Articles de revues : « 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, n^o 9 (4 septembre 2019) : 374. http://dx.doi.org/10.3390/antiox8090374.

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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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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.

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Reyes, Ronald L., Miyu Sato, Tomohiro Iwai, Kimichi Suzuki, Satoshi Maeda et Masaya Sawamura. « Asymmetric remote C–H borylation of aliphatic amides and esters with a modular iridium catalyst ». Science 369, n^o 6506 (20 août 2020) : 970–74. http://dx.doi.org/10.1126/science.abc8320.

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Site selectivity and stereocontrol remain major challenges in C–H bond functionalization chemistry, especially in linear aliphatic saturated hydrocarbon scaffolds. We report the highly enantioselective and site-selective catalytic borylation of remote C(sp3)–H bonds γ to the carbonyl group in aliphatic secondary and tertiary amides and esters. A chiral C–H activation catalyst was modularly assembled from an iridium center, a chiral monophosphite ligand, an achiral urea-pyridine receptor ligand, and pinacolatoboryl groups. Quantum chemical calculations support an enzyme-like structural cavity formed by the catalyst components, which bind the substrate through multiple noncovalent interactions. Versatile synthetic utility of the enantioenriched γ-borylcarboxylic acid derivatives was demonstrated.

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Wang, Geqing, Jilong Qin, Anthony D. Verderosa, Lilian Hor, Carlos Santos-Martin, Jason J. Paxman, Jennifer L. Martin, Makrina Totsika et Begoña Heras. « A Buried Water Network Modulates the Activity of the Escherichia coli Disulphide Catalyst DsbA ». Antioxidants 12, n^o 2 (4 février 2023) : 380. http://dx.doi.org/10.3390/antiox12020380.

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The formation of disulphide bonds is an essential step in the folding of many proteins that enter the secretory pathway; therefore, it is not surprising that eukaryotic and prokaryotic organisms have dedicated enzymatic systems to catalyse this process. In bacteria, one such enzyme is disulphide bond-forming protein A (DsbA), a thioredoxin-like thiol oxidase that catalyses the oxidative folding of proteins required for virulence and fitness. A large body of work on DsbA proteins, particularly Escherichia coli DsbA (EcDsbA), has demonstrated the key role that the Cys30-XX-Cys33 catalytic motif and its unique redox properties play in the thiol oxidase activity of this enzyme. Using mutational and functional analyses, here we identify that a set of charged residues, which form an acidic groove on the non-catalytic face of the enzyme, further modulate the activity of EcDsbA. Our high-resolution structures indicate that these residues form a water-mediated proton wire that can transfer protons from the bulk solvent to the active site. Our results support the view that proton shuffling may facilitate the stabilisation of the buried Cys33 thiolate formed during the redox reaction and promote the correct direction of the EcDsbA–substrate thiol–disulphide exchange. Comparison with other proteins of the same class and proteins of the thioredoxin-superfamily in general suggest that a proton relay system appears to be a conserved catalytic feature among this widespread superfamily of proteins. Furthermore, this study also indicates that the acidic groove of DsbA could be a promising allosteric site to develop novel DsbA inhibitors as antibacterial therapeutics.

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Wang, Shujiang, Ganesh N. Nawale, Oommen P. Oommen, Jöns Hilborn et Oommen P. Varghese. « Influence of ions to modulate hydrazone and oxime reaction kinetics to obtain dynamically cross-linked hyaluronic acid hydrogels ». Polymer Chemistry 10, n^o 31 (2019) : 4322–27. http://dx.doi.org/10.1039/c9py00862d.

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Wang, Guohong, Min Li, Wenmin Pang, Min Chen et Chen Tan. « Lewis acids in situ modulate pyridazine-imine Ni catalysed ethylene (co)polymerisation ». New Journal of Chemistry 43, n^o 34 (2019) : 13630–34. http://dx.doi.org/10.1039/c9nj01243e.

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The Lewis acid-base interaction between B(iii) Lewis acids and the pyridazine moiety reduced the electron density from the Ni center and in situ modulated the pyridazine-imine nickel catalyzed ethylene (co)polymerisation.

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Vu, Khanh B., Konstantin V. Bukhryakov, Dalaver H. Anjum et Valentin O. Rodionov. « Surface-Bound Ligands Modulate Chemoselectivity and Activity of a Bimetallic Nanoparticle Catalyst ». ACS Catalysis 5, n^o 4 (23 mars 2015) : 2529–33. http://dx.doi.org/10.1021/acscatal.5b00262.

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Smołka, Szymon, et Katarzyna Krukiewicz. « Catalyst Design through Grafting of Diazonium Salts—A Critical Review on Catalyst Stability ». International Journal of Molecular Sciences 24, n^o 16 (8 août 2023) : 12575. http://dx.doi.org/10.3390/ijms241612575.

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In the pursuit of designing a reusable catalyst with enhanced catalytic activity, recent studies indicate that electrochemical grafting of diazonium salts is an efficient method of forming heterogeneous catalysts. The aim of this review is to assess the industrial applicability of diazonium-based catalysts with particular emphasis on their mechanical, chemical, and thermal stability. To this end, different approaches to catalyst production via diazonium salt chemistry have been compared, including the immobilization of catalysts by a chemical reaction with a diazonium moiety, the direct use of diazonium salts and nanoparticles as catalysts, the use of diazonium layers to modulate wettability of a carrier, as well as the possibility of transforming the catalyst into the corresponding diazonium salt. After providing descriptions of the most suitable carriers, the most common deactivation routes of catalysts have been discussed. Although diazonium-based catalysts are expected to exhibit good stability owing to the covalent bond created between a catalyst and a post-diazonium layer, this review indicates the paucity of studies that experimentally verify this hypothesis. Therefore, use of diazonium salts appears a promising approach in catalysts formation if more research efforts can focus on assessing their stability and long-term catalytic performance.

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Sharp, Victoria, Lisa M. Thurston, Robert C. Fowkes et Anthony E. Michael. « 11β-Hydroxysteroid dehydrogenase enzymes in the testis and male reproductive tract of the boar (Sus scrofa domestica) indicate local roles for glucocorticoids in male reproductive physiology ». Reproduction 134, n^o 3 (septembre 2007) : 473–82. http://dx.doi.org/10.1530/rep-07-0126.

