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Ceylan, Yavuz Selim. "Exploration of Transition Metal-Containing Catalytic Cycles via Computational Methods." Thesis, University of North Texas, 2019. https://digital.library.unt.edu/ark:/67531/metadc1505287/.
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Styrene production by a (FlDAB)PdII(TFA)(η2-C2H4) complex was modeled using density functional theory (DFT). Benzene C-H activation by this complex was studied via five mechanisms: oxidative addition/reductive elimination, sigma-bond metathesis, concerted metalation deprotonation (CMD), CMD activation of ethylene, and benzene substitution of ethylene followed by CMD of the ligated benzene. Calculations provided evidence that conversion of benzene and ethylene to styrene was initiated by the fifth pathway, arylation via CMD of coordinated benzene, followed by ethylene insertion into the Ru-Ph bond, and then β-hydrogen elimination. Also, monomer (active species)/dimer equilibrium concentrations were analyzed. The results obtained from present study were compared with that of a recently reported RhI complex to help identify more suitable catalysts for the direct production of styrene from ethylene and benzene.
Second, theoretical studies of heterobimetallic {Ag–Fe(CO)5}+ fragments were performed in conjunction with experiments. The computational models suggested that for this first example of a heterodinuclear, metal-only FeAg Lewis pair (MOLP) that Fe(CO)5 acts as a Lewis base and AgI as a Lewis acid. The ῡCO bands of the studied molecules showed a blue shift relative to those measured for free Fe(CO)5, which indicated a reduction in Fe→CO backbonding upon coordination to silver(I). Electrostatic interaction is predicted via DFT as the dominant mode of Fe—Ag bonding augmented by a modest amount of charge transfer between Ag+ and Fe(CO)5.
Third, computational analyses of hypothetical transition metal-terminal boride [MB(PNPR)] complexes were reported. DFT, natural orbital analysis (NBO), and multiconfiguration self-consistent field (MCSCF) calculations were employed to investigate the structure and bonding of terminal boride complexes, in particular the extent of metal dπ - boron pπ bonding. Comparison of metal-boride, -borylene and –boryl bond lengths confirms the presence of metal-boron π bonds, albeit the modest shortening (~ 3%) of the metal-boron bond suggests that the π-bonding is weak. Their instabilities, as measured by free energies of H2 addition to make the corresponding boryl complexes, indicate terminal boride complexes to be thermodynamically weak. It is concluded that for the boride complexes studied, covering a range of 4d and 5d metals, that the metal-boride bond consisted of a reasonably covalent σ and two very polarized π metal-boron bonds. High polarization of the boron to metal π-bonds indicated that a terminal boride is an acceptor or Z type ligand.
Finally, anti-Markovnikov addition of water to olefins has been a long-standing goal in catalysis. The [Rh(COD)(DPEphos)]+ complex was found as a general and regioselective group 9 catalyst for intermolecular hydroamination of alkenes. The reaction mechanism was adapted for intermolecular hydration of alkenes catalyzed by a [Rh(DPEphos)]+ catalyst and studied by DFT calculations. Olefin hydration pathways were analyzed for anti-Markovnikov and Markovnikov regioselectivity. On the basis of the DFT results, the operating mechanism can be summarized as follows: styrene activation through nucleophilic attack by OHδ− of water to alkene with simultaneous Hδ+ transfer to the Rh; this is then followed by formation of primary alcohol via reductive elimination. The competitive formation of phenylethane was studied via a β-elimination pathway followed by hydrogenation. The origin of the regioselectivity (Markovnikov vs anti-Markovnikov) was analyzed by means of studying the molecular orbitals, plus natural atomic charges, and shown to be primarily orbital-driven rather than charge-driven.
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Bhawal, Benjamin Niladri. "Discovery and development of catalytic syntheses of aza-cycles." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708586.
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Shammas, Camille N. Y. A. "An investigation of the catalytic cycles of two dehydrogenases by X ray crystallography." Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274756.
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Stirling, Matthew John. "Coupled catalytic cycles : development of a procedure for the dynamic kinetic resolution of amines." Thesis, University of Huddersfield, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438067.
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Enantiomerically pure chiral amines are particularly important to the pharmaceutical and agrochemical industries. Due to the procedural operational simplicity the most common method for their synthesis on an industrial scale is kinetic resolution. However, this methodology has the inherent disadvantage of limiting the yield to a maximum of 50%. To overcome this drawback it is possible to combine the kinetic resolution with a simultaneous racemisation to give a theoretical yield of 100% in a procedure known as dynamic kinetic resolution. The most suitable method for amine resolution is via enzymatic acylation, however most known methods for amine racemisation require harsh conditions under which enzymes would be denatured. To date only three methods for amine dynamic kinetic resolution have been reported, all of which are not industrially viable. Herein we report the development of an amine dynamic kinetic resolution system using a novel iridium-based amine racemisation catalyst. Our initial attempts to utilise CATHyTM catalysts for amine racemisation proved unsuccessful, it did however reveal an unexpected property of the iridiumcatalysed CATHyTM of 6,7-dimethoxy- I -methyl-3,4-dihydroisoquinoline. During the asymmetric reduction of this substrate the enantiomeric excess of the product was observed to decrease with time. Initially this was suspected to be due to an in-situ racemisation, however our investigation disproved this and lead to the proposed system in which two catalytic species are present, one of which is (S)-selective and the other (R)-selective. During this investigation it was discovered that the iridium catalyst, pentamethylcyclopentadienyliridium (III) chloride dimer could be used as an amine racemisation catalyst. Further work found that the in-situ generation of the analogous iodo catalyst, pentamethylcyclopentadienyliridium (III) iodide dimer, led to a racemisation catalyst that was several orders of magnitude more active than the chloride species and more active than any previously reported amine racemisation catalyst. This iridium iodide catalyst was then synthesised and isolated and a standard amine racemisation protocol developed, which was utilised in the racemisation of a range of secondary amines and a tertiary amine. The catalyst also exhibited some activity towards the racemisation of amino acid esters. The attempted racemisation of primary amines led to the formation of dimeric impurities due to the reaction of the imine intermediate with the amine starting material. The catalyst was also shown to be able to racemise alcohols in the presence of a base, although the rate of hydrogen loss from the catalyst exceeded the rate of ketone hydrogenation and the reaction led to a quantitative conversion to ketone. The amine racemisation system using the pentamethylcyclopentadienyliridium (III) iodide dimer catalyst was then combined with an enzymatic resolution resulting in the dynamic kinetic resolution of 6,7-dimethoxy-l-methyl-1,2,3,4- tetrahydroisoquinoline in which the (R)-carbamate was isolated in 82% yield with 96% ee. This result constitutes the first example of a chemo-enzymatic dynamic kinetic resolution on a secondary amine using an organometallic amine racemisation catalyst.
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Parker, Mariah L. "The Investigation of Oxidative Addition Reactions of Metal Complexes in Cross-Coupling Catalytic Cycles Based on a Unique Methodology of Coupled Ion/Ion-Ion/Molecule Reactions." VCU Scholars Compass, 2018. https://scholarscompass.vcu.edu/etd/5651.
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Popular catalytic cycles, such as the Heck, Suzuki, and Negishi, utilize metal centers that oscillate between two oxidation states (II/0) during the three main steps of catalysis: reductive elimination, oxidative addition, and transmetallation. There has been a push to use less toxic, cheaper metal centers in catalytic cycles, leading to interest in first-row transition metals, such as nickel and cobalt. With these metals, the cycles can potentially pass through the +1 oxidation state, which acts as reactive intermediates, undergoing oxidative additions to form products, potentially with radical characteristics. The oxidative addition steps of catalytic cycles are critical to determining overall rates and products, however in many cases, these steps have not been amenable to study, in either condensed phase or gas phase, in the past. Through the use of electron transfer dissociation (ETD) technology on a modified Thermo Electron LTQ XLTM mass spectrometer, it is possible to generate intermediates in these catalytic cycles, including those in unusual oxidation states. Using sequentially coupled ion/ion-ion/molecule reactions, the reduced, reactive intermediate can be readily generated, isolated, and studied.As a model set of reactions, the mono- and bis-phenanthroline complexes of Fe(I), Co(I), Ni(I), Cu(I), and Zn(I) were formed by reduction of the corresponding M(II) species in an ion/ion reaction with the fluoranthenyl radical anion. The chemistry of the M(I) species was probed in ion/molecule reactions with allyl iodide. In order to explore ligand effects and the scope of oxidative addition reagents further, bipyridine and terpyridine were studied with these five first-row transition metal complexes while using an acetate series and other substrates for oxidative additions. Through these studies, the roles of the metal and ligand in dictating the product distributions and reaction rates were assessed. Metal electron count, ligand flexibility, and coordination number are critical factors. The overall reactivity is in accord with density functional theory calculations and mirrors that of proposed intermediates in condensed-phase catalytic cycles. In addition, second- and third-row transition metals (Ru(I), Pd(I), and Pt(I)) were explored with bipyridine, mono- and bis-triphenylphosphine, and 1,2-bis(diphenylphosphino)benzene ligation schemes. A variety of oxidative addition reagents were surveyed to determine the scope of reactivity and preference toward metal-carbon bond formation or carbon radical formation.
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Sullivan, Ryan. "Improving Efficiency by Using Continuous Flow to Enable Cycles: Pseudo-Catalysis, Catalysis and Kinetics." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40387.
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This thesis is centered around the use of flow chemistry to enable cycles in order to increase reaction or process efficiency. Chapter two describes the development of a pseudo-catalytic cycle in space; a strategy to achieve formal sub-stoichiometric loading of a chiral auxiliary. By telescoping auxiliary attachment, asymmetric transformation and auxiliary cleavage into one continuous flow process, coupled with separation of product and recovery of auxiliary, the reuse of the auxiliary can be automated by returning the recovered auxiliary back to the start of the process to achieve ‘turn-over.’ An asymmetric hydrogenation mediated by Oppolzer’s sultam is used to demonstrate this concept.
In order to achieve cycles such as the one discussed in Chapter two, the ability to telescope reactions in flow is paramount. However, solid handling challenges are frequent when transitioning to flow, leading to limitations in potential solvents or conditions in order to achieve homogeneity. This complicates the ability to telescope reactions, and to address this challenge the work in Chapter three focuses on the development of a general and simple solution to negate precipitation problems arising from precipitation of base·HX salts, a frequent reaction by-product of common reactions. By using bases that form low- to moderate-melting salts upon protonation, precipitation is precluded while reactions are performed above the melting point of the base·HX salt. This is shown to be applicable for a wide variety of substitution reactions and allow facile reaction telescoping.
Chapter four focus on overcoming severe scope limitations in palladium catalyzed transformations that result when rapid background reactions deplete the nucleophilic coupling partner faster than catalyst turnover. This work starts with real-time MS investigations to investigate why slow addition of Grignard or organolithium nucleophiles facilitates substantial scope expansion in Kumada-Corriu or Murahashi cross-couplings, and then uses the information gleaned from these studies to significantly expand the accessible scope of palladium catalyzed aryl halide–diazo cross-coupling, through controlled addition of the diazo reagent at a rate that approximates aryl halide oxidative addition, in combination with on-demand flow synthesis of non-stabilized diazo reagents.
