The main goal in my project was find out if the rate of zinc crossing the bilayer was either due to the fluidity of vesicles or the level of oxidation of the vesicles.To measure the oxidation a simple procedure called the TBA Test was used to measure each PC tested. The fluidity measurement was a calculation using the temperature the vesicles went from gel to liquid crystalline phase and the experimental temperature.Measuring the rate at which zinc crossed the bilayer was done using spectral changes that occur as zinc binds with APIII, a metal chelator entrapped inside the vesicles. To measure these rates we used k', the rate constant at which zinc is crossing the bilayer at a certain concentration and k, the second order diffusion rate constant which is the slope of k' vs. [Zn].The rates at which zinc was crossing the bilayer for each PC was then compared to the fluidity and oxidation levels for each PC. There was no direct correlation between the rates and fluidity but there was a good linear correlation between the rates and oxidation.So it seemed as if oxidation was the main reason zinc was crossing the bilayer so we wanted to see if our measurements could be obtained by biological cells. The comparison showed that rates obtained by biological cells can only be matched by the vesicle models when there oxidation levels are found to be high.In conclusion we believe that the reason zinc is crossing the bilayer is due to oxidation that occurs to the vesicle and as oxidation increases so do the rates at which zinc crosses the bilayer. / Department of Chemistry

Ozonation, or advanced oxidation processes (utilising ozone decomposition products as oxidants) are widely used in industrial waste water and drinking water treatment plants. In these applications the use of ozone is based on ozone and its decomposition by-products being strong oxidants. A case study revealed that several waterworks in South Africa successfully utilise ozone as a pre-oxidant for the treatment of raw waters. South Africa holds more than three quarters of the world’s viable chromium ore (chromite) reserves. Subsequently the Cr-related industry-within is considerable in size and a major producer of large volumes of waste materials. Chromium also occurs commonly in other industrial waste materials (e.g. fly ash and clinkers originating from coal combustion) and is a natural occurring element in natural sediments, since chromium is the 21st most abundant element in the earth’s crust with an average concentration of approximately 100 ppm. Considering the abundance of natural and anthropogenic Cr-containing materials in South Africa the possibility exists that some of these materials might be suspended in raw water entering water treatment facilities. In this dissertation, the possible oxidation of non-Cr(VI) Cr-containing materials suspended in water during ozonation, is presented within the context of water treatment applications (Chapter 4). The results indicate that in situ formation of hazardous Cr(VI) is possible during aqueous ozonation. pH had a significant influence, since the decomposition products of aqueous O3, i.e. hydroxyl radicals that form at higher pH levels, were found to be predominantly responsible for Cr(VI) formation. Increased ozonation contact time, water temperature and solid loading also resulted in elevated Cr(VI) concentrations being formed. Occasionally these values exceeded the drinking water standard 50 ppb Cr(VI). The results therefore indicate the importance of removing suspended particulates from water prior to ozonation. Additionally, pH-control could be used to mitigate the possible formation of Cr(VI) during ozonation. In Chapter 5, exploratory work is presented on the possibility of utilising Cr(VI) formation via ozonation as a means of recovering chromium from Cr-containing waste materials. Such a study is of particular interest within the local context, considering the large volumes of waste produced by the Cr-related industry in South Africa. This exploratory work is based on the fact that unlike Cr(0) and Cr(III), most Cr(VI) compounds are relatively soluble in water. Cr(VI) is a carcinogen if inhaled, however the probability of negative health effects are substantially reduced if it occurs in solution. Thus a hydrometallurgical route of recovering Cr-units via Cr(VI) generation represents the safest route with regard to Cr(VI) exposure. Such a hydrometallurgical route could also addresses the limitations of the physical separation methods currently applied, which fails to recover fine Cr-containing solids. The degree of Cr2O3-liberation achieved in this exploratory work was relatively low. However, the Cr2O3-liberation achieved for the ferrochromium slag (15%) indicated some promise, considering the limitations of this exploratory work. Several steps can be considered in future studies, which would in all likelihood improve the Cr2O3-liberation further. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2012

