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Sample records for 4alpha reaction mechanism

  1. Reaction mechanisms

    The 1988 progress report of the Reaction Mechanisms laboratory (Polytechnic School, France), is presented. The research topics are: the valence bond methods, the radical chemistry, the modelling of the transition states by applying geometric constraints, the long range interactions (ion - molecule) in gaseous phase, the reaction sites in gaseous phase and the mass spectroscopy applications. The points of convergence between the investigations of the mass spectroscopy and the theoretical chemistry teams, as well as the purposes guiding the research programs, are discussed. The published papers, the conferences, the congress communications and the thesis, are also reported

  2. Direct mechanism in solar nuclear reactions

    Oberhummer, H; Staudt, G.

    1994-01-01

    A short overview of the direct reaction mechanism and the models used for the analysis of such processes is given. Nuclear reactions proceeding through the direct mechanism and involved in solar hydrogen burning are discussed. The significance of these nuclear reactions with respect to the solar neutrino problem is investigated.

  3. Is EC class predictable from reaction mechanism?

    Nath Neetika; Mitchell John BO

    2012-01-01

    We thank the Scottish Universities Life Sciences Alliance (SULSA) and the Scottish Overseas Research Student Awards Scheme of the Scottish Funding Council (SFC) for financial support. Background: We investigate the relationships between the EC (Enzyme Commission) class, the associated chemical reaction, and the reaction mechanism by building predictive models using Support Vector Machine (SVM), Random Forest (RF) and k-Nearest Neighbours (kNN). We consider two ways of encoding the reaction...

  4. Heuristics-Guided Exploration of Reaction Mechanisms

    Bergeler, Maike; Proppe, Jonny; Reiher, Markus

    2015-01-01

    For the investigation of chemical reaction networks, the efficient and accurate determination of all relevant intermediates and elementary reactions is inevitable. The complexity of such a network may grow rapidly, in particular if reactive species are involved that might cause a myriad of side reactions. Without automation, a complete investigation of complex reaction mechanisms is tedious and possibly unfeasible. Therefore, only the expected dominant reaction paths of a chemical reaction network (e.g., a catalytic cycle or an enzymatic cascade) are usually explored in practice. Here, we present a computational protocol that constructs such networks in a parallelized and automated manner. Molecular structures of reactive complexes are generated based on heuristic rules and subsequently optimized by electronic-structure methods. Pairs of reactive complexes related by an elementary reaction are then automatically detected and subjected to an automated search for the connecting transition state. The results are...

  5. Reaction mechanism of -acylhydroxamate with cysteine proteases

    R Shankar; P Kolandaivel

    2007-09-01

    The gas-phase reaction mechanism of -acylhydroxamate with cysteine proteases has been investigated using ab initio and density functional theory. On the irreversible process, after breakdown of tetrahedral intermediate (INT1), small 1-2 anionotropic has been formed and rearranged to give stable by-products sulfenamide (P1) and thiocarbamate (P2) with considerable energy loss. While, on the reversible part of this reaction mechanism, intermediate (INT2) breaks down on oxidation, to form a stable product (P3). Topological and AIM analyses have been performed for hydrogen bonded complex in this reaction profile. Intrinsic reaction coordinates [IRC, minimum-energy path (MEP)] calculation connects the transition state between R-INT1, INT1-P1 and INT1-P2. The products P1, P2 and P3 are energetically more stable than the reactant and hence the reaction enthalpy is found to be exothermic.

  6. Is EC class predictable from reaction mechanism?

    2012-01-01

    Background We investigate the relationships between the EC (Enzyme Commission) class, the associated chemical reaction, and the reaction mechanism by building predictive models using Support Vector Machine (SVM), Random Forest (RF) and k-Nearest Neighbours (kNN). We consider two ways of encoding the reaction mechanism in descriptors, and also three approaches that encode only the overall chemical reaction. Both cross-validation and also an external test set are used. Results The three descriptor sets encoding overall chemical transformation perform better than the two descriptions of mechanism. SVM and RF models perform comparably well; kNN is less successful. Oxidoreductases and hydrolases are relatively well predicted by all types of descriptor; isomerases are well predicted by overall reaction descriptors but not by mechanistic ones. Conclusions Our results suggest that pairs of similar enzyme reactions tend to proceed by different mechanisms. Oxidoreductases, hydrolases, and to some extent isomerases and ligases, have clear chemical signatures, making them easier to predict than transferases and lyases. We find evidence that isomerases as a class are notably mechanistically diverse and that their one shared property, of substrate and product being isomers, can arise in various unrelated ways. The performance of the different machine learning algorithms is in line with many cheminformatics applications, with SVM and RF being roughly equally effective. kNN is less successful, given the role that non-local information plays in successful classification. We note also that, despite a lack of clarity in the literature, EC number prediction is not a single problem; the challenge of predicting protein function from available sequence data is quite different from assigning an EC classification from a cheminformatics representation of a reaction. PMID:22530800

  7. Is EC class predictable from reaction mechanism?

    Nath Neetika

    2012-04-01

    Full Text Available Abstract Background We investigate the relationships between the EC (Enzyme Commission class, the associated chemical reaction, and the reaction mechanism by building predictive models using Support Vector Machine (SVM, Random Forest (RF and k-Nearest Neighbours (kNN. We consider two ways of encoding the reaction mechanism in descriptors, and also three approaches that encode only the overall chemical reaction. Both cross-validation and also an external test set are used. Results The three descriptor sets encoding overall chemical transformation perform better than the two descriptions of mechanism. SVM and RF models perform comparably well; kNN is less successful. Oxidoreductases and hydrolases are relatively well predicted by all types of descriptor; isomerases are well predicted by overall reaction descriptors but not by mechanistic ones. Conclusions Our results suggest that pairs of similar enzyme reactions tend to proceed by different mechanisms. Oxidoreductases, hydrolases, and to some extent isomerases and ligases, have clear chemical signatures, making them easier to predict than transferases and lyases. We find evidence that isomerases as a class are notably mechanistically diverse and that their one shared property, of substrate and product being isomers, can arise in various unrelated ways. The performance of the different machine learning algorithms is in line with many cheminformatics applications, with SVM and RF being roughly equally effective. kNN is less successful, given the role that non-local information plays in successful classification. We note also that, despite a lack of clarity in the literature, EC number prediction is not a single problem; the challenge of predicting protein function from available sequence data is quite different from assigning an EC classification from a cheminformatics representation of a reaction.

  8. Reaction Mechanism Generator: Automatic construction of chemical kinetic mechanisms

    Gao, Connie W.; Allen, Joshua W.; Green, William H.; West, Richard H.

    2016-06-01

    Reaction Mechanism Generator (RMG) constructs kinetic models composed of elementary chemical reaction steps using a general understanding of how molecules react. Species thermochemistry is estimated through Benson group additivity and reaction rate coefficients are estimated using a database of known rate rules and reaction templates. At its core, RMG relies on two fundamental data structures: graphs and trees. Graphs are used to represent chemical structures, and trees are used to represent thermodynamic and kinetic data. Models are generated using a rate-based algorithm which excludes species from the model based on reaction fluxes. RMG can generate reaction mechanisms for species involving carbon, hydrogen, oxygen, sulfur, and nitrogen. It also has capabilities for estimating transport and solvation properties, and it automatically computes pressure-dependent rate coefficients and identifies chemically-activated reaction paths. RMG is an object-oriented program written in Python, which provides a stable, robust programming architecture for developing an extensible and modular code base with a large suite of unit tests. Computationally intensive functions are cythonized for speed improvements.

  9. Reaction mechanisms in heavy ion fusion

    Lubian J.

    2011-10-01

    Full Text Available We discuss the reaction mechanisms involved in heavy ion fusion. We begin with collisions of tightly bound systems, considering three energy regimes: energies above the Coulomb barrier, energies just below the barrier and deep sub-barrier energies. We show that channel coupling effects may influence the fusion process at above-barrier energies, increasing or reducing the cross section predicted by single barrier penetration model. Below the Coulomb barrier, it enhances the cross section, and this effect increases with the system’s size. It is argued that this behavior can be traced back to the increasing importance of Coulomb coupling with the charge of the collision partners. The sharp drop of the fusion cross section observed at deep sub-barrier energies is addressed and the theoretical approaches to this phenomenon are discussed. We then consider the reaction mechanisms involved in fusion reactions of weakly bound systems, paying particular attention to the calculations of complete and incomplete fusion available in the literature.

  10. New methods for quantum mechanical reaction dynamics

    Quantum mechanical methods are developed to describe the dynamics of bimolecular chemical reactions. We focus on developing approaches for directly calculating the desired quantity of interest. Methods for the calculation of single matrix elements of the scattering matrix (S-matrix) and initial state-selected reaction probabilities are presented. This is accomplished by the use of absorbing boundary conditions (ABC) to obtain a localized (L2) representation of the outgoing wave scattering Green's function. This approach enables the efficient calculation of only a single column of the S-matrix with a proportionate savings in effort over the calculation of the entire S-matrix. Applying this method to the calculation of the initial (or final) state-selected reaction probability, a more averaged quantity, requires even less effort than the state-to-state S-matrix elements. It is shown how the same representation of the Green's function can be effectively applied to the calculation of negative ion photodetachment intensities. Photodetachment spectroscopy of the anion ABC- can be a very useful method for obtaining detailed information about the neutral ABC potential energy surface, particularly if the ABC- geometry is similar to the transition state of the neutral ABC. Total and arrangement-selected photodetachment spectra are calculated for the H3O- system, providing information about the potential energy surface for the OH + H2 reaction when compared with experimental results. Finally, we present methods for the direct calculation of the thermal rate constant from the flux-position and flux-flux correlation functions. The spirit of transition state theory is invoked by concentrating on the short time dynamics in the area around the transition state that determine reactivity. These methods are made efficient by evaluating the required quantum mechanical trace in the basis of eigenstates of the Boltzmannized flux operator

  11. Angular correlation measurements for 4-{alpha} decaying states in {sup 16}O

    Wuosmaa, A.H.; Back, B.B.; Betts, R.R. [and others

    1995-08-01

    Previous measurements of the {sup 12}C({sup 12}C,{sup 8}Be){sup 16}O{sup *}(4 {alpha}) reaction identified discrete levels in {sup 16}O which decay by breakup into 4 {alpha} particles through a number of different decay sequences, including {sup 16}O{sup *} {yields} {sup 8}Be + {sup 8}Be and {alpha} + {sup 12}C (O{sub 2}{sup +}). These states are observed in a range of excitation energies where resonances are observed in inelastic {alpha} + {sup 12}C scattering leading to the {sup 8}Be + {sup 8}Be and {alpha} + {sup 12}C final states. These resonances were associated with 4 {alpha}-particle chain configurations in {sup 16}O. Should the states populated in the {sup 12}C + {sup 12}C reaction possess this same extended structure, it would serve as an important piece of evidence supporting the idea that even more deformed structures are formed in the {sup 24}Mg compound system. In order to more firmly make this association, it is important to determine the spins of the states populated in the {sup 12}C + {sup 12}C reaction.

  12. Knockout Reaction Mechanism for 6He+%Knockout Reaction Mechanism for 6He+

    吕林辉; 叶沿林; 曹中鑫; 肖军; 江栋兴; 郑涛; 华辉; 李智焕; 葛俞成; 李湘庆; 楼建玲; 李阔昂; 李奇特; 乔锐; 游海波; 陈瑞九

    2012-01-01

    A knockout reaction experiment was carried out by using the 6He beam at 82.5 MeV/nucleon impinging on CH2 and C targets. The a core fragments at forward angles were detected in coincidence with the recoiled protons at larger angles. From this exclusive measure- ment the valence nucleon knockout mechanism and the core knockout mechanism are separated. This study provides a basis for the exclusive spectroscopic investigation of the exotic nuclei.

  13. [Reaction mechanism studies of heavy ion induced nuclear reactions

    This report contains papers that discuss: Target Dependence of Complex Fragment Emission in 47-MeV/u La-Induced Reactions; Deconvolution of Time-of-Flight Data to Improve Mass Identification; and Study of the Reaction of La + Al at E/A = 50 MeV with Landau-Vlasov Dynamics

  14. Computerized approaches to enhance understanding of organic reaction mechanisms: CAN reaction mechanisms and CPLEX prelaboratory methodology

    Al-Shammari, Abdulrahman G. Alhamzani

    2008-10-01

    Two approaches to enhance the understanding of organic reaction mechanisms are described. First, a new method for teaching organic reaction mechanisms that can be used in a Computer-Assisted Instruction (CAI) environment is proposed and tested (Chapter 1). The method concentrates upon the important intermediate structures, which are assumed to be on the reaction coordinate, and which can be evaluated and graded by currently available computer techniques. At the same time, the "curved arrows" that show the electron flow in a reaction mechanism are neglected, since they cannot be evaluated and graded with currently available computer techniques. By allowing student practice for learning organic reaction mechanisms using the Curved Arrow Neglect (CAN) method within a "Practice Makes Perfect" CAI method, student performance in the drawing of traditional reaction mechanisms, in which students had to include the "curved arrows" on their written classroom exams, was significantly enhanced. Second, computerized prelaboratory experiments (CPLEX) for organic chemistry laboratory 1 & 2 courses have been created, used, and evaluated (Chapters 2 and 3). These computerized prelabs are unique because they combine both "dry lab" actions with detailed animations of the actual chemistry occurring at the molecular level. The "dry lab" serves to simulate the actual physical manipulations of equipment and chemicals that occur in the laboratory experiment through the use of drag-and-drop computer technology. At the same time, these physical actions are accompanied on a separate part of the computer screen by animations showing the chemistry at the molecular level that is occurring in the experiment. These CPLEX modules were made into Internet accessible modules. The students were allowed to access the CPLEX modules prior to performing the actual laboratory experiment. A detailed evaluation of students' perception of the modules was accomplished via survey methodology during the entire

  15. Carbonitriding reactions of diatomaceous earth: phase evolution and reaction mechanisms

    BRANKO MATOVIC

    2006-06-01

    Full Text Available The possibility of using diatomaceous earth as Si precursor for low temperature synthesis of non-oxide powders by carbothermal reduction-nitridation was studied. It was found that carbonitriding reactions produce phases of the Si–Al–O–N system. Already at 1300 °C, nanosized, non-oxide powders were obtained. The comparatively low reaction temperatures is attributred to the nano-porous nature of the raw material. The evolution of crystalline phases proceeded via many intermediate stages. The powders were characterized by X-ray and SEM investigations. The results showed that diatomaceous earth can be a very effective source for obtaining non-oxide powders.

  16. Reaction mechanism of dicofol removal by cellulase.

    Wang, Ziyuan; Yang, Ting; Zhai, Zihan; Zhang, Boya; Zhang, Jianbo

    2015-10-01

    It remains unclear whether dicofol should be defined as a persistent organic pollutant. Its environmental persistence has gained attention. This study focused on its degradation by cellulase. Cellulase was separated using a gel chromatogram, and its degradation activity towards dicofol involved its endoglucanase activity. By analyzing the kinetic parameters of cellulase reacting with mixed substrates, it was shown that cellulase reacted on dicofol and carboxyl methyl cellulose through two different active centers. Thus, the degradation of dicofol was shown to be an oxidative process by cellulase. Next, by comparing the impacts of tert-butyl alcohol (a typical OH free-radical inhibitor) on the removal efficiencies of dicofol under both cellulase and Fenton reagent systems, it was shown that the removal of dicofol was initiated by OH free radicals produced by cellulase. Finally, 4,4'-dichloro-dibenzophenone and chloride were detected using gas chromatography mass spectrometry and ion chromatography analysis, which supported our hypothesis. The reaction mechanism was analyzed and involved an attack by OH free radicals at the orthocarbon of dicofol, resulting in the degradation product 4,4'-dichloro-dibenzophenone. PMID:26456602

  17. The Blue Bottle Reaction as a General Chemistry Experiment on Reaction Mechanisms

    Engerer, Steven C.; Cook, A. Gilbert

    1999-11-01

    A kinetics/reaction mechanism experiment using the classic blue bottle reaction is described. Using the scientific method (observe, question, hypothesize, experiment, repeat) students propose and test possible reaction mechanisms for the methylene blue-catalyzed oxidation of dextrose with its dramatic color change. Students are led to discover the three-step mechanism through a series of questions. An advanced version for honors lab courses is also suggested.

  18. Deducing Reaction Mechanism: A Guide for Students, Researchers, and Instructors

    Meek, Simon J.; Pitman, Catherine L.; Miller, Alexander J. M.

    2016-01-01

    An introductory guide to deducing the mechanism of chemical reactions is presented. Following a typical workflow for probing reaction mechanism, the guide introduces a wide range of kinetic and mechanistic tools. In addition to serving as a broad introduction to mechanistic analysis for students and researchers, the guide has also been used by…

  19. Molecular analysis of a Clostridium butyricum NCIMB 7423 gene encoding 4-alpha-glucanotransferase and characterization of the recombinant enzyme produced in Escherichia coli.

    Goda, S K; Eissa, O; Akhtar, M; Minton, N P

    1997-10-01

    An Escherichia coli clone was detected in a Clostridium butyricum NCIMB 7423 plasmid library capable of degrading soluble amylose. Deletion subcloning of its recombinant plasmid indicated that the gene(s) responsible for amylose degradation was localized on a 1.8 kb NspHI-Scal fragment. This region was sequenced in its entirety and shown to encompass a large ORF capable of encoding a protein with a calculated molecular mass of 57,184 Da. Although the deduced amino acid sequence showed only weak similarity with known amylases, significant sequences identity was apparent with the 4-alpha-glucano-transferase enzymes of Streptococcus pneumoniae (46.9%), potato (42.9%) and E. coli (16.2%). The clostridial gene (designated maIQ) was followed by a second ORF which, through its homology to the equivalent enzymes of E. coli and S. pneumoniae, was deduced to encode maltodextrin phosphorylase (MaIP). The translation stop codon of MaIQ overlapped the translation start codon of the putative maIP gene, suggesting that the two genes may be both transcriptionally and translationally coupled. 4-alpha-Glucanotransferase catalyses a disproportionation reaction in which single or multiple glucose units from oligosaccharides are transferred to the 4-hydroxyl group of acceptor sugars. Characterization of the recombinant C. butyricum enzyme demonstrated that glucose, maltose and maltotriose could act as acceptor, whereas of the three only maltotriose could act as donor. The enzyme therefore shares properties with the E. coli MaIQ protein, but differs significantly from the glucanotransferase of Thermotoga maritima, which is unable to use maltotriose as donor or glucose as acceptor. Physiologically, the concerted action of 4-alpha-glucanotransferase and maltodextrin phosphorylase provides C. butyricum with a mechanism of utilizing amylose/maltodextrins with little drain on cellular ATP reserves. PMID:9353929

  20. Overview of ALD Precursors and Reaction Mechanisms

    Gordon, Roy Gerald

    2011-01-01

    Successful use of ALD requires suitable chemical precursors used under reaction conditions that are appropriate for them. There are many requirements for ALD precursors: sufficient volatility, thermal stability and reactivity with substrates and with the films being deposited. In addition, it is easier to produce the required vapors if the precursor is liquid at room temperature, or if it is a solid with melting point below the vaporization temperature, or if it is soluble in an inert solvent...

  1. Chemical kinetic reaction mechanism for the combustion of propane

    Jachimowski, C. J.

    1984-01-01

    A detailed chemical kinetic reaction mechanism for the combustion of propane is presented and discussed. The mechanism consists of 27 chemical species and 83 elementary chemical reactions. Ignition and combustion data as determined in shock tube studies were used to evaluate the mechanism. Numerical simulation of the shock tube experiments showed that the kinetic behavior predicted by the mechanism for stoichiometric mixtures is in good agrement with the experimental results over the entire temperature range examined (1150-2600K). Sensitivity and theoretical studies carried out using the mechanism revealed that hydrocarbon reactions which are involved in the formation of the HO2 radical and the H2O2 molecule are very important in the mechanism and that the observed nonlinear behavior of ignition delay time with decreasing temperature can be interpreted in terms of the increased importance of the HO2 and H2O2 reactions at the lower temperatures.

  2. A thermochemically derived global reaction mechanism for detonation application

    Zhu, Y.; Yang, J.; Sun, M.

    2012-07-01

    A 4-species 4-step global reaction mechanism for detonation calculations is derived from detailed chemistry through thermochemical approach. Reaction species involved in the mechanism and their corresponding molecular weight and enthalpy data are derived from the real equilibrium properties. By substituting these global species into the results of constant volume explosion and examining the evolution process of these global species under varied conditions, reaction paths and corresponding rates are summarized and formulated. The proposed mechanism is first validated to the original chemistry through calculations of the CJ detonation wave, adiabatic constant volume explosion, and the steady reaction structure after a strong shock wave. Good agreement in both reaction scales and averaged thermodynamic properties has been achieved. Two sets of reaction rates based on different detailed chemistry are then examined and applied for numerical simulations of two-dimensional cellular detonations. Preliminary results and a brief comparison between the two mechanisms are presented. The proposed global mechanism is found to be economic in computation and also competent in description of the overall characteristics of detonation wave. Though only stoichiometric acetylene-oxygen mixture is investigated in this study, the method to derive such a global reaction mechanism possesses a certain generality for premixed reactions of most lean hydrocarbon mixtures.

  3. Reaction Mechanism of Mycobacterium Tuberculosis Glutamine Synthetase Using Quantum Mechanics/Molecular Mechanics Calculations.

    Moreira, Cátia; Ramos, Maria J; Fernandes, Pedro Alexandrino

    2016-06-27

    This paper is devoted to the understanding of the reaction mechanism of mycobacterium tuberculosis glutamine synthetase (mtGS) with atomic detail, using computational quantum mechanics/molecular mechanics (QM/MM) methods at the ONIOM M06-D3/6-311++G(2d,2p):ff99SB//B3LYP/6-31G(d):ff99SB level of theory. The complete reaction undergoes a three-step mechanism: the spontaneous transfer of phosphate from ATP to glutamate upon ammonium binding (ammonium quickly loses a proton to Asp54), the attack of ammonia on phosphorylated glutamate (yielding protonated glutamine), and the deprotonation of glutamine by the leaving phosphate. This exothermic reaction has an activation free energy of 21.5 kcal mol(-1) , which is consistent with that described for Escherichia coli glutamine synthetase (15-17 kcal mol(-1) ). The participating active site residues have been identified and their role and energy contributions clarified. This study provides an insightful atomic description of the biosynthetic reaction that takes place in this enzyme, opening doors for more accurate studies for developing new anti-tuberculosis therapies. PMID:27225077

  4. Sugarcane bagasse gasification: Global reaction mechanism of syngas evolution

    Highlights: ► Gasification of sugarcane bagasse has been investigated using a semi batch reactor. ► Global reaction mechanism combining pyrolysis and gasification reactions is presented. ► High flow rates of syngas supported fragmentation and secondary reactions. ► CO flow rate increased at higher heating rates at the expense of CO2 production. ► At high temperatures merger between pyrolysis and char gasification occurs. -- Abstract: Steam gasification of sugarcane bagasse has been investigated. A semi batch reactor with a fixed amount of sugarcane bagasse sample placed in steady flow of high temperature steam at atmospheric pressure has been used. The gasification of bagasse was examined at reactor and steam temperatures of 800, 900 and 1000 °C. The evolution of syngas flow rate and chemical composition has been monitored. The evolution of chemical composition and total flow rate of the syngas has been used to formulate a global reaction mechanism. The mechanism combines pyrolysis reaction mechanisms from the literature and steam gasification/reforming reactions. Steam gasification steps include steam–hydrocarbons reforming, char gasification and water gas shift reactions. Evidence of fragmentation, secondary ring opening reactions and tertiary reactions resulting in formation of gaseous hydrocarbons is supported by higher flow rates of syngas and hydrogen at high heating rates and high reactor temperatures. Increase in carbon monoxide flow rate at the expense of carbon dioxide flow rate with the increase in reactor temperature has been observed. This increase in the ratio of CO/CO2 flow rate confirms the production of CO and CO2 from the competing reaction routes. At 1000 °C gasification a total merging between the pyrolysis step and the char gasification step has been observed. This is attributed to acceleration of char gasification reactions and acceleration of steam–hydrocarbons reforming reactions. These hydrocarbons are the precursors to char

  5. A comprehensive review of the heavy ion reaction mechanisms

    A general survey of the various heavy ion reaction mechanisms used to very high incident energy is given at an introductory level. The French heavy ion program centered for the eighties around the laboratory GANIL is outlined

  6. On reaction mechanisms involved in the deuteron–induced surrogate reactions

    An extended analysis of the nuclear reaction mechanisms involved within deuteron interaction with nuclei, namely the breakup, stripping, pick-up, pre-equilibrium emission, and evaporation from fully equilibrated compound nucleus, is presented in order to highlight the importance of the direct mechanisms still neglected in the analysis of deuteron-induced surrogate reactions. Particularly, the dominance of the breakup mechanism at low energies around the Coulomb barrier should be considered in the case of (d,x) surrogate reactions on actinide target nuclei

  7. On reaction mechanisms involved in the deuteron–induced surrogate reactions

    Avrigeanu, M.; Avrigeanu, V.; Mănăilescu, C. [Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O. Box MG-6, 077125 Bucharest-Magurele (Romania)

    2015-02-24

    An extended analysis of the nuclear reaction mechanisms involved within deuteron interaction with nuclei, namely the breakup, stripping, pick-up, pre-equilibrium emission, and evaporation from fully equilibrated compound nucleus, is presented in order to highlight the importance of the direct mechanisms still neglected in the analysis of deuteron-induced surrogate reactions. Particularly, the dominance of the breakup mechanism at low energies around the Coulomb barrier should be considered in the case of (d,x) surrogate reactions on actinide target nuclei.

  8. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Chapman, Piers; *Morse, John W. (*/deceased)

    2010-11-15

    1. Objective The general objective of this research was to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, carbon dioxide partial pressure (pCO2), and modest ranges of T and P. This would be done by studying both reaction rates and solubility from changes in solution chemistry. Also, nanoscale observations of calcite surface morphology and composition would be made to provide an understanding of rate controlling mechanisms.

  9. Reaction Mechanism of the Multi-channel Decomposition Reactions of 1-Pentenyl Free Radicals

    CHENG,Xue-Li; ZHAO,Yan-Yun; LI,Feng; LI,Li-Qing; TAO,Xiu-Jun

    2008-01-01

    The reactions of 1-pentenyl decomposition system have been studied extensively at the B3LYP/6-311++G** level with Gaussion 98 package. The potential energy surface with zero-point energy correction was drawn. All reaction channels were fully investigated with the vibrational mode analysis, frontier orbital analysis and electron population analysis to confirm the transition states and reveal the reaction mechanism.

  10. Density Functional Study on the Mechanism of Amadori Rearrangement Reaction

    BAO Xiu-Xiu; CHEN Zu-Qin; XIE Hu-Jun

    2011-01-01

    The reaction mechanism of amadori rearrangement in the initial stage of Maillard reaction has been investigated by means of density functional theory calculations in the gaseous phase and aqueous solution. Cyclic ribose and glycine were taken as the model in the amadori rearrangement. Reaction mechanisms have been proposed, and possibility for the formation of different compounds has been evaluated through calculating the relative energy changes for different steps of the reaction by following the total mass balance. The calculations reveal that the amadori rearrangement initialized via the intramolecular rearrangement, transferring one proton from N(3) to O(4) atom. In the next step, the second proton is also transferred from N(3) to O(4) atom,corresponding to the cleavage of C(4)-O(4) bond and the release of one water molecule. Then another proton is transferred from N(3) to C(5) atom via TS3 with the reaction barrier of 58.3kcal.mol-1 after tunneling the effect correction calculated at the B3LYP/6-31+G(d) level of theory,and this step is rate limiting for the whole catalytic cycle. Ultimately, the product is generated via keto-enolic tautomerization. Present calculation could provide insights into the reaction mechanism of Maillard reaction since experimental evaluation of the role of intermediates in the Maillard reaction is quite complicated.

  11. Reaction mechanisms in cellulose pyrolysis: a literature review

    Molton, P.M.; Demmitt, T.F.

    1977-08-01

    A bibliographic review of 195 references is presented outlining the history of the research into the mechanisms of cellulose pyrolysis. Topics discussed are: initial product identification, mechanism of initial formation of levoglucosan, from cellulose and from related compounds, decomposition of cellulose to other compounds, formation of aromatics, pyrolysis of levoglucosan, crosslinking of cellulose, pyrolytic reactions of cellulose derivatives, and the effects of inorganic salts on the pyrolysis mechanism. (JSR)

  12. Reaction mechanisms of ruthenium tetroxide mediated oxidations of organic compounds

    Froehaug, Astrid Elisabeth

    1995-12-31

    This thesis reports a study of the mechanism of ruthenium tetroxide mediated oxidations of saturated hydrocarbons, ethers, alkenes and alcohols. Several methods were used. The RuO{sub 4}-mediated oxidations of adamantane and cis-decalin were studied in CCl{sub 4}-CH{sub 3}CN-H{sub 2}O and in acetone-water. The rate of reaction was found to be moderately influenced by the polarity of the solvent. Solvent properties other than the polarity were also found to influence the reaction rates. From the oxidations of adamantane and adamantane-1,3,5,7-d{sub 4} two primary kinetic deuterium isotope effects were found. These were comparable with the deuterium isotope effects found for the analogous oxidations of cis-decalin and cis-decalin-d{sub 18}. The results seem to exclude both a one step hydride abstraction reaction mechanism and a one step concerted mechanism, as well as a scheme where two such mechanisms compete. The observations may be explained by a two step reaction mechanism consisting of a pre-equilibrium with formation of a substrate-RuO{sub 4} complex followed by a concerted rate determining reaction. The RuO{sub 4}-mediated oxidation of ethers was of kinetic second order with a small enthalpy of activation and a large negative entropy of activation. Oxidation of cyclopropylmethyl methyl ether gave methyl cyclopropanecarboxylate, no rearranged products were observed. On RuO{sub 4} oxidations in CCl{sub 4} with NaIO{sub 4} as stoichiometric oxidant, no chlorinated products were observed. Several observations not in agreement with a hydride or a hydrogen abstraction mechanism may be explained by assuming that the reaction proceeds by either a concerted reaction or by a reversible oxidative addition of the ether to RuO{sub 4} followed by a slow concerted step. 228 refs., 9 figs., 27 tabs.

  13. Quantum mechanics of chemical reactions: Recent developments in reactive scattering and in reaction path Hamiltonians

    Two recent developments in the theory of chemical reaction dynamics are reviewed. First, it has recently been discovered that the S- matrix version of the Kohn variational principle is free of the ''Kohn anomalies'' that have plagued other versions and prevented its general use. This has considerably simplified quantum mechanical reactive scattering calculations, which provide the rigorous characterizations of bimolecular reactions. Second, a new kind of reaction path Hamiltonian has been developed, one based on the ''least motion'' path that interpolates linearly between the reactant and product geometry of the molecule (rather than the previously used minimum energy, or ''intrinsic'' reaction path). The form of Hamiltonian which results is much simpler than the original reaction path Hamiltonian, but more important is the fact that it provides a more physically correct description of hydrogen atom transfer reactions. 44 refs., 4 figs

  14. The Electronic Flux in Chemical Reactions. Insights on the Mechanism of the Maillard Reaction

    Flores, Patricio; Gutiérrez-Oliva, Soledad; Herrera, Bárbara; Silva, Eduardo; Toro-Labbé, Alejandro

    2007-11-01

    The electronic transfer that occurs during a chemical process is analysed in term of a new concept, the electronic flux, that allows characterizing the regions along the reaction coordinate where electron transfer is actually taking place. The electron flux is quantified through the variation of the electronic chemical potential with respect to the reaction coordinate and is used, together with the reaction force, to shed light on reaction mechanism of the Schiff base formation in the Maillard reaction. By partitioning the reaction coordinate in regions in which different process might be taking place, electronic reordering associated to polarization and transfer has been identified and found to be localized at specific transition state regions where most bond forming and breaking occur.

  15. Reaction mechanism of light nuclei below 20 MeV

    The light nuclei are the elements in 1p shell. At the incident neutron energies below 20 MeV, the reaction mechanism could be classified as follows: 1. one particle emission, 2. sequential two particles emission, 3. the two cluster separation, when the residual are 8Be, 5He, 5Li, 4. three body break-up process, when the residual nuclei are 10Be, 6He. The Legendre expansion coefficients of the double differential cross section of outgoing particles in each type reaction mechanism are set up for the model calculating. The double differential cross section of secondary particle emission is calculated for light nuclei reaction and calculation formulation is also given. The problem on energy balance in light nuclear reaction is discussed

  16. Reaction mechanisms in the radiolysis of peptides, polypeptides and proteins

    The purpose of this review is to bring together and to correlate the wide variety of experimental studies that provide information on the reaction products and reaction mechanisms involved in the radiolysis of peptides, polypeptides and proteins (including chromosomal proteins) in both aqueous and solid-state systems. The comparative radiation chemistry of these systems is developed in terms of specific reactions of the peptide main-chain and the aliphatic, aromatic-unsaturated and sulfur-containing side-chains. Information obtained with the various experimental techniques of product analysis, competition kinetics, spin-trapping, pulse radiolysis and ESR spectroscopy is included. 147 refs

  17. Reaction mechanisms for on-surface synthesis of covalent nanostructures

    Björk, J.

    2016-03-01

    In recent years, on-surface synthesis has become an increasingly popular strategy to form covalent nanostructures. The approach has great prospects for facilitating the manufacture of a range of fascinating materials with atomic precision. However, the on-surface reactions are enigmatic to control, currently restricting its bright perspectives and there is a great need to explore how the reactions are governed. The objective of this topical review is to summarize theoretical work that has focused on comprehending on-surface synthesis protocols through studies of reaction mechanisms.

  18. Reaction mechanisms in the radiolysis of peptides, polypeptides and proteins

    Garrison, W.M.

    1985-01-01

    The purpose of this review is to bring together and to correlate the wide variety of experimental studies that provide information on the reaction products and reaction mechanisms involved in the radiolysis of peptides, polypeptides and proteins (including chromosomal proteins) in both aqueous and solid-state systems. The comparative radiation chemistry of these systems is developed in terms of specific reactions of the peptide main-chain and the aliphatic, aromatic-unsaturated and sulfur-containing side-chains. Information obtained with the various experimental techniques of product analysis, competition kinetics, spin-trapping, pulse radiolysis and ESR spectroscopy is included. 147 refs.

  19. A new comprehensive reaction mechanism for combustion of hydrocarbon fuels

    Ranzi, E.; Sogaro, A.; Gaffuri, P.; Pennati, G. [Politecnico di Milano (Italy). Dipt. di Chimica Industriale e Ingegneria Chimica; Westbrook, C.K.; Pitz, W.J. [Lawrence Livermore National Lab., CA (United States)

    1993-12-03

    A chemical kinetic model has been developed which describes pyrolysis, ignition and oxidation of many small hydrocarbon fuels over a wide range of experimental conditions. Fuels include carbon monoxide and hydrogen, methane and other alkane species up to n-butane, ethylene, propene, acetylene, and oxygenated species such as methanol, acetaldehyde and ethanol. Formation of some larger intermediate and product species including benzene, butadiene, large olefins, and cyclopentadiene has been treated in a semi-empirical manner. The reaction mechanism has been tested for conditions that do not involve transport and diffusional processes, including plug flow and stirred reactors, batch reactors and shock tubes. The present kinetic model and its validation differ from previous reaction mechanisms in two ways. First, in addition to conventional combustion data, experiments more commonly associated with chemical engineering problems such as oxidative coupling, oxidative pyrolysis and steam cracking are used to test the reaction mechanism, making it even more general than previous models. In addition, H atom abstraction and some other reaction rates, even for the smaller C{sub 2}, C{sub 3} and C{sub 4} species, are treated using approximations that facilitate future extensions to larger fuels in a convenient manner. Construction of the reaction mechanism and comparisons with experimental data illustrate the generality of the model.

  20. Thermal degradation reaction mechanism of xylose: A DFT study

    Huang, Jinbao; He, Chao; Wu, Longqin; Tong, Hong

    2016-08-01

    The thermal degradation reaction mechanism of xylose as hemicellulose model compound was investigated by using density functional theory methods M062X with the 6-31++G(d,p) basis set. Eight possible pyrolytic reaction pathways were proposed and the standard kinetic and thermodynamic parameters in all reaction pathways were calculated at different temperatures. In reaction pathway (1), xylose is first transformed into acyclic containing-carbonyl isomer, and then the isomer further decomposes through four possible pyrolysis pathways (1-1)-(1-4). Pathways (2) and (3) depict an immediate ring-opening process through the simultaneous breaking of C-O and C-C bonds. Pathways (4)-(7) describe the pyrolysis processes of various anhydro-xyloses through a direct ring-opening process. Pathway (8) gives the evolutionary process of pyranones. The calculation results show that reaction pathways (1), (2) and (5) are the major reaction channels and reaction pathways (3), (4), and (6)-(8) are the competitive reaction channels in pyrolysis of xylose. The major products of xylose pyrolysis are low molecular products such as 2-furaldehyde, glycolaldehyde, acetaldehyde, methylglyoxal and acetone, and the main competitive products are formaldehyde, formic acid, acetic acid, CO2, CH4, acetol, pyranone, and so on.

  1. Reaction mechanism study of 7Li(7Li, 6He) reaction at above Coulomb barrier energies

    V V Parkar; V Jha; S Santra; B J Roy; K Ramachandran; A Shrivastava; K Mahata; A Chatterjee; S Kailas

    2009-02-01

    The elastic scattering and the 6He angular distributions were measured in 7Li + 7Li reaction at two energies, lab = 20 and 25 MeV. FRDWBA calculations have been performed to explain the measured 6He data. The calculations were very sensitive to the choice of the optical model potentials in entrance and exit channels. The one-step proton transfer was found to be the dominant reaction mechanism in 6He production.

  2. A characterization of the two-step reaction mechanism of phenol decomposition by a Fenton reaction

    Valdés, Cristian; Alzate-Morales, Jans; Osorio, Edison; Villaseñor, Jorge; Navarro-Retamal, Carlos

    2015-11-01

    Phenol is one of the worst contaminants at date, and its degradation has been a crucial task over years. Here, the decomposition process of phenol, in a Fenton reaction, is described. Using scavengers, it was observed that decomposition of phenol was mainly influenced by production of hydroxyl radicals. Experimental and theoretical activation energies (Ea) for phenol oxidation intermediates were calculated. According to these Ea, phenol decomposition is a two-step reaction mechanism mediated predominantly by hydroxyl radicals, producing a decomposition yield order given as hydroquinone > catechol > resorcinol. Furthermore, traces of reaction derived acids were detected by HPLC and GS-MS.

  3. Physical Mechanism of Nuclear Reactions at Low Energies

    Oleinik, V P; Arepjev, Yu.D

    2002-01-01

    The physical mechanism of nuclear reactions at low energies caused by spatial extension of electron is considered. Nuclear reactions of this type represent intra-electronic processes, more precisely, the processes occurring inside the area of basic localization of electron. Distinctive characteristics of these processes are defined by interaction of the own field produced by electrically charged matter of electron with free nuclei. Heavy nucleus, appearing inside the area of basic localization of electron, is inevitably deformed because of interaction of protons with the adjoining layers of electronic cloud, which may cause nuclear fission. If there occur "inside" electron two or greater number of light nuclei, an attractive force appears between the nuclei which may result in the fusion of nuclei. The intra-electronic mechanism of nuclear reactions is of a universal character. For its realization it is necessary to have merely a sufficiently intensive stream of free electrons, i.e. heavy electric current, an...

  4. Reaction of niobium with hexane and methanol by mechanical grinding

    In mechanical alloying (MA) processing, alcohol, acetone and other organic solvents are often added as dispersants in order that powders will not stick to a vessel. It has been however considered that these organic solvents are simply additives. Enough attention has not been paid to the role or reaction of these dispersants. Recently, it was found that these organic solvents could react with some metals. For example, the authors reported that NbC is obtained by a reaction between Nb and methanol in the preparation of Al3Nb intermetallics by the MA method. Niobium hydrides are obtained by milling of Nb powders in hydrocarbon. In this paper, the authors discuss the reaction between Nb powder and hexane (C6H14) or methanol (CH3OH) during mechanical grinding (MG) processing

  5. Kinetics and Mechanism of the Chlorate-Bromide Reaction.

    Sant'Anna, Rafaela T P; Faria, Roberto B

    2015-11-01

    The chlorate-bromide reaction, ClO3(-) + 6Br(-) + 6H(+) → 3Br2 + Cl(-) + 3H2O, was followed at the Br3(-)/Br2 isosbestic point (446 nm). A fifth-order rate law was found: (1)/3 d[Br2]/dt = k[ClO3(-)][Br(-)][H(+)](3) (k = 5.10 × 10(-6) s(-1) L(4) mol(-4)) at 25 °C and I = 2.4 mol L(-1). At high bromide concentrations, the bromide order becomes close to zero, indicating a saturation profile on bromide concentration, similar to the chloride saturation profile observed in the chlorate-chloride reaction. A mechanism is proposed that considers the formation of the intermediate BrOClO2(2-), similar to the intermediate ClOClO2(2-) proposed in the mechanism of the chlorate-chloride reaction. PMID:26467822

  6. The mechanism of electronic excitation in the bacterial bioluminescent reaction

    The current state of the problem of formation of the electron-excited product in the chemiluminescent reaction that underlies the bacterial luminescence is analysed. Various schemes of chemical transformations capable of producing a bacterial bioluminescence emitter are presented. The problem of excitation of secondary emitters is considered; two possible mechanisms of their excitation are analysed.

  7. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Gorman, Brian P [Colorado School of Mines, Golden, CO (United States)

    2015-09-02

    Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO2, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO2, Ca2+, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO2 in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer

  8. Benzoxazinone-Mediated Triazine Degradation: A Proposed Reaction Mechanism.

    Willett, C D; Lerch, R N; Lin, C-H; Goyne, K W; Leigh, N D; Roberts, C A

    2016-06-22

    The role of benzoxazinones (Bx, 2-hydroxy-2H-1,4-benzoxazin-3(4H)-one) in triazine resistance in plants has been studied for over half a century. In this research, fundamental parameters of the reaction between DIBOA-Glc (2-β-d-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one) and atrazine (ATR, 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine) were examined. Through a series of experiments employing a variety of chromatographic and spectroscopic techniques, the DIBOA-Glc/ATR reaction was characterized in terms of reactant and product kinetics, stoichiometry, identification of a reaction intermediate, and reaction products formed. Results of these experiments demonstrated that the reaction mechanism proceeds via nucleophilic attack of the hydroxamic acid moiety of DIBOA-Glc at the C-2 position of the triazine ring to form hydroxyatrazine (HA, 2-hydroxy-4-ethylamino-6-isopropylamino-s-triazine), with associated degradation of DIBOA-Glc. Degradation of reactants followed first-order kinetics with a noncatalytic role of DIBOA-Glc. A reaction intermediate was identified as a DIBOA-Glc-HA conjugate, indicating a 1:1 DIBOA-Glc:ATR stoichiometry. Reaction products included HA and Cl(-), but definitive identification of DIBOA-Glc reaction product(s) was not attained. With these reaction parameters elucidated, DIBOA-Glc can be evaluated in terms of its potential for a myriad of applications, including its use to address the problem of widespread ATR contamination of soil and water resources. PMID:27215133

  9. Revealing Stepwise Mechanisms in Dipolar Cycloaddition Reactions: Computational Study of the Reaction between Nitrones and Isocyanates.

    Darù, Andrea; Roca-López, David; Tejero, Tomás; Merino, Pedro

    2016-01-15

    The mechanism of cycloaddition reactions of nitrones with isocyanates has been studied using density functional theory (DFT) methods at the M06-2X/cc-pVTZ level of theory. The exploration of the potential energy surfaces associated with two reactive channels leading to 1,2,4-oxadiazolidin-5-ones and 1,4,2-dioxazolidines revealed that the cycloaddition reaction takes place through a concerted mechanism in gas phase and in apolar solvents but a stepwise mechanism in polar solvents. In stepwise mechanisms, the first step of the reaction is a rare case in which the nitrone oxygen acts as a nucleophile by attacking the central carbon atom of the isocyanate (interacting with the π-system of the C═O bond) to give an intermediate. The corresponding transition structure is stabilized by an attractive electrostatic interaction favored in a polar medium. The second step of the reaction is the rate-limiting one in which the formation of 1,2,4-oxadiazolidin-5-ones or 1,4,2-dioxazolidines is decided. Calculations indicate that formation of 1,2,4-oxadiazolidin-5-ones is favored both kinetically and thermodynamically independently of the solvent, in agreement with experimental observations. Noncovalent interactions (NCI) and topological analysis of the gradient field of electron localization function (ELF) bonding confirmed the observed interactions. PMID:26682934

  10. Reaction mechanisms in the 6Li+ 52Cr system

    Pandey Bhawna

    2015-01-01

    Full Text Available Reactions induced by the weakly bound 6Li projectile interacting with the intermediate mass target 52Cr are investigated. The choice of this particular reaction in our study is because it is proposed as a surrogate reaction [6Li(52Cr, d56Fe*] for the measurement of 55Fe(n,p reaction cross-section, which has been found to be very important in fusion reactor studies. All the conditions which have to be satisfied for using the surrogate method have been checked. The energy of 6Li beam is selected in a way so as to get equivalent neutron energy in the region of 9-14 MeV, which is of primary interest in fusion reactor application. In the present work, statistical model calculations PACE (Projection-Angular-Momentum-Coupled-Evaporation, ALICE and Continuum-Discretized–Coupled-Channel (CDCC: FRESCO have been used to provide information for the 6Li + 52Cr system and the respective contributions of different reaction mechanisms. The present theoretical work is an important step in the direction towards studying the cross-section of the 55Fe(n, p55Mn reaction by surrogate method.

  11. Nuclear reaction mechanisms. Progress report, June 1975--May 1976

    Blann, M.

    1976-01-01

    Research under the subject contract has been directed along two major lines: (1) development and exploration of pre-equilibrium statistical models; (2) experimental measurement and theoretical investigation of heavy ion reaction mechanisms, with emphasis on the limits on compound nucleus formation. Much of the work under this contract has been published and a list of publications is part of this report. This work is not otherwise summarized herein. New unpublished results on heavy ion reactions are briefly summarized, as are results of precompound ..cap alpha.. emission. Colloquia and addresses are also summarized. Separate abstracts appear in ERA for six of the papers in this report.

  12. Structure and Reaction Mechanism of Pyrrolysine Synthase (PylD)

    Quitterer, Felix

    2013-05-29

    The final step in the biosynthesis of the 22nd genetically encoded amino acid, pyrrolysine, is catalyzed by PylD, a structurally and mechanistically unique dehydrogenase. This catalyzed reaction includes an induced-fit mechanism achieved by major structural rearrangements of the N-terminal helix upon substrate binding. Different steps of the reaction trajectory are visualized by complex structures of PylD with substrate and product. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Mechanisms of chemical reaction initiated by recoil implantation

    Mechanisms of chemical reactions initiated by recoil implantation were studied in the systems 51Cr+M(acac)3 yields 51Cr(acac)3 where M is a trivalent metal. The yield of 51Cr(acac)3 increased linearly with an increase of inverse of the force constant of metal-oxygen bonding K(M-O). This indicates that there is competition between the implanted 51Cr atom and M. However, exception for this trend was the case of Co(acac)3 catcher, for which the yield of 51Cr(acac)3 was much higher than that expected for a competition reaction. Complex features of the replacement reaction caused by implantation are discussed

  14. Facilitating effects of berberine on rat pancreatic islets through modulating hepatic nuclear factor 4 alpha expression and glucokinase activity

    Zhi-Quan Wang; Fu-Er Lu; San-Hua Leng; Xin-Sheng Fang; Guang Chen; Zeng-Si Wang; Li-Ping Dong; Zhong-Qing Yan

    2008-01-01

    AIM: To observe the effect of berberine on insulin secretion in rat pancreatic islets and to explore its possible molecular mechanism.METHODS: Primary rat islets were isolated from male Sprague-Dawley rats by collagenase digestion and treated with different concentrations (1, 3, 10 and 30 μmol/L) of berberine or 1 μmol/L Glibenclamide (GB) for 24 h. Glucose-stimulated insulin secretion (GSIS) assay was conducted and insulin was determined by radioimmunoassay. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (NTT) assay was performed to evaluate cytotoxicity. The mRNA level of hepatic nuclear factor 4 alpha (HNF4α) was determined by reverse transcription polymerase chain reaction (RT-PCR). Indirect immunofluorescence staining and Western blot analysis were employed to detect protein expression of HNF4α in the islets. Glucokinase (GK) activity was measured by spectrophotometric method.RESULTS: Berberine enhanced GSIS rather than basal insulin secretion dose-dependently in rat islets and showed no significant cytotoxicity on islet cells at the concentration of 10 μmol/L. Both mRNA and protein expressions of HNF4α were up-regulated by berberine in a dose-dependent manner, and GK activity was also increased accordingly. However, GB demonstrated no regulatory effects on HNF4α expression or GK activity.CONCLUSION: Berberine can enhance GSIS in rat islets, and probably exerts the insulinotropic effect via a pathway involving HNF4α and GK, which is distinct from sulphonylureas (SUs).

  15. Reactions of a stable dialkylsilylene and their mechanisms

    Mitsuo Kira

    2012-11-01

    Various reactions for a stable dialkylsilylene, 2,2,5,5-tetrakis(trimethylsilyl)silacyclopentane-1,1-diyl (1), are summarized and their mechanisms are discussed. Silylene 1 isomerizes to the corresponding silaethene via the 1,2-trimethylsilyl migration. Reduction of 1 with alkali metals affords the corresponding radical anion 1.− with a relatively small 29Si hfs constant (2.99 mT) and a large g-factor (g = 2.0077) compared with those for trivalent silyl radicals. Photo-excitation of 1 generates the corresponding singlet excited state (11*) with the lifetime of 80.5 ns. The excited state reacts with C=C double bond compounds including benzene, naphthalene, and ()- and ()-2-butenes. Although the thermal reactions of 1 with haloalkanes occur via radical mechanisms, the insertion into O-H, Si-H and Si-Cl bonds proceeds concertedly via the threemembered cyclic transition states. The reaction of 1 with H2SiCl2 gives the Si-Cl insertion product exclusively, while the quantitative insertion to Si-H bond occurs when Me2SiHCl is used as a substrate. The origin of the rather unusual Si-H/Si-Cl selectivity is elucidated using DFT calculations. Silylene 1 adds to C=C, C≡C, and C=O bonds to afford the corresponding silacycles as stable compounds. The importance of the carbonyl silaylides during the reactions of silylenes with aldehydes and ketones is emphasized.

  16. Mechanism of the Intramolecular Hexadehydro-Diels-Alder Reaction.

    Marell, Daniel J; Furan, Lawrence R; Woods, Brian P; Lei, Xiangyun; Bendelsmith, Andrew J; Cramer, Christopher J; Hoye, Thomas R; Kuwata, Keith T

    2015-12-01

    Theoretical analysis of the mechanism of the intramolecular hexadehydro-Diels-Alder (HDDA) reaction, validated against prior and newly measured kinetic data for a number of different tethered yne-diynes, indicates that the reaction proceeds in a highly asynchronous fashion. The rate-determining step is bond formation at the alkyne termini nearest the tether, which involves a transition-state structure exhibiting substantial diradical character. Whether the reaction then continues to close the remaining bond in a concerted fashion or in a stepwise fashion (i.e., with an intervening intermediate) depends on the substituents at the remaining terminal alkyne positions. Computational modeling of the HDDA reaction is complicated by the significant diradical character that arises along the reaction coordinate, which leads to instabilities in both restricted singlet Kohn-Sham density functional theory (DFT) and coupled cluster theory based on a Hartree-Fock reference wave function. A consistent picture emerges, however, from comparison of broken-symmetry DFT calculations and second-order perturbation theory based on complete-active-space self-consistent-field (CASPT2) calculations. PMID:26270857

  17. Reaction Kinetics and Mechanism of Magnetic Field Effects in Cryptochrome

    Ilia A Solov'yov; Schulten, Klaus

    2012-01-01

    Creatures as varied as mammals, fish, insects, reptiles, and birds have an intriguing ‘sixth’ sense that allows them to orient themselves in the Earth's magnetic field. Despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically sensitive radical pair reactions occurring in the retina, the light-sensitive part of animal eyes. A photoreceptor, cryptochrome, has been suggested to endow birds with magnetoreceptive abilities...

  18. Agricultural biochemistry: reaction mechanisms and pathways in biosynthesis

    Plant tracer studies in research concerning human food chains are reviewed in the following sections: tracer studies with 14C (photosynthesis and other biosynthesis pathways in plants, intermediary carbon pathways), tracer studies with 13C (13C NMR spectrometry and its applications in biosynthesis pathways), the fate of hydrogen, deuterium as a tracer, triton magnetic resonance spectrometry, double label isotope ratios (reaction mechanism studies and studies of precursor-product relationships), kinetic isotope effects, 18O and organic mass spectrometry, 18O and 31P NMR, precursor-product incorporation and dilution. (U.K.)

  19. Reaction mechanisms in the plasma focus - investigations on accelerated deuterons and reaction protons

    The Plasma focus POSEIDON (W0=280 kJ; U0=60 kV) exhibits two distinct phases of high suprathermal fusion production. The first, pinch or quiescent phase shows a stable, radially well confined plasma. The second, unstable phase corresponds to m=0 instabilities and subsequent break-up of the plasma. For an analysis of the mechanisms leading to the high fusion production in both phases, a new model, the ''Gyrating Particle Model'' (GPM), was developed. In the GPM the trajectories of fast deuterons in the time varying focus structures are determined by a ray-tracing code. The profiles nsub(e)(r,z,t) and Tsub(e)(r,z,t) for both phases are taken from measurements in a schematized form. The deuteron acceleration process is not treated, i.e. arbitrary initial distribution functions of the deuterons are taken at the beginning of each phase. Coulomb collisions with the thermal plasma electrons describing the energy loss of the fast deuterons and fusion collisions with the thermal deuterons are treated with the help of Monte Carlo methods. Other reaction mechanisms, such as beam-beam or thermal production, are neglected. The trajectories of the reaction protons in the focus-field are traced up to measuring positions outside of the focus pinch. Thus, measurable quantities such as spatial, angular and spectral distributions and time evolution of the reaction protons and neutrons are obtained and compared with experimental results. (orig./GG)

  20. The fast neutron induced (n, p) reaction cross sections. Compound reaction mechanism

    In the framework of the compound mechanism the general formula for fast neutron induced and particle emission reaction cross section was deduced. The evaporation model, constant nuclear temperature approximation, semi-classical approach to an inverse reaction cross section and Weizsaecker formula for nuclear binding energy were used. For the systematic analysis of known experimental (n, p) cross sections the obtained formula was used in the energy range from 6 to 16 MeV. It was found that discrepancy between the theoretical and experimental (n, p) cross sections increases with growth of the neutron relative excess parameter (N - Z + 1)/A. Levkovsky's conclusions were considered and revised for a wide energy range from 6 to 16 MeV

  1. Computational analysis of the mechanism of chemical reactions in terms of reaction phases: hidden intermediates and hidden transition States.

    Kraka, Elfi; Cremer, Dieter

    2010-05-18

    Computational approaches to understanding chemical reaction mechanisms generally begin by establishing the relative energies of the starting materials, transition state, and products, that is, the stationary points on the potential energy surface of the reaction complex. Examining the intervening species via the intrinsic reaction coordinate (IRC) offers further insight into the fate of the reactants by delineating, step-by-step, the energetics involved along the reaction path between the stationary states. For a detailed analysis of the mechanism and dynamics of a chemical reaction, the reaction path Hamiltonian (RPH) and the united reaction valley approach (URVA) are an efficient combination. The chemical conversion of the reaction complex is reflected by the changes in the reaction path direction t(s) and reaction path curvature k(s), both expressed as a function of the path length s. This information can be used to partition the reaction path, and by this the reaction mechanism, of a chemical reaction into reaction phases describing chemically relevant changes of the reaction complex: (i) a contact phase characterized by van der Waals interactions, (ii) a preparation phase, in which the reactants prepare for the chemical processes, (iii) one or more transition state phases, in which the chemical processes of bond cleavage and bond formation take place, (iv) a product adjustment phase, and (v) a separation phase. In this Account, we examine mechanistic analysis with URVA in detail, focusing on recent theoretical insights (with a variety of reaction types) from our laboratories. Through the utilization of the concept of localized adiabatic vibrational modes that are associated with the internal coordinates, q(n)(s), of the reaction complex, the chemical character of each reaction phase can be identified via the adiabatic curvature coupling coefficients, A(n,s)(s). These quantities reveal whether a local adiabatic vibrational mode supports (A(n,s) > 0) or resists

  2. A New Formulation of the Lindemann Mechanism of Unimolecular Reactions

    钱人元

    2003-01-01

    A new formulation of the Lindemann mechanism of unimolecular reactions in gaseous phase is presented, without the use of steady state hypothesis. It is hereby shown that the nature of applicability of steady state hypothesis in the regime of high reactant gas pressure is different from that in the regime of low gas pressure. In the former case it is an equilibrium approximation, while in the latter case it is a highly reactive intermediate approximation in no connection with a steady state. Furthermore for the latter case it is shown that in the classical formulation of Lindemann mecbRnism the use of steady state hypothesis is an ad hoc assumption. A highly reactive intermediate in the sense that its concentration is very small during the whole course of reaction is a necessary condition for the applicability of very reactive intermediate approximation. When the two distinctive nature of the applicability of steady state hypothesis is mlxed-up, wrong or useless conclusion may be arrived at. The only possible case of realizing a true steady state in a complex reaction is pointed out.

  3. Inelastic collisions of heavy ions and their reaction mechanisms

    This work is dedicated to the study of inelastic collisions of heavy ions. Most experiments took place in Ganil facility. The 2 first chapters introduce the notion of inelastic scattering of heavy ions. The third chapter deals with target excitation, giant monopolar or dipolar or quadrupolar resonances ant the multi-phonon concept and presents relevant experimental results from the Ca40 + Ca40 nuclear reaction at 50 MeV/A. The fourth chapter is dedicated to nuclear processes involved in inelastic collisions: pick-up break-up mechanisms, the angular distribution of emitted protons and the towing mode. These notions are applied to the reaction Zr90(Ar40, Ar40'). The fifth chapter presents the solving of the time dependent Schroedinger equation (TDSE) applied to the wave function of a particle plunged in a variable potential. TDSE solving is applied to the break-up of Be11. These calculations have been validated by comparing them with experimental results from the nuclear reaction Ti48(Be11, Be10 + n + γ) that is described in the chapter 6. The last chapter presents the advantages of inelastic scattering considered as a tool to study exotic nuclei

  4. Complete reaction mechanisms of mercury oxidation on halogenated activated carbon.

    Rungnim, Chompoonut; Promarak, Vinich; Hannongbua, Supa; Kungwan, Nawee; Namuangruk, Supawadee

    2016-06-01

    The reaction mechanisms of mercury (Hg) adsorption and oxidation on halogenated activated carbon (AC) have been completely studied for the first time using density functional theory (DFT) method. Two different halogenated AC models, namely X-AC and X-AC-X (X=Cl, Br, I), were adopted. The results revealed that HgX is found to be stable-state on the AC edge since its further desorption from the AC as HgX, or further oxidation to HgX2, are energetically unfavorable. Remarkably, the halide type does not significantly affect the Hg adsorption energy but it strongly affects the activation energy barrier of HgX formation, which obviously increases in the order HgIelimination significantly decreases as I-AC>Br-AC>Cl-AC. Thus, the study of the complete reaction mechanism is essential because the adsorption energy can not be used as a guideline for the rational material design in the halide impregnated AC systems. The activation energy is an important descriptor for the predictions of sorbent reactivity to the Hg oxidation process. PMID:26943019

  5. Kinetics and mechanisms of reactions involving small aromatic reactive intermediates

    Lin, M.C. [Emory Univ., Atlanta, GA (United States)

    1993-12-01

    Small aromatic radicals such as C{sub 6}H{sub 5}, C{sub 6}H{sub 5}O and C{sub 6}H{sub 4} are key prototype species of their homologs. C{sub 6}H{sub 5} and its oxidation product, C{sub 6}H{sub 5}O are believed to be important intermediates which play a pivotal role in hydrocarbon combustion, particularly with regard to soot formation. Despite their fundamental importance, experimental data on the reaction mechanisms and reactivities of these species are very limited. For C{sub 6}H{sub 5}, most kinetic data except its reactions with NO and NO{sub 2}, were obtained by relative rate measurements. For C{sub 6}H{sub 5}O, the authors have earlier measured its fragmentation reaction producing C{sub 5}H{sub 5} + CO in shock waves. For C{sub 6}H{sub 4}, the only rate constant measured in the gas phase is its recombination rate at room temperature. The authors have proposed to investigate systematically the kinetics and mechanisms of this important class of molecules using two parallel laser diagnostic techniques--laser resonance absorption (LRA) and resonance enhanced multiphoton ionization mass spectrometry (REMPI/MS). In the past two years, study has been focused on the development of a new multipass adsorption technique--the {open_quotes}cavity-ring-down{close_quotes} technique for kinetic applications. The preliminary results of this study appear to be quite good and the sensitivity of the technique is at least comparable to that of the laser-induced fluorescence method.

  6. Heavy ion reactions: an experimental vista. [Review, angular momentum, compound-nucleus decay, reaction mechanism

    Stokstad, R.G.

    1977-01-01

    Examples of recent experiments in the areas of fusion and deep-inelastic scattering are presented and discussed. Emphasis is placed on the importance of individual nucleons in the fusion process, the effects of high angular momentum, and the understanding of compound nuclear decay. Experiments on deep inelastic scattering are entering a new stage in which important parameters of the reaction mechanism are now open to investigation. Primarily through coincidence measurements, direct information on the angular momentum transferred in a collision and on the time scale of decay is being obtained.

  7. Study on the Reaction Mechanism of Naphthalene with Oxalyl Chloride

    2001-01-01

    The reaction of naphthalene with oxalyl chloride in the presence of anhydrous AlCl3 was investigated. The homolog of dinaphthyl methanone can be obtained mainly from this reaction. Naphthalene conversion does not have evident correlation with the amount of AlCl3. The results show that the reaction proceeds via carbon cation electrophilic substitution reaction-free radical substitution reaction pathway.

