Doctoral Degrees (Chemistry)

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    Phytochemistry and quorum sensing inhibitory studies of four vernonia species growing in Nigeria.
    (2017) Aliyu, Abubakar Babando; Moodley, Brenda.
    Abstract This thesis contains the phytochemical analysis of four medicinal Vernonia species growing in Nigeria and used in ethnomedicine to treat a variety of medical conditions. The four Vernonia species studied were Vernonia blumeoides, Vernonia perrottetii, Vernonia ambigua and Vernonia glaberrima. The thesis also contains a comprehensive review of the sesquiterpene lactones from the genus Vernonia, their structural diversity and biosynthetic considerations. For each of the plants, the crude extracts and selected compounds were tested for their antibacterial activity using the traditional disc diffusion and broth microdilution as well as anti-quorum sensing assays. Three of the four plants studied yielded sesquiterpene lactones, Vernonia blumeoides yielded four novel eudesmanolide sesquiterpene lactones (blumeoidolides A-D), Vernonia perrottettii yielded a novel keto-hirsutinolide 13-acetoxy-1(4β),5(6)β-diepoxy-8α-(senecioyloxy)-3-oxo-1,7(11)-germacradiene-12,6-olide B1 and the known keto-hirsutinolide 13-acetoxy-1,4β-epoxy-8α-(senecioyloxy)-3-oxo-1,5,7(11)-germacratriene-12,6-olide B2 and Vernonia ambigua yielded a novel glaucolide sesquiterpene, 5,6-dehydrobrachycalyxolide. The structures of the sesquiterpenes were determined from their 1H, 13C and 2D NMR spectra along with mass spectra. The crystal structure of one of the eudesmanolide sesquiterpenes allowed the configuration of the stereocentres in the molecule to be determined. In addition to the sesquiterpene lactones, some common sterols and flavonoids were isolated from the plants: stigmasterol was isolated from V. blumeoides, lupeol was isolated from V. blumeoides, V. ambigua and V. perrottettii and lupeol acetate from V. ambigua and V. perrottetti. The flavonoid apigenin was found in V. blumeoides, V. perrottetti and V. glaberrima, luteolin in V. blumeoides and V. perrottetti, velutin in V. perrottetti and V. glaberrima and chrysoeriol in V. ambigua and V. glaberrima. Chrysin was found only in V. blumeoides and luteolin 3',4'-dimethyl ether in V. glaberrima. Several of the isolated sesquiterpene lactones showed good anti-quorum sensing inhibition (QSI). QSI ≥80% was obtained for blumeoidolide A at a concentration ≥ 0.071 mg mL-1, blumeoidolide B (≥ 3.6 mg mL-1) and B1 (1.31 mg mL-1), QSI ≥75% for B2 (0.33 mg mL-1) and QSI ≥84% for 5,6-dehydrobrachycalyxolide (2.6 mg mL-1). The sterols, lupeol and lupeol acetate, were also found to have QSI ≥84% at 2.6 mg mL-1. Molecular docking studies carried out on blumeodolides A-D in the binding sites of CviR and CviR' (transcription activator proteins) suggested that these molecules are able to bind to certain domains in the target protein, thus eliciting an effect. The current work adds to the library of sesquiterpene lactones from the genus Vernonia and provides some lead compounds to antibacterial activity via quorum sensing inhibition.
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    NCC-based SERS substrate: fundamentals, preparation and applications.
    (2018) Ogundare, Segun Ajibola.; Van Zyl, Werner Ewald.
    This study reports the isolation and characterization of nanocrystalline cellulose (NCC) produced from discarded cigarette filters (DCF). The DCF were processed into cellulose via ethanolic extraction, hypochlorite bleaching, alkaline deacetylation, and then converted into NCC by sulphuric acid hydrolysis. The morphological structures of the isolated NCC, established with TEM, showed that the nanocrystals were needle-like with length in the range of between 62–258 nm. FEGSEM showed the morphological transition of the micro-sized DCF to a self-assembled NCC, while EDX revealed the presence of Ti (as TiO2) in DCF, which was retained in the NCC. A NCC sample that was freeze-dried showed a specific surface area of ~8 m2/g. The crystallinity of the NCC film and the freeze-dried samples were ~97% and ~94%, respectively. Crystallite sizes of the freeze-dried (8.4 nm) and film (7.6 nm) samples correlated with the mean width (8.3 nm) of the NCC, observed with the TEM. The isolated NCC was used in the dual role as a reducing- and stabilizing agent in the formation of silver nanoparticles (AgNPs). By this method, a notable size variation of the synthesized AgNPs was found over the pH range of between 5–10, ranging from 4.61 nm at pH = 9 and increasing to 19.93 nm diameter at pH = 5. The size and yield of the AgNPs were also affected by the reaction time and concentration. The spherically shaped AgNPs induced a localized surface plasmon resonance (LSPR) at around 416 nm. The Ag content in the dry AgNPs was 81.9 wt%, which correlated with 82.1 wt% mass left at 600 ºC. Further analysis showed that the dry AgNPs were macroporous with reduced surface area and porosity upon calcination. The sensitivity of the AgNPs showed excellent surface-enhanced Raman scattering (SERS) of riboflavin. The limit-of-detection (LOD) for riboflavin, based on a signal-to-background ratio of 3:1, was found to be 3 x 10-7 M. The intensities of SERS signals increased with increase in concentration. In addition, clusters of AgNPs were synthesized with NCC isolated from Whatman cellulose filter paper, which behaved as a dual reducing- and stabilizing agent, and Stӧber silica (SiO2) provided a suitable anchoring surface. The synthesized nanocomposite (AgNPs/SiO2/NCC) was evaluated as a substrate for surface-enhanced Raman scattering (SERS) of malachite green (MG) and compared with AgNPs/NCC nanocomposite. The FTIR spectra of both nanocomposites showed a weak carbonyl band (1754 cm-1), indicating partial oxidation of the NCC. The UV-vis spectrum of AgNPs/NCC showed a narrow peak at 412 nm, characteristicof LSPR of monodispersed AgNPs. However, this peak was broad with a shoulder at 490 nm in the spectrum of the AgNPs/SiO2/NCC, which indicated clustering of the plasmonic nanoparticles. TEM micrographs showed that the plasmonic nanoparticles were monodispersed with a mean diameter of 19.5 nm in AgNPs/NCC, while they aggregated into clusters on SiO2 in AgNPs/SiO2/NCC resulting in an approximately 20 nm increase in the mean diameter of the SiO2. The SEM/EDX spectra and XRD diffractograms of the nanocomposites showed Ag as the predominant element. The SERS performance of the nanocomposites was evaluated by using MG as a probe, showed AgNPs/SiO2/NCC as a superior substrate with significant improvement in intensities of Raman peaks of MG and high sensitivity as the LOD was 0.9 nm, while AgNPs/NCC showed a LOD of 5.2 nm, based on a signal-to-background ratio of 3:1. This result underscores the huge contribution of SERS “hot spots” as AgNPs assembled into clusters in contrast to monodispersed AgNPs in the absence of SiO2.
