Abstract available in pdf file.

The importance of alkyl methacrylates has been firmly established within the chemical industry. For example, free radical polymers, which contain the methacrylate backbone are more rigid than acrylate polymers. Several methods have been reported for the production of alkyl methacrylates. The aim of this project is focused on isolating a phase specific iron phosphate catalyst and thereafter testing its efficacy in oxidative reactions to form ethyl methacrylate in a one step process in the gas phase using a fixed bed continuous flow reactor. The catalyst was characterized by using Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), Brunauer-Emmett-Teller (BET) surface area measurements, Attenuated Total Reflection-Infrared (ATR-IR) Spectroscopy, Scanning Electron Microscopy (SEM), Temperature Programmed Reduction (TPR), Temperature Programmed Oxidation (TPO), Energy Dispersive X-ray (EDX) determination, Temperature Programmed Desorption (TPD), Room Temperature X-ray Diffraction (XRD), In situ X-ray Diffraction (In situ XRD), Thermogravimetric/Differential Thermal Analysis (TGA/DTA), Transmission Electron Microscopy (TEM), Mössbauer Spectroscopy and Raman Spectroscopy. A further venture included employing certain of the above techniques to characterize the cesium promoted iron phosphate catalyst as well as the spent catalysts. The catalytic activity of the iron phosphate based catalyst synthesized was investigated for the oxidative dehydrogenation (ODH) of ethyl isobutyrate (EIB) to ethyl methacrylate (EMA). Reaction conditions which were considered included variation in the contact time, co-feeding water at varying contact times, co-feeding ethanol at varying ratios, as well as co-feeding both ethanol and water and catalyst lifetime and regeneration studies. The cesium promoted iron phosphate catalyst was tested at optimal reaction conditions. The findings of the investigation showed that the tridymite-like FePO4 phase was the most suitable precursor to allow for the formation of the active α-phase during catalytic testing. It was found that the catalyst performed optimally at a contact time of 0.8 seconds and the beneficial effect of co-feeding water and ethanol primarily on conversion and selectivity towards EMA respectively, was demonstrated. Optimal results were obtained at a EIB:EtOH ratio of 1:5 with a conversion of 57 % and a yield of 34 mol %. The lifetime and regeneration studies showed that water had a significant effect on the regeneration of the catalyst after a specific time on stream and a shorter time on stream (i.e. 25 hours) prior to regeneration, minimized rapid deactivation of the catalyst. The characterization results obtained for the spent catalysts showed that under the reaction conditions considered with respect to co-feeds, the active α-phase and the Fe2P2O7 phase dominated. The cesium promoted iron phosphate catalyst was synthesized to favour stabilization of the tridymite-like structure. The results showed that a mixture of phases was observed for the synthesized promoted catalysts and there was an increase in EIB conversion as well as EMA selectivity with a decrease in cesium loading. However, the promoted catalyst with the lowest cesium loading (Cs/Fe = 0.10), showed a lower selectivity towards EMA relative to the unpromoted iron phosphate catalyst. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Multi-walled carbon nanotubes (MWCNTs) and other shaped carbon nanomaterials (SCNMs) were synthesized by the floating catalyst chemical vapour deposition (CVD) method, using either ferrocene [1] as the catalyst at 2.5 or 5 wt.%, or a synthesized heteroatom-containing ferrocene derivative, in toluene, in the range 750 to 950 °C. The derivatives used were ferrocenoyl imidazolide [3] (a source of N and O) at 2.5 and 5 wt.%, (N-phenylcarbamoyl)ferrocene [4] (a source of N and O) at 1.25 wt.% and S,S-bis(ferrocenylmethyl)dithiocarbonate [5] (a source of S and O) at 2.5 wt.%, which was synthesized from ferrocenylmethanol [2]. These were characterized by melting point, 1H- and 13C-NMR spectroscopy, IR spectroscopy and mass spectrometry (MS). The effects of variations in the CVD physicochemical reaction parameters, namely temperature, catalyst employed (and the effect of its heteroatoms, where applicable) and catalyst concentration, on the CVD products were investigated. These materials were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive Xray spectroscopy (EDX), Raman spectroscopy, thermogravimetric analysis (TGA) and some by the Brunauer, Emmett and Teller method (BET). The best temperature range, in terms of high yields of MWCNTs with relatively high thermal stabilities and surface areas, in general, was identified as being 800 to 900 °C, from results obtained with [1]. This temperature range was used for further experiments. Among other results, it was shown that [1] and [3], at 2.5 wt.%, and at 800 and 850 °C respectively, produced the best materials. Catalysts [4] and [5] produced primarily carbon spheres, however, in general, all experiments using N-containing catalysts produced bamboo-shaped MWCNTs. For [3], at 2.5 wt.%, smaller bamboo compartment lengths correlated with decreasing temperature and decreasing crystallinity, suggesting a larger incorporation of nitrogen with lowered temperature. Catalyst [3] at 2.5 wt.