Chapter five focuses on improving efficiency in the collection of kinetic data in flow, by developing a reaction cycling reactor. Conversion over time data is obtained by passing a discrete reaction slug back-and-forth between two residence coils, with analysis performed each time the solution passes from one coil to the other. In contrast to a traditional steady state flow system, which requires >5 X the total reaction time to collect data, this reactor design collects all the data during a single reaction. Multiple reactions can also be monitored at the same time by performing multiple reactions as sequential slugs in the reactor. The reactor is demonstrated by application to a wide variety of transformations and different methods of kinetic analysis.
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鄧文偉 and Man-wai Simon Tang. "Novel cyclic ketones for catalytic epoxidation of olefins." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1997. http://hub.hku.hk/bib/B31214654.
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Tang, Man-wai Simon. "Novel cyclic ketones for catalytic epoxidation of olefins /." Hong Kong : University of Hong Kong, 1997. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1853871X.
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Rothnie, Alice. "TM6 of Pgp : changes in topography during the catalytic cycle." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401107.
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Belcastro, Elizabeth Lynn. "Life Cycle Analysis of a Ceramic Three-Way Catalytic Converter." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/32342.
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The life cycle analysis compares the environmental impacts of catalytic converters and the effects of not using these devices. To environmentally evaluate the catalytic converter, the emissions during extraction, processing, use of the product are considered. All relevant materials and energy supplies are evaluated for the catalytic converter. The goal of this life cycle is to compare the pollutants of a car with and without a catalytic converter. Pollutants examined are carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and nitrogen oxides (NOx). The main finding is that even considering materials and processing, a catalytic converter decreases the CO, HC and NOx pollutant emissions. The CO2 emissions are increased with a catalytic converter, but this increase is small relative to the overall CO2 emissions. The majority of catalytic converter pollutants are caused by the use phase, not extraction or processing. The life cycle analysis indicates that a catalytic converter decreases damage to human health by almost half, and the ecosystem quality damage is decreased by more than half. There is no damage to resources without a converter, as there are no materials or energy required; the damages with a converter are so small that they are not a significant factor. Overall, catalytic converters can be seen as worthwhile environmental products when considering short term effects like human health effects of smog, which are their design intent. If broader environmental perspectives that include climate change are considered, then the benefits depend on the weighting of these different environmental impacts.Master of Science
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Miranda, Rojas Sebastián Esteban. "Theoretical insight into the catalytic cycle of cobalamin-glutamate mutase complex." Tesis, Universidad de Chile, 2012. http://repositorio.uchile.cl/handle/2250/105223.
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Tesis para optar al grado de Doctor en QuímicaLas enzimas son capaces de acelerar reacciones químicas con una gran selectividad, permitiendo que la vida sea posible como la conocemos. Glutamato mutasa (GM) es una enzima dependiente de adenosilcobalamina (AdoCbl), la cual cataliza la isomerización reversible de glutamato (glm) a metilaspartato (masp). AdoCbl es un cofactor que consiste en un macrociclo ubicado en el plano ecuatorial denominado corrina, el cual tiene como átomo central un Co+3. Este metal está axialmente coordinado por un ligando desoxiadenosina e intramolecularmente por un grupo 5,6-dimetilbenzimidazol. El mecanismo propuesto para la reacción de isomerización comienza con la unión del sustrato al sitio catalítico, la cual induce la ruptura homolítica del enlace cobalto-carbono (Co-C) del cofactor. Como producto de esta disociación homolítica se forma el radical desoxiadenosilo (Ado•) que luego abstrae un hidrógeno desde el sustrato, formando un radical derivado del sustrato y AdoH. Este radical sufre un reordenamiento que da origen al radical relacionado con el producto, el cual reabstrae el hidrógeno desde AdoH, regenerando Ado•. El ciclo catalítico termina con la formación del enlace Co-C. La generación de intermediarios radicalarios altamente reactivos hace que esta reacción sea muy difícil de llevar a cabo sin reacciones secundarias. Es así que la necesidad de una maquinaria catalítica capaz de controlar los caminos de reacción sea indispensable. Una interesante pregunta en química bioinorgánica es cómo luego de la unión del sustrato, el complejo cofactor-enzima es capaz de modificar su estructura electrónica debilitando el enlace Co-C hasta su disociación homolítica. Además, el camino de reacción exacto que conecta el rompimiento del enlace Co-C con el proceso de abstracción del hidrógeno desde el sustrato permanece incierto. Finalmente, el papel exacto que cumple el entorno enzimático en el mecanismo de isomerización está lejos de ser completamente comprendido. La necesidad de una mayor comprensión del mecanismo catalítico de GM, especialmente el proceso de control de la ruptura del enlace Co-C y el mecanismo para controlar la transformación química catalizada por GM son interesantes problemas para ser resueltos por métodos químico computacionales. En este trabajo presentamos un conjunto de modelos químico-cuánticos obtenidos con el propósito de responder a las preguntar presentadas anteriormente. Primero, exploramos la naturaleza del enlace Co-C mediante en estudio comparativo de AdoCbl y un cofactor análogo conocido como MeCbl, ambos en sus formas libres. Segundo, obtuvimos un conjunto de modelos del cofactor unido a GM para explorar las fuerzas involucradas en el proceso de ruptura catalítica del enlace Co-C, junto con la influencia del sustrato en esta. Tercero, con el fin de comprender las fuerzas que manejan el ciclo catalítico, llevamos a cabo el estudio del estado fundamental, intermediarios clave y estados de transición del ciclo catalítico usando modelos del complejo GM-Ado-glm obtenidos a partir de cálculos de estructura electrónica. Los estudios de la disociación del enlace Co-C en complejo con la enzima y del ciclo catalítico fueron enfocados en el efecto del entorno enzimático cercano. La aproximación de cluster fue usando en todos los cálculos que involucraron a GM como parte del modelo. Nuestros principales resultados revelaron que el enlace Co-C es debilitado por el reemplazo de base axial que sufre luego de unirse a la enzima por el par histidina-aspartato. Además existe un efecto electrostático ejercido por el par lisina-glutamato de la enzima que estabiliza al radical Ado•. La presencia de glm tiene un papel importante luego de la formación del radical Ado• ya que permite la formación del radical un radical glm• que es más estable, propagando el ciclo catalítico hacia la formación del producto. Finalmente, nuestros hallazgos revelaron que el entorno enzimático conduce la reacción de isomerización mediante una estabilización diferencial de los intermediarios y estados de transición asociados a la reacción. Además provee de un importante soporte estructural. Los antecedentes entregados en este trabajo permitirán en el futuro el diseño de bio-miméticos capaces de catalizar reacciones químicas extremadamente complejas
Enzymes accelerate chemical reactions with exceptional selectivity making life itself possible. Glutamate Mutase (GM) is an adenosylcobalamin (AdoCbl)-dependent enzyme that catalyzes the reversible isomerization of glutamate (glm) to methylaspartate (masp). The AdoCbl cofactor consists of an equatorial corrin ring, which has a Co+3 as the metal center axially coordinated by a deoxyadenosyl moiety and intramolecularly by a 5,6-dimethylbenzimidazole group. The accepted mechanism for the isomerization reaction begins with substrate binding to the catalytic site, which induces the homolytic cleavage of the cobalt carbon bond (Co-C) of AdoCbl, being this the first catalytic event. This generates an adenosyl radical (Ado•) that subsequently abstracts a hydrogen atom from the substrate, forming a substrate-derived radical and AdoH. The newly formed radical rearranges to a product-related radical, which eventually re-abstracts the hydrogen from AdoH, leading into Ado• regeneration. Finally, the catalytic cycle ends by Co-C bond formation. The generation of highly reactive radical intermediaries makes this reaction very difficult to occur without side reactions. Thus, the need of proper catalytic machinery able to control the reaction pathway is mandatory. An intriguing question in bioinorganic chemistry is how upon substrate binding, the cofactorenzyme complex modifies its electronic structure weakening the Co-C bond strength until its homolytic dissociation. In addition, the exact reaction pathway that connects the Co-C bond breaking with the hydrogen abstraction from the substrate remains uncertain. Finally, the exact role of the enzymatic environment on the isomerization reaction mechanism is far from been completely understood. The need of deeper insights about the GM catalytic reaction, especially the control of the Co- C bond dissociation process and the mechanism to manage the chemical transformation are interesting challenges to be solved by computational chemistry approaches. Here we present a large set of quantum chemical models obtained to answer the questions above presented. First, we explored the nature of the Co-C bond by the comparative study of AdoCbl and an analogous cofactor known as methylcobalamin (MeCbl), both in their free forms. Second, a set of models of AdoCbl in complex with GM were obtained to explore the forces involved in the catalytic Co-C bond dissociation process and the influence of the substrate on it. Third, in order to shed light into the driving forces of the catalytic cycle, we performed the study of models of ground state, key intermediates and transition states of the catalytic cycle using GM-Ado-glm complexes by means of modern electronic structure calculations. In all the calculation involving the GM as part of the model, the cluster approach was used. The studies of the Co-C bond dissociation in complex with the enzyme and the study of the catalytic cycle were focused on the effect of the nearby enzymatic environment. Our main results revealed that the Co-C bond is weakened in part by the axial ligand replacement involving a histidine-aspartate pair, and the electrostatic effect exerted by the lysine-glutamate pair from the enzyme which stabilizes the Ado• radical. After the formation of the Ado•, the presence of glm leads to the formation of glm• radical, which is largely more stable than Ado•. Thus, glm has an important role on the propagation of the catalytic cycle toward the product formation. Finally, our findings revealed that the near enzymatic environment provides differential stabilization of the reaction intermediaries and transition state mediated by the properties of the interactions with the catalytic site. Additionally, it provides of an important structural support. This understanding would allow in the future the design of bio-mimetic able to catalyze highly complex reactions
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Middleton, Ann Jenny. "Cyclic phosphines for hydroformylation catalysis." Thesis, University of Bristol, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412371.
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Griffin, Tim Robert. "Ab initio and density functional theory study of the Monsanto catalytic cycle." Thesis, University of Sheffield, 1997. http://etheses.whiterose.ac.uk/3445/.
