The nuclear magnetic resonance in single crystal magnesium has been studied at 4.2°K. The isotropic Knight shift, the anisotropic Knight shift and the quadrupole interaction have been investigated. The values for the parameters measured are K = (0.1127 ± 0.0005)%, K' = (0.0004 ± 0.0002)%, e²qQ/h = 324 ± 6 KHz. These results are compared with those of Rowland in powdered magnesium to reveal the Knight shift is independent of temperature. This contrasts directly with the behavior of cadmium. The quadrupole interaction is shown to increase by 40% as temperature is lowered to 4.2°K from room temperature. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Proton and fluorine nuclear magnetic resonance spectroscopy was used to investigate the favoured forms of several furanosyl fluorides. The low energy barrier to pseudo-rotation in these systems precludes the assignment of only one favoured conformation for each molecule. A systematic study of five membered ring sugar conformations was undertaken by examining three types of systems, varying from a relatively rigid molecule involving three fused rings, to more flexible molecules involving a "free" furanosyl fluoride ring. The spectral assignment was greatly facilitated by heteronuclear fluorine decoupling and computer analysis. 5-fluoro-3,6-anhydro-α-L-idofuranose was synthesized in good yield from several precursors and the molecule's furanose ring conformation of ₂T³was assigned on the basis of vicinal ¹H-¹H coupling constants. Using the values for vicinal ¹H- ¹⁹F couplings obtained from this molecule, together with data from other workers, a partial Karplus type curve was constructed relating vicinal ¹H- ¹⁹F couplings to dihedral angles. This curve - which was found to be more asymmetric than the Karplus relationship for vicinal ¹H-¹H couplings - was then used, together with the known Karplus curve for vicinal ¹H-¹H couplings, to determine the conformations of the triester furanosyl fluorides of ribose, arabinose and xylose. Assuming pure sp³ hybridization and maximum ring puckering, the conformations for most of the sugars studied were found to involve the displacement of C₂ and/or C₃ positions out of the plane of the ring formed by the other atoms. The conformation for α-fluoro-ribo-furanosyl triester ( ₃T⁴ ) was found to be different than that of the β-fluoro-ribofuranosyl triester (₃T⁴). A significant and apparently stereospecific long-range ⁴J[subscript H].₄,F coupling through oxygen of ca. 6.5 Hz, is observed when H₄ and F are in a trans arrangement, while a much smaller coupling for ⁴J[subscript H].₄,F of ca. 1.0 Hz. is observed when these two nuclei are in a cis or approximately "planar M" arrangement. On the other hand, ⁴J[subscript H].₃,F couplings were found to have a value of ca. 2.2 Hz. in the cis or "planar M" geometry, while in the trans geometry, ⁴J[subscript H].₄,F is ca. 0.5 Hz. / Science, Faculty of / Chemistry, Department of / Graduate

Resonance absorption spectra have been observed which may be interpreted as many-quantum transitions where the axis of quantization is along the effective magnetic field in the rotating frame. By this description, resonances which required up to five quanta were observed. The spin system used was that of conduction electrons of lithium metal in neutron irradiated lithium fluoride crystals. An analysis of the experimental results using a modified Bloch equation under the assumption that Ƭ₁= Ƭ₂= Ƭ 1.5x10 ̄⁷sec. and that the spin system relaxes toward the instantaneous field is presented. A brief outline of the concept of spin temperature is included. A comparison is made between some of the predictions of the spin temperature concept and the simple Bloch theory used in analyzing the experimental data. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Spin-lattice relaxation times have been measured in metal single crystals with a pulsed nuclear magnetic resonance apparatus at both room and liquid nitrogen- temperatures. The values obtained for aluminum and vanadium agreed well with the values given in the literature for powdered samples. The niobium value was slightly lower than the most reliable powder value, possibly because of impurities. Measurements were made on isotopically pure tin to see if any anisotropy could be detected in the spin-lattice relaxation time. No anisotropy could be detected, but the crystal orientation used was so unfavourable that an anisotropy of less than about 50% could not be detected. The spin-spin relaxation time was measured in the isotopically pure tin for five different magnetic field orientations. These showed that exchange narrowing occurred. With a suitable choice of operating conditions, the apparatus measured the equivalent of the absorption mode in steady state nuclear magnetic resonance as a function of magnetic field orientation. This was combined with the spin-spin measurements to give the complete orientation dependence of the latter. These measurements gave a value of (2.1±0.3)Kc/s. for the pseudo-exchange constant in tin. The pseudo-dipolar second moment was found to be twice the dipolar second moment. Spin echoes were observed in the isotopically pure tin and were used to measure the spin-spin relaxation time. These gave values which were much shorter than those measured by free induction decays. The reason for this was not determined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A new method of synthesizing organic fluorides stereospecifically was developed; the elements 'BrF' and 'IF' were added quantitatively across the double bond of simple olefins such as cyclohexene, using elemental halogen and silver fluoride at room temperature in benzene. Application of this reaction to the activated olefin, acenaphthylene, resulted in a variety of products, depending on solvent; with pure acetonitrile solvent, quantitative 'BrF' addition occurs, but with an increasing proportion of benzene various side reactions take