Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Mycotoxins have assumed worldwide importance due to the ubiquitous occurrence of toxigenic fungi, their infestation of plant-based foods and feeds and the subsequent economical and health impact it because of their contamination of commercial products. Ochratoxin A (OA) is a nephrotoxic mycotoxin produced by isolates of Aspergillus ochraceus and Penicillium verrucosum and occurs frequently in nature. The major target for toxicity of OA in mammalian species is the kidneys and it has been the major cause of Danish Porcine Nephropathy. OA has also been extensively implicated in the aetiology of Balkan Endemic Nephropathy and Chronic Interstitial Nephropathy in Northern-Africa. Furthermore, OA has been identified as a carcinogen, an immunosuppressant and a teratogen with respect to the foetal central nervous system. Although a large amount of research has been conducted into the chemical nature of the toxicity of OA, the exact molecular mechanism of action of OA is not yet conclusive. Numerous structure activity relationship studies have suggested that the toxicity of OA may be assigned to three major processes: (i) inhibition of ATP production; (ii) inhibition of protein synthesis; and (iii) the disruption of hepatic microsomal calcium homeostasis through the promotion of membrane lipid peroxidation. It is the aim of this thesis to gain a better understanding, through the synthesis ofOA analogues, of the chemical structure responsible for the toxic function of the ochratoxins. The halogen-group has extensively been implicated in the toxicity of the ochratoxins. This is evident in ochratoxin B (OB), the dechloro analogue of OA, which is approximately ten times less toxic than OA. Preliminary tests have indicated that bromo-ochratoxin B(BrOB), the bromo analogue of OA, is more toxic than ochratoxin A to renal cells. Fluoro-ochratoxin B and other analogues of OA, where other amino acids are incorporated, should provide invaluable information on the structure-activity relationships and the mode of action of the ochratoxins. Our research effort addresses both these aspects (i) fluorination of the dihydroisocoumarin moiety and (ii) the coupling of different amino acids and dipeptides to the non-toxic hydrolysed product of OA, ochratoxin a. Chapter one includes a review of the important biological aspects of OA that has served as a guideline to the synthesis of effective OA analogues. An overview of the relevant chemistry involved in the modification of OA will conclude the chapter. Chapter two entails a discussion of fluorine in bio-organic chemistry. This includes an overview of the impact that fluorine substitution has on the biological reactivity of molecules. A review on the synthesis of organofluorine compounds, which forms the emphasis of this study, concludes the chapter. Chapter three elaborates on the different methodologies used in our attempts to synthesise fluoro-ochratoxin B and other analogues. These included the direct electrophilic fluorination of OB and different analogous aromatic model compounds by xenon difluoride, N-fluorobenzenesulfonimides and Selectfluor™ as fluorinating agents. Also involved is an investigation into an alternative route for the synthesis of fluoro aromatic compounds from bromo and chloro analogues by means of palladium catalysed trimethyl- and tributylstannyl and trimethylsilylation which in tum may be substituted with fluorine by means of xenon difluoride. Efforts towards the direct catalytic fluorosubstitution of aryl halides are also investigated. The synthesis of a key intermediate, fluoroacetoacetaldehyde, in a de nova synthetic route to fluoroochratoxin B is also discussed. Furthermore, the synthesis of novel OA analogues with respect to the replacement of the L-phenylalanine moiety is addressed. This includes the conversion of OA to Oa, by acid hydrolysis, followed by the coupling of ortho-, meta- and para- substituted DL-fluorophenylalanine to the lactone acid. This is followed by the synthesis of histidylhistidine methyl ester and attempted coupling to Oa. The coupling of halosalicylic acids and salicylic acid to L-phenylalanine, for use as model aromatic substrates for fluorination, IS discussed. Peptide coupling by dicyclohexylcarbodiimide carboxyl activation, with reference to the protection of the phenolic hydroxyl group in 5-chlorosalicylic acid for application to Oa, concludes this work. / AFRIKAANSE OPSOMMING: Mikotoksiene is van wêreld-wye belang