годишник annuaire - Факултет по химия и фармация

Transcription

ГОД И Ш Н И К
НА
СОФИЙСКИЯ УНИВЕРСИТЕТ
„СВ. КЛИМЕНТ ОХРИДСКИ“
ХИМИЧЕСКИ ФАКУЛТЕТ
Том 102/103, 2011
ANNUAIRE
DE
L’UNIVERSITE DE SOFIA
“ST. KLIMENT OHRIDSKI“
FACULTE DE CHIMIE
Tome 102/103, 2011
СОФИЯ • 2011 • SOFIA
УНИВЕРСИТЕТСКО ИЗДАТЕЛСТВО „СВ. КЛИМЕНТ ОХРИДСКИ“
PRESSES UNIVERSITAIRE „ST. KLIMENT OHRIDSKI“
© St. Kliment Ohridski University of Sofia
Faculty of Chemistry
2011
ISSN 0584-0317
ГОДИШНИК НА СОФИЙСКИЯ УНИВЕРСИТЕТ „СВ. КЛИМЕНТ ОХРИДСКИ“
ANNUAIRE DE L’UNIVERSlTE DE SOFIA „ST. KLIMENT OHRIDSKI“
FACULTE DE CHIMIE
Editor-in-Chief
Prof. M. Miteva, D.Sc., Ph.D.
Department of Analytical Chemistry
Faculty of Chemistry, University of Sofia, 1 J. Bourchier Blvd., 1164 Sofia, BULGARIA
E-mail: [email protected]
Edited by Sophia Toudjarova
Faculty of Chemistry, University of Sofia, 1 J. Bourchier Blvd., 1164 Sofia, BULGARIA
Editorial Board
Prof. D. Todorovsky, D.Sc., Ph.D.
Department of Inorganic Chemistry
University of Sofia
[email protected]
Prof. B. V. Toshev, D.Sc., Ph.D.
Department of Physical Chemistry
University of Sofia
[email protected]
Prof. B. Galabov, D.Sc., Ph.D.
Department of Applied Organic Chemical
University of Sofia
[email protected]
Prof. T. Spassov, D.Sc., Ph.D.
Department of Applied Inorganic Chemical
University of Sofia
[email protected]
Prof. G. Petrov, D.Sc., Ph.D.
Department of Organic Chemistry, University of Sofia
[email protected]
AIMS AND SCOPE
Annuaire de l’University de Sofia ,,St. Kliment Ohridski“. Faculte de chimie (Ann.
Univ. Sofia. Fac. Chimie, formerly: Ann. Univ. Sofia. Fac. Phys.-Math.) is the first Bulgarian
journal publishing research papers in the field of chemistry. The aim of the Journal is to
encourage the submission of original, well-documented articles on all branches of chemistry.
Areas covered include inorganic chemistry, organic chemistry, analytical chemistry, physical
chemistry, and chemical technology.
The Journal publishes review papers from invited authors of international stature. The
Sofia University lecturers could also present such reviews but prior to submitting a manuscript,
please send an outline and table of contents of the proposed review. Our rubric Literary heritage contains research papers and documents on the history of chemical education and scientific
achievements at the University of Sofia. Lists of publications of our eminent professors, nowadays and in the past, are welcome.
The journal will also publish Book reviews.
3
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CONTENTS
1. Literary heritage. Lothar Beyer, Fritz Dietz. 600 Jahre Universität Leipzig (1409-2009)
und die Chemie .........................................................................................................9
2. Literary heritage. Bibliography of Professor DSc. Michail G. Arnaudov /dedicated to
the 70th anniversary of Prof. Michail G. Arnaudov/ ................................................13
3. Literary heritage. Bibliography of Professor DSc. Emil D. Manev /dedicated to the 70th
anniversary of Prof. Emil D. Manev/ ......................................................................23
4. Literary heritage. Bibliography of Professor DSc Ivan Panayotov. Dedicated to the 70
th anniversary of Prof. Ivan Panayotov....................................................................33
5. Literary heritage. Bibliography of Professor DSc S. Alexandrov. Dedicated to the 70 th
anniversary of Prof. S. Alexandrov ..........................................................................43
6. In Memoriam: Professor DSc. K. Kostadynov ........................................................... 55
7. In Memoriam: Professor DSc. V. Drianska ................................................................ 59
8. Prof. N. Tyutyulkov, F. Dietz. Nature of magnetic interaction in organic radical crystals.
Mixed radical crystals with polymethine radicals....................................................61
9. Konstantin Balashev, Martin Gudmand, Thomas Heimburg, Thomas Björnholm.
Measuring the liquid-gas line energy in Dipalmitoyl-sn-glycero-3-phosphocholine
(DPPC) Langmuir monolayers combining Wide-Field Fluorescence Microscopy and
Surface potential measurements 69
10. Georgi G. Yordanov, Ceco D. Dushkin. Quantum dots for bioimaging applications:
present status and prospects .....................................................................................81
11. Stoyan I. Karakashev, Dilyana S. Ivanova. Dynamic Effects in Thin Films with
Different Radii ......................................................................................................103
12. Yordanka B. Ivanova, Ognyan I. Petrov. Novel chalcone-like derivatives - 6-(3-aryl- or
hetaryl-2-propenoyl)-2(3H)-benzoxazolones - synthesis and evaluation of cytotoxicity on leukemia cells ..............................................................................................123
13. R. Todorovska, M. Uzunova-Bujnova, M. Milanova, D. Todorovsky. Spray-deposited
TiO2 films for phenol destruction in water ............................................................129
14. Milen G. Bogdanov, Ivan V. Svinyarov, Vasil N. Atanasov. Synthesis and mass spectral
stady of trans-and cis- (±)-3-phenyl-3,4-dihydroisocoumarin-4-carboxamides....145
15. Stoyan I. Karakashev, Emil D. Manev and Anh V. Nguyen. Effect of Thin Film Elasticity
on Foam Stability ...................................................................................................153
16. I. Dakova, I. Karadjova, V. Georgieva, G. Georgiev. Synthesis and Characterization of the
Hg(II)-ion imprinted microbeads and membranes for enrichment of inorganic Hg(II) ......165
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17. Roumen Tsekov. Electric double layer in highly concentrated solutions of ionic surfactants ........................................................................................................................177
18. Roumen Tsekov. Ermakov Equations in Quantum Mechanics ................................. 185
19. Marco Kostadinov, Gianluca Li Puma, Ceco Dushkin. Preliminary test of modified
TiO2 photocatalysts in gas-phase ............................................................................189
20. Jordan G. Petrov, Tonya D. Andreeva, Helmuth Moehwald. Interaction of hydrophobic
ions with Langmuir monolayers with opposite dipole moments of the hydrophilic
heads ......................................................................................................................195
21. Jordan G. Petrov, Gerald Brezesinski, Tonya D. Andreeva, Helmuth Moehwald.
Nanometer structure of binary Langmuir monolayers with opposite dipole moments
of the hydrophilic heads .........................................................................................205
22. S.K.Peneva, K.D.Djuneva, N.S.Neykov. Additional crystallographic data on some
metastable crystalline states of tin .........................................................................215
23. S. B. Iliev, G. S. Georgiev. Mechanism of the alternating copolymerization. V. Azeotrope comроsations at the donor-acceptor copolymerization of the maleic anhydride
with vinyl ester of 2,2,4-trimethylheptanoic acid .................................................231
24. Roumen Tsekov. Thermo-quantum diffusion in periodic potentials .........................247
25. Roumen Tsekov. Flocculation of vesicles ................................................................. 253
26. Ivan T. Ivanov, Iana Petkova, Borislav P. Soklev, Iliana V. Delcheva, Boyan Iliev,
Thomas J.S. Schubert, Milen G. Bogdanov, Radomir I. Slavchov.Wetting Properties
of Low-viscosity room temperature imidazolium ionic liquids .............................259
27. Roumen Tsekov. Adsorption component of the disjoining pressure in thin liquid films ....... 273
28. Snejana N. Merkova, Petko I. Bozov, Ilia N. Iliev. Chemical constituens of the aerial
parts of salvia splendenes.......................................................................................279
29. K. Genov, V. Blaskov, M. Shipochka, I. Boevski, A. Loukanov, I. Stambolova. C. Dushkin. Spray pyrolysis vs. ion-exchange methods: Decomposition of ozone over Cu
coated HEU- type zeolite in ambient conditions ................................................... 285
30. Nina Kaneva, Bozhidar Stefanov, Dimitre Dimitrov, Ceco Dushkin. Photocatalytic
degradation of Methylene Blue by ZnO photocatalyst doped with nickel ...........293
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СЪДЪРЖАНИЕ
1. Литературно наследство. 600 години Лайпцигски Университет (1409-2009) ....9
2. Литературно наследство. Библиография на проф. дхн М. Арнаудов (посвещава
се на 70 Годишния юбилей на проф. М. Арнаудов) ............................................13
3. Литературно наследство. Библиография на проф. дхн Е. Манев (посвещава се на
70 Годишния юбилей на проф. Е. Манев) ............................................................23
4. Литературно наследство. Библиография на проф. дхн И. Панайотов (посвещава
се на 70 Годишния юбилей на проф. И. Панайотов) ...........................................33
5. Литературно наследство. Библиография на проф. дхн Стоян Александров (посвещава се на 70 Годишния юбилей на проф. Стоян Александров) ...................43
6. В памет на проф. дхн К. Костадинов .......................................................................55
7. В памет на проф. дхн Венета Дрянска .....................................................................59
8. Н. Тютюлков, Фритц Диетц. Природа на магнитните взаимодействия в органични радикалкристали ...............................................................................................61
9. Константин Балашев, Мартин Гудман, Томас Хаймбург, Томас Бьорнхолм. Измерване на линейното напрежение на прехода течност – газ в дипалмитоилфосфатидилхолинови (DPPC)монослоеве с комбинирано измерване от флуорисцентна микроскопия и повърхностен потенциал ..........................................69
10. Георги Йорданов, Цецо Душкин. Биомедицинско приложение на полупроводникови квантови точки ...............................................................................................81
11. Стоян И. Каракашев, Дияна С. Иванова. Динамика на тънки филми с различни
радиуси ..................................................................................................................103
12. Йорданка Б. Иванова, Огнян Петров. Нови халконови производни: 6-(3-арилили хетарил-2-пропеноил)-2(3H)-бензоксазолони – синтез и цитотоксичност
върху лефкемични клетъчни линии....................................................................123
13. Р. Тодоровска, М. Узунова-Буйнова, М. Миланова, Д. Тодоровски. Пулверизационно отлагане на слоеве от TiO2 за фотокаталитично разлагане на фенол, разтворен във вода .....................................................................................................129
14. Милен Богданов, Иван Свиняров, Васил Атанасов. Синтез и мас-спектрално изследване на транс- и цис-(±)-3-фенил-3,4-дихидроизокумарин-4-карбоксамиди ..........145
15. Стоян Каракашев, Емил Манев, A. Hгуен. Влияние на еластичността на филмите
върху стабилността на пяна ................................................................................153
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16. И. Дакова, Ирина Караджова, В. Георгиева, Г. Георгиев. Синтез и характеризиране на Hg(II)-йон отпечатани микрочастици и мембрани ..............................165
17. Румен Цеков. Двоен електричен слой в концентрирани разтвори на йоногенни
повърхностно активни вещества ........................................................................177
18. Румен Цеков. Уравнения на Ермаков в квантовата механика ............................185
19. Марко Костадинов, Джанлука Ли Пума, Цецо Душкин. Предварителен тест на
модифицирани фотокатализатори от TiO2 в газова фаза .................................189
20. Йордан Г. Петров, Тоня Д. Андреева, Хелмут Мьовалд. Взаимодействие на
хидрофобни йони с Лангмюйрови монослоеве с противоположни диполни моменти на хидрофилните глави ............................................................................195
21. Йордан Г. Петров, Гералд Брецезински, Тоня Д. Андреева, Хелмут Мьовалд. Наномерна структура на бинерни Лангмюйрови монослоеве с противоположни
диполни моменти на хидрофилните глави ........................................................ 205
22. Ст. К. Пенева, К. Д. Джунева, Н.С. Нейков. Допълнителни кристалографски
данни за някои метастабилни кристални състояния на калая ......................... 215
23. Ст. Б. Илиев, Г. С. Георгиев. Азеотропни състави при донорно-акцепторната
съполимеризация на малеиновия анхидрид с винилов естер на 2,2,4-триметилхептанова киселина ..............................................................................................231
24. Румен Цеков. Термо-квантова дифузия в периодичните потенциали ............... 247
25. Румен Цеков. Флокулация на везикули ................................................................ 253
26. Иван Иванов, Яна Петкова, Борислав Соклев, Иляна Делчева, Боян Илиев, Томас
Шуберт, Милен Богданов, Радомир Славчов. Умокрящи свойства на нисковизкозни имидазолиеви йонни течности .................................................................259
27. Румен Цеков. Адсорбционен компонент на разклинящото налягане в тънки течни
филми ....................................................................................................................273
28. Снежана Н. Меркова, Петко И. Бозов, Илия Н. Илиев. Химичен състав на надземните части на “Salvia splendenes Ker.-Gawl” ................................................ 279
29. К. Генов, В. Блъсков, M. Шипочка, И. Боевски, А. Луканов, И. Стамболова, Ц.
Душкин. Сравняване на спрей пиролиза с йонен обмен: Разлагане на озон чрез
мед, нанесена върху HEU-тип зеолит при стайна температура...................... 285
30. Нина Кънева, Божидар Стефанов, Димитре Димитров, Цецо Душкин. Фотокаталитично разлагане на Метиленово синьо с помощта на фотокатализатор от
модифициран с никел ZnO ..................................................................................293
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Том 102/103, 2011
ANNUAIRE DE L’UNIVERSITÉ DE SOFIA “ST. KLIMENT OHRIDSKI”
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
600 JAHRE UNIVERSITДT LEIPZIG (1409–2009)
UND DIE CHEMIE
von Lothar Beyer und Fritz Dietz
Seit mehr als 30 Jahren kooperieren Chemiker der Universität Sofia und der
Universität Leipzig miteinander auf dem Gebiet der Theoretischen Chemie. Prof.
Dr. Nikolai Tyutyulkov (Sofia), seit dem Jahr 2000 Doktor honoris causa der Alma
mater Lipsiensis, und Prof. Dr. Fritz Dietz (Leipzig) als wissenschaftliche Leiter
der Zusammenarbeit erzielten dabei mit ihren Gruppen Forschungsergebnisse, die
in den letzten 40 Jahren in etwa 100 Arbeiten in nationalen und internationalen
Zeitschriften publiziert wurden und international große Beachtung gefunden haben. Zahlreiche bulgarische Studierende und graduierte Wissenschaftler, insbesondere in den Fachrichtungen analytische, technische und theoretische Chemie,
waren Gäste an der Fakultät für Chemie und Mineralogie der Universität Leipzig.
Das Gründungsjubiläum der Universität Leipzig ist ein geeigneter Anlass, interessierte bulgarische Wissenschaftler und Praktiker über die Geschichte ihrer deutschen Partneruniversität unter besonderer Berücksichtigung der Entwicklung der
Chemie zu informieren.
Im Mai 1409 verließen Professoren und Studenten sächsischer, bayerischer, und polnischer „Nation“, wegen des sie im Stimmrecht benachteiligten
„Kuttenberger Edikts“, vom böhmischen König Wenzel IV. protestierend die
Karls-Universität Prag und zogen nach Leipzig. Papst Alexander V. erteilte die
Genehmigung zur Gründung der Universität Leipzig. Markgraf Friedrich von
Sachsen stellte Gebäude im Stadtzentrum zur Verfügung und am 2. Dezember 1409
erfolgte der feierliche Gründungsakt mit der Wahl von Johann von Münsterberg
zum ersten Rektor. Leipzig besitzt nach Heidelberg die Zweitälteste Universität
in Deutschland mit ununterbrochenem Lehrbetrieb. Gottfried Wilhelm Leibniz,
Georgius Agricola und Johann Wolfgang von Goethe studierten hier. Aus den ursprünglich vier Fakultäten, der Theologischen, Juristischen, Medizinischen und
9
„Artistenfakultät“, haben sich dann im Laufe der Jahrhunderte die zahlreichen
Wissenschaftsdisziplinen entwickelt, die heute an der Universität Leipzig mit 456
Professoren und 30.000 Studenten in 14 Fakultäten beheimatet sind. Eine von ihnen
ist die Fakultät für Chemie und Mineralogie, an der gegenwärtig 23 Professoren
lehren und jährlich etwa 180 Chemiestudenten immatrikuliert werden. Das Profil
der Universität Leipzig ist auf Geistes-, Sozial- und Naturwissenschaften sowie
Medizin orientiert. Die Technikwissenschaften sind an den drei anderen sächsischen Universitäten in Dresden. Chemnitz und Freibera etabliert.
Die universitäre Leipziger Chemie blickt auf eine mehr als 300 jährige Geschichte zurück. Sie entwickelte sich seit der Ernennung des ersten
Chemieprofessors Michael Heinrich Horn 1668 mehr als 150 Jahre lang im
Schoße der Medizinischen Fakultät als eine Hilfswissenschaft derselben, ehe
sie dann im Zuge einer grundlegenden Universitätsreform um 1830 mit dem
Ordinarius Otto Linne Erdmann in der Philosophischen Fakultät eigenständig
wurde. Er war Wegbereiter für die Blütezeit der Naturwissenschaften an der
Leipziger Universität, speziell der Chemie und Physik, in der zweiten Hälfte des
19. und dem ersten Drittel des 20. Jahrhunderts. Den Chemikern in aller Welt sind
die klangvollen Namen der Protagonisten der Chemie jener Zeit und ihre fundamentalen, an der Universität Leipzig erzielten, wissenschaftlichen Leistungen
bekannt: Es sind Hermann Kolbe (Salicylsäuresynthese nach Kolbe-Schmitt),
Ernst Beckmann (Beckmannsche Molekulargewichtsbestimmung, BeckmannUmlagerung, Beckmann-Thermometer), Johannes Wislicenus (cis-trans Isomerie),
Arthur Hantzsch (Hantzsch’sche Pyridinsynthese) und die Nobelpreisträger
Wilhelm Ostwald (Katalyse, Ostwaldsches Verdünnungsgesetz, Ostwald-BrauerVerfahren der Ammoniakoxidation) Svante Arrhenius (Arrhenius-Gleichung),
Walther Nernst (Nernstsche Gleichung) sowie Max Le Blanc (Elektrochemie),
Hans Stobbe (Stobbe-Kondensation), Hans Kautsky (Singulett-Sauerstoff,
Kautsky-Kurve) und andere. Im Physikalischen Institut wirkten die der Chemie
nahestehenden Nobelpreisträger Peter Debye, Werner Heisenberg und Gustav
Hertz, weiterhin Friedrich Hund, Heinrich Wiener und Gustav Fechner.
Hermann Kolbe hatte 1868 das „Chemische Laboratorium der Universität
Leipzig“, in der Liebigstraße als damals größtes und modernstes in Deutschland
erbauen lassen. Wilhelm Ostwald, Mitbegründer der Physikalischen Chemie und
Begründer der weltbekannten „Leipziger Schule der Physikalischen Chemie“,
zog 1898 in das neuerbaute Physikalischchemische Institut in der Linnestraße.
Im Inferno des Bombenhagels auf Leipzig gegen Ende des II. Weltkrieges am
4. Dezember 1943 versanken beide Gebäude nahezu vollständig in Schutt und
Asche. Im Juni 1945 wurden fast alle Chemie-Professoren von einer Siegermacht
in die westliche Besatzungszone Deutschlands evakuiert. Der Neuaufbau der
Chemischen Institute in Leipzig verlief deshalb unter extrem schwierigen
Bedingungen. Umso höher sind die Leistungen jener Jahre in Lehre und Forschung
10
auf den Gebieten der Seltenen Erden (Leopold Wolf), der Naturstoff- und organischen Synthesechemie (Wilhelm Treibs), der Photografischen Chemie (Herbert
Staude) sowie der Braunkohlenveredelung (Eberhard Leibnitz) zu bewerten. Im
Zuge einer Hochschulreform wurde 1968 die „Sektion Chemie“, in Nachfolge
der ehemaligen Chemischen Institute bzw. des Chemischen Laboratoriums als
Institution an der 1953 so genannten Karl-Marx-Universität Leipzig gebildet.
Nach der Wiedervereinigung Deutschlands 1990 im Ergebnis der friedlich verlaufenen revolutionären Ereignisse von 1989 mit der Schaffung demokratischer
Verhältnisse und für die Universitäten mit der Herstellung der Freiheit von Lehre
und Forschung wurde am 15. Januar 1994 unter dem Rektorat des Theoretischen
Chemikers Cornelius Weiss die o.g. Fakultät für Chemie und Mineralogie an
der Universität Leipzig gegründet. Zum ersten Dekan wurde der Theoretische
Chemiker Joachim Reinhold gewählt. In dieser Fakultät sind die Institute für
Analytische Chemie, Anorganische Chemie, Organische Chemie, Physikalische
und Theoretische Chemie, Technische Chemie, Mineralogie und Chemiedidaktik
vereint. Ein großzügiger, moderner Chemie-Neubau in der Johannisallee wurde
im Jahre 2000 in einem naturwissenschaftlich geprägten Universitätsareal neben
dem Technikum Analytikum, dem rekonstruierten Wilhelm-Ostwald-Institut für
Physikalische und Theoretische Chemie, der Physik und den Biowissenschaften in
unmittelbarer Nähe zu den medizinischen Instituten und zum Forschungskomplex
der „Biocity Leipzig“, einem Max-Planck-Institut für evolutionäre Anthropologie
und der Deutschen Nationalbibliothek eingeweiht. Damit sind beste Bedingungen
für eine interdiszplinär angelegte universitäre Lehre und Forschung, besonders
in den „Life sciences“, und auf dem Gebiet der „Nanowissenschaften“, (multifunktionale Materialien, Nanoobjekte, Bausteine für die molekulare Elektronik)
geschaffen. Ein großzügiger Neubau für die Hauptgebäude der Universität im
Zentrum der Großstadt Leipzig, das neue „Paulinum“, wird im Jubiläumsjahr fertig gestellt. Eine Jubiläumsausstellung „Erleuchtung der Welt“, zeigt bis Dezember
2009 in beeindruckender Weise die gewichtigen Beiträge der Universität Leipzig
zur Entwicklung der modernen Wissenschaften im Zeitraum von Humanismus und
Aufklärung im 17./18. Jahrhundert. Leipzig mit seiner altehrwürdigen, modernen
Universität und seinem besonderen Flair als Musik-, Buch- und Messestadt ist
attraktiv für Studenten und Wissenschaftler aus Bulgarien und aus aller Welt.
10.10.09
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Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
LITERARY HERITAGE
BIBLIOGRAPHY OF PROFESSOR DSc. MICHAIL G. ARNAUDOV
Dedicated to the 70th anniversary of Prof. Michail G. Arnaudov
Prof. Michail Georgiev Arnaudov was born
on 17.04.1939 in Sofia. In 1963 he has graduated
as diploma engineer at the University of Chemical Technology and Metallurgy (former Institute
of Chemical Technology) in Sofia. In 1966 he was
enrolled as a Research Fellow at the Faculty of
Chemistry, University of Sofia “St. Kl. Ohridski”.
During the years 1966–1986 he was promoted to
scientific positions of Research Fellow 3rd degree
(1966–1969), 2nd degree (1969–1974) and 1st degree (1974–1986) in the Laboratory of Molecular Spectral Analysis, Department of Analytical
Chemistry, Faculty of Chemistry. He has founded this Laboratory as early as 1965
and headed it until his retirement in 2007. In 1986 he was habilitated as Associate
Professor of organic chemistry, position held until 2002. In 2002 Dr. Arnaudov became Full Professor in analytical chemistry. He has defended a thesis for a Ph.D.
degree in 1983 and a second thesis for Doctor of Sciences (D.Sc) in 2000.
Prof. M. Arnaudov has lectured in the following courses at the University
of Sofia: “Applied molecular spectroscopy” (1977–2001), “Physical methods in
organic chemistry” (1984–2001), “Molecular spectral analysis” (1993–2001),
“Instrumental methods of analysis” (from 2001), “Modern methods of molecular
spectroscopy” (since 2001), “Infrared and raman spectroscopy” (since 2001), and
(co-lecturer) on “Liquid crystals – background and applications”. At the Faculty
of Biology he has lectured in the course “Physical methods in biology and chem13
istry” (1987–1999). His has also lectured in 26 courses for postgraduate students:
“Physical methods in chemical research” and “Infrared spectral analysis”. Professor Arnaudov has supervised 30 individual post graduates in courses on “Infrared
spectral analysis”, 23 M.Sc. students and 4 Ph.D. students.
Professor Arnaudov has also lectured in several other universities in Bulgaria:
“Molecular spectroscopy” (1977–1981) at the University of Chemical Technology
and Metallurgy (Burgas); “Physical methods in organic chemistry” (1977–1980)
at the University of Shumen “St. Konstantin Preslavski”; and “Physical methods
in organic chemistry” (1989–2000) and “Organic analysis” (1996–2000) at the
South-West University “Neofit Rilski” (Blagoevgrad).
Research accomplishments of Prof. M. G. Arnaudov cover the scientific area
of molecular (mainly infrared) spectral analysis. He has been author and co-author
of over 87 scientific research papers and co-author of 3 authors’ certificates (BG
patents). Parts of his scientific results have been presented at 23 national and international conferences. His papers have been citied over 630 times in the scientific
literature. Professor Arnaudov has been author and co-author of two books and a
textbook section as listed below.
During his scientific career Professor Arnaudov has collaborated successfully
with numerous scientists from the Faculty, this country and abroad: Prof. Yanko
Dimitriev (University of Chemical Technology and Metallurgy, Sofia), Prof. Bojidar
Yordanov (Institute of Organic Chemistry, Bulgarian Academy of Sciences), Academician Panayot R. Bontchev, Prof. Alexander Dobrev and Assist. Prof. Bojidarka
Ivanova (Faculty of Chemistry, University of Sofia “St. Kl. Ohridski”), Academician Ivan Gutzov (Institute of Physical Chemistry, Bulgarian Academy of Sciences)
as well as with Prof. William Sheldrick (Ruhr-University Bochum, Germany).
Professor Arnaudov has been Vice Dean of the Faculty of Chemistry (1988–
1991) and Head of the School on Analysis of Inorganic and Organic Substances”,
organized by the Ministry of Chemical Industry and Sofia University (1980–1987).
He has been member of several committees and scientific councils: the National
Committee of Spectroscopy – Section of Molecular Spectroscopy (1981–1989);
Member of the Faculty Council and Scientific Council of the Faculty of Chemistry, University of Sofia (since 1987–2007); Member of the Specialized Council
Inorganic and Analytical Chemistry (since 1993).
Complete bibliography of Professor M. G. Arnaudov has been compiled and
given in chronological order below in this issue. Publications are given in their
original language of publication and translated in English.
14
THESES
1. Арнаудов, М. Г. ИЧ-спектрално изследване на стеричните ефекти при образуване на
водородни връзки в 2,3-заместените 3-бензоил-аминопропионови киселини и техни
естери. Дисертация за присъждане на научната степен “кандидат на химическите науки”,
ИОХ-БАН, София, 1983, 166 с.
Arnaudov, М. G. IR Spectral Study оn Steric Effects at H-bond Formation in 2,3-Substituted
3-Benzoylaminopropionic Acids and Their Esters. Ph. D. Thesis, Institute of Organic Chemistry,
Bulgarian Academy of Sciences, Sofia, 1983, pp. 166.
2. Арнаудов, М. Г. Приложение на ефектите на средата в инфрачервения спектрален анализ.
Дисертация за присъждане на научната степен “доктор на химическите науки” Химически факултет, СУ “Св. Климент Охридски”. Институт по Обща и Неорганична
Химия, Българска Академия на Науките, София, 1999, с. 349.
Arnaudov, M. G. Applications of the Medium Effects in the Infrared Spectral Analysis. Dissertation presented for obtaining the scientific degree “Doctor of Chemical Sciences”, D.Sc. - Faculty of
Chemistry, Sofia University). Institute of General and Inorganic Chemistry - Bulgarian Academy of
Sciences, Sofia, 1999, pp. 349.
MONOGRAPHS AND TEXTBOOKS
3.
4.
5.
Арнаудов, М. Приложение на инфрачервената спектроскопия в химията, Наука и
изкуство, София, 1981, 40 с.
Arnaudov, M. Application of Infrared Spectroscopy in Chemistry, Nauka i Izkustvo, Sofia,
1981, pp. 40 (in Bulgarian).
Спасов, Ст., М. Арнаудов. Приложение на спектроскопията в органичната химия. Наука
и изкуство, София, 1978, 382 с.
Spassov, St., M. Arnaudov. Application of Spectroscopy in Organic Chemistry. Nauka i Izkustvo, Sofia, 1978, pp. 382 (in Bulgarian).
Арнаудов, М. Приложение на ИЧ-спектроскопия в неорганичната технология. – В:
Ръководство по неорганична химична технология, Част 1, съставител Ал. Ленчев, редактор
Ст. Будуров. Унив. Изд. “Св. Климент Охридски”, С., 1988, Глава II.2.5, с. 151–160
Arnaudov, M. Application of Infrared Spectroscopy in Inorganic Technology. – In: Practice
in Inorganic Chemical Technology, Part 1, Al. Lenchev (Compiler), St. Budurov (Ed.), Univ.
Press “St. Kliment Ohridski”, Sofia, 1988, Chap. II.2.5, pp. 151–160 (in Bulgarian).
BIBLIOGRAPHY
6.
7.
8.
9.
Гуцов, Ив., М. Арнаудов, Б. Йорданов. Изследване на структурата и процеса на
сумарна кристализация на Гремово стъкло с помощта на инфрачервена спектроскопия,
Изв. Инст. Физикохим, БАН, 4, 1964, 13–22
Gutsov, Iv., M. Arnaudov, B. Yordanov. Study on the Structure and the Process of Crystallization of Graham Glass by Means of Infrared Spectroscopy. Izv. Inst. Fizikokhimiya, Bulg.
Acad. Sci., 4, 1964, 13–22.
Marinov, M., J. Dimitriev, M. Arnaudov. Einfluss der alkalischen Halogenide auf die
Glasbildung in Boratgläsern. Compt. Rend Bulg, Acad. Sci., 20,1967, 569–572.
Simov, D., V. Kalceva, M. Arnaudov, B. Galabov. Über Kinetik und Mechanismus der Aminolyse der Aryloxazolone. Compt. Rend, Bulg. Acad. Sci., 21, 1968, 877–880.
Besouhanova, Ts., Chr. Dimitrov, M. Arnaudov, B. Souroudjieva, B. Yanev. Catalytic Conversions of the Isomeric Diethylbenzenes on a Silica-Alumina Catalyst. Compt. Rend, Bulg.
Acad. Sci., 22, 1969, 555–558.
15
10. Димитров, Д., Л. Стефанова, Л. Халачева, М. Арнаудов, М. Попов. Върху разделянето
на синтетични нафтенови киселини чрез течнофазно окисление на деароматизирана
газьолова фракция от тюленовски нефт. Химия и индустрия, 9, 1969, 389–393.
Dimitrov D., A. Stefanova, L. Halatsheva, M. Arnaudov, M. Popov. On the Separation of
Synthetic Naphthenic Acids by Liquid Phase Oxidation of Dearomatized Naphtha Fraction in
Petrol from Tulenovo. Khimiya i Industriya, 9, 1969, 389–393 (in Bulgarian).
11. Kirilov, M., M. Arnaudov, G. Petrov, L. Shishkova. IR-Spektroskopische Untersuchungen
über die Kinetik der kationotropen Umwandlung von Mg-Diäthylphosphonoaceton in Lösung.
Chem. Ber., 103, 1970, 3190–3195.
12. Симов, Д., Б. Гълъбов, М. Арнаудов, В. Калчева. Исследование спектров поглощения
бензоксазолонов в средней ИК-области. Ж. прикл. спектроск., 13, 1970, 327–333.
Simov, D., B. Galabov, M. Arnaudov, V. Kalcheva. Study on Absorption Spectra of Benoxazoxalons in the Mid-Infrared Region. Zh. Prikl. Spektrosk., 13, 1970, 327–333 (in Russian).
13. Симов, Д., Б. Гълъбов, М. Арнаудов, В. Калчева. Изследване абсорбционните спектри
на арилоксазолони в средната инфрачервена област. Изв. Физ. И-тут с АНЕБ, БАН, 21,
1971, 265–275.
Simov, D., B. Galabov, M. Arnaudov, V. Kalcheva. Study on Absorption Spectra of Aryloxazolons in the Mid-Infrared Region. Izv. Fiz. Inst. s ANEB, Bulg. Acad. Sci,. 21, 1971, 265–275
(in Bulgarian).
14. Арнаудов, М., А. Добрев, Л. Шишкова, Хр. Иванов. ИЧ-спектрално изследване на
водородните връзки при 3-ациламинопропионови киселини. Год. СУ, ХФ, 65, 1972, 363–384.
Arnaudov, M., A. Dobrev, L. Shishkova, Chr. Ivanov. Infrared Spectral Study of Intramolecular Hydrogen Bonds of 3-benzoylaminopropionic Acids. Ann. Univ. Sofia, Fac. Chem., 65,
1972, 363–384 (in Bulgarian).
15. Арнаудов, М, А. Добрев, Л. Шишкова, Хр. Иванов. ИК-спектральное исследование
внутримолекулярных водородных связей 3-бензоиламино-пропионовых кислот. Ж. прикл.
спектроск., 18, 1973, 242–250.
Arnaudov, M., A. Dobrev, L. Shishkova, Chr. Ivanov. Infrared Spectral Study of Intramolecular Hydrogen Bonds of 3-benzoylaminopropionic Acids. Zh. Prikl. Spektrosk., 18, 1973,
242–250 (in Russian).
16. Dimitriev, J., M. Arnaudov, V. Dimitrov. IR-Spektralanalyse von Gläsern des Systems TeO2V2O5. Monatsh. Chem., 107, 1976, 1335–1343.
17. Димитриев, Я., М. Арнаудов, В. Димитров. ИЧ-спектрално изследване на стъкла от
системата TeO2-V2O5 и техните кристални продукти. Строит. матер. силик. пром., 16,
1976, 25–29.
Dimitriev, Ya., M. Arnaudov, V. Dimitrov. Infrared Spectral Study of Glasses in the TeO2V2O5 System and their Crystal Products. Stroit. Mater. Silik. Prom., 16, 1976, 25–29 (in Bulgarian).
18. Arnaudov, M., L. Shishkova, A. Dobrev, C. Ivanov. IR-Spectral Investigation of Steric
Effects on Hydrogen Bond Formation in Esters of 3-Benzoylaminopropionic Acids. I. NHsretching region. Spectrochim. Acta, 33 A , 1977, 437–443.
19. Dimitriev, J., V. Dimitrov, M. Arnaudov. Struktur von Glasern des Systems TeO2-VO2.
Monatsh. Chem., 109, 1978, 791–797.
20. Спасов, Ст., М. Арнаудов. Приложение на спектроскопията в органичната химия. Наука
и изкуство, София, 1978, 382 с.
Spassov, St., M. Arnaudov. Application of Spectroscopy in Organic Chemistry. Nauka i Izkustvo, Sofia, 1978, pp. 382 (in Bulgarian).
21. Dimitriev, Y., V. Dimitrov, M. Arnaudov. IR-Spectra of Crystalline Phases and Related
Glasses in the TeO2-V2O5-Me2O-System. J. Mater. Sci., 14, 1979, 723–727.
16
22. Markov, P., I. Petkov, M. Arnaudov. Influence of UV-Light on 3-Aminocrotonic Acid-Ethylester and its N-substituted Derivates. Spectral Evidance for a Photoinduced Hydrogen Transfer. Mol. Photochem., 9, 1979, 295–301.
23. Ivanov, C., M. Arnaudov, P. Markov, L. Shishkova. IR-Spektroskopische Angaben tber die
Metallotropie in Losung von Cu(II)- und Ca-Acetessigestern. Commun. Depart. Chem. Bulg.
Acad. Sci., 13, 1980, 198–204.
24. Арнаудов, М. Приложение на инфрачервената спектроскопия в химията. Наука и
изкуство, София, 1981, 40 с.
Arnaudov, M. Application of Infrared Spectroscopy in Chemistry. Nauka i Izkustvo, Sofia,
1981, pp. 40 (in Bulgarian).
25. Dimitriev, Y., M. Arnaudov, V. Dimitrov. Phase Diagram and IR-Spectral Investigation of
the 2TeO2.V2O5-Na2O.V2O5. 2TeO2 System. J. Solid State Chem., 38, 1981, 55 –61.
26. Димитриев, Я., В. Димитров, М. Арнаудов. Инфрачервени спектри и структура на
телуритни стъкла. – В: Тр. VI научно-техн. конф. “Стъкло и фина керамика”, ред. Св.
Бъчваров. Институт по стъкло и фина керамика, 1981, с. 272–278
Dimitriev, Ya., V. Dimitrov, M. Arnaudov. Infrared Spectra and Structure of Tellurite Glasses. – In: Proc. 6th Sci.-Techn. Conf. “Glass and Ceramics”, Sv. Bachvarov (Ed.). Institute for
Glass and Fine Ceramics, 1981, pp. 272–278 (in Bulgarian).
27. Dimitriev, Y., J. C. J. Bart, V. Dimitrov, M. Arnaudov. Structure of Glasses of the TeO2-MoO3
System. Z. Anorg. allgem. Chem., 479, 1981, 229–240.
28. Arnaudov, M., V. Dimitrov, Y. Dimitriev, L. Markova. IR-Spectral Investigation of Tellurites. Mater. Res. Bull., 17, 1982, 1121–1129.
29. Ivanov, P. M., M. G. Arnaudov, A. A. Dobrev. IR-Spectral Investigation of Steric Effects on Hydrogen Formation in Esters of 3-Benzoylaminopropionic Acids. II. Empirical Energy Calculations.
J. Mol. Struct. (Theochem), 88, 1982, 235–242.
30. Арнаудов, М. Г. ИЧ-спектрално изследване на стеричните ефекти при образуване на
водородни връзки в 2,3-заместените 3-бензоил-аминопропионови киселини и техни
естери. Дисертация за присъждане на научната степен “кандидат на химическите науки”,
ИОХ-БАН, София, 1983, 166 с.
Arnaudov, М. G. IR Spectral Study оn Steric Effects at H-bond Formation in 2,3-Substituted
3-Benzoylaminopropionic Acids and Their Esters. Ph. D. Thesis. Institute of Organic Chemistry,
Bulgarian Academy of Sciences, Sofia, 1983, pp. 166.
31. Dimitriev, Y., V. Dimitrov, M. Arnaudov, D. Topalov. IR-Spectral Study of Vanadate Vitreous Systems. J. Non-Cryst. Solids, 57, 1983, 147–156.
32. Dimitrov, V., M. Arnaudov, Y. Dimitriev. IR-Spectral Study of the Effect of WO3 on the
Structure of Tellurite Glasses. Monatsh. Chem., 115, 1984, 987–991.
33. Dimitriev, Y., V. Dimitrov, M. Arnaudov. IR-Spectra and Structures of Tellurite Glasses. J.
Mater. Sci., 18, 1983, 1353–1358.
34. Bontchev P.R., M. Boneva, M. Arnaudov, V. Nefedov. Palladium (II) Complexes of Hydrazides of Aspartic and Clutamic Acids. Inorg. Chim. Acta, 81, 1984, 75–81.
35. Diakovitch, Vl. A., M. G. Arnaudov, L. M. Shishkova, M. B. Ilieva. Correlations between
IR-characteristic Vibrations and Solvent Parameters. Koppel-Palm’s Multiparameter Equation. J. Mol. Liquids, 28, 1984, 115–118.
36. Arnaudov, M. G., L. M. Shishkova, A. A. Dobrev. IR-Spectral Investigation of Steric Effеcts
on Hydrogen Bond Formation in Esters of 3-Benzoylaminopropionic Acids. III. Correlation
between Amide-I Vibrations and Solvent Parameters. J. Mol. Struct., 114, 1984, 195–201.
37. Diakovitch, V., M. Arnaudov, L. Shishkova. Correlation between IR-characteristic Frequencies and Solvent Parameters. I. Analysis of the Koppel-Palm Polyparametric Equation. Commun. Depart. Chem. Bulg. Acad. Sci., 18, 1985, 336–344.
17
38. Bontchev, P. R., M. K. Boneva, M. G. Arnaudov, E. V. Golovinsky. Palladium (II) Complexes of Dihydrazide of Aspartic Acid. Compt. Rend. Bulg. Acad. Sci., 38, 1986, 707–710.
39. Arnaudov, M., Y. Dimitriev, V. Dimitrov, M. Dimitrova-Pankova. IR-Spectral Investigation of
Water in Tellurite Glasses. Phys. Chem. Glas., 27, 1986, 48–50.
40. Arnaudov, M., S. Hadjistoianova, P. Novakov. IR-Spectral Study of Diphenylether Polymers, J. Mater. Sci., 21, 1986, 3135–3138.
41. Arnaudov, M. G., L. M. Shishkova, B. O. Budevska. IR-Spectral Investigation of Steric Effects on Hydrogen Bond Formation in Fsters of 3-Benzoylaminopropionic Acids. IV. An Analysis of Conformational Equilibria in Solutions. J. Mol. Struct. (Theochem), 149, 1987, 111–119.
42. Павлова, М. П., М. Ас. Драганова, Хр. Ив. Константинов, М. Г. Арнаудов, Ш. Г.
Динков, Л. М. Шикова. Метод за получаване на блокиран изоцианат. Авторско
свидетелство, No 44598/1987.
Pavlova, M. P., M. A. Draganova, Chr. I. Konstantinov, M. G. Arnaudov, Sh. G. Dinkov, L. M.
Shishkova. Method for Production of Blocked Isocyanate. Author’s Certificate, No. 44598 /1987.
43. Павлова, М. П., М. Ас. Драганова, Хр. Ив. Константинов, М. Г. Арнаудов, Ш. Г. Динков,
Л. М. Шикова. Метод за получаване на полиизоцианатен полиуретанов адукт. Авторско
свидетелство, No 44613 /1987.
Pavlova, M. P., M. A. Draganova, Chr. I. Konstantinov, M. G. Arnaudov, Sh. G. Dinkov,
L. M. Shishkova. Method for Production of Polyisocyanate Polyurethane Adduct. Author’s
Certificate, No. 44613 /1987.
44. Павлова, М. П., Вл. Ст. Кабаиванов, Хр. Ив. Константинов, М. Ас. Драганова, П.
Г. Равелова, М. Г. Арнаудов, Ш. Г. Динков, Д. Ст. Димитров, Ал. Д. Ангелов, М. Р.
Христова. Двукомпонентна полиуретанова смола и метод за получаването й. Авторско
свидетелство, No 45123 /1987.
Pavlova, M. P., V. S. Kabaivanov, Chr. I. Konstantinov, M. A. Draganova, P. G. Ravelova, M.
G. Arnaudov, Sh. G. Dinkov, D. S. Dimitrov, A. D. Angelov, M. R. Christova. Two Component
Polyurethane Resin and Method for its Production. Author’s Certificate, No. 45123 /1987.
45. Арнаудов, М. Приложение на ИЧ-спектроскопия в неорганичната технология. – В:
Ръководство по неорганична химична технология, част 1, съставител Ал. Ленчев, pедактор
Ст. Будуров. Унив. Изд. “Св. Климент Охридски”, С., 1988, Глава II.2.5, с. 151–160.
Arnaudov, M. Application of Infrared Spectroscopy in Inorganic Technology – In: Practice in
Inorganic Chemical Technology, Part 1, Al. Lenchev (Compiler), St. Budurov (Ed.), University of Sofia Kliment Ohridski, Sofia, 1988, Chap. II.2.5, pp. 151–160 (in Bulgarian).
46. Tcholakova, I. F., A. G. Bakalova, M. G. Arnaudov, M. H. Karaivanova, B. V. Aleksiev.
New Biologically Active Complexes of Pt (II). Structure and Properties. Compt. Rend. Bulg.
Acad. Sci., 41, 1988, 45–48.
47. Arnaudov, M., Y. Dimitriev, V. Dimitrov, M. Dimitrova-Pankova, Ch. Petkov. IR-Spectral Investigation of Glasses of the TeO2-GeO2 System. Mater. Chem. and Phys., 21, 1989, 215–222.
48. Arnaudov, M. G., Vl. A. Diakovitch, L. M. Shishkova, M. B. Ilieva. Correlations between
IR-characteristic Frequencies and Solvent Parameters. 2. Empirical Parameters of Kamlet and
Taft. – In: Recent Developments in Molecular Spectroscopy, B. Jordanov, N. Kirov, P. Simova
(Eds.). World Scientific, Singapore–New Jersey–London–Hong Kong, 1989, pp. 107–120.
49. Dimitriev, Y., M. Arnaudov, V. Dimitrov, Ch. Petkov. IR-Spectral Study and Structure of Tellurite Glasses. – In: Disordered Systems and New Materials, M. Borisov, N. Kirov, A. Vavrek
(Eds.). World Scientific, Singapore–New Jersey–London–Hong Kong, 1989, pp. 530–538.
50. Tcholakova, I. F., A. G. Bakalova, M. G. Arnaudov, A. Florin, B. V. Aleksiev. Structure and Properties of New Complex Compounds of Pt(II). Compt. Rend. Bulg. Acad. Sci., 42, 1989, 73–76.
18
51. Dimitrova-Pankova, M., Y. Dimitriev, M. Arnaudov, V. Dimitrov. IR-Spectral Investigation of the Influence of Modifying Oxides on the Structure of Tellurite Glasses. Phys. Chem.
Glas., 30, 1989, 260–262.
52. Rogojerov, M. I., M. G. Arnaudov. Fourier Deconvolution of IR-Spectra Using a Reference
Band. Vibr. Sectrosc., 3, 1992, 239–244.
53. Rogojerov, M. I., M. G. Arnaudov. IR-LD Study of High-symmetry Molecules Dissolved in
a Liquid Crystal Solvent. I. Carbon Tetrabromide, J. Mol. Struct., 321, 1994, 147–155.
54. Rogojerov, M. I., M. G. Arnaudov. IR-LD Study of High-symmetry Molecules Dissolved in
a Liquid Crystal Solvent. II. Metal Hexacarbonyl Complexes M (CO) (M = Mo, Cr). J. Mol.
Struct., 321, 1994, 157–164.
55. Milanova, M., D. Todorovsky, M. Arnaudov, N. Minkova. The Possibility for Separation
of Lanthanium by Solid-State Complexes with 2-Ethylhexyl Phosphoric Acids. Separ. Sci.
Technol., 30, 1995, 821–832.
56. Milanova, M., D. Todorovsky, M. Arnaudov. Mixed Ligand Solid State Complexes of Cerium with bis-(2-ethylhehyl)-phosphoric Acid. J. Alloys Comp., 223, 1995, 118–121.
57. Arnaudov, M., Sh. Dinkov, L. Shishkova. IR-spectral Determination of the Degree of Oxyethylation in Nonylphenoxypoly-ethylene Glycols. Analytical Laboratory, 4, 1995, 18–22.
58. Milanova, M., D. Todorovsky, M. Arnaudov. Thermochemical Behaviour of Lanthanium Solid State Complexes with 2-Ethylhexyl-phosphoric Acids. J. Therm. Anal., 47, 1996 847–856.
59. Arnaudov M., M. Milanova and D. Todorovsky. IR-spectral Study of Lanthanium Solid
State Complexes with 2-Ethyl-hexyl-phosphoric Acids. Spectrosc. Lett., 29, 1996, 781–798.
60. Milanova, M., D. Todorovsky, M. Arnaudov. Yttrium Solid State Complexes Formation
in a Mixture of bis- and mono-(2-Ethylhexyl) Phosphoric Acids. Analytical Laboratory, 5,
1996, 94–97.
61. Arnaudov, M., M. Milanova, D. Todorovsky. Synthesis and IR-spectral Characterization of
Mixed Solid State Complexes of Some Lanthanoids with mono-(2-Ethylhexyl) Phosphoric
Acid. Spectrosc. Lett., 29, 1996, 1297–1305.
62. Arnaudova, R., T. Vladkova, M. Arnaudov. Influence of Oligoamide-phosphates on Some
Characteristics of Elastomer Compounds Based on NBR. KGK (Kautcshuk, Gummi, Kunststoffe), 49, 1996, 206–209.
63. Arnaudov, M. G., M. I. Rogojerov, L. G. Prangova. IR-Spectral Study of 4’-substituted
Thiobenzoates in Solution. Spectrosc. Lett., 30, 1997, 149–161.
64. Arnaudov, M., Sh. Dinkov, L. Shishkova, L. Pindeva, C. Petrov, E. Dobreva. IR- and UVSpectral Study of Palladium (II) Complexes with 2-Aminopyridine obtained in SulpuricAcid
and Alkaline Solutions. Spectrosc. Lett., 30, 1997, 1595–1607.
65. Dinkov, Sh., M. Arnaudov. IR- and UV-Spectral Study on the Mechanism of 2-Aminopyridine Complexation with Palladium(II). Spectrosc. Lett., 31, 1998, 529–546.
66. Milanova M.M., M. G. Arnaudov, M. M. Getsova, D. S. Todorovsky. Preparation and Characterization of Solid State Lanthanium-Titanium Citrate Complexes, J. Alloys Comp., 264,
1998, 95–103.
67. Arnaudov, M., M. Getsova, D. Todorovsky, M. Milanova. IR-spectral Study of the System Ethylene Glycol–Citric Acid. Analytical Laboratory, 2, 1998, 70–74.
68. Arnaudov, M., Sh. Dinkov. IR-Spectral Study of Self-Association Effects of 2-Aminopyridine in Solution. Spectrosc. Lett., 31, 1998, 1687–1703.
69. Arnaudov, M., Sh. Dinkov. IR-LD-Spectral Study of Self-Association Effects of 2-Aminopyridine. J. Mol. Struct., 476, 1998, 235–241.
70. Pavlova, M., M. Arnaudov, M. Draganova, Sh. Dinkov. Synthesis and Analysis of Blocked by
Phenol Urethanes. Analytical Laboratory, 4, 1998, 218–222.
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71. Sinclair, R.N., A. C. Wright, B. Bachra, Y. B. Dimitriev, V. V. Dimitrov, M. G. Arnaudov.
The structure of vitreous V2O5-TeO2. J. Non-Cryst. Solids, 232–234 (1998) 38–43.
72. Арнаудов, М. Г. Приложение на ефектите на средата в инфрачервения спектрален
анализ, Дисертация за присъждане на научната степен “доктор на химическите науки”
- Химически факултет, СУ “Св. Климент Охридски”). Институт по Обща и Неорганична
Химия - Българска Академия на Науките, София, 1999, с. 349
Arnaudov, M. G. Applications of the Medium Effects in the Infrared Spectral Analysis. Dissertation presented for obtaining the scientific degree “Doctor of Chemical Sciences”, D.Sc. – Faculty of
Chemistry, Sofia University). Institute of General and Inorganic Chemistry – Bulgarian Academy
of Sciences, Sofia, 1999, pp. 349.
73. Arnaudov, M., Sh. Dinkov. IR-LD-spectral Study of Self-association Effects of 2-Aminopyridine in Solution. J. Mol. Struct., 476, 1999, 235–339.
74. Dinkov, Sh., M. Arnaudov. IR-spectral Study of 2-Aminopyridine and Aniline Complexes
with Palladium(II). Spectrosc. Lett., 32, 1999, 165–180.
75. Getsova, M. M., D. S. Todorovsky, M. G. Arnaudov. Preparation and Characterization of
Yttrium-Titanium Citrate Complexes. Z. Anorg. Allg. Chem., 676 (2000) 1488–1492.
76. Arnaudov, M. Application of the Medium Effects to the Structural Analysis of Self- Associate
Systems by Means of Infrared Spectroscopy. Int. J. Vibr. Spectrosc., 5, 2001, 5–17.
77. Arnaudov M., Y. Dimitriev. Study of the Structural Transition in Binary Tellurite Glasses by
Means of Reduced IR-spectra. Phys. Chem. Glasses, 42, 2001, 99–105.
78. Arnaudov, M., V. Simeonov, R. Yontchev , St. Tsakovski. Cluster and Principal Component
Analysis of the Solvent Effects on the C=O-stretching Frequency of Acetophenone. Spectrosc.
Lett., 34, 2001, 93–107.
79. Arnaudov, M. G., B. Ivanova, L. Prangova . Linear-Dichroic Infrared Spectral and Theoretical
Analysis of Phenylthiolbenzoate. Bull. Chem. Technologists of Macedonia, 21, 2002, 151–155.
80. Kuleff, I., R. Djingova, M. Arnaudov, D. Gergova. Provinance Study of Iron Age Amber
from Bulgaria. In: Proc. Int. Symp. “Archaeometry, Budapest, 27 April - May 3, 1998. Archaeometry 98, E. Jerem, K. Biró (Eds.), Britain Archaeological Reports International Series 1043
(II) and Archaeolinqua Central European Series 1, Oxford, 2002, pp. 757–760.
81. Arnaudov, M., B. B. Ivanova, L. Prangova. Linear-Dichroic Infrared Spectral Analysis of
the Stereo Structures of 4’-cyanophenylthiolbenzoate. J. Mol. Struct., 661, 2003, 219–223.
82. Ivanova, B. B., A. Tchapkavov, M. G. Arnaudov, I. Petkov. IR-study of Photoinduced Tautomerization in 1,3-diphenyl-pyrazol-5-one. Centr. Europ. J. Chem., 1, 2003, 356–367.
83. Ivanova, B. B., M. G. Arnaudov. Theoretical Vibrational Assignment for Non-substituted and
4’-cyano- and 4’-methoxy-phenylthiolbenzoate. Centr. Europ. J. Chem., 2, 2003, 98–106.
84. Ivanova, B. B., M. G. Arnaudov, P. R. Bontchev. Linear-dichroic infrared spectral analysis of
Cu(I)-homocysteine complex. Spectrochim. Acta, Part A, 60, 2004, 855–862.
85. Arnaudov, M., Solid State Infrared Dichroic (IR-LD) Analysis of Samples Oriented as a Suspension in a Nematic Liquid Crystal. Bulg. Chem. Commn., 37, 2005, 283–288.
86. Arnaudov, M. G., B. B. Ivanova. The Effectiveness of the Reducing-difference Procedure as a
Tool for an IR-LD Spectra Interpretation of Solids. Bulg. Chem. Commun., 37, 2005, 283–288.
87. Arnaudov, M. G., B. B. Ivanova, Sh. G. Dinkov. A Linear Dichroic Infrared (IR-LD) Solid
State Spectral Study of 4-aminopyridine. Vibr. Spectrosc., 37, 2005, 145–147.
88. Ivanova, B. B., A. Chapkanov, M. G. Arnaudov, I. K. Petkov. IR-LD Spectral Study and ab
initio Calculations of 1-phenyl 3–substituted Pyrazol –5-ones. Struct. Chem., 16, 2005, 47–53.
89. Ivanova, B. B., M. G. Arnaudov, H. Mayer-Figge. Molecular Spectral Analysis and Crystal
Structure of 4-aminopyridinium Tetrachloropalladate(II) Complex Salt. Polyhedron, 24, 2005,
1624–1630.
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90. Arnaudov, M. G., B. B. Ivanova, St. T. Todorov, S. Io. Zareva. Reducing-difference Infrared Spectral Analysis of cis- and trans-configurated Lactams. Spectrochim. Acta, Part A, 63A,
2006, 491–500.
91. Ivanova, B. B., M. G. Arnaudov. Theoretical and Solid State Linear-dichroic Infrared Spectral Analysis of Aromatic Dipeptides and Their Protonated Forms. Prot. Pept. Lett., 13, 2006,
889–896.
92. Ivanova, B. B., M. G. Arnaudov. Solid State Linear-dichroic Infrared Spectral and Theoretical
Analysis of Methionine Containing Tripeptides. Spectrochim. Acta, Part B, 65A, 2006, 56–61.
93. Ivanova, B. B., M. G. Arnaudov, W. S. Sheldrick, H. Mayer-Figge. S-Phenyl 4-cyanothiobenzoate. Acta Crystallogr., E62, 2006, o3–o4.
94. Ivanova, B. B., M. G. Arnaudov, St. T. Todorov. Linear-dichroic Infrared and NMR Spectral
Analysis of Au3+-complex with the Tripeptide Glycyl-methionyl-glycine. J. Coord. Chem., 59,
2006, 1749–1755.
95. Ivanova, B. B., M. G. Arnaudov, St. Todorov, W. S. Sheldrick, H. Mayer-Figge. Structural
Analysis of the Tripeptide Glycyl-methionyl-glycine (H-Gly-Met-Gly-OH) and Its Hydrochloride. Struct. Chem., 17, 2006, 49–56.
96. Ivanova, B. B., D.L. Tsalev, M.G. Arnaudov. Validation of Reducing-Difference Procedure
for the Interpretation of Non-polarized Infrared Spectra of n-component Solid Mixtures. Talanta, 69, 2006, 822–828.
97. Koleva, B. B., E. N. Trendafilova, M. G. Arnaudov, W. S. Sheldrick, H. Mayer-Figge.
Structural Analysis of a Mononuclear Copper(II) Complex of 3-aminopyridine. Trans. Met.
Chem., 31, 2006, 866–873.
98. Ivanova, B. B., V. D. Simeonov, M. G. Arnaudov, D. L. Tsalev. Linear-dichroic Infrared
Spectroscopy – Validation and Experimental Design of the Orientation Technique as Suspension in Nematic Liquid Crystal. Spectrochim. Acta Part A, 67, 2007, 66–75.
99. Todorovsky, D. S., M. M. Getsova, M. M. Milanova, M. Kakihana, N. L. Petrova, M.
G. Arnaudov, V. G. Enchev. The Chemistry on the Processes Involved in the Production of
Lanthanide Titanates by the Polymerized Complex Method. Canadian J. Chem., 85, 2007,
547–559.
100. Chapkanov, A. G., B. B. Koleva, M. G. Arnaudov, I. K. Petkov. 1-phenyl-3-substitutedpyrazol-5-ones Tautomerism – Theoretical and Experimental UV Spectral Analysis. Photoinduced Products. Chem. Papers, 62, 2008, 1–8.
Prof. Dr. Dimiter L. Tsalev, DSc, C.M.
Chair of Analytical Chemistry,
Faculty of Chemistry,
University of Sofia
1, J. Bourchier blvd
1164 Sofia
14.05.09
21
22
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
LITERARY HERITAGE
BIBLIOGRAPHY OF PROFESSOR DSc. EMIL D. MANEV
Dedicated to the 70th anniversary of Prof. Emil D. Manev
Prof. Emil Deyanov Manev was born on 12th June 1939 in Sofia. In 1961 he has
graduated as diploma Chemist at Sofia University “St. Kliment Ohridski” (in Sofia).
In 1962 he was enrolled as an Assistant Professor at the Faculty of Chemistry of Sofia University. During the years 1966–1977 he was promoted to scientific positions
of Senior Assistant Professor (1966–1972), Chief Assistant Professor (1972–1977)
in the Department of Physical Chemistry. In 1986 he was habilitated as Associate
Professor of Physical chemistry, position held until 2002. In 2002 Dr. Emil Manev
became Full Professor in physical chemistry. He has defended a thesis for a Ph.D.
degree in 1973 and a second thesis for Doctor of Sciences (D.Sc.) in 2001.
Prof. E. Manev has lectured on varied courses at the University of Sofia.
To undergraduates in the Faculty of Chemistry:
“Physical Chemistry” and “Colloid Chemistry” to students in Chemistry
(1974–2007);
“Physical and “Colloid Chemistry” to the students in Chemistry and Physics
(1984–2007);
Physical and “Colloid Chemistry” to the students in Chemistry and Informatics (2004–2007);
Special Course on “Physical Chemistry of Liquid Surfaces” (1984–2007).
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To MSc students in the Faculty of Chemistry:
“Physic-chemical Problems of the Environmental Chemistry” (2002- till
present);
“Surfactants” (2004- 2009);
“Foams, Foamers and Antifoamers” (2004- 2009).
Prof. E. Manev has supervised 23 M.Sc. students, 5 individual postgraduate
students, and 2 PhD students.
At the Faculty of Biology he has lectured on Physical and “Colloid Chemistry” in 2001-2003.
Prof. E. Manev has also lectured in other universities in Bulgaria. Since 1995
in the Faculty of Natural Sciences of the Shumen University “Ep. Konstantin
Preslavski”:
Courses on “Physical Chemistry” and “Colloid Chemistry” to the students on
Chemistry.
Also: “Physical and Colloid Chemistry” to the students on “Chemistry and
Biology” and “Chemistry and Ecology”.
The Research accomplishments of prof. E. Manev cover the scientific area of
Physical Chemistry of Surfaces and Disperse Systems.
With the guidance of Alexei Scheludko, Emil Manev employed the so-called
dynamic method to determining the van-der-Waals component of the disjoining
pressure in thin foam films of aniline, benzene and chlorobenzene [3, 4, 6]. Together with I.B.Ivanov, B. Radoev and C. Vassilieff developed and tested the theory about the role of the surfactants in the regime of foam and emulsion film thinning (the Marangoni effect) [5, 13, 29-34]. He proved experimentally the theory
of Scheludko-Frij about the critical thickness of liquid film rupture [9, 11, 25, 50,
84, 100, 113]. E. Manev established the qualitatively different (from the Reynolds
equation) regime of thinning of the larger foam and emulsion films [44, 47, 48,
52, 95, 107] and (together with R. Tsekov and B. Radoev) offered a quantitative
explanation of the divergence, based on the inherent film thickness inhomogeneity
[80]. In the studies of equilibrium foam films stabilized with nonionic surfactants
E. Manev has established the correlation of the level of repulsive (positive) disjoining pressure with the surfactant adsorption, and the concentration of “black
spots” formation in particular [60, 63-68].
Up to now Emil Manev has been author and co-author of more than 110 scientific publications. His scientific results have been presented at 23 international
conferences. His papers have been citied over 800 times in the international scientific literature.
24
During his scientific career prof. E. Manev has successfully collaborated with
many scientists in Bulgaria and abroad. He has worked and specialized in a number of prestigious academic world centers:
• Great Britain (1968-69): Cambridge University (with prof. D. A. Haydon,
FRS) and Imperial College-London (with Dr. J. A. Kitchener);
• France (1976): Universitė Renė Descartes & Universitė Paris-Sud (with
prof. L. Ter-Minassian-Saraga;
• USA (1978-1981): Columbia University, New York (with prof. P. Somasundaran) and Illinois Institute of Technology, Chicago (with prof. D. Wasan);
• Germany (2000): Mining Academy-Freiberg (with Dr. H. J. Schulze);
• USA (2000-2001): University of California- Berkeley (with prof. C. Radke);
• The Netherlands (1989): Agricultural University, Wageningen with prof. J.
Liklema);
• Sweden (1989-1992): Institute for Surface Chemistry, YKI-Stockholm (with
prof. R. Pugh and prof. P. Claesson);
• Australia (2002, 2004, 2006): The University of Newcastle (with prof. A.
V. Nguyen).
Prof. E. Manev has been Member of the Faculty Council and Scientific Council of the Faculty of Chemistry, University of Sofia (1984-1989; 1996-2007);
Member of the Council on Education of the Faculty of Chemistry (1995-2003);
Member of the Attestation Commission of the Faculty of Chemistry (19841989; 2004-2007).
Complete bibliography of Professor E. D. Manev has been compiled and
given in chronological order below in this issue.
LIST OF SCIENTIFIC PUBLICATIONS
1.
2.
3.
4.
5.
6.
Platikanov, D., E. Manev. Investigation of Thin Liquid Films in another Liquid. Communications Phys. Chem., Bulg. Acad. Sci., 4, 185 (1964).
Platikanov, D., E. Manev. Study of Thin Liquid Films in another Liquid - a Model of Emulsions. Proc. 4th Intl. Cong. Surf. Active Subst. CID, Brussels, Gordon & Breach, London, 2,
1189 (1964).
Scheludko, A., D. Platikanov, E. Manev. Study of Disjoining Pressure in Thin Liquid Films.
Ann. Univ. Sofia, Fac. Chim., 59, 1 (1964/65).
Scheludko, A., D. Platikanov, E. Manev. Disjoining Pressure in Thin Liquid Films and the
Electromagnetic Retardation Effect on the Molecular Dispersion Interactions. Faraday Soc.
Discuss., 40, 253 (1965).
Radoev, B., E. Manev, I. Ivanov. On the Thinning of Liquid Films. Diffusion Kinetics. Ann.
Univ. Sofia, Fac. Chim, 60, 59 (1965/66).
Manev, E., M. Buleva. Neue Daten für den Einfluss der elektromagnetischen Verstätung aus
den Spaltdruck in Schaumfilmen. Abhandl. Deut. Akademie Wiss.Berlin, Klass Chemie, 6b,
557 (1966).
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7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
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E. Manev, M. Buleva. New Data about the Effect of Electromagnetic Retardation on the Disjoining Pressure in Aniline Films. Ann. Univ. Sofia, Fac. Chim., 62, 304 (1967/68).
Ivanov, I., B. Radoev, E. Manev, A. Scheludko. Theory of the Critical Thickness of Rupture of
Thin Liquid Films. Ann. Univ. Sofia, Fac. Chim., 62, 304 (1967/68).
Scheludko, A., E. Manev. Critical Thickness of Rupture of Chlorobenzene and Aniline Films.
Trans. Faraday Soc., 64, 1123 (1968).
Radoev, B., E. Manev, I. Ivanov. Effect of Surfactant Diffusion on The Rate of Drainage of
Microscopic Liquid Films. Ann. Univ. Sofia, Fac. Chim., (1968).
Scheludko, A., E. Manev. Critical Thickness of Rupture of Chlorobenzene and Aniline Films.
Commun. Chem. Sci., Bulg. Acad. Sci., 1 (2), 81, (1968).
Manev, E. Some Observations on the Formation of Polymolecular Adsorption Films on a
Solid Surface. Mineral Technology, London 39, 49 (1969).
Radoev, B., E. Manev, I.Ivanov. Geschwindigkeit der Verdünnung Flüssiger Filme. Kolloid Z.,
234(1), 1037 (1969).
Ivanov, I., B. Radoev, E. Manev, A. Scheludko. On the Theory of the Critical Thickness of
Rupture of Thin Liquid Films. Trans. Faraday Soc., 66, 1262 (1970).
Ivanov, I, B. Radoev, E. Manev, A. Scheludko. Comparison of the Theories of the Critical
Thickness of Rupture of Thin Liquid Films. Ann. Univ. Sofia, Fac. Chim., 64, 373 (1969/70).
Andrews, D.M., E.D. Manev, D.A. Haydon. Composition and Energy Relationships for Some
Thin Liquid Films and the Chain Comformation in Monolayers at Liquid-Liquid Interface.
Faraday Soc. Discuss. 1, 46 (1970).
Manev, E., A. Scheludko, V. Mavrodiev. Dependence of the Critical Thickness on Surfactant
Concentration for Foam Films of Fatty Acids Aqueous Solutions. Ann. Univ. Sofia, Fac. Chim.,
66, 303 (1971/72).
Manev, E., A. Scheludko, D. Exerowa. Crtitical Thickness of Rupture and of Black Spots Formation in Microscopic Aqueous Films. Commun. Chem. Sci., Bulgar. Academy Sci., 5, 585 (1972).
Manev, E., Chr. Vassilieff, I. Ivanov. Hydrodynamics of Thin Liquid Films - Effect of Surface
Diffusion. Ann. Univ. Sofia, Fac. Chim., 67, 169 (1972/73).
Manev, E., M. Kabakchieva, M. Ivanova. Investigation of Equilibrium Foam Films of Nitrobenzene. Ann. Univ. Sofia, Fac. Chim., 67, 273 (1972/73).
Manev, E., Chr. Vassilieff, I. Ivanov. Hydrodynamics of Thin Liquid Films - Effect of Surface
Diffusion. Ann. Univ. Sofia, Fac. Chim., 67, 169 (1972/73).
Manev, E., M. Buleva. Study of Binary Foam Films of Nitrobenzene-Hexane. Ann. Univ. Sofia,
Fac. Chim., 68, 32 (1973/74).
Manev, E.D., C.S. Vassilieff, I.B. Ivanov. Einfluss der Oberflächendiffision auf die Verdünnungsgeschwindigkeit von Schaumfilmen. Mitteilungsblatt der Chem. Geselsch., DDR 21, 6 (1974).
Manev, E. Study of Equilibrium Foam Films of Nitrobenzene. Proc. 4th Internl. Conference
Surface Activity, Berlin p.629 (1974).
Manev, E., A.Scheludko, D.Exerowa. Effect of the Surfactant Concentration on the Critical
Thickness of Rupture of Liquid Films. Colloid & Polymer Sci., 252, 586 (1974).
Traykov, T., E. Manev, I. Ivanov. Effect of Surfactant Concentration on the Hydrodynamic
Behavoiur of Emulsion Films. Ann. Univ. Sofia, Fac. Chim., 69, 32 (1974/75).
Ivanov, I., B. Radoev, D. Dimitrov, T. Traykov, E. Manev, Chr. Vassilieff. Hydrodynamics of
Thin Foam and Emulsion Films. Proc. Intl. Conference Surface Active Subst. IUPAC, Budapest 1, 583 (1975).
Yampolskaya, G. P., V. N. Izmailova, V. K. Mazo, E. D. Manev. Electroforeticал Study of
Small Plasma Albumine Complexes with Anionic Surfactant, Commun. Moscow State Univ.,
16/II/2, 211 (1975).
29. Vassilieff, Chr., E. Manev, Z. Abadjieva, I. Ivanov. Disjoining Pressure in Free Films of Hexadecane. Ann. Univ. Sofia, Fac. Chim., 70, 169 (1975/76).
30. Manev, E.D.: The Effect of Disjoining Presssure and Surfactant Diffusion on the Rate of Thinning of Aniline Foam Films. Ann. Univ. Sofia, Fac. Chim., 70, 97 (1975/76).
31. Manev, E.D., S. V. Sazdanova, C. S. Vassilieff, I. B. Ivanov. Hydrodynamics of Thin Liquid
Films. Effect of Surfactant on the Thinning of Microscopic Nitrobenzene Films. Ann. Univ.
Sofia, Fac. Chim., 71, 5 (1976/77).
32. Manev, E., Chr. Vassilieff, I. Ivanov. Hydrodynamics of Thin Liquid Films. Effect of Surface
Diffusion on the Rate of Thinning of Foam Films. Colloid & Polym. Sci., 254, 99 (1976).
33. Ivanov, I., T. Traykov, E. Manev. Hydrodynamics of Emulsion Films with Soluble Surfactants.
Proc. 7th Internl. Congress Surface Active Subst. Moscow, p. 183 (1976).
34. Traykov, T., E. Manev, I. Ivanov. Hydrodynamics of Emulsion Films. Experimental Investigation of the Effect of Surfactant Concentration on the Drainage of Emulsion Films. Intl. J.
Multiphase Flow, 3, 485 (1977).
35. Manev, E., J.-E. Proust, L. Terr-Minassian-Saraga. Study of Symmetrical and Asymmetrical
Equilibrium Films of Liquid Crystals. Colloid & Polymer Sci., 256, 1133 (1977).
36. Proust, J.-E., E. Perez, L. Terr-Minassian-Saraga, E. Manev. Structural Disjoining Pressure in
Thin Films of Liquid Crystals. Colloid & Polym. Sci., 256, 1003 –1004 (1977).
37. Manev, E., M. Buleva. Behaviour of Binary Free Liquid Films of Nitrobenzene-Hexane. Colloid & Polymer Sci., 257, 375 (1978).
38. Celik, M., A. Goyal, E. Manev, P. Somasundaran. The Role of Surfactant Precipitation and
Redissolution in The Adsorption of Sulfonate on Minerals. SPE Meetings, p.8263 (1979).
39. Manev, E., S. Sazdanova. Effect of Temperature on Precipitation and Redissolution of Surfactants in the Presence of Multivalent Metal Ions. Ann. Univ. Sofia, Fac. Chim., 74, 184
(1979/80).
40. Sazdanova, S.V., E.D. Manev. Precipitation and Micellar Redisolution of Sulphonates in the
Presence of Mono- and Multivalent Ions. Ann. Univ. Sofia, Fac. Chim., 75, 99 (1981).
41. Celik, M., E. Manev, P.Somasundaran. Sulfonate Precipitation-Redisolution-Represipitation
in Inorganic Electrolytes. Proc. 90th National AIChE Meeting, Houston, Paper 10a (1981).
42. Celik, M., K. P. Ananthapadmanabhan, P. Somasundaran, E. Manev. Mechanism of Dissolution of Calcium Sulfonates Precipitates by Micelles - Role of Counterion Binding. ACS 55th
Colloid Sci. Symposium, Cleveland, p. 25 (1981).
43. Rao, A.A., D.T. Wasan, E.D. Manev. Film Stability. Effect of the Liquid-Crystalline Phase on the
Drainage of Foam Films. Proc. 2nd Intern. Congress of Chem. Engineering, Montreal, p.1 (1981).
44. Manev, E. Study of Thickness Non-homogeneity and Rate of Thinning of Free Microscopic
Films. Ann. Univ. Sofia, Fac. Chim., 75, 174 (1981).
45. Radoev, B.P., A.D. Scheludko, E.D. Manev. Critical Thickness of Thin Liquid Films. Theory
and Experiment. Ann. Univ. Sofia, Fac. Chim., 75, 227 (1981).
46. Manev, E.D., M.S. Celik, K.P. Ananthapadmanabhan, P. Somasundaran. A Thermodynamic
Model of Redissolution of Calcium Sulfonate Precipitates in NaCl Solutions. SPE 4th Intl.
Symposium on Oilfield & Geothermal Chemistry, 43, 105 (1982).
47. Manev, E.D., D.T. Wasan, A.A. Rao. Foam Stability. Effect of Surfactant Composition on the
Drainage of Microscopic Aqueous Films. Chem. Eng. Communications, 15, 63 (1982).
48. Manev, E.D., S.V. Sazdanova, A.A. Rao, D.T. Wasan. Foam Stability. The Effect of LiquidCrystalline Phase on the Drainage and Transition Behaviour of Foam Films. J. Dispersion Sci.
& Technology, 3 (4), 435 (1982).
49. Manev, E.D., S.V. Sazdanova, D.T. Wasan. Multilayered Structuring in Foam and Emulsion
Films. Ann. Univ. Sofia, Fac. Chim., 76, 49 (1982).
27
50. Radoev, B., A. Scheludko, E. Manev. Critical Thickness of Thin Liquid Films. Theory and
Experiment. J. Colloid Interface Sci., 95, 254 (1983).
51. Manev, E.D., S.V. Sazdanova, D.T. Wasan. Stratification in Emulsion Films. J. Dispersion Sci.
& Technology, 5 (2), 111 (1984).
52. Manev, E.D., S.V.Sazdanova, D.T.Wasan. Emulsion and Foam Stability. The Effect of Film
Size on Film Drainage. J. Colloid Interface Sci., 97, 591 (1984).
53. Somasundaran, P., M.S. Chelik, A. Goyal, E.D. Manev. The Role of Surfactant Precipitation and
Redissolution in the Adsorption of Sulfonate on Milnerals. SPE Journal, 24 (2), 223 (1984).
54. Manev, E.D., R.A. Chapkanova. Dependence of the Rate of Thinning of Aniline and Nitrobenzene
Films on Their Radius and Surfactant Concentration. Ann. Univ. Sofia, Fac. Chim., 79, 3 (1985).
55. Manev, E.D. Dependence of the Critical Thickness of Aniline and Nitrobenzene Films on
Their Radius. Ann. Univ. Sofia, Fac. Chim., 79 (1985).
56. Vassilieff, C.S., E.D. Manev, I.B. Ivanov. Foam Film Drainage. Effect Surfactant Surface Diffusion on the Rate of Thinning, Proc. 6th Internl. Conference on Surface Active Subst. Badstuer’86, DAW Verlag (1987), p. 465.
57. Manev, E.D., S.D.Tchaliovska, J.C.Eriksson, B.P.Radoev. Study of the Interactions in Equilibrium Free Films from Aqueous Solutions of Dodecylammonium Chloride. Ann. Univ. Sofia,
Fac. Chim., 82 (1988).
58. Manev, E.D. Foam Films Stability - Dependence of the Critical Thickness on Film Size and
Surfactant Concentration. Proc. 5th Internl. Conference on Colloid Chemistry, Balatonfüred’88, Magyar Kémi, p.163 (1990).
59. Manev, E.D., R.A. Chapkanova. Thinning of Foam Films of Water/Glicol Mixtures of Different Composition. Ann. Univ. Sofia, Fac. Chim., 80, 106 (1991).
60. Manev, E.D., R.Pugh. Effect of Short-Chain Xanthate on Electrostatic Interactions and Equilibrium Thickness of Foam Films from Aqueous Solutions of Nonionic Frother. Surface and
Interface Analysis, 17, 681 (1991).
61. Manev, E.D., R.J. Pugh. Study of Drainage and Equilibrium Thickness of Single Foam Films
Containing Nonionic Frothers and aShort Chained Xanthate. Proc. Conference in Mineral
Technique, Luleå‘91 p. 111 (1991).
62. Pugh, R.J., E.D. Manev. The Study of Thin Aqueous Films as Models for Froths and Flotation.
Proc. NATO Conference on Advances in Flotation - Thessaloniki, May 1991, p.1
63. Manev, E.D., R.J. Pugh. The Diffuse Layer Electrostatic Potential and Stability of Thin Aqueous Films Containing a Nonionic Surfactant. Langmuir, 7, 2253 (1992).
64. Manev, E.D., R.J. Pugh. Drainage and Equilibrium Thickness of Aqueous Films Containing
Nonionic Frothers and Xanthate Collector. J. Colloid Interface Sci., 151, 505 (1992).
65. Pugh, R.J., E.D. Manev. Froth Stability in Aqueous Solutions of Non-ionic Surfactants and
Inorganic Electrolytes. J. Colloid Interface Sci., 152, 582 (1992).
66. Manev, E., R. Pugh. Frotter/Collector Interactions in Thin Froth Films and Flotation. Proc.
SME Annual Meeting, Feb.1992.
67. Manev, E., R.J. Pugh. Frother/Collector Interactions in Thin Froth Films and Flotation. Colloids and Surfaces, 70, 289 (1993).
68. Waltermo, Å., E. Manev, R. Pugh, P. Claesson. Foam Films and Surface Forces Studies in
Aqueous Solutions of Octyl-Glucoside. J. Dispersion Sci. Technology, 15(3), 273 (1994).
69. Tchaliovska, S., E.Manev, B.Radoev, J.C.Eriksson, P.Claesson. Interactions in Equilibrium
Free Films of Aqueous Dodecylammonium Chloride Solutions. J. Colloid Interface Sci., 168,
190 (1994).
70. Manev, E.D., S. Tchaliovska, J.C. Eriksson, P. Stenius. Study of the Stability of Free and Wetting Films on Mica from Aqueous Solutions of Dodecylammonium Chloride. Ann. Univ. Sofia,
Fac. Chim., 81, 165 (1994).
28
71. Manev, E.D.. Effect of Tetraalkylammonium Ions on Black Spots Formation is Aqueous Surfactant Films and the Related Foam Stability. Ann. Univ. Sofia, Fac. Chim., 88 (1995).
72. Vassilieff, C.S., E.D. Manev. Evolution of White Spots in Lipid Foam Black Films of DMPC.
Colloid & Polymer Sci., 273, 512-515 (1995)
73. Vassilieff, C.S., I. Panaiotov, E.D. Manev, J. Proust, Tz. Ivanova. Kinettics of Liposome
Desintegration from a Foam Films Studies. Effect of the Lipid Bilayer Phase State. Biophysical Chemistry, 58, 97 (1995).
74. Pugh, R.J., M.W. Rutland, E.D. Manev, P.M. Claesson. A Fundamental Study of Mica Flotation in Dodecylamine Collector. Progr. Colloid Polym. Sci., 98, 284-287 (1995).
75. Pugh, R. J., E. Manev. Nonionic Surfactant Monolayers. Tenside (Surfactants Detergents),
32(3), 278-284 (1995).
76. Pugh, R.J., M.W. Ruthland, E.D. Manev, P.M. Claesson. Dodecylamine Collector- pH Effect
on Mica Flotation and Correlation with Thin Aqueous Foam Film and Surface Force Measurements. Int. J. Mineral Process., 46, 245-262 (1996).
77. Waltermo, Å., P.M. Claesson, S. Simonsson, E. Manev, I. Johansson, V. Bergeron. Foam and
Thin-Liquid-Film Studies of Alkyl Glucoside Systems. Langmuir, 12(22), 5271-5278 (1996).
78. Pugh, R.J., M.W. Ruthland, E. Manev. Surface Force and Thin Aqueous Film Studies of Mica/
Dodecylammonium Flotation. Proc. 19th Int. Miner. Processing Congr.’ 95, SMME, Co, USA,
Vol.3, p. 73 (1997).
79. Manev, E., R. J. Pugh. The influence of tetraalkylammonium counter-ions on the drainage
and stability of thin films and foams stabilized by dilute aqueous solutions of sodium dodecyl
sulphate. J.Colloid Interface Sci., 186 (2), 493-497 (1997).
80. Manev, E., R. Tsekov and B. Radoev. Effect of Thickness Non-Homogeneity on the Kinetic
Behaviour of Microscopic Foam Films. J. Disper. Sci. Tech., 18, 769 (1997).
81. Tsekov, R., H.J. Schulze, B. Radoev, E. Manev. Linear Surface Waves on a Liquid-Vapour Interface: Role of Surfactant Permanent Dipole Moment. Colloids & Surf., 149, 475-479 (1998).
82. Manev, E.D., M. Sjoberg, M. Jonsson. Effect of Tetraalkylammonium Ions on Black Spots
Formation is Aqueous Surfactant Films and the Related Foam Stability. Ann.Univ. Sofia, Fac.
Chim., 88, 87 (2000).
83. Manev, E., S. Karakashev, A. Milushev. Influence of Some Organic and Inorganic Additives on the
Stability of Aqueous Tetraethyleneglycol-Octylether Foams. Bulg. Chem. Commun. , 32, 2 (2001).
84. Angarska, K., E.D. Manev. Effect of Surface Forces and Surfactant Adsorption on the Thinning and Critical Thickness of Foam Films. Colloids and Surfaces; A. Physicochemical and
Engineering Aspects, 190, 117 (2001).
85. Karakashev, S., R. Tsekov, E. Manev. Adsorption of alkali dodecylsulfates on air/water surface. Langmuir, 17, 5403 (2001).
86. Manev, E., S. Karakashev. Effect of Adsorption of Short-Chained Organic Ions on the Stability of Foam From Aqueous Solution of a Non-Ionic Surfactant. Ann. Univ. Sofia, Fac. Chim.,
92/93, 167 (2001).
87. Manev, E., S. Karakashev. Frothing Behaviour of Non-Ionic Surfactant Solutions in Presence
of Organic and Inorganic Electrolytes. J. Colloid Interface Sci., 235, 194 (2001).
88. Karakashev, S., E. Manev. On the Surface Interactions of the Adsorbed Nonionic Surfactant
Molecules. Ann. Univ. Sofia, Fac. Chim., 95, 12 9-134 (2002).
89. Karakashev, S., E. Manev. Effect of Interactions between the Adsorbed Species on the Propperties of Single and Mixed Surfactant Monolayers at the Air/Water Interface. J. Colloid Interface Sci., 248, 1-10, (2002).
90. Karakashev, S., E. Manev, G.Karakashev. Description of the Adsorption Behavior of Surfactant Species on Air/Water Interface. Bulg. Chem. Commun., 34, 32-49 (2002).
29
91. Angarska J., E. Manev. Thinning of microscopic foam films. Effect of the driving pressure,
Shumen University: Collection of Scientific works, Vol. Natural Sciences, p.132, 2002.
92. Karakashev, S., R. Tzekov, E. Manev. New model of adsorption of the adsorption behaviour of
ionic surfactants on the water/air interface, Shumen University: Collection of Scientific works,
Vol. Natural Sciences, p.146, 2002.
93. Karakashev, S., E. Manev. Adsorption of ionic surfactants on water/air interface, Shumen University: Collection of Scientific works, Vol. Natural Sciences, p.157, 2002.
94. Angarska, J.K., E.D. Manev. Effect of Тetrapentylammonium-Аdsrption on the Еlectrostatic
Interactions in Aqueous Octaethyleneglycol-Decylether Foam Films, Colloids and Surfaces,
A.: Physicochem. Eng. Aspects, 223, 73-82 (2003).
95. Angarska, J.K., E.D. Manev. Effect of the Driving Pressure on the Rate of Thinning of Microscopic Foam Films, Colloids and Surfaces, A.: Physicochem. Eng. Aspects, 223, 27-34 (2003).
96. Karakashev, S., E. Manev. Correlation in the Properties of Aqueous Single Films and Foam
Containing a Non-Ionic Surfactant and Organic/Inorganic Electrolytes. J. Colloid Interface
Sci., 259, 171-179, (2003).
97. Ангарска, Ж. и Е. Манев. Критична дебелина на тънък течен филм: сравнение между
теория и експеримент, Cборник научни трудове на Шуменския университет, Природни
науки - 2004.
98. Karakashev, S., E. Manev, A. Nguyen. Interpretation of negative values of the interaction parameter in the adsorption equation through the effects of surface layer heterogeneity. Advances
Colloid Interface Sci., 112, 31-36 (2004).
99. Karakashev, S.I., A.V. Nguyen, E.D. Manev, C.M. Phan. Surface Foam Films Waves Studied
with High-Speed Linescan Camera, Colloids & Surfaces, A 262, 23-32 (2005).
100. Angarska, J. and E. Manev. Critical Thickness of Thin Liquid Films: Comparison of Theory
and Experiment, Colloids & Surfaces, A 263/1-3 250-257 (2005).
101. Manev, E.D., and A.V. Nguyen. Critical Thickness of Microscopic Thin Liquid Films. Advances in Colloid and Interface Sci., 114-115, 133-146 (2005).
102. Manev, E.D., and A.V. Nguyen. Effects of Surfactant Adsorption and Surface Forces on Thinning and Rupture of Liquid Films. Int. J. Mineral Process. 77, 1-45 (2005).
103. Vasilieff, C.S., E.D. Manev, B.N. Nickolova. Experimental physicochemical hydrodynamics
of foam films. Effects of interfacial sources of surfactant molecules, Proc. 10th Jubilee National
Congress on Theoretical and Applied Mechanics (10th JNCTAM), Varna, Bulgaria, 13-16 September 2005; Vol.1, pp.612-617 (2005).
104. Radoev, B., E. Manev. Dynamic behaviour and stability of thin liquid films –Proc. 4th Eastern
Mediterranean Chemical Engineering Conference / EMCC4, 11-16 January 2006, Dead SeaIsrael рр.121-125 (2006).
105. Stubenrauch, C., D. Langevin, D. Exerowa, E. Manev, P. M. Claesson, L. B. Boinovich, R. v.
Klitzing. “Comment on “Hydrophobic Forces in the Foam Films Stabilized by Sodium Dodecyl
Sulfate: Effect of Electrolyte” and Subsequent Criticism”, Langmuir, 23, 12457-12460 (2007).
106. Karakashev, S.I., A.V. Nguyen, E. D. Manev. A novel technique for improving interferometric
determination of emulsion film thickness by digital filtration. Journal of Colloid and Interface
Science, 306, 449-453 (2007).
107. Angarska, J., C. Stubenrauch, E. Manev. Drainage of foam films stabilized with mixtures of nonionic surfactants. Colloids and Surfaces A: Physicochem. Eng. Aspects, 309 (2007) 189–197.
108. Angarska, J., D. Ivanova, E. Manev. Thinning of Foam Films Stabilized by Mixtures of Nonionic Surfactants, Ann. Konstantin Preslavski University, Shumen, Vol. XVII B 1, Natural
Sciences, pp. 69-82 (2007).