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    Production of nanocellulose composites and catalytic and microbial applications.
    (2018) Moodley, Vashen.; Van Zyl, Werner Ewald.
    This study describes the preparation, isolation, characterization and application of polysaccharide based nanocrystalline cellulose (NCC) from two source materials (filter paper and bleached pulp). The isolated NCCs were utilized as a composite/support material. Hydroxyapatite (HAp), titanium(IV) oxide (anatase phase, TiO2) and biologically synthesized silver nanoparticles were chosen as the preferred candidates for the incorporation of NCC into their respective matrices, which allowed for the preparation of three new materials. These newly prepared composites were applied in catalytic and anti-microbial studies. NCC formed the basis of this investigation and was prepared via a common acid hydrolysis treatment, using sulfuric acid as the preferred acid hydrolytic medium. The isolated NCCs were obtained in reasonable yields and were characterized using the following techniques: ATR-FTIR, XRD, TEM, HRTEM, FEGSEM equipped with EDX detector, TGA/DTA, NTA (zeta potential) and BET. The rod-shaped particles revealed a high crystallinity, small crystallite sizes and good thermal stabilities. These results led to use the prepared NCC’s as a composite material in the pursuit to prepare a new class of materials with a potential array of applications. The preparation of HAp and subsequently the NCC/HAp (in varied wt%) composite allowed for the use of this newly synthesized material as a versatile catalyst. The catalyst was well characterized and used in the preparation of the two-component one-pot synthesis of triazolidine-3-one derivatives. Preliminary reaction optimization established that the 40 w/w% NCC/HAp composite catalyst returned the best results. The eleven new triazolidine-3-one derivatives (4a - 4k) were synthesized in good yields and maintained good atom economy. The catalyst proved to be an effective tool in this protocol with the supplementary advantage of being recyclable. This approach to organic multicomponent reactions (MCRs) proved to be a cost-effective strategy and allowed for an easy work up with environment-friendly reaction conditions. Compared to non-catalytic protocols this approach required shorter reaction times. With the prospect of employing the optical properties of the prepared NCC, TiO2 was then considered for the use in the second newly prepared composite material as a potential photo-catalyst. The NCC/TiO2 material was synthesized in varying wt% and was characterized via a number of optical, spectroscopic and microscopic techniques to establish if it possessed the potential to be used as a photo-catalyst. Proceeding this evaluation, the NCC/TiO2 material was used in the solar-driven photo-degradation mineralization of o-chloranil (2,3,5,6-tetrachloro-2,5-cyclohexadiene-1,4-dione), a commonly used pesticide. The successful decomposition of o-chloranil led to the identifiable products to 2,3-dichloro-4,5-dioxohex-2-enedoic acid (DCA), 2,3-dioxosuccinic acid (DSA) and oxalic acid (OA). This proved that the 20 w/w% NCC/TiO2 composite could be employed as a successful photo-catalyst, and in particular that NCC could be used as a successful composite material together with TiO2. The rate of degradation was influenced by various parameters such as substrate concentration and photo-catalyst loading. The intermediate product (DCA) formed during the decomposition process was assumed to slow down the progression of the reaction and provided a useful insight into the degradation pathway of the contaminant. The final study demonstrated the synthesis of silver nanoparticles (AgNPs) via a biological (phyto-mediated) route using Lippia javanica plant extract (LPE). The preparation of the colloidal AgNPs involved a variation in the LPE (100 – 400 μL) and AgNO3 (1 – 10 mM) concentration to determine the ideal morphology of AgNPs formed. This biosynthetic approach proved successful in the formation of AgNPs in colloidal form, with superior advantages over the chemical formation. These AgNPs were used in several applications as demonstrated with the inclusion of NCC as a support. Samples were characterized via optical, spectroscopic and microscopic analyses, with the ideal colloidal solution C9 (400 μL LPE, 10 mM AgNO3) established as providing the greatest number of AgNPs with the lowest size. This colloid was chosen for the further incorporation of NCC. NCC (filter paper source) was then incorporated into the quasi-spherical shaped nanoparticle matrix and further characterized, analysed and applied as a catalyst to the synthesis of benzylidene-bis-(4-hydroxycoumarin) derivatives and as a potential bactericidal agent. All colloidal samples were biologically tested against 5 bacterial strains and demonstrated good activity, however, samples with the highest concentration of AgNPs were chosen for further Minimal Bactericidal Concentration (MBC) testing. The results showed that all samples were superior in relation to their anti-biotic counterparts used as standards. Sample C9e (1000 mg NCC, 4 mL of LPE in 10 mL of 10 mM AgNO3 and made up to 50 mL), proved to be an efficient catalyst for a three-component reaction. This led to the catalytic preparation of nine benzylidene-bis-(4-hydroxycoumarin) derivatives (6a – 6i).
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    Catalytic ring-opening polymerization of cyclic esters to biodegradable polyesters using N,N'- and N,O-ligand supported Cu(II), Mg(II) and Zn(II) complexes.
    (2018) Munzeiwa, Wisdom.; Owaga, Bernard Omondi.; Nyamori, Vincent Onserio.
