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Sample records for biochemical reaction kinetics

  1. The Chemical Master Equation Approach to Nonequilibrium Steady-State of Open Biochemical Systems: Linear Single-Molecule Enzyme Kinetics and Nonlinear Biochemical Reaction Networks

    Directory of Open Access Journals (Sweden)

    Lisa M. Bishop

    2010-09-01

    Full Text Available We develop the stochastic, chemical master equation as a unifying approach to the dynamics of biochemical reaction systems in a mesoscopic volume under a living environment. A living environment provides a continuous chemical energy input that sustains the reaction system in a nonequilibrium steady state with concentration fluctuations. We discuss the linear, unimolecular single-molecule enzyme kinetics, phosphorylation-dephosphorylation cycle (PdPC with bistability, and network exhibiting oscillations. Emphasis is paid to the comparison between the stochastic dynamics and the prediction based on the traditional approach based on the Law of Mass Action. We introduce the difference between nonlinear bistability and stochastic bistability, the latter has no deterministic counterpart. For systems with nonlinear bistability, there are three different time scales: (a individual biochemical reactions, (b nonlinear network dynamics approaching to attractors, and (c cellular evolution. For mesoscopic systems with size of a living cell, dynamics in (a and (c are stochastic while that with (b is dominantly deterministic. Both (b and (c are emergent properties of a dynamic biochemical network; We suggest that the (c is most relevant to major cellular biochemical processes such as epi-genetic regulation, apoptosis, and cancer immunoediting. The cellular evolution proceeds with transitions among the attractors of (b in a “punctuated equilibrium” manner.

  2. The chemical master equation approach to nonequilibrium steady-state of open biochemical systems: linear single-molecule enzyme kinetics and nonlinear biochemical reaction networks.

    Science.gov (United States)

    Qian, Hong; Bishop, Lisa M

    2010-01-01

    We develop the stochastic, chemical master equation as a unifying approach to the dynamics of biochemical reaction systems in a mesoscopic volume under a living environment. A living environment provides a continuous chemical energy input that sustains the reaction system in a nonequilibrium steady state with concentration fluctuations. We discuss the linear, unimolecular single-molecule enzyme kinetics, phosphorylation-dephosphorylation cycle (PdPC) with bistability, and network exhibiting oscillations. Emphasis is paid to the comparison between the stochastic dynamics and the prediction based on the traditional approach based on the Law of Mass Action. We introduce the difference between nonlinear bistability and stochastic bistability, the latter has no deterministic counterpart. For systems with nonlinear bistability, there are three different time scales: (a) individual biochemical reactions, (b) nonlinear network dynamics approaching to attractors, and (c) cellular evolution. For mesoscopic systems with size of a living cell, dynamics in (a) and (c) are stochastic while that with (b) is dominantly deterministic. Both (b) and (c) are emergent properties of a dynamic biochemical network; We suggest that the (c) is most relevant to major cellular biochemical processes such as epi-genetic regulation, apoptosis, and cancer immunoediting. The cellular evolution proceeds with transitions among the attractors of (b) in a "punctuated equilibrium" manner. PMID:20957107

  3. Biochemical toxicology studies of methomyl and its kinetic reaction with cholinesterase in rats

    International Nuclear Information System (INIS)

    The effect of the pesticide methomyl on acetylcholinesterase activities in brain and blood of male rats in vivo and the kinetics involved in their reaction in vitro were studied. Also, its effect on peroxidase action of catalase in vivo was studied using 14C- formate. The results showed that methomyl is a competitive inhibitor for acetylcholinesterase and the concentration levels that caused 50% inhibition of the enzyme activity were 2.1 x 10-2 M and 1.9 x 10-4 for brain and blood- Ache, respectively. The inhibition of acetylcholinesterase activity decreased to 67.5 % at the time of appearance of toxicity symptoms. The radioactivity eliminated in both the expired air and in urine was reduced

  4. Microfluidic Technology Platforms for Synthesizing, Labeling and Measuring the Kinetics of Transport and Biochemical Reactions for Developing Molecular Imaging Probes

    Energy Technology Data Exchange (ETDEWEB)

    Phelps, Michael E.

    2009-09-01

    for radiochemistry (macro to micro levels), biochemistry and biology to imaging principles, tracer kinetics, pharmacokinetics and biochemical assays. New generations of radiochemists will be immersed in the biochemistry and biology for which their labeled probes are being developed for assays of these processes. In this program engineers and radio-chemists integrate the principles of microfluidics and radiolabeling along with proper system design and chemistry rule sets to yield Synthesizers enabling biological and pharmaceutical scientists to develop diverse arrays of probes to pursue their interests. This progression would allow also radiochemists to focus on the further evolution of rapid, high yield synthetic reactions with new enabling technologies, rather than everyday production of radiotracers that should be done by technologists. The invention of integrated circuits in electronics established a platform technology that allowed an evolution of ideas and applications far beyond what could have been imagined at the beginning. Rather than provide a technology for the solution to a single problem, it is hoped that microfluidic radiochemistry will be an enabling platform technology for others to solve many problems. As part of this objective, another program goal is to commercialize the technologies that come from this work so that they can be provided to others who wish to use it.

  5. Propagation of kinetic uncertainties through a canonical topology of the TLR4 signaling network in different regions of biochemical reaction space

    Directory of Open Access Journals (Sweden)

    St Laurent Georges

    2010-03-01

    Full Text Available Abstract Background Signal transduction networks represent the information processing systems that dictate which dynamical regimes of biochemical activity can be accessible to a cell under certain circumstances. One of the major concerns in molecular systems biology is centered on the elucidation of the robustness properties and information processing capabilities of signal transduction networks. Achieving this goal requires the establishment of causal relations between the design principle of biochemical reaction systems and their emergent dynamical behaviors. Methods In this study, efforts were focused in the construction of a relatively well informed, deterministic, non-linear dynamic model, accounting for reaction mechanisms grounded on standard mass action and Hill saturation kinetics, of the canonical reaction topology underlying Toll-like receptor 4 (TLR4-mediated signaling events. This signaling mechanism has been shown to be deployed in macrophages during a relatively short time window in response to lypopolysaccharyde (LPS stimulation, which leads to a rapidly mounted innate immune response. An extensive computational exploration of the biochemical reaction space inhabited by this signal transduction network was performed via local and global perturbation strategies. Importantly, a broad spectrum of biologically plausible dynamical regimes accessible to the network in widely scattered regions of parameter space was reconstructed computationally. Additionally, experimentally reported transcriptional readouts of target pro-inflammatory genes, which are actively modulated by the network in response to LPS stimulation, were also simulated. This was done with the main goal of carrying out an unbiased statistical assessment of the intrinsic robustness properties of this canonical reaction topology. Results Our simulation results provide convincing numerical evidence supporting the idea that a canonical reaction mechanism of the TLR4

  6. Interfacial Reaction Kinetics

    OpenAIRE

    O'Shaughnessy, Ben; Vavylonis, Dimitrios

    1998-01-01

    We study irreversible A-B reaction kinetics at a fixed interface separating two immiscible bulk phases, A and B. We consider general dynamical exponent $z$, where $x_t\\sim t^{1/z}$ is the rms diffusion distance after time $t$. At short times the number of reactions per unit area, $R_t$, is {\\em 2nd order} in the far-field reactant densities $n_A^{\\infty},n_B^{\\infty}$. For spatial dimensions $d$ above a critical value $d_c=z-1$, simple mean field (MF) kinetics pertain, $R_t\\sim Q_b t n_A^{\\in...

  7. Modelling of biochemical reaction networks

    OpenAIRE

    Gloppen Jørgensen, Arne Gunnar

    2011-01-01

    This report investigates signalling in reaction kinetic networks. The main topic is signalling between a substance being controlled by another substance and how this can be related to control theory. Different types of so-called natural controllers are compared and certain properties are investigated. Natural controllers are models on how a catalyst enzyme controls, for example the concentration, of a substance. There are sixteen different combinations of signalling between these substanc...

  8. Chemical kinetics of gas reactions

    CERN Document Server

    Kondrat'Ev, V N

    2013-01-01

    Chemical Kinetics of Gas Reactions explores the advances in gas kinetics and thermal, photochemical, electrical discharge, and radiation chemical reactions. This book is composed of 10 chapters, and begins with the presentation of general kinetic rules for simple and complex chemical reactions. The next chapters deal with the experimental methods for evaluating chemical reaction mechanisms and some theories of elementary chemical processes. These topics are followed by discussions on certain class of chemical reactions, including unimolecular, bimolecular, and termolecular reactions. The rema

  9. Determination of Kinetic Parameters and Metal Ions in Urea-Urease System Based on the Biochemical Reaction Heat Induced Laser Beam Deflection

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    A new analytical method for the determination of urea-urease system based on biochemical reaction heat induced laser beam deflection is presented in this paper. With the method, the Michaelis constant (Km) of urease and apparent inhibition constant (Ki) of some metal ion inhibitors were measured respectively. This method was also used for the quantitative determination of metal ions with satisfactory result.

  10. Kinetics of Bio-Reactions

    DEFF Research Database (Denmark)

    Villadsen, John

    2015-01-01

    his chapter predicts the specific rates of reaction by means of a mathematical expression, the kinetics of the reaction. This expression can be derived through a mechanistic interpretation of an enzymatically catalyzed reaction, but it is essentially of empirical nature for cell reactions. The...... models can be used in mass balances for design of processes under process conditions not yet studied experimentally. The value of the predictive kinetic model depends on the quality of the experimental data on which the model is based, and well-founded kinetic models for enzyme reactions have a...... considerable predictive power. This is also true for cell reaction models, when the model is used in its proper context. The chapter first discusses the kinetics for enzymatically catalyzed reactions (“enzyme reactions”). The kinetics can be derived from a mechanistic model. Then, the chapter derives empirical...

  11. Reaction kinetics of polybutylene terephthalate polycondensation reaction

    NARCIS (Netherlands)

    Darda, P. J.; Hogendoorn, J. A.; Versteeg, G. F.; Souren, F.

    2005-01-01

    The kinetics of the forward polycondensation reaction of polybutylene terephthalate (PBT) has been investigated using thermogravimetric analysis (TGA). PBT - prepolymer with an initial degree of polymerization of 5.5 was used as starting material. The PBT prepolymer was prepared from dimethyl tereph

  12. Probabilistic sensitivity analysis of biochemical reaction systems

    OpenAIRE

    Zhang, Hong-Xuan; Dempsey, William P.; Goutsias, John

    2009-01-01

    Sensitivity analysis is an indispensable tool for studying the robustness and fragility properties of biochemical reaction systems as well as for designing optimal approaches for selective perturbation and intervention. Deterministic sensitivity analysis techniques, using derivatives of the system response, have been extensively used in the literature. However, these techniques suffer from several drawbacks, which must be carefully considered before using them in problems of systems biology. ...

  13. Kinetics of actinide complexation reactions

    International Nuclear Information System (INIS)

    Though the literature records extensive compilations of the thermodynamics of actinide complexation reactions, the kinetics of complex formation and dissociation reactions of actinide ions in aqueous solutions have not been extensively investigated. In light of the central role played by such reactions in actinide process and environmental chemistry, this situation is somewhat surprising. The authors report herein a summary of what is known about actinide complexation kinetics. The systems include actinide ions in the four principal oxidation states (III, IV, V, and VI) and complex formation and dissociation rates with both simple and complex ligands. Most of the work reported was conducted in acidic media, but a few address reactions in neutral and alkaline solutions. Complex formation reactions tend in general to be rapid, accessible only to rapid-scan and equilibrium perturbation techniques. Complex dissociation reactions exhibit a wider range of rates and are generally more accessible using standard analytical methods. Literature results are described and correlated with the known properties of the individual ions

  14. Simulation methods with extended stability for stiff biochemical Kinetics

    Directory of Open Access Journals (Sweden)

    Rué Pau

    2010-08-01

    Full Text Available Abstract Background With increasing computer power, simulating the dynamics of complex systems in chemistry and biology is becoming increasingly routine. The modelling of individual reactions in (biochemical systems involves a large number of random events that can be simulated by the stochastic simulation algorithm (SSA. The key quantity is the step size, or waiting time, τ, whose value inversely depends on the size of the propensities of the different channel reactions and which needs to be re-evaluated after every firing event. Such a discrete event simulation may be extremely expensive, in particular for stiff systems where τ can be very short due to the fast kinetics of some of the channel reactions. Several alternative methods have been put forward to increase the integration step size. The so-called τ-leap approach takes a larger step size by allowing all the reactions to fire, from a Poisson or Binomial distribution, within that step. Although the expected value for the different species in the reactive system is maintained with respect to more precise methods, the variance at steady state can suffer from large errors as τ grows. Results In this paper we extend Poisson τ-leap methods to a general class of Runge-Kutta (RK τ-leap methods. We show that with the proper selection of the coefficients, the variance of the extended τ-leap can be well-behaved, leading to significantly larger step sizes. Conclusions The benefit of adapting the extended method to the use of RK frameworks is clear in terms of speed of calculation, as the number of evaluations of the Poisson distribution is still one set per time step, as in the original τ-leap method. The approach paves the way to explore new multiscale methods to simulate (biochemical systems.

  15. Combustion kinetics and reaction pathways

    Energy Technology Data Exchange (ETDEWEB)

    Klemm, R.B.; Sutherland, J.W. [Brookhaven National Laboratory, Upton, NY (United States)

    1993-12-01

    This project is focused on the fundamental chemistry of combustion. The overall objectives are to determine rate constants for elementary reactions and to elucidate the pathways of multichannel reactions. A multitechnique approach that features three independent experiments provides unique capabilities in performing reliable kinetic measurements over an exceptionally wide range in temperature, 300 to 2500 K. Recent kinetic work has focused on experimental studies and theoretical calculations of the methane dissociation system (CH{sub 4} + Ar {yields} CH{sub 3} + H + Ar and H + CH{sub 4} {yields} CH{sub 3} + H{sub 2}). Additionally, a discharge flow-photoionization mass spectrometer (DF-PIMS) experiment is used to determine branching fractions for multichannel reactions and to measure ionization thresholds of free radicals. Thus, these photoionization experiments generate data that are relevant to both reaction pathways studies (reaction dynamics) and fundamental thermochemical research. Two distinct advantages of performing PIMS with high intensity, tunable vacuum ultraviolet light at the National Synchrotron Light Source are high detection sensitivity and exceptional selectivity in monitoring radical species.

  16. Chemical reaction network approaches to Biochemical Systems Theory.

    Science.gov (United States)

    Arceo, Carlene Perpetua P; Jose, Editha C; Marin-Sanguino, Alberto; Mendoza, Eduardo R

    2015-11-01

    This paper provides a framework to represent a Biochemical Systems Theory (BST) model (in either GMA or S-system form) as a chemical reaction network with power law kinetics. Using this representation, some basic properties and the application of recent results of Chemical Reaction Network Theory regarding steady states of such systems are shown. In particular, Injectivity Theory, including network concordance [36] and the Jacobian Determinant Criterion [43], a "Lifting Theorem" for steady states [26] and the comprehensive results of Müller and Regensburger [31] on complex balanced equilibria are discussed. A partial extension of a recent Emulation Theorem of Cardelli for mass action systems [3] is derived for a subclass of power law kinetic systems. However, it is also shown that the GMA and S-system models of human purine metabolism [10] do not display the reactant-determined kinetics assumed by Müller and Regensburger and hence only a subset of BST models can be handled with their approach. Moreover, since the reaction networks underlying many BST models are not weakly reversible, results for non-complex balanced equilibria are also needed. PMID:26363083

  17. Practical Enzyme Kinetics: A Biochemical Laboratory Experiment.

    Science.gov (United States)

    Rowe, H. Alan; Brown, Morris

    1988-01-01

    Describes an experiment that provides a fundamental understanding of the kinetics of the enzyme papain. Discusses background, materials, procedures and results. Mentions analogous experiments that can be conducted with enzymatic contact-lens cleaning solutions. (CW)

  18. Kinetics of heterogeneous catalytic reactions

    CERN Document Server

    Boudart, Michel

    2014-01-01

    This book is a critical account of the principles of the kinetics of heterogeneous catalytic reactions in the light of recent developments in surface science and catalysis science. Originally published in 1984. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase acc

  19. Mathematical treatment of isotopologue and isotopomer speciation and fractionation in biochemical kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Maggi, F.M.; Riley, W.J.

    2009-11-01

    We present a mathematical treatment of the kinetic equations that describe isotopologue and isotopomer speciation and fractionation during enzyme-catalyzed biochemical reactions. These equations, presented here with the name GEBIK (general equations for biochemical isotope kinetics) and GEBIF (general equations for biochemical isotope fractionation), take into account microbial biomass and enzyme dynamics, reaction stoichiometry, isotope substitution number, and isotope location within each isotopologue and isotopomer. In addition to solving the complete GEBIK and GEBIF, we also present and discuss two approximations to the full solutions under the assumption of biomass-free and enzyme steady-state, and under the quasi-steady-state assumption as applied to the complexation rate. The complete and approximate approaches are applied to observations of biological denitrification in soils. Our analysis highlights that the full GEBIK and GEBIF provide a more accurate description of concentrations and isotopic compositions of substrates and products throughout the reaction than do the approximate forms. We demonstrate that the isotopic effects of a biochemical reaction depend, in the most general case, on substrate and complex concentrations and, therefore, the fractionation factor is a function of time. We also demonstrate that inverse isotopic effects can occur for values of the fractionation factor smaller than 1, and that reactions that do not discriminate isotopes do not necessarily imply a fractionation factor equal to 1.

  20. Exact Results for Kinetics of Catalytic Reactions

    OpenAIRE

    Frachebourg, L.; Krapivsky, P. L.

    1995-01-01

    The kinetics of an irreversible catalytic reaction on substrate of arbitrary dimension is examined. In the limit of infinitesimal reaction rate (reaction-controlled limit), we solve the dimer-dimer surface reaction model (or voter model) exactly in arbitrary dimension $D$. The density of reactive interfaces is found to exhibit a power law decay for $D

  1. Turing-Hopf instability in biochemical reaction networks arising from pairs of subnetworks.

    Science.gov (United States)

    Mincheva, Maya; Roussel, Marc R

    2012-11-01

    Network conditions for Turing instability in biochemical systems with two biochemical species are well known and involve autocatalysis or self-activation. On the other hand general network conditions for potential Turing instabilities in large biochemical reaction networks are not well developed. A biochemical reaction network with any number of species where only one species moves is represented by a simple digraph and is modeled by a reaction-diffusion system with non-mass action kinetics. A graph-theoretic condition for potential Turing-Hopf instability that arises when a spatially homogeneous equilibrium loses its stability via a single pair of complex eigenvalues is obtained. This novel graph-theoretic condition is closely related to the negative cycle condition for oscillations in ordinary differential equation models and its generalizations, and requires the existence of a pair of subnetworks, each containing an even number of positive cycles. The technique is illustrated with a double-cycle Goodwin type model. PMID:22698892

  2. Reaction kinetics of isopropyl palmitate synthesis

    Institute of Scientific and Technical Information of China (English)

    Lili Fu; Yinge Bai; Gaozhi L; Denggao Jiang

    2015-01-01

    In this study, the kinetics of isopropyl palmitate synthesis including the reaction mechanism was studied based on the two-step noncatalytic method. The liquid-phase diffusion effect on the reaction process was eliminated by adjusting the stirring rate. The results showed that the two-step reaction followed a tetrahedral mechanism and conformed to second-order reaction kinetics. Nucleophilic attack on the carbonyl carbon afforded an intermedi-ate, containing a tetrahedral carbon center. The intermediate ultimately decomposed by elimination of the leav-ing group, affording isopropyl palmitate. The experimental data were analyzed at different temperatures by the integral method. The kinetic equations of the each step were deduced, and the activation energy and frequency factor were obtained. Experiments were performed to verify the feasibility of kinetic equations, and the result showed that the kinetic equations were reliable. This study could be very significant to both industrial application and determining the continuous production of isopropyl palmitate.

  3. Kinetic studies of elementary chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Durant, J.L. Jr. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    This program concerning kinetic studies of elementary chemical reactions is presently focussed on understanding reactions of NH{sub x} species. To reach this goal, the author is pursuing experimental studies of reaction rate coefficients and product branching fractions as well as using electronic structure calculations to calculate transition state properties and reaction rate calculations to relate these properties to predicted kinetic behavior. The synergy existing between the experimental and theoretical studies allow one to gain a deeper insight into more complex elementary reactions.

  4. Non-Markovian polymer reaction kinetics

    CERN Document Server

    Guérin, Thomas; Voituriez, Raphaël; 10.1038/NCHEM.1378

    2012-01-01

    Describing the kinetics of polymer reactions, such as the formation of loops and hairpins in nucleic acids or polypeptides, is complicated by the structural dynamics of their chains. Although both intramolecular reactions, such as cyclization, and intermolecular reactions have been studied extensively, both experimentally and theoretically, there is to date no exact explicit analytical treatment of transport-limited polymer reaction kinetics, even in the case of the simplest (Rouse) model of monomers connected by linear springs. We introduce a new analytical approach to calculate the mean reaction time of polymer reactions that encompasses the non-Markovian dynamics of monomer motion. This requires that the conformational statistics of the polymer at the very instant of reaction be determined, which provides, as a by-product, new information on the reaction path. We show that the typical reactive conformation of the polymer is more extended than the equilibrium conformation, which leads to reaction times sign...

  5. Hydrogen electrode reaction: A complete kinetic description

    International Nuclear Information System (INIS)

    The kinetic description of the hydrogen electrode reaction (HER) in the whole range of overpotentials (-0.2 < η (V) < 0.40) is presented. The Volmer-Heyrovsky-Tafel mechanism was solved considering simultaneously the following items: (i) the diffusional contribution of the molecular hydrogen from and towards the electrode surface, (ii) the forward and backward reaction rates of each elementary step and (iii) a Frumkin type adsorption for the reaction intermediate. In order to verify the descriptive capability of the kinetic expressions derived, an experimental study of the HER was carried out on a rotating platinum disc electrode in acid solution. From the correlation of these results the elementary kinetic parameters were evaluated and several aspects related to the kinetic mechanism were discussed. Finally, the use of these kinetic expressions to interpret results obtained on microelectrodes is also analysed

  6. Hydrogen electrode reaction: A complete kinetic description

    Energy Technology Data Exchange (ETDEWEB)

    Quaino, P.M. [Programa de Electroquimica Aplicada e Ingenieria Electroquimica (PRELINE), Facultad de Ingenieria Quimica, Universidad Nacional del Litoral, Santiago del Estero 2829, 3000 Santa Fe (Argentina); Gennero de Chialvo, M.R. [Programa de Electroquimica Aplicada e Ingenieria Electroquimica (PRELINE), Facultad de Ingenieria Quimica, Universidad Nacional del Litoral, Santiago del Estero 2829, 3000 Santa Fe (Argentina); Chialvo, A.C. [Programa de Electroquimica Aplicada e Ingenieria Electroquimica (PRELINE), Facultad de Ingenieria Quimica, Universidad Nacional del Litoral, Santiago del Estero 2829, 3000 Santa Fe (Argentina)]. E-mail: achialvo@fiqus.unl.edu.ar

    2007-09-15

    The kinetic description of the hydrogen electrode reaction (HER) in the whole range of overpotentials (-0.2 < {eta} (V) < 0.40) is presented. The Volmer-Heyrovsky-Tafel mechanism was solved considering simultaneously the following items: (i) the diffusional contribution of the molecular hydrogen from and towards the electrode surface, (ii) the forward and backward reaction rates of each elementary step and (iii) a Frumkin type adsorption for the reaction intermediate. In order to verify the descriptive capability of the kinetic expressions derived, an experimental study of the HER was carried out on a rotating platinum disc electrode in acid solution. From the correlation of these results the elementary kinetic parameters were evaluated and several aspects related to the kinetic mechanism were discussed. Finally, the use of these kinetic expressions to interpret results obtained on microelectrodes is also analysed.

  7. Chemical kinetics and reaction dynamics

    CERN Document Server

    Houston, Paul L

    2006-01-01

    This text teaches the principles underlying modern chemical kinetics in a clear, direct fashion, using several examples to enhance basic understanding. It features solutions to selected problems, with separate sections and appendices that cover more technical applications.Each chapter is self-contained and features an introduction that identifies its basic goals, their significance, and a general plan for their achievement. This text's important aims are to demonstrate that the basic kinetic principles are essential to the solution of modern chemical problems, and to show how the underlying qu

  8. Mean field interaction in biochemical reaction networks

    KAUST Repository

    Tembine, Hamidou

    2011-09-01

    In this paper we establish a relationship between chemical dynamics and mean field game dynamics. We show that chemical reaction networks can be studied using noisy mean field limits. We provide deterministic, noisy and switching mean field limits and illustrate them with numerical examples. © 2011 IEEE.

  9. SBMLsqueezer: A CellDesigner plug-in to generate kinetic rate equations for biochemical networks

    Directory of Open Access Journals (Sweden)

    Schröder Adrian

    2008-04-01

    Full Text Available Abstract Background The development of complex biochemical models has been facilitated through the standardization of machine-readable representations like SBML (Systems Biology Markup Language. This effort is accompanied by the ongoing development of the human-readable diagrammatic representation SBGN (Systems Biology Graphical Notation. The graphical SBML editor CellDesigner allows direct translation of SBGN into SBML, and vice versa. For the assignment of kinetic rate laws, however, this process is not straightforward, as it often requires manual assembly and specific knowledge of kinetic equations. Results SBMLsqueezer facilitates exactly this modeling step via automated equation generation, overcoming the highly error-prone and cumbersome process of manually assigning kinetic equations. For each reaction the kinetic equation is derived from the stoichiometry, the participating species (e.g., proteins, mRNA or simple molecules as well as the regulatory relations (activation, inhibition or other modulations of the SBGN diagram. Such information allows distinctions between, for example, translation, phosphorylation or state transitions. The types of kinetics considered are numerous, for instance generalized mass-action, Hill, convenience and several Michaelis-Menten-based kinetics, each including activation and inhibition. These kinetics allow SBMLsqueezer to cover metabolic, gene regulatory, signal transduction and mixed networks. Whenever multiple kinetics are applicable to one reaction, parameter settings allow for user-defined specifications. After invoking SBMLsqueezer, the kinetic formulas are generated and assigned to the model, which can then be simulated in CellDesigner or with external ODE solvers. Furthermore, the equations can be exported to SBML, LaTeX or plain text format. Conclusion SBMLsqueezer considers the annotation of all participating reactants, products and regulators when generating rate laws for reactions. Thus, for

  10. Kinetics of nitroxyl radical reactions

    International Nuclear Information System (INIS)

    Absolute rate-constants for the reaction of the nitroxyl free radicals TAN and TMPN with radiation-chemically-formed radicals and ions have been determined. k(TAN + X) (in M-1 sec-1) = 4.0 x 109 (for X =OH), 2.9 x 1010(esub(aq)-), 8.0 x 109 (H), 7.2 x 108 (CH2OH), 4.0 x 108 (CH3CHOH), 4.3 x 108 ((CH3)2COH), 2.8 x 108 (CH2(CH3)2COH), 5.9 x 107 (glucose radical), 4.0 x 108 (c-C5H9), and k(TMPN + X) = 3.4 x 109 (OH), 7.8 x 109 (esub(aq)-), 4.9 x 109 (H), 4.4 x 108 (CH2OH), 4.9 x 108 (CH3CHOH), 3.6 x 108 ((CH3)2COH), 1.5 x 108 (CH2(CH3)2COH), 4.9 x 107 (glucose radical), 4.3 x 108 (c-C5H9). Direct measurements by means of a pulse-radiolysis conductivity technique were based on the formation and destruction of charged species in these reactions within certain pH ranges. It is indicated that the radiosensitizing nitroxyles undergo both redox and addition reactions. (author)

  11. Modeling stochasticity in biochemical reaction networks

    Science.gov (United States)

    Constantino, P. H.; Vlysidis, M.; Smadbeck, P.; Kaznessis, Y. N.

    2016-03-01

    Small biomolecular systems are inherently stochastic. Indeed, fluctuations of molecular species are substantial in living organisms and may result in significant variation in cellular phenotypes. The chemical master equation (CME) is the most detailed mathematical model that can describe stochastic behaviors. However, because of its complexity the CME has been solved for only few, very small reaction networks. As a result, the contribution of CME-based approaches to biology has been very limited. In this review we discuss the approach of solving CME by a set of differential equations of probability moments, called moment equations. We present different approaches to produce and to solve these equations, emphasizing the use of factorial moments and the zero information entropy closure scheme. We also provide information on the stability analysis of stochastic systems. Finally, we speculate on the utility of CME-based modeling formalisms, especially in the context of synthetic biology efforts.

  12. Morphological, kinetic, membrane biochemical and genetic aspects of intestinal enteroplasticity

    Institute of Scientific and Technical Information of China (English)

    Laurie A Drozdowski; M Tom Clandinin; Alan BR Thomson

    2009-01-01

    The process of intestinal adaptation ("enteroplasticity") is complex and multifaceted. Although a number of trophic nutrients and non-nutritive factors have been identified in animal studies, successful, reproducible clinical trials in humans are awaited. Understanding mechanisms underlying this adaptive process may direct research toward strategies that maximize intestinal function and impart a true clinical benefit to patients with short bowel syndrome, or to persons in whom nutrient absorption needs to be maximized. In this review, we consider the morphological, kinetic and membrane biochemical aspects of enteroplasticity, focus on the importance of nutritional factors, provide an overview of the many hormones that may alter the adaptive process, and consider some of the possible molecular profiles. While most of the data is derived from rodent studies, wherever possible, the results of human studies of intestinal enteroplasticity are provided.

  13. Thermodynamically consistent Bayesian analysis of closed biochemical reaction systems

    Directory of Open Access Journals (Sweden)

    Goutsias John

    2010-11-01

    Full Text Available Abstract Background Estimating the rate constants of a biochemical reaction system with known stoichiometry from noisy time series measurements of molecular concentrations is an important step for building predictive models of cellular function. Inference techniques currently available in the literature may produce rate constant values that defy necessary constraints imposed by the fundamental laws of thermodynamics. As a result, these techniques may lead to biochemical reaction systems whose concentration dynamics could not possibly occur in nature. Therefore, development of a thermodynamically consistent approach for estimating the rate constants of a biochemical reaction system is highly desirable. Results We introduce a Bayesian analysis approach for computing thermodynamically consistent estimates of the rate constants of a closed biochemical reaction system with known stoichiometry given experimental data. Our method employs an appropriately designed prior probability density function that effectively integrates fundamental biophysical and thermodynamic knowledge into the inference problem. Moreover, it takes into account experimental strategies for collecting informative observations of molecular concentrations through perturbations. The proposed method employs a maximization-expectation-maximization algorithm that provides thermodynamically feasible estimates of the rate constant values and computes appropriate measures of estimation accuracy. We demonstrate various aspects of the proposed method on synthetic data obtained by simulating a subset of a well-known model of the EGF/ERK signaling pathway, and examine its robustness under conditions that violate key assumptions. Software, coded in MATLAB®, which implements all Bayesian analysis techniques discussed in this paper, is available free of charge at http://www.cis.jhu.edu/~goutsias/CSS%20lab/software.html. Conclusions Our approach provides an attractive statistical methodology for

  14. Metabolic control analysis of biochemical pathways based on a thermokinetic description of reaction rates

    DEFF Research Database (Denmark)

    Nielsen, Jens Bredal

    1997-01-01

    of the thermokinetic description of reaction rates to include the influence of effecters. Here the reaction rate is written as a linear function of the logarithm of the metabolite concentrations. With this type of rate function it is shown that the approach of Delgado and Liao [Biochem. J. (1992) 282......, 919-927] can be much more widely applied, although it was originally based on linearized kinetics. The methodology of determining elasticity coefficients directly from pool levels is illustrated with an analysis of the first two steps of the biosynthetic pathway of penicillin. The results compare well...

  15. Reaction kinetics of bond rotations in graphene

    KAUST Repository

    Skowron, Stephen T.

    2016-04-12

    The formation and healing processes of the fundamental topological defect in graphitic materials, the Stone-Wales (SW) defect, are brought into a chemical context by considering the rotation of a carbon-carbon bond as chemical reaction. We investigate the rates and mechanisms of these SW transformations in graphene at the atomic scale using transmission electron microscopy. We develop a statistical atomic kinetics formalism, using direct observations obtained under different conditions to determine key kinetic parameters of the reactions. Based on the obtained statistics we quantify thermally and irradiation induced routes, identifying a thermal process of healing with an activation energy consistent with predicted adatom catalysed mechanisms. We discover exceptionally high rates for irradiation induced SW healing, incompatible with the previously assumed mechanism of direct knock-on damage and indicating the presence of an efficient nonadiabatic coupling healing mechanism involving beam induced electronic excitations of the SW defect.

  16. Kinetics of catalytic reactions-solutions manual

    CERN Document Server

    Vannice, M Albert

    2008-01-01

    Including countless exercises and worked examples, this advanced reference work and textbook will be extremely useful for the work of many industrial scientists. It teaches readers to design kinetic experiments involving heterogeneous catalysts, to characterize these catalysts, to acquire rate data, to find heat and mass transfer limitations in these data, to select reaction models, to derive rate expressions based on these models, and to assess the consistency of these rate equations.

  17. Kinetics of rouleau formation. II. Reversible reactions.

    OpenAIRE

    Samsel, R W; Perelson, A. S.

    1984-01-01

    Red blood cells aggregate face-to-face to form long, cylindrical, straight chains and sometimes branched structures called rouleaux. Here we extend a kinetic model developed by R. W. Samsel and A. S. Perelson (1982, Biophys. J. 37:493-514) to include both the formation and dissociation of rouleaux. We examine thermodynamic constraints on the rate constants of the model imposed by the principle of detailed balance. Incorporation of reverse reactions allows us to compute mean sizes of rouleaux ...

  18. Modelling biochemical reaction systems by stochastic differential equations with reflection.

    Science.gov (United States)

    Niu, Yuanling; Burrage, Kevin; Chen, Luonan

    2016-05-01

    In this paper, we gave a new framework for modelling and simulating biochemical reaction systems by stochastic differential equations with reflection not in a heuristic way but in a mathematical way. The model is computationally efficient compared with the discrete-state Markov chain approach, and it ensures that both analytic and numerical solutions remain in a biologically plausible region. Specifically, our model mathematically ensures that species numbers lie in the domain D, which is a physical constraint for biochemical reactions, in contrast to the previous models. The domain D is actually obtained according to the structure of the corresponding chemical Langevin equations, i.e., the boundary is inherent in the biochemical reaction system. A variant of projection method was employed to solve the reflected stochastic differential equation model, and it includes three simple steps, i.e., Euler-Maruyama method was applied to the equations first, and then check whether or not the point lies within the domain D, and if not perform an orthogonal projection. It is found that the projection onto the closure D¯ is the solution to a convex quadratic programming problem. Thus, existing methods for the convex quadratic programming problem can be employed for the orthogonal projection map. Numerical tests on several important problems in biological systems confirmed the efficiency and accuracy of this approach. PMID:26920245

  19. Pozzolanic Reaction Kinetics of Coal Ashes

    Institute of Scientific and Technical Information of China (English)

    ZHENG Hongwei; WANG Zhijuan; QIAN Jueshi; SONG Yuanming; WANG Zhi

    2009-01-01

    The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO_2 and Al_2O_3 with lime were soluble in dilute hydrochloric acid.The results show that the pozzolanic reaction of active SiO_2 and Al2O3 of coal ashes follows apparent first-order kinetics.The reaction rate constant of FBC ashes is greater than that of PC ashes,while the activation energy of the former is lower than that of the latter.It is confirmed that the pozzolanic activity of fluidized bed combustion(FBC)ashes is significantly higher than that of PC ashes,and the reaction barrier of the former is lower than that of the latter,because the microstructures of FBC ashes,such as mineralogical composition,morphology and polymerization degree of [SiO_4]and[AlO_6]are more favorable to the pozzolanic activity development than those of PC ashes.

  20. Spectroscopy and reaction kinetics of HCO

    International Nuclear Information System (INIS)

    The high-resolution infrared spectrum of the C-H stretching fundamental of HCO has been studied by means of infrared flash kinetic spectroscopy. HCO was generated by flash photolysis of acetaldehyde or formaldehyde using a 308 nm (XeCl) excimer laser. The transient absorption was probed with an infrared difference frequency laser system. The high resolution spectra obtained were assigned and fitted with rotational, spin-rotational, and centrifugal distortion constants. The ν1 band origin is 2434.48 cm/sup /minus/1/. New ground state constants have been derived from a least-squares fit combining the ν1 data with previous microwave and FIR LMR measurements. A new set of spectroscopic constants for the (1, 0, 0) state, the equilibrium rotational constants, and the orientation of the transition dipole moment are also reported. The kinetics and product branching ratios of the HCO + NO2 reaction have been studied using visible and infrared laser flash kinetic spectroscopy. The rate constant for the disappearance of HCO radical at 296 K is (5.7 +- 0.9) /times/ 10/sup /minus/11/ cm3 molec/sup /minus/1/ sec/sup /minus/1/, and it is independent of the pressure of SF6 buffer gas up to 700 torr. Less than 10% of the reaction goes through the most exothermic product channel, HNO + CO2. The product channel, H + CO2 + NO, is responsible for 52% of the reaction. HONO has been observed, though not quantitatively, as a reaction product corresponding to the HONO + CO channel. 51 refs., 21 figs., 8 tabs

  1. Kinetics of rouleau formation. II. Reversible reactions

    Energy Technology Data Exchange (ETDEWEB)

    Samsel, R.W.; Perelson, A.S.

    1984-04-01

    Red blood cells aggregate face-to-face to form long, cylindrical, straight chains and sometimes branched structures called rouleaux. Here the authors extend a kinetic model developed by R.W. Samsel and A.S. Perelson to include both the formation and dissociation of rouleaux. Thermodynamic constraints on the rate constants of the model imposed by the principle of detailed balance were examined. Incorporation of reverse reactions allows computation of mean sizes of rouleaux and straight chain segments within rouleaux, as functions of time and at equilibrium. Using the Flory-Stockmayer method from polymer chemistry, a closed-form solution was obtained for the size distribution of straight chain segments within rouleaux at any point in the evolution of the reaction. The predictions of the theory compare favorably with data collected by D. Kernick, A.W.L. Jay, S. Rowlands, and L. Skibo on the kinetics of rouleaux formation. When rouleaux grow large, they may contain rings or loops and take on the appearance of a network. The importance of including the kinetics of ring closure in the development of realistic models of rouleaux formation was demonstrated.

  2. Bayesian inference of biochemical kinetic parameters using the linear noise approximation

    Directory of Open Access Journals (Sweden)

    Finkenstädt Bärbel

    2009-10-01

    Full Text Available Abstract Background Fluorescent and luminescent gene reporters allow us to dynamically quantify changes in molecular species concentration over time on the single cell level. The mathematical modeling of their interaction through multivariate dynamical models requires the deveopment of effective statistical methods to calibrate such models against available data. Given the prevalence of stochasticity and noise in biochemical systems inference for stochastic models is of special interest. In this paper we present a simple and computationally efficient algorithm for the estimation of biochemical kinetic parameters from gene reporter data. Results We use the linear noise approximation to model biochemical reactions through a stochastic dynamic model which essentially approximates a diffusion model by an ordinary differential equation model with an appropriately defined noise process. An explicit formula for the likelihood function can be derived allowing for computationally efficient parameter estimation. The proposed algorithm is embedded in a Bayesian framework and inference is performed using Markov chain Monte Carlo. Conclusion The major advantage of the method is that in contrast to the more established diffusion approximation based methods the computationally costly methods of data augmentation are not necessary. Our approach also allows for unobserved variables and measurement error. The application of the method to both simulated and experimental data shows that the proposed methodology provides a useful alternative to diffusion approximation based methods.

  3. Kinetics of elementary atom and radical reactions

    International Nuclear Information System (INIS)

    During the past three years we have been working on four problems in the general area of gas phase kinetics and energy transfer of small molecules. These are: (1) measurements of the fine structure populations of ground state oxygen atoms produced in photodissociation reactions; (2) quenching of the Rydberg B (1Σ+) state of CO; (3) vibrational relaxation of highly excited molecules; and (4) kinetics of hydrogen molecules. The first two topics, which involve transitions between different electronic states of the parent molecule, are a departure from our previous research interests. In the accompanying renewal proposal we discuss plans to pursue these new topics vigorously during the coming year. The third topic is a continuation of our long interest in the energy dependence of the rates laws governing vibrational-to-translational energy transfer of molecules having large initial amounts of vibrational excitation. The final topic is a continuation of our studies of the reaction of O(3P) + H2. In this work we measured the rate constant for the reaction O(3P) with deuterium and also analyzed spectroscopically different sources of vibrationally excited hydrogen for possible future work. We discuss each of these four studies in the following sections

  4. Reaction kinetics of dolomite rim growth

    Science.gov (United States)

    Helpa, V.; Rybacki, E.; Abart, R.; Morales, L. F. G.; Rhede, D.; Jeřábek, P.; Dresen, G.

    2014-04-01

    Reaction rims of dolomite (CaMg[CO3]2) were produced by solid-state reactions at the contacts of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals at 400 MPa pressure, 750-850 °C temperature, and 3-146 h annealing time to determine the reaction kinetics. The dolomite reaction rims show two different microstructural domains. Elongated palisades of dolomite grew perpendicular into the MgCO3 interface with length ranging from about 6 to 41 µm. At the same time, a 5-71 µm wide rim of equiaxed granular dolomite grew at the contact with CaCO3. Platinum markers showed that the original interface is located at the boundary between the granular and palisade-forming dolomite. In addition to dolomite, a 12-80 µm thick magnesio-calcite layer formed between the dolomite reaction rims and the calcite single crystals. All reaction products show at least an axiotactic crystallographic relationship with respect to calcite reactant, while full topotaxy to calcite prevails within the granular dolomite and magnesio-calcite. Dolomite grains frequently exhibit growth twins characterized by a rotation of 180° around one of the equivalent axis. From mass balance considerations, it is inferred that the reaction rim of dolomite grew by counter diffusion of MgO and CaO. Assuming an Arrhenius-type temperature dependence, activation energies for diffusion of CaO and MgO are E a (CaO) = 192 ± 54 kJ/mol and E a (MgO) = 198 ± 44 kJ/mol, respectively.

  5. Kinetic modelling of the Maillard reaction between proteins and sugars

    OpenAIRE

    Brands, C.M.J.

    2002-01-01

    Keywords: Maillard reaction, sugar isomerisation, kinetics, multiresponse modelling, brown colour formation, lysine damage, mutagenicity, casein, monosaccharides, disaccharides, aldoses, ketosesThe aim of this thesis was to determine the kinetics of the Maillard reaction between proteins and sugars, taking into account other simultaneously occurring sugar reactions. Model systems of foods, consisting of the protein casein and various sugars in a buffered solution, were studied. The reaction c...

  6. Understanding Chemical Reaction Kinetics and Equilibrium with Interlocking Building Blocks

    Science.gov (United States)

    Cloonan, Carrie A.; Nichol, Carolyn A.; Hutchinson, John S.

    2011-01-01

    Chemical reaction kinetics and equilibrium are essential core concepts of chemistry but are challenging topics for many students, both at the high school and undergraduate university level. Visualization at the molecular level is valuable to aid understanding of reaction kinetics and equilibrium. This activity provides a discovery-based method to…

  7. Computational analysis of the roles of biochemical reactions in anomalous diffusion dynamics

    Science.gov (United States)

    Naruemon, Rueangkham; Charin, Modchang

    2016-04-01

    Most biochemical processes in cells are usually modeled by reaction–diffusion (RD) equations. In these RD models, the diffusive process is assumed to be Gaussian. However, a growing number of studies have noted that intracellular diffusion is anomalous at some or all times, which may result from a crowded environment and chemical kinetics. This work aims to computationally study the effects of chemical reactions on the diffusive dynamics of RD systems by using both stochastic and deterministic algorithms. Numerical method to estimate the mean-square displacement (MSD) from a deterministic algorithm is also investigated. Our computational results show that anomalous diffusion can be solely due to chemical reactions. The chemical reactions alone can cause anomalous sub-diffusion in the RD system at some or all times. The time-dependent anomalous diffusion exponent is found to depend on many parameters, including chemical reaction rates, reaction orders, and chemical concentrations. Project supported by the Thailand Research Fund and Mahidol University (Grant No. TRG5880157), the Thailand Center of Excellence in Physics (ThEP), CHE, Thailand, and the Development Promotion of Science and Technology.

  8. A generalized kinetic model for heterogeneous gas-solid reactions

    Science.gov (United States)

    Xu, Zhijie; Sun, Xin; Khaleel, Mohammad A.

    2012-08-01

    We present a generalized kinetic model for gas-solid heterogeneous reactions taking place at the interface between two phases. The model studies the reaction kinetics by taking into account the reactions at the interface, as well as the transport process within the product layer. The standard unreacted shrinking core model relies on the assumption of quasi-static diffusion that results in a steady-state concentration profile of gas reactant in the product layer. By relaxing this assumption and resolving the entire problem, general solutions can be obtained for reaction kinetics, including the reaction front velocity and the conversion (volume fraction of reacted solid). The unreacted shrinking core model is shown to be accurate and in agreement with the generalized model for slow reaction (or fast diffusion), low concentration of gas reactant, and small solid size. Otherwise, a generalized kinetic model should be used.

  9. Unravelling the Maillard reaction network by multiresponse kinetic modelling

    OpenAIRE

    Martins, S.I.F.S.

    2003-01-01

    The Maillard reaction is an important reaction in food industry. It is responsible for the formation of colour and aroma, as well as toxic compounds as the recent discovered acrylamide. The knowledge of kinetic parameters, such as rate constants and activation energy, is necessary to predict its extent and, consequently, to optimise it. Each of the chapters presented in this thesis can be seen as a necessary step to succeed in applying multiresponse kinetic modelling in a complex reaction, su...

  10. Reaction schemes, escape times and geminate recombinations in particle-based spatial simulations of biochemical reactions

    International Nuclear Information System (INIS)

    Modeling the spatiotemporal dynamics of biochemical reaction systems at single-molecule resolution has become feasible with the increase of computing power and is applied especially to cellular signal transduction. For an association reaction the two molecules have to be in contact. Hence, a physically faithful model of the molecular interaction assumes non-overlapping molecules that interact at their surfaces (boundary scheme). For performance reasons, this model can be replaced by particles that can overlap and react when they are closer than a certain distance with a reaction probability (volume scheme). Here we present an analytical approximation for the reaction probability in the volume scheme and compare the volume- with the boundary scheme. A dissociation reaction, in contrast, creates two molecules next to each other. If the reaction is reversible, these two products can directly re-bind again, leading to an overestimation of the dimerized state in the simulation. We show how the correct recombination rate can be achieved if the products of the dissociation are placed at identical positions, but cannot react for a certain timespan. This refractory time corresponds to the completion of the diffusion-controlled dissociation of the two molecules to their contact distance ri + rj at t = τ-hat ×(ri+rj)2/(Di+Dj) with τ-hat = 1/10 for molecules with radii ri and rj and diffusion coefficients Di and Dj, respectively. (paper)

  11. Kinetics of the Exothermic Decomposition Reaction of s-Tripicryaminotrinitrobenzene

    Institute of Scientific and Technical Information of China (English)

    ZHAO Feng-qi; HU Rong-zu; GAO Hong-xu; LUO Yang; GAO Sheng-li; SONG Ji-rong; SHI Qi-zhen

    2007-01-01

    The kinetic parameters of the exothermic decomposition reaction of s-Tripicryaminotrinitrobenzene under linear temperature rise condition are studied by means of DSC. The results show that the empirical kinetic model function in difs-1, respectively. The critical temperature of thermal explosion of the compound is 267.36 ℃.

  12. Kinetics of Acid Reactions: Making Sense of Associated Concepts

    Science.gov (United States)

    Tan, Kim Chwee Daniel; Treagust, David F.; Chandrasegaran, A. L.; Mocerino, Mauro

    2010-01-01

    In chemical kinetics, in addition to the concepts related to kinetics, stoichiometry, chemical equilibrium and the characteristics of the reactants are often involved when comparing the rates of different reactions, making such comparisons very challenging for students at all levels, as well as for pre-service science teachers. Consequently, four…

  13. A moment-convergence method for stochastic analysis of biochemical reaction networks

    Science.gov (United States)

    Zhang, Jiajun; Nie, Qing; Zhou, Tianshou

    2016-05-01

    Traditional moment-closure methods need to assume that high-order cumulants of a probability distribution approximate to zero. However, this strong assumption is not satisfied for many biochemical reaction networks. Here, we introduce convergent moments (defined in mathematics as the coefficients in the Taylor expansion of the probability-generating function at some point) to overcome this drawback of the moment-closure methods. As such, we develop a new analysis method for stochastic chemical kinetics. This method provides an accurate approximation for the master probability equation (MPE). In particular, the connection between low-order convergent moments and rate constants can be more easily derived in terms of explicit and analytical forms, allowing insights that would be difficult to obtain through direct simulation or manipulation of the MPE. In addition, it provides an accurate and efficient way to compute steady-state or transient probability distribution, avoiding the algorithmic difficulty associated with stiffness of the MPE due to large differences in sizes of rate constants. Applications of the method to several systems reveal nontrivial stochastic mechanisms of gene expression dynamics, e.g., intrinsic fluctuations can induce transient bimodality and amplify transient signals, and slow switching between promoter states can increase fluctuations in spatially heterogeneous signals. The overall approach has broad applications in modeling, analysis, and computation of complex biochemical networks with intrinsic noise.

  14. A database of sources of information on mineral reaction kinetics

    OpenAIRE

    Rochelle, C. A.; Turner, G

    2005-01-01

    The rate and magnitude of geochemical reactions can be described by two main processes; thermodynamics which determines the end point of reaction (i.e. approach to equilibrium conditions), and kinetics which determines how rapidly the reaction proceeds. There have been many studies that have investigated equilibrium conditions and have generated a wealth of data. However, for many systems the rate at which the end point of the reaction is reached is of equal, and possibly greater importance (...

  15. SBMLsqueezer 2: context-sensitive creation of kinetic equations in biochemical networks

    DEFF Research Database (Denmark)

    Draeger, Andreas; Zielinski, Daniel C.; Keller, Roland;

    2015-01-01

    simplified the network reconstruction process, but building kinetic models for these systems is still a manually intensive task. Appropriate kinetic equations, based upon reaction rate laws, must be constructed and parameterized for each reaction. The complex test-and-evaluation cycles that can be involved...... during kinetic model construction would thus benefit from automated methods for rate law assignment. Results: We present a high-throughput algorithm to automatically suggest and create suitable rate laws based upon reaction type according to several criteria. The criteria for choices made by the...... algorithm can be influenced in order to assign the desired type of rate law to each reaction. This algorithm is implemented in the software package SBMLsqueezer 2. In addition, this program contains an integrated connection to the kinetics database SABIO-RK to obtain experimentally-derived rate laws when...

  16. Kinetics of Model Reactions for Interfacial Polymerization

    Directory of Open Access Journals (Sweden)

    Henry Hall

    2012-02-01

    Full Text Available To model the rates of interfacial polycondensations, the rates of reaction of benzoyl chloride and methyl chloroformate with various aliphatic monoamines in acetonitrile were determined at 25 °C. Buffering with picric acid slowed these extremely fast reactions so the rate constants could be determined from the rate of disappearance of picrate ion. The rates of the amine reactions correlated linearly with their Swain-Scott nucleophilicities.

  17. Kinetics of Model Reactions for Interfacial Polymerization

    OpenAIRE

    Henry Hall; Robert Bates; Jeffrey Robertson; Anne Padias; Trevor Centeno-Hall

    2012-01-01

    To model the rates of interfacial polycondensations, the rates of reaction of benzoyl chloride and methyl chloroformate with various aliphatic monoamines in acetonitrile were determined at 25 °C. Buffering with picric acid slowed these extremely fast reactions so the rate constants could be determined from the rate of disappearance of picrate ion. The rates of the amine reactions correlated linearly with their Swain-Scott nucleophilicities.

  18. Kinetics of photochromic reactions in condensed phases

    Czech Academy of Sciences Publication Activity Database

    Sworakowski, J.; Janus, K.; Nešpůrek, Stanislav

    2005-01-01

    Roč. 116, 1-3 (2005), s. 97-110. ISSN 0001-8686 R&D Projects: GA MŠk 1P04OCD14.30 Grant ostatní: Polish Committee for Scientific Research(PL) 18/2004; Polish Committee for Scientific Research(PL) 50/2004 Keywords : photochromism * kinetics * rate constant Subject RIV: CH - Nuclear ; Quantum Chemistry Impact factor: 4.198, year: 2005

  19. Kinetic analysis of temperature-programmed reactions

    OpenAIRE

    Kanervo, Jaana

    2003-01-01

    Temperature-programmed desorption (TPD), reduction (TPR) and oxidation (TPO) are thermoanalytical techniques for characterising chemical interactions between gaseous reactants and solid substances. The data collected by these techniques are commonly interpreted on a qualitative basis or by utilising simple, approximate kinetic methods. However, temperature-programmed techniques can also be regarded as transient response techniques and the experimental data can be utilised for dynamic modellin...

  20. Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives

    KAUST Repository

    Hisatomi, Takashi

    2014-10-16

    Abstract: Some particulate semiconductors loaded with nanoparticulate catalysts exhibit photocatalytic activity for the water-splitting reaction. The photocatalysis is distinct from the thermal catalysis because photocatalysis involves photophysical processes in particulate semiconductors. This review article presents a brief introduction to photocatalysis, followed by kinetic aspects of the photocatalytic water-splitting reaction.Graphical Abstract: [Figure not available: see fulltext.

  1. Adsorption Isotherms and Surface Reaction Kinetics

    Science.gov (United States)

    Lobo, L. S.; Bernardo, C. A.

    1974-01-01

    Explains an error that occurs in calculating the conditions for a maximum value of a rate expression for a bimolecular reaction. The rate expression is derived using the Langmuir adsorption isotherm to relate gas pressures and corresponding surface coverages. (GS)

  2. Kinetics of transuranium element oxidation-reduction reactions in solution

    International Nuclear Information System (INIS)

    A review of the kinetics of U, Np, Pu, Am oxidation-reduction reactions is proposed. The relations between the different activation thermodynamic functions (compensatory effect, formal entropy of the activated complex, magnitude of reactions velocities) are considered. The effects of acidity, ionic strength deuterium and mixed solvents polarity on reactions rates are described. The effect of different anions on reactions rates are explained by variations of the reaction standard free energy and variations of the activation free energy (coulombic interactions) resulting from the complexation of dissolved species by these anions. (author)

  3. Use of Competition Kinetics with Fast Reactions of Grignard Reagents

    DEFF Research Database (Denmark)

    Holm, Torkil

    2000-01-01

    Competition kinetics are useful for estimation of the reactivities of Grignard reagents if the reaction rates do not differ widely and if exact rates are not needed. If the rate of mixing is slower than the rate of reaction the ratios between the rates of fast and slow reagents are found to be too...... may account for almost all the product even when present as only 1 part in 100 parts of the competing agent. In this way allylmagnesium bromide is estimated to react with acetone, benzophenone, benzaldehyde, and diethylacetaldehyde ca. 1.5 x 105 times faster than does butylmagnesium bromide. The rates...... found for the four substrates do not differ significantly and it seems possible that there is a ceiling over the rate of reaction of this reagent, for example caused by diffusion control. This may explain that competition kinetics using allylmagnesium bromide have failed to show kinetic isotope effects...

  4. The influence of gas-kinetic evolution on plasma reactions

    CERN Document Server

    Diver, D A; MacLachlan, C S; Potts, H E

    2008-01-01

    Plasmas in which there is a threshold for a dominant reaction to take place (such as recombination or attachment) will have particle distributions that evolve as the reaction progresses. The form of the Boltzmann collision term in such a context will cause the distribution to drift from its initial form, and so cause for example temperature fluctuations in the plasma if the distribution is originally Maxwellian. This behaviour will impact on the relevant reaction rates in a feedback loop that is missing from simple chemical kinetic descriptions since the plasma cannot be considered to be isothermal, as is the case in the latter approach. In this article we present a simple kinetic model that captures these essential features, showing how cumulative differences in the instantaneous species levels can arise over the purely chemical kinetic description, with implications for process yields and efficiencies.

  5. Antibiogram, Biochemical Reactions and Biotyping of Biofield Treated Providencia rettgeri

    OpenAIRE

    Trivedi, Mahendra Kumar

    2015-01-01

    Providencia rettgeri (P. rettgeri) is the key organism for gastrointestinal tract infections due to its high virulence properties. The current study was designed to investigate the effect of Mr. Trivedi’s biofield energy treatment on P. rettgeri in lyophilized as well as revived state for antimicrobial susceptibility pattern, biochemical characteristics, and biotype number. The lyophilized strain of P. rettgeri (ATCC 9250) was divided into two parts, Group (Gr.)...

  6. Reduction of dynamical biochemical reactions networks in computational biology

    OpenAIRE

    Radulescu, O.; Gorban, A.N.; Zinovyev, A.; Noel, V.

