Radical scavenging activity of ascorbic acid analogs: kinetics and mechanisms

In the present work, the antioxidant activity of four ascorbic acid analogs has been studied at the M05-2X/6-31G+(d) computational level using the conventional transition state theory in different solvents, with different polarity and taking into account all possible mechanisms. The obtained results indicate that the antioxidant activity of the ascorbic acid analogs increases with the polarity of the environment. Additionally, their antioxidant activity is higher than ascorbic acid. This result is in line with experimental finding which supports the hypothesis that the analogs that had an endocyclic nitrogen atom instead of a ring oxygen may have a higher antioxidant activity than ascorbic acid. On the other hand, the results also indicate that compound 4 (designed by us) is predicted to be more antioxidant than ascorbic acid and the other analogs 1-3, in both lipid and aqueous solution. Finally, for the first time, pKa values, branching ratios and the rate constants for the reactions of ascorbic acid analogs with methylperoxyl radical CH3OO center dot are reported.