  8. Low Energy Electrons as Probing Tool for Astrochemical Reaction Mechanisms

    Hendrik Bredehöft, Jan; Swiderek, Petra; Hamann, Thorben

    The complexity of molecules found in space varies widely. On one end of the scale of molecular complexity is the hydrogen molecule H2 . Its formation from H atoms is if not understood than at least thoroughly investigated[1]. On the other side of said spectrum the precursors to biopolymers can be found, such as amino acids[2,3], sugars[4], lipids, cofactors[5], etc, and the kerogen-like organic polymer material in carbonaceous meteorites called "black stuff" [6]. These have also received broad attention in the last decades. Sitting in the middle between these two extremes are simple molecules that are observed by radio astronomy throughout the Universe. These are molecules like methane (CH4 ), methanol (CH3 OH), formaldehyde (CH2 O), hydrogen cyanide (HCN), and many many others. So far more than 40 such species have been identified.[7] They are often used in laboratory experiments to create larger complex molecules on the surface of simulated interstellar dust grains.[2,8] The mechanisms of formation of these observed starting materials for prebiotic chemistry is however not always clear. Also the exact mechanisms of formation of larger molecules in photochemical experiments are largely unclear. This is mostly due to the very complex chemistry going on which involves many different radicals and ions. The creation of radicals and ions can be studied in detail in laboratory simulations. They can be created in a setup mimicking interstellar grain chemistry using slow electrons. There is no free electron radiation in space. What can be found though is a lot of radiation of different sorts. There is electromagnetic radiation (UV light, X-Rays, rays, etc.) and there is particulate radiation as well in the form of high energy ions. This radiation can provide energy that drives chemical reactions in the ice mantles of interstellar dust grains. And while the multitude of different kinds of radiation might be a little confusing, they all have one thing in common: Upon

  9. Mechanism of the Ferrocyanide-Iodate-Sulfite Oscillatory Chemical Reaction.

    Horváth, Viktor; Epstein, Irving R; Kustin, Kenneth

    2016-03-31

    Existing models of the ferrocyanide-iodate-sulfite (FIS) reaction seek to replicate the oscillatory pH behavior that occurs in open systems. These models exhibit significant differences in the amplitudes and waveforms of the concentration oscillations of such intermediates as I(-), I3(-), and Fe(CN)6(3-) under identical conditions and do not include several experimentally found intermediates. Here we report measurements of sulfite concentrations during an oscillatory cycle. Knowing the correct concentration of sulfite over the course of a period is important because sulfite is the main component that determines the buffer capacity, the pH extrema, and the amount of oxidizer (iodate) required for the transition to low pH. On the basis of this new result and recent experimental findings on the rate laws and intermediates of component processes taken from the literature, we propose a mass action kinetics model that attempts to faithfully represent the chemistry of the FIS reaction. This new comprehensive mechanism reproduces the pH oscillations and the periodic behavior in [Fe(CN)6(3-)], [I3(-)], [I(-)], and [SO3(2-)]T with characteristics similar to those seen in experiments in both CSTR and semibatch arrangements. The parameter ranges at which stationary and oscillatory behavior is exhibited also show good agreement with those of the experiments. PMID:26949219

  10. Novel uses of isotope effects to elucidate enzyme reaction mechanisms

    A new technique (Multiple Isotope Effects) for determining enzyme reaction mechanisms and intrinsic isotope effects has been developed. By determining the 13C isotope effect on V/K with both a deuterated and unlabeled substrate, and the deuterium isotope effect on V/K, it is possible to tell whether the 13C-sensitive and deuterium-sensitive steps are the same or not and, if they are different, to determine which comes first in the mechanism. If the two isotope-sensitive steps are the same, 1) deuteration increases the size of the observed 13C isotope effect, and 2) the intrinsic 13C and deuterium isotope effects, and the commitments can be calculated. When the deuterium- and 13C-sensitive steps are different, deuteration decreases the size of the observed 13C isotope effect. The data fit the equation [13(V/K)/sub H/ - 1]/[13(V/K)/sub D/ - 1] = /sup D/(V/K)//sup D/K/sub eq/ when the deuterium-sensitive step comes first, but fit the equation [13(V/K)/sub H/ - 13K/sub eq/]/[13(V/K)/sub D/ - 13K/sub eq/] = /sup D/(V/K) when the 13C-sensitive step comes first

  11. Preparation by a Rheological Phase Reaction Method and Thermal Decomposition Reaction Mechanism of Nickelous Salicylate Tetrahydrate

    Wang Jin-long; Yuan Liang-jie; Yang Yi-yong; Sun Ju-tang; Zhang Ke-li

    2003-01-01

    The single crystal nickel salicylate tetrahydrate was prepared with the rheological phase reaction method from nickelous hydroxide and salicylic acid. The crystal structure was determined. It is monoclinic, space group P21 /n, a =0.67874(3), b=0. 515 91(2), c=2. 313 30(9) nm, β=90.9286(17)°, V=0. 809 94(6) nm3, Z=2, ρcalcd =0. 065 0[I >2a(I)]. The thermal decomposition mechanism in an inert atmosphere was investigated via TG, DTG and DTA. The thermal decomposition products were characterized with IR and micro-powder X-ray diffraction method. A new coordination polymer (NiC6 H4O)n as an intermediate product and nanoscale metal nickel were obtained in the ranges of 364-429 ℃ and 429-680 ℃, respectively.

  12. Human podocytes adhere to the KRGDS motif of the alpha3alpha4alpha5 collagen IV network.

    Borza, Corina M; Borza, Dorin-Bogdan; Pedchenko, Vadim; Saleem, Moin A; Mathieson, Peter W; Sado, Yoshikazu; Hudson, Heather M; Pozzi, Ambra; Saus, Juan; Abrahamson, Dale R; Zent, Roy; Hudson, Billy G

    2008-04-01

    Podocyte adhesion to the glomerular basement membrane is required for proper function of the glomerular filtration barrier. However, the mechanism whereby podocytes adhere to collagen IV networks, a major component of the glomerular basement membrane, is poorly understood. The predominant collagen IV network is composed of triple helical protomers containing the alpha3alpha4alpha5 chains. The protomers connect via the trimeric noncollagenous (NC1) domains to form hexamers at the interface. Because the NC1 domains of this network can potentially support integrin-dependent cell adhesion, it was determined whether individual NC1 monomers or alpha3alpha4alpha5 hexamers support podocyte adhesion. It was found that, although human podocytes did not adhere to NC1 domains proper, they did adhere via integrin alphavbeta3 to a KRGDS motif located adjacent to alpha3NC1 domains. Because the KRGDS motif is a site of phosphorylation, its interactions with integrin alphavbeta3 may play a critical role in cell signaling in physiologic and pathologic states. PMID:18235087

  13. Kinetics and Mechanism of Iodide Oxidation by Iron(III): A Clock Reaction Approach

    Bauer, Jurica; Tomisic, Vladislav; Vrkljan, Petar B. A.

    2008-01-01

    A simple method for studying the kinetics of a chemical reaction is described and the significance of reaction orders in deducing reaction mechanisms is demonstrated. In this student laboratory experiment, oxidation of iodide by iron(III) ions in an acidic medium is transformed into a clock reaction. By means of the initial rates method, it is…

  14. Reaction mechanisms in medium energy collisions: influence of dynamical fluctuations

    Dynamical fluctuations in heavy ion collisions at beam energies 20 - 200 MeV are discussed. The main topics are: fragment formation from dynamical instabilities; neck fragmentation and variances; dynamics of fluctuations. A detailed study between the fragment formation time and the freeze-out time has been performed. Different theoretical models are proposed. For more peripheral collisions a novel reaction mechanism is revealed, due to the onset of new neck instabilities coupled to an increasing amount of dynamical fluctuations. Expected consequences are: possibility of intermediate mass fragment emission from the neck region and larger variances in projectile-like and target-like observables. A great variety of sources for dynamically emitted particles are predicted. Isospin effects and possibilities of producing of highly exotic nuclear systems from neck ruptures are also expected. A fully consistent treatment of fluctuation dynamics is presented, including short range (Langevin type) and long range (mean field) correlations. A stochastic transport model is constructed with the presence of the random force related to consistent density fluctuations. The Boltzmann-Nordheim-Vlasov equation for a mean phase space trajectory is modified by a correlation term with the structure of a diffusion in momentum space. Effects for collective motions and for regions of mean field instabilities are discussed. Relevant contributions from fluctuations are predicted for the production of high energy photons with a coherent mechanism. In particular a soft component in the Bremsstrahlung gamma spectrum is strongly enhanced, with important consequences on the properties of hot giant resonances that can be extracted from experiments. 5 refs

  15. Reaction mechanisms in irradiated, precipitated, and mesoporous silica.

    Dondi, D; Buttafava, A; Zeffiro, A; Bracco, S; Sozzani, P; Faucitano, A

    2013-04-25

    A matrix EPR spectroscopy study of the low temperature γ radiolysis of precipitated (Zeosil) and mesoporous high surface silica has afforded evidence of the formation of trapped H-atoms, H-atom centers, siloxy radicals ≡Si-O(•), anomalous silyl peroxy radicals ≡Si-OO(•) with reduced g tensor anisotropy, siloxy radical-cations (≡Si-O-Si≡)(+•), E' centers, and two species from Ge impurity. Coordination of peroxyl radicals with diamagnetic ≡Si(+) centers is proposed and tested by DFT computations in order to justify the observed g tensor. Coordination of H-atoms to ≡Si(+) centers is also proposed for the structure of the H-atom centers as an alternative model not requiring the intervention of Ge, Sn, or CO impurities. The DFT method has been employed to assess the electronic structure of siloxy radical-cations and its similarity with that of the carbon radical-cation analogues; the results have prompted a revision of the structures proposed in the literature for ST1 and ST2 centers. The comparison between the two types of silica has afforded evidence of different radiolysis mechanisms leading to a greater yield of trapped H-atoms and H-atom centers in zeosil silica, which is reckoned with the 4-fold greater concentration of silanol groups. Parallel radiolysis experiments carried out by using both types of silica with polybutadiene oligomers as adsorbate have afforded evidence of free valence and energy migration phenomena leading to irreversible linking of polybutadiene chains onto silica. Reaction mechanisms are proposed based on the detection of SiO2-bonded free radicals whose structure has been defined by EPR. PMID:23521082

  16. Theoretical Study on the Mechanism of Sonogashira Coupling Reaction

    CHEN Li-Ping; HONG San-Guo; HOU Hao-Qing

    2008-01-01

    The mechanism of palladium-catalyzed Sonogashira cross-coupling reaction has been studied theoretically by DFT (density functional theory) calculations. The model system studied consists of Pd(PH3)2 as the starting catalyst complex, phenyl bromide as the substrate and acetylene as the terminal alkyne, without regarding to the co-catalyst and base. Mechanistically and energetically plausible catalytic cycles for the cross-coupling have been identified. The DFT analysis shows that the catalytic cycle occurs in three stages: oxidative addition of phenyl bromide to the palladium center, alkynylation of palladium(II) intermediate, and reductive elimination to phenylacetylene. In the oxidative addition, the neutral and anionic pathways have been investigated, which could both give rise to cis-configured palladium(II) diphosphine intermediate. Starting from the palladium(II) diphosphine intermediate, the only identifiable pathway in alkynylation involves the dissociation of Br group and the formation of square-planar palladium(II) intermediate, in which the phenyl and alkynyl groups are oriented cis to each other. Due to the close proximity of phenyl and alkynyl groups, the reductive elimination of phenylacetylene proceeds smoothly.

  17. The mechanism and kinetics of epoxy-amine reactions

    Full text.Silane coupling agents have an important role at the interface for improving the performance of composite materials based on polymer matrices reinforced with glass fibers or mineral fillers. The silanes are also used in some adhesive formulations or as substrate primers, giving higher strength of adhesives joints. In these interface or interphase problems, most of the data in the literature concerns the final properties of the composite materials, such as strength or young's modulus; there is very little information about the chemical properties of the interphase. The aim of this study is to try to provide some of this basic data. The coupling agent studied here is the γ-aminopropyltriethoxysilane (γ-APS) or A1100. It is the most commonly used coupling agents. During composite processing, it is frequently reacted with an epoxy prepolymer based on diglycidylether of bisphenol A. We have studied these reactions from a fundamental point of view and not in industrial conditions. First we compared the kinetics results of different analytical techniques. Secondly, we compared the reactivities of the epoxy in DGEBA and the amino-hydrogen functions in coupling agent to those of model reagents like phenylglycidylether and hexylamine. the third part consists of validating a kinetic mechanism and calculating the rate constants, activation energy and reactivity ratios

  18. Structure and reaction mechanism of basil eugenol synthase.

    Gordon V Louie

    Full Text Available Phenylpropenes, a large group of plant volatile compounds that serve in multiple roles in defense and pollinator attraction, contain a propenyl side chain. Eugenol synthase (EGS catalyzes the reductive displacement of acetate from the propenyl side chain of the substrate coniferyl acetate to produce the allyl-phenylpropene eugenol. We report here the structure determination of EGS from basil (Ocimum basilicum by protein x-ray crystallography. EGS is structurally related to the short-chain dehydrogenase/reductases (SDRs, and in particular, enzymes in the isoflavone-reductase-like subfamily. The structure of a ternary complex of EGS bound to the cofactor NADP(H and a mixed competitive inhibitor EMDF ((7S,8S-ethyl (7,8-methylene-dihydroferulate provides a detailed view of the binding interactions within the EGS active site and a starting point for mutagenic examination of the unusual reductive mechanism of EGS. The key interactions between EMDF and the EGS-holoenzyme include stacking of the phenyl ring of EMDF against the cofactor's nicotinamide ring and a water-mediated hydrogen-bonding interaction between the EMDF 4-hydroxy group and the side-chain amino moiety of a conserved lysine residue, Lys132. The C4 carbon of nicotinamide resides immediately adjacent to the site of hydride addition, the C7 carbon of cinnamyl acetate substrates. The inhibitor-bound EGS structure suggests a two-step reaction mechanism involving the formation of a quinone-methide prior to reduction. The formation of this intermediate is promoted by a hydrogen-bonding network that favors deprotonation of the substrate's 4-hydroxyl group and disfavors binding of the acetate moiety, akin to a push-pull catalytic mechanism. Notably, the catalytic involvement in EGS of the conserved Lys132 in preparing the phenolic substrate for quinone methide formation through the proton-relay network appears to be an adaptation of the analogous role in hydrogen bonding played by the equivalent

  19. Crystallization and melt behaviour of isotactic poly((4-alpha,alpha-dimethyl-benzyl)phenyl methacrylate)

    vanEkenstein, GORA; Tan, YY

    1997-01-01

    The crystallization and melting behaviour of practically 100% isotactic poly((4-alpha,alpha-dimethylbenzyl) phenyl methacrylate) has been studied by d.s.c. and light microscopy. Crystallization from the melt seemed to be non-spherulitic. The maximum crystallization rate, which could only be determin

  20. The reaction mechanism of the (3HE,T) reaction and applications to nuclear structure

    1986-01-01

    In this thesis we present a study on the reaction meachanism of the (3He,t) reaction at 70-80 MeV bombarding energy and on structures of the residual nuclei excited in this reaction: 24-Al, 26-Al, 28-P, 32-Cl, 40-Sc, 42-Sc and 58-Cu... Zie: Summary

  1. Novel P2 promoter-derived HNF4{alpha} isoforms with different N-terminus generated by alternate exon insertion

    Huang, Jianmin, E-mail: jmhuang@partners.org [Pediatric Endocrine Unit, MassGeneral Hospital for Children and Harvard Medical School, Boston, Massachusetts, 02114-2696 (United States); Levitsky, Lynne L. [Pediatric Endocrine Unit, MassGeneral Hospital for Children and Harvard Medical School, Boston, Massachusetts, 02114-2696 (United States); Rhoads, David B., E-mail: rhoads@helix.mgh.harvard.edu [Pediatric Endocrine Unit, MassGeneral Hospital for Children and Harvard Medical School, Boston, Massachusetts, 02114-2696 (United States)

    2009-04-15

    Hepatocyte nuclear factor 4{alpha} (HNF4{alpha}) is a critical transcription factor for pancreas and liver development and functions in islet {beta} cells to maintain glucose homeostasis. Mutations in the human HNF4A gene lead to maturity onset diabetes of the young (MODY1) and polymorphisms are associated with increased risk for type 2 diabetes mellitus (T2DM). Expression of six HNF4{alpha} variants, three each from two developmentally regulated promoters, has been firmly established. We have now detected a new set of HNF4{alpha} variants designated HNF4{alpha}10-12 expressed from distal promoter P2. These variants, generated by inclusion of previously undetected exon 1E (human = 222 nt, rodent = 136 nt) following exon 1D have an altered N-terminus but identical remaining reading frame. HNF4{alpha}10-{alpha}12 are expressed in pancreatic islets (and liver) and exhibit transactivation potentials similar to the corresponding {alpha}7-{alpha}9 isoforms. DNA-binding analyses implied much higher protein levels of HNF4{alpha}10-{alpha}12 in liver than expected from the RT-PCR data. Our results provide evidence for a more complex expression pattern of HNF4{alpha} than previously appreciated. We recommend inclusion of exon 1E and nearby DNA sequences in screening for HNF4{alpha} mutations and polymorphisms in genetic analyses of MODY1 and T2DM.

  2. Preparation by a Rheological Phase Reaction Method and Thermal Decomposition Reaction Mechanism of Nickelous Salicylate Tetrahydrate

    WangJin-long; YuanLiang-jie; YangYi-yong; SunJu-tang; ZhangKe-li

    2003-01-01

    The single crystal nickel salicylate tetrahydrate was prepared with the rheological phase reaction method from nickelous hydroxide and salicylic acid. The crystal structure was determinecL It is monoclinic, space group P21/n, α=0.678 74(3), b=0. 515 91(2), c=2. 313 30(9) nm, β=90.9286(17)°,V=0. 809 94(6) nm3, Z=2, ρcalod =1. 661 g· cm-3. Final R indices: R=0. 027 9 and ωR=0.065 0[Ⅰ>2σ(Ⅰ)]. The thermal decomposition mechanism in an inert atmosphere was investigated via TG, DTG and DTA. The thermal decomposition products were characterized with IR and micro-powder X-ray diffraction method. A new coordination polymer ( NiC6 H4 O)n as an intermediate product and nanoscale metal nickel were obtained in the ranges of 364-429℃ and 429-680℃, respectively.

  3. The mechanisms of delayed onset type adverse reactions to oseltamivir.

    Hama, Rokuro

    2016-09-01

    Oseltamivir is recommended for the treatment and prophylaxis of influenza in persons at higher risk for influenza complications such as individuals with diabetes, neuropsychiatric illnesses, and respiratory, cardiac, renal, hepatic or haematological diseases. However, a recent Cochrane review reported that reduction of antibody production, renal disorders, hyperglycaemia, psychiatric disorders, and QT prolongation may be related to oseltamivir use. The underlying mechanisms are reviewed. There is decisive evidence that administration of a clinically compatible dose of oseltamivir in mice challenged by a respiratory syncytial virus (RSV) that lacks a neuraminidase gene showed symptom-relieving effects and inhibition of viral clearance. These effects were accompanied by decreased level of T cell surface sialoglycosphingolipid (ganglioside) GM1 that is regulated by the endogenous neuraminidase in response to viral challenge. Clinical and non-clinical evidence supports the view that the usual dose of oseltamivir suppresses pro-inflammatory cytokines such as interferon-gamma, interleukin-6, and tumour necrosis factor-alpha almost completely with partial suppression of viral shedding in human influenza virus infection experiment. Animal toxicity tests support the clinical evidence with regard to renal and cardiac disorders (bradycardia and QT prolongation) and do not disprove the metabolic effect. Reduction of antibody production and cytokine induction and renal, metabolic, cardiac, and prolonged psychiatric disorders after oseltamivir use may be related to inhibition of the host's endogenous neuraminidase. While the usual clinical dose of zanamivir may not have this effect, a higher dose or prolonged administration of zanamivir and other neuraminidase inhibitors may induce similar delayed reactions, including reduction of the antibody and/or cytokine production. PMID:27251370

  4. Theoretical studies on reaction mechanisms of unstable nuclei

    Recent studies on reactions of unstable nuclei by means of the continuum-discretized coupled-channels method (CDCC) are briefly reviewed. The topics covered are: four-body breakup processes for 6He induced reaction, microscopic description of projectile breakup processes, and new approach to inclusive breakup processes. (author)

  5. Mechanism of reaction synthesis of Li-B alloys

    LIU; Zhijian; (刘志坚); QU; Xuanhui; (曲选辉); LI; Zhiyou; (李志友); HUANG; Baiyun; (黄伯云)

    2003-01-01

    A model for reaction synthesis of Li-B alloys has been presented. Results show that the first exothermal reaction can be divided into three stages. The first stage is an instantaneous reaction on the boundary between boron particles and lithium melting, in which the caloric released is inversely proportional to the particle size of the boron powder. The second stage is a reaction between the unreacted boron and the lithium that diffuses through the product LiB3 on the surface of the boron particle. This process can be described by Johnston model. The third stage is dissolution of the product LiB3 to Li liquid, which takes place at temperature up to 420℃. At the same time, the second exothermal reaction begins, which consists of nucleation and growth of the last Li-B compound. It can be divided into two substages, i.e. the nucleation pregnant stage and the exploded reaction stage. When the concentration of the particle nucleated is high enough, an exploding reaction takes place. The lower the temperature, the longer the time needed for the exploding reaction. By the model presented, the experimental phenomena in the synthesis are explained.

  6. Mechanisms in adverse reactions to food. The nose

    Høst, A

    1995-01-01

    Rhinitis is a common symptom in food allergic patients, but rhinitis is rarely the only symptom. Rhinitis due to adverse reactions to preservatives and colorants is very rare. In anaphylactic systemic reactions to foods the rhinitis symptoms are caused by inflammatory mediators transported by the...

  7. New mechanism of spiral wave initiation in a reaction-diffusion-mechanics system.

    Louis D Weise

    Full Text Available Spiral wave initiation in the heart muscle is a mechanism for the onset of dangerous cardiac arrhythmias. A standard protocol for spiral wave initiation is the application of a stimulus in the refractory tail of a propagating excitation wave, a region that we call the "classical vulnerable zone." Previous studies of vulnerability to spiral wave initiation did not take the influence of deformation into account, which has been shown to have a substantial effect on the excitation process of cardiomyocytes via the mechano-electrical feedback phenomenon. In this work we study the effect of deformation on the vulnerability of excitable media in a discrete reaction-diffusion-mechanics (dRDM model. The dRDM model combines FitzHugh-Nagumo type equations for cardiac excitation with a discrete mechanical description of a finite-elastic isotropic material (Seth material to model cardiac excitation-contraction coupling and stretch activated depolarizing current. We show that deformation alters the "classical," and forms a new vulnerable zone at longer coupling intervals. This mechanically caused vulnerable zone results in a new mechanism of spiral wave initiation, where unidirectional conduction block and rotation directions of the consequently initiated spiral waves are opposite compared to the mechanism of spiral wave initiation due to the "classical vulnerable zone." We show that this new mechanism of spiral wave initiation can naturally occur in situations that involve wave fronts with curvature, and discuss its relation to supernormal excitability of cardiac tissue. The concept of mechanically induced vulnerability may lead to a better understanding about the onset of dangerous heart arrhythmias via mechano-electrical feedback.

  8. Theoretical Study on Reaction Mechanism of Aluminum-Water System

    Yun-lan Sun; Yan Tian; Shu-fen Li

    2008-01-01

    A theoretical study on the reaction of aluminum with water in the gas phase was performed using the hybrid density functional B3LYP and QCISD(T) methods with the 6-311+G(d,p) and the 6-311++G(d,p) basis sets. The results show that there are three possible reaction pathways that involve four isomers, seven transition structures, and two possible products for the reaction of aluminum with water. The two most favorable reaction pathways were found, whose intermediates and products agreed quite well with experimental results. The enthalpy and Gibbs free energy change of the reaction between AI and H2O at 298 and 2000 K were calculated. Some results are also in good agreement with the previous calculations or experimental results.

  9. Mercury Methylation by Cobalt Corrinoids: Relativistic Effects Dictate the Reaction Mechanism.

    Demissie, Taye B; Garabato, Brady D; Ruud, Kenneth; Kozlowski, Pawel M

    2016-09-12

    The methylation of Hg(II) (SCH3 )2 by corrinoid-based methyl donors proceeds in a concerted manner through a single transition state by transfer of a methyl radical, in contrast to previously proposed reaction mechanisms. This reaction mechanism is a consequence of relativistic effects that lower the energies of the mercury 6p1/2 and 6p3/2 orbitals, making them energetically accessible for chemical bonding. In the absence of spin-orbit coupling, the predicted reaction mechanism is qualitatively different. This is the first example of relativity being decisive for the nature of an observed enzymatic reaction mechanism. PMID:27510509

  10. Pre-equilibrium nuclear reactions: An introduction to classical and quantum-mechanical models

    In studies of light-ion induced nuclear reactions one distinguishes three different mechanisms: direct, compound and pre-equilibrium nuclear reactions. These reaction processes can be subdivided according to time scales or, equivalently, the number of intranuclear collisions taking place before emission. Furthermore, each mechanism preferably excites certain parts of the nuclear level spectrum and is characterized by different types of angular distributions. This presentation includes description of the classical, exciton model, semi-classical models, with some selected results, and quantum mechanical models. A survey of classical versus quantum-mechanical pre-equilibrium reaction theory is presented including practical applications

  11. Boyer's Reaction and Transetherification: Mechanism and New Perspectives.

    Fraschetti, Caterina; Speranza, Maurizio; Guarcini, Laura; Roselli, Graziella; Filippi, Antonello

    2016-04-01

    The progress and stereochemistry of Boyer's reaction were analyzed using several simple, chiral, alcoholic substrates, a variable amount of BiBr3 and different solvents. Basic solvents inhibit the reaction, while cyclohexane works very well; thus, it was our choice for the present study. In contrast to previous works, BiBr3 behaves as a true catalyst, being not consumed during the reaction. Although poisoning of the catalyst occurs to some extent, it does not prejudice the reaction yields (>90%). Gas chromatography/mass spectrometry (GC-MS) monitoring of the reaction revealed that, for example, in the presence of alcohol , isomeric ethers transetherificate to . We propose a unifying mechanistic model for both Boyer's and transetherification reactions, in which the electronic properties of n-adducts intermediates, formed by combination of bismuth(III) of BiBr3 and oxygen atoms of alcohols and ethers, play the key role for both the reactivity and the stereochemical outcome of the reaction. Chirality 28:269-275, 2016. © 2016 Wiley Periodicals, Inc. PMID:26924771

  12. Reaction mechanisms for the synthesis of the heaviest elements from heavy ion reactions

    This review paper concerns fusion reactions with light heavy-ions, cold fusion, transfer reactions using light heavy-ions or heavy ions. In two appendices, methods for the separation and detection of nuclides in the domain of heaviest elements are described and a comment on the discovery of the element 104 is given. 51 figs., 10 tabs., 335 refs

  13. The Kabachnik–Fields Reaction: Mechanism and Synthetic Use

    György Keglevich

    2012-11-01

    Full Text Available The Kabachnik–Fields (phospha-Mannich reaction involving the condensation of primary or secondary amines, oxo compounds (aldehydes and ketones and >P(OH species, especially dialkyl phosphites, represents a good choice for the synthesis of α-aminophosphonates that are of significant importance due to their biological activity. In general, these three-component reactions may take place via an imine or an α-hydroxy-phosphonate intermediate. The monitoring of a few Kabachnik–Fields reactions by in situ Fourier transform IR spectroscopy has indicated the involvement of the imine intermediate that was also justified by theoretical calculations. The Kabachnik–Fields reaction was extended to >P(OH species, comprising cyclic phosphites, acyclic and cyclic H-phosphinates, as well as secondary phosphine oxides. On the other hand, heterocyclic amines were also used to prepare new α-amino phosphonic, phosphinic and phosphine oxide derivatives. In most cases, the synthesis under solvent-free microwave (MW conditions is the method of choice. It was proved that, in the cases studied by us, there was no need for the use of any catalyst. Moreover, it can be said that sophisticated and environmentally unfriendly catalysts suggested are completely unnecessary under MW conditions. Finally, the double Kabachnik–Fields reaction has made available bis(phosphonomethylamines, bis(phosphinoxidomethylamines and related species. The bis(phosphinoxidomethylamines serve as precursors for bisphosphines that furnish ring platinum complexes on reaction with dichlorodibenzonitriloplatinum.

  14. Assessment of existing H2/O2 chemical reaction mechanisms at reheat gas turbine conditions

    Weydahl, Torleif; Seljeskog, Morten; Haugen, Nils Erland L

    2011-01-01

    This paper provides detailed comparisons of chemical reaction mechanisms of H2 applicable at high preheat temperatures and pressures relevant to gas turbine and particularly Alstom's reheat gas turbine conditions. It is shown that the available reaction mechanisms exhibit large differences in several important elementary reaction coefficients. The reaction mechanisms are assessed by comparing ignition delay and laminar flame speed results obtained from CHEMKIN with available data, however, the amount of data at these conditions is scarce and a recommended candidate among the mechanisms can presently not be selected. Generally, the results with the GRI-Mech and Leeds mechanisms deviate from the Davis, Li, O'Conaire, Konnov and San Diego mechanisms, but there are also significant deviations between the latter five mechanisms that altogether are better adapted to hydrogen. The differences in ignition delay times between the dedicated hydrogen mechanisms (O'Conaire, Li and Konnov) range from approximately a maxim...

  15. Variation near the hepatocyte nuclear factor (HNF)-4alpha gene associates with type 2 diabetes in the Danish population

    Hansen, S K; Rose, C S; Glümer, C;

    2005-01-01

    The hepatocyte nuclear factor (HNF)-4alpha is an orphan nuclear receptor, which plays crucial roles in regulating hepatic gluconeogenesis and insulin secretion. The gene encoding HNF-4alpha (HNF4A) is located on chromosome 20q12-q13 in a region that in several studies has shown linkage with type 2...

  16. An ab initio molecular dynamics study of the roaming mechanism of the H2+HOC+ reaction

    Yu, Hua-Gen

    2011-08-01

    We report here a direct ab initio molecular dynamics study of the p-/o-H2+HOC+ reaction on the basis of the accurate SAC-MP2 potential energy surface. The quasi-classical trajectory method was employed. This work largely focuses on the study of reaction mechanisms. A roaming mechanism was identified for this molecular ion-molecule reaction. The driving forces behind the roaming mechanism were thoroughly investigated by using a trajectory dynamics approach. In addition, the thermal rate coefficients of the H2+HOC+ reaction were calculated in the temperature range [25, 300] K and are in good agreement with experiments.

  17. Recent developments in semiclassical mechanics: eigenvalues and reaction rate constants

    Miller, W.H.

    1976-04-01

    A semiclassical treatment of eigenvalues for a multidimensional non-separable potential function and of the rate constant for a chemical reaction with an activation barrier is presented. Both phenomena are seen to be described by essentially the same semiclassical formalism, which is based on a construction of the total Hamiltonian in terms of the complete set of ''good'' action variables (or adiabatic invariants) associated with the minimum in the potential energy surface for the eigenvalue case, or the saddle point in the potential energy surface for the case of chemical reaction.

  18. Molecular Mechanism by which One Enzyme Catalyzes Two Reactions

    Nishimasu, Hiroshi; Fushinobu, Shinya; Wakagi, Takayoshi

    Unlike ordinary enzymes, fructose-1,6-bisphosphate (FBP) aldolase/phosphatase (FBPA/P) catalyzes two distinct reactions : (1) the aldol condensation of dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate to FBP, and (2) the dephosphorylation of FBP to fructose-6-phosphate. We solved the crystal structures of FBPA/P in complex with DHAP (its aldolase form) and FBP (its phosphatase form). The crystal structures revealed that FBPA/P exhibits the dual activities through a dramatic conformational change in the active-site architecture. Our findings expand the conventional concept that one enzyme catalyzes one reaction.

  19. Mechanical effects of alkali silica reaction in concrete studied by SEM-image analysis

    Ben Haha, Mohsen

    2006-01-01

    The occurrence of alkali-silica and alkali-silicate reactions causes damage in concrete. Even though the reaction has been known for some time, the progress of reaction in affected structures is difficult to predict. This research programme aims to study the relationship between the progress of the reaction and the mechanical properties of the concrete in order to support better prognosis of the effect of ASR on affected structure. The basic principal of the research programme is to character...

  20. Mechanical effects of alkali silica reaction in concrete studied by SEM-image analysis

    Ben Haha, Mohsen; Scrivener, Karen

    2007-01-01

    The occurrence of alkali-silica and alkali-silicate reactions causes damage in concrete. Even though the reaction has been known for some time, the progress of reaction in affected structures is difficult to predict. This research programme aims to study the relationship between the progress of the reaction and the mechanical properties of the concrete in order to support better prognosis of the effect of ASR on affected structure. The basic principal of the research programme is to character...

  1. Assessment of deuteron-induced reaction mechanisms at low and medium energies

    Avrigeanu V.; Avrigeanu M.

    2010-01-01

    An extended analysis of the nuclear reaction mechanisms involved in the deuterons interaction with 63,65Cu is presented. First, the available elastic-scattering data analysis provided us the optical potential for reaction cross sections calculations. An increased effort has been devoted to the breakup mechanism, both the elastic breakup and the breakup fusion contributions to the different activation cross sections being carefully considered. Next, the direct reaction contributions throu...

  2. Alcali-silica reactions: Mechanisms for crack formations

    Goltermann, Per

    2006-01-01

    Alkali-silica reactions (ASR) are found all over the world and cause a large number of damage, which have lead to different sets of requirements in the different countries for the aggregates, the cements and the admixtures. One of the reasons for the damage and the different requirements is that...

  3. Heavy-ion reaction mechanisms studied with the spin spectrometer

    Experimental data and statistical-model calculations for xn and αxn products of the reaction 20Ne + 146Nd at 136 MeV are shown to be in generally good agreement, indicating that equilibrium processes are dominant. Preliminary results on the heavy-ion ejectiles from 19F + 159Tb are presented

  4. Unified connected theory of few-body reaction mechanisms in N-body scattering theory

    Polyzou, W. N.; Redish, E. F.

    1978-01-01

    A unified treatment of different reaction mechanisms in nonrelativistic N-body scattering is presented. The theory is based on connected kernel integral equations that are expected to become compact for reasonable constraints on the potentials. The operators T/sub +-//sup ab/(A) are approximate transition operators that describe the scattering proceeding through an arbitrary reaction mechanism A. These operators are uniquely determined by a connected kernel equation and satisfy an optical theorem consistent with the choice of reaction mechanism. Connected kernel equations relating T/sub +-//sup ab/(A) to the full T/sub +-//sup ab/ allow correction of the approximate solutions for any ignored process to any order. This theory gives a unified treatment of all few-body reaction mechanisms with the same dynamic simplicity of a model calculation, but can include complicated reaction mechanisms involving overlapping configurations where it is difficult to formulate models.

  5. Unified connected theory of few-body reaction mechanisms in N-body scattering theory

    A unified treatment of different reaction mechanisms in nonrelativistic N-body scattering is presented. The theory is based on connected kernel integral equations that are expected to become compact for reasonable constraints on the potentials. The operators T/sub +-//sup ab/(A) are approximate transition operators that describe the scattering proceeding through an arbitrary reaction mechanism A. These operators are uniquely determined by a connected kernel equation and satisfy an optical theorem consistent with the choice of reaction mechanism. Connected kernel equations relating T/sub +-//sup ab/(A) to the full T/sub +-//sup ab/ allow correction of the approximate solutions for any ignored process to any order. This theory gives a unified treatment of all few-body reaction mechanisms with the same dynamic simplicity of a model calculation, but can include complicated reaction mechanisms involving overlapping configurations where it is difficult to formulate models

  6. Studies on the mechanism of the peroxyoxalate chemiluminescence reaction

    Further consideration has been given to the reaction pathway of a model peroxyoxalate chemiluminescence system. Again utilising doubly labelled oxalyl chloride and anhydrous hydrogen peroxide, 2D EXSY 13C nuclear magnetic resonance (NMR) spectroscopy experiments allowed for the characterisation of unknown products and key intermediate species on the dark side of the peroxyoxalate chemiluminescence reaction. Exchange spectroscopy afforded elucidation of a scheme comprised of two distinct mechanistic pathways, one of which contributes to chemiluminescence. 13C NMR experiments carried out at varied reagent molar ratios demonstrated that excess amounts of hydrogen peroxide favoured formation of 1,2-dioxetanedione: the intermediate that, upon thermolysis, has been long thought to interact with a fluorophore to produce light

  7. Nuclear reaction mechanisms. Progress report, June 1976--July 1977

    Blann, M.

    1977-01-01

    Research under the subject contract is on heavy ion induced reactions, both on experimental measurement and theoretical interpretation. Measurements have included determination of elastic scattering, evaporation residue, fission, quasi elastic and deep inelastic scattering cross sections. From these data we have extracted information on fusion barrier heights and radii, nucleus-nucleus potentials and fission parameterizations at high angular momenta. We have started investigating influence of excitation energies on inverse cross sections and of precompound decay in heavy ion reactions, and have investigated multidimensional potential energy surfaces for heavy ion collisions. Work which has been published is listed in the Publications Section; work not yet published and/or in progress is discussed herein.

  8. Production mechanism of superheavy nuclei in massive fusion reactions

    FENG Zhao-Qing; JIN Gen-Ming; LI Jun-Qing; Werner Scheid

    2009-01-01

    Within the concept of the dinuclear system (DNS), a dynamical model is proposed for describing the formation of superheavy nuclei in complete fusion reactions by incorporating the coupling of the relative motion to the nucleon transfer process. The capture of two heavy colliding nuclei, the formation of the compound nucleus and the de-excitation process are calculated by using an empirical coupled channel model, solving a set of microscopically derived master equations numerically and applying statistical theory, respectively.Fusion-fission reactions and evaporation residue excitation functions of synthesizing superheavy nuclei (SHN) are investigated systematically and compared them with available experimental data. The possible factors that affecting the production cross sections of SHN are discussed in this workshop.

  9. Nuclear reaction mechanisms. Progress report, June 1976--July 1977

    Research under the subject contract is on heavy ion induced reactions, both on experimental measurement and theoretical interpretation. Measurements have included determination of elastic scattering, evaporation residue, fission, quasi elastic and deep inelastic scattering cross sections. From these data we have extracted information on fusion barrier heights and radii, nucleus-nucleus potentials and fission parameterizations at high angular momenta. We have started investigating influence of excitation energies on inverse cross sections and of precompound decay in heavy ion reactions, and have investigated multidimensional potential energy surfaces for heavy ion collisions. Work which has been published is listed in the Publications Section; work not yet published and/or in progress is discussed herein

  10. Novel error propagation approach for reducing H2S/O2 reaction mechanism

    A reduction strategy of hydrogen sulfide/oxygen reaction mechanism is conducted to simplify the detailed mechanism. Direct relation graph and error propagation methodology (DRGEP) has been used. A novel approach of direct elementary reaction error (DERE) has been developed in this study. The developed approach allowed for further reduction of the reaction mechanism. The reduced mechanism has been compared with the detailed mechanism under different conditions to emphasize its validity. The results obtained from the resulting reduced mechanism showed good agreement with that from the detailed mechanism. However, some discrepancies have been found for some species. Hydrogen and oxygen mole fractions showed the largest discrepancy of all combustion products. The reduced mechanism was also found to be capable of tracking the changes that occur in chemical kinetics through the change in reaction conditions. A comparison on the ignition delay time obtained from the reduced mechanism and previous experimental data showed good agreement. The reduced mechanism was used to track changes in mechanistic pathways of Claus reactions with the reaction progress.

  11. Experimental and Guided Theoretical Investigation of Complex Reaction Mechanisms in a Prins Reaction of Glyoxylic Acid and Isobutene

    Angelici, Gaetano; Nicolet, Stefan; Uda, Narasimha R.; Creus, Marc

    2014-01-01

    A laboratory experiment was designed for undergraduate students, in which the outcome of an easy single-step organic synthesis with well-defined conditions was not elucidated until the end of the exercise. In class, students predict and discuss the possible products using their knowledge of reaction mechanisms. In the laboratory, they learn how to…

  12. Illustration of reaction mechanism in polyatomic systems via computer movies

    The CD4 + T* systems is suited for classroom illustration of reaction dynamics. Questions about the system can be illustrated by reducing selected many-body trajectories to a 16 mm color movie that represents the six-body motion in projected coordinates. Such a movie has been produced for this system. The production procedure used is reported, and a detailed description of the contents of the movie is given. (U.S.)

  13. Elucidation of Reaction Mechanisms Far from Thermodynamic Equilibrium.

    Nagao, Raphael

    2016-04-01

    Far from equilibrium: This thesis provides a deep mechanistic analysis of the electrooxidation of methanol when the system is kept far from the thermodynamic equilibrium. Under an oscillatory regime, interesting characteristics between the elementary reaction steps were observed. We were able to elucidate the effect of the intrinsic drift in a potential time-series responsible for spontaneous transition of temporal patterns and the carbon dioxide decoupling from direct and indirect pathways. PMID:27308227

  14. Quantum-mechanical description of initial stage of fusion reaction

    Within the formalism of the reduced density matrix the process of capture of projectile by a target at energies near the Coulomb barrier is considered. The influence of dissipation and fluctuations is taken self-consistently into account. Using the calculated probabilities of the capture, averaged in all mutual orientations of the deformed colliding nuclei, the evaporation residue cross-sections are calculated for the asymmetric fusion reactions

  15. Kinetics and mechanism of the reaction of uranium hexafluoride and tritium

    Maienschein, Jon L.; Sunderland, William E.

    1985-03-01

    Using infrared analysis, we found that the reaction rate of gaseous uranium hexafluoride and tritium is determined solely by the rate at which energy from the radioactive decay of tritium is absorbed in the reaction mixture. Because uranium hexafluoride and tritium absorb β-energy with different efficiencies, the reaction rate is somewhat dependent on the initial reactant concentrations. Reaction products include uranium subfluorides and tritium fluoride. A radiochemistry model has been developed that includes β-energy production and absorption in the gas phase to allow calculation of the reaction yield per ion pair formed. With this model it was found that the reaction mechanism does not include lengthy chain propagation steps-only about 10 uranium hexafluoride molecules are consumed for each ion-pair formed in the gas phase. Many possible reaction steps are suggested that could contribute to the observed overall mechanism.

  16. Thermodynamic chemical energy transfer mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium chemical reactions

    Chemical energy transfer mechanisms at finite temperature are explored by a chemical energy transfer theory which is capable of investigating various chemical mechanisms of non-equilibrium, quasi-equilibrium, and equilibrium. Gibbs energy fluxes are obtained as a function of chemical potential, time, and displacement. Diffusion, convection, internal convection, and internal equilibrium chemical energy fluxes are demonstrated. The theory reveals that there are chemical energy flux gaps and broken discrete symmetries at the activation chemical potential, time, and displacement. The statistical, thermodynamic theory is the unification of diffusion and internal convection chemical reactions which reduces to the non-equilibrium generalization beyond the quasi-equilibrium theories of migration and diffusion processes. The relationship between kinetic theories of chemical and electrochemical reactions is also explored. The theory is applied to explore non-equilibrium chemical reactions as an illustration. Three variable separation constants indicate particle number constants and play key roles in describing the distinct chemical reaction mechanisms. The kinetics of chemical energy transfer accounts for the four control mechanisms of chemical reactions such as activation, concentration, transition, and film chemical reactions. - Highlights: • Chemical energy transfer theory is proposed for non-, quasi-, and equilibrium. • Gibbs energy fluxes are expressed by chemical potential, time, and displacement. • Relationship between chemical and electrochemical reactions is discussed. • Theory is applied to explore nonequilibrium energy transfer in chemical reactions. • Kinetics of non-equilibrium chemical reactions shows the four control mechanisms

  17. Film forming kinetics and reaction mechanism of γ-glycidoxypropyltrimethoxysilane on low carbon steel surfaces

    The film forming kinetics and reaction mechanism of γ-GPS on low carbon steel surfaces was investigated by FTIR-ATR, AFM, NSS and theoretical calculation method. The results from experimental section indicated that the reaction of γ-GPS on low carbon steel surfaces followed the conventional reaction mechanism, which can be described as reaction (I) (Me (Metal)-OH + HO-Si → Me-O-Si + H2O) and reaction (II) (Si-OH + Si-OH → Si-O-Si + H2O). During film forming process, the formation of Si-O-Fe bond (reaction (I)) exhibited oscillatory phenomenon, the condensation degree of silanol monomers (reaction (II)) increased continuously. The metal hydroxyl density had significant influence on the growth mechanisms and corrosion resisting property of γ-GPS films. The results from theoretical calculation section indicated that the patterns of reaction (I) and reaction (II) were similar, involving a nucleophilic attack on the silicon center. The formation of Si-O-Fe bond (reaction (I)) was kinetically and thermodynamically preferred, which had catalytic effect on its condensation with neighboring silanol monomers (reaction (II)). Our DFT calculations were good consistent with the experimental measurements.

  18. On the reaction of the nitroso group with olefins. Mechanisms of ene reactions

    Intra- and intermolecular isotope effects point to a two-step process for the reaction of pentafluoronitrosobenzene with tetramethylethylene to afford the ene product, rate-determining formation of an intermediate (for which the arizidine N-oxide is suggested) followed by C-H (or C-D) cleavage to the ene product

  19. On the reaction of the nitroso group with olefins. Mechanisms of ene reactions

    Seymour, C.A.; Greene, F.D.

    1982-11-15

    Intra- and intermolecular isotope effects point to a two-step process for the reaction of pentafluoronitrosobenzene with tetramethylethylene to afford the ene product, rate-determining formation of an intermediate (for which the arizidine N-oxide is suggested) followed by C-H (or C-D) cleavage to the ene product.

  20. Fasting induces basolateral uptake transporters of the SLC family in the liver via HNF4alpha and PGC1alpha.

    Dietrich, Christoph G; Martin, Ina V; Porn, Anne C; Voigt, Sebastian; Gartung, Carsten; Trautwein, Christian; Geier, Andreas

    2007-09-01

    Fasting induces numerous adaptive changes in metabolism by several central signaling pathways, the most important represented by the HNF4alpha/PGC-1alpha-pathway. Because HNF4alpha has been identified as central regulator of basolateral bile acid transporters and a previous study reports increased basolateral bile acid uptake into the liver during fasting, we hypothesized that HNF4alpha is involved in fasting-induced bile acid uptake via upregulation of basolateral bile acid transporters. In rats, mRNA of Ntcp, Oatp1, and Oatp2 were significantly increased after 48 h of fasting. Protein expression as determined by Western blot showed significant increases for all three transporters 72 h after the onset of fasting. Whereas binding activity of HNF1alpha in electrophoretic mobility shift assays remained unchanged, HNF4alpha binding activity to the Ntcp promoter was increased significantly. In line with this result, we found significantly increased mRNA expression of HNF4alpha and PGC-1alpha. Functional studies in HepG2 cells revealed an increased endogenous NTCP mRNA expression upon cotransfection with either HNF4alpha, PGC-1alpha, or a combination of both. We conclude that upregulation of the basolateral bile acid transporters Ntcp, Oatp1, and Oatp2 in fasted rats is mediated via the HNF4alpha/PGC-1alpha pathway. PMID:17640976

  1. Theoretical Studies of the Reaction Mechanisms of CH3S + NO2

    2002-01-01

    The potential energy surface for the CH3S + NO2 reaction has been studied using the ab initio G3 (MP2) method. A variety of possible complexes and saddle points along the minimum energy reaction paths have been characterized at UMP2 (full)/6-31G(d) level. The calculations reveal dominating reaction mechanisms of the title reaction: CH3S + NO2 firstly produce intermediate CH3SONO, then break up into CH3SO + NO. The results are valuable to understand the atmospheric sulfur compounds oxidation mechanism.

  2. Program Helps To Determine Chemical-Reaction Mechanisms

    Bittker, D. A.; Radhakrishnan, K.

    1995-01-01

    General Chemical Kinetics and Sensitivity Analysis (LSENS) computer code developed for use in solving complex, homogeneous, gas-phase, chemical-kinetics problems. Provides for efficient and accurate chemical-kinetics computations and provides for sensitivity analysis for variety of problems, including problems involving honisothermal conditions. Incorporates mathematical models for static system, steady one-dimensional inviscid flow, reaction behind incident shock wave (with boundary-layer correction), and perfectly stirred reactor. Computations of equilibrium properties performed for following assigned states: enthalpy and pressure, temperature and pressure, internal energy and volume, and temperature and volume. Written in FORTRAN 77 with exception of NAMELIST extensions used for input.

  3. Rescattering mechanisms for anti pd→pX reactions

    Inclusive proton spectra for the reactions anti pd→3πp, anti pd→5πd, and anti pd→Kanti Kmπp are calculated. In addition to nucleon exchange, the rescattering of pions and kaons, and the production and absorption of heavy mesons is evaluated. In the proton spectator momentum regime of 200 to 600 MeV, the role of heavy mesons is found to be negligible. The proper counting of the topological variants of pion and kaon rescattering can explain the cross sections with the exception of the anti pd→3πp channel. (orig.)

  4. Prevention of growth of human lung carcinoma cells and induction of apoptosis by a novel phenoxazinone, 2-amino-4,4alpha-dihydro-4alpha,7-dimethyl-3H-phenoxazine-3-one.

    Abe, A; Yamane, M; Tomoda, A

    2001-04-01

    Anti-tumor effects of a novel phenoxazinone, 2-amino-4,4-dihydro-4alpha,7-dimethyl-3H-phenoxazine-3-one (Phx), which was synthesized by the reaction of 2-amino-5-methylphenol with bovine hemoglobin, were studied in terms of suppression of the proliferation of human lung carcinoma cells and apoptosis induction. When Phx was added to cultures of the human lung carcinoma cell lines A549 (adenocarcinoma) and H226 (squamous carcinoma), it caused the growth inhibition and the death of these cells. Phx also fragmented the DNA of these cells to oligonucleosomal-sized fragments, which is characteristic of the apoptosis, dependent on the dose and exposure time. The cellular death caused by the administration of Phx was partially reversed by the addition of Z-VAD-fmk, a caspase family inhibitor. Present results suggest that Phx demonstrates anti-cancer activity against human lung carcinoma cell lines A549 and H226, by inhibiting growth and inducing apoptosis. PMID:11335795

  5. Nuclear and hadronic reaction mechanisms producing spin asymmetry

    Ken-Ichi Kubo

    2001-08-01

    We briefly review concept of the quark recombination (QRC) model and a general success of the model. To solve the existing problem, so called anomalous spin observables, in the high energy hyperon spin phenomena, we propose a mechanism; the primarily produced quarks, which are predominantly and quarks, act as the leading partons to form the hyperons. Extension of the quark recombination concept with this mechanism is successful in providing a good account of the anomalous spin observables. Another kind of anomaly, the non-zero analysing power and spin depolarization in the hyperon productions, are also discussed and well understood by the presently proposed mechanism. Recently, a further difficulty was observed in an exclusive K+ production and we will indicate a possible diagram for resolving it.

  6. Contribution of quantum effects to the mechanism of positronium reactions

    Quantum-mechanical effects in the mechanism of positronium spin conversion by FeCl2 in water-glycerol mixtures have been demonstrated by measurements of the rate constant of the process as a function of viscosity over the range 0.7-466 cP. Apparently these effects are due to the tunnelling of the positronium atom (Ps) as a whole from some trap to the corresponding level of the complex [Ps...Fe2+]. Similar effects have not been observed for oxidation of Ps by K2Cr2O7. (orig.)

  7. Reaction kinetics and mechanism of magnetic field effects in cryptochrome

    Solov'yov, Ilia; Schulten, Klaus

    2012-01-01

    Creatures as varied as mammals, fish, insects, reptiles, and birds have an intriguing sixth sense that allows them to orient themselves in the Earth's magnetic field. Despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically...

  8. Fission as a probe to understand heavy ion reaction mechanism and dynamics

    The study of nucleus-nucleus collisions provides a way to learn about the nuclear equilibration process in several collective degrees of freedom of much physical significance and their characteristics relaxation times. The reactions resulting from nucleus-nucleus collisions at intermediate energies can be broadly classified in four types: elastic (and quasi elastic) reaction, dinucleus reactions involving deep inelastic collisions, non-compound nucleus fusion reactions like fast-fission, quasi-fission and pre-equilibrium fission and true compound nucleus reactions. Experimentally, it is not always possible to identify uniquely the reaction products as belonging to the pre or post compound nucleus phase. This often leads to apparent anomaly in the interpretation of some of the experimental results in heavy ion reaction studies. Measurements of various observables in fission-like reactions provides information about the reaction mechanism and dynamics. Fission fragment angular distributions, which depend on the spin distributions and the shape parameters of the fissioning nucleus, give information about the fusion dynamics. Pre and post scission neutron multiplicities in fusion-fission reactions are used to determine pre-scission life times. Fragment-fragment angular correlation acts as a probe for linear momentum transfer characterising the reaction mechanism. The experimental results on the different aspects of the heavy ion fission studies and the information obtained on the dynamical features of the heavy ion collisions are summarised. (author). 36 refs., 12 figs

  9. Plant surface reactions: an ozone defence mechanism impacting atmospheric chemistry

    W. Jud

    2015-07-01

    Full Text Available Elevated tropospheric ozone concentrations are considered a toxic threat to plants, responsible for global crop losses with associated economic costs of several billion dollars per year. Plant injuries have been linked to the uptake of ozone through stomatal pores and oxidative damage of the internal leaf tissue. But a striking question remains: how much ozone effectively enters the plant through open stomata and how much is lost by chemical reactions at the plant surface? In this laboratory study we could show that semi-volatile organic compounds exuded by the glandular trichomes of different Nicotiana tabacum varieties are an efficient ozone sink at the plant surface. In our experiments, different diterpenoid compounds were responsible for a strongly variety dependent ozone uptake of plants under dark conditions, when stomatal pores are almost closed. Surface reactions of ozone were accompanied by prompt release of oxygenated volatile organic compounds, which could be linked to the corresponding precursor compounds: ozonolysis of cis-abienol (C20H34O – a diterpenoid with two exocyclic double bonds – caused emissions of formaldehyde (HCHO and methyl vinyl ketone (C4H6O. The ring-structured cembratrien-diols (C20H34O2 with three endocyclic double bonds need at least two ozonolysis steps to form volatile carbonyls such as 4-oxopentanal (C5H8O2, which we could observe in the gas phase, too. Fluid dynamic calculations were used to model ozone distribution in the diffusion limited leaf boundary layer under daylight conditions. In the case of an ozone-reactive leaf surface, ozone gradients in the vicinity of stomatal pores are changed in such a way, that ozone flux through the open stomata is strongly reduced. Our results show that unsaturated semi-volatile compounds at the plant surface should be considered as a source of oxygenated volatile organic compounds, impacting gas phase chemistry, as well as efficient ozone sink improving the ozone

  10. Monosaccharide templates for de novo designed 4-alpha-helix bundle proteins: template effects in carboproteins

    Brask, Jesper; Dideriksen, J.M.; Nielsen, John; Jensen, Knud Jørgen

    2003-01-01

    De novo design and total chemical synthesis of proteins provide powerful approaches to critically test our understanding of protein folding, structure, and stability. The 4-alpha-helix bundle is a frequently studied structure in which four amphiphilic alpha-helical peptide strands form a...... hydrophobic core. Assembly of protein models on a template has been suggested as a way to reduce the entropy of folding. We have previously developed the concept of carbohydrates as templates in the de novo design of protein models termed 'carboproteins'. Here we present the chemical synthesis of three 8.1 k...... melting points in chemical and thermal denaturation experiments....

  11. Interfacial reaction mechanism between matrix and reinforcement in B4C/6061Al composites

    The interfacial reaction mechanism in B4C/6061Al composites, fabricated by the powder metallurgy technique at 560 and 620 °C with various holding times, was subjected to detailed investigations using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and hardness tests. Results showed that complicated interfacial reactions occurred in the B4C/6061Al composites, forming Al3BC, MgAl2O4, MgB7, Mg0.78Al0.75B14, AlB12C2 and Al4SiC4 as the main products, which clearly deteriorated the age-hardening ability of the composites. The interfacial reactions involving Mg and Si could be divided into two series. The oxidation of Mg occurred at both 560 and 620 °C, whereas other reactions only occurred at 620 °C. The existence of the liquid phase at 620 °C activated the reaction between Al and B4C, leading to the generation of free B, and subsequent reactions involving B and Mg occurred. After the reactions involving B and Mg was completed, the reaction involving Al, Si and C took place. It was determined that the reactions involving B and Mg rather than the oxidation of Mg or the reaction involving Si were the main reasons for the consumption of Mg and the deterioration of age-hardening ability of the B4C/6061Al composites at 620 °C. - Highlights: • Complicated interfacial reactions occurred in B4C/6061Al composites. • Reactions involving Mg and Si were divided into oxidation of Mg and other reactions. • Al/B4C reaction produced free B and then activated B/Mg reactions. • B/Mg reactions rather than Mg oxidation were main reasons for Mg consumption. • Interfacial reactions definitely deteriorate age-hardening ability of composites

  12. The methanol-to-hydrocarbons reaction : Influence of acid strength on the mechanism of olefin formation

    2010-01-01

    The methanol-to-hydrocarbons (MTH) reaction is a flexible alternative step in the upgrading of natural gas, coal or biomass. By tuning the catalyst and process conditions, methanol can be converted into a variety of hydrocarbon products including gasoline and polymer-grade olefins. While the reaction has been known for many years, reaction mechanisms are still not fully understood. Most previous mechanistic studies have been performed on aluminosilicate zeolites, so the aim of the present wor...

  13. Theoretical study on the reaction mechanism of CN radical with ketene

    2008-01-01

    The bimolecular single collision reaction potential energy surface of CN radical with ketene (CH2CO) was investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH2CO to form the intermediate NCCH2CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH2CN+CO. The second is a direct addition reaction between CN and CH2CO to form the intermediate CH2C(O)CN followed by its isomerization into NCCH2CO via a CN-shift reaction, and subsequently, NCCH2CO dissociates into CH2CN+CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH2CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The present theoretical computation results, which give an available suggestion on the reaction mechanism, are in good agreement with previous experimental studies.

  14. Reaction mechanisms in 24.3 MeV/nucleon 238U induced reactions through a comprehensive study of fission

    Nuclear reaction mechanisms for system characterized by very different asymmetries (U+C, Si, Ni, Au) have been investigated at 24.3 MeV/nucleon, using as observables both the fission products and the neutron multiplicity. It is clearly observed that the fusion process-whatever its completeness- can only occur with rather light target nuclei, indicating the persistence of potential energy effects much above the interaction barrier. (authors). 22 refs., 1 fig

  15. Probing the Mechanism of 1,4-Conjugate Elimination Reactions Catalyzed by Terpene Synthases

    Faraldos, Juan A.; Gonzalez, Veronica; Li, Amang; Yu, Fanglei; Köksal, Mustafa; Christianson, David W.; Allemann, Rudolf K.

    2012-01-01

    The reaction mechanisms of (E)-β-farnesene synthase (EBFS) and isoprene synthase (ISPS), enzymes that catalyze a formal regioespecific 1,4-conjugate elimination of hydrogen-diphosphate from (E, E)-farnesyl and dimethylallyl diphosphate (FDP and DMADP) to generate the semiochemicals (E)-β-farnesene and isoprene, respectively, were probed with substrate analogs and kinetic measurements. The results support stepwise reaction mechanisms through analogous enzyme-bound allylic cationic intermediate...

  16. Reaction Mechanism of Oxygen Atoms with Unsaturated Hydrocarbons by the Crossed-Molecular-Beams Method

    Buss, R. J.; Baseman, R. J.; Guozhong, H.; Lee, Y. T.

    1982-04-01

    From a series of studies of the reaction of oxygen atoms with unsaturated hydrocarbons using the crossed molecular beam method, the dominant reaction mechanisms were found to be the simple substitution reactions with oxygen atoms replacing H, Cl, Br atom or alkyl groups. Complication due to secondary reaction was avoided by carrying out experiments under single collisions and observing primary products directly. Primary products were identified by measuring the angular and velocity distributions of products at all the mass numbers which could be detected by the mass spectrometer, and from comparison of these distributions, applying the requirement of energy and momentum conservation.

  17. Simulation of chemical reactions in solution by a combination of classical and quantum mechanical approach

    Onida, Giovanni; Andreoni, Wanda

    1995-09-01

    A classical trajectory mapping method was developed to study chemical reactions in solution and in enzymes. In this method, the trajectories were calculated on a classical potential surface and the free energy profile was obtained by mapping the classical surface to the quantum mechanical surface obtained by the semiempirical AM1 method. There is no need to perform expensive quantum mechanical calculations at each iteration step. This method was applied to proton transfer reactions both in aqueous solution and in papain. The results are encouraging, indicating the applicability of this hybrid method to chemical reactions both in solution and in enzymes.

  18. 2013 INORGANIC REACTION MECHANISMS GORDON RESEARCH CONFERENCE (MARCH 3-8, 2013 - HOTEL GALVEZ, GALVESTON TX)

    Abu-Omar, Mahdi M.

    2012-12-08

    The 2013 Gordon Conference on Inorganic Reaction Mechanisms will present cutting-edge research on the molecular aspects of inorganic reactions involving elements from throughout the periodic table and state-of-the art techniques that are used in the elucidation of reaction mechanisms. The Conference will feature a wide range of topics, such as homogeneous and heterogeneous catalysis, metallobiochemistry, electron-transfer in energy reactions, polymerization, nitrogen fixation, green chemistry, oxidation, solar conversion, alkane functionalization, organotransition metal chemistry, and computational chemistry. The talks will cover themes of current interest including energy, materials, and bioinorganic chemistry. Sections cover: Electron-Transfer in Energy Reactions; Catalytic Polymerization and Oxidation Chemistry; Kinetics and Spectroscopy of Heterogeneous Catalysts; Metal-Organic Chemistry and its Application in Synthesis; Green Energy Conversion;Organometallic Chemistry and Activation of Small Molecules; Advances in Kinetics Modeling and Green Chemistry; Metals in Biology and Disease; Frontiers in Catalytic Bond Activation and Cleavage.

  19. Theoretical Study on the Mechanism of CF2 Reaction with CH2O

    LI Zhi-Feng; Lü Ling-Ling; ZHU Yuan-Cheng; LIU Xin-Wen

    2008-01-01

    The insertion reaction mechanism of CF2 with CH2O was investigated at the B3LYP/6-311G(d)//MP2/6-311G(d) level.The geometric conformations at each stationary point in reaction potential surface were fully optimized and the transition states were verified by intrinsic reaction coordinate (IRC) and frequency analysis.The energies of all reactants were calculated with CCSD(T)/6-311G(d)//G2MP2 methods.Results indicated that the P1 reaction route with difuoroaldehyde as product is the dominant reaction pathway, which exhibits nucleophilic character.According to NBO analysis, the starting point of insertion reaction is the interaction between carbene LP(C3) and formaldehyde (*(C1-O2).Besides, the thermodynamic and dynamic properties of dominated reaction (1) at different temperature were studied with statistic thermo- dynamic method and Eyring transition state theory adjusted by Wigner means, from which the proper temperature (500~1200 K) of reaction (1) could be estimated.Finally, the thermo- dynamic and dynamic properties of insertion reaction mechanisms (CF2, CX2 (X = Cl, Br) with CH2O) were compared and discussed.

  20. The mechanism of the (p,α) reaction: pick-up or knock-out

    Several early studies of the (p,α) reaction to discrete states of the final nucleus indicated that it proceeds mainly by the pick-up mechanism, whereas more recent experiments provide qualitative arguments in favour of the knock-out mechanism. This paper reports calculations showing that the angular distributions and analysing powers of the sup(90,92)Zr(p,α)sup(87,89)Y and 118Sn(p,α)115In reactions can be equally well fitted by distorted wave calculations using either mechanism. (author)

  1. Mechanism of degradation and discoloration reaction of L-ascorbic acid

    The mechanisms of decomposition and coloration reaction of L-ascorbic acid are reviewed. At the initial stage of the decomposition, it can be classified roughly into oxidative and non-oxidative processes of decomposition. ASA forms furfural by being heated and decomposed in strong acid. The mechanism of the production of furfural at varying pH in acidic region was discussed. Furfural was produced through the enol form of 3-deoxy-L-pentosulose(3DP). 3DP seemed to be produced by two different routes: the one route consists of successive reactions from ASA through lactone ring-opening, dehydration, decarboxylation, to 3DP, and the other consists of reactions from the 3-keto form of ASA, through lactone ring-opening, decarboxylation, and dehydration, to the enol form of 3DP. ASA is easily reduced and decomposed through dehydro-ASA(DHA) by the presence of an oxidizing agent. The decomposition of DHA is discussed in cases of the systems of DHA alone, DHA and α-aminoacid, and DHA and amine. DHA was decomposed by the same reaction scheme as the decomposition of ASA and yielded 2-furoic acid. In the presence of an amino acid, DHA was decomposed by the Strecker decomposition, and yielded a red compound and a radical. In the presence of an amine, the discoloration reaction seemed to take place through radical reaction mechanism. The coloration reaction of ASA occurs in an acidic medium, and is accelerated by the oxidative process of decomposition. (Nishino, S.)

