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首页> 美国卫生研究院文献>Wiley-Blackwell Online Open >Accurate Bond Lengths to Hydrogen Atoms from Single‐Crystal X‐ray Diffraction by Including Estimated Hydrogen ADPs and Comparison to Neutron and QM/MM Benchmarks
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Accurate Bond Lengths to Hydrogen Atoms from Single‐Crystal X‐ray Diffraction by Including Estimated Hydrogen ADPs and Comparison to Neutron and QM/MM Benchmarks

机译：通过包括估计的氢ADP以及与中子和QM / MM基准的比较得出单晶X射线衍射与氢原子的准确键长

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摘要

Amino acid structures are an ideal test set for method‐development studies in crystallography. High‐resolution X‐ray diffraction data for eight previously studied genetically encoding amino acids are provided, complemented by a non‐standard amino acid. Structures were re‐investigated to study a widely applicable treatment that permits accurate X−H bond lengths to hydrogen atoms to be obtained: this treatment combines refinement of positional hydrogen‐atom parameters with aspherical scattering factors with constrained “TLS+INV” estimated hydrogen anisotropic displacement parameters (H‐ADPs). Tabulated invariom scattering factors allow rapid modeling without further computations, and unconstrained Hirshfeld atom refinement provides a computationally demanding alternative when database entries are missing. Both should incorporate estimated H‐ADPs, as free refinement frequently leads to over‐parameterization and non‐positive definite H‐ADPs irrespective of the aspherical scattering model used. Using estimated H‐ADPs, both methods yield accurate and precise X−H distances in best quantitative agreement with neutron diffraction data (available for five of the test‐set molecules). This work thus solves the last remaining problem to obtain such results more frequently. Density functional theoretical QM/MM computations are able to play the role of an alternative benchmark to neutron diffraction.
机译：氨基酸结构是用于晶体学方法开发研究的理想测试套件。提供了先前研究的八个遗传编码氨基酸的高分辨率X射线衍射数据，并辅以非标准氨基酸。对结构进行了重新研究，以研究一种广泛应用的处理方法，该方法可获取与氢原子精确的X-H键长度：此处理方法结合了对位置氢原子参数的细化与非球面散射因子以及受约束的“ TLS + INV”估计的氢各向异性位移参数（H‐ADP）。列表式不变散射因子无需进一步计算即可进行快速建模，并且当缺少数据库条目时，不受约束的Hirshfeld原子细化功能可提供计算要求较高的替代方案。两者都应包含估计的H-ADP，因为自由细化经常会导致过度参数化和非正定H-ADP，而与所使用的非球面散射模型无关。使用估计的H-ADP，这两种方法都能产生与中子衍射数据（适用于五个测试装置分子）的最佳定量一致性的精确X-H距离。因此，这项工作解决了最后剩下的问题，以便更频繁地获得这种结果。密度泛函理论QM / MM计算能够充当中子衍射的替代基准。

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