Bibliographies thématiques / Complex Reaction Mechanism

Littérature scientifique sur le sujet « Complex Reaction Mechanism »

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Publié le 7 septembre 2023

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Articles de revues sur le sujet "Complex Reaction Mechanism"

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Butuk, N., et J. P. Pemba. « Computing CHEMKIN Sensitivities Using Complex Variables ». Journal of Engineering for Gas Turbines and Power 125, no 3 (1 juillet 2003) : 854–58. http://dx.doi.org/10.1115/1.1469006.

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This paper discusses an accurate numerical approach based on complex variables for the computation of the Jacobian matrix of complex chemical reaction mechanisms. The Jacobian matrix is required in the calculation of low dimensional manifolds during kinetic chemical mechanism reduction. The approach is suitable for numerical computations of large-scale problems and is more accurate than the finite difference approach of computing Jacobians. The method is demonstrated via a nonlinear reaction mechanism for the synthesis of Bromide acid and a H2/Air mechanism using a modified CHEMKIN package. The Bromide mechanism consisted of five species participating in six elementary chemical reactions and the H2/Air mechanism consisted of 11 species and 23 reactions. In both cases it is shown that the method is superior to the finite difference approach of computing derivatives with an arbitrary computational step size h.
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Хамидуллина, Зульфия Абударовна, Альбина Сабирьяновна Исмагилова et Семен Израилевич Спивак. « Determination of the basis for nonlinear parametric functions of chemical reactions ». Вычислительные технологии, no 3 (15 juillet 2020) : 29–34. http://dx.doi.org/10.25743/ict.2020.25.3.004.

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Настоящая работа посвящена математическому и компьютерному моделированию кинетики сложных химических реакций. Сформулирована и доказана теорема о соответствии структуры механизма сложной химической реакции с матрицей связей. Разработан и автоматизирован алгоритм определения базиса нелинейных параметрических функций. Реализована теоретико-графовая интерпретация механизма сложной химической реакции Mathematical and computer modelling of the kinetics of complex chemical reactions is considered in the present study. It was formulated that the structural mechanism of complex chemical reaction corresponds to the matrix of bonds. The appropriate theorem was proved. A graph and theoretical technique that allows determining the functional dependences of kinetic parameters directly from the graph of the reaction mechanism is developed. Based on the proposed algorithm, a program for determining the basis of nonlinear parametric functions of kinetic parameters is proposed. The program implements a graph and theoretic interpretation of the mechanisms of complex chemical reactions for constructing stationary kinetic models of catalytic reactions. An algorithm for determining the basis of nonlinear parametric functions is developed and automated. A graph and theoretical interpretation of the mechanism of a complex chemical reaction is implemented
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Simoyi, Reuben H., Patricia Masvikeni et Angela Sikosana. « Complex kinetics in the bromate-iodide reaction : a clock reaction mechanism ». Journal of Physical Chemistry 90, no 17 (août 1986) : 4126–31. http://dx.doi.org/10.1021/j100408a058.

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Ratkiewicz, Artur, et Thanh N. Truong. « A canonical form of the complex reaction mechanism ». Energy 43, no 1 (juillet 2012) : 64–72. http://dx.doi.org/10.1016/j.energy.2012.02.029.

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Tsona, Narcisse Tchinda, et Lin Du. « A potential source of atmospheric sulfate from O<sub>2</sub><sup>−</sup>-induced SO<sub>2</sub> ; oxidation by ozone ». Atmospheric Chemistry and Physics 19, no 1 (17 janvier 2019) : 649–61. http://dx.doi.org/10.5194/acp-19-649-2019.

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Abstract. It was formerly demonstrated that O2SOO− forms at collisions rate in the gas phase as a result of SO2 reaction with O2-. Here, we present a theoretical investigation of the chemical fate of O2SOO− by reaction with O3 in the gas phase, based on ab initio calculations. Two main mechanisms were found for the title reaction, with fundamentally different products: (i) formation of a van der Waals complex followed by electron transfer and further decomposition to O2 + SO2 + O3- and (ii) formation of a molecular complex from O2 switching by O3, followed by SO2 oxidation to SO3- within the complex. Both reactions are exergonic, but separated by relatively low energy barriers. The products in the former mechanism would likely initiate other SO2 oxidations as shown in previous studies, whereas the latter mechanism closes a path wherein SO2 is oxidized to SO3-. The latter reaction is atmospherically relevant since it forms the SO3- ion, hereby closing the SO2 oxidation path initiated by O2-. The main atmospheric fate of SO3- is nothing but sulfate formation. Exploration of the reactions kinetics indicates that the path of reaction (ii) is highly facilitated by humidity. For this path, we found an overall rate constant of 4.0×10-11 cm3 molecule−1 s−1 at 298 K and 50 % relative humidity. The title reaction provides a new mechanism for sulfate formation from ion-induced SO2 oxidation in the gas phase and highlights the importance of including such a mechanism in modeling sulfate-based aerosol formation rates.
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Taylor, Annette F. « Mechanism and Phenomenology of an Oscillating Chemical Reaction ». Progress in Reaction Kinetics and Mechanism 27, no 4 (décembre 2002) : 247–326. http://dx.doi.org/10.3184/007967402103165414.

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Chemical reactions, which are far from equilibrium, are capable of displaying oscillations in species concentrations and hence in colour, electrode potential, pH and/or temperature. The oscillations arise from the interplay between positive and negative kinetic feedback. Mechanisms for such reactions are presented, along with the rich phenomenology that these systems exhibit, from complex oscillations and chemical waves, to stationary concentration patterns. This review will focus on the Belousov-Zhabotinksy reaction but reference to other reactions will be made where appropriate.
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Back, M. H. « 1996 Clara Benson Award Lecture The kinetics of the reaction of carbon with oxygen ». Canadian Journal of Chemistry 75, no 3 (1 mars 1997) : 249–57. http://dx.doi.org/10.1139/v97-028.

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The results of studies of the kinetics of the reaction of oxygen with thin films of carbon are described with special emphasis on the role, in the mechanism of the reaction, of the stable complex formed between oxygen and the carbon surface. A key part of the proposed mechanism is the reaction between gaseous oxygen and the stable complex to form the product carbon dioxide. Measurements of the total pressure and the products formed as a function of time of the reaction have allowed estimates of the rate constants for the elementary reactions that make up the mechanism. This in turn has led to the application of computer modelling to the mechanism of the reaction and to the development of a more detailed mechanism involving two types of reactive sites on the carbon surface. Keywords: carbon, oxygen, kinetics, mechanism, computer modelling.
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Gromotka, Zoë, Gregory Yablonsky, Nickolay Ostrovskii et Denis Constales. « Integral Characteristic of Complex Catalytic Reaction Accompanied by Deactivation ». Catalysts 12, no 10 (20 octobre 2022) : 1283. http://dx.doi.org/10.3390/catal12101283.