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The results of an effective core potential ab initio and Density Functional Theory (DFT) quantum mechanical study of the rhodium- and iodide- catalysed Monsanto acetic acid cycle are presented. The geometries and energetics of the intermediates and transition states have been determined for the key steps of the cycle. The potential influence of variables such as solvent and ligands, and the controlling electronic structure features have been examined. Theoretical data for the analogous iridium system are also reported. The lowest energy transition state determined at the restricted Hartree-Fock (RHF) level for the oxidative addition Of C1131 to CiS-[M(CO)2121- (M=Rh, Ir) is a "linear" structure, involving classical SN2 back- side attack by the transition metal. Secondary a-Deuterium kinetic isotope effects calculated for this mechanism are in excellent agreement with experiment. Both electron correlation and an electrostatic medium have a significant influence on the nucleophilic substitution reaction energetics. Second-order Moller-Plesset theory (MP2) calculations, with the effect of solvent included, using the self-consistent reaction field (SCRF) model, predict activation barriers in good agreement with experiment. The overall oxidative addition process is found to be exothermic at the MP2 level for both metal systems, but more so for iridium. The transition state and intrinsic reaction co-ordinate (IRC) calculated for migratory insertion in [CH3M(CO)2131- (M=Rh, Ir), indicate that the reaction proceeds via a concerted movement of CH3 and CO groups toward each other. In the rhodium system this reaction is predicted to take place with a low activation barrier and lead to exothermic formation of a five co-ordinate acyl complex in agreement with experiment. By contrast, migratory insertion in the iridium system has a high barrier and is endothermic. Analyses suggest that the difference in reactivity of rhodium and iridium complexes can be correlated to the greater strength of metal-carbon bonds for the heavier transition metal. DFT calculations of the strongly bound ground state complexes yield geometrical structures and carbonyl vibrational frequencies which are comparable, or superior, to those obtained at the RHF and MP2 levels in the same Gaussian basis. However, calculations of the transition states and reaction co-ordinates have not been successful. It is proposed that the currently used functionals are not suitable for the calculation of transition states when weak interactions become important.
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Wilkinson, Craig. "Understanding the catalytic cycle of membrane pyrophosphatases through structural and functional studies." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/19131/.
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Membrane pyrophosphatases (M-PPases) couple pyrophosphate hydrolysis to the translocation of sodium ions/protons, using the resulting ion gradients to drive abiotic stress resistance and in the infectivity of protozoan parasites. I have solved two M-PPase structures in different catalytic states, combining these with previous structures to update the model of the catalytic cycle of M-PPases. These new structures confirm previous findings that substrate binding breaks interactions between K12.50 and D6.43 due to motion of helix 12, leading to a rearrangement of helix 6 and priming the enzyme for hydrolysis. Previously this information was only visible between the structures of two-distinct M-PPases, a H+-PPase and Na+-PPase. The current structures allow for comparisons to be made between structures of the same type of M-PPase. Electrometric data was acquired using the Nanion SURFE2R technique, which showed a proton-pumping signal was generated by the non-hydrolysable inhibitor, imidodiphosphate. This provided sufficient information to update the model of the complete catalytic cycle, favouring the hypothesised Binding change mechanism, in which substrate binding induces a series of conformational changes during which ion pumping occurs first, followed by substrate hydrolysis. Additionally, crystal optimisation techniques improved the resolution of the Pyrobaculum aerophilum M-PPase structure to 3.8, providing an overview of the K+-independent M-PPase. The hydrolytic centre and ion gate regions showed similar coordination to previous structures, with differences seen in the conformation of several outer ring helices, potentially linked to K+-independence. I also carried out mutational studies investigating K12.46 and T12.49, both involved in K+-independence and found that both mutations were required to generate a K+-dependent variant of PaPPase. Overall, this information has improved our understanding of the structure and function of the membrane pyrophosphatases, providing a basis for drug-design programmes targeting protozoan parasites, to which the membrane pyrophosphatases are a vital part of growth and infectivity.
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Daff, Simon N. "Analysis of the catalytic cycle & manipulation of substrate specificity in flavocytochrome b2." Thesis, University of Edinburgh, 1996. http://hdl.handle.net/1842/12172.
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The physiological role of flavocytochrome b2 from Saccharomyes cerevisiae is to couple L-lactate dehydrogenation to respiration via the ubiquitous electron carrier cytochrome c. For each L-lactate molecule dehydrogenated two cytochrome c. molecules are reduced, and as such the enzyme acts as a 'bio-electrical transformer'. The mechanism through which this process occurs can be simplified into five separate electron transfer events which form the catalytic cycle. L-lactate dehydrogenation results in the two electron reduction of flavin at the enzyme's active site. These electrons are passed individually to the b2-haem (intramolecular electron transfer) and on to two cytochrome c molecules (intermolecular electron transfer). Using stopped-flow spectrophotometry, the intramolecular electron transfer steps have been investigated using several different experimental procedures. Electron transfer from fully reduced FMN to b2-haem has been studied by monitoring both haem reduction and haem re-reduction (following oxidation by cytochrome c). In each situation this step proved too fast to be observed, and appeared only as a slight lag (relative to flavin reduction) in the b2-haem reduction trace. Nevertheless a lower estimate for this rate constant was derived to be 1500±500 s-1. The second intramolecular electron transfer step takes place from flavin semiquinone to b2 haem and was observed as a component of the flavin oxidation process. This proved to be the slowest step in the catalytic cycle (at 120 s-1) and is therefore responsible for determining the overall turnover rate. The product, pyruvate, was found to be an inhibitor of the flavin oxidation reaction (Ki= 40 ± 15 mM) consistent with reports that it acts as a non-competitive inhibitor in the steady-state. Stopped-flow studies on the cytochrome c reductase activity of flavocytochrome b2 yielded a second-order rate constant of 35 μM-1s-1, which represents the rate constant for cytochrome c association.
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Navarro-Fernandez, Oscar. "Synthesis, Activation and Catalytic Activity of N-Heterocyclic Carbene Bearing Palladium Catalysts." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/330.
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The syntheses and characterization of a series of (NHC)Pd(II) complexes (NHC = N-heterocyclic carbene) are described. A variety of architectures and precursors have been employed to lead to numerous air- and moisture-stable complexes. The use of those complexes as pre-catalysts in cross-coupling (Suzuki- Miyaura, Buchwald-Hartwig) and related (catalytic dehalogenation, £-ketone arylation) reactions is also discussed. A comparison of the activity of a variety of (NHC)Pd complexes as pre-catalysts for cross-coupling reactions was carried out. The results indicate that the activation of those pre-catalysts, leading to the catalytically active [(NHC)Pd(0)] species, was key in assuring high catalytic performance under mild reaction conditions. For the first series of complexes described, (NHC)Pd(allyl)Cl complexes, a better understanding of the process leading to the catalytically active species has permitted us to introduce simple modifications (alkyl or aryl groups at the allyl moiety) that dramatically alter the performance of the complexes by facilitating their activation, decreasing reaction times, catalyst loadings and even allowing reactions to be conducted at room temperature. Catalyst loadings as low as 0.05 mol% can be used for the Suzuki-Miyaura crosscoupling of aryl chlorides and aryl boronic acids at room temperature, leading to the synthesis of poly-ortho-substituted biaryls in excellent yields. This catalyst loading is the lowest ever used for this purpose. The system also allows for the first examples of coupling between aryl chlorides and alkenyl boronic acids at room temperature. When the temperature is raised to 80 ¢ XC for these reactions, a catalyst loading as low as 50 ppm can be used to effectively carry out Suzuki-Miyaura cross-couplings in remarkably short reaction times. As an added advantage, these complexes are air- and moisture-stable and can be prepared in a facile one-pot, multigram scale synthesis from commercially available starting materials in very high yields. The second series of complexes described revolves around the (NHC)Pd(acac)n framework. These complexes are also air- and moisture-stable and can be prepared in a one-step synthesis in high yields from commercially available materials. These complexes were tested forƒn £-ketone arylation and Buchwald-Hartwig amination reactions affording high yields of the desired products, in short reaction times and mild reaction conditions.
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Martin, Catherine Anne. "P-glycoprotein transport cycle : 'cross-talk' between multiple binding sites and the catalytic domains." Thesis, Open University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369076.
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Bowen, Laura Christine. "Cyclic AMP-dependent protein kinase catalytic subunit in the nematode 'Caenorhabditis elegans'." Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402303.
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Mohamad, Noh N. "Catalytic route for the synthesis of cyclic organic carbonates from renewable polyols." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3012167/.
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Kong, Jianfeng. "Evidence for pH-dependent conformations in the catalytic cycle of cytochrome caa¦3 from B. subtilis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0004/MQ45281.pdf.
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Yeamin, Md Bin. "Catalytic CO2 Cycloaddition with Epoxides into Cyclic Carbonates: Synergies from Computational to Experimental Studies." Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/672267.
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La utilització d'el CO2 com a matèria primera química ha demostrat ser una estratègia important per reduir les emissions de CO2 a l'atmosfera i, per tant, per trobar un equilibri en el cicle natural de l'carboni. No obstant això, l'activació d'aquesta petita molècula estable és molt difícil. De fet, els substrats reactius amb alta energia interna poden facilitar les transformacions químiques de el CO2 per compensar la seva estabilitat termodinàmica. A més, es necessiten catalitzadors eficaços per superar l'elevada barrera cinètica de l'activació. Entre els molts mètodes catalítics, la catàlisi tèrmica segueix sent el mètode més utilitzat per ampliar els processos de fixació de CO2 a nivell industrial. Es necessiten catalitzadors amb més activitat i selectivitat en condicions de reacció més suaus. Per tant, el nostre objectiu és avaluar l'eficiència dels materials de baix cost i abundants en terra com a catalitzadors per a la cicloaddició de CO2 amb epòxids d'alt contingut energètic. També pretenem entendre el comportament d'aquests catalitzadors a partir d'estudis mecanístics computacionals, i millorar el seu disseny corroborant amb el seu rendiment catalític experimental per aquesta reacció de transformació de el CO2.
En aquesta Tesi estudiem 3 catalitzadors diferents per a la reacció de cicloaddició de CO2 amb epòxids sota gradient tèrmic. Els catalitzadors són biomasses lignocelulósiques com materials vegetals més abundants, 1,10-fenatronina derivada de quatre donants de nitrogen que contenen complexos de zinc, i un complex derivat de ciclam de l'element més abundant, el ferro. Els efectes cooperatius d'aquests catalitzadors binaris en combinació amb un cocatalizador, el bromur de tetrabutilo i amoni (TBAB), s'han dilucidat a partir d'estudis mecanístics computacionals. En els estudis experimentals, les reaccions catalítiques s'optimitzen per substrats estàndard, i els percentatges de conversió dels substrats es corroboren amb les barreres d'energia d'activació dels mecanismes de reacció, quan s'apliquen. També s'analitza la naturalesa dels diferents llocs actius catalítics des del punt de vista de l'abast de l'substrat.La utilización del CO2 como materia prima química ha demostrado ser una estrategia importante para reducir las emisiones de CO2 a la atmósfera y, por tanto, para encontrar un equilibrio en el ciclo natural del carbono. Sin embargo, la activación de esta pequeña molécula estable es muy difícil. De hecho, los sustratos reactivos con alta energía interna pueden facilitar las transformaciones químicas del CO2 para compensar su estabilidad termodinámica. Además, se necesitan catalizadores eficaces para superar la elevada barrera cinética de la activación. Entre los muchos métodos catalíticos, la catálisis térmica sigue siendo el método más utilizado para ampliar los procesos de fijación de CO2 a nivel industrial. Se necesitan catalizadores con mayor actividad y selectividad en condiciones de reacción más suaves. Por lo tanto, nuestro objetivo es evaluar la eficiencia de los materiales de bajo coste y abundantes en tierra como catalizadores para la cicloadición de CO2 con epóxidos de alto contenido energético. También pretendemos entender el comportamiento de estos catalizadores a partir de estudios mecanísticos computacionales, y mejorar su diseño corroborando con su rendimiento catalítico experimental para esta reacción de transformación del CO2. En esta Tesis estudiamos tres catalizadores diferentes para la reacción de cicloadición de CO2 con epóxidos bajo gradiente térmico. Los catalizadores son biomasas lignocelulósicas como materiales vegetales más abundantes, 1,10-fenatronina derivada de cuatro donantes de nitrógeno que contienen complejos de zinc, y un complejo derivado de ciclam del elemento más abundante, el hierro. Los efectos cooperativos de estos catalizadores binarios en combinación con un cocatalizador, el bromuro de tetrabutilo y amonio (TBAB), se han dilucidado a partir de estudios mecanísticos computacionales. En los estudios experimentales, las reacciones catalíticas se optimizan para sustratos estándar, y los porcentajes de conversión de los sustratos se corroboran con las barreras de energía de activación de los mecanismos de reacción, cuando se aplican. También se analiza la naturaleza de los diferentes sitios activos catalíticos desde el punto de vista del alcance del sustrato.