% also produced very “clean” MWCNTs and this was attributed to optimal levels of oxygen being able to convert amorphous carbons to gas. Certain MWCNT properties were shown to be dependent on the combined, or synergistic, effects of catalyst concentration and temperature. The best undoped MWCNTs that were synthesized and commercially produced MWCNTs were loaded with Pd nanoparticles using a metal organic CVD (MOCVD) method. Results revealed well dispersed metal nanoparticles of narrow size distribution. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: Ruthenium, as one of the platinum group metals, was investigated to determine the aquation rate constant of [RuCl6]3- and the anation rate constant of [RuCl5(H2O)]2-. This two reactions represent the equilibrium reaction [RuCl6]3- + H2O ⇄ [RuCl5(H2O)]2- + Cl-. The reactions were followed, using stopped-flow injection and UV/Visible spectroscopy, at different temperatures. The aquation and anation rate constants were determined with good precision and thermodynamic values for the reactions were calculated. The pseudo first order aquation rate constant, k65, was determined by calculation from the regression line as k65 = 52.1 (±3.7) x10-3 s-1 at 25°C. The activation energy, Ea, is 90.1 (±1.2) kJ.mol-1 and the enthalpy and entropy of activation is 87.7 (±1.2) kJ.mol-1 and 24.7 (±4.3) J.K-1.mol-1, respectively. The aquation rate constant was found to be dependent on the hydrochloric acid concentration, decreasing with increasing hydrochloric acid concentration. From the regression line at 25°C the second order anation rate constant, k56, was calculated as 1.62 (±0.11) x10-3 M-1s-1. The activation energy is 88.0 (±1.4) kJ.mol-1, with the enthalpy and entropy of activation 85.6 (±1.4) kJ.mol-1 and –11.2 (±4.7) J.K-1.mol-1, respectively. The influence of the hydrochloric acid concentration of the solution on the anation rate constant was not investigated. The equilibrium constant for the reaction studied was calculated from the rate constants for the aquation and anation reactions. The equilibrium constant, K6, was calculated as 0.0311 M-1 at 25°C. The equilibrium constant, when compared to literature, was found to be dependent on the hydrochloric acid concentration. It was then used, in conjunction with data from the literature, to construct two distribution diagrams. Distribution diagrams for the Ru(III) aquachloro species show between 79.9% to 72.3% [RuCl6]3- present in 12M HCl. The two distribution diagrams were very similar and it is not possible to resolve the issue of a final distribution diagram for the aqua-chloro Ru(III) system without further investigation into the all the other rate constants of the Ru(III) aqua-chloro species. The rate constants and thermodynamic values for the Ru(III) reaction were compared to corresponding data (from literature) for Rh(III) and Ir(III) because several comparisons between these platinum group metals have been noted. It was found that for both the aquation and anation rate constants, the following trend was observed: Ru(III) > Rh(III) > Ir(III). These differences are in certain cases exploited in the refining of these platinum group metals. Crystals of diethylenetriamine hexachlororuthenate(III) was prepared and characterised by x-ray crystallography and CHN analysis. The average Cl-Ru bond length for the crystal was 2.371 Å. The crystal structure was compared to hexaaquaaluminium hexachlororuthenate(III) tetrahydrate and diethylenetriamine hexachlororhodate(III). The metal-chloride bond lengths of all the crystals were found to be similar (2.350 Å – 2.375 Å). The diethylenetriamine crystal structures compared well. The conclusion was that the crystals prepared were diethylenetriamine hexachlororuthenate(III). / AFRIKAANSE OPSOMMING: Ruthenium(III), een van die platinum groep metaal-ione, is in hierdie studie ondersoek om die akwasie tempo konstante van [RuCl6]3- en die anasie tempo konstante van [RuCl5(H2O)]2- te bepaal. Dié twee reaksies verteenwoordig die ewewigsreaksie [RuCl6]3- + H2O ⇄ [RuCl5(H2O)]2- + Cl-. Die verloop van die reaksies is met behulp van UV/Sigbare spektroskopie by verskillende temperature gevolg. Die akwasie en anasie tempo konstantes is bepaal met goeie presisie en die termodinamiese konstantes van die reaksies is bereken. Die pseudo-eerste orde akwasie tempo konstante, k65, is bepaal deur middel van regressie, as 52.1 (±3.7) x10-3 s-1 by 25°C. Die aktiverings energie, Ea, is bereken as 90.1 (±1.2) kJ.mol-1 en die entalpie en entropie van aktivering is onderskeidelik 87.7 (±1.2) kJ.mol-1 en 24.7 (±4.3) J.K-1.mol-1. Daar is gevind dat die akwasie reaksie konstante afhanklik was van die soutsuur konsentrasie: dit neem af soos die soutsuur konsentrasie toeneem. Met behulp van die regressie lyn is die anasie tempo konstante bepaal by 25°C as 1.62 (±0.11) x10-3 M-1s-1. Die aktiveringsenergie is bepaal as 88.0 (±1.4) kJ.mol-1 en die entalpie en entropie van aktivering, onderskeidelik as 85.6 (±1.4) kJ.mol-1 en –11.2 (±4.7) J.K-1.mol-1. Die invloed van die soutsuur konsentrasie op die anasie tempo konstante is nie bepaal nie. Die ewewigskonstante vir die reaksie wat ondersoek is, is bereken met die tempo konstantes vir die akwasie en anasie reaksies. Die ewewigskonstante, K6, is bereken as 0.0311 M-1 by 25°C. Toe die ewewigskonstante vergelyk is met die literatuur waardes, is gevind dat die ewewigskonstante afhanklik is van die soutsuur konsentrasie. Saam met die waardes wat in die literatuur