Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / The focus of this study was the pathways for β-alanine production in Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. The major pathway for β-alanine production is the decarboxylation of L-aspartate by L-aspartate-α-decarboxylase (PanD). This enzyme is not essential for the survival for Mtb which implies that an alternative pathway for β-alanine production must exist. We postulated that such a secondary pathway may be based on the oxidation of various polyamines by a polyamine oxidase to give the β-alanine precursor 3-aminopropanal, and therefore set out to find data in support of this hypothesis. Based on sequence homology to the FAD-dependent Saccharomyces cerevisiae polyamine oxidase Fms1, Mtb AofH was identified as a likely candidate. The soluble expression and purification of AofH proved troublesome and lead to the investigation of various techniques to increase protein yield. These methods include fusion to various tags, coexpression with the protein chaperones, addition of scarce codon tRNA’s to the translation mixture and protein refolding. AofH was eventually purified as fusions to the Nus and MBP proteins and its activity determined by analysis of the enzymatic reactions by TLC, reverse phase HPLC, ESI-MS and LC-MS. TLC analysis indicated that 3- aminopropanol formed as a product during polyamine oxidation, but this could not be confirmed by any of the more sensitive analytical techniques. We set out to confirm the presence of the FAD cofactor in the enzyme by various methods and concluded that the AofH fusions did not contain FAD. Efforts to refold the protein in the presence of FAD also failed. From this study it is clear that the biochemical confirmation of the presumed activity of AofH will remain elusive until the enzyme can be purified in its active form, i.e. with FAD bound. A genetic test for activity based on functional complementation studies of Escherichia coli ΔpanD strains proved inconclusive since no difference in growth rate was found between cell transformed with the aofH gene and the negative control. We continued our studies of β-alanine biosynthesis by attempting the design of mechanism-based inhibitors for the PanD enzyme. Various structural analogues were identified and tested by qualitative and quantitative methods. Our results show that β- substituted aspartate analogues may be good potential inhibitors of Mtb’s PanD protein and can thus be used in rational drug design.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / This work focuses on the biocatalytic production of coenzyme A (CoA) analogues with different tether lengths in its pantetheine moiety, and on analogues where the cysteamine moiety has been replaced with a range of other amines. An attempt was made to develop a simple biocatalytic method for the optimum production of such CoA analogues by chemo-enzymatic means. Pantothenic acid ethyl thioesters with different tether lengths were first synthesized as substrates of the CoA biosynthetic enzymes, CoaA, CoaD and CoaE. The acceptability of these compounds as substrates for the pantothenate kinase (CoaA) from prokaryotic and eukaryotic organisms was investigated through kinetic studies. These substrates were subsequently exposed to CoaA, CoaD and CoaE to produce various general CoA synthons (ethyl pre-CoAs). Finally aminolysis of these ethyl pre-CoAs by cysteamine and homocysteamine gave the various CoA analogues of different tether lengths in their pantetheine moiety. The identical production of a second type of CoA synthon (phenyl pre-CoA) from pantothenic acid phenyl thioesters was also investigated as a means to increase reactivity of the thioester substrates. Aminolysis of the phenyl pre-CoA produced the corresponding CoA derivative, but reactivity was lower than expected. A second strategy was also developed where the pantothenic acid phenyl thioesters were first aminolyzed, resulting in various pantothenamide intermediates. Aminolysis was attempted with thiol-bearing amines such as cysteamine and homocysteamine as well as with amines without sulfhydryl functionalities. These pantothenamide intermediates were then used in the biosynthesis of the corresponding CoA analogues by addition of CoaA, CoaD and CoaE. The ideal method of CoA analogue production will utilize a continuous bioreactor system in which these analogues can be prepared on large scale. However, to construct a bioreactor the enzymes involved need to be immobilized on a matrix in order to transform substrate to product. The enzymes CoaA, CoaD and CoaE can be immobilized on cellulose via a cellulose binding domain (CBD) affinity tag. Various types of CBDs were investigated and used in the construction of suitable expression vectors. Optimum expression conditions to obtain soluble CBD-fused enzymes were developed.