Methane Formation by Reaction of a Methyl Thioether with a Photo-Excited Nickel Thiolate—A Process Mimicking Methanogenesis in Archaea
Methane Formation by Reaction of a Methyl Thioether with a Photo-Excited Nickel Thiolate—A Process Mimicking Methanogenesis in Archaea
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甲基硫醚与光激发硫醇镍反应形成甲烷——模拟古细菌产甲烷作用的过程
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发表时间：
2000
期刊：
影响因子：
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通讯作者：
B. Jaun
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作者：
L. Signor;C. Knuppe;R. Hug;B. Schweizer;A. Pfaltz;B. Jaun
硫酰自由基中间体的形成，随后甲基转移到辅酶F430的镍（I）中心，并产生二硫化物已被提出作为一种可能的机制，在产甲烷古菌中由甲基辅酶M还原酶催化甲烷的形成。为了验证这一假设，合成了一种含有甲基硫醚和巯基官能团的空间屏蔽的双官能模型底物，其可以根据假设的机制形成五元环硫酰基自由基。相应的硫醇盐与Ni（II）盐反应，得到抗磁性的正方形平面二硫代镍（II）配合物，其结构经X-射线衍射表征。在用λ> 300 nm的光照射该络合物时，形成甲烷和环状二硫化物，而在不存在镍的情况下照射硫醇盐仅得到痕量的甲烷而没有环状二硫化物。所观察到的产品是一致的假设的机制，通过一个sulfuranyl自由基，和光的作用被解释为形成一个Ni（I）/巯基自由基对后，激发的电荷转移带的Ni（II）二硫醇盐。在大量过量的硫醇盐的存在下，反磁性复合物被转化成顺磁性的，五或六配位复合物，被证明是更活跃的生成甲烷和环状二硫化物，比正方形平面的反磁性二硫醇盐。
The formation of a sulfuranyl radical intermediate followed by methyl transfer to the nickel(I) center of coenzyme F430 and generation of the disulfide has been proposed as a possible mechanism for the formation of methane catalyzed by methyl coenzyme M reductase in methanogenic archaea. In order to test this hypothesis, a sterically shielded, bifunctional model substrate that contained a methyl thioether and a sulfhydryl functional group, which could form a five-membered cyclic sulfuranyl radical according to the postulated mechanism, was synthesized. The corresponding thiolate reacted with Ni(II) salts to give a diamagnetic, square-planar Ni(II) dithiolate complex, which was characterized by X-ray diffraction. Upon irradiation of this complex with light of lambda > 300 nm, methane and the cyclic disulfide were formed, whereas irradiation of the thiolate in the absence of nickel gave only traces of methane and no cyclic disulfide. The observed products are consistent with the postulated mechanism via a sulfuranyl radical, and the role of light is interpreted as the formation of a Ni(I)/thiyl radical pair upon excitation of a charge-transfer band of the Ni(II) dithiolate. In the presence of a large excess of thiolate, the diamagnetic complex was transformed into a paramagnetic, five- or six-coordinate complex that proved to be more active in the generation of both methane and the cyclic disulfide, than the square-planar diamagnetic dithiolate.