Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Positron annihilation lifetime spectroscopy (PALS) is well established as a novel method currently available for the study of polymers at a molecular level because of its sensitivity to the microstructural changes in the polymer matrix. The technique provides unique, but limited, information of the solid state structure – primarily on the nature of the free volume (or unoccupied space) in the polymer due to the less dense packing of polymer chains relative to in other solid materials. In the case of completely homogeneous polymer materials the measurement and interpretation of the positron annihilation parameters is relatively simple. However, in the case of polymers with more complex morphologies the situation becomes less clear. This is due to the possibility of the formation, localization and subsequent annihilation of o-Ps (ortho-positronium) within different areas of the complex morphology. This can result in more than one o-Ps lifetime component being present, and each of the different components corresponds to areas with differing types and amounts of 'open spaces'. In this study a detailed and systematic approach was taken to study the positron annihilation parameters in various semi-crystalline polymers and to correlate these to the chain structure and morphology of the materials. The study focused specifically on polyolefin polymers as these are the most widely used semi-crystalline materials, but more importantly, they offer the possibility to produce a variety of morphological complexity by simple manipulation of the chain structure – while there is essentially no difference in the chemical composition of the materials. The copolymers were selected to study the influence of short-chain branching (amount and length), short-chain branching distribution and tacticity on the morphology, and subsequent positron annihilation lifetime parameters. Three separate topics were addressed. First, preparative temperature rising elution fractionation was used to isolate polymer samples that are homogeneously crystallisable and to produce a series of polymers with differing chain structure and resultant morphologies. Second, additional series were produced by removing specific crystallisable fractions from the bulk materials. Third, the temperature variation of the samples as they approach and go through the crystalline melting point was studied. All the raw positron data were found to be best fitted with a four-component positron annihilation lifetime analysis. The longest lifetime (which is attributed to annihilation of o-Ps in the amorphous phase of the materials) showed systematic variations with the degree and nature of the short-chain branding, tacticity variation, a combination of both short-chain branching and tacticity, and changes in the amorphous phase as a result of heating. The third lifetime component (which is attributed to o-Ps annihilation in or around the crystalline areas of the materials) showed less variation across the sample series. Typically, greater variations were observed in the propylene copolymers than in the ethylene copolymers, which are reflective of the more complex chain structure and corresponding morphology in the propylene copolymer series. Direct evidence for a contribution from the nature of the amorphous phase to the bulk microhardness of the sample was also found. / AFRIKAANSE OPSOMMING: Positronvernietigingsleeftydspektroskopie (PALS) is goed gevestig as ‘n nuwe metode vir die studie van polimere op molekulêrevlak agv die sensitiwiteit van die metode vir mikrostrukturele veranderings in die polimeermatriks. Hierdie tegniek verskaf unieke, maar beperkte, inligting aangaande die vastetoestandstruktuur – veral aangaande die aard van die vryevolume (of onbesette spasie) in die polimeer as gevolg van die minder digte verpakking van polimeerkettings relatief tot in ander vastestowwe. In die geval van volledig homogene polimeriese materiale is die meet en interpretasie van die positronvernietigingsparameters relatief eenvoudig. Maar in die geval van polimere met meer komplekse morfologieë is die situasie minder duidelik. Die rede hiervoor is die moontlikheid vir die formasie, lokalisering en gevolglike vernietiging van o-Ps (orto-positronium) in die verskillende areas van die komplekse morfologie. Dit kan tot