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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Electron Densities of Three B_(12) Vitamins
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Electron Densities of Three B_(12) Vitamins

机译：三种B_（12）维生素的电子密度

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The electron densities of the three natural B_(12)-vitamins, two of them being essential cofactors for animal life, were determined in a procedure combining high-order X-ray data collection at low to very low temperatures with high-level density functional calculations. In a series of extensive experimental attempts, a high-order data set of adenosylcobalamin (AdoCbl) could be collected to a resolution of sin θ/λ = 1.00 _~(-1) at 25 K. This modification contains only minor disorder at the solvent bulk. For methylcobalamin (MeCbl), only a severely disordered modification was found (sin θ/λ = 1.00 _~(-1), 100 K, measured with synchrotron radiation). The already published data set of cyanocobalamin (CNCbl) (sin θ/λ = 1.25 _~(-1), 100 K) was reintegrated to guarantee similar treatment of the three compounds and cut to sin θ/λ= 1.11 _~(-1) to obtain a higher degree of completeness and redundancy. On the basis of these accurate experimental geometries of AdoCbl, MeCbl, and CNCbl, state-of-the-art density functional calculations, single-point calculations, and geometry optimizations were performed on model compounds at the BP86/TZVP level of theory to evaluate the electronic differences of the three compounds. AdoCbl and MeCbl are known to undergo different reaction paths in the body. Thus, the focus was directed toward the characterization of the dative Co-C_(ax) and Co-N_(ax) bonds, which were quantifed by topological parameters, including energy densities; the source function including local source; and the electron localizability indicator (ELI-D), respectively. The source function reveals the existence of delocalized interactions between the corrin macrocycle and the axial ligands. The ELI-D indicates unsaturated Co_C_(ax) bonding basins for the two biochemically active cofactors, but not for CNCbl, where a population of 2.2e is found. This may be related to significant π-backbonding, which is supported by the delocalization index, δ, of 0.15 between the Co atom and the N atom of the cyano ligand. Considering all results, the inherent electronic differences between AdoCbl and MeCbl are found to be small thus, supporting earlier findings that the interaction with the protein site mainly controls the type of Co-C_(ax) bond cleavage.
机译：三种天然B_（12）-维生素的电子密度，其中两种是动物生命必不可少的辅助因子，是通过将低温至极低温下的高阶X射线数据收集与高水平密度功能相结合的程序确定的计算。在一系列广泛的实验尝试中，可以收集高位腺苷钴胺素（AdoCbl）数据集，其分辨率为25 K时sinθ/λ= 1.00 _〜（-1）。溶剂散装。对于甲基钴胺素（MeCbl），仅发现了严重无序的修饰（用同步加速器辐射测量，sinθ/λ= 1.00〜（-1），100 K）。重新整合了氰钴胺素（CNCbl）（sinθ/λ= 1.25 _〜（-1），100 K）的数据集，以确保对这三种化合物进行类似处理并切成sinθ/λ= 1.11 _〜（- 1）获得更高的完整性和冗余度。在AdoCbl，MeCbl和CNCbl的这些精确实验几何的基础上，以BP86 / TZVP的理论水平对模型化合物进行了最先进的密度泛函计算，单点计算和几何优化。三种化合物的电子差异。已知AdoCbl和MeCbl在体内会经历不同的反应路径。因此，研究的重点是表征Co-C_（ax）键和Co-N_（ax）键的特征，这些键通过包括能量密度在内的拓扑参数进行定量。源函数包括本地源;和电子可定位性指示器（ELI-D）。源函数揭示了corrin大环与轴向配体之间存在离域相互作用。 ELI-D表示两个生化活性辅因子的不饱和Co_C_（ax）结合盆地，但CNCbl则没有，那里有2.2e的人口。这可能与显着的π回键有关，这由氰基配体的Co原子和N原子之间的0.15的离域指数δ所支持。考虑到所有结果，因此发现AdoCbl和MeCbl之间固有的电子差异很小，从而支持较早的发现，即与蛋白质位点的相互作用主要控制Co-C_（ax）键裂解的类型。

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