Department of Inorganic and Analytical Chemistry, University of Debrecen, P.O. Box 21, Debrecen H-4010, Hungary.
Inorg Chem. 2013 Feb 18;52(4):2150-6. doi: 10.1021/ic302544y. Epub 2013 Jan 30.
The haloperoxidase-catalyzed in vivo oxidation of thiocyanate ion (SCN(-)) by H(2)O(2) is important for generation of the antimicrobial hypothiocyanite ion (OSCN(-)), which is also susceptible to oxidation by strong in vivo oxidizing agents (i.e., H(2)O(2), OCl(-), OBr(-)). We report a detailed mechanistic investigation on the multistep oxidation of excess SCN(-) with peroxomonosulfate ion (HSO(5)(-) in the form of Oxone) in the range from pH 6.5 to 13.5. OSCN(-) was detected to be the intermediate of this reaction under the above conditions, and a kinetic model is proposed. Furthermore, by kinetic separation of the consecutive reaction steps, the rate constant of the direct oxidation of OSCN(-) by HSO(5)(-) was determined: k(2) = (1.6 ± 0.1) × 10(2) M(-1) s(-1) at pH 13.5 and k(2)(H) = (3.3 ± 0.1) × 10(3) M(-1) s(-1) at pH 6.89. A critical evaluation of the estimated activation parameters of the elementary steps revealed that the oxidations of SCN(-) as well as the consecutive OSCN(-) by HSO(5)(-) are more likely to proceed via 2e(-)-transfer steps rather than 1e(-) transfer.
过氧化物酶催化的硫氰酸根离子（SCN(-)）在体内被 H(2)O(2)氧化，对于生成具有抗菌作用的次碘酸根离子（OSCN(-)）很重要，而 OSCN(-)也容易被体内的强氧化剂（如 H(2)O(2)、OCl(-)、OBr(-)）氧化。我们报道了在 pH 6.5 到 13.5 的范围内，用过氧单硫酸盐离子（Oxone 形式的 HSO(5)(-)）对过量的 SCN(-)进行多步氧化的详细机理研究。在上述条件下，检测到 OSCN(-)是该反应的中间体，并提出了一个动力学模型。此外，通过连续反应步骤的动力学分离，确定了 OSCN(-)被 HSO(5)(-)直接氧化的速率常数：在 pH 13.5 时，k(2) = (1.6 ± 0.1) × 10(2) M(-1) s(-1)，在 pH 6.89 时，k(2)(H) = (3.3 ± 0.1) × 10(3) M(-1) s(-1)。对各基元步骤估计的活化参数的严格评估表明，SCN(-)的氧化以及 HSO(5)(-)对连续的 OSCN(-)的氧化更可能通过 2e(-)转移步骤而不是 1e(-)转移步骤进行。