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New theoretical relationships for a complex catalytic reaction accompanied by deactivation are obtained, using as an example the two-step catalytic mechanism (Temkin–Boudart mechanism) with irreversible reactions and irreversible deactivation. In the domain of small concentrations, Alim=NSk1CAkd, where Alim is the limit of the integral consumption of the gas substance, NS is the number of active sites per unit of catalyst surface; k1 and kd, are kinetic coefficients which relate to two reactions which compete for the free active site Z. CA is the gas concentration. One reaction belongs to the catalytic cycle. The other reaction with kinetic coefficient kd is irreversible deactivation. The catalyst lifetime, τcat=1CZ′1kd, where CZ′ is the dimensionless steady-state concentration of free active sites. The main conclusion was formulated as follows: the catalyst lifetime can be enhanced by decreasing the steady-state (quasi-steady-state) concentration of free active sites. In some domains of parameters, it can also be achieved by increasing the steady-state (quasi-steady-state) reaction rate of the fresh catalyst. We can express this conclusion as follows: under some conditions, an elevated fresh catalyst activity protects the catalyst from deactivation. These theoretical results are illustrated with the use of computer simulations.
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Parker, Vernon D. « Is the single transition-state model appropriate for the fundamental reactions of organic chemistry ? » Pure and Applied Chemistry 77, no 11 (1 janvier 2005) : 1823–33. http://dx.doi.org/10.1351/pac200577111823.

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In recent years, we have reported that a number of organic reactions generally believed to follow simple second-order kinetics actually follow a more complex mechanism. This mechanism, the reversible consecutive second-order mechanism, involves the reversible formation of a kinetically significant reactant complex intermediate followed by irreversible product formation. The mechanism is illustrated for the general reaction between reactant and excess reagent under pseudo-first-order conditions in eq. i where kf' is the pseudo-first-order rate constant equal to kf[Excess Reagent].Reactant + Excess reagent = Reactant complex = Products (i)The mechanisms are determined for the various systems, and the kinetics of the complex mechanisms are resolved by our "non-steady-state kinetic data analysis". The basis for the non-steady-state kinetic method will be presented along with examples. The problems encountered in attempting to identify intermediates formed in low concentration will be discussed.
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Tsutsui, Minoru. « π-COMPLEX MECHANISM OF CATALYSIS : THE ARYL-COUPLING REACTION ». Annals of the New York Academy of Sciences 93, no 4 (15 décembre 2006) : 135–46. http://dx.doi.org/10.1111/j.1749-6632.1961.tb30517.x.

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Thèses sur le sujet "Complex Reaction Mechanism"

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Ishino, So. « Physicochemical studies on reaction mechanism of molecular chaperone GroE ». 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199490.

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Henry, Marc. « Application du concept d'electronegativite aux processus d'hydrolyse et de condensation en chimie minerale ». Paris 6, 1988. http://www.theses.fr/1988PA066293.

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Utilisation des procedes sol-gel pour elabour des materiaux a base d'oxydes et a proprietes optimisees. Mecanismes d'hydrolyse et de condensation des precurseurs moleculaires (alcoxydes ou sels metalliques) aboutissant a l'obtention de materiaux mixtes organiques/inorganiques
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Giraudon, Jean-Marc. « Complexes mono et dinucléaires du molybdene avec les ligands macrocycliques : synthèse, structure, réactivité et propriétés redox ». Brest, 1988. http://www.theses.fr/1988BRES2019.

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Preparation des complexes avec le coordinat tetraazaannulene; cas de complexes a liaison quadruple du mo ou le coordinat organique presente une coordination tetradentee. On envisage les mecanismes d'interconversion monomere oxo-dinucleaire. Etudes rpe et uv-visible
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Nuel, Didier. « Etude de la reactivite de fragments alkylidynes dans des clusters trinucleaires du fer ». Toulouse 3, 1986. http://www.theses.fr/1986TOU30206.

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Reactivite des complexes fe::(3)(co)::(9)(cch::(3))(coc::(2)h::(5)) ou fe::(3)(co)::(10)(cch::(3))(h). Les reactions de couplage des groupes alkylidynes avec les algues sont faciles. L'action de co a mis en evidence le couplage reversible dans des conditions douces de 2 fragments alkylidynes. En general, la presence du coordinat hydruro rend les reactions plus complexes
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Yadnum, Sudarat. « Tailoring complex heterogeneous metal-organic framework structures ». Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0299/document.

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Dans cette thèse, de nouvelles stratégies pour la préparation de matériaux de type Metal-Organic-Frameworks (MOF) ont été étudiés et développés. L’électrodeposition bipolaire indirecte (IBED) a été utilisé pour préparer ZIF-8 et HKUST-1 sur des substrats métalliques de façon simple et avec une sélectivité spatiale. Ce concept devrait pouvoir être généralisée pour la synthèse de nombreux autres composés MOF, permettant ainsi une synthèse pas chère et verte, conduisant à de nouvelles générations de composites de type Janus basés sur des MOFs. En outre, des électrodes avec une structure hiérarchique macro-/ microporeux de HKUST-1 ont été préparées par une technique de dissolution-dépôt électrochimique. L'approche de synthèse mis au point est très pratique en ce qui concerne la durée des expériences, et ouvre diverses applications pour les MOFs. Enfin des nanoparticules de métaux nobles sur un substrat à base de MIL-101 ont été préparées comme la dernière partie de l'étude expérimentale par dépôt colloïdal. Ce concept peut être généralisé pour la synthèse d'autres composites nanoparticules métalliques / MOF, et pourrait améliorer l'activité catalytique des MOFs. En dehors de l'étude expérimentale, afin de comprendre mieux la catalyse de matériaux MOF, le comportement catalytique de Cu (II) dans le MOF-505 a été théoriquement étudié pour la réaction d'aldolisation Mukayiama par la théorie de densité fonctionnelle et comparé à celui d'un autre catalyseur, Cu-ZSM-5. En outre, le comportement catalytique d'amas homo- et hétéro-bimétalliques, qui sont des complexes métalliques qui représentent les agrégats métalliques dans les MOFs, a également été étudié théoriquement pour la réaction de cycloaddition de dioxyde de carbone et des oxydes d'éthylène
In this thesis, new strategies for the preparation of Metal 0rganic Frameworks (MOF) materials with designed structures were studied and developed. Indirect bipolar electrodeposition (IBED) was used to prepare ZIF-8 and HKUST-1 on metal substrates in a straightforward and site-selective way. This concept is expected to be able to be generalized for the synthesis of many other MOF compounds, thus allowing a cheap and green synthesis, leading to new generations of MOF-based Janus-type composites. Furthermore, rationally designed hierarchical macro-/microporous HKUST-1 electrodes were prepared via an electrochemical dissolution-deposition technique. The developed synthesis approach is very practical in terms of the time consumption, and opens up MOFs for various applications. Finally, MIL-101-supported noble metal nanoparticles were prepared as the last part of the experimental studies via a simple colloidal deposition technique. This concept might be generalized for the synthesis of other metal nanoparticle/MOF composites, and might improve the catalytic activity of MOFs. Apart from the experimental study, in order to gain a deeper insight into the catalysis of MOF materials, the catalytic behavior of Cu(II) in the paddle-wheel unit of MOF-505 was theoretically investigated for the Mukaiyama aldol reaction via the density functional theory and compared to that of another catalyst, Cu-ZSM-5 zeolite. Besides, the catalytic behavior of homo-metallic clusters and hetero-bimetallic clusters, that are the metal complexes representing the metal clusters in MOFs, were also theoretically investigated for the cycloaddition reaction of carbon dioxide and ethylene oxides
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Schoettel, Guy. « Complexes alkylidenes du molybdene ». Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13125.