CO2 utilization as a chemical feedstock has been proven as a major strategy to reduce CO2 emissions to the atmosphere, and therefore to find an equilibrium in the natural carbon cycle. However, activating this stable small molecule is very challenging. In fact, high internal energy-containing reactive substrates can facilitate chemical transformations of CO2 to compensate its thermodynamic stability. Moreover, efficient catalysts are needed to overcome the high kinetic barrier of activation. Among many catalytic methods, thermal catalysis is still the mostly used method to scale up the CO2 fixation processes at industrial level. Catalysts with higher activity and selectivity in milder reaction conditions are required. Therefore, we aim to assess the efficiency of low-cost earth-abundant materials as catalysts for CO2 cycloaddition with high energy-containing epoxides. We also aim to understand the behavior of these catalysts from computational mechanistic studies, and to improve on their design corroborating with their experimental catalytic performance for this CO2 transformation reaction. In this Thesis we study three different catalysts for CO2 cycloaddition reaction with epoxides under thermal gradient. The catalysts are lignocellulosic biomasses as most abundant plant materials, 1,10-phenathronine derived four nitrogen donor containing complexes of zinc, and a cyclam derived complex of the most abundant element iron. The cooperative effects of these binary catalysts in combination of a co-catalyst, tetrabutyl ammonium bromide (TBAB) are elucidated from computational mechanistic studies. In experimental studies, the catalytic reactions are optimized for standard substrates, and %substrate conversions are corroborated with the activation energy barriers from reaction mechanisms, where applies. Also, the nature of different catalytic active sites is analyzed from substrate scope standpoint.
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Natarajan, Nallusamy. "Ligands build on macrocyclic platforms : can the macro cyclic unit influence the catalytic properties ?" Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF052.
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Cette thèse présente la synthèse de ligands originaux construits sur des plateformes coniques de type résorcin[4]arène ou calix[4]arène étant susceptibles de positionner un métal à proximité d'une unité réceptrice: a) des bis-binaphtylphosphites optiquement actifs dont les centres phosphorés ont été greffés sur le bord supérieur de cavités génériques. Ces coordinats ont été testés en hydroformylation asymétrique d’arènes vinyliques et ont conduit à une sélectivité iso très élevée avec de bons, voire très bons excès énantiomériques; b) des carbènes N- hétérocycliques ayant soit un, soit les deux atomes d'azote substitués par des unités résorcinarényle (variante cavitand) et leur utilisation pour la formation d'espèces comportant un centre métallique supramoléculairement piégé dans la partie cavitaire (complexes du type [NiXCpL] (X = Br ou Cl, Cp = cyclopentadiényle, LH = NHC). Ces complexes se sont avérés efficaces en dimérisation de l'éthylène; c) des carbènes N-hétérocyliques anormaux obtenus à partir de sels de triazolium comportant un ou deux substituants résorcinarène. Ces composés à fort encombrement ont été efficacement employés en couplage croisé de Suzuki-Miyaura entre des chlorures d'aryles volumineux et des acides arylboroniques stériquement encombrés. Les activités les plus importantes ont été obtenues avec le sel de triazolium stériquement le moins encombré, celui portant un seul substituant résorcinarène. Sa plus grande efficacité est due à une approche plus facile des substrats dans les intermédiaires catalytiques correspondants ainsi que de la présence de groupes pentyles flexibles pouvant interagir stériquement avec le centre métallique de manière à faciliter l'étape d'élimination réductriceThis thesis describes the synthesis of a series of compounds built on conical resorcin[4]arene and calix[4]arene platforms: a) diphosphites derived from optically active binol, in which the phosphite moieties have been grafted to the wider rim of the generic cones. These ligands were assessed in asymmetric hydroformylation of vinyl arenes and led to high iso selectivity with good to excellent enantiomeric excess; b) N-heterocyclic carbenes bearing either one or two cavitand moieties and their use for the synthesis of [NiXCpL] complexes (X = Br or Cl, Cp = cyclopentadienyl, LH = NHC) in which the NiCp moiety has been supramolecularly trapped in a resorcinarene bowl. These complexes were found active in ethylene dimerization; c) bulky triazolium salts with one or two resorcinarene substituents that were found suitable for the synthesis of complexes with abnormal NHCs. The latter were tested in palladium-catalysed Suzuki-Miyaura cross-coupling of bulky aryl chlorides with sterically hindered aryl boronic acids. Better activities were observed with the sterically less hindered triazolium salt, which bears a single resorcinarene substituent. Its higher efficiency arises from a higher substrate accessibility in the resulting catalytic intermediates as well as the presence of flexible pentyl groups that may interact with the metal centre so as to facilitate the reductive elimination step
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Wagner, Tristan. "Structural insights into mycobacterial central carbon metabolism : the catalytic mechanisms and regulatory properties of α-ketoglutarate decarboxylase (KGD)." Paris 6, 2011. http://www.theses.fr/2011PA066421.
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Le nœud métabolique au croisement du cycle de Krebs et de l’assimilation de l’azote est régi par l’α-kétoglutarate déshydrogénase (KDH), un complexe constitué des composants E1o, E2o et E3. Chez les actinobactéries le composant E2o n’existe pas, son domaine catalytique est fusionné à E1o (α-kétoglutarate décarboxylase : KGD). La liaison de KGD au complexe de la pyruvate déshydrogénase assure l’activité KDH dont la régulation est cruciale pour coordonner le flux de carbone. Les corynebactéries ont développé un système de contrôle unique par GarA, une protéine à domaine en tête de fourche (ce domaine appelé FHA reconnait les thréonines phosphorylées) régulé par phosphorylation. GarA coordonne la synthèse du glutamate en bloquant KGD via une reconnaissance ne passant pas par une phospho-thréonine. Le but de cette thèse est de comprendre au niveau moléculaire comment GarA inhibe KGD. Nous avons résolu la première structure d’un composant E1o avec son cofacteur. L’analyse de la catalyse de KGD montre d’importants changements conformationnels passant par la translocation d’une hélice externe (αE). GarA s’ancre à un site allostérique grâce à la reconnaissance d’un aspartate mimant la charge phosphate contenu sur l’hélice αE, sa fixation bloquera l’événement de translocation de l’hélice. L’inhibition est accentuée par un effet synergique avec le domaine E2o qui verrouille la position de l’hélice αE. Néanmoins ce phénomène peut être contrecarré par l’action d’un nouveau type d’activateur propre à KGD : l’acétyl-CoA. Sa fixation sur un autre site allostérique aidera la translocation de l’hélice αE en déplaçant des résidus impliqués dans le changement conformationnel
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LaBarre, Michael James. "Investigation of the catalytic cycle of the molybdoenzyme sulfite oxidase: Synthesis and spectroscopic study of model systems." Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/186051.
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This research has been directed at the study of the catalytic cycle of the molybdoenzyme, sulfite oxidase, through the use of both functional and structural model chemistry. A biologically relevant synthetic model for the first two steps of the proposed catalytic cycle of sulfite oxidase has been developed. A rapid oxygen atom transfer reaction from a dioxo-molybdenum(VI) center to triphenylphosphine is followed by an intermolecular electron/halogen exchange reaction between tetratolylporphinatoiron(III)-chloride and the now reduced oxo-molybdenum(IV) center. The kinetic and thermo-dynamic parameters of these reactions in dimethylformamide and toluene have been investigated and a self consistent mechanism has been proposed. Structural models for intramolecular electron transfer between the oxo-molybdenum center of the cofactor and the iron heme of sulfite oxidase have been prepared. Modified tetratolylporphyrins have been designed in order to contain a chelating catecholate functionality at discreet distances from the central cavity of the porphyrin ring. An oxo-molybdenum(V) group (which is stabilized by the facially coordinating, hydrotris(3,5-dimethyl-1-pyrazolyl)borate ligand) has been attached to the porphyrin through this catecholate functionality and the resulting bimetallic compounds have been investigated by NMR, EPR, UV/Vis, and electrochemical methods. The use of ³¹P-NMR spectroscopy as a probe of molybdenum-phosphate interactions in sulfite oxidase has been investigated through the synthesis and spectroscopic investigation of a series of six mononuclear oxo-molybdenum(V) and dioxo-molybdenum(VI) compounds which contain pendant phosphate esters. The ³¹P-NMR spectra of the Mo(V) compounds exhibit line broadening due to the absolute distance to the paramagnetic d¹ Mo(V) center. The relaxation times (T₁ and T₂) of the ³¹P center have been determined and are sensitive to the overall structure of the model compounds. The Mo-P distances have been calculated using the relaxation data and the Solomon equation and yield distances which are in reasonable agreement with the structures as determined by computer molecular modeling.
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Martorell, Colomer Aina. "Chiral biaryl monodentate cyclic phosphonites and phosphites for asymmetric catalysis." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/c3c79146-8c6a-4ba1-9eb6-6d5779456813.
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A serieso f chiral biaryl cyclic monophosphoniteli gands of type RP(OAr)2 (R = Ph, Me, t-Bu, o-anisyl and Cy; (OAr)2 = 1,1'-binaphthyl-2,2'-diyl, 9,9'- biphenanthryl- 10,1 0'-diyl) have been prepared. The ligands have been synthesised by reaction of the dichlorophosphine precursor with the corresponding biphenol (HOAr)2. Chiral biaryl diphosphonite ligand (ArO)2PCH2CH2(OAr)2 derived from binaphthol has also been prepared. Platinum(II), palladium(II) and rhodium(I) complexes of these ligands are described and the X-ray crystal structures of five of these complexes are reported and discussed.T he electronic propertieso f the phosphonitesa re betweent hose of phosphite and phosphine, and this is reflected in their coordination chemistry. The new chiral biaryl monophosphites of type (Ar'O)P(OAr)2 have been synthesised straightforwardly by condensation of a phenol and the corresponding chlorophosphites in the presence of NEt3. Preliminary studies of their coordination chemistry with platinum(II) and rhodium(I) have been carried out. The twist on the seven membered P(OCCCCO) ring leads to a deshielding of the 31P signal for the biaryl ligands and in the complexes studied here. The asymmetric hydrogenation of a-enamides with rhodium(I) complexes of the phosphonites and diphosphonites as catalysts is discussed. The ligands have been screened in the asymmetric hydrogenation of two substrates: methyl-2-acetamido acrylate and methyl-(Z)-2-acetamido cinnamate. Monodentate phosphonite systems show, in some cases, higher enantioselectivity (up to 92% ee) than the analogous bidentate. The results presented here challenge the long-accepted wisdom that chelating ligands are necessary to achieve high enantioselectivities in asymmetric hydrogenation. NMR studies and X-ray crystallographic data show that the asymmetric ligand profile caused by the biaryl units in these phosphonites has three consequences: (i) rotation about the M-P bond in monodentate phosphonites is inhibited; (ii) a different rotamer for the monodentate from that in the chelate analogues is favoured; (iii) the favoured rotamer in the monodentate causes more effective chiral induction in the hydrogenation catalyses. The generality of these new concepts has been probed with some preliminary catalytic studiesw ith monodentatep hosphitel igands. The phosphonite ligands have also been tested in the copper(I) catalysed 1,4- addition of diethylzinc to enones and nitro-olefins in an attempt to extend their potential use in asymmetric catalysis. The phosphonite ligands show moderate to high ee's for the ethyl transfer to enones (cyclic and acyclic). The monophosphonite ligands induce higher enantioselectivity for acyclic enones: ee's up to 82% are the highest obtained with a monodentate phosphonite ligand in asymmetric 1,4-addition of diethylzinc to chalcone.