gevind is, is die ewewigskonstante gebruik om twee distribusie diagramme te bereken. Die distribusie diagramme vir die Ru(III) spesies toon onderskeidelik 79.9% en 72.3% [RuCl6]3- in 12M HCl. Die twee distribusie diagramme is baie eenders en dit is nie moontlik om ‘n finale distribusie diagram op te trek totdat die uitstaande tempo konstantes tussen die akwachloro Ru(III) spesies bepaal word nie. Die tempo konstantes en termodinamiese waardes wat bepaal is vir die Ru(III) reaksie is vergelyk met gelyksoortige waardes in die literatuur van Rh(III) en Ir(III) omdat daar ooreenkomste tussen die platinum groep metale opgemerk is. Daar is bevind dat die akwasie én anasie reaksies die volgende patroon volg: Ru(III) > Rh(III) > Ir(III). Die verskille word in sekere gevalle benut in die raffinering van hierdie metale. Kristalle van dietileentriamien heksachlororuthenaat(III) is berei en gekarakteriseer met behulp van CHN analise en x-straal kristallografie. Die gemiddelde Cl-Ru bindingsafstand vir die kristal was 2.371 Å. Die kristalstruktuur is vergelyk met dié van heksaäkwaäluminium hexachlororuthenaat(III) tetrahidraat en diëtileentriamien heksachlororhodaat(III). Die chloried-metaal bindingsafstand vir die kristalle was soortgelyk (2.350 Å – 2.375 Å). Die diëtileentriamien kristalstrukture stem goed ooreen. Die gevolgtrekking was dat die kristalle wat voorberei is wel diëtileentriamien heksachlororuthenaat(III) was.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007. / Excitation functions and production rates are presented for various Ce and Pr radionuclides formed in the bombardment of 141Pr, natLa and natCe with protons. Extensive measure- ments were performed for 141Pr + p up to 100 MeV and for natLa + p up to 20 MeV. The possibility is investigated to utilize tandem targetry for the production of no-carrier-added 139Ce of high radionuclidic purity, having a Pr target in the higher energy slot followed by a La target in a lower energy slot. 141Pr(p,3n)139mNd!139Pr is investigated as an al- ternative to the direct production route 140Ce(p,2n)139Pr for producing no-carrier-added 139Pr of high radionuclidic purity. The advantages and disadvantages of both production routes are discussed. The simultaneous production of 139Pr and 140Nd using Pr as target is also investigated. Experimental thick-target production rates are presented for Pr ra- dionuclides formed in the bombardment of natCe with protons at incident energies of 20, 26 and 32 MeV. All the experimental excitation functions obtained in this work are compared with theoretical predictions by means of the geometry-dependent hybrid (GDH) model as implemented in the code ALICE-IPPE. The results of this work are also compared with previous literature experimental data, if available.

Thesis (PhD)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: A study was undertaken to investigate the radiochemical stability of the βiodoethoxyl moiety, a relatively novel prosthetic group employed in radiopharmaceutical chemistry, in which an oxygen atom in a β-position relative to the radioiodine atom has a stabilising effect on the aliphatic carbon-iodine bond. The investigation was started as a pilot study by synthesising various model compounds containing a β-radioiodoethoxyl moiety, as well as two reference compounds lacking such a moiety. The purpose was to determine the influence of various groups in the vicinity of the β-oxygen atom on the stability of the abovementioned moiety. Radiochemical stability tests were carried out in vitro at 37°C in human blood serum. The results confirmed the superior stability of such a moiety compared to that of the reference compounds and also showed that the branching of such an aliphatic unit resulted in a considerable improvement in its stability, especially over a longer period. The investigation was extended to the synthesis of other compounds containing a few selected β-iodoethoxyl moieties that showed improved stability in the pilot study work. Reference compounds containing the classical iodovinyl unit, as well as those lacking a stabilising β- oxygen atom, were also prepared. The carrier molecules used in this part of the work was a benzamide containing a phenolic oxygen atom which acted as the β-oxygen atom, as well as two heterocyclic amines, benzotriazole and 2-methyl-5-nitroimidazole, in which the β- iodoethoxyl moiety was linked to a secondary nitrogen atom. Various suitable alkylating agents were prepared, chemically linked to the carrier molecules, the resulting intermediate compounds converted into tosylate or triflate iodination precursors and labelled with radioiodine by means of iodide-for-tosylate/triflate exchange. In vitro stability tests of these compounds showed similar trends to those obtained with the model compounds. Moreover, the stability of the stabilised β-iodoethoxyl moiety compared favourably with that of the iodovinyl unit, especially when incorporated into a heterocyclic amine. The results of this study have shown that some of the radioiodinated compounds synthesized in this work, especially the nitroimidazole derivatives, have the potential to be considered as novel radiopharmaceuticals. / AFRIKAANSE OPSOMMING: 'n Studie is onderneem om die radiochemiese stabiliteit van die β-jodium-etoksi-eenheid te ondersoek. Dié eenheid is 'n relatief nuwe prostetiese groep wat in radiofarmaseutiese chemie gebruik word. Die suurstofatoom