    Over the past decades, there has been a tremendous increase in market demand for polyesters and their co-polymers. Of interest, polycaprolactone (PCL) and polylactides (PLA) which are biodegradable have found widespread applications in the packaging and biomedical fields. Polyesters are produced via ring-opening polymerization (ROP) process using metal-based metal-catalyst/initiators, with industrial production relying on tin(II) compounds. Despite the intense research efforts devoted to this area, there are still considerable limitations. For example, in case of chiral lactides monomers very few catalytic systems are capable of stereoselective synthesis. In addition, there is also lack of control of the polymerization process to curb side reactions which results in low molecular weight polymers with broad molecular distributions. Furthermore, the toxicological effects associated with tin compounds pose a danger if polymers are applied in the biomedical field since it is difficult to completely remove remnant catalyst from the polymer matrices. Thus, this thesis investigated the synthesis of less toxic metal complexes such as zinc, copper and magnesium supported by strategically designed ligands and their application in ROP. Four different class of ligands were explored as supports namely formamidine, N-hydroxy formamidine, Schiff base phenoxide and chiral amino pyridyl ligands and thirty complexes were synthesized and reported in this thesis. The steric and electronic properties of the ligands were fine-tuned to influence the catalytic activity and the polymer properties. The effect of the nature of the metal—oxygen bond which is prerequisite for ring-opening polymerization was investigated. Complexes with acetate and alkoxide reactive ligands were synthesised where the oxygen was not part of the ligand system. N-hydroxy formamidine and Schiff base phenoxide ligands contain the oxygen heteroatom as part of the ligand backbone. All the complexes polymerized caprolactone and lactides with appreciable activity, however for hydroxy formamidine ligands the polymerization complexes were more active only in the presence of co-initiator. The effect of auxiliary ligands such as acetates, alkoxides was also investigated. The polymerization data showed that catalytic activity depended on the metal identity, steric crowding and auxiliary ligands. Generally, zinc acetate complexes were more active achieving complete monomer conversion within 68 h compared to 120 h for the copper analogues.Magnesium-amino phenolate complexes showed greater activity, attaining 99% monomer conversion in less than 32 h as compared to 55 h for the zinc analogues. The zinc pyridyl alky and alkoxide complexes showed excellent activity, achieving 100% monomer conversion within 1 min at room temperature. Bulk substituents and electron withdrawing substituent resulted in reduced catalytic activity. All catalytic systems produced low molecular weight polymers ranging from 1200 to 10 500 g mol-1 with relatively broad molecular weight distributions and PDIs that lie between 1.2 and 2 pointing to semi-living polymerization. Chiral ligand supported catalysts showed good stereoselectivity in polymerization of rac-lactide (rac-LA) with Pr values ca 0.70. The role of the solvent was studied, and it was observed that coordinating solvent such as THF retards the polymerization as they compete with the monomer for catalytic active sites. Detailed abstracts are given in each of chapters 3 to 6.
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    Phytochemical, elemental and biological studies of three ficus species (moraceae) found in KwaZulu-Natal, South Africa.
    (2017) Ogunlaja, Olumuyiwa Olufisayo.; Jonnalagadda, Sreekantha Babu
    ABSTRACT Ficus (Moraceae), with over 800 species, is one of the understudied genera in modern pharmacognosy. Rural households depend on their fruits for food while other plant parts such as leaves and bark are utilised for medicinal purposes. Phytochemical analyses and biological activities of different plant parts, as well as the nutritional value of the edible fruits of many of the species are yet to be investigated. This study aimed at investigating three Ficus species (Ficus burtt-davyi, Ficus sur Forssk and Ficus sycomorous Linn) that produce edible fruits and are indigenous to KwaZulu-Natal, South Africa, as a source of secondary metabolites and essential dietary elements, due to their claimed medicinal and nutritional value. Plant material was subjected to chromatographic analyses and isolated compounds were identified using spectroscopic techniques and by comparison with previously reported data. Fruit and soil samples that were collected from sites within KwaZulu-Natal, were digested and analysed for macro, micro and toxic elements by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The phytochemical investigation of F. burtt-davyi revealed the bark to be rich in pentacyclic triterpenoids (lupeol and lupeol acetate) and the known antioxidant flavonoid ((+)-catechin) whilst the leaves were rich in sterols (β-sitosterol, campesterol, and stigmasterol). Both leaves and fruits also contained phaeophytin a, lutein and α-amyrin. This is the first phytochemical report on this species. The cytotoxic results indicated that lupeol and (+)-catechin, the most abundant bioactive compounds in the stem bark, were responsible for its synergistic cytotoxic effects against breast and colorectal adenocarcinoma cell lines. This study supports the use of this plant species as a substitute for antioxidant supplements and as an alternative medicine for oxidative stress related iv non-communicable chronic diseases in vulnerable communities. The phytochemical analysis of F. sur revealed two pharmacologically active triterpenoids (lupeol and sitosterol), one pheaophytin (pheaphytin a) and one flavonoid (epicatechin). The analytical results indicated that the fruits of F. burtt-davyi, F. sur and F. sycomorous are good sources of essential dietary elements and can contribute significantly (p < 0.05) to the recommended dietary allowances (RDAs) for most nutrients. The fruits of F. sur and F. burttdavyi are good dietary sources of Se and Mn, respectively. The concentrations of As, Cd, and Pb were below the instrument detection limits in all three figs indicating that the species do not tend to accumulate these toxic elements. Data from this study showed that metal interactions in soil influenced their availability, but uptake was to a greater extent controlled by the plant. Statistical analyses revealed synergistic relationships in the plants, thereby confirming that uptake of elements is controlled to meet metabolic needs. Overall, this study validates the ethnomedicinal use of these figs and reveals the nutritional and medicinal benefits of consuming the indigenous edible fruits. It also addressed the need for analytical information on the elemental concentrations in indigenous edible fruits consumed in South Africa.
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    Final stage CO removal by oxidation or hydrogenation using supported PGM catalysts for fuel cell applications.
    (2015) Mohamed, Ziyaad.; Friedrich, Holger Bernhard.; Singh, Sooboo.
    Hydrogen has recently become a promising alternative fuel for small scale energy generation with the aid of fuel cells. The most prefered method for on-board production of pure hydrogen from methane is through a series of catalytic reactions. However, prior to entering the fuel cell stack, the CO concentration in the reformate gas must not exceed 10 ppm. Concentrations of CO greater than 10 ppm poison the Pt anode which results in the loss of activity and, the power output. Post water-gas shift reaction, two methods show promise for the effective CO removal to the desired levels of less than 10 ppm. In the first method, known as preferential oxidation (PROX), CO is oxidized to CO2, whereas in the second method, known as selective methanation (SMET), CO is hydrogenated to CH4. The catalysts for these reactions must be highly active and selective for the specific reaction (CO oxidation and/or CO hydrogenation), since unwanted side reactions could result in the additional loss of hydrogen. This study presents the synthesis, characterization and testing of Pt, Ir and Ru supported on reducible oxides, TiO2 and ZrO2, for both the oxidation and hydrogenation of CO in H2 rich streams. The effect of synthesis methods (wet impregnation and deposition precipitation), controlling the isoelectric points of the supports, the nature of the active metals (metal dispersion, particle sizes, CO chemisorption capacities) and the metal support interactions were investigated. The catalysts were characterized by ICP-OES, BET, XRD, XPS, temperature programmed studies, FTIR-CO, CO chemisorption and HRTEM. Catalytic testing of these materials included CO oxidation, CO oxidation in the presence of H2 and the hydrogenation of CO in dry and realistic water-gas shift reformate feeds. All the catalysts showed appreciable activy for the total oxidation of CO below 200 °C, but in the presence of H2, the activity decreased significantly. The Pt and Ir catalysts, although showing low CO conversions, favoured the undesired oxidation of H2, which was due to the strong metal support interactions of these materials, resulting in higher H2 spillover on the supports, reducing them and thus forming H2O. The Ru systems showed slightly better activity but tend to simultaneously hydrogenate CO and oxidize it, which is not selective or desired since increased H2 consumption takes place.CO hydrogenation, on the other hand, showed promising results for all the catalysts in the dry reactions. However, the Pt and Ir systems tested with realistic water-gas shift feeds, which included CO2 and H2O, favoured the forward and reverse water-gas shift reaction, as well as CO2 hydrogenation. The Ru systems showed the best activity towards the selective methanation of CO with realistic feeds at a temperature 100 °C lower than the Pt and Ir systems, giving 99.9 % CO conversions and 99.9 % selectivity towards CH4. CO2 methanation was only observed once all CO in the feed was converted. The superior results of the Ru systems were attributed to the active metal which has a lower heat of CO adsorption and a higher CO dissociative adsorption energy compared to that of Pt and Ir. The CO content in the feed stream was effectively reduced to less than 10 ppm over the Ru catalysts which is crucial for fuel cell applications.