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Thesis submitted in partial fulfilment for the degree of Master of Science (polymer science) at Stellenbosch University / ENGLISH ABSTRACT: The goal of this study was to synthesize hybrid hydrogels via a chemical crosslinking mechanism through use of chain end functional poly(N-vinyl pyrrolidone)(PVP) with various topologies. The crosslinking chemistries should be benign in nature i.e. at physiological pH ranges and at 37 °C. The degradation products should be biologically tolerable and renal clearance should be possible (< 30 000 g/mol PVP0. PVP of various topologies, controlled molar mass and quantitative chain end functionality was obtained via Reversible Addition Fragmentation chain Transfer (RAFT) mediated polymerization (PDI = 1.1- 1.4). The synthesized polymers were chain end functionalized to introduce thiol or aldehyde moieties. Thiol chain ends were obtained through post polymerization modification of xanthate functional PVP with either aminolysis or reduction. The aldehyde moiety was obtained by post polymerization modification of xanthate end functional PVP with sequential hydrolysis and thermolysis. Thiol functional four arm star PVP was reacted with acrylate difunctional poly(ethylene glycol) (DIAC PEG) crosslinker under standard Michael addition conditions. In order to obtain thioether crosslinked hydrogels from tetra functional star PVP molecules it was found that a minimum thiol functionalization of 30% and a molar ratio of acrylate:thiol of 1:1.1 is required. The Schiff base reaction was used to synthesize imine or secondary amine (after reduction) crosslinks with the lysine residues on either lysozyme or bovine serum albumin (BSA) or the primary amines of bis-(2-amino ethyl)amine). Hydrogels were obtained from aldehyde functionalized PVP molecules with a fraction of functional aldehyde chain ends of 0.88 for difunctional molecules and 0.50 for tetra functional star PVP molecules with lysozyme or BSA crosslinkers. The reaction rate was favoured by lowered pH (<6.0) and an optimum molar ratio of amine : aldehyde of 1:0.8. Hydrogels were analyzed by equilibrium swelling calculations to determine the molar mass between crosslinks and the estimated pore size. In both crosslinking systems the properties of the formed hydrogels were seen to be affected by molar ratio used and by the topology of the crosslinking agent. PVP BSA and PVP PEG hydrogels were tested for 24 h and 48 h cell viability by using H9C2 myoblast cells. A concentration range of 0.25 x 10(2) to 0.01 g/mL was studied. Cell mortality was tested by Trypan blue staining and results were verified with MTT assay. A very low cell death precentage (<37%)was observed. Cells even appeared to experience a stimulatory effect after 48 h of exposure at low concentrations of PVP PEG hydrogel treatments. The properties of the formed hydrogel could be tuned by the molar mass ratios of PVP and crosslinker. The functionality of the crosslinker directly affects the molar mass between crosslinks and thus indirectly the degradation profile. It was concluded that PVP molecules with various topologies, well-defined molar masses and chain end functionality could be obtained via RAFT mediated polymerization. Obtained polymers were successfully modified and crosslinked to obtain hydrogels with stoichiometrically tuneable properties i.e. initial swelling ratio, degradation time, molar mass between crosslinks. The hydrogels had very positive cell viability results that would definitely justify further research into these materials as “tissue-mimetic” materials. / AFRIKAANSE OPSOMMING: Die doel van die studie is om poli(N-viniel pirollidoon) (PVP) gebaseerde hibried hidrogelle te sintetiseer deur middel van kovalente kruisbindings met toepaslike kruisverbinder molekules. Die chemiese reaksies betrokke in die vorming van hierdie kovalente kruisbindings moet gematig van aard wees, by fisiologiese pH en by 37 °C plaasvind. Die degradasieprodukte van die hibried-hidrogel moet biologies verdraagsaam en ook uitskeibaar deur die endokrinologiese sisteem wees. PVP van verskillende topologieë, beheerde molêre massa en kwantitatiewe kettingendfunksionaliteit is berei deur ‘n omkeerbare addisie-fragmentasiekettingoordrag (OAFO)-beheerde polimerisasieproses (PDI = 1.1-1.4). Xantaat-kettingend-PVP is aangepas na thiol of aldehied kettingendfunksies. Thiolendfunksies is verkry deur middel van ‘n aminolisasie-reaksie. Xantaat kettingend-PVP is stapsgewys gemodifiseer deur hidroliese en verhittingstappe om die aldehied ketting-endfunksionaliteit te bekom. Thiol ketting-endfunksionele vier-armige ster-PVP is kovalent gebind aan difunksionele poly(etileen glikol) deur middel van die Michael-addisiereaksie. PVP PEG hidrogelle het slegs gevorm met vier-armige ster-PVP molekules wat oor ‘n minimum van 30 % thiol-funksionaliteit beskik het en ‘n optimale molêre massa verhouding van 1:1.1 vir ankrilaat to thiol. Die Schiff-basisreaksie is gebruik om hidrogel te sintetiseer wat met imiene of amiene (na redusering) kovalente bindings gekruisbind is. In hierdie sisteme het hidrogel slegs