Antioxidant activity of anthraquinones and anthrone

The antioxidant properties of anthraquinones (AQs) and anthrone were evaluated using different model systems. The antioxidant activity of these compounds (200 ppm) on the inhibition of peroxidation of linoleic acid was found to be in the order of BHA (96%), anthrone (95%), alizarin (93%) > aloe-emodin (78%) > rhein (71%) > emodin (36%) > anthraquinone (8%). Chrysophanol accelerated the peroxidation of linoleic acid. Anthrone and alizarin exhibited a reducing power, although the other AQs did not show any reducing power. AQs and anthrone exhibited a weak chelating ability on iron (II). At a concentration of 0.25 mg/ml, the scavenging effects of anthrone, aloe-emodin and emodin, on hydroxyl radicals produced by the Fenton reaction were 26.2, 16.6 and 41.8%, respectively. However, at the same concentration, anthraquinone, alizarin, chrysophanol and rhein accelerated the production of hydroxyl radicals. These results suggest that the antioxidant mechanism, for both emodin and aloe-emodin, possibly depends on scavenging hydroxyl radicals. The strong activity shown by anthrone could be due to its reducing power and scavenging effects on hydroxyl radicals. The pro-oxidant activity exhibited by chrysophanol might be due to the enhanced production of free radicals. (C) 2000 Elsevier Science Ltd. All rights reserved.