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Castro, Pastrana Lucila Isabel. "Mycobacterial adenylyl cyclases Rv1625c and Rv0386 othodox vs. unorthodox catalysis /." [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11051883.
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Lawrence, Christopher Ralph. "Studies towards the catalysis of cationic cyclisations using monoclonal antibodies." Thesis, University of Cambridge, 1994. https://www.repository.cam.ac.uk/handle/1810/272265.
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Sarkisian, Ryan Gregory. "MULTICOMPONENT REACTIONS OF SALICYLALDEHYDE, CYCLIC KETONES, AND ARYLAMINES THROUGH COOPERATIVE ENAMINE-METAL LEWIS ACID CATALYSIS." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1409236804.
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Liu, Kun. "Catalytic Asymmetric Synthesis of Chiral Cyclic Amines and Axially Chiral Anilides by Phase-Transfer Catalyzed Reactions." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/158098.
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Carberry, Brendan Patrick. "A theoretical and experimental investigation of the characteristics of automotive catalytic converters for use on two-stroke cycle engines." Thesis, Queen's University Belfast, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310149.
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Liu, Rui. "Ruthenium (II) - catalysed enyne carbocyclization reactions." Thesis, Ecole centrale de Marseille, 2017. http://www.theses.fr/2017ECDM0004/document.
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Cette thèse porte sur les réactions de cyclisation des 1,6-enynes impliquant des catalyseurs de ruthénium. Trois types différents de cyclisation ont été élaborés à partir de précurseurs facilement disponibles, tels que les 1,6-enynes et alcynes. Dans un premier temps, une nouvelle cyclisation hydroalcynylante des 1,6-enynes, à l'aide d'alcynes terminaux comme co-réactifs, catalysée par le ruthenium a été explorée. Cette réaction fournit une méthode de synthèse de cycles à cinq chaînons doté d'un motif 1,5-enyne exocyclique. Un complexe du ruthenium neutre et riche en électrons, Cp*Ru(cod)Cl, s'est avéré être le catalyseur de choix de ces transformations. Dans un deuxième temps, en utilisant le même complexe, la cycloaddition [2+2+2] des 1,6-enynes et alcynes catalysée par le ruthénium a été développée. Les alcynes internes et terminaux sont appropriés pour accéder en une seule étape aux bicyclohexadienes avec de hauts rendements. Une bicycloannulation inhabitelle des 1,6-enynes, intégrant un atome d’azote, catalysée par le ruthénium a également été élaborée. Pour ces cyclisations, seul un complexe du ruthénium électrophile et alkynophile tel que [RuCl2(CO)3]2 a été en mesure d'effectuer la réaction. La formation exclusive des 3-azabicylo[4.1.0]hept-1-enes a été observée avec les 1,6-enynes dotés d'une unité alcyne interne. Ces réactions de cyclisation, respectant le principe des réactions à économie d’atome, sont discutées et sur la base de leur mécanisme de formationThis dissertation focuses on cyclization reactions of 1,6-enynes involving ruthenium catalysts. Three different types of cyclization were developed from readily available precursors, such as 1,6-enynes and alkynes. In one application, a novel ruthenium-catalyzed hydroalkynylative cyclization of 1,6-enynes using terminal alkynes as co-reactants was explored. This reaction provides and entry to five-membered rings featuring an exocyclic 1,5-enyne motif. A neutral electron-rich ruthenium complex Cp*Ru(cod)Cl proved to be the catalyst of choice for these transformations. In another application, using the same complex, the ruthenium-catalyzed [2+2+2] cycloaddition of 1,6-enynes and alkynes was developed. Both internal and terminal alkynes were suitable substrates to access bicyclohexadienes with high yields in a single step. An intriguing ruthenium-catalyzed bicycloannulation of nitrogen-tethered 1,6-enynes has also been developed. For these cyclizations, only the electrophilic and alkynophilic ruthenium complex [RuCl2(CO)3]2 was able to perform the reaction. The exclusive formation of 3-azabicylo[4.1.0]hept-1-enes was observed with 1,6-enynes featuring an internal alkyne unit. These cyclization reactions fulfil the atom-economical reactions principle and are discussed on the basis of their mechanisms of formation
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Pitaval, Anthony. "Gold catalysis for the synthesis of protoilludane sesquiterpenes and other cyclic systems." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/145765.
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Homogeneous gold catalysis emerged as a powerful tool in organic chemistry, offering new perspectives for the synthesis of natural products. In this Doctoral Thesis, I present the application of the cycloisomerization of substituted alkynes with vinylcyclopropanes towards the synthesis of Repraesentin F. As an extension of this methodology, I studied the cycloisomerization of allenes with vinylcyclopropanes aim at constructing the carbon skeleton of several sesquiterpinoids belonging to the protoilludane family. In addition to these projects, I revisited the cycloisomerization of 1,6-enynes that does not proceed by 1,5-migration of alkoxy group at the propargylic position. The mechanism of this reaction was studied by deuteration of the alkyne terminus y appeared to be an endo-type single cleavage rearrangement.La catálisis homogénea con oro ha emergido como una poderosa herramienta en síntesis orgánica, dando a lugar muchosnuevosmétodospara la síntesis de productos naturales. En esta Tesis Doctoral, presentolaaplicación de la cicloisomerización de alquinos sustituidos con vinilciclopropanospara la síntesis de la repraesentina F. Como extensión de estas investigaciones, estudié la cicloisomerización de alenos con vinilciclopropanos con el objetivo de construir el esqueleto de varios sesquiterpenoides de la familia de los protoilludanos. Además de estos proyectos, he re-visitado la cicloisomerización de 1,6-eninos en la que no ocurre una 1,5-migración de grupos OR en posición propargílica. El mecanismo de la reacción se estudió por deuteración del alquino terminal, resultando ser un reordenamiento de tipo endopor ruptura simple.
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Kumano, Takeshi. "Enantioselective Synthesis of Cyclic α-Amino Acids through Asymmetric Phase-Transfer Catalysis." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/179375.
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Walter, Christopher John. "Stereoselective acceleration of Diels-Alder reactions by synthetic enzymes." Thesis, University of Cambridge, 1994. https://www.repository.cam.ac.uk/handle/1810/272679.
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Nyadanu, Aude. "Nouvelles réactions multicomposants et ouverture de cycles contraints pour la synthèse d’hétérocycles." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX065/document.
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Les réactions multicomposants (MCR) constituent une réponse à deux grands défis rencontrés par la chimie pharmaceutique : la découverte de nouvelles molécules bioactives ainsi que leur production à moindre coût dans le respect de l’environnement. En effet, en combinant plusieurs réactifs de façon monotope, les MCR permettent de synthétiser une grande diversité de molécules complexes par des procédés simples et rapides, avec de bons rendements, et en limitant fortement les déchets de réaction. Dans le cadre de cette thèse, nous avons mis au point de nouvelles réactions multicomposants impliquant des isonitriles, composés à la réactivité exceptionnellement riche.Nous nous sommes d’abord intéressés à l’utilisation d’acides forts dans la réaction de Ugi. Les premiers essais ont été réalisés avec des acides sulfiniques, sulfoniques, phosphiniques et phosphoniques, sans succès. Mais grâce à l’introduction de l’acide nitrique comme composant acide dans la réaction de Ugi, nous avons décrit une synthèse monotope de nitramines hautement fonctionnalisées à partir d’un aldéhyde, un isonitrile et un nitrate d’ammonium. Nous avons ainsi développé la première réaction multicomposant conduisant à la formation d’une liaison N-N.Nous avons également proposé une nouvelle variante de la réaction de Passerini impliquant des dérivés thiocarbonylés. Ces derniers étant généralement peu stables, nous avons mis au point une stratégie pour générer un thiocarbénium in situ à partir d’un 3-sulfanyl phthalide, en présence de tétrachlorure de titane. Le couplage de ce thiocarbénium avec un isonitrile et un acide carboxylique a conduit à la synthèse divergente de deux types d’hétérocycles soufrés : les thiophthalides et les 3-amino-4-sulfanyl isocoumarines. Cette étude constitue la première approche formelle de la réaction de Thio-Passerini.Enfin, dans la continuité de notre intérêt pour les dérivés soufrés, nous avons décrit une nouvelle synthèse de thiovinyléthers. Ces composés, synthétiquement équivalents à des dérivés thiocarbonylés, ont été obtenus par l’ouverture palladocatalysée de thiocyclopropanes. Si le recours à des métaux de transition pour l’ouverture de cycles contraints est bien connue pour des dérivés oxygénés ou azotés, il s’agit de la première réaction de ce type pour des dérivés soufrés.Ainsi, trois méthodologies originales ont été développées. Elles donnent accès à différents types de composés fonctionnalisés, potentiellement utiles en pharmacie et en agrochimie. Ces travaux s’appuient fortement sur la réactivité unique des isonitriles et viennent compléter cette chimie particulièrement richeMulticomponent reactions (MCR) are a response to two big challenges faced by pharmaceutical chemistry : the discovery of new bioactive molecules and their production with reduced costs in a environmentally acceptable way. Indeed, by combining several reactants in one pot, MCR allow the synthesis of a wide diversity of complex molecules by simple and quick procedures, with good yields, and with limited amounts of reaction waste. In the framework of this thesis, we have developed new isocyanide-based multicomponent reactions, these compounds having an exceptionnaly rich reactivity.First, we were interested in the use of strong acids in the Ugi reaction. The first trials were made with sulfinic, sulfonic, phosphinic and phosphonic acids, and they failed. Nevertheless, thanks to the introduction of nitric acid as the acid component in the Ugi reaction, we described a one-pot synthesis of highly functionalized nitramines starting from an aldehyde, an isocyanide and an ammonium nitrate. This transformation is the first multicomponent reaction leading to a N-N bond formation.We also proposed a new variant for the Passerini reaction, involving thiocarbonyl derivatives. These compounds generally being quite unstable, we imagined a strategy in order to generate a thiocarbenium in situ from a 3-sulfanyl phthtalide, in the presence of titanium chloride. The coupling of this thiocarbenium with an isocyanide and a carboxylic acid leads to a divergent synthesis of two types of sulfur-containing heterocycles : thiophthalides and 3-amino-4-sulfanyl isocoumarines. This study represents the first formal approach of a Thio-Passerini reaction.Finally, as part of our continuing interest in in sulfur-containing derivatives, we described a new synthesis of thiovinylethers. These compounds, synthetically equivalent to thiocarbonyl derivatives, were obtained by the palladium-catalyzed ring opening of thiocyclopropanes.While the use of transition metals for constrained ring opening is well known for oxygen or nitrogen derivatives, this is the first reaction of this type for sulfur derivatives.Overall, we developed three original methodologies that give access to different types of functionalized compounds, potentially useful in pharmacy and agrochemistry. This work relies on the unique reactivity of isocyanides and adds on this especially rich chemistry
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Karlsson, Erik. "Catalysts for Oxygen Production and Utilization : Closing the Oxygen Cycle: From Biomimetic Oxidation to Artificial Photosynthesis." Doctoral thesis, Stockholms universitet, Institutionen för organisk kemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-56917.