place, including difluorination and dimerization. Another series of compounds was synthesized from fluoro- acenaphthylene by various addition and substitution reactions, and all together fifteen acenaphthene fluorides were made, including thirteen new compounds. The ¹H and ¹⁹F N.M.R. spectra of these substances were measured and a set of ³JHF values obtained for a wide variation in the electronegativity of the substituents, and for two values of dihedral angle (0°and 100°). This data showed that the dependence of ³JHF upon electronegativity was far from linear, as had hitherto been supposed, but rather exponential, which is in retrospect more logical. Application of this data on ³JHF to some flexible systems, derivatives of indene and benzofuran, allowed their conformations to be determined. In all cases the pucker of the five-membered ring is small (∼25°), except in the cis-bromofluoride of benzofuran where it is much larger, (45-50°). A separate study was made of the conformational inversion of trans-1-fluoro-2-iodocyclohexane (I) and its specifically deuterated analogue, derived from 3,3,6,6-tetradeutero-cyclohexene. Several methods were employed to measure the position of the conformational equilibrium and this permitted a comparison of the methods themselves. It was found that all chemical shifts and coupling constants were temperature dependent, those involving ¹⁹F being particularly susceptible. The only reliable methods were found to be area measurements (at -90°C), linewidth measurements (at -45°C), and temperature-corrected ¹⁹F chemical shift measurements; thus the compound in question was found to have a preference for the diequatorial form, with ∆G° = 0.650 ± 0.025 kcal./mole (at -90°C to 0°C), and a near zero entropy, ∆S° = 0.0 ± 0.5 e.u. This value of ∆G° is only 0.1 kcal./mole smaller than the sum of the A-values for iodine and fluorine, and indicates that the repulsion between these two halogens in the diequatorial form is quite small, about one tenth that between iodine and chlorine, or between chlorine and chlorine, etc. A kinetic study of I was made by applying the general lineshape equation of Gutowsky and Holm for two-site exchange; calculated line-widths and positions were matched to the experimental ¹⁹F spectra (with all ¹H couplings removed by irradiation) at various temperatures, and thus an Arrhenius plot was made and activation parameters derived. ∆FƗ = 10.38 kcal./mole; ∆SƗ = 2.1 e.u. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis was initiated in an attempt to overcome the limitations imposed upon NMR spectroscopy by magnetic field inhomogeneity in two specific areas: high resolution spectroscopy in isotropic liquids, and chemical shift resolved NMR imaging in isotropic liquids. In both cases magnetic field inhomogeneity may degrade the resolution of spectra to such an extent that no useful information can be obtained from them. In high resolution NMR spectroscopy it is necessary to be able to extract accurately the parameters present within the spectrum such as chemical shifts, coupling constants and peak areas. In chemical shift resolved imaging experiments the requirements are less stringent; and it is only necessary that the resonances of different chemical species be resolved. However, even the less stringent requirements of NMR imaging are often difficult to meet as the sample volumes required are often several orders of magnitude larger than those required in conventional high resolution NMR spectroscopy. The use of zero-quantum coherence has been investigated as a potential solution to the magnetic field inhomogeneity problem in both of these areas. Zero-quantum coherences are independent of magnetic field inhomogeneity and contain the parameters desired in both cases, though they are displayed in a way which differs from conventional NMR spectra. In this thesis, existing zero-quantum coherence experiments have been evaluated for use with inhomogeneous magnetic fields, and, where necessary, adapted for this purpose. Several completely new experiments have been developed for producing broad-band decoupled zero-quantum coherence spectra and also for presenting coupling constants and chemical shifts in a manner which is as close to conventional NMR spectra as possible, hence facilitating ease of use. Zero-quantum coherence has been evaluated as a tool for identifying unknown compounds and also for identifying the components of complex mixtures by "signature" recognition. Both decoupled and non-decoupled zero-quantum coherence experiments are adapted to provide imaging experiments which allow the separation of the images of different chemical species in inhomogeneous magnetic fields. The two-dimensional J-resolved experiment is also adapted for this purpose. / Science, Faculty of / Chemistry, Department of / Graduate

The work described in this thesis is divided into two parts: testing and evaluation of some surface coils, and application of the surface coils to in-vivo studies. In particular, the localization properties of surface coils were examined and optimized using the highest performance coil geometry and wire. Application of the surface coil technique to in-vivo studies involved measuring changes in metabolic status of muscle and brain tissue in rats using ³¹P spectroscopy. The properties of surface coils have been studied by evaluating their excitation patterns with ¹H and ³¹P NMR spectroscopy. Surface coils, manufactured in different sizes, geometries, and materials were tested for Q factors, signal-to-noise ratios, and pulse widths required for excitation of the sample. A silver plating on the copper wire used to fabricate the surface coils was found to increase the Q and signal-to-noise of the coil. Examination of the excitation patterns of the surface coils with point samples characterized the B₁ field of the coils as decreasing axially and radially from the coil. Calculations of the magnitude of the B₁ field