ANTIOXIDANT MECHANISMS OF FLAVONOIDS: STRUCTURE–ACTIVITY RELATIONSHIP (SAR)
Keywords:
flavonoids; antioxidant activity; structure–activity relationship (SAR); hydrogen atom transfer (HAT); single electron transfer (SET); radical scavenging.Abstract
Flavonoids are plant-derived phenolic secondary metabolites synthesized via the phenylpropanoid pathway and characterized by a C6–C3–C6 carbon skeleton. Their antioxidant properties are directly associated with their molecular structure. The present study analyzes the principal structural determinants governing the antioxidant activity of flavonoids and elucidates their radical-scavenging mechanisms. The results indicate that the presence of a 3′,4′-ortho-dihydroxy (catechol) moiety in the B ring, conjugation between the C2–C3 double bond and the 4-oxo functional group, as well as the 3-hydroxyl substituent, enhance electron delocalization and contribute to the stabilization of the corresponding phenoxyl radical. These structural features increase the efficiency of hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms. The findings support a structure–activity relationship (SAR)-based evaluation of the antioxidant potential of flavonoids and provide a theoretical framework for the rational design of bioactive molecules.
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