Dispersed niobia catalysts were prepared via a non-aqueous synthesis route. The effects of the type of oxide support, the support thermal pre-treatment, the calcination temperature and the niobia loading on the activity and selectivity for mesityl oxide (MO) synthesis at 160C were investigated in an autoclave reactor. The morphological and chemical properties of the catalysts were characterized via EDXRF, XRD, BET and Raman spectroscopy. The strength and nature of the acid sites were elucidated via in situ DRIFT spectra of the adsorption of pyridine as well as the temperature programmed desorption of NH3 interacting with the surface oxide phase. All four catalyst parameters had significant effects on the catalytic properties. Significantly, the nature of the acidity was clearly linked to the catalyst activity and particularly the catalyst stability. Catalysts exhibiting predominantly Lewis acidity invariably deactivated despite good initial activity, with the final acetone conversion dependent on the catalyst formulation. In contrast, catalysts exhibiting Bronsted acidity showed no evidence of catalyst deactivation after 8 hours of reaction. A plausible mechanism which explains these observations is proposed. Catalysts exhibiting Lewis acidity were more active when the supports were first activated at elevated temperature, likely due to a stronger support-surface oxide interaction as a consequence of increased surface coordinative unsaturation of the support. SiO¬2 supported catalysts exhibiting Bronsted acidity were more active if the supports were initially activated at 100C. Evidently, the hydroxyl groups on the oxide support contribute to the generation of Bronsted acidity. Different oxide supports gave rise to distinct acidic and catalytic properties in the niobia overlayer. The most striking example of this was the direct comparison of niobia dispersed onto two kinds of silica supports following the same preparative method. Unique and very strong acid sites were observed in niobia dispersed onto a commercial SiO¬2 catalyst carrier that were not observed in niobia dispersed onto fumed SiO¬2. For SiO2 catalysts, the activity increased linearly with niobia loading regardless of calcination temperature. In contrast, Al2O3 catalysts exhibited an initial increase in activity for MO synthesis with niobia loading followed by a decrease in activity after reaching a maximum activity below 1/3 monolayer coverage. The effect was more pronounced for catalysts exhibiting Bronsted acidity. It is proposed that adlineation sites are primarily responsible for catalytic activity in Nb2O5/-Al2O3 catalysts exhibiting Bronsted acidity. Niobia catalysts were developed using commercially available catalyst carriers as supports. The macrokinetics of MO and MIBK syntheses were investigated in a benchtop fixed bed flow reactor. The catalysts showed excellent activity for MO and MIBK syntheses at 160°C, typically 0.9 to 1.3 [g/hr*gcat]. However, the MIBK selectivity was constrained from 82 to 85% due to the coproduction of 2-propanol and diisobutyl ketone. The productivity for MO synthesis was found to be strongly dependent on the space velocity suggesting product inhibition. The intrinsic kinetics of the one-step synthesis of MIBK over a 15.2 wt% Pd/Nb2O5/SiO2 catalyst was investigated in an autoclave reactor. A kinetic model was developed and is reported. The one step synthesis of MIBK was investigated at the pilot plant scale via catalytic distillation (CD). An important finding was that while operating at 100% reflux, the accumulation of water in the reactive section resulted in the suppression of the DAA dehydration reaction. The in situ removal of water from the reactive section via an overhead distillate stream operating at 83 to 97% reflux directly resulted in an increase in MIBK productivity and hydrogen uptake efficiency by factors of about 20 yielding a moisture free reboiler product stream with as high as 53 wt% MIBK. The process was found to be controlled by the external mass transfer of hydrogen. Interestingly, the results suggest that the catalyst wetting efficiency affects the transport of hydrogen to the active sites as evidenced by the dependence of MO conversion on the reflux flow rate. The condition of minimum reflux flow rate and maximum hydrogen flow rate resulted in 97% MO conversion and 90 wt% MIBK selectivity.

