Masters Degrees (Chemistry)

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2,4,6-Trichloro-1,3,5-triazine as a triorthogonal chemoselective linker.
(2019) Rotimi, Sheyi Ebenezer.; Albericio, Fernando.; Garcia de la Torre, Beatriz.
Abstract available in PDF.
A highly efficient, low-cost, and sustainable method of water purification and desalination using solar-driven interfacial evaporation.
(2024) Nnaeme, Esther Uchechukwu.; Van Zyl, Werner Ewald.; Bissessur, Ajay Bissessur.
Water scarcity has become one of the most daunting global challenges, and as a result, a continuous supply of potable water has become a bane to most societies. Techniques such as distillation and reverse osmosis have been adopted in the production of potable water but these processes are energy-consuming and highly expensive making them less attractive to many households. A viable economical technique is the removal of salt from seawater or brackish water through a solar distiller. This research was based on the design of a low-cost and new improved solar distiller which was made up of a wooden basin and an inclined glass cover. In the basin is contained sea or brackish water and photothermal materials which include recycled materials that act as an insulation material, an evaporation structure, and a solar absorber. These photothermal materials were designed and fabricated to meet with the current state-of-the-art method of evaporation which is solar interfacial evaporation. The fabricated materials were characterized using scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The solar distiller and photo thermal materials were evaluated for their efficiencies via real-time outdoor experiments using solar energy. The rate of evaporation was calculated, while parameters such as pH, conductivity, Total dissolved solids (TDS) and salinity were analyzed on the freshwater collected and compared with the standard of drinking water by the World Health Organisation (WHO) and South African National Standard (SANS241). Heavy metal concentration in the water samples and remediated water collected were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES) and compared with the WHO and SANS241 standards as well. The findings could provide adequate and affordable potable water to all households irrespective of societal status and it will reduce the cost of health management, as many diseases associated with consumption of untreated water can be drastically reduced. This is in-line with South Africa’s National Development Plan (NDP) 2030 and the United Nations’ Sustainable Development Goals (SDGs).
A phytochemical and elemental analysis of senecio serratuloides DC, and its antidiabetic potential.
(2024) Gumede, Andile.; Koorbanally, Neil Anthony.; Moodley, Roshila.; Mshengu, Bongiwe Pridesworth.
Senecio serratuloides DC, from the Asteraceae, has been widely used in South African traditional medicine for the treatment of various conditions such as swollen gums, chest pains, sores, cuts, burns and ulcers. This study was conducted to determine a chemical profile of the plant, both in terms of the secondary metabolites and essential and toxic elements contained in the plant. The plant extracts were further tested for their antibacterial (minimal inhibitory concentrations) and antidiabetic potential (α-amylase and α-glucosidase inhibitory activity). The phytochemical analysis of the leaves and stems resulted in the isolation of the sterols, β- sitosterol (S1) from the stems, and stigmasterol (S2) and stigmasterol glucoside (S3) from the leaves. A further rare sterol, 18α-ursa-12,20(30)-dien-3β-ol (S4) was also isolated from the leaves. Three flavonoids, quercetin (S5), quercetin-3-O-glucoside (S6) and hesperidine (S7) were also isolated from the leaves, along with an aromatic acid, caffeic acid (S8). Extracts of the plant showed good in vitro antidiabetic activity, with the methanol extract from the leaves exhibiting the highest activity against α-glucosidase and α-amylase. However, the extracts did not exhibit any significant antibacterial activity in the assays carried out. The elemental analysis of the plant indicated a decreasing order of Ca > Mg > Zn > Fe > Co > Cu > Cr > Mn > Ni > As > Se. The leaves also showed good quantities of vitamin C, with an appreciable amount being extracted during the cooking phase. The results also show that moderate consumption of the leaves pose no probable threats of metal poisoning. The extracts obtained from S. serratuloides DC were found to have no antibacterial activity. This is surprising, since some of the isolated compounds were reported to have shown some antibacterial properties, however, these may have been too low to have any significant effect in the crude extracts.
Amino-, amido- and oxy-bipyridyl complexes of copper, ruthenium, molybdenum and rhodium.
(1996) Bernardis, Francesco Luigi.; Haines, Raymond John.