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109. Simulescu, V., J. Angarska, E. Manev. Kinetic Stability of Foam Films from Aqueous Solutions of Single and Mixed Nonionic Surfactants. Ann. Konstantin Preslavski University, Shumen, Vol.XVII B1, Natural Sciences, pp. 132-148 (2007).
110. Ангарска, Ж., Д. Иванова, Е. Манев. Влияние на нейонно ПАВ върху изтъняването на
пенни филми от n-додецил—малтозид. Ann. Konstantin Preslavski University, Shumen,
Vol. XVIII B2, Fac. Nat. Sciences, pp. 27-42 (2008).
111. Karakashev, S. I., E.D. Manev, R. Tsekov, A.V. Nguyen. Effect of ionic surfactants on drainage
and equilibrium thickness of emulsion films. J. Colloid Interface Sci., 318, 358–364 (2008).
112. Vassilieff, C.S., B.N. Nickolova, E.D. Manev. Thinning of Foam Films of Micellar Surfactant Solutions. 1. Nonionic surfactants C10H21(OC2H4)8OH and C12H25(OC2H4)8OH. Colloid &
Polym. Sci., 286, 475-480 (2008).
113. Simulescu, V., J. Angarska, E. Manev. Drainage and Critical Thickness of Foam Films from
Aqueous Solutions of Mixed Nonionic Surfactants. Colloids and Surfaces A: Physicochem.
Eng. Aspects, 319 (2008), 21–28.
114. Manev, E.D., S.V. Sazdanova, R. Tsekov, S.I. Karakashev, A.V. Nguyen. On the Adsorption
Behaviour of Ionic urfactants. Colloids and Surfaces A: Physicochem. Eng. Aspects, 319
(2008), 29–33.
115. Karakashev, S.I., E.D. Manev, A.V. Nguyen. Influence of Double-Layer Repulsion at Constant
Surface Charge on Foam Film Drainage. Colloids and Surfaces A: Physicochem. Eng. Aspects,
319 (2008), 34–42.
116. Vassileiff, C.S., B.N. Nickolova, E.D. Manev. Interfacial disintegration of Submicro- and
Nano-sized Amphiphilic Aggregates: Kinetic Foam Film Studies, (Proc. 9th Nat’l Workshop
“Nano-science and Nano-technology“, Sofia, 28-30 Nov. 2007). Nanoscience & Nanotechnology, 8 (2008), 227-230.
Prof. Boryan Radoev
University of Sofia
1164 Sofia
08.09.09
31
32
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
LITERARY HERITAGE
BIBLIOGRAPHY OF PROFESSOR DSc IVAN PANAYOTOV
Dedicated to the 70 th anniversary of Prof. Ivan Panayotov
Prof. Ivan Panayotov was born on 21 February
1940 in V. Tarnovo (Bulgaria). In 1964 he has graduated MSc in Chemistry at Sofia University “St. Kliment Ohridski”. He was enrolled as Assistant Professor (1964) and was habilitated as Associate Professor
(1979) and Full Professor (1989) of Physical chemistry in the Department of Physical Chemistry at the
Faculty of Chemistry of Sofia University. Prof. Panayotov is the founder and head of the Laboratory of
Biophysical Chemistry. He has Vice-Dean of the center of Biotechnology (1987−1990) and Dean of the
Faculty of Chemistry (1999−2003), Member of the
Council of the Faculty of Chemistry (1979−2010).
Member of the Academic Council of the University of Sofia (1999−2003), Member
of the Council of the Institute of Biophysics (1982−2010), Member of the State
Commission of Physical Chemistry (1987−2010), Member of the State Commission of Biophysics, Biochemistry and Molecular Biology (2006−2010). In 2004
Prof. Panayotov was appointed as President of the Bulgarian National Evaluation
and Accreditation Agency (NEAA) with a six years term of office.
Prof. Panayotov is author and co-author of more than 135 scientific publications in the field of Physical Chemistry of interfaces and disperse systems and
Biophysical Chemistry (dynamic phenomena at fluid interfaces; surface archeology; interfacial organization of photochemical and enzymatic reactions; micro−
33
and nanocapsules etc …) published in collaboration with leading bulgarian and
international laboratories and cited more than 900 times.
Prof. Panayotov is also author of more than 15 publications devoted to the
problems of the quality assurance of Higher education.
Prof. Panayotov spent many years as invited professor in french universities in Paris, Marseilles and Angers. He is member of the Chemical Society of
France (1975), expert in the nomination procedures for Nobel Prize in Chemistry
(2000−2003) member of the Steering Committee of the Central and Eastern European Network of the agencies for quality assurance CEEN (2006−2010), member
of the Editorial board of QA Review ARACIS, Bucharest etc … omplete bibliography of Prof. Ivan Panayotov has been compiled and given in chronological
order below in this issue.
LIST OF SCIENTIFIC PUBLICATIONS
1. Платиканов, Д., Ив. Панайотов. Метод за измерване на еластичността на адсорбционни
слоеве върху течни повърхности. Год. СУ., ХФ., 59, 1964/65, 219.
2. Platikanov, D., I. Panajotov, A. Scheludko. Über die Elastizität der Adsorptionsschichten bei
Lösungen von grenzflächenaktiven Stoffen, III Internationale Vortragstagung über Grenzflächenaktive Stoffe, Acad. Verlag, Berlin, 1966, 773.
3. Платиканов, Д., Ив. Панайотов. Еластичност на мономолекулни слоеве от неразтворими
вещества върху течнa подложка. Год. СУ., ХФ., 60, 1965/66, 85.
4. Панайотов, Ив., Д. Платиканов. Еластичност на адсорбционни слоеве на повърхността на
разтвори. Год. СУ., ХФ., 61, 1966/67, 203.
5. Platikanov, D., I. Panajotov. Elasticité des couches d’adsorption et d’étalement d’acides gras,
Proc. Vth Int. Congr.on Surface Activity, Barcelona, 1968, 361.
6. Панайотов, Ив., И. Иванов. Влияние на дифузионния обмен при промяна на повърхностната
концентрация на разтворими адсорбционни слоеве. Год. СУ., ХФ, 62, 1967/68, 121.
7. Platikanov, D., I. Panaiotov. Transformation de phase des couches monomoléculaires sur un
support liquide en couches polymoléculaires. Compt. Rend. de l, Acad. Bulg. Sci., 22, 1969,
N 10, 1141.
8. Панайотов, Ив., Й. Петров. Кинетика на адсорбцията на границата разтвор-въздух. I.
Теория. Год. СУ., ХФ., 63, 1968/69, 115.
9. Панайотов, Ив., Й. Г. Петров. Кинетика на адсорбцията на границата разтвор-въздух. II.
Експериментално изследване, Год. СУ., ХФ., 64, 1969/70, 385.
10. Панайотов, Ив. Влияние на холестерол върху свойствата на молекулни слоеве от лецитин,
Год. СУ., ХФ., 65, 1970/71, 309.
11. Panaiotov, I. Elasticité des films étalés monomoléculaires de L - α dipalmitillécithine et de
cholesterol., VI. Int. Congr. für Grenzildchenaktive Stoffe, Zürich, 1972, 123.
12. Петров, Й. Г., Ив. Панайотов, Сл. Чальовска, А. Шелудко. Пренос на адсорбционни слоеве
между течни и твърди повърхности. Изследване на системата кварц/воден разтвор на
додециламин. Год. СУ., ХФ., 66, 1971/72, 191.
13. Панайотов, Ив., М. Иванова. Метод за изследване на разпространението на деформации
на мономолекулни слоеве върху течна повърхност. Год. СУ., ХФ, 66, 1971/72, 335.
14. Панайотов, Ив., Д. Платиканов. I. Динамични свойства на неразтворими мономолекулни
слоеве върху течни повърхности. Год. Соф. Унив., Хим. фак., 67, 1972/73, 99.
34
15. Панайотов, Ив., Д. Платиканов. II. Динамични свойства на разтворими адсорбционни
слоеве на граница разтвор/въздух. Год. СУ., ХФ., 67, 1972/73, 109.
16. Георгиев, Г., Ив. Панайотов, Ек. Евтимова, Р. Матеева, Н. Хаджииванова. Динамични
свойства на монослоеве от алвеоларен сърфактант. Год. СУ., ХФ., 67, 1972/73, 121.
17. Панайотов, Ив., М. Иванова. Взаимодействие на яйчен албумин и L -α-дипалмитиллецитин
в смесен мономолекулен слой на течна подложка. Год. СУ., ХФ., 67, 1972/73, 265.
18. Петров, Й., Ив. Панайотов. Хистерезисни явления при преноса на монослоеве от течна
върху твърда повърхност. I. Поведение на линията на трифазен контакт при изграждане
на Лангмюир-Блоджетови мултислоеве. Год. СУ., ХФ., 68, 1973/74, 191.
19. Петров, Й.Г., Ив. Панайотов, Д. Платиканов. Хистерезисни явления при преноса на
монослоеве от течна върху твърда повърхност. II.Пренос на адсорбционни слоеве от
флотореагенти и хистерезисни отнасяния на трифазния контакт. Год. СУ., ХФ., 69,
1974/75, 27.
20. Mateeva, R., I. Panaiotov, M. Ivanova, E. Loshtilova, V. Prokopov, G. Georgiev. Measurement
of Dynamic Properties of Alveolar Surfactant Monolayers. Compt. rend. de l’Acad. bulg. Sci.,
28, 1975, N 9, 1223.
21. Panaiotov, I., M. Ivanova, D. Platikanov, A. Nikolov. Dynamic Properties of Monolayers of
PVAc at the air-water Interface. IV. Int. Taging uber Grenzfldchenaktive Stoffe, Acad. Verlag,
Berlin, 1975, p.455.
22. Панайотов, Ив., М. Иванова, Л. Сарага. Ролята на повърхностния вискозитет на
разширение при динамичните отнасяния на неразтворими монослоеве. Год. СУ., ХФ,
69, 1974/75, 7.
23. Panaiotov, I., M. Ivanova, R. Mateeva, G. Georgiev. Proprietés viscoélastiques des couches
monomoléculaires de L- α-dipalmitoyl lecithine et serum albumin. Proc. Int. Symp., Varna,
1976, 184.
24. Panaiotov, I., R. Stefanova, R. Mateeva, G. Georgiev. Proprietés dynamiques de couches monomoléculaires des lipides et du surfactant total alveolaire. Proc. Int. Symp., Varna, 1976, 128.
25. Димитров, Д.С., Ив. Панайотов. Хидродинамично взаимодействие между еластичен
неразтворим монослой и течна подложка при динамични измервания с лангмюирови
везни., Год. СУ., ХФ., 70, 1975/76, 103.
26. Димитров, Д.С., Ив. Панайотов. Теоретично изследване на динамичното двумерно
налягане при надлъжни деформации на неразтворими вискоеластични монослоеве. Год.
СУ., ХФ., 70, 1975/76, 115.
27. Иванова, М., Ив. Панайотов, П. Исаев. Експериментално изследване на динамичното
двумeрно налягане и динамичния повърхностен потенциал при надлъжни деформации на
монослоеве от поливинилацетат върху течна подложка. Год. СУ., ХФ., 70, 1975/76, 137.
28. Dimitrov, D.S., I. Panaiotov, P. Richmond, L. Ter-Minassian Saraga. Dynamics of Insoluble
Monolayers. I. Dilatational or Elastic Modulus, Friction Coefficient and Marangoni Effect for
Dipalmitoyllecithin Monolayers. J. Coll. Int. Sci., 65, 1978, N3, 483.
29. Panaiotov, I., D.S. Dimitrov, G. Georgiev. Viscoelastic Relaxation in Mixed Dipalmitoyllecithin/Serum albumin Monolayers Modeling the Lung Surface Film. Berlin, Studia Biophysica,
band 78 (2), 1980, 95.
30. Матеева, Р., Е. Лощилова, Ив. Панайотов, Г. Георгиев. Влияние на продължителната
хипероксия върху свойствата на монослой от липидите на алвеоларен сърфактант при
заек. Фтизиатрия, 4 (1978).
31. Панайотов, Ив., М. Иванова, Р. Мутафчиева, Г. Георгиев. Изследване на смесени
мономолекулни слоеве от L-α-дипалмитоиллецитин, свингомиелин и серумалбумин
като модели на адсорбционния монослой на границата въздух/течност на алвеоларната
мембрана. Год. СУ., ХФ., 71, 1976/77, 101.
35
32. Панайотов, Ив., Д.С. Димитров, М. Иванова. Изследване на динамичното повърхностно
напрежение при надлъжни деформации на разтворими адсорбционни слоеве. Год. СУ.,
ХФ., 71, 1976/77, 89.
33. Panaiotov, I., D.S. Dimitrov, M. Ivanova. Influence of Bulk to Surface Diffusion Interchange
on Dynamic Surface Tension Excess at Uniformly Compressed Interface . J. Coll. Int. Sci.,
69, 1979, 318.
34. Панайотов, Ив., Д.С. Димитров, М. Иванова, Св. Танева. Динамични отнасяния на
бинерни смеси от разтворими и неразтворими адсорбционни слоеве при надлъжни
деформации. Год. СУ., ХФ., 71, 1976/77, 27.
35. Panaiotov, I., D.S. Dimitrov, L. Ter-Minassian Saraga. Propagation of Longitudinal Deformations along Insoluble and Soluble Adsorption Layers. Ann. Univ. Sofia, Fac. Chim., 72,
1977/78, 81.
36. Panaiotov, I. Model Monomolecular Investigations of the Alveolar Surfactant. Ann. Univ.
Sofia, Fac. Chim., 72, 1977/78, 95.
37. Panaiotov, I., D.S. Dimitrov, L. Ter-Minassian Saraga. Dynamics of Insoluble Monolayers. II.
Viscoelastic Behaviour and Marangoni Effect for Mixed Protein Phospholipid Films. J. Coll.
Int. Sci., 72, 1979, N1, 49.
38. Saraga, L. Ter-Minassian, I. Panaiotov , J.S. Abitboul. Dynamics of Insoluble Monolayers. III. Dynamic Surface Potentials of Elastic and Viscoelastic Monolayers. J. Coll. Int. Sci., 72, 1979, N 1, 54.
39. Dimitrov, D.S., I. Panaiotov. Model Investigations of the Alveolar Surface. I. Elastic and Viscoelastic Behaviour of Dipalmitoyllecithin Monolayers at Small Deformations. Proc. IInd Int.
Symp., Varna (1979), p.19, Publ. House Bulg. Acad. Sci., Sofia (1980).
40. Taneva, S., D.S. Dimitrov, I. Panaiotov. Model Investigations of the Alveolar Surface. II. Surface Pressure Hysteresis of Monolayers of Dipalmitoyllecithin., Proc. IInd Int. Symp.”Lung
lipid metabolisms, mechanisms of its regulation and alveolar surfactant”, Varna (1979), p.27,
Publ. House Bulg. Acad. Sci., Sofia (1980).
41. Panaiotov, I., D.S. Dimitrov. Model Investigations of the Alveolar Surface. III. Viscoelastic
Behaviour and Surface Pressure Hysteresis of Serum Albumin Monolayers. Proc. IInd Int.
Symp.”Lung lipid metabolisms, mechanisms of its regulation and alveolar surfactant”, Varna
(1979), p.48, Publ. House Bulg. Acad. Sci., Sofia (1980).
42. Panaiotov, I., A. Bikov, S. Taneva, G. Georgiev. Model Investigations of the Alveolar Surface. IV.
Effects of Bulk-Surface Diffusion Interchange of the Surface Pressure of the Main Alveolar Surfactant Components. Proc. IInd Int. Symp.Lung lipid metabolisms, mechanisms of its regulation
and alveolar surfactant”, Varna (1979), p.54, Publ. House Bulg. Acad. Sci., Sofia (1980).
43. Mutafchieva, R., I. Panaiotov, D.S. Dimitrov, G. Georgiev. Model Investigations of the Alveolar
Surface. V. Equilibrium and Dynamic Properties of the Mixed Binary Monolayers formed
by Dipalmitoyllecithin, sphingomyelin and serum albumin. Proc. IInd Int. Symp.”Lung lipid
metabolisms, mechanisms of its regulation and alveolar surfactant”, Varna (1979), p.61, Publ.
House Bulg. Acad. Sci., Sofia (1980).
44. Panaiotov, I., D.S. Dimitrov, S. Taneva, R. Mutafchieva, P. Vassilev, G. Georgiev. Model Investigations of the Alveolar Surface. VI. Dynamic Behaviour of the Alveolar Lining Layer - “Plane
Surface Model”. Proc. IInd Int. Symp.”Lung lipid metabolisms, mechanisms of its regulation and
alveolar surfactant”, Varna (1979), p.67, Publ. House Bulg. Acad. Sci., Sofia (1980).
45. Vassilev, P., S. Taneva, I. Panaiotov, G. Georgiev. Dilatational viscoelastic Properties of Tubulin
and Mixed Tubulin-Lipid Monolayers. J. Coll. Int. Sci., 84, 1981, 169.
46. Димитров, Д.С., Ив. Панайотов, Цв. Иванова, Г. Георгиев. Релаксация на повърхностното
налягане на монослоеве от дипалмитоиллецитин. Год. СУ., ХФ, 72, 1977/78, 119.
47. Танева, С., Д.С. Димитров, Ив. Панайотов. Хистерезисни цикли на повърхностното
налягане на монослоеве от L-α-дипалмитоиллецитин. Год. СУ., ХФ., 73, 1978/79, 2, 155.
36
48. Hadjiivanova, N., K. Koumanov, I. Panaiotov, M. Ivanova. Insulin Effect on Some Biochemical
and Biophysical Characteristics of Lung Surfactant. Int. J. Biochem., 16, 1984, 195.
49. Panaiotov, I., A. Sanfeld, A. Bois, J.F. Baret. Influence of Desorption-Controlled Interchange
on Dynamic Surface Tension Axcess: Calculation of Kinetic Desorption Constant. J. Coll. Int.
Sci., 96, 1983, 315.
50. Sanfeld, A., M. Lin, A. Bois, I. Panaiotov, J.F. Baret. Mechanical and Electrochemical Effects on
Surface Convection and on Emulsification - new criteria. Adv. Coll. Int. Sci., 20, 1984, 101.
51. Sanfeld, A., M. Lin, I. Panaiotov, A. Bois, J.F. Baret. Effects méchaniques et électriques sur la
convection interfaciale et sur l’émulsification. C.R. Acad. Sci. Paris, 296, II (1984), 609.
52. Bois, A., I. Panaiotov, J.F. Baret. Relaxation in LE-LC Transition of Fatty Acid Monolayers.
Chemistry and Physics of Lipids, 34, 1984, 265.
53. Taneva, S., I. Panaiotov, L. Ter-Minassian Saraga. Effect of Surface Pressure on Mixed Dipalmitoyllecithin-Serum albumin Monolayer Composition. Colloids ans Surfaces, 10, 1984, 101.
54. Ivanova, M., I. Panaiotov, T. Trifonova, M. Echkenazi. Interaction of Antilipid A immunoglobulin G and Normal Immunoglobulin G Incorporated in Lipid A Monolayer. Colloids and
Surfaces, 10, 1984, 269.
55. Mutafchieva, R., I. Panaiotov, D.S. Dimitrov. Surface Pressure Hysteresis of Mixed Lipid/
Protein Monolayers: Applications to the Alveolar Dynamics. Zeitschrift fur Naturforschung,
Section C, 39 (9-10), 1984, 965.
56. Томова, Г., М. Кънчева, Ив. Панайотов. Растежна кинетика на микроорганизмова
популация Candida tropicalis при периодично култивиране бърху твърда хранителна
среда. Acta microbiologica Bulgarica, Bul. Acad., 15, 1984, 62.
57. Танева, Св., Ив. Панайотов. Дилатационни свойства на бинерен монослой от неразтворим
и разтворим компонент - адсорбционно-десорбционно определен обмен на молекули.
Год. СУ., ХФ., 78, N1, 1984, 8.
58. Kolev, V., Tz. Ivanova, I. Panaiotov, D. Kafalieva. Mixed Monolayers of β-caroten and α-Llecithin at the air-water Interface. Доклади на БАН, 38 N9, 1985, 1239.
59. Panaiotov, I., L. Ter-Minassian Saraga. Association of Vinblastine Sulphate to Phospholipid
Membrane Models. I. Vinblastine sulphate Penetration into Egg Lecithine Monolayers. A Surface Pressure Study (сборник посветен на проф. Отеро) Ed. Département de Chimie Physique de la Fac. Farm. de Madrid (1985).
60. Panaiotov, I., L. Ter-Minassian Saraga , G. Albrecht. Soluble Vinblastine Sulphate Penetration
into Insoluble Egg-Lecithin Monolayers. II. Surface Tension and Surface Pressure Studies.,
Langmuir, 1, 1985, 395.
61. Panaiotov, I., M. Ivanova - Dilatational Mechano-Chemical Properties of Lipid-Protein Monolayers., VI Internationale Tagung uber Grenzfldchenaktive Stoffe (22-27 april 1985), Bad Stuer, 357.
62. Stoitcheva, N., I.Tsoneva, D.S. Dimitrov, I. Panaiotov. Kinetics of Calcium - Induced Fusion
of Cellsize Liposomes with Monolayers in solutions of Different Osmolarity. Z. Naturforsch.,
40, 1985, 92
63. Ivanova, M., I. Panaiotov, M. Eshkenazy, R. Tekelieva, R. Ivanova. Interaction of Lipid A with
antilipid A Immunoglobulin G and Normal Immunoglobulin G in Mixed Monolayers. Colloids
and Surfaces, 17, 1986, 159.
64. Bois, A.G., M.G. Ivanova, I. Panaiotov. Marangoni effect and Relaxation of Surface Potential in
Pentadecanoic Acid and Octadecanol Monolayers. Langmuir, 3, 1987, 215.
65. Танева, Св., Ив. Панайотов. Состояние и продольньiе динамические свойства смешенньiх
мономолекулярньiх слоев из холестерина и дипальмитоиллецитина на границе раздела
вода/воздух. Год. СУ., ХФ., 82, 1988, 51.
66. Bois, A., J.F. Baret, V. Kulkarni, I. Panaiotov, M. Ivanova. Relaxation of Surface Pressure and
Surface Potential in 12-Hydroxystearic Acid Alkil Ester monolayers. Langmuir, 4, 1988, 1358.
37
67. Ivanova, Tz., G.Georgiev, I. Panaiotov, M. Ivanova, M.A. Surpas, J. Proust, F. Puisieux. Behaviour of liposomes prepared fron lung surfactant analogues and spread at the air-water interface.
Prog. Coll. Polym. Sci., 79, 1989, 24.
68. Ivanova, M., I.Panaiotov, A.Bois, Y. Gargouri, R.Verger. Inhibition of Pancreatic Lipase by
ovalbumin and β-lactoglobulin A at the air-water interface. J. Coll. Int. Sci., 136, 1990, 363.
69. Ivanova, M., R.Verger, A.Bois, I.Panaiotov. Proteins at the air-water interface and their inhibitory effects on enzyme lipolysis. Coll. and Surf., 54, 1991, 279.
70. Panaiotov, I., S.Taneva, A.Bois, F. Rondelez. Photoinduced dilatational motion in monolayers
of poly (methylmethacrylate) having benzospiropyran side groupe. Macromolecules, 24 (15),
1991, 4250.
71. Ivanova, Tz., I.Panaiotov, G.Georgiev, M.A.Launois-Surpas, J.E.Proust and F.Puisieux. Surface pressure-area hysteresis of surface films formed by spreading of phospholipid liposomes.
Colloids & Surfaces, 60, 1991, 263.
72. Vassilieff, C., I.Momtchiliva, I.Panaiotov, Tz.Ivanova. Thinning of foam films of liposomal
suspensions. Communications of the Bulgarian Academy of Sciences, 24 (4), 1991, 519.
73. Ivanova, Tz., I.Panaiotov. The kinetics of surface film formation from small unilamellar liposomes spread or adsorbed at the air-water interface. Communications of the Bulgarian Academy of Sciences, 24, 1991, 590.
74. Launois-Surpas, M.A., Tz.Ivanova, I.Panaiotov, J.E.Proust, F.Puisieux, G.Georgiev. Behavior
of pure or mixed DPPC liposomes spread or adsorbed at the air-water interface. Colloid &
Polymer Sci., 270, 1992, 901.
75. Panaiotov, I., Tz.Ivanova, A.Sanfeld. Interfacial orientation of DOPC liposomes spread at the
air-water interface. Advances in Colloid and Interface Sciences, 40, 1992, 147.
76. Ivanova, Tz., V.Raneva, I.Panaiotov, R.Verger. Kinetics of spreading of DOPC liposomes at
the air-water interface subjected to pospholipase A2 hydrolysis. Colloid Polymer Sci., 271,
1993, 290.
77. Panaiotov, I., J.E.Proust, V.Raneva, Tz.Ivanova. Kinetics of spreading at the air-water interface
of dioleoylphosphatidylcholine liposomes influenced by photodynamic lipid peroxidation.
Thin Solid Films, 244, 1994, 845-851.
78. Raneva, V., Tz.Ivanova, I.Panaiotov. Lipolytic hydrolysis of medium and long chain phosphatidylcholine monolayers under barostatic conditions. Ann. Univ. Sofia, Fac.Chem., 87, 1994, 99.
79. Raneva, V., Tz.Ivanova, G.Lazarova, J.E.Proust, I.Panaiotov. Kinetic of spreading of photodamaged DOPC liposomes at the air-water interface. Colloid and Polymer Sci., 273, 1995, 150.
80. Boury, F., Tz.Ivanova, I.Panaiotov, J.E.Proust, A.Bois, J.Richou. Dynamic Properties of
Poly(D,L lactide) and Polyvinyl Alcohol Monolayers at the air/water and at Dichloromethane/
Water interfaces. J.of Coll. Int. Sci., 169, 1995, 380.
81. Boury, F., Tz.Ivanova, I.Panaiotov, J.E.Proust. Dilatational Properties of Poly (D,L lactic acid) and
Bovin Serum Albumin Monolayers spread at the air/water interface. Langmuir, 11, 1995, 599.
82. Boury, F., Tz.Ivanova, I.Panaiotov, J.E.Proust, A.Bois, J.Richou-Dilatational Properties of Adsorbed Poly (D,L lactide) and Bovine Serum Albumin Monolayers at the Dichloromethane/water interface. Langmuir, 11 (5), 1995, 1636.
83. Boury, F., Tz. Ivanova, I. Panaiotov, J. Proust. Dilatational properties of Poly (D,L-lactic acid)
and Bovine Serum Albumin monolayers formed from spreading an oil-in water emulsion at the
air/water interface. Langmuir, 11, 1995, 2131.
84. Panaiotov, I., Tz.Ivanova, K.Balachev and J.E.Proust. Spreading kinetics of dimyristoylphosphatidylcholine liposomes at the air/water interface below and above the main phase-transition
temperature. Coll.and Surf. B:Biointerfaces, 102, 1995, 159.
38
85. Raneva, V., Tz.Ivanova, R.Verger, I.Panaiotov. Comparative kinetics of phospholipase A2 action
on liposomes and monolayers of phosphatidylcholine spread at the air-water interface. Coll.
and Surfaces B: Biointerface, 3, 1995, 357.
86. Raneva, V., M.Ivanova, Tz.Ivanova, E.Rogalska, R.Verger, I.Panaiotov. Kinetics of the spreading of IntralipidTM emulsions at the air-water interface. Coll. and Surf. B: Biointerface, 4,
1995, 213.
87. Bois, A., I. Panaiotov. Nonsteady effects due to a small surface pressure perturbation in an
elastic insoluble monolayer. J.Coll.Int.Sci., 170, 1995, 25.
88. Proust, J.E., I Panaiotov, F. Boury, Tz. Ivanova. A study of structural properties (AFM) of
mixed Polymer Monolayers in Relation with its viscoelastic properties. Journal of Trace and
Microprobe Techniques., 13, N3, 1995, 367.
89. Vassilieff, C., I.Panaiotov, E.D. Manev, J.E.Proust and Tz.Ivanova. Kinetics of liposome desintegration from foam film studies: Effect of the lipid bilayer phase state. Biophysical Chemistry., 58, 1996, 97.
90. Panaiotov, I., Tz. Ivanova, J.Proust, F Boury, B. Denizot, K. Keough, S Taneva. Effect of hydrophobic protein SP-C on structure and dilatational properties of the model monolayers of
pulmonary surfactant.. Coll. & Surf. B: Biointerfaces, 6, 1996, 243.
91. Doisy, A., J.E.Proust, Tz.Ivanova, I.Panaiotov and J.L.Dubois-Phospholipid/Drug Interaction in
Liposomes Studied by Rheological Properties of Monolayers, Langmuir, 12 (25) (1996) 6098.
92. Ivanova, M., Tz. Ivanova, R. Verger, I. Panaiotov. Hydrolysis of monomolecular film of long
chain phosphatidylcholine by phospholipase A2 in the presence of β - cyclodextrin. Coll. and
Surfaces B:Biointerfaces, 6, 1996, 9.
93. Balashev, K., I. Panaiotov, J.E. Proust. Propagation of photoinduced surface perturbation along
a mixed benzospiripyran-octadecanol monolayer. Langmuir, 13, (20), 1997, 5373.
94. Balashev, K., A.Bois, J.E.Proust, Tz. Ivanova, I.Petkov, S.Masuda, I.Panaiotov. Comparative
study of polyacryloylacetone monolayers at Dichloromethane-Water and Air-Water interfaces.
Langmuir, 13 (20), 1997, 5362.
95. Balashev, K., I.Panaiotov, M. Ivanova, I.Petkov, J.E.Proust, F. Boury, S. Masuda. Influence of
pH and presence of Ca++ ions on the properties of polyacryloylacetone (PAA) monolayers. J.
of Disperssion Sci. and Tech., 18 (6&7), 1997, 661.
96. Ivanova, Tz., I. Panaiotov, F. Boury, J.E. Proust, J.P. Benoit, R. Verger. Hydrolysis kinetics of
poly(D,L-lactide) monolayers spread on basic or acidic aqueous subphases. Coll. and Surfaces
Biointerfaces, 8, 1997, 217.
97. Ivanova, Tz., I. Panaiotov, F. Boury, J.E. Proust, R. Verger. Enzymatic hydrolysis of poly(D,Llactide) spread monolayers by cutinase. Coll. and Polym. Sci., 275, 1997, 449.
98. Ransac, S., M. Ivanova, R. Verger, I. Panaiotov. Monolayer techniques for studying lipase kinetics , “ Methods in Enzymology”, vol. 286, 1997, 263
99. Ivanova, M., R. Verger, I. Panaiotov. Mechanisms underlying the desorption of long chain
lipolytic products by cyclodextrins: application to lipase kinetics in monolayers. Coll. and
Surfaces B: Biointerfaces, 10, 1997, 1.
100. Panaiotov, I., M. Ivanova, R. Verger. Interfacial and temporal organization of enzymatic lipolysis. Current Opinion in Colloid & Interface Sci., Vol. 2 (5), 1997, 517.
101. Proust, J.E., F. Boury, P. Saulnier, J.P. Benoit, I.Panaiotov, Tz. Ivanova. Structure, morphology
and degradation of poly (α-hydroxy acid)s microspheres in relation with monolayer. Current
Topics in Coll. & Int. Sci., 1, 1997, 195.
102. Balashev, K., I. Panaiotov, I. Petkov. Interfacial photochemical tautomerization in polyacryloyl
acetone monolayers. Coll. Polym. Sci., 276 (8), 1998, 984.
103. Ransac, S., M. Ivanova, R. Verger, I. Panaiotov. Monolayers Thechniques for studing Lipase
Kinetics. Methods in Molecular Biology, vol. 109, 1998, 279.
39
104. Boury, F., P. Saulnier, J.E. Proust, I. Panaiotov, Tz. Ivanova, C. Postel, O. Abillon. Characterization
of the Morphology of poly (α-hydroxy acid)s Langmuir-Blodgett Films by Atomic Force Microscopy Measurements. Coll. and Surfaces A: Phys. Chem. Engineer. Asp. , 155, 1999, 117.
105. Ivanova, Tz., N. Grozev I. Panaiotov, J.E. Proust. Role of the molecular weight and the compozition on the hydrolysis kinetics of monolayers of poly(α-hydroxy acid)s. Coll. Polym. Sci,
277, 1999, 709.
106. Панайотов, Ив. Увод в биофизикохимията. Наука и изкуство, 1982; Унив. изд., 2000.
107. Panaiotov, I. Continuous compression of single-component monolayers at air-water interface.
Ann. Univ. Sofia, Fac. Chem., 88, 2000, 121-143.
108. Ivanova, M., Tz. Ivanova, I. Panaiotov. Organization of enzymatic catalyse and photoperoxidation reactions at the interface. Ann. Univ. Sofia, Fac. Chem., 88, 2000, 145.
109. Panaiotov, I., R. Verger. Enzymatic reactions at the interface. - In: Physical Chemistry of
Biological Interfacers, W. Norde, A. Baszkin (Eds.), Elzevier, 2000, 359.
110. Ivanova, M., A. Svendsen, R. Verger, I. Panaiotov. Hydrolysis of 1,2-rac-dicaprin monomolecular films by Humicola lanuginosa lipase, as reflected in the surface potential. Coll. And
Surfs B : Biointerfaces, 19, 2000, 137.
111. Balashev, K., N. Panchev, I. Petkov, I. Panaiotov. Photochemical behaviour of polyacryloylacetone and polyethylacrylacetate monolayers at the air-water interface. Coll. Polym. Sci., 278,
2000, 301.
112. Ivanova, Tz., I. Panaiotov, F. Boury, P. Saulnier, J.E. Proust. Role of the electrostatic interaction on the basic or acidic hydrolysis kinetics of poly(D,L-lactide) monolayers. Coll. and
Surfaces B: Biointerfaces, 17, 2000, 241.
113. Ivanova, Tz., A. Svendsen, R. Verger, I. Panaiotov. Enzymatic hydrolysis by Humicola lanuginosa lipase of poly (lactic acid) – poly(glicolic acid) monolayers. Coll. Polym. Sci., 278,
2000, 719.
114. Zheliaskova, A., I. Peeva, K. Balachev, I. Panaiotov, A.G. Petrov. Photoconductance Effects in
Bilayer Lipid Membranes, Containing Amphiphilic Hexadecylbenzospiropyrane Derivatives.
Mol. Crys. Liq. Cryst., 352, 2000, 471.
115. Ivanova, Tz., P. Saulnier, A. Malzert, F. Boury, J. E. Proust, I. Panaiotov. Basic and enzymatic
hydrolysis in mixed polyethylene glycol/ poly(D.L-co-glycolide) films spread at the air-water
interface. Coll. and Surf. B: Biointerfaces, 23, 2002, 7.
116. Saulnier, P., F. Boury, A. Malzert, B. Heurtault, Tz. Ivanova, A. Cagna, I. Panaiotov, J. E.
Proust. Rheological Model for the study of dilational properties of monolayers.Comportment
of DPPC at the DCM/Water interface under conditions or sinusoidal perturbations. Langmuir,
17, 2001, 8104.
117. Ivanova, A., A. Tadjer, B. Radoev, I. Panaiotov. A Theoretical study of model lipid monolayers,
SAR and QSAR in Environmental research. 13(2), 2002, 237.
118. Grozev, N., A.Svendsen, R.Verger, I.Panaiotov. Enzymatic hydrolysis by Humicola lanuginosa lipase of polycaprolactonе monolayers. Colloid Polym. Sci., 280, 2002, 7.
119. Ivanova, M., A. Svendsen, R. Verger, I. Panaiotov. Action of Humicola lanuginisa lipase on
long-chain lipid substrates : 1. Hydrolysis of monoolein monolayers. Coll. and Surfaces B :
Biointerfaces, 26, 2002, 301
120. Grozev, N., V. Aguié-Béghin, Tz. Ivanova, S. Baumberger, B. Cathala, R. Douillard, I. Panaiotov. State, electrical and rheological properties of model and dioxan isolated lignin films at the
air-water interface. Coll. and Polym. Sci., 280, 2002, 798.
121. Hambardzumyan, A., V. Aguié-Béghin, I. Panaiotov, R. Douillard. Effect of Frequency and Temperature on Rheological Properties of Casein Adsorption Layers. Langmuir, 19(1), 2003, 72.
40
122. Ivanova, Tz., A. Malzert, F. Boury, J. E. Proust, R. Verger, I. Panaiotov. Enzymatic hydrolysis
by cutinase of PEG-co PLA copolymers spread monolayers. Coll. and Surfaces B : Biointerfaces, 32, 2003, 307.
123. Malzert, A., F.Boury, P.Saulnier, Tz.Ivanova, I.Panaiotov, J.P.Benoit, J.E. Proust. Interfacial
propreties of adsorbed films made of a PEG2000 and PLA50 mixture or a copolymer at the
dichloromethane -water interface. J. of Coll.and Int. Sci., 259, 2003, 398.
124. Ivanova, M., A. Detcheva, R. Verger, I. Panaiotov. Action of Humicola lanuginisa lipase on
long-chain lipid substrates : 2. Hydrolysis of diolein monolayers. Coll. and Surfaces B : Biointerfaces, 33(2), 2004, 89.
125. Grozev, N., V. Aguié-Béghin, B. Cathala, R. Douillard, I. Panaiotov. Kinetics and layer organization during the polymerization of coniferyl alcohol at the air-water interface. Coll. Polym.
Sci., 282, 2004, 429.
126. Grozev, N., I. Panaiotov. Dilatational behavior of monolayers undergoing relaxation processes
with different characteristic times. Ann. Univ. Sofia, Fac.Chem., 96, 2004, 213.
127. Ivanova, Tz., I. Minkov, I. Panaiotov, P. Saulnier, J.E. Proust. Dilatational properties and
morphology of surface films spread from clinically used lung surfactants. Colloid Polym. Sci.,
282, 2004, 1258-1267.
128. Minkov, I., J. Proust , P. Saulnier , Tz. Ivanova , I. Panaiotov. Behaviour of lipid nanocapsules
of a novel class at air – water interface, Nanoscience&Nanotechnology 4, E. Balabanova, I.
Dragieva (Eds.), Heron Press, Sofia, 2004, 284.
129. Alahverdjieva, V., M. Ivanova, R. Verger, I. Panaiotov. A kinetic study of the formation of βcyclodextrin complexes with monomolecular films of fatty acids and glycerides spread at the
air/water interface. Colloids and Surfaces B: Biointerfaces, 42(1), 2005, 9-20.
130. Minkov, I., Tz. Ivanova, I. Panaiotov, J. Proust, P. Saulnier. Reorganisation of lipid nanocapsules at air-water interface: 1. Kinetics of surfac film formation. Colloids and Surfaces B:
Biointerfaces, 45, 2005, 14-23.
131. Minkov, I., Tz. Ivanova, I. Panaiotov, J. Proust, P. Saulnier. Reorganisation of lipid nanocapsules at air-water interface: 2. Properties of the formed surface film. Colloids and Surfaces B:
Biointerfaces, 44, 2005, 197-123.
132. Minkov, I., Tz. Ivanova, I. Panaiotov, J. Proust, R. Verger. Reorganisation of lipid nanocapsules at air-water interface: 3. Action of hydrolytic enzymes HLL and PLA2. Colloids and
Surfaces B: Biointerfaces, 45, 2005, 23-34.
133. Minkov, I., Tz. Ivanova, I. Panaiotov, J. Proust, P. Saulnier. Role of the lipid content on the interfacial stabilisation of lipid nanocapsules. Nanoscience&Nanotechnology, 5, E. Balabanova,
I. Dragieva (eds.), Heron Press Sci. Series, Sofia, 2005, 250-253.
134. Ivanova, Tz., K. Mircheva, G. Dobreva, I. Panaiotov, J.E. Proust, R. Verger. Action of Humicola lanuginosa lipase on mixed monomolecular films of tricaprylin and polyethylene glycol
stearate. Colloids and Surfaces B: Biointerfaces, 63, 2008, 91–100.
135. Mircheva, K., I. Minkov, Tz. Ivanova, I. Panaiotov, J.E.Proust, R. Verger. Comparative study
of lipolysis by PLA2 of DOPC substrates organized as monolayers, bilayer vesicles and nanocapsules. Colloids and Surfaces B:Biointerfaces, 67, 2008, 107-114.
136. Minkov, I., Tz. Ivanova, I. Panaiotov, J.E. Proust, P. Saulnier. Kinetics of reorganization of
lipid nanocapsules at air–water interface. Ann. Univ. Sofia, Fac.Chem., 101, 2009, 45-57.
41
Selected publications and contributions in the field of Quality
Assurance (QA) in Higher Education (HE)
1. Panayotov, I. The University Idea during the Centuries. Nauka (Science), Sofia, 4, 2003, 6 (in
Bulg.).
2. Panayotov, I. NEAA approach of QA in HE. – In: Seminar “Cooperation between accreditation
agencies, 14-16 February, 2005, Warsaw (Poland).
3. Panayotov, I. Doctoral studies in Bulgaria in the context of the Eastern European countries. – In:
Seminar ‘Doctoral studies in the European Higher Education Area”, 23-24 March, 2006, Murcia
(Spain).
4. Panayotov, I. Institutional evaluation and accreditation in Bulgaria. – In: Int. Conference “Institutional Evaluation in the European Higher Education Area”, 14-16 June, 2006, Sofia.
5. Panayotov, I. Evaluation and Accreditation of HE Institutions in Bulgaria, 2nd Athens Int. Conf.
on University Assessment, 12-14 October, 2007. – In: QA in HE – An Antology of Best Practice,
Hellenic American Union, 2008, 149.
6. Panayotov, I. – “Assessment of research activity in the procedures of the NEAA (in Bulgarian)”
in Assessment in Science”, ed. by V. Prodanov, Marin Drinov Academic publishing House, Sofia
(2007) 149.
7. Panayotov, I. Formation doctorale en Bulgaria dans le contexte européen, Conférence internationale” L’enseignement supérieur en Europe”, 8-9 juin 2007, Sofia.
8. Panayotov, I. National system of HE-how to face the global challenges (in Russian). – In: Accreditation of HE (Akkreditatsia v obrasovanii), Iochkar-Ola (Russia), N 20, February, 2008, 20.
9. Golovinsky, E., I. Tchorbadjisky, I. Panayotov. 10 Jahre Akkreditierung der Hochschulausbildung in Bulgarien” (in German). – In: “Forschung in Bulgarien and Rumänien – Probleme und
Perspektiven nach dem EU-Beitritt”, Humboldt – Kolleg 30 November 2007, Sofia, Craft House
Bulgaria Ltd, Sofia (2008) 43.
10. Panayotov, I. Evaluation of Master and Doctoral Programmes (in Bulg.), National Forum of
Science, 27-29 April 2009, ed. by Union of Scientists in Bulgaria, Sofia, 2009, 186.
Prof. B. Radoevq PhD, DSc
University of Sofia
1164 Sofia
26.04.2010
42
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
LITERARY HERITAGE
BIBLIOGRAPHY OF PROFESSOR DSc. STOYAN ALEXANDROV
Dedicated to the 70th anniversary of Prof. Stoyan ALEXANDROV Nedeltchev
Stoyan ALEXANDROV Nedeltchev was born on 11 September 1940 in Strazha, Targovishte District. He is a graduate of the Faculty
of Chemistry, “St. Kliment Ohridski” University of Sofia
(1966). In 1973 he has defended a Ph.D. thesis in the field
of radiochemistry entitled “Study of the Separation of the
Noble Metals Using Some Sulphides by the Radioactive
Indicator Method” as a post graduate student at the Department of Chemistry, University of Moscow, Russia. Dr. Alexandrov defended a D.Sc. thesis in the field of Analytical
Chemistry on “Separation and Preconcentration by Using
of Some Low Soluble Inorganic Sulphides, Chlorides and
Oxides and Development of Combined and Hydrid Methods for Anaysis” in 1989
in Sofia. He has been lecturing and specializing in the field of analytical chemistry
and radiochemistry in Laboratoire Pierre Sue, C.E.N. Saclay, France (6 months in
1970), Faculty of Chemistry, Moscow State University, Russia (4 months in 1971)
and University of Batna, Algerie (1978–1981).
Mr. Stoyan Alexandrov has been Assistant Professor of Analytical Chemistry
(1966–1980), Associate Professor (1980–1990) and Full Professor of Analytical
Chemistry (from 1990 until his retirement in 2008). He has served as a Head of
the Chair of Analytical Chemistry (1982–1991) and Deputy Dean of the Faculty
of Chemistry. During the period 1986–1990 Prof. Alexandrov has been member
of the Specialized Scientific Council on Inorganic and Analytical Chemistry.
43
Scientific research of Professor Alexandrov has been mailly in the field of
analytical chemistry and partly in radiochemistry and radioanalytical chemistry:
separation and enrichment methods by precipitation, co-precipitation, sorption
and extraction, followed by quantitative determination by atomic spectroscopic
methods such as arc source atomic emission spectrography, inductively coupled
plasma atomic emission spectrometry, atomic absorption spectrometry and neutron activation analysis. Professor Alexandrov has published 91 journal and conference papers in Bulgarian, English, Russian and German, including 5 author
certificates (BG Patents) and 13 textbooks and student laboratory guides (4 of
them with co-authors). He has participated in 10 projects in various fields, mainly
on analyses of high-purity materials.
Professor Alexandrov has lectured in Analytical Chemistry: a short course for
all students from the Faculty of Biology; Analytical Chemistry Part II (Qualitative
Analysis and Instrumental Methods for Quantitative Analysis); Separation and
Preconcentration. He has supervised 4 Ph.D. students. During his professional
career Professor Alexandrov has cooperated with scientists from the Universities
of Thessaloniki, Habana, Moscow and Brno.
Complete bibliography of Professor Stoyan Alexandrov, including 2 theses,
13 books and textbooks and 91 papers has been compiled and given in chronological order below in this issue. Publications are given in their original language of
publication and translated in English.
Theses
1. Александров Неделчев, С. Изучение разделения благородных металлов с помощью
сульфидов методом радиоактивных индикаторов. Химический факультет, Московский
государственный университет, Москва 1973, 160 с.; Alexandrov Nedeltchev, S. Study of
the Separation of the Noble Metals Using Some Sulphides bу Radiotracer Method, Department
of Chemistry, Moscow State University, USSR, Moscow 1973, pp. 160 (in Russian).
2. Александров Неделчев, Стоян. Разделяне и концентриране с изпoлзване на някoи малко
разтворими неорганични сулфиди, хлориди и оксиди при създаване на комбинирани и
хибридни методи за анализ. Доктор на химическите науки, ИOНХ-БАН, София 1989,
271 с.; Alexandrov Nedelchev, S. Separation and Preconcentration bу Using of Some Low
Soluble Inorganic Sulphides, Chlorides and Oxides at Development of Combined and Hybrid
Methods for Analysis. D. Sc. Dissertation, Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1989, pp. 271 (in Bulg.).
Textbooks
3. Александров, Ст. Лекционен курс по методи за разделяне и концентриране при анализ на
неорганични вещества (учебник за студентите от специалността “Химия” и курсистите
от курсовете по следдипломна специализация и квалификация при Катедрата по
аналитична химия), СУ “Св. Кл. Охридски”, С., 1977, 252 с.; Alexandrov, St. Lecture
Course on Methods for Separation and Preconcentration in Analysis of Inorganic Substances
(Textbook for Students on Chemistry and Post-Graduate Studies at the Department of Analytical Chemistrey), St. Kl. Ohridski University of Sofia, Sofia, 1977, pp. 252 (in Bulg.).
44
4. Христова, Р., Д. Цалев, Б. Желязкова, В. Михайлова, Ст. Александров. Ръководство по
количествен анализ, Наука и изкуство, С., 1979, 318 с.; Христова, Р., Ст. Александров,
Д. Цалев, Б. Желязкова, В. Михайлова. Ръководство по количествен анализ, Второ
преработено издание, Наука и изкуство, С., 1986, 274 с.; Христова, Р., Ст. Александров,
Д. Цалев, Б. Желязкова, В. Михайлова. Ръководство по количествен анализ, Трето
издание, Унив. изд. “Св. Кл. Охридски”, София, 1991, 255 с.; Христова, Р., Ст.
Александров, Д. Цалев, Б. Желязкова, В. Михайлова. Ръководство по количествен
анализ, Четвърто издание, 2000, 266 с. ISBN 954-07-0799-4; Христова, Р., Ст.
Александров, Д. Цалев, Б. Желязкова, В. Михайлова. Ръководство по количествен
анализ. Пето издание, Унив. изд. “Св. Кл. Охридски”, С., 2003, 266 с. ISBN 954-07-07995; Christova, R., S. Alexandrov, D. Tsalev, B. Jeljazkova, V. Mihajlova. Practice of Quantitative Analysis. 4th Edition. St. Kl. Ohridski University Press, Sofia, 2000, pp. 266. ISBN 95407-0799-4 (in Bulg.); Christova, R., S. Alexandrov, D. Tsalev, B. Jeljazkova, V. Mihajlova.
Practice in Quantitative Analysis. 5th Edition, St. Kl. Ohridski University Press, Sofia, 2003,
pp. 266. ISBN 954-07-1829-5 (in Bulg.).
5. Александров, Ст. Аналитична химия (учебник и ръководство за студентите от Биологическия
факултет на СУ “Св. Кл. Охридски”, Софийски университет “Св. Кл. Охридски”, С.,
1984, 313 с.; Александров, Ст. “Аналитична химия”, Второ издание, Унив. изд. “Св. Кл.
Охридски”, С., 1991, 244 с. (in Bulg.).
6. Александров, Ст. Аналитична химия, Унив. изд. “Св. Кл. Охридски”, С., 1993, 159 с.; Alexandrov, St. Analytical Chemistry, St. Kl. Ohridski University Press, Sofia, 1993, pp. 159
(in Bulg.).
7. Александров, Ст. Ръководство по аналитична химия, Унив. изд. “Св. Кл. Охридски”, С.,
1993, 159 с.; Alexandrov, St. Practice in Analytical Chemistry, St. Kl. Ohridski University
Press, Sofia, 1993, pp. 159, ISBN 954-07-0066-3 (in Bulg.).
8. Александров, Ст. Методи за разтваряне, разделяне и концентриране в аналитичната
химия, С., Народна култура, 1995, 240 с., ISBN 954-04-0103-8; Alexandrov, St. Methods
for Dissolution, Separation and Preconcentration in Analytical Chemistry, Sofia, Narodna
Kultura, 1995, pp. 240 с., ISBN 954-04-0103-8 (in Bulg.).
9. Александров, С. Сборник от решени задачи по аналитична химия, Печатна база на СУ “Св.
Кл. Oхридски”, С., 1982; Александров, Ст. Сборник от решени задачи по аналитична
химия, С., Унив. изд. Св. Кл. Охридски, 1996, 395 с. ISBN 054-07-0788-9; Alexandrov, S.
Solved Problems in Analytical Chemistry, St. Kl. Ohridski University Press, Sofia, 1982 (in
Bulg.); Alexandrov, S. Solved Problems in Analytical Chemistry, St. Kl. Ohridski University
Press, Sofia, 1996, pp. 395, ISBN 054-07-0788-9 (in Bulg.).
10. Александров, Ст. Аналитична химия, Унив. изд. “Св. Кл. Охридски”, София, 1998, 255
с. ISBN 954-07-1059-6; Alexandrov, St. Analytical Chemistry, St. Kl. Ohridski University
Press, Sofia, 1998, pp. 255 (in Bulg.).
11. Александров, Ст. Аналитична химия с инструментални методи за анализ. (Програма
екология и опазване на околната среда), Нов български университет. Център по
дистанционно обучение, С., 2001, 200 с., ISBN 954-535-224-8; Alexandrov, S. Analitical
Chemistry and Instrumental Methods of Analysis. New Bulgarian University, Center for elearning. Sofia, 2001, pp. 200. ISBN 954-535-224-8 (in Bulg.).
12. Александров, С. Ръководство по аналитична химия. Второ издание, Унив. изд. “Св. Кл.
Охридски”, С., 2001, 162 с., ISBN 954-07-1519-9: Alexandrov, S. Practice in Analytical
Chemistry. 2nd Edition. St. Kl. Ohridski University Press, Sofia, 2001, pp. 162, ISBN 954-071519-9 (in Bulg.).
13. Нейков, Г. Д., О. М. Пешев, С. А. Неделчев, С. Т. Бенева, Л. Н. Станоева. Химия и
опазване на околната среда. Учебник за 11. клас профилирана подготовка. Булвест
45
2000, С., 2002, 307 с., ISBN 954-18-0264-8; Nejkov, G. D., O. M. Pechev, St. A. Nedelchev,
S. T. Beneva, L. N. Stanoeva. Chemistry and Environmental Protection. 11th School Class
Textbook. Bulvest 2002, Sofia, 2002, pp. 307. ISBN 954-18-0264-8 (in Bulg.).
14. Шишиньова, М., М. Градинарова, Е. Илиева, Л. Банчева, И. Враджалиева, С. Александров.
Човекът и природата за пети клас. Анубис, С., 2006, 167 с. ISBN-10: 954-426-692-5, ISBN13: 978-954-426-692-9; Shishinyova, M., M. Gradinarova, E. Ilieva, L. Bancheva, I. Vradzhalieva, S. Alexandrov. Man and Nature for 5th Grade. Anubis Publishing House, Sofia, 2006, pp.
167, ISBN-10: 954-426-692-5, ISBN-13: 978-954-426-692-9 (in Bulg.).
15. Шишиньова, М., М. Градинарова, Е. Илиева, Л. Банчева, И. Враджалиева, С.
Александров. Човекът и природата за пети клас. Тетрадка. Анубис, С., 2006, 65 с.;
Shishinyova, M., M. Gradinarova, E. Ilieva, L. Bancheva, I. Vradzhalieva, S. Alexandrov. Man
and Nature for 5th Grade. A Notebook. Anubis Publishing House, Sofia, 2006, pp. 65 (in Bulg).
Scientific Papers
16. Daiev, Ch., S. Alexandrov, L. Daieva. Zerstörungsfreie aktivierungsanalytische Bestimmung
von Mikro- und Ultramikromengen Indium in Reinstthallium und Thalliumverbindungen, Fresenius Z. Anal. Chem., 239, 1968, 369–377.
17. Даиев, Х., С. Александров, М. Михайлов. Метод за недеструктивен неутронноактивационен анализ, Авт. свидетелство № 13593 (1968), Рег. № 9634/21.03.1968 г.;
Daiev, Ch., S. Alexandrov, M. Michailov. Method for Non-destructive Activation Analysis,
Author’s Certificate No. 13593 (1968), Reg. No. 9634/21.03.1968 (in Bulg.).
18. Даиев, Хр., Ст. Александров. Неутронно-активационное определение платины по золоту199. В: Симпозиум по использованию методов меченных атомов для совершенствования
технологических процессов производства и по применению ядерено-физических
методов анализа состава веществ. Познань, Польша, Польша-Познан, 12–15.ХI.1968
г., СЭВ, Варшава, 1969, 325–332; Daiev, Ch., S. Alexandrov. Determination par activation
neutronique du Pt à l’aide du 199Au, In: Conference sur l’utilisation des isotopes radioactives
pour prefectionnement des prossesus technologiques et l’utilisation des methodes physiques
radiochimiques pour l’analyse des substances. Poznan, Polane, Warssovie, 1969, 325–332 (in
Russian).
19. Alexandrov, S., J. N. Barrandon, I. N. Bourelly, Ch. Cleyrergue, N. Deschamps, H. Jaffrezic, B. Vialatte. Etude du comportement de quelques metaux nobles sur le sulfure de cuivre
en milieu acide forte. Radiochem. Radioanal. Lett., 5, 1970, 51–58.
20. Alexandrov, S., N. Krasnobaeva. Zur Analyse von Reinstblei. Spectrochemische Bestimmung
von Kupfer, Eisen, Zinn und Wismut mit Anreicherung durch Ionenaustausch, Acta Chim. Sci.
Hung., 64, 1970, 11–16.
21. Bourelly, I.N., Ch. Cleyrergue, N. Deschamps, H. Jaffrezic, B. Vialatte, S. Alexandrov, J. N.
Barrandon. Etude de la fixation des metaux alcalins sur le pentoxide d’antimoine hidrate en
milieu acide forte, Radiochem. Radioanal. Lett., 5, 1970, 43–49.
22. Krasnobaeva, N., S. Alexandrov. Zur Analyse von Reinstblei. Spectrochemische Bestimmung
von Kupfer, Eisen und Antimon mit Anreicherung durch Ausfällung des Bleichlorids. Acta
Chim. Sci. Hung., 64, 1970, 1–9.
23. Vialatte, B., J. N. Barrandon, S. Alexandrov, I. N. Bourelly, Ch. Cleyrergue, N. Deschamps,
H. Jaffrezic. Etude de la fixation du fluor sur le pentoxide d’antimoine hidrate en milieu chlorhydrique. Radiochem. Radioanal. Lett., 5, 1970, 59–62.
24. Cleyrergue, Ch., N. Deschamps, H. Jaffrezic, B. Vialatte, S. Alexandrov, J. N. Barrandon,
I. N. Bourelly. Etude de la fixation du fer sur le dioxide d’etain hidrate en milieu nitrique.
Radiochem. Radioanal. Lett., 6, 1971, 15–20.
46
25. Александров, С., И. В. Голубцов. Изучаване сорбцията на благородните метали върху
някои неорганични сорбенти. Съобщ. III. Сорбция на сребро(I), злато(III), рутений(IV),
родий(III), паладий(II) и платина (IV) върху оловен сулфид. Год. Соф. Унив., Хим. фак.,
65, 1970–1971, 105–112; Alexandrov, S., I.V. Golobtzov. Study of the Sorption of Noble
Metals on Some Inorganic Sorbents. Communication III. Sorption of Silver(I), Gold(III),
Ruthenium(IV), Rhodium(III), Palladium(II) and Platinum(IV) on Lead Silphide. Ann. Univ.
Sofia, Fac. Chim., 65, 1970–1971, 105–112 (in Bulg.).
26. Александров, С., И. В. Голубцов. Изучаване сорбцията на благородните метали върху
някои неорганични сорбенти. Съобщ. IV. Сорбция на сребро(I), злато(III), рутений(IV),
родий(III), паладий(II) и платина(IV) върху живачен сулфид. Год. Соф. Унив., Хим. фак.,
65, 1970–1971, 113–118; Alexandrov, S., I.V. Golobtzov. Study of the Sorption of Noble
Metals on Some Inorganic Sorbents. Communication IV. Sorption of Silver(I), Gold(III),
Ruthenium(IV), Rhodium(III), Palladium(II) and Platinum(IV) on Mercury Sulphide. Ann.
Univ. Sofia, Fac. Chim., 65, 1970–1971, 113–118 (in Bulg.).
27. Александров, С., И. Иванов. Изучаване сорбцията на благородните метали върху някои
неорганични сорбенти. Съобщ. V. Сорбция на сребро(I), злато(III) и на платиновите
метали върху оловен, меден и живачен сулфид. Год. Соф. унив., Хим. Фак., 65, 1970–1971,
319–328; Alexandrov, S., I. Ivanov. Study of the Sorption of Noble Metals on Some Inorganic
Sorbents. Communication V. Sorption of Silver(I), Gold(III) and Platinum Metals on Lead, Copper and Mercury Sulphide. Ann. Univ. Sofia, Fac. Chim., 65, 1970–1971, 319–328 (in Bulg.).
28. Александров, С. Изучаване сорбцията на благородните метали върху някои неорганични
сорбенти. Съобщ. VI. Сорбция на осмий(IV) и иридий (IV) върху оловен и живачен
сулфид. Год. Соф. Унив., Хим. Фак., 66, 1971–1972, 107–117. Alexandrov, S. Study of
the Sorption of Noble Metals on Some Inorganic Sorbents. Communication VI. Sorption of
Osmium(IV) and Iridium(IV) on Lead and Mercury Sulphide. Ann. Univ. Sofia, Fac. Chim.,
66, 1971–1972, 107–117 (in Bulg.).
сорбенти. Съобщ. VII. Върху механизма на процеса на сорбция на йоните на благородните
метали върху оловен, меден и живачен сулфид в кисела среда. Год. Соф. унив., Хим.
фак., 67, 1972–1973, 83–91. Alexandrov, S. Study of the Sorption of Noble Metals on Some
Inorganic Sorbents. Communication VII. On the Mechanism of the Sorption Process of Noble
Metal Ions on Lead, Copper and Mercury Sulphide in Acidic Medium. Ann. Univ. Sofia, Fac.
Chim., 67, 1972–1973, 83–91 (in Bulg.).
30. Александров, С., И. В. Голубцов. Сорбция на среброто, златото и на платиновите метали
на неорганични йонообменни материали. Химия и индустрия, 44, 1972, 365–370; Alexandrov, S., I.V. Golubtzov. Sorption of Silver, Gold and Noble Metals on Inorganic Ion
Exchange Materials. Khimiya i Industriya, 44, 1972, 365–370 (in Bulg.).
сорбенти. Съобщ. II. Сорбция на рутений(IV), родий(III), паладий(II) и осмий(IV) върху
меден сулфид в кисела среда. Год. Соф. унив., Хим. фак., 68, 1973–1974, 281–290. Alexandrov, S. Study of the Sorption of Noble Metals on Some Inorganic Sorbents. Communication II.
Sorption of Ruthenium(IV), Rhodium(III), Palladium(II) and Osmium(IV) on Copper Sulphide
in Acidic Medium. Ann. Univ. Sofia, Fac. Chim., 68, 1973–1974, 281–290 (in Bulg.).
сорбенти. Съобщ. VIII. Радиохимично разделяне на иридий(IV) от сребро(II), злато(III),
платина(IV) и паладий(II) c помощта на меден сулфид като cорбент. Год. Соф. унив.,
Хим. фак., 68, 1973–1974, 291–297. Alexandrov, S. Study of the Sorption of Noble Metals
on Some Inorganic Sorbents. Communication VIII. Radiochemical Separation of Iridium(IV)
47
from Silver(I), Gold(III), Platinum(IV) and Palladium(II) by Means of Copper Sulphide as a
Sorbent. Ann. Univ. Sofia, Fac. Chim., 68, 1973–1974, 291–297 (in Bulg.).
33. Александров, С., С. Илиев. Неутронно-активационен метод за определяне на злато в
морска вода, Авт. свидетелство № 20503 (1974), Рег. №. 26837 / 31.05.1974 г.; Alexandrov, S., S. Iliev. Neutron Activation Method for Determination of Gold in Sea Water, Author’s Certificate No. 20503 (1974), Reg. No. 26837/31.05.1974 (in Bulg.).
34. Александров, С., А. Константинова, Д. Цалев. Сравнително изследване на емисионноспектралния, атомно-абсорбционния и неутронно-активационния анализ при определяне
на някои микроелементи в биологични обекти. Год. Соф. Унив., Хим. Фак., 69 (1), 1974/1975,
153–163; Alexandrov, S., A Konstantinova, D. Tsalev. Comparative Study of Atomic Emission,
Atomic Absorption and Neutron Activation Analysis for Determination of Some Microelements
in Biological Materials. Ann. Univ. Sofia, Fac. Chim., 69 (1), 1974/1975, 153–163 (in Bulg.).
35. Александров, С. Нейтронно-активационное определение иридия в бедных медноникелевых рудах. Ж. аналит. химии, 30, 1975, 322–325; Alexandrov, S. Neutron Activation Determination of Iridium in Low-Grade Copper-Nickel Ores, Zh. Anal. Khim., 30, 1975,
322–325 (in Russian).
36. Александров, С. Сорбция йонов благородных металлов сульфидами свинца, меди и ртути
из сильнокислых растворов. Ж. аналит. химии, 30, 1975, 528–532; Alexandrov, S. Sorption of Noble Metal Ions on Sulphides of Lead, Copper and Mercury from Highly Acidic Solutions. Zh. Anal. Khim., 30, 1975, 528–532 (in Russian).
37. Александров, С. Емисионно спектрален метод за определяне на живак в природни води,
Авт. свидетелство № 22961 (1975), Рег. №.30329/18.06.1975 г.; Alexandrov, S. Atomic
Emission Spectrographic Method for Determination of Mercury in Natural Waters, Author’s
Certificate No. 22961 (1975), Reg. No. 30329/18.06.1975 (in Bulg.).
38. Alexandrov, S. Dosage par spectrometrie gamma non destructive du mercure et de l’or dans
l’eau de mer aprеs preconcentration par le sulfur de plomb. Talanta, 23, 1976, 684–686.
39. Alexandrov, S. Atomic Emission Spectroscopic Determination of Mercury in Fish. Compt.
Rend. Acad. Bulg. Sci., 29, 1976, 1309–1312.
40. Alexandrov, S., Z. Milenova, V. Simeonov. Optimized condition for emission-spectral determination of mercury by the use of iron electrode cell. Ann. Univ. Sofia, Fac. Chim., 70,
1975–1976, 44–49.
41. Динев, И., С. Александров, С. Cлавов. Изследване съдържанието на микроелементи в
биологични материали при болни от ендемична нефропатия. Сб. доклади на II национален
конгрес с международно участие по клинична лаборатория, 15–17 май, София, 1975,
35–41; Dinev, I., S. Alexandrov, S. Slavov. Study on Microelement Content in Biological Materials from Endemic Nephropathy Patientrs, In: Procedings of the Second National Congress
with International Participation on Clinical Laboratory, 15–17 May, Sofia, 1975, 35–41.
42. Alexandrov, С., M. T. Petrova. Spectrochemical Determination of Mercury Content in Bulgarian Mineral Waters. Compt. Rend. Acad. Bulg. Sci., 30, 1977, 1435–1437.
43. Александров, С., Г. Боснев. Проучване на възможността за използване на оловен и
кадмиев сулфид при концентриране на малки количества арсен из водни разтвори. Год.
Соф. Унив., Хим. Фак., 71, 1976–1977, 101–107; Alexandrov, S., G. Bosnev. A Study on the
Possibility of Using Lead and Cadmium Supphide in Concentrating Small Amounts of Arsenic
from Aqueous Solutions, Ann. Univ. Sofia, Fac. Chim., 71, 1976–1977, 101–107.
44. Alexandrov, S., G. L. Gyulmezova, J. Sanabria. A study on the possibility for emission-spectral and atomic-absorption determination of silver, gold and palladium in anode slime. Compt.
Rend. Acad. Bulg. Sci., 31, 1978, 73–76.
45. Alexandrov, S. Study of conditions for spectrochemical determination of mercury in urine after
preconcentration. Compt. Rend. Acad. Bulg. Sci., 31 1978, 691–694.
48
46. Монева, М., С. Александров , C . Войнова. Преглед на методите за определяне на живак
във води. Химия и индустрия, 50, 1978, 162–166; Moneva, M., S. Alexandrov, S. Voynova.
Determination of Mercury in Water – A review, Knimiya i Industriya, 50, 1978, 162–166.
47. Страхилова, Т., С. Александров, З. Малчева. За изучаване на аналитичната химия в
общообразователното училище. Биология и химия, 21, 1978, 25–30; Strakhilova, T., S.
Alexandrov, Z. Malcheva. On the Studying of Analytical Chemistry in the School., Khimiya
i Biologiya, 21, 1978, 25–30 (in Bulg.).
48. Тасев, А., П. Червенаков, С. Александров, К. Колев, Б. Гълъбов, К. Янкова, Н.
Козарева, Х. Танабе, Е. Панева, Ц. Кирилова. Употреба на Na2S2O4 в синтезата на
аналгин, Химия и индустрия, 53, 1981, 13–16; Tassev, A., P. Tchervenakov, S. Alexandrov,
K. Kolev, B. Galabov, K. Jankova, N. Kozareva, J. Tanabe, E. Paneva, Z. Kirilova. Using
of Na2S2O4 in the Synthesis of Analginum, Khimiya i Industriya, 53, 1981, 13–16 (in Bulg.).
49. Александров, С. Емисионен спектрален метод за определяне на живачни пари във
въздуха, Авт. свидетелство № 35227 (1982), Рег. №. 58097/27.09.1982 г.; Alexandrov, S.
Atomic Emission Spectroscopic Method for Determination of Mercury Vapours in Air, Author’s Certificate No. 35227 (1982), Reg. No. 58097/27.09.1982 (in Bulg.).
50. Страхилова, Т., С. Александров. Аналитична химия и проблемът за опазване на околната
среда. Биология и химия, 25, 1982, 24–30; Strakhilova, T., S. Alexandrov. Analytical Chemistry and Environmental Protection Problem, Biologiya i Khimiya, 25, 1982, 24–30 (in Bulg.).
51. Александров, С. Атомно-эмисионное определение паров ртути в воздухе после
предварительного концентрирования. Ж. аналит. химии, 38, 1983, 1003–1007; Alexandrov, S. Determination of Mercury Vapour in Aior by Arc-Source Atomic Emission Spectroscopy after Preconcentration, Zh. Anal. Khim., 38, 1983, 1003–1007 (in Russian).
52. Алекандров, С., И. Караджова. Хибриден метод за определяне на мед, желязо, кобалт,
никел, манган, цинк, ванадий и хром в бариев хлорид и бариев карбонат с висока чистота.
Год. Соф. Унив., Хим. Фак., 77, 1983, 218–225; Alexandrov, S., I. Karadjova. Hybride
method for Determinaqtion of Copper, Iron, Cobalt, Nickel, Manganese, Zinc, Vanadium and
Chromium in High Purity Barium Chloride and Sodium Carbonate, Ann. Univ. Sofia, Fac.
Chim., 77, 1983, 218–225 (in Bulg.).
53. Севова, Н., С. Александров, С. Севов. Атомноемиионно спектрално определяне на
живак в почви. Год. Соф. Унив., Хим. Фак., 78, 1984, 203–213; Sevova, N., S. Alexandrov,
S. Sevov. Atomic Emission Spectroscopic Determination of Mercury in Soils, Ann. Univ. Sofia, Fac. Chim., 78, 1984, 203–213(in Bulg.).
54. Христова, Р., С. Александров. Фотометрично определяне на сулфатни йони с ортанилово-К
в чисти и особено чист бариев хлорид, борна киселина, калиево-натриев тартарат, натриев
карбонат и калиев карбонат. Год. Соф. Унив., Хим. Фак., 78, 1984, 195–201; Christova, R.,
S. Alexandrov. Photometreic Determination of Sulphate Ions with Ortanilic Acid in Pure and
Ultrapure Barium Chloride, Boric Acid, Potassium Sodium Tartarate, Sodium Carbonate and
Potassium Carbonate, Ann. Univ. Sofia, Fac. Chim., 78, 1984, 195–201(in Bulg.).
55. Алекандров, С., Г. Георгиев, В. Симеонов. Химичен контрол на смазочно-охлаждащи
течности в производствени уловия. Машиностроене, 34, 1985, 351–353; Alexandrov, S.,
G. Georgiev, V. Simeonov. Chemical Control of Lublricating-Cooling Fluid in Industrial Conditions, Mashinostroene, 34, 1985, 351–353 (in Bulg.).
56. Alexandrov, S. Lead Sulphide as a Sorbent for the Preconcentration of Mercury from Air and
Determination of Mercury by Atomic Emission Spectroscopy. Fresenius Z. Anal. Chem., 321,
1985, 578–580.
57. Simeonov, V., I. Karadjova, S. Alexandrov. Model for Designed Emission Spectroscopic Determination of Trace Metals in Pure Substances after Coprecipitation with Cadmium Sulphide.
Fresenius Z. Anal. Chem., 320, 1985, 330–333.
49
58. Arpadjan, S., I. Karadjova, S. Alexandrov, D. Tsalev. Extractions-Flammenabsorptionsbestimmung von Spurenverunreingungen in Salzen. Fresenius Z. Anal. Chem., 320, 1985,
581–583.
59. Александров, С., Г. Георгиев, В. Симеонов. Контрол и анализ на инхибитор за водноохлаждащи системи ИВС-4 в производствени условия. Машиностроене, 34, 1985, 312–
353; Alexandrov, S., G. Georgiev, V. Simeonov. Control and Analysis of Inhibitor for Water
Cooling Systems IVC-4 in Industrial Conditions. Mashinostroene, 34, 1985, 312–353 (in Bulg).
60. Александров, С., Г. Георгиев. Извличане и оползотворяване на паладий, сребро и мед
от промишлени отпадъци с ниско процентно съдържание на тези елементи. Год. Соф.
Унив., Хим. Фак., 79, 1985, 89–94; Alexandrov, S., G. Georgiev. Extraction and Utilization
of Silver, Palladium and Copper from Low Content Industrial Waste, Ann. Univ. Sofia, Fac.
Chim., 79, 1985, 89–94.
61. Анева, З., С. Арпаджян, С. Алекандров. Моделиране и оптимизиране на процеса на
синергична екстракция на платина(IV) със смес от изоамилов алкохол и метилизобутил
кетон. Год. Соф. Унив., Хим. Фак., 79, 1985, 83–88; Aneva, Z., S. Arpadjan, S. Alexandrov.
Modelling and Optimization of the Process of Synergetic Extraction of Pt(IV) with a Mixture of Isoamylalcohol and Methylisobutylketon. Ann. Univ. Sofia, Fac. Chim., 79, 1985, 83–88 (in Bulg.).
62. Александров, С., С.Арпаджян, М. Иванова. Атомноемисионно и атомноабсорбционно
определяне на примеси в сребро с висока чстота. Год. Соф. Унив., Хим. Фак., 79, 1985,
205–212; Alexandrov, S., S. Arpadjan, M. Ivanova. Emission Spectroscopic and Atomic
Absorption Determination of Impurities in High-Purity Silver. Ann. Univ. Sofia, Fac. Chim.,
79, 1985, с. 205–212 (in Bulg.).
63. Alexandrov, S., I. Kuleff, R. Djingova, S. Arpadjan, E. Taskaev. Impurity Determination in
Bi2O3 and PbCl2 by Neutron Activation Analysis and Atomic Absorption Spectrometry. First
Balkan Conference on Activation Analysis, Proceedings, Varna, May 6–8 1985, pp. 60–62.
64. Arpadjan, S., M. Novkirischka, S. Alexandrov, P. Petkov. Über die Bestimmung von Spurenverunreinigungen (Fe, Cu, Co, Ni, Mn, Zn, Pb, Cd, Cr,Cl–) in reiner Borsäure mit Einsatz der
Extraction-Flammen- AAS und Spectralphotometrie. White-spirit als organisches Lösungsmittel. Zeitschrift f. Chemie, 26 (12), 1986, 430–433.
65. Колев, Н., И. Хавезов, С. Александров, И. Илиева, Ст. Загаров, Хр. Иванов, Н.
Врачева, С. Ганева. Спектрални методи за атестиране съдържанията на примеси в
стандартни образци за спектрален анализ на сребро. Годишник на института по цветна
металургия, Пловдив, 24, 1986, 94–98; Kolev, N., I. Havezov, S. Alexandrov, I. Ilieva, St.
Zagarov, Chr. Ivanov, N. Vraceva, S. Ganeva. Methods for Spectrochemical Determination
of Impurities in Certified Reference Materials for Spectral Analysis of Silver. In: Annuaire of
the Institute of Non-Ferrous Metallurgy, Plovdiv, 24, 1986, 94–98 (in Bulg.).
66. Alexandrov, S., S. Sevov, S. Peneva, E. Tsukeva. Sorption of Mercury on Lead Sulphide:
RHEED investigation of the Hg-Pb system. Fresenius Z. Anal. Chem., 326, 1987, 358–361.
67. Анева, З., С. Арпаджян, С. Александров. Метод за екстракционно отделяне на платина
от алуминий, калций, магнезий, никел, манган и хром., Авт. свидетелство № 80839, 1987,
Рег. №. 80839/04.08.1987; Aneva, Z., S. Arpadjan, S. Alexandrov. Method for Extraction
Separation of Platinum from Aluminium, Calcium, Magnesium, Nickel, Manganese and Chromium, Author’s Certificate No. 80839 (1987), Reg. No. 80839/04.08.1987 (in Bulg.).
68. Aneva, Z., S. Arpadjan, S. Alexandrov, K. Kovatscheva. Synergetic Extraction of Platinum
(IV) from Dilute Hydrochloric Acid by Isoamyl alcohol-Methylisobutylcetone mixture. Mikrochim. Acta (Wien), 1987, I, 341–350.
69. Александров, С., Г. С. Георгиев, Л. Стойнова, Е. Каменска, Е. Белева. Химичен контрол
на съдържанието на компонентите на охлаждащата смес при закаляване на детайли в
машиностроенето. Машиностроене, 36 (9), 1987, 415–417; Alexandrov, S. Chemical Con-
50
trol of the Composition of the Cooling Fluid in the Quenchuing of Details in Mashine Building, Mashinostroene, 36 (9), 1987, 415–417
70. Djingova R., I. Kuleff, S. Arpadjan, S. Alexandrov, A. Voulgaropoulos, T. Sawidis. Neutron
Activation and Atomic Absorption Analysis of Ulva Lactuca and Gracilaria Verrucosa from
Thermaikos Gulf, Greece, Toxicol. Environ. Chem., 15, 1987, 149–158.
71. Alexandrov, S., E. Vassileva. Atomic Spectroscopic Determination of Impurities in Nickel
Sulphate after Separation and Preconcentration by the Precipitation of the Macrocomponent.
Compt. Rend. Acad. Bulg. Sci., 40 (10), 1987, 75–78.
72. Simeonov, V., S. Alexandrov. Philosophical Aspects of Chemometrical Strategy in Analytical
Chemistry. Fresenius Z. Anal. Chem., 326, 1987, 314–316.
73. Aneva, Z., M. Pankova, S. Arpadjan, S. Alexandrov. Bestimmung von Spurenverunreinigungen (Al, Ca, Cr, Cu, Mg, Mn, Ni, Pb) in Reinstplatin durch Flammen-AAS. Fresenius Z. Anal.
Chem., 1987, 326, 561–562.
74. Alexandrov, S., L. B. Baeva. Studying the Mechanism of the Process of Preconcentration of Mercury from Solution with Lead Sulphide. Compt. Rend. Acad. Bulg. Sci., 41 (1), 1988, 47–50.
75. Alexandrov, S., A. Voulgaropoulus. Atomic Emission Spectroscopic Determination of Mercury
in Water and Sediment Samples from the River Strimon. Chimika Chronika. New Series, 17,
1988, 143–148.
76. Aneva Z., S. Arpadjan, S. Alexandrov. Extraction AAS Determination of Traces of Elements
in Pure Platinum. In: International Solvent Extraction Conference, Moscow, USSR, July 18–
24, 1988. Conference Papers, Vol. IV, Moscow, Nauka, 1988, 88–93.
77. Alexandrov, S. Sorption Mechanism of Ions of Some Heavy Metals and Mercury Vaopours on
Lead Sulphide. Extention of the Fajans-Panet-Hahn Rule. Compt. Rend. Acad. Bulg. Sci., 43
(12), 1990, 45–48.
78. Alexandrov, S., I. Gafur, N. Koleva. Separation and Preconcentration of Impurities in Analysis
of High-Purity Zinc Compounds. Compt. Rend. Acad. Bulg. Sci., 43 (11), 1990, 69–72.
79. Alexandrov, S., E. Vassileva. Study on the Co-precipitation Mechanism of Ag(I) and Fe(III)
with Cobalt and Nickel Sulphides for Atomic Emission Spectroscopic Determination in High
Purity Cobalt and Nicklel Salts, Compt. Rend. Acad. Bulg. Sci., 43 (7), 1990, 45–48.
80. Александров, С., С. Арпаджян, М. Матова. Атомноемисионно спектрално определяне
на сребро и паладий след концентриране с меден сулфид. Год. Соф. Унив., Хим. Фак., 80,
1991, 134–143; Alexandrov, S., S. Arpadjan, M. Matova. Atomic Emission Spectroscopic
Determination of Ag and Pd after Preconcentration with CuS. Ann. Univ. Sofia, Fac. Chim.,
80, 1991, 143–149.
81. Александров, С., Л. Баева. Атомноемисионно спектрално определяне на живак в соли
след предварително концентриране с оловен сулфид. Год. Соф. Унив., Хим. Фак., 80,
1991, 143–149; Alexandrov, S., L. Baeva. Atomic Emission Spectroscopic Determination of
Mercury in Salts after Preconcentration with Lead Sulphide. Ann. Univ. Sofia, Fac. Chim., 80,
1991, 143–149 (in Bulg.).
82. Василева, Е., С. Александров. Съвременно състояние на методите за анализ на никел и някои
никелови съединения с голяма чистота. Год. Соф. Унив., Хим. Фак., 80, 1991, 208–218; Vassileva, E., S. Alexandrov. Current State of the Methods for Analysis of Nickel and Some High Purity
Nickel Compounds. Ann. Univ. Sofia, Fac. Chem., 80, 1991, 208–218 (in Bulg.).
83. Страхилова, Т., С. Александров. Обучението по химия в средното училище и проблемът
чисти и особено чисти вещества. Биология и химия, 3, 1991, 1–9; Strakhilova, T., S. Alexandrov. Chemical Education in tjhe School and the Problem of Pure and High Purity Substances. Biologiya i Khim iya, 3, 1991, 1–9 (in Bulg.).
84. Александров, С., И. Гафур. Методи за анализ на кадмий и кадмиеви съединения с висока
чистота. Analytical Laboratory, 1 (2), 1992, 59–69; Alexandrov, S., I. Gafur. Methods for
51
Analysis of High Purity Cadmium and Cadmium Compounds. Analytical Laboratory, 1 (2),
1992, 59–69 (in Bulg.).
85. Александров, С., И. Гафур. Методи за анализ на цинк и цинкови съединения с висока чистота.
Химия и индустрия, 63 (10), 1992, 8–15; Alexandrov, S., I. Gafur. Methods for Analysis of High
Purity Zinc and Zinc Compounds. Khimiya i Industriya, 63 (10), 1992, 8–15 (in Bulg).
86. Alexandrov, S., I. Gafur, D. Luchanska. Investigation of the Пossibility of Separation and
Preconcentration in High Purity Cadmium Salts Analysis. Compt. Rend. Acad. Bulg. Sci., 45,
(5), 1992, 55–58.
87. Alexandrov, S., I. Gafur, P. Mandjukov, O. Nedelchev. Study on the Hydride Generation
Atomic Absorption Spectrometry of As, Sb, Bi, Se, Sn, Te and Hg in the Presence of Cadmium
and Zinc Salts. Frezenius J. Anal. Chem., 347, 1993, 303–304.
88. Костуркова, П., С. Александров, Н. Панчева. Изследвания върху атомноабсорбционното
определяне на злато в геоложки проби, съдържащи органични вещества. Analytical Laboratory, 4 (2), 1995, 108–111; Kosturkova, P., S. Alexandrov, N. Pancheva. Investigation
on Atomic Absorption Determination of Gold in Geological Samples Containing Organic Substances. Analytical Laboratory, 4 (2), 1995, 108–111 (in Bulg).
89. Александров, С., П. Костуркова. Изследвания върху методи за определяне на мед, олово
и цинк в геоложки проби от почви. В: Сб. 25 години Шуменски университет “Еп. К.
Преславски”, 1996, Шумен, 151–156; Alexandrov, S. P. Kosturkova. Investigation on
Methods for Determination of Cu, Pb and Zn in Soil Samples. In: 25 Years of the University of
Shoumen “Episkop K. Preslavski”, Shoumen, 1996, Шумен, 151–156 (in Bulg.).
90. Александров, С., П. Костуркова. Изследвания върху методи за определяне на сребро в
геоложки проби. В: Сб. 25 години Шуменски университет “Еп. К. Преславски”, 1996,
Шумен, 156–161; Alexandrov, S. P. Kosturkova. Investigation on Methods for Determination of Silver in Geological Samples. In: 25 Years of the University of Shoumen “Episkop K.
Preslavski”, Shoumen, 1996, Шумен, 156–161 (in Bulg.).
91. Александров, С., П. Костуркова. Сравнителни изследвания върху някои методи за
определяне на злато в геоложки проби. Год. Соф. Унив., Хим. Фак., 89, 1997, 119–127.
92. Alexandrov, S., P. Kosturkova. Comparative Study of Several Methods for Determination of
Gold in Geological Samples. Ann. Univ. Sofia, Fac. Chim., 89, 1997, 119–127 (in Bulg.).
93. Костуркова, П., С. Александров. Сравнително изследване на някои методи за определяне
на желязо в железни руди. Год. Соф. Унив., Хим. Фак., 89, 1997, 129–135; Kosturkova, P.,
S. Alexandrov. Comparative Study of Several Methods for Determination of Gold in Geological Samples. Ann. Univ. Sofia, Fac. Chim., 89, 1997, 129–135 (in Bulg.).
94. Александров, С. Приложение на методите на атомната спектроскопия за определяне на
живак в сребро и сребърни съединения. Год. Соф. Унив., Хим. Фак., 90, 1998, 67–77; Alexandrov, S. Application of Atomic Spectroscopic Methods for Determination of Mercury in
Silver and Silver Compounds. Ann. Univ. Sofia, Fac. Chim., 90, 1998, 67–77 (in Bulg.).
95. Александров, Ст. Конкурсен изпит по химия в Химически факултет на СУ „Св. Кл.
Охридски“ – 1998. Химия, VIII (1), 1999, 1–4; Alexandrov, St. Chemistry Exam in the
Faculty of Chemistry, University of Sofia “St. Kl. Ohridski” 1998. Khimiya, VIII (1), 1999,
1–4 (in Bulg.).
96. Alexandrov, S. Investigation on Extraction-Chromatographic Determination of Tetrabutyltin in
Sea Water. Ann. Univ. Sof., Fac. Chim., 92–94, 2001, 107–112 (in Bulg.).
97. Александров, С. Правило Файанса–Панета–Хана для системы сульфид свинца–йоны
серебра, золота, ртути и платиовых металлов в кислой среде. Ж. аналит. химии, 54,
1999, 1037–1041; Alexandrov, S. Fajans-Paneth-Hahn Rule for System Containing Lead
Sulphide and Silver, Gold, Mercury and Platinum-Group Metal Ions in Acid Media. Zh. Anal.
Khim., 54, 1999, 1037–1041 (in Russian).
52
98. Александров, С., Кр. Монтини. Определяне на съдържанието на някои органокалаени
съединения в проби от водата на Черно море в пристанището на г. Варна, Хигиена и
Здравеопазване, XLII, 1999, 25–28; Alexandrov, S., C. Montiny. Determination of Some
Organotin Compounds in the Black-Sea Water Samples of the Harbour-Varna, Higiena i Zdraveopazvane, XLII, 1999, 25–28 (in Bulg.).
99. Александров, Ст. Изследване на разпределението на някои елементи между почва и
растение. Българска медицина, Знание, 3, 2002, 22–26; Alexandrov, St. Study on the Distribution of Some Elements Among Soil and Plant, Bulgarska Meditzina, Znanie, 3, 2002,
22–26 (in Bulg.).
100. Александров, Ст. Определяне на съдържанието на някои метали в проби от почви в
близост до промишлено предприятие. В: Сборник научни трудове. Природни науки.
Химия. Унив. Изд. “Еп. К. Преславски”, Шумен, 2002, ISBN 954-577-155-0, с. 9–19; Alexandrov, St. Determination of Some Metals Content in Soil Samples Near to Industrial Plants.
In: Sbornik Nauchni Trudove. Prirodni Nauki. Khimiya, University of Shoumen “Ep. Konstantin Preslavski”, Shoumen, 2002, ISBN 954-577-155-0, pp. 9–19 (in Bulg).
101. Alexandrov, St. Study on the Distribution of Some Elements Between Soil and Lavandula
angustifolia – Miler plant. Ann. Univ. Sofia, Fac. Chim, 96, 2003, 13–16.
102. Pavlova, D. K., St. Alexandrov. Metal Uptake in Some Plants Growing on Serpentine Areas
in the Eastern Rhodopes Mountains (Bulgaria), The Herb Journal of Systematic Botany, 10,
2003, 14–30.
103. Alexandrov, St. Study on the Distribution of Some Elements between Soil and Lavandula
angustifolia – Miller Plant. Ann. Univ. Sof., Fac. Chim., 96, 2004, 269–274.
