Flavonoids as hydroxyl radical scavengers, iron reductants and chelators: in vitro antioxidant action

Flavonoids are phytochemicals, which exhibit antioxidant potential due to their ability to donate a hydrogen atom and/or a single electron, and to interact with other antioxidants.The aim of this study was to evaluate the antioxidant potential of two subclasses of pure flavonoids: flavonols (quercetin, rhamnetin, isorhamnetin) and flavones (luteolin, apigenin) in vitro.Particularly, using spectrophotometric methods, we determined the ability of these flavonoids to scavenge hydroxyl radical, reduce ferric ions (Fe (III)) and chelate ferrous ions (Fe (II)).Obtained results showed that tested flavonoids are good scavengers of hydroxyl radical and reductants (Fe (III) → Fe (II)) but relatively poor chelators of ferrous ions.Quercetin, which belongs to the group of flavonols was the most efficient antioxidant among tested flavonoids, while luteolin from the flavone group was the second one.We found that the number of hydroxyl groups and the presence of hydroxyl group at the C3 position of ring C corresponds with better hydroxyl radical scavenging activity and reduces the power of flavonoids.Catechol structure in the B ring was important for higher reducing power and chelating activity of flavonoids, but surprisingly it did not influence the hydroxyl radical scavenging activity of tested compounds.In contrary, the presence of the methoxy group in the structure of rhamnetin and isorhamnetin decreases their reducing power and chelating activity.Interestingly, the hydroxyl group at the C5 position of ring A was more important for the chelating activity of flavonoids than the hydroxyl group at the C3 position of ring C. Our research may enrich knowledge about the therapeutic potential of flavonoids as antioxidants.