scholarly journals The application of tailor-made force fields and molecular dynamics for NMR crystallography: a case study of free base cocaine

IUCrJ ◽  
2017 ◽  
Vol 4 (2) ◽  
pp. 175-184 ◽  
Author(s):  
Xiaozhou Li ◽  
Marcus A. Neumann ◽  
Jacco van de Streek

Motional averaging has been proven to be significant in predicting the chemical shifts inab initiosolid-state NMR calculations, and the applicability of motional averaging with molecular dynamics has been shown to depend on the accuracy of the molecular mechanical force field. The performance of a fully automatically generated tailor-made force field (TMFF) for the dynamic aspects of NMR crystallography is evaluated and compared with existing benchmarks, including static dispersion-corrected density functional theory calculations and the COMPASS force field. The crystal structure of free base cocaine is used as an example. The results reveal that, even though the TMFF outperforms the COMPASS force field for representing the energies and conformations of predicted structures, it does not give significant improvement in the accuracy of NMR calculations. Further studies should direct more attention to anisotropic chemical shifts and development of the method of solid-state NMR calculations.

2017 ◽  
Vol 73 (3) ◽  
pp. 168-175 ◽  
Author(s):  
Hannah E. Kerr ◽  
Lorna K. Softley ◽  
Kuthuru Suresh ◽  
Paul Hodgkinson ◽  
Ivana Radosavljevic Evans

Naproxen (NPX) is a nonsteroidal anti-inflammatory drug with pain- and fever-relieving properties, currently marketed in the sodium salt form to overcome solubility problems; however, alternative solutions for improving its solubility across all pH values are desirable. NPX is suitable for cocrystal formation, with hydrogen-bonding possibilities via the COOH group. The crystal structure is presented of a 1:1 cocrystal of NPX with picolinamide as a coformer [systematic name: (S)-2-(6-methoxynaphthalen-2-yl)propanoic acid–pyridine-2-carboxamide (1/1), C14H14O3·C6H6N2O]. The pharmaceutically relevant physical properties were investigated and the intrinsic dissolution rate was found to be essentially the same as that of commercial naproxen. An NMR crystallography approach was used to investigate the H-atom positions in the two crystallographically unique COOH–CONH hydrogen-bonded dimers. 1H solid-state NMR distinguished the two carboxyl protons, despite the very similar crystallographic environments. The nature of the hydrogen bonding was confirmed by solid-state NMR and density functional theory calculations.


2021 ◽  
Vol 60 (8) ◽  
pp. 6016-6026
Author(s):  
Aydar Rakhmatullin ◽  
Maxim S. Molokeev ◽  
Graham King ◽  
Ilya B. Polovov ◽  
Konstantin V. Maksimtsev ◽  
...  

2016 ◽  
Vol 52 (12) ◽  
pp. 2577-2580 ◽  
Author(s):  
Farhan Ahmad Pasha ◽  
Anissa Bendjeriou-Sedjerari ◽  
Edy Abou-Hamad ◽  
Kuo-Wei Huang ◽  
Jean-Marie Basset

Density functional theory calculations and 2D 1H–13C HETCOR solid state NMR spectroscopy prove that CO2 can be used to probe, by its own reactivity, different types of N-donor surface ligands on SBA15-supported ZrIV hydrides: [(Si–O–)(Si–N)[Zr]H] and [(Si–NH–)(Si–X–)[Zr]H2] (XO or NH).


2021 ◽  
Author(s):  
Kent Griffith ◽  
Fenghua Ding ◽  
Steven Flynn

Indium and bismuth are technologically important elements, in particular as oxides for optoelectronic applications. <sup>115</sup>In and <sup>209</sup>Bi are both I = 9/2 nuclei with high natural abundances and moderately high frequencies but large nuclear electric quadrupole moments. Leveraging the quadrupolar interaction as a measure of local symmetry and polyhedral distortions for these nuclei could provide powerful insights on a range of applied materials. However, the absence of reported NMR parameters on these nuclei, particularly in oxides, hinders their use by the broader materials community. In this contribution, solid-state <sup>115</sup>In and <sup>209</sup>Bi NMR of three recently discovered quaternary bismuth or indium oxides are reported, supported by density functional theory calculations, numerical simulations, diffraction, and additional multinuclear (<sup>27</sup>Al, <sup>69,71</sup>Ga, <sup>121</sup>Sb) solid-state NMR measurements. The compounds LiIn<sub>2</sub>SbO<sub>6</sub>, BiAlTeO<sub>6</sub>, and BiGaTeO<sub>6</sub> are measured without special equipment at 9.4 T, demonstrating that wideline techniques such as the QCPMG pulse sequence and frequency-stepped acquisition can enable straightforward extraction of quadrupolar tensor information in I = 9/2 <sup>115</sup>In and <sup>209</sup>Bi even in sites with large quadrupolar coupling constants. Relationships are described between the NMR observables and local site symmetry. These are amongst the first reports of the NMR parameters of <sup>115</sup>In, <sup>121</sup>Sb, and <sup>209</sup>Bi in oxides.


2020 ◽  
Author(s):  
Giovanna Pope ◽  
Demetrius Vazquez ◽  
Fernando Uribe-Romo ◽  
James K. Harper

Since its initial synthesis in 2005, COF-5 has been known to have intrinsic disorder in the placement of the 2D layers relative to one another (i.e. turbostratic disorder). Prior studies of have demonstrated that the eclipsed layering found in the space group originally assigned to COF-5 (<i>P</i>6<i>/mmm</i>) is inconsistent with energy considerations. Herein it is demonstrated that eclipsed layers are also inconsistent with<sup> 13</sup>C solid-state NMR data. Crystal structure predictions are made in five alternative space groups and good agreement is obtained in <i>P</i>21<i>/m</i>, <i>Cmcm</i>, and <i>C</i>2<i>/m</i>. We posit that all three space groups are present within the stacked 2D layers and show that this conclusion is consistent with evidence from <sup>13</sup>C solid-state NMR linewidths and chemical shifts, powder x-ray diffraction data and energy considerations. An alternative explanation involving a mixture of multiple pure phases is rejected because the observed NMR spectra don’t exhibit the characteristic features of such mixed phase materials.


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