gevolg hê dat meer as een o-Ps komponent teenwoordig is en waar elk van die verskillende komponente ooreenstem met areas met verskillende tipes en hoeveelhede 'oop spasies'. In hierdie studie is ‘n sistematiese, in-diepte benadering gebruik om die positronvernietigingsparameters in verskeie semikristallyne polimere te bestudeer en hulle te korreleer met dié van die kettingstruktuur en die morfologieë van die materiale. Hierdie studie het spesifiek gefokus op poliolefiene aangesien hulle die mees algemene semikristallyne materiale is wat gebruik word en, nog meer belangrik, hulle bied die geleentheid om verskeie komplekse morfologieë te lewer dmv eenvoudige manipulasie van die kettingstrukture – terwyl daar basies geen verandering in die chemiesesamestelling van die materiale is nie. Die kopolimere is gekies om die invloed van kort-ketting vertakking (lengte en hoeveelheid), kort-ketting vertakking verspreiding en taktisiteit op die morfologie en vervolgens die positronvernietigingsleeftyd parameters te bestudeer. Drie onderwerpe is aangespreek. Eerstens, preparatiewe temperatuurstygingelueringsfraksionering (prep-TREF) is gebruik om polimeermonsters wat homogeenkristalliseerbaar is te isoleer om sodoende 'n reeks polimere met verskillende kettingstrukture, en gevolglike morfologieë, te lewer. Tweedens, 'n addisionele reekse monsters is berei deur die verwydering van spesifieke kristalliseerbare fraksies vanaf die grootmaatmonsters. Derdens, die temperatuurverandering van die monsters wanneer die monsters naby aan die kristallyne smeltpunt is en wanneer hulle deur die kristallyne smeltpunt gaan is bestudeer. Daar is bevind dat alle rou positrondata ten beste gepas het in 'n vier-komponent positronvernietigingsleeftydanalise. Die langste leeftyd (wat toegeskryf is aan vernietiging van o-Ps in die amorfe fase van die materiaal) het sistematiese variasies getoon met die volgende: hoeveelheid en aard van die kort-kettingvertaking, verandering in taktisiteit, 'n kombinasie van beide kort-kettingvertakking en taktisiteit en veranderings in die amorfiesefase as gevolg van verhitting. Die derde leeftyd komponent (wat toegeskryf is aan die o-Ps vernietiging in of rondom die kristallyne areas van die materiale) het minder variasie in hierdie reeks monsters getoon. Daar is tipies meer variasie waargeneem in die propileenkopolimere as in die etileenkopolimere, wat ’n weerspieëling is van die meer komplekse kettingstruktuur en ooreenstemmende morfologie in die propileenkopolomeerreeks. Direkte bewys vir 'n bydrag van die aard van die amorfe fase tot die grootmaat mikrohardheid van monsters is ook bevind.

Thesis (PhD)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The crystallization of polyolefins is an important parameter in determining the properties of such materials. The crystallization phenomenon generally depends on the molecular symmetry (tacticity) and molecular weight of the material. In this study, a series of polypropylenes was prepared using heterogeneous MgCl2-supported Ziegler catalysts with two different external donors, diphenyldimethoxysilane (DPDMS) and methyl-phenyldimethoxysilane (MPDMS), and two different homogeneous metallocene catalysts, racethylene- bis(indenyl) zirconium dichloride, Et(Ind)2ZrCl2 (EI), and rac-ethylene-bis(4,5,6,7- tetrahydro-1-indenyl) zirconium dichloride, Et(H4Ind)2ZrCl2 (EI(4H)). Molecular hydrogen was used as terminating agent. In order to establish a correlation between the molecular weight and the crystallization of these polymers, fractionation of the materials according to crystallizability was performed by means of temperature rising elution fractionation (TREF). This affords the opportunity of blending materials of different molecular weights but similar symmetry. These materials were characterized using various analytical techniques: differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), 13C nuclear magnetic resonance spectroscopy (13C-NMR), high temperature gel permeation chromatography (HT-GPC) and Fourier-transform infrared spectroscopy (FT-IR). DSC was used to study the bulk crystallization of different polypropylene blends, most of which showed only one melting peak. The latter is usually associated with a high degree of cocrystallization. Turbidity analysis of the different polypropylene polymers, obtained using solution crystallization