Ekaterina I. Yackevich

Design of supramolecular biomimetic catalysts of high substrate specificity by noncovalent self-assembly of calix[4]arenes with amphiphilic and polymeric amines.

Supramolecular biomimetic catalysts of high substrate specificity are developed based on amphiphilic oxyethylated calix[4]arene bearing iso-nonyl fragments at the upper rim and hexadeca(ethylene glycol) fragments at lower rim (9CO16), and amines of amphiphilic or polymeric nature. Two critical concentrations determined by tensiometry and dye solubilization methods are probably reflect the onset of association process and transition from bimodal to monomodal size distribution revealed by the dynamic light scattering method. Amine components used may form aggregates as well, which is mediated by hydrophobic effect due to occurrence of long-chain alkyl tails. The micellar rate effect of the designed systems toward the cleavage of carboxylic acid ester is shown to be contributed by the formation of mixed aggregates with the reactive functional groups, as well as by the pKa shift of the amine and the character of the distribution of reagents in functional micelles. In the case of long-chain primary amines, an inversion of micellar rate effect (catalysis to inhibition) occurs upon transferring from the less hydrophobic substrate, p-nitrophenyl acetate, to the more hydrophobic analogs, p-nitrophenyl laurate and p-nitrophenyl caprinate. The opposite effect (inhibition of the reaction of p-nitrophenyl acetate and the acceleration of the process of hydrophobic analogs) was observed in systems based on polyethyleneimine.

Solubilizing and catalytic properties of supramolecular systems based on gemini surfactants

Quantitative parameters characterizing the aggregation behavior of dicationic surfactants of the 12-s-12 type in aqueous solutions were determined: critical micelle concentrations, aggregation numbers, and surface potentials. The effects of the spacer length of the surfactants on their solubilizing effect with respect to hydrophobic (dye Orange OT) and water-soluble (p-nitrophenol) spectral probes and on their ability to shift acid-base equilibria were studied. The kinetics of alkaline hydrolysis of p-nitrophenyl acetate and p-nitrophenyl caprinate in 12-s-12 solutions was studied by spectrophotometry. A correlation between the micellar catalytic effect and the surface potential of micelles was established. The pronounced substrate specificity was revealed: the maximum acceleration of hydrolysis is observed in solutions of 12-6-12, attaining 1760 times for p-nitrophenyl caprinate.

Solubility and hydrolytic stability of indomethacin in aqueous micellar solutions

The solubility of the indomethacin drug in aqueous micellar solutions of a series of dicationic surfactants was characterized by spectrophotometry. The use of these surfactants can significantly increase the indomethacin content in aqueous solutions without destruction of the drug. The increase in the solubility can be explained by the multifactorial mechanism of the influence of micelles involving the solubilization of the drug and its binding with surfactants due to electrostatic and specific interactions. The use of dicationic surfactants in alkaline solutions was shown to markedly accelerate the hydrolytic cleavage of indomethacin. The highest catalytic effect is observed for N,N´-(hexane-1,6-diyl)bis(2-hydroxyethyl)(methyl)(cetyl)ammonium dibromide: a 1200-fold increase in the reaction rate of alkaline hydrolysis of the drug.

Effect of surfactant micelles on solubility and spectral characteristics of 2,2’-bibenzimidazole

The solubilization capacity of surfactants of different types was quantitatively characterized by spectrophotometry toward 2,2’-bibenzimidazole (BBI), whose derivatives possess a wide range of pharmacological activity. 2,2’-Bibenzimidazole solubilized by sodium dodecyl sulfate micelles is characterized by a high molar absorption coefficient (9400 mol−1 L cm−1) at the absorbance maximum (342 nm at pH 4–10), which may serve as a basis for the development of procedures for analytical monitoring of the BBI content in aqueous solutions and biosystems. The ability of surfactants to enhance the solubility of BBI in water and, as a consequence, to increase its bioavailability in the series sodium dodecyl sulfate < cetyltrimethylammonium bromide < Tween-80.

Polyelectrolyte micro- and nanocapsules with varied shell permeability controlling the rate of esters hydrolysis

Two variants of layer-by-layer deposition of polyelectrolytes (polyacrylic acid and polyethyleneimine) for the encapsulation of low-molecular-weight hydrophobic substrates (carboxylic acid esters) were proposed. The spectrophotometric method was used to study the kinetics of alkaline hydrolysis of the esters by monitoring the permeability of microcapsule shells. The first procedure provides a preliminary microencapsulation of substrates into the carbonate matrix to form stable capsules 7–10 μm in size with a low wall permeability. According to the second procedure, the polyelectrolytes were adsorbed directly on the dispersed substrate. In this case, nanosized capsules are formed, whose permeability is controlled by the ultrasonic treatment and the number of deposited layers.

Effect of 14- s -14 dicationic surfactants on the solubility and acid–base properties of thymolphthalein in water

The solubilization effect of 14-s-14 series dicationic surfactants is quantified via spectrophotometry using a thymolphthalein hydrophobic indicator. It is shown that the solubilization capacity of the studied micellar solutions with respect to the neutral form of thymolphthalein increases along with the length of the spacer moiety and grows by as much as five times upon transitioning from 14-2-14 to 14-6-14. It is concluded that the solubilization of thymolphthalein is accompanied by a shift in the acid-base equilibria in which this compound participates, as is reflected in the drop of its pKa value and the shift of the region of color change.

Polyfunctional supramolecular systems based on surfactants containing the hydroxyalkyl moiety in the head group

The critical micelle concentration, surface potential, and degree of binding of counterions in aqueous micellar solutions of N-cetyl-N-methylmorpholinium bromide and its analog containing the hydroxyethyl moiety in the head group were determined using a complex of physicochemical methods. The aggregation behavior of these compounds was found to vary insignificantly, whereas the catalytic effect of the hydroxyethyl derivative on the hydrolysis of carboxylic acid esters more than an order of magnitude exceeds the effect of the non-functionalized surfactant. One of the reasons for this phenomenon can be an increase in the micropolarity in the chemical reaction zone detected by fluorescence spectroscopy.