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Sample records for activated chemical reactions

  1. Microfluidic chemical reaction circuits

    DOEpatents

    Lee, Chung-cheng; Sui, Guodong; Elizarov, Arkadij; Kolb, Hartmuth C.; Huang, Jiang; Heath, James R.; Phelps, Michael E.; Quake, Stephen R.; Tseng, Hsian-rong; Wyatt, Paul; Daridon, Antoine

    2012-06-26

    New microfluidic devices, useful for carrying out chemical reactions, are provided. The devices are adapted for on-chip solvent exchange, chemical processes requiring multiple chemical reactions, and rapid concentration of reagents.

  2. X-ray imaging of chemically active valence electrons during a pericyclic reaction.

    PubMed

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-11-26

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.

  3. X-ray imaging of chemically active valence electrons during a pericyclic reaction

    PubMed Central

    Bredtmann, Timm; Ivanov, Misha; Dixit, Gopal

    2014-01-01

    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions. PMID:25424639

  4. Spatiotemporal regulation of chemical reaction kinetics of cell surface molecules by active remodeling of cortical actin

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Bhaswati; Chaudhuri, Abhishek; Gowrishankar, Kripa; Mayor, Satyajit; Rao, Madan

    2010-03-01

    Cell surface proteins such as lipid tethered GPI-anchored proteins and Ras-proteins are distributed as monomers and nanoclusters on the surface of living cells. Recent work from our laboratory suggests that the spatial distribution and dynamics of formation and breakup of these nanoclusters is controlled by the active remodeling dynamics of the underlying cortical actin. To explain these observations, we propose a novel mechanism of nanoclustering, involving the transient binding to and advection along constitutively occuring ``asters'' of cortical actin. Here we study the consequences of such active actin based clustering, in the context of chemical reactions involving conformational changes of cell surface proteins. We find that active remodeling of cortical actin, can give rise to a dramatic increase in the reaction efficiency and output levels. In general, such actin driven clustering of membrane proteins could be a cellular mechanism to spatiotemporally regulate and amplify local chemical reaction rates, in the context of signalling and endocytosis.

  5. Chemical Reaction Problem Solving.

    ERIC Educational Resources Information Center

    Veal, William

    1999-01-01

    Discusses the role of chemical-equation problem solving in helping students predict reaction products. Methods for helping students learn this process must be taught to students and future teachers by using pedagogical skills within the content of chemistry. Emphasizes that solving chemical reactions should involve creative cognition where…

  6. Chemical activity induces dynamical force with global structure in a reaction-diffusion-convection system.

    PubMed

    Mahara, Hitoshi; Okada, Koichi; Nomura, Atsushi; Miike, Hidetoshi; Sakurai, Tatsunari

    2009-07-01

    We found a rotating global structure induced by the dynamical force of local chemical activity in a thin solution layer of excitable Belousov-Zhabotinsky reaction coupled with diffusion. The surface flow and deformation associated with chemical spiral waves (wavelength about 1 mm) represents a global unidirectional structure and a global tilt in the entire Petri dish (100 mm in diameter), respectively. For these observations, we scanned the condition of hierarchal pattern selection. From this result, the bromomalonic acid has an important role to induce the rotating global structure. An interaction between a reaction-diffusion process and a surface-tension-driven effect leads to such hierarchal pattern with different scales. PMID:19658764

  7. Oscillating Chemical Reactions

    ERIC Educational Resources Information Center

    Hawkins, M. D.; And Others

    1975-01-01

    Describes several oscillating chemical reactions which can be used in undergraduate chemistry laboratories. In one such reaction, ferroin oscillates from red (reducing solution) to blue (oxidizing solution) for about an hour at a frequency which can readily be shown to depend on such factors as the temperature, type of solvent, and concentration…

  8. Translated chemical reaction networks.

    PubMed

    Johnston, Matthew D

    2014-05-01

    Many biochemical and industrial applications involve complicated networks of simultaneously occurring chemical reactions. Under the assumption of mass action kinetics, the dynamics of these chemical reaction networks are governed by systems of polynomial ordinary differential equations. The steady states of these mass action systems have been analyzed via a variety of techniques, including stoichiometric network analysis, deficiency theory, and algebraic techniques (e.g., Gröbner bases). In this paper, we present a novel method for characterizing the steady states of mass action systems. Our method explicitly links a network's capacity to permit a particular class of steady states, called toric steady states, to topological properties of a generalized network called a translated chemical reaction network. These networks share their reaction vectors with their source network but are permitted to have different complex stoichiometries and different network topologies. We apply the results to examples drawn from the biochemical literature.

  9. Heat and mass transfer in unsteady rotating fluid flow with binary chemical reaction and activation energy.

    PubMed

    Awad, Faiz G; Motsa, Sandile; Khumalo, Melusi

    2014-01-01

    In this study, the Spectral Relaxation Method (SRM) is used to solve the coupled highly nonlinear system of partial differential equations due to an unsteady flow over a stretching surface in an incompressible rotating viscous fluid in presence of binary chemical reaction and Arrhenius activation energy. The velocity, temperature and concentration distributions as well as the skin-friction, heat and mass transfer coefficients have been obtained and discussed for various physical parametric values. The numerical results obtained by (SRM) are then presented graphically and discussed to highlight the physical implications of the simulations. PMID:25250830

  10. Heat and Mass Transfer in Unsteady Rotating Fluid Flow with Binary Chemical Reaction and Activation Energy

    PubMed Central

    Awad, Faiz G.; Motsa, Sandile; Khumalo, Melusi

    2014-01-01

    In this study, the Spectral Relaxation Method (SRM) is used to solve the coupled highly nonlinear system of partial differential equations due to an unsteady flow over a stretching surface in an incompressible rotating viscous fluid in presence of binary chemical reaction and Arrhenius activation energy. The velocity, temperature and concentration distributions as well as the skin-friction, heat and mass transfer coefficients have been obtained and discussed for various physical parametric values. The numerical results obtained by (SRM) are then presented graphically and discussed to highlight the physical implications of the simulations. PMID:25250830

