Multiple pulse line-narrowing

Shown herein are the first 2D multiple-pulse NMR images following a chemical reaction for which the image contrast is Ti rather than T2. A multiple pulse line narrowing sequence is critical to efficient image acquisition where broad lines are expected. The gas-solid reaction between ammonia and a crystal of 4-bromobenzoic acid was monitored optically and by NMR imaging. Some anisotropy in the reaction... 

Butler, L. G., Cory, D. G., Dooley, K. M., Miller, J. B. and Garroway, A. N. (1992). NMR imaging of anisotropic solid-state chemical-reactions using multiple-pulse line-narrowing techniques and H-1 T1-weighting. J. Am. Chem. Soc., 114, 125-35. [238]... 

Bernd Tesche (1994) has verified in the meantime that approximately the same values are valid for H4. These values agree remarkably well with those from the (old) multiple-pulse line-narrowing experiment and one might be tempted to conclude that this is it. It would be an illusion to expect still better agreement because the calculation was done for an isolated molecule, whereas the measurement includes intermolecular shielding contributions. These contributions can be estimated (but not more than that) on the basis of a point dipole model (Post, 1978 Avara-mudhan and Haeberlen, 1979). For malonic acid we expect that these contributions do not exceed 0.5 ppm for the various elements of the a tensor. 

Phase considerations intrude even in the simplest experiments of observing an FID or an echo. Accurately adjusting the phases of rf pulses can be very important, particularly in experiments involving trains of pulses such as the Carr-Purcell Meiboom-Gill train or the multiple pulse line narrowing sequences. In other sections we have considered how phase shifts originate and how to cope with them. 

The Si NMR [19] cross-polarization magic-angle spinning (CP MAS) and H NMR magic-angle spinning with multiple-pulsed line narrowing (CRAMPS for combined rotation and multiple-pulse spectroscopy) techniques of Maciel et al. [20,21] indicate that FS-662... 

Measurements have included relaxation times, and absorption spectra and (in cases where lines are already narrowed by translation of protonic species) application of combined magic-angle-rotation and multiple-pulse line-narrowing CRAMPS NMR). For the fastest self-diffusions (D > 10 cm s ) direct measurement of D is possible using the pulsed field gradient (PFG) technique (see Chapters 26 28). 

FIGURE 1.10 CRAMPS NMR spectra, obtained by combined MAS and multiple-pulse line narrowing, of silica gel at various degrees of water content. (Adapted with permission from Chem. Rev., 99, Brown Jr., G.E., Henrich, V.E., Casey, W.H. et al.. Metal oxide surfaces and their interactions with aqueous solutions and microbial organisms, 77-174, 1999. Copyright 1999, American Chemical Society.)... 

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