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Synthese de complexes de mo(vi) de type mo(ntbu)(=chtbu)(or)::(n)(ch::(2)tbu)::(2-n)(n=0,1,2), s'inscrivant dans le cadre de l'activation catalytique des reactions de metathese des olefines. Le type de reaction observee varie selon le complexe et la nature, cyclique, terminale, interne ou fonctionnalisee de l'olefine etudiee
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EL, AMOURI HANZ. « Synthese et reactivite catalytique de composes homo- et heterobinucleaires ». Université Louis Pasteur (Strasbourg) (1971-2008), 1987. http://www.theses.fr/1987STR13156.

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Utilisation du ligand tripode ch(pph::(2))::(3) pour synthetiser des complexes mononucleaires (rh(i), ir(i) et mo(0)), homobinucleaires (rh(i)-rh(i)), heterobinuclaires (rh(i)-cu(i), rh(i)-au(i), ir(i)-au(i) et polynucleaires (rh(i)::(4), rh(i)-cu(i)::(2)). Etude des proprietes catalytiques en hydrogenation des olefines et acetylene
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Etienne, Michel. « Réactivité de complexes dinucléaires hydrure et alcénylidène ponte du fer vis-a-vis d'hydrocarbures cyanes insatures (mono et dicyanoacétylène, tétracyanoethylène) ». Brest, 1988. http://www.theses.fr/1988BRES2009.

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Preparation de complexes avec des coordinats cyano-4 butadienyldene portants. On obtient egalement des complexes dinucleaires avec le tricyano-3,4,4 butadienylidene-1,3. Mecanisme ses reactions de migration de l'hydrogene allylique
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Grytsyk, Natalia. « Development of the surface-enhanced infrared spectroscopic approach and surface-enhanced Raman spectroscopy coupled with electrochemistry to study reaction mechanism of membrane proteins ». Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAF057/document.

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Cette thèse concerne le développement d’approches spectroscopiques infrarouge et Raman exaltées de surface: la spectroscopie infrarouge exaltée de surface (SEIRAS) combinée avec une cellule de perfusion et la spectroscopie Raman exaltée de surface (SERS) couplée avec l’électrochimie. Dans le cadre du premier projet, différentes protéines ont été étudiées : lactose perméase (LacY), complexe I et IM30. Nous avons déterminé le pKa de Glu325 dans LacY sauvage et dans différents mutants portant des mutations dans le centre actif de translocation des protons. Sauvage complexe I a été oxydé avec différents agents oxydants et réduit avec NADH. Spectres différentiels correspondants ont été analysés. Des changements conformationnels dans la protéine IM30, induits par la présence des ions Mg2+, ont été observés.Dans le cadre du deuxième projet, une cellule spectroélectrochimique contenant une grille d’or a été adaptée pour étudier des protéines redox actives. Cette grille d’or sert à la fois de substrat SERS et d’électrode de travail. Cyt c, Hb et Mb ont d'abord été utilisés pour valider la configuration, puis l'approche a été étendue pour étudier une protéine membranaire
This thesis concerns the development of surface-enhanced infrared and Raman spectroscopic approaches: surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with perfusion cell and surface-enhanced Raman spectroscopy (SERS) combined with electrochemistry. Within the first project different proteins were studied: Lactose Permease (LacY), complex I and IM30.The pKa of Glu325 in LacY WT and in different mutants carrying mutations in the proton translocation active center was determined. WT complex I was oxidized with different oxidizing agents and reduced with NADH. Corresponding redox-induced conformational changes were studied. The evidence was given that Mg2+ ions induce conformational changes in the protein IM30.Within the second project the spectroelectrochemical cell containing gold grid electrode was adopted for the studies of redox active proteins. This gold grid serves both as working electrode and as SERS active substrate. First Cyt c, Hb and Mb were used to validate the setup and then the approach was extended to study a membrane protein
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Coldren, William Henry. « Theoretical Studies of Reactive Intermediates in Complex Reaction Mechanisms ». The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531497707269833.

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Livres sur le sujet "Complex Reaction Mechanism"

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Vicario, Jose L. Organocatalytic enantioselective conjugate addition reactions : A powerful tool for the stereocontrolled synthesis of complex molecules. Cambridge : Royal Society of Chemistry, 2010.

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John, Ross. Determination of complex reaction mechanisms : Analysis of chemical, biological, and genetic networks. New York : Oxford University Press, 2005.

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Elena, Soriano, José Marco-Contelles et B. Alcaide. Computational mechanisms of Au and Pt catalyzed reactions. Heidelberg : Springer, 2011.

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Ross, John. Determination of complex reaction mechanisms : Analysis of chemical, biological, and genetic networks. New York, NY : Oxford University Press, 2005.

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Wilkins, Ralph G. Kinetics and mechanism of reactions of transition metal complexes. 2e éd. Weinheim : VCH, 1991.

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Wilkins, Ralph G. Kinetics and mechanism of reactions of transition metal complexes. 2e éd. Weinheim : VCH, 1991.

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Wilkins, Ralph G. Kinetics and mechanisms of reactions of transition metal complexes. 2e éd. Weinheim : VCH Publishers, 1991.

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Busacca, Maurizio, et Roberto Paladini. Collaboration Age. Venice : Fondazione Università Ca’ Foscari, 2020. http://dx.doi.org/10.30687/978-88-6969-424-0.

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Recently, public policies of urban regeneration have intensified and multiplied. They are being promoted with the aim to start social and economic dynamics within the local context which is subject to intervention. From the empirical analysis, we realise that such activities are mainly implemented by three subjects or by mixed coalitions (public institutions, actors of the third sector and companies). Within them, each player is moved by a multiplicity of interests and goals that go beyond their own nature – public interest, market and mutualism – and tend to redefine themselves, thus becoming hybrid forms of production of value (social, economic, cultural). By studying a number Italian and Catalan cases, this essay deals with the theory that, under specific conditions and configurations, a collaborative direction – of organization, production and design – would give life to successful procedures, even without the identification of a one-best-way. The collaboration is not simply a choice of operation, but a real production method which mobilises social resources to create hybrid solutions – between state, market and society – to complex issues that could not be faced solely with the use of the rationale of action of one among the three actors. In this framework, the systems of relations and interactions between players and shared capital become an essential condition for the success of every initiative of urban redevelopment, or failure thereof. Such initiatives are brought to life by the strategic role of individuals who foster connections as well as the dissemination of non-redundant information between social networks, and collective and individual actors which would otherwise be separated and barely able to communicate and collaborate with each other. In addition to the functions carried out by knowledge brokers, that have been extensively described in organisational studies and economic sociology, the aforementioned figures act as real social enzymes, that is to say, they handle the available information and function as catalysts of social processes of production of knowledge. Moreover, they increase the reaction speed, working on mechanisms which control the spontaneity.
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Ross, John, Igor Schreiber et Marcel O. Vlad. Determination of Complex Reaction Mechanisms. Oxford University Press, 2006. http://dx.doi.org/10.1093/oso/9780195178685.001.0001.

