Particle precipitation involves the injection of energetic particles into the ionosphere which could increase the ionisation and conductivity of the upper atmosphere. The goal of this study was to examine the ionospheric response and changes due to particle precipitation in the region over South Africa, using a combination of groundbased and satellite instruments. Particle precipitation events were identified from satellite particle flux measurements of the Defence Meteorological Satellite Program (DMSP). Comprehensive studies were done on the events of 5 April, 2000 and 7 October, 2000. Analysis of the data from the satellite instruments indicates that no particle precipitation was observed over the South African region during these events and that it is unlikely to occur during other such events. To validate the data, methods and tools used in this study, precipitation in the South Atlantic anomaly (SAA) region is used. Satellite ion density measurements revealed that strong density enhancements occurred over the SAA region at satellite altitudes during the precipitation events, but this did not occur in the South African region. The measurements also revealed how the ionisation enhancements in the SAA region correlated with geomagnetic and solar activities. Particle precipitation and convective electric fields are two major magnetospheric energy sources to the upper atmosphere in the auroral and the SAA regions. These increase dramatically during geomagnetic storms and can disturb thermospheric circulation in the atmosphere and alter the rates of production and recombination of the ionised species. Ionosonde observations at Grahamstown, South Africa (33.30S, 26.50E), provided the data to build a picture of the response of the ionosphere over the South African region to particle precipitation during the precipitation events. This analysis showed that, within the confines of the available data, no direct connections between particle precipitation events and disturbances in the ionosphere over this region were revealed.

Thesis (M.Sc. (Chemistry)) --University of Limpopo, 2014 / This study deals with the synthesis and characterisation of cobalt complexes of nitrogen-donor imidazolyl- salicylaldimine ligands and their potential catalytic activity in the oxidation reactions of phenol and styrene. Five ligands were used in the study, four of which are new. Compound 2,4-di-tert-butyl-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1), was synthesised according to a literature procedure. The other imidazole-based salicylaldimine compounds 2-ethoxy-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L2), 4-methoxy-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3), 1{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-benzene (L4) and 4-methyl-1{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-benzene (L5) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3-ethoxy-2-hydroxybenzaldehyde, 5-methoxy-2-hydroxybenzaldehyde, benzaldehyde, 4-methylbenzaldehyde respectively. L1-L5 were characterised by 1H and 13C{1H} NMR, IR and UV-vis spectroscopy and high resolution mass spectrometry (HRMS). Reactions of L1-L5 with CoCl2 yielded complexes C1-C5, while complexes C6-C10 were synthesised by reactions of L1-L5 with CoBr2 all in a ratio of 1:1 of ligand to metal precursor. The cobalt(II) complexes were characterised by IR and UV-vis spectroscopy, elemental analysis and high resolution mass spectrometry due to their paramagnetic nature. All the characterisation data point to complexes C1-C10 being formulated as [Co(3-L)X] (where L = ligand and X = halide). However, single crystal X-ray diffraction showed that the prolonged stay of complex C6 in a solution gave a new structure as complex C11. The imidazole-based salicylaldimine cobalt(II) complexes (C1-C10) were tested as catalysts for the oxidation reactions of phenol and styrene with H2O2, O2 and 3-chloroperbenzoic acid as oxidants. The complexes were found not to be active for the oxidation of both substrates (phenol and styrene) with 0% conversion, even when the reactions were left for 1 week. Analysis of the oxidation reactions were performed with GC and 1H NMR spectroscopy. Both analysis methods showed the presence of unreacted substrates at the end of the reaction period. Effects of concentration of pre-catalysts, substrates and oxidants, time and temperature of reaction and nature of solvent on catalytic activity were also investigated, however the conversions remained at 0% conversion. / Sasol Inzalo Foundation

Thesis (MSc. (Chemistry)) --University of Limpopo, 2014 / This study deals with the synthesis and characterisation of cobalt complexes of nitrogen-donor imidazolyl- salicylaldimine ligands and their potential catalytic activity in the oxidation reactions of phenol and styrene. Five ligands were used in the study, four of which are new. Compound 2,4-di-tert-butyl-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L1), was synthesised according to a literature procedure. The other imidazole-based salicylaldimine compounds 2-ethoxy-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L2), 4-methoxy-6{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-phenol (L3), 1{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-benzene (L4) and 4-methyl-1{[2-(1H-imidazol-4-yl)-ethylimino]-methyl}-benzene (L5) were prepared by Schiff base condensation reaction of histamine dihydrochloride with 3-ethoxy-2-hydroxybenzaldehyde, 5-methoxy-2-hydroxybenzaldehyde, benzaldehyde, 4-methylbenzaldehyde respectively. L1-L5 were characterised by 1H and 13C{1H} NMR, IR and UV-vis spectroscopy and high resolution mass spectrometry (HRMS). Reactions of L1-L5 with CoCl2 yielded complexes C1-C5, while complexes C6-C10 were synthesised by reactions of L1-L5 with CoBr2 all in a ratio of 1:1 of ligand to metal precursor. The cobalt(II) complexes were characterised by IR and UV-vis spectroscopy, elemental analysis and high resolution mass spectrometry due to their paramagnetic nature. All the characterisation data point to complexes C1-C10 being formulated as [Co(3-L)X] (where L = ligand and X = halide). However, single crystal X-ray diffraction showed that the prolonged stay of complex C6 in a solution gave a new structure as complex C11. The imidazole-based salicylaldimine cobalt(II) complexes (C1-C10) were tested as catalysts for the oxidation reactions of phenol and styrene with H2O2, O2 and 3-chloroperbenzoic acid as oxidants. The complexes were found not to be active for the oxidation of both substrates (phenol and styrene) with 0% conversion, even when the reactions were left for 1 week. Analysis of the oxidation reactions were performed with GC and 1H NMR spectroscopy. Both analysis methods showed the presence of unreacted substrates at the end of the reaction period. Effects of concentration of pre-catalysts, substrates and oxidants, time and temperature of reaction and nature of solvent on catalytic activity were also investigated, however the conversions remained at 0% conversion.