    2012-01-01

    Biochemical networks are used in computational biology, to model mechanistic details of systems involved in cell signaling, metabolism, and regulation of gene expression. Parametric and structural uncertainty, as well as combinatorial explosion are strong obstacles against analyzing the dynamics of large models of this type. Multiscaleness, an important property of these networks, can be used to get past some of these obstacles. Networks with many well separated time scales, can be reduced to...

  7. Stochastic Modeling and Simulation of Reaction-Diffusion Biochemical Systems

    OpenAIRE

    LI Fei

    2016-01-01

    Reaction Diffusion Master Equation (RDME) framework, characterized by the discretization of the spatial domain, is one of the most widely used methods in the stochastic simulation of reaction-diffusion systems. Discretization sizes for RDME have to be appropriately chosen such that each discrete compartment is "well-stirred" and the computational cost is not too expensive. An efficient discretization size based on the reaction-diffusion dynamics of each species is derived in this disserta...

  8. Reaction kinetics of nanostructured silicon carbide

    Science.gov (United States)

    Wallis, K. L.; Patyk, J. K.; Zerda, T. W.

    2008-08-01

    SiC nanowires were produced from carbon nanotubes and silicon by two different methods at high temperature. X-ray powder diffraction was used to determine SiC concentration. The reaction rate using the Avrami-Erofeev method was determined for samples sintered at temperatures ranging from 1313 to 1823 K. The activation energy was found to be (254 ± 36) kJ mol-1. The limiting factor in SiC formation is diffusion of silicon and carbon atoms through the produced layer of SiC.

  9. Reaction kinetics of nanostructured silicon carbide

    International Nuclear Information System (INIS)

    SiC nanowires were produced from carbon nanotubes and silicon by two different methods at high temperature. X-ray powder diffraction was used to determine SiC concentration. The reaction rate using the Avrami-Erofeev method was determined for samples sintered at temperatures ranging from 1313 to 1823 K. The activation energy was found to be (254 ± 36) kJ mol-1. The limiting factor in SiC formation is diffusion of silicon and carbon atoms through the produced layer of SiC

  10. Fast stochastic simulation of biochemical reaction systems by alternative formulations of the chemical Langevin equation

    KAUST Repository

    Mélykúti, Bence

    2010-01-01

    The Chemical Langevin Equation (CLE), which is a stochastic differential equation driven by a multidimensional Wiener process, acts as a bridge between the discrete stochastic simulation algorithm and the deterministic reaction rate equation when simulating (bio)chemical kinetics. The CLE model is valid in the regime where molecular populations are abundant enough to assume their concentrations change continuously, but stochastic fluctuations still play a major role. The contribution of this work is that we observe and explore that the CLE is not a single equation, but a parametric family of equations, all of which give the same finite-dimensional distribution of the variables. On the theoretical side, we prove that as many Wiener processes are sufficient to formulate the CLE as there are independent variables in the equation, which is just the rank of the stoichiometric matrix. On the practical side, we show that in the case where there are m1 pairs of reversible reactions and m2 irreversible reactions there is another, simple formulation of the CLE with only m1 + m2 Wiener processes, whereas the standard approach uses 2 m1 + m2. We demonstrate that there are considerable computational savings when using this latter formulation. Such transformations of the CLE do not cause a loss of accuracy and are therefore distinct from model reduction techniques. We illustrate our findings by considering alternative formulations of the CLE for a human ether a-go-go related gene ion channel model and the Goldbeter-Koshland switch. © 2010 American Institute of Physics.

  11. Chemical kinetic reaction mechanism for the combustion of propane

    Science.gov (United States)

    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.

  12. Kinetic of the reaction between bitumen and sulphur

    International Nuclear Information System (INIS)

    The utilization of sulphur in bituminous binders has been tried for many years in a number of countries, mainly USA and Canada. The overall purpose of this study was to evaluate the kinetics of the reaction between elemental sulphur and bitumen, with the production of hydrogen sulfide. The work was carried out with the help of a thermo balance. It was shown that H2S evolution starts immediately after sulphur melting and that the rate of reaction is of second order

  13. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Energy Technology Data Exchange (ETDEWEB)

    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.

  14. Exact results for noise power spectra in linear biochemical reaction networks

    OpenAIRE

    Warren, Patrick B.; Tanase-Nicola, Sorin; Wolde, Pieter Rein ten

    2005-01-01

    We present a simple method for determining the exact noise power spectra in linear chemical reaction networks. We apply the method to networks which are representative of biochemical processes such as gene expression and signal detection. Our results clarify how noise is transmitted by signal detection motifs, and indicate how to coarse-grain networks by the elimination of fast reactions.

  15. Penicillin Hydrolysis: A Kinetic Study of a Multistep, Multiproduct Reaction.

    Science.gov (United States)

    McCarrick, Thomas A.; McLafferty, Fred W.

    1984-01-01

    Background, procedures used, and typical results are provided for an experiment in which students carry out the necessary measurements on the acid-catalysis of penicillin in two hours. By applying kinetic theory to the data obtained, the reaction pathways for the hydrolysis of potassium benzyl penicillin are elucidated. (JN)

  16. REACTION KINETICS OF CA-BASED SORBENTS WITH HC1

    Science.gov (United States)

    The kinetics of the reaction between CaO and HCl were investigated under conditions that minimize bulk mass transfer and pore diffusion limitations. Reactivity data from 0.2- to 1-s exposure to 5000 ppm HCl in a fixed bed reactor were analyzed by a shrinking core model of diffusi...

  17. Kinetics of interfacial reaction between uranium dioxide and zircaloy-2

    International Nuclear Information System (INIS)

    Solid state reaction between UO2 pellets and zircaloy-2 has been studied at temperature between 1270 and 1775 K. It has been observed that the reaction results in the formation of three layers. The kinetics of growth of these layers have been studied in depth and are found to obey parabolic relatjon with annealing time. The temperature dependence of the growth rate of these reaction layers obeys an Arrhenius type of relation. Micro cracks and longitudinal gaps were observed in some of the couples (towards UO2 pellet side) annealed for longer period. The presence of gaps and cracks suggests that the reaction is assisted by a process involving stress and strain in the reaction zone set up by differential contraction between uranium dioxide and reaction layers. (author)

  18. Intermediate-high energy nuclear reaction kinetics simulation and QMD

    International Nuclear Information System (INIS)

    The main features of the IHENRKS and its application in the study of thermalization for reaction of 830 MeV P + 56Fe are described. IHENRKS is the abbreviation of intermediate-high energy nuclear reaction kinetic simulation. It combines the idea and method of MCM, SSIENC and QMD. These kind of models treat the movement of each particle (nucleon and meson) and their collisions in time and space and concern with the new particle production. From calculations for 830 MeV proton bombarding reactions, it can be concluded that the nucleus is not wholly thermalized, but locally thermalized. (1 fig.)

  19. Evolutionary origin of power-laws in Biochemical Reaction Network; embedding abundance distribution into topology

    OpenAIRE

    Furusawa, Chikara; Kaneko, Kunihiko

    2005-01-01

    The evolutionary origin of universal statistics in biochemical reaction network is studied, to explain the power-law distribution of reaction links and the power-law distributions of chemical abundances. Using cell models with catalytic reaction network, we find evidence that the power-law distribution in abundances of chemicals emerges by the selection of cells with higher growth speeds. Through the further evolution, this inhomogeneity in chemical abundances is shown to be embedded in the d...

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

    Science.gov (United States)

    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.

  1. Kinetics of fast reactions of excited species. Final report

    International Nuclear Information System (INIS)

    This report contains brief summaries of findings in the following areas: gamma radiation induced decomposition of chloroform; proton transfer and ion neutralization reactions in gaseous hydrocarbons; kinetics of thremal D-atom reactions with CH4 C2H6; the gamma radiation induced decomposition of liquid n-pentane; pulse radiolysis of rare gases and liquid n-pentane and n-pentane-O2 solutions; rate constants and activation energies for second order decay of pentyl and peroxypentyl radicals; pulse radiolysis fo aromatic solutes in halogenated solvents; the gamma radiation induced decomposition of nitromethane; the radiolysis of heavy water vapor; pulse radiolysis of solvated electrons in binary liquid solutions; collisional quenching of rare gas excimers by small foreign molecules; kinetics and mechanism for decay of Paschen-1s argon atoms; detection and monitoring of excited atoms in pulse irradiated rare gases

  2. EFFECTIVE SOLUTION METHOD OF CHEMICAL REACTION KINETICS WITH DIFFUSE

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The time integration method with four-order accuracy, self-starting and implicit for the diffuse chemical reaction kinetics equation or the transient instantaneous temperature filed equation was presented. The examples show that both accuracy and stability are better than Runge-Kutta method with four-order. The coefficients of the equation are stored with sparse matrix pattern, so an algorithm is presented which combines a compact storage scheme with reduced computation cost. The computation of the competitive and consecutive reaction in the rotating packed bed, taken as examples,shows that the method is effective.

  3. Some kinetics aspects of chlorine-solids reactions

    OpenAIRE

    Kanari, N.; Mishra, D.; Mochón, J.; Verdeja, L. F.; Diot, F.; Allain, E.

    2011-01-01

    The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl2+N2 (chlorination), Cl2+O2 (oxychlorination), and Cl2+CO (...

  4. Variable elimination in chemical reaction networks with mass action kinetics

    OpenAIRE

    Feliu, Elisenda; Wiuf, Carsten

    2011-01-01

    We consider chemical reaction networks taken with mass action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination of variables. The procedure reduces the variables in the system to a set of "core" variables by eliminating variables corresponding to a set of non-interacting species. The steady states are paramet...

  5. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    Science.gov (United States)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  6. The reaction kinetics of amino radicals with sulfur dioxide

    DEFF Research Database (Denmark)

    Gao, Yide; Glarborg, Peter; Marshall, Paul

    2015-01-01

    Application of the laser photolysis-laser-induced fluorescence method to the reaction NH2+SO2 in argon bath gas yields pressure-dependent, third-order kinetics which may be summarized as k = (1.49 ± 0.15) × 10-31 (T/298 K)-0.83cm6 molecule-2 s-1 over 292-555K, where the uncertainty is the 95% con...

  7. Kinetics of the reversible reaction of struvite crystallisation.

    Science.gov (United States)

    Crutchik, D; Garrido, J M

    2016-07-01

    The crystallisation of struvite could be a sustainable and economical alternative for recovering phosphorus from wastewater streams with high phosphate concentrations. Knowledge regarding the kinetics and thermodynamics that are involved in the crystallisation of struvite is the key to determine the optimal conditions for obtaining an efficient process. This study was conducted in a continuous stirred batch reactor. Different sets of experiments were performed in which struvite was either dissolved (undersaturated) or precipitated (oversaturated). These experiments were conducted at different temperatures (25, 30 and 35 °C) and pH values (8.2, 8.5 and 8.8) to determine the kinetics of struvite precipitation and dissolution. Struvite crystallisation was modelled as a reversible reaction. The kinetic rate parameters of struvite precipitation were 1.03·10(-4), 1.25·10(-4) and 1.54·10(-4) mol m(-2) min(-1) at 25, 30 and 35 °C, respectively. Similar kinetic rate parameters were determined for struvite dissolution. Struvite heterogeneous crystallisation can be represented by a first-order kinetic model that fitted well the experimental data. PMID:27085317

  8. Temperature Control System for Biochemical Reactions in Microchip-Based Devices

    Institute of Scientific and Technical Information of China (English)

    荆高山; 张坚; 朱小山; 冯继宏; 谭智敏; 刘理天; 程京

    2001-01-01

    A silicon-glass chip based microreactor has been designed and fabricated for biochemical reactions such as polymerase chain reactions (PCR). The chip based microreactor has integrated resistive heating elements. The computer-controlled temperature control system is highly reliable with precise temperature control, excellent temperature uniformity, and rapid heating and cooling capabilities. The development of the microreaction system is an important step towards the construction of a lab-on-a-chip system.

  9. Radical-ion-pair reactions are the biochemical equivalent of the optical double slit experiment

    OpenAIRE

    Kominis, I. K.

    2010-01-01

    Radical-ion-pair reactions were recently shown to represent a rich biophysical laboratory for the application of quantum measurement theory methods and concepts. We here show that radical-ion-pair reactions essentially form a non-linear biochemical double slit interferometer. Quantum coherence effects are visible when "which-path" information is limited, and the incoherent limit is approached when measurement-induced decoherence sets in. Based on this analogy with the optical double slit expe...

  10. OCCURING SOME BIOCHEMICAL REACTIONS IN FERMENTED MEAT PRODUCTS AND THEIR EFFECTS ON AROMA DEVELOPMENT

    OpenAIRE

    Gökalp, Hüsnü Yusuf; Hüdayi ERCOŞKUN; Ahmet Hilmi ÇON

    1998-01-01

    Glycolysis, lipolysis and proteolysis are the main biochemical reactions which effect characteristic flavour, aroma, color and texture development of fermented meat products. These reactions are results of the microorganisms or endogenous meat enzymes. The products which are results of glycolysis are firstly responsible from decreasing of pH. Volatile compounds from glycolysis effect aroma. Compounds formed by lipolysis are the main reason that effect aroma. 60 % volatile compounds formed...

  11. Reaction Path Optimization with Holonomic Constraints and Kinetic Energy Potentials

    International Nuclear Information System (INIS)

    Two methods are developed to enhance the stability, efficiency, and robustness of reaction path optimization using a chain of replicas. First, distances between replicas are kept equal during path optimization via holonomic constraints. Finding a reaction path is, thus, transformed into a constrained optimization problem. This approach avoids force projections for finding minimum energy paths (MEPs), and fast-converging schemes such as quasi-Newton methods can be readily applied. Second, we define a new objective function - the total Hamiltonian - for reaction path optimization, by combining the kinetic energy potential of each replica with its potential energy function. Minimizing the total Hamiltonian of a chain determines a minimum Hamiltonian path (MHP). If the distances between replicas are kept equal and a consistent force constant is used, then the kinetic energy potentials of all replicas have the same value. The MHP in this case is the most probable isokinetic path. Our results indicate that low-temperature kinetic energy potentials (7eq-to-Cax isomerization of an alanine dipeptide, the 4C1-to-1C4 transition of an α-D-glucopyranose, and the helix-to-sheet transition of a GNNQQNY heptapeptide. By applying the methods developed in this work, convergence of reaction path optimization can be achieved for these complex transitions, involving full atomic details and a large number of replicas (>100). For the case of helix-to-sheet transition, we identify pathways whose energy barriers are consistent with experimental measurements. Further, we develop a method based on the work energy theorem to quantify the accuracy of reaction paths and to determine whether the atoms used to define a path are enough to provide quantitative estimation of energy barriers.

  12. A Note on the Kinetics of Diffusion-mediated Reactions

    CERN Document Server

    Naqvi, K Razi

    2014-01-01

    The prevalent scheme of a diffusion-mediated bimolecular reaction $A+B\\rightarrow P$ is an adaptation of that proposed by Briggs and Haldane for enzyme action [{\\em Biochem J.\\/}, 19:338--339, 1925]. The purpose of this Note is to explain, {\\em by using an argument involving no mathematics\\/}, why the breakup of the encounter complex cannot be described, except in special circumstances, in terms of a first-order process $\\{AB\\}\\rightarrow A+B$. Briefly, such a description neglects the occurrence of re-encounters, which lie at the heart of Noyes's theory of diffusion-mediated reactions. The relation $k=\\alpha k_{\\mbox{\\scriptsize e}}$ becomes valid only when $\\alpha$ (the reaction probability per encounter) is very much smaller than unity (activation-controlled reactions), or when $\\beta$ (the re-encounter probability) is negligible (as happens in a gas-phase reaction). References to some works (by the author and his collaborators) which propound the correct approach for finding $k$ are also supplied.

  13. Reaction kinetics of resveratrol with thiyl and alkoxyl radicals

    International Nuclear Information System (INIS)

    Complete text of publication follows. Plant derived resveratrol (trans-3,5,4'-trihydroxystilbene) possesses a broad spectrum of biological activities, one of them are very well known its antioxidative properties. Our work aims to provide kinetic data with regard to the reactivity of resveratrol with uninvestigated short-lived bioradicals, identified as mediators in oxidative lipid degradation processes. Radicals of our interest are alkoxyl radicals, well known propagators of the chain free radical reactions in lipids, and thiyl radicals which protect lipids from their degradation pathway, but at the same time cause the isomerization of the double bonds. In order to investigate these reactions of resveratrol laser flash photolysis was used. On the basis of competitive kinetics the rate constants were determined under pseudo-first order conditions in acetonitrile solutions at room temperature. Thiyl radicals were generated indirectly in solution containing 1-octadecanthiol and photosensitive benzophenone in acetonitrile using the light pulses at 347 nm from ruby laser. Tert-butoxyl radicals were generated directly by peroxide bond cleavage from di-tert-butyl peroxide in acetonitrile by light pulses of Nd:YAG at 355 nm, and ruby at 347 nm. Obtained rate constants for the reactions of resveratrol and radicals generated by laser flash photolysis will be summarized and compared with rare literature data for the rate constants of investigated reactions of resveratrol and other radicals generated by pulse radiolysis.

  14. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Energy Technology Data Exchange (ETDEWEB)

    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

  15. An investigation of kinetic reaction and decomposition of sodium uranate

    International Nuclear Information System (INIS)

    For the management of severe accidents of sodium-cooled fast breeder reactor, the coolability of the fuel debris bed on a core support plate is a key concern during the post-accident heat removal phase. In an air ingress scenario, the reactions between the fuel and highly oxidized sodium are likely to form sodium uranoplutonate. This would negatively influence the coolability of the fuel debris bed due to a lowering of the thermal conductivity and density. This study has focused on the formation kinetics of sodium uranate from UO2 and liquid sodium including oxygen at a high concentration. In this paper, the experiments on reaction initiation temperatures, reaction rates, and the decomposition of sodium uranate are reported. (author)

  16. Variation of kinetic isotope effect in multiple proton transfer reactions

    Indian Academy of Sciences (India)

    B Saritha; M Durga Prasad

    2012-01-01

    Recently, we had suggested that the motion along the promoter mode in the first part of the IRC of proton transfer reaction enhances the delocalization of electrons on the acceptor atom into the * orbital of the donor-hydrogen covalent bond, and as a consequence weakens it. This leads to a reduction of the barrier to the proton transfer as well as the stretching frequency of donor-hydrogen bond. An extension of this to the concerted multiple proton transfer reactions implies that the kinetic isotope effect in such reaction depends exponentially on the number of protons that are being transferred. Computational evidence on three systems, (HF)3, formic acid dimer, and (H2O) clusters is provided to support this assertion.

  17. Biochemical features and kinetic properties of α-amylases from marine organisms.

    Science.gov (United States)

    Homaei, Ahmad; Ghanbarzadeh, Mehri; Monsef, Ferial

    2016-02-01

    Marine organisms have the ability of producing enzymes with unique properties compared to those of the same enzymes from terrestrial organisms. α-Amylases are among the most important extracellular enzymes found in various groups of organisms such as plants, animals and microorganisms. They play important roles in their carbohydrates metabolism of each organism. Microbial production of α-amylases is more effective than other sources of the enzyme. Many microorganisms are known to produce α-amylase including bacteria, yeasts, fungi and actinomycetes. However, enzymes from fungal and bacterial sources have dominated applications in industrial sectors. This review deals with what is known about the kinetics, biochemical properties and applications of these enzymes that have only been found in them and not in other α-amylases, and discussing their mechanistic and regulatory implications. PMID:26657843

  18. Simulation of biochemical reactions with time-dependent rates by the rejection-based algorithm

    International Nuclear Information System (INIS)

    We address the problem of simulating biochemical reaction networks with time-dependent rates and propose a new algorithm based on our rejection-based stochastic simulation algorithm (RSSA) [Thanh et al., J. Chem. Phys. 141(13), 134116 (2014)]. The computation for selecting next reaction firings by our time-dependent RSSA (tRSSA) is computationally efficient. Furthermore, the generated trajectory is exact by exploiting the rejection-based mechanism. We benchmark tRSSA on different biological systems with varying forms of reaction rates to demonstrate its applicability and efficiency. We reveal that for nontrivial cases, the selection of reaction firings in existing algorithms introduces approximations because the integration of reaction rates is very computationally demanding and simplifying assumptions are introduced. The selection of the next reaction firing by our approach is easier while preserving the exactness

  19. Radical-ion-pair reactions are the biochemical equivalent of the optical double-slit experiment.

    Science.gov (United States)

    Kominis, Iannis K

    2011-05-01

    Radical-ion-pair reactions were recently shown to represent a rich biophysical laboratory for the application of quantum measurement theory methods and concepts. Here we show that radical-ion-pair reactions essentially form a nonlinear biochemical double-slit interferometer. Quantum coherence effects are visible when "which-path" information is limited, and the incoherent limit is approached when measurement-induced decoherence sets in. Based on this analogy with the optical double-slit experiment we derive and elaborate on the fundamental master equation of spin-selective radical-ion-pair reactions that covers the continuous range from complete incoherence to maximum singlet-triplet coherence. PMID:21728616

  20. Simulation of the kinetics of precipitation reactions in ferritic steels

    International Nuclear Information System (INIS)

    Computer simulations of diffusion-controlled phase transformations in model alloys of Fe-Cr-C, Fe-Cr-W-C, Fe-Cr-Si-C, and Fe-Cr-Co-V-C are presented. The compositions considered are typical for ferritic steels. The simulations are performed using the software DICTRA and the thermodynamic calculations of phase equilibria are performed using Thermo-Calc. The thermodynamic driving forces and the kinetics of diffusion-controlled precipitation reactions of M23C6, M7C3, cementite and Laves-phase (Fe, Cr)2W are discussed. The simultaneous growth of stable and metastable phases is treated in a multi-cell approach. The results show remarkable effects on the growth kinetics due to the competition during simultaneous growth

  1. Hybrid Differential Evolution for Estimation of Kinetic Parameters for Biochemical Systems

    Institute of Scientific and Technical Information of China (English)

    ZHAO Chao; XU Qiaoling; LIN Siming; LI Xuelai

    2013-01-01

    Determination of the optimal model parameters for biochemical systems is a time consuming iterative process.In this study,a novel hybrid differential evolution(DE)algorithm based on the differential evolution technique and a local search strategy is developed for solving kinetic parameter estimation problems.By combining the merits of DE with Gauss-Newton method,the proposed hybrid approach employs a DE algorithm for identifying promising regions of the solution space followed by use of Gauss-Newton method to determine the optimum in the identified regions.Some well-known benchmark estimation problems are utilized to test the efficiency and the robustness of the proposed algorithm compared to other methods in literature.The comparison indicates that the present hybrid algorithm outperforms other estimation techniques in terms of the global searching ability and the convergence speed.Additionally,the estimation of kinetic model parameters for a feed batch fermentor is carried out to test the applicability of the proposed algorithm.The result suggests that the method can be used to estimate suitable values of model parameters for a complex mathematical model.

  2. Kinetics of the gas-phase tritium oxidation reaction

    International Nuclear Information System (INIS)

    Homogeneous gas-phase kinetics of tritium oxidation (2T2 + O2 →2T2O) have been studied with a model that accounts explicitly for radiolysis of the major species and the kinetics of the subsequent reactions of ionic, excited-state, and neutral species. Results from model calculations are given for 10-4 -1.0 mol% T2 in O2 (298 K, 1 atm). As the reaction evolves three different mechanisms control T2O production, each with a different overall rate expression and a different order with respect to the T2 concentration. The effects of self-radiolysis of pure T2 on the tritium oxidation reaction were calculated. Tritium atoms, the primary product of T2 self-radiolysis, altered the oxidation mechanism only during the first few seconds following the initiation of the T2-O2 reaction. Ozone, an important intermediate in T2 oxidation, was monitored in-situ by U.V. absorption spectroscopy for 0.01-1.0 mol% T2 an 1 atm O2. The shape of the experimental ozone time profile agreed with the model predictions. As predicted, the measured initial rate of ozone production varied linearly with initial T2 concentration ([T2]0.6o), but at an initial rate one-third the predicted value. The steady-state ozone concentration ([O3]ss) was predicted to be dependent on [T2]0.3o, but the measured value was [T2]0.6o, resulting in four times higher [O3]ss than predicted for a 1.0% T2-O2 mixture. Adding H2 to the T2-O2 mixture, to provide insight into the differences between the radiolytic and chemical behavior of the tritium, produced a greater decrease in [O3]ss than predicted. Adjusting the reaction cell surface-to-volume ratio showed implications of minor surface removal of ozone

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  4. Kinetics of the reactions of hydrated electrons with metal complexes

    International Nuclear Information System (INIS)

    The reactivity of the hydrated electron towards metal complexes is considered. Experiments are described involving metal EDTA and similar complexes. The metal ions studied are mainly Ni2+, Co2+ and Cu2+. Rates of the reactions of the complexes with e-(aq) were measured using the pulse radiolysis technique. It is shown that the reactions of e-(aq) with the copper complexes display unusually small kinetic salt effects. The results suggest long-range electron transfer by tunneling. A tunneling model is presented and the experimental results are discussed in terms of this model. Results of approximate molecular orbital calculations of some redox potentials are given, for EDTA chelates as well as for series of hexacyano and hexaquo complexes. Finally, equilibrium constants for the formation of ternary complexes are reported. (Auth./G.J.P.)

  5. Bayesian inference of chemical kinetic models from proposed reactions

    KAUST Repository

    Galagali, Nikhil

    2015-02-01

    © 2014 Elsevier Ltd. Bayesian inference provides a natural framework for combining experimental data with prior knowledge to develop chemical kinetic models and quantify the associated uncertainties, not only in parameter values but also in model structure. Most existing applications of Bayesian model selection methods to chemical kinetics have been limited to comparisons among a small set of models, however. The significant computational cost of evaluating posterior model probabilities renders traditional Bayesian methods infeasible when the model space becomes large. We present a new framework for tractable Bayesian model inference and uncertainty quantification using a large number of systematically generated model hypotheses. The approach involves imposing point-mass mixture priors over rate constants and exploring the resulting posterior distribution using an adaptive Markov chain Monte Carlo method. The posterior samples are used to identify plausible models, to quantify rate constant uncertainties, and to extract key diagnostic information about model structure-such as the reactions and operating pathways most strongly supported by the data. We provide numerical demonstrations of the proposed framework by inferring kinetic models for catalytic steam and dry reforming of methane using available experimental data.

  6. Modified Step Variational Iteration Method for Solving Fractional Biochemical Reaction Model

    Directory of Open Access Journals (Sweden)

    R. Yulita Molliq

    2011-01-01

    Full Text Available A new method called the modification of step variational iteration method (MoSVIM is introduced and used to solve the fractional biochemical reaction model. The MoSVIM uses general Lagrange multipliers for construction of the correction functional for the problems, and it runs by step approach, which is to divide the interval into subintervals with time step, and the solutions are obtained at each subinterval as well adopting a nonzero auxiliary parameter ℏ to control the convergence region of series' solutions. The MoSVIM yields an analytical solution of a rapidly convergent infinite power series with easily computable terms and produces a good approximate solution on enlarged intervals for solving the fractional biochemical reaction model. The accuracy of the results obtained is in a excellent agreement with the Adam Bashforth Moulton method (ABMM.

  7. Extension of a Kinetic-Theory Approach for Computing Chemical-Reaction Rates to Reactions with Charged Particles

    Science.gov (United States)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

    Recently introduced molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction rate information) are extended to include reactions involving charged particles and electronic energy levels. The proposed extensions include ionization reactions, exothermic associative ionization reactions, endothermic and exothermic charge exchange reactions, and other exchange reactions involving ionized species. The extensions are shown to agree favorably with the measured Arrhenius rates for near-equilibrium conditions.

  8. HRSSA - Efficient hybrid stochastic simulation for spatially homogeneous biochemical reaction networks

    Science.gov (United States)

    Marchetti, Luca; Priami, Corrado; Thanh, Vo Hong

    2016-07-01

    This paper introduces HRSSA (Hybrid Rejection-based Stochastic Simulation Algorithm), a new efficient hybrid stochastic simulation algorithm for spatially homogeneous biochemical reaction networks. HRSSA is built on top of RSSA, an exact stochastic simulation algorithm which relies on propensity bounds to select next reaction firings and to reduce the average number of reaction propensity updates needed during the simulation. HRSSA exploits the computational advantage of propensity bounds to manage time-varying transition propensities and to apply dynamic partitioning of reactions, which constitute the two most significant bottlenecks of hybrid simulation. A comprehensive set of simulation benchmarks is provided for evaluating performance and accuracy of HRSSA against other state of the art algorithms.

  9. Some kinetics aspects of chlorine-solids reactions

    Energy Technology Data Exchange (ETDEWEB)

    Kanari, N.; Mishra, D.; Mochon, J.; Verdeja, L. F.; Diot, F.; Allain, E.

    2010-07-01

    The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl{sub 2}+N{sub 2} (chlorination), Cl{sub 2}+O{sub 2} (oxy chlorination), and Cl{sub 2}+CO (carbochlorination). Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III) oxide was possible only above 500 degree centigrade. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.. (Author) 12 refs.

  10. Kinetics of the Self Reaction of Cyclopentadienyl Radicals.

    Science.gov (United States)

    Knyazev, Vadim D; Popov, Konstantin V

    2015-07-16

    The kinetics of the self-reaction of cyclopentadienyl radicals (c-C5H5) was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 304-600 K and at bath gas densities of (3.00-12.0) × 10(16) molecules cm(-3). The room-temperature value of the rate constant, (3.98 ± 0.41) × 10(-10) cm(3) molecule(-1) s(-1), is significantly higher than the rate constants for most hydrocarbon radical-radical reactions and coincides with the estimated collision rate. The observed overall c-C5H5 + c-C5H5 rate constant demonstrates an unprecedented strong negative temperature dependence: k1 = 2.9 × 10(-12) exp(+1489 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainty increasing with temperature, from 13% at 304 to 32% at 600 K. Formation of C10H10 as the primary product of cyclopentadienyl self-reaction was observed. In additional experiments performed at the temperature of 800 K, formation of C10H10, C10H9, and C10H8 was observed. Final product analysis by gas chromatography/mass spectrometry detected two isomers of C10H8 at 800 K: naphthalene (major) and azulene (minor). PMID:25760686

  11. Biochemical Properties and Inhibition Kinetics of Phosphatase from Wheat Thylakoid Membranes

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A phosphatase that hydrolyses phosphate monoesters has been isolated from wheat thylakoid membranes.Biochemical properties and inhibition kinetics of the phosphatase were investigated using several ions, organic solvents, and inhibitors. Wheat (Triticum aestivum L. cv. PH82-2-2) thylakoid membrane phosphatase activity was activated by Mg2+, Ca2+, and Fe2+ and was inhibited by Mn2+ and Cu2+. For example, enzyme activity was activated 34.81% by 2 mmol/L Mg2+, but was inhibited 22.3% and 8.5% by 2 and 1 mmol/L Cu2+, respectively.Methanol, ethanol and glycol were all able to activate enzyme activity. Enzyme activity was activated 58.5%, 48.2%,and 8.7% by 40% ethanol, methanol and glycol, respectively. From these results, it can be seen that the degree of activation of the phosphatase was greatest for ethanol and the type of activation was uncompetitive. Moreover,the activity of the thylakoid membrane phosphatase was inhibited by molybdate, vanadate, phosphate, and fluoride and the type of inhibition produced by these elements was uncompetitive, non-competitive, competitive and mixed, respectively.

  12. Biochemical reactions in crowded environments: Revisiting the effects of volume exclusion with simulations

    Directory of Open Access Journals (Sweden)

    David eGomez

    2015-06-01

    Full Text Available Molecular crowding is ubiquitous within cells and affects many biological processes including protein-protein binding, enzyme activities and gene regulation. Here we revisit some generic effects of crowding using a combination of lattice simulations and reaction-diffusion simulations with the program ReaDDy. Specifically, we implement three reactions, simple binding, a diffusion-limited reaction and a reaction with Michaelis-Menten kinetics. Histograms of binding and unbinding times provide a detailed picture how crowding affects these reactions and how the separate effects of crowding on binding equilibrium and on diffusion act together. In addition, we discuss how crowding affects processes related to gene expression such as RNA polymerase-promoter binding and translation elongation.

  13. Biochemical reactions in crowded environments: Revisiting the effects of volume exclusion with simulations

    Science.gov (United States)

    Gomez, David; Klumpp, Stefan

    2015-06-01

    Molecular crowding is ubiquitous within cells and affects many biological processes including protein-protein binding, enzyme activities and gene regulation. Here we revisit some generic effects of crowding using a combination of lattice simulations and reaction-diffusion simulations with the program ReaDDy. Specifically, we implement three reactions, simple binding, a diffusion-limited reaction and a reaction with Michaelis-Menten kinetics. Histograms of binding and unbinding times provide a detailed picture how crowding affects these reactions and how the separate effects of crowding on binding equilibrium and on diffusion act together. In addition, we discuss how crowding affects processes related to gene expression such as RNA polymerase-promoter binding and translation elongation.

  14. Spectator Ions ARE Important! A Kinetic Study of the Copper-Aluminum Displacement Reaction

    Science.gov (United States)

    Sobel, Sabrina G.; Cohen, Skyler

    2010-01-01

    Surprisingly, spectator ions are responsible for unexpected kinetics in the biphasic copper(II)-aluminum displacement reaction, with the rate of reaction dependent on the identity of the otherwise ignored spectator ions. Application of a published kinetic analysis developed for a reaction between a rotating Al disk and a Cu(II) ion solution to the…

  15. Reaction Kinetics of Meteoric Sodium Reservoirs in the Upper Atmosphere.

    Science.gov (United States)

    Gómez Martín, J C; Garraway, S A; Plane, J M C

    2016-03-10

    The gas-phase reactions of a selection of sodium-containing species with atmospheric constituents, relevant to the chemistry of meteor-ablated Na in the upper atmosphere, were studied in a fast flow tube using multiphoton ionization time-of-flight mass spectrometry. For the first time, unambiguous observations of NaO and NaOH in the gas phase under atmospheric conditions have been achieved. This enabled the direct measurement of the rate constants for the reactions of NaO with H2, H2O, and CO, and of NaOH with CO2, which at 300-310 K were found to be (at 2σ confidence level): k(NaO + H2O) = (2.4 ± 0.6) × 10(-10) cm(3) molecule (-1) s(-1), k(NaO + H2) = (4.9 ± 1.2) × 10(-12) cm(3) molecule (-1) s(-1), k(NaO + CO) = (9 ± 4) × 10(-11) cm(3) molecule (-1) s(-1), and k(NaOH + CO2 + M) = (7.6 ± 1.6) × 10(-29) cm(6) molecule (-2) s(-1) (P = 1-4 Torr). The NaO + H2 reaction was found to make NaOH with a branching ratio ≥ 99%. A combination of quantum chemistry and statistical rate theory calculations are used to interpret the reaction kinetics and extrapolate the atmospherically relevant experimental results to mesospheric temperatures and pressures. The NaO + H2O and NaOH + CO2 reactions act sequentially to provide the major atmospheric sink of meteoric Na and therefore have a significant impact on the underside of the Na layer in the terrestrial mesosphere: the newly determined rate constants shift the modeled peak to about 93 km, i.e., 2 km higher than observed by ground-based lidars. This highlights further uncertainties in the Na chemistry cycle such as the unknown rate constant of the NaOH + H reaction. The fast Na-recycling reaction between NaO and CO and a re-evaluated rate constant of the NaO + CO2 sink should be now considered in chemical models of the Martian Na layer. PMID:25723735

  16. Variable elimination in chemical reaction networks with mass action kinetics

    CERN Document Server

    Feliu, Elisenda

    2011-01-01

    We consider chemical reaction networks taken with mass action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination of variables. The procedure reduces the variables in the system to a set of "core" variables by eliminating variables corresponding to a set of non-interacting species. The steady states are parameterized algebraically by the core variables, and a graphical condition is given for when a steady state with positive core variables necessarily have all variables positive. Further, we characterize graphically the sets of eliminated variables that are constrained by a conservation law and show that this conservation law takes a specific form.

  17. Reaction kinetics of annealing of high energy implantation by XRD

    International Nuclear Information System (INIS)

    The annealing of structural defects caused by high energy implantation is studied using X-ray diffraction. The implanted sample (dose: 1 x 1014 ions/cm2) was isochronally annealed in flowing nitrogen in steps of 50 K up to 823 K for 10 min each, using a RTA system developed in Mumbai University. XRD patterns were recorded after each annealing and analyzed for strain and curvature. Also, the screw dislocation density was estimated at each stage of annealing using the FWHM of w scans in high resolution mode. The XRD profiles were simulated using the dynamical theory of X-ray diffraction for layer damage i.e. thickness, mismatch with respect to substrate, Debye Waller factor and sample curvature. The activation energy and characteristic temperature of annealing were estimated through reaction kinetics, utilizing the experimental XRD for progressive changes with temperature, of strain and dislocation density

  18. Kinetic Deuterium Isotope Effects in Cytochrome P450 Oxidation Reactions

    Science.gov (United States)

    Guengerich, F. Peter

    2016-01-01

    Cytochrome P450 (P450) enzymes account for ~ 75% of the metabolism of drugs. Most of the reactions catalyzed by P450s are mixed-function oxidations, and a C-H bond is (usually) broken. The rate-limiting nature of this step can be analyzed using the kinetic isotope effect (KIE) approach. The most relevant type of KIE is one termed intermolecular non-competitive, indicative of rate-limiting C-H bond breaking. A KIE vs. kcat for several P450s showed a correlation coefficient (r2) of 0.62. Deuterium substitution has been considered as a potential means of slowing drug metabolism or redirecting sites of metabolism in some cases, and several general points can be made regarding the potential for application of deuterium in drug design/development based on what is known about P450 KIEs. PMID:24285515

  19. The mechanism and kinetics of epoxy-amine reactions

    International Nuclear Information System (INIS)

    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

  20. Nuclear quantum effects and kinetic isotope effects in enzyme reactions.

    Science.gov (United States)

    Vardi-Kilshtain, Alexandra; Nitoker, Neta; Major, Dan Thomas

    2015-09-15

    Enzymes are extraordinarily effective catalysts evolved to perform well-defined and highly specific chemical transformations. Studying the nature of rate enhancements and the mechanistic strategies in enzymes is very important, both from a basic scientific point of view, as well as in order to improve rational design of biomimetics. Kinetic isotope effect (KIE) is a very important tool in the study of chemical reactions and has been used extensively in the field of enzymology. Theoretically, the prediction of KIEs in condensed phase environments such as enzymes is challenging due to the need to include nuclear quantum effects (NQEs). Herein we describe recent progress in our group in the development of multi-scale simulation methods for the calculation of NQEs and accurate computation of KIEs. We also describe their application to several enzyme systems. In particular we describe the use of combined quantum mechanics/molecular mechanics (QM/MM) methods in classical and quantum simulations. The development of various novel path-integral methods is reviewed. These methods are tailor suited to enzyme systems, where only a few degrees of freedom involved in the chemistry need to be quantized. The application of the hybrid QM/MM quantum-classical simulation approach to three case studies is presented. The first case involves the proton transfer in alanine racemase. The second case presented involves orotidine 5'-monophosphate decarboxylase where multidimensional free energy simulations together with kinetic isotope effects are combined in the study of the reaction mechanism. Finally, we discuss the proton transfer in nitroalkane oxidase, where the enzyme employs tunneling as a catalytic fine-tuning tool. PMID:25769515

  1. Kinetic study of hydrated lime reaction with HCl.

    Science.gov (United States)

    Yan, Rong; Chin, Terence; Liang, David Tee; Laursen, Karin; Ong, Wan Yean; Yao, Kaiwen; Tay, Joo Hwa

    2003-06-01

    Hydrochloride (HCl) is an acidic pollutant present in the flue gas of most municipal or hazardous waste incinerators. Hydrated lime (Ca(OH)2) is often used as a dry sorbent for injection in a spray reactor to remove HCI. However, due to the short residence time encountered, this control method has generally been found to have low conversion efficiencies which results in the high lime usage and generates large amount of fly ash as solid wastes. A fundamental study was carried outto investigate the kinetics of HCl-lime reaction under simulated flue gas conditions in order to better understand the process thereby providing a basis for an optimized lime usage and reduced fly ash production. The initial reaction rate and conversion of three limes were studied using a thermogravimetric analyzer by varying the gas flow rate, temperature (170-400 degrees C), and HCI concentrations (600-1200 mg/m3) as well as the associated particle size and surface area of the limes. The initial lime conversions were found to rely mostly on the residence time, while the ultimate lime conversions were strongly influenced by temperature and the reaction products. CaOHCI was found to be the primary product in most cases, while for one specific lime, CaCl2 was the ultimate conversion product after an extended time period. The true utilization of lime in flue gas cleanup is thus higher when CaOHCl is considered as the final product than those based on CaCl2 as the final product, which has been commonly used in previous studies. The initial reaction was controlled by diffusion of HCl in gas phase and the subsequent reaction by gaseous diffusion through the developing product layer. Increasing the HCI concentration raised the initial rate as well as conversion. However, overloading the lime with excessive HCI caused clogging at its surface and a drop in the ultimate conversion. Limes with smaller particle diameters and higher surface areas were found to be more reactive. The effect of gas

  2. Thin film reaction kinetics of niobium/aluminum multilayers

    International Nuclear Information System (INIS)

    Phase formation kinetics in Nb/Al multilayered thin films having overall compositions of 25, 33, 50, and 75 at. % Al have been investigated using scanning calorimetry, x-ray diffraction, and cross-sectional transmission electron microscopy. The first phase to form upon annealing the Nb/Al layered structure of all samples is the NbAl3 intermetallic. Calorimetry clearly identifies the NbAl3 formation to be a two-stage process. The first stage is the formation of a planar layer by nucleation and growth to coalescence while the second stage is the thickening of the planar layer. The large amount of heat released (and hence large volume fraction of NbAl3 formed) during the first reaction stage is consistent with heterogeneous nucleation at well-isolated sites in the Nb/Al interface. This is surprising in light of the large thermodynamic driving force expected for nucleation and suggests that the local nonequilibrium nature of the Nb/Al interface greatly reduces the driving force for nucleation. The next phase observed in samples of 25 and 33 at. % Al is the A15 superconducting phase, Nb3Al. The Nb3Al growth completes a first reaction stage similar to the NbAl3, but the subsequent thickening reaction stage is not observed without simultaneous Nb2Al growth. The high interface velocities derived from the calorimetry for formation of both NbAl3 and the A15 Nb3Al indicate that atomic transport must be by grain boundary diffusion

  3. Effects of temperature on biochemical reactions and drug resistance of virulent and avirulent Aeromonas salmonicida

    Science.gov (United States)

    Hahnel, G.B.; Gould, R.W.

    1982-01-01

    Incubation temperatures of 11°, 18° and 28° did not substantially affect biochemical reactions of either virulent or avirulent forms of Aeromonas salmonicida subspecies salmonicida. The only change observed, amygdalin fermentation, was positive at 11° and 18° but negative at 28°C. Several isolates utilized sucrose, a characteristic not normally recognized for A. salmonicida subspecies salmonicida.Antimicrobial susceptibility screening indicated resistance to novobiocin increased at the higher incubation temperatures. Standardized drug sensitivity testing procedures and precise zone diameter interpretive standards for bacterial fish pathogens are needed.

  4. Introduction to dynamic spin chemistry magnetic field effects on chemical and biochemical reactions

    CERN Document Server

    Hayashi, Hisaharu

    2004-01-01

    This book presents a detailed account of one of the most mysterious problems in science - whether ordinary magnetic fields can exert an appreciable influence on chemical and biochemical reactions. The first aim of the book is to introduce this research, through theoretical and dynamic spin chemistry, to graduate students and researchers, by means of detailed theoretical and experimental descriptions. The second aim is to review typical recent investigations, which will stimulate new interest and applications in the 21st century. Because dynamic spin chemistry is based on established science, i

  5. Reaction kinetics of dual setting α-tricalcium phosphate cements.

    Science.gov (United States)

    Hurle, Katrin; Christel, Theresa; Gbureck, Uwe; Moseke, Claus; Neubauer, Juergen; Goetz-Neunhoeffer, Friedlinde

    2016-01-01

    Addition of ductile polymers to calcium-deficient hydroxyapatite (CDHA)-forming bone cements based on α-tricalcium phosphate (α-TCP) is a promising approach to improve the mechanical performance of α-TCP cements and extend their application to load-bearing defects, which is else impeded by the brittleness of the hardened cement. One suitable polymer is poly-(2-hydroxyethylmethacrylate) (p-HEMA), which forms during cement setting by radical polymerisation of the monomer. In this study the hydration kinetics and the mechanical performance of α-TCP cements modified with addition of different HEMA concentrations (0-50 wt% in the cement liquid) was investigated by quantitative in situ XRD and four-point bending tests. Morphology of CDHA crystals was monitored by scanning electron microscopy. The hydration of α-TCP to CDHA was increasingly impeded and the visible crystal size of CDHA increasingly reduced with increasing HEMA concentration. Modification of the cements by adding 50 wt% HEMA to the cement liquid changed the brittle performance of the hardened cement to a pseudoplastic behaviour, reduced the flexural modulus and increased the work of fracture, while lower HEMA concentrations had no significant effect on these parameters. In such a composite, the extent of CDHA formation was considerably reduced (34.0 ± 1.8 wt% CDHA with 50 % HEMA compared to 54.1 ± 2.4 wt% CDHA in the reference formed after 48 h), while the general reaction kinetics were not changed. In conclusion, while the extent of CDHA formation was decreased, the mechanical properties were noticeably improved by addition of HEMA. Hence, α-TCP/HEMA composites might be suitable for application in some load-bearing defects and have adequate properties for mechanical treatment after implantation, like insertion of screws. PMID:26610924

  6. Proton mediated control of biochemical reactions with bioelectronic pH modulation

    Science.gov (United States)

    Deng, Yingxin; Miyake, Takeo; Keene, Scott; Josberger, Erik E.; Rolandi, Marco

    2016-04-01

    In Nature, protons (H+) can mediate metabolic process through enzymatic reactions. Examples include glucose oxidation with glucose dehydrogenase to regulate blood glucose level, alcohol dissolution into carboxylic acid through alcohol dehydrogenase, and voltage-regulated H+ channels activating bioluminescence in firefly and jellyfish. Artificial devices that control H+ currents and H+ concentration (pH) are able to actively influence biochemical processes. Here, we demonstrate a biotransducer that monitors and actively regulates pH-responsive enzymatic reactions by monitoring and controlling the flow of H+ between PdHx contacts and solution. The present transducer records bistable pH modulation from an “enzymatic flip-flop” circuit that comprises glucose dehydrogenase and alcohol dehydrogenase. The transducer also controls bioluminescence from firefly luciferase by affecting solution pH.

  7. Proton mediated control of biochemical reactions with bioelectronic pH modulation

    Science.gov (United States)

    Deng, Yingxin; Miyake, Takeo; Keene, Scott; Josberger, Erik E.; Rolandi, Marco

    2016-01-01

    In Nature, protons (H+) can mediate metabolic process through enzymatic reactions. Examples include glucose oxidation with glucose dehydrogenase to regulate blood glucose level, alcohol dissolution into carboxylic acid through alcohol dehydrogenase, and voltage-regulated H+ channels activating bioluminescence in firefly and jellyfish. Artificial devices that control H+ currents and H+ concentration (pH) are able to actively influence biochemical processes. Here, we demonstrate a biotransducer that monitors and actively regulates pH-responsive enzymatic reactions by monitoring and controlling the flow of H+ between PdHx contacts and solution. The present transducer records bistable pH modulation from an “enzymatic flip-flop” circuit that comprises glucose dehydrogenase and alcohol dehydrogenase. The transducer also controls bioluminescence from firefly luciferase by affecting solution pH. PMID:27052724

  8. Kinetics of the self reaction of cyclohexyl radicals.

    Science.gov (United States)

    Loginova, Ksenia A; Knyazev, Vadim D

    2011-08-11

    The kinetics of the self-reaction of cyclohexyl radicals was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 303-520 K and at bath gas (helium with up to 5% of radical precursors) densities (3.00-12.0) × 10(16) molecules cm(-3). Cyclohexyl radicals were produced by a combination of the 193 nm photolysis of oxalyl chloride ((CClO)(2)) with the subsequent fast reaction of Cl atoms with cyclohexane, and their initial concentrations were determined from real-time profiles of HCl. The observed overall c-C(6)H(11) + c-C(6)H(11) rate constants demonstrate negative temperature dependence, which can be described by the following expressions: k(1) = 4.8 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainty of 16% over the 303-520 K temperature range. The fraction of disproportionation equal to 41 ± 7% was determined at 305 K; analysis of earlier experimental determinations of the disproportionation-to-recombination branching ratio leads to recommending this room-temperature value for other temperatures. The corresponding temperature dependences of the recombination (1a, bicyclohexyl product) and the disproportionation (1b, cyclohexene and cyclohexane products) channels are k(1a) = 2.8 × 10(-12) exp(+542 K/T) and k(1b) = 2.0 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainties of 20% and 29%, respectively. PMID:21702489

  9. Constraining kinetic rates of mineral reactions using reactive transport models

    Science.gov (United States)

    Bolton, E. W.; Wang, Z.; Ague, J.; Bercovici, D.; Cai, Z.; Karato, S.; Oristaglio, M. L.; Qiu, L.

    2012-12-01

    We use a reactive transport model to better understand results of experiments to obtain kinetic rates of mineral reactions in closed systems. Closed system experiments pose special challenges in that secondary minerals may form that modify the fluid composition evolution and may grow on the dissolving minerals thus armoring the surface. Even so, such closed system experiments provide critical data for what minerals would actually form in field applications and how coupled dissolution and precipitation mineral reactions are strongly linked. Comparing to experimental observations can test the reactive transport model, and the experimental observations can be better understood by comparing the results to the modeling. We apply a 0D end member of the model to understand the dissolution of single crystals of forsterite in a variety of settings (low pH, high pH, or NaHCO3 initial fluids, at 100 C and 1 bar, or 200 C and 150 bar). Depending on the initial conditions, we observe the precipitation of talc, brucite, amorphous silica, chrysotile, or magnesite, in various combinations. We compare simulation results to fluid compositions and the presence of secondary minerals experimentally sampled at various times. Insight from the simulations helped create an inverse model to extract the rates of forsterite dissolution and to create a simple forward model useful for exploring the influence of system size, secondary mineral surface areas, etc. Our reactive transport model allows secondary minerals to armor the forsterite surface, which can strongly decrease the dissolution rate as the system evolves. Tuning our model with experimentally derived rates and assuring relevant processes are included so as to reproduce experimental observations is necessary before upscaling to heterogeneous field conditions. The reactive transport model will be used for field-scale sequestration simulations and coupled with a geomechanical model that includes the influence of deformation.

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

    Science.gov (United States)

    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…

  11. Theory of Square-wave Voltammetry of Kinetically Controlled Two-step Electrode Reactions

    OpenAIRE

    Lovrić, Milivoj; Komorsky-Lovrić, Šebojka

    2012-01-01

    An influence of electron transfer kinetics on square-wave voltammograms of two-step electrode reaction is investigated theoretically. A phenomenon of “kinetic burden” of potential inversion is described for the case of equal kinetic parameters. A linear relationship between standard rate constant and the difference between standard potentials of the second and the first charge transfers is demonstrated for the reactions with thermodynamically unstable intermediate. (doi: 10.5562/cca2126)

  12. Kinetics of the Uninhibited Reaction of 2-Chloropropene-Part II: Comparison with Inhibited Reaction

    International Nuclear Information System (INIS)

    The kinetics of the uninhibited reaction of 2-chloropropene in the gas-phase has been studied between 662 and 747 K at pressures ranging from 11 to 76 Torr with the object of determining the overall mechanism using static system. The reaction was found to be accurately of the first order at the high pressures and the observed rate coefficient is expressed by the following Arrhenius equation:K sub total (uninhibited) = 10 super 7.98 ± 0.6 (s super -1) exp super -167 ± 7.8 (kJ/mole)/RT The activation energy was calculated at 167 ± 7.98kJ/mol and identified with the dissociation of C-Cl bond. The reaction is pressured to be unimolecular at lower temperature with formation of propyne and elimination of hydrogen chloride. However, at high temperature C-Cl bond fission takes place and this changes the mechanism of the reaction. Two mechanisms dehydrohalogenation molecular elimination and C-Cl bond fission are discussed. (author)

  13. Reaction of Phenyl Radical with O2: Thermodynamic Properties, Important Reaction Paths and Kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Bozzelli, J; Sebbar, N; Pitz, W; Bockhorn, H

    2001-04-12

    The Phenyl + O{sub 2} association results in a chemically activated phenyl-peroxy radical which can dissociate to phenoxy radical + O, undergo intramolecular addition of the peroxy radical to several unsaturated carbon sites or react back to phenyl + O{sub 2}. The intramolecular addition channels further react through several paths to ring opening (unsaturated + carbonyl moieties) as well as cyclopentadieny radical + CO{sub 2}. Enthalpy ({Delta}H{sub f(298)}{sup o}), Entropy (S{sub 298}), and heat capacities Cp(T) for species in the decomposition of the ring are evaluated using density functional and ab initio calculations and by comparisons to vinyl + O{sub 2} data of Mebel et al, and phenyl + O{sub 2} data of Hadad et al. Isodesmic reaction analysis is used to estimate enthalpy values of the intermediates and well depths of the adducts. High Pressure limit kinetic parameters are obtained from the calculation results using canonical Transition State Theory. Quantum RRK analysis is utilized to obtain k(E) and modified strong collision or master equation analysis is used for evaluation of pressure fall-off in this complex bimolecular, chemical activation, reaction system. Uncertainty in key barriers is discussed, resulting variations in important reaction product ratios are illustrated, and changes in these branching ratios are evaluated with a detailed reaction mechanism.

  14. Kinetic analysis of complex solid-state reactions. A new deconvolution procedure

    OpenAIRE

    Perejón, Antonio; Sánchez-Jiménez, P.E.; Criado, J. M.; Pérez-Maqueda, Luis A

    2011-01-01

    The kinetic analysis of complex solid-state reactions that involve simultaneous overlapping processes is challenging. A method that involves the deconvolution of the individual processes from the overall differential kinetic curves obtained under linear heating rate conditions, followed by the kinetic analysis of the discrete processes using combined kinetic analysis, is proposed. Different conventional mathematical fitting functions have been tested for deconvolution, paying special attentio...

  15. Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

    Institute of Scientific and Technical Information of China (English)

    Fandong Meng; Genhui Xu; Zhenhua Li; Pa Du

    2002-01-01

    The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.

  16. Soil solid materials affect the kinetics of extracellular enzymatic reactions

    Science.gov (United States)

    Lammirato, C.; Miltner, A.; Kästner, M.

    2009-04-01

    INTRODUCTION Soil solid materials affect the degradation processes of many organic compounds by decreasing the bioavailability of substrates and by interacting with degraders. The magnitude of this effect in the environment is shown by the fact that xenobiotics which are readily metabolized in aquatic environments can have long residence times in soil. Extracellular enzymatic hydrolysis of cellobiose (enzyme: beta-glucosidase from Aspergillus niger) was chosen as model degradation process since it is easier to control and more reproducible than a whole cell processes. Furthermore extracellular enzymes play an important role in the environment since they are responsible for the first steps in the degradation of organic macromolecules; beta-glucosidase is key enzyme in the degradation of cellulose and therefore it is fundamental in the carbon cycle and for soil in general. The aims of the project are: 1) quantification of solid material effect on degradation, 2) separation of the effects of minerals on enzyme (adsorption →change in activity) and substrate (adsorption →change in bioavailability). Our hypothesis is that a rate reduction in the enzymatic reaction in the presence of a solid phase results from the sum of decreased bioavailability of the substrate and decreased activity of enzyme molecules. The relative contribution of the two terms to the overall effect can vary widely depending on the chemical nature of the substrate, the properties of the enzyme and on the surface properties of the solid materials. Furthermore we hypothesize that by immobilizing the enzyme in an appropriate carrier the adsorption of enzymes to soil materials can be eliminated and that therefore immobilization can increase the overall reaction rate (activity loss caused by immobilization activity loss caused by adsorption to soil minerals). MATERIALS AND METHODS Enzymatic kinetic experiments are carried out in homogeneous liquid systems and in heterogeneous systems where solid

  17. Evaluating the effect of potassium on cellulose pyrolysis reaction kinetics

    International Nuclear Information System (INIS)

    This paper proposes modifications to an existing cellulose pyrolysis mechanism in order to include the effect of potassium on product yields and composition. The changes in activation energies and pre-exponential factors due to potassium were evaluated based on the experimental data collected from pyrolysis of cellulose samples treated with different levels of potassium (0–1% mass fraction). The experiments were performed in a pyrolysis reactor coupled to a molecular beam mass spectrometer (MBMS). Principal component analysis (PCA) performed on the collected data revealed that cellulose pyrolysis products could be divided into two groups: anhydrosugars and other fragmentation products (hydroxyacetaldehyde, 5-hydroxymethylfurfural, acetyl compounds). Multivariate curve resolution (MCR) was used to extract the time resolved concentration score profiles of principal components. Kinetic tests revealed that potassium apparently inhibits the formation of anhydrosugars and catalyzes char formation. Therefore, the oil yield predicted at 500 °C decreased from 87.9% from cellulose to 54.0% from cellulose with 0.5% mass fraction potassium treatment. The decrease in oil yield was accompanied by increased yield of char and gases produced via a catalyzed dehydration reaction. The predicted char and gas yield from cellulose were 3.7% and 8.4%, respectively. Introducing 0.5% mass fraction potassium treatment resulted in an increase of char yield to 12.1% and gas yield to 33.9%. The validation of the cellulose pyrolysis mechanism with experimental data from a fluidized-bed reactor, after this correction for potassium, showed good agreement with our results, with differences in product yields of up to 5%

  18. Growth kinetics of forsterite reaction rims at high-pressure

    Science.gov (United States)

    Nishihara, Yu; Maruyama, Genta; Nishi, Masayuki

    2016-08-01

    Growth kinetics of forsterite (Fo) reaction rims between periclase (Per) and enstatite (En) were studied experimentally at pressure (P) and temperature (T) conditions of 3.0-11.1 GPa and 1473-1873 K, respectively. Pt markers originally placed at the Per-En interface were always observed at the Per-Fo interface, which indicates that Mg and O are the diffusing species in Fo rim growth (Mg-O coupled diffusion). The presence of some En inclusions in Fo grains and the growth rate of the Fo rim suggests that grain boundary diffusion is dominant rather than lattice diffusion. Considering the very fast grain boundary diffusion of O in olivine, the Mg-O coupled grain boundary diffusion in Fo is deduced to be rate-limited by the diffusivity of Mg. Based on an analysis of data collected under dry conditions, the product of the Mg grain boundary diffusion coefficient (Dgb) and the effective grain boundary width (δ) was determined to be δDgb = δDgb,0exp[-(E∗ + PV∗)/RT] with δDgb,0 = 10-9.68 ± 1.51 m3/s, E∗ = 379 ± 44 kJ/mol and V∗ = -1.9 ± 1.4 cm3/mol. Our results, combined with previously reported data on Mg lattice diffusion in Fo, suggest that for Mg, the significance of grain boundary diffusion increases with depth in the Earth's upper mantle, although lattice diffusion is still dominant for typical mantle grain sizes of 1-10 mm.