  11. Experimental Demonstrations in Teaching Chemical Reactions.

    ERIC Educational Resources Information Center

    Hugerat, Muhamad; Basheer, Sobhi

    2001-01-01

    Presents demonstrations of chemical reactions by employing different features of various compounds that can be altered after a chemical change occurs. Experimental activities include para- and dia-magnetism in chemical reactions, aluminum reaction with base, reaction of acid with carbonates, use of electrochemical cells for demonstrating chemical…

  12. The activation strain model and molecular orbital theory: understanding and designing chemical reactions.

    PubMed

    Fernández, Israel; Bickelhaupt, F Matthias

    2014-07-21

    In this Tutorial Review, we make the point that a true understanding of trends in reactivity (as opposed to measuring or simply computing them) requires a causal reactivity model. To this end, we present and discuss the Activation Strain Model (ASM). The ASM establishes the desired causal relationship between reaction barriers, on one hand, and the properties of reactants and characteristics of reaction mechanisms, on the other hand. In the ASM, the potential energy surface ΔE(ζ) along the reaction coordinate ζ is decomposed into the strain ΔEstrain(ζ) of the reactants that become increasingly deformed as the reaction proceeds, plus the interaction ΔEint(ζ) between these deformed reactants, i.e., ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). The ASM can be used in conjunction with any quantum chemical program. An analysis of the method and its application to problems in organic and organometallic chemistry illustrate the power of the ASM as a unifying concept and a tool for rational design of reactants and catalysts.

  13. Biological and chemical assessment of antioxidant activity of sugar-lysine model maillard reaction products.

    PubMed

    Kitts, David D; Hu, Chun

    2005-06-01

    The antioxidant activity of Maillard reaction products (MRPs) is often associated with increased stability and shelf life of food systems vulnerable to oxidation reactions. In this study, nondialyzed, high-molecular weight (HMW = >3500 Da) MRPs were recovered from three model sugar-lysine (glucose-lysine, Glc-Lys; fructose-lysine, Fru-Lys; and ribose-lysine, Rib-Lys) reactions, heated at 121 degrees C for one hour. Samples were characterized by UV and fluorescence spectra and assessed for antioxidant activity using both standard chemical methods (1,1-diphenyl-2-picryl-hydrazyl [DPPH] and oxygen radical absorbing capacity [ORAC]). In addition, biochemical (e.g., cell culture for intracellular oxidation in RAW264.7 cells and protection against metal ion-induced cytotoxicity in C3H/10T1/2 mouse embryo fibroblast cells) assays were used. Patterns of change for fluorescence and multiple colorimetric parameters corresponded to the recovery yield of HMW MRPs and indicated that Rib was more (P < 0.05) reactive than Glc, which in turn was greater (P < 0.05) than Fru. These characteristics of rate of browning did not parallel the significant (P < 0.05) antioxidant activity noted for different sugar-derived HMW MRPs to scavenge DPPH radical, or exhibit total antioxidant activity using the ORAC (e.g., 800-1000 micromol Trolox/gm MRP) method. Antioxidant activity of Glc-, Fru-, and Rib-Lys HMW-MRPs (50 microg/mL) produced protection (P < 0.05) against both H2O2- and AAPH-induced intracellular oxidation reactions in cultured RAW 264.7 cells. Metal chelating activity of all three sugar-derived HMW MRPs (0.01% w/v) was attributed to similar protection (P < 0.05) against Fe2+ and Cu2+-induced cytotoxicity in cultured mouse embryonic fibroblasts. The reducing activity of all three HMW-MRPs indicated the potential for prooxidant activity that could explain enhanced cytotoxicity of Fe3+ in cultured cells. PMID:16037272

  14. Chemical Reactions at Surfaces

    SciTech Connect

    Michael Henderson and Nancy Ryan Gray

    2010-04-14

    Chemical reactions at surfaces underlie some of the most important processes of today, including catalysis, energy conversion, microelectronics, human health and the environment. Understanding surface chemical reactions at a fundamental level is at the core of the field of surface science. The Gordon Research Conference on Chemical Reactions at Surfaces is one of the premiere meetings in the field. The program this year will cover a broad range of topics, including heterogeneous catalysis and surface chemistry, surfaces in environmental chemistry and energy conversion, reactions at the liquid-solid and liquid-gas interface, electronic materials growth and surface modification, biological interfaces, and electrons and photons at surfaces. An exciting program is planned, with contributions from outstanding speakers and discussion leaders from the international scientific community. The conference provides a dynamic environment with ample time for discussion and interaction. Attendees are encouraged to present posters; the poster sessions are historically well attended and stimulate additional discussions. The conference provides an excellent opportunity for junior researchers (e.g. graduate students or postdocs) to present their work and interact with established leaders in the field.

  15. Enhancing chemical reactions

    DOEpatents

    Morrey, John R.

    1978-01-01

    Methods of enhancing selected chemical reactions. The population of a selected high vibrational energy state of a reactant molecule is increased substantially above its population at thermal equilibrium by directing onto the molecule a beam of radiant energy from a laser having a combination of frequency and intensity selected to pump the selected energy state, and the reaction is carried out with the temperature, pressure, and concentrations of reactants maintained at a combination of values selected to optimize the reaction in preference to thermal degradation by transforming the absorbed energy into translational motion. The reaction temperature is selected to optimize the reaction. Typically a laser and a frequency doubler emit radiant energy at frequencies of .nu. and 2.nu. into an optical dye within an optical cavity capable of being tuned to a wanted frequency .delta. or a parametric oscillator comprising a non-centrosymmetric crystal having two indices of refraction, to emit radiant energy at the frequencies of .nu., 2.nu., and .delta. (and, with a parametric oscillator, also at 2.nu.-.delta.). Each unwanted frequency is filtered out, and each desired frequency is focused to the desired radiation flux within a reaction chamber and is reflected repeatedly through the chamber while reactants are fed into the chamber and reaction products are removed therefrom.

