Littérature scientifique sur le sujet « Catalyse modulable »
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Articles de revues sur le sujet "Catalyse modulable"
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Rodríguez-Ruiz, Marta, Salvador González-Gordo, Amanda Cañas, María Jesús Campos, Alberto Paradela, Francisco J. Corpas et José M. Palma. « Sweet Pepper (Capsicum annuum L.) Fruits Contain an Atypical Peroxisomal Catalase That Is Modulated by Reactive Oxygen and Nitrogen Species ». Antioxidants 8, no 9 (4 septembre 2019) : 374. http://dx.doi.org/10.3390/antiox8090374.
Texte intégralRésumé :
During the ripening of sweet pepper (Capsicum annuum L.) fruits, in a genetically controlled scenario, enormous metabolic changes occur that affect the physiology of most cell compartments. Peroxisomal catalase gene expression decreases after pepper fruit ripening, while the enzyme is also susceptible to undergo post-translational modifications (nitration, S-nitrosation, and oxidation) promoted by reactive oxygen and nitrogen species (ROS/RNS). Unlike most plant catalases, the pepper fruit enzyme acts as a homodimer, with an atypical native molecular mass of 125 to 135 kDa and an isoelectric point of 7.4, which is higher than that of most plant catalases. These data suggest that ROS/RNS could be essential to modulate the role of catalase in maintaining basic cellular peroxisomal functions during pepper fruit ripening when nitro-oxidative stress occurs. Using catalase from bovine liver as a model and biotin-switch labeling, in-gel trypsin digestion, and nanoliquid chromatography coupled with mass spectrometry, it was found that Cys377 from the bovine enzyme could potentially undergo S-nitrosation. To our knowledge, this is the first report of a cysteine residue from catalase that can be post-translationally modified by S-nitrosation, which makes it especially important to find the target points where the enzyme can be modulated under either physiological or adverse conditions.
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Ilani, Tal, Assaf Alon, Iris Grossman, Ben Horowitz, Elena Kartvelishvily, Sidney R. Cohen et Deborah Fass. « A Secreted Disulfide Catalyst Controls Extracellular Matrix Composition and Function ». Science 341, no 6141 (23 mai 2013) : 74–76. http://dx.doi.org/10.1126/science.1238279.
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Disulfide bond formation in secretory proteins occurs primarily in the endoplasmic reticulum (ER), where multiple enzyme families catalyze cysteine cross-linking. Quiescin sulfhydryl oxidase 1 (QSOX1) is an atypical disulfide catalyst, localized to the Golgi apparatus or secreted from cells. We examined the physiological function for extracellular catalysis of de novo disulfide bond formation by QSOX1. QSOX1 activity was required for incorporation of laminin into the extracellular matrix (ECM) synthesized by fibroblasts, and ECM produced without QSOX1 was defective in supporting cell-matrix adhesion. We developed an inhibitory monoclonal antibody against QSOX1 that could modulate ECM properties and undermine cell migration.
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Ramirez-Ramirez, Joaquin, Javier Martin-Diaz, Nina Pastor, Miguel Alcalde et Marcela Ayala. « Exploring the Role of Phenylalanine Residues in Modulating the Flexibility and Topography of the Active Site in the Peroxygenase Variant PaDa-I ». International Journal of Molecular Sciences 21, no 16 (10 août 2020) : 5734. http://dx.doi.org/10.3390/ijms21165734.
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Unspecific peroxygenases (UPOs) are fungal heme-thiolate enzymes able to catalyze a wide range of oxidation reactions, such as peroxidase-like, catalase-like, haloperoxidase-like, and, most interestingly, cytochrome P450-like. One of the most outstanding properties of these enzymes is the ability to catalyze the oxidation a wide range of organic substrates (both aromatic and aliphatic) through cytochrome P450-like reactions (the so-called peroxygenase activity), which involves the insertion of an oxygen atom from hydrogen peroxide. To catalyze this reaction, the substrate must access a channel connecting the bulk solution to the heme group. The composition, shape, and flexibility of this channel surely modulate the catalytic ability of the enzymes in this family. In order to gain an understanding of the role of the residues comprising the channel, mutants derived from PaDa-I, a laboratory-evolved UPO variant from Agrocybe aegerita, were obtained. The two phenylalanine residues at the surface of the channel, which regulate the traffic towards the heme active site, were mutated by less bulky residues (alanine and leucine). The mutants were experimentally characterized, and computational studies (i.e., molecular dynamics (MD)) were performed. The results suggest that these residues are necessary to reduce the flexibility of the region and maintain the topography of the channel.
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Carpena, Xavier, Ben Wiseman, Taweewat Deemagarn, Rahul Singh, Jacek Switala, Anabella Ivancich, Ignacio Fita et Peter C. Loewen. « A molecular switch and electronic circuit modulate catalase activity in catalase‐peroxidases ». EMBO reports 6, no 12 (décembre 2005) : 1156–62. http://dx.doi.org/10.1038/sj.embor.7400550.
