published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Indirect nuclear spin-spin coupling constants in high resolution nuclear magnetic resonance (NMR) spectroscopy provide the most powerful method for determining conformations and structures of molecules in solution. The research described in this dissertation establishes the conformational and substituent dependencies of several new types of nuclear spin-spin coupling for use in structural studies. It was also of interest to determine the electronic factors which lead to the observed experimental trends. Geminal, vicinal, and four-bond carbon-carbon nuclear magnetic resonance coupling constants were studied experimentally with fifty carbon-13 enriched alicyclic compounds. Because of the small magnitudes of many of these coupling constants it ~vas necessary to modify existing Fourier transform NMR equipment to perform J-resolved two-dimensional NMR experiments. With the greater spectral resolution it was possible to determine 56 intercarbon geminal (²J(cc)), 107 vicinal (³J(cc)) and 26 four-bond (⁴J(cc)) coupling constants. These data represent the largest collection of ²J(cc), the only known data for ⁴J(cc), and the most accurate compilation of vicinal ¹³C-¹³C coupling constants. In combination with molecular orbital methods, the relevant conformational and substituent trends in each of these series were elucidated. Because of the great amount of interest in the importance of bridgehead interactions in "strained" molecules, a study is presented of coupling transmitted via nonbonded interactions between the bridgehead carbons in a series of l-substituted-bicycloalkanes. The two-dimensional Fourier transform methods were again used to obtain the experimental coupling constants and molecular orbital methods were used to determine the importance of the intercarbon bridgehead interactions on ¹H-¹H, ¹³c-¹H, ¹³C-¹³C, ¹³c-¹⁹F , and ¹H-¹⁹F coupling constants. In all cases the nonbonded interactions increased dramatically as the separation between the bridgehead carbons decreased. Further understanding of mechanisms of "through space" coupling were based on NMP. studies of the long range coupling constants (⁵J(HF) and ⁴J(HF)) in N-methyl-8-fluoroquinolinium halides. The X-ray structure of N-methyl-8-fluoroquinolinium chloride was determined in an attempt to calculate the observed ⁵J(HF) and ⁴J(HF). A selective population inversion mIR method was used to show that the sign of ⁵J(HF) in N-ethyl-8- fluoroquinolinium iodide is positive.

Carbon-13 nuclear magnetic resonance is a very useful spectroscopic technique in studying organic compounds, especially when the proton NMR does not provide much information. In this study of multicyclic lactams, different NMR techniques were used: broadband decoupled spectra, single-frequency off-resonance decoupling (SFORD), and the attached proton test (APT). Lanthanide shift reagents and lanthanide relaxation reagents were also used. Almost all the carbon-13 resonances of mono-, bi-, and polycyclolactams were unambiguously assigned. The most powerful method in the assignments was based on the use of the lanthanide induced shifts (LIS) which confirmed the assignments qualitatively and quantitatively. The quantitative confirmation comes from the calculations of LIS and their comparison with the observed shifts. The carbon-13 chemical shielding of the studied lactams was analyzed and compared with analogous compounds. The results presented provide a consistent picture and the major influences in the trends of the ¹³C chemical shifts. However, no empirical relationships were derived for this series of compounds. The solution conformations of most of these lactams have been investigated using the shifts induced in their carbon-13 NMR by Yb(dpm)₃. These conformations were compared with structures obtained from X-ray data and MINDO/3 calculations. The structural analyses of ε-caprolactam and 3-azabicyclo[4.3.1]decan-4-one showed that these molecules have at least two conformations in solution. The LIS structural analyses were confirmed by using ¹³C T₁ relaxation times in Gd(dpm)₃ and Gd(fod)₃ relaxation reagents. The different contributions to the ¹³C NMR lanthanide induced shifts (LIS) were studied with emphasis in determining the importance of the ligand pseudocontact contribution. This was found to be important, especially in carbons in proximity to the complexation site.

