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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Bioinspired Activation of Oxygen with Pyrazole-Supported Dinuclear Copper Complexes

Dalle, Kristian Erwin 22 October 2014 (has links)
No description available.
2

INVESTIGATION OF NICKEL (II)-OXIMATE COMPLEXES THAT REACT WITH MOLECULAR OXYGEN

EDISON, SARA ELIZABETH 01 July 2004 (has links)
No description available.
3

A Structural and Mechanistic Study of Two Members of Cupin Family Protein

Liu, Fange 18 June 2013 (has links)
is a functionally diverse large group of proteins sharing a jelly roll β-barrel fold. An enzymatic member 3-hydroxyanthranilate-3,4-dioxygenase (HAO) and a non-enzymatic member pirin, which is a human nuclear metalloprotein of unknown function present in all human tissues, were selected for structural and functional studies in this dissertation work. HAO is an important enzyme for tryptophan catabolism and for 2-nitrobenzoic acid biodegradation. In this work, seven catalytic intermediate were captured in HAO single crystals, enabling for the first time a nearly complete structural snapshot viewing of the entire molecular oxygen activation and insertion mechanism in an iron- and O2-depedent enzyme. The rapid catalytic turnover rate was found achieved in large part by protein dynamics that facilitates O2 binding to the catalytic iron, which is bound to the enzyme by a facile 2-His-1-carboxylate ligand motif. An iron storage and chaperon mechanism was also discovered in the bacterial source of this enzyme, which led to a proposed novel biological function of a mononuclear iron-sulfur center. Although human pirin protein shares the same structural fold with HAO, its iron ion is coordinated by a 3-His-1-carboxylate ligand motif. Pirin belongs to a subset of proteins whose members are playing regulatory functions in the superfamily. In this work, pirin is shown to act as a redox sensor for the NF-κB transcription factor, a critical mediator of intracellular signaling that has been linked to cellular responses to pro-inflammatory signals which controls the expression of a vast array of genes involved in immune and stress responses.
4

A Structural and Mechanistic Study of Two Members of Cupin Family Protein

Liu, Fange 18 June 2013 (has links)
is a functionally diverse large group of proteins sharing a jelly roll β-barrel fold. An enzymatic member 3-hydroxyanthranilate-3,4-dioxygenase (HAO) and a non-enzymatic member pirin, which is a human nuclear metalloprotein of unknown function present in all human tissues, were selected for structural and functional studies in this dissertation work. HAO is an important enzyme for tryptophan catabolism and for 2-nitrobenzoic acid biodegradation. In this work, seven catalytic intermediate were captured in HAO single crystals, enabling for the first time a nearly complete structural snapshot viewing of the entire molecular oxygen activation and insertion mechanism in an iron- and O2-depedent enzyme. The rapid catalytic turnover rate was found achieved in large part by protein dynamics that facilitates O2 binding to the catalytic iron, which is bound to the enzyme by a facile 2-His-1-carboxylate ligand motif. An iron storage and chaperon mechanism was also discovered in the bacterial source of this enzyme, which led to a proposed novel biological function of a mononuclear iron-sulfur center. Although human pirin protein shares the same structural fold with HAO, its iron ion is coordinated by a 3-His-1-carboxylate ligand motif. Pirin belongs to a subset of proteins whose members are playing regulatory functions in the superfamily. In this work, pirin is shown to act as a redox sensor for the NF-κB transcription factor, a critical mediator of intracellular signaling that has been linked to cellular responses to pro-inflammatory signals which controls the expression of a vast array of genes involved in immune and stress responses.
5

DEVELOPMENT OF NICKEL (II) COMPLEXES OF OXIME CONTAINING LIGANDS FOR THE ACTIVATION OF DIOXYGEN

GOLDCAMP, MICHAEL JOSEPH 16 September 2002 (has links)
No description available.
6