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Ochoa, Elba, Wilson Henao, Sara Fuertes, Daniel Torres, Tomas van Haasterecht, Elinor Scott, Harry Bitter, Isabel Suelves et Jose Luis Pinilla. « Synthesis and characterization of a supported Pd complex on carbon nanofibers for the selective decarbonylation of stearic acid to 1-heptadecene : the importance of subnanometric Pd dispersion ». Catalysis Science & ; Technology 10, no 9 (2020) : 2970–85. http://dx.doi.org/10.1039/d0cy00322k.
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Evaluation of the dispersion of Pd active sites on the catalyst performance during fatty acids decarbonylation to α-olefins was explored in this work. Pd subnanometric particles, clusters and aggregates were found to modulate the catalyst activity.
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Wang, T. S., Y. F. Shu, Y. C. Liu, K. Y. Jan et H. Huang. « Glutathione peroxidase and catalase modulate the genotoxicity of arsenite ». Toxicology 121, no 3 (septembre 1997) : 229–37. http://dx.doi.org/10.1016/s0300-483x(97)00071-1.
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Xu, Zheng, So Fun Chau, Kwok Ho Lam, Ho Yin Chan, Tzi Bun Ng et Shannon W. N. Au. « Crystal structure of the SENP1 mutant C603S–SUMO complex reveals the hydrolytic mechanism of SUMO-specific protease ». Biochemical Journal 398, no 3 (29 août 2006) : 345–52. http://dx.doi.org/10.1042/bj20060526.
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SUMO (small ubiquitin-related modifier)-specific proteases catalyse the maturation and de-conjugation processes of the sumoylation pathway and modulate various cellular responses including nuclear metabolism and cell cycle progression. The active-site cysteine residue is conserved among all known SUMO-specific proteases and is not substitutable by serine in the hydrolysis reactions demonstrated previously in yeast. We report here that the catalytic domain of human protease SENP1 (SUMO-specific protease 1) mutant SENP1CC603S carrying a mutation of cysteine to serine at the active site is inactive in maturation and de-conjugation reactions. To further understand the hydrolytic mechanism catalysed by SENP1, we have determined, at 2.8 Å resolution (1 Å=0.1 nm), the X-ray structure of SENP1CC603S–SUMO-1 complex. A comparison of the structure of SENP2–SUMO-1 suggests strongly that SUMO-specific proteases require a self-conformational change prior to cleavage of peptide or isopeptide bond in the maturation and de-conjugation processes respectively. Moreover, analysis of the interface of SENP1 and SUMO-1 has led to the identification of four unique amino acids in SENP1 that facilitate the binding of SUMO-1. By means of an in vitro assay, we further demonstrate a novel function of SENP1 in hydrolysing the thioester linkage in E1-SUMO and E2-SUMO complexes. The results disclose a new mechanism of regulation of the sumoylation pathway by the SUMO-specific proteases.
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Sun, He, Mengfan Wang, Xinchuan Du, Yu Jiao, Sisi Liu, Tao Qian, Yichao Yan et al. « Modulating the d-band center of boron doped single-atom sites to boost the oxygen reduction reaction ». Journal of Materials Chemistry A 7, no 36 (2019) : 20952–57. http://dx.doi.org/10.1039/c9ta06949f.
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A boron dopant is experimentally and theoretically confirmed to effectively modulate the d-band center of a single-atom catalyst, enabling favorable adsorption kinetics of oxygen intermediates and thus greatly improving the ORR performance.
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Thomson, Martha, Khaled Al-Qattan, Mohamed H. Mansour et Muslim Ali. « Green Tea Attenuates Oxidative Stress and Downregulates the Expression of Angiotensin II AT1Receptor in Renal and Hepatic Tissues of Streptozotocin-Induced Diabetic Rats ». Evidence-Based Complementary and Alternative Medicine 2012 (2012) : 1–10. http://dx.doi.org/10.1155/2012/409047.
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This study investigates the potential of green tea to modulate oxidative stress and angiotensin II AT1receptor expression in renal and hepatic tissues of diabetic rats. Three groups of rats were studied after 8 weeks following diabetes induction: normal, streptozotocin-induced diabetic (diabetic control), and green-tea-treated diabetic rats. Total antioxidant, catalase, and malondialdehyde levels were assayed by standard procedures. Levels of AT1receptor labeling, in renal and hepatic tissues of the three rat groups, were immunohistochemically investigated using an anti-AT1receptor antibody. Levels of total antioxidant and catalase were significantly reduced, whereas malondialdehyde levels and AT1receptor labeling were significantly increased in renal and hepatic tissues of diabetic control rats compared to normal rats. Compared to diabetic control rats, total antioxidant and catalase levels were significantly increased, whereas malondialdehyde levels and AT1receptor labeling in the green-tea-treated diabetic group were significantly reduced throughout hepatic lobules and renal cortical and medullary vascular and tubular segments to levels comparable to those observed in normal rats. The capacity of green tea to modulate diabetes-induced oxidative stress and AT1receptor upregulation may be beneficial in opposing the deleterious effects of excessive angiotensin II signaling, manifested by progressive renal and hepatic tissue damage.
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Fang, Wei, Chengtao Wang, Zhiqiang Liu, Liang Wang, Lu Liu, Hangjie Li, Shaodan Xu et al. « Physical mixing of a catalyst and a hydrophobic polymer promotes CO hydrogenation through dehydration ». Science 377, no 6604 (22 juillet 2022) : 406–10. http://dx.doi.org/10.1126/science.abo0356.