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This thesis describes the development and study of catalysts for redox reactions, which either utilize oxygen or hydrogen peroxide for the purpose of selectively oxidizing organic substrates, or produce oxygen as the necessary byproduct in the production of hydrogen by artificial photosynthesis. The first chapter gives a general introduction about the use of environmentally friendly oxidants in the field of organic synthesis, and about the field of artificial photosynthesis. The second chapter describes a computational study of the mechanism of palladium-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes. The proposed mechanism, which was supported by DFT calculations, involves an unusual water attack on a (π-allyl)palladium complex. The third chapter describes a computational study of the oxidation of unfunctionalized hydrocarbons, ethers and alcohols with hydrogen peroxide, catalyzed by methyltrioxorhenium (MTO). The mechanism was found to proceed via rate-limiting hydride abstraction followed by hydroxide transfer in a single concerted, but highly asynchronous, step as shown by intrinsic reaction coordinate (IRC) scans. The fourth chapter describes the use of a new hybrid (hydroquinone-Schiff base)cobalt catalyst as electron transfer mediator (ETM) in the palladium-catalyzed aerobic carbocyclization of enallenes. Covalently linking the two ETMs gave a fivefold rate increase compared to the use of separate components. The fifth chapter describes an improved synthetic route to the (hydroquinone-Schiff base)cobalt catalysts. Preparation of the key intermediate 5-(2,5-hydroxyphenyl)salicylaldehyde was improved by optimization of the key Suzuki coupling and change of protecting groups from methyl ethers to easily cleaved THP groups. The catalysts could thus be prepared in good overall yield from inexpensive starting materials. Finally, the sixth chapter describes the preparation and study of two catalysts for water oxidation, both based on ligands containing imidazole groups, analogous to the histidine residues present in the oxygen evolving complex (OEC) and in many other metalloenzymes. The first, ruthenium-based, catalyst was found to catalyze highly efficient water oxidation induced by visible light. The second catalyst is, to the best of our knowledge, the first homogeneous manganese complex to catalyze light-driven water oxidation.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted.
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Grogan, Gideon James. "Microbial biotransformations : oxygenation of cyclic ketones by Baeyer-Villiger monooxygenases from camphor-grown Pseudomonas putida NCIMB 10007." Thesis, University of Exeter, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261493.
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Spielmann, Kim. "Synthèse asymétrique de petits cycles et leur réarrangement via des extensions cycliques." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2018. http://www.theses.fr/2018ENCM0015.
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Ce manuscrit de thèse est consacré à l’élaboration asymétrique de petits cycles et à leur fonctionnalisation. En premier lieu, la synthèse énantiosélective de δ-lactones α,β-insaturées par une réaction de Mukaiyama vinylogue catalytique asymétrique a été examinée. Une étude pluridisciplinaire a permis de déterminer le cycle catalytique de cette transformation dans son ensemble. Par ailleurs, grâce à une hydrogénolyse stéréospécifique de ces lactones, la synthèse totale de deux produits naturels, (R)-curcumène et (R)-ar-himachalène, a pu être réalisée. Dans un second temps, une réaction de cycloaddition (3+2) palladocatalysée sur des vinyl-aziridines et cyclopropanes a été développée. Ainsi, des imidazolidines et des pyrrolidines hautement fonctionnalisées ont pu être isolées avec de bons rendements. En fonction du substrat utilisé, des comportements réactionnels différents ont pu être mis en évidence. Ces petits cycles peuvent être considérés comme des « briques moléculaires » polyvalentes pour accéder à des molécules plus complexesThis manuscript deals with the asymmetrical synthesis of small cyclic compounds and their functionalization. In a first part, the enantioselective synthesis of α,β-unsaturated δ-lactones by a catalytic asymmetric vinylogous Mukaiyama reaction was examined. A multidisciplinary study made possible the elucidation of the whole catalytic cycle. Moreover, thanks to a stereospecific hydrogenolysis of these lactones, the total synthesis of two natural products, (R)-ar-Himachalene and (R)-curcumene, could be achieved.In a second part, a palladocatalyzed (3+2) cycloaddition reaction of vinyl aziridines and cyclopropanes was developed. Thus, highly functionalized imidazolidines and pyrrolidines could be isolated with good yields. Depending on the substrate used, different reaction behaviors could be highlighted. These small cycles can be considered as versatile "building blocks" to access more complex molecules
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Guan, Shaoliang. "Determination of the role of nanoparticle active sites in catalytic hydrogenation reactions by cyclic voltammetry and novel in-situ surface spectroscopy." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/73388/.
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Cyclic Voltammetry, Surface Enhanced Raman Spectroscopy and SHell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) have been used to investigate two types of heterogeneously catalysed hydrogenation reactions – hydrogenation of selected alkynes and the Orito reaction. Using a spectro-electrochemical flowcell, which is designed and built in-house, the selectivity and reactivity of the reactions on platinum surfaces have been truly discovered. By studying hydrogenation of a range of alkyne molecules, including 2-butyne-1,4-diol, 2-pentyne, 4-octyne, propargyl alcohol and 2-methyl-3-butyn-2-ol, on different platinum surfaces, it was found that alkyne adsorption on Pt defect sites produces a long-lived di-sigma/pi- alkene complex which may undergo further hydrogenation to produce alkane. This complex may form on different surfaces with various orientations. However, depending on the specific molecules, the intermediate may not survive on some surfaces due to the steady state conditions arising from the catalytic reaction whereby adsorption of alkyne and hydrogenative desorption of reaction intermediates determines the overall surface coverage of intermediate as a function of potential. Alkene selectivity can be increased by blocking defect sites, using polyvinylpyrrolidone or bismuth, leaving only platinum{111} terraces available for catalysis. By studying ethyl pyruvate (EP) adsorption on different surfaces of platinum and palladium, it was found that EP half-hydrogenated state (HHS) is a critical intermediate of the hydrogenated product which only forms on the step sites of the platinum surface at the hydrogen evolution reaction potential. However, another new intermediate adsorbate, which is believed to be a η1 species and is believed to be a precursor of the HHS only forms on the terraces of the surface. By studying the surface intermediates formed during hydrogenation of EP at palladium modified platinum single crystal electrodes, it was found that there was no unequivocal evidence for bands pertaining to EP adsorption on palladium could be identified under hydrogenating conditions due to the reconstruction of the palladium adlayer to reveal Pt subsurface sites.
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Chung, Yongseong. "Diene substituent effects on the retro-Diels-Alder reaction and a formal catalytic cycle for ester hydrolysis based on the Michael/retro-Michael reaction /." The Ohio State University, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487668215805488.
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Castro, Pastrana Lucila Isabel. "Mycobacterial adenylyl cyclases Rv1625c and Rv0386 orthodox vs. unorthodox catalysis = Die mycobakteriellen Adenylatcyclasen Rv1625c und Rv0386 /." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=970608837.
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Carvalho, Rocha Catarina. "Towards a catalytic system allowing the "one-pot" conversion of alkenes into cyclic carbonates in the presence of dioxygen/carbon dioxide mixtures." Paris 6, 2013. http://www.theses.fr/2013PA066758.
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This work aims to develop a heterogeneous catalyst for the direct conversion of an alkene to the corresponding cyclic carbonate in the presence of O2 and CO2. A MnIII salen complex and quaternary ammonium salts (QAS) bearing a -(CH2)2OH function were considered as active phases for the epoxidation and epoxide cyclocarbonatation, respectively. The activity of several QAS was measured to study the influence of the ammonium structure, as well as that of counter-ions. The C16H33N(CH3)2(CH2CH2OH)+Br- salt (HEA16Br) turned out to be more active than choline chloride (HEA1Cl). DFT calculations were used to support the influence of the -(CH2)2OH function and the unexpected reactivity of the HCO3- ion. SBA-15-type materials bearing CxHyN(CH3)2(CH2CH2OH)+ groups were obtained by: i) the impregnation of Al-SBA-15 by aqueous HEA16Cl or ii) covalent anchoring of -C3H6N(CH3)2(CH2CH2OH)+Cl- (HEA3Cl) groups on SBA-15. In both cases, the yields of cyclic carbonate were higher than those obtained in solution, a priori because of a synergistic effect due to the presence of silanols. The catalytic performances of MnIII complex, anchored onto silica through i) dihydroimidazole or ii) phosphonate ligands, were equivalent to that measured in solution, but with a high rate of leached active species. Finally, preliminary "one-pot" studies, involving ,simultaneously, the MnIII salen complex and HEA1Cl with an O2/CO2 mixture were carried out with an in-situ temperature variation from 80 to 120°C. Under these conditions, it appeared that the sacrificial aldehyde not consumed in the epoxidation step could induce side reactionsCes travaux visent à mettre au point un catalyseur hétérogène permettant la transformation directe d’un alcène en son carbonate cyclique en présence d’O2 et de CO2. Un complexe salen du MnIII et des sels d’ammonium quaternaires (SAQ) porteurs de groupements -(CH2)2OH ont été considérés comme phases actives pour les réactions d’époxydation et de cyclocarbonatation des époxydes, respectivement. L’activité de nombreux SAQ a été mesurée afin d’étudier l’influence de la structure de l’ammonium ainsi que des contre-ions. Le sel C16H33N(CH3)2(CH2CH2OH)+Br- (HEA16Br) est plus actif que la choline (HEA1Cl). Les calculs DFT ont permis d’étayer l’influence du groupement -(CH2)2OH ainsi que la réactivité particulière de l’ion HCO3-. Des matériaux siliciques de type SBA-15 porteurs de groupements CxHyN(CH3)2(CH2CH2OH)+ ont été obtenus : i) par imprégnation de Al-SBA-15 par HEA16Cl, ii) par ancrage covalent de groupements -C3H6N(CH3)2(CH2CH2OH)+Cl- (HEA3Cl) sur SBA-15. Dans les deux cas, les rendements en carbonate cyclique sont supérieurs à ceux obtenus en solution, a priori en raison d’un effet de synergie lié à la présence de silanols. Le complexe de MnIII ancré sur silice par le biais de ligands : i) dihydroimidazole, ii) phosphonate a donné des activités équivalentes à celle mesurée en solution mais avec un fort taux de lessivage de la phase active. Enfin, les premières études « one-pot » impliquant simultanément le salen du MnIII et HEA1Cl avec un mélange O2/CO2 ont été réalisées en faisant varier la température de 80 à 120°C en cours de réaction. Dans ces conditions, il apparait que l’aldéhyde sacrificiel non consommé lors de l’étape d’époxydation induit des réactions secondaires
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Cook, Terry Ann. "Function and regulation of the delta subunit of PDE6 /." Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/6287.