  2. Toward an Automatic Determination of Enzymatic Reaction Mechanisms and Their Activation Free Energies.

    Zinovjev, Kirill; Ruiz-Pernía, J Javier; Tuñón, Iñaki

    2013-08-13

    We present a combination of the string method and a path collective variable for the exploration of the free energy surface associated to a chemical reaction in condensed environments. The on-the-fly string method is employed to find the minimum free energy paths on a multidimensional free energy surface defined in terms of interatomic distances, which is a convenient selection to study bond forming/breaking processes. Once the paths have been determined, a reaction coordinate is defined as a measure of the advance of the system along these paths. This reaction coordinate can be then used to trace the reaction Potential of Mean Force from which the activation free energy can be obtained. This combination of methodologies has been here applied to the study, by means of Quantum Mechanics/Molecular Mechanics simulations, of the reaction catalyzed by guanidinoacetate methyltransferase. This enzyme catalyzes the methylation of guanidinoacetate by S-adenosyl-l-methionine, a reaction that involves a methyl transfer and a proton transfer and for which different reaction mechanisms have been proposed. PMID:26584125

  3. Intramolecular Lactonization of Poly(α-hydroxyacrylic acid: Kinetics and Reaction Mechanism

    Heli Virkki

    2015-01-01

    Full Text Available Poly(α-hydroxyacrylic acid, PHA, is one of the few polymers with biodegradable properties used in mechanical pulp bleaching to stabilize hydrogen peroxide. A new method for the in situ follow-up of the lactone ring formation of PHA has been developed. The results have further been applied to describe the reaction kinetics of the lactonization and hydrolysis reactions through parameter estimation. In addition, the reaction mechanism is elucidated by multivariate data analysis. Satisfactory identification and semiquantitative separation of the lactone ring as well as the acyclic (carboxyl and hydroxyl groups forms have been established by 1H NMR in the pH range of 1–9. The lactonization reaction approaching equilibrium can be described by pseudo-first-order kinetics in the pH range of 1–6. The rate constants of the pseudo-first-order kinetic model have been estimated by nonlinear regression. Due to the very low rates of lactonization as well as the weak pH dependency of the reaction, an addition-elimination mechanism is proposed. Additionally, the presence of a transient reaction intermediate during lactonization reaction could be identified by subjecting the measurement data to multivariate data analysis (PCA, principal component analysis. A good correlation was found between the kinetic and the PCA models in terms of model validity.

  4. Synergetic mechanism of methanol–steam reforming reaction in a catalytic reactor with electric discharges

    Highlights: • Methanol–steam reforming was performed on Cu catalysts under an electric discharge. • Discharge had a synergetic effect on the catalytic reaction for methanol conversion. • Discharge lowered the temperature for catalyst activation or light off. • Discharge controlled the yield and selectivity of species in a reforming process. • Adsorption triggered by a discharge was a possible mechanism for a synergetic effect. - Abstract: Methanol–steam reforming was performed on Cu/ZnO/Al2O3 catalysts under an electric discharge. The discharge occurred between the electrodes where the catalysts were packed. The electric discharge was characterized by the discharge voltage and electric power to generate the discharge. The existence of a discharge had a synergetic effect on the catalytic reaction for methanol conversion. The electric discharge provided modified reaction paths resulting in a lower temperature for catalyst activation or light off. The discharge partially controlled the yield and selectivity of species in a reforming process. The aspect of control was examined in view of the reaction kinetics. The possible mechanisms for the synergetic effect between the catalytic reaction and electric discharge on methanol–steam reforming were addressed. A discrete reaction path, particularly adsorption triggered by an electric discharge, was suggested to be the most likely mechanism for the synergetic effect. These results are expected to provide a guide for understanding the plasma–catalyst hybrid reaction

  5. Interest of uranium complexes for the mechanism study of the McMurry reaction

    The reducing coupling reactions of ketones in diols and olefins are generally carried out with titanium or samarium compounds. In this work uranium complexes have been used. They have allowed to study the chemical reaction mechanism. This thesis is divided into three parts: 1) the reduction mechanism of uranium tetrachloride by cyclic voltametry has been studied at first. It has been shown that this reduction is followed by a transfer reaction of chlorides between the reduced specie of the higher electronic density and UCl . 2) In the second part is described: the synthesis, the crystal structure, the reactivity of the chemical agents, the stereochemistry of diols and alkenes formation and the pinacolisation reaction catalysis. 3) In the last part, the limits of the McMurry reaction are given by the study of the aromatic ketones pinacolisation reaction by-products. The obtained results show that the complexes of the metals which present a high reducing and oxo-philic (Ti, Sm, U..) character react in a similar way with the carbonyl compounds. If the uranium compounds are less used than those of the titanium in the field of the organic synthesis applications, they are precious auxiliaries and excellent models for reactions mechanisms study and for the synthesis methods optimization. (O.M.)

  6. Quantum mechanical investigations on the role of neutral and negatively charged enamine intermediates in organocatalyzed reactions

    Highlights: • M06-2X functional is suitable to model key steps of proline-catalyzed reactions. • Investigation of the proline-catalyzed aldol reaction mechanism. • Influence of water molecules on the C–C bond formation step. • Mechanism for the reaction of proline-derived enamines with benzhydrylium cations. - Abstract: The proline-catalyzed aldol reaction is the seminal example of asymmetric organocatalysis. Previous theoretical and experimental studies aimed at identifying its mechanism in order to rationalize the outcome of this reaction. Here, we focus on key steps with modern first principle methods, i.e. the M06-2X hybrid exchange–correlation functional combined to the solvation density model to account for environmental effects. In particular, different pathways leading to the formation of neutral and negatively charged enamine intermediates are investigated, and their reactivity towards two electrophiles, i.e. an aldehyde and a benzhydrylium cation, are compared. Regarding the self-aldol reaction, our calculations confirm that the neutral enamine intermediate is more reactive than the negatively charged one. For the reaction with benzhydrylium cations however, the negatively charged enamine intermediate is more reactive

  7. Quantum mechanical investigations on the role of neutral and negatively charged enamine intermediates in organocatalyzed reactions

    Hubin, Pierre O., E-mail: pierre.hubin@unamur.be [Laboratoire de Physico-Chimie Informatique (PCI), Unité de Chimie Physique Théorique et Structurale, University of Namur, 61 rue de Bruxelles, 5000 Namur (Belgium); Jacquemin, Denis [Laboratoire CEISAM – UMR CNRS 6230, Université de Nantes, 2 rue de la Houssinière, BP92208, 44322 Nantes Cedex 3 (France); Institut Universitaire de France 103, Boulevard St Michel, 75005 Paris Cedex 5 (France); Leherte, Laurence; Vercauteren, Daniel P. [Laboratoire de Physico-Chimie Informatique (PCI), Unité de Chimie Physique Théorique et Structurale, University of Namur, 61 rue de Bruxelles, 5000 Namur (Belgium)

    2014-04-15

    Highlights: • M06-2X functional is suitable to model key steps of proline-catalyzed reactions. • Investigation of the proline-catalyzed aldol reaction mechanism. • Influence of water molecules on the C–C bond formation step. • Mechanism for the reaction of proline-derived enamines with benzhydrylium cations. - Abstract: The proline-catalyzed aldol reaction is the seminal example of asymmetric organocatalysis. Previous theoretical and experimental studies aimed at identifying its mechanism in order to rationalize the outcome of this reaction. Here, we focus on key steps with modern first principle methods, i.e. the M06-2X hybrid exchange–correlation functional combined to the solvation density model to account for environmental effects. In particular, different pathways leading to the formation of neutral and negatively charged enamine intermediates are investigated, and their reactivity towards two electrophiles, i.e. an aldehyde and a benzhydrylium cation, are compared. Regarding the self-aldol reaction, our calculations confirm that the neutral enamine intermediate is more reactive than the negatively charged one. For the reaction with benzhydrylium cations however, the negatively charged enamine intermediate is more reactive.

  8. Reaction mechanism of manganese superoxide dismutase studied by combined quantum and molecular mechanical calculations and multiconfigurational methods

    Srnec, Martin; Aquilante, F.; Ryde, U.; Rulíšek, Lubomír

    2009-01-01

    Roč. 113, č. 17 (2009), s. 6074-6086. ISSN 1520-6106 R&D Projects: GA MŠk LC512 Institutional research plan: CEZ:AV0Z40550506 Keywords : reaction mechanism * QM/MM calculations * MnSOD * multireference calculations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.471, year: 2009

  9. Reduction of very large reaction mechanisms using methods based on simulation error minimization

    Nagy, Tibor; Turanyi, Tamas [Institute of Chemistry, Eoetvoes University (ELTE), P.O. Box 32, H-1518 Budapest (Hungary)

    2009-02-15

    A new species reduction method called the Simulation Error Minimization Connectivity Method (SEM-CM) was developed. According to the SEM-CM algorithm, a mechanism building procedure is started from the important species. Strongly connected sets of species, identified on the basis of the normalized Jacobian, are added and several consistent mechanisms are produced. The combustion model is simulated with each of these mechanisms and the mechanism causing the smallest error (i.e. deviation from the model that uses the full mechanism), considering the important species only, is selected. Then, in several steps other strongly connected sets of species are added, the size of the mechanism is gradually increased and the procedure is terminated when the error becomes smaller than the required threshold. A new method for the elimination of redundant reactions is also presented, which is called the Principal Component Analysis of Matrix F with Simulation Error Minimization (SEM-PCAF). According to this method, several reduced mechanisms are produced by using various PCAF thresholds. The reduced mechanism having the least CPU time requirement among the ones having almost the smallest error is selected. Application of SEM-CM and SEM-PCAF together provides a very efficient way to eliminate redundant species and reactions from large mechanisms. The suggested approach was tested on a mechanism containing 6874 irreversible reactions of 345 species that describes methane partial oxidation to high conversion. The aim is to accurately reproduce the concentration-time profiles of 12 major species with less than 5% error at the conditions of an industrial application. The reduced mechanism consists of 246 reactions of 47 species and its simulation is 116 times faster than using the full mechanism. The SEM-CM was found to be more effective than the classic Connectivity Method, and also than the DRG, two-stage DRG, DRGASA, basic DRGEP and extended DRGEP methods. (author)

  10. Hepatocyte nuclear factor 4 alpha is a key factor related to depression and physiological homeostasis in the mouse brain.

    Kyosuke Yamanishi

    Full Text Available Major depressive disorder (MDD is a common psychiatric disorder that involves marked disabilities in global functioning, anorexia, and severe medical comorbidities. MDD is associated with not only psychological and sociocultural problems, but also pervasive physical dysfunctions such as metabolic, neurobiological and immunological abnormalities. Nevertheless, the mechanisms underlying the interactions between these factors have yet to be determined in detail. The aim of the present study was to identify the molecular mechanisms responsible for the interactions between MDD and dysregulation of physiological homeostasis, including immunological function as well as lipid metabolism, coagulation, and hormonal activity in the brain. We generated depression-like behavior in mice using chronic mild stress (CMS as a model of depression. We compared the gene expression profiles in the prefrontal cortex (PFC of CMS and control mice using microarrays. We subsequently categorized genes using two web-based bioinformatics applications: Ingenuity Pathway Analysis and The Database for Annotation, Visualization, and Integrated Discovery. We then confirmed significant group-differences by analyzing mRNA and protein expression levels not only in the PFC, but also in the thalamus and hippocampus. These web tools revealed that hepatocyte nuclear factor 4 alpha (Hnf4a may exert direct effects on various genes specifically associated with amine synthesis, such as genes involved in serotonin metabolism and related immunological functions. Moreover, these genes may influence lipid metabolism, coagulation, and hormonal activity. We also confirmed the significant effects of Hnf4a on both mRNA and protein expression levels in the brain. These results suggest that Hnf4a may have a critical influence on physiological homeostasis under depressive states, and may be associated with the mechanisms responsible for the interactions between MDD and the dysregulation of

  11. Unified connected theory of few-body reaction mechanisms in N-body scattering theory

    A unified treatment of different reaction mechanisms in nonrelativistic N-body scattering is presented. The theory is based on connected kernel integral equations that are expected to become compact for reasonable constraints on the potentials. These equations can be formulated for any important set of asymptotic channels. The operators T/sub +-//sup ab/(A) are approximate transition operators that describe the scattering proceeding through an arbitrary reaction mechanism A. These operators are uniquely determined by a connected kernel equation and satisfy an optical theorem consistent with the choice of reaction mechanism. Connected kernel equations relating T/sub +-//sup ab/(A) to the full T/sub +-//sup ab/ allow correction of the approximate solutions for any ignored process to any order. This theory gives a unified treatment of all few-body reaction mechanisms with the same dynamic simplicity of a model calculation, but can include complicated reaction mechanisms involving overlapping configurations where it is difficult to formulate models. 1 figure

  12. Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

    LI ZhiFeng; L(U) LingLing; KANG JingWan; LU XiaoQuan

    2007-01-01

    The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions, transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal reaction coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path, which proceeds via two steps: i) two reactants form an intermediate (IM1), which is an exothermal reaction of 8.62 kJ·mol-1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift, in which the energy barrier is 44.53 kJ·mol-1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm, in which the reaction has a bigger spontaneity capability, equilibrium constant (K) and higher rate constant (k).

  13. Formation reaction mechanisms of hydroxide anions from Mg(OH){sub 2} layers

    Vaiss, Viviane S. [Departamento de Química, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, 36036-330 (Brazil); Borges, Itamar [Departamento de Química, Instituto Militar de Engenharia, Rio de Janeiro, RJ, 22290-270 (Brazil); Wypych, Fernando [Departamento de Química, Universidade Federal do Paraná, Curitiba, PR, 81531-990 (Brazil); Leitão, Alexandre A., E-mail: alexandre.leitao@ufjf.edu.br [Departamento de Química, Universidade Federal de Juiz de Fora, Juiz de Fora, MG, 36036-330 (Brazil)

    2013-06-03

    Highlights: • Mg(OH){sub 2} hydroxide anion migrates to the surface thus producing an adsorbed free hydroxide anion. • Orbital contributions from adsorbed free hydroxide anion dominate the shape of total DOS in the region near the Fermi level. • The hydroxide anion formation reaction in Mg(OH){sub 2} from Mg(OH){sub 2} dissociation is slower than the formation from H{sub 2}O dissociation. • Formation of hydroxide anions in a layered hydroxide would involve reaction of H{sub 2}O molecules with layer hydroxide anions. - Abstract: DFT calculations with periodic boundary conditions were used to study two formation reaction mechanisms of adsorbed free hydroxide anions on the surface of the brucite, Mg(OH){sub 2}. In the first mechanism, we investigated the migration of a hydroxide anion present in the structure of Mg(OH){sub 2} to the layer surface. In the second, a mechanism composed of three elementary reactions was examined for the reaction of H{sub 2}O molecules with the brucite layer surface. The result in both mechanisms is the formation of hydroxide anions and a hydroxide vacancy in the positively charged Mg(OH){sub 2} layer. The global reaction is the same in both cases and the computed Gibbs free energy variation equals 37.5 kcal/mol at room temperature. The reaction barrier for the formation of hydroxide anion on Mg(OH){sub 2} surface from H{sub 2}O dissociation (27.6 kcal/mol) is lower than the reaction barrier for the formation of hydroxide anions from Mg(OH){sub 2} dissociation (43.2 kcal/mol)

  14. Reaction Mechanism and Kinetics of Aqueous Solutions of Primary and Secondary Alkanolamines and Carbon Dioxide

    BAVBEK, Olgac; ALPER, Erdoğan

    1999-01-01

    The mechanism and kinetics of the reaction between aqueous solutions of CO2 and the alkanolamines 1-amino-2-propanol, 3-amino-1-propanol,2-methyl aminoethanol and 2-ethyl aminoethanol were investigated using a stopped flow technique. It was found that the reaction orders according to power law kinetics were between 1.1 and 2.0, depending on the alkanolamine and the concentration ranges investigated. This fractional order was therefore considered to be further evidence that carbamate ...

  15. Structural snapshots of the SCR reaction mechanism on Cu-SSZ-13.

    Günter, Tobias; Carvalho, Hudson W P; Doronkin, Dmitry E; Sheppard, Thomas; Glatzel, Pieter; Atkins, Andrew J; Rudolph, Julian; Jacob, Christoph R; Casapu, Maria; Grunwaldt, Jan-Dierk

    2015-06-01

    The structure of copper sites in Cu-SSZ-13 during NH3-SCR was unravelled by a combination of novel operando X-ray spectroscopic techniques. Strong adsorption of NH3 on Cu, its reaction with weakly adsorbed NO from the gas phase, and slow re-oxidation of Cu(I) were proven. Thereby the SCR reaction mechanism is significantly different to that observed for Fe-ZSM-5. PMID:25951966

  16. Formation reaction mechanisms of hydroxide anions from Mg(OH)2 layers

    Highlights: • Mg(OH)2 hydroxide anion migrates to the surface thus producing an adsorbed free hydroxide anion. • Orbital contributions from adsorbed free hydroxide anion dominate the shape of total DOS in the region near the Fermi level. • The hydroxide anion formation reaction in Mg(OH)2 from Mg(OH)2 dissociation is slower than the formation from H2O dissociation. • Formation of hydroxide anions in a layered hydroxide would involve reaction of H2O molecules with layer hydroxide anions. - Abstract: DFT calculations with periodic boundary conditions were used to study two formation reaction mechanisms of adsorbed free hydroxide anions on the surface of the brucite, Mg(OH)2. In the first mechanism, we investigated the migration of a hydroxide anion present in the structure of Mg(OH)2 to the layer surface. In the second, a mechanism composed of three elementary reactions was examined for the reaction of H2O molecules with the brucite layer surface. The result in both mechanisms is the formation of hydroxide anions and a hydroxide vacancy in the positively charged Mg(OH)2 layer. The global reaction is the same in both cases and the computed Gibbs free energy variation equals 37.5 kcal/mol at room temperature. The reaction barrier for the formation of hydroxide anion on Mg(OH)2 surface from H2O dissociation (27.6 kcal/mol) is lower than the reaction barrier for the formation of hydroxide anions from Mg(OH)2 dissociation (43.2 kcal/mol)

  17. Interfacial reaction mechanism between matrix and reinforcement in B{sub 4}C/6061Al composites

    Li, Y.Z. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Wang, Q.Z., E-mail: qzwang@imr.ac.cn [Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Wang, W.G.; Xiao, B.L. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Ma, Z.Y., E-mail: zyma@imr.ac.cn [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

    2015-03-15

    The interfacial reaction mechanism in B{sub 4}C/6061Al composites, fabricated by the powder metallurgy technique at 560 and 620 °C with various holding times, was subjected to detailed investigations using optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and hardness tests. Results showed that complicated interfacial reactions occurred in the B{sub 4}C/6061Al composites, forming Al{sub 3}BC, MgAl{sub 2}O{sub 4}, MgB{sub 7}, Mg{sub 0.78}Al{sub 0.75}B{sub 14}, AlB{sub 12}C{sub 2} and Al{sub 4}SiC{sub 4} as the main products, which clearly deteriorated the age-hardening ability of the composites. The interfacial reactions involving Mg and Si could be divided into two series. The oxidation of Mg occurred at both 560 and 620 °C, whereas other reactions only occurred at 620 °C. The existence of the liquid phase at 620 °C activated the reaction between Al and B{sub 4}C, leading to the generation of free B, and subsequent reactions involving B and Mg occurred. After the reactions involving B and Mg was completed, the reaction involving Al, Si and C took place. It was determined that the reactions involving B and Mg rather than the oxidation of Mg or the reaction involving Si were the main reasons for the consumption of Mg and the deterioration of age-hardening ability of the B{sub 4}C/6061Al composites at 620 °C. - Highlights: • Complicated interfacial reactions occurred in B{sub 4}C/6061Al composites. • Reactions involving Mg and Si were divided into oxidation of Mg and other reactions. • Al/B{sub 4}C reaction produced free B and then activated B/Mg reactions. • B/Mg reactions rather than Mg oxidation were main reasons for Mg consumption. • Interfacial reactions definitely deteriorate age-hardening ability of composites.

  18. Development and validation of a reduced combined biodiesel–diesel reaction mechanism

    Ng, Hoon Kiat; Gan, Suyin; Ng, Jo-Han;

    2013-01-01

    In this study, a compact combined biodiesel–diesel (CBD) reaction mechanism for diesel engine simulations is proposed through the combination of three component mechanisms using a chemical class-based approach. The proposed mechanism comprises the reaction mechanisms of methyl crotonate (MC......), methyl butanoate (MB) and n-heptane which are the surrogate fuel models of unsaturated fatty acid methyl ester, saturated fatty acid methyl ester and straight chain hydrocarbon (HC), respectively. The MC and MB mechanisms are adopted to represent biodiesel fuels, while n-heptane is utilised to...... computational fluid dynamics studies involving a light-duty diesel engine fuelled with biodiesel of different feedstock types, diesel as well as their blends....

  19. Study of the mechanism of muon catalyzed t + t fusion reaction

    The mechanism for the muon catalyzed fusion reaction t + t → 4He + 2n + 11.33 MeV is investigated. The model of the cascade reaction with 5He as an intermediate state is considered. Both the ground and the first excited states of 5He are taken into account. The neutron energy spectrum measured in the recent experiment is compared with the Monte Carlo-simulated one. Varying reaction parameters, we obtain optimum values for the relative weights of the 5He ground and excited states and for the excitation energy and width of the excited state

  20. Chemical reaction of hexagonal boron nitride and graphite nanoclusters in mechanical milling systems

    Muramatsu, Y.; Grush, M.; Callcott, T.A. [Univ. of Tennessee, Knoxville, TN (United States)] [and others

    1997-04-01

    Synthesis of boron-carbon-nitride (BCN) hybrid alloys has been attempted extensively by many researchers because the BCN alloys are considered an extremely hard material called {open_quotes}super diamond,{close_quotes} and the industrial application for wear-resistant materials is promising. A mechanical alloying (MA) method of hexagonal boron nitride (h-BN) with graphite has recently been studied to explore the industrial synthesis of the BCN alloys. To develop the MA method for the BCN alloy synthesis, it is necessary to confirm the chemical reaction processes in the mechanical milling systems and to identify the reaction products. Therefore, the authors have attempted to confirm the chemical reaction process of the h-BN and graphite in mechanical milling systems using x-ray absorption near edge structure (XANES) methods.

  1. Investigation of the CH3Cl + CN− reaction in water: Multilevel quantum mechanics/molecular mechanics study

    The CH3Cl + CN− reaction in water was studied using a multilevel quantum mechanics/molecular mechanics (MM) method with the multilevels, electrostatic potential, density functional theory (DFT) and coupled-cluster single double triple (CCSD(T)), for the solute region. The detailed, back-side attack SN2 reaction mechanism was mapped along the reaction pathway. The potentials of mean force were calculated under both the DFT and CCSD(T) levels for the reaction region. The CCSD(T)/MM level of theory presents a free energy activation barrier height at 20.3 kcal/mol, which agrees very well with the experiment value at 21.6 kcal/mol. The results show that the aqueous solution has a dominant role in shaping the potential of mean force. The solvation effect and the polarization effect together increase the activation barrier height by ∼11.4 kcal/mol: the solvation effect plays a major role by providing about 75% of the contribution, while polarization effect only contributes 25% to the activation barrier height. Our calculated potential of mean force under the CCSD(T)/MM also has a good agreement with the one estimated using data from previous gas-phase studies

  2. The Mechanisms of Oxygen Reduction and Evolution Reactions in Nonaqueous Lithium-Oxygen Batteries

    Cao, Ruiguo; Walter, Eric D.; Xu, Wu; Nasybulin, Eduard N.; Bhattacharya, Priyanka; Bowden, Mark E.; Engelhard, Mark H.; Zhang, Jiguang

    2014-09-01

    The oxygen reduction/evolution reaction (ORR/OER) mechanisms in nonaqueous Li-O2 batteries have been investigated by using electron paramagnetic resonance spectroscopy in this work. We identified the superoxide radical anion (O2•-) as an intermediate in the ORR process using 5,5-dimethyl-pyrroline N-oxide as a spin trap, while no O2•- in OER was detected during the charge process. These findings provide insightful understanding on the fundamental oxygen reaction mechanisms in rechargeable nonaqueous Li-O2 batteries.

  3. Solid state reactions of V75Si25 driven by mechanical alloying

    The solid state reactions of V75Si25 mixture during mechanical alloying were investigated by X-ray diffraction, scanning and transmission electron microscopy. Two different pathways of V/Si reaction under different milling conditions were observed, i.e., high energy milling led to formation of intermetallic compounds while relatively low energy milling resulted in formation of amorphous phase. The thermal responses of the milled products were studied through differential thermal analysis. The thermodynamics and kinetics related to the different phase transition are discussed. Finally, the effect of air contamination on phase transformation in both mechanical alloying and annealing processes was investigated. (orig.)

  4. Identification of mechanisms in heavy ion reactions by measurement of angular correlations

    The identification of reaction mechanisms in light heavy-ion collisions has been performed within the framework of the three body kinematics, by means of angular correlation measurements. The 16O+27Al, 16+O+28Si and 10B+27Al reactions were investigated at Laboratory bombarding energies of 64 MeV, 64 and 48 MeV, respectively. Contributions of transfer-reemission and projectile sequential decay mechanisms were identified by the analysis of the relative kinetic energy of the final state components, excitation energies of the system at the intermediate stages, and also by means of fits to theoretical predictions for the angular correlations. (author)

  5. Ab initio Mechanism Study on the Reaction of Chlorine Atom with Formic Acid

    于海涛; 付宏刚; 等

    2003-01-01

    The potential energy surface(PES) for the reaction of Cl atom with HCOOH is predicted using ab initio molecular orbital calculation methods at UQCIDS(T,full)6-311++G(3df,2p)//UMP2(full)/6-311+G(d,P) level of theory with zero-point vibrational energy (ZPVE) correction.The calculated results show that the reaction mechanism of Cl atom with formic acid is a C-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom with a 3.73kJ/mol reaction barrier height,leading to the formation of cis-HOCO radical which will reacts with Cl atom or other molecules in such a reaction system.Because the reaction barrier height of O-site hydrogen abstraction reaction from cis-HOC(H)O molecule by Cl atom which leads to the formation of HCO2 radical is 67.95kJ/mol,it is a secondary reaction channel in experiment,This is in good agreement with the prediction based on the previous experiments.

  6. Unified connected theory of few-body reaction mechanisms in N-body scattering theory

    A complete N-body reaction theory is described for any reaction mechanism, based on a system of connected kernel integral equations; one describing the dynamics of the reaction mechanism in a unitary way, one describing the dynamics of the excluded processes in a unitary way, and one combining these to get the full N-body dynamics. A new democratic decomposition of the full Hamiltonian is introduced in terms of proper partition Hamiltonians as follows: H=Σ/sub a/C/sub a/H/sub a/ where the C/sub a/'s are combinatoric coefficients. The set of asympototic channels, A0, may be divided into the physically important channels A, and the remainder A'. The sets A and A' of asymptotic channels are referred to as reaction mechanisms (RM's). By making a spectral resolution of each partition Hamiltonian, parts corresponding to each RM may be identified. Using the above expansion this gives a decomposition of full Hamiltonian by reaction mechanism, H=H (A)+H (A'), depending only on the spectral properties of the partition Hamiltonians. We define the RM resolvent by G (A) = (Z-H (A)-1) and G (A') = (Z-H (A')-1). We derived connected kernel equations for these operators. The full resolvent may then be obtained as the solution of a connected kernel equation involving G (A) and G (A'). Transition operators associated with G (A) and G (A') are shown to satisfy optical theorems where all of the scattered flux comes through the channels of A and A' respectively. If A is chosen to only include channels having no more than three or four clusters, the equations for G (A) have the numerical simplicity of a few body problem. This formulation should be useful for serious evaluations of existing reaction models, and in developing new reaction models that can emphasize any given RM including breakup, rearrangement, and those involving overlapping clustering

  7. Reaction mechanism of the reverse water-gas shift reaction using first-row middle transition metal catalysts L'M (M = Fe, Mn, Co): a computational study.

    Liu, Cong; Cundari, Thomas R; Wilson, Angela K

    2011-09-19

    The mechanism of the reverse water-gas shift reaction (CO(2) + H(2) → CO + H(2)O) was investigated using the 3d transition metal complexes L'M (M = Fe, Mn, and Co, L' = parent β-diketiminate). The thermodynamics and reaction barriers of the elementary reaction pathways were studied with the B3LYP density functional and two different basis sets: 6-311+G(d) and aug-cc-pVTZ. Plausible reactants, intermediates, transition states, and products were modeled, with different conformers and multiplicities for each identified. Different reaction pathways and side reactions were also considered. Reaction Gibbs free energies and activation energies for all steps were determined for each transition metal. Calculations indicate that the most desirable mechanism involves mostly monometallic complexes. Among the three catalysts modeled, the Mn complex shows the most favorable catalytic properties. Considering the individual reaction barriers, the Fe complex shows the lowest barrier for activation of CO(2). PMID:21838224

  8. Dynamics of the molecular and atomic mechanisms for the hydrogen-iodine exchange reaction.

    Raff, L. M.; Thompson, D. L.; Sims, L. B.; Porter, R. N.

    1972-01-01

    The molecular and atomic mechanisms for the hydrogen-iodine exchange reaction are treated theoretically by means of extensive classical trajectories calculated on a reasonable potential energy surface on which the single adjustable parameter is the iodine-core effective charge. The analysis shows the molecular mechanism to be dynamically forbidden, but gives an over-all rate constant for the atomic mechanism that is in agreement with the experimental values. It is indicated that the formation of a weak H2I complex plays an important dynamical role if the atomic mechanism is limited to reactions with collision complexes involving no more than two hydrogen atoms and two iodine atoms. Excellent agreement with experiment is obtained for the rate constant for the recombination I+I+H2 yields I2+H2 and its negative temperature coefficient.

  9. Formation of degradation compounds from lignocellulosic biomass in the biorefinery: sugar reaction mechanisms.

    Rasmussen, Helena; Sørensen, Hanne R; Meyer, Anne S

    2014-02-19

    The degradation compounds formed during pretreatment when lignocellulosic biomass is processed to ethanol or other biorefinery products include furans, phenolics, organic acids, as well as mono- and oligomeric pentoses and hexoses. Depending on the reaction conditions glucose can be converted to 5-(hydroxymethyl)-2-furaldehyde (HMF) and/or levulinic acid, formic acid and different phenolics at elevated temperatures. Correspondingly, xylose can follow different reaction mechanisms resulting in the formation of furan-2-carbaldehyde (furfural) and/or various C-1 and C-4 compounds. At least four routes for the formation of HMF from glucose and three routes for furfural formation from xylose are possible. In addition, new findings show that biomass monosaccharides themselves can react further to form pseudo-lignin and humins as well as a wide array of other compounds when exposed to high temperatures. Hence, several aldehydes and ketones and many different organic acids and aromatic compounds may be generated during hydrothermal treatment of lignocellulosic biomass. The reaction mechanisms are of interest because the very same compounds that are possible inhibitors for biomass processing enzymes and microorganisms may be valuable biobased chemicals. Hence a new potential for industrial scale synthesis of chemicals has emerged. A better understanding of the reaction mechanisms and the impact of the reaction conditions on the product formation is thus a prerequisite for designing better biomass processing strategies and forms an important basis for the development of new biorefinery products from lignocellulosic biomass as well. PMID:24412507

  10. The hadron-nucleus collision reaction mechanism memorized by fast nucleons emitted from target nuclei

    It is shown in this work that: 1. The target-nucleus damaged in a hadron-nucleus nuclear collision memorizes information about the collision mechanism; 2. Similar information is contained in characteristics of the incident hadron passage through the target nucleus. The mechanism of the hadron-nucleus collision process is presented - as experimentally based, from the collision reaction starting up to the destroyed target-nucleus transmutation into stable fragments. 34 refs., 2 figs

  11. Reaction Mechanisms of Metalloenzymes and Synthetic Model Complexes Activating Dioxygen : A Computational study

    Georgiev, Valentin

    2009-01-01

    Quantum chemistry has nowadays become a powerful and efficient tool that can be successfully used for studies of biosystems. It is therefore possibleto model the enzyme active-site and the reactions undergoing into it, as well as obtaining quite accurate energetic profiles. Important conclusions can be drawn from such profiles about the  plausibility of different putative mechanisms. Density Functional Theory is used in the present thesis for investigation of the catalytic mechanism of dioxyg...

  12. Theoretical Study on the Mechanism of the Cycloaddition Reaction between Stannylene and Ethylene or Formaldehyde

    卢秀慧; 翟利民; 王沂轩

    2001-01-01

    The mechanism of the cycloaddition reaction of singlet stannylene and ethylene or formaldehyde has been studied by using density functional theory, The geometrical parameters, h-armonic vibrational frequencies and energies of stationary points for potential energy surface are calculated by RB3LYP/3-21G* method. The results show that the two reaction proceesses are both two steps: (1) stannylene and ethylene or formaldehyde form an energy-rich intermediate complex respectively, which is an exothermal reaction with no barrier;(2) two intermediate complexes isomerize to the product, respectively, with the barriers of these two reactions being 52.97and 45.15 kJ/mol at RB3LYP/3-21G* level.

  13. Reaction mechanism of 3-chlorophenol with OH, H in aqueous solution

    2003-01-01

    The reaction mechanism of 3-chlorophenol with OH, H inaqueous solution was studied by transient technology. The3-chlorophenol aqueous solutions have been saturated with air or N2previously. Under alkaline condition, the reaction of OH radicalwith 3-chlorophenol produces 3-chlorinated phenoxyl radical, withthe absorption peaks at 400 nm and 417 nm. Under neutral condition,the reaction of OH radical with 3-chlorophenol produces OH-adductwith the maximal absorption at about 340 nm. And in acid solution,the reaction of H with 3-chlorophenol produces H-adduct with themaximal absorption at about 320 nm. 3-chlorophenol is compared with4- and 2-chlorophenols from the free radical pathways. The resultsshow that the positions of chlorine on the aromatic ring stronglyinfluence the dehalogenation and degradation process.

  14. Mechanisms of branching reactions in melanin formation - Ab initio quantum engineering approach -

    Kishida, Ryo; Menez Aspera, Susan; Kasai, Hideaki

    Melanin, a pigment found in animals, consists of two types of oligomeric unit: eumelanin and pheomelanin. The color of the skin, the hair, and the eyes is controlled by the ratio of eumelanin/pheomelanin production. Especially, dopachrome and dopaquinone are the precursor molecules of melanin which directly affect the composition of melanin through their branching reactions. Dopachrome is converted into two possible monomers of eumelanin. Dopaquinone can undergo both eumelanin and pheomelanin synthesis. To understand the mechanisms and controlling factors that govern the conversions, reactions of the two molecules are investigated using density functional theory-based first-principles calculations. Our results deepen mechanistic understanding of the reactions and open possibilities to design properties and functions of melanin. In this talk, we will discuss about the competitions of the branching reactions.

  15. Kinetics and Mechanism of the Reaction of Ozone with Double Bonds

    Razumovskii, S. D.; Zaikov, Gennadii E.

    1980-12-01

    Analysis of the results of recent studies has shown that the reaction of ozone with the double bonds of organic compounds apparently takes place not by a synchronous addition mechanism but through a reversible stage involving the formation of an intermediate complex of ozone with the double bond. The subsequent stages of the reaction involve the formation of a primary ozonide, its decomposition into two fragments, their combination, and a number of other transformations. The properties of the intermediate products, the relationship between the structure of the original alkenes and their reactivity towards ozone, the influence of the nature of the solvent on the direction and rate of the reaction, and the practical application of the reaction of ozone with double bonds in research and chemical technology have been examined. The bibliography contains 205 references.

  16. A DFT Study Toward the Reaction Mechanisms of TNT With Hydroxyl Radicals for Advanced Oxidation Processes.

    He, Xi; Zeng, Qun; Zhou, Yang; Zeng, Qingxuan; Wei, Xianfeng; Zhang, Chaoyang

    2016-05-26

    The degradation pathway of environmental contaminant 2,4,6-trinitrotoluene (TNT) was investigated computationally at the SMD(Pauling)/M06-2X/6-311+G(d,p) level of theory. The dominant decomposition pathway of TNT → 4,6-dinitro-o-cresol → 4,6-dinitro-2-hydroxybenzylalcohol → 4,6-dinitro-2-hydroxybenzaldehyde was provided, and the corresponding predicted products and their distributions are in a good agreement with available experimental data on TNT degradation by Fenton reaction. It was shown that the mechanism of addition-elimination is crucial for this stage of the reaction. The reaction of H atom abstraction is a minor competing pathway. The details on transition states, intermediate radicals, and free energy surfaces for all proposed reactions are given and make up for a lack of experimental knowledge. PMID:27135259

  17. Molecular dynamics simulations of the reaction mechanism in Ni/Al reactive intermetallics

    We present an atomistic level description of the reaction mechanisms in thermally ignited samples of reactive core/shell Ni/Al wires. The combination of very long simulation times (up to 0.1 μs) and very reactive core/shell nanostructures enables ignition at unprecedentedly low temperatures for molecular dynamics simulations. Samples ignited at low temperatures (900 K or less) follow a multi-stage reaction process involving solid-phase diffusion and the formation of the B2 NiAl phase, while samples ignited at higher temperatures, follow a direct reaction path with accelerated diffusion of Ni into molten Al, leading to a completely molten final state. Interestingly, NiAl nucleates and grows under a significant concentration gradient, which may explain the absence of other phases like AlNi3. The formation of the B2 intermetallic slows atomic diffusion and consequently the reaction rates

  18. Kinetics and Mechanism of the Exothermic First-stage Decomposition Reaction of Dinitroglycoluril

    ZHAO,Feng-Qi(赵凤起); HU,Rong-Zu(胡荣祖); CHEN,Pei(陈沛); LUO,Yang(罗阳); GAO,Sheng-Li(高胜利); SONG,Ji-Rong(宋纪蓉); SHI,Qi-Zhen(史启祯)

    2004-01-01

    Under linear temperature increase condition, the thermal behavior, mechanism and kinetic parameters of the exothermic decomposition reaction of the title compound have been studied by means of DSC and IR. The initial stage of the mechanism was proposed. The empirical kinetic model function in differential form, apparent activation energy and pre-exponential constant of the exothermic decomposition reaction are α 0.526, 207.0 kJ·mol-1 and 1018.49 s-1, respectively. The critical temperature of thermal explosion of the compound is 252.87 ℃. The values of △S≠, △H≠ and △G≠ of the reaction are 128.4 J·mol-1·K-1, 218.9 kJ·mol-1 and 152.7 kJ·mol-1, respectively.

  19. Chemical dynamics in the gas phase: Time-dependent quantum mechanics of chemical reactions

    Gray, S.K. [Argonne National Laboratory, IL (United States)

    1993-12-01

    A major goal of this research is to obtain an understanding of the molecular reaction dynamics of three and four atom chemical reactions using numerically accurate quantum dynamics. This work involves: (i) the development and/or improvement of accurate quantum mechanical methods for the calculation and analysis of the properties of chemical reactions (e.g., rate constants and product distributions), and (ii) the determination of accurate dynamical results for selected chemical systems, which allow one to compare directly with experiment, determine the reliability of the underlying potential energy surfaces, and test the validity of approximate theories. This research emphasizes the use of recently developed time-dependent quantum mechanical methods, i.e. wave packet methods.

  20. The Mechanism of the Eeffect of Mineral Admixtures on the Expansion of Aalkali-silica Reaction

    WANG Aiqin; Niu Jishou; ZHANG Chengzhi

    2008-01-01

    On the base of the influence rule of silica fume, slag and fly ash on alkali-silica reaction under the condition of 70℃, the mechanism of the effect of mineral admixtures on alkali-silica reaction is studied further in the paper. The results show that the effects of mineral admixtures on alkali-silica reaction are mainly chemistry effect and surface physichemistry effect. Under suitable condition, the chemistry effect may make alkali-silica reaction to be inhibited effectively, but the physichemistry effect only make alkali-silica reaction to be delayed. The chemistry effect and the physichemistry effect of minerals admixture are relative to the content of Ca(OH)2 in system. Under the condition that there is a large quantity of Ca(OH)2, mineral admixture cannot inhibit alkali-silica reaction effectively. Only when Ca(OH)2 in the system is very less, it is possible that mineral admixture inhibits alkali-silica reaction effectively.

  1. Differences in the Abilities to Mechanically Eliminate Activation Energies for Unimolecular and Bimolecular Reactions

    Kochhar, Gurpaul S.; Mosey, Nicholas J.

    2016-03-01

    Mechanochemistry, i.e. the application of forces, F, at the molecular level, has attracted significant interest as a means of controlling chemical reactions. The present study uses quantum chemical calculations to explore the abilities to mechanically eliminate activation energies, ΔE‡, for unimolecular and bimolecular reactions. The results demonstrate that ΔE‡ can be eliminated for unimolecular reactions by applying sufficiently large F along directions that move the reactant and/or transition state (TS) structures parallel to the zero-F reaction coordinate, S0. In contrast, eliminating ΔE‡ for bimolecular reactions requires the reactant to undergo a force-induced shift parallel to S0 irrespective of changes in the TS. Meeting this requirement depends upon the coupling between F and S0 in the reactant. The insights regarding the differences in eliminating ΔE‡ for unimolecular and bimolecular reactions, and the requirements for eliminating ΔE‡, may be useful in practical efforts to control reactions mechanochemically.

  2. Hydrogen-air detonation cells computed using skeletal and reduced reaction mechanisms

    Kessler, David; Taylor, Brian; Gamezo, Vadim; Oran, Elaine

    2011-11-01

    The multidimensional instability of gas-phase detonations results in a complex dynamic structure at the detonation front that leaves behind characteristic cellular patterns as it propagates. In fuel-air mixtures with high effective activation energies, such as hydrogen and air, these detonation cells can become irregular and modelling this behavior using reduced chemical reaction mechanisms can be challenging. Using complex reaction mechanisms, however, can be computationally overwhelming for problems of practical interest. We compare the reaction front structures and dynamic behavior of two-dimensional detonations in a stoichiometric hydrogen-air mixture computed using a 12-step skeletal mechanism and several reduced mechanisms, including a calibrated one-step model. We pay particular attention to how transverse instabilities that form in this high-activation-energy mixture are affected by the details of the chemistry model. We then discuss how to adjust the parameters in reduced reaction models to better describe irregular triple point behavior. NAS/NRC Postdoctoral Research Associate.

  3. Mechanisms of oxygen reduction reactions for carbon alloy catalysts via first principles molecular dynamics

    Carbon alloy catalysts (CACs) are one of promising candidates for platinum-substitute cathode catalysts for polymer electrolyte fuel cells. We have investigated possible mechanisms of oxygen reduction reactions (ORRs) for CACs via first-principles-based molecular dynamics simulations. In this contribution, we review possible ORRs at likely catalytic sites of CACs suggested from our simulations. (author)

  4. Ego Defenses and Reaction to Stress: A Validation Study of the Defense Mechanisms Inventory

    Gleser, Goldine C.; Sacks, Marilyn

    1973-01-01

    This study investigated the relationship between scores on the Defense Mechanisms Inventory and reaction to an experimental conflict situation in which Ss (85 undergraduate college students) were led to believe that their performance was deficient on a new test of scholastic ability. The pattern of defenses predicted residual posttest estimates of…

  5. Unravelling the reaction mechanism of matrix metalloproteinase 3 using QM/MM calculations

    Feliciano, Gustavo Troiano; da Silva, Antônio José Roque

    2015-07-01

    The matrix metalloproteinase family (MMP) constitutes a family of zinc (Zn) proteases that catalyze the breaking of peptide bonds in proteins. These enzymes are very promising drug targets, since they are involved in remodeling and degradation of the extracellular matrix, which is a key process required for cancer metastasis, and thus, their reaction mechanism has been an area of intensive research. Early proposal based on acid base catalyzed hydrolysis, suggested that a conserved zinc bound water molecule acted as the nucleophile attacking the peptide bond carbon, after being activated by essential glutamate. The possibility of a direct nucleophilic attack by the enzyme, performed by the glutamate was also suggested. These are the key yet unsolved issues about MMP reaction mechanism. In the present work, we used hybrid quantum/classical calculations to analyze the structure and energetics of different possible hydrolysis reaction paths. The results support a water mediated mechanism, where both the nucleophile water molecule and the carbonyl oxygen of the scissile peptide bond are coordinated to zinc in the reactive configuration, while the essential glutamate acts as the base accepting the proton from the nucleophilic water. Formation of the carbon-oxygen bond and breaking of carbon-nitrogen bond were found to be concerted events, with a computed barrier of 14.8 kcal/mol. Substrate polarization was found to be important for the observed reaction mechanism, and a substantial change in the metal coordination environment was observed, particularly, regarding the zinc-histidine coordination.

  6. Reaction mechanism and influence factors analysis for calcium sulfide generation in the process of phosphogypsum decomposition

    Ma, Liping, E-mail: lpma2522@hotmail.com [Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China); Niu, Xuekui; Hou, Juan; Zheng, Shaocong; Xu, Wenjuan [Faculty of Environmental Science and Engineering, Kunming University of Science and Technology, Kunming 650093 (China)

    2011-11-10

    Highlights: Black-Right-Pointing-Pointer Reusing phosphogypsum is to decompose and recycle Ca and sulfur. Black-Right-Pointing-Pointer FactSage6.1 software was used to simulate the decomposition reactions. Black-Right-Pointing-Pointer Experiments had been taken with high sulfur concentration coal as reducing agent. Black-Right-Pointing-Pointer The reaction mechanism of CaS generation had been analysis, 1100 Degree-Sign C could be the best temperature for PG decomposition. - Abstract: FactSage6.1 software simulation and experiments had been used to analysis the reaction mechanism and influence factors for CaS generation during the process of phosphogypsum decomposition. Thermodynamic calculation showed that the reaction for CaS generation was very complex and CaS was generated mainly through solid-solid reaction and gas-solid reaction. The proper CO and CO{sub 2} have benefit for improving the decomposition effects of phosphogypsum and reducing the generation of CaS at 1100 Degree-Sign C. Using high sulfur concentration coal as reducer, the proper reaction conditions to control the generation of CaS were: the coal particle size was between 60 mesh and 100 mesh, reaction temperature was above 1100 Degree-Sign C and the heating rate was 5 Degree-Sign C/min. Experimental and theoretical calculation indicated that the concentration of CaS was only ten percents in the solid product at 1100 Degree-Sign C, which is favorable for the further cement producing using solid production.

  7. Preparation and Reaction Mechanism of LaB6 Powder by Solid―state Reaction at Atmospheric Pressure

    XU Xiu-Hua,XIAO Han-Ning,GUO Wen-Ming,GAO Peng-Zhao,PENG Su-Hua

    2011-04-01

    Full Text Available The lanthanum hexaboride (LaB6) powders were synthesized under atmospheric pressure using B4C and La2O3 powder as the precursors. The thermodynamic conditions for preparing LaB6 at atmospheric pressure were calculated. The effects of temperature and holding time on the phase composition, morphology, particle size and distribution of LaB6 powders were characterized by X―ray diffraction (XRD), scanning electron microscope(SEM) and laser particle size anslyzer. The reaction mechanism was investigated. The results show that LaB6 powders obtained under atmospheric pressure at 1650 ¡䟦or 2h have cube structure with 99.22% purity after washed by hydrochloric acid. When the particle size of La2O3 powder is much smaller than that of B4C particle, the synthesis of LaB6 starts on the surface of B4C particle, then the residual La2O3 and LaBO3 will diffuse through LaB6 shell onto B4C core until the reaction is completely with the temperature rising and holding time prolonged. The initial shape and particle size of LaB6 powders are depending on that of B4C particles.

  8. Theoretical Study on the Reaction Mechanism of F2+2HBr=2HF+Br2

    2005-01-01

    The gas phase reaction mechanism of F2 + 2HBr = 2HF + Br2 has been investigated by (U)MP2 at 6-311G** level, and a series of four-center and three-center transition states have been obtained. The reaction mechanism was achieved by comparing the activation energy of seven reaction paths, i.e. the dissociation energy of F2 is less than the activation energy of the bimolecular elementary reaction F2 + HBr → HF + BrF. Thus it is theoretically proved that the title reaction occurs more easily inthe free radical reaction with three medium steps.

  9. Automated Prediction of Catalytic Mechanism and Rate Law Using Graph-Based Reaction Path Sampling.

    Habershon, Scott

    2016-04-12

    In a recent article [ J. Chem. Phys. 2015 , 143 , 094106 ], we introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modeling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths enable automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resultant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the reaction mechanism and the associated rate law in an automated fashion, without the need for either presupposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; furthermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pressure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles. PMID:26938837

  10. Fasten-induzierte Regulation hepatischer basolateraler Gallensäuretransporter in Ratten vermittelt über PGC-1[alpha]/HNF-4[alpha

    Porn, Anne Christine

    2008-01-01

    Fasting induces numerous adaptive changes in metabolism by several central signaling pathways, the most important represented by the HNF4-alpha PGC-1-alpha-pathway. Because HNF4-alpha has been identified as central regulator of basolateral bile acid transporters and a previous study reports increased basolateral bile acid uptake into the liver during fasting, we hypothesized that HNF4-alpha is involved in fasting-induced bile acid uptake via upregulation of basolateral bile acid transporters....

  11. Cluster reaction of [Ag8]-/[Cu8]- with chlorine: Evidence for the harpoon mechanism?

    Luo, Zhixun; Berkdemir, Cüneyt; Smith, Jordan C.; Castleman, A. W.

    2013-09-01

    To examine the question whether the harpoon mechanism can account for the reactive behavior of microscopic charged systems, we have investigated the reactivity of coinage metal clusters in gas phase. Our studies reveal that the reactivity between [Cu8]-/[Ag8]- and chlorine gas is consistent with the harpoon mechanism. An increased reactive cross section is noted through our theoretical estimation based on two methods, ascribed to a long-range transfer of valence electrons from the [Cu8]-/[Ag8]- cluster to chlorine. Insights into this reactivity will be of interest to other researchers working on obtaining a better understanding of the reaction mechanisms of such superatomic species.

  12. Theoretical study of the reaction mechanism of a series of 4-hydroxycoumarins against the DPPH radical

    Rodríguez, Sergio A.; Baumgartner, Maria T.

    2014-05-01

    Structural, electronic and energetic characteristics of a series of 4-hydroxycoumarin derivatives have been studied using DFT to elucidate the mechanisms involved in their antiradical activities against DPPH radical. Different mechanisms were examined. The thermodynamic parameters obtained were BDE, IP, ETE, PA and PDE, both in gas and methanolic phase. The evaluation of these parameters allowed to conclude that the most probable mechanism was HAT. In addition, the transition state (TS) and pre-TS complex for the reaction of hydroxycoumarins and DPPHrad were calculated. The results provide a physicochemical understanding of the hydrogen abstraction of a no-phenolic hydroxyl.

  13. Quantitative interpretation to the chain mechanism of free radical reactions in cyclohexane pyrolysis

    Yingxian Zhao; Bo Shen; Feng Wei

    2011-01-01

    Pyrolysis of cyclohexane was conducted with a plug flow tube reactor in the temperature range of 873-973 K.Based on the experimental data,the mechanism and kinetic model of cyclohexane pyrolysis reaction were proposed.The kinetic analysis shows that overall conversion of cyclohexane is a first order reaction,of which the rate constant increased from 0.0086 to 0.0225 to 0.0623 s- 1 with the increase of temperature from 873 to 923 to 973 K,and the apparent activation energy was determined to be 155.0+1.0 kJ.mo1-1.The mechanism suggests that the cyclohexane is consumed by four processes:the homolysis of C-C bond (Path Ⅰ),the homolysis of C-H bond (Path Ⅱ) in reaction chain initiation,the H-abstraction of various radicals from the feed molecules in reaction chain propagation (Path Ⅲ),and the process associated with coke formation (Path Ⅳ).The reaction path probability (RPP) ratio of Xpath Ⅰ ∶ Xpath Ⅱ∶ XPath Ⅲ ∶ XPath Ⅳ was 0.5420 ∶ 0.0045 ∶ 0.3897 ∶ 0.0638 at 873 K,and 0.4336 ∶ 0.0061 ∶ 0.4885 ∶ 0.0718 at 973 K,respectively.

  14. Pharmacoepidemiological characterization of drug-induced adverse reaction clusters towards understanding of their mechanisms.

    Mizutani, Sayaka; Noro, Yousuke; Kotera, Masaaki; Goto, Susumu

    2014-06-01

    A big challenge in pharmacology is the understanding of the underlying mechanisms that cause drug-induced adverse reactions (ADRs), which are in some cases similar to each other regardless of different drug indications, and are in other cases different regardless of same drug indications. The FDA Adverse Event Reporting System (FAERS) provides a valuable resource for pharmacoepidemiology, the study of the uses and the effects of drugs in large human population. However, FAERS is a spontaneous reporting system that inevitably contains noise that deviates the application of conventional clustering approaches. By performing a biclustering analysis on the FAERS data we identified 163 biclusters of drug-induced adverse reactions, counting for 691 ADRs and 240 drugs in total, where the number of ADR occurrences are consistently high across the associated drugs. Medically similar ADRs are derived from several distinct indications for use in the majority (145/163=88%) of the biclusters, which enabled us to interpret the underlying mechanisms that lead to similar ADRs. Furthermore, we compared the biclusters that contain same drugs but different ADRs, finding the cases where the populations of the patients were different in terms of age, sex, and body weight. We applied a biclustering approach to catalogue the relationship between drugs and adverse reactions from a large FAERS data set, and demonstrated a systematic way to uncover the cases different drug administrations resulted in similar adverse reactions, and the same drug can cause different reactions dependent on the patients' conditions. PMID:24534381

  15. A theoretical study of the mechanism of the addition reaction between carbene and azacyclopropane

    XIAOJUN TAN

    2010-05-01

    Full Text Available The mechanism of the addition reaction between carbene and azacyclopropane was investigated using the second-order Moller–Plesset perturbation theory (MP2. By using the 6-311+G* basis set, geometry optimization, vibrational analysis and the energy properties of the involved stationary points on the potential energy surface were calculated. From the surface energy profile, it can be predicted that there are two reaction mechanisms. The first one (1 is carbene attack at the N atom of azacyclopropane to form an intermediate, 1a (IM1a, which is a barrier-free exothermic reaction. Then, IM1a can isomerize to IM1b via a transition state 1a (TS1a, in which the potential barrier is 30.0 kJ/mol. Subsequently, IM1b isomerizes to a product (Pro1 via TS1b with a potential barrier of 39.3 kJ/mol. The other one (2 is carbene attack at the C atom of azacyclopropane, firstly to form IM2 via TS2a, the potential barrier is 35.4 kJ/mol. Then IM2 isomerizes to a product (Pro2 via TS2b with a potential barrier of 35.1 kJ/mol. Correspondingly, the reaction energy for the reactions (1 and (2 is –478.3 and –509.9 kJ/mol, respectively. Additionally, the orbital interactions are also discussed for the leading intermediate.

  16. Pulse radiolysis study on the mechanisms of reactions of CCl3OO· radical with quercetin, rutin and epigallocatechin gallate

    2001-01-01

    The mechanisms of reactions between CCl3OO· radical and quercetin, rutin and epigallocatechin gallate (EGCG) have been studied using pulse radiolytic technique. It is suggested that the electron transfer reaction is the main reaction between CCl3OO· radical and rutin, EGCG, but there are two main pathways for the reaction of CCl3OO· radical with quercetin, one is the electron transfer reaction, the other is addition reaction. The reaction rate constants were determined. It is proved that quercetin and rutin are better CCl3OO· radical scavengers than EGCG.

  17. Genetic evidence that HNF-1alpha-dependent transcriptional control of HNF-4alpha is essential for human pancreatic beta cell function

    Hansen, Sara K; Párrizas, Marcelina; Jensen, Maria L; Pruhova, Stepanka; Ek, Jakob; Boj, Sylvia F; Johansen, Anders; Maestro, Miguel A; Rivera, Francisca; Eiberg, Hans; Andel, Michal; Lebl, Jan; Pedersen, Oluf; Ferrer, Jorge; Hansen, Torben

    2002-01-01

    Mutations in the genes encoding hepatocyte nuclear factor 4alpha (HNF-4alpha) and HNF-1alpha impair insulin secretion and cause maturity onset diabetes of the young (MODY). HNF-4alpha is known to be an essential positive regulator of HNF-1alpha. More recent data demonstrates that HNF-4alpha...... human islets and exocrine cells is primarily mediated by the P2 promoter. Furthermore, we describe a G --> A mutation in a conserved nucleotide position of the HNF-1alpha binding site of the P2 promoter, which cosegregates with MODY. The mutation results in decreased affinity for HNF-1alpha, and...

  18. Nuclear structure and reaction mechanisms studied on alpha-particle transitions

    Since the observation of the natural alpha decay of atomic nuclei the alpha particle was and is considered as an important component of the nuclear matter. The modern studies of alpha-particle transfer reactions are devoted to the question on four-particle correlations (alpha-particle clusters) generally in nuclear matter or also on nuclear surfaces. Thereby one is today yet absolutely far away from a unified picture of the mechanism of the alpha transfer: It is shown that different reaction and nuclear models must be used with different success for the interpretation of the data. Theoretical and experimental determination of spectroscopic strength distribution were thereby developed mutually supportingly each other. On the experimental side the question of the reaction mechanism and the determination of its details is to be clarified. Here approaches were developed which lead to a unified description in the sd shell. Calculations in the formalism of the coupled channels with spectroscopic factors calculated in the framework of the shell model lead to convincing agreements between theoretical and experimental angular distributions regarding both their shape and their amplitude. Hereby it was shown that beside the determination of the potential parameters a two-stage reaction mechanism as in an alpha-particle transition after or before an inelastic excitation of the target or residual nucleus is of decicive importance. (HSI)

  19. Centripetal Acceleration Reaction: An Effective and Robust Mechanism for Flapping Flight in Insects.

    Chao Zhang

    Full Text Available Despite intense study by physicists and biologists, we do not fully understand the unsteady aerodynamics that relate insect wing morphology and kinematics to lift generation. Here, we formulate a force partitioning method (FPM and implement it within a computational fluid dynamic model to provide an unambiguous and physically insightful division of aerodynamic force into components associated with wing kinematics, vorticity, and viscosity. Application of the FPM to hawkmoth and fruit fly flight shows that the leading-edge vortex is the dominant mechanism for lift generation for both these insects and contributes between 72-85% of the net lift. However, there is another, previously unidentified mechanism, the centripetal acceleration reaction, which generates up to 17% of the net lift. The centripetal acceleration reaction is similar to the classical inviscid added-mass in that it depends only on the kinematics (i.e. accelerations of the body, but is different in that it requires the satisfaction of the no-slip condition, and a combination of tangential motion and rotation of the wing surface. Furthermore, the classical added-mass force is identically zero for cyclic motion but this is not true of the centripetal acceleration reaction. Furthermore, unlike the lift due to vorticity, centripetal acceleration reaction lift is insensitive to Reynolds number and to environmental flow perturbations, making it an important contributor to insect flight stability and miniaturization. This force mechanism also has broad implications for flow-induced deformation and vibration, underwater locomotion and flows involving bubbles and droplets.

  20. Theoretical investigation on H abstraction reaction mechanisms and rate constants of Isoflurane with the OH radical

    Ren, Hongjiang; Li, Xiaojun

    2015-12-01

    The mechanism of H abstraction reactions for Isoflurane with the OH radical was investigated using density functional theory and G3(MP2) duel theory methods. The geometrical structures of all the species were fully optimised at B3LYP/6-311++G** level of theory. Thermochemistry data were obtained by utilising the high accurate model chemistry method G3(MP2) combined with the standard statistical thermodynamic calculations. Gibbs free energies were used for the reaction channels analysis. All the reaction channels were confirmed throughout the intrinsic reaction coordinate analysis. The results show that two channels were obtained, which correspond to P(1) and P(2) with the respective activation barriers of 63.03 and 54.82 kJ/mol. The rate constants for the two channels over a wide temperature range of 298.15-2000 K were predicted and the calculated data are in agreement with the experimental one. The results show that P(2) is the dominant reaction channel under 800 K and above 800 K, it can be found that P(1) will be more preferable reaction channel.

  1. Theoretical Studies on the Reaction Mechanism of 1-Chloroethane with Hydroxyl Radical

    WANG Bing-Xing; WANG Li

    2007-01-01

    The reaction mechanism of 1-chloroethane with hydroxyl radical has been investigated by using density functional theory (DFT) B3LYP/6-31G (d, p) method. All bond dissociation enthalpies were computed at the same theoretical level. It was found that hydrogen abstraction pathway is the most favorable. There are two hydrogen abstraction pathways with activation barriers of 0.630 and 4.988 kJ/mol, respectively, while chlorine abstraction pathway was not found. It was observed that activation energies have a more reasonable correlation with the reaction enthalpy changes (ΔHr) than with bond dissociation enthalpies (BDE).

  2. Alkali-Silica Reaction Inhibited by LiOH and Its Mechanism

    2003-01-01

    A high alkali reactive aggregate-zeolitization perlite was used to test the long-term effectiveness of LiOH in inhibiting alkali-silica reaction.In this paper,the rigorous conditions were designed that the mortar bars had been cured at 80℃ for 3 years after autoclaved 24 hours at 150℃.Under this condition,LiOH was able to inhibit the alkali-silica reaction long-term effectiveness.Not only the relationship between the molar ratio of n(Li)/(Na) and the alkali contents in systems was established, but also the governing mechanism of such effects was also studied by SEM.

  3. Mechanism and kinetics in reactions of caffeic acid with radicals by pulse radiolysis and calculation

    The interaction of caffeic acid with eaq-, (CH3)2(OH) CCH2·, CO2·-, H·, ·OH and N3· radicals were studied by γ-, pulse radiolysis and molecular orbital calculation. UV-visible spectra of electron/·OH adducts, semi-quinone radicals of caffeic ions, and the stable products from the reactions were derived. The rate constants were determined. The attacked sites and the most favorable structures of the transient radicals were predicted. Reaction mechanisms were proposed. (author)

  4. Mechanism of carbon monoxide reactions under high pressure catalyzed by acids and bases

    Takezaki, Y.

    1978-05-01

    A review, based mainly on work done at Kyoto University, covers the mechanisms and kinetics of acid-catalyzed carbonylations, including the hydrogen fluoride-catalyzed addition of carbon monoxide to methallyl chloride, the sulfuric acid-catalyzed synthesis of succinic acid from acrylic acid, and the conversion of toluene to p-tolualdehyde in hydrogen fluoride/boron trifluoride by the Gattermann-Koch reaction; and of base-catalyzed reactions, including the production of methyl formate from methanol with 1,8-diazabicyclo (5,4,0)undec-7-ene catalyst and of malonic acid from potassium acetate and potassium carbonate. Graphs, tables, and 34 references.

  5. Quantum mechanical/molecular mechanical free energy simulations of the self-cleavage reaction in the hepatitis delta virus ribozyme.