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In many reactions restricted by water, selective removal of water from the reaction system is critical and usually requires a membrane reactor. We found that a simple physical mixture of hydrophobic poly(divinylbenzene) with cobalt-manganese carbide could modulate a local environment of catalysts for rapidly shipping water product in syngas conversion. We were able to shift the water-sorption equilibrium on the catalyst surface, leading to a greater proportion of free surface that in turn raised the rate of syngas conversion by nearly a factor of 2. The carbon monoxide conversion reached 63.5%, and 71.4% of the hydrocarbon products were light olefins at 250°C, outperforming poly(divinylbenzene)-free catalyst under equivalent reaction conditions. The physically mixed CoMn carbide/poly(divinylbenzene) catalyst was durable in the continuous test for 120 hours.
Thèses sur le sujet "Catalyse modulable"
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Colin, Olivier. « Plateforme pyridylalkylamine modulable : un outil pour la catalyse ». Thesis, Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS023V/document.
Texte intégralRésumé :
Les travaux exposés dans ce manuscrit s’articulent autour de l’élaboration de nouvelles plateformes pyridylalkylamines polyfonctionelles et chirales afin de permettre le développement d’un nouveau processus de réactions catalysées en cascade. La première partie de ce document décrit la synthèse de plateformes pyridylméthylamines (pma) portant des motifs chiraux et (thio)urées. La seconde partie traite de leur utilisation dans des réactions d’organocatalyse et de métallocatalyse asymétriques, puis dans des réactions catalysées en cascade séquencée. La troisième partie porte sur la synthèse de plateformes pyridyléthylamines (pea) via l’utilisation d’une réaction d’amination électrophile organocatalysée et une réaction de cyclisation de PrinsThe works described in this manuscript is dealing with the construction of new polyfunctional chiral pyridylmethylamine (pma) platforms in order to allow the development of new one-pot catalytic reaction sequences. The first part of this document focuses on the synthesis of pyridylméthylamine platforms carrying chiral motifs and (thio)ureas. The second part reports their use in asymmetric organocatalysis and metallocatalysis and then in catalyzed cascade reaction sequences. The third part deals with the synthesis of pyridyléthylamine (pea) platforms through an organocatalyzed electrophilic reaction followed by a Prins cyclisation
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Mongin, Cédric. « Synthèse et étude de cages moléculaires photo-modulables et génération de nano-cristaux d’or par photo-catalyse supramoléculaire ». Thesis, Bordeaux 1, 2013. http://www.theses.fr/2013BOR14996/document.
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Les objectifs de cette thèse sont articulés autour de deux axes principaux : la synthèse et l’étude de cages moléculaires photo-modulables, et la génération de nano-cristaux d’or par photo-catalyse supramoléculaire. Ces deux thématiques sont reliées entre elles par l’exploitation des propriétés photophysiques et photochimiques d’un motif commun, le 9,10-diphénylanthracène (DPA). Dans un premier temps, de nouvelles architectures tridimensionnelles photo-modulables de type cage moléculaire ont été conçues et étudiées. En présence d’oxygène, l’irradiation directe ou sensibilisée du DPA permet de former réversiblement le dérivé endoperoxyde et ainsi moduler les propriétés de complexation de la cage. Les différentes stratégies de synthèse mises en place reposent sur l’exploitation conjuguée de la réactivité de la 2,4,6-trichloro-1,3,5-triazine, et de réactions de chimie « click » (métathèse des oléfines, cycloaddition de Huisgen). L’étude et la modulation des propriétés des reconnaissances ont été effectuées sur des sels de cations alcalins (sodium et césium) et suivies par émission de fluorescence et spectroscopie d’absorption UV-visible. Les résultats obtenus avec deux cages possédant des constantes d'associations élevées (logK = 8,7 pour le cation sodium) montrent une augmentation de la constante d’association d’un facteur 10 et 20 pour respectivement le sodium et le césium entre la forme DPA et la forme endoperoxyde. Dans un second temps, des photocatalyseurs supramoléculaires basés sur le chromophore DPA ont été étudiés en vue de la synthèse de nano-cristaux d’or nus. L’association du chromophore avec des thioéthers permet de former un complexe en phase organique par extraction de sels d’or(III) depuis une phase aqueuse. L’irradiation à 400nm permet la réduction de l’or(III) par transfert d’énergie depuis le 9,10-diphénylanthracène. Les atomes d’or sont ensuite relargués en phase aqueuse pour former des nano-cristaux nus qui ont pu être caractérisés par MET, XPS, AFM et DLS. Par ailleurs, ce procédé est catalytique dans le toluène et un système de réduction en flux continu a été mis au point permettant un turnover moyen de 150The goals of this thesis are organized around two major axes: the synthesis and study of photo-gated molecular cages, and the generation of gold nanocrystals by supramolecular photocatalysis. These two themes are connected by the use of the photochemical and photophysical properties of a common chromophore, 9,10-diphenylanthracene (DPA). Three-dimensional photo-gated cage-like architectures were designed and synthesized. Various synthetic strategies based on the combined use of the 2,4,6-trichloro-1,3,5-triazine unit and "click" chemistry reactions (olefin metathesis, Huisgen cycloaddition) were employed for the synthesis. In the presence of oxygen, sensitized or direct irradiation of the DPA chromophore forms the corresponding endoperoxide derivative, thereby modulating the binding properties of the cage. The study and the modulation of the recognition properties were performed on various alkali metal cations and a strong binding of sodium and cesium was evidenced by fluorescence emission and UV-visible absorption spectroscopy. The cages investigated possessed high association constants towards sodium and cesium