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11β-Hydroxysteroid dehydrogenase (11βHSD) enzymes modulate the target cell actions of corticosteroids by catalysing metabolism of the physiological glucocorticoid (GC), cortisol, to inert cortisone. Recent studies have implicated GCs in boar sperm apoptosis. Hence, the objective of this study was to characterise 11βHSD enzyme expression and activities in the boar testis and reproductive tract. Although 11βHSD1 and 11βHSD2 mRNA transcripts and proteins were co-expressed in all tissues, cortisol–cortisone interconversion was undetectable in the corpus and cauda epididymides, vas deferens, vesicular and prostate glands, irrespective of nucleotide cofactors. In contrast, homogenates of boar testis, caput epididymidis and bulbourethral gland all displayed pronounced 11βHSD activities in the presence of NADPH/NADP+ and NAD+, and the penile urethra exhibited NAD+-dependent 11β-dehydrogenase activity. In kinetic studies, homogenates of boar testis, caput epididymidis and bulbourethral gland oxidised cortisol with Km values of 237–443 and 154–226 nmol/l in the presence of NADP+ and NAD+ respectively. Maximal rates of NADP+-dependent cortisol oxidation were 7.4- to 28.5-fold greater than the Vmax for NADPH- dependent reduction of cortisone, but were comparable with the rates of NAD+-dependent cortisol metabolism. The relatively low Km estimates for NADP+ -dependent cortisol oxidation suggest that either the affinity of 11βHSD1 has been increased or the cortisol inactivation is catalysed by a novel NADP+-dependent 11βHSD enzyme in these tissues. We conclude that in the boar testis, caput epididymidis and bulbourethral gland, NADP+- and NAD+-dependent 11βHSD enzymes catalyse net inactivation of cortisol, consistent with a physiological role in limiting any local actions of GCs within these reproductive tissues.

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Lu, Xiaodong, Guofu Wang, Yu Yang, Xiangpeng Kong et Jiangang Chen. « A boron-doped carbon aerogel-supported Cu catalyst for the selective hydrogenation of dimethyl oxalate ». New Journal of Chemistry 44, n^o 8 (2020) : 3232–40. http://dx.doi.org/10.1039/c9nj05956c.

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Zhang, Zicong, Xiangli Ru, Xiaoli Yang, Zhengyu Bai et Lin Yang. « Red Blood Cells-Derived Iron Self–Doped 3D Porous Carbon Networks for Efficient Oxygen Reduction ». Catalysts 12, n^o 3 (28 février 2022) : 273. http://dx.doi.org/10.3390/catal12030273.

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In addition to C, H and O, some biomass is also rich in mineral elements. The recovery and utilization of special mineral elements is of great significance to prepare functional materials and alleviate the current energy shortage. Herein, we describe a facile strategy for making full use of the chemical composition (C, Fe) and special structure of red blood cells (RBCs) from waste pig blood to fabricate a dual metal (Fe, Co)-nitrogen (N)-doped porous carbon catalyst by pyrolysis of a mixture of RBCs biomass, cobaltous acetate, and melamine. The porous catalyst displays a comparable activity for oxygen reduction reaction (ORR) to that of commercial Pt/C catalyst, with a half-wave potential of 0.821 VvsRHE in alkaline media and 0.672 VvsRHE in acid electrolyte. Especially, the as-prepared catalyst shows excellent methanol tolerance and stability in both acidic and alkaline electrolytes, which is superior to commercial Pt/C catalysts. The excellent ORR activity of FeCo-N/C(RBC) can be ascribed to the porous morphology and the cooperation between metal and nitrogen species. This work provides a novel idea of exploiting the composition of renewable biomass to modulate the activity and stability of carbon-based ORR catalysts.

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Jussupow, Alexander, Andrea Di Luca et Ville R. I. Kaila. « How cardiolipin modulates the dynamics of respiratory complex I ». Science Advances 5, n^o 3 (mars 2019) : eaav1850. http://dx.doi.org/10.1126/sciadv.aav1850.

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Cardiolipin modulates the activity of membrane-bound respiratory enzymes that catalyze biological energy transduction. The respiratory complex I functions as the primary redox-driven proton pump in mitochondrial and bacterial respiratory chains, and its activity is strongly enhanced by cardiolipin. However, despite recent advances in the structural biology of complex I, cardiolipin-specific interaction mechanisms currently remain unknown. On the basis of millisecond molecular simulations, we suggest that cardiolipin binds to proton-pumping subunits of complex I and induces global conformational changes that modulate the accessibility of the quinone substrate to the enzyme. Our findings provide key information on the coupling between complex I dynamics and activity and suggest how biological membranes modulate the structure and activity of proteins.

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Rey, Yannick P., et Ryan Gilmour. « Modulating NHC catalysis with fluorine ». Beilstein Journal of Organic Chemistry 9 (6 décembre 2013) : 2812–20. http://dx.doi.org/10.3762/bjoc.9.316.

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Fluorination often confers a range of advantages in modulating the conformation and reactivity of small molecule organocatalysts. By strategically introducing fluorine substituents, as part of a β-fluoroamine motif, in a triazolium pre-catalyst, it was possible to modulate the behaviour of the corresponding N-heterocyclic carbene (NHC) with minimal steric alterations to the catalyst core. In this study, the effect of hydrogen to fluorine substitution was evaluated as part of a molecular editing study. X-ray crystallographic analyses of a number of derivatives are presented and the conformations are discussed. Upon deprotonation, the fluorinated triazolium salts generate catalytically active N-heterocyclic carbenes, which can then participate in the enantioselective Steglich rearrangement of oxazolyl carbonates to C-carboxyazlactones (e.r. up to 87.0:13.0).

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Ji, Junhyuk, Minseon Park, Minho Kim, Song Kyu Kang, Gwan Hyeon Park, Min Ho Seo et Won Bae Kim. « Cationic-Dependent Cooperative Catalysis of Ni_0.261Co_0.739S₂/N-Doped Carbon Nanotubes for Achieving Superior Electrocatalytic Activity and Cycling Stability at High Rate in Li-S Batteries ». ECS Meeting Abstracts MA2024-02, n^o 67 (22 novembre 2024) : 4447. https://doi.org/10.1149/ma2024-02674447mtgabs.