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    Synthesis, characterization and antibacterial activity of benzimidazole Derivatives.
    (2018) Cheddie, Adele.; Koorbanally, Neil Anthony.
    Three series of benzimidazole hybrids were synthesised, two of which contained either thiazolidinone or amino acids tethered to the benzimidazole at C-2 by a phenyl linker and the third contained a thiazolidinone moiety at C-5 on the core structure of the benzimidazole. A total of 35 new compounds were synthesised. Variety was introduced into the molecules by using different benzaldehydes when forming the thiazolidinones or different amino acids substituted on the phenyl linker. Many of the reaction steps were carried out using microwave reactions and in one series, a comparative study was carried out between conventional synthesis and microwave irradiation. In all cases, the microwave methods had many advantages over conventional methods, having shorter reaction times, improved yields and use of green solvents. The synthesized compounds were characterised using mainly Nuclear Magnetic Resonance Spectroscopy and confirmed by High Resolution Mass Spectroscopy. All compounds were tested for their antimicrobial properties against two Gram positive bacteria (Staphylococcus aureus ATCC 25923 and Staphylococcus aureus Rosenbach ATCC BAA-1683 (methicillin resistant S. aureus)) and four Gram negative bacteria (Pseudomonas aeruginosa ATCC 27853, Klebsiella pneumonia ATCC 31488, Escherichia coli ATCC 25922 and Salmonella typhimurium ATCC 14026). A disc diffusion assay was used to first screen the compounds for bacterial activity, followed by the Minimum Bactericidal Concentration (MBC) assay. Among the three series, the thiazolidinones linked to the benzimidazole via the phenyl group at C-2 showed the lowest activity in the mM range. Both the amino acid derivatives linked to the phenyl group at C-2 and the thiazolidinone attached to C-5 of the benzimidazole showed antimicrobial activity in the M range. Although the benzimidazole amino acid hybrids were inactive against the Gram positive bacteria, B7c and B7d (the methionine derivatives) showed excellent inhibitory activity against S. typhimurium (MBC = 0.25 and 0.05 μM respectively), along with compounds B7a (valine derivative) and B7j (tryptophan derivative) which were active against K. pneumoniae with MBC values of 0.27 and 0.10 μM respectively. The benzimidazole–thiazolidinone hybrids, containing a trifluoromethyl group at C-2 and a thiazolidinone group at C-5, showed excellent activity with most compounds exhibiting activity ranging from 3 to over 100 fold higher than the standards. Among these, C3d, C3f and C3j (0.14-35.46 μM), containing bromine and nitro groups, displayed broad range activity against all strains tested. These findings are a major contribution and a good lead to developing new and better antimicrobial drugs.
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    Catalytic ozonation of hazardous halogenated compounds with mixed-metal oxides.
    (2018) Gounden, Asogan Nokan.; Jonnalagadda, Sreekantha Babu.; Singh, Sooboo.
    The study compares degradation of four hazardous halogenated pollutants, namely 2,3-DBP, 1,3-DCP, 2,4,6-TBP and 2,4-DCPA Acid in water, by ozonation alone and catalytic ozonation using Co and Ni loaded on Fe respectively by co-precipitation and a simple mixing method. The brominated pollutants showed a higher reactivity during ozonation than the chlorinated pollutants. In ozonation alone dehalogenation of each compound improved with an increase in the amount of hydroxide ions. TOC removal and DBP minimization was difficult to achieve in ozonation alone, however, in catalytic ozonation with Fe:Co (Co-ppt) and Fe:Ni (Co-ppt) significant improvements were noted. Fe:Ni (Co-ppt) catalyst material showed the best activity for conversion of the pollutants, TOC removal and DBP minimization in water during ozone treatment. BET and SEM data showed that the mixed metal oxides catalyst prepared by coprecipitation had better textural properties than the mixed metal oxide catalyst prepared by simple mixing, hence more superior catalytic activity for degradation of pollutants, TOC removal and DBP minimization, however, Fe:Co (Mixed) was the only catalyst material to effectively minimize bromate formation through lowering of solution pH. The chloride ion was found be refractory towards ozone, which is an added advantage during water treatment processes. NH3-TPD analysis and pZc values reveal that Fe alone has negligible acidic sites, whereas, Fe:Co (Co-ppt) and Fe:Ni (Co-ppt) have more acidic sites than Fe:Co (Mixed) and Fe:Ni (Mixed), hence improved decomposition of ozone to hydroxyl radicals on these active sites. The presence of 𝐻2𝑂2 showed an improvement in the debromination efficiency of 2,4,6- TBP. TOC data indicated that total mineralization of OBP’s occurred in the 𝑂3/𝐻2𝑂2 process, which was not achievable in ozonation alone. Only 10% 𝐻2𝑂2 was able to effectively lessen 𝐵𝑟𝑂3 − formation. In basic water both 2,4,6-TBP conversion and TOC removal decreased with an increase in 𝐶𝑂3 2−, hence minimizing 𝐵𝑟𝑂3 − formation.
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    Synthesis, characterisation and antibacterial activity of new quinoline and quinoxaline hybrid molecules.
    (2018) Sewpersad, Shirveen.; Koorbanally, Neil Anthony.
