A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2014. / The seemingly simple proton abstraction reactions underpin many chemical transformations including isomerization reactions and are thus of immense biological significance. Despite the energetic cost, enzyme-catalyzed proton abstraction reactions show remarkable rate enhancements. The pathways leading to these accelerated rates are numerous and on occasion partly enigmatic. The isomerization of the steroid, Δ5- androstene-3,17-dione by the human glutathione transferase A3-3 in mammals was investigated to gain insight into the mechanism. Particular emphasis was placed on the nature of the transition state, the intermediate suspected of aiding this process and the hydrogen bonds postulated to be the stabilizing forces of these transient species. Kinetics studies on Δ5-androstene-17-one, a substrate that is incapable of forming hydrogen bonds reveal that such stabilizing forces are not a requirement to explain the observed rate enhancements. The UV-Vis detection of the intermediate places this specie in the catalytic pathway while fluorescence spectroscopy is used to obtain the binding constant of the intermediate analogue equilenin. Analysis of the kinetics data in terms of the Marcus formalism indicates that the human glutathione transferase A3-3 lowers the intrinsic kinetic barrier by 3 kcal/mole. The results lead to the conclusion that this reaction proceeds through an enforced concerted mechanism in which the barrier to product formation is kinetically insignificant.

Title from PDF of title page (University of Missouri--Columbia, viewed on March 10, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Michael Harmata. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 112-126). Available also in a digital version from Dissertation Abstracts.

No description available.

This thesis focuses on the investigation of the optoelectronic, photo and thermal- responsive properties of organoboron compounds. In search of blue phosphors for phosphorescent organic light emitting diodes, new triarylboron functionalized phosphorescent Pt(II) complexes were synthesized and their device performances were evaluated. In Pt(II) complexes with the 2-phenylpyridyl N,C-chelate ligand and an acetylacetonato ancillary ligand, it was found that BMes2 substitution at the 4’ position of the phenyl ring can increase the phosphorescent emission energy, compared to the 5’-BMes2 substituted analogue. This occurred without substantial loss of luminescent quantum efficiency. At 100 cdm-2 luminance, electroluminescence devices with the newly synthesized Pt(II) complexes as emitters have achieved external quantum efficiency of ~ 4.7-13.4%. Tuning of the photo-responsive properties of biaryl N,C-chelate dimesitylboron compounds was achieved by functionalization with either a bisthienyl moiety or ferrocene unit. It was demonstrated that the bisthienyl unit has the ability to completely stabilize a N,C-chelate boryl chromophore toward photoisomerization. With the ferrocene unit being part of the chelation backbone of BMes2 moiety, the B−N bond of molecule B(2-ferrocenyl-N-Me-benzimidazolyl)Mes2 was found to undergo a dynamic dissociation/association process in solution, leading to its slow hydrolysis under ambient conditions. The oxidized ferrocenium species has a notable spin delocalization through space from the Fe(III) center to a flanking mesityl group. To further expand the photochromic family based on pyridyl N,C-chelate dimesityboron compounds, a systematic study was carried out with the pyridyl N donor replaced by N-heterocyclic carbene donor and azolyl, benzoazolyl N donors. These new classes of organoboranes all underwent transformation to their corresponding dark isomer in a similar fashion as the pyridyl N,C-chelate dimesitylboron. However, a second-step photoisomerization was observed in the NHC,C-chelate dark isomer via a “borylene”-like intermediate. The thiazolyl, benzoazolyl N,C-chelate dark isomers demonstrate multi-structural transformations, which include hydrogen atom transfer, 1,3-boryl shift and diastereomer interconversion via a spiropyran type ring-opening/closure process. The imidazolyl N,C-chelate dark isomer exhibits a consecutive photochromism phenomenon, namely an interconversion between azaboratabisnorcaradiene and azabenzotropilidene derivatives. The calculated mechanism for this bares an interesting resemblance to that of the “walk” rearrangement in norcaradiene. / Thesis (Ph.D, Chemistry) -- Queen's University, 2014-06-23 20:55:20.399

This thesis describes three types of reactions that were carried out using iridium catalysts. The first type is the iridium-catalyzed asymmetric hydrogenation of olefins. In paper I, the preparation of a new type of bicyclic thiazole-phosphine based iridium complex was described. The new catalysts have displayed high activity and enantioselectivity in the asymmetric hydrogenation of unfunctionalized olefins. Papers II and III focus on the expansion of the substrate scope for the iridium catalyzed asymmetric hydrogenation in which a number of heterocyclic olefins were evaluated. In paper IV, the enantioselective asymmetric hydrogenation of α, β-unsaturated esters was described. The chiral products bearing tertiary stereogenic centers obtained by hydrogenation have great synthetic value and have been used in the synthesis of pharmaceuticals as well as in the total synthesis of natural products. The second type is the asymmetric isomerization of allylic alcohols. In paper V, both cis and trans primary allylic alcohols were isomerized to the corresponding β-chiral aldehydes in high enantioselectivities by an N,P-chelating iridium complex. The third type is the selective mono-N-alkylation of amines with alcohols. In paper VI, a phosphine/NHC based iridium catalyst was synthesized and applied in the alkylation of amines. It is the first time that this type of transformation is carried out at room temperature.

Thesis (Ph. D.)--University of Nevada, Reno, 2007. / "August 2007." Includes bibliographical references. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2008]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.

Thesis (M.S.)--Bowling Green State University, 2005. / Document formatted into pages; contains ix, 79 p. : ill. Includes bibliographical references.

M.Sc. (Chemistry) / At Sasol the zeolite catalyst HZ-1 is used to isomerize short-chain hydrocarbons. In this reaction unwanted organic acids are also formed. This investigation has as focal point the interaction between one of these acids, n-butyric acid, and the catalyst. This experimental study consisted of kinetic experiments with a continuous reactor as well as a pulse reactor. In addition to this, temperature programmed desorption was used ...

M.Sc. (Chemistry) / Please refer to full text to view abstract