as gevolg van die alomteenwoordige voorkoms van toksigeniese fungi, hul besmetting van plantaardige kossoorte en voerstowwe en die gevolglike ekonomiese en gesondheidsimpak deur die besoedeling van kommersiële produkte. Ochratoksien A (OA) is 'n nefrotoksiese mikotoksien wat geproduseer word deur isolate van Aspergillus ochraceus en Penicillium verrucosum en kom algemeen in die natuur voor. Die niere is die hoof teiken vir vergifiting deur OA in soogdierspesies en is as die vername oorsaak van "Danish Porcine Nephropathy" aangewys. OA word verder aangedui as die oorsaak vir "Balkan Endemic Nephropathy" en "Chronic Interstitial Nephropathy" in Noord- Afrika. OA is verder geïdentifiseer as 'n karsinogeen, immuno-onderdrukker en is teratogenies ten opsigte van die sentrale senuweestelsel van fetusse. Alhoewel aansienlike navorsing alreeds gewei is aan die chemiese natuur van die toksisiteit van OA, is die presiese molekulêre meganisme van OA reaktiwiteit onbeslis. Verskeie struktuur-aktiwitweit verwantskaps studies dui daarop dat die toksisiteit van OA hoofsaaklik toegeskryf kan word aan drie hoof prosesse: (i) inhibisie van ATP produksie; (ii) inhibisie van proteïen sintese; en (iii) die ontwrigting van hepatiese mikrosomale kalsiumhomeostase deur die bevordering van membraanlipiedperoksidasie. Hierdie tesis het ten doel, deur die sintese van OA analoë, om 'n beter insig oor die chemiese struktuur wat verantwoordelik is vir die toksiese funksionaliteit van ochratoksiene te verkry. Die halogeen substituent is grootliks geïmpliseer in die toksisiteit van OA. 'n Bewys hiervan is ochratoksien B (OB), die dechlooranaloog van OA, wat ongeveer tien maal minder toksies is as OA. Voorlopige ondersoeke het aangetoon dat bromoochratoksien B (BrOB), die broomanaloog van OA, meer toksies is vir nierselle as OA. Fluoorochratoksien B en ander analoë van OA, waar ander aminosure geïnkorporeer word, behoort waardevolle inligting te voorsien met betrekking tot die struktuur-aktiwiteitsverwantskappe en die wyse waarop ochratoksiene funksioneer. Hierdie navorsingspoging spreek beide aspekte aan; (i) die fluorering van die dihidroïsokumarien gedeelte en, (ii) die koppeling van verskillende armnosure en dipeptiede aan die nie-toksiese hidrolieseproduk van OA, nl. ochratoksien a. Hoofstuk een vervat 'n oorsig van die belangrike biologiese aspekte van OA wat dien as riglyn vir die sintese van doeltreffende OA analoë. Die hoofstuk word afgesluit met 'n oorsig van die relevante chemie betrokke by die modifisering van die struktuur van OA. Hoofstuk twee bevat 'n bespreking van die aanwending van fluoor in bio-organiese chemie. Dit bevat 'n oorsig van die impak wat fluoorsubstitusie het op die biologiese reaktiwiteit van molekules. 'n Opsomming oor die sintese van organofluoorverbindings, wat die essensie van hierdie studie is, beëindig die hoofstuk. Hoofstuk drie handeloor die veskillende metodes wat toegepas is in pogings om fluoorochratoksien B en ander analoë te sintetiseer. Dit sluit in die direkte elektrofiliese fluorering van OB en ander verwante aromatiese modelverbindings deur gebruik te maak van xenondifluoried, N-fluoorbenseensulfonimied en Selectfluor™ as fluoreringsreagense. Dit behels verder ook 'n ondersoek na 'n alternatiewe roete tot die sintese van fluooraromatiese verbindings vanaf broom- en chlooranaloë. Vir die doel word palladiumgekataliseerde trimetiel- en tributielstannilering, en trimetielsililering wat vervolgens deur middel van xenondifluoried met fluoor gesubstitueer kan word, aangewend. Pogings tot die direkte katalitiese fluoorsubstitusie van arielhaliede word ook bespreek. Die sintese van 'n sleutelintermediêr, fluoroasetoasetaldehied, in 'n de nova sintese roete tot fluoorochratoksien B word bespreek. Die sintese van nuwe OA analoë, met betrekking to die vervangmg van die Lfenielalanien (L-Phe) groep word ondersoek. Dit bevat die omsetting van OA na Oa, deur suurhidrolise, gevolg deur die koppeling van orto-, meta- en paragesubstitueerde DL-fluoorfenielalanien aan die laktoonsuur, Oa. Daarna word die sintese van histidielhistidienmetielester en die verdere pogings aangaande koppeling met Oa bespreek. Die koppeling van halosalisielsure en salisielsuur aan L-Phe wat dien as model aromatiese verbindings vir fluorering, word behandel. Peptiedkoppeling met behulp van disikloheksielkarbodiimied-karboksielaktivering, met inbegrip van die beskerming van die fenoliese hidroksiel groep m 5-chloorsalisielsuur Vir die toepassing op Oa, beëindig hierdie werk.

