Nano drug modeling: Ab initio and DFT studies on ionization of ampicillin in aqueous solution

In this article, pKa values of the drug ampicillin were determined in aqueous solution by an ab initio method. The quantitative behavior of acids and bases in solution can be understood only if their pKa values are known. We used density functional theory (DFT) methods and polarizable continuum solvation model (PCM) to explain the effects of aqueous solvation. For the analyze the formation of intermolecular hydrogen bonds (IHBs) between the existent species and water molecules, Tomasi,s method (B3LYP/6-31+G(d)) was used. It was shown that anion, and neutral species of ampicillin are solvated with one, two, three, and four molecules of water in alkaline aqueous solutions. In this research work, we obtained there is comparable agreement between the experimentally determined pKa values for the acid-base reactions selected by potentiometric and those reported in the literature demonstrating the theoretically calculated pKa values.