THEORETICAL ELUCIDATION OF THE STRUCTURE - ACTIVITY RELATIONSHIP FOR TANNINS USED TO SCAVENGE RADICALS

摘要

Tannin extracts have been used to scavenge free radicals and prevent chromium VI formation in leathers tanned with chrome salts, but their structure-activity relationship has not been clarified theoretically. In this paper, model tannin compounds representing condensed tannins and hydrolysable tannins were evaluated using the approach of computational chemistry. By using the B3LYP/6-31G(d) method, two kinds of theoretical parameters, i.e. O-H bond dissociation energy (BDE) and adiabatic ionization potential (IP), were obtained to characterize H-atom transfer and concerted proton electron transfer mechanisms respectively in the free radical scavenging process. Both BDE and IP, gave the order of free radical scavenging activity: EGCG>ECG>EGC>EC, and digallic acid >ellagic acid. Furthermore, all the calculation results from electron transfer mechanism and H-abstraction mechanism indicated that the condensed tannins that contain galloyl groups seem to possess the highest free radical scavenging activity.