analysis by laser light scattering (SCALLS), provided good crystallization information – similar to that provided by crystallization analysis fractionation (CRYSTAF) and TREF. It was also possible to differentiate between polypropylenes with similar chemical structure but different tacticity and molecular weight. SCALLS results also showed that the blends of different isotactic polypropylene polymers were miscible and cocrystallization had occurred, whereas, the blends of syndiotactic polypropylene and different isotactic polypropylenes were not miscible and some interaction between phases had occurred. Optical microcopy (OM) and scanning electronic microscopy (SEM) were used to study the morphological properties of different isotactic polypropylenes. Results revealed a welldefined and large spherulitic morphology of mixed a1 (disordered) and a2 (ordered) crystal form structures. OM and SEM images also clearly showed an effect of molecular weight and tacticity on the crystal structure of the different polypropylene samples. Finally, various homopolymers and blends were studied to investigate the effect of molecular weight on the mechanical properties of these materials. This was done using microhardness testing and dynamic mechanical analysis. / AFRIKAANSE OPSOMMING: Die kristallisasie van poliolefiene is ‘n belangrike faktor wat die eienskappe van hierdie tipe materiale bepaal. In die algemeen hang kristallisasie af van die molekulêre simmetrie (taktisiteit) en molekulêre massa van die materiaal. ‘n Reeks polipropilene is berei deur gebruik te maak van heterogene MgCl2-ondersteunde Ziegler-kataliste met twee verskillende elektron donors, difenieldimetoksisilaan (DPDMS) en metielfenieldimetoksisilaan (MPDMS), en twee verskillende homogene metalloseenkataliste, rac-etileen-bis(indeniel) sirkoniumdichloried, Et(Ind)2ZrCl2 (EI), en rac-etileen-bis(4,5,6,7-tetrahidro-1-indeniel) sirkoniumdichloried, Et(H4Ind)2ZrCl2 (EI(4H)). Molekulêre waterstof is gebruik as termineringssagent. Ten einde ‘n verband te bepaal tussen die molekulêre massa en kristallisasie van hierdie polimere is hulle gefraksioneer op die basis van hulle kristallisseerbaarheid deur gebruik te maak van temperatuurstyging-elueringsfraksionering (TREF). Deur hierdie tegniek verkry ons materiale van verskillende molekulêre massa maar met dieselfde taktisiteit wat ons kan vermeng. Verskeie tegnieke is gebruik om hierdie materiale te karakteriseer: differensiële skandeerkalorometrie (DSC), wyehoek X-straal diffraksie (WAXS), 13C-kernmagnetiese resonansspektroskopie (13C-KMR), hoë-temperatuur gelpermeasiechromotagrafie (HT-GPC) en Fourier-transform-infrarooispektroskopie (FT-IR). DSC is gebruik om die vaste-toestand kristallisasie van verskeie vermengde polipropilene te bestudeer., en net een smeltpunt is in meeste gevalle waargeneem. Laasgenoemde word gewoonlik verbind met ‘n hoë mate van kokristallisasie. Oplossingkristallisasie analise, dmv laserligverstrooiing (SCALLS), is gebruik om die turbiditeit van die verskillende polipropileen kopolimeervermengings te bepaal. Goeie inligting aangaande die kristallisasie in oplossing – soortgelyk aan dié wat dmv die kristallisasie-analise-fraksioneringstegniek (CRYSTAF) en TREF bepaal is, is verkry. Dit was ook moontlik om te onderskei tussen polipropilene met soortgelyke chemiese strukture maar verskillende taktisiteit en molekulêre massas. SCALLS data het ook getoon dat die vermengings van verskeie isotaktiese polipropileen polimere versoenbaar was en dat kokristallisasie plaasgevind het, terwyl vermengings van sindiotaktiese polipropileen en verskeie isotaktiese polipropilene nie versoenbaar was nie en dat ‘n mate van fase-skeiding plaasgevind het. Optiese mikroskopie (OM) en skandeer-elektronmikroskopie (SEM) is gebruik om die morfologiese eienskappe van verskillende isotaktiese polipropilene te bepaal. Goed gedefineerde en groot sferulitiese morfologie van gemengde a1 (onordelike struktuur) en a2 (ordelike struktuur) kristal-strukture is waargeneem. OM en SEM beelde het ook gewys dat molekulêre massa en taktisiteit ‘n effek het op die kristalstruktuur van die verskillende polipropileenmonsters. Laastens is die meganiese eienskappe van ‘n verskeidenheid homopolimere en vermengde materiale bestudeer, deur gebruik te maak van mikro-hardheid metings en dinamiesmeganiese analise (DMA).

