Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Controol and Remediation Technology, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-Sen University, Guangzhou 510006, China.
UFZ Department of Ecological Chemistry, Helmholtz Centre for Environmental Research, Permoserstraße 15, 04318 Leipzig, Germany.
Environ Sci Technol. 2020 Dec 15;54(24):15751-15758. doi: 10.1021/acs.est.0c04404. Epub 2020 Nov 25.
Several anaerobic bacteria can couple the reduction of aromatic halides to energy conservation. This organohalide respiration is catalyzed by enzymes containing cob(I)alamin, an activated supernucleophilic form of the coenzyme vitamin B. However, the mechanism underlying the electron transfer (inner-sphere vs outer-sphere ET) still remains elusive. To clarify this issue, we selected 36 fluoro-, chloro-, and bromobenzenes as representative substrates and calculated their free-energy barriers at the quantum chemical density functional theory level, considering a wide range of theoretically possible outer-sphere ET mechanisms. Across all 336 reaction routes addressed, 334 routes involve free-energy barriers larger than 20 kcal/mol. For two reaction routes with highly brominated benzenes, free-energy barriers below 20 kcal/mol imply abiotic reduction as observed in experiments. Thus, microbial B-dependent aromatic reductive dehalogenation does not proceed through an outer-sphere ET mechanism. Instead, the present study strongly suggests that microbe-catalyzed reductive dehalogenation of aromatic halides is governed by inner-sphere ET.
几种厌氧细菌可以将芳香卤化物的还原与能量守恒联系起来。这种有机卤化物呼吸由含有 cob(I)alamin 的酶催化，cob(I)alamin 是辅酶维生素 B 的一种活化超亲核形式。然而，电子转移（内球与外球 ET）的机制仍然难以捉摸。为了澄清这个问题，我们选择了 36 个氟代、氯代和溴代苯作为代表性的底物，并在量子化学密度泛函理论水平上计算了它们的自由能势垒，考虑了广泛的理论上可能的外球 ET 机制。在所涉及的 336 个反应途径中，有 334 个途径的自由能势垒大于 20 kcal/mol。对于两个高度溴化苯的反应途径，自由能势垒低于 20 kcal/mol 意味着如实验中观察到的非生物还原。因此，微生物 B 依赖性芳香族还原脱卤反应不是通过外球 ET 机制进行的。相反，本研究强烈表明，微生物催化的芳香卤化物还原脱卤反应受内球 ET 控制。