cations (logK = 8.7 for the sodium cation) which could be reversibly increased by a factor 10 and 20 for sodium and cesium, respectively, upon formation of the endoperoxide. Supramolecular photocatalysis of gold(III) reduction based on the DPA chromophore was also studied for the preparation of uncapped gold nanocrystals. The combination of the DPA chromophore with thioether chains allows the formation of a complex in the organic phase by extraction of gold(III) chloride from an aqueous phase. Irradiation at 400 nm enables the reduction gold(III) by energy transfer from the 9,10-diphenylanthracene followed by oxidation of the solvent. The gold atoms are subsequently released in the aqueous phase to form uncapped nanocrystals characterized using TEM, XPS, AFM, and DLS techniques. Furthermore, the process is catalytic in toluene, where a continuous flow reactor was developed. The latter allowed an average catalytic turnover of 150 to be determined
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Cayla, Mattéo. « Catalyseurs contrôlables par l’oxygène singulet : conception, synthèse et propriétés ». Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0419.
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La catalyse modulable vise à contrôler l’activité catalytique par la modification réversible du site catalytique, sous le contrôle d’un stimulus. Les stimuli connus pour les systèmes artificiels sont chimiques (molécules, ions), physiques (température, lumière) ou électrochimiques (rédox). Ces stimulus contrôlent le passage d’un état à l’autre du catalyseur, donc, par conséquence, l’activité du système catalytique en termes de cinétique et de sélectivités des réactions. Afin d’élargir le champ des applications de la catalyse modulable, une stratégie innovante serait d’introduire un nouveau stimulus pour engendrer des modulations inédites. Ces travaux de doctorat ont ainsi visé à montrer que la catalyse peut être modulée par l’oxygène singulet. Les réactions de cycloaddition [4+2] entre 1O2 et les dérivés du 9,10-diphénylanthracène permettent la formation de 9,10-endopéroxydes de façon quantitative et réversible par le biais d’une cycloréversion thermique. De plus, cette réaction engendre une modification structurelle importante, en transformant un composé polyaromatique plan en un produit endopéroxyde à géométrie concave. Ainsi, un site catalytique pourvu de dérivés anthracènes pourrait avoir deux arrangement spatiaux différents, contrôlé par 1O2 et la chaleur. Une nouvelle famille de catalyseurs modulables a été conçue à partir d’acides phosphoriques chiraux dérivés du (R)-BINOL (1,1’-bi-2-naphtol) substitués par des dérivés anthracènes. La cycloaddition de l’oxygène singulet sur ces dérivés a été optimisée pour obtenir des molécules dont la géométrie et la nature du site catalytique sont modifiés. Les propriétés catalytiques des édifices anthracènes et endopéroxydes ont ensuite été évaluées à l’aide de trois réactions modèles (désymétrisation d’oxétane, aza-Friedel-Crafts et désaromatisation de 2-naphtols). Ces réactions ont ensuite été étudiées par modélisation moléculaire pour une compréhension fine des relations entre la structure et l’activité catalytique. Sur la base des calculs DFT, une optimisation des structures des catalyseurs et de nouvelles réactions modèles ont aussi été proposés. Les résultats obtenus constituent une avancée vers une preuve de concept pour l’utilisation de 1O2 en tant que stimulus en organocatalyse, malgré la complexité chimique induite sur les catalyseurs modèles dérivés des acides phosphoriques chirauxSwitchable catalysis aims to control catalytic activity by modulating the system’s catalytic site, when under the influence of a stimulus. The known stimuli that regulate artificial catalytic systems are chemical (molecules, ions), physical (temperature, light) or electrochemical (redox). These stimuli control the switch between states of the catalyst and of its activity, with effects on its catalytic efficiency, regio- or stereo- selectivity. To broaden the field of applications of switchable catalysis, an innovative strategy would consist in introducing a new stimulus that induces unprecedented modulations. This doctoral work aimed to show that catalysis can be modulated by singlet oxygen. [4+2] cycloaddition reactions between 1O2 and 9,10-diphenylanthracene derivatives allows the formation of the corresponding endoperoxides in a quantitative and reversible (with a cycloreversion via thermolysis) manner. Furthermore, this reaction induces a consequent structural modification, transforming a flat polyaromatic into a endoperoxide product with a concave geometry. Thereby, a catalytic site bearing anthracenes could have two spatial arrangements, controlled by 1O2 and heat. A new family of modular catalysts have been designed from (R)-BINOL (1,1’-bi-2-naphtol) based chiral phosphoric acids, substituted by anthracene moieties. The cycloaddition reaction of singlet oxygen onto these derivatives was optimized to efficiently obtain molecules whose geometry and nature of the catalytic site are modified. The catalytic properties of the anthracene- and endoperoxide-based architectures were then evaluated using three model reactions (oxetane desymmetrization, aza-Friedel-Crafts and 2-naphtol derivatives dearomatization). These reactions were then studied by molecular modelling to refine the comprehension of the structure-activity relation of these catalysts. On the basis of DFT calculations, paths of improvement for the catalysts and the optimisation of the catalysed reactions were proposed. The obtained results are an initial base for the proof of concept for the use of 1O2 as a stimulus in organocatalysis, despite the chemical complexity induced on the model catalysts derived from chiral phosphoric acids
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César, Vincent. « Ligands carbènes n-hétérocycliques chiraux par assemblage modulaire d'unités oxazolines et imidazol-2-ylidènes : Synthèse et application en catalyse homogène ». Université Louis Pasteur (Strasbourg) (1971-2008), 2004. https://publication-theses.unistra.fr/public/theses_doctorat/2004/CESAR_Vincent_2004.pdf.
