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An important task in technology of chemical-pharmaceutical preparations is the improvement of drug formulations, the development of new alternative drug delivery methods for biologically active substances as well as the changes in the delivery systems of active components. A search and implementation of nano-size systems for the delivery of drug formulations related to nootropic series is in fact an actual task in medicine. Correct interpretation of the experimental data in the study of the reactant release from the delivery systems such as nanoparticles is impossible without the comprehension of physico-chemical processes occurring at the molecular level. The purpose of the study is a comparative analysis of thermodynamic characteristics of vinpocetine binding with the surface of silicon and silicon oxide in aqueous medium. Calculations of the enthalpy, entropy and Gibbs energy were performed for the process of vinpocetine desorption from the surface of an adsorbent. First, the values of enthalpy and entropy were calculated for the initial and final stages of the process. Gibbs energy of vinpocetine desorption from the surface of silicon oxide is of a greater value as compared with its desorption from silicon surface under corresponding pH values. It can be explained by the ability of silicon oxide surface to ionization at pH 6.8 and 7.0, as well as by a large number of hydroxyl groups on the surface of this adsorbent. The obtained data enables to make a conclusion on the more tight vinpocetine binding with the surface of silicon oxide as compared with pure silicon surface.

Quantum-chemical calculation of the free energy of binding of vinpocetine molecules with surface of silicon and silicon dioxide