104. Bozhanov, S., S. Alexandrov. Analysis of Lavender and Rose Oil. Studies on the Possibility
for Elaboration of a Method for Kinetic Spectrophotometric Determination of Mn(II) in Bulgarian Lavender and Rose Oil. J. Univ. Chem. Technol. Metall. (Sofia), 41, 2006, 457–460.
105. Bozhanov, S., S. Arpadjan, S. Alexandrov. Determination of mercury in geritamin, fish oil
and essential oils by electrothermal atomic absorption spectrometry. Compt. Rend. Acad. Bulg.
Sci., 60, 2007, 979–982.
106. Bozhanov, S., I. Karadjova, S. Alexandrov. Determination of Trace Elements in the Lavender
Inflorescence (Lavandula angustifolia Mill.) – Lavender Oil System. Microchem. J., 86, 2007,
119–123.
107. Bozhanov, S., St. Alexandrov, I. Dakova. A Study on the Distribution of Some Metals in Soil,
Lavender Plant and Lavender Oil. Ann. Univ. Sofia, Fac. Chim., 100, 2008, 253–258.
Prof. Dr. Dimiter L. Tsalev, DSc, C.M.
Chair of Analytical Chemistry,
University of Sofia
1, J. Bourchier Blvd.
1164 Sofia
01.06.2010
53
54
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
In memoriam: Prof. KOSTADIN NIKOLOV KOSTADINOV, D. Sc.
1931–2009
Prof. D. Sc. Kostadin Nikolov Kostadinov deceased on 7.10.2009.
Prof. Kostadinov was born in 1931. He graduated
in Chemistry at the University of Sofia in 1955 and
started his carrier as a research associate in the Institute of Physics of the Bulgarian Academy of Sciences.
Under the supervision of the great Bulgarian scientist
Prof. Elisaveta Karamihajlova he worked on natural
radioactivity, mainly on the determination of the uranium and radium content in fallout, water sources,
thermal and cold underground waters and medicinal
mud and its influence on humans.
Prof. Kostadinov has a significant contribution to
the start of the Bulgarian Research Nuclear Reactor IRT-1000 in Sofia and particularly in the preparation and the control of the first cooling water loop. He was
a founder and head of the Radiochemical Laboratory of the Institute of Physics
with Atomic Scientific Experimental Basis (now Institute of Nuclear Research
and Nuclear Energy), in which for the first time in Bulgaria radioactive isotopes
(gold-198, fluorine-18, yttrium-90) and labelled compounds for medical purposes
were produced.
Since 1964 he was an associate professor and in 1980 became professor in Radiochemistry in the Department of General and Inorganic Chemistry of the Faculty
of Chemistry. He was the founder and for many years head of the Radiochemical
Laboratory of the Department. In the sixties he was a vice dean of the Faculty.
In 1968-1973 Prof. Kostadinov took a responsible position in the International Atomic Energy Agency in Vienna as a coordinator of research and technological projects related to uranium mining.
55
In 1975-1980 he was Chairman of the Bulgarian Committee for Peaceful
Uses of Atomic Energy (now Nuclear Regulatory Agency).
Prof. Kostadinov had various scientific interests in the field of natural radioactivity, the production and characterization of radionuclides and labelled compounds,
chemistry and radiochemistry of the cooling water from the first loop of nuclear
reactors, radioanalytical chemistry (radiochemical and neutron activation analysis,
low-energy beta-emitters measurement), nuclear chemistry and radioecology.
In the seventies-eighties of the last century he and his collaborators continued the investigations on natural radioactivity started in the very beginning of his
carrier, with development of methods for low-energy beta-emitter measurement,
particularly of tritium. Problems related with its determination by means of internal filling counters and liquid scintillation spectrometry were solved. The main
attention was paid to its monitoring in the environment and application for the
evaluation of the radioecological conditions around nuclear facilities as well as
for solving hydrological issues.
The studies in the field of the chemistry of the research reactor were continued and extended for analysis of some radionuclides in the cooling water of the
Kozloduj Nuclear Power Plant.
The gamma spectrometers supplied through contracts with the International
Atomic Energy Agency made possible a successful development of radiochemical
and non-destructive neutron activation analysis methods for analysis of uranium,
mercury and lithium in waters, low-content uranium materials (phosphorites, copper ores, lignite coal ash), coal, etc. as well as methods for multicomponent analysis of different samples. Later on these investigations were fruitfully carried out
and extended by his former collaborators. However they were limited after closing of the research nuclear reactor in Sofia.
Prof. Kostadinov inspired investigations in nuclear chemistry (chemical effects of nuclear transformation), studying hot atom chemistry of sulfur-35 as well
as mercury-203.
After his retirement (1999) Prof. Kostadinov concentrated his interests mainly in radioecology, including radiostrontium determination in bones, etc.
In 1964 Prof. Kostadinov delivered lectures in the first course in radiochemistry
in the Faculty of Chemistry and after that in other radiochemical subjects. Under his
supervision M. Sc. and Ph. D. theses were elaborated. The training of radiochemists,
started by Prof. Kostadinov with a single optional course, has successful development: in 1972 a specialization in radiochemistry was established, followed by a
masters program and since 2006 the bachelor program in Nuclear Chemistry.
Prof. Kostadinov is an author of 125 scientific papers and of a number of
reports on national and international scientific forums, and of a few books in the
field of radiochemistry and transuranium elements. He translated the fundamental
text-book of Fridlander, Kennedy and Miller into Bulgarian. The bibliography of
56
his works can be found in Annuaire de l’Université de Sofia “St. Kliment Ohridski”, Faculté de Chimie 96 (2004) 9-19.
Prof. Kostadinov considered secondary school education and especially the
radioecological education of young people as very important. He was a co-author
of textbooks for secondary education and of papers devoted to the methodological
problems in this field.
For his scientific and pedagogical work and his contributions in the development and recognition of Bulgarian radiochemistry, Prof. Kostadinov was decorated with the Sign of Merit of the University of Sofia with a blue ribbon.
Prof. Kostadinov, along with other Bulgarians, gave his contribution to turn
Bulgaria into nuclear state. The future belongs to the new generations and depends
on their will and efforts.
Prof. D. Tododrovsy, DSc, PhD
Department of Inorganic Chemistry,
University of Sofia
1164 Sofia
30.03.2010
57
58
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
In memoriam: Prof. VENETA DRIANSKA D. Sc.
1937–2010
Prof. D.Sc. Veneta Drianska Ph. D. was born on
the 28th of March 1937 in Oreshak village, Lovech
region. In the year of 1960 she graduated from the
faculty of Physics and Mathematics of the University
of Sofia with a degree in Chemistry. Afterwards she
taught for a year and later worked as a chemist in the
Chemical-Pharmaceutical factory in Troyan.
After a successfully won a contest in 1962 she was
appointed an assistant- Professor in the department of
Organic Chemistry of the Chemical Faculty of the University of Sofia. She attained the academic rank of Associate Professor in 1987, and
in 2001 she was elected as Professor in the department of Organic Chemistry.
In 1975 after a successful defense of Ph. D. dissertations she was awarded the scientific degree PhD. In 1998 she defended the degree “Doctor of Chemical Sciences”.
Prof. Drianska increased her scientific qualification during a 4-month specialization at the University of Paris VII in 1976 and in 1988 she specialized for
3 months at the University of Biefeld with Prof. Demlow. She delivered scientific
reports on her own researches at the Jagiellonian University in Krakow as well as
universities in Bielfeld and Saarland.
Prof. Drianska was a prominent researcher in the field of Organic Synthesis.
She had a great contribution for the introduction and the development of phase
transfer catalysis and its application to reactions of aldole type and reactions of
conjugated 1,4 incorporation. The obtained results are summarized in more than
70 scientific publications; she was a co-author of 6 auto certificates. Her contributions to the field of organic synthesis are cited more than 220 times in scientific
articles and monographs. More than 20 diploma works and 2 PhD dissertations
were defended successfully under her directions.
59
Throughout her long period as a member of staff of the department of Organic
Chemistry Prof. D.Sc. Veneta Drianska proved to be a prominent scientist in the field
of organic synthesis as well as a respected by the student’s teacher and lecturer and a
tolerant and responsible member of staff of the department of Organic Chemistry.
Prof. M. Miteva, DSc, PhD
Department of Analytical Chemistry,
University of Sofia
1164 Sofia
30.03.2010
60
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
NATURE OF THE MAGNETIC INTERACTION IN ORGANIC
RADICAL CRYSTALS.
5. MIXED RADICAL CRYSTALS WITH POLYMETHINE RADICALS #
N.TYUTYULKOV1, F.DIETZ2
University of Sofia, Faculty of Chemistry, Department of Physical Chemistry,
1, J. Bourchier blvd, BG-1164, Sofia, Bulgaria.
E-mail adress:[email protected]
2
Universität Leipzig, Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie,
D-04103 Leipzig, Johannisallee 29, Deutschland.
# Part 5, see ref. 3.
1
Dedicated to the 70th anniversary of Prof. Dr. Michail G. Arnaudov
Abstract. The magnetic characteristics of a class 1-D mixed radical crystals composed
of stable polymethine radicals and polycyclic aromatic hydrocarbons are investigated
theoretically by means of many electron band theory of magnetism. The ferromagnetic
interaction between the electrons within the half-filled-band is characterized. The
contributions to the effective exchange integral: direct (Hund,s), kinetic and indirect, are
calculated. For some structures, the values of the effective exchange integral in the order
of magnitude of ~ 102 meV.
Keywords: molecular ferromagnets
INTRODUCTIONS
Although with very low critical temperature, Tc, the known pure organic high
spin systems with ferromagnetic coupled electrons and macroscopic ferromagnetism are crystals with inter-molecular π-system of conjugation [1,2].
In our earlier paper (see ref.3 and references given therein) the band theory
of magnetism is applied to study the nature of the intermolecular magnetic in61
teraction in 1-D mixed radical crystals (MRC) composed of polycyclic aromatic
hydrocarbons (PAH) and π-radicals or π−ion radicals. In all systems investigated
in the papers cited in ref.3, the magnetic interaction between theelectrons in the
half-filled-band (HFB) is weak. The effective exchange integral Jeff (see eq.4) has
a low value: Jeff < 40 meV.
The aim of the present paper is to extend the investigation for MRC characterised by strongly coupled electrons (large values of Jeff) – necessary condition for
high values for critical (Curie) temperature, Tc.
OBJECTS OF INVESTIGATION
The investigated mixed radical crystals are composed of polymethine radicals (see ref.4, and refs. given therein): Weitz -1, 2, Wurster- 3, shown in Fig.1,
and PAHs-nanographenes [5], shown in Fig.2.
.
H
N
X
+
N
H
H
N
N
.
.
Y
1
+
2
3a , X= NH2, Y= NH2
3b, X= O , Y = O -
Fig. 1. Invesstigated polymethine radicals.
T
C
HBC
Fig. 2. Invesstigated PAHs : triphenylene (T), coronene (C), and hexabenzocoronene.(HBC)
62
Models of the 1-D stacks
The stacks of the disk-type π-systems are considered to be 1-D crystals, for
which the Born-Karman cyclic conditions are fulfilled. The arrangement of the
stacks is of the slipped face-to-face type.
The intermolecular distances between the planes of two neighboring monoradicals in different pure molecular radical crystals (MRC) vary in the range between 3.1 Å in the stacks of Wurster ’s radicals [6] up to 3.71 Å in the galvinoxyl
stacks [7]. Because the results of the magnetic characteristics qualitatively are
identical obtained with different values of the inter-planar distance R (see Table 2)
in the other Tables are given the results for a value of R = 3.35 Å as for the 2-D
layer of graphite [8] (Scheme 1):
HBC
o
3.35 A
Radical
o
3.35 A
Scheme 1
All radicals and PAHs are assumed to have ideal geometry: all bond lengths, R= 140 Å, valence
bond angles 120°.
METHOD OF INVESTIGATION
Energy Spectra
If the MOs of the 1-D system have the form of Bloch running waves
Ψ(κ) = N-1/2 ΣΣCr(k) exp(-ikμ)|r,μ>
(1)
μ r
(k ∈[-π, π] is the wave vector, μ denotes the number of the elementary units (EU)
and |r,μ> is the r-th AO within the μ-th EU), in the Hückel-Hubbard version of the
Bloch method the MO energies e(k) are eigenvalues of the energy matrix [9]:
E(k) = Eo + V exp(ik) + V+exp(-ik),
(2)
where Eo is the energy matrix for the EU, V is the interaction matrix between
neighbouring EUs (μ-th and μ+1-th), V+ is the transposed matrix.
Spin-exchange Interaction in the Half Filled Band
In accordance with Anderson’s theory of magnetism [10] it was shown (see
ref.11 and references given therein) that the effective exchange integral, Jeff , in the
Heisenberg-Dirac-Van Fleck Hamiltonian ( i and j denote the EUs):
H = -2 Σ Jeff (i,j) Si Sj = -2 Σ Jeff (i,j) Si Sj = -2 Σ Jeff (τ) Si Sj
i,j
i,j
i,j
(3)
63
can be expressed as a sum of three contributions:
Jeff = J - Jkin + Jind
(4)
J is the direct (Coulomb, Hund) exchange integral between the Wannier states
localized at the i-th and j-th sites.
Jkin (Jkin < 0) is the kinetic exchange parameter representing the antiferromagnetic contribution to the spin exchange:
Jkin = -Δε2 / 2U = -Δε2 / 2(Uo - U1 ),
(5)
where Δε is the NBMO band width and U is the renormalized Hubbard parameter
[12]. Uo and U1 are the Coulomb repulsion integrals of to electrons, residing in the
same Wannier state and occupying adjacent Wannier states (τ = 1).
The term Jind expresses the indirect exchange (superexchange) via delocalized π−electrons in the filled energy bands. The sign of Jind is determined by the
structure and the interaction between the EUs. The terms can be calculated using
a formalism described in ref. 13.
The calculations have been carried out using a standard set of parameters [11,
14]. The exchange parameter in eq. (4) was calculated by means of the screened
Mataga-Nishimoto potential [16] for the two-centre Coulomb atomic integrals:
γrs (M) = e2/(a+DRrs),
(6)
where D is the screening constants.
The results obtained by means of the Ohno potential [17] do not differ substantially from the results calculated using the Mataga-Nishimoto approximation.
Whangbo – Nubbard condition.
Whangbo has derived a condition [18], allowing a simple determination of
the relative stability of localised high spin (magnetic) and loe spin (non- magnetic) states in the half-filled-band (HFB). Let us denote the Coulomb repulsion
integral of two electrons occupying the same Wannier state and adjacent states
by Uo and U1 , respectively, and the HFB width by Δε. Wangho,s condition reads
(U = Uo – U1 is the renormalized Hubbard integral):
Δε \ U < π/4
(7)
Similar condition is derived by Hubbard [12]:
Δε \ U < 2. 2-1/2
64
(8)
Eqs. (7) and (8) have the following physical meaning: if the HFB width Δε is
small compared with the Coulomb repulsion Uo – U1 , the magnetic, high-spin
state is favoured.
NUMERICAL RESULTS AND DISCUSSION
In Tables 1–6 are given the numerical results of the calculated values of the
components to the effective exchange integral between the electrons in the delocalized HFB of radical crystals, consisting of different radicals and PAHs.
Table 1. Calculated values of the exchange parameter (in meV) of the 1-D
mixed radical crystals consisting of the Weitz radical 1, and coronene. The results
are obteined Mataga-Nishimoto approximation for the two-center Coulomb integrals (see eq. 6). The results obteined by means of the Ohno potential are given
only in Table 5.
Δr1
0.7*
0.7**
1.4*
1.4*
2.1*
Δr2
0
0
0
1.4
0
J
50
91
256
121
0.6
Jind
1
2
69
3
0
Jkin
0
0
0
0
0.8
Jeff
51
93
325
124
1.4
* The interaction only between first neighbouring π-centers is taken into account.
** The interaction between first and second π-centers is taken into account.
mixed radical crystals consisting of Weitz radical 1 and hexabenzocoronene.
65
Δr1
1.4*
1.4**
0*
Δr2
0
0
0
J
Jind
184
247
180
6
7
5
- Jkin
4
0
2
Jeff
186
254
183
mixed radical crystals consisting of Weitz radical 1 and triphenylene.
T-n
Δr
J
T- 1*
T- 1*
T- 1**
T- 2*
T- 2**
T- 2**
0
1.4
1.4
0
0
1.4
11.6
56
35
53
26
8
Jind
0.4
16
1
2
1
0
- Jkin
0
0
0
0
0
0
Jeff
12
72
36
55
27
8
66
mixed radical crystals consisting of Weitz radical 2 and coronene.
Δr1
0*
0**
1.4*
1.4*
2.8*
2.8**
Δr2
0
0
0
1.4
0
0
J
114
52
38
54
30
12
Jind
8
3
3
4
2
1
- Jkin
6
1
0
1
0
0
Jeff
116
54
41
57
32
13
mixed radical crystals consisting of Wurster radicals 3a,3b and triphenylene. I all
cases Δy1 = 0.
Radical
3a*
3a**
3a**,#
3b*
3b**
3b**,#
Δy
0
1.4
1.4
0
1.4
1.4
J
21
18
22
35
22
27
Jind
1
1
2
2
1
2
- Jkin
~0
~0
~0
~0
~0
~0
Jeff
22
19
24
37
23
29
# The results are obteined by means of Ohno potential.
67
The Whangbo- Hubbard condition is fullfiled for all considered 1D stacks. For
instance the HFB width and the renolmalised Hubbard integral for stacks shown
in Table 5 (Δy =1.4) Å) have the values : Δε = 21 meV , and U = 2.195 eV.
CONCLUSIONS
The results in this paper illustrate the possibility for the existence of mixed
radical crystals with polymethine radicals with ferromagnetic ordering. The numerical results should be consi-dered as quantitative illustrations of qualitative
correct results.
The main factors that determine the magnitude of the effective exchange integral are the slip parameters (Δr, Δx and Δy, respectively).
The high values of the effective exchange integral (in some stacks in the
order of magnitude of ~102 meV) corresponds to for high values for the crytical temperature, Tc of the experimentally accsesible mixed radical crystals with
polymethine radicals.
REFERENCES
1. Dekker, Marcel. Magnetic Properties of Organic Materials. Lahti, P. M. ed, Inc., New York, 1999.
2. Itoh, K, M. Kinoshita. Molecular Magnetism. Kodansha, Tokio, 2000.
3. Dietz, F., N.Tyutyulkov, M.Staneva, M.Baumgarten, K.Muellen. J.Phys.Chem., B 105, 2001, 7972.
4. Tyutyulkov, N., J. Fabian, A. Mehlhorn, F. Dietz, A. Tadjer. Polymethine Dyes. Structure and
Properties. University Press, Sofia, 1991.
5. Muellen, K., J. P.Rabe. Accounts Chem. Research, 41, 2008, 511.
6. Tanaka, J., N. Sakabe. Acta Crystallogr. Sect. B 24, 1968, 1345.
7. Williams, D. Mol. Phys., 16, 1969, 145.
8. Kelly, B. T. K. Physic of Graphite. Applied Science Publishers. London, 1981.
9. Polansky, O.E., N.Tyutyulkov. MATCH (Mathematical Comm.), 3, 1977, 149.
10. Anderson, P. W. Phys. Rev., 79, 1950,350; 115, 1959, 2.
11. Tyutyulkov, N., F. Dietz. – In: Magnetic Properties of Organic Materials, P. M. Lahti, ed., Marcel
Dekker, Inc., New York,1999, Chapt. 18.
12. Hubbard, J. Proc.Roy.Soc.London, A276, 1963, 238; A277, 1964, 401.
13. Tyutyulkov, N., S. Karabunarliev. J.Chem.Phys.,112, 1987, 293.
14. Dietz, F., K.Muellen, M.Baumgarten, V.Georgiev, N.Tyutyulkov. Chem.Phys. Lett., 389, 2004, 135.
15. Minkov, I., A. Tadjer. Int.J.Quantum Chem., 99, 2004, 667.
16. Mataga, N., K.Nishimoto. Z. Phys. Chem., 13, 1957, 140.
17. Ohno, K. Theoret. Chim.Acta, 11, 1964,145.
18. Whangbo, M.H. J.Chem.Phys., 70, 1979, 4963.
Received on April 27, 2009
68
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
MEASURING THE LIQUID-GAS LINE ENERGY IN
DIPALMITOYL-SN-GLYCERO-3-PHOSPHOCHOLINE (DPPC)
LANGMUIR MONOLAYERS COMBINING WIDE-FIELD
FLUORESCENCE MICROSCOPY AND SURFACE POTENTIAL
MEASUREMENTS
KONSTANTIN BALASHEV a, MARTIN GUDMAND b, THOMAS HEIMBURGc AND
THOMAS BJORNHOLMb
Sofia University, Faculty of Chemistry, Department of Physical Chemistry, Lab. Of Biophysical
Chemistry, Sofia 1164, 1, James Bourchier Ave., Bulgaria
b
Nano-Science Center, Department of Chemistry, University of Copenhagen, Universitetsparken 5,
2100 Copenhagen Ø, Denmark
c
Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark
a
Abstract. The evolution of two dimensional bubble-like domains in DPPC Langmuir
monolayers were observed during the compression of the monolayer in areas corresponding
to the coexisting region gas- liquid expanded (G - LE) phase. On the basis of previously
developed theory [1–3] we determine the values of the line tension, λ , between the two
phases within the monolayer. For that purpose we combined two experimental methods:
Wide-Field Fluorescence Microscopy adapted with Langmuir trough and surface potential
measurements. We used the first method to evaluate the radii and areas of the gas phase
domains. In the same time using data from the surface potential measurements the electrostatic
interactions within coexisting phases were distinguished from the mechanical ones.
Key words: Wide-Field Fluorescence Microscopy, Langmuir monolayers, Line tension,
Surface potential, Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), two-dimensional systems
69
INTRODUCTION
Phospholipid molecules with long C − chains (i.e. C14 to C20 ) form at airwater interface stable water-insoluble Langmuir monolayers. If sufficiently small
amount of these molecules is spread at the interface as a result a monolayer is
formed in molecular state where individual molecules are separated at distances
from each other far enough that no force interactions between them could exist.
This thermodynamic state is considered as 2D − gas. Further compression of the
monolayer leads to appearance of different phases or states, depending on the
surface concentration (or surface pressure), temperature, and molecular structure.
It is now generally accepted that a DPPC monolayer can exist in four different
pure phases below the critical temperature (~ 40 o C ). These are; gas (G), liquid
expanded LE, liquid condensed LC, and solid S. In addition to these there are two
mixed phases; a gas/liquid-expanded phase co-existence (G-LE), and the liquidexpanded/liquid-condensed phase co-existence (LE-LC).If lipid monolayers exist in a two phase regime, then using different experimental techniques one can
observe discrete domains of one phase surrounded by a second, coexisting phase.
Moreover, such lipid domains have been observed in a wide variety of shapes,
ranging from simple, circular disks to complex fractal patterns [1].
In the last two decades a big step forward in understanding two dimensional
microstructures has been done after emergence of some powerful experimental
methods such as Brewster angle and Fluorescence Microscopy. It is known that
equilibrium shape of the phase domains in monolayers is a result of a competition
between certain molecular interactions, particularly the line tension and electrostatic
forces. Explicitly speaking in such force competition at the interface, the line tension
prevails in phase domains with circular shapes as the line tension tends to minimize
the perimeter of the boundary between the two coexisting phases. On a contrary
for the coarsening of the domains are responsible long range repulsive electrostatic
forces between the dipoles carried by the surfactant molecules [1–3].
In two-phase equilibrium system line tension λ is defined as an excessive
energy quantity at the line of contact. Correspondingly λ is equal to the force
acting per unit length (line of contact of two the phases) [4]. Estimation of the line
tension λ of the interface between two coexisting phases always has been a demanding experimental problem [5]. First report for the measurement of the liquidsolid line energy in a Langmuir monolayer was presented by Muller et al. [6]. The
authors observed the homogeneous 2D − nucleation of solid anisotropic domains
from a liquid phase in an amphiphilic nitrobenzoxadiazole steric acid monolayer
and measured the line tension λ between the two phases. Discher B.M. et al [7]
while studying the effect of neutral lipids on coexisting phases in monolayers of
pulmonary surfactant by surface potential measurements along with fluorescence
microscopy calculated the interfacial tension between the two coexisting phases.
70
More recently, Stottrup et al. [8] used a method for extracting the interfacial line
tension between coexisting monolayer phases through direct observations of thermal fluctuations. The backbone theory describing these two-dimensional systems
has been developed by McConnell [1–3]. In his model the definitive state of the
system corresponds to the minimum of the free-energy function F , which is sum
of the domain shaped-dependant electrostatic energy- Fel and line tension energyFλ . The theory also assumes that there is a sharp well defined boundary between
coexisting phases and that those phases are isotropic.
As an experimental approach for studying coexisting fluid phases at the airwater interface McConnell and others proposed monolayer perturbation of the
monolayer, either by a rotating disk or more recently by the manipulation of a
glass bead with optical tweezers. The line tension was determined by monitoring
the relaxation of the interface between coexisting monolayer phases. [9, 10]
In the present paper we present the use Wide-Field Fluorescence Microscopy (WFFM) technique adapted with Langmuir trough and surface potential
measurements for studying the nature of the region of coexisting liquid-expanded
(LE) and gas (G) phases in Dipalmitoylphosphatidylcholine (DPPC) monolayers
spread at air-water interface. Here we propose an adaptation of the theoretical and
experimental approaches developed by McConnell [1] and Meunier respectively
[5] to determine the values of the line tension, λ , between the two phases within
the monolayer. Our analysis required fluorescent images obtained during the slow
(quasi-statically) compression of DPPC monolayer.
Following an approach which allows to keep the monolayer at a strict equilibrium, the discontinuous phase occurs as circular domains with radius R determined by both line tension and the difference in dipole moment densities between
the two phases - λ and Δμ , respectively. Therefore for the purposes of the current
study we used the images obtained from Wide-Field Fluorescence Microscopy
in order to determine domain radius R and on the other hand we used the surface
potential measurements to determine Δμ .
THEORETICAL APPROACH
Surface potential ΔV is defined as a difference between potentials of the water substrate and that of the monomolecular layer spread at the air/water interface.
It is proportional to the effective dipole density μ for uncharged monolayer (Fig.
1). In a continuum approximation Helmholtz equation gives:
ΔV =
μ
,
εε 0
(1)
where ε is the local dielectric constant;ε0 is the dielectric constant of the vacuum;
ε 0 = 8.854 × 10−12 C 2 N −1m −2 ); μ = nμ , with n corresponding to the number of
molecules at the surface, respectively to the surface concentration Γ and μ is the
71
Figure 1. (a) Surface potential ΔV is proportional to the effective dipole density μ for
uncharged monolayer. ΔV is the difference between potentials of the water substrate and that of
the monomolecular layer spread at the air/water interface. The difference in the effective dipolar
surface density μ of LE and G phases leads to repulsion between neighboring domains (b) The
surface potential ΔV describes the potential difference between the plates of a parallel capacitor
separated at distance d while the interfacial film represents flat array of dipoles with area.
effective dipole moment perpendicular to the surface[11]. The interpretation of the
surface potential is not as strict straightforward as the physical meaning surface
pressure. Equation (1) is analogous to the equation describing potential difference
between the plates of a parallel capacitor separated at distance d with assumption
that the interfacial film represents flat array of dipoles with area A = kl (Fig.1B).
Two main limitations of Helmholtz equation are considered. First one arises
from the assumption that the dielectric constant is unity. The second limitation
comes from the elimination of the contribution of the dipoles of water molecules
at the interface. [12]. It is also been shown that hydrocarbon and end-group dipolar
moments in the monolayer can influence the surface potential [13]. In order to use
the interpretation of the surface potential in terms of molecular dipole moments as
a first approximation we will take the dielectric constant ε as unity and equal to
the dielectric constant of the air ( ε air = 1 ). Surface potential measurements thus
give a good measure of long-range repulsion within a monolayer [9].
Following McConnell [1] we consider DPPC monolayer in which LE and G
phases are present. If the two-dimensional dipole moment density in the LE − and
72
G − phases are denoted as μ LE and μG respectively then the dipole moment density in the monolayer can be considered as μ = μ LE − μG (Fig. 1a). In the equivalent
dipole model, the dipole densities μ LE and μG in each of the two coexisting phases
are related to the measured surface potentials ΔVLE and ΔVG by means of the
Helmholtz equation (1). Therefore using (1) and substituting ε = 1 one can write:
μ LE = ε00 ΔVLE
(2)
μG = εε00 ΔVG
(3)
From the experimental data (see further) for ΔVG ≈ 0 therefore (3) can be
approximate with:
μG = 0
(4)
Or from μ = μ LE − μG therefore we’ll have:
μ = μ LE
LE
(5)
Because the purpose of this study is to obtain values of the line tension, λ,
between the two coexisting phases, we assumed that DPPC monolayer is in thermodynamic equilibrium-or at least quasi equilibrium because of a slow rate of
compression- in the coexisting region LE/G phase. In this state gas phase occurs
as circular domains with radii R determined by λ and, the difference in dipole
densities between the two phases μ . Therefore we need an expression for μ in
terms of measurable quantities, and for λ in terms of R and μ .
When DPPC monolayer is split into liquid expanded and gas phases, the average dipole moment density, μ , in terms of the values μ LE and μG for each phase,
and the fraction of the interfacial area, φLE, occupied by the liquid expanded phase
[7] may be expressed as:
μ = μΕ φLE + μG (1 – φLE)
(6)
By appropriately combining equations (1) to (6) one can obtain:
μ = μ LE =
ε00 ΔV
(7)
φ
φLE
LE
Eventually, the line tension λ is determined from Req and μ as follows [7]:
λ=
⎛ 4 Req
μ2
ln ⎜⎜ 3 cq
4πε
4π
ε 00 ⎝ e δ
⎞
⎟⎟ ,
⎠
(8)
73
where Req is equilibrium radius of the gas domains and might be determined as it explained in [7], e is the base of the Naperian logarithm, and δ is an effective distance
between neighboring dipoles at the interface, taken approximately 10 Е [14].
Substituting (7) in (8) leads to:
2
1 ⎛ ΔV ⎞ ⎛ 4 Req ⎞
λ=
⎜
⎟ ln ⎜
⎟
4πε 0 ⎝ φLE ⎠ ⎝ e3δ ⎠
(9)
Therefore to calculate λ our theoretical approach required experimental values for Req and μ . The first one was estimated from the images obtained with the
WFFM and the second one from the measurements of the surface potential ΔV .
MATERIALS AND METHODS
Materials
1, 2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) was purchased from
Avanti Polar Lipids (Alabaster, AL) and used as received. Chloroform for phospholipid solutions was purchased from Merck (Germany).
Methods
Isotherm measurements
Initially, DPPC was dissolved in chloroform to a concentration of 1 mg/ml.
The lipids were spread using a Hamilton microsiringe on a pure MilliQ (Millipore Corp., Bedford, MA) water surface, and 15–30 min was allowed for
chloroform evaporation. The monolayers were compressed at a constant
speed of 1Å2 / molecule / min . Surface pressure ( π ) versus area per molecule (Å2 / molecule ) and surface potential ( ΔV ) versus area per molecule
(Å2 / molecule ) isotherms were measured using commercial Langmuir trough
(KSV 5000, KSV, Helsinki, Finland) with platinum plate. The surface potential
( ΔV ) was measured using a gold-coated 241 Am ionizing electrode and a reference calomel electrode. For surface potential data storage an electrometer (KP
511, Kriona, Bulgaria) connected to a PC with home made software for real-time
data acquisition was utilized. The accuracy of the initial surface potential, V0 ,
measurement was about 15 mV . However, the accuracy of the surface potential
variation rate, d V / d t , was 1 mV / s . As usual, the surface potential of the pure
water surface fluctuated for about 30 min. When it became constant the spreading
of the monolayer was performed.
Wide-Field Fluorescence Microscopy(WFFM) measurements
Thorough explanation of the experimental method is given at [15,16]. Here
we present only the schematics of the experimental setup (Fig. 2).
74
Figure 2. A. Illustration of the central part of the microscope setup, with the two beam paths. One
for Fluorescence correlation spectroscopy (FCS) and one for Wide-Field Fluorescence Microscopy
(WFFM). B: Detailed illustration with the constructional elements removed. The objective is placed
just beneath the Langmuir trough. C: Schematic of the complete setup with the lenses in WFM
mode. Only one laser line is shown for simplicity. Lens 1 (L1) and lens 2 (L2) compose the beam
expander. Lens 3 (L3) focuses the laser on the objective (Köhler illumination). For FCS mode Lens
3 is removed and a focused spot is created ~200 μm above the objective. The signal is directed to
either an EMCCD camera (WFM), or an APD (FCS)
75
Image analysis
Image analysis was carried out using public domain PC program- ImageJ,
available on the Internet web site. (http://rsb.info.nih.gov/ij/index.html)
RESULTS AND DISCUSSIONS
Typical isotherms, surface pressure versus mean molecular area (MMA)
(curve 1) and surface potential vs. MMA (curve 2) at Figure 3 confirmed previously published data (see for example [17]). All the phase transitions during
60
800
1
700
600
G
G-LE
LE-C
LC
S
Surface pressure (mN/m)
40
1
LE
2
2
30
500
400
300
Surface potential (mV)
50
20
200
10
100
0
30
40
50
60
70
80
90
100
0
110
2
MMA (Å /mol)
Figure 3. Surface pressure versus mean molecular area (MMA) (curve 1) and surface potential vs.
MMA (curve 2). Phase transitions during the compression of DPPC monolayer are shown – gas
(G), gas-liquid expanded (G-LE) , liquid expanded (LE), liquid expanded –condensed (LE-C) ,
condensed (C) and solid (S). The cartoon representation of lipid molecules illustrates the lipid
organization during the compression. The monolayer is initially in a gas-phase where the lipids
have negligible interaction. After full compression the lipid monolayer is shifted into a solid-phase
where both lipid headgroups and aliphatic chains are highly ordered. Images: In the first image
(G-LE) phase co-existence) the dark areas are gas-bubbles (i.e. exposed air-water interface). In the
second image the dark areas are LC-domains (condensed lipid structure) in a LE matrix. Images
were recorded with the WFM
76
the compression of DPPC monolayer are clearly distinguishable. In our study we
take into consideration only the gas-liquid expanded phase transition. It is known
from, simulation and experimental data that in gas phase the hydrocarbon chains
of DPPC molecules make significant contact with the water subphase. Further,
the compression of this 2D gas leads to a raise of hydrocarbon chains but they
still remain largely disordered. This phase transition to a liquid phase is identified as liquid expanded phase. We will concentrate on surface potential ΔV
versus area isotherm data since these are used in our theoretical approach. For
values of MMA from 180 to about 100 Å2 / molecule the surface potential remains constant with values about 15 mV . The obtained small values of the surface potential at these MMAs allowed us to use equation (9) as an approximation in the proposed theoretical model. At areas smaller than 100 Å2 / molecule
a rapid increase of the surface potential begins in values starting from 15 mV up
to 300 mV . The value of the surface potential equal to 300 mV corresponded to
area of about 95Å2 / molecule . At this point a kink of surface potential appeared.
During further compression of the monolayer from areas from 95Å2 / molecule
down to about 75Å2 / molecule the alteration of the surface potential was not so
sharp and eventually reached a broad plateau in the area of LE-C phase coexisting
region corresponding to 50Å2 / molecule . The values from 300 mV and corresponding area of 95Å2 / molecule to 380 mV with corresponding area about
75Å2 / molecule are observed. It is also clear from the surface pressure vs. MMA
isotherm that at area up to 95Å2 / molecule surface pressures remains undetectable with values altering around instrumental sensitivity.
The series of images obtained with WFFM at certain areas during the compression of the DPPC monolayer are presented at Figure 4. In this experiment,
the relaxation was done at the highest possible rate at which the monolayer plane
could be kept in the optical focus of the microscope (~ 5Å2 / molecule / min ). As
shown, fast relaxation caused quite large gas-bubbles to form at mean molecular areas just a few square-angstroms from the LE-phase. In contrast, when the
relaxation was done at 0.5Å2 / molecule / min , then the homogenous appearing
phase seen in (data not shown) could be maintained for much larger molecular
areas (at least 150Å2 . A general explanation for this may be that in the G-LE region which is close to the LE-phase, small air bubbles spontaneously form (due
to density fluctuations) and collapse (due to line tension) in a highly dynamic
process. These dynamic gas-bubbles were never observed in the microscope images and are therefore expected to be below the optical resolution. However, if the
monolayer was relaxed at high rate (> 2Å2 / molecule / min ), some of these dynamic gas-bubbles were stretched to a size where they became meta-stable. This is
comparable to the phenomena of undercooling of (3D-) fluids, where a substance
may retain its fluid structure below its freezing temperature if the temperature is
shifted too quickly for the molecules to arrange into an ordered (solid) structure.
77
ММА [Å2/DPPC molecule]
ММА [Å2/DPPC molecule]
Figure 4. Wide-Field Fluorescence Microscopy (WFFM) images obtained during the compression
of DPPC monolayers at corresponding surface areas. The areas at which the images were recorded
are pointed with the arrows. The dark and the bright areas at the images represent the gas and liquid
expanded phases, respectively.
Gas-bubbles with a size on the order of the diffraction limit were observed to be at
least meta-stable, so the critical size at which the meta-stable bubbles are reached
must be on the order of 0.5 μ m .
From the Wide-Field Fluorescence Microscopy images and from surface potential measurements we can conclude that the rapid change of surface potential
at area around 100Å2 / molecule is a result of a phase transition from gas phase
to the coexisting G-LE phase. [14]. Further monolayer compression and the appearance of the kink in the surface potential isotherm correspond to the end of the
coexisting phase G-LE region and the beginning of the liquid expanded phase.
Finally, at Figure 5 are presented data for the change of line tension calculated
according to equation (9).
The obtained values for the line tension varied from 0.15 to 1.15 pN . As
it was expected line tension plays dominant role when gas domains are circular
(MMA from 75Å2 / molecule to 95Å2 / molecule ). Afterwards the domains start
coarsening and the line tension drops down to minimum values. Accordingly in
this situation the dipole-dipole interactions become dominant. Finally it should be
78
1.2
Line tension λ (pN)
1
0.8
0.6
0.4
0.2
0
70
80
90
100
110
120
130
140
150
160
170
180
2
MMA (A /molecule)
λ plotted versus corresponding mean molecular area
2
1 ⎛ ΔV ⎞ ⎛ 4 Req ⎞
(MMA). λ was calculated according to the equation λ =
⎜
⎟ ln ⎜
⎟ . In
4πε 0 ⎝ φLE ⎠ ⎝ e3δ ⎠
order to plot data points, the values for the equilibrium radius Req of the gas domains were
determined using procedure explained elsewhere [7], and the values for ΔV were obtained from
Figure 5. The variation of the line tension
surface potential measurement as explained in Materials and Methods.
mentioned that the obtained values of line tension are in the range measured by
Riviere et al. [5]. Still, as these authors pointed out the straightforward comparison is difficult because the investigated systems are different.
Acknowledgements. The work was funded by the National Council “Scientific Research”
Project HT 1-01 “Nanotechnologies and new materials”.
1.
2.
3.
4.
5.
6.
7.
8.
REFERENCES
Harden M. McConnell., Annu. Rev. Phys. Chem, 42, 1991, 171–195
Harden M. McConnell and Vincent T. Moy, J. Phys. Chem., 92, 1988, 4520–4525
Harden M. McConnell, Proc. Natl. Acad. Sci., 86, 1989, 3452–3455
Toshev, B. V., D. Platikanov, A. Scheludko. Langmuir, 4(3), 1988, 489–499
Rivière, S., S. Hénon, J. Meunier G. Albrecht, M. M. Boissonnade, A. Baszkin. Phys. Rev. Lett.
75, 1995, 2506–2509
Muller P., F. Gallet. Phys. Rev. Lett., 67, 1991, 1106–1109
Discher, B. M., K. M. Maloney, D. W. Grainger, S. B. Hall. Biophysical Chemistry, 101–102,
2002, 333–345
Stottrup, B., A. Heussler, T. Bibelnieks. J. Phys. Chem., 4, 2007, 3
79
9.
10.
11.
12.
13.
14.
15.
Benvegnu, D. J., McConnell, H. M. J. Phys. Chem., 96, 1992, 6820-6824
Wurlitzer, S., P. Steffen, Th. M. Fischer. J. Chem. Phys., 112, 2000, 5915–5918
Adamsonq A. W., A. P. Gast. Physical Chemistry of Surfaces (Wiley, New York, 1997), 6ed
Daviesq J.T., E. K Rideal. Interfacial phenomena. (Academic press, New York, 1963, p71
Vogel, V., Dietmar Möbius. J. Colloid Interface Sci. 126, 1988, 408
Benvegnu, D. J., H. M. McConnell. J. Phys. Chem., 96, 1992, 6820–6824
Hac, A. Diffusion Processes in Membranes Containing Coexisting Domains Investigated by
Fluorescence Correlation Spectroscopy, PhD Thesis, Göttingen 2003
16. Gudmand, M. Phase behavior and enzyme dynamics at the lipid-water interface - a monolayer,
fluorescence microscopy, and spectroscopy study, PhD Thesis, Copenhagen, 2008
17. Mohwald, H. Annu. Rev.Phys.Chem. 41, 1990, 441
Received on June 1, 2009
80
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
QUANTUM DOTS FOR BIOIMAGING APPLICATIONS: PRESENT
STATUS AND PROSPECTS
GEORGI G. YORDANOV*, CECO D. DUSHKIN
Faculty of Chemistry, University of Sofia, 1164 Sofia, Bulgaria
* Corresponding author:
Abstract. This review considers the present status and the prospects for future
development of the bioimaging applications of quantum dots. The preparation and optical
characteristics of quantum dots are discussed, as well as the general strategies for their
post-synthetic chemical modifications, which are required in order to obtain biocompatible
fluorescent probes. Special attention is given to the problem with the cytotoxicity of
quantum dots, which is the major limitation toward their utilization in biological research.
Recently developed applications of quantum dots as fluorescent markers for colloidal drug
carriers are reviewed. Despite the currently existing problems, it is expected that quantum
dots will reveal many important details about the mechanisms of interaction between
biological cells and nanosized materials.
Key words: quantum dots, semiconductors, nanoparticles, nanocrystals, fluorescence,
bioimaging.
INTRODUCTION
The quantum dots (QDs) are spherical nanocrystals (2–10 nm in diameter)
made of semiconductor materials. A nanocrystal consists of about few hundreds
to few thousands of atoms and is thus an intermediate between a molecule and
the bulk. Since their first discovery in 1981 [1], the QDs and their chemical
synthesis is a rapidly expanding area of research in materials science [2–4]. These
81
nanocrystals represent a novel type of inorganic fluorophores. QDs were first
utilized as fluorescent biolabels in 1998 [5, 6], which promoted further extensive
research in this area. Bioimaging applications of QDs also represent a rapidly
developing field and up to date there are many reviews concerning different aspects
of the problem [7–18]. In this report we review the influence of synthesis methods
on the optical characteristics of quantum dots, their subsequent processing and
suitability for different bioimaging applications. The general principles and ideas
in bioimaging with QD-probes are illustrated. The barriers restricting further
progress are discussed taking into account the significant potential for cytotoxicity
of QDs both in vitro and in vivo. The potential of QD-probes for revealing the
mechanisms of interactions between biological cells and nanosized materials is
discussed from the viewpoints of recent advancements in the fields of cancer cell
biology and drug delivery research.
QUANTUM DOTS FOR BIOIMAGING
1. Optical properties
Quantum dots absorb and emit visible light at room temperature due to a
quantum effect, known as the size-confinement of the exciton [14, 19–24]. The most
impressive for QDs are their size-dependent optical properties. Their absorbance
and emission wavelengths depend on the nanocrystals diameter [25]. After an
electron is excited, some of its energy is lost to atomic vibrations. This energy
is typically converted to heat. When the electron decays into the ground state, it
emits light at longer wavelength, because of its energy loss – this is the so-called
normal band-edge emission [26]. Typical absorbance and fluorescence spectra of
CdSe QDs prepared by us using the hot-matrix method are shown in Fig. 1. Due
to the thermal energy loss, the fluorescence spectrum is red-shifted with respect
to the absorbance spectrum (so-called Stokes shift). The nanoparticles can exhibit
also a unique type of fluorescence resulting from a trapping of an electron at the
crystal surface [26, 27]. When a defect is entrapped into the crystal, it introduces
a potential energy state in the band gap. Electrons are trapped at this state. The
emission from this state leads to an electron decay to the ground state and is thus
called trap-state emission. The respective fluorescence band is broader than the
band-edge emission and located at a longer wavelength, respectively. A QD can
exhibit both band-edge and trap-state emission simultaneously.
82
Absorbance, a.u.
0.7
a
160
0.6
0.5
120
0.4
b
0.3
0.2
80
40
Fluorescence, a.u.
200
0.8
0.1
0
450
550
650
0
750
wavelength, nm
Fig. 1. Typical absorbance (a) and fluorescence (b) spectra of CdSe QDs with average size of
4.5 nm. The QDs are prepared by hot-matrix method in liquid paraffin at 250 °C.
The quantum confinement effect results in unique optical and electronic properties
of QDs, giving them numerous advantages over the current fluorophores. The
conventional dyes have narrow excitation spectra. It requires an excitation by light of
a specific wavelength, corresponding to the maximum in the absorbance spectrum.
Also, the conventional organic fluorophores have broad emission spectra, meaning that
the spectra of different dyes may overlap thus limiting the possibilities for multicolor
labelling. Furthermore, most of the organic fluorophores have a poor photostability
and usually photobleach after only a few minutes of exposure to UV-light. Also,
the organic dyes have a fast fluorescence emission (~5 ns), which is similar to the
fluorescence lifetime of the background from many naturally occurring substances,
which leads to reduction of the signal-to-noise ratio in fluorescent bioimaging.
Now, let us summarize the advantages of QDs [16]. They have broad absorption
spectra, allowing excitation by light of a wide range of wavelengths. This may be
used to excite simultaneously multiple coloured QDs using a single wavelength
of light. The QDs have narrow emission spectra, which can be easily controlled
by varying the core size and composition, and also by variation of the surface
coatings. Furthermore, the QDs are extremely stable against photobleaching and
can remain fluorescent for hours under UV-light illumination. Finally, the QDs
have a long fluorescent lifetime after excitation, which can be advantageous
in time-gated imaging [14]. In the time-gated analysis, the photons hitting the
detector in the first few nanoseconds are disregarded to decrease the background
noise and increase sensitivity.
83
The most pronounced advantage of QDs over the organic fluorophores is their
superior photostability, demonstrated in a number of reports [5, 6, and 28]. This may
be exploited in situations where a long-term monitoring of labelled substances is
required, and is an area in which QDs may find use. For example, the comparison of
the photostability of silica-coated QDs and Rhodamine 6G at excitation wavelength
of 488 nm shows that the QDs exhibit a stable emission for at least 4 h, while
the Rhodamine dye bleaches after 10 min [8]. This difference in the photostability
is clearly illustrated by photographs comparing organic fluorophore vs. QDs in
fluorescent tracking of cells in the course of embryogenesis [28] and in fluorescent
labelling of cell structures [29]. Another example represents dihydrolipoic acidcapped CdSe-ZnS QDs, which show no loss in intensity after 14 h, and are nearly
100-fold as stable as, and also 20-fold as bright as, Rhodamine 6G [6].
2. Synthesis of core-only quantum dots
Most of the classical biological applications of QDs involve Cd-based
nanoparticles. The CdSe QDs are produced in the 90s by the organometallic
synthesis using dimethylcadmium as the Cd-precursor and toxic organic solvents,
such as trioctylphosphine oxide (TOPO) and aliphatic amines [2,30–32]. In the
2000s, the organometallics are replaced with CdO [3,4]. We have developed a
new approach using liquid paraffin as a solvent for the QDs synthesis [33], which
allows the systematic investigation of nanocrystal growth and studies of the effects
of various factors on this process [34–38]. The liquid paraffin solvent possesses a
number of advantages in comparison with the classical solvents used in nanocrystal
synthesis. The liquid paraffin is cheap, natural, non-toxic, chemically inert, and
has a high boiling temperature (>320 °C). The synthesis of QDs in liquid paraffin
leads to the formation of relatively monodisperse in size nanocrystals of high
fluorescence quantum yield (~25%) and well-controllable size. The size of QDs,
respectively their optical properties, can be controlled by various factors, such as the
synthesis temperature [2-4, 35–37, 39], the precursor molar ratio [36, 39–41], and
the composition of reaction medium (matrix) [38, 39, 42, 43]. Different in size QDs
can be obtained by simply taking aliquots from the matrix at different times of their
growth, or by rapidly cooling down the reaction mixture. After the synthesis, the QDs
can be easily purified and isolated applying simple extraction procedures [4,44]. A
synthesis of QDs, suitable for biological applications, has been proposed directly in
water dispersions [45–48]. In this case, the obtained QDs carry functionalities (like
thioglycolic acid) on their surface, which can serve as linkers with biomolecules.
Some commercially available QDs for bioimaging applications are also
non-cadmium. Recent report deals with the potential bioapplication of Zn-based
QDs [49]. Particular interest represents the nanoparticle synthesis of AIIIBV
semiconductors. The colloidal synthesis of various AIIIBV QDs is less studied
and needs more effort in order to obtain high-quality nanocrystals for extended
84
bioimaging applications [50]. For example, colloidal QDs of InAs (diameters
~2.5–6 nm) are synthesized in a hot matrix of trioctylphosphine (TOP) [51]
serving as both the solvent and capping agent. The colloidal InAs QDs show
absorbance and fluorescence affected by the quantum confinement. InGaP2 based
QDs are commercial products for applications as markers in infrared light, where
the biological tissues are more transparent.
3. Synthesis of core-shell quantum dots
A core-shell quantum dot consists of a semiconductor nanocrystal core,
coated with a shell of another semiconductor material. The core-shell QDs have
a core of a narrow band-gap semiconductor like CdSe and a shell of a wide bandgap semiconductor like ZnS or CdS [52]. The core-shell nanocrystals typically
have brighter fluorescence [52–59] and are more stable against photodegradation
[54] than the core-only QDs. The fluorescence quantum yield of core-shell
nanocrystals can be 50–80%, however a fluorescence quantum yield of up to
40% is usually achieved [5, 60–63].
Core-shell CdSe/ZnS QDs have been first synthesized in a hot matrix of TOPO
[52]. A wide spectral range of bright fluorescence from different in size samples
of CdSe/ZnS can be obtained (the fluorescence peaks occur from 470 to 620 nm).
The position of maximum in the fluorescence spectrum shifts to red with increasing
of the shell thickness. The overcoating of CdSe QDs with either ZnS [52,53] or
CdS [54,64] shell has become routine and usually results in almost an order-ofmagnitude enhancement in the fluorescence quantum yield compared to the initial
core-only QDs. Recently, we prepared CdSe/CdS QDs by a novel approach using
the hot-matrix method in liquid paraffin [65]. In this procedure, the sulfur precursor
is injected at once to a dispersion of CdSe cores and cadmium stearate in liquid
paraffin at ~100 °C. Then, the temperature is gradually raised up to 250 °C, resulting
in CdS shell growth. The gradual heating, allows the successful preparation of highly
fluorescent (florescence quantum yield ~65%) core-shell QDs relatively fast, at the
same time avoiding dissolution and size defocusing of the CdSe cores.
4. Hydrophilization of quantum dots
The QDs, synthesized in a hot organic matrix, have the disadvantage of being
capped with hydrophobic organics, which do not allow their dispersion in aqueous
medium for the biological applications. Further special treatment is necessary to
replace the hydrophobic organic layer with a hydrophilic one [8]. Water-insoluble
QDs can be grown easily in hydrophobic solvents, but the solubilization in water
requires sophisticated surface chemistry alterations and presents a significant
challenge. There are three general strategies for water solubilization of QDs: (i)
ligand exchange, (ii) micelle formation through hydrophobic interaction, and (iii)
silica encapsulation. One should take into account that some types of QDs, such
85
as CdTe suitable for biological applications, can be synthesized directly in water
dispersions, however they are less stable and easily undergo aggregation [45–48].
4.1. Ligand exchange
Usually, the QDs synthesized in organic solvents have hydrophobic surface
ligands, such as trioctylphosphine oxide (TOPO), trioctylphosphine (TOP) [2, 43,
66], tetradecylphosphonic acid (TDPA) [3] or various long-chain fatty acids (lauric,
stearic, oleic, etc.) [4, 33, 43, 65, 67]. These hydrophobic ligands could be replaced
by some water-soluble bifunctional molecules, in which the one end is connected
to the nanocrystal surface and the other end is hydrophilic and may also be reactive
to biomolecules. Examples of some water-soluble bifunctional molecules used
are mercaptocarboxylic acids (HS-(CH2) n-COOH, n=1–15) [6, 8, 48, 68, 69], 2aminoethanethiol [68], dithiothreitol [70], dihydrolipoic acid [61], hydrophilic
phosphines [71], peptides [72], neoglycoconjugates with a reactive thiol group [73],
etc. (Fig. 2). The thioglycolic acid (TGA) was used in the first bioapplication of
QDs [6], while recently dihydrolipoic acid (DHLA) is more used, because of its
biocompatibility, lower toxicity and higher stability of the obtained QD-dispersions
in water [61]. However, TGA is widely used to obtain hydrophilic QDs (Fig. 3).
Our experience shows that such TGA-capped QDs can be prepared by extraction
of stearate-coated QDs (synthesized by the hot-matrix method in liquid paraffin,
purified and dispersed in chloroform) with water solution of sodium thioglycolate.
However, the ligand exchange in most cases dramatically decreases the fluorescence
quantum yield of QDs. Also, the thiol-based molecules (e.g. mercaptocarboxylic
acids) may form disulfides over time and come off from the quantum dot surface
and finally the QDs aggregate and precipitate out of water; the other water-soluble
bifunctional molecules are expensive and instable, either.
OH
HS
COOH
thioglycolic acid
H2N
SH
SH
HS
OH
dithiothreitol
2-aminoethanethiol
O
OH
SH
SH
dihydrolipoic acid (DHLA)
Fig. 2. Chemical structures of various bifunctional ligands used for hydrophilization of QDs.
86
HOOC
O O O OO
O
O
O
O
O
O
O
O
O
O
O
O
O
O
OO
OO O
QD
HOOC
HOOC
HOOC
HOOC
S
S
COOH
S
S
S
QD
S
HOOC
S
S
S
S
S
S
COOH
COOH
COOH
COOH
COOH
Fig. 3. Schematic representation of a hydrophobic stearate-coated QD (left) and a hydrophilic
QD, coated with thioglycolic acid (right) obtained after ligand exchange reaction. Stearate-coated
QDs can be prepared by hot-matrix synthesis in liquid paraffin (see the text for details).
4.2. Encapsulation in micelles
Phospholipids, such as 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N[methoxy(polyethylene glycol)] or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine
has both hydrophobic and hydrophilic ends. They could encapsulate QDs in the
core by forming oil-in-water micelles through hydrophobic interaction between
their hydrophobic ends and the surface ligands of QDs thus providing waterdispersibility [28]. Recent work reports on the preparation of water-dispersible
QDs, coated with Gemini surfactants [74]. These QDs are biocompatible,
photostable, and suitable for live cell imaging.
A more promising approach is to use amphiphilic polymers to form micellelike structures for transferring the hydrophobic QDs into water [75, 76]. A triblock
polymer, containing segments of poly(butylacrylate), poly(ethylacrylate) and
poly(methacrylic acid), is used to transfer hydrophobic TOPO-coated QDs into
water, in which the methacrylic acid segments were also partially derivatized with
octylamine and PEG-NH2 through a two-step EDC-coupling [76]. The hydrophobic
side chain is directly attached to the hydrophilic acrylic acid segment and interacts
strongly with the hydrophobic tails of TOPO. The strategy of using amphiphilic
polymers is generally superior to the ligand exchange, because:
(i) There is no direct interaction with the atoms on the nanocrystal surface and
therefore can preserve the original fluorescence quantum yield to the highest extent.
87
(ii) The large number of hydrophobic side chains on the polymer strengthens
the hydrophobic interaction to form more steadily structures and stable waterdispersible QDs.
(iii) The amphiphilic polymers can be carboxylate or amine functionalized in
order to attach various ligands or biomolecules [77].
Other relatively large organic molecules, such as amphiphilic dendrimers
[78] and amphiphilic hyperbranched polyethylenimine [79], are also used for
hydrophilization and stabilization of QDs in water dispersions.
4.3. Encapsulation in silica
A layer of silica can also encapsulate the fluorescent QDs in order to make them
biocompatible [5, 80]. Functional organosilicone molecules, containing –NH2 or –SH, can
be incorporated into the silica shell thus providing surface functionalities for biomedical
applications. The silanization method includes replacement of the hydrophobic organics
on the nanocrystal surface with mercaptopropyl-tris(methyloxy)silane (MPS). The
methoxysilane groups (Si-OCH3) hydrolyze into silanol groups (Si-OH), which form
siloxane bonds upon heating, thus releasing water molecules. Then, fresh silane precursors,
containing a functional group (F) -SH, -NH2; -PO- (O-CH3), are incorporated into the shell.
The remaining –OH groups are converted in –OCH3 groups; this last step blocks further
the silica growth. This method seems to stand in between the above two strategies, but is
much closer to the ligand exchange. The quantum dot surface changes once introducing
the organosilicone molecules and usually results in a decrease of the fluorescence quantum
yield. The procedures to make a controllable silica coating around the hydrophobic QDs
are complicated. The silica coating needs to be carried out at dilute conditions, which is
a limitation for large quantity production. However, the fluorescence of silanized QDs is
much more stable in comparison with the organic fluorophores [80].
A simple aqueous synthesis of silica-capped, highly fluorescent CdTe
quantum dots is developed [81]. The synthesis of silica shell in this case is carried
out through a modified Stöber method. The photoluminescence studies show
that the silica shell results in greatly increased photostability in tris-borate-eth
ylenediaminetetraacetate and phosphate-saline buffers. To further improve their
biocompatibility, the silica-capped QDs are functionalized with poly(ethylene
glycol) and thiol-terminated biolinkers. Through the use of these linkers, antibody
proteins are successfully conjugated.
Another general method for silica encapsulation in toluene is also reported
[82]. The biocompatible modification and multi-functionalization of QDs has
been carried out through direct reaction of organic silanes on the surface of QDs.
Functionalized QDs, including CdSe/ZnS, CdSe/CdS core/shell and PbS QDs,
have been prepared at a high concentration up to 10-4 M in toluene. Different
organic silanes can be used to prepare various organosiloxane shells.
88
5. Bioconjugation of functionalized quantum dots
Various water-dispersible functionalized QDs have been used in both in vitro
and in vivo bioimaging and detection. A number of published review articles
provide excellent overviews about a variety of biomedical applications of QDs [7,
8, 14, 76, 83]. Here, we will summarize the bioconjugation reactions used for the
preparation of functionalized QDs.
5.1. Bioconjugation of carboxyl-functionalized QDs
The bioconjugation reactions involving amino-functionalized QDs are summarized
and represented schematically in Fig. 4. The carboxyl-functionalized QDs are
usually conjugated to biological molecules by using the reaction with 1-ethyl-3-(3dimethylaminopropyl)-carbodiimide (EDC), known as EDC-coupling. EDC is a watersoluble derivative of carbodiimide. Carbodiimide catalyzes the formation of amide
bonds between carboxylic acids or phosphates and amines by activating carboxyl or
phosphate to form an O-urea derivative. This derivative reacts readily with nucleophiles
(usually amine groups). Historically, EDC-coupling was first used to conjugate TGAcoated QDs with transferrin and IgG [6]. Now EDC-coupling is among the most used
techniques for direct conjugation of QDs with various proteins, including antibodies [6,
48, 72, 77, 84], or small biomolecules, such as γ-aminobutyric acid [85].
Antibodies can be conjugated to carboxyl-functionalized QDs by three different
ways (Fig. 4): (i) directly, by covalent attachment via EDC-coupling [6]; (ii)
indirectly, by using streptavidin (or avidin)-coated QDs and biotinylated antibodies
NR'
H 2N
COOH
C NR''
QD
COO
C
COOH
molecule
QD
NHR''
COOH
H
O
N
C
molecule
COOH
NR'
COO-
COOH
QD
COOH
COOH
streptavidin
(avidin)
QD
+
COO+
COO - +
COO-
QD
adapter protein
COO-
+
biotinylated
antibody
COO-
QD
antibody
+
COO-
COO-
+
+
COO+
COO - +
QD
+
+
+
+
COOCOO-
+
+
+
Fig. 4. Schematic view of some bioconjugation reactions involving carboxyl-functionalized
QDs (see the text for details).
89
[9, 53]; (iii) indirectly, by using a special adapter protein, which is electrostatically
adsorbed on the carboxyl-functionalized QDs (see for more details section 4.4.).
The avidin-biotin and streptavidin-biotin interaction is widely used for conjugation
of QDs to various biomolecules and ligands [72]. Most of the QDs, currently used in
immunofluorescent assays, are streptavidin-coated for interaction with biotinylated
ligands and antibodies. The avidin-biotin and streptavidin-biotin interaction is among
the strongest known non-covalent, specific interaction between protein and ligand. The
bond formation between biotin and avidin is very rapid and, once formed, is unaffected
by wide extremes of pH, temperature, organic solvents and other denaturating agents.
The complex can withstand incubation in 2 M urea and is not significantly affected
by pH values between 2 and 13. Streptavidin is a biotin-binding protein, which has a
molecular weight of ~60,000 Da and consists of 4 subunits. Each subunit is capable of
binding of one biotin molecule. The streptavidin protein has 32 lysine residues and can
be conjugated to various molecules, as well as with QDs, using EDC-coupling. Biotin,
a naturally occurring vitamin with a molecular weight of 244 Da, can be conjugated
to proteins using hydrophobic or hydrophilic linkers with different lengths. Usually
biotinylated antibodies are used as primary antibodies in a sandwich immunoassay for
binding with the streptavidin-QD conjugates. Various applications of QDs-biomolecule
conjugates via biotin-streptavidin interaction are discussed in the next chapters.
5.2. Bioconjugation of thiol-functionalized QDs
Thiol-functionalized QDs can be conjugated to proteins (as well as any other molecules
containing amine groups), using 4-(N-maleimidomethyl)cyclohexane-1-carboxylic acid
O
O
H 2N
N
molecule
N
O
O
O
O
O
O
4-(N-maleimidomethyl)cyclohexane-1-carboxylic
acid 3-sulfo-N-hydroxysuccinimide
SH
QD
SO3 H
O
molecule
HN
N
SH
SH
O
SH
QD
S
SH
N
O
O
HN
molecule
Fig. 5. Schematic representation of a bioconjugation reaction involving thiol-functionalized QDs.
90
3-sulfo-N-hydroxysuccinimide [81]. The scheme of conjugation reactions is shown in
Fig. 5. First, the linker molecule reacts with the amine to form an amide derivative. Then,
the obtained derivative reacts with a thiol group from the QD-surface to form the QDconjugate.
5.3. Bioconjugation of amino-functionalized QDs
The bioconjugation reactions involving amino-functionalized QDs are
summarized and represented schematically in Fig. 6. The reaction of aminefunctionalized QDs with N-(β-maleimidopropyloxyl)succinimide ester is used for
the conjugation of QDs to ligands, bearing a thiol (–SH) group [77]. For example,
the ligand Deltorphin-II targeting G-protein coupled receptor is successfully
conjugated to amine-functionalized QDs in order to observe the distribution of
human δ-opioid receptors expressed in living cells.
EDC
OH
P
nucleotide
O
OH
P
Imidazole
-
O
O
O
N
O
O
QD-nucleotide
conjugate
NH 2
QD
NH2
N-(3-maleimidopropyloxyl)
succinimide ester
H
H N
NH2
N
O
H
N
H
O
O
HO3S
N
O
O
O
NH
S
H
O
O
NH 2
NH
NH2
NH2
N
O
O
NH
QD
N O
NH2
P
N
O
QD
OH
biotinamidocaproic acid 3-sulf oN-hydroxysuccinimide ester
O
O
N
molecule
HS
HO3 S
NH2
QD
NH 2
NH
O
OH
O
H
H N
NH2
O
N
O
QD-thiol conjugate
S
molecule
QD
NH 2
HN
O
O
S
H
O
NH
H
N
H
biotinylated QD
Fig. 6. Schematic view of some bioconjugation reactions involving amino-functionalized QDs
(see the text for details).
91
A reaction involving the EDC reagent is used also as a first stage in the conjugation
of amino-functionalized QDs to oligonucleotides [86]. The 5’-phosphate group of
the oligonucleotides is activated with EDC, followed by a reaction with imidazole to
obtain a reactive phosphorimidazolide derivative. The obtained phosphorimidazolide
derivative reacts with amino-functionalized QDs in order to produce the phosphoramide
conjugate.
One of the first bioapplication of amino-functionalized QDs as fluorescent
biolabels utilizes biotinylated nanocrystals [5]. Biotinylated QDs may be used as
markers attached to different streptavidin (or avidin)-conjugated molecules.
CYTOTOXICITY OF QUANTUM DOTS
As the range of biomedical applications of QDs expands to in vivo
measurements, questions concerning their short and long-term cytotoxicity
are raised. All known studies are focused on the toxic effects of colloidal QDs
dispersed in aqueous solution on cells. The extent of cytotoxicity has been found
to depend upon a number of factors including size, capping materials, color, dose
of QDs, surface chemistry, coating bioactivity and processing parameters (for
detailed review see ref. [87]). Recent reports have indicated that bare CdSe QDs
are indeed toxic to cells [88, 89, 91–99].
A number of mechanisms have been postulated as responsible for QD
cytotoxicity [91,100]. These include:
1. Release of free Cd (II) ions (QD core degradation) [88, 95]. When
appropriately coated, the CdSe-core QDs can be made less toxic and used to track
cell migration and reorganization in vitro.
2. Free radical formation [95,101]. It is proposed that the mechanism for QDinduced cell death involves the generation of reactive oxygen species (ROS) in
the extracellular environment and intracellularly. These ROS can cause plasma
membrane damages and intracellular organelle damages.
3. DNA damage caused by CdSe QDs has been observed under exposure
to UV-light, most probably due to the production of free radicals and reactive
oxygen species [97].
4. QDs, such as CdTe, were found to induce apoptosis in human cells by
affecting various biochemical pathways [93, 96].
5. Cytotoxicity of QDs can be rendered significantly by due nature of the
surface coating material [87, 89]. For example, compounds such as thioglycolic
acid are found to be toxic to a number of cells. For that reason the QDs must be
purified from any excess of a free surface coating ligand, which may have toxic
effects on the living cells.
The reviewed literature suggests that the engineered QDs cannot be considered
a uniform group of substances. QD absorption, distribution, metabolism, excretion,
92
and toxicity depend on multiple factors derived from both inherent physicochemical
properties and environmental conditions; QD size, charge, concentration, outer coating
bioactivity (capping material and functional groups), and oxidative, photolytic, and
mechanical stability have been implicated as determining factors in QD toxicity.
APPLICATIONS OF QUANTUM DOTS IN BIOIMAGING
1. Fluorescence resonance energy transfer (FRET) assays
The fluorescence resonance energy transfer (FRET) represents energy transfer
from a donor to an acceptor, which takes place at small enough distance between
them [20]. As a result, the donor’s fluorescence intensity decreases and that of
the acceptor increases. The first investigation, concerning the QD fluorescence
quenching by FRET, involves attachment of a chromophore (QSY-7) labeled
maltose-binding protein (MBP) and IgG to QDs capped with dihydrolipoic
acid [102]. Later research demonstrated that the gold nanoparticles could act as
fluorescence quenchers in QDs-based FRET sensors [103]. It must be pointed
out that the QD-based FRET-probes are utilized also in gene technology for
investigation of the telomerization dynamics and DNA replication [104].
Recently, advanced QD-based FRET systems for investigation of enzymatic
activity are developed, providing easily controlled FRET efficiency, as well as
data about the enzymatic velocity, Michaelis–Menten kinetic parameters, and the
mechanisms of enzymatic inhibition [105,106]. The QDs-FRET-based enzymatic
activity probes are used to determine the activity of collagenase in solution [107].
In this study, rhodamine-labeled peptide-coated CdSe/ZnS QDs are synthesized
and used as FRET probes to monitor the proteolytic activity of extracellular matrix
metalloproteinases (MMPs) in normal and cancerous cell cultures. Taking into
account that the MMPs activity in breast cancer cultures is significantly higher
compared to normal cells, it is possible to distinguish a normal and cancerous
tissue in less than 15 min by using this FRET assay.
2. Cell tracking during embryogenesis
The cell tracking during embryogenesis is an extremely important topic in
developmental biology, where the QDs have been used as fluorescent labels with
superior photostability. In a pioneering study, highly fluorescent QDs have been
encapsulated in phospholipid micelles and used to label individual blastomere
cells in Xenopus embryos [28]. These encapsulated QDs are stable in vivo, do not
aggregate and are able to label all cell types in the embryo. At the levels required
for fluorescence visualization (2×109 QDs/cell), the QD-micelles are not toxic to
the cells, but concentrations higher than 5×109 QDs/cell produce abnormalities.
The QDs are confined to the injected cell and the respective daughter cells.
Interesting translocation of the QDs to the cell nucleus is observed at a particular
93
stage in the embryo development. Recent studies report the use of QDs on the
Xenopus embryo development to image mesoderm migration in vivo with single
cell resolution and provide in vivo quantitative data regarding the migration rates
[108]. Fluorescent labelling of cells with QDs is also applied in studies of the
Zebrafish embryo development [109].
3. Labeling of cell surface receptors
Ligand-conjugated QDs are first used to label cell surface receptors in 2002
[110]. It is demonstrated that serotonin-capped QDs interact with the serotonin
transporter protein in transfected HeLa cells and oocytes in vitro. A serotoninlinker arm ligand is synthesized and used to modify the QDs. It is found that
the serotonin-modified QDs inhibit the serotonin transport activity in transfected
cells. More recently, new high-affinity ligands for serotonin transporter protein are
created, which are then conjugated to QDs (functionalized with -COOH groups)
through EDC-coupling [111,112].
QDs are used to track the individual glycine receptors and analyze their
lateral dynamics in the neuronal membrane of living cells [113]. This receptor is
the main inhibitory neurotransmitter receptor in the adult spinal cord. The issue
of lateral mobility of the receptors for neurotransmitters has become central to
understand the development and plasticity of synapses. The properties of QDs
make it possible to record the mobility of individual molecules at the neuronal
surface, even in confined cellular compartments.
A practical method is reported for generating water-soluble QDs and the
necessary chemistry for covalently coupling them with ligands targeting Gprotein coupled receptors (GPCRs) [77]. GPCRs constitute a large and diverse
family of proteins, whose primary function is to transduce extracellular stimuli
into intracellular signals. Since 50 % of the pharmaceuticals target GPCRs, new
methods for the imaging of GPCRs at the cell surfaces are of interest. As a proof
of principle, the QDs are chosen to target the human melanocortin and δ-opioid
receptors. It is demonstrated that the QDs could be used for effective imaging
of melanocortin receptors. It is also demonstrated that the QDs, conjugated to
Deltrophin-II analogs, could be utilized for the selective imaging of δ-opioid
receptors on the cell surfaces and for single molecule imaging.
Recent reports describe the development of QD-based probe for fluorescent
detection of apoptosis [114]. The QDs are conjugated to Annexin V for specific
targeting of apoptotic cells. For that purpose, streptavidin-conjugated QDs are
coupled to biotinylated Annexin V, a protein that specifically recognizes and binds
to phosphatidylserine moieties present on the outer membrane of apoptotic cells
and not on healthy or necrotic cells. This makes the QDs excellent candidates to
continuously follow the fast changes occurring at the membrane of apoptotic cells
and facilitates the time-lapse imaging as they alleviate any bleaching issue. The
94
investigation of molecular events that take place during apoptosis is extremely
important for understanding the programmed cell death, which is usually disrupted
in cancer cells and represents a major problem.
4. Immunofluorescent bioimaging
The application of QDs in immunofluorescent detection is demonstrated
with one of the two first bioimaging applications of QDs in 1998 by conjugating
TGA-capped QDs with IgG by EDC-coupling [6]. In this study, antibodyinduced agglutination of QDs, conjugated to human IgG, is clearly observed
for the first time. This “proof of principle” paved the way for further research
and improvements of the QDs applications in immunofluorescent labeling [29,
72,115–119]. The reactions for conjugation of QDs to antibodies are discussed in
section 2.5. Streptavidin-coated QDs are found as the most suitable ones, because
they can be easily conjugated to different commercially available biotinylated
antibodies. The QD-antibody conjugate can be used for immunofluorescent
bioimaging by two general approaches. In the first approach, a streptavidin-coated
QD is conjugated to a biotinylated primary antibody, which recognizes directly
the targeted antigen. The second approach for a QD-mediated labeling of antigens
involves secondary and primary antibodies. The primary antibody targets the
antigen, and is then recognized by a biotinylated secondary antibody, which binds
a streptavidin-coated QD (Fig. 7).
QD
QD
secondary antibody
primary antibody
antigen
cell membrane
Fig. 7. Schematic representation of the application of QDs for immunofluorescent bioimaging
using biotinylated primary antibody (left) or a combination of a primary antibody and a
biotinylated secondary antibody (right).
95
5. In vivo imaging
Fluorescent QDs are used for whole body imaging, however relatively little work
is done due the potential for toxicity of QDs [10, 12, 76,120-122]. It is worth noting
that successful labeling of lymph nodes in pigs is achieved by using NIR-emitting
QD-probes [123]. This strategy may be useful for successful surgical resection
of lymph nodes containing metastatic cancer cells. A number of complications
exist with the QD imaging in animals due to the absorbance and scatter of light
by the tissues, as well as observation of autofluorescence upon their excitation.
This may be partially overcome by using QDs that emit in the near infrared region
(700–1000 nm) [108,120,122]. Another barrier to use in vivo QDs is the extensive
reticuloendothelial uptake of QDs introduced into the bloodstream [121].
Multifunctional nanoparticle QD-based probes for cancer imaging in living
animals are also developed [76]. The structural design involves encapsulation of
luminescent QDs with an ABC triblock copolymer and linking of this amphiphilic
polymer to tumor-targeting ligands. For active tumor targeting, antibodyconjugated QDs are used to target a prostate-specific membrane antigen (PSMA).
Immunocytochemical studies of QD-PSMA Ab binding activity in cultured prostate
cancer cells confirmed PSMA as a cell surface–specific marker for some prostate
cancer cell lines, like C4-2 cells. In vivo targeting studies of the human prostate cancer
growing in nude mice indicate that the QD-probes accumulate at the tumors both
by the enhanced permeability and retention of tumor sites and by antibody binding
to cancer-specific cell surface biomarkers. Using both subcutaneous injection of
QD-tagged cancer cells and systemic injection of multifunctional QD-probes, the
authors have achieved sensitive and multicolor fluorescence imaging of cancer cells
under in vivo conditions. These results raise new possibilities for ultrasensitive and
multiplexed imaging of molecular targets in vivo.
The tumour vasculature plays an important role in determining the tumour
pathophysiology and drug delivery. Angiogenesis, the formation of new blood
vessels from preexisting vasculature, is essential for the tumor growth and
progression. Integrin αVβ3, which binds to arginine-glycine-aspartic acid (RGD)containing components of the interstitial matrix, plays a key role in the tumor
angiogenesis and metastasis. It is significantly upregulated in invasive cancer cells
but not in normal tissues. The in vivo targeting and imaging of tumor vasculature
using RGD peptide-labeled QDs is reported [122]. Athymic nude mice, bearing
subcutaneous U87MG human glioblastoma tumors, are administered QD-RGD
intravenously. The tumor fluorescence intensity reaches a maximum at 6 h post
injection with a good contrast. The reported results open up new perspectives for
integrin-targeted near-infrared optical imaging and may aid in cancer detection
and management including imaging-guided surgery.
The in vivo applications of QDs are limited from several factors. First,
the QDs, including their capping materials, may be immunogenic, which may
96
result in acute immune response as well as massive uptake of QDs by the
reticuloendothelial system. Second, the QD core material, as well as the capping
organics, may be toxic to the organism or individual cells. Third, the size of QD
complexes precludes renal excretion, making clearance from the blood stream
unlikely. This may increase the QDs uptake by the liver, which may result in a
dangerous hepatic toxicity. Taking into account these serious barriers against the
in vivo applications of QDs, it is clear that the QD-based fluorescent probes may
be more useful for in vitro assays.
6. Applications of quantum dots in cancer cell research
Attempts for fluorescent in vivo imaging of cancer cells are reported [76,
90,124]; some of them are described in the previous section. Also, there are
many reports concerning the in vitro fluorescent labelling of cancer cells by
using antibodies and other targeting ligands [125–128]. Here, we shortly describe
representative examples of these latter cases.
The epidermal growth factor receptor (EGFR) can be a molecular marker
for cancerous cells. It is expressed ubiquitously in cells and is overexpressed in
human malignancies including breast cancer, glioma and lung cancer, making it a
promising biomarker. A successful direct targeting of EGFR with QDs, conjugated
to anti-EGFR antibodies, is carried out and compared to appropriate controls
[125]. Also, QD-lectin conjugates are synthesized and applied for identification of
leukemia cells from normal lymphocytes using fluorescent confocal microscopy
and flow cytometry [126]. The results are compared with commercially available
FITC-lectin. Lectins are found to possess a high affinity to several leukemia cell
lines, without or with low affinity to normal lymphocytes. The results clearly
demonstrate that the QD-lectin conjugates are appropriate fluorescent markers
for identification of several leukemia cell lines. It is found that the QD-lectins
give higher quality images and possess higher stability against photobleaching in
comparison with the commercially available FITC-labeled lectin.
7. Fluorescent labeling of colloidal drug carriers
Nanosized drug carrier systems like liposomes, polymer nanoparticles, and
solid-lipid nanoparticles have been optimistically considered as “magic bullets”, not
only because a wide range of biologically active substances can be encapsulated and
targeted to the desired site of action, but also because they can be injected into human
or animals without adverse effects [129]. The fluorescent labeling of these nanosized
carriers offers a possibility to gain an insight into the mechanisms of their interaction
with the biological cells and tissues by visual tracking of the labeled nanoparticles
[130, 131]. The QDs can serve as highly effective fluorescent markers for such
a purpose. For example, a relatively simple approach is reported concerning the
efficient encapsulation of CdSe QDs in liposomes, which are stable in biocompatible
97
water buffer [132]. The stable liposome-encapsulated QDs could be used as bright
fluorescent labels in biological applications, involving the conjugation of biomolecules
such as enzymes, antibodies, and DNA molecules to the liposomes.
Another report considers the preparation of polylactide (PLA) particles,
loaded with fluorescent QDs [133, 134]. In this study, CdSe QDs are encapsulated
in PLA particles and studied in vitro and in vivo. The PLA-coated QDs are waterdispersible and highly fluorescent – the fluorescence is stable in aqueous solution
for more than 30 days. The results obtained in the course of this investigation
clearly demonstrate that the PLA-encapsulated CdSe QDs have a high potential
for biological labeling and diagnostics.
Poly(alkylcyanoacrylate) (PACA) nanoparticles are considered as ones of the most
promising polymer carriers for drug delivery [135]. The poly(alkylcyanoacrylates) are
biocompatible, biodegradable and relatively non-toxic. These advantages make them
appropriate materials for biocompatibilization of QDs. Highly fluorescent CdSe/CdS
core-shell QDs are embedded into poly(butylcyanoacrylate) nanoparticles in order to
prepare novel fluorescent nanocomposite particles for bioimaging applications [136].
The investigations with fluorescent microscopy allow the successful visual tracking of
the QD-labeled polymer particles in the course of their interaction with biological cells.
A recent report considers the development of a new strategy to prepare folatedecorated nanoparticles of biodegradable polymers for QDs encapsulation, targeted
and sustained imaging of cancer cells [137]. Copolymers of poly(lactide)-vitamin
E are synthesized, which are then blended at various weight ratios to make QDsloaded nanoparticles, which are further decorated with folate for targeted and
sustained imaging. This study shows that the QDs formulated in folate-decorated
nanoparticles are feasible for targeted imaging. These QDs improve imaging
specificity and sensitivity with reduced side effects of QDs to normal cells.
Taking into account the above-mentioned examples, one can conclude that
the fluorescent labeling of colloidal drug carrier systems with QDs could open a
possibility to investigate the mechanisms of carrier-cell interactions, penetration
and localization of the colloidal particles in various biological cells.
CONCLUSIONS
The applications of quantum dots as a novel generation of fluorescent markers
for bioimaging may provide important information about the mechanisms of
interactions between the biological cells and nanosized materials. They can
be especially important in the cases, where a long-term imaging and a high
photostability of the fluorophore are required. The quantum dots may be useful
also for imaging in the near infrared region, as well for visual tracking of single
molecules and investigation of complicated biological processes, such as embryonic
development. However, one should take into account the possible toxic effects of
quantum dots or their coating material on the living cells and organisms. The
98
recent advancements in development of non-toxic and biocompatible quantum
dots reveal a great possibility for extension of the exciting biological applications
of these nanoparticles. It is expected that the quantum dots will increase our
knowledge about the molecular mechanisms of many biological processes and will
be important tools in fluorescent diagnosis of cancer and other severe diseases.
Acknowledgements. The authors are thankful to COST Action D43. The financial support of
the Bulgarian Ministry of Education and Science (Project DO 02-168) is greatly acknowledged.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
Kalyanasundaram, K., E. Borgarello, D. Duonghong, M. Gratzel. Angew. Chem. Int. Ed., 20,
1981, 987.
Murray, C.B., D.J. Norris, M.G. Bawendi. J. Am. Chem. Soc., 115, 1993, 8706.
Peng, Z.A., X. Peng. J. Am. Chem. Soc., 123, 2001, 183.
Yu, W.W., X. Peng. Angew. Chem. Int. Ed., 41, 2002, 2368.
Bruchez, M., M. Moronne, P. Gin, S. Weiss, A.P Alivisatos. Science, 281, 1998, 2013.
Chan, W.W., S. Nie. Science, 281, 1998, 2016.
Gao X., Chan W., Nie S. (2002) J. of Biomed. Opt. 7(4), 532–537.
Chan W.W., Maxwell D.J., Gao X., Bailey R.E., Han M., Nie S. (2002) Curr. Opin. Biotech.
13, 40–46.
Jaiswal, J.K., S.M. Simon. Trends Cell Biol., 14 (9), 2004, 497.
Jiang, W., E. Papa, H. Fischer, S. Mardyani, W. Chan. Trends Biotechnol., 22 (12), 2004, 607.
Wang, Y., Z. Tang, N.A. Kotov. Materials Today, 8 (5), 2005, 20.
Gao, X., L. Yang, J. Petros, F. Marshall, J. Simons, S. Nie. Curr. Opin. Biotechnol., 16 (1),
2005, 63.
Sharma, P., S. Brown, G. Walter, S. Santra, B. Moudgil. Adv. Colloid Interf. Sci., 123-126,
2006, 471.
Pinaud, F., X. Michalet, L.A. Bentolila, J.M. Tsay, S. Doosel, J.J. Li, G. Iyer, S. Weiss. Biomaterials, 27, 2006, 1679.
Zajac, A., D. Song, W. Qian, T. Zhukov. Colloids Surf. B: Biointerfaces, 58 (2), 2007, 309.
Jamieson, T., R. Bakhshi, D. Petrova, R. Pocock, M. Imani, A. Seifalian. Biomaterials, 28 (31),
2007, 4717.
Smith, A., H. Duan, A. Mohs, S. Nie. Adv. Drug Deliv. Rev., 60 (11), 2008, 1226.
Hild, W.A., M. Breunig, A. Goepferich. Eur. J. Pharm. Biopharm., 68 (2), 2008, 153.
Yoffe, A.D. Adv. Phys., 42, 1993, 173.
Gaponenko, S.V., Optical Properties of Semiconductor Nanocrystals, Cambridge University
Press, 2005.
Rogach, A.L. (Ed.). Semiconductor nanocrystal quantum dots: synthesis, assembly, spectroscopy and applications, 2008, Springer.
Brus, L.E. J. Chem. Phys., 80, 1984, 4403.
Rossetti, R., S. Nakahara, L. Brus. J. Chem. Phys., 79, 1983, 1086.
Rossetti, R., J.L. Ellison, J.M. Gibson, L.E. Brus. J. Chem. Phys., 80, 1984, 4464.
Nirmal, M., L. Brus. Acc. Chem. Res., 32, 1999, 407.
Ramsden, J.J., S.E. Webber, M. Grätzel. J. Phys. Chem., 89, 1985, 2740.
Hässelbarth, A., A. Eychmüller, H. Weller. Chem. Phys. Lett., 203, 1993, 271.
Dubertret, B., P. Skourides, D.J. Norris, V. Noireaux, A.H. Brivanlou, A. Libchaber. Science,
298, 2002, 1759.
99
29. Wu, X., H. Liu, J. Liu, K.N. Haley, J.A. Treadway, J.P. Larson, N. Ge, F. Peale, M.P. Bruchez.
Nature Biotechnol., 21, 2003, 41.
30. Alivisatos, A.P., A.L. Harris, N.J. Levinos, M.L. Steigerwald, L.E. Brus. J. Chem. Phys., 89,
1988, 4001.
31. Dushkin, C., S. Saita, K. Yoshie, Y. Yamaguchi. Adv. Colloid Interf. Sci., 88, 2000, 37.
32. Yordanov, G., C. Dushkin, B. Bochev, G. Gicheva, E. Adachi. Annuire L’Universite Sofia,
Faculte Chimie, 98-99, 2006, 131.
33. Yordanov, G., C. Dushkin, G. Gicheva, B. Bochev, E. Adachi. Colloid Polymer Sci., 284, 2005, 229.
34. Yordanov, G., E. Adachi, C. Dushkin. Mater. Character., 58, 2007, 267.
35. Yordanov, G., G. Gicheva, B. Bochev, C. Dushkin, E. Adachi. Colloids Surfaces A, 273, 2006, 10.
36. Yordanov, G., C. Dushkin, E. Adachi. Colloids Surfaces A, 316, 2008, 37.
37. Yordanov, G., E. Adachi, C. Dushkin. Colloids Surfaces A, 289, 2006, 118.
38. Yordanov, G., H. Yoshimura, C. Dushkin. Colloids Surfaces A, 322, 2008, 177.
39. Donega, C.M., S.G. Hickey, S.F. Wuister, D. Vanmaekelbergh, A. Meijerink. J. Phys. Chem. B,
107, 2003, 489.
40. Qu, L., X. Peng. J. Am. Chem. Soc., 124, 2002, 2049.
41. Peng, Z.A., X. Peng. J. Am. Chem. Soc., 124, 2002, 3343.
42. Qu, L., Z. Peng, X. Peng. Nanoletters, 1, 2001, 333.
43. Yu, W., Y. Wang, X. Peng. Chem. Mater., 15, 2003, 4300.
44. Munro, A., J. Bardecker, M. Liu, Y.-J. Cheng, Y.-H. Niu, I. Plante, A. Jen, D. Ginger. Microchim. Acta, 160, 2008, 345.
45. Li, L., H.F. Qian, J. Ren. Chem. Commun., 2005, 528.
46. Weng, J., X. Song, L. Li, H. Qian, K. Chen. Talanta, 70, 2006, 397.
47. Rogach, A., T. Franzl, T. Klar, J. Feldmann, N. Gaponik, V. Lesnyak, A. Shavel, A. Eychmüller, Y. Rakovich, J. Donegan. J. Phys. Chem. C, 111, 2007, 14628.
48. Li, H. Ind. Eng. Chem. Res., 46, 2007, 2013.
49. Pradhan, N., D.M. Battaglia, Y. Liu, X. Peng. Nanoletters, 7, 2007, 312.
50. Micic, O.I., J. Sprague, C. Curtis, K. Jones, J. Machol, A. Nozik, H. Giessen, B. Fluegel, G.
Mohs, N. Peyghambarian. J. Phys. Chem., 99, 1995, 7754.
