Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005. / This thesis begins with the description of the preparation of thirteen dithioesters (of the form Z- (C=S)-S-R) which were characterized via Fourier-transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (NMR) and ultraviolet spectroscopy (UV). The dithioesters were then used as reversible addition-fragmentation chain transfer (RAFT) mediating agents in the bulk polymerization of styrene, in order to observe differences in the kinetic behaviour of the polymerizations and, as a result, the efficiencies of the dithioesters in mediating the polymerizations.

Thesis (PhD (Chemistry and Polymer Science))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Due to the commercial, nutritional and health value of vegetable oils, seeds and beans, the analysis of their components is of much interest. In this dissertation oil-containing food products, specifically vegetable oils, seeds and beans, were investigated. Selected minor components of three locally produced vegetable oils, namely apricot kernel, avocado pear and macadamia nut oils were investigated using 31P NMR spectroscopy. These minor components, including 1,2 diacylglycerols, 1,3 diacylglycerols and free fatty acids, were identified in the 31P NMR spectra of each of the three vegetable oils for the first time. Two approaches were used for the quantification of the minor components present in the spectra. A calibration curve approach used known concentrations of standard minor components to establish calibration curves while a direct correlation approach calculated the unknown concentration of minor components in the vegetable oils using a known amount of standard compound within the analysis solution. These approaches aided in determining the concentration of minor components during storage studies in which vegetable oils were stored in five different ways: exposed to light, in a cupboard, in a cupboard wrapped in tin foil, at -8 °C and at 5 °C. It was found that determining the best storage condition for each oil was difficult since individual minor components were affected differently by the various storage conditions. However, in general the best storage conditions appeared to be 5 °C and -8 °C. The oil, protein and carbohydrate contents of sesame, sunflower, poppy, and pumpkin seeds, and soy, mung, black and kidney beans were analysed by thermogravimetric analysis and 13C NMR solid state NMR spectroscopy. It was shown that the first derivative of TGA data for seeds and beans can give valuable information about the carbohydrate, moisture, protein and fat content. This has not been previously demonstrated. For the seeds, the integration of a region between 270–480 ºC was equal to the sum of the oil and protein content and compared well to quantitative results obtained by other conventional methods. For beans the integration of a region between 180-590 ºC, gave a value which represented the sum of the oil, protein and carbohydrate content. 13C solid state NMR spectroscopy, including SPE-MAS, CP-MAS and variable contact time experiments, was carried out on these seeds and beans and gave valuable information on the solid-like and liquid-like components. To our knowledge these seeds and beans have never been previously analysed using this technique. 13C SPE-MAS NMR spectroscopy indicated that the seeds contained more liquid-like components than the beans. In turn the 13C CP-MAS NMR spectra indicated that beans had higher levels of solid-like components than the seeds. These conclusions correlated well with the quantities of liquid-like components and solid-like components that were determined by conventional methods and TGA. Preliminary studies using T1pH experiments on the components present in the seeds and beans led to a few observations. Most interesting is that a model using a two- phase fit in order to determine T1pH values appears to be more accurate than a one-phase model. / AFRIKAANSE OPSOMMING: Groente olies, sade en bone is ‘n onderwerp van groot belang omrede hul kommersiële, voeding en gesondheidswaardes. In hierdie tesis is olie-bevattende voedselprodukte, spesifiek groente-olies, sade en bone geanaliseer. Geselekteerde komponente teenwoordig in klein