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In a chemical system with many chemical species several questions can be asked: what species react with other species: in what temporal order: and with what results? These questions have been asked for over one hundred years about simple and complex chemical systems, and the answers constitute the macroscopic reaction mechanism. In Determination of Complex Reaction Mechanisms authors John Ross, Igor Schreiber, and Marcel Vlad present several systematic approaches for obtaining information on the causal connectivity of chemical species, on correlations of chemical species, on the reaction pathway, and on the reaction mechanism. Basic pulse theory is demonstrated and tested in an experiment on glycolysis. In a second approach, measurements on time series of concentrations are used to construct correlation functions and a theory is developed which shows that from these functions information may be inferred on the reaction pathway, the reaction mechanism, and the centers of control in that mechanism. A third approach is based on application of genetic algorithm methods to the study of the evolutionary development of a reaction mechanism, to the attainment given goals in a mechanism, and to the determination of a reaction mechanism and rate coefficients by comparison with experiment. Responses of non-linear systems to pulses or other perturbations are analyzed, and mechanisms of oscillatory reactions are presented in detail. The concluding chapters give an introduction to bioinformatics and statistical methods for determining reaction mechanisms.
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Sanguanruang, Oravan. [Lambda hyperon]-((R)-cysteinesulfenamido-N,S) bis (ethylenediamine) cobalt(III) complex : Characterization of the complex and kinetics and mechanism of formation and base-catalyzed decomposition. 1988.

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Chapitres de livres sur le sujet "Complex Reaction Mechanism"

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Kramer, David M., et Antony R. Crofts. « A Chain Reaction Mechanism for Oxidation of the Fully Reduced Cytochrome b6f Complex ». Dans Photosynthesis : from Light to Biosphere, 1553–56. Dordrecht : Springer Netherlands, 1995. http://dx.doi.org/10.1007/978-94-009-0173-5_365.

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Yoshikawa, Shinya, Satoshi Nitta, Kyoko Nishiyama, Norihiro Ohnishi, Katsuhito Takeshima, Yasuhiko Ishii, Makoto Nakamura, Hiroshi Matsuara et Keiun Kodo. « Mechanism of ferredoxin-NADP+ reductase reaction NADP radical, semiquinone and fully reduced enzyme-NADP+ charge transfer complex as the reaction intermediates ». Dans Flavins and Flavoproteins 1987, sous la direction de D. E. Edmondson et D. B. McCormick, 341–44. Berlin, Boston : De Gruyter, 1987. http://dx.doi.org/10.1515/9783110884715-058.

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Tsuge, Hideaki, et Toshiharu Tsurumura. « Reaction Mechanism of Mono-ADP-Ribosyltransferase Based on Structures of the Complex of Enzyme and Substrate Protein ». Dans Endogenous ADP-Ribosylation, 69–87. Cham : Springer International Publishing, 2014. http://dx.doi.org/10.1007/82_2014_415.

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Ulrich, Magda M. W. « Fetal Wound Healing ». Dans Textbook on Scar Management, 3–9. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44766-3_1.

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AbstractFirst- and second-trimester fetal skin wounds are known to heal without scarring.Research has excluded factors like the sterile uterine environment as the cause of scarless repair, and it is believed that scarless healing is an intrinsic property of early fetal skin. However, increasing wound size and induction of the inflammatory reaction can evoke a scar response in the fetus.For decades, research is performed to elucidate the mechanisms responsible for scarless healing in fetuses. Much research has been performed in animal studies, and several mechanisms have been proposed to be involved such as the microenvironment and the extracellular matrix, a reduced inflammatory response, differences in growth factor profile, and differences in fibroblast phenotype.It is clear that the wound healing process leading to scarless healing cannot be attributed to just one factor or mechanism but will be the result of a complex of interconnected processes.This chapter describes some of the possible mechanisms which may play a role in scarless healing.
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Varfolomeev, Sergey, Bella Grigorenko, Sofya Lushchekina, Patrick Masson, Galina Mahaeva et Alexander Nemuchin. « Human cholinesterases ». Dans ORGANOPHOSPHORUS NEUROTOXINS, 69–126. ru : Publishing Center RIOR, 2020. http://dx.doi.org/10.29039/21_069-126.

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The work is devoted to modeling the elementary stages of the hydrolysis reaction in the active site of enzymes belonging to the class of cholinesterases — acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The study allowed to describe at the molecular level the effect of the polymorphic modification of BChE, causing serious physiolog ical consequences. Cholinesterase plays a crucial role in the human body. AChE is one of the key enzymes of the central nervous system, and BChE performs protective functions in the body. According to the results of calculations using the combined method of quantum and molecular mechanics (KM/MM), the mechanism of the hydrolysis of the native acetylcholine substrate in the AChE active center was detailed. For a series of ester substrates, a method for estimation of dependence of the enzyme reactivity on the structure of the substrate has been developed. The mechanism of hydrolysis of the muscle relaxant of succininylcholine BChE and the effect of the Asp70Gly polymorph on it were studied. Using various computer simulation methods, the stability of the enzyme-substrate complex of two enzyme variants with succinylcholine was studied.
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Varfolomeev, Sergey, Bella Grigorenko, Sofya Lushchekina et Alexander Nemuchin. « Human cholinesterases ». Dans Organophosphorous Neurotoxins, 63–120. ru : Publishing Center RIOR, 2020. http://dx.doi.org/10.29039/chapter_5e4132b5f22366.15634219.

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The work is devoted to modeling the elementary stages of the hydrolysis reaction in the active site of enzymes belonging to the class of cholinesterases — acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The study allowed to describe at the molecular level the effect of the polymorphic modification of BChE, causing serious physiolog ical consequences. Cholinesterase plays a crucial role in the human body. AChE is one of the key enzymes of the central nervous system, and BChE performs protective functions in the body. According to the results of calculations using the combined method of quantum and molecular mechanics (KM/MM), the mechanism of the hydrolysis of the native acetylcholine substrate in the AChE active center was detailed. For a series of ester substrates, a method for estimation of dependence of the enzyme reactivity on the structure of the substrate has been developed. The mechanism of hydrolysis of the muscle relaxant of succininylcholine BChE and the effect of the Asp70Gly polymorph on it were studied. Using various computer simulation methods, the stability of the enzyme-substrate complex of two enzyme variants with succinylcholine was studied.
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Gallego, Mar Gómez, et Miguel A. Sierra. « Level 1 — Case 7 NaBH4 Reduction of α,β-Unsaturated Chromium Carbene Complexes ». Dans Organic Reaction Mechanisms, 39–45. Berlin, Heidelberg : Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-642-18788-9_7.

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Turányi, Tamás, et Alison S. Tomlin. « Computer Codes for the Study of Complex Reaction Systems ». Dans Analysis of Kinetic Reaction Mechanisms, 337–51. Berlin, Heidelberg : Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-662-44562-4_9.

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Ašperger, Smiljko. « Metal Complexes in Tumor Therapy ». Dans Chemical Kinetics and Inorganic Reaction Mechanisms, 281–91. Boston, MA : Springer US, 2003. http://dx.doi.org/10.1007/978-1-4419-9276-5_11.

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Ašperger, Smiljko. « Substitution Reactions on Metal Complexes ». Dans Chemical Kinetics and Inorganic Reaction Mechanisms, 105–59. Boston, MA : Springer US, 2003. http://dx.doi.org/10.1007/978-1-4419-9276-5_3.

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Actes de conférences sur le sujet "Complex Reaction Mechanism"

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Bian, Weiwei. « Discussion on reaction mechanism of enoxacine-terbium complex ». Dans 2015 International Conference on Automation, Mechanical Control and Computational Engineering. Paris, France : Atlantis Press, 2015. http://dx.doi.org/10.2991/amcce-15.2015.333.

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Mazumder, Sandip, et Ankan Kumar. « The In Situ Adaptive Tabulation (ISAT) Algorithm for Reacting Flow Computations With Complex Surface Chemistry ». Dans ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17694.