The work described in this thesis concerns the synthesis and study of the coordination behaviour of the 6-anilino-2,2'-bipyridyl (Habipy), 6-N-methylanilino-2,2'-bipyridyl (mabipy), 6-piperidyl2,2'.- bipyridyl (pipbipy) and 2,2'-bipyridin-6-one (Hobipy) ligands. Chapter one reviews the coordination chemistry of the 2-aminopyridyl (Rap), 2-hydroxypyridyl (Hhp) and the 2-(2-pyridyl)-I,8-naphthyridine (pynp) ligands. These ligands are closely related to Habipy, mabipy, pipbipy and Hobipy in that they share a common NCN or NCO fragment. Thus the review of their coordination behaviour provides insight into the expected coordination of the Habipy, mabipy, pipbipy and Hobipy ligands. The synthesis and characteristaion of the novel Habipy, mabipy and pipbipy ligands are reported in Chapter two. X-ray crystal structure determinations of mabipy and pipbipy reveal that the geometry about the exocyclic nitrogen atom in both ligands is nearly planer, suggesting substantial overlap of the nitrogen lone pair orbital with the 1t electron system of the bipyridyl rings. In both mabipy and pipbipy the N3-C 10 bond lengths are shorter then normal N-C single bonds. In Chapter three -the synthesis and characterisation of copper(I) complexes containing mabipy, pipbipy and Habipy, and a copper(II) complex containing mabipy are reported. The copper(I) complexes have the general formula [Cu(l12-L)2r, where L= mabipy 1, pipbipy 2 or Habipy 3. The structures of complexes 1 and 2 are determined by X-ray crystallography. In complexes 1- 3 the bipyridyl fragments of mabipy, pipbipy and Habipy chelate while the exocyclic nitrogen atoms remain free. The crystal structures of 1 and 2 reveal that the exocyclic nitrogens have a planar geometry as was the case in the uncoordinated ligand. The crystal structure of [Cu(1l2-mabipY)2f+ (4) is determined by X-ray crystallography and is very similar to that of the copper(I) species. Coordination of the mabipy ligand in 4 is the same as that in 1 and the exocyclic nitrogen in 4 is also planar. The redox couple 4/1 is shown to be electrochemically reversible with EV2= 0.45 V. In Chapter four the synthesis and chararcterisation of dinuclear complexes containing the Ru2 2+, Ru/+, Mo24+and ~4+ cores are reported in which the abipy ligand bridges two metal centres. The complexes [Rulll-L)lCO)4], where L= abipy 5 or obipy 6, were synthesised by the r~action of the free ligands with [{RuiCO)102CCH3)2}n] in toluene. The structures of5 and 6 are determined by X-ray crystallography and show the ligands bridging the Ru(I) atoms in a head to tail fashion and occupy mutually cis positions about the octahedral Ru(I) atoms. The Ru-Ru separations in 5 and 6 are 2.668(1) and 2.671(1) A respectively. The reaction of Habipy with [Rui02CCH3)4CI]n was found to afford the mixed valence species [Ruill-abipy)(02CCH3)3CI] (7), the structure of which is determined by X-ray diffraction methods. The structure of7 reveals one abipy ligand bridging the two ruthenium atoms as in 5. The Ru-Ru separation in 7 is 2.294(2) A. The reaction of [Moi02CCH3)4] with habipy in methanol affords (Moill-abipy)(02CCH3)3] (8). The structure of 8 is determined by X-ray diffraction methods and reveals one abipy ligand bridging two quadruply bonded molybdenum atoms which have a Mo-Mo separation of 2.094(2) A. The [Rhlll~abipy)(02CCH3)iH20)] (9) is formed from the reaction of [Rh i02CCH3)4] with Habipy in methanol. The structure of [Rh2(Il-abipy)(02CCH3)iNCPh)] is determined by X-ray diffraction methods and shows the abipy ligand bridging two Rh(II) atoms which are separated by 2.399(1) A. This chapter is concluded with a discussion of the possiblity of substitution of more than one acetate ligand by the abipy ligand in terms of 'hard' and' soft' acid-base theory and synthetic methods.
