GIPAW

T. Charpentier, The PAW/GIPAW approach for computing NMR parameters a new dimension added to NMR study of solids. Solid State Nucl. Magn. Reson., 2011,40,1-20. 

Eor each predicted structure, chemical shifts were generated with the GIPAW approach described in detail elsewhere [39]. For the set of CM-isomers this included 14 structures, and for the trani -isomers this involved 20 structures. For each structure, measured and calculated shifts were then compared and the corresponding RMSD was obtained. 

D N- H HMQC experiments recorded at a 60kHz MAS rate were recently performed, in drugs (acetaminophen), polymer (PVP), and polymer-drug dispersions, to assess proximities between nitrogen and proton nuclei involved in H-bonds [44], This 2D N- H HETCOR NMR experiment considerably shortens the acquisition time required compared to a N-H HETCOR spectrum (6h vs 48h) [45]. The GIPAW-DFT approach was employed to calculate N ICSs and N EFG parameters (C and... 

The vast majority of applications of GIPAW so far have focused on the ICS and the quadrupolar coupling (for nuclei with spin quantum number I> 1/2), and there have been far fewer studies that have exploited interactions such as the CSA. This is mainly a result related to the difficulty in accurately measuring such interactions for all but the simplest systems, although developments in experimental methodologies will enable the determination of parameters across a wider range of increasingly complex systems. 

Uldry etal. on uracil and 4-cyano-4 -ethynylbiphenyl, andMafraetal. on ciprofloxacin polymorphs, GIPAW CST and NICS calculations on the piece-wise deconstructed crystalline lattice are used to deconvolute these effects [20, 59]. 

The GIPAW calculated H CS differences between the complete crystal... 

FIGURE 12.14 (Left) A5(ppm) plot showing crystal packing contributions (blue stems) and hydration contributions (red stems) to the GIPAW calculated H ICS of ciprofloxacin Form I and Form II. In II, each of the three stems per proton corresponds to a crystallographic unique molecule (Z = 3). Right Detailed view of intermolecular interactions in the ciprofloxacin Forms I and II structures. Reprinted with permission from Ref. [20]. Copyright 2012, American Chemical Society. 

Keywords 2D NMR, Very fast MAS, invHfTCOR, Recoupling sequences. Molecular motion, Dynamics, Polymorphism, Solvatomorphism, NMR shielding parameters. Theoretical calculations, GIPAW, GIAO, ONIOM... 

Figure 2.29 CP MAS NMR spectra of (A) Leu-enkephalin H20 and (B) Leu-enkephalin-2H20-2DMF, recorded at a spinning rate of 12 kHz. The resonances are assigned employing GIPAW method. Reprinted from Ref. [96]. Copyright 2014 American Chemical Society.

On the other hand, very recently Asakura et al. reported application of high-resolution H SS NMR performed under F-MAS and GIPAW chemical shift calculations for assignment of resonances and structure of alanine tripeptides [168]. The information on the exact H positions is important for fine refinement of peptides because their higher order structure is determined mainly by the intramolecular and intermolecular hydrogen bonds. The homonuclear DQMAS experiment allowed to precisely assign proton signals in the H spectra of (Ala)3 (Fig. 2.34). 

Recent years have witnessed the incredible progress in advance of calculation of NMR parameters in the soHd matter. State-of-the-art in this field was recendy exhaustively discussed in review article published hy Bonhomme et al. [170]. In the cited paper, which mostly focuses on latest applications of GIPAW method approach, there is also short section dedicated to study of amino acids and peptides. Thus, in our report we wiU draw attention to those works which were pubhshed last years or employed other techniques than GIPAW. 

First-principles calculations of NMR parameters for solid peptides have a long-standing history. Number of spectacular results was pubhshed during last 20 years. Review articles of Sitkoff et al. and Ando and coworkers summarize the apphcabihty and power of GIAO approach for study of different peptides at that time [183,184]. Today, the modem methodologies are rather oriented on appHcations of GIPAW method. As shown by Zeng... 

Potrzebowski and coworkers have published number of papers showing applications of GIPAW for structural assignment oftri-, tetra- andpentapep-tides [94-96]. It was confirmed that the best results are obtained for fuUy optimized structures. The most spectacular achievement was refinement of enkephalins which as discussed in Section 4 in the crystal lattice form very complex, multi-component systems. 

In papers discussed supra, GIPAW method implemented in CASTEP was exploited for computing of NMR parameters. CASTEP is commercial... 

The X-ray molecular disorder is immediately recognized by GIPAW method when experimental and theoretical shielding NMR parameters are compared. The scatter of points shown in Fig. 2.42B and C, both for tensor parameters and isotropic values exclude the drawing of acceptable linear correlation. These correlations have been greatly improved when periodic model with fuU optimization of position of heavy atoms and protons was used for calculation of GIPAW parameters. 

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