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The In Situ Adaptive Tabulation (ISAT) procedure, originally developed for the efficient computation of homogeneous reactions in chemically reacting flows, is adapted and demonstrated for reacting flow computations with complex heterogeneous (or surface) reactions. The treatment of heterogeneous reactions within a reacting flow calculation requires solution of a set of nonlinear differential algebraic equations at boundary faces/nodes, as opposed to the solution of an initial value problem for which the original ISAT procedure was developed. The modified ISAT algorithm, referred to as ISAT-S, is coupled to a three-dimensional unstructured reacting flow solver, and strategies for maximizing efficiency without hampering accuracy and convergence are developed. These include use of multiple binary tables, use of dynamic tolerance values to control errors, and periodic deletion and/or re-creation of the binary tables. The new procedure is demonstrated for steady-state catalytic combustion of a methane-air mixture on platinum using a 24-step reaction mechanism with 19 species, and for steady-state three-way catalytic conversion using a 61-step mechanism with 34 species. Both reaction mechanisms are first tested in simple 3D channel geometry with reacting walls, and the impact of various ISAT parameters is investigated. As a final step, the catalytic combustion mechanism is demonstrated in a laboratory-scale monolithic catalytic converter geometry with 57 channels discretized using 354,300 control volumes (4.6 million unknowns). For all of the cases considered, the reduction in the time taken to perform surface chemistry calculations alone was found to be a factor of 5–11.
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Inomoto, Osamu, Kazuyuki Fujii et Shoichi Kai. « Physicochemical mechanism of accelerating chemical wave in Belousov-Zhabotinsky reaction ». Dans The 8th tohwa university international symposium on slow dynamics in complex systems. AIP, 1999. http://dx.doi.org/10.1063/1.58463.

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Butuk, Nelson, et JeanPaul Pemba. « Computing CHEMKIN Sensitivities Using Complex Variables ». Dans ASME 2001 Engineering Technology Conference on Energy. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/etce2001-17013.

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Abstract This paper discusses an accurate numerical approach of computing the Jacobian Matrix for the calculation of low dimensional manifolds for kinetic chemical mechanism reduction. The approach is suitable for numerical computations of large scale problems and is more accurate than the finite difference approach of computing Jacobians. The method is demonstrated via a highly stiff reaction mechanism for the synthesis of Bromide acid and a H2/Air mechanism using a modified CHEMKIN package. The Bromide mechanism consisted of five species participating in six elementary chemical reactions and the H2/Air mechanism consisted of 11 species and 23 reactions. In both cases it is shown that the method is superior to the finite difference approach of computing derivatives with an arbitrary computational step size, h.
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Elliott, L., D. B. Ingham, A. G. Kyne, N. S. Mera, M. Pourkashanian et C. W. Wilson. « A Novel Approach to Mechanism Reduction Optimisation for Aviation Fuel/Air Reaction Mechanism Using a Genetic Algorithm ». Dans ASME Turbo Expo 2004 : Power for Land, Sea, and Air. ASMEDC, 2004. http://dx.doi.org/10.1115/gt2004-53053.

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This study presents the use of a genetic algorithm to produce a new reduced chemical kinetic reaction mechanism to simulate aviation fuel combustion under various operating conditions. The mechanism is used to predict the flame structure of a aviation fuel/O2/N2 flame in both spatially homogeneous and one-dimensional premixed combustion. Complex hydrocarbon fuels, such as aviation fuel, involve large numbers of reaction steps with many species. As all the reaction rate data is not well known, there is a high degree of uncertainty in the results obtained using these large detailed reaction mechanisms. In this study a genetic algorithm approach is employed for determining new reaction rate parameters for a reduced reaction mechanism for the combustion of aviation fuel/air mixtures. The genetic algorithm employed incorporates both perfectly stirred reactor and laminar premixed flame data in the inversion process, thus producing an efficient reaction mechanism. This study provides an optimised reduced aviation fuel/air reaction scheme whose performance in predicting experimental major species profiles and ignition delay times is not only an improvement on the starting reduced mechanism but also on the full mechanism.
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TOLSTOV, G. I., I. A. MEDVEDKOV, D. P. PORFLRIEV, M. V. ZAGIDULLIN, A. M. MEBEL et V. N. AZYAZOV. « MODELING OF THE COMPLETE MECHANISM OF OXIDATION OF PHENYL RADICAL UNDER COMBUSTION CONDITIONS ». Dans 9th International Symposium on Nonequilibrium Processes, Plasma, Combustion, and Atmospheric Phenomena. TORUS PRESS, 2020. http://dx.doi.org/10.30826/nepcap9b-08.

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Quantum chemical calculations, computational fluid dynamics (CFD) simulations, and isothermal approximation were applied for the interpretation of experimental measurements of the reaction of C6H5+O2 in the high-temperature microreactor and of the pressure drop in the flow tube of the reactor. Applying isothermal approximation allows the derivation of analytical relationships between the kinetic, gas flow, and geometrical parameters of the microreactor which, along with CFD simulations, accurately predict the experimental observations. The analysis showed that at the first stage, mainly C6H5O is formed in reaction C6H5+O2→C6H5O+O and C5H5 in reaction C6H5+O2→C5H5+CO2. С6Н5О decomposes either with the formation of C5H5 in reaction C6H5O→C5H5+CO or into other components. The decrease in С5Н5 in secondary reactions is insignificant. It has been demonstrated that CFD modeling is a powerful tool for understanding the complex physical and chemical processes inside a microreactor.
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Peswani, Mohnish, et Brian McN Maxwell. « Performance of a Generic 4-Step Global Reaction Mechanism With Equilibrium Effects for Detonation Applications ». Dans ASME 2020 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/imece2020-23786.

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Abstract A reduced 4-species, 4-step Global Reaction Mechanism (GRM) [1], derived from detailed chemistry using a thermochemical approach, is investigated for three different reactive mixtures. The trade-off between preciseness of Elementary Reaction Mechanisms (ERMs), and low computational overhead requirements of GRMs remains a dilemma in the application of chemical kinetic models to detonation problems. Reducing a reaction mechanism often compromises the chemical details, and reduces the scope of applicability of the derived model. This is largely due to the mixture chemistry having a vital influence on several key aspects of the detonation phenomenon like initiation, quenching, and the dynamics of the wave front and hydrodynamic structure during propagation. For detonation problems in particular, there has been an insufficient replication of the complex reality of the phenomenon through numerical simulations which has lead to a constant demand for more accurate and affordable models. Three separate stoichiometric combustion mixtures are investigated, each involving acetylene, methane, or propane mixed with oxygen. Each mixture exhibits very different global activation energies, heat release, and ignition characteristics.
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Kubota, Tomohiro, Yoshiyuki Kikuchi et Seiji Samukawa. « Transition metal complex reaction etching with neutral beam and its mechanism investigated by first-principles calculation ». Dans 2016 IEEE 16th International Conference on Nanotechnology (IEEE-NANO). IEEE, 2016. http://dx.doi.org/10.1109/nano.2016.7751342.

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Zapata-Romero, Gilberto A., Markus Doerr et Martha C. Daza. « Enantioselective lipase-catalyzed O-acylation of (RS)-propranolol : analysis of the hydrogen bonds essential for catalysis ». Dans VIII Simpósio de Estrutura Eletrônica e Dinâmica Molecular. Universidade de Brasília, 2020. http://dx.doi.org/10.21826/viiiseedmol2020131.