gevorm as die aldehied-PVP molekules oor ‘n fraksie funksionele kettingend-waarde van 0.88 vir dialdehied-PVP molekules en 0.5 vir vier armige ster-PVP molekules beskik het. Die reaksie snelheid van die Schiff-basis kovalente bindings is bevoordeel deur die pH te verlaag (≤ 6.0) en ‘n gunstige molêre massa verhouding van 1:0.8 vir die nukleofiel teen oor die akseptor molekule is waargeneem. Ewewigswel berekeninge is gebruik om die molêre massa tussen kruisbindings en die gemiddelde benaderde porieë binne die drie-dimensionele interne struktuur van die hydrogel te bepaal. Die seltoksisiteit van PVP-BSA en PVP-PEG hidrogelle is oor 24 h en 48 h in die teenwoordigheid van H9c2 mioblast-selle getoets. Die hydrogel behandelings is uitgevoer in ‘n konsentrasie reeks van 0.25 x 10(2) tot 0.01 g/mL. Selmortaliteit is getoets deur ‘n Trypan-blou verkleuringstudie. Hierdie resultate is ondersteun deur MTT sel-lewensvatbaarheidstoetse. ‘n Lae selmortaliteit (≤ 37 %) is waargeneem en, opspraakwekkend, het van die selle na 48 h verhoogde vitaliteit getoon in die teenwoordigheid van lae konsentrasies PVP-PEG hidrogelle. Dit is bevind dat hidrogel eienskappe deur stoichiometriese molêre massa verhoudings asook die keuse in die topologie van kruisverbinder beïnvloed word. Hierdie eienskappe het ‘n direkte effek op die degradasieprofiel van die gevormde hidrogel. Samevattend dus is PVP molekules met ‘n variasie van topologieë, spesifieke molêre massas en kettingfunksionalitete deur middel van OAFO-gemedieerde polimerisasies gesintetiseer. Xantaatkettingendfunksionele PVP-molekules kon suksesvol omgeskakel word na die kettingendfunksionaliteit van ons keuse om ‘n hibriedhidrogel met stoichiometries-manupileerbare eienskappe te sintetiseer. Die positiewe sel-lewensvatbaarbheidstudie resultate staaf verdere ondersoeke in hierdie PVPgebaseerde hibried hidrogelmateriaal as ‘n weefsel nabootsingsmateriaal.

Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Resorcinarenes are tetramers, belonging to a class of [1]4metacyclophanes, easily formed by the acid- or base-catalysed condensation of resorcinol and aldehydes. Properties include, amongst others; bowl-like shape, adhesion to hydrophilic surfaces and formation of hexameric capsules. Their uses are, to mention some: components in liquid crystals, photoresistors, selective membranes, surface reforming agents, HPLC stationary phases, ion-channel mimics, metal-ion extraction, molecular switches and ligands for metal catalysts. Selective functionalization of resorcinarenes has been explored and achieved via relatively inefficient methodologies which limit studies, structural architecture and new applications. In this work, synthesis of C4v symmetric resorcinarene ethers was performed which were used as templates in undertaking studies towards selective derivatisation of resorcinarenes via an ortholithiation approach. Conditions for the efficient synthesis of distally substituted resorcinarenes using ortholithiation were optimized and tested with a range of electrophiles, lower rim lengths, scale, base equivalents, reaction times and solvent effects. Ortholithiation gave distally substituted resorcinarenes in reasonable yields (>80%). Ortholithiation and its ability to form distal-resorcinarene esters could possibly be used as a way to synthesize distal-chloromethyl resorcinarene precursors whose further functionalization would furnish a range of distal-resorcinarene imidazolium salts, a class of distal bidentate carbene ligand staring materials for transition metal coordination. / AFRIKAANSE OPSOMMING: Resorsinarene is sikliese tetramere, wat deel uitmaak van 'n klas van [1]4metasiklofane, en kan maklik gevorm word deur die suur- of basis-gekataliseerde kondensasie van resorsinol en aldehiede. Eienskappe sluit onder andere in: bak-vormig, adhesie aan hidrofiliese oppervlakke en die vormasie van heksameriese kapsules. Tipiese voorbeelde van gebruike sluit die volgende in: komponente van vloeistof kristalle, fotoresistors, selektiewe membrane, oppervlak hervormings agente, HDVC stationêre fases, ioon-kanaal nabootsers, metaal-ioon ekstraksie, molekulêre skakelaars en ligande vir metaalkatalise. Selektiewe funksionalisering van resorsinarene was al voorheen bestudeer, maar die metodologieë was beperkend ten opsigte van die struktuele argitektuur en nuwe toepassings wat daaruit gekom het. In hierdie werk was C4v simmetriese resorsinareen eters gesintetiseer wat gebruik was as uitgangstowwe om selektiewe funksionalisering deur orto-litiëring te bewerkstellig. Kondisies vir die effektiewe sintese van distaal gesubstitueerde resorsinarene, deur gebruik te maak van orto-litiëring, was bepaal en ge-optimaliseer deur gebruik te maak van 'n wye reeks elektrofiele, laer rand lengtes, reaksieskale, basis ekwivalente en reaksie tye. Deur dié proses was dit moontlik om distaal gesubstitueerde resorsinareen produkte te bekom in redelike opbrengste (>80%) met meeste funksionele goepe. Daar word voorsien om orto-litiëring, en sy vermoë om distale-resorsinareen esters te vorm,van gebruik te maak as 'n beginpunt in die sintese van distale-chlorometiel resorsinarene, wat op hulle beurt weer sal dien as uitgangstowwe vir die sintese van distale-resorsinareen imidasolium soute. Hierdie distale, bidentale soute kan gebruik word as karbeen ligande in oorgangsmetaal koordinasie.