Theoretical elucidation of activity differences of five phenolic antioxidants.

To verify the effectiveness of structure-activity relationship (SAR) and theoretical calculation methods for antioxidants.Preliminary elucidation on the differences of activities of 5 antioxidants was performed by SAR. Then semiempirical quantum chemistry method AM1 was employed to calculate the delta HOF value, the difference between the heat of formation of antioxidant and its free radical, which was used as a theoretical parameter to elucidate the differences of activities of the antioxidants thoroughly.delta HOF values of antioxidants were obtained as follows: ferulic acid, 150.58 kJ.mol-1; anion of ferulic acid, 122.64 kJ.mol-1; modified ferulic acid, 137.70 kJ.mol-1; anion of modified ferulic acid, 118.99 kJ.mol-1; salvianic acid, 134.17 kJ.mol-1; rutin, 137.83 kJ.mol-1, L-EGCG, 124.39 kJ.mol-1; paeonol, 176.79 kJ.mol-1. The differences of the antioxidant activities were elucidated, and how to further enhance the antioxidant activity was investigated as well.The SAR and calculation methods are rather effective to elucidate the differences of antioxidant activities, and present some new clues for structural modification of antioxidants to increase their activities.