The pathogenic bacterium Mycobacterium tuberculosis (Mt) is the causative agent of tuberculosis, a widespread and fatal infectious disease. Today, treatment against tuberculosis involves a combination of drugs, which need to be taken for at least six months and which often causes severe side effects. Therefore, new drugs that are more effective and that give fewer side effects are needed. A characteristic feature of the Mt bacterium is its very complex and thick cell wall, which prevents many potential drug molecules from penetrating it. Inhibiting any one of the enzymes that are involved in its biosynthesis would therefore seem to be a good strategy for eliminating the Mt bacteria. The aim of this study was to characterize four enzymes involved in Mt cell wall biosynthesis. In order to do that, they were produced recombinantly in E. coli and purified. Crystallization experiments were set up in order to produce diffracting crystals, with the aim of structure determination and drug design.

Fractional crystallization, magma mixing, assimilation of continental crust, and how those processes modify volatile budgets, control the evolution of magma. As a consequence, the understanding of these processes, their magnitudes, and timescales is critical for interpreting ancient magma systems, their eruptions, and the potential future volcanic activity. In this dissertation I present the results of three projects. The first explores how magmatic processes affect magma reservoirs and eruption dynamics. The second explores where in the storage system and how often these processes occur. The third explores how volatile budgets are modified by processes such as crystallization, mixing, and assimilation. Volcán Popocatépetl (central México) erupted ~14100 14C yr BP producing the Tutti Frutti Plinian Eruption (TFPE). The eruption tapped two different silicic magmas that mixed just prior and during the eruption. The influx of mass and volatiles generated during the mixing of both magmas overpressured the reservoir, which was weakened at the top. The weakened reservoir relaxed while magma was tapped and collapsed to form a caldera at the surface. Although it is known that fractional crystallization, mixing, and assimilation can greatly modify magmas, the frequency and intensity of these events is not known. I investigated the magmatic processes responsible for the evolution of magmas erupted during five Plinian events of Popocatépetl volcano. Results show that during the last 23 ky magma was stored in two different zones, and was variably modified by replenishments of mafic magma. Interestingly, little evidence for large mafic inputs triggering explosive eruptions was found. Each of these processes alters the abundances of volatiles and introduces different types of volatiles to the system. Hence, the volatile budget of magma can have a rich and complex history. To investigate how volatile budgets evolve in active magma systems, I analyzed the abundances of volatiles (H2O, CO2, F, Cl, and S) in numerous glass inclusions trapped in phenocrysts. Results show that the magmas that produced the last five Plinian eruptions at Popocatépetl volcano evolved by crystallization and magma mixing, assimilation of the local carbonate basement is not chemically appreciable. Mixing with mafic magmas added substantial CO2 and S to the system, dewatered the magma, yet produced little change in the F contents of the magmas. / text

Lactose is used in many food/pharmaceutical products, despite powders containing amorphous lactose being difficult to handle because they tend to be sticky and are prone to crystallization and powder caking. There is therefore a market for lactose powder with improved functionality to facilitate powder handling. The aim of the proposed project was to produce a value-added, free-flowing and non-caking lactose powder that can be easily blended into other dairy products, such as dry-powder soups or drinks, and non-dairy products such as chocolate bars. The principle of particle coating during spray drying (in-situ coating), which exploits the phenomenon of solute segregation of different components within the drying droplet, was used for the purpose of producing such powders. In this work, spray-dried lactose powders containing low concentrations of edible additives, such as proteins, polymers or fat, were produced in order to investigate the ability of these additives to accumulate at the droplet surface during drying to form a coating that improves powder functional properties and limits powder caking. This thesis presents the results of the trials necessary to develop these coated powder by the use of an

The objectives of this work are to characterize and model the solvent-mediated phase transformation process of theophylline anhydrous crystals to the monohydrate crystals in an aqueous system. In order to model the transformation, the following processes are taken into account: (1) the dissolution kinetics of theophylline anhydrous crystals, (2) the kinetics of the formation of theophylline monohydrate nuclei, and (3) the growth kinetics of the monohydrate crystals. The driving forces for the above processes are determined from the concentration of theophylline in the solution and the solubilities of theophylline anhydrous and monohydrate. The solubilities of theophylline anhydrous and the monohydrate, and these three distinct processes along with the overall transformation phenomena were investigated in the present study. By using theophylline as a model compound we have gained some understanding of the kinetics of the solvent-mediated phase transformation between the metastable anhydrous form and the stable hydrated form of an organic compound and we were able to model the transformation process. By identifying the mechanisms for nucleation, growth of the hydrate form and the dissolution of the anhydrous form one can predict and control the transformation process. The growth kinetics of thymine monohydrate crystals at various temperatures are also investigated in the present study.