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Les carbènes N-hétérocycliques représentent une alternative intéressante aux ligands phosphinés en catalyse homogène. Le développement d'une version chirale de ces ligands carbènes constitue le but principal de ce travail de thèse. Tout d'abord, une large gamme de sels d'oxazolinyl/imidazolium, précurseurs des ligands bidentates cibles, a été synthétisée à l'aide d'une approche modulaire. Nous avons ensuite réalisé la complexation du représentant achiral de cette famille de ligands sur divers centres métalliques tels que du palladium(II) ou du rhodium(I). Le complexe de palladium(II) permet le couplage des chlorures d'aryles activés pour les réactions catalytiques de Heck et Suzuki. Les études réalisées sur les complexes neutres pentacoordinés de rhodium(I) ont mis en lumière deux processus fluxionnels que sont la pseudo-rotation de Berry et un échange intermoléculaire de ligand bromure. Nous avons également étudié la réaction d'hydrosilylation asymétrique des cétones à l'aide des complexes chiraux de rhodium(I). Le système catalytique a été optimisé grâce notamment à la modularité des ligands. Il présente une activité catalytique remarquable et montre un excellent caractère énantiosélectif pour les cétones prochirales à substituants aryle-alkyle et surtout dialkyle avec des excès énantiomériques atteignant 95%. Enfin, la dernière partie décrit la synthèse d'un ligand carbène/bisoxazoline tridentate chiral qui pourrait posséder un fort pouvoir d'induction asymétrique. Un complexe de rhodium(III) a été préparé. Sa structure moléculaire obtenue par diffraction des rayons X confirme la coordination tridentate et méridionale du ligandThis work, part of the field of homogeneous catalysis, describes the development of chiral N heterocyclic carbenes based on a modular assembly between oxazoline and imidazolylidene units. First a large library of imidazolium salts, precursors for the bidentate ligands oxazolinyl-imidazolylidene, was obtained by a single coupling step. The second part is devoted to the coordination chemistry of the achiral representative of this family of ligands. Several transition metal complexes were synthesized and analyzed by X-ray diffraction studies. The palladium(II) complex was found to catalyze the coupling of activated aryl chlorides in catalytic Heck and Suzuki reactions. Cationic, chiral rhodium(I) complexes were then applied as catalysts in the asymmetric catalytic hydrosilylation reaction of prochiral ketones. The optimized catalytic system is remarkably active and induces high enantioselectivity for aryl-alkyl ketones and, in particular, for dialkyl ketones (enantiomeric excess up to 95%). In the last part the synthesis and complexation on a rhodium(III) centre of a chiral, tridentate bisoxazoline-carbene ligand are reported. This carbene is effectively tridentate with a quasi planar skeleton and could be highly efficient as a stereoinducting ligand for asymmetric catalysis
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BRISSE-LE, MENN FRANCOISE. « Contribution a l'etude de la catalyse biphasique au moyen de colloides de rhodium stabilises par des trisulfonates aux proprietes tensioactives modulables ». Rennes 1, 1990. http://www.theses.fr/1990REN10101.
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La stabilisation de colloides metalliques dans l'eau ou sur un support dans le but de realiser des reactions de catalyse en milieu biphasique constitue l'objet des recherches decrites dans ce memoire. Pour cela des methodes generales de synthese de derives du triphenylmethane et leurs sulfonations ont ete mises au point. Les nouveaux triphenylmethyl trisulfonates de sodium substitues (r-tpmts) ainsi prepares ont ete caracterises; la determination de leurs proprietes tensioactives permet de les classer en deux categories: les r-tpmts hydrotropes et les r-tpmts tensioactifs. Les triphenylsulfonates stabilisent dans l'eau des metaux colloidaux soit sous forme oxydee, soit a l'etat zerovalent. Dans les deux cas, leur interet pour la catalyse biphasique liquide-liquide a ete evalue en etudiant l'hydrogenation d'alcenes dans des conditions douces de temperature et de pression. Avec les r-tmpts hydrotropes et des poly(oxydes-hydroxydes) de rhodium colloidal, l'emploi sequentiel de h2, d2, h20 et d20 permet de montrer que l'eau intervient pendant la formation du colloide et pendant la catalyse. Il est aussi prouve que l'isomerisation des substrats olefiniques se produit de facon constante. Les r-tpmts tensioactifs sont de tres bons stabilisants pour les colloides metalliques zerovalents. En faisant varier la balance hydrophile-lipophile et la concentration en trisulfonates, il est possible de preparer des particules metalliques monodispersees de diametre compris entre 20 a et 1 um caracterisees par microscopie electronique. Les colloides zerovalents peuvent etre deposes sur silice et dans ces conditions, ils presentent une bonne activite catalytique pour l'hydrogenation d'olefines et de cetones en systeme solide-liquide
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Foli, Giacomo. « Modulazione reversibile dell'attivita catalitica di sistemi tioureidici chirali mediante interazioni con anioni ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8608/.
