Abstract: In order to estimate the activity of scavenging free radicals of EGCG and its stereisomer GCG,the hybrid density functional theory B3LYP method at 6-311++G(d,p) level has been used to calculate O-H bond dissociation energies (BDE),ionization potentials (IP),electronic affinities (EA),E0HUMO energies and E-LUMO energies. Results showed that the B ring of EGCG and GCG was the most active site and the free radical reaction was most likely to occur on the B ring on the basis of stability of dehydrogenated EGCG and GCG radicals.This relatively high activity could be attributed to weak hydrogen-bond interactions between two nearby hydroxyls in the B ring of EGCG and GCG.Moreover,GCG was more stable than EGCG and has the same activity of scavenging free radicals as EGCG based on the HAT mechanism and ET-PT mechanism.

Key words: density functional theory, catechin, antioxidant, dissociation energy