LibRar.Org.Ua — Бібліотека українських авторефератів

Загрузка...

Головна Хімічні науки → Різнорідна асоціація іонів барвників у водних розчинах

(энергетика ассоциации, молекулярные диаграммы) предложено решение проблемы прогнозирования устойчивости ионных ассоциатов красителей. Показано, что с применением принципов "тетрафениларсоний-тетрафенилборатной" гипотезы можно оценивать DGо(Ct+) и DGо(An–) по экспериментально полученным значениям равновесных констант ассоциации Kas. На основании данных об ассоциации "стандартных" катиона тетрафениларсония и аниона тетрафенилбората предложены расчётные маршруты оценки DGо ионов красителей. Показано удовлетворительное согласие прогнозируемых значений Kas с их экспериментальными значениями.

Ключевые слова: ионная ассоциация, краситель, растворы, спектральные методы, квантовохимические расчёты, константа ассоциации, термодинамика, кинетика, поверхностно-активные вещества.

Shapovalov S.A. Heteroassociation of ions of dyes in aqueous solutions. – Manuscript.

Thesis for a doctor's degree work by speciality 02.00.04 – physical chemistry. – Kharkiv V.N. Karazin National University, Kharkiv, 2008.

This work was aimedto reveal the main factors (such as structural characteristics of counter ions, the charge, presence of ionic surfactants), governing the formation and stability of dissimilar ionic associates of dyes (IA), and thus to elucidate the fundamental regularities of the above process.

In order to develop approaches for predicting (or "a priori" estimation) of IA stability, a systematic study of heteroassociation (e.g. dissimilar association) was undertaken for different classes of dyes (cyanines, rhodamines, oxyxanthenes, sulfonephtaleins, thiazines).

Literary data on IA formation confirm the necessity of search of correlations between structural features of counter ions and properties of IA; there is no clearness in what characteristics of counter ions are of essential importance for formation IA in aqueous solutions. The lack of spectral, thermodynamic, and kinetic characterization of heteroassociation of dyes hinders the utilization of this process in various branches of chemistry.

Systematic research of association with participation of ionic forms of dyes has been offered by use of the "model ions". The last-named were chosen from dyes belonging to different classes: pinacyanol, astrafloxin, rhodamine 110, tetrabromophenylfluoron; colourless ions: tetrabutylammonium, tetraphenylarsonium, tetraphenylborate. The (cation+anion) association was treated in terms of the equilibrium model. It was experimentally ascertained the intensive interaction between cations and anions within the concentration range of (5–500)10 7 mol/l can be accompanied by pinacyanol, quinaldine red, carbocyanines, and rhodamines can be arranged in a sequence according to their ΔНhydr values.

The comparison of experimentally found thermodynamic values (∆Ноas, ∆Gоas, ∆Sоas) with structural characteristics of counter ions demonstrates that dispersion and hydrophobic interactions play an essential role in association. Along with the increase in the contribution of hydrophobic interactions, the IA structure can alter from solvent-separated ionic pairs (e.g., pinacyanol cation + sulfonephtalein anion) to contact ones (pinacyanol cation + rose Bengal anion).

Polythermal studies within the range of 292 – 329 K show, that increase in temperature results in Kas values decrease. This tendency is sharper than for inorganic ions association. Using the cyanine ions-containing IA it was revealed that at certain temperatures there coexistence of associates with composition 2:1 and 1:1 takes place. Also it was found, that formation of stable IA is accompanied by an essential isolation of energy.

The restoration of the absorption spectra of IA components on adding of cationic (cetylpyridinium bromide, etc.) or anionic (sodium dodecylsulfate) surfactants indicate the decay of the associate, owing to the interaction of dye ions with the oppositely charged surface-active ions. Such competition between a dye and a surfactant takes place even at concentrations below CMC; it was utilized for developing two methods of determination of surfactants in aqueous solutions.

The Kas values and the kinetic constants of IA decay were used to explain the reasons of unequal sensitivity of the dye associates towards the addition of cationic and anionic surfactants. The established kinetic regularities agree with the association constants: the IA with high Kas values are characterized by lower rates of decomposition.

A method of pre-experimental estimations of IA stability was proposed. It is based on experimental (Kas values) and simulated (the association energy, molecular diagrams) data. The "tetraphenylarsonium-tetraphenylborate" approach is used to estimate the set DGo(Ct+) and DGo(An–) values for single charged ions.

The routes of DGo estimation of counter-ions have been shown with the help of the data on association "standard" ions such as tetraphenylarsonium or tetraphenylborate. The constancy of DGo(Сt+) and DGo(Аn–) contributions have been analyzed on a basis of experimentally obtained Kas values for IA of different structure. The satisfactory agreement between theoretically predicted values Kas and their experimental values is observed.

Key words: ionic association, dye, solutions, spectral methods, simulations, constant of association, thermodynamics, kinetics, surfactants.

*) В англомовній літературі для позначення однорідної асоціації, або самоасоціації, використовується термін "self-association", а різнорідної асоціації – "heteroassociation", рідше "dissimilar association".

*) Ґрунтується на інтерпретації спектральних ефектів; див. монографію: Ищенко А.А. Строение и спектрально–люминесцентные свойства полиметиновых красителей / А.А. Ищенко. – К. : Наукова думка, 1994. – 232 с.

*) Ці зміни відбуваються у відповідності з раніше виявленими ефектами; див.: Саввин С.Б.Поверхностно-активные вещества / С.Б. Саввин,Р.К. Чернова,С.Н. Штыков.– М. : Наука, 1991. – 251 с.

*)Взаємозв'язок стійкості асоціатів з хімічною будовою барвників раніше не вивчався. Відомі лише дослідження впливу довжини поліметинового ланцюга на спектрально-люмінесцентні властивості барвників; див.: Ищенко А.А. Влияние длины полиметиновой цепи на ширину полос поглощения симметричных цианиновых красителей / А.А.Ищенко, Н.А.Деревянко, В.М.Зубаровский, А.И.Толмачёв // Теор. и эксперим. химия. – 1984. – Т. 20, № 4 – С. 443 – 451.

** В дужках тут і далі – особистий внесок здобувача.