Solid-state nuclear magnetic pulse sequences

All the powerful methods of magnetic resonance, from solid-state nuclear magnetic resonance (NMR) to medical magnetic resonance imaging, depend on measuring the time evolution of a spin system following the application of one or more radio frequency pulses. In the visible and ultraviolet, ultrafast optical pulse sequences have been used for many years to measure both population dynamics and coherence phenomena. At low... 

T. Karlsson, J. M. Popham, J. R. Long, N. Oyler and G. P. Drobny, A study of homonuclear dipolar recoupling pulse sequences in solid-state nuclear magnetic resonance. J. Am. Chem. Soc., 2003, 125, 7394-7407. 

Solid-state C variable-amplitude cross polarization magic-angle spinning (VACP/MAS) nuclear magnetic resonance (NMR) spectra were acquired for the sorbitol samples. Proton decoupling was achieved by a two-pulse phase modulation (TPPM) sequence. Identical C spectra were measured for the y-form sorbitol samples, and a representative spectrum is shown in Figure 9. 

These advances, mainly in hardware, along with developments of pulse sequences, have tremendous potential in virtually every aspect of solid-state NMR and nuclear magnetic resonance imaging. Each will be covered in the following sections. 

The major breakthroughs, however, have come from the use of high magnetic fields and further from the use of different multiple pulse sequences to manipulate the nuclear spins in order to generate more and more information time domain NMR spectroscopy, that is used to probe molecular dynamics in solutions. The latter made it also possible to "edit" sub-spectra and to develop different two-dimensional (2D) techniques, where correlation between different NMR parameters can be made in the experiment (e.g. SH versus 813c, see later). Solid state NMR spectroscopy is used to determine the molecular structure of solids. 

M. H. Levitt, Symmetry-based pulse sequences in magic-angle spinning solid-state NMR. in Encyclopedia of Nuclear Magnetic Resonance, D. M. Grant and R. K. Harris (eds.), Supplementary Volume, Wiley, Chichester, 2002, pp. 165-196. 

The ultimate molecular level characterization of a pharmaceutical material is performed on the level of individual chemical environments of each atom in the compound, and this information is best obtained using nuclear magnetic resonance (NMR) spectroscopy. Advances in instrumentation and computer pulse sequences currently allow these studies to be carried out routinely in the solid state.2 Although any nucleus that can be studied in the solution phase also can be studied in the solid state, most work has focused on studies. H-NMR remains an extremely difficult measurement in the solid state, and the data obtained from such work can be obtained only at medium resolution. The main problem is that H-NMR has one of the smallest isotropic chemical shift ranges (12 ppm), but has peak broadening effects that can span several parts per million in magnitude. 

Nuclear magnetic resonance (NMR) spectrometers offer spectral capabilities to elucidate polymeric structures. This approach can be used to perform experiments to determine comonomer sequence distributions of polymer products. Furthermore, the NMR can be equipped with pulsed-liied gradient technology (PFG-NMR), which not only allows one to determine self-diffusion coefficients of molecules to better understand complexation mechanisms between a chemical and certain polymers, but also can reduce experimental time for acquiring NMR data. Some NMR instruments can be equipped with a microprobe to be able to detect microgram quantities of samples for analysis. This probe has proven quite useful in GPC/NMR studies on polymers. Examples include both comonomer concentration and sequence distribution for copolymers across their respective molecular-weight distributions and chemical compositions. The GPC interface can also be used on an HPLC, permitting LC-NMR analysis to be performed too. Solid-state accessories also make it possible to study cross-linked polymers by NMR. 

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