    Ganguly, Abir; Thaplyal, Pallavi; Rosta, Edina; Bevilacqua, Philip C; Hammes-Schiffer, Sharon

    2014-01-29

    The hepatitis delta virus (HDV) ribozyme catalyzes a self-cleavage reaction using a combination of nucleobase and metal ion catalysis. Both divalent and monovalent ions can catalyze this reaction, although the rate is slower with monovalent ions alone. Herein, we use quantum mechanical/molecular mechanical (QM/MM) free energy simulations to investigate the mechanism of this ribozyme and to elucidate the roles of the catalytic metal ion. With Mg(2+) at the catalytic site, the self-cleavage mechanism is observed to be concerted with a phosphorane-like transition state and a free energy barrier of ∼13 kcal/mol, consistent with free energy barrier values extrapolated from experimental studies. With Na(+) at the catalytic site, the mechanism is observed to be sequential, passing through a phosphorane intermediate, with free energy barriers of 2-4 kcal/mol for both steps; moreover, proton transfer from the exocyclic amine of protonated C75 to the nonbridging oxygen of the scissile phosphate occurs to stabilize the phosphorane intermediate in the sequential mechanism. To explain the slower rate observed experimentally with monovalent ions, we hypothesize that the activation of the O2' nucleophile by deprotonation and orientation is less favorable with Na(+) ions than with Mg(2+) ions. To explore this hypothesis, we experimentally measure the pKa of O2' by kinetic and NMR methods and find it to be lower in the presence of divalent ions rather than only monovalent ions. The combined theoretical and experimental results indicate that the catalytic Mg(2+) ion may play three key roles: assisting in the activation of the O2' nucleophile, acidifying the general acid C75, and stabilizing the nonbridging oxygen to prevent proton transfer to it. PMID:24383543

  6. Hepatitis C virus suppresses Hepatocyte Nuclear Factor 4 alpha, a key regulator of hepatocellular carcinoma.

    Vallianou, Ioanna; Dafou, Dimitra; Vassilaki, Niki; Mavromara, Penelope; Hadzopoulou-Cladaras, Margarita

    2016-09-01

    Hepatitis C Virus (HCV) infection presents with a disturbed lipid profile and can evolve to hepatic steatosis and hepatocellular carcinoma (HCC). Hepatocyte Nuclear Factor 4 alpha (HNF4α) is the most abundant transcription factor in the liver, a key regulator of hepatic lipid metabolism and a critical determinant of Epithelial to Mesenchymal Transition and hepatic development. We have previously shown that transient inhibition of HNF4α initiates transformation of immortalized hepatocytes through a feedback loop consisting of miR-24, IL6 receptor (IL6R), STAT3, miR-124 and miR-629, suggesting a central role of HNF4α in HCC. However, the role of HNF4α in Hepatitis C Virus (HCV)-related hepatocarcinoma has not been evaluated and remains controversial. In this study, we provide strong evidence suggesting that HCV downregulates HNF4α expression at both transcriptional and translational levels. The observed decrease of HNF4α expression correlated with the downregulation of its downstream targets, HNF1α and MTP. Ectopic overexpression of HCV proteins also exhibited an inhibitory effect on HNF4α levels. The inhibition of HNF4α expression by HCV appeared to be mediated at transcriptional level as HCV proteins suppressed HNF4α gene promoter activity. HCV also up-regulated IL6R, activated STAT3 protein phosphorylation and altered the expression of acute phase genes. Furthermore, as HCV triggered the loss of HNF4α a consequent change of miR-24, miR-629 or miR-124 was observed. Our findings demonstrated that HCV-related HCC could be mediated through HNF4α-microRNA deregulation implying a possible role of HNF4α in HCV hepatocarcinogenesis. HCV inhibition of HNF4α could be sustained to promote HCC. PMID:27477312

  7. Mechanism of electron transfer reaction of ternary dipicolinatochromium(III) complex involving oxalate as secondary ligand

    Hassan Amroun Ewais; Iqbal Mohamed Ibrhium Ismail

    2013-09-01

    Mechanism of electron transfer reaction of ternary Mechanism of the oxidation of [CrIII(DPA)(OX)(H2O)]− (DPA = dipicolinate and OX = oxalate) by periodate in aqueous acidic medium has been studied spectrophotometrically over the pH range of 4.45-5.57 at different temperatures. The reaction is first order with respect to both [IO$^{−}_{4}$] and the complex concentration, and it obeys the following rate law: $$d[{\\text Cr}^{\\text{VI}}]/dt = k_6K_4K_6[{\\text IO}^−_4][{\\text{Cr}}^{\\text{III}}]_{\\text{T}}/\\{([H^+] + K_4) + (K_5[H+] + K_6K_4)[{\\text{IO}}^{−}_{4}]\\}.$$ The rate of the reaction increases with increasing pH due to the deprotonation equilibria of the complex. The experimental rate law is consistent with a mechanism in which the deprotonated form [CrIII(DPA)(OX)(OH)]2− is more reactive than the conjugated acid. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO$^{−}_{4}$ to chromium(III). Thermodynamic activation parameters were calculated using the transition state theory equation.dipicolinatochromium(III) complex involving oxalate as secondary ligand

  8. Reactions of the OOH radical with guanine: Mechanisms of formation of 8-oxoguanine and other products

    Kumar, Nagendra; Shukla, P. K.; Mishra, P. C.

    2010-09-01

    The mutagenic product 8-oxoguanine (8-oxoGua) is formed due to intermediacy of peroxyl (OOR) radicals in lipid peroxidation and protein oxidation-induced DNA damage. The mechanisms of these reactions are not yet understood properly. Therefore, in the present study, the mechanisms of formation of 8-oxoGua and other related products due to the reaction of the guanine base of DNA with the hydroperoxyl radical (OOH) were investigated theoretically employing the B3LYP and BHandHLYP hybrid functionals of density functional theory and the polarizable continuum model for solvation. It is found that the reaction of the OOH radical with guanine can occur following seven different mechanisms leading to the formation of various products including 8-oxoGua, its radicals, 5-hydroxy-8-oxoguanine and CO 2. The mechanism that yields 8-oxoGua as an intermediate and 5-hydroxy-8-oxoGua as the final product was found to be energetically most favorable.

  9. Modeling a halogen dance reaction mechanism: A density functional theory study.

    Jones, Leighton; Whitaker, Benjamin J

    2016-07-01

    Since the discovery of the halogen dance (HD) reaction more than 60 years ago, numerous insights into the mechanism have been unveiled. To date however, the reaction has not been investigated from a theoretical perspective. Density functional theory (DFT) was used to model the potential energy surface linking the starting reagents to the lithiated products for each step in the mechanism using a thiophene substrate. It was found that the lithium-halogen exchange mechanism is critical to understand the HD mechanism in detail and yielded the knowledge that SN 2 transition states (TS) are favored over the four-center type for the lithium-bromine exchange steps. The overall driving force for the HD is thermodynamics, while the kinetic factors tightly control the reaction path through temperature. The SN 2 lithium-bromide TS are barrierless, except the second, which is the limiting step. Finally, the model for the HD is discovered to be a pseudo-clock type, due to a highly favorable bromide catalysis step and the reformation of 2-bromothiophene. © 2016 Wiley Periodicals, Inc. PMID:27075112

  10. A reaction mechanism for gasoline surrogate fuels for large polycyclic aromatic hydrocarbons

    Raj, Abhijeet

    2012-02-01

    This work aims to develop a reaction mechanism for gasoline surrogate fuels (n-heptane, iso-octane and toluene) with an emphasis on the formation of large polycyclic aromatic hydrocarbons (PAHs). Starting from an existing base mechanism for gasoline surrogate fuels with the largest chemical species being pyrene (C 16H 10), this new mechanism is generated by adding PAH sub-mechanisms to account for the formation and growth of PAHs up to coronene (C 24H 12). The density functional theory (DFT) and the transition state theory (TST) have been adopted to evaluate the rate constants for several PAH reactions. The mechanism is validated in the premixed laminar flames of n-heptane, iso-octane, benzene and ethylene. The characteristics of PAH formation in the counterflow diffusion flames of iso-octane/toluene and n-heptane/toluene mixtures have also been tested for both the soot formation and soot formation/oxidation flame conditions. The predictions of the concentrations of large PAHs in the premixed flames having available experimental data are significantly improved with the new mechanism as compared to the base mechanism. The major pathways for the formation of large PAHs are identified. The test of the counterflow diffusion flames successfully predicts the PAH behavior exhibiting a synergistic effect observed experimentally for the mixture fuels, irrespective of the type of flame (soot formation flame or soot formation/oxidation flame). The reactions that lead to this synergistic effect in PAH formation are identified through the rate-of-production analysis. © 2011 The Combustion Institute.

  11. Elastic scattering and reaction mechanisms of the halo nucleus $^{11}$Be around the Coulomb barrier

    Di Pietro, A; Fisichella, M; Borge, M J G; Randisi, G; Milin, M; Figuera, P; Gomez-Camacho, J; Raabe, R; Amorini, F; Fraile, L M; Rizzo, F; Zadro, M; Torresi, D; Wenander, F; Pellegriti, M G; Papa, M; Jeppesen, H; Santonocito, D; Scuderi, V; Acosta, L; Perez-Bernal, F; Tengblad, O; Lattuada, M; Musumarra, A; Scalia, G; Maira Vidal, A; Voulot, D

    2010-01-01

    Collisions induced by $^{9}$Be, $^{10}$Be, $^{11}$Be on a $^{64}$Zn target at the same c. m. energy were studied. For the first time, strong effects of the $^{11}$Be halo structure on elastic-scattering and reaction mechanisms at energies near the Coulomb barrier are evidenced experimentally. The elastic-scattering cross section of the $^{11}$Be halo nucleus shows unusual behavior in the Coulomb-nuclear interference peak angular region. The extracted total-reaction cross section for the $^{11}$Be collision is more than double the ones measured in the collisions induced by $^{9}$Be, $^{10}$Be. It is shown that such a strong enhancement of the total-reaction cross section with $^{11}$Be is due to transfer and breakup processes.

  12. The Kabachnik-Fields reaction: synthetic potential and the problem of the mechanism

    Cherkasov, Rafael A; Galkin, Vladimir I [Department of Chemistry, Kazan State University, Kazan (Russian Federation)

    1998-10-31

    The published data of the last decade concerning the mechanism of the Kabachnik-Fields reaction and its significance for the chemistry of organophosphorus compounds as a method for the synthesis of {alpha}-amino phosphonates and their numerous functionally substituted derivatives and analogues, such as phosphinates and phosphine oxides, are generalised and systematised. The review discusses the classical version of the Kabachnik-Fields reaction, its modifications with the use of phosphorus chlorides, neutral esters and inorganic phosphorus acids, as well as chemical processes simulating separate steps of the reaction, viz., hydrophosphorylation of imines and amination of {alpha}-hydroxy phosphonates. Data on the practical application of {alpha}-amino phosphonates are presented. The bibliography includes 253 references.

  13. Mechanisms and Kinetics of Radical Reaction of O(1D,3P) + HCN System

    HUANG Yu-Cheng; DU Jin-Yan; JU Xue-Hai; YE Shi-Yong; ZHOU Tao

    2008-01-01

    The reaction of HCN with O(1D, 3P) radical has been investigated by density functional theory (DFT) and ab initio methods. The stationary points on the reaction paths(reactants, intermediates and products) were optimized at the (U)B3LYP/aug-cc-pVTZ level.Single-point calculations were performed at the (U)QCISD(T)/aug-cc-pVTZ level for the optimized structures and all the total energies were corrected by zero-point energy. It is shown that there exist three competing mechanisms of oxygen attacking nitrogen O→N, oxygen attacking carbon O→C and oxygen attacking hydrogen O→H. The rate constants were obtained via Eyring transition-state theory in the temperature range of 600~2000 K. The linear relationship between lnk and 1/T was presented. The results show that path 1 is the main reaction channel and the product of NCO + H is predominant.

  14. Quantum Chemical Study on the Reaction Mechanism of OBrO Radical with OH Radical

    ZhAO,Min(赵岷); ZHAO,Yan-Ling(赵艳玲); LIU,Peng-Jun(刘朋军); CHANG,Ying-Fei(常鹰飞); PAN,Xiu-Mei(潘秀梅); SU,Zhong-Min(苏忠民); WANG,Rong-Shun(王荣顺)

    2004-01-01

    The reaction mechanism of OBrO with OH has been studied using the B3LYP/6-31 l+G(d,p) and the high-level electron-correlation CCSD(T)/6-311 +G(d,p) at single-point. The results show that the title reaction could probably proceed by four possible schemes, generating HOBr+O2, HBr+O3, BrO+HO2 and HOBrO2 products, respectively. The main channel is the one to yield HOBr+ O2. The whole reaction involves the formation of three-membered, four-membered and five-membered rings, followed by the complicated processes of association,H-shift, Br-shift and dissociation. All routes are exothermic.

  15. Theoretical Study on the Mechanism of the Cycloaddition Reaction between Alkylidene Carbene and Ethylene

    LU,Xiu-Hui(卢秀慧); ZHAI,Li-Min(翟利民); WU,Wei-Rong(武卫荣)

    2004-01-01

    The mechanism of cycloaddition reaction between singlet alkylidene carbene and ethylene has been investigated with second-order Moller-Plesset perturbation theory (MP2). By using 6-31G* basis , geometry optimization, vibrational analysis and energetics have been calculated for the involved stationary points on the potential energy surface. The results show that the title reaction has two major competition channels. An energy-rich intermediate (INT) is firstly formed between alkylidene carbene and ethylene through a barrier-free exothermic reaction of 63.62 kJ/mol, and the intermediate then isomerizes to a three-membered ring product (P1) and a four-memberd ring product (P2) via transition state TS1 and TS2, in which energy barriers are 47.00 and 51.02 kJ/mol, respectively. P1 is the main product.

  16. Studies on Mechanism of Hoesch Reaction with Mass Spectrometry and Its Improvement

    LI,Shao-Bai; ZHENG,Hong-Yan

    2004-01-01

    @@ It has been about ninety years since Hoesch reaction was first discovered in 1915. To our knowledge, although several authors[1,2] have studied the mechanism of Hoesch reaction, it has not been explained clearly. Here we represent an investigation on the mechanism with isotopic mass spectrometry. The effects of isotopes on mass spectra were illustrated obviously. FAB spectrum contained intermediate molecular ions at m/z 336 (M+, 19.3), 338 (M+, 18.2), 340 (M+, 12.3),etc and the peak 364 had already arose. This isotopic cluster demonstrated the positive ion 4 (M+, 336) was in existence (isotopes of Zn: 64, 66, 67, 68, 70). A possible intermediate molecular structure of the signal at m/z 364 could be assigned to 3 (M+, 364). Ions peaks of a possible intermediate negative ions suggested the structure 7.

  17. Light particle emission as a probe of reaction mechanism and nuclear excitation

    The central part of these lectures will be dealing with the problem of energy dissipation. A good understanding of the mechanisms for the dissipation requires to study both peripheral and central collisions or, in other words, to look at the impact paramenter dependence. This should also provide valuable information on the time scale. In order to probe the reaction mechanism and nuclear excitation, one of the most powerful tool is unquestionably the observation of light particle emission, including neutrons and charged particles. Several examples will be discussed related to peripheral collisions (the fate of transfer reactions, the excitation energy generation, the production of projectile-like fragments) as well as inner collisions for which extensive studies have demonstrated the strength of intermediate energy heavy ions for the production of very hot nuclei and detailed study of their decay properties

  18. Hybrid direct carbon fuel cells and their reaction mechanisms - a review

    Deleebeeck, Lisa; Kammer Hansen, Kent

    2014-01-01

    with carbon capture and storage (CCS) due to the high purity of CO2 emitted in the exhaust gas. Direct carbon (or coal) fuel cells (DCFCs) are directly fed with solid carbon to the anode chamber. The fuel cell converts the carbon at the anode and the oxygen at the cathode into electricity, heat and...... efforts is discussed on the fuel cell stack and system levels. The range of DCFC types can be roughly broken down into four fuel cell types: aqueous hydroxide, molten hydroxide, molten carbonate and solid oxide fuel cells. Emphasis is placed on the electrochemical reactions occurring at the anode and the...... proposed mechanism(s) of these reactions for molten carbonate, solid oxide and hybrid direct carbon fuel cells. Additionally, the criteria of choosing the ‘best’ DCFC technology is explored, including system design (continuous supply of solid fuel), performance (power density, efficiency), environmental...

  19. Mechanism of nuclear dissipation in fission and heavy-ion reactions

    Recent advances in the theoretical understanding of nuclear dissipation at intermediate excitation energies are reviewed, with particular emphasis on a new surface-plus-window mechanism that involves interactions of either one or two nucleons with the moving nuclear surface and also, for dumbbell-like shapes encountered in fission and heavy-ion reactions, the transfer of nucleons through the window separating the two portions of the system. This novel dissipation mechanism provides a unified macroscopic description of such diverse phenomena as widths of isoscalar giant quadrupole and giant octupole resonances, mean fission-fragment kinetic energies and excitation energies, dynamical thresholds for compound-nucleus formation, enhancement in neutron emission prior to fission, and widths of mass and charge distributions in deep-inelastic heavy-ion reactions. 41 refs., 8 figs

  20. Modeling of the Reaction Mechanism of Enzymatic Radical C-C Coupling by Benzylsuccinate Synthase.

    Szaleniec, Maciej; Heider, Johann

    2016-01-01

    Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C-C coupling catalyzed by benzylsuccinate synthase (BSS). BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD) simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i) What mechanistic details of the BSS reaction yield the most probable molecular model? (ii) What is the molecular basis of enantiospecificity of BSS? (iii) Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R)-benzylsuccinate as a product and a kinetic isotope effect (KIE) ranging between 2 and 4? The quantum mechanics (QM) modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C-H activation and not C-C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R) orientation and reverse preference of benzyl radical attack on fumarate in pro(S) pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5) is still higher than the experimentally observed values (4.0) which suggests that both C-H activation and radical quenching may jointly be involved in the kinetic control of the reaction. PMID:27070573

  1. Modeling of the Reaction Mechanism of Enzymatic Radical C–C Coupling by Benzylsuccinate Synthase

    Szaleniec, Maciej; Heider, Johann

    2016-01-01

    Molecular modeling techniques and density functional theory calculations were performed to study the mechanism of enzymatic radical C–C coupling catalyzed by benzylsuccinate synthase (BSS). BSS has been identified as a glycyl radical enzyme that catalyzes the enantiospecific fumarate addition to toluene initiating its anaerobic metabolism in the denitrifying bacterium Thauera aromatica, and this reaction represents the general mechanism of toluene degradation in all known anaerobic degraders. In this work docking calculations, classical molecular dynamics (MD) simulations, and DFT+D2 cluster modeling was employed to address the following questions: (i) What mechanistic details of the BSS reaction yield the most probable molecular model? (ii) What is the molecular basis of enantiospecificity of BSS? (iii) Is the proposed mechanism consistent with experimental observations, such as an inversion of the stereochemistry of the benzylic protons, syn addition of toluene to fumarate, exclusive production of (R)-benzylsuccinate as a product and a kinetic isotope effect (KIE) ranging between 2 and 4? The quantum mechanics (QM) modeling confirms that the previously proposed hypothetical mechanism is the most probable among several variants considered, although C–H activation and not C–C coupling turns out to be the rate limiting step. The enantiospecificity of the enzyme seems to be enforced by a thermodynamic preference for binding of fumarate in the pro(R) orientation and reverse preference of benzyl radical attack on fumarate in pro(S) pathway which results with prohibitively high energy barrier of the radical quenching. Finally, the proposed mechanism agrees with most of the experimental observations, although the calculated intrinsic KIE from the model (6.5) is still higher than the experimentally observed values (4.0) which suggests that both C–H activation and radical quenching may jointly be involved in the kinetic control of the reaction. PMID:27070573

  2. A coupled mechanical and chemical damage model for concrete affected by alkali–silica reaction

    To model the complex degradation phenomena occurring in concrete affected by alkali–silica reaction (ASR), we formulate a poro-mechanical model with two isotropic internal variables: the chemical and the mechanical damage. The chemical damage, related to the evolution of the reaction, is caused by the pressure generated by the expanding ASR gel on the solid concrete skeleton. The mechanical damage describes the strength and stiffness degradation induced by the external loads. As suggested by experimental results, degradation due to ASR is considered to be localized around reactive sites. The effect of the degree of saturation and of the temperature on the reaction development is also modeled. The chemical damage evolution is calibrated using the value of the gel pressure estimated by applying the electrical diffuse double-layer theory to experimental values of the surface charge density in ASR gel specimens reported in the literature. The chemo-damage model is first validated by simulating expansion tests on reactive specimens and beams; the coupled chemo-mechanical damage model is then employed to simulate compression and flexure tests results also taken from the literature. -- Highlights: •Concrete degradation due to ASR in variable environmental conditions is modeled. •Two isotropic internal variables – chemical and mechanical damage – are introduced. •The value of the swelling pressure is estimated by the diffuse double layer theory. •A simplified scheme is proposed to relate macro- and microscopic properties. •The chemo-mechanical damage model is validated by simulating tests in literature

  3. Reaction mechanism for the free-edge oxidation of soot by O 2

    Raj, Abhijeet

    2012-11-01

    The reaction pathways for the oxidation by O 2 of polycyclic aromatic hydrocarbons present in soot particles are investigated using density functional theory at B3LYP/6-311++G(d,p) level of theory. For this, pyrene radical (4-pyrenyl) is chosen as the model molecule, as most soot models present in the literature employ the reactions involving the conversion of 4-pyrenyl to 4-phenanthryl by O 2 and OH to account for soot oxidation. Several routes for the formation of CO and CO 2 are proposed. The addition of O 2 on a radical site to form a peroxyl radical is found to be barrierless and exothermic with reaction energy of 188kJ/mol. For the oxidation reaction to proceed further, three pathways are suggested, each of which involve the activation energies of 104, 167 and 115kJ/mol relative to the peroxyl radical. The effect of the presence of H atom on a carbon atom neighboring the radical site on the energetics of carbon oxidation is assessed. Those intermediate species formed during oxidation with seven-membered rings or with a phenolic group are found to be highly stable. The rate constants evaluated using transition state theory in the temperature range of 300-3000K for the reactions involved in the mechanism are provided. © 2012 The Combustion Institute.

  4. New Insights into Reaction Mechanisms of Ethanol Steam Reforming on Co-ZrO2

    Sun, Junming; Karim, Ayman M.; Mei, Donghai; Engelhard, Mark H.; Bao, Xinhe; Wang, Yong

    2015-01-01

    The reaction pathway of ethanol steam reforming on Co-ZrO2 has been identified and the active sites associated with each step are proposed. Ethanol is converted to acetaldehyde and then to acetone, followed by acetone steam reforming. More than 90% carbon was found to follow this reaction pathway. N2-Sorption, X-ray Diffraction (XRD), Temperature Programmed Reduction (TPR), in situ X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy, as well as theoretical Density Functional Theory (DFT) calculations have been employed to identify the structure and functionality of the catalysts, which was further used to correlate their performance in ESR. It was found that metallic cobalt is mainly responsible for the acetone steam reforming reactions; while, CoO and basic sites on the support play a key role in converting ethanol to acetone via dehydrogenation and condensation/ketonization reaction pathways. The current work provides fundamental understanding of the ethanol steam reforming reaction mechanisms on Co-ZrO2 catalysts and sheds light on the rational design of selective and durable ethanol steam reforming catalysts.

  5. Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

    Cahoon, James Francis

    2008-12-16

    One and two dimensional time-resolved vibrational spectroscopy has been used to investigate the elementary reactions of several prototypical organometallic complexes in room temperature solution. The electron transfer and ligand substitution reactions of photogenerated 17-electron organometallic radicals CpW(CO){sub 3} and CpFe(CO){sub 2} have been examined with one dimensional spectroscopy on the picosecond through microsecond time-scales, revealing the importance of caging effects and odd-electron intermediates in these reactions. Similarly, an investigation of the photophysics of the simple Fischer carbene complex Cr(CO){sub 5}[CMe(OMe)] showed that this class of molecule undergoes an unusual molecular rearrangement on the picosecond time-scale, briefly forming a metal-ketene complex. Although time-resolved spectroscopy has long been used for these types of photoinitiated reactions, the advent of two dimensional vibrational spectroscopy (2D-IR) opens the possibility to examine the ultrafast dynamics of molecules under thermal equilibrium conditions. Using this method, the picosecond fluxional rearrangements of the model metal carbonyl Fe(CO){sub 5} have been examined, revealing the mechanism, time-scale, and transition state of the fluxional reaction. The success of this experiment demonstrates that 2D-IR is a powerful technique to examine the thermally-driven, ultrafast rearrangements of organometallic molecules in solution.

  6. Competition between heavy-ion reaction mechanisms as a function of the system isospin

    Simone Valdre'

    2016-01-01

    The thesis describes the complex procedure of data reduction and analysis of a heavy-ion nuclear physics experiment performed at LNL in Legnaro (Italy). The experiment was focused on the reaction mechanism characterization at energies between the mean field region and the Fermi energy regime. Pre-equilibrium and isospin transport phenomena were also put into evidence. The results were compared with the literature and with advanced dynamical models.

  7. Stochastic innovation as a mechanism by which catalysts might self-assemble into chemical reaction networks

    Bradford, Justin A; Dill, Ken A.

    2007-01-01

    We develop a computer model for how two different chemical catalysts in solution, A and B, could be driven to form AB complexes, based on the concentration gradients of a substrate or product that they share in common. If A's product is B's substrate, B will be attracted to A, mediated by a common resource that is not otherwise plentiful in the environment. By this simple physicochemical mechanism, chemical reactions could spontaneously associate to become chained together in solution. Accord...

  8. Statistical mechanics of neocortical interactions: Reaction time correlates of the g factor

    L. Ingber

    2000-01-01

    A statistical mechanics of neuronal interactions (SMNI) is explored as providing some substance to a physiological basis of the g factor. Some specific elements of SMNI, previously used to develop a theory of short-term memory (STM) and a model of electroencephalography (EEG) are key to providing this basis. Specifically, Hick's Law, an observed linear relationship between reaction time (RT) and the information storage of STM, in turn correlated to a RT-g relationship, is derived.

  9. An ab initio molecular dynamics study of the roaming mechanism of the H{sub 2}+HOC{sup +} reaction

    Yu Huagen, E-mail: hgy@bnl.gov [Department of Chemistry, Brookhaven National Laboratory, Upton, NY 11973 (United States)

    2011-08-01

    We report here a direct ab initio molecular dynamics study of the p-/o-H{sub 2}+HOC{sup +} reaction on the basis of the accurate SAC-MP2 potential energy surface. The quasi-classical trajectory method was employed. This work largely focuses on the study of reaction mechanisms. A roaming mechanism was identified for this molecular ion-molecule reaction. The driving forces behind the roaming mechanism were thoroughly investigated by using a trajectory dynamics approach. In addition, the thermal rate coefficients of the H{sub 2}+HOC{sup +} reaction were calculated in the temperature range [25, 300] K and are in good agreement with experiments.

  10. Mechanism of catalytic action of oxide systems in reactions of aldehyde oxidation to carboxylic acids

    Mechanism of selective action of oxide catalysts (on the base of V2O4, MoO3) of aldehyde oxidation to acids is considered, reaction acrolein oxidation to acrylic acid is taken as an example. Multistage mechanism of the process is established; it involves consequent transformation of coordination-bonded aldehyde into carbonyl-bonded aldehyde and symmetric carboxylate. Principles of active surface construction are formulated, they take into account the activity of stabilization center of concrete intermediate compound and bond energy of oxygen with surface. (author)

  11. DFT studies on the SCR reaction mechanism of nitrogen monoxide with propylene catalyzed by copper oxide

    TIAN Ying; XU Jing; ZHAO Jing-xiang

    2007-01-01

    The SCR reaction mechanism of NO with C3H6catalyzed by CuO was studied by the method of Density Functional Theory (DFT) at the B3LYP/LanL2DZ levels. The optimized geometries of the stationary points on the potential surface were obtained and the transition state was confirmed by IRC and vibration analysis. The activation energy was calculated being 34. 26 kJ/mol. It was shown that propylene reacted firstly with Cu forming intermediate, and then nitrogen monoxide immediately reacted with the intermediate to be reduced. It was proved to be a direct interaction mechanism.

  12. Comparison of automatically generated reaction mechanism for oxidation of simple hydrocarbons in IC engine

    Muhammad Mansha

    2011-10-01

    Full Text Available In this work, a detailed kinetic reaction mechanism, consisting of 208 reactions and 79 species, has been developed todescribe the oxidation of simple hydrocarbon fuel (natural gas in IC engine. The performance of the proposed mechanismis tested using simulation, tool CHEMKIN 4.1.1, and experimental measurements. The simulation results of the proposedreaction scheme were compared with those of reference mechanisms (GRI v3.0 and Konnov 0.5 version as well as experimentaldata. Based upon simulation results, it can be concluded that the proposed mechanism shows good concordanceswith GR I3.0 mechanism especially in the prediction of temperature, pressure, and major product species (H2O, CO2 profilesat stoichiometric conditions (= 1.0. Although, there are some discrepancies among each predicted profile, the proposeddetailed mechanism is good to describe the oxidation of natural gas in IC engine. The experimental data also showed favorableresults for prediction of major product species (CO2, H2O & CO at various engine operating speeds in idle mode.

  13. Telaprevir may induce adverse cutaneous reactions by a T cell immune-mediated mechanism.

    Federico, Alessandro; Aitella, Ernesto; Sgambato, Dolores; Savoia, Alfonso; De Bartolomeis, Fabio; Dallio, Marcello; Ruocco, Eleonora; Pezone, Luciano; Abbondanza, Ciro; Loguercio, Carmela; Astarita, Corrado

    2015-01-01

    The HCV protease inhibitor telaprevir associated with peginterferon-alpha and ribavirin, was widely used in the recent past as standard treatment in HCV genotype-1 infected patients. Telaprevir improves the sustained virology response rates, but at the same time increases the frequency of adverse cutaneous reactions. However, mechanisms through which telaprevir induces cutaneous lesions are not yet defined. A 50-year-old woman, affected by HCV genotype 1b, was admitted to our Department for a telaprevir-related severe cutaneous eruptions, eight weeks after starting a triple therapy (telaprevir associated with Peginterferon-alpha and ribavirin). Mechanisms of cutaneous reactions were investigated by skin tests with non-irritating concentrations of telaprevir and by activating in vitro T lymphocyte with different concentrations. Immediate and delayed responses to skin testing were negative, but the drug-induced lymphocytes activation was significantly higher as compared to patient's baseline values and to parallel results obtained in three healthy subjects (p < 0.05). In conclusion, adverse cutaneous reactions of our patient were caused by a telaprevir-induced T-cell dependent immune mechanism. PMID:25864225

  14. Kinetics and mechanism of oxygen reduction reaction at CoPd system synthesized on XC72

    Studies are presented of the kinetics and mechanism of oxygen electroreduction reaction on CoPd catalysts synthesized on carbon black XC72. As shown both in model conditions and in the tests within the cathodes of hydrogen-oxygen fuel cells with proton conducting electrolyte, CoPd/C system features a higher activity, as compared to Co/C. The highest activity in the oxygen reduction reaction is demonstrated by the catalysts with the Pd:Co atomic ratio being 7:3 and 4:1. The structural studies (XPS and XRD, and also the data of CO desorption measurements) evidence the CoPd alloy formation, which is reflected in the negative shift of the bonding energy maximum as compared to Pd/C and in the appearance of the additional CO desorption maximums on the voltammograms. It is found by means of structural research that CoPd alloy is formed in the course of the catalyst synthesis which features a higher catalytic activity of the binary systems. Besides, CoPd/C catalyst is more stable in respect to corrosion than Pd supported on carbon black. The measurements on the rotating disc electrode and rotating ring-disc electrode evidence that CoPd/C system provides the predominant oxygen reduction to water in the practically important range of potentials (E > 0.7 V). The proximity of kinetic parameters of the oxygen reduction reaction on CoPd/C and Pt/C catalysts points to the similar reaction mechanism. The slow step of the reaction is the addition of the first electron to the adsorbed and previously protonated O2 molecule. The assumptions are offered about the reasons causing the higher activity and selectivity of the binary catalyst towards oxygen reduction to water, as compared to Co/C. The studies of the most active catalysts within the fuel cell cathodes are performed

  15. Quantum Mechanical and Molecular Dynamics Studies of the Reaction Mechanism of the Nucleophilic Substitution at the Si Atom.

    Matsubara, Toshiaki; Ito, Tomoyoshi

    2016-05-01

    The mechanism of the nucleophilic substitution at the Si atom, SiH3Cl + Cl*(-) → SiH3Cl* + Cl(-), is examined by both quantum mechanical (QM) and molecular dynamics (MD) methods. This reaction proceeds by two steps with the inversion or retention of the configuration passing through an intermediate with the trigonal bipyramid (TBP) structure, although the conventional SN2 reaction at the C atom proceeds by one step with the inversion of the configuration passing through a transition state with the TBP structure. We followed by the QM calculations all the possible paths of the substitution reaction that undergo the TBP intermediates with the cis and trans forms produced by the frontside and backside attacks of Cl(-). As a result, it was thought that TBPcis1 produced with a high probability is readily transformed to the energetically more stable TBPtrans. This fact was also shown by the MD simulations. In order to obtain more information concerning the trajectory of Cl(-) on the dissociation from TBPtrans, which we cannot clarify on the basis of the energy profile determined by the QM method, the MD simulations with and without the water solvent were conducted and analyzed in detail. The QM-MD simulations without the water solvent revealed that the dissociation of Cl(-) from TBPtrans occurs without passing through TBPcis1'. The ONIOM-MD simulations with the water solvent further suggested that the thermal fluctuation of the water solvent significantly affects the oscillation of the kinetic and potential energies of the substrate to facilitate the isomerization of the TBP intermediate from the cis form to the trans form and the subsequent dissociation of Cl(-) from TBPtrans. PMID:27046773

  16. Methanol synthesis on ZnO(0001{sup ¯}). IV. Reaction mechanisms and electronic structure

    Frenzel, Johannes, E-mail: johannes.frenzel@theochem.rub.de; Marx, Dominik [Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum (Germany)

    2014-09-28

    Methanol synthesis from CO and H{sub 2} over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partially hydroxylated and defective ZnO(0001{sup ¯}) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving “near-surface” molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H{sub 2} stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are

  17. Methanol synthesis on ZnO(0001¯). IV. Reaction mechanisms and electronic structure

    Methanol synthesis from CO and H2 over ZnO, which requires high temperatures and high pressures giving rise to a complex interplay of physical and chemical processes over this heterogeneous catalyst surface, is investigated using ab initio simulations. The redox properties of the surrounding gas phase are known to directly impact on the catalyst properties and thus, set the overall catalytic reactivity of this easily reducible oxide material. In Paper III of our series [J. Kiss, J. Frenzel, N. N. Nair, B. Meyer, and D. Marx, J. Chem. Phys. 134, 064710 (2011)] we have qualitatively shown that for the partially hydroxylated and defective ZnO(0001¯) surface there exists an intricate network of surface chemical reactions. In the present study, we employ advanced molecular dynamics techniques to resolve in detail this reaction network in terms of elementary steps on the defective surface, which is in stepwise equilibrium with the gas phase. The two individual reduction steps were investigated by ab initio metadynamics sampling of free energy landscapes in three-dimensional reaction subspaces. By also sampling adsorption and desorption processes and thus molecular species that are in the gas phase but close to the surface, our approach successfully generated several alternative pathways of methanol synthesis. The obtained results suggest an Eley-Rideal mechanism for both reduction steps, thus involving “near-surface” molecules from the gas phase, to give methanol preferentially over a strongly reduced catalyst surface, while important side reactions are of Langmuir-Hinshelwood type. Catalyst re-reduction by H2 stemming from the gas phase is a crucial process after each reduction step in order to maintain the catalyst's activity toward methanol formation and to close the catalytic cycle in some reaction channels. Furthermore, the role of oxygen vacancies, side reactions, and spectator species is investigated and mechanistic details are discussed based on extensive

  18. Products and mechanism of the reaction of ozone with phospholipids in unilamellar phospholipid vesicles

    Santrock, J.; Gorski, R.A.; O' Gara, J.F. (Biomedical Science Department, General Motors Research Laboratories, Warren, MI (United States))

    1992-01-01

    While considerable effort has been expended on determining the health effects of exposure to typical urban concentrations of O3, little is known about the chemical events responsible for toxicity. Phospholipids containing unsaturated fatty acids in the cell membranes of lung cells are likely reaction sites for inhaled ozone (O3). In this study, we examined the reaction of O3 with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in unilamellar phospholipid vesicles. Reaction of ozone with the carbon-carbon double bond of POPC yielded an aldehyde and a hydroxy hydroperoxide. The hydroxy hydroperoxide eliminated H2O2 to yield a second aldehyde. Upon further ozonolysis, the aldehydes were oxidized to the corresponding carboxylic acids. A material balance showed that no other reaction consumed POPC and O3 or produced these products. As a mechanistic probe, we measured incorporation of oxygen-18 from 18O3 into aldehyde, carboxylic acid, and H2O2. Approximately 50% of the aldehyde oxygen atoms were derived from O3. Oxygen in H2O2 was derived solely from O3, where both oxygen atoms in a molecule of H2O2 were from the same molecule of O3. One of the carboxylic acid oxygen atoms was derived from the precursor aldehyde, while the other was derived from O3. These results support the following mechanism. Cleavage of the carbon-carbon double bond of POPC by O3 yields a carbonyl oxide and an aldehyde. Reaction of H2O with the carbonyl oxide yields a hydroxy hydroperoxide, preventing formation ozonide by reaction of the carbonyl oxide and aldehyde. Elimination of H2O2 from the hydroxy hydroperoxide yields a second aldehyde. Oxidation of the aldehydes by O3 yields carboxylic acids.

  19. (3He,α) reaction mechanism at high energy and neutron inner shell structure

    The (3He,α) reaction on 12C, 16O, 28Si, 58Ni, 90Zr, 118Sn, 124Sn and 208Pb targets has been studied at Esub(3He) = 217 MeV (or 205 MeV) in order to investigate the reaction mechanism at high energy and large momentum transfer. The reaction yields large cross sections at very forward angles and strongly enhances the largest orbital momentum transfer. The angular distribution shapes are well reproduced in the frame-work of the Z-R- D.W.B.A. analysis if we use a unique empirical α-potential: Vsub(α)(Esub(α)) = Vsub(3He)(3/4 Esub(α)) + Vsub(n)(1/4 Esub(α)). The excitation energy spectra have been measured up to 100 MeV in the residual light and medium nuclei and up to about 16 MeV in heavy nuclei. In addition to the well-known low-lying levels, peaks or broad structures are observed for each nucleus at higher excitation energies. They are attributed to pick up from inner shells: 1s(11C and 15O), 1p(27Si), 1d5/2 + 1p(57Ni), 1f7/2(89Zr) 1g9/2117Sn, 123Sn and 1h11/2(207Pb). Selectivity and localization of direct and indirect pick up (3He,α) reactions were studied. Finite range calculations show that this reaction is not very sensitive to the details of the range from function but only to D0 coefficient and range R. A microscopic α-nucleus optical potential calculated with n-n dependent and independent density forces is able to reproduce both elastic scattering and pick up reaction angular distributions

  20. Elimination Reactions of (E)-2,4,6-Trinitrobenzaldehyde O-benzoyloximes Promoted by R2NH in MeCN. Change of Reaction Mechanism

    We have studied the nitrile-forming elimination reactions from 1 promoted by R2NH in MeCN. The reaction proceeded by (E1cb)irr mechanism. Change of the β-aryl group from 2,4-dinitrophenyl to a more strongly electron-withdrawing 2,4,6-trinitrophenyl increased the reaction rate by 470-fold, shifted the transition state toward more reactant-like, and changed the reaction mechanism from E2 to (E1cb)irr. To the best of our knowledge, this is the first example of nitrile-forming elimination reaction that proceeds by the (E1cb)irr mechanism in MeCN. Noteworthy is the carbanion stabilizing ability of the 2,4,6-trinitrophenyl group in aprotic solvent. Nitrile-forming elimination reactions of (E)-benzaldoxime derivatives have been extensively investigated under various conditions. The reactions proceeded by the E2 mechanism in MeCN despite the fact that the reactants have syn stereochemistry, poor leaving, and sp2 hybridized β-carbon atom, all of which favor E1cb- or E1cb-like transition state. Moreover, the transition state structures were relatively insensitive to the variation of the reactant structures. The results have been attributed to the poor anion solvating ability of MeCN, which favors E2 transition state with maximum charge dispersal. For eliminations from strongly activated (E)-2,4-(NO2)2C6H3CH=NOC(O)C6H4X, a change in the reaction mechanism from E2 to (E1cb)irr was observed as the base-solvent was changed from R2NH in MeCN to R2NH/R2NH2+ in 70 mol % MeCN(aq). A combination of a strong electron-withdrawing β-aryl group and anion-solvating protic solvent was required for the mechanistic change

  1. Studies of reaction mechanism in 12C + 12C system at intermediate energy of 28.7 MeV/N

    The reaction mechanism in 12C + 12C system at intermediate energy of about 30 MeV/nucleon was studied. The contribution of various reaction mechanisms (inelastic scattering, transfer reactions, compound nucleus reactions, sequential decay following inelastic excitation and transfer) to the total reaction cross section were found. The analysis of inclusive and coincidence spectra shows that sequential fragmentation processes dominate

  2. Characteristics and mechanism of explosive reactions of Purex solvents with Nitric Acid at elevated temperatures

    This investigation was undertaken to make clear the energetic properties and mechanism of explosive decomposition of Purex solvent systems (TBP/n-Dodecane/HNO3) by Nitric Acid at elevated temperatures using a calorimetric technique (DSC, ARC) and a chromatographic technique (GC, GC/MS). The measurement of exothermic events of solvent-HNO3 reactions using DSC with a stainless steel sealed cell showed distinct two peaks with maxima at around 170 and 320degC, respectively. The peak at around 170degC was mainly attributed to the reactions of dealkylation products (n-butyl nitrate) of TBP and the solvent with nitric acid, and the peak at around 320degC was attributed to the exothermic decomposition of nitrated dodecanes formed in the foregoing exothermic reaction of dodecane with nitric acid. By using the data obtained in ARC experiments, activation energies of 123.2 and 152.5 kJ/mol were determined for the exothermic reaction of TBP with nitric acid and for the exothermic pyrolysis of n-butyl nitrate, respectively. Some possible pathways were considered for the explosive decomposition of TBP by nitric acid at elevated temperatures. (author)

  3. Research on the Thermal Decomposition Reaction Kinetics and Mechanism of Pyridinol-Blocked Isophorone Diisocyanate

    Sen Guo

    2016-02-01

    Full Text Available A series of pyridinol-blocked isophorone isocyanates, based on pyridinol including 2-hydroxypyridine, 3-hydroxypyridine, and 4-hydroxypyridine, was synthesized and characterized by 1H-NMR, 13C-NMR, and FTIR spectra. The deblocking temperature of blocked isocyanates was established by thermo-gravimetric analysis (TGA, differential scanning calorimetry (DSC, and the CO2 evaluation method. The deblocking studies revealed that the deblocking temperature was increased with pyridinol nucleophilicity in this order: 3-hydroxypyridine > 4-hydroxypyridine > 2-hydroxypyridine. The thermal decomposition reaction of 4-hydroxypyridine blocked isophorone diisocyanate was studied by thermo-gravimetric analysis. The Friedman–Reich–Levi (FRL equation, Flynn–Wall–Ozawa (FWO equation, and Crane equation were utilized to analyze the thermal decomposition reaction kinetics. The activation energy calculated by FRL method and FWO method was 134.6 kJ·mol−1 and 126.2 kJ·mol−1, respectively. The most probable mechanism function calculated by the FWO method was the Jander equation. The reaction order was not an integer because of the complicated reactions of isocyanate.

  4. Toward Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction.

    Mauguière, Frédéric A L; Collins, Peter; Stamatiadis, Stamatis; Li, Anyang; Ezra, Gregory S; Farantos, Stavros C; Kramer, Zeb C; Carpenter, Barry K; Wiggins, Stephen; Guo, Hua

    2016-07-14

    The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or "roam" to the MgHH minimum from where the molecule may react. PMID:26918375

  5. Study on the mechanism of coal liquefaction reaction and a new process concept

    SHI Shi-dong; LI Wen-bo; WANG Yong; GUO Zhi; LI Ke-jian

    2008-01-01

    The coal hydrogenation reaction process is simply considered as three steps. In the first step, the smaller molecules associated with coal structure units are released as some gases and water in the condition of solvent and heating. In this step, some weaker bonds of the coal structure units are ruptured to form free radicals. The radicals are stabi-lized by hydrogen atoms from donor solvent and/or H2. In the second step, chain reaction occurs quickly. In the process of chain reaction, the covalent bonds of coal structure units are attacked by the radicals to form some asphaltenes. In the third step, asphaltenes are hydrogenated form more liquids and some gases. In coal liquefaction, the second step of coal hydrogenation reaction should be controlled to avoid integration of radicals, and the third step of coal hydrogenation should be accelerated to increase the coal conversion and the oil yield. A new concept of coal liquefaction process named as China direct coal lique-faction (CDCL) process is presented based on the mechanism study of coal liquefaction.

  6. Calcium-Magnesium-Aluminosilicate (CMAS) Reactions and Degradation Mechanisms of Advanced Environmental Barrier Coatings

    Ahlborg, Nadia L.; Zhu, Dongming

    2013-01-01

    The thermochemical reactions between calcium-magnesium-aluminosilicate- (CMAS-) based road sand and several advanced turbine engine environmental barrier coating (EBC) materials were studied. The phase stability, reaction kinetics and degradation mechanisms of rare earth (RE)-silicates Yb2SiO5, Y2Si2O7, and RE-oxide doped HfO2 and ZrO2 under the CMAS infiltration condition at 1500 C were investigated, and the microstructure and phase characteristics of CMAS-EBC specimens were examined using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). Experimental results showed that the CMAS dissolved RE-silicates to form crystalline, highly non-stoichiometric apatite phases, and in particular attacking the silicate grain boundaries. Cross-section images show that the CMAS reacted with specimens and deeply penetrated into the EBC grain boundaries and formed extensive low-melting eutectic phases, causing grain boundary recession with increasing testing time in the silicate materials. The preliminary results also showed that CMAS reactions also formed low melting grain boundary phases in the higher concentration RE-oxide doped HfO2 systems. The effect of the test temperature on CMAS reactions of the EBC materials will also be discussed. The faster diffusion exhibited by apatite and RE-doped oxide phases and the formation of extensive grain boundary low-melting phases may limit the CMAS resistance of some of the environmental barrier coatings at high temperatures.

  7. Reaction mechanism for the symmetric breakup of 24Mg following an interaction with 12C

    Data on the yield of the symmetric breakup of 24Mg as a function of beam energy are presented and compared with detailed calculations of the energy dependence. The 24Mg states seen in symmetric breakup agree with previously observed breakup states having spin and parities Jπ=4+,(6+),8+. The data allow the variations of yield for indivual states to be judged, as the beam energy is varied. The variation in the yield of the 4+ states is compared in detail with calculations assuming several possible compound nuclear or direct reaction mechanisms. It is concluded that a massive (12C) transfer or a simple statistical compound process are unlikely mechanisms, but that each of several other mechanisms is consistent with the data. ((orig.))

  8. Probing the Reaction Mechanism of Aluminum/Poly(vinylidene fluoride) Composites.

    DeLisio, Jeffery B; Hu, Xiuli; Wu, Tao; Egan, Garth C; Young, Gregory; Zachariah, Michael R

    2016-06-23

    Energetic thin films with high mass loadings of nanosized components have been recently fabricated using electrospray deposition. These films are composed of aluminum nanoparticles (nAl) homogeneously dispersed in an energetic fluoropolymer binder, poly(vinylidene fluoride) (PVDF). The nascent oxide shell of the nAl has been previously shown to undergo a preignition reaction (PIR) with fluoropolymers such as polytetrafluoroethylene (PTFE). This work examines the PIR between alumina and PVDF to further explain the reaction mechanism of the Al/PVDF system. Temperature jump (T-jump) ignition experiments in air, argon, and vacuum environments showed that the nAl is fluorinated by gas phase species due to a decrease in reactivity in a vacuum. Thermogravimetric analysis coupled with differential scanning calorimetry (TGA/DSC) was used to confirm the occurrence of a PIR, and gas phase products during the PIR and fluorination of nAl were investigated with temperature jump time-of-flight mass spectrometry (T-jump TOFMS). Results show a direct correlation between the amount of alumina in the PVDF film and the relative signal intensity of hydrogen fluoride release (HF). Although the PIR between alumina and PVDF plays an important role in the Al/PVDF reaction mechanism, burn speeds of Al/PVDF films containing additional pure alumina particles showed no burn speed enhancement. PMID:27228361

  9. Memorable Experiences with Sad Music—Reasons, Reactions and Mechanisms of Three Types of Experiences

    Peltola, Henna-Riikka

    2016-01-01

    Reactions to memorable experiences of sad music were studied by means of a survey administered to a convenience (N = 1577), representative (N = 445), and quota sample (N = 414). The survey explored the reasons, mechanisms, and emotions of such experiences. Memorable experiences linked with sad music typically occurred in relation to extremely familiar music, caused intense and pleasurable experiences, which were accompanied by physiological reactions and positive mood changes in about a third of the participants. A consistent structure of reasons and emotions for these experiences was identified through exploratory and confirmatory factor analyses across the samples. Three types of sadness experiences were established, one that was genuinely negative (Grief-Stricken Sorrow) and two that were positive (Comforting Sorrow and Sweet Sorrow). Each type of emotion exhibited certain individual differences and had distinct profiles in terms of the underlying reasons, mechanisms, and elicited reactions. The prevalence of these broad types of emotional experiences suggested that positive experiences are the most frequent, but negative experiences were not uncommon in any of the samples. The findings have implications for measuring emotions induced by music and fiction in general, and call attention to the non-pleasurable aspects of these experiences. PMID:27300268

  10. Memorable Experiences with Sad Music-Reasons, Reactions and Mechanisms of Three Types of Experiences.

    Tuomas Eerola

    Full Text Available Reactions to memorable experiences of sad music were studied by means of a survey administered to a convenience (N = 1577, representative (N = 445, and quota sample (N = 414. The survey explored the reasons, mechanisms, and emotions of such experiences. Memorable experiences linked with sad music typically occurred in relation to extremely familiar music, caused intense and pleasurable experiences, which were accompanied by physiological reactions and positive mood changes in about a third of the participants. A consistent structure of reasons and emotions for these experiences was identified through exploratory and confirmatory factor analyses across the samples. Three types of sadness experiences were established, one that was genuinely negative (Grief-Stricken Sorrow and two that were positive (Comforting Sorrow and Sweet Sorrow. Each type of emotion exhibited certain individual differences and had distinct profiles in terms of the underlying reasons, mechanisms, and elicited reactions. The prevalence of these broad types of emotional experiences suggested that positive experiences are the most frequent, but negative experiences were not uncommon in any of the samples. The findings have implications for measuring emotions induced by music and fiction in general, and call attention to the non-pleasurable aspects of these experiences.

  11. Reaction mechanisms in the radiolysis of peptides, polypeptides and proteins II reactions at side-chain loci in model systems

    The major emphasis in radiation biology at the molecular level has been on the nucleic acid component of the nucleic acid-protein complex because of its primary genetic importance. But there is increasing evidence that radiation damage to the protein component also has important biological implications. Damage to capsid protein now appears to be a major factor in the radiation inactivation of phage and other viruses. And, there is increasing evidence that radiation-chemical change in the protein component of chromation leads to changes in the stability of the repressor-operator complexes involved in gene expression. Knowledge of the radiation chemistry of protein is also of importance in other fields such as the application of radiation sterilization to foods and drugs. Recent findings that a class of compounds, the α,α'-diaminodicarboxylic acids, not normally present in food proteins, are formed in protein radiolysis is of particular significance since certain of their peptide derivatives have been showing to exhibit immunological activity. The purpose of this review is to bring together and to correlate our present knowledge of products and mechanisms in the radiolysis of peptides, polypeptides and proteins both aqueous and solid-state. In part 1 we presented a discussion of the radiation-induced reactions of the peptide main-chain in model peptide and polypeptide systems. Here in part 2 the emphasis is on the competing radiation chemistry at side-chain loci of peptide derivatives of aliphatic, aromatic-unsaturated and sulfur-containing amino acids in similar systems. Information obtained with the various experimental techniques of product analysis, competition kinetics, spin-trapping, pulse radiolysis, and ESR spectroscopy are included

  12. Requirements for charged particle light isotopes reaction data for advanced fuel cycles including two step reaction mechanism

    Requirements for light charged isotopes nuclear reaction data for advanced fusion fuel cycles are identified. This is performed in the frame of the compilation of charged particle nuclear reaction data. Those reactions are considered which determine the nuclear energy production, burn kinetics, neutron- and radionuclide production among fuel and ash isotopes. Emphasis is put on the fuel p-11B for which a review of the status of existing data is given. Other exotic fuel candidates (e.g. p-6Li) and some exotic reactions occurring in D-3He based fuels are also considered, however in less detail. We conclude that there is a lack of experimental and evaluated data for several important reactions. It is recommended that evaluations be performed, existing ones reexamined, and that they are made easily accessible for the increasing number of researchers studying advanced fuels. (author). 52 refs, 10 figs, 6 tabs

  13. From Sound to Significance: Exploring the Mechanisms Underlying Emotional Reactions to Music.

    Juslin, Patrik N; Barradas, Gonçalo; Eerola, Tuomas

    2015-01-01

    A common approach to studying emotional reactions to music is to attempt to obtain direct links between musical surface features such as tempo and a listener's responses. However, such an analysis ultimately fails to explain why emotions are aroused in the listener. In this article we explore an alternative approach, which aims to account for musical emotions in terms of a set of psychological mechanisms that are activated by different types of information in a musical event. This approach was tested in 4 experiments that manipulated 4 mechanisms (brain stem reflex, contagion, episodic memory, musical expectancy) by selecting existing musical pieces that featured information relevant for each mechanism. The excerpts were played to 60 listeners, who were asked to rate their felt emotions on 15 scales. Skin conductance levels and facial expressions were measured, and listeners reported subjective impressions of relevance to specific mechanisms. Results indicated that the target mechanism conditions evoked emotions largely as predicted by a multimechanism framework and that mostly similar effects occurred across the experiments that included different pieces of music. We conclude that a satisfactory account of musical emotions requires consideration of how musical features and responses are mediated by a range of underlying mechanisms. PMID:26442337

  14. Reaction Mechanisms in Petroleum: From Experimentation to Upgrading and Geological Conditions

    Lannuzel, Frédéric; Bounaceur, Roda; Marquaire, Paul-Marie; Michels, Raymond

    2009-01-01

    Among the numerous questions that arise concerning the exploitation of petroleum from unconventional reservoirs, lie the questions of the composition of hydrocarbons present in deep seated HP-HT reservoirs or produced during in-situ upgrading steps of heavy oils and oil shales. Our research shows that experimental hydrocarbon cracking results obtained in the laboratory cannot be extrapolated to geological reservoir conditions in a simple manner. Our demonstration is based on two examples: 1) the role of the hydrocarbon mixture composition on reaction kinetics (the "mixing effect") and the effects of pressure (both in relationship to temperature and time). The extrapolation of experimental data to geological conditions requires investigation of the free-radical reaction mechanisms through a computed kinetic model. We propose a model that takes into account 52 reactants as of today, and which can be continuously improved by addition of new reactants as research proceeds. This model is complete and detailed enou...

  15. Kinetics and mechanism of hydrogen evolution reaction on cobalt silicides in alkaline solutions

    Cathodic polarisation curves and impedance spectra for cobalt silicides Co2Si and CoSi2 in 0.5–2 M KOH at ambient temperature were obtained. It was shown that electrocatalytic activity of both silicides in hydrogen evolution reaction (HER) is higher than that of cobalt. The dependences of equivalent circuit elements on the electrode potential were analysed. The conclusion was made that the atomic hydrogen adsorption on the surface of cobalt silicides is described by the Langmuir isotherm, and hydrogen evolution proceeds through the Volmer–Heyrovsky mechanism (at α1 ≠ α2 for Co2Si and α1 = α2 for CoSi2; α1 and α2 are the transfer coefficients for the Volmer and Heyrovsky steps respectively). The Heyrovsky reaction is probably the rate-determining step. The values of the kinetic parameters of HER on Co2Si and CoSi2 in 1 M KOH were estimated

  16. Reaction mechanism studies on isoquinoline with hydroxyl radical in aqueous solutions

    ZHU Dazhang; WANG Shilong; SUN Xiaoyu; NI Yarning; YAO Side

    2007-01-01

    The reaction mechanism between isoquinoline and .OH radical in aqueous dilute solutions under different conditions was studied by pulse radiolysis. The main chara-cteristic peaks in these transient absorption spectra were attributed and the growth-decay trends of several transient species were investigated. Under neutral or alkaline condi-tions, the reaction of-OH radical and isoquinoline produces OH-adducts with respective rate constants of 3.4 × 109 and 6.6× 109 mol-1.dm3·s-1 while under acidic conditions, the isoquinoline was firstly protonated and then -OH added to the benzene ring and produced protonated isoquinoline OH-adducts with a rate constant of 3.9× 109 mol-1.dm3·s-1.With a better understanding on radiolysis ofisoquinoline, this study is of help for its degradation and for environmental protection.

  17. Quantum interference between H + D2 quasiclassical reaction mechanisms

    Jambrina, Pablo G.; Herráez-Aguilar, Diego; Aoiz, F. Javier; Sneha, Mahima; Jankunas, Justinas; Zare, Richard N.

    2015-08-01

    Interferences are genuine quantum phenomena that appear whenever two seemingly distinct classical trajectories lead to the same outcome. They are common in elastic scattering but are seldom observable in chemical reactions. Here we report experimental measurements of the state-to-state angular distribution for the H + D2 reaction using the ‘photoloc’ technique. For products in low rotational and vibrational states, a characteristic oscillation pattern governs backward scattering. The comparison between the experiments, rigorous quantum calculations and classical trajectories on an accurate potential energy surface allows us to trace the origin of that structure to the quantum interference between different quasiclassical mechanisms, a phenomenon analogous to that observed in the double-slit experiment.

  18. Evolution of reaction mechanisms for the reaction 36Ar + 58Ni studied from 32 to 95 A*MeV with the INDRA multidetector

    In the context of the multifragmentation study program with the 4π INDRA detector at GANIL, the reaction 36Ar + 58Ni has been studied at seven different energies ranging from 32 to 95 A*MeV. After a brief description of the detector characteristics and of the data treatment, results on the evolution of intermediate mass fragments (IMF) distributions with incident energy and a first outlook about reaction mechanisms are presented. (author). 15 refs., 10 figs

  19. Mechanisms of emission of particles charged in 6Li + 6Li and 6Li + 10B reactions at low energies

    The lithium 6 nucleus is a projectile of interest to study nuclear reactions at low energy due to the possibility to obtain high heats of reaction, and to its structure which can play an important role in the projectile-target interaction. This research thesis focused on the study of two low-energy reactions provoked by lithium projectiles. These reactions are studied within the framework of the theoretical model of aggregates. The first part presents the experimental conditions of both reactions, reports the development and analysis of nuclear plates, and the transformation of a given type of particle histogram into a spectrum in the mass centre system. The next parts report the study of the 6Li + 6Li reaction (previous results, kinematic analysis, spectrum of secondary particles, theoretical analysis of results) and of the 6Li + 10B reaction (previous results, experimental results, study of the continuous spectrum of alpha particle, reaction mechanisms)

  20. Reaction pathway and oxidation mechanisms of dibutyl phthalate by persulfate activated with zero-valent iron.

    Li, Huanxuan; Wan, Jinquan; Ma, Yongwen; Wang, Yan

    2016-08-15

    This study investigated reaction pathway and oxidation mechanisms of dibutyl phthalate (DBP) by persulfate (PS) activated with zero-valent iron (ZVI). The DBP degradation was studied at three pH values (acidic, neutral and basic) in the presence of different organic scavengers. Using a chemical probe method, both sulfate radical (SO4(-)) and hydroxyl radical (·OH) were found to be primary oxidants at pH3.0 and pH7.0, respectively while ·OH was the major specie to oxidize DBP at pH11.0. A similar result was found in an experiment of Electron Spin Resonance spin-trapping where in addition to OH, superoxide radical (O2(-)) was detected at pH11.0. The transformation of degradation products including dimethyl phthalate (DMP), diethyl phthalate (DEP), phthalic anhydride, and acetophenone exhibited diverse variation during the reaction processes. The phthalic anhydride concentration appeared to be maximum at all pHs. Another eleven intermediate products were also found at pH3.0 by GC-MS and HPLC analysis, and their degradation mechanisms and pathways were proposed. It was suggested that dealkylation, hydroxylation, decarboxylation and hydrogen extraction were the dominant degradation mechanisms of DBP at pH3.0. PMID:27125682

  1. Mechanism of prooxidant reaction of vitamin E. Kinetic, spectroscopic, and ab initio study of proton-transfer reaction

    Nagoaka, Shin-ichi; Sawada, Kouhei; Fukumoto, Youji [Ehime Univ., Matsuyama (Japan)] [and others

    1992-08-06

    This paper discusses using kinetic, spectroscopic, and ab initio studies of the prooxidant reaction of vitamin E derivatives to determine second-order rate constants for the reaction of six tocopheroxyl radicals with five alkyl hydroperoxides in benzene along with the first adiabatic ionization potentials of the alkyl hydroperoxides. These results suggest that charge transfer and proton tunneling play important roles in this prooxidant reaction, with proton tunneling taking place below the transition state and allowing the proton to cut a corner on the potential energy surface. 31 refs., 10 figs., 2 tabs.

  2. Study of the reaction mechanisms leading to projectile fragmentation in 40 Ar + Ag nat reactions at 30 MeV and 60 MeV per nucleon

    This work is devoted to a study of the reaction mechanisms leading to projectile fragmentation in heavy ion collisions at intermediate energy (less than 100 MeV per nucleon). In contradiction with some theoretical calculations, inclusive measurements of projectile fragments as well as correlation measurements between projectile and target fragments in the reaction 40Ar + natAg at 30 MeV and 60 MeV per nucleon do not show any evidence for a change in the reaction mechanism in this energy range. Angular, mass and velocity correlations between projectile and target fragments enable us to reject mass transfer from projectile to target as a leading mechanism in projectile fragmentations. However, a coherent description of the data can be given either in the framework of an abrasion-ablation model in which the primary fragments of the projectile and of the target are produced with very low excitation energies, or assuming a two-body reaction, reminiscent of the first steps of deeply inelastic collisions, in which the dissipated energy is shared about equally between strongly excited projectile and target. The high excitation energies deduced from the two-body analysis bring in question our description of the fragmentation process. Thus, the excitation energy of the primary fragment is a key parameter which may be used in future experiments to distinguish between different reaction mechanisms

  3. Reaction mechanism on reduction surface of mixed conductor membrane for H2 production by coal-gas

    The reaction mechanism on surface of BaCo0.7Fe0.2Nb0.1O3-δ membrane for reforming coal-gas was studied. The effects of metal particle on membrane surface were concluded. 'Activation mechanism' was proposed to be the key for enhancing oxygen permeation of membrane; while the catalyst-bed only takes charge of the reforming reaction. Though not as important as 'activation mechanism', the 'space charge mechanism' still affects the oxygen permeation of membrane. According to these mechanisms, the new design and surface-modifying strategy of membrane reactor were proposed.

  4. Formation of degradation compounds from lignocellulosic biomass in the biorefinery: sugar reaction mechanisms

    Rasmussen, Helena; Sørensen, Hanne R.; Meyer, Anne S.

    2014-01-01

    -(hydroxymethyl)-2-furaldehyde (HMF) and/or levulinic acid, formic acid and different phenolics at elevated temperatures. Correspondingly, xylose can follow different reaction mechanisms resulting in the formation of furan-2-carbaldehyde (furfural) and/or various C-1 and C-4 compounds. At least four routes for...... the formation of HMF from glucose and three routes for furfural formation from xylose are possible. In addition, new findings show that biomass monosaccharides themselves can react further to form pseudo-lignin and humins as well as a wide array of other compounds when exposed to high temperatures...