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Lithium-sulfur (Li-S) batteries are increasingly recognized for their exceptional energy storage capabilities, offering an energy density of approximately 2600 Wh kg-1. This is largely attributed to the use of sulfur in the cathode—a material both abundantly available and cost-effective. However, the widespread adoption of Li-S batteries faces significant challenges, including the low electrical conductivity of sulfur and its discharge byproducts (e.g., Li2S2, Li2S), the migration of polysulfides within the electrolyte, and electrode volume expansion, which collectively impede their practical application. In the realm of recent advancements, transition metal (TM) sulfides have attracted considerable interest for their superior electrical conductivity and the presence of effective binding sites for lithium polysulfides (LiPSs), arising from a high density of valence electrons. This is a consequence of the soft basic nature of S2-/S2 2- anions, as opposed to the hard basic O2- ions. Particularly, TM sulfides with pyrite-type cubic crystalline structures, including NiS2 and CoS2, have proven to be potent electrocatalysts. They facilitate enhanced polysulfide redox reactions owing to their conductivity surpassing that of TM oxides. Furthermore, the integration of multi-cationic species into a single composite electrocatalyst has emerged as a strategic approach to refine the electronic configuration and augment the catalytic synergy of TM sulfides. Despite these developments, the discrete roles and synergistic contributions of cations within bimetallic TM sulfides remain largely unexplored, especially in comparison to the unveiled catalytic mechanisms of TM oxides. This study introduces a novel, highly active, and durable sulfur catalyst system composed of NixCo1-xS2 nanocrystals dispersed on N-doped porous carbon nanotubes (NixCo1-xS2@NPCTs). This system serves as an efficient cathode electrocatalyst for rechargeable Li-S batteries. The carbonized, porous architecture offers extensive surface area and buffering capacity for cyclic redox processes, alongside numerous chemical binding sites on the CNT framework. The ingeniously designed dual-active TM sulfides, characterized by NiOh 2+−S−CoOh 2+ bonds within the octahedral TMS6 structure, effectively catalyze sulfur cathode reactions. They fulfill multifaceted roles; specifically, CoOh 2+ sites with vacancies robustly interact with LiPSs to mitigate the shuttle effect. Concurrently, the NiOh 2+ species, with an optimal doping concentration, precisely modulate the chemical interaction with LiPSs to facilitate a sequential redox reaction, thereby promoting sustained cooperative catalysis and reducing Li2S passivation on the catalyst surface. The Ni0.261Co0.739S2 catalyst, supported by NPCT carbon, excels by achieving excellent discharge capacity and exhibiting remarkable long-term electrochemical stability. Even under harsh conditions with a low electrolyte-to-sulfur ratio (E/S = 10.0 μL mg-1), this catalyst system demonstrates superior cycling performance and durability. Notably, the Ni0.261Co0.739S2@NPCTs catalyst system showcases exceptional cyclic endurance, maintaining a capacity of 511 mAh g-1 with a mere 0.055% decay per cycle at a 5.0 C rate over 1000 cycles, alongside a significant areal capacity of 2.20 mAh cm-2 under a sulfur loading of 4.61 mg cm-2 after 200 cycles at 0.2 C. Complementary theoretical DFT calculations corroborate the experimental results, enhancing our understanding of the efficacy of the catalyst system, particularly in terms of weakend sulfur bonding strength and optimzed binding energy which are pivotal for the catalytic performance of NixCo1-xS2@NPCTs in interactions with TM sulfides and lithium polysulfides. Our findings could highlight the importance of leveraging the synergistic potential of advanced carbon hosts and optimized bimetallic sulfide electrocatalysts, while also illuminating the intricate atomic configurations crucial for augmenting the redox activity of Li-S batteries in practical applications. Figure 1

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Muro, Silvia, Madalina Mateescu, Christine Gajewski, Mary Robinson, Vladimir R. Muzykantov et Michael Koval. « Control of intracellular trafficking of ICAM-1-targeted nanocarriers by endothelial Na+/H+ exchanger proteins ». American Journal of Physiology-Lung Cellular and Molecular Physiology 290, n^o 5 (mai 2006) : L809—L817. http://dx.doi.org/10.1152/ajplung.00311.2005.

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Targeting nanocarriers (NC) loaded by antioxidant enzymes (e.g., catalase) to endothelial cell adhesion molecules (CAM) alleviates oxidative stress in the pulmonary vasculature. However, antioxidant protection is transient, since CAM-targeted catalase is internalized, delivered to lysosomes, and degraded. To design means to modulate the metabolism and longevity of endothelial cell (EC)-targeted drugs, we identified and manipulated cellular elements controlling the uptake and intracellular trafficking of NC targeted to ICAM-1 (anti-ICAM/NC). BAPTA, thapsigargin, amiloride, and EIPA inhibited anti-ICAM/NC uptake by EC and actin rearrangements induced by anti-ICAM/NC (required for uptake), suggesting that member(s) of Na+/H+ exchanger family proteins (NHE) regulate these processes. Consistent with this hypothesis, an siRNA specific for the plasmalemma NHE1, but not the endosome-associated NHE6, inhibited actin remodeling induced by anti-ICAM/NC and internalization. Anti-ICAM/NC binding to EC stimulated formation of a transient ICAM-1/NHE1 complex. One hour after uptake, ICAM-1 dissociated from NHE1, and anti-ICAM/NC were transported to NHE6-positive vesicles en route to lysosomes. Inhibition of PKC (an activator of intracellular NHE) accelerated nanocarrier lysosomal trafficking. In contrast, monensin, which enhances the endosomal sodium influx and proton efflux maintained by NHE6, inhibited delivery of anti-ICAM/NC to lysosomes by switching their trafficking to a plasma membrane recycling pathway. This markedly prolonged the protective effect of catalase-coated anti-ICAM/NC. Therefore, 1) NHE1 and NHE6 regulate distinct phases of anti-ICAM/NC uptake and trafficking; 2) pharmacological agents affecting these regulatory elements alter the itinerary of anti-ICAM/NC intracellular trafficking; and 3) these agents modulate duration of the therapeutic effects of targeted drugs.

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Kwon, Youngkook. « (Invited, Digital Presentation) Interface Rich Catalyst Design for Enhanced CO₂ Conversion ». ECS Meeting Abstracts MA2022-02, n^o 48 (9 octobre 2022) : 1863. http://dx.doi.org/10.1149/ma2022-02481863mtgabs.

