ESR study on the structure–antioxidant activity relationship of tea catechins and their epimers

• Published in: Biochimica et biophysica acta Vol. 1427; no. 1; pp. 13 - 23
• Main Authors: Guo, Qiong, Zhao, Baolu, Shen, Shengrong, Hou, Jingwu, Hu, Jungai, Xin, Wenjuan
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 14.03.1999
• Subjects: Amidines; Amidines - chemistry; analogs & derivatives; antioxidants; Antioxidants - chemistry; Bepridil; Bepridil - analogs & derivatives; Bepridil - chemistry; Biphenyl Compounds; Catechin; Catechin - analogs & derivatives; Chemical structure; chemistry; Electron spin resonance; Electron Spin Resonance Spectroscopy; Epimer; flavonols; Free Radical Scavengers; Free Radical Scavengers - chemistry; Gallate group; Isomerism; Oxidation-Reduction; Oxygen; Oxygen - chemistry; Picrates; Scavenging activity; Singlet Oxygen; Structure-Activity Relationship; structure-activity relationships; Superoxides; Superoxides - chemistry; tea; Tea - chemistry; Tea catechin; EGC, (−)-epigallocatechin; EC, (−)-epicatechin; Electron spin resonance; TEMPONE, 2,2,6,6-tetramethyl-4-piperidone; Epimer; Chemical structure; DMPO, 5,5-dimethyl-1-pyrroline-1-oxide; TC, tea catechin; GC, (−)-gallocatechin; (+)-C, (+)-catechin; Tea catechin; GCG, (−)-gallocatechin gallate; ESR, electron spin resonance; Gallate group; Scavenging activity; 4-POBN, α-(4-pyridyl-1-oxide)- N- t-butylnitrone; EGCG, (−)-epigallocatechin gallate; DPPH, 1,1-diphenyl-2-picrylhydrazyl; AAPH, 2,2′-azobis(2-amidinopropane)hydrochloride
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/S0304-4165(98)00168-8

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( 1O 2) 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 ( a N=15.6 G and a H β =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 1O 2, especially in the case with EGCG and GCG with more bulky steric hindrance.