Determination of antioxidant activity of some herbal compunds by using DFT methods

The aim of this study is to compare and to interpret reaction results, obtained through the DFT methods, of some plant-based compounds that have antioxidant activity (gallic acid, kampherol, resveratrol, hydroxythrosol, epicatechin) and radical-scavenging compounds (Abts, Cuprac, Dpph, Frap), with experimental (laboratory) data results. Accordingly, we have determined which antioxidant molecule give better interaction with radicals and which were in consistent with the experimental data. As a result, the highest occupied molecular orbital (HOMO), the lowest unoccupied moleculer orbital (LUMO), reaction energy, UV graphics of studied molecules are investigated by using Gaussian 03W. Geometric structures of the studied molecules are drawn by using GaussView5.0 package program. The molecules in gaseous phase are optimized by using 6-31G(d) set and density functional theory (DFT), that is coded in Gaussian 03W, and B3LYP, that consist of Becke's three parametres energy functional approach, and Lee-Yang-Parr's correlation function are used for calculations. In gaseous phase, in comparing with 6-31G(d), the reaction enegry is calculated by using 6-311G+(d,p) set. The spectroscopic graphics are made by using ZBYFT (Time Dependent Density Functional Theory) method. In solvent phase, reaction energy is calculated and their graphics are drawn by using IEFPCM (Integral Equation Formalism Polarizable Continuum Model) code. As a result, except ABTS, the other radicals that are used in our study do react with antioxidant properly. According to our study, thus, the molecules which have the best antioxidant property, are resveratrol and hydroxytyrosol.