    This thesis focussed on the synthesis of three series of hybrid molecules, all related to the quinoline or quinoxaline scaffolds. These are (i) 2-(1H-benzo[d]imidazol-2-yl)quinolines, (ii) quinoxaline-chalcones and their pyrazoline derivatives, and (iii) 5-(quinolin-2-ylmethylene)- 2-thioxothiazolidin-4-ones. The target molecules were fully characterized particularly by 2D NMR and verified by high resolution mass spectrometry. The synthesised compounds were tested for their antibacterial activity against two Gram +ve species, Staphylococcus aureus and MRSA and four Gram -ve bacteria, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli and Salmonella typhimurium to identify lead compounds which could be developed into active pharmaceutical ingredients for antibiotics. A total of fifty-six compounds were synthesised based on these scaffolds. The 2-(1H-benzo[d]imidazol-2-yl)quinolines were synthesised by the Doebner-Miller reaction of crotonaldehyde and substituted anilines, followed by oxidation and benzimidazole formation with o-phenylenediamine. The series of compounds consisted of 6- and 8- substituted halogen, methoxy and methyl groups. A complete structural elucidation of all compounds was carried out and the effects that the different substituents had on the resonances of the quinoline scaffold reported. The quinoxaline-chalcone and quinoxaline-chalcone-quinoline hybrids were synthesised from a quinoxaline acetophenone derivative and various 2- or 4- substituted benzaldehydes and 6- or 8- substituted quinoline-2-carbaldehydes via the Claisen-Schmidt condensation. These molecules were then converted to their respective pyrazoline derivatives using hydrazine hydrate. The 5-(quinolin-2-ylmethylene)-2-thioxothiazolidin-4-ones were synthesised from the Knoevenagel reaction of various 8- and 6-substituted quinoline-2- carbaldehydes and rhodanine. The method described is a convenient way to tag a rhodanine moeity onto a quinoline ring.Of the three sets of compounds synthesised, only the quinoxaline-chalcone-quinoline hybrids showed appreciable antibacterial activity, being active against the Gram +ve S. aureus and MRSA and not against the Gram -ve species, with the activity against S. aureus being much higher than that for MRSA. Quinoxaline chalcones showed no activity against the bacterial strains tested, however, when a quinoline moiety replaced the aromatic ring, eight derivatives showed enhanced antibacterial activity, having MBC values between 0.151-0.360 M against S. aureus and 10.9-618 M against MRSA. The quinoxaline-chalcone-quinoline hybrids showed antibacterial activity two orders of magnitude greater than ciprofloxacin and levofloxacin against S. aureus and comparable activity to these standards against MRSA. Interestingly, the 4'-Br and 4'-Cl pyrazoline derivatives of the quinoxaline chalcones (having MBC values of 11 and 12 M, respectively) showed comparable activity to levofloxacin and ciprofloxacin.
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    2D3V electromagnetic particle-in-cell simulations of plasmas having kappa velocity distributions.
    (2018) Abdul, Reginald Francis.; Mace, Richard Lester.
    It is now well established that the kappa distribution is a more appropriate kinetic model for space plasmas than the Maxwellian distribution. In particular it possesses a power-law tail, frequently observed in space plasmas. The research presented in this thesis outlines the development of a two-dimensional electromagnetic particle-in-cell (PIC) simulation code, designed to run on general purpose graphics processing units (GPGPUs), and presents results from simulations of waves and instabilities obtained using it. While PIC simulations are not new, the majority have focussed on the old paradigm of initial particle loadings with a Maxwellian velocity distribution, or one of its variants. Distinguishing this research from previous PIC simulations is the use of the kappa distribution for the initial particle loading. To achieve this, a fast and e cient algorithm for generating multi-dimensional kappa distributed deviates was developed. The code is rst applied to the study of waves in an electron-ion plasma, in a stable equilibrium con guration with a constant background magnetic eld. Both species are modelled by isotropic (a) kappa and (b) Maxwellian velocity distributions. In each case, spectral analysis of the eld uctuations is performed, allowing mode identi cation. For parallel propagation, the maximum uctuation intensities follow the dispersion relations for the L and R modes, respectively, while those at perpendicular propagation follow the dispersion relations for the X, O and electromagnetic electron and ion Bernstein waves. The variation of wave intensity for the oblique angles is also investigated. For the kappa case, this yields new and important information presently unavailable by analysis alone. The e ects of the kappa distribution on wave intensity, as well as its e ect on the dispersion relations of the modes is discussed in detail. The second application is to the simulation of the electron temperature anisotropy driven whistler instability in an electron-ion plasma, where the electron species is modelled by the (a) bi-kappa and (b) bi-Maxwellian velocity distribution. For parallel propagation, the maximum eld uctuation intensities agree well with the dispersion relation for the whistler instability in a kappa plasma. While most of the wave intensity is in the parallel whistler mode, the oblique modes also contribute signi cantly to the overall uctuation spectrum, but their intensities vary with angle of propagation relative to the magnetic eld. The dependence of the growth rate on the index e of the electron kappa distribution is discussed in detail and compared with the well known Maxwellian results. Saturation of the instability via pitch angle scattering, reducing the electron temperature anisotropy, is observed.
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    Synthesis and biological activity of quinoline derivatives.
    (2018) Govender, Hogantharanni.; Koorbanally, Neil Anthony.
    A total of 42 compounds, which include 12 quinoline-3-carboxamides (A5a-l), 15 quinolone thiosemicarbazones (B5a-o) and 15 tetrazoloquinoline phenylhydrazones (C5a-o) were successfully synthesized and characterised. Of these 42 compounds, 36 have been prepared for the first time in this work, with 4 thiosemicarbazones and 2 phenylhydrazones being previously reported. The 2-chloroquinoline-3-carbaldehyde intermediate was the basic scaffold on which the three types of quinoline hybrids were based on. Various substituents were placed at C-6 on this substituent to create small libraries of compounds. This key intermediate was prepared using the Vilsmeier-Haack reaction, which resulted in a quinoline with a carbaldehyde at C-3. In the case of the quinoline-3-carboxamides, the aldehyde at position 3 was oxidized to the acid functionality via the Pinnick Oxidation. This was followed by the preparation of carboxamides using a coupling reaction with different substituted anilines and using the coupling reagents EDC∙HCl and HOBt in the presence of triethylamine used as a base. The thiosemicarbazones were prepared by condensing the 2-quinolone carbaldehydes with thiosemicarbazides and the tetrazolophenylhydrazones prepared by first forming a tetrazolo ring with sodium azide on the quinoline and then forming phenylhydrazones from the carbaldehyde moiety and phenylhydrazines. The quinoline scaffold was varied at C-6 with Cl, F, Br and CH3 groups and the various hybrids were varied again using different anilines, thiosemicarbazides and phenylhydrazines. The structures of the synthesised compounds were elucidated using 1D and 2D NMR spectroscopy. The synthesised compounds were tested for their antibacterial activity against two Gram positive (Staphylococcus aureus and S. aureus Rosenbach (MRSA)) and four Gram negative species, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli and Salmonella typhimurium. Although compounds in all three classes of hybrids showed antibacterial activity, these were not as good as current drugs being used as antibiotics. The synthesised compounds showed antibacterial activity in the range of 0.80 to 36.49 mM.