Ozonation, or advanced oxidation processes (utilising ozone decomposition products as oxidants) are widely used in industrial waste water and drinking water treatment plants. In these applications the use of ozone is based on ozone and its decomposition by-products being strong oxidants. A case study revealed that several waterworks in South Africa successfully utilise ozone as a pre-oxidant for the treatment of raw waters. South Africa holds more than three quarters of the world’s viable chromium ore (chromite) reserves. Subsequently the Cr-related industry-within is considerable in size and a major producer of large volumes of waste materials. Chromium also occurs commonly in other industrial waste materials (e.g. fly ash and clinkers originating from coal combustion) and is a natural occurring element in natural sediments, since chromium is the 21st most abundant element in the earth’s crust with an average concentration of approximately 100 ppm. Considering the abundance of natural and anthropogenic Cr-containing materials in South Africa the possibility exists that some of these materials might be suspended in raw water entering water treatment facilities. In this dissertation, the possible oxidation of non-Cr(VI) Cr-containing materials suspended in water during ozonation, is presented within the context of water treatment applications (Chapter 4). The results indicate that in situ formation of hazardous Cr(VI) is possible during aqueous ozonation. pH had a significant influence, since the decomposition products of aqueous O3, i.e. hydroxyl radicals that form at higher pH levels, were found to be predominantly responsible for Cr(VI) formation. Increased ozonation contact time, water temperature and solid loading also resulted in elevated Cr(VI) concentrations being formed. Occasionally these values exceeded the drinking water standard 50 ppb Cr(VI). The results therefore indicate the importance of removing suspended particulates from water prior to ozonation. Additionally, pH-control could be used to mitigate the possible formation of Cr(VI) during ozonation. In Chapter 5, exploratory work is presented on the possibility of utilising Cr(VI) formation via ozonation as a means of recovering chromium from Cr-containing waste materials. Such a study is of particular interest within the local context, considering the large volumes of waste produced by the Cr-related industry in South Africa. This exploratory work is based on the fact that unlike Cr(0) and Cr(III), most Cr(VI) compounds are relatively soluble in water. Cr(VI) is a carcinogen if inhaled, however the probability of negative health effects are substantially reduced if it occurs in solution. Thus a hydrometallurgical route of recovering Cr-units via Cr(VI) generation represents the safest route with regard to Cr(VI) exposure. Such a hydrometallurgical route could also addresses the limitations of the physical separation methods currently applied, which fails to recover fine Cr-containing solids. The degree of Cr2O3-liberation achieved in this exploratory work was relatively low. However, the Cr2O3-liberation achieved for the ferrochromium slag (15%) indicated some promise, considering the limitations of this exploratory work. Several steps can be considered in future studies, which would in all likelihood improve the Cr2O3-liberation further. / Thesis (MSc (Chemistry))--North-West University, Potchefstroom Campus, 2012

The importance of alkyl methacrylates has been firmly established within the chemical industry. For example, free radical polymers, which contain the methacrylate backbone are more rigid than acrylate polymers. Several methods have been reported for the production of alkyl methacrylates. The aim of this project is focused on isolating a phase specific iron phosphate catalyst and thereafter testing its efficacy in oxidative reactions to form ethyl methacrylate in a one step process in the gas phase using a fixed bed continuous flow reactor. The catalyst was characterized by using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) surface area measurements, Attenuated Total Reflection-Infrared (ATR-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Temperature Programmed Reduction (TPR), Temperature Programmed Oxidation (TPO), Energy Dispersive X-ray (EDX) determination, Temperature Programmed Desorption (TPD), Room Temperature X-ray Diffraction (XRD), In situ X-ray Diffraction (In situ XRD), Thermogravimetric/Differential Thermal Analysis (TGA/DTA), Transmission Electron Microscopy (TEM), Mössbauer Spectroscopy and Raman Spectroscopy. A further venture included employing certain of the above techniques to characterize the cesium promoted iron phosphate catalyst as well as the spent catalysts. The catalytic activity of the iron phosphate based catalyst synthesized was investigated for the oxidative dehydrogenation (ODH) of ethyl isobutyrate (EIB) to ethyl methacrylate (EMA). Reaction conditions which were considered included variation in the contact time, co-feeding water at varying contact times, co-feeding ethanol at varying ratios, as well as co-feeding both ethanol and water and catalyst lifetime and regeneration studies. The cesium promoted iron phosphate catalyst was tested at optimal reaction conditions. The findings of the investigation showed that the tridymite-like FePO4 phase was the most suitable precursor to allow for the formation of the active α-phase during catalytic testing. It was found that the catalyst performed optimally at a contact time of 0.8 seconds and the beneficial effect of co-feeding water and ethanol primarily on conversion and selectivity towards EMA respectively, was demonstrated. Optimal results were obtained at a EIB:EtOH ratio of 1:5 with a conversion of 57 % and a yield of 34 mol %. The lifetime and regeneration studies showed that water had a significant effect on the regeneration of the catalyst after a specific time on stream and a shorter time on stream (i.e. 25 hours) prior to regeneration, minimized rapid deactivation of the catalyst. The characterization results obtained for the spent catalysts showed that under the reaction conditions considered with respect to co-feeds, the active α-phase and the Fe2P2O7 phase dominated. The cesium promoted iron phosphate catalyst was synthesized to favour stabilization of the tridymite-like structure. The results showed that a mixture of phases was observed for the synthesized promoted catalysts and there was an increase in EIB conversion as well as EMA selectivity with a decrease in cesium loading. However, the promoted catalyst with the lowest cesium loading (Cs/Fe = 0.10), showed a lower selectivity towards EMA relative to the unpromoted iron phosphate catalyst. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

