Solid-state 33S NMR spectroscopy

The majority of studies on 33S NMR spectroscopy have been limited to liquid samples. 33S solid-state NMR spectroscopy remained substantially unexplored until 2003, when the first systematic studies began to be published. 

Problems encountered in the acquisition of 33S solid-state spectra are common to most of the quadrupolar nuclei, with the addition of the great inconvenience of the low sensitivity of 33S.105 In 33S solid-state NMR,69 the outer (—3/2 - —1/2) and (1/2 - 3/2) transitions are normally very broad as a consequence of 

The first application of 33S solid-state NMR spectroscopy is, of course, the determination of precise values of the 33S nuclear quadrupole coupling constants that, as previously outlined, cannot be easily determined from liquid phase spectra. Jakobsen et al.106 have demonstrated that it is possible to obtain very precise values of nuclear quadrupole coupling constants and asymmetry 

Very recent studies have examined the possibility of using 33S MAS spectroscopy in the study of some structural problems in cementitious materials107 108 and in sulphur speciation in silicate melts.109 Several processes of the deterioration of cements and more generally lapideous materials can be correlated to the stability of sulphate, to changes in the sulphate phase and to the interaction of sulphate ions with water molecules and hydrates.108 Since sulphate anion is one of the species that can be studied more easily by 33S NMR solid-state spectroscopy, this technique can be a valuable tool in studying 

In these studies, the parameters that could provide the most interesting information are likely to be the electric field gradient (nuclear quadrupole coupling constant) at the 33S nucleus and its asymmetry parameter. Indeed, modifications of the lattice structure in different cement matrixes are expected to influence the symmetry of the electronic distribution around the sulphur nucleus more than the chemical environment of sulphur. 

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Many of the difficulties encountered in the acquisition of 33S NMR spectra can now be circumvented by the use of modern spectrometers operating at very high magnetic fields, as the early successes of solid-state 33S NMR spectroscopy have demonstrated. 

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