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Thesis (MSc)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Glycerol metabolism is paramount to the physiological adaptation by Saccharomyces cerevisiae to hyper-osmotic stress conditions. Glycerol metabolism also -plays a fundamental role in maintaining a redox state favourable for growth under fermentative conditions. All aspects of the relationship between redox balancing and glycerol metabolism are not yet fully defined and attempts to manipulate this relationship, i.e., to increase or decrease glycerol yields from fermentation, result in a redox disturbance that is often detrimental to other aspects of metabolism. Another aspect of glycerol metabolism that is not thoroughly understood, is how the various parameters of the glycerol synthesis pathway, each independently and in conjunction with each other, control the rate at which glycerol is synthesized. Addressing these questions has been the topic of this thesis. In this regard, the theory of metabolic control analysis (MeA) was adopted and calculations were performed with the aid of an experimentally validated kinetic model. To ascertain the in vivo substrate, product, coenzyme and known modifier concentrations of the glycerol synthesis pathway, reliable techniques to halt metabolism, extract and measure these metabolites had to be established. The metabolite concentrations constitute a portion of the parameters of the pathway and are necessary to construct a detailed kinetic model. Measuring the concentration of an intracellular metabolite enzymatically requires the cell extract to have an adequate quantity of the metabolite in question. This may be achieved by concentrating the cells, before extracting the metabolite, by means of rapid filtration. Then by freezing the cells with liquid nitrogen, metabolism can be halted instantly. It was found that when metabolites were measured, yields were largely dependent on the method of extraction, since different metabolites are sensitive to different pH and temperature conditions. Methods of extraction found to be reliable for the metabolites of interest in this study are presented in Chapter 3. Metabolic control coefficients calculated by the model helped identify the parameters that control flux through the glycerol synthesis pathway most rigidly. The first reaction of the pathway, catalyzed by NAO+-dependent glycerol 3- phosphate dehydrogenase, had a flux control coefficient ( c; )of 0.83 to 0.87 and exercises the majority of control of flux through the pathway, while the subsequent reaction, catalyzed by glycerol 3-phosphatase, had far less control (C:2 = 0.13 to 0.17). The response coefficients (RJ ) of various parameter metabolites indicate [x] that flux through the pathway is most responsive to the concentration of the substrate, DHAP (RJ = 0.48 to 0.69), followed by the concentration of the [DHAP] inhibitor, ATP (RJ =-0.21 to -0.5). Interestingly, the model also predicts that [ATP] the pathway responds far more severely to the ATP/ADP ratio than to the NADH/NAD ratio, because of the weak response coefficient attributed to NADH (RJ = 0.03 to 0.08). Thus, the model suggests that the targets most strategic [NADH] for altering glycerol synthesis would be the Vmax of the glycerol 3-phosphate dehydrogenase reaction and the concentrations of DHAP and ATP. Ideally, the approach would entail manipulating each of these parameters to their optimal levels in conjunction with each other, with the least detrimental physiological effect possible. / AFRIKAANSE OPSOMMING: Gliserolmetabolisme is noodsaaklik tydens die fisiologiese aanpassing van gis onder hiperosmotiese strestoestande. Dit speelook 'n fundamentele rol in die handhawing van 'n voordelige redokstoestand, tydens groei onder fermentatiewe kondisies. Alle aspekte rondom die verwantskap tussen redoksbalansering en gliserolmetabolisme is nog nie ten volle gedefinieer nie en pogings om hierdie verwantskap te manipuleer, m.a.w. om gliserolproduksie tydens fermentasie te verhoog of verlaag, het In redoksversteuring tot gevolg, wat dikwels nadelig teenoor ander aspekte van metabolisme is. Verder is die meganisme van hoe verskeie parameters in die gliserolsintese pad, beide afsonderlik en gesamentlik, die tempo van gliserolsintese beheer, nie ten volle duidelik nie. Die doel van hierdie studie was dus om die bogenoemde onduidelikhede te probeer verklaar. In hierdie verband is die teorie van metaboliese kontrole analise (MeA) gebruik, en berekeninge is uitgevoer met behulp van 'n eksperimenteel gevalideerde kinetiese model. Ten einde, die in vivo substraat-, produk-, koensiem-, asook bekende aktiveerder en inhibeerder-konsentrasies van die gliserolsintese pad te bepaal, moes betroubare tegnieke ontwikkel word om die metabolisme vinnig te stop en sodoende metaboliete te ekstraheer en te meet. Dié metabolietkonsentrasies vorm 'n deel van die parameters in die pad, en word dus benodig om 'n gedetailleerde kinetiese model saam te stel. Die ensiematiese bepaling van intrasellulêre metabolietkonsentrasies vereis dat die selekstrak genoegsame hoeveelhede van die metaboliete bevat. Dit kan verkry word deur die selle te konsentreer deur middel van 'n vinnige filtrasiestap voordat ekstraksie van die metaboliete plaasvind. Metabolisme word onmiddellik gestop deur die selle te vries met vloeibare stikstof. Die metaboliet-hoeveelhede het grootliks afgehang van die ekstraksie-metode gebruik, aangesien verskillende metaboliete gevoelig is vir verskeie pH en temperatuurkondisies. Betroubare ekstraksiemetodes vir die metaboliete van belang vir hierdie studie word aangedui in Hoofstuk 3 van die tesis. Metaboliese kontrole koëeffisiënte wat met die model bereken is, het daardie parameters geïdentifiseer wat die fluksie deur die gliserolsintese pad die meeste beïnvloed. pie eerste reaksie in die pad, wat deur NAD+-afhanklike gliserol 3-fosfaat dehidrogenase gekataliseer word, besit 'n fluksie kontrolekoëeffisiënt ( C~) van 0.83 tot 0.87, en oefen die grootste beheer uit oor fluksie deur die pad. Die daaropvolgende reaksie, gekataliseer deur gliserol 3-fosfatase, handhaaf minder kontrole oor fluksie deur die pad (C;2 = 0.13 tot 0.17). Responskoëeffisiënte (RJ ) van verskeie parametermetaboliete dui [x) daarop dat die fluksie deur die pad die sterkste deur substraat (DHAP) konsentrasie beïnvloed word (RJ = 0.48 tot 0.69), gevolg deur inhibeerder [DHA?) (ATP) konsentrasie (RJ =-0.21 tot -0.5). Daarbenewens dui die model oak aan [AT?) dat die pad meer sensitief is teenoor die ATP/ADP verhouding, relatief tot die NADH/NAD+ verhouding, wat die gevolg is van die klein responskoëeffisiënt teenoor NADH (RJ =0.03 tot 0.08). Die model suggereer dus dat die Vmaks [NADH) van die gliserol 3-fosfaat dehidrogenase reaksie, asook die DHAP en ATP konsentrasies, die mees strategiese teikens vir manipulering van gliserolsintese behoort te wees. Die ideale benadering sal dus wees om al hierdie parameters in samehang met mekaar te kan manipuleer tot huloptimale vlakke, met die minste ontwrigting van die sel se fisiologie.