  16. Chemically Activated Formation of Organic Acids in Reactions of the Criegee Intermediate with Aldehydes and Ketones

    SciTech Connect

    Jalan, Amrit; Allen, Joshua W.; Green, William H.

    2013-08-08

    Reactions of the Criegee intermediate (CI, .CH2OO.) are important in atmospheric ozonolysis models. In this work, we compute the rates for reactions between .CH2OO. and HCHO, CH3CHO and CH3COCH3 leading to the formation of secondary ozonides (SOZ) and organic acids. Relative to infinitely separated reactants, the SOZ in all three cases is found to be 48–51 kcal mol-1 lower in energy, formed via 1,3- cycloaddition of .CH2OO. across the CQO bond. The lowest energy pathway found for SOZ decomposition is intramolecular disproportionation of the singlet biradical intermediate formed from cleavage of the O–O bond to form hydroxyalkyl esters. These hydroxyalkyl esters undergo concerted decomposition providing a low energy pathway from SOZ to acids. Geometries and frequencies of all stationary points were obtained using the B3LYP/MG3S DFT model chemistry, and energies were refined using RCCSD(T)-F12a/cc-pVTZ-F12 single-point calculations. RRKM calculations were used to obtain microcanonical rate coefficients (k(E)) and the reservoir state method was used to obtain temperature and pressure dependent rate coefficients (k(T, P)) and product branching ratios. At atmospheric pressure, the yield of collisionally stabilized SOZ was found to increase in the order HCHO o CH3CHO o CH3COCH3 (the highest yield being 10-4 times lower than the initial .CH2OO. concentration). At low pressures, chemically activated formation of organic acids (formic acid in the case of HCHO and CH3COCH3, formic and acetic acid in the case of CH3CHO) was found to be the major product channel in agreement with recent direct measurements. Collisional energy transfer parameters and the barrier heights for SOZ reactions were found to be the most sensitive parameters determining SOZ and organic acid yield.

  17. Chemical Reactions in DSMC

    SciTech Connect

    Bird, G. A.

    2011-05-20

    DSMC simulations of chemically reacting gas flows have generally employed procedures that convert the macroscopic chemical rate equations to reaction cross-sections at the microscopic level. They therefore depend on the availability of experimental data that has been fitted to equations of the Arrhenius form. This paper presents a physical model for dissociation and recombination reactions and a phenomenological model for exchange and chain reactions. These are based on the vibrational states of the colliding molecules and do not require any experimentally-based data. The simplicity of the models allows the corresponding rate equations to be written down and, while these are not required for the implementation of the models, they facilitate their validation. The model is applied to a typical hypersonic atmospheric entry problem and the results are compared with the corresponding results from the traditional method. It is also used to investigate both spontaneous and forced ignition as well as the structure of a deflagration wave in an oxygen-hydrogen mixture.

  18. Concordant Chemical Reaction Networks

    PubMed Central

    Shinar, Guy; Feinberg, Martin

    2015-01-01

    We describe a large class of chemical reaction networks, those endowed with a subtle structural property called concordance. We show that the class of concordant networks coincides precisely with the class of networks which, when taken with any weakly monotonic kinetics, invariably give rise to kinetic systems that are injective — a quality that, among other things, precludes the possibility of switch-like transitions between distinct positive steady states. We also provide persistence characteristics of concordant networks, instability implications of discordance, and consequences of stronger variants of concordance. Some of our results are in the spirit of recent ones by Banaji and Craciun, but here we do not require that every species suffer a degradation reaction. This is especially important in studying biochemical networks, for which it is rare to have all species degrade. PMID:22659063

  19. Nanoreactors for simultaneous remote thermal activation and optical monitoring of chemical reactions.

    PubMed

    Vázquez-Vázquez, Carmen; Vaz, Belén; Giannini, Vincenzo; Pérez-Lorenzo, Moisés; Alvarez-Puebla, Ramon A; Correa-Duarte, Miguel A

    2013-09-18

    We report herein the design of plasmonic hollow nanoreactors capable of concentrating light at the nanometer scale for the simultaneous performance and optical monitoring of thermally activated reactions. These reactors feature the encapsulation of plasmonic nanoparticles on the inner walls of a mesoporous silica capsule. A Diels-Alder cycloaddition reaction was carried out in the inner cavities of these nanoreactors to evidence their efficacy. Thus, it is demonstrated that reactions can be accomplished in a confined volume without alteration of the temperature of the bulk solvent while allowing real-time monitoring of the reaction progress.

  20. Mass Transfer with Chemical Reaction.

    ERIC Educational Resources Information Center

    DeCoursey, W. J.

    1987-01-01

    Describes the organization of a graduate course dealing with mass transfer, particularly as it relates to chemical reactions. Discusses the course outline, including mathematics models of mass transfer, enhancement of mass transfer rates by homogeneous chemical reaction, and gas-liquid systems with chemical reaction. (TW)

  1. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen–Popper, Dion–Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  2. Photocatalytic activity of layered perovskite-like oxides in practically valuable chemical reactions

    NASA Astrophysics Data System (ADS)

    Rodionov, I. A.; Zvereva, I. A.