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Bailey, Gwendolyn Anne. "Inside the Cycle: Understanding and Overcoming Decomposition of Key Intermediates in Olefin Metathesis." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37501.
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Ru-catalyzed olefin metathesis is an exceptionally powerful, versatile methodology for the assembly of carbon–carbon bonds. The N-heterocyclic carbene (NHC)-stabilized, “second-generation” Ru catalysts have enabled groundbreaking recent advances, ranging from the RCM assembly of cyclic peptides as hepatitis C virus therapeutics, to the elaboration of renewable seed oils and phenylpropanoids into value-added products and chemicals. However, key limitations arise from facile catalyst decomposition. Despite a plethora of studies on the synthesis of new catalysts, and on the decomposition processes accessible to the precatalyst and resting-state species, the underlying principles that govern decomposition of the active intermediates have been surprisingly little examined. One important reason for this is their incredible reactivity: the four-coordinate methylidene intermediate RuCl2(H2IMes)(=CH2) is too short-lived to be observed, while the metallacyclobutane (MCB) intermediate RuCl2(H2IMes)(2-C3H6) can only be observed below –40 °C. This makes them extremely challenging, but also fascinating targets for study. Understanding the underlying chemistry that dictates their reactivity and decomposition is essential for informed catalyst and process redesign, and is thus of fundamental interest, but also considerable practical importance.
This thesis work thus aims at understanding the decomposition of active intermediates relevant to the highly-active, second-generation class of catalysts. Emphasis is placed on examining a variety of metathesis contexts, as well as providing solutions. Treated first are the decomposition pathways that arise during metathesis of electron-deficient olefins, a frontier area in organic synthesis, and in the utilization of renewable resources. An unexpected correlation is revealed between rapid catalyst decomposition, and the presence of a stabilizing PCy3 ligand in the standard catalyst for this reaction. The nucleophilic phosphine ligand is shown to attack an acrylate olefin, forming enolates that function as potent Brønsted bases. Literature evidence suggests that such strong bases are innocuous towards the precatalyst, pointing towards a key role for the active intermediates in Brønsted base-induced catalyst decomposition.
Precisely which intermediate is involved, as well as the site of deprotonation, is elucidated next. Prior to this work, the NHC ligand was widely believed to be the target for attack. However, through labelling experiments, analysis of the Ru and organic byproducts, and computational studies, deprotonation is shown to occur at the MCB ring. Moreover, MCB deprotonation is revealed to be unexpectedly general, and not contingent on the presence of either an exceptionally strong base, or an electron-deficient substrate. This understanding is key, given recent reports from pharma highlighting the adverse impact of base contaminants, as well as current interest in metathesis of amine-containing substrates.
Next examined are the intrinsic decomposition pathways operative for the MCB and four-coordinate methylidene. Prior to this work, the only reported pathway for decomposition of these two species involved beta-elimination of the MCB ring as propene. However, beta-elimination is shown to play an unexpectedly minor role in catalyst decomposition: less than 40% propenes are observed, even under conditions expected to favour MCB elimination. Bimolecular coupling of the methylidene, with loss of the methylidene moiety as ethylene, is proposed to account for the difference. Thus, transiently-stabilized adducts RuCl2(H2IMes)(=CH2)(L)n (L = o-dianiline or pyridine) are synthesized at temperatures down to –120 °C. On warming, these adducts lose Ln and rapidly decompose via bimolecular coupling, with loss of the methylidene moiety as ethylene. These experiments provide the first unambiguous evidence for bimolecular coupling in the important "second-generation" Ru systems, nearly two decades after which this pathway was dismissed in leading papers and reviews.
The last two sections focus on solutions. First, a powerful, straightforward solution to the “enolate problem” is developed, whereby the acrylate enolates are quenched and sequestered via reaction with a polyphenol resin. Then, methods for preventing catalyst decomposition during matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS) are developed, via elucidation of the instrumental and experimental factors that promote successful analysis. As one of the only MS methods capable of affording insight into neutral metal complexes and catalysts, MALDI has unique potential to enable routine analysis of catalyst speciation and decomposition in situ, under real catalytic conditions, for a wide range of catalytic reactions.
Collectively, the findings in this thesis offer a much more complete understanding of the fundamental pathways accessible to the important, highly-active metathesis intermediates, and offer strategies likely to inform practice in both academic and industrial settings. This understanding is key to harnessing the full potential of metathesis methodologies.
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Elbert, Bryony L. "The synthesis and applications of cyclic alkenylsiloxanes." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a332365e-22f2-4449-b517-3fd8a62ea8a3.
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This thesis describes the development of robust methodology to access cyclic alkenylsiloxanes, and their subsequent application in Hiyama-Denmark cross couplings. An early chapter shows the identification of Lindlar reduction conditions capable of generating cyclic alkenylsiloxanes from alkynylsiloxanes in high yields. The use of such species in Hiyama-Denmark cross coupling is then examined, with particular emphasis on the development of fluoride-free conditions, previously unreported for this class of organosilane. A ring-size dependent orthogonality is revealed, where 5-membered cyclic alkenylsiloxanes cross couple under basic conditions, while 6-membered analogues are inert. The origins of this effect are investigated experimentally and theoretically, leading to the proposal of detailed mechanisms for coupling. In the final chapter, the methodology that has been developed is applied to total synthesis. The great potential of the orthogonality uncovered is demonstrated with the highly convergent construction of anti-inflammatory natural product resolvin D3 by sequential, one-pot, orthogonal cross couplings.
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Chen, Li. "New developments in green asymmetric catalysis : Application to Michael reaction and ring opening polymerisation." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS162.
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La synthèse asymétrique organo-catalysée est un domaine de recherche en pleine expansion visant une chimie plus verte. Nous nous sommes intéressés au développement d’une réaction de Michael asymétrique organocatalysée en mettant à profit la catalyse par liaison hydrogène et l’activation énamine afin de contrôler en une seule étape la formation d’adduits portant un centre carboné quaternaire à partir de cétones non activées. Ainsi, nous avons développé des organocatalyseurs bifonctionnels de type squaramide qui ont permis d’obtenir les adduits de Michael attendu à partir de cycloalcanones alpha-substituées avec une bonne énantiosélectivité et une grande régiosélectivité dans un processus sous micro-ondes et sans solvant. Nous avons développé de nouveaux systèmes catalytiques sur la base du motif squaramide qui sont simples, efficaces et opérationnels. Nous avons étudié également l'utilité de nos systèmes organocatalytiques dans d'autres transformations comme la polymérisation verte. Afin de réduire l'utilisation de métaux toxiques pour produire des polymères bien définis sans trace de métaux et d'importance environnementale ou médicale, nous avons également étudié comment nos organo-catalyseurs de type squaramide pourraient contrôler la polymérisation verte par ouverture de cycle. Les systèmes organocatalytiques basés sur des squaramides étaient également applicables à la polymerisation par ouverture de cycle afin de donner des polylactides de dispersité étroite et de masses moléculaires contrôléesOrganocatalyzed asymmetric synthesis is a growing and rapidly expanding research field for a greener chemistry. In this respect, we were interested in developing an organocatalyzed asymmetric Michael reaction taking advantage of H-bond catalysis and enamine activation allowing control of quaternary carbon center from unactivated ketones. Hence compared with well-known H-bond donor urea and thiourea organocatalysts, we first propose bifunctional squaramide organocatalysts for the one-pot transformation of unsymmetrical ketones to produce Michael adducts exhibiting a stereocontrolled quaternary carbon center in a neat microwave process. We also developped new catalytic systems based on the squaramide motive that are efficient and operationnaly simple, and produce Michael adducts in a good regioselectivity with an excellent enantio-selectivity. We also studied the usefulness of our systems in other transformations like green polymerization. In order to reduce the use of toxic metals to produce metal-free and well-defined polymers of environmental and medical significance, we also studied how our squaramide organocatalysts could control the green ring opening polymerization (ROP.The squaramide organocatalyst-based systems were also applicable to ROP to give polylactides of narrow dispersity and controlled molecular masses
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Pankhurst, James Richard. "Complexes of Schiff-base macrocycles and donor-expanded dipyrrins for catalysis and uranyl reduction." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/28887.
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The modern world faces a number of challenges related to energy and the environment. Atmospheric levels of carbon dioxide have now surpassed the 400 ppm mark due to the burning of fossil fuels, yet despite its abundance and potential use as a C1 feedstock for value-added products, there are both thermodynamic and kinetic barriers associated with the strong carbon-oxygen bonds that preclude its widespread deployment in industry. Nuclear energy is an alternative power source that reduces carbon emissions by billions of tonnes each year, but there are widespread concerns regarding the treatment of the radioactive waste that it accrues (of which the main component is uranyl, [UO2]2+). Most of the work presented in this thesis concerns the synthesis of transition-metal complexes, with the aim of directing catalytic reactivity to convert CO2 to useful products. Part of this thesis also concerns the synthesis of uranyl complexes and the study of uranyl reduction chemistry, which is relevant to uranyl remediation and nuclear waste treatment at a fundamental level. Making use of Earth-abundant metals to carry out hydrocarbon oxidation catalysis is a further focus of this work, as the efficient production of oxygenated compounds under mild conditions is of importance to the fine-chemical industry. Chapter 1 reviews important complexes reported in the literature that successfully convert CO2 to useful products through molecular, homogenous electro-catalysis and ring-opening copolymerisation catalysis. Reactions that exemplify a two-electron reduction of uranyl (i.e. uranium(VI) to uranium(IV)) are reviewed, along with uranyl complexes that undergo ligand-centred redox to give ligand-based radicals. The state of the literature on hydrocarbon oxidation catalysis is reviewed in the introduction. The development of multinuclear, macrocyclic complexes and the reactivity of dinuclear Pacman complexes are also presented. Chapter 2 reports the synthesis and characterisation of a new set of Schiff-base macrocycles and acyclic dipyrrin ligands. A number of attempted synthetic routes towards incorporating a dipyrrin coordination compartment in a macro-cyclic setting are discussed. Differences in electronic structures between dipyrromethanes and dipyrromethenes are also examined by theoretical and experimental methods. Chapter 3 introduces the coordination chemistry of these new macrocycles with zinc(II), where the isolation of dinuclear and tetranuclear complexes is demonstrated using different zinc(II) precursors. Tetranuclear zinc-alkyl complexes presented here are shown to be resistant to insertion chemistry with small molecules, but readily form zinc-oxo, -hydroxyl and -alkoxide clusters upon protonolysis with water and alcohols. These molecular clusters display reactivity towards CO2: a zinc-hydroxyl complex precipitates ZnCO3 at high temperature; and zinc-alkoxide complexes have been used to catalyse the copolymerisation reaction between CO2 and cyclohexene oxide to form polycarbonates. Chapter 4 describes the synthesis of late-transition-metal complexes of macrocyclic ligands and dipyrrins, and explores the relationship between macrocycle geometry and electronic structure. Their reactivities towards CO2 are assessed here, using cyclic voltammetry to assess the electro-catalytic activity of a number of the complexes. Chapter 5 reports the oxidation chemistry of hydrocarbon substrates catalysed by copper(II) complexes. High-temperature catalysis occurs with bimetallic copper(II) complexes, and this chapter describes how added FeCl3 acts as a co-catalyst, leading to greater catalyst stability and allowing the catalytic reaction to occur at room temperature. A range of analytical methods have been used to deduce the catalytically active species, and chemical kinetic measurements have been used to deduce a possible reaction mechanism. Chapter 6 reports the synthesis of a uranyl(VI) dipyrrin complex and details characterisation of its electronic structure by theoretical and experimental methods. Theoretical modelling has indicated that the observed two-electron reduction of uranium(VI) to uranium(IV) is facilitated by the dipyrrin ligand, representing a novel uranyl reduction mechanism.
