Spectroscopic and computational studies on [Ni(tmc)CH3]OTf: implications for Ni-methyl bonding in the A cluster of acetyl-CoA synthase.
Spectroscopic and computational studies on [Ni(tmc)CH3]OTf: implications for Ni-methyl bonding in the A cluster of acetyl-CoA synthase.
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[Ni(tmc)CH3]OTf 的光谱和计算研究：对乙酰辅酶 A 合酶 A 簇中 Ni-甲基键合的影响。
DOI：
10.1021/ic0483996
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发表时间：
2005
影响因子：
4.6
通讯作者：
Brunold,ThomasC
中科院分区：
文献类型：
--
作者：
Schenker,Ralph;Mock,MichaelT;Kieber-Emmons,MatthewT;Riordan,CharlesG;Brunold,ThomasC
五配位高自旋（S= 1）Ni 2+配合物[Ni（tmc）CH 3]+（1）（tmc = 1，4，8，11-四甲基-1，4，8，11-四氮杂环十四烷）作为乙酰辅酶A合酶（ACS）A簇活性反应中间体的模型，其中远端镍中心被甲基化。光谱和密度泛函理论（DFT）计算研究提供了一个定量的成键描述1，揭示了一个高度共价的Ni− CH 3键。从对1的共振拉曼数据的简正坐标分析中，得到该物种的Ni−C伸缩力常数kNi-C = 1.44 mdyn/m3。该值小于thankCo-C= 1.85 mdyn/dyn，这是在ACS催化循环中作为A簇的甲基供体的甲基辅酶酰胺辅因子（5）中的Co-C伸缩的报告。实验校准的DFT计算可行的甲基化A簇模型显示，甲基结合到近端（NIP），而不是远端（NID）镍中心，并提供一个简单的电子参数为这种偏好。通过将实验力常数与1和5中计算的M-C键的键级相关联，预测具有正方形平面Nip构象的A簇模型的Nip 2 +-CH 3键强度与CH 3-CoFeSP中的Co 3 +-CH 3键强度相似，这是基于空间和能量考虑的甲基化A簇的最可能结构。这种相似性可能是酶促甲基转移反应可逆性的关键热力学先决条件。
The five-coordinate high-spin (S= 1) Ni2+complex [Ni(tmc)CH3]+(1) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) serves as a model for a viable reaction intermediate of the A cluster of acetyl-CoA synthase (ACS) in which the distal nickel center is methylated. Spectroscopic and density functional theory (DFT) computational studies afford a quantitative bonding description for1that reveals a highly covalent Ni−CH3bond. From a normal coordinate analysis of resonance Raman data obtained for1, a value ofkNi-C= 1.44 mdyn/Å is obtained for the Ni−C stretch force constant of this species. This value is smaller thankCo-C= 1.85 mdyn/Å, which is reported for the Co−C stretch in the methylcobinamide cofactor (5) that serves as the methyl donor to the A cluster in the ACS catalytic cycle. Experimentally calibrated DFT computations on viable methylated A cluster models reveal that the methyl group binds to the proximal (Nip) rather than the distal (Nid) nickel center and afford a simple electronic argument for this preference. By correlating the experimental force constants with the computed bond orders of the M−C bonds in1and5, the Nip2+−CH3bond strength for an A cluster model with a square-planar Nipconformation, which is the most probable structure of the methylated A cluster on the basis of steric and energetic considerations, is predicted to be similar to the Co3+−CH3bond strength in CH3−CoFeSP. This similarity could be a crucial thermodynamic prerequisite for the reversibility of the enzymatic transmethylation reaction.