Pathways for C—H Activation and Functionalization by Group 9 Metals

Pahls, Dale R. 05 1900 (has links)
As fossil fuel resources become more and more scarce, attention has been turned to alternative sources of fuels and energy. One promising prospect is the conversion of methane (natural gas) to methanol, which requires an initial activation of a C-H bond and subsequent formation of a C-O bond. The most well studied methodologies for both C-H activation and C-O bond formation involve oxidation of the metal center. Metal complexes with facile access to oxidation states separated by four charge units, required for two subsequent oxidations, are rare. Non-oxidative methods to perform C-H bond activation or C-O bond formation must be pursued in order for methane to methanol to become a viable strategy. In this dissertation studies on redox and non-redox methods for both C-H activation and C-O bond formation are discussed. In the early chapters C-O bond formation in the form of reductive functionalization is modeled. Polypyridine ligated rhodium complexes were studied computationally to determine the properties that would promote reductive functionalization. These principles were then tested by designing an experimental complex that could form C-O bonds. This complex was then shown to also work in acidic media, a critical aspect for product stabilization. In the later chapters, non-oxidative C-H activation is discussed with Ir complexes. Both sigma bond metathesis and concerted metalation deprotonation were investigated. For the former, the mechanism for an experimentally known complex was elucidated and for the latter the controlling factors for a proposed catalyst were explored.
7

Réactivité biomimétique du dioxygène au sein de complexes du fer et du cuivre en vue de l’activation des liaisons C-H / Biomimetic reactivity of dioxygen with iron and copper complexes for C-H bond activation

Ayad, Massinissa 02 June 2017 (has links)
L’oxydation catalytique des liaisons C-H, en condition aérobie est l’une des réactions « phare » de la chimie, aussi bien d’un point de vue fondamental qu’industriel. Le principal défi consiste en l’utilisation de l’oxygène moléculaire comme oxydant « vert » pour l’activation de ces liaisons C-H. De nombreuses métalloprotéines, telles que les mono-oxygénases (Fe, Cu), sont capables de réaliser ces réactions dans des conditions douces. Une stratégie actuelle consiste à développer des systèmes synthétiques capables de reproduire de manière efficace les propriétés catalytiques de ces enzymes. L’objectif principal de nos travaux a été de synthétiser et de caractériser des modèles de mono-oxygénases solubles (sMMO) et membranaires (pMMO). Deux approches ont été développées. La première a consisté à élaborer des ligands ditopiques dissymétriques, dont les deux sites de coordination tris-(2-pyridymethyl)amine “TPA” et pyridinedicarboxamide “PydCA”, sont enclavés dans un seul macrocycle afin de favoriser une distance intermétallique optimale. La seconde stratégie est basée sur la synthèse de ligands ditopiques où les motifs coordinants, tetraazacyclotetradecane “cyclam” et dipicolylamine “DPA”, sont séparés par un espaceur de type phényle. Ces deux approches ont conduit à l’obtention et à la caractérisation, à l’état solide (structure aux rayons X) et en solution (spectroscopie, électrochimie), de nombreux complexes mono et dinucléaires du fer, du cuivre et du cobalt. L’étude de la réactivité de certains complexes mononucléaires vis-à-vis des oxydants tels que O2 et H2O2, en l’absence de substrats organiques, a permis d’identifier des espèces métal-oxygène. L’oxydation catalytique de substrats organiques a également été réalisée. / Catalytic oxydation of C-H bonds using molecular oxygen as ‘green’ oxidant remains a great challenge from both fundamental and industrial point of views. Many metalloproteins, such as copper end iron-based mono-oxygenases are able to perform these reactions under mild conditions. A current strategy is to develop synthetic complexes which can reproduce the efficiency of such enzymes. The main objective of our work has been to synthesize and characterize new models of soluble (sMMO) and particulate (pMMO) mono-oxygenases. Two approaches have been developed. The first strategy was to synthesize unsymmetrical dinucleating ligands bearing two coordination sites, tris-(2-pyridylmethyl)amine “TPA” and pyridinedicarboxamide “PydCA”, which are embedded in a single macrocycle to favor intermetallic interaction. The second strategy is based on the synthesis of dinucleating ligands where coordinating patterns, tetraazacyclotetradecane “cyclam” and dipicolylamine “DPA”, are separated by a phenyl type spacer. These two approaches have led to the formation and characterization in the solid state (X-ray structure) and in solution (spectroscopy, electrochemistry) of many mononuclear and dinuclear iron, copper and cobalt complexes. The study of the reactivity of some mononuclear complexes towards oxidants such as O2 and H2O2, in absence of organic substrates, has led to the identification of metal-oxygen species. Catalytic oxidation of organic substrates was also conducted.
8