    2016-03-01

    The photocatalytic properties of layered perovskite-like oxides corresponding to the Ruddlesen-Popper, Dion-Jacobson and Aurivillius phases are considered. Of the photocatalytic reactions, the focus is on the reactions of water splitting, hydrogen evolution from aqueous solutions of organic substances and degradation of model organic pollutants. Possibilities to conduct these reactions under UV and visible light in the presence of layered perovskite-like oxides and composite photocatalysts based on them are shown. The specific surface area, band gap energy, particle morphology, cation and anion doping and surface modification are considered as factors that affect the photocatalytic activity. Special attention is paid to the possibilities to enhance the photocatalytic activity by intercalation, ion exchange and exfoliation, which are inherent in this class of compounds. Conclusions are made about the prospects for the use of layered perovskite-like oxides in photocatalysis. The bibliography includes 253 references.

  3. Catalytically active polymers obtained by molecular imprinting and their application in chemical reaction engineering.

    PubMed

    Brüggemann, O

    2001-08-01

    Molecular imprinting is a way of creating polymers bearing artificial receptors. It allows the fabrication of highly selective plastics by polymerizing monomers in the presence of a template. This technique primarily had been developed for the generation of biomimetic materials to be used in chromatographic separation, in extraction approaches and in sensors and assays. Beyond these applications, in the past few years molecular imprinting has become a tool for producing new kinds of catalysts. For catalytic applications, the template must be chosen, so that it is structurally comparable with the transition state (a transition state analogue, TSA) of a reaction, or with the product or substrate. The advantage of using these polymeric catalysts is obvious: the backbone withstands more aggressive conditions than a bio material could ever survive. Results are presented showing the applicability of a molecularly imprinted catalyst in different kinds of chemical reactors. It is demonstrated that the catalysts can be utilized not only in batch but also in continuously driven reactors and that their performance can be improved by means of chemical reaction engineering. PMID:11429307

  4. More on Chemical Reaction Balancing.

    ERIC Educational Resources Information Center

    Swinehart, D. F.

    1985-01-01

    A previous article stated that only the matrix method was powerful enough to balance a particular chemical equation. Shows how this equation can be balanced without using the matrix method. The approach taken involves writing partial mathematical reactions and redox half-reactions, and combining them to yield the final balanced reaction. (JN)

  5. Chemical burn or reaction

    MedlinePlus

    Burn from chemicals ... in contact with the toxic substance Rash , blisters , burns on the skin Unconsciousness or other states of ... Make sure the cause of the burn has been removed. Try not to come ... yourself. If the chemical is dry, brush off any excess. Avoid ...

  6. Singular characteristics and unique chemical bond activation mechanisms of photocatalytic reactions on plasmonic nanostructures

    NASA Astrophysics Data System (ADS)

    Christopher, Phillip; Xin, Hongliang; Marimuthu, Andiappan; Linic, Suljo

    2012-12-01

    The field of heterogeneous photocatalysis has almost exclusively focused on semiconductor photocatalysts. Herein, we show that plasmonic metallic nanostructures represent a new family of photocatalysts. We demonstrate that these photocatalysts exhibit fundamentally different behaviour compared with semiconductors. First, we show that photocatalytic reaction rates on excited plasmonic metallic nanostructures exhibit a super-linear power law dependence on light intensity (rate ∝intensityn, with n > 1), at significantly lower intensity than required for super-linear behaviour on extended metal surfaces. We also demonstrate that, in sharp contrast to semiconductor photocatalysts, photocatalytic quantum efficiencies on plasmonic metallic nanostructures increase with light intensity and operating temperature. These unique characteristics of plasmonic metallic nanostructures suggest that this new family of photocatalysts could prove useful for many heterogeneous catalytic processes that cannot be activated using conventional thermal processes on metals or photocatalytic processes on semiconductors.

  7. Reduction of chemical reaction models

    NASA Technical Reports Server (NTRS)

    Frenklach, Michael

    1991-01-01

    An attempt is made to reconcile the different terminologies pertaining to reduction of chemical reaction models. The approaches considered include global modeling, response modeling, detailed reduction, chemical lumping, and statistical lumping. The advantages and drawbacks of each of these methods are pointed out.

  8. Programmability of Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    Cook, Matthew; Soloveichik, David; Winfree, Erik; Bruck, Jehoshua

    Motivated by the intriguing complexity of biochemical circuitry within individual cells we study Stochastic Chemical Reaction Networks (SCRNs), a formal model that considers a set of chemical reactions acting on a finite number of molecules in a well-stirred solution according to standard chemical kinetics equations. SCRNs have been widely used for describing naturally occurring (bio)chemical systems, and with the advent of synthetic biology they become a promising language for the design of artificial biochemical circuits. Our interest here is the computational power of SCRNs and how they relate to more conventional models of computation. We survey known connections and give new connections between SCRNs and Boolean Logic Circuits, Vector Addition Systems, Petri nets, Gate Implementability, Primitive Recursive Functions, Register Machines, Fractran, and Turing Machines. A theme to these investigations is the thin line between decidable and undecidable questions about SCRN behavior.

  9. Chemical characteristics and enhanced hepatoprotective activities of Maillard reaction products derived from milk protein-sugar system.

    PubMed

    Oh, Nam Su; Young Lee, Ji; Lee, Hyun Ah; Joung, Jae Yeon; Shin, Yong Kook; Kim, Sae Hun; Kim, Younghoon; Lee, Kwang Won

    2016-02-01

    The objective of this study was to investigate the characteristics, antioxidative properties, and hepatoprotective effects of Maillard reaction products (MRP) from milk protein reacted with sugars. The MRP were obtained from milk protein, whey protein concentrates and sodium caseinate, using 2 types of sugars, lactose and glucose, by heating the mixture at 55°C for 7d in a sodium phosphate buffer (pH 7.4). Changes in the chemical modification of the milk protein were monitored by measuring the protein-bound carbonyls and PAGE protein profiles. The results showed that the amount of protein-bound carbonyls increased after Maillard reaction (MR). In addition, sodium dodecyl sulfate-PAGE analysis indicated a formation of high-molecular weight complexes through MR. The modification sites induced by MR of milk protein were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis of tryptic-digested gel spots of MRP. As a result, modification and their localization in AA sequence of MRP was identified. Also, the MRP showed higher antioxidant activities than the intact milk protein, and they reduced intracellular reactive oxygen species production and inhibited the depletion of the reduced glutathione concentrations in the HepG2 cells. In particular, glucose-sodium caseinate MRP showed the highest biological activities among all MRP. Therefore, these results suggest that the MRP from milk protein reacting with sugars possess effective antioxidant activity and have a protective ability against oxidative damage.

