Mechanistic studies of catechins as antioxidants against radical oxidation
Mechanistic studies of catechins as antioxidants against radical oxidation
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DOI：
10.1006/abbi.1998.1015
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发表时间：
1999-02-01
影响因子：
3.9
通讯作者：
Toyoda, M
中科院分区：
文献类型：
--
作者：
Kondo, K;Kurihara, M;Toyoda, M
通过研究2，2‘-偶氮二(2-氨基丙烷)盐酸盐(AAPH)诱导自由基氧化的第一阶段产物，采用LC/MS、分光光度和PM3半经验分子轨道计算，研究了儿茶素的抗氧化机理。在脂质体和水体系中，除(-)-表没食子儿茶素(EGC)外，EGC的清除能力最差。根据LC/MS和光谱研究的结果，(-)表儿茶素(EC)将被温和地转化为花青素类化合物。从机理上讲，EC自由基氧化生成的化合物也具有抗氧化剂的作用。结果表明，EC具有较长的抑制期(t(Inh)=9360 S)。另一方面，氧化后不久EGC降低(t(Inh)=3420 S)，并转变为类似苯醌的化合物。超氧化物歧化酶(SOD)的加入降低了EGC氧化过程中的化学发光。在鸡蛋的情况下，可能会产生包括超氧阴离子自由基(O-2(-))在内的活性氧，但在EC的情况下不会。然而，EGC对过氧化自由基(k(Inh)/k(P)=232)的清除作用比EC(k(Inh)/k(P)=41)更快，计算的C-2位儿茶素的C-H键离解热CBDEs(65kcal/mol)出人意料地低于酚位的O-HBDEs(70kcal/Mel)，这表明C-2位的氢可能被自由基带走。作者根据实验结果和理论计算提出了儿茶素的初步抗氧化机理，(C)1999年学术出版社。
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 (t(inh) = 9360 s). On the other hand, EGC decreased shortly after oxidation (t(inh) = 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 EGG, but not in the case of EC. However, EGC has a more rapid scavenging effect on peroxyl radicals (k(inh)/k(p), = 232) than EC (k(inh)/k(p) = 41), The calculated C-H bond dissociation enthalpies CBDEs) for catechins at the C-2 position were unexpectedly low (65 kcal/ mol) compared to O-H BDEs at phenolic sites (70 kcal/ mel), 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, (C) 1999 Academic Press.