Dispersed niobia catalysts were prepared via a non-aqueous synthesis route. The effects of the type of oxide support, the support thermal pre-treatment, the calcination temperature and the niobia loading on the activity and selectivity for mesityl oxide (MO) synthesis at 160C were investigated in an autoclave reactor. The morphological and chemical properties of the catalysts were characterized via EDXRF, XRD, BET and Raman spectroscopy. The strength and nature of the acid sites were elucidated via in situ DRIFT spectra of the adsorption of pyridine as well as the temperature programmed desorption of NH3 interacting with the surface oxide phase. All four catalyst parameters had significant effects on the catalytic properties. Significantly, the nature of the acidity was clearly linked to the catalyst activity and particularly the catalyst stability. Catalysts exhibiting predominantly Lewis acidity invariably deactivated despite good initial activity, with the final acetone conversion dependent on the catalyst formulation. In contrast, catalysts exhibiting Bronsted acidity showed no evidence of catalyst deactivation after 8 hours of reaction. A plausible mechanism which explains these observations is proposed. Catalysts exhibiting Lewis acidity were more active when the supports were first activated at elevated temperature, likely due to a stronger support-surface oxide interaction as a consequence of increased surface coordinative unsaturation of the support. SiO¬2 supported catalysts exhibiting Bronsted acidity were more active if the supports were initially activated at 100C. Evidently, the hydroxyl groups on the oxide support contribute to the generation of Bronsted acidity. Different oxide supports gave rise to distinct acidic and catalytic properties in the niobia overlayer. The most striking example of this was the direct comparison of niobia dispersed onto two kinds of silica supports following the same preparative method. Unique and very strong acid sites were observed in niobia dispersed onto a commercial SiO¬2 catalyst carrier that were not observed in niobia dispersed onto fumed SiO¬2. For SiO2 catalysts, the activity increased linearly with niobia loading regardless of calcination temperature. In contrast, Al2O3 catalysts exhibited an initial increase in activity for MO synthesis with niobia loading followed by a decrease in activity after reaching a maximum activity below 1/3 monolayer coverage. The effect was more pronounced for catalysts exhibiting Bronsted acidity. It is proposed that adlineation sites are primarily responsible for catalytic activity in Nb2O5/-Al2O3 catalysts exhibiting Bronsted acidity. Niobia catalysts were developed using commercially available catalyst carriers as supports. The macrokinetics of MO and MIBK syntheses were investigated in a benchtop fixed bed flow reactor. The catalysts showed excellent activity for MO and MIBK syntheses at 160°C, typically 0.9 to 1.3 [g/hr*gcat]. However, the MIBK selectivity was constrained from 82 to 85% due to the coproduction of 2-propanol and diisobutyl ketone. The productivity for MO synthesis was found to be strongly dependent on the space velocity suggesting product inhibition. The intrinsic kinetics of the one-step synthesis of MIBK over a 15.2 wt% Pd/Nb2O5/SiO2 catalyst was investigated in an autoclave reactor. A kinetic model was developed and is reported. The one step synthesis of MIBK was investigated at the pilot plant scale via catalytic distillation (CD). An important finding was that while operating at 100% reflux, the accumulation of water in the reactive section resulted in the suppression of the DAA dehydration reaction. The in situ removal of water from the reactive section via an overhead distillate stream operating at 83 to 97% reflux directly resulted in an increase in MIBK productivity and hydrogen uptake efficiency by factors of about 20 yielding a moisture free reboiler product stream with as high as 53 wt% MIBK. The process was found to be controlled by the external mass transfer of hydrogen. Interestingly, the results suggest that the catalyst wetting efficiency affects the transport of hydrogen to the active sites as evidenced by the dependence of MO conversion on the reflux flow rate. The condition of minimum reflux flow rate and maximum hydrogen flow rate resulted in 97% MO conversion and 90 wt% MIBK selectivity.

The objective of the study presented here was to develop either enzymatic or whole cell mediated green procedures for the syntheses of a-hydroxy ketones. Production of optically active synthons is crucial for the preparation of fine chemicals. Enzymes and whole-cell biocatalysts have proven to be excellent vehicles with their chiral nature for the biotransformations. Under the light of this discussion, firstly benzaldehyde lyase [BAL, (EC 4.1.2.38)] was used in novel C-C bond formation reactions to obtain interesting and biologically important precursors / 2-Hydroxy-1-arylethan-1-ones and functionalized aliphatic acyloin derivatives. All the compounds were obtained with high yields and in the case of aliphatic acyloin derivatives with high enantiomeric excesses (ee&rsquo / s). Another strategy was to use whole cell biocatalysis. A.flavus 200120 was found to be a promising biocatalyst with the ability to catalyze a broad range of reactions / reduction, hydrolysis and deracemization, while another fungus / A. oryzae 5048 was utilized in bioreduction reactions of benzil and its derivatives. Each reaction was investigated, optimized and thus enhanced via medium design. Products were obtained with high yields and ee&rsquo / s. To sum up, in this study novel efficient green procedures were developed to synthesize various ahydroxy ketones with high yield and stereoselectivity. These newly established methods present promising alternatives to classical chemical methodologies.