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The efficient electrochemical conversion of CO2 to fuels or stock chemicals with high-energy density would be a major step forward in the introduction of a carbon neutral energy cycle. Especially, understanding the role of electrocatalysts, supports, and electrolytes that can efficiently reduce CO2 to fuels with high selectivity is a subject of significant interest. Copper is the only known catalyst for producing a reasonable quantity of hydrocarbons, which means that designing proper electrode interfaces would modulate the catalytic reactivity and product selectivity. One of the observations on copper catalyst interface is that copper catalyst with a specific atomic-scale gap accelerates the reaction kinetics and selectivity to C2+ products, by confining CO2 and reaction intermediates within a sub-nanoscale reactor in which the reaction energy for CO formation and subsequent C-C coupling can be accelerated. However, the selectivity control toward a target product such as ethylene or ethanol is a remaining issue to be resolved. Recently, we have designed interface rich CuO-Al2CuO4 catalyst and were able to reach about 80% FE of ethylene. In-situ ATR-FTIR and DFT calculation supported that CO2 was selectively converted to CO on CuO and subsequently CO was coupling on Al2CuO4 to ethylene. Therefore, designing interface rich catalysts offers efficient, yet cheap electrochemical CO2 reduction systems.

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Li, Haobo, Jianping Xiao, Qiang Fu et Xinhe Bao. « Confined catalysis under two-dimensional materials ». Proceedings of the National Academy of Sciences 114, n^o 23 (22 mai 2017) : 5930–34. http://dx.doi.org/10.1073/pnas.1701280114.

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Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces.

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Warren, Averil Y., Balwir Matharoo-Ball, Robert W. Shaw et Raheela N. Khan. « Hydrogen peroxide and superoxide anion modulate pregnant human myometrial contractility ». Reproduction 130, n^o 4 (octobre 2005) : 539–44. http://dx.doi.org/10.1530/rep.1.00437.

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Reactive oxygen species (ROS) have the propensity to cause macromolecular damage with consequent modification of cellular function. We investigated the effects of two particular oxidants, superoxide (O2−) anions and hydrogen peroxide (H2O2), on oxytocin-induced myometrial contractility using biopsies from women undergoing Caesarean section at term gestation. Isometric tension recordings were performed and concentration–response curves derived after addition of test agents. A maximal reduction in myometrial contractility to 27.2 ± 4.5% of control was observed followed application of H2O2. The enzyme scavenger catalase (CAT) reduced the inhibitory effect of H2O2but had little effect at 10-fold lower concentrations. Addition of dialysed xanthine oxidase ± hypoxanthine significantly inhibited contractility to 23.8.0 ± 4.2% compared with control. Pre-incubation with superoxide dismutase and CAT diminished this effect. The non-specific potassium channel blocker, tetraethylammonium chloride (1 mM), had no effect on myometrial contractility. We conclude that human myometrium is susceptible to the effects of ROS, which may be produced by reperfusion–ischaemic episodes during labour. Our findings could, in part, explain the weak or prolonged depression of contractions characteristic of myometrial dysfunction culminating in difficult labours.

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Montserrat-de la Paz, Sergio, Gabriela Carrillo-Berdasco, Fernando Rivero-Pino, Alvaro Villanueva-Lazo et Maria C. Millan-Linares. « Hemp Protein Hydrolysates Modulate Inflammasome-Related Genes in Microglial Cells ». Biology 12, n^o 1 (27 décembre 2022) : 49. http://dx.doi.org/10.3390/biology12010049.

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A prolonged inflammatory response can lead to the development of neurodegenerative diseases such as Alzheimer’s disease. Enzymatic hydrolysis is a sustainable way to increase the value of protein sources by obtaining peptides that can exert bioactivity. Hemp (Cannabis sativa L.) protein hydrolysates have been proven to exert anti-inflammatory activity. In this study, two hemp protein hydrolysate (HPHs), obtained with Alcalase as sole catalyst, or with Alcalase followed by Flavourzyme, were evaluated as inflammatory mediators (TNFα, IL-1β, IL-6, and IL-10), microglial polarization markers (Ccr7, iNos, Arg1, and Ym1), and genes related to inflammasome activation (Nlrp3, Asc, Casp1, and Il18), employing the lipopolysaccharide (LPS)-induced neuroinflammation model in murine BV-2 microglial cells. A significant decrease of the expression of proinflammatory genes (e.g., Tnfα, Ccr7, inos, and Nlrp3, among others) and increase of the expression anti-inflammatory cytokines in microglial cells was observed after treatment with the test HPHs. This result in the cell model suggests a polarization toward an anti-inflammatory M2 phenotype. Our results show that the evaluated HPHs show potential neuroprotective activity in microglial cells via the inflammasome.

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Chen, Billy T., Marat V. Avshalumov et Margaret E. Rice. « H2O2 Is a Novel, Endogenous Modulator of Synaptic Dopamine Release ». Journal of Neurophysiology 85, n^o 6 (1 juin 2001) : 2468–76. http://dx.doi.org/10.1152/jn.2001.85.6.2468.

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Recent evidence suggests that reactive oxygen species (ROS) might act as modulators of neuronal processes, including synaptic transmission. Here we report that synaptic dopamine (DA) release can be modulated by an endogenous ROS, H2O2. Electrically stimulated DA release was monitored in guinea pig striatal slices using carbon-fiber microelectrodes with fast-scan cyclic voltammetry. Exogenously applied H2O2reversibly inhibited evoked release in the presence of 1.5 mM Ca2+. The effectiveness of exogenous H2O2, however, was abolished or decreased by conditions that enhance Ca2+ entry, including increased extracellular Ca2+ concentration ([Ca2+]o; to 2.4 mM), brief, high-frequency stimulation, and blockade of inhibitory D2 autoreceptors. To test whether DA release could be modulated by endogenous H2O2, release was evoked in the presence of the H2O2-scavenging enzyme, catalase. In the presence of catalase, evoked [DA]o was 60% higher than after catalase washout, demonstrating that endogenously generated H2O2 can also inhibit DA release. Importantly, the Ca2+ dependence of the catalase-mediated effect was opposite to that of H2O2: catalase had a greater enhancing effect in 2.4 mM Ca2+ than in 1.5 mM, consistent with enhanced H2O2 generation in higher [Ca2+]o. Together these data suggest that H2O2production is Ca2+ dependent and that the inhibitory mechanism can be saturated, thus preventing further effects from exogenous H2O2. These findings show for the first time that endogenous H2O2 can modulate vesicular neurotransmitter release, thus revealing an important new signaling role for ROS in synaptic transmission.

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Van-Brunt, Alexander John. « A Lifetime Prediction Model for the Anode Catalyst Layer in PEM Electroyzers ». ECS Meeting Abstracts MA2024-02, n^o 45 (22 novembre 2024) : 3164. https://doi.org/10.1149/ma2024-02453164mtgabs.

