Kalakewich, Keyton; Iuliucci, Robbie; Mueller, Karl T.; Eloranta, Harriet; Harper, James K. published the article 《Monitoring the refinement of crystal structures with 15N solid-state NMR shift tensor data》. Keywords: monitoring refinement crystal structure solid state NMR shift tensor.They researched the compound: DL-Histidine monohydrochloride monohydrate( cas:123333-71-1 ).Related Products of 123333-71-1. Aromatic heterocyclic compounds can be divided into two categories: single heterocyclic and fused heterocyclic. In addition, there is a lot of other information about this compound (cas:123333-71-1) here.
The 15N chem. shift tensor is extremely sensitive to lattice structure and a powerful metric for monitoring d. functional theory refinements of crystal structures. These refinements include lattice effects and are applied here to five crystal structures. All structures improve based on a better agreement between exptl. and calculated 15N tensors, with an average improvement of 47.0 ppm. Structural improvement is further indicated by a decrease in forces on the atoms by 2-3 orders of magnitude and a greater similarity in atom positions to neutron diffraction structures. These refinements change bond lengths by more than the diffraction Errors including adjustments to X-Y and X-H bonds (X, Y = C, N, and O) of 0.028 ± 0.002 Å and 0.144 ± 0.036 Å, resp. The acquisition of 15N tensors at natural abundance is challenging and this limitation is overcome by improved 1H decoupling in the FIREMAT method. This decoupling dramatically narrows linewidths, improves signal-to-noise by up to 317%, and significantly improves the accuracy of measured tensors. A total of 39 tensors are measured with shifts distributed over a range of >400 ppm. Overall, exptl. 15N tensors are at least 5 times more sensitive to crystal structure than 13C tensors due to N’s greater polarizability and larger range of chem. shifts. (c) 2015 American Institute of Physics.
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Reference:
Metal catalyst and ligand design,
Ligand Template Strategies for Catalyst Encapsulation – NCBI