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A study of the n.m.r. absorption of oleic acid has been carried out between 77°K. and 287°K. A sharp increase in line width and second moment is observed below 100°K. indicative of an increase in the intramolecular interactions. A narrow line, indicative of liquid-like motion, is observed at temperatures above 208°K. The second moment and line width decrease rapidly as the melting point is approached, dropping to liquid-like values at 287°K. The experimental data are compared with the theoretical data obtained from the known crystal structure. From this comparison, a crystal transition is proposed to take place below 100°K., and heteronuclear premelting is proposed to take place above 208°K. It is likely that end methyl group rotation takes place at all temperatures but there is no extensive torsional oscillation or vibration below 26o°K. and there is little apparent change in the cell dimensions between 260°K. and 100°K. Elaidic acid has been studied between 77°K. and 315°K. The line width and second moment increase slightly below 170GK. and a narrow component is observed above 225°K. The line width and second moment fall sharply only at the melting point, decreasing to a liquid-like line. As no crystal structure is available for elaidic acid, the experimental data are compared with experimental and theoretical data for oleic acid and stearic acid. Some form of molecular vibration or hindered rotation is proposed to account for the transition at 170°K., and heteronuclear premelting is proposed to take place above 225°K. The difference in the behaviour of oleic acid and elaidic acid near the melting point is explained in terms of the molecular shape. / Science, Faculty of / Chemistry, Department of / Graduate

A series of bis(ethene)rhodium(I) complexes of β-diketonates and similar ligands were prepared. The complexes were characterized by elemental analysis, ¹H NMR spectroscopy and mass spectrometry. Crystal structures are reported for bis(η²-ethene)-(1,3(1-ferrocenyl)butanedionato-0.0 ')rhodium(I), 13, (1,5-cyclooctadieiie)(2-acetylphen-oxy-0,0')rhodium(I),18, and some related molecules. [FORMULA OMITTED] The complexes are catalyst precursors for the homogeneous hydrogenation of olefins and the hydrosilylation of ketones. The generated hydrogenation catalysts are effective for the reduction of sterically unhindered carbon-carbon double bonds. These catalysts are active in the presence of alcohol, aromatic and carboxylic acid functional groups on the olefin substrate. The catalysts decompose to give a heterogeneously active rhodium precipitate when reducing olefinic substrates which are too sterically hindered. Study of the hydrosilylation reaction revealed that the complexes generate active hydrosilylation catalysts. A series of optically active ligands were tested for their ability to effect asymmetry in the silyl ether products. The bis(ethene)rhodium(I) complexes are fluxional in the NMR time scale due to the motion of the ethylene ligands. A detailed ¹H NMR study was conducted on one of the complexes, bis(η²-ethene)(2-acetylphenoxy-0,0 ')rhodium(I) 15 to explore the nature of the rearrangement. [FORMULA OMITTED] The ¹H NMR study revealed the presence of two different modes of fluxionality. The first type of motion is intramolecular in nature and is due to the rotation of the ethylene ligands about the rhodium-ethylene bond axis. The second type is intermolecular in nature and is due to exchange of the ethylene ligands. This exchange is a measure of the lability of the ethylene ligands. The system allowed the separate study of the ethylene ligands and ΔG‡ values were obtained for each ligand for both of the exchange processes. The results of the study indicate the independance of the ethylene ligands with respect to both fluxional processes. / Science, Faculty of / Chemistry, Department of / Graduate

The pathogenesis of low back pain is complex but likely involves the intervertebral disc (Nachemson, 1976). Direct evidence for its importance is lacking because an accurate in vivo method of imaging the lumbar intervertebral disc has not been established. The objective of this research was to develop classifications of gross morphologic appearance and magnetic resonance image (MRI) of the disc that describe the changes associated with aging and degeneration, thereby permitting interpretation of the MRI in terms of gross morphology and allowing correlation of morphologic, chemical, mechanical, radiologic and epidemiologic data with a standard reference of disc aging and degeneration. The classifications were developed on the basis of literature review, detailed examination of 55 discs and expert advice. Two sets of three observers, one for the morphologic classification and one for the MRI classification evaluated 68 life size randomized duplicates of discs making detailed observations about overall category and 17 regional morphologic parameters and 11 regional MRI parameters. The data was tested to demonstrate the validity of the classifications using established criteria (Tugwell & Bombardier, 1982; Guyatt 4 Kirschner, 1985; Feinstein, 1985). The consistency with which the classifications could be applied was evaluated by calculating weighted kappa, a statistical test of agreement that corrects for agreement by chance; the ability of the classifications to distinguish stages in the process of ageing and degeneration by stepwise discriminant analysis; their conformity with other measures by comparisons within and between classifications and, comparisons with histologic and chemical data. The degree of agreement for all six intra-observer pairs was 'almost perfect' (weighted kappa > 0.80); for 5 interobserver pairs 'substantial' (weighted kappa > 0.60) and for one MRI interobserver pair 'moderate' (weighted kappa > 0.50). This represented a satisfactory level of agreement and indicated the classifications could be applied consistently (Feinstein, 1981). The linear regression model developed by stepwise discriminant analysis clearly demonstrated the ability of the classifications to distinguish distinct stages in disc aging and degeneration. Wilk's lambda, a likelihood ratio statistic reflecting discriminatory function, approached zero in both the morphologic (0.0408) and MRI (0.0H80) classifications. In both models, parameters pertaining to the nucleus pulposus of the disc accounted for the majority of the variance (morphologic partial R² 0.8598 and MRI partial R² 0.8811) suggesting nuclear parameters are the most important in distinguishing overall category. The correlation table generated by principal component analysis demonstrated that the categories assigned to regional parameters correlated significantly (p > 0.0001) with each other and with the overall category. From the linear combinations of parameters (principal components) generated the weighting of the nucleus pulposus behaved independently attesting to its importance. Comparisons of the morphologic and MRI classifications yielded high indices of trend (Pearson correlation coefficient of 0.81) and concordance (kappa of 0.62). Trends in the histologic and chemical data were consistent with the classifications but could not be evaluated statistically because only 15 specimens were studied. This research suggests that the classifications are valid and will form a basis for the interpretation of MRI. Preliminary evidence suggested MRI is sensitive to early changes in extracellular matrix composition not apparent in gross morphology. / Medicine, Faculty of / Graduate