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    Partitioning studies of polychlorinated biphenyls between aqueous solution and soil and sediment systems of Umngeni river, KwaZulu-Natal, South Africa.
    (2018) Adeyinka, Gbadebo Clement.; Moodley, Brenda.
    The significance of soil and sediment physicochemical properties and the environmental parameters such as pH, temperature, ionic strength, humic acid (HA) and time on the partitioning action of eight selected polychlorinated biphenyl (PCB) congeners were critically evaluated in this study to better understand the mobility, transportation, fate and distribution of hydrophobic organic pollutants in environmental media. Natural soil samples used in this study were collected along uMngeni River of KwaZulu-Natal province of South Africa. The mineral properties of soil samples were determined using the Walkley Black method, barium chloride compulsive exchange method and Brunauer-Emmet-Teller (BET) adsorption-desorption isotherm. All these were employed to observe the surface characteristics of the modeled individual soil particle sizes. Scanning electron microscopy (SEM) equipped with energy disperse X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) were used for the internal morphology and qualitative elemental analysis, as well as identification of possible functional groups in soil samples and commercial HA. Batch adsorption experiments were used for sorption studies. The results revealed that the amount of PCBs sorbed by soil was found to increase with an increase in contact time reaching equilibrium within 8 h. Among the soil chemical properties, soil organic matter was observed to correlate positively and play a more significant role in the sorption of PCBs. Soil samples with highest BET surface areas were related to the soil particle grain size. The sorption of PCBs onto soil was also found to decrease with an increase in the aqueous HA concentrations, and a change in the aqueous concentration of ionic strength was found to be less significant. Other important factors found to be more significant in the sorption were the degree of chlorination as well as stereochemistry of PCB congeners. The more hydrophobic and non-ortho (planar) congeners were found to contribute more significantly to sorption relative to the less hydrophobic and more ortho-substituted (nonplanar) congeners. Moreover, a decrease in the ratio of Si: (Al + Fe) was found to contribute positively to the sorption of PCBs. The kinetic studies on the partitioning of PCBs onto the soils was found to fit best with pseudo-second order, suggesting that the partitioning process of the selected PCBs between aqueous solution and active components in soil, involved more than onestep. Logarithmic values of organic carbon normalized sorption coefficient (log Koc) of the selected PCBs were found to decrease with an increase in the solution pH. The partitioning of PCBs onto the soils was also said to be temperature driven, where low aqueous temperatures encouraged morepartitioning of hydrophobic PCBs onto the soil. The Gibbs free energy (ΔG°) was found to be negative. Therefore, the thermodynamic studies showed that the PCB interaction with soil particle sizes was a spontaneous process. The role of initial PCB concentration on the partitioning was found to be L-type. This indicated that an increase in PCB concentration in the aqueous phase made it more difficult for PCB molecules to find a vacant site available for sorption onto the soil SOM.
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    Synthesis, characterization and antibacterial activity of curcumin and curcumin-like derivatives.
    (2018) Kannigadu, Christina.; Koorbanally, Neil Anthony.
    This thesis consists of the synthesis, characterization and antibacterial activity of three series of curcumin and curcumin-like compounds. The curcumins were synthesised from acetylacetone and benzaldehydes whilst curcumin-like compounds were synthesised from acetone and either benzaldehydes or quinoline aldehydes. The curcumins were derivatised to pyrazolines and the curcumin-like compounds to ketopyrazoles with hydrazine hydrate and to spiro barbiturates with barbituric acid. The spiro barbiturates in turn were converted to oximes using hydroxylamine hydrochloride. A total of 52 new compounds were synthesised in this work. These compounds were characterized using 1H, 13C and 2D NMR spectroscopy and mass spectrometry. Both the ketopyrazoles and the spiro barbiturates contained sterogenic centers. Single crystal XRD was used to determine the configuration of these stereogenic centers, where the pyrazole was found to be in the 5S and the spiro barbiturates in the 7R,11R configuration. The three sets of synthesised compounds was tested for their antibacterial activity against two Gram +ve strains (Staphylococcus aureus and methicillin resistant S. aureus (MRSA)) and four Gram -ve strains (Salmonella typhimurium, Pseudomonas aeruginosa, Klebsiella pneumonia and Escherichia coli). The best activity was seen by the 6-chloro, 6-bromo and 6- methyl derivatives of quinoline ketodienes, which were active against all six strains of Gram +ve and Gram -ve species at 0.98-31.3 g mL-1, with the exception of the 6-bromo derivative having lower activity against S. aureus at 250 g mL-1. This was followed by the curcumin pyrazolines where several compounds showed good antibacterial activity: the 3-Cl pyrazoline showed activity against both the Gram +ve MRSA (31.3 μg mL-1) and Gram –ve K. pneumonia (7.8 μg mL-1), the 2,4-difluoro pyrazoline showed activity against Gram –ve K. pneumonia (0.98 μg mL-1), and the 3-methoxy-4-(4-chlorobenzyloxy) curcumin derivativeand 3-methoxy-4-hydroxy pyrazoline showed activity against both S. aureus and MRSA at 31.3-62.5 μg mL-1. A further compound the 4-trifluoro curcumin pyrazoline was also active against the Gram –ve E. coli with a MBC of 31.3 μg mL-1. Amongst the ketopyrazoles, the chloro derivatives were active at low concentrations with MBC's between 15.6-62.5 g mL-1 against either S. aureus or MRSA. In addition, the 4- bromo derivative was also active against MRSA and the 2-chloro derivative against P. aeruginosa, both with a MBC value of 31.3 g mL-1. In contrast, the spiro barbiturates showed activity against the Gram –ve E. coli and P. aeruginosa with MBC values ranging from 0.98-125 g mL-1. In particular, the 4-bromo derivative showed excellent activity, better than the standards levofloxacin and ciprofloxacin with MBC values of 0.98 g mL-1. Conversion to the oximes resulted in loss of activity against all the Gram –ve bacteria. However the 4-trifluoro and 4-bromo spiro barbiturate oximes showed weak activity against MRSA.
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    Development of efficient and chemoselective quasi-heterogeneous catalytic systems for C-C cross-coupling reactions mediated by Pd/Ce based solidsolution catalysts.
    (2018) Mpungose, Philani Perfect.; Friedrich, Holger Bernhard.; Maguire, Glenn Eamonn Mitchel.