This thesis provides investigation into the interaction between quartz lamp emitters and polyether ether ketone (PEEK) powder. Calculations and experiments concerning the conductivity and emissivity of the powder at various temperatures are performed. The thermal profile of the emitter on a flat powder bed is captured using thermal imaging. The effect of exposing a pile of powder to the emitter and the subsequent thermal gradient through the pile is measured and analyzed. Based on these results, ramifications for the application of these emitters to selective laser sintering (SLS) machines for processing high temperature polymers such as PEEK are discussed. / text

Pyrithiamine-induced thiamine deficiency in rats is a well-established animal model of Wernicke's Encephalopathy (WE). This thesis project, submitted as four articles, presents an examination of metabolic events that contribute to the selective neuronal lesions observed in the medial thalamus (MT) of thiamine-deficient (TD) rat. In addition, the phenomenon of glucose-precipitated worsening of neurological status in WE patients (Wallis et al., 1978; Watson et al., 1981) is explored. / Lactate accumulation is known to occur selectively in regions of the TD brain, which ultimately express neuronal cell death (McCandless, 1982; Munujos et al., 1996). In Article 1, the metabolic origin and cellular localization of region-selective lactate accumulation in the MT of TD rats was studied using combined 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Parallel studies were performed to examine the effects of glucose loading on regional brain lactate synthesis in TD animals. Thiamine deficiency caused focal increases in the de novo synthesis of lactate via elevated glycolytic flux in the MT, while contribution via pyruvate recycling and the periphery remained nominal. Lactate levels remained unaltered in the frontal cortex (FC), a brain region that is spared in thiamine deficiency. Administration of a glucose load intensified the selective increases in lactate de novo synthesis and accumulation in the MT of TD rats, positing a role for lactic acidosis in the glucose-precipitated worsening of neurological status in TD patients. Accordingly, Article 2 addresses the effect of glucose loading on local cerebral pH in the vulnerable MT, compared to the FC, of TD rats. Administration of a glucose load resulted in detrimental decreases in regional pH selectively in the MT, implying that alterations of brain pH contribute to the pathogenesis of thalamic neuronal damage and consequent cerebral dysfunction in WE. / Region-specific alterations in the steady state levels of cerebral amino acid neurotransmitters have been well-documented in experimental animal models of thiamine deficiency (Butterworth et al., 1979; Butterworth & Heroux, 1989; Gaitonde et al., 1975; Plaitakis et al., 1979); however, the dynamics of these changes have never been systematically explored. In Article 3, we examined the metabolic fluxes through thiamine-dependent pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) using multinuclear NMR spectroscopy. Furthermore the cellular localization of the metabolic changes in relation to regional vulnerability to thiamine deficiency was addressed. Our studies clearly demonstrate that early decreases m metabolic flux through alpha-KGDH result in commensurate declines in aspartate concentrations in the MT of TD rats. Impairments to PDH flux manifest secondarily to the metabolic block at alpha-KGDH, likely due to depleted oxaloacetate pools. As a result of impaired pyruvate oxidation, declines in the de novo synthesis of glutamate and GABA ensue. The present findings also suggest that inhibition of flux through alpha-KGDH in TD brain occurs primarily in the neurons, while astrocytes possess compensatory mechanisms, i.e. the anaplerotic pathway, to replenish oxaloacetate concentrations via metabolic pathways that do not involve thiamine-dependent enzymes. / In Article 4, we investigated the regional effects of thiamine deficiency on the activity of thiamine-dependent branched-chain alpha-ketoacid dehydrogenase (BCKDH) and the resultant effects on regional cerebral branched-chain amino acid (BCAA) oxidation. Thiamine deficiency resulted in significant impairments in BCKDH activity; while parallel studies on enzyme distribution confirmed a lower oxidative capacity for BCAAs in the MT compared with the Fe. / The data presented in these four articles confirm and extend findings for the region-selective impairments in thiamine-dependent metabolic processes as the foundation of vulnerability of the MT to thiamine deficiency. In addition, glucose loading of TD rats exacerbates both lactic acidosis and impaired pyruvate oxidation in this vulnerable brain region, positing a role for these processes in the glucose-precipitated worsening of neurological status in TD patients. Impaired oxidative metabolism of glucose and BCAAs in the MT leads to the accumulation of potentially harmful metabolic intermediates, contributing to the mitochondrial dysfunction, cellular energy failure and ultimately neuronal cell death observed in thiamine deficiency.

