13C-cross-polarization magic angle spinning

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. 

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.

Asakura, T., Kuzuhara, A., Tabeta, R., and Saito, H. (1985). Conformation characteriz-tion of Bombyx mod silk fibroin in the solid state by high-frequency 13C cross polarization-magic angle spinning NMR, x-ray diffraction, and infrared spectroscopy. Macromolecules 18, 1841-1845. 

Asakura, T., Ohgo, K., Ishida, T., Taddei, P., Monti, P., and Kishore, R. (2005). Possible implications of serine and tyrosine residues and intermolecular interactions on the appearance of silk I structure of Bombyx mod silk fibroin-derived synthetic peptides High-resolution 13C cross-polarization/magic-angle spinning NMR study. Biomacromolecules 6, 468-474. 

Pfeffer, P. E., Hicks, K. B. and Earl, W. L. 1983. Solid state structures of keto-disacchar-ides as probed by 13C cross-polarization, magic angle spinning NMR spectroscopy. Carbohydr. Res. 11, 181-194. 

Correlating positively with the hydrophobicity of the solvent, different fractions of inactivated active centers were measured in different solvents with solid-state NMR spectroscopy (13C-cross-polarization/magic angle spinning (MAS) NMR) (Burke, 1992). Just as with tritiated water (see above), immediate desorption of water molecules from the protein surface was observed after addition to the organic solvent. 

Figure 9.3 Conventional 13C cross-polarization magic angle spinning (CP/MAS) solid-state NMR spectra of mangrove leaves at different stages of decomposition in estuarine waters. Differences in carbon functionality are defined by the following key characteristic resonances carbohydrates (50-90 ppm) carboxyl (175 ppm) aromatic (90-170 ppm). (Modified from Benner et al., 1990.)...

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). 

C-cross polarization magic angle spinning (CP-MAS) spectra were obtained on a Bruker CXP-100 instrument. A rotor consisting of a barrel of boron nitride and a base of Kel-F was used. Rotor speed was 3.8 kHz. Recycle time was varied from 0.3 to 1 s. A variety of contact times from 0.5 to 3ms were employed. The Hartmann-Hahn condition was set using a sample of hexamethylbenzene. Chemical shifts were measured with respect to external hexamethylbenzene (by storing the hexamethylbenzene spectrum in another computer memory block) but are quoted with respect to TMS. It is assumed that the chemical shifts of hexamethylbenzene with respect to TMS are the same in solution as in the solid state. 

Kallury K, MacDonald P, Thompson M (1994) Effect of surface water and base catalysis on the silaniation of silica by (aminopropyl)alkoxysilanes studied by x-ray photoelectron spectroscopy and 13C cross-polarization/magic angle spinning nuclear magnetic resonance. Langmuir 10(2) 492 99... 

Szeverenyi NM, Sullivan MJ, Maciel GE (1982) Observation of spin exchange by two-dimensional fourier transform 13C cross polarization-magic-angle spinning. J Magn Reson 47 462-475... 

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. 

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... 

High-resolution 13C NMR studies have been conducted on intact cuticles from limes, suberized cell walls from potatoes, and insoluble residues that remain after chemical depolymerization treatments of these materials. Identification and quantitation of the major functional moieties in cutin and suberin have been accomplished with cross-polarization magic-angle spinning as well as direct polarization methods. Evidence for polyester crosslinks and details of the interactions among polyester, wax, and cell-wall components have come from a variety of spin-relaxation measurements. Structural models for these protective plant biopolymers have been evaluated in light of the NMR results. 

The cross-polarization, magic-angle spinning method (CP MAS) has been applied by Myhre and Yannoni50 to cation 19 in the solid state at very low temperatures using 13C NMR spectroscopy. In the initial study, no convincing evidence for a frozen 2-butyl cation was obtained even at — 190°C. However, subsequently they managed to freeze out the equilibration of the 2-butyl cation (19) at —223°C.62 It behaves like a normal secondary trivalent carbocation. 

Both of these methods have been used for DOM isolation from major rivers and the surface ocean, and the general characteristics of these fractions of DOM are presented in Table I. The major C functional groups of humic substances and ultrafiltered DOM (UDOM) have been characterized by solid-state, cross-polarization magic angle spinning 13C nuclear magnetic resonance (NMR) spectroscopy. The samples of humic substances that were characterized by NMR spectroscopy were collected from the Amazon River... 

Knicker, H. (2000). Double cross polarization magic angle spinning 15N 13C NMR spectroscopic studies for characterization of immobilized nitrogen in soils. Proceedings, 10th IHSS International Conference (Toulouse), France, pp. 1105-1108. 

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