Amperometric determination of selected persistent organic pollutants and heavy metals using horseradish peroxidase biosensor.
(2010) Nomngongo, Philiswa Nosizo.; Ngila, Jane Catherine.
Persistent organic pollutants and heavy metals are released into the environment through different anthropogenic processes. They are of concern because they tend to bioaccumulate in the food chain and show adverse health effects ranging from acute to chronic toxicity. These pollutants need therefore to be monitored to conserve the environment. Conventionally, samples are sent to a laboratory for analysis by standard techniques such as chromatography and spectroscopy. Although these conventional techniques display high accuracy and low detection limits, they are expensive, require the use of highly trained personnel and tedious sample preparation. In comparison, electrochemical methods such as biosensors are sensitive, low cost and simple to operate. In this thesis, the determination of selected persistent organic pollutants (polybrominated diphenyl ethers, polybrominated biphenyls and polychlorinated biphenyls) and heavy metals (Cd, Pb and Cu) was achieved by the use of amperometric inhibition biosensor based on horseradish peroxidase (HRP) immobilized on the surface of platinum-polyaniline modified electrode. Polyaniline (PANI) film was electrochemically deposited on the platinum electrode surface. The film was characterized by cyclic voltammetry and spectrometric techniques. The CV results proved that the PANI was electroactive and exhibited a fast reversible electrochemistry. Characteristic Ultraviolet–Visible and Fourier Transform Infrared features of the polymer film were identified. They revealed that PANI film synthesized in this study is the conductive emeraldine salt. Horseradish peroxidase based biosensor was constructed by electrostatic attachment of the enzyme onto Pt-PANI electrode surface. Spectrometric and cyclic voltammetric results indicated that the immobilized HRP retained its bioelectrocatalytic activity towards the reduction of hydrogen peroxide. The Pt/PANI/HRP biosensor showed a linear response over a concentration range of 0.05 to 3.17 mM with a detection limit of 36.8 nM. Apparent Michaelis- Menten constant ( app M K ) was calculated as 1.04 mM. This implied that the HRP biosensor had a high affinity for H2O2. Furthermore, the fabricated biosensor showed high sensitivity, good reproducibility, repeatability and long-term stability. The Pt/PANI/HRP biosensor was applied to the determination of selected persistent organic pollutants and heavy metals. The latter was found to inhibit the HRP enzyme’s activity. The percentage inhibition of the investigated persistent organic pollutants decreases in the following order: 2,2´4,4´,6-pentabrominated diphenyl ether> 2-brominated biphenyl> 2-chlorinated biphenyl> 2,2´,4,5,5´-pentachlorinated biphenyl> 2,4,4´-trichlorinated biphenyl. In the case of heavy metals, the degree of inhibition of heavy metals was highest for Cd2+, followed by Cu2+ and then Pb2+. Kinetic study for the amperometric response to H2O2, recorded in the absence and presence of persistent organic pollutants and heavy metals revealed that for polybrominated diphenyl ethers, the inhibition process corresponded to a competitive type whereas for polybrominated biphenyls, polychlorinated biphenyls and heavy metals, it corresponded to the on-competitive type. The biosensor exhibited high sensitivity towards the determination of the metals and persistent organic pollutants as pollutants in real water samples, namely tap water and landfill leachate samples.
The analysis of organometallic compounds using SFC-ICPMS.
(1994) Blake, Earl.; Raynor, Mark W.; Cornell, David H.; Ross, Graham.
Supercritical fluid chromatography has recently been coupled to an ICPMS detector. The method has been shown to be suitable for the speciation and analysis of organometallic compounds at trace levels. This study has attempted to further the research initiated by other groups in this field by developing a new interface for coupling these two instruments. The new interface makes use of a modified join between the nebuliser and the torch in the ICP unit. The effect of the mobile phase on the plasma with time has been investigated and little spectral background interference has been observed. The chromatographic conditions were optimised using a flame ionisation detector and a series of tin, arsenic, iron, and mercury compounds were analysed using SFC-ICPMS. Mter focusing the ICP-MS on the element of interest, each compound was evaluated in terms of the change in peak intensity with change in concentration and the theoretical detection limits were compared to the practical detection limit. The restrictor temperature was determined using a rough calibration procedure with bench top experiments. The effect of the restrictor temperature on the peak intensity of each compound was then studied. All results were plotted and a theory for the observed trends and observations is proposed. The results obtained and the interface used have been compared to the results and interfaces of other groups and differences have been explained. Attempts to extract relevant compounds from topsoil using supercritical fluid extraction were made. Finally, sediment samples were collected from relevant points in Durban Bay and an attempt was made to extract these samples using supercritical fluid extraction. The extracted samples were analysed using SFC-ICPMS although little success was obtained. Reasons for the failure of this method on the real samples have been proposed. In the concluding section of this study SFC~ICPMS has been evaluated in terms of its future applicability and use as a viable analytical method.
