Radical Scavenging Activity Of Natural Anthraquinones: A Theoretical Insight

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 center dot 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(center dot-) 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 x 10(6) to 3.70 x 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(center dot-) radical scavengers in polar media.