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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. 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. [Univ. of California, Los Angeles, CA (United States)

    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.

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

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    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

  5. Biochemical reaction engineering for redox reactions.

    Science.gov (United States)

    Wandrey, Christian

    2004-01-01

    Redox reactions are still a challenge for biochemical engineers. A personal view for the development of this field is given. Cofactor regeneration was an obstacle for quite some time. The first technical breakthrough was achieved with the system formate/formate dehydrogenase for the regeneration of NADH2. In cases where the same enzyme could be used for chiral reduction as well as for cofactor regeneration, isopropanol as a hydrogen source proved to be beneficial. The coproduct (acetone) can be removed by pervaporation. Whole-cell reductions (often yeast reductions) can also be used. By proper biochemical reaction engineering, it is possible to apply these systems in a continuous way. By cloning a formate dehydrogenase and an oxidoreductase "designer bug" can be obtained where formate is used instead of glucose as the hydrogen source. Complex sequences of redox reactions can be established by pathway engineering with a focus on gene overexpression or with a focus on establishing non-natural pathways. The success of pathway engineering can be controlled by measuring cytosolic metabolite concentrations. The optimal exploitation of such systems calls for the integrated cooperation of classical and molecular biochemical engineering.

  6. 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

  7. 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.

  8. Kinetic modeling of reactions in Foods

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    2008-01-01

    The level of quality that food maintains as it travels down the production-to-consumption path is largely determined by the chemical, biochemical, physical, and microbiological changes that take place during its processing and storage. Kinetic Modeling of Reactions in Foods demonstrates how to effec

  9. 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...

  10. 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

  11. Characterizing multistationarity regimes in biochemical reaction networks.

    Directory of Open Access Journals (Sweden)

    Irene Otero-Muras

    Full Text Available Switch like responses appear as common strategies in the regulation of cellular systems. Here we present a method to characterize bistable regimes in biochemical reaction networks that can be of use to both direct and reverse engineering of biological switches. In the design of a synthetic biological switch, it is important to study the capability for bistability of the underlying biochemical network structure. Chemical Reaction Network Theory (CRNT may help at this level to decide whether a given network has the capacity for multiple positive equilibria, based on their structural properties. However, in order to build a working switch, we also need to ensure that the bistability property is robust, by studying the conditions leading to the existence of two different steady states. In the reverse engineering of biological switches, knowledge collected about the bistable regimes of the underlying potential model structures can contribute at the model identification stage to a drastic reduction of the feasible region in the parameter space of search. In this work, we make use and extend previous results of the CRNT, aiming not only to discriminate whether a biochemical reaction network can exhibit multiple steady states, but also to determine the regions within the whole space of parameters capable of producing multistationarity. To that purpose we present and justify a condition on the parameters of biochemical networks for the appearance of multistationarity, and propose an efficient and reliable computational method to check its satisfaction through the parameter space.

  12. 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.

  13. Simulation methods with extended stability for stiff biochemical Kinetics

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    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.

  14. 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

    Background: The size and complexity of published biochemical network reconstructions are steadily increasing, expanding the potential scale of derived computational models. However, the construction of large biochemical network models is a laborious and error-prone task. Automated methods have...... 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...

  15. 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

  16. A study for multiple steady states of biochemical reactions under substrate and product inhibition.

    Science.gov (United States)

    Chien

    2000-08-01

    This paper combines Sturm's method with the tangent analysis method to solve a biochemical reaction involving multiplicity. This method can easily derive the necessary conditions for multiplicity. In addition, we find a starting bifurcation point for multiplicity which cannot be obtained by the tangent method alone. Moreover, a start-up strategy is suggested to obtain a high conversion and unique steady state in four selected kinetic models of biochemical reactions, with inhibition.

  17. Nonequilibrium steady state of biochemical cycle kinetics under non-isothermal conditions

    CERN Document Server

    Jin, Xiao

    2016-01-01

    Nonequilibrium steady state of isothermal biochemical cycle kinetics has been extensively studied, but much less investigated under non-isothermal conditions. However, once the heat exchange between subsystems is rather slow, the isothermal assumption of the whole system meets great challenge, which is indeed the case inside many kinds of living organisms. Here we generalize the nonequilibrium steady-state theory of isothermal biochemical cycle kinetics, in the master-equation models, to the situation in which the temperatures of subsystems can be far from uniform. We first obtain a new thermodynamic relation between the chemical reaction rates and thermodynamic potentials under such a non-isothermal circumstances, which immediately implies simply applying the isothermal transition-state rate formula for each chemical reaction in terms of only the reactants' temperature, is not thermodynamically consistent. Therefore, we mathematically derive several revised reaction-rate formulas which not only obey the new ...

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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...

  3. 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.

  4. 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

  5. Reaction Kinetics of Nanostructured Silicon Carbide

    Science.gov (United States)

    Wallis, Kendra; Zerda, T. W.

    2006-10-01

    Nanostructured silicon carbide (SiC) is of interest particularly for use in nanocomposites that demonstrate high hardness as well as for use in semiconductor applications. Reaction kinetics studies of solid-solid reactions are relatively recent and present a method of determining the reaction mechanism and activation energy by measuring reaction rates. We have used induction heating to heat quickly, thus reducing the error in reaction time measurements. Data will be presented for reactions using silicon nanopowder (melting point of silicon. Using the well-known Avrami-Erofeev model, a two-parameter chi- square fit of the data provided a rate constant (k) and parameter (n), related to the reaction mechanism, for each temperature. From these data, an activation energy of 138 kJ/mol was calculated. In addition, the parameter n suggests the reaction mechanism, which will also be discussed. Experiments are continuing at higher temperatures to consider the liquid- solid reaction as well.

  6. 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)

  7. Biochemical reaction engineering and process development in anaerobic wastewater treatment.

    Science.gov (United States)

    Aivasidis, Alexander; Diamantis, Vasileios

    2005-01-01

    Developments in production technology have frequently resulted in the concentrated local accumulation of highly organic-laden wastewaters. Anaerobic wastewater treatment, in industrial applications, constitutes an advanced method of synthesis by which inexpensive substrates are converted into valuable disproportionate products. A critical discussion of certain fundamental principles of biochemical reaction engineering relevant to the anaerobic mode of operation is made here, with special emphasis on the roles of thermodynamics, kinetics, mass and heat transfer, reactor design, biomass retention and recycling. The applications of the anaerobic processes are discussed, introducing the principles of an upflow anaerobic sludge bed reactor and a fixed-bed loop reactor. The merits of staging reactor systems are presented using selected examples based on two decades of research in the field of anaerobic fermentation and wastewater treatment at the Forschungszentrum Julich (Julich Research Center, Germany). Wastewater treatment is an industrial process associated with one of the largest levels of mass throughput known, and for this reason it provides a major impetus to further developments in bioprocess technology in general.

  8. SABRE: A Tool for Stochastic Analysis of Biochemical Reaction Networks

    CERN Document Server

    Didier, Frederic; Mateescu, Maria; Wolf, Verena

    2010-01-01

    The importance of stochasticity within biological systems has been shown repeatedly during the last years and has raised the need for efficient stochastic tools. We present SABRE, a tool for stochastic analysis of biochemical reaction networks. SABRE implements fast adaptive uniformization (FAU), a direct numerical approximation algorithm for computing transient solutions of biochemical reaction networks. Biochemical reactions networks represent biological systems studied at a molecular level and these reactions can be modeled as transitions of a Markov chain. SABRE accepts as input the formalism of guarded commands, which it interprets either as continuous-time or as discrete-time Markov chains. Besides operating in a stochastic mode, SABRE may also perform a deterministic analysis by directly computing a mean-field approximation of the system under study. We illustrate the different functionalities of SABRE by means of biological case studies.

  9. Inferring biochemical reaction pathways: the case of the gemcitabine pharmacokinetics

    Directory of Open Access Journals (Sweden)

    Lecca Paola

    2012-05-01

    Full Text Available Abstract Background The representation of a biochemical system as a network is the precursor of any mathematical model of the processes driving the dynamics of that system. Pharmacokinetics uses mathematical models to describe the interactions between drug, and drug metabolites and targets and through the simulation of these models predicts drug levels and/or dynamic behaviors of drug entities in the body. Therefore, the development of computational techniques for inferring the interaction network of the drug entities and its kinetic parameters from observational data is raising great interest in the scientific community of pharmacologists. In fact, the network inference is a set of mathematical procedures deducing the structure of a model from the experimental data associated to the nodes of the network of interactions. In this paper, we deal with the inference of a pharmacokinetic network from the concentrations of the drug and its metabolites observed at discrete time points. Results The method of network inference presented in this paper is inspired by the theory of time-lagged correlation inference with regard to the deduction of the interaction network, and on a maximum likelihood approach with regard to the estimation of the kinetic parameters of the network. Both network inference and parameter estimation have been designed specifically to identify systems of biotransformations, at the biochemical level, from noisy time-resolved experimental data. We use our inference method to deduce the metabolic pathway of the gemcitabine. The inputs to our inference algorithm are the experimental time series of the concentration of gemcitabine and its metabolites. The output is the set of reactions of the metabolic network of the gemcitabine. Conclusions Time-lagged correlation based inference pairs up to a probabilistic model of parameter inference from metabolites time series allows the identification of the microscopic pharmacokinetics and

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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

  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. 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...

  18. 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.

  19. 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

  20. 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

  1. Reaction rates for mesoscopic reaction-diffusion kinetics.

    Science.gov (United States)

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-01

    The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

  2. Reaction rates for mesoscopic reaction-diffusion kinetics

    Science.gov (United States)

    Hellander, Stefan; Hellander, Andreas; Petzold, Linda

    2015-02-01

    The mesoscopic reaction-diffusion master equation (RDME) is a popular modeling framework frequently applied to stochastic reaction-diffusion kinetics in systems biology. The RDME is derived from assumptions about the underlying physical properties of the system, and it may produce unphysical results for models where those assumptions fail. In that case, other more comprehensive models are better suited, such as hard-sphere Brownian dynamics (BD). Although the RDME is a model in its own right, and not inferred from any specific microscale model, it proves useful to attempt to approximate a microscale model by a specific choice of mesoscopic reaction rates. In this paper we derive mesoscopic scale-dependent reaction rates by matching certain statistics of the RDME solution to statistics of the solution of a widely used microscopic BD model: the Smoluchowski model with a Robin boundary condition at the reaction radius of two molecules. We also establish fundamental limits on the range of mesh resolutions for which this approach yields accurate results and show both theoretically and in numerical examples that as we approach the lower fundamental limit, the mesoscopic dynamics approach the microscopic dynamics. We show that for mesh sizes below the fundamental lower limit, results are less accurate. Thus, the lower limit determines the mesh size for which we obtain the most accurate results.

  3. 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.

  4. Reaction kinetic analysis of reactor surveillance data

    Energy Technology Data Exchange (ETDEWEB)

    Yoshiie, T., E-mail: yoshiie@rri.kyoto-u.ac.jp [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); Sato, K.; Xu, Q. [Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka-fu 590-0494 (Japan); Nagai, Y. [The Oarai Center, Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan)

    2015-06-01

    In reactor pressure vessel surveillance data, it was found that the concentration of matrix defects was very low even after nearly 40 years of operation, though a large number of precipitates existed. In this paper, defect structures obtained from surveillance data of A533B (high Cu concentration) were simulated using reaction kinetic analysis with 11 rate equations. The coefficients used in the equations were quite different from those obtained by fitting a Fe-0.6 wt%Cu alloy irradiated by the Kyoto University Reactor. The difference was mainly caused by alloying elements in A533B, and the effect of alloying elements was extracted. The same code was applied to low-Cu A533B irradiated with high irradiation damage rate, and the formation of voids was correctly simulated.

  5. Computer prediction system on solid/solid reaction kinetics

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A computer software system of kinetic predication of solid/solid reaction, KinPreSSR, was developed using Visual C++ and FoxPro. It includes two main modules, REACTION and DIFFUSION. KinPreSSR deals with the kinetics on the diffusion in solids as well as solid/solid reactions. The REACTION module in KinPreSSR was mainly described, which has organized the commonly recognized kinetic models, parameters, and employed both numerical and graphical methods for data analyses. The proper combination between the kinetic contents and the analytical methods enables users to use KinPreSSR for the evaluation and prediction of solid/solid reactions interested. As an example to show some of functions of KinPreSSR, the kinetics analysis for the reaction between SrCO3 and TiO2 powders to form SrTiO3 with a series of kinetic data from isothermal measurements was demonstrated.

  6. 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...

  7. Mathematics analysis of polymerase chain reaction kinetic curves.

    Science.gov (United States)

    Sochivko, D G; Fedorov, A A; Varlamov, D A; Kurochkin, V E; Petrov, R V

    2016-01-01

    The paper reviews different approaches to the mathematical analysis of polymerase chain reaction (PCR) kinetic curves. The basic principles of PCR mathematical analysis are presented. Approximation of PCR kinetic curves and PCR efficiency curves by various functions is described. Several PCR models based on chemical kinetics equations are suggested. Decision criteria for an optimal function to describe PCR efficiency are proposed.

  8. Reaction of nitrile pollutants in high temperature water: Reaction pathway analysis and kinetic modeling

    Energy Technology Data Exchange (ETDEWEB)

    Izzo, B.; Harrell, C.; Klein, M.T. [Univ. of Delaware, Newark, DE (United States); LaMarca, C. [E.I. du Pont de Nemours & Co., Wilmington, DE (United States)

    1996-12-31

    The reaction chemistry of acetonitrile and benzonitrile in High Temperature Water (HTW) was investigated. The reaction products were the associated amides and carboxylic acids. A kinetic model incorporating two autocatalytic steps captured the kinetics observed. The optimized rate constants highlighted differences in the reaction chemistry of aliphatic and aromatic nitrites at these reaction conditions. 6 refs., 3 figs., 2 tabs.

  9. 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…

  10. Kinetics of ozone-phenol reaction in aqueous solutions

    Energy Technology Data Exchange (ETDEWEB)

    Joshi, M.G.; Shambaugh, R.L.

    1982-01-01

    The kinetics of the reaction of ozone and phenol in aqueous medium was studied. The reaction was first order with respect to both ozone and phenol. The rate constant was found to increase with increase in the pH of the reaction mixture. Four different catalysts were examined for their effect on the rate of reaction. 30 refs.

  11. Nitrile reaction in high-temperature water: Kinetics and mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Izzo, B.; Harrell, C.L.; Klein, M.T. [Univ. of Delaware, Newark, DE (United States). Dept. of Chemical Engineering

    1997-08-01

    The reaction pathways, kinetics and mechanisms underlying the hydrolysis of aliphatic and aromatic nitriles in high-temperature water (HTW) were investigated. The reaction products were the associated amides and carboxylic acids. Autocatalytic kinetics were observed and confirmed by experiment and analysis of the physical chemistry of the HTW reaction environment. A model incorporating two autocatalytic steps captured the observed kinetics well, and the associated optimized rate constants highlighted the key differences in the reaction chemistry of aliphatic and aromatic nitriles. The rate behavior of nitrile hydrolysis at these conditions has tangible consequences regarding optimal processing strategies.

  12. 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...

  13. 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.

  14. Plant Glutathione Biosynthesis: Diversity in Biochemical Regulation and Reaction Products

    Directory of Open Access Journals (Sweden)

    Ashley eGalant

    2011-09-01

    Full Text Available In plants, exposure to temperature extremes, heavy metal-contaminated soils, drought, air pollutants, and pathogens results in the generation of reactive oxygen species that alter the intracellular redox environment, which in turn influences signaling pathways and cell fate. As part of their response to these stresses, plants produce glutathione. Glutathione acts as an antioxidant by quenching reactive oxygen species, and is involved in the ascorbate-glutathione cycle that eliminates damaging peroxides. Plants also use glutathione for the detoxification of xenobiotics, herbicides, air pollutants (sulfur dioxide and ozone, and toxic heavy metals. Two enzymes catalyze glutathione synthesis: glutamate-cysteine ligase (GCL, and glutathione synthetase (GS. Glutathione is a ubiquitous protective compound in plants, but the structural and functional details of the proteins that synthesize it, as well as the potential biochemical mechanisms of their regulation, have only begun to be explored. As discussed here, the core reactions of glutathione synthesis are conserved across various organisms, but plants have diversified both the regulatory mechanisms that control its synthesis and the range of products derived from this pathway. Understanding the molecular basis of glutathione biosynthesis and its regulation will expand our knowledge of this component in the plant stress response network.

  15. The thermodynamic natural path in chemical reaction kinetics

    Directory of Open Access Journals (Sweden)

    Moishe garfinkle

    2000-01-01

    Full Text Available The Natural Path approach to chemical reaction kinetics was developed to bridge the considerable gap between the Mass Action mechanistic approach and the non-mechanistic irreversible thermodynamic approach. The Natural Path approach can correlate empirical kinetic data with a high degree precision, as least equal to that achievable by the Mass-Action rate equations, but without recourse mechanistic considerations. The reaction velocities arising from the particular rate equation chosen by kineticists to best represent the kinetic behavior of a chemical reaction are the natural outcome of the Natural Path approach. Moreover, by virtue of its thermodynamic roots, equilibrium thermodynamic functions can be extracted from reaction kinetic data with considerable accuracy. These results support the intrinsic validity of the Natural Path approach.

  16. Moment equations for chromatography based on Langmuir type reaction kinetics.

    Science.gov (United States)

    Miyabe, Kanji

    2014-08-22

    Moment equations were derived for chromatography, in which the reaction kinetics between solute molecules and functional ligands on the stationary phase was represented by the Langmuir type rate equation. A set of basic equations of the general rate model of chromatography representing the mass balance, mass transfer rate, and reaction kinetics in the column were analytically solved in the Laplace domain. The moment equations for the first absolute moment and the second central moment in the real time domain were derived from the analytical solution in the Laplace domain. The moment equations were used for predicting the chromatographic behavior under hypothetical HPLC conditions. The influence of the parameters relating to the adsorption equilibrium and to the reaction kinetics on the chromatographic behavior was quantitatively evaluated. It is expected that the moment equations are effective for a detailed analysis of the influence of the mass transfer rates and of the Langmuir type reaction kinetics on the column efficiency.

  17. 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 ℃.

  18. 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…

  19. Belousov-Zhabotinsky oscillatory reaction. Kinetics of malonic acid decomposition

    Directory of Open Access Journals (Sweden)

    LJILJANA KOLAR-ANIC

    2000-10-01

    Full Text Available The kinetics of the Belousov-Zhabotinsky (BZ oscillatory reaction was analyzed. With this aim, the time evolution of a reaction mixture composed of malonic acid, bromate, sulfuric acid and cerium(III was studied at 298 K. Pseudo-first order kinetics with respect to malonic acid as the species undergoing decomposition with a corresponding rate constant, k = 7.5×10-3 min-1, was found.

  20. 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 (...

  1. 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.

  2. 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.

  3. 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...

  4. 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.

  5. 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 to...

  6. 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.

  7. 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)

  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. 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.

  11. 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

  12. 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...

  13. 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)

  14. Diagnostic Appraisal of Grade 12 Students' Understanding of Reaction Kinetics

    Science.gov (United States)

    Yan, Yaw Kai; Subramaniam, R.

    2016-01-01

    The study explored grade 12 students' understanding of reaction kinetics, a topic which has not been extensively explored in the chemistry education literature at this level. A 3-tier diagnostic instrument with 11 questions was developed--this format is of very recent origin and has been the subject of only a handful of studies. The findings…

  15. 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...

  16. Developing the reaction kinetics for a biodiesel reactor.

    Science.gov (United States)

    Slinn, Matthew; Kendall, Kevin

    2009-04-01

    The aim of this paper was to investigate the kinetics of the biodiesel reaction in order to find out how best to reach 96.5% methyl ester. The purity of the biodiesel product was examined using gas chromatography to the EN14214 FAME standard and real-time optical microscopy was used to observe the reaction. The problem was the reaction does not reach completion and the mechanism is not understood. It was observed that droplet size had a major influence on reaction end point and that the reaction was mass-transfer limited. This observation was confirmed by developing a mass-transfer based reaction model using the data from the batch reactor which agreed with results from other researchers. The model predicted better conversion with more mixing intensity. The results show that significant improvements could be made to the conventional FAME process.

  17. 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.

  18. 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.

  19. Reaction kinetics of cellulose hydrolysis in subcritical and supercritical water

    Science.gov (United States)

    Olanrewaju, Kazeem Bode

    The uncertainties in the continuous supply of fossil fuels from the crisis-ridden oil-rich region of the world is fast shifting focus on the need to utilize cellulosic biomass and develop more efficient technologies for its conversion to fuels and chemicals. One such technology is the rapid degradation of cellulose in supercritical water without the need for an enzyme or inorganic catalyst such as acid. This project focused on the study of reaction kinetics of cellulose hydrolysis in subcritical and supercritical water. Cellulose reactions at hydrothermal conditions can proceed via the homogeneous route involving dissolution and hydrolysis or the heterogeneous path of surface hydrolysis. The work is divided into three main parts. First, the detailed kinetic analysis of cellulose reactions in micro- and tubular reactors was conducted. Reaction kinetics models were applied, and kinetics parameters at both subcritical and supercritical conditions were evaluated. The second major task was the evaluation of yields of water soluble hydrolysates obtained from the hydrolysis of cellulose and starch in hydrothermal reactors. Lastly, changes in molecular weight distribution due to hydrothermolytic degradation of cellulose were investigated. These changes were also simulated based on different modes of scission, and the pattern generated from simulation was compared with the distribution pattern from experiments. For a better understanding of the reaction kinetics of cellulose in subcritical and supercritical water, a series of reactions was conducted in the microreactor. Hydrolysis of cellulose was performed at subcritical temperatures ranging from 270 to 340 °C (tau = 0.40--0.88 s). For the dissolution of cellulose, the reaction was conducted at supercritical temperatures ranging from 375 to 395 °C (tau = 0.27--0.44 s). The operating pressure for the reactions at both subcritical and supercritical conditions was 5000 psig. The results show that the rate-limiting step in

  20. 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

  1. 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.

  2. 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.

  3. 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...

  4. 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

  5. Biochemical kinetics of fermentative hydrogen production by Clostridium butyricum W5

    Energy Technology Data Exchange (ETDEWEB)

    Wang, X. [School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005 (Australia); Monis, P.T. [Australian Water Quality Centre, SA Water, Bolivar, SA 5110 (Australia); Saint, C.P.; Jin, B. [School of Earth and Environmental Sciences, The University of Adelaide, Adelaide, SA 5005 (Australia)]|[Australian Water Quality Centre, SA Water, Bolivar, SA 5110 (Australia)

    2009-01-15

    The fermentation process for hydrogen production has been widely reported. However, there is lack of information related to detailed kinetic studies. The aim of this work was to investigate biochemical kinetics of fermentative hydrogen production by a newly isolated strain of Clostridium butyricum W5. The research objectives were to clarify relationships between hydrogen fermentation and biochemical parameters and hydrogenases, and consequently to seek an index for hydrogen production. Time profiles of hydrogen production, cell growth, volatile fatty acid accumulation and [FeFe]hydrogenase expression level were described. The amount of hydrogen produced in a laboratory batch process was 45.45 mmol/L at 10 h and peak production rate was 7.61 mmol/l/h at 9 h. Cell growth rate peaked at 8 h. Lactic acid was a main by-product, followed by butyric acid and acetic acid. Quantification of [FeFe]hydrogenase mRNA was optimized by a real-time reverse transcriptase-PCR. Statistical analysis showed that [FeFe]hydrogenase mRNA levels peak earlier than hydrogen production rate, and cell growth has a linear positive relationship with hydrogen production. (author)

  6. 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

  7. 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.

  8. 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.

  9. 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)

  10. 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.

  11. 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

  12. 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.

  13. KINETIC MODELS STUDY OF HYDRODESULPHURIZATION VACUUM DISTILLATE REACTION

    OpenAIRE

    AbdulMunem A. Karim

    2013-01-01

       This study deals with  kinetics of hydrodesulphurization (HDS) reaction of vacuum gas oil (611-833) K which was distillated from Kirkuk crude oil and which was obtained by blending the fractions, light vacuum gas oil (611 - 650) K, medium vacuum gas oil (650-690) K, heavy vacuum gas oil (690-727) K and very heavy vacuum gas oil (727-833) K.   The vacuum gas oil was hydrotreated on a commercial cobalt-molybdenum alumina catalyst presulfied at specified conditions in a laboratory trickle bed...

  14. Kinetics of Reduction Reaction in Micro-Fluidized Bed

    Institute of Scientific and Technical Information of China (English)

    LINYin-he; GUOZhan—cheng; TANGHui—qing; REN Shan; LIJing—wei

    2012-01-01

    Micro-fluidized bed reactor is a new research method for the reduction of iron ore fines. The reactor is op- erated as a differential reactor to ensure a constant gas concentration and temperature within the reactor volume. In order to understand the dynamic process of the reduction reaction in micro-fluidized bed, a series of kinetic experi- ments were designed. In the micro fluidized bed, the use of shrinking core model describes the dynamic behavior of reduction of iron ore. And the apparent activation energy is calculated in the range of 700--850 ~C while the initial atmosphere is 100% content of CO.

