Magic-angle spinning 13C NMR

It was reasoned that the polymer must consist of a, a -coupled pyrrole units, with fi coupling less important, because of the fact that oc-substituted pyrroles do not polymerise whereas -substituted species do, and on the basis of magic angle spinning 13C nmr and IR techniques. The method of labelling the monomer ring positions is also shown in Scheme 3.9. 

Griffin, J.L. and Corcoran, O., High-resolution magic-angle spinning 13C NMR spectroscopy of cerebral tissue, Magn. Reson. Mater. Phys. Biol. Med., 18,1352, 2005. 

Cook, R.L., Langford, C.H., Yamdagni, R. and Preston, C.M. (1996) A modified crosspolarization magic angle spinning 13C NMR procedure for the study of humic materials. Anal. Chem., 68, 3979-3986. 

Knicker, H. (2000) Solid-state 2D double cross polarization magic angle spinning 13C NMR spectroscopy on degraded algal residues. Org. Geochem. 31, 337-340. 

Table 2. Relative Intensities of the Crystalline Signal in the Magic-Angle Spinning 13C NMR Spectra of Alkane n-Ci6 H33 (ref 95)...

DA Middleton, CS Duff, F Berst, DG Reid. Cross-polarization magic-angle spinning 13C NMR characterization of the stable solid state forms of cimetidine. J Pharm Sci 86 1400-1402, 1997. 

Shefer, A., Shefer, S., Kost, J. and Langer, R. (1992) Structural characterization of starch networks in tlic solid state by cro.s.s-polarization magic-angle spinning 13C NMR spectroscopy and wide angle X-rav diffraction. Macromolecules, 25, 6756-6760. 

Four narrow lines are observed in the high-resolution cross-polarization magic-angle spinning 13C NMR spectra of intact, lyophilized samples of Pseudomonas sp. LBr, in addition to the broader lines normally associated with bacterial cellular material. These narrow lines arise from poly-3-hydroxybutyrate. The cellular carbon contained in this storage material can be measured quantitatively and nondestructively from the... 

Although limited by sensitivity, chemical reaction monitoring via less sensitive nuclei (such as 13C) has also been reported. In 1987 Albert et al. monitored the electrochemical reaction of 2,4,6-tri-t-butylphenol by continuous flow 13C NMR [4]. More recently, Hunger and Horvath studied the conversion of vapor propan-2-ol (13C labeled) on zeolites using 1H and 13C in situ magic angle spinning (MAS) NMR spectroscopy under continuous-flow conditions [15]. 

Structure identification, quantifying relative cage occupancies. 1II NMR has been used for ethane, propane, and isobutane hydrates (Davidson et al., 1977 Garg et al., 1977), while 2H, 19F, 31P, and 77 Se NMR have been used for several si guests (Collins et al., 1990). 13C cross-polarization and magic angle spinning (MAS) NMR techniques have been applied to study hydrates of carbon dioxide, methane, and propane (Ripmeester and Ratcliffe, 1988, 1999 Wilson et al., 2002 Kini et al., 2004). 

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. 

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... 

Barron, P. F., and Wilson, M. A. (1981). Humic soil and coal structure study with magic-angle spinning 13C CP NMR. Nature 289, 275-276. 

Finally, 13C-NMR with cross-polarization and magic angle spinning (13C-CP/MAS) has been used to examine changes in the mesomorphic states of phospholipids at various temperatures in the absence and presence of the two drugs. Three effects were followed ... 

Magic angle spinning (MAS) NMR brings the power of H NMR to solid-phase chemistry [2,25], A simple MAS spectrum, that of the reaction product of succinic anhydride and TentaGel S NH2, is shown in Fig. 2. Presaturation of the PEG resonance at 3.6 ppm is critical to spectral quality. The complex peaks from 3.4 to 3.9 ppm are due to residual PEG, 13C satellites and the terminal CH2 of the PEG chain. The characteristic doubling of the solution-phase CDC1, and TMS resonances can be seen. 

In summary, for this area to move forward, methods need to be introduced to provide information additional to 2H lineshapes when studying more complex systems. Calculations such as those just described are one real possibility experimental possibilities include use of magic-angle spinning 2H NMR, and using the full anisotropy of 2H 7j measurements and 13C NMR. A very nice illustration of the use of several different techniques in a motional study examined the slow alkane motions in a urea/alkane inclusion compound via 2H relaxation measurements, selective inversion experiments and two-dimensional 2H exchange.125... 

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. 

Figure 1 Schematic representation of the 13C (or 15N) spin-lattice relaxation times (7"i), spin-spin relaxation (T2), and H spin-lattice relaxation time in the rotating frame (Tlp) for the liquid-like and solid-like domains, as a function of the correlation times of local motions. 13C (or 15N) NMR signals from the solid-like domains undergoing incoherent fluctuation motions with the correlation times of 10 4-10 5 s (indicated by the grey colour) could be lost due to failure of attempted peak-narrowing due to interference of frequency with proton decoupling or magic angle spinning.

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