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: There is limited experimental and computational information available on the structures of compounds of the form R2GeX2, where X is a halogen and R an alkyl group. Gas phase electron diffraction studies of the dihalo(dimethyl)germanes (R=Me)consistently give C-Ge-C angles in the range of 120-125°, about 10° larger than the corresponding C-C-C angles in the 2,2-dihalopropanes. However, in dimethylgermane, where the halogen atoms are substituted by hydrogen, the value of the C-Ge-C is very similar to the corresponding C-C-C angle in propane and deviates little from the tetrahedral value of 109.47°. The unusually large influence of atomic substituents on the value of the valence angles in these compounds introduces a serious challenge to the development of empirical force fields, where the size of an angle is traditionally determined only by the atoms directly involved in the formation of the angle and not by the other substituents attached to the central atom. Unfortunately, the large experimental errors in the gas phase electron diffraction studies and the lack of representative crystalline compounds in the Cambridge Structural Database make it impossible to establish conclusively whether these large valence angles are significant or just statistical anomalies. A systematic ab initio study of a number of compounds of the general form Me2AX2with A=C, Si or Ge and X=H, F, Cl, Br or I has been initiated to verify the experimental results and to try to explain this observed deviation in valence angle in terms of electronic effects and existing theories of structure and bonding. The carbon and silicon analogs of the dimethylated germanes were included in the calculations to ascertain whether the observed effect is an anomaly or merely a periodic trend in the group IVelements. To obtain a clearer overall view, identical calculations were also performed on compounds of the form AHnX4-n,MeAH2X, MeAHX2and Me2AHX,where Aand X have the same meaning as before. The ab initio calculations confirmed that there is in fact a significant increase in the C-A-C angle from A=C to A=Ge in the compounds Me2AX2,although the calculated increase is smaller than the experimentally determined increase by a few degrees. Together with this observed increase in the C-A-C angle there is a corresponding decrease in the X-A-X angle. Calculation of the electron density of three representative compounds revealed a significant difference in electron distribution between the germanium compounds and their carbon analogs, suggesting that the ionicity of the bonds and the electronegativity of the substituents may playa role in the size of the C-A-C angle in compounds of this form. This is supported by a statistical analysis of compounds in the Cambridge Structural Database containing a C2GeYZ fragment, where Y and Z may be any elements except carbon, which showed that the average C-Ge-C angle in compounds where Y and Z are electronegative is approximately 7° larger than in compounds where Y and Z are electropositive. The qualitative trends in the C-A-C and X-A-X angles have also been discussed in terms of three different bonding models. To verify the results of the ab initio calculations experimentally, a representative compound, dichlorobis(phenethyl)germane, has been synthesized and its crystal structure determined by X-ray diffraction. The C-Ge-C angle was found to be 121.2°, which is in good agreement with both the ab initio and the gas phase electron diffraction results. Furthermore, a force field for halogenated organic carbon, silicon and germanium compounds has also been developed based on the structural and vibrational data obtained from the ab initio calculations. Molecules of the form AHnX4-nand Me2AX2with A=C, Si, Ge and X=H, F, Cl and Br were used in the training set and the bond lengths, bond angles and vibrational frequencies were used to optimize the force field. Calculations performed with the force field reproduce the C-A-C angles to within 1° of the observed values and the reproducibility for the rest of the experimental data is also good. Force fields have been developed for some of the simpler molecules in our training set and where this is the case, the force field parameters have been compared to the previously determined values. / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Please refer to fulltext for abstract. / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISCH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (MSc)--Stellenbosch University, 1967. / ENGLISH ABSTRACT: no abstract available / AFRIKAANSE OPSOMMING: geen opsomming

