コンドウ　カズナリ    KONDO KAZUNARI
   近藤 一成
   所属
食健康科学部 食安全マネジメント学科
   職種
教授
言語種別 英語
発行・発表の年月 1999
形態種別 学術雑誌
査読 査読あり
標題 Mechanistic Studies of Catechins as Antioxidants against Radical Oxidation
執筆形態 共著
掲載誌名 Archives of Biochemistry and Biophysics
掲載区分国外
巻・号・頁 362,pp.79-86
担当区分 筆頭著者,責任著者
著者・共著者 Kondo K, Kurihara M, Miyata N, Suzuki T, Toyoda M
概要 The antioxidative mechanisms of catechins were studied by investigating products generated at the first stages by 2, 2'-azobis(2-aminopropane)hydrochloride (AAPH)-induced radical oxidation, without any isolation, using LC/MS, spectrophotometry, and PM3 semiempirical molecular orbital (MO) calculations. Catechins were quite effective in scavenging peroxyl radicals in a liposomal system and in an aqueous system except for (-)-epigallocatechin (EGC). EGC was the least effective among four catechins tested. From the results of LC/MS and spectroscopic studies, (-)-epicatechin (EC) would be gently converted to an anthocyanin-like compound. According to the mechanisms, the compound produced from EC by radical oxidation can also function as an antioxidant. As a result, EC has a longer inhibition period (tinh = 9360 s). On the other hand, EGC decreased shortly after oxidation (tinh = 3420 s) and was transformed to a quinone-like compound. The addition of superoxide dismutase (SOD) reduced the chemiluminescence from EGC during oxidation. Active oxygen including superoxide anion radicals (O-2) may be produced in the case of EGC, but not in the case of EC. However, EGC has a more rapid scavenging effect on peroxyl radicals (kinh/kp = 232) than EC (kinh/kp = 41). The calculated C-H bond dissociation enthalpies (BDEs) for catechins at the C-2 position were unexpectedly low (65 kcal/mol) compared to O-H BDEs at phenolic sites (70 kcal/mol), suggesting that hydrogen at the C-2 position may be abstracted by free radicals. The authors propose the tentative antioxidative mechanisms of catechins depending on the experimental results and theoretical calculations.