Combined rotation and multipulse

Lesage et al. have shown that the resolution of the proton NMR spectroscopy of powdered solids can be improved significantly when multi-pulse sequences are employed [44a]. In the approach based on combined rotation and multipulse spectroscopy (CRAMPS) (Figure 7.9) the problem of dipolar line broadening is usually overcome. 

Recently, the relation between the amide proton shift and the conformation of synthetic polypeptides has been studied in the solid state using H combined rotation and multipulse spectroscopy (CRAMPS). It has been determined that the amide chemical shifts of a synthetic polypeptide are 8.0-8.1 ppm for the a helix and 8.6-9.1 ppm for the P sheet. It was shown that high-resolution solid-state H NMR such as CRAMPS is also a useful tool for studying the molecular structure of polypeptides in addition to high-resolution solid-state C NMR. 

Tip filters for the longitudinal relaxation time in the rotating frame by applying spin-lock fields or multisolid echoes combinations of relaxation-time filters and multipulse excitation chemical-shift selective excitation ... 

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