No description available.

No description available.

The purpose of this work has been the determination of structure in solids using the technique of solid-state nuclear magnetic resonance spectroscopy. High-resolution (^31) p NMR spectra have been obtained for a range of phosphate species. A number of techniques have been applied to these systems including cross-polarization, magic angle spinning, and high power proton decoupling. Characterisation using additional NMR techniques such as (^1) H cramps has been carried out wherever possible. The results obtained yield molecular and crystallographic information consistent with data from X-ray diffraction when known. Shielding tensor components were determined from static and/or spinning spectra wherever possible. The phosphate species studied include a series of precipitated calcium phosphates. A particular model for the structure of amorphous calcium phosphate is favoured in the light of (^31) p NMR measurements. One sample showed NMR evidence for changes in composition whilst in the solid state. The origins of (^31) p NMR line widths in high-resolution solid-state spectra have been considered in some detail. Variation of (^31) p NMR linewidth as function of spinning rate has been noted for a number phosphate compounds. Multiple pulse techniques have been applied on the phosphorus channel with pleasing improvements in spectral resolution. Five solid binary phosphorus sulphides have also been studied using phosphorus MAS NMR, and the results compared to solution state data wherever possible. A number of anomalies between solution and solid-state data have been noted and discussed.

The push toward higher magnetic fields in MRI has consistently thrown up new challenges in hardware development. The recent development of a new generation of ultra-high field scanners for human imaging is no exception. The earch presented in this thesis aims to provide solutions to new technical challenges in radio-frequency probe design. All probe designs were developed for use at 7T on a Philips Acheiva full body scanner.

A novel imaging modality is introduced, using Radio-Frequency Longitudinally Detected Electron Spin Resonance (RF-LODESR), capable of providing qualitative and semi-quantitative information on a variety of parameters reflecting physiological function, the most significant being tissue oxygenation. Effective spin-lattice (T_1e*) and spin-spin (T_2e*) electronic relaxation time maps of the abdomen of living 200 g rats were generated after intravenous administration of a triarylmethyl free radical (TAM). These maps were used to evaluate oxygen distribution. Differences between the liver, kidneys and bladder were noted. Conclusions were made regarding distribution, perfusion and excretion rate of the contrast medium. Ligature induced anoxia in the kidney was also visualised. LODESR involves transverse ESR irradiation with a modulated excitation and observing oscillations in the spin magnetisation parallel to the main magnetic field. The T_1e* and T_2e* maps were calculated from a set of LODESR signal phase images collected at different detection frequencies. Each phase image also provides qualitative information on tissue oxygen level without any further processing. Additionally, a new method is introduced for measuring T_1e, valid for inhomogeneous spectra, based on measuring the spectral area as a function of detection frequency. These methods present alternatives to the conventional transverse ESR linewidth-based oximetry methods, particularly for animal whole body imaging applications.

No description available.

No description available.

Alkali borosilicate glass is used to immobilise high-level radioactive waste generated from the reprocessing of spent nuclear fuel. However, poorly soluble waste products such as molybdenum present issues for long-term storage of the material, whereby phase separation of water-soluble crystalline aggregates truncate the glass network and offer leaching opportunities for the escape of radionuclides into the environment. Solid-state NMR is an effective technique for studying the phase separation in nuclear waste glasses, as it is able to distinguish glassy and crystalline environments using nuclei-specific probes. The presence of paramagnetic transition metal cations within the waste glass compromises the efficacy of NMR, as unpaired electrons can cause broadening and chemical shift effects. This work engages in a multinuclear magnetic resonance characterisation of paramagnetically-doped (by Cr2O3, MnO2, Fe2O3, NiO, or Nd2O3) model nuclear waste glasses and explores the partitioning of transition-metal components. Characterisation of the separated heterogeneous crystalline phase was accomplished principally by 133Cs, 23Na, and 95Mo NMR, where it was determined that Cr substitutes into mixed-alkali molybdates. Furthermore, paramagnetic broadening and relaxation effects were observed and quantified by 11B and 29Si NMR.

The purpose of this thesis is to describe research into the extension and development of methods in solid state NMR, and their application to chemical systems where, for various reasons, analysis was difficult, incomplete, or impossible by other spectroscopic techniques. In particular silicon-29, sodium-23, fluorine-19 and proton nuclei have been used as molecular probes in inorganic silicates, macrocyclic polyether crown complexes and fluoropolymer chemical systems. The sodium-23 chemical shift and lineshape have been shown to be sensitive to coordination and local symmetry. The cross-polarization experiment has also been applied to the sodium-23 nucleus, and shown to exhibit the same steric selectivity which has been observed in carbon-13 andsilicon-29 experiments. A probe has been configured at 4.7 Tesla to perform proton and fluorlne-19 CRAMPS experiments. Multiple pulse sequences and CRAMPS experiments have been used to investigate the molecular motions and chemical environments of the systems investigated. Conclusions are drawn upon the results which support the utility of these methods in application to difficult solid state systems.

A range of 1D and 2D MAS NMR experiments have been carried out in conjunction with X-ray diffraction experiments on a number of materials from the AM(_2)O(_7) family, which exhibit the unusual phenomenon of negative thermal expansion. It has been shown that ZrP(_2)O(_7) and HfP(_2)O(_7) exist with space group Pbca rather than Pa3 as proposed in the literature, and a full structure solution has been possible for ZrP(_2)O(_7) from a combination of NMR and X-ray and neutron powder diffraction. 2D MAS NMR has been used to differentiate at least 108 unique phosphorus sites within the asymmetric unit of SnP(_2)O(_7), supporting a recent powder diffraction study presented in the literature. PbP(_2)O(_7) has been shown, by NMR, to exist as an incommensurate phase at room temperature. ZrW(_2)O(_8), a material which also shows negative thermal expansion, has been studied here primarily with variable-temperature (^17)O MAS NMR. The results presented shed important new light on oxygen migration processes occurring at the a I β-phase transition of this material. A full structure solution is presented for 2-[4-(2-hydroxy-ethylamino)-6-phenylamino-[1,3,5]triazin-2-ylamino]-ethanol from powder X-ray data, an organic material investigated as part of a study of ink-jet-dyes.