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Electrolyzer stacks (ELY stacks) are anticipated to form a key component in the hydrogen economy by providing a clean hydrogen source which may be deployed modularly. Currently, proton-exchange-membrane (PEM) electolyzers are a promising candidate to meet this demand on account of their high performance relative other electrolysis methods. Amongst other considerations, economic barriers preventing the uptake of PEM ELY stacks are the durability and cost of the precious catalyst materials, especially iridium-loaded catalysts. Additionally, due to the ever-growing uptake of intermittent power sources, dynamic operation of the ELY stack is an attractive economic option, yet may also accelerate degradation. Taken together, a key question in the design and deployment of ELY stacks is predicting the lifetime of the anode catalyst layer under dynamic power loads. In this presentation we present a simple model for lifetime prediction of the anode catalyst layer of a PEM electrolyzer with iridium dissolution as the principal degradation mechanism. The model is parameterized from data in the literature and wind and solar profiles are used as validation. Implications in the design of accelerated stress tests are also discussed.

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Hamkins, Kiran, et Xiaolin Zheng. « Metal Supported Metal Oxide Catalysts for Hydrogen Peroxide Production Via Water Splitting ». ECS Meeting Abstracts MA2024-01, n^o 48 (9 août 2024) : 3101. http://dx.doi.org/10.1149/ma2024-01483101mtgabs.

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The two-electron water oxidation reaction (WOR) has drawn recent attention as an efficient, simple method of producing on-site hydrogen peroxide through electrochemical water splitting. However, finding electrocatalysts with high activity and stability in the reaction’s harsh oxidizing environment is challenging. This is made especially difficult due to the competing four-electron and one-electron WOR, which necessitate a catalyst material with high selectivity towards the hydrogen peroxide production pathway. Here, we utilize metal/metal oxide coupling interactions to tune metal oxide catalysts to be active for 2 e- WOR via the creation of a Mott-Schottky junction. Metal/metal oxide interactions have been well studied for supported metal catalysts, but their behavior has been less investigated for catalysts where the metal oxide provides the active sites, called inverse catalysts. In this case, the difference in work functions between the metal support and metal oxide semiconductor catalyst drives electron transfer between the two, facilitating electronic interactions which can modulate the binding energy of reaction intermediates at the interface and thus tune the catalytic ability of the metal oxide. In this work, we investigate a variety of metal oxide catalyst and metal support materials and find that a thin layer of indium tin oxide (ITO) supported by a layer of platinum (Pt) has excellent catalytic ability towards 2 e- WOR. The activity, selectivity, and stability of the ITO/Pt catalyst shows significant improvement over the unsupported ITO catalyst and yields hydrogen peroxide production rates greater than those reported in literature using other standard catalysts for this reaction. This method of catalyst engineering also provides a future pathway to create new catalysts for this electrochemical reaction. Figure 1

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Samuni, Amram, Eric Maimon et Sara Goldstein. « Nitroxides protect horseradish peroxidase from H2O2-induced inactivation and modulate its catalase-like activity ». Biochimica et Biophysica Acta (BBA) - General Subjects 1861, n^o 8 (août 2017) : 2060–69. http://dx.doi.org/10.1016/j.bbagen.2017.03.021.

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Cottone, Grazia, Sergio Giuffrida, Stefano Bettati, Stefano Bruno, Barbara Campanini, Marialaura Marchetti, Stefania Abbruzzetti et al. « More than a Confinement : “Soft” and “Hard” Enzyme Entrapment Modulates Biological Catalyst Function ». Catalysts 9, n^o 12 (4 décembre 2019) : 1024. http://dx.doi.org/10.3390/catal9121024.

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Catalysis makes chemical and biochemical reactions kinetically accessible. From a technological point of view, organic, inorganic, and biochemical catalysis is relevant for several applications, from industrial synthesis to biomedical, material, and food sciences. A heterogeneous catalyst, i.e., a catalyst confined in a different phase with respect to the reagents’ phase, requires either its physical confinement in an immobilization matrix or its physical adsorption on a surface. In this review, we will focus on the immobilization of biological catalysts, i.e., enzymes, by comparing hard and soft immobilization matrices and their effect on the modulation of the catalysts’ function. Indeed, unlike smaller molecules, the catalytic activity of protein catalysts depends on their structure, conformation, local environment, and dynamics, properties that can be strongly affected by the immobilization matrices, which, therefore, not only provide physical confinement, but also modulate catalysis.

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Li, Shilin, Yuxin Wang, Kun Tang, Han Guo, Yifan Guo, Long You, Zhi Lu et Guangxin Wang. « Preparation of nickel-manganese based bimetallic hydroxide nanosheets for enhanced electrocatalytic oxygen evolution reaction ». Journal of Physics : Conference Series 2838, n^o 1 (1 septembre 2024) : 012002. http://dx.doi.org/10.1088/1742-6596/2838/1/012002.

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Abstract This paper uses a common one-step hydrothermal method to prepare NiMn-LDH/NF (Layered Double Hydroxide, LDH) oxygen evolution catalyst with outstanding performance. The NiMn-LDH grows into a nanosheet array structure on nickel foam (NF) and it has a big surface area and exceptional ion transport function that could accelerate the diffusion rate of electrocatalytic products. It attempted to modulate the molar proportion of Ni and Mn to explore the oxygen evolution reaction (OER) performance of the NiMn-LDH/NF catalysts. It was found that when Ni:Mn=4:1 (molar ratio, hereinafter), the nanosheets grew more densely and had better OER performance and stability. The electrochemical test results show that the Ni4Mn-LDH/NF catalyst exhibits an overvoltage of 341 mV at a current density of 10 mA cm−2, and the Tafel slope is only 98.99 mV dec−1.

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Yang, Zixuan, Huijuan Su, Yanan Cheng, Xun Sun, Libo Sun, Lijun Zhao et Caixia Qi. « Performance, Reaction Pathway, and Pretreatment of Au Catalyst Precursor in H2/O2 Atmosphere for the Epoxidation of Propylene ». Catalysts 12, n^o 5 (15 mai 2022) : 540. http://dx.doi.org/10.3390/catal12050540.

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Gas-phase epoxidation of propylene in the copresence of H2 and O2 was performed over the catalyst of Au on as-synthesized TS-1 that contained a small amount of anatase TiO2. The catalytic performance was studied by washing or nonwashing the catalyst precursor to modulate the content of purity (K, Cl) and then calcining the samples in O2 or H2 prior to reaction. The results show that the catalytic performance of Au/TS-1 can be improved without washing (more K+ and Au maintained) and O2 pretreatment. It was found that the calcination in O2 was able to maintain more metallic Au and form more surface-active oxygen species and thus providing a better yield of propylene oxide with the assistance of potassium. Interestingly, more acrolein can be produced over the catalysts with respect to the in situ calcination in O2 than that in H2 when the feed only contained 10% O2 and 10% propylene in argon, while there was no formation of propylene oxide. On the other hand, the catalyst precursor calcined in H2 prefers the formation of successive oxygenates of PO.