  5. Reaction mechanisms and production of exotic nuclei using 200 MeV/n 40Ar

    Experiments using the fragmentation of 40Ar at 200 MeV/n have proved to be a powerful new tool for the investigation of both the dynamics of nuclear interactions at high energies and the limits of nuclear stability. In order to study the reaction mechanism, C and Th targets were bombarded by 213 MeV/n 40Ar. Energy spectra were measured at lab angles from 00 to 40 in a telescope. Isotope production cross sections were obtained by integrating the energy spectra and angular distributions. (orig./AH)

  6. First-principles modeling of catalysts: novel algorithms and reaction mechanisms

    Richard, Bryan Goldsmith

    A molecular level understanding of a reaction mechanism and the computation of rates requires knowledge of the stable structures and the corresponding transition states that connect them. Temperature, pressure, and environment effects must be included to bridge the 'materials gap' so one can reasonably compare ab initio (first-principles, i.e., having no empirical parameters) predictions with experimental measurements. In this thesis, a few critical problems pertaining to ab initio modeling of catalytic systems are addressed; namely, 1) the issue of building representative models of isolated metal atoms grafted on amorphous supports, 2) modeling inorganic catalytic reactions in non-ideal solutions where the solvent participates in the reaction mechanism, and 3) bridging the materials gap using ab initio thermodynamics to predict the stability of supported nanoparticles under experimental reaction conditions. In Chapter I, a background on first-principles modeling of heterogeneous and homogenous catalysts is provided. Subsequently, to address the problem of modeling catalysis by isolated metal atoms on amorphous supports, we present in Chapter II a sequential-quadratic programming algorithm that systematically predicts the structure and reactivity of isolated active sites on insulating amorphous supports. Modeling solution phase reactions is also a considerable challenge for first-principles modeling, yet when done correctly it can yield critical kinetic and mechanistic insight that can guide experimental investigations. In Chapter III, we examine the formation of peroxorhenium complexes by activation of H2O2, which is key in selective oxidation reactions catalyzed by CH3ReO3 (methyltrioxorhenium, MTO). New experiments and density functional theory (DFT) calculations were conducted to better understand the activation of H2O2 by MTO and to provide a strong experimental foundation for benchmarking computational studies involving MTO and its derivatives. It was found

  7. Reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts revealed by an FeO(111)/Pt(111) inverse model catalyst.

    Xu, Lingshun; Wu, Zongfang; Jin, Yuekang; Ma, Yunsheng; Huang, Weixin

    2013-08-01

    We have employed XPS and TDS to study the adsorption and surface reactions of H2O, CO and HCOOH on an FeO(111)/Pt(111) inverse model catalyst. The FeO(111)-Pt(111) interface of the FeO(111)/Pt(111) inverse model catalyst exposes coordination-unsaturated Fe(II) cations (Fe(II)CUS) and the Fe(II)CUS cations are capable of modifying the reactivity of neighbouring Pt sites. Water facilely dissociates on the Fe(II)CUS cations at the FeO(111)-Pt(111) interface to form hydroxyls that react to form both water and H2 upon heating. Hydroxyls on the Fe(II)CUS cations can react with CO(a) on the neighbouring Pt(111) sites to produce CO2 at low temperatures. Hydroxyls act as the co-catalyst in the CO oxidation by hydroxyls to CO2 (PROX reaction), while they act as one of the reactants in the CO oxidation by hydroxyls to CO2 and H2 (WGS reaction), and the recombinative reaction of hydroxyls to produce H2 is the rate-limiting step in the WGS reaction. A comparison of reaction behaviors between the interfacial CO(a) + OH reaction and the formate decomposition reaction suggest that formate is the likely surface intermediate of the CO(a) + OH reaction. These results provide some solid experimental evidence for the associative reaction mechanism of WGS and PROX reactions catalyzed by Pt/oxide catalysts. PMID:23576093

  8. Theoretical Study on the Reaction Mechanism of SiCl4 with H in the Gas Phase

    2006-01-01

    The reaction mechanism of SiCl4 with H2 has been studied theoretically using Gaussian 98 program at B3LYP/6-311G* level. Three different reaction paths (a, b, c) in the gas phase were obtained. The geometries, vibrational frequencies and energies of every stagnation point in the reaction channel were calculated and the mechanisms have been confirmed. The results show that path a has an activation energy of 79.12 kcal/mol, which was considered as the main reaction path. Comparably, paths b and c have the energy barriers of 125.07 and 136.25 kcal/mol, res- pectively. The reaction rate constant was calculated by TST method over a wide temperature range of 900~1600 K, which further confirmed that path a was the main reaction channel.

  9. Dissipative structure of mechanically stimulated reaction; Kikaiteki reiki hanno ni okeru san`itsu kozo

    Hida, M. [Okayama Univ., Okayama (Japan). Faculty of Engineering

    1994-12-20

    Recently various studies have been conducted concerning the state changes of materials obtained through mechanical alloying (MA) or mechano-chemical (MC) processing. What is noticeable is the quasi-steady state of almost all the materials obtained through various processes including MA and MC, and that the super cooling, supersaturating and high residue distortion realized under unbalanced conditions have not been clarified. In other words, the tracing capability to the external binding conditions is low. In this report, the appearance of the high temperature phase and high pressure phase obtained through MA or MC processing, the forming of amorphous, the mesomerism of the amorphous materials, the interesting phenomena generated by combination between the mechanical disturbance and chemical reactions were discussed with concrete examples, and a steady dissipative organization theory was approached from the viewpoint of dissipative structure development which is equal to the forming process of the quasi-steady phase. 34 refs., 2 figs.

  10. A Theoretical Investigation on the Reaction Mechanism of the C9H+ 12·Side-chain Decomposition

    CHENG,Xueli; ZHAO,Yanyun; LI,Feng; ZHANG,Dongsheng

    2009-01-01

    n-Phenylpropane cation C9H+·12 serves as a prototype to investigate the reaction mechanisms of alkylbenzene cations.The decomposition reactions of C9H+·12 system have been studied extensively at the B3LYP/6-311 + + G**level with Gaussian 98 program package.All reaction channels were fully investigated with the vibrational mode analysis to confirm the transition states and with electron population analysis to discuss the electron redistribution,and to elucidate the reaction mechanism.The reaction mechanism shows that there is a non-barrier channel of C9H+·12→C7H+7+C2H·5,which is thermodynamically most favorable.

  11. Automatic analysis and reduction of reaction mechanisms for complex fuel combustion

    Nilsson, Daniel

    2001-05-01

    This work concentrates on automatic procedures for simplifying chemical models for realistic fuels using skeletal mechanism construction and Quasi Steady-State Approximation (QSSA) applied to detailed reaction mechanisms. To automate the selection of species for removal or approximation, different indices for species ranking have thus been proposed. Reaction flow rates are combined with sensitivity information for targeting a certain quantity, and used to determine a level of redundancy for automatic skeletal mechanism construction by exclusion of redundant species. For QSSA reduction, a measure of species lifetime can be used for species ranking as-is, weighted by concentrations or molecular transport timescales, and/or combined with species sensitivity. Maximum values of the indices are accumulated over ranges of parameters, (e.g. fuel-air ratio and octane number), and species with low accumulated index values are selected for removal or steady-state approximation. In the case of QSSA, a model with a certain degree of reduction is automatically implemented as FORTRAN code by setting a certain index limit. The code calculates source terms of explicitly handled species from reaction rates and the steady-state concentrations by internal iteration. Homogeneous-reactor and one-dimensional laminar-flame models were used as test cases. A staged combustor fuelled by ethylene with monomethylamine addition is modelled by two homogeneous reactors in sequence, i.e. a PSR (Perfectly Stirred Reactor) followed by a PFR (Plug Flow Reactor). A modified PFR model was applied for simulation of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with four-component natural gas, whereas a two-zone model was required for a knocking Spark Ignition (SI) engine powered by Primary Reference Fuel (PRF). Finally, a laminar one-dimensional model was used to simulate premixed flames burning methane and an aeroturbine kerosene surrogate consisting of n-decane and toluene. In

  12. Computational study of the reaction mechanism and kinetics of ethyl acrylate ozonolysis in atmosphere

    Sun, Yanhui; Cao, Haijie; Han, Dandan; Li, Jing; He, Maoxia; Wang, Chen

    2012-06-01

    The reaction mechanism for the ozonolysis of ethyl acrylate (EA) has been investigated at the CCSD(T)/6-31G(d)+CF//B3LYP/6-31+G(d,p) level of theory. The profile of the potential energy surface (PES) is constructed. Ozone adds to EA via a cyclic transition state to produce a highly unstable primary ozonide which can decompose readily. Over the temperature range of 200-2000 K, the total and individual rate constants are obtained by employing multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The calculated rate constants are 1.37 × 10-18 cm3 molecule-1 s-1 at 294 K and 1.65 × 10-18 cm3 molecule-1 s-1 at 298 K under the pressure of 760 Torr. The main products of the reactions are ethyl glyoxylate and formaldehyde. These results are in good agreement with the previous experimental data. Several experimental uncertain products are identified. The branching ratios of main reaction paths are also discussed at different temperatures and pressures.

  13. Study of transfer reactions (α,t), (α,3He) in the f-p shell: mechanism and spectroscopic use

    We describe an experimental study of (α,t), (α,3He) reactions at 44 MeV using a solid-state identifier, on the target-nuclei 54Fe and 58,60,62,64Ni. A critical study of optical model and of disturbed wave analysis has been performed. We show the complementarity of different transfer-reactions, the ambiguity of spectroscopic factors, the importance of the problem of the reaction mechanism. (author)

  14. Detailed Chemical Kinetic Reaction Mechanisms for Primary Reference Fuels for Diesel Cetane Number and Spark-Ignition Octane Number

    Westbrook, C K; Pitz, W J; Mehl, M; Curran, H J

    2010-03-03

    For the first time, a detailed chemical kinetic reaction mechanism is developed for primary reference fuel mixtures of n-hexadecane and 2,2,4,4,6,8,8-heptamethyl nonane for diesel cetane ratings. The mechanisms are constructed using existing rules for reaction pathways and rate expressions developed previously for the primary reference fuels for gasoline octane ratings, n-heptane and iso-octane. These reaction mechanisms are validated by comparisons between computed and experimental results for shock tube ignition and for oxidation under jet-stirred reactor conditions. The combined kinetic reaction mechanism contains the submechanisms for the primary reference fuels for diesel cetane ratings and submechanisms for the primary reference fuels for gasoline octane ratings, all in one integrated large kinetic reaction mechanism. Representative applications of this mechanism to two test problems are presented, one describing fuel/air autoignition variations with changes in fuel cetane numbers, and the other describing fuel combustion in a jet-stirred reactor environment with the fuel varying from pure 2,2,4,4,6,8,8-heptamethyl nonane (Cetane number of 15) to pure n-hexadecane (Cetane number of 100). The final reaction mechanism for the primary reference fuels for diesel fuel and gasoline is available on the web.

  15. On Cosmic-Ray-Driven Electron Reaction Mechanism for Ozone Hole and Chlorofluorocarbon Mechanism for Global Climate Change

    Lu, Qing-Bin

    2012-01-01

    Numerous laboratory measurements have provided a sound physical basis for the cosmic-ray driven electron-induced reaction (CRE) mechanism of halogen-containing molecules for the ozone hole. And observed spatial and time correlations between polar ozone loss or stratospheric cooling and cosmic rays have shown strong evidence of the CRE mechanism [Q.-B. Lu, Phys. Rep. 487, 141-167(2010)]. Chlorofluorocarbons (CFCs) were also long-known greenhouse gases but were thought to play only a minor role in climate change. However, recent observations have shown evidence of the saturation in greenhouse effect of non-CFC gases. A new evaluation has shown that halocarbons alone (mainly CFCs) could account for the rise of 0.5~0.6 deg C in global surface temperature since 1950, leading to the striking conclusion that not CO2 but CFCs were the major culprit for global warming in the late half of the 20th century [Q.-B. Lu, J. Cosmology 8, 1846-1862(2010)]. Surprizingly, a recent paper [J.-W. Grooss and R. Muller, Atmos. Envir...

  16. Gas-Phase Reactions of Methoxyphenols with NO3 Radicals: Kinetics, Products, and Mechanisms.

    Zhang, Haixu; Yang, Bo; Wang, Youfeng; Shu, Jinian; Zhang, Peng; Ma, Pengkun; Li, Zhen

    2016-03-01

    Methoxyphenols, a group of important tracers for wood smoke, are emitted to the atmosphere in large quantities, but their transformations are rarely studied. In this study, the kinetics and products of the gas-phase reactions of eugenol and 4-ethylguaiacol with NO3 radicals were investigated online using a vacuum ultraviolet photoionization gas time-of-flight mass spectrometer. The rate coefficients of the gaseous reactions of eugenol and 4-ethylguaiacol with NO3 radicals were (1.6 ± 0.4) × 10(-13) and (1.1 ± 0.2) × 10(-12) cm(3) molecule(-1) s(-1) (at 298 K), indicating that the atmospheric lifetimes of the NO3 radicals were 3.5 and 0.5 h, respectively. With the aid of gas-chromatography-mass-spectrometry analysis, several types of degradation products were identified with nitro derivatives as the major products. The configurations of the nitro-product isomers and their formation mechanisms were determined via theoretical calculations. On the basis of these products, degradation pathways of the methoxyphenols with NO3 radicals were proposed. This study determines the degradation rates and mechanisms of the methoxyphenols at night and implies the significant NO3 nighttime chemistry. PMID:26845070

  17. TDDFT Study on Different Sensing Mechanisms of Similar Cyanide Sensors Based on Michael Addition Reaction

    Guang-yue Li; Ping Song; Guo-zhong He

    2011-01-01

    The solvents and substituents of two similar fluorescent sensors for cyanide, 7-diethylamino-3-formylcoumarin (sensor a) and 7-diethylamino-3-(2-nitrovinyl)coumarin (sensor b), are proposed to account for their distinct sensing mechanisms and experimental phenomena.The time-dependent density functional theory has been applied to investigate the ground states and the first singlet excited electronic states of the sensor as well as their possible Michael reaction products with cyanide, with a view to monitoring their geometries and photophysical properties. The theoretical study indicates that the protic water solvent could lead to final Michael addition product of sensor a in the ground state, while the aprotic acetonitrile solvent could lead to carbanion as the final product of sensor b. Furthermore,the Michael reaction product of sensor a has been proved to have a torsion structure in its first singlet excited state. Correspondingly, sensor b also has a torsion structure around the nitrovinyl moiety in its first singlet excited state, while not in its carbanion structure. This could explain the observed strong fluorescence for sensor a and the quenching fluorescencefor the sensor b upon the addition of the cyanide anions in the relevant sensing mechanisms.

  18. Formation mechanisms of 3,4-dinitrofuroxan via nitration reaction of furoxan

    Peng, Yajing; Ye, Yuqing; Liu, Jianyong; Lai, Weipeng

    2016-03-01

    A systematic investigations on the nitration of furoxan by two typical nitration reagents nitronium tetrafluoroborate (BF4NO2) and dilute nitric acid (HNO3) in chloroform (CHCl3) solvent using density functional theory (DFT) method to reveal the formation mechanism of 3,4-dinitrofuroxan (DNFO) and explore new synthesis routes. The geometry optimizations of the minima and transition states involved in the two nitration reactions are performed at the B3LYP/6-311++G** basis set level. The CCSD single-point energy corrections at the same level are carried out on top of the optimized geometries to obtain the accurate energy. Calculated results demonstrate that the electrophilic substitutions of nitronium ions from the nitration reagents and the abstractions of protons in the complex intermediates are the main formation mechanism of DNFO. BF4- is shown to be a better proton abstracter than HNO3 and H2O due to its no barrier combination with H+. The abstraction of proton by HNO3 is predicted to be more feasible than H2O because it can supply the nitration attacker (NO2+) and release more heat. Chloroform is a feasible solvent and heating properly is necessary for the two reactions due to the relatively high barrier of 37 kcal/mol. These conclusions provide some significant indications on the new experimental synthesis of DNFO.

  19. Amorphous and crystalline polyetheretherketone: Mechanical properties and tissue reactions during a 3-year follow-up.

    Nieminen, Tuomo; Kallela, Ilkka; Wuolijoki, Erkki; Kainulainen, Heikki; Hiidenheimo, Ilmari; Rantala, Immo

    2008-02-01

    The study was aimed to test the mechanical strength, structural stability, and tissue reactions of optically amorphous and crystalline polyetheretherketone (PEEK) plates during a 3-year follow-up in vivo and in vitro. The injection-moulded PEEK plates were implanted to the dorsal subcutis of 12 sheep, which were sacrificed at 6-156 weeks. Thereafter, the plates were subjected to tensile tests, and levels of crystallinity were assessed by differential scanning calorimetry (DSC). Histological evaluation was carried out using the paraffin technique. In vitro properties were examined with the tensile test and DSC at 0-156 weeks. Tissue reactions were mild and fairly similar for the amorphous and crystalline plates at corresponding points in time. The mechanical characteristics of the plates remained stable over the entire follow-up. The tensile yield load and elongation at the yield load of the crystalline plates were roughly double ( approximately 500 vs. 270 N and 2.4 vs. 1.4 mm, respectively) in comparison to the amorphous plates. The elongation at break load of the crystalline plates was smaller than that of the amorphous ones (6 vs. 10). The level of crystallinity in both the optically amorphous ( approximately 15%) and crystalline (32-34%) plates remained invariable during the follow-up. The in vitro and in vivo data coincided remarkably well. In conclusion, both optically amorphous and crystalline PEEK plates are suitable for the fixation of fractures and osteotomies. PMID:17618477

  20. Reaction Mechanism for m- Xylene Oxidation in the Claus Process by Sulfur Dioxide

    Sinha, Sourab

    2015-09-24

    In the Claus process, the presence of aromatic contaminants such benzene, toluene, and xylenes (BTX), in the H2S feed stream has a detrimental effect on catalytic reactors, where BTX form soot particles and clog and deactivate the catalysts. Among BTX, xylenes are proven to be most damaging contaminant for catalysts. BTX oxidation in the Claus furnace, before they enter catalyst beds, provides a solution to this problem. A reaction kinetics study on m-xylene oxidation by SO2, an oxidant present in Claus furnace, is presented. The density functional theory is used to study the formation of m-xylene radicals (3-methylbenzyl, 2,6-dimethylphenyl, 2,4-dimethylphenyl, and 3,5-dimethylphenyl) through H-abstraction and their oxidation by SO2. The mechanism begins with SO2 addition on the radicals through an O-atom rather than the S-atom with the release of 180.0-183.1 kJ/mol of reaction energies. This exothermic reaction involves energy barriers in the range 3.9-5.2 kJ/mol for several m-xylene radicals. Thereafter, O-S bond scission takes place to release SO, and the O-atom remaining on aromatics leads to CO formation. Among four m-xylene radicals, the resonantly stabilized 3-methylbenzyl exhibited the lowest SO2 addition and SO elimination rates. The reaction rate constants are provided to facilitate Claus process simulations to find conditions suitable for BTX oxidation. © 2015 American Chemical Society.

  1. Reaction intermediates in the catalytic mechanism of Escherichia coli MutY DNA glycosylase.

    Manuel, Raymond C; Hitomi, Kenichi; Arvai, Andrew S; House, Paul G; Kurtz, Andrew J; Dodson, M L; McCullough, Amanda K; Tainer, John A; Lloyd, R Stephen

    2004-11-01

    The Escherichia coli adenine DNA glycosylase, MutY, plays an important role in the maintenance of genomic stability by catalyzing the removal of adenine opposite 8-oxo-7,8-dihydroguanine or guanine in duplex DNA. Although the x-ray crystal structure of the catalytic domain of MutY revealed a mechanism for catalysis of the glycosyl bond, it appeared that several opportunistically positioned lysine side chains could participate in a secondary beta-elimination reaction. In this investigation, it is established via site-directed mutagenesis and the determination of a 1.35-A structure of MutY in complex with adenine that the abasic site (apurinic/apyrimidinic) lyase activity is alternatively regulated by two lysines, Lys142 and Lys20. Analyses of the crystallographic structure also suggest a role for Glu161 in the apurinic/apyrimidinic lyase chemistry. The beta-elimination reaction is structurally and chemically uncoupled from the initial glycosyl bond scission, indicating that this reaction occurs as a consequence of active site plasticity and slow dissociation of the product complex. MutY with either the K142A or K20A mutation still catalyzes beta and beta-delta elimination reactions, and both mutants can be trapped as covalent enzyme-DNA intermediates by chemical reduction. The trapping was observed to occur both pre- and post-phosphodiester bond scission, establishing that both of these intermediates have significant half-lives. Thus, the final spectrum of DNA products generated reflects the outcome of a delicate balance of closely related equilibrium constants. PMID:15326180

  2. Reaction mechanisms and kinetics of the iminovinylidene radical with NO: Ab initio study

    Hsiao, Ming-Kai; Chung, Yi-Hua; Hung, Yu-Ming; Chen, Hui-Lung, E-mail: chl3@faculty.pccu.edu.tw [Department of Chemistry and Institute of Applied Chemistry, Chinese Culture University, Taipei 111, Taiwan (China)

    2014-05-28

    The nitric oxide (NO) is a notorious compound for polluting environment. Recent year, removing nitric oxide from the atmosphere becomes a focus of the investigation. In our work, we study the iminovinylidene (HNCC) radical reacted with NO molecule. The mechanism and kinetic for reaction of the HNCC radical with the NO molecule is investigated via considering the possible channels of the N and O atoms of NO attacking the N and C atoms of the HNCC based on the high level ab initio molecular orbital calculations in conjunction with variational TST and RRKM calculations. The species involved have been optimized at the B3LYP/6-311++G(3df,2p) level and their single-point energies are refined by the CCSD(T)/aug-cc-PVQZ//B3LYP/6-311++G(3df,2p) method. The calculated potential energy surfaces indicated that energetically the most favorable channel for the HNCC + NO reaction was predicted to be the formation of HNC+CNO (P8) product via the addition reaction of the C atom of HNCC radical and the N atom of NO with the head to head orientation. To rationalize the scenario of the calculated results, we also employ the Fukui functions and HSAB theory to seek for a possible explanation. In addition, the reaction rate constants were calculated using VariFlex code, and the results show that the total rate coefficient, k{sub total}, at Ar pressure 760 Torr can be represented with an equation: k{sub total} = 6.433 × 10{sup −11} T {sup 0.100} exp(0.275 kcal mol{sup −1}/RT) at T = 298–3000 K, in units of cm{sup 3} molecule{sup −1} s{sup −1}.

  3. Mechanisms before Reactions: A Mechanistic Approach to the Organic Chemistry Curriculum Based on Patterns of Electron Flow

    Flynn, Alison B.; Ogilvie, William W.

    2015-01-01

    A significant redesign of the introductory organic chemistry curriculum at the authors' institution is described. There are two aspects that differ greatly from a typical functional group approach. First, organic reaction mechanisms and the electron-pushing formalism are taught before students have learned a single reaction. The conservation of…

  4. Conversion Reaction Mechanisms in Lithium Ion Batteries: Study of the Binary Metal Fluoride Electrodes

    Materials that undergo a conversion reaction with lithium (e.g., metal fluorides MF2: M = Fe, Cu, ...) often accommodate more than one Li atom per transition-metal cation, and are promising candidates for high-capacity cathodes for lithium ion batteries. However, little is known about the mechanisms involved in the conversion process, the origins of the large polarization during electrochemical cycling, and why some materials are reversible (e.g., FeF2) while others are not (e.g., CuF2). In this study, we investigated the conversion reaction of binary metal fluorides, FeF2 and CuF2, using a series of local and bulk probes to better understand the mechanisms underlying their contrasting electrochemical behavior. X-ray pair-distribution-function and magnetization measurements were used to determine changes in short-range ordering, particle size and microstructure, while high-resolution transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) were used to measure the atomic-level structure of individual particles and map the phase distribution in the initial and fully lithiated electrodes. Both FeF2 and CuF2 react with lithium via a direct conversion process with no intercalation step, but there are differences in the conversion process and final phase distribution. During the reaction of Li+ with FeF2, small metallic iron nanoparticles (2. In contrast to FeF2, no continuous Cu network was observed in the lithiated CuF2; rather, the converted Cu segregates to large particles (5-12 nm in diameter) during the first discharge, which may be partially responsible for the lack of reversibility in the CuF2 electrode.

  5. EFFECT OF FLUORINE AND CHLORINE IONS ON THE REACTION SINTERING OF MECHANICALLY ACTIVATED ZIRCON-ALUMINA MIXTURE

    R. Zamani Foroshani

    2015-09-01

    Full Text Available The aim of this work was to study the effect of fluorine and chlorine ions on the formation of mullite during the reaction sintering of mechanically activated zircon-alumina powder mixture. The results showed that mechanical activation of zirconalumina powder mixture for 20 h led to grain refinement and partial amorphization. In the presence of fluorine and chlorine ions, complete formation of mullite in the mechanically activated sample occurred after 2 h of reaction sintering at 1300oC and 1400oC, respectively. In the sample lacking fluorine and chlorine ions, mullitization was not completed even after 2 h of reaction sintering at 1400oC. It was concluded that presence of fluorine and chlorine ions enhance the dissociation of zircon and formation of mullite during the reaction sintering of mechanically activated zircon-alumina mixture.

  6. The reaction mechanism and mechanical properties of the composites fabricated in an Al-ZrO2-C system

    The in situ composites with the reinforcement volume fraction of 30 vol.% and the C/ZrO2 mole ratio of 0, 0.5 and 1.0 have been fabricated by using exothermic dispersion synthesis in an Al-ZrO2-C system. The reaction mechanism and mechanical properties of the composites have also been studied. When the reinforcement volume fraction of the composites is 30 vol.% and the C/ZrO2 mole ratio is zero, the Al first reacts with ZrO2 to produce the α-Al2O3 particles and the active Zr atoms, and then the Zr atoms react with Al to form the Al3Zr blocks, which are distributed uniformly throughout the aluminum matrix. The ultimate tensile strength and elongation of the composites at room temperature are 215.2 MPa and 3.0%, respectively. The fracture mechanism of the composite can be characterized by a crack nucleus initiating in the Al3Zr blocks and then propagating to the interface because of the poor properties of Al3Zr. With increasing the C/ZrO2 mole ratios, the ZrC is formed previous to the Al3Zr due to its lower Gibbs free energy, and its formation peak becomes bigger in the DSC curve. The amount of the Al3Zr blocks decreases, which leads to the improvement in the tensile properties of the composites. When the C/ZrO2 mole ratio is up to 1, the Al3Zr blocks have almost disappeared in the composites. The reinforcements are composed of α-Al2O3 and ZrC. At the same time, the ultimate tensile strength and elongation increase to 245.4 MPa and 8.0%, respectively. The tensile fracture surface is composed of fine ductile dimples.

  7. Reaction mechanism and influence of the experimental variables for solvothermal synthesized LiMnPO4 nanoplates

    Zhu, Kunlei; Zhang, Wenxuan; Du, Jiangyong; Liu, Xiaoyan; Tian, Jianhua; Ma, Huanmei; Liu, Shengzhong; Shan, Zhongqiang

    2015-12-01

    Plate-like LiMnPO4 nanomaterial for Li-ion batteries is synthesised successfully via a facile solvothermal process in mixed water-diethylene glycol (DEG) solvents at 190 °C for 3 h. Experimental variables, including reaction time, reaction temperature and reactant mole ratio, are discussed in detail. A tentative reaction mechanism is proposed on the basis of the time dependent trials. It is found that, with the increase of reaction temperature, the formation of LiMnPO4 phase is accelerated and the reaction for synthesizing LiMnPO4 can be finished in a shorter time. Studies on the effect of reactant mole ratio further support the proposed mechanism. The electrochemical properties of obtained LiMnPO4 are examined after a carbon coating process. Electrochemical tests show that the obtained LiMnPO4 at 190 °C for 3 h exhibits better electrochemical performances than the LiMnPO4 synthesized at 170 °C for 4.5 h or 150 °C for 6 h. It is clear that an improved electrochemical performance can be obtained with the increase of reaction temperature and the decrease of reaction time. This result provides us thoughts and guidance to optimize the reaction conditions by harmonizing the reaction temperature and reaction time, which is beneficial for the practical application.

  8. The Effect of Exertion and Sex on Vertical Ground Reaction Force Variables and Landing Mechanics.

    Bell, David R; Pennuto, Anthony P; Trigsted, Stephanie M

    2016-06-01

    Bell, DR, Pennuto, AP, and Trigsted, SM. The effect of exertion and sex on vertical ground reaction force variables and landing mechanics. J Strength Cond Res 30(6): 1661-1669, 2016-The purpose of this investigation was to determine how exertion and sex affected a variety of vertical ground reaction force (VGRF) parameters during a jump-landing task, including peak VGRF, peak VGRF asymmetry, loading rate, and loading rate asymmetry. Additionally, we wanted to determine whether landing mechanics changed after exertion as measured by the Landing Error Scoring System (LESS). Forty recreationally active participants (20 men and 20 women) completed jump landings from a 30-cm-high box onto force plates before and after repeated bouts of an exercise circuit until a specific rating of perceived exertion was achieved. Three-way (sex × time × limb) analyses of variance were used to analyze variables pre-exertion to postexertion. No significant 3-way interactions were observed for peak VGRF (p = 0.31) or loading rate (p = 0.14). Time by sex interactions were observed for peak VGRF (p = 0.02) and loading rate (p = 0.008). Post hoc analysis revealed that men increased landing force and loading rate after exertion while women did not. Landing mechanics, as assessed by total LESS score, were worse after exertion (p < 0.001) with increased frequency of errors for knee flexion <30° at initial contact, lateral trunk flexion, and not flexing the hip during landing. Women may be more resistant to exertion compared with men and use different joint controls' strategies to cope with VGRF after exertion. However, VGRF asymmetry is not affected by sex and exertion. Limiting peak VGRF and addressing landing postures, especially after exertion, should be components of injury prevention strategies. PMID:26562710

  9. Shrinkage Cracking: A mechanism for self-sustaining carbon mineralization reactions in olivine rocks

    Zhu, W.; Fusseis, F.; Lisabeth, H. P.; Xing, T.; Xiao, X.; De Andrade, V. J. D.; Karato, S. I.

    2015-12-01

    The hydration and carbonation of olivine results in an up to ~44% increase in solid molar volume, which may choke off of fluid supply and passivate reactive surfaces, thus preventing further carbonation reactions. The carbonation of olivine has ben studied extensively in the laboratory. To date, observations from these experimental studies indicate that carbonation reaction rates generally decrease with time and the extent of carbonation is limited in olivine rocks. Field studies, however, show that 100% hydration and carbonation occur naturally in ultramafic rocks. The disagreement between the laboratory results under controlled conditions and the field observations underlines the lack of understanding of the mechanisms responsible for the self-sustaining carbonation interaction in nature. We developed a state-of-the-art pressurized hydrothermal cell that is transparent to X-rays to characterize the real-time evolution of pore geometry during fluid-rock interaction using in-situ synchrotron-based X-ray microtomography. Through a time series of high-resolution 3-dimensional images, we document the microstructural evolution of a porous olivine aggregate reacting with a sodium bicarbonate solution at elevated pressure and temperature conditions. We observed porosity increases, near constant rate of crystal growth, and pervasive reaction-induced fractures. Based on the nanometer scale tomography data, we propose that shrinkage cracking is the mechanism responsible for producing new reactive surface and keep the carbonation reaction self-sustaining in our experiment. Shrinkage cracks are commonly observed in drying mud ponds, cooling lava flows and ice wedge fields. Stretching of a contracting surface bonded to a substrate of nearly constant dimensions leads to a stress buildup in the surface layer. When the stress exceeds the tensile strength, polygonal cracks develop in the surface layer. In our experiments, the stretching mismatch between the surface and interior of

  10. Preparation of Polystyrenylphosphonous Acid of Low Polymerization Degree and Influence of Initiators upon the Free Radical Reaction Mechanism

    2002-01-01

    The polystyrenylphosphonous acid (PSPA) of low polymerization degree was prepared with one step reaction. The reaction mechanism was changed with different initiators. For the reaction with AIBN or BPO as the initiator, there are 2 or 3 series of radical reaction chains and 5 or 9 series of polystyrenyl products. The main products are PSPA without or with the fragment of the initiator H[CH(C6H5)-CH2]n-PO2H2 and C6H5CO2-[CH2CH (C6H5)]n-PO2H2 respectively.

  11. Surftherm: A program to analyze thermochemical and kinetic data in gas-phase and surface chemical reaction mechanisms

    Coltrin, M.E.; Moffat, H.K.

    1994-06-01

    This report documents the Surftherm program that analyzes transport coefficient, thermochemical- and kinetic rate information in complex gas-phase and surface chemical reaction mechanisms. The program is designed for use with the Chemkin (gas-phase chemistry) and Surface Chemkin (heterogeneous chemistry) programs. It was developed as a ``chemist`s companion`` in using the Chemkin packages with complex chemical reaction mechanisms. It presents in tabular form detailed information about the temperature and pressure dependence of chemical reaction rate constants and their reverse rate constants, reaction equilibrium constants, reaction thermochemistry, chemical species thermochemistry and transport properties. This report serves as a user`s manual for use of the program, explaining the required input and the output.

  12. A Theoretical Investigation on the Reaction Mechanism of the C8H+·10 Side-Chain Decomposition Processes

    CHENG Xue-Li; ZHAO Yan-Yun; LI Feng

    2008-01-01

    The dissociation of ethylbenzene cation C8H+·10 served as a prototype to investigate the decompasition mechanisms of alkylbenzene cations.The reactions of C8H+·10 decomposition reaction system have been studied extensively at the B3L YP/6-311++G** level with Gaussion 98 package.The chain reaction of C8H+·10 dissociation is initiated by C-H bond rupture.All reaction channels were fully investigated with the vibrational mode analysis to confirm the transition states and reveal the reaction mechanism.The energetically most favorable pathway is C8H+·10→TS4→·P2+H· and the channel ieading to C8H+·10 and C2H4 is also competitive.

  13. Palladium/N-heterocyclic carbene catalysed regio and diastereoselective reaction of ketones with allyl reagents via inner-sphere mechanism.

    Bai, Da-Chang; Yu, Fei-Le; Wang, Wan-Ying; Chen, Di; Li, Hao; Liu, Qing-Rong; Ding, Chang-Hua; Chen, Bo; Hou, Xue-Long

    2016-01-01

    The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism-nucleophilic attack of enolate oxygen on Palladium followed by C-C bond-forming [3,3']-reductive elimination. PMID:27283477

  14. Structures and reaction mechanisms of the two related enzymes, PurN and PurU.

    Sampei, Gen-ichi; Kanagawa, Mayumi; Baba, Seiki; Shimasaki, Toshiaki; Taka, Hiroyuki; Mitsui, Shohei; Fujiwara, Shinji; Yanagida, Yuki; Kusano, Mayumi; Suzuki, Sakiko; Terao, Kayoko; Kawai, Hiroya; Fukai, Yoko; Nakagawa, Noriko; Ebihara, Akio; Kuramitsu, Seiki; Yokoyama, Shigeyuki; Kawai, Gota

    2013-12-01

    The crystal structures of glycinamide ribonucleotide transformylases (PurNs) from Aquifex aeolicus (Aa), Geobacillus kaustophilus (Gk) and Symbiobacterium toebii (St), and of formyltetrahydrofolate hydrolase (PurU) from Thermus thermophilus (Tt) were determined. The monomer structures of the determined PurN and PurU were very similar to the known structure of PurN, but oligomeric states were different; AaPurN and StPurN formed dimers, GkPurN formed monomer and PurU formed tetramer in the crystals. PurU had a regulatory ACT domain in its N-terminal side. So far several structures of PurUs have been determined, yet, the mechanisms of the catalysis and the regulation of PurU have not been elucidated. We, therefore, modelled ligand-bound structures of PurN and PurU, and performed molecular dynamics simulations to elucidate the reaction mechanisms. The evolutionary relationship of the two enzymes is discussed based on the comparisons of the structures and the catalytic mechanisms. PMID:24108189

  15. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    solving complex problems and proposing new detailed reaction mechanisms that rationalize the experimental findings. For each of the considered reactions, a consistent mechanism is presented, the experimentally observed selectivities are reproduced, and their sources are identified. Reproducing selectivities requires high accuracy in computing relative transition state energies. As demonstrated by the results summarized in this Account, this accuracy is possible with the use of the presented methodology, benefiting of course from a large extent of cancellation of systematic errors. It is argued that as the employed models become larger, the number of rotamers and isomers that have to be considered for every stationary point increases and a careful assessment of their energies is therefore necessary in order to ensure that the lowest energy conformation is located. This issue constitutes a bottleneck of the investigation in some cases and is particularly important when analyzing selectivities, since small energy differences need to be reproduced. PMID:27082700

  16. Computerized pathway elucidation for hydroxyl radical-induced chain reaction mechanisms in aqueous phase advanced oxidation processes.

    Li, Ke; Crittenden, John

    2009-04-15

    The radical reaction mechanism that is involved in advanced oxidation processes is complex. An increasing number of trace contaminants and stringent drinking water standards call for a rule-based model to provide insight to the mechanism of the processes. A model was developed to predict the pathway of contaminant degradation and byproduct formation during advanced oxidation. The model builds chemical molecules as graph objects, which enables mathematic abstraction of chemicals and preserves chemistry information. The model algorithm enumerates all possible reaction pathways according to the elementary reactions (built as reaction rules) established from experimental observation. The method can predict minor pathways that could lead to toxic byproducts so that measures can be taken to ensure drinking water treatment safety. The method can be of great assistance to water treatment engineers and chemists who appreciate the mechanism of treatment processes. PMID:19475958

  17. The mechanism of chemisorption of hydrogen atom on graphene: Insights from the reaction force and reaction electronic flux

    At the PBE-D3/cc-pVDZ level of theory, the hydrogen chemisorption on graphene was analyzed using the reaction force and reaction electronic flux (REF) theories in combination with electron population analysis. It was found that chemisorption energy barrier is mainly dominated by structural work (∼73%) associated to the substrate reconstruction whereas the electronic work is the greatest contribution of the reverse energy barrier (∼67%) in the desorption process. Moreover, REF shows that hydrogen chemisorption is driven by charge transfer processes through four electronic events taking place as H approaches the adsorbent surface: (a) intramolecular charge transfer in the adsorbent surface; (b) surface reconstruction; (c) substrate magnetization and adsorbent carbon atom develops a sp3 hybridization to form the σC-H bond; and (d) spontaneous intermolecular charge transfer to reach the final chemisorbed state

  18. Reaction mechanisms in the reduction of Winterveld chrome spinel with graphite and carbon

    The reduction of mixtures of various sizes of gangue-free Winterveld chrome spinel and graphite under an argon atmosphere at 1300 degrees Celsius was studied by use of a recording thermobalance. The partially reduced material was examined by scanning electron microscopy, and the observations were analysed in terms of reaction mechanism. A four-stage sequence was deduced, as follows. In the first stage, the ferric iron is reduced to ferrous iron with no metallization. This stage is inherently variable and is controlled by the random packing of particles of reducing agent round the chromite. The second stage starts with a burst of metal nucleation, which is also inherently variable. This is followed by the reaction of carbon monoxide with the relatively highly reducible oxide at the perimeters of the metal nuclei, and is controlled by the regeneration of carbon monoxide by the Boudouard reaction. The second stage merges into the third, with no change in the form of the product until the removal of iron decreases the reducibility of the remaining oxide to such an extent that the activity of the carbon monoxide is not sufficient for reduction to proceed. Reduction is then accomplished by the carbon dissolved in the reduced metallic product, the rate of reduction being limited by the rate of carburization of the metal. The fourth stage is reached at a reduction of about 50 per cent. In that stage the rate is controlled by the diffusion of chromium ions in the oxide, and the reduced product becomes saturated with carbon as the mixed (Fe,Cr)7C3 carbide

  19. The alloantigenic sites of alpha3alpha4alpha5(IV) collagen: pathogenic X-linked alport alloantibodies target two accessible conformational epitopes in the alpha5NC1 domain.

    Kang, Jeong Suk; Kashtan, Clifford E; Turner, A Neil; Heidet, Laurence; Hudson, Billy G; Borza, Dorin-Bogdan

    2007-04-01

    Anti-glomerular basement membrane (GBM) antibody nephritis is caused by an autoimmune or alloimmune reaction to the NC1 domains of alpha3alpha4alpha5(IV) collagen. Some patients with X-linked Alport syndrome (XLAS) develop post-transplant nephritis mediated by pathogenic anti-GBM alloantibodies to collagen IV chains present in the renal allograft but absent from the tissues of the patient. In this work, the epitopes targeted by alloantibodies from these patients were identified and characterized. All XLAS alloantibodies recognized conformational epitopes in the NC1 domain of alpha5(IV) collagen, which were mapped using chimeric alpha1/alpha5 NC1 domains expressed in mammalian cells. Allograft-eluted alloantibodies mainly targeted two conformational alloepitopes mapping to alpha5NC1 residues 1-45 and 114-168. These regions also encompassed the major epitopes of circulating XLAS alloantibodies, which in some patients additionally targeted alpha5NC1 residues 169-229. Both kidney-eluted and circulating alloantibodies to alpha5NC1 distinctively targeted epitopes accessible in the alpha3alpha4alpha5NC1 hexamers of human GBM, unlike anti-GBM autoantibodies, which targeted sequestered alpha3NC1 epitopes. The results identify two immunodominant alpha5NC1 epitopes as major alloantigenic sites of alpha3alpha4alpha5(IV) collagen specifically implicated in the pathogenesis of post-transplant nephritis in XLAS patients. The contrast between the accessibility of these alloepitopes and the crypticity of autoepitopes indicates that distinct molecular forms of antigen may initiate the immunopathogenic processes in the two forms of anti-GBM disease. PMID:17293596

  20. Studies on the Reaction Mechanism of CPP and the Factors Affecting the Yields of Ethylene and Propylene

    2002-01-01

    The reaction mechanisms of Catalytic Pyrolysis Process and the ethylene and propylene forma-tion reaction are analyzed, and ethylene and propylene are produced through both the free radical reac-tion and carbenium ion reaction. The factors affecting the yields of ethylene and propylene are discussed.The results showed that greater yields of ethylene and propylene can be obtained on ZSM-5 catalystsrather than USY and REY catalysts, and the modified ZSM-5 could improve the ethylene yield. A highertemperature is favorable for enhancement of the free radical reaction as opposed to carbenium ion reaction,and change in temperature can adjust the ratio of ethylene and propylene production. A higher steamamount could produce more ethylene and propylene and less coke, and lowering the catalyst/oil ratio isfavorable for producing ethylene.

  1. Studies on the Reaction Mechanism of CPP and the Factors Affecting the Yields of Ethylene and Propylene

    Hou Dianguo; Wang Xieqing; Xie Chaogang; Shi Zhicheng

    2002-01-01

    The reaction mechanisms of Catalytic Pyrolysis Process and theethylene and propylene forma-tion reaction are analyzed, and ethylene and propylene are produced through both the free radical reac-tion and carbenium ion reaction. The factors affecting the yields of ethylene and propylene are discussed.The results showed that greater yields of ethylene and propylene can be obtained on ZSM-5 catalystsrather than USY and REY catalysts, and the modified ZSM-5 could improve the ethylene yield. A highertemperature is favorable for enhancement of the free radical reaction as opposed to carbenium ion reaction,and change in temperature can adjust the ratio of ethylene and propylene production. A higher steamamount could produce more ethylene and propylene and less coke, and lowering the catalyst/oil ratio isfavorable for producing ethylene.

  2. Thermal analysis experiment for elucidating sodium-water chemical reaction mechanism in steam generator of sodium-cooled fast reactor

    For the purpose of elucidating the mechanism of the sodium-water surface reaction in steam generator of sodium-cooled after reactors, kinetic study of the sodium (Na)-sodium hydroxide (NaOH) reaction has been carried out by using Differential Thermal Analysis (DTA) technique. The parameters, including melting point of Na and NaOH, transition temperature of NaOH, Na-NaOH reaction temperature, and the decomposition temperature of sodium hydride (NaH) have been identified from DTA curves. Based on the measured reaction temperature, rate constant of Na2O generation was obtained. Thermal analysis results indicated that Na2O generation at the secondary overall reaction would be considered during the sodium-water reaction. (author)

  3. Kinetics and mechanisms of reactions between H2O2 and copper and copper oxides.

    Björkbacka, Åsa; Yang, Miao; Gasparrini, Claudia; Leygraf, Christofer; Jonsson, Mats

    2015-09-28

    One of the main challenges for the nuclear power industry today is the disposal of spent nuclear fuel. One of the most developed methods for its long term storage is the Swedish KBS-3 concept where the spent fuel is sealed inside copper canisters and placed 500 meters down in the bedrock. Gamma radiation will penetrate the canisters and be absorbed by groundwater thereby creating oxidative radiolysis products such as hydrogen peroxide (H2O2) and hydroxyl radicals (HO˙). Both H2O2 and HO˙ are able to initiate corrosion of the copper canisters. In this work the kinetics and mechanism of reactions between the stable radiolysis product, H2O2, and copper and copper oxides were studied. Also the dissolution of copper into solution after reaction with H2O2 was monitored by ICP-OES. The experiments show that both H2O2 and HO˙ are present in the systems with copper and copper oxides. Nevertheless, these species do not appear to influence the dissolution of copper to the same extent as observed in recent studies in irradiated systems. This strongly suggests that aqueous radiolysis can only account for a very minor part of the observed radiation induced corrosion of copper. PMID:26287519

  4. Removal of Cr (VI) with wheat-residue derived black carbon: Reaction mechanism and adsorption performance

    The removal of Cr (VI) from aqueous solutions using black carbon (BC) isolated from the burning residues of wheat straw was investigated as a function of pH, contact time, reaction temperature, supporting electrolyte concentration and analytical initial Cr (VI) concentration in batch studies. The effect of surface properties on the adsorption behavior of Cr (VI) was investigated with scanning electron microscope (SEM) equipped with the energy dispersive X-ray spectroscope (EDS) and Fourier transform-infrared (FTIR) spectroscopy. The removal mechanism of Cr (VI) onto the BC was investigated and the result showed that the adsorption reaction consumed a large amount of protons along the reduction of Cr (VI) to Cr (III). The oxidation of the BC took place concurrently to the chromium reduction and led to the formation of hydroxyl and carboxyl functions. An initial solution pH of 1.0 was most favorable for Cr (VI) removal. The adsorption process followed the pseudo-second order equation and Freundlich isotherm very well. The Cr (VI) adsorption was temperature-dependent and almost independent on the sodium chloride concentrations. The maximum adsorption capacity for Cr (VI) was found at 21.34 mg/g in an acidic medium, which is comparable to other low-cost adsorbents.

  5. Nuclear structure and reaction mechanism effects in quasi continuum gamma decay

    In this thesis an investigation of nuclear structure and reaction mechanism effects is presented as they manifest themselves in the gamma-ray quasi-continua of residual nuclei produced in 12C induced reactions. The author has studied the nuclear structure at high angular momentum and excitation energy of two heavy nuclei (152Dy,156Dy) that have a very different structure at low angular momentum and excitation energy. In addition the effect of the quasi-continuous gamma-decay process on the feeding of the yrast states (the states with the lowest excitation energy at a certain angular momentum) in these two rare earth nuclei has been investigated. The results are discussed in terms of collective and non-collective excitation modes. The interplay between these two types of motion of the nucleons in nuclei in the same mass region and its influence on the structure of the yrast states has been investigated in a search for high-spin isomeric states. (Auth.)

  6. Kinetics and Mechanism of Deoxygenation Reactions over Proton-Form and Molybdenum-Modified Zeolite Catalysts

    Bedard, Jeremy William

    The depletion of fossil fuel resources and the environmental consequences of their use have dictated the development of new sources of energy that are both sustainable and economical. Biomass has emerged as a renewable carbon feedstock that can be used to produce chemicals and fuels traditionally obtained from petroleum. The oxygen content of biomass prohibits its use without modification because oxygenated hydrocarbons are non-volatile and have lower energy content. Chemical processes that eliminate oxygen and keep the carbon backbone intact are required for the development of biomass as a viable chemical feedstock. This dissertation reports on the kinetic and mechanistic studies conducted on high and low temperature catalytic processes for deoxygenation of biomass precursors to produce high-value chemicals and fuels. Low temperature, steady state reaction studies of acetic acid and ethanol were used to identify co-adsorbed acetic acid/ethanol dimers as surface intermediates within specific elementary steps involved in the esterification of acetic acid with ethanol on zeolites. A reaction mechanism involving two dominating surface species, an inactive ethanol dimeric species adsorbed on Bronsted sites inhibiting ester formation and a co-adsorbed complex of acetic acid and ethanol on the active site reacting to produce ethyl acetate, is shown to describe the reaction rate as a function of temperature (323 -- 383 K), acetic acid (0.5 -- 6.0 kPa), and ethanol (5.0 -- 13.0 kPa) partial pressure on proton-form BEA, FER, MFI, and MOR zeolites. Measured differences in rates as a function of zeolite structure and the rigorous interpretation of these differences in terms of esterification rate and equilibrium constants is presented to show that the intrinsic rate constant for the activation of the co-adsorbed complex increases in the order FER dehydrogenation reaction sequences results instead in a two-zone, stratified bed reactor configuration consisting of upstream

  7. NATO Advanced Research Workshop on the Mechanisms of Reactions of Organometallic Compounds with Surfaces

    Williams, J

    1989-01-01

    A NATO Advanced Research Workshop on the "Mechanisms of Reactions of Organometallic Compounds with Surfaces" was held in St. Andrews, Scotland in June 1988. Many of the leading international researchers in this area were present at the workshop and all made oral presentations of their results. In addition, significant amounts of time were set aside for Round Table discussions, in which smaller groups considered the current status of mechanistic knowledge, identified areas of dispute or disagreement, and proposed experiments that need to be carried out to resolve such disputes so as to advance our understanding of this important research area. All the papers presented at the workshop are collected in this volume, together with summaries of the conclusions reached at the Round Table discussions. The workshop could not have taken place without financial support from NATO, and donations were also received from Associated Octel, Ltd., STC Ltd., and Epichem Ltd., for which the organisers are very grateful. The orga...

  8. Catapult mechanism for fast particle emission in fission and heavy ion reactions

    The fission processes of slabs of nuclear matter is modelled in the Hartree-Fock time dependence approximation by adding an initial collective velocity field to the static self-consistent solution. In dependence on its amplitude either large amplitude density oscillations are excited or fission occurs. The final disintegration of the slab proceeds on a time scale 10-22 s and is characterized by a sharp peak in the actual velocity field in the region of the ''snatching'' inner low density tails. A characteristic time later a low density lump correlated with a peak in the velocity field energies in front of the fragments. These particles are called ''catapult particles''. Recent experimental results possibly provide evidence for catapult neutrons in low-energy fission. The significance of the catapult mechanism for fast particle emission in the exit channel of heavy ion reactions is discussed

  9. Structrue and Characteristics of Mesoporous Silica Synthesized in Acid Medium and Its Reaction Mechanism

    LEI Jia-heng; ZHAO Jun; CHEN Yong-xi; GUO Li-ping; LIU Dan

    2004-01-01

    Structrue and pore characteristics of the mesoporous silica synthesized in acid medium were studied by means of XRD, HRTEM, BET, FT-IR, DSC-TGA, and the reaction mechanism was also investigated deeply. The results show that mesopores in the sample possess hexagonal arrays obviously, whereas the structure of silica matrix is amorphous. The results also show that the acting mode of silica and CTMA+ inside the mesopores was chemical bonding force. The structure of mesoporous silica was mainly dependent on the aggregational condition of micelle of CTMA+ as well as their liquid-crystallized status. In addition, condensation and dehydration of silicate radicals were accompanied in the process of calcination, which resulted in the mesoporous structure ordered in local range and the pore sizes largening.

  10. Catalytic mechanism of transition-metal compounds on Mg hydrogen sorption reaction.

    Barkhordarian, Gagik; Klassen, Thomas; Bormann, Rüdiger

    2006-06-01

    The catalytic mechanisms of transition-metal compounds during the hydrogen sorption reaction of magnesium-based hydrides were investigated through relevant experiments. Catalytic activity was found to be influenced by four distinct physico-thermodynamic properties of the transition-metal compound: a high number of structural defects, a low stability of the compound, which however has to be high enough to avoid complete reduction of the transition metal under operating conditions, a high valence state of the transition-metal ion within the compound, and a high affinity of the transition-metal ion to hydrogen. On the basis of these results, further optimization of the selection of catalysts for improving sorption properties of magnesium-based hydrides is possible. In addition, utilization of transition-metal compounds as catalysts for other hydrogen storage materials is considered. PMID:16771356

  11. Mechanism of recoil implantation reactions of technetium and ruthenium in metal acetylacetonates

    Recoil implantation of Tc and Ru in metal acetylacetonates were performed using ruthenium metal as a source and MIII(acac)3 and MII(acac)2 complexes as catchers. The recoil atoms were obtained by 100Ru(γ,p)99mTc and 98Ru(γ,n)97Ru reactions. The yields of Tc(acac)3 and Ru(acac)3 were clearly dependent on the force constant of the bond between the central metal atom and oxygen in acetylacetone K(M-O). A plot of the yield vs. 1/K(M-O) showed a linear relationship. However, the yield of Tc(acac)2 implanted in M(acac)2 did not show such a dependence on the force constant. The difference of the mechanism of complex formation between Tc(acac)3 and Tc(acac)2 was discussed. (author)

  12. Alkene Cleavage Catalysed by Heme and Nonheme Enzymes: Reaction Mechanisms and Biocatalytic Applications

    Francesco G. Mutti

    2012-01-01

    Full Text Available The oxidative cleavage of alkenes is classically performed by chemical methods, although they display several drawbacks. Ozonolysis requires harsh conditions (−78°C, for a safe process and reducing reagents in a molar amount, whereas the use of poisonous heavy metals such as Cr, Os, or Ru as catalysts is additionally plagued by low yield and selectivity. Conversely, heme and nonheme enzymes can catalyse the oxidative alkene cleavage at ambient temperature and atmospheric pressure in an aqueous buffer, showing excellent chemo- and regioselectivities in certain cases. This paper focuses on the alkene cleavage catalysed by iron cofactor-dependent enzymes encompassing the reaction mechanisms (in case where it is known and the application of these enzymes in biocatalysis.

  13. Revisitation of the βCl-Elimination Reaction of d-Amino Acid Oxidase: NEW INTERPRETATION OF THE REACTION THAT SPARKED FLAVOPROTEIN DEHYDROGENATION MECHANISMS*

    Ghisla, Sandro; Pollegioni, Loredano; Molla, Gianluca

    2011-01-01

    d-Amino acid oxidase (DAAO) from pig has been reported to catalyze the β-elimination of Cl− from βCl-d-alanine via abstraction of the substrate α-H as H+ (“carbanion mechanism”) (Walsh, C. T., Schonbrunn, A., and Abeles, R. H. (1971) J. Biol. Chem. 246, 6855–6866). In view of the fundamental mechanistic importance of this reaction and of the recent reinterpretation of the DAAO dehydrogenation step as occurring via a hydride mechanism, we reinvestigated the elimination reaction using yeast DAA...

  14. Theoretical Study of the Scattering Resonance State, Reaction Mechanism and Partial Potential Energy Surface of the F+CH4→HF +CH3 Reaction

    Qiang WANG; Zheng Ting CAI; Da Cheng FENG

    2006-01-01

    The partial potential energy surface was constructed by ab initio method [QCISD(T)/6-311++G(2df,2pd)]for F+CH4→HF+CH3 reaction system. It not only explained the reaction mechanism brought forward by Diego Troya by means of quasiclassical trajectory (QCT) but also successfully validated Kopin Liu's experimental phenomena about the existence of the reactive resonance. The lifetime of the scattering resonance state was about 0.07 ps. All these were in agreement with the experiments.

  15. Probing the reaction mechanism of IspH protein by x-ray structure analysis

    Gräwert, Tobias

    2009-12-28

    Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) represent the two central intermediates in the biosynthesis of isoprenoids. The recently discovereddeoxyxylulose 5-phosphate pathway generates a mixture of IPP and DMAPP in its final step by reductive dehydroxylation of 1-hydroxy-2-methyl- 2-butenyl 4-diphosphate. This conversion is catalyzed by IspH protein comprising a central iron-sulfur cluster as electron transfer cofactor in the active site. The five crystal structures of IspH in complex with substrate, converted substrate, products and PPi reported in this article provide unique insights into the mechanism of this enzyme. While IspH protein crystallizes with substrate bound to a [4Fe-4S] cluster, crystals of IspH in complex with IPP, DMAPP or inorganic pyrophosphate feature [3Fe-4S] clusters. The IspH:substrate complex reveals a hairpin conformation of the ligand with the C(1) hydroxyl group coordinated to the unique site in a [4Fe-4S] cluster of aconitase type. The resulting alkoxide complex is coupled to a hydrogen-bonding network, which serves as proton reservoir via a Thr167 proton relay. Prolonged x-ray irradiation leads to cleavage of the C(1)-O bond (initiated by reducing photo electrons). The data suggest a reaction mechanism involving a combination of Lewis-acid activation and proton coupled electron transfer. The resulting allyl radical intermediate can acquire a second electron via the iron-sulfur cluster. The reaction may be terminated by the transfer of a proton from the β-phosphate of the substrate to C(1) (affording DMAPP) or C(3) (affording IPP).

  16. Mechanism of coupling drug transport reactions located in two different membranes

    Helen I. Zgurskaya

    2015-02-01

    Full Text Available Gram- negative bacteria utilize a diverse array of multidrug transporters to pump toxic compounds out of cells. Some transporters together with periplasmic membrane fusion proteins (MFPs and outer membrane channels assemble trans-envelope complexes that expel multiple antibiotics across outer membranes of Gram-negative bacteria and into the external medium. Others further potentiate this efflux by pumping drugs across the inner membrane into the periplasm. Together these transporters create a powerful network of efflux that protect bacteria against a broad range of antimicrobial agents. This review is focused on the mechanism of coupling transport reactions located in two different membranes of Gram-negative bacteria. Using a combination of biochemical, genetic and biophysical approaches we have reconstructed the sequence of events leading to the assembly of trans-envelope drug efflux complexes and characterized the roles of periplasmic and outer membrane proteins in this process. Our recent data suggest a critical step in the activation of intermembrane efflux pumps, which is controlled by MFPs. We propose that the reaction cycles of transporters are tightly coupled to the assembly of the trans-envelope complexes. Transporters and MFPs exist in the inner membrane as dormant complexes. The activation of complexes is triggered by MFP binding to the outer membrane channel, which leads to a conformational change in the membrane proximal domain of MFP needed for stimulation of transporters. The activated MFP-transporter complex engages the outer membrane channel to expel substrates across the outer membrane. The recruitment of the channel is likely triggered by binding of effectors (substrates to MFP or MFP-transporter complexes. This model together with recent structural and functional advances in the field of drug efflux provides a fairly detailed understanding of the mechanism of drug efflux across the two membranes.

  17. Implicit coupling of turbulent diffusion with chemical reaction mechanisms for prognostic atmospheric dispersion models

    Berlowitz, D.R.

    1996-11-01

    In the last few decades the negative impact by humans on the thin atmospheric layer enveloping the earth, the basis for life on this planet, has increased steadily. In order to halt, or at least slow down this development, the knowledge and study of these anthropogenic influence has to be increased and possible remedies have to be suggested. An important tool for these studies are computer models. With their help the atmospheric system can be approximated and the various processes, which have led to the current situation can be quantified. They also serve as an instrument to assess short or medium term strategies to reduce this human impact. However, to assure efficiency as well as accuracy, a careful analysis of the numerous processes involved in the dispersion of pollutants in the atmosphere is called for. This should help to concentrate on the essentials and also prevent excessive usage of sometimes scarce computing resources. The basis of the presented work is the EUMAC Zooming Model (ETM), and particularly the component calculating the dispersion of pollutants in the atmosphere, the model MARS. The model has two main parts: an explicit solver, where the advection and the horizontal diffusion of pollutants are calculated, and an implicit solution mechanism, allowing the joint computation of the change of concentration due to chemical reactions, coupled with the respective influence of the vertical diffusion of the species. The aim of this thesis is to determine particularly the influence of the horizontal components of the turbulent diffusion on the existing implicit solver of the model. Suggestions for a more comprehensive inclusion of the full three dimensional diffusion operator in the implicit solver are made. This is achieved by an appropriate operator splitting. A selection of numerical approaches to tighten the coupling of the diffusion processes with the calculation of the applied chemical reaction mechanisms are examined. (author) figs., tabs., refs.

  18. Kinetics and Reaction Mechanisms of High-Temperature Flash Oxidation of Molybdenite

    Wilkomirsky, Igor; Otero, Alfonso; Balladares, Eduardo

    2010-02-01

    The kinetics and reaction mechanism of the flash oxidation of +35/-53 μm molybdenite particles in air, as well as in 25, 50, and 100 pct oxygen higher than 800 K, has been investigated using a stagnant gas reactor and a laminar flow reactor coupled to a fast-response, two-wavelength pyrometer. The changes in the morphology and in the chemical composition of partially reacted particles were also investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential thermal analysis (DTA), and electron microprobe. High-speed photography was also used to characterize the particle combustion phenomena. The effects of oxygen concentration and gas temperature on ignition and peak combustion temperatures were studied. The experimental results indicate that MoS2 goes through a process of ignition/combustion with the formation of gaseous MoO3 and SO2 with no evidence of formation of a molten phase, although the reacting molybdenite particles reach temperatures much higher than their melting temperature. This effect may be a result of the combustion of gaseous sulfur from partial decomposition of molybdenite to Mo2S3 under a high gas temperature and 100 pct oxygen. In some cases, the partial fragmentation and distortion of particles also takes place. The transformation can be approximated to the unreacted core model with chemical control and with activation energy of 104.0 ± 4 kJ/mol at the actual temperature of the reacting particles. The reaction was found to be first order with respect to the oxygen concentration. The rate constant calculated at the actual temperatures of the reacting particles shows a good agreement with kinetic data obtained at lower temperatures. The ignition temperature of molybdenite shows an inverse relationship with the gas temperature and oxygen content, with the lowest ignition temperature of 1120 K for 100 pct oxygen. Increasing the oxygen content from 21 to 100 pct increases the particle combustion temperature from 1600 K

  19. A Detailed Chemical Kinetic Reaction Mechanism for Oxidation of Four Small Alkyl Esters in Laminar Premixed Flames

    Westbrook, C K; Pitz, W J; Westmoreland, P R; Dryer, F L; Chaos, M; Osswald, P; Kohse-Hoinghaus, K; Cool, T A; Wang, J; Yang, B; Hansen, N; Kasper, T

    2008-02-08

    A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions in each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules.

  20. Isospin transport and reaction mechanism in nuclear reactions in the range 20–40 MeV/n

    Barlini, S., E-mail: barlini@fi.infn.it; Piantelli, S.; Casini, G.; Olmi, A.; Bini, M.; Pasquali, G.; Poggi, G.; Stefanini, A. A.; Valdré, S.; Pastore, G. [Dipartimento di Fisica ed Astronomia dell’Università and INFN Sezione di Firenze, Firenze (Italy); Bougault, R.; Lopez, O.; Le Neindre, N.; Parlog, M.; Vient, E. [LPC, IN2P3-CNRS, ENSICAEN et Université de Caen, F-14050 Caen-Cedex (France); Bonnet, E.; Chibhi, A.; Frankland, J. D. [GANIL, CEA/DSM-CNRS/IN2P3, B.P.5027, F-14076 Caen cedex (France); Borderie, B.; Rivet, M. F. [Institut de Physique Nucléaire, CNRS/IN2P3, Université Paris-Sud 11, F-91406 Orsay cedex (France); and others

    2015-10-15

    In recent years, many efforts have been devoted to the investigation of the isospin degree of freedom in nuclear reactions. Comparing systems involving partners with different N/Z, it has been possible to investigate the isospin transport process and its influence on the final products population. This can be then related to the symmetry energy term of the nuclear EOS. From the experimental point of view, this task requires detectors able to measure both charge and mass of the emitted products, in the widest possible range of energy and size of the fragments. With this objective, the FAZIA and GARFIELD+RCo apparatus have been used with success in some recent experiments.

  1. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior

  2. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    Xiong, Wei; Zhang, Xianfeng, E-mail: lynx@mail.njust.edu.cn; Wu, Yang; He, Yong; Wang, Chuanting; Guo, Lei

    2015-11-05

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior.