In most countries, as many as 15 to 25% of the adult population have raised blood pressure. People with hypertension, and even those with mild elevation of blood pressure, are at an increased risk of cardiovascular disease, whether or not the symptoms are present. The risk of serious cardiovascular disease varies greatly among individuals and is also determined by a variety of concomitant risk factors other than the level of blood pressure. Hypertension develops as a result of disturbances of the body's blood pressure regulating system. The biological activity of the renin-angiotensin systems results from a series of specific enzymatic cleavages leading to the generation of angiotensin II, a potent vasoconstrictor. In the treatment of hypertension, inhibition of the angiotensin converting enzyme is established as one modern therapeutic principle. Angiotensin converting enzyme inhibitors act by inhibiting the conversion of angiotensin I to angiotensin II. The in vitro assay, developed by ELBL and WAGNER (1991) for the detection of angiotensin converting enzyme inhibitors in plant extracts was successfully established during this study. Plants used by traditional healers in South Africa for the treatment of high blood pressure were investigated for their antihypertensive properties, utilizing the established angiotensin converting enzyme assay. Twenty plants were investigated for their angiotensin converting enzyme inhibitory activity. The highest inhibition (97%) was obtained by Adenopodia spicata leaves. A further seven plants exhibited an inhibition greater than 70% and five more over 50%. Plants exhibiting inhibition levels greater than 50% were further tested for the presence of tannins in order to eliminate possible false positives. The leaves of Tulbaghia violacea were chosen for bioassay-guided fractionation in an attempt to isolate the active compound(s). Serial extractions were made of ground Tulbaghia violacea leaves using polar to non-polar solvents to establish the solvent giving optimum extraction of the active compound(s). Distilled H2O was selected as the extractant and a bulk extract was performed on 0.7 kg ground leaves. The extracted residue was partitioned against butanol, fractionated using cation exchange resin chromatography, Sephadex ® LH-20 and high performance liquid chromatography. Fractions collected after each purification step were assayed using the angiotensin converting enzyme assay. Fractions exhibiting high levels of angiotensin converting enzyme inhibition were selected for further purification. The active fraction from the final high performance liquid chromatography step used in this study requires further attention in order to purify and identify the active compound(s). The chromatographic and chemical properties of the compound(s) present in the isolated active fraction are discussed. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1998.

A dissertation submitted to the faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science. / Unable to load abstract.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science August 2017. / Streamwater chemistry is influenced by several factors that include: geology, soil-geology interactions, land use, climate change, topography, vegetation, mechanical and chemical weathering. The dominance of these factors when determining the chemistry of streamwater varies from one situation to the other. Four different catchments in the Drakensberg were monitored to identify the processes determining temporal and seasonal patterns in streamwater chemistry. The land uses of the catchment include: CP03 (previously afforested, degraded), CP04 (pristine grasslands), CP06 (pristine grasslands) and CP09 (protection from fire). All the catchments were investigated for differences in major ion concentrations, streamwater temperatures, dissolved organic carbon (DOC), dissolved oxygen, pH, conductivity. There were comparisons made between historical and recent data collected at the Cathedral Peak Research Site. Comparisons were made between CP03 and CP06 to identify effects of storm events on streamwater chemistry. CP03 and CP09 had significant statistical differences in terms of major ions. Land use and stormflow path ways were most influential in determining the streamwater chemistry across catchments. / LG2018