hoeveelhede in drie lokaal geproduseerde groente-olies, naamlik appelkoos-pit, avokadopeer en makadamia-neut olies is geanaliseer met behulp van 31P KMR spektroskopie. Hierdie komponente, insluitend 1,2 diasielglyserole, 1,3 diasielglyserole en ongebonde vetsure, is vir die eerste keer geïdentifiseer in die 31P KMR spektra van die drie groente olies. Twee benaderings is gebruik vir die hoeveelheids-bepaling van die komponente in die spektra. ‘n Yking-kurwe metode het gebruik gemaak van bekende hoeveelhede konsentrasies standaard komponente vir die opstel van yking-kurwes, terwyl ‘n direkte korrelasie metode gebruik is om die onbekende konsentrasie van komponente in groente olies te bepaal met behulp van ‘n bekende hoeveelheid standaard verbinding teenwoordig in die oplossing. Hierdie metodes het gelei tot die bepaling van die konsentrasies van die komponente gedurende vyf verskillende berging toestande wat ingesluit het: Blootgestel aan lig, in ‘n donker kas, in ‘n donker kas toegevou in tin foelie, bevries by -8 °C en in ’n koelkas by 5 °C. Dit was bevind dat bepaling van die beste bergingstoestand vir elke olie moeilik is aangesien die individuele komponente verskillend geaffekteer word deur die verskeie berging toestande. Die beste bergings toestand oor die algemeen blyk egter om by 5 °C en -8 °C te wees. Sesamsaad, sonneblomsaad, papawersaad en pampoensaad sowel as sojaboontjie, mungboontjie, swartboontjie en pronkboontjie se olie, protein en koolhidraat komponente was geanaliseer met behulp van termogravimetriese analise (TGA) en 13C soliede toestand KMR spektroskopie. Dit was bevind dat die eerste afgeleide van die TGA data waardevolle inligting lewer oor die komponent inhoud van elk van die sade en bone. Hierdie is nog nie vantevore bevind nie. Vir die sade, was die integrasie van ‘n area tussen 270–480 ºC gelyk aan die som van die olie en proteïen inhoud en het goed vergelyk met die waardes verky deur algemene analitiese metodes. Vir die boontjies, was die integrasie van ‘n area tussen 180-590 ºC gelyk aan die som van die olie, protein en koolhidraat inhoud. 13C vaste staat KMR spektroskopie, insluitende SPE-MAS, CP-MAS en variëerbare kontak-tyd eksperimente, was gedoen en het waardevolle inligting gelewer omtrent die solied-agtige en mobiel-agtige komponente. Hierdie sade en bone is tot ons kennis nog nie van te vore met die tegnieke ondersoek nie. 13C SPE-MAS NMR spektroskopie het aangedui dat daar ‘n groter hoeveelheid mobiel-agtige komponente in sade as in bone teenwoordig is. 13C CP-MAS NMR spektroskopie het weer aangedui dat daar ‘n groter hoeveelheid solied-agtige komponente in bone as in sade teenwoordig is. Hierdie gevolgtrekkings het goed vergelyk met die waarnemings verkry deur konvensionele analitiese metodes en TGA. Voorlopige studies op die komponente van sade en bone deur T1pH eksperimente het tot ‘n paar gevolgtrekkings gelei waarvan die mees interessantste was dat ‘n twee-fase model vir die bepaling van T1pH waardes beter resultate lewer as ‘n een-fase model.

Thesis (PhD)--Stellenbosch University, 2012. / See full text for abstract. / Sien volteks vir opsomming

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis, the recovery of RhIII from both synthetically prepared and authentic industrial PGM-containing solutions was systematically investigated via organic precipitation methods using several commercially available, N-containing organic receptors including (amongst others) diethylenetriamine (Deta), triethylenetetramine (Teta), tetraethylenepentamine (Tepa) and tris(2-aminoethyl)amine (Tren). These organic receptors act as precipitating agents in the presence of an appropriate protonating agent (HCl) by lowering the solubility of the PGM chlorido-anions through an ion-pairing mechanism. The recovery of RhIII from synthetically prepared PGM (RhIII and PtIV) containing solutions using these precipitants was excellent, while poor Rh recovery from authentic industrial process solutions was achieved. The poor Rh recovery from these process solutions was ascribed to the species distribution of the [RhCln(H2O)6-n]3-n complexes. In order to validate the proposition that RhIII speciation effects are responsible for the poor Rh recovery observed during the