An analysis of Sappi Saiccor's effluent streams.
(2003) Ismail, Fathima.; Marsh, Jeremy J.; Mulholland, Dulcie Aca.
SAPPI SAICCOR is a pulp and paper mill situated in Umkomaas, 50 kms south of the port of Durban in South Africa. It was the first company to produce high grade dissolving pulp from the Eucalyptus tree and is currently the world's largest manufacturer of chemical cellulose. SAICCOR is one of the few pulp and paper mills that produces its dissolving pulp by the acid sulphite process using both calcium and magnesium as bases in the form of calcium bisulphite and magnesium bisulphite. Four streams of effluent are produced during their process, namely, the calcium spent liquor, the magnesium pulp condensate and two streams from the bleaching stages. An acid hydrolysis of the effluent streams yielded a range of organic compounds such as lignans and lignin - type precursors as well as a triterpenoid. Column chromatography and thin layer chromatography, using various ratios of hexane, dichloromethane, ethyl acetate and methanol, were carried out in isolating and purifying the compounds. The structures of these compounds were determined using NMR spectroscopic and mass spectrometric techniques.
Analysis of skin preparations.
(2015) Navondo, Funani Thelma.; Martincigh, Bice Susan.
Abstract available in PDF file.
Analysis of targeted pharmaceuticals and metabolites at a wastewater treatment plant in KwaZulu-Natal, South Africa.
(2022) Inarmal, Nikitha.; Moodley, Brenda.
Globally, surface water bodies are shown to be severely contaminated by chemical compounds as a result of human activity. Some of these compounds are inclusive of pharmaceuticals and their metabolites which are classified as emerging contaminants (ECs). A major contributor to this pollution event is treated wastewater effluent. This is an area of growing concern, particularly for emerging economies, due to an increase in demand for clean and potable water arising from rapid urbanisation and significant population growth. In South Africa, there is limited information outlining concentrations of various pharmaceuticals in treated wastewater effluent and surface water bodies and there is currently no legislation indicating maximum concentrations to be allowed in wastewater effluent. This research study aimed to identify and quantify concentrations of selected pharmaceuticals and metabolites present at various stages within the Wastewater Treatment Plant (WWTP). Additionally, the study aimed to determine seasonal pharmaceutical trends in relation to SARS-CoV-2 (COVID-19) and influenza infections, removal efficiencies and undertake an environmental risk assessment (ERA). The pharmaceuticals that were analysed included metformin, caffeine, sulfamethoxazole hydroxylamine, sulfamethoxazole, nevirapine, prednisolone, valsartan, rifampicin, 17α ethinylestradiol (EE2) and ivermectin, all of which being pharmaceuticals that are commonly prescribed for the treatment of medical conditions that are prevalent in South Africa and for the treatment and prevention of COVID-19. Analyte concentrations were assessed in wastewater samples taken from the inlet, balancing tank, secondary effluent, and maturation river over three sampling seasons. Analytes were extracted using a solid phase extraction (SPE) method and extracts were analysed using liquid chromatography – mass spectrometry (LC – MS). Method percentage recoveries ranged from 73.53 – 100.70% while limit of detection (LOD) and limit of quantification (LOQ) overall ranged from 0.0330 – 0.886 mg L-1 and 0.0990 – 2.68 mg L-1, respectively. Analyte concentrations quantified in inlet samples ranged from 0.007587 – 1.243 mg L-1 while balancing tank concentrations ranged from 0.007599 – 1.042 mg L-1. Secondary effluent and maturation river concentrations ranged from 0.0005244 – 0.9483 mg L-1 and 0.0002507 – 0.9286 mg L-1, respectively. Non-detection of certain analytes in some samples could imply the possibility that the pharmaceutical converted into transformation products and thus evaded detection. Influent pharmaceutical concentrations showed distinct seasonal variation, and this was statistically shown using a one-way ANOVA analysis. P-values were recorded as < 0.05 for caffeine, sulfamethoxazole hydroxylamine, sulfamethoxazole, EE2 and ivermectin, thus implying that significant differences were observed between seasonal levels of pharmaceutical compounds and in relation to the COVID-19 and influenza infection peaks. Analyte removal efficiencies based on the plant treatment processes ranged from 7.70 – > 99.99 %. The ERA performed indicated ratios within the range of 0.0863 and 10.5x 108, which is of significant concern as values greater than 1 would severely impact the health of aquatic organisms and ecosystems within the receiving surface water body.