  19. Kinetics of exciplex formation/dissipation in reaction following Weller Scheme II

    Energy Technology Data Exchange (ETDEWEB)

    Fedorenko, S. G. [Voevodsky Institute of Chemical Kinetics and Combustion, Novosibirsk (Russian Federation); Burshtein, A. I. [Weizmann Institute of Science, 76100, Rehovot (Israel)

    2014-09-21

    Creation of exciplexes from the charged products of photoionization is considered by means of Integral Encounter Theory. The general kinetic equations of such a reaction following the Weller scheme II are developed. The special attention is given to the particular case of irreversible remote ionization of primary excited electron donor. Kinetics of exciplex formation is considered at fast biexponential geminate transformation of exciplexes in cage that gives way to subsequent bulk reaction of equilibrated reaction products controlled by power law recombination of ions. It is shown that the initial geminate stage of exciplex kinetics is observed only in diffusion controlled regime of the reaction and disappears with increasing mobility of ions in passing to kinetic regime. The quantum yield of exciplexes is studied along with their kinetics.

  20. A computational approach to persistence, permanence, and endotacticity of biochemical reaction systems.

    Science.gov (United States)

    Johnston, Matthew D; Pantea, Casian; Donnell, Pete

    2016-01-01

    We introduce a mixed-integer linear programming (MILP) framework capable of determining whether a chemical reaction network possesses the property of being endotactic or strongly endotactic. The network property of being strongly endotactic is known to lead to persistence and permanence of chemical species under genetic kinetic assumptions, while the same result is conjectured but as yet unproved for general endotactic networks. The algorithms we present are the first capable of verifying endotacticity of chemical reaction networks for systems with greater than two constituent species. We implement the algorithms in the open-source online package CoNtRol and apply them to a large sample of networks from the European Bioinformatics Institute's BioModels Database. We use strong endotacticity to establish for the first time the permanence of a well-studied circadian clock mechanism. PMID:25986743

  1. Kinetic Modelling of the Maillard Browning Reaction in Pekmez (Grape Molasses)

    OpenAIRE

    Bozkurt, Hüseyin; Göğüş, Fahrettin; Eren, Sami

    1998-01-01

    The effects of pH, temperature and total solube solids on the Maillard reactions which occurred during the storage of Pekmez were determined using accelerated storage test. The reaction was followed measurement of by the amount of 5-Hydroxymethyl furfural, an intermediate product of the Maillard reaction. The change in the reaction rate was defined with a kinetic model as a function of pH, temperature and the total soluble solids. The reaction rate was correlated with the independen...

  2. Reaction kinetics of the iron-catalysed decomposition of SO3 / Abraham Frederik van der Merwe

    OpenAIRE

    Van der Merwe, Abraham Frederik

    2014-01-01

    In this study the performance of pure, very fine iron (III) oxide powder was investigated as catalyst for the decomposition of sulphur trioxide into sulphur dioxide and oxygen. This highly endothermic reaction requires a catalyst to lower the reaction temperature. This reaction forms part of the HyS (Hybrid Sulphur) cycle, a proposed thermochemical process for the industrial scale production of hydrogen and oxygen from water. The study aimed at obtaining reaction kinetics for this reaction...

  3. Some kinetics aspects of chlorine-solids reactions

    Directory of Open Access Journals (Sweden)

    Kanari, N.

    2010-02-01

    Full Text Available The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl2+N2 (chlorination, Cl2+O2 (oxychlorination, and Cl2+CO (carbochlorination. Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III oxide was possible only above 500 °C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.

    Este trabajo describe detalladas investigaciones cinéticas en algunas reacciones seleccionadas de cloro-sólido a través de medidas termogravimétricas. Los sólidos estudiados en este artículo incluyen óxidos químicos puros y sulfuros, así como sus materiales naturales de soporte. Los agentes de cloración empleados son mezclas de gases de Cl2+N2 (cloración, Cl2+O2 (oxicloración y Cl2+O2 (carbocloración. Los resultados se presentan como efecto de varios parámetros en el porcentaje de reacción de estos sólidos con los agentes de cloración. Se ha observado que la reactividad de estos sólidos a través de diferentes agentes de cloración varía ampliamente. Los sulfuros se pudieron

  4. Reaction kinetics of oxygen on single-phase alloys, oxidation of nickel and niobium alloys

    International Nuclear Information System (INIS)

    This research thesis first addresses the reaction kinetics of oxygen on alloys. It presents some generalities on heterogeneous reactions (conventional theory, theory of jumps), discusses the core reaction (with the influence of pressure), discusses the influence of metal self-diffusion on metal oxidation kinetics (equilibrium conditions at the interface, hybrid diffusion regime), reports the application of the hybrid diffusion model to the study of selective oxidation of alloys (Wagner model, hybrid diffusion model) and the study of the oxidation kinetics of an alloy forming a solid solution of two oxides. The second part reports the investigation of the oxidation of single phase nickel and niobium alloys (phase α, β and γ)

  5. Kinetics of the γ-radiation-initiated reaction of 2-propanol with tri- and hexafluoropropylene

    International Nuclear Information System (INIS)

    The initiation of telomerization reactions by ionizing radiation provides good opportunities for studying the kinetics of free radical reactions. The fluoroalcohols and their derivatives prepared using fluoroolefins and aliphatic alcohols find wide practical application. The object of this exercise was to study the reactivity of trifluoropropylene and hexafluoropropylene with 2-propanol. The reaction products were analyzed gas chromatographically

  6. Influence of hydrogen fluoride on kinetics of thermal reaction of hydrogen with chlorine monofluoride

    Energy Technology Data Exchange (ETDEWEB)

    Zhitneva, G.P.

    1986-07-01

    The influence of HF on the kinetics of the thermal reaction of H/sub 2/ with ClF in a fused quartz vessel was studied. It was shown that HF inbibits the reaction by blocking the reaction centers on the vessel surface, which lowers the rate of the heterogeneous generation of chains.

  7. Stochastic focusing coupled with negative feedback enables robust regulation in biochemical reaction networks.

    Science.gov (United States)

    Milias-Argeitis, Andreas; Engblom, Stefan; Bauer, Pavol; Khammash, Mustafa

    2015-12-01

    Nature presents multiple intriguing examples of processes that proceed with high precision and regularity. This remarkable stability is frequently counter to modellers' experience with the inherent stochasticity of chemical reactions in the regime of low-copy numbers. Moreover, the effects of noise and nonlinearities can lead to 'counterintuitive' behaviour, as demonstrated for a basic enzymatic reaction scheme that can display stochastic focusing (SF). Under the assumption of rapid signal fluctuations, SF has been shown to convert a graded response into a threshold mechanism, thus attenuating the detrimental effects of signal noise. However, when the rapid fluctuation assumption is violated, this gain in sensitivity is generally obtained at the cost of very large product variance, and this unpredictable behaviour may be one possible explanation of why, more than a decade after its introduction, SF has still not been observed in real biochemical systems. In this work, we explore the noise properties of a simple enzymatic reaction mechanism with a small and fluctuating number of active enzymes that behaves as a high-gain, noisy amplifier due to SF caused by slow enzyme fluctuations. We then show that the inclusion of a plausible negative feedback mechanism turns the system from a noisy signal detector to a strong homeostatic mechanism by exchanging high gain with strong attenuation in output noise and robustness to parameter variations. Moreover, we observe that the discrepancy between deterministic and stochastic descriptions of stochastically focused systems in the evolution of the means almost completely disappears, despite very low molecule counts and the additional nonlinearity due to feedback. The reaction mechanism considered here can provide a possible resolution to the apparent conflict between intrinsic noise and high precision in critical intracellular processes. PMID:26609065

  8. Removal of triclosan via peroxidases-mediated reactions in water: Reaction kinetics, products and detoxification.

    Science.gov (United States)

    Li, Jianhua; Peng, Jianbiao; Zhang, Ya; Ji, Yuefei; Shi, Huanhuan; Mao, Liang; Gao, Shixiang

    2016-06-01

    This study investigated and compared reaction kinetics, product characterization, and toxicity variation of triclosan (TCS) removal mediated by soybean peroxidase (SBP), a recognized potential peroxidase for removing phenolic pollutants, and the commonly used horseradish peroxidase (HRP) with the goal of assessing the technical feasibility of SBP-catalyzed removal of TCS. Reaction conditions such as pH, H2O2 concentration and enzyme dosage were found to have a strong influence on the removal efficiency of TCS. SBP can retain its catalytic ability to remove TCS over broad ranges of pH and H2O2 concentration, while the optimal pH and H2O2 concentration were 7.0 and 8μM, respectively. 98% TCS was removed with only 0.1UmL(-1) SBP in 30min reaction time, while an HRP dose of 0.3UmL(-1) was required to achieve the similar conversion. The catalytic performance of SBP towards TCS was more efficient than that of HRP, which can be explained by catalytic rate constant (KCAT) and catalytic efficiency (KCAT/KM) for the two enzymes. MS analysis in combination with quantum chemistry computation showed that the polymerization products were generated via CC and CO coupling pathways. The polymers were proved to be nontoxic through growth inhibition of green alga (Scenedesmus obliquus). Taking into consideration of the enzymatic treatment cost, SBP may be a better alternative to HRP upon the removal and detoxification of TCS in water/wastewater treatment. PMID:26921508

  9. Kinetic determination of iodide by the oxidation reaction of benzidine with chloramine B

    International Nuclear Information System (INIS)

    Iodide catalyzed oxidation of benzidine with Chloramine B is studied for its possible application to kinetic determination of iodides. Based on the results of kinetic studies performed, optimal conditions for the catalytic reaction are revealed and a kinetic method for iodide determination is developed. The determination limit of iodide is 2x10-4 μg/ml. It was demonstrated that the proposed method can be used for the determination of iodides in water, soil, and kelp

  10. Study of the kinetics of the steam-zirconium reaction using a one rod assembly model

    International Nuclear Information System (INIS)

    The results of the investigation of steam-zirconium reaction kinetics at the HPE simulator surface are presented in the paper. The dynamic characteristics of the hydrogen production resulted from the heated surface dryout are determined. (author)

  11. Kinetics and thermodynamics of chemical reactions in Li/SOCl2 cells

    Science.gov (United States)

    Hansen, Lee D.; Frank, Harvey

    1987-01-01

    Work is described that was designed to determine the kinetic constants necessary to extrapolate kinetic data on Li/SOCl2 cells over the temperature range from 25 to 75 C. A second objective was to characterize as far as possible the chemical reactions that occur in the cells since these reactions may be important in understanding the potential hazards of these cells. The kinetics of the corrosion processes in undischarged Li/SOCl2 cells were determined and separated according to their occurrence at the anode and cathode; the effects that switching the current on and off has on the corrosion reactions was determined; and the effects of discharge state on the kinetics of the corrosion process were found. A thermodynamic analysis of the current-producing reactions in the cell was done and is included.

  12. A Model of Hydrogen Desorption Kinetics Controlled both by Interface and Surface Reactions for Metal Hydrides

    CERN Document Server

    Drozdov, I

    2014-01-01

    The desorption kinetics was modelled with the both interface- and surface reactions as rate-controlling steps. It has been shown analytically, that in the model of 'shrinking core' desorption, the finite hydride-decomposition-rate causes a modified slope of kinetics. The dependence of desorption time on the powder particle size has the same power of order as for the surface controlled desorption.

  13. Physico-Geometrical Kinetics of Solid-State Reactions in an Undergraduate Thermal Analysis Laboratory

    Science.gov (United States)

    Koga, Nobuyoshi; Goshi, Yuri; Yoshikawa, Masahiro; Tatsuoka, Tomoyuki

    2014-01-01

    An undergraduate kinetic experiment of the thermal decomposition of solids by microscopic observation and thermal analysis was developed by investigating a suitable reaction, applicable techniques of thermal analysis and microscopic observation, and a reliable kinetic calculation method. The thermal decomposition of sodium hydrogen carbonate is…

  14. The Mechanisms, Products, and Kinetics of Triclosan-Free Chlorine Reactions

    OpenAIRE

    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...

  15. Kinetics of Nonenzymatic Browning Reaction in Citrus Juice Concentrates during Storage

    OpenAIRE

    KOCA, Nuray; BURDURLU, Hande Selen; KARADENİZ, Feryal

    2003-01-01

    The kinetics of nonenzymatic browning in citrus juice concentrates (orange, lemon, grapefruit and tangerine) during 8 weeks of storage at 28, 37 and 45 ºC were investigated. Browning development was followed by measuring absorbance at 420 nm (A420) and using CIE-Lab color system. Analysis of kinetic data from A420 values suggested a zero-order reaction for nonenzymatic browning, while changes in L* and b* parameters followed a first-order reaction. Activation energy for nonenzymatic browning...

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

    OpenAIRE

    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 ...

  17. The renneting of milk. A kinetic study of the enzymic and aggregation reactions.

    OpenAIRE

    Hooydonk, van, V.E.

    1987-01-01

    The rennet-induced clotting of milk was studied under various conditions. The kinetics of the enzymic and aggregation reactions was analysed separately and, where possible, related to the physico-chemical properties of the casein micelle and its environment.The effects of important variables, such as temperature, pH, divalent cations, ionic strength, casein concentration and pre-heat treatment of milk, are given and discussed in relation to the reaction kinetics and to the implications for th...

  18. Stochastic reaction-diffusion kinetics in the microscopic limit

    OpenAIRE

    Fange, David; Berg, Otto G.; Sjöberg, Paul; Elf, Johan

    2010-01-01

    Quantitative analysis of biochemical networks often requires consideration of both spatial and stochastic aspects of chemical processes. Despite significant progress in the field, it is still computationally prohibitive to simulate systems involving many reactants or complex geometries using a microscopic framework that includes the finest length and time scales of diffusion-limited molecular interactions. For this reason, spatially or temporally discretized simulations schemes are commonly u...

  19. Probing Aluminum Reactions in Combustion and Explosion Via the Kinetic Isotope Effect

    Science.gov (United States)

    Tappan, Bryce

    2015-06-01

    The mechanism that controls the reaction speed of aluminum in explosion and combustion is poorly understood, and experimentally difficult to measure. Recently, work in our laboratory has demonstrated that during the combustion of nanoparticulate aluminum with H2O or D2O, different reaction rates due to the kinetic isotope effect are observed. This result is the first-ever observed kinetic isotope effect in a metal combustion reaction and verifies that chemical reaction kinetics play a major role in determining the global burning rate. During or shortly after a detonation, however, the reaction rates are dramatically faster and the physical mechanism controlling Al reaction is likely different than during combustion events. To utilize the kinetic isotope effect to probe Al reactions in detonation, formulations were produced that contain powdered Al in deuterated high explosives and high-fidelity detonation velocity were determined along with PDV measurements to observe early wall velocity expansion measurements. The JWL equation of state was solved to determine temperature, pressure and energies at specific time periods, in addition of Gurney energies, which enables the elucidation of Al reaction extent. By comparison of the Al oxidation with LiF, data indicate that Al oxidation occurs on an extremely fast time scale and isotope effects in both the HE detonation and post-detonation Al reactions are discussed.

  20. Ion-neutral gas reactions in a collision/reaction cell in inductively coupled plasma mass spectrometry: Correlation of ion signal decrease to kinetic rate constants

    International Nuclear Information System (INIS)

    Reaction gas flow rate dependent Ar2+ and Ar+ signals are correlated to fundamental kinetic rate coefficients. A simple calculation, assuming that gas exits the reaction cell due only to effusion, is described to estimate the gas pressure in the reaction cell. The value of the product of the kinetic rate constant and the ion residence time in the reaction cell can be determined from experimental measurement of the decrease in an ion signal as a function of reaction gas flow rate. New kinetic rate constants are determined for the reaction of CH3F with Ar+ and Ar2+. - Highlights: • How to determine pressure and the product of the kinetic rate constant times the ion residence time in reaction cell • Relate measured ICP-DRC-MS signals versus gas flow rate to kinetic rate constants measured previously using SIFT-MS • Describe how to determine previously unmeasured kinetic rate constants using ICP-DRC-MS

  1. Kinetics of the reaction between carbon dioxide and tertiary amines

    Energy Technology Data Exchange (ETDEWEB)

    Crooks, J.E.; Donnellan, J.P. (King' s Coll., London (England))

    1990-02-16

    The reaction between carbon dioxide and amines is of great technical importance and has been the subject of many investigations. The authors have shown that the reaction for secondary amines in anhydrous ethanol and in aqueous solution is exclusively second-order in amine and that the zwitterion intermediate postulated by Danckwerts is probably of negligible significance in the mechanism. The reaction with tertiary amines has also been studied, but the data are less controversial. In order to complete their studies of the reactions of carbon dioxide with amines, using their conductimetric stopped-flow apparatus, they have studied this reaction for MDEA (methyldiethanolamine, IUPAC name N-methyl-2,2{prime}-iminodiethanol) and TEA (triethanolamine, IUPAC name 2,2{prime},2{double prime}-nitrilotris(ethanol)).

  2. Kinetic Monte Carlo studies of the reaction kinetics of crystal defects that diffuse one-dimensionally with occasional transverse migration

    DEFF Research Database (Denmark)

    Heinisch, H.L.; Trinkaus, H.; Singh, Bachu Narain

    2007-01-01

    The reaction kinetics of the various species of mobile defects in irradiated materials are crucially dependent on the dimensionality of their migration. Sink strengths for one-dimensionally (1D) gliding interstitial loops undergoing occasional direction changes have been described analytically and...... transverse to their 1D glide direction. Their transition from 1D to 3D kinetics is significantly different from that due to direction changes. The KMC results are compared to an analytical description of this diffusion mode in the form of a master curve relating the 1D normalized sink strength to the...

  3. Comparison of four commercialized biochemical systems for clinical yeast identification by colour-producing reactions.

    Science.gov (United States)

    Paugam, A; Benchetrit, M; Fiacre, A; Tourte-Schaefer, C; Dupouy-Camet, J

    1999-02-01

    We compared the ability of four commercially available yeast identification systems for routine laboratory hospital use: Auxacolor (AUX) (Sanofi Diagnostics Pasteur, Marne-la-Coquette), Fungichrom I (FUC) and Fungifast I Twin (FUF) (International Microbio, Toulon), Api Candida (API) (bioMérieux, Lyon). These systems are based on obtaining a biochemical profile easily defined by colorimetric reactions. We tested 202 yeasts belonging to 19 species which were included or were not included in the manufacturer's data base of the identification systems. Without extra tests, for all the organisms tested, after 24 h of incubation, the percentage of organisms correctly identified was 48% for AUX, 75% for FUC, 77% for FUF and 81% for API. However, if we consider the ratio of the number of correct identifications without extra tests with the number of yeasts included in the manufacturers' data bases (sensitivity) the results increased to 61% for AUX, 81% for FUC, 91% for FUF and 83% for API. These systems are particularly well adapted to medical use, they are simple to set up, interpret, and have very good efficiency for the yeasts most commonly isolated in clinical specimens. The findings reported here indicate that the most favourable results were obtained with FUF and API systems. PMID:10200929

  4. Nonlinear stochastic dynamics of mesoscopic homogeneous biochemical reaction systems—an analytical theory

    International Nuclear Information System (INIS)

    The nonlinear dynamics of biochemical reactions in a small-sized system on the order of a cell are stochastic. Assuming spatial homogeneity, the populations of n molecular species follow a multi-dimensional birth-and-death process on Zn. We introduce the Delbrück–Gillespie process, a continuous-time Markov jump process, whose Kolmogorov forward equation has been known as the chemical master equation, and whose stochastic trajectories can be computed via the Gillespie algorithm. Using simple models, we illustrate that a system of nonlinear ordinary differential equations on Rn emerges in the infinite system size limit. For finite system size, transitions among multiple attractors of the nonlinear dynamical system are rare events with exponentially long transit times. There is a separation of time scales between the deterministic ODEs and the stochastic Markov jumps between attractors. No diffusion process can provide a global representation that is accurate on both short and long time scales for the nonlinear, stochastic population dynamics. On the short time scale and near deterministic stable fixed points, Ornstein–Uhlenbeck Gaussian processes give linear stochastic dynamics that exhibit time-irreversible circular motion for open, driven chemical systems. Extending this individual stochastic behaviour-based nonlinear population theory of molecular species to other biological systems is discussed. (invited article)

  5. Biological and within-subject variability of calcium kinetics and biochemical markers of bone turnover

    Science.gov (United States)

    Bone loss is a critical issue during space flight. Evaluating changes in bone and calcium metabolism in astronauts often requires multiple preflight data collection points. Bone turnover and calcium kinetics were measured in 4 healthy subjects, and the day-to-day and between-subject variations were ...

  6. Nitrite-Driven Nitrous Oxide Production Under Aerobic Soil Conditions: Kinetics and Biochemical Controls

    Science.gov (United States)

    Nitrite (NO2-) can accumulate during nitrification in soil following fertilizer application. While the role of NO2- as a substrate regulating nitrous oxide (N2O) production is recognized, kinetic data are not available that allow for estimating N2O production or soil-to-atmosphere fluxes as a functi...

  7. Kinetics of liquid-solid reactions in naphthenic acid conversion and Kraft pulping

    Science.gov (United States)

    Yang, Ling

    Two liquid-solid reactions, in which the morphology of the solid changes as the reactions proceeds, were examined. One is the NA conversion in oil by decarboxylation on metal oxides and carbonates, and the other is the Kraft pulping in which lignin removal by delignification reaction. In the study of the NA conversion, CaO was chosen as the catalyst for the kinetic study from the tested catalysts based on NA conversion. Two reaction mixtures, carrier oil plus commercial naphthenic acids and heavy vacuum gas oil (HVGO) from Athabasca bitumen, were applied in the kinetic study. The influence of TAN, temperature, and catalyst loading on the NA conversion and decarboxylation were studied systematically. The results showed that the removal rate of TAN and the decarboxylation of NA were both independent of the concentration of NA over the range studied, and significantly dependent on reaction temperature. The data from analyzing the spent catalyst demonstrated that calcium naphthenate was an intermediate of the decarboxylation reaction of NA, and the decomposition of calcium naphthenate was a rate-determining step. In the study on the delignification of the Kraft pulping, a new mechanism was proposed for the heterogeneous delignification reaction during the Kraft pulping process. In particular, the chemical reaction mechanism took into account the heterogeneous nature of Kraft pulping. Lignin reacted in parallel with sodium hydroxide and sodium sulfide. The mechanism consists of three key kinetic steps: (1) adsorption of hydroxide and hydrosulfide ions on lignin; (2) surface reaction on the solid surface to produce degraded lignin products; and (3) desorption of degradation products from the solid surface. The most important step for the delignification process is the surface reaction, rather than the reactions occurring in the liquid phase. A kinetic model has, thus, been developed based on the proposed mechanism. The derived kinetic model showed that the mechanism

  8. A simultaneous one pot synthesis of two fractal structures via swapping two fractal reaction kinetic states.

    Science.gov (United States)

    Ghosh, Subrata; Dutta, Mrinal; Ray, Kanad; Fujita, Daisuke; Bandyopadhyay, Anirban

    2016-06-01

    We introduce a new class of fractal reaction kinetics wherein two or more distinct fractal structures are synthesized as parts of a singular cascade reaction in a single chemical beaker. Two examples: sphere ↔ spiral & triangle ↔ square fractals, grow 10(6) orders from a single dendrimer (8 nm) to the visible scale. PMID:27166589

  9. Kinetics of the reaction between dissolved sodium sulfide and biologically produced sulfur

    NARCIS (Netherlands)

    Kleinjan, W.E.; Keizer, de A.; Janssen, A.J.H.

    2005-01-01

    The kinetics of the heterogeneous reaction between dissolved sodium sulfide and biologically produced sulfur particles has been studied by measuring the formation of polysulfide ions, Sx2-, in time (pH = 8.0, T = 30-50 °C). Detailed knowledge of this reaction is essential to understand its effect on

  10. Mechanistic interpretation of glass reaction: Input to kinetic model development

    International Nuclear Information System (INIS)

    Actinide-doped SRL 165 type glass was reacted in J-13 groundwater at 90 degree C for times up to 278 days. The reaction was characterized by both solution and solid analyses. The glass was seen to react nonstoichiometrically with preferred leaching of alkali metals and boron. High resolution electron microscopy revealed the formation of a complex layer structure which became separated from the underlying glass as the reaction progressed. The formation of the layer and its effect on continued glass reaction are discussed with respect to the current model for glass reaction used in the EQ3/6 computer simulation. It is concluded that the layer formed after 278 days is not protective and may eventually become fractured and generate particulates that may be transported by liquid water. 5 refs., 5 figs. , 3 tabs

  11. Ab Initio Calculations of Hydrocarbon Thermochemistry and Reaction Kinetics

    OpenAIRE

    Aguilera Iparraguirre, Jorge

    2009-01-01

    In the framework of the SFB 551 "Carbon from the Gas Phase: Elementary Reactions, Structures, Materials" several areas of carbon related chemistry have been studied with help of computational tools. They include the exploration of different ways of building PAHs, the attempt to check the limits of quantum chemistry methods in hydrocarbon chemistry using explicitly-correlated methods and the calculation of accurate reaction rates.

  12. A study on reaction kinetics of the radicals produced in the laser-induced silane plasma

    International Nuclear Information System (INIS)

    The reaction kinetic processes of species produced in a pulsed TEA CO2 laser induced silane plasma were studied with the time-resolved OES. It is showed that the time position of main peaks for different fragments' characteristic lines are appreciably different. The reaction kinetic processes are discussed based on the results. By comparing the time evolution of the lines of the fragments and considering the other results of OES, the authors infer that the final reaction channel of the laser-induced silane plasma is a Si producing channel

  13. Kinetics of the Bray-Liebhafsky oscillatory reaction perturbed by polymer supported cobalt catalyst

    OpenAIRE

    Maksimović J.P.; Čupić Ž.D.; Lončarević D.; Pejić N.; Vasiljević-Radović D.; Anić S.

    2011-01-01

    The Bray-Liebhafsky (BL) oscillatory reaction generated in the batch reactor at 62- 68 oC was perturbed by cobalt(II)-nitrate, supported on the macroreticular copolymer of poly-4-vinylpyridine with divinylbenzene (Co-PVPDVB). The kinetic data was analyzed of the complex pathways of the hydrogen peroxide decomposition in the examined BL reaction. The obtained results confirm that the kinetics of the BL reaction in the presence Co-PVPDVB comes partially from the Co-catalyst and partially ...

  14. Kinetics of the Bray-Liebhafsky oscillatory reaction perturbed by polymer supported cobalt catalyst

    Directory of Open Access Journals (Sweden)

    Maksimović J.P.

    2011-01-01

    Full Text Available The Bray-Liebhafsky (BL oscillatory reaction generated in the batch reactor at 62- 68 oC was perturbed by cobalt(II-nitrate, supported on the macroreticular copolymer of poly-4-vinylpyridine with divinylbenzene (Co-PVPDVB. The kinetic data was analyzed of the complex pathways of the hydrogen peroxide decomposition in the examined BL reaction. The obtained results confirm that the kinetics of the BL reaction in the presence Co-PVPDVB comes partially from the Co-catalyst and partially from the macroreticular copolymer support.

  15. Kinetic and mechanistic studies of free-radical reactions in combustion

    Energy Technology Data Exchange (ETDEWEB)

    Tully, F.P. [Sandia National Laboratories, Livermore, CA (United States)

    1993-12-01

    Combustion is driven by energy-releasing chemical reactions. Free radicals that participate in chain reactions carry the combustion process from reactants to products. Research in chemical kinetics enables us to understand the microscopic mechanisms involved in individual chemical reactions as well as to determine the rates at which they proceed. Both types of information are required for an understanding of how flames burn, why engines knock, how to minimize the production of pollutants, and many other important questions in combustion. In this program the authors emphasize accurate measurements over wide temperature ranges of the rates at which ubiquitous free radicals react with stable molecules. The authors investigate a variety of OH, CN, and CH + stable molecule reactions important to fuel conversion, emphasizing application of the extraordinarily precise technique of laser photolysis/continuous-wave laser-induced fluorescence (LP/cwLIF). This precision enables kinetic measurements to serve as mechanistic probes. Since considerable effort is required to study each individual reaction, prudent selection is critical. Two factors encourage selection of a specific reaction: (1) the rates and mechanisms of the subject reaction are required input to a combustion model; and (2) the reaction is a chemical prototype which, upon characterization, will provide fundamental insight into chemical reactivity, facilitate estimation of kinetic parameters for similar reactions, and constrain and test the computational limits of reaction-rate theory. Most studies performed in this project satisfy both conditions.

  16. A COMPUTERIZED SYSTEM ON KINETIC ANALYSIS AND EVALUATION OF GAS/SOLID REACTIONS

    Institute of Scientific and Technical Information of China (English)

    J.H. Liu; J. Y. Zhang; S.K. Wei

    2003-01-01

    The present paper presents the structure, features and functions of a computerized system on kinetic analysis and evaluation of gas/solid reactions, KinPreGSR. KinPreGSR is a menu driven system, can be operated with MS Windows as workbench in a PC computer. It has been developed using visual C++ with FoxPro hybrid coding technique.KinPreGSR combines the characteristics of gas/solid reactions with the kinetic models as well as mass and heat transfer equations. The database files were established for the apparent activation energies of some reduction and decomposition reactions to allow the prediction of the reaction kinetics to some extents. Outputs can be displayed using graphical or numerical forms. Examples regarding the oxide reduction and carbonate decomposition under isothermal conditions are given to show those functions.

  17. Kinetics and optimization on discoloration of dyeing wastewater by schorl-catalyzed fenton-like reaction

    Directory of Open Access Journals (Sweden)

    Xu Huan-Yan

    2014-01-01

    Full Text Available Kinetics and optimization on the discoloration of an active commercial dye, Argazol Blue BFBR (ABB by heterogeneous Fenton-like reaction catalyzed by natural schorl were investigated in this study. Kinetic investigations revealed that the first-order kinetic model was more favorable to describe the discoloration of ABB at different reaction conditions than the second-order and Behnajady-Modirshahla-Ghanbery models. The relationship between the reaction rate constant k and reaction temperature T followed the Arrhenius equation, with the apparent activation energy Ea of 51.31kJ•mol-1. The central composite design under the response surface methodology was employed for the experimental design and optimization of the ABB discoloration process. The significance of a second order polynomial model for predicting the optimal values of ABB discoloration was evaluated by the analysis of variance and 3D response surface plots for the interactions between two variables were constructed. Then, the optimum conditions were determined.

  18. Explaining the atypical reaction profiles of heme enzymes with a novel mechanistic hypothesis and kinetic treatment.

    Directory of Open Access Journals (Sweden)

    Kelath Murali Manoj

    Full Text Available Many heme enzymes show remarkable versatility and atypical kinetics. The fungal extracellular enzyme chloroperoxidase (CPO characterizes a variety of one and two electron redox reactions in the presence of hydroperoxides. A structural counterpart, found in mammalian microsomal cytochrome P450 (CYP, uses molecular oxygen plus NADPH for the oxidative metabolism (predominantly hydroxylation of substrate in conjunction with a redox partner enzyme, cytochrome P450 reductase. In this study, we employ the two above-mentioned heme-thiolate proteins to probe the reaction kinetics and mechanism of heme enzymes. Hitherto, a substrate inhibition model based upon non-productive binding of substrate (two-site model was used to account for the inhibition of reaction at higher substrate concentrations for the CYP reaction systems. Herein, the observation of substrate inhibition is shown for both peroxide and final substrate in CPO catalyzed peroxidations. Further, analogy is drawn in the "steady state kinetics" of CPO and CYP reaction systems. New experimental observations and analyses indicate that a scheme of competing reactions (involving primary product with enzyme or other reaction components/intermediates is relevant in such complex reaction mixtures. The presence of non-selective reactive intermediate(s affords alternate reaction routes at various substrate/product concentrations, thereby leading to a lowered detectable concentration of "the product of interest" in the reaction milieu. Occam's razor favors the new hypothesis. With the new hypothesis as foundation, a new biphasic treatment to analyze the kinetics is put forth. We also introduce a key concept of "substrate concentration at maximum observed rate". The new treatment affords a more acceptable fit for observable experimental kinetic data of heme redox enzymes.

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Science.gov (United States)

    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

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

    Energy Technology Data Exchange (ETDEWEB)

    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. Kinetics of the decomposition reaction of phosphorite concentrate

    Directory of Open Access Journals (Sweden)

    Huang Run

    2014-01-01

    Full Text Available Apatite is the raw material, which is mainly used in phosphate fertilizer, and part are used in yellow phosphorus, red phosphorus, and phosphoric acid in the industry. With the decrease of the high grade phosphorite lump, the agglomeration process is necessary for the phosphorite concentrate after beneficiation process. The decomposition behavior and the phase transformation are of vital importance for the agglomeration process of phosphorite. In this study, the thermal kinetic analysis method was used to study the kinetics of the decomposition of phosphorite concentrate. The phosphorite concentrate was heated under various heating rate, and the phases in the sample heated were examined by the X-ray diffraction method. It was found that the main phases in the phosphorite are fluorapatiteCa5(PO43F, quartz SiO2,and dolomite CaMg(CO32.The endothermic DSC peak corresponding to the mass loss caused by the decomposition of dolomite covers from 600°C to 850°C. The activation energy of the decomposition of dolomite, which increases with the increase in the extent of conversion, is about 71.6~123.6kJ/mol. The mechanism equation for the decomposition of dolomite agrees with the Valensi equation and G-B equation.

  3. Minimal moment equations for stochastic models of biochemical reaction networks with partially finite state space

    Science.gov (United States)

    Ruess, Jakob

    2015-12-01

    Many stochastic models of biochemical reaction networks contain some chemical species for which the number of molecules that are present in the system can only be finite (for instance due to conservation laws), but also other species that can be present in arbitrarily large amounts. The prime example of such networks are models of gene expression, which typically contain a small and finite number of possible states for the promoter but an infinite number of possible states for the amount of mRNA and protein. One of the main approaches to analyze such models is through the use of equations for the time evolution of moments of the chemical species. Recently, a new approach based on conditional moments of the species with infinite state space given all the different possible states of the finite species has been proposed. It was argued that this approach allows one to capture more details about the full underlying probability distribution with a smaller number of equations. Here, I show that the result that less moments provide more information can only stem from an unnecessarily complicated description of the system in the classical formulation. The foundation of this argument will be the derivation of moment equations that describe the complete probability distribution over the finite state space but only low-order moments over the infinite state space. I will show that the number of equations that is needed is always less than what was previously claimed and always less than the number of conditional moment equations up to the same order. To support these arguments, a symbolic algorithm is provided that can be used to derive minimal systems of unconditional moment equations for models with partially finite state space.

  4. Kinetics of thermal decomposition and kinetics of substitution reaction of nano uranyl Schiff base complexes

    Czech Academy of Sciences Publication Activity Database

    Asadi, Z.; Zeinali, A.; Dušek, Michal; Eigner, Václav

    2014-01-01

    Roč. 46, č. 12 (2014), s. 718-729. ISSN 0538-8066 R&D Projects: GA ČR(CZ) GAP204/11/0809 Institutional support: RVO:68378271 Keywords : uranyl * Schiff base * kinetics * anticancer activity Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.517, year: 2014

  5. Oxygen Diffusion and Reaction Kinetics in Continuous Fiber Ceramic Matrix Composites

    Science.gov (United States)

    Halbig, Michael C.; Eckel, Andrew J.; Cawley, James D.

    1999-01-01

    Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.

  6. Kinetic characterization of the photosynthetic reaction centres in microalgae by means of fluorescence methodology.

    Science.gov (United States)

    Gargano, Immacolata; Olivieri, Giuseppe; Spasiano, Danilo; Andreozzi, Roberto; Pollio, Antonino; Marotta, Raffaele; D'Ambrosio, Nicola; Marzocchella, Antonio

    2015-10-20

    The kinetic characterization of the photosynthetic activity in autotrophic microalgae plays a key role in the design of optimized photobioreactors. This paper presents a procedure to assess kinetic parameters of a three-state photosynthetic reaction centres model. Four kinetic parameters of the model were assessed by processing the time-series measurements of pulse-amplitude modulation fluorimetry. The kinetic parameters were assessed for several microalgal strains (Stichococcus bacillaris, Scenedesmus vacuolatus, Chlamydomonas reinhardtii, Chlorella vulgaris) growth in vertical and inclined bubble columns and irradiated by white-light or red/blue light. The procedure was successfully applied to the investigated strains. The assessed parameters allow identifying the irradiance range under which: the photochemical process is controlled by the photons capture; the photoinhibition competes with the photochemical quenching. The analysis of the time-scale of the photosynthetic reaction centres as a function of the irradiance allows interpreting the performances of photobioreactors characterized by non-homogeneous irradiance. PMID:26216180

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

    International Nuclear Information System (INIS)

    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.

  8. LSENS, a general chemical kinetics and sensitivity analysis code for gas-phase reactions: User's guide

    Science.gov (United States)

    Radhakrishnan, Krishnan; Bittker, David A.

    1993-01-01

    A general chemical kinetics and sensitivity analysis code for complex, homogeneous, gas-phase reactions is described. The main features of the code, LSENS, are its flexibility, efficiency and convenience in treating many different chemical reaction models. The models include static system, steady, one-dimensional, inviscid flow, shock initiated reaction, and a perfectly stirred reactor. In addition, equilibrium computations can be performed for several assigned states. An implicit numerical integration method, which works efficiently for the extremes of very fast and very slow reaction, is used for solving the 'stiff' differential equation systems that arise in chemical kinetics. For static reactions, sensitivity coefficients of all dependent variables and their temporal derivatives with respect to the initial values of dependent variables and/or the rate coefficient parameters can be computed. This paper presents descriptions of the code and its usage, and includes several illustrative example problems.

  9. Determination of a global kinetics for the sodium-water reaction using heat transfer statuses

    International Nuclear Information System (INIS)

    The aim of this study is the determination of a global kinetics for the sodium (solid) - water (vapor) reaction in diffusional regime. One of the methods used consists in implementing a temperature evolution measurement. Because of the exo-thermal property of the reaction, the use of the heat transfer status of a small reactor allows to evaluate the kinetics of the reaction. The heat dissipated by the reaction is shared among the sodium support and the gas. The main component is the flux inside the support. In order to evaluate this flux, an inverse method is used. A flux estimation inside the support is performed using a minimization algorithm applied to the differences between the temperatures measured on different points of the support and the calculated temperatures. This non-intrusive measurement technique allows to follow up the evolution of temperatures with time, and thus the heat flux of the reaction. (J.S.)

  10. THE ROLES OF REACTION INHOMOGENEITY IN PHASE SEPARATION KINETICS AND MORPHOLOGY OF REACTIVE POLYMER BLENDS

    Institute of Scientific and Technical Information of China (English)

    Qui Tran-Cong-Miyata; Dan-Thuy Van-Pham; Kei Noma; Tomohisa Norisuye; Hideyuki Nakanishi

    2009-01-01

    The roles of reaction inhomogeneity in phase separation of polymer mixtures were described and summarized via two examples:photocross-link of polymer mixtures in the bulk state and photopolymerization of monomer in the liquid state.The reaction kinetics,the reaction-induced elastic strain and the phase separation kinetics were monitored respectively by UV-Vis spectroscopy,Mach-Zehnder interferometry and laser-scanning confocal microscopy.It was found that phase separation in the bulk state was strongly influenced by the elastic strain associated with the intrinsic inhomogeneity of the reaction,whereas the autocatalytic behavior of the polymerization plays an important role in the resulting morphology in the liquid state.These experimental results are discussed in conjunction with the morphology control of polymer mixtures by using chemical reactions.

  11. Effect of temperature on kinetic parameters of decomposition reaction of calcium carbonate

    Institute of Scientific and Technical Information of China (English)

    CHEN Hongwei; CHEN Jiangtao; WEI Riguang; SUO Xinliang

    2013-01-01

    In order to investigate the influence of temperature on behavior of calcium carbonate decomposition,especially on kinetic parameters of the decomposition reaction,the analytically pure calcium carbonate was calcined on a self-built large dose thermogravimetric analyzer.The results indicated that,with an increase in the reaction temperature,the reactivity index of calcium carbonate decomposition increased at stage state while the kinetic parameters decreased at stage state.Moreover,both the reaction indices and the kinetic parameters can be divided into three stages and the temperature turning points in different stages were the same.The phase boundary reaction (cylindrical symmetry) theory was more suitable for calcium carbonate calcination under N2 atmosphere.The change trend of the logarithm of reaction activation with temperature was similar as that of the pre-exponential factor.There existed good liner relationship and kinetic compensation effect between them.The isokinetic temperature of the CaCO3 calcination was 842 ℃ and the reaction rate constant was 0.104 9 min-1 derived by the compensation coefficients.

  12. An investigation of the general regularity of size dependence of reaction kinetics of nanoparticles

    International Nuclear Information System (INIS)

    In the processes of preparation and application of nanomaterials, the chemical reactions of nanoparticles are often involved, and the size of nanoparticles has dramatic influence on the reaction kinetics. Nevertheless, there are many conflicts on regularities of size dependence of reaction kinetic parameters, and these conflicts have not been explained so far. In this paper, taking the reaction of nano-ZnO (average diameter is from 20.96 to 53.31 nm) with acrylic acid solution as a system, the influence regularities of the particle size on the kinetic parameters were researched. The regularities were consistent with that in most literatures, but inconsistent with that in a few of literatures, the reasons for the conflicts were interpreted. The reasons can be attributed to two factors: one is improper data processing for fewer data points, and the other is the difference between solid particles and porous particles. A general regularity of the size dependence of reaction kinetics for solid particles was obtained. The regularity shows that with the size of nanoparticles decreasing, the rate constant and the reaction order increase, while the apparent activation energy and the pre-exponential factor decrease; and the relationships of the logarithm of rate constant, the logarithm of pre-exponential factor, and the apparent activation energy to the reciprocal of the particle size are linear, respectively

  13. Investigation of the kinetics of the reactions of oxidation, nitration, and hydrogenation of uranium

    International Nuclear Information System (INIS)

    Various physico-chemical methods have been used to investigate the kinetics of the oxidation hydridation and nitridation of uranium. The experimental results show that the kinetics of these reactions are influenced by many factors also the Pilling and Bedworth rule is valid only under very limited conditions. The disagreement between this rule and the experimental results could be explained by the existence of numerous mechanical faults in the compounds obtained by the dry corrosion of the metal. (author)

  14. Measuring the Electrode Kinetics of Surface Confined Electrode Reactions at a Constant Scan Rate

    OpenAIRE

    Guziejewski, Dariusz; Mirceski, Valentin; Jadresko, Dijana

    2014-01-01

    Abstract: The kinetics of surface confined electrode reactions of alizarin, vitamin B12, and vitamin K2 is measured with square-wave voltammetry over a wide pH interval, by applying the recent methodology for kinetic analysis at a constant scan rate [V. Mirceski, D. Guziejewski, K. Lisichkov, Electrochim. Acta 2013, 114, 667–673]. The reliability and the simplicity of the recent methodology is confirmed. The methodology requires analysis of the peak potential separation o...

  15. Ab initio studies of the kinetic isotope effect of the CH4 + OH atmospheric reaction

    Science.gov (United States)

    Lasaga, Antonio C.; Gibbs, G. V.

    1991-07-01

    High level ab initio calculations have been carried out on the C-13 - C-12 kinetic isotope effect of the CH4 + OH reaction in the atmosphere. The results agree quite well with both the absolute value of the isotope effect and the temperature dependence of the effect, based on new experimental data. The calculated kinetic isotope effect supports a bigger effect of biomass burning on the methane global budget.

  16. Optimization and kinetic studies of sea mango (Cerbera odollam) oil for biodiesel production via supercritical reaction

    International Nuclear Information System (INIS)

    Highlights: • Sea mango oil as feedstock for biodiesel via non-catalytic supercritical reaction. • Extracted sea mango oil with high FFA could produce high yield of FAME. • Employment of Response Surface Methodology for optimization of FAME. • Kinetic study for reversible transesterification and esterification reactions. - Abstract: Sea mango (Cerbera odollam) oil, which is rich in free fatty acids, was utilized to produce fatty acid methyl esters (FAME) via supercritical transesterification reaction. Sea mango oil was extracted from seeds and was subsequently reacted with methanol in a batch-type supercritical reactor. Response surface methodology (RSM) analysis was used to optimize important parameters, including reaction temperature, reaction time and the molar ratio of methanol to oil. The optimum conditions were found as 380 °C, 40 min and 45:1 mol/mol, respectively, to achieve 78% biodiesel content. The first kinetic modelling of FAME production from sea mango oil incorporating reversible transesterification and reversible esterification was verified simultaneously. The kinetic parameters, including reaction rate constants, k, the pre-exponential constant, A, and the activation energy, Ea, for transesterification and esterification were determined using an ordinary differential equation (ODE45) solver. The highest activation energy of 40 kJ/mol and the lowest reaction rate constant of 2.50 × 10−5 dm3/mol s verified that the first stepwise reaction of TG to produce DG was the rate-limiting step

  17. Complex Cure Kinetics of the Hydroxyl-Epoxide Reaction in DGEBA Epoxy Hardened with Diethanolamine

    Science.gov (United States)

    Ancipink, Windy; McCoy, John; Kropka, Jamie; Celina, Mathias

    The curing of a diglycidyl ether of bisphenol-A Epoxy (Epon 828) with diethanolamine (DEA) involves a fast amine-epoxide reaction followed by a slower hydroxyl-epoxide reaction. At curing temperatures below 100°C, the time scales of these two reactions are well separated, and the hydroxyl addition can be studied as an ''isolated'' reaction. The hydroxyl-epoxide reaction is of great interest due to the complex kinetics involved, which are brought about by competing reactions. The reaction kinetics are believed to be tertiary amine catalyzed and are well fit to a modified form of the Kamal-type equation. Here we study the complex long term reaction kinetics at various temperatures, by using isothermal modulated differential scanning calorimetry, micro calorimetry, and infrared spectroscopy. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

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

    OpenAIRE

    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...

  19. Reaction Kinetic Parameters and Surface Thermodynamic Properties of Cu2O Nanocubes

    Directory of Open Access Journals (Sweden)

    Xingxing Li

    2015-07-01

    Full Text Available Cuprous oxide (Cu2O nanocubes were synthesized by reducing Cu(OH2 in the presence of sodium citrate at room temperature. The samples were characterized in detail by field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray powder diffraction, and N2 absorption (BET specific surface area. The equations for acquiring reaction kinetic parameters and surface thermodynamic properties of Cu2O nanocubes were deduced by establishment of the relations between thermodynamic functions of Cu2O nanocubes and these of the bulk Cu2O. Combined with thermochemical cycle, transition state theory, basic theory of chemical thermodynamics, and in situ microcalorimetry, reaction kinetic parameters, specific surface enthalpy, specific surface Gibbs free energy, and specific surface entropy of Cu2O nanocubes were successfully determined. We also introduced a universal route for gaining reaction kinetic parameters and surface thermodynamic properties of nanomaterials.

  20. Multiresponse kinetic modelling of Maillard reaction and caramelisation in a heated glucose/wheat flour system.

    Science.gov (United States)

    Kocadağlı, Tolgahan; Gökmen, Vural

    2016-11-15

    The study describes the kinetics of the formation and degradation of α-dicarbonyl compounds in glucose/wheat flour system heated under low moisture conditions. Changes in the concentrations of glucose, fructose, individual free amino acids, lysine and arginine residues, glucosone, 1-deoxyglucosone, 3-deoxyglucosone, 3,4-dideoxyglucosone, 5-hydroxymethyl-2-furfural, glyoxal, methylglyoxal and diacetyl concentrations were determined to form a multiresponse kinetic model for isomerisation and degradation reactions of glucose. Degradation of Amadori product mainly produced 1-deoxyglucosone. Formation of 3-deoxyglucosone proceeded directly from glucose and also Amadori product degradation. Glyoxal formation was predominant from glucosone while methylglyoxal and diacetyl originated from 1-deoxyglucosone. Formation of 5-hydroxymethyl-2-furfural from fructose was found to be a key step. Multi-response kinetic modelling of Maillard reaction and caramelisation simultaneously indicated quantitatively predominant parallel and consecutive pathways and rate limiting steps by estimating the reaction rate constants. PMID:27283710

  1. Reaction kinetics of solid fuels during entrained flow gasification

    Energy Technology Data Exchange (ETDEWEB)

    Tremel, Alexander

    2012-10-24

    Despite the application of entrained flow gasification on larger scales, the reaction rates in the hot conversion zone are almost unknown. But the knowledge of the rates of the gasification reactions at high temperature and high pressure is crucial for the detailed design and optimisation of these gasifiers. This dissertation provides measurements of fuel conversion under operation conditions relevant to industrial gasifiers and aims at the transfer of the data to larger scale applications. A novel pilot-scale research reactor is developed that enables the study of gasification reactions at high temperature, high pressure and under entrained flow conditions. The Pressurised High Temperature Entrained Flow Reactor (PiTER) is operated at up to 1600 C and 4.0 MPa in pyrolysis and gasification experiments. The data set is extended by measurements in an atmospheric entrained flow reactor and a pressurised wire mesh reactor. Devolatilisation and gasification behaviour of a wide range of fuels is analysed including anthracite, bituminous coal, lignite, biocoal (from hydrothermal carbonisation), and biomass; however, Rhenish lignite is used in most of the experiments. The pyrolysis data enable the validation of a simple first order reaction model that describes the influence of pressure, temperature, and residence time on volatile yield. Char samples collected from the three reactors are analysed using laboratory procedures and bench-scale setups. Specific char surface area is measured by CO{sub 2} adsorption at 273 K, and is found to be significantly influenced by char conversion, reaction temperature, and devolatilisation pressure. The surface data are described by an extension of the Random Pore Model. Intrinsic char reactivity is measured in a pressurised thermogravimetric analyser and the influence of reactant partial pressure and temperature on the char-CO{sub 2} and char-H{sub 2}O reaction is studied. The intrinsic reaction rate is described by nth order and

  2. Reaction diffusion and solid state chemical kinetics handbook

    CERN Document Server

    Dybkov, V I

    2010-01-01

    This monograph deals with a physico-chemical approach to the problem of the solid-state growth of chemical compound layers and reaction-diffusion in binary heterogeneous systems formed by two solids; as well as a solid with a liquid or a gas. It is explained why the number of compound layers growing at the interface between the original phases is usually much lower than the number of chemical compounds in the phase diagram of a given binary system. For example, of the eight intermetallic compounds which exist in the aluminium-zirconium binary system, only ZrAl3 was found to grow as a separate

  3. Self-triggering reaction kinetics between nitrates and aluminium powder

    International Nuclear Information System (INIS)

    During the night between the 19 and 20 September 2003, a loud explosion occurred at about 3 km from the town of Carignano that was clearly heard at a distance of some tens of kilometres. The explosion almost completely destroyed most of the laboratories of the Panzera Company that were used for the production of fireworks. The results of the research activities that were carried out using a differential scanning calorimeter (DSC) on the same raw materials that made up the pyrotechnical mixture that exploded are reported in this paper. This activity was carried out to identify the dynamics of the accident. It proved possible to verify how the event was produced because of a slow exothermic reaction which, after about 8 h, caused the self-triggering of 120 kg of finished product. The detonation can therefore be put down to a runaway reaction in the solid phase, whose primogenial causes can be attributed to a still craftsman type production system, not conformed to the rigorous controls and inspections as those required by a safety management system for major risk plants, as the Panzera Company was

  4. Glycerol acetals, kinetic study of the reaction between glycerol and formaldehyde

    International Nuclear Information System (INIS)

    The acetalization reaction between glycerol and formaldehyde using Amberlyst 47 acidic ion exchange resin was studied. These acetals can be obtained from renewable sources (bioalcohols and bioalcohol derived aldehydes) and seem to be good candidates for different applications such as oxygenated diesel additives. A preliminary kinetic study was performed in a batch stirred tank reactor studying the influence of different process parameters like temperature, feed composition and the stirring speed. A pseudo homogenous kinetic model able to explain the reaction mechanism was adjusted. Thus, the corresponding order of reaction was determined. Amberlyst 47 acidic ion exchange resin showed a fairly good behavior allowing 100% of selectivity towards acetals formation. However, the studied acetalization reaction showed high thermodynamic limitations achieving glycerol conversions around 50% using a stoichiometric feed ratio at 353 K. The product is a mixture of two isomers (1,3-Dioxan-5-ol and 1,3-dioxolane-4-methanol) and the conversion of 1,3-dioxolane-4-methanol into 1,3-Dioxan-5-ol was also observed. -- Highlights: → The reaction between glycerol and acetaldehyde shows thermodynamic limitations. → Amberlyst 47 ion exchange resins show 100% of selectivity. → A pseudo-homogeneous kinetic model is able to predict the reaction progress. → Isomerization reactions were observed from dioxalanes to dioxanes.

  5. Kinetics of pozzolanic reaction for preparation of flue gas desulfurizer from fly ash and Ca(OH)2

    Institute of Scientific and Technical Information of China (English)

    WANG Jingang; HU Jinbang; WANG Daobin; DUAN Zhenya

    2007-01-01

    A kinetic model of the pozzolanic reaction for the preparation of flue gas desulfurizers from fly ash and Ca(OH)2 was deduced on the basis of solid phase reaction kinetic theory.Kinetic expressions and parameters were obtained and verified by experiment.A comparison of calculated results with experimental results showed that precision in kinetic expressions was good.The apparent reaction rate constants of the pozzolanic reaction could be raised by increasing the specific surface area of fly ash and the hydration temperature,and by using a suitable additive.

  6. DME Dissociation Reaction on Platinum Electrode Surface : A Quantitative Kinetic Analysis by In Situ IR Spectroscopy

    OpenAIRE

    Zhang, Yi; Tong, Yujin; Lu, Leilei; Osawa, Masatoshi; Ye, Shen

    2010-01-01

    The kinetics of electrocatalytic dissociation reaction of dimethyl ether (DME) on a platinum (Pt) polycrystalline electrode in an acidic solution yielding carbon monoxide (CO) has been quantitatively analyzed by in situ IR spectroscopy in the potential region between 100 and 500 mV (vs reversible hydrogen electrode). A two-step consecutive reaction model, an initial dehydrogenation step followed by a CO formation step, is proposed for the dissociation process of the DME molecule. The mechanis...

  7. A kinetic model for chemical reactions without barriers : transport coefficients and eigenmodes

    OpenAIRE

    Alves, Giselle M.; Marques Júnior, Wilson; Soares, A. J.; Kremer, Gilberto M.

    2011-01-01

    The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solution of the Boltzmann equation is determined through an expansion in Sonine polyn...

  8. On the Mathematical Structure of Balanced Chemical Reaction Networks Governed by Mass Action Kinetics

    OpenAIRE

    der Schaft, Arjan van; Rao, Shodhan; Jayawardhana, Bayu

    2011-01-01

    Motivated by recent progress on the interplay between graph theory, dynamics, and systems theory, we revisit the analysis of chemical reaction networks described by mass action kinetics. For reaction networks possessing a thermodynamic equilibrium we derive a compact formulation exhibiting at the same time the structure of the complex graph and the stoichiometry of the network, and which admits a direct thermodynamical interpretation. This formulation allows us to easily characterize the set ...