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Rectangular components were produced by both standard injection moulding and by a process called Lomolding. Both moulding grade polypropylene homopolymer and glass-filled polypropylene were used. The effect of processing parameters on material properties, as measured by tensile and impact strength, and warpage were determined for both injection moulding and lomolding, for both unfilled and glass-filled polypropylene materials. Sampling of the components allowed for critical evaluation of processing parameters’ effect on material properties at points close to and distant from the injection point, as well as in the direction of materials flow and transverse to material flow. Glass-filled components were also evaluated in terms of glass fibre length and fibre distribution (post-injection). Overall conclusions could be drawn with respect to the 2 different processes and the materials used. It was seen, inter alia, that the specimen orientation had no effect on the mechanical properties when using unfilled polypropylene, but that the orientation of the glass fibres in the testing direction resulted in an increase in the tensile strength and the impact strength for the injection moulded samples. Similar results were seen for lomolded samples, except that the fibre orientation effects were different. In the same vein, other notable differences could be observed for samples produced by lomolding and injection molding. Fibre length and distributions obtained by polymer burn-off experiments served to help explain differences in properties of glass-filled products produced by the two processes.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Polyurethanes (PUs) are finding increasing application and use in many industries due to their advantageous properties, such as a wide range of flexibility combined with toughness, high chemical resistance, excellent weatherability, and very low temperature cure. PUs do however have some disadvantages, for instance, PU is considered an expensive polymer, especially when considered for solvent based adhesives. A motivation for this study was to consider a largely unstudied area of PU chemistry by combining PUs with polyacrylates. Polyacrylates are well known adhesives and can carry specific functionality, but have the disadvantage that their flexible backbones impart limited thermal stability and mechanical strength. In this study PU was incorporated into acrylates in an effort to obtain acrylate-g-urethanes with good properties. The mode of incorporation chosen was urethane macromonomers (UMs), a hardly mentioned substance in literature, yet one deserving investigation. UMs having different urethane chain lengths (X) were synthesized by the polyaddition polymerization of toluene diisocyanate (TDI) and ethylene glycol (EG) by the prepolymer method, which was terminated by 2-hydroxy ethyl methacrylate (HEMA) and isopropanol. The UMs were characterized by Fourier-transform infrared spectroscopy (FTIR), proton NMR (1H NMR), carbon NMR (13C NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Various percentages of the respective UMs (0-40 wt % according to acrylate monomers) were then incorporated into methyl methacrylate (MMA) and into normal butyl methacrylate (n-BMA) backbones via solution free radical copolymerization. The resulting methyl methacrylate-urethane graft copolymers (PMMA-g-urethane) and normal butyl methacrylate-urethane graft copolymers (n-PBMA-g-urethane) were characterized by GPC, 1H NMR and 13C NMR, FTIR, TGA, and DMA. Phase separation between the urethane segment and acrylate segment in the yield of graft copolymerization products was investigated by DMA and transmission electron microscopy (TEM). As the concentration of the UMs in the free radical copolymerization feed increased, lower yields of both graft copolymers PMMA-g-urethane and n-PBMA-g-urethane were observed and more UM was incorporated into the PMMA and n-PBMA backbones. It also was found that the thermal stability of the PMMA-g-urethane and n-PBMA-gurethane copolymers increased with increasing UM concentration. DMA results showed that in most graft copolymer products the two respective component parts of PMMA-g-urethane or n-PBMA-g-urethane were completely compatible as only one Tg was observed. Two glass transitions, at temperatures of 22.0 and 76.0 oC, corresponding to the n-PBMA and urethane moieties, were observed when the chain length of the UMs was increased from X=4 to X=32 [the amount of this UM used in the copolymerization feed was increased to 40%, and microphase separation was indicated].