  3. A computational linear elastic fracture mechanics-based model for alkali-silica reaction

    This article presents a fracture mechanics model for Alkali-Silica Reaction (ASR). The model deals with the case of a concrete made up of dense aggregates submitted to chemical attack. The chemistry and diffusion (of ions and gel) are not modelled. The focus is put on the mechanical consequences of the progressive replacement of the outer layer of the aggregate by a less dense gel. A schematic cracking pattern is assumed: a ring-shaped crack appears in the cement paste surrounding the spherical aggregate depending on the pressure build-up. The onset of cracking is determined using an incremental energy criterion. The stored elastic energy and deformation of a given configuration are determined assuming that each aggregate behaves as if it was embedded in an infinite cement paste matrix. The calculations are performed by Finite Element Analysis. We note a very different behaviour of aggregates of different sizes. Adding the contributions of different aggregate sizes leads to an estimation of the global free expansion of a concrete of given aggregate size distribution. A rate of attack is identified that leads to recover the usual sigmoid ASR expansion curve. (authors)

  4. Reaction Mechanism of Siderite Lump in Coal-Based Direct Reduction

    Zhu, Deqing; Luo, Yanhong; Pan, Jian; Zhou, Xianlin

    2016-02-01

    Siderite is one of the significant iron ore resources in China and yet is difficult to upgrade by traditional beneficiation processes. A process of coal-based direct reduction-magnetic separation was successfully developed for the beneficiation of siderite. However, few studies have thoroughly investigated the mechanism of the direct reduction of siderite. In order to reveal the reaction mechanism of coal-based direct reduction of siderite lump, thermodynamics of direct reduction was investigated with coal as the reductant. The thermodynamics results indicate that coal-based direct reduction process of siderite lump at 1,050°C follows the steps as FeCO3→ Fe3O4→ FeO → Fe, which is verified by chemical titration analysis, X-ray diffraction and scanning electron microscope. The microstructure of siderite sample varies with different reduction stages and some 45% porosity induced by thermal decomposition of siderite is conductive to subsequent reduction. The conversion of FeO to Fe is the main reduction rate-controlling step. The reduced product with the metallic iron size over 30 μm can be effectively beneficiated by wet magnetic separation after grinding. The obvious layered structure of reduced product is due to different heat transfer resistance, CO and CO2 concentration.

  5. [The reactions of hypersensitivity: the mechanisms of development, clinical manifestations, principles of diagnostic (a lecture)].

    Tukavkina, S Yu; Kharseyeva, G G

    2014-05-01

    The article considers the principles of modern classification of hypersensitivity, pathogenic mechanisms of formation of its various types resulting in development of typical clinical symptoms and syndromes. The knowledge and comprehension of these issues is important for physicians of different specializations since it permits to properly make out and formulate diagnosis and timely send patient for examination and treatment to such specialist as allergist-immunologist. The particular attention was paid to description of pathogenesis of diseases and syndromes underlaid by IgE-mediated type of hypersensitivity since their share is highest and clinical manifestations frequently require emergency medical care. The diagnostic of allergic diseases is to be implemented sequentially (step-by-step) and include common clinical and special (specific) methods. In case of choosing of extent of specialized allergological examination the diagnostic significance of techniques and their safety is to be taken into account concerning condition of patient. The diagnosis is objectively formulated only by complex of examination results. It is worth to remember about possibility of development of syndromes similar to IgE-mediated allergy by their clinical manifestations but belonging to non-allergic type of hypersensitivity. It is important to know main causes, mechanisms and ways of formation of such reactions previously named as anaphylactoid ones. PMID:25338461

  6. O2 activation by binuclear Cu sites: Noncoupled versus exchange coupled reaction mechanisms

    Chen, Peng; Solomon, Edward I.

    2004-09-01

    Binuclear Cu proteins play vital roles in O2 binding and activation in biology and can be classified into coupled and noncoupled binuclear sites based on the magnetic interaction between the two Cu centers. Coupled binuclear Cu proteins include hemocyanin, tyrosinase, and catechol oxidase. These proteins have two Cu centers strongly magnetically coupled through direct bridging ligands that provide a mechanism for the 2-electron reduction of O2 to a µ-2:2 side-on peroxide bridged species. This side-on bridged peroxo-CuII2 species is activated for electrophilic attack on the phenolic ring of substrates. Noncoupled binuclear Cu proteins include peptidylglycine -hydroxylating monooxygenase and dopamine -monooxygenase. These proteins have binuclear Cu active sites that are distant, that exhibit no exchange interaction, and that activate O2 at a single Cu center to generate a reactive CuII/O2 species for H-atom abstraction from the C-H bond of substrates. O2 intermediates in the coupled binuclear Cu enzymes can be trapped and studied spectroscopically. Possible intermediates in noncoupled binuclear Cu proteins can be defined through correlation to mononuclear CuII/O2 model complexes. The different intermediates in these two classes of binuclear Cu proteins exhibit different reactivities that correlate with their different electronic structures and exchange coupling interactions between the binuclear Cu centers. These studies provide insight into the role of exchange coupling between the Cu centers in their reaction mechanisms.

  7. New insights into atrazine degradation by cobalt catalyzed peroxymonosulfate oxidation: kinetics, reaction products and transformation mechanisms.

    Ji, Yuefei; Dong, Changxun; Kong, Deyang; Lu, Junhe

    2015-03-21

    The widespread occurrence of atrazine in waters poses potential risk to ecosystem and human health. In this study, we investigated the underlying mechanisms and transformation pathways of atrazine degradation by cobalt catalyzed peroxymonosulfate (Co(II)/PMS). Co(II)/PMS was found to be more efficient for ATZ elimination in aqueous solution than Fe(II)/PMS process. ATZ oxidation by Co(II)/PMS followed pseudo-first-order kinetics, and the reaction rate constant (k(obs)) increased appreciably with increasing Co(II) concentration. Increasing initial PMS concentration favored the decomposition of ATZ, however, no linear relationship between k(obs) and PMS concentration was observed. Higher efficiency of ATZ oxidation was observed around neutral pH, implying the possibility of applying Co(II)/PMS process under environmental realistic conditions. Natural organic matter (NOM), chloride (Cl(-)) and bicarbonate (HCO3(-)) showed detrimental effects on ATZ degradation, particularly at higher concentrations. Eleven products were identified by applying solid phase extraction-liquid chromatography-mass spectrometry (SPE-LC/MS) techniques. Major transformation pathways of ATZ included dealkylation, dechlorination-hydroxylation, and alkyl chain oxidation. Detailed mechanisms responsible for these transformation pathways were discussed. Our results reveal that Co(II)/PMS process might be an efficient technique for remediation of groundwater contaminated by ATZ and structurally related s-triazine herbicides. PMID:25544494

  8. Reaction Mechanism Underlying Atomic Layer Deposition of Antimony Telluride Thin Films.

    Han, Byeol; Kim, Yu-Jin; Park, Jae-Min; Yusup, Luchana L; Ishii, Hana; Lansalot-Matras, Clement; Lee, Won-Jun

    2016-05-01

    The mechanism underlying the deposition of SbTe films by alternating exposures to Sb(NMe2)3 and Te(GeMe3)2 was investigated. Sb(NMe2)3 and Te(GeMe3)2 were selected because they have very high vapor pressure and are free of Si, Cl, and O atoms in the molecules. The mechanism of deposition was proposed by density functional theory (DFT) calculation and was verified by in-situ quartz crystal microbalance (QCM) analysis. DFT calculation expected the ligand-exchange reactions between the Sb and Te precursors to form Me2NGeMe3 as the byproduct. QCM analysis indicated that a single -NMe2 group in Sb(NMe2)3 reacts with -TeGeMe3 on the surface to form an Sb2Te3 film, and that a small fraction of Sb is incorporated into the film by the thermal decomposition of Sb(NMe2)3. The Te(GeMe3)2 molecules were thermally stable up to 120 degrees C, while the Sb(NMe2)3 molecules decomposed at temperatures of 60 degrees C and higher. Sb-rich SbTe films with different Sb contents were prepared by controlling the partial decomposition of Sb(NMe2)3 molecules, which was enhanced by increasing the pulse time of the precursor. PMID:27483847

  9. Detailed mechanism of the CH2I + O2 reaction: Yield and self-reaction of the simplest Criegee intermediate CH2OO

    Ting, Wei-Lun; Chang, Chun-Hung; Lee, Yu-Fang; Matsui, Hiroyuki; Lee, Yuan-Pern; Lin, Jim-Min, Jr.

    2014-09-01

    The application of a new reaction scheme using CH2I + O2 to generate the simplest Criegee intermediate, CH2OO, has stimulated lively research; the Criegee intermediates are extremely important in atmospheric chemistry. The detailed mechanism of CH2I + O2 is hence important in understanding kinetics involving CH2OO. We employed ultraviolet absorption to probe simultaneously CH2I2, CH2OO, CH2I, and IO in the reaction system of CH2I + O2 upon photolysis at 248 nm of a flowing mixture of CH2I2, O2, and N2 (or SF6) in the pressure range 7.6-779 Torr to investigate the reaction kinetics. With a detailed mechanism to model the observed temporal profiles of CH2I, CH2OO, and IO, we found that various channels of the reaction CH2I + O2 and CH2OO + I play important roles; an additional decomposition channel of CH2I + O2 to form products other than CH2OO or ICH2OO becomes important at pressure less than 60 Torr. The pressure dependence of the derived rate coefficients of various channels of reactions of CH2I + O2 and CH2OO + I has been determined. We derived a rate coefficient also for the self-reaction of CH2OO as k = (8 ± 4) × 10-11 cm3 molecule-1 s-1 at 295 K. The yield of CH2OO from CH2I + O2 was found to have a pressure dependence on N2 and O2 smaller than in previous reports; for air under 1 atm, the yield of ˜30% is about twice of previous estimates.

  10. Studies of reaction mechanism in {sup 12}C + {sup 12}C system at intermediate energy of 28.7 MeV/N

    Magiera, A. [Inst. of Physics, Jagiellonian Univ., Cracow (Poland)

    1996-12-31

    The reaction mechanism in {sup 12}C + {sup 12}C system at intermediate energy of about 30 MeV/nucleon was studied. The contribution of various reaction mechanisms (inelastic scattering, transfer reactions, compound nucleus reactions, sequential decay following inelastic excitation and transfer) to the total reaction cross section were found. The analysis of inclusive and coincidence spectra shows that sequential fragmentation processes dominate. 100 refs, 45 figs, 1 tab

  11. Simulation mechanisms of low energy nuclear reaction using super flow energy external fields

    Full text: The review of possible stimulation mechanisms of the LENR (low energy nuclear reactions) is represented. We have concluded that transamination of nuclei at low energies and excess heat are possible in the framework of the modern physical theory - the universal resonance synchronization principle and based on its different enhancement mechanisms of reaction rates are responsible for these processes. The excitation nd ionization of atom may play role as trigger for LERN. Investigation of this phenomenon requires knowledge of different branches if science: nuclear and atomic physics, chemistry and electrochemistry, condensed matter and solid state physics. The results of this research field can provide a new source of energy, substances and technologies. The puzzle of poor re-productivity of experimental data in due ti the fact LENR occurs in open systems and it is extremely sensitive to parameters of external fields and systems. Classical re-productivity principle should be reconsidered for LENR experiments. Poor re-productivity and unexpected results do not means that the experiment is wrong. Our main conclusion: LENR may be understand in terms of the modern theory without any violation of the basic physics. 2) Weak and electromagnetic interactions may show the strong influence of the surrounding conditions on the nuclear processes. 3) Universal resonance synchronization principle is a key issue to make a bridge between various scales of interactions and it is responsible for self-organization of hierarchical systems independent of substances, fields and interactions. We bring some arguments in favor of the mechanism - order based on order - declared by Schroedinger in fundamental problem of contemporary science. 4) The universal resonance synchronization principle became a fruitful interdisciplinary science of general laws of self-organized processes in different branches of physics because it is consequence of the energy conservation law and resonance

  12. Insights into the reaction mechanism of 3-O-sulfotransferase through QM/MM calculations.

    Sousa, Rui P; Fernandes, Pedro A; Ramos, Maria J; Brás, Natércia F

    2016-04-20

    3-O-Sulfotransferase (3-OST) is one of the enzymes involved in heparan sulfate (HS) biosynthesis. HSs are polysaccharides with variable patterns of sulfation and acetylation that serve as entry receptors for herpes simplex virus type 1 (HSV-1). 3-OST is responsible for the transfer of a sulfate group from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) to glucosamine units of HS. In this work, the catalytic mechanism of 3-OST was studied with atomic detail, using computational methods. We investigated the protonation state of key residues using the H++ web-based pKa prediction tool and molecular dynamics (MD) simulations and estimated the most relevant protonation state of the catalytic residues during catalysis. Catalytic histidine (His186) is predominantly protonated, while catalytic aspartate and glutamate (Asp189 and Glu184) are predominantly deprotonated. Subsequently, to study the catalytic mechanism, we applied a QM/MM method at the ONIOM(B3LYP/6-31G(d):ff94) level, starting from three geometries extracted from the 3, 6 and 8 ns point on the MD simulation. The results show that the reaction mechanism of 3-OST occurs by a single elementary step, consisting of an associative SN2 transfer of the sulfate group from PAPS to the HS glucosamine units, with the transfer of a proton from glucosamine to the catalytic Glu184. The activation free energies for this reaction were determined at the ONIOM(M06-2X-D3/6-311++G(2d,2p):ff94//B3LYP/6-31G(d):ff94) level of theory. Despite the free energy differences among the three conformations (10.2, 20.9 and 16.1 kcal mol(-1)), our results are consistent with the upper limit determined experimentally for the full cycle (20.4 kcal mol(-1)). The data obtained in this study will be useful for further studies on the inhibition of this enzyme, which is a useful target for drugs that block HSV-1 viral infections. PMID:27063019

  13. Effect of the Ti/B4C mole ratio on the reaction products and reaction mechanism in an Al–Ti–B4C powder mixture

    The effect of the Ti/B4C mole ratio on the fabrication behavior of Al composites is investigated using Al–Ti–B4C powder mixtures as reactants. The quick spontaneous infiltration (QSI) process combined with the combustion reaction and DTA analysis were used. According to the thermodynamic predictions, which are verified in the experimental results, TiB2 is formed in all the samples whereas TiC is only formed in reactants with a Ti/B4C mole ratio of more than two. The C atoms from the reacted B4C do not move into TiC but instead they move into Al3BC or Al4C3 when the Ti/B4C mole ratio is less than two. In addition, the reaction mechanism with a Ti/B4C mole ratio of 0.75 is investigated extensively. - Highlights: • The critical role of the Ti/B4C mole ratio on the reaction products of Al–Ti–B4C was studied using experiments. • The experimental results are also supported by thermodynamic calculations presented in this paper. • The reaction mechanism with a Ti/B4C mole ratio of 0.75 is investigated extensively

  14. Reaction site and mechanism in the UV or visible light induced TiO2 photodegradation of Orange G

    YANG Shi-ying; LOU Li-ping; WU Xiao-na; CHEN Ying-xu

    2006-01-01

    For TiO2 heterogeneous reaction, the reaction site and the detailed mechanism are interesting and controversy topics. In this paper, effects of surface fluorination of TiO2 on the photocatalytic degradation of an azo dye, Orange G(OG) under UV or visible light irradiation were investigated, and the possible reaction site and mechanism were elucidated. The adsorption of OG on TiO2 was nearly inhibited by fluoride but its UV light induced photodegradation rate was greatly increased by a factor of about 2.7, which was due to the more generated free hydroxyl radicals. It supported the views that fluoride could desorb the oxidant species from surface and that the reaction sites could move to the bulk solution. In TiO2/Vis system, the observed inhibition effects of fluorination could be interpreted by the competitive adsorption, which provided additional evidences that the visible light sensitized photodegradation of dye pollutants on the catalyst surface.

  15. Mechanically activated SHS reaction in the Fe-Al system: in-situ time resolved diffraction using synchrotron radiation

    The mechanical activation self propagating high temperature synthesis (M.A.S.H.S.) processing is a new way to produce nanocrystalline iron aluminide intermetallic compounds. This process is maily the combination of two steps; in the one hand, a mechanical activation where the Fe - Al powder mixture was milled during a short time at given energy and frequency of shocks and in the other hand, a self propagating high temperature synthesis (S.H.S.) reaction, for which the exothermicity of the Fe + Al reaction is used. This fast propagated MASHS reaction has been in-situ investigated using the time resolved X-ray diffraction (TRXRD) using a X-ray synchrotron beam and an infrared thermography camera, allowing the coupling of the materials structure and the temperature field. The effects of the initial mean compositions, of the milling conditions as well as of the compaction parameters on the MASHS reaction are reported. (orig.)

  16. Final Report: Dominant Mechanisms of Uranium-Phosphate Reactions in Subsurface Sediments

    Catalano, Jeffrey G. [Washington Univ., St. Louis, MO (United States); Giammar, Daniel E. [Washington Univ., St. Louis, MO (United States); Wang, Zheming [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2016-03-08

    Phosphate addition is an in situ remediation approach that may enhance the sequestration of uranium without requiring sustained reducing conditions. However, the geochemical factors that determine the dominant immobilization mechanisms upon phosphate addition are insufficiently understood to design efficient remediation strategies or accurately predict U(VI) transport. The overall objective of our project is to determine the dominant mechanisms of U(VI)-phosphate reactions in subsurface environments. Our research approach seeks to determine the U(VI)-phosphate solid that form in the presence of different groundwater cations, characterize the effects of phosphate on U(VI) adsorption and precipitation on smectite and iron oxide minerals, examples of two major reactive mineral phases in contaminated sediments, and investigate how phosphate affects U(VI) speciation and fate during water flow through sediments from contaminated sites. The research activities conducted for this project have generated a series of major findings. U(VI) phosphate solids from the autunite mineral family are the sole phases to form during precipitation, with uranyl orthophosphate not occurring despite its predicted greater stability. Calcium phosphates may take up substantial quantities of U(VI) through three different removal processes (adsorption, coprecipitation, and precipitation) but the dominance of each process varies with the pathway of reaction. Phosphate co-adsorbs with U(VI) onto smectite mineral surfaces, forming a mixed uranium-phosphate surface complex over a wide range of conditions. However, this molecular-scale association of uranium and phosphate has not effect on the overall extent of uptake. In contrast, phosphate enhanced U(VI) adsorption to iron oxide minerals at acidic pH conditions but suppresses such adsorption at neutral and alkaline pH, despite forming mixed uranium-phosphate surface complexes during adsorption. Nucleation barriers exist that inhibit U(VI) phosphate

  17. Low-Pressure Photolysis of 2,3-Pentanedione in Air: Quantum Yields and Reaction Mechanism.

    Bouzidi, Hichem; Djehiche, Mokhtar; Gierczak, Tomasz; Morajkar, Pranay; Fittschen, Christa; Coddeville, Patrice; Tomas, Alexandre

    2015-12-24

    Dicarbonyls in the atmosphere mainly arise from secondary sources as reaction products in the degradation of a large number of volatile organic compounds (VOC). Because of their sensitivity to solar radiation, photodissociation of dicarbonyls can dominate the fate of these VOC and impact the atmospheric radical budget. The photolysis of 2,3-pentanedione (PTD) has been investigated for the first time as a function of pressure in a static reactor equipped with continuous wave cavity ring-down spectroscopy to measure the HO2 radical photostationary concentrations along with stable species. We showed that (i) Stern-Volmer plots are consistent with low OH-radical formation yields in RCO + O2 reactions, (ii) the decrease of the photodissociation rate due to pressure increase from 26 to 1000 mbar is of about 30%, (iii) similarly to other dicarbonyls, the Stern-Volmer analysis shows a curvature at the lower pressure investigated, which may be assigned to the existence of excited singlet and triplet PTD states, (iv) PTD photolysis at 66 mbar leads to CO2, CH2O and CO with yields of (1.16 ± 0.04), (0.33 ± 0.02) and (0.070 ± 0.005), respectively, with CH2O yield independent of pressure up to 132 mbar and CO yield in agreement with that obtained at atmospheric pressure by Bouzidi et al. (2014), and (v) the PTD photolysis mechanism remains unchanged between atmospheric pressure and 66 mbar. As a part of this work, the O2 broadening coefficient for the absorption line of HO2 radicals at 6638.21 cm(-1) has been determined (γO2 = 0.0289 cm(-1) atm(-1)). PMID:26608471

  18. Strongly correlated mechanisms of a photoexcited radical reaction from the anti-Hermitian contracted Schroedinger equation

    Photoexcited radical reactions are critical to processes in both nature and materials, and yet they can be challenging for electronic structure methods due to the presence of strong electron correlation. Reduced-density-matrix (RDM) methods, based on solving the anti-Hermitian contracted Schroedinger equation (ACSE) for the two-electron RDM (2-RDM), are examined for studying the strongly correlated mechanisms of these reactions with application to the electrocyclic interconversion of allyl and cyclopropyl radicals. We combine recent extensions of the ACSE to excited states [G. Gidofalvi and D. A. Mazziotti, Phys. Rev. A 80, 022507 (2009)] and arbitrary spin states [A. E. Rothman, J. J. Foley IV, and D. A. Mazziotti, Phys. Rev. A 80, 052508 (2009)]. The ACSE predicts that the ground-state ring closure of the allyl radical has a high 52.5 kcal/mol activation energy that is consistent with experimental data, while the closure of an excited allyl radical can occur by disrotatory and conrotatory pathways whose transition states are essentially barrierless. Comparisons are made with multireference second- and third-order perturbation theories and multireference configuration interaction. While predicted energy differences do not vary greatly between methods, the ACSE appears to improve these differences when they involve a strongly and a weakly correlated radical by capturing a greater share of single-reference correlation that increases the stability of the weakly correlated radicals. For example, the ACSE predicts a -39.6 kcal/mol conversion of the excited allyl radical to the ground-state cyclopropyl radical in comparison to the -32.6 to -37.3 kcal/mol conversions predicted by multireference methods. In addition, the ACSE reduces the computational scaling with the number of strongly correlated orbitals from exponential (traditional multireference methods) to quadratic. Computed ground- and excited-state 2-RDMs are nearly N-representable.

  19. Theoretical investigation of the mechanism of tritiated methane dehydrogenation reaction using nickel-based catalysts

    Dong, Liang; Li, Jiamao; Deng, Bing; Yang, Yong; Wang, Heyi [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China); Li, Weiyi [School of Physics and Chemistry, Xihua University, Chengdu 610065 (China); Li, Shuo, E-mail: lishuo@cqut.edu.cn [School of Chemical Engineering, Chongqing University of Technology, Chongqing 400054 (China); Tan, Zhaoyi, E-mail: tanzhaoyi@caep.cn [Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang 621900 (China)

    2015-06-15

    Graphical abstract: - Highlights: • Four-step dehydrogenation of CT{sub 4} catalyzed by Ni to form Ni–C by releasing T{sub 2}. • The process of Ni + CT{sub 4} → NiCT{sub 2} + T{sub 2} is more achievable than that of NiCT{sub 2} → NiC + T{sub 2}. • TNiCT → T{sub 2}NiC step is the RDS with the rate constant of k = 2.8 × 10{sup 13} exp(−313,136/RT). • The hydrogen isotope effect value of k{sub H}/k{sub T} is 2.94, and k{sub D}/k{sub T} is 1.39. • CH{sub 4} and CD{sub 4} dehydrogenations are likely to occur, accompanied by the CT{sub 4} cracking. - Abstract: The mechanism of tritiated methane dehydrogenation reaction catalyzed by nickel-based catalyst was investigated in detail by density functional theory (DFT) at the B3LYP/[6-311++G(d, p), SDD] level. The computational results indicated that the dehydrogenation of tritiated methane is endothermic. The decomposition of tritiated methane catalyzed by Ni to form Ni-based carbon (Ni–C) after a four-step dehydrogenation companied with releasing tritium. After the first and second dehydrogenation steps, Ni + CT{sub 4} formed NiCT{sub 2}. After the third and fourth dehydrogenation steps, NiCT{sub 2} formed NiC. The first and second steps of dehydrogenation occurred on both the singlet and triplet states, and the lowest energy route is Ni + CT{sub 4} → {sup 1}COM → {sup 1}TS1 → {sup 3}IM1 → {sup 3}TS2 → {sup 3}IM2. The third and fourth steps of dehydrogenation occurred on both the singlet and quintet states, and the minimum energy reaction pathway appeared to be IM3 → {sup 1}TS4 → {sup 5}IM4 → {sup 5}TS5 → {sup 5}IM5 → {sup 5}pro + T{sub 2}. The fourth step of dehydrogenation TNiCT → T{sub 2}NiC was the rate-determining step of the entire reaction with the rate constant of k{sub 2} = 2.8 × 10{sup 13} exp(−313,136/RT) (in cm{sup 3} mol{sup −1} s{sup −1}), and its activation energy barrier was calculated to be 51.8 kcal/mol. The Ni-catalyzed CH{sub 4} and CD{sub 4} cracking

  20. The Effect of Mechanical Vibration Stimulation of Perception Subthreshold on the Muscle Force and Muscle Reaction Time of Lower Leg

    Kim, Huigyun; Kwak, Kiyoung; Kim, Dongwook

    2016-01-01

    The objective of this study is to investigate the effect of mechanical vibration stimulation on the muscle force and muscle reaction time of lower leg according to perception threshold and vibration frequency. A vibration stimulation with perception threshold intensity was applied on the Achilles tendon and tibialis anterior tendon. EMG measurement and analysis system were used to analyze the change of muscle force and muscle reaction time according to perception threshold and vibration frequ...

  1. A DFT study on the mechanisms for the cycloaddition reactions between 1-aza-2-azoniaallene cations and acetylenes.

    Wang, Jing-mei; Li, Zhi-ming; Wang, Quan-rui; Tao, Feng-gang

    2013-01-01

    The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions. PMID:22810049

  2. MiRNA-Based Regulation of Hemostatic Factors through Hepatic Nuclear Factor-4 Alpha

    Salloum-Asfar, Salam; Arroyo, Ana B.; Teruel-Montoya, Raúl; García-Barberá, Nuria; Roldán, Vanessa; Vicente, Vicente; Martínez, Constantino; González-Conejero, Rocío

    2016-01-01

    MiRNAs have been reported as CIS-acting elements of several hemostatic factors, however, their mechanism as TRANS-acting elements mediated by a transcription factor is little known and could have important effects. HNF4α has a direct and important role in the regulation of multiple hepatic coagulation genes. Previous in vitro studies have demonstrated that miR-24-3p and miR-34a-5p regulate HNF4A expression. Here we aimed to investigate the molecular mechanisms of miR-24 and miR-34a on coagulation through HNF4A. Transfections with miR-24 and miR-34a in HepG2 cells decreased not only HNF4A but also F10, F12, SERPINC1, PROS1, PROC, and PROZ transcripts levels. Positive and significant correlations were observed between levels of HNF4A and several hemostatic factors (F5, F8, F9, F11, F12, SERPINC1, PROC, and PROS1) in human liver samples (N = 104). However, miR-24 and miR-34a levels of the low (10th) and high (90th) percentiles of those liver samples were inversely correlated with HNF4A and almost all hemostatic factors expression levels. These outcomes suggest that miR-24 and miR-34a might be two indirect elements of regulation of several hemostatic factors. Additionally, variations in miRNA expression profiles could justify, at least in part, changes in HNF4A expression levels and its downstream targets of coagulation. PMID:27135744

  3. Global-through-urban nested three-dimensional simulation of air pollution with a 13,600-reaction photochemical mechanism

    Jacobson, Mark Z.; Ginnebaugh, Diana L.

    2010-07-01

    To date, gas photochemistry has not been simulated beyond a few hundred reactions in a three-dimensional (3-D) atmospheric model. Here, we treat 4675 gases and 13,626 tropospheric and stratospheric reactions in the 3-D GATOR-GCMOM climate-pollution model and compare results with data and with results from a condensed 152-gas/297-reaction mechanism when the model was nested at increasing resolution from the globe to California to Los Angeles. Gases included C1-C12 organic degradation products and H-, O-, N-, Cl-, Br-, Fl-, and S-containing inorganics. Organic reactions were from the Master Chemical Mechanism. Photolysis coefficients for 2644 photoprocesses and heating rates for 1909 photolyzing gases were solved with an online radiative code in each grid cell using quantum yield/cross section data over 86 UV/visible wavelengths. Spatial/temporal emissions of > 110 gases were derived from the 2005 U.S. National Emission Inventory. The condensed mechanism was a modified Carbon-Bond IV (MCBIV). Three-day simulation results indicate that the more-explicit mechanism reduced the O3 gross error against data versus the MCBIV error against data by only ˜2 percentage points (from 28.3% to 26.5%) and NO2 and HCHO by ˜6 percentage points in Los Angeles. While more-explicit photochemistry improved results, the condensed mechanism was not the main source of ozone error. The more explicit mechanism, which treated absorptive heating by more photolyzing gases, also resulted in a different magnitude of feedbacks to meteorological variables and back to gases themselves than did the less-explicit mechanism. The computer time for all processes in GATOR-GCMOM with the more explicit mechanism (solved with SMVGEAR II in all domains) was only ˜3.7 times that with the MCBIV despite the factors of 31 and 46 increases in numbers of species and reactions, respectively.

  4. The Role of Various Stressors in the Trigger Mechanism of Raynaud's Disease (Hemorheological and Vascular Reactions

    Mantskava M.M.

    2014-05-01

    Full Text Available The emergence and spread of stress reactions are provided by the blood circulation system. In its turn, the adequacy of blood circulation depends on the hemorheological and vascular mechanisms. The changeability of their properties appears to be the basis of the increasing of stress stages. From the viewpoint of biophysical reactions, any change and movement occur with the expenditure and accumulation of energy. Higher level of adaptation energy waste and secondary level take place, when a small stressor entails a small expenditure. There is a maximum possible rate of adaptive energy consumption and at this maximum the organism cannot cope with any additional stimulus. At the same time adaptive and stress diseases develop. Let’s consider the duration and manifestation of Raynaud's disease from the perspective of adaptation diseases and diseases of the third grade, which appears to be the cause of the double stress effect - cold and emotional- physical and psychic. Total of 97 patients with Raynaud's disease were examined. For a new vision of the problem it was necessary to find out how the streessors of various nature impact the hemoreheological status and vascular resistance. For this purpose all the patients were examined for a resistance index of resistive arteries of the hand and the indices of erythrocyte aggregation and deformability. The patients were divided into four subgroups. The first subgroup – the patients after chilblain, the second subgroup – the patients with psychic strerssor, the third subgroup – the patients with prolonged chronic stress, and the fourth subgroup – the patients without the differentiation of the stressors. According to the obtained results, it is obvious that at cold and emotional stress (I and II subgroups the hemorheological and vascular parameters are changed. However, this change (hemorheological and vascular is more pronounced at chronic emotional stress (III subgroup as compared both to the

  5. Mechanism of sperm capacitation and the acrosome reaction: role of protein kinases

    Debby Ickowicz; Maya Finkelstein; Haim Breitbart

    2012-01-01

    Mammalian sperm must undergo a series of biochemical and physiological modifications,collectively called capacitation,in the female reproductive tract prior to the acrosome reaction (AR).The mechanisms of these modifications are not well characterized though protein kinases were shown to be involved in the regulation of intracellular Ca2+ during both capacitation and the AR.In the present review,we summarize some of the signaling events that are involved in capacitation.During the capacitation process,phosphatidyl-inositol-3-kinase (P13K) is phosphorylated/activated via a protein kinase A (PKA)-dependent cascade,and downregulated by protein kinase C α (PKCα).PKCα is active at the beginning of capacitation,resulting in P13K inactivation.During capacitation,PKCα as well as PP1γ2 is degraded by a PKA-dependent mechanism,allowing the activation of P13K.The activation of PKA during capacitation depends mainly on cyclic adenosine monophosphate (cAMP) produced by the bicarbonate-dependent soluble adenylyl cyclase.This activation of PKA leads to an increase in actin polymerization,an essential process for the development of hyperactivated motility,which is necessary for successful fertilization.Actin polymerization is mediated by PIP2 in two ways:first,P(I)P2 acts as a cofactor for phospholipase D (PLD) activation,and second,as a molecule that binds and inhibits actin-severing proteins such as gelsolin.Tyrosine phosphorylation of gelsolin during capacitation by Src family kinase (SFK) is also important for its inactivation.Prior to the AR,gelsolin is released from P(I)P2 and undergoes dephosphorylation/activation,resulting in fast F-actin depolymerization,leading to the AR.

  6. Kinetics and mechanisms of the acid-base reaction between NH$_3$ and HCOOH in interstellar ice analogs

    Bergner, Jennifer B; Rajappan, Mahesh; Fayolle, Edith C

    2016-01-01

    Interstellar complex organic molecules (COMs) are commonly observed during star formation, and are proposed to form through radical chemistry in icy grain mantles. Reactions between ions and neutral molecules in ices may provide an alternative cold channel to complexity, as ion-neutral reactions are thought to have low or even no energy barriers. Here we present a study of a the kinetics and mechanisms of a potential ion-generating acid-base reaction between NH$_{3}$ and HCOOH to form the salt NH$_{4}^{+}$HCOO$^{-}$. We observe salt growth at temperatures as low as 15K, indicating that this reaction is feasible in cold environments. The kinetics of salt growth are best fit by a two-step model involving a slow "pre-reaction" step followed by a fast reaction step. The reaction energy barrier is determined to be 70 $\\pm$ 30K with a pre-exponential factor 1.4 $\\pm$ 0.4 x 10$^{-3}$ s$^{-1}$. The pre-reaction rate varies under different experimental conditions and likely represents a combination of diffusion and or...

  7. Multiconfiguration molecular mechanics algorithm for potential energy surfaces of chemical reactions

    We present an efficient algorithm for generating semiglobal potential energy surfaces of reactive systems. The method takes as input molecular mechanics force fields for reactants and products and a quadratic expansion of the potential energy surface around a small number of geometries whose locations are determined by an iterative process. These Hessian expansions might come, for example, from ab initio electronic structure calculations, density functional theory, or semiempirical molecular orbital theory. A 2x2 electronic diabatic Hamiltonian matrix is constructed from these data such that, by construction, the lowest eigenvalue of this matrix provides a semiglobal approximation to the lowest electronically adiabatic potential energy surface. The theory is illustrated and tested by applications to rate constant calculations for three gas-phase test reactions, namely, the isomerization of 1,3-cis-pentadiene, OH+CH4→H2O+CH3, and CH2Cl+CH3F→CH3Cl+CH2F. (c) 2000 American Institute of Physics

  8. Reaction bonding and mechanical properties of mullite/silicon carbide composites

    Based on the RBAO technology, low-shrinkage mullite/SiC/Al2O3/ZrO2 composite were fabricated. A powder mixture of 40 vol% Al, 30 vol% Al2O3, and 30 vol% SiC was attrition milled in acetone with TZP balls which introduced a substantial ZrO2 wear debris into the mixture. The precursor powder was isopressed at 300--900 MPa and heat-treated in air by two different cycles resulting in various phase ratios in the final products. During heating, Al oxidizes to Al2O3 completely, while SiC oxidizes to SiO2 only on its surface. Fast densification (at > 1300 C) and mullite formation (at 1400 C) prevent further oxidation of the SiC particles. Because of the volume expansion associated with the oxidation of Al (28%), SiC (108%), and the mullitization (4.2%), sintering shrinkage is effectively compensated. The reaction-bonded composites exhibit low linear shrinkages and high strengths: shrinkages of 7.2%, 4.8%, and 3%, and strengths of 610, 580, and 490 MPa, corresponding to compaction pressure of 300, 600, and 900 MPa, respectively, were achieved in samples containing 49--55 vol% mullite. HIPing improved significantly the mechanical properties: a fracture strength of 490 MPa and a toughness of 4.1 MPa·m1/2 increased to 890 MPa and 6 MPa·m1/2, respectively

  9. Quantum mechanical investigation of the atmospheric reaction CH3O2 + NO.

    Lesar, Antonija; Hodoscek, Milan; Drougas, Evangelos; Kosmas, Agnie M

    2006-06-29

    The important stationary points on the potential energy surface of the reaction CH(3)O(2) + NO have been investigated using ab initio and density functional theory techniques. The optimizations were carried out at the B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory while the energetics have been refined using the G2MP2, G3//B3LYP, and CCSD(T) methodologies. The calculations allow the proper characterization of the transition state barriers that determine the fate of the nascent association conformeric minima of methyl peroxynitrite. The main products, CH(3)O + NO(2), are formed through either rearrangement of the trans-conformer to methyl nitrate and its subsequent dissociation or via the breaking of the peroxy bond of the cis-conformer to CH(3)O + NO(2) radical pair. The important consequences of the proposed mechanism are (a) the allowance on energetic grounds for nitrate formation parallel to radical propagation under favorable external conditions and (b) the confirmation of the conformational preference of the homolytic cleavage of the peroxy bond, discussed in previous literature. PMID:16789778

  10. Reaction products and mechanisms for the reaction of n-butyl vinyl ether with the oxidants OH and Cl: Atmospheric implications

    Colmenar, Inmaculada; Martín, Pilar; Cabañas, Beatriz; Salgado, Sagrario; Tapia, Araceli; Martínez, Ernesto

    2015-12-01

    A reaction product study for the degradation of butyl vinyl ether (CH3(CH2)3OCHdbnd CH2) by reaction with chlorine atoms (Cl) and hydroxyl radicals (OH) has been carried out using Fourier Transform Infrared absorption spectroscopy (FTIR) and/or Gas Chromatography-Mass Spectrometry with a Time of Flight analyzer (GC-TOFMS). The rate coefficient for the reaction of butyl vinyl ether (BVE) with chlorine atoms has also been evaluated for the first time at room temperature (298 ± 2) K and atmospheric pressure (708 ± 8) Torr. The rate coefficient obtained was (9.9 ± 1.5) × 10-10 cm3 molecule-1 s-1 and this indicates the high reactivity of butyl vinyl ether with Cl atoms. However, this value may be affected by the dark reaction of BVE with Cl2. The results of a qualitative study of the Cl reaction show that the main oxidation products are butyl formate (CH3(CH2)3OC(O)H), butyl chloroacetate (CH3(CH2)3OC(O)CH2Cl and formyl chloride (HCOCl). Individual yields in the ranges ∼16-40% and 30-70% in the absence and presence of NOx, respectively, have been estimated for these products. In the OH reaction, butyl formate and formic acid were identified as the main products, with yields of around 50 and 20%, respectively. Based on the results of this work and a literature survey, the addition of OH radicals and Cl atoms at the terminal C atom of the double bond in CH3(CH2)3OCHdbnd CH2 has been proposed as the first step in the reaction mechanism for both of the studied oxidants. The tropospheric lifetime of butyl vinyl ether is very short and, as a consequence, it will be rapidly degraded and will only be involved in tropospheric chemistry at a local level. The degradation products of these reactions should be considered when evaluating the atmospheric impact.

  11. Investigation of the kinetics and mechanism of the glycerol chlorination reaction using gas chromatography–mass spectrometry

    JUN WANG

    2010-01-01

    Full Text Available As a primary by-product in biodiesel production, glycerol can be used to prepare an important fine chemical, epichlorohydrin, by the glycerol chlorination reaction. Although this process has been applied in industrial production, unfortunately, less attention has been paid to the analysis and separation of the compounds in the glycerol chlorination products. In this study, a convenient and accurate method to determine the products in glycerol chlorination reaction was established and based on the results the kinetic mechanism of the reaction was investigated. The structure of main products, including 1,3--dichloropropan-2-ol, 2,3-dichloropropan-1-ol, 3-chloro-1,2-propanediol, 2-chloro-1,3-propanediol and glycerol was ascertained by gas chromatography–mass spectrometry and the isomers of the products were distinguished. Apidic acid was considered as the best catalyst because of its excellent catalytic effect and high boiling point. The mechanism of the glycerol chlorination reaction was proposed and a new kinetic model was developed. Kinetic equations of the process in the experimental range were obtained by data fitting and the activation energies of each tandem reaction were 30.7, 41.8, 29.4 and 49.5 kJ mol-1, respectively. This study revealed the process and mechanism of the kinetics and provides the theoretical basis for engineering problems.

  12. Solid-state Reaction of Azolium Hydrohalogen Salts with Silver Dicyanamide - Unexpected Formation of Cyanoguanidine-azoles, Reaction Mechanism and Their Hypergolic Properties

    Liu, Wei; Lin, Qiu-Han; Li, Yu-Chuan; Chen, Peng-Wan; Fang, Tao; Zhang, Ru-Bo; Pang, Si-Ping

    2015-06-01

    Cyanoguanidines as well as azoles are important bioactive groups, which play an important role in the medical application; meanwhile, the high nitrogen content makes them excellent backbones for energetic materials. A Novel and simple method that combined these two fragments into one molecular compound was developed through the transformation of dicyanamide ionic salts. In return, compounds 4-11 were synthesized, and fully characterized by IR, MS, NMR and elemental analysis. Meanwhile, the structures of compounds 4, 8 and 11 were confirmed by X-ray crystal diffraction. Detailed reaction mechanisms were studied through accurate calculations on the reaction energy profiles of the azolium cations and DCA anion, which revealed the essence of the transformation proceeding. Meanwhile, compound 8 exhibits excellent hypergolic property, which could be potentially novel molecular hypergolic fuel.

  13. 2007 Inorganic Reaction Mechanisms Gordon Research Conference-February 18-23

    Andreja Bakac

    2008-01-01

    This conference focuses on kinetic, mechanistic, and thermodynamic studies of reactions that play a role in fields as diverse as catalysis, energy, bioinorganic chemistry, green chemistry, organometallics, and activation of small molecules (oxygen, nitrogen, carbon monoxide, carbon dioxide, alkanes). Participants from universities, industry, and national laboratories present results and engage in discussions of pathways, intermediates, and outcome of various reactions of inorganic, organic, coordination, organometallic, and biological species. This knowledge is essential for rational development and design of novel reactions, compounds, and catalysts.

  14. Expanding the Enzyme Universe: Accessing Non-Natural Reactions by Mechanism-Guided Directed Evolution

    Renata, Hans; Wang, Z. Jane; Arnold, Frances H

    2015-01-01

    High selectivities and exquisite control over reaction outcomes entice chemists to use biocatalysts in organic synthesis. However, many useful reactions are not accessible because they are not in nature’s known repertoire. We will use this review to outline an evolutionary approach to engineering enzymes to catalyze reactions not found in nature. We begin with examples of how nature has discovered new catalytic functions and how such evolutionary progressions have been recapitulated in the la...

  15. A Unified Approach to Mechanical Compaction, Pressure Solution, Mineral Reactions and the Temperature Distribution in Hydrocarbon Basins

    Yang, Xin-She

    2010-01-01

    In modelling sediment compaction and mineral reactions, the rheological behaviour of sediments is typically considered as poroelastic or purely viscous. In fact, compaction due to pressure solution and mechanical processes in porous media is far more complicated. A generalised model of viscoelastic compaction and the smectite to illite mineral reaction in hydrocarbon basins is presented. A one-step dehydration model of the mineral reaction is assumed. The obtained nonlinear governing equations are solved numerically and different combinations of physical parameters are used to simulate realistic situations in typical sedimentary basins. Comparison of numerical simulations with real data has shown very good agreement with respect to both the porosity profile and the mineral reaction.

  16. Kinetic Approach to the Mechanism of Redox Reaction of Pyrocatechol Violet and Nitrite Ion in Aqueous Hydrochloric Acid

    A. Adetoro

    2011-10-01

    Full Text Available The kinetics of the oxidation of Pyrocatechol violet (PCVH by nitrite ion (NO2- in aqueous acidic medium has been studied at 24±1ºC, I = 0.50 mol/dm3(NaCl, [H+] = 1.0×10-3 mol/dm3. The reaction is first order to [PCVH] and half order to [NO2-]. The redox reaction displayed a 1:1 stoichiometry and obeys the rate law: d[PCVH]/dt = (a + b[H+] [PCVH][NO2-]½. The second-order rate constant increases with increase in acid concentration and ionic strength. This system displayed positive salt effect while spectroscopic investigation and Michaelis-Menten plot showed evidence of intermediate complex formation in the course of the reaction. A plausible mechanism has been proposed for the reaction.

  17. Degradation of quinoline by wet oxidation - kinetic aspects and reaction mechanisms

    Thomsen, A.B.

    1998-01-01

    The high temperature, high pressure wet oxidation reaction of quinoline has been studied as a function of initial concentration, pH and temperature. At neutral to acidic pH, it is effective in the oxidation of quinoline at 240 degrees C and above, whereas under alkaline conditions the reaction is...... markedly slowed down. The results indicate that the reaction is an auto-catalysed, free radical chain reaction transforming 99% of quinoline to other substances. Of the quinoline. 30-50% was oxidised to CO2 and H2O depending on the initial concentration. Wet oxidation of deuterium-labelled quinoline was...

  18. REACTION MECHANISMS OF MAGNESIUM SILICATES WITH CARBON DIOXIDE IN MICROWAVE FIELDS

    William B. White; Michael R. Silsbee; B. Joe Kearns

    2004-02-18

    The objective of the investigation was to determine whether microwave fields would enhance the reactions of CO{sub 2} with silicates that are relevant to the sequestration of carbon dioxide. Three sets of experiments were conducted. (1) Serpentine and CO{sub 2} were reacted directly at one atmosphere pressure in a microwave furnace. Little reaction was observed. (2) Serpentine was dehydroxylated in a microwave furnace. The reaction was rapid, reaching completion in less than 30 minutes. A detailed investigation of this reaction produced an S-shaped kinetics curve, similar to the kinetics from dehydroxylating serpentine in a resistance furnace, but offset to 100 C lower temperature. This set of experiments clearly demonstrates the effect of microwaves for enhancing reaction kinetics. (3) Reactions of serpentine with alkaline carbonates and in acid solution were carried out in a microwave hydrothermal apparatus. There was a greatly enhanced decomposition of the serpentine in acid solution but, at the temperature and pressure of the reaction chamber (15 bars; 200 C) the carbonates did not react. Overall, microwave fields, as expected, enhance silicate reaction kinetics, but higher CO{sub 2} pressures are needed to accomplish the desired sequestration reactions.

  19. Adsorbate thermodynamics as a determinant of reaction mechanism: Pentamethylene sulfide on Mo(110)

    Wiegand, B.C.; Friend, C.M.; Roberts, J.T. (Harvard Univ., Cambridge, MA (USA))

    The reactions of the totally unstrained, six-membered cyclic sulfide pentamethylene sulfide on Mo(110) have been investigated by using temperature-programmed reaction spectroscopy and X-ray photoelectron spectroscopy in an effort to identify the roles of ring size and strain in dictating reaction selectivity. Four gases products are detected in the temperature-programmed reaction of pentamethylene sulfide: dihydrogen at 380 and 590 K, pentane at 350 K, pentene at 345 K, and pentamethylene sulfide at 190 and 280 K. The kinetics for hydrocarbon production from pentamethylene sulfide are qualitatively different than for the four- and five-membered cyclic sulfides, trimethylene sulfide and tetrahydrothiophene.

  20. Curing reaction and mechanism of phenol-formaldehyde novolac resins for foundry

    Yan Shi

    2016-05-01

    Full Text Available In this study on the curing dynamics of phenol-formaldehyde novolac resins (PFNR and hexamethylene tetramine (HMTA, two typical commercial PFNR were selected as examples and the curing reactions of the resins with HMTA were studied by differential scanning calorimetry (DSC. Based on the data calculated by the Kissinger equation and the Crane equation, a thermocuring dynamic model was established, from which the process conditions, activation energy, reaction kinetics equation and a first-order reaction of the curing reactions were derived.

  1. The Mechanisms, Products, and Kinetics of Triclosan-Free Chlorine Reactions

    Rule, Krista Lynn

    2004-01-01

    The kinetics, products, and reaction pathways of triclosan/free chlorine reactions were investigated for the pH range 3.5-11. Although pH dependent speciation occurs in both triclosan and free chlorine, only the reaction between HOCl and the phenolate-triclosan was found to play a significant role in the kinetics. The second order rate constant for the reaction between phenolate-triclosan and HOCl was found to be 5.40 (±1.82) à 103 M-1s-1. Three chlorinated triclosan intermediates were t...

  2. Study of the mechanisms in heavy ion reactions in the energy range of 20 to 100 MeV/u

    The evolution in heavy ion reactions, for energies higher than 20 MeV/u, is investigated. The experimental results of the Xe + Ag and Xe + Au interactions, at 23.7 and 27 MeV/u, are presented. Inclusive interactions and coincidence measurements are carried out. A mechanism to explain the inclusive interactions results is proposed. It is based on a high energy mechanism, in which the mean field created by the nucleons is taken into account. A model describing the evolution of inelastic interactions towards multiple-fragmentation, in high energy reactions, is provided. The multiple-fragmentation percentage, at the end of the reaction, is obtained by means of a percolation model combined with a hydrodynamic model

  3. Kinetics and Mechanism of the Thermal Decomposition Reaction of 3,3-Bis(azidomethyl)oxetane/Tetrahydrofuran Copolymer

    LUO, Yang(罗阳); CHEN, Pei(陈沛); ZHAO, Feng-Qi(赵凤起); HU, Rong-Zu(胡劳祖); LI, Shang-Wen(李上文); GAO, Yin(高茵)

    2004-01-01

    The thermal behavior, mechanism and kinetic parameters of the exothermic decomposition reaction of 3,3-bis(azidomethyl)oxetane/tetrahydrofuran (BAMO/THF) copolymer in a temperature-programmed mode have been investigated by means of DSC, TG-DTG, fast and lower thermolysis/FTIR and TG-MS. The reaction mechanism was proposed. The apparent activation energy and pre-exponential constant of exothermic decomposition reaction of the compound at 0.1 MPa are 167.04 kJ·mol-1 and 1014.41 s-1, respectively. The corresponding critical temperatures of thermal explosion obtained from the onset temperature Te and the peak temperature Tp are 223.20 and 245.78 ℃, respectively. The kinetic equation of the exothermic decomposition process of BAMO/THF at 0.1 MPa could be expressed as:dα/dT= 1015.19 [-ln(1-α)]2/3e-2.009×104/T

  4. The influence of the “cage effect” on the mechanism of reversible bimolecular multistage chemical reactions in solutions

    Manifestations of the “cage effect” at the encounters of reactants are theoretically treated by the example of multistage reactions in liquid solutions including bimolecular exchange reactions as elementary stages. It is shown that consistent consideration of quasi-stationary kinetics of multistage reactions (possible only in the framework of the encounter theory) for reactions proceeding near reactants contact can be made on the basis of the concepts of a “cage complex.” Though mathematically such a consideration is more complicated, it is more clear from the standpoint of chemical notions. It is established that the presence of the “cage effect” leads to some important effects not inherent in reactions in gases or those in solutions proceeding in the kinetic regime, such as the appearance of new transition channels of reactant transformation that cannot be caused by elementary event of chemical conversion for the given mechanism of reaction. This results in that, for example, rate constant values of multistage reaction defined by standard kinetic equations of formal chemical kinetics from experimentally measured kinetics can differ essentially from real values of these constants

  5. Toward Determining ATPase Mechanism in ABC Transporters: Development of the Reaction Path–Force Matching QM/MM Method

    Zhou, Y.; Ojeda-May, P.; Nagaraju, M.; Pu, J.

    2016-01-01

    Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are ubiquitous ATP-dependent membrane proteins involved in translocations of a wide variety of substrates across cellular membranes. To understand the chemomechanical coupling mechanism as well as functional asymmetry in these systems, a quantitative description of how ABC transporters hydrolyze ATP is needed. Complementary to experimental approaches, computer simulations based on combined quantum mechanical and molecular mechanical (QM/MM) potentials have provided new insights into the catalytic mechanism in ABC transporters. Quantitatively reliable determination of the free energy requirement for enzymatic ATP hydrolysis, however, requires substantial statistical sampling on QM/MM potential. A case study shows that brute force sampling of ab initio QM/MM (AI/MM) potential energy surfaces is computationally impractical for enzyme simulations of ABC transporters. On the other hand, existing semiempirical QM/MM (SE/MM) methods, although affordable for free energy sampling, are unreliable for studying ATP hydrolysis. To close this gap, a multiscale QM/MM approach named reaction path–force matching (RP–FM) has been developed. In RP–FM, specific reaction parameters for a selected SE method are optimized against AI reference data along reaction paths by employing the force matching technique. The feasibility of the method is demonstrated for a proton transfer reaction in the gas phase and in solution. The RP–FM method may offer a general tool for simulating complex enzyme systems such as ABC transporters. PMID:27498639

  6. Toward Determining ATPase Mechanism in ABC Transporters: Development of the Reaction Path-Force Matching QM/MM Method.

    Zhou, Y; Ojeda-May, P; Nagaraju, M; Pu, J

    2016-01-01

    Adenosine triphosphate (ATP)-binding cassette (ABC) transporters are ubiquitous ATP-dependent membrane proteins involved in translocations of a wide variety of substrates across cellular membranes. To understand the chemomechanical coupling mechanism as well as functional asymmetry in these systems, a quantitative description of how ABC transporters hydrolyze ATP is needed. Complementary to experimental approaches, computer simulations based on combined quantum mechanical and molecular mechanical (QM/MM) potentials have provided new insights into the catalytic mechanism in ABC transporters. Quantitatively reliable determination of the free energy requirement for enzymatic ATP hydrolysis, however, requires substantial statistical sampling on QM/MM potential. A case study shows that brute force sampling of ab initio QM/MM (AI/MM) potential energy surfaces is computationally impractical for enzyme simulations of ABC transporters. On the other hand, existing semiempirical QM/MM (SE/MM) methods, although affordable for free energy sampling, are unreliable for studying ATP hydrolysis. To close this gap, a multiscale QM/MM approach named reaction path-force matching (RP-FM) has been developed. In RP-FM, specific reaction parameters for a selected SE method are optimized against AI reference data along reaction paths by employing the force matching technique. The feasibility of the method is demonstrated for a proton transfer reaction in the gas phase and in solution. The RP-FM method may offer a general tool for simulating complex enzyme systems such as ABC transporters. PMID:27498639

  7. Reaction mechanisms and microstructures of ceramic-metal composites made by reactive metal penetration

    Fahrenholtz, W.F. [Univ. of New Mexico, Albuquerque, NM (United States). Advanced Materials Lab.; Ewsuk, K.G.; Loehman, R.E. [Sandia National Labs., NM (United States)] [and others

    1996-12-31

    Ceramic-metal composites can be made by reactive penetration of molten metals into dense ceramic performs. The metal penetration is driven by a large negative Gibbs energy for reaction, which is different from the more common physical infiltration of porous media. Reactions involving Al can be written generally as (x+2)Al + (3/y)MO{sub y} {yields} Al{sub 2}O{sub 3} + M{sub 3/y}Al{sub x}, where MO{sub y} is an oxide that is wet by molten Al. In low Po{sub 2} atmospheres and at temperature above about 900{degrees}c, molten Al reduces mullite to produce Al{sub 2}O{sub 3} + M{sub 3/y}Al{sub x}, where MO is an oxide that is wet by molten Al. In low Po{sub 2} atmospheres and at temperatures above about 900{degrees}C, molten al reduces mullite to produce Al{sub 2}O{sub 3} and Si. The Al/mullite reaction has a {Delta}G{sub r}{degrees} (1200K) of -1014 kJ/mol and, if the mullite is fully dense, the theoretical volume change on reaction is less than 1%. A microstructure of mutually-interpenetrating metal and ceramic phases generally is obtained. Penetration rate increases with increasing reaction temperature from 900 to 1150{degrees}C, and the reaction layer thickness increases linearly with time. Reaction rate is a maximum at 1150{degrees}C; above that temperature the reaction slows and stops after a relatively short period of linear growth. At 1300{degrees}C and above, no reaction layer is detected by optical microscopy. Observations of the reaction front by TEM show only al and Al{sub 2}O{sub 3} after reaction at 900{degrees}C, but Si is present in increasing amounts as the reaction temperature increases to 1100{degrees}C and above. The kinetic and microstructural data suggest that the deviation from linear growth kinetics at higher reaction temperatures and longer times is due to Si build-up and saturation at the reaction front. The activation energy for short reaction times at 900 to 1150{degrees}C varies from {approximately}90 to {approximately}200 kJ/mole.

  8. Retention mechanism of technetium-99m-HM-PAO: intracellular reaction with glutathione

    Preparations of d,l- and meso-hexamethylpropyleneamine oxime (HM-PAO) labeled with technetium-99m were added to rat brain homogenates diluted with phosphate buffer (1:10). The conversion of d,l-HM-PAO to hydrophilic forms took place with an initial rate constant of 0.12 min-1. Incubation of the brain homogenate with 2% diethyl maleate for 5 h decreased the homogenate's measured glutathione (GSH) concentration from 160 to 16 microM and decreased the conversion rate to 0.012 min-1. Buffered aqueous solutions of glutathione rapidly converted the HM-PAO tracers to hydrophilic forms having the same chromatographic characteristics as found in the brain homogenates. The rate constant for the conversion reaction of d,l-HM-PAO in GSH aqueous solution was 208 and 317 L/mol/min in two different assay systems and for meso-HM-PAO the values were 14.7 and 23.2 L/mol/min, respectively. Rat brain has a GSH concentration of about 2.3 mM and the conversion of the d,l-HM-PAO due to GSH alone should proceed with a rate constant of 0.48 to 0.73 min-1 and be correspondingly 14-fold slower for meso-HM-PAO. In human brain, the in vivo data of Lassen et al. show a conversion rate constant of 0.80 min-1. This correspondence of values supports the notion that GSH may be important for the in vivo conversion of 99mTc-labeled HM-PAO to hydrophilic forms and may be the mechanism of trapping in brain and other cells. A kinetic model for the trapping of d,l- and meso-HM-PAO in tissue is developed that is based on data of GSH concentration in various organs

  9. A Detailed Chemical Kinetic Reaction Mechanism for n-Alkane Hydrocarbons from n-Octane to n-Hexadecane

    Westbrook, C K; Pitz, W J; Herbinet, O; Silke, E J; Curran, H J

    2007-09-25

    Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of the n-alkanes, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for n-heptane, using the same reaction class mechanism construction developed initially for n-heptane. Individual reaction class rules are as simple as possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms, and there is an intent to develop these mechanisms further in the future to incorporate greater levels of accuracy and predictive capability. Several of these areas for improvement are identified and explained in detail. These mechanisms are validated through comparisons between computed and experimental data from as many different sources as possible. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare processes in all of the n-alkane fuels. The mechanisms for all of these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, will be available on our web page when the paper is accepted for publication.

  10. Investigation of Pd-catalyzed Co(III)-EDTA/hypophosphite inhibition reaction kinetics, mechanism and the evaluation of its analytical application possibilities

    M. AKCAY; T. ALTUNATA; R. GURKAN; N. BICER

    2004-01-01

    The reaction between Co(III)-EDTA and hypophosphite ion, catalyzed by Pd(II) was chosen as the indicator reaction. The inhibition kinetics of this catalytic reaction have been investigated by a mechanistic approach in the presence of some inhibitors. Catalysts other than PdCl2, that is Pt, Au, Ni salts, did not exhibit any effect on the reaction. An original reaction mechanism is proposed based on the experimental data. The important variables were optimized for maximum sensitivity. The calib...

  11. Role of the direct mechanisms in the deuteron-induced surrogate reactions

    Avrigeanu, M

    2015-01-01

    An extended analysis of the key role of direct interactions, i.e., breakup, stripping and pick-up processes, for the deuteron–induced surrogate reactions is presented. Particular comments concern the deuteron breakup which is dominant in the case of the ( d; p g ) surrogate reactions on actinides target nuclei, around the Coulomb barrier.

  12. Microstructure and mechanical properties of mullite-zirconia reaction-sintered composites

    The flexural strength, fracture toughness (KIC), creep behavior and thermal shock of mullite-zirconia and mullite-zirconia-alumina composites obtained by reaction-sintering of zircon + alumina mixtures have been studied in the temperature interval ranging from room temperature to 1,400C. The results are discussed in terms of the microstructural features of the reaction-sintered composites

  13. Kinetics and Mechanism of Interfacial Reaction in a SiCf/Ti Composite

    Guoxing ZHANG; Qiang KANG; Nanlin SHI; Geping LI; Dong LI

    2003-01-01

    In order to evaluate the interfacial reaction, a SiCf/Ti (TA1) composite was fabricated by a vacuum hot pressingmethod and then heat-treated in vacuum at 800℃ for up to 100 h. The elemental distributions of C, Si and Ti at theinterfacial reaction zone were investigated. It was found that the reaction zone occurs during the fabrication processand continuously grows at high temperature because the Si and C atoms diffuse from SiC fibers to the matrix and Tiatoms diffuse in the opposite direction. The growth of the reaction zone is diffusion controlled and the mechanismof the reaction can be described by a reactive diffusion model of solid-state growth of an AmBn layer between twoelementary substances A and B.

  14. Theoretical studies of the reactions of O(3p) with halogenated methyl (Ⅰ)——Reaction mechanism of the O(3p) + CH2Cl reaction

    侯华; 王宝山; 顾月姝

    1999-01-01

    The reaction of O(3P) with CH2Cl radical has been studied using ab initio molecular orbital theory. G2 (MP2) method is used to calculate the geometrical parameters, vibrational frequencies and energies of various stationary points on the potential energy surface. The reaction mechanism is revealed. The addition of O(3P) with CH2Cl leads to the formation of an energy rich intermediate OCH2Cl which can subsequently undergo decomposition or isomerization to the final products. The calculated heat of reaction for each channel is in agreement with the experimental value. The production of H+CHClO and Cl+CH2O are predicted to be the major channels. The overall rate constants are calculated using transition state theory on the basis of ab initio data. The rate constant is pressure independent and exhibits negative temperature dependence at lower temperatures, in accordance with the experimental results.

  15. Large scale synthesis and formation mechanism of silver nanoparticles in solid-state reactions at ambient temperature

    Highlights: • AgNPs were prepared by solid state reaction at ambient temperature. • Only silver nitrate and ascorbic acid were needed in this reaction. • The size of the AgNPs can be tuned conveniently. • Formation mechanism of the AgNPs was investigated. - Abstract: A one-step strategy for preparing Ag nanoparticles (AgNPs) on large scale is demonstrated successfully, based on solid-state reactions at ambient temperature. The environmentally friendly synthesis can be achieved by simply grinding AgNO3 and ascorbic acid (AA) for about 30 min without adding any solvent and organic protectors. The size of AgNPs can be readily controlled by adjusting the reaction parameters such as AgNO3/AA molar ratio and reaction time. The nanostructures of AgNPs and their formation mechanism have been also investigated with XRD, FTIR, FESEM, HRTEM and HPLC–MS. It was found that AA can reduce Ag+ into Ag0 to form AgNPs directly in accompanying with its first oxidation into 2,3-diketogulonic acid (2,3-DKG) and then a series of fragmentary species of 2,3-DKG

  16. Large scale synthesis and formation mechanism of silver nanoparticles in solid-state reactions at ambient temperature

    Zhang, Aiqin, E-mail: zhangaiqin@zzuli.edu.cn [State Laboratory of Surface and Interface Science and Technology, Henan Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); Tian, Yakun; Xiao, Yuanhua; Sun, Yuan [State Laboratory of Surface and Interface Science and Technology, Henan Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); Li, Feng [State Laboratory of Surface and Interface Science and Technology, Henan Collaborative Innovation Center of Environmental Pollution Control and Ecological Restoration, Zhengzhou University of Light Industry, Zhengzhou 450002 (China); American Advanced Nanotechnology, Houston, TX 77459 (United States)

    2015-07-15

    Highlights: • AgNPs were prepared by solid state reaction at ambient temperature. • Only silver nitrate and ascorbic acid were needed in this reaction. • The size of the AgNPs can be tuned conveniently. • Formation mechanism of the AgNPs was investigated. - Abstract: A one-step strategy for preparing Ag nanoparticles (AgNPs) on large scale is demonstrated successfully, based on solid-state reactions at ambient temperature. The environmentally friendly synthesis can be achieved by simply grinding AgNO{sub 3} and ascorbic acid (AA) for about 30 min without adding any solvent and organic protectors. The size of AgNPs can be readily controlled by adjusting the reaction parameters such as AgNO{sub 3}/AA molar ratio and reaction time. The nanostructures of AgNPs and their formation mechanism have been also investigated with XRD, FTIR, FESEM, HRTEM and HPLC–MS. It was found that AA can reduce Ag{sup +} into Ag{sup 0} to form AgNPs directly in accompanying with its first oxidation into 2,3-diketogulonic acid (2,3-DKG) and then a series of fragmentary species of 2,3-DKG.

  17. Complementarity between Quantum and Classical Mechanics in Chemical Modeling. The H + HeH+ → H2 + + He Reaction: A Rigourous Test for Reaction Dynamics Methods.

