Conversion of methane to methanol at the mononuclear and dinuclear copper sites of particulate methane monooxygenase (pMMO): A DFT and QM/MM study
Conversion of methane to methanol at the mononuclear and dinuclear copper sites of particulate methane monooxygenase (pMMO): A DFT and QM/MM study
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DOI：
10.1021/ja061604r
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发表时间：
2006-08-02
影响因子：
15
通讯作者：
Shiota, Yoshihito
中科院分区：
文献类型：
--
作者：
Yoshizawa, Kazunari;Shiota, Yoshihito
利用量子力学和QM/MM计算讨论了pMMO单核和双核铜中心的甲烷羟基化反应。可能的机制提出了相对于反应性铜氧代的形成，以及它们如何激活甲烷。将分子氧引入Cu（I）物种中以得到Cu（II）- superoxo物种，然后从靠近单铜活性位点的酪氨酸残基转移H-原子。所得的CuII-氢过氧物种接下来通过从另一个酪氨酸残基提取H-原子而转化为Cu（III）-氧代物种和水分子。在生理条件下，这一过程在能量上是可以实现的。分子氧也被引入到二铜位点中以形成（μ-η（2）：η（2）-过氧）二铜物质，然后将其转化为双（μ-氧代）二铜物质。该物种的形成在能量上比单铜氧物种更有利。如果在蛋白质环境中形成，Cu（III）-氧代物种的反应性足以将甲烷转化为甲醇。由于位于Cu-O键区域的σ * 轨道在三重态中被单独占据，因此该轨道在甲烷的C-H键的均裂中起作用。双（μ-氧代）二铜物质的反应性也足以将甲烷转化为甲醇。混合价的双（μ-氧代）Cu（II）Cu（III）物种是反应性的甲烷，因为幅度的σ * 单占据MO本地化的桥接氧代部分起着至关重要的作用，在C-H活化。
Methane hydroxylation at the mononuclear and dinuclear copper sites of pMMO is discussed using quantum mechanical and QM/MM calculations. Possible mechanisms are proposed with respect to the formation of reactive copper-oxo and how they activate methane. Dioxygen is incorporated into the Cu(I) species to give a Cu(II)- superoxo species, followed by an H-atom transfer from a tyrosine residue near the monocopper active site. A resultant CuII- hydroperoxo species is next transformed into a Cu(III)-oxo species and a water molecule by the abstraction of an H-atom from another tyrosine residue. This process is accessible in energy under physiological conditions. Dioxygen is also incorporated into the dicopper site to form a (mu-eta(2):eta(2)-peroxo)dicopper species, which is then transformed into a bis(mu-oxo) dicopper species. The formation of this species is more favorable in energy than that of the monocopper- oxo species. The reactivity of the Cu(III)-oxo species is sufficient for the conversion of methane to methanol if it is formed in the protein environment. Since the sigma* orbital localized in the Cu-O bond region is singly occupied in the triplet state, this orbital plays a role in the homolytic cleavage of a C-H bond of methane. The reactivity of the bis(mu-oxo) dicopper species is also sufficient for the conversion of methane to methanol. The mixed-valent bis(mu-oxo)Cu(II)Cu(III) species is reactive to methane because the amplitude of the sigma* singly occupied MO localized on the bridging oxo moieties plays an essential role in C-H activation.