precipitation studies, attempt were made to describe the species distribution of the [RhCln(H2O)6-n]3-n (n=3-6) by means of high-resolution 103Rh NMR spectroscopy. A detailed high-resolution 103Rh NMR spectroscopic study of the series of [RhCln(H2O)6-n]3-n (n=3-6) complexes was conducted. During this study, all six RhIII aqua chlorido-complexes have unambiguously been characterized by means of high-resolution 103Rh NMR spectroscopy, proving the powerful analytical capability of this technique. Characterization of these complexes is based on the detailed analysis of the 35Cl/37Cl isotope effects which is observed in the 19.11 MHz 103Rh NMR resonances of the [RhCln(H2O)6-n]3-n (n=3-6) complexes in aqueous HCl solutions at 292 K. These resonances show that the “finestructure” of each of the 103Rh resonances may be understood in terms of its unique isotopologue, and in certain cases, the isotopomer distribution of each complex, which manifests as a result of its statistically expected 35Cl/37Cl isotopologue and isotopomer distributions. As a result, the 103Rh NMR resonance structure serves as a unique “NMRfingerprint”, which allows for the unambiguous assignment of [RhCln(H2O)6-n]3-n (n=3-6) complexes, without the reliance on accurate δ(103Rh) chemical shifts. Furthermore, this study reports the first direct species distribution diagram for the [RhCln(H2O)6-n]3-n (n=3-6) series of complexes (in aqueous HCl solutions at 292 K) as a function of the “free” (unbound) chloride concentration, constructed from 103Rh NMR measurements. The need for a revised speciation diagram of [RhCln(H2O)6-n]3-n (n=3-6) complexes is clearly reflected by the vast differences observed in the literature reported species distribution diagrams, which makes it difficult to decide which set of experimental conditions (if any) is required for the quantitative and “selective” recovery of RhIII from aqueous HCl solutions containing associated PGMs (Pt, Pd, Ir, Ru) as well as other transition metals. The documented species distribution diagrams for RhIII have been generally constructed via data from indirect (kinetic and spectrophotometric) measurements using dilute RhIII solutions at relatively high HCl concentrations, which implies that the RhIII:Clmole ratio is higher than what may be expected in authentic process solutions – an important aspect to consider when optimizing RhIII recovery methods. In addition, RhIII kinetic investigations reported in this study shows that ionic strength and temperature effects are important factors that dramatically influences the rate of RhIII ligand exchange (i.e. RhIII aquation reactions) which, in turn, have contributing effects on the species distribution of [RhCln(H2O)6-n]3-n complexes. Notable differences exist between the speciation diagram reported in this study and those documented in literature, especially at a “free” chloride concentration of 1.0 M. At this “free” chloride concentration, the [RhCl5(H2O)]2- complex anion was found to have an abundance of 34%, while literature reports an abundance of 80%. In order to ascertain its practical relevance, the proposed 103Rh NMR speciation method was extended, for the first time, to authentic industrial Rh feed solutions (Anglo Platinum PLC). Each of the 103Rh resonances was unambiguously assigned, and each species quantified. Moreover, the RhIII species distribution of the industrial Rh feed solution was accurately predicted by the “direct” speciation diagram constructed form 103Rh NMR measurements. After careful optimization of the Heraeus industrial feed solutions (optimal chloride concentration followed by thermal treatment for enhancing RhIII chloride anation reactions), the recovery of Rh via precipitation was repeated. In this instance, Rh recovery improved dramatically, with up to 95% of Rh removed from solution. This improvement is ascribed primarily to the increased “free” (unbound) chloride concentration. The presence of associated PGMs as well as other transition metals would lower the effective “free” chloride concentration, since these metals would act as “chloride binders”. By adjusting the total chloride concentration, RhIII chloride anation reactions is enhanced which leads to the [RhCln(H2O)6-n]3-n (n=5,6) complex