Antioxidant Activity Mechanism Studies On Medicinal Plants Flavones

This dissertation includes two aspects of study:The first part is the theoretical study of quercetin and methyl hydroperoxide free radical, and analysised the order of the antioxidant activity on five hydroxyl sites of quercetin, from the static and dynamic methods. The second part is the theoretical study of four flavones A-glucosides and methyl hydroperoxide on 4'site, it maked comparation with quercetin.The antioxidant activity of quercetin and related activity-structure relationships were investigated in this study by the DMOLJ calculation, based on the density functional theory (DFT). Quercetin exerts its antioxidant activity through the capacity of donating H atom to inhibit reactive oxygen species (ROS) that act as free radicals. So the interaction of the most reactive quercetin with methyl peroxyl radical (CH3OO) is studied. The geometries of quercetin and its five phenoxy radicals were obtained at the Generalized Gradient Approximation (GGA) level, medium of quality, with the spin unrestricted approach and BLYP/DND method. Five possible reactions of scavenging methyl peroxyl radicals, in terms of H-atom-transfer mechanism, were designed. The transition state(TS) for each reaction was determined. The spin density, the intrinsic reaction coordinate and structure properties of stationary points were analyzed. The activation energy, thermodynamic state functions and kinetic reaction rate constant k were calculated. Results show that, the anti-oxidation strength order of five different reaction sites is 4'-OH> 3'-OH> 3-OH> 7-OH> 5-OH, which is in agreement with the experiment results. In addition, whatever 3',4'-ortho-hydrogexyl in the B-ring donates a hydrogen atom firstly and finally becomes to be 3',4'-double radicals, their BDE values, spin density and transition state are less than others. We conclude quercetin is attacked two methyl peroxyl radical (CH3OO) continuously, which explains that why ortho-hydrogexyl positions (especially 4'site) are most reactive and competitive, which had been reported by many experimental studies.The antioxidant activity of flavones A-glucosides and related activity-structure relationships were investigated in this study by the DMOL3 calculation, They exerts its antioxidant activity through the capacity of donating H atom to inhibit free radicals. So the interaction of flavones A-glucosides with methyl peroxyl radical (CH3OO) is studied. The geometries of They and their phenoxy radicals at 4'site were obtained at the Generalized Gradient Approximation (GGA) level, medium of quality, with the spin unrestricted approach and BLYP/DND method. Four possible reactions of scavenging methyl peroxyl radicals, in terms of H-atom-transfer mechanism, were designed. The transition state(TS) for each reaction was determined. The spin density, the intrinsic reaction coordinate and structure properties of stationary points were analyzed. The activation energy, thermodynamic state functions and kinetic reaction rate constant k were calculated. In the end, the results maked comparation with quercetin.