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We investigated the effect of the acyl group size in the enantioselectivity of the acylation of propranolol, an amino alcohol used as β-adrenergic blocking agent. We applied a methodology frequently used to model enantioselectivity that is based on the hydrogen bonds present in the tetrahedral intermediate, which occurs in lipase-catalyzed reactions. We sampled the conformations of the tetrahedral intermediate corresponding to the esterification of both enantiomers of propranolol with ethanoyl and butanoyl, employing molecular dynamics simulation together with a quantum mechanics/molecular mechanics approach. We found that the population of these hydrogen bonds provides insight into the mechanism of the reaction. However, they are not conclusive about the role of the acyl group in the enantioselectivity. For both acyl groups, we found that the reaction from the Michaelis complex to the tetrahedral intermediate is more favorable for (R)-propranolol and the reaction from the tetrahedral intermediate to the enzyme/product complex is more favorable for (S)-propranolol.
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Elliott, L., D. B. Ingham, A. G. Kyne, N. S. Mera, M. Pourkashanian et C. W. Wilson. « A Novel Approach to the Optimisation of Reaction Rate Parameters for Methane Combustion Using Multi-Objective Genetic Algorithms ». Dans ASME Turbo Expo 2003, collocated with the 2003 International Joint Power Generation Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/gt2003-38018.

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This study uses a multi-objective genetic algorithm to determine new reaction rate parameters (A’s, β’s and Ea’s in the non-Arrhenius expressions) for the combustion of a methane/air mixture. The multi-objective structure of the genetic algorithm employed allows for the incorporation of both perfectly stirred reactor and laminar premixed flames data in the inversion process, thus enabling a greater confidence in the predictive capabilities of the reaction mechanisms obtained. Various inversion procedures based on reduced sets of data are investigated and tested on methane/air combustion in order to generate efficient inversion schemes for future investigations concerning complex hydrocarbon fuels. The inversion algorithms developed are first tested on numerically simulated data. In addition, the increased flexibility offered by this novel multi-objective GA has now, for the first time, allowed experimental data to be incorporated into our reaction mechanism development. A GA optimised methane air reaction mechanism is presented which offers a remarkable improvement over a previously validated starting mechanism in modelling the flame structure in a stoichiometric methane-air premixed flame (http://www.leeds.ac.uk/ERRI/research/res.html). In addition, the mechanism outperforms the predictions of more detailed schemes and is still capable of modelling combustion phenomena that were not part of the optimisation process. Therefore, the results of this study demonstrate that the genetic algorithm inversion process promises the ability to assess combustion behaviour for fuels where the reaction rate coefficients are not known with any confidence and, subsequently, accurately predict emission characteristics, stable species concentrations and flame characterisation. Such predictive capabilities will be of paramount importance within the gas turbine industry.
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Rapports d'organisations sur le sujet "Complex Reaction Mechanism"

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Day, Marcus. Improving Gas Reactor Design with Complex Non-Standard Reaction Mechanisms in a Reactive Flow Model. Office of Scientific and Technical Information (OSTI), mars 2020. http://dx.doi.org/10.2172/1605427.

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Christopher, David A., et Avihai Danon. Plant Adaptation to Light Stress : Genetic Regulatory Mechanisms. United States Department of Agriculture, mai 2004. http://dx.doi.org/10.32747/2004.7586534.bard.

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Original Objectives: 1. Purify and biochemically characterize RB60 orthologs in higher plant chloroplasts; 2. Clone the gene(s) encoding plant RB60 orthologs and determine their structure and expression; 3. Manipulate the expression of RB60; 4. Assay the effects of altered RB60 expression on thylakoid biogenesis and photosynthetic function in plants exposed to different light conditions. In addition, we also examined the gene structure and expression of RB60 orthologs in the non-vascular plant, Physcomitrella patens and cloned the poly(A)-binding protein orthologue (43 kDa RB47-like protein). This protein is believed to a partner that interacts with RB60 to bind to the psbA5' UTR. Thus, to obtain a comprehensive view of RB60 function requires analysis of its biochemical partners such as RB43. Background & Achievements: High levels of sunlight reduce photosynthesis in plants by damaging the photo system II reaction center (PSII) subunits, such as D1 (encoded by the chloroplast tpsbAgene). When the rate of D1 synthesis is less than the rate of photo damage, photo inhibition occurs and plant growth is decreased. Plants use light-activated translation and enhanced psbAmRNA stability to maintain D1 synthesis and replace the photo damaged 01. Despite the importance to photosynthetic capacity, these mechanisms are poorly understood in plants. One intriguing model derived from the algal chloroplast system, Chlamydomonas, implicates the role of three proteins (RB60, RB47, RB38) that bind to the psbAmRNA 5' untranslated leader (5' UTR) in the light to activate translation or enhance mRNA stability. RB60 is the key enzyme, protein D1sulfide isomerase (Pill), that regulates the psbA-RN :Binding proteins (RB's) by way of light-mediated redox potentials generated by the photosystems. However, proteins with these functions have not been described from higher plants. We provided compelling evidence for the existence of RB60, RB47 and RB38 orthologs in the vascular plant, Arabidopsis. Using gel mobility shift, Rnase protection and UV-crosslinking assays, we have shown that a dithiol redox mechanism which resembles a Pill (RB60) activity regulates the interaction of 43- and 30-kDa proteins with a thermolabile stem-loop in the 5' UTR of the psbAmRNA from Arabidopsis. We discovered, in Arabidopsis, the PD1 gene family consists of II members that differ in polypeptide length from 361 to 566 amino acids, presence of signal peptides, KDEL motifs, and the number and positions of thioredoxin domains. PD1's catalyze the reversible formation an disomerization of disulfide bonds necessary for the proper folding, assembly, activity, and secretion of numerous enzymes and structural proteins. PD1's have also evolved novel cellular redox functions, as single enzymes and as subunits of protein complexes in organelles. We provide evidence that at least one Pill is localized to the chloroplast. We have used PDI-specific polyclonal and monoclonal antisera to characterize the PD1 (55 kDa) in the chloroplast that is unevenly distributed between the stroma and pellet (containing membranes, DNA, polysomes, starch), being three-fold more abundant in the pellet phase. PD1-55 levels increase with light intensity and it assembles into a high molecular weight complex of ~230 kDa as determined on native blue gels. In vitro translation of all 11 different Pill's followed by microsomal membrane processing reactions were used to differentiate among PD1's localized in the endoplasmic reticulum or other organelles. These results will provide.1e insights into redox regulatory mechanisms involved in adaptation of the photosynthetic apparatus to light stress. Elucidating the genetic mechanisms and factors regulating chloroplast photosynthetic genes is important for developing strategies to improve photosynthetic efficiency, crop productivity and adaptation to high light environments.
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Bays, John, Amity Andersen, Jonathan Egbert, John Linehan et Richard Overstreet. Elucidation of the Reaction Mechanisms of Autooxidative Processes in Complex Condensed-Phase Mixtures. Office of Scientific and Technical Information (OSTI), novembre 2020. http://dx.doi.org/10.2172/1985293.

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Wicker, Louise, Ilan Shomer et Uzi Merin. Membrane Processing of Citrus Extracts : Effects on Pectinesterase Activity and Cloud Stability. United States Department of Agriculture, octobre 1993. http://dx.doi.org/10.32747/1993.7568754.bard.