    Esposito, Fabrizio; Coppola, Carla Maria; De Fazio, Dario

    2015-12-24

    In this work we present a dynamical study of the H + HeH+ → H2+ + He reaction in a collision energy range from 0.1 meV to 10 eV, suitable to be used in applicative models. The paper extends and complements a recent work [ Phys. Chem. Chem. Phys. 2014, 16, 11662] devoted to the characterization of the reactivity from the ultracold regime up to the three-body dissociation breakup. In particular, the accuracy of the quasi-classical trajectory method below the three-body dissociation threshold has been assessed by a detailed comparison with previous calculations performed with different reaction dynamics methods, whereas the reliability of the results in the high energy range has been checked by a direct comparison with the available experimental data. Integral cross sections for several HeH+ roto-vibrational states have been analyzed and used to understand the extent of quantum effects in the reaction dynamics. By using the quasi-classical trajectory method and quantum mechanical close coupling data, respectively, in the high and low collision energy ranges, we obtain highly accurate thermal rate costants until 15 000 K including all (178) the roto-vibrational bound and quasi-bound states of HeH+. The role of the collision-induced dissociation is also discussed and explicitly calculated for the ground roto-vibrational state of HeH+. PMID:26583384

  18. Theoretical study on the reaction mechanism of CH4 with CaO

    The reaction pathways and energetics for the reaction of methane with CaO are discussed on the singlet spin state potential energy surface at the B3LYP/6-311+G(2df,2p) and QCISD/6-311++G(3df,3pd)//B3LYP/6-311+G(2df,2p) levels of theory. The reaction of methane with CaO is proposed to proceed in the following reaction pathways: CaO + CH4→ CaOCH4→ [TS] → CaOH + CH3, CaO + CH4→ OCaCH4→ [TS] → HOCaCH3→ CaOH + CH3 or [TS] → CaCH3OH → Ca + CH3OH, and OCaCH4→ [TS] → HCaOCH3→ CaOCH3 + H or [TS] → CaCH3OH → Ca + CH3OH. The gas-phase methane-methanol conversion by CaO is suggested to proceed via two kinds of important reaction intermediates, HOCaCH3 and HCaOCH3, and the reaction pathway via the hydroxy intermediate (HOCaCH3) is energetically more favorable than the other one via the methoxy intermediate (HCaOCH3). The hydroxy intermediate HOCaCH3 is predicted to be the energetically most preferred configuration in the reaction of CaO + CH4. Meanwhile, these three product channels (CaOH + CH3, CaOCH3 + H and Ca + CH3OH) are expected to compete with each other, and the formation of methyl radical is the most preferable pathway energetically. On the other hand, the intermediates HCaOCH3 and HOCaCH3 are predicted to be the energetically preferred configuration in the reaction of Ca + CH3OH, which is precisely the reverse reaction of methane hydroxylation

  19. Theoretical Study of CH3CH=CH2+O(1D) Reaction:Mechanism and Kinetics

    WU Nai-nan; LIU Hong-xia; DUAN Xue-mei; LIU Jing-yao

    2012-01-01

    The mechanism and kinetics for the reaction of propene(CH3CH=CH2) molecule with O(1D) atom were investigated theoretically.The electronic structure information of the potential energy surface(PES) was obtained at the B3LYP/6-31 l+G(d,p) level,and the single-point energies were refined by the multi-level MCG3-MPWB method.The calculated results show that O(1D) atom can attack CH3CH=CH2 via the barrierless insertion mechanism to form four energy-riched intermediates CH3C(OH)CH2(IM1),CH3CHCHOH(IM2),CH2OHCHCH2(IM3)and cycloCH2OCHCH3(IM4),respectively,on the singlet PES.The branching ratios as well as the pressure- and temperaturedependence of various product channels for this multi-well reaction were predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus(RRKM) theories.The present results will be useful to gain a deep insight into the reaction mechanism and kinetics of CH3CH=CH2+O(1D) reaction.

  20. Mechanical stimulated reaction of metal/polymer mixed powders; Kinzoku/kobunshi kongo funmatsu no kikaiteki reiki hanno

    Tobita, M.; Sakakibara, A.; Takemoto, Y. [Okayama University, Okayama (Japan). Faculty of Engineering; Iwabu, H. [Kurare Co. Ltd., Osaka (Japan)

    1999-12-15

    Mechanical grinding (MG) with mechanically stimulated reaction was performed on metal/polymer mixed powders. The starting materials used in this study were the metals of Mg, Ti and Mg{sub 2}Ni powders, arid polymer of PTFE, PVC and PE powders. The MG process was investigated using XRD, IR, SEM and TEM. According to XRD results, magnesium fluoride (MgF{sub 2}, TiF{sub 2}) and chloride (MgCl{sub 2}) were detected from MG products of the Mg/PTFE, Ti/PTFE and Mg/PVC blending systems, respectively. Explosive reaction was found during MG of both Mg/PTFE and Ti/PTFE. It was also confirmed by XRD results that the production of MgF{sub 2} had already been formed just before the explosive reaction in Mg/PTFE system. It was found from IR analysis that C-C single bond in the polymers, not only both in PTFE and PVC but also in PE, changed to double bond C=C. Hydrogen produced due to decomposition of PE on blending Mg{sub 2}Ni/PE was absorbed into C-Mg{sub 2}Ni-H as amorphous solutes. These mechanically stimulated reaction was powerful method for decomposition of engineering plastics. (author)

  1. Exploring reaction mechanisms and their competition in 58Ni + 48Ca collisions at E=25 AMeV

    Latest results concerning the study of central collisions in 58Ni+48Ca reactions at Elab(Ni)=25 AMeV are presented. The experimental data, collected with the CHIMERA 4π device, have been analyzed in order to investigate the competition among different reaction mechanisms for central collisions in the Fermi energy domain. The method adopted to perform the centrality selection refers to the global variable 'flow angle', that is related to the event shape in momentum space, as it is determined by the eigenvectors of the experimental kinetic-energy tensor. The main features of the reaction products were explored by using different constraints on some of the relevant observables, such as mass and velocity distributions and their correlations. Much emphasis was devoted to the competition between fusion-evaporation processes with subsequent identification of a heavy residue and a prompt multifragmentation mechanism. The reaction mechanism was simulated in the framework of transport theories (dynamical stochastic BNV calculations, followed by sequential SIMON code) and further comparison with dynamical calculations from transport model (QMD, CoMD) are in progress. Moreover, an extension of this study taking into account for the light particles has been envisaged. (authors)

  2. Nuclear excitations and reaction mechanisms. Progress report, 1 November 1979-30 September 1980

    Among the topics investigated were the following: photon scattering and consistency condition between seagull quadrupole terms and the absorption sum rule; Raman scattering to negative-parity states; nonlocal terms due to exchange and retardation effects in charge-transfer reactions; consistency and meaning of various approximate channel coupling array equations; derivation of equations used in empirical nuclear reaction analyses; multicluster, n-particle scattering theory; converged molecular bound state calculations; consistency of approximate channel coupling array equations; derivations of equations used in empirical nuclear reaction analyses; and WKB-type approximation in angular momenta for central potentials. References to publications are given

  3. Study on Reaction Mechanism for Cracking FCC Gasoline on Acid Catalyst

    Xu Youhao; Wang Xieqing

    2004-01-01

    This article is based on the experimental data on reaction of FCC naphtha in the presence of acid catalysts. The data published in the literature were reprocessed and compared with experimental data and the relationship of hydrogen and methane contained in the dry gas with the conversion rate was identified.The similarity between the route for cracking of olefin enriched FCC gasoline and the route for reaction of individual hydrocarbons was deduced, while the route for formation of ethylene in dry gas was also proposed to identify the relationship between the reaction path for formation of ethylene and the conversion rate.

  4. Kinetic Study on Aminolysis of 4-Nitrophenyl Isonicotinate in Acetonitrile: Effect of Amine Basicity on Reactivity and Reaction Mechanism

    A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl isonicotinate with a series of cyclic secondary amines in MeCN. The plots of kobsd vs. [amine] curve upward for the reactions with weakly basic amines (e. g., morpholine, 1-(2-hydroxyethyl)piperazine, and piperazine) but are linear for those with strongly basic amines (e. g., piperidine and 3-methylpiperidine). The curved plots for the reactions with the weakly basic amines are typical for reactions reported previously to proceed through uncatalyzed and catalyzed routes with two intermediates (e. g., a zwitterionic tetrahedral intermediate T± and its deprotonated form T-). In contrast, the linear plots for the reactions with the strongly basic amines indicate that the catalytic route (i. e., the deprotonation process to yield T- from T± by a second amine molecule) is absent. The Brφnsted-type plots for Kk2 and Kk3 (i. e., the rate constants for the uncatalyzed and catalyzed routes, respectively) exhibit excellent linear correlations with βnuc = 0.99 and 0.69, respectively. The effect of amine basicity on the reaction mechanism is discussed in detail

  5. Study of the mechanism of Pb + Au reaction at 29 A.MeV; Etude du mecanisme de la reaction Pb + Au a 29 A.MeV

    Aboufirassi, M.

    1994-07-01

    The aim of this thesis is to demonstrate the binary character of Pb + Au reaction at 29 A.MeV and to study the decay modes of very excited nuclei produced. The experiment set up was performed at the GANIL in the scattering chamber NAUTILUS. It was composed by multi detectors of fragments (Z {>=}8) and multi detectors of light charged particles. (Z<8). The analysis of events which lead to detection of more then 80 % of both total charge and total parallel momentum proved that two body final state is still present at this incident energy. This mechanism is similar to the mechanism of heavy ion reaction at low bombarding energy. We have shown that complete damping occurred leading to excitation energy as high as 6 Me V/u. The decay modes of deep inelastic products are evaporation residue or binary fission or multifragmentation. Analysing the fission products, we have estimated the aligned spin of deep inelastic products (45 h). Finally, the study of light charged particles detected with fission fragments has demonstrated that these particles are emitted essentially before fission. The temperature value of hot nuclei emitted at foreword angle is deduced of light particle spectra. (author). 59 refs.

  6. Theoretical study on the reaction mechanism and thermodynamics of tin oxidation by oxygen species and chlorine species

    Li, Lai-Cai; Deng, Ping; Zhu, Yuan-Qiang; Zha, Dong; Tian, An-Min; Xu, Ming-Hou; Wong, Ning-Bew

    In this work ab initio molecular orbital methods were employed to study the coal combustion reaction mechanisms of tin oxidized by different oxidants, including HOCl, HCl, ClO, ClO2, NO3, CO2, and O2. Eleven reaction pathways were identified. The results show that Sn can react with HCl, ClOO, CO2, O2, and NO3 to form SnO and SnCl. SnO can be oxidized into SnCl by HOCl and HCl. SnCl can be further oxidized into a soluble compound, SnCl2.

  7. Reaction Mechanism and Kinetics of Aqueous Solutions of 2-Amino -2 Methyl-1,3- Propanediol and Carbonyl Sulphide

    ALPER, E

    2001-01-01

    The mechanism and kinetics of the reaction between aqueous solutions of COS and a sterically hindered primary amine, 2-amino-2-methyl-1,3-propanediol (AMPD), were investigated at 288-303 K using a stopped-flow technique. It was found that the reaction order according to power law kinetics was between 1.12 and 1.16 for an amine concentration range of 0.5 to 1.5 kmol m-3 . This overall order indicated that the thiocarbamate formation was complex and possibly involved a zwitterion inter...

  8. New insight into the ZnO sulfidation reaction: mechanism and kinetics modeling of the ZnS outward growth.

    Neveux, Laure; Chiche, David; Pérez-Pellitero, Javier; Favergeon, Loïc; Gay, Anne-Sophie; Pijolat, Michèle

    2013-02-01

    Zinc oxide based materials are commonly used for the final desulfurization of synthesis gas in Fischer-Tropsch based XTL processes. Although the ZnO sulfidation reaction has been widely studied, little is known about the transformation at the crystal scale, its detailed mechanism and kinetics. A model ZnO material with well-determined characteristics (particle size and shape) has been synthesized to perform this study. Characterizations of sulfided samples (using XRD, TEM and electron diffraction) have shown the formation of oriented polycrystalline ZnS nanoparticles with a predominant hexagonal form (wurtzite phase). TEM observations also have evidenced an outward development of the ZnS phase, showing zinc and oxygen diffusion from the ZnO-ZnS internal interface to the surface of the ZnS particle. The kinetics of ZnO sulfidation by H(2)S has been investigated using isothermal and isobaric thermogravimetry. Kinetic tests have been performed that show that nucleation of ZnS is instantaneous compared to the growth process. A reaction mechanism composed of eight elementary steps has been proposed to account for these results, and various possible rate laws have been determined upon approximation of the rate-determining step. Thermogravimetry experiments performed in a wide range of H(2)S and H(2)O partial pressures have shown that the ZnO sulfidation reaction rate has a nonlinear variation with H(2)S partial pressure at the same time no significant influence of water vapor on reaction kinetics has been observed. From these observations, a mixed kinetics of external interface reaction with water desorption and oxygen diffusion has been determined to control the reaction kinetics and the proposed mechanism has been validated. However, the formation of voids at the ZnO-ZnS internal interface, characterized by TEM and electron tomography, strongly slows down the reaction rate. Therefore, the impact of the decreasing ZnO-ZnS internal interface on reaction kinetics has been

  9. Reactions of the simple nitroalkanes with hydroxide ion in water. Evidence for a complex mechanism.

    Li, Zhao; Cheng, Jin-Pei; Parker, Vernon D

    2011-06-21

    Conventional kinetic analysis of the reactions of nitromethane (NM), nitroethane (NE) and 2-nitropropane (2-NP) with hydroxide ion in water revealed that the reactions are complex and involve kinetically significant intermediates. Kinetic experiments at the isosbestic points where changes in reactant and product absorbance cancel indicate the evolution and decay of absorbance characteristic of the formation of reactive intermediates. The deviations from 1st-order kinetics were observed to increase with increasing extent of reaction and in the reactant order: NM < NE < 2-NP. The apparent deuterium kinetic isotope effects for proton/deuteron transfer approach unity near zero time and increased with time toward plateau values as the reaction kinetics reach steady state. It is proposed that the initially formed preassociation complexes are transformed to more intimate reactant complexes which can give products by two possible pathways. PMID:21519607

  10. Kinetics and mechanism of the reaction of fluorine atoms with pentafluoropropionic acid.

    Vasiliev, E S; Knyazev, V D; Karpov, G V; Morozov, I I

    2014-06-12

    The kinetics of the reaction between fluorine atoms and pentafluoropropionic acid has been studied experimentally at T = 262-343 K. The overall reaction rate constant decreases with temperature: k1(T) = 6.1 × 10(-13) exp(+1166 K)/T) cm(3) molecule(-1) s(-1). The potential energy surface of the reaction has been studied using quantum chemistry. The results were used in transition state theory calculations of the temperature dependences of the rate constants of the two channels of the reaction. The abstraction channel ultimately producing HF, C2F5, and CO2 is dominant at the experimental temperatures; the addition-elimination channel producing C2F5 and CF(O)OH becomes important above 1000 K. PMID:24819330

  11. Nuclear excitations and reaction mechanisms: Progress report: [1 August 1986-31 July 1987

    Completed and ongoing research includes various theoretical and numerical studies of few-nucleon systems; nuclear reaction models; photon scattering from nuclei, including sum rules and current conservation; and properties of the pion

  12. Mechanism of anti-influenza virus activity of Maillard reaction products derived from Isatidis roots

    Ke, Lijing

    2011-01-01

    The cyto-protective compositions and effects of antiviral Maillard reaction products (MRPs) derived from roots of Isatis indigotica F. were examined using biochemical and biophysical methods. The Maillard reaction was identified as the main source of compounds with antiviral activity, an observation which has led to the proposal of a new class of active compounds that protect cells from influenza virus infection. In the roots, arginine and glucose were revealed to be the predom...

  13. Generalization of the Activated Complex Theory of Reaction Rates. I. Quantum Mechanical Treatment

    Marcus, R. A.

    1964-01-01

    In its usual form activated complex theory assumes a quasi-equilibrium between reactants and activated complex, a separable reaction coordinate, a Cartesian reaction coordinate, and an absence of interaction of rotation with internal motion in the complex. In the present paper a rate expression is derived without introducing the Cartesian assumption. The expression bears a formal resemblance to the usual one and reduces to it when the added assumptions of the latter are introduced.

  14. Graphene Facilitated Removal of Labetalol in Laccase-ABTS System: Reaction Efficiency, Pathways and Mechanism

    Dong, Shipeng; Xiao, Huifang; Huang, Qingguo; Zhang, Jian; Mao, Liang; Gao, Shixiang

    2016-02-01

    The widespread occurrence of the beta-blocker labetalol causes environmental health concern. Enzymatic reactions are highly efficient and specific offering biochemical transformation of trace contaminants with short reaction time and little to none energy consumption. Our experiments indicate that labetalol can be effectively transformed by laccase-catalyzed reaction using 2, 2-Azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator, while no significant removal of labetalol can be achieved in the absence of ABTS. A total of three products were identified. It is interesting that the presence of graphene greatly increased the reaction rate while not changed the products. In the presence of 100 μg/L graphene, the pseudo-first-order reaction rate constant was increased ~50 times. We found that the enhancement of graphene is probably attributed to the formation and releasing of ABTS2+ which has a much greater reactivity towards labetalol when graphene is present. This study provides fundamental information for laccase-ABTS mediated labetalol reactions and the effect of graphene, which could eventually lead to development of novel methods to control beta-blocker contamination.

  15. Modulation of the transient receptor potential vanilloid channel TRPV4 by 4alpha-phorbol esters: a structure-activity study

    Klausen, Thomas Kjaer; Pagani, Alberto; Minassi, Alberto;

    2009-01-01

    , affecting the orientation of the diterpenoid core into the ligand binding pocket, while the nature of the A,B ring junction plays an essential role in the Ca(2+)-dependence of the TRPV4 response. Taken together, our results show that 4alpha-phorbol is a useful template to investigate the molecular details...

  16. Kinetic mechanism of molecular energy transfer and chemical reactions in low-temperature air-fuel plasmas.

    Adamovich, Igor V; Li, Ting; Lempert, Walter R

    2015-08-13

    This work describes the kinetic mechanism of coupled molecular energy transfer and chemical reactions in low-temperature air, H2-air and hydrocarbon-air plasmas sustained by nanosecond pulse discharges (single-pulse or repetitive pulse burst). The model incorporates electron impact processes, state-specific N2 vibrational energy transfer, reactions of excited electronic species of N2, O2, N and O, and 'conventional' chemical reactions (Konnov mechanism). Effects of diffusion and conduction heat transfer, energy coupled to the cathode layer and gasdynamic compression/expansion are incorporated as quasi-zero-dimensional corrections. The model is exercised using a combination of freeware (Bolsig+) and commercial software (ChemKin-Pro). The model predictions are validated using time-resolved measurements of temperature and N2 vibrational level populations in nanosecond pulse discharges in air in plane-to-plane and sphere-to-sphere geometry; temperature and OH number density after nanosecond pulse burst discharges in lean H2-air, CH4-air and C2H4-air mixtures; and temperature after the nanosecond pulse discharge burst during plasma-assisted ignition of lean H2-mixtures, showing good agreement with the data. The model predictions for OH number density in lean C3H8-air mixtures differ from the experimental results, over-predicting its absolute value and failing to predict transient OH rise and decay after the discharge burst. The agreement with the data for C3H8-air is improved considerably if a different conventional hydrocarbon chemistry reaction set (LLNL methane-n-butane flame mechanism) is used. The results of mechanism validation demonstrate its applicability for analysis of plasma chemical oxidation and ignition of low-temperature H2-air, CH4-air and C2H4-air mixtures using nanosecond pulse discharges. Kinetic modelling of low-temperature plasma excited propane-air mixtures demonstrates the need for development of a more accurate 'conventional' chemistry mechanism

  17. Tyree-body mechanisms in the 3^He(e,e'p) reactions at high missing momentum

    Laget, J M

    2004-01-01

    A particular three-body mechanism is responsible for the missing strength which has been reported in $^3$He(e,e$'$p) reactions at missing momentum above 700 MeV/c. It corresponds to the absorption of the virtual photon by a nucleon at rest which subsequently propagates on-shell and emits a meson which is reabsorbed by the pair formed by the two other nucleons. Its amplitude, which is negligible in photon induced reactions as well as in the electro-production of an on-shell meson, becomes maximal in the quasi-free kinematics (X=1). It relates the amplitude of the $^3$He(e,e$'$p)D reaction to the amplitude of $pD$ elastic scattering at backward angles.

  18. On the importance of steady-state isotopic techniques for the investigation of the mechanism of the reverse water-gas-shift reaction.

    Tibiletti, Daniele; Goguet, Alexandre; Meunier, Frederic C; Breen, John P; Burch, Robbie

    2004-07-21

    The formation and reactivity of surface intermediates in the reverse water-gas-shift reaction on a Pt/CeO2 catalyst are critically dependent on the reaction conditions so that conclusions regarding the reaction mechanism cannot be inferred using ex operando conditions. PMID:15263955

  19. Application of radioisotopes to the investigation of the kinetics and mechanism of reactions of some inorganic complex compounds

    Radioisotopes are invaluable tools in the study of many types of inorganic chemical reactions, particularly those involving complex ionic substances in aqueous solution. One important approach is through research on the rates and mechanisms of isotopic exchange processes. For example, a series of studies has been made of the exchange between carbon-14-labelled ''free'' carbonate and the ligand carbonate in octahedral complex ions of the type CoA2CO3+, where A = 2 NH3, ethylenediamine (en), propylenediamine (pn), or trimethylenediamine (tn). These studies have led to a rather thorough understanding of the nature of this kind of ligand substitution reaction, and of the part played by the non-exchanging amine ligands in the process. Similar studies of oxalate exchange with tris-oxalato complexes of the form M (C2O4)3-3, where M = Co (III), Cr (III), or Rh (III), have been equally fruitful. An alternative technique, applicable only when using low-atomic-weight radioisotopes such as carbon-14, is to observe the equilibrium or kinetic isotope effects in the reaction of interest. I t has, for instance, been possible to interpret differences in the ligand carbonate exchange mechanism of Coen2CO3+ and Cotn2CO3+ on the basis of equilibrium isotope-effect measurements made on the carbonate exchange reaction. Similarly, data on the kinetic isotope effect in the acid-catalysed aquation of the Co (NH3)4CO3+ ion has supported deductions as to the nature of the rate-determining bond-breakage step in such reactions. Finally, the mechanistic path of certain atoms or radicals in inorganic reactions, where a choice between alternative explanations must be made, is frequently facilitated by a radioactive tracer experiment. An example is the proof that cyanide does not appear as a rapidly exchanging intermediate in the oxidation of thiocyanate ion by hydrogen peroxide, although cyanide is an important end-product. (author)

  20. Reaction mechanism and nuclear correlations study by low energy pion double charge exchange

    In pion double-charge-exchange (DCX) reactions, a positive (negative) pion is incident on a nucleus and a negative (positive) pion emerges. These reactions are of fundamental interest since the process must involve at least two nucleons in order to conserve charge. Although two nucleon processes are present in many reactions they are usually masked by the dominant single nucleon processes. DCX is unique in that respect since it is a two nucleon process in lowest order and thus may be sensitive to two-nucleon correlations. Measurements of low energy pion double-charge-exchange reactions to the double-isobaric-analog-state (DIAS) and ground-state (GS) of the residual nucleus provide new means for studying nucleon-nucleon correlations in nuclei. At low energies (Tπ 7/2 shell at energies ranging from 25 to 65 MeV. Cross sections were measured on 42,44,48Ca, 46,50Ti and 54Fe. The calcium isotopes make a good set of nuclei on which to study the effects of correlations in DCX reactions

  1. Study of the 16O(16O,12C)20Ne reaction mechanism by polarization measurements

    The 16O(16O,12C)20Ne reaction has been studied at beam energies of 68 and 90 MeV. At these energies, this reaction is selective for populating high spin states well known to have a large overlap with α+16O. The angular distributions have been analyzed with an EFR-DWBA code. Good fits are obtained and the resulting relative α particle spectroscopic factors for the 20Ne states are in good agreement with shell model predictions, and with other results from different α transfer reactions. The polarization of the 20Ne has been measured by angular correlations between 12C and 16O (product of the 20Ne decay). As expected from a semi-classical view of the transfer, a strong 20Ne polarization, on an axis perpendicular to the reaction plane has been found. This polarization remains constant on a wide span of 12C angles. Different nuclear reaction models have been tested. With selected potentials, the DWBA predicts a strong polarization in this case of a heavy ion transfer, but not as strong as the one observed in the experiment. Some possible reasons for this difference are indicated

  2. Ion beam irradiation effect on polymers. LET dependence on the chemical reactions and change of mechanical properties

    High-energy ions of H, He, C, O, Ne, Ar with 10-460 MeV from an AVF cyclotron accelerator were used to irradiate polymer films of 100x100 mm2 area by beam scanning. The changes of mechanical properties and also the chemical reactions such as chain scission or double bond formation were investigated. The linear energy transfer (LET) dependence of the changes of polymer properties was found to be very small when compared with adsorbed dose and was the same as that under gamma ray or electron beam irradiation. It means that the probability and also the mechanisms of chemical reaction should be almost the same even if LET was different. The ion energy would be dispersed widely in the polymer material, where the chemical reaction proceeds rather homogeneously. The chemical reaction sites are not so concentrated in a local area under high LET radiation, and the concentration in the local area might be the same as under low LET radiation. If the track model along the ion path is applied, the diameter may be a few 100 nm for C5+ (220 MeV) ion irradiation and is proportional to the square root of LET

  3. Reaction Mechanisms of Synthesis of 3,4-Epoxybutyric Acid from 3-Hydroxy-{\\gamma}-Butyrolactone by Density Functional Theory

    Yu-Chol, Jong; Yun-Hui, Ju; Kye-Ryong, Sin

    2016-01-01

    In this paper, carried out were the investigations on the synthetic reaction mechanisms of 3,4-epoxybutyric acid (EBA) from 3-hydroxy-{\\gamma}-butyrolactone (HBL) with two different activating agents, methanesulfonyl chloride (MC) or acetic acid (AA), respectively, and on the convertion of EBA to L-carnitine by density functional theory (DFT/B3LYP). The theoretical calculations showed that the two reaction mechanisms of EBA synthesis with MC or AA as an activating agent were nearly the same. If activated HBL is hydrolysed, not only ring cleavage reaction, but also reverse reaction to HBL can take place. In the case of AA as the activating agent, the activation energy ( energy barrier ) for EBA synthesis is 1.8 times larger than that with MC. It means that the synthesis of EBA with AA may make more by-products with less yield of EBA than that with MC, that can be one reason why AA gave the less yield than MC in EBA synthesis, as reported in the previous experimental study.

  4. Kinetics and mechanism of the gas-phase reaction of Cl atoms and OH radicals with fluorobenzene at 296 K

    Andersen, Mads Peter Sulbæk; Nielsen, Ole John; Hurley, MD;

    2002-01-01

    radical and adduct formation to give the C6H5F-Cl adduct. At 296 K the rate constant for the abstraction channel is k(5a)(Cl+C6H5F) = (1.1 +/- 0.1) x 10(-17) cm(3) molecule(-1) s(-1). The C6H5F-Cl adduct undergoes rapid (k similar to 10(8) s(-1)) decomposition to reform C6H5F and Cl atoms and reaction......Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms and OH radicals with fluorobenzene, C6H5F, in 700 Torr of N-2 or air diluent at 296 K. Reaction of Cl atoms with C6H5F proceeds via two pathways: H-atom abstraction to give HCl and the C6H4F...... with Cl atoms via a mechanism which, at least in part, leads neither to production of C6H5Cl nor to reformation of C6H5F. As the steady-state Cl atom concentration is increased, the fraction of the C6H5F-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate...

  5. Hydrothermal synthesis of cubic α-Fe2O3 microparticles using glycine: Surface characterization, reaction mechanism and electrochemical activity

    Graphical abstract: Highlights: → We synthesize cubic α-Fe2O3 (hematite) microparticles. → Their morphological, mineralogical and surface properties are determined. → Reaction mechanism based on thermodynamics and ionic equilibrium concepts are described. → Microparticles have charge capacity of 160 mAh/g and good columbic efficiency of 94%. - Abstract: Cubic α-Fe2O3 (hematite) microparticles (side lengths = 0.3-1.3 μm) have been synthesized using glycine and ferric chloride via a simple one-step hydrothermal reaction. Their morphological, mineralogical and surface properties have been determined using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). XRD analysis indicated that the synthesized α-Fe2O3 microparticles were minerallogically pure. An increase in hydrothermal reaction duration from 10 to 24 h increased the atomic percentages of α-Fe2O3 on the surface of the microparticles by almost 8%. The mechanism concerning reactions of species to produce this microparticles precipitate was elucidated based on thermodynamics and ionic equilibrium aspects. In the electrochemical analysis, the synthesized α-Fe2O3 microparticles (as cathode material) exhibit an approximate charge capacity of 160 mAh/g and excellent coulombic efficiency of 94%.

  6. Simulation of biodiesel combustion in a light-duty diesel engine using integrated compact biodiesel–diesel reaction mechanism

    Ng, Hoon Kiat; Gan, Suyin; Ng, Jo-Han;

    2013-01-01

    This computational fluid dynamics (CFD) study is performed to investigate the combustion characteristics and emissions formation processes of biodiesel fuels in a light-duty diesel engine. A compact reaction mechanism with 80 species and 303 reactions is used to account for the effects of chemical...... kinetics. Here, the mechanism is capable of emulating biodiesel–diesel mixture of different blending levels and biodiesel produced from different feedstock. The integrated CFD-kinetic model was validated against a test matrix which covers the entire saturated–unsaturated methyl ester range typical...... of biodiesel fuels, as well as the biodiesel–diesel blending levels. The simulated cases were then validated for in-cylinder pressure profiles and peak pressure values/timings. Errors in the peak pressure values did not exceed 1%, while the variations in peak pressure timings were kept within 1.5 crank angle...

  7. FEARCF a multidimensional free energy method for investigating conformational landscapes and chemical reaction mechanisms

    NAIDOO Kevin J.

    2012-01-01

    The development and implementation of a computational method able to produce free energies in multiple dimensions,descriptively named the free energies from adaptive reaction coordinate forces (FEARCF) method is described in this paper.While the method can be used to calculate free energies of association,conformation and reactivity here it is shown in the context of chemical reaction landscapes.A reaction free energy surface for the Claisen rearrangement of chorismate to prephenate is used as an illustration of the method's efficient convergence.FEARCF simulations are shown to achieve fiat histograms for complex multidimensional free energy volumes.The sampling efficiency by which it produces multidimensional free energies is demonstrated on the complex puckering of a pyranose ring,that is described by a three dimensional W(θ1,θ2,θ3) potential of mean force.

  8. Theoretical study on the reaction mechanism of the gas-phase H2/CO2/Ni(3D) system.

    Qin, Song; Hu, Changwei; Yang, Huaqing; Su, Zhishan

    2005-07-28

    The ground-state potential energy surface (PES) in the gas-phase H2/CO2/Ni(3D) system is investigated at the CCSD(T)//B3LYP/6-311+G(2d,2p) levels in order to explore the possible reaction mechanism of the reverse water gas shift reaction catalyzed by Ni(3D). The calculations predict that the C-O bond cleavage of CO2 assisted by co-interacted H2 is prior to the dissociation of the H2, and the most feasible reaction path for Ni(3D) + H2 + CO2 --> Ni(3D) + H2O + CO is endothermic by 12.5 kJ mol(-1) with an energy barrier of 103.9 kJ mol(-1). The rate-determining step for the overall reaction is predicted to be the hydrogen migration with water formation. The promotion effect of H2 on the cleavage of C-O bond in CO2 is also discussed and compared with the analogous reaction of Ni(3D) + CO2 --> NiO + CO, and the difference between triplet and singlet H2/CO2/Ni systems is also discussed. PMID:16833994

  9. Light Particle Emission Mechanisms in Heavy-Ion Reactions at 5-20 MeV/u

    Fotina O.V.

    2010-03-01

    Full Text Available Light Charged Particle emission mechanisms were studied for different mass entrance channel nuclear reactions. The 300, 400, 500 MeV 64Ni + 68Zn and 130, 250 MeV 16O + 116Sn reactions were measured at the Legnaro National Laboratory using the beams from the TANDEM-ALPI acceleration system. Light Charged Particles were measured in coincidence with Evaporation Residues and their spectra were analyzed using the global moving source fit technique. The characterization of different emission sources (evaporative, pre-equilibrium, break-up is discussed. The behavior of pre-equilibrium emission as a function of projectile energy, excitation energy and mass-asymmetry in the entrance channel was studied, evaluating the energy, mass and charge lost by the composite systems and using Griffin exciton model for the pre-equilibrium neutron emission. The present results are compared with the systematics of the asymmetric mass entrance channel reactions. The present work shows that also at the onset the pre-equilibrium emission depends not only on the projectile velocity but also on the reaction entrance channel mass-asymmetry. The first attempt of the particle spectra analysis using the Griffin exciton model is demonstrated for the case of proton emission in the 130 MeV 16O + 116Sn reaction.

  10. Oxidative removal of acetaminophen using zero valent aluminum-acid system:Efficacy, influencing factors, and reaction mechanism

    Honghua Zhang; Beipei Cao; Wanpeng Liu; Kunde Lin; Jun Feng

    2012-01-01

    Commercial available zero valent aluminum under air-equilibrated acidic conditions (ZVA1/H+/air system) demonstrated an excellent capacity to remove aqueous organic compounds.Acetaminophen (ACTM),the active ingredient of the over-the-counter drug Tylenol(R),is widely present in the aquatic environment and therefore the treatment of ACTM-contaminated water calls for further research.Herein we investigated the oxidative removal of ACTM by ZVAl/H+/air system and the reaction mechanism.In acidic solutions (pH < 3.5),ZVAl displayed an excellent capacity to remove ACTM.More than 99% of ACTM was eliminated within 16 hr in pH 1.5 reaction solutions initially containing 2.0 g/L aluminum and 2.0 mg/L ACTM at 25 ± 1℃.Higher temperature and lower pH facilitated ACTM removal.The addition of different iron species Fe0,Fe2+ and Fe3+ into ZVAl/H+/air system dramatically accelerated the reaction likely due to the enhancing transformation of H2O2 to HO·via Fenton's reaction.Furthermore,the primary intermediate h.ydroquinone and the anions formate,acetate and nitrate,were identified and a possible reaction scheme was proposed.This work suggested that ZVA1/H+/air system may be potentially employed to treat ACTM-contaminated water.

  11. Kinetics and mechanisms of heterogeneous reaction of NO2 on CaCO3 surfaces under dry and wet conditions

    Z. M. Chen

    2009-03-01

    Full Text Available Calcium nitrate (Ca(NO32 was observed in mineral dust and could change the hygroscopic and optical properties of mineral dust significantly due to its strong water solubility. The reaction of calcium carbonate (CaCO3 with nitric acid (HNO3 is believed the main reason for the observed Ca(NO32 in the mineral dust. In the atmosphere, the concentration of nitrogen dioxide (NO2 is orders of magnitude higher than that of HNO3; however, little is known about the reaction of NO2 with CaCO3. In this study, the heterogeneous reaction of NO2 on the surface of CaCO3 particles was investigated using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS combined with X-ray photoelectron spectroscopy (XPS and scanning electron microscopy (SEM under wet and dry conditions. Nitrate formation was observed in both conditions, and nitrite was observed under wet conditions, indicating the reaction of NO2 on the CaCO3 surface produced nitrate and probably nitrous acid (HONO. Relative humidity (RH influenced both the initial uptake coefficient and the reaction mechanism. With RH52%, a monolayer of water formed on the surface of the CaCO3 particles, which reacted with NO2 as a first order reaction, forming HNO3 and HONO. The initial uptake coefficient γ0 was determined to be (1.66±0.38×10−7 under dry conditions and up to (0.84±0.44×10−6 under wet conditions. Considering that NO2 concentrations in the atmosphere are orders of magnitude higher than those of HNO3, the reaction of NO2 on CaCO3 particle should have similar importance as that of HNO3 in the atmosphere and could also be an important source of HONO in the atmosphere.

  12. Anxiety sensitivity and post-traumatic stress reactions: Evidence for intrusions and physiological arousal as mediating and moderating mechanisms.

    Olatunji, Bunmi O; Fan, Qianqian

    2015-08-01

    A growing body of research has implicated anxiety sensitivity (AS) and its dimensions in the development of post-traumatic stress disorder (PTSD). However, the mechanism(s) that may account for the association between AS and PTSD remains unclear. Using the "trauma film paradigm," which provides a prospective experimental tool for investigating analog intrusion development, the present study examines the extent to which intrusions mediate the association between AS and the development of posttraumatic stress reactions. After completing a measure of AS and state mood, unselected participants (n = 45) viewed a 10 min film of graphic scenes of fatal traffic accidents and then completed a second assessment of state mood. Participants then kept a daily diary to record intrusions about the film for a one-week period. Post-traumatic stress reactions about the film were then assessed after the one-week period. The results showed that general AS and physical and cognitive concerns AS predicted greater post-traumatic stress reactions about the film a week later. Furthermore, the number of intrusions the day after viewing the traumatic film, but not fear and disgust in response to the trauma film, mediated the association between general AS (and AS specifically for physical and cognitive concerns) and post-traumatic stress reactions a week later. Subsequent analysis also showed that physiological arousal during initial exposure to the traumatic film moderated the association between general AS and the number of intrusions reported the day after viewing the film. The implications of these analog findings for conceptualizing the mechanism(s) that may interact to explain the role of AS in the development of PTSD and its effective treatment are discussed. PMID:26121496

  13. Investigating Glutamatergic Mechanism in Attention and Impulse Control Using Rats in a Modified 5-Choice Serial Reaction Time Task

    Abigail Benn; Emma S J Robinson

    2014-01-01

    The 5-choice serial reaction time task (5CSRTT) has been widely used to study attention and impulse control in rodents. In order to mimic cognitive impairments in psychiatry, one approach has been to use acute administration of NMDA antagonists. This disruption in glutamatergic transmission leads to impairments in accuracy, omissions, and premature responses although findings have been inconsistent. In this study, we further investigated glutamatergic mechanisms using a novel version of the 5...

  14. Benzyl alcohol oxidation in supercritical carbon dioxide: spectroscopic insight into phase behaviour and reaction mechanism.

    Caravati, Matteo; Grunwaldt, Jan-Dierk; Baiker, Alfons

    2005-01-21

    Selective oxidation of benzyl alcohol to benzaldehyde with molecular oxygen over an alumina-supported palladium catalyst was performed with high rate at about 95% selectivity in supercritical carbon dioxide. The experiments in a continuous flow fixed-bed reactor showed that the pressure has a strong influence on the reaction rate. A marked increase of the rate (turnover frequency) from 900 h(-1) to 1800 h(-1) was observed when increasing the pressure from 140 to 150 bar. Video monitoring of the bulk fluid phase behavior and the simultaneous investigation by transmission and attenuated total reflection (ATR) infrared spectroscopy at two positions of the view cell showed that the sharp increase in activity is correlated to a transition from a biphasic to a monophasic reaction mixture. In the single phase region, both oxygen and benzyl alcohol are dissolved in the supercritical CO2 phase, which leads to a reduction of the mass transport resistances (both in the external fluid film and in the catalyst pores) and thus to the high reaction rate measured in the catalytic experiments. The phase transition could be effectively and easily monitored by transmission and ATR-IR spectroscopy despite the small concentration of the dense liquid like phase. Deposition of the Pd/Al2O3 catalyst on the ATR-crystal at the bottom of the view cell allowed to gain insight into the chemical changes and mass transfer processes occurring in the solid/liquid interface region during reaction. Analyzing the shift of the upsilon2 bending mode of CO2 gave information on the fluid composition in and outside the catalyst pores. Moreover, the catalytic reaction could be investigated in situ in this spectroscopic batch reactor cell by monitoring simultaneously the reaction progress, the phase behaviour and the catalytic interface. PMID:19785149

  15. A mechanism for excitation of metastable levels by(γ,γ') reactions

    The analysis of the cross-section of 77Se and 87Sr isomeric states excitation in the (γ, γ') reaction, was carried out using neutron pick-up and stripping reaction results. It allows the shell configurations of the transitions to the activation states to be determined. To check thus obtained conclusions the energies of Jπ=1- excited states for 90Zr and 138Ba were calculated, which are in good agreement with the resonance structure at the γ-quanta elastic scattering in the 5 to 10 MeV energy range

  16. Two-step mechanism of meson production in pd → 3HeX reaction

    It is shown that the two-step model of the reaction pd→3HeX (X η, η', ω, φ), involving the subprocesses pp → dπ+ and π+n →Xp allows to explain the form of energy dependence of experimental cross sections above the thresholds under assumption that the singlet part of the pp→dπ+ amplitude dominates in collinear kinematics. The spin-spin asymmetry for the reaction dp→3HeX has been found to be ∼ -1 in the forward-backward approximation. (author)

  17. Mechanism for the stabilization of protein clusters above the solubility curve: the role of non-ideal chemical reactions

    Lutsko, J. F.

    2016-06-01

    Dense protein clusters are known to play an important role in nucleation of protein crystals from dilute solutions. While these have generally been thought to be formed from a metastable phase, the observation of similar, if not identical, clusters above the critical point for the dilute-solution/strong-solution phase transition has thrown this into doubt. Furthermore, the observed clusters are stable for relatively long times. Because protein aggregation plays a central role in some pathologies, understanding the nature of such clusters is an important problem. One mechanism for the stabilization of such structures was proposed by Pan, Vekilov and Lubchenko and was investigated using a dynamical density functional theory model which confirmed the viability of the model. Here, we revisit that model and incorporate additional physics in the form of state-dependent reaction rates. We show by a combination of numerical results and general arguments that the state-dependent rates disrupt the stability mechanism. Finally, we argue that the state-dependent reactions correct unphysical aspects of the model with ideal (state-independent) reactions and that this necessarily leads to the failure of the proposed mechanism.

  18. Mechanism for the stabilization of protein clusters above the solubility curve: the role of non-ideal chemical reactions.

    Lutsko, J F

    2016-06-22

    Dense protein clusters are known to play an important role in nucleation of protein crystals from dilute solutions. While these have generally been thought to be formed from a metastable phase, the observation of similar, if not identical, clusters above the critical point for the dilute-solution/strong-solution phase transition has thrown this into doubt. Furthermore, the observed clusters are stable for relatively long times. Because protein aggregation plays a central role in some pathologies, understanding the nature of such clusters is an important problem. One mechanism for the stabilization of such structures was proposed by Pan, Vekilov and Lubchenko and was investigated using a dynamical density functional theory model which confirmed the viability of the model. Here, we revisit that model and incorporate additional physics in the form of state-dependent reaction rates. We show by a combination of numerical results and general arguments that the state-dependent rates disrupt the stability mechanism. Finally, we argue that the state-dependent reactions correct unphysical aspects of the model with ideal (state-independent) reactions and that this necessarily leads to the failure of the proposed mechanism. PMID:27115119

  19. International conference: Features of nuclear excitation states and mechanisms of nuclear reactions. 51. Meeting on nuclear spectroscopy and nuclear structure. The book of abstracts

    Results of the LI Meeting on Nuclear Spectroscopy and Nuclear Structure are presented. Properties of excited states of atomic nuclei and mechanisms of nuclear reactions are considered. Studies on the theory of nucleus and fundamental interactions pertinent to experimental study of nuclei properties and mechanisms of nuclear reactions, technique and methods of experiment, application of nuclear-physical method, are provided

  20. Supercritical water oxidation of Quinazoline: Effects of conversion parameters and reaction mechanism.

    Gong, Yanmeng; Guo, Yang; Wang, Shuzhong; Song, Wenhan

    2016-09-01

    The supercritical water oxidation reaction of quinazoline and a set of related reaction products were investigated in batch reactors by varying the temperature (T, 400-600 °C), time (t, 0-400 s), water density (ρ, 70.79-166.28  kg m(-3)) and oxidation coefficient (OC, 0-4.0). The TOC removal efficiency (CRE) increased significantly as the OC increased, whereas this effect was very limited at high OC (>2.0). Lack of oxygen resulted in low CRE and TN removal efficiency (NRE), also cause coke-formation, and giving high yield of NH3 and nitrogenous organic intermediates. Prolonging reaction time did not provide an appreciable improvement on CRE but remarkably increased NRE at temperature higher than 500 °C. Pyrimidines and pyridines as the nitrogenous intermediates were largely found in GC-MS spectrum. Polymerization among benzene, phenyl radical and benzyl radical played important roles in the formation of PAHs, such as naphthalene, biphenyl, phenanthrene. These collective results showed how the yield of intermediate products responded to changes in the process variables, which permitted the development of a potential reaction network for supercritical water oxidation of quinazoline. PMID:27179598

  1. Theoretical study on the mechanism of CH3NH2 and O3 atmospheric reaction

    Samira Valehi; Morteza Vahedpour

    2014-07-01

    Reaction pathways of methylamine with ozone on the singlet potential energy profile have been investigated at the RB3LYP/6-311++G (3df-3pd) computational level. Calculated results reveal that six kinds of products P1 (CH3NO + H2O2), P2 (CH3NH + OH + O2), P3 (NH2CH + HO2+ OH), P4 (CH2NH + H2O +O2), P5 (NH2CH2OH + O2), P6 (NH3+ CH2O +O2) are obtained through variety of transformation of one reactant complex C1. Cleavage and formation of the chemical bonds in the reaction pathways have been discussed using the structural parameters. Based on the calculations, the title reaction leads to NH3+ CH2O + O2 as thermodynamic adducts in an exothermic process by −76.28 kcal/mol in heat realizing and spontaneous reaction by −86.71 kcal/mol in standard Gibbs free energy. From a kinetic viewpoint, the production of CH3NH + OH + O2 adducts with one transition state is the most favoured path.

  2. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    Kinnison, Douglas E.; Wuebbles, Donald J.

    1994-01-01

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated.

  3. Quantum statistical mechanical theory of diffusion and reaction on solid surfaces

    Lin, S. H.; Ziv, Alan R.; Eyring, H.

    1981-01-01

    We present the derivation of the general kinetic equations of diffusion and diffusion with interaction (or chemical reaction) on solid surfaces (or in dense media) by using the density matrix method. We indicate several problems to which this formalism applies and, in particular, discuss the damping effect on diffusion.

  4. Dynamic quenching as a simple test for the mechanism of excited-state reaction

    We report on comparative studies of dynamic fluorescence quenching of 3-hydroxyflavone (3HF) and of its novel analogs by nitric oxide spin compound TEMPO. These dyes exhibit the excited-state intramolecular proton transfer (ESIPT) reaction that allows observation of two separate bands in fluorescence emission - of initially excited form and of the product of ESIPT reaction. In the frame of two-state excited-state reaction formalism, we develop the theory predicting different dependence of intensities at two bands in steady-state spectra in the cases of thermodynamic and kinetic control of ESIPT. In line with these predictions, the quenching changes strongly the distribution of intensities between these bands for 3HF but does not change it for the novel compounds whose excited states exhibit strong charge transfer character. Based on these findings, we suggest that the quenching of fluorescence by an efficient collisional quencher can be a simple and convenient method using only the steady-state experiment for distinguishing the excited-state reactions occurring under thermodynamic or under kinetic controls. This method can be used for large-scale screening of a series of compounds - potential candidates for application in fluorescence sensor and biosensor technologies

  5. Generalization of the Activated Complex Theory of Reaction Rates. II. Classical Mechanical Treatment

    Marcus, R. A.

    1964-01-01

    In its usual classical form activated complex theory assumes a particular expression for the kinetic energy of the reacting system -- one associated with a rectilinear motion along the reaction coordinate. The derivation of the rate expression given in the present paper is based on the general kinetic energy expression.

  6. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NOx, Clx, HCl, N2O5, ClONO2 are calculated

  7. Insights into the Mechanism of Type I Dehydroquinate Dehydratases from Structures of Reaction Intermediates

    Light, Samuel H.; Minasov, George; Shuvalova, Ludmilla; Duban, Mark-Eugene; Caffrey, Michael; Anderson, Wayne F.; Lavie, Arnon (NWU); (UIC)

    2012-02-27

    The biosynthetic shikimate pathway consists of seven enzymes that catalyze sequential reactions to generate chorismate, a critical branch point in the synthesis of the aromatic amino acids. The third enzyme in the pathway, dehydroquinate dehydratase (DHQD), catalyzes the dehydration of 3-dehydroquinate to 3-dehydroshikimate. We present three crystal structures of the type I DHQD from the intestinal pathogens Clostridium difficile and Salmonella enterica. Structures of the enzyme with substrate and covalent pre- and post-dehydration reaction intermediates provide snapshots of successive steps along the type I DHQD-catalyzed reaction coordinate. These structures reveal that the position of the substrate within the active site does not appreciably change upon Schiff base formation. The intermediate state structures reveal a reaction state-dependent behavior of His-143 in which the residue adopts a conformation proximal to the site of catalytic dehydration only when the leaving group is present. We speculate that His-143 is likely to assume differing catalytic roles in each of its observed conformations. One conformation of His-143 positions the residue for the formation/hydrolysis of the covalent Schiff base intermediates, whereas the other conformation positions the residue for a role in the catalytic dehydration event. The fact that the shikimate pathway is absent from humans makes the enzymes of the pathway potential targets for the development of non-toxic antimicrobials. The structures and mechanistic insight presented here may inform the design of type I DHQD enzyme inhibitors.

  8. Studies of (p,t) reaction mechanism employing the realistic deuteron and triton wave functions

    The roles of the simultaneous (one-step) and the sequential (two-step) transfer processes in the (p,t) reactions were investigated. For this purpose, the exact evaluations of both processes were carried out employing the realistic light-ion wave functions and the interaction which causes the transfer. (author)

  9. Kinetics and mechanism of bimolecular electron transfer reaction in quinone-amine systems in micellar solution

    Photoinduced electron transfer (ET) reactions between anthraquinone derivatives and aromatic amines have been investigated in sodium dodecyl sulphate (SDS) micellar solutions. Significant static quenching of the quinone fluorescence due to high amine concentration in the micellar phase has been observed in steady-state measurements. The bimolecular rate constants for the dynamic quenching in the present systems kqTR, as estimated from the time-resolved measurements, have been correlated with the free energy changes ΔG0 for the ET reactions. Interestingly it is seen that the kqTR vs ΔG0 plot displays an inversion behavior with maximum kqTR at around 0.7 eV, a trend similar to that predicted in Marcus ET theory. Like the present results, Marcus inversion in the kqTR values was also observed earlier in coumarin-amine systems in SDS and TX-100 micellar solutions, with maximum kqTR at around the same exergonicity. These results thus suggest that Marcus inversion in bimolecular ET reaction is a general phenomenon in micellar media. Present observations have been rationalized on the basis of the two-dimensional ET (2DET) theory, which seems to be more suitable for micellar ET reactions than the conventional ET theory. For the quinone-amine systems, it is interestingly seen that kqTR vs ΔG0 plot is somewhat wider in comparison to that of the coumarin-amine systems, even though the maxima in the kqTR vs ΔG0 plots appear at almost similar exergonicity for both the acceptor-donor systems. These observations have been rationalized on the basis of the differences in the reaction windows along the solvation axis, as envisaged within the framework of the 2DET theory, and arise due to the differences in the locations of the quinones and coumarin dyes in the micellar phase

  10. A STUDY OF FUNDAMENTAL REACTION PATHWAYS FOR TRANSITION METAL ALKYL COMPLEXES. I. THE REACTION OF A NICKEL METHYL COMPLEX WITH ALKYNES. II. THE MECHANISM OF ALDEHYDE FORMATION IN THE REACTION OF A MOLYBDENUM HYDRIDE WITH MOLYBDENUM ALKYLS

    Huggins, John Mitchell

    1980-06-01

    I. This study reports the rapid reaction under mild conditions of internal or terminal alkynes with methyl (acetyl~ acetonato) (triphenylphosphine) nickel (1) in either aromatic or ether solvents. In all cases vinylnickel products 2 are formed by insertion of the alkyne into the nickel=methyl bond. These complexes may be converted into a variety of organic products (e.g. alkenes, esters, vinyl halides) by treatment with appropriate reagents. Unsymmetrical alkynes give selectively the one regioisomer with the sterically largest substituent next to the nickel atom. In order to investigate the stereochemistry of the initial insertion, a x-ray diffraction study of the reaction of 1 with diphenylacetylene was carried out. This showed that the vinylnickel complex formed by overall trans insertion was the product of the reaction. Furthermore, subsequent slow isomerization of this complex, to a mixture of it and the corresponding cis isomer, demonstrated that this trans addition product is the kinetic product of the reaction. In studies with other alkynes, the product of trans addition was not always exclusively (or even predominantly) formed, but the ratio of the stereoisomers formed kinetically was substantially different from the thermodynamic ratio. Isotope labeling, added phosphine, and other experiments have allowed us to conclude that the mechanism of this reaction does involve initial cis addition. However, a coordinatively unsaturated vinylnickel complex is initially formed which can undergo rapid, phosphine-catalyzed cis-trans isomerization in competition with its conversion to the isolable phosphine-substituted kinetic reaction products. II. The reaction of CpMo(CO){sub 3}H (1a) with CpMo(CO){sub 3}R (2, R= CH{sub 3}, C{sub 2}H{sub 5}) at 50{degrees} C in THF gives the aldehyde RCHO and the dimers [CpMo(CO){sub 3}]{sub 2} (3a) and [CpMo(CO){sub 2}]{sub 2} (4a). Labeling one of the reactants with a methylcyclopentadienyl ligand it was possible to show that the

  11. Mechanism for the growth of polycyclic aromatic hydrocarbons from the reactions of naphthalene with cyclopentadienyl and indenyl.

    Xu, Fei; Shi, Xiangli; Zhang, Qingzhu; Wang, Wenxing

    2016-11-01

    Polycyclic aromatic hydrocarbons (PAHs) are globally concerned atmospheric particle-bound pollutants due to their toxicities. A mechanistic understanding of their formation from other environmental sources is of crucial importance for successful prevention of PAH. In the present work, the formation and growth mechanism of PAHs from the reactions of naphthalene with the cyclopentadienyl and indenyl radicals was investigated by using the hybrid density functional theory (DFT) at the MPWB1K/6-311+G(3df,2p)//MPWB1K/6-31+G(d,p) level. The rate constants for the crucial elementary steps were deduced with the aid of the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) contribution. The formation of PAHs was involved in six elementary processes including: the addition reaction, ring closure, intramolecular H-shift, C-C cleavage, intramolecular H-shift and unimolecular elimination of CH3 or H. The C-C cleavage steps were revealed as the rate determining steps due to the extremely high barrier. At high temperature conditions like the combustion and pyrolysis of many hydrocarbons, the main products are phenanthrene, 4-methyl-phenanthrene and 1-methyl-phenanthrene from the reactions of naphthalene and cyclopentadienyl, and benzo(a)anthracene, 12-methyl-phenanthrene and 7-methyl-phenanthrene from the reactions of naphthalene and indenyl radicals. The reaction of naphthalene with indenyl radical is slightly more difficult than the reaction of naphthalene with cyclopentadienyl radical because of the bigger HOMO-LUMO orbital energy difference of naphthalene with indenyl relative to that of naphthalene with cyclopentadienyl. PMID:27538266

  12. Reaction Force/Torque Sensing in a Master-Slave Robot System without Mechanical Sensors

    Kyoko Shibata

    2010-07-01

    Full Text Available In human-robot cooperative control systems, force feedback is often necessary in order to achieve high precision and high stability. Usually, traditional robot assistant systems implement force feedback using force/torque sensors. However, it is difficult to directly mount a mechanical force sensor on some working terminals, such as in applications of minimally invasive robotic surgery, micromanipulation, or in working environments exposed to radiation or high temperature. We propose a novel force sensing mechanism for implementing force feedback in a master-slave robot system with no mechanical sensors. The system consists of two identical electro-motors with the master motor powering the slave motor to interact with the environment. A bimanual coordinated training platform using the new force sensing mechanism was developed and the system was verified in experiments. Results confirm that the proposed mechanism is capable of achieving bilateral force sensing and mirror-image movements of two terminals in two reverse control directions.

  13. Protonation states of intermediates in the reaction mechanism of [NiFe] hydrogenase studied by computational methods.

    Dong, Geng; Ryde, Ulf

    2016-06-01

    The [NiFe] hydrogenases catalyse the reversible conversion of H2 to protons and electrons. The active site consists of a Fe ion with one carbon monoxide, two cyanide, and two cysteine (Cys) ligands. The latter two bridge to a Ni ion, which has two additional terminal Cys ligands. It has been suggested that one of the Cys residues is protonated during the reaction mechanism. We have used combined quantum mechanical and molecular mechanics (QM/MM) geometry optimisations, large QM calculations with 817 atoms, and QM/MM free energy simulations, using the TPSS and B3LYP methods with basis sets extrapolated to the quadruple zeta level to determine which of the four Cys residues is more favourable to protonate for four putative states in the reaction mechanism, Ni-SIa, Ni-R, Ni-C, and Ni-L. The calculations show that for all states, the terminal Cys-546 residue is most easily protonated by 14-51 kJ/mol, owing to a more favourable hydrogen-bond pattern around this residue in the protein. PMID:26940957

  14. Study of components and statistical reaction mechanism in simulation of nuclear process for optimized production of {sup 64}Cu and {sup 67}Ga medical radioisotopes using TALYS, EMPIRE and LISE++ nuclear reaction and evaporation codes

    Nasrabadi, M. N., E-mail: mnnasrabadi@ast.ui.ac.ir; Sepiani, M. [Department of Nuclear Engineering, Faculty of Advanced Sciences and Technologies, University of Isfahan, Hezarjerib Street, 81746-73441, Isfahan (Iran, Islamic Republic of)

    2015-03-30

    Production of medical radioisotopes is one of the most important tasks in the field of nuclear technology. These radioactive isotopes are mainly produced through variety nuclear process. In this research, excitation functions and nuclear reaction mechanisms are studied for simulation of production of these radioisotopes in the TALYS, EMPIRE and LISE++ reaction codes, then parameters and different models of nuclear level density as one of the most important components in statistical reaction models are adjusted for optimum production of desired radioactive yields.

  15. Study of components and statistical reaction mechanism in simulation of nuclear process for optimized production of 64Cu and 67Ga medical radioisotopes using TALYS, EMPIRE and LISE++ nuclear reaction and evaporation codes

    Production of medical radioisotopes is one of the most important tasks in the field of nuclear technology. These radioactive isotopes are mainly produced through variety nuclear process. In this research, excitation functions and nuclear reaction mechanisms are studied for simulation of production of these radioisotopes in the TALYS, EMPIRE and LISE++ reaction codes, then parameters and different models of nuclear level density as one of the most important components in statistical reaction models are adjusted for optimum production of desired radioactive yields

  16. Reaction mechanisms in collisions induced by 8B beam close to the barrier

    The aim of the proposed experiment is to investigate on the reaction dynamics of proton-halo induced collisions at energies around the Coulomb barrier where coupling to continuum effects are expected to be important. We propose to measure $^{8}$B+$^{64}$Zn elastic scattering angular distribution together with the measurement, for the first time, of p-$^{7}$Be coincidences coming from transfer and/or break-up of $^{8}$B. The latter will allow a better understanding of the relative contribution of elastic $\\textit{vs}$ non-elastic break-up in reactions induced by extremely weakly-bound nuclei. We believe that with the availability of the post accelerated $^{8}$B beam at REX-ISOLDE we will be able to collect for the first time high quality data for the study of such an important topic.

  17. Communication: Enhanced oxygen reduction reaction and its underlying mechanism in Pd-Ir-Co trimetallic alloys

    Ham, Hyung Chul; Hwang, Gyeong S., E-mail: gshwang@che.utexas.edu [Department of Chemical Engineering, The University of Texas at Austin, Austin, Texas 78712 (United States); Manogaran, Dhivya [Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712 (United States); Lee, Kang Hee; Jin, Seon-ah; You, Dae Jong; Pak, Chanho [Energy Lab, Samsung Advanced Institute of Technology, Samsung Electronics Co., Ltd., Suwon (Korea, Republic of); Kwon, Kyungjung [Department of Energy and Mineral Resources Engineering, Sejong University, Seoul 143-747 (Korea, Republic of)

    2013-11-28

    Based on a combined density functional theory and experimental study, we present that the electrochemical activity of Pd{sub 3}Co alloy catalysts toward oxygen reduction reaction (ORR) can be enhanced by adding a small amount of Ir. While Ir tends to favorably exist in the subsurface layers, the underlying Ir atoms are found to cause a substantial modification in the surface electronic structure. As a consequence, we find that the activation barriers of O/OH hydrogenation reactions are noticeably lowered, which would be mainly responsible for the enhanced ORR activity. Furthermore, our study suggests that the presence of Ir in the near-surface region can suppress Co out-diffusion from the Pd{sub 3}Co substrate, thereby improving the durability of Pd-Ir-Co catalysts. We also discuss the relative roles played by Ir and Co in enhancing the ORR activity relative to monometallic Pd catalysts.

  18. Communication: Enhanced oxygen reduction reaction and its underlying mechanism in Pd-Ir-Co trimetallic alloys

    Based on a combined density functional theory and experimental study, we present that the electrochemical activity of Pd3Co alloy catalysts toward oxygen reduction reaction (ORR) can be enhanced by adding a small amount of Ir. While Ir tends to favorably exist in the subsurface layers, the underlying Ir atoms are found to cause a substantial modification in the surface electronic structure. As a consequence, we find that the activation barriers of O/OH hydrogenation reactions are noticeably lowered, which would be mainly responsible for the enhanced ORR activity. Furthermore, our study suggests that the presence of Ir in the near-surface region can suppress Co out-diffusion from the Pd3Co substrate, thereby improving the durability of Pd-Ir-Co catalysts. We also discuss the relative roles played by Ir and Co in enhancing the ORR activity relative to monometallic Pd catalysts

  19. Actinide complexation kinetics: rate and mechanism of dioxoneptunium (V) reaction with chlorophosphonazo III

    Rates of complex formation and dissociation in NpO2+- Chlorophosphonazo III (2,7-bis(4-chloro-2-phosphonobenzeneazo)-1,8- dihydroxynapthalene-3,6-disulfonic acid)(CLIII) were investigated by stopped-flow spectrophotometry. Also, limited studies were made of the rates of reaction of La3+, Eu3+, Dy3+, and Fe3+ with CLIII. Rate determining step in each system is an intramolecular process, the NpO2+-CLIII reaction proceeding by a first order approach to equilibrium in the acid range from 0.1 to 1.0 M. Complex formation occurs independent of acidity, while both acid dependent and independent dissociation pathways are observed. Activation parameters for the complex formation reaction are ΔH=46.2±0.3 kJ/m and ΔS=7± J/mK (I=1.0 M); these for the acid dependent and independent dissociation pathways are ΔH=38.8±0.6 kJ/m, ΔS=-96±18 J/mK, ΔH=70.0± kJ/m, and ΔS=17±1 J/mK, respectively. An isokinetic relationship is observed between the activation parameters for CLIII complex formation with NpO2+, UO22+, Th4+, and Zr4+. Rates of CLIII complex formation reactions for Fe3+, Zr4+, NpO2+, UO22+, Th4+, La3+, Eu3+, and Dy3+ correlate with cation radius rather than charge/radius ratio

  20. Ultrahigh Vacuum Studies of the Kinetics and Reaction Mechanisms of Ozone with Surface-Bound Fullerenes

    Davis, Erin Durke

    2011-01-01

    Acquiring in depth knowledge of the ozone oxidation of surface-bound fullerenes advances the understanding of fullerene fate in the environment, as well as the reactivity of ozone with carbonaceous nanomaterials. Recent ultrahigh vacuum studies of the reaction of gasphase ozone with surface-bound fullerenes have made it possible to observe the formation and subsequent thermal decomposition of the primary ozonide (PO). As the use of nanomaterials, such as C60, continues to incre...