  15. KINETIC MODELS STUDY OF HYDRODESULPHURIZATION VACUUM DISTILLATE REACTION

    Directory of Open Access Journals (Sweden)

    AbdulMunem A. Karim

    2013-05-01

    Full Text Available    This study deals with  kinetics of hydrodesulphurization (HDS reaction of vacuum gas oil (611-833 K which was distillated from Kirkuk crude oil and which was obtained by blending the fractions, light vacuum gas oil (611 - 650 K, medium vacuum gas oil (650-690 K, heavy vacuum gas oil (690-727 K and very heavy vacuum gas oil (727-833 K.   The vacuum gas oil was hydrotreated on a commercial cobalt-molybdenum alumina catalyst presulfied at specified conditions in a laboratory trickle bed reactor. The reaction temperature range (583-643 K,liquid hourly space velocity range (1.5-3.75 h-1 and hydrogen pressure was kept constant at 3.5 MPa with hydrogen to oil ratio about 250 lt/lt.           The conversion results for desulphurization reaction appeared to obey the second order reaction. According to this model, the rate constants for desulphurization reaction were determined. Finally, the apparent activation energy (Ea, enthalpy of activation ( H* and entropy ( S* were calculated based on the values of rate constant (k2 and were equal 80.3792 KJ/mole, 75.2974 KJ/mole and 197.493 J/mole, respectively.

  16. 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.)

  17. Kinetics of the reaction of hydroxyl radicals with nitric acid

    Science.gov (United States)

    Margitan, J. J.; Watson, R. T.

    1982-01-01

    An extensive study was made of the reaction of hydroxyl radicals with nitric acid in a laser photolysis-resonance fluorescence system. A 266 nm laser was used to photolyze HNO3 in the temperature range 225-415 K at pressures of 20-300 torr. A temperature dependence was detected below room temperature, with a leveling off at 298 K and a wide spread in the rate constants. A pressure dependence was observed over the entire range and was more pronounced at lower temperatures. The results are noted to be in agreement with those of previous investigations. However, the wide range of rate constants are suggested to be a problem for stratospheric HO(x) modeling for anthropogenic effects. No explanation could be given of the varying results obtained by other investigators regarding the kinetics of the reactions.

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

    Energy Technology Data Exchange (ETDEWEB)

    Thanh, Vo Hong, E-mail: vo@cosbi.eu [The Microsoft Research - University of Trento Centre for Computational and Systems Biology, Piazza Manifattura 1, Rovereto 38068 (Italy); Priami, Corrado, E-mail: priami@cosbi.eu [The Microsoft Research - University of Trento Centre for Computational and Systems Biology, Piazza Manifattura 1, Rovereto 38068 (Italy); Department of Mathematics, University of Trento, Trento (Italy)

    2015-08-07

    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. 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.

  20. 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.

  1. Reaction route graphs. III. Non-minimal kinetic mechanisms.

    Science.gov (United States)

    Fishtik, Ilie; Callaghan, Caitlin A; Datta, Ravindra

    2005-02-24

    The concept of reaction route (RR) graphs introduced recently by us for kinetic mechanisms that produce minimal graphs is extended to the problem of non-minimal kinetic mechanisms for the case of a single overall reaction (OR). A RR graph is said to be minimal if all of the stoichiometric numbers in all direct RRs of the mechanism are equal to +/-1 and non-minimal if at least one stoichiometric number in a direct RR is non-unity, e.g., equal to +/-2. For a given mechanism, four unique topological characteristics of RR graphs are defined and enumerated, namely, direct full routes (FRs), empty routes (ERs), intermediate nodes (INs), and terminal nodes (TNs). These are further utilized to construct the RR graphs. One algorithm involves viewing each IN as a central node in a RR sub-graph. As a result, the construction and enumeration of RR graphs are reduced to the problem of balancing the peripheral nodes in the RR sub-graphs according to the list of FRs, ERs, INs, and TNs. An alternate method involves using an independent set of RRs to draw the RR graph while satisfying the INs and TNs. Three examples are presented to illustrate the application of non-minimal RR graph theory.

  2. 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.

  3. Kinetics and reaction mechanism of hydroxyl radical reaction with methyl formate

    Energy Technology Data Exchange (ETDEWEB)

    Good, D.A.; Hanson, J.; Francisco, J.S.; Li, Z.; Jeong, G.R.

    1999-12-16

    Ab initio molecular orbital theory has been used to examine the kinetics and mechanism for the reaction of hydroxyl radical with methyl formate. From the ab initio parameters the room temperature rate constant is calculated and found to be in good agreement with the experimental determination. It is found that 86% of the reaction proceeds via abstraction of the carbonyl hydrogen from methyl formate by hydroxyl radical, resulting in the formation of CH{sub 3}OCO radical. CH{sub 3}OCO is expected to oxidize to formaldehyde and carbon dioxide under tropospheric conditions.

  4. The Reaction Kinetics of LiD with Water Vapor

    Energy Technology Data Exchange (ETDEWEB)

    Balooch, M; Dinh, L N; Calef, D F

    2003-04-01

    The interaction of LiD with water vapor in the partial pressure range of 10{sup -7} Torr to 20 Torr has been investigated. The reaction probability of water with pure LiD cleaved in an ultra high vacuum environment was obtained using the modulated molecular beam technique. This probability was 0.11 and independent of LiD surface temperature suggesting a negligible activation energy for the reaction in agreement with quantum chemical calculations. The value gradually reduced, however, to .007 as the surface concentration of oxygen containing product (LiOH), which was monitored in-situ by Auger electron spectroscopy on the reaction zone, approached full coverage. As the hydroxide film grew beyond a monolayer, the phase lag of hydrogen product increased from zero to 20 degrees and the reaction probability reduced further until it approached our detection limit ({approx} 10{sup -4}). This phase lag was attributed to a diffusion limited process in this regime. In separate experiments, the film growth has been studied in nitrogen atmosphere with 100% relative humidity using thermogravimetric analysis (TGA) and in air with 50% relative humidity utilizing scanning electron microscopy (SEM). For exposures to environment with high water concentrations and for micrometer thick films, the reaction probability reduced to 4 x 10{sup -7} and was independent of exposure time, The lattice diffusion through the film was no longer controlling the transport of water to the LiD/LiOH interface. Microcracks generated in the film to release stress provided easier pathways to the interface. A modified microscope, capable of both atomic force microscopy (AFM) and nanoindentation, was employed to investigate the surface morphology of LiOH.H{sub 2}O grown on LiOH at high water vapor partial pressures and the kinetics of this growth.

  5. 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

  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. Real-time monitoring of mass-transport-related enzymatic reaction kinetics in a nanochannel-array reactor.

    Science.gov (United States)

    Li, Su-Juan; Wang, Chen; Wu, Zeng-Qiang; Xu, Jing-Juan; Xia, Xing-Hua; Chen, Hong-Yuan

    2010-09-01

    To understand the fundamentals of enzymatic reactions confined in micro-/nanosystems, the construction of a small enzyme reactor coupled with an integrated real-time detection system for monitoring the kinetic information is a significant challenge. Nano-enzyme array reactors were fabricated by covalently linking enzymes to the inner channels of a porous anodic alumina (PAA) membrane. The mechanical stability of this nanodevice enables us to integrate an electrochemical detector for the real-time monitoring of the formation of the enzyme reaction product by sputtering a thin Pt film on one side of the PAA membrane. Because the enzymatic reaction is confined in a limited nanospace, the mass transport of the substrate would influence the reaction kinetics considerably. Therefore, the oxidation of glucose by dissolved oxygen catalyzed by immobilized glucose oxidase was used as a model to investigate the mass-transport-related enzymatic reaction kinetics in confined nanospaces. The activity and stability of the enzyme immobilized in the nanochannels was enhanced. In this nano-enzyme reactor, the enzymatic reaction was controlled by mass transport if the flux was low. With an increase in the flux (e.g., >50 microL min(-1)), the enzymatic reaction kinetics became the rate-determining step. This change resulted in the decrease in the conversion efficiency of the nano-enzyme reactor and the apparent Michaelis-Menten constant with an increase in substrate flux. This nanodevice integrated with an electrochemical detector could help to understand the fundamentals of enzymatic reactions confined in nanospaces and provide a platform for the design of highly efficient enzyme reactors. In addition, we believe that such nanodevices will find widespread applications in biosensing, drug screening, and biochemical synthesis.

  8. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction

    Directory of Open Access Journals (Sweden)

    Cobbs Gary

    2012-08-01

    Full Text Available Abstract Background Numerous models for use in interpreting quantitative PCR (qPCR data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented. Results Two models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the

  9. 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

  10. 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

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. Reaction kinetics and validity of BOD test for domestic wastewater released in marine ecosystems.

    Science.gov (United States)

    Dhage, Shivani S; Dalvi, Amita A; Prabhu, Damodar V

    2012-09-01

    With urbanization of coastal cities, marine pollution is becoming a severe problem. The rates of biodegradation, decomposition, and ratification of pollutants get slowed down due to salinity. The higher temperatures prevalent in tropical regions significantly affect reaction rates. Multiple factors influence the rate of biodegradation, making the process complex. Hence, prediction and evaluation of the assimilative capacity of the marine environment due to wastewater discharges is becoming a difficult task. Biochemical oxygen demand (BOD) is a wet oxidation process, which follows first-order kinetics. The values of kinetic rate constants are expected to differ with varying salinities and temperatures. Research is carried out using glucose-glutamic acid and domestic wastewater to evaluate the impact of salinity on biodegradation of carbonaceous waste at 20°C and 27°C. The findings confirm the hypothesis of slow biodegradation of carbonaceous organic matter in marine waters. An inverse relationship between rate of biodegradation and salinity was observed. BOD exertion at 20°C (5 days) and 27°C (3 days) for the marine environment is comparable at selected salinities thereby confirming the validity of BOD test of shorter duration at elevated temperature.

  16. Combustion reaction kinetics of guarana seed residue applying isoconversional methods and consecutive reaction scheme.

    Science.gov (United States)

    Lopes, Fernanda Cristina Rezende; Tannous, Katia; Rueda-Ordóñez, Yesid Javier

    2016-11-01

    This work aims the study of decomposition kinetics of guarana seed residue using thermogravimetric analyzer under synthetic air atmosphere applying heating rates of 5, 10, and 15°C/min, from room temperature to 900°C. Three thermal decomposition stages were identified: dehydration (25.1-160°C), oxidative pyrolysis (240-370°C), and combustion (350-650°C). The activation energies, reaction model, and pre-exponential factor were determined through four isoconversional methods, master plots, and linearization of the conversion rate equation, respectively. A scheme of two-consecutive reactions was applied validating the kinetic parameters of first-order reaction and two-dimensional diffusion models for the oxidative pyrolysis stage (149.57kJ/mol, 6.97×10(10)1/s) and for combustion stage (77.98kJ/mol, 98.611/s), respectively. The comparison between theoretical and experimental conversion and conversion rate showed good agreement with average deviation lower than 2%, indicating that these results could be used for modeling of guarana seed residue. PMID:27513645

  17. 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

  18. Cr stable isotope fractionation and reaction kinetics in aqueous milieu

    Science.gov (United States)

    Zink, S.; Schoenberg, R.; Staubwasser, M.

    2009-12-01

    Mass-dependent stable Cr isotope variations show great potential to monitor the natural attenuation of anthropogenic chromate pollution as well as to investigate changes in environmental conditions in the present and the past. However, accurate interpretation of mass-dependent Cr isotope variations requires profound knowledge of the Cr isotope fractionation behaviour during redox transitions and the isotope exchange kinetics of the reactions involved. Here, we present a comprehensive dataset of stable Cr isotope fractionation and reaction kinetics during Cr(III) oxidation, Cr(VI) reduction and isotopic exchange between soluble Cr(III) and Cr(VI) in aqueous milieu. All experiments were carried out with both oxidation states (i.e. Cr(III) and Cr(VI)) in solution, using H2O2 as oxidising as well as reducing agent. The pH conditions were varied to investigate the influence of the different Cr(III) and Cr(VI) species on the Cr isotope fractionation and on the reaction mechanisms during the enforced redox transitions. All Cr stable isotope measurements were performed by high-resolution MC-ICP-MS [1]. The reduction of Cr(VI) to Cr(III) with H2O2 under strongly acidic conditions shows an equilibrium isotope fractionation of Δ(53,52Cr)Cr(III)-Cr(VI) of -3.54 ± 0.35 ‰. This value is within uncertainty equal to that of -3.4 ± 0.1 ‰ reported by Ellis et al. [2], who used natural sediment and magnetite as reducing agents at pH 6 to 7. At pH = 7 our reduction experiments show a unidirectional, kinetic isotope fractionation Δ(53,52Cr)Cr(III)-Cr(VI) of approximately -5 ‰ for reduction rates of up to 80 %, but a strong deviation from this Rayleigh-type process for higher reduction rates. However, at a pH value of 7 H2O2 supports the temporary formation and decomposition of Cr(V)-peroxo complexes that might explain this fractionation behaviour and deviation from a single Rayleigh type trend. The oxidation experiments of Cr(III) to Cr(VI) were carried out in alkaline media

  19. 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

  20. Review of computer simulations of isotope effects on biochemical reactions: From the Bigeleisen equation to Feynman's path integral.

    Science.gov (United States)

    Wong, Kin-Yiu; Xu, Yuqing; Xu, Liang

    2015-11-01

    Enzymatic reactions are integral components in many biological functions and malfunctions. The iconic structure of each reaction path for elucidating the reaction mechanism in details is the molecular structure of the rate-limiting transition state (RLTS). But RLTS is very hard to get caught or to get visualized by experimentalists. In spite of the lack of explicit molecular structure of the RLTS in experiment, we still can trace out the RLTS unique "fingerprints" by measuring the isotope effects on the reaction rate. This set of "fingerprints" is considered as a most direct probe of RLTS. By contrast, for computer simulations, oftentimes molecular structures of a number of TS can be precisely visualized on computer screen, however, theoreticians are not sure which TS is the actual rate-limiting one. As a result, this is an excellent stage setting for a perfect "marriage" between experiment and theory for determining the structure of RLTS, along with the reaction mechanism, i.e., experimentalists are responsible for "fingerprinting", whereas theoreticians are responsible for providing candidates that match the "fingerprints". In this Review, the origin of isotope effects on a chemical reaction is discussed from the perspectives of classical and quantum worlds, respectively (e.g., the origins of the inverse kinetic isotope effects and all the equilibrium isotope effects are purely from quantum). The conventional Bigeleisen equation for isotope effect calculations, as well as its refined version in the framework of Feynman's path integral and Kleinert's variational perturbation (KP) theory for systematically incorporating anharmonicity and (non-parabolic) quantum tunneling, are also presented. In addition, the outstanding interplay between theory and experiment for successfully deducing the RLTS structures and the reaction mechanisms is demonstrated by applications on biochemical reactions, namely models of bacterial squalene-to-hopene polycyclization and RNA 2'-O

  1. Kinetics of the Reaction of CO2 with Aqueous Potassium Salt of Taurine and Glycine

    NARCIS (Netherlands)

    Kumar, P.S.; Hogendoorn, J.A.; Versteeg, G.F.; Feron, P.H.M.

    2003-01-01

    The kinetics of the reaction between CO2 and aqueous potassium salts of taurine and glycine was measured at 295 K in a stirred-cell reactor with a flat gas–liquid interface. For aqueous potassium taurate solutions, the temperature effect on the reaction kinetics was measured at 285 and 305 K. Unlike

  2. Kinetics of the reaction of CO2 with aqueous potassium salt of taurine and glycine

    NARCIS (Netherlands)

    Kumar, P.S.; Hogendoorn, J.A.; Versteeg, G.F.; Feron, P.H.M.

    2003-01-01

    The kinetics of the reaction between CO2 and aqueous potassium salts of taurine and glycine was measured at 295 K in a stirred-cell reactor with a flat gas-liquid interface. For aqueous potassium taurate solutions, the temperature effect on the reaction kinetics was measured at 285 and 305 K. Unlike

  3. 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)

  4. 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.

  5. 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

  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. 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.

  8. Study of Zircaloy-4: steam oxidation reaction kinetics. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Biederman, R.R.; Sisson, R.D. Jr.; Jones, J.K.; Dobson, W.G.

    1978-04-01

    Experimental studies utilizing a ''Gleeble'' have been performed to evaluate the oxidation of reactor grade Zircaloy-4 tubing in steam throughout the 1200/sup 0/F (649/sup 0/C) to 1800/sup 0/F (982/sup 0/C) temperature range. Oxidation behavior in this temperature range was found to be substantially different from that predicted by either the Baker-Just equation or extrapolation of oxidation data from temperatures above 1800/sup 0/F (982/sup 0/C). Preoxidation of Zircaloy-4 below the ..cap alpha../..beta.. Zircaloy transformation was found to have a substantial effect on the rate of subsequent oxidation at temperatures above 1800/sup 0/F (982/sup 0/C) with this effect increasing as the preoxidation thickness increased. Furthermore, a preoxidation treatment prior to clad rupture has been observed to reduce the extent of swelling prior to clad rupture in internal pressurization studies. Evaluation of the load carrying ability of Zircaloy-4 for both as-received and 10 ..mu..m preoxidized cladding has been made under both internal pressurization and axial loading conditions. Results of these rupture studies agree well with reported data from several other research programs indicating that once the ..beta.. phase of Zircaloy-4 begins to form, the load carrying ability of the cladding is rapidly reduced. Microstructural analysis and alumina marker studies have been used to develop a more complete understanding of the oxidation reaction of Zircaloy-4 in steam. These studies in combination with the low activation energy for oxygen diffusion through the oxide phase obtained from oxidation kinetics, strongly suggest a pore or surface diffusion mechanism for the oxidation of Zircaloy-4 in steam.

  9. 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

  10. 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...

  11. Cure Reaction Kinetics of Low Pressure Sheet Molding Compound System Thickened by Crystalline Polymer

    Institute of Scientific and Technical Information of China (English)

    QIN Yan; LIU Haihua; HUANG Zhixiong; MEI Qilin

    2007-01-01

    Several kinetic models for unsaturated polyester cure reaction and some existing parameter estimation techniques of these models were introduced. Correlated kinetic parameters and kinetic equations of the autocatalytic empirical kinetic model of LPSMC system were determined by using isothermal DSC to scan the system which was thickened by crystalline polymer (PEG-MAH). Through using a serial curing degree of the system to validate the model, the experimental results were basically identical with the predictions of the autocatalytic empirical kinetic model. This model could provide a theoretical reference to the determination of molding techniques of low pressure SMC.

  12. 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.

  13. 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.

  14. 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

  15. Kinetic isotope effect of low-temperature reactions of carbenes in solid polymers

    Energy Technology Data Exchange (ETDEWEB)

    Korshak, V.V.; Vorotnikov, A.P.; Davydov, E.Ya.; Kozyreva, N.M.; Kirilin, A.I.; Skubina, S.B.; Toptygin, D.Ya.

    1987-05-01

    The kinetics of dark quenching of diphenylcarbene (DPC) and 2,6-di-tert-butylcyclohexadiene carbene (CHC) in polymethyl methacrylate (PMMA) and polystyrene (PS) with protonated and totally deuterated units were studied to determine the mechanism of the reactions of carbenes in the polymer matrix. A comparison of the kinetic data on quenching of DPC and CHC in proton- and deuterium-containing polymers indicates the complex dependence of the kinetic isotope effect on both the temperature and the degree of conversion.

  16. 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 an...

  17. 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.

  18. 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…

  19. Utilization of the Recycle Reactor in Determining Kinetics of Gas-Solid Catalytic Reactions.

    Science.gov (United States)

    Paspek, Stephen C.; And Others

    1980-01-01

    Describes a laboratory scale reactor that determines the kinetics of a gas-solid catalytic reaction. The external recycle reactor construction is detailed with accompanying diagrams. Experimental details, application of the reactor to CO oxidation kinetics, interphase gradients, and intraphase gradients are discussed. (CS)

  20. Learning the Fundamentals of Kinetics and Reaction Engineering with the Catalytic Oxidation of Methane

    Science.gov (United States)

    Cybulskis, Viktor J.; Smeltz, Andrew D.; Zvinevich, Yury; Gounder, Rajamani; Delgass, W. Nicholas; Ribeiro, Fabio H.

    2016-01-01

    Understanding catalytic chemistry, collecting and interpreting kinetic data, and operating chemical reactors are critical skills for chemical engineers. This laboratory experiment provides students with a hands-on supplement to a course in chemical kinetics and reaction engineering. The oxidation of methane with a palladium catalyst supported on…

  1. 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

  2. Estimation of kinetic parameters related to biochemical interactions between hydrogen peroxide and signal transduction proteins

    Science.gov (United States)

    Brito, Paula; Antunes, Fernando

    2014-10-01

    The lack of kinetic data concerning the biological effects of reactive oxygen species is slowing down the development of the field of redox signaling. Herein, we deduced and applied equations to estimate kinetic parameters from typical redox signaling experiments. H2O2-sensing mediated by the oxidation of a protein target and the switch-off of this sensor, by being converted back to its reduced form, are the two processes for which kinetic parameters are determined. The experimental data required to apply the equations deduced is the fraction of the H2O2 sensor protein in the reduced or in the oxidized state measured in intact cells or living tissues after exposure to either endogenous or added H2O2. Either non-linear fittings that do not need transformation of the experimental data or linearized plots in which deviations from the equations are easily observed can be used. The equations were shown to be valid by fitting to them virtual time courses simulated with a kinetic model. The good agreement between the kinetic parameters estimated in these fittings and those used to simulate the virtual time courses supported the accuracy of the kinetic equations deduced. Finally, equations were successfully tested with real data taken from published experiments that describe redox signaling mediated by the oxidation of two protein tyrosine phosphatases, PTP1B and SHP-2, which are two of the few H2O2-sensing proteins with known kinetic parameters. Whereas for PTP1B estimated kinetic parameters fitted in general the present knowledge, for SHP-2 results obtained suggest that reactivity towards H2O2 as well as the rate of SHP-2 regeneration back to its reduced form are higher than previously thought. In conclusion, valuable quantitative kinetic data can be estimated from typical redox signaling experiments, thus improving our understanding about the complex processes that underline the interplay between oxidative stress and redox signaling responses.

  3. 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...

  4. Kinetically influenced terms for solute transport affected by heterogeneous and homogeneous classical reactions

    Science.gov (United States)

    Bahr, J.M.

    1990-01-01

    This paper extends a four-step derivation procedure, previously presented for cases of transport affected by surface reactions, to transport problems involving homogeneous reactions. Derivations for these classes of reactions are used to illustrate the manner in which mathematical differences between reaction classes are reflected in the mathematical derivation procedures required to identify kinetically influenced terms. Simulation results for a case of transport affected by a single solution phase complexation reaction and for a case of transport affected by a precipitation-dissolution reaction are used to demonstrate the nature of departures from equilibrium-controlled transport as well as the use of kinetically influenced terms in determining criteria for the applicability of the local equilibrium assumption. A final derivation for a multireaction problem demonstrates the application of the generalized procedure to a case of transport affected by reactions of several classes. -from Author

  5. 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

  6. 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

  7. 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

  8. Graphene liquid marbles as photothermal miniature reactors for reaction kinetics modulation.

    Science.gov (United States)

    Gao, Wei; Lee, Hiang Kwee; Hobley, Jonathan; Liu, Tianxi; Phang, In Yee; Ling, Xing Yi

    2015-03-23

    We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble's surface temperature between 21-135 °C and its encapsulated water temperature between 21-74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12-fold superior reaction rate constant for methylene blue degradation than at room temperature.

  9. Kinetic equation for the reaction of titanium tetrachloride with hydride functional groups of diamond

    Energy Technology Data Exchange (ETDEWEB)

    Zhidkov, A.B.; Smirnov, E.P.

    1989-02-01

    This work is devoted to the study of the kinetics of the reaction of titanium tetrachloride with the hydride functional groups of diamond. The research was performed on submicron powders of ASM 0.7/0.3 grade synthetic diamond with a specific surface area of 8.0 m/sup 2//g as measured from the adsorption of nitrogen. The reaction was carried out in a flow-through quartz reactor in a flow of dry He. The content of the titanium in the samples was determined by a photocolorimetric method. A kinetic equation for the reaction of diamond with titanium tetrachloride was found on the basis of a statistical approach.

  10. 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.

  11. 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.

  12. Circumventing Diffusion in Kinetically Controlled Solid-State Metathesis Reactions.

    Science.gov (United States)

    Martinolich, Andrew J; Kurzman, Joshua A; Neilson, James R

    2016-08-31

    Solid-state diffusion is often the primary limitation in the synthesis of crystalline inorganic materials and prevents the potential discovery and isolation of new materials that may not be the most stable with respect to the reaction conditions. Synthetic approaches that circumvent diffusion in solid-state reactions are rare and often allow the formation of metastable products. To this end, we present an in situ study of the solid-state metathesis reactions MCl2 + Na2S2 → MS2 + 2 NaCl (M = Fe, Co, Ni) using synchrotron powder X-ray diffraction and differential scanning calorimetry. Depending on the preparation method of the reaction, either combining the reactants in an air-free environment or grinding homogeneously in air before annealing, the barrier to product formation, and therefore reaction pathway, can be altered. In the air-free reactions, the product formation appears to be diffusion limited, with a number of intermediate phases observed before formation of the MS2 product. However, grinding the reactants in air allows NaCl to form directly without annealing and displaces the corresponding metal and sulfide ions into an amorphous matrix, as confirmed by pair distribution function analysis. Heating this mixture yields direct nucleation of the MS2 phase and avoids all crystalline binary intermediates. Grinding in air also dissipates a large amount of lattice energy via the formation of NaCl, and the crystallization of the metal sulfide is a much less exothermic process. This approach has the potential to allow formation of a range of binary, ternary, or higher-ordered compounds to be synthesized in the bulk, while avoiding the formation of many binary intermediates that may otherwise form in a diffusion-limited reaction. PMID:27490369

  13. 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.

