Department of Chemistry, Jadavpur University, Kolkata, 700 032, India.
Dalton Trans. 2010 Mar 14;39(10):2692-6. doi: 10.1039/b918582h. Epub 2010 Feb 3.
In weakly acidic media ([H(+)], 0.01-0.06 M), 2-mercaptoethanol (mercap, RSH), thioglycolic acid (tga, R'SH) and L-cysteine (cys, R''SH) reduce the superoxo ligand of the complex ion, {mu-amido-mu-superoxo-bis[tetraamminecobalt(III)]}(4+) (1) to its corresponding hydroperoxo complex, {mu-amido-mu-hydroperoxo-bis[tetraamminecobalt(III)]}(3+) (2). During this act, RSH and R'SH are quantitatively oxidized to their respective disulfides. However, cysteine (R''SH) is converted to a mixture of approximately 80% of the disulfide, cystine and approximately 20% to cystine sulfinic acid. Cystine itself is not a source of the sulfinic acid. Dissolved copper, even at the impurity level, dramatically catalyzes the reaction such that the direct reactions are inaccessible. Nevertheless, the catalyzed path can be masked completely with 0.20 mM dipicolinic acid and it can be determined for the first time that, the direct reactions are first-order in [1], in [total thiol] and in basicity. Rate decreases linearly with increasing mol% of D(2)O in the solvent. H-atom (H(+) + e) transfer from thiols to superoxide in 1 seems logical for the conversion of 1 to 2.
在弱酸性介质中（[H(+)]，0.01-0.06 M），2-巯基乙醇（mercap，RSH）、硫代甘醇酸（tga，R'SH）和 L-半胱氨酸（cys，R''SH）将配合物离子{μ-酰胺-μ-超氧双[四氨合钴（III）]}(4+)（1）中的超氧配体还原为其相应的过氧配合物，{μ-酰胺-μ-过氧双[四氨合钴（III）]}(3+)（2）。在这个过程中，RSH 和 R'SH 被定量氧化为它们各自的二硫化物。然而，半胱氨酸（R''SH）转化为大约 80%的二硫化物胱氨酸和大约 20%的胱氨酸亚磺酸的混合物。胱氨酸本身不是亚磺酸的来源。即使在杂质水平下，溶解的铜也会显著催化反应，使得直接反应无法进行。然而，用 0.20 mM 二吡啶甲酸可以完全掩蔽催化途径，并且可以首次确定直接反应在[1]、[总巯基]和碱度方面是一级反应。随着溶剂中 D(2)O 摩尔%的增加，速率呈线性下降。在 1 中，从硫醇到超氧的 H-原子（H(+) + e）转移似乎对于 1 向 2 的转化是合理的。
