Antioxidant activity and free radical scavenging reactions of hydroxybenzyl alcohols. Biochemical and pulse radiolysis studies.

Comparative studies on free radical scavenging by isomers of hydroxybenzyl alcohols (HBAs) were carried out to understand the molecular mechanisms involved in the antioxidant action. Using rat liver mitochondria as model systems, we have examined the radioprotective and antioxidant effects of hydroxybenzyl alcohols. Apart from their ability to scavenge free radicals and ferric reducing power, HBAs have shown good protection against radiation and oxidative stress. Using peroxyl radicals as initiator of reactive oxygen species (ROS), studies were carried out to evaluate antioxidant properties of HBAs against rat liver mitochondrial membrane components such as lipid and protein. Our results show that HBAs are potent inhibitor of lipid peroxidation and protein oxidation thus suggesting their role as free radical scavengers. In the presence of HBAs, restoration of depleted activity of Mn-SOD has also been investigated. In the presence of 2-hydroxybenzyl alcohol (2-HBA) complete restoration in the activity of Mn-SOD was observed on exposure to 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). Free radical scavenging ability of HBAs were found to be comparable to alpha tocopherol. Pulse radiolysis technique has been used to study the reactions of HBAs with various biologically relevant reactive species such as hydroxyl radical (OH) and trichloromethyl peroxyl radical (CCl3O2). HBAs could scavenge OH radical giving initially OH-adducts which in turn decays to phenoxyl radicals. Reactions of phenoxyl radicals of HBAs with ascorbic acid have been also studied. Redox potential of HBAs has been evaluated with cyclic voltammetry. Studies clearly suggest a structural reactivity correlation between radical scavenging and antioxidant properties of these isomers of HBA. Among the 3 isomers of HBAs, 4-HBA and 2-HBA are found to have better radical scavenging and antioxidant properties than 3-HBA.