  9. Excluded volume effects on the intrachain reaction kinetics.

    Science.gov (United States)

    Kim, Ji-Hyun; Lee, Woojin; Sung, Jaeyoung; Lee, Sangyoub

    2008-05-15

    On the basis of the recently developed optimized Rouse-Zimm theory of chain polymers with excluded volume interactions, we calculate the long-time first-order rate constant k(1) for end-to-end cyclization of linear chain polymers. We first find that the optimized Rouse-Zimm theory provides the longest chain relaxation times tau(1) of excluded volume chains that are in excellent agreement with the available Brownian dynamics simulation results. In the free-draining limit, the cyclization rate is diffusion-controlled and k(1) is inversely proportional to tau(1), and the k(1) values calculated using the Wilemski-Fixman rate theory are in good agreement with Brownian dynamics simulation results. However, when hydrodynamic interactions are included, noticeable deviations are found. The main sources of errors are fluctuating hydrodynamic interaction and correlation hole effects as well as the non-Markovian reaction dynamic effect. The physical natures of these factors are discussed, and estimates for the magnitudes of required corrections are given. When the corrections are included, the present theory allows the prediction of accurate k(1) values for the cyclization of finite-length chains in good solvents as well as the correct scaling exponent in the long-chain limit. PMID:18419166

  10. Approximation and inference methods for stochastic biochemical kinetics - a tutorial review

    CERN Document Server

    Schnoerr, David; Grima, Ramon

    2016-01-01

    Stochastic fluctuations of molecule numbers are ubiquitous in biological systems. Important examples include gene expression and enzymatic processes in living cells. Such systems are typically modelled as chemical reaction networks whose dynamics are governed by the Chemical Master Equation. Despite its simple structure, no analytic solutions to the Chemical Master Equation are known for most systems. Moreover, stochastic simulations are computationally expensive, making systematic analysis and statistical inference a challenging task. Consequently, significant effort has been spent in recent decades on the development of efficient approximation and inference methods. This article gives an introduction to basic modelling concepts as well as an overview of state of the art methods. First, we motivate and introduce deterministic and stochastic models for chemical networks, and give an overview of simulation and exact solution methods. Next, we discuss several approximation methods, including the chemical Langev...

  11. Variable elimination in chemical reaction networks with mass-action kinetics

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Wiuf, C.

    2012-01-01

    We consider chemical reaction networks taken with mass-action kinetics. The steady states of such a system are solutions to a system of polynomial equations. Even for small systems the task of finding the solutions is daunting. We develop an algebraic framework and procedure for linear elimination...

  12. Kinetic Study of the Reaction between Tert-butyl Hydrazine and Nitrous Acid

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The kinetic study of the reaction between tert-butyl hydrazine(TBH)and nitrous acid in nitric acid system is performed by spectrophotometry. The effect of some factors such as the concentration of TBH, the concentration of nitric acid, ionic strength, temperature and the

  13. Interfacial reaction kinetics of coated SiC fibers with various titanium alloys

    Science.gov (United States)

    Gundel, D. B.; Wawner, F. E.

    1991-01-01

    The kinetics of the reaction between the silicon carbide fibers and the titanium-based alloy matrix was investigated at temperatures from 800 to 1000 C for several titanium-based alloys (including Ti-1100 alloy and BETA 21S) and unalloyed Ti, reinforced with coated silicon carbide fiber SCS-6. The reaction zone growth kinetics was studied by exposing vacuum encapsulated samples to temperatures from 700 to 1000 C for times up to 150 hrs, followed by SAM observations of samples which were polished perpendicular to the fiber axis and etched. It was found that the reaction zone growth kinetics of the alpha (hcp) and beta (bcc) phases of unalloyed titanium reacting with SCS-6 fibers exhibited different values of the apparent activation energy and of the preexponential factor. Additions of other metals to Ti was found to slow down the reaction kinetics. Among the alloys studied, the Ti-1100 was the slowest reacting conventional alloy and the Ti-14Al-21Nb (in wt pct) was the slowest overall.

  14. On the graph and systems analysis of reversible chemical reaction networks with mass action kinetics

    NARCIS (Netherlands)

    Rao, Shodhan; Jayawardhana, Bayu; Schaft, Arjan van der

    2012-01-01

    Motivated by the recent progresses on the interplay between the graph theory and systems theory, we revisit the analysis of reversible chemical reaction networks described by mass action kinetics by reformulating it using the graph knowledge of the underlying networks. Based on this formulation, we

  15. Employing Magnetic Levitation to Monitor Reaction Kinetics and Measure Activation Energy

    Science.gov (United States)

    Benz, Lauren; Cesafsky, Karen E.; Le, Tran; Park, Aileen; Malicky, David

    2012-01-01

    This article describes a simple and inexpensive undergraduate-level kinetics experiment that uses magnetic levitation to monitor the progress and determine the activation energy of a condensation reaction on a polymeric solid support. The method employs a cuvette filled with a paramagnetic solution positioned between two strong magnets. The…

  16. Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

    Science.gov (United States)

    Silverstein, Todd P.

    2012-01-01

    Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

  17. A Gas-Kinetic Scheme for Multimaterial Flows and Its Application in Chemical Reaction

    Science.gov (United States)

    Lian, Yongsheng; Xu, Kun

    1999-01-01

    This paper concerns the extension of the multicomponent gas-kinetic BGK-type scheme to multidimensional chemical reactive flow calculations. In the kinetic model, each component satisfies its individual gas-kinetic BGK equation and the equilibrium states of both components are coupled in space and time due to the momentum and energy exchange in the course of particle collisions. At the same time, according to the chemical reaction rule one component can be changed into another component with the release of energy, where the reactant and product could have different gamma. Many numerical test cases are included in this paper, which show the robustness and accuracy of kinetic approach in the description of multicomponent reactive flows.

  18. Kinetics of deso/sub x/ reaction on copper and cerium-based sorbent-catalysts

    International Nuclear Information System (INIS)

    Kinetics of SO/sub 2/ removal using a copper-based sorbent CuO/gamma-AI/sub 2/O/sub 3/ and a cerium modified copper sorbent CuO-CeO/sub 2/gamma-AI/sub 2/O, were measured on a TGA and their kinetics behaviors were simulated with a proposed empirical rate model (ERM). The purpose of cerium addition to the copper sorbent was to study the difference of sorbent's kinetics. The cerium modified copper sorbent showed a higher reaction rate on initial sulfation than the regular copper sorbent. Both sorbents however had similar calculated activation energy. The proposed ERM model appeared to describe the SO/sub 2/ removal kinetics well in the temperature range 250-400 degree C. (author)

  19. 生化反应的五行归属%Anfive elements classification of bio-chemical reactions

    Institute of Scientific and Technical Information of China (English)

    徐天成

    2015-01-01

    五行学说提供了对事物进行系统分类的合理方法。人类体内充满了复杂的生物化学反应体系,能否用五行学说的基本规律归纳生物化学反应体系值得探讨。在以往相关研究的基础上,本文利用五行思想对生化反应的物质和反应类型进行分类,用简洁的中医学规律研究复杂的生化反应过程,这种新思路对药物研究、中西医结合学科的发展等具有挖掘价值。%Thefive elements theory provides us a system classification of all things so we can do the research in a much reasonable way. Further more, our bodies are full of complicated bio-chemical reactions and thefive elements theory should also be applicable to those reaction systems. This paper will try to make use of thefive elements theory to carry on an innovative classification of different types of bio-chemical reactions with the help of the former foundation of related researches, to make the complicated bio-chemical reactions easy to understand, and point out that this kind of lately academic thought is of great significance to the medicine researches as well as the integrated traditional Chinese and western medicine.

  20. Prediction of Reaction Kinetic of Al- Doura Heavy Naphtha Reforming Process Using Genetic Algorithm

    Directory of Open Access Journals (Sweden)

    Ramzy H. Saihod

    2015-07-01

    Full Text Available In this study, genetic algorithm was used to predict the reaction kinetics of Iraqi heavy naphtha catalytic reforming process located in Al-Doura refinery in Baghdad. One-dimensional steady state model was derived to describe commercial catalytic reforming unit consisting of four catalytic reforming reactors in series process. The experimental information (Reformate composition and output temperature for each four reactors collected at different operating conditions was used to predict the parameters of the proposed kinetic model. The kinetic model involving 24 components, 1 to 11 carbon atoms for paraffins and 6 to 11 carbon atom for naphthenes and aromatics with 71 reactions. The pre-exponential Arrhenius constants and activation energies were determined after fine tuning of the model results with experimental data. The input to the optimization is the compositions for 21 components and the temperature for the effluent stream for each one of the four reactors within the reforming process while the output of optimization is 142 predicted kinetic parameters for 71 reactions within reforming process. The differential optimization technique using genetic algorithm to predict the parameters of the kinetic model. To validate the kinetic model, the simulation results of the model based on proposed kinetic model was compared with the experimental results. The comparison between the predicted and commercially results shows a good agreement, while the percentage of absolute error for aromatics compositions are (7.5, 2, 8.3, and 6.1% and the temperature absolute percentage error are (0.49, 0.5, 0.01, and 0.3% for four reactors respectively.

  1. Biochemical and morphological changes during the growth kinetics of Araucaria angustifolia suspension cultures

    Directory of Open Access Journals (Sweden)

    André Luis Wendt dos Santos

    2010-06-01

    Full Text Available Embryogenic cultures of Araucaria angustifolia were established in a BM liquid medium supplemented with 2 µM 2,4-dichlorophenoxyacetic acid, 1 µM 6-benzylaminopurine and 1 µM kinetin (BM2 and in a BM medium free of growth regulators (BM0. During 42 days in culture, the cell growth pattern of both cultures was similar. The pH of the culture medium of both BM0 and BM2 underwent progressive reduction during culture time. For both the embryogenic cultures a preferential uptake of glucose in the late stages of cell growth kinetics was observed. The extracellular protein content was similar for both the embryogenic cultures. Acetocarmine and Evan's blue double stain showed major differences for early somatic embryo organisation, in which only the embryogenic culture grown in a liquid culture medium free of plant growth regulators showed the presence of bipolar somatic pro-embryos.Culturas embriogênicas de Araucaria angustifolia foram estabelecidas em meio de cultura líquido BM suplementado com 2 µM Ácido 2,4 Diclorofenoxiacético, 1 µM 6-Benzilaminopurina e 1 µM Cinetina (BM2 e em meio BM isento de reguladores de crescimento (BM0. Durante 42 dias de cultivo, o padrão de crescimento celular em ambas as culturas foi similar. O pH do meio de cultura BM0 e BM2 sofreu uma progressiva redução durante o período de cultivo. Em ambas as culturas embriogênicas foram observadas um consumo preferencial de glicose no período final da curva de crescimento celular. O nível de proteínas extracelulares foi similar para ambas as culturas embriogênicas. A dupla coloração com carmin acético e azul de Evans revelou diferenças na organização das linhagens celulares embriogênicas, sendo que a presença de proembriões somáticos bipolares foi apenas evidenciada nas culturas embriogênicas mantidas em meio de cultura líquido sem reguladores de crescimento.

  2. Thermodynamic and Kinetic Studies on the SiH + XH3 (X=N, P) Reactions

    Institute of Scientific and Technical Information of China (English)

    Wei Jiang SI; hu Ping ZHUO; Guan Zhi JU

    2004-01-01

    Based on the quantum chemical study of the silylidyne insertion reaction with NH3 or PH3, the general statistical thermodynamics and Eyring transition state theory with Wigner correction are used to compute the changes of thermodynamic functions, equilibrium constants, A factors and rate constants of the two reactions in the temperature range 200-2000K. The results show that both of these reactions are thermodynamically dominant at low temperatures and kinetically favored at higher temperatures. The comparison between these two reactions shows that the SiH reaction with NH3 is more exothermic than SiH with PH3, while the rate constant of SiH reaction with NH3 is lower than that of SiH with PH3 at the same temperature.

  3. SurfKin: an ab initio kinetic code for modeling surface reactions.

    Science.gov (United States)

    Le, Thong Nguyen-Minh; Liu, Bin; Huynh, Lam K

    2014-10-01

    In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. PMID:25111729

  4. Bench-scale Kinetics Study of Mercury Reactions in FGD Liquors

    Energy Technology Data Exchange (ETDEWEB)

    Gary Blythe; John Currie; David DeBerry

    2008-03-31

    This document is the final report for Cooperative Agreement DE-FC26-04NT42314, 'Kinetics Study of Mercury Reactions in FGD Liquors'. The project was co-funded by the U.S. DOE National Energy Technology Laboratory and EPRI. The objective of the project has been to determine the mechanisms and kinetics of the aqueous reactions of mercury absorbed by wet flue gas desulfurization (FGD) systems, and develop a kinetics model to predict mercury reactions in wet FGD systems. The model may be used to determine optimum wet FGD design and operating conditions to maximize mercury capture in wet FGD systems. Initially, a series of bench-top, liquid-phase reactor tests were conducted and mercury species concentrations were measured by UV/visible light spectroscopy to determine reactant and byproduct concentrations over time. Other measurement methods, such as atomic absorption, were used to measure concentrations of vapor-phase elemental mercury, that cannot be measured by UV/visible light spectroscopy. Next, a series of bench-scale wet FGD simulation tests were conducted. Because of the significant effects of sulfite concentration on mercury re-emission rates, new methods were developed for operating and controlling the bench-scale FGD experiments. Approximately 140 bench-scale wet FGD tests were conducted and several unusual and pertinent effects of process chemistry on mercury re-emissions were identified and characterized. These data have been used to develop an empirically adjusted, theoretically based kinetics model to predict mercury species reactions in wet FGD systems. The model has been verified in tests conducted with the bench-scale wet FGD system, where both gas-phase and liquid-phase mercury concentrations were measured to determine if the model accurately predicts the tendency for mercury re-emissions. This report presents and discusses results from the initial laboratory kinetics measurements, the bench-scale wet FGD tests, and the kinetics modeling

  5. Oxygen exchange reaction kinetics for cerium(IV) oxide at 1000 °C

    International Nuclear Information System (INIS)

    Bulk oxygen exchange rate kinetics on CeO2 at 1000 °C were observed to have a first order dependence on the fraction of reaction remaining and to be independent of oxygen partial pressure, total pressure, particle size, and specific surface area. This suggests that the exchange reaction is dominated by an internal chemical reaction that is occurring throughout the bulk of the material, and not at the material surface. Oxygen exchange rates were limited by this internal chemical reaction for all CeO2 powders studied (15 nm to −325 mesh), and had a rate constant of 1.19×10−2 s−1 with a time to completion of 617 s. These results are similar to the exchange rates observed previously on PuO2, suggesting that oxygen exchange on PuO2 may also be dominated by an internal chemical reaction under similar conditions. This work will help guide future experiments on 238PuO2 oxygen exchange reactions. - Graphical abstract: Oxygen exchange kinetics on CeO2 at 1000 °C are independent of a wide range of experimental conditions and exhibit first-order chemical reaction kinetics. - Highlights: • Stable oxygen exchange rates obtained on a variety of CeO2 powders at 1000 °C. • Exchange rates are independent of atmospheric composition and specific surface area. • Exchange rates are limited by an internal chemical reaction, not a surface reaction. • CeO2 exchange rates appear similar to the rates observed on PuO2 at 1000 °C

  6. Coherent chemical kinetics as quantum walks. I. Reaction operators for radical pairs

    Science.gov (United States)

    Chia, A.; Tan, K. C.; Pawela, Ł.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.

    2016-03-01

    Classical chemical kinetics uses rate-equation models to describe how a reaction proceeds in time. Such models are sufficient for describing state transitions in a reaction where coherences between different states do not arise, in other words, a reaction that contains only incoherent transitions. A prominent example of a reaction containing coherent transitions is the radical-pair model. The kinetics of such reactions is defined by the so-called reaction operator that determines the radical-pair state as a function of intermediate transition rates. We argue that the well-known concept of quantum walks from quantum information theory is a natural and apt framework for describing multisite chemical reactions. By composing Kraus maps that act only on two sites at a time, we show how the quantum-walk formalism can be applied to derive a reaction operator for the standard avian radical-pair reaction. Our reaction operator predicts the same recombination dephasing rate as the conventional Haberkorn model, which is consistent with recent experiments [K. Maeda et al., J. Chem. Phys. 139, 234309 (2013), 10.1063/1.4844355], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010), 10.1016/j.cplett.2010.01.063]. The standard radical-pair reaction has conventionally been described by either a normalized density operator incorporating both the radical pair and reaction products or a trace-decreasing density operator that considers only the radical pair. We demonstrate a density operator that is both normalized and refers only to radical-pair states. Generalizations to include additional dephasing processes and an arbitrary number of sites are also discussed.

  7. The analysis of Al-based alloys by calorimetry: quantitative analysis of reactions and reaction kinetics

    OpenAIRE

    Starink, M.J.

    2004-01-01

    Differential scanning calorimetry (DSC) and isothermal calorimetry have been applied extensively to the analysis of light metals, especially Al based alloys. Isothermal calorimetry and differential scanning calorimetry are used for analysis of solid state reactions, such as precipitation, homogenisation, devitrivication and recrystallisation; and solid–liquid reactions, such as incipient melting and solidification, are studied by differential scanning calorimetry. In producing repeatable calo...

  8. A small-scale, inexpensive method for detecting formaldehyde or methanol in biochemical reactions containing interfering substances.

    Science.gov (United States)

    Jiang, Wen Zhi; Adamec, Jiri; Weeks, Donald P

    2013-11-15

    A simple, inexpensive microdistillation device is described for capturing methanol or formaldehyde as end products of biochemical reactions or in environmental samples. We demonstrate that the microdistillation protocol, coupled with the use of alcohol oxidase and the formaldehyde-sensitive reagent Purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole), serves as a quick and inexpensive alternative to chromatographic and mass spectrometer analyses for determining if formaldehyde or methanol is a product of reactions that contain substances that interfere with the Purpald reaction. These techniques were used to affirm formaldehyde as the end product of the dicamba monooxygenase-catalyzed O-demethylation of the herbicide dicamba (2-methoxy-3,6-dichlorobenzoic acid). PMID:23938775

  9. A Kinetic Study of the Gas-Phase Reaction of OH with Br2

    OpenAIRE

    Bryukov, Mikhail G.; Dellinger, Barry; Knyazev, Vadim D.

    2006-01-01

    An experimental, temperature-dependent kinetic study of the gas-phase reaction of the hydroxyl radical with molecular bromine (reaction 1) has been performed using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over a wide temperature range of 297 – 766 K, and at pressures between 6.68 and 40.29 kPa of helium. The experimental rate coefficients for reaction 1 demonstrate no correlation with pressure and exhibit a negative temperature dependence with a slight negative cu...

  10. A kinetic study of the reaction of water vapor and carbon dioxide on uranium

    International Nuclear Information System (INIS)

    The kinetic study of the reaction of water vapour and carbon dioxide with uranium has been performed by thermogravimetric methods at temperatures between 160 and 410 deg G in the first case, 350 and 1050 deg C in the second: Three sorts of uranium specimens were used: uranium powder, thin evaporated films, and small spheres obtained from a plasma furnace. The experimental results led in the case of water vapour, to a linear rate of reaction controlled by diffusion at the lower temperatures, and by a surface reaction at the upper ones. In the case of carbon dioxide, a parabolic law has been found, controlled by diffusional processes. (author)

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

    Institute of Scientific and Technical Information of China (English)

    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.

  12. A hydrodynamics-reaction kinetics coupled model for evaluating bioreactors derived from CFD simulation.

    Science.gov (United States)

    Wang, Xu; Ding, Jie; Guo, Wan-Qian; Ren, Nan-Qi

    2010-12-01

    Investigating how a bioreactor functions is a necessary precursor for successful reactor design and operation. Traditional methods used to investigate flow-field cannot meet this challenge accurately and economically. Hydrodynamics model can solve this problem, but to understand a bioreactor in sufficient depth, it is often insufficient. In this paper, a coupled hydrodynamics-reaction kinetics model was formulated from computational fluid dynamics (CFD) code to simulate a gas-liquid-solid three-phase biotreatment system for the first time. The hydrodynamics model is used to formulate prediction of the flow field and the reaction kinetics model then portrays the reaction conversion process. The coupled model is verified and used to simulate the behavior of an expanded granular sludge bed (EGSB) reactor for biohydrogen production. The flow patterns were visualized and analyzed. The coupled model also demonstrates a qualitative relationship between hydrodynamics and biohydrogen production. The advantages and limitations of applying this coupled model are discussed. PMID:20727741

  13. New method for spectrophotometric determination of quinones and barbituric acid through their reaction. A kinetic study

    Science.gov (United States)

    Medien, H. A. A.

    1996-11-01

    A new and sensitive spectrophotometric method is described for the determination of p-benzoquinone, p-chloranil and 1.4-naphthoquinone. The method is based on the reaction between quinones and barbituric acid, by which a color is developed with maximum absorption between 485 and 555 nm in 50% methyl alcohol-water mixture. The absorption of the product obeys Beer's law within the concentration range 0.025-05 mM of orginal quinone. The kinetics of the reaction between p-benzoquinone and barbituric acid was studied in a range of methyl alcohol-water mixtures. The reaction follows overall second order kinetics, first order in each of the reactants. The rate increases with increasing dielectric constant. The method was applied for determination of barbituric acid with p-benzoquinone in the concentration range of 0.025-0.345 mM. Other barbiturates do not interfere.

  14. Kinetics of phyllosemiquinone oxidation in the Photosystem I reaction centre of Acaryochloris marina.

    Science.gov (United States)

    Santabarbara, Stefano; Bailleul, Benjamin; Redding, Kevin; Barber, James; Rappaport, Fabrice; Telfer, Alison

    2012-02-01

    Light-induced electron transfer reactions in the chlorophyll a/d-binding Photosystem I reaction centre of Acaryochloris marina were investigated in whole cells by pump-probe optical spectroscopy with a temporal resolution of ~5ns at room temperature. It is shown that phyllosemiquinone, the secondary electron transfer acceptor anion, is oxidised with bi-phasic kinetics characterised by lifetimes of 88±6ns and 345±10ns. These lifetimes, particularly the former, are significantly slower than those reported for chlorophyll a-binding Photosystem I, which typically range in the 5-30ns and 200-300ns intervals. The possible mechanism of electron transfer reactions in the chlorophyll a/d-binding Photosystem I and the slower oxidation kinetics of the secondary acceptors are discussed. PMID:22037394

  15. Hydrolysis of Surfactants Containing Ester Bonds: Modulation of Reaction Kinetics and Important Aspects of Surfactant Self-Assembly

    Science.gov (United States)

    Lundberg, Dan; Stjerndahl, Maria

    2011-01-01

    The effects of self-assembly on the hydrolysis kinetics of surfactants that contain ester bonds are discussed. A number of examples on how reaction rates and apparent reaction orders can be modulated by changes in the conditions, including an instance of apparent zero-order kinetics, are presented. Furthermore, it is shown that the examples on…

  16. The kinetic model for slow photoinduced electron transport in the reaction centers of purple bacteria.

    Science.gov (United States)

    Serdenko, T V; Barabash, Y M; Knox, P P; Seifullina, N Kh

    2016-12-01

    The present work is related to the investigation of slow kinetics of electron transport in the reaction centers (RCs) of Rhodobacter sphaeroides. Experimental data on the absorption kinetics of aqueous solutions of reaction centers at different modes of photoexcitation are given. It is shown that the kinetics of oxidation and reduction of RCs are well described by the sum of three exponential functions. This allows to suggest a two-level kinetic model for electron transport in the RC as a system of four electron-conformational states which correspond to three balance differential equations combined with state equation. The solution of inverse problem made it possible to obtain the rate constant values in kinetic equations for different times and intensities of exciting light. Analysis of rate constant values in different modes of RC excitation allowed to suggest that two mechanisms of structural changes are involved in RC photo-oxidation. One mechanism leads to the increment of the rate of electron return, another one-to its drop. Structural changes were found out to occur in the RCs under incident light. After light was turned off, the reduction of RCs was determined by the second mechanism. PMID:27271854

  17. Determination of Carbohydrazide and Kinetics of Condensation reaction of Carbohydrazide with Malachite Green by Spectrophotometry

    Institute of Scientific and Technical Information of China (English)

    伍涛; 张同来; 陈红艳; 张建国

    2005-01-01

    The kinetics of the condensation reaction of malachite green and carbohydrazide was studied by spectrophotometry in aqueous solution in the temperature range of 15.0-22.0℃. The reaction was found to be second-order overall, first-order with respect to each reactant. The effect of ionic strength on the reaction has negative salt effect in the range of 0.2-1.0 mol·L-1. A mechanism of the reaction between malachite green and carbohydrazide was proposed, and the rate equation derived from the mechanism can explain all experimental observations properly. Based on this reaction, a method of determining the content of carbohydrazide in the concentration range of (0.02-0.5) )<10-3 mol·L-1 was proposed.

  18. Kinetic analysis of the reactions of hypobromous acid with protein components

    DEFF Research Database (Denmark)

    Pattison, David I; Davies, Michael Jonathan

    2004-01-01

    proteins isolated from patients with atherosclerosis, asthma, and cystic fibrosis, implicating the production of HOX in these diseases. The quantitative significance of these findings requires knowledge of the kinetics of reaction of HOX with protein targets, and such data have not been previously...... more, and Cys and Met much less, important targets for HOBr than HOCl. Kinetic models have been developed to predict the targets of HOX attack on proteins and free amino acids. Overall, these results shed light on the mechanisms of cell damage induced by HOX and indicate, for example, that the 3-chloro...

  19. Thermal decomposition of sugarcane straw, kinetics and heat of reaction in synthetic air.

    Science.gov (United States)

    Rueda-Ordóñez, Yesid Javier; Tannous, Katia

    2016-07-01

    The aim of this work was to analyze the thermal decomposition, kinetics and heat of reaction of sugarcane straw in synthetic air by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG and DSC experiments were carried out using heating rates of 2.5°C/min, 5°C/min, and 10°C/min, and particle diameter of 0.250mm. In the study of the smoldering reaction were identified three consecutive stages, drying, oxidative pyrolysis, and combustion. Thus, the kinetic pathway was composed by six independent parallel reactions, three for each stage after drying, in which the activation energies were 176, 313, 150, 80, 150, and 100kJ/mol. The heat of reaction in synthetic air was completely exothermic releasing 8MJ/kg. The modeled curves of thermal decomposition of sugarcane straw presented good agreement with experimental data. Then, the kinetic parameters obtained could be used to analyze different processes involving smoldering. PMID:27019126

  20. Sensitivity of Polar Stratospheric Ozone Loss to Uncertainties in Chemical Reaction Kinetics

    Science.gov (United States)

    Kawa, S. Randolph; Stolarksi, Richard S.; Douglass, Anne R.; Newman, Paul A.

    2008-01-01

    Several recent observational and laboratory studies of processes involved in polar stratospheric ozone loss have prompted a reexamination of aspects of our understanding for this key indicator of global change. To a large extent, our confidence in understanding and projecting changes in polar and global ozone is based on our ability to simulate these processes in numerical models of chemistry and transport. The fidelity of the models is assessed in comparison with a wide range of observations. These models depend on laboratory-measured kinetic reaction rates and photolysis cross sections to simulate molecular interactions. A typical stratospheric chemistry mechanism has on the order of 50- 100 species undergoing over a hundred intermolecular reactions and several tens of photolysis reactions. The rates of all of these reactions are subject to uncertainty, some substantial. Given the complexity of the models, however, it is difficult to quantify uncertainties in many aspects of system. In this study we use a simple box-model scenario for Antarctic ozone to estimate the uncertainty in loss attributable to known reaction kinetic uncertainties. Following the method of earlier work, rates and uncertainties from the latest laboratory evaluations are applied in random combinations. We determine the key reactions and rates contributing the largest potential errors and compare the results to observations to evaluate which combinations are consistent with atmospheric data. Implications for our theoretical and practical understanding of polar ozone loss will be assessed.

  1. Chemical kinetic analysis of hydrogen-air ignition and reaction times

    Science.gov (United States)

    Rogers, R. C.; Schexnayder, C. J., Jr.

    1981-01-01

    An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

  2. Kinetic method for enzymatic analysis by predicting background with uricase reaction as model

    Institute of Scientific and Technical Information of China (English)

    LIAO Fei; ZHAO Yun-sheng; ZHAO Li-na; TAO Jia; ZHU Xiao-yun; WANG Yong-mei; ZUO Yu-ping

    2005-01-01

    Objective:To investigate the reliability for kinetic assay of substance with background predicted by the integrated method using uricase reaction as model. Methods: Absorbance before uricase action (A0) was estimated by extrapolation with given lag time of steady-state reaction. With Km fixed at12.5 μmol/L, background absorbance (Ab) was predicted by nonlinearly fitting integrated MichaelisMenten equation to Candida utilis uricase reaction curve. Uric acid in reaction solution was determined by the difference (ΔA) between A0 and Ab. Results :Ab usually showed deviation <3% from direct assay with residual substrate <one-fifth of initial substrate for analysis. ΔA showed CV <5% with resistance to common interferences except xanthine, and it linearly responded to uric acid with slope consistent to the absorptivity of uric acid. The lower limit was 2.0 μmol/L and upper limit reached 30 μmol/L in reaction solution with data monitored within 8 min reaction at 0. 015 U/ml uricase. Preliminary application to serum and urine gave better precision than the direct equilibrium method without the removal of proteins before analysis. Conclusion:This kinetic method with background predicted by the integrated method was reliable for enzymatic analysis, and it showed resistance to common interferences and enhanced efficiency at much lower cost.

  3. CP: AN INVESTIGATION OF COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS, AND REACTION TO VARIOUS STIMULI

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K; Burnham, A K; Fontes, A T

    2005-03-23

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear heating rates, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Using differential scanning calorimetry, DSC, CP was decomposed at linear heating rates of 1, 3, and 7 C/min and the kinetic triplet calculated using the LLNL code Kinetics05. Values are also reported for spark, friction, and impact sensitivity.

  4. Kinetics of free radical decay reactions in lactic acid homo and copolymers irradiated to sterilization dose

    International Nuclear Information System (INIS)

    The kinetics of free radical decay reactions of poly(L-Lactic acid), poly(DL-Lactic acid) and random copolymer of lactic and glycolic acid have been investigated for decays taking place in air and in vacuum. The change in ESR lines of γ-irradiated polymers have been followed over a long time period. The decay has been found to follow neither simple first-order nor second-order kinetics. Various kinetic approaches including composite first or second-order mechanisms and diffusion-controlled first or second-order equations were determined to be also unsatisfactory. The decay of radicals in bulk irradiated lactic acid homo and copolymers was found to be best described when the second-order non-classical equation with time dependent rate constant approach was used. (Author)

  5. Stochastic modeling of biochemical systems with multistep reactions using state-dependent time delay.

    Science.gov (United States)

    Wu, Qianqian; Tian, Tianhai

    2016-01-01

    To deal with the growing scale of molecular systems, sophisticated modelling techniques have been designed in recent years to reduce the complexity of mathematical models. Among them, a widely used approach is delayed reaction for simplifying multistep reactions. However, recent research results suggest that a delayed reaction with constant time delay is unable to describe multistep reactions accurately. To address this issue, we propose a novel approach using state-dependent time delay to approximate multistep reactions. We first use stochastic simulations to calculate time delay arising from multistep reactions exactly. Then we design algorithms to calculate time delay based on system dynamics precisely. To demonstrate the power of proposed method, two processes of mRNA degradation are used to investigate the function of time delay in determining system dynamics. In addition, a multistep pathway of metabolic synthesis is used to explore the potential of the proposed method to simplify multistep reactions with nonlinear reaction rates. Simulation results suggest that the state-dependent time delay is a promising and accurate approach to reduce model complexity and decrease the number of unknown parameters in the models. PMID:27553753

  6. On the ultrafast kinetics of the energy and electron transfer reactions in photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Slavov, Chavdar Lyubomirov

    2009-07-09

    The subject of the current work is one of the main participants in the light-dependent phase of oxygenic photosynthesis, Photosystem I (PS I). This complex carries an immense number of cofactors: chlorophylls (Chl), carotenoids, quinones, etc, which together with the protein entity exhibit several exceptional properties. First, PS I has an ultrafast light energy trapping kinetics with a nearly 100% quantum efficiency. Secondly, both of the electron transfer branches in the reaction center are suggested to be active. Thirdly, there are some so called 'red' Chls in the antenna system of PS I, absorbing light with longer wavelengths than the reaction center. These 'red' Chls significantly modify the trapping kinetics of PS I. The purpose of this thesis is to obtain better understanding of the above-mentioned, specific features of PS I. This will not merely cast more light on the mechanisms of energy and electron transfer in the complex, but also will contribute to the future developments of optimized artificial light-harvesting systems. In the current work, a number of PS I complexes isolated from different organisms (Thermosynechococcus elongatus, Chlamydomonas reinhardtii, Arabidopsis thaliana) and possessing distinctive features (different macroorganisation, monomers, trimers, monomers with a semibelt of peripheral antenna attached; presence of 'red' Chls) is investigated. The studies are primarily focused on the electron transfer kinetics in each of the cofactor branches in the PS I reaction center, as well as on the effect of the antenna size and the presence of 'red' Chls on the trapping kinetics of PS I. These aspects are explored with the help of several ultrafast optical spectroscopy methods: (i) time-resolved fluorescence ? single photon counting and synchroscan streak camera; and (ii) ultrafast transient absorption. Physically meaningful information about the molecular mechanisms of the energy trapping in PS I is

  7. Role of reaction kinetics and mass transport in glucose sensing with nanopillar array electrodes

    Directory of Open Access Journals (Sweden)

    Rao Yeswanth L

    2007-10-01

    Full Text Available Abstract The use of nanopillar array electrodes (NAEs for biosensor applications was explored using a combined experimental and simulation approach to characterize the role of reaction kinetics and mass transport in glucose detection with NAEs. Thin gold electrodes with arrays of vertically standing gold nanopillars were fabricated and their amperometric current responses were measured under bare and functionalized conditions. Results show that the sensing performances of both the bare and functionalized NAEs were affected not only by the presence and variation of the nanoscale structures on the electrodes but also by the reaction kinetics and mass transport of the analyte species involved. These results will shed new light for enhancing the performance of nanostructure based biosensors.

  8. Constrained reaction volume approach for studying chemical kinetics behind reflected shock waves

    KAUST Repository

    Hanson, Ronald K.

    2013-09-01

    We report a constrained-reaction-volume strategy for conducting kinetics experiments behind reflected shock waves, achieved in the present work by staged filling in a shock tube. Using hydrogen-oxygen ignition experiments as an example, we demonstrate that this strategy eliminates the possibility of non-localized (remote) ignition in shock tubes. Furthermore, we show that this same strategy can also effectively eliminate or minimize pressure changes due to combustion heat release, thereby enabling quantitative modeling of the kinetics throughout the combustion event using a simple assumption of specified pressure and enthalpy. We measure temperature and OH radical time-histories during ethylene-oxygen combustion behind reflected shock waves in a constrained reaction volume and verify that the results can be accurately modeled using a detailed mechanism and a specified pressure and enthalpy constraint. © 2013 The Combustion Institute.

  9. Reaction kinetics and modeling of photoinitiated cationic polymerization of an alicyclic based diglycidyl ether

    Energy Technology Data Exchange (ETDEWEB)

    Harikrishna, R., E-mail: r.harikrishna@ncl.res.in [Polymer Science and Engineering Division, National Chemical Laboratory, Pune 411008 (India); Ponrathnam, S. [Polymer Science and Engineering Division, National Chemical Laboratory, Pune 411008 (India); Tambe, S.S. [Chemical Engineering and Process Development Division, National Chemical Laboratory, Pune 411008 (India)

    2014-01-01

    Highlights: • Photocationic polymerization of alicyclic based diglycidyl ether was carried out. • Kinetic parameters were influenced by gelation and diffusional restrictions. • Applicability of autocatalytic model was established by nonlinear regression. • System showed higher activation energy than cycloaliphatic and aromatic diepoxides. -- Abstract: Photoinitiated cationic polymerization of cycloaliphatic diepoxides had received tremendous attention, while studies with lesser polymerizable diglycidyl ethers are comparatively less reported. The present work deals with the photoinitiated cationic polymerization of cyclohexane dimethanol diglycidyl ether followed by estimation of kinetic parameters. The effects of concentration of photoinitiator and temperature on curing performance were studied using photo differential scanning calorimeter or photo DSC with polychromatic radiation. It was observed that the rate of polymerization as well as ultimate conversion increased with increasing concentration of photoinitiator and temperature. The influences of gelation as well as diffusional restrictions have remarkable effect on cure performance. The kinetic parameters as per autocatalytic kinetic model were studied by Levenberg–Marquardt nonlinear regression method instead of conventional linear method for obtaining more accurate values of apparent rate constant. It was observed that the model fits with data from initial stages to almost towards the end of the reaction. The activation energy was found to be higher than the values reported for more reactive cycloaliphatic diepoxides. The value of pre-exponential factor increased with increase in activation energy showing influence of gelation at early stages of reaction.

  10. Purification and characterization of Fab fragments with rapid reaction kinetics against myoglobin.

    Science.gov (United States)

    Song, Hyung-Nam; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon

    2015-01-01

    Myoglobin is an early biomarker for acute myocardial infarction. Recently, we isolated the antibody IgG-Myo2-7ds, which exhibits unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid dissociation kinetics are thought to be premature IgG forms that are produced during the early stage of in vivo immunization. In the present study, we identified the epitope region of the IgG-Myo2-7ds antibody to be the C-terminal region of myoglobin, which corresponds to 144-154 aa. The Fab fragment was directly purified by papain cleavage and protein G affinity chromatography and demonstrated kinetics of an association constant of 4.02 × 10(4) M(-1) s(-1) and a dissociation constant of 2.28 × 10(-2) s(-1), which retained the unique reaction kinetics of intact IgG-Myo2-7ds antibodies. Because a rapid dissociation antibody can be utilized for antibody recycling, the results from this study would provide a platform for the development of antibody engineering in potential diagnostic areas such as a continuous monitoring system for heart disease. PMID:25561012

  11. Single-Site Palladium(II) Catalyst for Oxidative Heck Reaction: Catalytic Performance and Kinetic Investigations

    Energy Technology Data Exchange (ETDEWEB)

    Duan, Hui; Li, Mengyang; Zhang, Guanghui; Gallagher, James R.; Huang, Zhiliang; Sun, Yu; Luo, Zhong; Chen, Hongzhong; Miller, Jeffrey T.; Zou, Ruqiang; Lei, Aiwen; Zhao, Yanli

    2015-01-01

    ABSTRACT: The development of organometallic single-site catalysts (SSCs) has inspired the designs of new heterogeneous catalysts with high efficiency. Nevertheless, the application of SSCs in certain modern organic reactions, such as C-C bond formation reactions, has still been less investigated. In this study, a single-site Pd(II) catalyst was developed, where 2,2'-bipyridine-grafted periodic mesoporous organosilica (PMO) was employed as the support of a Pd(II) complex. The overall performance of the single-site Pd(II) catalyst in the oxidative Heck reaction was then investigated. The investigation results show that the catalyst displays over 99% selectivity for the product formation with high reaction yield. Kinetic profiles further confirm its high catalytic efficiency, showing that the rate constant is nearly 40 times higher than that for the free Pd(II) salt. X-ray absorption spectroscopy reveals that the catalyst has remarkable lifetime and recyclability.

  12. Kinetics and mechanism of the reaction of fluorine atoms with pentafluoropropionic acid.

    Science.gov (United States)

    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

  13. Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles

    International Nuclear Information System (INIS)

    Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology

  14. Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Bartling, Stephan, E-mail: stephan.bartling@uni-rostock.de; Meiwes-Broer, Karl-Heinz; Barke, Ingo [Department of Physics, University of Rostock, Universitätsplatz 3, D-18051 Rostock (Germany); Pohl, Marga-Martina [Leibniz-Institut für Katalyse e.V. an der Universität Rostock (LIKAT), Albert-Einstein-Str. 29a, D-18059 Rostock (Germany)

    2015-09-21

    Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology.

  15. Chlorine transfert reactions between chloramine and piperidine: Kinetic reactivity and characterization in a Raschig medium

    OpenAIRE

    Darwich, Chaza; Elkhatib, Mazen; Steinhauser, Georg; Delalu, Henri

    2009-01-01

    the kinetics of the Cl-transfert reaction between chloramine and piperidine in a Raschig medium was studied at various temperatures, with variable concentrations of the two reactants. The influence of the pH on the interaction was examined at a pH ranging between 8.25 and 12.89. The Cl-transfert reaction resulted in the formation of 1-chloropiperidine, which, in the presence of NaOH, underwent a dehydrohalogenation leading to an endocyclic imine derivative: 2,3,4,5-tetrahydropyridine. The kin...

  16. Fischer-Tropsch Reaction Kinetics of Cobalt Catalyst in Supercritical Phase

    Institute of Scientific and Technical Information of China (English)

    Abdullah Irankhah; Ali Haghtalab; Ebrahim Vasheghani Farahani; Kambiz Sadaghianizadeh

    2007-01-01

    Fischer-Tropsch synthesis under supercritical phase condition was examined in a continuous and a high-pressure fixed bed reactor by employing a cobalt catalyst (Co-Ru/γ-Al2O3). An integral reactor model involving Fischer-Tropsch reaction kinetics in the supercritical fluid n-hexane was used to describe the overall performance. On the basis of Langmuir-Hinshelwood-Hougen-Watson (LHHW) model, the reaction rate constants were obtained for the rate equations of CO conversion to CH4 formation under supercritical conditions.

  17. Kinetics of the photoprotolytic reaction in a solution of coumarin dye

    International Nuclear Information System (INIS)

    The radiation kinetics of various ionic forms of the conmarin dye, aesculin, in ethanol under addition of acid was studied with the aid of a photoelectric rapid convertor (probably a photomultiplier with coupled oscillograph). The sweeps of radiation intensity were determined for sub-nanosecond resolution time. It was shown that the proton addition reaction from solution can be described by a simple one-step scheme. Rate constants for the photoprotolytic reaction were calculated from the measured time dependences of radiation intensity. (orig.)

  18. A novel reactor for determination of kinetics for solid catalyzed gas reactions

    OpenAIRE

    Borman, P.C.; Bos, A.N.R.; Westerterp, K.R.

    1994-01-01

    A novel perfectly mixed laboratory reactor for determining kinetics of heterogeneously catalyzed gas-phase reactions has been developed. Perfect mixing is achieved by circulating the gas in the reactor using an axial flow impeller in a well streamlined enclosure. Pellets are fixed in a rectangular opening in the blades of the impeller. They rotate with the impeller, thus realizing high particle velocities in the reactor. Interparticle mass transfer was studied experimentally by vaporization o...

  19. Data quality objectives for the reaction kinetics studies of K West fuel samples

    International Nuclear Information System (INIS)

    The Data Quality Objectives (DQOs) were established for the reaction kinetics studies of the first group of fuel samples shipped from the K West Basin to the Hanford 327 Building hot cells for examinations. A Thermo-Gravimetric Analysis (TGA) system was selected for these measurements and associated hydrogen release and ignition temperature testing. These examinations are an extension of the conditioning testing of sibling samples described in WHC-SD-SNF-DQO-004, Data Quality Objectives for the Initial Fuel Conditioning Examinations

  20. Kinetics of barium sulphate reaction crystallization in crystallizers with internal circulation

    OpenAIRE

    Koralewska, J.; Piotrowski, K; B. Wierzbowska; A. Matynia

    2008-01-01

    Kinetic calculation results describing the observed nucleation and growth rates of barium sulphate crystals precipitated in an integrated reaction-crystallization process in a barium sulphate-ammonium chloride-water system are presented and analyzed. The scope of experiments included two continuous model DTM-type crystallizers (Draft Tube Magma) with internal circulation of the suspension forced by a liquid jet-pump device responsible for stable and intensive enough ascending/descending flow ...

  1. On the graph and systems analysis of reversible chemical reaction networks with mass action kinetics

    OpenAIRE

    Rao, Shodhan; Jayawardhana, Bayu; der Schaft, Arjan van

    2012-01-01

    Motivated by the recent progresses on the interplay between the graph theory and systems theory, we revisit the analysis of reversible chemical reaction networks described by mass action kinetics by reformulating it using the graph knowledge of the underlying networks. Based on this formulation, we can characterize the space of equilibrium points and provide simple dynamical analysis on the state space modulo the space of equilibrium points.

  2. Design Of A Simple Apparatus For Reaction Kinetics And Reactor Design Experiments

    OpenAIRE

    Vavanellos, T. D.

    1990-01-01

    Tubular reactor experiments arc an integral part of an undergraduate course in reaction kinetics and reactor design. However, the successful design of such experiments necessitates meeting a set of criteria regarding safety, simplicity of design and aniytical needs, acceptable cost, and instuctional value. The design of a tubular reactor experiment satisfying the above criteria is presented here. It is hoped that this design can serve as the basis for assembling the necessary experimental app...

  3. Role of reaction kinetics and mass transport in glucose sensing with nanopillar array electrodes

    OpenAIRE

    Rao Yeswanth L; Kim Euihyeon; Yang Xiaoling; Anandan Venkataramani; Zhang Guigen

    2007-01-01

    Abstract The use of nanopillar array electrodes (NAEs) for biosensor applications was explored using a combined experimental and simulation approach to characterize the role of reaction kinetics and mass transport in glucose detection with NAEs. Thin gold electrodes with arrays of vertically standing gold nanopillars were fabricated and their amperometric current responses were measured under bare and functionalized conditions. Results show that the sensing performances of both the bare and f...

  4. Total kinetic energy distribution of fission fragments in 6,7Li + 238U reactions

    International Nuclear Information System (INIS)

    The shape and width of fission-fragment (FF) mass and kinetic energy distribution provides a lot of information on the fission reaction mechanism and the structure of the compound nucleus (CN), the fragments as well as the interacting nuclei. The shape of the mass distribution of the fission fragments for the actinides induced by the proton or neutron is known to change with the incident energy. At low energies, it shows a double humped distribution which changes slowly to a single humped distribution as energy increases. However, for a reaction involving a weakly bound projectile (i.e., 6Li + 232Th), a sharp change in the shape of the mass distribution with energy was observed. The sharp increase in the peak to valley ratio (P:V) in the fission-fragment mass distribution in 6Li + 232Th reaction by Itkis et al. and in 6,7Li + 238U reactions by Santra et al. was concluded to be due to the reduced energy transfer to the composite system caused by incomplete fusion (ICF) of alpha or deuteron/triton followed by fissions. Total Kinetic Energy (TKE) distribution of fission fragments is another important observable on which the effect of projectile breakup is not explored yet. In this contribution, the study of breakup/transfer effect on average TKE distribution for 6,7Li + 238U reactions is presented

  5. Reactions of plutonium and uranium with water: Kinetics and potential hazards

    International Nuclear Information System (INIS)

    The chemistry and kinetics of reactions between water and the metals and hydrides of plutonium and uranium are described in an effort to consolidate information for assessing potential hazards associated with handling and storage. New experimental results and data from literature sources are presented. Kinetic dependencies on pH, salt concentration, temperature and other parameters are reviewed. Corrosion reactions of the metals in near-neutral solutions produce a fine hydridic powder plus hydrogen. The corrosion rate for plutonium in sea water is a thousand-fold faster than for the metal in distilled water and more than a thousand-fold faster than for uranium in sea water. Reaction rates for immersed hydrides of plutonium and uranium are comparable and slower than the corrosion rates for the respective metals. However, uranium trihydride is reported to react violently if a quantity greater than twenty-five grams is rapidly immersed in water. The possibility of a similar autothermic reaction for large quantities of plutonium hydride cannot be excluded. In addition to producing hydrogen, corrosion reactions convert the massive metals into material forms that are readily suspended in water and that are aerosolizable and potentially pyrophoric when dry. Potential hazards associated with criticality, environmental dispersal, spontaneous ignition and explosive gas mixtures are outlined

  6. Kinetic study of the reaction of uranium with various carbon-containing gases

    International Nuclear Information System (INIS)

    The kinetic study of the reaction U + CO2 and U + CO has been performed by a thermogravimetric method on a spherical uranium powder, in temperature ranges respectively from 460 to 690 deg. C and from 570 to 850 deg. C. The reaction with carbon dioxide leads to uranium dioxide. A carbon deposition takes place at the same time. The global reactions is the result of two reactions: U + 2 CO2 → UO2 + 2 CO U + CO2 → UO2 + C The reaction with carbon monoxide leads to a mixture of dioxide UO2, dicarbide UC2 and free carbon. The main reaction can be written. U + CO → 1/2 UO2 + 1/2 UC2 The free carbon results of the disproportionation of the carbon monoxide. A remarkable separation of the two phases UO2 and UC2 can be observed. A mechanism accounting for the phenomenon has been proposed. The two reactions U + CO2 and U + CO begin with a long germination period, after which, the reaction velocity seems to be limited in both cases by the ionic diffusion of oxygen through the uranium dioxide. (author)

  7. Refolded scFv Antibody Fragment against Myoglobin Shows Rapid Reaction Kinetics

    Directory of Open Access Journals (Sweden)

    Hyung-Nam Song

    2014-12-01

    Full Text Available Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the VH–VL sequence with a (Gly4Ser3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10−4 M−1·s−1 and 6.29 × 10−3 s−1, respectively, with an affinity value exceeding 107 M−1 (kon/koff, maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor.

  8. Kinetics of reaction of gold nanoparticles following partial removal of stabilizers

    International Nuclear Information System (INIS)

    Citrate-stabilized gold nanoparticles (Au NPs) of 17-nm diameter were allowed to react following partial depletion of the stabilizer using dialysis. Kinetics of the reaction was investigated by following time-dependent changes in the visible extinction spectrum. Thus, surface plasmon resonance peak (SPR) of isolated Au NPs (reactant) at 522 nm decreased, while SPR peak due to product—which was agglomerated Au NPs—occurring at 600 nm increased with time. The reaction followed first-order kinetics with respect to concentration of reactant (Au NP) with a rate constant on the order of (2.10 ± 0.34) × 10−3 min−1. Further, product concentration correspondingly increased with time. Transmission electron microscopy investigation indicated the presence of individual NPs, along with agglomerated structures in the beginning of reaction—the extent of which increased with time, rather than the formation of smaller agglomerates. A model has been proposed based on reaction of individual NPs with agglomerated structures which accounted for the observed kinetics.

  9. Kinetics of reaction of gold nanoparticles following partial removal of stabilizers

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, Anushree [Indian Institute of Technology Guwahati, Department of Chemistry (India); Das, Subhojit [National Institute of Technology, Department of Chemistry (India); Paul, Anumita, E-mail: anumita@iitg.ernet.in; Chattopadhyay, Arun, E-mail: arun@iitg.ernet.in [Indian Institute of Technology Guwahati, Department of Chemistry (India)

    2015-06-15

    Citrate-stabilized gold nanoparticles (Au NPs) of 17-nm diameter were allowed to react following partial depletion of the stabilizer using dialysis. Kinetics of the reaction was investigated by following time-dependent changes in the visible extinction spectrum. Thus, surface plasmon resonance peak (SPR) of isolated Au NPs (reactant) at 522 nm decreased, while SPR peak due to product—which was agglomerated Au NPs—occurring at 600 nm increased with time. The reaction followed first-order kinetics with respect to concentration of reactant (Au NP) with a rate constant on the order of (2.10 ± 0.34) × 10{sup −3} min{sup −1}. Further, product concentration correspondingly increased with time. Transmission electron microscopy investigation indicated the presence of individual NPs, along with agglomerated structures in the beginning of reaction—the extent of which increased with time, rather than the formation of smaller agglomerates. A model has been proposed based on reaction of individual NPs with agglomerated structures which accounted for the observed kinetics.

  10. Refolded scFv antibody fragment against myoglobin shows rapid reaction kinetics.

    Science.gov (United States)

    Song, Hyung-Nam; Jang, Jun-Hyuck; Kim, Young-Wan; Kim, Dong-Hyung; Park, Sung-Goo; Lee, Myung Kyu; Paek, Se-Hwan; Woo, Eui-Jeon

    2014-01-01

    Myoglobin is one of the early biomarkers for acute myocardial infarction. Recently, we have screened an antibody with unique rapid reaction kinetics toward human myoglobin antigen. Antibodies with rapid reaction kinetics are thought to be an early IgG form produced during early stage of in vivo immunization. We produced a recombinant scFv fragment for the premature antibody from Escherichia coli using refolding technology. The scFv gene was constructed by connection of the V(H)-V(L) sequence with a (Gly4Ser)3 linker. The scFv fragment without the pelB leader sequence was expressed at a high level, but the solubility was extremely low. A high concentration of 8 M urea was used for denaturation. The dilution refolding process in the presence of arginine and the redox reagents GSH and GSSH successfully produced a soluble scFv protein. The resultant refolded scFv protein showed association and dissociation values of 9.32 × 10⁻⁴ M⁻¹·s⁻¹ and 6.29 × 10⁻³ s⁻¹, respectively, with an affinity value exceeding 10⁷ M⁻¹ (k(on)/k(off)), maintaining the original rapid reaction kinetics of the premature antibody. The refolded scFv could provide a platform for protein engineering for the clinical application for diagnosis of heart disease and the development of a continuous biosensor. PMID:25530617

  11. Reaction kinetics of the double perovskite Sr2FeMoO6 by gas–solid reactions

    International Nuclear Information System (INIS)

    Double perovskite Sr2FeMoO6 is characterized by its colossal magnetoresistance, however, its production route is not well established. Therefore, the objective of this work is to study the reaction kinetics involved in the formation of Sr2FeMoO6. Firstly, precursor phases Sr2Fe2O5 and SrMoO4 were synthesized by gas-solid reactions from starting reagents such as SrCO3, Fe2O3 y MoO3. The thermogravimetric technique was employed to analyze the kinetics of formation of the double perovskite from the precursor phases given the optimized process variables. Microstructural characterization of the products obtained was performed by X-ray diffraction and Rietveld analysis. Results showed that the instability of SrFeO2.5 during the reduction stage led to a formation of a disordered double perovskite Sr2Fe0.71Mo1.29O6

  12. Surface Reaction Kinetics of Steam- and CO2-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

    OpenAIRE

    Karla Herrera Delgado; Lubow Maier; Steffen Tischer; Alexander Zellner; Henning Stotz; Olaf Deutschmann

    2015-01-01

    An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO2 as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented i...

  13. Kinetics of reactions of Np and Pu ions with hydrazine derivatives. XVI. Reaction between Np(V) and phenylhydrazine

    International Nuclear Information System (INIS)

    The rate of reduction of Np(V) by phenylhydrazine in perchloric acid solution is described by kinetic equation d[Np(IV)]/dt=k1[Np(V)][C6H5N2H4+] + k3[Np(V)][C6H5N2H4+][H+]2 + k2[Np(V)][Np(IV)], where k1=1.27x10-3, 2.81x10-3 and 5.86x10-3 l/(mol min); k3=2.32x10-2, 1.21x10-2 and 5.75x10-2 l3/(mol3 min) and k2=1.1, 8.3 and 50 l/(mol min) at ionic strength μ=4 and at 40, 60 and 80 Deg C respectively. Activation energies of three reaction ways are: E1=35±7, E3=74±17 and E2=88±1 kJ/mol. Reaction is autocatalyzed due to formation of intermediate product - hydroquinone, which concentration in reaction solution is proportional to concentration of the end product - Np(IV) ions. Possible slow stages of two basic and autocatalytic ways of reaction are discussed

  14. Some biochemical reactions of strawberry plants to infection with Botrytis cinerea and salicylic acid treatment

    OpenAIRE

    Urszula Małolepsza; Henryk Urbanek; Justyna Polit

    2013-01-01

    The reactions of strawberry plants to infection with B. cinerea and treatment with salicylic acid has been studied. Infection of leaves with B. cinerea resulted in early increases in active oxygen species generation, superoxide dismutase and peroxidase activities and phenolic compounds content. Some increases of the above reactions were noticed in plants treated with salicylic acid but not in the plants treated with SA and then later infected with B. cinerea.

  15. Some biochemical reactions of strawberry plants to infection with Botrytis cinerea and salicylic acid treatment

    Directory of Open Access Journals (Sweden)

    Urszula Małolepsza

    2013-12-01

    Full Text Available The reactions of strawberry plants to infection with B. cinerea and treatment with salicylic acid has been studied. Infection of leaves with B. cinerea resulted in early increases in active oxygen species generation, superoxide dismutase and peroxidase activities and phenolic compounds content. Some increases of the above reactions were noticed in plants treated with salicylic acid but not in the plants treated with SA and then later infected with B. cinerea.

  16. Reaction kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers

    International Nuclear Information System (INIS)

    The study of the kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers is presented. The model system was Pt submonolayer deposition on Au(1 1 1) via red-ox replacement of Pb and Cu UPD monolayers on Au(1 1 1). The kinetics of a single replacement reaction was studied using the formalism of the comprehensive analytical model developed to fit the open circuit potential transients from deposition experiments. The practical reaction kinetics parameters like reaction half life, reaction order and reaction rate constant are determined and discussed with their relevance to design and control of deposition experiments. The effects of transport limitation and the role of the anions/electrolyte on deposition kinetics are investigated and their significance to design of effective deposition process is discussed.

  17. A kinetic study of the CH2OO Criegee intermediate self-reaction, reaction with SO2 and unimolecular reaction using cavity ring-down spectroscopy.