Dipolar and quadrupolar couplings measured from NMR experiments, and order parameters obtained from these couplings, are reported for a number of small solutes dissolved in several nematic liquid crystals. These results are discussed in terms of the solute-solvent interactions. It has been shown that the interaction between the solute molecular quadrupole moment and a mean external electric field gradient due to the liquid crystal accounts for most but not all of the ordering of molecular hydrogen. The remaining contribution to ordering is discussed in terms of possible mechanisms. The anisotropic couplings observed for methane and acetylene are discussed in terms of a model which takes into account the interaction between the vibrations and rotations of the solute. Excellent agreement between the observed and calculated dipolar couplings is obtained. Evidence is given that these two solutes experience the same field gradient as molecular hydrogen. In a mixture of 55wt per cent 1132 (Merck ZLI 1132) and 45wt per cent EBBA (N-(4-ethoxybenzylidene)-4'-n-butylaniline at 301.4K the deuterons in D₂ experience no external electric field gradient. The order parameters of a series of solutes in this mixture are calculated in terms of a simple model for the short range interactions which depend on the size and shape of the solute. These calculated order parameters are in very good agreement with the experimental results. In liquid crystals where the field gradient is not zero it is shown that the combination of the short range interaction model and the electric field gradient - molecular quadrupole moment mechanism predicts the order parameters very well. / Science, Faculty of / Chemistry, Department of / Graduate

The experiments to be described here were undertaken for the purpose of determining, if possible, by NMR techniques whether or not the hydroxyl protons in mica are bound in a regular crystalline array, and, if so, whether or not the hydroxyl protons occur in reasonably isolated pairs as in waters of hydration.

Magister Scientiae - MSC (Biochemistry) / Proteins play an important role in cells, as the morphology, function and activities of the cell depend on the proteins they express. The key to understanding how different proteins function lies in an understanding of the molecular structure. The overall aim of this thesis was the determination of the structure of DWNN domains. This thesis described the preparation of samples of human DWNN suitable for structural analysis by nuclear magnetic resonance spectroscopy (NMR), as well as NMR analysis. / South Africa

Neste trabalho foi estudado o condutor protônico HPb2Nb3O10. nH2O , por Ressonância Magnética Nuclear pulsada do próton \'ANTPOT.1H\'. Tanto o estudo da forma de linha como a relaxação spin-rede, em função da temperatura, refletem a mobilidade das espécies protônicas neste material. O início dos movimentos iônicos e moleculares produzem um forte estreitamento da largura de linha acima de 130 K. Os dados da taxa de relaxação spin-rede (1/T1) mostra um máximo entre 253 K e 273 K que depende da hidratação (n). As energias de ativação obtidas dos resultados de relaxação e largura de linha variam entre 0,14eV e 0,4eV, dependendo da hidratação. Os resultados de condutividade e RMN são consistente com um mecanismo de condução do tipo Grotthus, que consiste numa sucessão de movimentos reorientacionais e saltos de prótons. O coeficiente de difusão protônica foi estimado dos parâmetros obtidos de RMN sendo da ordem de 10-8 cm2/s. Este valor leva a uma condutividade da ordem de 10-3 S/ cm. / The protonic conductor HPb2Nb3O10. nH2O , was studied by pulsed Nuclear Magnetic Resonance (NMR) of \'ANTPOT.1H\'. The temperature dependence of the spin-lattice relaxation rate (1/\'T IND.1\') and line width, reflect the mobility of the protonic species present in this material. The onset of ionic and molecular motions produces a strong narrowing of the line at temperatures above 130 K. The spin-lattice relaxation data, obtained above 200 K, shows a maximum in 1/\'T IND.1\', peaking in the range 253 K to 273 K, depending on the value of n. Activation energies of protonic motions, measured from line width and relaxation data, are n dependent and lies in the range of 0,14 eV to 0,4 eV. Results of NMR and conductivity are consistent with the Grotthus conduction mechanism, consisting of a succession of molecular re-orientations and proton jumps. The protonic diffusion coefficient was estimated from the parameters obtained from NMR relaxation and found to be of the order of 10-8 cm2/s, leading to a conductivity of about 10-3 S/ cm.