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Gerna, Davide, Thomas Roach, Birgit Mitter, Wolfgang Stöggl et Ilse Kranner. « Hydrogen Peroxide Metabolism in Interkingdom Interaction Between Bacteria and Wheat Seeds and Seedlings ». Molecular Plant-Microbe Interactions® 33, n^o 2 (février 2020) : 336–48. http://dx.doi.org/10.1094/mpmi-09-19-0248-r.

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In endophytes, the abundance of genes coding for enzymes processing reactive oxygen species (ROS), including hydrogen peroxide (H2O2), argues for a crucial role of ROS metabolism in plant-microbe interaction for plant colonization. Here, we studied H2O2 metabolism of bread wheat (Triticum aestivum L.) seeds and their microbiota during germination and early seedling growth, the most vulnerable stages in the plant life cycle. Treatment with hot steam diminished the seed microbiota, and these seeds produced less extracellular H2O2 than untreated seeds. Using a culture-dependent approach, Pantoea and Pseudomonas genera were the most abundant epiphytes of dry untreated seeds. Incubating intact seedlings from hot steam–treated seeds with Pantoea strains triggered H2O2 production, whereas Pseudomonas strains dampened H2O2 levels, attributable to higher catalase activities. The genus Pantoea was much less represented among seedling endophytes than genus Pseudomonas, with other endophytic genera, including Bacillus and Paenibacillus, also possessing high catalase activities. Overall, our results show that certain bacteria of the seed microbiota are able to modulate the extracellular redox environment during germination and early seedling growth, and high catalase activity is proposed as a key trait of seed endophytes.

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Zhou, Huang, Nannan Zhang, Hui Bai, Hai Ming, Qin Zhang, Jun Du, Xing Fan et Changyuan Tao. « A pulse modulatable self-oscillation kinetics for water oxidation at large current on manganese catalyst ». Electrochimica Acta 337 (mars 2020) : 135798. http://dx.doi.org/10.1016/j.electacta.2020.135798.

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Zhao, Jun, Baozhan Wang et Zhongjun Jia. « Phylogenetically Distinct Phylotypes Modulate Nitrification in a Paddy Soil ». Applied and Environmental Microbiology 81, n^o 9 (27 février 2015) : 3218–27. http://dx.doi.org/10.1128/aem.00426-15.

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ABSTRACTPaddy fields represent a unique ecosystem in which regular flooding occurs, allowing for rice cultivation. However, the taxonomic identity of the microbial functional guilds that catalyze soil nitrification remains poorly understood. In this study, we provide molecular evidence for distinctly different phylotypes of nitrifying communities in a neutral paddy soil using high-throughput pyrosequencing and DNA-based stable isotope probing (SIP). Following urea addition, the levels of soil nitrate increased significantly, accompanied by an increase in the abundance of the bacterial and archaealamoAgene in microcosms subjected to SIP (SIP microcosms) during a 56-day incubation period. High-throughput fingerprints of the total 16S rRNA genes in SIP microcosms indicated that nitrification activity positively correlated with the abundance ofNitrosospira-like ammonia-oxidizing bacteria (AOB), soil group 1.1b-like ammonia-oxidizing archaea (AOA), andNitrospira-like nitrite-oxidizing bacteria (NOB). Pyrosequencing of13C-labeled DNA further revealed that13CO2was assimilated by these functional groups to a much greater extent than by marine group 1.1a-associated AOA andNitrobacter-like NOB. Phylogenetic analysis demonstrated that active AOB communities were closely affiliated withNitrosospirasp. strain L115 and theNitrosospira multiformislineage and that the13C-labeled AOA were related to phylogenetically distinct groups, including the moderately thermophilic “CandidatusNitrososphaera gargensis,” uncultured fosmid 29i4, and acidophilic “CandidatusNitrosotalea devanaterra” lineages. These results suggest that a wide variety of microorganisms were involved in soil nitrification, implying physiological diversification of soil nitrifying communities that are constantly exposed to environmental fluctuations in paddy fields.

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Morimoto, Tatsuki, Hidemitsu Uno et Hiroyuki Furuta. « Benzene Ring Trimer Interactions Modulate Supramolecular Structures ». Angewandte Chemie International Edition 46, n^o 20 (11 mai 2007) : 3672–75. http://dx.doi.org/10.1002/anie.200604371.

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Peng, Lechao, Lan Zhou, Wenjun Kang, Rui Li, Konggang Qu, Lei Wang et Haibo Li. « Electrospinning Synthesis of Carbon-Supported Pt3Mn Intermetallic Nanocrystals and Electrocatalytic Performance towards Oxygen Reduction Reaction ». Nanomaterials 10, n^o 9 (22 septembre 2020) : 1893. http://dx.doi.org/10.3390/nano10091893.

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To realize the large-scale application of fuel cells, it is still a great challenge to improve the performance and reduce the cost of cathode catalysts towards oxygen reduction reaction (ORR). In this work, carbon-supported ordered Pt3Mn intermetallic catalysts were prepared by thermal annealing electrospun polyacrylonitrile nanofibers containing Platinum(II) acetylacetonate/ Manganese(III) acetylacetonate. Compared with its counterparts, the ordered Pt3Mn intermetallic obtained at 950 °C exhibits a more positive half-potential and higher kinetic current density during the ORR process. Benefiting from their defined stoichiometry and crystal structure, the Mn atoms in Pt3Mn intermetallic can modulate well the geometric and electronic structure of surface Pt atoms, endowing Pt3Mn catalyst with an enhanced ORR catalytic activity. Moreover, it also has a better catalytic stability and methanol tolerance than commercial Pt/C catalyst. Our study provides a new strategy to fabricate a highly active and durable Pt3Mn intermetallic electrocatalyst towards ORR.

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Olson, C. E., M. C. Chen, D. A. Amirian et A. H. Soll. « Oxygen metabolites modulate prostaglandin E2 production by isolated gastric mucosal cells ». American Journal of Physiology-Gastrointestinal and Liver Physiology 256, n^o 5 (1 mai 1989) : G925—G930. http://dx.doi.org/10.1152/ajpgi.1989.256.5.g925.

