scholarly journals Polymorphic Forms of Valinomycin Investigated by NMR Crystallography

2020 ◽  
Vol 21 (14) ◽  
pp. 4907
Author(s):  
Jiří Czernek ◽  
Jiří Brus
Keyword(s):  
Solid State Nmr ◽  
Large Scale ◽  
Solid Phase ◽  
Chemical Shifts ◽  
Conformational Stability ◽  
Structural Factors ◽  
Polymorphic Forms ◽  
Isotropic Chemical Shifts ◽  
Nmr Crystallography ◽  
Crystalline Forms

A dodecadepsipeptide valinomycin (VLM) has been most recently reported to be a potential anti-coronavirus drug that could be efficiently produced on a large scale. It is thus of importance to study solid-phase forms of VLM in order to be able to ensure its polymorphic purity in drug formulations. The previously available solid-state NMR (SSNMR) data are combined with the plane-wave DFT computations in the NMR crystallography framework. Structural/spectroscopical predictions (the PBE functional/GIPAW method) are obtained to characterize four polymorphs of VLM. Interactions which confer a conformational stability to VLM molecules in these crystalline forms are described in detail. The way how various structural factors affect the values of SSNMR parameters is thoroughly analyzed, and several SSNMR markers of the respective VLM polymorphs are identified. The markers are connected to hydrogen bonding effects upon the corresponding (13C/15N/1H) isotropic chemical shifts of (CO, Namid, Hamid, Hα) VLM backbone nuclei. These results are expected to be crucial for polymorph control of VLM and in probing its interactions in dosage forms.

A 13C solid-state NMR investigation of four cocrystals of caffeine and theophylline

2017 ◽  
Vol 73 (3) ◽  
pp. 234-243 ◽  
Author(s):  
Nicolas J. Vigilante ◽  
Manish A. Mehta
Keyword(s):  
Solid State ◽  
Chemical Shift ◽  
Solid State Nmr ◽  
Chemical Shifts ◽  
Active Pharmaceutical Ingredient ◽  
Magic Angle Spinning ◽  
Chemical Shift Tensor ◽  
Magic Angle ◽  
Isotropic Chemical Shifts ◽  
Angle Spinning

We report an analysis of the 13C solid-state NMR chemical shift data in a series of four cocrystals involving two active pharmaceutical ingredient (API) mimics (caffeine and theophylline) and two diacid coformers (malonic acid and glutaric acid). Within this controlled set, we make comparisons of the isotropic chemical shifts and the principal values of the chemical shift tensor. The dispersion at 14.1 T (600 MHz 1H) shows crystallographic splittings in some of the resonances in the magic angle spinning spectra. By comparing the isotropic chemical shifts of individual C atoms across the four cocrystals, we are able to identify pronounced effects on the local electronic structure at some sites. We perform a similar analysis of the principal values of the chemical shift tensors for the anisotropic C atoms (most of the ring C atoms for the API mimics and the carbonyl C atoms of the diacid coformers) and link them to differences in the known crystal structures. We discuss the future prospects for extending this type of study to incorporate the full chemical shift tensor, including its orientation in the crystal frame of reference.

Assigning solid-state NMR spectra of aligned proteins using isotropic chemical shifts

2006 ◽  
Vol 183 (2) ◽  
pp. 329-332 ◽  
Author(s):  
Anna A. De Angelis ◽  
Stanley C. Howell ◽  
Stanley J. Opella
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Isotropic Chemical Shifts

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
Keyword(s):  
Molecular Dynamics ◽  
Solid State ◽  
Force Field ◽  
Solid State Nmr ◽  
Density Functional ◽  
Chemical Shifts ◽  
Density Functional Theory Calculations ◽  
Free Base ◽  
Nmr Crystallography

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.

scholarly journals Characterizing the Turbostratic Disorder in COF-5 with NMR Crystallography

2020 ◽  
Author(s):  
Giovanna Pope ◽  
Demetrius Vazquez ◽  
Fernando Uribe-Romo ◽  
James K. Harper
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chemical Shifts ◽  
X Ray Diffraction ◽  
Space Groups ◽  
Turbostratic Disorder ◽  
Characteristic Features ◽  
Nmr Crystallography ◽  
Pure Phases ◽  
Three Space

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.

Obtaining accurate chemical shifts for all magnetic nuclei (1H, 13C, 17O, and 27Al) in tris(2,4-pentanedionato-O,O′)aluminium(III) — A solid-state NMR case study

2011 ◽  
Vol 89 (9) ◽  
pp. 1087-1094 ◽  
Author(s):  
Alan Wong ◽  
Mark E. Smith ◽  
Victor Terskikh ◽  
Gang Wu
Keyword(s):  
Solid State ◽  
High Resolution ◽  
Solid State Nmr ◽  
Nmr Spectra ◽  
Chemical Shifts ◽  
Dft Method ◽  
Magic Angle Spinning ◽  
Magic Angle ◽  
Multiple Quantum ◽  
Isotropic Chemical Shifts

We report a complete set of high-resolution solid-state NMR spectra for all magnetic nuclei (1H, 13C, 17O, and 27Al) in the α-form of tris(2,4-pentanedionato-O,O′)aluminium(III), α-Al(acac)3. These high-resolution NMR spectra were obtained by using a host of solid-state NMR techniques: standard cross-polarization under the magic-angle spinning (CPMAS) method for 13C, 1-D homonuclear decoupling using the windowed DUMBO sequence for 1H, double-rotation (DOR) for 17O and 27Al, and multiple-quantum MAS for 27Al. Some experiments were performed at multiple magnetic fields. We show that the isotropic chemical shifts obtained for 1H, 13C, 17O, and 27Al nuclei in α-Al(acac)3 are highly resolved and accurate, regardless of the nature of the targeted nuclear spins (i.e., spin-1/2 or quadrupolar) and, as such, can be treated equally in comparison with computational chemical shifts obtained from a gauge-including projector-augmented wave (GIPAW) plane-wave pseudopotential DFT method.

scholarly journals Characterizing the Turbostratic Disorder in COF-5 with NMR Crystallography

2020 ◽  
Author(s):  
Giovanna Pope ◽  
Demetrius Vazquez ◽  
Fernando Uribe-Romo ◽  
James K. Harper
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Chemical Shifts ◽  
X Ray Diffraction ◽  
Space Groups ◽  
Turbostratic Disorder ◽  
Characteristic Features ◽  
Nmr Crystallography ◽  
Pure Phases ◽  
Three Space

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.

Strong Intermolecular Ring Current Influence on 1H Chemical Shifts in Two Crystalline Forms of Naproxen: a Combined Solid-State NMR and DFT Study

2013 ◽  
Vol 117 (34) ◽  
pp. 17731-17740 ◽  
Author(s):  
Elisa Carignani ◽  
Silvia Borsacchi ◽  
Jonathan P. Bradley ◽  
Steven P. Brown ◽  
Marco Geppi
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Ring Current ◽  
Chemical Shifts ◽  
Dft Study ◽  
Crystalline Forms
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