Magic-angle spinning experiment

We used modifications of the standard solid-state CP-MAS (cross-polarisation, magic-angle spinning) experiment to allow the proton relaxation characteristics to be measured for each peak in the C spectrum. It is known that highly mobile, hydrated polymers can not be seen using either usual CP-MAS C spectrum or solution NMR (6). We found, however, that by a combination of a long-contact experiment and a delayed-contact experiment we could reconstruct a C spectrum of the cell-wall components that are normally too mobile to be visible. With these techniques we were able to determine the mobility of pectins and their approximate spatial location in comparison to cellulose. 

The line broadening caused by partial motional narrowing can be distinguished from that due to isotropic reorientation at a reduced rate by appropriate magic angle spinning experiments. 

By combining all of the above techniques into the so-called cross-polarization magic-angle spinning experiment (CP/MAS), relatively high-resolu-tion solid-state NMR spectra can be obtained. It should be pointed out, however, that the best solid-state spectra are still of substantially lower resolution than routine liquid-state spectra, and therefore additional information not present in the solid-state spectra can be obtained from liquid spectra. 

B Wehrle, F Aguilar-Parrilla, H-H Limbach. A novel 15N chemical-shift NMR thermometer for magic angle spinning experiments. J Magn Reson 87 584-591, 1990. 

R. D. Kendrick, R. A. Wind, and C. S. Yannoni, "A simple method for measuring the spinning frequency in magic angle spinning experiments," J. Magn. Resonance 40, 585 (1980). 

The chemical shift anisotropies for the carbonyl and aromatic carbons of Hytrel were reconstructed from a Herzfeld-Beiger analysis (24) of the intensities of the sidebands from NMR magic angle spinning experiments. The results in Table III indicate that the carbonyl carbon chemical shift anisotropy is axially symmetric for each terephthalate ester. We attribute this axial symmetry to a general property of terephthalate esters, rather than as a consequence of molecular motion, as the highly crystalline dimethyl terephthalate also has an axially symmetric carbonyl carbon chemical shift tensor. 

Solution NMR techniques have been extensively used in the literature for the determination of precise structures of bioactive polysaccharides [90,129,131]. However, it should be noted that the technique is applicable only if the polysaccharides are soluble in a suitable solvent. Nonsoluble polysaccharides can be analyzed using solid state NMR techniques [134]. Normally, magic-angle spinning experiments with cross-polarizaticHi from proton to nuclei are employed in high-resolution solid-state NMR to enable the structural analysis of insoluble polysaccharides. 

S. Wimperis, Quadrupolar NMR of Inorganic Materials The Multiple-Quantum Magic Angle Spinning Experiment , in Modem Magnetic Resonance, Part 3, ed. G. A. Webb, Springer, Dordrecht, Netherlands, 2006, p. 1487. 

The multiple-quantum magic-angle spinning experiment... 

---