  10. A continuous sirtuin activity assay without any coupling to enzymatic or chemical reactions

    PubMed Central

    Schuster, Sabine; Roessler, Claudia; Meleshin, Marat; Zimmermann, Philipp; Simic, Zeljko; Kambach, Christian; Schiene-Fischer, Cordelia; Steegborn, Clemens; Hottiger, Michael O.; Schutkowski, Mike

    2016-01-01

    Sirtuins are NAD+ dependent lysine deacylases involved in many regulatory processes such as control of metabolic pathways, DNA repair and stress response. Modulators of sirtuin activity are required as tools for uncovering the biological function of these enzymes and as potential therapeutic agents. Systematic discovery of such modulators is hampered by the lack of direct and continuous activity assays. The present study describes a novel continuous assay based on the increase of a fluorescence signal subsequent to sirtuin mediated removal of a fluorescent acyl chain from a modified TNFα-derived peptide. This substrate is well recognized by human sirtuins 1–6 and represents the best sirtuin 2 substrate described so far with a kcat/KM-value of 176 000 M−1s−1. These extraordinary substrate properties allow the first determination of Ki-values for the specific Sirt2 inhibitory peptide S2iL5 (600 nM) and for the quasi-universal sirtuin inhibitor peptide thioxo myristoyl TNFα (80 nM). PMID:26940860

  11. Chemical reactions confined within carbon nanotubes.

    PubMed

    Miners, Scott A; Rance, Graham A; Khlobystov, Andrei N

    2016-08-22

    In this critical review, we survey the wide range of chemical reactions that have been confined within carbon nanotubes, particularly emphasising how the pairwise interactions between the catalysts, reactants, transition states and products of a particular molecular transformation with the host nanotube can be used to control the yields and distributions of products of chemical reactions. We demonstrate that nanoscale confinement within carbon nanotubes enables the control of catalyst activity, morphology and stability, influences the local concentration of reactants and products thus affecting equilibria, rates and selectivity, pre-arranges the reactants for desired reactions and alters the relative stability of isomeric products. We critically evaluate the relative advantages and disadvantages of the confinement of chemical reactions inside carbon nanotubes from a chemical perspective and describe how further developments in the controlled synthesis of carbon nanotubes and the incorporation of multifunctionality are essential for the development of this ever-expanding field, ultimately leading to the effective control of the pathways of chemical reactions through the rational design of multi-functional carbon nanoreactors.

  12. A reversible nanoconfined chemical reaction.

    PubMed

    Nielsen, Thomas K; Bösenberg, Ulrike; Gosalawit, Rapee; Dornheim, Martin; Cerenius, Yngve; Besenbacher, Flemming; Jensen, Torben R

    2010-07-27

    Hydrogen is recognized as a potential, extremely interesting energy carrier system, which can facilitate efficient utilization of unevenly distributed renewable energy. A major challenge in a future "hydrogen economy" is the development of a safe, compact, robust, and efficient means of hydrogen storage, in particular, for mobile applications. Here we report on a new concept for hydrogen storage using nanoconfined reversible chemical reactions. LiBH4 and MgH2 nanoparticles are embedded in a nanoporous carbon aerogel scaffold with pore size Dmax approximately 21 nm and react during release of hydrogen and form MgB2. The hydrogen desorption kinetics is significantly improved compared to bulk conditions, and the nanoconfined system has a high degree of reversibility and stability and possibly also improved thermodynamic properties. This new scheme of nanoconfined chemistry may have a wide range of interesting applications in the future, for example, within the merging area of chemical storage of renewable energy.

  13. A mechanistic model for hydrogen activation, spillover, and its chemical reaction in a zeolite-encapsulated Pt catalyst.

    PubMed

    Shin, Hyeyoung; Choi, Minkee; Kim, Hyungjun

    2016-03-14

    The hydrogen (H) spillover phenomenon has attracted considerable attention in the catalysis field. Many researchers have focused on the phenomenon itself, as well as its applications for advanced catalytic systems. In particular, H spillover on non-reducible materials, such as alumina, silica, and zeolites, is a controversial issue owing to the lack of understanding regarding its mechanistic properties. In this study, we use density functional theory calculations to propose the entire mechanism of H spillover from H2 activation on a platinum to its participation in chemical reactions on the external surface of a zeolite. We determined that surface hydroxyl groups of the zeolites, such as Brønsted acid sites, play a role in initiating H spillover, and the Lewis acid sites facilitate the entire process by allowing H to be transferred as a H(+)/e(-) charge pair, as well as providing good binding sites for organic reactants. Theoretical results explain the key experimental features, and we expect that this work will help to elucidate the H spillover phenomenon on non-reducible support materials and to utilize it for catalytic systems. PMID:26735140

  14. Chemical reactions at aqueous interfaces

    NASA Astrophysics Data System (ADS)