wat in 'n β-posisie relatief tot die radiojodiumatoom voorkom, oefen 'n stabiliserende invloed op die alifatiese koolstof-jodiumbinding uit. Die ondersoek het met 'n loodsstudie begin deur verskillende modelverbindings te sintetiseer wat 'n β-radiojodium-etoksi-eenheid bevat, asook twee verwysingsverbindings waarin so 'n eenheid ontbreek. Die doel hiermee was om die invloed van verskillende groepe, wat in die omgewing van die β-suurstofatoom voorkom, op die stabiliteit van die eenheid te bepaal. Radiochemiese stabiliteitstoetse is uitgevoer deur middel van inkubering in menslike bloedserum by 37°C. Die resultate het die groter stabiliteit van so 'n eenheid in vergelyking met dié van die verwysingsverbindings aangetoon, en het ook uitgewys dat vertakking van so 'n alifatiese eenheid 'n aansienlike verbetering in die stabiliteit tot gevolg gehad het, veraloor 'n langer periode. Die ondersoek is vervolgens uitgebrei deur verdere verbindings te sintetiseer wat beskik oor bepaalde uitgesoekte β-jodium-etoksi-eenhede, wat verbeterde stabiliteit in die loodsstudie getoon het. Verwysingsverbindings wat die klassieke jodiumvinieleenheid bevat het, sowel as dié waarin 'n stabiliserende β-suurstofatoom ontbreek het, is ook berei. Die draermolekules wat in hierdie deel van die studie gebruik is, was 'n bensamied met 'n fenoliese suurstofatoom wat as die β-suurstofatoom gedien het, sowel as twee heterosikliese amiene, bensotriasool en 2- metiel-5-nitroimidasool, waarin die β-jodium-etoksi-eenheid aan 'n sekondêre stikstofatoom geheg is. Verskillende geskikte alkileermiddels is berei, aan die draermolekules geheg, die tussenprodukte omskep in tosilate of triflate en met radiojodium gemerk deur middel van jodium-vir-tosilaatltriflaat-uitruiling. Stabiliteitstoetse van hierdie verbindings in bloedserum het soortgelyke tendense as dié van die aanvanklike modelverbindings getoon. Daarbenewens het die stabiliteit van die gestabiliseerde β-jodium-etoksi-eenheid gunstig vergelyk met dié van die jodiumviniel-eenheid, veral wanneer dit deel gevorm het van 'n heterosikliese amien. Die resultate van die studie het getoon dat sommige van die radiogejodeerde verbindings wat berei is, veral die nitroimidasoolderivate, die potensiaal het om as nuwe radiofarmaseutiese verbindings gebruik te kan word.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Even capillary gas chromatography does not always give complete separation of the components of complex mixtures. During the last few decades several two-dimensional gas chromatographic techniques were developed to circumvent this problem and towards the end of the previous century, a technique that became known as comprehensive twodimensional gas chromatography, was introduced with which the peak capacity of capillary gas chromatography could be increased by at least two orders of magnitude. This technique is based on utilizing different separation mechanisms of two coupled chromatographic columns to get a better separation of complex mixtures than would be possible with the individual columns. To be classified as comprehensive twodimensional gas chromatography, the analytes eluted from the first or primary column must al be transferred to the second column as sharp sample pulses by, for example, focusing of analytes. Focusing of the analytes can be achieved by trapping or immobilizing the analytes in a short capillary tube that serves as a connection between the two columns, after which the trapped material is released as a sharp pulse into the secondary column by rapidly, i.e. within a fraction of a second, heating this capillary which therefore serves to modulate the effluent from the primary column. This ensures optimum separation on the secondary column and the independence of retention times of the analytes on the two columns. A modulator consisting of a capillary (modulator capillary) coated with a thick film of an apolar stationary phase was used in the present project to immobilize or trap the analytes. This capillary was housed in a stainless-steel tube (heater) which was subdivided into a number of segments of equal lengths (maximum of 10). These segments were heated sequentially to desorb the analytes from the inlet end of the modulator to its outlet end at such a rate as to generate and transfer a sharply focused analyte pulse into the secondary column. In a typical analysis each of the 10 segments of a lO-segment heater would, for example, be heated to a temperature 50°C higher than that of the gas chromatograph's oven (50°C temperature increment) within 200 milliseconds, after which each segment would be allowed to immediately cool down to the temperature of the oven. After the last segment had been heated, a pause of, for example, two seconds followed to allow analytes to be trapped in the modulator capillary after which the cycle was repeated until the analysis had been completed. For several reasons, heating the segments resistively by using a current of between 1 and 20 Ampere was preferred to the application of high voltages. A computer controlled power supply was developed with which any combination of duration of the energizing pulses of the segments from 10 to 2500 milliseconds, pause times from 100 milliseconds to 100 seconds and temperature increments of 100°C or higher could be used with acceptable precision and high reproducibility in comprehensive two-dimensional gas chromatographic analyses. The