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Paschkewitz, Timothy Michael. "Ammonia Production at Ambient Temperature and Pressure: An Electrochemical and Biological Approach." Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/4893.
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The majority of power generated worldwide is from combustion of fossil fuels. The sustainability and environmental impacts of this non renewable process are severe. Alternative fuels and power generation systems are needed, however, to cope with increasing energy demands. Ammonia shows promise for use in power generation, however it is costly to produce and very few methods of using it as a fuel are developed. To address the need for alternative methods of ammonia synthesis, this research designed and tested a bioelectrochemical device that generates NH3 through electrode induced enzyme catalysis. The ammonia generating device consists of an electrode modified with a polymer that contains whole cell Anabaena variabilis, a photosynthetic cyanobacterium. A. variabilis contains nitrogenase and nitrate/nitrite reductase, catalysts for the production of ammonia. In this system, the electrode supplies driving force and generates a reductive microenvironment near cells to facilitate enzymatic production of NH3 at ambient temperatures and pressures.
Farm animal wastes contain significant amounts of NO2- and NO3-, which can leech into groundwater sources and contaminate them. The system described here recycles NO2- and NO3- to NH4sup+ by the nitrate/nitrite reductase enzyme. Unlike nitrogen fixation by the nitrogenase enzyme whose substrate is atmospheric N2, the substrates for nitrate/nitrite reductase are NO2- and NO3-. The ammonia produced by this system shows great potential as a crop fertilizer.
While the substrates and enzymatic basis for ammonia production by nitrogenase and nitrate/nitrite reductase are very different, there is utility in the comparison of commercially produced ammonia by the Haber Bosch synthesis and by the bioelectrocatalytic device described here. In one day, the Haber Bosch process produces 1800 tons of NH3 at an energetic cost of $500/ton. Per ton of ammonia, the Haber Bosch process consumes 28 GJ of energy. The bioelectrocatalytic device produces 1 ton of NH3 for $10/ton, consuming only 0.04 GJ energy, which can be obtained by sunlight via installation of a photovoltaic device. Thus, the system presented here demonstrates ammonia production with significant impact to the economy.
NH3 production by the bioelectrocatalytic is dependent upon A. var. cell density and electrode polarization. The faradaic current response from cyclic voltammetry is linearly related to cell density and ammonia production. Without electrode polarization, immobilized A. var. do not produce ammonia above the basal level of 2.8 ± 0.4 ΜM. Ten minutes after cycled potential is applied across the electrode, average ammonia output increases to 22 ± 8 ΜM depending on the mediator and substrate chemicals present. Ammonia is produced by this system at 25 °℃ and 1 atm. The electrochemical basis for enhanced NH3 by immobilized cyanobacteria is complex with multiple levels of feedback.
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Griffiths, Owen Glyn. "Environmental life cycle assessment of engineered nanomaterials in carbon capture and utilisation processes." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629663.
Full textAbstract:
CO2 is a waste product from a number of human activities such as fossil fuel power generation, industrial manufacturing processes, and transport. The rising concentration of CO2 in the atmosphere is heating the planet’s surface via the well-established greenhouse effect; a mechanism for many irreversible climate change impacts. Coupled to this is the ever-increasing global pressure over the availability and access to fossil fuel reserves; the foundations of modern society. In recognition of this CO2 is gaining renewed interest as a carbon feedstock, a changing of attitude viewing it as an asset rather than waste. Carbon capture and utilisation (CCU) technologies are attempting to make use of it. However, little quantitative assessment work has been done to assessand verify such potentials. This thesis applies the principles and framework of the life cycle assessment (LCA) - environmental management tool to early stage CO2 utilisation laboratory processes. All processes employ engineered nanomaterials (ENM) to perform this function, a material class leading the way in the challenges of efficient and feasible CO2 chemistry. The LCA contribution in this thesis acts as a measuring and a guiding tool for technology developers, in the first instance to document the cradle-to-gate impacts of a number of formed ENMs. Appreciating the net environmental benefits of ENM uptake within society has yet to be wholly established, and the unavailability of data is recognised as a major factor. The work of this thesis will thus contribute to knowledge gaps, and be informative to wider community seeking to quantify technical performance benefits of ENMs in the context of net life cycle impact burdens. Finally the actual CCU processes are assessed, initially within the confines of the laboratory but further expanded for consideration at more industrially relevant scales. The potential for sound CCU performance were found achievable under best case conditions, with net GHG impact reductions over the life cycle, and the potential for lower impact carbon products, even carbon negative. However other environmental impacts such as ozone depletion, toxic emissions and the consumption of precious metalores are impacts that require consideration in the use of such technologies.
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Zhu, Jie. "Metal-cyclam based Metal-Organic Frameworks for CO₂ Chemical Transformations." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/86838.
Full textAbstract:
Designing new materials for CO₂ capture and utilization is one of the most challenging research topics. Metal-organic frameworks (MOFs) are one of the most efficient CO₂ adsorbents, as well as an emerging class of heterogeneous catalysts for CO₂ chemical transformations. Highlighted by their high content of active centers, large internal surface areas, tunable pore size, and versatile chemical functionalities, MOFs can serve as highly stable and reusable heterogeneous catalysts and provide a great platform to explore the structure-function relationships for transforming CO₂ into useful chemicals. In this dissertation, we aim to develop a new class of metal-cyclam based robust MOFs as porous materials for CO₂ uptake as well as efficient catalysts for CO₂ chemical transformations, including CO₂ chemical fixation, CO₂ photo- and electroreduction.
Chapter 1 introduces the concept and main challenges of CO₂ capture and conversion. The potential of metal-cyclam complexes as molecular catalysts for CO₂ conversion is also mentioned. The current state of the art in designing stable MOFs and azamacrocyclic-based MOFs is briefly discussed. Finally, the strategies, challenges and future outlook of using MOF as catalysts in CO₂ chemical transformation are summarized.
Metal-organic frameworks (MOFs) as highly ordered, tunable hybrid materials have shown great promise in photon collection, energy transfer and photocatalytic reactions. In Chapter 2, the fundamental principles of energy transfer in the condensed phase are summarized, and a series of studies in light-harvesting, excited state quenching and photo-excited reactivity occurring within ruthenium-polypyridyl-doped zirconium MOFs are reviewed. The application of MOFs in energy conversion devices such as dye-sensitized solar cells (DSSC) is also discussed.
Chapter 3 reports two new robust 3D porous metal-cyclam based Zr-MOFs, VPI-100 (Cu) and VPI-100 (Ni) with potential as heterogeneous catalysts for CO2 chemical fixation. The frameworks are prepared by a modulated synthetic strategy and the structure highlighted by eight-connected Zr₆ clusters and metallocyclams as organic linkers. The VPI-100 MOFs exhibit excellent chemical stability in various organic and aqueous solvents over a wide pH range and show high CO₂ uptake capacity (up to ∼9.83 wt% adsorption at 273 K under 1 atm). Moreover, VPI-100 MOFs demonstrate some of the highest reported catalytic activity values (turnover frequency and conversion efficiency) among Zr-based MOFs for the chemical fixation of CO₂ with epoxides. The MOFs, which bear dual catalytic sites (Zr and Cu/Ni), enable chemistry not possible with the cyclam ligand under the same conditions and can be used as recoverable stable heterogeneous catalysts without losing performance.
A follow-up study of CO₂ chemical fixation using Hf analogs of VPI-100 is presented in Chapter 4. Structural characterization and catalytic performance of Hf-VPI-100 are summarized. Moreover, a detailed comparison of VPI-100 and Hf-VPI-100 is made. In situ powder X-ray diffraction (PXRD), quartz crystal microbalance (QCM) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) have been used to probe the interaction between the guest molecules (CO₂/epoxide) and Hf-VPI-100. For CO₂, no specific chemical binding sites in MOFs has been observed and the uptake of CO₂ does not change the crystal structure of Hf-VPI-100. Both QCM and DRIFTs revealed the irreversible binding between the framework and 1,2-epoxybutane. The epoxide uptake per unit cell of VPI-100 MOFs and diffusion coefficients have been calculated by QCM analysis.
Transition metal complexes capable of visible light-triggered cytotoxicity are appealing potential candidates for photodynamic therapy (PDT) of cancer. In Chapter 5, two monometallic polyazine complexes, [(Ph₂phen)₂Ru(dpp)]²⁺ and [(Ph₂phen)₂Os(dpp)]⁺ (Ph₂phen = 4,7-diphenyl-1,10-phenanthroline; dpp =2,3-bis(2-pyridyl)pyrazine), were synthesized, characterized and studied as light activated drugs to kill rat malignant glioma F98 cells. Both compounds display strong absorption in visible spectrum, oxygen-mediated DNA and BSA photocleavage and significant photocytotoxicity under blue light irradiation along with negligible activity in the dark. The compounds show approximately five-fold higher cytotoxicity compared the traditional chemotherapeutic drug, cisplatin. Furthermore, [(Ph₂phen)₂Os(dpp)]⁺ shows promising photocytotoxicity in F98 rat malignant glioma cells within the phototherapeutic window with an IC50 value of (86.07±8.48) µM under red light (625 nm) irradiation.
In Chapter 6, the mixed-metal supramolecular complex, [(Ph₂phen)₂Ru-(dpp)PtCl₂]²⁺, was found to display significant DNA modification, cell growth inhibition, and toxicity towards F98 malignant glioma cells following visible light irradiation. The design of this complex has a significantly higher potential for membrane permeability than three other FDA-approved anti-cancer agents, including cisplatin, and exhibited a dramatic ten-fold higher uptake by F98 cells than cisplatin in a two-hour window. Based on studies with a rat glioma cell line, the compound has very low cytotoxicity in the dark, but results in substantial cell death upon light treatment. The complex is thus among the first to exhibit all the hallmarks of a very promising new class of PDT agents.Ph. D.