  14. 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...

  15. 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 ...

  16. Stimulating kinetic of aerobic reactions skilled athlete in sport dance

    Directory of Open Access Journals (Sweden)

    Lee Bo

    2010-10-01

    Full Text Available Changes speed of development of reaction of frequency of heart-throbs are appraised under act of the program of trainings facilities. Directions stimulation of the cardiorespiratory system of sportsmen are rotined. In research took part 2 homogeneous groups of sportsmen for 12 sportsmen (6 pair. It is set that the high-rate of development of reactions of aerobic power providing reflects reactive properties of the cardiorespiratory system and influences on efficiency of functional preparation on the whole. Possibilities of estimation of reactive properties of the cardiorespiratory system are rotined in the natural terms of training process.

  17. 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)

  18. 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.

  19. Effect of mixing on reaction-diffusion kinetics for protein hydrogel-based microchips.

    Science.gov (United States)

    Zubtsov, D A; Ivanov, S M; Rubina, A Yu; Dementieva, E I; Chechetkin, V R; Zasedatelev, A S

    2006-03-01

    Protein hydrogel-based microchips are being developed for high-throughput evaluation of the concentrations and activities of various proteins. To shorten the time of analysis, the reaction-diffusion kinetics on gel microchips should be accelerated. Here we present the results of the experimental and theoretical analysis of the reaction-diffusion kinetics enforced by mixing with peristaltic pump. The experiments were carried out on gel-based protein microchips with immobilized antibodies under the conditions utilized for on-chip immunoassay. The dependence of fluorescence signals at saturation and corresponding saturation times on the concentrations of immobilized antibodies and antigen in solution proved to be in good agreement with theoretical predictions. It is shown that the enhancement of transport with peristaltic pump results in more than five-fold acceleration of binding kinetics. Our results suggest useful criteria for the optimal conditions for assays on gel microchips to balance high sensitivity and rapid fluorescence saturation kinetics.

  20. 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.

  1. Parallel Kinetic Resolution of Racemic Aldehydes by Use of Asymmetric Horner-Wadsworth-Emmons Reactions

    DEFF Research Database (Denmark)

    Pedersen, Torben Møller; Jensen, Jakob Feldthusen; Humble, Rikke Eva;

    2000-01-01

    A racemic aldehyde can undergo parallel kinetic resolution (PKR) by simultaneous reaction with two different chiral phosphonates, differing either in the structure of the chiral auxiliary or in the structure of the phosphoryl group (i.e., one (E)- and one (Z)-selective reagent). This strategy all...... allows conversion of a racemic aldehyde to two different, synthetically useful chiral products with essentially doubled material throughput and similar or improved selectivities as compared to conventional kinetic resolution....

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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...

  8. Chlorination of tramadol: Reaction kinetics, mechanism and genotoxicity evaluation.

    Science.gov (United States)

    Cheng, Hanyang; Song, Dean; Chang, Yangyang; Liu, Huijuan; Qu, Jiuhui

    2015-12-01

    Tramadol (TRA) is one of the most detected analgesics in environmental matrices, and it is of high significance to study the reactivity of TRA during chlorination considering its potential toxicity to the environment. The chlorine/TRA reaction is first order with respect to the TRA concentration, and a combination of first-order and second-order with respect to chlorine concentration. The pH dependence of the observed rate constants (kobs) showed that the TRA oxidation reactivity increased with increasing pH. kobs can be quantitatively described by considering all active species including Cl2, Cl2O and HOCl, and the individual rate constants of HOCl/TRA(0), HOCl/TRAH(+), Cl2/TRA and Cl2O/TRA reactions were calculated to be (2.61±0.29)×10(3)M(-1)s(-1), 14.73±4.17M(-1)s(-1), (3.93±0.34)×10(5)M(-1)s(-1) and (5.66±1.83)×10(6)M(-1)s(-1), respectively. Eleven degradation products were detected with UPLC-Q-TOF-MS, and the corresponding structures of eight products found under various pH conditions were proposed. The amine group was proposed to be the initial attack site under alkaline pH conditions, where reaction of the deprotonated amine group with HOCl is favorable. Under acidic and neutral pH conditions, however, two possible reaction pathways were proposed. One is an electrophilic substitution on the aromatic ring, and another is an electrophilic substitution on the nitrogen, leading to an N-chlorinated intermediate, which can be further oxidized. Finally, the SOS/umu test showed that the genotoxicity of TRA chlorination products increased with increasing dosage of chlorine, which was mostly attributed to the formation of some chlorine substitution products.

  9. 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

  10. 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.

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

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Schulten, Klaus

    2012-01-01

    Creatures as varied as mammals, fish, insects, reptiles, and birds have an intriguing sixth sense that allows them to orient themselves in the Earth's magnetic field. Despite decades of study, the physical basis of this magnetic sense remains elusive. A likely mechanism is furnished by magnetically...... absorption and electron-spin-resonance observations together with known facts on avian magnetoreception. The reaction cycle permits one to predict magnetic field effects on cryptochrome activation and deactivation. The suggested analysis method gives insight into structural and dynamic design features...... required for optimal detection of the geomagnetic field by cryptochrome and suggests further experimental and theoretical studies....

  12. 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

  13. 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.

  14. Reaction Kinetic Equation for Char Combustion of Underground Coal Gasification

    Institute of Scientific and Technical Information of China (English)

    YU Hong-guan; YANG Lan-he; FENG Wei-min; LIU Shu-qin; SONG Zhen-qi

    2006-01-01

    Based on the quasi-steady-state approximation, the dynamic equation of char combustion in the oxidation zone of underground coal gasification (UCG) was derived. The parameters of the dynamic equation were determined at 900℃ using a thermo-gravimetric (TG) analyzer connected to a flue gas analyzer and this equation. The equation was simplified for specific coals, including high ash content, low ash content, and low ash fusibility ones. The results show that 1) the apparent reaction rate constant increases with an increase in volatile matter value as dry ash-free basis, 2) the effective coefficient of diffusion decreases with an increase in ash as dry basis, and 3) the mass transfer coefficient is independent of coal quality on the whole. The apparent reaction rate constant, mass-transfer coefficient and effective coefficient of diffusion of six char samples range from 7.51×104 m/s to 8.98×104 m/s, 3.05×106 m/s to 3.23×106 m/s and 5.36×106 m2/s to 8.23×106 m2/s at 900℃, respectively.

  15. Biochemical, immunological and kinetic characterisation of thiol protease inhibitor (cystatin) from liver.

    Science.gov (United States)

    Shah, Aaliya; Priyadarshini, Medha; Khan, Mohd Shahnawaz; Aatif, Mohammad; Amin, Fakhra; Bano, Bilqees

    2013-10-01

    Regulation of the cysteine protease activity is imperative for proper functioning of the various organ systems. Elevated activities of cysteine proteinases due to impaired regulation by the endogenous cysteine proteinase inhibitors (cystatins) have been linked to liver malignancies. To gain an insight into these regulatory processes, it is essential to purify and characterise the inhibitors, cystatins. Present study was undertaken to purify the inhibitor from the liver. The purification was accomplished in four steps: alkaline treatment, ammonium sulphate fractionation, acetone precipitation and gel filtration column (Sephacryl S-100 HR). The eluted protein exhibited inhibitory activity towards papain, and its purity was further reaffirmed using western blotting and immunodiffusion. The purified inhibitor (liver cystatin (LC)) was stable in the pH range of 6-8 and temperature up to 45 °C. In view of the significance of kinetics parameters for drug delivery, the kinetic parameters of liver cystatin were also determined. LC showed the greatest affinity for papain followed by ficin and bromelain. UV and fluorescence spectroscopy results showed that binding of LC with thiol proteases induced changes in the environment of aromatic residues. Recent advances in the field of proteinase inhibitors have drawn attention to the possible use of this collected knowledge to control pathologies.

  16. 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.

  17. PIERO ontology for analysis of biochemical transformations: effective implementation of reaction information in the IUBMB enzyme list.

    Science.gov (United States)

    Kotera, Masaaki; Nishimura, Yosuke; Nakagawa, Zen-ichi; Muto, Ai; Moriya, Yuki; Okamoto, Shinobu; Kawashima, Shuichi; Katayama, Toshiaki; Tokimatsu, Toshiaki; Kanehisa, Minoru; Goto, Susumu

    2014-12-01

    Genomics is faced with the issue of many partially annotated putative enzyme-encoding genes for which activities have not yet been verified, while metabolomics is faced with the issue of many putative enzyme reactions for which full equations have not been verified. Knowledge of enzymes has been collected by IUBMB, and has been made public as the Enzyme List. To date, however, the terminology of the Enzyme List has not been assessed comprehensively by bioinformatics studies. Instead, most of the bioinformatics studies simply use the identifiers of the enzymes, i.e. the Enzyme Commission (EC) numbers. We investigated the actual usage of terminology throughout the Enzyme List, and demonstrated that the partial characteristics of reactions cannot be retrieved by simply using EC numbers. Thus, we developed a novel ontology, named PIERO, for annotating biochemical transformations as follows. First, the terminology describing enzymatic reactions was retrieved from the Enzyme List, and was grouped into those related to overall reactions and biochemical transformations. Consequently, these terms were mapped onto the actual transformations taken from enzymatic reaction equations. This ontology was linked to Gene Ontology (GO) and EC numbers, allowing the extraction of common partial reaction characteristics from given sets of orthologous genes and the elucidation of possible enzymes from the given transformations. Further future development of the PIERO ontology should enhance the Enzyme List to promote the integration of genomics and metabolomics.

  18. Mechanism and kinetics of the NOCO reaction on Rh

    Science.gov (United States)

    Zhdanov, V. P.; Kasemo, B.

    During the past 15 years, the NOCO reaction on Rh has attracted considerable attention of the researchers working in academic and applied surface science. The practical importance of this reaction is connected with its relevance for environmental chemistry. From the point of view of academic studies, the NOCO reaction on Rh is of interest because it represents one of the simplest examples from the class of catalytic reactions occurring via decomposition of adsorbed species. At present, the detailed kinetic data for this reaction are available both for single-crystal and supported Rh, at ultrahigh vacuum (UHV) conditions and also at realistic pressures. For this reason, the NOCO reaction on Rh has become one of the major testing platforms for a microscopic, surface-science based approach to heterogeneous catalysis. The present review shows how far the progress in this field has come. In particular, the review describes in detail the evolution of the ideas for the mechanism of the reaction and also presents the data for the elementary reaction steps, obtained primarily on Rh(1 1 1) at UHV conditions. Then, the possibility of using these data for simulation of the reaction kinetics at moderate pressures, P NO ⋍ P CO ⋍ 0.01 bar, is discussed. The technological aspects of application of Rh in the automotive exhaust systems are surveyed as well, but only briefly.

  19. 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...

  20. 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 ...

  1. 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...

  2. Kinetics of Thermochemical Reactions Important in the Venus Atmospheric Sulfur Cycle

    Science.gov (United States)

    Fegley, Bruce, Jr.

    1997-01-01

    The purpose of this project was to experimentally measure the rates of several thermochemical gas-solid reactions between sulfur gases in the Venus atmosphere and reactive minerals on the hot Venus surface. Despite the great importance of these reactions for the maintenance of significant amounts of sulfur gases (and thus for the maintenance of the global cloud cover) in the atmosphere of Venus, essentially no kinetic data are currently available for them.

  3. Modelling and simulation of a transketolase mediated reaction: Sensitivity analysis of kinetic parameters

    DEFF Research Database (Denmark)

    Sayar, N.A.; Chen, B.H.; Lye, G.J.;

    2009-01-01

    In this paper we have used a proposed mathematical model, describing the carbon-carbon bond format ion reaction between beta-hydroxypyruvate and glycolaldehyde to synthesise L-erythrulose, catalysed by the enzyme transketolase, for the analysis of the sensitivity of the process to its kinetic par....... (C) 2009 Elsevier B.V. All rights reserved....

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

    DEFF Research Database (Denmark)

    Pattison, David I; Davies, Michael Jonathan

    2004-01-01

    in 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...

  5. Investigation of Coal-biomass Catalytic Gasification using Experiments, Reaction Kinetics and Computational Fluid Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, Francine [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Agblevor, Foster [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Klein, Michael [Univ. of Delaware, Newark, DE (United States); Sheikhi, Reza [Northeastern Univ., Boston, MA (United States)

    2015-09-30

    A collaborative effort involving experiments, kinetic modeling, and computational fluid dynamics (CFD) was used to understand co-gasification of coal-biomass mixtures. The overall goal of the work was to determine the key reactive properties for coal-biomass mixed fuels. Sub-bituminous coal was mixed with biomass feedstocks to determine the fluidization and gasification characteristics of hybrid poplar wood, switchgrass and corn stover. It was found that corn stover and poplar wood were the best feedstocks to use with coal. The novel approach of this project was the use of a red mud catalyst to improve gasification and lower gasification temperatures. An important results was the reduction of agglomeration of the biomass using the catalyst. An outcome of this work was the characterization of the chemical kinetics and reaction mechanisms of the co-gasification fuels, and the development of a set of models that can be integrated into other modeling environments. The multiphase flow code, MFIX, was used to simulate and predict the hydrodynamics and co-gasification, and results were validated with the experiments. The reaction kinetics modeling was used to develop a smaller set of reactions for tractable CFD calculations that represented the experiments. Finally, an efficient tool was developed, MCHARS, and coupled with MFIX to efficiently simulate the complex reaction kinetics.

  6. 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

  7. 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…

  8. A Molecular Reaction Cycle with a Solvatochromic Merocyanine Dye: An Experiment in Photochemistry, Kinetics, and Catalysis.

    Science.gov (United States)

    Abdel-Kader, M. H.; Steiner, U.

    1983-01-01

    Three experiments using merocyanine M suitable as an integrated laboratory experience for undergraduates are described. Experiments demonstrate: complete molecular cycle composed of photochemical, thermal, and protolytic reaction steps; kinetics of cis-trans isomerization of the dye; and mechanism of base catalysis for thermal isomerization of the…

  9. 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

  10. Investigation of Coal-biomass Catalytic Gasification using Experiments, Reaction Kinetics and Computational Fluid Dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, Francine [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Agblevor, Foster [Virginia Polytechnic Inst. and State Univ. (Virginia Tech), Blacksburg, VA (United States); Klein, Michael [Univ. of Delaware, Newark, DE (United States); Sheikhi, Reza [Northeastern Univ., Boston, MA (United States)

    2015-12-31

    A collaborative effort involving experiments, kinetic modeling, and computational fluid dynamics (CFD) was used to understand co-gasification of coal-biomass mixtures. The overall goal of the work was to determine the key reactive properties for coal-biomass mixed fuels. Sub-bituminous coal was mixed with biomass feedstocks to determine the fluidization and gasification characteristics of hybrid poplar wood, switchgrass and corn stover. It was found that corn stover and poplar wood were the best feedstocks to use with coal. The novel approach of this project was the use of a red mud catalyst to improve gasification and lower gasification temperatures. An important results was the reduction of agglomeration of the biomass using the catalyst. An outcome of this work was the characterization of the chemical kinetics and reaction mechanisms of the co-gasification fuels, and the development of a set of models that can be integrated into other modeling environments. The multiphase flow code, MFIX, was used to simulate and predict the hydrodynamics and co-gasification, and results were validated with the experiments. The reaction kinetics modeling was used to develop a smaller set of reactions for tractable CFD calculations that represented the experiments. Finally, an efficient tool was developed, MCHARS, and coupled with MFIX to efficiently simulate the complex reaction kinetics.

  11. 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.

  12. 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...

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

    NARCIS (Netherlands)

    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 o

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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...

  20. 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.

  1. 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...

  2. 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)

  3. 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

  4. 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

  5. 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.

  6. 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...

  7. 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…

  8. 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

  9. Kinetic modeling of mechanisms of industrially important organic reactions in gas and liquid phase

    Energy Technology Data Exchange (ETDEWEB)

    Vahteristo, K.

    2010-07-01

    -trans and skeletal isomerization. Minor side reaction were dimerization and fragmentation. Monomolecular and bimolecular reaction mechanisms for skeletal isomerization explained experimental results almost equally well. Pseudohomogeneous kinetic parameters of reactions 1 and 2 were estimated by usual least squares fitting. Concerning reactions 3 and 4 kinetic parameters were estimated by the leastsquares method, but also the possible cross-correlation and identifiability of parameters were determined using Markov chain Monte Carlo (MCMC) method. Finally using MCMC method, the estimation of model parameters and predictions were performed according to the Bayesian paradigm. According to the fitting results suggested reaction mechanisms explained experimental results rather well. When the possible cross-correlation and identifiability of parameters (Reactions 3 and 4) were determined using MCMC method, the parameters identified well, and no pathological cross-correlation could be seen between any parameter pair. (orig.)

  10. 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.

  11. 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.

  12. Differential scanning calorimetry and reaction kinetics studies of {gamma} + {alpha}{sub 2} Ti aluminide

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, R.K., E-mail: rohitkumar_gupta@vssc.gov.in [Vikram Sarabhai Space Centre, ISRO, Trivandrum 695 022 (India); Pant, Bhanu [Vikram Sarabhai Space Centre, ISRO, Trivandrum 695 022 (India); Agarwala, Vijaya [Indian Institute of Technology Roorkee, Roorkee 247 667 (India); Sinha, P.P. [Vikram Sarabhai Space Centre, ISRO, Trivandrum 695 022 (India)

    2012-12-14

    Reaction synthesis method for titanium aluminide processing consists of an exothermic reaction among alloying elements present and primarily between titanium and aluminium particles at specific temperature range. Study of this reaction helps in understanding the process of aluminide formation. Differential scanning calorimetry (DSC) study is the suitable method to study such reactions. In the present work, five different alloy mixtures based on Ti48Al2Cr2Nb0.1B are prepared and DSC study is carried out. Onset temperature, peak temperature and completion temperature of the major exothermic reaction is analyzed at different heating rates. Further, kinetics of the reaction is studied using Johnson-Mehl-Avrami equation. Activation energy and Avrami parameter are calculated and compared with the reported works on binary alloy. It has been observed that exothermic reaction is triggered by melting of aluminium. Boron assists in increasing the enthalpy of reaction by boride formation. Primary reaction product is found to be TiAl{sub 3}. Activation energy as well as Avrami parameter is found to have marginal variation due to small change in alloying elements in different alloys and due to heating rates in the same alloy. -- Highlights: Black-Right-Pointing-Pointer Reaction kinetics studies of Ti-aluminide alloy powder mixtures carried out. Black-Right-Pointing-Pointer Five compositions studied through non-isothermal differential scanning calorimetry. Black-Right-Pointing-Pointer Effect of minor boron addition and role of Ti particle size is noted. Black-Right-Pointing-Pointer Activation energies using JMA equations are between 169.5 and 192.49 kJ mol{sup -1}.

  13. 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

  14. 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.

  15. Kinetics and mechanism of the reaction of gold(III chloride complexes with formic acid

    Directory of Open Access Journals (Sweden)

    Pacławski K.

    2015-01-01

    Full Text Available In this work, the results of kinetic studies of the redox reaction of gold(III chloride complexes ([AuCl4]- with formic acid, are presented. Obtained data suggest the complex character of the reaction which leads to the [AuCl2]- and [AuCl3(COOH]- ions formation as intermediates. In the pH range over 2.5, the final product of the reaction is metallic gold. From the analysis of kinetic data, the rate limiting step is found to be the gold metallic phase formation. The stage of Au(III reduction is relatively fast with the second-order rate constant equal to 61.8 M-1s-1 at temperature 50ºC. The rate of the studied reaction depends on the temperature, reactants concentration and chloride ions concentration. As a result of the data analysis, the scheme of the reaction path has been suggested. Also, the values of enthalpy and entropy of activation for the reaction have been determined.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Heterogeneous photocatalysis of real textile wastewater: evaluation of reaction kinetics and characterization.

    Science.gov (United States)

    Sahoo, Chittaranjan; Gupta, Ashok K; Pillai, Indu M Sasidharan

    2012-01-01

    Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag(+) doped TiO(2) (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. Kinetics of the First Order Autocatalytic Decomposition Reaction of Nitrocellulose (13.86% N)

    Institute of Scientific and Technical Information of China (English)

    GUO,Peng-Jiang(郭鹏江); HU,Rong-Zu(胡荣祖); NING,Bin-Ke(宁斌科); YANG,Zheng-Quan(杨正权); SONG,Ji-Rong(宋纪蓉); SHI,Qi-Zhen(史启祯); LU,Gui-E(路桂娥); JIANG,Jin-You(江劲勇)

    2004-01-01

    The kinetics of the first order autocatalytic decomposition reaction of nitrocellulose (NC, 13.86% N) was studied by using DSC. The results show that the DSC curve for the initial 50% of conversion degree of NC can be described by the first order autocatalytic equation dy/dt=-1016.3exp(-181860/RT)y-1016.7exp(-173050)y(1-y) and that for the latter 50% conversion degree of NC described by the reaction equations dy/dt=-1016.4exp(-154820/RT)y(n=1) and dy/dt=-1016.9exp(-155270/RT)y2.80(n≠1).

  9. A temperature dependent kinetic study of the reaction of the hydroxyl radical with CH2Br

    Science.gov (United States)

    Zhang, Zhengyu; Saini, Rameshwar D.; Kurylo, Michael; Huie, Robert E.

    1992-01-01

    Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH3Br over the temperature range 250 to 400 K. The Arrhenius expression k = (5.79 x 10 exp -12) exp(-1560/T) cu cm/molecule per sec was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH3Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years.

  10. 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.)

  11. 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.

  12. 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...

  13. 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 ...

  14. 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

    is therefore 'mixed 1D/3D migration' along a 3D path consisting of 1D segments, The defect reaction kinetics under mixed 1D/3D diffusion are different from pure 1D diffusion and pure 3D diffusion, both of which can be formulated within analytical rate theory models of microstructure evolution under irradiation...... of an analytical expression describing this transition region. (C) 2000 Elsevier Science B.V. All rights reserved....

  15. 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...

  16. 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...... 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....

  17. The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

    OpenAIRE

    Huang, D.; X. Zhang; Chen, Z M; Zhao, Y.; X. L. Shen

    2011-01-01

    Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA). Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and ...

  18. 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.

  19. 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...

  20. Kinetics of the reaction of CH3O2 radicals with NO2

    DEFF Research Database (Denmark)

    Wallington, T.J.; Nielsen, O.J.; Sehested, K.

    1999-01-01

    The kinetics of the gas-phase reaction of CH3O2 radicals with NO2 were studied at 295 K in 0.5-14 arm of SF6 diluent using pulse radiolysis combined with time-resolved UV-VIS spectroscopy. Rate data were obtained by following the loss of CH3O2 using a monitoring wavelength of 260 nm. The results...

  1. 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

  2. Reaction kinetics for synthesis of sec-butyl alcohol catalyzed by acid-functionalized ionic liquid

    Institute of Scientific and Technical Information of China (English)

    Ting Qiu; Wenli Tang; Chenggang Li; Chengming Wu; Ling Li

    2015-01-01

    The acid-functionalized ionic liquid ([HSO3Pmim]HSO4) was synthesized by a two-step method. Nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FT-IR) show that the synthesis method is feasible and high purity of ionic liquid can be obtained. Using [HSO3Pmim]HSO4 as the catalyst, we studied the reaction kinetics of synthesizing sec-butyl alcohol from sec-butyl acetate and methanol by transesterification in a high-pressure batch reactor. The effects of temperature, initial molar ratio of methanol to ester, and catalyst concentration on the conversion of sec-butyl acetate were studied. Based on its possible reaction mechanism, a ho-mogeneous kinetic model was established. The results show that the reaction heatΔH is 10.94 × 103 J·mol−1, so the reaction is an endothermic reaction. The activation energies Ea+and Ea−are 60.38 × 103 and 49.44 × 103 J·mol−1, respectively.

  3. Reaction mechanism and kinetics of the NCN +NO reaction: Comparison of theory and experiment

    Science.gov (United States)

    Huang, Chih-Liang; Tseng, Shiang Yang; Wang, Tzu Yi; Wang, Niann S.; Xu, Z. F.; Lin, M. C.

    2005-05-01

    The rate constants for the NCN +NO reaction have been measured by laser photolysis/laser-induced fluorescence technique in the temperature range of 254-353K in the presence of He (40-600Torr) and N2 (30-528Torr) buffer gases. The NCN radical was produced from the photodissociation of NCN3 at 193nm and monitored with a dye laser at 329.01nm. The reaction was found to be strongly positive-pressure dependent with negative-temperature dependence, as was reported previously. The experimental data could be reasonably accounted for by dual-channel Rice-Ramsperger-Kassel-Marcus calculations based on the predicted potential-energy surface using the modified Gaussian-2 method. The reaction is predicted to occur via weak intermediates, cis- and trans-NCNNO, in the A″2 state which crosses with the A'2 state containing more stable cis- and trans-NCNNO isomers. The high barriers for the fragmentation of these isomers and their trapping in the A'2 state by collisional stabilization give rise to the observed positive-pressure dependence and negative-temperature effect. The predicted energy barrier for the fragmentation of the cis-NCNNO (A'2) to CN +N2O also allows us to quantitatively account for the rate constant previously measured for the reverse process CN +N2O→NCN+NO.