The mechanisms of the deterioration of cellulose acetate compounded with triphenyl phosphate were investigated. A key peak shift of 726cm⁻¹ to 718cm⁻¹ in the Raman spectrum of triphenyl phosphate (726cm-1 uncompounded) when compounded in cellulose acetate (718cm⁻¹) was tied to the action of C-O bonds in triphenyl phosphate. The molecular bonds responsible for the 726cm⁻¹ peak were identified by collecting and examining spectra of chemicals with functional groups similar to triphenyl phosphate. Initially it was hypothesized that triphenyl phosphate acts as nucleophilic catalyst of deacetylation. This mechanism was evaluated by dissolving triphenyl phosphate in solvents that served as functional group analogues of cellulose acetate. These liquid-solution systems have a faster rate of reaction and complete mixing with triphenyl phosphate compared with what is seen in cellulose acetate solid-solution systems. The results of the cellulose acetate analogue experiments did not support the hypothesis of triphenyl phosphate acting as a nucleophilic catalyst of deacetylation. The results instead support a new theory of deterioration induced by the recrystallization of triphenyl phosphate. Additionally, the prevailing theory of triphenyl phosphate induced deterioration as proposed by Shinagawa et al. in 1992 was reviewed. The experiments conducted here do not support Shinagawa's theory.

Synthesebedingt fällt die DTPMP als dunkelbraune, zähflüssige Lösung mit zahlreichen Verunreinigungen an. Diese Arbeit beschäftigt sich mit der Herstellung einer hochreinen, festen DTPMP. Hierfür wurden zwei unterschiedliche Reinigungsmethoden untersucht. Durch Umkristallisation und anschließendes Rühren in Ethanol konnte mit 95 % eine höhere Reinheit als bisher veröffentlicht erzielt werden. Eine alternative Reinigungsmethode stellt die Ausfällung als Erdalkali-DTPMP-Salz und anschließende Auflösung in Schwefelsäure und Abtrennung des entstehenden Erdalkalisulfats dar, wobei eine Reinheit > 99 % erzielt wurde. Zur strukturellen Charakterisierung wurden zahlreiche Kristallisationsexperimente zur Züchtung von Kristallen der DTPMP als Säure und deren Alkali- und Erdalkalisalzen durchgeführt. Weiterhin wurde das thermische Verhalten der DTPMP und deren Salzen charakterisiert. Unter den zahlreichen möglichen Anwendungen der DTPMP wurde beispielhaft die Wirksamkeit auf die Gipskristallisation untersucht.

The spatio-temporal attributes of intracellular calcium (Ca2+) transients activate various biological functions. These Ca2+ signaling events are triggered extracellularly through different stimuli and controlled intracellularly by the major Ca2+ storage organelle and by numerous Ca2+ pumps, channels, and Ca2+ binding proteins. Ca2+ transients can be significantly altered as a result of defects with signal modulation, leading to different diseases. Because of the fragility and intricacy of the Ca2+ signaling system, with the endo- and sarcoplasmic reticulum at the center, genetically-encoded Ca2+ probes that have been optimized for mammalian expression and fast kinetics are needed to observe global and local Ca2+ changes in different cells. Here, we first report the crystal structure determination of our genetically-encoded Ca2+ sensor CatchER which utilizes EGFP as the scaffold protein. Crystal structures of CatchER were resolved in the Ca2+-free, Ca2+-loaded, and gadolinium-loaded forms at 1.66, 1.20, and 1.78 Å, respectively. Analysis of all three structures established conformational changes in T203 and E222 produce the varying ratios of the neutral and anionic chromophore reflected in the absorbance spectrum where Ca2+ stabilizes the anionic chromophore and enhances the optical output. Since CatchER has miniscule fluorescence when expressed at 37˚C in mammalian cells, we enhanced its brightness by improving the folding at 37˚C, facilitating better chromophore formation. The resulting mutants are the CatchER-T series of Ca2+ sensors with CatchER-T’ having the most improvement in brightness at 37˚C. We also introduced the N149E mutation in the binding site to alter the Kd along with the brightness mutations. The resulting mutants were characterized and found to have weaker Kds compared to wild-type CatchER, similar quantum yields, and altered ratios of the neutral and anionic chromophore in the apo form. Then, CatchER-T’ was applied in situ to monitor Ca2+ changes globally in the ER/SR of C2C12, HEK293, and Cos-7 cells. A new construct consisting of CatchER-T’ and JP-45 was created to monitor local Ca2+ dynamics in the SR lumen of skeletal muscle cells. The results showed a difference between global and local SR Ca2+ release. We also examined the potential and spectroscopic properties to utilize some of our sensors in T cells to monitor the magnesium (Mg2+) flux in immune cells with faulty MagT1 receptors to understand the role of Mg2+ in the immune response.

