Formation Of Molecular Associates Research Articles

Analysis of xylitol – citric acid system forming deep eutectic solvent: Application for dissolving poorly water-soluble drugs. A combination of calorimetric and Raman investigations

The phase diagram of the xylitol – citric acid system was determined from microcalorimetry experiments performed on mixtures prepared by co-milling. Raman investigations in the stretching regions of carbonyl and hydroxyl groups have shown a close relationship between the formation of molecular associations between the two molecular species and the drastic negative deviation from ideality for high citric acid content, responsible for obtaining a deep eutectic solvent (DES). It was shown that a great amount of poorly water-soluble drugs (ibuprofen and paracetamol) could be dissolved in that DES, providing a strategy for stabilizing a great amount of amorphous drugs or for obtaining unusual crystalline forms of drugs.

Аминокислоты в условиях ионизации при электрораспылении: использование хлорида никеля для инициирования кластерообразования

Проведено систематическое исследование ионизации аминокислот методом ионизации элек- трораспылением (ESI-MS) в присутствии хлорида никеля. Проведено исследование влияния состава подвижной фазы на качество и состав масс-спектров. Состав смеси ацетонитрил-вода варьировался от 5 до 95% воды. Установлено, что изменение состава подвижной фазы существенно оказывает некото- рое влияние на интенсивность масс-спектров, но не на качественный состав. Качество масс-спектра значительно зависит от чистоты используемого ацетонитрила, который в больших количествах уве- личивает химический шум и затрудняет идентификацию. Наилучшим для работы соотношением было 45% воды и 55% ацетонитрила. Показано, что для ароматических аминокислот (тирозина, триптофа- на) наиболее характерны как процессы фрагментации (декарбоксилирование, деаминирование, распад по α-углероду), так и в некоторой степени и процессы кластерообразования с участием атомов нике- ля. Также показано, что наиболее интенсивно кластерообразование проходит в простых неароматиче- ских аминокислотах. Видно, что кластерообразование в таких случаях идёт по трём различным на- правлениям: образование молекулярных ассоциатов аминокислот с несущим заряд протоном, образо- вание молекулярных ассоциатов аминокислот с несущим заряд атомом никеля и образование поли- молекулярных координированных структур, координируемых двумя ионами никеля. В работе пока- зано, что результаты полученные при исследовании могут быть использованы не только для более чувствительного и информативного поиска аминокислот в растворах сложных смесей с хроматогра- фическим разделением и при использовании прямого ввода, но для более надёжной идентификации целевых соединений благодаря образованию кластеров целевых соединений (в случае неароматиче- ских соединений) и характерной фрагментации (в случае ароматических соединений).

Photosensitizing properties of supramolecular systems based on chlorin e6

The novel supramolecular systems based on chlorine e 6 (Ce 6 ) are presented, and their optical absorption and fluorescence have been investigated. The influence of different excipients as poly-N-vinylpyrrolidone (PVP), polyethyleneglycol (PEG), bovine serum albumin (BSA), chitosan, Triton X-100 (TX-100) on spectral characteristics of these systems has been studied. The obtained spectral-fluorescence characteristics of Ce 6 -PVP, Ce 6 -PEG, Ce 6 -BSA, Ce 6 -TX-100 indicate disaggregation of chlorine e 6 molecules and their consecutive interaction with excipients in solutions and formation of molecular associates and molecular complexes. The system Ce 6 -chitosan is characterized by aggregation of pigments in solution that reduces photochemical activity of a photosensitizer. The fluorescence quantum yield j k of mentioned above supramolecular systems has been calculated. The results can be useful during the new method of controlled aggregation of photosensitizers as a part of supramolecular complexes development as well as for the purposes of new medicines of predictable photodynamic activity creation.

Molecular dynamics study of the structure and mechanism of formation of molecular associates in aqueous solutions of surfactants

The process of micelle formation in an aqueous solution of the surfactant was simulated by the computer experiment. It was established by the molecular dynamics method that micelles are formed through the formation of premicellar associates of the surfactant. The practical absence of an attraction between single molecules of sodium pentadecyl sulfonate (SPDS) and premicellar associates dissolved in water was shown for a SPDS—water system. The function of the radial distribution of Na+ counterions towards polar groups of SPDS molecules in water and on the surfaces of micelles and premicellar associates was studied by the molecular dynamics method. The presence of dissociated and non-dissociated polar groups of the SPDS molecular on the micelle surface was found. The data obtained are consistent with the existence concepts on micelle formation processes.

The state and phase transitions of an adsorbate on a homogeneous solid surface. Part 1.—A model of a two-dimensional associated van der Waals gas and of a two-dimensional phase transition

The state of an adsorbate on a mathematically homogeneous surface of a non-specific adsorbent over a wide range of temperature and surface coverage is considered. A model of a two-dimensional associated van der Waals gas is used. Besides the averaged long-distance intermolecular attraction considered in the usual van der Waals gas model, the new model also takes into account the formation of molecular associates at short distances (in a quasi-chemical approximation). These associates are formed not only as a result of the non-specific intermolecular interactions, but also additional specific intermolecular interactions, especially hydrogen bonds and complexing processes depending on the specific structure of the adsorbate molecule. Expressions have been derived for the thermodynamic characteristics of a two-dimensional associated van der Waals gas at temperatures above and below the two-dimensional critical temperature. A method is proposed for the determination of the critical parameters of the two-dimensional state, and the thermodynamic properties of a two-phase, two-dimensional system are considered.

Rate of formation of condensation nuclei in a supersaturated vapor

The dynamics of the condensation process are analyzed, and the kinetic equations of phase transformations (transitions) in a supersaturated vapor are derived. The formation of molecular associates is described by means of the well-known chains of A. A. Markov.

A spectrophotometric study of the formation of molecular associations

A spectrophotometric study of the formation of molecular associations