UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research , Permoserstraße 15, 04318 Leipzig, Germany.
Technical University Bergakademie Freiberg , Institute for Organic Chemistry, Leipziger Straße 29, 09596 Freiberg, German y.
Environ Sci Technol. 2018 Feb 20;52(4):1834-1843. doi: 10.1021/acs.est.7b04278. Epub 2018 Jan 31.
The bacterium Dehalococcoides, strain CBDB1, transforms aromatic halides through reductive dehalogenation. So far, however, the structures of its vitamin B-containing dehalogenases are unknown, hampering clarification of the catalytic mechanism and substrate specificity as basis for targeted remediation strategies. This study employs a quantum chemical donor-acceptor approach for the Co(I)-substrate electron transfer. Computational characterization of the substrate electron affinity at carbon-halogen bonds enables discriminating aromatic halides ready for dehalogenation by strain CBDB1 (active substrates) from nondehalogenated (inactive) counterparts with 92% accuracy, covering 86 of 93 bromobenzenes, chlorobenzenes, chlorophenols, chloroanilines, polychlorinated biphenyls, and dibenzo-p-dioxins. Moreover, experimental regioselectivity is predicted with 78% accuracy by a site-specific parameter encoding the overlap potential between the Co(I) HOMO (highest occupied molecular orbital) and the lowest-energy unoccupied sigma-symmetry substrate MO (σ*), and the observed dehalogenation pathways are rationalized with a success rate of 81%. Molecular orbital analysis reveals that the most reactive unoccupied sigma-symmetry orbital of carbon-attached halogen X (σ) mediates its reductive cleavage. The discussion includes predictions for untested substrates, thus providing opportunities for targeted experimental investigations. Overall, the presently introduced orbital interaction model supports the view that with bacterial strain CBDB1, an inner-sphere electron transfer from the supernucleophile B Co(I) to the halogen substituent of the aromatic halide is likely to represent the rate-determining step of the reductive dehalogenation.
细菌 Dehalococcoides 株 CBDB1 通过还原脱卤化作用转化芳香卤化物。然而，到目前为止，其含维生素 B 的脱卤酶的结构仍然未知，这阻碍了对催化机制和底物特异性的澄清，而这些是靶向修复策略的基础。本研究采用量子化学给体-受体方法研究 Co(I)-底物电子转移。对碳-卤键上的底物电子亲合性的计算特征描述使我们能够以 92%的准确率区分 CBDB1 菌株可进行脱卤化作用的芳香卤化物（活性底物）和不可进行脱卤化作用的（非活性）对应物，涵盖 86 个溴苯、氯苯、氯苯酚、氯苯胺、多氯联苯和二苯并对二恶英。此外，通过对 Co(I) HOMO（最高占据分子轨道）和最低能量非占据 σ 对称底物 MO（σ*）之间重叠势的特定位置参数进行编码，可以以 78%的准确率预测实验的区域选择性，并且观察到的脱卤化途径的成功率为 81%。分子轨道分析表明，与碳相连的卤原子 X（σ）的最反应性非占据 σ 对称轨道介导其还原断裂。讨论包括对未经测试的底物的预测，从而为有针对性的实验研究提供了机会。总的来说，目前引入的轨道相互作用模型支持这样的观点，即对于细菌株 CBDB1，来自超亲核试剂 B Co(I)到芳香卤化物的卤原子取代基的内球电子转移可能代表还原脱卤化作用的速率决定步骤。
