Abstract
The protective activities of 6 different catechins on the singlet oxygen induced photooxidation of α-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 1.31×108 and 1.66×107/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 3.23×105–1.64×106/M·s.
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