    Science.gov (United States)

    Chhantyal-Pun, Rabi; Davey, Anthony; Shallcross, Dudley E; Percival, Carl J; Orr-Ewing, Andrew J

    2015-02-01

    Criegee intermediates are important species formed during the ozonolysis of alkenes. Reaction of stabilized Criegee intermediates with various species like SO2 and NO2 may contribute significantly to tropospheric chemistry. In the laboratory, self-reaction can be an important loss pathway for Criegee intermediates and thus needs to be characterized to obtain accurate bimolecular reaction rate coefficients. Cavity ring-down spectroscopy was used to perform kinetic measurements for various reactions of CH2OO at 293 K and under low pressure (7 to 30 Torr) conditions. For the reaction CH2OO + CH2OO (8), a rate coefficient k8 = (7.35 ± 0.63) × 10(-11) cm(3) molecule(-1) s(-1) was derived from the measured CH2OO decay rates, using an absorption cross section value reported previously. A rate coefficient of k4 = (3.80 ± 0.04) × 10(-11) cm(3) molecule(-1) s(-1) was obtained for the CH2OO + SO2 (4) reaction. An upper limit for the unimolecular CH2OO loss rate coefficient of 11.6 ± 8.0 s(-1) was deduced from studies of reaction (4). SO2 catalysed CH2OO isomerization or intersystem crossing is proposed to occur with a rate coefficient of (3.53 ± 0.32) × 10(-11) cm(3) molecule(-1) s(-1). PMID:25553776

  18. Multiplexed detection of two proteins by a reaction kinetics-resolved chemiluminescence immunoassay strategy.

    Science.gov (United States)

    Wang, Wenwen; Ouyang, Hui; Yang, Shijia; Wang, Lin; Fu, Zhifeng

    2015-02-21

    A multiplexed immunoassay method was proposed for the sequential detection of two proteins in a single run based on a novel chemiluminescence (CL) reaction kinetics-resolved strategy. This method was established using acridinium ester (AE) and alkaline phosphatase (ALP) as the signal probes due to the significant difference in their CL reaction kinetics characteristics. Mouse IgG (MIgG) and mouse IgM (MIgM) were detected as the model analytes with a competitive immunoassay format. AE and ALP were used to tag goat anti-mouse IgG and rabbit anti-mouse IgM, respectively, to form two immunocomplexes. The two CL reactions with flash type and glow type kinetics characteristics were triggered simultaneously by adding the coreactants, then the CL signals from the two reactions were recorded after 0.2 s and 500 s of the reaction triggering, respectively. The multiplexed CL immunoassay provided a wide range of 0.50-200 ng mL(-1), with a low detection limit of 0.16 ng mL(-1) (S/N = 3) for both MIgG and MIgM. Additionally, no obvious signal overlap was observed in the multiplexed immunoassay. The proposed method was successfully applied for the detection of MIgG and MIgM levels in mouse serums, and the results were in good agreement with those from the reference ELISA method. We anticipate that it can be used in some other areas such as drug screening, food safety, environment monitoring and clinical diagnosis. PMID:25531210

  19. Statistical deduction and experimental verification on kinetic equations for the curing reactions of epoxy resins/amines

    Institute of Scientific and Technical Information of China (English)

    CHEN Ping; LU Zu-shun; YU Da-shu; HU Li-jiang

    2005-01-01

    Based on three typical mechanisms (second-order, third-order and competitive mechanisms) for the curing reactions of the epoxy resins with amines, a pair of the kinetic equations (for primary and secondary aminations) was presented to explain the uniformity and relationship among the three different kinetic mechanisms of the reactions. The presented macro-equations were deduced from the kinetic micro-equations by the statistics method. And the constitutive equations were verified by experimental data at different reaction times and temperatures (95℃, 60℃ and 39℃), taking diglycidyl ether of bisphenol A (DGEBA) /ethyleneamine (EA) as a model.

  20. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    Science.gov (United States)

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the…

  1. Kinetics of Imidazole Catalyzed Ester Hydrolysis: Use of Buffer Dilutions to Determine Spontaneous Rate, Catalyzed Rate, and Reaction Order.

    Science.gov (United States)

    Lombardo, Anthony

    1982-01-01

    Described is an advanced undergraduate kinetics experiment using buffer dilutions to determine spontaneous rate, catalyzed rate, and reaction order. The reaction utilized is hydrolysis of p-nitro-phenyl acetate in presence of imidazole, which has been shown to enhance rate of the reaction. (Author/JN)

  2. Kinetics of diamond-silicon reaction under high pressure-high temperature conditions

    Science.gov (United States)

    Pantea, Cristian

    In this dissertation work, the kinetics of the reaction between diamond and silicon at high pressure-high temperature conditions was investigated. This study was motivated by the extremely limited amount of information related to the kinetics of the reaction in diamond-silicon carbide composites formation. It was found that the reaction between diamond and melted silicon and the subsequent silicon carbide formation is a two-stage process. The initial stage is a result of direct reaction of melted silicon with carbon atoms from the diamond surface, the phase boundary reaction. Further growth of SiC is much more complicated and when the outer surfaces of diamond crystals are covered with the silicon carbide layer it involves diffusion of carbon and silicon atoms through the SiC layer. The reaction takes place differently for the two regions of stability of carbon. In the graphite-stable region, the reaction between diamond and melted silicon is associated with the diamond-to-graphite phase transition, while in the diamond-stable region there is no intermediary step for the reaction. The data obtained at HPHT were fitted by the Avrami-Erofeev equation. It was found that the reaction is isotropic, the beta-SiC grown on different faces of the diamond crystals showing the same reaction rate, and that the controlling mechanism for the reaction is the diffusion. In the graphite-stable region the activation energy, 402 kJ/mol is slightly higher than in the diamond-stable region, 260 kJ/mol, as the reaction between diamond and melted silicon is associated with the diamond-to-graphite phase transition, which has higher activation energy. In the diamond-stable region, the calculated activation energy is higher for micron size diamond powders (≈260 kJ/mol), while for nanocrystalline diamond powders a lower value of 170 kJ/mol was obtained. This effect was attributed to nanocrystalline structure and strained bonds within grain boundaries in SiC formed from nanosize diamond

  3. Polycyclic aromatic hydrocarbon (PAH) formation from benzyl radicals: a reaction kinetics study.

    Science.gov (United States)

    Sinha, Sourab; Raj, Abhijeet

    2016-03-01

    The role of resonantly stabilized radicals such as propargyl, cyclopentadienyl and benzyl in the formation of aromatic hydrocarbons such as benzene and naphthalene in the high temperature environments has been long known. In this work, the possibility of benzyl recombination to form three-ring aromatics, phenanthrene and anthracene, is explored. A reaction mechanism for it is developed, where reaction energetics are calculated using density functional theory (B3LYP functional with 6-311++G(d,p) basis set) and CBS-QB3, while temperature-dependent reaction kinetics are evaluated using transition state theory. The mechanism begins with barrierless formation of bibenzyl from two benzyl radicals with the release of 283.2 kJ mol(-1) of reaction energy. The further reactions involve H-abstraction by a H atom, H-desorption, H-migration, and ring closure to gain aromaticity. Through mechanism and rate of production analyses, the important reactions leading to phenanthrene and anthracene formation are determined. Phenanthrene is found to be the major product at high temperatures. Premixed laminar flame simulations are carried out by including the proposed reactions for phenanthrene formation from benzyl radicals and compared to experimentally observed species profiles to understand their effects on species concentrations. PMID:26923612

  4. A Kinetic Study of the Gas-Phase Reaction of OH with Br2

    Science.gov (United States)

    Bryukov, Mikhail G.; Dellinger, Barry; Knyazev, Vadim D.

    2011-01-01

    An experimental, temperature-dependent kinetic study of the gas-phase reaction of the hydroxyl radical with molecular bromine (reaction 1) has been performed using a pulsed laser photolysis/pulsed-laser-induced fluorescence technique over a wide temperature range of 297 – 766 K, and at pressures between 6.68 and 40.29 kPa of helium. The experimental rate coefficients for reaction 1 demonstrate no correlation with pressure and exhibit a negative temperature dependence with a slight negative curvature in the Arrhenius plot. A non-linear least-squares fit with two floating parameters of the temperature dependent k1(T) data set using an equation of the form k1(T) = ATn yields the recommended expression k1(T) = 1.85×10−9T − 0.66 cm3 molecule−1 s−1 for the temperature dependence of the reaction 1 rate coefficient. The potential energy surface (PES) of reaction 1 was investigated using quantum chemistry methods. The reaction proceeds through formation of a weakly bound OH···Br2 complex and a PES saddle point with an energy below that of the reactants. Temperature dependence of the reaction rate coefficient was modeled using the RRKM method on the basis of the calculated PES. PMID:16854030

  5. Numerical kinetic model including equilibrium and rate equations for chemical reactions of actinide elements

    International Nuclear Information System (INIS)

    Numerical simulation method was examined for chemical reactions of actinide elements U, Pu, Np, and Tc etc. in an aqueous nitric acid solution. It is known that the numerical calculation for the Purex process with chemical reactions and liquid flow becomes stiff, because time constant for the chemical reactions is two to three order of magnitude smaller due to the very fast reactions than that of mass transfer or of reaching distribution equilibrium. Recently in order to increase a time step Δt the partial equilibrium (P.E.) model, in which some very fast reactions are treated by the equilibrium law whereas other reactions are by the rate law, has been proposed. In the present study concentration change of the solutes in an aqueous solution with 30 chemical reactions, of which 4 are expressed by equilibrium equations, has been calculated. Description of the P.E. model and the comparison of the results and cpu time between the kinetic and the P.E. models are given. (author)

  6. Kinetics of barium sulphate reaction crystallization in crystallizers with internal circulation

    Directory of Open Access Journals (Sweden)

    J. Koralewska

    2008-06-01

    Full Text Available Kinetic calculation results describing the observed nucleation and growth rates of barium sulphate crystals precipitated in an integrated reaction-crystallization process in a barium sulphate-ammonium chloride-water system are presented and analyzed. The scope of experiments included two continuous model DTM-type crystallizers (Draft Tube Magma with internal circulation of the suspension forced by a liquid jet-pump device responsible for stable and intensive enough ascending/descending flow of BaSO4 crystal magma in a mixing chamber. For comparison purposes the experimental data corresponding to a continuous DT (Draft Tube crystallizer with propeller agitator are presented and discussed. The various types of laboratory crystallizers used were fed with concentrated water solution of barium chloride (of 10 or 24 mass % and - in a stoichiometric proportion - crystalline ammonium sulphate, assuming isothermal (348 K and hydrodynamic (average residence time of suspension in a crystallizer: 900 s process conditions. The observed nucleation and growth rates of barium sulphate crystals were estimated on the basis of crystal size distributions (CSDs using convenient calculation scheme derived for an MSMPR (Mixed Suspension Mixed Product Removal model approach. Considering the experimental population density distribution courses, a size-dependent growth (SDG phenomenon was taken into account in the kinetic calculations. Five SDG kinetic models recommended in the accessible literature were used for kinetic parameter values estimation. It was proved statistically, that Rojkowski’s two SDG models (hyperbolic and exponential best suit for our own experimental data description. The experimental data presented can be practically applied for improving the constructions of liquid jet-pump DTM crystallizers recommended for reaction crystallization of sparingly soluble inorganic salts (especially for high concentrations of reaction substrates in the modern

  7. Searching out the hydrogen absorption/desorption limiting reaction factors: Strategies allowing to increase kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Zeaiter, Ali, E-mail: ali.zeaiter@femto-st.fr; Chapelle, David; Nardin, Philippe

    2015-10-05

    Highlights: • A macro scale thermodynamic model that simulates the response of a FeTi-X hydride tank is performed, and validated experimentally. • A sensibility study to identify the most influent input variables that can changes very largely the reaction rate. - Abstract: Hydrogen gas has become one of the most promising energy carriers. Main breakthrough concerns hydrogen solid storage, specially based on intermetallic material use. Regarding the raw material abundance and cost, the AB type alloy FeTi is an auspicious candidate to store hydrogen. Its absorption/desorption kinetics is a basic hindrance to common use, compared with more usual hydrides. First, discussions based on literature help us identifying the successive steps leading to metal hydriding, and allow to introduce the physical parameters which drive or limit the reaction. This analysis leads us to suggest strategies in order to increase absorption/desorption kinetics. Attention is then paid to a thermofluidodynamic model, allowing to describe a macroscopic solid storage reactor. Thus, we can achieve a simulation which describes the overall reaction inside the hydrogen reactor and, by varying the sub-mentioned parameters (thermal conductivity, the powder granularity, environment heat exchange…), we attempt to hierarchy the reaction limiting factors. These simulations are correlated to absorption/desorption experiments for which pressure, temperature and hydrogen flow are recorded.

  8. First steps towards the reaction kinetics of HMDSO in an atmospheric pressure plasma jet in argon

    Science.gov (United States)

    Loffhagen, Detlef; Becker, Markus M.; Foest, Rüdiger; Schäfer, Jan; Sigeneger, Florian

    2014-10-01

    Hexamethyldisiloxane (HMDSO) is a silicon-organic compound which is often used as precursor for thin-film deposition by means of plasma polymerization because of its high deposition rate and low toxicity. To improve the physical understanding of the deposition processes, fundamental investigations have been performed to clarify the plasma-chemical reaction pathways of HMDSO and their effect on the composition and structure of the deposited film. The current contribution represents the main primary and secondary plasma-chemical processes and their reaction products in the effluent region of an argon plasma jet at atmospheric pressure. The importance of the different collision processes of electrons and heavy particles are discussed. Results of numerical modelling of the plasma jet and the Ar-HMDSO reaction kinetics indicate that the fragmentation of HMDSO is mainly initiated by collisions with molecular argon ions, while Penning ionization processes play a minor role for the reaction kinetics in the effluent region of the jet. The work has been supported by the German Research Foundation (DFG) under Grant LO 623/3-1.

  9. Kinetics of acid-catalyzed aldol condensation reactions of aliphatic aldehydes

    Science.gov (United States)

    Casale, Mia T.; Richman, Aviva R.; Elrod, Matthew J.; Garland, Rebecca M.; Beaver, Melinda R.; Tolbert, Margaret A.

    Field observations of atmospheric aerosols have established that organic compounds compose a large fraction of the atmospheric aerosol mass. However, the physical/chemical pathway by which organic compounds are incorporated into atmospheric aerosols remains unclear. The potential role of acid-catalyzed reactions of organic compounds on acidic aerosols has been explored as a possible chemical pathway for the incorporation of organic material into aerosols. In the present study, ultraviolet-visible (UV-vis) spectroscopy was used to monitor the kinetics of formation of the products of the acid-catalyzed aldol condensation reaction of a range of aliphatic aldehydes (C 2-C 8). The experiments were carried out at various sulfuric acid concentrations and a range of temperatures in order to estimate the rate constants of such reactions on sulfuric acid aerosols under tropospheric conditions. The rate constants were generally found to decrease as the chain length of the aliphatic aldehyde increased (except for acetaldehyde, which had an unusually small rate constant), increase as a function of sulfuric acid concentration as predicted by excess acidity theory, and showed normal Arrhenius behavior as a function of temperature. While the kinetic data are generally consistent with previous laboratory reports of aldehyde reactivity in various sulfuric acid media, the aldol condensation reactions involving aliphatic aldehydes do not appear fast enough to be responsible for significant transfer of organic material into atmospheric aerosols.

  10. Searching out the hydrogen absorption/desorption limiting reaction factors: Strategies allowing to increase kinetics

    International Nuclear Information System (INIS)

    Highlights: • A macro scale thermodynamic model that simulates the response of a FeTi-X hydride tank is performed, and validated experimentally. • A sensibility study to identify the most influent input variables that can changes very largely the reaction rate. - Abstract: Hydrogen gas has become one of the most promising energy carriers. Main breakthrough concerns hydrogen solid storage, specially based on intermetallic material use. Regarding the raw material abundance and cost, the AB type alloy FeTi is an auspicious candidate to store hydrogen. Its absorption/desorption kinetics is a basic hindrance to common use, compared with more usual hydrides. First, discussions based on literature help us identifying the successive steps leading to metal hydriding, and allow to introduce the physical parameters which drive or limit the reaction. This analysis leads us to suggest strategies in order to increase absorption/desorption kinetics. Attention is then paid to a thermofluidodynamic model, allowing to describe a macroscopic solid storage reactor. Thus, we can achieve a simulation which describes the overall reaction inside the hydrogen reactor and, by varying the sub-mentioned parameters (thermal conductivity, the powder granularity, environment heat exchange…), we attempt to hierarchy the reaction limiting factors. These simulations are correlated to absorption/desorption experiments for which pressure, temperature and hydrogen flow are recorded

  11. Reaction Kinetics of Ozonation of Trichloroethylene and Benzene in Gas and Liquid Phases

    Institute of Scientific and Technical Information of China (English)

    钟理; KuoChiane-Hai

    2000-01-01

    The kinetics of ozonation reactions of trichloroethylene (TCE) and benzene in gas and liquid phases at 101.3 kPa and 298 K was investigated in this paper. The ozonation of TCE is first order with respect to the ozone concentration and one and half order to TCE in the gas phase with the average rate constant 57.30 (mol·L-1 )-l.5·s-1,and the TCE ozonation in aqueous medium is first order with respect to both ozone and trichloroethylene with the average rate constant 6.30 (mol·L-1)-l·s-1. The ozonation of benzene in the gas phase is first order in ozone but independent of the benzene concentration with the average reaction rate constant 0.0011s-1. The overall kinetics of reaction between ozone and benzene in aqueous solution is found to be first order with one-half order in both ozone and bezene, with the average reaction rate constant 2.67s-1. It is found that the ozonation rate of pallutants is much quicker than that of self-decomposition of ozone in both gas and aqueous phase.

  12. Steady-state analysis of kinetic isotope effects in enzymic reactions

    International Nuclear Information System (INIS)

    The decrease in the rate of bond cleavage resulting from the presence of heavy isotopes is expressed to a greater or lesser extent as an isotope effect on steady-state kinetic parameters of enzyme-catalyzed reactions, depending upon complex relationships between individual rate constants. This paper describes these relationships and derives general kinetic expressions which allow the determination of the limits of the relative contribution of different reaction components to V/sub max/ and V/sub max//K/sub m/. The value of the true isotope effect on a carbon-hydrogen bond breaking step, the rate of this step, and its percentage of partial rate limitation of the overall reaction, plus the dissociation constant of the enzyme-substrate complex, can be determined from the derived expressions by comparing deuterium and tritium isotope effects on V/sub max//K/sub m/. In the absence of a measure of the true isotope effect, the lower limit of primary isotope effects of deuterium which may be interpreted as identifying the slowest or ''rate-determining'' step in an enzyme-catalyzed reaction is found to be k/sub H//k/sub D/ = 8, and not k/sub H//k/sub D/ = 2 as is currently supposed. (U.S.)

  13. A data base for the reaction kinetics of iodine in aqueous solution

    International Nuclear Information System (INIS)

    This paper describes the setting up of a data base for the reaction kinetics of inorganic iodine species in solution for use in the simulation of iodine chemistry in the laboratory or in water-cooled reactor faults. A number of specific problems are highlighted. These include the rather poor quality of much of the literature kinetic data, the paucity of data for a number of key reactions (gas-liquid partitioning, radiolytic processes, metal ion catalysis, production of organic iodides), and the difficulties inherent in extrapolating laboratory data obtained at relatively high iodine concentrations (>10-4 M) to the concentrations typical of reactor faults (-6 M). Specific examples are given to illustrate these points. Despite the shortcomings the data base established reproduces well a number of alternative results including those obtained in radiolytic systems, and in the oscillating Bray-Liebhafsky reaction, the latter a particularly severe test of any mechanism. Typical applications in reaction safety analysis are indicated with reference to fuel pond faults. (author)

  14. Kinetics of the Reaction Between Ozone and Cationic Red X-GRL

    Institute of Scientific and Technical Information of China (English)

    赵伟荣; 史惠祥; 汪大翚

    2003-01-01

    The ozonation of Cationic Red X-GRL in a semi-batch reactor was studied with variation of the gas flow rate, initial Cationic Red X-GILL concentration, temperature, and pH value. By the evaluation of the liquid mass transfer coefficient, the interfacial area, and the stoichiometric ratio between ozone and Cationic Red X-GRL, the rate constants and the kinetic regime of the reaction between ozone and Cationic Red X-GRL were investigated by applying the experimental data to a model based on the film mass transfer theory. The results obtained support a second order overall reaction, first order with respect to both ozone and dye, and the rate constants were correlated by a modified Arrhenius Equation of temperature and pH value with activation energy of 18.06kJ·mo1-1. Hatta number of the reaction was found to he between 0.026 and 0.041, it indicates that the reaction occurs in the liquid bulk,corresponding to the slow kinetic regime.

  15. Reaction Kinetics of Ozonation of Trichloroethylene and Benzene in Gas and Liquid Phase

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The kinetics of ozonation reactions oftrichloroethylene (TCE) and benzene in gas and liquid phases at101.3 kPa and 298 K was investigated in this paper. The ozonation ofTCE is first order with respect to the ozone concentration and one andhalf order to TCE in the gas phase with the average rate constant 57.30(mol*L-1)-1.5 *s-1, and the TCE ozonation inaqueous medium is first order with respect to both ozone andtrichloroethylene with the average rate constant 6.30(mol*L-1)-1 *s-1. The ozonation of benzene inthe gas phase is first order in ozone but independent of the benzeneconcentration with the average reaction rate constant 0.0011 s-1.The overall kinetics of reaction between ozone and benzene in aqueoussolution is found to be first order with one-half order in both ozoneand bezene, with the average reaction rate constant 2.67 s-1. Itis found that the ozonation rate of pallutants is much quicker than that ofself-decomposition of ozone in both gas and aqueous phase.

  16. Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

    Energy Technology Data Exchange (ETDEWEB)

    Basilevsky, M. V.; Mitina, E. A. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); Odinokov, A. V. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow (Russian Federation); Titov, S. V. [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)

    2013-12-21

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ{sub 0} < 1 − 3) and for low (ξ{sub 0}≫ 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T→ 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the

  17. Reaction Rates and Kinetic Isotope Effects of H$_2$ + OH $\\rightarrow$ H$_2$O + H

    CERN Document Server

    Meisner, Jan

    2016-01-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling (CVT/$\\mu$OMT) were applied using a fitted potential energy surface [J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval $ 4 \\cdot 10^{-20}$ to $4 \\cdot 10^{-17}$ cm$^3$ s$^{-1}$ , demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures.

  18. Kinetics of reaction between acetic acid and Ag2+ in nitric acid medium

    International Nuclear Information System (INIS)

    The reaction kinetics between acetic acid and Ag2+ in nitric acid medium is studied by spectrophotometry. The effects of concentrations of acetic acid (HAc), H+, NO3- and temperature on the reaction are investigated. The rate equation has been determined to be -dc(Ag2+)/dt=kc(Ag2+)c(HAc)c-1(H+), where k = (610±15) (mol/L)-1·min-1 with an activation energy of about (48.8±3.5) kJ·mol-1 when the temperature is 25degC and the ionic strength is 4.0 mol/L. The reduction rate of Ag2+ increases with the increase of HAc concentration or temperature and the decrease of HNO3 concentration. However, the effect of NO3- concentrations on the reaction rate is negligible. (author)

  19. Reaction rates and kinetic isotope effects of H2 + OH → H2O + H.

    Science.gov (United States)

    Meisner, Jan; Kästner, Johannes

    2016-05-01

    We calculated reaction rate constants including atom tunneling of the reaction of dihydrogen with the hydroxy radical down to a temperature of 50 K. Instanton theory and canonical variational theory with microcanonical optimized multidimensional tunneling were applied using a fitted potential energy surface [J. Chen et al., J. Chem. Phys. 138, 154301 (2013)]. All possible protium/deuterium isotopologues were considered. Atom tunneling increases at about 250 K (200 K for deuterium transfer). Even at 50 K the rate constants of all isotopologues remain in the interval 4 ⋅ 10(-20) to 4 ⋅ 10(-17) cm(3) s(-1), demonstrating that even deuterated versions of the title reaction are possibly relevant to astrochemical processes in molecular clouds. The transferred hydrogen atom dominates the kinetic isotope effect at all temperatures. PMID:27155636

  20. Kinetic characteristics of continuous flow polymerase chain reaction chip: A numerical investigation

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Continuous flow PCR (polymerase chain reaction) chip holds impressive advantages compared to micro chamber PCR chip. In order to have better understanding of kinetic characteristics of continuous flow PCR chip, a comprehensive mathematical model is presented in this paper, including melting, annealing and extension phases of a typical PCR process which has the essence of a convection-diffusion-reaction system. Using this model, we can simulate the PCR process in series of reaction cycles. Numerical results show that the average sample velocity plays a significant role in affecting the amplification efficiency. Also, appropriate combination of the PCR mixture is important for high-quality DNA amplification. Giving a large initial DNA concentration range, the continuous flow PCR scheme holds excellent real-time detection ability theoretically. The present numerical model bridges the temperature distribution to the real DNA amplification, and thereby is able to successfully predict continuous flow PCR properties which are important for the chip design.

  1. Kinetics and intermediates of the reaction of fully reduced Escherichia coli bo₃ ubiquinol oxidase with O₂.

    Science.gov (United States)

    Szundi, Istvan; Kittredge, Clive; Choi, Sylvia K; McDonald, William; Ray, Jayashree; Gennis, Robert B; Einarsdóttir, Ólöf

    2014-08-26

    Cytochrome bo₃ ubiquinol oxidase from Escherichia coli catalyzes the reduction of O₂ to water by ubiquinol. The reaction mechanism and the role of ubiquinol continue to be a subject of discussion. In this study, we report a detailed kinetic scheme of the reaction of cytochrome bo₃ with O₂ with steps specific to ubiquinol. The reaction was investigated using the CO flow-flash method, and time-resolved optical absorption difference spectra were collected from 1 μs to 20 ms after photolysis. Singular value decomposition-based global exponential fitting resolved five apparent lifetimes, 22 μs, 30 μs, 42 μs, 470 μs, and 2.0 ms. The reaction mechanism was derived by an algebraic kinetic analysis method using frequency-shifted spectra of known bovine states to identify the bo3 intermediates. It shows 42 μs O₂ binding (3.8 × 10(7) M(-1) s(-1)), producing compound A, followed by faster (22 μs) heme b oxidation, yielding a mixture of PR and F, and rapid heme b rereduction by ubiquinol (30 μs), producing the F intermediate and semiquinone. In the 470 μs step, the o₃ F state is converted into the o₃(3+) oxidized state, presumably by semiquinone/ubiquinol, without the concomitant oxidation of heme b. The final 2 ms step shows heme b reoxidation and the partial rereduction of the binuclear center and, following O₂ binding, the formation of a mixture of P and F during a second turnover cycle. The results show that ubiquinol/semiquinone plays a complex role in the mechanism of O₂ reduction by bo₃, displaying kinetic steps that have no analogy in the CuA-containing heme-copper oxidases. PMID:25076393

  2. Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

    Science.gov (United States)

    Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

    2016-06-23

    It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination. PMID:27243380

  3. A global reaction route mapping-based kinetic Monte Carlo algorithm

    Science.gov (United States)

    Mitchell, Izaac; Irle, Stephan; Page, Alister J.

    2016-07-01

    We propose a new on-the-fly kinetic Monte Carlo (KMC) method that is based on exhaustive potential energy surface searching carried out with the global reaction route mapping (GRRM) algorithm. Starting from any given equilibrium state, this GRRM-KMC algorithm performs a one-step GRRM search to identify all surrounding transition states. Intrinsic reaction coordinate pathways are then calculated to identify potential subsequent equilibrium states. Harmonic transition state theory is used to calculate rate constants for all potential pathways, before a standard KMC accept/reject selection is performed. The selected pathway is then used to propagate the system forward in time, which is calculated on the basis of 1st order kinetics. The GRRM-KMC algorithm is validated here in two challenging contexts: intramolecular proton transfer in malonaldehyde and surface carbon diffusion on an iron nanoparticle. We demonstrate that in both cases the GRRM-KMC method is capable of reproducing the 1st order kinetics observed during independent quantum chemical molecular dynamics simulations using the density-functional tight-binding potential.

  4. Characterization of excited-state reactions with instant spectra of fluorescence kinetics

    International Nuclear Information System (INIS)

    Comprehensible knowledge of the excited-state proton transfer processes in organic compounds is overwhelmingly important not only for physics, but also chemistry and Life Sciences, since they play a key role in main processes of photosynthesis and functioning of biological organisms. Moreover compounds with Excited-State Intramolecular Proton Transfer (ESIPT) are in the focus of the interest of scientists throughout the world, because dual fluorescence spectra of such objects corresponding to two forms of molecular structure (normal and photoproduct) are very sensitive to characteristics of molecular microenvironment. This property allows to use such substances as fluorescent probes for diverse applications in chemistry and Life Sciences. But at the same time studying of proton transfer processes is not simple, because this process is characterized by extremely fast times (on picoseconds time scale and less order) and very often contribution of reverse reactions is essentially complicates an interpretation of observed properties of dual fluorescence. Hence, understanding of a role of reversible reactions is crucial for a comprehensive description of all processes accompanying excited state reactions. We discuss new approach for treatment ESIPT reaction on the basis of experimentally measured instant spectra of dual fluorescence and temporal behavior of ratiometric signal of normal to tautomer form intensities. Simple analytical expressions show in transparent way how to distinguish a degree of reverse reaction contribution to ratiometric signal. A validation of the approach under consideration is fulfilled with two different flavonols – 3-hydroxyflavone and 4′-(Dimethylamino)-3-hydroxyflavone – representing two extreme cases in affecting reversible reaction on dual emission. A comparing of new approach and traditional method when we analyze kinetics of separate the N* and T* fluorescence bands decays, has been carried out. - Highlights: • The excited

  5. Characterization of excited-state reactions with instant spectra of fluorescence kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Tomin, Vladimir I., E-mail: tomin@apsl.edu.pl; Ushakou, Dzmitryi V.

    2015-10-15

    Comprehensible knowledge of the excited-state proton transfer processes in organic compounds is overwhelmingly important not only for physics, but also chemistry and Life Sciences, since they play a key role in main processes of photosynthesis and functioning of biological organisms. Moreover compounds with Excited-State Intramolecular Proton Transfer (ESIPT) are in the focus of the interest of scientists throughout the world, because dual fluorescence spectra of such objects corresponding to two forms of molecular structure (normal and photoproduct) are very sensitive to characteristics of molecular microenvironment. This property allows to use such substances as fluorescent probes for diverse applications in chemistry and Life Sciences. But at the same time studying of proton transfer processes is not simple, because this process is characterized by extremely fast times (on picoseconds time scale and less order) and very often contribution of reverse reactions is essentially complicates an interpretation of observed properties of dual fluorescence. Hence, understanding of a role of reversible reactions is crucial for a comprehensive description of all processes accompanying excited state reactions. We discuss new approach for treatment ESIPT reaction on the basis of experimentally measured instant spectra of dual fluorescence and temporal behavior of ratiometric signal of normal to tautomer form intensities. Simple analytical expressions show in transparent way how to distinguish a degree of reverse reaction contribution to ratiometric signal. A validation of the approach under consideration is fulfilled with two different flavonols – 3-hydroxyflavone and 4′-(Dimethylamino)-3-hydroxyflavone – representing two extreme cases in affecting reversible reaction on dual emission. A comparing of new approach and traditional method when we analyze kinetics of separate the N* and T* fluorescence bands decays, has been carried out. - Highlights: • The excited

  6. Kinetics of Reaction Between Tc(Ⅶ) and Monomethylhydrazine or Dimethylhydroxylamine in Nitric Acid Medium Containing Plutonium

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    <正>The chemical reaction kinetics research of Tc(Ⅶ) with monomethylhydrazine or dimethylhydroxy-lamine in nitric acid medium demonstrated that Tc(Ⅶ) hardly reacts with the salt-free reagents during the

  7. Kinetics and Product Yields of the Gas-Phase Reactions of Isoprene Hydroxynitrates and Isoprene Carbonynitrates

    Science.gov (United States)

    Abdelhamid, A.; Addala, R.; Vizenor, N.; Scruggs, A.; Tyndall, G. S.; Orlando, J. J.; Le, T.; Cardenas, E.; Maitra, S.; Hasson, A. S.

    2013-12-01

    Isoprene nitrates are formed in the troposphere from the reactions of isoprene with OH in the presence of NOx during the day and with NO3 during the night. Depending on their subsequent reactions, these compounds may be reservoirs or sinks for NOx, and may contribute to secondary organic aerosol formation. In this work, two isoprene hydroxynitrates (CH2=CHC(ONO2)(CH3)CH2OH, 1,2-IHN and CH2OHCH(ONO2)C(CH3)=CH2, 4,3-IHN ) and one isoprene carbonyl nitrate (CH2=CHC(ONO2)(CH3)CHO, ICN)) were synthesized. The kinetics and product yields from their reaction with O3, OH, NO3 and Cl were then investigated in a photochemical reactor using a combination of long-path Fourier transform infra-red spectroscopy, proton transfer reaction mass spectrometry and gas chromatography with flame ionization detection. Measured rate coefficients are consistent with reaction with OH and NO3 as the major chemical sinks for these compounds. Measured product yields imply that NOx is not released from these compounds in their reactions with atmospheric oxidants.

  8. A TGA study on the chlorination reaction kinetics of Zircaloy-4 cladding hulls

    International Nuclear Information System (INIS)

    The chlorination reaction kinetics of Zircaloy-4 cladding hulls were investigated using a home-made thermogravimetric analysis for a hull chlorination (TGA-HC) system. The reproducibility of the TGA-HC system was verified by repeated measurements at an identical condition, which showed only 6.6% of maximum difference. The effect of total flow rate (Q) was investigated for Q of 120 and 240 mL/min, and it was revealed that the reaction rate is not influenced in this condition. Using the Sharp–Hancock plot, the volumetric contraction model was identified as the most suitable model for the Zircaloy-4 chlorination reaction. The influence of chlorine partial pressure was studied at 9.21, 16.9, and 23.4 kPa of Cl2 partial pressure conditions, and it was identified that the reaction rate is proportional to the chlorine partial pressure on the order of (0.669). The effect of reaction temperature was investigated for 300–450 °C, and it was revealed that the chlorination reaction exhibits an activation energy of 26.2 kJ/mol. Using the experimental and fitting results, the reaction rate equation for the Zircaloy-4 chlorination reaction was achieved, but the equation was valid only until the conversion fraction (α) reaches up to (0.60). When α is higher than 0.60, the volumetric contraction model was not applicable. A second-order reaction rate equation was suggested for the 0.6 < α region, although it needs further investigation

  9. A new method for studying caffeine's antioxygenic property: Peroxidase-Oxidase biochemical reaction

    Institute of Scientific and Technical Information of China (English)

    WANG Jun; CAI Ruxiu; LIN Zhixin; LIU Zhihong

    2003-01-01

    The effect of Caffeine on Peroxidase-Oxidase (PO) reaction was studied systematically in this paper. We proved that the valley of PO oscillation is the best phase angle which was used to research antioxygenic property by the Analyte Pulse Perturbation Technique (APP), based on investigating the mechanism. Area integral calculus was proposed to use in quantitative analysis for the first time. There is a good linear relationship (R = 0.9950) between the ratio of amplitude changes of PO oscillation and the concentration of caffeine in the range 4.61×10-7 mol/L-1.84×10-5 mol/L. A new method for analysis by PO oscillation was set up. We also investigated two-dimensional projections and Fourier spectrum of nonlinear complicate system--PO reaction which was perturbed by caffeine, in order to provide a theoretical basis for studying effects of kinds of antioxidants on life system.

  10. On multistage homotopy-perturbation method applied to nonlinear biochemical reaction model

    International Nuclear Information System (INIS)

    The total time evolution of the reactant concentrations in the basic enzyme-substrate reaction is simulated by an adaptation of the standard analytic homotopy-perturbation method (HPM). The standard HPM is converted into a hybrid numeric-analytic method called the multistage HPM (MHPM). The numerical results obtained from the MHPM and the classical fourth-order Runge-Kutta (RK4) method are in complete agreement

  11. Reaction from Dimethyl Carbonate (DMC) to Diphenyl Carbonate (DPC). 2. Kinetics of the Reactions from DMC via Methyl Phenyl Carbonate to DPC

    NARCIS (Netherlands)

    Haubrock, J.; Wermink, W.; Versteeg, G.F.; Kooijman, H.A.; Taylor, R.; Sint Annaland, M. van; Hogendoorn, J.A.

    2008-01-01

    The kinetics of the reaction of dimethyl carbonate (DMC) and phenol to methyl phenyl carbonate (MPC) and the subsequent disproportion and transesterification reaction of methyl phenyl carbonate (MPC) to diphenyl carbonate (DPC) have been studied. Experiments were carried out in a closed batch reacto

  12. The effects of one-dimensional glide on the reaction kinetics of interstitial clusters

    DEFF Research Database (Denmark)

    Heinisch, H.L.; Singh, B.N.; Golubov, S.I.

    2000-01-01

    . Atomic-scale kinetic Monte Carlo (kMC) defect migration simulations are used to investigate the effects of mixed 1D/3D migration on defect reaction kinetics as a guide for implementing mixed 1D/3D migration into the analytical rate theory. The functional dependence of the sink strength on the size and...... concentration of sinks under mixed 1D/3D migration is shown to lie between that for pure 1D and pure 3D migration and varies with L, the average distance between direction changes of the gliding defects. It is shown that the sink strength in simulations for spherical sinks of radius R under mixed 1D/3D...

  13. Kinetic Isotope Effects for the Reactions of Muonic Helium and Muonium with H2

    Energy Technology Data Exchange (ETDEWEB)

    Fleming, Donald G.; Arseneau, Donald J.; Sukhorukov, Oleksandr; Brewer, Jess H.; Mielke, Steven L.; Schatz, George C.; Garrett, Bruce C.; Peterson, Kirk A.; Truhlar, Donald G.

    2011-01-28

    The neutral muonic helium atom may be regarded as the heaviest isotope of the hydrogen atom, with a mass of ~4.1 amu (4.1H), because the negative muon screens one proton charge. We report the reaction rate of 4.1H with 1H2 to produce 4.1H1H + 1H at 295 to 500 K. The experimental rate constants are compared with the predictions of accurate quantum mechanical dynamics calculations carried out on an accurate Born-Huang potential energy surface and with previously measured rate constants of 0.11H (where 0.11H is shorthand for muonium). Kinetic isotope effects can be compared for the unprecedentedly large mass ratio of 36. The agreement with accurate quantum dynamics is quantitative at 500 K, and variational transition state theory is used to interpret the extremely low (large inverse) kinetic isotope effects in the 10-4 to 10-2 range.

  14. HTP kinetics studies on isolated elementary combustion reactions over wide temperature ranges

    Energy Technology Data Exchange (ETDEWEB)

    Fontijn, A.; Adusei, G.Y.; Hranisavlevic, J.; Bajaj, P.N. [Rensselaer Polytechnic Institute, Troy, NY (United States)

    1993-12-01

    The goals of this project are to provide accurate data on the temperature dependence of the kinetics of elementary combustion reactions, (i) for use by combustion modelers, and (ii) to gain a better fundamental understanding of, and hence predictive ability for, the chemistry involved. Experimental measurements are made mainly by using the pseudo-static HTP (high-temperature photochemistry) technique. While continuing rate coefficient measurements, further aspects of kinetics research are being explored. Thus, starting from the data obtained, a method for predicting the temperature dependence of rate coefficients of oxygen-atom olefin experiment and confirms the underlying mechanistic assumptions. Mechanistic information of another sort, i.e. by product analysis, has recently become accessible with the inauguration of our heated flow tube mass spectrometer facility; early results are reported here. HTP experiments designed to lead to measurements of product channels by resonance fluorescence have started.

  15. Formic Acid Decomposition on Au catalysts: DFT, Microkinetic Modeling, and Reaction Kinetics Experiments

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Suyash; Li, Sha; Carrasquillo-Flores, Ronald; Alba-Rubio, Ana C.; Dumesic, James A.; Mavrikakis, Manos

    2014-04-01

    A combined theoretical and experimental approach is presented that uses a comprehensive mean-field microkinetic model, reaction kinetics experiments, and scanning transmission electron microscopy imaging to unravel the reaction mechanism and provide insights into the nature of active sites for formic acid (HCOOH) decomposition on Au/SiC catalysts. All input parameters for the microkinetic model are derived from periodic, self-consistent, generalized gradient approximation (GGA-PW91) density functional theory calculations on the Au(111), Au(100), and Au(211) surfaces and are subsequently adjusted to describe the experimental HCOOH decomposition rate and selectivity data. It is shown that the HCOOH decomposition follows the formate (HCOO) mediated path, with 100% selectivity toward the dehydrogenation products (CO21H2) under all reaction conditions. An analysis of the kinetic parameters suggests that an Au surface in which the coordination number of surface Au atoms is 4 may provide a better model for the active site of HCOOH decomposition on these specific supported Au catalysts.

  16. Mass action realizations of reaction kinetic system models on various time scales

    Energy Technology Data Exchange (ETDEWEB)

    Hangos, K M; Szederkenyi, G, E-mail: hangos@scl.sztaki.hu, E-mail: szeder@scl.sztaki.hu [Process Control Research Group, Computer and Automation Reseach Institute, Kende u. 13-17, H-1111 Budapest (Hungary)

    2011-01-01

    Complex chemical reaction networks often exhibit different dynamic behaviour on different time scales. A combined approach is proposed in this work for determining physically meaningful mass action realizations of complex chemical reaction networks that describe its dynamic behaviour on different time scales. This is achieved by appropriately reducing the detailed overall mass action kinetic scheme using quasi steady state assumptions fit to the particular time scale, and then searching for an optimal realization using mixed integer linear programing. Furthermore, the relationship between the properties (reversibility, deficiency, stability) of the obtained realizations of the same system on different time scales are also investigated and related to the same properties of the detailed overall model. It is shown that the reduced models obtained by quasi steady state assumptions may show exotic nonlinear behaviour, such as oscillations, when the original detailed is globally asymptotically stable. The proposed methods are illustrated by using a simple Michaelis-Menten type reaction kinetic example. The simplified versions of the well known Brusselator model have also been investigated and presented as a case study.

  17. Reaction kinetics of selected micropollutants in ozonation and advanced oxidation processes.

    Science.gov (United States)

    Jin, Xiaohui; Peldszus, Sigrid; Huck, Peter M

    2012-12-01

    Second-order reaction rate constants of micropollutants with ozone (k(O3)) and hydroxyl radicals (k(OH)) are essential for evaluating their removal efficiencies from water during ozonation and advanced oxidation processes. Kinetic data are unavailable for many of the emerging micropollutants. Twenty-four micropollutants with very diverse structures and applications including endocrine disrupting compounds, pharmaceuticals, and personal care products were selected, and their k(O3) and k(OH) values were determined using bench-scale reactors (at pH 7 and T = 20 °C). Reactions with molecular ozone are highly selective as indicated by their k(O3) values ranging from 10(-2)-10(7) M(-1) s(-1). The general trend of ozone reactivity can be explained by micropollutant structures in conjunction with the electrophilic nature of ozone reactions. All of the studied compounds are highly reactive with hydroxyl radicals as shown by their high k(OH) values (10(8)-10(10) M(-1) s(-1)) even though they are structurally very diverse. For compounds with a low reactivity toward ozone, hydroxyl radical based treatment such as O(3)/H(2)O(2) or UV/H(2)O(2) is a viable alternative. This study contributed to filling the data gap pertaining kinetic data of organic micropollutants while confirming results reported in the literature where available. PMID:23079129

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

    International Nuclear Information System (INIS)

    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

  19. Cyclopentadienone Oxidation Reaction Kinetics and Thermochemistry for the Alcohols, Hydroperoxides, and Vinylic, Alkoxy, and Alkylperoxy Radicals.

    Science.gov (United States)

    Yommee, Suriyakit; Bozzelli, Joseph W

    2016-01-28

    Cyclopentadienone has one carbonyl and two olefin groups resulting in 4n + 2 π-electrons in a cyclic five-membered ring structure. Thermochemical and kinetic parameters for the initial reactions of cyclopentadienone radicals with O2 and the thermochemical properties for cyclopentadienone-hydroperoxides, alcohols, and alkenyl, alkoxy, and peroxy radicals were determined by use of computational chemistry. The CBS-QB3 composite and B3LYP density functional theory methods were used to determine the enthalpies of formation (ΔfH°298) using the isodesmic reaction schemes with several work reactions for each species. Entropy and heat capacity, S°(T) and Cp°(T) (50 K ≤ T ≤ 5000 K) are determined using geometric parameters, internal rotor potentials, and frequencies from B3LYP/6-31G(d,p) calculations. Standard enthalpies of formation are reported for parent molecules as cyclopentadienone, cyclopentadienone with alcohol, hydroperoxide substituents, and the cyclopentadienone-yl vinylic, alkoxy, and peroxy radicals corresponding to loss of a hydrogen atom from the carbon and oxygen sites. Entropy and heat capacity vs temperature also are reported for the parent molecules and for radicals. The thermochemical analysis shows The R(•) + O2 well depths are deep, on the order of 50 kcal mol(-1), and the R(•) + O2 reactions to RO + O (chain branching products) for cyclopentadienone-2-yl and cyclopentadienone-3-yl have unusually low reaction (ΔHrxn) enthalpies, some 20 or so kcal/mol below the entrance channels. Chemical activation kinetics using quantum RRK analysis for k(E) and master equation for falloff are used to show that significant chain branching as a function of temperature and pressure can occur when these vinylic radicals are formed. PMID:26784854

  20. Reactions of the CN Radical with Benzene and Toluene: Product Detection and Low-Temperature Kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Trevitt, Adam J.; Goulay, Fabien; Taatjes, Craig A.; Osborn, David L.; Leone, Stephen R.

    2009-12-23

    Low temperature rate coefficients are measured for the CN + benzene and CN + toluene reactions using the pulsed Laval nozzle expansion technique coupled with laser-induced fluorescence detection. The CN + benzene reaction rate coefficient at 105, 165 and 295 K is found to be relatively constant over this temperature range, 3.9 - 4.9 x 10-10 cm3 molecule-1 s-1. These rapid kinetics, along with the observed negligible temperature dependence, are consistent with a barrierless reaction entrance channel and reaction efficiencies approaching unity. The CN + toluene reaction is measured to have a slower rate coefficient of 1.3 x 10-10 cm3 molecule-1 s-1 at 105 K. At room temperature, non-exponential decay profiles are observed for this reaction that may suggest significant back-dissociation of intermediate complexes. In separate experiments, the products of these reactions are probed at room temperature using synchrotron VUV photoionization mass spectrometry. For CN + benzene, cyanobenzene (C6H5CN) is the only product recorded with no detectable evidence for a C6H5 + HCN product channel. In the case of CN + toluene, cyanotoluene (NCC6H4CH3) constitutes the only detected product. It is not possible to differentiate among the ortho, meta and para isomers of cyanotoluene because of their similar ionization energies and the ~;; 40 meV photon energy resolution of the experiment. There is no significant detection of benzyl radicals (C6H5CH2) that would suggest a H-abstraction or a HCN elimination channel is prominent at these conditions. As both reactions are measured to be rapid at 105 K, appearing to have barrierless entrance channels, it follows that they will proceed efficiently at the temperatures of Saturn?s moon Titan (~;;100 K) and are also likely to proceed at the temperature of interstellar clouds (10-20 K).

  1. Photochemistry and kinetics of gas phase reactions involving HO and Cl radicals

    Energy Technology Data Exchange (ETDEWEB)

    Nelson, H.H.

    1980-11-01

    The kinetics of the reaction of the HO radical with HNO/sub 3/ and H/sub 2/O/sub 2/, the kinetics of Cl atom reactions with ClNO and ClNO/sub 2/, and the photochemistry of ClNO/sub 2/ and ClONO/sub 2/ were examined. The ultraviolet absorption cross sections of HNO/sub 3/ and ClNO/sub 2/ were also determined as part of the kinetics work. The rate constant for the reaction of HO with HNO/sub 3/ at room temperature was measured to be (8.2 +- 1.8) x 10/sup -14/ cm/sup 3/ molecule/sup -1/ s/sup -1/, where the uncertainty reported here and in all cases reflects twice the experimental standard deviation plus an estimate of systematic errors. The rate constant for the reaction HO + H/sub 2/O/sub 2/ was measured as (1.57 +- 0.23) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/. This agrees well with the two latest determinations and serves as a calibration of the experimental apparatus used. The Cl + ClNO reaction rate constant was determined to be (1.65 +- 0.32) x 10/sup -11/ cm/sup 3/ molecule/sup -1/ s/sup -1/. The rate constant for the reaction of Cl + ClNO/sub 2/ was found to be (5.05 +- 0.75) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/. This is the first direct measurement of this rate constant. The photodissociation of ClNO/sub 2/ was studied in great detail. The absorption cross sections were measured in the ultraviolet and found to be substantially lower than the literature values in the Cl/sub 2/ absorption region (300 to 360 nm). Two product channels were investigated; products representative of the two channels were Cl and O atoms. Absolute calibration for the product detection systems was provided by Cl/sub 2/ and NO/sub 2/ photolysis respectively. The quantum uields measured for photolysis at 350 nm, calcualted using the absorption spectrum measured in this work, are: 0.93 +- 0.1 for Cl and less than or equal to 0.025 for O. An upper limit of 0.1 was measured for the O atom channel in ClOHO/sub 2/ photolysis.

  2. Thermochemical Properties and Non-isothermal Decomposition Reaction Kinetics of N-Guanylurea Dinitramide (GUDN)

    Institute of Scientific and Technical Information of China (English)

    ZHAO, Feng-Qi(赵凤起); CHEN, Pei(陈沛); YUAN, Hong-An(袁宏安); GAO, Sheng-Li(高胜利); HU, Rong-Zu(胡荣祖); SHI, Qi-Zhen(史启祯)

    2004-01-01

    The constant-volume combustion energy,(△) cU(GUDN, s, 298.15 K), enthalpy of solution in acetic ether,(△)solHm(I) and kinetic behavior of the exothermic decomposition reaction of the title compound (GUDN) are determined by a precise rotating bomb calorimeter, a Calvet microcalorimeter and DSC, respectively. Its standard enthalpy of combustion,(△)cHm(I) (GUDN, s, 298.15 K), standard enthalpy of formation,(△)fHm(I) (GUDN, s, 298.15 K) and kinetic parameters of the exothermic main decomposition reaction in a temperature-programmed mode [the apparent activation energy (Ea) and pre-exponential factor (A)] are calculated. The values of (△)cU(GUDN, s, 298.15 K), (△)cHm(I)(GUDN, s, 298.15 K),(△)fHm(I) (GUDN, s, 298.15 K) and (△)solHm(I)of GUDN are (-7068.64±2.37) J·g-1, (-1467.66±0.50) kJ·mol-1, (-319.76±0.58) kJ·mol-1 and (165.737±0.013) kJ·mol-1, respectively. The kinetic model function in integral form and the value of and A of the exothermic main decomposition reaction of GUDN are 220.20 kJ·mol-1 and 1021.18 s-1, respectively. The critical temperature of thermal explosion of GUDN is 217.6 ℃

  3. Kinetics and Thermodynamic Studies of Depolymerization of Nylon Waste by Hydrolysis Reaction

    Directory of Open Access Journals (Sweden)

    D. B. Patil

    2014-01-01

    Full Text Available Depolymerization reaction of nylon waste was carried out by hydrolysis reaction. Yield of depolymerization products was up to 72.20% for a two-hour reaction time. The products obtained were characterized by melting point and FTIR spectra. The values obtained for dibenzoyl derivative of hexamethylenediamine (DBHMD agreed with those of the pure substance. Chemical kinetics of this reaction shows that it is a first-order reaction with respect to hexamethylenediamine (HMD concentration with velocity constant 7.32×10-3 min−1. The energy of activation and Arrhenius constant obtained by Arrhenius plot were 87.22 KJg−1 and 0.129, respectively. The other thermodynamic parameters such as enthalpy of activation (ΔH‡ and entropy of activation (ΔS‡ and free energy of activation were 5975.85 J and −270.86 J·K−1·mol−1 and 101.59 KJ·mol−1, respectively.

  4. Kinetic study of the reaction of plutonium(IV) with hydroxylamine

    International Nuclear Information System (INIS)

    The kinetics of the one-equivalent reduction of plutonium(IV) with a large excess of hydroxylamine in nitric acid solution was studied. The form of the experimental rate law implies that a multi-step reaction mechanism is involved. Using the equilibrium-steady-state approximation, a rate law with the above form can be derived from a mechanism in which the reduction reaction rapidly approaches equilibrium with the reverse reaction. As this equilibrium is neared, the rate-controlling step becomes the dimerization of the NH2O radical intermediate to form H2N2O2 which then decomposes to nitrogen gas and water. Measurements of initial reaction rates give results which are consistent with this mechanism. The values for k' and K/sub d/ (dissociation constant for PuNO33+) at 300C are 0.029 +- 0.008M5 sec-1 and 0.33 +- 0.15M, respectively. The apparent activation energy for the reaction is 31 +- 1 kcal/mole

  5. Direct hydroxylation of benzene to phenol - aspects of catalysts development and reaction kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Unger, A.; Hiemer, U.; Schwieger, W. [Lehrstuhl fuer Technische Chemie 1, Erlangen-Nuernberg, Erlangen (Germany); Reitzmann, A. [Inst. fuer Chemische Verfahrenstechnik (CVT), Karlsruhe Univ. (Germany); Klemm, E. [DEGUSSA AG, Service Unit Process Technology, Hanau-Wolfgang (Germany)

    2002-07-01

    An alternative route for phenol synthesis is the direct hydroxylation of benzene with nitrous oxide over zeolite catalysts of the ZSM5-type. The disadvantage of this pathway to phenol is the fact that a technically suitable catalyst is not yet available. This is due to low yields and fast deactivation behaviour of the presently-used catalysts. From a scientific point of view one has to state that the reaction mechanism of this single-step reaction is still not clear. The catalyst development requires a systematic study with respect to the chemical, structural and/or morphological properties of the catalytic materials that might have an influence on the performance of the catalyst and/or on the reaction itself. The chance to design the catalyst in a desired way is given by the large variety of parameters that can influence the properties of the zeolite during the synthesis itself or during following post-modification processes. Kinetic measurements offer the possibility to identify mechanism of the reaction and therefore allow conclusions for further improvements of the catalyst design and the reaction conditions itself. The combination of results of both research directions should open an opportunity to derive structure-activity relationships to provide a suitable catalyst for an industrial application. In the present paper we will show first results of an attempt following this described way. (orig.)

  6. The efficiency of driving chemical reactions by a physical non-equilibrium is kinetically controlled.

    Science.gov (United States)

    Göppel, Tobias; Palyulin, Vladimir V; Gerland, Ulrich

    2016-07-27

    An out-of-equilibrium physical environment can drive chemical reactions into thermodynamically unfavorable regimes. Under prebiotic conditions such a coupling between physical and chemical non-equilibria may have enabled the spontaneous emergence of primitive evolutionary processes. Here, we study the coupling efficiency within a theoretical model that is inspired by recent laboratory experiments, but focuses on generic effects arising whenever reactant and product molecules have different transport coefficients in a flow-through system. In our model, the physical non-equilibrium is represented by a drift-diffusion process, which is a valid coarse-grained description for the interplay between thermophoresis and convection, as well as for many other molecular transport processes. As a simple chemical reaction, we consider a reversible dimerization process, which is coupled to the transport process by different drift velocities for monomers and dimers. Within this minimal model, the coupling efficiency between the non-equilibrium transport process and the chemical reaction can be analyzed in all parameter regimes. The analysis shows that the efficiency depends strongly on the Damköhler number, a parameter that measures the relative timescales associated with the transport and reaction kinetics. Our model and results will be useful for a better understanding of the conditions for which non-equilibrium environments can provide a significant driving force for chemical reactions in a prebiotic setting. PMID:27147197

  7. Kinetics of the Gas-Phase Reaction of OH with Chlorobenzene

    OpenAIRE

    Bryukov, Mikhail G.; Knyazev, Vadim D.; Gehling, William M.; Dellinger, Barry

    2009-01-01

    The kinetics of the reaction of hydroxyl radicals with chlorobenzene was studied experimentally using a pulsed laser photolysis/pulsed laser induced fluorescence technique over a wide range of temperatures, 298-670 K, and at pressures between 13.33 and 39.92 kPa. The bimolecular rate constants demonstrate different behavior at low and high temperatures. At room temperature, T = 298.8±1.5 K, the rate constant is equal to (6.02 ± 0.34)×10-13 cm3 molecule-1 s-1; at high temperatures (474 - 670 K...

  8. Theoretical Study of the Kinetics of the Pyrolytic Elimination Reaction of Ethyl Chloride

    OpenAIRE

    Isaiah Ajibade Adejoro; Emmanuel Ekeh

    2010-01-01

    The products of the gas-phase elimination of ethyl chloride are hydrogen chloride and ethane. Using AM1, MNDO and PM3 Hamiltonians of quantum mechanical computer code called MOPAC, a procedure for the kinetics and computation of the Arrhenius parameters for the pyrolytic elimination reaction of ethyl chloride was devised in order to evaluate the predictive ability of the three Hamiltonians used. The first-order rate coefficient for the three Hamiltonians are 1.15x10-8s-1, 4.55x10-15s-1 and 5....