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The U.S. team studied the role of cations and pH on thermolabile (TL-PE) and thermostable (TS-PE), permeation in ultrafiltration (UF) membranes, affinity to ion exchange membranes, mechanism of cation and pH activation, and effect on PE stability. An optimum pH and cation concentration exists for activity and UF permeation, which is specific for each cation type. Incomplete release of PE from a pectin complex resulted in low PE binding to cationic and anionic membranes. Incubation of PE at low pH increases the surface hydrophobicity, especially TL-PE, but the secondary structure of TL-PE is not greatly affected. The Israeli team showed that stable cloud colloidal constituents flocculate following the conversion of soluble to insoluble biopolymers. First, formation of pectic acid by pectinesterase activity is followed by the formation of calcium pectate gel. This process initiates a myriad of poorly defined reactions that result in juice clarification. Second, protein coagulation by heat resulted in flocculation of proteinacous bound cloud constituents, particularly after enzymatic pectin degradation. Pectinesterase activity is proposed to be an indirect cause for clarification; whereas binding of cloud constituents is the primary event in clarification by pectate gel and coagulated proteins. Understanding the mechanism of interaction of protein and pectic polymers is key to understanding cloud instability. Based on the above, it was hypothesized that the structure of pectin-protein coagulates plays a key role in cloud instability.
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Kelley, D. Kinetics and mechanisms of the reactions of alkyl radicals with oxygen and with complexes of Co(III), Ru(III), and Ni(III). Office of Scientific and Technical Information (OSTI), octobre 1990. http://dx.doi.org/10.2172/6454295.

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Wallace, Kevin C., Andy H. Liu, John C. Dewan et Richard R. Schrock. Preparation and Reactions of Tantalum Alkylidene Complexes Containing Bulky Phenoxide or Thiolate Ligands. Controlling Ring-Opening Metathesis Polymerization Activity and Mechanism Through Choice of Anionic Ligand. Fort Belvoir, VA : Defense Technical Information Center, juillet 1988. http://dx.doi.org/10.21236/ada198293.

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Morrison, Mark, et Joshuah Miron. Molecular-Based Analysis of Cellulose Binding Proteins Involved with Adherence to Cellulose by Ruminococcus albus. United States Department of Agriculture, novembre 2000. http://dx.doi.org/10.32747/2000.7695844.bard.

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At the beginning of this project, it was clear that R. albus adhered tightly to cellulose and its efficient degradation of this polysaccharide was dependent on micromolar concentrations of phenylacetic acid (PAA) and phenylpropionic acid (PPA). The objectives for our research were: i) to identify how many different kinds of cellulose binding proteins are produced by Ruminococcus albus; ii) to isolate and clone the genes encoding some of these proteins from the same bacterium; iii) to determine where these various proteins were located and; iv) quantify the relative importance of these proteins in affecting the rate and extent to which the bacterium becomes attached to cellulose. BARD support has facilitated a number of breakthroughs relevant to our fundamental understanding of the adhesion process. First, R. albus possesses multiple mechanisms for adhesion to cellulose. The P.I.'s laboratory has discovered a novel cellulose-binding protein (CbpC) that belongs to the Pil-protein family, and in particular, the type 4 fimbrial proteins. We have also obtained genetic and biochemical evidence demonstrating that, in addition to CbpC-mediated adhesion, R. albus also produces a cellulosome-like complex for adhesion. These breakthroughs resulted from the isolation (in Israel and the US) of spontaneously arising mutants of R. albus strains SY3 and 8, which were completely or partially defective in adhesion to cellulose, respectively. While the SY3 mutant strain was incapable of growth with cellulose as the sole carbon source, the strain 8 mutants showed varying abilities to degrade and grow with cellulose. Biochemical and gene cloning experiments have been used in Israel and the US, respectively, to identify what are believed to be key components of a cellulosome. This combination of cellulose adhesion mechanisms has not been identified previously in any bacterium. Second, differential display, reverse transcription polymerase chain reaction (DD RT-PCR) has been developed for use with R. albus. A major limitation to cellulose research has been the intractability of cellulolytic bacteria to genetic manipulation by techniques such as transposon mutagenesis and gene displacement. The P.I.'s successfully developed DD RT- PCR, which expanded the scope of our research beyond the original objectives of the project, and a subset of the transcripts conditionally expressed in response to PAA and PPA have been identified and characterized. Third, proteins immunochemically related to the CbpC protein of R. albus 8 are present in other R. albus strains and F. intestinalis, Western immunoblots have been used to examine additional strains of R. albus, as well as other cellulolytic bacteria of ruminant origin, for production of proteins immunochemically related to the CbpC protein. The results of these experiments showed that R. albus strains SY3, 7 and B199 all possess a protein of ~25 kDa which cross-reacts with polyclonal anti-CbpC antiserum. Several strains of Butyrivibrio fibrisolvens, Ruminococcus flavefaciens strains C- 94 and FD-1, and Fibrobacter succinogenes S85 produced no proteins that cross-react with the same antiserum. Surprisingly though, F. intestinalis strain DR7 does possess a protein(s) of relatively large molecular mass (~200 kDa) that was strongly cross-reactive with the anti- CbpC antiserum. Scientifically, our studies have helped expand the scope of our fundamental understanding of adhesion mechanisms in cellulose-degrading bacteria, and validated the use of RNA-based techniques to examine physiological responses in bacteria that are nor amenable to genetic manipulations. Because efficient fiber hydrolysis by many anaerobic bacteria requires both tight adhesion to substrate and a stable cellulosome, we believe our findings are also the first step in providing the resources needed to achieve our long-term goal of increasing fiber digestibility in animals.
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Kanner, Joseph, Edwin Frankel, Stella Harel et Bruce German. Grapes, Wines and By-products as Potential Sources of Antioxidants. United States Department of Agriculture, janvier 1995. http://dx.doi.org/10.32747/1995.7568767.bard.

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Several grape varieties and red wines were found to contain large concentration of phenolic compounds which work as antioxidant in-vitro and in-vivo. Wastes from wine production contain antioxidants in large amounts, between 2-6% on dry material basis. Red wines but also white wines were found to prevent lipid peroxidation of turkey muscle tissues stored at 5oC. The antioxidant reaction of flavonoids found in red wines against lipid peroxidation were found to depend on the structure of the molecule. Red wine flavonoids containing an orthodihydroxy structure around the B ring were found highly active against LDL and membrane lipid peroxidation. The antioxidant activity of red wine polyphenols were also found to be dependent on the catalyzer used. In the presence of H2O2-activated myoglobin, the inhibition efficiency was malvidin 3-glucoside>catechin>malvidin>resveratol. However, in the presence of an iron redox cycle catalyzer, the order of effectiveness was resveratol>malvidin 3-glucoside = malvidin>catechin. Differences in protein binding were found to affect antioxidant activity in inhibiting LDL oxidation. A model protein such as BSA, was investigated on the antioxidant activity of phenolic compounds, grape extracts, and red wines in a lecithin-liposome model system. Ferulic acid followed by malvidin and rutin were the most efficient in inhibiting both lipid and protein oxidation. Catechin, a flavonal found in red-wines in relatively high concentration was found to inhibit myoglobin catalyzed linoleate membrane lipid peroxidation at a relatively very low concentration. This effect was studied by the determination of the by-products generated from linoleate during oxidation. The study showed that hydroperoxides are catalytically broken down, not to an alcohol but most probably to a non-radical adduct. The ability of wine-phenolics to reduce iron and from complexes with metals were also demonstrated. Low concentration of wine phenolics were found to inhibit lipoxygenase type II activity. An attempt to understand the bioavailability in humans of antocyanins from red wine showed that two antocyanins from red wine were found unchanged in human urine. Other antocyanins seems to undergo molecular modification. In hypercholesterolemic hamsters, aortic lipid deposition was significantly less in animals fed diets supplemented with either catechin or vitamin E. The rate of LDL accumulation in the carotid arteries was also significantly lower in the catechin and vitamin E animal groups. These results suggested a novel mechanism by which wine phenolics are associated with decreased risk of coronary heart diseases. This study proves in part our hypothesis that the "French Paradox" could be explained by the action of the antioxidant effects of phenolic compounds found at high concentration in red wines. The results of this study argue that it is in the interest of public health to increase the consumption of dietary plant falvonoids. Our results and these from others, show that the consumption of red wine or plant derived polyphenolics can change the antioxidant tone of animal and human plasma and its isolated components towards oxidative reactions. However, we need more research to better understand bioavailability and the mechanism of how polyphenolics affect health and disease.
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Steffens, John C., et Eithan Harel. Polyphenol Oxidases- Expression, Assembly and Function. United States Department of Agriculture, janvier 1995. http://dx.doi.org/10.32747/1995.7571358.bard.