effectivity of the focusing that can be achieved with heaters having different numbers of segments, modulator capillaries with different inside diameters, different heating increments, as well as different rates at which the modulators are heated, were investigated. The best results were obtained with heaters having 8 and 10 segments, a modulator capillary with an inside diameter of 0.2 mm, a heating increment between 50°C and 10Goe, and a heating cycle composed of a total heating time of two seconds followed by a pause time of two to three seconds before the next cycle is started. A light petroleum oil fraction was used in a preliminary evaluation of the comprehensive two-dimensional system that was developed. At this stage of the project the influence of various parameters such as the average carrier gas velocity, the temperature program and the length of the secondary column was investigated. It was found that changing one parameter required the re-optimization of the other parameters. The concentrations of the sample also had a marked influence on the parameters that had to be used to achieve optimum results. A low sample concentration appeared to require a higher carrier gas velocity, a higher temperature-programming rate or considerably longer pause times to achieve satisfactory focusing of analytes, whereas too high a concentration resulted in breakthrough of the analytes from the modulator capillary. The two-dimensional gas chromatographic device was also interfaced to a quadrupole mass spectrometer. A GC-MS analysis of a petroleum oil sample gave mass spectra of surprisingly good quality in spite of the high scanning speed that was required by the sharp constituent peaks produced by the gas chromatographic component of the system. The two-dimensional system that was developed therefore appears to offer a costeffective alternative to other systems that have been developed elsewhere in which other modulation mechanisms are used. One remaining problem that still has to be solved is the unsatisfactory synchronization of the timing device of the power supply with that of the computer on which data are accumulated. Although the difference in timing may seem negligible, the result is that certain software packages cannot be used for the two-dimensional visualization of the data Of several possible solutions to the problem, redesigning the control circuitry of the power supply will be the first option to be explored. An important consideration in the development of the system was to avoid having moving parts so that the modulator could be installed in any gas chromatograph without requiring structural alterations to the instrument. No provision was therefore made to install the two columns and the modulator in separate temperature-programmable compartments in the oven of the gas chromatograph. During the evaluation of the present system it was, however, found that the parameters which gave acceptable results were confined to rather narrow limits. Not being able to cool the modulator to temperatures below that of the oven was found to be the most important limiting factor. A simple solution to this problem is to cool the modulator to a selected suitable temperature below the oven temperature with compressed air, the flow of which is regulated by a computer controlled mass flow regulator to maintain the same increment below the oven temperature right through an analysis. As this development was considered to be outside the scope of the present project, this idea was not implemented and evaluated. However, successful exploratory experiments were done in which the flow was mechanically regulated. A prototype of the component in which the modulator can be cooled was built and the mass flow regulator, control unit and software will be commissioned shortly. / AFRIKAANSE OPSOMMING: Volledige skeiding van die verbindings in 'n komplekse mengsel is selfs met kapillêre gaschromatografie nie altyd moontlik nie. Oor die afgelope paar dekades is verskillende tweedimensionele gaschromatografiese tegnieke ontwikkel om hierdie probleem te bowe te kom en redelik onlangs is 'n tegniek bekend gestel wat as omvattende tweedimensionele gaschromatografie bekend staan en wat die piekkapasiteit van 'n kapillêre gaschromatografiese skeiding teoreties met sowat twee ordegroottes kan verhoog. Hierdie tegniek berus op die aanwending van die verskillende skeidingsmeganismes van twee chromatografiese kolomme wat aan mekaar gekoppel word en waardeur verbeterde skeiding van komplekse mengsels verkry kan word. Hierdie tegniek kan egter slegs as omvattende tweedimensionele gaschromatografie beskou word as die analiete wat van die primêre kolom elueer volledig na die sekondêre kolom oorgedra word in die vorm van skerp gedefinieerde monsterpulse, byvoorbeeld deur fokussering van analiete. Fokussering van die analiete kan verkry word deur die eluaat van die primêre kolom te immobiliseer in 'n kort kapillêr tussen die twee kolomme waarna dit as 'n skerp puls op die sekondêre kolom ingelaat kan word deur die kapillêr, wat dus as modulator dien, vinnig, dit wil sê binne breuke van 'n sekonde, te verhit. Hierdeur word optimum skeiding in die sekondêre kolom verseker asook die onafhanklikheid van die retensietye van verbindings op die twee kolomme. In hierdie projek is gebruik gemaak van 'n modulator wat bestaan uit 'n kapillêr (modulatorkapillêr) belaag met 'n dik laag van 'n