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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Chemoprotectant, Sodium 2?Mercaptoethanesulfonate, MESNA, by Acidic Bromate and Aqueous Bromine
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Oxyhalogen-Sulfur Chemistry: Kinetics and Mechanism of Oxidation of Chemoprotectant, Sodium 2?Mercaptoethanesulfonate, MESNA, by Acidic Bromate and Aqueous Bromine

机译：氧卤硫化学：酸性溴酸盐和溴水溶液对化学保护剂2？巯基乙磺酸钠MESNA氧化的动力学和机理

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The oxidation of a well-known chemoprotectant in anticancer therapies, sodium 2-mercaptoethanesulfonate, MESNA, by acidic bromate and aqueous bromine was studied in acidic medium. Stoichiometry of the reaction is: BrO_3~- + HSCH_2CH_2SO_3H → Br- + HO_3SCH_2CH_2SO_3H. In excess bromate conditions the stoichiometry was deduced to be: 6BrO_3~- + 5HSCH_2CH_2SO_3H + 6H~+ → 3Br_2 + 5HO_3SCH_2CH_2SO_3H + 3H_2O. The direct reaction of bromine and MESNA gave a stoichiometric ratio of 3:1: 3Br_2 + HSCH_2CH_2SO_3H + 3H_2O → HO_3SCH_2CH_2SO_3H + 6Br~- + 6H~+. This direct reaction is very fast; within limits of the mixing time of the stopped-flow spectrophotometer and with a bimolecular rate constant of 1.95 ± 0.05 × 10~4 M~(-1) s~(-1). Despite the strong oxidizing agents utilized, there is no cleavage of the C-S bond and no sulfate production was detected. The ESI-MS data show that the reaction proceeds via a predominantly nonradical pathway of three consecutive 2-electron transfers on the sulfur center to obtain the product 1,2-ethanedisulfonic acid, a well-known medium for the delivery of psychotic drugs. Thiyl radicals were detected but the absence of autocatalytic kinetics indicated that the radical pathway was a minor oxidation route. ESI-MS data showed that the S-oxide, contrary to known behavior of organosulfur compounds, is much more stable than the sulfinic acid. In conditions where the oxidizing equivalents are limited to a 4-electron transfer to only the sulfinic acid, the products obtained are a mixture of the S-oxide and the sulfonic acid with negligible amounts of the sulfinic acid. It appears the S-oxide is the preferred conformation over the sulfenic acid since no sulfenic acids have ever been stabilized without bulky substituent groups. The overall reaction scheme could be described and modeled by a minimal network of 18 reactions in which the major oxidants are HOBr and Br_2(aq).
机译：研究了在酸性介质中酸性溴酸盐和含水溴对抗癌疗法中众所周知的化学保护剂2-巯基乙磺酸钠（MESNA）的氧化作用。反应的化学计量为：BrO_3〜-+ HSCH_2CH_2SO_3H→Br- + HO_3SCH_2CH_2SO_3H。在过量的溴酸盐条件下，化学计量推导为：6BrO_3〜-+ 5HSCH_2CH_2SO_3H + 6H〜+→3Br_2 + 5HO_3SCH_2CH_2SO_3H + 3H_2O。溴与MESNA的直接反应的化学计量比为3：1：3Br_2 + HSCH_2CH_2SO_3H + 3H_2O→HO_3SCH_2CH_2SO_3H + 6Br〜-+ 6H〜+。这种直接反应非常快。在停止流式分光光度计的混合时间限制内，双分子速率常数为1.95±0.05×10〜4 M〜（-1）s〜（-1）。尽管使用了强氧化剂，但没有裂解C-S键，也未检测到硫酸盐的产生。 ESI-MS数据显示，该反应通过硫中心上三个连续的2-电子转移的主要非自由基途径进行，从而获得了产物1,2-乙烷二磺酸，这是一种用于输送精神药物的众所周知的介质。可以检测到巯基自由基，但是缺乏自催化动力学表明自由基途径是次要的氧化途径。 ESI-MS数据显示，与有机硫化合物的已知行为相反，S-氧化物比亚磺酸稳定得多。在将氧化当量限制为仅向亚磺酸的4-电子转移的条件下，获得的产物为S-氧化物和磺酸与少量亚磺酸的混合物。似乎S-氧化物是优于亚磺酸的优选构象，因为没有亚硫酸在没有庞大的取代基的情况下从未被稳定过。整个反应方案可以通过18个反应的最小网络来描述和建模，其中主要氧化剂为HOBr和Br_2（aq）。

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