Ab Initio Studies of Complexation of Gallic Acid in Aqueous Solutions

Abstract

By an ab initio Hartree-Fock method at the (6-311+G*) level of theory the structural and energy characteristics of gallic acid (GA) complexes are calculated with and without taking into account the first hydration shell: GA–GA, GA–H2O, GA–H2O–GA and GA–H2O–GA (+6 water molecules), GA–GA (+8 water molecules). The calculations are carried out in the vacuum and aqueous solutions by the selfconsistent reaction field method (SCRF calculations). The solvent effect is studied using the Onsager model. The effect of the medium on the geometry, dipole moment, and stability of the considered complexes is estimated. The most stable structures of the complexes, their geometric parameters and atomic charges are determined and the vibrational spectra are calculated. In the aqueous medium, the GA–GA complex (ΔEint =–12.9758 kcal/mol) is found to be the most stable as compared to GA–H2O and GA–H2O–GA. It is shown that the involvement of solvent molecules as the first hydration shell significantly affects the structure and stability of GA complexes.