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)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Trace amounts of soluble Pt(II/IV) ions are not recovered using current refining processes. There are both economic and environmental incentives to recover these Pt(II/IV) ions from effluent. The work presented in this dissertation was aimed at producing functionalised electrospun nanofibre webs for the extraction of trace amounts of Pt(II/IV) ions in the form of [PtCl6]2- from acidic solutions. An insoluble, low molecular weight oligomeric compound, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was synthesised from relatively inexpensive starting reagents using a “one-pot” two step synthesis procedure. Interest in this compound lies in its ability to extract Pt(II/IV) ions from acidic, chloride-rich solutions, as may be encountered in real process solutions in platinum group metal refineries. The product was isolated and characterised with an array of techniques, including GPC, elemental analysis, 1H and 13C NMR, as well as FTIR, and it was found to be a mixture of various molecular weight fractions with a degree of chemical variance between oligomer chains. The poly(N-terephthaloylthiourea)-N’,N’-piperazine was blended with polyacrylonitrile (PAN) and electrospun using both the classical single needle approach as well as a high throughput free-surface electrospinning process, called ball electrospinning. The nanofibres consisted of the oligomer which provided the affinity for [PtCl6]2- while PAN provided sufficient polymer chain entanglement which allowed the formation of fibrous structures. Two different solutions were found to produce nanofibres with the desired dimensions, namely: 6 wt% and 8 wt% PAN solution, both having a PAN to oligomer ratio of 7:3. The fibres produced by needle electrospinning and ball electrospinning had average fibre diameters of 172 ± 35 nm and 210 ± 49 nm, respectively. The ball electrospinning process had 86 times greater fibre production rates compared to needle electrospinning. The effects of three experimental conditions on the recovery of Pt(II/IV) ions by the poly(N-terephthaloylthiourea)-N’,N’-piperazine-containing nanofibres were determined. The conditions were: (i) the effects of specific surface area and available coordination sites over time, (ii) the effect of extraction temperature, and (iii) the effect of hydrochloric acid (HCl) concentration on [PtCl6]2- extraction. Increased availability of coordination sites caused an increase in Pt ion extraction. The Pt ion extraction also increased from 0.007 g to 0.023 g for each gram of nanofibres used as the temperature was increased from 20 °C to 60 °C when using a 114 mg/L Pt stock solution. The HCl concentration had no effect on Pt ion extraction when varied between 1.0 x 10-3 M to 1 M, while increased extraction as well as fibre damage was caused at HCl concentrations greater than 1 M. Nanofibres containing an oligomeric compound with affinity for [PtCl6]2- in acidic solutions were successfully synthesised and used to extract trace amounts of Pt(II/IV) ions from solutions under various conditions. / AFRIKAANSE OPSOMMING: In huidige verfynings prosesse word spoorelemente van oplosbare Pt(II/IV) nie herwin nie. Daar is beide ekonomiese en omgewings insentiewe om hierdie Pt(II/IV) ione te verhaal uit die afval oplossings. Hierdie tesis was gemik daarop om funksionele elektrospinde nanovesel webbe te produseer vir die herwinning van Pt(II/IV) ioon spoorelemente in die vorm van [PtCl6]2- uit aangesuurde oplossings. ‘n Onoplosbare oligomeriese verbinding met ‘n lae molukulêre gewig, poly(N-terephthaloylthiourea)-N’,N’-piperazine, was uit relatief goedkoop begin reagense gesintetiseer deur gebruik te maak van ‘n “een-pot” twee stap prosedure. Die belangrikheid van die verbinding lê in sy vermoë om Pt(II/IV) ione uit aangesuurde, chloried-ryke oplossing te onttrek, soos wat in alledaagse afval oplossings van platinum-groep metalurgiese raffinaderye ondervind kan word. Die sintese produk was geisoleer en gekarakariseer deur gebruik te maak van ‘n verskeidenheid tegnieke, waaronder GPC, elementêre analise, 1H en 13C NMR sowel as FTIR, en daar was bepaal dat die produk bestaan uit ‘n mengsel van verskeie molukulêre gewig kettings met ‘n mate van chemiese variansie tussen hulle. Die gesintetiseerde oligometriese verbinding was gemeng met poliakrielonitriel (PAN) en elektrospin deur gebruik te maak van beide die klasieke naald spin proses, sowel as ‘n hoë-produksie vrye oppervlak