This work takes a closer look at ceria catalyst synthesis through micelle self-assembly. We compare surfactants, precursors, solvent systems, and doping. The surfactants are the building blocks upon which the ceria can crystallize. The samples are calcinated to test their thermal stability. Characterization is performed using pXRD as well as physisorption. The samples that exhibited a higher thermal stability were characterized to have a high surface area as well as low fluctuations in crystallite size, pore volume, and pore size. Ceria synthesized with cerium (III) nitrate hexahydrate and CTAB in a water:ethanol mixture using sodium hydroxide showed to be the most effective at providing a thermally stable product. Doping the catalyst with titanium increased the thermal stability significantly. Select samples were run in a variety of fuel to oxygen ratios to determine the best conditions in which we could perform partial methane oxidation to recuperate hydrogen gas. Most of the experiments show oxygen depletion with minor changes in other gas levels indicating that there is no oxidation occurring. Curiously the oxygen levels do decrease. There is a possibility that there is a reaction occurring initially at room temperature and being exacerbated with further temperature increase.

The osmium-mediated aminohydroxylation reaction is a powerful oxidation that introduces a hydroxyl group and a protected amino group in a syn relationship across an olefinic double bond. This study concerns one approach to controlling the regioselectivity of this oxidation. Introduction I The mechanism, scope and limitations of the aminohydroxylation reaction are discussed, with particular attention to the asymmetric version, providing a background from which the newly developed methodology has emerged. Results and Discussion I Development of the reaction This section concerns the original attempts to perform the tethered aminohydroxylation reaction, and early process optimisation to maximise the yield of aminohydroxylated product produced. Scope of the reaction This section details the results of the TA reaction as applied to further allylic carbamates demonstrating the applicability of the reaction to other olefinic geometries. The diastereoselectivity of the reaction in cyclic and acyclic systems is reported, and a model to explain the observed results discussed. Also covered within are the syntheses of the various substrates and proof of the stereochemistry of the products. Mechanistic investigations Work involving attempts to isolate a catalytic intermediate from the reaction is described. A crystal structure of this intermediate is discussed. Introduction II The isolation and physiological properties of the antibiotic compound hygromycin A are described. Prior synthetic routes towards this compound are discussed. Results and Discussion II Three approaches towards the aminocyclitol unit of hygromycin A, employing the tethered aminohydroxylation reaction, are outlined. Two of these allow for potential future development and completion of the synthesis.

This thesis describes investigations into the use of electrochemical oxidation as a method for the activation of glycosyl donors, and in particular the application of this technique to the selective activation of one electrochemically active glycoside over another. The synthesis of twenty eight electrochemically active monosaccharide donors, including thio-, seleno- and O-glycosides with varying protecting group patterns and anomeric substituents is described, together with the synthesis of three electrochemically active monosaccharides with the potential to act as both glycosyl donors and glycosyl acceptors. The electrochemical analysis of these monosaccharides is reported and gives a detailed insight into the effect of various factors on the oxidation potentials of the monosaccharide donors and allows some general conclusions to be drawn. In addition the analysis of six monosaccharides by cyclic voltammetry at scan rates of up to 25 000 Vs^-1 allows their homogenous kinetics to be outrun and formal oxidation potentials obtained. Investigations into selective electrochemical glycosylations are reported, and the applicability of the analytical electrochemical studies to synthetic electrochemical reactions is demonstrated. Selective glycosylations are possible with selenoglycoside donors and either thio- or O-glycoside acceptors to give disaccharides. However the selective activation of selenoglycosides over thioglycosides is shown to be complicated by some underlying pathway for indiscriminate activation of both donor and acceptor. In contrast the use of an O-glycoside donor experiences no such problems. More detailed work on the underlying problems experienced with the thioglycoside acceptor was conducted, and the results are reported here. Investigations into electrochemical activation of the disaccharides are discussed, and the thioglycoside is shown to be easily activated to give a trisaccharide. At the time of writing this is believed to be the only electrochemically mediated trisaccharide synthesis reported in the literature. The O-glycoside however is shown to be inactive under the electrochemical oxidation conditions employed.

