Theoretical Study of antioxidant properties of three isomers flavonoids: kaempferol, luteolin and fisetin

Abstract

Fisetin, luteolin and kaempferol are three flavonoids isomers known for their antioxidant properties. To determine the most likely mechanism and the most important sites of demonstration of the antioxidant activity of the molecules, a theoretical study of these properties was carried out by functional B3LYP of DFT in three bases set more and more widened 6-311G, 6-311G (d, p) and 6-311 ++ G (d, p). Based on the electronic and thermodynamic calculated parameters, three elimination mechanisms of the peroxide radical (O2°) were investigated for each of the molecules: electron elimination followed by proton elimination by the molecule, then trapping of free radical; proton elimination followed by electron elimination, then trapping of the free radical; elimination of hydrogen atom by homolytic rupture of OH bond, then trapping of the free radical. The results confirmed that fisetin was the best antioxidant of the three molecules. The mechanism through the elimination of atomic hydrogen by homolytic bond breaking, the most likely for the removal of a peroxide radical by each of the two molecules and the most important sites of demonstration of the antioxidant activity of both flavonols were especially their catechol hydroxyl groups.