Analytical and biochemical studies of selected seaweeds obtained from the eastern coast of South Africa`s Indian Ocean in KwaZulu-Natal.
(2015) Magura, Judie.; Jonnalagadda, Sreekantha Babu.; Moodley, Roshila.
Abstract available in PDF file.
Antidiabetic compounds from Hypoxis colchicifolia and Terminalia sericea.
Cumbe, Jaime Tomás.; Van Heerden, Fanie Retief.
In this project two medicinal plant species, namely Hypoxis colchicifolia Bak (Hypoxidaceae) and Terminalia sericea Burch. (Combretaceae), have been investigated and different compounds isolated and characterised. The aim of this study was to investigate the phytochemistry and antidiabetic activity of H. colchicifolia and T. sericea. H. colchicifolia (H. latifolia) is after H. hemerocallidea (African Potato) the second most important Hypoxis medicinal species with commercial value in South Africa. From the methanol extract of the corms, four phenolic derivatives, hypoxoside, a mixture of dehydroxyhypoxoside A and B and bis-dehydroxyhypoxoside were isolated, as well as an environmental impurity bisphenol A diglycidyl ether. This is the first study on the isolation of the dehydroxyhypoxoside B. The methanol extract of H. colchicifolia showed glucose lowering effects and low toxicity in vitro against C2C12 muscle cells and Chang liver cells. Of the pure compounds, only the mixture of dehydroxyhypoxoside A and B showed an increase in glucose utilization by the muscle cell line C2C12. T. sericea is an important plant in traditional medicine and is in the top 50 most important African medicinal plants. From the methanol extract of the roots, one known compound, sericic acid, was isolated. The methanol extract of T. sericea roots showed an increase in glucose utilization by C2C12 muscle cells and Chang liver cells but the extract also showed some cytotoxicity towards these cells. Structural elucidation of the different compounds was achieved by using NMR spectroscopy in one and two dimensions, high-resolution mass spectrometry, infrared spectroscopy and ultraviolet spectroscopy.
Antioxidant activity of Maillard reaction products.
(1994) Devchand, Kamlashkumar.; de Muelenaere, H. J. H.
