氮氧自由基研究 XX.哌啶氧铵溴化物与半胱氨酸于酸性水溶液中的反应和机理

Studies on Nitroxides XX. A Mechanistic Study on Reaction between 2, 2, 6, 6-Tetramethyl-4-hydroxypiperidine Oxoammonium Bormide and Cysteine in Acidic Aqueous Medium

氧铵盐是氮氧自由基失去单电子后生成的高价化合物,其氧化性较氮氧自由基强。据报道,氧铵盐可氧化醇成醛或酮,相应氮氧自由基无此特性。Stier等指出,氮氧自由基可作为反应中间体存在于生物细胞的某些酶作用过程。Yamaguchi等发现,氮氧自由基可被H_2O_2/Fe^(2+)/氨基酸或H_2O_2/血红蛋白体系氧化为氧铵盐。鉴于Fe^(2+),·OH以及氨基酸存在于生物体内,因此研究氧铵盐与生物分子间的反应是有一定意义的。本文从反应产物,化学反应计量关系,电化学模拟和动力学测定诸方面对氧铰盐1与dl-半胱氨酸(2)于盐酸水溶液中的反应作了研究。

The products of the reaction between 2, 2, 6, 6-tetramethyl-4-hydroxypiperidine oxoammonium bromide (1) and dl-cysteine (2) in aqueous HCl solution have been identified as the corresponding hydroxylamine and cysteic acid. The stoichiometry of the reaction was determined by TLC scan method to be 3:1. According to tho cyclovoltam- metric study, one-electron transfer process is assumed to be involved in the reaction. The flow-stop UV kinetic experiments showed that the reaction was first order to both 1 and 2, the reaction rate decreased with the increase of the acidity of the medium. A mechanism for the reaction is proposed.