spin proses, genaamd die bal elektrospin proses. Die nanovesels bestaan uit die oligomeer wat die affiniteit vir die [PtCl6]2- voorsien terwyl die PAN genoegsame polimeer ketting verstrengeling veroorsaak het om die veselagtige struktuur te vorm. Nanovesels met die gewensde dimensies was gevorm deur die elektrospin proses toe te pas op twee verskillende oplossings, naamlik: ‘n 6 massa persent PAN en ‘n 8 massa persent PAN oplossing, beide met ‘n PAN tot oligomeer verhouding van 7:3. Die vesels geproduseer deur die naald en bal elektrospin prosesse het ‘n gemiddelde vesel deursneë gehad van 172 ± 35 nm en 210 ± 49 nm, onderskeidelik. Die bal spin proses het egter ‘n 86 keer groter produksie kapasiteit van vesels gehad in vergelyking met die naald spin proses. Die effek van drie verskillende toestande op die effektiwiteit van die nanovesels, wat poly(N-terephthaloylthiourea)-N’,N’-piperazine bevat, om Pt(II/IV) ione te onttrek uit die oplossings was ondersoek. Die toestande was: (i) die effekte van spesifieke oppervlak area asook beskikbare ontginnings setels oor tyd, (ii) die effek van die ontginnings temperatuur, en (iii) die effek van die soutsuur (HCl) konsentrasie op die Pt ioon ontginning. ‘n Toename in die beskikbaarheid van die ontginnings setels het gelei tot ‘n toename in die Pt ioon ontginning. Die Pt ioon ontginning het toegeneem van 0.007 g tot 0.023 g vir elke gram van nanovesels gebruik soos die temperatuur verhoog was van 20 °C tot 60 °C wanneer ‘n 114 ppm (m/v) Pt ioon oplossing gebruik was. Daar was geen effek op die Pt ioon ontginning toe die HCl konsentrasie tussen 1.0 x 10-3 M en 1 M HCl varieer was nie, alhoewel daar by konsentrasies hoër as 1M ‘n verhoogde ontginning sowel as vesel skade was. Nanovesels wat ‘n oligemetriese verbinding bevat met ‘n affiniteit vir [PtCl6]2- in ‘n aangesuurde oplossing, was suksesvol gesintetiseerd en gebruik om spoorelemente van Pt(II/IV) te onttrek onder verskillende omstandighede.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The main aim of this study was to use poly (ethylene-co-vinyl alcohol) (EVOH) as vehicle to incorporate nanofillers into low density polyethylene (LDPE). For this purpose, chitin and cellulose nanowhiskers were prepared through a process of acid hydrolysis and then incorporated into different EVOH copolymers with varying ethylene contents by means of two different experimental methods, namely solution casting and electrospinning. The extremely small dimensions of nanowhiskers make it difficult to observe the degree of dispersion in the electrospun fibers using methods such as transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Fluorescence microscopy was therefore investigated as an alternative characterization technique to obtain better results with regard to tracking the filler dispersion. TEM analysis proved to be the most successful method for observing the dispersion of nanowhiskers for solution cast EVOH nanocomposites as well as electrospun EVOH nanocomposites. Clear differences between EVOH composites with low nanowhisker and high nanowhisker loading were observed in TEM images for these nanocomposites. Thermal analysis of solution cast as well as electrospun fibers were carried out using techniques such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). These results revealed changes in crystallization behaviour as well as changes in thermal stability of the EVOH nanocomposites compared to the pure polymer matrix. The incorporation of cellulose and chitin nanowhiskers indicated a general increase in percentage crystallization which probably resulted from the nanowhiskers acting as nucleating agents and therefore increasing the crystallization of most EVOH nanocomposites. The thermal stability is observed to increase as the cellulose nanowhisker loading is increased. This increase in thermal stability proved to be partly attributed to the presence of sulphuric acid which were not completely removed during dialysis of cellulose nanowhiskers. Neutralisation of cellulose nanowhiskers and the treatment with a strong base was therefore further investigated to improve degradation within the EVOH nanocomposites during thermal treatment. The last step in this study involved the incorporation of electrospun EVOH nanofibers containing cellulose nanowhiskers into LDPE in order to improve the mechanical properties. The tensile strength and Young’s modulus of these LDPE nanocomposites were seen to improve quite significantly while a decrease in elongation at break was observed. / AFRIKAANSE OPSOMMING: Die hoofdoel van hierdie studie was