Bacterial resistance to antibiotics is an emerging epidemic throughout the world and there is a desperate need for new antibiotics and new strategies to maintain the effectiveness of current agents. ??-Lactams, such as the penicillins and cephalosporins, have been the most important class of antibiotic for several decades and represent half of the global antibacterial market, but the continued use of ??-lactams is threatened by ??-lactamases, enzymes that efficiently inactivate ??-lactams through hydrolysis. Class A, C, and D ??-lactamases use an active-site serine residue for hydrolysis and achieve turnover through an acylenzyme intermediate while the class B metallo-??-lactamases (MBLs) use a zinc-bound hydroxide as the active-site nucleophile. Two successful approaches to combat ??-lactamase-mediated resistance have involved the development of ??-lactam antibiotics which bind poorly to ??-lactamases and the combination of ??-lactams with ??-lactamase inhibitors. These strategies have been effective for overcoming resistance due to class A ??-lactamases, but the ever-increasing prevalence of extended-spectrum ??-lactamases (ESBLs), metallo-??-lactamases, and carbapenemases compromises the effectiveness of current penicillins, cephalosporins, carbapenems, and mechanism-based ??-lactamase inhibitors. Cyclobutanone analogues of ??-lactam antibiotics were explored in the early 1980s as potential inhibitors of ??-lactamases and D-Ala-D-Ala transpeptidases, but simple analogues showed only weak inhibitory activity and this approach was subsequently abandoned. The increasing threat of multidrug-resistant ??-lactamase-producing organisms in recent years, however, has inspired a re-evaluation of these inhibitors since cyclobutanones have the potential to exhibit broad-spectrum inhibition of both serine- and metallo-??-lactamases through the formation of enzyme-bound hemiketals or hydrates. 7,7-Dichloro-2-thia-bicyclo[3.2.0]heptan-6-one-4-carboxylic acid (65), a dichlorocyclobutanone that had shown modest inhibition of the class B and D ??-lactamases IMP-1 and OXA-10 in earlier work in this laboratory, was prepared in an efficient seven-step sequence from triethyl phosphonoacetate (103) with an overall yield of 28%. Initial efforts to improve upon the potency of the cyclobutanones involved functionalization at C3 and a highly stereoselective chlorination with sulfuryl chloride provided the 3??-chloro derivative 117?? in nearly quantitative yield. Elimination of HCl from 117?? was achieved under a variety of conditions and 3-alkoxy derivatives were prepared from 117?? through diastereoselective substitution reactions with alcohols. Cyclobutanones with 3??-OR substituents were found to favour an endo envelope conformation while the 3??-OR derivatives adopt the exo envelope conformation. Evidence from X-ray crystal structures and ab initio molecular orbital calculations suggests that an anomeric effect contributes to the large conformational preference of the tetrahydrothiophene ring that favours the 3-alkoxy substituent in an axial orientation. In addition, the conformation of the bicyclic system was found to have a dramatic effect on the tendency of the cyclobutanone to undergo hemiketal formation. Cyclobutanone analogues of penicillins, including 3-alkoxy derivatives, and cyclobutanone analogues of penems were evaluated against class A, B, C, and D ??-lactamases and found to be moderate inhibitors of KPC-2, IMP-1, GC1, and OXA-10. The cyclobutanones found to be most potent were those which are hydrated to a larger extent in aqueous solution. Dichlorocyclobutanones were found to be better inhibitors than dechlorinated cyclobutanones and a 3??-methoxy derivative 152??, which favours the exo envelope conformation in which the C4 carboxylate is equatorial, was found to be a better inhibitor than cyclobutanones that favour the endo envelope conformation. A 3,4-unsaturated penem analogue, 153, showed comparable potency to that of 152?? and molecular models of enzyme-inhibitor complexes indicate that an equatorial carboxylate is required for binding to ??-lactamases. An X-ray crystal structure of 152?? bound to the class D ??-lactamase OXA-10 confirms that a serine hemiketal is formed in the active site and that the inhibitor adopts the exo envelope. The biochemical data described above demonstrate that cyclobutanones can indeed act as inhibitors of serine- and metallo-??-lactamases and these cyclobutanones represent the first class of reversible inhibitors to show moderate inhibition of all four classes of ??-lactamase. Although the inhibitory potency of these compounds is modest (low micromolar IC50 values), penem analogue 153 was able to enhance the potency of meropenem against carbapenem-resistant MBL-producing clinical isolates of Chryseobacterium meningosepticum and Stenotrophomonas maltophilia and the synergy demonstrated in these antimicrobial assays is encouraging. Synthetic studies toward other C3-alkyl and C3-thioalkyl-substituted inhibitors are described and the design and synthesis of C7-monochloro- and 7??-hydroxymethyl-7??-chloro cyclobutanone derivatives is presented.