Structural and biochemical insights into catalytic mechanisms of carotenoid cleavage oxygenases

Sui, Xuewu 08 February 2017 (has links)
No description available.
9

Etude du mécanisme d’activation de l’oxygène par les NO-Synthases / Study of oxygen activation mechanism by nitric-oxide synthases

Brunel, Albane 30 November 2012 (has links)
Le monoxyde d'azote est exclusivement synthétisé chez les mammifères par une famille d’hémoprotéines, les NO-Synthases. Le cœur de l’activité des NO-Synthases est l’activation de l’oxygène c'est-à-dire l’activation de l’intermédiaire réactionnel FeIIO2. Cette étape est contrôlée par la réactivité intrinsèque du fer, par les transferts de proton et les transferts d’électron. Elle doit être parfaitement maîtrisée car elle contrôle le chemin catalytique emprunté et la nature du produit final. Comprendre l’étape d’activation de l’oxygène est essentiel à la compréhension du rôle biologique et/ou pathologique de la NO-Synthase de mammifère. Cette question s'étend aux NO-Synthases bactériennes pour lesquelles on ne connait ni le mécanisme moléculaire ni la fonction biologique. Ce manuscrit propose une analyse approfondie de l’étape d’activation de l’oxygène de la NO-Synthase. Dans un premier temps, nous avons étudié l’influence de l’environnement proximal sur la réactivité intrinsèque du fer et l’activation de l’oxygène. Nous avons généré des protéines mutées qui modifient les propriétés électroniques de la liaison proximale de l’hème. Ces protéines mutées ont été caractérisées par différentes spectroscopies (résonance paramagnétique électronique, Raman de résonance). Dans un second temps nous avons directement étudié le complexe FeIIO2, en présence d’analogues de substrat, grâce à des analyses de cinétique rapide en flux continu et en flux arrêté (stopped-flow). Dans un troisième temps, le rôle du cofacteur tetrahydrobioptérine dans le transfert de proton et d’électron a été étudié par une méthode de piégeage à des temps très courts : le freeze-quench. L'ensemble de nos résultats montrent que l’activation de l’oxygène est régulée par les propriétés électro-donneuses du ligand proximal et par le réseau de liaisons H distal. Nous mettons en évidence des différences dans le rôle redox du cofacteur tetrahydrobioptérine entre la NO-Synthase de mammifère et la NO-Synthase bactérienne. La difficulté majeure pour comprendre l’étape d’activation de l’oxygène de la NO-Synthase réside dans la complexité et la rapidité de la réaction catalytique. Dans ce contexte, nous avons cherché à adapter une méthodologie qui a prouvé son efficacité dans le cas des cytochromes P450 : la cryo-réduction couplée à des sauts en température. / Nitric oxide is exclusively synthesized by NO-Synthases in mammals. The heart of the NO-synthase activity is oxygen activation, which corresponds to the activation of the FeIIO2 intermediate. This step depends on the heme electronic properties and on the electron and proton transfers. Oxygen activation has to be well mastered to control exactly the nature of the end-product. Understanding the oxygen activation step is necessary to better understand the biological/pathological role of the mammalian NO-Synthases. Furthermore, bacterial NO-Synthases function and oxygen activation mechanism are unknown. This PhD work proposes a deep analysis of the oxygen activation step in NO-Synthases. First, proximal environment has been studied with mutated proteins. These mutations impact the electronic properties of the heme proximal bond. Spectroscopic analyses of these mutants have been done by electron paramagnetic resonance and resonance Raman. Then, we have studied the FeIIO2 intermediate with substrate analogs which has necessitated continuous flow and stopped-flow analyses. Finally, the role of the tetrahydrobiopterin cofactor in the electron and proton transfer has been studied and clarified thanks to a very fast trapping method : the freeze-quench. Our results show that the oxygen activation step is elaborately controlled by the proximal bond electron donation and the distal H bond network. At the same time we show some differences between mammalian and bacterial NO-Synthases concerning the redox role of the tetrahydrobiopterin cofactor. The major obstacle to understand the oxygen activation step resides in the complexity of the active site chemistry and the rate of catalytic reactions. For this reason, we propose to adapt an already successful protocol to trap some intermediates in the cytochromes P450 mechanism : cryo-reduction coupled with temperature jumps.
10