reveal that its dome-like shape extends to approximately one coil radius above the surface coil. It was found that samples lying outside the domain of this "sensitive volume" did not contribute to a spectrum. These data were all correlated and the "0.9" silver plated coil was deemed to be the most efficient coil with which to pursue further in-vivo studies. In-vivo ³¹P studies of rat tissues were preceded by in-vitro spectral measurements of various metabolites at physiological concentrations. These standards were used to aid in the identification of resonances in the in-vivo spectra. Metabolic changes such as artificially induced ischemia in muscle, deceased brain, and artificially induced brain dementia were compared with "normal" ³¹P spectra of anaesthetized rat tissues. It was found that oxygen deprivation is readily observed with this technique whereas the preparation of brain dementia cannot be diagnosed with ³¹P NMR spectroscopy. / Science, Faculty of / Chemistry, Department of / Graduate

NMR spectra of many systems governed by axially symmetric second rank tensor interactions exhibit P2(cos θ) dependence on the angle 9 between the symmetry axis and the externally applied magnetic field. For the so-called "powder samples" consisting of many randomly oriented domains the resulting spectrum is the superposition of contributions from each such domain. This study deals with a numerical technique enabling one to obtain the lineshapes of such individual contributions responsible for the given powder spectrum. The electric dipolar interaction between two spin 1/2 nuclei produces a characteristic powder lineshape called "Pake doublet", after G.E.Pake, hence the name "de-pake-ing". An iterative algorithm capable of dealing with spectra produced by a variety of systems is developed and checked by applying it to a wide range of simulated NMR spectra. A set of characteristic "signatures" associated with different experimental situations is established and the limits of the applicability of the technique are determined. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Bibliography: [appendix A-1 to A-2]. / This thesis was motivated by the idea of employing non-invasive investigations of atherosclerosis using Magnetic Resonance Imaging (MRI). MRI has the advantage of being able to detect atheroma in blood vessels with no risk to the patient but is still limited in its application to large blood vessels by the low geometrical resolution obtainable. The capability of MRI to measure velocities as well leads to the idea of correlating atheroma dimensions with measured velocities downstream of the blockage. This thesis makes a first step towards obtaining results that can be applied in investigations of atherosclerosis employing MRI. The fluid dynamics of arterial blood flow, the medical procedure of diagnosing and treating atherosclerotic diseases, and the physical principle of MRI are investigated to find out "if' and "how" the correlation between a blockage and the resulting downstream velocities can contribute to the diagnosis of atheroma. Parallel to this background research, experimental and numerical modeling of atheroma is carried out. These two approaches use identical geometrical and fluid parameters to enable a direct validation of the results. An experimental test-rig is designed. Experiments with different types of blockages are performed. The measured flow parameters are pressure and velocity profiles in a crosssection of the modeled artery. A commercial software package is employed for the numerical simulation of blockages with similar geometries to those used in the experiments. The pressure and absolute velocities are again the derived parameters. Both approaches are validated with analytical results obtainable for flow without any blockages. Blockages are then inserted and the results are compared and analyzed for their potential to contribute to the medical application. The results obtained with the two models give good correspondence. The transitional length of the laminar pipe flow corresponds very well to the expectations. A laminar velocity profile is completely built up before the fluid enters a blockage. Blockages with a small flow area cause a high peak velocity and a large wake. Blockages that slightly reduce the flow area have only a small influence on the flow. The length of a blockage has only a secondary influence on the downstream velocity distribution, while the influence of the surface roughness of the blockage is small. The peak velocities and pressure loss caused by the different blockages give good correlation. The prediction of the diameter of the blockage from peak velocities measured with MRI is an improvement on that which is possible from the theory only. In particular, the results obtained in this thesis show that the true maximum velocities are significantly lower than those obtained with theoretical predictions. The change in the velocity profiles, due to angioplasty, is shown in a simplified form with the models. Typical values of reduced areas before and after such surgery, where the atheroma is squeezed against the arterial walls, are analysed. The influence of the post-surgery blockage on the flow is very small, while the pre-surgery blockage shows a dominant influence. A prominent wake exists downstream of a highly reduced flow area, and high velocities occur. A wake is a potential risk area for atherosclerosis, as low shear rates and high turbulence intensities are possible. The blockage with the less reduced area has almost no influence on the flow, and a wake is hardly formed. The influence of different shapes of atheroma, while having a similar reduced area, is also demonstrated. The perfectly symmetrical blockage has less negative influence on the flow than one which is highly asymmetrical. The asymmetrical blockage causes a larger wake and higher maximum velocities.

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