Separated Local Field NMR

Organic Solids. - Separated local-field NMR spectroscopy under MAS... 

Lobo and Ramanathan have combined adiabatic and Hartmann-Hahn cross-polarization for sensitivity enhancement in solid-state separated local field 2D NMR experiments of partially ordered systems The magnetization in double- and zero-quantum reservoirs of an ensemble of spin-1/2 nuclei has been examined and their role in determining the sensitivity of a class of separated local field NMR experiments based on Hartmann-Hahn cross-polarization has been described. Lobo and Ramanathan report that for the liquid crystal system studied, a large dilute spin-polarization, obtained initially by the use of adiabatic cross-polarization, can enhance the sensitivity of the above experiment. The signal enhancement factors, however, are found to vary and depend on the local dynamics. The experimental results have been utilized to obtain the local order-parameters of the system. 

Two-dimensional separated-local-field NMR experiments have been applied to magnetically aligned bicelles to measure dipolar cou-... 

J. Grinshtein, C. V. Grant, L. Frydman, Separate-local-field NMR spectroscopy on half-integer quadrupolar nuclei, J. Am. Chem. Soc., 124, 13344-13345 (2002). 

SEPARATED LOCAL FIELD NMR SPECTROSCOPY IN COLUMNAR LIQUID CRYSTALS... 

S. V. Dvinskikh, K. Yamamoto, and A. Ramamoorthy, Separated local field NMR spectroscopy by windowless isotropic mixing, Chem. Phys. Lett. 419 168-173 (2006). 

Dynamic parameters for heterogeneous systems have been explored in the liquid, liquid like, solid like, and solid states, based on analyses of the longitudinal or transverse relaxation times, chemical exchange based on line-shape analysis and separated local field (SLF), time domain 1H NMR, etc., as summarized in Figure 3. It is therefore possible to utilize these most appropriate dynamic parameters, to explore the dynamic features of our concern, depending upon the systems we study. 

ID, 2D and 3D experiments, all H, and Sn chemical shifts for four postulated Sn species could be resolved unambiguously. Variable temperature and variable stress NMR spectroscopic and imaging studies are reported for a sample of high impact polystyrene. NMR microscopy and solid state stray field imaging studies indicated that imposed stress affects the molecular chain dynamics only of the polybutadiene region and not of the polystyrene(PS) matrix.The principal values of the chemical shift tensors and the separated-local field pattern are reported for the all-... 

Several new assignment techniques for C solid-state NMR spectra have recently been proposed Spectral Editing by Multiple-Quantum Traps (SEMUT) [15], separated local field MAS [17-19], Windowless /sotropic Mixing for Spectral Editing (WIMSE) [20], Off-/ esonance Proton /rradiation (ORPI) [21,22], and cross-polarization with fast MAS ]23]. Their detailed performance has yet to be assessed, but it is already clear that the latter two methods are simple and eminently worthwhile. 

An interesting three-dimensional separated-local-field/dilute-spin-exchange solid state NMR experiment has been reported where homonuclear spin-exchange cross-peaks provide correlation in the un u>z plane. Resonances are resolved along the u> axis by their heteronuclear dipolar couplings. The experiment was demonstrated experimentally with the heteronuclear and N- N homonuclear dipole-dipole interactions in... 

A novel MAS NMR approach has been presented for the determination of motionally averaged heteronuclear dipolar couplings in unoriented materials. The technique is based on the proton-detected local field protocol and achieves dipolar recoupling by R-type RF irradiation. The experiment, which is called R-PDLF spectroscopy, is demonstrated on solid and liquid-crystalline systems. For mobile systems, it is shown that the R-PDLF scheme provides better dipolar resolution as compared to techniques combining conventional separated local field spectroscopy with R-type recoupling. 

One way to determine heteronuclear dipolar couplings with MAS is to perform separated local field spectroscopy (SEE) experiments, a 2D NMR protocol which resolves for... 

Other apphcations of covariance NMR include natural abundance deuterium NMR spectroscopy in chiral polypeptide liquid crystals [78] and three-dimensional experiments of combined homonuclear spin-exchange and separated-local-field spectroscopies [79]. These works also presented new sampling schemes and will be introduced in the next section. 

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