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<p> Approximately 80 percent of all synthetic polymers used are cross-linked polymers, unfortunately the characterization of cross-linked polymers has not kept up with their use. This study tries to help in the characterization of cross-linked polymer systems. More specifically the interactions of cross-linked polymer systems with solvents will be probed. Nuclear Magnetic Resonance (NMR) spectrometric techniques will be used to characterize solvent-polymer interactions.</p> <p> The cross-linked polymer system studied was the polymer ethylene glycol dimethacrylate (EGDMA) with methylmethacrylate (MMA). A splitting of the solvent signals was observed in the NMR spectrum which can be used to understand these solvent-polymer interactions. Several NMR parameters and swelling of the polymers were measured in order to understand these interactions. The chemical shift differences between the solvent types and the peak linewidths were measured. As the polymer becomes more highly cross-linked the chemical shift differences and the linewidths increases. This compactness can be monitored by measuring the degree of swelling of the polymer. In addition the possibility of an isotope effect was explored by monitored by placing the polymer in solvent mixture of CHCl3/JCDCl3 and varying the temperature. No isotope dependence was found to exist for chloroform over the temperature range analyzed. The degree of splitting and the occurrence of splitting was found to be dependent on the solvent system. In general, solvent splitting is present for solvents that are able to cause the polymer to swell appreciably. For 4.8 weight percent EGDMA in EGDMA/MMA polymer a splitting is usually observed for a solvent that is able to swell the polymer to twice its dry size. The association between the solvents and the polymers can be best explained by breaking the interactions into a number of components.</p> <p> The explanation is based on the presence of three interactions. A weak chemical interaction exists between the solvent and the polymer to account for the field dependent linewidths. A second chemical interaction that results is a binding between the solvent and the polymer and causes the solvent splitting to occur. The third interaction is a result of the increased rigidity and compactness of the polymer as the weight percent EGDMA in EGDMA/MMA polymer increases. Alternatively as the polymer becomes more compact the chemical shift difference between the two types of solvents increases.</p> <p> Ultimately, it is shown that NMR is a useful aid in understanding solvent-polymer interactions.</p> / Thesis / Master of Science (MSc)

<p> Quantitation by nuclear magnetic resonance (NMR) has been frequently done with integrals. The use of peak heights has been thought to be unreliable. The aim of this thesis is to examine the reliability of peak height method in achieving quantitative NMR measurements for small molecules such as water and sucrose.</p> <p> Isotope measurements have been traditionally done by isotope-ratio mass spectrometry. This is no doubt a highly sensitive technique for analyzing pure samples but the analysis of mixtures is not as straight-forward as it would be for the former. Ontario Hydro has encountered problems in measuring deuterium in DMSO/water mixtures. To solve the problem with NMR, an analytical method has been established to measure the deuterium content in waters and in DMSO/water mixtures. This involved testing a linear model for analyzing waters which were enriched or depleted with deuterium as well as applying the model to quantify DMSO/water mixtures. Both 1H and 2H NMR were employed. Satisfactory accuracy and precision of the results were obtained.</p> <p> For quantitative 13C work, the peak height method is often not recommended due to the variations in signal width, which is a result of varied T2 values and nuclear Overhauser enhancement (NOE). Sucrose molecules in cane sugar and beet sugar have different 13C isotopic ratios because they are synthesized by different photosynthetic pathways. To see the usefulness and limitation of the peak height method, 13C spectra of sucrose were acquired and the carbon peaks were quantified. Good precision was achieved but no predictable trend in the isotope difference could be found.</p> / Thesis / Master of Science (MSc)

The F19 NMR spectrum of SF4 at - 101° C has been assigned as an A2B2 type spectrum, rather than A2X2 as previously reported. Sulphur and boron isotope effects on F19 NMR spectra have been observed for the first time and a new silicon isotope effect has been measured. An expression has been derived for the shape of the spectrum of a nucleus of spin I = 1/2 spin-spin coupled to a nucleus of spin I = 3/2 which is undergoing quadrupole relaxation. The derived expression is used to interpret the F19 spectra of BF3 and Cl03F over a wide temperature range. A new compound, IOF5, has been prepared, and identified by means of its F19 NMR spectrum. / Thesis / Doctor of Philosophy (PhD)

The studies of enzymes from extreme sources have gained significance due to their increasing potential applications. The proteins from halophiles (salt loving) have adapted to challenging environmental conditions and require salt for their structure and function. How halophilic proteins adapt to a hypersaline environment is still an intriguing question. It is important to mimic the environmental conditions of the sample under investigation with experimental techniques. In this study, structure and dynamic features of a halophilic enzyme have been investigated under high salt conditions. The acquisition of NMR data on high salt samples has always been problematic. We have devised a simple and elegant approach for obtaining NMR data for a protein in a high salt buffer that allows for virtually complete 1H, 13C, and 15N assignments. These data were then used to calculate the NMR derived structure of Haloferax volcanii dihydrofolate reductase in 3.5 M NaCl. Structure calculations showed that this protein folds in a similar manner as investigated in the crystal structures of Haloferax volcanii dihydrofolate reductase and Escherichia coli dihydrofolate reductase. To understand the effect of salt on flexibility as well as activity, NMR relaxation studies at 3.5 M and 1.0 M salt concentration were carried out. NMR dynamics of this enzyme revealed that the loss of activity as the salt concentration is lowered is due to lose in the inherent flexibility across the backbone, particularly in the catalytic loops.

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