La compréhension de la relation structure-propriété est un élément indispensable pour la conception et l'amélioration des matériaux, notamment ceux utilisés dans le domaine de l'emballage alimentaire. Afin de contribuer à la compréhension des phénomènes de transport dans le polylactide (PLA), les travaux de ce mémoire se sont portés sur la modulation de la microstructure du PLA en lien avec ses propriétés barrière aux gaz (oxygène, hélium) et aux composés organiques (esters éthyliques, sondes fluorescentes). La microstructure a été modulée i) par l'ajout de plastifiant (ATBC, PEG), ii) par la cristallisation selon trois procédés, le traitement thermique, la cristallisation induite par des composés organiques et le biétirage. Ces approches ont permis, respectivement, de faire varier le pourcentage de phase amorphe par rapport à la phase cristalline, la fraction de volume libre au sein de la phase amorphe, et la structure cristalline. L'augmentation de la cristallinité par recuit à partir du vitreux n'a pas conduit à une diminution systématique et importante des coefficients de transport des molécules de gaz (oxygène, hélium). Deux hypothèses principales ont ainsi été formulées pour expliquer ce comportement : la dédensification de la phase amorphe et la présence d'une phase amorphe mobile et d'une phase rigide. L'influence du biétirage sur les propriétés barrière aux gaz a été très limitée même au plus fort ratio d'étirage (4×4). Néanmoins cette technique a l'avantage de pouvoir réaliser des morphologies différentes.L'étude des coefficients de transport par plusieurs méthodes (sorption, perméation, diffusion par contact solide/solide) a mis en évidence la loi d'échelle ( ) dans le cas des molécules fluorescentes et a permis une première estimation du coefficient alpha. Une approche par Résonance Paramagnétique Electronique a permis de mettre en évidence des séparations de phase des systèmes plastifiés par ATBC et PEG. Cette méthode pourrait constituer un des moyens de sonder les hétérogénéités locales et les changements microstructuraux liés à l'interaction de molécules perméantes et de la matrice polymère, lors du transport. / The understanding of the relationship between structure and properties is fundamental for materials conception and improvement, in particular for those used in food packaging industry. To contribute to the understanding of the transport phenomena in polylactide (PLA), this study was focused on the adjustment of PLA microstructure modulation related to its gas (oxygen, helium) and organic compounds (ethyl esters, fluorescent molecules) barrier properties. The microstructure was modulated i) by adding plasticizers (ATBC, PEG), ii) by crystallizing according to 3 processes, thermal treatment, organic compounds induced crystallization and biaxially orientation. These approaches, respectively enabled to vary, the ratio of amorphous phase and crystalline phase, free volume fraction into amorphous phase and the crystalline structure. The increase in crystallinity degree, by annealing from cold state, did not result in a systematic and significant decrease of the gas molecules transport coefficient (oxygen, helium). Two main hypotheses were formulated to explain this behaviour: de-densification of amorphous phase and the presence of a mobile and a rigid amorphous phase. The influence of biaxially orientation on gas barrier properties was strongly limited even at the highest stretching ratio (4×4). Nevertheless several morphologies can be formed thanks to this technique.The transport coefficient study by several methods (sorption, permeation and diffusion by solid/solid contact) highlighted a scale law with the fluorescent molecules and allowed to a first estimation of the α coefficient. Thanks to Electronic Spin Resonance approach, phase separation of plasticized systems by ATBC and PEG were highlighted. This method could be one of the means to probe the local heterogeneities and the micro-structural changes related to the interaction of permeating molecules and polymer matrix during transport.