Texte intégralRésumé :
In questo lavoro di tesi viene proposto un approccio semplice e innovativo allo sviluppo di un sistema catalitico modulabile in maniera reversibile, basato su catalizzatori tioureidici chirali. La modulazione dell’attività catalitica avviene attraverso interazioni tra un determinato anione e i due protoni tioureidici di questi catalizzatori. A seconda del carattere coordinante di un anione, l’interazione che si viene a creare con le tiouree può essere forte, nel caso di anioni coordinanti come gli alogenuri, o debole, nel caso di anioni debolmente coordinanti quali borati. Una forte interazione da parte dell’anione con il catalizzatore si traduce in una inibizione dell’attività catalitica, dal momento che il sito tioureidico non è più disponibile per promuovere eventuali reazioni. Al contrario, un anione debolmente coordinante lascia l’attività catalitica fondamentalmente inalterata, anche in termini di stereoselezione. La reversibilità di questa modulazione è ottenuta sfruttando reazioni di metatesi tra due sali che, risultando nella precipitazione di un sale insolubile, riescono a rimuovere un determinato anione dall’ambiente di reazione per sostituirlo con un altro.
Chapitres de livres sur le sujet "Catalyse modulable"
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Taber, Douglass. « Enantioselective Synthesis of Alcohols and Amines ». Dans Organic Synthesis. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199764549.003.0036.
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Enantiomerically-enriched alkoxy stannanes such as 3 are versatile intermediates for synthesis. John R. Falck of UT Southwestern found (Angew. Chem. Int. Ed. 2008, 47, 6586) that the simple combination of Bu3 SnH and Et2Zn generated a reagent that added to aldehydes such as 1 under catalysis by the MIB amino alcohol introduced by Nugent (Chem. Commun. 1999, 1369) to give the adduct 3 in high ee. Gonzalo Blay and José R. Pedro of the Universitat de València showed (Chem. Commun. 2008, 4840) that it was possible to modulate the reactivity of the acidic 4, allowing catalyzed formation of the high ee adduct 5 to dominate. Xiaoming Feng of Sichuan University developed (J. Am. Chem. Soc. 2008, 130, 15770) a Ni catalyst for the intermolecular ene reaction of 6 with 7 to give 8 in high ee. Enantioselective allylation is a key transformation in current organic synthesis. Yoshito Kishi of Harvard University optimized (Organic Lett. 2008, 10, 3073) enantioselective Cr-mediated allylation, with a ligand that can be easily recovered and recycled. Michael J. Krische of UT Austin devised (J. Am. Chem. Soc. 2008, 130, 14891) a ligand-catalyst combination for effecting the enantioselective allylation of alcohols such as 12 . Brian M. Stoltz of Caltech developed (Angew. Chem. Int. Ed. 2008, 47, 6873) a protocol for the enantioselective allylation of the enol ether 15, leading to the construction of oxygenated quaternary centers. Adducts such as 11 and 17 are of interest, inter alia , as direct precursors, by elimination, of the corresponding alkynes. Simon Blakey of Emory University designed (Angew. Chem. Int. Ed. 2008, 47, 6825) a Ru catalyst that mediated enantioselective intramolecular C-H amination, converting the simple alcohol derivative 18 into the versatile secondary amine 19 in high ee. We established (J. Org. Chem. 2008, 73, 9334) a procedure, based on diazo transfer followed by Rh-mediated intermolecular N-H insertion, for aminating menthyl esters and separating the product diastereomers. The menthyl group, easily removed (TFA) from 21, served as a useful reporter of ee, by 1H NMR of the upfield methyl doublets. Wolfgang Kroutil of the University of Graz found (Adv. Synth. Cat. 2008, 350, 2761) that ω-transaminases could effect the reductive amination of methyl ketones such as 22 in high ee.
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Bisht, Ruchi, et Dr G. C. Joshi. « GAMMA-IRRADIATION EFFECTS ON DIFFERENT METAL OXIDE NANOPARTICLES ». Dans Futuristic Trends in Physical Sciences Volume 3 Book 2, 212–36. Iterative International Publishers, Selfypage Developers Pvt Ltd, 2024. http://dx.doi.org/10.58532/v3bkps2p2ch7.
