<i>Ab initio</i> and DFT studies on ionization of octopamine and 6-aminopenicillanic acid in aqueous solution

Abstract

619-626The existing quantum chemical methods to accurately predict pKa and to determine the trade-off between accuracy and computational cost have been evaluated by ab initio and density functional theory with the B3LYP functional and 6-31+G(d) basis sets and polarizable continuum solvation model. The calculated free energies for determination of pKa values, and intermolecular hydrogen bonds in aqueous solutions of octopamine and 6-aminopenicillanic acid have been computed. This study shows that there is reasonable agreement between the theoretically calculated pKa values and the experimentally determined pKa values for the acid-base reactions obtained by potentiometric and spectrophotometric methods reported in the literature