    Construction of carbon-carbon bonds is of pivotal importance in chemistry and their careful assembly can allow complex molecules such as peptides to be created. As a result, the development of carbon-carbon bond forming reactions has turned into an area appreciated by Chemists both in academia and industry. In addition, numerous Nobel prizes in chemistry have been awarded for this area of research. The C-C forming reactions have also facilitated the synthesis of natural products, pharmaceuticals, agrochemicals, conjugated polymers and nanomaterials. In this study, the intention is to synthesize heterogeneous palladium based catalysts that can efficiently catalyze Heck-Mizoroki, Sonogashira and Suzuki- Miyaura C-C cross-coupling reactions. The heterogenisation of these coupling reactions improves their overall efficiency, since it allows for easy work-up and the reusability of the expensive palladium catalysts. In this direction, we used palladium and ceria based solid-solution oxides, PdxCe1-xO2-δ, as heterogeneous nanocrystalline catalysts for the three C-C cross-coupling reactions. The PdxCe1- xO2-δ based solid solution oxides were synthesized in one-step using a ureaassisted solution combustion method. These PdxCe1-xO2-δ solid solution oxides were fully characterized by XRD, ICP-OES, BET, XPS, SEM, EDX, TEM, TGA and Raman spectroscopy. All characterization techniques strongly suggested that Pd2+ was successfully incorporated into the lattice structure of ceria. The effect of reaction conditions on the catalytic properties of the PdxCe1-xO2-δ solid-solution oxide catalysts was studied in detail with the model Heck- Mizoroki, Sonogashira and Suzuki-Miyaura cross-coupling reactions to obtain the optimum reaction conditions for each transformation. Then, a wide range of aryl halides was efficiently coupled to various alkenes or alkynes or boric acids. All the PdxCe1-xO2-δ based solid solution oxide catalysts exhibited high activity and afforded the desired products in good to excellent yields. A careful investigation through a series of suitable tests clearly showed that the C–C crosscoupling is accomplished via a quasi-homogeneous mechanism by leached palladium(0) species. Characterization of the used catalyst suggests that Pd2+ in PdxCe1-xO2-δ is reduced in situ to Pd0 when employed in the cross-coupling reactions. However, the PdxCe1-xO2-δ catalysts were found to be both recoverable and recyclable.
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    Targeting the tumour extracellular environment through rational modification of the SNX class of HSP90 inhibitors.
    (2022) Mathenjwa, Gciniwe Sindiswa.; Akerman, Matthew Piers.; Veale, Clinton Gareth Lancaster.; Bode, Moira L.
    HSP90 remains a valuable target for cancer therapy. Unfortunately, targeting intracellular HSP90 has proven not to be a viable chemotherapeutic approach. Compensatory HSR induction and HSP70 overexpression are the main limitations of this approach. A growing body of evidence suggests that targeting the extracellular environment would be of advantage and devoid of the drawbacks observed with intracellular HSP90 inhibition. As a result, the development of extracellular HSP90 inhibitors represents a novel opportunity for cancer therapeutics. In view of this hypothesis, we aimed to design and synthesise extracellular inhibitors and to assay these compounds against HSP90. To develop extracellular HSP90 inhibitors, cell-impermeable analogues of the well-developed benzamide HSP90 inhibitor (SNX 2112) were designed, synthesised and biologically evaluated. The desired target compounds were synthesized using developed methodology, as well as modified methodology. In Chapter 3 we compared and evaluated a variety of reported synthetic methods to deliver the analogues of SNX 2112. Interested in a general procedure for the synthesis of our analogues, we initially attempted to afford both the methyl and the trifluoromethyl containing analogues via a β-triketone mediated procedure. Despite the success observed with the methyl analogues, the instability of a trifluoromethyl containing β-triketone, deemed this procedure not feasible for this class of compounds. Our continued effort towards a general procedure led to the investigation of a tosylhydrazone mediated tetrahydroindazolone condensation; unexpectedly attempts to synthesise the methyl containing analogues via this procedure led to a 1—5 nitrogen to carbon tosyl migration, which was further investigated for varying substrates, and these results are explained in detail in this thesis. It then became apparent that each of the reported methods had its merits and shortcomings, there was no one best method, rather the synthetic approach was mainly determined by the C-3 substituent. The key intermediates were then converted into the desired targeted compounds by tethering the HSP90 pharmacophore to flexible alkyl groups, attached to polar sulfonate and phosphonate functionalities. Hypothetically, introduction of polar alkyl groups, would inhibit cell penetration thus limiting them to the extracellular environment. Based on the goals of our study we were interested in three biological evaluations; to confirm that our modified compounds were still capable of inhibiting HSP90s ATPase activity, to evaluate if our modifications reduced intracellular HSP90 activity, whether they stimulated the pro-oncogenic HSR, and to evaluate their cytotoxicity. Preliminary biological assessment of our compounds was consistent with our hypothesis. Here we showed that our compounds did not inhibit intracellular HSP90, and did not stimulate HSP70 expression, a marker of induction of the compensatory HSR. Furthermore, our analogues displayed cytotoxicity in the nanomolar range against the HeLa cell line. These preliminary data support the feasibility of targeting extracellular HSP90 as a novel anticancer strategy.
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    Synthesis, characterization and reactivity of metal modified heteropolyacid catalysts for organic transformation reactions.
    (2018) Pedada, Jhansi.; Friedrich, Holger Bernhard.; Singh, Sooboo.