51. Guzelian, A., U. Banin, A. Kadavanich, X. Peng, A. Alivisatos. Appl. Phys. Lett., 69, 1996, 1432.
52. Dabbousi, B., J. Rodriguez-Viejo, F. Mikulec, J. Heine, H. Mattoussi, R. Ober, K. Jensen, M.
Bawendi. J. Phys. Chem. B, 101, 1997, 9463.
53. Hines, M.A., P. Guyot-Sionnest. J. Phys. Chem., 100, 1996, 468.
54. Peng, X., M. Schlamp, A. Kadavanich, A. Alivisatos. J. Am. Chem. Soc., 119, 1997, 7019.
55. Micic, O., B. Smith, A. Nozik. J. Phys. Chem. B, 104, 2000, 12149.
56. Cao, Y.W., U.J. Banin. J. Am. Chem. Soc., 122, 2000, 9692.
57. Cumberland, S.L., K.M. Hanif, A. Javier, G.A. Khitrov, G.F. Strouse, S.M. Woessner, C.S.
Yun. Chem. Mater., 14, 2002, 1576.
58. Manna, L., E.C. Scher, L.S. Li, A.P. Alivisatos. J. Am. Chem. Soc., 124, 2002, 7136.
59. Reiss, P., J. Bleuse, A. Pron. Nano Lett., 2, 2002, 781.
60. Schlamp, M.C., X. Peng, A.P. Alivisatos. J. Appl. Phys., 82, 1997, 5837.
61. Mattoussi, H., J.M. Mauro, E.R. Goldman, G.P. Anderson, V.C. Sundar, F.V. Mikulec, M.G.
Bawendi. J. Am. Chem. Soc., 122, 2000, 12142.
62. Lee, J., V.C. Sundar, J.R. Heine, M.G. Bawendi, K.F. Jensen. Adv. Mater., 12, 2000, 1102.
63. Coe, S., W.K. Woo, M. Bawendi, V. Bulovic. Nature, 420, 2002, 800.
64. Li, J., Y. Wang, W. Guo, J. Keay, T. Mishima, M. Johnson, X. Peng. J. Am. Chem. Soc., 125,
2003, 12567.
65. Yordanov, G., H. Yoshimura, C. Dushkin. Colloid Polymer Sci., 286, 2008, 1097.
66. Peng, X., J. Wickham, A.P. Alivisatos. J. Am. Chem. Soc., 120, 1998, 5343.
100
67.
68.
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
82.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94.
95.
96.
97.
98.
99.
100.
101.
102.
103.
104.
Yu, W., J. Falkner, B. Shih, V. Colvin. Chem. Mater., 16, 2004, 3318.
Wuister, S.F., I. Swart, F. Driel, S.G. Hickey, C.M. Donega. Nanoletters, 3, 2003, 503.
Zhang, H., Z. Zhou, B. Yang, M. Gao. J. Phys. Chem. B, 107, 2003, 8.
Pathak, S., S.-K. Choi, N. Arnheim, M. Thompson. J. Am. Chem. Soc., 123, 2001, 4103.
Kim, S., M.G. Bawendi. J. Am. Chem. Soc., 125, 2003, 14652.
Zhou, M., I. Ghosh. Biopolymers (Peptide Science), 88, 2006, 325.
Babu, P., S. Sinha, A. Surolia. Bioconjugate Chem., 18, 2007, 146.
Li, H., X. Wang, Z. Gao, Z. He. Nanotechnology, 18, 2007, 205603.
Pellegrino, T., L. Manna, S. Kudera, T. Liedl, D. Koktysh, A.L. Rogach, S. Keller, J. Radler, G.
Natile, W.J. Parak. Nanoletters, 4, 2004, 703.
Gao, X., Y. Cui, R. Levenson, L. Chung, S. Nie. Nat. Biotechnol., 22, 2004, 969.
Zhou, M., E. Nakatani, L. Gronenberg, T. Tokimoto, M. Wirth, V. Hruby, A. Roberts, R. Lynch,
I. Ghosh. Bioconjugate Chem., 18, 2007, 323.
Zhang, C., S. O’Brien, L. Balogh. J. Phys. Chem. B, 106, 2002, 10316.
Nann, T. Chem. Commun., 2005, 1735.
Gerion, D., F. Pinaud, S. C. Williams, W. Parak, D. Zanchet, S. Weiss, A.P. Alivisatos. J. Phys.
Chem. B, 105, 2001, 8861.
Wolcott, A., D. Gerion, M. Visconte, J. Sun, A. Schwartzberg, S. Chen, J.Z. Zhang. J. Phys.
Chem. B, 110, 2006, 5779.
Zhu, M.-Q., E. Chang, J. Sun, R.A. Drezek. J. Mater. Chem., 17, 2007, 800.
Parak, W.J., T. Pellegrino, C. Plank. Nanotechnology, 16, 2005, R9.
Ravindran, S., S. Kim, R. Martin, E.M. Lord, C.S. Ozkan. Nanotechnology, 16, 2005, 1.
Yu, G., J. Liang, Z. He, M. Sun. Chem. Biol., 13, 2006, 723.
Schroedter, A., H. Weller. Nano Lett., 2, 2002, 1363.
Hardman, R. Environmental Health Perspectives, 114, 2006, 165.
Derfus, A.M., W.C.W. Chan, S.N. Bhatia. Nano Lett., 4, 2004, 11.
Hoshino, A., K. Fujioka, T. Oku, M. Suga, Y.F. Sasaki, T. Ohta, M. Yasuhara, K. Suzuki, K.
Yamamoto. Nano Lett., 4, 2004, 2163.
Hoshino, A., K. Hanaki, K. Suzuki, K. Yamamoto. Biochem. Biophys. Res. Comm., 314, 2004, 46.
Kirchner, C., Liedl T., Kudera S., Pellegrino T., Javier A.M., Gaub H.E., Stolzle S., Fertig N.,
W.J. Parak. Nano Lett., 5, 2005, 331.
Tsay, J.M., X. Michalet. Chemistry & Biology, 12, 2005, 1159.
Lu, H.-Y., N.-H. Shiao, W.-H. Chan. J. Med. Biol. Eng., 26, 2006, 89.
Zhang, T., J.L. Stilwell, D. Gerion, L. Ding, O. Elboudwarej, P.A. Cooke, J.W. Gray, A.P.
Alivisatos, F.F. Chen. Nano Lett., 6, 2006, 800.
Cho, S.J., D. Maysinger, M. Jain, B. Roder, S. Hackbarth, F.M. Winnik. Langmuir, 23, 2007, 1974.
Choi, A., S.J. Cho, J. Desbarats, J. Lovrić, D. Maysinger. J. Nanobiotech., 5, 2007, 1.
Liang, J., Z. He, S. Zhang, S. Huang, X. Ai, H. Yang, H. Han. Talanta, 71, 2007, 1675.
Ryman-Rasmussen, J., J. Riviere, N. Monteiro-Riviere. J. Investigative Dermatology, 127,
2007, 143.
Ryman-Rasmussen, J., J. Riviere, N. Monteiro-Riviere. Nano Lett., 7, 2007, 1344.
Duan, H., S. Nie. J. Am. Chem. Soc., 129, 2007, 3333.
Lovric, J., S.J. Cho, F.M. Winnik, D. Maysinger. Chemistry & Biology, 12, 2005, 1227.
Tran, P.T., E.R. Goldman, J.P. Anderson, J.M. Mauro, H. Mattoussi. Phys. Stat. Sol., 229, 2002, 427.
Chang, E., J.S. Miller, J. Sun, W.W. Yu, V.L. Colvin, R. Drezek, J.L. West. Biochem. Biophys.
Res. Comm., 334, 2005, 1317.
Patolsky, F., R. Gill, Y. Weizmann, T. Mokari, U. Banin, I. Willner. J. Am. Chem. Soc., 125,
2003, 13918.
101
105. Medintz, I.L., A.R. Clapp, F.M. Brunel, T. Tiefenbrunn, H.T. Uyeda, E.L. Chang, J.R. Deschamps, P.E. Dawson, H. Mattoussi. Nat. Mater., 5, 2006, 581.
106. Shi, L., N. Rosenzweig, Z. Rosenzweig. Anal. Chem., 79, 2007, 208.
107. Shi, L., V. Paoli, N. Rosenzweig, Z. Rosenzweig. J. Am. Chem. Soc., 128, 2006, 10378.
108. Stylianou, P., P.A. Skourides. Mechanisms Development, 126, 2009, 828.
109. Rieger, S., R.P. Kulkarni, D. Darcy, S.E. Fraser, R.W. Koster. Dev. Dyn., 234, 2005, 670.
110. Rosenthal, J., I. Tomlinson, E. Adkins, S. Schroeter, S. Adams, L. Swafford, J. McBride, Y.
Wang, L. DeFelice, R. Blakely. J. Am. Chem. Soc., 124, 2002, 4586.
111. Tomlinson, I.D., J.N. Mason, R.D. Blakely, S.J. Rosenthal. Bioorg. Med. Chem. Lett., 15,
2005, 5307.
112. Tomlinson, I.D., M.R. Warnerment, J.N. Mason, M.J. Vergne, D.M. Hercules, R.D. Blakely,
S.J. Rosenthal. Bioorg. Med. Chem. Lett., 17, 2007, 5656.
113. Dahan, M., S. Lévi, C. Luccardini, P. Rostaing, B. Riveau, A. Triller. Science, 302, 2003, 442.
114. Gac, S.L., I. Vermes, A. Berg. Nano Lett., 6, 2006, 1863.
115. Goldman, E.R., E.D. Balighian, H. Mattoussi, M.K. Kuno, J.M. Mauro, P.T. Tran, G.P. Anderson. J. Am. Chem. Soc., 124, 2002, 6378.
116. Goldman, E.R., E.D. Balighian, M.K. Kuno, S. Labrenz, P.T. Tran, G.P. Anderson, J.M. Mauro, H. Mattoussi. Phys. Stat. Sol. B, 229, 2002, 407.
117. Sukhanova, A., J. Devy, L. Venteo, H. Kaplan, M. Artemyev, V. Oleinikov, D. Klinov, M.
Pluot, J. Cohen, I. Nabiev. Analyt. Biochem., 324, 2004, 60.
118. Zhu, L., S. Ang, W-T Liu. Appl. Environ. Microbiol., 70, 2004, 597.
119. Lao, U.L., A. Mulchandani, W. Chen. J. Am. Chem. Soc., 128, 2006, 14756.
120. Frangioni, J.V. Curr. Opinion Chem. Biol., 7, 2003, 626.
121. Ballou, B., B. Lagerholm, L. Ernst, M. Bruchez, A. Waggoner. Bioconjugate Chem., 15, 2004, 79.
122. Cai, W., D.-W. Shin, K. Chen, O. Gheysens, Q. Cao, S.X. Wang, S.S. Gambhir, X. Chen. Nano
Lett., 6, 2006, 669.
123. Parungo, C.P., S. Ohnishi, S.W. Kim, S. Kim, R.G. Laurence, E.G. Soltesz. J. Thoracic Cardiovasc. Surg., 129, 2005, 844.
124. Ballou, B., L.A. Ernst, S. Andreko, T. Harper, J.A.J. Fitzpatrick, A.S. Waggoner, M.P. Bruchez.
Bioconjugate Chem., 18, 2007, 389.
125. Nida, D.L., M.S. Rahman, K.D. Carlson, R. Richards-Kortum, M. Follen. Gynecologic Oncology, 99, 2005, S89.
126. Zhelev, Z., H. Ohba, R. Bakalova, R. Jose, S. Fukuoka, T. Nagase, M. Ishikawa, Y. Baba.
Chem. Commun., 2005, 1980.
127. Li, Z., K. Wang, W. Tan, J. Li, Z. Fu, C. Ma, H. Li, X. He, J. Liu. Anal. Biochem., 354, 2006, 169.
128. Kerman, K., T. Endo, M. Tsukamoto, M. Chikae, Y. Takamura, E. Tamiya. Talanta, 71, 2007, 1494.
129. Amiji, M.M. (Ed.). Nanotechnology for Cancer Therapy. CRC Press, Boca Raton, 2006.
130. Miyazaki, S., A. Takahashi, W. Kubo, J. Bachynsky, R. Löbenberg. J. Pharm. Pharmaceut.
Sci., 6, 2003, 238.
131. Kreuter, J., R. Alyautdin, D. Kharkevich, A. Ivanov. Brain Res., 674, 1995, 171.
132. Feng, L., X. Kong, K. Chao, Y. Sun, Q. Zeng, Y. Zhang. Mater. Chem. Phys., 93, 2005, 310.
133. Nehilla, B., P. Allen, T. Desai. ACS Nano, 2, 2008, 538.
134. Guo, G., W. Liu, J. Liang, H. Xu, Z. He, X. Yang. Mater. Lett., 60, 2006, 2565.
135. Vauthier, C., C. Dubernet, E. Fattal, H. Pinto-Alphandary, P. Couvreur. Adv. Drug Deliv. Rev.,
55, 2003, 519.
136. Yordanov, G., M. Simeonova, R. Alexandrova, H. Yoshimura, C. Dushkin. Colloids Surfaces
A, 339, 2009, 199.
137. Pan, J., S.-S. Feng. Biomaterials, 30, 2009, 1176.
Received of July 22, 2009
102
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
DYNAMIC EFFECTS IN THIN FILMS WITH DIFFERENT RADII
STOYAN I. KARAKASHEV1* AND DILYANA S. IVANOVA2
Department of Physical Chemistry, Sofia University, 1 James Bourchier Avenue, Sofia 1126, Bulgaria
2
Faculty of Natural Sciences, Shumen University, 9712 Shumen, Bulgaria
*To whom correspondence should be addressed. Email: [email protected]
1
Abstract. The strong influence of surfactants on foam film drainage has been quantified
by the Marangoni stress. This paper reviews and experimentally validates the theoretical
developments aimed to describe the Marangoni effect on foam film drainage. They have been
presented by four models, namely, 1) the Scheludko model developed on the basis of the StefanReynolds lubrication theory for liquid films confined between plane-parallel solid surfaces, 2)
the model of Radoev, Dimitrov and Ivanov (RDI model) for foam films confined between
partially mobile plane-parallel gas-liquid surfaces under the Marangoni stress generated by
adsorbed surfactants, 3) the model of Ruckenstein and Sharma (RSh model) for foam films
with surfaces wrinkled by capillary waves, pumping out peristaltically the liquid to the film
periphery, thus causing faster drainage, and 4) the model of Manev, Tsekov and Radoev
(MTR model) for foam films with surfaces corrugated by quasi-stationary inhomogeneities
in the local film thickness which reduce the hydrodynamic resistance and accelerate drainage
Experimental data on foam film drainage stabilized with nonionic surfactants, imposing
variety of different experimental conditions were compiled and used in validating the models.
A systematic validation based on the statistical level of uncertainty of the model predictions as
compared to the experimental results was preformed. The experimental data were collected for
foam films containing hexaethyleneglycol monododecyl ether (C12E6). The test on the model
kinetic equations confirmed their validations reported in the literature. Thus, the applicability
of each one of the models to different experimental conditions of film drainage was specified.
Ultimately, it was concluded that thin film drainage is a complex phenomenon, which should
be studied further by different experimental techniques and modelling approaches.
Key words: foam film drainage, thin liquid films, Marangoni effect, surfactants.
103
1. INTRODUCTION
Thin liquid films (TLF) have been widely studied [1-4]. It was established during
the past century that “Scheludko-Exerowa cell” is an efficient and productive model
for studying properties, behaviour and stability of dispersion systems [1, 5, 6].
Disjoining pressure acting between the film surfaces was experimentally determined and validated against the DLVO theory [7, 8]. Other properties of film
surfaces and the kinetics of film thinning were also studied and modelled using the
microinterferometric method [9–25]. These important studies were focussed on the
effect of the mechanical properties of the film surfaces (e.g., the Marangoni stress,
the surface diffusivity and the surface viscosity), the film geometry, and the type and
concentration of surfactants and electrolytes on the film drainage and stability.
A number of developments have been introduced in the theory of foam film
drainage during the last century. For example, Scheludko [26] applied the StefanReynolds equation [27, 28] to describe the film drainage. He considered plane
parallel rigid and tangentially immobile surfaces of the film due to the Marangoni
effect produced by the surface tension gradient. It was established that this assumption is valid for foam films with small radii (below 0.05 mm)[20, 29, 30].
Furthermore, Radoev et al. [31, 32] developed the theory by considering mobile
film surfaces. According to this model, the velocity on the film surfaces is a result
of the combined effects of the liquid outflow, Marangoni effect, and surfactant
adsorption. Later, Radoev et al. [11] included the effect of the surface diffusion on
the interfacial velocity. Manev [33] observed experimentally that the increase in
the film radius correlates with the film thickness fluctuations, which accelerate the
film drainage. Analytical solutions for the limiting cases of small and large deformation of the bubble caps were also obtained by Ivanov, Dimitrov, Somasundaran
and Jain [34]. The evolution of thin film with dimple was analytically obtained by
Tsekov and Ruckenstein [35]. Empirical equations along with numerical solutions
on film thinning between approaching drops were obtained by Davies, Schoneberg and Ralison [36] and Jeelani and Hartland [37].
The influence of the thickness fluctuations on the film drainage has been modelled by Manev et al. [20] and Tsekov [30, 38]. In these models the film surfaces
are assumed fully immobile.
These theoretical models are valid for nonionic surfactants and are based on
the lubrication and steady-state approximations valid at very small Reynolds and
Peclet numbers [39]. Contribution to the theory was the introduction of the effect
of surface viscosity on the film drainage firstly by Ivanov and Dimitrov and later
re-established by Karakashev and Nguyen [40, 41]. However, the surface viscosity appears to be less important when the Marangoni effect is dominant for typical
surfactant systems even with low concentrations.
104
Moreover, experiments preformed by Manev [42, 43] established that the
thinning rate of films with radius larger then 50μm is inversely proportional to the
film radius raised to the power 4/5, instead of power 2, as in the Stefan-Reynolds
equation. This problem was analysed in different ways in the literature. Malhotra
and Wasan [44] attributed the experimentally established dependence to the modulation of the pressure distribution in the adjacent meniscus by the film drainage,
while Ruckenstein and Sharma [15] tried to explain it with the peristaltic action of
surface hydrodynamic waves, formed during the film drainage and derived analytical kinetic equation (containing an empirical term). The problem was attacked
from a different angle by Manev, Tsekov and Radoev [20], who assumed that
quasi-stationary steady and static thickness inhomogeneities are the driving force
for the faster film drainage. They solved the problem analytically and obtained
another kinetic equation for the film drainage. All the above works assume tangentially immobile film surfaces.
With the development of computers, the general differential equation for
drainage of films with deformable surfaces was solved numerically in number of
works (e.g. [45–48]). Thus the corrugation of the film surfaces was explained [46,
47] later with formation of surface instability caused by the Marangoni effect.
Numerical simulation of this instability causing asymmetric drainage of foam film
was performed by Joye, Hirasaki and Miller [46, 47]. They indicated that asymmetric film drainage is faster than the axisymmetric, i.e. non-planar foam films
drain faster than the planar ones. Valkovska and Danov [49] included an electrical
term into the bulk pressure stress tensor and the electrostatic potential into the
film, thus making the theory valid for ionic surfactants. Due to the complexity of
the problem the differential equations were solved only numerically.
The above scrutiny on the literature shows that surfactants adsorbed at the
film surfaces play the critical role in foam film drainage. In many cases, the effect of surfactant adsorption can be sufficiently accounted for by considering the
Marangoni stress. The available theories for the Marangoni effect on foam film
drainage can be represented by four characteristic models specified as follows:
1. The model of Scheludko [10, 50] which is based on the Stefan-Reynolds lubrication theory [51]. A capillary “squeezing” force presses the film surfaces towards
each other. The surfaces are assumed to be planar, rigid and tangentially immobile.
2. The model of Radoev, Dimitrov and Ivanov (RDI) [11]. The film drainage
driven by the capillary pressure is controlled by the mobile but planar rigid film
surfaces. The mobility of the film surfaces depends on the Marangoni stress, surface diffusion and surfactant adsorption.
3. The model of Ruckenstein and Sharma (RSh) [15]. The capillary pressure pushes the two immobile film surfaces towards each other. The surfaces are
wrinkled by capillary waves pumping the liquid out peristaltically towards the
film periphery, thus making the film draining faster.
105
4. The model of Manev, Tsekov and Radoev (MTR) [20]. The capillary force
presses immobile film surfaces, which are corrugated by quasi-stationary inhomogeneities in film thickness which reduce the hydrodynamic repulsion between the
film surfaces and, therefore, make the film draining faster.
These models do not account for the dynamic effects produced by the electrical double layer, which can arise in TLF with ionic surfactants. For this reason,
non-ionic surfactants are used for stabilizing the foam films here.
The aim of this paper is to review these four milestones on the way to further
development of the theory. They are also critically validated using the experimental results obtained with a number of non-ionic surfactants.
2. FOAM FILM DRAINAGE THEORIES
The key considerations and assumptions used to establish the foam film drainage theories can be summarised as follows [39]:
– The use of a cylindrical coordinate system simplifies the film geometry
(Figure 1).
– The liquid is an incompressible Newtonian fluid.
– The pressure within the gas phase is constant.
– The viscous forces dominate over the inertial forces, which are neglected.
– The local variation of film thickness with radial coordinate is weak,
i.e. ∂h / ∂r << 1 .
– The lubrication approximation is assumed, i.e., (h0 / R0 ) << 1 , where h0
is the initial thickness at the film centre and R0 is the film radius (the Reynolds
number << 1).
– The rate of liquid outflow is lower than the rate of mass diffusion (the Peclet
number << 1). The convective and time derivative terms in the film mass balance
equation are neglected. This is the so-called “quasi-steady” approximation, imposing that the time dependences of all quantities can be expressed through the
thickness h alone.
– The surfactant adsorption layers on the film surfaces are close to equilibrium.
– The effect from the surface viscosity is negligible compared to the Marangoni effect.
All of the above assumptions lead to a simplified system of differential equations solvable analytically with appropriate boundary conditions [4, 39] as follows:
– Radial component of the Navier-Stokes equation with omitted convective
and time derivative terms.
– Normal component of the Navier-Stokes equation in the lubrication approximation: ∂P / ∂z = 0 .
– Continuity equation, mass balance equation in the film with omitted convective and time derivative terms.
106
– Mass balance equation on film surfaces and tangential stress boundary
equation with omitted surface viscosity term.
The solutions of the governing equations are then used to calculate the total
drag force on the film surfaces, which is the response of the film to external force
pushing the bubbles towards each other. In the case of the Scheludko-Exerowa
experimental methodology [1], this applied pressure is equal to the sum of the
Figure 1. Evolution of a foam film in
time (top left to right down).
2R
Pumping
out
2Rc
Double concave drop
2R
Non-planar film
2Rc
2Rc
Dimpled film
2R
Equilibrium
2Rc
107
capillary pressure and the (total) disjoining pressure. Each of the four representative models are described below.
2.1 The Model of Scheludko [10, 39, 50] Based on the Stefan-Reynolds Theory
The classical lubrication theory of Stefan and Reynolds [27, 28] focused on
the kinetics of thinning of liquid films, confined between two parallel flat solid
discs, compressed by an external force. The thin liquid films between the bubbles
and/or oil droplets exhibit certain similarities to the Stefan-Reynolds assumptions
during their drainage, viz., they have a cylindrical shape; their surfaces can be
planar at small radii (less than 50 μm [42]); their surfaces become stagnant by
the Gibbs elasticity values larger than 2 mN/m, which is fulfilled for most surfactants, starting from their diluted aqueous solutions [10]. Bearing in mind all these
features, Scheludko adopted the Stefan-Reynolds theory and applied it to liquid
films between fluid phases [10, 50]. The final formula about the velocity of film
drainage, derived after solving the simplified system of the Navier-Stokes and
continuity equations with the assumption that the drag force equals the external
pressing force is given as
VRe = −
dh
2h 3
=
(Pσ − Π )
dt 3μR 2f
(1)
where VRe is the velocity of drainage, h is film thickness, t is time, μ is the bulk
kinematic viscosity, R f is film radius, Pσ = 2σ / RC is capillary pressure, σ
is surface tension, RC is the radius of the capillary tube ( see Figure 1), and Π
is the total disjoining pressure. This is the first theory applied to thin liquid film
drainage but as mentioned above, it is valid for film radii less then ca. 50 μm,
where the films are nearly planar [42]. Experimentally[43, 50, 52, 53] it is proved
that the real rate of drainage V is greater than that theoretically predicted by Eq. ,
due to the deviations of the real TLF from the conditions required by the model.
Deviations from the Stefan-Reynolds equation due to tangential surface mobility were theoretically predicted and experimentally established [31, 43, 54, 55].
It is shown that the gradient of concentration (respectively the surface tension
gradient) which can slow down or even to stop the flow on the surface is partially
compensated by bulk [31] or surface diffusion [39, 56]. As shown in [57], the influence of the solution composition (the type of surfactant, a mixture of surfactant
and their concentration) on the time of thinning was significant. It was found to be
substantially affected by surface tension, surface dynamic viscosity and surface
elasticity. Any deviation from the planar shape of the film originates dimple in
its centre. The problem of the dimple formation and its evolution with the time
was treated theoretically in a number of studies [58–60]. In the earlier studies it
was assumed that the dimple in the foam films decreases and even disappears at a
108
smaller thickness. More recent investigations [20, 61] show however that the film
thickness inhomogeneity persists to the critical thickness. The film inhomogeneity
increases strongly with the film radius. It is shown in Ref. [42] that the StefanReynolds drainage equation is only applicable for films with diameter of up to 0.1
mm. The hydrodynamic regime of thinning becomes more complicated for films
of larger radii.
2.2 The Model of Radoev, Dimitrov and Ivanov (RDI) [11]
This drainage model assumes planar and mobile film surfaces being controlled
by the Marangoni stress, surface diffusion and adsorption of surfactant molecules.
The final expression for the velocity of film drainage can be described as [11]
V =−
dh
2h 3
=
(Pσ − Π ) f
dt 3μR 2f
where f = 1 +
6D f μ
hEG
(2)
is the mobility factor. Here, EG = − d σ / d ln Γ is the
Gibbs elasticity, which governs the Marangoni stress and, therefore, controls the
mobility of the film surfaces.
Dh dC
In the equation for the mobility factor, D f = DS +
is an effective
2 dΓ
film diffusion coefficient. Here, DS and D are the surface and bulk diffusion coefficients of the surfactant molecules, respectively, and d Γ / dC is the first derivative of the adsorption regarding the surfactant concentration, known as the adsorption length. The surface tension isotherm is usually measured to derive the value
of the capillary pressure, the Gibbs elasticity and the adsorption length. However,
the values of DS and D are usually unknown. Moreover, it is known that the
effect of DS on the drainage velocity is significant. There is no experimental way
to reliably determine DS . Therefore, in this paper a simulation approach is taken
for estimation of these two parameters.
The surfactant molecule with the hydrophilic and hydrophobic parts is assumed
with cylindrical shape. Its length, L, can be calculated via the HyperChem software
for quantum chemistry and MD simulations. In this way, for SDS (sodium dodecyl
sulphate) molecule as an example, we obtained LSDS = 1.76 nm for the molecular
length and d = 0.137 nm for the distance between two methylene groups.
The bulk diffusion coefficient depends on the shape and size of molecules,
bulk viscosity and temperature. For cylindrical molecules it can be expressed by:
D=
k BT
⎛L⎞
ln ⎜ ⎟
3πμL ⎝ d ⎠
(3)
109
where k B is the Boltzmann constant, T is temperature, L is the length of the cylinder and d is its diameter. The calculated bulk diffusion coefficient for SDS agree
with the measured value DSDS = 6 × 10−10 m 2 /s [62, 63]. Knowing DSDS for SDS
molecules, the bulk diffusion coefficient of other surfactants can be calculated as
D = DSDS
ln (L / d )
LSDS
L ln (LSDS / d SDS )
(4)
Regarding the surface diffusion coefficient, DS , it can be calculated from the
bulk diffusion coefficient as Ds = 1.5 D [64].
The RDI model should be valid for small films, i.e., R f ≤ 50μm , because
larger films are usually not plane-parallel [11, 39, 65, 66]. If the film surfaces are
very rigid, the Gibbs elasticity becomes significantly large and the RDI model
reduces to the Scheludko model.
2.3 The Model of Ruckenstein and Sharma (RSh) [15]
This drainage model was developed based on the experimental findings of
Manev [42, 52] which show that foam films usually thin faster than the StefanReynolds prediction. The model assumes tangentially immobile film surfaces,
wrinkled by capillary waves which move from the film centre towards its periphery, thus peristaltically pumping out the liquid from the film centre faster.
Ruckenstein and Sharma [15] introduced the van der Waals disjoining pressure in
the tangential and normal components of the Navier-Stokes equations. No electrostatic disjoining pressure was considered by the authors. The film thickness heterogeneity was introduced by the substantial time derivative of the film thickness
as dh / dt = ∂h / ∂t + vr ∂h / ∂r , where vr is radial velocity of the liquid outflow.
This stipulates a weak variation of the local film thickness over the film surfaces.
In addition, a balance between the local capillary pressure and the pressure in the
film at the film surface, p = − (σ / 2 )∂ 2 h / ∂r 2 , was made. Due to the fact that the
capillary waves are naturally periodical, the pressure in the film should be periodically decaying function of the radial coordinate. It is assumed that the capillary
waves oscillate around the average film thickness, which leads to two governing
differential equations: the first one for the rate of thinning of a foam film with the
average thickness (same as the Stefan-Reynolds model) and the second one for
the oscillation of the local film thickness around its average value. The van der
Waals disjoining and the local capillary pressures play significant roles in this
model equation. The solution of this second differential equation illustrated the
existence of decaying and growing surface waves, moving from the centre toward
the periphery of the film. The authors introduced an empirical correction for the
solution of this equation [38], using a characteristic wavelength of the surface
110
waves. The wavelength is equal to the maximum radius ( R f = 50μm ), at which
the film still can be plane-parallel [42]. An empirical equation for the amplitude,
εt , of the inhomogeneity as a function of the film radius was introduced to exploit
the experimental data obtained by Manev [42] as
εt = 797 R 0.25
− 209
f
(5)
where the film radius Rf is given centimetre and the amplitude εt is in Å. In this
model, the wavelength ( λ = 50 μ m ) and the amplitude of the surface waves do
not vary during the film drainage, while the frequency decays as follows:
ω
ω=
3π
3π
λ
3 R f dh
2 h dt
(6)
However, the experimental findings by Karakashev et al. [67] who studied
foam film surface waves with high speed line-scan camera microscopy indicated
that both the wavelength and frequency change during the film drainage. In addition, the film wavelengths measured are in the range of 50–120 μm [67] and to
some extent contradict to the stipulations of the RSh model. This does not mean
that the model is wrong. Only validation with experimental data, as it is done in
this paper, can justify or reject the validity of the RSh model. After estimating the
contributions of the different terms in the general differential equation, the following equation for the drainage velocity was obtained:
⎡
⎛ Rf
2h 3
dh
1
7.35
V =−
=
P
−
Π
+
(
)
⎢
⎜
σ
dt 3μR 2f
⎝ λ
⎣⎢
⎞ ⎛ εt
⎟⎜
⎠⎝ h
⎞⎤
⎟⎥
⎠ ⎦⎥
(7)
−5
where λ = 5 × 10 m is the characteristic wavelength of the thickness inhomogeneity. Finally, it is noted that the surface waves in this model are generated by the
liquid outflow during drainage and are suppressed by the hydrodynamic and other
repulsions between the film surfaces. This model should be valid for foam films
with rigid film surfaces and was compared with experimental data [15, 68]. It was
shown that the RSh model agrees well with the experimental data when the radii
of the films are in the range from 40 to 450 μm.
2.4 The Model of Manev, Tsekov and Radoev (MTR) [20]
At the first glance this model appears equivalent to the RSh model as far as
it stipulates immobile and deformable film surfaces. However, the MTR model is
different. The model derivation starts with the general differential equation giving the speed of film evolution with deformable surfaces [20, 39]. The normal
111
force balance for a nearly flat thin liquid film ( (∂H / ∂r ) << 1 ) is expressed as
p = − (σ / 2 )∂ 2 H / ∂r 2 − Π (H ) . The local film thickness, H, is assumed to be a
homogeneous function of the average film thickness, h, expressed as
2
H =h
∂H
∂h
(8)
In the MTR model, the surface corrugations are static rather than running
waves as considered in the RSh model. The solution of the governing differential
equation for the wave number of the capillary waves is given as
k=
2π
Π′
Π′2 24 μV
=
+
+
λ
σ
σ2
σ h4
(9)
Equation (9) shows that the there is a steady-state capillary wave, which
changes slowly during the film thinning. The drainage rates close to and far from
equilibrium present two important limits. At equilibrium the velocity of film drainage is zero and hence
λ=
2π
2Π′ / σ
(10)
which corresponds to the Scheludko critical wave [10]. When the film is far from
equilibrium and relatively thick, Eq. (9) reduces to
1/4
⎛ σ h4 ⎞
λ = 2π ⎜
⎟
⎝ 24 μV ⎠
(11)
Equation (11) shows that the wavelength decreases with the film drainage and
the theoretical wavelength is of the same order of magnitude as the experimental
data [67]. With the existence of variable wavelength, this model differs from the
RSh model, which stipulates a single (constant) wavelength. When substituting
VRe for V into Eq. (11) and following the mathematical procedure given in [20],
one obtains the critical radius of the foam film (about 40 μ m ), below which the
film becomes planar and follows the Stefan-Reynolds model for drainage. The
latter was confirmed by the experimental data [42]. Integrating the general driving
differential equation yields the final equation of the film drainage as [20]
1/5
8
12
dh 1 ⎛ h (Pσ − Π ) ⎞
=
V =−
⎜
⎟
⎟
dt 6 μ ⎜⎝ 4σ 3 R 4f
⎠
112
(12)
Similar to the RSh model, the MTR model is valid for foam films with any
radii and immobile film surfaces and was compared against experimental data
[22, 30, 68].
2.5 The Disjoining Pressure
The disjoining pressure is an important parameter for thin liquid films. Approximate equations are not universal and are not used in this paper. Instead, the
advanced models for both electrical double layer and van der Waals components
of the disjoining pressure are described below.
The electrostatic disjoining pressure Πel is obtained by numerically solving
the Poisson-Boltzmann equation employing appropriate boundary conditions at
the film surfaces. Under the condition of constant surface potential, the numerical
solution of the non-linear Poisson-Boltzmann equation can be semi-analytically
represented as [69]
y
1
⎛ y ⎞⎧
⎫
Π el (h) = 32cel Rg T tanh 2 ⎜ 0 ⎟ ⎨
+ f ( y0 )sinh 2 0 exp[− f ( y0 )kh]⎬(13)
4
⎝ 4 ⎠ ⎩1 + cosh κ h
⎭
where Rg is the universal gas constant, cel is the molar concentration of electrolytes
in the solution, T is the absolute temperature. The Debye constant for a binary elec-
{
}
2 2
trolyte of valence z is defined as κ = 2cel F z / (εε 0 Rg T )
1/ 2
, where ε0 is the di-
electric permittivity of the vacuum. The normalized surface potential is defined as
y0 = zFψ s / (Rg T ), where F is the Faraday constant and ψs is the surface potential.
For y0 ≤ 7 , the function f ( y0 ) is defined as f ( y0 ) = 2cosh(0.332 y0 − 0.779) .
Under the condition of constant surface charge, the exact numerical solution to the
Poisson-Boltzmann equation gives [69]:
2cel Rg TA
Π el (h) =
(14)
[cosh(κ hC ) − 1] 1 + B 2 coth (κ hC / 2)
The model constants in Eq. (14) are functions of the surface potential, y0, at infinite separation (i.e., the single air-water surface) which are described for y0 ≤ 5
(
2
3
as follows: A = BC sinh 1.854 y0 − 0.585 y0 + 0.1127 y0 − 0.00815 y0
(
B = 0.571 y0 exp −0.095 y0
1.857
) and C = 1 − 0.00848 y
0
4
),
.
The van der Waals disjoining pressure, ΠvdW, as a function of the film thickness, h, for both the non-retarded and retarded regimes can be described as [70]
Π vdW = −
A (h, κ )
1 dA (h, κ )
+
6π h3
12π h 2
dh
(15)
113
where А(h,κ) is the Hamaker-Lifshitz function, which depends on the film thickness and the Debye constant, κ, due to the electromagnetic retardation effect and
is described as
3k T
A (h, κ ) = (1 + 2κ h )e −2κ h B
4
∞
∑
j =1
2
2
⎛ ε −ε ⎞
3 ω (n1 − n2 )
j −3 ⎜ 1 2 ⎟ +
3/2
16 2 (n12 + n22 )
⎝ ε1 + ε 2 ⎠
2
2j
q
⎪⎧ ⎛ h ⎞ ⎪⎫
⎨1 + ⎜ ⎟ ⎬
⎪⎩ ⎝ λ ⎠ ⎪⎭
−1/ q
(16)
where ε1 is the static dielectric permittivity of the dispersion phase (2.379 for
toluene at 298.15 K), ε2 is the static dielectric permittivity of the disperse medium
(80 for water),
= 1.055 × 10-34 Js/rad is the Planck constant (divided by 2π),
ω is the absorption frequency in the UV region – typically around 2.068 × 1016
rad/s for water, n1 and n2 are the characteristic refractive indices of the dispersion
phase and the medium: n12 = 1 for air and n 22 = 1.887 for water, and q = 1.185. The
characteristic wavelength is defined as λ = 2v 2 / n22 (n12 + n22 ) / (π 2ω ), where v is
the speed of light.
2.6 Numerical Solution
Knowing the total disjoining pressure, Π = Π el + Π vdW , as a function of the
film thickness, Eqs. (1), (2), (7), (12) were numerically integrated to obtain the
transient film thickness using the 4th order Runge-Kutta algorithm. A program
was written using the VBA (Visual Basic for Application) programming language
available in Microsoft Excel. In some cases, the concentration of the background
electrolytes was so significantly high that the electrical double layer interaction
was fully compressed. In these cases, the surface potential is not required.
The models were statistically evaluated using the Chi-square test and the statistical uncertainty [71] described as
⎛ hiExp − hiTh ⎞
χ = ∑⎜
⎟
αi
i =1 ⎝
⎠
2
N
2
(17)
Exp
Th
where N is the number of the experimental points, hi and hi are the experimental and theoretical film thicknesses, respectively, αi is the experimental error
for each one of the points. The average experimental error is estimated to be about
±2 nm . The level of statistical uncertainty can be calculated as
α = χ 2 / (N − ϑ )
(18)
where ϑ is the number of fitting parameters. Since there are no fitting parameters
used in this paper, ϑ = 0 .
The smaller the α value, the greater is the statistical reliability of the theoretical model. The α value for each one of the cases was calculated. The validation
114
of the above models for foam films containing weak, moderate and strong surfactants at different concentrations and film radii was carried out.
3. EXPERIMENTAL PART
The drainage models reviewed in Section 2 were validated using the experimental data. The data were obtained in the present work using the micro interferometric
technique with the Scheludko cell. Foam films with hexathyleneglycol monododecyl ether (C12E6: CMC = 7.3 × 10-5 M) at ionic strength 0.024 M were studied.
The micro interferometric method was used to determine the transient behaviour of foam films. The full description of the experimental apparatus was
previously reported [1, 4, 25, 42, 72, 73] and is not fully repeated here. Briefly, the
apparatus consists of a glass cell, with an inner diameter of 4 mm, for producing
horizontal foam films, normal to gravity. First, a droplet of surfactant solution was
formed inside the film holder. Then the amount of liquid was regulated by means
of a gastight microsyringe connected to the film holder through a glass capillary.
Finally, a microscopic film was formed between the apexes of the double-concave meniscus by pumping out the liquid from the drop. A metallurgical inverted
microscope was used for illuminating and observing the film and the interference
fringes (the Newton rings) in reflected light by means of wavelength λ = 546 nm
and a digital camera system connected with computer for storage of the data. The
interferograms were processed offline using the “Image J” software for image processing delivering the pixel signal from a given small area of the film as a function
of the time, thus producing temporal interferograms, which was used for further
calculation of the film thickness versus time.
4. RESULTS AND DISCUSSION
Figure 2 presents the experimental data for foam films obtained with three
different radii (50 μm, 100 μm and 150 μm), which should produce plane parallel
films (with small radii) and then should increase the film thickness inhomogeneity
with increasing the film radius from 100 μm to 150 μm. According to the theoretical expectation the RDI and Scheludko models should better fit with the data for
the smallest foam film (Rf = 50 μm) than for the films with the larger radii. It is
noted that the drainage curves predicted by the RSh model are very close to the
experimental data for the three cases shown in Figure 4. On the other hand, the
MTR model, which is basically valid for inhomogeneous foam films with immobile surfaces and large radius, predicts significantly faster drainage than the
experimental data.
115
116
Figure 2. Comparison between the model predictions (curves) and the experimental results (points) for transient thickness of C12E6 + 0.024 M
NaCl foam film with radius of 0.05 mm, 0.1 mm and 0.15 mm.
5. STATISTICAL EVALUATION OF THE THEORETICAL MODELS
Now the comparison and the validation of the models are checked by the statistical analysis. The statistical evaluation of the theoretical models is performed
by means of Eqs. and . This criterion is not absolute, but it is significantly indicative regarding the applicability of the models. Table 1 summarizes the level of
statistical uncertainty for all the presented cases along with the surface tension,
adsorption, the Gibbs elasticity, the adsorption length, the film radii, the CMCs,
the adsorption parameters and the bulk and surface diffusion coefficients. It is
noted that the smaller is the level of uncertainty, α, the closer is the theoretical
model to the experimental data. This statistical evaluation is expected to provide
the better measure of the significance and precision of the models than the visual
observation of the theoretical and experimental results presented in Figure 2.
Table 1 summarize the data for C12E6. Drainage of foam films with three different radii (50μm, 100μm and 150μm), keeping the same surfactant concentration,
is shown. This allows the estimation of the α value as a function of the film radius.
The α values for the Scheludko and RDI models increase with increasing the film
radius, which is expectable. Such dependence is not manifested with the other two
models. The RSh model agrees reasonably with the experimental data regardless of
the film radius, while the MTR model describes poorly the experimental data.
In summary: Scheludko and RDI models are with well defined validity – they
are valid for planar films of small size; in most cases such films are with radii up
to 50 μm. RSh model is empirically parameterized with experimental data and is
valid for films with tangentially immobile surfaces. For this reason this model
fits well to the experiment in many of the investigated here cases, although not
perfectly. MTR is a purely analytical model which should have validity similar to
the RSh model. However, in the particular studied range of small films, not being
empirically adjusted, it has lost here the advantages that it distinctly exhibits with
larger films. For this reason it needs further development.
6. CONCLUSION AND REMARKS
The available models for foam film drainage due to the Marangoni effect
were reviewed and validated using the experimental data obtained with non-ionic
surfactant. The evaluation of theoretical models was based on several criteria in
terms of dependence of the statistical uncertainty, α, on the Gibbs elasticity (at
similar film radii), the film radii (at the similar Gibbs elasticities) and for films
with film surface aggregates.
The validity of the Scheludko, RDI, RSh and MTR models was evaluated via
experiments on drainage of foam films with C12E6 in the range of small film radii
(50–150μm).
The evaluation of the theoretical models indicated that the foam film drainage
is crucially dependent on two factors: film radius and Gibbs elasticity. The film
117
118
RSh
α± 0.26
1.31
3.97
2.53
2.52
1.21
2.50
2.11
1.04
4.47
MTR
α ± 0.24
8.87
4.08
6.00
12.53
6.43
4.41
12.46
10.11
10.57
Table 1. Experimental and model parameters, and statistical uncertainty, α, evaluated for the model thickness predictions for C12E6 foam films
RDI
1133.12 3.67 × 10-10 5.51 × 10-10 Scheludko
7.3 × 10-5
3 × 10-6
2
Csurf, M σ,mN/m Γ, μmol/m Eg, mN/m dΓ/dc, μm
Rf, μm
α± 0.16
α ± 0.15
50
1.26
1.26
-5
100
9.61
9.61
48.25
2.94
370
8.08
1 × 10
150
10.35
10.35
50
2.24
2.24
39.40
2.98
1150
0.95
100
6.15
6.15
3 × 10-5
150
10.81
10.81
50
1.82
1.82
-4
100
5.49
5.49
33.09
2.99
3400
0.11
1 × 10
150
10.81
11.67
C12E6 (Film radii = 50, 100 & 150 μm, Ionic strength = 0.024 M)
CMC, M Γ∞, mol/m2 K, m3/mol D, m2/s
Ds, m2/s
radius determines the thickness inhomogeneities, which make the film draining
faster. The formation of thickness inhomogeneity starts at film radius if ca. 50 μm
and increases upon the enlargement of the films as indicated by the experiment of
Manev [42]. The Gibbs elasticity controls the mobility of the film surfaces. They
become practically rigid at Eg = 1 mN/m. This is fulfilled with majority of the
surfactants at concentrations of CMC/1000.
The tests on the Scheludko and RDI models confirmed the theoretical expectations that these models are only valid in plane parallel films ( R f ≤50 μ m ).
The Scheludko model is only valid in the case with rigid film surfaces, i.e.,
Eg ≥ 1mN / m .
The RSh model gives good agreement with the theory with both small and
large foam films. In the case of small foam films ( R f ≤50 μ m ) the RSh model
agrees with the experimental data even for foam films with mobile film surfaces. At larger film radii the RSh model agrees well with the experiments when
Eg ≥ 10 mN / m , which is in accord with the theoretical stipulations of the model (for rigid film surfaces). It should be noted that the film surfaces become practically immobile, starting from Eg = 1 mN / m . The requirement for higher value
of the Gibbs elasticity with the RSh model most probably concerns the mechanical strength of the film surfaces. Again Eg ≥ 10 mN / m is fulfilled with most of
the cases, which makes RSh model very applicable for variety of different cases.
It should be noted here that MTR model was inducted by the experiments of
Manev [42]. In addition, empirical correction originating from Ref. [42] was introduced in the RSh model thus becoming semi-empirical. In this term it is not surprising that this model agree with the similar experiments in most of the cases.
The MTR model was developed for inhomogeneous foam films with immobile
surfaces. In most of the cases in the present work, these requirements are fulfilled
yet the model predicts significantly faster drainage. It should be noted that according
to Ref. [30] the MTR model agrees better with experiments on films with larger radii
(e.g. 200–500μm) than the other models observed in the present work.
The present work brings together the basic theoretical models for evaluation
with experiment on foam film drainage with seven different surfactants. Therefore, it calls upon the further development of the theory of thin liquid films.
Acknowledgments. Dr Stoyan Karakashev gratefully acknowledges the EC “Marie Curie Actions” for the financial support through DETLIF – Project No. 200688/2009. The authors thank Dr.
Alia Tadjer for her help in calculating the bulk diffusion coefficients of the surfactants.
REFERENCES
1. Exerowa, D.,P.M. Kruglyakov, Foam and Foam Films: Theory, Experiment, Application. Marcel
Dekker, New York, NY,1997.
2. Weaire, D.,S. Hutzler, Physics of Foams. Oxford University Press, USA, Oxford,1999.
119
3. Binks, B.P., Modern aspects of emulsion science. The Royal Society of Chemistry, Cambridge,1998.
4. Nguyen, A.V.,H.J. Schulze, Colloidal science of flotation. Marcel Dekker, New York,2003.
5. Mittal, K.L.,P. Kumar, Emulsions, Foams, and Thin Films. CRC, New York,2000.
6. Karakashev, S.I.,E.D. Manev, Journal of Colloid and Interface Science, 259 (1), 2003:171-179.
7. Derjaguin, B., Acta Phys.-chim., 10 (3), 1939:333-346.
8. Verwey, E.J.W.,J.T.G. Overbeek, Theory of the Stability of Lyophobic Colloids. Elsevier, Amsterdam,1948.
9. Ekserova, D., I. Ivanov,A. Sheludko, Issled. v Obl. Poverkhn. Sil, Akad. Nauk SSSR, Inst. Fiz.
Khim., Sb. Dokl. na Vtoroi Konf., Moscow, 1962, 1964:158-63.
10. Scheludko, A., Adv. Colloid Interface Sci., 1 (4), 1967:391-464.
11. Radoev, B.P., D.S. Dimitrov,I.B. Ivanov, Colloid Polym. Sci., 252 (1), 1974:50-5.
12. Traykov, T.T., E.D. Manev,I.B. Ivanov, International Journal of Multiphase Flow, 3 (5),
1977:485-94.
13. Ivanov, I.B., Pure and Applied Chemistry, 52 (5), 1980:1241-62.
14. Wasan, D.T.,A.K. Malhotra, AIChE Symp. Ser., 82 (252, Thin Liquid Film Phenom.), 1986:5-13.
15. Ruckenstein, E.,A. Sharma, J. Colloid Interface Sci., 119 (1), 1987:1-13.
16. Bergeron, V.,C.J. Radke, Langmuir, 8 (12), 1992:3020-6.
17. Manev, E.,R.J. Pugh, Colloids Surf., A, 70 (3), 1993:289-95.
18. Tchaliovska, S., E. Manev, B. Radoev, J.C. Eriksson,P.M. Claesson, Journal of Colloid & Interface Science, 168 (1), 1994:190-197.
19. Bergeron, V., A. Waltermo,P. Claesson, Langmuir, 12, 1996:1336-1342.
20. Manev, E., R. Tsekov,B. Radoev, J. Dispersion Sci. Technol., 18 (6 & 7), 1997:769-788.
21. Tsekov, R.,H.J. Schulze, Langmuir, 13 (21), 1997:5674-5677.
22. Angarska, J.K.,E.D. Manev, Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 223 (1-3), 2003:27-34.
23. Stubenrauch, C.,R. von Klitzing, Journal of Physics: Condensed Matter, 15 (25), 2003;
24. Wang, L.,R.-H. Yoon, Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 263
(1-3), 2005:267-274.
25. Karakashev, S.I.,A.V. Nguyen, Colloids & Surfaces A - Physicochemical & Engineering Aspects, 293 (1-3), 2007;
26. Sheludko, A., Adv. Colloid Interface Sci., 1 (4), 1967:391-464.
27. Stefan, M.J., Sitzungsberichte der Mathematisch-naturwissenschaften Klasse der Kaiserlichen
Akademie der Wissenschaften, II. Abteilung (Wien), 69, 1874:713-735.
28. Reynolds, O., Philos. Trans. R. Soc. London, Ser. A, 177, 1886:157-234.
29. Manev, E.D.,J.K. Angarska, Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 263 (1-3), 2005:250-257.
30. Tsekov, R., Colloids Surf., A, 141 (2), 1998:161-164.
31. Radoev, B.P., E.D. Manev,I.B. Ivanov, Godishnik na Sofiiskiya Universitet Sv. Kliment Okhridski, Khimicheski Fakultet, 60, 1968:59-72.
32. Radoev, B., D. Manev Emil,I. Ivanov, B., Kolloid Z., 234, 1969:1039-1045.
33. Manev, E.D.,A.V. Nguyen, International Journal of Mineral Processing, 77 (1), 2005:1-45.
34. Ivanov, I., D. Dimitrov, P. Somasundaran,R.K. Jain, Chem. Eng. Sci., 40 (1), 1985:137-50.
35. Tsekov, R.,E. Ruckenstein, Colloids Surf., A, 82 (3), 1994:255-61.
36. Davies, R.H., J.A. Schonberg,J.M. Rallison, Phys. Fluids A, 1 (1), 1989:77.
37. Jeelani, S.A.K.,S. Hartland, J. Colloid Interface Sci., 206 (1), 1998:83-93.
38. Tsekov, R.,E. Evstatieva, Progress in Colloid & Polymer Science, 126, 2004:93-96.
39. Ivanov, I.B.E., Thin Liquid Films. Marcel Dekker, New York, N. Y.,1988.
40. Ivanov, I.B.,D.S. Dimitrov, Colloid Polym. Sci., 252 (11), 1974:982-90.
120
41. Karakashev Stoyan, I.,A. Nguyen Anh, Colloids & Surfaces A - Physicochemical & Engineering
Aspects, 293 (1-3), 2007;
42. Radoev, B., A. Scheludko,E. Manev, J. Colloid Interface Sci., 95 (1), 1983:254-65.
43. Manev, E.D., S.V. Sazdanova,D.T. Wasan, J. Colloid Interface Sci., 97 (2), 1984:591-4.
44. Malhotra, A.K.,D.T. Wasan, AIChE J., 33 (9), 1987:1533-41.
45. Li, D., Chemical Engineering Science, 51 (14), 1996:3623.
46. Joye, J.-L., G.J. Hirasaki,C.A. Miller, Journal of Colloid and Interface Science, 177, 1996:542.
47. Joye, J.-L., G.J. Hirasaki,C.A. Miller, Langmuir, 10, 1994:3174-79.
48. Yeo, L.Y., O.K. Matar, E.S. Perez de Ortiz,G.F. Hewitt, J. Colloid Interface Sci., 241 (1),
2001:233-247.
49. Valkovska, D.S.,K.D. Danov, Journal of Colloid and Interface Science, 241, 2001:400.
50. Scheludko, A., G. Desimirov,K. Nikolov, Godishnik Sofiiskiya Univ. Fiz. Mat. Fak. Kniga 2Khim., 49, 1956:127-41.
51. Nguyen, A.V., J. Colloid Interface Sci., 231 (1), 2000:195.
52. Manev, E.D.,R.J. Pugh, J. Colloid Interface Sci., 151 (2), 1992:505-16.
53. Manev, E., K. Vasil’ev,I. Ivanov, Colloid and Polymer Science, 254 (1), 1976:99-102.
54. Hartland, S.,S.A.K. Jeelani, Journal of Colloid and Interface Science, 164 (2), 1994:196-298.
55. Davis, R.H., J.A. Schonberg,J.M. Rallison, Physics of Fluids A: Fluid Dynamics, 1 (1), 1989:77-81.
56. Radoev, B.P., D.S. Dimitrov,I.B. Ivanov, God. Sofii. Univ., Khim. Fak., 66, 1975:87-98.
57. Rao, A.A., D.T. Wasan,E.D. Manev, Chemical Engineering Communications, 15 (1-4), 1982:63-81.
58. Frankel, S.P.,K.J. Mysels, J. Phys. Chem., 66, 1962:190-1.
59. Hartland, S., Chem. Eng. Progr., Symp. Ser., 65 (91), 1969:82-9.
60. Joye, J.-L.,C.A. Miller, Langmuir, 8, 1992:3083-92.
61. Kashtiev, D.,D. Ekhzerova, J. Colloid Interface Sci., 77 (2), 1980:501-11.
62. Sonin, A.A., A. Bonfillon,D. Langevin, Journal of Colloid and Interface Science, 162,
1994:323.
63. Lindman, B., N. Kamenka, M.-C. Puyal, B. Brun,B. Jonsson, Journal of Physical Chemistry,
88, 1984:53.
64. Nelson, P., Biological Physics. Energy, Information, Life. W. H. Freeman and Company, New
York,2008.
65. Danov, K.D., D.S. Valkovska,I.B. Ivanov, J. Colloid Interface Sci., 211 (2), 1999:291-303.
66. Stoyanov, S.D.,N.D. Denkov, Langmuir, 17 (4), 2001:1150-1156.
67. Karakashev, S.I., A.V. Nguyen, E.D. Manev,C.M. Phan, Colloids and Surfaces, A: Physicochemical and Engineering Aspects, 262 (1-3), 2005:23-32.
68. Coons , J.E., P.J. Halley, S.A. McGlashan,T.T. Cong, Colloids and Surfaces A, 263, 2005:197-204.
69. Nguyen, A.V., G.M. Evans,G.J. Jameson, Approximate calculations of electrical double-layer
interaction between spheres, in Encyclopedia of Surface and Colloid Science,2002, A.T. Hubbard, Editor Marcel Dekker: New York.
70. Nguyen, A.V.,H.J. Schulze, Colloidal science of flotation. Marcel Dekker, New York,2004.
71. Phan, C.M., A.V. Nguyen,G.M. Evans, Journal of Colloid & Interface Science, 296, 2006:669-676.
72. Karakashev, S.I.,A.V. Nguyen, Colloids Surfaces A, 293, 2007:229-240.
73. Karakashev Stoyan, I., D. Manev Emil,A. Nguyen Anh, Colloids and Surfaces A, in press, 2007;
Received on September 15, 2009
121
122
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
NOVEL CHALCONE-LIKE DERIVATIVES: 6-(3-ARYL- OR
HETARYL-2-PROPENOYL)-2(3H)-BENZOXAZOLONES SYNTHESIS AND
EVALUATION OF CYTOTOXICITY ON LEUKEMIA CELLS
Y. IVANOVA, O. PETROV*
a
Department of Applied Organic Chemistry, Faculty of Chemistry, Sofia University, 1164 Sofia,
Bulgaria
*[email protected]
Abstract: The synthesis of novel 1,3-diaryl propenone derivatives and their cytotoxic
activity in vitro against tumor cell lines BV-173 and SKW-3 are described. Chalcone
derivatives are prepared via Claisen-Schmidt condensation of substituted aldehydes with
6-acetyl-2(3H)-benzoxazolone.
Keywords: Chalcones; 2(3H)-Benzoxazolone; Cytotoxic activity;
INTRODUCTION
Chalcones are biosynthetic precursors of flavonoids found to possess cytotoxic and chemopreventive activities [1]. Viewed from a historical perspective,
the chalcones are best known as the yellow to orange colored flower pigments of
some species of Coreopsis and other Asteraceae taxa. The distribution of these
compounds is not restricted to flowers, however, and examples of this class can be
found in many different plant tissues. The chalcones are structurally one of most
diverse groups of flavonoids, as witnessed by the formation of a wide range of
dimers, oligomers, Diels–Alder adducts, and conjugates of various kinds. At the
same time, they are of great significance biosynthetically as the immediate precursors of all other classes of flavonoid [2]. Interest in chalcones as cytotoxic agents
was initiated by the discovery of some natural chalcones as Calythropsin, which
showed cytotoxicity against 60 cell lines, a small effect on tubulin polymerization
123
and antimitotic activity. Therefore attempts have been made to find new synthetic cytotoxic analogues. In our earlier works we have synthesized and evaluated
novel heterocyclic chalcone as cytotoxic agents against several human cell lines.
Most of the tested chalcones showed cytotoxic activity where for compound 1 it
was comparable with anticancer drug etoposide[3–6].
OH
N
N
HO
HO
OCH3
Cl
OCH3
N
O
O
O
O
Calythropsin
1
In diversifying our work we have designed and synthesized new chalcone
derivatives and evaluated their cytotoxic ability in vitro.
RESULT AND DISCUSSION
The Claisen-Schmidt condensation method was employed for the synthesis
of 7 chalcone derivatives (compounds 2a-g, Table 1). Two step synthesis protocols, as depicted in scheme 1, were used to prepare the compounds. The first
step involved direct acylation of 2(3H)-benzoxazolone in Friedel-Crafts condition using acetyl chloride and the complex AlCl3-DMF as Lewis acid to yield 6acetyl-2(3H)-benzoxazolone [7]. In the next step, 6-acetyl-2(3H)-benzoxazolone
was condensed with a suitable aldehyde using aqueous potassium hydroxide as
catalyst in ethanol at room temperature to yield chalcone [8]. These conditions
were found to be satisfactory for the synthesis of chalcones in good yields. The
structure of the newly synthesized compound was confirmed by IR- and 1H-NMR
spectroscopy and elemental analyses.
Scheme 1. Schematic representation of the synthesis of chalcones 2a-g.
H
N
O
O
H
N
CH3COCl
AlCl3 /DMF
O
CH3
O
O
124
R1-CHO
aq. KOH, EtOH
H
N
O
R1
O
O
2a-g
Table 1. Physical properties, elemental analysis and cytotoxic activity of compounds 2a-g
Compd
R1
2a
O
2b
S
2c
N
2d
CH3
O
2e
O
CH3
N
2f
O
Elemental analysis
[Calc./Found]
C 65.88 H 3.55 N 5.49
C14H9NO4
65.95
3.69
5.55
C 61.98 H 3.43 N 5.16
C14H9NO3S
62.36
3.43
5.34
Molecular
formula
C15H10N2O3
C 67.67 H 3.79 N 10.52
67.70
4.01
10.20
C17H13NO3
logP**
[Calc.]
n.d.*
31.8±2.5 2.83±0.42
n.d.*
39.4±3.4 3.02±0.59
n.d.*
1.84±0.44
C 73.10 H 4.69 N 5.02
35.1±3.3
73.54
4.84
5.09
n.d.*
3.67±0.40
C17H11NO5
C 66.02 H 3.59 N 4.53
66.18
3.81
4.63
n.d.*
3.33±0.50
C18H12N2O5
C 64.29 H 3.60 N 8.33
440±24.3
64.20
3.73
8.48
n.d.*
2.17±0.48
C20H13NO3
C 76.18 H 4.15 N 4.44
76.19
4.35
4.79
O
2g
IC50(μM)
BV-173 SKW-3
n.d.*
n.d.*
n.d.*
15.3±1.8 4.44±0.40
- Not determined
- calculated with ACD Labs
*
**
Inspection of 1H NMR spectral data clearly indicated that the compounds
were both geometrically pure and were configured trans- (JHα-Hβ = 15–16 Hz). The
aromatic ring protons were observed at the expected values at the area of 7.0–8.0
ppm. The IR spectra taken in nujol showed one characteristic vibrational frequency for the carbonyl group at about 1650 cm-1 and for the lactam C=O stretching
band at about 1760 сm-1.
Some of the synthesized compounds were evaluated for cytotoxicity in the
human chronic myeloid leukemia cell line BV-173 and the human chronic lymphoid leukemia derived SKW-3 cell using the MTT-dye reduction assay [9]. The
tested compounds exhibited concentration-dependent cytotoxic effects at different
concentrations. In both leukemia cell lines, the intensity of cytotoxicity of the heterocyclic chalcones is not governed by the substituents R1. Compound 2f, containing two azolone cycles in the chalcone core structure, showed decreasing in the
activity, which probably due to low lipophilicity as indicated logP values (Table
1). The comparative evaluation of the chalcones 2a-f revealed that the most active
one is 2g with IC50 value 15.3 μM, in accordance with the highest logP value.
125
EXPERIMENTAL PART
Chemistry
The melting points were determined on a Boetius hot-stage microscope. IR
spectra were recorded in nujol on a Specord 75 spectrometer. 1H NMR spectra
(DMSO-d6; δ [ppm]; J [Hz]) were recorded on a Bruker Avance DRX 250 with
tetramethylsilane as internal standard. Elemental analyses were performed on a
Vario III microanalyzer. Obtained results were within 0.4% of theoretical values.
The synthesis of 6-acetyl-2(3H)-benzoxazolone [7] were described previously.
6-(3-(Furan-2-yl)-2-propenoyl)-2(3H)-benzoxazolone (2a) General procedure
To a solution of 0.35 g (2 mmol) 6-acetyl-2(3H)-benzoxazolone in 2 ml 10%
aq. KOH, 0.18 ml (2.2 mmol) furan-2-carbaldehyde in 3 ml EtOH was added.
After stirring a few hours at room temperature, the mixture precipitated. The reaction mixture was poured into 10 ml hot water and acidified with 10% HCl.
After cooling, the crystalline product was filtered, washed with water to pH 7 and
dried. Yield 0.48 g (96%); M.p. 199–201oC ; IR (nujol) 1771, 1660 cm-1, 1H NMR
(DMSO-d6): δ [ppm] 6.41 (m, 1H, furan); 6.70 (m, 1H, furan); 7.22 (d, 1H, arom.
H, J=8.5 Hz); 7.50 (m, 2H,furan, =CHCO); 7.71 (d, 1H, ArCH=, J=15.4 Hz); 7.92
(d, 1H, arom. H, J=1.5 Hz); 7.99 (m, 1H, arom. H); 12.05 (brs, 1H, NH);
6-(3-(Thiophen-2-yl)-2-propenoyl)-2(3H)-benzoxazolone (2b)
Yield 0.51 g (94%); M.p. 224–226 oC; IR (nujol) 1771, 1650 cm-1;1H NMR
(DMSO-d6): δ [ppm] 7.19 (m, 1H, thiophen); 7.22 (d, 1H, arom. H, J=8.2 Hz);
7.62 (d, 1H, =CHCO, J=15.3 Hz); 7.71 (m, 1H, thiophen); 7.79 (m, 1H, thiophen);
7.91 (d, 1H, ArCH=, J=15.3 Hz); 8.01 (dd, 1H, arom. H, J=8.2 Hz, J=1.5 Hz);
8.04 (d, 1H, arom. H, J=1.2 Hz); 12.10 (brs, 1H, NH);
6-(3-(Pyridin-2-yl)-2-propenoyl)-2(3H)-benzoxazolone (2c)
Yield 0.29 g (72%); M.p. 207–211 oC; IR (nujol) 1740, 1650 cm-1, 1H NMR
(DMSO-d6): δ [ppm] 7.24 (d, 1H, arom. H, J=8.1 Hz); 7.43 (m, 1H, pyridin); 7.70
(d, 1H, =CHCO, J=15.4 Hz); 7.94 (m, 4H, pyridin, arom. H); 8.16 (d, 1H, ArCH=,
J=15.4 Hz); 8.68 (m, 1H, pyridin);
6-(3-(4-Methylphenyl)-2-propenoyl)-2(3H)-benzoxazolone (2d)
(DMSO-d6): δ [ppm] 2.36 (s, 3H, CH3); 7.24 (d, 1H, arom. H, J=8.2 Hz); 7.28 (d,
2H, arom. H, J=8 Hz); 7.72 (d, 1H, =CHCO, J=15.5 Hz); 7.81 (d, 2H, arom. H,
J=8 Hz); 7.95 (d, 1H, ArCH=, J=15.5 Hz); 8.07 (dd, 1H, arom. H, J=8.2 Hz, J=1.5
Hz); 8.11 (d, 1H, arom. H, J=1.4 Hz); 12.1 (brs, 1H, NH);
126
6-(3-(3,4-Methylendioxyphenyl)-2-propenoyl)-2(3H)-benzoxazolone (2e)
(DMSO-d6): δ [ppm] 6.12 (s, 2H, CH2); 7.01 (d, 1H, arom.H, J=8.0 Hz); 7.23 (d,
1H, arom.H, J=8.2 Hz); 7.34 (dd, 1H, arom.H, J=8.2 Hz, J=1.5 Hz);7.68 (m, 2H,
=CHCO, arom.H); 7.87 (d, 1H, ArCH=, J=15.5 Hz); 8.06 (dd, 1H, arom.H, J=8.2
Hz, J=1.6 Hz); 8.11 (d, 1H, arom.H, J=1.5 Hz);
3-Methyl-6-(3-oxo-3-(2-oxo-2,3-dihydrobenzo[d]oxazol-6-yl))-2-propenoyl)-2(3H)-benzoxazolone (2f)
Yield 0.31 g (91%); M.p. >350 oC; IR (nujol) 1770, 1620 cm-1, 1H NMR
(DMSO-d6): δ [ppm] 3.37 (s, 3H, CH3); 7.22 (d, 1H, arom.H, J=8.2 Hz); 7.31 (d,
1H, arom.H, J=8.2 Hz); 7.73 (m, 2H, arom.H, =CHCO); 7.95 (d, 1H, ArCH=,
J=15.4 Hz); 8.06 (m, 3H, arom.H); 12.06 (brs, 1H, NH);
6-(3-(Naphthalen-2-yl)-2-propenoyl)-2(3H)-benzoxazolone (2g)
(DMSO-d6): δ [ppm] 7.25 (d, 1H, arom.H, J=8.1 Hz); 7.62 (m, 3H, arom.H); 8.07
(m, 5H, =CHCO, аром.H); 8.57 (d, 1H, ArCH=, J=15.3 Hz); 12.12 (brs, 1H, NH);
Cytotoxic activity
The cytotoxic activity of the tested compounds was assessed by the MTT-dye
reduction assay as described by Mosmann, with minor modifications [10]. Briefly,
exponentially growing cells were seeded into 96-well plates (100 μl aliquotes/
well at a density of 1×105 cells/ml). Following 24 h adaptation period they were
exposed to various concentrations of the tested compounds for 72 h. After the
exposure period, MTT-solution (10 mg/ml in PBS) was added (10 μl/well). Plates
were further incubated for 4 h at 37 oC and the MTT-formazan crystals formed
were dissolved by adding 100 μl/well of 5% formic acid in 2-propanol. Absorption was measured on an ELISA reader (Uniscan® Titertek, Helsinki, Finland) at
540 nm. For each concentration at least 8 wells were used. A mixture of 100 μl
RPMI 1640 medium with 10 μl MTT stock and 100 μl 5% formic acid in 2-propanol served as a blank solution. The cell viability (% of untreated control) for each
treatment group was calculated using the formula:
% of
of untreated control =
AT
× 100
AC
AT – MTT-formazan absorption of the test sample
AC – MTT-formazan absorption of the control (solvent treated) sample
Concentration response curves were generated and the corresponding IC50
values were extrapolated, using Origin plot Software for PC.
127
REFERENCES
1.
2.
Han, Y., M. Riwanto, M. Go, P. Rachel. Eur. J. Pharm. Sci., 35, 2008, 30.
Davies, K. M., K.E. Schwinn. – In:. Flavonoids: Chemistry, Biochemistry and Applications.
O.M. Andersen, K. R. Markham, ed. Taylor & Francis, FL, 2006, 143.
3. Ivanova, Y., G. Momekov, O. Petrov, M. Karaivanova, V. Kalcheva. Eur. J. Med. Chem., 42,
2007, 1382.
4. Ivanova, Y., O. Petrov, M. Gerova, G. Momekov. Comp. rend. Acad. bulg. Sci., 60, 2007, 642.
5. Ivanova, Y., V. Kalcheva, O. Petrov. Comp. rend. Acad. bulg. Sci., 61, 2008, 41.
6. Petrov, O., Y. Ivanova, G. Momekov, V. Kalcheva. Lett. Drug Des. Disc., 5, 2008, 358.
7. Aichaou, H., J.H. Poupeart, D. Lesieur, J.P. Henichart. Tetrahedron, 47, 1991, 6649.
8. Bonte, J.P., D. Lesieur, C. Lespagnol, J.C. Cazin, M. Cazin. Eur. J. Med. Chem. – Chim. Ther.,
9, 1974, 497.
9. Mosmann, T. J. Immunol. Methods, 65, 1983, 55.
10. Bakalova, A., R. Buyukliev, I. Tcholakova, G. Momekov, S. Konstantinov, M. Karaivanova.
Eur. J. Med. Chem., 38, 2003, 627.
Received on Oktober 22, 2009
128
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
SPRAY-DEPOSITED TiO2 FILMS FOR PHENOL DESTRUCTION
IN WATER
R. TODOROVSKA1, M. UZUNOVA-BUJNOVA, M. MILANOVA, D. TODOROVSKY*
Faculty of Chemistry, University of Sofia., 1, J. Bourchier Blvd., Sofia 1164, Bulgaria
Institute of Electronics, Bulgarian Academy of Sciences, 72, Tsarigradsko Shose Blvd., Sofia 1784,
Bulgaria
Corresponding author, e-mail: [email protected]
1
Abstract. The influence of the preparation conditions of films produced from commercially
available TiO2 by spray drying (particularly the role of the titania phase composition, the
nature of the suspension medium and of the substrate, temperatures of the deposition and postdeposition annealing) on their photocatalytic activity to the degradation of phenol dissolved in
water are studied. On the ground of the results reported and the data from the literature survey,
optimal conditions for photocatalytic TiO2 layers production are recommended.
Keywords: photocatalysis, TiO2, thin films, spray-pyrolysis, phenol, SEM
ПУЛВЕРИЗАЦИОННО ОТЛАГАНЕ НА СЛОЕВЕ ОТ TiO2
ЗА ФОТОКАТАЛИТИЧНО РАЗЛАГАНЕ НА ФЕНОЛ, РАЗТВОРЕН
ВЪВ ВОДА
Р. ТОДОРОВСКА, М. УЗУНОВА-БУЙНОВА, М. МИЛАНОВА, Д. ТОДОРОВСКИ
Абстракт. Изследвано е влиянието на условията на спрей-пиролизно получаване на филми от търговски продукти TiO2 (по-специално ефекта на фазовия състав на
оксида, състава на суспендиращата среда, природата на подложката, температурата
на отлагане на слоя и на следващото му нагряване) върху тяхната фотокаталитична
активност по отношение на разлагането на фенол, разтворен във вода. На основата
129
на получените резултати и данни от литературното проучване са предложени оптимални условия за отлагане на фотокаталигични слоеве от TiO2.
INTRODUCTION
Amongst various oxide semiconductor photocatalysts, TiO2 has proven to be
the most widely used due to its strong oxidizing power, non-toxicity and longterm photostability [1]. Intensive investigations are carried out on the various factors influencing its photocatalytic efficiency. A critical review of different routes
for its modification as to enhance the activity towards the degradation of organic
dyes at wastewater treatment is reported recently [2]. Due to its high toxicity, wide
spreading and difficult destruction, phenol is used often as a model pollutant in
testing the peculiarities of the photocatalysts and photocatalytic processes conductions. The amount of literature devoted to this problem is rather huge.
The present work aims: (i) to make a short overview of some, more or less
representative papers revealing some of the main factors responsible particularly
for phenol degradation; (ii) by means of an additional experimental study to help
in elucidation of the influence of the TiO2 films preparation conditions on their
photocatalytic activity.
1. Photocatalyst
Slurry and films. TiO2 is used for phenol degradation as coatings on appropriate substrates or as slurry. The comparison between the effectiveness of the
catalyst used as slurry or as thin films correlated with its phase composition and
oxygen-source (O2 or H2O2) is made in [3].
Degradation of phenol derivates. A review of some papers dealing with degradation of 2-chlorphenol, 4-chlorphenol, 2,4-dichlorphenol, 3,5-dichlorphenol,
2,4,6-trichlorphenol, 2,3,5-trichlorphenol, pentachlorphenol, 4-nitrophenol is
made in [4]. Quantum yields for the photooxidation of 4-chlorophenol on spincoated films is studied [5].
Films substrates. Degussa P25 TiO2 is widely used for phenol degradation [6,
7] attached to glass mesh or spiral [8, 9], glass pearls [10], porous ceramic pellets
(there heating to 800 0C has a positive effect on the catalytic activity) [11], silica
[12], Si wafer [13, 14].
Influence of the catalyst preparation conditions. The catalyst preparation conditions are of great importance for its performance. The study [15] on the effect of the
calcination temperatures ranging from 350 to 750 0C on the structure and photocatalytic activity in visible and ultraviolet light show that samples calcinated at 350 0C
are active in vis region and had anatase structure, about 200 m2/g specific surface
area, absorb light above 400 nm and contain 10.1 mol% of C–C species. Photocatalyst processed at 450 0C had the best activity in UV light (250 ÷ 400 nm).
130
Catalyst with smallest particle size, highest surface area and highest porevolume has been produced by ultrasonic-assisted sol-gel method showing to be
the rather active for the phenol derivates degradation [16].
Influence of the catalyst morphology. No proportional dependence between
films roughness and its activity has been found. Degradation of the pollutant to
CO2 after 2 h at 25 0C using films which roughness decreases in the order A>B>C
is 64% (B), 17% (A), 2% (C) due to the different surface properties has been observed [13].
The pores structure of the catalyst plays important role in the activity of TiO2.
Micro-/nano-composite hierarchical films deposited on glass by electro-hydrodynamic method, consisting of 100–1000 nm spheres (with macropores among
them) assembled by nanoparticles with nanopores have shown higher activity
than the nanofilms (rate constants 0.36 and 0.21 h-1, respectively) due to the increase of light collection above 380 nm and higher specific surface. The role of the
molecular transport is elucidated and a mathematical model is proposed [6].
It is found that the particle size of about 10 nm is an optimal for maximum
photocatalytic efficiency of anatase (prepared through sol–gel hydrolysis precipitation of titanium isopropoxide, followed by peptization, reflux or hydrothermal
treatment) [17]. UV pretreatment of the so obtained TiO2 samples leads to 40 %
higher activity than the one obtained with not treated samples.
Nanosized TiO2 photocatalysts (with 79–98% anatase, 48–63 nm in diameter
and specific surface area of 20–32 m2/g) are also synthesized via hydrogen–air
flame hydrolysis. It is found that catalysts with spherical particles have lower
activity compared with ones with polyhedral (cubic or hexagonal) shapes. Some
of the produced catalysts have a better photocatalytic performance than that of
Degussa P25 [18]. Nanocrysalline TiO2 (18 nm) was tested for phenol derivates
degradation under UV illumination [19].
Photocatalyst crystallite size has not significant influence on its catalytic activity. The low Fermi level is not favorable for phenol transformation [13].
The interrelation of influences of the type of the TiO2, the substrate nature,
the deposition and post-deposition annealing temperatures, the type of suspension
medium and additives serving as binders and pore-makers on the film photodegradation performance is shown [20].
Influence of the doping of the catalyst A number of doping agents and TiO2
doping methods are proposed.
F-doped commercial powder has been deposited on Ti plate [21].
The twist-like helix W, N-codoped TiO2 photocatalysts has been prepared
by a hydrolysis of TiCl4 using (NH4)2WO4 as W- and N- sources. The probable
mechanism of codoping effect is proposed considering the narrowing the band
gap between the valence and conduction band, the formation of trapping sites by
the tungsten ions with changing valences and the special twist-like helix structure
131
with regular holes on the wall, high surface area, large pore volume and wellcrystallized anatase phase. Codoped 1 %-W, N-TiO2 sample has shown the best
photocatalytic activity, which is much superior to Degussa P25 under both visible
and ultraviolet light irradiation [22].
The N-doped TiO2 prepared using TiCl3 as the precursor and ethylenediamine
as N-source shows red-shiftting to the visible region. The nitrogen atoms are located
at the oxygen site in the TiO2 lattice to form an O-Ti-N structure. As a result ~98%
of the present phenol is degraded for 6 h under visible light irradiation [23].
A wide number of different TiO2 (Degussa P25, Hombikat UV-100 and Rutile Aldrich as well as TiO2 prepared by sol–gel method) have been modified by
photodeposition of platinum from H2PtCl6, using isopropanol as reducting agent
under N2- atmosphere, thus depositing an amount of 0.5% Pt. The photocatalytic
activity has been studied in correlation with the results of structural and surface
characterisation [24].
The effect of sulphatization on the structural and surface characteristics and
photocatalytic properties of Degussa and sol–gel produced TiO2 has been studied
in [25]. Sulphatization process stabilizes TiO2 catalyst phase against sintering,
maintaining anatase phase until higher calcination temperatures and relatively
high surface area values. Better conversion values for phenol oxidation have been
obtained for samples calcined at 700 0C or (for the sol-gel samples) at 600 0C.
Further improvement of the photocatalytic activity of sol–gel prepared TiO2 has
been achieved by sulphate pre-treatment, calcination at high temperature and following platinisation (0.5–2.5% Pt) of the samples. Synergetic effect of the co-doping is
registered, the activity of the samples being several orders of magnitude higher than
that of the commercial TiO2 Degussa P25 (platinised or unmodified) [26].
The influence of pH and doppant concentration on the activity of the sol–gel
prepared titania nanopowders co-dopped with Zn(II) and Fe(III) has been investigated and a mechanism has been proposed explaining the enhanced activity [27].
The synergetic effect of B-Fe co-doping of titania/silica photocatalyst has been
found in [28]. The dopants inhibit phase transformation of TiO2 and enhance the
intimate interaction between titania and silica thus increasing the photoactivity. The
doping with boron leads to the response to visible light and with iron (existing as
Fe2O3 dispersed on the TiO2 surface) increases the photoquantum efficiency. Codopping with boron and nitrogen is also used for the same purpose. The presence of
the dopants leads to the band gap decrease and respective rise of the photocatalytic
activity. The calcination temperature influences the photoactivity [29].
Improving of the photocatalytic activity (compared with Degussa product or
the sample prepared by the same method but without dopant) has been reached
by a composite consisting of TiO2 coated onto a magnetic Fe3O4 core with a SiO2
layer between the core and shell. The photocatalytic-degraded ratio of phenol is
132
still higher than 80 % after six cycles. The activity of the product without the buffer SiO2 layer has been found to be lower than the referent materials [30].
The presence of SnO2 in the composites TiO2/SnO2 efficiently suppresses the
electron-hole recombination [31].
The system of porphyrin/TiO2 complexes has significant efficiency for photocatalytic degradation for some hazardous or recalcitrant pollutants, under visible
light (λ = 419 nm) irradiation. The degradation of 2, 4-dichlorphenol has reached
42–81% at pH 10 for 4 h [32].
Fe- and Eu-doped (≤1 mol %) TiO2 nanoparticles powders have been synthesized by a hydrothermal route at 200 0C, using chlorides as starting materials.
XRD patterns reveal that the as-prepared samples consist of TiO2 with particle
size as low as 15 nm with iron and europium ions substituting for titanium in the
tetragonal anatase structure. A decrease of Eg from 2.9 eV found for Degussa photocatalyst to 2.8 eV for the titania doped with 1 mol% Fe has been evidenced, indicating a valuable absorption shift ( 20 nm) towards visible light region. However, the best photocatalytic activity in the photodegradation reaction of phenol
has been found for hydrothermal sample of TiO2 with 1 mol% Fe and 0.5 mol%
Eu, in both UV and visible light regions. The photocatalytic activities of Fe-doped
and Fe–Eu-codoped samples are practically the same only in visible light [33].
La-doped nanocrystalline TiO2 photocatalyst has been developed by sol-gel
method. The photocatalytic activity has been evaluated by the photocatalytic degradation of phenol in solution under sunlight irradiation. The results have shown
that La doping improves the crystallinity of anatase, suppresses phase transition
from anatase to rutile and exhibits an absorption in the >400 nm range. So produced photocatalysts exceeds the activity of pure TiO2 prepared by the same method when the molar ratio of La to Ti has been kept at 0.3 % [34].
Nd3+–TiO2 nanocolloids (sol particles of 10 nm prepared by chemical coprecipitation–peptization method) have exhibited photocatalytic activity in the visible range.
It has been found that after 2 h photocatalysis the concentrations (mg/l) decreased
from initial 100 to final 5.29 for phenol and 75.2 for phenol derivatives and from 37.1
to final 29.3 for the total organic carbon value. The reaction mechanism has been proposed as the process of self-sensitization and sub-bandgap overlapping [35].
The composite consisting of 10 % TiO2 and 0.3 % Ce loaded on molecular
sieve has shown maximum phenol degradation activity. The possible mechanism
of the degradation process has been proposed [36]. Nanocrystalline TiO2 incorporated with Pr(NO3)3 has been prepared by an ultrasound method in a sol–gel
process [37] and tested for the phenol derivates degradation.
Modified sol–gel method has been used to produce multi-walled carbon nanotubes (MWNT) - TiO2 catalyst. The synergetic effect (strongest at weight ratio
MWNT/TiO2 equal to 20 %) induced by a strong interphase interaction between
MWNT and TiO2 (preventing TiO2 particle agglomeration) has led under visible
133
light irradiation to an increase in the first-order rate constant by a factor of 4.1.
A correlation exists between the MWNT content and the changes in the UV–vis
absorption properties. [38, 39].
Carbon-containing catalysts of semiconductor nature with large surface areas, capable to photodegrade p-chlorphenol under visible light, with long-time
stability have been obtained by a modified sol–gel process. A highly condensed,
carbonaceous species formed during calcination are responsible for the photosensitisation. Commercially available TiO2 can be photosensitised by impregnation
with suitable alcohols followed by pyrolysis [40].
2. Photocatalytic process
Excitation light wavelength. Using 15 W UV lamps, higher degradation rates
have been obtained at 254 nm than at 350 nm [41].
Excitation source. Different types of black light UV fluorescent tubes (15–20 W)
are usually applied along with Hg lamp (125 [10] – 500 W [42]). Solar parabolic
trough [8] or other sources of concentrated sunlight [7] are used for a sunlight
excitation.
Value of pH of the pollutant solution. Using Degussa P25 TiO2, attached to
glass spiral and fluorescent tube or solar energy as excitation source, maximum
rate was observed above pH 3.4 [8]. Further increase of pH to 8.5 has not shown
essential effect at near-UV illumination [43].
Temperature. The apparent degradation rate constant Kd registered using
TiO2-x (prepared by direct current reactive sputtering on different supports) has
changed with the temperature increasing more than twice between 298 K and 343
K at x = 0. The differences in the catalytic activity is connected with the electrical
properties and depends on the value of x, for example Kd = 1 h-1 at 298 K and 105
h-1 at 343 K at x = 0.07 when slurry with 1.5 % anatase nanoprecipitate is irradiated with visible light. However the temperature increase has an opposite effect
applying a rutile/anatase mixture with x = 0.03: 1.2 h-1 at 298 K and 0.5 h-1 at 343
K. In some cases the increase of the temperature has led to slower phenol transformation but with improved mineralization [13].
Influence of other components in the purified liquid. The presence of different
modifications of MnO2 (20 mg/l) in the purified water has inhibited completely the
activity of Degussa P25 in the first 20-60 min due to photoelectron and photohole
recombination [44].
Influence of the reactor construction. The role of the photochemical reactor
construction has been studied [42]. Coil-type reactor with 374 cm2 effective area
and 0.44 mg/cm2 TiO2 coating has been proposed for phenol (17,8 μM) degradation at illumination with light above 340 nm [45].
Kinetics. The kinetics of the photodegradation process is usually described
by the Langmuir–Hinshelwood. Montoya et al. [46] has shown that literature data
134
concerning TiO2 photocatalytic oxidation of phenol and formic acid, are incompatible with the behavior predicted by this model. They have reanalyzed these
data from the point of view of the alternative model [47], developed as an addition to the L–H model. Two interfacial charge transfer mechanisms are considered
by the last model: the indirect transfer mechanism, which is concerned with the
adiabatic transfer of holes trapped at TiO2 terminal oxygen ions to dissolved substrate species, and the direct transfer mechanism dealing with the inelastic transfer
of free holes to specifically adsorbed substrate species.
According to [48] the apparent first-order rate constant depends on the phenol
concentration [Ph]0 in the starting solution, indicating that the reaction is not a simple first-order one. Up to the high conversion the reaction apparently has proceeded
according to the first-order kinetics. The dependence K/[Ph]0 has been affected by
TiO2 concentration and light intensity. The rate determining step has been considered to be the formation of OH because it reacts very rapidly with the phenol.
The first-order kinetics has been accepted in [49] but the rate constant decreased with increasing solute concentration. The effect is explained in terms of
the integrated form of Langmuir adsorption isotherm. A marked dependence of
the destruction rate on flow rate has been observed.
The kinetics of the photodegradation of substituted phenols has been studied in [50]. A nano-sized, high surface area combustion synthesized pure anatase
TiO2 has a higher photocatalytic activity than the commercial Degussa P-25. No
intermediates have been observed when so produced catalyst has been used for
the photocatalytic degradation of phenols, while several intermediates have been
observed for the same reactions catalyzed by Degussa P-25. Chlorphenols and
methylphenols degrade much faster than phenol. The mechanisms and the kinetic
parameters of the process have been determined [50].
Despite the positive effect of the doping of TiO2 with some dopants and/or
application of special methods for its production or treatment on its photocatalytic
activity, the commercially available Degussa P25 stays one of the best catalysts,
often used as referent material for this purpose. In the same time the constant
quality and detailed characterization of this product turns it into rather convenient
system to be used in investigations on the influence of preparation conditions
on the catalyst films photocatalytic performance. Spray-drying as film deposition
method, applied in this work, is preferred because it does not causes significant
changes in the catalyst phase composition and crystallites size thus permitting the
influence of other deposition conditions to be elucidated.
The aim of this work is to study the influence of the preparation conditions
of films produced from commercially available TiO2 by spray drying (particularly
the role of the type of the titania, the nature of the suspension medium and of the
substrate, temperatures of the deposition and post-deposition annealing) on their
photocatalytic activity to the degradation of phenol dissolved in water.
