High-pressure NMR studies of isomerizational exchange rates in liquids
Campbell, Douglas Michael
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Permalink
https://hdl.handle.net/2142/21823
Description
Title
High-pressure NMR studies of isomerizational exchange rates in liquids
Author(s)
Campbell, Douglas Michael
Issue Date
1991
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
The effect of pressure on exchange rates, of varied systems in condensed media, were observed and typically related to stochastic theoretical models of exchange processes. Rates of exchange were determined using, the total line shape analysis method in chapters two and three, peak areas and saturation transfer in chapter four, and rotating frame spin lattice relaxation measurements in chapter five. Chapter six details some properties of high pressure high resolution NMR probes. Increasing solvent pressure on N,N-dimethyltrichloroacetamide (chapter two) was shown to decrease the rate of rotation about the amide bond. In order to fit the data favorably the Grote-Hynes model, which takes into account the frequency dependence of the friction, was applied. The opposite effect was seen for the rotation of coordinated ethylene in $\pi$-cyclopentadienyldiethylenerhodium (chapter three). In this case the data was fit best using the model developed by Skinner and Wolynes. The effect of pressure on the denaturation of lysozyme was determined using the peak areas of the histidine-15$\sp{1\varepsilon}$ resonance in both the native and denatured forms. The data indicated the possibility of a second major denatured structure under these conditions, while thermal denaturation techniques indicated only one major denatured structure. Individual rate constants of folding and unfolding were also determined using saturation transfer experiments on this same resonance. The effect of pressure on the conformational isomerization of cyclohexane in CS2 was studied using rotating frame spin lattice relaxation techniques (chapter five). By using this method rate constants were obtained which were two orders of magnitude larger than those which could be obtained by the line shaper analysis technique. Increasing solvent pressure increased the isomerization rate by combining this data with previously collected data, it was determined that the barrier to isomerization is pressure independent, and that eyclohexane falls in the inertial regime of the Kramers' model.
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