apolêre stasionêre fase om die analiete te immobiliseer. Die kapillêr is in 'n vlekvrye staalbuis (verhitter) geplaas wat in 'n aantal gelyke segmente verdeel is (maksimum van 10) en die segmente is vinnig opeenvolgend verhit om die analiete vanaf die inlaat- na die uitlaatkant van die modulator uit die stasionêre fase in die kapillêr te desorbeer en as 'n skerp gefokusseerde puls na die sekondêre kolom oor te dra In 'n tipiese analise sou elkeen van die segmente van 'n 10- segment verhitter, byvoorbeeld, binne 200 millisekondes tot 'n temperatuur 500e hoër as die temperatuur van die gaschromatograafoond (500e verhittingsinkrement) verhit word, waarna die betrokke segment toegelaat word om oombliklik tot die oondtemperatuur af te koel. Na verhitting van die laaste segment volg 'n wagtyd van, byvoorbeeld, twee sekondes om analiete wat uit die primêre kolom elueer toe te laat om in die modulatorkapillêr gesorbeer te word waarna die siklus herhaal word tot die einde van die analise. Om verskeie redes is besluit om die segmente elektries te verhit deur verkieslik hoë stroomsterktes van tussen 1 en 20 Ampere te gebruik in plaas daarvan om van hoë spannings gebruik te maak. 'n Gerekenariseerde kragbron is ontwikkel wat dit moontlik gemaak het om enige kombinasie van verhittingstyd per segment tussen 10 en 2500 millisekondes, wagtye van 100 millisekondes tot 100 sekondes tussen verhittings en temperatuurinkremente van 100°C en selfs hoër met bevredigende presisie en hoë reproduseerbaarheid vir omvattende tweedimensionele gaschromatografiese skeidings te gebruik. Ondersoek is ingestel na die effektiwiteit van fokussering wat verkry word deur verhitters met verskillende getalle segmente, modulatorkapillêre met verskillende binnedeursnitte, verskillende verhittingsinkremente, asook verskillende tempo's waarteen die modulatorkapillêr verhit word, te gebruik. Die beste resultate is verkry met 8- en 10- segment verhitters, 'n modulatorkapillêr met 0.2 mm binnedeursnit, 'n verhittingsinkrement tussen 50°C en 100°C en 'n verhittingsiklus bestaande uit 'n twee sekonde totale verhittingstyd gevolg deur twee tot drie sekondes wagtyd voor die volgende siklus begin. 'n Ligte aardolie-fraksie is gekies as die eerste monster vir die evaluering van die omvattende tweedimensionele sisteem wat ontwikkel is. In hierdie stadium van die projek is die invloed van verskillende parameters soos die gemiddelde vloeisnelheid van die draergas, die temperatuurprogram, asook die lengte van die sekondêre kolom ondersoek. Daar is gevind dat verandering van een parameter, byvoorbeeld die lengte van die sekondêre kolom, die heroptimering van die ander parameters vereis. Die konsentrasie van die monster het ook 'n bepalende invloed op die parameters wat 'n optimum skeiding van verbindings lewer. 'n Lae konsentrasie mag 'n hoër vloei, vinniger temperatuurprogram of heelwat langer wagtyd vereis om bevredigende fokussering van die analiete te verkry, terwyl 'n te hoë konsentrasie tot deurbraak van die analiete in die modulatorkapillêr kan lei. Die tweedimensionele gaschromatografiese sisteem IS ook aan 'n kwadrupoolmassaspektrometer gekoppel en analise van 'n aardolie-monster het massaspektra van verbasende goeie kwaliteit gelewer ten spyte van die hoë skandeerspoed wat deur die baie smal gaschromatografiese pieke wat deur die sisteem geproduseer word, vereis word. Die tweedimensionele sisteem wat ontwikkel is, stel klaarblyklik 'n kosteeffektiewe alternatief daar vir die enkele ander sisteme wat deur ander navorsingsgroepe ontwikkel is en waarin van ander modulatortipes gebruik gemaak word. Een oorblywende probleem is egter die onbevredigende sinchronisasie van die tydhousisteme van die kragbron en die rekenaar waarmee die data versamel word. Hoewel uiters gering, bring die verskil in tydsmeting van die twee komponente mee dat sekere sagtewarepakette nie vir die tweedimensionele voorstelling van die data gebruik kan word nie. Vanverskillende moontlike oplossings vir hierdie probleem, sal die herontwerp van die beheerstelsel van die kragbron eerste ondersoek word. 'n Belangrike oorweging ill die ontwikkeling van die huidige sisteem was om 'n modulator sonder bewegende dele te ontwikkel wat sonder moeite in enige gaschromatograaf geïnstalleer sou kon word. Daar is dus nie voorsiening gemaak vir die installering van die twee kapillêre kolomme en die modulator in afsonderlik temperatuurprogrammeerbare kompartemente in die gaschromatograafoond rue. Gedurende die ondersoek het dit egter geblyk dat die parameters wat bevredigende resultate lewer, as gevolg van hierdie ontwerpskriterium, tussen redelike nou grense lê. Die mees beperkende faktor is die feit dat die modulator nie benede die oondtemperatuur afgekoel kan word nie. 'n Eenvoudige oplossing vir hierdie probleem is afkoeling van dié modulator tot 'n geskikte selekteerbare temperatuur benede dié van die gaschromatograafoond met druklug waarvan die vloei met behulp van 'n rekenaarbeheerde klep geprogrammeer kan word. Aangesien hierdie ontwikkeling buite die bestek van die huidige ondersoek geval het, is die idee nie geïmplementeer en volledig geëvalueer nie. Voorlopige eksperimente waarin die lugvloei meganies beheer is, is wel suksesvol uitgevoer. 'n Prototipe van 'n geskikte onderdeel waarin die modulator afgekoel word, is vervaardig en die massavloeiregulerende klep, beheereenheid en sagteware sal eersdaags in gebruik geneem word.

