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ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers.
Biochim Biophys Acta. 1999 Mar 14; 1427(1):13-23.BB

Abstract

The purpose of this study is to examine the relationship between the free radical scavenging activities and the chemical structures of tea catechins ((-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)) and their corresponding epimers ((-)-gallocatechin gallate (GCG), (-)-gallocatechin (GC) and (+)-catechin ((+)-C)). With electron spin resonance (ESR) we investigated their scavenging effects on superoxide anions (O-.2) generated in the irradiated riboflavin system, singlet oxygen(1O2) generated in the photoradiation-hemoporphyrin system, the free radicals generated from 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. The results showed that the scavenging effects of galloylated catechins (EGCG and GCG) on the four free radicals were stronger than those of nongalloylated catechins (EGC, GC, EC, (+)-C), and the scavenging effects of EGC and GC were stronger than those of EC and (+)-C. Thus, it is suggested that the presence of the gallate group at the 3 position plays the most important role in their free radical-scavenging abilities and an additional insertion of the hydroxyl group at the 5' position in the B ring also contributes to their scavenging activities. Moreover, the corresponding phenoxyl radicals formed after the reaction with O-.2 were trapped by DMPO and the ESR spectra of DMPO/phenoxyl radical adducts were observed (aN=15.6 G and aHbeta=21.5 G). No significant differences were found between the scavenging effects of the catechins and their epimers when their concentrations were high. However, significant differences were observed at relatively low concentrations, and the lower their concentrations, the higher the differences. The scavenging abilities of GCG, GC and (+)-C were stronger than those of their corresponding epimers (EGCG, EGC and EC). The differences between their sterical structures played a more important role in their abilities to scavenge large free radicals, such as the free radicals generated from AAPH and the DPPH radical, than to scavenge small free radicals, such as O-.2 and 1O2, especially in the case with EGCG and GCG with more bulky steric hindrance.

Authors+Show Affiliations

Institute of Biophysics, Academia Sinica, 15 Datun Road, Beijing 100101, People's Republic of China.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Comparative Study
Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

10082983

Citation

Guo, Q, et al. "ESR Study On the Structure-antioxidant Activity Relationship of Tea Catechins and Their Epimers." Biochimica Et Biophysica Acta, vol. 1427, no. 1, 1999, pp. 13-23.
Guo Q, Zhao B, Shen S, et al. ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers. Biochim Biophys Acta. 1999;1427(1):13-23.
Guo, Q., Zhao, B., Shen, S., Hou, J., Hu, J., & Xin, W. (1999). ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers. Biochimica Et Biophysica Acta, 1427(1), 13-23.
Guo Q, et al. ESR Study On the Structure-antioxidant Activity Relationship of Tea Catechins and Their Epimers. Biochim Biophys Acta. 1999 Mar 14;1427(1):13-23. PubMed PMID: 10082983.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - ESR study on the structure-antioxidant activity relationship of tea catechins and their epimers. AU - Guo,Q, AU - Zhao,B, AU - Shen,S, AU - Hou,J, AU - Hu,J, AU - Xin,W, PY - 1999/3/20/pubmed PY - 1999/3/20/medline PY - 1999/3/20/entrez SP - 13 EP - 23 JF - Biochimica et biophysica acta JO - Biochim Biophys Acta VL - 1427 IS - 1 N2 - The purpose of this study is to examine the relationship between the free radical scavenging activities and the chemical structures of tea catechins ((-)-epigallocatechin gallate (EGCG), (-)-epigallocatechin (EGC) and (-)-epicatechin (EC)) and their corresponding epimers ((-)-gallocatechin gallate (GCG), (-)-gallocatechin (GC) and (+)-catechin ((+)-C)). With electron spin resonance (ESR) we investigated their scavenging effects on superoxide anions (O-.2) generated in the irradiated riboflavin system, singlet oxygen(1O2) generated in the photoradiation-hemoporphyrin system, the free radicals generated from 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) and 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical. The results showed that the scavenging effects of galloylated catechins (EGCG and GCG) on the four free radicals were stronger than those of nongalloylated catechins (EGC, GC, EC, (+)-C), and the scavenging effects of EGC and GC were stronger than those of EC and (+)-C. Thus, it is suggested that the presence of the gallate group at the 3 position plays the most important role in their free radical-scavenging abilities and an additional insertion of the hydroxyl group at the 5' position in the B ring also contributes to their scavenging activities. Moreover, the corresponding phenoxyl radicals formed after the reaction with O-.2 were trapped by DMPO and the ESR spectra of DMPO/phenoxyl radical adducts were observed (aN=15.6 G and aHbeta=21.5 G). No significant differences were found between the scavenging effects of the catechins and their epimers when their concentrations were high. However, significant differences were observed at relatively low concentrations, and the lower their concentrations, the higher the differences. The scavenging abilities of GCG, GC and (+)-C were stronger than those of their corresponding epimers (EGCG, EGC and EC). The differences between their sterical structures played a more important role in their abilities to scavenge large free radicals, such as the free radicals generated from AAPH and the DPPH radical, than to scavenge small free radicals, such as O-.2 and 1O2, especially in the case with EGCG and GCG with more bulky steric hindrance. SN - 0006-3002 UR - https://www.unboundmedicine.com/medline/citation/10082983/ESR_study_on_the_structure_antioxidant_activity_relationship_of_tea_catechins_and_their_epimers_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0304-4165(98)00168-8 DB - PRIME DP - Unbound Medicine ER -