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首页> 外文学位 >Investigation on the mechanism of formation and consumption of vinylcobalamins involved in vitamin B(12)-catalyzed reductive dechlorination of perchloroethylene.
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Investigation on the mechanism of formation and consumption of vinylcobalamins involved in vitamin B(12)-catalyzed reductive dechlorination of perchloroethylene.

机译：关于维生素B（12）催化的全氯乙烯还原脱氯反应中乙烯基钴胺素形成和消耗机理的研究。

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摘要

Vitamin B12 reductively dechlorinates perchloroethylene (PCE), a common environmental pollutant and human carcinogen, into less toxic molecules, such as ethene, making B12 a possible catalyst for the bioremediation of PCE from contaminated sites. Application of B12 as a catalyst requires a detailed understanding of the mechanism by which B12 dechlorinates PCE. While vitamin B12 dechlorinates PCE to form trichloroethylene (TCE) via an electron transfer mechanism, further dechlorination of TCE to form ethene involves chlorovinylcobalamins as intermediates. Despite their detection, the structure and reactivity of these cobalamin intermediates is poorly understood.; Cobaloximes, B12 model complexes, were used to investigate the cobalamin intermediates. It was found that cob(I)aloxime catalyzed the dechlorination of PCE to TCE, and TCE reacted with cob(I)aloxime to form dichlorinated vinylcobaloxime 4. Cob(I)aloxime further catalyzed the dechlorination of 4 to monochlorinated vinylcobaloximes (5 and 6) and could fully dechlorinate 5 and 6 to vinylcobaloxime 7. Electrochemical reduction of the chlorinated vinylcobaloximes indicated that the reduction of the cobaloximes became more facile as the number of chlorides on the vinyl ligand increased.; Similar experiments were undertaken using cobalamins to further investigate the vitamin B12-catalyzed dechlorination of PCE. Chlorovinylcobalamin 16, previously detected in the PCE dechlorination reaction, was synthesized by treating cob(I)alamin with chloroacetylene. The structure of 16 was confirmed by X-ray crystallography, and is the first reported structure of an organocobalamin containing a bond to a sp2 hybridized carbon in its axial ligand. Although treating cobalamin 16 with either titanium(III)citrate or cob(I)alamin led to the formation of vinylcobalamin 17, cob(I)alamin was found to catalyze this transformation at a much faster rate. Vinylcobalamin 17 was resistant toward reduction by titanium(III)citrate or cob(I)alamin, which prevents efficient dechlorination of PCE by sequestering the active catalyst. Electrochemical experiments on 16 and 17 indicate that the chlorovinylcobalamins become more susceptible to reduction as the number of chlorides on the vinyl ligand increases. It would be expected that the presence of three chlorines on the vinyl ligand would further shift the peak potential toward the CoII /CoI couple of B12 making reduction of a polychlorinated vinylcobalamins by cob(I)alamin even more facile.
机译：维生素B 12 将常见的环境污染物和人类致癌物全氯乙烯（PCE）还原为毒性较小的分子（例如乙烯），使B 12 成为生物修复的可能催化剂来自受污染场地的PCE。 B 12 作为催化剂的应用需要对B 12 对PCE进行脱氯的机理的详细理解。维生素B 12 通过电子转移机理使PCE脱氯形成三氯乙烯（TCE），而将TCE进一步脱氯形成乙烯则需要氯乙烯钴胺素作为中间体。尽管检测到了这些钴胺素中间体的结构和反应性，但了解甚少。 Cobaloximes，B 12 模型复合物，用于研究钴胺素中间体。结果表明，钴（I）肟能够催化PCE脱氯成三氯乙烯，三氯乙烯（TCE）与钴（I）肟反应生成二氯化乙烯基钴肟 4 。 Cob（I）aloxime进一步催化 4 脱氯为单氯代乙烯基钴肟（ 5 和 6 ），并且可以将 5 完全脱氯。粗体>和 6 表示乙烯基钴肟 7 。氯化乙烯基钴氧肟的电化学还原表明，随着乙烯基配体上氯化物数目的增加，钴氧肟的还原变得更容易。使用钴胺素进行了类似的实验，以进一步研究维生素B 12 催化的PCE脱氯。氯乙炔钴胺 16 以前是在PCE脱氯反应中检测到的，是通过用氯乙炔处理钴（I）丙胺来合成的。 X射线晶体学证实了 16 的结构，这是第一个报道的有机钴胺素结构，其轴向配体中包含与sp 2 杂化碳键。尽管用柠檬酸钛（III）或钴（I）阿拉明处理钴胺素 16 会导致乙烯基钴胺素 17 的形成，但发现钴（I）alamin可以催化这种转化以更快的速度。乙烯基钴胺素 17 不能被柠檬酸钛（III）或钴（I）alamin还原，从而通过隔离活性催化剂阻止了PCE的有效脱氯。在 16 和 17 上进行的电化学实验表明，随着乙烯基配体上氯离子数量的增加，氯乙烯基钴胺素变得更易于还原。可以预料，乙烯基配体上存在三个氯会进一步将峰值电势移向B 12 / Co / Co I 对。使得通过钴（I）丙氨酸还原多氯乙烯钴胺素更加容易。

著录项

  • 作者

    McCauley, Kevin Michael.;

  • 作者单位

    University of Illinois at Urbana-Champaign.;

  • 授予单位 University of Illinois at Urbana-Champaign.;
  • 学科 Chemistry Organic.; Chemistry Inorganic.
  • 学位 Ph.D.
  • 年度 2003
  • 页码 106 p.
  • 总页数 106
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 有机化学;无机化学;
  • 关键词

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