Thesis (PhD)--Stellenbosch University , 1990. / ENGLISH ABSTRACT: Monatin, or 4-hydroxy-4-(3-indolylmethyl) glutamic acid is a high-intensity sweet tasting amino acid found in the root bark of the indigenous plant Schlerochiton ilicifolius. In the thesis the isolation, structure elucidation and a number of synthetic approaches toward the total synthesis of monatin are described. Extensive fractionation of an aqueous extract of the root bark of S. ilicifolius using AG50WX8 strong acid cation exchange resin followed by successive gel filtration procedures using Biogel P2- and Sephadex G10 gels and guided by the intense sweet taste resulted in the isolation of monatin as a mixture of salts in which the sodium salt predominates. Potassium and calcium are the two other cations present. The structure elucidation is based mainly on the analysis of data obtained for monatin and the lactone ester of the N-2,4-dinitrophenyl derivative, prepared by reaction of monatin with Sangers reagent and diazomethane, by 1H and 13C n.m.r. techniques. The X-ray crystallographic study of both monatin and the derivative proved disappointing in that the reflections measured were weak and as a consequence refinement of the data was severely curtailed. However the resultant structures do show the skeletal atoms of the two compounds and in each case the relative stereochemistry of the two chiral centres could be deduced. A comparison of the specific rotation of monatin with those of related 4-hydroxy-4-methylglutamic acids indicates that monatin could have the (2S,4S) configuration. Retrosynthetic analysis of the monatin molecule identified a number of routes which could be utilized for the synthesis of monatin and analogues in which the indole moiety is replaced by a phenyl or aryl group. Seven approaches toward the synthesis of monatin were investigated using in most instances model compounds to establish optimum reaction conditions. Only the last approach, based on a 1,3-dipolar cyclo-addition reaction met with a measure of success: reaction of the 1,3-dipolar compound formed by reaction of N-t-Boc-indole-3-aldehyde with methyl N-benzylglycinate, with the dipolarophile methyl 2-acetoxyacrylate, generated a pyrrolidine with the requisite substituents needed for the monatin structure. In the event the final step, the cleavage of the C-2--N bond of the substituted pyrrolidine ring to give monatin, failed. During the investigation of the 1,3-dipolar cycloaddition reaction several substituted pyrrolidines were prepared. In each case several racemic stereoisomers were formed. In addition a number of substituted oxazolines and pyrrolizidines were obtained as minor by-products during these reactions. The stereochemistry of these compounds was deduced from the proton-proton nuclear Overhauser effect studies and X-ray crystallographic data. / AFRIKAANSE OPSOMMING: Monatien, of 4-hidroksi-4-(3-indolielmetiel) glutamicnsuur is 'n aminosuur met 'n hoëintensiteit soet smaak, wat in die wortelbas van die inheemse plant Schlerochiton ilicifolius voorkom. In die proefskrif word die isolasie, struktuuropklaring en 'n aantal sintetiese benaderings tot die totaalsintese daarvan beskryf. Omvattende fraksionering van 'n waterige ekstrak van die wortelbas van S. ilicifolius met behulp van AG50WX8 sterksuur-katioonuitruilhars gevolg deur opeenvolgende gelfiltrasies op Biogel P2 en Sephadex G10 filtrasiegel met die intense soet smaak as indikator, het gelei tot die isolasie van monatien as 'n mengsel van soute waarin die natriumsout oorheers het. Kalium en kalsium is die ander twee katione wat ook voorgekom het. Die struktuuropklaring is hoofsaaklik gebaseer op 1H en 13C k.m.r.-data wat vir monatien en die laktoonester van die N-2,4-dinitrofeniel derivaat verkry is. Laasgenoemde verbinding is berei deur reaksie van monatien met Sanger se reagens en diasometaan. Die X-straalkristallografiese studie van beide monatien en die derivaat het teleurstellende resultate gelewer aangesien swak refleksie-intensiteite die daaruitspruitende verfyning beperk het. Die verkreë strukture toon egter weI die raamwerkatome van beide verbindings waaruit die relatiewe stereochemie van die twee chirale sentra afgelei kon word. Vergelyking van die spesifieke rotasie van monatien met die van die verwante 4-hidroksi-4-metielglutamiensure dui daarop dat monatien die (2S,4S) konfigurasie mag besit. Retrosintetiese analises van monatien het 'n aantal sintetiese roetes aangedui wat gevolg kon word vir die sintese van monatien en/of monatienanaloë waarin die indoolbrokstuk denr 'n feniel of arielgroep vervang is. Sewe benaderings waarin modelverbindings gebruik is om die gunstigste reaksietoestande te bepaal, is ondersoek. Slegs die laaste benadering, gebaseer op 'n 1,3-dipolêre siklo-addisiereaksie was gedeeltelik suksesvol, naamlik reaksie van die 1,3-dipolêre verbinding gevorm uit N-t-Boc-indool-3-aldehied en metiel N-bensielglisinaat met 'n dipolarofiel, metiel-2-asetoksi-akrilaat, wat 'n pirrolidien gelewer het met die vereiste substituente benodig vir die monatienstruktuur. Die laaste stap, naamlik splyting van die C-2--N binding van die gesubstitueerde pirrolidienring was onsuksesvol. Die ondersoek van die 1,3-dipolêre siklo-addisiereaksie het verskeie gesubstitueerde pirrolidiene as rasemiese sterioisomere gelewer. Hiermee saam het 'n aantal oksasoliene en pirrolisidiene as byprodukte gevorm en hulle strukture is met behulp van proton/proton kern-Overhauser-effekstudies en X-straalkristallografis afgelei.

