Cross-polarization magic-angle-spinning CP-MAS

Table 1. Structural carbon distribution (%) of the humic acids extracted from soil horizons, adopted from Xing (2001). The distribution was calculated from solid state 13C Cross-Polarization Magic-Angle-Spinning (CP/MAS) NMR spectra. Chemical shift assignment for carbon functional groups alkyl 0-50 ppm O-alkyl 50-117 ppm aromatic 107-165 ppm.

The 13C NMR study utilized cross polarization-magic angle spinning (CP-MAS) with spin counting. The elemental and functional group analyses provided input for a series of analytical constraints calculations that yield an absolute upper limit for the amount of aromatic carbon and most probable estimates of both aromatic and non-carboxyl aliphatic carbon in each sample. Spin counting experiments demonstrate that less than 50% of the... 

Fig. 13.9 Carbon-13 solid-state NMR spectra of poly(ethylene) (a) cross-polarization magic angle spinning (CP/MAS), (b) progressive saturation, and (c) Torchia T, experiment.

The X-ray and solution structures of lithium fluorenide (68) have been reported earlier125,126. It was found that whereas the X-ray study suggested that the lithium is asymmetrically positioned above the fluorenyl unit, calculations and solution 13C NMR showed a symmetrical structure. Thus, Johnels and Edlund used 13C cross-polarization/magic angle spinning (CP/MAS) NMR in order to get further insight about the structure 68. 

The solid-phase 13C cross-polarization/magic angle spinning (CP/MAS) NMR, as a tool for conformation prediction, revealed that the solid-phase conformation of the nine-membered ring crown cavity in naphtho-9-crown-3 is different from benzo-9-crown-3. The two key C-0-CH2 units are predicted to be out of naphthalene plane, and the two C-C-O-CH2 torsion angle values are close to each other <2000JST(526)185>. 

Several physical methods have been employed to ascertain the existence and nature of ICs infrared (IR) absorption spectroscopy nuclear magnetic resonance (NMR) spectroscopy,14 including JH nuclear Overhauser effect (NOE) difference spectroscopy, H 2-D rotating-frame Overhauser effect spectroscopy (2-D ROESY),15 and solid-state 13C cross-polarization/magic angle spinning (CP/MAS) spectroscopy 16 induced circular dichroism (ICD) absorption spectroscopy 17 powder and singlecrystal X-ray diffraction 18 and fast atom bombardment mass spectrometry (FAB MS). 

A 13C nuclear magnetic resonance (NMR) study in solution and in the solid state has been reported for three thermochromic spirooxazines, 29-31.32 From a quantitative analysis of I3C cross-polarization/magic-angle-spinning (CP-MAS) NMR spectra shielding anisotropies were estimated and a correlation of these characteristics with thermochromic activity was suggested. 

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