  4. 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)

  5. 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.

  6. 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

  7. 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...

  8. Influence of diffusive porosity architecture on kinetically-controlled reactions in mobile-immobile models

    Science.gov (United States)

    Babey, T.; Ginn, T. R.; De Dreuzy, J. R.

    2014-12-01

    Solute transport in porous media may be structured at various scales by geological features, from connectivity patterns of pores to fracture networks. This structure impacts solute repartition and consequently reactivity. Here we study numerically the influence of the organization of porous volumes within diffusive porosity zones on different reactions. We couple a mobile-immobile transport model where an advective zone exchanges with diffusive zones of variable structure to the geochemical modeling software PHREEQC. We focus on two kinetically-controlled reactions, a linear sorption and a nonlinear dissolution of a mineral. We show that in both cases the structure of the immobile zones has an important impact on the overall reaction rates. Through the Multi-Rate Mass Transfer (MRMT) framework, we show that this impact is very well captured by residence times-based models for the kinetic linear sorption, as it is mathematically equivalent to a modification of the initial diffusive structure; Consequently, the overall reaction rate could be easily extrapolated from a conservative tracer experiment. The MRMT models however struggle to reproduce the non-linearity and the threshold effects associated with the kinetic dissolution. A slower reaction, by allowing more time for diffusion to smooth out the concentration gradients, tends to increase their relevance. Figure: Left: Representation of a mobile-immobile model with a complex immobile architecture. The mobile zone is indicated by an arrow. Right: Total remaining mass of mineral in mobile-immobile models and in their equivalent MRMT models during a flush by a highly under-saturated solution. The models only differ by the organization of their immobile porous volumes.

  9. 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

  10. 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

  11. 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.

  12. 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

  13. 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…

  14. 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

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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)

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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)

  6. Kinetic behavior of the reaction between hydroxyl radical and the SV40 minichromosome

    Science.gov (United States)

    Ly, A.; Aguilera, J. A.; Milligan, J. R.

    2011-01-01

    Aqueous solutions containing the minichromosomal form of the virus SV40 and the radical scavenger DMSO were subjected to gamma-irradiation, and the resulting formation of single strand breaks (SSB) was quantified. Under the irradiation conditions, most SSBs were produced as a consequence of hydroxyl radical (•OH) reactions. By controlling the competition between DMSO and the viral DNA substrate for •OH, we are able to estimate the rate coefficient for the reaction of •OH with the SV40 minichromosome. The results cannot be described adequately by homogeneous competition kinetics, but it is possible to describe the rate coefficient for the reaction as a function of the scavenging capacity of the solution. The experimentally determined rate coefficient lies in the range 1×109 – 2×109 L mol−1 s−1 at 107 s−1, and increases with increasing scavenging capacity. PMID:21960732

  7. 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

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

    Science.gov (United States)

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

    2016-07-14

    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. PMID:27421395

  9. A novel approach to modeling the reaction kinetics of tetracycline antibiotics with aqueous ozone.

    Science.gov (United States)

    Hopkins, Zachary R; Blaney, Lee

    2014-01-15

    Tetracycline antibiotics represent one of the most successful classes of pharmaceuticals and are extensively used around the world for human and veterinary health. Ozone-based processes have emerged as a selective water treatment process for many pharmaceuticals. The primary objective of this study was to determine the reaction kinetics for transformation of five tetracycline antibiotics (i.e., chlortetracycline, doxycycline, oxytetracycline, rolitetracycline, and tetracycline) by ozone across the pH2 to 9 range. The apparent second-order rate constant for tetracycline was on the order of 1-6 × 10(4) M(-1) s(-1) at low pH, and 0.6-2.0 × 10(6) M(-1) s(-1) at near neutral pH. The apparent second-order rate constants did not fit a conventional pKa-based model, presumably due to the complex acid/base speciation of tetracycline antibiotics. A model that considers the net charge on tetracycline molecules in solution provided a nice fit to experimental data for all five tetracyclines. The five tetracycline antibiotics demonstrated similar reaction kinetics with ozone, and a cumulative analysis of all kinetics data provides a baseline model for other tetracycline compounds. The ozone exposure required for complete transformation of tetracycline antibiotics (10(-5) M-s) is well below that achieved during ozone disinfection processes (10(-3) M-s), indicating that ozone is an effective treatment for tetracycline antibiotics.

  10. 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.

  11. 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

  12. 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

  13. 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

  14. 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

  15. Kinetic stabilization against the oxidation reaction induced by a silaalkane cage in a thiophene-bridged molecular gyroscope.

    Science.gov (United States)

    Setaka, Wataru; Ohmizu, Soichiro; Kira, Mitsuo

    2014-02-01

    Macrocage molecules with a bridged rotor have been synthesized as molecular gyroscopes. The kinetics of the oxidation reaction of the thiophene-bridged molecular gyroscope, whose thiophene ring was bridged inside a silaalkane cage, was investigated. A remarkable kinetic stabilization against the oxidation of the thiophene moiety induced by the molecular cage framework was observed.

  16. 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.

  17. Removal of Hg~0 with sodium chlorite solution and mass transfer reaction kinetics

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    The absorption behavior of Hg0 was studied experimentally by using sodium chlorite solution(NaClO2) as the absorbent in a bubble reactor.Primary influencing factors on removal efficiency of Hg0 such as NaClO2 concentration,pH,reaction temperature and the concentration of Hg0 were investigated.The results indicated that 72.91% of Hg0 removal efficiency could be achieved in acidic NaClO2 solution.The removal mechanism of Hg0 was proposed by analyzing of Hg2+ concentration in ab-sorption solution after reaction and comparing the electrode potentials between NaClO2 species and Hg2+/Hg0.The experimental results of mass transfer-reaction kinetics on oxidation of Hg0 by NaClO2 solution showed that with the increase of NaClO2 concentration and the decrease of pH value,the enhancement factor(E) and ratio of KG(Hg0)/kG(Hg0) increased and the liquid phase mass transfer resistance decreased,which is benefit to the mass transfer adsorption reaction.Although the increase of reaction temperature could improve the enhancement factor(E),but the ratio of KG(Hg0)/kG(Hg0) decreased;as a result,the liquid phase mass transfer resistance increased,therefore,the reaction rate for removal of Hg0 decreased.

  18. Stability analysis of a PFTR reactor for a first order kinetic reaction using the Lyapunov functionals

    Directory of Open Access Journals (Sweden)

    Héctor Armando Durán Peralta

    2010-04-01

    Full Text Available The stability of reactors having encompassing concentration and temperature parameters, such as continuous flow stirred tank reactors (CSTR, has been widely explored in the literature; however, there are few papers about the stability of tubular reactor having distributed spatial concentration and temperature parameters such as the plow flow tubular reactor (PFTR. This paper analyses the stability of isothermal and non-isothermal PFTR reactors using the Lyapunov functional method. The first order kinetic reaction was selected because one of this paper’s oblectives was to apply Lyapunov functionals to stability analysis of distributed parameter reactors (technique used in electrical engineering systems’ stability analysis. The stability analysis revealed asymptotically stable tempe- rature and concentration profiles for isothermal PFTR, non-isothermal PFTR with kinetic constant independent of temperature and adiabatic non-isothermal PFTR. Analysis revealed an asymptotically stability region for the heat exchange reactor and an uncertain region where it may have oscillations.

  19. 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.

  20. 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

  1. Kinetic Reaction Mechanism of Sinapic Acid Scavenging NO2 and OH Radicals: A Theoretical Study

    Science.gov (United States)

    Lu, Yang; Wang, AiHua; Shi, Peng; Zhang, Hui; Li, ZeSheng

    2016-01-01

    The mechanism and kinetics underlying reactions between the naturally-occurring antioxidant sinapic acid (SA) and the very damaging ·NO2 and ·OH were investigated through the density functional theory (DFT). Two most possible reaction mechanisms were studied: hydrogen atom transfer (HAT) and radical adduct formation (RAF). Different reaction channels of neutral and anionic sinapic acid (SA-) scavenging radicals in both atmosphere and water medium were traced independently, and the thermodynamic and kinetic parameters were calculated. We find the most active site of SA/SA- scavenging ·NO2 and ·OH is the –OH group in benzene ring by HAT mechanism, while the RAF mechanism for SA/SA- scavenging ·NO2 seems thermodynamically unfavorable. In water phase, at 298 K, the total rate constants of SA eliminating ·NO2 and ·OH are 1.30×108 and 9.20×109 M-1 S-1 respectively, indicating that sinapic acid is an efficient scavenger for both ·NO2 and ·OH. PMID:27622460

  2. 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

  3. 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.

  4. 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.

  5. Study on the reaction kinetics in pulsed RF discharges under RIE conditions

    Science.gov (United States)

    Baggerman, Jacobus Antonius Gijsbertus

    1993-10-01

    In the present-day electronics industry, reactive ion etching (RIE) is a technique widely used to etch thin films anisotropically. The subject of this thesis is the determination of (reaction) kinetics of rf discharges under RIE conditions. Special attention is given to determining quantitatively the rise and decay of densities and energy distributions of plasma particles. A production-type RIE reactor was used for all experiments. In chapter 2 the ion density is determined by LIF spectroscopy in a model (N2) discharge under RIE conditions. Chapter 3 concerns energy-flux density measurements on the various parts of the etch reactor in contact with a 30 Pa nitrogen rf discharge. Chapter 4 concerns the etch mechanism of various organic polymers in oxygen and argon of discharges under RIE conditions studied by performing energy-flux density and ion-flux density measurements on the powered electrode. The polymers of interest are a novolac-based photoresist, polyimide and polymethylmethacrylate (PMMA). The density and the reaction kinetics of ground-state methylidyne (CH radical) are determined by LIF in order to determine whether small molecules in addition to atoms are sputtered from the polymer surface. In chapter 5 a model is set up in which diffusion of CH from the substrate into the gas phase and chemical reactions in the gas phase are taken into account.

  6. 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

  7. 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).

  8. 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 ℃

  9. 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

  10. Study of Zircaloy 4: steam oxidation reaction kinetics. Final report. [PWR; BWR

    Energy Technology Data Exchange (ETDEWEB)

    Biederman, R.R.; Ballinger, R.G.; Dobson, W.G.

    1976-09-01

    Experimental studies utilizing a Gleeble have been performed to evaluate the oxidation of reactor grade Zircaloy-4 tubing in steam under both isothermal and transient oxidizing conditions. Metallographic examination including measurements of oxide, stabilized ..cap alpha.. and xi thicknesses has been used as the principal method of characterizing the extent of oxidation and in the development of reaction rate kinetics. A variety of test specimens have been analyzed by alternative methods including weight gain analysis, total oxygen analysis by vacuum fusion and high resolution neutron activation analysis as a check on the metallographic method.

  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. 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

  13. 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.

  14. Evaluated kinetic and photochemical data for atmospheric chemistry: Volume IV – gas phase reactions of organic halogen species

    Directory of Open Access Journals (Sweden)

    R. Atkinson

    2008-08-01

    Full Text Available This article, the fourth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of organic halogen species, which were last published in 1997, and were updated on the IUPAC website in 2006/07. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and four appendices containing the data sheets, which provide information upon which the recommendations are made.

  15. Evaluated kinetic and photochemical data for atmospheric chemistry: Volume II – gas phase reactions of organic species

    Directory of Open Access Journals (Sweden)

    R. Atkinson

    2006-01-01

    Full Text Available This article, the second in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of Organic species, which were last published in 1999, and were updated on the IUPAC website in late 2002, and subsequently during the preparation of this article. The article consists of a summary table of the recommended rate coefficients, containing the recommended kinetic parameters for the evaluated reactions, and eight appendices containing the data sheets, which provide information upon which the recommendations are made.

  16. The influence of stressors on biochemical reactions--a review of present scientific findings with noise.

    Science.gov (United States)

    Maschke, C; Rupp, T; Hecht, K

    2000-03-01

    For every faculty of perception there is, according to the degree of irritation, a biochemical or psychobiological activation. This is also true for the perception of sound or noise. Initially, these processes allow for the adjustment of the organism to a changed situation (eustress). Prolonged effects of stressors may ultimately lead to regulatory disturbances and induce pathological processes (distress). The pathogenetic concept that psychobiological stresses (e.g. noise) may be connected with the well-known risk factors of cardiovascular diseases, through excitation of the central nervous system, is based on the known stress models. The central connective factors are the activation hormones of the adrenal gland, also referred to as stress hormones. From blood and urine parameters recorded in epidemiological and experimental studies under the influence of acute or chronic noise, a simplified model of the pathogenetic mechanism has been developed. Fundamental conditions for future assessing the "stress hormones" have been derived, by means of which premorbid conditions can be determined on a population or group basis.

  17. 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.

  18. 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.

  19. 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)

  20. Atmospheric chemistry of CF3COOH. Kinetics of the reaction with OH radicals

    DEFF Research Database (Denmark)

    Møgelberg, T.E.; Nielsen, O.J.; Sehested, J.;

    1994-01-01

    Two different experimental techniques were used to study the kinetics of the reaction of OH radicals with trifluoroacetic acid, CF3COOH. Using a pulse radiolysis absolute rate technique, rate constants at 315 and 348 K were determined to be (1.6 +/- 0.4) x 10(-13) and (1.5 +/- 0.2) x 10(-13) cm3...... molecule-1 s-1, respectively. Using a long path-length FTIR relative rate technique a rate constant of (1.7 +/- 0.5) x 10(-13) cm3 molecule-1 s-1 was obtained at 296 K. In the atmosphere, reaction with OH radicals in the gas phase is estimated to account for 10%-20% of the loss of CF3COOH. The major fate...... of CF3COOH is rainout....

  1. 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.

  2. Reaction of a sterically hindered iron(III porphyrin with peroxyacetic acid: degradation kinetics

    Directory of Open Access Journals (Sweden)

    P. PRAKASH

    2005-09-01

    Full Text Available A kinetic analysis of the reaction between peracetic acid (AcOOH, and tetrakis (pentafluorophenyl - 21H, 23H-porphine iron(III chloride, Fe(F20TPPCl, in acetonitrile showed that the peracetic acid oxidatively destroys Fe(F20TPPCl. This is in contrast to an assumption that the oxidative degradation of metalloporphyrins can be prevented by the introduction of electron-withdrawing substituents into the phenyl groups of the porphyrin ligand. A UV-visible spectroscopic study showed a degree of macro cycle destruction of the tetrapyrrole conjucation of the metalloporphyrin. The degradation takes place via oxoperferryl species. The first step of the reaction mechanism is the reversible formation of an adduct ’X’(k1/k-1 between Fe(F20TPPCl and peracetic acid, followed by an irreversible step (k2 for the formation of oxoperferryl species.

  3. 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.

  4. 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

  5. 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

  6. Gas-phase thermolysis reaction of formaldehyde diperoxide. Kinetic study and theoretical mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Jorge, Nelly Lidia [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Av. Las Palmeras 4, 18100 Armilla, Granada (Spain); Area de Quimica Fisica Facultad de Ciencias Exactas y Naturales y Agrimensura, UNNE, Avda. Libertad 5460, 3400 Corrientes (Argentina); Romero, Jorge Marcelo [Area de Quimica Fisica Facultad de Ciencias Exactas y Naturales y Agrimensura, UNNE, Avda. Libertad 5460, 3400 Corrientes (Argentina); Grand, Andre [INAC, SCIB, Laboratoire ' Lesions des Acides Nucleiques' , UMR CEA-UJF E3, CEA-Grenoble, 17 Rue des Martyrs, 38054 Grenoble cedex 9 (France); Hernandez-Laguna, Alfonso, E-mail: ahlaguna@ugr.es [Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Av. Las Palmeras 4, 18100 Armilla, Granada (Spain)

    2012-01-17

    Highlights: Black-Right-Pointing-Pointer Kinetic and mechanism of the gas-phase thermolysis of tetroxane were determined. Black-Right-Pointing-Pointer Gas chromatography and computational potential energy surfaces were performed. Black-Right-Pointing-Pointer A mechanism in steps looked like the most probable mechanism. Black-Right-Pointing-Pointer A spin-orbit coupling appeared at the singlet and triple diradical open structures. Black-Right-Pointing-Pointer A non-adiabatic crossing from the singlet to the triplet state occurred. - Abstract: Gas-phase thermolysis reaction of formaldehyde diperoxide (1,2,4,5-tetroxane) was performed in an injection chamber of a gas chromatograph at a range of 463-503 K. The average Arrhenius activation energy and pre-exponential factor were 29.3 {+-} 0.8 kcal/mol and 5.2 Multiplication-Sign 10{sup 13} s{sup -1}, respectively. Critical points and reaction paths of the ground singlet and first triplet potential energy surfaces (PES) were calculated, using DFT method at BHANDHLYP/6-311+G{sup Asterisk-Operator Asterisk-Operator} level of the theory. Also, G3 calculations were performed on the reactant and products. Reaction by the ground-singlet and first-triplet states turned out to be endothermic and exothermic, respectively. The mechanism in three steps seemed to be the most probable one. An electronically non-adiabatic process appeared, in which a crossing, at an open diradical structure, from the singlet to the triplet state PES occurred, due to a spin-orbit coupling, yielding an exothermic reaction. Theoretical kinetic constant coming from the non- adiabatic transition from the singlet to the triplet state agrees with the experimental values.

  7. 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.

  8. Oxidation of ferrous nitrilotriacetic acid with oxygen : A model for oxygen mass transfer parallel to reaction kinetics

    NARCIS (Netherlands)

    Demmink, JF; Beenackers, AACM

    1997-01-01

    The kinetics of the reaction of ferrous chelate of nitrilotriacetic acid (NTA) and gaseous oxygen were studied in a stirred-cell reactor. The initial concentration of ferrous chelate was 0.100 kmol/m(3). Other reaction conditions include 293

  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. Ground reaction forces and lower-limb joint kinetics of turning gait in typically developing children.

    Science.gov (United States)

    Dixon, Philippe C; Stebbins, Julie; Theologis, Tim; Zavatsky, Amy B

    2014-11-28

    Turning is a common locomotor task essential to daily activity; however, very little is known about the forces and moments responsible for the kinematic adaptations occurring relative to straight-line gait in typically developing children. Thus, the aims of this study were to analyse ground reaction forces (GRFs), ground reaction free vertical torque (TZ), and the lower-limb joint kinetics of 90° outside (step) and inside (spin) limb turns. Step, spin, and straight walking trials from fifty-four typically developing children were analysed. All children were fit with the Plug-in Gait and Oxford Foot Model marker sets while walking over force plates embedded in the walkway. Net internal joint moments and power were computed via a standard inverse dynamics approach. All dependent variables were statistically analysed over the entire curves using the mean difference 95% bootstrap confidence band approach. GRFs were directed medially for step turns and laterally for spin turns during the turning phase. Directions were reversed and magnitudes decreased during the approach phase. Step turns showed reduced ankle power generation, while spin turns showed large TZ. Both strategies required large knee and hip coronal and transverse plane moments during swing. These kinetic differences highlight adaptations required to maintain stability and reorient the body towards the new walking direction during turning. From a clinical perspective, turning gait may better reveal weaknesses and motor control deficits than straight walking in pathological populations, such as children with cerebral palsy, and could potentially be implemented in standard gait analysis sessions.

  12. 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)

  13. Kinetics of microbially mediated reactions: dissimilatory sulfate reduction in saltmarsh sediments (Sapelo Island, Georgia, USA)

    Science.gov (United States)

    Roychoudhury, Alakendra N.; Van Cappellen, Philippe; Kostka, Joel E.; Viollier, Eric

    2003-04-01

    A sediment disk reactor was tested in once flow-through mode to retrieve kinetic parameters for the Monod rate law that describes sulfate reduction. The experimental method was compared with a previously described procedure by the authors where a sediment plug-flow reactor was operated in a recirculation mode. In recirculation mode, accumulation of metabolic byproducts in certain cases may result in negative feedback, thus preventing accurate determination of kinetic information. The method described in this article provides an alternative to the recirculation sediment plug-flow-through reactor technique for retrieving kinetic parameters of microbially mediated reactions in aquatic sediments. For sulfate reduction in a saltmarsh site, a maximum estimate of the half-saturation concentration, Ks, of 204±26 μM and a maximum reaction rate, Rm, of 2846±129 nmol cm( wet sediment ) 3 d-1 was determined. The Ks value obtained was consistent with the one estimated previously (K s=240±20 μM) from a different site within the same saltmarsh mud flat using a recirculating reactor. From the Rm value and reduction rates determined using 35SO 42- incubation experiments, we infer that sulfate reduction is limited in the field. Substrate availability is not the main contributor for the limitation, however. Competition from other microbes, such as iron reducers affects the activity of sulfate reducers in the suboxic to anoxic zones, whereas aerobes compete in the oxic zone. High sulfide concentration in the pore water may also have acted as a toxin to the sulfate reducers in the field.

  14. 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.

  15. 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.

  16. 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.

  17. A study on the reaction kinetics of mineral surface adsorption in mix system

    Institute of Scientific and Technical Information of China (English)

    吴大清; 刁桂仪; 彭金莲

    1999-01-01

    The experimental results on adsorption of ions Pb2+, Zn2+ and Ag+ onto mineral surfaces in a mix system show that the reaction kinetics of adions adsorbed onto mineral surfaces was mainly controlled by their diffusion rates in solution. The concentration variations can be fit for the second-order rate equation with good determined coefficients r=0.800 5—0.979 7. In the near neutral solution, the concentration of exchanged ions K+ and Na+ related to reaction time can be described by the first-order rate equation with r=0.855 7—0.997 7. Meanwhile, the complex diffusionexchange rate equation is suitable for describing the Ca2+ concentration variation, as ions Ph2+ and Zn2+ were adions. Experimental data show that the amount of ions K+, Na+ and Ca2+ release is much more than that of adion decrement in solution. This fact may suggest that the complexation reaction of adions Pb2+, Zn2+ and Ag+ with the mineral surfaces was the major reaction process while adions were not enteri

  18. 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.

  19. Kinetics of thermochemical gas-solid reactions important in the Venus sulfur cycle

    Science.gov (United States)

    Fegley, Bruce, Jr.

    1988-01-01

    The thermochemical net reaction CaCO3 + SO2 yields CaSO4 + CO is predicted to be an important sink for incorporation of SO2 into the Venus crust. The reaction rate law was established to understand the dependence of rate on experimental variables such as temperature and partial pressure of SO2, CO2, and O2. The experimental approach was a variant of the thermogravimetric method often employed to study the kinetics of thermochemical gas-solid reactions. Clear calcite crystals were heated at constant temperature in SO2-bearing gas streams for varying time periods. Reaction rate was determined by three independent methods. A weighted linear least squares fit to all rate data yielded a rate equation. Based on the Venera 13, 14 and Vega 2 observations of CaO content of the Venus atmosphere, SO2 at the calculated rate would be removed from the Venus atmosphere in about 1,900,00 years. The most plausible endogenic source of the sulfur needed to replenish atmospheric SO2 is volcanism. The annual amount of erupted material needed for the replenishment depends on sulfur content; three ratios are used to calculate rates ranging from 0.4 to 11 cu km/year. This geochemically derived volcanism rate can be used to test if geophysically derived rates are correct. The work also suggests that Venus is less volcanically active than the Earth.

  20. 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.

  1. 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

  2. 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...

  3. 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

  4. Thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates of BTATz-CMDB propellant

    Energy Technology Data Exchange (ETDEWEB)

    Yi Jianhua [Xi' an Modern Chemistry Research Institute, Xi' an 710065 (China); Zhao Fengqi, E-mail: yiren@nwu.edu.cn [Xi' an Modern Chemistry Research Institute, Xi' an 710065 (China); Wang Bozhou; Liu Qian; Zhou Cheng; Hu Rongzu [Xi' an Modern Chemistry Research Institute, Xi' an 710065 (China); Ren Yinghui [School of Chemical Engineering, Northwest University, Xi' an 710069 (China); Xu Siyu [Xi' an Modern Chemistry Research Institute, Xi' an 710065 (China); Xu, Kang-Zhen [School of Chemical Engineering, Northwest University, Xi' an 710069 (China); Ren Xiaoning [Xi' an Modern Chemistry Research Institute, Xi' an 710065 (China)

    2010-09-15

    The composite modified double base (CMDB) propellants (nos. RB0601 and RB0602) containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) without and with the ballistic modifier were prepared and their thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates were investigated. The results show that there are three mass-loss stages in TG curve and two exothermic peaks in DSC curve for the BTATz-CMDB propellant. The first two mass-loss stages occur in succession and the temperature ranges are near apart, and the decomposition peaks of the two stages overlap each other, inducing only one visible exothermic peak appear in DSC curve during 350-550 K. The reaction mechanisms of the main exothermal decomposition processes of RB0601 and RB0602 are all classified as chemical reaction, the mechanism functions are f({alpha}) = (1 - {alpha}){sup 2}, and the kinetic equations are d{alpha}/dt=10{sup 19.24}(1-{alpha}){sup 2}e{sup -2.32x10{sup 4/T}} and d{alpha}/dt=10{sup 20.32}(1-{alpha}){sup 2}e{sup -2.43x10{sup 4/T}}. The thermal safety evaluation on the BTATz-CMDB propellants was obtained. With the substitution of 26% RDX by BTATz and with the help of the ballistic modifier in the CMDB propellant formulation, the burning rate can be improved by 89.0% at 8 MPa and 47.1% at 22 MPa, the pressure exponent can be reduced to 0.353 at 14-20 MPa.