    Vecitis, Chad David

    2009-12-01

    Interfaces or phase boundaries are a unique chemical environment relative to individual gas, liquid, or solid phases. Interfacial reaction mechanisms and kinetics are often at variance with homogeneous chemistry due to mass transfer, molecular orientation, and catalytic effects. Aqueous interfaces are a common subject of environmental science and engineering research, and three environmentally relevant aqueous interfaces are investigated in this thesis: 1) fluorochemical sonochemistry (bubble-water), 2) aqueous aerosol ozonation (gas-water droplet), and 3) electrolytic hydrogen production and simultaneous organic oxidation (water-metal/semiconductor). Direct interfacial analysis under environmentally relevant conditions is difficult, since most surface-specific techniques require relatively `extreme' conditions. Thus, the experimental investigations here focus on the development of chemical reactors and analytical techniques for the completion of time/concentration-dependent measurements of reactants and their products. Kinetic modeling, estimations, and/or correlations were used to extract information on interfacially relevant processes. We found that interfacial chemistry was determined to be the rate-limiting step to a subsequent series of relatively fast homogeneous reactions, for example: 1) Pyrolytic cleavage of the ionic headgroup of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) adsorbed to cavitating bubble-water interfaces during sonolysis was the rate-determining step in transformation to their inorganic constituents carbon monoxide, carbon dioxide, and fluoride; 2) ozone oxidation of aqueous iodide to hypoiodous acid at the aerosol-gas interface is the rate-determining step in the oxidation of bromide and chloride to dihalogens; 3) Electrolytic oxidation of anodic titanol surface groups is rate-limiting for the overall oxidation of organics by the dichloride radical. We also found chemistry unique to the interface, for example: 1

  15. Analytic study of the chain dark decomposition reaction of iodides - atomic iodine donors - in the active medium of a pulsed chemical oxygen-iodine laser: 1. Criteria for the development of the branching chain dark decomposition reaction of iodides

    SciTech Connect

    Andreeva, Tamara L; Kuznetsova, S V; Maslov, Aleksandr I; Sorokin, Vadim N

    2009-02-28

    The scheme of chemical processes proceeding in the active medium of a pulsed chemical oxygen-iodine laser (COIL) is analysed. Based on the analysis performed, the complete system of differential equations corresponding to this scheme is replaced by a simplified system of equations describing in dimensionless variables the chain dark decomposition of iodides - atomic iodine donors, in the COIL active medium. The procedure solving this system is described, the basic parameters determining the development of the chain reaction are found and its specific time intervals are determined. The initial stage of the reaction is analysed and criteria for the development of the branching chain decomposition reaction of iodide in the COIL active medium are determined. (active media)

  16. Chemical computing with reaction-diffusion processes.

    PubMed

    Gorecki, J; Gizynski, K; Guzowski, J; Gorecka, J N; Garstecki, P; Gruenert, G; Dittrich, P

    2015-07-28

    Chemical reactions are responsible for information processing in living organisms. It is believed that the basic features of biological computing activity are reflected by a reaction-diffusion medium. We illustrate the ideas of chemical information processing considering the Belousov-Zhabotinsky (BZ) reaction and its photosensitive variant. The computational universality of information processing is demonstrated. For different methods of information coding constructions of the simplest signal processing devices are described. The function performed by a particular device is determined by the geometrical structure of oscillatory (or of excitable) and non-excitable regions of the medium. In a living organism, the brain is created as a self-grown structure of interacting nonlinear elements and reaches its functionality as the result of learning. We discuss whether such a strategy can be adopted for generation of chemical information processing devices. Recent studies have shown that lipid-covered droplets containing solution of reagents of BZ reaction can be transported by a flowing oil. Therefore, structures of droplets can be spontaneously formed at specific non-equilibrium conditions, for example forced by flows in a microfluidic reactor. We describe how to introduce information to a droplet structure, track the information flow inside it and optimize medium evolution to achieve the maximum reliability. Applications of droplet structures for classification tasks are discussed.

  17. Dynamic Reaction Figures: An Integrative Vehicle for Understanding Chemical Reactions

    ERIC Educational Resources Information Center

    Schultz, Emeric

    2008-01-01

    A highly flexible learning tool, referred to as a dynamic reaction figure, is described. Application of these figures can (i) yield the correct chemical equation by simply following a set of menu driven directions; (ii) present the underlying "mechanism" in chemical reactions; and (iii) help to solve quantitative problems in a number of different…

  18. Suppression of Ostwald Ripening by Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Zwicker, David; Hyman, Anthony A.; Jülicher, Frank

    2015-03-01

    Emulsions consisting of droplets immersed in a fluid are typically unstable and coarsen over time. One important coarsening process is Ostwald ripening, which is driven by the surface tension of the droplets. Ostwald ripening must thus be suppressed to stabilize emulsions, e.g. to control the properties of pharmaceuticals, food, or cosmetics. Suppression of Ostwald ripening is also important in biological cells, which contain stable liquid-like compartments, e.g. germ granules, Cajal-bodies, and centrosomes. Such systems are often driven away from equilibrium by chemical reactions and can thus be called active emulsions. Here, we show that non-equilibrium chemical reactions can suppress Ostwald Ripening, leading to stable, monodisperse emulsions. We derive analytical approximations of the typical droplet size, droplet count, and time scale of the dynamics from a coarse-grained description of the droplet dynamics. We also compare these results to numerical simulations of the continuous concentration fields. Generally, we thus show how chemical reactions can be used to stabilize emulsions and to control their properties in technology and nature.

  19. High Chemical Activity of a Perovskite Surface: Reaction of CO with Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Stöger, Bernhard; Hieckel, Marcel; Mittendorfer, Florian; Wang, Zhiming; Fobes, David; Peng, Jin; Mao, Zhiqiang; Schmid, Michael; Redinger, Josef; Diebold, Ulrike

    2014-09-01

    Adsorption of CO at the Sr3Ru2O7(001) surface was studied with low-temperature scanning tunneling microscopy (STM) and density functional theory. In situ cleaved single crystals terminate in an almost perfect SrO surface. At 78 K, CO first populates impurities and then adsorbs above the apical surface O with a binding energy Eads=-0.7 eV. Above 100 K, this physisorbed CO replaces the surface O, forming a bent CO2 with the C end bound to the Ru underneath. The resulting metal carboxylate (Ru-COO) can be desorbed by STM manipulation. A low activation (0.2 eV) and high binding (-2.2 eV) energy confirm a strong reaction between CO and regular surface sites of Sr3Ru2O7; likely, this reaction causes the "UHV aging effect" reported for this and other perovskite oxides.