Synthesis, structure and reactivity of novel CuI, CuII and CuIII complexes containing triaza and hexaaza macrocyclic ligands

Ribas Salamaña, Xavi 17 December 2001 (has links)
El treball de tesi s'emmarca dins del camp de la bioinorgànica, disciplina que estudia les propietats estructurals i de reactivitat dels centres actius dels enzims, servint-se de models síntètics de baix pes molecular per tal d'intentar reproduïr la reactivitat presentada per l'enzim i conèixer els mecanismes de reacció a nivell molecular que tenen lloc en els processos biològics.1 Més concretament el treball posa especial èmfasi en els processos d'activació d'oxigen molecular que tenen lloc en les metaloproteïnes de Coure del Tipus 3, com són l'hemocianina i la tirosinasa, ambdues presentant un complex dinuclear de Cu(I)) en el centre actiu de la forma reduïda, capaç d'activar l'O2 cap a espècies de tipus peròxid.2 Un altre camp d'interès ha estat l'estudi dels processos d'activació d'enllaços C-H no activats en hidrocarburs, tant per la seva importàcia a nivell industrial com per comprendre els mecanismes intrínsecs d'aquesta activació a través de metalls de trancisió.3,4 Durant el treball de tesi presentat s'ha desenvolupat la síntesi de nous complexes de Coure(I), Coure(II) y Cu(III) utilitzant lligands macrocíclics de tipus triaza i hexaaza, i s'han estudiat la seves propietats estructurals així com la seva reactivitat. La reacció dels lligands triazacíclics H32m, H2Me33m i H33m amb sals de coure(II) dóna lloc a una reacció de desproporció de Cu(II) per obtenir-se en quantitats equimolars un complex organometàl·lic de Cu(III) i un complex de Cu(I). La caracterizació estructural exhaustiva dels complexes del tipus aryl-Cu(III) evidencia la formació d'un enllaç organometàl·lic entre l'àtom de Cu(III) i el carboni més próxim de l'anell aromàtic del lligand. Aquesta reacció, a més de representar una nova forma de desproporció en la química del Cu, suposa l'activació d'un enllaç C-H aromàtic a temperatura ambient que, mitjançant l'estudi cinètic d'aquesta desproporció per espectroscòpia UV-Vis, dels càlcul de l'efecte cinètic isotòpic utilitzant el lligand deuterat en el C-H de l'anell, juntament amb el recolzament teòrics dels càlculs DFT per a la optimització de geometries d'intermedis de reacció, ens permeten proposar un mecanisme de reacció pel nostre sistema, on l'activació de l'enllaç C-H aromàtic transcorre per la formació d'un enllaç de tipus agòstic C-H ? Cu(II),5 seguit de la desprotonació del C-H aromàtic per acció d'una base i posterior transferència electrònica per obtenir el complex organometàlic de Cu(III) i el complex de de Cu(I). En quant a la reactivitat d'aquests complexes organometàl·lics aryl-Cu(III) s'ha observat que una base en medi aquós causa la inestabilitat d'aquests compostos, evolucionant cap a la inserció d'un àtom d'oxigen sobre la posició activada de l'anell aromàtic, per a donar lloc a un complex dinuclear de Cu(II) amb dos grups fenoxo actuant de pont entre els àtoms metàl·lics. La reacció transcorre per un intermedi colorejat, caracteritzat com el complex ayl-Cu(III) monodesprotonat en una de les seves amines benzíliques, els quals s'observen igualment en la reacció dels correponents complexos de Cu(I) amb oxigen molecular (O2). És en els nostres sistemes en els quals es descriu per primera vegada la participació d'intermedis organometàl·lics Cu(III)-C en processos d'hidroxilació aromàtica, tals com el desenvolupat per l'enzim tirosinasa o per alguns dels seus models químics de síntesi.6,7,8 S'han estudiat les propietats magnètiques dels quatre bis(fenoxo)complexes de Cu(II) descrits, obtenint-se uns acoplaments de tipus antiferromagnètic o ferromagnètic de diversa magnitud, depenent del solapament orbitalari a l'enllaç Cu-O, a través del qual es produeix el superintercanvi. Nous complexos de Cu(I) sintetitzats amb lligands hexaazamacrocíclics han estat estudiats, i posant especial èmfasi a la seva reactivitat respecta a l'activació d'oxigen molecular (O2). S'ha observat una reactivitat diferenciada segons la concentració de complex de Cu(I) utilitzada, de manera que a altes concentracions s'obté un carbonato complex tetranuclear de Cu(II) per fixació de CO2 atmosfèric, mentre que a baixes concentracions s'observa la hidroxilació aromàtica intramolecular d'un dels anells benzílics del lligand, reacció que presumiblement transcorre per atac electrofílic d'un peroxo complex intermedi sobre el sistema ? de l'anell.6Els resultats obtinguts en aquest treball ens mostren la facilitat per activar enllaços C-H aromàtics per metalls de transició de la primera sèrie (Cu, Ni) quan aquests estan suficientment pròxims a l'enllaç C-H, en unes condicions de reacció molt suaus (1atm., temperatura ambient). Els nous complexos organometàl·lics Aryl-Cu(III) són el producte d'una nova reacció de desproporció de Cu(II), així com un posició aromàtica activada que podria ser el punt de partida per l'estudi de funcionalització selectiva d'aquests grups aromàtics. / In the present thesis the synthesis of novel Cu(I), Cu(II) and Cu(III) complexes containing triaza and hexaaza macrocyclic ligands is described, as well as the study of their structural and reactivity properties. Ligands H32m, H2Me33m and H33m react with Cu(II) salts at room temperature in CH3CN to afford an organometallic Cu(III) complex and a Cu(I) complex in equimolar amounts, constituting a new disproportionation reaction for Cu(II). An exhaustive structural characterization of Aryl-Cu(III) complexes shows the formation of an organometallic between theCu(III) center and the carbon form the aromatic ring. This reaction represents a novel disproportionation in copper chemistry and moreover, evidenciates the activation of an aromatic C-H bond at room temperature. Throughout kinetic studies by UV-Vis spectroscopy, determination of the KIE value by using the corresponding deuterated ligand and theoretical calculations at DFT level for the optimization of intermediate geometries, we have proposed a mechanism for this disproportionation reaction: the aromatic C-H bond activation occurs through the formation of an agostic C-H ? Cu(II) interaction, followed by the deprotonation of the aromatic proton by the action of a base and final electron transfer to obtain the Cu(III) and Cu(I) final complexes. The organometallic Cu(III) synthesized are stable in protic media, but react with aqueous base to afford the insertion of an oxygen atom at the C-Cu(III) bond and finally obtain a dinuclear Cu(II) complex where two phenoxo groups are bridging between the metal centers. The reaction undergoes through the formation of a colored intermediate characterized as an Aryl-Cu(III) complex deprotonated in one of the benzylic amines. These intermediates are also observed in the reaction of the corresponding Cu(I) complexes with molecular oxygen (O2). The intermediacy of organometallic aryl-Cu(III) in aromatic hydroxylation processes such as the reactivity displayed by tyrosinase or some synthetic model systems, is first described in the present work. Magnetic properties for the four bis(phenoxo)Cu(II) complexes have alse been investigated. Different magnetic couplings are observed yielding ferromagnetic and antiferromagnetic behavior of variable magnitudes, depending on orbital overlapping on the Cu-O bond, through which the superexchange occurs. Novel Cu(I) complexes containing the hexaazamacrocyclic ligand H33+33m have been studied, with special attention on the reactivity towards the O2 activation. It has been observed a differential reactivity depending on the concentration of Cu(I) complex: if high Cu(I) concentration are used the product obtained consists on a tetranuclear carbonato complex by atmospheric CO2 fixation, while if low concentrations are used the intramolecular aromatic hydroxylation is observed, reaction that is proposed to undergo through an electrophilic attack of the peroxo group to the ? system of the aromatic ring.

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