om poliëtileen (ko-viniel alkohol) (EVOH) as voertuig te gebruik om nanofillers in lae digtheid poliëtileen (LDPE) te inkorporeer. Kitien en sellulose nanokristalle is vir hierdie doel geproduseer deur middel van ʼn suurhidrolise proses en daarna in verskillende EVOH-kopolimere met verskillende etileeninhoude geïnkorporeer met behulp van twee verskillende eksperimentele metodes, naamlik ʼn drogings- en elektrospinproses. Die uiters klein dimensies van die nanokristalle maak dit uitdagend om die mate van verspreiding van die nanokristalle binne in die elekrogespinde vesels waar te neem m.b.v. metodes soos transmissieelektronmikroskopie (TEM) en skandeerelektronmikroskopie (SEM). Fluoressensie is dus as ʼn moontlike alternatiewe karakteriserings tegniek bestudeer om beter resultate rakende die verspreiding van die nanokristalle te kan waarneem. In hierdie studie is gevind dat TEM-analise die suksesvolste metode was om die verspreiding van nanokristalle te bestudeer en dit geld vir beide die gedroogte en gespinde EVOH-nanosamestellings. Duidelike verskille is waargeneem vir monsters wat hoër en laer nanokristalinhoude gehad het. Saambondeling van die nanokristalle kom duideliker voor by dié wat ʼn hoër inhoud van nanokristalle bevat. Termiese analises van gedroogte EVOH-nanosamestellings en ook die gespinde nanosaamgestelde vesels is uitgevoer d.m.v. tegnieke soos differensieëlskandeerkalorometrie (DSC) en termiese-gravimetriese analise (TGA). Die resultate wat verkry is vanaf die bogenoemde tegnieke het bewys dat daar verandering in die kristallisasie, sowel as die degradasie temperatuur, van die EVOH-nanosamestelling is. Die byvoeging van sellulose en kitien nanokristalle het ʼn algemene verhoging in die persentasie kristallisasie van die EVOH-nanosamestelling te wee gebring. Die byvoeging van nanokristalle tree waarskynlik gedeeltelik op as kernvormings agent vir die EVOH-molekules. TGA analises toon dat die termiese stabiliteit van die EVOH-nanosamestelling verhoog met die byvoeging van nanokristalle. Die teenwoordigheid van die sulfaatgroepe wat nie heeltemal verwyder is tydens die wasproses nie, is bewys om gedeeltelik verantwoordelik te wees vir die verhoging in termiese stabiliteit van die EVOH-nanosamestellings. Die neutralisasie en behandeling van die nanokristalle met ʼn sterk basis is dus verder ondersoek om die degradasie van die EVOH-nanosamestellings tydens verhitting te verbeter. Die laaste stap in hierdie studie het behels dat elektrogespinde EVOH vesels wat verskillende hoeveelhede sellulose nanokristalle bevat, geïnkorporeer is in LDPE ten einde die meganiese eienskappe te verbeter. Die treksterkte en die Young’s modulus het met ʼn beduidendende hoeveelheid verbeter terwyl die verlenging by breekpunt verlaag het. / National Research Foundation

It has been shown that alkaloids from various sources are vital as lead compounds in medicinal research and thus also the efficient synthesis of these. With the goal of developing a general synthetic route that can potentially access pyrrolizidine, indolizidine, quinolizidine and possibly lehmizidine alkaloid skeletons, a modified route that has been shown to produce pyrrolizidines was employed towards the synthesis of indolizidine alkaloid 223AB. Within this synthesis, a 6-endo-dig hydroamination-cyclization step was attempted for construction of the bicyclic system. For this purpose, a selection of titanium-based catalysts were synthesized in order to determine their regiochemical outcome. For the purpose of investigating ab initio the mechanism of regioselective hydroamination, the skills and methods involved in computational chemistry were acquired through a study into amide rotational barriers: A range of novel 2-oxo-2H-chromen-7-yl dimethylcarbamates were synthesised containing either an oxygen or sulphur in the α-position to the carbonyl or thiocarbonyl group of the amide moiety. Microwave synthesis was essential for the successful synthesis of some of the sulphur containing carbamates. The barriers to internal rotation of each of these compounds were investigated as follows. Variable Temperature and Exchange Spectroscopy NMR was performed on these compounds and the barrier to free amide rotation was calculated. Each of these compounds were also modeled ab initio and the gas phase barrier to rotation calculated. These three sets of data were compared and the influence of the α-heteroatom on rotation for amides and thioamides evaluated. / Thesis (M.Sc.) - University of KwaZulu-Natal, Pietermaritzburg, 2008.

Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.