anions being the dominant species in solution, therefore leading to improved Rh recovery. Moreover, it was shown that, under carefully controlled conditions, “selective” recovery of Rh is achieved using tris(2-aminoethyl)amine (Tren). Considering the fact that Rh is the last precious metal recovered in all PGM refineries, this can possibly provide a cost-effective route for the “upfront” (early stage) recovery of Rh from industrial PGM feed solutions. / AFRIKAANSE OPSOMMING: In hierdie tesis word die herwinning van RhIII uit laboratorium voorbereide sowel as ware industriële PGM-bevattende oplossings sistematies ondersoek deur middel van organiese neerslag metodes, deur gebruik te maak van verskeie kommersieël beskikbare, Nbevattende organiese reseptore insluitende dietileentriamien (Deta), tri-etileentetramien (Teta), tetra-etileenpentamien (Tepa) en tris(2-aminoetiel)amien (Tren). Hierdie organiese reseptore tree op as neerslag-agente in die teenwoordigheid van 'n geskikte protoneringsagent (in hierdie geval HCl) deur 'n verlaging van die oplosbaarheid van die PGM chloriedanione deur middel van 'n ioon parings meganisme. Die herwinning van RhIII vanuit laboratorium voorbereide PGM (RhIII en PtIV) oplossing met behulp van hierdie organiese neerslag-agente was uitstekend, terwyl Rh herwinning vanuit ware industriële oplossings swak was. Die onvolledige Rh herwinning uit hierdie industriële oplossings word toegeskryf aan die spesie-verspreiding van die [RhCln(H2O)6-n]3-n komplekse. Ten einde die effek van RhIII spesie-verspreiding op die herwinning van Rh te bestudeer, is gepoog om die spesieverspreiding van [RhCln(H2O)6-n]3-n (n=3-6) komplekse, deur middel van hoë resolusie 103Rh KMR spektroskopie, te beskryf. 'n Gedetailleerde hoë resolusie 103Rh KMR spektroskopiese studie van die reeks van [RhCln(H2O)6-n]3-n (n=3-6) komplekse was uitgevoer. Tydens hierdie studie was al ses RhIII aqua chlorido-komplekse ondubbelsinnig gekarakteriseer deur middel van hoë resolusie 103Rh KMR spektroskopie, wat bewys lewer van die kragtige analitiese vermoë van hierdie tegniek. Karakterisering van hierdie komplekse is gebaseer op die gedetailleerde analise van die 35Cl/37Cl isotoop effekte wat waargeneem word in die 19.11 MHz 103Rh KMR resonansies van die [RhCln(H2O)6-n]3-n (n=3-6) komplekse in HCl oplossings by 292 K. Hierdie resonansies toon dat die "fyn struktuur" van elk van die 103Rh resonansies verstaan kan word in terme van die unieke isotopoloog, en in sekere gevalle, die isotopomeer verspreiding van elke kompleks, wat manifesteer as 'n gevolg van die die statisties verwagte 35Cl/37Cl isotopoloog en isotopomeer verspreiding. Die 103Rh KMR resonansie-struktuur kan sodoende dien as 'n unieke "KMR-vingerafdruk", wat voorsiening maak vir die ondubbelsinnige karakterisering van [RhCln(H2O)6-n]3-n (n=3-6) komplekse, sonder om vertroue op akkurate δ(103Rh) chemiese verskuiwings te plaas. Hierdie studie rapporteer verder die eerste direkte spesie-verspreiding-diagram vir die [RhCln(H2O)6-n]3-n (n=3-6) reeks komplekse (in HCl oplossings by 292 K) as 'n funksie van die "vrye"(ongebonde) chloried-konsentrasie, verkry van 103Rh KMR metings. Die behoefte vir 'n aangepasde spesiasie-diagram vir die [RhCln(H2O)6-n]3-n (n=3-6) komplekse word duidelik weerspieël deur die groot verskille waargeneem in die literatuur gerapporteerde verspreidings diagramme, wat dit moeilik maak om te besluit watter stel eksperimentele toestande (indien enige) benodig word vir die kwantitatiewe en “selektiewe” herwinning van RhIII in HCl oplossings in die teenwoordigheid van gepaardgaande PGM (Pt, Pd, Ir, Ru) sowel as ander oorgangsmetale. Die gedokumenteerde spesie-verspreiding-diagramme vir RhIII is oor die algemeen verkry via data vanaf indirekte (kinetiese en spektrofotometriese metings) deur gebruik te maak van verdunde RhIII oplossings in relatiewe hoë HCl konsentrasies, wat impliseer dat die RhIII:Cl mol verhouding hoër is as wat verwag kan word in ware industriële proses oplossings - 'n belangrike aspek om te oorweeg gedurende die optimalisering van RhIII herwinning-metodes. Verder, die RhIII kinetiese ondersoeke gerapporteer in hierdie studie toon dat ioniese sterkte sowel as temperatuur effekte belangrike faktore is wat