Texte intégralRésumé :
Metal Oxide Nanoparticles (MONPs) have attracted significant attention due to their unique optical, magnetic, and electrical properties and wide-ranging applications in optoelectronic devices, supercapacitors, Li-ion batteries, solar cells, catalysts, liquid crystal displays, drug delivery, sensors, etc. The ability to modulate both the physical as well as chemical properties of MONPs plays a vital role in the designing of novel devices, consequently enhancing their significance in various industries and scientific fields. Recently, gamma (y)-irradiation has emerged as a promising technique for modifying the physicochemical properties of nanomaterials. This chapter presents the γ-irradiation effect on different MONPs such as TiO2, ZnO, SnO2, MoO3, CuO, WO3, MgO, etc. highlighting the modification in their structure, morphology, composition and functional properties. These modifications can be ascribed to various underlying mechanisms, including the generation of defects, phase change, surface modification, and grain growth
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V. S, Gavhane, et Amolik K. K. « RECENT TRENDS IN FASCINATING USE OF NANOTECHNOLOGY ». Dans Futuristic Trends in Chemical, Material Sciences & ; Nano Technology Volume 2 Book 12, 173–78. Iterative International Publishers, Selfypage Developers Pvt Ltd, 2023. http://dx.doi.org/10.58532/v2bs12p2ch1.
Texte intégralRésumé :
The tunable optical, morphological and external properties of nanoscopic delivery enhance the quality of integrated nanodevices as well as sensors. They are later tried in optical electronics, biomedicine and catalysis. Nanomaterials used to fabricate organic and inorganic active nanomaterials holds great promise. They possess outstanding electronic and surface reactivity. It may be attractive to modify the surface, structure and physicochemical properties of nanometamaterials. Nanoparticle technology will be particularly useful in developing useful cancer treatments that can control the various biological, biophysical as well as biomedical barriers that the body stages against standard interventions. Their various proposals include metal- and metal oxide-based nanoparticles, wires, clusters such as carbon nanotubes. Recently, hybrid nanomaterials are extended to modulate sensory work functions in the fields of nanomedicine and pharmaceutical companies. Nanotechnology incorporation into food packaging shows promise for improving food quality
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Maret Wolfgang. « 4. Human Zinc Biochemistry ». Dans Biomedical and Health Research. IOS Press, 2011. https://doi.org/10.3233/978-1-60750-816-8-45.
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Zinc is nutritionally essential and indispensable to growth, development, and maintenance of human functions. There is hardly any cellular process that does not depend on zinc in some way. As a constituent of at least 2800 human proteins and with cellular concentrations of a few hundred micromolar, zinc has unparalleled significance in protein structure, enzymatic catalysis, and cellular regulation. The largest group of zinc metalloenzymes are proteinases. Zinc has a major role in the structural organization of protein domains that interact with DNA/RNA, other proteins, and lipids. Several dozen proteins control cellular and subcellular zinc homeostasis and re-distribution. The control is a prerequisite for regulatory functions of free zinc (II) ions. Fluctuations of cellular free zinc ion concentrations modulate the biological activity of a yet unknown number of additional proteins, suggesting roles of zinc in information transfer.
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Wang, Xinlong, Francisco Gonzalez-Lima et Hanli Liu. « Transcranial Infrared Laser Stimulation ». Dans The Oxford Handbook of Transcranial Stimulation, Second Edition, C10.S1—C10.S19. 2e éd. Oxford University Press, 2022. http://dx.doi.org/10.1093/oxfordhb/9780198832256.013.10.
Texte intégralRésumé :
Abstract As part of transcranial photobiomodulation, transcranial infrared laser stimulation (TILS) refers to the non-invasive delivery of 1064 nm wavelength infrared laser light to the brain to modulate energy metabolism and hemodynamics. The primary mechanism rests on the photo-oxidation of cytochrome-c-oxidase, the key mitochondrial enzyme that catalyzes oxygen utilization in animal cells. Since brain physiology is dependent on oxygenation for energy production, TILS modulates brain activity. Placebo-controlled TILS effects were demonstrated in vivo by broadband near-infrared spectroscopy and electroencephalography. We showed the ability of TILS to upregulate cerebral metabolism and hemodynamics, as well as electrophysiological activity in the human brain. TILS effects were proven safe and not caused by thermal effects. We also showed improved behavioral performance, learning, and cognition by TILS in animal models, healthy humans, and patients with psychiatric symptoms. However, several key questions should be addressed before TILS becomes an effective therapeutic tool for enhancing healthy aging and treating brain disorders.
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Gómez, Hansel, Fernanda Mendoza, José M. Lluch et Laura Masgrau. « QM/MM Studies Reveal How Substrate–Substrate and Enzyme–Substrate Interactions Modulate Retaining Glycosyltransferases Catalysis and Mechanism ». Dans Combined Quantum Mechanical and Molecular Mechanical Modelling of Biomolecular Interactions, 225–54. Elsevier, 2015. http://dx.doi.org/10.1016/bs.apcsb.2015.06.004.
Texte intégral
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DUNN, MICHAEL F., PETER BRZOVIC', CATHERINE LEJA, KARL HOUBEN, MELINDA ROY, ALEN AGUILAR et WILLIAM F. DREWE. « Allosteric Interactions Coordinate Covalent Steps in Catalysis and Modulate Indole Transfer Between the α- and β-Sites of the Tryptophan Synthase Bienzyme Complex ». Dans Enzymes Dependent on Pyridoxal Phosphate and Other Carbonyl Compounds As Cofactors, 257–64. Elsevier, 1991. http://dx.doi.org/10.1016/b978-0-08-040820-0.50055-8.