For the last two decades, the possibility of using synthetic membranes for industrial gas separations has attracted considerable interest since membrane separation technologies have the advantages of energy efficiency, simplicity and low cost. However, for wider commercial utilization there is still a need to develop membranes with higher permeant fluxes and higher transport selectivities. Conductive polymers, due to their high gas transport selectivities, give rise to a new class of polymeric materials for membrane based gas separation though poor mechanical properties obstruct the applications for this purpose of use. This problem led researches to a new idea of combining the conducting polymers with insulating polymers forming mixed matrix composite membranes. In the previous studies in our group, polypyrrole was chosen as the conductive polymer, and different preparation techniques were tried and optimized for membrane application. As the insulating polymer, previously poly(bisphenol-Acarbonate) was used to support the conductive polymer filler in order to constitute a conductive composite membrane. For this study, as the polymer matrix, hexafluorobisphenol A based poly(arylene ether ketone) was targeted due to its physical properties and temperature resistance which can be important for industrial applications. First of all, permeabilities of N2, CH4, Ar, H2, CO2, and H2 were measured at varying temperatures ranging from 25&deg / C to 85&deg / C through a homogenous dense membrane of chosen polymeric material to characterize its intrinsic properties. Measurements were done using laboratory scale gas separation apparatus which makes use of a constant volume variable pressure technique. The permeability results were used for the calculations of permeation activation energies for each gas. These permeation activation energies were found to be differing slightly for each gas independently from the kinetic diameters of gases. In this study, mixed matrix membranes of conducting polymer, polypyrrole (PPy) and insulating polymer, hexafluorobisphenol A based poly(arylene ether ketone) (PAEK) were also prepared. It was observed that PAEK and PPy form a composite mixed matrix structure, which can function as permselective membrane. The effect of conducting polymer filler content was investigated with two different filler ratios. When comparing with the pure PAEK membranes, meaningful increases for both permeability and selectivity were obtained for some of the gases.

Universiẗat, Diss., 2002--Bielefeld.

Abstract The synthesis of α-hydroxy aldehydes and hydroxymethyl ketones as well as their interconversion to each other are discussed in this thesis. The literature survey of the monograph reviews the synthetic methods for the preparation of 1,2-bifunctionalized hydroxy aldehydes and ketones. The keto-aldehyde isomerisation reaction catalyzed by Triosephosphate isomerase enzyme (TIM) and organic compounds that interact with the TIM are also introduced. In addition, the microwave heating techniques in organic syntheses are reviewed. The practical work consists of two entities: The synthesis of new substrate candidates and transition state analogues for a mutated monomeric TIM. These compounds are model compounds for the catalytic activity and the structural studies of the mutated monomeric TIM. The synthesis of the sulphonyl α-hydroxy ketone-based substrate candidates consists of four successive syntheses. The microwave-activation was utilized in the preparation of a carbon-sulphur bond and the synthesis of hydroxymethyl ketones. The improved synthesis of the terminal α-hydroxy ketone functionality with microwave activation is presented. The formation of charged compounds was utilized to improve the absorption of microwave energy of reaction mixtures. The design and the synthetic work were carried out in accordance to principles of green chemistry. The second part of the practical work is the development of an organocatalytic α-oxybenzoylation reaction of aldehydes with high enantiomeric selectivity. This novel method generated enantiomerically pure α-hydroxy aldehydes in the stable benzoate-protected form from achiral starting materials under mild conditions at the presence of air and moisture.

No description available.