die tempo van RhIII ligand uitruiling (d.w.s. RhIII “aquation” reaksies), wat ‘n betekenisvolle invloed hê op die spesie-verspreiding van [RhCln(H2O)6-n]3-n komplekse. Aansienlike verskille bestaan tussen die spesiasie-diagram gerapporteer in hierdie studie en dit gedokumenteer in die literatuur, veral by 'n "vrye" chloried-konsentrasie van 1.0 M. By hierdie "vrye" chloried-konsentrasie was die [RhCl5(H2O)]2- komplekse anioon gevind om in 34% teenwoordig te wees (hierdie studie), terwyl die publiseerde verslae 80% rapporteer. Ten einde die praktiese toepaslikheid van die voorgestelde 103Rh KMR spesiasiemetode te bepaal, was (vir die eerste keer) ware industriële Rh oplossings (Anglo Platinum PLC) gebruik. Elk van die 103Rh resonansies was ondubbelsinnig gekarakteriseer, en elke Rh spesie teenwoordig gekwantifiseer. Daarbenewens is die RhIII spesie-verspreiding van die industriële Rh oplossing deur die "direkte" spesiasie-diagram saamgestel vanuit 103Rh KMR metings akkuraat voorspel. Die berekende RhIII spesie-verspreiding van die industriële Rh oplossings was akkuraat voorspel deur die voorgestelde “direkte” spesiasie-diagram soos saamgestel vanuit die 103Rh KMR metings. Na deeglike optimalisering van Heraeus industriële oplossings (optimale chloriedkonsentrasie gevolg deur termiese behandeling vir effektiewe RhIII chloried anasie reaksies), is die herwinning van Rh via neerslag metodes herhaal. In hierdie geval, het die Rh herwinning dramaties verbeter, met tot 95% van die Rh uit oplossing verwyder. Hierdie verbetering is hoofsaaklik toegeskryf aan die verhoogde "vry" (ongebonde) chloriedkonsentrasie. Die teenwoordigheid van geassosieerde PGM's sowel as ander oorgangsmetale sal die effektiewe "vrye" chloried-konsentrasie verlaag, aangesien hierdie metale sou optree as "chloried-binders". Deur die aanpassing van die totale chloried-konsentrasie, word RhIII chloried anasie reaksies verbeter, wat daartoe lei dat [RhCln(H2O)6-n]3-n (n = 5,6) komplekse anione die dominante spesies in oplossing word, en dus lei tot verbeterde Rh herwinning. Daarbenewens word verder aangetoon dat, onder noukeurig gekontroleerde voorwaardes, "selektiewe" herwinning van Rh bereik word deur gebruik te maak van tris(2-aminoetiel)amien (Tren). Met inagneming van die feit dat Rh die laaste edelmetaal is wat verhaal word in alle PGM-raffinaderye, kan dit 'n koste-effektiewe roete word vir die "vooraf" (vroeë-stadium) herwinning van Rh vanuit industriële PGM bevattende oplossings.

Thesis (PhD)--Stellenbosch University, 2013. / Please refer to full text to view abstract.

Submitted by admin tede (tede@pucgoias.edu.br) on 2017-08-21T12:12:23Z No. of bitstreams: 1 LUCAS CAMILO SILVA.pdf: 1027283 bytes, checksum: 4d040e2a5bb41a7711feb0c0686ea851 (MD5) / Made available in DSpace on 2017-08-21T12:12:23Z (GMT). No. of bitstreams: 1 LUCAS CAMILO SILVA.pdf: 1027283 bytes, checksum: 4d040e2a5bb41a7711feb0c0686ea851 (MD5) Previous issue date: 2017-03-10 / The complexity of biodiesel production processes through alkaline transesterification generates undesirable components to the process and increases the cost of quality control. The objective of this study is to analyze the biodiesel production process throughout the intermediate stages and propose analytical methodologies based on Nuclear Magnetic Resonance (NMR) and spectroscopy since these demanding less time for analysis and provide reliable information on various parameters without requiring large laboratory structure. The residual fatty acids and glycerol produced during transesterification of oils to biodiesel production can be raw material for glycerides synthesis by esterification reaction, an alternative technology to aggregate the biodiesel market. This paper presents an alternative to add value to these two byproducts under reaction conditions to easy control. It was used glycerol and fatty acids derived from the production of biodiesel and pure soybean fatty acid and glycerol pharmaceutical standard for evaluation of esterification with glycerol of fatty acids. For analysis of the NMR results was used factorial experimental design where was confirmed the gradually increasing concentration of glycerides in all batches getting to have 94.65% of glycerides