135
EXPERIMENTAL
1. Materials. Matted microscopic slides, 20×25×1 mm (Isolab, Germany),
silica glass (18×18×2 mm, optical grade) and stainless steel type 316 plates
(20×15×0.5 mm) were used as substrates. All of them were carefully washed with
detergent, water, distilled water and treated in ultrasonic bath consecutively with
dichlorethylene, i-propanol, ethanol and acetone for 10 min in each of them.
Commercially available TiO2 Degussa P-25 and Tronox were used as starting
material for the films deposition. Ethylene glycol (EG, p.a grade) or polyethylene
glycol with molecule mass 2000 (PEG) or acetylacetone (AA, puriss. p.a., Fluka)
were added to increase the porosity and to improve the adhesion of the films.
Aqueous solution of freshly purified phenol (10-4 M) were used as model pollutant.
2. Films deposition. Aqueous or methanol suspension containing 1% TiO2
[51] and 0.24 % EG or PEG was used for the films deposition. In some of the
experiments sonication for 20 min by means of ultrasonic disintegrator UD 20
(Technopan, Poland) was applied before spraying.
The spraying device shown in Ref. [52] was used for films deposition. The
optimal coating conditions were found at preliminary experiments and were similar to the ones used in [20]. The suspension was passed through a pneumatic
nebulizer with a nozzle diameter 1 mm using pressurized O2 as a carrier gas. The
substrate was situated at 20 cm from the nozzle at an angle of 45 0 and heated at
temperatures (shown in the text) depending on the nature of the substrate and of
the spraying material and kept within the limits of ± 5 0C. The suspension was
sprayed for 30 s followed by 5 min interval. The deposited films were undergone
to heating at 300 0C ÷ 500 0C for 1 h in static air. The so-prepared films have a
very good adhesion with the substrate as proven by the standard tests with scotch
tape and brass edge. The films thickness is controlled by the number of spraying
cycles. Typically 10 cycles were applied to produce 0.5 mg/cm2 layers or approximately 1.5 μm in thickness.
3. Films characterization. X-ray diffractograms of the films were taken by
Siemens D-500 powder diffractometer (CuKα, 40 kV, 30 mA). The diffraction
spectra of rutile (JCPDS 77-0442) and anatase (JCPDS 84-1286) were used as
referent database for films phase-composition determination. The crystallites size
was evaluated by the broadening of (100) and (110) reflections of anatase and
rutile, respectively. The weight fraction f of anatase was calculated using the integrated intensities of (101) reflection of anatase IA and (110) reflection of rutile
IR according to the equation [53]: f = 1/(1 + 1.26IR/IA). The film morphology was
observed by scanning electron microscopy (JEOL JSM 5510, Japan).
4. Photocatalytic tests. The prepared films were placed in 250 cm3 model pollutant solution, magnetically stirred (360 min-1) at bubbling with air (45 dm3/h).
After 30 min “dark” period (for the establishing of equilibrium of the sorption pro136
Intensity at 297 nm (a.u.)
cess), the system was UV-illuminated by a lamp (Sylvania, 18 W BLB T8), situated
at 9.5 cm from the film (light intensity at the film surface 50 μW/cm2). Periodically
5 cm3 aliquot was taken from the solution, filtered through 0.22 μm membrane filter
and the phenol concentration was determined by the fluorescence microspectrometer PC2000 of Ocean Optics, USA (excitation at 273 nm, emission band at 297 nm).
The results were managed by the specialized program OOI BASL. The calibration
curves for different measuring time (2–8 s) are shown on Fig. 1.
2s
4s
5s
6s
8s
700
600
500
400
300
200
100
1E-5
Concentration (mol/l)
Fig. 1
1E-4
Fig.1. Calibration curves for phenol concentration determination at different measuring times (2–8 s).
RESULTS AND DISCUSSION
Fig. 2 shows the typical changes in the fluorescence spectra of the purified solution during the photochemical test thus revealing the performance of the catalyst
used. The data obtained permit the kinetic curves to be plotted and the degradation
rate constants to be derived (Fig. 3).
SEM images (Fig. 4) permits the morphology of the films to be evaluated.
They are relatively uniform, porous, in some cases (film 1) with wave-like surface
and with morphological grains size and agglomeration ability depending on the
titania type.
Table 1 represents data for the TiO2 type, film preparation mode and degradation rate constant for some of the prepared films. Aiming a greater value of the
phenol degradation rate constant, results reported lead to the following general
recommendations for the films preparation:
Catalyst phase composition. The comparison of the data for films 1 and 2 (Table 1) confirms the earlier reported results [54] that the presence of some amount
of rutile in the photocatalysts (i.e. applying the product of Degussa instead of the
137
Fluorescence intensity (a.u.)
0 min
30 min
60 min
120 min
180 min
210 min
500
400
300
200
100
280
300
320
340
Wavelength (nm)
Fig. 2. Typical fluorescent spectra of the purified solution in the course of the photocatalytic test.
Fig. 3. Typical kinetic curve lnC/C0 vs UV-irradiation time.
pure anatase of Tronox) is an advantage despite the fact that anatase is an active
polymorph. In the same time, SEM observation (Fig. 4) show that the morpho138
a
1
2
8
Fig. 4. SEM images of the initial Degussa P25 TiO2 (powder) (a) and of films 1, 2, 8 (see Table 1).
Table 1. Preparation conditions, phase composition and photocatalytic activity of spray-pyrolysis deposited TiO2 films
Film Sub№
strate
1
2
3
4
5
6
7
8
Steel 2
Steel 4
Steel
Steel
Steel
Steel
Silica
Glass 3
1
2
Suspension
medium
H2O
H2O
CH3OH
CH3OH
CH3OH
H2O
CH3OH
H2O
Additive
PEG
PEG
PEG
PEG
AA
PEG
Sonication1
+
+
+
+
+
Temperature (0C) of Rate con- Type
stant,
of
deposianneal- n.10-3
TiO22
-1
-2
min
.cm
tion
ing
100
500
2.07
D
100
500
1.81
T
100
500
2.72
D
25
500
1.94
D
100
500
1.49
D
100
500
1.06
D
25
500
3.14
D
300
500
2.42
T
+ applied, – not applied
D – Degussa P25, T – Tronox
logical grains size of the film, produced from Degussa P25 is smaller than that of
the film from Tronox (films 1, 2) thus ensuring higher specific surface area. Obviously, the latter factor will favor a higher photocatalytic activity.
139
Suspension medium. Methanol is advantageous in comparison with water and
ensures two-fold higher decomposition rate at medium deposition temperatures
(100 0C, films 1 and 3, Table 1). The effect could be connected with the difference
in the boiling temperatures and, respectively, the drying rate [20].
Deposition temperature. The deposition temperature should be chosen as a
compromise, accounting for the established decrease (with approx. 20 %) of the rate
constant with the increase of the deposition temperature from 25 to 100 0C (films 4,
5) and the requirement a good adhesion of the film to be obtained. The latter is, to
some extend, favored by the higher deposition temperature and 100 0C seems to be
an acceptable compromise for films produced from Degussa, titania. The observation of the films morphology (Fig. 4) shows a lower trend of the Tronox product to
agglomerate. No significant difference is seen in the morphology of the films deposited at 100 0C and at 300 0C. The higher rate constant achieved at higher temperature
of deposition (films 2, 8, Fig. 4) might be due to the appearance of small amount of
rutile. Commonly the anatase → rutile transformation proceeds above 500 0C. It has
to be supposed that shock-like heating of the microdrops in the course of spraying
may provoke some recrystallization at substantially lower temperature.
Annealing temperature. Fig. 5 illustrates the influence of the annealing temperature on the effectiveness of the film deposited on the glass. The increase of the
temperature from 300 0C to 400 0C has not a significant effect on the rate constant
value but further increase to 500 0C leads to its decrease. However such dependence
is valid only for films on glass substrate and is possibly due to diffusion of sodium
(which negative effect on the photocatalytic activity is known [55]) from the glass
into the layer. On other substrates 500 0C is the optimal temperature (Fig. 6). Possible introduction of Fe when steel substrate is used may have a positive effect.
Fig. 5. Influence of the post deposition annealing temperature on the photocatalytic activity of
films on glass: 1- 400 0C, 2 – 500 0C
140
Fig. 6. The comparison of the apparent rate constants of the films, produced on different
supports and different temperature of post-deposition annealing; all other coating conditions
are the same
Presence of additives into the suspension medium. Among the studied by
us PEG, ethylene glycol and AA as binders and porosity enhancement reagents,
the PEG is to be preferred because it ensures two times higher activity of the film
probably due to higher boiling point and, respectively, slower degradation leading
to substantial effect on the film porosity (films 1, 6).
The highest value of the constant is registered for film from Degussa P25
product deposited on silica substrate at ambient temperature and post-deposition
heated at 500 0C (film 7, Table 1). This temperature is high enough a strong adhesion of the film to be obtained without (according to the X-ray diffractometry
data) any significant increase of the rutile relative content.
CONCLUSION
Applying commercially available TiO2 as starting material at spray-drying
method uniform, porous films can be produced. The agglomeration of the grains
depends on the oxide type. The films morphology slightly depends on the thermal
conditions applied in the course of the overall process. Substances with higher
decomposition temperatures (PEG) are to be preferred as additives to the starting
suspension. The temperature of films deposition has to be determined accounting
141
for the agglomeration trend of the oxide and for the requirements a good adhesion to be achieved. The annealing temperature strongly depends on the substrate
nature and mainly on the possibility ions suppressing photocatalytic activity to
penetrate in the layer deposited.
Silica glass as substrate, Degussa P25 suspended in methanol (1 %) with addition of 0.25 % PEG 2000, deposition at conditions described in the text at 100
0
C and annealing for 1 h at 500 0C could be recommended as optimal conditions
for preparation of films for phenol degradation.
Acknowledgment. The study is performed with the financial support of NATO “Science for
Peace” Program (contracts SfP 977986 and SfP 982835).
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
142
Pirkanniemi, K., M. Sillanpaa. Chemosphere, 48, 2002, 1047.
Han, F., V. S. R. Kambala, M. Srinivasan, D. Rajarathnam, R. Naidu. Appl. Catalysis A: General, 359, 2009, 25–40.
Scotti, R., M. D’Arienzo, F. Morazzoni, I. R. Bellobono. Applied Catalysis B: Environmental,
88, 2009, 323.
Bhatkhande, D. S., V. G. Pangarcar, A. A. C. M. J. Chem. Techn. Biotechnol., 77, 2002, 102.
Fretwell, R., P. Douglas. J. Photochem. Photobiology A: Chemistry, 143, 2001, 229-240.
Zhao, Y., X. Zhang, J. Zhai, J. He, L. Jiang, Zh. Liu, Sh. Nishimoto, T. Murakami, A. Fujishima, D. Zhu. Appl. Catalysis B: Environmental, 83, 2008, 24.
Yawlakar, A. A., D. S. Bhatkhande, V. G. Pangarcar, A. A. C. M. Beenackers. J. Chem. Technol. Biotechnol., 76, 2001, 363.
Matthews, R. W. Solar Energy, 38, 1987, 405.
Abdullah, M., K. C. L. Gary, R.W. Matthews. J. Phys. Chem., 94, 1990, 231.
Trilas, M., J. Peral, X. Donenech. J. Chem. Technol. Biotechnol., 67, 1996, 237.
Kim, H., H. Jeong, J. Park. J. Korean Soc. Geosystem, 40, 2003, 103.
Matthews, R. W., S. R. McEvoy. Destruction of phenol in water with sun sand and photocatalysis. Solar Energy, 49, 1992, 507-513.
Dumitriu, A., R. Bally, C. Ballif, P. Hones, P. E. Schmid, R. Sanjinés, F. Lévy, V. I. Pârvulescu.
Appl. Catalysis B: Environmental, 25, 2000, 83.
Choi, Y. L., S. H. Kim, Y. S Song, D. Y. Lee. J. Mater. Sci., 39, 2004, 5695.
Goґrska, P., A. Zaleska, E. Kowalska, T. Klimczuk, J. W. Sobczak, E. Skwarek, W. Janusz, J.
Hupka. Appl. Catalysis B: Environmental, 84, 2008, 440.
Neppolian, B., Q. Wang, H. Jung, H. Choi. Ultrasonics Sonochemistry, 15, 2008, 649.
Liu, S., N. Jaffrezic, C. Guillard. Appl. Surface Sci., 255, 2008, 2704.
Balaґzs, N., K. Mogyoroґsi, D. F. Srankoґ, A. Pallagi, TuЁnde Alapi, A. Oszkoґ, A. Dombi, P.
Sipos. Appl. Catalysis B: Environmental, 84, 2008, 356.
Orendorz, A., Ch. Ziegler, H. Gnaser . Appl. Surface Science, 255, 2008, 1011.
Uzunova-Bujnova, M., R. Todorovska, M. Milanova, D. Todorovsky. On the spray-drying
deposition of TiO2 photocatalytic films. Appl. Surface Science (in press).
Park, H., W. Choi. J. Phys. Chem. B, 108, 2004, 4086.
Lia, J., J. Xua, W.-L. Daia, H. Lib, K. Fana. Applied Catalysis B: Environmental, 81, 2008, 258.
Wang, Z., F. Zhang, Y. Yang, J. Cui, Q. Sun, N. Guan. Chinese J. Catalysis, 27, 2006, 1091.
Hidalgo, M. C., M. Maicua, J. A. Navíoa, G. Colóna. Catalysis Today, 129, 2007, 43.
25. Colón, G., M. C. Hidalgo, J. A. Navío. Appl. Catalysis B: Environmental, 45, 2003, 39.
26. Hidalgo, M. C., M. Maicua, J. A. Navíoa, G. Colóna. Appl. Catalysis B: Environmental, 81,
2008, 49.
27. Yuan, Z.-h., J.-h. Jia, Li-de Zhang. Materials Chem. Physics, 73, 2002, 323-326.
28. Linga, Q., J. Sun, Q. Zhoua, H. Rena, Q. Zhaoa. Appl. Surface Sciences, 251, 2008, 6731.
29. Ling, Q., J. Sun, Q. Zhou. Appl. Surface Science, 254, 2008, 3236.
30. Xua, J., Y. Aoa, D. Fua, Ch. Yuan. J. Physics Chem. Solids, 69, 2008, 1980.
31. Ou, H.-H., Sh.-L. Lo, Ch.-H. Wu. J. Hazardous Materials, 137, 2006, 1362.
32. Chang, M.-Yi, Y.-H. Hsieh, Ta-C. Cheng, K.-S. Yao, M.-C. Wei, Ch.-Yu Thin Solid Films, 517,
2009, 3888.
33. Diamandescua, L., F. Vasiliua, D. Tarabasanu-Mihailaa, M. Federa, A. M. Vlaicua, C. M. Teodorescu, D. Macovei, I. Enculescu, V. Parvulescu, E. Vasile. Materials Chem. Physics, 112,
2008, 146.
34. Wen, Ch., H. Deng, J.-y. Tian, Ji-m. Ang. Trans. Nonferrous Met. SOC. China, 16, 2006, 728.
35. Xie, Y., Ch. Yuan. Appl. Surface Sci., 221, 2004, 17.
36. Reddy, J. K., V. Durgakumari, M. Subrahmanyam, B. Sreedhar. Mater. Res. Bull., 44, 2009, 1540.
37. Su, W., J. Chen, L. Wu, X. Wang, X. Wang, X. Fu. Appl. Catalysis B: Environmental, 77, 2008, 264.
38. Wang, W., Ph. Serp, Ph. Kalck, J. L. Faria. Appl. Catalysis B: Environmental, 56, 2005, 305.
39. Wang, W., Ph. Serp, Ph. Kalck, J. L. Faria. J. Molecular Catalysis, 235, 2005, 194.
40. Lettmann, Ch., K. Hildenbrand, H. Kisch, W. Macyk, W. F. Maier. Appl. Catalysis B: Environmental, 32, 2001, 215.
41. Matthews, R. W., S. R. McEvoy. J. Photochem. Photobiol. A: Chem., 66, 1992, 355.
42. Satuf, M. L., R. J. Brandi, A. E. Cassano, O. M. Alfano. Catalysis Today, 129, 2007, 110.
43. Matthews, R.W., S. R. McEvoy. J. Photochem. Photobiol. A: Chem., 64, 1992, 231.
44. Li, Sh., Z. Ma, J. Zhang, Y. Wu, Y. Gong. Catalysis Today, 139, 2008, 109.
45. Al-Ekabi, H., N. Serpone. J. Phys. Chem., 92, 1988, 5726.
46. Montoya, J. F., J. A. Velaґsquez, P. Salvador. TApplied Catalysis B: Environmental, 88, 2009, 50.
47. Monllor-Satoca, D., R. Gomez, M. Gonzalez-Hidalgo, P. Salvador. Catalysis. Today, 129,
2007, 247
48. Okamoto, K.-I., Y. Yamamoto, H. Tanaka, A. Itaya. Bull. Chem. Soc. Jpn., 58, 1985, 2023.
49. Matthews, R. W. J. Phys. Chem., 91, 1987, 3328.
50. Sivalingam, G., M. H. Priya, G. Madras. Appl. Catalysis B: Environmental, 51, 2004, 67.
51. Byrne, J. A., B. R. Eggins, N. M. D. Brown, B. McKinney, M. Rouse. Appl Catalysis B, 17,
1998, 125.
52. Todorovska, R. V., St. Groudeva-Zotova, D. S. Todorovsky. Mat. Lett., 56, 2002, 770.
53. Spurr, K., H. Myers. Analyt. Chem., 29, 1957, 760.
54. Ohno, T., K. Sarukawa, K Tokieda, M. Matsumura. J. Catal., 203, 2001, 82.
55. Tomaszewski, H., K. Eufinger, H. Poelman, D. Poelman, R. De Gryse, P.F. Smet, G.B. Marin.
Int. J. Photoenergy, 2007, 2007, Article ID 95213, doi: 10.1155/2007/95213.
Received on November 10, 2009
143
144
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
SYNTHESIS AND MASS SPECTRAL STUDY OF TRANS- AND CIS(±)-3-PHENYL-3,4-DIHYDROISOCOUMARIN-4-CARBOXAMIDES
MILEN G. BOGDANOV*, IVAN V. SVINYAROV, VASIL N. ATANASOV
a
Faculty of Chemistry, Sofia University, 1, J. Bourchier Blvd., 1164 Sofia, Bulgaria
* Corresponding author, E-mail: [email protected]
Abstract. A series of trans- and cis- (±)-3-phenyl-3,4-dihydroisocoumarin-4carboxamides (4a-c) were synthesized and the electron impact (EI) ionization mass spectral
fragmentation was described. For all studied compounds, both diastereomers follow the
same fragmentation pattern, but differ on the abundance of the base peaks, which shows the
opportunity to distinguish 3,4-dihydroisocoumarin diastereomers using mass spectrometry.
Key words: Isocoumarin, Dihydroisocoumarin, Diastereomers, Homophthalic
anhydride, Mass Specrometry.
INTRODUCTION
3,4-dihydroisocoumarins possess an aryl substituent in position 3 are the core
of various natural [1] and synthetic [2] compounds which exhibit a wide variety
of pharmacological activitiess [1–5]. Because C-3 and C-4 carbon atoms are stereogenic centers both diastereomers (cis- and trans-) are possible for this type of
compounds (see Fig. 1). The relative configuration can be attributed on the basis of
the value of the vicinal coupling constant (3J3,4) between H-3 and H-4 atoms in the
1
H NMR spectra [6, 7], but in some cases [8] the intermediate value (2–6 Hz) of the
observed coupling constant (being characteristic both for the trans- and cis- diastereomers in synclinal conformation) can lead to wrong interpretation of the experimental data and thus to erroneously proposed relative configuration. This problem
can be avoided if another spectral method distinguishes both diastereomers. Thus,
the aim of this work is to study the fragmentation pattern of trans- and cis-(±)145
3-phenyl-3,4-dihydroisocoumarin-4-carboxamides (4a-c) by electron impact mass
spectrometry (EIMS) in order to distinguish trans- and cis- diastereomers.
Synthesis of compounds
Scheme 1 shows the reaction outcome and the synthetic path to compounds
4a-c. In the first synthetic step, following a previously reported by us protocols,
[9,10] homophthalic anhydride (1) reacts with benzaldehyde to give the corresponding trans- and cis-(±)-3-phenyl-3,4-dihydroisocoumarin-4-carboxylic acids
(2). It is noteworthy that the ratio among the isomers depends on the catalyst
used in the reaction, so both basic (DMAP) and acidic catalysts (BF3•Et2O) were
used. The cis-/trans-isomeric products were separate successfully by fractional recrystallization and the separated isomers were converted into corresponding acyl
chlorides 3a-c in boiling benzene in the presence of thionyl chloride. Treatment
of the latter with cyclic secondary amines (NuH) gave the target products 4a-c,
which were isolated as crystalline products and purified by recrystallization from
appropriate solvents.
O
O
O
O
Catalist
+
OH
O
OH
+
CHCl3 , rt
O
O
O
O
O
cis-2
1
Catalyst
trans-2
SOCl2/C6H6
Yield (%)
cis-2
trans-2
DMAP
12
70
BF3.Et2O
35
54
O
O
Cl
NuH
CH2Cl2
O
O
O
cis-/ trans-4a-c
O
cis-/ trans-3a-c
Compd.
Nu
N
ci s-4a
trans-4a
Yield (%)
61
72
Nu
Compd.
Nu
O
N
cis-4b
trans-4b
Yield (%)
56
85
Compd.
Nu
C6 H13
H
N
cis-4c
tr ans-4c
Yield (%)
67
61
Scheme 1. Reaction scheme for the preparation of compounds 4a-c.
The structure of the newly synthesized products was characterized by spectral
methods (IR and 1H NMR) and elemental analysis. The interpretation of the 1H
NMR spectra is in agreement with the literature data for compounds of this class
[9,10] and showed the following characteristic signals: the signals for H-4 and H-3
protons appear as doublets within 3.99–4.61 and 5.67–5.94 ppm respectively; the
146
two groups of protons close to the amide nitrogen are unequivalent and thus independent signals in the region 2.43–3.62 ppm are observed for each proton; the
signals for proton H-8 appear at lower field (7.77–8.04) compared to the other aromatic protons. This phenomenon is an indication for proximity of H-8 to the lactone
carbonyl group. The relative configuration of trans- and cis-4a-c can be defined on
the basis of the vicinal coupling constant value (3J3,4) between H-3 and H-4 atoms in
the 1H NMR spectra (see Fig. 1). In general, values of 10–13 Hz suggest trans-configuration [6,7] and preferred antiperiplanar (ax,ax) conformation of the H-3 and H4 atoms, but values of 3J3,4 = 3–6 Hz suggest, synclinal (sc or gauche) conformation
and did not allow a distinction between cis (eq,ax) and trans (eq,eq) configuration of
H-3 and H-4 atoms. On the other hand, 3,4-dihydroisocoumarins are conformationally flexible compounds, [8] and thus one can define incorrect relative configuration
if the existing conformational equilibrium between conformers I and II is neglected.
However, to overcome this problem another spectral method could be applied. It is
known that the mass spectrometry is a proven technique for the differentiation of
stereoisomers, but to the best of our knowledge no literature data is available for
diastereomeric differentiation by MS of 3,4-disubstituted 3,4-dihydroisocoumarins.
In this direction, we carried out preliminary mass spectral study on three of the synthesized diastereomeric couples.
Nu
O
Nu
O
Ph
Ph
O
O
O
O
cis-I,II
trans-I,II
O H
O
Ph
3
O
4
Nu
H O
H-3ax, H-4ax (ap)
3J = 10-13 Hz
3,4
trans-I
O
H
Nu
O
O
3
O
3
4
H
Ph
H
trans-II
4
Nu
H O
Ph
H-3eq, H-4eq (sc)
3J = 3-6 Hz
3,4
O
H-3eq, H-4ax (sc)
3
J3,4= 3-6 Hz
cis-I
O
Ph
Nu
O
3
4
H
H
H-3ax, H-4eq (sc)
3J = 3-6 Hz
3,4
cis-II
Ph = Phenyl, Nu = amino groups
Figure 1. Possible conformational equilibrium for trans- and cis-4-a-c.
147
Mass spectral characterization
The fragmentation pattern for the studied compounds is shown in Scheme 2
and is summarized in Table 1. The molecular ion peaks (M•+) for 4a, 4b and 4c
appear at m/z 335, 337 and 351, respectively. The relative abundances of M•+ is in
the range 1–12%, so that, only a small fraction of the total ion current is carried by
those peaks. Тhe fragmentation proceeds further in two directions – path a, due to
ionization of the amide group, and path b – due to ionization of the pyranone ring.
The most important fragmentation in 4a-c arises from α-cleavage of the amide
function, resulting in the formation of isocoumarinе fragment [i-cum] of mass
222, 223 and 224 for 4b, 4a and 4c, respectively. Following the fragmentation
path a, further elimination of phenyl radical yield a cation at m/z 145. This is followed by consequent elimination of two CO molecules furnishing cations at m/z
117 and 89. The loss of CO2 and CO from [i-cum] furnished radical cations at m/z
178 and 194. The fragmentation path b gives characteristic fragments regarding
the amide group. Loss of a molecule benzaldehyde from M•+ yield radical cations
of type i in all cases, which afford radical cations ii and iii after consequent loss
of two molecules CO. It is noteworthy that the fragmentation pattern shown in
Scheme 2 is followed by all the compounds studied, and thus, not characteristic
fragment can be attributed towards one of the isomers. However, an interesting
result appears from the analysis of Table 1. Although the isomeric compounds
show the same characteristic fragment ions, clear differences are observed in the
relative abundance for the base peaks. The [i-cum] fragment appears as the base
peak in the spectra of the cis-isomers only. In contrast, the formed [i-cum] fragments from the trans-isomers are always of less abundance. That difference in
the formation of [i-cum] could be explained by the different stability of the two
diastereomers. According to the observed values of 3J3,4 of about 11 Hz we assign
conformation in solution with both equatorial bulky substituents at C3 and C4
atoms (trans-I) for compound trans-4a-d (see Fig. 1). In the case of compounds
cis-4a-d the preferred conformation in solution can not be determined only from
3
J3,4, because of the same value (3–6 Hz) in conformations cis-I and cis-II, but
since one of the substituents is always in axial position (unpreferable conformation) it could be concluded that the cis-isomers are of higher energy (related to
the trans-isomers). Thus, the formation of the [i-cum] fragment from cis-4a-c is
expected to be faster than those formed from trans-4a-c, since the formation of
[i-cum] from the cis-isomers needs less activation energy.
148
Table 1. EI mass spectra of trans- and cis-4a-c.
m/z (relative abundance, %)
M
[i-cum]
cis-4a
335 (12)
223 (100)
290(9), 229(29), 222(92), 205(17), 201(40), 194(15), 178(20), 172(52),
165(15), 158(9), 145(17), 117(22), 112(79), 105(37), 89(74), 84(28),
69(36), 56(10), 41(17)
trans-4a
335 (2)
223 (2)
290(1), 229(8), 206(30), 205(20), 201(8), 194(4), 178(15), 172(12),
165(9), 145(5), 117(6), 112(100), 105(12), 89(24), 84(12), 69(33),
56(5), 41(13)
cis-4b
337 (12)
222 (100)
292(9), 231(26), 207(18), 203(28), 194(8), 178(8), 174(19), 165(8),
145(29), 117(17), 114(48), 105(62), 89(53), 86(7), 77(12), 70(20),
56(6), 42(5)
trans-4b
337 (2)
223 (2)
292(9), 231(20), 207(20), 203(28), 194(20), 178(21), 174(40), 165(15),
145(42), 117(35), 114(48), 105(62), 89(100), 86(19), 77(36), 70(53),
56(12), 42(5)
cis-4c
351 (1)
224 (100)
245(2), 206(8), 195(7), 178(29), 165(8), 152(4), 145(5), 133(18),
118(4), 105(14), 89(15), 77(11), 55(2), 43(3)
trans-4c
351 (9)
224 (61)
307(11), 245(8), 223(75), 206(19), 195(39), 178(61), 165(23), 152(11),
145(18), 133(36), 118(31), 105(100) , 89(61), 77(41), 55(9), 43(12)
Compound
Nu
Other ions
O
Nu
O
O
4a 2 29
4b 231
4a 2 45
i
path b
- CO
Nu
- CO2
4 a 201
4 b 203
O
ii
O
O
4a 335
4b 3 37
4c 351
4a 172
4b 174
path a
M
165
77
Nu
- CH 3
O
4a 112
4b 1 14
Nu
O
i-cum
4a 290
4b 292
4c 307
iii
89
O
- CO
Nu
- CO
117
O
145
O
O
- CO
O
O
4a 223
4b 2 22
4c 224
O
iv
O
105
- CO 2
178
- CO
- H2O
117
O
194
O
2 06
Scheme 2. EI fragmentation pattern of trans- and cis-4a-c.
CONCLUSION
The present mass spectral study on isomeric 3,4-disubstituted 3,4-dihydroisocoumarins shows that trans- and cis-isomers of this type could be differentiated
by mass spectral analysis, since under EI conditions, the relative abundance of the
149
[i-cum] fragment is greater in the cis-isomers. In order to understand the observed
phenomenon in details, the synthesis of more complete series of diastereomeric
couples of dihydroisocoumarine type is now in progress.
EXPERIMENTAL
Melting points were determined on a Kofler microscope Boetius PHMK 0.5
and are uncorrected. The IR spectra were acquired in chloroform on a Specord 75
and are reported in reciprocal centimeters. The 1H-NMR spectra were obtained on
a DRX Bruker Avance NMR spectrometer at 250 MHz in corresponding solvents
given in parentheses. The chemical shift is given in ppm (δ) relative to tetramethylsilane as internal standard. Elemental analyses were obtained in the relevant
laboratories at the Faculty of Chemistry, University of Sofia. The mass spectra
were obtained after preliminary GC separation on Trace GC (Thermo Electron)
instrument equipped with a quadruple MS detector DSQ (Thermo Electron). The
separation was carried out on DB-5 MS column. The mass spectrometer operates
in scan-mode (70 eV ionization potential).
cis/trans-1-Oxo-3-phenyl-isochroman-4-carboxylic acid (cis-/trans-2).
DMAP catalyzed reaction: To a mixture of homophthalic anhydride (1) (1
g, 0.006 mol) and 1.1 equiv. of benzaldehyde (0.72 g, 0.007 mol) in 7 ml dry
chloroform 1 equiv. DMAP was added. The reaction mixture was stirred for 2 h at
room temperature. At the end of the reaction (TLC) the obtained carboxylic acids
were extracted with 10 % sodium hydrogen carbonate. The aqueous layer was
acidified (pH = 3) with 15 % hydrochloric acid and extracted with ethyl acetate.
The organic layer was dried with sodium sulfate, filtered and then the solvent was
evaporated under reduced pressure. The mixture of cis-2 and trans-2 isomers was
separated by fractional crystallization from dichloromethane (yield: cis-2 0.124 g,
12%; trans-2 0.698 g, 70 %).
BF3.Et2O catalyzed reaction: To a mixture of homophthalic anhydride (1)
(1.81 g, 0.011 mol) and benzaldehyde (1.19 g, 0.011 mol) in 15 ml dry chloroform
BF3.Et2O (15,78 g, 0.111 mol) was added. The reaction mixture was stirred for
8 h at room temperature. At the end of the reaction (TLC) the reaction mixture
was diluted with ethyl acetate and was washed with 15 % hydrochloric acid and
then with water (pH = 7). The organic layer was dried (sodium sulfate), filtered
and then evaporated under reduced pressure. The mixture of cis-2 and trans-2
isomers was separated by fractional crystallization from dichloromethane (yield:
cis-2 1.053 g, 35 %; trans-2 1.608 g, 54 %).
150
General procedure for synthesis of compounds (cis-/trans-4a-c). To a suspension of cis-/trans-2 acid in dry benzene, thionyl chloride (4 equiv.) was added.
The reaction mixture was stirred at 80 ºC for 2 h. Then, the solvents were evaporated under reduce pressure and the residue was dissolved in dry chloroform. To
the cooled solution (0 ºC, ice bath) 3 equiv. of the coresponding amine were added
and the reaction mixture was stirred for 30 minutes. At the end of the reaction
(TLC), the reaction mixture was diluted with ethyl acetate and washed with water
(pH = 7). The organic layer was dried (sodium sulfate), filtered and the solvent
was then evaporated under reduced pressure. The products cis-/trans-4a-c were
isolated after recrystallization.
trans-4-(Piperidine-4-carbonyl)-3-phenyl-isochroman-1-on (trans-4a). This
compound was obtained as colorless needles from ethyl acetate (yield: 0.216 g,
72 %), mp 181-182 ºC; IR: 1620 cm-1 (CONH), 1720 cm-1 (COOR); 1H NMR
(CDCl3): δ = 0.64-0.90 (1H, m, CH2), 1.06-1.31 (1H, m, CH2), 1.31-1.60 (4H,
m, CH2), 3.13-3.39 (3H, m, CH2), 3.80-3.93 (1H, m, CH2), 4.61 (1H, d, H-C, J =
10.8), 5.84 (1H, d, H-C, J = 10.8), 7.10 (1H, d, H-Ar, J = 7.7), 7.34-7.44 (3H, m,
H-Ar), 7.44-7.54 (3H, m, H-Ar), 7.59 (1H, dt, , H-Ar, J = 1.5, 7.6), 8.19 (1H, dd,
H-Ar, J = 1.4, 7.7). Anal. Calcd. For C21H21NO3 (335.40): C, 75.20; H, 6.31; N,
4.18. Found: C, 75.50; H, 5.98; N, 4.18.
cis-4-(Piperidine-4-carbonyl)-3-phenyl-isochroman-1-on (cis-4a). This compound was obtained as colorless needles from ethyl acetate (yield: 0.184 g, 61 %),
mp 281-282 ºC; IR: 1630 cm-1 (CONH), 1730 cm-1 (COOR); 1H NMR (CDCl3): δ
= 1.17-1.46 (6H, m, CH2), 2.70-2.80 (1H, m, CH2), 3,08-3.29 (2H, m, CH2), 3.373.46 (1H, m, CH2), 4.50 (1H, d, H-C, J = 3.5), 5.74 (1H, d, H-C, J = 3.5), 7.20 (1H,
dd, H-Ar, J = 1.3, 7.4), 7.38-7.52 (6H, m, H-Ar), 7.57 (1H, dt, H-Ar, J = 1.6, 7.4),
8.18 (1H, dd, H-Ar, J = 1.6, 7.5). Anal. Calcd. For C21H21NO3 (335.40): C, 75.20;
H, 6.31; N, 4.18. Found: C, 75.40; H, 5.90; N, 4.16.
trans-4-(Morpholine-4-carbonyl)-3-phenyl-isochroman-1-on
(trans-4b).
This compound was obtained as white crystals from dichloromethane/ethyl acetate (yield: 0.255 g, 85 %), mp 221-223 ºC; IR: 1630 cm-1 (CONH), 1720 cm-1
(COOR); 1H NMR (CDCl3): δ = 2.60-2.73 (1H, m, CH2), 3.04-3.49 (5H, m, CH2),
3.58 (1H, ddd, CH2, J = 2.9, 5.1, 11.4 Hz), 3.69-3.77 (1H, m, CH2), 4.56 (1H, d,
H-C, J = 10.9), 5.74 (1H, d, H-C, J = 10.9), 7.05 (1H, d, H-Ar, J = 7.7), 7.33-7.39
(3H, m, H-Ar), 7.41-7.46 (3H, m, H-Ar), 7.56 (1H, dt, , H-Ar, J = 1.5, 7.6), 8.30
(1H, dd, H-Ar, J = 1.3, 7.8, H-8). Anal. Calcd. For C20H19NO4 (337.37): C, 71.20;
H, 5.68; N, 4.15. Found: C, 71.67; H, 5.48; N, 4.14.
151
cis-4-(Morpholine-4-carbonyl)-3-phenyl-isochroman-1-on (cis-4b). This compound was obtained as colorless prisms from dichloromethane/methanol (yield:
0.167 g, 56 %), mp 302-303 ºC; IR: 1635 cm-1 (CONH), 1720 cm-1 (COOR); 1H
NMR (CDCl3): δ = 2.44-2.61 (1H, m, CH2), 2.63-2.77 (1H, m, CH2), 3.14-3.41 (4H,
m, CH2), 3.43-3.63 (2H, m, CH2), 4.42 (1H, d, H-C, J = 3.5), 5.76 (1H, d, H-C, J =
3.5), 7.19 (1H, dd, H-Ar, J = 1.4, 7.3), 7.37-7.54 (6H, m, H-Ar), 7.58 (1H, dt, H-Ar,
J = 1.7, 7.4), 8.22 (1H, dd, H-Ar, J = 1.7, 7.5). Anal. Calcd. For C20H19NO4 (337.37):
C, 71.20; H, 5.68; N, 4.15. Found: C, 71.20; H, 5.35; N, 4.33.
trans-4-(Hexyl-4-carbonyl)-3-phenyl-isochroman-1-on (trans-4c). This compound was obtained as colorless needles from ethyl acetate (yield: 0.183 g, 61 %),
mp 171-172 ºC; IR: 1540 cm-1 (NH), 1650 cm-1 (CONH), 1720 cm-1 (COOR); 1H
NMR (CDCl3): δ = 0.89 (3H, t, CH3, J = 6,8), 1.03-1.39 (8H, m, CH2), 3.06-3.33 (2H,
m, CH2-N), 3.99 (1H, d, H-C, J = 8.3), 5.59 (1H, brs, H-N), 5.94 (1H, d, H-C, J =
8.3), 7.28 (1H, d, H-Ar, J = 7.5), 7.32-7.44 (5H, m, H-Ar), 7.45-7.54 (1H, m, H-Ar),
7.63 (1H, dt, H-Ar, J = 1.5, 7.6), 8.19 (1H, dd, , H-Ar, J = 1.4, 7.7). Anal. Calcd. For
C22H25NO3 (351.44): C, 75.19; H, 7.17; N, 3.99. Found: C, 75.48; H, 6.65; N, 4.12.
cis-4-(Hexyl-4-carbonyl)-3-phenyl-isochroman-1-on (cis-4c). This compound
was obtained as white crystals from ethyl acetate (yield: 0.202 g, 67 %), mp 200-201
ºC; IR: 1540 cm-1 (NH), 1650 cm-1 (CONH), 1730 cm-1 (COOR); 1H NMR (CDCl3):
δ = 0.85 (3H, t, CH3, J = 7,0), 0.91-1.04 (2H, m, CH2), 1.94-1.33 (6H, m, CH2),
2.84-3.06 (2H, m, CH2-N), 4.00 (1H, d, H-C, J = 3.4), 5.43 (1H, brs, H-N), 5.83
(1H, d, H-C, J = 3.4), 7.34-7.49 (4H, m, H-Ar), 7.49-7.59 (3H, m, H-Ar), 7.64 (1H,
dt, H-Ar, J = 1.5, 7.5), 8.24 (1H, dd, H-Ar, J = 1.5, 7.7). Anal. Calcd. For C22H25NO3
(351.44): C, 75.19; H, 7.17; N, 3.99. Found: C, 75.40; H, 6.47; N, 3.99
REFERENCES
1.
2.
3.
4.
Hill R. A. Fortschr. Chem. Org. Naturst., 49, 1986, 1.
Napolitano E. Org. Prep. Proced. Int., 29, 1997, 631.
Nozawa K., M. Yamada, Y. Tsuda, K. Kawai, S. Nakajima. Chem. Pharm. Bull., 29, 1981, 2689.
Yoshikawa M., H. Matsuda, H. Shimoda, H. Shimada, E. Harada, Y. Naitoh, A. Miki, J. Yamahara, N. Murakami. Chem. Pharm. Bull., 44, 1996, 1440.
5. Bogdanov M. G., M. I. Kandinska, B. T. Gocheva, D. B. Dimitrova, M. D., Z. Palamareva.
Naturforsch., 62c, 2007, 477.
6. Karplus, M. J. Chem. Phys., 30, 1959, 11.
7. Karplus, M. J. Am. Chem. Soc., 85, 1963, 2870.
8. Bogdanov M. G., I. S. Todorov, P. G. Manolova, D. V. Cheshmedzhieva, M. D. Palamareva.
Tetrahedron Lett., 45, 2004, 8383.
9. Bogdanov M. G., M. D. Palamareva. Tetrahedron, 60, 2004, 2525.
10. Bogdanov M. G., B. T. Gocheva, D. B. Dimitrova, M. D. Palamareva. J. Heterocyclic Chem.
44, 2007, 673.
Received on December 11, 2009
152
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
EFFECT OF THIN FILM ELASTICITY ON FOAM STABILITY
STOYAN I. KARAKASHEV1, EMIL D. MANEV1 AND ANH V. NGUYEN2
Department of Physical Chemistry, Faculty of Chemistry, St. Kliment Ohridski University of
Sofia, 1126 Sofia, Bulgaria
2
School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072,
Australia
*To whom correspondence should be addressed. Email: [email protected]
1
Abstract. The effect of the elastic modulus on the stability of foam stabilized with
tetraethyleneglycol-octylether (C8E4) was studied in the concentration range 2x10-3 – 10-2
M. The life-time of foam was measured by the standard shaking method. The elasticity of
soap bubbles was measured by vibration using pendant drop tensiometer (PAT 1D module of
Sinterface Technologies, Ltd., Germany) with a frequency 0.1 Hz and an amplitude volume
2 mm3 in the same concentration range. A good correlation was found between the soap
film elasticity and the foam life-time profiles. The Gibbs elasticity and the elastic modulus
were compared. It was found that the Gibbs elasticity values are by an order of magnitude
larger that values of the elasticity modulus. The latter should be due to the faster adsorption/
desorption of the surfactant molecules compared to the speed of change of the bubble area.
Key words: Gibbs elasticity, Foam life-time, Surfactant, Soap Bubble, Thin Liquid
Film, elastic modulus
1. INTRODUCTION
The foam lifetime depends on the properties of the adsorption layers on the
liquid film surfaces separating the gas bubbles. It was found for example, that
upon increasing surfactant concentration the stability of foam sharply rises at the
onset of black films formation [1–3]. The latter formation enhances the Gibbs
elasticity and, consequently, the foam stability. The relation between the elastic
modulus of single bubbles in surfactant solutions and the durability of wet foams
153
has been studied in the past decades see e.g. Refs. [4–13]. The elastic modulus
was measured by the vibration of bubbles with frequency up to 75 Hz [7]. It was
found that the wet foam becomes more durable with increasing elasticity of the
bubbles. The elasticity of planar foam films in a frame was measured firstly by
Mysels et al. [14, 15]. Fruhner et al. [11] found correlation between the lifetime of
foam lamellae and the dilational viscosity of the water/air interface as well. The
elasticity of single foam films was studied theoretically [16–21]. A correlation
between the elasticity of model planar foam films and the durability of wet foams
was found by Wang and Yoon [22]. However, experimental data on Gibbs elasticity of soap bubble are scarce in the literature. The present work aims at studying
the properties of soap bubbles, stabilized by C8E4 and correlating them with the
life-time of foam column generated from the respective surfactants solution.
2. THEORETICAL BACKGROUND
2.1. Elasticity modulus obtained by bubble vibration method
The Gibbs elasticity can be determined in two ways: (i) by sufficiently fast
expansion and/or compression of single or a foam bubble [21, 23]; and (ii) by
measuring the surface tension isotherm, coupled with theoretical processing of the
experimental data by means of an appropriate adsorption model (e.g. Ref. [24]).
The Gibbs elasticity as defined by Gibbs [16] can be presented as:
EG =
2dσ
d ln At
(1)
Where σ is the tension on each of the film surfaces, and At is the total area
of the film divided by the total amount of surfactant adsorbed on the two film
surfaces. For a mono-component system (one solute) Eq. (1) can be presented in
the following form:
EG = 4Γ 2
dμ
dG
(2)
Where Γ is Gibbs surface excess of the surfactant as regards the single water/air interface, G is Gibbs surface excess of the surfactant as regards the foam
film, and μ is the chemical potential of the surfactant at equilibrium. When the
foam film is sufficiently thick the film surfaces do not interact with each other and
the Gibbs elasticity of the film can be assumed to be the doubled Gibbs elasticity
of the single water/air interface. Such condition of the foam films can be observed
in wet foams at their very generation. Inversely, sufficiently dry foam consists of
thin films with interacting surfaces. In the latter case the disjoining pressure also
contributes to the Gibbs elasticity of the film. The Gibbs elasticity of the single
water/air interface, as mentioned above, can be measured by fast expansion and/or
compression of single (in the liquid phase) or soap bubble (in the gas phase). If
154
the rate of expansion and/or contraction of the bubble surface is much larger than
the rate of surfactant adsorption, the bubble responds with maximal increase and/
or decrease of the surface tension, without any lag of the phase angle. This case
corresponds to the limiting dilatational modulus ε 0 , which is equal to the Gibbs
elasticity ( EG = 2ε 0 = −2dσ / d ln Γ )[25]. However, if the bubble is expanded
and/or compressed at a speed commensurable to or slightly less than the speed of
surfactant adsorption, a smaller change in the value of the surface tension, and a
certain phase lag, will be detected (in a case of repetitive expansions and compressions). In such a case the bubble has dilatational modulus ε .The dilation modulus
ε is a function of the frequency ω of bubble vibration [25]:
ε=
ε0
1 + 2 ω0 / ω + 2ω0 / ω
(3)
Where ω0 is adsorption frequency [26], which can be considered as the frequency of expansion/contraction with the same speed as adsorption/desorption
occurs. It is defined by:
ω0 =
D
⎛ ∂Γ ⎞
2⎜ ⎟
⎝ ∂c ⎠
2
(4)
Here D is surfactant diffusion coefficient and ∂Γ / ∂c is adsorption length.
Eq. has been derived for the case of adsorption layer near equilibrium [25, 27].
If ω = ω0 then ε / ε 0 = 1/ 5 = 0.446 . If the vibration of the bubble is as fast
as the adsorption of the surfactant molecules then ε = 0.446ε 0 . The adsorption is
considered as diffusion controlled process. The model of Lucassen and van den
Tempel [26] is derived on the assumption of diffusion controlled adsorption. Of
course the latter is approximation, due to the fact that an adsorption controlled
mechanism is possible as well. The surfactant under study in the present work is
tetraethyleneglycol octylether (C8E4). The adsorption length ∂Γ / ∂c was calculated by processing the experimental surface tension isotherm with SzyskowskiLangmuir adsorption model.
2.2. Elasticity modulus obtained by periodical expanding and shrinking
of foam film.
Mysels et. al.[14, 28, 29] were the first to develop an experimental method
for measuring the elastic modulus of soap films in a rectangular frame. Kitchener proved that one can measure the Gibbs elasticity by this method [30]. The
same method was adopted and applied by Prins et al. [31, 32]. The method was
advanced by adjusting it to spherical foam films (soap bubbles) [17, 20]. The sur-
155
face tension of the film surfaces of an expanding bubble can be presented by the
expression [17]:
4
ΔP = σ ∑1/ Ri
(5)
i =1
Where ΔP is the pressure difference between the internal and the external
sides of the soap bubble, σ is the surface tension of each film surface, and Ri are
the radii of curvature – two for the internal and two for the external surfaces of
the soap bubble. The experiment consists in determining the surface tension as a
function of the total bubble surface A . The film volume is assumed constant. The
total number of surfactant molecules is kept constant with the expression [17]:
V0 c0 = V0 c + AΓ
(6)
Where c0 bulk concentration of the surfactant is V0 is volume of the film, c
is surfactant concentration within the film, Γ is total surfactant adsorption on the
two film surfaces. The following expression for Gibbs elasticity is thus derived
from Eq. (1) [17]:
At dσ
dc
(7)
V0 dc d ( At / V0 )
where c is the surfactant concentration within the soap bubble given by the
EG = 2
expression:
c=
1⎡
2
(1/ k + Γ ∞ At / V0 − c0 ) + 4c0 / k − (1/ k + Γ ∞ At / V − c0 )⎤⎥
⎢
⎦
2⎣
(8)
Where Γ ∞ is the surfactant adsorption close to CMC; k is the equilibrium
adsorption constant. The surface tension isotherm of the surfactant should be measured and the quantities Γ ∞ and k can be determined via Szyszkowski-Langmuir
equation of state. Hence, dσ / dc and dc / ( At / V0 ) can be determined to calculate EG . This approach is approximated because the contribution of gravity is
neglected. The latter force causes non-uniform distribution of the film thickness
and surfactant concentration upon the soap bubble surface. The contribution of
gravity was accounted later in Ref. [20] and a commercial apparatus for automatic
determination of the film tension was developed [20]. According to Eq. (7) the
Gibbs elasticity depends on the total area of the soap bubble. However, this should
be valid for small and sufficiently fast expansion of the soap bubble, as compared
with the speed of surfactant adsorption, i.e. at minute deviations from the thermodynamic equilibrium. At non-uniform film thickness distribution, due to the
gravity, a non-uniform distribution along the soap bubble of the Gibbs elasticity
156
is present. Due to gravity, non-uniform allocation of the Gibbs elasticity over the
soap bubble is present at non-uniform film thickness distribution.
2.3. Gibbs elasticity obtained by a surface tension isotherm
The Gibbs elasticity is often presented in the form of Eq. (1). The Gibbs surfaces excess (adsorption) Γ can be obtained from the experimental surface tension isotherm ( σ vs c ) by means of an appropriate adsorption model. The basic
equation giving the relation between surface tension and Gibbs surface excess is
the Gibbs adsorption isotherm:
n
d σ = −∑ Γi d μi
(9)
i =1
where Γi is the surface excess of the ith component in the system, and μi is its
chemical potential. The adsorption model of Szyskowski-Langmuir was applied
in the present work. For a mono-component (one solute) system this model can
be expressed with:
(i) Langmuir adsorption isotherm
Γ = Γ∞
Kc
1 + Kc
(10),
and (ii) Szyskowski equation:
σ = σ0 − RT Γ ∞ ln (1 + Kc )
(11)
The equation of state (EOS, Eq. 11) can be presented as:
⎛
Γ ⎞
σ = σ 0 + Γ ∞ RT ln ⎜1 −
⎟
⎝ Γ∞ ⎠
(12)
Here Γ∞ is the maximum adsorption, at complete saturation of the monolayer;
c is the bulk concentration of surfactant; K is the equilibrium constant of adsorption and σ 0 is the surface tension of the pure solvent (water), R is the gas constant,
and T is the absolute temperature.
Hence the adsorption length d Γ / dc can be expressed by:
Γ∞ K
∂Γ
=
∂c (1 + Kc )2
(13)
This model accepts that the surfactant molecule have finite sizes, but do not interact. If one combines Eqs. and by the relation A = 1/ Γ , the limiting elastic modulus
ε 0 (called limiting Gibbs elasticity[20]) for soluble surfactants can be obtained:
ε0 = −
Γ ΓRT
dσ
= ∞
d ln Γ Γ ∞ − Γ
(14)
157
3. EXPERIMENTAL
The stability of foams produced by aqueous solutions of C8E4 (produced by
Sigma-Aldrich Ltd) in the concentration range of 2x10-3 – 10-2 M and in the presence 10-5 M NaCl (produced by Sigma-Aldrich Ltd), was measured. The temperature during the experiment was kept constant at 25 °C.
The shaking test method was used to determine the foam stability. It includes
standartized (10-fold) shaking of flask of 50 ml volume, containing 20 ml of the
studied solution. The time interval from the formation of foam to the appearance
of free water surface is measured. This operation is repeated 10-times, and an
average value of the foam decay time is obtained. This method is very simple to
use and gives sufficiently good reproducibility. The surface tension isotherm was
determined by the Harkins-Brown method [33].
All the measurements were obtained using a commercially available profile
analysis tensiometer, (PAT 1 D module of Sinterface Technologies, Ltd., Germany) with a frequency of 0.1 Hz and amplitude of 2 mm3. The tensiometer consists
of (1) a mechanical unit for creating and controlling the test fluid–liquid interface
in a 2 cm x 2 cm x 2 cm cuvette made of optical grade silica, (2) an optical unit
for monitoring the evolution of the interface profile and (3) a computer with the
Sinterface software, PAT-1D and a data acquisition system for operating the instrument, storing the raw data for the interface profiles, and processing the data
off-line. The mechanical unit has a water bath for controlling the temperature. The
soap bubble is produced (see Fig.1) by a dual tube – a narrower internal tube situated in a wider external tube. The surfactant solution flowing in the external tube
is controlled by a syringe, while air flows through the internal tube, controlled
by another syringe. The two syringes are mounted on the panel of a motorized
pump, controlled by the computer. Once formed, the soap bubble was illuminated,
equilibrated and its image was captured by the CCD video camera, stored, and
processed by the computer software. The edge (the interface profile) of the bubble
was digitally identified with sub-pixel resolution and fitted with the numerical solution of the Young–Laplace equation, allowing the determination of the film tension, volume and area of the bubble. The cyclic time dependence of film tension
was determined by changing the bubble volume as a sinusoidal function of time.
158
Figure 1. Sketch of the Profile analysis tensiometer system for studying elastic modulus of soap
bubble (not to scale).
The surface tension isotherm of C8E4 is presented in Fig. 2 (the circles).
80
Surface tension, mN/m
70
60
50
40
30
20
1.E-05
1.E-04
1.E-03
1.E-02
C8E4 concentration, M
Figure 2. Surface tension isotherm of C8E4 – experimental (circles) and computed.
159
These experimental data were processed with the Szyskowski-Langmuir
equation of state:
σ = σ 0 − Γ ∞ RT ln (1 + kc )
(15)
2000
2.0
1600
1.6
1200
1.2
800
0.8
400
0.4
0
0.E+00
2.E-03
4.E-03
6.E-03
8.E-03
1.E-02
dГ/dc,
d /dc, ìm
m
EG, mN/m
Fitting procedure with two matching parameters Γ ∞ and k was conducted via “Solver” option of Microsoft Excel. The theoretical curve is situated in Fig.1. The obtained values of the fitting parameters are Γ ∞ = 3.42 x10−6 mol/m2 and k = 25 m3/mol.
The corresponding adsorption length (see Eq. 13) and Gibbs elasticity (see Eq. 14)
are presented in Fig. 3.
0.0
1.E-02
Figure 3. Adsorption length and Gibbs elasticity vs. concentration of C8E4
The experiments on expanding a soap bubble were conducted in the concentration range of 2x10-3–10-2 M C8E4. At lower surfactant concentrations the data
were either redundant or the soap bubbles were not stable.
By the present experimental procedure conducted with the commercial Profile Analysis Tensiometer (PAT 1 D module of Sinterface Technologies, Ltd., Germany), expressed in periodical expansion and contraction of the soap bubble with
frequency of 0.1 Hz, an average value of the film tension and Gibbs elasticity is
produced. The values of the Gibbs elasticity and the Foam life-time versus C8E4
concentration is presented in Fig. 4.
160
100
160
Foam lifetime, min
Elastic modulus, mN/m
200
10
120
80
1
Elastic modulus
40
0
2.E-03
Foam lifetime
4.E-03
6.E-03
8.E-03
1.E-02
Concentration of C8E4, M
0.1
1.E-02
Figure 4. Gibbs elasticity and foam life-time as a function of C8E4 concentration
One can see clear correlation between the foam lifetime and the elastic modulus curves. It should be noted here that the elastic modulus values obtained by this
method are averaged, due to the variable in time film thickness inhomogeneity
over the soap bubble during its expansion and shrinking.
The comparison between the Gibbs elasticity and the limiting elasticity (see
Eq. 14) is presented in Fig. 5:
200
4500
160
3500
3000
120
2500
2000
80
1500
1000
40
Gibbs elasticity, mN/m
Elastic modulus, mN/m
4000
500
0
2.E-03
0
4.E-03
6.E-03
8.E-03
1.E-02
1.E-02
Figure 5. Gibbs elasticity
EG and elastic modulus ε vs. surfactant concentration.
161
One can see the Gibbs elasticity is significantly larger than the elastic modulus.
5. CONCLUSIONS
The results hold several noteworthy points:
1. Evident correlation between the film elasticity modulus and the foam lifetime (see Fig. 4). The film elasticity profile has a minimum and maxima.
2. The Gibbs elasticity values are about 10-fold larger than the values of the
film elasticity modulus. This must be due to difference in the rates of surfactant
adsorption/desorption as regards to the speed of expansion/ compression of the
soap bubble. The speed of surface area variation is smaller as compared to the
surfactant adsorption/desorption.
The elastic modulus and the film tension of soap bubble, produced by aqueous
solution of C8E4 + 10-5 M NaCl, was found by cyclic expansion and compression
of soap bubble with a frequency of 0.1 Hz. A good correlation between the elasticity of soap bubble and foam lifetime was found. In addition, the Gibbs elasticity
and the elastic modulus were compared. It was found that the Gibbs elasticity values are by an order of magnitude larger that values of the elasticity modulus. The
latter should be due to the faster adsorption/desorption of the surfactant molecules
compared to the speed of change of the bubble area.
Acknowledgments. Dr Stoyan Karakashev gratefully acknowledges the EC “Marie Curie
Actions” for the financial support through DEFFED – Project No. 230626/2009. The authors thank
to Assoc. Prof. R. Tsekov for the fruitful discussions.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
162
REFERENCE
Scheludko, A. Adv. Colloid Interface Sci. 1(4) (1967) p. 391–464.
Schick, M. Nonionic Surfactants. New York: Marcel Dekker Inc., 1988.
Exerowa, D. and P. M. Kruglyakov. Foam and Foam Films: Theory, Experiment, Application.
New York, NY: Marcel Dekker. 1997.
Mysels, K. J., J. Amer. Oil Chem. Soc. 45(3) (1968) p. 139–40.
Mysels K. J. and B.R. Vijayendran. J. Phys. Chem. 77(13), (1973) p. 1692–4.
Malysa, K., K. Lunkenheimer, R. Miller, and C. Hartenstein. Colloids and Surfaces, 3(4),
(1981) p. 329–338.
Malysa, K. K., Lunkenheimer, R. Miller, and C. Hempt. Coll. Surf. 16(1) (1985) p. 9–20.
Malysa, R. K., Miller, and K. Lunkenheimer. Colloids and Surfaces. 53(1–2) (1991) p. 47–62.
Lucassen-Reyndersq E. H. and D.T. Wasan. Food Structure. 12(1) (1993) p. 1–12.
Lyklema, J. Fundamentals of Interface and Colloid Science. Vol. 2: Academic Press, 1995.
Fruhner, H., K. D. Wantke, and K. Lunkenheimer. Colloids Surf., A. 162(1–3) (2000) p. 193–202.
Lucassen-Reynders, E. H., A. Cagna, and J. Lucassen. Colloids Surf., A. 186(1–2) (2001) p. 63–72.
Georgieva, D., A. Cagna, and D. Langevin. Soft Matter. 5(10) (2009) p. 2063–2071.
Mysels, K. J., M. C. Cox, and J. D. Skewis. J. Appl. Phys. 65(7) (1961) p. 1107-&.
Malysa, K., K. Lunkenheimer, R. Miller, and C. Hartenstein. Colloids and Surfaces. 3 (1981),
p. 329–338.
Gibbs, J.W. The Scientific Papers of J. Willard Gibbs. New York: Dover, 1961.
Bianco, H. and A. Marmur. J. Coll. Interface Sci. 158(2), (1993), p. 295–302.
18. Rusanov, A. I. and V. V. Krotov. Doklady Physical Chemistry. 393(4–6), (2003), p. 350–352.
19. Rusanov, A. I. and V. V. Krotov. Mendeleev Communications. (1), (2004), p. 16–17.
20. Kovalchuk, V. I., A. V. Makievski, J. Kragel, P. Pandolfini, G. Loglio, L. Liggieri, F. Ravera,
and R. Miller. Coll. Surf. A.261(1–3), (2005), p. 115–121.
21. Lucassen-Reynders, E. H., A. Cagna, and J. Lucassen. Coll. Surf. A.186(1–2), (2001), p. 63.
22. Wang, L. and R.-H. Yoon, Int. J. Min. Process. 85 (101), (2008) p.
23. Stubenrauch C., R. Miller, J. Phys. Chem. B.108(20), (2004), p. 6412–6421.
24. Ivanov, I. B. Thin Liquid Films. New York, N. Y.: Marcel Dekker. 1988.
25. Veer, F. A., M. Van Den Tempel. J Colloid Interface Sci. 42(2), (1972), p. 418–426
26. Lucassen, J., M. Van Den Tempel. Chem. Eng. Sci. 27(6), (1972), p. 1283–1291.
27. Lucassen, J., M. van den Tempel. Chem. Eng. Sci. 26(6), (1972), p. 1283.
28. Razouk, R. I., K. J. Mysels, J. Am. Oil Chem. Soc. 43(3), (1966), p. A130-&.
29. Razouk, R. I., K. J. Mysels. Journal of the American Oil Chemists Society. 45(5), (1968),
p. 381–&.
30. Kitchener, J.A. Nature. 194 (1962), p. 676–7.
31. Prins, A., C. Arcuri, M. van den Tempel. J Colloid Interface Sci. 24, (1967), p. 84.
32. Prins, A., M. van den Tempel. The Journal of Physical Chemistry. 73(9), (1968), p. 2828.
33. Mori, Y. H. Aiche Journal. 36(8), (1990), p. 1272–1274.
Received on March 17, 2010
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164
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
SYNTHESIS AND CHARACTERIZATION OF THE Hg(II)-ION IMPRINTED MICROBEADS AND MEMBRANES FOR ENRICHMENT
OF INORGANIC Hg(II)
I. DAKOVA1*, I. KARADJOVA1, V. GEORGIEVA2, G. GEORGIEV2
Department of Analytical Chemistry, 1 J. Bourchier, 1164 Sofia
Department of Organic Chemical Technology, Laboratory for Water Soluble Polymers,
Polyelectrolytes and Biopolymers, 1 J. Bourchier, 1164 Sofia
* Coresponding author, e-mail: [email protected]
1
2
Abstract: Hg(II)-ion imprinted polymer microbeads have been prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2’-azobisisobutyronitrile as initiator, in the presence of Hg(II)-1-(2thiazolylazo)-2-naphthol complex. The separation and preconcentration characteristics of
the copolymers for inorganic mercury have been investigated by batch procedure. The optimal pH value for the quantitative sorption is 7. The selectivity of the copolymer toward
inorganic mercury(II) ion is confirmed through the comparison of the competitive adsorptions of CH3Hg(II), Cd(II), Cu(II), Ni(II), Pb(II) and high values of the selectivity and
distribution coefficients have been calculated. The recognition properties of the Hg(II)-ion
imprinted microspheres are compared to those of the Hg(II)-ion imprinted membranes.
The membranes are prepared by loading of Hg(II)-imprinted microbeads in the bulk or on
the surface of chitosan membranes.
Hg(II)-отпечатани микрочастици са получени чрез съполимeризация на метакрилова киселина като мономер, триметилолпропан триметакрилат като омрежващ
агент и 2,2’-азобисизобутиронитрил като инициатор, в присъствие на комплекса
Hg(II)-1-(2-тиазолиазо)-2-нафтол. Съполимерите са приложени за разделяне и концентриране на неорганичен живак(II). Оптималната pH стойност за количествена
сорбция на живак е 7. Установени са високи стойности на коефициентите на селективност на неорганичния живак спрямо CH3Hg(II), Cd(II), Cu(II), Ni(II) и Pb(II).
165
Свойствата на Hg(II)-отпечатаните микросфери са сравнени с тези на Hg(II)-отпечатани мембрани. Мембраните са получени чрез включване на Hg(II)-отпечатаните
микрочастици в обема или върху повърхността на хитозанови мембрани.
Keywords: Solid phase extraction; Ion-imprinted polymer; Membrane; Preconcentration;
Inorganic mercury
INTRODUCTION
Mercury is one of the most toxic heavy metals for animals and humans, even
at low concentrations. It is included in all lists of priority pollutants, and different regulation and guidelines have been developed for limiting its level in water
and sediments [1]. Due to its trace amount and the influence of coexisting substances in real samples, the selective preconcentration and separation of mercury
ion are of great significance prior to analysis. Selective removal of toxic metal
from aqueous solutions is usually achieved by solvent extraction and solid phase
extraction (SPE). For metal extraction from dilute solution, the adsorption technique has greater applicability than traditional solvent extraction processes due to
its several advantages, such as higher enrichment factor, high retention capacity,
speed and simplicity, absence of emulsion, minimal cost due to low consumption
of reagents, flexibility and easy automation [2]. However, it should be noted that
the extraction efficiency and selectivity of this technique is strongly dependent on
the sorbent material used. Ion-imprinted polymers (IIP), as selective sorbents for
a particular chemical form of given element, help the solution of this problem.
The high selectivity of IIP could be related to the polymer memory effect toward
the metal ion interaction with a specific ligand, coordination geometry, metal ion
coordination number, charge and size [3]. Traditional application of IIPs in separation/preconcentration utilize polymer particles obtained by grinding and sieving
of synthesized block polymers [4], suspension [5] or precipitation [6] copolymerization. Generally, use of small polymer particles in separation processing is often
associated with generation of too high backpressures. The combination of the imprinting and membrane techniques would solve this problem. Kimaro et al. reported a uranyl ion (UO22+) selective membrane prepared by imprinting techniques
[7]. Goto et al. prepared a metal IIPM with porous solid support material through
water-in-oil emulsion polymerization using Zn(II) as a template ion [8]. Zhai et
al. proposed Zn(II)-2,2’-bipyridyl complex as the template, 4-vinylpyridyne as a
monomer and polyvinylidene fluorid membranes as a supporting material [9].
In the first part of this paper we report the synthesis of microspheric polymer
particles using methacrylic acid (MAA) as a monomer, trimethylolpropane trimethacrylate (TMPTMA) as a cross-linking agent, and 1-(2-thiazolylazo)-2-naphthol (TAN) as a specific ligand for Hg(II). The carboxylic group of methacrylic
acid were used to create the necessary interaction between the copolymer matrix
and the template. The extraction characteristics of the non-imprinted (blank P(B)),
166
imprinted with TAN alone (P(TAN)), and imprinted with Hg(II)-TAN complex
(P(TAN-Hg)) polymer gels have been compared. The sorption and desorption
characteristics have been investigated using batch procedures. The mercury selectivity versus other interfering metal ions (Cd(II), Cu(II), Ni(II), Pb(II)) and
methylmercury (CH3Hg(I)) has been studied.
In the second part of the communication, the recognition properties of the
Hg(II)-imprinted microspheres are compared to those of the Hg(II)-imprinted membranes. The membranes are prepared by loading of Hg(II)-imprinted microbeads
in the bulk or on the surface of chitosan membranes. A method for the application
of inorganic mercury imprinted (P(TAN-Hg)) polymer gel for the determination of
inorganic and methylmercury in water samples has also been developed.
EXPERIMENTAL
REAGENTS
All reagents used were of analytical reagent grade. The stock standard solutions for Hg (II), Cd(II), Cu(II), Ni(II) and Pb(II) (1000 μg mL-1) were Titrisol, Merck (Germany), in 2 % HNO3. MAA, TMPTM, 2,2’-azobisisobutyronitrile
(AIBN), chitosan (Merck, Darmstadt, Germany), TAN, glutaraldehyde (25 %)
(Fluka A.G., Switzerland), methylmercury chloride (CH3HgCl) (Sigma-Aldrich,
USA) and acetonitrile (ACN) (Labscan, Ireland) were used without further purification. Redistilled water was used in all experiments.
APPARATUS
Flame atomic absorption spectrometric (FAAS) measurements were carried out
on a Perkin Elmer Zeeman 1100 B spectrometer (Germany) with an air/acetylene
flame. Continuous flow (CF) cold vapor atomic absorption spectrometric (CV AAS)
measurements were carried out on a Varian AA 240 atomic absorption spectrometer.
The centrifuge K-1000 (KUBOTA Corporation, Osaka, Japan, www.centrifuge.jp) was used to separate modified silica and extracted metal solution in batch
experiments.
A microprocessor pH meter (Hanna Instruments, Portugal) was used for pH
measurements.
A scanning electron microscope (SEM, JEOL JSM-5500, Japan) was used for
the determination of the microbead shape and size.
PREPARATION OF Hg(II)-IMPRINTED MICROBEADS
The imprinted polymer materials were synthesized as described earlier [10].
As template species (0.024 mmol) the complexes of the imprinted ion (Hg(II))
with TAN or TAN only were used (Fig. 1). Hg(II)-IIPs were prepared via dispersion polymerization using ACN (5 mL) as solvent, AIBN (3.45 mg) as initia167
tor, MAA (0.116 mmol) as monomer and TMPTM (0.186 mmol) as crosslinking
agent at T=60 ºC for 24 h. Non imprinted polymer sorbent (P(B)) was synthesized
in the same way as described above, in the absence of template.
Hg(II) was eluted from the prepared polymer networks by stirring with 10 mL 4
M HNO3 for 2 h. Then ion imprinted polymer particles were dried in a vacuum
oven at 60 ºC. The non-imprinted (P(B)) polymer particles were treated in the
same way. The yields were 88.6 % for P(TAN-Hg), 86,5 % P(TAN) and 85.7 %
for P(B). Using scanning electron microscopy, it has been shown that in all cases
the obtained microparticles are in the shape of microspheres. Their average diameters, determined from the micrographs, vary between 210 nm and 330 nm.
O
S
O
N N
HO
O
+
O
+
+
N
Hg
O
O
TMPTM
OH
HO
O
O
OH
HO
Elution
S
N
N
N
N
N
O
+
O
S
N
O
Polymerization
MAA
TAN-Hg
O
O
O
HO
O
Hg
OH
OH
P(TAN-Hg)
A
Fig. 1. Scheme of the Hg(II)-IIP preparation.
PREPARATION OF MICROBEADS-MODIFIED
CHITOSAN MEMBRANES
The chitosan membranes M(CH) were obtained by a direct solvent evaporation of 2 g of chitosan solution (2 % w/w in 2 % acetic acid) in a Petri dishes
(internal diameter 3 cm). The formed membranes were then immersed for 24 h in
168
1 M NaOH, in order to neutralize the excess of acid and they were washed twice
with bidistilled water. One of the membranes was modified by the deposition/
loading of P(TAN-Hg) imprinted microparticles (Fig. 2) after Hg(II) extraction.
Microspheres (10 mg) were suspended in acetone and deposited on the membrane
surface. After acetone evaporation the membrane-particles system (M(TAN-HgsCH)) was washed with disilled water to remove not perfectly attached particles.
The third membrane (M(TAN-Hg-iCH)) was prepared by loading of Hg(II)-imprinted microbeads in the bulk of chitosan membrane (Fig. 2) in the same way as
M(CH), but in the presence of P(TAN-Hg) microparticles.
A
B
C
Fig. 2. Schemes of the chitosan membrane – microbeads systems: A: Chitosan membrane
(M(CH); B: Hg(II)-IIP on the chitosan membrane surface (M(TAN-Hg-sCH)); C: Hg(II)-IIP in
the bulk of chitosan membrane (M(TAN-Hg-iCH)).
STATIC ADSORPTION AND DESORPTION TEST
A portion of the solution containing 0.1 μg Hg(II) was diluted to a 10 mL total
volume and pH was adjusted with buffer solution to the desired value. Polymer
particles of ca. 25 mg were added to this solution and stirred for 15 min with a
magnetic stirrer. The sample was centrifuged (3000 rpm), the supernatant was removed and the polymer gel was washed twice with redistilled water. The Hg(II)
was eluted from the sorbents with 2 mL 4 M HNO3. The eluate was transferred
in 10 mL volumetric flask and diluted up to the mark with doubly distilled water.
Hg(II) content in the eluate was determined by CV AAS.
Batch membrane studies were conducted by soaking chitosan membranes in
10 mL of Hg(II) solution at pH 7 for 24 h at a room temperature and with stirring
at 200 rpm. This period of time was chosen based on kinetics studies that showed
that the required time to reach equilibrium was approximately 10 h. The supernatant was removed and the membrane was washed twice with redistilled water.
169
The Hg(II) was eluted from the membrane with 2 mL 4 M HNO3. The eluate was
transferred in 10 mL volumetric flask and diluted up to the mark with doubly distilled water. Hg(II) content in the eluate was determined by CV AAS.
SELECTIVITY EXPERIMENTS
A 20 mL solutions containing 0.1 μg Hg(II), 0.1 μg CH3Hg(I) and 20 μg Cd(II),
Cu(II), Ni(II) and Pb(II) were stirred with ca. 25 mg P(TAN-Hg), P(TAN), P(B)
(for 15 min) or M(CH), M(TAN-Hg-iCH) and M(TAN-Hg-sCH) (for 24 h) at
pH 7. The solutions were separated, sorbent materials washed twice with doubly
distilled water and elution performed with 2 mL 4 M HNO3. The concentration of
Hg(II) and CH3Hg(II) in the supernatant and eluate solutions was determined by
CV/HG AAS respectively. The concentration of metal ions in the supernatant and
eluate solutions was measured by FAAS.
EXTRACTION EFFICIENCY AND SELECTIVITY CHARACTERISTICS
The extraction efficiency (E) of Hg(II) ions is
E (%) = [(Ai _ Aeff)/ Ai] . 100 ,
(1)
where Aeff (μg) is the cation amount in the effluate solution after extraction by
P(X) (X = TAN-Hg, TAN, B) or by the different membranes from a solution with
a total cation amount Ai (μg).
The distribution ratio (D) is defined as
D = (Ai _ Aeff)/ Aeff
(2)
The binding capacity of the Hg(II)-IIPs is defined as the amount of the adsorbed Hg(II) ions per gram of the sorbent.
1. Hg(II)- IMPRINTED AND NON-IMPRINTED MICROBEADS
1.1. Influence of pH on the sorption of Hg(II) with imprinted and non-imprinted polymer gels
Three synthesized sorbents: P(TAN-Hg) – imprinted with Hg-TAN; P(TAN) –
imprinted only with ligand (TAN) and non-imprinted P(B) were tested for Hg(II)
sorption from aqueous solution at various pH (3-9) in batch experiments, using
the procedure described in 2.4. The results obtained for the influence of pH on the
Hg(II) extraction efficiency (E) are presented in Table 1. It can be seen that E and
D values registered, when P(TAN-Hg) was used as a sorbent, are well above those
170
for P(TAN) and P(B). These large differences in the values obtained confirm the
advantages of the imprinted with the TAN-Hg complex IIP – (P(TAN-Hg)) over
the imprinted with TAN (P(TAN)) and the non-imprinted one P(B) in the separation and preconcentration of Hg(II) ions.
Table 1. Comparison of the efficiency (E) and the distribution ratio (D) of Hg(II) extraction by
the polymer gels used. 25 mg polymer gel, 0.1 μg Hg(II), 2 mL 4 M M HNO3 as eluent.
Polymer
E, %
D
gel
pH 3 pH 4 pH 5 pH 6 pH 7 pH 8 pH 9 pH 3 pH 4 pH 5 pH 6 pH 7 pH 8 pH 9
P(TAN-Hg) 25±2 58±2 76±1 92±1 98±1 90±1 76±1 0.3
1.4
3.2 11.5 49.0 10.0 3.2
P(TAN) 24±2 46±2 53±2 48±2 39±2 35±2 33±2 0.3
0.9
1.1
0.9
0.6
0.5
0.4
P(B)
23±2 50±2 62±2 70±1 75±1 73±1 68±2
0.3
1.0
1.3
2.3
3.0
2.7
2.1
The values of E show that the polymer imprinted with TAN is not so effective
as those of the imprinted with the TAN-Hg complex (Table 1). Probably, EP(TAN-Hg)
>EP(TAN) (DP(TAN-Hg)>DP(TAN)) due to the configurations of the TAN molecules immobilized in gels using the Hg(II)-TAN complex and TAN molecules alone as
template species, are quite different. In the first case, the TAN molecule configuration in P(TAN-Hg) exhibits maximum activity for such complex formation as this
configuration is the same as in the complex. If the imprinting is performed with
TAN molecules only as the template species (P(TAN)), the fraction of the active
TAN molecule configuration for the complex formation is less than one. Some of
the gel-immobilized TAN molecules in this case are blocked for the formation of
the TAN-Hg complex (see Fig. 1). The reason for the inequality between P(TANHg) and P(B) (Table 1) is, however, quite different. Evidently, if P(B) is used for
Hg(II) sorption, the specific interaction between TAN and Hg(II) does not take
place, thus explaining low extraction efficiency observed.
The ratios EP(TAN-Hg)/E P(B) and DP(TAN-Hg)/DP(B) show maximum values in the pH
range from 6 to 7, but extraction efficiency reaches its highest value at pH 7 (Table 1). Therefore, pH 7 was selected for our further investigations. Comparison of
the extraction efficiencies (Table 1) of the tested sorbents shows that at higher pH
values (7–9) the E values decrease for P(TAN-Hg) and P(B), while for P(TAN) –
this decrease is at wider pH (5–9) interval. This could be related to the precipitation of the metal hydroxide and its quick decomposition to oxide.
1.2. Optimization of the experimental conditions for preconcentration of Hg(II)
The influence of various parameters (eluent volume and concentration, sorption and
desorption time) on the solid phase extraction efficiencies of P(TAN-Hg) for the preconcentration of Hg(II) from a 10 mL 1 μg mL-1 Hg(II) solution at pH 7 is investigated.
The effect of the eluent volume on the metal desorption was investigated in
the range of 2–10 mL 4 M HNO3 and the eluent acidity influence – in the range of
1.0–5.0 M HNO3. The full extraction efficiency of Hg(II) was reached when the
adsorbed Hg(II) was eluted with 2 mL 4 M HNO3.
171
The kinetics of the Hg(II) sorption and desorption were investigated in a
batch system with 25 mg of the P(TAN-Hg) particles for 5–40 min. The adsorbed
Hg(II) ions were desorbed by treatment with 4 M HNO3 at continuous stirring.
The loading half time (t1/2), defined as the time required for reaching 50% of the
sorbent total loading capacity, is 3 min. It was established that the saturation values (i.e., equilibrium extraction efficiency) were gradually reached within 20 min,
so the Hg(II) adsorption was sufficiently fast for practical applications. The Hg(II)
ions could be quantitatively eluted for 20 min.
1.3. Competitive adsorption
In order to prove the selectivity of P(TAN-Hg), a competitive adsorption of
Cd(II), Cu(II), Ni(II), Pb(II) and CH3Hg(II) from their model mixture was investigated as well. Although these ions have the same charge, similar chemical properties and ionic radii, significant differences in their extraction characteristic E
were observed. The extraction efficiencies of Hg(II) with P(TAN-Hg) are much
higher than those of Cd(II), Cu(II), Ni(II), Pb(II), and CH3Hg(II). The greatest
difference is established between extraction efficiencies of Hg(II) and CH3Hg(II)
(97.5 % and < 3 %, respectively). The large size of CH3Hg(I) probably hinders
the ion diffusion and the ions can not reach the functional groups. The selectivity coefficients (calculated by eq. SHg/Me = DHg/DMe) are 1633, 114, 233, 73 and
132 for CH3Hg(II), Cu(II), Ni(II), Pb(II) and Cd(II), respectively. These results
unambiguously confirm the very good selectivity of P(TAN-Hg) toward the target
(imprinter Hg(II)) ions.
2. MEMBRANE – MICROBEADS SYSTEMS
Chitosan, (1→4)-2-amino-2-deoxy-b-D-glucan (Fig. 3), is a semisynthetic
polymer derived from chitin by deacetylation [11]. Chitosan–metal ion complex
formation occurs primarily through the amino groups of chitosan functioning as
ligands. Among factors controlling the level of this complex formation the most
important are: (1) the total amino group concentration in chitosan, which is dependent on the degree of deacetylation of chitosan, and (2) availability of amino
groups, which is dependent on the geometrical configuration of chitosan matrix
(powder, beads, fibers, membranes or soluble chitosan) and on the rate of metal
ion diffusion through the matrix [12]. Due to the presence of amino groups in
its molecules, chitosan is a cationic polyelectrolyte and it is soluble in aqueous
acidic media [13]. Therefore, the effect of pH on Hg(II) adsorption onto chitosan
membranes was studied in the pH range from 5–8 and the results are presented
in Fig. 5. As shown in Fig. 4, the extraction efficiency of mercury ions increased
with a pH ncreasing from pH 5 to pH 7. In acidic solutions, a strong competition
existed between metal ions and protons for sorption sites and the extraction efficiency was decreased. Moreover, the protonation of amine groups induced an
172
electrostatic repulsion of metal cations and reduced the number of binding sites
available for mercury metal ion uptake. When the pH of the solution increased,
the competition effect as well as the electrostatic repulsion decrease. The decrease
in extraction efficiency above pH 7.0 seems due to the precipitation of the metal
hydroxide. Therefore, the pH was adjusted to 7.0 in all subsequent studies.
Fig. 3. Molecular structure of chitosan.
E, % 100
90
80
70
60
4
5
6
7
8
9
pH
Fig. 4. pH-dependence of the extraction efficiencies of Hg(II) ions with M(CH): 20 mg M(CH),
d = 3 cm, 0.1 μg mL-1 Hg(II), 24 h.
173
Extraction efficiencies, distribution and selectivity coefficients of Hg(II),
Cd(II), Cu(II), Ni(II), Pb(II)and CH3Hg(II) of polymer microspheres (P(TANHg)) and of membranes non-loaded (M(CH) and loaded with Hg(II)-imprinted
microbeads in the bulk (M(TAN-Hg-iCH)) or on the surface (M(TAN-Hg-sCH))
are shown in Tables 2 and 3. Comparing the results obtained in these different kinds of membranes, it is evident that membranes prepared by loading with
P(TAN-Hg) on the surface of chitosan membrane have higher extraction efficiency and selectivity for Hg(II), than M(CH) and M(TAN-Hg-iCH), though they are
lower than those showed by free microparticles. These results could be related
to the fact that the loading itself reduces the exposed surface of the microspheres.
This effect is still greater when the loaded in the bulk membrane was used.
The comparison of the presented results in Table 2 shows, that the chitosan
high sorption ability suppresses the expected specific sorption of the investigated
ions (including of the imprinted ions) on the ion-imprinted particles included in
the chitosan membranes. Therefore, in the subsequent development of this investigation the chitosan will be exchanged with other suitable polymer membrane.
Table 2. Comparison of the efficiency (E) of metal ions extraction by the polymer particles and
membanes used (pH 7; 2 mL 4 M HNO3 as eluent; sorption time 24 h).
E, %
Sorbent
P(TAN-Hg)
M(CH)
M(TAN-Hg-sCH)
M(TAN-Hg-iCH)
Hg(II)
98±1
96±2
95±1
90±1
HgCH3(II)
<3
<3
<3
<3
Cu(II)
30±2
68±2
55±2
58±2
Ni(II)
17±3
50±3
42±3
39±3
Pb(II)
40±2
65±2
53±2
55±2
Cd(II)
27±2
46±2
40±2
41±2
Table 3. Distribution (D) and selectivity coefficients (SHg/Me) of
P(TAN-Hg), M(CH), M(TAN-Hg-sCH) and M(TAN-Hg-iCH) for Hg(II).
Me ion
Hg(II)
CH3Hg(II)
Cu(II)
Ni(II)
Pb(II)
Cd(II)
P(TAN-Hg)
D
SHg/Me
49
0.03
0.43
0.21
0.67
0.37
1633
113.9
233.3
73.1
132.4
D
M(CH)
SHg/Me
24
0.03
2.12
1.00
1.80
0.85
1633
23.1
49
27.2
57.6
M(TAN-Hg-sCH)
D
SHg/Me
13
0.03
1.22
0.12
1.12
0.67
1633
40.2
408.3
44.5
73.1
M(TAN-Hg-iCH)
D
SHg/Me
9
0.03
1.38
0.64
1.22
0.69
1633
35.5
76.6
40.2
71.0
ANALYTICAL FIGURES OF MERIT
The accuracy and precision of the proposed analytical procedure has been checked
by spike recovery method. Mineral water samples ca 200 mL were spiked with Hg(II)
and CH3Hg(II). Results obtained are presented in Table 4. The limit of detection
174
achieved for Hg(II) determination (calculated as 3 times standard deviation of the
blank, 100 ml water sample) is 0.006 μg L–1 and the limit of determination is 0.02 μg L–1.
The relative standard deviation varied in the range 5–9 %. Neither Hg(II) nor CH3Hg(II)
were found in mineral waters above the presented determination limits.
Table 4. Added/found method for Hg(II) and CH3Hg(I) determination in mineral water “Bankya”
(pH 7, water samples 200 mL, elution with 2 mL 4M HNO3, three parallel determinations)
Sorbent
P(TAN-Hg)
M(TAN-Hg-sCH)
Added
0.1μg L-1 Hg(II) and
0.05 μg L-1 CH3Hg(II)
0.1μg L-1 Hg(II) and
0.05 μg L-1 CH3Hg(II)
Found Hg(II) (μg L-1)
Found CH3Hg(II) (μg L-1)
0.095±0.009
0.052±0.004
0.114±0.013
0.019±0.002
CONCLUSIONS
In the present paper the preparation of microspheric Hg(II)-IIP by crosslinking dispersion copolymerization of methacrylic acid and trimethylolpropane
trimethacrylate in acetonitrile and its application as adsorbent for the selective
separation and preconcentration of Hg(II) in water samples is reported. The most
important characteristic of the Hg(II)-IIP is its excellent selectivity towards Hg(II)
over Cd(II), Cu(II), Ni(II), Pb(II) and CH3Hg(II).
The recognition properties of the Hg(II)-imprinted microspheres are compared to those of the Hg(II)-imprinted membranes. The membranes, prepared by
loading of Hg(II)-imprinted microbeads on the surface of chitosan membranes,
showed the best extraction efficiency and selectivity to mercury ions.
Acknowledgement: Financial support of this work was provided by a Project DO-02-82/2008UNION and EC project (NMP4-ct-2007-033168).
REFERENCES
1. Hayes, R.B. Cancer Causes control, 8, 1997, 371.
2. Prasada Rao, T., R. Kala, S. Daniel. Anal. Chim Acta, 578, 2006, 105.
3. Wulff, G. Angew. Chem., Int. Ed. Engl., 34, 1995, 1812.
4. Chianella, I., S.A. Pyletsky, I.E. Tothill, B. Chen, A.P.F. Turner. Biosens. Bioelectron., 18, 2003, 119.
5. Lai, J.P., X. Yu. Lu, Ch.Ya. Ju, X.W. He. Anal. Chim. Acta, 442, 2001, 105.
6. Tamayo, F.G., J.L. Casillas, A. Martin-Esteban, C. Perez-Conde, C. Camara. J. Chromatogr. A,
1069, 2005, 173.
7. Kimaro, A., L. Kelly, G.M. Murray. Chem. Commun., 14, 2001, 1282.
8. Araki, K., T. Maruyama, N. Kamiya, M. Goto. J. Chromatogr. B, 818, 2005, 141.
9. Zhai, Yu., Yo. Liu, X. Chang, X. Ruan, J. Liu. React. Func. Polym., 68, 2008, 284.
10. Dakova I., I. Karadjova, V. Georgieva, G. Georgiev. Talanta, 78, 2009, 523.
11. Ravi Kumar, M. N.V. React. Func. Polym., 46, 2000, 1.
12. Vieira, R. S., M. M. Beppu. Wat. Res., 40, 2006, 1726.
13. Krajewska, B. React. Func. Polym., 47, 2001, 37.
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Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
ELECTRIC DOUBLE LAYER IN CONCENTRATED SOLUTIONS OF
IONIC SURFACTANTS
ROUMEN TSEKOV
Department of Physical Chemistry, University of Sofia, 1 J. Bourchier Blvd, 1164 Sofia, Bulgaria
Abstract. A simple non-local theoretical model is developed considering concentrated ionic surfactant solutions as regular ones. Their thermodynamics is described by the Cahn-Hilliard theory coupled with electrostatics. It is discovered that unstable solutions possess two critical temperatures, where
the temperature coefficients of all characteristic lengths are discontinuous. At temperatures below the
lower critical temperature ionic surfactant solutions separate into thin layers of oppositely charged
liquids spread across the whole system and the electric potential is strictly periodic. At temperatures
between the two critical temperatures separation can occur only near the solution surface thus leading
to an oscillatory-decaying electric double layer. At temperatures above the higher critical temperature
as well as in stable solutions there is no separation and the electric potential decays exponentially.