  20. Chemical reactions in low-g

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.; Facemire, B. R.

    1978-01-01

    The Apollo-Soyuz flight experiment, 'Chemical Foams' demonstrated that foams and air/liquid dispersions are much more stable in low-gravity than on the ground. It thus should be possible to conduct unique chemical reactions in space foams. The low-g results and subsequent ground work on the formaldehyde clock reaction indicate that the reaction is strongly influenced by (1) dissociated and undissociated solution species being adsorbed at solid/liquid and gas/liquid surfaces and (2) chemical reaction rates apparently being affected by long-range forces determined by the liquid mass and the extent and nature of all surface interfaces.

  1. Microfabricated electrochemiluminescence cell for chemical reaction detection

    DOEpatents

    Northrup, M. Allen; Hsueh, Yun-Tai; Smith, Rosemary L.

    2003-01-01

    A detector cell for a silicon-based or non-silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The detector cell is an electrochemiluminescence cell constructed of layers of silicon with a cover layer of glass, with spaced electrodes located intermediate various layers forming the cell. The cell includes a cavity formed therein and fluid inlets for directing reaction fluid therein. The reaction chamber and detector cell may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The ECL cell may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  2. 'GREENER' CHEMICAL SYNTHESES USING ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a greener chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation t...

  3. Chemical potential and reaction electronic flux in symmetry controlled reactions.

    PubMed

    Vogt-Geisse, Stefan; Toro-Labbé, Alejandro

    2016-07-15

    In symmetry controlled reactions, orbital degeneracies among orbitals of different symmetries can occur along a reaction coordinate. In such case Koopmans' theorem and the finite difference approximation provide a chemical potential profile with nondifferentiable points. This results in an ill-defined reaction electronic flux (REF) profile, since it is defined as the derivative of the chemical potential with respect to the reaction coordinate. To overcome this deficiency, we propose a new way for the calculation of the chemical potential based on a many orbital approach, suitable for reactions in which symmetry is preserved. This new approach gives rise to a new descriptor: symmetry adapted chemical potential (SA-CP), which is the chemical potential corresponding to a given irreducible representation of a symmetry group. A corresponding symmetry adapted reaction electronic flux (SA-REF) is also obtained. Using this approach smooth chemical potential profiles and well defined REFs are achieved. An application of SA-CP and SA-REF is presented by studying the Cs enol-keto tautomerization of thioformic acid. Two SA-REFs are obtained, JA'(ξ) and JA'' (ξ). It is found that the tautomerization proceeds via an in-plane delocalized 3-center 4-electron O-H-S hypervalent bond which is predicted to exist only in the transition state (TS) region. © 2016 Wiley Periodicals, Inc.

  4. Quantum mechanics/molecular mechanics investigation of the chemical reaction in Dpo4 reveals water-dependent pathways and requirements for active site reorganization.

    PubMed

    Wang, Yanli; Schlick, Tamar

    2008-10-01

    The nucleotidyl-transfer reaction coupled with the conformational transitions in DNA polymerases is critical for maintaining the fidelity and efficiency of DNA synthesis. We examine here the possible reaction pathways of a Y-family DNA polymerase, Sulfolobus solfataricus DNA polymerase IV (Dpo4), for the correct insertion of dCTP opposite 8-oxoguanine using the quantum mechanics/molecular mechanics (QM/MM) approach, both from a chemistry-competent state and a crystal closed state. The latter examination is important for understanding pre-chemistry barriers to interpret the entire enzyme mechanism, since the crystal closed state is not an ideal state for initiating the chemical reaction. The most favorable reaction path involves initial deprotonation of O3'H via two bridging water molecules to O1A, overcoming an overall potential energy barrier of approximately 20.0 kcal/mol. The proton on O1A-P(alpha) then migrates to the gamma-phosphate oxygen of the incoming nucleotide as O3' attacks P(alpha), and the P(alpha)-O3A bond breaks. The other possible pathway in which the O3'H proton is transferred directly to O1A on P(alpha) has an overall energy barrier of 25.0 kcal/mol. In both reaction paths, the rate-limiting step is the initial deprotonation, and the trigonal-bipyramidal configuration for P(alpha) occurs during the concerted bond formation (O3'-P(alpha)) and breaking (P(alpha)-O3A), indicating the associative nature of the chemical reaction. In contrast, the Dpo4/DNA complex with an imperfect active-site geometry corresponding to the crystal state must overcome a much higher activation energy barrier (29.0 kcal/mol) to achieve a tightly organized site due to hindered O3'H deprotonation stemming from larger distances and distorted conformation of the proton acceptors. This significant difference demonstrates that the pre-chemistry reorganization in Dpo4 costs approximately 4.0 to 9.0 kcal/mol depending on the primer terminus environment. Compared to the higher

  5. Chemical-reaction model for Mexican wave

    NASA Astrophysics Data System (ADS)

    Nagatani, Takashi

    2003-05-01

    We present a chemical-reaction model to describe the Mexican wave ( La Ola) in football stadia. The spectator's action is described in terms of chemical reactions. The model is governed by three reaction rates k 1, k 2, and k3. We study the nonlinear waves on one- and two-dimensional lattices. The Mexican wave is formulated as a clockwise forwardly propagating wave. Waves are growing or disappear, depending on the values of reaction rates. In the specific case of k1= k2= k3=1, the nonlinear-wave equation produces a propagating pulse like soliton.