The use of natural antioxidants to improve the oxidative stability of food lipids has received special attention because of the worldwide trend to avoid the use of synthetic food additives. A wide range of natural sources has been shown to contain antioxidant properties, these include plant extracts, herbs and spices, citrus fruits, oilseeds and legumes. Some antioxidants have been found to be fonned during the heat processing of foods, including the Maillard reaction products that are formed by the reaction of amino acids, peptides and proteins with reducing carbohydrates. A study was undertaken to investigate the antioxidant activity of Maillard reaction products fonned during extrusion of soyabeans. A preliminary oxidation study carried out to identify a suitable substrate revealed that sunflower oil stripped of antioxidants was a suitable substrate with a low induction period of 15 minutes via the Rancimat Method and 4.5 hours via the method of Ross and de Muelenaere. Methyllinoleate was found to be sensitive to oxidation, but not readily available and costly. Storage test of antioxidant stripped sunflower oil under various headspace conditions showed that the substrate stability was best at 4°C under nitrogen or vacuum. Under such conditions the product could be stored for a period of 136 days. Nitrogen was chosen as the most suitable for this exercise as it was not easy to remove all residual air from the samples by vacuum. Furthermore with nitrogen headspace residual 02 could be measured based on Ni02 ratio changes. Hexane solvent was found to be able to remove all lipids from soyabeans. Under the experimental conditions practised it was found that the induction periods for extruded and unextruded soya flour hexane extracted lipids were very similar. Addition of glucose or fructose to the extrusion mixture increased induction period of hexane extracted lipids by 37.5% and 1.5% respectively as measured by the Ross and de Muelenaere method and by 50% and 6.5% respectively as measured by the Rancimat Method. Available lysine of glucose containing extrudate was reduced by 69% while that of the fructose containing extrudate was reduced by 23%. Residual glucose and fructose analysis of extrudates showed that 66% of glucose was utilized in the formation of the Maillard reaction products while only 21% of fructose was utilized during extrusion processing. Comparison of induction periods of soya glucose and soya fructose extrudates to induction period of TBHQ antioxidants (200ppm) in antioxidant stripped sunflower oil gave antioxidant activity of 86ppm and 9ppm for soya glucose extrudates and soya fructose extrudates respectively. The observed antioxidant activity of Maillard reaction products could be utilized with success in different types of processed foods without the need for extensive testing as required for synthetic antioxidants but supplementation of lysine may be required to maintain nutritional balance.
Application of analytical chemistry and waste minimisation techniques in a paint drier plant.
(2009) Rasalanavho, Muvhango
Environmental sustainability, strict Municipal bylaws, ever-increasing waste disposal
Application of analytical chemistry to waste minimisation in the powder coating industry.
(2005) Moodley, Kuveshnie.; Spankie, Sally A. R.
A local company instituted a new chemical procedure in their spray phosphating system used in the pretreatment of large components for industrial racking systems. An inorganic conversion coating is deposited on the workpiece surface during phosphating and this prepares the surface to receive an organic top-coat. The organic coating is applied to the workpiece surface in the form of a powder and cured to form a continuous film about 80 u.m thick. The solution chemistry of the phosphating system was monitored by sampling and chemical analysis and taking direct reading instrumental measurements on the process and rinse solutions. The process was also evaluated using the results of a waste minimisation audit. This involved gathering data on composition, flow rates and costs of inputs and outputs of the process. Two types of information were collected and used during the audit, namely chemical monitoring (concentration levels of Na, Fe, Zn, Mo, Mn and Cr and measurements of conductivity, TDS, SS and pH) and water usage data on the Phosphating Line and existing data (raw materials, workpieces and utility inputs as well as domestic waste, factory waste and scrap metal outputs). The data were analysed using four established waste minimisation techniques. The Scoping Audit and the Water Economy Assessment results were determined using empirically derived models. The Mass Balance and the True Cost of Waste findings were obtained through more detailed calculations using the results of the chemical analysis. The results of the audit showed that the most important area for waste minimsation in the Phosphating Line was the (dragged-out phosphating chemicals present in) wastewater stream. According to the scoping audit, water usage had the third highest waste minimisation potential behind powder and steel consumption for the entire powder coating process. While the scoping audit and the specific water intake value showed that water consumption for the process was not excessive, it did not indicate that the pollution level in the rinse waters was high. Further, drag-out calculations showed that drag-out volumes were typical of those found in the metal finishing industry. However the presence of high levels of metal species in the rinse waters was highlighted through the chemical monitoring of the Phosphating Line. The True Cost of Waste Analysis estimated potential financial savings for the effluent stream at about R8000 for a period of 105 days. However this does not take into consideration the cost of the liability associated with this stream when exceeding effluent discharge limits (given in the Trade Effluent Bylaws) or of the chemical treatment necessary to render this stream suitable for discharge to sewer. Intervention using only "low-cost-no-cost" waste minimisation measures was recommended as a first step before contemplating further areas for technical or economic feasibility studies. However, a further study involving monitoring the sludge was recommended in order to establish the potential financial savings offered by this waste stream.
Application of chemical analysis as an aid to waste minimisation in the electroplating industry.
(2009) Mudaly, Prenesha.; Southway, Colin.; Spankie, Sally A. R.
