M.Tech. (Microbiology) / Please refer to full text to view abstract

Organic semiconductors (OSCs), compared to the more traditional silicon, are enticing materials for the fabrication of optoelectronic devices (e.g., transistors, photovoltaic cells, light-emitting diodes) due notably to the lower cost associated with their preparation and purification, as well as their increased solubility in solvents which can accommodate large-scale fabrication. However, a higher degree of molecular disorder typically results in lower performance than silicon and remains an issue to be adressed. As the structure of an OSC is crucial to its performance, understanding the nature of this structure-property relationship is key to further the field of OSCs. In this regard, this thesis explores the optoelectronic properties of different π-conjugated organic frameworks which incorporate sulphur and nitrogen atoms along the rigid conjugated backbone for their desirable impacts on charge mobilities and stability. After a brief review of both small-molecule OSCs as well as key experimental techniques employed in the course of this work, chapter three covers the synthesis and characterization of dithiatetrazocines (DTTA), electron-deficient sulphur-nitrogen heterocycles, which were functionalized with various (oligo)thienyls pendants. The impact of both the substitution patterns and the degree of conjugation on the optoelectronic and solid-state properties of the ring system was investigated. The fourth chapter expands on previous work from the Brusso group that focused on extending the 2D conjugation of tetrathienoanthracene. While oligothienyls were previously shown to effectively increase the degree of conjugation, little to no change in device performance were observed, which was ascribed to disorder of the rotatable pendants. Here, rigid thieno[3,2-b]thiophene was used instead to increase both the degree of conjugation while maintaining structural rigidity, as assessed by optical, electrochemical and theoretical studies. The fifth chapter introduces preliminary work toward expanding the electron-deficient hexaazatrinaphtylene core with thiophene rings. The resulting concentric donor-acceptor structure promotes luminescent behavior with pronounced emission solvatochromism. Optical measurements were performed before and after intramolecular cyclization of the thiophene rings, to study the impact of aromatization on the optoelectronic properties of the system.

Please read the abstract in the section front of this document / Thesis (PhD (Chemistry))--University of Pretoria, 2006. / Chemistry / unrestricted

Pentafluorosulfur (VI) bromide (SF5Br) adds to olefins of the form CX2=CX2, where X= H or F, with the pentafluorosulfur group usually adding to the carbon with more hydrogens attached to it. This series of compounds was used in an attempt to prepare the corresponding sulfonic acid hydrates of the general formula SF5CX2CX2SO3H·nH2O, in order to have these compounds tested as possible fuel cell electrolytes. The reaction scheme involved reflux of the SF5Br adduct with an equimolar amount of sodium sulfite in 50% ethanol for two days, followed by acidification of the recovered solid material using HCl or H2SO4.

Part I describes the preparation of a number of useful intermediates from the sultone F5SCHCF2OSO2 (1). These intermediates include the following: the ketene F5SC(SO2)=C=O (21), the unique sultone F4S=CCF2OSO2 (23), and various ionic intermediates of the form Y+ [F5SC(SO2F) COX]-. These intermediates play an important role in providing new pathways for preparing fluorosulfonic acid precursors. Fluorosulfonic acids are excellent candidates to improve the efficiency of environmentally safe fuel cells. It was possible to obtain new derivatives of 1 by various reactions of 21, 23 and the ionic intermediates, but it was not possible to introduce an alkyl substituent with either of the intermediates. Part II is concerned with the synthesis of SF5 containing epoxides as possible monomers. When polymerized, materials of high dielectric strength and high chemical resistance should be obtained. The reaction chemistry of one of the epoxides was investigated and it was found that all reactions studied were accompanied by the loss of the SF5 group. Thus, it was not possible to obtain any polymeric materials. Part III deals with the synthetic accessibility of SF$\sb5$ malonic esters and thence of SF$\sb5$ acrylic esters. These compounds should serve as building blocks in the synthesis of SF$\sb5$ containing pyrimidines. The CF3 analogue, 5-trifluoromethyl uracil, is used as an antiviral drug. In order to synthesize either SF5 malonic ester or 2-SF5 acrylic ester an SF5 group has to be introduced at a secondary carbon. A secondary SF$\sb5$ compound could be synthesized (F5SCH (COOC2H5) (CHBrOAc)) but could not be converted to the respective malonic ester F5SCH (COOC2H5) compound. Part IV describes the reactions and preparations of Parts I-III.

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Equilibrium exchange constants were calculated for exchange of sulphite with other sulphur compounds. The equilibrium constant for sulphur Isotope exchange between sulphate in solution and solid calcium sulphate was calcu­lated and measured experimentally. In the chemical reduc­tion of sulphate to sulphide S^32O-4 reacted 2.5% faster than S340-4 , in agreement with the calculated kinetic isotope effect for the step sulphate to sulphite. The isotope effect in the reduction of sulphate by Desulphovibrio desulphuricans was found to vary from 0.0 to 2.5% The results were inter­preted on the basis of a mechanism involving two consecutive steps, pick-up of sulphate and reduction of sulphate to sul-phite, competing for control of the rate. The isotope effect in bacterial reduction of sulphite was studied briefly. / Thesis / Doctor of Philosophy (PhD)

yes / A simulation was conducted using Aspen HYSYS® software for an industrial scale condensate stabilization unit and the results of the product composition from the simulation were compared with the plant data. The results were also compared to the results obtained using PRO/II software. It was found that the simulation is closely matched with the plant data and in particular for medium range hydrocarbons. The effects of four process conditions, i.e. feed flow rate, temperature, pressure and reboiler temperature on the product Reid Vapour Pressure (RVP) and sulphur content were also studied. The operating conditions which gave rise to the production of off-specification condensate were found. It was found that at a column pressure of 8.5 barg and reboiler temperature of 180°C, the condensate is successfully stabilised to a RVP of 60.6 kPa (8.78 psia). It is also found that as compared to the other parameters the reboiler temperature is the most influential parameter control the product properties. Among the all sulphur contents in the feed, nP-Mercaptan played a dominant role for the finishing product in terms of sulphur contents. / The full text will be available at the end of the publisher's embargo, 12 months after publication.

Yes / A simulation was conducted using Aspen HYSYS® software for an industrial scale condensate stabilization unit and the results of the product composition from the simulation were compared with the plant data. The results were also compared to the results obtained using PRO/II software. The results show that the simulation is in good agreement with the plant data, especially for medium range hydrocarbons. For hydrocarbons lighter than C5, the simulation results over predict the plant data while for hydrocarbons heavier than C9 this trend is reversed. The influences of steam temperature and pressure, as well as feed conditions (flow rate, temperature and pressure) for the product specification (RVP and sulphur content) were also investigated. It was reported that the operating conditions gave rise to the production of off-specification condensate and it was also found that the unit could be utilized within 40–110% of its normal throughput without altering equipment sizing and by the operating parameters.

Ore specimens from the cupriferous zone of the basal Nonesuch shale at the White Pine Mine were analysed for sulphur isotopes, carbon and sulphide contents and boron. The results of the analyses were discussed in relation to a biogenic-syngenetic mineralization process for the ore body. A model, based on the δS³⁴sulphide frequency distribution, was developed to determine the δS³⁴ sulphate value of the lower Nonesuch paleoenvironment. A transmitted light microscopic examination of chlorite was undertaken in order to present a more complete picture of this proposed source for copper in the cupriferous zone of the Nonesuch shale. / Thesis / Master of Science (MSc)