Vanadium-51 NMR spectroscopy

Although NMR is a notoriously insensitive technique, vanadium is a highly responsive nucleus, and it is quite feasible to get spectra from a few micromolar concentration of vanadium in solution. Frequently, there is no necessity for such low concentrations, and more typically NMR studies utilize 0.5 mM, and above, total vanadium concentrations. 

Vanadium-51 is a spin 7/2 nucleus, and consequently it has a quadrupole moment and is frequently referred to as a quadrupolar nucleus. The nuclear quadrupole moment is moderate in size, having a value of -0.052 x 10 2S m2. Vanadium-51 is about 40% as sensitive as protons toward NMR observation, and therefore spectra are generally easily obtained. The NMR spectroscopy of vanadium is influenced strongly by the quadrupolar properties, which derive from charge separation within the nucleus. The quadrupole moment interacts with its environment by means of electric field gradients within the electron cloud surrounding the nucleus. The electric field gradients arise from a nonspherical distribution of electron density about the 

FIGURE 2.1 51V NMR spectrum showing aqueous vanadate in the presence of A/fV-dimeth-ylhydroxylamine and dithiothreitol. The wide spectral dispersion of the signals is characteristic of vanadium NMR spectra. 

FIGURE 2.2 51V NMR spectrum showing vanadate in the presence of cysteine at pH 8.4. Signals of varying linewidth are frequently found in vanadium spectra. 

As a result of the short relaxation times of most vanadate species, 51V 2D exchange spectroscopy is limited to dynamic processes that occur within a few tens of milliseconds. This timescale is conveniently lengthened to 1 sec or longer in cases where proton (or other) NMR spectroscopy can be employed, for instance, in ligand exchange reactions. 

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Howarth OW (1990) Vanadium-51 NMR. Progress in Nuclear Magnetic Resonance Spectroscopy 22 453-485. 

J. Canny, R. Thouvenot, A. Teze, G. Herve, M. Leparulo-Loftus, M. T. Pope, Disubstituted tungstosilicates. 2. y- and P-Isomers of tungstovanadosilicate, [SiV2Wio04o] Syntheses and structure determinations by tungsten-183, vanadium-51 and silicon-29 NMR spectroscopy, Inorg. Chem. 30 (1991) 976. 

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