Abstract Antioxidant activity of gentisic acid has been studied using fast chemical kinetics and two in vitro models, namely the isolated rat liver mitochondria (RLM) and the human erythrocytes. The presence of gentisic acid (GA) during irradiation significantly reduced the levels of gamma radiation induced damages to lipids and proteins in RLM. Further, GA imparted protection to the human erythrocytes against exposure to gamma radiation. Molecular mechanism of free radical scavenging reactions has been evaluated with the help of rate constants and transients obtained from gentisic acid using pulse radiolysis technique. GA efficiently scavenged hydroxyl radical (k = 1.1 × 10(10) dm(3)mol(-1)s(-1)) to produce reducing adduct radical (~76%) and oxidizing phenoxyl radical (~24%). GA has also scavenged organohaloperoxyl radical (k = 9.3 × 10(7) dm(3) mol(-1)s(-1)). Ascorbate has been found to repair phenoxyl radical of GA (k = 1.0 × 10(7) dm(3)mol(-1)s(-1)). Redox potential value of GA(•)/GA couple (0.774 V vs NHE) obtained by cyclic voltammetry is less than those of physiologically important oxidants, which supports the observed antioxidant capacity of GA. We, therefore, propose that the antioxidant and radioprotective properties of GA are exerted by its phenoxyl group.
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