  9. New indicator reaction for kinetic determination of micro amounts of Sn(II)

    OpenAIRE

    VESNA P. STANKOV-JOVANOVIC; TODOR G. PECEV; VIOLETA D. MITIC; RANGEL P. IGOV

    2001-01-01

    A new reaction is suggested and a new method is elaborated for determination of micro amounts of Sn(II) based on its inhibiting effect on the oxidation of {4-bis[n-(dimethylamino) phenyl ]methylene-2,5-cyclohexadiene-1-ilydene}dimethyl-ammonium chloride (crystal violet CV) by H2O2. The method sensibility is 0.4 mg/cm3. The probable relative error is 2.812.8 % for Sn(II) in the concentration interval of 3 to 0.8 mg/cm3. The kinetic equation for this process is given. The influence of some oth...

  10. Struvite Precipitation and Phosphorous Removal from Urine Synthetic Solution: Reaction Kinetic Study

    Directory of Open Access Journals (Sweden)

    Marwa Saied Shalaby

    2015-03-01

    Full Text Available Phosphorus, like oil, is a non-renewable resource that must be harvested from finite resources in the earth’s crust. An essential element for life, phosphorus is becoming increasingly scarce, contaminated, and difficult to extract. Struvite or magnesium ammonium phosphate (MgNH4PO4.6H2O is a white, crystalline phosphate mineral that can be used as a bio-available fertilizer. The main objective of this research is to indicate the most important operating parameters affecting struvite precipitation by means of chemical reaction kinetics. The present study explores struvite precipitation by chemical method under different starting molar ratios, pH and SSR. It is shown that an increase of starting Mg: PO4: NH4 with respect to magnesium (1.6:1:1 strongly influences the growth rate of struvite and so the efficiency of the phosphate removal. This was attributed to the effect of magnesium on the struvite solubility product and on the reached supersaturation Super Saturation Ratio at optimum starting molar ratio and pH. It was also shown, by using chemical precipitation method that the determined Super Saturation Ratio (SSR values of struvite, at 8, 8.5, 9, 9.5 and 10 are 1.314, 4.29, 8.89, 9.87 and 14.89 respectively are close to those presented in the literature for different origins of wastewater streams. The results show that SSR , pH, and starting molar ratio strongly influences the kinetics of precipitation and so phosphorous removal to reach 93% removal percent , 5.95 mg/lit as a minimum PO4 remained in solution, and 7.9 gm precipitated struvite from feed synthetic solution of 750 ml . The product was subjected to chemical analysis by means of EDIX-FTIR, SEM and XRD showing conformity with published literature. First-order kinetics was found to be sufficient to describe the rate data. The rates increased with increasing pH and so SSR and the apparent rate constants for the reaction were determined. © 2015 BCREC UNDIP. All rights reserved

  11. Kinetics of the Esterification Reaction Catalyzed by Lipase in W/O Microemulsions of Alkyl Polyglucoside

    Institute of Scientific and Technical Information of China (English)

    Jin Ling CHAI; Shou Qing WANG; Gan Zuo LI; Qing XU; Yan Hong GAO

    2004-01-01

    A novel kinetic mechanism of esterification reaction of 1-hexanoic acid with 1-butanol, catalyzed by lipase, was studied in water-in-oil microemulsions. The microemulsions were formed by alkyl polyglucoside C10G1.54 /1-butanol / cyclohexane/phosphate buffer solution. The result shows that when the ratio of mol concentration of 1-butanol to 1-hexanoic acid is about 3.0, the initial rate V0 get the maximum values. This phenomenon was explained by the modified fishlike phase diagrams.

  12. Physiological and biochemical reactions of Hordeum vulgare seedlings to the action of silver nanoparticles

    Directory of Open Access Journals (Sweden)

    N. O. Khromykh

    2015-07-01

    Full Text Available Morphometrical indexes, and spectrophotometrically measured protein and glutathione (GSH, GSSG contents and activity of peroxidase (POD, EC 1.11.1.7, glutathione-reductase (GR, EC 1.6.4.2 and glutathione S-transferase (GST, EС 2.5.1.18 were examined in Hordeum vulgare L. seedlings after 0.01 and 0.1 mg/l AgNPs treatment during 24 h. We tested the hypothesis that the action of nanoparticles has a stressful effect on the physiological and biochemical processes of seedlings. Growth of roots was inhibited and fresh weight decreased by 29% and 21% under low and high concentrations respectively. Conversely, leaf growth was intensified, and leaf length (16% and 18% and fresh weight (35% and 44% increased at low and high concentrations respectively. POD activity in roots increased by 26% and 7%, and decreased in leaves to 57% and 81% of control at low and high concentrations respectively. GSH content changed insignificantly, but GSSG content increased in roots (2 and 2.5-fold and in leaves (13% and 30% at both AgNPs concentrations. GSH/GSSG-ratio decreased in roots (1.9 and 2.6-fold and in leaves (1.1 and 1.3-fold at low and high concentrations respectively. GR activity decreased at a concentration of 0.01 mg/l (7% in roots and 17% in leaves respectively and increased at 0.1 mg/l (52% in roots and 6% in leaves. GST activity increased in leaves (52% and 78% at low and high concentrations but decreased by 17% in roots under high concentration of nanosilver. Thus, the action of AgNPs on barley seedlings had a dose-dependent and organ-specific character. The various directions of changes in growth, metabolic processes and activity of antioxidant defense systems appear to be a stress response of barley seedlings to the impact of AgNPs, which underlines the necessity of detailed study of plant intracellular processes exposed to the action of nanomaterial.

  13. The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

    Science.gov (United States)

    Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

    2013-12-01

    During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer

  14. Kinetics of the epoxy–thiol click reaction initiated by a tertiary amine: Calorimetric study using monofunctional components

    Energy Technology Data Exchange (ETDEWEB)

    Loureiro, Roi Meizoso; Amarelo, Tánia Carballeira [Gairesa, Outeiro 1, Lago (Valdoviño), 15551 A Coruña (Spain); Abuin, Senen Paz, E-mail: senen@gairesa.com [Gairesa, Outeiro 1, Lago (Valdoviño), 15551 A Coruña (Spain); Soulé, Ezequiel R. [Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and National Research Council (CONICET), J. B. Justo 4302, 7600 Mar del Plata (Argentina); Williams, Roberto J.J., E-mail: williams@fi.mdp.edu.ar [Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and National Research Council (CONICET), J. B. Justo 4302, 7600 Mar del Plata (Argentina)

    2015-09-20

    Graphical abstract: - Highlights: • Reaction kinetics of a monoepoxy and a monothiol was studied by DSC. • Benzyldimethylamine (BDMA) was used as initiator. • Reaction exhibited a long induction period followed by a fast autocatalytic rate. • A mechanistic kinetic model provided a reasonable fitting of the kinetic behavior. • The formulation simulates the behavior of room-temperature-cure commercial epoxies. - Abstract: An analysis of the kinetics of the epoxy–thiol reaction in a model stoichiometric system of monofunctional reagents, 3-mercaptopropionate (BMP) and phenylglycidylether (PGE) is reported. Benzyldimethylamine (BDMA) was employed as initiator in amounts ranging from 0.5 to 2 wt%. These formulations showed a kinetic behavior qualitatively similar to that of commercial adhesives and coatings formulated for a room-temperature cure. Isothermal DSC scans revealed the existence of a relatively long induction period preceding a fast autocatalytic reaction step. Dynamic DSC scans showed that the reaction was shifted to a lower temperature range by increasing the storage period of the initial formulation at 20 °C. This unusual kinetic behavior could be modeled assuming that thiolate anions, slowly generated during the induction period, initiated a fast autocatalytic propagation/proton transfer reaction. The kinetic model included a pseudo-steady state for the initiator concentration and an equilibrium reaction between epoxy and OH groups generated by reaction. A reasonable fitting of isothermal and dynamic DSC runs was achieved in a broad range of temperatures and amine concentrations. In particular, both the length of the induction time and the effect of the storage period were correctly predicted.

  15. Kinetics of the epoxy–thiol click reaction initiated by a tertiary amine: Calorimetric study using monofunctional components

    International Nuclear Information System (INIS)

    Graphical abstract: - Highlights: • Reaction kinetics of a monoepoxy and a monothiol was studied by DSC. • Benzyldimethylamine (BDMA) was used as initiator. • Reaction exhibited a long induction period followed by a fast autocatalytic rate. • A mechanistic kinetic model provided a reasonable fitting of the kinetic behavior. • The formulation simulates the behavior of room-temperature-cure commercial epoxies. - Abstract: An analysis of the kinetics of the epoxy–thiol reaction in a model stoichiometric system of monofunctional reagents, 3-mercaptopropionate (BMP) and phenylglycidylether (PGE) is reported. Benzyldimethylamine (BDMA) was employed as initiator in amounts ranging from 0.5 to 2 wt%. These formulations showed a kinetic behavior qualitatively similar to that of commercial adhesives and coatings formulated for a room-temperature cure. Isothermal DSC scans revealed the existence of a relatively long induction period preceding a fast autocatalytic reaction step. Dynamic DSC scans showed that the reaction was shifted to a lower temperature range by increasing the storage period of the initial formulation at 20 °C. This unusual kinetic behavior could be modeled assuming that thiolate anions, slowly generated during the induction period, initiated a fast autocatalytic propagation/proton transfer reaction. The kinetic model included a pseudo-steady state for the initiator concentration and an equilibrium reaction between epoxy and OH groups generated by reaction. A reasonable fitting of isothermal and dynamic DSC runs was achieved in a broad range of temperatures and amine concentrations. In particular, both the length of the induction time and the effect of the storage period were correctly predicted

  16. Oxygen isotope exchange between metabolites and water during biochemical reactions leading to cellulose synthesis

    International Nuclear Information System (INIS)

    Cellulose was produced heterotrophically from different carbon substrates by carrot tissue cultures and Acetobacter xylinum (a cellulose-producing bacterium) and by castor bean seeds germinated in the dark, in each case in the presence of water having known concentration of oxygen-18 (18O). We used the relationship between the amount of 18O in the water and in the cellulose that was synthesized to determine the number and 18O content of the substrate oxygens that exchanged with water during the reactions leading to cellulose synthesis. Our observations support the hypothesis that oxygen isotope ratios of plant cellulose are determined by isotopic exchange occurring during hydration of carbonyl groups of the intermediates of cellulose synthesis. (author)

  17. Biochemical properties of Paracoccus denitrificans FnrP: reactions with molecular oxygen and nitric oxide.

    Science.gov (United States)

    Crack, Jason C; Hutchings, Matthew I; Thomson, Andrew J; Le Brun, Nick E

    2016-03-01

    In Paracoccus denitrificans, three CRP/FNR family regulatory proteins, NarR, NnrR and FnrP, control the switch between aerobic and anaerobic (denitrification) respiration. FnrP is a [4Fe-4S] cluster-containing homologue of the archetypal O2 sensor FNR from E. coli and accordingly regulates genes encoding aerobic and anaerobic respiratory enzymes in response to O2, and also NO, availability. Here we show that FnrP undergoes O2-driven [4Fe-4S] to [2Fe-2S] cluster conversion that involves up to 2 O2 per cluster, with significant oxidation of released cluster sulfide to sulfane observed at higher O2 concentrations. The rate of the cluster reaction was found to be ~sixfold lower than that of E. coli FNR, suggesting that FnrP can remain transcriptionally active under microaerobic conditions. This is consistent with a role for FnrP in activating expression of the high O2 affinity cytochrome c oxidase under microaerobic conditions. Cluster conversion resulted in dissociation of the transcriptionally active FnrP dimer into monomers. Therefore, along with E. coli FNR, FnrP belongs to the subset of FNR proteins in which cluster type is correlated with association state. Interestingly, two key charged residues, Arg140 and Asp154, that have been shown to play key roles in the monomer-dimer equilibrium in E. coli FNR are not conserved in FnrP, indicating that different protomer interactions are important for this equilibrium. Finally, the FnrP [4Fe-4S] cluster is shown to undergo reaction with multiple NO molecules, resulting in iron nitrosyl species and dissociation into monomers. PMID:26790880

  18. Reaction kinetics of irradiation prepolymerized MMA-PU IPN by 5DXC FTIR

    International Nuclear Information System (INIS)

    The reaction kinetics of irradiation-prepolymerized MMA-PU (polyether) IPNs have been studied by FTIR. The results indicate that the polymerization of each component in the IPN follows its normal distinct reaction mechanism with no mutual interference. Increasing the concentration of TMPTAM (crosslinking agent of PMMA) increased the formation rate of PMMA, while the formation rate of PU networks remained almost the same. Increasing the concentration of TMP (crosslinking agent of PU) increased the formation rate of PU, while the formation rate of PMMA networks decreased. The formation rate of PU was obviously faster than that of PMMA. A theory for the cage effect of the PU network has been proposed. (author)

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

    International Nuclear Information System (INIS)

    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

  20. The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications

    KAUST Repository

    Ebner, Davidâ C.

    2009-12-07

    The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-to-excellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.

  1. New indicator reaction for kinetic determination of micro amounts of Sn(II

    Directory of Open Access Journals (Sweden)

    VESNA P. STANKOV-JOVANOVIC

    2001-09-01

    Full Text Available A new reaction is suggested and a new method is elaborated for determination of micro amounts of Sn(II based on its inhibiting effect on the oxidation of {4-bis[n-(dimethylamino phenyl ]methylene-2,5-cyclohexadiene-1-ilydene}dimethyl-ammonium chloride (crystal violet CV by H2O2. The method sensibility is 0.4 mg/cm3. The probable relative error is 2.8–12.8 % for Sn(II in the concentration interval of 3 to 0.8 mg/cm3. The kinetic equation for this process is given. The influence of some other ions on the reaction rate was tested. The method was applied to the determination of Sn(II in a sample of microalloy.

  2. Kinetic Monte Carlo simulations of surface reactions on supported nanoparticles: A novel approach and computer code

    Science.gov (United States)

    Kunz, Lothar; Kuhn, Frank M.; Deutschmann, Olaf

    2015-07-01

    So far most kinetic Monte Carlo (kMC) simulations of heterogeneously catalyzed gas phase reactions were limited to flat crystal surfaces. The newly developed program MoCKA (Monte Carlo Karlsruhe) combines graph-theoretical and lattice-based principles to be able to efficiently handle multiple lattices with a large number of sites, which account for different facets of the catalytic nanoparticle and the support material, and pursues a general approach, which is not restricted to a specific surface or reaction. The implementation uses the efficient variable step size method and applies a fast update algorithm for its process list. It is shown that the analysis of communication between facets and of (reverse) spillover effects is possible by rewinding the kMC simulation. Hence, this approach offers a wide range of new applications for kMC simulations in heterogeneous catalysis.

  3. Kinetics of the elementary act of electrochemical reactions at the semiconductor--electrolyte solution interface

    CERN Document Server

    Kovalenko, Sergii

    2013-01-01

    In the framework of the quantum-mechanical theory of elementary act of non-adiabatic electrochemical reactions, it is carried out the calculation of the discharge current of ions at the semiconductor--electrolyte solution interface using the model of isotropic spherically symmetric band. It is shown that our results generalize the well-known formulae for the current density obtained by R.R. Dogonadze, A.M. Kuznetsov, and Yu.A. Chizmadzhev [R.R. Dogonadze, A.M. Kuznetsov, and Yu.A. Chizmadzhev, The kinetics of some heterogeneous reactions at semiconductor--electrolyte interface, Zhur. Fiz. Khim. 38 (1964) 1195--1202]. The average densities of states in the valence band and the conduction band of the semiconductor electrode in the heterogeneous charge transfer are found.

  4. Two-scale large deviations for chemical reaction kinetics through second quantization path integral

    Science.gov (United States)

    Li, Tiejun; Lin, Feng

    2016-04-01

    Motivated by the study of rare events for a typical genetic switching model in systems biology, in this paper we aim to establish the general two-scale large deviations for chemical reaction systems. We build a formal approach to explicitly obtain the large deviation rate functionals for the considered two-scale processes based upon the second quantization path integral technique. We get three important types of large deviation results when the underlying two timescales are in three different regimes. This is realized by singular perturbation analysis to the rate functionals obtained by the path integral. We find that the three regimes possess the same deterministic mean-field limit but completely different chemical Langevin approximations. The obtained results are natural extensions of the classical large volume limit for chemical reactions. We also discuss its implication on the single-molecule Michaelis-Menten kinetics. Our framework and results can be applied to understand general multi-scale systems including diffusion processes.

  5. Kinetics and energetics of one-electron-transfer reactions involving tryptophan neutral and cation radicals

    International Nuclear Information System (INIS)

    Reversible one-electron-transfer reactions involving the tryptophan cation and neutral radicals were investigated by pulse radiolysis. The one-electron-reduction potential of the neutral tryptophan radical at pH 7 was determined to be E7 = 1.01 ± 0.03 V by using the bis(1,4,7-triazacyclononane)nickel(III/II) redox couple with E = 0.95 V as a standard. The value obtained with promethazine (E = 0.89 V) as a standard at pH 6 was E6 = 1.11 V. From these measurements, a mean value E7 = 1.03 V results, in agreement with some earlier determinations (1.05 and 1.08 V) obtained in experiments with inorganic redox standards. The kinetics and energetics of the reactions of the tryptophan neutral and cation radicals with selected electron donors were also investigated

  6. Kinetics of the gas-phase reaction of OH with chlorobenzene.

    Science.gov (United States)

    Bryukov, Mikhail G; Knyazev, Vadim D; Gehling, William M; Dellinger, Barry

    2009-10-01

    The kinetics of the reaction of hydroxyl radicals with chlorobenzene was studied experimentally using a pulsed laser photolysis/pulsed laser induced fluorescence technique over a wide range of temperatures, 298-670 K, and at pressures between 13.33 and 39.92 kPa. The bimolecular rate constants demonstrate different behavior at low and high temperatures. At room temperature, T = 298.8 +/- 1.5 K, the rate constant is equal to (6.02 +/- 0.34) x 10(-13) cm3 molecule(-1) s(-1); at high temperatures (474-670 K), the rate constant values are significantly lower and have a positive temperature dependence that can be described by an Arrhenius expression k1(T) = (1.01 +/- 0.35) x 10(-11) exp[(-2490 +/- 170 K)/T] cm3 molecule(-1) s(-1). This behavior is consistent with the low-temperature reaction being dominated by reversible addition and the high-temperature reaction representing abstraction and addition-elimination channels. The potential energy surface of the reaction was studied using quantum chemical methods, and a transition state theory model was developed for all reaction channels. The temperature dependences of the high-temperature rate constants obtained in calculations using the method of isodesmic reactions for transition states (IRTS) and the CBS-QB3 method are in very good agreement with experiment, with deviations smaller than the estimated experimental uncertainties. The G3//B3LYP-based calculated rate constants are in disagreement with the experimental values. The IRTS-based model was used to provide modified Arrhenius expressions for the temperature dependences of the rate constant for the abstraction and addition-elimination (Cl replacement) channels of the reaction. PMID:19728723

  7. The chemical kinetics of the reactions of lithium with steam-air mixtures

    International Nuclear Information System (INIS)

    This work involved the experimental and analytical determination of the consequences of lithium fires in the presence of steam. Experiments were performed to characterize the chemical reactions of lithium with steam-nitrogen and steam-air mixtures. Models were introduced in the LITFIRE code to describe lithium fires in the presence of steam inside the containment building and plasma chamber of a hypothetical fusion reactor. The code was also equipped with the capability to determine the effects of decay heat and lithium fire on the temperature response of the reactor first wall in the event of a coolant disturbance. Forty-two kinetics experiments were performed in which a stream of steam-nitrogen or steam-air was passed over and reacted with approximately three grams of lithium heated to a predetermined temperature. The lithium reaction rates with the constituent gases were measured and characterized for a wide range of lithium temperatures and gas compositions. Experiments were performed with steam molar concentrations of 5, 15 and 30% and lithium temperatures ranging from 400 to 1100 degree C, inclusive. The LITFIRE code was modified to enable it to model the interactions of lithium with steam-air atmospheres. Results of the reaction kinetics experiments were used in the reaction model, and the heat transfer model was expanded to allow it to handle condensible atmospheres. Three groups of accidents were investigated: a spill on the containment building floor, a spill inside the reactor plasma chamber, and a spill inside the plasma chamber with steam injection to the containment building simulating a steam line break. The results were compared to dry air cases under the same conditions. 23 refs., 66 figs., 18 tabs

  8. PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS, AND REACTION TO SPARK, FRICTION AND IMPACT

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K; Burnham, A K

    2005-09-28

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear and isothermal heating, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Differential scanning calorimetry, DSC, was used to monitor CP decomposition at linear heating rates of 1-7 C min{sup -1} in perforated pans and of 0.1-1.0 C min{sup -1} in sealed pans. The kinetic triplet was calculated using the LLNL code Kinetics05, and predictions for 210 and 240 C are compared to isothermal thermogravimetric analysis (TGA) experiments. Values are also reported for spark, friction, and impact sensitivity.

  9. Study of the kinetics and equilibria of the oligomerization reactions of 2-methylglyceric acid

    Directory of Open Access Journals (Sweden)

    A. W. Birdsall

    2012-11-01

    Full Text Available The presence of a variety of chemical species related to the gaseous precursor isoprene in ambient secondary organic aerosol (SOA has stimulated investigations of the nature of SOA-phase chemical processing. Recent work has demonstrated that 2-methylglyceric acid (2-MG is an important isoprene-derived ambient SOA component and atmospheric chamber experiments have suggested that 2-MG may exist in oligomeric form (as oligoesters under conditions of low SOA water content. In order to better understand the thermodynamic and kinetic parameters of such oligomerization reactions, nuclear magnetic resonance techniques were used to study the bulk phase acid-catalyzed aqueous reactions (Fischer esterification of 2-MG. While the present results indicate that 2-MG oligoesters are formed in the bulk phase with similar water content equilibrium dependences as observed in atmospheric chamber SOA experiments, the acid-catalyzed rate of the Fischer esterification mechanism may be too slow to rationalize the 2-MG oligoester production timescales observed in the atmospheric chamber experiments. Furthermore, it appears that unrealistically high ambient SOA acidities would also be required for significant 2-MG oligoester content to arise via Fischer esterification. Therefore, the present results suggest that other, more kinetically facile, esterification mechanisms may be necessary to rationalize the existence of 2-MG oligomers in atmospheric chamber-generated and ambient SOA.

  10. Study of the kinetics and equilibria of the oligomerization reactions of 2-methylglyceric acid

    Directory of Open Access Journals (Sweden)

    A. W. Birdsall

    2013-03-01

    Full Text Available The presence of a variety of chemical species related to the gaseous precursor isoprene in ambient secondary organic aerosol (SOA has stimulated investigations of the nature of SOA-phase chemical processing. Recent work has demonstrated that 2-methylglyceric acid (2-MG is an important isoprene-derived ambient SOA component and atmospheric chamber experiments have suggested that 2-MG may exist in oligomeric form (as oligoesters under conditions of low SOA water content. In order to better understand the thermodynamic and kinetic parameters of such oligomerization reactions, nuclear magnetic resonance techniques were used to study the bulk phase acid-catalyzed aqueous reactions (Fischer esterification of 2-MG. While the present results indicate that 2-MG oligoesters are formed in the bulk phase with similar water content equilibrium dependences as observed in atmospheric chamber SOA experiments, the acid-catalyzed rate of the Fischer esterification mechanism may be too slow to rationalize the 2-MG oligoester production timescales observed in the atmospheric chamber experiments. Furthermore, it appears that unrealistically high ambient SOA acidities would also be required for significant 2-MG oligoester content to arise via Fischer esterification. Therefore, the present results suggest that other, more kinetically facile, esterification mechanisms may be necessary to rationalize the existence of 2-MG oligomers in atmospheric chamber-generated and ambient SOA.

  11. A study of redox kinetic in silicate melt; Etude cinetique des reactions d'oxydoreduction dans les silicates

    Energy Technology Data Exchange (ETDEWEB)

    Magnien, V

    2005-12-15

    The aim of this thesis is to understand better iron redox reactions and mechanisms in silicate glasses and melts. Particular interest has been paid to the influence of temperature and chemical composition. For this purpose, the influence of alkali element content, iron content and network formers on the kinetics of redox reactions has been determined through XANES and Raman spectroscopy experiments performed either near the glass transition or above the liquidus temperature. As a complement, electrical conductivity and RBS spectroscopy experiments have been made to characterize the diffusivity of the species that transport electrical charges and the reaction morphology, respectively. Temperature and composition variations can induce changes in the dominating redox mechanism. At a given temperature, the parameters that exert the strongest influence on redox mechanisms are the presence or lack of divalent cations and the existing decoupling between the mobility of network former and modifier elements. Near Tg, the diffusion of divalent cations, when present in the melt, controls the kinetics of iron redox reactions along with a flux of electron holes. Composition, through the degree of polymerization and the silicate network structure, influences the kinetics and the nature of the involved cations, but not the mechanisms of the reaction. Without alkaline earth elements, the kinetics of redox reactions are controlled by the diffusion of oxygen species. With increasing temperatures, the diffusivities of all ionic species tend to become similar. The decoupling between ionic fluxes then is reduced so that several mechanisms become kinetically equivalent and can thus coexist. (author)

  12. Kinetics of the Reactions of IO Radicals with NO and NO2

    Science.gov (United States)

    Daykin, E. P.; Wine, P. H.

    1997-01-01

    A laser flash photolysis-long path absorption technique has been employed to study the kinetics of the reactions of IO radicals with NO and NO2 as a function of temperature and pressure. The IO and NO rate coefficient is independent of pressure over the range 40-200 Torr of N2, and its temperature dependence over the range 242-359 K is adequately described by the Arrhenius expression k(sub 1) = (6.9 +/- 1.7) x 10(exp -12) exp[(328 +/- 71)/T] cu cm/(molecule.s) (errors are 2 sigma, precision only). These Arrhenius parameters are similar to those determined previously for the ClO + NO and BrO + NO reactions. The IO and NO2 association reaction is found to be in the falloff regime over the temperature and pressure ranges investigated (254-354 K and 40-750 Torr of N2). Assuming F(sub c) = 0.4 independent of temperature, a physically reasonable set of falloff parameters which adequately describe the data are k(sub 0) = 7.7 x 10(exp -31)(T/300)(exp -5.0) cm(exp 6)/(molecule(exp 2).s) and k(sub infinity) = 1.55 x 10(exp -11)cu cm/(molecule.s) independent of temperature. The IO + NO2 rate coefficients determined in this study are about a factor of 2 faster than those reported in the only previous study of this reaction.

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

    Directory of Open Access Journals (Sweden)

    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.

  14. Study on the Size-Dependent Oxidation Reaction Kinetics of Nanosized Zinc Sulfide

    Directory of Open Access Journals (Sweden)

    Qing-Shan Fu

    2014-01-01

    Full Text Available Numerous oxidation problems of nanoparticles are often involved during the preparation and application of nanomaterials. The oxidation rate of nanomaterials is much faster than bulk materials due to nanoeffect. Nanosized zinc sulfide (nano-ZnS and oxygen were chosen as a reaction system. The influence regularities were discussed and the influence essence was elucidated theoretically. The results indicate that the particle size can remarkably influence the oxidation reaction kinetics. The rate constant and the reaction order increase, while the apparent activation energy and the preexponential factor decrease with the decreasing particle size. Furthermore, the logarithm of rate constant, the apparent activation energy and the logarithm of preexponential factor are linearly related to the reciprocal of particle diameter, respectively. The essence is that the rate constant is influenced by the combined effect of molar surface energy and molar surface entropy, the reaction order by the molar surface area, the apparent activation energy, by the molar surface energy, and the preexponential factor by the molar surface entropy. The influence regularities and essence can provide theoretical guidance to solve the oxidation problems involved in the process of preparation and application of nanomaterials.

  15. Probing the kinetics for thiol desulfurization: The reactions of 2-methyl-2-propanethiol on Mo(110)

    Energy Technology Data Exchange (ETDEWEB)

    Wiegand, B.C.; Uvdal, P.; Friend, C.M. [Harvard Univ., Cambridge, MA (United States)

    1992-05-28

    The reactions of 2-methyl-2-propanethiol on Mo(110) were studied using temperature programmed reaction, high resolution electron energy loss, and X-ray photoelectron spectroscopies. The sulfur-hydrogen bond breaks upon adsorption at 120 K, yielding adsorbed 2-methyl-2-propyl thiolate and hydrogen. Thiolate hydrogenolysis produces isobutane, while cleavage of the C-S and selective C-H bond breaking {beta} to the sulfur yields isobutene. Nonselective decomposition to adsorbed carbon, sulfur, and gaseous dihydrogen is a competing channel. At reaction saturation, the selectivity for hydrocarbon for hydrocarbon formation patterns is 80%. The specific butane and butene isomers were identified on the basis of the differences in the fragmentation patterns of the various isomers when an electron energy of 27 eV was used in the mass spectrometer. The isometric selectivity corroborates the authors general mechanism for thiolate reaction. Isobutane formation preceded ethane formation for a 2-methyl-2-propanethiol/ethanethiol mixture. The kinetics for 2-methyl-2-propyl thiolate desulfurization were found to increase with increasing 2-methyl-2-propyl thiolate coverage. 38 refs., 6 figs., 4 tabs.

  16. Kinetic measurements on elementary fossil fuel combustion reactions over wide temperatures ranges

    Energy Technology Data Exchange (ETDEWEB)

    Fontijin, A.

    1992-01-01

    The goals of this work are to provide accurate data on the temperature dependence of the kinetics of elementary combustion reactions (i) for use by combustion modelers, and (ii) to gain a better fundamental understanding of, and hence predictive ability for, the chemistry involved. Experimental measurements are made using the pseudo-static HTP (high-temperature photochemistry) technique. This approach allows observations on single reactions in the 300 to 1800 K temperature range to be made. Typical total (bath gas) pressures are in the 100 to 1000 mbar range. Ground-state O and H atoms are produced by flash or excimer laser photolysis of suitable precursors (O{sub 2}, CO{sub 2}, SO{sub 2}, NH{sub 3}). The relative atom concentrations are monitored by resonance fluorescence pumped by a cw microwave discharge flow lamp. The molecular reactant-in-excess is introduced through a cooled inlet. Adequate time for mixing, 0.1 to 10 s, between this inlet and the photolysis/observation zone is achieved by using slow flows (typically less than 20 cm s{sup {minus}1}). Results are reported for: O-Atom Reactions with the Four Isomeric Butenes, H + HCl {yields} H{sub 2} + Cl, and the O-atom 1,3-butadiene reaction.

  17. Kinetic limit for incubation period of primary phase produced by the combination reaction between two solid heterogeneous pure metals

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    An irreversible thermodynamics model was constructed to study the combination reaction of two heterogeneous pure metals in diffusion bonding based on the theorem of minimum entropy production and the Curie principle.The correlation between the irreversible reaction and diffusion was discussed,which provided the kinetic inevitability of an incubation period of a primary phase.The analytical descriptions of the incubation period and the kinetically critical grain size of the primary phase were deduced.Comparison of the experimental results of Al/Mo interfacial reaction with the calculations indicated that the performed theoretical analysis was reliable.

  18. KINETIC MONTE CARLO SIMULATIONS OF THE EFFECTS OF 1-D DEFECT TRANSPORT ON DEFECT REACTION KINETICS AND VOID LATTICE FORMATION DURING IRRADIATION

    International Nuclear Information System (INIS)

    Within the last decade molecular dynamics simulations of displacement cascades have revealed that glissile clusters of self-interstitial crowdions are formed directly in cascades. Also, under various conditions, a crowdion cluster can change its Burgers vector and glide along a different close-packed direction. In order to incorporate the migration properties of crowdion clusters into analytical rate theory models, it is necessary to describe the reaction kinetics of defects that migrate one-dimensionally with occasional changes in their Burgers vector. To meet this requirement, atomic-scale kinetic Monte Carlo (KMC) simulations have been used to study the defect reaction kinetics of one-dimensionally migrating crowdion clusters as a function of the frequency of direction changes, specifically to determine the sink strengths for such one-dimensionally migrating defects. The KMC experiments are used to guide the development of analytical expressions for use in reaction rate theories and especially to test their validity. Excellent agreement is found between the results of KMC experiments and the analytical expressions derived for the transition from one-dimensional to three-dimensional reaction kinetics. Furthermore, KMC simulations have been performed to investigate the significant role of crowdion clusters in the formation and stability of void lattices. The necessity for both one-dimensional migration and Burgers vectors changes for achieving a stable void lattice is demonstrated.

  19. Kinetics of CO2–fluid–rock reactions in a basalt aquifer, Soda Springs, Idaho

    International Nuclear Information System (INIS)

    Highlights: • We model reaction progress in a basalt aquifer by using changes in groundwater. • We use U-series isotope ratios to determine the surface area of plagioclase. • Calculated dissolution rates for plagioclase compare to other CO2-charged systems. - Abstract: The dissolution of silicate minerals by CO2-rich fluids and the subsequent precipitation of CO2 as carbonate minerals represent a means of permanently storing anthropogenic CO2 waste products in a solid and secure form. Modelling the progression of these reactions is hindered by our poor understanding of the rates of mineral dissolution–precipitation reactions and mineral surface properties in natural systems. This study evaluates the chemical evolution of groundwater flowing through a basalt aquifer, which forms part of the leaking CO2-charged system of the Blackfoot Volcanic Field in south-eastern Idaho, USA. Reaction progress is modelled using changes in groundwater chemistry by inverse mass balance techniques. The CO2-promoted fluid–mineral reactions include the dissolution of primary plagioclase, orthoclase, pyroxene and gypsum which is balanced by the precipitation of secondary albite, calcite, zeolite, kaolinite and silica. Mineral mole transfers and groundwater flow rates estimated from hydraulic head data are used to determine the kinetics of plagioclase and orthoclase feldspar dissolution. Plagioclase surface area measurements were determined using the evolution of the U-series isotope ratios in the groundwater and are compared to published surface area measurements. Calculated rates of dissolution for plagioclase range from 2.4 × 10−12 to 4.6 × 10−16 mol/m2/s and orthoclase from 2.0 × 10−13 to 6.8 × 10−16 mol/m2/s respectively. These feldspar reaction rates, correlate with the degree of mineral–fluid disequilibrium and are similar to the dissolution rates for these mineral measured in other natural CO2-charged groundwater systems

  20. KINETIC MODELING OF TRANSESTERFICATION REACTION FOR BIODIESEL PRODUCTION USING HETEROGENEOUS CATALYST

    Directory of Open Access Journals (Sweden)

    N. JAYA,

    2011-04-01

    Full Text Available Biodiesel derived from renewable plant sources is monoalkyl esters of long chain fatty acids which fall in the carbon range of C12-C22. It has similar properties as mineral diesel. Various processes exist to convert vegetable oils into biodiesel. Transesterification of such vegetable oils using alcohol in the catalytic environment is most commonly used method for producing biodiesel. The equilibrium conversion of triglycerides is affected by various factors namely feed Quality (like free fatty acid content, water content etc.,type of alcohol used, molar ratio of alcohol to triglycerides, type of catalyst, amount of catalyst, reaction temperature, reaction time and stirring rates. The present work reports on the characterization of cotton seed oil and production of biodiesel. This study also reports on the optimal operating parameter for cotton seed oil inbatch reactor. The main thrust of present work was to study the kinetics, modeling and simulation of anionic ion exchange resin catalyzed transesterification of cotton seed oil. Experiments were carried out in batch reactor to generate kinetic data and a kinetic model was developed. The effect of temperature, catalyst concentration and molar ratio of methanol to triglycerides and stirring rates were investigated. A few fuel properties were alsomeasured for biodiesel to observe its competitiveness with onventional diesel fuel. The equilibrium conversions of triglycerides were observed to be in the range of 85%. It was also observed that higher conversion was achieved at 6:1 molar ratio of ethanol to oil, 2 wt.% of anionic resin catalyst ,temperature at 338 K, reaction time of 180 minutes with stirring speed 10 Hz. Model parameters such as order, activation energy and rate constants were calculated, the overall activation energy was also estimated. The rate constants werefound to increase with an increase in temperature and catalyst concentration. Various simulations were also carried out at

  1. Advanced glycation end product ligands for the receptor for advanced glycation end products: Biochemical characterization and formation kinetics

    NARCIS (Netherlands)

    Valencia, J.V.; Weldon, S.C.; Quinn, D.; Kiers, G.H.; Groot, J. de; TeKoppele, J.M.; Hughes, T.E.

    2004-01-01

    Advanced glycation end products (AGEs) accumulate with age and at an accelerated rate in diabetes. AGEs bind cell-surface receptors including the receptor for advanced glycation end products (RAGE). The dependence of RAGE binding on specific biochemical characteristics of AGEs is currently unknown.

  2. Biochemical ripening of dredged sediments. Part 1. Kinetics of biological organic matter mineralization and chemical sulfur oxidation

    NARCIS (Netherlands)

    Vermeulen, J.; Gool, M.P.M. van; Dorleijn, A.S.; Joziasse, J.; Bruning, H.; Rulkens, W.H.; Grotenhuis, J.T.C.

    2007-01-01

    After dredged sediments have settled in a temporary upland disposal site, ripening starts, which turns waterlogged sediment into aerated soil. Aerobic biological mineralization of organic matter (OM) and chemical oxidation of reduced sulfur compounds are the major biochemical ripening processes. Qua

  3. Characterisation and reaction kinetics of high ash chars derived from inertinite-rich coal discards / Rufaro Kaitano

    OpenAIRE

    Kaitano, Rufaro

    2007-01-01

    An investigation was undertaken to determine the gasification and combustion characteristics of chars derived from an inertinite-rich coal discard sample with a high ash content. Fundamental knowledge of the reaction rate kinetics for char conversion at reactions conditions used in fluidised bed gasification and combustion was obtained. For this purpose, characterisation of the parent coal and derived chars, reactivity determinations of the chars and detailed reaction rate mode...

  4. Sensitivity of polar stratospheric ozone loss to uncertainties in chemical reaction kinetics

    Directory of Open Access Journals (Sweden)

    S. R. Kawa

    2009-06-01

    Full Text Available The impact and significance of uncertainties in model calculations of stratospheric ozone loss resulting from known uncertainty in chemical kinetics parameters is evaluated in trajectory chemistry simulations for the Antarctic and Arctic polar vortices. The uncertainty in modeled ozone loss is derived from Monte Carlo scenario simulations varying the kinetic (reaction and photolysis rate parameters within their estimated uncertainty bounds. Simulations of a typical winter/spring Antarctic vortex scenario and Match scenarios in the Arctic produce large uncertainty in ozone loss rates and integrated seasonal loss. The simulations clearly indicate that the dominant source of model uncertainty in polar ozone loss is uncertainty in the Cl2O2 photolysis reaction, which arises from uncertainty in laboratory-measured molecular cross sections at atmospherically important wavelengths. This estimated uncertainty in JCl2O2 from laboratory measurements seriously hinders our ability to model polar ozone loss within useful quantitative error limits. Atmospheric observations, however, suggest that the Cl2O2 photolysis uncertainty may be less than that derived from the lab data. Comparisons to Match, South Pole ozonesonde, and Aura Microwave Limb Sounder (MLS data all show that the nominal recommended rate simulations agree with data within uncertainties when the Cl2O2 photolysis error is reduced by a factor of two, in line with previous in situ ClOx measurements. Comparisons to simulations using recent cross sections from Pope et al. (2007 are outside the constrained error bounds in each case. Other reactions producing significant sensitivity in polar ozone loss include BrO+ClO and its branching ratios. These uncertainties challenge our confidence in modeling polar ozone depletion and projecting future changes in response to changing halogen

  5. Reaction Kinetics of LiOH· H2O and CO2 Improved with Composite Silica Gel of Lanthanum Chloride

    Institute of Scientific and Technical Information of China (English)

    Zhao Zhuo; Fu Pingfeng; Wang Jingxin

    2007-01-01

    Reaction kinetics of LiOH·H2O and C·2 within a closed system were studied under the adsorption of water vapor by composite silica gel of lanthanum chloride. At the reaction temperature of 273~323K and initial CO2 pressures of 40~100kPa, reaction kinetics obeyed the Erofeev model. The reaction rate decreased slightly while the initial CO2 pressure reduced. When the reaction occurred at 273~299K, the reaction rate was so low that it was almost independent of the reaction temperature. However, as the temperature rose up to 300~323K, LiOH·H2O dehydrated its crystal water, and both the dehydrated and reaction-generated water were evaporated from solid reactant. For the dehydration rate increased, the reaction rate also increased as the reaction temperature rose. While the temperature was higher than 323K, the reaction apparent activation energy of LiOH·H2O and CO2, was higher than 52.5kJ·mol-1 and close to 61.4kJ·mol-1 of the LiOH·H2O dehydrated enthalpy variable at 298K, in which anhydrous LiOH was the major reactant and showed the reaction characteristics of LiOH crystals.

  6. Kinetics of the monomer-dimer reaction of yeast hexokinase PI.

    Science.gov (United States)

    Hoggett, J G; Kellett, G L

    1992-10-15

    Kinetic studies of the glucose-dependent monomer-dimer reaction of yeast hexokinase PI at pH 8.0 in the presence of 0.1 M-KCl have been carried out using the fluorescence temperature-jump technique. A slow-relaxation effect was observed which was attributed from its dependence on enzyme concentration to the monomer-dimer reaction; the reciprocal relaxation times tau-1 varied from 3 s-1 at low concentrations of glucose to 42 s-1 at saturating concentrations. Rate constants for association (kass.) and dissociation (kdiss.) were determined as a function of glucose concentration using values of the equilibrium association constant of the monomer-dimer reaction derived from sedimentation ultracentrifugation studies under similar conditions, and also from the dependence of tau-2 on enzyme concentration. kass. was almost independent of glucose concentration and its value (2 x 10(5) M-1.s-1) was close to that expected for a diffusion-controlled process. The influence of glucose on the monomer-dimer reaction is entirely due to effects on kdiss., which increases from 0.21 s-1 in the absence of glucose to 25 s-1 at saturating concentrations. The monomer and dimer forms of hexokinase have different affinities and Km values for glucose, and the results reported here imply that there may be a significant lag in the response of the monomer-dimer reaction to changes in glucose concentrations in vivo with consequent hysteretic effects on the hexokinase activity. PMID:1445216

  7. Oxidation of triclosan by ferrate: Reaction kinetics, products identification and toxicity evaluation

    Energy Technology Data Exchange (ETDEWEB)

    Yang Bin [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Ying Guangguo, E-mail: guang-guo.ying@csiro.au [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Zhao Jianliang; Zhang Lijuan; Fang Yixiang [State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640 (China); Nghiem, Long Duc [School of Civil Mining and Environmental Engineering, University of Wollongong, Wollongong, NSW 2522 (Australia)

    2011-02-15

    Research highlights: {yields} Triclosan reacted rapidly with ferrate. {yields} Oxidation resulted in a decrease in algal toxicity. {yields} No inhibition of algae growth from ferrate. - Abstract: The oxidation of triclosan by commercial grade aqueous ferrate (Fe(VI)) was investigated and the reaction kinetics as a function of pH (7.0-10.0) were experimentally determined. Intermediate products of the oxidation process were characterized using both GC-MS and RRLC-MS/MS techniques. Changes in toxicity during the oxidation process of triclosan using Fe(VI) were investigated using Pseudokirchneriella subcapitata growth inhibition tests. The results show that triclosan reacted rapidly with Fe(VI), with the apparent second-order rate constant, k{sub app}, being 754.7 M{sup -1} s{sup -1} at pH 7. At a stoichiometric ratio of 10:1 (Fe(VI):triclosan), complete removal of triclosan was achieved. Species-specific rate constants, k, were determined for reaction of Fe(VI) with both the protonated and deprotonated triclosan species. The value of k determined for neutral triclosan was 6.7({+-}1.9) x 10{sup 2} M{sup -1} s{sup -1}, while that measured for anionic triclosan was 7.6({+-}0.6) x 10{sup 3} M{sup -1} s{sup -1}. The proposed mechanism for the oxidation of triclosan by the Fe(VI) involves the scission of ether bond and phenoxy radical addition reaction. Coupling reaction may also occur during Fe(VI) degradation of triclosan. Overall, the degradation processes of triclosan resulted in a significant decrease in algal toxicity. The toxicity tests showed that Fe(VI) itself dosed in the reaction did not inhibit green algae growth.

  8. Oxidation of triclosan by ferrate: Reaction kinetics, products identification and toxicity evaluation

    International Nuclear Information System (INIS)

    Research highlights: → Triclosan reacted rapidly with ferrate. → Oxidation resulted in a decrease in algal toxicity. → No inhibition of algae growth from ferrate. - Abstract: The oxidation of triclosan by commercial grade aqueous ferrate (Fe(VI)) was investigated and the reaction kinetics as a function of pH (7.0-10.0) were experimentally determined. Intermediate products of the oxidation process were characterized using both GC-MS and RRLC-MS/MS techniques. Changes in toxicity during the oxidation process of triclosan using Fe(VI) were investigated using Pseudokirchneriella subcapitata growth inhibition tests. The results show that triclosan reacted rapidly with Fe(VI), with the apparent second-order rate constant, kapp, being 754.7 M-1 s-1 at pH 7. At a stoichiometric ratio of 10:1 (Fe(VI):triclosan), complete removal of triclosan was achieved. Species-specific rate constants, k, were determined for reaction of Fe(VI) with both the protonated and deprotonated triclosan species. The value of k determined for neutral triclosan was 6.7(±1.9) x 102 M-1 s-1, while that measured for anionic triclosan was 7.6(±0.6) x 103 M-1 s-1. The proposed mechanism for the oxidation of triclosan by the Fe(VI) involves the scission of ether bond and phenoxy radical addition reaction. Coupling reaction may also occur during Fe(VI) degradation of triclosan. Overall, the degradation processes of triclosan resulted in a significant decrease in algal toxicity. The toxicity tests showed that Fe(VI) itself dosed in the reaction did not inhibit green algae growth.

  9. Thermal Behavior,Nonisothermal Decomposition Reaction Kinetics of Mixed Ester Double-base Gun Propellants

    Institute of Scientific and Technical Information of China (English)

    YI Jian-hua; ZHAO Feng-qi; XU Si-yu; GAO Hong-xu; HU Rong-zu

    2008-01-01

    The thermal decomposition behavior and nonisothermal reaction kinetics of the double-base gun propellants containing the mixed ester of triethyleneglycol dinitrate(TEGDN) and nitroglycerin(NG) were investigated by thermogravimetry(TG) and differential thermogravimetry(DTG),and differential scanning calorimetry(DSC) under the high-pressure dynamic ambience.The results show that the thermal decomposition processes of the mixed nitric ester gun propellants have two mass-loss stages.Nitric ester evaporates and decomposes in the first stage,and nitrocellulose and centralite Ⅱ(C2) decompose in the second stage.The mass loss,the DTG peak points,and the terminated temperatures of the two stages are changeable with the difference of the mass ratio of TEGDN to NG.There is only one obvious exothermic peak in the DSC curves under the different pressures.With the increase in the furnace pressure,the peak temperature decreases,and the decomposition heat increases.With the increase in the content of TEGDN,the decomposition heat decreases at 0.1 Mpa and rises at high pressure.The variety of mass ratio of TEGDN to NG makes few effect on the exothermic peak temperatures in the DSC curves at different pressures.The kinetic equation of the main exothermal decomposition reaction of the gun propellant TG0601 was determined as:da/dt-=1021.59(1-a)3e-2.60×104/T The reaction mechanism of the process can be classified as chemical reaction.The critical temperatures of the thermal explosion(Tbe and Tbp) obtained from the onset temperature(Te) and the peak temperature(Tp) are 456.46 and 473.40 K,respectively.△S≠,△H≠,and △G≠of the decomposition reaction are 163.57 J·mol-1·K-1,209.54 kJ·mol-1,and 133.55kJ·mol-1,respectively.

  10. REACTION KINETICS OF VERSATILE PEROXIDASE FOR THE DEGRADATION OF LIGNIN COMPOUNDS

    Directory of Open Access Journals (Sweden)

    N. Busse

    2013-01-01

    Full Text Available The H2O2 dependent degradation of adlerol by a crude versatile peroxidase from Bjerkandera adusta, a new ligninolytic enzyme, was investigated. Adlerol (1-(3,4-dimethoxyphenyl-2-(2-methoxyphenoxy-1,3-propanediol is a non phenolic β-O-4 dimer whose structural architecture represents the most abundant unit (50-65% of the valuable renewable biopolymer lignin. Lignin removel plays a key role in utilizing lignocellulosic biomass in biorefineries. Steady state analyses in the µL scale showed saturation kinetics for both, H2O2 and adlerol with quite sensitive response to H2O2. This was characterized through slow transient states (lag phases prior steady state and were enhanced by increasing H2O2 concentration. The major reason for such phenomena was found to be an accumulation of compound III (EIII via reaction of compound II (EII with H2O2; instead with adlerol to the enzyme’s ground state E0 in order to restart another catalytic cycle. As result, the enzyme deviated from its normal catalytic cycle. A corresponding threshold was determined at ≥ 50 μM H2O2 and an adlerol to H2O2 ratio of 15:1 for the given conditions. Furthermore, EIII did not represent a catalytical dead end intermediate as it is generally described. By an additional decrease of the adlerol to H2O2 ratio of ca. 3 at the latest, considerable irreversible enzyme deactivations occurred promoted through reaction of EIII with H2O2. At a mL scale deactivation kinetics by H2O2 were further examined in dependence on adlerol presence. The course followed a time dependent irreversible deactivation (two step mechanism and was diminished in the presence of adlerol. The deactivation could be sufficiently described by an equation similar to the Michaelis Menten type, competitive inhibited by adlerol. Finally, first estimates of the kinetic parameters vmax, KmS1 (S1: H2O2, KmS2 (S2: adlerol, kiapp and Kiapp were made. Moreover, the peroxidase reaction mechanism was reviewed and

  11. A kinetic study of the complexation reaction between the dioxoururanium(VI) ion and arsenazo III

    International Nuclear Information System (INIS)

    The rates of formation of the 1:1 complexes between the aquo UO22+ ion and Arsenazo III were determined in 2.0 M perchloric acid solutions. The kinetic data are consistent with a first-order approach to equilibrium due to the concentration conditions under which the reaction was studied. Rate and activation parameters for the forward reaction at 25.0deg C are kf=2.14 ± (0.08)x105 M-1 sec-1, ΔH*f=30.1 ± (6.0) kJ/mol and ΔS*f=-42.2 ± (20.2) J/molxK, respectively. For the corresponding reverse reaction at 25.0deg C, kr=8.86 ± (0.44) sec-1, ΔH*r=48.2 ± (0.1) kJ/mol and ΔS*r=-65.3 ± (4.1) J/molxK. Equilibrium parameters are used to calculate at 25deg C, ΔG0=-25.0 ± (5.3) J/mol, ΔH0=-18.1 ± (0.3) kJ/mol, and ΔS0=23.1 ± (10.6) J/molxK. (orig.)

  12. Kinetics of the high-temperature combustion reactions of dibutylether using composite computational methods

    KAUST Repository

    Al Rashidi, Mariam J.

    2015-01-01

    This paper investigates the high-temperature combustion kinetics of n-dibutyl ether (n-DBE), including unimolecular decomposition, H-abstraction by H, H-migration, and C{single bond}C/C{single bond}O β-scission reactions of the DBE radicals. The energetics of H-abstraction by OH radicals is also studied. All rates are determined computationally using the CBS-QB3 and G4 composite methods in conjunction with conventional transition state theory. The B3LYP/6-311++G(2df,2pd) method is used to optimize the geometries and calculate the frequencies of all reactive species and transition states for use in ChemRate. Some of the rates calculated in this study vary markedly from those obtained for similar reactions of alcohols or alkanes, particularly those pertaining to unimolecular decomposition and β-scission at the α-β C{single bond}C bond. These variations show that analogies to alkanes and alcohols are, in some cases, inappropriate means of estimating the reaction rates of ethers. This emphasizes the need to establish valid rates through computation or experimentation. Such studies are especially important given that ethers exhibit promising biofuel and fuel additive characteristics. © 2014.

  13. Kinetically constrained ring-polymer molecular dynamics for non-adiabatic chemical reactions

    International Nuclear Information System (INIS)

    We extend ring-polymer molecular dynamics (RPMD) to allow for the direct simulation of general, electronically non-adiabatic chemical processes. The kinetically constrained (KC) RPMD method uses the imaginary-time path-integral representation in the set of nuclear coordinates and electronic states to provide continuous equations of motion that describe the quantized, electronically non-adiabatic dynamics of the system. KC-RPMD preserves the favorable properties of the usual RPMD formulation in the position representation, including rigorous detailed balance, time-reversal symmetry, and invariance of reaction rate calculations to the choice of dividing surface. However, the new method overcomes significant shortcomings of position-representation RPMD by enabling the description of non-adiabatic transitions between states associated with general, many-electron wavefunctions and by accurately describing deep-tunneling processes across asymmetric barriers. We demonstrate that KC-RPMD yields excellent numerical results for a range of model systems, including a simple avoided-crossing reaction and condensed-phase electron-transfer reactions across multiple regimes for the electronic coupling and thermodynamic driving force

  14. Kinetically constrained ring-polymer molecular dynamics for non-adiabatic chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

    Menzeleev, Artur R.; Bell, Franziska; Miller, Thomas F., E-mail: tfm@caltech.edu [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)

    2014-02-14

    We extend ring-polymer molecular dynamics (RPMD) to allow for the direct simulation of general, electronically non-adiabatic chemical processes. The kinetically constrained (KC) RPMD method uses the imaginary-time path-integral representation in the set of nuclear coordinates and electronic states to provide continuous equations of motion that describe the quantized, electronically non-adiabatic dynamics of the system. KC-RPMD preserves the favorable properties of the usual RPMD formulation in the position representation, including rigorous detailed balance, time-reversal symmetry, and invariance of reaction rate calculations to the choice of dividing surface. However, the new method overcomes significant shortcomings of position-representation RPMD by enabling the description of non-adiabatic transitions between states associated with general, many-electron wavefunctions and by accurately describing deep-tunneling processes across asymmetric barriers. We demonstrate that KC-RPMD yields excellent numerical results for a range of model systems, including a simple avoided-crossing reaction and condensed-phase electron-transfer reactions across multiple regimes for the electronic coupling and thermodynamic driving force.

  15. Kinetics of chemi-ionization reactions of lanthanide metals (Nd, Sm) from 150 to 450 K

    International Nuclear Information System (INIS)

    The kinetics of chemi-ionization reactions of neodymium and samarium atoms with an oxygen atom to yield a metal monoxide cation and electron were studied using a flow tube apparatus over a temperature range of 150–450 K. Nd reacts efficiently with O, near the hard-sphere collision limit at all temperatures, with a rate constant of 3 × 10−10 cm3 s−1 at 300 K and a slight positive temperature dependence. No chemi-ionization of Nd with N2O was observed, despite the reaction being exothermic. Chemi-ionization of Sm with O is slow, with a rate constant at 300 K determined to be 7 × 10−12 cm3 s−1, although with large uncertainty. The Sm reaction also shows a slightly positive temperature dependence, described by a small activation energy of 60 meV. Although not definitive, the data suggest that excited states of Sm react efficiently whereas ground state Sm reacts inefficiently

  16. Esterification with ethanol to produce biodiesel from high acidity raw materials. Kinetic studies and analysis of secondary reactions

    Energy Technology Data Exchange (ETDEWEB)

    Pisarello, M.L.; Dalla Costa, B.; Mendow, G.; Querini, C.A. [Instituto de Investigaciones en Catalisis y Petroquimica (INCAPE)-(FIQ-UNL, CONICET), Santiago del Estero 2654-Santa Fe, S3000AOJ (Argentina)

    2010-09-15

    In this work, the esterification reaction of free fatty acids (FFA) in sunflower oil, coconut oil and concentrated FFA, with ethanol, methanol and ethanol 96%, using homogeneous acid catalysts to produce biodiesel is studied. Kinetic parameters are estimated with a simplified model, and then used to predict the reaction behavior. Reactions other than the reversible esterification are considered to explain the behavior that this system displays. Such reactions are the triglycerides conversion by acid catalyzed transesterification and hydrolysis. In addition, we include kinetic studies of the reaction that occur between the sulphuric acid and methanol (or ethanol), forming mono and dialkylsulphates. This reaction produces water and consumes methanol (or ethanol), and consequently has a direct impact in the esterification reaction rate and equilibrium conversion. The concentration of sulphuric acid decreases to less than 50% of the initial value due to the reaction with the alcohol. A minimum in the acidity due to the free fatty acids as a function of time was clearly observed during the reaction, which has not been reported earlier. This behavior is related to the consecutive reactions that take place during the esterification of FFA in the presence of triglycerides. The phase separation due to the presence of water, which is generated during the reaction, is also studied. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  18. Kinetic study on bonding reaction of gelatin with CdS nanopaticles by UV-visible spectroscopy

    Science.gov (United States)

    Tang, Shihua; Wang, Baiyang; Li, Youqun

    2015-04-01

    The chemical kinetics on gelatin-CdS direct conjugates has been systematically investigated as a function of different temperature and reactant concentration (i.e. Cd2+, S2- and gelatin) by UV-visible spectroscopy, for the first time. The nonlinear fitting and the differential method were used to calculate the initial rate based on the absorbance-time data. A double logarithmic linear equation for calculating the rate constant (k) and the reaction order (n) was introduced. The reaction kinetic parameters (n, k, Ea, and Z) and activation thermodynamic parameters (ΔG≠, ΔH≠, and ΔS≠) were obtained from variable temperature kinetic studies. The overall rate equation allowing evaluation of conditions that provide required reaction rate could be expressed as:

  19. Kinetics of solid-gas reactions characterized by scanning AC nano-calorimetry with application to Zr oxidation

    International Nuclear Information System (INIS)

    Scanning AC nano-calorimetry is a recently developed experimental technique capable of measuring the heat capacity of thin-film samples of a material over a wide range of temperatures and heating rates. Here, we describe how this technique can be used to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59 ± 0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.

