A quantum chemical study on the antioxidant properties of aureusidin and bracteatin

摘要

The radical scavenging activities of the two flavonoids, aureusidin and bracteatin, have been explored by using density functional theory (DFT) with the B3LYP exchange correlation functional. These compounds are characterized by a high antioxidant activity which confers to them pharmacological properties that are useful for the treatment of several diseases. The minimum energy conformations obtained from the energy scan is a further geometry optimization performed at the B3LYP-DFT level with 6-311G** basis set. Harmonic vibrational frequencies have been performed on the optimized structures to ensure that the geometries obtained were real minima. For radicals, the geometry optimizations and frequency calculations were also done at the same mode of theory. Single point energy was calculated at the same level of theory in the gas phase and in two solvents with different polarities (water and benzene) with the aim of computing the bond dissociation enthalpy (BDE) for the O-H bonds and the ionization potentials (IPs). The O-H BDE parameter calculated for each OH group seems to be the best indicator of the antiradical property of these compounds. This demonstrates the importance of the H-atom transfer mechanism to explain their capacity to scavenge the free radicals. The active sites are identified. BDE for these systems do not follow the same trends in gas and solution phases. The values of reactivity-based descriptors such as total energy, orbital energy gap, maximum hardness principle, and electronegativity are also related with the antioxidant activity.