On the primary and secondary antioxidant activity from hydroxy‐methylcoumarins: experimental and theoretical studies

Abstract In this work, the experimental and theoretical study on the primary and secondary antioxidant activities of three hydroxy‐4‐methylcoumarins were carried out. According to the experimental results obtained in the TEAC test employing ABTS, DPPH and galvinoxyl radicals, coumarin with the most important radical scavenging activity was 7,8‐dihydroxy‐4‐methylcoumarin (HMD), even observing a radical scavenging activity greater than that demonstrated by the Trolox antioxidant. The theoretical results on primary antioxidant capability shown that the HMD has a good radical scavenging activity in lipid media when compared to other molecules with known antioxidant activity. It was also highlighted that HMD showed an excellent radical scavenging capability in aqueous media considering the physiological pH, the results indicated that it even has a more important radical scavenging capability than others coumarins that are considered excellent antioxidants. Hence, HMD showed a great versatility to stabilize different kinds of important biological radicals, in these results were highlighted their great antioxidant activity. In addition to the previous results, the secondary antioxidant activity was studied, the results showed that HMD could inhibit the reduction of the copper and in this way avoid the Haber‐Weiss reactions, which leads to the increase of the hydroxyl radical concentration, and then, to oxidative stress. Therefore, this study shows that the HMD is able to stabilize the radicals in the primary antioxidant activity and avoid the generation of radicals through the Fenton reaction in the secondary antioxidant activity.