Stabilization of weakly associated water forms by the surface of compacted methylsilica and its composites with Betulin

Abstract

A complex of physicochemical methods was used to study the morphology and structure of the surface of methylsilica AM-1. Hydration of methylsilica was carried out by mechanochemical activation in the presence of water. The structure of the hydrate layer was studied using low-temperature 1H NMR spectroscopy. It has been established that adsorbed water is present in the form of nanosized clusters with a radii R = 0.4–20 nm, some of which are in a strongly associated state (SAW), and the other in a weakly associated state (WAW). The properties of the weakly associated state of water are similar to the supercritical state, which exists at high temperatures and pressures in the form of nanosized surface clusters. A method has been developed for the formation of a hydrated composite system AM-1/Betulin, which provides it possible for a significant amount of weakly associated water forms to exist in the surface layer. The contact of composite particles with a liquid hydrophobic medium (modeling hydrophobic areas of the gastrointestinal mucosa) further increases the amount of WAW even more. The binding energy of water and the size of adsorbed water clusters depend on the method of hydration. In the case of soft hydration by shaking with water, large clusters of SAW are formed on the surface, localized on the molecules of adsorption-fixed Betulin. During hard hydration (grinding with water in a porcelain mortar), water penetrates into the gaps between hydrophobic particles of methylsilica or methylsilica with immobilized Betulin and forms clusters of WAW, the radii of which can be 0.4–8 nm. This type of interfacial water exists in a wide temperature range, its amount increases with increasing temperature. Thus, a new type of composites has been created, promising for use as antiviral and anticancer drugs.