<p>The Application of Magnetic Resonance (MRI) and Computed Tomography Imaging (CT) in the Diagnosis and Management of Maxillofacial Tumours. For decades maxillofacial surgeons over the world have been frustrated by the high and often fatal recurrence of certain advanced jaw tumours. This study conclusively proves that Computed Tomography and especially Magnetic Resonance Imaging significantly decreases recurrence of Odontogenic Keratocyst and Ameloblastoma and allows surgical planning to avoid these recurrences.</p>

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.

A 1H, 13C, and 6Li NMR study of 2-ethyl-1-butyllithium indicated that 2-ethyl-1-butyllithium exists only as a hexameric aggregate over the entire temperature range of 25 to - 92.1 ° C in cyclopentane. Reacting 2-ethyl-1-butyllithium with 2-ethyl-1-butanol resulted in alkyllithium/lithium alkoxide mixed aggregates, apparently of the form Ra(RO)bLia+b. A multinuclear, variable temperature NMR study of samples with O:Li ratios of 0.2 and 0.4 showed, in addition to the alkyllithium, the formation of four mixed aggregates, one of them probably an octamer. Higher O:Li ratio samples showed the formation of several other mixed aggregates. Mixing 2-ethyl-1-butyllithium with independently prepared lithium 2-ethyl-1-butoxide formed the same mixed aggregates formed by in situ synthesis of lithium alkoxide. Lithium 2-ethyl-1-butoxide also exists as aggregates in cyclopentane.

It has been demonstrated that by using 1H NMR spectroscopy in combination with multivariate statistical modelling (PLS) it is possible, using urine samples obtained from rats, to distinguish between different types of CNS lesions. Against this background this thesis will explore whether the combination of 1H NMR and PLS modelling on biofluids can be used q-1eientify biomarkers in .. - different neurological diseases and in clinically relevant animal models of neurologic disease. The results in this thesis demonstrate that it is possible to separate sets of animals at different stages of disease in models of multiple sclerosis and to identify the presence of early brain metastasis. The same methodology was also applied to human biofluids. In MS patient cohorts (RR- MS, PP-MS and SP-MS) it was also possible to differentiate between RR-MS and SP-MS as well between MS and healthy controls. Therapy for these two stages of MS are very different and therefore a rapid test to determine a patient's stage of MS would be hugely beneficial in the clinic. Further investigation revealed that it is possible to separate MS patients from individuals with Alzheimer's disease. Metabolomics was then combined with other eo- variants in a study of cerebrospinal fluid obtained from patients with HIV associated dementia (HAD) to discover whether disease progression could be followed in this manner. The results show that it is possible to detect neurocognitive changes in patients with HAD. Indeed, the results demonstrate. that metabolomics is a far more sensitive tool for the following progression than other non-PLS biomarker techniques and should provide a useful method for early diagnosis of CNS disease and the evaluation of therapy in prospective studies.

