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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

DOI: 10.1002/chem.201604705 DOI Help

Authors: Birger Dittrich (Heinrich-Heine Universität Düsseldorf) , Jens Lübben (Heinrich-Heine Universität Düsseldorf) , Stefan Mebs (Institut für Chemie und Biochemie–Anorganische Chemie der, Freien Universität Berlin) , Armin Wagner (Diamond Light Source) , Peter Luger (Institut für Chemie und Biochemie–Anorganische Chemie der, Freien Universität Berlin) , Ralf Flaig (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemistry - A European Journal , VOL 42

State: Published (Approved)
Published: March 2017

Open Access Open Access

Abstract: 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.

Journal Keywords: amino acids; density functional theory; neutron diffraction; structure elucidation; X-ray diffraction

Subject Areas: Chemistry

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Added On: 17/03/2017 08:49


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