Orientador: Leandro Martins / Banca: Dulce Helena Siqueira Silva / Banca: Dilson Cardoso / Resumo: As propriedades catalíticas de zeólitas micro e micro-mesoporoas foram avaliadas pela desidratação do glicerol em fase gasosa. A dessilicação foi a metodologia utilizada para criar mesoporos nas zeólitas, diminuir as limitações difusionais e aumentar a conversão de glicerol devido a esse sistema hierárquico de poros criados no cristal zeolítico. A composição química e estrutural dos catalisadores foi estudada por difração de raios-X, isotermas de adsorção-dessorção de nitrogênio, TPD-NH3 e quimissorção de piridina seguida por espectroscopia IV. Embora o objetivo fosse dessilicar para criar mesoporosidade nos cristais zeolíticos, a dessilicação promoveu a firmação de alumínio extra-rede que afeta a conversão e a distribuição dos produtos. Os resultados mostram claramente que zeólitas mesoporosas permitem a rápida difusão e consequentemente melhoram a cinética da reação. Entretanto, uma atenção especial foi dada à dessilicação porque tratamentos severos afetam negativamente, interferindo na distribuição relativa dos sítios ácidos de Brønsted e Lewis e, consequentemente, na ineficiência catalítica promovida por esses materiais. Contudo, durante a reação catalítica, os mesoporos intra-cristalisnos permitem compostos carbonáceos serem depositados dentro dos mesmos, resultando em microporos menos bloqueados por coque e aumentando a sua estabilidade / Abstract: The catalytic properties of monomodal microporous and bimodal micro-mesoporous zeolites were investigated in the gas-phase dehydration of glycerol. The desilication methodology used to produce the mesoporous zeolites minimized diffusion limitations and increased glycerol conversion in the catalytic reaction due to the hierarchical system of secondary pores created in the zeolite crystals. The chemical and structural properties of the catalyst were studied by X-ray diffraction, nitrogen adsorption-desorption isotherms, NH3-TPD and pyridine chemisorption followed by IR-spectroscopy. Although the aim was to desilicate to create mesoporosity in the zeolite crystals, the desilication promoted the formation of extra-framework aluminum species that affected the conversion of glycerol and the products distribution. The results clearly show that the mesoporous zeolites with designed mesopore structure allowed a rapid diffusion and consequently improved the reaction kinetics. However, especial attention must be given to the desilication procedure because the severity of the treatment negatively interfered on the Brønsted and Lewis acid sites relative concentration and, consequently, in the efficiency of the catalysis performed by these materials. On the other hand, during the catalytic reaction, the intracrystalline mesopores allowed carbonaceous compounds to be deposited herein, resulting in less blocked micropores and catalysts with higher long-term stability / Mestre

