Influence of structural characteristics of substituents on the antioxidant activity of some anthraquinone derivatives

Abstract

The antioxidant activity of chrysophanol (CH), emodin (EM), aloe-emodin (AE), and 1,3,8-trihydroxyanthraquinone (THA) was examined in water and pentyl ethanoate by using the M052X/6-311++G(d,p) level of theory. It was shown that hydrogen bonds are of significant importance for the stability of the radical and anionic species obtained in the HAT and SPLET mechanisms. Consequently, all radicals and anions formed with retention of O9⋯H1–O1 and O9⋯H8–O8 hydrogen bonds are more stable than those where the hydrogen bonds are disturbed. The exceptions are the radical and anion of AE, the unpaired electron or negative charge is poorly delocalized.The high IP values for all investigated compounds undoubtedly discredit the SET-PT mechanism. Since the PA values are notably lower than the BDE values, one can conclude that SPLET is more favorable reaction pathway than the HAT mechanism in both solvents. In the case of CH and AE 1-OH and 8-OH are the most reactive sites for radical inactivation, while 3-OH is the most reactive site for EM and THA. The examined compounds are moderate antioxidants.