The theory of the electric double layer [1] dates back to the classical works
of Helmholtz, Gouy, Chapman, Stern, Debye, Hückel and others. Due to general mathematical complications in dense systems, however, the applications are
mainly restricted to dilute ionic solutions, where the electric potential is described
via the Poisson-Boltzmann equation. The interactions between electric double
layers are also intensively studied as an important component of the inter-particle and colloidal forces [2]. Recently, significant attention has been attracted by
highly charged Coulomb mixtures, where many specific phenomena take place [3]
among them mono-species electric double layers [4]. General theories of charged
fluids are also developed [5–8], which account for ion correlations going beyond
the Poisson-Boltzmann theory. An interesting aspect here is the effect of nonelectrostatic interactions between the ions in the electric double layer expected
to become important in concentrated solutions. The aim of the present paper is
to develop a simple theoretical approach to concentrated ionic surfactant solutions based on electrostatics coupled with the regular solution model. The lat177
ter is described in accordance to the Cahn-Hilliard theory [9]. It is shown that a
temperature region exists where the electric potential is an oscillatory-decaying
function. At temperatures below this temperature region the spatial arrangement
of the ions is purely periodic thus indicating a complete phase separation to oppositely charged layers. On the contrary, at temperatures above this temperature
region the oscillations are completely damped and the electric potential decays
exponentially. On the borders of this temperature region the temperature coefficients of all characteristic lengths exhibit singularities, thus indicating a new type
of second-order phase-transitions.
The structure of concentrated solutions is rather complex and, for this reason,
it is difficult for theoretical modeling. Hereafter a simple model is developed,
which aims to describe the main features of the electric double layer in concentrated solutions of symmetric ionic surfactants. The latter dissociate in water completely to cations and anions with charges ± z , respectively. The electric potential
φ is related to the local charge density via the Poisson equation
ε0 εΔφ = ze(c− − c+ )
(1)
where ε 0 ε is the dielectric permittivity of the solution, Δ is the Laplace operator
and c− and c+ are the local concentrations of anions and cations. The further application requires a relation between the local ion concentrations and the electric
potential. In the frames of the regular solution model the electrochemical potentials of the ions can be presented in the forms
μ + = μ 0+ + k BT ln c+ + zeφ + ωc−2 / 2c∞2 − λΔc+ / 2c∞
(2)
μ − = μ 0− + k BT ln c− − zeφ + ωc+2 / 2c∞2 − λΔc− / 2c∞
(3)
Here T is temperature, c∞ is the in the bulk concentration far away from the
surface, ω is the interaction energy excess between ions and the last terms follow
from the Cahn-Hilliard gradient theory [9]. Note that the non-negative parameter λ is proportional to the surface tension between the two possible oppositely
charged solutions dominantly containing cations and anions, respectively. Since
these two charged liquids contribute equally to the surface tension on their common dividing surface, the elastic constant λ is the same in both electrochemical
potentials above. The presence of the last terms in Eqs. (2) and (3) is an indication
of non-locality because the electrochemical potential depends not only on the local concentration but also on the concentration distribution all over the solution.
The Cahn-Hilliard theory is an extension to mixtures of the general van der Waals
178
density functional theory of non-homogeneous fluids [10]. It is a first approximation for non-locality but a very general one accounting for the leading effects of
the ion correlations. There are no restrictions of its application due to high concentrations. On the contrary, the Cahn-Hilliard theory is usually applied to condensed
phases since in dilute systems λ is negligibly small. If the explicit potentials of
the ion interactions are known it is a matter of integration [9] only to calculate
rigorously ω and λ .
The thermodynamic equilibrium requires constant values of the electrochemical potentials along the solution, which can be determined from Eqs. (2) and (3)
far away from the surface, where c− = c+ = c∞ and φ = 0 , i.e.
μ + = μ 0+ + k BT ln c∞ + ω / 2
μ − = μ 0− + k BT ln c∞ + ω / 2
(4)
Introducing these expressions back into Eqs. (2) and (3), respectively, leads to the
following expression for the electric potential
2 zeφ = k BT ln(c− / c+ ) − ω(c−2 − c+2 ) / 2c∞2 − λΔ (c− − c+ ) / 2c∞
(5)
Due to the strong electrostatic effects the local concentrations differ slightly from
c∞ and the first entropic and second enthalpic terms in Eq. (5) can be linearized
to obtain
2 zec∞ φ = (k BT − ω)(c− − c+ ) − λΔ (c− − c+ ) / 2
(6)
Finally, substituting the local concentration variations in Eq. (6) by Eq. (1) leads
to the following differential equations for the electric potential φ
−βλΔΔφ + 2(1 − βω)Δφ = 2κ 2φ
(7)
Here β ≡ 1/ k BT and κ ≡ (2 z e c∞ / ε 0 εk BT ) are the reciprocal thermal energy and Debye length, respectively. Note that Eq. (7) reduces to the linearized
Poisson-Boltzmann equation from the Debye-Hückel theory in the case of dilute
solutions, where ω = 0 and λ = 0 . Due to the first non-local term, however, it
goes beyond the local screening theories being proven to be inaccurate in concentrated ionic solutions.
Deep inside the solution the molar fraction of cations and anions are equal
due to electro-neutrality. Close to the surface, however, the specific adsorption of
surfactant ions induces decrease of surfactant ions concentration and increase of
the counterions one. To analyze the spatial patterns in the electric double layer
2 2
1/ 2
179
close to the surface it is more convenient to apply the Fourier transform of Eq. (7)
which reflects into the following dispersion relation
βλq 4 + 2(1 − βω)q 2 + 2κ 2 = 0
(8)
for the wave vector q . In general Eq. (8) has four roots
q=±
± (1 − βω) 2 − 2βλκ 2 − (1 − βω)
βλ
(9)
Physically relevant roots are, however, ones with non-negative imaginary parts
since the Fourier components with qIm < 0 diverge at infinity. Since the real parts
of the physically relevant roots appear with opposite signs ± qRe , the dependence
of the electric potential near a flat surface acquires the form
φ = φs exp(qIm z ) cos(qRe z )
(10)
where φs is the surface potential and the solution occupies the lower half-space
z ≤ 0 . The boundary conditions of Eq. (7) to obtain Eq. (10) are a fixed surface
potential and purely exponential decay very near to the surface due to the requirement of space needed for building of another layer similarly charged to the surface.
If ω ≤ 0 , the solution is stable at any temperature. Since in this case the cation-anion attraction is stronger than the cation-cation and anion-anion ones, the
surface tension between the possible oppositely charged liquids should vanish.
Hence, in this case one can accept generally λ = 0 and Eq. (9) reduces to
q = i κ / 1 − βω
(11)
As seen, the wave vector is purely imaginary thus indicating simple exponential
2 2
1/ 2
decay of the potential. The decay length [ε 0 ε(k BT − ω) / 2 z e c∞ ] , however, is
larger than the Debye one due to the ion interactions, which obviously help the
entropy to diffuse the electric double layer.
More interesting is the case ω > 0 , where the solution can separate in two oppositely charged liquids at low temperatures. This case is especially relevant to surfactant
solutions since the surfactant ions are usually complex organic species. Hence, the
strong non-electrostatic attraction between them as well as the hydrophobic repulsion
between surfactant and strongly hydrated counter ions can result in a positive ω . If the
material parameters ω , λ , c∞ and ε are temperature independent constants, one can
introduce the following characteristic temperatures: the classical critical temperature
180
Tc ≡ ω / k B and the split temperature Ts ≡ 2(λz 2 e 2 c∞ / ε 0 ε)1/ 2 / k B . Alternatively the
2
2 2
1/ 4
latter can be presented as Ts = 2λκ s / k B , where κ s ≡ κ(Ts ) = ( z e c∞ / ε 0 ελ ) .
Hence, k BTs is proportional to the mean energy of the electrostatic contribution to the
surface tension between the oppositely charged liquids. Using these notations Eq. (9)
can be rewritten as
q / κ s = ± 2(± t 2 − 1 − t )
(12)
where t ≡ (T − Tc ) / Ts . The Cahn-Hilliard parameter λ ∼ ωa = k BTc a is proportional to interaction energy ω and a length a , reflecting the typical distance of
the intermolecular interactions. Hence, introducing κ c ≡ κ(Tc ) the ratio between
1/2
the split and critical temperatures scales as Ts / Tc ∼ κ c a , while κ s ∼ ( κ c / a ) .
At c∞ = 0.1 M, z = 1 and a room critical temperature these estimates lead to
κ s ∼ κc = 1 nm-1 and Ts / Tc ∼ 0.1 at a ∼ 0.1 nm.
2
2
Fig. 1 The universal temperature dependence of the dimensionless components of the wave
vector
qRe / κ s
(dashed line) and
qIm / κ s
(solid line) on
t ≡ (T − Tc ) / Ts
In Fig. 1 the corresponding universal dependence of the physically relevant
real and imaginary parts of the dimensionless wave vector q / κ s are presented as
functions of the dimensionless temperature difference t . As seen for temperatures
below Tcb ≡ Tc − Ts the system decomposes of layers of oppositely charged liquids,
which spread out periodically across the whole liquid. In this case qIm = 0 and
181
qRe is inverse proportional to the thickness of the layers. Since the upper branch
corresponds to extremely thin layers, a realistic structure will be described by the
2
2
lower branch qRe ≤ 2 κ s . Such layers are a particular example of the lamellar structures formed by surfactants at high concentrations. For temperature above Tcb but
1/ 2
1/ 2
bellow Tcs ≡ Tc + Ts both imaginary qIm = κ s (1 + t ) and real qRe = κ s (1 − t )
parts are not zero thus indicating an oscillatory-decaying propagation of the electric
potential as described in Eq. (10). In this case the liquid separates to oppositely
charged layers only near the surface. At T ≥ Tcs , however, qRe = 0 and the potential becomes purely exponentially decaying but its decay length differs from the
2
2
Debye one. Here again the realistic value is qIm ≤ 2 κ s since at large temperatures
it tends asymptotically to κ . In general the symmetry rule qIm (t ) = qRe (−t ) holds.
At both new critical temperatures, the bulk one Tcb and the surface one Tcs , the
temperature coefficients of qRe and qIm are discontinuous, while at T = Tc the real
and imaginary parts are both equal to κ s . Note that a decrease of the ionic surfactant
concentration reflects in decrease of Ts . Hence, in relatively dilute solutions both
the new critical temperatures tend to the classical one Tc .
The present non-local model of concentrated ionic surfactant solutions as
regular ones is a simple and effective tool for description and understanding of
the complex structure of the electric double layer. Essential innovation in addition
of the Cahn-Hilliard gradient term is the coupling with electrostatics. The main
limitation of the theory is a linearization but even so it demonstrates interesting
and important results. In general, the described phase transitions are related to
spinodal decomposition of the ionic surfactant solutions to oppositely charged
liquids. However, in contrast to simple non-charged liquids it is favorable for the
ions to form thin layers instead of bulk phases since the coexisting phases are
charged solutions. The interplay between thermodynamic instability and electrostatics leads also to appearance of two critical temperatures spanning a temperature region, where the decomposition is only possible near the solution surface.
Such boundary induced phase-transition generates an oscillatory-decaying electric
double layer. Similar oscillatory-decaying dependence of the electrical potential
is observed in room temperature ionic liquids via computer simulations [11–13].
Moreover, singularities of the interfacial polarization are experimentally detected
in ionic liquids [14–16], which are explained also by demixing criticality [17]. An
interesting question remained open is what happens in highly concentrated solutions without non-electrostatic interactions between ions. Intuitively one would
expect that ω < 0 due to electrostatic repulsion and attraction between similar and
dissimilar charges, respectively. Computer simulations [18] have shown, however, that due to strong correlation effects purely Coulomb mixtures possess also
critical temperatures, under which phase separation takes place.
182
Acknowledgement. The author is grateful to the Bulgarian NSF for financial support through
grant DRG 02/3.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
REFERENCES
Ohshima, H. Theory of Colloid and Interfacial Electric Phenomena. Academic: London, 2006.
Hansen, J.-P., H. Löwen. Annu. Rev. Phys., Chem. 2000, 51, 209.
Levin. Y. Rep. Prog. Phys., 2002, 65, 1577.
Tsekov, R., O.I. Vinogradova. J. Chem. Phys., 2007, 126, 094901.
Narayanan, T., K.S. Pitzer. Phys. Rev. Lett., 1994, 73, 3002.
Weingärtner, H., W. Schröer. Adv. Chem. Phys., 2001, 116, 1.
Ramirez, R., R. Kjellander. J. Chem. Phys., 2003, 119, 11380.
Levin, Y. Braz. J. Phys., 2004, 34, 1158.
Cahn, J.W., J.E. Hilliard. J. Chem. Phys., 1958, 28, 258.
Rowlinson, J.S., B. Widom. Molecular Theory of Capillarity. Clarendon: Oxford, 1982.
Lynden-Bell, R.M., J. Kohanoff, M.G. Del Popolo. Faraday Discussions, 2005, 129, 57.
Pinilla, C., M.G. Del Popolo, R.M. Lynden-Bell, J. Kohanoff. J. Phys. Chem., B 2005, 109, 17922.
Koslowski, T., U. Beck. J. Phys.: Condens. Matter., 1999, 11, 3019.
Halka, V., R. Tsekov, W. Freyland. Phys. Chem. Chem. Phys., 2005, 7, 2038.
Halka, V., R. Tsekov, W. Freyland. J. Phys.: Condens. Matter., 2005, 17, S3325.
Halka, V., R. Tsekov, I. Mechdiev, W. Freyland, Z. Phys. Chem., 2007, 221, 549.
Tsekov, R. J. Chem. Phys., 2007, 126, 191110.
Hynninen, A. P., M. Dijkstra, A.Z. Panagiotopoulos. J. Chem. Phys., 2005, 123, 084903.
183
184
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
ERMAKOV EQUATIONS IN QUANTUM MECHANICS
ROUMEN TSEKOV
Department of Physical Chemistry, University of Sofia, 1 James Bourchiers Blvd., 1164 Sofia, Bulgaria
Abstract. The Ermakov equation, appearing in quantum mechanics of a harmonic oscillator, is
extended via dissipative and thermal terms to take into account the effect of an environment.
More than a century ago Ermakov [1] has introduced an equation, which appears in many branches of modern physics [2, 3]. In quantum mechanics the Ermakov equation comes out in the case of a harmonic oscillator [4, 5]. The evolution of
the latter is usually described by the time-dependent Schrödinger equation
i ∂ t ψ = (− 2 ∂ 2x / 2m + mω02 x 2 / 2)ψ
(1)
where m is the particle mass and ω0 is the oscillator own frequency. The complex wave function ψ ( x, t ) can be presented generally in the polar form
ψ = ρ exp(iS / )
(2)
where ρ is the probability density and S is the wave function phase. Introducing
Eq. (2) in Eq. (1) the latter splits in two equations [6]
∂ t ρ = −∂ x (ρV )
(3)
m∂ tV + mV ∂ xV + mω02 x = −∂ x Q
(4)
185
corresponding to the imaginary and real parts. The first equation is a continuity
one and V ≡ ∂ x S / m is the hydrodynamic-like velocity in the probability space.
Equation (4) is a macroscopic force balance, where Q = − 2 ∂ 2x ρ / 2m ρ
is the Bohm quantum potential. The solution of these Madelung equations
ρ = exp(− x 2 / 2σ 2 ) / 2πσ is a Gaussian probability density, which introduced
in Eq. (3) leads to an expression V = xσ / σ for the hydrodynamic-like velocity.
Substituting now both expressions for ρ and V in Eq. (4) results in the Ermakov
equation describing the evolution of the rms displacement σ
mσ + mω02 σ =
2
/ 4mσ3
(5)
Pinney [7] has found a general solution of the Ermakov equation. In the case of a
free quantum particle (ω0 = 0) the solution of Eq. (5) is the well-known expression,
describing ballistic spreading of a Gaussian wave packet, σ 2 = σ02 + ( t / 2mσ0 ) 2
.
The Madelung presentation of the Schrödinger equation opens a door for introduction of dissipative forces in quantum mechanics. Usually the friction force
of a particle in a classical environment depends linearly on the particle velocity.
Hence, one can add a friction force −bV in Eq. (4) to obtain [8, 9]
m∂ tV + mV ∂ xV + bV + mω02 x = −∂ x Q
(6)
where b is the particle friction coefficient. Thus one arrives to dissipative Madelung hydrodynamics. Substituting the expressions for ρ and V in Eq. (6) yields
a dissipative Ermakov equation [8-10, 3]
mσ + bσ + mω02 σ =
2
/ 4mσ3
(7)
In the case of a strong friction one can neglect the first inertial term in Eq. (7) and
the solution of the remaining equation is σ 2 = ( / 2mω0 ) 1 − exp(−4mω02t / b)
[11]. It describes the relaxation of an initially excited oscillator to the ground state.
In the case of a free dissipative quantum particle ( ω0 = 0 ) this solution reduces to
a known sub-diffusive law σ 2 =
t / mb [11].
Equation (7) describes a dissipative quantum oscillator at zero temperature.
In the case of a finite temperature the following thermal dissipative Ermakov
equation is obtained [9]
186
mσ + bσ + mω02 σ = 2∂ β (1/ σ)b +
2
/ 4mσ3
(8)
where β = 1/ k BT and the subscript b indicates that the differentiation on β is
carried out at constant friction coefficient. This equation reduces to Eq. (7) at
T → 0 and its equilibrium solution σ∞2 = ( / 2mω0 ) coth(β ω0 / 2) corre-
sponds to the well-known expression from the quantum statistical thermodynamics. However, in the classical limit Eq. (8) differs from a well-known result. In the
case of thermo-quantum diffusion Eq. (6) can be generalized to [12]
β
m∂ tV + mV ∂ xV + bV + mω02 x = −∂ x (ln ρ + ∫ Qd β)b / β
(9)
0
Substituting here the expressions for ρ and V yields another Ermakov-like equation which provides the correct classical limit
β
mσ + bσ + mω02 σ = [1/ σ + σ ∫ (
0
2
/ 4mσ 4 )b d β] / β
(10)
The equilibrium solution of Eq. (10) is again σ∞2 = ( / 2mω0 ) coth(β ω0 / 2) .
In the high temperature limit both equations (8) and (10) reduces to
mσ + bσ + mω02 σ = k BT / σ +
2
/ 4mσ3
(11)
The equilibrium solution of Eq. (11) σ∞2 = [ 1 + (β ω0 ) 2 + 1] / 2β mω02 provides
the correct limits at low and high temperatures. This thermal dissipative Ermakov
equation is solved in the case of strong friction, where the first inertial term is
neglected [13].
Finally, the Ermakov equation allows exploring other dissipative models in
quantum mechanics. For instance, one can add in Eq. (5) a jerk term, heuristically
corresponding to the Abraham-Lorentz force [14], to obtain
mσ − r σ + mω02 σ =
2
/ 4mσ3
(12)
where r = e 2 / 6πε 0 c 3 , e is the particle charge and c is the speed of light. Thus,
Eq. (12) describes a charged quantum harmonic oscillator dissipating energy via
electromagnetic radiation.
187
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Ermakov, V. P. Univ. Izv. (Kiev), 20, 1880, 1.
Leach, P.G.L. and K. Andriopoulos. Appl. Anal. Discrete Math., 2 2008, 146.
Haas, F. Phys. Scr., 81, 2010 025004.
Nassar, A. B. Phys. Rev., 32, 1985, 1986 Phys. Rev., 33 1986, 4433.
Schuch, D. SIGMA, 4, 2008, 043.
Madelung, E. Z. Phys., 40, 1927, 322.
Pinney, E. Proc. Am. Math. Soc., 1, 1950, 681.
Nassar, A. B. J. Phys. A: Math. Gen., 18, 1985, L509.
Tsekov, R. and G.N. Vayssilov. Chem. Phys. Lett., 195, 1992, 423.
Nassar, A. B. J. Math. Phys., 27, 1986, 755.
Tsekov, R. Int. J. Theor. Phys., 48, 2009, 630.
Tsekov, R. Int. J. Theor. Phys., 48, 2009, 85.
Messer, J.A. GEB Univ. Giessen, 2008, 6328.
Abraham, M. Theorie der Elektrizität (Leipzig: Teubner), 1905.
188
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
PRELIMINARY TEST OF MODIFIED TiO2 PHOTOCATALYSTS IN
GAS-PHASE
MARCO KOSTADINOV1,2, GIANLUCA LI PUMA1, CECO DUSHKIN2
Photocatalysis & Photoreaction Engineering, Department of Chemical and Environmental
Engineering, The University of Nottingham, Nottingham NG7 2RD, United Kingdom
2
University of Sofia, Faculty of Chemistry, Department of General and Inorganic Chemistry,
Laboratory of Nanoparticle Science and Technology, 1 James Bourchier blvd., Sofia 1164, Bulgaria
1
Abstract: Vanadium and nitrogen doped TiO2 catalysts are synthesized and their
photocatalytic activity for destruction of trichloroethylene in gas-phase is tested for the
first time in a flat-plate flow-through reactor.
Keywords: photocatalysis, gas-phase, TiO2, V and N doped
INTRODUCTION
The titanium dioxide has been extensively investigated as a photocatalyst for
water and air purification. However, due to its wide band-gap, only ultraviolet light
(λ<390 nm) can be utilized to induce electrons and holes, which subsequently take
part in the destruction of pollutants. For the process to be more efficient and economical, the photocatalyst should be active in the visible region light, thus making use of
a greater part of the solar spectrum. One approach to achieve band-gap narrowing is
doping of TiO2 with transition metals ions such as V, Cr, Fe, etc. [1]. The transitionmetal-ion energy levels are positioned slightly below the lower edge of the conduction
band of TiO2. Another approach is to dope titania with anions of p-elements, such as
N, S, F [2–5]. Their energy levels are located slightly above the upper edge of the
valence band of TiO2. The photocatalyst can also be modified with both p- and d-ions
189
[6–8]. The prevailing number of papers in the literature deals with photocatalysis in
aqueous phase [1–3,7,8], whereas a few authors report results in gas phase [4–6].
Here, the photocatalytic action of TiO2 doped with V, N, and both V and N
for destructing trichloroethylene in gas phase is investigated in a flat-plate flowthrough reactor using UV and visible light. The sophisticated experiments show
noticeable activity of doped photocatalysts in the UV-light region only.
EXPERIMENTAL
Titanium tetraisopropoxide (Aldrich) was used as precursor for TiO2. Doping with V was made with vanadylacetylacetonate, VO(acac)2, (Aldrich); triethylamine (Aldrich) was used as a source of nitrogen.
100 mL bidistilled water (Millipore) was transferred in a two-neck round-bottom
flask and H2SO4 was added to adjust pH to 2. Above the flask, an additional funnel
with a pressure equilibration tube was attached and Ti(OCH(CH3)2)4 was added in
the funnel. Then the precursor was added to the aqueous phase at a rate of about 1
mL/min. In the synthesis of V-doped photocatalyst, VO(acac)2 was dissolved in the
isopropoxide prior to the addition to the aqueous phase. The amount of V was 1% mol/
mol of that of Ti. The molar ratio H2O:Ti was approximately 56 times greater than the
stoichiometric one [9]. The mixture was kept at room temperature and under vigorous
stirring. When nitrogen was to be included as dopant, triethylamine was added in excess [2] two hours after the isopropoxide, N:Ti ratio being 2:1. Several hours later the
mixture was divided; one part was kept in the flask, the other one was put in a PTFE
autoclave and was hydrothermally treated at 137 °C for 24 hours [9]. Then the samples
were centrifuged and subsequently washed or they were evaporated, respectively, and
dry photocatalysts were obtained. They were calcined either at 400 °C for 1 hour or
just heated to 400 °C (for the hydrothermally treated samples) to burn out the remaining organic matter. Finally, the samples were ground in a mortar.
The photocatalyst powders were suspended in ethanol, sonicated for 1 hour
and supported on glass slides via drop-coating.
The activities photocatalytic films were valuated by measuring the rate of
decomposition of trichloroethylene (TCE) (Fisher, for analysis, > 99.8%), in air
in the presence of water vapor. The experiments were carried out in a narrow slit,
flat-plate, single-pass, flow-through photocatalytic reactor. The reactor set-up has
been described in detail elsewhere [10, 11].
Dry compressed air (BOC gases) was divided in three streams, one stream
passing through a Drechsel bottle containing ultrapure water for saturating the
stream with water vapor, the second stream passing through a gas washing Drechsel bottle to carry out the pollutant. These two streams were reunited to the third
stream and fed to the reactor. The humidity and TCE concentration were adjusted
by controlling the flowrates of these three streams, by means of electronic mass
flow controllers (Cole Parmer). The experiments were conducted in the reaction
190
controlled regime, using a total gas flow rate of 1.23 l/min, relative humidity
6.5%, initial concentration of TCE of 15 μM. The reactor was illuminated through
a pyrex glass window (T%≈86%). Five fluorescent lamps (Philips TL 8W/08
F8T5/BLB, 1.2 W UV-A output, λmax≈365-370 nm) were used as the source of UV
irradiation. Five halophosphor fluorescent lamps (Sylvania, 8W, F8W/154 Daylight, λmax1≈405 nm, λmax2≈440 nm, λmax3≈545 nm, λmax4≈580 nm) were used as the
source of visible light, λ∈(390÷680 nm). Both lamps have identical input power
and dimensions (0.0155 m bulb diameter, 0.26 m effective bulb length). The pollutant concentration was monitored through GC-FID (Agilent Technologies, GC6890N equipped with a Flame Ionization Detector (250°C), with helium as the
carrier gas, and fitted with a GS-GASPRO capillary column, 30m and 0.32mm
i.d.). The reactor outlet gas samples were injected at 200°C through an automatic
sampling system. The reactor outlet stream was vented to the atmosphere.
The conversion of TCE was calculated from the reactor outlet GC signal for TCE
at steady state, in the absence and in the presence of irradiation. The as-prepared photocatalysts were compared with the commercial photocatalyst Degussa P25.
Figure 1 shows the XRD diagram of TiO2 Degussa P25 and selected photocatalysts samples. All of the synthesized photocatalysts are of anatase crystalline
structure, whereas P25 consists of both anatase and rutile phases. No other phases
were formed as a result of the presence of the dopants.
Fig. 1. XRD diagrams for Degussa P25 and TiO2 doped with: 1%V/N; 1%V; N.
Figure 2 shows the conversion of TCE with time for P25 under UV light illumination. Figure 3 presents the data for the TCE destruction with time for TiO2 doped
with N under UV and visible light illumination. The maximum TCE conversion for
191
several catalysts under UV illumination is presented in Table 1. It is clear that, under
the conditions of the experiment, all of the synthesized samples performed worse than
the commercial material. No activity under visible light irradiation was detected in our
experiment. Joung et al. [4] and Li et al. [5] have also reported visible light driven photocatalytic destruction of TCE in gas-phase, the former using N-doped TiO2 with ammonia
as source of nitrogen, and the latter using N and N-F doped TiO2 with urea and NH4F as
dopant precursors. It should be pointed out that they used recirculation reactor systems.
For the overall low rates of the photocatalytic processes under visible light, this could be
an important factor as in the flow-through reactor type the residence time of the pollutant
could not be enough for the degradation to be detected. However, this should not be the
case when UV light is utilized. This suggests that, in our experiment, either the synthesis
procedure has to be improved, or the conditions of photocatalytic experiments have to
be optimized, or the reason is a combination of factors.
Fig. 2. Conversion of TCE under UV irradiation with Degussa P25 as photocatalyst.
Fig. 3. Conversion of TCE with TiO2/N as photocatalyst.
192
Table 1. Maximum conversion of TCE for different photocatalysts.
Catalyst
P25
N
1%V
2%V
1%V/N
TCE conversion, UV light (%)
~15
~9
~1.5
~1.5
~1.5
Acknowledgements. The financial support from NATO (Project CBP.EAP.SFPP 982835) and
project DO02-252 of the National Science Fund of Bulgaria (NSFB) is gratefully acknowledged. M.
Kostadinov is grateful to the Researcher Exchange Programme of the British Council for the visiting grant to the University of Nottingham. C. Dushkin is thankful to projects TK-X-1702-07 and
UNION DO02-82 of NSFB.
REFERENCES
1. Wu, J.C.-S., C.-H. Chen. J. Photochem. Photobiol. A, 163, 2004, 509.
2. Burda. C., Y. Lou, X. Chen, A. Samia, J. Stout, J. Gole. Nanolett., 3, 2003, 1049.
3. Cong, Y., J. Zhang, F. Chen, M. Anpo. J. Phys. Chem. C, 111, 2007, 6976.
4. Joung, S.-K., T. Amemiya, M. Murabayashi, K. Itoh. Appl. Catal. A, 312, 2006, 20.
5. Li, D., H. Haneda, S. Hishita, N. Ohashi. Mater. Sci. Eng., 117, 2005, 67.
6. Yang, X., C. Cao, K. Hohn, L. Erickson, R. Maghirang, D. Hamal. K. Klabunde. J. Catal., 252,
2007, 296.
7. Cong, Y., J. Zhang, F. Chen, M. Anpo, D. He. J. Phys. Chem. C, 111, 2007, 10618.
8. Gu, D.-E., B.-C. Yang, Y.-D. Hu. Catal. Commun., 9, 2008, 1472.
9. Wang, C.-C., J. Ying. Chem. Mater., 11, 1999, 3113.
10. Salvado-Estivill, I., D. M. Hargreaves, G. Li Puma. Env. Sci. Technol., 41, 2007, 2028.
11. Puddu, V., R. Mokaya, G. Li Puma. Chem. Comm., 45, 2007, 4749.
193
194
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
INTERACTION OF HYDROPHOBIC IONS WITH LANGMUIR
MONOLAYERS WITH OPPOSITE DIPOLE MOMENTS OF THE
HYDROPHILIC HEADS
JORDAN G. PETROV,1* TONYA D. ANDREEVA1, AND HELMUTH MOEHWALD2
1) Institute of biophysics of the Bulgarian Academy of Sciences
1 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
2) Max-Planck Institue of Colloids and Interfaces, D-14476 Golm/Potsdam, Germany
*) Corresponding author, E-mail: [email protected]
Abstract. We investigate the interaction of the hydrophobic tetraphenylborate
anion (TPhB–) and tetraphenylphosphonate cation (TPhP+) with Langmuir monolayers
having positive and negative dipoles in the hydrophilic heads. The latter are created via
fluorination of the terminal CH3 groups of docosyl ethyl ester and docosyl N-ethyl amide.
Surface pressure/area and surface potential/area isotherms on pure water are compared
with those for subsolutions containing TPhB– or TPhP+. Small shifts of ΔVmax(H2O) at
maximum density of the films are found. As compared to the DPPC monolayers their
values are 4.1 times smaller for the ethyl amide and 9.5 times smaller for the ethyl ester
monolayer, which as DPPC show positive surface potentials on water. The negative dipoles
of the fluorinated FED heads do not reverse the specificity of the anion-cation interaction
of TPhB− and TPhP+ as predicted by the theory.
A non-electrostatic adsorption of both TPhB− and TPhP+ is registered for the ethyl
ester and DPPC monolayers, bearing CH3 terminals of the hydrophilic heads, but not for
the N-ethyl amide films having the same CH3 end groups. This observation suggests that
hydrophobic attraction between the CH3 terminals and the phenyl ligands causes the nonelectrostatic adsorption of both ions at ED and DPPC films, but the network of NH…O=C
hydrogen bonds of EA monolayers hampers this effect.
The surprising decrease of the positive values of ΔVmax(H2O) of the ED and DPPC
monolayers caused by adsorption of the cation TPhP+, is ascribed to its chaotropic action
195
destroying the hydration structure of the polar heads and eliminating (reducing) the
contribution of oriented water dipoles to ΔVmax.
Keywords: Langmuir monolayers, Hydrophobic ions, Surface potential, Fluorinated
amphiphiles, Phospholipids.
INTRODUCTION
The hydrophobic ions are charged organic molecules which specifically interact with native and model membranes. It has been found that the anions adsorb
much stronger and traverse the membrane much faster than the cations with the
same charge and similar structure [1–3]. This specificity is ascribed to the positively oriented dipoles (plus sign inside) at the membrane surface [4]. The dipoleion interaction accelerates the transmembrane transport of the hydrophobic anions
but slows up the shipping of the cation. A decrease of the membrane dipole potential by 300 mV increases the rate of the anion traverse 100 000 times and slows
dawn the transport of the cation 1000 times [5].
In this paper we investigate the interaction of a couple of structurally similar
hydrophobic anion and cation with Langmuir films with positive and negative dipolar moments of the hydrophilic heads. The negative dipoles are created via fluorination of the CH3 terminals of the polar heads in a long chain ethyl ester and an
N-ethyl amide. The CF3 for CH3 substitution decreases the surface dipole potential
ΔV of the ethyl ester monolayer by 200% and yields a strongly negative ΔV value,
but increases the positive dipole potential in the N-ethyl amide films by 300%
retaining its positive sign [6,7]. One could expect that the corresponding dramatic
changes of the head-group dipole moments should significantly affect their interaction with hydrophobic ions, reversing the anion-cation specificity in the case of
trifluoroethylester, and increasing the adsorption of the anions at the monolayer/
solution boundary in the case of N-trifluoroethylamide. The ethyl docosanoate,
trifluoroethyl docosanoate, N-ethyldocosanamide, and N-trifluoroethyldocosanamide have the same С21Н43 straight chains and polar heads with similar size,
but both amide heads develop lateral networks via hydrogen bonds NH…O=C,
whereas the ethyl and trifluoroethyl ester heads do not form such bonds.
We chose to compare the interaction of the tetraphenylborate anion (TPhB–)
and tetraphenylphosphonate cation (TPhP+) with the above monolayers. They were
widely used to determine the dipole potential of lipid bilayers [4,8–11], because
of the same ligands, equal effective radii of 4.2 Å [12], and very close electrochemical properties [13, 14]. Their phenyl ligands (Figure 1a,b) simulate the hydrophobic core of such ion carriers as valinomicin and nonactin, which transport
inorganic ions through the hydrocarbon parts of the membranes. The K-nonactin
complex (Figure 1c,d) has four tetrahydrofuran nuclei forming a hydrophobic external core, which facilitates the transport of K+ ion through the membrane.
196
B
P+
(a)
(b)
(c)
(d)
−
Figure 1. Molecular models of: a) tetraphenylborate anion TPhB , b) tetraphenylphosphonium
cation TPhP+, c) nonactin, d) К+-nonactin complex.
The ion-film interaction was characterized through the difference between the
surface pressure/molecular area π/A and surface potential/molecular area ΔV/A
isotherms on pure water and aqueous solutions of TPhB–and TPhP+.
MATERIALS AND METHODS
The following lipids were used as model monolayer membranes with positive
and negative dipoles of their polar hydrophilic heads:
- Ethyl docosanoate (ЕD), CH3(CH2)19CH2C(=O)OCH2CH3
- Trifluoroethyl docosanoate (FED), CH3(CH2)19CH2C(=O)OCH2CF3
- N-Ethyldocosanamide (EA), CH3(CH2)19CH2C(=O)NHCH2CH3
- N-Trifluoroethyldocosanamide (FEA), CH3(CH2)19CH2C(=O)NHCH2CF3
- 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)
The FED, EA and FEA were synthesized at the Max-Planck Institute of
Colloids and Interfaces, Golm/Potsdam, Germany as described previously [6,7].
Synthetic ED with 99% purity and DPPC with 99% purity were purchased from
Sigma-Aldrich, Germany and used as received.
Tetraphenylphosphonium chloride (Aldrich, 98%) and sodiumtetraphenylborate (Fluka, ≥ 99.5%) were used without further purification. Mili-Q Millipore
water with specific receptivity of 18 MΩ was used for preparation of 1x10-4 M
ionic solutions. The monolayers were spread from 1х10-3 M chloroform solutions.
Five minutes were left for evaporation of CHCl3 before the films were compressed
at a speed of 2.2 Å2/molecule.min.
The π/А isotherms were recorded with a computer controlled Langmuir balance with a Teflon trough and Wilhelmy dynamometric system yielding sensitivity
of 0.2 mN/m. Each measurement was repeated 3-5 times until the molecular area at
given surface pressure coincided within 0.3 Å2/molecule. Parallel surface potential
isotherms ΔV/A were recorded using Kelvin’s vibrating plate method (at electrode
frequency of 150–200 Hz). The circular electrode with diameter of 5 mm was placed
1 mm above the aqueous phase, and ΔV was measured with resolution of 5 mV. The
liquid substrate was kept at 20.0 ± 0.1° C via temperature control system.
197
THEORETICAL BACKGROUND
The free energy change of interaction of a hydrophobic ion with a membrane
ΔG can be written as a sum of two electrical and one non-electrical terms [4,15]:
ΔG = ΔGB+I + ΔGD + ΔGN
(1)
ΔGB+I is the Born-Image free energy change of transfer of the hydrophobic
ion from the aqueous phase with dielectric permeability ε = 80 into the hydrocarbon interior of the membrane with ε = 2. It is proportional to the square of the
ionic charge q2, its radius r and the depth of its penetration into the membrane x, so
it is positive and the same for the cation TPhP+ and the anion TPhB− having q = 1
and r = 4.2 Å.
ΔG B − I (x ) =
q2
2rεhfhf
2
⎡
r
⎛ r ⎞⎛ x ⎞ ⎤
1
1
.
2
−
−
⎜ ⎟⎜ ⎟ ⎥
⎢
⎝ d ⎠⎝ d ⎠ ⎦⎥
⎣⎢ 2 x
(2)
The neutral energy ΔGN accounts for the hydrophobic interaction between the
ligands of the hydrophobic ions and the hydrocarbon interior of the membrane. It
strongly depends on the depth of ion penetration x, ion radius r, and the constant
ΔGN0 standing for ΔGN at x = 0 that has values between −4 and −8 kcal/mol. Since
ΔGN0 < 0, ΔGN is negative for each penetration x > 0, i. e. it facilitates the adsorption and penetration of both hydrophobic ions into the membrane.
ΔG N0
ΔG N (x ) =
1 + 10
10 − 2 x / r
(3)
The dipolar free energy change ΔGD accounts for the interaction between the
hydrophobic ion and the membrane dipoles and depends on the dipole moment μ
of the latter and the charge of the ion q:
ΔG D ( x ) =
qμ
L
ε ( x)
(4)
ε(х) is a dielectric function characterizing the transition region between the
aqueous solution and the hydrophobic interior of the membrane, L is a lattice
function of the 2D-dipole layer on its surface. Equation 4 shows that when μ and
q have opposite signs ΔGD < 0 and the hydrophobic ion and the membrane dipoles
attract each other. The same sign of the hydrophobic ion and membrane dipoles
yields ΔGD > 0 and electrostatic repulsion.
Interaction of the hydrophobic ions with monolayers with fluorinated and
non-fluorinated hydrophilic polar heads. Figure 2 presents the π/А and ΔV/А iso198
ΔV, mV
ΔV, mV
π, mN/m
π, mN/m
therms of ЕD and FED monolayers on pure water, 1х10-4 М TPhB– and 1х10-4
М TPhP+. The anion and cation cause practically equal shifts of the ED π/А isotherm on water to larger molecular areas, symptomatic of the same adsorption
or penetration into the film. The
50
350
collapse surface pressure πcol on
ED 300
water increases in the same extent,
40
demonstrating that both TPhP+ and
250
ΔV
TPhB– stabilize the ЕD monolayer
30
200
causing lateral repulsion. The effect
150
π
20
on the ΔV/А isotherms depends on
100
the density of the ЕD-monolayer.
10
50
For uncompressed films at A >
0
32
Å2 the ΔV/А plateaus for both
0
ions stay above the plateau for wa10
20
30
40
50
ter. After the sharp rise of ΔV the
20
50
anion causes a larger shift of the
0
15
surface potential than the cation,
-50
ΔV
but this relation changes when the
π
-100
10
ED-monolayer achieves maximum
-150
density and constant ΔVmax values.
-200
5
Under such conditions the effect of
FED -250
the cation TPhP+ on the surface po-300
0
tential is stronger than the effect of
-350
the anion TPhB–. This relationship
10
20
30
40
50
contradicts to eq. 4. Moreover, the
2
charging of the densest ED memA, Е /molecule
brane through adsorption of the
Figure 2. π/А and ΔV/А isotherms of ЕD
hydrophobic
ions is unexpected; the
monolayers (top) and FED films (bottom) on water
negatively
charged
TPhB– increases
(●), and aqueous solutions of the hydrophobic
the positive value of ΔVmax(H2O),
anion TPhB− (◊), and cation TPhP+ (∆).
and the positively charged TPhP+
decreases the positive ΔVmax(H2O) value.
The bottom panel of Figure 2 shows that TPhP+ and TPhB– do not displace
the π/А isotherms of the FED monolayer on water. This fact indicates a negligible
adsorption and penetration at/between the fluorinated polar heads. Nevertheless,
the cation TPhP+ increases the collapse surface pressure and stabilizes the FED
film, whereas the πcol values on water and TPhB– solution are the same. The ΔV/
А isotherms demonstrate that at the highest film density the cation TPhP+ does
not change ΔVmax(H2O), whereas the anion TPhB– increases the negative value of
ΔVmax(H2O). This result also contradicts the theory, because the dipole moments
of the FED monolayer μ < 0, the charge of the anion q < 0 and ΔGD > 0.
199
The effect of TPhP+ and TPhB– on ΔVmax(H2O) of the FED monolayer again
depends on its density. At 27 Å2/molecule one finds the following relationship of
the absolute values ⏐ΔV27TPhB–)⏐ > ⏐ΔV27TPhP+)⏐ > ⏐ΔV27(H2O)⏐. At the maximum film density before collapse one finds that⏐Vmax(TPhB–)⏐ > ⏐ΔVmax(TPhP+)⏐
= ⏐ΔVmax(H2O)⏐ (Table 1). As expected the adsorption of the anion TPhB– increases the negative value of ΔVmax(H2O) because of the negative charging of the
monolayer/solution boundary.
The effect of TPhP+ and TPhB– on ΔVmax(H2O) of the positive head-group
dipoles of EA again depends on the density of the films (Figure 3). At 48 Å2/molecule ΔV48(TPhB–) < ΔV48(H2O) < ΔV48(TPhP+), at 40 Å2 all three values match,
and at the maximum film density before collapse, ΔVmax(TPhB–) < ΔVmax(TPhP+)
= ΔVmax(H2O) (Table 1). The negative shift caused by the anion TPhB– is in qualitative agreement with eq. 4.
The impact of both hydrophobic ions on ΔVmax(H2O) of the fluorinated FEA is
smaller despite the almost five times higher ΔVmax(H2O) as compared to ΔVmax(H2O)
of the non-fluorinated amide (see Table 1). Below 30 Å2/molecule, where the films
are compact, the relationship ΔVmax(H2O) < ΔVmax(TPhP+) < ΔVmax(TPhB–) holds
up to the densest film packing. The absolute values of the shifts qualitatively follow the theory, but the adsorption of the negatively charged TPhB– increases the
positive value of ΔVmax(H2O).
Interaction of the hydrophobic ions with phospholipid monolayers. The influence of TPhP+ and TPhB– on the π/А and ΔV/А isotherms of DPPC monolayer is shown in Figure 4, confirming the previous literature data for these systems [16,17]. The π/A curve on water shows the well known phase transition
from liquid-expanded (LE) phase with chaotic chains to liquid-condensed (LC)
phase with closely packed zwiterionic heads and uniformly tilted closely packed
chains. The cation TPhP+ slightly shifts the low-pressure section of the steep part
of the isotherm to higher molecular area in contrast to the anion TPhB– which
considerably changes the region of the LE-LC phase transition. This difference
is probably due to the penetration of the TPhB– into the monolayer, caused by
the opposite signs of μ and q yielding a favorable negative dipolar term ΔGD <
0. The effect of TPhB– and TPhP+ on the ΔV/A isotherms again depends on the
density of the monolayer. At 90 Å2/molecule, where the surface pressure starts
rising, ΔV90(TPhB–) << ΔV90(H2O) < ΔV90(TPhP+). The same relationship holds
until the end of LE-LC phase transition, but changes below 50 Å2/molecule. At
42 Å2/molecule (dashed line) corresponding to maximal density before collapse
ΔVmax(TPhB–) << ΔVmax(TPhP+) < ΔVmax(H2O). Under such conditions TPhP+ also
decreases ΔVmax(H2O), but the effect of cation is 4.4 times larger than the one
of the anion. The fact that ΔVmax(TPhB–) << ΔVmax(TPhP+) qualitatively follows
the theory, because the DPPC heads have large μ > 0 and their interaction with
TPhB– , whose charge q < 0, yields large ΔGD < 0. The interaction of the DPPC
200
30
300
ΔV
10
200
π
100
0
0
π, mN/m
10
30
20
30
40
50
60
1200
FEA
ΔV
1000
800
20
600
10
ΔV, mV
20
π
400
ΔV, mV
π, mN/m
EA
200
0
0
10
20
30
40
50
Figure 3. π/А and ΔV/А isotherms of ЕA
(top) и FEA (bottom) monolayers on water
(●), and aqueous solutions of the hydrophobic anion TPhB− (◊), and cation TPhP+ (∆).
60
A, Е2/molecule
Table 1. Average surface potentials at maximum density of ED, FED, ЕA, FEA and DPPC
monolayers on water and TPhB− and TPhP+ solutions.
ED
Subphase
solution ΔVmax
mV
FED
EA
FEA
Δ(ΔVmax) ΔVmax Δ(ΔVmax) ΔVmax Δ(ΔVmax)
mV
mV
mV
mV
mV
ΔVmax
mV
DPPC
Δ(ΔVmax) ΔVmax Δ(ΔVmax)
mV
mV
mV
Water
+315
±8
−
-295
±5
−
+200
±12
−
+965
±42
−
1x10-4 M
TPhB-
+325
±4
+10
(3 %)
-310
±9
+15
(5 %)
+170
±15
-30
(15 %)
+1025
±20
+60
(6 %)
1x10-4 M
TPhP+
+290
±1
-25
(8 %)
-295
±3
0
+200
±7
0
+1000
±29
+35
(4 %)
+605
±10
+260
±2
+525
±5
−
−345
(57 %)
−80
(13 %)
heads with the cation TPhP+ is much weaker because μ > 0, q > 0, and ΔGD > 0.
Similar specificity was previously found also for DPPC leptosomes [18], but the
authors of this study assume a complex formation between TPhB− and the choline
group that adds to the electrostatic attraction.
Comparison of the effects for all systems studied. The effect of the hydrophobic ions on the maximum surface potentials of the investigated monolayers
201
700
50
600
40
30
500
π
400
300
20
200
10
ΔV, mV
π, mN/m
60
100
0
0
30 40 50 60 70 80 90 100 110 120
A, Е2/molecule
Figure 4. π/А and ΔV/А isotherms of DPPC monolayers on water (●) and TPhB− (◊) and
TPhP+ (∆) aqueous solutions. The dash line designates the molecular area and surface pressure at the
maximal density of the films.
is compared in Table 1, presenting the average of 3-5 values of ΔVmax, as well
as their scatter and the percentage of change ΔVmax(ion) − ΔVmax(H2O) from the
ΔVmax(H2O) value. The main result is that the magnitude of the shifts for the ED,
EA, FEA и DPPC films having positive ΔVmax(H2O) and μ values dramatically
differ. The shift ΔVmax(TPhB–) − ΔVmax(H2O) = −345 mV, caused by the adsorption and penetration of the anion at the DPPC film is six times larger and opposite
in sign as compared to the shift of +60 mV on TPhB– solution for the fluorinated
amide FEA in spite of the largest ΔVmax(H2O) of the latter. The shift caused by the
anion TPhB− on ΔVmax(H2O) of the ethyl ester monolayer has also opposite sign
but a 35 times smaller value as the shift for the DPPC film.
A non-electrostatic adsorption that is not accounted by the theory is found
for the cation TPhP+ which specifically interacts with the ED, FEA and DPPC
monolayers having positive value of ΔVmax(H2O). However, one observes that
positively charged cation decreases the positive ΔVmax(H2O) values of the ED and
DPPC films, but increases the ΔVmax(H2O) of the FEA monolayer. Similar unexpected direction of the observed shifts were found for the anion TPhB–, whose
adsorption on the ED and FEA monolayers increases the corresponding positive
values of ΔVmax(H2O).
The unusual signs of the Δ(ΔVmax(H2O)) shifts point to an additional effect that
overcompensates the charging of the monolayer/solution boundary caused by the
adsorption/penetration of the hydrophobic ions. We hypothesize that this could be
202
the chaotropic action of TPhP+ and TPhB– that (partially) destroys the hydration
structure of the polar heads and eliminates (reduces) its contribution to ΔVmax.
Our previous in situ investigation of the ЕD, FED, EA and FEA monolayers on
water via Grazing Incidence X-Ray Diffraction (GIXD) showed [19,20], that at maximum density they exist in the same S-phase with closely packed chains and the same
area per molecule. This similarity determines the same structural function L in eq
4. The dielectric functions ε(х) might differ but cannot change the sigh of ΔGN that
should be negative in all cases. However, due to the polycrystalline structure of the
ЕD, FED, EA and FEA monolayers the penetration of the large TPhB− and TPhP+ ions
is strongly delimited. This probably occurs along the “border lines” of the crystallites,
which are built up after spreading and form the uncompressed films.
CONCLUSIONS
The interaction of the hydrophobic ions TPhB− and TPhP+ with monolayers
of FED, ED, FEA and EA, whose polar heads have negative or positive dipole
moments, is weak and not always follows the theory. In spite of the huge range
(from −295 mV for FED to +965 mV for FEA) covered by their ΔVmax(H2O) values at maximum film density, the changes they cause vary from 10 to 60 mV. The
negative dipoles of the fluorinated FED heads do not reverse the specificity of the
anion-cation interaction of TPhB− and TPhP+ with this monolayer as the theory
predicts. The cation TPhP+ dos not change ΔVmax(H2O), the anion TPhB− adsorbs
causing a positive shift of +15 mV.
As found before the hydrophobic anion adsorbs at the zwiterionic heads of
DPPC much stronger as the cation; TPhB− reduces the positive ΔVmax(H2O) by
−345 mV, the shift caused by TPhP+ is −80 mV. Previous studies with DPPC liposomes [18] ascribe the predominant anion adsorption to steric reasons; TPhB−
easily approaches the terminal +N(CH3)3 groups of the zwiterionic heads, whereas
TPhP+ has to overcome a steric barrier of the latter in order to get closer to the
negatively charged РО4− groups.
The unusual signs of the Δ(ΔVmax(H2O)) shifts point to an additional effect that
overcompensates the charging of the monolayer/solution boundary caused by the
adsorption/penetration of the hydrophobic ions. We hypothesize that this could be
the chaotropic action of TPhP+ and TPhB– that (partially) destroys the hydration
structure of the polar heads and eliminates (reduces) its contribution to ΔVmax.
Acknowledgment. The authors appreciate the financial support of project NT-1-03 by the
National Science Fund of the Bulgarian Ministry of Education and Science. The Max-Planck
Institute of Colloids and Surfaces is acknowledged for the ΔV measurements.
REFERENCES
1.
2.
Liberman, E. A., V. P. Topaly. Biochim. Biophys. Acta, 163, 1968, 125.
Liberman, E. A., V. P. Topaly. Biophysics, 13, 1968, 1195.
203
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
LeBlanc, O. H. Biophys. J., 14, 1970, 2.
Flewelling, R. F., W. L. Hubbell. Biophys. J., 49, 1986, 541.
Andersen, O. S., A. Finkelstein, I. Katz, A. Cass. J. Gen. Physiol., 67, 1976, 749.
Petrov, J. G.; H. Möhwald. J. Phys. Chem., 100, 1996, 18458.
Petrov, J. G., E. E. Polymeropoulos, H. Möhwald. Langmuir, 23, 2007, 2623.
Andersen, O. S., M. Fuchs. Biophys. J., 15, 1975, 795.
Pickar, A. D., R. Benz. J. Membr. Biol., 44, 1978, 353.
Gawrisch, K., D. Ruston, J. Zimmerberg, V. A. Parsegian, R. P. Rand, N. Fuller. Biophys. J.,
61, 1992, 1213.
Franklin, J. C., D. S. Cafiso. Biophys. J., 65, 1993, 289.
Grunwald, E., G. Baughmen, G. Kohnstam. J. Am. Chem. Soc., 82, 1960, 5801.
Parker, A. J. Chem. Rev., 69, 1969, 1.
Popovych, O. CRC Crit. Rev. Anal. Chem., 1, 1970, 73.
Schamberger, J, R. J. Clarke. Biophys. J., 82, 2002, 3081.
Shapovalov, V. L. Russ. Chem. Buil., 45, 1996, 1611.
Shapovalov, V. L. Thin Solid Films, 327-329, 1998, 599.
Elena, J. F., R. N. Dominey, S. J. Archer, Zh. Ch. Xu, D. S. Cafiso. Biochemistry, 26, 1987, 4584.
Petrov, J. G., G. Brezesinski, N. Krasteva, H. Möhwald. Langmuir, 17, 2001, 4581.
Andreeva T. D., J. G. Petrov, G. Brezesinski, H. Möhwald. Langmuir, 24 (15), 2008, 8001.
Received on May 26, 2010
204
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
NANOMETER STRUCTURE OF BINARY LANGMUIR
MONOLAYERS WITH OPPOSITE DIPOLE MOMENTS OF THE
HYDROPHILIC HEADS
JORDAN G. PETROV,*,1 GERALD BREZESINSKI,2 TONYA D. ANDREEVA,1 AND
HELMUTH MOEHWALD2
1) Institute of biophysics of the Bulgarian Academy of Sciences
1 Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
2) Max-Planck Institute of Colloids and Interafces
D-14476 Golm/Potsdam, Germany
*) Corresponding author E-mail: [email protected]
Abstract. Langmuir monolayers of docosyl trifluororethyl ether (FEE) and docosyl
ethyl ether (EE) with the same CH3(CH2)21 hydrocarbon chains but fluorinated -O-CH2CF3,
respectively non-fluorinated -O-CH2CH3 polar heads, exhibit negative versus positive
dipole potentials and molecular dipole moments. The opposite dipoles of the FEE and
EE heads imply unusual behaviors of their mixtures, because the polar heads of almost
all natural amphiphiles have the same dipole orientation. Here we investigate the effect of
the head-head interactions between the FEE and EE heads on the phase state, miscibility,
and nanometer-scale structure of the FE-FEE binary films in uncompressed state after
spreading and in compressed state at 15 mN/m. Our Grazing Incidence X-Ray Diffraction
(GIXD) experiments show that the uncompressed films exist in L2’ and S solid phases
depending on composition, and only in the S-phase when the monolayers are compressed
to 15 mN/m. All areas per molecule determined via GIXD are determined by the hydrated
polar heads because they exceed the cross-section of the solid n-alkanes which do not have
polar terminals. The composition dependencies of the crystal lattice parameters point to
non-monotonous rotation of the all-trans -C-C-C- backbones with increasing of the FEE
molar fraction XFEE. The areas per molecule determined via GIXD at all compositions
205
exceed the cross-section of the solid n-alkanes without polar terminals, demonstrating
the determining role of the hydrated polar heads. The calculated coherence lengths show
that the crystalline domains of both the uncompressed and compressed monolayers
are elongated in direction towards nearest neighbors. Specific composition effects are
observed at XFEE = 0.8, where the GIXD area per molecule Axy matches the molecular
area Aπ determined in the Langmuir balance, but significantly exceeds the cross-section
of the long n-alkanes in 3D crystals. This fact again relates the observed specificity to the
interactions between the polar heads which are absent in the alkanes.
Keywords: Dipole-dipole interactions in Langmuir films, Mixed Langmuir
monolayers, Fluorinated amphiphiles.
INTRODUCTION
Multicomponent Langmuir monolayers are useful models of biomembranes
[1–5]. Films containing fluorinated components are particularly interesting because
of their medical, environmental, and industrial applications [6-8]. Here we investigate binary mixtures of docosyl ethyl ether C21H43CH2OCH2CН3 (EE) and docosyl
trifluoroethyl ether C21H43CH2OCH2CF3 (FEE), whose polar heads yield positive,
respectively negative molecular dipole moments in Langmuir films [9], and the same
hydrocarbon chains keep the van der Waals interaction independent on composition.
Since almost all polar heads of the natural and synthetic amphiphiles have positively
oriented dipoles in spread or adsorbed monolayers [10], the dipolar interactions between the EE and FEE heads are extremely unusual. On this basis one could expect
non-trivial molecular structure and phase behaviors of the EE-FEE binary films.
Although weaker as the ion-ion and dipole-ion interaction the dipole-dipole interaction might be significant in Langmuir monolayers. It was shown that about 40% of
the spreading surface pressure of phosphatidylcholine vesicles originates from dipolar
repulsion between the zwiterionic heads [11]. The dipolar interaction determines the
size and shape of the liquid domains in cholesterol-phospholipid mixtures [12], and
plays a crucial role in the polymorphism of solid monolayers [13].
Our previous paper [14] has shown that the EE monolayer on water forms
a crystal L2’ phase with tilted closely packed chains after spreading, whereas
the uncompressed FEE film organizes in a crystal S-phase with closely packed
upright chains, which do not change their organization under compression. In
contrast, the EE monolayer exhibits L2’−S solid phase transition at 10 mN/m
adopting the molecular structure of the FEE film. The features of the individual
substances suggest that the binary monolayers might separate in tilted and upright
solid phases at low surface pressures, but form isomorphic molecular mixtures
with upright closely packed chains at high surface pressures. Our recent analysis
of the surface pressure-molecular area isotherms showed a non-ideal miscibility and specific molecular interactions at particular compositions of the FEE-EE
films [15]. In the present study we perform Grazing Incidence X-Ray Diffraction
206
(GIXD) experiments in order to investigate the effect of the dipolar attractions on
the nanometer scale architecture of the FEE-EE binary films.
EXPERIMENTAL PART
C21H43CH2OCH2CН3 and C21H43CH2OCH2CF3 were synthesized and characterized at the Max-Planck Institute of Colloids and Interfaces as described in ref. 9.
Milimolar chloroform solutions of EE and FEE were mixed in particular ratios prier
to the experiment and the mixture was spread on Milli-Q-Millipore at molecular area
of ca. 70 Å2/molecule. After five minutes left for evaporation of the solvent the films
were compressed at 2.2 Å2/molecule.min. The GIXD experiments were performed
at fixed surface pressures automatically kept constant during the measurement by a
computerized Langmuir balance. The temperature of the water substrate in the Teflon
trough was maintained at 20.0 ± 0.1°C by a temperature control system.
The nanometer scale structure of the binary films was studied on the liquid
surface diffractometer at the undulator beam line BW1, at HASYLAB, DESY in
Hamburg, Germany. The phase state was determined from the number and position of the diffraction peaks [16]. A hexagonal LS phase consisting of upright molecules yields a single trifold-degenerate peak. The orthorhombic crystal phases
with tilted chains, L2’, L2”, and upright chains, S, CS, show two peaks, a nondegenerate Qn and a two-fold degenerate Qd one. The orientation of the chains is
determined from the vertical components Qz of the scattering vector. The LS, S
and CS phases are characterized by Qzn = Qzd = 0, the L2’ and L2” have at least one
non-zero Qz coordinate. A tilt to the next-neighbors (NN) yields Qzn = 0 and Qzd > 0,
the one to the next-nearest-neighbors (NNN) gives Qzn > 0 and Qzd > 0.
The positions of the maxima of the horizontal component of the scattering vector Qxy yield the repeat distances dhk = 2π/Qxyhk at given Miller indices h,k, and the
parameters of the primitive unit cell a, b, c, α, β, γ of the monolayer crystal lattice.
The orthorhombic (centered rectangular) lattice discussed latter is better described
by the distances between the nearest neighbors ar = a, the next-nearest neighbors
br = 2bcos(γ-90o), and the area per molecule at the water surface Axy = arbr/2.
For the NNN azimuth the tilt angle of the chains from the surface normal is determined from the formula τ = arctan(Qzn / Qxyn). When comparing the packing of
tilted and upright phases one uses the reciprocal lattice that is normal to the long
chain axes, because it removes the effect of the tilt. The reciprocal unit cell lattice
parameters are ar,n = ar, br,n = brcosτ, A0 = Axycosτ.
The full width at half maximum intensity (FWHM) of the horizontal peak
ΔQxy gives the coherent length ζ = 1.8π/ΔQxyhk characterizing the mean dimension
of the crystalline domains in a polycrystalline films [16]. The intrinsic FWHM
used to calculate ζ is obtained from the measured FWHM and the instrumental
resolution (ΔQxy)2 = (ΔQxy,msd)2 – (ΔQxy,ins)2. When ΔQxy{11} is used one obtains
ζ11 representing the average dimension of the crystalline domains in direction to207
wards the nearest neighbors, whereas ΔQxy{02} yields the average dimension ζ02
in direction next-nearest neighbors.
Surface pressure/molecular area isotherms π/A at different composition of the binary films. Figure 1 presents several π/A isotherms illustrating the changes caused by
increasing of the molar fraction XFEE of the fluorinated ether. Our previous study [15]
has shown that the isotherms of the films with composition ХFEE ≤ 0.3 have kinks at πt,
typical for a solid-solid phase transition from tilted to upright closely packed chains. The
monolayers with ХFEE > 0.3 do not show such kinks, suggesting that they are organized
in a solid phase with upright chains in the whole range between π ≈ 0 and the collapse
surface pressure. This conclusion was supported by BAM images, demonstrating that
films with ХFEE ≤ 0.3 exhibit optical anisotropy at low surface pressure and isotropic
behaviors at high surface pressure. The monolayers compressed above πt are optically
isotropic at all compositions. The above findings determine the conditions of the present
GIXD study. They correspond to uncompressed monolayers at π = 0.2–0.3 mN/m and
A = 23 –25 Ǻ2, and compressed films at π = 15 mN/m (the dashed line).
60
π, mN/m
50
0.0
0.2
0.5
0.7
1.0
40
30
20
10
πt
0
18 21 24 18 21 24 18 21 24 18 21 24 18 21 24
A, Е2/molecule
Figure 1. Isotherms surface pressure / molecular area π/A of binary EE-FEE films with different
molar fractions of FEE indicated in the plot. The dash lines denote an uncompressed state at
π = 0.2–0.3 mN/m, A = 23-25 Ǻ2, and compressed state at π = 15 mN/m.
GIXD analyses of the phase state and molecular structure of the binary films.
Figure 2 shows the contour plots of the diffraction for the uncompressed and compressed films which present the peak intensity as a function of the horizontal QXY
and vertical QZ coordinates of the scattering vector. The top left-side panel holds
for uncompressed films with 0 ≤ XFEE < 0.5, the bottom left-side panel stands for
uncompressed monolayers with XFEE ≥ 0.5. The right-side panels hold for compressed monolayers with 0 ≤ XFEE ≤ 1.0 at 15 mN/m.
Only two peaks, whose positions are characteristic for the crystal L2’and
S-phases having orthorhombic lattices, were found at all compositions for both
208
0.2 - 0. 3 mN/m
15 m N/m
XF EE = 0.3
L2’- phase
S- phase
XF EE = 0.5
XF EE = 0.5
S- phase
S- phase
Qx, cm–1
Q,xycm
-1
xy
QQ,
, cm–1
x cm
-1
XF EE = 0.3
Qz, cm
-1
Qz, cm
-1
Figure 2. Contour plots of the diffraction peak intensity versus the coordinates of the horizontal QXY
and vertical QZ scattering vector. Left: uncompressed films at 0.2 - 0.3 mN/m; left top holds for 0
≤ XFEE ≤ 0.3, left bottom for XFEE ≥ 0.5. Right: compressed films at 15 mN/m - the position of the
peaks is the same for 0 ≤ XFEE ≤ 1.0.
uncompressed and compressed states. This fact shows a phase independent complete miscibility. The chains in the uncompressed L2’ phase are tilted towards
the next-nearest neighbours at 0 ≤ XFEE < 0.5, but upright at XFEE > 0.5. The films
compressed to 15 mN/m are organized in the same S-phase with upright closely
packed chains at all compositions (see the inserts).
Figure 3a shows that at π = 0.2 mN/m the tilt angle τ of the chains from the
surface normal decreases linearly with increasing XFEE and vanishes for XFEE ≥
0.5. Above this molar fraction the uncompressed monolayers exist in S-phase. At
15 mN/m the chains are upright for 0 ≤ XFEE < 1.0. For the L2’ phase the area per
chain on the water surface AXY decreases with increasing XFEE and levels out to a
plateau at XFEE ≥ 0.5 (Figure 3b). The plateau values at 0.2 and 15 mN/m differ by
less then 0.1 Ǻ2, but exceed by 0.7 Ǻ2 the cross-section AHC of the long n-alkanes
in 3D crystals. Since the latter do not have polar terminals we conclude that the hydrated polar heads or gauche defects in the adjacent sections of the chains, which
cannot be registered via GIXD, determine the values of AXY. Figure 3c shows
that the composition dependencies of the chain cross-section A0 = Axycosτ, which
209
30
ar = ar,n, Å
Е2
25
τ, degree
5.03
a
20
15
10
5
5.00
8.4
0.0 0.2 0.4 0.6 0.8 1.0
8.2
br Å
Е
21
Axy, Å
Е22
5.01
4.99
0,0 0,2 0,4 0,6 0,8 1,0
b
20
19
b
8.0
7.8
7.6
AHC
18
5.02
a
0
22
0.2 mN/m
15 mN/m
7.4
0,0 0,2 0,4 0,6 0,8 1,0
19,4
0.0 0.2 0.4 0.6 0.8 1.0
7.75
c
c
7.70
br, n, Å
Е
Å22
A0, Е
19,3
19,2
19,1
19,0
7.60
0,0 0,2 0,4 0,6 0,8 1,0
XFEE
Figure 3.
7.65
7.55
0.0 0.2 0.4 0.6 0.8 1.0
XFEE
Figure 4.
Figure 3. Composition dependences of the lattice characteristics for uncompressed monolayers
(squares) and compressed films (circles). a) tilt angle τ of the chains from the surface normal,
b) GIXD area per molecule on the water surface AXY, c) cross-section of the chains A0 normal
to their long axis which is independent on the tilt.
Figure 4. Composition dependence of the distances between the nearest ar and next-nearest
neighbors br in the horizontal crystal lattice (Fig. 4a,b). The variation of the parameters of the
reciprocal lattice ar,n and br,n with XFEE is shown in Fig. 4a,c.
does not depend on the tilt, exhibits small but detectable via GIXD maxima. At
0.2 mN/m they display two maxima at XFEE = 0.1 and 0.8, at 15 mN/m they show
210
only one maximum at XFEE = 0.8. Such extrema reflect conformation of the heads
which causes specific orientation, respectively interaction of their dipoles.
The unit cell parameters of the rectangular lattice ar and br and those of the
reciprocal lattice normal to the chains ar,n and br,n are presented in Figure 4 as a function of XFEE. Increasing the surface pressure from 0.2 mN/m to 15 mN/m enlarges
the distance ar = ar,n between the nearest neighbors, and shortens the distances br and
br,n between the next-nearest neighbors. The longer side of the unit cell br decreases
up to XFEE = 0.5 due to erection of the chains during the continuous L2’-S transition
occurring at 0.2 mN/m, and levels out in the S-phase at XFEE ≥ 0.5 (Fig. 4b). The ar,n/
XFEE and br,n/XFEE dependencies (Fig. 4a,c) have opposite curvatures which point to a
non-monotonous rotation of the all-trans -C-C-C- backbones with composition.
Figure 5 presents the composition dependence of the coherence lengths of the
crystalline domains in directions toward the nearest neighbors ζ11, respectively
next-nearest neighbors ζ02. The crystalline domains in both uncompressed and
compressed states are elongated in direction towards nearest neighbors. In the
uncompressed films their larger dimension varies between 445 and 1370 Ǻ, the
smaller one changes between 165 and 750 Ǻ. Compression to 15 mN/m improves
the crystalline order in both directions, increasing ζ11 and ζ02 up to, and above the
maximum values of the uncompressed monolayers.
The top panel ζ / XFEE dependencies can be qualitatively explained via dipolar
interactions of the EE and FEE heads. The number of the EE-FEE pairs increases
and their dipolar attraction rises up to XFEE = 0.5 and falls down above this molar
fraction. The number of EE-EE and FEE-FEE couples experiencing dipolar repulsion reaches minimum at XFEE = 0.5, so that the sum of all dipolar interactions
becomes most favorable for the crystalline order at this composition. Since the
above interactions depend on the orientation of the molecular dipoles they could
be responsible also for the observed anisotropy of the coherence lengths. The
maxima at XFEE = 0.2-0.3 and 0.8 of the ζ02 / XFEE dependence of the compressed
films (Figure 5b) demonstrate structural effects resulting from specific conformations of the head-groups, which improve the dipolar attraction.
Similar specificity was observed in the composition dependence of the mean
molecular area Aπ/XFEE obtained from the isotherms [16]. Figure 6 compares the Aπ/
XFEE and Axy/XFEE curves recorded at 15 mN/m. The molecular area measured in the
Langmuir trough strongly decreases above XFEE = 0.5, reaching a deep minimum at
XFEE = 0.8. In contrast Axy slightly rises above XFEE > 0.5 also reaching a week maximum at the same composition (c. Fig. 3c). The values of Aπ and Axy at the extrema
match, demonstrating that a limiting density of the upright solid S-phase is achieved
at XFEE = 0.8. The fact that even this limiting molecular area significantly exceeds
the cross-section AHC of the long n-alkanes in 3D crystals means that the above effect of the composition is due to specific reorganization of the head groups region.
However, this part of the binary films is “invisible” for the GIXD technique and
shall be investigated via IR reflection-adsorption spectrometry in our next paper.
211
2000
CONCLUSIONS
Coherence
Е
Coherence
length,length,
Å
1. Only two peaks, characteristic for
the centred rectangular crystal lattice of
1500
the L2’or S-phase, were found for both
uncompressed and compressed films at
1000
all compositions. This fact demonstrates
complete miscibility independent of the
phase state of the mixtures. The uncom500
pressed films with 0 ≤ XFEE < 0.5 have
closely packed chains tilted towards next0
nearest neighbors; those with XFEE ≥ 0.5
0.0 0.2 0.4 0.6 0.8 1.0
have upright closely packed chains. The
2000
compressed monolayers are organized in
ζ11
15 mN/m
the crystal S-phase with upright closely
ζ02
packed chains at all compositions.
1500
resolution limmited
2. The composition dependencies of
the rectangular unit cell parameters of
1000
the reciprocal lattice ar,n/XFEE and br,n/XFEE
have opposite curvature, which indicate
500
rotation of the all-trans -C-C-C- backbones. Since the hydrocarbon part of the
mixtures does not change with composi0
0.0 0.2 0.4 0.6 0.8 1.0
tion (EE and FEE have the same chains)
the rotation should be related to variation
XFEE
of the number and orientation of the posiFigure 5. Composition dependences of the tive and negative head-group dipoles.
coherence lengths ζ11 and ζ02 representing the
3. The cross-section of the chains
average dimensions of the crystalline domains
A0 = Axycosτ, which does not depend on
in directions toward the nearest neighbors,
the tilt, exhibits week but measurable via
respectively next-nearest neighbors.
GIXD maxima; at XFEE = 0.1 and 0.8 for
the uncompressed, and at XFEE = 0.8 for
the compressed state. These extrema reflect specific interactions of the head-group
dipoles caused by changes of their conformation at particular compositions.
4. Both the uncompressed and compressed mixtures have longer coherence
lengths towards nearest neighbors, showing that the crystalline domains are elongated in this direction. The longer dimension of the uncompressed domains varies
between 445 and 1370 Ǻ, the shorter one - between 165 and 750 Ǻ. Compression
of the films to 15 mN/m improves the crystalline order, increasing both coherent
lengths to the maximum values of the uncompressed monolayers, and at particular
compositions even above them.
212
ζ11
ζ02
0.2 mN/m
2
A , Axy, Å
Е2
π
20,5
20,0
Aπ
19,5
Axy
19,0
18,5
AHC
0,0
0,2
0,4
0,6
XFEE
0,8
1,0
Figure 6. Comparison of the composition dependence of the
molecular area recorded via Langmuir balance Aπ/XFEE at 15
mN/m and the corresponding Axy/XFEE dependence obtained via
GIXD.
5. The composition dependence of the molecular area recorded via Langmuir
balance Aπ/XFEE is much stronger then the corresponding dependence Axy/XFEE obtained via GIXD. The value of Aπ strongly decreases at XFEE > 0.5, reaching a
deep minimum at XFEE = 0.8, whereas Axy slightly goes up above XFEE > 0.5 and
achieves week maximum at the same composition. The values of Aπ and Axy at the
extrema are equal showing that the compressed mixtures achieve highest density
at XFEE = 0.8. Since the cross-section of all-trans n-alkanes in 3D crystals, which
do not have polar heads, is below Aπ = Axy we conclude that the above extrema are
due to specific changes of the interactions of the head-group dipoles which affect
their cross-section.
Acknowledgment. The authors appreciate the financial support of project NT-1-03 by the National Science Fund of the Bulgarian Ministry of Education and Science. The Max-Planck Institute
of Colloids and Surfaces is acknowledged for the performance of the GIXD measurements.
213
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
214
Vanounou, S., A. H. Parola, I. Fishov. Molec. Microbiology, 49, 2003, 1067.
Heimburg, T., B. Angerstein, D. Marsh. Biophys. J., 76, 1999, 2575.
Sennato, S., F. Bordi, C. Cametti, C. Coluzza, A. Desideri, S. Rufini. J. Phys. Chem. B, 109,
2005, 15950.
Discher, B. M., W. R. Schief, V. Vogel, S. B. Hall. Biophys. J., 77, 1999, 2051.
Kuzmenko, I., H. Rapapport, K. Kjaer, J. Als-Nielsen, I. Weissbuch, M. Lahav, L. Leserowitz.
Chem. Rev., 101, 2001, 1659.
Gerber, F., M. P. Kraft, T. F. Vandamme, M. Goldmann, P. Fontaine. Angew. Chem. Int. Ed., 44,
2005, 2749.
Rontu, N., V. Vaida. J. Phys. Chem. C, 111, 2007, 9975.
Kissa, E., Marcel Dekker. – In: Fluorinated Surfactants: Synthesis, Properties, Applications.
New York, 1994.
Petrov, J. G., T. D. Andreeva, D. G. Kurth, H. Möhwald. J. Phys. Chem. B, 109, 2005, 14102.
Haydon, D. A., S. B. Hladky. Q. Rev. Biophys., 5, 1972, 187.
Panaiotov, I., Tz. Ivanova, A. Sanfeld. Adv. Colloid Interface Sci., 40, 1992, 147.
Kellner, S. L., H. M. McConnel. Phys. Rev. Lett., 82, 1999, 1602.
Roan, J.-R., T. Kawakatsu. J. Phys. Soc. Japan, 70, 2001, 738.
Petrov, J. G., G. Brezesinski, T. D. Andreeva, H. Möhwald. J. Phys. Chem. B, 108, 2004,
16154.
Petrov, J. G., T. D. Andreeva, H. Möhwald. Langmuir, 25, 2009, 3659.
Kaganer, V. M., H. Möhwald, P. Dutta. Rev. Modern Physics, 71, 1999, 779.
Kitaigorodsky, A. I. - In: Molecular Crystals and Molecules. New York and London, Academic
Press, 1973, 48.
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
ADDITIONAL CRYSTALLOGRAPHIC DATA ON
SOME METASTABLE CRYSTALLINE STATES OF TIN
S.K.PENEVA1, K.D.DJUNEVA1, N.S.NEYKOV2,
University of Sofia, Chemical Faculty, Department of Physical Chemistry,
University of Sofia, Chemical Faculty, Department of Applied Inorganic Chemistry,
1, James Bourcher Rd., Sofia 1126, Bulgaria
(e-mail address of S. K. Peneva – [email protected] )
1
2
Abstract. Metastable tin structures, designated as αin-Sn and βin-Sn , grown as small
particles by different reduction processes are investigated with transmission electron microscopy
and selected area electron diffraction (TEM with SAD) during long time of aging at room
temperature. The results are compared to the depth selective Mössbauer spectroscopy (DSMS)
and reflection high energy electron diffraction (RHEED) data registered from unheated and
heated vacuum evaporated thin 119Sn films. Series of cubic tin structures, αin-Sn close to α2-Sn,
and their structural transitions to βin-Sn, close to β2-Sn, and their transformations to other tin
structures during aging are described. Comparison of the electron diffraction results with the
DSMS data permits the identification of α3-Sn and its β3-Sn. Structural transitions of an αinSn to β-Sn and of a βin-Sn to γo-Sn are described. The data on different αin-Sn and βin-Sn are
expected to help further studies on the p / T diagram of tin.
Keywords. Sn / αj-Sn , βj-Sn / Electron diffraction/ Mössbauer effect /
1. INTRODUCTION
This report is a continuation of our efforts to gain additional crystallographic
information on some metastable structures of tin. These structures are detected
in thin tin films [1, 2] and are grown as small particles by different reduction
processes [3–6]. Some metastable tin states are found in other tin containing thin
215
films [7] and are observed to grow under the oxide crust of partially oxidized massive tin samples [8]. Information of these structures does not exist in the tin p /T
diagram [9, 10]. The growth conditions of thin tin films and small tin particles lead
to formation of metastable tin states which are expected to be stable at elevated
pressures /and temperatures/, according to the Oswald’s rule of stages [11].
Thin tin films: The results were obtained by depth selective Mössbauer spectroscopy (DSMS) and reflection high energy electron diffraction (RHEED) from
unheated and heated from 260 ºC to 600 ºC vacuum evaporated thin 119Sn films [1, 2,
12]. The DSMS data show unusually high values of the isomeric shifts δ explained
by participation of d electrons into the chemical bindings of the tin structures [1,2].
The tin structures were designated as αj-Sn, βj-Sn, (j = 1,2,3..), and γo-Sn:
– α1-Sn is the known α-Sn [13], 5-390. β-Sn [13], 4-637, was defined initially
as β1-Sn [1], but it appears that β1-Sn is to be a different structure.
– Each αj-Sn has a particular βj-Sn state.
– αj-Sn are considered as diamond cubic structures, isostructural to the known
α-Sn.
– the diamond cubic α2-Sn has lattice parameter a = 5.42 ± 0.06 Å and isomeric shift δ = + 4.4 ± 0.02 mm/s, (here and further relative to SnO2), [1,2]. Some
unheated 119Sn films can consist entirely of the diamond cubic α2-Sn, [2]. The
conditions for α2-Sn films growth are described in [14].
– β2-Sn is tetragonal with lattice parameters a = 5.42 Å and c = 4.95 Å and
with δ = + 5.2 ± 0.2 mm/s [2, 5]. It grows by heating of α2-Sn films up to 400°C.
– αj-Sn and βj -Sn with j ≥ 2 are with high values of the isomeric shifts.
– Crystallographic data of other αj-Sn and βj-Sn are not obtained by the thin
tin films studies. Part of the unusual isomeric shifts observed in heated 119Sn films
[2] remained unexplained by the hypothesis in [1].
– γo-Sn are several tin structures. They are treated as a tin / tin intermetallic
structures since theirs isomeric shifts are low, δ slightly more than + 1.0 mm/s.
Tin structures grown by different reduction processes: Conventional
Mössbauer spectroscopy, X-ray diffraction and TEM with SAD are used in the
studies of the metastable tin structures grown as small particles by different reduction processes [3-6].
Depending on the values of the isomeric shifts δ of the Mössbauer spectral
lines the metastable tin structures grown by a reduction process are defined as
α2-Sn-types and β-Sn-types [5]. α2-Sn-types and β-Sn-types are coexisting with
SnO2 in the reduction products of SnCl2 (or SnSO4) with Mg. The upper portion of
the reduction products of SnCl4 with NaBH4 contain α2-Sn-types, β-Sn-types and
SnO2, while the lower portion consists of SnO2 and β-Sn-types [6]. β-Sn-types,
SnO2 and a hint of α2-Sn- types are observed in the Mössbauer spectra of products
grown by reduction of SnCl2 with Al [4].
216
Mössbauer and XPS data registered from products of all investigated reduction processes show that their later oxidation in air observed during many months
of aging at room temperature, is to tetravalent tin oxides only [5,6]. The tetravalent oxides grown on the surfaces of many metastable tin structures, especially on
the surfaces of the α2-Sn-types, are amorphous.
The reduction products of SnCl2 with Mg are the most thoroughly investigated systems since they contain the largest amount of α2-Sn-types. The products are
referred to as products type-A when α2-Sn is the prevailing α2-Sn-type of structure
and products type-B (C) when the α2-Sn-types are other αj-Sn and βj-Sn states [5].
One cannot predict in advance the type of tin structures which will grow after a
particular reduction of SnCl2 with Mg.
The initial studies of the metastable tin states in the various reduction products reveal that the polycrystalline α2-Sn is no more with a diamond structure, [5].
An α2-Sn → β2-Sn structural transition is observed during aging of polycrystalline
α2-Sn, [5]. Some structural changes of β2-Sn during aging are also reported, [5].
The existence of some tin states, resembling, but different from the known β-Sn is
described in [4]. These structures are defined as “excited β-Sn”. The high resolution Mössbauer spectra registered from the reduction products of SnCl2 with Mg
[15] show different values of the isomeric shifts δ as compared to the values
observed during the thin tin films studies [2]. The only exception is the value of
δ of β2-Sn - δ = + 5.2 ± 0.2 mm/s. It is observed both in heated thin tin films
consisting of β2-Sn [2] and in the reduction products of SnCl2 with Mg [15].
Tin structures grown by heating of massive tin: Some metastable states
of tin grow under the oxide crust of partially oxidized at 800 – 950ºC massive
tin samples where the strain between the solid oxide crust and the molten tin
promotes their growth. α2-Sn, β2-Sn, the α2-Sn → β2-Sn structural transition and
a polycrystalline cubic tin structure resembling the polycrystalline α2-Sn, with
a = 5.72 Å, are observed by TEM with SAD and by X-ray diffraction, [8].
The present report includes some new crystallographic data on a number of
metastable tin structures and their structural transformations during aging. The
DSMS data registered from the surfaces and the depths of unheated and heated
α2-Sn films [2] are the guide for interpretation of the structural transformations of
α2-Sn micro-particles observed during aging of different reduction products.
2. EXPERIMENTAL DETAILS
The experimental conditions for the growth of tin micro-particles are described in [3,4,5,6]. 20% aqueous solutions of SnCl2 or SnCl4 or SnSO4 are reduced with Mg or Al. Solid SnCl4 is added to a 5% aqueous solution of NaBH4.
The samples were investigated by X-ray photoelectron spectroscopy (XPS)
[6], Mössbauer spectroscopy [3,4,5,6], X-ray diffraction [3,4,5] and TEM with
SAD [3,4,5]. There are ambiguities in the interpretation of the electron diffraction
217
results registered from tin products grown by using a metal as a reducing agent.
The last reduction products contain some chloride. The ambiguities are overcome
by analysis of the electron diffraction data obtained from the reduction products
of SnCl4 with NaBH4, [6]. The X-ray and electron diffraction investigations show
that the tin structures formed during the reduction of SnCl4 with NaBH4, [6],are
identical to the metastable tin states detected in the products grown by reduction
of SnCl2 with Mg and Al (or SnCl4 or SnSO4 with Mg), [3,4,5], a result which
permits to compare unambiguously the electron diffraction results on different tin
structures during aging.
The tin structures grown by different reduction processes are investigated
after their growth and during many months of aging. A TESLA BS-540 electron
microscope working at 80 kV is used for the TEM with SAD observations. The
errors in the interplanar distance measurements are about 1% for interplanar distances of the order of 1.5 Å or lower but are about 2% for interplanar distances of
the order of 3 Å. Interplanar distances which are equal or larger than 3 Å are corrected by the values of higher order reflection.
3. EXPERIMENTAL RESULTS
αin-Sn, βin– Sn structures
A number of polycrystalline Sn structures with cubic lattices are observed in
the products of different reduction experiments resembling closely the polycrystalline α2-Sn, [5]. They are detected either after a particular reduction process or after
aging of the reduction products. As discussed later in the text, we have observed
cubic structures with lattice parameters varying from a = 5.72 Å to a = 5.10 Å. The
notation αj-Sn requires an hole number of d electrons participating into the chemical bondings, (j =1,2,3..) [1]. αin-Sn, (intermediate Sn structures), is introduced for
those tin structures with lattice parameters different from those of α1 -Sn and α2-Sn.
βin– Sn defines the beta state of a particular αin-Sn. Later in the text they are described as: αin-Sn/ lattice parameter in Å, and βin– Sn/ both lattice parameters in Å.
Table 1 is a summary of the polycrystalline electron diffraction data of the
αin-Sn structures observed to grow during different reduction experiments. There
is also an αin-Sn /5.10 Å, which is not included in Table 1 since it is detected relatively rarely. The polycrystalline αin-Sn do not possess a diamond cubic structure.
Their electron diffraction patterns are similar to that of the defect polycrystalline
α2-Sn, [5]. As a rule, the permitted for a diamond cubic structure 111 reflection is
absent, but the weak forbidden 110 reflections appear occasionally in the diffraction pictures, Table 1.
Diffraction data of the observed βin-Sn states are included in Tables 2a and
2b. Occasionally, the strong 111 reflection of a βin-Sn is detected in the diffraction
218
Table 1
Electron diffraction data registered from different αin – Sn micro-particles observed in the
products of reduction of tin chlorides with Mg, Al and NaBH4. αin- Sn are defect (see the presence
of the forbidden for the diamond structure 110 reflection and the absence of the permitted 111 reflection). Abbreviations for the relative intensities Irel: vs – very strong; s – strong; m-s – medium-strong;
m – medium; m-w – medium-weak; w – weak; vw – very weak. (dhkl )spots – Debye ring consisting
of limited number of diffraction spots.Such ring is either the 111 reflection of the βin – Sn of the
respective αin – Sn or rarely of another βin – Sn. Relative error: Δa/a ≈ 1 %.
Experimental values of dhkl Å / Irel, registered from different αin – Sn islands and compared to
the theoretical dhkl Å / hkl values
1
αin - Sn
a = 5.72 ± 0.06 Å
experiment / theory
dhkl Å/Irel; dhkl Å/hkl;
(3.23)spots
2.86/vs
2.02/vs
1.73/m
1.43/m-s
3.30 /111
2.86/200
2.02/220
1.73/311
1.43/400
1.27/w
1.28/420
2
αin - Sn
a = 5.54 ± 0.06 Å
experiment / theory
3.85/vw 3.91/110
(3.11)spots 3.18/111
2.76 /s
2.77/200
1.96/vs 1.96/220
1.68/s-m 1.67/311
1.38/m 1.39/400
1.25/m 1.27/331
1.23/m
1.24/420
0.97/m
0.98/440
0.92/600,
442
0.87/620
0.92/m
0.86/m
3
4
α2 - Sn
αin - Sn
a = 5.42 ± 0.05 Å
a = 5.35 ± 0.05 Å
experiment / theory experiment / theory
dhkl Å/Irel; dhkl Å/hkl; dhkl Å/Irel; dhkl Å/hkl;
3.80/vw 3.83/110
(3.02)spots 3.13/111
2.70/s
2.71/200 2.69/s 2.68/200
1.91/s
1.93/220 1.90/s 1.89/220
1.62/m 1.65/311
1.35/m 1.37/400 1.33/m 1.34/400
1.23/m 1.25/331
1.21/m
1.21/420
1.10/w
1.11/422
0.90/w
0.94/m 0.95/440
0.90/600,
0.89/600,
0.89/w
442
442
0.86/620 0.84/w 0.85/620
0.85/w
1.20/m
1.20/420
5
αin - Sn
a = 5. 22 ± 0.05 Å
experiment / theory
3.68/w 3.69/110
2.63/vs
1.84/vs
2.61/200
1.85/220
1.30/s
1.31/400
1.16/
m-s
1.17/420
0.92/w
0.86/w
0.82/w
0.92/440
0.86/600,
442
0.83/620
patterns of its or other αin - Sn, (compare the data in Table 1 with the values of d111
of the different βj-Sn in Tables 2a and 2b).
