Separated-local-field spectroscopy

Fig. 1. A two-dimensional pulse sequence for separated-local-field spectroscopy. The pulse sequence correlates the chemical shift of a low-sensitive nuclei S (e.g., or with the dipolar coupling between S and the abundant nuclei I (e.g., or F). During the delays before (r—q) and after (t) the 7t-pulse, / spins are decoupled from S spins by continuous rf irradiation on S spins. The details of this pulse sequence are discussed in the text.

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... 

Figure 53 Separated local field spectroscopy correlating heteronuclear dipoledipolecoupling with chemical shifts (a) 2D spectrum of highly oriented pol)

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. 

S. V. Dvinsldldi, H. Zimmermann, A. Matmiak, and D. Sandstrom, Separated local field spectroscopy of columnar and nematic liquid crystals, J. Magn. Reson. 163 46-55 (2003). 

A. A. Nevzorov and S. J. Opella, A "Magic Sandwich" pulse sequence with reduced offset dependence for high-resolution separated local field spectroscopy, J. Magn. Reson. 164 182-186 (2003). 

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

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). 

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