PECULARITIES OF MICELLE FORMATION OF PENTACYCLIC GLYCOSIDES IN AQUEOUS SOLUTIONS

Abstract

The regularities of changes in structural characteristics during the formation of associates in micellar aqueous solutions of triterpene saponins Quillaja Saponin and Sapindus Mukorossi are considered. The dependence of surface tension and adsorption on the concentration of an aqueous saponin solution is analyzed, and the values of surface activity and parameters of the adsorption layer are calculated. The average values of diffusion coefficients for spherical and cylindrical micelles are determined based on the measurement of the solution viscosity. The effect of the electrolyte solution on the surface tension and viscosity of glycoside solutions is studied: when the electrolyte is introduced into the saponin solution, the surface tension decreases, which leads to a shift in the critical concentration of micelle formation towards lower concentrations. The introduction of potassium chloride electrolyte reduces the degree of ionization and, as a result of suppressing the electroviscosity effect, leads to a decrease in the viscosity of the solution. The dynamic light scattering method is used to determine the size of glycoside aggregates. It is established that there are aggregates of several sizes in an aqueous solution of saponin. The size and shape of aggregates were calculated using the concepts of micelle packing parameters. In the region of very low concentrations of glycoside solutions, when approaching the critical concentration of micelle formation in the solution, there are spherical micelles. A further increase in the saponin concentration in the solution leads to a decrease in the content of structures with a hydrodynamic radius of 50-80 nm and the appearance of larger agglomerates with sizes greater than 100 nm. It was found that micelles acquire a less hydrated and more densely packed cylindrical shape in the concentration range of 1.7-2.6 mmol/dm3. Compaction of associates leads to an increase in the content of particles with a hydrodynamic radius of 150-250 nm and larger ones, and their presence predicts the appearance of larger agglomerates. Analyzing the data obtained using the dynamic light scattering method, it can be concluded that aggregates of several sizes co-exist in the volume of aqueous saponin solutions at certain concentrations.