The kinetics and mechanism of the [RuIII(edta)(H2O)]â-mediated oxidation of cysteine (RSH) by hydrogen peroxide (edta4â = ethylenediaminetetraacetate), were studied in detail as a function of both the hydrogen peroxide and cysteine concentrations at pH 5.1 and room temperature. The kinetic traces reveal clear evidence for a catalytic process in which hydrogen peroxide reacts directly with cysteine coordinated to the RuIII(edta) complex in the form of [RuIII(edta)SR]2â. A parallel process in which [RuIII(edta)(H2O)]â first reacts with H2O2 to produce [RuV(edta)O]â and subsequently oxidizes cysteine, is orders of magnitude slower than the [RuIII(edta)(H2O)]â-mediated oxidation in which cysteine rapidly coordinates to [RuIII(edta)(H2O)]â prior to the reaction with H2O2. HPLC product analyses revealed the formation of cystine (RSSR) as major product along with cysteine sulfinic acid (RSO2H) in the reaction system, and established the catalytic role of [RuIII(edta)(H2O)]â. Simulations were performed to account for the rather complex kinetic traces in terms of the suggested reaction mechanism. The results of the simulations support the proposed reaction mechanism that involves the oxidation of coordinated cysteine to cysteine sulfenic acid (RSOH), which subsequently rapidly reacts with H2O2 and RSH to form RSO2H and RSSR, respectively.
详细研究了[RuIII(edta)(
H2O)]-介导的
过氧化氢(edta4-=
乙二胺四乙酸)氧化半胱
氨酸(RSH)的动力学和机制,作为
过氧化氢和
乙二胺四乙酸的函数。 pH 5.1 和室温下的半胱
氨酸浓度。动力学痕迹揭示了催化过程的清晰证据,其中
过氧化氢直接与以 [RuIII(edta)SR]2- 形式配位到 RuIII(edta) 复合物的半胱
氨酸反应。 [RuIII(edta)( )]→ 首先与 2 反应生成 [RuV(edta)O]→ 并随后氧化半胱
氨酸的并行过程比 [RuIII(edta) 慢几个数量级( )]‐介导的氧化反应,其中半胱
氨酸在与 2 反应之前快速与 [RuIII(edta)( )]‐ 配位。 HPLC 产物分析表明,反应体系中主要产物为胱
氨酸 (RSSR) 和半胱
氨酸亚
磺酸 (RSO2H),并确定了 [RuIII(edta)( )] 的催化作用。进行模拟以解释所建议的反应机制中相当复杂的动力学轨迹。模拟结果支持了所提出的反应机制,其中涉及配位半胱
氨酸氧化为半胱
氨酸
磺酸(RSOH),随后与 2和RSH快速反应,分别形成RSO2H和RSSR。