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / Please refer to full text for abstract

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / A comprehensive, comparative structural study of gold(I), gold(II) and gold(III) compounds with the general formula [Aux(C6F5)y(tht)z] (tht = tetrahydrothiophene) was performed. The series of compounds included the unprecedented dinucleur gold(II) compound, tetrakis(pentafluorophenyl)bis(tetrahydrothiophene)digold(II), which could be prepared in a rational manner. This very unique compound represents the first example of an unbridged dinucleur gold(II) compound in which the gold(II) centres are not stabilised by chelating ligands. Formation of this compound was postulated to have taken place by radical pentafluorophenyl (pfp) ligand migration along with AuII–AuII bond formation. It may therefore be regarded as a rare example of labile behaviour by a generally inert pfp ligand. In addition to this compound, the crystal and molecular structures of the wellknown gold(I) and gold(III) precursor compounds, (pentafluorophenyl)(tetrahydrothiophene) gold(I) and tris(pentafluorophenyl)(tetrahydrothiophene)gold(III) were carried out and are described for the first time. The latter underwent a unique mononuclear ligand rearrangement (metathesis or disproportionation) reaction in solution to yield the novel rearrangement product, bis(pentafluorophenyl)bis(tetrahydrothiophene)gold(III)tetrakis- (pentafluorophenyl)gold(III). In all the complexes, the Au–C and Au–S bond lengths displayed a variation which appears to be dependent on the oxidation state of the central gold atom. Both of these bond types were found to descrease in the order Au(II) > Au(III) > Au(I)...

Thesis (MSc (Chemistry and Polymer Science))--Stellenbosch University, 2008. / There are various mercury species in the environment and their toxicity and availability relies on their chemical form and oxidation states. Inorganic and organic mercury is found to co-exist in water and body tissue of some organisms. Among them inorganic mercury has a lower toxicity than the organic mercury. Methyl mercury (CH3Hg+) is the most toxic species found in the environment because it can enter the food chain accumulating and contaminating humans. Hence the total mercury concentration does not reflect the important information and thus the needs for the development of methods for the simultaneously separating and determination of mercury species. A study of the electrochemistry of mercury and organo mercury complexes with cysteine and dithizone indicated the formation of stable complexes, which can be utilized for the determination of the species in environmental matrices. Cyclic voltammetry is used to determine the electrochemical properties of the complexes. A technique based on capillary electrophoresis and amperometric detection (CE-AD) has been developed for the speciation of mercury. This technique has the capability to detect mercury species that are electrochemically active. Using capillary electrophoresis in combination with electrochemical detection makes speciation of the complexes possible at lower than normal concentrations. For CE-AD the detection limits were 0.005 μg/L for Hg2+ and 0.4 μg/L for MeHg+. These detection sensitivities are attractive for environmental monitoring.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Synthesis of a series of poly (methylmethacrylate)-graft-poly (styrene) polymer was carried out via free radical polymerization of methylmethacrylate and polystyrene macromonomers. The macromonomers were synthesized via living anionic polymerization techniques. Two series of macromonomers where synthesized with different polymerizable end group functionalities, by termination with p-vinyl benzyl chloride and 3-(dimethyl chloro silyl) propyl methacrylate. The branch density was varied by controlling the composition feed ratio of the macromonomers to comonomer. Liquid chromatographic techniques were used to fully characterize the chemical composition and branch distributions of the graft polymer. Liquid chromatography under critical conditions of adsorption of styrene coupling with Fourier Transform Infrared Spectra was used to investigate the chemical composition and distribution of the branches in the graft. Physical properties of the graft copolymers such as Tg and free volume were determined using differential scanning calorimetry and positron lifetime spectrometry respectively. The relationship between the chemical composition and the graft copolymer properties such as Tg and free volume were investigated. The results show that for long chain macromonomers phase segregation occurs in the graft copolymers. In the case of shorter chain macromonomers at low content no phase segregation is observed and the macromonomers have an antiplasticization effect on the graft polymers.