A dissertation submitted to the Faculty of Science, University of Witwatersrand, in fulfilment of the requirements for the degree of Masters of Science Johannesburg, 2012. / Amplified loads of sulfate and nitrate have caused increased stress on soil systems in many areas of the world, as both are dominant components of acid rain. This is a critical environmental stress due to the damage caused to soil, water quality and ecosystem functioning. Issues concerning the rising emissions of these elements from local industries have begun to attract increasing attention in South Africa, as the rates of deposition in the Mpumalanga Highveld region alone is comparable to those experienced in First World countries. This study sought to investigate the use of natural stable isotopes of sulfur and nitrogen to identify the process transformations that these species undergo in environmental cycles. Total δ34S, δ15N and δ13C isotope signature of soils in the Mpumalanga region were combined with total elemental concentrations to determine the effect of deposition on the soil system. Soil samples from two soil depths (0 – 10 cm and 20 – 40 cm) were taken along a distance gradient from an identified pollution source, the Majuba power station. Long-term air quality data from the study area were also obtained from Eskom’s air quality monitoring stations, as well as sulfur and nitrogen deposition data from selected literature. Elemental concentrations decreased with soil depth as expected, while sites located approximately 25 km downwind of the power station were seen to contain higher concentrations of both soil sulfur and nitrogen. The mean per site soil sulfur concentration across all depths ranged from 0.009 % to 0.048 %, while the mean per site nitrogen concentration across all depths ranged from 0.056 % to 0.346 %. The mean soil carbon concentration in the top-soils ranged from 0.97 % to 7.93 %, and decreased in the sub-soils to 0.490 % to 3.270 %.The mean δ34S value for the top-soils was found to be 8.28 ‰ and increased to 10.78 ‰ in the sub-soils. Soil δ15N also increased with soil depth from 6.55 ‰ to 8.28 ‰. Soil δ13C values were seen to increase from -12.83 ‰ in the top-soils to -11.90 ‰ in the sub-soils. Lighter δ34S values at the surface may be due to anthropogenic deposition. The positive δ34S shift was attributed to a two-source mixing model (atmospheric deposition and bedrock) and isotopic fractionation processes that occur within the soil profile. The δ15N values of the top-soil were higher than what is expected if all nitrogen was derived from atmospheric nitrogen gas fixation. The increase in δ15N with depth suggested that isotope fractionation occurred during nitrogen export due to the faster reaction rate of 14N compared to 15N. The soil δ13C values indicated a typical C4 grassland system. New carbon at the top-soil depths was enriched in 13C due to the slower decay of 13C-depleted lignin; whereas in the sub-soils microbial recycling of carbon dominates and explained the higher 13C content of the older carbon. The conceptual framework presented for this project involves simultaneous processes of deposition and export in the soil system. This was particularly true for sulfur, where sites with lower isotope values had lower soil sulfur concentrations and vice versa. This indicates that high levels of deposition correspond to high net export. The sulfur and nitrogen isotopic signatures could not be used to as a direct means of source identification; however, the effectiveness of isotopes in elucidating transfer of these nutrients in the soil system was illustrated.

Abstract available on PDF file. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1978.

Thesis (MSc. (Soil Science)) -- University of Limpopo, 2015 / There exists a considerable level of spatial variability in soil physical and chemical properties within the research block; and the soils are generally shallow. Of all the measured parameters, electrical conductivity, Bray-1 P, exchangeable potassium, calcium and sodium as well as extractable iron and zinc showed a huge percent of variation across the field. Soil variability maps indicated the degree of variability within the research block. The spatial variability of the characterized parameters was significant across the research block. A correlation study was conducted to investigate the relationship between the measured soil physical and chemical properties. Regular soil analyses should be conducted to avoid failure/delay of experiments. It is recommended that inputs such as irrigation and fertilizer application must be varied based on varying soil conditions across the research block. / VLIR project 6 leaders

The HIV-1 pandemic affects millions of people worldwide with approximately 70% of those affected residing in sub-Saharan Africa (SSA) relying on traditional medicines for treatment. The key aim of the study was to isolate and characterise an active phyto-pharmaceutical ingredient (API) from L. trigonus for use as a vaginal microbicide. The aerial parts of L. trigonus were oven-dried at 80°C, ground and then extracted with boiling water for 30 minutes. Aqueous extracts were screened using an HIV-1 neutralization assay in TZM bl cells. Chromatographic and spectroscopic techniques were used to purify, isolate and identify the API. The API (BP36-117-26464C) was identified as a polymeric macromolecule with IC50 = 0.04 μg/ml against HIV-1 HXB 2 subtype B. This activity is comparable to the ARV drug, enfuvirtide (IC50 = 0.02 μg/ml). The API consists of galacturonic acid polymer and a mixture of seven compounds. Its mode of action may involve inhibiting virus attachment. The activity of this precipitate (BP36-117-26464C) tested against HIV-1 subtype C pseudovirions and shown to compare favorably with that of enfuvirtide (T20). The water-soluble nature of this API and its mode of action identified it as a potential microbicide. In the current form, the precipitate (API) would be difficult to develop as an oral treatment for HIV, as high-molecular weight agents often have poor bioavailability following oral administration. However, large molecules with potent anti-HIV activity are ideal for topical use and potent development as a microbicide. / Life & Consumer Sciences / M.Sc (Life Sciences)