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Polyphenol oxidases (PPOs) participate in the preparation of many plant products on the one hand and cause considerable losses during processing of plant products on the other hand. However, the physiological functions of plant PPO were still a subject of controversy at the onset of the project. Preliminary observations that suggested involvement of PPOs in resistance to herbivores and pathogens held great promise for application in agriculture but required elucidation of PPO's function if modulation of PPO expression is to be considered for improving plant protection or storage and processing of plant products. Suggestions on a possible role of PPO in various aspects of chloroplast metabolism were also relevant in this context. The characterization of plant PPO genes opened a way for achieving these goals. We reasoned that "understanding PPO targeting and routing, designing ways to manipulate its expression and assessing the effects of such modifications will enable determination of the true properties of the enzyme and open the way for controlling its activity". The objective of the project was to "obtain an insight into the function and biological significance of PPOs" by examining possible function(s) of PPO in photosynthesis and plant-pest interactions using transgenic tomato plants; extending our understanding of PPO routing and assembly and the mechanism of its thylakoid translocation; preparing recombinant PPOs for use in import studies, determination of the genuine properties of PPOs and understanding its assembly and determining the effect of PPO's absence on chloroplast performance. Results obtained during work on the project made it necessary to abandon some minor objectives and devote the effort to more promising topics. Such changes are mentioned in the 'Body of the report' which is arranged according to the objectives of the original proposal. The complex expression pattern of tomato PPO gene family was determined. Individual members of the family are differentially expressed in various parts of the plant and subjected to developmentally regulated turnover. Some members are differentially regulated also by pathogens, wounding and chemical wound signals. Wounding systemically induces PPO activity and level in potato. Only tissues that are developmentally competent to express PPO are capable of responding to the systemic wounding signal by increased accumulation of PPO mRNA. Down regulation of PPO genes causes hyper susceptibility to leaf pathogens in tomato while over expression regulation of PPO expression in tomato plants is their apparent increased tolerance to drought. Both the enhanced disease resistance conferred by PPO over expression and the increased stress tolerance due to down regulation can be used in the engineering of improved crop plants. Photosynthesis rate and variable fluorescence measurements in wild type, and PPO-null and over expressing transgenic tomato lines suggest that PPO does not enable plants to cope better with stressful high light intensities or reactive oxygen species. Rather high levels of the enzyme aggravate the damage caused under such conditions. Our work suggests that PPO's primary role is in defending plants against pathogens and herbivores. Jasmonate and ethylene, and apparently also salicylate, signals involved in responses to wounding and defense against herbivores and pathogens, enhance markedly and specifically the competence of chloroplasts to import and process pPPO. The interaction of the precursor with thylakoid membranes is primarily affected. The routing of PPO shows other unusual properties: stromal processing occurs in two sites, resulting in intermediates that are translocated across thylakoids by two different mechanisms - a DpH- and a Sec-dependent one. It is suggested that the dual pattern of processing and routing constitutes a'fail safe' mechanism, reflecting the need for a rapid and flexible response to defense challenges. Many of the observations described above should be taken into consideration when manipulation of PPO expression is contemplated for use in crop improvement.
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Kirchhoff, Helmut, et Ziv Reich. Protection of the photosynthetic apparatus during desiccation in resurrection plants. United States Department of Agriculture, février 2014. http://dx.doi.org/10.32747/2014.7699861.bard.

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In this project, we studied the photosynthetic apparatus during dehydration and rehydration of the homoiochlorophyllous resurrection plant Craterostigmapumilum (retains most of the photosynthetic components during desiccation). Resurrection plants have the remarkable capability to withstand desiccation, being able to revive after prolonged severe water deficit in a few days upon rehydration. Homoiochlorophyllous resurrection plants are very efficient in protecting the photosynthetic machinery against damage by reactive oxygen production under drought. The main purpose of this BARD project was to unravel these largely unknown protection strategies for C. pumilum. In detail, the specific objectives were: (1) To determine the distribution and local organization of photosynthetic protein complexes and formation of inverted hexagonal phases within the thylakoid membranes at different dehydration/rehydration states. (2) To determine the 3D structure and characterize the geometry, topology, and mechanics of the thylakoid network at the different states. (3) Generation of molecular models for thylakoids at the different states and study the implications for diffusion within the thylakoid lumen. (4) Characterization of inter-system electron transport, quantum efficiencies, photosystem antenna sizes and distribution, NPQ, and photoinhibition at different hydration states. (5) Measuring the partition of photosynthetic reducing equivalents between the Calvin cycle, photorespiration, and the water-water cycle. At the beginning of the project, we decided to use C. pumilum instead of C. wilmsii because the former species was available from our collaborator Dr. Farrant. In addition to the original two dehydration states (40 relative water content=RWC and 5% RWC), we characterized a third state (15-20%) because some interesting changes occurs at this RWC. Furthermore, it was not possible to detect D1 protein levels by Western blot analysis because antibodies against other higher plants failed to detect D1 in C. pumilum. We developed growth conditions that allow reproducible generation of different dehydration and rehydration states for C. pumilum. Furthermore, advanced spectroscopy and microscopy for C. pumilum were established to obtain a detailed picture of structural and functional changes of the photosynthetic apparatus in different hydrated states. Main findings of our study are: 1. Anthocyan accumulation during desiccation alleviates the light pressure within the leaves (Fig. 1). 2. During desiccation, stomatal closure leads to drastic reductions in CO2 fixation and photorespiration. We could not identify alternative electron sinks as a solution to reduce ROS production. 3. On the supramolecular level, semicrystalline protein arrays were identified in thylakoid membranes in the desiccated state (see Fig. 3). On the electron transport level, a specific series of shut downs occur (summarized in Fig. 2). The main events include: Early shutdown of the ATPase activity, cessation of electron transport between cyt. bf complex and PSI (can reduce ROS formation at PSI); at higher dehydration levels uncoupling of LHCII from PSII and cessation of electron flow from PSII accompanied by crystal formation. The later could severe as a swift PSII reservoir during rehydration. The specific order of events in the course of dehydration and rehydration discovered in this project is indicative for regulated structural transitions specifically realized in resurrection plants. This detailed knowledge can serve as an interesting starting point for rationale genetic engineering of drought-tolerant crops.
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