A carne bovina é considerada um alimento altamente nutritivo, sendo uma fonte de proteínas e vitaminas, além de minerais tal como ferro e zinco. Por outro lado, a carne vermelha atualmente tem sido associada a doenças cardiovasculares e ao câncer. No entanto, essa associação vem sendo contestada, pois a carne de ruminantes bem como o leite são fontes naturais do ácido linoléico conjugado (CLA, do inglês \"conjugated linoleic acid\"), o qual possui várias propriedades benéficas, como atividade anticarcinogênica, redução de gordura corporal, entre outras. Essas propriedades têm sido observadas em estudos com animais modelos, mas também pesquisas apontam tais benefícios para os humanos. Vários estudos têm sido realizados para aumentar a produção de CLA pelos ruminantes no Brasil. Nesse contexto, se faz necessário o desenvolvimento de métodos rápidos e eficazes para a determinação de CLA em carnes de ruminantes e no leite, pois o método atual é baseado na análise dos ésteres metílicos dos ácidos graxos por cromatografia gasosa, que envolve várias etapas, sendo um método laborioso. Assim, o principal objetivo deste trabalho foi o desenvolvimento de uma metodologia rápida, baseada na técnica de ressonância magnética nuclear de hidrogênio (RMN de 1H) para a determinação do teor do CLA na gordura de carne bovina. Para isso foi avaliada a influência dos principais parâmetros experimentais de RMN de 1H, como a largura do pulso de radiofrequência, o tempo de repetição, método de excitação seletiva, entre outros parâmetros que podem interferir na razão sinal/ruído e na reprodutibilidade das medidas. Os resultados mostraram que a utilização da RMN de 1H para a determinação do teor de CLA em carne bovina, além de ser coerente com os dados obtidos por cromatografia gasosa, representa uma abordagem mais rápida e simples para a determinação do teor de CLA em carne bovina. / Beef is considered a very nutritive food, since it is a source of proteins and vitamins, besides minerals such as iron and zinc, on the other hand it has been associated to heart diseases and cancer. However, this association has been contested because ruminant meat as well as milk, is a natural source of conjugated linoleic acid (CLA), that has several benefic properties such as anticarcinogenic activity, reduction of body fat and others. These properties have been observed in studies with animals and can be extended to humans. Several studies have been done to increase the concentration of CLA in Brazilian ruminant meat. In this context, it is necessary to develop fast and effective analytical methods to determine CLA in ruminant meat and milk, because the current method, based on the analysis of fatty acid methyl esters by gas chromatography (GC), involves several stages, being laborious. Thus, the main purpose of this work was the development of a fast methodology, based on hydrogen nuclear magnetic resonance technique (1H NMR) to determine CLA content in beef fat. In consequence, it was evaluated the influence of main experimental parameters from 1H NMR, such as radiofrequency pulse width, repetition time, method of selective excitation, between others that may interfere in signal-to-noise ratio and reproducibility. The results indicated that the use of 1H NMR spectroscopy to determine CLA content in beef have high correlation to data obtained by gas chromatography, representing a much faster and simpler methodology to determine CLA content in beef.

Phosphorus (³¹P) metabolites are emerging liver disease biomarkers. This work aims to develop a quantification protocol for human hepatic ³¹P magnetic resonance spectroscopy (MRS) at 7 tesla (T). It should have high SNR, deliver robust measurements of metabolite concentrations with high reproducibility, and be feasible to use in clinical studies. This will allow detailed characterization of liver metabolism in diseases such as cirrhosis, increasing the utility of ³¹P-MRS as a clinical tool. A 3D chemical shift imaging method using a 16 channel ³¹P array at 7 T is chosen to give high SNR ³¹P spectra from the human liver in vivo, while also providing good spatial localization and spectral resolution. The Oxford Spectroscopy Analysis (OXSA) toolbox, our MATLAB-based processing software package, is introduced and adaptations for analysis of liver spectra are described. Five volunteers were scanned to determine T₁s for the ten visible ³¹P metabolites. Simulations were used to determine design criteria for calibration phantoms at 1.5, 3 and 7 T. I compare three candidate approaches to give "absolute" concentrations in mmol/L wet tissue using a 10 cm loop coil, and then extend these approaches to data acquired using the 16 element receive array. The final protocol was applied to data acquired in ten healthy volunteers and eleven patients with cirrhosis to determine reproducibility and the differences between healthy and diseased livers. This protocol allows distinction between healthy and cirrhotic livers with 90% specificity and sensitivity, using cut-offs in either Î3-adenosine triphosphate or inorganic phosphate concentrations. This ³¹P-MRS absolute quantification protocol is an important first step in fully utilising the increased SNR afforded by the 7 T scanner, offering valuable insight into liver metabolism, and paving the way for other novel ³¹P-MRS methods to be developed in the liver at 7 T.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by William Paul Rothwell. / Ph.D.