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We previously found that the small cell fraction of isolated cells from canine gastric mucosa is a major producer of prostaglandin E2 (PGE2) and identified macrophages as the predominant cellular source. Prostaglandin-H synthase activity is dependent on the continuous presence of hydroperoxides. Because reactive oxygen metabolites may mediate mucosal injury in inflammatory or ischemic disease, we studied the release of PGE2 by isolated gastric cells during exposure to an oxygen metabolite-generating system, xanthine and xanthine oxidase. We found a concentration-dependent relationship between xanthine oxidase concentration and PGE2 production without cell lysis. The maximum PGE2 production stimulated by oxidants was equivalent to the maximum PGE2 response to bradykinin and A23187. The chief and parietal cell fractions produced very little PGE2 with xanthine oxidase concentrations that stimulated maximal PGE2 production in the small cell fraction. Uric acid did not stimulate PGE2 production. Catalase completely inhibited the response, while superoxide dismutase had a partial inhibitory effect. Hydrogen peroxide stimulated concentration-dependent PGE2 production with an ED50 of approximately 5 microM. We concluded that reactive oxygen metabolites stimulate PGE2 production by the small cell fraction of gastric mucosa.

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Wang, Tianzuo, Lun Pan, Xiangwen Zhang et Ji-Jun Zou. « Insights into the Pt (111) Surface Aid in Predicting the Selective Hydrogenation Catalyst ». Catalysts 10, n^o 12 (16 décembre 2020) : 1473. http://dx.doi.org/10.3390/catal10121473.

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The d-band center position of the metal catalyst is one of the most important factors for catalytic selective hydrogenation, e.g., the conversion of nitrostyrene to aminostyrene. In this work, we modulate the d-band center position of the Pt surface via H coverage manipulation in order to assess the highly efficient selective hydrogenation catalyst using density functional theory (DFT) calculation, which is validated experimentally. The optimal transition metal catalysts are first screened by comparing the adsorption energy values of two ideal models, nitrobenzene and styrene, and by correlating the adsorption energy with the d-band center positions. Among the ten transition metals, Pt nanoparticles have a good balance between selectivity and the conversion rate. Then, the surface hydrogen covering strategy is applied to modulate the d-band center position on the Pt (111) surface, with the increase of H coverage leading to a decline of the d-band center position, which can selectively enhance the adsorption of nitro groups. However, excessively high H coverage (e.g., 75% or 100%) with an insufficiently low d-band center position can switch the chemisorption of nitro groups to physisorption, significantly reducing the catalytic activity. Therefore, a moderate d-band center shift (ca. −2.14 eV) resulted in both high selectivity and catalytic conversion. In addition, the PtSn experimental results met the theoretical expectations. This work provides a new strategy for the design of highly efficient metal catalysts for selective hydrogenation via the modulation of the d-band center position.

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Singh, Ashish Kumar, Kirti Sad, Shailendra Kumar Singh et Sisinthy Shivaji. « Regulation of gene expression at low temperature : role of cold-inducible promoters ». Microbiology 160, n^o 7 (1 juillet 2014) : 1291–96. http://dx.doi.org/10.1099/mic.0.077594-0.

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Psychrophilic micro-organisms are the most dominant flora in cold habitats. Their unique ability to survive and multiply at low temperatures (<5 °C) is based on their ability to modulate the rigidity of the membrane, to transcribe, to translate and to catalyse biochemical reactions at low temperature. A number of genes are known to be upregulated during growth at low temperature and cold-inducible promoters are known to regulate the expression of genes at low temperature. In this review, we attempted to compile promoter sequences of genes that are cold-inducible so as to identify similarities and to compare the distinct features of each type of promoter when microbes are grown in the cold.

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Mondal, Rakesh, Himanshu Ratnawat, Sarvesh Kumar, Anil Kumar et Preetam Singh. « Ni stabilized rock-salt structured CoO ; Co1−xNixO : tuning of eg electrons to develop a novel OER catalyst ». RSC Advances 10, n^o 30 (2020) : 17845–53. http://dx.doi.org/10.1039/d0ra03050c.

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Kwak, Mi-Sun, Hisaaki Mihara et Nobuyoshi Esaki. « A novel regulatory function of selenocysteine lyase, a unique catalyst to modulate major urinary protein ». Journal of Molecular Catalysis B : Enzymatic 23, n^o 2-6 (septembre 2003) : 367–72. http://dx.doi.org/10.1016/s1381-1177(03)00100-0.

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Ge, Xiao, Dongqin Zhou, Jie Wang, Weiqin Yin, Xiaozhi Wang et Yuen Wu. « Rational regulation of the electronic structure of Cu1 sites catalyst to modulate persulphate activation pathway ». Chemical Engineering Journal 481 (février 2024) : 148587. http://dx.doi.org/10.1016/j.cej.2024.148587.

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Swanwick, Richard S., Giovanni Maglia, Lai-hock Tey et Rudolf K. Allemann. « Coupling of protein motions and hydrogen transfer during catalysis by Escherichia coli dihydrofolate reductase ». Biochemical Journal 394, n^o 1 (27 janvier 2006) : 259–65. http://dx.doi.org/10.1042/bj20051464.

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The enzyme DHFR (dihydrofolate reductase) catalyses hydride transfer from NADPH to, and protonation of, dihydrofolate. The physical basis of the hydride transfer step catalysed by DHFR from Escherichia coli has been studied through the measurement of the temperature dependence of the reaction rates and the kinetic isotope effects. Single turnover experiments at pH 7.0 revealed a strong dependence of the reaction rates on temperature. The observed relatively large difference in the activation energies for hydrogen and deuterium transfer led to a temperature dependence of the primary kinetic isotope effects from 3.0±0.2 at 5 °C to 2.2±0.2 at 40 °C and an inverse ratio of the pre-exponential factors of 0.108±0.04. These results are consistent with theoretical models for hydrogen transfer that include contributions from quantum mechanical tunnelling coupled with protein motions that actively modulate the tunnelling distance. Previous work had suggested a coupling of a remote residue, Gly121, with the kinetic events at the active site. However, pre-steady-state experiments at pH 7.0 with the mutant G121V-DHFR, in which Gly121 was replaced with valine, revealed that the chemical mechanism of DHFR catalysis was robust to this replacement. The reduced catalytic efficiency of G121V-DHFR was mainly a consequence of the significantly reduced pre-exponential factors, indicating the requirement for significant molecular reorganization during G121V-DHFR catalysis. In contrast, steady-state measurements at pH 9.5, where hydride transfer is rate limiting, revealed temperature-independent kinetic isotope effects between 15 and 35 °C and a ratio of the pre-exponential factors above the semi-classical limit, suggesting a rigid active site configuration from which hydrogen tunnelling occurs. The mechanism by which hydrogen tunnelling in DHFR is coupled with the environment appears therefore to be sensitive to pH.