A chromium plating line used by a local company was monitored to identify any potential waste minimisation opportunities. Plating of the workpiece surface is carried out by immersing the workpiece in seven process (treatment) solutions including nickel and chromium plating baths. Between each process step the workpieces are rinsed. The chromium plating process was evaluated using the results of a waste minimisation audit. This involved gathering data on the composition, flow rates and costs of the inputs of the process. Two types of data were collected namely new and existing data. The new data included chemical monitoring (concentration levels of Ni, Cr, Na, S, B, P, Si, Fe, Cu, Zn, Pb as well as conductivity, TDS, SS and pH measurements) and water usage data. The existing data included raw materials, utility inputs, composition of process solutions and product outputs. The data were analysed using three established waste minimisation techniques. The Water Economy Assessment (a form of Monitoring and Targeting) results were determined using an empirically derived model. The Water Balance and True Cost of Waste results were obtained through more detailed calculations using the results of the chemical analysis. The results from the audit showed that the water usage on the chromium plating line has the highest waste minimisation potential. The True Cost of Waste analysis showed there is no significant chemical wastage in the effluent stream. The potential savings of the effluent stream was negligible (approximately R10 for 238 days). Drag-out calculations were also performed and showed that the drag-out volumes were in good agreement with the typical volumes found in the metal finishing industry. Intervention using simple lowcost and no-cost waste minimisation opportunities were recommended as a first step before contemplating further focus areas for technical or feasibility studies.
Application of cobalt complexes containing SNS ligands as catalysts for biomimetic paraffin activation.
(2012) Komarsamy, Lynette.; Bala, Muhammad Dabai.; Friedrich, Holger Bernhard.
A series of SNS ligands have been successfully synthesised and characterised by IR, NMR and MS. The ligands are divided into two groups and represented by the general formulae: 2,6- bis(RSCH2)pyridine [R= methyl, ethyl, butyl, cyclohexyl, phenyl] and bis(RSCH2CH2)amine [R= ethyl, butyl, decyl]. Cobalt complexes of the respective ligands with the general formulae Co[2,6-bis(RSCH2)pyridine]Cl2 and Co[bis(RSCH2CH2)amine]Cl2 were synthesised and characterised by IR, elemental analysis and X-ray crystallography (for selected complexes). Thus, to investigate the electronic and steric effects of the ligand structure on the chemistry and reactivity of the complexes, the substituents bonded to the two sulfur donor atoms were sequentially varied and two different nitrogen sources were chosen. Crystal structures of Co[2,6- bis(CH2SCH2)pyridine]Cl2 (Ia), Co[2,6-bis(CH2CH2SCH2) pyridine]Cl2 (IIa) and Co[2,6- bis(CH2CH2CH2CH2SCH2)pyridine]Cl2 (IIIa) were obtained. It was found that complex Ia exists as a molecular dimer linked through two chloride bridges resulting in an octahedral geometry around each metal centre, while complexes IIa and IIIa are monomers exhibiting a trigonal bypyrimidal geometry. The complexes were tested as catalysts for the activation of paraffinic C−H bonds towards the formation of oxygenated products: octanol, octanone, octanal and octanoic acid from the substrate n-octane. Gas chromatography was utilised to quantify the products formed and also to calculate the conversion and selectivity of each catalyst system. The catalytic testing revealed that the ketone products were the most dominant with selectivities of ca. 90%. The catalyst that was the most active was Co[bis(CH2CH2SCH2CH2)amine]Cl2 (Ib) with a total n-octane conversion of 23%.
Application of metallocenes for the synthesis of multiwalled carbon nanotubes.
(2016) Ngidi, Nonjabulo Philile Dominica.; Nyamori, Vincent Onserio.; Owaga, Bernard Omondi.
Abstract available in PDF file.
An application of modern analytical solution techniques to nonlinear partial differential equations.
(2014) Augustine, Jashan M.; Sibanda, Precious.