formation when the catalyst used Methanesulfonic acid (M.S.A.) for reaction between Soybean distilled fatty acids (A.G.D.S.) and pharmaceutical standard glycerol. Was evaluated the esterification of Methyl Esters (ME) present in olein where it was found that the use of glycerol and standard pharmaceutical M.S.A. was the best reaction route where only 16.50% of the ME was not consume to generate glycerides. There was evaluation of the stages of the biodiesel production process and analysis of quality parameters by NMR where was possible to find contaminants in the raw material and determine the biodiesel quality results. Was make analysis of the standard glycerol pharmaceutical by xiv spectroscopy. For the treatment of the spectroscopy data, the PLSR model assembled and the results verified by the RMSEP calculation. It verified that the use of 20 components to construct the model showed RMSEP values ranging from the highest value referring to Color parameter and the lowest for the acidity analysis being 0.5659 and 0.00115 respectively, low values indicating that the model was satisfactory for predicting the quality results. It concluded that the synthesis of glycerides through reaction between glycerol and fatty acids occurred significantly. NMR and Spectroscopy techniques present potential for quality evaluation and reaction route for biodiesel production and synthesis of glycerides through esterification of esters and fatty acids as well as for quality control analyzes of glycerol pharmaceutical standard. / A complexidade de processos de produção de biodiesel através de transesterificação alcalina gera compostos indesejáveis. O objetivo deste trabalho é analisar o processo de produção de biodiesel ao longo das etapas e propor metodologias analíticas baseadas em Ressonância Magnética Nuclear (NMR) e espectroscopia visto que estas demandam menor tempo para análise e forneçam informações confiáveis de vários parâmetros. Ácidos graxos residuais e glicerol produzido durante a transesterificação de óleos para produção de biodiesel podem ser matérias-primas para síntese de glicerídeos através de reação de esterificação, uma alternativa tecnológica para agregar valor ao biodiesel no mercado. Este trabalho apresenta uma condição reacional de fácil controle para síntese de glicerídeos. Utilizou-se glicerol e ácidos graxos oriundos da produção de biodiesel e ácido graxos puros de soja e glicerol padrão farmacêutico para avaliação da esterificação de ácidos graxos com glicerol. Para análise dos resultados de NMR fez-se planejamento fatorial onde confirmou-se aumento gradativo de concentração de glicerídeos em todas bateladas chegando a ter-se um total de 94,65% de formação de glicerídeos. Avaliou-se a esterificação de metilésteres (ME) presentes na oleína onde verificou-se que a utilização de glicerol padrão farmacêutico e Ácido Metatoluenosulfônico M.S.A. foi a melhor rota reacional onde apenas 16,50% do ME não foi consumido para geração de glicerídeos. Fez-se avaliação das etapas do processo de produção de biodiesel e análise de parâmetros de qualidade através de NMR onde foi possível encontrar contaminantes na matériaprima e determinar resultados de qualidade do biodiesel. Fez ainda análise de glicerol padrão farmacêutico por espectroscopia. Para tratamento dos dados de espectroscopia, montou-se modelo de Regressão por Mínimos Quadrados Parciais (PLSR) e verificou-se os resultados através do cálculo do Erro Médio Quadrático de Previsão xii (RMSEP).Verificou-se que a utilização de 20 componentes para construção do modelo observou-se valores de RMSEP variando entre o maior valor referente ao parâmetro cor e o menor para a análise de acidez sendo 0,5659 e 0,00115 respectivamente, valores baixos que indicam que o modelo apresentou-se satisfatório para predição dos resultados de qualidade. Concluiu-se que a síntese de glicerídeos através de reação entre o glicerol e ácidos graxos ocorreram de maneira significativa. Técnicas de NMR e Espectroscopia apresentam potencial para avaliação de qualidade e rota reacional para produção de biodiesel e síntese de glicerídeos através de esterificação de ésteres e ácidos graxos assim como para análises de controle de qualidade de glicerol padrão farmacêutico.