  20. Kinetic and Reaction Pathway Analysis in the Application of Botulinum Toxin A for Wound Healing

    Directory of Open Access Journals (Sweden)

    Frank J. Lebeda

    2012-01-01

    Full Text Available A relatively new approach in the treatment of specific wounds in animal models and in patients with type A botulinum toxin is the focus of this paper. The indications or conditions include traumatic wounds (experimental and clinical, surgical (incision wounds, and wounds such as fissures and ulcers that are signs/symptoms of disease or other processes. An objective was to conduct systematic literature searches and take note of the reactions involved in the healing process and identify corresponding pharmacokinetic data. From several case reports, we developed a qualitative model of how botulinum toxin disrupts the vicious cycle of muscle spasm, pain, inflammation, decreased blood flow, and ischemia. We transformed this model into a minimal kinetic scheme for healing chronic wounds. The model helped us to estimate the rate of decline of this toxin's therapeutic effect by calculating the rate of recurrence of clinical symptoms after a wound-healing treatment with this neurotoxin.

  1. A model for lignin alteration - Part I: A kinetic reaction-network model

    Science.gov (United States)

    Payne, D.F.; Ortoleva, P.J.

    2001-01-01

    A new quantitative model is presented which simulates the maturation of lignin-derived sedimentary organic matter under geologic conditions. In this model, compositionally specific reactants evolve to specific intermediate and mobile products through balanced, nth order processes, by way of a network of sequential and parallel reactions. The chemical kinetic approach is based primarily on published observed structural transformations of naturally matured, lignin-derived, sedimentary organic matter. Assuming that Upper Cretaceous Williams Fork coal in the Piceance Basin is primarily lignin-derived, the model is calibrated for the Multi-Well Experiment(MWX) Site in this basin. This kind of approach may be applied to other selectively preserved chemical components of sedimentary organic matter. ?? 2001 Elsevier Science Ltd. All rights reserved.

  2. Programming chemical kinetics: engineering dynamic reaction networks with DNA strand displacement

    Science.gov (United States)

    Srinivas, Niranjan

    Over the last century, the silicon revolution has enabled us to build faster, smaller and more sophisticated computers. Today, these computers control phones, cars, satellites, assembly lines, and other electromechanical devices. Just as electrical wiring controls electromechanical devices, living organisms employ "chemical wiring" to make decisions about their environment and control physical processes. Currently, the big difference between these two substrates is that while we have the abstractions, design principles, verification and fabrication techniques in place for programming with silicon, we have no comparable understanding or expertise for programming chemistry. In this thesis we take a small step towards the goal of learning how to systematically engineer prescribed non-equilibrium dynamical behaviors in chemical systems. We use the formalism of chemical reaction networks (CRNs), combined with mass-action kinetics, as our programming language for specifying dynamical behaviors. Leveraging the tools of nucleic acid nanotechnology (introduced in Chapter 1), we employ synthetic DNA molecules as our molecular architecture and toehold-mediated DNA strand displacement as our reaction primitive. Abstraction, modular design and systematic fabrication can work only with well-understood and quantitatively characterized tools. Therefore, we embark on a detailed study of the "device physics" of DNA strand displacement (Chapter 2). We present a unified view of strand displacement biophysics and kinetics by studying the process at multiple levels of detail, using an intuitive model of a random walk on a 1-dimensional energy landscape, a secondary structure kinetics model with single base-pair steps, and a coarse-grained molecular model that incorporates three-dimensional geometric and steric effects. Further, we experimentally investigate the thermodynamics of three-way branch migration. Our findings are consistent with previously measured or inferred rates for

  3. Preclusion of switch behavior in reaction networks with mass-action kinetics

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Wiuf, C.

    2012-01-01

    We study networks taken with mass-action kinetics and provide a Jacobian criterion that applies to an arbitrary network to preclude the existence of multiple positive steady states within any stoichiometric class for any choice of rate constants. We are concerned with the characterization of...... injective networks, that is, networks for which the species formation rate function is injective in the interior of the positive orthant within each stoichiometric class. We show that a network is injective if and only if the determinant of the Jacobian of a certain function does not vanish. The function...... precludes the existence of degenerate steady states. Further, we relate injectivity of a network to that of the network obtained by adding outflow, or degradation, reactions for all species....

  4. An improved equilibrium-kinetics speciation algorithm for redox reactions in variably saturated subsurface flow systems

    International Nuclear Information System (INIS)

    Reactive chemical transport occurs in a variety of geochemical environments, and over a broad range of space and time scales. Efficiency of the chemical speciation and water-rock-gas interaction calculations is important for modeling field-scale multidimensional reactive transport problems. An improved efficient model, REACT, for simulating water-rock-gas interaction under equilibrium and kinetic conditions, has been developed. In this model, equilibrium and kinetic reactions are solved simultaneously by Newton-Raphson iteration. The REACT speciation model was coupled with the multidimensional nonisothermal multiphase flow and mass transport code TOUGH2, resulting in the general purpose reactive chemical transport simulator TOUGHREACT. An application to supergene copper enrichment of a typical copper protore that includes the sulfide minerals pyrite (FeS2) and chalcopyrite (CuFeS2) is presented. The efficiency and convergence of the present model is demonstrated from this numerically difficult application that involves very large variations in the concentrations of oxygen, and sulfide and sulfate species. TOUGHREACT provides a detailed description of water-rock-gas interactions during fully transient, multiphase, nonisothermal flow and transport in hydrologically and geochemically heterogeneous media. The code is helpful for assessment of acid mine drainage remediation, geothermal convection, waste disposal, contaminant transport and water quality. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

  5. An improved equilibrium-kinetics speciation algorithm for redox reactions in variably saturated subsurface flow systems

    Science.gov (United States)

    Xu, Tianfu; Pruess, Karsten; Brimhall, George

    1999-07-01

    Reactive chemical transport occurs in a variety of geochemical environments, and over a broad range of space and time scales. Efficiency of the chemical speciation and water-rock-gas interaction calculations is important for modeling field-scale multidimensional reactive transport problems. An improved efficient model, REACT, for simulating water-rock-gas interaction under equilibrium and kinetic conditions, has been developed. In this model, equilibrium and kinetic reactions are solved simultaneously by Newton-Raphson iteration. The REACT speciation model was coupled with the multidimensional nonisothermal multiphase flow and mass transport code TOUGH2, resulting in the general purpose reactive chemical transport simulator TOUGHREACT. An application to supergene copper enrichment of a typical copper protore that includes the sulfide minerals pyrite (FeS 2) and chalcopyrite (CuFeS 2) is presented. The efficiency and convergence of the present model is demonstrated from this numerically difficult application that involves very large variations in the concentrations of oxygen, and sulfide and sulfate species. TOUGHREACT provides a detailed description of water-rock-gas interactions during fully transient, multiphase, nonisothermal flow and transport in hydrologically and geochemically heterogeneous media. The code is helpful for assessment of acid mine drainage remediation, geothermal convection, waste disposal, contaminant transport and water quality.

  6. A simplified kinetic model for the side reactions occurring during the enzymatic synthesis of ampicillin

    Directory of Open Access Journals (Sweden)

    A.L.O. Ferreira

    2000-12-01

    Full Text Available This work presents a kinetic study of the side reactions of the ampicillin enzymatic synthesis, from phenylglycine methyl ester and 6-aminopenicillanic acid using penicillin G acylase immobilized on agarose. A Michaelis-Menten model with competitive inhibition was fitted to initial rates of ester and antibiotic hydrolysis, at pH 6.5 and 25ºC. Inherent kinetic parameters were estimated for low enzymatic loads, to assure that diffusional resistance was not important. It was observed that ampicillin inhibits the hydrolysis of PGME, but the inhibitory effect of the ester on ampicillin hydrolysis was almost negligible. The obtained parameters were: k cat1= 0.025 mM/UI min, Km1 = 155.4mM, K AE = 16.18mM, k cat2= 4.67x10-3 mM/UI min, Km2 = 11.47, K EA = 0.68 mM. Parameter values are in the range reported in the literature, except for Km1, which is much higher. The large confidence interval for this parameter denotes that the model presents low sensitivity with respect to it.

  7. Coupled transport and reaction kinetics control the nitrate source-sink function of hyporheic zones

    Science.gov (United States)

    Zarnetske, Jay P.; Haggerty, Roy; Wondzell, Steven M.; Bokil, Vrushali A.; GonzáLez-Pinzón, Ricardo

    2012-11-01

    The fate of biologically available nitrogen (N) and carbon (C) in stream ecosystems is controlled by the coupling of physical transport and biogeochemical reaction kinetics. However, determining the relative role of physical and biogeochemical controls at different temporal and spatial scales is difficult. The hyporheic zone (HZ), where groundwater-stream water mix, can be an important location controlling N and C transformations because it creates strong gradients in both the physical and biogeochemical conditions that control redox biogeochemistry. We evaluated the coupling of physical transport and biogeochemical redox reactions by linking an advection, dispersion, and residence time model with a multiple Monod kinetics model simulating the concentrations of oxygen (O2), ammonium (NH4), nitrate (NO3), and dissolved organic carbon (DOC). We used global Monte Carlo sensitivity analyses with a nondimensional form of the model to examine coupled nitrification-denitrification dynamics across many scales of transport and reaction conditions. Results demonstrated that the residence time of water in the HZ and the uptake rate of O2 from either respiration and/or nitrification determined whether the HZ was a source or a sink of NO3 to the stream. We further show that whether the HZ is a net NO3 source or net NO3 sink is determined by the ratio of the characteristic transport time to the characteristic reaction time of O2 (i.e., the Damköhler number, DaO2), where HZs with DaO2 < 1 will be net nitrification environments and HZs with DaO2 ≪ 1 will be net denitrification environments. Our coupling of the hydrologic and biogeochemical limitations of N transformations across different temporal and spatial scales within the HZ allows us to explain the widely contrasting results of previous investigations of HZ N dynamics which variously identify the HZ as either a net source or sink of NO3. Our model results suggest that only estimates of residence times and O2uptake rates

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

    Energy Technology Data Exchange (ETDEWEB)

    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}.

  9. Reaction Kinetics of LiOH Improved with Composite Silica Gel of Lanthanum Chloride for Absorbing CO2

    Institute of Scientific and Technical Information of China (English)

    Zhao Zhuo; Fu Pingfeng; Wang Jingxin

    2007-01-01

    A static method was employed to study the reaction kinetics of anhydrous lithium hydroxide (LiOH) and CO2. The reaction generated water was absorbed with the composite silica gel of lanthanum chloride to make the experiment repeatable. At the reaction temperature of 15~60℃ and initial CO2 pressures of 25~100kPa, the reaction rate of anhydrous LiOH and CO2 decreased slightly with the reduction of initial CO2 pressure and the rise of reaction temperature, indicating that the reaction activation energy of LiOH and CO2 was negative and close to zero. During the middle period (1~5 min) of the isothermal reaction, the ratio of reaction efficiency was approximately the power of 0.4 to that of initial CO2 pressures. As anhydrous LiOH reacted to CO2, the solid product Li2CO3 covered on the surface of LiOH was not compact, so it did not hinder the subsequent reaction of absorbing the CO2 gas. The reaction kinetics of anhydrous LiOH and CO2 obeyed the Erofeev's model.

  10. alfa-Deuterium kinetic isotope effects in reactions of methyllithium. Is better aggregation the cause of lower reactivity?

    DEFF Research Database (Denmark)

    Holm, Torkil

    1996-01-01

    The value of kH/kD for alfa deuterium kinetic isotope effects for the reaction of methyllithium and methylmagnesium iodid with a series of substrates are consistently ca. 10-15 % higher for the lithium reagent. This may indicate a pre-equilibrium......The value of kH/kD for alfa deuterium kinetic isotope effects for the reaction of methyllithium and methylmagnesium iodid with a series of substrates are consistently ca. 10-15 % higher for the lithium reagent. This may indicate a pre-equilibrium...

  11. Process and kinetics of the fundamental radiation-electrochemical reactions in the primary coolant loop of nuclear reactors

    International Nuclear Information System (INIS)

    In spite of the rather broad title of this report, its major part is devoted to the corrosion problems at the RA reactor, i.e. causes and consequences of the reactor shutdown in 1979 and 1982. Some problems of reactor chemistry are pointed out because they are significant for future reactor operation. The final conclusion of this report is that corrosion processes in the primary coolant circuit of the nuclear reactor are specific and that radiation effects cannot be excluded when processes and reaction kinetics are investigated. Knowledge about the kinetics of all the chemical reactions occurring in the primary coolant loop are of crucial significance for safe and economical reactor operation

  12. Reaction Mechanism and Kinetics of Aqueous Solutions of 2-Amino -2 Methyl-1,3- Propanediol and Carbonyl Sulphide

    OpenAIRE

    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...

  13. Synthesis Of Magnesium-Aluminum Layered Double Hydroxides By Mechanochemical Method And Its Solid State Reaction Kinetics

    Directory of Open Access Journals (Sweden)

    Hongbo Y.

    2015-06-01

    Full Text Available A mechanochemical method is developed in preparing magnesium-aluminum-layered double hydroxides (MgAl-LDHs. This approach includes activation process and diffusion process. In order to verify the LDHs structure and study the reaction kinetics, X-ray diffraction (XRD patterns, inductively coupled plasma(ICP and physical adsorption instrument were characterized. The results show that activation time can change the surface of particles and affect the reaction grade. During the diffusion process, reaction time is the most important factor. The reaction energy (ΔQ was calculated that is 6kJ/mol.

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

    Directory of Open Access Journals (Sweden)

    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.

  15. New insight into the ZnO sulfidation reaction: mechanism and kinetics modeling of the ZnS outward growth.

    Science.gov (United States)

    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

  16. RMBNToolbox: random models for biochemical networks

    Directory of Open Access Journals (Sweden)

    Niemi Jari

    2007-05-01

    Full Text Available Abstract Background There is an increasing interest to model biochemical and cell biological networks, as well as to the computational analysis of these models. The development of analysis methodologies and related software is rapid in the field. However, the number of available models is still relatively small and the model sizes remain limited. The lack of kinetic information is usually the limiting factor for the construction of detailed simulation models. Results We present a computational toolbox for generating random biochemical network models which mimic real biochemical networks. The toolbox is called Random Models for Biochemical Networks. The toolbox works in the Matlab environment, and it makes it possible to generate various network structures, stoichiometries, kinetic laws for reactions, and parameters therein. The generation can be based on statistical rules and distributions, and more detailed information of real biochemical networks can be used in situations where it is known. The toolbox can be easily extended. The resulting network models can be exported in the format of Systems Biology Markup Language. Conclusion While more information is accumulating on biochemical networks, random networks can be used as an intermediate step towards their better understanding. Random networks make it possible to study the effects of various network characteristics to the overall behavior of the network. Moreover, the construction of artificial network models provides the ground truth data needed in the validation of various computational methods in the fields of parameter estimation and data analysis.

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

    Science.gov (United States)

    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

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

    Science.gov (United States)

    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

  19. Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans.

    Science.gov (United States)

    Lizama, H M; Suzuki, I

    1989-11-01

    Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 muM Fe per min per FeS(2) percent pulp density for the spontaneous pyrite dissolution, 10 muM Fe per min per mM Fe for the indirect leaching with Fe, 90 muM O(2) per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 muM O(2) per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K(m) values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K(i) value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe production from Fe plus pyrite. PMID:16348054

  20. Kinetic study of the hydrogen electrode reaction on a porous material in a flow cell

    International Nuclear Information System (INIS)

    The present work deals with the determination of the electrocatalytic activity of porous electrodes.This problem cannot be appropriately treated with the conventional methods because the reaction is not uniform in the whole electrodic surface.Therefore, it is proposed the evaluation of the variation of the equilibrium polarization resistance with pH.As the current - potential dependences are obtained around the equilibrium condition, current values are very low, gaseous evolution is negligible and the ohmic effects can be avoided through a suitable electrolyte solution.In this context a simple model of a porous electrode was developed, consisting in a tubular electrode operating with a laminar flow of electrolyte, where the mass transfer processes towards and/or from the electrode surface are clearly defined as a function of the mean flow rate of the electrolyte.This method was applied to the study of the hydrogen electrode reaction.The experimental determinations were carried out in a flow cell with a platinum tubular electrode and a regulation of the electrolyte flow saturated with hydrogen gas.The apparent polarization resistance was calculated at different flow rate and pH.The application of the flow model together with a kinetic formalism corresponding to the Volmer - Heyrovsky - Tafel mechanism allowed the evaluation of the intrinsic electrocatalytic activity

  1. Two-scale large deviations for chemical reaction kinetics through second quantization path integral

    International Nuclear Information System (INIS)

    Motivated by the study of rare events for a typical genetic switching model in systems biology, in this paper we aim to establish the general two-scale large deviations for chemical reaction systems. We build a formal approach to explicitly obtain the large deviation rate functionals for the considered two-scale processes based upon the second quantization path integral technique. We get three important types of large deviation results when the underlying two timescales are in three different regimes. This is realized by singular perturbation analysis to the rate functionals obtained by the path integral. We find that the three regimes possess the same deterministic mean-field limit but completely different chemical Langevin approximations. The obtained results are natural extensions of the classical large volume limit for chemical reactions. We also discuss its implication on the single-molecule Michaelis–Menten kinetics. Our framework and results can be applied to understand general multi-scale systems including diffusion processes. (paper)

  2. A Stopped-Flow Kinetics Experiment for the Physical Chemistry Laboratory Using Noncorrosive Reagents

    Science.gov (United States)

    Prigodich, Richard V.

    2014-01-01

    Stopped-flow kinetics techniques are important to the study of rapid chemical and biochemical reactions. Incorporation of a stopped-flow kinetics experiment into the physical chemistry laboratory curriculum would therefore be an instructive addition. However, the usual reactions studied in such exercises employ a corrosive reagent that can over…

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

    Science.gov (United States)

    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

  4. Influence of various metallic oxides on the kinetic of the oxygen evolution reaction on platinum electrodes

    Directory of Open Access Journals (Sweden)

    Kambire Ollo

    2015-08-01

    Full Text Available Pt, 50Pt-50RuO2 and 50Pt-50IrO2 electrodes were prepared on titanium (Ti substrate by thermal decomposition techniques. The micrographs of 50Pt-50RuO2 and 50Pt-50IrO2 have revealed that their surfaces are rough with cracked structures. That of platinum was smooth, compact and homogeneous. The richer the electrode ‘surface in platinum, thinner is the crack size and also more compact is the electrode’surface. The electrodes have also been characterized electrochemically by cyclic voltammetry in acid (HClO4 and in alkaline (KOH electrolytes. These characterizations showed that the surface of the 50Pt-50RuO2 and 50Pt-50IrO2 electrodes were composed by platinum and metal dioxide active sites. The Tafel slope obtained on Pt, 50Pt-50RuO2 and 50Pt-50IrO2 for the oxygen evolution reaction (OER were respectively 120, 90 and 44 mV/dec in acid electrolyte. In the alkaline electrolyte, they were 119, 87 and 42 mV/dec respectively on Pt, 50Pt-50RuO2 and 50Pt-50IrO2 electrodes indicating that for the prepared electrodes, Tafel slopes are the same in acid and in alkaline media. Moreover, in acid and in alkaline media, the kinetic of the oxygen evolution reaction was rapid on 50Pt-50RuO2 and 50Pt-50IrO2 than Pt owing to a synergetic effect of Pt and the oxides. That additional effect of the surface component 50Pt-50RuO2 and 50Pt-50IrO2 electrodes let them possess high electrocatalytic activity towards OER than Pt in the two media. Though the kinetic of the oxygen evolution reaction is practically the same in acidic and alkaline media for all the electrodes, OER occurred at lower overpotential in alkaline electrolyte than in acidic electrolyte on the prepared electrodes.

  5. HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, G.T.; Salvage, K.M. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil and Environmental Engineering; Gwo, J.P. [Oak Ridge National Lab., TN (United States); Zachara, J.M.; Szecsody, J.E. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-07-01

    The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.

  6. Mechanistic Studies on the Reaction of Nitrocobalamin with Glutathione: Kinetic evidence for formation of an aquacobalamin intermediate

    OpenAIRE

    Walker, David T.; Dassanayake, Rohan S.; Garcia, Kamille A.; Mukherjee, Riya; Brasch, Nicola E.

    2013-01-01

    The essential but also toxic gaseous signaling molecule nitric oxide is scavenged by the reduced vitamin B12 complex cob(II)alamin. The resulting complex, nitroxylcobalamin (NO−-Cbl(III)), is rapidly oxidized to nitrocobalamin (NO2Cbl) in the presence of oxygen; however it is unlikely that nitrocobalamin is itself stable in biological systems. Kinetic studies on the reaction between NO2Cbl and the important intracellular antioxidant, glutathione (GSH), are reported. In this study, a reaction ...

  7. Synthesis Of Magnesium-Aluminum Layered Double Hydroxides By Mechanochemical Method And Its Solid State Reaction Kinetics

    OpenAIRE

    Hongbo Y.; Meiling C.; Xiuhui W.; Hong G.

    2015-01-01

    A mechanochemical method is developed in preparing magnesium-aluminum-layered double hydroxides (MgAl-LDHs). This approach includes activation process and diffusion process. In order to verify the LDHs structure and study the reaction kinetics, X-ray diffraction (XRD) patterns, inductively coupled plasma(ICP) and physical adsorption instrument were characterized. The results show that activation time can change the surface of particles and affect the reaction grade. During the diffusion proce...

  8. Kinetic regimes and limiting cases of gas uptake and heterogeneous reactions in atmospheric aerosols and clouds: a general classification scheme

    Directory of Open Access Journals (Sweden)

    T. Berkemeier

    2013-01-01

    Full Text Available Heterogeneous reactions are important to atmospheric chemistry and are therefore an area of intense research. In multiphase systems such as aerosols and clouds, chemical reactions are usually strongly coupled to a complex sequence of mass transport processes and results are often not easy to interpret.

    Here we present a systematic classification scheme for gas uptake by aerosol or cloud particles which distinguishes two major regimes: a reaction-diffusion regime and a mass-transfer regime. Each of these regimes includes four distinct limiting cases, characterized by a dominant reaction location (surface or bulk and a single rate-limiting process: chemical reaction, bulk diffusion, gas-phase diffusion or mass accommodation.

    The conceptual framework enables efficient comparison of different studies and reaction systems, going beyond the scope of previous classification schemes by explicitly resolving interfacial transport processes and surface reactions limited by mass transfer from the gas phase. The use of kinetic multi-layer models instead of resistor model approaches increases the flexibility and enables a broader treatment of the subject, including cases which do not fit into the strict limiting cases typical of most resistor model formulations. The relative importance of different kinetic parameters such as diffusion, reaction rate and accommodation coefficients in this system is evaluated by a quantitative global sensitivity analysis. We outline the characteristic features of each limiting case and discuss the potential relevance of different regimes and limiting cases for various reaction systems. In particular, the classification scheme is applied to three different data sets for the benchmark system of oleic acid reacting with ozone. In light of these results, future directions of research needed to elucidate the multiphase chemical kinetics in this and other reaction systems are discussed.

  9. Kinetic regimes and limiting cases of gas uptake and heterogeneous reactions in atmospheric aerosols and clouds: a general classification scheme

    Directory of Open Access Journals (Sweden)

    T. Berkemeier

    2013-07-01

    Full Text Available Heterogeneous reactions are important to atmospheric chemistry and are therefore an area of intense research. In multiphase systems such as aerosols and clouds, chemical reactions are usually strongly coupled to a complex sequence of mass transport processes and results are often not easy to interpret. Here we present a systematic classification scheme for gas uptake by aerosol or cloud particles which distinguishes two major regimes: a reaction-diffusion regime and a mass transfer regime. Each of these regimes includes four distinct limiting cases, characterised by a dominant reaction location (surface or bulk and a single rate-limiting process: chemical reaction, bulk diffusion, gas-phase diffusion or mass accommodation. The conceptual framework enables efficient comparison of different studies and reaction systems, going beyond the scope of previous classification schemes by explicitly resolving interfacial transport processes and surface reactions limited by mass transfer from the gas phase. The use of kinetic multi-layer models instead of resistor model approaches increases the flexibility and enables a broader treatment of the subject, including cases which do not fit into the strict limiting cases typical of most resistor model formulations. The relative importance of different kinetic parameters such as diffusion, reaction rate and accommodation coefficients in this system is evaluated by a quantitative global sensitivity analysis. We outline the characteristic features of each limiting case and discuss the potential relevance of different regimes and limiting cases for various reaction systems. In particular, the classification scheme is applied to three different datasets for the benchmark system of oleic acid reacting with ozone in order to demonstrate utility and highlight potential issues. In light of these results, future directions of research needed to elucidate the multiphase chemical kinetics in this and other reaction systems

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  11. Reaction kinetics of free fatty acids esterification in palm fatty acid distillate using coconut shell biochar sulfonated catalyst

    Science.gov (United States)

    Hidayat, Arif; Rochmadi, Wijaya, Karna; Budiman, Arief

    2015-12-01

    Recently, a new strategy of preparing novel carbon-based solid acids has been developed. In this research, the esterification reactions of Palm Fatty Acid Distillate (PFAD) with methanol, using coconut shell biochar sulfonated catalyst from biomass wastes as catalyst, were studied. In this study, the coconut shell biochar sulfonated catalysts were synthesized by sulfonating the coconut shell biochar using concentrated H2SO4. The kinetics of free fatty acid (FFA) esterification in PFAD using a coconut shell biochar sulfonated catalyst was also studied. The effects of the mass ratio of catalyst to oil (1-10%), the molar ratio of methanol to oil (6:1-12:1), and the reaction temperature (40-60°C) were studied for the conversion of PFAD to optimize the reaction conditions. The results showed that the optimal conditions were an methanol to PFAD molar ratio of 12:1, the amount of catalyst of 10%w, and reaction temperature of 60°C. The proposed kinetic model shows a reversible second order reaction and represents all the experimental data satisfactorily, providing deeper insight into the kinetics of the reaction.

  12. Dominant particles and reactions in a two-temperature chemical kinetic model of a decaying SF6 arc

    Science.gov (United States)

    Wang, Xiaohua; Gao, Qingqing; Fu, Yuwei; Yang, Aijun; Rong, Mingzhe; Wu, Yi; Niu, Chunping; Murphy, Anthony B.

    2016-03-01

    This paper is devoted to the computation of the non-equilibrium composition of an SF6 plasma, and determination of the dominant particles and reactions, at conditions relevant to high-voltage circuit breakers after current zero (temperatures from 12 000 K to 1000 K and a pressure of 4 atm). The non-equilibrium composition is characterized by departures from both thermal and chemical equilibrium. In thermal non-equilibrium process, the electron temperature (T e) is not equal to the heavy-particle temperature (T h), while for chemical non-equilibrium, a chemical kinetic model is adopted. In order to evaluate the reasonableness and reliability of the non-equilibrium composition, calculation methods for equilibrium composition based on Gibbs free energy minimization and kinetic composition in a one-temperature kinetic model are first considered. Based on the one-temperature kinetic model, a two-temperature kinetic model with the ratio T e/T h varying as a function of the logarithm of electron density ratio (n e/n\\text{e}\\max ) was established. In this model, T* is introduced to allow a smooth transition between T h and T e and to determine the temperatures for the rate constants. The initial composition in the kinetic models is obtained from the asymptotic composition as infinite time is approached at 12 000 K. The molar fractions of neutral particles and ions in the two-temperature kinetic model are consistent with the equilibrium composition and the composition obtained from the one-temperature kinetic model above 10 000 K, while significant differences appear below 10 000 K. Based on the dependence of the particle distributions on temperature in the two-temperature kinetic model, three temperature ranges, and the dominant particles and reactions in the respective ranges, are determined. The full model is then simplified into three models and the accuracy of the simplified models is assessed. The simplified models reduce the number of species and

  13. Chemical kinetics

    International Nuclear Information System (INIS)

    This book gives descriptions of chemical kinetics. It starts summary of chemical kinetics and reaction mechanism, and explains basic velocity law, experiment method for determination of reaction velocity, temperature dependence of reaction velocity, theory of reaction velocity, theory on reaction of unimolecular, process of atom and free radical, reaction in solution, catalysis, photochemical reaction, such as experiment and photochemical law and rapid reaction like flame, beam of molecule and shock tube.

  14. Thermodynamics and kinetics of reactions involving vanadium in natural systems: Accumulation of vanadium in sedimentary rocks

    Science.gov (United States)

    Wanty, R.B.; Goldhaber, M.B.

    1992-01-01

    A critical review of thermodynamic data for aqueous and solid V species is presented to evaluate dissolution, transport, and precipitation of V under natural conditions. Emphasis is given to results of experimental studies of V chemistry, especially those for which the experimental conditions are near those found in nature. Where possible, data are obtained for or corrected to the reference conditions of 298.15K, 1 atm (1.01325 bar) and zero ionic strength. Vanadium [IV] (VIV) and vanadium[V] (VV) are the most soluble forms of V in nature, and their complexes with fluoride, sulfate, and oxalate may act to increase V solubility under oxidizing conditions. Because redox behavior is of fundamental importance to understanding natural V chemistry, the kinetics of reduction of VIV to VIII H2S were studied. Although H2S is predicted from thermodynamic data to be capable of reducing VIV to VIII, this reaction has not been demonstrated experimentally. Experiments were carried out under conditions of temperature (45??C), pH (3.6-6.8), ionic strength (0.05-0.1 m), and V concentrations (9.8-240 ??molar) likely to be found in nature. Because the reaction is very slow, H2S concentrations in excess of natural conditions were used (8.1 ?? 10-4 to 0.41 atm). The results show that VIV is reduced to VIII under a variety of conditions. The rate increases with increasing pH, but is not appreciably affected by ionic strength (as represented by the concentration of KCl, which was used as the supporting electrolyte in all cases). Prior to initiation of the reaction, there is an induction period, the length of which increases with increasing KCl concentration or decreasing pH. Attempts to model the reaction mechanism by numerical methods have failed to produce a satisfying fit of the results, indicating partial reaction orders, a complex mechanism, or involvement of a variety of intermediate species. The results of the thermodynamic and kinetic studies were applied to understanding the

  15. In situ synchrotron powder diffraction study of the setting reaction kinetics of magnesium-potassium phosphate cements

    Czech Academy of Sciences Publication Activity Database

    Viani, Alberto; Pérez-Estébanez, Marta; Pollastri, S.; Gualtieri, A. F.

    2016-01-01

    Roč. 79, January (2016), s. 344-352. ISSN 0008-8846 R&D Projects: GA MŠk(CZ) LO1219 Keywords : kinetics * reaction * X-ray diffraction * MgO * chemically bonded ceramics Subject RIV: JN - Civil Engineering Impact factor: 2.864, year: 2014 http://www.sciencedirect.com/science/article/pii/S0008884615002690

  16. LSENS: A General Chemical Kinetics and Sensitivity Analysis Code for homogeneous gas-phase reactions. Part 3: Illustrative test problems

    Science.gov (United States)

    Bittker, David A.; Radhakrishnan, Krishnan

    1994-01-01

    LSENS, the Lewis General Chemical Kinetics and Sensitivity Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 3 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 3 explains the kinetics and kinetics-plus-sensitivity analysis problems supplied with LSENS and presents sample results. These problems illustrate the various capabilities of, and reaction models that can be solved by, the code and may provide a convenient starting point for the user to construct the problem data file required to execute LSENS. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions.

  17. Kinetic Analysis of Parallel-Consecutive First-Order Reactions with a Reversible Step: Concentration-Time Integrals Method

    Science.gov (United States)

    Mucientes, A. E.; de la Pena, M. A.

    2009-01-01

    The concentration-time integrals method has been used to solve kinetic equations of parallel-consecutive first-order reactions with a reversible step. This method involves the determination of the area under the curve for the concentration of a given species against time. Computer techniques are used to integrate experimental curves and the method…

  18. Reaction Kinetics of Acetone Peroxide Formation and Structure Investigations Using Raman Spectroscopy and X-ray Diffraction

    DEFF Research Database (Denmark)

    Jensen, Lars; Mortensen, Peter Mølgaard; Trane, Rasmus;

    2009-01-01

    Triacetone triperoxide (TATP) has been prepared in order to study the effect of pH and temperature on the reaction kinetics. Raman spectra of liquid mixtures of acetone and hydrogen peroxide were recorded versus time throughout the experiments. The spectral data of the liquid phases indicate that...

  19. Asymmetric Synthesis of 1,3-Oxazolidine Derivatives with Multi-Component Reaction and Research of Kinetic Resolution

    Directory of Open Access Journals (Sweden)

    Xiao-Wei Hong

    2015-09-01

    Full Text Available An efficient multi-component reaction to synthesize multi-substituted 1,3-oxazolidine compounds of high optical purity was described. All the products were well-characterized and the absolute configuration of one chiral center was determined. The plausible mechanism was proposed and a kinetic resolution of epoxides process was confirmed.

  20. Kinetic Model of Biomass Pyrolysis Based on Three-component Independent Parallel First-order Reactions

    Institute of Scientific and Technical Information of China (English)

    王新运; 万新军; 陈明强; 王君

    2012-01-01

    The pyrolysis behavior of two kinds of typical biomass (pine wood and cotton stalk) was studied in nitrogen atmosphere at various heating rates by thermogravimetric analysis (TGA).The pyrolysis process can be divided into three stages:evolution of moisture (<200 ℃),devolatilization (200~400 ℃) and carbonization (>400 ℃).The comparison of DTG curves of two biomass materials show that the higher the hemicellulose content of biomass,the more evident the shoulder peak of DTG curve.The weight loss process of two materials was simulated by the kinetic model assuming cellulose,hemicellulose and lignin pyrolyzing independently and in parallel,obeying first-order reactions.The pyrolysis kinetic parameters corresponding to the three components were estimated by the nonlinear least square algorithm.The results show that their fitting curves are in good agreement with the experimental data.Their activation energy values for pine wood and cotton stalk are in the range of 188~215,90~102,29~49 and 187~214,95~101,30~38 kJ/mol,respectively.The corresponding pre-exponential factors are in the range of 1.8×1015~2.0×1016,1.6×107~7.1×108,9.3×101~l.5×103 and 1.2× 1015~6.7×1017,1.2× 108~1.4×109,1.4× 102~4.6× 102 min-1,respectively.In addition,the activation energy of cellulose and lignin increased and their contributions to volatile tended to fall,whereas the activation energy of herricellulose decreased and its contribution to volatile tended to rise with increasing of heating rate.

  1. Prediction and validation of burnout curves for Goettelborn char using reaction kinetics determined in shock tube experiments

    Energy Technology Data Exchange (ETDEWEB)

    Moors, J.H.J.; Banin, V.E.; Haas, J.H.P.; Weber, R.; Veefkind, A. [Eindhoven University of Technology, Eindhoven (Netherlands). Dept. of Applied Physics

    1999-01-01

    Using a shock tube facility the combustion characteristics of pulverised char ({lt} 10 {mu}m) were measured. A prediction was made for the burnout behaviour of a commercial sized char particle (75-90 {mu}m) in different ambient conditions using a `pseudo kinetic` approach. In this approach the kinetic rate of a surface containing micro pores is determined and these `pseudo kinetics` are then applied to the larger particle not taking into account the micro pores. Comparison of the predictions with measurements done with an isothermal plug flow reactor showed this approach to be valid within experimental error for low burnout. A linear decrease of the kinetic reaction rate with burnout is shown to predict the burnout behaviour in the complete range of burnout. A possible explanation for this linear decrease could be a growing fraction of non-combustible material in the char particles during burnout. 11 refs., 6 figs., 2 tabs.

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

    CERN Document Server

    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...

  3. Kinetics of isotopic exchange reaction between hydrogen and water vapor over hydrophobic catalyst in a Co-current bed

    International Nuclear Information System (INIS)

    The kinetics of isotopic exchange reaction between hydrogen and water vapor over Pt- SDB as a hydrophobic catalyst was investigated in a fixed co-current bed. The influence of vari- ous factors on the rate constant of water vapor-hydrogen co-current exchange reaction were studied, including rate equation, order of reaction, temperature dependence of reaction and the species of catalysts. The results show that the overall reaction is first order. The relation of apparent rate constant with temperature accorded with Arrhenius and the apparent rate constant increases with temperature rising. The apparent activation energy of Pt-SDB is lower than Pt-C-PTFE and the rate constant of water vapor-hydrogen co-current exchange reaction increases when the apparent activation energy of the hydrophobic catalyst decreases. (authors)

  4. The Effect of Kinetic Energy on the Reactions of Nucleogenic Carbon Atoms with Hydrocarbons

    International Nuclear Information System (INIS)

    The basic technique for studying the effect of kinetic energy on reactions of C atoms produced by nuclear transformation involves the well-known method of moderation with inert gases. However, this can be combined with other techniques such as (1) the use of scavengers to detect processes involving long- lived radicals, (2) degradative studies that serve to fix the position occupied by the labelled atom, (3) double tracer studies in which a reactant is partially labelled with deuterium and the isotopic composition of the labelled products is determined in order to establish the origin of the hydrogen which they contain. In this paper new results on product yields in two systems, neon-ethylene and neon-ethane, will be presented, and the relation of these results to other work involving degradative studies and double tracer experiments will be discussed. The discussion of the neon-ethylene results is in terms of the two previously postulated insertion mechanisms, insertion of the C atom into the C = C and into the C-H bonds to give C-C2H4 adducts, As neon concentration is increased no product is eliminated, but the relative yields of products are altered markedly. Those products such as acetylene and vinyl acetylene which can be formed from the initial C-C2H4 adducts via processes with a high energy requirement decrease in importance, and the yields of products formed in low energy processes, such as C5 compounds, increase. The ethane pattern is similar. Degradative studies have already shown that the intramolecular C11 distribution in allene and methyl- acetylene formed from ethylene is affected by neon moderation. These results imply both participation of the C = C and C-H bonds in formation of these products, and a dependence of the ratio of attack at the two bond types on the kinetic energy of the reacting C atom. Other work involving double tracer studies on acetylene formation from single molecules such as CH2CD2, CH3CH2D, CD9CDH2 and from various mixtures of

  5. The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading

    International Nuclear Information System (INIS)

    Highlights: • Detailed analysis of cyclic and monotonic loading of thermochemical heat stores. • Fully coupled reactive heat and mass transport. • Reaction kinetics can be simplified in systems limited by heat transport. • Operating lines valid during monotonic and cyclic loading. • Local integral degree of conversion to capture heterogeneous material usage. - Abstract: Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a reactor level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the reactor level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the reactor behaviour. The degree of material usage within the reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes

  6. The kinetics of the photo-induced solid-state chemical reaction in Ag/As33S67 bilayers and its reaction products

    Science.gov (United States)

    Wagner, T.; Marquez, E.; Fernandez-Pena, J.; Gonzalez-Leal, J. M.; Ewen, P. J. S.; Kasap, S. O.

    1999-02-01

    The kinetics of the photo-induced solid-state chemical reaction of silver with amorphous As33S67 films in a conventional sandwich structure was measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflection technique. The reaction between silver and the chalcogenide layer was induced by an Ar-ion laser. The Ag As33S67 sample was illuminated by the laser beam coming from the chalcogenide side of the sample. The consumption of the elemental silver source in the course of the reaction was monitored by the simultaneous measurement of the electrical resistance of the silver layer. The kinetic data obtained show that there are two stages in the photoreaction process, with the second stage having a sublinear dependence. The exhaustion of the elemental silver source in the course of the reaction does not significantly influence the reaction rate. The reaction rates characterizing each stage have been measured, and a comparison of the composition and structure has been made. All the structure-sensitive parameters, Tg, Cp and Delta Cp, measured by the temperature modulated differential scanning calorimetry (MDSC) technique, show a change in the structure of As33S67 as silver is introduced by photodoping or in melt-quenched Ag-As-S glasses. Further, by using far-infrared spectroscopy it was possible to correlate the MDSC results to the structure of As33S67 and Ag-As-S glasses.

  7. Experimental study of the reaction kinetics between CO2-bearing solution and picrite cubes

    Science.gov (United States)

    Zhang, S.; Wang, Z.; Qiu, L.; Karato, S.; Johnson, K. T.; Ague, J. J.; Oristaglio, M. L.; Bolton, E. W.; Bercovici, D. A.

    2013-12-01

    Shuang Zhang1*, Zhengrong Wang1, Lin Qiu1, Shun-ichiro Karato1, Kevin Johnson2, Jay Ague1, Michael Oristaglio1, Edward Bolton1, and David Bercovici1 1Department of Geology and Geophysics and Energy Science Institute, Yale University, New Haven, CT 06520, USA 2Department of Geology and Geophysics, University of Hawai';i at Mānoa, Honolulu, HI 96822, USA *presenting author: shuang.zhang@yale.edu Picrites are potential repositories for permanent storage of anthropogenic CO2 because they contain large amounts of olivine which dissolves faster than other coexisting minerals (e.g., clinopyroxene or plagioclase), and they have relatively higher porosity and permeability than ultramafic rocks. In order to understand the kinetics of reacting CO2-bearing fluid with picrites and its carbonation potential, this study investigated the reactions between CO2-bearing solution and picrite cubes under various experimental conditions, including temperature, the concentration of DIC, reaction time and water/rock ratio. Hawaiian picrite cubes (~ 4 mm × 4 mm) and different concentrations of NaHCO3 solution (0.5 M, 1 M, and 3 M) were sealed in gold capsules and placed in an autoclave at 100-200 oC for 5-10 days. After each run, the solids were dried and characterized by Scanning Electron Microprobe (SEM) and Electron Probe Micro Analyzer (EPMA). The coexisting solutions were titrated to quantify the consumption of dissolved inorganic carbon (DIC) during the carbonation process. Several phenomena have been observed from these experiments. First, high concentrations of DIC can significantly raise the carbonation fraction ((Mg+Fe+Ca (consumed by carbonate))/(Mg+Fe+Ca (in picrite before reaction))×100%) in these experiments. For example, the carbonation fraction (~ 0.5%) is negligible using the 0.5 or 1 M NaHCO3 even in experiments conducted at 200 oC for 10 days, but is significantly higher (~ 10%) than the detection limit of our titration method (0.5%) for 3 M NaHCO3. Second, most

  8. Iron Reduction and Radionuclide Immobilization: Kinetic, Thermodynamic and Hydrologic controls & Reaction-Based Modeling - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    William D. Burgos

    2004-06-18

    that the hydrated surface of nano-particles of hematite (prepared according to well-cited recipes and confirmed to be 100% hematite by Mossbauer spectroscopy and XRD) exhibited the solubility of hydrous ferric oxide (HFO). Jang (2004) also demonstrated that the sorptive reactivity of hematite and HFO were identical except for different specific surface area and pHzpc, and that the reduction of U(VI) by sorbed Fe(II) in the presence of the two phases was also similar in spite of theoretical predictions of large differences in Nernst potential. These results are consistent with the modeling of hematite bioreduction experiments where the thermodynamic potential of hematite had to be adjusted to represent a more disordered surface phase in order to accurately model bioreduction kinetics (Burgos et al, 2002, 2003). We have demonstrated that humic substances enhance solid-phase Fe(III) bioreduction via both electron shuttling and Fe(II) complexation(Royer et al, 2002a, b). We have found that humic substances were shown to inhibit the bioreduction of dissolved U(VI) and that soluble humic-U(IV) complexes were likely formed (Burgos et al, 2004). Kirkham (2004) measured and modeled complexation of U(VI) by humic substances as a function of pH, pCO2, U(VI) concentration, and humic concentration, and demonstrated that humic substances can complex U(VI) even at neutral pH values and in the presence of high (ca.30 mM) carbonate concentrations. Jang(2004) measured the abiotic reduction of U(VI) by Fe(II) sorbed to Fe(III) oxides in the presence/absence of humic substances and demonstrated that humic substances inhibited the heterogeneous reduction of U(VI). We have recently developed, validated, and documented a series of diagonalized reaction-based reactive transport computer models (HYDROGEOCHEM; Yeh et al,2004a,b). We demonstrated that parallel kinetic reactions could be modeled if separate experiments are used to independently measure each contributing kinetic reaction (Burgos

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

    Science.gov (United States)

    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

  10. Kinetics of formation of a platelet-reinforced ceramic composite prepared by the directed reaction of zirconium with boron carbide

    International Nuclear Information System (INIS)

    In this paper the kinetics of formation of a new class of ceramic composite material, zirconium diboride platelet-reinforced zirconium carbides, are discussed. These materials are prepared by the directed reaction of molten zirconium with boron carbide to form a ceramic material composed of zirconium diboride platelets approximately uniformly distributed in a zirconium carbide matrix containing a controlled amount of residual zirconium metal. Results from interrupted growth studies, differential thermal analysis, adiabatic reaction temperature calculations, and kinetic measurements have been used to study the kinetics of the process. The reaction is very fast and proceeds parabolically with time with a rate constant between 1.6 x 10-2 and 3.9 x 10-2 cm2/s. The proposed mechanism suggests that when molten zirconium contacts boron carbide, the molten zirconium exothermically reacts with the boron carbide to form a boron-rick liquid. Further reaction is sustained by the continuous dissolution of the boron carbide as the boron-rich liquid is drawn into the boron carbide. The product is a zirconium diboride/zirconium carbide/zirconium composite which homogenizes quickly at the reaction temperature to yield a uniform product microstructure throughout the composite. Two alternative rate-limiting steps are discussed and the implications of each are explored

  11. Modeling of reaction kinetics in bubbling fluidized bed biomass gasification reactor

    Energy Technology Data Exchange (ETDEWEB)

    Thapa, R.K.; Halvorsen, B.M. [Telemark University College, Kjolnes ring 56, P.O. Box 203, 3901 Porsgrunn (Norway); Pfeifer, C. [University of Natural Resources and Life Sciences, Vienna (Austria)

    2013-07-01

    Bubbling fluidized beds are widely used as biomass gasification reactors as at the biomass gasification plant in Gussing, Austria. The reactor in the plant is a dual circulating bubbling fluidized bed gasification reactor. The plant produces 2MW electricity and 4.5MW heat from the gasification of biomass. Wood chips as biomass and olivine particles as hot bed materials are fluidized with high temperature steam in the reactor. As a result, biomass undergoes endothermic chemical reaction to produce a mixture of combustible gases in addition to some carbon-dioxide (CO2). The combustible gases are mainly hydrogen (H2), carbon monoxide (CO) and methane (CH4). The gas is used to produce electricity and heat via utilization in a gas engine. Alternatively, the gas is further processed for gaseous or liquid fuels, but still on the process of development level. Composition and quality of the gas determine the efficiency of the reactor. A computational model has been developed for the study of reaction kinetics in the gasification rector. The simulation is performed using commercial software Barracuda virtual reactor, VR15. Eulerian-Lagrangian approach in coupling of gas-solid flow has been implemented. Fluid phase is treated with an Eulerian formulation. Discrete phase is treated with a Lagrangian formulation. Particle-particle and particle-wall interactions and inter-phase heat and mass transfer have been taken into account. Series of simulations have been performed to study model prediction of the gas composition. The composition is compared with data from the gasifier at the CHP plant in Güssing, Austria. The model prediction of the composition of gases has good agreements with the result of the operating plant.

  12. Electrodeposited ultrafine TaOx/CB catalysts for PEFC cathode application: Their oxygen reduction reaction kinetics

    KAUST Repository

    Seo, Jeongsuk

    2014-12-01

    Ultrafine TaOx nanoparticles were electrodeposited on carbon black (CB) powder in a nonaqueous Ta complex solution at room temperature, and the resultant TaOx/CB catalysts were assessed as oxygen reduction reaction (ORR) electrocatalysts for polymer electrolyte fuel cell (PEFC) cathodes. The Ta electrodeposition process was scaled up using a newly designed working electrode containing a CB dense layer, without introducing any binder such as the ionomer Nafion in the electrode for electrodeposition. The electrodeposited TaOx/CB powders were removed from the deposition electrode and subsequent H2 treatment at varying temperatures between 523 and 1073 K was attempted to increase the ORR performance. The TaOx/CB samples were characterized by SEM, STEM, XPS, and EELS measurements. XPS and EELS results indicated the reduced nature of the Ta species caused by the high-temperature treatment in H2, while STEM images clearly revealed that the TaOx particles aggregated as the treatment temperature increased. When the TaOx/CB catalyst, which was treated at 873 K for 2 h, was deposited on a glassy carbon substrate with Nafion ionomer, it resulted in the highest activity among the samples investigated, giving an onset potential of 0.95 VRHE at -2 μA cm-2 in a 0.1 M H2SO4 solution. Moreover, the long-term stability test with 10,000 cycles of the voltammetry only led to a 6% loss in the ORR currents, demonstrating the high stability of the TaOx/CB catalysts. Kinetic analysis by R(R)DE indicated that the four-electron transfer pathway in the ORR process was dominant for this TaOx/CB catalyst, and Tafel plots showed a slope corresponding to a one-electron reaction for the rate-determining step.

  13. Kinetics and Mechanism of the Thermal Decomposition Reaction of 3,3-Bis(azidomethyl)oxetane/Tetrahydrofuran Copolymer

    Institute of Scientific and Technical Information of China (English)

    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

  14. Mechanistic and full Kinetic Study of the reaction between 4-chlorobenzaldehyde, malononitrile and dimedone using caffeine as a green catalyst

    Directory of Open Access Journals (Sweden)

    Halimeh Yaghoubian

    2015-12-01

    Full Text Available This article was conducted to investigate spectrophotometrically the kinetic and mechanism of the reaction synthesis of tetrahydrobenzo[b] pyrans via one-pot, three-component condensation of malononitrile, dimedone and 4-chlorobenzaldehyde in the presence of caffeine, as a new green catalyst. The effect of various parameters such as temperature, solvent, concentration and catalyst was determined. Pursuant to obtained data the reaction rate was obeyed second order kinetics and automatically calculated rate constants were in agreement with the Arrhenius and Eyring equations. From these the activation parameters (Ea, ΔG‡, ΔS‡, and ΔH‡ were determined. Also, in a mixture of water: ethanol (2:1, the rate constant was increased with respect to ethanol solvent that has lower dielectric constant. Furthermore, experimental data and steady state approximation corroborated the proposed mechanism. The results showed that the first step of the reaction mechanism is a rate determining step (RDS.

  15. Stereodynamical Origin of Anti-Arrhenius Kinetics: Negative Activation Energy and Roaming for a Four-Atom Reaction.

    Science.gov (United States)

    Coutinho, Nayara D; Silva, Valter H C; de Oliveira, Heibbe C B; Camargo, Ademir J; Mundim, Kleber C; Aquilanti, Vincenzo

    2015-05-01

    The OH + HBr → H2O + Br reaction, prototypical of halogen-atom liberating processes relevant to mechanisms for atmospheric ozone destruction, attracted frequent attention of experimental chemical kinetics: the nature of the unusual reactivity drop from low to high temperatures eluded a variety of theoretical efforts, ranking this one among the most studied four-atom reactions. Here, inspired by oriented molecular-beams experiments, we develop a first-principles stereodynamical approach. Thermalized sets of trajectories, evolving on a multidimensional potential energy surface quantum mechanically generated on-the-fly, provide a map of most visited regions at each temperature. Visualizations of rearrangements of bonds along trajectories and of the role of specific angles of reactants' mutual approach elucidate the mechanistic change from the low kinetic energy regime (where incident reactants reorient to find the propitious alignment leading to reaction) to high temperature (where speed hinders adjustment of directionality and roaming delays reactivity). PMID:26263312

  16. Thermodynamic and kinetic study on interfacial reaction and diamond graphitization of Cu-Fe-based diamond composite

    Institute of Scientific and Technical Information of China (English)

    Li Wen-Sheng; Zhang Jie; Dong Hong-Feng; Chu Ke; Wang Shun-Cai; Liu Yi; Li Ya-Ming

    2013-01-01

    Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressureassisted sintering.The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu-Fe matrix.The interfacial reactions between diamond/graphite and Cr or Ti,and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods.The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically.The Cr3C2,Cr7C3,Cr23C6,and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.

  17. The role of high temperature heterogeneous reaction kinetics in the rate of radionuclide vaporisation during core-concrete interactions

    International Nuclear Information System (INIS)

    Heterogeneous reactions may cause enhanced release of radionuclides during the core-concrete interaction (CCl) stage of a PWR severe accident. The VANESA computer code models these CCI releases using chemical equilibrium assumptions; however, the possibility that chemical kinetics could prevent equilibrium from being achieved is considered in this report. Direct experimental evidence is lacking on these reactions. Therefore, some analogues studies are reviewed, including examples of Eyring's surface reaction rate theory; sequential vaporisation-oxidation processes; iron and steelmaking chemistry; radionuclide evaporation from solid UO2. This circumstantial evidence appeared to agree with the current assumptions, in VANESA and some UK modelling studies, that mass transfer, rather than chemical kinetics will limit the rate at which equilibrium is attained. (author)

  18. Laccase-catalyzed removal of the antimicrobials chlorophene and dichlorophen from water: Reaction kinetics, pathway and toxicity evaluation.

    Science.gov (United States)

    Shi, Huanhuan; Peng, Jianbiao; Li, Jianhua; Mao, Liang; Wang, Zunyao; Gao, Shixiang

    2016-11-01

    As active agents in cleaning and disinfecting products, antimicrobials have been widely spread in the environment and have drawn extensive attention as potential threats to the ecological system and human health. In this study, the laccase-catalyzed removal of two emerging antimicrobials, chlorophene (CP) and dichlorophen (DCP), was investigated under simulated environmental conditions. Intrinsic reaction kinetics showed that the removal of CP and DCP followed second-order reaction kinetics, first-order with respect to both the enzyme and the substrate concentration. It was also found that fulvic acid could suppress the transformation of CP and DCP by reversing the oxidation reactions through its action as a scavenger of the free radical intermediates produced from reactions between laccase and the substrates. Several reaction products were identified by a quadrupole time-of-flight mass spectrometer, and detailed reaction pathways were proposed. For both CP and DCP, direct polymerization was the principal pathway, and the coupling patterns were further corroborated based on molecular modeling. The nucleophilic substitution of chlorine by the hydroxyl group was observed, and further oxidation products capable of coupling with each other were also found. Additionally, toxicity evaluation tests using Scenedesmus obliquus confirmed that the toxicity of CP and DCP was effectively eliminated during the reaction processes. PMID:27262275

  19. On kinetics of reactions in HV circuit breakers after current zero

    Science.gov (United States)

    Adamec, L.; Coufal, O.

    1999-07-01

    An analysis of six different definitions of the rate of reaction is made and it is shown that some of the definitions are not consistent with the mass action law. Kinetic equations are derived whose solution is the time dependence of the composition of an arbitrary closed gaseous system icons/Journals/Common/calS" ALT="calS" ALIGN="TOP"/> in an ideal state for a given time dependence of temperature on the assumption that either the time dependence of pressure in icons/Journals/Common/calS" ALT="calS" ALIGN="TOP"/> or the time dependence of the volume of icons/Journals/Common/calS" ALT="calS" ALIGN="TOP"/> is given. Results are given of the computation of composition of a system of SF6 dissociation and ionization products at a temperature drop from 12 000 K to room temperature and a comparison is made of the time-dependent composition with equilibrium composition for pressures of 0.1, 0.5, 1 and 2 MPa.

  20. Thermodynamics and kinetics of internal reactions: nitridation of Ni-Cr alloys

    International Nuclear Information System (INIS)

    The implementation of Wagner's theory of internal precipitation for evaluating nitriding kinetics has been discussed. Nitriding experiments on Ni-Cr alloys were carried out in the range of 1-6000 bar of hydrostatic N2-pressure and under a flowing NH3+H2 gas mixture at 873-1398 K. When a moderately stable phase is precipitated out during an internal reaction, the behaviour of the penetrating atoms within the diffusion zone can be interpreted based on thermodynamic considerations. The thermodynamic assessment of the Ni-Cr-N system was performed using the Thermo-Calc databank and the results were verified experimentally. However, ''up-hill'' diffusion of the penetrating species through the matrix towards the precipitation front can be predicted in certain cases and then Wagner's treatment cannot be utilised. It was demonstrated that under suitable experimental conditions of solute content, temperature and external activity of the penetrating element, Wagner's analysis can be applied to internal precipitation process in any material system. (orig.)

  1. Influence of reaction kinetics and mesh refinement on the numerical modelling of concrete/clay interactions

    Science.gov (United States)

    Marty, Nicolas C. M.; Tournassat, Christophe; Burnol, André; Giffaut, Eric; Gaucher, Eric C.

