Predicting the antioxidant activity of curcumin and curcuminoids

The curcuminoids, which include curcumin and related molecules, are effective antioxidants with demonstrated medicinal effects. The curcumin structure contains a variety of functional groups including the P-diketo group, carbon-carbon double bonds and phenyl rings containing varying amounts of hydroxyl and methoxy substituents. The literature on the site of activity and the reaction mechanism(s) responsible for the antioxidant effects is controversial, with some authors claiming that the activity is due to the hydroxyl moiety while others invoke carbon-centered radicals or involvement of the carbonyl groups. We present a systematic theoretical study of these molecules, aimed at clarifying the active sites, and discuss the validity of proposed mechanisms based on our calculations. We also discuss more general aspects of free radical chemistry, especially the selectivity arising from choice of the free radical/antioxidant system. (C) 2002 Elsevier Science B.V. All rights reserved.