CTG repeat is one of the most common triplet repeat sequences that have been found to form slipped-strand structures leading to self-expansion during DNA replication. The lengthening of these repeats causes the onset of neurodegenerative diseases such as myotonic dystrophy. Through designing a series of CTG repeat sequences with high hairpin populations, systematic analysis of imino and methyl proton spectra study has been carried out to investigate the length and structural roles of CTG repeats in affecting the propensity of hairpin formation. Direct NMR evidence has been obtained to support three types of hairpin structures in sequences containing one to ten CTG repeats. The differences in loop structures and extent of interactions observed in the hairpins account for the differences in hairpin formation propensity and explain how slippage occurs that lead to triplet repeat expansion. / DNA has been found to adopt unusual structures leading to different types of mutations, which can ultimately cause genetic diseases and cancers. In this thesis, investigations on (i) structural role of CTG repeats in trinucleotide repeat expansion, (ii) primer-template structures in strand slippage during low fidelity replication and (iii) sequence effect of nucleotide downstream of thymine templates on primer-template structures have been carried out using NMR spectroscopy. / In addition, NMR structural investigations have also been carried out to determine solution structures of primer-template models. NMR evidence confirms misalignment can occur in primer-templates upon misincorporation of dNTP opposite a template sequence, leading to bulge formation in the primer-template. Depending on the template sequence, further incorporation of dNTP can bring about either realignment or further stabilization of the primer-template structure. Consequently, either mismatch or deletion errors will occur, leading to base substitution or frameshift mutation. These results imply that DNA sequences do not only play a passive role to store genetic information in the replication process, they also play an active structural role in governing the types of mutation during low-fidelity DNA replication. / Some of the results in this thesis have been reported in the following peer-reviewed journals: (1) Chi, L. M. and Lam, S. L. (2005) Structural roles of CTG repeats in slippage expansion during DNA replication. Nucleic Acids Res, 33, 1604-1617. (2) Chi, L. M. and Lam, S. L. (2006) NMR investigation of DNA primer-template models: structural insights into dislocation mutagenesis in DNA replication. FEBS Lett. , 580, 6496-6500. (3) Chi, L. M. and Lam, S. L. (2007) NMR investigation of primer-template models: structural effect of sequence downstream of a thymine template on mutagenesis in DNA replication. Biochemistry, 46, 9292-9300. / Chi, Lai Man. / "August 2007." / Adviser: Lam Sik Lok. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 0877. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references (p. 102-112). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

Over the past few decades, amorphous solid dispersions (ASDs) have been of great interest to pharmaceutical scientists to address bioavailability issues associated with poorly water-soluble drugs. ASDs consist of an active pharmaceutical ingredient (API) that is typically dispersed in an inert polymeric matrix. Despite promising advantages, a major concern that has resulted in limited marketed formulations is the physical instability of these complex formulations. Physical instability is often manifested as phase heterogeneity, where the drug and carrier migrate and generate distinct phases, which can be a prelude to recrystallization. One important factor that dictates the physical stability of ASDs is the spatial distribution of API in the polymeric matrix. It is generally agreed that intimate mixing of the drug and polymer is necessary to achieve maximum stabilization, and thus understanding the factors controlling phase mixing and nano-domain structure of ASDs is crucial to rational formulation design. The focus of this thesis work is to better understand the factors involved in phase mixing on the nanometric level and get insights on the role of excipients on overall stabilization of these systems. The central hypothesis of this research is that an intimately mixed ASD will have better physical stability as compared to a partially homogeneous or a non-homogeneous system. Our approach is to probe and correlate phase homogeneity and intermolecular drug-excipient interactions to better understand the physical stability of ASDs primarily using solid-state nuclear magnetic resonance (SSNMR) spectroscopy and other solid-state characterization tools. A detailed investigation was carried out to understand the role of hydrogen bonding on compositional homogeneity on different model systems. A comprehensive characterization of ternary ASDs in terms of molecular interactions and physical stability was studied. Finally, long-term physical stability studies were conducted in order to understand the impact of different grades of a cellulosic polymer on phase homogeneity for two sets of samples prepared via different methods. Overall, through this research an attempt has been made to address some relevant questions pertaining to nano-phase heterogeneity in ASDs and provide a molecular level understanding of these complex systems to enable rational formulation design.

The aim of this research project was to use 15N nuclear magnetic resonance (NMR) spectroscopy to better understand nitrogen (N) cycling processes in forest plantations. In particular, the studies were designed to link to the effects of forest management practices and environmental conditions. 15N NMR cross polarization/magic angle spinning (CPMAS) and dipolar dephasing (DD)-CPMAS experiments of some simple N-containing compounds found widely in nature were first undertaken. This was done in order to understand how different sample conditions, such as the presence of moisture, sample mixing and dilution, affected the intensity and the observability of the NMR peaks corresponding to N containing functional groups. Our results exhibited changes in NMR signal intensities and various time constants calculated. In the case of variable contact time experiments, use of an equation that predicts both a bi-exponential rise and decay was found to fit the data obtained more accurately. The optimised parameters for 15N NMR CPMAS were then used along with other analytical techniques such as ion chromatography, total C and N and elemental analyses to study plant nutrient uptake, plant decomposition and the effect of forest ecosystem disturbances, in this case an insect infestation. These analytical data were also correlated with the changes in the 13C NMR spectra in order to gain a more comprehensive understanding of the chemical transformations in the forest ecosystem. / Doctor of Philosophy (PhD)

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