The errors in the dhkl measurements by electron diffraction and the complex
diffraction pictures of coexisting αin-Sn and βin - Sn structures registered during
aging of the reduction products makes it difficult to determine unambiguously the
number of all metastable αin-Sn structures. There are indications that an αin-Sn
/5.28 Å is formed during the gradual transformation of αin-Sn / 5.35 Å during aging. Similarly, aging of αin-Sn /5.22 Å leads to an αin-Sn with lattice dimensions
around a = 5.15 Å. There are data that the number of αin-Sn structures with lattice
dimensions from a = 5.54 Å to a = 5.66 Å could be three: αin-Sn /5.54 Å, αin-Sn
/5.60 Å and αin-Sn /5.66 Å. Further in the text these last αin-Sn structures are referred to as αin-Sn /(5.54–5.66) Å.
α2-Sn is the prevailing α2-Sn-type observed immediately after a reduction in
reaction products type-A. Small quantity of α2-Sn exists in the upper fraction of
the products of reduction of SnCl4 with NaBH4 where it coexists with αin-Sn /5.35
Å, αin-Sn / 5.22 Å, αin-Sn / 5.54–5.66 Å and with some βin-Sn states.
219
Table 2a
Electron diffraction data registered from different βin - Sn islands observed in the products of reduction of tin
chlorides. The experimental values dhkl Å / Irel are compared to the theoretical dhkl Å / hkl values. The abbreviations and the relative errors are defined in the caption of Table 1. Additional abbreviation: l.sp. - local splitting
of the respective Debye ring; dhkl Å/partly - partly registered Debye ring.
1
2
3
4
5
βin - Sn
βin - Sn
βin - Sn
βin - Sn
βin – Sn (β2 – Sn)
a = 5.42 ± 0.05 Å
a = 5.31 ± 0.05 Å
a = 5.22 ± 0.05 Å
a = 5.22 ± 0.05 Å
a = 5.12 ± 0.05 Å
c = 4.95 ± 0.05 Å
c = 4.93 ± 0.05 Å
c = 4.77 ± 0.05 Å
c = 4.64 ± 0.05 Å
c = 4.64 ± 0.05 Å
experiment/theory
experiment/theory experiment/theory
experiment/theory
experiment/theory
dhkl Å / Irel; dhkl /hkl; dhkl Å / Irel; dhkl Å/ hkl; dhkl Å / Irel; dhkl Å / hkl; dhkl Å / Irel; dhkl Å /hkl; dhkl Å / Irel; dhkl Å /hkl;
4.82/w 4.93/001
3.05/s
3.03/111
2.99/s 2.99/111 2.95/s 2.97/111 2.94/s; 2.92/111 2.85/vs 2..85/111
l.sp.2.99
2. 72/s
2.71/200
2.65/s 2.66/200 2.64/m 2.63/200
2.61/s
2.62/200 2.57/vs 2.56/200
(2.40/w)s 2.39/002 (2.36)т 2.32/002
2.41/vw 2.38/210
2.29/w 2.29/201 2.23/m-w 2.24/201
1.96/w 2.00/112 1.95/vw 1.95/112
1.94/s
1.92/220 1.88/m 1.88/220 1.85/m 1.86/220 1.85/ partly 1.85/220 1.81/vs 1.81/220
1.85/m-w 1.83/022; 1.81/m-w 1.81/022 1.78/m 1.80/022 1.76/s; 1.76/022 1.69/s; 1.69/221
l. sp.1.80 1.79/221
l.sp.1.72
l.sp..1.73
1.63/partly 1.64/301
1.63/s
1.62/311
1.59/s 1.59/311 1.58/s 1.57/311
1.55/s
1.56/311 1.53/vs 1.53/311
1.52/m 1.52/222 1.50/m-s 1.51/113 1.49/m 1.49/222;
1.42/m 1.42/113
1.42/w 1.41/203 1.40/m-w 1.40/203
1.41/vw 1.41/320 1.32/w 1.32/203
1.36/w 1.36/400 1.34/m-w 1.33/400 1.33/m 1.31/400 1.30/m 1.31/400 1.28/m-s 1.28/400
1.31/w 1.31/401
1.24/m-w 1.24/004 1.22/m-w 1.23/004
1.16/s
1.16/004
1.22/m-w 1.20/331 1.19/m-w 1.19/331;
004
1.22/w 1.21/420
1.14/s
1.15/420
1.18/m 1.19/402 1.16/w 1.17/133 1.16/m-w 1.16/402 1.13/l.sp. 1.15/133 1.11/s
1.12/402
1.14;1.12
1.05/partly 1.06/204
1.10/m 1.09/422 1.07/w 1.07/422 1.06/m-w 1.06/422 1.04/m 1.05/422 1.02/s
1.03/422
1.04/m 1.04/511; 1.02/w 1.03/224 1.01/m-w 1.01/511 1.00/w 1.00/511; 0.98/s
0.98/511
224
224
αin-Sn /5.35 Å, αin-Sn /5.22 Å, αin-Sn /5.54 - 5.66 Å and rarely αin-Sn /5.10
Å and their respective βin-Sn exist in the reduction products type-B (C). Small
quantities of the former αin-Sn and βin-Sn states, predominantly αin-Sn /5.22 Å and
αin-Sn /5.54 - 5.66 Å, are observed in the reduction products of SnCl2 with Al.
αin-Sn /5.72 Å is observed in the reduction products of SnCl2 with Al only.
Systematic electron diffraction studies performed during many months of aging of different reduction products at room temperature have shown that α2-Sn
is the most stable metastable cubic tin structure. αin-Sn /5.72 Å appears to be the
next in the row of stability.
220
Table 2b
The same as Table 2a, but the observed βin - Sn lattice parameters are larger then that of β2 - Sn. The abbreviations
and the relative error are defined in the captions of Tables 1 and 2a.
1
βin - Sn ( β2 - Sn)
a = 5.42 ± 0.05 Å
c = 4.95 ± 0.05 Å
experiment / theory
dhkl Å / Irel dhkl /hkl
2
βin - Sn
a = 5.60 ± 0.05 Å
c = 5.07 ± 0.05 Å
experiment / theory
dhkl Å / Irel dhkl Å/ hkl
3.05/s
2. 72/s
1.94/s
1.85/m-w
л.сц.1.80
1.63/s
3.03/111
2.71/200
1.92/220
1.83/022;
1.79/221
1.62/311
1.52/m
1.52/222
1.55/w
1.42/w
1.36/w
1.41/203
1.36/400
1.38/w
1.31/w
1.31/401
1.24/m-w
1.24/004
1.27/w
1.22/w
1.21/420
1.21/w
1.18/m
1.10/m
1.19/402
1.09/422
1.04/511;
224
1.04/m
3
βin - Sn
a = 5.72 ± 0.05 Å
c = 5.02 ± 0.05 Å
experiment / theory
dhkl Å / Irel
dhkl Å / hkl
4
βin - Sn
a = 5.80 ± 0.05 Å
c = 5.23 ± 0.05 Å
experiment / theory
dhkl Å / Irel
dhkl Å /hkl
4.04/vw
4.08/110
3.23/vs
3.23/111
2.89/vs
2.90/200
2.05/vs
2.05/220
3.11/s
2..81/s
1.97 /s
3.12/111
2.80/200
1.98/220
3.16/s
2.86/s
2.02/ s
3.15/111
2.86/200
2.02/220
1.87/m
1.87/022
1.90/m
1.89/022
1.94/m
1.94/022
1.67/s
1.67/311
1.55/222;
113
1.70/s
1.70/311
1.73/s
1.73/311
1.58/m
1.58/222
1.62/m
1.60/113
1.43/m
1.43/400
1.39/410;
1.38/401
1.44/m-s
1.45/400
1.30/m-s
1.30/331
1.33/m-w
1.31/004;
1.32/331
1.27/m-s
1.28/420
1.30/m-w
1.30/420
1.40/400
1.38/m-s
1.28/004;
331
1.20/133;
1.22/402
1.11/w
1.12/422
1.24/m-s
1.14/m
1.24/402
1.14/422
1.28m-w
1.16/w
1.27/402
1.16/422
1.06/w
1.07/511
1.09/m-s
1.10/511
1.12/w
1.11/511
The changes of the structures of α2-Sn and β2-Sn during aging are the first
source of information of the interrelations between the different αin-Sn and βin-Sn.
All αin-Sn transform themselves in their respective βin-Sn by an αin-Sn → βinSn structural transition almost identical to the α2-Sn → β2-Sn transition discussed
in [5], Fig. 1. As the α2-Sn → β2-Sn transition, the αin-Sn → βin-Sn transitions
are complicated coexistences of sheet textures of the respective αin-Sn and βin-Sn
structures. These structural transitions appear to be of the displacement type.
Beginning of an α2-Sn→ αin-Sn /5.22 Å structural transition is shown in Fig. 2.
Such a transition is detected relatively rarely. Fig. 2 shows the splitting of the 200 and
220 reflections of α2-Sn in a particular direction on the sample surface. The data are :
α2-Sn a = 5.42 Å
hkl / dhkl Å
200 / 2.71
220 / 1.92
αin-Sn / 5.22 Å
hkl / dhkl Å
200 / 2.63
220 / 1.86
221
Fig. 1 αin-Sn /5.25 Å → βin-Sn /a =
5.25 Å, c = 4.77 Å structural transition
observed after three months of aging of
the reduction products of SnCl2 with Al.
It is almost identical to the α2-Sn → β2-Sn
transition discussed in [5]. Part of the tin
products are at the boundary crystalline /
amorphous state of the matter.
Fig. 2 SAD showing an α2-Sn → αin-Sn /5.22 Å structural transition observed in an α2-Sn
island.
Fig. 3 Structural transition observed by
splitting the diffraction lines registered
for the relatively more unstable αj-Sn
/5.54 Å. A β-Sn is formed during that
transition.
αj – Sn /5.35 Å is unstable. Structural transition of α2-Sn to αin-Sn /5.35 Å has
not been observed.
Structural transition observed by splitting the diffraction lines as shown in
Fig.2, is registered for the relatively more unstable αin-Sn /5.54 Å, Fig. 3. It was
provoked by the electron beam radiation. A β-Sn is formed during that transition.
Structural transitions of the type illustrated by Figs 2 and 3 appear to be first order
phase transitions.
Complicated α2-Sn supper-lattices are observed in large flat α2-Sn drops several days after a reduction experiment type-A. Flat tin drops are formed either dur222
ing the reduction process or some α2-Sn single crystals transform themselves into
drops during the electron beam radiation. β-Sn crystallizes after a while in molten
under the electron beam α2-Sn single crystals.
The structural changes of αinSn /5.72 Å are of the same type as those of α2-Sn
but they take place about ten days after a reduction of SnCl2 with Al.
The initial βin-Sn structures described in Tables 2a and 2b can be considered
as tetragonal with a (βin-Sn) ≈ a (αin-Sn) but with c (βin-Sn) < a (αin-Sn).
A βin-Sn /a = 5.80 Å, c = 5.23 Å is described in Table 2b. It is detected in the
products of reduction of SnCl2 with Al and is observed side by side with αin-Sn
/5.72 Å and its βin-Sn structure. The αin-Sn /5.80 Å is observed in heated above
400°C thin tin films where the DSMS spectra show the line of β-Sn only, [2].
β2 – Sn is the most stable βj – Sn structure. Several months of aging decrease
its lattice symmetry, [5]. A structural change of β2 – Sn can lead to formation of
another tetragonal structure with lattice parameters a = 4.80 Å and c = 4.40 Å. The
structural change involves disappearance of the 111 reflection of the initial β2 – Sn.
Table 3 includes diffraction data of β2 – Sn, (columns 1) and diffraction data of the
transformed to the new tetragonal lattice βin – Sn/ a = 4.80 Å and c = 4.40 Å, (columns 2). Similar structural changes are observed for βin - Sn /а = 5.66 Å, с = 5.15 Å,
(columns 3). The structural change of βin – Sn /а = 5.66 Å, с = 5.15 Å leads to formation of βin – Sn /а = 5.12 Å, с = 4.64 Å, as shown by the indexing in column 4.
Diffraction photographs of the initial βin – Sn structures and the resulting structures
formed after the structural transformations are illustrated in Figs. 4.
Other structural changes of β2 – Sn are taking place after several months of
aging leading to formation to different βin – Sn states, coexisting with β2 – Sn.
They are βin – Sn /а = 5.25 Å, с = 4.95 Å and βin – Sn /a = 5.04 Å, с = 4.60 Å.
Separate islands of βj – Sn /а = 5.04 Å, с = 4.60 Å are detected in reduction products of SnCl2 with Mg, type B (C).
βin – Sn /а = 5.35 Å, с = 4.95 Å shows a tendency for transition to βin – Sn /а
= 5.25 Å, с = 4.95 Å. The changes of βin – Sn /а = 5.25 Å, с = 4.95 Å during aging are via a series of transitional βin – Sn structures and follow approximately the
following pattern:
βin – Sn /а = 5.25 Å, с = 4.95 Å → βin – Sn І /а ≈ 5.25 Å, с ≈ 4.80 Å →
βin – Sn ІІ /а ≈ 5.25 Å, с ≈ 4.60 Å →
βin – Sn III /а ≈ 5.15 – 5.10 Å, с ≈ 4.60 Å → βin – Sn IV /а ≈ 5.05 Å, с ≈ 4.60 Å.
The lattice parameters of the last two βin – Sn structures are very close which
leads to ambiguities in the interpretation of the structural composition of reduction
products containing both structures.
It is observed that βin - Sn І and βin – Sn ІІ coexist with β2 – Sn when α2 – Sn
→ β2 – Sn structural transition takes place after more than an year of aging of reduction products of SnCl2 with Mg, type A.
223
Table 3
Electron diffraction data illustrating the change of the structure of β2 - Sn and βin - Sn / a = 5.66 Å, c = 5.15 Å
to other crystalline states of tin. The abbreviations and the relative errors are defined in the captions of Tables 1 and 2.
1
β2 – Sn
a = 5.42 ± 0.05 Å
c = 4.95 ± 0.05 Å
experiment / theory
dhkl Å / Irel
dhkl /hkl
3.02/s
3.03/111
2.70/s
2.71/200
2.49/vw
2.49/002
2.42/210
2.38/w
2.38/201
2.08/vw
2.08/112
1.90/s
1.92/220
1.82/m
1.83/022;
1.78/w
1.79/221
1.70/122;310
1.63/s
1.62/311
1.58/103
1.52/m
1.52/222
1.48/w
1.46/302
1.43/w
1.44/321
1.38/w
1.36/400
1.32/w
1.25/m-w
1.23/w
1.19/m
1.12/w
1.09/m
1.04/m
1.32/410
1.24/004;331
1.21/420
1.19/402
1.16/412
1.13/204
1.09/422
1.08/430
1.04/511
2
transformed state
a = 4.80 ± 0.05 Å
c = 4.40 ± 0.05 Å
experiment / theory
dhkl Å / Irel
dhkl Å/ hkl
2.70/s
2.69/111
2.41/vs
2.40/200
1.71/vs
1.63/w
1.60/w
1.70/220
1.62/022
-
1.45/vs
1.44/311
1.35/w
1.35/222;113
1.20/m
1.20/400
1.16/w
1.16/410
1.10/w
1.08/w
1.05/w
1.10/004;531
1.07/420
1.04/402
3
βin - Sn
a = 5.66 ± 0.05 Å
c = 5.15 ± 0.05 Å
experiment / theory
dhkl Å / Irel dhkl Å / hkl
2.85/m-s
2.55/m-s
1.81/m-s
1.72/m
1.68/w
1.53/s
1.42/m
2.83 / 200
2.57 / 002
1.81 / 122
1.71 / 310
1.69 / 311
1.52 / 302
1.42 / 400
1.28/m
1.17/m
1.14/m
1.11/m
1.02/m
0.97/m
0.85/w
1.29 / 331
1.17 / 204
1.14 / 422
1.11 / 510
1.00 / 440
0.95 / 044
0.86 / 006
4
transformed state
a = 5.12 Å
c = 4.64 Å
experiment / theory
dhkl Å / hkl
2.85 / 111
2.56 / 200
1.81 / 220
1.72 / 022
1.69 / 221
1.53 / 311
1.42 / 113;
1.43 / 222;
1.28 / 400
1.16 / 004
1.145 / 420
1.12 / 402
1.03 / 422
0.98 / 224;511
0.86 / 531;
0.85 / 600
Complicated sheet texture, suggesting displacement type structural transition
of βin – Sn /a = 5.72 Å, c = 5.02 Å is observed in reduction products of SnCl2
with Al after several days of aging. Figs. 5 show the observed diffraction photograph and its indexed sketch. A γo – Sn /a = 4.04 Å, c = 3.76 Å is formed. The
[110] texture axis of βj - Sn /a = 5.72 Å, c = 5.02 Å is at right angle to the [001]
texture axis of γo – Sn /a = 4.04 Å, c = 3.76 Å. Separate single crystal diffraction
photographs of γo – Sn /a = 4.05 Å, c = 3.76 Å are detected suggesting that it is a
relatively stable crystalline state of tin.
224
Figs. 4
4.a Diffraction photograph of β2 – Sn (the data are included in columns 1, Table 3);
4.b Diffraction photograph of a tetragonal tin structure with lattice parameters a = 4.80 Å and
c = 4.40 Å, obtained after a structural transformation of β2 – Sn (data in columns 2, Table 3)
4.c βin – Sn /а = 5.66 Å, с = 5.15 Å diffraction photograph, (data in columns 3, Table 3);
4.d βin – Sn /а = 5.12 Å, с = 4.64 Å diffraction photograph, (data in column 4,
Table 3), obtained after a structural change of βin – Sn /а = 5.66 Å, с = 5.15 Å.
225
Figs. 5
5.a
Sheet
texture,
suggesting
displacement type structural transition of
βin – Sn / a = 5.72 Å, c = 5.02 Å to γo – Sn
/a = 4.04 Å, c = 3.76 Å. The [110] texture
axis of the βin – Sn is at right angle to the
[001] texture axis of γo – Sn.
5.b Indexed sketch of the structural
transition.
226
4. DISCUSSIONS
The structural changes of α2-Sn and β2-Sn microparticles grown by different reduction processes observed during aging can be compared directly to the
structural transitions observed by DSMS and RHEED in heated α2-Sn thin films,
[2]. α2-Sn thin films are grown from a tin source at 830°C, at an evaporation
rate 2 Å/s, [14]. They do not change their structure during months of aging at
room temperature. α2-Sn clusters are to be responsible for the growth of α2-Sn
films. High temperature /high pressure macroscopic experiments at temperatures
< 830°C should be performed to establish the area of existence of α2-Sn in the
/ /T diagram of tin.
Heating of α2-Sn thin 119Sn films leads to faster structural changes of α2-Sn
than the disorder introduced into its lattice during the gradual structural transformations of the α2-Sn micro-particles observed during aging at room temperature.
The isomeric shift δ of α2-Sn increases gradually during heating at 260°C and
reaches a value of 4.9 mm/s for 6 hours heating time. The main quantity of α2-Sn
in the observed reduction products of various reduction processes is defect. It is
no more diamond cubic and one should not expect its isomeric shift to be the
theoretical δ = + 4.4 ± 0.02 mm/s, [1]. The data in [2] suggest that its value is to
be larger. Therefore, the interpretation of the precise Mössbauer results in [15] are
to to be modified according these results.
The observations in the present investigation confirm the former results in [5]
that the disproportion of α2-Sn to β2-Sn in the reduction products requires several
months of aging at room temperature. The disproportion of α2-Sn (isomeric shift
δ = 4.4 mm/s) to β2-Sn (isomeric shift δ = 5.2 mm/s) is observed in heated upto
400°C 119Sn films, [2]. β2-Sn is the only one metastable tin structure grown by a
reduction process with the theoretical value of its isomeric shift observed both from
thin films and from tin products grown by different reduction processes, [1,2, 15].
The results of the present investigations define the lattice parameters of α3-Sn
and β3-Sn. α2-Sn (δ = 4.40 mm/s) transforms itself into α3-Sn (δ = 6.3 mm/s) in
heated for more than five hours at 300°C 119Sn films, [1, 2]. This structural change
of α2-Sn to α3-Sn is about an order of magnitude more rare as compared to the disproportion of α2-Sn to β2-Sn. αin-Sn / 5.22 Å is to be α3-Sn according to the rarely
observed structural transition α2-Sn→ αin-Sn /5.22 Å shown in Fig. 2. β3-Sn (δ =
6.82 mm/s) is observed in heated for about 6 hours at 260°C tin films, coexisting
with a tin state with δ = 4.78 mm/s,[2]. The lattice parameters of β3-Sn grown by
an α3-Sn → β3-Sn structural transformation are to be β3-Sn/a = 5.22 Å , c = 4.77
Å according to the results of the present investigations. It would be interesting to
analyse the existence of α3-Sn and its α3-Sn state in the phase diagram of tin.
The DSMS data confirmed by the electron diffraction results suggest that these
structures could be also high temperature, high pressure tin states.
227
The DSMS results show that isomeric shifts in the region of δ of γo – Sn are
observed in heated α2-Sn films, [2]. DSMS and RHEED show that γo – Sn exist in
thin tin films with initial γo – Sn and α1-Sn / γo – Sn structures, [2]. The structural
transformation of β2-Sn discussed in connection with Table 3 show that tin structures with lattice parameters close to the lattice parameters of γo – Sn can grow
by a structural transformation of β2-Sn. Fig.5 shows that a γo – Sn is formed by a
structural transformation of βin – Sn/ a = 5.72 Å, c = 5.02 Å.
The precise Mössbauer data in [15] do not consider the existence of α1-Sn
micro-particles in the investigated reduction products. The registered isomeric
shift δ = 2.2 mm/s is considered as part of the α-SnO doublet. α1-Sn micro-particles could exist inside the investigated reduction products, but interpretations of
the existing supper-lattices are ambiguous.
5. CONCLUSIONS
Series of αin – Sn have been identified by TEM with SAD. There are indications that their number may be larger, but the limited resolution of the electron
diffraction studies does not permit to establish their exact number. Their number
is more than the numbers of αj - Sn structures introduced in [1]. The conditions a
particular αin – Sn to grow in different reduction products are not clear.
All αin – Sn are with diamond cubic structure which is distorted when they
exist as small particles in products of chemical reductions. One can consider that
the diamond cubic structure is a property of tin itself, with or without d electrons
participation into the chemical bondings.
α2 – Sn is the most stable αj – Sn structure. αin – Sn / 5.72 Å appears to be the
next in the row of stability. It was established that αin – Sn/ 5.72 Å is observed in
the reduction products of SnCl2 with Al only. The Mössbauer results from these
reaction products show that they are predominantly β-Sn-types. The change of
the enthalpies during the reaction of SnCl2 with Al is larger than that during the
reaction of SnCl2 with Mg. This result is in accordance with the thin tin films
results. α2 – Sn films require a temperature of 830ºC of the tin source and a particular distance /growth rate/ of the growing films, [14]. At temperatures ≥ 930 ºC
are growing β– Sn films, [14].
Data on α1 – Sn micro-particles eventually existing in the products of chemical reductions are not obtained in the present investigations.
TEM with SAD show that the observed rare disproportions of some αin-Sn to
β– Sn require either electron beam radiation leading to structural changes of the
initial αin-Sn lattice or it grows after melting under the electron beam.The data
suggest that formation of β– Sn is not a displacement type phase transition. The
main quantity of β– Sn is formed during the respective reduction processes.
All αI -Sn transform themselves into their respective βin-Sn by an αin-Sn →
βin-Sn structural transition identical to the α2-Sn → β2-Sn transition . The αin-Sn
228
→ βin-Sn transitions are complicated coexistences of sheet textures of the respective αin-Sn and βin-Sn structures.
Electron diffraction studies of aging at room temperature of α2-Sn particles
have revealed an α2 – Sn → α3-Sn structural transition, an order of magnitude
more rare than the α2 – Sn → β2-Sn structural transition. The diffraction data suggest that it may be a first order phase transition.
αin-Sn / 5.22 Å is to be α3-Sn according to the rarely observed structural transition α2-Sn→ αin-Sn /5.22 Å. The lattice parameters of β3-Sn grown by an α3-Sn
→ β3-Sn structural transformation are to be β3-Sn/a = 5.22 Å , c = 4.77 Å.
Structural transition of the same type of the more unstable αin-Sn/ 5.54 Å
leads to formation of β-Sn.
Complicated sheet texture, suggesting displacement type structural transition
of βin – Sn/ a = 5.72 Å, c = 5.02 Å to γo – Sn / a = 4.04 Å, c = 3.76 Å is detected.
Separate single crystal diffraction photographs of γo – Sn /a = 4.04 Å, c = 3.76 Å
are detected suggesting that it is a relatively stable crystalline state of tin.
β2 – Sn is the most stable βj – Sn structure. Several months of aging decrease
its lattice symmetry and different structural changes are observed. Disappearance
of the 111 reflection of the initial β2 – Sn is leading to formation of tetragonal lattice with lattice parameters a = 4.80 Å and c = 4.40 Å. Similar structural change
is observed an for βin – Sn / а = 5.66 Å, с = 5.15 Å leading to formation of the β in
– Sn /а = 5.12 Å, с = 4.64 Å.
Aging leads to a gradual formation of different βin – Sn states via a series of
transitional βin - Sn structures.
The results of the present study suggest a complicated phase diagram of tin in
the high pressure/ high temperature region. High temperature /high pressure macroscopic experiments at temperatures < 830°C should be performed to establish
the area of existence of α2-Sn and its transformation to β2-Sn and the existence of
α3-Sn and its β3-Sn. The region of existence of αin-Sn / 5.72 Å is to be at T ≥ 800
– 900 ˚C, following the data in [8, 14].
REFERENCES
1.
2.
3.
4.
Bonchev, Ts., S.K.Peneva, K.D.Djuneva. On the possibility of formation of chemical bonds
with electrons from low lying orbitals, KINAM 3 (1981), 389–401.
Peneva, S.K., K.D.Djuneva. Some RHEED and DSMS investigations on the structures inevaporated thin tin films before and after their heating in vacuum, Thin Solid Films, 113 (1984), 297–326.
Rusanov, V., Ts. Bonchev, S.K.Peneva, K.H.Chakarova, L.A.Spasov, S.L.Petrov. Some Mössbauer and X-ray investigations of α2 – Sn formation during the reduction of SnCl2 water
solutions, J. Solid State Chem., 51 (1984), 336– 344.
Neykov, N.S., S.K.Peneva, K.D.Djuneva. Electrochemically obtained tin – Part II: TEM,
Mössbauer and X-ray investigations of some β – Sn type of structures, Z. Kristallogr. 202
(1992), 215–225.
229
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Peneva, S. K., N. S. Neykov, K. D. Djuneva, V. Rusanov. Electrochemically obtained tin – Part
I: TEM, Mössbauer and X-ray investigations of α2 – Sn and β2 – Sn grown during the reduction of SnCl2, Z. Kristallogr. 202 (1992), 191–213.
Peneva, S. K., N. S. Neykov, V. Rusanov, D. D.Chakarov. Mössbauer spectroscopy investigations of the oxidation of α2 – Sn and β – Sn types of structure at room temperature, J. Phys.:
Condens. Mater. 6 (1994) 2083–2092.
Popova, LI., S. K. Peneva, C. A. Dimitriadis, V. K. Gueorgiev, S. K. Andreev. TEM structural
characterization of Sn-Te-O thin films on monocrystalline silicon wafers, Thin Solid Films,
441 (2003), 25–31.
Peneva, S. K., K .D. Djuneva and T. Kazakova. Metastable crystalline states of tin grown by
fast cooling of molten tin – electron and X-ray diffraction investigations, Ann.Univ. Sofia, Fac.
Chem., 88 (2000b), 183–193.
Gmelins Handbuch der Anorganische Chemie, begrundet von Leopold Gmelin, (Verlag Chemie, GMB Weinheim, Bergstrasse – 1971) Vol. 46, (Zinn ), Teil B.
Young, David A. Phase Diagrams of the Elements (University of California Press, Berkeley,
Los Angeles, Oxford, 1991.
Gutzov, I., J. Schmelzer. The vitreous state – Thermodinamics, Structure, Rheology and Crystallization, Springer Verlag, Berlin, 1995.
Djuneva, K. D., S. K. Peneva, E. A. Tsukeva and I. Batov. Some investigations of the heterojunctions in AIVBIV systems. Thin Solid Films, 67 (1980), 371–383.
PDF, Powder Diffraction File 1988, International Centre for Diffraction Data, 601 Park Lane,
Swarthmore, Pa 19081-2389, USA.
Tsukeva, E. A., E. Tsakin, S. K. Peneva, K. D. Djuneva. On the possibility to grow thin tin
films with unusual tin structures from the vapours, Z. Kristallogr., 187 (1989), 63–70.
Rusanov, V., I. Mandjukov, Ts. Bonchev, K. Kantchev. On the phase and structural composition of electrochemically obtained tin samples, J. Phys. F: Met. Phys., 18 (1988), 1311–1316.
230
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
MECHANISM OF THE ALTERNATING COPOLYMERIZATION.
V. AZEOTROPE COMPOSITIONS AT THE DONOR-ACCEPTOR
COPOLYMERIZATION OF MALEIC ANHYDRIDE WITH VINYL
ESTER OF 2,2,4-TRIMETHYLHEPTANOIC ACID
S. B. ILIEV, G. S. GEORGIEV
University of Sofia, Faculty of Chemistry,
Laboratory of Water-Soluble Polymers, Polyelectrolytes and Biopolymers,
1 J. Baurchier Avenue, 1164-Sopfia, Bulgaria
Abstract. It was established that maleic anhydride (MA) – vinyl ester of 2,2,4trimethylheptanoic acid (VH) copolymerization in bulk or in a solution is characterized
with two copolymerization rate maximums as a function of the monomer feed composition
and considerable deviation of the copolymer composition from equimole one, registered
when the initial monomer mole ratio [MA]/[VA] is 0,5. These peculiarities find its
reasonable explanation assuming the formation of two comonomer complexes (C1 = MAVH and C2 = VH-MA-VH) and their participation in the chain propagation with constants
larger than these characterizing the monomer addition to the propagation chains. The
results of this analysis is generalized proving that similar peculiarities are in force for each
copolymerization in which chain propagation two or more comonomer complexes with a
arbitrarily composition take part. From these considerations the azeotropy of the donoracceptor copolymerization is defined for the first time. It essence is that the copolymer
compositions are the same of that of the monomer feeds which compositions are equal
to the complex compositions. This azeotropy allows a clear definition of the difference
between alternating and donor-acceptor copolymerizations.
Keywords: Alternating copolymerization, radical pairs, azeotropy, donor-acceptor
complex.
231
INTRODUCTION
As the alternating copolymerization (AC) is one of the few successful methods for the production of the regular composed copolymers [1-3], the investigation of the AC mechanism continues to be attractive and actual. Most commonly,
AC is considered as a consequence of the equimole donor-acceptor complex (C)
formation between electrondonor (D) and electronacceptor (A) comonomers, and
its dominating participation in the chain propagation reactions [4]. In a previous
work on this series [5] the kinetic method for the estimation of the C contribution
in the formation of the alternating copolymer macromolecule was shown. Later
to this aim another method, using the experimental results for triad-pentad compositional mole fractions of the copolymers produced, has been developed [6, 7],
as well as a general model for a radical copolymerization [8, 9] also. The main
characteristic of the donor-acceptor copolymerization (DAC; copolymerization in
which chain propagation reactions C takes part) is the maximum of DAC rate at
the equimole composition of the initial monomer feed. It is explained just with a
formation and participation in the chain propagation of C with an equimole composition [1, 3]. As this peculiarity characterizes a large number of AC also [4, 5],
the both copolymerizations (DAC and AC) are considered as synonyms.
However, C can have nonequimole composition. What will be the influence
of this C nonequimole composition on DAC? Will be the copolymerization alternating? Partial answer of these questions was proposed in the mentioned above
work [5]. In this communication these problems are analyzed with a necessary
details and sequence. This analysis is performed on the basis of experimental results on the DAC kinetics and composition of the copolymers of vinyl acetate
(VA) and vinyl ester of 2,2,4-trimethylheptane acid (VH) in bulk and in a dioxan
solutions. It is established that the DAC rate as a function of the monomer feed
composition, has two maximums and that the most considerable deviation of the
copolymer composition from the equimole one takes place at monomer mole ratio
[MA]/[VH] = 0.5. These both peculiarities are related to the formation of two
comonomer complexes (C1 = MA-VH and C2 = MA-(VH)2) and their participation in the propagation reactions. In terms of this suggestion the more general
relationships for DAC with arbitrary number of C and copolymer compositions
different from equimole one are deduced. This generalization allows to introduce
a new concept for the azeotropy of DAC, according with which the participation
of each complex in the chain propagation, results in the tendency for the equality of the copolymer composition, with that of the monomer feed (azeotropy) for
those monomer feed, which composition coincides with that of C only. By this
way, the DAC azeotropy allows clear demarcation between DAC and AC. The
both copolymerizations coincide only when one equimole comonomer complex,
participating in the propagation reaction, is formed.
232
EXPERIMENTAL
Vinyl ester of 2,2,4-trimethylheptanoic acid (VH, Shell) was dried and distilled just before the usage. The used electronacceptor monomer (maleic anhydride, MA) was purified by sublimation just before its application also. Benzoyl
peroxide (BPO, Merck) used as an initiator, was recrystallized from the saturated
at 50˚ C solution in ethanol. Dioxan, which was used as a solvent, was dried and
distilled also before the usage.
The copolymerizations in bulk and in dioxan were performed in seald glass
ampoules (containing comonomers and initiator) at temperature 80˚ C in a nitrogen atmosphere. The copolymerization rates were determined gravimetrically. To
this aim the copolymers were isolated and purified by the double precipitation
from their dioxan solutions in a mixed ethanol/water (2/1 volume ratio) precipitator. After a drying of the purified copolymers (at temperature 45˚ C under vacuum)
they were analyzed. The copolymer compositions were determined by the carboxylic group titration of the solved in acetone copolymer samples.
q, %
The kinetics of MA-VH copolymerization at dеfined monomer feeds in bulk are
presented on Fig. 1. It is clear that the concentration ratio between comonomers
1
2
15
3
4
10
5
6
5
7
8
9
0
0
5
10
15
20
25
30
t, min
Figure 1. Conversion (q) as a function of the time of the MA-VH copolymerization at different
maleic anhydride mole fractions (MMA) in a monomer feed. MMA = 0.50 (curve 1); 0.33
(curve 2); 0.35 (curve 3); 0.30 (curve 4); 0.65 (curve 5); 0.25 (curve 6); 0.40 (curve 7); 0.20
(curve 8); 0.80 (curve 9).Temperature: 80˚ C; Initiator: BPO (0.2%, wt); The error’s measures
are the vertical lines of the cross points.
233
V, % conv. / min
(MMA) influences not only the initial copolymerization rates (V), but the induction period length (τ) as well as the critical moments, after which self-acceleration as
a result of the gel-effect takes place. Clearly, the relationship between initial copolymerization rate and MA mole fraction in the monomer feed (MMA) is presented on
Fig. 2. Two maximums are the peculiarity of this dependence. From the curves, presented on Fig. 1, it is seen that the critical time for the copolymerization decreases
with the increase of the V values. It means that the dependence of this time as a
0,25
0,20
0,15
0,10
0,05
0,00
0,0
0,2
0,4
0,6
0,8
1,0
MMA
Figure 2. Relationship between the initial MA-VH copolymerization rate (V) and MA mole
fraction in the initial monomer feed (MMA). Temperature: 80˚ C; Initiator: BPO (0.2%, wt);
The error’s measures are the vertical lines of the cross points.
function of MMA would be the mirror of that, presented on Fig. 2.. As the accuracy
of the determination of these times (as abscissае of the crossing points of the relative linear fragments of the presented on Fig. 1 curves) is less, this dependence
doesn’t presented. It is notеworthy that the appearance of the induction periods (τ)
takes place for the copolymerization which rates are smaller. The larger τ values,
234
the smaller V. This antisymmetry between V and critical times for the copolymerization self-acceleration is a result of the reaction medium viscosity importance
(it depends on a monomer conversion q) for the gel-effect and a sharp increase of
the termination constant.
The above outlined two maximums of the demonstrated on Fig. 2 curve are the
first peculiarity of the discussed MA-VH copolymerization. In general, for the most
of the DAC investigated [1-3, 5] the curve “copolymerization rate – mole fraction of
one of the monomers” has one maximum at equimole monomer feed. This is a result
of the formation of 1:1 donor-acceptor complex (C1) between D and A:
A+D
K1
C1
[C1] = K1[A][D]
(1)
From the necessary condition for an extreme (d[C1]/dMA = 0; MA is the mole
fraction of A; in this case MA = MMA) it follows:
K1([A] + [D])2(1 - 2MA) = 0
(2)
As K1 = const and [A] + [D] = const also it follows that MA = 0.5 from the last
equation (2). By this way, it is proved that at MA = 0.5 (equimole composition of
the monomer feed) the C1 concentration is maximal. The second part of the proof
of the experimental established maximum of V at MA = 0.5 is based on the early
registered fact [1-3, 5, 9] that the propagation rate constants for the complex (C1)
addition to the propagation chains (kAC1 and kDC1) are larger than those for the comonomer (A and D) addition to the same propagation chains (kAD and kDA).
k
(3)
DC1
~ D i + C1 ⎯⎯⎯
→ ~ Di
k
(4)
k AD
~ Ai + D ⎯⎯→
~ Di
(5)
k DA
~ D i + A ⎯⎯→
~ Ai
(6)
AC1
~ Ai + C1 ⎯⎯⎯
→ ~ Ai
The values of the determined kAC1/kAD and kDC1/kDA) rations by the kinetic
method, proposed in the first part of this series of works [5] for different DAC
confirm this statement. The values of both ratios are more than unity: kAC1/kAD >
1; kDC1/kDA > 1. By this way, the existence of one maximum V value at equimole
monomer feed (MA = 0.5 in this case) is proved.
However, the curve in Fig. 2 shows the maximum at MA = 0.33, the fact
demonstrating the peculiarity of this copolymerization. To explain the latter the
suggestion for the formation and participation in the propagation reactions of
235
one new donor-acceptor complex C2 = MA-(VH)2 could be discussed, along with
C1 = MA-VH.
C1 + D
K2
C2
K2 = [C2] / [C1][D]
(7)
The result of the substitution of C1 in the last equation with its expression by
Eqn. (1) is:
K2 =
[C2 ]
[C2 ]
=
[ D]K1 [ A][ D] K1 [ A][ D]2
(8)
from which:
K = K1 K 2 =
[C2 ]
[ A][ D]2
(9)
and
[C2 ] = K [ A][ D]2 = K ([ A] + [ D])3 M A (1 − M A ) 2
(10)
where MA is a mole fraction of A in monomer feed. MA ≡ MMA for the discussed
MA-VH copolymerization. As earlier, from the C2 extreme condition (d[C2]/dMA
= 0) the next quadratic equation can be deduced:
4
1
M A2 − M A + = 0
3
3
(11)
which two decisions are MA = 1 and MA = 0.33. The first one is without physical
meaning as the C2 formation is not possible without D (MA = 1) in the monomer
feed. However, the second decision is just that MMA value at which the second
maximum of the “V – MMA” dependence takes place (Fig. 2).
This curve has its full proof if, as in the previous case, the suggestion that the
rate constant for the C2 addition to A (kC2A) is greater than kDA is accepted. Therefore,
the both experimental maxima of the “V – MMA” dependence (Fig. 2) could be related substantially to the formation of two donor-acceptor complexes (C1 = MA-VH
and C2 = VH-MA-VH) and their participation in the propagation reactions with rate
constants for their addition to the propagation chains greater than those for the comonomers (MA and VH in this case). The kinetic scheme for the formation of the
alternating copolymer chain in this case can be presented as follow:
k
VH ,MA
~ VH i + MA ⎯⎯⎯
→ ~ MAi
k
VH −C1
~ VH i + ( MA − VH ) ⎯⎯⎯
→ ~ VH i
236
(12)
(13)
kMA−VH
~ MAi + VH ⎯⎯⎯
→ ~ VH i
k
MA−C1
~ MAi + (VH − MA) ⎯⎯⎯
→ ~ MAi
k
MA−C2
~ MAi + (VH − MA − VH ) ⎯⎯⎯
→ ~ VH i
(14)
(15)
(16)
From this scheme it is clear that as a result of the donor-acceptor interaction
between the propagation ends, comonomers and complexes, the propagation end
~VH• interact with MA and MA-VH (C1) only, while the other propagation end
~MA• can interact with both VH, VH-MA (C1) and VH-MA-VH (C2) also. The
quantitative analysis of the similar kinetic scheme of donor-acceptor copolymerization, accounting the participation of two and more donor-acceptor complexes
in the chain propagation was not discussed up to now. This does not performed
in our previous work [5] also. The reason for this situation is not the lack of the
wish for the full analysis of such possibility, but first of all it is a result of the fact
that the participation of the nonequimole comonomer complex (C2 = MA-(VH)2
is a such complex) in the propagation reaction results in a deviation of the copolymer composition from equimole one. It means that the copolymer obtained is
not alternative, and the copolymerization is not alternating, the general product
of the donor-acceptor copolymerization. As in general the alternating copolymerization was the subject for an analysis and simulation it becomes clear why such
nonequimole copolymers were not included in different type of the models for
the alternating copolymerization. For the kinetic scheme presented above (Eqs.
12-16) the deviation from the alternation in the copolymer composition can be a
result of the relation (16) for the macromolecule formation. Each addition of the
complex C2 (MA-(VH)2) to the propagation end ~MA• contributes the shift of the
copolymer composition to that which mMA = 0.33. This shift is more considerable
for the greater number of these additions. The effect has maximum at MMA = 0.33
when the VH-MA-VH concentration is the greatest (it was proved above) and
kMA-C2 > kMA-VH and kMA-C2 > kMA-C1. The experimental copolymer composition (mole
fraction of MA monomer units in copolymers mMA) as a function of the monomer
feed (Fig. 3) confirmed this expectation. It is seen in fact that at MA = 0.33 the
deviation of the copolymer composition from the equimole one is the greatest and,
at the same time, mMA value is the closest to mMA = 0.33. This is the second very
important peculiarity of the copolymerization discussed.
237
mMA
0,5
0,4
0,3
0,0
0,2
0,4
0,6
0,8
1,0
MMA
Figure 3. Copolymer (produced by MA copolymerization with VH in bulk) composition (mole
fraction of the MA monomer units, mMA) as a function of the monomer feed one (mole fraction
of MA in it, MMA). Temperature: 80 ˚C; Initiator: BPO (0.2%, wt); The error’s measures are
the vertical lines of the cross points
The common characteristic for the both mentioned above peculiarities (the
maximum of V and minimum of mMA) is the fact that the both extremes appears
at MMA = 0.33. It is a result of the common reasons for these peculiarities: the
formation of the nonequimolar donor-acceptor complex between the comonomers
and its participation in the chain propagation reactions with rate constants greater
then those of the addition of the single (not incorporated in the complexes) comonomer molecules. Therefore, these peculiarities can be regarded as two different
appearances of the both, mentioned above reasons for the shift of the discussed
copolymerization from the classical alternating copolymerization.
It is noteworthy the possibility for a generalization of the analysis presented
for the complexes with an arbitrary composition, e. g. for each m/n (AmDn; m ≠
n) different from unity.
K mn
⎯⎯
⎯
→ C ; K mn =
mA + nD ←⎯⎯
⎯
[C ]
[ A]m [ D]n
(17)
Let for clarity m > n. Then:
[C ] = K mn [ A]m [ D]n = K mn ([ A] + [ D]) m + n M Am (1 − M A ) n
From the necessary for the extreme condition:
238
(18)
d [C ]
m
= 0 = K mn n([ A] + [ D]) m + n M Am −1 (1 − M A ) n −1{ (1 − M A ) − M A } (19)
dM A
n
it follows that:
MA =
m
n
and M D = 1 − M A =
m+n
m+n
(20)
The same expression is obtained also if m < n. The extreme condition in this
case is:
n
(1 − M D ) − M D = 0
m
(21)
which is identical with Eqn. (20). In such a way the following, common for DAC
peculiarities, were proved:
1. The relationship between the rate of this copolymerization and monomer
feed has one maximum only if one donor-acceptor complex between the comonomers is formed and its addition to the propagating chains takes place with rate
constants greater than those of the single monomer molecules.
2. The position of this maximum depends on the composition of this complex,
and if C = AmDn, the mole fraction of A at which V = Vmax is MA = m/(m+n).
3. The composition of the copolymer obtained at these conditions and if the
addition of the complex C = AmDn to the propagation ends dominates is close to
the same monomer feed at which the copolymerization rate has maximum.
4. When m = n (the equimole complex C) the copolymerization rate maximum should to be appeared at equimole monomer feed (MA = 0.5), and the composition of the copolymer produced is equimole and alternated also.
5. If two and more donor-acceptor complexes are formed between the comonomers, and they take part in the propagation reactions with rate constants
greater than those of the “free” (unincorporated in the complexes) monomer molecules, the number of the maximums of the copolymerization rate as a function
of the monomer feed is equal to the number of the donor-acceptor complexes.
The monomer feed compositions at which the copolymerization rate has maximal
values are equal just to the donor-acceptor complex compositions.
6. The compositions of the copolymers, producing by DAC with two and
more donor-acceptor complexes change between the compositions of the these
complexes. If the monomer feed composition is equal to a given complex, the
composition of the copolymer produced approximates the composition of this
complex. The fastness of the transition of the copolymer composition from one
to another complex composition depends on the ratio between the rate constants
of the complex additions to different propagation ends. The quantitative analysis
of this behaviour of the copolymer composition curves is under a development. It
allows the decision both the right and opposite kinetic tasks of DAC.
239
q, %
The deduced above common for DAC characteristics are in force for the discussed DAC of MA with VH also. In fact, they were defined during the analysis of
the experimental results just of this copolymerization. The consequences 5 and 6
are in force also, and the number of the complexes in this case are two: equimole
one (MA-VH) and MA-(VH)2. According to a consequence 5, two maximums are
appeared in the copolymer composition curve (Fig. 2) as a function of the monomer
feed; just at MMA = 0.5 (the composition of the equimole complex) and MMA = 0.33,
the composition of the complex MA-(VH)2. In accordance to the consequence 6 the
composition of the copolymers obtained are changed between equimole one (mMA
= 0.5) and mMA = 0.33, corresponding to the composition of the other, nonequimole
complex MA-(VH)2. As it can be seen from the date presented in Fig. 3, the equimole copolymer composition dominates. This fact shows the C1 relativity to the
propagation ends is higher than those of the complex C2. In other words, it means
that kMA-C1 > kMA-C2 (Eqns (15) and (16)) and kVH-C1 > kVH-MA (Eqns (12) and (13)) also.
Another possible reason for the established domination of the equimole copolymer
composition in a wide interval of the monomer feed composition could be related to
the inequality K1 > K2, providing the C1 excess over C2 (C1 > C2).
70
1
2
3
4
5
6
7
8
9
60
50
40
30
20
10
0
0
10
20
30
40
50
60
t, min
Figure 4. Kinetics of MA copolymerization with VH in dioxan (the total monomer concentration
is 50% wt) in coordinates “conversion (q) - time (t)” at different monomer feed compositions
(mole fraction of MA in it, MMA). MMA = 0.20 (curve 7); 0.25 (curve 6); 0.30 (curve 4);
0.33 (curve 2); 0.35 (curve 3); 0.40 (curve 5); 0.50 (curve 1); 0.65 (curve 8); 0.80 (curve 9);
Temperature: 80 ˚C; Initiator: BPO (0.4%, wt); The error’s measures are the vertical lines of the
cross points.
240
V, % conv. / min
It appears that the established peculiarities of MA copolymerization with VH
in bulk are in force for the copolymerization of the same monomers in dioxan
(Fig. 4 and Fig. 5) too. However, it is seen that the convexity of the curves, presented in Fig. 4 is opposite to that of the conversion curves for the copolymerization in bulk (Fig. 1). This difference can be related to the characteristic for the
copolymerization in bulk gel-effect (Fig. 1) which is not, if the copolymerization
is performed in solution (Fig. 4). The higher conversion of the monomers, the less
concentration of the complexes C1 and C2 as a result of which, the copolymerization rate reduces. By this way the negative (upwards) convexity of the curves,
shown in Fig. 4, can be explained.
0,6
0,5
0,4
0,3
0,2
0,0
0,2
0,4
0,6
0,8
1,0
MMA
Figure 5. Initial MA-VH copolymerization rate in dioxan as a function of the monomer feed
composition (MMA – mole fraction of MA in it). The total monomer concentration: 50% wt;
Temperature: 80 ˚C; Initiator: BPO (0.4%, wt); The error’s measures are the vertical lines of
the cross points.
Interesting and even unexpected result is revealed by the comparison of the
initial rates of copolymerization in bulk (Figs. 1, 2) and in dioxan (Figs. 4, 5). The
initial rates in dioxan are more than twice higher than those of the copolymerization in bulk. This could be related to the both greater values of the mentioned
above rate constants of the complex (C1 = MA-VH) and (C2 = MA-(VH)2) additions to the propagation ends and to the increase of the complex stability constants
(K1 for C1 and K2 for C2) at the transition from a medium without solvent to the
241
medium with solvent (dioxan). Another reason for this result could be the initiation rate increase at this transition.
The curve in Fig. 5 is similar to that in Fig. 3 and is characterized with two
maximums again at the monomer feed compositions (MMA) equal to the both complex compositions: MA-VH (C1) and MA-(VH)2 (C2). It is interesting to follow
the influence of other solvents on this copolymerization, the task under a development at the moment.
Another challenge of the results obtained and more precisely – the formation
of two donor-acceptor complexes (C1 = MA-VH and C2 = MA-(VH)2) and their
participation in the propagation chains, is connected with a possibility for the C2
participation in the defined by Hall et al [11-14] bond-forming initiation of DAC.
A
A
A
A
+
(22)
D
D
The forming by this scheme covalent-bounded radical pairs is a prerequisite
for both the spontaneous DAC initiation and for the biradical copolymer chain
propagation trough the reactions (12-16). According to the Huisgen [15] the radical pair is one of the possible intermediates of the interaction of two olefines with
electronodonor and elektronoacceptor substituents. It is reasonably to regard this
intermediate as a product of the decomposition of the donor-acceptor complex C1
= MA-VH (23).
A
A
A
A
A
A
+
(23)
D
D
D
(C1)
If it is so, the proved above formation and participation of the complex C2 =
VH-MA-VH in the chain propagations creates a hypothesis for the formation of
the following covalent-bonded radical pair from the complex C2 = MA-(VH)2:
242
o
oc
o
c
+ 2(
c o
o c
o
o
o
c o oc
o
o
c
)
c o c
R
R
o
o
o
R
o
c o
(24)
c o
R
R
R = C9H19
(C2)
There is not a theoretical analysis of the possibility for the formation of such
radical pair. This is in force for the experimental verification of this possibility. This
new type radical pair is the essence of the possible answer of the pointed out above
challenge. Maybe the presence of two acceptor groups at the double bond of the
acceptor (MA in this case) is a reason for the formation of longer conjugation chain
between one acceptor (MA) and two donor (VH) molecules, and for the simultaneous break of the both double bonds of the both donor molecules (VH), connected
together trough the π-bond of A (MA) (24). It is seen (24) that the both uncoupled
electrons of the radical pair produced are localized at the carbon atoms belonging to
the both electrondonor molecules (VH) included in the initial donor-acceptor complex C2. In means that if the donor-acceptor interaction in the propagation reactions
dominates, the first chain propagation steps of this radical pairs are the reactions
(12) and (13), demonstrating the interaction of the propagation end ~VN • either
with MA (12) or with MA component of the MA-VH complex (13).
DAC AZEOTROPY
The experimental results obtained for the presence of the maximums of the
MA-VH copolymerization rate as a function of the monomer feed in bulk (Fig. 2)
and in a solution (Fig. 5) at MMA = 0.50 and 0.33 as well as of the minimum of the
MA mole fraction (mMA) in the copolymers produced at MMA = 0.33 (Fig. 3) can
be explained reasonably with suggestion for the formation of two donor-acceptor
complexes (equimole one MA-VH and nonequimole one MA-(VH)2) and their
participation in the chain propagation reactions. The identification of these complexes, and their detailed structure organization and determination of their stability constants are the tasks which are under study. In spite of this, the suggestion
is already fruitful as it allows to explain simultaneously both the kinetic results
obtained (Figs. 1, 2–5) and that for the dependence of the copolymer composition on the monomer feed (Fig. 3). These are the both peculiarities of the DAC
243
discussed. According to the literature information available, such polymerization
peculiarities for DAC between a strong electronacceptor (MA) and strong electrondonor (VH) were obtained and explained for the first time. This is in force
for the defined above suggestion for their explanation. In the present work the
quantitative generalization of the discussed results was made also. It was proved
strictly the statement that at the formation of the any nonequimolar comonomer
complex AmDn (m ≠ n) its concentration as a function of the monomer feed composition has maximum at acceptor mole fraction MA = m/(m+n) (Eqn 20). From
this statement and a preposition for the participation of the complex in the chain
propagation reactions with rate constants higher than those for the single monomer molecule additions to the same propagation chains, it follows: i. clear maximum of the copolymerization rate dependence as a function of the monomer feed
at the same composition of the latter (MA = m/(m + n), and ii. the composition of
the copolymer produced at this monomer feed (MA = m/(m + n)) is, if not strictly
equal, very close to that of the complex (mA = MA = m/(m + n)). By this way, the
azeotropy (Fig. 6) for DAC was defined and proved. Its essence is that the copolymer composition is equal to that of the monomer
Donor-Acceptor Complex
(C = AmDn) formation
Registration of the [C]max at monomer feed composition
[A]/[D] = m/n
C takes part in the chain propagation reactions and
kpC > kpA and kpD
Registration of Vmax at the same monomer feed
composition [A]/[D] = m/n
AZEOTROPY means that mA/mD = m/n at the same
monomer feed composition [A]/[D/ = m/n
Figure 6. Algorithm for the proof of the azeotropy of DAC in which chain propagation
reactions the donor-acceptor complex C = AmDm takes place. MFC - monomer feed
composition; mA, mD – mole fractions of A and D monomer units in the copolymer; kpA,
kpD, kpC are the rate constants of the A, D and C addition reactions to the propagation ends;
Vmax is the maximal copolymerization rate.
feed composition if the latter is identical to that of the donor-acceptor complex
AmDn. The established peculiarities of DAC between MA and VH in bulk and
244
in dioxin underlines this common for such copolymerization azeotropy. For this
copolymerization the both azeotropy copolymer compositions are equimole one
(m/n = 1) and nonequimole when m/n = 0.5. If the monomer feed compositions
are equal to the azeotropy ones, the rate of this DAC adopts its local maximums.
As a result just of the higher rates of the complex inclusion in the copolymer chain
in comparison with single monomer molecules, the copolymer composition seeks
to the complex one. This striving, according to the discussion above, provides the
tendency to equilification of the monomer feed composition and that of the copolymers obtained at the azeotropy points (monomer feed compositions). In this
work the azeotropy of the DAC was defined only. The strict quantitative analysis
of this phenomenon, including the influence of the complex stability constants and
of the difference between the propagation rate constants for forecasts and is the
new, third challenge for the future DAC theory.
In the light of this phenomenon the developed kinetic method for the determination of the complex participation in the chain formation of the alternating copolymerization developed in our previous work of this series [5] could be regarded as
a partial case of the quantitative analysis of the azeotropy of this copolymerization,
those when m = n. The extension of this method accounting DAC azeotropy for
nonequimole comonomer complex composition (when m ≠ n) is forthcoming.
The DAC azeotropy, defined above, provides a new light on the relationship between DAC and AC. Usually these two names are regarded as synonyms.
However, from the discussion above it becomes clear that the identity between
these copolymerizations takes place if only one, equimole (m = n) comonomer
complex is formed and participates in the propagation reactions. In all other cases
these two definitions characterize two different copolymerizations. DAC is not
identical with AC even only one donor-acceptor but not equimole (m ≠ n) complex is formed. Because of the azeotropy in this case the copolymer produced
is not equimole, and thus it is not alternating. The difference between DAC and
AC becomes more considerable when two and more comonomer complexes are
formed and take place in the chain propagation. By this way, the introduced and
used in this work category azeotropy of the donor-acceptor copolymerization allows clear deviation and definition of DAC and AC.
CONCLUSION
For MA-VH DAC in bulk and dioxan it was shown the existence of two
copolymerization rate maximums as a function of monomer feed at MA = 0.50
and MA = 0.33. This fact was explained with the formation of two donor-acceptor
complexes (MA-VH and VH-MA-VN) and their participation in the chain propagation reactions. This suggestion was confirmed by the results for the copolymer
composition. The latter follows the complex composition one and thus it is equal
to the monomer feed composition also. The equality of the copolymer and mono245
mer feed composition is the essence of the azeotropy, which was established and
explained for DAC for the first time.
Acknowledgements: This work was funded by EC, 6FP (STREP, PhotoNanoTech, Contr. No:
NMPC-ct-2007-033168).
REFERENCES
1. Cowie, J. M. G. Alternating Copolymers. Plenum Press, New York, 1985.
2. Kabanov, V. A., V. P. Zubov, Yu. D. Semchikov. Complex-Radical Copolymerization. Chemistry,
Moscow, 1987.
3. Barton, B., E. Borsig. Complexes in Eree-Radikal Polymerization. Elsevier, Amsterdam, 1988.
4. Georgiev, G. S. Models and Control of the Radical Polymerization. Thesis. University of Sofia,
Department of Chemistry, 2001.
5. Georgiev, G. S., V. P. Zubov. Eur. Polym. J., 14, 1978, 93.
6. Georgiev, G. S. Macromolecules, 28, 1995, 6883.
7. Georgiev, G. S. Polymer Bull., 6, 1981, 29.
8. Georgieva, V. T., G. S. Georgiev. Polym. J., 29(3), 1997, 270.
9. Georgiev, G. S., V. T. Georgieva. Polym. Int., 48, 1999, 819.
10. Ratch, M. Progr. Polym. Sci., 13, 1988, 277.
11. Hall, H. K. Jr., A. B. Padias. Acc. Chem. Res., 23, 1990, 3.
12. Hall, H. K. Jr., P. Ykman. Macromolecules., 10, 1977, 464.
13. Hall, H. K. Jr., P. Ykman. J. Am. Chem. Soc., 97, 1975, 800.
14. Hall, H. K. Jr., A. B. Padias, A. Pandya, H. Tanaka. Macromolecules, 20, 1987, 247.
15. Huisgen, R. Acc. Chem. Res., 10, 1977, 199.
246
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
THERMO-QUANTUM DIFFUSION IN PERIODIC POTENTIALS
ROUMEN TSEKOV
Department of Physical Chemistry, University of Sofia, 1 James Bourchier Blvd., 1164 Sofia, Bulgaria
Abstract. Quantum Brownian motion in a periodic cosine potential is studied and
a simple estimate of the tunneling effect is obtained in the frames of a semiclassical
quasi-equilibrium approach. It is shown that the latter is applicable for heavy particles
but electrons cannot be described properly since the quantum effects dominate over the
thermal ones. The electron purely quantum diffusion is investigated at zero temperature
and demonstrates that electrons do not obey the classical Einstein law of Brownian
motion in the field of periodic potentials, since the dispersion of the Gaussian wave packet
increases logarithmically in time.
Diffusion in the field of periodic potentials is important for particle transport
via ordered structures, typical in condensed matter. The underlying mechanism
is Brownian motion. If the diffusing particles are quantum ones, e.g. electrons,
protons, light atoms, etc., their migration is described via the theory of quantum
Brownian motion [1, 2], which is significantly affected by the tunneling effect
[3]. Hereafter an alternative approach to the problem of quantum Brownian motion in periodic potentials is developed based on the Bohm quantum potential
[4]. In contrast to the WKB theory valid in vacuum the present paper describes
tunneling in a dissipative environment. The starting point is a nonlinear quantum
Smoluchowski-like equation [5, 6]
β
∂ t ρ = ∂ x [ρ∂ x ∫ (V + Q)b d β + ∂ xρ] / β b
0
(1)
247
describing the overdamped evolution of the probability density ρ( x, t ) to
find a quantum particle at a given place under the action of an arbitrary external potential V . Here b is the particle friction coefficient, β = 1/ k BT and
Q ≡ − 2 ∂ 2x ρ / 2m ρ is the Bohm quantum potential with m being the particle mass. Thus, due to the quantum potential the diffusion becomes mass-sensitive. The goal of the present analysis is to estimate the diffusion coefficient from
Eq. (1) for the case of a periodic cosine potential V ( x) = U cos(qx) .
Since Eq. (1) is nonlinear due to the quantum potential, obtaining its general
solution is mathematically frustrated. In a semiclassical approach one could estimate Q by using the classical solution of Eq. (1). However, even in the classical
case it is impossible to obtain a simple physically transparent expression for the
probability density. For this reason, we are going to apply a stronger approximation
by employing the equilibrium classical Boltzmann distribution ρ B ∼ exp(−β V )
in the quantum potential to obtain
Q(ρ B ) = (β
2
/ 4m)[∂ 2xV − β(∂ xV ) 2 / 2] = −λT2 q 2 [V + β(U 2 − V 2 ) / 2] (2)
The first expression here is general, while the last one is valid for the present
particular cosine potential; the thermal de Broglie wave length is introduced by
the expression λT ≡ / 2 mk BT . Note that because of this quasi-equilibrium
approximation the quantum potential (2) becomes temperature-dependent. Substituting Eq. (2) in Eq. (1) and performing the integration over β results in the
following semiclassical quasi-equilibrium Smoluchowski equation
∂ t ρ = ∂ x (βρ∂ xW + ∂ xρ) / β b
(3)
where the new effective potential is given by W ≡ [1 − λT2 q 2 (1 − β V / 3) / 2]V and
possesses the same periodicity as the external potential V . Owing to the Boltzmann
distribution employed, Eq. (3) is a quasi-equilibrium one and in the case of a free
quantum Brownian particle ( V = 0 ) it reduces to the classical diffusion equation.
Hence, its application is restricted to relatively strong external potentials, where
the semiclassical quantum effects still play a role. For instance, in a harmonic potential V = mω02 x 2 / 2 the effective potential W = [1 − (β ω0 / 2) 2 / 3]V is harmonic as well. Thus, the average equilibrium position dispersion, following from
Eq. (3), σ 2x = 1/ β mω02 [1 − (β ω0 / 2) 2 / 3] is the high temperature approximation
of the exact thermodynamic expression σ 2x = ( / 2mω0 ) coth(β ω0 / 2) .
Lifson and Jackson [7] and later Festa and d’Agliano [8] have derived a general formula for calculation of the diffusion coefficient D from Eq. (3) applied
for periodic potentials
1/ D = β b < exp(β W ) >< exp(−β W ) >
248
(4)
where the brackets < ⋅ > indicate spatial geometric average. At room temperature
one can usually neglect the small nonlinear contribution of the external potential
V to W and thus the latter acquires the simplified form W = (1 − λT2 q 2 / 2)V .
In this case the spatial averaging in Eq. (4) can be analytically accomplished and
the result reads
1/ D = β bI 02 [β(1 − λT2 q 2 / 2)U ]
(5)
where I 0 is the modified Bessel function of first kind and zero order. In the case
of free Brownian motion ( U = 0 ) Eq. (5) provides the classical Einstein formula D = 1/ β b , which is due to the semiclassical quasi-equilibrium approach [9].
At large arguments the modified Bessel function can be approximated well as
I 0 ( x) ≈ exp( x) / 2πx and Eq. (5) reduces in this case to the Arrhenius law
D = π(2 − λT2 q 2 )(U / b) exp[−β(2 − λT2 q 2 )U ]
(6)
As is seen, both the effective activation energy Ea ≡ (2 − λT2 q 2 )U and the
pre-exponential factor π(2 − λT2 q 2 )U / b from Eq. (6) are affected by the quantum
effect. In the classical limit λT = 0 and the activation energy Ea = 2U equals to
the difference between the maximal and minimal value of the external potential.
The quantum effect decreases effectively the activation energy due to the quantum
tunneling. For instance, the thermal de Broglie wave length for a proton at room
temperature equals to λT ≈ 0.2 Å. If protons are diffusing in a structured medium
with a lattice constant 3 Å then λT2 q 2 / 2 ≈ 0.1 . Hence, the tunneling effect will
decrease the activation energy by 10 % as well as the pre-exponential factor. Note
that if λT2 q 2 = 2 the diffusion is free since W = 0 , which corresponds for a proton
to T ≈ 25 K. For electrons the thermal de Broglie wave length at room temperature
is λT ≈ 8.6 Å and hence λT2 q 2 / 2 ≈ 162 . Since this number is much larger than 1,
the conclusion is that the theory above is not applicable to electrons since they are
essentially quantum particles and cannot be described by a quasi-equilibrium semiclassical approach, unless they are moving in very flat potentials with q < 1/ λT .
For electrons one should solve directly Eq. (1) instead of Eq. (3). To simplify
now the problem we will consider the case of zero temperature, where Eq. (1)
reduces to
∂ t ρ = ∂ x [ρ∂ x (V + Q)] / b = ∂ x [ρ∂ xV / b −
2
∂ x (ρ∂ 2x ln ρ) / 4mb]
(7)
This is still a nonlinear equation, which is not easy to solve. To linearize it one
can use the fact that the effective shape of the probability density is expected to
be Gaussian in the case of relatively low U , which corresponds to lack of localization. Hence, one can employ the approximation ∂ 2x ln ρ = −1/ σ 2x , where σ 2x
249
is the dispersion of the probability density. Introducing this expression in Eq. (7)
yields a Smoluchowski equation
∂ t ρ = ∂ x (ρ∂ xV + βQ−1∂ xρ) / b
(8)
with a new quantum temperature βQ−1 ≡ 2 / 4mσ 2x corresponds to the momentum
dispersion from the minimal Heisenberg relation valid for Gaussian processes.
Since βQ depends on time via σ 2x one should use a more general expression of
the Festa-d’Agliano formula [8]
∂ t σ2x / 2 = [βQ b < exp(βQV ) >< exp(−βQV ) >]−1 = 1/ βQ bI 02 (βQU )
(9)
Integration of Eq. (9) on time yields the relation
(βQU ) 2 [ I 02 (βQU ) − I12 (βQU )] = 16mU 2t /
2
b
(10)
where I1 is the modified Bessel function of first kind and first order.
If U = 0 , Eq. (10) reduces to the already known expression σ 2x =
t / mb
for the purely quantum diffusion in a non-structured environment [6]. Note that
this dispersion does not depend linearly on time and hence no diffusion constant
exists. In the opposite case 2βQU > 1 the modified Bessel functions difference is
well approximated by I 02 ( x) − I12 ( x) ≈ exp(2 x) / 2πx 2 . Thus according to Eq.
(10) the dispersion of the purely quantum diffusion in a strong cosine potential
depends logarithmically on time
σ2x = (
2
/ 8mU ) ln(32πmU 2t /
2
b)
(11)
This result demonstrates again the lack of classical diffusive behavior. As seen
from Eq. (11) the magnitude of the deviation σ x scales with the de Broglie wave
length λU = / 2 2mU of the activation energy [9], while its relaxation time
b / mωU2 corresponds to that of a harmonic oscillator with an own frequency
ωU = 4U / . Even if this logarithmic dependence is derived here particularly for
a cosine external potential we believe that it is general for any periodic potential
and reflects the Arrhenius law. Indeed the latter holds in any periodic potential
when the potential barriers are much higher than the thermal energy and the particular type of the potential affects the pre-exponential factor only [7, 8]. Hence,
the quantum diffusion does not obey the classical linear Einstein law of Brownian
motion in periodic potentials as well [10]. The account for the nonlinear term in
the potential W will introduce some aperiodic behavior, which certainly will accelerate the diffusion process [11].
250
In the case of a free quantum Brownian particle ( V = 0 ) an alternative way to
simplify Eq. (7) is, instead of the quantum pressure, to linearize the quantum potential
around the homogeneous equilibrium distribution. In this way, Eq. (7) reduces to
∂ t ρ = − 2 ∂ 4xρ / 4mb
(12)
This equation is not parabolic one and hence it does not describe an ordinary diffusion process. Since the Fourier image ρq = exp(− 2 q 4t / 4mb) of the solution
of Eq. (12) corresponds to a probability density, which is not positively defined, it
seems that Eq. (12) is a worse approximation than the diffusive Eq. (8). The solution of ∂ t ρ =
2
∂ 2x ρ / 4mbσ 2x is a Gaussian distribution density with dispersion
σ2x =
t / mb . Equation (7) is also exactly solvable for a free quantum Brownian
particle and its solution is, of course, the same Gaussian distribution [6].
Acknowledgement. The author is grateful to the Bulgarian NSF for financial support through
grant DRG 02/3.
REFERENCES
1. Fisher, M. P. A., W. Zwerger. Phys. Rev. B., 32, 1985, 6190.
2. Coffey, W. T., Yu. P. Kalmykov, S. V. Titov, B. P. Mulligan. Phys. Rev. E, 75, 2007, 041117.
3. Coffey, W. T., Yu. P. Kalmykov, S. V. Titov, L. Cleary. Phys. Rev. E, 78, 2008, 031114.
4. Bohm, D. Phys. Rev., 85, 1952, 166.
5. Tsekov, R. J. Phys. A: Math. Gen., 28, 1995, L557.
6. Tsekov, R. Int. J. Theor. Phys., 48, 2009, 630.
7. Lifson, S., J. L. Jackson. J. Chem. Phys. 36, 1962, 2410.
8. Festa, R., E. G. d’Agliano. Physica A, 80, 1978, 229.
9. Tsekov, R. J. Phys. A: Math. Theor., 40, 2007, 10945.
10. Tsekov, R. Phys. Scr., 85, 2011, 035004.
11. Tsekov, R., E. Ruckenstein. J. Chem. Phys., 101, 1994, 7844.
251
252
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
FLOCCULATION OF VESICLES
ROUMEN TSEKOV
Department of Physical Chemistry, University of Sofia, 1, J. Bourchier Blvd., 1164 Sofia, Bulgaria
Abstract. The flocculation of liposomes is theoretically studied. An expression for the
flocculation activation energy is derived, accounting for the electrostatic and hydrophobic
interactions as well as for the correlation area of floc-spots.
INTRODUCTION
In water phospholipid molecules form spontaneously spheroid structures
called vesicles or liposomes [1, 2]. Their body is filled by maternal solution and
surrounded by a closed bilayer surface. The liposome wall is not penetrable for
large molecules and for this reason vesicles are used as original carrier of drags
and other substances in medicine and cosmetics [3, 4]. Hence, the stability of liposome suspensions is important for these applications and this is the reason for
intensive studies on the flocculation kinetics of vesicles in solutions.
The problem of coalescence of two liposomes is equivalent to the problem
of rupture of the liquid film formed between two vesicles (see Fig. 1). Because
vesicles possess almost zero surface tension, they are easily deformable and the
hydrodynamics resistance due to the vesicles approach deforms liposomes naturally to form a thin liquid film. Similar picture is observed in deformable droplets,
which possess, however, large surface tension [5]. When the film ruptures, the
liposomes attach to each other and a primary floc is formed. A very useful idea in
colloid science is to consider the film stability as a result of competition of interfacial forces [6]. The classical DLVO theory considers van der Waals and electrostatic components only. It has been recognized further that there are many other
macroscopic interactions in the films such as hydration, hydrophobic, etc. forces
[5]. Knowledge of all these components is important to answer the questions how
253
do the liposomes flocculate and what is the role of polymers and other substances
in the floc-formation.
h
Fig. 1 Schema of a collision of two liposomes or droplets [5]
THEORY
Let W is the free energy excess per unit area of a film as compared to the
corresponding bulk liquid. The simplest expression for the van der Waals excess
energy is
WVW = − A /12πh 2
(1)
where h is the film thickness and A is the Hamaker constant, which is always
positive for symmetric films. Hence, the van der Waals force in films dividing
two liposomes or droplets is attraction. However, since the bulk phase of the vesicles possesses the same composition like the film solution, the Hamaker constant
should be negligibly small for liposomes. Therefore, the van der Waals interaction
is not important for the flocculation kinetics of vesicles, in contrast to the case of
droplets. The classical expression for electrostatic energy at constant and relatively weak surface charge q per unit vesicle area is [7]
WEL = 2( Dq 2 / ε 0 ε) exp(− h / D)
(2)
where D is the Debye length and ε 0 ε is the dielectric permittivity of the suspension. As is seen there are two different kinds of electrolyte effects on the electrostatic interaction. An increase of the concentration of ions not adsorbing specifically on the film interfaces decreases the Debye length and thus suppresses the
electrostatic repulsion. Ions adsorbed specifically on the film interfaces change
the surface charge density q and depending on their sign can lead to increase
or decrease of WEL. This can be a reasonable explanation of the relative stability
254
of liposome suspensions on ionic strength variations [8] and of the aggregation
induced by calcium and beryllium cations [9].
Tsekov and Schulze have demonstrated that any adsorption of species on the
film interfaces causes a hydrophobic force. The corresponding excess energy is
given by [10, 11]
WHP = 2ΔEG exp(− h / a )
(3)
where a is the adsorption length and ΔEG is the difference of the Gibbs elasticity on the surface of a vesicle and on the surface between two liposomes in a floc.
The adsorption length and ΔEG depend strongly on the concentration of species
in the bulk. If ΔEG is negative the hydrophobic force is attraction and the liposome suspensions could become unstable. Indeed, flocculation induced by addition of polymers was experimentally observed [12, 13]. Equation (3) is applicable
also for description of the solvent adsorption effect. The corresponding force is
known as hydration force [14] and some authors put forward an explanation of the
relative stability of phospatitylcholine liposome suspensions by a strong repulsive
hydration interaction [8]. The vesicle bilayers themselves are source of hydrophobic force. For instance, Alexandrova and Tsekov [15] have demonstrated that
liposomes induce attractive forces in an aqueous wetting film on a quartz surface
which lead to rupture of the films. The latter are stable without vesicles. Moreover,
this interaction is very sensitive to small temperature changes due to many phase
transitions occurring in the lipid bilyaers [16].
The total excess of free energy W= WVW + WEL + WHP in a film dividing two
liposomes takes the following form
W = 2( Dq 2 / ε 0 ε) exp(− h / D) + 2ΔEG exp(− h / a )
(4)
after neglecting the contribution of the van der Waals force. Since we are interested in unstable liposome suspensions the hydrophobic force here should be attractive and ΔEG is considered further to be negative. Usually at relatively low
electrolyte concentrations the electrostatic force is longer ranged as compared to
the hydrophobic one, i.e. D ≥ a . In this case W exhibits a maximum as shown in
Fig. 2 if − ε 0 εΔEG ≥ a
q 2 . Using eq. (4) one can calculate the film thickness h *
corresponding to the maximum energy and the height W * of the energy barrier
a
h* =
ε εΔE
Da
2( D − a ) q 2
aq 2 D −a
(−
)
ln(− 0 2 G ) W * =
ε0ε
ε 0 εΔEG
D−a
aq
(5)
Since the pressures inside and outside a liposome are equal, the only force
pushing the vesicles to each other is due to the Brownian motion and the maximum W * represents the activation energy per unit area of the liposome floccula255
tion. As seen from eq. (5) W * is an increasing function on D , q 2 and ΔEG . The
dependence W * vs. a is more complicated.
W
*
W
0
0
*
h
h
Fig. 2 Energy profile of two liposomes separated by a film with thickness
h
The initial rate of flocculation is given by V = K n , where n is the liposome
concentration and K is the rate constant of flocculation. Using the well-known
expression
2
K = (8k BT / 3η) exp(− E * / k BT )
(6)
one is able to calculated the activation energy E * of the process from the temperature dependence of K [17]. The activation energy is related to W * and to the
area o of the first floc-spot formed in the film, E * = oW * . Hence, to calculate the
activation energy it is necessary to calculate the correlation area o , as well. The
shape in Fig. 1 is an average profile, while the real shape fluctuates permanently.
From the theory of film thickness fluctuations is known that it is proportional
to the lipid bilayer bending elasticity κ and the second derivative of the free
energy in the film in respect to its thickness. Since the fluctuations close to the
barrier top are important for the flocculation kinetics the correlation area is equal
to o = −κ / W ′′(h* ) . Note that according to the Scheludko wavelength the correlation area in droplet films is equal to o = −σ / W ′′(h* ) , where σ is the drop
surface tension. Calculating the second derivative of W from eq. (4) one yields
W ′′( h * ) = −W */aD and the correlation area amounts to
o = κaD / W *
256
(7)
Finally, introducing eq. (7) in the relation E * = oW * we acquire an expression for
the activation energy
E * = κaDW *
(8)
It is interesting that for droplets the activation energy E * = σaD is independent
of W * .
The effects of other substances to the flocculation can be seen in the activation energy from eq. (8). Using eq. (5) it can be rewritten in the form
E * = κDa
2( D − a )q 2
aq 2 Da− a
(−
)
ε0ε
ε 0 εΔEG
(9)
Firstly, by addition of electrolytes the Debye length D decreases. This screening
of the electrostatic interaction decreases the stabilising force between two vesicles. As a result the films become less stable and the activation energy E * goes
down. This is the case of electrolyte induced fast coagulation in disperse systems.
If some ions adsorb specifically on the liposome surface and if their charge has
opposite sign than the surface one, then they diminish the surface charge density
q and in this way decrease the activation energy. Secondly, addition of uncharged
species like polymers, aionic surfactants, etc. affects the hydrophobic force. If
they decrease, the value of the resulting ΔE G the activation energy decreases,
too. A dramatic effect, however, will appear if they change also the value of the
effective adsorption length. For instance, if a becomes larger than D there is no
more maximum in the energy as a function of the film thickness. The result is barrier-less flocculation being much more rapid than the usual one. Such an increase
of a is expected in the case of adsorption of long polymers on the vesicle wall.
And the effect is known as bridging flocculation being inter-mediated by polymer
bridges. Finally, adsorption of species affects the elastic properties of the vesicle
bilayers. Usually they increase the bending elastic modulus κ , which reflects in
lower flocculation rate. The effect of the liposome size on flocculation can also be
accounted for [18].
Acknowledgement
The author is grateful to the Bulgarian NSF for financial support through grant DRG 02/3. He
is also thankful to Dr. Hideo Matsumura for stimulating discussions and to the Referee for valuable
comments.
257
REFERENCES
1. Lasic, D. Liposomes: from Physics to Applications, Elsevier, Amsterdam, 1993
2. Blanschtein, D., A. Shiloach and N. Zoeller. Curr. Opin. Colloid Interface Sci., 2 (1997), 294
3. Pozannsky, M. and R. Juliano. Pharmacol. Rev., 36 (1984), 277
4. Allen, T. Curr. Opin. Colloid Interface Sci., 1 (1996), 645
5. Petsev D.N., N.D. Denkov and P. A. Kralchevsky. J. Colloid Interface Sci., 176 (1995), 201
6. van Oss, C. Interfacial Forces in Aqueous Media. Dekker, New York, 1994
7. Verwey, E. and J. Overbeek. Theory of the Stability of Lyophobic Colloids. Elsevier, Amsterdam, 1948
8. Matsumura, H., K. Watanabe and K. Furusawa. Colloid Surf. A, 98 (1995), 175
9. Minami, H., T. Inoue and R. Shimozawa. Langmuir. 12 (1996), 3574
10. Tsekov, R. and H. J. Schulze. Langmuir., 13 (1997), 5674
11. Tsekov, R. Ann. Univ. Sofia, Fac. Chem. 102/103 (2011), 273
12. Massenberg, D. and B. Lentz. Biochem. 32 (1993), 9172
13. Viguera, A., A. Alonso and F. Goni. Colloid Surf. B 3 (1995), 263
14. Besseling, N. Langmuir, 13 (1997), 2113
15. Alexandrova, L. and R. Tsekov. Colloid Surf. A 131 (1998), 289
16. Alexandrova, L., R. Koynova, L. Grigorov and B. Tenchov, Colloid Surf. A 149 (1999), 239
17. Dimitrova, M., H. Matsumura and V. Neitchev. Langmuir., 13 (1997), 6516
18. Dimitrova, M., R. Tsekov, H. Matsumura and K. Furusawa. J. Colloid Interface Sci., 226 (2000), 44.
Received on April 4, 2011
258
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
WETTING PROPERTIES OF LOW-VISCOSITY ROOM
TEMPERATURE IMIDAZOLIUM IONIC LIQUIDS
IVAN T. IVANOVa, IANA S. PETKOVAa, BORISLAV P. SOKLEVa, ILIANA V. DELCHEVAa,
BOYAN ILIEVb, THOMAS J. S. SCHUBERTBb, MILEN G. BOGDANOVa,
RADOMIR I. SLAVCHOV*,a
b
a
Faculty of Chemistry, University of Sofia, 1, J. Bourchier Blvd., 1164 Sofia, Bulgaria
Iolitec Ionic Liquid technologies GmbH, Salzstrasse 184, D-74081 Heilbronn, Germany
*Corresponding author: [email protected], +359 2 8161613
Abstract. The wetting properties of six low viscosity room temperature ionic liquids (RTIL) were
investigated by means of dynamic three-phase contact (TPC) angle measurements of RTIL droplets
sliding at an inclined surface. Well-defined solid surfaces of different hydrophobicity were used. Hydrophobicity strongly increased TPC line mobility. Molecular kinetic (Blake-Haynes) model compares
well with the experimental data for TPC line rate of propagation as a function of dynamic TPC angle,
while hydrodynamic (Voinov) model does not. Comparison with water droplets at the same surfaces
shows qualitatively similar, but quantitatively different wetting properties of RTILs.
Keywords: room temperature ionic liquids; imidazolium; wetting kinetics; three-phase contact
angle; contact angle hysteresis; drop on inclined surfaces
1. INTRODUCTION
Room temperature ionic liquids (RTIL) have numerous applications, due to
their unique properties – low volatility, high thermal and chemical stability, possibility for regeneration [1–3]. These properties make them good solvents in organic
synthesis [2]. They have the ability to dissolve otherwise insoluble molecules,
such as cellulose [3]. New recently developed applications include their use in
microfluidic devices [4]. RTILs’ excellent properties as solvents and their appli259
cations, such as microfluidics [4], are a reason to investigate their cleaning and
wetting properties.
From the surface properties of the RTILs, surface tension of the ionic liquid/air
interface was the first to receive scientific attention (review of experimental and
theoretical studies: [1,5]). No surprises were found: surface tension values are of the
same order, but lower, compared with water/air interface. The temperature dependence of the surface tension is linear [6–9]. With homologues, σ decreases with carbon chain length [7]. Surfactant aggregation behavior in RTIL’s and its effect on the
RTIL’s surface tension is similar to that of surfactant in water [11–13]. Fluorinated
surfactants were found to reduce the surface tension more than hydrocarbon-based
surfactants [13]. Capillary waves at the interface RTIL/gas were investigated [8–9].
The dispersion law of the capillary waves at RTILs surfaces deviated strongly from
dispersion law of simple liquids, due to the strong normal dipole moment surface
density. The temperature dependence of the surface dipole moment indicated interfacial order-disorder transition at a certain temperature [10].
During the last two years, RTIL’s wetting properties became a major focus
of scientific literature [14]. The studies in this field started with the electrowetting
properties of RTILs [14–20]. The main results from these studies can be summed
up as follows: (1) electrowetting typically follows Young-Lippmann equation; (2)
saturation contact angle and potential are observed, at which the effect of further
increase of the potential has small effect on the contact angle. Another important
direction of study was the electrocapillary properties of RTILs [21–23]. A model
for the electric double layer in ionic liquid was proposed [22], trying to explain the
camel-shaped double layer capacitance curve, found with certain ionic liquids.
Furthermore, few recent works deal with the static wetting properties of ionic
liquids (mostly imidazolium based) at surfaces of different hydrophobicity [2425]. The current work investigates the dynamics of wetting of RTILs at glass
surfaces. From rheological viewpoint, the relationship between the three-phase
contact (TPC) line rate and the applied driving force is of main interest here. According to the known studies, TPC rheology model can be successfully presented
by two dissipative elements in series: the first one entirely in the TPC bulk zone
determined by the bulk viscosity (Voinov’s model [26]) and the second, localized
in the contact line obeying a barrier (Eyring) mechanism (Blake-Haynes model
[27, 28]). Due to the relatively high bulk viscosities of ionic liquids (higher in
comparison with the water viscosity) one could expect more pronounced bulk
drag compared to water. On the other hand, large TPC contact angles (>20 deg)
advantage the contact line barrier mechanism [29–32]. To the best of our knowledge, only one work dealt with dynamic contact angle measurements of RTILs
[16], and it confirms these expectations. In the current article, we are investigating
the dynamic contact angle in greater detail.
260
2. MATERIALS AND EXPERIMENTAL SETUP
2.1. Synthesis of the ionic liquids
RTILs under study (Fig. 1) were synthesized by metathesis reactions from
the coresponding imidazolium or pyridinium chlorides or bromides, which were
obtained from Iolitec GmbH in a >98% purity and used without further purification. The determination of the ion purity was achieve by means of ion chromatography (IC) from Metrohm GmbH und Co. KG consisting of a 733 IC separation
center, a 732 IC detector and a 753 suppressor module. All starting chlorides and
bromides were obtained from Iolitec GmbH in a >98% purity and used without
further purification.
Fig. 1 Structure and abbreviation of ions used to form the ILs under study.
(a) Syntesis of 1-Allyl-3-methylimidazolium dicyanamide (AllMIM DCA)
1-Allyl-3-methylimidazolium chloride (100 g, 0.63 mol) was dissolved in dry
acetonitrile and sodium dicyanamide (57.9 g, 0.65 mol) was added portionwise.
The reaction mixture was stirred at RT for 3 days, filtered off and the solvent was
removed in a rotary evaporator, and the purification process was completed by one
more filtration and heating the ionic liquid at 50ºC for 24 h under high vacuum. A
liquid with a yellowish coloration was obtained. The purity of the desired product
was confirmed by IC and was found to be 98.7 DCA and 98.9% AllMIM. A water
content of 1020 ppm in the final product was measured by Karl Fischer titration.
(b) Syntesis of 1-Ethyl-3-methylimidazolium dicyanamide (EMIM DCA)
1-Ethyl-3-methylimidazolium bromide (100 g, 0.507 mol) was dissolved in
dry acetonitrile and sodium dicyanamide (49 g, 0.55 mol) was added portionwise.
The reaction mixture was stirred at RT for 3 days, filtered off and the solvent was
removed in a rotary evaporator, and the purification process was completed by one
261
more filtration and heating the ionic liquid at 50 ºC for 24 h under high vacuum. A
liquid with a yellowish coloration was obtained. The purity of the desired product
was confirmed by IC and was found to be 98,3% DCA and 98.8% EMIM . A water
content of 980 ppm in the final product was measured by Karl Fischer titration.
(c) Syntesis of 1-Ethyl-3-methylimidazolium thiocyanate (EMIM SCN)
1-Ethyl-3-methylimidazolium bromide (100 g, 0.507 mol) was dissolved in dry
acetonitrile and sodium thiocyanate (44.6 g, 0.55 mol) was added portionwise. The
reaction mixture was stirred at RT for 3 days, filtered off and the solvent was removed
in a rotary evaporator, and the purification process was completed by one more filtration and heating the ionic liquid at 50ºC for 24 h under high vacuum. A liquid with a
red-brown coloration was obtained. The purity of the desired product was confirmed
by IC and was found to be 98.4% for SCN and 98.6 for EMIM. A water content of
1920 ppm in the final product was measured by Karl Fischer titration.
(d) Syntesis of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfony
l)imide (EMIM BTA)
1-Ethyl-3-methylimidazolium bromide (100 g, 0.507 mol) was dissolved in
dichloromethane (299 ml) and lithium bis(trifluoromethylsulfonyl)imide (157.9
g, 0.55 mol) in 200 ml water was added. . The reaction mixture was stirred at RT
for 2 hours, the phases separated and the organic phase washed 5x50ml water.