No description available.

Chapter I contains a brief introduction to the applications of dioxirane chemistry and outlines the mechanistic investigations carried out to date. Chapter 2 describes investigations into the dimethyldioxirane oxidation of para-substituted N,N-dimethylanilines in acetone. The N-oxides were found to be the only products. Relative rates were determined and compared with those of reactions with methyl iodide and other oxidants. The dimethyldioxirane reactions followed the Hammett relationship with a p value of -1.0. The reaction rates are strongly accelerated in the presence of water and the overall reaction mechanism is electrophilic in nature and does not involve free radical species or electron transfer. Chapter 3 looks at the regioselectivity of dimethyldioxirane when used to oxidise several polyfunctionalised nitrogenous drugs with a view to developing a system for use in oxidative degradation studies. The regioselectivity of dimethyldioxirane in the oxidation of polyhydroxy steroids, namely a series of bile acid methyl esters, is discussed in chapter 4. No evidence for preferential oxidation of axial over equatorial hydroxyls or vice versa was seen. Instead the least hindered hydroxyl at C3 was oxidised preferentially with some oxidation also occurring at C6 and C7. Hydroxyls at the sterically hindered C 12 were not oxidised. This provides further evidence for the proposed butterfly transition state. Finally, chapter 5 discusses the use of novel trifluoromethyl aryl ketones as promoters for Oxone®mediated epoxidations. 4-(trifluoroacetyl)benzoic acid was used succesfully and can be readily isolated for re-use by simple base extraction.

The type and extent of surface oxidation of carbon fibres has been determined after electrochemically treating fibres in a variety of electrolyte solutions. The chemical and physical characteristics of these fibres have been evaluated using XPS, SEM, FTIR and UV spectroscopy. The fibres were anodically treated, both in a laboratory and in a commercial type cell. Fibres that have undergone commercial treatment were then incorporated into epoxy composites, the ILSSs of which were then measured. The extent of oxidation and type of surface functionality produced as a result of electrochemical treatment is shown to depend upon several factors, ie the nature of the electrolyte, the anodic potential, reaction time, the structure of the fibre surface, the pH of the electrolyte solution, and the electrolyte concentration. Surface nitrogen functionality is not produced as a result of polarising the fibres in nitric acid. It is produced, however, with treatments in solutions containing ammonium ions. The amount of surface nitrogen depends upon the concentration of these ammonium ions in the solution. In most cases, polarisations in salt solutions produce similar changes in the fibre surfaces as treatment in the acid alone. The presence of bicarbonate ions tend to inhibit fibre surface oxidation. In acidic solutions the fibres are shown to be extensively oxidised. Although the functionality of the oxide layer produced is very similar Ge. consisting of keto- and carboxyl/ester groups) after all the acidic treatments studied, the surface topography of the oxide layer produced is very different. In all cases this oxide layer is loosely bound to the bulk fibre. In general, as reaction time increases, oxidation of the fibre surfaces also increases. Surface oxidation also increases with potential. However at high potentials (-3V) and long reaction times (>15mins) the detected functionality of type 11 fibres decreases. This is thought to be due to the formation of gaseous products such as carbon dioxide. The reactivity of type I and type II fibre is shown to be different. The amount of carboxyl/ester functionality produced is far greater for type 11 fibres. It is concluded that carboxyl functionality is produced at the edge sites and keto-type functionality on the basal planes. The amount of oxidation decreases as the pH increases. In alkaline solutions carboxyl and alcohol groups are produced, (the former being in greater quantities). The physical mechanism of oxidation is also different. Instead of an overall oxide layer being produced (in acidic solutions), holes are produced in the fibre surfaces. These holes are thought to be areas of localised attack. It is also shown, using a small pilot plant, that both galvanostatic and. potentiostatic control of electrolysis are satisfactory in producing treated fibres, which when incorporated into resins form composites with a high ILSS. The ILSS of the composites produced are dependent neither upon the amount of surface oxygen present nor upon the number of carboxyl groups present.