Reactive Sulfur Species: Kinetics and Mechanism of the Equilibrium between Cysteine Sulfenyl Thiocyanate and Cysteine Thiosulfinate Ester in Acidic Aqueous Solution
作者:Kelemu Lemma、Michael T. Ashby
DOI:10.1021/jo702345u
日期:2008.4.1
The kinetics and mechanism of the hydrolysis of cysteine sulfenyl thiocyanate (CySSCN) to give cysteine thiosulfinate ester (CyS(O)SCy) have been investigated between pH 0 and 4. The reaction is reversible. The hydrolysis of CySSCN is second-order in [CySSCN] and inverse first-order in [H+] and [SCN-]. The following mechanism is proposed for the hydrolysis of CySSCN (where the charge depends upon the
研究了在pH 0至4之间水解半胱氨酸硫基硫氰酸酯(CySSCN)生成半胱氨酸硫亚磺酸酯(CyS(O)SCy)的动力学和机理。该反应是可逆的。CySSCN的水解是二阶在[CySSCN]和逆第一阶中[H + ]和[SCN - ]。提出了一种用于CySSCN(其中电荷取决于pH值)的水解如下机理:CySSCN 0 / + + H 2 ö⇌CySOH 0 / + + SCN - + H +,CySOH 0 / + + CySSCN 0 / + → CYS(O)SCY 0 / + / 2 + + SCN - + H +; k 1= 3.36±0.01×10 -3 s -1,K 1 k 2= 0.13±0.05Ms -1(产生k 2 / k -1= 39M)。观察到的速率定律排除了1≤pH≤4的替代机制,包括两个分子的半胱氨酸亚磺酸(CySOH)缩合生成CyS(O)SCy的机制。可以从相反的方向达到平衡。CYS的反应(O)SCY与SCN