Approach to Determination a Structure – Antioxidant Activity Relationship of Selected Common Terpenoids Evaluated by ABTS•+Radical Cation Assay

Data available in the literature indicated various biological activities of terpenes. One of the most frequently investigated activities is the ability to scavenge free radicals. To date, studies based on the DPPH • method indicated conjugated double bonds as moieties responsible for antioxidant activity of selected terpenes. In order to verify this theory, studies based on 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS •+ ) were performed. The spectrophotometric investigations explicitly revealed relatively high antioxidant activity of terpenes possessing conjugated double bonds in comparison with substances without this structural element. It has been shown that the chain-breaking antioxidant activity of terpenes strictly depends on π bonds. TEAC values and percentage scavenging of the free radicals revealed that the most promising antioxidants are α-terpinene, ocimene, pulegone and farnesene. In order to explain the reaction between terpenes and ABTS •+ free radical cation, a possible antioxidant mechanism has been proposed.