Cross-polarization magic-angle spinning CPMAS

As a consequence of restricted internal mobility in molecules in the crystalline state, nuclei in different conformation environments, but identical in other respects, can produce different signals in 13C cross polarization, magic angle spinning (CPMAS) solid-state NMR. This analysis is not necessarily limited to crystalline regions, since signals of different conformations are resolved if the exchange is slow with respect to the time scale of the NMR experiment. 

Sometimes decomposition reactions can be avoided by carrying out diazotizations in concentrated sulfuric acid. By this method Law et al. (1991) obtained the 1,5-bisdiazonium salt (incorrectly called tetrazonium salt) of l,5-diamino-4,8-dihy-droxy-anthraquinone, which is deprotonated to 2.28. The structure was verified by cross-polarization magic angle spinning (CPMAS) 13C NMR spectroscopy. 

NMR experiment is generally termed the cross-polarization magic-angle spinning, CPMAS, experiment. 

During the last 15 years, the cross-polarization magic-angle spinning (CPMAS) technique (2) has been used with increasing frequency to provide detailed structural information about solid polymers and biopolymers... 

Another, perhaps clearer indication for isostructural character is given by solid-state,, 3C cross-polarization magic angle-spinning (CPMAS) NMR. A comparison of the high-field spectra revealed strong similarities for the decaphenylgermanium and tin compounds (the amorphous lead complex produced broader lines) (120). 

Solid-state experiments use a dry sample that is packed into a rotor and spun at high frequency inside the spectrometer s magnetic field. This approach is termed cross-polarization magic angle spinning (CPMAS), and is the standard protocol for solids. It relies on transfer of magnetization from protons to C (or other nuclei) in order to achieve rapid analyses with reasonably narrow spectral lines. Cody et al. 

Cross-Polarization/Magic-Angle Spinning (CPMAS) Techniques. 212... 

FIGURE 12. 29Si cross polarization/magic angle spinning (CPMAS) spectra of (a) poly(methyl-w-hexylsilane) and (b) poly(di-n-hexylsilane)124... 

We emphasize here that NMR spectroscopy is very useful for determining the conformation of polymer chains in the gel state, although very little work has been done along with this line (5-9,21, ). In particular, chemical shifts of C-1 and C-3 carbons were found to be very sensitive to predict the portion of single helix conformation, with reference to those obtained in the solid state by cross-polarization magic-angle spinning (CPMAS)... 

C-1-0 and C-3-0 linkages is allowed (6). We attempted here to compare the chemical shifts of the gel with those of solid state curdlan, the conformation of which is mainly single helix at ambient temperature and triple-helix at higher temperature above 120°, as studied by X-ray diffraction (14>I5)- The newly emerging technique, cross-polarization magic angle spinning (CPMAS) ... 

Si NMR spectroscopy of 12 in solution demonstrated that the six skeletal silicons are equivalent, with a single resonance appearing at —22.3 ppm. However, cross polarization magic-angle spinning (CPMAS) Si NMR in the solid state shows two signals at —22.2 and —30.8 ppm with relative intensity of 2 1. Similarly, CPMAS Si NMR of 18a... 

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