  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. Dehydriding reaction kinetic mechanism of MgH2-Nb2O5 by Chou model

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Chou model was used to investigate the dehydriding reaction kinetic mechanism of MgH2-Nb2O5 hydrogen storage materials at 573 K.A new conception,"characteristic absorption/desorption time(yc)"was introduced to characterize the reaction rate.The fitting results show that for the hydrogen desorbing mechanism.the surface penetration iS the rate.controlling step.The mechanism remains the same even when the original particle size of Nb2O5 is before ball milling(BM)or when the BM time changes.And tc indicates that the desorption rate of MgH2-Nb2O5 will be faster than that of MgH2-Nb2O5 by BM.The dehydriding reaction rate of MgH2-Nb2O5(micro particle)BMed for 50 h is 4.76 times faster than that of the MgH2-Nb2O5(micro particle)BMed for 0.25 h,while the dehydriding reaction rate of MgH2-Nb2O5(nano particle)BMed for 50 h is only 1.1 8 times as that of the MgH2-Nb2O5 (nano particle)BMed for 0.25 h.The dehydriding reaction rate of the BMed MgH2-Nb2O5(nano particle)is 1-9 times faster than that of the BMed MgH2-Nb2O5(micro particle).

  8. 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.

  9. 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

  10. 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.

  11. Kinetic behavior of the reaction between hydroxyl radical and the SV40 minichromosome

    Energy Technology Data Exchange (ETDEWEB)

    Ly, A. [Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States); Aguilera, J.A. [Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States); Milligan, J.R. [Department of Radiology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0610 (United States)]. E-mail: jmilligan@ucsd.edu

    2007-06-15

    Aqueous solutions containing the minichromosomal form of the virus SV40 and the radical scavenger DMSO were subjected to {gamma}-irradiation, and the resulting formation of single-strand breaks (SSB) was quantified. Under the irradiation conditions, most SSBs were produced as a consequence of hydroxyl radical ( {sup {center_dot}}OH) reactions. By controlling the competition between DMSO and the viral DNA substrate for {sup {center_dot}}OH, we are able to estimate the rate coefficient for the reaction of {sup {center_dot}}OH with the SV40 minichromosome. The results cannot be described adequately by homogeneous competition kinetics, but it is possible to describe the rate coefficient for the reaction as a function of the scavenging capacity of the solution. The experimentally determined rate coefficient lies in the range 1x10{sup 9}-2x10{sup 9} L mol{sup -1} s{sup -1} at 10{sup 7} s{sup -1}, and increases with increasing scavenging capacity.

  12. Non-Isothermal Kinetics of Reduction Reaction of Oxidized Pellet Under Microwave Irradiation

    Institute of Scientific and Technical Information of China (English)

    HUANG Zhu-cheng; WU Kai; HU Bing; PENG Hu; JIANG Tao

    2012-01-01

    The microwave heating characteristics of the mixture with oxidized pellet and coal was studied, and the non-isothermal reduction dynamics is discussed. The results show that, the slow-heating stage of the temperature rising process can be segmented into two heating temperature curves approximately that have good linear relation- ship. They can be seen as temperature programming. In the first stage, between 827 and 1073 K, the reaction mechanism obeys diffusion controlled model. In the second stage, between 1 093 and 1 323 K, the reaction mecha- nism also obeys diffusion controlled model. The apparent activation energies are found to be 75.13 kJ/mol for the first stage and 53.17 kJ/mol for the second stage. That is lower than the apparent activation energy under conven- tional heating. The microstructure of the reduced pellets shows that microwave can improve the kinetics of the reduc- tion. Microwave has anxo-action to the reaction obviously.

  13. 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.

  14. 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

  15. 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)

    NARCIS (Netherlands)

    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 wa

  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. Correlation of Impact Conditions, Interface Reactions, Microstructural Evolution, and Mechanical Properties in Kinetic Spraying of Metals: A Review

    Science.gov (United States)

    Kim, Jaeick; Lee, Changhee

    2016-09-01

    In the past, most studies into kinetic spraying technology focused on basic research, but a large portion of current research is devoted to industrial applications of the technology. To advance, however, studies about industrial applications of kinetic spraying require profound understanding of the scientific foundations of the kinetic spray process. Nevertheless, no one has yet provided a well-organized summary of the correlations among impact conditions, interface reactions, microstructural evolution, and mechanical properties across the whole field of kinetic spraying technology. This paper provides such an overview of these correlations for kinetic spraying of metals. For each correlation, the interactions between the given conditions and the material properties of the metal feedstock powder are the most influential. These interactions are so complicated that it is difficult to systematically classify all cases into certain types. Nonetheless, we try to explain and summarize the critical factors and their roles in each relationship.

  18. Mechanism and Kinetics Analysis of NO/SO2/N2/O2 Dissociation Reactions in Non-Thermal Plasma

    Institute of Scientific and Technical Information of China (English)

    WANG Xinliang; LI Tingting; WEI Dongxiang; WEI Yanli; GU Fan

    2008-01-01

    The kinetics mechanism of the dissociation reactions in a NO/SO2/N2/O2 system was investigated in consideration of energetic electrons' impacts on a non-thermal plasma. A model was derived from the Boltzmann equation and molecule collision theory to predict the dissociation reaction rate coefficients. Upon comparison with available literature, the model was confirmed to be acceptably accurate in general. Several reaction rate coefficients of the NO/SO2/N2/O2 dissociation system were derived according to the Arrhenius formula. The activation energies of each plasma reaction were calculated by quantum chemistry methods. The relation between the dissociation reaction rate coefficient and electron temperature was established to describe the importance of each reaction and to predict relevant processes of gaseous chemical reactions. The sensitivity of the mechanism of NO/SO2/N2/O2 dissociation reaction in a non-thermal plasma was also analysed.

  19. Decolorization kinetics of Procion H-exl dyes from textile dyeing using Fenton-like reactions.

    Science.gov (United States)

    Ntampegliotis, K; Riga, A; Karayannis, V; Bontozoglou, V; Papapolymerou, G

    2006-08-10

    The decolorization kinetics of three commercially used Procion H-exl dyes was studied using a Fenton-like reagent. The effect of the major system parameters (pH, concentration of H(2)O(2) and Fe(3+) and initial dye concentration) on the kinetics was determined. For comparison, the effect of the use of UV irradiated Fenton-like reagent and of Fenton reagent on the kinetics was also examined. In addition, mineralization rates and the biodegradability improvement as well as the effect of the addition of Cl(-), CO(3)(2-) or HCO(3)(-) on the decolorization rates was studied. The reactions were carried out in a 300 ml stirred cylindrical reactor with the capability of UV irradiation. The dye half-life time goes through a minimum with respect to the solution pH between 3 and 4. It also exhibits a broad minimum with respect to Fe(3+) and H(2)O(2) at molar ratios of H(2)O(2)/Fe(3+) from about 100 to 10. The addition of CO(3)(2-) and HCO(3)(-) substantially reduces the decolorization rates, while this effect is significantly less pronounced with Cl(-). At an optimum range of parameters, the mineralization rate (TOC reduction) is very slow for the Fenton-like process (TOC decrease from an initial 49.5 to 41.1 mg/l after 30 min and to only 35.2 mg/l after 600 min), but it increases significantly for the photo-Fenton-like process (to TOC values of 39.7 and 11.4 mg/l, respectively). The biodegradability, as expressed by the BOD/COD ratio, increases significantly from an initial value of 0.11-0.55 for the Fenton-like and to 0.72 for the photo-Fenton-like processes.

  20. Kinetics of solid-gas reactions characterized by scanning AC nano-calorimetry with application to Zr oxidation

    Science.gov (United States)

    Xiao, Kechao; Lee, Dongwoo; Vlassak, Joost J.

    2014-10-01

    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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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}.

  6. 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

  7. 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.

  8. 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.

  9. Kinetics and reaction pathways of formaldehyde degradation using the UV-fenton method.

    Science.gov (United States)

    Liu, Xiangxuan; Liang, Jiantao; Wang, Xuanjun

    2011-05-01

    This study was based on the purpose of investigating the reaction rules of formaldehyde (HCHO) as an intermediate product in the degradation of many other organic wastewaters. The process conditions of UV-Fenton method for the degradation of the low concentrations of HCHO were studied in a batch photochemical reactor. The results showed that, when the original HCHO concentration was 30 mg/L, at an operating temperature of 23 degrees C, pH = 3, an H202 dosage of 68 mg/L, and an H2O2-to-Fe2+ mole ratio (H2O2:Fe2+) of 5, 91.89% of the HCHO was removed after 30 minutes. The degradation of HCHO in the UV-Fenton system was basically in accordance with the exponential decay. The kinetic study results showed that the reaction orders of HCHO, Fe2+, and H2O2 in the system were 1.054, 0.510, and 0.728, respectively, and the activation energy (Ea) was 9.85 kJ/mol. The comparison of UV/H2O2, Fenton, and UV-Fenton systems for the degradation of HCHO, and the results of iron catalyst tests showed that the mechanism of UV-Fenton on the degradation of HCHO was through a synergistic effect of Fe2+ and UV light to catalyze the decomposition of H2O2. The introduction of UV irradiation to the Fenton system largely increased the degradation rate of HCHO, mainly as a result of the accelerating effect on the formation of the Fe2+/Fe3+ cycle. The reaction products were analyzed by gas chromatography-mass spectrometry and a chemical oxygen demand (COD) analyzer. The effluent gases also were analyzed by gas chromatography. Based on those results, the reaction pathways of HCHO in the UV-Fenton system were proposed. The qualitative and quantitative analysis of the reaction products and the COD showed that the main intermediate product of the reaction was formic acid, and the further oxidation of it was the rate-limiting step for the degradation of HCHO.

  10. 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.

  11. 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

  12. 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

  13. 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

  14. 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

  15. Studies on adsorption, reaction mechanisms and kinetics for photocatalytic degradation of CHD, a pharmaceutical waste.

    Science.gov (United States)

    Sarkar, Santanu; Bhattacharjee, Chiranjib; Curcio, Stefano

    2015-11-01

    The photocatalytic degradation of chlorhexidine digluconate (CHD), a disinfectant and topical antiseptic and adsorption of CHD catalyst surface in dark condition has been studied. Moreover, the value of kinetic parameters has been measured and the effect of adsorption on photocatalysis has been investigated here. Substantial removal was observed during the photocatalysis process, whereas 40% removal was possible through the adsorption route on TiO2 surface. The parametric variation has shown that alkaline pH, ambient temperature, low initial substrate concentration, high TiO2 loading were favourable, though at a certain concentration of TiO2 loading, photocatalytic degradation efficiency was found to be maximum. The adsorption study has shown good confirmation with Langmuir isotherm and during the reaction at initial stage, it followed pseudo-first-order reaction, after that Langmuir Hinshelwood model was found to be appropriate in describing the system. The present study also confirmed that there is a significant effect of adsorption on photocatalytic degradation. The possible mechanism for adsorption and photocatalysis has been shown here and process controlling step has been identified. The influences of pH and temperature have been explained with the help of surface charge distribution of reacting particles and thermodynamic point of view respectively.

  16. 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)

  17. 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.

  18. 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

  19. 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.

  20. 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...

  1. The kinetics and mechanism of an aqueous phase isoprene reaction with hydroxyl radical

    Directory of Open Access Journals (Sweden)

    D. Huang

    2011-08-01

    Full Text Available Aqueous phase chemical processes of organic compounds in the atmosphere have received increasing attention, partly due to their potential contribution to the formation of secondary organic aerosol (SOA. Here, we analyzed the aqueous OH-initiated oxidation of isoprene and its reaction products including carbonyl compounds and organic acids, regarding the acidity and temperature as in-cloudy conditions. We also performed a laboratory simulation to improve our understanding of the kinetics and mechanisms for the products of aqueous isoprene oxidation that are significant precursors of SOA; these included methacrolein (MACR, methyl vinyl ketone (MVK, methyl glyoxal (MG, and glyoxal (GL. We used a novel chemical titration method to monitor the concentration of isoprene in the aqueous phase. We used a box model to interpret the mechanistic differences between aqueous and gas phase OH radical-initiated isoprene oxidations. Our results were the first demonstration of the rate constant for the reaction between isoprene and OH radical in water, 1.2 ± 0.4 × 1010 M−1 s−1 at 283 K. Molar yields were determined based on consumed isoprene. Of note, the ratio of the yields of MVK (24.1 ± 0.8 % to MACR (10.9 ± 1.1% in the aqueous phase isoprene oxidation was approximately double that observed for the corresponding gas phase reaction. We hypothesized that this might be explained by a water-induced enhancement in the self-reaction of a hydroxy isoprene peroxyl radical (HOCH2C(CH3(O2CH = CH2 produced in the aqueous reaction. The observed yields for MG and GL were 11.4 ± 0.3 % and 3.8 ± 0.1 %, respectively. Model simulations indicated that several potential pathways may contribute to the formation of MG and GL. Finally, oxalic acid increased steadily throughout the course of the study, even after isoprene was consumed completely. The observed yield of oxalic acid was 26.2 ± 0

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. Validation of a kinetic-diffusive model to characterize pozzolanic reaction kinetics in sugar cane straw-clay ash/lime systems

    Directory of Open Access Journals (Sweden)

    Villar-Cociña, E.

    2005-06-01

    Full Text Available A kinetic-diffusive model proposed by the authors in previous papers to describe pozzolanic reaction kinetics in sugar cane straw-clay ash (SCSCA/calcium hydroxide (CH systems is validated in this study. Two different methods (direct and indirect for determining pozzolanic activity were applied and their effect on pozzolanic reaction rate kinetic constants evaluated. Determined by fitting a model to the data, these constants are used to quantitatively characterize pozzolanic activity. The values of the kinetic constants calculated with the model were similar for the two methods. Classic kinetic models, such as the Jander, modified Jander and Zhuravlev models, were also applied to the system studied and the results were compared to the figures calculated with the model proposed. The kinetic-diffusive approach proposed was found to be valid regardless of the method for determining pozzolanic activity used, and to be the most suitable model for describing pozzolanic reaction kinetics in the SCSCA/lime system.

    Se valida la aplicación de un modelo cinético-difusivo propuesto por los autores en trabajos anteriores para describir la cinética de reacción puzolánica en sistemas ceniza de paja de caña-arcilla (CPCAñúdróxido de calcio (CH. Se aplican 2 métodos diferentes de actividad puzolánica (directo e indirecto y se valora el efecto que pudieran tener los mismos sobre las constantes cinéticas de velocidad de reacción de la reacción puzolánica. Estas constantes cinéticas son determinadas en el proceso de ajuste del modelo y permiten caracterizar cuantitativamente la actividad puzolánica. Los resultados muestran la similitud de las constantes cinéticas de velocidad de reacción calculadas, aplicando el modelo a los resultados experimentales obtenidos por ambos métodos. Además, fueron aplicados al sistema estudiado modelos cinéticos el chicos como: modelo de Jander, modelo de Jander Modificado y el modelo de Zhuravlev y

  8. Electron transport between plastoquinone and chlorophyll Ai in chloroplasts. II. Reaction kinetics and the function of plastocyanin in situ.

    Science.gov (United States)

    Haehnel, W

    1977-03-11

    The light-induced reaction kinetics of electron carriers between the two light reactions were studied in spinach chloroplasts. 1. The difference spectrum of the absorbance changes of plastocyanin in situ was separated from superimposing absorbance changes by flash titration described in the preceding paper (Haehnel, W. (1973) Biochim. Biophys. Acta 305, 618-631). Relative amounts of 2 : 1 electron equivalents were observed for plastocyanin and chlorophyll a1 (P-700). 2. A balance of the electron equivalents released from reduced plastoquinone and simultaneously accepted by oxidized plastocyanin, cytochrome f and chlorophyll a1 indicated a quantitative electron transfer. Additional electron carriers between plastoquinone and light reaction I can be excluded with an accuracy of about +/-0.3 electron equivalents per light reaction II. 3. The time course of the absorbance changes of plastocyanin was measured at 584 nm with negligible interference with other absorbance changes. The reduction kinetics show an initial lag followed by a rise with a half time of about 20 ms. The redox states of plastocyanin and chlorophyll a1 during this reduction via the rate-limiting step between the light reactions and during oxidation by weak far-red light suggest a true equilibrium constant of about 20. 4. The simultaneous oxidation and reduction kinetics of plastoquinone, cytochrome f, plastocyanin and chlorophyll a1 induced by two successive groups of saturating flashes after far-red illumination were measured. The oxidation kinetics of plastocyanin and the simultaneous reduction kinetics of chlorophyll a1 after the single flashes indicate a quantitative electron transfer with a half time of 200 mus. 5. The fast reduction of chlorophyll a1 by plastocyanin showed no effect of the inhibitors 3-(3',4'-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone or of reduced phenazine methosulfate. But it was completed inhibited after KCN incubation. 6. The

  9. 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.

  10. Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400° C and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, Al and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300° C, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300° C. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatures increased from 25 to 300° C and decreased when the temperatures increase from 300 to 400° C. At some flow velocities, the dissolution rates rose as the temperature surpassed 374° C. Albite dissolution was incongruent in water at most temperatures. It was only at 300° C that albite dissolution was congruent. The albite dissolution from 25 to 300° C (at 23 MPa) will change from incongruent to congruent, whereas from subcritical 300 to 400° C (at 23 MPa), the dissolution will change from congruent to incongruent. The release ratio of Al/Si (or Na/Si) is positive at T300° C. The dissolution rates of magnetite in water increased with increasing T until T at the critical point of water or around it. The authors believe that this is caused by the wide fluctuations in water properties under the conditions from the near-critical to supercritical state.

  11. 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…

  12. 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

  13. 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.

  14. 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…

  15. 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.

  16. Decolorization kinetics of Procion H-exl dyes from textile dyeing using Fenton-like reactions

    Energy Technology Data Exchange (ETDEWEB)

    Ntampegliotis, K. [Department of Physical Sciences, Technological and Educational Institute of Larisa, T.K 411 10 Larisa (Greece); Riga, A. [Department of Physical Sciences, Technological and Educational Institute of Larisa, T.K 411 10 Larisa (Greece); Karayannis, V. [Department of Physical Sciences, Technological and Educational Institute of Larisa, T.K 411 10 Larisa (Greece); Bontozoglou, V. [Department of Mechanical and Industrial Engineering, University of Thessaly, Pedion Areos, T.K 383 34 Volos (Greece); Papapolymerou, G. [Department of Physical Sciences, Technological and Educational Institute of Larisa, T.K 411 10 Larisa (Greece)]. E-mail: papapoly@teilar.gr

    2006-08-10

    The decolorization kinetics of three commercially used Procion H-exl dyes was studied using a Fenton-like reagent. The effect of the major system parameters (pH, concentration of H{sub 2}O{sub 2} and Fe{sup 3+} and initial dye concentration) on the kinetics was determined. For comparison, the effect of the use of UV irradiated Fenton-like reagent and of Fenton reagent on the kinetics was also examined. In addition, mineralization rates and the biodegradability improvement as well as the effect of the addition of Cl{sup -}, CO{sub 3} {sup 2-} or HCO{sub 3} {sup -} on the decolorization rates was studied. The reactions were carried out in a 300 ml stirred cylindrical reactor with the capability of UV irradiation. The dye half-life time goes through a minimum with respect to the solution pH between 3 and 4. It also exhibits a broad minimum with respect to Fe{sup 3+} and H{sub 2}O{sub 2} at molar ratios of H{sub 2}O{sub 2}/Fe{sup 3+} from about 100 to 10. The addition of CO{sub 3} {sup 2-} and HCO{sub 3} {sup -} substantially reduces the decolorization rates, while this effect is significantly less pronounced with Cl{sup -}. At an optimum range of parameters, the mineralization rate (TOC reduction) is very slow for the Fenton-like process (TOC decrease from an initial 49.5 to 41.1 mg/l after 30 min and to only 35.2 mg/l after 600 min), but it increases significantly for the photo-Fenton-like process (to TOC values of 39.7 and 11.4 mg/l, respectively). The biodegradability, as expressed by the BOD/COD ratio, increases significantly from an initial value of 0.11-0.55 for the Fenton-like and to 0.72 for the photo-Fenton-like processes.

  17. Kinetics and Mechanisms of the Acid-base Reaction Between NH3 and HCOOH in Interstellar Ice Analogs

    Science.gov (United States)

    Bergner, Jennifer B.; Öberg, Karin I.; Rajappan, Mahesh; Fayolle, Edith C.

    2016-10-01

    Interstellar complex organic molecules 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 the kinetics and mechanisms of a potential ion-generating, acid-base reaction between NH3 and HCOOH to form the salt NH{}4+HCOO-. We observe salt growth at temperatures as low as 15 K, 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 ± 30 K with a pre-exponential factor 1.4 ± 0.4 × 10-3 s-1. The pre-reaction rate varies under different experimental conditions and likely represents a combination of diffusion and orientation of reactant molecules. For a diffusion-limited case, the pre-reaction barrier is 770 ± 110 K with a pre-exponential factor of ˜7.6 × 10-3 s-1. Acid-base chemistry of common ice constituents is thus a potential cold pathway to generating ions in interstellar ices.

  18. 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...

  19. 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)

  20. Synthesis of Toluene-2,4-Bisurea from 2,4-Toluene Diamine and Urea and the Reaction Kinetics

    Institute of Scientific and Technical Information of China (English)

    王娜; 耿艳楼; 安华良; 赵新强; 王延吉

    2013-01-01

    Toluene-2,4-bisurea (TBU) is an important intermediate for urea route to dimethyl toluene-2,4-dicarbamate and the study on TBU synthesis via the reaction of 2,4-toluene diamine (TDA) and urea is of great significance. Firstly, thermodynamic analysis shows that the reaction is exothermic and a high equilibrium conversion of TDA is expected due to its large reaction equilibrium constant. Secondly, under the suitable reaction conditions, 130 °C, 7 h, and molar ratio of TDA/zinc acetate/urea/sulfolane=1/0.05/3.5/10, TDA conversion is 54.3%, and TBU yield and selectivity are 39.8%and 73.3%respectively. Lastly, the synthesis of TBU is a 1st order reaction with respect to TDA and the reaction kinetics model is established. This work will provide useful information for commercializing the urea route to toluene-2,4-dicarbamate (TDC).

  1. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    Science.gov (United States)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

  2. Modeling of reaction kinetics in bubbling fluidized bed biomass gasification reactor

    Directory of Open Access Journals (Sweden)

    R.K. Thapa, C. Pfeifer, B. M. Halvorsen

    2014-01-01

    Full Text Available Bubbling fluidized beds are widely used as biomass gasification reactors as at the biomass gasification plant in Güssing, 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.

  3. 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.

  4. 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.

  5. Ozonation of benzotriazole and methylindole: Kinetic modeling, identification of intermediates and reaction mechanisms.

    Science.gov (United States)

    Benitez, F Javier; Acero, Juan L; Real, Francisco J; Roldán, Gloria; Rodríguez, Elena

    2015-01-23

    The ozonation of 1H-benzotriazole (BZ) and 3-methylindole (ML), two emerging contaminants that are frequently present in aquatic environments, was investigated. The experiments were performed with the contaminants (1μM) dissolved in ultrapure water. The kinetic study led to the determination of the apparent rate constants for the ozonation reactions. In the case of 1H-benzotriazole, these rate constants varied from 20.1 ± 0.4M(-1)s(-1) at pH=3 to 2143 ± 23 M(-1)s(-1) at pH=10. Due to its acidic nature (pKa=8.2), the degree of dissociation of this pollutant was determined at every pH of work, and the specific rate constants of the un-dissociated and dissociated species were evaluated, being the values of these rate constants 20.1 ± 2.0 and 2.0 ± 0.3 × 10(3)M(-1)s(-1), respectively. On the contrary, 3-methylindole does not present acidic nature, and therefore, it can be proposed an average value for its rate constant of 4.90 ± 0.7 × 10(5)M(-1)s(-1) in the whole pH range 3-10. Further experiments were performed to identify the main degradation byproducts (10 mg L(-1) of contaminants, 0.023 gh(-1) of ozone). Up to 8 intermediates formed in the ozonation of 3-methylindole were identified by LC-TOFMS, while 6 intermediates were identified in the ozonation of 1H-benzotriazole. By considering these intermediate compounds, the reaction mechanisms were proposed and discussed. Finally, evaluated rate constants allowed to predict and modeling the oxidation of these micropollutants in general aquatic systems.

  6. 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)

  7. 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

  8. A kinetic study of the electron-transfer in the reaction of tribenzylchlorotin with [COW12O40]5-

    Institute of Scientific and Technical Information of China (English)

    Fatemeh F. Bamoharram; Mohammad M. Heravi; Touran Ardalan; Pouran Ardalan

    2009-01-01

    A kinetic study of the electron-transfer in the reaction of tribenzylchlorotin with potassium 12-tungsto cobalt (Ⅲ) ate ion, K5[CoW12O40], abbreviated as Co(Ⅲ)W, has been performed in different solvents. The studies were carried out in methanol, ethanol, acetonitrile and acetic acid/water. The rate constants, reaction rates and activation parameters were calculated. Our findings show that the rate of disappearance of the Co(Ⅲ) is pseudo-first order. The kinetic data is strongly affected by used solvents. The maximum and minimum rate constants were achieved in the ethanol and acetic acid/water (70/30) as a solvent, respectively. In all of the used solvents, negative value of activation entropies was observed, but negative activation enthalpies are observed in methanol, ethanol and acetonitrile. The reaction rate is increased with increase of Co(Ⅲ) concentration.