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Zalavras, Athanasios, Ioannis G. Fatouros, Chariklia K. Deli, Dimitris Draganidis, Anastasios A. Theodorou, Dimitrios Soulas, Yiannis Koutsioras, Yiannis Koutedakis et Athanasios Z. Jamurtas. « Age-Related Responses in Circulating Markers of Redox Status in Healthy Adolescents and Adults during the Course of a Training Macrocycle ». Oxidative Medicine and Cellular Longevity 2015 (2015) : 1–17. http://dx.doi.org/10.1155/2015/283921.

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Redox status changes during an annual training cycle in young and adult track and field athletes and possible differences between the two age groups were assessed. Forty-six individuals (24 children and 22 adults) were assigned to four groups: trained adolescents, (TAD,N=13), untrained adolescents (UAD,N=11), trained adults (TA,N=12), and untrained adults (UA,N=10). Aerobic capacity and redox status related variables [total antioxidant capacity (TAC), glutathione (GSH), catalase activity, TBARS, protein carbonyls (PC), uric acid, and bilirubin] were assessed at rest and in response to a time-trial bout before training, at mid- and posttraining. TAC, catalase activity, TBARS, PC, uric acid, and bilirubin increased and GSH declined in all groups in response to acute exercise independent of training status and age. Training improved aerobic capacity, TAC, and GSH at rest and in response to exercise. Age affected basal and exercise-induced responses since adults demonstrated a greater TAC and GSH levels at rest and a greater rise of TBARS, protein carbonyls, and TAC and decline of GSH in response to exercise. Catalase activity, uric acid, and bilirubin responses were comparable among groups. These results suggest that acute exercise, age, and training modulate the antioxidant reserves of the body.

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Wang, Xiong, Wenqian Kang, Lin Gao, Guangquan Li, Xuerong Chen et Yi Guo. « Highly Flowable Nano TiO2/Porous Organic Polymer (POP) Supports for Efficient Metallocene Catalysts ». Nanomaterials 11, n^o 1 (29 décembre 2020) : 60. http://dx.doi.org/10.3390/nano11010060.

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Porous organic polymers (POPs) have proven to be an efficient support in the olefin polymerization catalyst field. In this paper, nano TiO2 beads were used to modulate the pore structure, bulk density, and surface morphology and flowability of the prepared POPs. With the incorporation of the hydrophilic nano TiO2 beads, the prepared TiO2/POP supports obtained reasonable specific surface area (100–300 m2/g) and higher bulk density (0.26–0.35 g/mL) and flowability than the pure POP supports. The results show that bulk density of the prepared TiO2/POP particles increased when adding an increased amount of TiO2, and when 37.5% TiO2 (weight percent to the total comonomers divinylbenzene (DVB) and 2-hydroxyethyl methacrylate (HEMA)) and 3:1 DVB/HEMA (molar ratio) were added, highly flowable TiO2/POP composites (POP-6 and POP-7) were obtained. With the modulation of the nano TiO2 template during the support synthesis, the prepared POP-7 particles successfully achieved a normal distribution with a narrow particle size distribution (PSD) of 0.717 and average particle size of 24.1 m, a specific surface area (SSA) of 279 m2/g, and relatively high bulk density of 0.30 g/mL. Furthermore, all the prepared TiO2/POP supports obtained higher ethylene polymerization activity than silica gel-supported commercial metallocene catalyst. The immobilized (n-BuCp)2ZrCl2/MAO@POP-7 catalyst exhibited the highest ethylene polymerization activity of 4794 kg PE/mol Zr.bar.h and productivity of 389 g PE/g cat, more than twice that of the commercial counterpart. Even higher catalyst productivity (3197 g PE/g cat) and bulk density of the produced PE (0.36 g/mL) could be obtained in higher ethylene partial pressure at 80 ∘C for 2 h, and the prepared TiO2/POP catalyst shows no obvious Zr+ active sites decay during the ethylene polymerization.

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Heroven, Christina, Victoria Georgi, Gaurav K. Ganotra, Paul Brennan, Finn Wolfreys, Rebecca C. Wade, Amaury E. Fernández-Montalván, Apirat Chaikuad et Stefan Knapp. « Halogen-Aromatic π Interactions Modulate Inhibitor Residence Times ». Angewandte Chemie International Edition 57, n^o 24 (9 mai 2018) : 7220–24. http://dx.doi.org/10.1002/anie.201801666.

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Tian, Yiying, Zhiyuan Jiao, Fangfang Qi, Wendi Ma, Yuming Hao, Xinyu Wang, Liyang Xie, Tao Zhou et Zaifeng Fan. « Maize catalases are recruited by a virus to modulate viral multiplication and infection ». Molecular Plant Pathology 25, n^o 3 (mars 2024). http://dx.doi.org/10.1111/mpp.13440.

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AbstractGiven the detrimental effects of excessive reactive oxygen species (ROS) accumulation in plant cells, various antioxidant mechanisms have evolved to maintain cellular redox homeostasis, encompassing both enzymatic components (e.g., catalase, superoxide dismutase) and non‐enzymatic ones. Despite extensive research on the role of antioxidant systems in plant physiology and responses to abiotic stresses, the potential exploitation of antioxidant enzymes by plant viruses to facilitate viral infection remains insufficiently addressed. Herein, we demonstrate that maize catalases (ZmCATs) exhibited up‐regulated enzymatic activities upon sugarcane mosaic virus (SCMV) infection. ZmCATs played crucial roles in SCMV multiplication and infection by catalysing the decomposition of excess cellular H2O2 and promoting the accumulation of viral replication‐related cylindrical inclusion (CI) protein through interaction. Peroxisome‐localized ZmCATs were found to be distributed around SCMV replication vesicles in Nicotiana benthamiana leaves. Additionally, the helper component‐protease (HC‐Pro) of SCMV interacted with ZmCATs and enhanced catalase activities to promote viral accumulation. This study unveils a significant involvement of maize catalases in modulating SCMV multiplication and infection through interaction with two viral factors, thereby enhancing our understanding regarding viral strategies for manipulating host antioxidant mechanisms towards robust viral accumulation.

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Articles de revues sur le sujet « Catalyse modulable »

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