Thesis (MSc )--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Thesis (PhD)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The use of solar distillation as a means of desalination to provide potable water to communities in remote and arid regions has often been discarded on economic grounds mainly because of the inherent low efficiency of relatively expensive solar distillation units (solar stills). Closer analysis of this constraint showed that by following a mainly Physical Chemistry approach (rather than the traditional engineering one), the technology could be made more economically attractive through (1) lowering the construction cost of the solar still and / or (2) increasing its operational life and / or (3) increasing its efficiency. The study into different solar still designs showed that, despite its limitations, the basin solar still is preferred due to its simplicity, ease of operation and low maintenance. Given the solar distillation process as formulated in this study, substitute durable components could be identified and optimised for this design. A basin solar still that costs about 80% less than a reference unit without an apparent drop in performance was consequently developed and successfully tested up to full plant scale. An in-house experimental facility that simulates solar still behaviour under controlled environmental conditions was developed to simulate conditions of lower radiation intensity and productivity, which enabled research into performance enhancement and microbiological water quality. It was found that (a) absorption of the radiation by the water plays an important part in productivity and that a productivity decrease of up to 33% can be expected as the black interior lining becomes contaminated, (b) the simulated winter productivity of the basin still was about 25% of the summer value due to the lesser amount of solar radiation hours, the lower angles of radiation incidence onto the cover and the decrease in water area receiving direct radiation, (c) an annual productivity increase of about 10% can be obtained when a particular reflector configuration is fixed behind the basin, and (d) the microbiological pasteurisation temperature is less than the distillation onset temperature. This study played an important role in making solar still technology affordable for use by poor, rural communities, as was demonstrated by the successful use of the research product (basin solar still) in a pilot drinking water plant at a typical target community. This was made possible through the use of evaluation models developed as part of this research, which addressed relevant construction and performance factors influencing the economic viability of the specific solar still. The following outcomes of this study can be regarded as new contributions to the field of solar distillation technology, namely (a) a test matrix that can be used to screen solar still construction materials at component level, (b) an evaluation model that can be used to determine the economic viability of solar stills at a given location, (c) a laboratory testing facility to study solar still behaviour under controlled conditions and (d) a solar still design that has been optimised and tested for local field application. / AFRIKAANSE OPSOMMING: Die gebruik van son-energie om brakwater deur middel van distillasie te ontsout en sodoende drinkwater aan afgeleë gemeenskappe te verskaf, is herhaaldelik in die verlede as ekonomies nie-lewensvatbaar aangetoon. Dit is hoofsaaklik toeskryfbaar aan die inherente lae effektiwiteit van sodanige stelsels, asook die hoë kapitaalkoste daaraan verbonde. Die hoofsaaklike faktore wat die tegnologie bekostigbaar kan maak, is egter hieruit afgelei en volgens 'n Fisiese Chemie benadering geoptimeer, naamlik (1) vermindering van die konstruksiekoste van die sondistilleerder-eenhede, en / of (2) verlenging van die operasionele leeftyd daarvan, en / of (3) verhoging van effektiwiteit van die stelsel. Die literatuurstudie het aangetoon dat die pan-tipe sondistilleerder-eenheid verkieslik as navorsingsbasis is omdat dit eenvoudig en maklik bedryf- en onderhoudbaar is. Vanuit die geformuleerde beskrywing van die sondistillasie-proses kon plaasvervangende komponente vir die sondistilleerder-eenheid geïdentifiseer en getoets word, wat daartoe gelei het dat 'n eenheid met dieselfde funksioneringseienskappe vir sowat 80% goedkoper ontwikkel kon word. 'n Laboratoriumopstelling waarmee lae bestralingskondisies gesimuleer kan word, is ontwikkel om navorsing op produktiwiteitsverbetering en mikrobiologiese produkwaterkwaliteit te doen. Dit is aangetoon dat (a) absorpsie van die inkomende bestraling deur die water belangrik is en dat 'n sondistilleerder-eenheid tot 33% minder produktief kan wees indien die swart voering binne die eenheid besoedel sou word, (b) winterproduktiwiteit daal tot 25% van somerproduktiwiteit as gevolg van die verminderde sonlig-ure, die laer invalshoek van die bestraling op die glasdeksel, en die gepaardgaande verkleining van die blootgestelde water-oppervlakte, (c) 'n gemiddelde produktiwiteitsverhoging van 10% deur weerkaatsers agter die sondistilleerder-eenheid teweeggebring kan word, en (d) die distillasie-temperatuur die water-ontsmettingstemperatuur oorskry. Hierdie navorsmg het 'n belangrike rol gespeelom sondistilleerder-tegnologie bekostigbaar vir behoeftge gemeenskappe in landelike gebiede te maak. Dit is gedemonstreer deur die suksesvolle toepassing van die navorsingsproduk (sondistilleerder-eenheid) in 'n drinkwatervoorsieningsprojek by 'n tipiese teikengemeenskap. Dit is vermag deur die gebruikmaking van evaluasie-modelle wat gedurende hierdie studie ontwikkel is, en wat die toepaslike konstruksie- en funksioneringsfaktore wat die ekonomiese lewensvatbaarheid van die eenheid beïnvloed, aanspreek. Die volgende navorsingsprodukte kan beskou word as nuut in die veld van sondistillasie-tegnologie, naamlik (a) 'n toetsmatriks wat gebruik kan word om komponente vir sondistilleeerders te evalueer, (b) 'n ekonomiese evalueringsmodel wat gebruik kan word om die bekostigbaarheid van sondistilleerders in 'n bepaalde gebied te bepaal, (c) 'n laboratorium-toetsfasiliteit om die werking van sondistilleerders onder beheerde kondisies te ondersoek en (d) 'n sondistilleerdereenheid wat doelgeskik vir plaaslike omstandighede ontwikkel en getoets is.