    2009-01-01

    SummaryLarge quantities of cements and concretes need to be incorporated in geological disposal facilities for long-lived radwaste. An alkaline plume diffusing from an aged concrete (pH ˜ 12.5) through argillite-type rocks has been modelled considering feedback of porosity value variations on transport properties using the reactive transport code TOUGHREACT. The mineralogical composition of the argillite is modified at the interface with the concrete. Diffusion of cementitious elements leads to rapid and strong porosity occlusion in the argillite. Numerical results show that both reaction rates and spatial refinement affect mineralogical transformation pathways. The variations in porosity and the extension of the zone affected by the alkaline perturbation are compared at different times. The major effects of mineral precipitation under kinetic constraints, rather than local equilibrium, are a delay in the porosity clogging and an increase in the extension of the alkaline perturbation in the clay formation. The same time-delay rise for the porosity occlusion also appears for the roughest spatial resolutions. A simulation as representative as possible of temporal and spatial scales of cementation processes must then be supported by more comparative data such as long term experimental investigations or natural analogues.

  2. Influence of surface acoustic waves induced acoustic streaming on the kinetics of electrochemical reactions

    Science.gov (United States)

    Tietze, Sabrina; Schlemmer, Josefine; Lindner, Gerhard

    2013-12-01

    The kinetics of electrochemical reactions is controlled by diffusion processes of charge carriers across a boundary layer between the electrode and the electrolyte, which result in a shielding of the electric field inside the electrolyte and a concentration gradient across this boundary layer. In accumulators the diffusion rate determines the rather long time needed for charging, which is a major drawback for electric mobility. This diffusion boundary can be removed by acoustic streaming in the electrolyte induced by surface acoustic waves propagating of the electrode, which results in an increase of the charging current and thus in a reduction of the time needed for charging. For a quantitative study of the influence of acoustic streaming on the charge transport an electropolishing cell with vertically oriented copper electrodes and diluted H3PO4-Propanol electrolytes were used. Lamb waves with various excitation frequencies were exited on the anode with different piezoelectric transducers, which induced acoustic streaming in the overlaying electrolytic liquid. An increase of the polishing current of up to approximately 100 % has been obtained with such a set-up.

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

    Science.gov (United States)

    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

  4. Low-temperature oxidation of alkali overlayers: Ionic species and reaction kinetics

    International Nuclear Information System (INIS)

    Clean and oxidized alkali metal films have been studied using X-ray photoelectron spectroscopy (XPS). Thin films, typically 10 nm thick, of lithium, sodium, potassium, rubidium and cesium have been deposited on silicon substrates and oxidized at 120 K. Plasmon losses were found to dress the primary photo emission structures of the metals’ core lines which confirms the metallic, bulk like nature of the films. The emission from the O 1s core levels was used to determine the chemical composition and the reaction kinetics during the exposure to molecular oxygen at low pressures. Molecular oxide ions O2− and O22− as well as atomic oxygen ions O2− were detected in varying amounts depending on the alkali metal used. Diffusive transport of material in the film is shown to greatly determine the composition of the oxides. Especially, the growth of potassium superoxide is explained by the diffusion of potassium atoms to the surface and growth at the surface in a Deal–Grove like model.

  5. Kinetic and isotopic studies of the oxidative half-reaction of phenol hydroxylase.

    Science.gov (United States)

    Taylor, M G; Massey, V

    1991-05-01

    Phenol hydroxylase, an FAD-containing monooxygenase, catalyzes the conversion of substituted phenols to the corresponding catechol. Use of metapyrocatechase, capable of dioxygenation of several catechols to give highly absorbing products, permitted determination of the time course of product release from phenol hydroxylase. Product dissociated prior to complete reoxidation of the enzyme, most likely concomitant with formation of the 4a-hydroxyflavin species (intermediate III). Deuterated phenol and thiophenol exhibited no kinetic isotope effect during the oxidative half-reaction. Isotope effects of 1.7 to 3.7 were found with resorcinol for the conversion of the second intermediate to intermediate III. These effects limited the possible models for phenol hydroxylation. An attempt was made to distinguish whether the spectrum of intermediate II is due entirely to that of the flavin moiety of phenol hydroxylase or whether some radical intermediate form involved in the formation of catechol makes a significant visible contribution. Reduced native and 6-hydroxy-FAD phenol hydroxylase were reacted with oxygen and resorcinol in order to provide evidence for the identity of intermediate II. PMID:2022646

  6. Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetic, and Rate Rule Optimizations for 2-Methylhexane

    KAUST Repository

    Mohamed, Samah Y

    2016-03-21

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxy-alkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model’s performance. The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model.

  7. Influence of chemical kinetics on postcolumn reaction in a capillary Taylor reactor with catechol analytes and photoluminescence following electron transfer.

    Science.gov (United States)

    Jung, Moon Chul; Weber, Stephen G

    2005-02-15

    Postcolumn derivatization reactions can enhance detector sensitivity and selectivity, but their successful combination with capillary liquid chromatography has been limited because of the small peak volumes in capillary chromatography. A capillary Taylor reactor (CTR), developed in our laboratory, provides simple and effective mixing and reaction in a 25-microm-radius postcolumn capillary. Homogenization of reactant streams occurs by radial diffusion, and a chemical reaction follows. Three characteristic times for a given reaction process can be predicted using simple physical and chemical parameters. Two of these times are the homogenization time, which governs how long it takes the molecules in the analyte and reagent streams to mix, and the reaction time, which governs how long the molecules in a homogeneous solution take to react. The third characteristic time is an adjustment to the reaction time called the start time, which represents an estimate of the average time the analyte stream spends without exposure to reagent. In this study, laser-induced fluorescence monitored the extent of the postcolumn reaction (reduction of Os(bpy)3(3+) by analyte to the photoluminescent Os(bpy)3(2+)) in a CTR. The reaction time depends on the reaction rates. Analysis of product versus time data yielded second-order reaction rate constants between the PFET reagent, tris(2,2'-bipyridine)osmium, and standards ((ferrocenylmethyl)trimethylammonium cation and p-hydroquinone) or catechols (dopamine, epinephrine, norepinephrine, 3, 4-dihydroxyphenylacetic acid. The extent of the reactions in a CTR were then predicted from initial reaction conditions and compared to experimental results. Both the theory and experimental results suggested the reactions of catechols were generally kinetically controlled, while those of the standards were controlled by mixing time (1-2 s). Thus, the extent of homogenization can be monitored in a CTR using the relatively fast reaction of the reagent and p

  8. Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts

    KAUST Repository

    Khan, Abdulaziz M.

    2016-04-26

    With the increasing production of natural gas as a result of the advancement in the technology, methane conversion to more valuable products has become a must. One of the most attractive processes which allow the utilization of the world’s most abundant hydrocarbon is the oxidative coupling. The main advantage of this process is the ability of converting methane into higher paraffins and olefins (primarily C2) in a direct way using a single reactor. Nevertheless, low C2+ yields have prevented the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized in improving the catalysts’ performance. The reaction involves the formation of methyl radicals that undergo gas-phase radical reactions. CH4 activation is believed to be done the surface oxygen species. However, recent studies showed that, in addition to the surface oxygen mediated pathway, an OH radical mediated pathway have a large contribution on the CH4 activation. The experiments of Li/MgO, Sr/La2O3 and NaWO4/SiO2 catalysts revealed variation of behavior in activity and selectivity. In addition, water effect analysis showed that Li/MgO deactivate at the presence of water due to sintering phenomena and the loss of active sites. On the other hand, negative effect on the C2 yield and CH4 conversion rate was observed with Sr/La2O3 with increasing the water partial pressure. Na2WO4/SiO2 showed a positive behavior with water in terms of CH4 conversion and C2 yield. In addition, the increment in CH4 conversion rate was found to be proportional with PO2 ¼ PH2O ½ which is consistent with the formation of OH radicals and the OH-mediated pathway. Experiments of using ring-dye laser, which is used to detect OH in combustion experiments, were tried in order to detect OH radicals in the gas-phase of the catalyst. Nevertheless

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

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Surface Reaction Kinetics of Steam- and CO2-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

    Directory of Open Access Journals (Sweden)

    Karla Herrera Delgado

    2015-05-01

    Full Text Available An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO2 as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented in a one-dimensional flow field description of a fixed bed reactor. The model is evaluated by comparison of numerical simulations with data derived from isothermal experiments in a flow reactor over a powdered nickel-based catalyst using varying inlet gas compositions and operating temperatures. Furthermore, the influence of hydrogen and water as co-feed on methane dry reforming with CO2 is also investigated.

  11. On the dynamics of immobilized enzyme kinetics in a microreactor: A study of AP-catalyzed reactions

    Directory of Open Access Journals (Sweden)

    Pratap R Patnaik

    2011-11-01

    Full Text Available Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} The kinetics of immobilized enzyme-catalyzed reactions in microreactors differ from those in macro-scale reactors. Recognizing this, a recent study (Patnaik 2011 based on a new interpretation of the kinetics of AP-catalyzed reactions showed that dynamic behavior is feasible only certain loci relating key kinetic parameters. That work has been extended here, and the kinetic parameters have now been related to bulk phase concentrations, thereby providing a link with the reaction system per se. It has also been shown that under certain conditions the reaction may become self-quenching but either monotonically or as damped oscillations. These two studies thus establish the importance of understanding kinetic dynamics in microreactors and in selecting feasible operating conditions.

  12. Biochemical, Kinetic, and Spectroscopic Characterization of Ruegeria pomeroyi DddW--A Mononuclear Iron-Dependent DMSP Lyase.

    Directory of Open Access Journals (Sweden)

    Adam E Brummett

    Full Text Available The osmolyte dimethylsulfoniopropionate (DMSP is a key nutrient in marine environments and its catabolism by bacteria through enzymes known as DMSP lyases generates dimethylsulfide (DMS, a gas of importance in climate regulation, the sulfur cycle, and signaling to higher organisms. Despite the environmental significance of DMSP lyases, little is known about how they function at the mechanistic level. In this study we biochemically characterize DddW, a DMSP lyase from the model roseobacter Ruegeria pomeroyi DSS-3. DddW is a 16.9 kDa enzyme that contains a C-terminal cupin domain and liberates acrylate, a proton, and DMS from the DMSP substrate. Our studies show that as-purified DddW is a metalloenzyme, like the DddQ and DddP DMSP lyases, but contains an iron cofactor. The metal cofactor is essential for DddW DMSP lyase activity since addition of the metal chelator EDTA abolishes its enzymatic activity, as do substitution mutations of key metal-binding residues in the cupin motif (His81, His83, Glu87, and His121. Measurements of metal binding affinity and catalytic activity indicate that Fe(II is most likely the preferred catalytic metal ion with a nanomolar binding affinity. Stoichiometry studies suggest DddW requires one Fe(II per monomer. Electronic absorption and electron paramagnetic resonance (EPR studies show an interaction between NO and Fe(II-DddW, with NO binding to the EPR silent Fe(II site giving rise to an EPR active species (g = 4.29, 3.95, 2.00. The change in the rhombicity of the EPR signal is observed in the presence of DMSP, indicating that substrate binds to the iron site without displacing bound NO. This work provides insight into the mechanism of DMSP cleavage catalyzed by DddW.

  13. KINETIC UNDERSTANDING OF THE SYNGAS-TO-DME REACTION SYSTEM AND ITS IMPLICATIONS TO PROCESS AND ECONOMICS

    Energy Technology Data Exchange (ETDEWEB)

    Xiang-Dong Peng

    2002-12-01

    In a single-step synthesis gas-to-dimethyl ether process, synthesis gas (or syngas, a mixture of H{sub 2} and CO) is converted into dimethyl ether (DME) in a single reactor. The three reactions involved in this process, methanol synthesis, methanol dehydration and water gas shift, form an interesting reaction network. The interplay among these three reactions results in excellent syngas conversion or reactor productivity. A fundamental understanding of this interplay helps to explain many experimental and simulation observations, to identify optimal reaction conditions, and to provide guidelines for process development. The higher syngas conversion or reactor productivity in the syngas-to-DME reaction system, compared to that in the syngas-to-methanol reaction system, is referred to as chemical synergy. This synergy exhibits a strong dependence on the composition of the reactor feed. To demonstrate the extent of this dependence, simulations with adjusted activity for each reaction were performed to reveal the relative rate of each reaction. The results show that the water gas shift reaction is the most rapid, being practically controlled by the equilibrium. Both methanol synthesis and methanol dehydration reactions are kinetically controlled. The kinetics of the dehydration reactions is greater than that of the methanol synthesis reaction in the CO-rich regime. However, the rates of these two reactions come closer as the H{sub 2} concentration in the reactor feed increases. The role of the dehydration reaction is to remove the equilibrium barrier for the methanol synthesis reaction. The role of the water gas shift reaction is more complex; it helps the kinetics of methanol dehydration by keeping the water concentration low, which in turn enhances methanol synthesis. It also readjusts the H{sub 2}:CO ratio in the reactor as the reactions proceed. In the CO-rich regime, the water gas shift reaction supplements the limiting reactant, H{sub 2}, by reacting water with

  14. DYNAMIC MATHEMATICAL MODELLING OF REACTION KINETICS FOR CYCLODEXTRINS PRODUCTION FROM DIFFERENT STARCH SOURCES USING BACILLUS MACERANS CYCLODEXTRIN GLUCANOTRANSFERASE

    Directory of Open Access Journals (Sweden)

    Syahinaz Shahrazi

    2013-01-01

    Full Text Available This study relates to the mathematical modelling of enzymatic production of Cyclodextrins (CDs by Cyclodextrin Glucanotransferase (CGTase from Bacillus macerans. The experiments were carried out in batch mode using different starch sources and the results were used to estimate unknown parameters using linearization and dynamic simulation methods. α- and β-CD produced from tapioca were found to give the highest Michaelis-Menten constant, KM,i of 58.23 and 54.07 g L-1, respectively and maximum velocity, Vmax,i of 3.45 and 2.76 g L-1.min, respectively, while sago resulted in the highest KM,i and Vmax,i values of 342.35 g L-1 and 5.97 g L-1.min, respectively, for γ-CD obtained by the linearization method. Value of product inhibition, K1,i and CD degradation coefficient rate, δCD,i, were estimated using dynamic simulation, indicating that exponential reaction kinetics could be fitted better with the experimental data. Sensitivity analysis revealed that the product inhibition parameter in the exponential reaction kinetic equation is more significant in the process. For validation, the production of CDs by fed batch method was undertaken and starch and enzyme were added into the reaction medium. Then, the predicted profiles generated by simulation were compared with the experimental values. The proposed exponential reaction kinetics shows good fitting with the experimental data.

  15. Mass Transfer and Chemical Reaction Approach of the Kinetics of the Acetylation of Gadung Flour using Glacial Acetic Acid

    Directory of Open Access Journals (Sweden)

    Andri Cahyo Kumoro

    2015-03-01

    Full Text Available Acetylation is one of the common methods of modifying starch properties by introducing acetil (CH3CO groups to starch molecules at low temperatures. While most acetylation is conducted using starch as anhidroglucose source and acetic anhydride or vinyl acetate as nucleophilic agents, this work employ reactants, namely flour and glacial acetic acid. The purpose of this work are to study the effect of pH reaction and GAA/GF mass ratio on the rate of acetylation reaction and to determine its rate constants. The acetylation of gadung flour with glacial acetic acid in the presence of sodium hydroxide as a homogenous catalyst was studied at ambient temperature with pH ranging from 8-10 and different mass ratio of acetic acid : gadung flour (1:3; 1:4; and 1:5. It was found that increasing pH, lead to increase the degree of substitution, while increasing GAA/GF mass ratio caused such decreases in the degree of substitution, due to the hydrolysis of the acetylated starch. The desired starch acetylation reaction is accompanied by undesirable hydrolysis reaction of the acetylated starch after 40-50 minutes reaction time. Investigation of kinetics of the reaction observed that the value of mass transfer rate constant (Kcs is smaller than the surface reaction rate constant (k. Thus, it can be concluded that rate controlling step is mass transfer.  © 2015 BCREC UNDIP. All rights reservedReceived: 7th August 2014; Revised: 8th September 2014; Accepted: 14th September 2014How to Cite: Kumoro, A.C., Amelia, R. (2015. Mass Transfer and Chemical Reaction Approach of the Kinetics of the Acetylation of Gadung Flour using Glacial Acetic Acid. Bulletin of Chemical Reaction Engineering & Catalysis, 10 (1: 30-37. (doi:10.9767/bcrec.10.1.7181.30-37Permalink/DOI: http://dx.doi.org/10.9767/bcrec.10.1.7181.30-37

  16. On the formal correctness of the reaction kinetics model and its solution in HV circuit breakers after current zero

    Science.gov (United States)

    Coufal, O.; Sezemský, P.

    2001-07-01

    Five necessary conditions for the so-called formal correctness of solutions of kinetic equations are formulated, which form a mathematical model of the reaction kinetics in HV circuit breakers after current zero for a given time-dependence of temperature and a given time-dependence of pressure or volume. The conditions are based on the mass action law, knowledge obtained from mathematical analysis of a system of ordinary differential equations, the principles of numerical analysis and the equilibrium-state principle of thermodynamics. Concrete solutions of kinetic equations are given and analysed for the products of SF6 dissociation and ionization. Two models are considered. In one model, the temperature drops from 10 000 to 2500 K, in the other it drops from 12 000 K to room temperature. A comparison of the time-dependent composition with the equilibrium composition is offered for both models.

  17. Kinetics and mechanism of reaction between water vapor, carbon monoxide and a chromia-forming nickel base alloy

    International Nuclear Information System (INIS)

    The kinetic aspects of the competitive reaction of CO and H2O in the formation of chromia layer on a nickel base alloy at high temperature were studied by thermogravimetry combined to gas phase chromatography. It was shown that competitive adsorption occurred between both molecules and that whatever P(CO)/P(H2O) ratio, CO mainly reacted in the first instants of oxidation and H2O became the main long-term oxidant species. After an interfacial and diffusion mixed kinetic regime, the long-term oxidation rate was parabolic and did not depend on the water vapor content in the gas phase. The oxidation kinetics was well described by considering that the rate limiting step was the outwards diffusion of interstitial chromium cations in the oxide layer. (authors)

  18. Deduction of kinetic mechanism in multisubstrate enzyme reactions from tritium isotope effects. Application to dopamine beta-hydroxylase

    International Nuclear Information System (INIS)

    Primary tritium isotope effects have been measured for the hydroxylation of [2-3H] dopamine catalyzed by dopamine beta-hydroxylase. Experimental values vary from 8.8 +/- 1.4 at 0.02 mM oxygen to 4.1 +/- 0.6 at 1.0 mM oxygen. It is shown that the observed dependence of the isotope effect on oxygen concentration provides unequivocal evidence for a kinetically significant dissociation of both dopamine and oxygen from enzyme, ternary complex. This approach, which is applicable to any multisubstrate enzyme characterized by detectable kinetic isotope effects, provides an alternate to classical methods for the elucidation of kinetic order in enzyme-catalyzed reactions

  19. A STUDY OF THE PROPERTIES OF CP: COEFFICIENT OF THERMAL EXPANSION, DECOMPOSITION KINETICS AND REACTION TO SPARK, FRICTION AND IMPACT

    Energy Technology Data Exchange (ETDEWEB)

    Weese, R K; Burnham, A K; Fontes, A T

    2005-03-30

    The properties of pentaamine (5-cyano-2H-tetrazolato-N2) cobalt (III) perchlorate (CP), which was first synthesized in 1968, continues to be of interest for predicting behavior in handling, shipping, aging, and thermal cook-off situations. We report coefficient of thermal expansion (CTE) values over four specific temperature ranges, decomposition kinetics using linear heating rates, and the reaction to three different types of stimuli: impact, spark, and friction. The CTE was measured using a Thermal Mechanical Analyzer (TMA) for samples that were uniaxially compressed at 10,000 psi and analyzed over a dynamic temperature range of -20 C to 70 C. Using differential scanning calorimetry, DSC, CP was decomposed at linear heating rates of 1, 3, and 7 C/min and the kinetic triplet calculated using the LLNL code Kinetics05. Values are also reported for spark, friction, and impact sensitivity.

  20. High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes.

    Science.gov (United States)

    Chen, Chang-Hui; Meadows, Katherine E; Cuharuc, Anatolii; Lai, Stanley C S; Unwin, Patrick R

    2014-09-14

    The scanning droplet-based technique, scanning electrochemical cell microscopy (SECCM), combined with electron backscatter diffraction (EBSD), is demonstrated as a powerful approach for visualizing surface structure effects on the rate of the oxygen reduction reaction (ORR) at polycrystalline platinum electrodes. Elucidating the effect of electrode structure on the ORR is of major interest in connection to electrocatalysis for energy-related applications. The attributes of the approach herein stem from: (i) the ease with which the polycrystalline substrate electrode can be prepared; (ii) the wide range of surface character open to study; (iii) the possibility of mapping reactivity within a particular facet (or grain), in a pseudo-single-crystal approach, and acquiring a high volume of data as a consequence; (iv) the ready ability to measure the activity at grain boundaries; and (v) an experimental arrangement (SECCM) that mimics the three-phase boundary in low temperature fuel cells. The kinetics of the ORR was analyzed and a finite element method model was developed to explore the effect of the three-phase boundary, in particular to examine pH variations in the droplet and the differential transport rates of the reactants and products. We have found a significant variation of activity across the platinum substrate, inherently linked to the crystallographic orientation, but do not detect any enhanced activity at grain boundaries. Grains with (111) and (100) contributions exhibit considerably higher activity than those with (110) and (100) contributions. These results, which can be explained by reference to previous single-crystal measurements, enhance our understanding of ORR structure-activity relationships on complex high-index platinum surfaces, and further demonstrate the power of high resolution flux imaging techniques to visualize and understand complex electrocatalyst materials. PMID:25072300

  1. Reactions of chlorine (III) and their kinetics in the chlorine dioxide bleaching of kraft pulps

    OpenAIRE

    Lehtimaa, Tuula

    2010-01-01

    The reactions of Cl(III) were investigated utilizing iodometric titration in combination with DMSO and EDTA to prevent undesired side reactions. Among a large group of suggested Cl(III) decomposition reactions, two reactions were found to be adequate to describe the Cl(III) decomposition in the absence of metals and HOCl. The rate parameters (k - rate coefficient, Ea - activation energy) were determined for these reactions. The reaction between Cl(III) and HOCl is known to start with the...

  2. Kinetics of the Exothermic Decomposition Reaction of N-Methyl-N-nitro-2,2,2- trinitroethanamine

    Institute of Scientific and Technical Information of China (English)

    陈三平; 胡荣祖; 宋纪蓉; 杨得琐; 高胜利; 赵宏安; 史启祯

    2003-01-01

    The thermal behavior and kinetic parameters of the exothermic decomposition reaction of N-methyl-N-nitro-2,2,2-trinitroethanamine in a temperature-programmed mode have been investigated by means of differential scanning calorimetry (DSC).The kinetic equation of the exothermic decomposition process of the compound is proposed. The values of the apparent activation energy (Ea), pre-exponential factor (A), entropy of activation (ΔS≠ ), enthalpy of activation (ΔH≠ ), and free energy of activation (ΔG≠ ) of this reaction and the critical temperature of thermal explosion of the compound are reported. Information is obtained on the mechanism of the initial stage of the thermal decomposition of the compound.

  3. Simulation Experiments on the Reaction of CH4-CaSO4 and Its Carbon Kinetic Isotope Fractionation

    Institute of Scientific and Technical Information of China (English)

    YueChangtao; LiShuyuan; DingKangle; ZhongNingning

    2005-01-01

    Thermochemical sulfate reduction (TSR) in geological deposits can account for the accumulation of H,S in deep sour gas reservoirs. In this paper, thermal simulation experiments on the reaction of CH4-CaSO4 were carried out using an autoclave at high temperatures and high pressures. The products were characterized with analytical methods including carbon isotope analysis. It is found that the reaction can proceed to produce H2S, H2O and CaCO3 as the main products. Based on the experimental results, the carbon kinetic isotope fractionation was investigated, and the value of Ki(kinetic isotope effect) was calculated. The results obtained in this paper can provide useful information to explain the occurrence of H2S in deep carbonate gas reservoirs.

  4. Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

    International Nuclear Information System (INIS)

    The effects of duration (1–100 days) and temperature (20 and 50 °C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by 29Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C–S–H and then C–A–S–H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 °C, corresponding to an apparent activation energy of 40–50 kJ/mol

  5. Kinetics of lime/bentonite pozzolanic reactions at 20 and 50 °C: Batch tests and modeling

    Energy Technology Data Exchange (ETDEWEB)

    De Windt, Laurent, E-mail: laurent.dewindt@mines-paristech.fr [Mines-ParisTech (Ecole des Mines de Paris), Centre de Géosciences, 35 Rue St-Honoré, 77305 Fontainebleau Cedex (France); Deneele, Dimitri [LUNAM, IFSTTAR, Institut Français des Sciences et des Technologies des Transports, de l' Aménagement et des Réseaux, BP 4129, route de Bouaye, 44332 Bouguenais (France); Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322 Nantes Cedex 3 (France); Maubec, Nicolas [LUNAM, IFSTTAR, Institut Français des Sciences et des Technologies des Transports, de l' Aménagement et des Réseaux, BP 4129, route de Bouaye, 44332 Bouguenais (France)

    2014-05-01

    The effects of duration (1–100 days) and temperature (20 and 50 °C) were assessed from batch tests for Ca-bentonite mixed with 10 wt.% lime. The pozzolanic processes were monitored over time by {sup 29}Si NMR (Cement Concr. Res. 42, 2012), TGA-DTA, XRD and chemical analysis. Modeling considered kinetics and thermodynamics of mineralogical transformations and cation exchange. Kinetic laws were dependent on pH and temperature (Arrhenius energy). Lime hydration occurs within hours, modifying the bentonite exchangeable population and increasing the pH. These alkaline conditions initiate the pozzolanic reactions in a second stage. The rate-limiting step is the dissolution kinetics of the bentonite minerals, i.e. a relatively fast and total consumption of cristobalite in parallel to a long-term slower dissolution of montmorillonite. First C–S–H and then C–A–S–H are formed consequently. Temperature speeds up the pozzolanic reaction kinetics by a factor 5 from 20 to 50 °C, corresponding to an apparent activation energy of 40–50 kJ/mol.

  6. Kinetic Approach to the Mechanism of Redox Reaction of Pyrocatechol Violet and Nitrite Ion in Aqueous Hydrochloric Acid

    Directory of Open Access Journals (Sweden)

    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.

  7. The kinetics of the O2/CO2 reaction in molten carbonate - Reaction orders for O2 and CO2 on NiO. [in fuel cells

    Science.gov (United States)

    Winnick, J.; Ross, P. N.

    1980-01-01

    The kinetics of the O2/CO2 reaction in molten carbonate is investigated using paste electrolytes and nickel sinter electrodes. A two-step approach to the determination of reaction orders is employed. First, exchange currents at various P(CO2) and P(O2) were measured using the low polarization method. Second, alpha(+) and alpha(-) values were obtained from the slope of the Allen-Hickling plot for current densities low enough so that concentration polarization within the electrode can be neglected. The reaction orders are + 1/4 in CO2 and + 5/8 in O2 in the cathodic direction, and - 3/4 in CO2 and + 1/8 in O2 in the anodic direction.

  8. A Study on the Kinetics of the Catalytic Reforming Reaction of CH4 with CO2: Determination of the Reaction Order

    Institute of Scientific and Technical Information of China (English)

    Chunyang Ji; Lihong Gong; Jiawei Zhang; Keying Shi

    2003-01-01

    The kinetics of the catalytic reforming reaction of methane with carbon dioxide to produce synthesis gas on a Ni/α-Al2O3 and a HSD-2 type commercial catalyst has been studied. The results indicate that the reaction orders are one and zero for methane and carbon dioxide, respectively, when the carbon dioxide partial pressure was about 12.5-30.0 kPa and the temperature was at 1123-1173 K. However,when the carbon dioxide partial pressure was changed to 30.0-45.0 kPa under the same temperature range of 1123 1173 K, the reaction orders of methane and carbon dioxide are one. Furthermore, average rate constants at different temperatures were determined.

  9. Determination of the residence time distribution for a solar reactor and its use for deriving reaction kinetics

    Energy Technology Data Exchange (ETDEWEB)

    Frey, Th.; Guesdon, Ch.; Sturzenegger, M.

    2001-03-01

    The residence time distribution of a solar reactor was experimentally determined by measuring the response function at the reactor outlet after applying a step input of a tracer. The results have shown that the reactor behaves like an ideal stirred tank with a mean residence time of 90{+-}2 s and they were used to derive reaction kinetics from high temperature experiments in the solar furnace. (author)

  10. Kinetic Analysis of Some Chalcones and Synthetic Chalcone Analogues on the Fenton-Reaction Initiated Deoxyribose Degradation Assay1

    OpenAIRE

    Perjési, Pál; Rozmer, Zsuzsanna

    2011-01-01

    Investigation of in vitro hydroxyl radical scavenging (antioxidant) effect 4-methoxychalcone (1a) and its cyclic analogues (2a-4a), as well as their hydroxyl substituted counterparts (1b-4b) was performed by means of the Fenton-reaction initiated deoxyribose degradation assay in short term (10 minute) and long term (240 minute) experiments. The kinetic deoxyribose method provides possibility to investigate not only the short term antioxidant (hydroxyl radical scavenger) effect but the possibl...

  11. Inverse Secondary Deuterium Kinetic Isotope Effect in Diels-Alder Reaction of Orthonaphtho [3.3] orthoanthracenophane with Maleic Anhydride

    OpenAIRE

    Mataka, Shuntaro; Ma, Jiang; Tsuzuki, Hirohisa; Nishiyama, Kozaburo; Thiemann, Thies; Tashiro, Masashi

    1996-01-01

    The Diels-Alderreactions of rigid [3.3] orthoanthracenophanes 1 and 2 with maleic anhydride and deuterium-labeled maleic anhydride-d_2, were studied. In the reaction of naphtophane 1, a large inverse secondary kinetic isotope effect (SDKIE) (kH_2/kD_2=0.78) was observed, while benzophane 2 shows a SDKIE similar to that of anthracene itself (kH_2/kD_2=0.95 and 0.96).

  12. Field-controlled electron transfer and reaction kinetics of the biological catalytic system of microperoxidase-11 and hydrogen peroxide

    OpenAIRE

    Yongki Choi; Siu-Tung Yau

    2011-01-01

    Controlled reaction kinetics of the bio-catalytic system of microperoxidase-11 and hydrogen peroxide has been achieved using an electrostatic technique. The technique allowed independent control of 1) the thermodynamics of the system using electrochemical setup and 2) the quantum mechanical tunneling at the interface between microperoxidase-11 and the working electrode by applying a gating voltage to the electrode. The cathodic currents of electrodes immobilized with microperoxidase-11 showed...

  13. Kinetics and Product Selectivity (Yield) of Second Order Competitive Consecutive Reactions in Fed-Batch Reactor and Plug Flow Reactor

    OpenAIRE

    Selvamony, Subash Chandra Bose

    2013-01-01

    This literature compares the performance of second order competitive consecutive reaction in Fed-Batch Reactor with that in continuous Plug Flow Reactor. In a kinetic sense, this simulation study aims to develop a case for continuous Plug Flow Reactor in pharmaceutical, fine chemical, and related other chemical industries. MATLAB is used to find solutions for the differential equations. The simulation results show that, for certain cases of nonelementary scenario, product selectivity is highe...

  14. Kinetic model of deactivation of a nickel catalyst in the reaction of hydrogenation of benzene

    Energy Technology Data Exchange (ETDEWEB)

    Masagutov, R.M.; Spivak, S.I.; Kovaleva, L.V.; Morozov, B.V.; Yaropolova, E.A.

    1988-12-01

    The kinetics of hydrogenation of benzene on a nickel catalyst in conditions of poisoning with thiophene were investigated. A mechanism of deactivation of the catalyst was proposed. A kinetic model of the process was constructed. The numerical values of the constants of the deactivation stages which satisfactorily describe the experimental data were found.

  15. Non-isothermal Kinetics of the First-stage Decomposition Reaction of Cobalt Oxalate Dihydrate

    Institute of Scientific and Technical Information of China (English)

    ZHANG Jian-jun; REN Ning; BAI Ji-hai

    2005-01-01

    @@ Introduction Solid state kinetics has been extensively studied by means of thermal analysis methods[1]. The aim of the study is to determine the mechanism function f(α) , the activation energy E and the pre-exponential factor A. In recent years there have been many methods of processing thermal analysis kinetic data[2-11].

  16. Insight into the kinetics and thermodynamics of the hydride transfer reactions between quinones and lumiflavin: a density functional theory study.

    Science.gov (United States)

    Reinhardt, Clorice R; Jaglinski, Tanner C; Kastenschmidt, Ashly M; Song, Eun H; Gross, Adam K; Krause, Alyssa J; Gollmar, Jonathan M; Meise, Kristin J; Stenerson, Zachary S; Weibel, Tyler J; Dison, Andrew; Finnegan, Mackenzie R; Griesi, Daniel S; Heltne, Michael D; Hughes, Tom G; Hunt, Connor D; Jansen, Kayla A; Xiong, Adam H; Hati, Sanchita; Bhattacharyya, Sudeep

    2016-09-01

    The kinetics and equilibrium of the hydride transfer reaction between lumiflavin and a number of substituted quinones was studied using density functional theory. The impact of electron withdrawing/donating substituents on the redox potentials of quinones was studied. In addition, the role of these substituents on the kinetics of the hydride transfer reaction with lumiflavin was investigated in detail under the transition state (TS) theory assumption. The hydride transfer reactions were found to be more favorable for an electron-withdrawing substituent. The activation barrier exhibited a quadratic relationship with the driving force of these reactions as derived under the formalism of modified Marcus theory. The present study found a significant extent of electron delocalization in the TS that is stabilized by enhanced electrostatic, polarization, and exchange interactions. Analysis of geometry, bond-orders, and energetics revealed a predominant parallel (Leffler-Hammond) effect on the TS. Closer scrutiny reveals that electron-withdrawing substituents, although located on the acceptor ring, reduce the N-H bond order of the donor fragment in the precursor complex. Carried out in the gas-phase, this is the first ever report of a theoretical study of flavin's hydride transfer reactions with quinones, providing an unfiltered view of the electronic effect on the nuclear reorganization of donor-acceptor complexes. PMID:27491848

  17. Implementation of steady state approximation for modelling of reaction kinetic of UV catalysed hydrogen peroxide oxidation of starch

    Science.gov (United States)

    Kumoro, Andri Cahyo; Retnowati, Diah Susetyo; Ratnawati, Budiyati, Catarina Sri

    2015-12-01

    With regard to its low viscosity, high stability, clarity, film forming and binding properties, oxidised starch has been widely used in various applications specifically in the food, paper, textile, laundry finishing and binding materials industries. A number of methods have been used to produce oxidised starch through reactions with various oxidizing agents, such as hydrogen peroxide, air oxygen, ozone, bromine, chromic acid, permanganate, nitrogen dioxide and hypochlorite. Unfortunately, most of previous works reported in the literatures were focused on the study of reaction mechanism and physicochemical properties characterization of the oxidised starches produced without investigation of the reaction kinetics of the oxidation process. This work aimed to develop a simple kinetic model for UV catalysed hydrogen peroxide oxidation of starch through implementation of steady state approximation for the radical reaction rates. The model was then verified using experimental data available in the literature. The model verification revealed that the proposed model shows its good agreement with the experimental data as indicated by an average absolute relative error of only 2.45%. The model also confirmed that carboxyl groups are oxidised further by hydroxyl radical. The carbonyl production rate was found to follow first order reaction with respect to carbonyl concentration. Similarly, carboxyl production rate also followed first order reaction with respect to carbonyl concentration. The apparent reaction rate constant for carbonyl formation and oxidation were 6.24 × 104 s-1 and 1.01 × 104 M-1.s-1, respectively. While apparent reaction rate constant for carboxyl oxidation was 4.86 × 104 M-1.s-1.

  18. The Application of Transient-State Kinetic Isotope Effects to the Resolution of Mechanisms of Enzyme-Catalyzed Reactions

    Directory of Open Access Journals (Sweden)

    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.

  19. Effect of Maillard reaction on biochemical properties of peanut 7S globulin (Ara h 1) and its interaction with a human colon cancer cell line (Caco-2)

    OpenAIRE

    Teodorowicz, M.; Fiedorowicz, E.; Kostyra, H.; Wichers, H J; Kostyra, E.

    2013-01-01

    Purpose The purpose of this study was to determine the influence of Maillard reaction (MR, glycation) on biochemical and biological properties of the major peanut allergen Ara h 1. Methods Three different time/temperature conditions of treatment were applied (37, 60, and 145 °C). The extent of MR was assessed by SDS-PAGE, loss of free amino groups, fluorescence intensity, content of bound sugar and fructosamine. The Caco-2 model system was applied to study effects of hydrolysed and non-hydrol...

  20. Investigation of Pd-catalyzed Co(III)-EDTA/hypophosphite inhibition reaction kinetics, mechanism and the evaluation of its analytical application possibilities

    OpenAIRE

    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...

  1. Muonium Addition Reactions and Kinetic Isotope Effects in the Gas Phase: k∞ Rate Constants for Mu + C2H2.

    Science.gov (United States)

    Arseneau, Donald J; Garner, David M; Reid, Ivan D; Fleming, Donald G

    2015-07-16

    The kinetics of the addition reaction of muonium (Mu) to acetylene have been studied in the gas phase at N2 moderator pressures mainly from ∼800 to 1000 Torr and over the temperature range from 168 to 446 K, but also down to 200 Torr at 168 K and over a much higher range of pressures, from 10 to 44 bar at 295 K, demonstrating pressure-independent rate constants, kMu(T). Even at 200 Torr moderator pressure, the kinetics for Mu + C2H2 addition behave as if effectively in the high-pressure limit, giving k∞ = kMu due to depolarization of the muon spin in the MuC2H2 radical formed in the addition step. The rate constants kMu(T) exhibit modest Arrhenius curvature over the range of measured temperatures. Comparisons with data and with calculations for the corresponding H(D) + C2H2 addition reactions reveal a much faster rate for the Mu reaction at the lowest temperatures, by 2 orders of magnitude, in accord with the propensity of Mu to undergo quantum tunneling. Moreover, isotopic atom exchange, which contributes in a major way to the analogous D atom reaction, forming C2HD + H, is expected to be unimportant in the case of Mu addition, a consequence of the much higher zero-point energy and hence weaker C-Mu bond that would form, meaning that the present report of the Mu + C2H2 reaction is effectively the only experimental study of kinetic isotope effects in the high-pressure limit for H-atom addition to acetylene. PMID:25664674

  2. Kinetics and mechanisms of the reactions of alkyl radicals with oxygen and with complexes of Co(III), Ru(III), and Ni(III)

    International Nuclear Information System (INIS)

    The kinetics of the reactions of C2H5 radical with Co(NH3)5X2+, Ru(NH3)5X2+, and Co(dmgH)2 (X) (Y) (X = Br, Cl, N3, SCN; Y = H2O, CH3CN) complexes were studied using laser flash photolysis of ethylcobalt complexes. The kinetics were obtained by the kinetic probe method. Some relative rate constants were also determined by a competition method based on ethyl halide product ratios. The kinetics of colligation reactions of a series of alkyl radicals with β-Ni(cyclam)2+ were studied using flaser flash photolysis of alkylcobalt complexes. Again, the kinetics were obtained by employing the kinetic probe competition method. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H2O2+ were studied. Activation parameters were obtained for the unimolecular homolysis of C2H5Ni(cyclam)H2O2+. Kinetic and thermodynamic data obtained from these reactions were compared with those for the σ-bonded organometallic complexes. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H2O2+ complexes were studied by monitoring the formation of the oxygen insertion product RO2Ni(cyclam)H2O2+. The higher rate constants for the reactions of alkyl radicals with oxygen in solution, as compared with those measured in the gas phase, were discussed. 30 refs

  3. Impacts of carbon nanotubes on biochemical reactions: insight into interaction between carbon nanotubes and DNA polymerase enzyme

    OpenAIRE

    Uysal, Ebru; Meral, Yüce; Meral, Yuce; Hasan KURT

    2014-01-01

    Recently, the Polymerase Chain Reaction technique has begun to benefit from nanotechnology. In this paper, effects of carbon nanotubes in the Polymerase Chain Reaction were investigated by Electrophoresis, Circular Dichroism Spectrometry and Dynamic Light Scattering Techniques. The unique ability to amplify low copy number DNA within minutes has made in vitro Polymerase Chain Reaction (PCR) one of the most essential techniques in modern biology. In order to harness this technique to its full ...

  4. Reaction of Human Cd7metallothionein and N-Ethylmaleimide: Kinetic and Structural Insights from Electrospray Ionization Mass Spectrometry.

    Science.gov (United States)

    Chen, Shu-Hua; Russell, David H

    2015-10-01

    The reaction of cadmium-binding human metallothionein-2A (Cd₇MT) and N-ethylmaleimide (NEM) is investigated by electrospray ionization-ion mobility-mass spectrometry (ESI IM-MS). MS provides a direct measure of the distribution of the kinetic intermediates as the reaction proceeds and provides new insights into the relative kinetic stability of the individual metal-thiolate bonds in Cd₇MT. The rate constants for the various metal-retaining intermediates (Cd(i), intermediate with i Cd²⁺ ions attached) differ by >3 orders of magnitude: Cd₄NEM₁₀MT was observed as the least reactive intermediate during the entire displacement process. "MS-CID-IM-MS", a top-down approach that provides two-dimensional dispersion (size to charge by IM; mass to charge by MS) of the CID fragment ions, was used for direct analysis of the kinetic intermediate [Cd₄NEM₁₀MT]⁵⁺ ion. The results provide direct evidence that the four Cd²⁺ ions located in the α-domain are retained, indicative of the greater kinetic stability for the α-domain. Further, the mapping of the alkylation sites in the [Cd₄NEM₁₀MT]⁵⁺ ion reveals that not only the nine cysteines in the β-domain but Cys33 in the α-domain is selectively labeled. The kinetic lability of the Cd-Cys33 bond is unexpected. The structural and functional implications of these findings are discussed. PMID:26375382

  5. Isolating Reactions at the Picoliter Scale: Parallel Control of Reaction Kinetics at the Liquid-Liquid Interface.

    Science.gov (United States)

    Phan-Quang, Gia Chuong; Lee, Hiang Kwee; Ling, Xing Yi

    2016-07-11

    Miniaturized liquid-liquid interfacial reactors offer enhanced surface area and rapid confinement of compounds of opposite solubility, yet they are unable to provide in situ reaction monitoring at a molecular level at the interface. A picoreactor operative at the liquid-liquid interface is described, comprising plasmonic colloidosomes containing Ag octahedra strategically assembled at the water-in-decane emulsion interface. The plasmonic colloidosomes isolate ultrasmall amounts of solutions (<200 pL), allowing parallel monitoring of multiple reactions simultaneously. Using the surface-enhanced Raman spectroscopy (SERS) technique, in situ monitoring of the interfacial protonation of dimethyl yellow (p-dimethylaminoazobenzene (DY)) is performed, revealing an apparent rate constant of 0.09 min(-1) for the first-order reaction. The presence of isomeric products with similar physical properties is resolved, which would otherwise be indiscernible by other analytical methods. PMID:27239973

  6. Curing Reaction Kinetics of Epoxy Resin Using Dicyandiamide Modified by Aromatic Amines

    Institute of Scientific and Technical Information of China (English)

    CHEN Lianxi; TIAN Hua; LIU Quanwen; Wang Jun

    2007-01-01

    The curing reaction and reaction mechanism of epoxy resin E-44, for which aromatic amine modified dicyandiamide was used as a curing reagent, were investigated by means of differential scanning calorimetry (DSC). The results showed that the modified dicyandiamide had better curing characteristic than ummodified dicyandiamide for epoxy resin E-44, and the curing reaction could be carried out at moderate temperature. Apparent activation energy of the curing reaction was decreased appreciably from 123.829 kJ/mol to 61.550-64.405 kJ/mol, and reaction order was decreased from 0.941 to 0.896-0.900. Curing reaction mechanism also was discussed.

  7. LSENS, a general chemical kinetics and sensitivity analysis code for homogeneous gas-phase reactions. 2: Code description and usage

    Science.gov (United States)

    Radhakrishnan, Krishnan; Bittker, David A.

    1994-01-01

    LSENS, the Lewis General Chemical Kinetics Analysis Code, has been developed for solving complex, homogeneous, gas-phase chemical kinetics problems and contains sensitivity analysis for a variety of problems, including nonisothermal situations. This report is part 2 of a series of three reference publications that describe LSENS, provide a detailed guide to its usage, and present many example problems. Part 2 describes the code, how to modify it, and its usage, including preparation of the problem data file required to execute LSENS. Code usage is illustrated by several example problems, which further explain preparation of the problem data file and show how to obtain desired accuracy in the computed results. LSENS is a flexible, convenient, accurate, and efficient solver for chemical reaction problems such as static system; steady, one-dimensional, inviscid flow; reaction behind incident shock wave, including boundary layer correction; and perfectly stirred (highly backmixed) reactor. In addition, the chemical equilibrium state can be computed for the following assigned states: temperature and pressure, enthalpy and pressure, temperature and volume, and internal energy and volume. For static problems the code computes the sensitivity coefficients of the dependent variables and their temporal derivatives with respect to the initial values of the dependent variables and/or the three rate coefficient parameters of the chemical reactions. Part 1 (NASA RP-1328) derives the governing equations describes the numerical solution procedures for the types of problems that can be solved by lSENS. Part 3 (NASA RP-1330) explains the kinetics and kinetics-plus-sensitivity-analysis problems supplied with LSENS and presents sample results.

  8. Primary Ion Depletion Kinetics (PIDK Studies as a New Tool for Investigating Chemical Ionization Fragmentation Reactions with PTR-MS.

    Directory of Open Access Journals (Sweden)

    Erna Schuhfried

    Full Text Available We report on a new approach for studying fragmentation channels in Proton Transfer Reaction-Mass Spectrometry (PTR-MS, which we name primary ion depletion kinetics (PIDK. PTR-MS is a chemical ionization mass spectrometric (CIMS technique deploying hydronium ions for the chemical ionization. Induced by extremely high concentrations of analyte M, depletion of the primary ions in the drift tube occurs. This is observed as quasi zero concentration of the primary ion H3O(+, and constant MH(+. Under these non-standard conditions, we find an overall changed fragmentation. We offer two explanations. Either the changed fragmentation pattern is the result of secondary proton transfer reactions. Or, alternatively, the fast depletion of H3O(+ leads to reduced heating of H3O(+ in the drift field, and consequently changed fragmentation following protonation of the analyte M. In any case, we use the observed changes in fragmentation as a successful new approach to fragmentation studies, and term it primary ion depletion kinetics, PIDK. PIDK easily yields an abundance of continuous data points with little deviation, because they are obtained in one experimental run, even for low abundant fragments. This is an advantage over traditional internal kinetic energy variation studies (electric field per number density (E/N variation studies. Also, some interpretation on the underlying fragmentation reaction mechanisms can be gleamed. We measure low occurring fragmentation (<2% of MH(+ of the compounds dimethyl sulfide, DMS, a compound that reportedly does not fragment, diethyl sulfide DES, and dipropyl sulfide DPS. And we confirm and complement the results with traditional E/N studies. Summing up, the new approach of primary ion depletion kinetics allows for the identification of dehydrogenation [MH(+ -H2] and adduct formation (RMH(+ as low abundant fragmentation channels in monosulfides.

  9. Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

    Energy Technology Data Exchange (ETDEWEB)

    Martin del Campo, Julia S. [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico); Patino, Rodrigo, E-mail: rtarkus@mda.cinvestav.mx [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico)

    2011-04-20

    Research highlights: {yields} The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. {yields} A spectrophotometric method is proposed for kinetic and thermodynamic analysis. {yields} The pH and the temperature influences are reported on physical chemical properties. {yields} Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD{sub ox}) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD{sub ox} as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, {Delta}{sub f}G{sup o} = -1784 {+-} 5 kJ mol{sup -1}.

  10. Theoretical Study of CH3CH=CH2+O(1D) Reaction:Mechanism and Kinetics

    Institute of Scientific and Technical Information of China (English)

    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.

  11. Curing behavior and reaction kinetics of binder resins for 3D-printing investigated by dielectric analysis (DEA)

    Science.gov (United States)

    Möginger, B.; Kehret, L.; Hausnerova, B.; Steinhaus, J.

    2016-05-01

    3D-Printing is an efficient method in the field of additive manufacturing. In order to optimize the properties of manufactured parts it is essential to adapt the curing behavior of the resin systems with respect to the requirements. Thus, effects of resin composition, e.g. due to different additives such as thickener and curing agents, on the curing behavior have to be known. As the resin transfers from a liquid to a solid glass the time dependent ion viscosity was measured using DEA with flat IDEX sensors. This allows for a sensitive measurement of resin changes as the ion viscosity changes two to four decades. The investigated resin systems are based on the monomers styrene and HEMA. To account for the effects of copolymerization in the calculation of the reaction kinetics it was assumed that the reaction can be considered as a homo-polymerization having a reaction order n≠1. Then the measured ion viscosity curves are fitted with the solution of the reactions kinetics - the time dependent degree of conversion (DC-function) - for times exceeding the initiation phase representing the primary curing. The measured ion viscosity curves can nicely be fitted with the DC-function and the determined fit parameters distinguish distinctly between the investigated resin compositions.

  12. Human immunodeficiency virus-1 protease. 1. Initial velocity studies and kinetic characterization of reaction intermediates by 18O isotope exchange

    International Nuclear Information System (INIS)

    The peptidolytic reaction HIV-1 protease has been investigated by using four oligopeptide substrates, Ac-Ser-Gln-Asn-Pro-Val-Val-NH2, Ac-Arg-Ala-Ser-Gln-Asn-Tyr-Pro-Val-Val-NH2, Ac-Ser-Gln-Ser-Tyr-Pro-Val-Val-NH2, and Ac-Arg-Lys-Ile-Leu-Phe-Leu-Asp-Gly-NH2 that resemble two cleavage sites found within the naturally occurring polyprotein substrates Pr55gag and Pr160gag-pol. By use of a variety of inorganic salts, it was concluded that the peptidolytic reaction is nonspecifically activated by increasing ionic strength. V/K increased in an apparently parabolic fashion with increasing ionic strength, while V was either increased or decreased slightly. From product inhibition studies, the kinetic mechanism of the protease is either random or ordered uni-bi, depending on the substrate studied. The protease-catalyzed exchange of an atom of 18O from H218O into the re-formed substrates occurred at a rate which was 0.01-0.12 times that the forward peptidolytic reaction. The results of these studies are in accord with the formation of a kinetically competent enzyme-bound amide hydrate intermediate, the collapse of which is the rate-limiting chemical step in the reaction pathway

  13. Cytologic-Biochemical Radiation Dosimeters in Man

    International Nuclear Information System (INIS)

    The result of radiation interacting with living tissue is the deposition of energy therein. This energy triggers numerous chemical reactions within the molecules of the target tissues. We have measured in man the results of some of these reactions at doses up to 300 rads: chromosome aberrations; alterations in the kinetics of specific human cell populations; changes in 37 biochemical constituents of serum and/or urine. The utilization of chromosomes as a biological dosimeter is partially perfected but there are numerous discrepancies in data between different laboratories. Etiocholanolone can be used to evaluate marrow injury before the white-cell count falls below 5000/mm3. Most biochemical dosimeters evaluated gave negative or inconsistent results. However, salivary amylase is a promising indicator of human radiation injury from doses as low as 100 rads. (author)

  14. Incorporation of aqueous reaction and sorption kinetics and biodegradation into TOUGHREACT

    OpenAIRE

    Xu, Tianfu

    2006-01-01

    The needs for considering aqueous and sorption kinetics and microbiological processes arises in many subsurface problems, such as environmental and acid mine remediation. A general rate expression has been implemented into TOUGHREACT, which considers multiple mechanisms (pathways) and includes multiple product, Monod, and inhibition terms. In this paper, the formulation for incorporating kinetic rates among primary species into the mass balance equations is presented. A batch sulfide oxi...

  15. Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions. Part I. Modeling

    OpenAIRE

    Gleeson, M. R.; Sheridan, John T.

    2009-01-01

    The photochemical processes present during free-radical-based holographic grating formation are examined. A kinetic model is presented, which includes, in a more nearly complete and physically realistic way, most of the major photochemical and nonlocal photopolymerization-driven diffusion effects. These effects include: (i) nonsteady-state kinetics (ii) spatially and temporally nonlocal polymer chain growth (iii) time varying photon absorption (iv) diffusion controlled viscosity effects (v) m...

  16. Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damk\\"ohler numbers

    CERN Document Server

    Bandopadhyay, Aditya; Méheust, Yves; Dentz, Marco

    2016-01-01

    Mixing fronts, where fluids of different chemical compositions mix with each other, are typically subjected to velocity gradients, ranging from the pore scale to the catchment scale due to permeability variations and flow line geometries. A common trait of these processes is that the mixing interface is strained by shear. Depending on the P\\'eclet number $Pe$, which represents the ratio of the characteristic diffusion time to the characteristic advection time, and the Damk\\"ohler number $Da$, which represents the ratio of the characteristic diffusion time to the characteristic reaction time, the local reaction rates can be strongly impacted by the dynamics of the mixing interface. This impact has been characterized mostly either in kinetics-limited or in mixing-limited conditions, that is, for either very low or very high $Da$. Here the coupling of shear flow and chemical reactivity is investigated for arbitrary Damk\\"ohler numbers, for a bimolecular reaction and an initial interface with separated reactants....

  17. Analysis of Absorption and Reaction Kinetics in the Oxidation of Organics in Effluents Using a Porous Electrode Ozonator

    Institute of Scientific and Technical Information of China (English)

    Alexander P. Mathews; ishora K. Panda

    2012-01-01

    A novel electrode design for the in situ generation of ozone in the reaction zone of a tubular reactor is described in this work. The ozone generator uses a porous inner electrode tube in the corona discharge assembly, and the ozone generated around the outer periphery of the porous tube diffuses into the tubular reactor and reacts with the contaminants in the fluid that is being treated. A mathematical model that includes absorption and second order reaction in the film is developed to describe ozonation kinetics of a contaminant dye in the tubular reactor. The model describes the experimental data for dye decolorization, oxidation byproducts, dissolved ozone, and ozone gas concentrations well. Model analysis indicates that the fast dye decolorization reaction occurs partly in the liquid film and partly in the bulk fluid. The model can be used in the selection of appropriate gas-liquid contactors for efficient oxidation of contaminants in effluents.

  18. Application of chemometrics methods with kinetic constraints for estimation of rate constants of second order consecutive reactions.

    Science.gov (United States)

    Kompany-Zareh, Mohsen; Khoshkam, Maryam

    2008-05-01

    To determine the rate constants for the second order consecutive reactions of the form U + V -(k1)--> W -(k2)--> P, a number of chemometrics and hard modeling-based methods are described. The absorption spectroscopic data from the reaction were utilized for performing the analysis. Concentrations and extinctions of components were comparable, and all of them were absorbing species. The number of steps in the reaction was less than the number of absorbing species, which resulted in a rank-deficient response matrix. This can cause difficulties for some of the methods described in the literature. The standard MATLAB functions were used for determining the solutions of the differential equations as well as for finding the optimal rate constants to describe the kinetic profiles. The available knowledge about the system determines the approaches described in this paper. The knowledge includes the spectra of reactants and products, the initial concentrations, and the exact kinetics. Some of this information is sometimes not available or is hard to estimate. Multiple linear regression for fitting the kinetic parameters to the obtained concentration profiles, rank augmentation using multiple batch runs, a mixed spectral approach which treats the reaction using a pseudo species concept, and principal components regression are the four groups of methods discussed in this study. In one of the simulated datasets the spectra are quite different, and in the other one the spectra of one reactant and of the product share a high degree of overlap. Instrumental noise, sampling error are the sources of error considered. Our aim was the investigation of the relative merits of each method. PMID:18469471

  19. Application of radioisotopes to the investigation of the kinetics and mechanism of reactions of some inorganic complex compounds

    International Nuclear Information System (INIS)

    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. Field-controlled electron transfer and reaction kinetics of the biological catalytic system of microperoxidase-11 and hydrogen peroxide

    Directory of Open Access Journals (Sweden)

    Yongki Choi

    2011-12-01

    Full Text Available Controlled reaction kinetics of the bio-catalytic system of microperoxidase-11 and hydrogen peroxide has been achieved using an electrostatic technique. The technique allowed independent control of 1 the thermodynamics of the system using electrochemical setup and 2 the quantum mechanical tunneling at the interface between microperoxidase-11 and the working electrode by applying a gating voltage to the electrode. The cathodic currents of electrodes immobilized with microperoxidase-11 showed a dependence on the gating voltage in the presence of hydrogen peroxide, indicating a controllable reduction reaction. The measured kinetic parameters of the bio-catalytic reduction showed nonlinear dependences on the gating voltage as the result of modified interfacial electron tunnel due to the field induced at the microperoxidase-11-electrode interface. Our results indicate that the kinetics of the reduction of hydrogen peroxide can be controlled by a gating voltage and illustrate the operation of a field-effect bio-catalytic transistor, whose current-generating mechanism is the conversion of hydrogen peroxide to water with the current being controlled by the gating voltage.