Many physics and engineering problems are modeled by differential equations. In many instances these equations are nonlinear and exact solutions are difficult to obtain. Numerical schemes are often used to find approximate solutions. However, numerical solutions do not describe the qualitative behaviour of mechanical systems and are insufficient in determining the general properties of certain systems of equations. The need for analytical methods is self-evident and major developments were seen in the 1990’s. With the aid of faster processing equipment today, we are able to compute analytical solutions to highly nonlinear equations that are more accurate than numerical solutions. In this study we discuss solutions to nonlinear partial differential equations with focus on non-perturbation analytical methods. The non-perturbation methods of choice are the homotopy analysis method (HAM) developed by Shijun Liao and the variational iteration method (VIM) developed by Ji-Huan He. The aim is to compare the solutions obtained by these modern day analytical methods against each other focusing on accuracy, convergence and computational efficiency. The methods were applied to three test problems, namely, the heat equation, Burgers equation and the Bratu equation. The solutions were compared against both the exact results as well as solutions generated using the finite difference method, in some cases. The results obtained show that the HAM successfully produces solutions which are accurate, faster converging and requires less computational resources than the VIM. However, the VIM still provides accurate solutions that are also in good agreement with the closed form solutions of the test problems. The FDM also produced good results which were used as a further comparison to the analytical solutions. The findings of this study is in agreement with those published in the literature.
Application of N-doped TiO₂/Bi₂O₃/rGO nanocomposites as a photoanode material in dye- sensitized solar cells.
(2021) Ngwenya, Simphiwe Ntokozo.; Nyamori, Vincent Onserio.; Martincigh, Bice Susan.
Abstract available in PDF.
Application of the Noyori annulation reaction to the cephalotaxine spirocycle.
(2001) McKenzie, Jean Mary-Anne.; Gravestock, David.; Robinson, Ross Stuart.
Cephalotaxine is a naturally occurring alkaloid which is the structural motif of a number of compounds which have shown promising anti-cancer properties. This fact together with its relatively complex pentacyclic structure, which incorporates an azaspirocycle annular to a benzazepine moiety, has resulted in its popularity as a synthetic target. The aim of this project was to synthesise the azaspirocycle of cephalotaxine using a Noyori annulation method involving the reaction of an enamine and an a,a' -dibromo ketone in the presence of Fe2{CO)9. In the first attempt the reaction of l-benzyl-2-methylenepyrrolidine (117) with methyl 2,4-dibromo-3-oxobutanoate (116) proved to be unsuccessful, the electron withdrawing ester functionality of methyl 2,4-dibromo-3-oxobutanoate (116) being unable to stabilise the intermediates formed during the reaction and thus resulting in its failure. Reaction of l-benzyl-2-methylenepyrrolidine (117) and 2,4-dibromo-3-pentanone (114) resulted in the formation of an azaspirocycle though in an extremely poor yield and the reaction was deemed inefficient for the synthesis of the cephalotaxine spirocycle. Finally, reaction of 2-(l-benzyl-2-pyrrolidinylidene)acetonitrile (129) and 2,4-dibromo-3-pentanone (114) resulted in the successful synthesis of a novel azaspirocycle. The product, l-benzyl-7,9-dimethyl-8-oxo-1-azaspiro[4.4]nonane-6-carbonitrile (130), contained four stereogenic centres and one of the diastereomers was successfully crystallised out. The X-ray structure in conjunction with NOESY NMR experiments showed the relative stereochemistry to be 5s', 6s', 7s', 9s'. Significant progress was made in the application of this methodology to the construction of the cephalotaxine pentacyclic skeleton with the synthesis of a novel lactam, 1-[2-(6-iodo-I,3-benzodioxol- 5-yl)ethyl]-2-pyrrolidinone, being achieved. In the course of this work a novel compound, 2-(6-Iodo-1 ,3-benzodioxol-5-yl)ethyl 4-methylbenzenesulfonate (98), was also synthesised and its X-ray structure revealed it to be conformationally interesting. As a result a conformation analysis study was carried out on this compound as well as 2-(6-Iodo-I,3-benzodioxol- 5-yl)ethyI 4-nitrobenzenesulfonate (15a). The Noyori annulation reaction was not implemented in the route to the basic pentacyclic structure of cephalotaxine due to time constraints, however synthesis of analogues of cephalotaxine and other alkaloids possessing azaspirocycles should now be possible based on the methodology developed in this project.

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