School of Geology and Geophysics, University of Oklahoma , 100 E. Boyd Street, SEC 710, Norman, Oklahoma 73019, United States.
Environ Sci Technol. 2013 Sep 3;47(17):9668-77. doi: 10.1021/es400463p. Epub 2013 Aug 23.
Carbon (C), chlorine (Cl), and hydrogen (H) isotope effects were determined during dechlorination of TCE to ethene by a mixed Dehalococcoides (Dhc) culture. The C isotope effects for the dechlorination steps were consistent with data published in the past for reductive dechlorination (RD) by Dhc. The Cl effects (combined with an inverse H effect in TCE) suggested that dechlorination proceeded through nucleophilic reactions with cobalamin rather than by an electron transfer mechanism. Depletions of (37)Cl in daughter compounds, resulting from fractionation at positions away from the dechlorination center (secondary isotope effects), further support the nucleophilic dechlorination mechanism. Determination of C and Cl isotope ratios of the reactants and products in the reductive dechlorination chain offers a potential tool for differentiation of Dhc activity from alternative transformation mechanisms (e.g., aerobic degradation and reductive dechlorination proceeding via outer sphere mechanisms), in studies of in situ attenuation of chlorinated ethenes. Hydrogenation of the reaction products (DCE, VC, and ethene) showed a major preference for the (1)H isotope. Detection of depleted dechlorination products could provide a line of evidence in discrimination between alternative sources of TCE (e.g., evolution from DNAPL sources or from conversion of PCE).
利用混合脱卤球菌（Dhc）培养物研究了三氯乙烯（TCE）脱氯生成乙烯过程中的碳（C）、氯（Cl）和氢（H）同位素效应。脱氯步骤的 C 同位素效应与过去 Dhc 介导的还原脱氯（RD）数据一致。Cl 效应（与 TCE 中的逆 H 效应结合）表明脱氯是通过钴胺素的亲核反应进行的，而不是通过电子转移机制。由于脱氯中心以外位置的分馏导致（37）Cl 在子化合物中的消耗（次级同位素效应），进一步支持亲核脱氯机制。还原脱氯链中反应物和产物的 C 和 Cl 同位素比的测定为区分 Dhc 活性与替代转化机制（例如，好氧降解和通过外球机制进行的还原脱氯）提供了一种潜在的工具，在研究氯化乙烯的原位衰减时。反应产物（DCE、VC 和乙烯）的加氢显示出对（1）H 同位素的主要偏好。耗尽脱氯产物的检测可提供区分 TCE 替代来源的证据（例如，从非水相液体（DNAPL）来源演变而来或从 PCE 转化而来）。