  9. 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.

  10. 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

  11. 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

  12. Reaction Kinetics of Aniline Synthetic Wastewater Treatment by Moving Bed Biofilm Reactor

    Directory of Open Access Journals (Sweden)

    H Ganjidoust

    2009-07-01

    Full Text Available "n "nBackground and Objectives: Experiments were conducted to investigate the behavior of Moving Bed Biofilm Reactor (MBBR as a novel aerobic process for treatment of aniline synthetic wastewater as a hard biodegradable compound is commonly used in number of industrial processes. The objective of this paper is evaluation of MBBR in different conditions for treatment of aniline and determination of reaction kinetics."nMaterials and Methods: In the MBBRs, different carriers are used to maximize the active biofilm surface area in the reactors. In this study, the reactor was filled with Light Expanded Clay Aggregate (LECA as carriers. Evaluation of the reactor efficiency was done at different retention time of 8, 24, 48 and 72 hours with an influent COD from 100 to 3500 mg/L (filling ratio of 50%. After obtaining removal efficiencies, effluent concentration of aniline was measured by adsorption spectrum and maladaptive municipal wastewater treatment plant sludge in batch conditions for confidence of aniline biodegradation and its adsorption to the sludge mass. "nResults:The maximum obtained removal efficiencies were 91% (influent COD=2000 mg/L after 72 hours. Biodegradation of aniline in MBBR has been also approved by NMR spectrum tests. Finally experimental data has indicated that Grau second order model and Stover-Kincannon were the best models to describe substrate loading removal rate for aniline."nConclusion:biological treatment of aniline wastewater compared to other researchers methods.

  13. 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.

  14. 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

  15. 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

  16. 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.

  17. 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 at 25 degrees C the reaction between acetone and hydrogen peroxide proceeds to form intermediates within one day. Based on the assumption that a likely reaction path involves a sequence of reaction steps between acetone and hydrogen peroxide, calculations of Raman spectra were performed using a density...... functional theory (DFT)/Hartree-Fock approach. It was not possible from this to assess with certainty which intermediate products formed most extensively in an acetone/hydrogen peroxide mixture. However, it was concluded that the most likely reaction mixture is a mixture of the different intermediate...

  18. 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.

  19. 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.

  20. Exchange Reaction Between Selenite and Hydroxyl Ion of Variable Charge Soil Surfaces: Ⅱ. Kinetics of Hydroxyl Release

    Institute of Scientific and Technical Information of China (English)

    ZHOU Shi-Wei; ZHANG Gang-Ya; ZHANG Xiao-Nian

    2003-01-01

    A self-made constant pH automated titration instrument was used to study the kinetics of hydroxyl release during selenite reacting with variable charge soils. The rate of hydroxyl release was very rapid at the first several minutes, then gradually slowed down, and at last did not change any more. The experimental data was well fitted by the Langmuir kinetic equation, and with increasing selenite concentration or decreasing solution pH, the reaction lasted longer, the maximum of hydroxyl release (xm) increased, and the binding constant (k) decreased. The time of hydroxyl release with Xuwen latosol was much longer than that with Jinxian red soil.

  1. 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

  2. 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.

  3. Hybrid quantum and classical methods for computing kinetic isotope effects of chemical reactions in solutions and in enzymes.

    Science.gov (United States)

    Gao, Jiali; Major, Dan T; Fan, Yao; Lin, Yen-Lin; Ma, Shuhua; Wong, Kin-Yiu

    2008-01-01

    A method for incorporating quantum mechanics into enzyme kinetics modeling is presented. Three aspects are emphasized: 1) combined quantum mechanical and molecular mechanical methods are used to represent the potential energy surface for modeling bond forming and breaking processes, 2) instantaneous normal mode analyses are used to incorporate quantum vibrational free energies to the classical potential of mean force, and 3) multidimensional tunneling methods are used to estimate quantum effects on the reaction coordinate motion. Centroid path integral simulations are described to make quantum corrections to the classical potential of mean force. In this method, the nuclear quantum vibrational and tunneling contributions are not separable. An integrated centroid path integral-free energy perturbation and umbrella sampling (PI-FEP/UM) method along with a bisection sampling procedure was summarized, which provides an accurate, easily convergent method for computing kinetic isotope effects for chemical reactions in solution and in enzymes. In the ensemble-averaged variational transition state theory with multidimensional tunneling (EA-VTST/MT), these three aspects of quantum mechanical effects can be individually treated, providing useful insights into the mechanism of enzymatic reactions. These methods are illustrated by applications to a model process in the gas phase, the decarboxylation reaction of N-methyl picolinate in water, and the proton abstraction and reprotonation process catalyzed by alanine racemase. These examples show that the incorporation of quantum mechanical effects is essential for enzyme kinetics simulations.

  4. 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.

  5. 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

  6. 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

  7. 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.

  8. 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...

  9. 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.

  10. Synthesis of Aluminum-Aluminum Nitride Nanocomposites by Gas-Liquid Reactions I. Thermodynamic and Kinetic Considerations

    Science.gov (United States)

    Borgonovo, Cecilia; Makhlouf, Makhlouf M.

    2016-10-01

    In-situ fabrication of the reinforcing particles directly in the metal matrix is an answer to many of the challenges encountered in manufacturing metal matrix nanocomposite materials. In this method, the nanosized particles are formed directly within the melt by means of a chemical reaction between a specially designed metallic alloy and a reactive gas. The thermodynamic and kinetic characteristics of this chemical reaction dictate the particle size and distribution in the matrix alloy, as well as the nature of the particle/matrix interface, and consequently, they govern many of the material's mechanical and physical properties. This article focuses on aluminum-aluminum-nitride nanocomposite materials that are synthesized by injecting a nitrogen-bearing gas into a molten aluminum alloy. The thermodynamic and kinetic aspects of the process are modeled, and the detrimental role of oxygen is elucidated.

  11. 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.

  12. 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].

  13. 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.

  14. 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.

  15. 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.

  16. 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).

  17. 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...

  18. 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

  19. Reaction condition optimization and kinetic investigation of roasting zinc oxide ore using (NH4)2SO4

    Science.gov (United States)

    Shao, Hong-mei; Shen, Xiao-yi; Sun, Yi; Liu, Yan; Zhai, Yu-chun

    2016-10-01

    An orthogonal test was used to optimize the reaction conditions of roasting zinc oxide ore using (NH4)2SO4. The optimized reaction conditions are defined as an (NH4)2SO4/zinc molar ratio of 1.4:1, a roasting temperature of 440°C, and a thermostatic time of 60 min. The molar ratio of (NH4)2SO4/zinc is the most predominant factor and the roasting temperature is the second significant factor that governs the zinc extraction. Thermogravimetric-differential thermal analysis was used for (NH4)2SO4 and zinc mixed in a molar ratio of 1.4:1 at the heating rates of 5, 10, 15, and 20 K·min-1. Two strong endothermic peaks indicate that the complex chemical reactions occur at approximately 290°C and 400°C. XRD analysis was employed to examine the transformations of mineral phases during roasting process. Kinetic parameters, including reaction apparent activation energy, reaction order, and frequency factor, were calculated by the Doyle-Ozawa and Kissinger methods. Corresponding to the two endothermic peaks, the kinetic equations were obtained.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  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. Influence of air-drying temperature on drying kinetics, colour, firmness and biochemical characteristics of Atlantic salmon (Salmo salar L.) fillets.

    Science.gov (United States)

    Ortiz, Jaime; Lemus-Mondaca, Roberto; Vega-Gálvez, Antonio; Ah-Hen, Kong; Puente-Diaz, Luis; Zura-Bravo, Liliana; Aubourg, Santiago

    2013-08-15

    In this work the drying kinetics of Atlantic salmon (Salmo salar L.) fillets and the influence of air drying temperature on colour, firmness and biochemical characteristics were studied. Experiments were conducted at 40, 50 and 60°C. Effective moisture diffusivity increased with temperature from 1.08×10(-10) to 1.90×10(-10) m(2) s(-1). The colour difference, determined as ΔE values (from 9.3 to 19.3), as well as firmness (from 25 to 75 N mm(-1)) of dried samples increased with dehydration temperature. The lightness value L(∗) and yellowness value b(∗) indicated formation of browning products at higher drying temperatures, while redness value a(∗) showed dependence on astaxanthin value. Compared with fresh fish samples, palmitic acid and tocopherol content decreased in a 20% and 40%, respectively, with temperature. While eicosapentaenoic acid (EPA) content remained unchanged and docosahexaenoic acid (DHA) content changed slightly. Anisidine and thiobarbituric acid values indicated the formation of secondary lipid oxidation products, which is more relevant for longer drying time than for higher drying temperatures. PMID:23561093

  6. 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.

  7. 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.

  8. 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

  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. 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.

  13. 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...

  14. 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.

  15. 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....

  16. 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.

  17. Kinetics and reaction mechanism of phenol hydroxylation catalyzed by La-Cu4FeAlCO3

    Institute of Scientific and Technical Information of China (English)

    CHEN; Chunxia; XU; Chenghua; FENG; Liangrong; SUO; Jishua

    2005-01-01

    The present work synthesizes La-Cu4FeAlCO3 catalyst under microwave irradiation and characterizes its structure using XRD and IR techniques. The results show that the obtained La-Cu4FeAlCO3 has a hydrotalcite structure. In the phenol hydroxylation with H2O2 catalyzed by La-Cu4FeAlCO3, the effects of reaction time and phenol/H2O2 molar ratio on the phenol hydroxylation, and relationships between the initial hydroxylation rate with concentration of the catalyst, phenol, H2O2 and reaction temperature are also investigated in details. It is shown the phenol conversion can reach 50.09% (mol percent) in the phenol hydroxylation catalyzed by La-Cu4FeAlCO3, under the reaction conditions of the molar ratio of phenol/H2O2 1/2, the amount ratio of phenol/catalyst 20, reaction temperature 343 K, reaction time 120 min, 10 mL distilled water as solvent. Moreover, a kinetic equation of and the activation energy of Ea=58.37 kJ/mol are obtained according to the kinetic studies. Due to the fact that the HO-Cu+-OH species are detected in La-Cu4FeAlCO3/H2O2 system by XPS, the new mechanism about the generation of hydroxyl free radicals in the phenol hydroxylation is proposed, which is supposed that HO-Cu+-OH species are transition state in this reaction.

  18. A kinetic study on the potential of a hybrid reaction mechanism for prediction of NOx formation in biomass grate furnaces

    Science.gov (United States)

    Zahirović, Selma; Scharler, Robert; Kilpinen, Pia; Obernberger, Ingwald

    2011-10-01

    This paper presents the verification of a hybrid reaction mechanism (28 species, 104 reactions) by means of a kinetic study with a view to its application for the CFD-based prediction of gas phase combustion and NOx formation in biomass grate furnaces. The mechanism is based on a skeletal kinetic scheme that includes the subsets for H2, CO, NH3 and HCN oxidation derived from the detailed Kilpinen 97 reaction mechanism. To account for the CH4 breakdown two related reactions from the 4-step global mechanism for hydrocarbons oxidation by Jones and Lindstedt were adopted. The hybrid mechanism was compared to the global mechanism and validated against the detailed Kilpinen 97 mechanism. For that purpose plug flow reactor simulations at conditions relevant to biomass combustion (atmospheric pressure, 1200-1600 K) for approximations of the flue gases in a grate furnace at fuel lean and fuel rich conditions were carried out. The hybrid reaction mechanism outperformed the global one at all conditions investigated. The most striking differences obtained in predictions by the hybrid and the detailed mechanism at the residence times prior to ignition were attributed to the simplified description of the CH4 oxidation in the case of the former. The overall agreement regarding both combustion and NOx chemistry between the hybrid and the detailed mechanism was better at fuel lean conditions than at fuel rich conditions. However, also at fuel rich conditions, the agreement was improving with increasing temperature. Moreover, it was shown that an improvement in the prediction of NOx formation by the N-subset of the hybrid reaction mechanism can be achieved by replacing its C-H-O subset with that of the detailed one.

  19. Kinetics, Reaction Orders, Rate Laws, and Their Relation to Mechanisms: A Hands-On Introduction for High School Students Using Portable Spectrophotometry

    Science.gov (United States)

    Carraher, Jack M.; Curry, Sarah M.; Tessonnier, Jean-Philippe

    2016-01-01

    Teaching complex chemistry concepts such as kinetics using inquiry-based learning techniques can be challenging in a high school classroom setting. Access to expensive laboratory equipment such as spectrometers is typically limited and most reaction kinetics experiments have been designed for advanced placement (AP) or first-year undergraduate…

  20. Kinetics studies of the reactions of main fourth-period monocations (Ga+, Ge+, As+, and Se+) with methyl fluoride.

    Science.gov (United States)

    Barrientos, Carmen; Rayón, Víctor Manuel; Largo, Antonio; Sordo, José Ángel; Redondo, Pilar

    2013-08-22

    Thermodynamics and kinetics theoretical studies on the gas-phase reactions of fluoromethane with main fourth-period monocations (Ga(+), Ge(+), As(+), and Se(+)) have been carried out. Density functional theory (in particular mPW1K functional) was employed in the description of the potential energy surfaces, and refinement of the energies were done at the CCSD(T) level. The reaction rate constants were estimated using variational/conventional microcanonical transition state theory. From a thermodynamic viewpoint, the fluorine abstraction product is predicted for Ga(+) and Ge(+), whereas for As(+) and Se(+) the elimination product, MCH2(+) (M = As, Se) + HF, is the preferred one. Nevertheless, the most favorable channel for the reactions of CH3F with Ga(+) and Se(+) cations present a net activation barrier. In the case of Ga(+), the reaction proceeds via an addition channel forming the adduct complex, CH3FGa(+), whereas for Se(+) no reaction is found, in agreement with the experiments. The predicted reaction rate constants are in reasonable good agreement with the experimental values available. Apart from the harpoon-like mechanism, our results suggest that an oxidative addition mechanism seems to play a relevant role.

  1. Kinetic Study on Aminolysis of 4-Nitrophenyl Isonicotinate in Acetonitrile: Effect of Amine Basicity on Reactivity and Reaction Mechanism

    International Nuclear Information System (INIS)

    A kinetic study is reported on nucleophilic substitution reactions of 4-nitrophenyl isonicotinate with a series of cyclic secondary amines in MeCN. The plots of kobsd vs. [amine] curve upward for the reactions with weakly basic amines (e. g., morpholine, 1-(2-hydroxyethyl)piperazine, and piperazine) but are linear for those with strongly basic amines (e. g., piperidine and 3-methylpiperidine). The curved plots for the reactions with the weakly basic amines are typical for reactions reported previously to proceed through uncatalyzed and catalyzed routes with two intermediates (e. g., a zwitterionic tetrahedral intermediate T± and its deprotonated form T-). In contrast, the linear plots for the reactions with the strongly basic amines indicate that the catalytic route (i. e., the deprotonation process to yield T- from T± by a second amine molecule) is absent. The Brφnsted-type plots for Kk2 and Kk3 (i. e., the rate constants for the uncatalyzed and catalyzed routes, respectively) exhibit excellent linear correlations with βnuc = 0.99 and 0.69, respectively. The effect of amine basicity on the reaction mechanism is discussed in detail

  2. Water formation reaction on Pt(111): Near edge x-ray absorption fine structure experiments and kinetic Monte Carlo simulations

    International Nuclear Information System (INIS)

    The catalytic water formation reaction was investigated by the energy dispersive near-edge x-ray absorption fine structure (dispersive NEXAFS) spectroscopy. An oxygen covered Pt(111) surface with the (2x2) structure was exposed to gaseous hydrogen (5.0x10-9 Torr) at constant surface temperatures (120-140 K). O K-edge NEXAFS spectra were measured during the reaction with a time interval of 35 s. Quantitative analyses of the spectra provided the coverage changes of the adsorbed species (O, OH, and H2O). The reaction is composed of three steps, which are characterized by an induction period (I), fast increase in coverage of OH and H2O with consuming O (II), and slow conversion of OH to H2O after the complete consumption of O (III). It was also found that the maximum OH coverage becomes smaller at a higher temperature. The kinetic Monte Carlo simulation has reproduced the three characteristic reaction steps; in the first step OH domains are created through two-dimensional aggregation of H2O (I), after the nucleation process the second step sets in where the OH domains propagate by the autocatalytic cycle until they contact with each other (II), and finally the merged OH domains convert to H2O (III). The reaction diffusion method was also applied to this system. It explained the reaction behavior in a wide surface area

  3. Detailed Reaction Kinetics for CFD Modeling of Nuclear Fuel Pellet Coating for High Temperature Gas-Cooled Reactors

    Energy Technology Data Exchange (ETDEWEB)

    Battaglia, Francine

    2008-11-29

    The research project was related to the Advanced Fuel Cycle Initiative and was in direct alignment with advancing knowledge in the area of Nuclear Fuel Development related to the use of TRISO fuels for high-temperature reactors. The importance of properly coating nuclear fuel pellets received a renewed interest for the safe production of nuclear power to help meet the energy requirements of the United States. High-temperature gas-cooled nuclear reactors use fuel in the form of coated uranium particles, and it is the coating process that was of importance to this project. The coating process requires four coating layers to retain radioactive fission products from escaping into the environment. The first layer consists of porous carbon and serves as a buffer layer to attenuate the fission and accommodate the fuel kernel swelling. The second (inner) layer is of pyrocarbon and provides protection from fission products and supports the third layer, which is silicon carbide. The final (outer) layer is also pyrocarbon and provides a bonding surface and protective barrier for the entire pellet. The coating procedures for the silicon carbide and the outer pyrocarbon layers require knowledge of the detailed kinetics of the reaction processes in the gas phase and at the surfaces where the particles interact with the reactor walls. The intent of this project was to acquire detailed information on the reaction kinetics for the chemical vapor deposition (CVD) of carbon and silicon carbine on uranium fuel pellets, including the location of transition state structures, evaluation of the associated activation energies, and the use of these activation energies in the prediction of reaction rate constants. After the detailed reaction kinetics were determined, the reactions were implemented and tested in a computational fluid dynamics model, MFIX. The intention was to find a reduced mechanism set to reduce the computational time for a simulation, while still providing accurate results

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

    Science.gov (United States)

    Maienschein, Jon L.; Sunderland, William E.

    1985-03-01

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

  5. Pulse radiolysis study of reaction of bull serum albumin electron adduct with oxygen. Polychromatic kinetics of reaction with adsorbed oxygen

    International Nuclear Information System (INIS)

    By the method of pulse radiolysis the reaction of bull serum albumin electron adduct with oxygen is investigated. As pulsed radiation source electron linear accelerators with particle energy of 8.0 and 4.5 MeV and pulse time of 40 ns and 2.2 μs, respectively have been used. It is assumed that the disappearance of protein electron adduct occurs in the course of its interaction with oxygen adsorbed on protein globular molecule

  6. Pressure dependence of the oxygen reduction reaction at the platinum microelectrode/nafion interface - Electrode kinetics and mass transport

    Science.gov (United States)

    Parthasarathy, Arvind; Srinivasan, Supramaniam; Appleby, A. J.; Martin, Charles R.

    1992-01-01

    The investigation of oxygen reduction kinetics at the platinum/Nafion interface is of great importance in the advancement of proton-exchange-membrane (PEM) fuel-cell technology. This study focuses on the dependence of the oxygen reduction kinetics on oxygen pressure. Conventional Tafel analysis of the data shows that the reaction order with respect to oxygen is unity at both high and low current densities. Chronoamperometric measurements of the transport parameters for oxygen in Nafion show that oxygen dissolution follows Henry's isotherm. The diffusion coefficient of oxygen is invariant with pressure; however, the diffusion coefficient for oxygen is lower when air is used as the equilibrating gas as compared to when oxygen is used for equilibration. These results are of value in understanding the influence of O2 partial pressure on the performance of PEM fuel cells and also in elucidating the mechanism of oxygen reduction at the platinum/Nafion interface.

  7. Hamiltonian formulation for the classical EM radiation-reaction problem: application to the kinetic theory for relativistic collisionless plasmas

    CERN Document Server

    Cremaschini, Claudio; 10.1140/epjp/i2011-11063-3

    2012-01-01

    A notorious difficulty in the covariant dynamics of classical charged particles subject to non-local electromagnetic (EM) interactions arising in the EM radiation-reaction (RR) phenomena is due to the definition of the related non-local Lagrangian and Hamiltonian systems. The lack of a standard Lagrangian/Hamiltonian formulation in the customary asymptotic approximation for the RR equation may inhibit the construction of consistent kinetic and fluid theories. In this paper the issue is investigated in the framework of Special Relativity. It is shown that, for finite-size spherically-symmetric classical charged particles, non-perturbative Lagrangian and Hamiltonian formulations in standard form can be obtained, which describe particle dynamics in the presence of the exact EM RR self-force. As a remarkable consequence, based on axiomatic formulation of classical statistical mechanics, the covariant kinetic theory for systems of charged particles subject to the EM RR self-force is formulated in Hamiltonian form....

  8. The deacetylation reaction in Eucalyptus wood: kinetics and effects on the effective diffusion.

    Science.gov (United States)

    Inalbon, María Cristina; Mocchiutti, Paulina; Zanuttini, Miguel

    2009-04-01

    The removal of native acetyl groups from hardwood O-acetyl-glucuronoxylan has a strong effect on physical characteristics, accessibility and structure of this polymer. The removal also has effects on the swelling and ion transport capacity of the cell wall of hardwoods. In this work, a kinetic expression for Eucalyptus wood deacetylation is determined. Two liquid mediums are considered: a simple alkaline one and another with a higher sodium concentration. The kinetic expression is a power law for the acetyl content and the concentrations in the liquid medium dependence, and is an Arrhenius type expression for temperature dependence. The kinetic expression can be useful to predict the physical properties of wood since the analysis of deacetylation effects on effective capillarity (ECCSA) shows that the acetyl content is a determining factor of wood ionic transport capacity. PMID:19095440

  9. Polarity controlled reaction path and kinetics of thermal cis-to-trans isomerization of 4-aminoazobenzene.

    Science.gov (United States)

    Joshi, Neeraj Kumar; Fuyuki, Masanori; Wada, Akihide

    2014-02-20

    Spectral and kinetic behavior of thermal cis-to-trans isomerization of 4-aminoazobenzene (AAB) is examined in various solvents of different polarities. In contrast to azobenzene (AB), it is found the rate of thermal isomerization of AAB is highly dependent on solvent polarity. Accelerated rates are observed in polar solvents as compared to nonpolar solvents. Moreover, a decrease in the barrier height with an increase in medium polarity is observed. Our observations suggest that inversion is the preferred pathway in cis-to-trans thermal isomerization in a nonpolar medium; however, in a polar medium, the isomerization path deviates from the inversion route and rotational behavior is incorporated. Differences in the kinetics and in mechanisms of isomerization in different media are rationalized in terms of modulation in barrier height by polarity of the medium and solute-solvent interaction. It is found that kinetics as well as the mechanism of thermal isomerization in AAB is controlled by the polarity of the medium.

  10. Nonlinear Stochastic Dynamics of Complex Systems, I: A Chemical Reaction Kinetic Perspective with Mesoscopic Nonequilibrium Thermodynamics

    CERN Document Server

    Qian, Hong

    2016-01-01

    We distinguish a mechanical representation of the world in terms of point masses with positions and momenta and the chemical representation of the world in terms of populations of different individuals, each with intrinsic stochasticity, but population wise with statistical rate laws in their syntheses, degradations, spatial diffusion, individual state transitions, and interactions. Such a formal kinetic system in a small volume $V$, like a single cell, can be rigorously treated in terms of a Markov process describing its nonlinear kinetics as well as nonequilibrium thermodynamics at a mesoscopic scale. We introduce notions such as open, driven chemical systems, entropy production, free energy dissipation, etc. Then in the macroscopic limit, we illustrate how two new "laws", in terms of a generalized free energy of the mesoscopic stochastic dynamics, emerge. Detailed balance and complex balance are two special classes of "simple" nonlinear kinetics. Phase transition is intrinsically related to multi-stability...

  11. Reaction kinetics of the double perovskite Sr{sub 2}FeMoO{sub 6} by gas–solid reactions

    Energy Technology Data Exchange (ETDEWEB)

    Valenzuela, J.L. [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico); Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Soto, T.E. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Facultad de Ciencias Físico-Matemáticas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Río, C.P. 58030 Morelia (Mexico); Lemus, J. [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico); Navarro, O. [Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, 04510 Mexico D.F. (Mexico); Morales, R., E-mail: rmorales@umich.mx [Instituto de Investigaciones Metalúrgicas, Universidad Michoacana de San Nícolas de Hidalgo, Ciudad Universitaria, Francisco J. Mújica S/N, Colonia Felicitas del Ro, C.P. 58030 Morelia (Mexico)

    2014-12-15

    Double perovskite Sr{sub 2}FeMoO{sub 6} 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 Sr{sub 2}FeMoO{sub 6}. Firstly, precursor phases Sr{sub 2}Fe{sub 2}O{sub 5} and SrMoO{sub 4} were synthesized by gas-solid reactions from starting reagents such as SrCO{sub 3}, Fe{sub 2}O{sub 3} y MoO{sub 3}. 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 SrFeO{sub 2.5} during the reduction stage led to a formation of a disordered double perovskite Sr{sub 2}Fe{sub 0.71}Mo{sub 1.29}O{sub 6}.