Biomass is a renewable resource as an alternative to fossil fuels for chemical and fuel production. Through depolymerization, such as hydrolysis and pyrolysis, biomass can be converted to numerous oxygenates, which can be further upgraded into value-added products. This thesis processes a fundamental study to investigate the upgrading of two platform chemicals, furfural and glycerol, which are produced from hemicellulose and triglyceride, respectively. The ring-opening of tetrahydrofurfuryl alcohol (THFA), formed by full hydrogenation of furfural, produces a valuable monomer, 1,5-pentanediol (1,5-PeD). This thesis reveals that the ring-opening of partially hydrogenated furfural to produce 1,5-pentanediol is a promising pathway, which has a lower activation barrier than that from the furfural-THFA-1,5-PeD pathway. The surface with strong interaction with furan ring can enhance the ring-opening reaction. However, a proper binding with the furan ring is also critical to avoid further decomposition. The hydrodeoxygenation (HDO) reaction can convert furfural to 2-methylfuran, a promising fuel additive. A comparison of bimetallic catalysts consisting of 3d transition metal over platinum, 3d/Pt(111) surfaces suggests that the 3d-terminated surfaces with strong oxophilic metal modifier have high HDO activity. However, Pt is a precious metal and the 3d-terminated 3d/Pt(111) is unstable due to the diffusion of the 3d metal. The two drawbacks make 3d/Pt catalysts unpractical for industrial use. Molybdenum carbide (Mo2C) shows Pt-like properties as a substrate and has high diffusion barrier to stabilize the surface 3d atoms, making it an ideal material to replace Pt. The 3d/Mo2C shows similar furfural HDO activity to 3d/Pt(111) with an enhanced stability in both surface science experiment and reactor evaluations. Due to the promising performance of 3d/Mo2C catalysts, they can be utilized in the HDO reaction of glycerol. Glycerol has three C-O bonds, and the selective HDO reaction upgrades glycerol into various products by cleaving different numbers of C-O bonds. The strong oxophilicity makes Mo2C active to break all C-O bonds of glycerol forming propylene. The Cu modifier can reduce the oxophilictiy of the Cu/Mo¬2C surface and products with fewer C-O bonds cleaved are observed as Cu coverage increases.

Zugl.: Bonn, Univ., Diss., 2008

Much work has been done towards the hydrogenolysis of glycerol to 1,2-PDO and 1,3-PDO using various heterogeneous systems including Rh, Ru, Pt, PtRu, copper systems and Raney Ni in batch systems. However, routes to lower alcohols, such as 1-propanol and ethanol have been less discussed. From an industry point of view, the production of lower alcohols, such as propanol and ethanol, is very interesting. Different ruthenium, palladium and platinum catalysts were employed to study the effect of the support on the catalytic performance in batch mode. These catalysts were evaluated for their production of lower alcohols, especially 1-propanol using concentrated glycerol solutions. Among the other solid acids tested in combination with Ru/C, Amberlyst DT gave the most promising results from a 1-PO point of view, achieving a 34.9 mol% glycerol conversion with a selectivity of 38 mol% selectivity to 1-propanol. Despite the low glycerol conversion (1.3 mol%), Pd/C gave a promising 1-PO selectivity (> 85 mol%). The use of supported Ni catalysts, an inexpensive system, towards the chemical transformation of glycerol to lower alcohols, has appeared less frequently in the literature. The activity of Ni supported catalysts on silica and alumina was studied for the transformation of glycerol to lower alcohols, primarily 1-propanol and ethanol in a fixed bed continuous flow reactor. Several characterisation techniques were performed on the fresh and used catalyst, such as BET, XRD, TPD, TPR, TGA and electron microscopy. The objective was also to continue the development of a more detailed mechanistic understanding of the formation of lower alcohols from glycerol. In an endeavour to understand the process better, the role of proposed intermediates, 1,2-propanediol, 1,3- propanediol, ethylene glycol and ethanol was investigated, as well as the influence of the hydrogen partial pressure. Under the reaction conditions employed, it was clear that the hydrogenolysis of C-C and C-O bonds of glycerol took place to a lesser extent when compared to dehydrogenation and dehydration which are seen as the dominating initial steps. Ethanol was produced in high selectivities with 1,2-propanediol as feed and 1-propanol was the main product obtained when 1,3-propanediol was used as feed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2010.

Zugl.: Kaiserslautern, Techn. Univ., Diss., 2008

Thesis (Ph. D.)--Johns Hopkins University. / Biography. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1966. / Typescript eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 59-62)

Thesis (Ph. D.)--Johns Hopkins University. / Biography. Includes bibliographical references.