Predicting the antioxidant activity of some flavonoids of Arbutus plant: A theoretical approach

In this work, the antioxidant activity, free radical-scavenging capacity, molecular geometry and intramolecular hydrogen bonding interaction were explored for three natural flavonoid compounds of Arbutus unedo L. plant, Fisetin (3,3',4',7-tetrahydroxy flavone), Catechin (Flavan-3,3',4',5,7-pentol) and Apigenin (4',5,7-trihydroxy flavone). Three potential mechanisms of antioxidant activity, hydrogen atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET), have been explored. The physicochemical parameters (BDE, IP, PA, PD, ETE, HOMO and LUMO), as well spin density distribution, were calculated in different solvents. The mechanisms involved in the radical scavenging activity, taking into account the position of the most active OH hydroxyl group, are in accordance with the experimental tests. HAT mechanism is most favorable in the gas phase and benzene solvent. B-ring of the three flavonoids is the active center for the antioxidant activity. Fisetin presents the best antioxidant activity with high free radical scavenging capacity followed by Catechin and Apigenin, respectively.