Texte intégralActes de conférences sur le sujet "Catalyse modulable"
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Loprete, Jason, Rodrigo Ristow Hadlich, Amanda Sirna, Dimitris Assanis, Tala Mon et Eleni Kyriakidou. « Exhaust Slip-Stream Sampling System for Aftertreatment Device Testing ». Dans WCX SAE World Congress Experience. 400 Commonwealth Drive, Warrendale, PA, United States : SAE International, 2024. http://dx.doi.org/10.4271/2024-01-2703.
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<div class="section abstract"><div class="htmlview paragraph">Design, testing, and implementation of new aftertreatment devices under various engine operating conditions is necessary to meet increasingly stringent regulatory mandates. One common aftertreatment device, the catalytic converter, is typically developed at a reduced scale and tested using predefined fluid compositions sourced from bottle gases and can undergo both species and temperature cycling in addition to steady-state testing. However, these bench-top conditions may differ from real-world operation in terms of flow-rates, species composition, and temperatures experienced. Transitioning from small-scale bench-top testing to full-scale engine applications requires larger monoliths that therefore have a significant amount of catalyst slurry to be washcoated, which increases cost and fabrication time. Being able to experience realistic emission streams under scaled flowrates would allow for a physically smaller catalyst testing at matched space velocities resulting in faster, more cost-effective determination of aftertreatment device effectiveness. This work documents the design and performance of an intermediary-scale (5-50 SLPM) setup to aid in the catalyst testing process. This is accomplished using a secondary exhaust branch to flow a variable percentage of exhaust from the main branch. The system siphons exhaust via a slip-stream approach driven by a venturi ejector, which is commonly used in automotive applications to dilute samples for emissions analysis. Instead, the pre-diluted flow from the ejector is routed through the catalyst, where post catalyst emissions testing occurs. The system is evaluated under a range of engine operating conditions with varied equivalence ratio and intake pressures to affect exhaust out temperatures / catalyst inlet temperature which is critical for testing catalyst activation. Emissions are recorded in both the main and secondary branch with no aftertreatment device installed to verify compositional parity. Initial results show that the two branches produce self-similar engine-out emissions, but with the ability to scale flow and modulate temperature through the secondary catalyst testing branch.</div></div>
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Campanelli, Veronica, Ciro Magliulo, Claudio Albanese et Ignazio Arces. « High Conversion Refineries : An Approach to Reduce the Carbon Footprint by Hydrogen Network Optimization and Flexibility Enhancement ». Dans ADIPEC. SPE, 2023. http://dx.doi.org/10.2118/216436-ms.
Texte intégralRésumé :
Abstract The momentum behind hydrogen as strategic vector to satisfy refining sector needs remains strong over the years. Indeed, hydrogen is a key feedstock in refining operations particularly for a complex conversion configuration such as that of Eni Sannazzaro Refinery, with one of the highest levels of complexity and capacity conversion in Europe, comprising of more than ten hydrogen consuming technologies out of which two hydrocracking, three diesel/kero hydrotreaters, three naphtha hydrotreaters, a FCC naphtha selective hydrogenation and other minor hydrogen consuming processes. The Sannazzaro Refinery is a hydrogen self-sustaining hub thanks to a robust hydrogen producing system that includes technologies such as steam reforming, catalytic reforming and gasification that feed a hydrogen network structured in three hydrogen grids at different pressures and purities. Targeting an excellent hydrogen network management and aiming at optimizing as possible the site energy consumption thus minimizing associated GHG emissions, the Sannazzaro Refinery has implemented a Dynamic Matrix Control (DMC) system monitoring the hydrogen network pressure to reduce the steam reforming throughput while maximizing the consumption of hydrogen produced by catalytic reforming units avoiding overpressures and hydrogen discharges towards the fuel gas network. The project has resulted in an overall increased stability of hydrogen network, achieving a noteworthy hydrogen production saving of 900 ton/year with a reduction of 8500 ton/year of CO2 associated emissions towards an increase of site sustainability, parallel resulting in an enhanced stability of hydrocracker recycle gas purity (always maintained over 85%vol hydrogen content in order to preserve catalyst activity), determining a remarkable reduced standard deviation for controlled variables such as the high purity hydrogen grid pressure, succeeding in minimizing the hydrogen content into the fuel gas network, thus increasing relative fuel gas Wobbe index by 3 MJ/Nm3, hence positively impacting the site energy efficiency and enhancing its flexibility to closer tackle the variations on hydrogen refinery needs. All results have been achieved thanks to a fast controller run time (ca. 30 seconds) and an average service factor > 70%. In conclusion, the overall project demonstrates how the implementation of a Dynamic Matrix Control system interestingly contributes to reduce a high conversion refinery carbon footprint and its hydrogen production cost via a fast-track and a low-cost project, being the site characterized by a complex hydrogen network with multiple hydrogen grids and steam reforming units to modulate the hydrogen production.