Quantum-Chemical Modeling of Vinpocetine Desorption from Silicon and Silicon-Dioxide Particle Surfaces

Abstract

Activation energies for desorption of vinpocetine from silicon (Si) and silicon-dioxide (SiO₂) surfaces were analyzed and compared. The molecular mechanism of vinpocetine desorption was found to differ depending on the adsorbent and ionization state, which in turn depended on the pH. Nonpolar interactions between the adsorbent and vinpocetine played a decisive role during desorption from a hydrophobic Si surface without substituents. Quantum-chemical estimates of the activation energy led to the conclusion that vinpocetine in aqueous solution at pH 6.8 and 7 was bound more strongly to SiO₂ than to Si. The activation energies for vinpocetine desorption from Si and SiO₂ surfaces at pH 2 were statistically indistinguishable and statistically significantly less than the activation energies at pH 6.8 and 7.