The solvent was removed in a rotary evaporator, and the purification process was
completed by heating the ionic liquid at 90 ºC for 24 h under high vacuum. A
liquid with a slightly yellowish coloration was obtained. The purity of the desired
product was confirmed by Ion chromatography and was found to be 99.9% TFSI
and 99.8% EMIM . A water content of 90 ppm in the final product was measured
by Karl Fischer titration.
(e) Syntesis of 1,3-Diethylimidazolium bis(trifluoromethylsulfonyl)imide
(DiEIM BTA)
1,3-Diethylimidazolium bromide (100 g, 0.49 mol) was dissolved in dichloromethane (299 ml) and lithium bis(trifluoromethylsulfonyl)imide (157.9 g, 0.55
mol) in 200 ml water was added. The reaction mixture was stirred at RT for 2 hours,
the phases separated and the organic phase washed 5x50 ml water. The solvent was
removed in a rotary evaporator, and the purification process was completed by heating the ionic liquid at 90 ºC for 24 h under high vacuum. A liquid with a slightly
yellowish coloration was obtained. The purity of the desired product was confirmed
by IC and was found to be 99.9% TFSI and 99.7% DiEIM. A water content of 80
ppm in the final product was measured by Karl Fischer titration.
(f) Syntesis of 1-Ethyl-3-methylpyridinium bis(trifluoromethylsulfonyl)i
mide (Et3Pic BTA)
1-Ethyl-3-methylpyridinium bromide (100 g, 0.49 mol) was dissolved in dichloromethane (299 ml) and lithium bis(trifluoromethylsulfonyl)imide (157.9 g,
0.55 mol) in 200 ml water was added. . The reaction mixture was stirred at RT for
262
2 hours, the phases separated and the organic phase washed 5x50 ml water. The
solvent was removed in a rotary evaporator, and the purification process was completed by heating the ionic liquid at 90 ºC for 24 h under high vacuum. A liquid with
a slightly yellowish coloration was obtained. The purity of the desired product was
confirmed by IC and was found to be 99.9% TFSI and 99.6% Et3Pic. A water content of 70 ppm in the final product was measured by Karl Fischer titration.
2.2. Experimental setup
Surface tension and viscosity measurements
Surface tension was measured using pendant drop method on Rame-Hart instrument No.290. All experiments were performed at temperature 22 °C. Every
measurement was carried out in a triplicate (with 3 pendant drops). 200 measurements were made with every drop. The surface tension was determined by surface
profile analysis. No special care was taken to reduce the humidity of the surrounding environment. The viscosities were measured on BROOKFIELD DV-II+ Pro
Programmable Viscometer.
Solid surface preparation
Coverglasses 20x20 mm from “Knittelgläser” (borosilicate glass) were used
for substrates. They were not very hydrophylic even before the hydrophobization
took place (water TPC angle was 13.5˚). The solid surfaces preparation includes
hydrophobization and further cleaning of both hydrophobic and hydrophilic surfaces. The glass surfaces were hydrophobized with bistrimethylsilcylacetamide
(BSA). About 70% hydrophobization is achieved with this method [33–35]. The
surfaces were cleaned with ethanol and dried at room temperature.
Contact angle measurements
All measurements of both static and dynamic TPC angles were performed
at standard volume of the drop V = 5 μl at temperature 22 °C. The drop profiles
were processed with ImageJ “DropSnake” plug-in [33]. Every measurement was
carried out in a triplicate.
Static contact angle (θst) measurement. The contact angle of a drop on a flat
surface (at tilt α = 0) is called static contact angle θst (Fig. 2).
Static advancing and receding angles (θa,st and θr,st) measurement at critical tilt αcr. As we incline the surface, the contact receding and advancing angles
change while the TPC line remains pinned. At a certain critical tilt angle, αcr, the
droplet starts to move. We will refer to the contact angles measured at this tilt αcr
as “static advancing angle” θa,st (at the front of the droplet) and “static receding
angle” θr,st (at the rear of the droplet, Fig. 2) [34, 35].
Dynamic contact angle and TPC line propagation rate measurements.
At tilt angles α > αcr, the droplets were moving with observable velocities. The
dynamic advancing and receding TPC angles of these moving droplets were measured. The higher the velocity, the more θa and θr deviate from their static values.
263
Rate of the TPC line propagation v was determined directly through the TPC line
positions ya (at the droplet front) and yr (at the droplet rear) dependence on time t (see
Fig. 2). The dynamic advancing and receding angles θa and θr were simultaneously
measured. The rate of TPC line propagation was calculated as ya(t) and yr(t) derivatives with respect to time t. The rate, v, could be controlled by changing the tilt angle
α from a minimal value αcr (corresponding to v = 0) to maximal value α = 90˚, corresponding to a certain maximal velocity of vmax; with our method, velocities higher
than vmax cannot be observed. The rate of the droplet rear propagation was taken with
negative sign (the TPC line recedes). The rate v, plotted versus the dynamic contact
angles’ cosines, cosθa and cosθr, represents the dynamic TPC rate low [26–32, 34].
The advantage of this method is that (1) only a small quantity of the ionic
liquid is needed for the measurements (compared with the well-established techniques, e.g. [30]), and (2) it makes it possible to measure also the receding angles
(compared to [16]).
Fig. 2 Definition of the TPC angles measured. (a) Static contact angle measurements. At tilt
α = 0, the droplet shape is symmetric with angle θst. (b) Static advancing and receding angles
measurement at the critical tilt αcr. At any tilt 0 < α < αcr, the droplet has no observable velocity.
(c) Dynamic contact angle measurements. At tilt α > αcr, the droplet is in motion. From its
profile, the dynamic advancing and receding angles θa and θr were determined. Simultaneously,
the position of the TPC at the front of the drop, ya(t), and at its rear, yr(t), were measured as
functions of time t. From the dependence y(t), the corresponding TPC line rate of propagation
v was determined by differentiation. The rate v can be easily controlled by shifting the tilt α
(the larger the tilt, the higher the velocity of the drop).
264
3.1. Quasi-static wetting properties of ionic liquids
The results are given in Table 1.
(a) The surface tension measurements can be compared to other authors
data: EMIM DCA 64.0 mJ/m2 [36] vs. 53.8 mN/m; EMIM SCN: 57.76 mN/m
[37] vs. 54.01 mN/m; EMIM BTA: 35.71 mN/m [17], 36.1 mN/m [38], 41.9 mN/
m [39] vs. 33.60 mN/m; Water at 22˚C: 72.30 mN/m [40] vs. 71.81 mN/m. The
surface tensions measured by us are lower than the cited ones. This is due to contamination of surfactants in our measurements or/and high concentration of water
in the other authors’ measurements.
(b) Upon hydrophobization of the glass, the static TPC angles increase significantly for all ionic liquids. There is one exception: EMIM BTA has nearly
the same contact angle on both hydrophilic and hydrophobic surfaces (only 3.3˚
increase of the TPC angle upon hydrophobization). What is most striking is that
only the combination of EMIM+ cation and BTA– anion is not reacting to hydrophobization. Even with the structurally very similar DiEIM BTA, there is a 25.0˚
increase of the contact angle.
(c) The difference between the surface energies of the dry surfaces Δσ = σSG
– σSL is estimated by assuming that θst is approximately equal to the equilibrium
(Young) TPC angle θY: Δσ ≈ σ cos θY. This estimate is reasonable if hysteresis is
small and especially when contact angle is not close to 90˚. For EMIM DCA and
EMIM SCN angles are about 86˚ and a small change of θ results in large change
of the value of σ cos θY, therefore, we cannot give reasonable estimation of Δσ.
The same is valid for the hydrophilic surface, where the hysteresis is larger.
(d) It seems that the anion determines the wetting properties of RTIL at
hydrophobic surface. EMIM BTA, Et3Pic BTA and DiEIM BTA have remarkably
similar wetting properties at the hydrophobized glass surface; AllMIM DCA and
EMIM DCA are also similar while EMIM DCA, EMIM SCN and EMIM BTA are
not, even though they have common cation. This is not so on hydrophilic surface,
where a small change in the cation structure leads to strong effect on the wettability (e.g. DiEIM BTA vs. EMIM BTA).
(e) We use the critical tilt αcr as a measure for the barrier for TPC line motion. The higher the critical tilt the higher the energetic barrier. There seems to
exist a loose positive correlation between the critical tilt αcr and the hysteresis θa,st
– θr,st. The effect of hydrophobization on the energetic barrier of all RTIL drops is
very pronounced: on hydrophilic surfaces, all drops were nearly immobile at any
tilt (except for EMIM BTA and DiEIM BTA, which were in motion at α > 50˚).
On hydrophobic surfaces, the barrier was obviously lower (20˚ > α > 10˚).
265
Table 1. Properties of the investigated ionic liquids. (1) density, ρ; (2) viscosity η; (3) surface
tension σ; (4) static contact angle θst, measured at tilt α = 0 on the hydrophilic surface; (5) static
contact angle θst, measured at tilt α = 0 on the hydrophobic surface; (6) Δσ ≈ σ cos θst, difference of
the surface energies of wet and dry hydrophobic surface; (7) critical tilt of the substrate αcr, at which
the drop starts to move on the hydrophobic surface; (8) the static advancing contact angle θa,st at tilt
αcr; (9) the static receding contact angle θr,st at tilt αcr on the hydrophobic surface; (10) hysteresis
θa,st – θr,st. No data for αcr, θa,st and θr,st were obtained because on hydrophilic surface, droplets were
nearly immobile at any tilt, with two exceptions: EMIM BTA and DiEIM BTA. For these two ionic
liquids, the critical tilt angle was around 50˚, but that value was not well reproducible (neither was
the corresponding values for θa,st and θr,st). All data were obtained at temperature 22˚C, except the
viscosities, which were measured at 21˚C.
liquid
AllMIM
DCA
EMIM
DCA
EMIM
SCN
EMIM
BTA
DiEIM
BTA
Et3Pic
BTA
water
η
ρ
kg/m3 mPa·s
σ
mN/m
hydrophilic
θst
deg
θst
deg
Δσ
mN/m
αcr
deg
θa,st
deg
θr,st
deg
hysteresis
hydrophobic
1071
16
37.6
45.9
82.5
4.9
10.0
82.7
82.0
0.7
1107
16.8
53.8
40.7
86.4
-
16.0
87.6
83.4
4.2
1145
24.7
54.0
62.7
86.3
-
22.0
88.3
81.0
7.3
1548
39.4
33.6
63.5
66.8
13.2
18.0
68.5
65.8
2.7
1450
27.9
31.6
40.3
65.3
13.2
11.0
67.5
62.4
5.1
1512
36.6
32.9
42.0
67.1
12.8
19.0
69.4
64.2
5.2
998
0.98
72.3
13.5
86.5
–13.5
-
21
-
86.0
3.2. Dynamic contact angle of ionic liquids. Mechanism of wetting
The dependence of the front and rear position ya and yr on time t is shown in
Fig. 3. The derivative v = dy/dt was determined from the experimental data using
three adjacent ya or yr points, yj+1, yj, yj–1, as the divided difference
v j ≡ dy / dt j =
(t
(t
j +1
j
− t j −1 )y j+1
− t j −1 )(t j +1 − t j
(t
) (t
+
j +1
j +1
− 2t j + t j −1 )y j
− t j )(t j − t j −1 )
−
(t
(t
j +1
j +1
− t j )y j −1
− t j −1 )(t j − t j −1 )
(1)
Typically, droplets kept the difference ya–yr constant during the observation,
therefore v, determined as dya/dt was the same as dyr/dt (the velocity of the receding TPC line is taken with negative sign). Simultaneously, both the dynamic
advancing and the receding angles were measured. Using the vj and θj values, determined in this way, the dependence of rate v on cosθ was plotted (Fig. 4). Often,
in the initial stage drops were accelerating before reaching constant velocity (as
in Fig. 3). We assumed that the contact angle depends only on v and not on the
acceleration, so we included these initial points in the rate law v(θ) plot.
266
Fig. 3 (a) Position of the TPC line at the droplet front (ya) and the droplet rear (yr) as functions of
time at tilt α = 90° (DiEIM BTA, hydrophobic surface). The corresponding rate of propagation
can be extracted by differentiation. (b) The corresponding θa and θr dependence on time, see
also Fig. 2. In the first few frames, not the whole droplet was within the field of view of the
camera, therefore in the initial moments, only ya and θa could be determined. The moving droplet
maintained constant velocity at most tilts, except for tilts close to αcr, where acceleration was
observed (the figure on the left is an example for such behavior). Analogously, the dynamic
contact angles were constant at larger tilts, while they might change with time at α ~ αcr.
The v(θ) dependence gives information about the mechanism of the TPC line
motion and the dissipative processes at the TPC.
(a) If hydrodynamic friction is the main dissipative mechanism, then
Voinov’s model for the TPC line motion gives the relation
v = A (θ3 − θ3Y ), where
A=
σ
.
9η ln r∞ / r0
267
Here r∞ is a characteristic length of the order of the droplet length, and r0 is a
cut-off parameter of the order of a few molecular sizes. It should be pointed, that
Voinov’s equation assumes the liquid is Newtonian fluid. Whether the RTILs under investigation are Newtonian fluids or not requires a separate study, but taking
into account that the RTILs under investigation do not posses long alkyl chains, it
could be assumed that they behave as Newtonian fluids [2].
Experimental data for DiEIM BTA at hydrophobized glass surface were compared with Voinov’s equation, and it was found that it is in qualitative disagreement with the experimentally obtained v(θ) dependence.
(b) If dissipation is localized in the TPC contact line and motion is obeying
barrier (Eyring) mechanism, then according to Blake-Haynes adsorption-desorption model [28]
v = 2v 0 sinh ⎡⎣ b (cos θY − cos θ )⎤⎦ , where
(2)
v 0 = λνe − FA /k BT .
(3)
Here the characteristic frequency ν can be identified with Eyring’s frequency
ν=
k BT
;
h
(4)
h is the Planck constant, and kB is the Boltzmann constant. The b coefficient
is related to surface tension and temperature via
b=
λ 2σ
,
2k BT
(5)
where λ, according to Blake and Haynes, is the average distance between the adsorption sites at the solid surface. Finally, FA is the barrier for jump of a molecule
from one adsorption site to another.
A step mechanism for TPC line motion on chemically heterogeneous or rough
surface was proposed [41], which led to precisely the same form of the dependence v(θ) as given by (2). However, the interpretation of the parameters ν and λ
is different. The length λ is identified with a characteristic length of the TPC line
corrugation (related to the structure of the substrate). The frequency ν was identified with the frequency of the capillary wave with length λ at the liquid surface,
given by the formula [42,43]
ν cap =
π σ
,
4 ρλ 3
where ρ is the ionic liquid density.
268
(6)
The rate law (2) compares well to the experimental data for dynamic contact
angles measured for DiEIM BTA at hydrophobized glass surface (Fig. 4). The best
fit parameters are given by
θY = 61.9˚, b = 10.1, v0 = 0.269 mm/s.
These values are of the right order [31,32,41]. No asymmetry between advancing
and receding [41] is observed. Compared to the static advancing and receding angles,
Young angle, θY, is closer to θr,st (the same is valid for θst, which also has value closer
to θr,st than to θa,st, see Table 1). From the values of b, the length λ can be calculated.
Taking σ = 31.58 mN/m (see Table 1) at T = 275.15 K, from (5) we obtain the value
λ = 1.6 nm. From the value of v0, we can estimate the energetic barrier for TPC line
propagation, FA, using (3). If the frequency ν is identified with Eyring’s frequency
(4) (ν= 6.1·1012 Hz at 22˚C), then we can calculate FA = 17.4×kBT from (3). If we take
the capillary wave frequency (6) (using the value of the density ρ = 1450 kg/m3 in (6),
we obtain νcap = 6.5·1010 Hz), from (3), the value FA = 12.9×kBT will be obtained.
At low spreading velocities, there are deviations between the experimental
velocities and the model predictions. They can be explained with switching from
one dynamic regime to another, which is a widespread behavior [41,28,32].
Fig. 4 Rate of TPC propagation v vs. dynamic TPC angle cosine cos(θ). Exemplary curve
for DiEIM BTA at hydrophobized glass surface. Red points are experimental. Solid line is
comparison with Blake-Haynes model.
269
Acknowledgements
This study is financially supported by the Sofia University (Faculty of Chemistry) project
069/2010. The authors are indebted to Dr. Hristo Chanev for the preparation of hydrophobic substrates. We are also thankful to Miss Valeria Yaneva for processing some of the experimental data.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
270
Kirchner B (2009) Ionic Liquids, Topics in Current Chemistry vol 290. Springer-Verlag, Berlin
Heidelberg
Wasserscheid P, Welton T (2008) Ionic Liquids in Synthesis. Wiley-VCH Verlag GmbH & Co
KGaA, Weinheim
Freemantle M (2009) An Introduction to Ionic Liquids. Royal Society of Chemistry, Cambridge
Chatterjee D, Hetayothin B, Wheeler AR, King DJ, Garrell RL (2006) Lab Chip 6:199–206
Castner EW, Wishart JF (2010) J Chem Phys 132:120901
Restolho J, Mata JL, Saramago B (2009) J Colloid Interface Sci 340:82-86
Law G, Watson RP (2001) Langmuir 17:6138
Halka V, Tsekov R, Freyland W (2005) Phys Chem Chem Phys 7:2038-2043
Halka V, Tsekov R, Freyland W (2005) J Phys: Condens Matter 17:S3325-S3331
Halka V, Tsekov R, Mechdiev I, Freyland W (2007) Z Phys Chem 221:549-558
Evans DF, Yamauchi A, Jason Wel, GJ, Bloomfield VA (1983) J Phys Chem 87:3537
Wu JP, Li N, Zheng LQ, Li XW, Gao Y, Inoue T (2008) Langmuir 24:9314
Dong SL, Li X, Xu GY, Hoffmann H (2007) J Phys Chem B 111:5903
Millefiorini S, Tkaczyk AH, Sedev R, Efthimiadis J, Ralston J (2006) J Am Chem Soc 128:3098-3101
Paneru M, Priest C, Sedev R, Ralston J (2010) J Phys Chem C 114:8383–8388
Paneru M, Priest C, Sedev R, Ralston J (2010) J Am Chem Soc 132:8301-8308
Restolho J, Mata JL, Saramago B (2009) J Phys Chem C 113:9321-9327
Halka V, Freyland W (2008) Z Phys Chem 222:117-127
Nanayakkara YS, Perera S, Bindiganavale S, Wanigasekara E, Moon H, Armstrong DW (2010)
Anal Chem 82:3146–3154
Zhang S, Hu X, Qu C, Zhang Q, Ma X, Lu L, Li X, Zhang X, Deng Y (2010) ChemPhysChem
11:2327–2331
Lockett V, Sedev R, Ralston J, Horne M, Rodopoulos T (2008) J Phys Chem C 112:7486-95
Kornyshev AA (2007) J Phys Chem B 111:5545-5557
Fedorov MV, Georgi N, Kornyshev AA (2010) Electrochem Commun 12:296–299
Carrera GVSM, Afonso CAM, Branco LC (2010) J Chem Eng Data 55:609-615
Batchelor T, Cunder J, Fadeev AY (2009) J Colloid Interface Sci 330:415-420
Voinov OV (1976) Fluid Dyn 11:714-721
Blake TD, Haynes JM (1969) J Colloid Interface Sci 30:421-423
Blake TD (1993) In: Berg JC (ed) Wettability, Surfactant Science Series vol 49. Marcel Dekker,
New York, p 291
Brochard-Wyart F, de Gennes PG (1992) Adv Colloid Interface Sci 39:1
Schneemilch M, Hayes RA, Petrov JG, Ralston J (1998) Langmuir 14:7047-7051
Petrov JG, Ralston J, Schneemilch M, Hayes RA (2003) J Phys Chem B 107:1634-1645
Petrov JG, Petrov PG (1992) Colloids Surf 64:143-149
Horning EC, Moscatelli EA, Sweeley CC (1959) Chem. Ind. London, p 751
Supina WR, Henly RS, Kruppa RF (1966) J Am Oil Chemists’ Soc 43:202A
MacLeod WD Jr, Nagy B (1968) Anal Chem 40:841-842
36. Stalder AF, Kulik G, Sage D, Barbieri L, Hoffmann P (2006) Colloids Surf A 286:92-103;
http://bigwww.epfl.ch/demo/dropanalysis/, accesssed 03 Jan 2010
37. De Gennes PG (1985) Rev Mod Phys 57:827-863
38. Extrand CW, Kumagai Y (1995) J Colloid Interface Sci 170:515-521
39. Fletcher SI, Sillars FB, Hudson NE, Hall PJ (2010) J Chem Eng Data 55 (2):778-782
40. Domanska U, Królikowska M, Królikowski M (2010) Fluid Phase Equilib 294:72–83
41. Klomfar J, Souckova M, Patek J (2010) J Chem Thermodyn 42 (3):323-329
42. Kilaru P, Baker GA, Scovazzo P (2007) J Chem Eng Data 52 (6):2306-2314
43. “IAPWS Release on Surface Tension of Ordinary Water Substance, International Association
for the Properties of Water and Steam”, September 1994
44. Slavchov R, Heinrich G, Dutschk V, Radoev B (2009) Colloids Surf A 354:252-260
45. Levich VG (1964) Physicochemical Hydrodynamics. Prentice-Hall, Englewood Cliffs
46. Lamb H (1994) Hydrodynamics, 6th ed. Cambridge University Press
271
272
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
ADSORPTION COMPONENT OF THE DISJOINING PRESSURE IN
THIN LIQUID FILMS
ROUMEN TSEKOV
Department of Physical Chemistry, University of Sofia, 11, J. Bourchier Blvd., 1164 Sofia, Bulgaria
Abstract. The disjoining pressure isotherm in foam films is theoretically studied and an
important contribution of adsorption is discovered. On the basis of interfacial thermodynamics an
adsorption disjoining pressure component is derived, which is repulsive and exponentially decaying
by the film thickness. Expressions for its magnitude and decay length are derived in terms of wellknown thermodynamic characteristics such as the partial Gibbs elasticity and adsorption length.
Several adsorption isotherms are considered and the corresponding adsorption disjoining pressure
components are calculated. An important coupling between the interfacial layer phases and wetting
transitions is discussed as well.
INTRODUCTION
Thin liquid films are anisotropic structures and the pressure tensor inside a
film possesses distinct components [1]. The normal component PN of the pressure tensor is constant equal to the pressure in the neighboring homogeneous bulk
phases. The tangential component PT of the pressure tensor exhibits non-monotonous profile across the film. If the liquid film is thin enough, the transition regions
of the two film surfaces overlap thus leading to appearance of disjoining pressure
[2]. The overall excess of PN against PT defines the film tension γ [3]
∞
γ=
∫ (P
N
− PT )dz = 2σ + Π h
(1)
−∞
where the interfacial part of γ equals to twice the film surface tension σ and Π
is the disjoining pressure (Fig. 1). The Gibbs-Duhem relation for the film at constant temperature reads [4]
2d σ = −Π dh − 2∑ Γi d μi
(2)
273
where {Γi , μi } are the adsorptions and electrochemical potentials of all the film
components excluding the solvent, whose adsorption is set to be zero. Equation
(2) provides straightforward an important definition of the disjoining pressure as
the thickness derivative of the film surface tension
Π = −2(∂ h σ)T ,μ
(3)
as well as the following Maxwell relationship
2(∂hГi)TT,μ,μ = (∂∂ μ П)T,h
(4)
i
which hints already the important contribution of adsorption on the disjoining
pressure [5, 6].
PN
bulk phase
PT
σ
h
thin film
Π
σ
bulk phase
Fig. 1 Schema of the pressure tensor distribution in a symmetric thin liquid film.
In the present paper a shorter notation ∂ x ≡ ∂ / ∂x , used often in the physics
literature, is adopted everywhere for the partial derivatives.
Disjoining Pressure Isotherm
According to Eq. (2) the film surface tension depends on temperature, film
thickness and electrochemical potentials of dissolved species. In theory, however, it
is more suitable to consider T , h and adsorptions as variables, i.e. σ = σ(T , h, Γ) .
Hence, the film surface tension depends on the film thickness either explicitly or
via the thickness dependence of the adsorptions. Thus, the definition (3) can be
split into two distinct components of the disjoining pressure
274
Π = −2(∂ h σ)T ,Γ − 2∑ (∂ Γi σ)T ,h (∂ h Γ i )T ,μ
(5)
Considering small deviations of the adsorption on the film surfaces with
respect to the case of a single surface, one can replace the term (∂ Γi σ)T ,h by
(∂ Γi σ)T ,h =∞ = − EG ,i / Γi (h = ∞) − zi F φ / 2 in Eq. (5), where EG ,i and φ are, respectively, the partial Gibbs elasticity and the surface potential on a single surface.
Thus, Eq. (5) acquires the approximate form
Π = −2(∂ h σ)T ,Γ + φ(∂ h q )T ,μ + 2∑ EG ,i (∂ h Γ i )T ,μ / Γ i (h = ∞)
(6)
∑
zi F Γi is the surface charge density.
where q =
Obviously the first term in Eq. (6) accounts for the solvent interactions. In the
case of foam film from pure solvent −2(∂ h σ)T ,Γ=0 reduces to the van der Waals
component of the disjoining pressure ΠVW = − A / 6πh3 with A being the corresponding Hamaker constant [7]. Since the films consist usually by dilute solutions,
their Hamaker constants do not differ substantially for those of pure solvents. It
is interesting to note that the van der Waals component can be also derived solely
from consideration of the adsorption in pure liquid films [6]. One can easily recognize the electrostatic disjoining pressure component in the second term of Eq.
(6). Indeed, substituting the well-known expression for the surface charge density
q = ε 0 εκφ tanh( κh / 2) , following from the linearized Poisson-Boltzmann equation, yields the classical expressions for the electrostatic disjoining pressure at low
surface potentials or surface charge densities, respectively, [8]
Π EL =
ε 0 εκ 2 φ2
q2
=
2 cosh 2 ( κh / 2) 2ε 0 ε sinh 2 ( κh / 2)
(7)
where κ is the reciprocal value of the Debye length.
Let us consider now the last adsorption term of the disjoining pressure in Eq.
(6). To calculate its thickness dependence one can employ the Maxwell relation (4).
Introducing the following definition for the difference ΔX ≡ X (h) − X (h = ∞)
between the values of a property in the film and in the bulk liquid one can write
that Π = −Δp where p is the film pressure. Thus, the Maxwell relation (4) can
be consecutively modified to
2(∂ h Γi )T ,μ = (∂ μi Π )T ,h = −Δ (∂ μi p )T ,h = −ΔCi = −α i ΔΓ i
(8)
where {Ci } are the concentrations of components and {α i } are the reciprocal values of adsorption lengths depending on the adsorption equilibrium con275
stants. Hence, the adsorption component of the disjoining pressure and adsorption
changes are due to the difference ΔCi in the surfactant concentration in the film
as compared to the corresponding bulk phase in the meniscus. Solving the linear
differential equation (8) under the obvious condition Γi (h = 0) = 0 yields
Γi = Γi (h = ∞)[1 − exp(−α i h / 2)]
(9)
As is seen, the adsorption in films is lower than the adsorption on a single
interface due to overlap of the concentration transition regions. Now substituting
this expression into the definition of the adsorption disjoining pressure, i.e. the last
term of Eq. (6), leads to
Π AD = ∑ α i EG ,i exp(−α i h / 2)
(10)
The similarity of this expression with the electrostatic Eq. (7) at large κh is
due to the existence of adsorption diffusive layers at the film surfaces [9].
Adsorption Disjoining Pressure
To describe the contribution of the specifically adsorbed species knowledge for
the corresponding adsorption isotherms is required. Henry’s isotherm K i Ci = Γ i
is the simplest model, which is valid for dilute solutions. In this case α i = 1/ K i
is a constant and the partial Gibbs elasticity depends linearly on the concentration,
EG ,i = RTK i ci , where {ci ≡ Ci (h = ∞)} are the surfactant concentrations of the
solution used to make the films. Introducing these expressions in Eq. (10) yields
the adsorption disjoining pressure component in the form
Π AD = RT ∑ ci exp(− h / 2 K i )
(11)
As is seen, Π AD is positive and represents the osmotic pressure difference between
the meniscus liquid and film, which is due to different concentrations equilibrated
by different adsorptions. A typical value for the Henry constant K i is of the order
of hundreds of microns. This means that the adsorption disjoining pressure from
Eq. (11) is extremely long-ranged repulsion. However, since the Henry isotherm
is valid for very dilute solutions, the concentrations {ci } should be small and thus
Π AD from Eq. (11) is practically negligible.
As is expected the adsorption disjoining pressure becomes important for relatively concentrated solutions. In this case, however, the Henry isotherm is no
more applicable. A reasonable model here is the Langmuir adsorption isotherm,
which for the case of presence of a single surfactant reads
KC = Γ / (1 − aΓ)
276
(12)
where a is the molar area in the saturated layer. The partial Gibbs elasticity of
the Langmuir layer is the same as above, EG = RTKc , but the adsorption length
1/ α = K / (1 + aKc) 2 is substantially decreased. For instance, at concentrations
about 1 mM the adsorption length is of the order of hundreds of Angstroms. This
value is commensurable with the Debye length at the same electrolyte concentrations. Also the pre-exponential factor is significantly increased with respect to Eq.
(11). Hence, at large surfactant concentrations the adsorption disjoining pressure
Π AD = RTc(1 + aKc) 2 exp[−(1 + aKc) 2 h / 2 K ]
(13)
becomes important. Note that Π AD exhibits now a maximum with respect to the
surfactant concentration. Equation (13) reduces naturally to Eq. (11) at low concentrations.
Since in the example above the meaningful adsorption corresponds to about
90 % of the maximal one, additional complications can arise from the interactions
between the adsorbed molecules. They could be accounted for by a more complicate adsorption isotherm, such as the Frumkin one
KC = exp(−β aΓ)Γ / (1 − aΓ)
(14)
where the coefficient β accounts for the interactions in the adsorption layer. The
corresponding partial Gibbs elasticity and reciprocal adsorption length can be expressed as functions of the adsorption
EG = RT Γ
1 − β aΓ(1 − aΓ)
1 − β aΓ(1 − aΓ)
α = exp(−β aΓ)
K (1 − aΓ) 2
1 − aΓ
(15)
and replaced in the disjoining pressure model (10) the latter acquires the form
Π AD = RT
Γ[1 − β aΓ(1 − aΓ)]2
[1 − β aΓ(1 − aΓ)]
exp{−β aΓ − exp(−β aΓ)
h} (16)
3
K (1 − aΓ)
2 K (1 − aΓ) 2
The relevant concentration dependence can be obtained by combining this
expression with Eq. (14). In the case of a positive and sufficiently large β the
Frumkin isotherm describes a phase-transition in the interfacial layer which reflects in an abrupt change of the adsorption. Thus in the two-phase coexistence region Π AD will possess two different values, which will induce film stratification.
Hence, the interfacial and wetting phase-transitions are coupled and cross-linked
effects are expected to occur [10].
Finally, the adsorption disjoining pressure is very sensitive to the interfacial
properties. Any surface modifications will reflect in changes of the adsorption
and, hence, in Π AD . This is especially significant for wetting films, where the socalled hydrophobic disjoining pressure Π HP is observed [11]. It decays exponen277
tially with the film thickness increase and has short- and long-ranged components
[12]. A previous analysis [13] showed that the adsorption disjoining pressure is an
important part of Π HP . In contrast to the present case, however, Π AD in wetting
films could be either attractive or repulsive depending on the hydrophobicity of
the two film surfaces. A further description of the adsorption component of the
disjoining pressure could take into account the dependence of the specific adsorption constants on the film thickness as well, which is week in general [6].
Acknowledgements. The author is grateful to the Bulgarian NSF for financial support through
the grant DRG 02/3.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
REFERENCES
Ivanov, I. B. (ed.). Thin Liquid Films, Dekker, New York, 1988.
Derjaguin, B. V. and M. M. Kussakov. Acta Phys. Chem. USSR, 10 (1939), 153.
Rusanov, A. I. Phasengleichgewichte und Grenzflächenerscheinungen. Akademie, Berlin, 1978.
Toshev, B. V. and I. B. Ivanov. Colloid Polym. Sci., 253 (1975), 558.
Derjaguin, B. V., V. M. Starov and N.V. Churaev. Colloid J. USSR, 38 (1976), 411.
Vassilieff, C. S., B. V. Toshev and I. B. Ivanov. Proc. Phys. Chem. Surf. Act. Subst., B 2 (1976), 91
C.S. Vassilieff, E. T. Toshev and I. B. Ivanov, in Surface Forces and Boundary Liquid Layers,
B.V. Derjaguin (ed.), Nauka, Moscow, 1983, p. 168.
Hamaker, H. C. Physics, 4 (1937), 1058.
Verwey, E. J. W. and J. Th. G. Overbeek. The Theory of Stability of Liophobic Colloids. Elsevier, Amsterdam, 1948.
Derjaguin, B. V. Pure Appl. Chem., 61 (1989), 1955.
Mileva, E. Curr. Opin. Colloid Interface Sci., 15 (2010), 315.
Israelachvili, J. and R. Pashley. J. Colloid Interface Sci., 98 (1984), 500.
Tsao, Y., D. Evans and H. Wennerström. Langmuir, 9 (1993), 779.
Tsekov, R. and H. J. Schulze. Langmuir, 13 (1997), 5674.
278
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
CHEMICAL CONSTITUENTS OF THE AERIAL PARTS OF SALVIA
SPLENDENES
SNEJANA N. MERKOVA, PETKO I. BOZOV*, ILIA N. ILIEV
Department of Biochemistry and micro-biology, Plovdiv University, 24 Tsar Assen str. 4000,
Plovdiv, Bulgaria
* Auther to whom correspondence should be addressed: [email protected]
Аbstract. First time in Bulgaria was studied species of genus Salvia. Four furoclerodane
diterpenoids – Salviаrin (1), Splenolide A (2) Splenolide B (3) and Splendidin (4) were isolated from
the aerial parts of Salviа splendens. The structure and configuration of compounds were established
by spectroscopic methods and by comparison (Mps, TLC) with authentic samples.
Key Word Index. Salvia splendens; Labiatae; neo-clerodane diterpenes; Salviаrin; Splenolide
A; Splenolide B; Splendidin.
Резюме. За първи път в България е изследван представител на род Salviа за наличие на
дитерпени. От наземните части на Salviа splendens бяха изолирани четири нео-клероданови
дитерпеноиди – Salviarin, Splenolide A, Splenolide B и Splendidin, структурата на които беше
доказана чрез спектрални анализи и сравнение (Тт, TLC) с автентични проби. Тези съединения до сега не са били изолирани от български растителни видове
Ключови думи. Salvia splendens; Labiatae; нео-клероданови дитерпеноиди; – Salviarin;
Splenolide A; Splenolide B; Splendidin.
INTRODUCTION
Clerodane, neo-clerodane and labdane diterpenes isolated from species of different genera of family Lamiaceae are of interest on account of their biological activity
as insect anti-feedants against some economically important lepidopterous and lepti279
notarsa decemlineata say – pests; and as antifungal, antitumor, antimicrobial and molluscicidal agents. Continuation of our search of diterpenoids we have now investigated
Salviа splendens. From the aerial parts of the plant were isolated four furoclerodane
diterpenoids – Salviаrin (1), Splenolide A (2), Splenolide B (3) and Splendidin (4).
15
O
14
16
R
R
1
1
2
1 2
H O
H
17
O
8
10
20
4
H
O
18
19
O
H
1
2
3
4
R1 = R2 = H
R1 = OH, R2 = H
R1 = H, R2 = OAc
R1 = R2 = OAc
IR spectra of the compounds were consistent with the presence of a γ-lactone
(1780–1754 cm-1), δ-lactone (1736–1714 cm-1), ester groups for compounds 2 and 3
(1736 br., 1729 br., 1289, 1228 cm-1) and a olefinic double bond (1653–1601 cm-1).
Assignment of the 1H and 13C NMR spectral data (tables 1 and 2) together with the
heteronuclear multiple bond connectivity (HMBC), the heteronuclear single quantum coherence (HSQC) spectra and 1H double resonance experiments, confirming
the relative stereochemistry and evaluating the conformation for the rings of these
compounds. Presence of only one methyl group (δ 0.97–1.02) reveale furoclerodane skeleton with two lactones. The δ-lactone confirmed of characteristic signals
at δH 5.28 dd (12β –H), 2.60 d dd (8β-H); δC 50.10 d (C-8), 71.20 d (C-12), 170.10
s (C-17) and the absent of signals for protons of Me-17 group. The γ-lactone is in
good agreement with the data: δH 2.86 dd dd (4β-H), 4.27 d (19A), 4.15 dd (19B);
δC 52.10 d (C-4), 41.60 s (C-5), 175.15 s (C-18), 70.50 t (C-19) and the absent of
signals for protons of Me-18 group. Signals in 1H NMR (δ 7.39 dd, 7.36 t, 6.35 dd)
iand 13C NMR (125.16 s, 108.74 d, 140.03 d, 144.24 d) were assigned for furane
moity. For double bond betwen C-2 and C-3 were assigned signals at δH 5.87–6.00
d dd, 5.55–5.72 dd dd; δC 128.80–136.19d, 120.28–122.35 d.
280
ЕXPERIMENTAL
The aerial material of Salviа splendens were collected in August 2011 in Plovdiv and voucher specimens were deposited in the Herbarium of the Higher Institute of Agriculture of Plovdiv, Bulgaria.
Melting points were determined on a Kofler block and are uncorrected.
IR spectra √max (KBr) cm-1 were run on a Perkin-Elmer 1750 (Infrared Fourier
trunsform spectrometer). 1H and 13C NMR spectra were recored in CDCL3 (TMS
as int. standard, 400 MHz).
Extraction and isolation. Dride and finely powdered aerial parts Salviа splendens L. (600 g) were extracted with Me2CO (3 x 3l) at room temp. For a week.
After filtration, the solvent was evapd under redused pressure and low temp. (50 °C)
yielding a gum (11,7 g), which was dissolved in aq. Me2CO (40%, H2O w/v, 200
ml). The soln was cooled to 3–4 °C for 24 hr and filtered. The filtrate was extracted
with CHCl3 (4 x 40 ml) and the organic extract was dried (Na2SO4) and evapd. In
vaquum giving a residue (4.2 g, biter fr.). This residue was subjected to CC (silica
gel Merck № 7734, deactivated with 10 % H2O, w/v 50g) eluting with hexane and
hexane – CHCl3 mixt (from 10:2 to 2 :1), yielding 120 mg of crude 1, 110 mg of 2
and 90 mg of 3. Pure compounds were obtained after crystallization from MeOH.
Salviarin (1). Colourless needles (acetone-n-hexane); mp 185–188 °C; IR √max
(KBr) cm-1 : 3151, 3110, 2925, 2856, 1778, 1714, 1653, 1508, 1464, 1291, 1211,
1180, 1154, 1016, 875, 811, 786, 705, 604, 486. 1H NMR: see table 1. 13C NMR: see
table 2. (Found: C. 70.52; H. 5.88. C20H19O5 requires: C. 70.79; H. 5.64 %).
Splenolide A (2). Colourless prisms, mp 224–228 °C; IR √max (KBr) cm-1 :
3183, 2930, 2830, 1779, 1729, 1606, 1517, 1448, 1303, 1255, 1178, 1142, 1032,
876, 836, 797, 742, 649, 488. 1H NMR: see table 1. 13C NMR: see table 2. (Found:
C. 67.25; H. 6.35. C20H22O6 requires: C. 67.03; H. 6.18 %).
Splenolide B (3). Colourless needles, mp 148-152 0C; IR √max (KBr) cm-1 :
3144, 2925, 2871, 1780, 1729, 1601, 1507, 1449, 1293, 1246, 1177, 1142, 1021,
874, 838, 790, 740, 699, 492. 1H NMR: see table 1. 13C NMR: see table 2. (Found:
C. 63.57; H. 5.17. C24H23O9 requires: C. 63.29; H. 5.09 %).
Splendidin (4). Colourless prisms, mp 160-1630C; IR √max (KBr) cm-1 : 2923,
2854, 1754, 1736, 1634, 1508, 1448, 1289, 1228, 1180, 1147, 1019, 875, 814,
787, 705, 692, 480. 1H NMR: see table 1. 13C NMR: see table 2. (Found: C. 66.59;
H. 5.67. C22H21O7 requires: C. 66.49; H. 5.33 %).
281
Spectral Assigments and Reference Data
Table 1. 1H NMR chemical shifts, δ (ppm), and coupling constants, J (H,H) (Hz),
for compounds 1–4a (400 MHz, CDCl3, TMS as int. standard)
proton
1
2
3
4
J (H,H)
1
2
3
4
1α
2.06
4.29 dddd
2.02 dddd
5.44 dddd
1α,1β
d
-
18.2
-
1β
2.06b
-
2.53 dddd
-
1α,2
2.2
2.4
2.1
2.6
2
5.94 dddd
5.87 ddd
5.96 dddd
5.83 ddd
1α,3
~2.0
2.0
2.8
1.3
3
5.58 brdd
5.51 ddd
5.58 dddd
5.68 ddd
1α,4β
2.4
2.1
2.4
2.6
4β
2.73 dddd
2.76 ddd
2.75 dddd
2.82 ddd
1α,10β
12.0
10.0
12.0
9.3
6α
1.88b
1.74 dddd
1. 83dddd
1.81 dddd
1β,2
5.6
-
5.8
-
1.29 dddd 1.26 dddd
1.29 dddd
1.40 dddd
1β,3
~1.0
-
1.2
-
2.4
-
2.4
-
b
6β
7α
1.85b
1.87 dddd
1.85 dddd
1.92 dddd
1β,4β
7β
2.40
2.35 dddd
2.41 dddd
2.45 dddd
1β,10β
4.3
-
4.8
-
8α
10β
11α
11β
12β
14
15
16
19A
19B
Me-20
1β-OAc
2.41 brdd
1.95 dd
1.71 dd
2.17 dd
5.30 dd
6.36 dd
7.36 t
7.40 dd
4.20 d
4.14 dd
0.96 s
-
2.44 ddd
1.96 d
1.63 dd
3.00 dd
5.69 dd
6.36 dd
7.35 t
7.40 dd
4.33 d
4.16 dd
1.07 s
-
2.62 ddd
2.15 dd
5.14 d
5.22 d
6.34 dd
7.35 t
7.43 dd
4.17 d
4.14 dd
0.93 s
-
2.74 ddd
2.45 dddd
5.33 d
5.83 ddd
6.35 dd
7.36 t
7.43 dd
4.32 d
4.09 dd
1.03 s
2.00 s
2,3
2,4β
3,4β
6α,6β
6α,7α
6α,7β
6α,8α
6β,7α
6β,7β
6β,19B
7α,7β
7α,8α
10.0
2.4
2.7
14.6
d
d
<1.0
13.0
4.0
1.6
d
4.0
10.0
2.4
2.8
14.0
3.6
3.2
1.2
14.1
3.3
2.0
14.2
4.4
10.0
2.1
2.8
14.8
4.0
4.0
1.0
13.6
4.0
1.7
14.4
4.0
10.0
2.6
2.6
14.2
4.0
2.8
1.2
14.0
3.6
1.9
14.4
4.0
11β-OAc
-
-
1.94 s
1.86 s
7β,8α
2.8
2.8
2.8
3.3
-
-
-
-
-
11α,11β
11α,12β
11β,12β
14,15
14,16
15,16
19A,19B
14.3
10.0
2.8
1.7
0.9
1.7
9.0
14.4
12.2
3.4
1.9
0.8
1.9
9.0
10.8
1.8
0.8
1.8
9.0
11.2
1.8
0.9
1.8
9.0
b
a
b
282
All these assignments were in agreement with COSY, HSQC and HMBC spectra.
Overlepped signals; δ values were measured from the HSQC spectra.
Spectral Assigments and Reference Data
Table 2. 13C NMR chemical shifts, δ (ppm), for compounds 1-4(CDCl3)
carbon
1
2
3
4
1
22.33 t
66.15 d
24.17 t
67.13 d
2
129.20d
136.56d
129.61d
129.27d
3
121.76d
120.61d
121.92d
122.78d
4
52.56 d
53.33 d
52.59 d
51.76 d
5
41.79 s
43.44 s
42.03 s
42.83 s
6
32.84 t
33.01 t
32.47 t
32.06 t
7
19.26 t
19.58 t
19.87 t
19.77 t
8
49.45 d
51.33 d
49.50 d
50.61 d
9
35.58 s
36.56 s
39.41 s
40.41 s
10
38.64 d
44.61 d
38.30 d
41.82 d
11
41.31 t
44.39 t
74.09 d
73.67 d
12
70.38 d
73.58 d
71.93 d
71.60d
13
125.17s
126.45s
121.10s
121.89s
14
108.71d
109.21d
108.90d
108.96d
15
144.24d
144.66d
144.43d
144.66d
16
140.02d
140.56d
141.76d
142.13d
17
171.76s
174.43s
169.85s
169.46s
18
175.8 s
177.3 s
175.7 s
174.4 s
19
70.90 t
71.93 t
70..38 t
70.87 t
20
24.08 q
24.62 q
19.44 q
19.56 q
1β-Oac
11β-Oac
-
-
-
170.4 s
-
-
-
22.15 q
-
-
169.4 s
170.1 s
-
-
21.15 q
20.41 q
All assignments were in agreement with HSQC and HMBC spectra.
Acknowlegewments. We thak Prof. Maurizio Bruno for measurement of NMR spectra and
thank Prof. Georgi Papanov for material support and given advices.
283
REFERENCES
1. Munro, T. A., M. A. Rizzacasa. J. Nat. Prod. 2003, 703–705.
2. Bigham, A. K., T. A. Munro, M. A. Rizzacasa, R. M. Robins-Browne. J. Nat. Prod., 66, 2003;
1240:1242.
3. Butelman, E. R., T. J. Harris, M. J. Kreek. Psychopharmacology. 2004; 172: 220.
4. Piozzi, F., M. Bruno, S. Rosselli, A. Maggio. Heterocycles., 65, 2005, 1221.
5. Harding, W. W., K. Tidgewell, N. Byrd, H. Cobb, C. M. Dersch, E. R. Butelman, R. B. Rothman,
T. E. Prisinzano. J. Med. Chem., 48, 2005, 4765–4771.
6. Fontana, G., G. Savona, B. Rodriguez. J. Nat. Prod., 48, 2006, 1734–1738.
7. Fontana, G., G. Savona, B. Rodriguez. Magn. Reson. Chem., 44, 2006, 962–965.
8. Fontana, G., G. Savona, B. Rodriguez, C. M. Dershch, R. B. Rothman, T. E. Prisinzano. Tetrahedron. 65, 2009, 1708–1715.
9. Fontana, G., G. Savona, B. Rodriguez. Magn. Reson. Chem., 44, 2006, 962–965.
284
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
SPRAY PYROLYSIS VS. ION-EXCHANGE METHODS:
DECOMPOSITION OF OZONE OVER Cu COATED HEU-TYPE
ZEOLITE IN AMBIENT CONDITIONS.
K. GENOV1, V. BLASKOV,1 M. SHIPOCHKA1, I. BOEVSKI1, A. LOUKANOV2,
I. STAMBOLOVA1*. C. DUSHKIN3
Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences,
Acad. G. Bomchev St. bl. 11, 1113, Sofia, Bulgaria
2
Laboratory of Geoecology University of Mining and Geology, S. Edrev St., 1700 Sofia, Bulgaria
3
Laboratory of Nanoparticle Science and Technology,
Department of General and Inorganic Chemistry
Faculty of Chemistry, Univ. of Sofia 1164, Sofia, Bulgaria
*E-mail: [email protected]
1
Abstract. A clinoptilolite zeolite was coated with copper via ion exchange and spray
pyrolysis methods. Cu-clinoptilolites were tested as catalysts for decomposition of gas phase
ozone. Catalytic activity up to 90% ozone conversion was observed for samples loaded via
spray pyrolysis and at the same time the catalysts remained active over time. Ion exchanged
form Cu-clinoptilolite shows smaller activity 15% ozone conversion. D.C. arc-AES, XRD,
SEM and XPS analysis were carried on for chemical characterization of the samples.
Key words: zeolite, spray pyrolysis, ion exchange, ozone decomposition, waste gases
1. INTRODUCTION
The Bulgarian clinoptilolite (CL) (CAS No.:12173-10-3) is a natural zeolite
with HEU–type framework and some of its structure and properties were widely
investigated and discussed in literature since last century up to day [2,1,3]. As an
agent of zeolite class, clinoptilolite can be used as catalyst support, adsorbent and
ion exchanger. Clinoptilolite is naturally formed mineral and it is cheaper than
new synthetic zeolites such as ZSM-5; Cu2+ loaded into the channels can be used
as catalytic centre for several types of reactions. So our interest in copper coated
285
or loaded clinoptilolite is provoked by these facts: In last work Boevski et.al.
2011 [4], revealed that Cu, introduced as T-atom into the channels via the ionexchanged method, could decompose ozone concerning over the reaction 2O3 →
3O2. Ozone is widely used as an oxidant for waste water treatment, drinking water
sterilization, industrially and in the laboratory for purification and sterilization
[5]. Conversely, ozone a highly toxic gas, is harmful for all living organisms and
particularly dangerous for the human health on direct exposure. The exhaust gases
from such processes described above contain residual ozone and in addition, may
give rise to air pollution problems that must be solved [6]. However, the conversion of O3 over Cu2+ion-exchanged zeolite - clinoptilolite (Cu-CL), started first
with higher percentage but during the time prolongation decreases [4]. So here,
with this work we present another method to incorporate Cu over natural CL by
simple and fast spray pyrolysis method, and to characterize of Cu loaded zeolite
(Cu/CL). The new catalytic experiments were carried out and compared with the
results of Cu2+-CL samples. Over the last decades spray pyrolysis has been one of
the mainstream chemical methods applied for formation of thin layers and particles (powders) of different compounds, alongside with the sol-gel method [7,8,9].
One of the reasons for the interest towards this method is the fact that it is a
cheap one and it incorporates simplified equipment in comparison to the physical
methods for formation of thin layers (vacuum evaporation, magnetron sputtering,
etc.) The method allows mixing of initial components at a molecular level. It also
enables easy formation of multicomponental materials having a complex chemical and phase composition, such as ferrites, superconductors, spinel types, etc.
for application as catalysts, sensors, optical elements, and others. Spray pyrolysis
allows doping, in practice, with any chemical element and in various proportions,
and a distinctive feature of sprayed catalysts is the homogeneous distribution of
the ingredients throughout the entire particle since all ingredients are formed from
a homogeneous solution [10,11].
2. EXPERIMENTAL
2.1. Samples preparation
2.1.1. Spray pyrolysis.
10 g substrate – (CL) fraction 3–5 mm) obtained from Bentonit AD in Beli
Plast deposit, was put in crucible and situated in pot furnace, which was heated
to the decomposition temperature (300 oC) of the precursor Tetra-μ2-aceatodiaqu
adicopper(II)). The aerosol of precursor solution in water was generated by pneumatic glass nebulizer and transported to the substrate. The spray coating process
was repeated 5 times at a 10-second interval at the same time the sample were
mechanically stirred in order to obtain homogeneous distribution of the drops
over the all surface of zeolite particles.. The final treatment at 300–400 oC was
carried out for 60 min for decomposition of all rest acetate and calcination. The
286
Cu content in the acetate precursor was calculated so to obtain 7.5 Cu wt % in the
final product Cu/Clinoptilolite (Cu/CL).
2.1.2. Ion exchange
Same CL, were put in an Erlenmeyer flask over magnetic stirrer, closed and
mixed with 250 mL aqueous solution of ammonia (Valerus, Bulgaria) overnight. After
filtration over sintered glass filter (3 MO 4) and washing with distilled water, the NH4+
form (NH4-CL) was obtained. After this step the sample was calcined at 600 oC (24 h)
to become the H+ form (H-CL). This form was exchanged once again with Cu water
soluble salts (0.2 M, sources: Cu(NO3)2.3 H2O (Institute of Pure Compounds, Univ. of
Sofia), on a rotatory evaporator device. Cu2+-CL were thus obtained.
2.2. Analysis of the samples.
D.C. arc – AES method. This method was conducted on spectrograph PGS-2
(Carl Zeiss-Jena) equipped with a ruled grating (650 grooves mm-1 and λ blaze
570 nm). The crystalline phase composition of the samples was studied by XRD,
using X-ray diffractometer Philips PW 1050 with CuKα-radiation. XPS measurements were performed in VG ESCALAB II electron spectrometer using AlKα radiation with an energy of 1486.6.eV. The binding energies were determined with
an accuracy of ±0.1 eV utilizing the C1s line at 285.0 eV (from an adventitious
carbon) as a reference. SEM JSM-5510 of JEOL was used for morphology observations of the samples.
2.3 Catalytic test
Room temperature ozone decomposition experiments were investigated via
an isothermal plug flow reactor under steady-state conditions without temperature
gradients. The catalyst Cu/CL (m=0.5318 g, /circa 1 cm3/) particles size (5–6 mm)
was chosen taking into account the reactor diameter (6 mm) and the volume rate
of O3 was 6 L/h. Ozone was synthesized in a flow of oxygen (99.7 %), dried with
silica gel, using an ozone generator (with a silent discharge of 15–20 kV between
the electrodes). The inlet concentration of ozone in the flow of oxygen was ca
24000 ppm. Ozone concentration was analyzed with an ozone analyzer BMT 964
(Germany) with an accuracy of ±3 ppm. The reaction temperature was ambient
(20 °C) and was maintained with an accuracy of ±0.2 °C. The activity of the
catalysts was measured every 5 min and was calculated on the basis of equation
(where C refers to concentration):
⎡ C − Coutlet ⎤
Conversion[%] = 100x ⎢ inlet
⎥
Cinlet
⎣
⎦
287
3.1. Samples analysis
3.1.1. DC arc AES method: The characteristic atomic lines are presented
in Table 1.
Table 1. Characteristic emission lines, determined by DC arc-AES
Sample
Characteristic lines at [pm]
Correspond to:
Cu/CL
324.754 & 327.396
Cu
CL and Cu/CL
308.215 & 309.271
Al
CL and Cu/CL
288.157
Si
Mg and Pb in Clinoptilolite were determined by DC arc AES method – and
correspond to the 17% impurities specified and declared by the producer. This
analysis is not enough to show where and how the Cu was distributed over zeolite
or into zeolite channels. In this case one was made further XRD to investigate the
zeolite structure and eventually Cu distributed crystalites over it coated surface.
3.1.2. XRD analysis also shows that the natural form of Bulgarian clinoptilolite contains the impurity of cristobalite, quartz, albite and microcline less then
17%. The samples contained over 5 wt % copper on the surface and XRD can
detect Cu phases. So it can be observed some Cu, CuO Cu2O crystallites over the
surface via XRD (Figure 1a.).
Cu2O
CuO CuO
Cu CuO
10
20
30
40
Figure 1a. XRD patterns of Cu/CL and XRD from
reference (CL from refer.) generated on http://www.
iza-structure.org/databases/
50
2θ
HEU
http://www.iza-structure.org/
CL
Figure 1b. XRD patterns of Cu2+CL, CL and XRD from reference
(CL from refer.) generated on http:// 10
www.iza-structure.org/databases
288
Cu2+-CL
20
30
2θ
40
50
XRD analysis (Figure 1b) shows
the iso-structures of investigated samples
O
and reference to the zeolite atlas guide.
Si
AlThe absence of other signals proved that
O Cu2+
O
the transitional metals were loaded as TAlSi
Si
Si
ions into zeolite channels. (Scheme 1.)
O
O
O
O
3.1.3. XPS. The chemical composiO
tion of the CL and Cu/CL were investiSi
gated on the basis of areas and binding
energies of C1s, O1s, Si 2s, Si 2p, Al
O
2+
2s Al 2p and Cu2p photoelectron peaks
Scheme 1. A model of Cu ion exchenged
(after linear subtraction of the backaluminum-silicate
ground) and Scofield’s photoionisation
cross-sections. Aluminium and silicon measurements were made using the integrated line intensities of the Al(2s) and Si(2p) photoelectron lines (Figure 2 a)).
O
a)
O 1s
Si 2p
Al 2s
Al 2p
0
50
Si 2s
100
150
500
550
600
Binding Energy (eV)
Figure 2a. XPS spectrum of CL
The surface atomic concentrations of O, Al, Si, Cu, Na, Ka and Ca estimated
from these data, along with the binding energy values of different photoelectron
lines are shown in Table 2.
Table 2. Chemical analysis of samples according XPS
O [at.%]
Si [at.%]
Al [at.%]
Na [at.%]
K [at.%]
Ca [at.%]
CL
60.5
31.6
4.2
Cu/CL
40.8
36.0
3.8
Cu [at.%]
<0.5
1.9
1.5
-
<0.5
<0.5
1.1
17.8
289
Cu 2p
b)
900
920
940
960
Binding Energy (eV)
980
1000
Figure 2b. XPS spectrum of Cu/CL
Figure 3. SEM of Cu/P
On Figure 2 b) is clearly visible that the Cu exists in form of oxide CuO. It
can be seen that Cu concentration on the zeolite surface is the several times higher
then that inside the channels. In order to clear this result from the XPS analysis
scanning electron microscopy has been used.
3.1.4. On SEM image (Figure 3.) one can see the agglomeration of many
particles over the porous zeolitic surface:
Probably, they can be better catalytic centres then Cu2+ loaded as T- ions on
Brønstedt’ acidic Al sites. In this case we have chosen spray pyrolysis method for
coating a higher zeo surface with metal particles.
3.2. Catalytic test obtained by different methods.
In a catalytic test (Fig. 4) the natural form (CL) was practically inactive (less
than 5% conversion). In the beginning it was started at 3% and decreased during
the time prolongation to 2–3%. As one can see, the clinoptilolite is not good catalyst for ozone decomposition at room temperature in spite of its porous structures.
Some molecules of O3 adsorbed on it channels and decompose but the main gas290
100
O3 conversion [%]
90
- Cu/CL
- Cu2+-CL
- CL
80
15
10
5
0
0 10 20 30 40 50 60 70 80 90 100110
Time [min]
Figure 4. Ozone
conversion at room
temperature (20 oC)
over the samples
flow contains decomposed ozone. Cu2+-CL shows about 10% conversions (ca.
15% at the reaction start) but deactivation of the samples was observed. The possible reason is the nature of the metal: Cu can be found in the Cu(I) and Cu(II)
form. This means that during the reaction it can change itself coordination and we
expected more high activity among this kind of sample. Cu2+-CL samples did not
meet to our expectations. However, these samples can be optimized as catalysts.
In this case the spray pyrolysis method was chosen – to load active centers of Cu
not only as T-ions but also as Cu, CuO and Cu2O aggregates over the surface on
zeolite. Thus, not such is the situation, when the Cu/CL sample was used. At 1st
5 to 10 minutes the conversion was very low ca 2.5% and after that increased to
76% (at 15th minute) May be here, the possible reason for lower initial conversion
was the time needs for coordination of O3 over Cu centers loaded on zeolite surface. The zeolite gives the same conversion as unloaded form. Then the conversion was going to 87% (25th minutes) and stay stable during the time prolongation.
This means that Cu was changed its coordination state and decomposed ozone to
oxygen (1st step of process) and then the O2 molecules leave the system and new
molecules O3 coordinate with Cu centers (Scheme 2).
So, the conversion was higher as the previously founded by Cu2+ - CL when
Cu was ion exchanged and stays stable somewhere against Brønsted Al centre in
zeolite channels (Scheme 1).
4. CONCLUSION
Zeolite loaded with copper particles on its surface was prepared using spray
pyrolysis method. The existence of Cu, loaded on the clinoptilolite from Beli Plast
was proved by D.C. arc – AES and XPS methods. XR Diffractograms show that
the HEU structure is not broken in the process of Cu loading.
291
Scheme 2. A possible mechanism for ozone decomposition over Cu/CL
SEM photographs reveal that Cu particles were coated on the zeo surface as
agglomerations.
So, obtained samples used further as catalyst in ozone decomposition reaction with very good activities 88–90 % conversion. We consider that the spray
pyrolysis is very fast and flexible method to obtain catalysts with higher activity
than tested before Cu(II) ion exchanged zeolite form.
Acknowledgements. The authors are grateful to UNION project (No DO-02-82/2008), NATO
Project (CBP.EAP.RIG.981670) and FNI No DVU-02/36 (DVU_10_0334)
REFERENCES
1. Vassileva, P., D. Voikova. J. Hazard. Mat. 170, 2009, 948.
2. Kanazirski, M., M. J. Y. Janev. Compt. rend. Acad. bulg. Sci., 36, 1983, 1571.
3. Lihareva, N., L. Dimova,O. Petrov, Y.Tzvetanova. Micropor. Mesopor. Mat., 130, 2010, 32.
4. Boevski, I., K. Genov, N. Boevska, K. Milenova, T. Batakliev, V. Georgiev, P. Nikolov,
D. K Sarker. Compt. rend. Acad. bulg. Sci., 64, 2011, 33.
5. Imamura, S., M. Ikebata, T. Ito T. Ogita. Ind. Eng. Chem. Res., 30, 1991, 217.
6. Naydenov, A., P. Konova, P. Nikolov, F. Klingstedt, N. Kumar, D. Kovacheva, P. Stefanov, R.
Stoyanova, D. Mehandjiev. Catal. Today 137 2008, 471.
7. Kaneva, N., I. Stambolova, V. Blaskov, Y.Dimitriev, S.Vassilev, C. Dushkin. J. Alloys Comp., 500,
2010, 252.
8. Stambolova, I., V.Blaskov, M. Shipochka, S.Vassilev, C. Dushkin, Y. Dimitriev. Mat.Chem.Phys.,
121, 2010, 447
9. Stambolova, I., V. Blaskov, S.Vassilev, M.Shipochka, C. Dushkin. J Alloys Comp., 489, 2010, 257.
10. Li, D., H. Haneda. J. Photochem. Photobiol. A, 155, 2003, 171.
11. Li, D., N. Ichikuni, S. Shimazu, T.Uematsu. Appl. Catal. A, 172, 1998, 351.
292
Том 102/103, 2011
FACULTE DE CHIMIE
Tome 102/103, 2011
_______________________________
PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE BY
ZnO PHOTOCATALYST DOPED WITH NICKEL
NINA V. KANEVA , BOZHIDAR I. STEFANOV, DIMITRE T. DIMITROV*, CECO D. DUSHKIN
Laboratory of Nanoparticle Science and Technology, Department of General and Inorganic
Chemistry, Faculty of Chemistry, University of Sofia, 1 James Bourchier Blvd., 1164 Sofia, Bulgaria
*E-mail: [email protected]
Абстракт: За да се изучи влиянието на примесите от никел на фотокаталитичните свойства на цинковия оксид върху подложки от стъкло, използвйки метода на
потапянето, бяха приготвени наноструктурирани слоеве Ni-ZnO с четири различи
брои потапяния при добавяне на 1mol.% от NiNO3·6H2O по отношение на ZnO. Така
получените слоеве бяха охарактеризирани с помощта на сканираща електронна микроскопия и рентгеновска дифрактометрия. Фотокаталитичните свойства на получените слоеве бяха изучени в зависимост от интензитета на падащата ултравиолетова светлина. Получените резултати от фотокаталитичните тестове са сравнени
с тези на чист ZnO и на публикуваните вече данни за слоеве от TiO2 с примеси от
Ni. Показано е че примесите от Ni понижават фотокаталитичната активност както
на слоевете от ZnO, така и на TiO2. При експерименталните условия на представеното изследване чистият ZnO показва по-висока фотокаталитична активност от
ZnO и TiO2 с примеси от Ni както и от слоеве на филми от чист TiO2. Резултатите от
представеното изследване показват, че скоростните константи на процеса на фотокатализа са пропорционални на интензитета на падащата светлина, въпреки че няма
поддаваща се на измерване зависимост, свързана с порядъка на реакцията, която да
бъде получена от дадения експеримент.
Abstract: For studying the effect of doping with nickel on photocatalytical properties
of zinc oxide, four nanofilm samples Ni-ZnO having different loading with 1 at.% of
NiNO3·6H2O added with respect to ZnO. They were deposited on the glass slide substrates
have been prepared by the dip coating technique. Films were characterized by means of
SEM and XRD. The samples were photocatalytically tested at different incident UV
293
light intensity. Obtained data was compared with the performance of pure ZnO films as
well as with the previous data from pure and Ni-doped TiO2 films. It was shown that Nidoping decreases the photocatalytic activity of the both of ZnO and TiO2. At the presented
experimental conditions the pure ZnO film showed the highest activity than the both of Ni
doped ZnO and TiO2 as well as than pure TiO2 films. Also was observed that the intensity of
the incident light is proportional to the rate constant of the process, although the measurable
relation, such as reaction order, could not be concluded from the experiments.
Keywords: ZnO, thin films, nickel doping, TiO2, photocatalysis, Methylene Blue
INTRODUCTION
Using semiconductors such as TiO2 and ZnO for photocatalytic degradation
of organic pollutants in water and air, has attracted extensive attention in the past
two decades [1–20]. Previous studies have proved that under ultraviolet (UV)
light irradiation such semiconductors are able to degrade most kinds of persistent organic pollutants such as detergents, dyes, pesticides and volatile organic
compound. A photocatalytic process is based on the generation under irradiation
of electron–hole pairs into the band-gap of the oxide that can give rise to redox
reactions with the species adsorbed on the surface of the photocatalysts. It is well
known that the doping the semiconductor oxides with various transition metal
ions may lead to an enhanced efficiency of the photocatalytic systems [2].
One of these semiconductors oxides is zinc oxide. Its stable structure is hexagonal, and the bulk, thin film and powder growth techniques greatly affect its chemical
and physical properties [21,22]. Its piezoelectricity is another property that has various applications in the industry such as acousto-optic modulator, force sensing and
acoustic wave resonator. Its crystal structure gives rise to piezoelectricity because
the oxygen and zinc atoms are bound on a tetrahedral shape, which moves the center
of positive and negative charges with an external pressure on the lattice constants
of its crystal structure, which produces a localized dipole momentum in the crystal
[23т29]. Due to point intrinsic defects such as oxyge n vacancies or zinc interstitials, undoped ZnO is an semiconductor of n-type [30)]. In the wavelength between
400 and 800 nm, ZnO crystal is transparent, which changes with increase of the
concentration of the various doping atoms. It is mention at ref. [31] that gas sensors,
based on ZnO layers are more suitable for detection of CH3 radicals than many other
semiconductors oxides such as TiO2, CdO, WO3 and MoO2.
For Ni doping into ZnO thin films very much attention has been paid in order
to understand the magnetic properties of diluted magnetic semiconductors [32–34].
For Ni doping ferromagnetic ordering in ZnO is predicted to occur without the need
of additional charge carriers. It was found out that the ferromagnetism becomes
weaker for Ni-doped ZnO with increasing the hole concentration, coming from Nidoping, which play a role of acceptor impurity into ZnO. It was also found that the
294
ferromagnetic state was stable ground state for Ni-doped ZnO [33]. To investigate
the magneto-optical properties, Ando et al. [34] measured the magnetic circular dichroism (MCD) spectra of ZnO films alloyed with Ni by using pulsed-laser deposition. MCD detects the relative difference of the circular polarization-dependent
optical absorption under an applied magnetic field. The films alloyed with Ni had
pronounced negative MCD peaks near the band edge of the host ZnO. However,
despite of the fact that for such a classical photocatalysis as TiO2 there are many papers dealing with application of Ni-doped TiO2 for degradation of hazardous organic
compounds, production of hydrogen or oxygen gas [1−7], to the best of our knowledge the photocatalytic activity of Ni-doped ZnO powder was presented only by
authors of ref. [8]. There was presented that doping of ZnO with Ni may reduce its
photoactivity. How was stated above, Ni play a role of acceptor impurity into ZnO.
By this way, how it is observed experimentally and interpreted theoretically previously by our team, adding the acceptor admixture to the n-type oxide photocatalysis
will decrease the photocatalytic activity for the samples [9].
The photocatalysis with ZnO represents a perspective research field, because
ZnO can be as efficient as TiO2 in the photocatalytic degradation of some dyes
in aqueous solution [10,11]. Therefore, according to some authors ZnO has been
found to be a better photocatalyst than TiO2 [12]. ZnO thin films decompose reactive dyes in their aqueous solutions [13], chlorophenol [14], methyl-blue [15],
malachite green [16] and other organic environmental pollutants [17−20]. The advantages of using powder catalyst are increased reaction rate due to the increased
surface area and simplicity of application. The use of conventional powder catalyst has also disadvantages in stirring during the photocatalytic reaction and in
separation of powder after the reaction. The preparation of film catalyst makes it
possible to overcome these disadvantages and extend the industrial applications
[35]. Furthermore, ZnO is of special interest, because of the possibilities for modification and control of various ZnO-based nanostructures [36–38].
In this paper we investigate the photocatalytic activity of commercial ZnO
powder in the form of thin films. The films are deposited on glass substrates by
dip coating. The ZnO material is further modified by mixing it with nickel nitrate,
NiNO3.6H2O. The decolorization kinetics of methylene blue dye in water is studied
as a model system. The kinetics of photocatalysis is systematically investigated in
novel photocatalytic reactor under UV-light illumination at two different variable
system parameters, the thickness of ZnO films and incident UV light intensity.
EXPERIMENTAL PROCEDURES
Materials and reagents. The following chemicals were used: zinc oxide
powder (>99.0%) from Fluka; polyethyleneglycol (PEG 4000) from the Institute
of Pure Compounds (University of Sofia, Bulgaria); Methylene Blue (MB) and
absolute ethanol (100%), both from Fluka. Glass slides (ca. 76x26 mm) for sub295
strates of ZnO films were from ISO-LAB (Germany). Distilled water was used in
all experiments. All other chemicals and reagents were of analytical grade.
Preparation of ZnO and ZnO/Ni films. The films were deposited from alcoholic suspension of the commercial zinc oxide powder [39]. For this purpose
polyethyleneglycol (PEG-4000; 7.0 g) was dissolved in absolute ethanol (50 ml)
upon stirring and heating at 70 °C for 30 min. Non-annealed pure ZnO powder
7.0 g in weight was dispersed in 60 ml of ethanol and the resulting dispersion was
mixed together with the clear solution of PEG-4000. The obtained suspension was
stirred for 10 min and sonicated at frequency 15 kHz for additional 30 min.
For the films doped with Ni(II) at 1 mol.% NiNO3.6H2O was added in respect
of ZnO. Pure ZnO powder or ZnO/Ni mixture was dispersed in 60 ml of ethanol
and the resulting dispersion was mixed with the solution of PEG-4000. The obtained suspension was stirred for 10 min and sonicated at 15 kHz for additional 30
min. The suspensions can be stored at room temperature in the long term and used
for multiple dip-coating procedures after homogenization.
To prepare the film, a glass substrate it was dipped the suspension and withdrawn at a rate of 0.9 cm/min at room temperature. The films with 1, 3, 5 and 7
number of coatings were produced. The films were dried at 80 °C for 30 min after
each coating. The dried films were annealed at 500 °C for 60 min in order to fire
any organics and to get ZnO films suitable for photocatalytic tests.
Characterization of ZnO films. Scanning electron microscopy (SEM) and
X-ray powder diffraction (XRD) were used to characterize all powder materials,
as well as the obtained films. The SEM images were obtained by a Scanning Electron Microscope JSM-5510 (JEOL) operated at 10 kV of acceleration voltage. The
investigated samples were coated with a thin film of gold by a fine coater JFC1200 (JEOL) before observation. X-Ray diffraction (XRD) spectra were recorded
at room temperature on a powder diffractometer Siemens D500 with CuKα radiation within 2θ range 10-80 deg and step 0.05 deg 2θ and counting time 2 s/step.
Photocatalytic tests. The photocatalytic activities upon UV light illumination
of pure ZnO and ZnO/Ni films were investigated by the photoinitiated decolorization of methylene blue (MB) dye in aqueous solution. The photocatalytic tests
were conducted inside the novel reactor described in our previous paper [7]. The
experimental conditions were the following: the reaction volume of 100 ml with
1 ppm solution of the model dye pollutant; stirring rate of 300 rpm; irradiation by
4W UVA tube at different levels in respect to the reactor to achieve the intensity
of 3.145, 1.178, 0.733 and 0.568 mW/cm2, which were measured by a radiometer.
Reaction time was 60 minutes with the first 30 in the dark to reach adsorption/desorption equilibrium and to estimate the rate constants the latter 30 with UV light
on was done. Measurements of the remaining dye concentration during the reactions were done at intervals of each 5 minutes by measuring at wavelength of 670
nm done by using the integrated colorimetric system of the reactor.
296
RESULTS AND DISCUSSIONS
Structure characterization. The
SEM reveals that the surface of ZnO and
ZnO/Ni films has a homogenous morphology (Fig. 1a,c). The higher magnification
shows the fine granular nanostructure of
the film surface. The cross-section view of
the film shows that the films interior also
consists of fine granules (Fig. 1b,d). No
significant difference in the morphology
of films, prepared with different number
of coatings, can be observed. However,
the films obtained of ZnO having a thickness of 10 μm which is much bigger than
those obtained of ZnO/Ni which thickness
is in the range of 2.5–3 μm.
From the XRD analysis of pure and
doped ZnO films (Figs. 2a,b) were estimated that the average sizes of crystallites
are about 80.8 nm for pure ZnO and 75.5
nm for doped with Ni ZnO films. The Xray diffraction studies reveal that all films
obtained are polycrystalline without a preferred orientation and the spectral peaks
at 2θ =31.9, 34.6 and 36.4 deg having
Miller’s index of (100), (002) and (101)
respectively, correspond to hexagonal
wurtzite structure. The mean crystallite
size was estimated by the Scherer’s formula. We suppose that heating for 1 hour
at 500 °C leads to the decomposition of
Zn(II) hydroxide and further crystallization of hexagonal ZnO in the film as seen
from the diffraction patterns.
The comparison of catalyst loading
on the slides versus the number of coating
cycles applied is shown at Figure 3. It can
a
b
c
Fig. 1. SEM images of the: 1) surface of
nanostructured ZnO films (a) undoped; (c)
doped with Ni2+; 2) cross-section of ZnO films
(b) pure ZnO; (d) with Ni2+.
d
297
Fig. 2. XRD spectra of ZnO films annealed at 500 °C
for 1 hour (a) pure ZnO, (b) ZnO/Ni. The crystallite
sizes are about 80.81 nm and 75.5 nm in both cases.
Fig. 3. Dependence of the catalyst loading and
number coating of ZnO and ZnO/Ni films.
298
be noticed that the addition of Ni2+
affects catalyst loading by reducing the amount of ZnO deposited.
Possible explanation for this can be
found by looking at the point-ofzero-charge (pzc) ot ZnO which is
about pH 9. Nickel ions are weak
Lewis acid and lower the pH of
the suspension leading to repulsion
forces between the ZnO nanoparticles and less material being deposited onto the glass slides.
Effect of Ni-doping. Light absorption characteristics of both ZnO
and ZnO/Ni films was measured
with UV–Vis diffuse reflectance
spectrophotometer (Fig. 4). It is observed that the absorption of light
by ZnO/Ni in the visible region is
more compared to pure ZnO.
Nickel doping also affects the
photocatalytical properties of the
prepared films. Figure 5 shows
a comparison between ZnO and
ZnO/Ni films. The shown kinetic
curves are measured at different
UV light intensities. It can be noticed that the addition of Nickel
worsens the photocatalytical performance of the prepared films.
Effect of light intensity. The
influence of light intensity has
been examined by varying the
height of the UV tube in respect of
the coating as 8.5, 13.5, 18.5 and
23.5 cm. The achieved intensities
were the 3.145, 1.178, 0.733 and
0.568 mW/cm2, measured with
a radiometer (Easton). On Figs.
6 and 7 are shown the linear fits
for the degradation of Methylene
blue at different light intensities
and the rate constants, as bars.
As can be expected the rate
constant increases with the increase of light intensity - the reason is that in photocatalysis light
is actually a reagent, which is
being consumed during the process. Increasing the quantity of
this reagent increases the rate of
the reaction. The increase is with
a non-linear manner, which indicates that the process of photo- Fig. 4. Comparison of the absorbance spectra of ZnO
thin films (undoped and doped) used in the decoloroxidation is surface-controlled.
ization
of dye methylene blue.
The numeric values of the
rate constants, related to catalyst
loading and light intensity are presented in Tables 1(a) and (b) respectively for
Fig. 5. Decolorization kinetics of MB aqueous solutions and comparison of ZnO and ZnO/Ni
films under UV light illumination with seven coatings at different intensity: (a) 3.145 mW; (b)
1.178 mW; (c) 0.733 mW and (d) 0.568 mW.
299
ZnO and ZnO/Ni, as well as the results of the non-linear fits for the reaction order
by light intensity. It was done using the following equation:
k’ = k.In
where k’ is the observed reaction rate, I is the incident light intensity, k is the normalization factor and n is the power of the light intensity, hence the reaction order.
As can be concluded from Fig. 6 and Fig. 7 the reaction rate increases with
light intensity. However it must be noted that for constant intensities the reaction
Fig. 6. Bleaching kinetics of MB aqueous solutions by ZnO films under UV-light illumination
at different intensity with: (a) one; (b) three; (c) five and (d) seven coatings. The rate constants
are inserted as bars.
rate decreases with the increase of catalyst loading. A possible explanation for that
is that the excess of deposited photocatalytic material can not be activated in depth
by the incident light thus serving for an electron-hole recombination area which
is leading to energy-loss.
Comparison with TiO2 film activity. There are not many studies which have
been attempted to compare the efficiency of two or more catalysts for a given organic compound under identical experimental conditions. This is why we decided
to compare the activity of ZnO and ZnO/Ni from current work with our previous
results for TiO2 (Degussa P25) and TiO2/Ni [7]. As is reported also by other authors
[1], adding of Ni to TiO2 powder, worsening its photocatalytic activity. The results,
shown on Figure 8, clearly indicate that unmodified ZnO film is found to be the
most active. The order of photocatalytic activity of the investigated photocatalysts
300
Fig. 7. Bleaching kinetics of MB aqueous solutions by ZnO/Ni films under UV-light illumination
at different intensity with: (a) one; (b) three; (c) five and (d) seven coatings.
for Methylene blue is ZnO>TiO2
>TiO2/Ni>ZnO/Ni. The reason for
greater activity of ZnO in comparison with TiO2 is due to the absorption of more light quanta. Since the
band gap of previous ZnO is 3.17
eV, the quantum efficiency of ZnO
films is significantly larger than
TiO2 films and hence higher efficiencies have been reported for
ZnO. For explanation of quenching of the photocatalytic activity of
Ti2O/Ni, mentioned also in [1] the
electronic structures of Ni-doped Fig. 8. Comparison of photocatalytic activity by
undoped and doped TiO , ZnO films with seven
TiO2, presented in [40] should be coatings at 3.145 mW 2intensity under UV-light
considered. How is stated there, as illumination.
well as in [41] for pure TiO2 the upper valence bands showed a strong hybridization between O 2p and Ti 3d orbitals.
The top of the valence bands was dominated by the O 2p orbitals, while the conduction bands, especially the bottom, contained significant contributions from the Ti 3d
301
Table 1. Rate constants at different light intensity of:
(a) undoped ZnO thin films
Rate constants
Number
of
coatings
One
Three
Five
Seven
3.145 mW/
1.178 mW/
cm2
cm2
0.0136
0.0131
0.0130
0.0120
0.0129
0.0117
0.0118
0.0111
0.733 mW/cm2
0.0082
0.0095
0.0113
0.0105
0.568 mW/
k, x 10-3
n
0.0079
0.0065
0.0100
0.0092
17.6355
17.0456
14.1162
16.0873
0.3725
0.3792
0.1464
0.2648
cm2
(b) doped ZnO thin films with Ni2+
Rate constants
Number
of
coatings
One
Three
Five
Seven
3.145 mW/
cm2
1.178 mW/
cm2
0.733 mW/cm2
0.568 mW/
cm2
k, x 10-3
n
0.0115
0.0066
0.0070
0.0078
0.0092
0.0060
0.0063
0.0071
0.0091
0.0051
0.0060
0.0062
0.0084
0.0047
0.0044
0.0053
12.4412
7.8474
8.3555
9.6395
0.1934
0.2301
0.2476
0.2467
orbitals. After Ni doping, two dopant bands which appeared in the band gap of TiO2.
These bands were unoccupied, so they would be acceptor levels upon visible light
excitation, because they are located in the middle of the band gap. By this way, how
it is observed experimentally and interpreted theoretically previously by our team,
adding the acceptor admixture to the n-type oxide photocatalysis will decrease the
photocatalytic activity for the samples [9].
CONCLUSIONS
Pure and Ni-doped ZnO nanofilms on glass substrates are successfully prepared from ZnO powder solution by using dip-coating technique. The films are
characterized by scanning electron microscopy and X-ray diffraction. The films
comprise ZnO crystallites with a hexagonal crystal structure. The kinetics of photocatalytic reaction is systematically studied under varied UV-light illumination at
two different variable system parameters, the thickness of ZnO films and incident
UV light intensity. The photo-initiated bleaching of methylene blue in aqueous
solutions is studied by the obtained ZnO films as a model system.
The ZnO films, prepared from suspension with 7 coatings show best activity
and highest photocatalytic performance than those prepared with 5, 3 and 1 coatings. The reason probably is related to the increasing the degree of crystallization
of the film with increasing number of coatings. Different kinds of defects could
302
work as recombination centers and by this way decreasing the photocatalytic performance [42]. In general, we can conclude that the obtained results are promising
for the development of ZnO photocatalysts by the sol-gel method, by which produced layers that have smoothness, continuity and a homogeneous composition
and ensuring formation of functional nanostructures at the molecular level [43].
Acknowledgements. This work is financially supported by projects TK-X-1702/07 and DDVU
02-36/10 of the Bulgarian Ministry of Education and Science. CD is also thankful to COST D-43 Action
of the European Community and project UNION DO02-82 of the National Science Fund of Bulgaria.
REFERENCES
1. Hoffmann M. R., S. T. Martin, W. Y Choi, D. W. Bahnemann. Chem. Rev., 95, 1995, 69.
2. Carp O., C. L Huisman, A. Reller. Progress in Solid State Chemistry, 32, 2004, 33.
3. Sharma S. D., D. Singh, K. K. Saini, C. Kant, V. Sharma, S. C. Jain, C. P. Sharma. Appl. Catal.
A, 314, 2006, 40.
4. Jing D. W., Y. J. Zhang, L. J. Guo. Chem. Phys. Lett., 415, 2005, 74.
5. Yamashita H., M. Harada, J. Misaka, M. Takeuchi, K. Ikeue, M. Anpo. Photochem Photobiol A,
148, 2002, 257.
6. Niishiro R., H. Kato, A. Kudo. 2005 Phys Chem. Chem. Phys., 7, 2005, 2241.
7. Stefanov B. I., N.V. Kaneva, G. Li Puma, C.D. Dushkin. Colloids and Surfaces A, 382, 2011, 219.
8. Casey P., S. Boskovic, K. Lawrence, T. Turney. 2004 NSTI-Nanotech, www.nsti.org, ISBN 09728422-9-2, 3, 2004, 370.
9. Donkova B., D. Dimitrov, M. Kostadinov, E. Mitkova, D. Mehandjiev. Mater. Chem. Phys., 123,
2010, 563.
10. Gouvea C. A. K., F. Wypych, S. G. Moraes, N. Duran, N. Nagata, P. Peralta-Zamora. Chemosphere, 40, 2000, 433.
11. Dindar B., S. Icli. J. Photochem. Photobiol. A, 140, 2001, 263.
12. Kansal S. K., M. Singh, D. Sud. J. Hazard. Mater., 153, 2008, 412.
13. Lizama C., F. Ferrer, J. Baeza, H. D. Mansilla. Catal. Today, 76 , 2002, 235.
14. Lathasree S., A. N. Rao, B. Siva-Sankar, B. Sadasivam, K. Rengaraj. J. Mol. Catal. A, 223,
2004, 101.
15. Jang Y. J., C. Simer, T. Ohm. Mater. Res. Bull., 41, 2006, 67.
16. N. Kaneva, I. Stambolova, V. Blaskov, Y. Dimitriev, S. Vassilev, C. Dushkin. Alloy Comp., 500,
2010, 252.
17. Khalil L. B., W. E. Mourad, M.W. Rophael. Appl. Catal. B, 17, 1998, 267.
18. Sirtori C., P. K. Altvater, A.M.de Freitas, P. G. Peralta-Zamora. J. Hazardous Mater., 129, 2006, 110.
19. Akyol A., H. C. Yatmaz, M. Bayramoglu. Appl. Catal. B, 54, 2004, 19.
20. Daneshvar N., D. Salari, A.R. Khataee. Appl. Catal. B, 162, 317.
21. Wang X. –H., J. Shi, S. Dai, Y. Yang. Thin Solid Films, 429, 2003, 102.
22. Yuonesi M., M. E. Ghazi, M. Izadifard, M. Yaghobi. JOAM, 10, 2008, 2603.
23. Catti M., Y. Noel, R. Dovesi. J. Phys. Chem. Solids, 64, 2003, 2183.
24. Yuonesi M., A. Pakdel. Physica B, 405, 2010, 2083.
25. Gardeniers J. G. E., Z. M. Rittersma, G. J. Burger. J. Appl. Phys., 83, 1998, 7844.
26. Molarius J., J. Kaitila, T. Pensala, M. Ylilammi. J. Mater. Sci. Mater. Electron., 14, 2003, 431.
27. Wuethrich C. R., C. A. P. Muller, G. R. Fox, H. G. Limberger. Sens. Actuators A, 66, 1998, 114.
28. Itoh T., T. Suga. Appl. Phys. Lett., 64, 1994, 37.
29. Paneva R., G. Temmel, E. P. Burte, H. Ryssel. Sens. Actuators A, 62, 1997, 765.
303
30. Norton D. P., M. Ivill, Y. Li, Y. W. Kwon, J. M. Erie, H.S. Kim, K. Ip, S. J. Pearton, Y. W. Heo,
S. Kim, B. S. Kang, F. Ren, A.F. Hebard, J. Kelly. 2006 Thin Solid Films, 496, 2006, 160.
31. Davidov S. Yu., V. A. Moshnikov, V. V. Tamaev. 1998 Semiconductor Adsorption Sensors.
North-Ossetia State University Publ., Vladikavkaz, 1998. (in Russian)
32. Özgür Ü., Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S. –J. Cho, H.
Morkoç. J. Appl. Phys., 98, 2005, 041301.
33. Sato K., H. Katayama-Yoshida. Semicond. Sci. Technol., 17, 2002, 367.
34. Ando K., H. Saito, Z. Jin, T. Fukumura, M. Kawasaki, Y. Matsumoto H. Koinuma. J. Appl. Phys.,
89, 2001, 7284.
35. Iketani K., R. D. Sun, M. Toki, K. Hirota, O. Yamaguchi. Mater. Sci. Eng. B, 108, 2004, 187.
36. Andres-Verges M., A. Mifsud, C. Serna. Mater. Letters, 8, 1989, 115.
37. Kaneva N., G. Yordanov, C. Dushkin. Bull. Mater. Sci., 33, 2010, 111.
38. Djurišić A. B., A. M. C. Ng, X. Y. Chen. Progress in Quantum Electronics, 34 , 2010, 191.
39. Kaneva N. V., C. D. Dushkin. Nanoscience and Nanotechnology, E. Balabanova, I. Dragieva
(eds.), Marin Drinov Publ. House, Sofia, 10, 2010, 59-64.
40. Liu M., Z. Zhou, M. Li, L. Guo. Proceedings of the WHEC Essen, 2010, 613.
41. Zhao Z., Q. Liu. J. Phys. D, 41, 2008, 085417.
42. Uzunova-Bujnova M., R. Todorovska, D. Dimitrov, D. Todorovsky. Appl. Surf. Sci., 254, 2008, 7296.
43. Moshnikov V. A., I. E. Gracheva, V. V. Kuznezov, A. I. Maximov, S. S. Karpova, A. A. Ponomareva. J. Non-Crystal Solids, 356, 2010, 2020.
304
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