Protective Activities of Catechins on Singlet Oxygen Induced Photooxidation of α-Terpinene in Methanol: Structure and Singlet Oxygen Quenching Activity Relationship

The protective activities of 6 different catechins on the singlet oxygen induced photooxidation of alpha-terpinene in methanol were studied to find out the relation between their structure and singlet oxygen quenching activity. The total singlet oxygen quenching abilities (k(r) + k(q) values) in the same system were also calculated by using a Stern-Volmer plot. The protective activities were in order of epigallocatechin gallate (EGCG)=epigallocatechin (EGC) > gallocatechin gallate (GCG) > epicatechin gallate (ECG) > epicatechin (EC) > catechin (C). The k(r) + k(q) values of EGCG and C were 1.31 x 10(8) and 1.66 x 10(7)/M.s, respectively. The pyrogallol (B) ring structure was the most influencing factor for the k(r) + k(q) values. Stereospecific configuration also provided a considerable influence on the values. The G-ring structure did not show significant influence in the value for EGCG and EGC. The k(r) values of the catechins were 3.23 x 10(5)-1.64 x 10(6)/M.s.