New theoretical perspective for easy evaluation of the antioxidant properties of typical flavonoids

To intensively investigate the antioxidant property of flavonoids and their different phenolic hydroxyl groups, we selected six types of typical flavonoids and carried out experimental analysis and quantum chemical calculations. By calculating the Mulliken charges, frontier molecular orbitals, molecular dipole moments, and interaction model hydrogen bond lengths of the compounds, the theoretical analysis results were compared with the free radical scavenging assays. Results show that the three flavonoids with different numbers of hydroxyl groups on the B ring are ranked in antioxidant activity as myricetin > quercetin > kaempferol. The glycoside linked in the C ring has a great effect on bioavailability, and the antioxidant activity is ranked as quercetin > isoquercetin > rutin. Besides, the results of the novel interaction model calculations show that quercetin with an meta-hydroxy group on the B ring structure has stronger antioxidant capacity than morin with an ortho-hydroxy group. The theoretical evaluation method established in this work is expected to provide new ideas and references for the evaluation of antioxidant properties of natural active substances from the electronic structure perspective.