  12. Gas-Phase Photocatalytic Oxidation of Dimethylamine: The Reaction Pathway and Kinetics

    Directory of Open Access Journals (Sweden)

    Anna Kachina

    2007-01-01

    Full Text Available Gas-phase photocatalytic oxidation (PCO and thermal catalytic oxidation (TCO of dimethylamine (DMA on titanium dioxide was studied in a continuous flow simple tubular reactor. Volatile PCO products of DMA included ammonia, formamide, carbon dioxide, and water. Ammonia was further oxidized in minor amounts to nitrous oxide and nitrogen dioxide. Effective at 573 K, TCO resulted in the formation of ammonia, hydrogen cyanide, carbon monoxide, carbon dioxide, and water. The PCO kinetic data fit well to the monomolecular Langmuir-Hinshelwood model, whereas TCO kinetic behaviour matched the first-order process. No deactivation of the photocatalyst during the multiple long-run experiments was observed.

  13. Time-Resolved O3 Chemical Chain Reaction Kinetics Via High-Resolution IR Laser Absorption Methods

    Science.gov (United States)

    Kulcke, Axel; Blackmon, Brad; Chapman, William B.; Kim, In Koo; Nesbitt, David J.

    1998-01-01

    Excimer laser photolysis in combination with time-resolved IR laser absorption detection of OH radicals has been used to study O3/OH(v = 0)/HO2 chain reaction kinetics at 298 K, (i.e.,(k(sub 1) is OH + 03 yields H02 + 02 and (k(sub 2) is H02 + 03 yields OH + 202). From time-resolved detection of OH radicals with high-resolution near IR laser absorption methods, the chain induction kinetics have been measured at up to an order of magnitude higher ozone concentrations ([03] less than or equal to 10(exp 17) molecules/cu cm) than accessible in previous studies. This greater dynamic range permits the full evolution of the chain induction, propagation, and termination process to be temporally isolated and measured in real time. An exact solution for time-dependent OH evolution under pseudo- first-order chain reaction conditions is presented, which correctly predicts new kinetic signatures not included in previous OH + 03 kinetic analyses. Specifically, the solutions predict an initial exponential loss (chain "induction") of the OH radical to a steady-state level ([OH](sub ss)), with this fast initial decay determined by the sum of both chain rate constants, k(sub ind) = k(sub 1) + k(sub 2). By monitoring the chain induction feature, this sum of the rate constants is determined to be k(sub ind) = 8.4(8) x 10(exp -14) cu cm/molecule/s for room temperature reagents. This is significantly higher than the values currently recommended for use in atmospheric models, but in excellent agreement with previous results from Ravishankara et al.

  14. Amplification of enantiomeric excess, mirror-image symmetry breaking and kinetic proofreading in Soai reaction models with different oligomeric orders.

    Science.gov (United States)

    Micheau, Jean-Claude; Coudret, Christophe; Cruz, José-Manuel; Buhse, Thomas

    2012-10-14

    A comprehensive kinetic analysis of three prototypical autocatalytic cycle models based on the absolute asymmetric Soai reaction is presented. The three models, which can give rise to amplification of enantiomeric excess and mirror-image symmetry breaking, vary by their monomeric, dimeric or trimeric order of the assumed catalytic species. Our numerical approach considered the entire chiral combinatorics of the diastereomeric interactions in the models as well as the multiplicity of coupled reversible reactions without applying fast equilibration or quasi-steady state approximations. For the simplest monomeric model, an extensive range of parameters was explored employing a random grid parameter scanning method that revealed the influence of the parameter values on the product distribution, the reaction-time, the attenuation or amplification of enantiomeric excess as well as on the presence or absence of mirror-image symmetry breaking. A symmetry breaking test was imposed on the three models showing that an increase in the catalytic oligomer size from one to three leads to a higher tolerance to poorer chiral recognition between the diastereoisomers and identifies the greater impact of the diastereoisomeric energy difference over an imperfect stereoselectivity in the catalytic step. This robustness is understood as a particular case of so-called kinetic proofreading in asymmetric autocatalysis.

  15. Power optimization of chemically driven heat engine based on first and second order reaction kinetic theory and probability theory

    Science.gov (United States)

    Zhang, Lei; Chen, Lingen; Sun, Fengrui

    2016-03-01

    The finite-time thermodynamic method based on probability analysis can more accurately describe various performance parameters of thermodynamic systems. Based on the relation between optimal efficiency and power output of a generalized Carnot heat engine with a finite high-temperature heat reservoir (heat source) and an infinite low-temperature heat reservoir (heat sink) and with the only irreversibility of heat transfer, this paper studies the problem of power optimization of chemically driven heat engine based on first and second order reaction kinetic theory, puts forward a model of the coupling heat engine which can be run periodically and obtains the effects of the finite-time thermodynamic characteristics of the coupling relation between chemical reaction and heat engine on the power optimization. The results show that the first order reaction kinetics model can use fuel more effectively, and can provide heat engine with higher temperature heat source to increase the power output of the heat engine. Moreover, the power fluctuation bounds of the chemically driven heat engine are obtained by using the probability analysis method. The results may provide some guidelines for the character analysis and power optimization of the chemically driven heat engines.

  16. Kinetics characterization of YBCO thin films growth on LAO (100) single crystals by the TFA-MOD reaction

    International Nuclear Information System (INIS)

    We have studied in detail the kinetics parameters of the YBa2Cu3O7-x (YBCO) thin films growth on LaAlO3 (100) single crystals by the TFA-MOD method, using an i.n-situ fluoride selective electrode. We have considered: temperature, flow carrier gas rates and water partial pressure dependences in the reaction. Kinetics curves show that it exist an intermediate step before the YBCO formation. This step, which starts during the heating ramp (∼400deg. C) consists in a partial elimination of F from the BaF2 precursor to forms an oxyfluoride intermediate compound. The total YBCO formation appears at temperatures as higher as 700deg. C. We have found that at low flow carrier gas rates, the reaction is controlled by diffusion mechanisms and the apparent order of YBCO formation is n = 1 respect to the stirring rate, but at higher flow rates the YBCO formation is controlled chemically, then the apparent order is zero. The apparent reaction order of YBCO formation respect to the water pressure also has been studied

  17. Recrossing and tunnelling in the kinetics study of the OH + CH4 -> H2O + CH3 reaction

    CERN Document Server

    Suleimanov, Yury V

    2015-01-01

    Thermal rate constants and several kinetic isotope effects were evaluated for the OH + CH4 hydrogen abstraction reaction using two kinetics approaches, ring polymer molecular dynamics (RPMD), and variational transition state theory with multidimensional tunnelling(VTST/MT), based on a refined full-dimensional analytical potential energy surface, PES-2014, in the temperature range 200-2000 K. For the OH + CH4 reaction, at low temperatures, T = 200 K, where the quantum tunnelling effect is more important, RPMD overestimates the experimental rate constants due to problems associated with PES-2014 in the deep tunnelling regime and to the known overestimation of this method in asymmetric reactions, while VTST/MT presents a better agreement, differences about 10%, due to compensation of several factors, inaccuracy of PES-2014 and ignoring anharmonicity. In the opposite extreme, T = 1000 K, recrossing effects play the main role, and the difference between both methods is now smaller, by a factor of 1.5. Given that R...

  18. Kinetic Models Study of Hydrogenation of Aromatic Hydrocarbons in Vacuum Gas Oil and Basrah Crude Oil Reaction

    Directory of Open Access Journals (Sweden)

    Muzher M. Ibraheem

    2013-05-01

    Full Text Available             The aim of this research is to study the kinetic reaction models for catalytic hydrogenation of aromatic content for Basrah crude oil (BCO and vacuum gas oil (VGO derived from Kirkuk crude oil which has the boiling point rang of (611-833K.            This work is performed using a hydrodesulphurization (HDS pilot plant unit located in AL-Basil Company. A commercial (HDS catalyst cobalt-molybdenum (Co-Mo supported in alumina (γ-Al2O3 is used in this work. The feed is supplied by North Refinery Company in Baiji. The reaction temperatures range is (600-675 K over liquid hourly space velocity (LHSV range of (0.7-2hr-1 and hydrogen pressure is 3 MPa with H2/oil ratio of 300 of Basrah Crude oil (BCO, while the corresponding conditions for vacuum gas oil (VGO are (583-643 K, (1.5-3.75 hr-1, 3.5 MPa and 250  respectively .            The results showed that the reaction kinetics is of second order for both types of feed. Activation energies are found to be 30.396, 38.479 kJ/mole for Basrah Crude Oil (BCO and Vacuum Gas Oil (VGO respectively.

  19. A kinetic model for the competitive reactions of ozone with amino acid residues in proteins in reverse micelles

    Energy Technology Data Exchange (ETDEWEB)

    Pryor, W.A.; Uppu, R.M. (Louisiana State Univ., Baton Rouge (United States))

    1993-02-15

    Lysozyme and 10 other proteins are solubilized in reverse micelles formed by 0.1 M sodium di-2-ethyl-hexylsulfosuccinate and 2.0-2.5 M water (pH 7.4) in isooctane solvent. Exposure of the protein-containing reverse micellar solutions to ozone causes oxidative damage to the proteins, as assessed by the oxidation of tryptophan residues. The oxidation product of the protein-bound tryptophan has a molar absorption coefficient of 3275 +/- 81 M-1 cm-1 (mean +/- S.D., n = 6) at 320 nm. The product is suggested to be a Criegee ozonide or a tautomer of the Criegee ozonide and not N-formylkynurenine. Ozonation of lysozyme in reverse micelles results in the formation of hydrogen peroxide in yields of only approximately 0.07 mol/mol of tryptophan residues oxidized. The recovery of hydrogen peroxide added as an internal standard to the lysozyme-containing reverse micellar solutions ranges from 84 to 88%, whether or not the samples are subjected to ozonation. This suggests that hydrogen peroxide is neither destroyed during the process of ozonation nor consumed by the protein to a significant extent in an adventitious reaction. A kinetic model for the overall reaction of ozone with the proteins is developed, taking into account the concentrations and the reactivities of individual amino acid residues toward ozone. The model predicts the fractional reaction of ozone with tryptophan residues in the proteins, despite differences in amino acid composition, molecular weight, and tertiary structures. The lack of influence of protein structure is confirmed further by the observation that the native lysozyme (with and without external S-carboxymethylcysteine) and S-carboxymethylated lysozyme give identical values of the fractional reaction of ozone with tryptophan residues. The kinetic equations for the competitive reactions of ozone with amino acid residues in proteins, with some minor modification, are applicable to ozonations on complex mixtures of lipids, proteins, and antioxidants.

  20. Radioiodination of 5-nitroimidazole Derivative (Ornidazole); Labeling Reaction Optimization, Reaction Kinetic Calculation and In-Vivo Characterization

    International Nuclear Information System (INIS)

    The aim of this study was to localize the inflammatory foci caused by the fungal infections, Ornidazole (ORN) was labeled with iodine-125, the prepared tracer had radiochemical yield greater than 96%. The labeling reaction was carried out at 45 degree c for 30 minutes. The electrophilic radioiodination of ORN was done using iodogen as oxidizing agent. The activation energy Efor this electrophilic substitution reaction was calculated and equal to 4.1 k Cal / mol (17.2 KJ/ mol) at 45 degree c after 30 min reaction time, An in-vivo inflammation models and hypoxic tumor were prepared by the intramuscular injection of E. Coli, C. Albicans, sterile turpentine oil, and Erlich cell line into the thigh muscle of the mice. The biological investigation of the 125IORD tracer in the different inflammatory modalities demonstrated that this tracer is able to distinguish C. Albicans infections from bacterial, sterile, and hypoxic tumor. The difference in target/ non-target (T/NT) ratios between the fungal infected muscle and that of hypoxic tumor, bacterial infected muscle, and sterile inflammation were significant (ι = 2.9, ρ ≤ 0.025, ι= 26.6, ρ <0.005, and (ι = 74,01, ρ <0.005, respectively). The tracer is suitable in imaging of serious fungal infections and in monitoring the efficacy of antifungal therapy during an infection with C. Albicans. In addition, ornidazole can be used to concentrate the therapeutic radionuclide in the site of the hypoxic tumor (1.2 % g and T/NT = 6.3 at 24 h post injection)

  1. Kinetics and Mechanism of the Gas-Phase Reaction of Selected Carbonyls with Cl Atoms between 250 and 340 K

    Science.gov (United States)

    Hasson, A. S.; Algrim, L.; Abdelhamid, A.; Tyndall, G. S.; Orlando, J. J.

    2013-12-01

    Carbonyls are important products from the gas phase degradation of most volatile organic compounds. Their atmospheric reactions therefore have a significant impact on atmospheric composition, particularly in aged air masses. While the reactions of short-chain linear carbonyls are well understood, the chemistry of larger (> C6) and branched carbonyl is more uncertain. To provide insight into these reactions, the reactions of three carbonyls (methyl isopropyl ketone, MIK; di-isopropyl ketone, DIK; and diethyl ketone, DEK) with chlorine atoms were investigated between 250 and 340 K and 1 atm in the presence and absence of NOx and an HO2 source (methanol). Experiments were performed 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. The kinetics were studied using the relative rate technique with butanone and isopropanol as the reference compounds. The Arrhenius expression for the three rate coefficients was determined to be k(DEK+Cl) = 3.87 x 10-11e(2 × 7 kJ/mol)/RT cm3 molecules-1 s-1 , k(MIPK+Cl) = 7.20 x 10-11e(0.2× 8 kJ/mol)/RT cm3 molecules-1 s-1 , and k(DIPK+Cl) = 3.33 x 10-10e(-3× 8 kJ/mol)/RT cm3 molecules-1 s-1 . Measured reaction products accounted for 38-72 % of the reacted carbon and were consistent with strong deactivation of the carbon atom adjacent to the carbonyl group with respect to H-atom abstraction by Cl atoms. The product distributions also provide insight into radical recycling from the organic peroxy + HO2 reaction, and the relative rates of isomerization, fragmentation and reaction with O2 for carbonyl-containing alkoxy radicals. Implications of these results will be discussed.

  2. 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)

  3. Kinetic parameters of oscillating reaction of amino acid-BrO-3-Mn2+-H2SO4-acetone system

    Institute of Scientific and Technical Information of China (English)

    LI Zongxiao; YUAN Chunlan; NIE Fei

    2005-01-01

    The oscillating behavior of thirteen amino acids [leucine (Leu), threonine (Thr), arginine (Arg), lysine (Lys), histidine (His), alanine (Ala), glutamine (Glu), glycine (Gly), methionine (Met), cystine (Cys), tryptophan (Trp), serine (Ser) and tyrosine (Tyr)] in amino acid--Mn2+-H2SO4-acetone system is studied by using a potentiometric determination. With the help of the oscillatory induction period and oscillation period obtained by the oscillating wave, and Arrhenius equation, the kinetic parameters [the apparent activation energy (E) and pre-exponential constant (A)] and rate constant (k) of the above-mentioned oscillating reaction are estimated.

  4. Evaluating the performance of a stopped-flow near-infrared spectrophotometer for studying fast kinetics of actinide reactions

    International Nuclear Information System (INIS)

    A stopped-flow rapid mixing device interfaced to a high performance miniature fibre optic CCD NIR detector permits the study of fast redox kinetics of actinide reactions at minimal cost. The use of fibre optics enables the stopped-flow device to be readily used in a glove-box. The system has been evaluated at 980 nm by observing the in-growth of Np(V) from a fast reduction of Np(VI), and has been shown to perform well in this spectral region. (author)

  5. On the Hydrophobicity of Nitrogen Dioxide: Could there be a “lens” effect for NO2 reaction kinetics?

    OpenAIRE

    Squadrito, Giuseppe L.; Postlethwait, Edward M.

    2009-01-01

    Solvent “lens” effects for the reaction kinetics of NO2 can be evaluated on the basis of published Henry’s law constants for nitrogen dioxide in various solvents. Water-to-organic solvent partition coefficients were derived from Henry’s law constants and used to assess the tendencies of NO2 toward fleeing the aqueous environments and concentrating in biological hydrophobic media. It is concluded, based only on the estimated aqueous medium-to-cell membrane partition coefficient for NO2, that s...

  6. Estimating the turnover number in enzyme kinetic reactions using transient and stationary state data

    Directory of Open Access Journals (Sweden)

    Sibel Uludag-Demirer

    2009-12-01

    Full Text Available Substrate and product concentration data obtained by simulating enzyme-substrate reaction rate equations were used to test two proposed kinetic rate constant estimation techniques in this study. In the first technique, the turnover number, k3, was calculated using early transient time domain data, which are difficult to obtain experimentally. The technique used an iterative approach to calculate k3 with a pair of data and the value of k3 could be retrieved with 35% error. The second technique calculated k3 using stationary domain data and the value of k3 could be retrieved with less than 5% error. This second technique also offered internal consistency in the calculation of k3 by calculating k3 both from the intercept and the slope of the linear plot derived in this study. A series of sensitivity analyses was conducted to understand the robustness of the second technique in estimating k3 from simulated data to the changes in the reaction rate constants (k1, k2, and k3 and the initial concentration of enzyme used for simulation. It was found that the second technique generally worked well in the estimation of k3 except for the simulated data for fast substrate conversions such as in the large k3 and [E]0 cases . This latter method, thus, shows promise for the use of late time experimental substrate/product concentration data to obtain k3. Exclusively using late time data avoids the need for difficult and expensive rapid early time measurement techniques for estimating k3. Once a reasonable estimate for k3 is obtained, the initial enzyme value can easily be determined from the maximum velocity constant established from fitting the Michaelis-Menten or Briggs-Haldane equations to substrate and product stationary state domain (late time data. While the first technique can estimate k3 with only one point in the transient domain, it is suggested that the second method generally be favored since it only requires late-time stationary domain data and

  7. Kinetic study of the reaction of nitrogen with uranium monocarbide; Etude cinetique de la reaction de l'azote sur le monocarbure d'uranium

    Energy Technology Data Exchange (ETDEWEB)

    Herrmann, F.J. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1968-07-01

    The nitridation of uranium monocarbide pieces, microspheres and powder as well, is investigated in the temperature range 700 - 1200 deg. C and the kinetics of this reaction specified, using a thermogravimetric experimental procedure. In every case; the kinetics appears to be linear, except for massive monocarbide at temperatures above 950 deg. C which obeys following the rate law: {delta} m{sup x} = Kt, with x = 1.5 {+-} 0.1 Accordingly, the activation energy varies from 15 to 30 Kcal/mole. Furthermore, as evidenced by the curves K = F(P), the rate of nitridation increases proportionally to the square root of nitrogen pressure. The particular behaviour of the powders can be accounted for through a study of their 'over-temperature'. On the basis of all experimental results, the author suggests a reactional mechanism. (author) [French] L'etude thermogravimetrique de nitruration du monocarbure d'uranium sous differentes formes: massif, billes, poudre, entre 700 et 1200 deg. C, permet de connaitre la cinetique de cette reaction. Dans tous les cas la loi est lineaire sauf pour le monocarbure massif aux temperatures superieures a 950 deg. C, ou elle peut s'exprimer sous la forme: {delta} m{sup x} = Kt avec x = 1,5 {+-} 0,1 L'energie d'activation varie de 15 a 30 Kcal/mole suivant le type de loi rencontre. Les courbes K = F(P) montrent que la vitesse de nitruration croit avec la racine carree de la pression d'azote. L'etude de surtemperature des poudres permet d'expliquer leur comportement particulier. L'auteur propose un mecanisme reactionnel regroupant l'ensemble des resultats experimentaux. (auteur)

  8. Isotopic Effect on the Kinetics of the Belousov-Zhabotinsky Reaction

    Directory of Open Access Journals (Sweden)

    Enzo Tiezzi

    2007-09-01

    Full Text Available In this work we present results about the deuterium isotope effect on the globalkinetics of a Belousov-Zhabotinsky reaction in batch conditions. A nonlinear dependenceof the Induction Period upon the percentage of deuterated reactants was found. The isotopiceffect on the bromination reaction of malonic acid was evaluated.

  9. Study of the Kinetics of an S[subscript N]1 Reaction by Conductivity Measurement

    Science.gov (United States)

    Marzluff, Elaine M.; Crawford, Mary A.; Reynolds, Helen

    2011-01-01

    Substitution reactions, a central part of organic chemistry, provide a model system in physical chemistry to study reaction rates and mechanisms. Here, the use of inexpensive and readily available commercial conductivity probes coupled with computer data acquisition for the study of the temperature and solvent dependence of the solvolysis of…

  10. Degradation of quinoline by wet oxidation - kinetic aspects and reaction mechanisms

    DEFF Research Database (Denmark)

    Thomsen, A.B.

    1998-01-01

    of succinic acid is suggested to be a result of a coupling reaction of the acetic acid radical A reaction mechanism is suggested for the degradation of quinoline: it involves hydroxyl radicals and the possible interaction with autoclave walls is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved....

  11. Kinetics of the oxidation-reduction reactions of uranium, neptunium, plutonium, and americium in aqueous solutions

    International Nuclear Information System (INIS)

    This is a review with about 250 references. Data for 240 reactions are cataloged and quantitative activation parameters are tabulated for 79 of these. Some empirical correlations are given. Twelve typical reactions are discussed in detail, along with the effects of self-irradiation and ionic strength. (U.S.)

  12. The reductive decomposition of calcium sulphate I. Kinetics of the apparent solid-solid reaction

    NARCIS (Netherlands)

    Kamphuis, B.; Potma, A.W.; Prins, W.; Swaaij, van W.P.M.

    1992-01-01

    The reductive decomposition of calcium sulphate by hydrogen is used for the regeneration of calcium-based atmospheric fluidized bed combustion (AFBC) SO2 sorbents. The apparent solid¿solid reaction between CaS and CaSO4, one of the steps involved in the reaction mechanism of the reductive decomposit

  13. Kinetics and Mechanism of Interfacial Reaction in a SiCf/Ti Composite

    Institute of Scientific and Technical Information of China (English)

    Guoxing ZHANG; Qiang KANG; Nanlin SHI; Geping LI; Dong LI

    2003-01-01

    In order to evaluate the interfacial reaction, a SiCf/Ti (TA1) composite was fabricated by a vacuum hot pressingmethod and then heat-treated in vacuum at 800℃ for up to 100 h. The elemental distributions of C, Si and Ti at theinterfacial reaction zone were investigated. It was found that the reaction zone occurs during the fabrication processand continuously grows at high temperature because the Si and C atoms diffuse from SiC fibers to the matrix and Tiatoms diffuse in the opposite direction. The growth of the reaction zone is diffusion controlled and the mechanismof the reaction can be described by a reactive diffusion model of solid-state growth of an AmBn layer between twoelementary substances A and B.

  14. Mass Transfer and Reaction Kinetics in the Carbonization of Magnesium Oxide from Light Calcined Magnesia with Mechanical Force Enhancement

    Institute of Scientific and Technical Information of China (English)

    张焕军; 朱国才

    2004-01-01

    The carbonization of magnesium oxide particles by CO2 was investigated using a stirring mill reactor.The effects of the system temperature, stirring rotation speed, influx rate of CO2 and initial diameter of the magnesium oxide particles on the carbonization process were determined. The results show that the system temperature and the stirring rotation speed are the most significant influencing factors on the carbonization rate. The determination of critical decomposition temperature (CDT) gives the maximum carbonization rate with other conditions fixed. A theoretical model involving mass transfer and reaction kinetics was presented for the carbonization process.The apparent activation energy was calculated to be 32.8kJ·mo1-1. The carbonization process is co-controlled by diffusive mass transfer and chemical reaction. The model fits well with the experimental results.

  15. Kinetics of the BrO + NO2 Association Reaction. Temperature and Pressure Dependence in the Falloff Regime

    Science.gov (United States)

    Thron, R. P.; 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 reaction BrO + NO2 + M yields (k1) products as a function of temperature (248-346 K), pressure (16-800 torr), and buffer gas identity (N2,CF4) The reaction is found to be in the falloff regime between third and second-order over the entire range of conditions investigated This is the first study where temperature-dependent measurements of k1(P,T) have been reported at pressures greater than 12 torr; hence, our results help constrain choices of k1(P,T) for use in models of lower stratospheric BrO(x) chemistry. Approximate falloff parameters in a convenient form for atmospheric modeling are derived.

  16. A temperature dependent kinetic study of the reaction of the hydroxyl radical with CH[sub 3]Br

    Energy Technology Data Exchange (ETDEWEB)

    Zhengyu Zhang; Saini, R.D.; Kurylo, M.J.; Huie, R.E. (National Inst. of Standards and Technology, Gaithersburg, MD (United States))

    1992-12-24

    Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH[sub 3]Br over the temperature range 250 to 400 K. The Arrhenius expression k = 5.79 [times] 10[sup [minus]12] exp([minus]1,560/T) cm[sup 3] molecule[sup [minus]1] s[sup [minus]1] was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH[sub 3]Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years. 20 refs., 1 fig., 1 tab.

  17. UV absorption spectrum and kinetics of the self-reaction of neopentyl radicals in the gas phase at 298 K

    DEFF Research Database (Denmark)

    Nielsen, O.J.; Ellermann, T.; Wallington, T.J.

    1993-01-01

    Neopentyl radicals were produced via the reaction F+(CH3)4C-->(CH3)3CCH2+HF, which was initiated by pulse radiolysis of neopentane/SF6 gas mixtures at 298 K. The ultraviolet absorption spectrum of neopentyl radicals has been recorded over the wavelength range 220-270 nm. An absorption cross section......, sigma((CH3)3CCH2) (240 nm) = (4.88 +/- 0.42) x 10(-18) cm2 molecule-1, has been obtained based on absolute yields using CH3O2 as a reference. The decay of neopentyl radicals was found to follow second-order kinetics in accordance with the self-reaction 2(CH3)3CCH2--> products, with an absolute...