  1. Studies of Atmospheric Chemistry and Reaction Mechanisms Using Optical Spectroscopy and Mass Spectrometry

    Liu, Yingdi

    2011-01-01

    This thesis mainly focuses on (1) development and applications of cavity ringdown spectroscopy (CRDS) to study atmospheric trace gases; (2) reactive intermediates in the alkene ozonolysis reactions using photoionization time-of-flight mass spectrometry (TOFMS); and (3) development of new methods using CRDS for thin film studies.Specifically, CRDS based instruments are developed to measure and characterize peroxy radicals in atmosphere. By combining the chemical amplification detection of pero...

  2. Nuclear excitations and reaction mechanisms. Progress report, 1 August-31 July 1984

    This progress report describes activities of the Nuclear Theory group at Brown University during the period 1 August 1983 to 31 July 1984. Completed and ongoing research include various theoretical and numerical studies of few-particle systems, nuclear reaction models, nuclear electroexcitation and photon scattering from nuclei. In addition, research on atomic and molecular structure has essentially been concluded and no further DOE-supported research in this area is anticipated

  3. Chemical mechanism and specificity of the C5-mannuronan epimerase reaction.

    Jerga, Agoston; Stanley, Matthew D; Tipton, Peter A

    2006-08-01

    C5-mannuronan epimerase catalyzes the formation of alpha-L-guluronate residues from beta-D-mannuronate residues in the synthesis of the linear polysaccharide alginate. The reaction requires the abstraction of a proton from C5 of the residue undergoing epimerization followed by re-protonation on the opposite face. Rapid-mixing chemical quench experiments were conducted to determine the nature of the intermediate formed upon proton abstraction in the reaction catalyzed by the enzyme from Pseudomonas aeruginosa. Colorimetric and HPLC analysis of quenched samples indicated that shortened oligosaccharides containing an unsaturated sugar residue form as transient intermediates in the epimerization reaction. This suggests that the carbanion is stabilized by glycal formation, concomitant with cleavage of the glycosidic bond between the residue undergoing epimerization and the adjacent residue. The time dependence of glycal formation suggested that slow steps flank the chemical steps in the catalytic cycle. Solvent isotope effects on V and V/K were unity, consistent with a catalytic cycle in which chemistry is not rate-limiting. The specificity of the epimerase with regard to neighboring residues was examined, and it was determined that the enzyme showed no bias for mannuronate residues adjacent to guluronates versus those adjacent to mannuronates. Proton abstraction and sugar epimerization were irreversible. Existing guluronate residues already present in the polysaccharide were not converted to mannuronates, nor was incorporation of solvent deuterium into existing mannuronates observed. PMID:16866359

  4. The Effect of Mechanical Vibration Stimulation of Perception Subthreshold on the Muscle Force and Muscle Reaction Time of Lower Leg

    Kim, Huigyun; Kwak, Kiyoung; Kim, Dongwook

    2016-01-01

    The objective of this study is to investigate the effect of mechanical vibration stimulation on the muscle force and muscle reaction time of lower leg according to perception threshold and vibration frequency. A vibration stimulation with perception threshold intensity was applied on the Achilles tendon and tibialis anterior tendon. EMG measurement and analysis system were used to analyze the change of muscle force and muscle reaction time according to perception threshold and vibration frequency. A root-mean-square (RMS) value was extracted using analysis software and Maximum Voluntary Contraction (MVC) and Premotor Time (PMT) were analyzed. The measurement results showed that perception threshold was different from application sites of vibration frequency. Also, the muscle force and muscle reaction time showed difference according to the presence of vibration, frequency, and intensity. This result means that the vibration stimulation causes the change on the muscle force and muscle reaction time and affects the muscles of lower leg by the characteristics of vibration stimulation. PMID:27382244

  5. Theoretical Studies on the Reaction Mechanisms of C3H2 (cyclopropenylidene) and O(3P) Radicals

    XlE Xiaohua; SHEN Wei; HE Rongxing; ZHANG Jinsheng; LI Ming

    2009-01-01

    The complex potential energy surface for the reaction of C3H2 (cyclopropenylidene) with O(3p) was explored computationally using a density functional and ab initio QCISD(T) methods. The geometries of all the stationary points (transition states, intermediates and products) were fully optimized at the B3LYP/6-311++G** computa-tional level, and the single point calculation including full population analysis was performed by employing QCISD(T). Our results show that the product P1 (C2H+HCO) is the major product, while the products P2 (C2H2+ CO) and P3 (HC3O+H) are minor products, as confirmed by experiment. Product P1 could be gained through the path: R→IM1→IM2→P1, and the C3H2+O(3P) reaction was expected to be rapid. So, the C3H2+O(3p) reaction may be an efficient strategy for producing C2H using cyclopropenylidene in atmosphere. The present results can lead us to understand deeply the mechanism of the title reaction.

  6. Effect of Nonleaving Group on the Reaction Rate and Mechanism: Aminolyses of 4-Nitrophenyl Acetate, Benzoate and Phenyl Carbonate

    Second-order rate constants have been determined spectrophotometrically for the reaction of phenyl 4- nitrophenyl carbonate with a series of primary amines in H2O containing 20 mol % DMSO at 25.0 .deg. C. The Brφnsted-type plot is linear with a βnuc 0.69 ± 0.04, which is slightly smaller than the βnuc values for the reactions of 4-nitrophenyl acetate (βnuc = 0.82 ± 0.03) and benzoate (βnuc = 0.76 ± 0.01), indicating that the reaction proceeds through a tetrahedral zwitterionic intermediate T±. The carbonate is more reactive than the corresponding acetate and benzoate. The changing Me (or Ph) to PhO has resulted in a decrease in the βnuc value without changing the reaction mechanism but an increase in the reactivity. The electronic effect of the substituent in the nonleaving group appears to be responsible for the enhanced reactivity of the carbonate compared with the corresponding acetate and benzoate

  7. A DFT study on the mechanism of palladium-catalyzed divergent reactions of 1,6-enyne carbonates

    Xing Hui Zhang; Zhi Yuan Geng; Teng Niu; Ke Tai Wang

    2015-03-01

    The reaction mechanisms of palladium-catalyzed divergent reactions of 1,6-enyne carbonates have been investigated using DFT calculations at the B3LYP/6-31G(d,p) (LanL2DZ for Pd) level. Solvent effects on these reactions have been considered by the polarizable continuum model (PCM) for the solvent (DMF). The formation of vinylidenepyridines and vinylidenepyrrolidines were generated through 5-exo-dig cyclization or 6-endo-dig cyclization. Our calculation results suggested the following: (i) The first step of the whole cycle is the rate-determining step, which causes allenic palladium intermediate through two plausible pathways. This intermediate provides the corresponding products and releases the palladium catalyst by a subsequent hydrogen transfer and elimination process. (ii) For the catalyst CH3OPdH, the reaction could occur through two possible pathways, but 5-exo-dig cyclization is favoured over 6-endo-dig cyclization. However, when the hydrogen atom is substituted with a phenyl group, the energy barriers for 5-exo-dig cyclization or 6-endo-dig cyclization become relatively high, 18.0–28.5 kcal/mol. The computational results provide good explanation for the experimental observations.

  8. Mechanism and kinetic study on the gas-phase reactions of OH radical with carbamate insecticide isoprocarb

    Zhang, Chenxi; Yang, Wenbo; Bai, Jing; Zhao, Yuyang; Gong, Chen; Sun, Xiaomin; Zhang, Qingzhu; Wang, Wenxing

    2012-12-01

    As one of the most important carbamate insecticides, isoprocarb [2-(1-methylethyl) phenyl methylcarbamate, MIPC] is widely used in agricultural and cotton spraying. The atmospheric chemical reaction mechanism and kinetics of MIPC with OH radical have been researched using the density functional theory in this paper. The study shows that OH radical is more easily added to the C atoms of aromatic ring than to carbon-oxygen double bond, while the H atom is abstracted more difficulty from -CONH- group and aromatic ring than from the -CH3- group and the -CH- group. At room temperature, the total rate constant of MIPC with OH radical is about 5.1 × 10-12 cm3 molecule-l s-l. OH radical addition reaction and H atom abstraction reaction are both important for the OH-initiated reaction of MIPC. The energy-rich adducts (MIPC-OH) and the MIPC's radical isomers are open-shell activated radicals and can be further oxidized in the atmosphere.

  9. Mechanism of formation of Fe-N alloy in the solid-state reaction process between iron and boron nitride

    Processes and resulting products of solid-state reaction between Fe and hexagonal boron nitride (h-BN) were studied by ball milling a mixture of Fe and h-BN with an Fe to h-BN volume ratio of 1:12.5 and/or heat-treating under normal or high pressure. The 30 h-milled mixture was annealed for 1 h under an atmospheric pressure at 770 and 1170 K, respectively. A small amount of γ'-Fe4N was observed in the mixture annealed at 770 K and a little γ-Fe(N) was obtained at 1170 K. All Fe atoms in the mixture reacted with N atoms in the BN to form a single phase of ε-FexN when the mixture was milled for 60 h or annealed for 1 h under 4 GPa at temperatures of 690-800 K. However, no Fe-B phase was observed in the present experiment. Formation and phase transition of Fe-N alloy in the solid-state reaction process as well as effect of pressure on the reaction and resulting products are discussed in the present paper. The mechanism of formation of Fe-N and Fe-B alloys in the reaction processes are also investigated in terms of the Miedema model and thermodynamics and kinetics

  10. Energy transfer mechanisms in photobiological reactions. Final report, 1 April 1960--31 March 1979. [Photodynamic processes in selected biomolecules

    Spikes, J.D.

    1979-03-31

    This project was concerned primarily with studies of the mechanisms of the sensitized photooxidation of selected biomolecules using a variety of phtosensitizers. Such reactions are often termed photodynamic processes. In particular we have carried out steady-state kinetic studies, flash photolysis and spectral studies, and product formation studies of the sensitized photooxidation of the five susceptible amino acids (cycteine, histidine, methonine, tryptophan, and tyrosine) and their derivatives, as well as purines and pyrimidines. A number of studies were also carried out on the mechanisms of the photodynamic inactivation of enzymes (trypsin, ribonuclease, lysozyme). Mechanism of photosensitization were studied using a variety of sensitizers including flavins, porphyrins, and a number of synthetic dyes (substituted fluoresceins, acridines, thyazines).

  11. Studies on the kinetics and mechanism of complex formation in the reactions of ferron with iron (III) and uranium (VI)

    The equilibria and kinetics of the reactions of ferron (7-iodo-8-hydroxyquindine-5-sulphonic acid) with iron(III) and uranium(VI) have been followed by stopped flow spectrophotometry under the conditions of mono-complex formation. The equilibrium constants obtained spectrophotmetrically have been compared with those obtained from kinetic studies. In the case of iron(III), in the acidity range, [H+]=(2.8-10.0)x10-2 mol dm-3, among the different possible reaction path-ways, the reaction has been found to proceed mainly through the interaction of Fe(OH)(aq)2+ and partially deprotonated form (LH-) of the ligand. In the case of uranium(VI), in the acidity range, [H+]=(2.5-25.0)x10-5 mol dm-3, a dual path mechanism involving UO2(aq)2+ and UO2(OH)(aq)- and the partially deprotonated (LH-) form of the ligand is consistent with the observations. The results in each case are in agreement with the Eigen mechanism and the characteristic water exchange rates have been obtained in each case, as a rough estimate, from the experimental data. Activation parameters (ΔHsup(≠) and ΔSsup(≠) for each path have been determined and compared. (author). 23 refs., 5 figs., 2 tabs

  12. The Application of Transient-State Kinetic Isotope Effects to the Resolution of Mechanisms of Enzyme-Catalyzed Reactions

    Harvey F. Fisher

    2013-07-01

    Full Text Available Much of our understanding of the mechanisms of enzyme-catalyzed reactions is based on steady-state kinetic studies. Experimentally, this approach depends solely on the measurement of rates of free product appearance (d[P]/dt, a mechanistically and mathematically complex entity. Despite the ambiguity of this observed parameter, the method’s success is due in part to the elaborate rigorously derived algebraic theory on which it is based. Transient-state kinetics, on the other hand, despite its ability to observe the formation of intermediate steps in real time, has contributed relatively little to the subject due in, some measure, to the lack of such a solid mathematical basis. Here we discuss the current state of existing transient-state theory and the difficulties in its realistic application to experimental data. We describe a basic analytic theory of transient-state kinetic isotope effects in the form of three novel fundamental rules. These rules are adequate to define an extended mechanism, locating the isotope-sensitive step and identifying missing steps from experimental data. We demonstrate the application of these rules to resolved component time courses of the phenylalanine dehydrogenase reaction, extending the previously known reaction by one new prehydride transfer step and two new post hydride transfer steps. We conclude with an assessment of future directions in this area.

  13. A mechanically coupled reaction-diffusion model for predicting the response of breast tumors to neoadjuvant chemotherapy

    Weis, Jared A.; Miga, Michael I.; Arlinghaus, Lori R.; Li, Xia; Bapsi Chakravarthy, A.; Abramson, Vandana; Farley, Jaime; Yankeelov, Thomas E.

    2013-09-01

    There is currently a paucity of reliable techniques for predicting the response of breast tumors to neoadjuvant chemotherapy. The standard approach is to monitor gross changes in tumor size as measured by physical exam and/or conventional imaging, but these methods generally do not show whether a tumor is responding until the patient has received many treatment cycles. One promising approach to address this clinical need is to integrate quantitative in vivo imaging data into biomathematical models of tumor growth in order to predict eventual response based on early measurements during therapy. In this work, we illustrate a novel biomechanical mathematical modeling approach in which contrast enhanced and diffusion weighted magnetic resonance imaging data acquired before and after the first cycle of neoadjuvant therapy are used to calibrate a patient-specific response model which subsequently is used to predict patient outcome at the conclusion of therapy. We present a modification of the reaction-diffusion tumor growth model whereby mechanical coupling to the surrounding tissue stiffness is incorporated via restricted cell diffusion. We use simulations and experimental data to illustrate how incorporating tissue mechanical properties leads to qualitatively and quantitatively different tumor growth patterns than when such properties are ignored. We apply the approach to patient data in a preliminary dataset of eight patients exhibiting a varying degree of responsiveness to neoadjuvant therapy, and we show that the mechanically coupled reaction-diffusion tumor growth model, when projected forward, more accurately predicts residual tumor burden at the conclusion of therapy than the non-mechanically coupled model. The mechanically coupled model predictions exhibit a significant correlation with data observations (PCC = 0.84, p statistically significant >4 fold reduction in model/data error (p = 0.02) as compared to the non-mechanically coupled model.

  14. Expression of Putative Stem Cell Marker, Hepatocyte Nuclear Factor 4 Alpha, in Mammary Gland of Water Buffalo.

    Choudhary, Ratan K; Choudhary, Shanti; Kaur, Harmanjot; Pathak, Devendra

    2016-01-01

    Buffaloes account for more than 56% of total milk production in India. Cyclic remodeling of mammary glands of human, mice, cow, sheep, and goat is determined by mammary stem cells. It is logical to assume that buffalo mammary gland will have mammary stem/progenitor cells. Thus far, no report exists on identification of buffalo mammary stem cells. Hepatocyte nuclear factor 4 alpha (HNF4A) is a candidate marker for hepatic progenitor cells and has recently been suggested as a marker of bovine mammary stem/progenitor cells. We hypothesized that ( 1 ) HNF4A identifies putative buffalo mammary stem/progenitor cells and ( 2 ) the number of HNF4A-positive cells increases during mastitis. Sixteen buffalo mammary samples were collected from a local slaughterhouse. Hematoxylin and eosin staining were performed on 5-micron thick sections and on the basis of gross examination and histomorphology of the mammary glands, physiological stages of the animals were estimated as non-lactating (n = 4), mastitis (n = 9), and prepubertal (n = 3). In total, 24048 cells were counted (5-10 microscopic fields/animal; n = 16 animals) of which, 40% cells were mammary epithelial cells (MEC) and 60% cells were the stromal cells. The percentage of MEC in non-lactating animals was higher compared to mastitic animals (47.3% vs. 37.3%), which was likely due to loss of MEC in mastitis. HNF4A staining was observed in nuclei of MEC of ducts, alveoli, and stromal cells. Basal location and low frequency of HNF4A-positive MEC (ranges from 0.4-4.5%) were consistent with stem cell characteristics. Preliminary study showed coexpression of HNF4A with MSI1 (a mammary stem cell marker in sheep), suggesting HNF4A was likely to be a putative mammary stem/progenitor cell marker in buffalo. HNF4A-positive MEC (basal and luminal; light and dark stained) tended to be higher in non-lactating than the mastitic animals (8.73 ± 1.71% vs. 4.29 ± 1.19%; P = 0.07). The first hypothesis that HNF4A identify

  15. Dwarf Ball: a 4π light-charged particle multidetector system for heavy-ion reaction mechanisms and spectroscopy

    The design and construction of a new spectrometer for heavy-ion reaction mechanism studies and for high spin spectroscopy is reported. The first version of this spectrometer consists of 72 fast-slow scintillator phoswiches packed with the same geometry as the spin spectrometer at the Holifield Heavy-Ion Research Facility and is small enough to fit inside the spin spectrometer. An improved version of the Dwarf Ball incorporates up to 85 detectors consisting primarily of CsI(T1) scintillators in a 4π arrangement and provides far superior performance in terms of energy resolution, particle identification, and dynamic range for energy measurements. The capabilities of the device for recording proton and α-particle spectra is discussed. The new possibilities for heavy-ion reaction studies and for nuclear spectroscopy that this device offers will be discussed

  16. Reaction Kinetics and Oxidation Mechanisms of the Conversion of Pyrite to Ferrous Sulphate: A Moessbauer Spectroscopy Study

    Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 deg. C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S-S and Fe-S bonds in pyrite.

  17. Reaction Kinetics and Oxidation Mechanisms of the Conversion of Pyrite to Ferrous Sulphate: A Moessbauer Spectroscopy Study

    Ferrow, Embaie A., E-mail: embaie.ferrow@geol.lu.se; Mannerstrand, Maria [Lund University, GeoBiosphere Science Centre, Department of Geology, Lithosphere Biosphere Science (Sweden); Sjoeberg, Bosse [Swedish Museum of Natural History (Sweden)

    2005-06-15

    Pyrite undergoes a series of exothermic reactions during mine roasting to porous hematite. At low temperatures, the first non-refractive phase to form is ferrous sulphate and could be a cheaper alternative to hematite roasting for the mining industry. In this study, pyrite powder is heated in air at temperatures between 200 and 370 deg. C for 1 to 256 h in a temperature and time series. The rate of oxidation of pyrite to ferrous sulphate is modelled by combining the Arrhenius equation with the Weibull function to extract reliable thermodynamic data, including the energy of activation, the frequency factor and the overall order of reaction. From the thermodynamic data obtained, two possible oxidation mechanisms are recognized, depending on the bond dissociation energies of the S-S and Fe-S bonds in pyrite.

  18. Reaction mechanisms of fast neutrons on stable Mo isotopes below 21 MeV

    A large number of new measurements with the activation technique were performed for (n,2n) and neutron-induced ΔZ=1,2 reaction cross sections on the stable molybdenum isotopes in the energy range from 13.5 to 21 MeV. First results were obtained for the 92Mo(n,2n)91Mom,92Mo(n,α)89Zrm,94Mo(n,2n)93Mom,95Mo(n,p)95Nbm,96Mo(n,p) 96Nb,96Mo(n,x)95Nbm, 97Mo(n,p)97Nb, 97Mo(n,p)97Nbm, 97Mo(n,x)96Nb, 98Mo(n,p)98Nbm, 98Mo(n,x)97Nb, 98Mo(n,x)97Nbm, and 100Mo(n,α)97Zr reactions, above 16 MeV. A significant number of high-accuracy 14 MeV measurements were performed which are in good agreement with the measurements above 16 MeV for reactions studied in both energy ranges. The rather complete database for the molybdenum isotopes was analyzed with two different sets of consistent model calculations: a local and a global approach. The global approach (a blind calculation with the TALYS code) provides a good overall description of the dominant reaction channels, although the (n,α) reactions for the heavy isotopes are overpredicted. The local approach (an adjusted calculation with the STAPRE-H code) describes the shapes and magnitudes of the excitation functions well from the reaction thresholds up to 21 MeV using a consistent parameter set, which was optimized based on all experimental information for the nuclei at hand and their immediate neighbors. The agreement between experimental and calculated data is, in general, good both at the maxima and at the tails of the excitation functions, and both for total activation cross sections of a particular channel and for cross sections leading to isomers, showing the viability of the level densities, the optical models, and the γ widths. Comparison of the two model calculations with the data indicates the relevance of an appropriate treatment for preequilibrium (PE) α-particle emission for the description of the data above 14 MeV. Comparison between the model calculations shows largely different PE deuteron emission contributions to the

  19. T(T,2n)4He and 3He(3He,2p)4He: The Reaction Mechanism from Solar Energies to 10 MeV

    Bacher, A. D.; Brune, C. R.; Sayre, D. B.; Hale, G. M.; Frenje, J. A.; Gatu Johnson, M.

    2016-03-01

    We have studied the energy dependence of the reaction mechanism of the T(t,2n)4He reaction at stellar energies and of its charge symmetric analog reaction 3He(3He,2p)4He at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state. This contribution is dedicated to the memory of Tom Tombrello, my Ph.D. advisor at Cal Tech, who died in 2014.

  20. Analysis of Reaction Mechanisms in Flames Using Combined - and Lif-Spectroscopy

    Brockhinke, Andreas; Nau, Patrick; Köhler, Markus; Kohse-Höinghaus, Katharina

    2009-06-01

    Laser-based non-intrusive diagnostic techniques are firmly established as the most versatile tools to study high-temperature gas-phase reactions in general and combustion processes in particular. While fossil fuels remain the most important primary energy carriers, alternative fuels gain in importance. Usually, these fuels contain significant amounts of oxygen, nitrogen and sulphur, leading to different reaction pathways than in the established combustion of hydrocarbons. In order to minimize the formation of pollutants and hazardous compounds (soot, CO, NO_{x}) and increase efficiency, a deeper understanding of these reaction processes is essential. Optical measurements, in particular Cavity Ring-Down Spectroscopy (CRDS) and Laser Induced Fluorescence spectroscopy (LIF), have proven to be well suited for quantitative radical measurements in flames (e.g. OH, ^1CH_2, C_2, HCO). Both techniques provide high sensitivity and selectivity. Our revised experimental setup is designed for quasi-simultaneous measurements, combining the positive features of both complementary techniques. In addition, invasive methods like mass-spectrometry are performed in order to gain a complete understanding of the flame species. In this contribution, we will focus on the quantitative determination of important minor species such as CN, NH_2, CH and formaldehyde in low-pressure flat flames. In addition to investigations of flames with hydrocarbon fuels, we present the first optical measurements in morpholine- and ethylamine-flames. Aim of these measurements is to study the conversion of fuel nitrogen to NO_{x}. Experimental results will be compared with numerical CHEMKIN-II simulations.

  1. Photodeamination Reaction Mechanism in Aminomethyl p-Cresol Derivatives: Different Reactivity of Amines and Ammonium Salts.

    Škalamera, Đani; Bohne, Cornelia; Landgraf, Stephan; Basarić, Nikola

    2015-11-01

    Derivatives of p-cresol 1-4 were synthesized, and their photochemical reactivity, acid-base, and photophysical properties were investigated. The photoreactivity of amines 1 and 3 is different from that for the corresponding ammonium salts 2 and 4. All compounds have low fluorescence quantum yields because the excited states undergo deamination reactions, and for all cresols the formation of quinone methides (QMs) was observed by laser flash photolysis. The reactivity observed is a consequence of the higher acidity of the S1 states of these p-cresols and the ability for excited-state intramolecular proton transfer (ESIPT) to occur in the case of 1 and 3, but not for salts 2 and 4. In aqueous solvent, deamination depends largely on the prototropic form of the molecule. The most efficient deamination takes place when monoamine is in the zwitterionic form (pH 9-11) or diamine is in the monocationic form (pH 7-9). QM1, QM3, and QM4 react with nucleophiles, and QM1 exhibits a shorter lifetime when formed from 1 (τ in CH3CN = 5 ms) than from 2 (τ in CH3CN = 200 ms) due to the reaction with eliminated dimethylamine, which acts as a nucleophile in the case of QM1. Bifunctional QM4 undergoes two types of reactions with nucleophiles, giving adducts or new QM species. The mechanistic diversity uncovered is of significance to biological systems, such as for the use of bifunctional QMs to achieve DNA cross-linking. PMID:26461794

  2. The mechanism of the reaction B10 (d,p) B11 at low deuteron energies

    Excitation functions and angular distributions were measured for the four most energetic proton groups from the reaction B10 (d,p) B11 in the deuteron energy range Ed = 0.8 to 2.4 MeV. The excitation functions for all the measured groups showed no noticeable resonance structure. Spectroscopic factors for the states at 0.00 and 4.46 MeV of B11 were extracted from a DWBA analysis of the angular distributions. The average values of the spectroscopic factors were compared with those predicted theoretically. (orig.)

  3. Electron spin interactions in chemistry and biology fundamentals, methods, reactions mechanisms, magnetic phenomena, structure investigation

    Likhtenshtein, Gertz

    2016-01-01

    This book presents the versatile and pivotal role of electron spin interactions in nature. It provides the background, methodologies and tools for basic areas related to spin interactions, such as spin chemistry and biology, electron transfer, light energy conversion, photochemistry, radical reactions, magneto-chemistry and magneto-biology. The book also includes an overview of designing advanced magnetic materials, optical and spintronic devices and photo catalysts. This monograph appeals to scientists and graduate students working in the areas related to spin interactions physics, biophysics, chemistry and chemical engineering.

  4. Reaction mechanisms in massive nuclei collisions and perspectives for synthesis of heavier superheavy elements

    We discuss a hardship in synthesis of heaviest super heavy elements in massive nuclei reactions due to the hindrance to complete fusion of reacting nuclei caused on the onset of quasifission process which strongly competes with complete fusion and due to the strong increase of fission yields along the de-excitation cascade of the compound nucleus in comparison with the evaporation residue formation. The hindrance to formation of compound nucleus and evaporation residue is determined by the characteristic of the entrance channel. (authors)

  5. Photon absorption mechanism in the 4He(γ, npp)n reaction

    We measured the 4He(γ, npp)n reaction in a kinematically complete way for the first time using the large-acceptance TAGX spectrometer and tagged photons at Eγ = 135-455 MeV. The momentum and angular distributions of the nucleons are explained by assuming that photons are absorbed either on the two-nucleon systems (np and pp) or on the three nucleon system (npp). The data can not be reproduced well by the photon absorption on the np system only. (author)

  6. Nuclear excitations and reaction mechanisms: a research proposal (renewal) and report of progress

    Research progress is reported on the following subjects: (1) diamagnetism, gauge transformations and sum rules, (2) quantal motion in an electric field, (3) a theorem concerning quadrupole absorption and scattering of photons, (4) excitation of natural parity states by Raman scattering in nuclei, (5) retarded E1 transitions and isoscaler giant dipole resonances, (6) low energy photon scattering from nuclei, (7) few-body models of nuclear reactions, (8) three- and four-nucleon configuration space calculations, (9) time-dependent few-body calculations, (10) atomic and molecular structure calculations, (11) bound state approximations, (12) extended Faddeev theory, (13) configuration-space techniques, and (14) time-dependent approach to scattering problems

  7. Proposed chemical mechanisms leading to secondary organic aerosol in the reactions of aliphatic amines with hydroxyl and nitrate radicals

    Price, Derek J.; Clark, Christopher H.; Tang, Xiaochen; Cocker, David R.; Purvis-Roberts, Kathleen L.; Silva, Philip J.

    2014-10-01

    The presence and importance of amines in the atmosphere, including aliphatic amines, continues to gain more attention. The atmospheric reaction mechanisms of these amines with key atmospheric radicals are important to predict both daytime and nighttime atmospheric chemistry. While previous studies have focused on the production of amine salts, this analysis looks at the importance of peroxy radical reactions to the formation of secondary organic aerosol. Atmospheric oxidation mechanisms are presented to explain the observed chemistry. A series of environmental chamber experiments were conducted in which aliphatic tertiary and secondary amines were reacted with either hydroxyl radical (OH) or nitrate radical (NO3). Chemical composition of the aerosol products was obtained with a High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and a Particle Into Liquid Sampler Time of Flight Mass Spectrometer (PILS-ToF-MS), while the chemical composition of the gas-phase products was obtained with a Selected Ion Flow Tube Mass Spectrometer (SIFT-MS). A number of aerosol-phase mass spectra showed highly oxidized fragments at a much higher molecular weight (MW) than the amine precursor. It is proposed that these larger compounds are oligomers formed through peroxy radical reactions with hydrogen rearrangement. Another reaction pathway observed was the formation of amine salts. The relative importance of each pathway to the overall production of aerosol is found to be dependent on the type of amine and oxidant. For example, the oligomers were observed in the tertiary methyl amines, while the formation of amine salts was more prevalent in the secondary and tertiary ethyl amines.

  8. Reactions of clofibric acid with oxidative and reductive radicals—Products, mechanisms, efficiency and toxic effects

    The degradation of clofibric acid induced by hydroxyl radical, hydrated electron and O2−∙/HO2∙ reactive species was studied in aqueous solutions. Clofibric acid was decomposed more effectively by hydroxyl radical than by hydrated electron or O2−∙/HO2∙. Various hydroxylated, dechlorinated and fragmentation products have been identified and quantified. A new LC–MS method was developed based on 18O isotope labeling to follow the formation of hydroxylated derivatives of clofibric acid. Possible degradation pathways have been proposed. The overall degradation was monitored by determination of sum parameters like COD, TOC and AOX. It was found that the organic chlorine degrades very effectively prior to complete mineralization. After the treatment no toxic effect was found according to Vibrio fischeri tests. However, at early stages some of the reaction products were more harmful than clofibric acid. - Highlights: • Clofibric acid is effectively degraded by OH radical. • Main primary and secondary products are hydroxylated and dihydroxylated phenyl type derivatives of clofibric acid. • In air saturated aqueous solutions O2 plays an important role in decomposition of the aromatic structure. • A new LC–MS method with 18O-labeling was developed. • Early stage reaction products are more toxic to bacteria Vibrio fischeri than clofibric acid

  9. Polyoxymetalate liquid-catalyzed polyol fuel cell and the related photoelectrochemical reaction mechanism study

    Wu, Weibing; Liu, Wei; Mu, Wei; Deng, Yulin

    2016-06-01

    A novel design of liquid catalyzed fuel cell (LCFC), which uses polyoxometalates (POMs) as the photocatalyst and charge carrier has been reported previously. In this paper, the adaptability of biomass fuels (e.g., glycerol and glucose) to the LCFC and corresponding cell performance were studied in detail here. An interesting finding that greatly differs from conventional fuel cell is that high molecular weight fuels rather than small molecule fuels (e.g., methanol and ethylene glycol) are favored by the novel LCFC with respect to the power densities. The power output of LCFC strongly depends on the number and structure of hydroxyl groups in the biomass fuels. The evidence of UV-Vis and 1H NMR spectra shows that the preassociation between POM and alcohol fuels, which determines the photoelectrochemical reaction pathway of POM, is enhanced as the number of hydroxyl increases. Experimental results also demonstrate that more hydroxyl groups in the molecules lead to faster photoelectrochemical reaction between POM and fuels, higher reduction degree of POM, and further higher power output of LCFC. Our study reveals that biomass-based polyhydroxyl compounds such as starch, hemicellulose and cellulose are potential high-performance fuels for LCFC.

  10. Transmission electron microscopy study of the reaction mechanisms involved in the carbothermal reduction of anatase

    The carbothermal reduction of anatase in titanium oxycarbide was studied by transmission electron microscopy (TEM). This study emphasizes that the reaction proceeds through complex solid–gas equilibria involving three main steps. During the first step, the carbon-monoxide-enriched atmosphere prevailing within the furnace provokes the direct transformation of anatase into the Magnéli phase. This transformation is accompanied by abnormal oxide grain growth showing a high number of stacking defects. The ordering tendency of such defects and their progressive increasing density lead to the final Ti3O5 compound. The second step of the reaction concerns the destabilization of Ti3O5 and carbon black in a high pCO atmosphere to form the oxycarbide. The titanium oxycarbide (TixOyCz) nucleates in the carbon black aggregates, giving rise to a first generation of defect-free faceted crystals (automorphous habit) characterized by a constant chemical composition. During the third step, Ti3O5 is missing and the primary carbide enters a maturation step characterized by carbon enrichment, attested by an increase in its cell parameter. This third step is characterized by the recrystallization phenomenon of the primary oxycarbide into the secondary one with an abrupt change in stoichiometry. The latter is characterized by rounded crystals (xenomorphous habit) bearing either a high density of dislocations or geometrical internal porosity linked to the migration of vacancies through the Kirkendall effect. Its further enrichment in carbon is assumed to be assisted by dislocation motion

  11. Identification of noncollagenous sites encoding specific interactions and quaternary assembly of alpha 3 alpha 4 alpha 5(IV) collagen: implications for Alport gene therapy.

    Kang, Jeong Suk; Colon, Selene; Hellmark, Thomas; Sado, Yoshikazu; Hudson, Billy G; Borza, Dorin-Bogdan

    2008-12-12

    Defective assembly of alpha 3 alpha 4 alpha 5(IV) collagen in the glomerular basement membrane causes Alport syndrome, a hereditary glomerulonephritis progressing to end-stage kidney failure. Assembly of collagen IV chains into heterotrimeric molecules and networks is driven by their noncollagenous (NC1) domains, but the sites encoding the specificity of these interactions are not known. To identify the sites directing quaternary assembly of alpha 3 alpha 4 alpha 5(IV) collagen, correctly folded NC1 chimeras were produced, and their interactions with other NC1 monomers were evaluated. All alpha1/alpha 5 chimeras containing alpha 5 NC1 residues 188-227 replicated the ability of alpha 5 NC1 to bind to alpha3NC1 and co-assemble into NC1 hexamers. Conversely, substitution of alpha 5 NC1 residues 188-227 by alpha1NC1 abolished these quaternary interactions. The amino-terminal 58 residues of alpha3NC1 encoded binding to alpha 5 NC1, but this interaction was not sufficient for hexamer co-assembly. Because alpha 5 NC1 residues 188-227 are necessary and sufficient for assembly into alpha 3 alpha 4 alpha 5 NC1 hexamers, whereas the immunodominant alloantigenic sites of alpha 5 NC1 do not encode specific quaternary interactions, the findings provide a basis for the rational design of less immunogenic alpha 5(IV) collagen constructs for the gene therapy of X-linked Alport patients. PMID:18930919

  12. The kinetics and mechanism of the reaction of uranium(VI) with 8-quinolinol and 8-hydroxy-5-quinolinesulfonic acid

    The kinetics of the reaction of uranium(VI) with 8-quinolinol and 8-hydroxy-5-quinolinesulfonate under the conditions of 1:1 chelate formation in the pH range 3.6-4.6 at different temperatures (20-30degC) and ionic strength I = 0.1 moldm-3 (KNO3) have been studied. A dual path mechanism involving both UO2(aq)2+ and UO2(OH)(aq)+ and the partially deprotonated ligand (LH, LH-) is consistent under the experimental conditions. The different rate constants under the condition of equilibrium have been determined. The results conform to kobs/B = k1[H+] + k2Kh; where B = (1/Q) + Ka(1)TU / ([H+] + Ka(1)) (Kh + [H+]); Kh = hydrolysis constant of UO2(aq)2+; Ka(1) = first deprotonation constant of the ligand, LH2 (charges are omitted); k1 and k2 are the second order forward rate constants of UO2(aq)2+ and UO2(OH)(aq)+ respectively and Q is the equilibrium constant of the reaction, UO22+ + LH ↔ UO2L+ + H+, where LH represents the partially deprotonated form of the ligand, 8-quinolinol and a similar reaction occurs for deprotonated 8-hydroxy-5-quinolinesulfonate (LH-). Thermodynamic parameters for each of the steps have been determined. The results have been compared with those of recent findings in the interaction of cerium(VI) and iron(III) with these ligands. UO2(aq)2+ has been argued to react through a dissociative interchange (Id) mechanism and its characteristic water exchange rate has been found as a rough estimate. Similarly for UO2(OH)(aq)+, a dissociative mechanism has been speculated. (author)

  13. Reaction mechanism of Ru(II) piano-stool complexes: umbrella sampling QM/MM MD study.

    Futera, Zdeněk; Burda, Jaroslav V

    2014-07-15

    Biologically relevant interactions of piano-stool ruthenium(II) complexes with ds-DNA are studied in this article by hybrid quantum mechanics-molecular mechanics (QM/MM) computational technique. The whole reaction mechanism is divided into three phases: (i) hydration of the [Ru(II) (η(6) -benzene)(en)Cl](+) complex, (ii) monoadduct formation between the resulting aqua-Ru(II) complex and N7 position of one of the guanines in the ds-DNA oligomer, and (iii) formation of the intrastrand Ru(II) bridge (cross-link) between two adjacent guanines. Free energy profiles of all the reactions are explored by QM/MM MD umbrella sampling approach where the Ru(II) complex and two guanines represent a quantum core, which is described by density functional theory methods. The combined QM/MM scheme is realized by our own software, which was developed to couple several quantum chemical programs (in this study Gaussian 09) and Amber 11 package. Calculated free energy barriers of the both ruthenium hydration and Ru(II)-N7(G) DNA binding process are in good agreement with experimentally measured rate constants. Then, this method was used to study the possibility of cross-link formation. One feasible pathway leading to Ru(II) guanine-guanine cross-link with synchronous releasing of the benzene ligand is predicted. The cross-linking is an exergonic process with the energy barrier lower than for the monoadduct reaction of Ru(II) complex with ds-DNA. PMID:24865949

  14. Study of Reaction Mechanism in the Interaction 86 MeV/A $^{12}$C with Heavy Targets

    2002-01-01

    Using the thin target-thin catcher techniques and the off-line analysis of the activities induced in the irradiated foils by means of singles and coincidences spectra recorded with Ge(Li) @g-rays and Si X-rays detectors, we will measure: 1) The target fragment mass and charge distribution from the interact 2) 86 MeV/A |1|2C with silver, tin and gold. 3) The target fragment average kinetic energy. 4) The target fragment angular and differential kinetic energy distributions. These measurements should allow us to better understand the heavy ion reaction mechanisms at intermediate energy.

  15. Shape-Controlled Synthesis and Related Growth Mechanism of Pb(OH)2 Nanorods by Solution-Phase Reaction

    We present a simple method to synthesize Pb(OH)2 nanorods by solution-phase reaction. Rod-like lead hydroxide precipitates are obtained by mixing lead nitrate with a concentration of about 0.01 M and potassium hydroxide with concentration of about 0.03 M in an aqueous solution. Sodium chloride as an additive is premixed with the lead nitrate aqueous solution. The presence of chloride ions in the precursor solution results in the rod-like morphology of lead hydroxide precipitates. The growth mechanism of the lead hydroxide nanorods is discussed

  16. Apparent anti-Woodward-Hoffmann addition to a nickel bis(dithiolene) complex: the reaction mechanism involves reduced, dimetallic intermediates.

    Dang, Li; Shibl, Mohamed F; Yang, Xinzheng; Harrison, Daniel J; Alak, Aiman; Lough, Alan J; Fekl, Ulrich; Brothers, Edward N; Hall, Michael B

    2013-04-01

    Nickel dithiolene complexes have been proposed as electrocatalysts for alkene purification. Recent studies of the ligand-based reactions of Ni(tfd)2 (tfd = S2C2(CF3)2) and its anion [Ni(tfd)2](-) with alkenes (ethylene and 1-hexene) showed that in the absence of the anion, the reaction proceeds most rapidly to form the intraligand adduct, which decomposes by releasing a substituted dihydrodithiin. However, the presence of the anion increases the rate of formation of the stable cis-interligand adduct, and decreases the rate of dihydrodithiin formation and decomposition. In spite of both computational and experimental studies, the mechanism, especially the role of the anion, remained somewhat elusive. We are now providing a combined experimental and computational study that addresses the mechanism and explains the role of the anion. A kinetic study (global analysis) for the reaction of 1-hexene is reported, which supports the following mechanism: (1) reversible intraligand addition, (2) oxidation of the intraligand addition product prior to decomposition, and (3) interligand adduct formation catalyzed by Ni(tfd)2(-). Density functional theory (DFT) calculations were performed on the Ni(tfd)2/Ni(tfd)2(-)/ethylene system to shed light on the selectivity of adduct formation in the absence of anion and on the mechanism in which Ni(tfd)2(-) shifts the reaction from intraligand addition to interligand addition. Computational results show that in the neutral system the free energy of activation for intraligand addition is lower than that for interligand addition, in agreement with the experimental results. The computations predict that the anion enhances the rate of the cis-interligand adduct formation by forming a dimetallic complex with the neutral complex. The [(Ni(tfd)2)2](-) dimetallic complex then coordinates ethylene and isomerizes to form a Ni,S-bound ethylene complex, which then rapidly isomerizes to the stable interligand adduct but not to the intraligand adduct

  17. Hydrogenation of n-butyraldehyde on copper-containing catalysts. III. Isotope investigation of the reaction mechanism

    The mechanism of the hydrogenation of n-butyraldehyde on a nickel-promoted copper-zinc-aluminum-calcium catalyst at 120-200 degree C was investigated by the isotope method using deuterium. Analysis of the mass spectra and the PMR spectra of the products of the reactions of deuteration and isotope exchange show that isotope in dissociatively adsorbed form is added directly at the C=O bond of the adsorbed aldehyde, and not at the C=C bond of the enol form

  18. Anaerobic reductive dechlorination of tetrachloroethene: how can dual Carbon-Chlorine isotopic measurements help elucidating the underlying reaction mechanism?

    Badin, Alice; Buttet, Géraldine; Maillard, Julien; Holliger, Christof; Hunkeler, Daniel

    2014-05-01

    Chlorinated ethenes (CEs) such as tetrachloroethene (PCE) are common persistent groundwater contaminants. Among clean-up strategies applied to sites affected by such pollution, bioremediation has been considered with a growing interest as it represents a cost-effective, environmental friendly approach. This technique however sometimes leads to an incomplete and slow biodegradation of CEs resulting in an accumulation of toxic metabolites. Understanding the reaction mechanisms underlying anaerobic reductive dechlorination would thus help assessing PCE biodegradation in polluted sites. Stable isotope analysis can provide insight into reaction mechanisms. For chlorinated hydrocarbons, carbon (C) and chlorine (Cl) isotope data (δ13C and δ37Cl) tend to show a linear correlation with a slope (m ≡ ɛC/ɛCl) characteristic of the reaction mechanism [1]. This study hence aims at exploring the potential of a dual C-Cl isotope approach in the determination of the reaction mechanisms involved in PCE reductive dechlorination. C and Cl isotope fractionation were investigated during anaerobic PCE dechlorination by two bacterial consortia containing members of the Sulfurospirillum genus. The specificity in these consortia resides in the fact that they each conduct PCE reductive dechlorination catalysed by one different reductive dehalogenase, i.e. PceADCE which yields trichloroethene (TCE) and cis-dichloroethene (cDCE), and PceATCE which yields TCE only. The bulk C isotope enrichment factors were -3.6±0.3 o for PceATCE and -0.7±0.1o for PceADCE. The bulk Cl isotope enrichment factors were -1.3±0.2 o for PceATCE and -0.9±0.1 o for PceADCE. When applying the dual isotope approach, two m values of 2.7±0.1 and 0.7±0.2 were obtained for the reductive dehalogenases PceATCE and PceADCE, respectively. These results suggest that PCE can be degraded according to two different mechanisms. Furthermore, despite their highly similar protein sequences, each reductive dehalogenase seems

  19. Photochemical generation of a primary vinyl cation from (E)-bromostyrene: Mechanisms of formation and reaction

    Gronheid, R.; Zuilhof, H.; Hellings, M.G.

    2003-01-01

    The photochemistry of (E)-bromostyrene was investigated to determine the nature of the product-forming intermediates and to clarify the mechanism of formation of vinylic cations and vinylic radicals. Both a cation- and a radical-derived product are formed, and the ionic origin of the former product

  20. Energy transfer mechanisms in photobiological reactions. Progress report, 1 August 1976--31 July 1977

    Spikes, J.D.

    1977-07-31

    Progress is reported on the following studies: chemical structure of biomolecules and mechanisms of their sensitized photo-oxidation; relationships between the structure and photosensitizing efficiencies of porphyrins; effects of photodynamic treatment on mammalian tendons; and sensitized photo-oxidation of substituted uracils, methionine, other amino acids, and horse-radish peroxidase. (HLW)

  1. Solid-state reactions during mechanical milling of Fe-Al under nitrogen atmosphere

    Jirásková, Yvonna; Buršík, Jiří; Čížek, J.; Jančík, D.

    2013-01-01

    Roč. 568, AUG (2013), s. 106-111. ISSN 0925-8388 R&D Projects: GA ČR(CZ) GAP108/11/1350 Institutional support: RVO:68081723 Keywords : milling * mechanical alloying * Mössbauer phase analysis * Fe-Al alloy * microstructure Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.726, year: 2013

  2. Reaction mechanisms of fast neutrons on stable Mo isotopes below 21 MeV

    Reimer, P.; Avrigeanu, V.; Chuvaev, S. V.; Filatenkov, A. A.; Glodarin, T.; de Koning, A; Plompen, A. J. M.; Qaim, S. M.; Smith, D. L.; Weigmann, H.

    2005-01-01

    A large number of new measurements with the activation technique were performed for (n,2n) and neutron-induced Delta Z=1,2 reaction cross sections on the stable molybdenum isotopes in the energy range from 13.5 to 21 MeV. First results were obtained for the Mo-92(n,2n)Mo-91(m),Mo-92(n,alpha)Zr-89(m),Mo-94(n,2n)Mo-93(m),Mo-95(n,p)Nb-95(m),Mo-96(n,p)Nb-96,Mo-96(n,x)Nb-95(m), Mo-97(n,p)Nb-97, Mo-97(n,p)Nb-97(m), Mo-97(n,x)Nb-96, Mo-98(n,p)Nb-98(m), Mo-98(n,x)Nb-97, Mo-98(n,x)Nb-97(m), and Mo-100...

  3. Water mediated hydrogen abstraction mechanism in the radical reaction between HOSO and NO2

    Lesar, Antonija; Tušar, Simona

    2016-05-01

    The effect of water molecules on the direct hydrogen abstraction from HOSO by NO2 was investigated for the first time. Stationary points were located at the B3LYP/6-311+G(2df,2pd) and CCSD/aug-cc-pVDZ levels of theory whereas energetics was further improved by CBS-QB3 and G4 composite methods. The fractions of hydrated radical complexes were estimated in order to assess atmospheric relevance of the title reaction. The energy barrier of the water mediated process becomes negligible. The formations of post-reactive complexes from pre-reactive complexes are energetically very favorable and the processes are spontaneous suggesting that they should be very feasible under atmospheric conditions.

  4. Atomistic Conversion Reaction Mechanism of WO3 in Secondary Ion Batteries of Li, Na, and Ca.

    He, Yang; Gu, Meng; Xiao, Haiyan; Luo, Langli; Shao, Yuyan; Gao, Fei; Du, Yingge; Mao, Scott X; Wang, Chongmin

    2016-05-17

    Intercalation and conversion are two fundamental chemical processes for battery materials in response to ion insertion. The interplay between these two chemical processes has never been directly seen and understood at atomic scale. Here, using in situ HRTEM, we captured the atomistic conversion reaction processes during Li, Na, Ca insertion into a WO3 single crystal model electrode. An intercalation step prior to conversion is explicitly revealed at atomic scale for the first time for Li, Na, Ca. Nanoscale diffraction and ab initio molecular dynamic simulations revealed that after intercalation, the inserted ion-oxygen bond formation destabilizes the transition-metal framework which gradually shrinks, distorts and finally collapses to an amorphous W and Mx O (M=Li, Na, Ca) composite structure. This study provides a full atomistic picture of the transition from intercalation to conversion, which is of essential importance for both secondary ion batteries and electrochromic devices. PMID:27071488

  5. The efficiency of self-phoretic propulsion mechanisms with surface reaction heterogeneity.

    Kreissl, Patrick; Holm, Christian; de Graaf, Joost

    2016-05-28

    We consider the efficiency of self-phoretic colloidal particles (swimmers) as a function of the heterogeneity in the surface reaction rate. The set of fluid, species, and electrostatic continuity equations is solved analytically using a linearization and numerically using a finite-element method. To compare spherical swimmers of different size and with heterogeneous catalytic conversion rates, a "swimmer efficiency" functional η is introduced. It is proven that in order to obtain maximum swimmer efficiency, the reactivity has to be localized at the pole(s). Our results also shed light on the sensitivity of the propulsion speed to details of the surface reactivity, a property that is notoriously hard to measure. This insight can be utilized in the design of new self-phoretic swimmers. PMID:27250326

  6. Mechanism for the stabilization of protein clusters above the solubility curve: the role of non-ideal chemical reactions

    Lutsko, James F

    2016-01-01

    Dense protein clusters are known to play an important role in nucleation of protein crystals from dilute solutions. While these have generally been thought to be formed from a metastable phase, the observation of similar, if not identical, clusters above the critical point for the dilute-solution/strong-solution phase transition has thrown this into doubt. Furthermore, the observed clusters are stable for relatively long times. Because protein aggregation plays an important role in some pathologies, understanding the nature of such clusters is an important problem. One mechanism for the stabilization of such structures was proposed by Pan, Vekilov and Lubchenko and was investigated using a DDFT model which confirmed the viability of the model. Here, we revisit that model and incorporate additional physics in the form of state-dependent reaction rates. We show by a combination of numerical results and general arguments that the state-dependent rates disrupt the stability mechanism. Finally, we argue that the s...

  7. Polymerization-induced phase separation in polyether-sulfone modified epoxy resin systems: effect of curing reaction mechanism

    2007-01-01

    Polyethersulfone (PES)-modified epoxy systems with stepwise reaction were studied throughout the entire curing process by using optical microscopes, time-resolved light scattering (TRLS), and a rheolometry instrument compared with that of chainwise polymerization. The results suggested that the phase separation process is mainly controlled by the diffusion of epoxy oligomers for stepwise mechanism system and by that of epoxy monomers for chainwise mechanism system. In case of high PES content (SPES-20%) light-scattering results showed a viscoelastic phase separation and the characteristic relaxation time of phase separation can be described well by the WLF equation. However, in the case of low PES content (SPES-14%) secondary phase separation phenomenon was observed by Optical Microscope and further demonstrated by rheological study.

  8. Sintering by SPS of ultrafine TiCxN1-x powders obtained using mechanically induced self sustaining reaction

    In this work high purity and nanometer character titanium carbonitride TiCxN1-x powders were obtained by mechanically induced self sustaining reaction (MSR) in a high-energy planetary ball mill, from a mixture of titanium with graphite or carbon nano fiber (CNFs) in a nitrogen atmosphere. A promising method for developing these materials is the coupling of the MSR with SPS sintering technique. The product is sintered at 1400 degree centigrade and 1700 degree centigrade, obtaining a completely dense monolithic ceramic (>99% t.d). In this work, the influence of SPS treatment and carbon precursor on material microstructures was studied and the main mechanical properties of the end material were evaluated. (Author) 21 refs.

  9. Study of the 20Ne+12C system reaction mechanisms for E(lab)20Ne=160MeV

    Coincidences between light particles (z8) are measured. The analysis of the single and coincident events shows that binary and sequentiel three body reactions, like the sequentiel break-up of the projectile, are responsible of the non relaxed part of the spectras. The relaxed component can be extracted and is compared with statistical model calculations obtained by Monte Carlo codes using the Hauser-Feshbach formalism. This prediction are consistent with the experiment for all the data. The slight discrepancies observed are reduced after a research on the parameter of the model. No evidences for incomplete fusion mechanism are observed. Even at this energy, fusion evaporation is the dominant mechanism for the system studied in this work

  10. Cure kinetics, morphologies, and mechanical properties of thermoplastic/MWCNT modified multifunctional glassy epoxies prepared via continuous reaction methods

    Cheng, Xiaole

    The primary goal of this dissertation is to develop a novel continuous reactor method to prepare partially cured epoxy prepolymers for aerospace prepreg applications with the aim of replacing traditional batch reactors. Compared to batch reactors, the continuous reactor is capable of solubilizing and dispersing a broad range of additives including thermoplastic tougheners, stabilizers, nanoparticles and curatives and advancing epoxy molecular weights and viscosities while reducing energy consumption. In order to prove this concept, polyethersulfone (PES) modified 4, 4'-diaminodiphenylsulfone (44DDS)/tetraglycidyl-4, 4'-diaminodiphenylmethane (TGDDM) epoxy prepolymers were firstly prepared using both continuous reactor and batch reactor methods. Kinetic studies confirmed the chain extension reaction in the continuous reactor is similar to the batch reactor, and the molecular weights and viscosities of prepolymers were readily controlled through reaction kinetics. Atomic force microscopy (AFM) confirmed similar cured network morphologies for formulations prepared from batch and continuous reactors. Additionally tensile strength, tensile modulus and fracture toughness analyses concluded mechanical properties of cured epoxy matrices produced from both reactors were equivalent. Effects of multifunctional epoxy compositions on thermoplastics phase-separated morphologies were systematically studied using a combination of AFM with nanomechanical mapping, spectroscopic and calorimetric techniques to provide new insights to tailor cured reaction induced phase separation (CRIPS) in multifunctional epoxy blend networks. Furthermore, how resultant crosslinked glassy polymer network and phase-separated morphologies correlated with mechanical properties are discussed in detail. Multiwall carbon nanotube (MWCNT)/TGDDM epoxy prepolymers were further prepared by combining the successful strategies for advancing epoxy chemistries and dispersing nanotubes using the continuous reactor

  11. Evolution mechanism of the interfacial reaction layers in the joints of diffusion bonded Mo and Ai foils

    LI Jinglong; ZHAO Fengkuan; YANG Weihua; XIONG Jiangtao; ZHANG Fusheng; Lü Xuechao

    2009-01-01

    Mo foil (10-20 μm in thickness) and Al foil (20-60 μm in thickness) were vacuum diffusion bonded at 600-640 ℃ under 20 MPa for 54 min-6 h. The joints were examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) to study the evolution mechanism of the reaction layers. The results show that Al atoms diffuse into Mo grain boundaries and form reaction products as Mo3Als, MoAl4, MoAl5 and MoAl12. The surface oxide film is eroded by the growths of the reaction products that plow into the lamellar texture of Mo grain boundaries. Mo3Al8 layer grows by "taking root" downwards and transforms into MoAl4 and MoAl5 phases upwards by absorbing Al atoms. MoAl12 layer grows up from MoAl5 layer in the same way. When the supplement of Al atoms ceases, MoAl12 transforms reversely into MoAl5 and MoAl3 into MoAl4 via the loss of Al atoms. However, MoAl4 continues to precipitate from Mo3Al8 layer. At last, there are MoAl4 and Mo3Al8 remained on the joint interface.

  12. Effect of ferrous/ferric ions molar ratio on reaction mechanism for hydrothermal synthesis of magnetite nanoparticles

    N Mizutani; T Iwasaki; S Watano; T Yanagida; H Tanaka; T Kawai

    2008-10-01

    Magnetite nanoparticles were prepared by hydrothermal synthesis under various initial ferrous/ferric molar ratios without adding any oxidizing and reducing agents in order to clarify effects of the molar ratio on the reaction mechanism for the formation of magnetite nanoparticles. The magnetite nanoparticles prepared were characterized by a scanning electron microscope, powder X-ray diffractometer, and superconducting quantum interference device (SQUID). At the molar ratio corresponding to the stoichiometric ratio in the synthesis reaction of magnetite from ferrous hydroxide and goethite, the nucleation of magnetite crystals progressed rapidly in an initial stage of the hydrothermal synthesis, resulting in formation of the magnetite nanoparticles having a smaller size and a lower crystallinity. On the other hand, at higher molar ratios, the particle size and crystallinity increased with increasing molar ratio because using surplus ferrous hydroxide the crystallites of magnetite nanoparticles grew up slowly under hydrothermal conditions according to the Schikorr reaction. The magnetite nanoparticles prepared under various molar ratios had good magnetic properties regardless of the molar ratio.

  13. Insights into Reaction Mechanism of Na2CO3 in Foaming Process of Cullet Powder

    Petersen, Rasmus Rosenlund; König, Jakob; Smedskjær, Morten Mattrup;

    prior to glass melting, the resulting decomposition product Na2O has strong impact on the melt viscosity, phase separation and crystallisation behaviour, and also mechanical properties of the final glass. This is relatively well understood in literature. In contrast, when Na2CO3 is added as a foaming...... in the glass, making the studied cullet powder potentially suitable for producing insulation materials. Finally, we discuss these results based on supplementary x-ray diffraction and scanning electron microscopy analyses....

  14. New approaches to chemical reaction mechanisms by means of radiation chemistry

    Since active species generated during radiolysis can be used as oxidative or reductive regents of various organic and inorganic compounds, radiation chemistry has been applied to wide range of research fields. We have studied charge-delocalization process in molecular systems, properties of intermediates in the excited states, mechanism of light emitting device, photo-catalyst for degradation of toxic compounds and so on by means of radiation chemistry. In the present paper, we summarize our recent research results. (author)

  15. Study on the Reaction Mechanism for Carbon Dioxide Reforming of Methane over supported Nickel Catalyst

    Ling QIAN; Zi Feng YAN

    2003-01-01

    The adsorption and dissociation of methane and carbon dioxide for reforming on nickelcatalyst were extensively investigated by TPSR and TPD experiments. It showed that thedecomposition of methane results in the formation of at least three kinds of surface carbon specieson supported nickel catalyst, while CO2 adsorbed on the catalyst weakly and only existed in onekind of adsorption state. Then the mechanism of interaction between the species dissociatedfrom CH4 and CO2 during reforming was proposed.

  16. The Al-Al3Ni Eutectic Reaction: Crystallography and Mechanism of Formation

    Fan, Yangyang; Makhlouf, Makhlouf M.

    2015-09-01

    The characteristics of the Al-Al3Ni eutectic structure are examined with emphasis on its morphology and crystallography. Based on these examinations, the mechanism of formation of this technologically important eutectic is postulated. It is found that a thin shell of α-Al forms coherently around each Al3Ni fiber. The excellent thermal stability of the Al-Al3Ni eutectic may be attributed to the presence of this coherent layer.

  17. Potential Mechanisms for IgG4 Inhibition of Immediate Hypersensitivity Reactions.

    James, Louisa K; Till, Stephen J

    2016-03-01

    IgG4 is the least abundant IgG subclass in human serum, representing less than 5 % of all IgG. Increases in IgG4 occur following chronic exposure to antigen and are generally associated with states of immune tolerance. In line with this, IgG4 is regarded as an anti-inflammatory antibody with a limited ability to elicit effective immune responses. Furthermore, IgG4 attenuates allergic responses by inhibiting the activity of IgE. The mechanism by which IgG4 inhibits IgE-mediated hypersensitivity has been investigated using a variety of model systems leading to two proposed mechanisms. First by sequestering antigen, IgG4 can function as a blocking antibody, preventing cross-linking of receptor bound IgE. Second IgG4 has been proposed to co-stimulate the inhibitory IgG receptor FcγRIIb, which can negatively regulate FcεRI signaling and in turn inhibit effector cell activation. Recent advances in our understanding of the structural features of human IgG4 have shed light on the unique functional and immunologic properties of IgG4. The aim of this review is to evaluate our current understanding of IgG4 biology and reassess the mechanisms by which IgG4 functions to inhibit IgE-mediated allergic responses. PMID:26892721

  18. Electrochemical oxidation of americium in nitric medium: study of reaction mechanisms

    One alternative selected by the CEA for partitioning minor actinides from aqueous solutions containing fission products is the selective extraction of oxidized americium. This is the SESAME process (Selective Extraction and Separation of Americium by Means of Electrolysis) aimed to convert americium to oxidation state (VI) and then extract it with a specific extractant of high valences. This paper presents the study of the electrochemical oxidation of americium in nitric medium which represents an important stage of the process. The reaction can be divided into two main steps: oxidation of americium (III) to americium (IV), and then of americium (IV) to americium (VI). For the first oxidation step, a ligand L is needed to stabilize the intermediate species americium (IV) which disproportionates in its free form into americium (III) and (V). Phospho-tungstate or silico-tungstate are appropriate ligands because they are stable in concentrated nitric acid and show a great affinity for metallic cations at oxidation state (IV) (Table 1 lists the stability constants of americium (IV) complexes). The presence of the lacunary poly-anion lowers the potential of the americium (IV) / americium (Ill) redox pair (see Figure 5 for the diagram of the apparent formal potential of americium versus ligand concentration). This makes it thermodynamically possible to oxidize americium (III) into americium (IV) at the anode of an electrolyzer in nitric acid. For the second oxidation step, a strong oxidant redox mediator, like silver (II), is needed to convert complexed americium at oxidation state (IV) to oxidation state (V). The AmVL complex is then hydrolyzed to yield americyle (V) aqua ion. A spectroscopic Raman study with 18O labeled species showed that the oxygen atoms of the americyle moiety came from water. This indicates that water hydrolyzes the americium (V) complex to produce americyle (V) aqua ion, AmO2+. This cation reacts with silver (Il) to give americyle (VI) ion. Figure

  19. Hydrolysis of Guanosine Triphosphate (GTP) by the Ras·GAP Protein Complex: Reaction Mechanism and Kinetic Scheme.

    Khrenova, Maria G; Grigorenko, Bella L; Kolomeisky, Anatoly B; Nemukhin, Alexander V

    2015-10-01

    Molecular mechanisms of the hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) and inorganic phosphate (Pi) by the Ras·GAP protein complex are fully investigated by using modern modeling tools. The previously hypothesized stages of the cleavage of the phosphorus-oxygen bond in GTP and the formation of the imide form of catalytic Gln61 from Ras upon creation of Pi are confirmed by using the higher-level quantum-based calculations. The steps of the enzyme regeneration are modeled for the first time, providing a comprehensive description of the catalytic cycle. It is found that for the reaction Ras·GAP·GTP·H2O → Ras·GAP·GDP·Pi, the highest barriers correspond to the process of regeneration of the active site but not to the process of substrate cleavage. The specific shape of the energy profile is responsible for an interesting kinetic mechanism of the GTP hydrolysis. The analysis of the process using the first-passage approach and consideration of kinetic equations suggest that the overall reaction rate is a result of the balance between relatively fast transitions and low probability of states from which these transitions are taking place. Our theoretical predictions are in excellent agreement with available experimental observations on GTP hydrolysis rates. PMID:26374425

  20. Design Paradigm Utilizing Reversible Diels-Alder Reactions to Enhance the Mechanical Properties of 3D Printed Materials.

    Davidson, Joshua R; Appuhamillage, Gayan A; Thompson, Christina M; Voit, Walter; Smaldone, Ronald A

    2016-07-01

    A design paradigm is demonstrated that enables new functional 3D printed materials made by fused filament fabrication (FFF) utilizing a thermally reversible dynamic covalent Diels-Alder reaction to dramatically improve both strength and toughness via self-healing mechanisms. To achieve this, we used as a mending agent a partially cross-linked terpolymer consisting of furan-maleimide Diels-Alder (fmDA) adducts that exhibit reversibility at temperatures typically used for FFF printing. When this mending agent is blended with commercially available polylactic acid (PLA) and printed, the resulting materials demonstrate an increase in the interfilament adhesion strength along the z-axis of up to 130%, with ultimate tensile strength increasing from 10 MPa in neat PLA to 24 MPa in fmDA-enhanced PLA. Toughness in the z-axis aligned prints increases by up to 460% from 0.05 MJ/m(3) for unmodified PLA to 0.28 MJ/m(3) for the remendable PLA. Importantly, it is demonstrated that a thermally reversible cross-linking paradigm based on the furan-maleimide Diels-Alder (fmDA) reaction can be more broadly applied to engineer property enhancements and remending abilities to a host of other 3D printable materials with superior mechanical properties. PMID:27299858