    In the present investigation, eco-friendly, sustainable and recyclable heteropolyacid catalysts have been developed for a series of organic transformations such as the production of ethyl acetate by solvent free liquid phase esterification and the formation of benzaldehyde by the oxidation of styrene and benzyl alcohol. All these reactions were carried out at room temperature. Various metal exchanged heteropolyacid catalysts with different metal loadings were prepared by the ion-exchange method and characterized by spectroscopic and adsorptions methods such as powder X-ray diffraction, scanning electron and transition electron microscopy, 31P NMR spectroscopy, elemental analysis, Bright Field-STEM analysis, infrared spectroscopy, ex-situ pyridine adsorbed infrared spectroscopy, pore size distribution studies and BET surface area measurements to understand their structural and surface properties, together with their acidity and to relate this to the catalytic performance. A series of K and Cs exchanged phosphotungstic acid (PTA) and phosphomolybdic acid (PMA) catalysts were synthesized for the esterification reaction. XRD patterns and infrared spectra showed that the crystallites and characteristic bands of the Keggin ion, respectively, were maintained after exchange of protons in the heteropolyacids with metal at all loadings of the catalysts. From pyridine adsorbed infrared spectroscopy, Brønsted and Lewis acid sites were present on the surface of the catalyst. Bright field STEM analysis showed a uniform distribution of the chemical composition which correlated well with theoretical atomic values of the metal loadings of all the catalysts, verified by ICP results. The efficiency of various metal exchanged heteropolyacid catalysts were assessed for the esterification reaction using various substrates and the Cs exchanged phosphotungstic acid catalysts showed superior activity compared to the other catalysts. In particular, the Cs exchanged phosphotungstic acid with a 1 wt.% loading showed the highest activity and was most tolerant to the presence of water that was produced in the reaction. The catalytic activity showed some correlation to the Brønsted and Lewis acidity, as well as Keggin ion density of catalysts. A series of alkali metal exchanged phosphomolybdic acid catalysts were synthesized by ion exchange, characterized by various physico-chemical techniques and used in the solvent freeoxidation of styrene to benzaldehyde. XRD and infrared results showed that the primary structure of the Keggin ion usually present in phosphomolybdic acid is retained after metal exchange. HR-TEM analysis show a well-constructed spherical morphology of the materials with a lower degree of crystalinity. Type IV isotherms with mesoporous structure are observed from nitrogen adsorption-desorption isotherm studies and ex-situ pyridine adsorption experiments reveal that Brønsted acidic sites increased after metal exchange. The K exchanged phosphomolybdic acid catalysts were most efficient in the conversion of styrene to benzaldehyde and the order of reactivity of the alkali metal exchanged phosphomolybdic acid catalysts was K > Rb > Cs. Insight into the reaction pathway was obtained by investigating the oxidation styrene oxide. The results showed that phenyl acetaldehyde together with benzaldehyde are produced, providing some evidence that styrene oxidation proceeds via C=C cleavage to selectively produce benzaldehyde. The catalyst was easily recovered and was reused for up to three cycles showing stable activity. Copper and zinc exchanged heteropolyacid catalysts were used in the oxidation of benzyl alcohol to benzaldehyde. The Zn exchanged phosphomolybdic acid catalysts showed higher oxidation activity that correlated well with the acidity of the catalysts. The catalysts were synthesized by the ion exchange method and were subjected to X-ray diffraction, infrared spectroscopy, pyridine adsorbed infrared spectroscopy, BET surface studies, 31P NMR spectroscopy and inductively coupled plasma-optical emission spectroscopy to determine its physico-chemical properties. XRD diffractograms showed that crystallites of the Keggin ion of the heteropolyacid were present and were retained after metal modification, as observed by infrared spectroscopy. From pyridine adsorbed infrared, the Brønsted/Lewis acid site ratio increased in the metal exchanged phosphomolybdic acid catalysts, whereas there was a decrease in the ratio for the modified phosphotungstic acid catalysts. 31P NMR spectra results showed that the metal was successfully exchanged with protons and was not incorporated in the primary structure of heteropolyacid catalyst, thus maintaining the Keggin ion. ICP analysis indicated a correlation of the theoretical metal content with the experimental loadings of the catalysts.
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    Detection and quantification of emerging contaminants in Mgeni and Msunduzi rivers by gas chromatography-mass spectrometry in KwaZulu-Natal, South Africa.
    (2018) Gumbi, Bhekumuzi Prince.; Ndungu, Patrick Gathura.; Moodley, Brenda.; Birungi, Grace.
    This work concerns the development, optimization and validation of simple and affordable analytical methods for determination of different classes of emerging contaminants in environmental waters and solids. Occurrence of emerging contaminants in the African environment has received much attention recently. However, there is paucity of detailed analytical methods for determination and regulation of emerging contaminants in the environment and wastewater effluents in South Africa today some parts of the world. The developed methods included, extraction with solid phase (clean-up), ultrasound-centrifuge assisted extraction (sediments), detection with gas chromatography-mass spectrometry (after derivatization of polar analytes) and ecological risk assessment technique associated with emerging contaminants. For all developed methods, recoveries (60% - 130%), R2 (> 0.99) and precisions (< 25%) within acceptable limits were achieved. This study was undertaken to determine the occurrence and concentration of major classes of emerging contaminants (pharmaceuticals, personal care products and stimulants) between 2014 and 2016 in Mgeni and Msunduzi Rivers, KwaZulu-Natal, South Africa. Surface water, wastewater (influent and effluent), sediment and biosolid samples were collected from these rivers and wastewater treatment plants along both rivers. The developed methods were combined and applied to qualitative and quantitative analysis of pharmaceuticals (acidic/ non-steroidal antiinflammatory drugs, antibiotic and hormones), stimulants (caffeine) and personal care products (paraben and triclosan). Approximately 50 emerging contaminants of different classes were detected and only 15 were quantified. Environmental concentration of contaminants were found to range from 0.02 μg L-1 to 68 μg L-1 and 0.12 to 220 ng g-1 in water and sediments respectively. Acidic drugs, antibiotic and hormones were detected in all samples analysed in both water and sediments, however, stimulant and PPC were not detected in some of the samples. Wastewater treatment plants were recognised as one of the main routes of emerging contaminants into the aquatic environment. The developed methods can be used to monitor emerging contaminants in the environment.
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    Synthesis, characterization and application of novel nano-materials for the electrochemical determination of antimalarial drugs.
    (2019) Chiwunze, Tirivashe Elton.; Karpoormath, Rajshekhar.
    ABSTRACT This thesis reports the development of electroanalytical methods applicable for determination of selected antimalarial drugs; primaquine, mefloquine and amodiaquine. The electrochemical behaviour of the drugs were carried out using three differently modified glassy carbon electrodes (GCE) as working electrodes. First working electrode was modified using synthesized gold nano-urchins (AuNU/GCE) and was used for the determination of mefloquine and primaquine separately. The second and third working electrodes were both used for the quantification of amodiaquine and were modified using the following composites; multi-walled carbon nanotubes with poly(methyl orange) (MWCNT/PMO/GCE) and gold nanoparticles decorated graphene oxide with poly-cysteamine (rGO-AuNP/Poly-Cyst/GCE). All measurements were carried out with a Ag/AgCl (3 M KCl)) reference using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) linear sweep voltammetry (LSV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV). The designed sensors showed enhanced voltammetric responses and very low limits of detection which are attributed to the high surface area and high conductivity of the nanomaterials. The proposed sensors also demonstrated practical utility in quantification of the antimalarial drug in pharmaceutical formulations and human urine sample. Thus, the present study demonstrates a promising and alternative approach for clinical analysis and quality control of primaquine, mefloquine and amodiaquine.
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    An experimental study of graphitic carbon nitride-based materials and selected metal-based semiconductors in organic solar cells combined with a computational study of perovskite solar cells.
    (2023) Rono, Nicholas.; Nyamori, Vincent Onserio.; Martincigh, Bice Susan.; Kibet, Joshua K.
    Abstract available in PDF.
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    Synthesis of selective N-heterocyclic scaffolds under green conditions using zirconia supported bimetallic catalysts.
    (2019) Bhaskaruni, Venkata Hanumath Sai Sandeep.; Jonnalagadda, Sreekantha Babu.; Van Zyl, Werner Ewald.
    Abstract available in PDF.