NMR of other nuclei

In diamagnetic vanadium complexes, information on the mode of coordination of the ligand(s) can be obtained from magnetic nuclei in the coordination sphere by both one-and two-dimensional (homo- and heteronuclear) methods. In model complexes for biorelevant vanadium compounds, informative spin probes are the spin-i/2 nuclei H, and (the last preferably in N-enriched samples), and the quadrupolar nuclei H (7 = 1), (7 = 1) and (7 = 72). NMR is a powerful tool in characterising 

Whereas V gives rise to resonances which are substantially shifted but still sufficiently sharp to be detected, greatly broadens signals but does not cause appreciable shifts. 

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Future applications will also be considered, in particular with respect to the use of these techniques combined with the NMR of other nuclei (Na, Al, Si) for the investigation of zeolite synthesis mechanisms (12-14). 

High Resolution Solid State NMR of Other Nuclei... 

NMR of other nuclei. NMR studies of rare earth intermetallic compounds utilizing non-rare earth nuclei not included in previous subsections are summarized in table 18.18 and in the following remarks about each element. 

In the following 55 problems, the chemical shift value (ppm) is given in the scale below the spectra and the coupling constant (Hz) is written immediately above or below the appropriate multi-plet. Proton NMR data are italicised throughout in order to distinguish them from the parameters of other nuclei ( C, N). 

Although the proton is the most extensively studied nucleus, NMR spectra of other nuclei have been investigated. 

Some other nuclei. Here are a few reported uses of NMR on other nuclei. 3He, binding into little cavities in fullerenes 478 nB, binding of boronic acids to active sites 479 23Na, measurement of intracellular [Na1] 180 482 35C1 and 37C1, binding to serum albumin 483 113Cd,... 

New techniques for data analysis and improvements in instrumentation have now made it possible to carry out stmctural and conformational studies of biopolymers including proteins, polysaccharides, and nucleic acids. NMR, which may be done on noncrystalline materials in solution, provides a technique complementary to X-ray diffraction, which requires crystals for analysis. One-dimensional NMR, as described to this point, can offer structural data for smaller molecules. But proteins and other biopolymers with large numbers of protons will yield a very crowded spectrum with many overlapping lines. In multidimensional NMR (2-D, 3-D, 4-D), peaks are spread out through two or more axes to improve resolution. The techniques of correlation spectroscopy (COSY), nuclear Overhausser effect spectroscopy (NOESY), and transverse relaxation-optimized spectroscopy (TROSY) depend on the observation that nonequivalent protons interact with each other. By using multiple-pulse techniques, it is possible to perturb one nucleus and observe the effect on the spin states of other nuclei. The availability of powerful computers and Fourier transform (FT) calculations makes it possible to elucidate structures of proteins up to 40,000 daltons in molecular mass and there is future promise for studies on proteins over 100,000... 

The potential of other nuclei for the study of surfaces is yet to be explored. Gottlieb and Luz (388) measured 2H spectra of a number of perdeuterated molecules adsorbed on active alumina and interpreted the results in terms of quadrupolar tensors. Yesinowski and Mobley (369) have shown that 19F MAS NMR can provide useful information about fluorinated surfaces of calcium hydroxyapatite, Cas(0H)(P04)3. In particular, l9F, 2H, and H MAS NMR may become powerful techniques for the study of interface systems in general. 

There are a number of other nuclei which can be detected by NMR in vivo. However, these have been used to a much lesser extent (see Szwergold, 1992, and references cited therein). 

H NMR spectrometry is the foundation upon which we will build an understanding of the magnetic resonance of other nuclei, especially 13C, which leads to the important advanced correlation experiments. We began by describing the magnetic properties of nuclei, noting the special importance of spin 1/2 nuclei. For practical... 

We start by acknowledging that our goals are modest as we confront such a vast field as multinuclear NMR. In Section 3.7, we have seen the impact of other nuclei that possess a magnetic moment (especially those with spin one-half) on proton spectra. We will briefly examine the NMR spectrometry of four spin one-half nuclei, which were selected for their historic importance in organic chemistry (and related natural products and pharmaceutical fields), biochemistry, and polymer chemistry. These four nuclei, l5N, 19F, 29Si, and 31P, are presented with a few simple examples and a brief consideration of important experimental factors and limitations. 

The use of NMR spectrometry of nuclei other than 3H and 13C to characterize and identify organic compounds is now commonplace. The use of other nuclei in NMR experiments ranges from such diverse areas as simply determining whether an unknown compound contains nitrogen to more complex questions of stereochemistry and reaction mechanisms. Although our discussions will be limited to four other nuclei, we should not limit our outlook with respect to the possibilities of other nuclei or other experiments. In fact, our intention here is to broaden our outlooks to the nearly limitless possibilities with NMR and the periodic table. 

As already outlined in Chapter 3, the variation in 33S chemical shift with molecular structure has been quite extensively studied in sulphinyl, -SO-, sulphonyl, -S02-, and sulphonic, — SO3, moieties. It has been found that the 33S chemical shift is much more sensitive to structural variation than the chemical shift of other nuclei, such as 13C, 15N or 170. For this reason, 33S NMR is a powerful method for structural elucidation and in many cases a unique probe for assessing the properties of the electronic distribution around the sulphur atom. 

MQMAS studies are at present relatively rare. However, MQMAS techniques have been applied in studies of other nuclei such as Al and Mo (see Section 5.3.2). The success of these studies suggests that MQMAS NMR may play a role in future investigations of vanadium oxide catalysts. 

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