  18. Ion-Isotopic Exchange Reaction Kinetics using Anion Exchange Resins Dowex 550A LC and Indion-930A

    Directory of Open Access Journals (Sweden)

    P.U. Singare

    2014-06-01

    Full Text Available The present paper deals with the characterization of ion exchange resins Dowex 550A LC and Indion-930A based on kinetics of ion-isotopic exchange reactions for which the short lived radioactive isotopes 131I and 82Br were used as a tracers. The study was performed for different concentration of ionic solution varying from 0.001 mol/L to 0.004 mol/L and temperature in the range of 30.0 °C to 45.0 °C. The results indicate that as compared to bromide ion-isotopic exchange reaction, iodide exchange reaction take place at the faster rate. For both the ion-isotopic exchange reactions, under identical experimental conditions, the values of specific reaction rate increases with increase in the ionic concentration and decreases with rise in temperature. It was observed that at 35.00C, 1.000 g of ion exchange resins and 0.002 mol/L labeled iodide ion solution for iodide ion-isotopic exchange reaction, the values of specific reaction rate (min-1, amount of ion exchanged (mmol, initial rate of ion exchange (mmol/min and log Kd were 0.270, 0.342, 0.092 and 11.8 respectively for Dowex 550A LC resin, which was higher than the respective values of 0.156, 0.241, 0.038 and 7.4 as that obtained for Indion-930A resins. From the results, it appears that Dowex 550A LC resins show superior performance over Indion-930A resins under identical experimental conditions.

  19. Kinetic study of the reaction of uranium with various carbon-containing gases; Etude cinetique de la reaction sur l'uranium de differents gaz carbones

    Energy Technology Data Exchange (ETDEWEB)

    Feron, G. [Commissariat a l' Energie Atomique, Grenoble (France). Centre d' Etudes Nucleaires

    1963-09-15

    The kinetic study of the reaction U + CO{sub 2} 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 CO{sub 2} {yields} UO{sub 2} + 2 CO U + CO{sub 2} {yields} UO{sub 2} + C The reaction with carbon monoxide leads to a mixture of dioxide UO{sub 2}, dicarbide UC{sub 2} and free carbon. The main reaction can be written. U + CO {yields} 1/2 UO{sub 2} + 1/2 UC{sub 2} The free carbon results of the disproportionation of the carbon monoxide. A remarkable separation of the two phases UO{sub 2} and UC{sub 2} can be observed. A mechanism accounting for the phenomenon has been proposed. The two reactions U + CO{sub 2} 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) [French] L'etude cinetique des reactions U sol + CO{sub 2} gaz et U sol + CO gaz a ete effectuee par thermogravirnetrie sur une poudre d'uranium a grains spheriques, les domaines de temperature etudies s'etendant respectivement de 460 a 690 deg. C et de 570 a 850 deg. C. L'action du dioxyde de carbone conduit au dioxyde d'uranium UO{sub 2}; il se produit en meme temps un depot de carbone. La reaction globale resulte des deux reactions: U + 2 CO{sub 2} {yields} UO{sub 2} + 2 CO U + CO{sub 2} {yields} UO{sub 2} + C Le mono-oxyde de carbone conduit a un melange de dioxyde UO{sub 2}, de dicarbure UC{sub 2} et de carbone libre. La reaction principale s'ecrit: U + CO {yields} 1/2 UO{sub 2} + 1/2 UC{sub 2} Le carbone libre provient de la dismutation du mono-oxyde de carbone. On observe une separation remarquable des deux phases UO{sub 2} et UC{sub 2}; un mecanisme

  20. Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide.

    Science.gov (United States)

    Huang, Liubin; Zhao, Yue; Li, Huan; Chen, Zhongming

    2015-09-15

    Heterogeneous reaction of SO2 on mineral dust seems to be an important sink for SO2. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H2O2) in this reaction. Here, we investigated the uptake kinetics of SO2 on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H2O2 at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γc). We found that with increasing RH, the γc decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H2O2 can promote the uptake of SO2 on mineral dust at different RHs. The probable explanations are that H2O2 rapidly reacts with SO2 on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H2O2 on the mineral dust, immediately react with adsorbed SO2 as well. Our results suggest that the removal of SO2 via the heterogeneous reaction on mineral dust is an important sink for SO2 and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere. PMID:26281003

  1. Thermodynamic and Kinetic Study of Crystallization Reaction of Fe/Dy Multilayers Form Amorphous State

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    To give further insight into the behavior of Fe/Dy multilayers in the crystallization from as-deposited amorphous state, free energy diagram of Fe/Dy system was constructed based on Miedema semiempirical theory. It is shown that the crystallization of amorphous films is controlled by both thermodynamic and kinetic conditions. The calculated free energies of crystalline Fe and Dy are significantly lower than those in the amorphous states, which provide thermodynamic driving force for crystallization. During annealing, the kinetic phase evolution of the multilayers is controlled by free energy barrier of nucleation and critical-size of new phase nucleus. Thus it explains the experimental results that Fe crystallites formed first followed by Dy grains, whereas crystalline Fe-Dy intermetallic compounds were not observed during annealing at moderate temperatures.

  2. Reaction kinetics of the formation of intermetallic Fe – Zn during hot - dip galvanizing of steel

    Directory of Open Access Journals (Sweden)

    P. Pokorny

    2016-01-01

    Full Text Available This review article mainly describes the composition of intermetallic Fe - Zn, i.e. zeta (ζ, delta (δ1k + δ1p, gamma1 (Γ1 and gamma (Γ on galvanized steel during low temperature galvanization (t ~ 450 °C. It gives detailed the formation, growth of individual phases during galvanization and their interaction. In terms of the kinetics, the formation of the coating is defined by a parabolic kinetic equation of the growth of different intermetallic phases under ideal conditions. From the available literature the rate constants of the formation of individual intermetallic phases and also for the total coating are cited. The composition of the intermetallic phases, iron content, crystal structure, and group symmetry in which the surface of galvanized steel forms.

  3. Steam reforming of methane over Ni catalysts prepared from hydrotalcite-type precursors:Catalytic activity and reaction kinetics

    Institute of Scientific and Technical Information of China (English)

    Yang Qi; Zhenmin Cheng; Zhiming Zhou

    2015-01-01

    Ni/Mg–Al catalysts derived from hydrotalcite-type precursors were prepared by a co-precipitation technique and applied to steam reforming of methane. By comparison with Ni/γ-Al2O3 and Ni/α-Al2O3 catalysts prepared by in-cipient wetness impregnation, the Ni/Mg–Al catalyst presented much higher activity as a result of higher specific surface area and better Ni dispersion. The Ni/Mg–Al catalyst with a Ni/Mg/Al molar ratio of 0.5:2.5:1 exhibited the highest activity for steam methane reforming and was selected for kinetic investigation. With external and inter-nal diffusion limitations eliminated, kinetic experiments were carried out at atmospheric pressure and over a temperature range of 823–973 K. The results demonstrated that the overal conversion of CH4 and the conversion of CH4 to CO2 were strongly influenced by reaction temperature, residence time of reactants as wel as molar ratio of steam to methane. A classical Langmuir–Hinshelwood kinetic model proposed by Xu and Froment (1989) fitted the experimental data with excellent agreement. The estimated adsorption parameters were consistent thermodynamical y.

  4. Kinetics of synthesis of Li4Ti5O12 through solid-solid reaction

    Institute of Scientific and Technical Information of China (English)

    CHOU Kuo-Chih; QIU Weihua; WU Ke; ZHANG Guohua

    2006-01-01

    Solid-solid reaction under low heat or low temperature is an approach to synthesize various kinds of materials that were widely used in electrochemistry field. In this paper a theoretical treatment has been presented for analyzing the mechanism of solid-solid reaction and deriving a series of formulae to describe the variation and rate of reactions. This new model has been used in the manufacturing of spinel Li4Ti5O12. The results show that this new model works very well and will play a useful role for guiding the manufacturing of electrochemical materials.

  5. Kinetic modelling of hydro-treatment reactions by study of different chemical groups; Modelisation cinetique des reactions d`hydrotraitement par regroupement en familles chimiques

    Energy Technology Data Exchange (ETDEWEB)

    Bonnardot, J.

    1998-11-19

    Hydro-treatment of petroleum shortcuts permits elimination of unwanted components in order to increase combustion in engine and to decrease atmospheric pollution. Hydro-desulfurization (HDS), Hydro-denitrogenation (HDN) and Hydrogenation of aromatics (HDA) of a LCO (Light Cycle Oil)-Type gas oil have been studied using a new pilot at a fixed temperature with a NiMo/Al{sub 2}O{sub 3} catalyst. A hydrodynamic study showed that reactions occurring in the up-flow fixed bed reactor that has been used during the experiments, were governed exclusively by chemical reaction rates and not by diffusion. Through detailed chemical analysis, height chemical groups have been considered: three aromatics groups, one sulfided group, one nitrogenized and NH{sub 3}, H{sub 2}S, H{sub 2}. Two Langmuir-Hinshelwood-type kinetic models with either one or two types of sites have been established. The model with two types of site - one site of hydrogenation and one site of hydrogenolysis - showed a better fit in the modeling of the experimental results. This model enables to forecast the influence of partial pressure of H{sub 2}S and partial pressure of H{sub 2} on hydro-treatment reactions of a LCO-type gas oil. (author) 119 refs.

  6. Instrumented sphere method for measuring thermal pressure in fluids and isotropic stresses and reaction kinetics in thermosetting resins

    Science.gov (United States)

    Merzlyakov, Mikhail; Meng, Yan; Simon, Sindee L.; McKenna, Gregory B.

    2004-10-01

    A novel technique is described for measuring thermal pressure in fluids and for measuring isotropic stress development and reaction kinetics in thermosetting resins during cure and thermal cycling. The method uses a 12.7-mm-diam sealed stainless steel spherical pressure vessel to impose three-dimensional isotropic constraints. The vessel is instrumented with strain gauges and thermocouples. Both isotropic stresses and reaction kinetics during cure at cure temperatures as high as 300 °C can be measured. In addition, measurement of the isotropic stress as a function of temperature yields the thermal pressure coefficient in both the glassy and rubbery (or liquid) states. Experimental results are presented for sucrose benzoate, a pressure-transmitting oil di-2-ethylhexylsebacate and an epoxy resin. The method provides reproducible estimates for the thermal pressure coefficient and the stresses are highly isotropic. A suggestion for improved versions of the device is: thicker walled vessels can be used to increase the upper stress limit (currently at 30 MPa). Also if a lower temperature range is to be studied, then aluminum can be used as a vessel material. Since epoxy resins have better adhesion to aluminum than to stainless steel, there may be an advantage to this.

  7. Incorporation of Reaction Kinetics into a Multiphase, Hydrodynamic Model of a Fischer Tropsch Slurry Bubble Column Reactor

    Energy Technology Data Exchange (ETDEWEB)

    Donna Guillen, PhD; Anastasia Gribik; Daniel Ginosar, PhD; Steven P. Antal, PhD

    2008-11-01

    This paper describes the development of a computational multiphase fluid dynamics (CMFD) model of the Fischer Tropsch (FT) process in a Slurry Bubble Column Reactor (SBCR). The CMFD model is fundamentally based which allows it to be applied to different industrial processes and reactor geometries. The NPHASE CMFD solver [1] is used as the robust computational platform. Results from the CMFD model include gas distribution, species concentration profiles, and local temperatures within the SBCR. This type of model can provide valuable information for process design, operations and troubleshooting of FT plants. An ensemble-averaged, turbulent, multi-fluid solution algorithm for the multiphase, reacting flow with heat transfer was employed. Mechanistic models applicable to churn turbulent flow have been developed to provide a fundamentally based closure set for the equations. In this four-field model formulation, two of the fields are used to track the gas phase (i.e., small spherical and large slug/cap bubbles), and the other two fields are used for the liquid and catalyst particles. Reaction kinetics for a cobalt catalyst is based upon values reported in the published literature. An initial, reaction kinetics model has been developed and exercised to demonstrate viability of the overall solution scheme. The model will continue to be developed with improved physics added in stages.

  8. The preparation and chemical reaction kinetics of tungsten bronze thin films and nitrobenzene with and without a catalyst

    Science.gov (United States)

    Materer, Nicholas F.; Apblett, Allen; Kadossov, Evgueni B.; Khan, Kashif Rashid; Casper, Walter; Hays, Kevin; Shams, Eman F.

    2016-06-01

    Microcrystalline tungsten bronze thin films were prepared using wet chemical techniques to reduce a tungsten oxide thin film that was prepared by thermal oxidation of a sputter deposited tungsten metal film on a quartz substrate. The crystallinity of these films was determined by X-ray diffraction and the surface was characterized by X-ray and Ultra-Violet Photoelectron spectroscopy. The total amount of hydrogen incorporated in the film was monitored using absorbance spectroscopy at 900 nm. The oxidation kinetics of the film and the hydrogenation of nitrobenzene in hexane were measured as a function of film thickness. A satisfactory fit of the resulting kinetics was obtained using a model that involves two simultaneous processes. The first one is the proton diffusion from the bulk of the film to the surface, and the second is a reaction of the surface protons with the oxidants. Finally, the dependence of the reaction rates on the presence of catalytic amounts of first row transition metals on the surface of the film was explored.

  9. Optimization of time–temperature schedule for nitridation of silicon compact on the basis of silicon and nitrogen reaction kinetics

    Indian Academy of Sciences (India)

    J Rakshit; P K Das

    2000-08-01

    A time–temperature schedule for formation of silicon–nitride by direct nitridation of silicon compact was optimized by kinetic study of the reaction, 3Si + 2N2 = Si3N4 at four different temperatures (1250°C, 1300°C, 1350°C and 1400°C). From kinetic study, three different temperature schedules were selected each of duration 20 h in the temperature range 1250°–1450°C, for complete nitridation. Theoretically full nitridation (100% i.e. 66.7% weight gain) was not achieved in the product having no unreacted silicon in the matrix, because impurities in Si powder and loss of material during nitridation would result in 5–10% reduction of weight gain. Green compact of density < 66% was fully nitrided by any one of the three schedules. For compact of density > 66%, the nitridation schedule was maneuvered for complete nitridation. Iron promotes nitridation reaction. Higher weight loss during nitridation of iron doped compact is the main cause of lower nitridation gain compared to undoped compact in the same firing schedule. Iron also enhances the amount of -Si3N4 phase by formation of low melting FeSi phase.

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

    Science.gov (United States)

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

    1980-12-01

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

  11. High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

    NARCIS (Netherlands)

    Chen, C.H.; Meadows, K.E.; Cuharuc, A.; Lai, S.C.S.; Unwin, P.R.

    2014-01-01

    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 platin

  12. Dynamic order reduction of thin-film deposition kinetics models: A reaction factorization approach

    Energy Technology Data Exchange (ETDEWEB)

    Adomaitis, Raymond A., E-mail: adomaiti@umd.edu [Department of Chemical and Biomolecular Engineering, Institute for Systems Research, University of Maryland, College Park, Maryland 20742 (United States)

    2016-01-15

    A set of numerical tools for the analysis and dynamic dimension reduction of chemical vapor and atomic layer deposition (ALD) surface reaction models is developed in this work. The approach is based on a two-step process where in the first, the chemical species surface balance dynamic equations are factored to effectively decouple the (nonlinear) reaction rates, a process that eliminates redundant dynamic modes and that identifies conserved quantities. If successful, the second phase is implemented to factor out redundant dynamic modes when species relatively minor in concentration are omitted; if unsuccessful, the technique points to potential model structural problems. An alumina ALD process is used for an example consisting of 19 reactions and 23 surface and gas-phase species. Using the approach developed, the model is reduced by nineteen modes to a four-dimensional dynamic system without any knowledge of the reaction rate values. Results are interpreted in the context of potential model validation studies.

  13. 加氢脱硫反应动力学研究进展%Research progress on hydrodesulfurization reaction kinetics

    Institute of Scientific and Technical Information of China (English)

    高玉瑛

    2011-01-01

    It is very important to study the process of hydrodesulphurization reaction in order to adapt to the increasingly strict environmental regulations. This paper focuses on reviewing hydrodesulphu-rization reaction kinetics of the sulfides in the model compounds and in oil respectively, and deeply studying the hydrogenation reaction dynamic behavior of all kinds of sulfides, which can enlarge the understanding of hydrodesulphurization reaction process and provide the guidance to the industrial production.%为了适应日益严格的环境法规,对加氢脱硫反应过程的研究十分重要.作者对模型化合物和实际油品中硫化物的加氢脱硫反应动力学研究进展分别进行评述,深入探讨了各硫化物的加氢反应动力学行为.通过本文可以提高对加氢脱硫反应过程的认识,更好地指导实际工业生产.

  14. Mechanism and kinetic study on the gas-phase reactions of OH radical with carbamate insecticide isoprocarb

    Science.gov (United States)

    Zhang, Chenxi; Yang, Wenbo; Bai, Jing; Zhao, Yuyang; Gong, Chen; Sun, Xiaomin; Zhang, Qingzhu; Wang, Wenxing

    2012-12-01

    As one of the most important carbamate insecticides, isoprocarb [2-(1-methylethyl) phenyl methylcarbamate, MIPC] is widely used in agricultural and cotton spraying. The atmospheric chemical reaction mechanism and kinetics of MIPC with OH radical have been researched using the density functional theory in this paper. The study shows that OH radical is more easily added to the C atoms of aromatic ring than to carbon-oxygen double bond, while the H atom is abstracted more difficulty from -CONH- group and aromatic ring than from the -CH3- group and the -CH- group. At room temperature, the total rate constant of MIPC with OH radical is about 5.1 × 10-12 cm3 molecule-l s-l. OH radical addition reaction and H atom abstraction reaction are both important for the OH-initiated reaction of MIPC. The energy-rich adducts (MIPC-OH) and the MIPC's radical isomers are open-shell activated radicals and can be further oxidized in the atmosphere.

  15. Kinetics and mechanism of the gas-phase reaction of Cl atoms and OH radicals with fluorobenzene at 296 K

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Nielsen, Ole John; Hurley, MD;

    2002-01-01

    radical and adduct formation to give the C6H5F-Cl adduct. At 296 K the rate constant for the abstraction channel is k(5a)(Cl+C6H5F) = (1.1 +/- 0.1) x 10(-17) cm(3) molecule(-1) s(-1). The C6H5F-Cl adduct undergoes rapid (k similar to 10(8) s(-1)) decomposition to reform C6H5F and Cl atoms and reaction......Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms and OH radicals with fluorobenzene, C6H5F, in 700 Torr of N-2 or air diluent at 296 K. Reaction of Cl atoms with C6H5F proceeds via two pathways: H-atom abstraction to give HCl and the C6H4F...... with Cl atoms via a mechanism which, at least in part, leads neither to production of C6H5Cl nor to reformation of C6H5F. As the steady-state Cl atom concentration is increased, the fraction of the C6H5F-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate...

  16. Theoretical analysis of kinetic isotope effects on proton transfer reactions between substituted alpha-methoxystyrenes and substituted acetic acids.

    Science.gov (United States)

    Wong, Kin-Yiu; Richard, John P; Gao, Jiali

    2009-10-01

    Primary kinetic isotope effects (KIEs) on a series of carboxylic acid-catalyzed protonation reactions of aryl-substituted alpha-methoxystyrenes (X-1) to form oxocarbenium ions have been computed using the second-order Kleinert variational perturbation theory (KP2) in the framework of Feynman path integrals (PI) along with the potential energy surface obtained at the B3LYP/6-31+G(d,p) level. Good agreement with the experimental data was obtained, demonstrating that this novel computational approach for computing KIEs of organic reactions is a viable alternative to the traditional method employing Bigeleisen equation and harmonic vibrational frequencies. Although tunneling makes relatively small contributions to the lowering of the free energy barriers for the carboxylic acid catalyzed protonation reaction, it is necessary to include tunneling contributions to obtain quantitative estimates of the KIEs. Consideration of anharmonicity can further improve the calculated KIEs for the protonation of substituted alpha-methoxystyrenes by chloroacetic acid, but for the reactions of the parent and 4-NO(2) substituted alpha-methoxystyrene with substituted carboxylic acids, the correction of anharmonicity overestimates the computed KIEs for strong acid catalysts. In agreement with experimental findings, the largest KIEs are found in nearly ergoneutral reactions, DeltaG(o) approximately 0, where the transition structures are nearly symmetric and the reaction barriers are relatively low. Furthermore, the optimized transition structures are strongly dependent on the free energy for the formation of the carbocation intermediate, that is, the driving force DeltaG(o), along with a good correlation of Hammond shift in the transition state structure.

  17. Kinetics study of heterogeneous reactions of ozone with erucic acid using an ATR-IR flow reactor.

    Science.gov (United States)

    Leng, Chunbo; Hiltner, Joseph; Pham, Hai; Kelley, Judas; Mach, Mindy; Zhang, Yunhong; Liu, Yong

    2014-03-01

    The ozone initiated heterogeneous oxidation of erucic acid (EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy (ATR-IR) over wide ranges of ozone concentrations (0.25-60 ppm), thin film thickness (0.1-1.0 μm), temperatures (263-298 K), and relative humidities (0-80% RH) for the first time. Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained through changes in the absorbance of C[double bond, length as m-dash]O stretching bands at 1695 cm(-1), which is assigned to the carbonyl group in carboxylic acid. Results showed that the reaction followed the Langmuir-Hinshelwood mechanism and kapp was largely dominated by surface reaction over bulk phase reaction. In addition, both the kapp and the γ values showed very strong temperature dependences (∼two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, the activation energy for the heterogeneous reaction was estimated to be 80.6 kJ mol(-1). Our results have suggested that heterogeneous reactions between ozone and unsaturated solid surfaces likely have a substantially greater temperature dependence than liquid ones. Moreover, the hygroscopic properties of EA thin films before and after exposure to ozone were also studied by measurement of water uptake. Based on the hygroscopicity data, the insignificant RH effect on reaction kinetics was probably due to the relatively weak water uptake by the unreacted and reacted EA thin films.

  18. Integrated microfluidic system enabling (bio)chemical reactions with on-line MALDI-TOF mass spectrometry

    NARCIS (Netherlands)

    Brivio, Monica; Fokkens, Roel H.; Verboom, Willem; Reinhoudt, David N.; Tas, Niels R.; Goedbloed, Martijn; Berg, van den Albert

    2002-01-01

    A continuous flow micro total analysis system (μ-TAS) consisting of an on-chip microfluidic device connected to a matrix assisted laser desorption ionization [MALDI] time-of-flight [TOF] mass spectrometer (MS) as an analytical screening system is presented. Reaction microchannels and inlet/outlet re

  19. Effect of fluorescently labeling protein probes on kinetics of protein-ligand reactions.

    Science.gov (United States)

    Sun, Y S; Landry, J P; Fei, Y Y; Zhu, X D; Luo, J T; Wang, X B; Lam, K S

    2008-12-01

    We studied the effect of fluorescently labeling proteins on protein-ligand reactions. Unlabeled ligands (streptavidin-binding peptides and rabbit immunoglobulin G (IgG) as antigen targets) are immobilized on epoxy-functionalized glass slides. Unlabeled and Cy3-labeled protein probes from the same batch (streptavidin and goat antibodies) subsequently react with the surface-immobilized targets. By monitoring in situ the surface mass density change using an oblique-incidence reflectivity difference scanning microscope (a label-free detector), we measured k(on) and k(off) for streptavidin-peptide reactions and antibody-antigen reaction. We found that (1) equilibrium dissociation constants, defined as K(D) = k(off)/k(on), for streptavidin-peptide reactions increases by a factor of 3-4 when the solution-phase streptavidin is labeled with Cy3 dye and (2) K(D) for reactions of solution-phase goat anti-rabbit antibodies with rabbit IgG targets also change significantly when the goat antibodies are labeled with Cy3 dye. PMID:18991423

  20. Permanganate oxidation of α-amino acids: kinetic correlations for the nonautocatalytic and autocatalytic reaction pathways.

    Science.gov (United States)

    Perez-Benito, Joaquin F

    2011-09-01

    The reactions of permanganate ion with seven α-amino acids in aqueous KH(2)PO(4)/K(2)HPO(4) buffers have been followed spectrophotometrically at two different wavelengths: 526 nm (decay of MnO(4)(-)) and 418 nm (formation of colloidal MnO(2)). All of the reactions studied were autocatalyzed by colloidal MnO(2), with the contribution of the autocatalytic reaction pathway decreasing in the order glycine > l-threonine > l-alanine > l-glutamic acid > l-leucine > l-isoleucine > l-valine. The rate constants corresponding to the nonautocatalytic and autocatalytic pathways were obtained by means of either a differential rate law or an integrated one, the latter requiring the use of an iterative method for its implementation. The activation parameters for the two pathways were determined and analyzed to obtain statistically significant correlations for the series of reactions studied. The activation enthalpy of the nonautocatalytic pathway showed a strong, positive dependence on the standard Gibbs energy for the dissociation of the protonated amino group of the α-amino acid. Linear enthalpy-entropy correlations were found for both pathways, leading to isokinetic temperatures of 370 ± 21 K (nonautocatalytic) and 364 ± 28 K (autocatalytic). Mechanisms in agreement with the experimental data are proposed for the two reaction pathways.