Radical Scavenging Activity of Natural Anthraquinones: a Theoretical Insight

[Image: see text] Anthraquinones (ANQs) isolated from Paederia plants are known to have antidiarrheal, antitussive, anthelmintic, analgesic, anti-inflammatory, antihyperlipidemic, antihyperglycaemic, and antimicrobial activities. The antioxidant properties were also noted but not confirmed thus far. In this study, the superoxide and hydroperoxide radical scavenging activities of six ANQs were evaluated using a computational approach. The results suggest that the ANQs exhibit low HOO(•) antiradical activity in all environments, including the gas phase (k < 10(2) M(–1) s(–1)). In contrast, the ANQs might exert excellent O(2)(•–) radical scavenging activity, particularly in aqueous solution. The rate constants of the superoxide anion scavenging in water (at pH = 7.4) range from 3.42 × 10(6) to 3.70 × 10(8) M(–1) s(–1). Compared with typical antioxidants such as ascorbic acid and quercetin, the superoxide anion scavenging activity of ANQs is significantly higher. Thus, the ANQs are promising O(2)(•–) radical scavengers in polar media.