  6. Microfabricated sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen

    2003-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and non-silicon based materials to provide the thermal properties desired. For example, the chamber may combine a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  7. Modeling of turbulent chemical reaction

    NASA Technical Reports Server (NTRS)

    Chen, J.-Y.

    1995-01-01

    Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.

  8. Chemical Reactions at Surfaces. Final Progress Report

    SciTech Connect

    2003-02-21

    The Gordon Research Conference (GRC) on Chemical Reactions at Surfaces was held at Holiday Inn, Ventura, California, 2/16-21/03. Emphasis was placed on current unpublished research and discussion of the future target areas in this field.

  9. Kinetic studies of elementary chemical reactions

    SciTech Connect

    Durant, J.L. Jr.

    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.

  10. Chemical Principles Revisited: Annotating Reaction Equations.

    ERIC Educational Resources Information Center

    Tykodi, R. J.

    1987-01-01

    Urges chemistry teachers to have students annotate the chemical reactions in aqueous-solutions that they see in their textbooks and witness in the laboratory. Suggests this will help students recognize the reaction type more readily. Examples are given for gas formation, precipitate formation, redox interaction, acid-base interaction, and…

  11. Entropy Generation in a Chemical Reaction

    ERIC Educational Resources Information Center

    Miranda, E. N.

    2010-01-01

    Entropy generation in a chemical reaction is analysed without using the general formalism of non-equilibrium thermodynamics at a level adequate for advanced undergraduates. In a first approach to the problem, the phenomenological kinetic equation of an elementary first-order reaction is used to show that entropy production is always positive. A…

  12. Chemical reactions in perfume ageing.

    PubMed

    Blakeway, J M; Frey, M L; Lacroix, S; Salerno, M S

    1987-10-01

    Summary The interactions between a typical range of perfume materials, alcohol, water, air, elevated temperatures and daylight have been studied. The changes of composition, acidity, peroxide content and the formation of new molecules were followed. The stabilizing effects of UV absorbers, antioxidants and sequestering agents were examined; - the formation of acid reaction products was accelerated by air, temperature, daylight and the presence of natural products; - peroxide formation was accelerated by heat and light and the presence of air; as the acidity increased, the peroxides decomposed; - the acetalization of other aldehydes was accelerated by temperature and daylight and the presence of natural products up to 40% of certain aldehydes may be converted into acetals after 3 months at 37 degrees C; - many stereoisomerizations occur, e.g., transisoeugenol is converted up to 10% into the cis isomer after 3 months at 37 degrees C and 58% in daylight; - evaluation of antioxidants UV absorbers and sequestering agents showed a significant protection against deterioration only by EDTA dipotassium salt; - ethanol was converted into acetaldehyde and its diethylacetal by peroxides present and formed on ageing up to 0.08%. Natural products accelerated this formation; - the reaction between benzoyl peroxide and ethanol was shown to yield up to 63% of acetaldehyde+diethyl acetal whilst di-t-butyl peroxide gave only 23% under the same conditions. These results go some way to explaining odour changes in perfume ageing.

  13. Effects of Chemical versus Electrochemical Delithiation on the Oxygen Evolution Reaction Activity of Nickel-Rich Layered LiMO2.

    PubMed

    Augustyn, Veronica; Manthiram, Arumugam

    2015-10-01

    Nickel-rich layered LiMO2 (M = transition metal) oxides doped with iron exhibit high oxygen evolution reaction (OER) activity in alkaline electrolytes. The LiMO2 oxides offer the possibility of investigating the influence of the number of d electrons on OER by tuning the oxidation state of M via chemical or electrochemical delithiation. Accordingly, we investigate here the electrocatalytic behavior of LiNi0.7Co0.3O2 and LiNi0.7Co0.2Fe0.1O2 before and after chemical delithiation. In addition to varying the oxidation state of the transition-metal ions, we find that chemical delithiation also affects the local chemical environment and morphology. The electrochemical response differs depending on whether the delithiation occurred ex situ chemically or in situ during the electrocatalysis. The results point to the important role of in situ transformation in LiMO2 in alkaline electrolytes during electrocatalytic cycling.

  14. Gas-phase reactions of doubly charged actinide cations with alkanes and alkenes--probing the chemical activity of 5f electrons from Th to Cm.

    PubMed

    Marçalo, Joaquim; Santos, Marta; Gibson, John K

    2011-11-01

    Small alkanes (methane, ethane, propane, n-butane) and alkenes (ethene, propene, 1-butene) were used to probe the gas-phase reactivity of doubly charged actinide cations, An(2+) (An = Th, Pa, U, Np, Pu, Am, Cm), by means of Fourier transform ion cyclotron resonance mass spectrometry. Different combinations of doubly and singly charged ions were observed as reaction products, comprising species formed via metal-ion induced eliminations of small molecules, simple adducts and ions resulting from electron, hydride or methide transfer channels. Th(2+), Pa(2+), U(2+) and Np(2+) preferentially yielded doubly charged products of hydrocarbon activation, while Pu(2+), Am(2+) and Cm(2+) reacted mainly through transfer channels. Cm(2+) was also capable of forming doubly charged products with some of the hydrocarbons whereas Pu(2+) and Am(2+) were not, these latter two ions conversely being the only for which adduct formation was observed. The product distributions and the reaction efficiencies are discussed in relation to the electronic configurations of the metal ions, the energetics of the reactions and similar studies previously performed with doubly charged lanthanide and transition metal cations. The conditions for hydrocarbon activation to occur as related to the accessibility of electronic configurations with one or two 5f and/or 6d unpaired electrons are examined and the possible chemical activity of the 5f electrons in these early actinide ions, particularly Pa(2+), is considered.

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

    ERIC Educational Resources Information Center

    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…

  16. Thermodynamic performance for a chemical reactions model

    NASA Astrophysics Data System (ADS)

    Gonzalez-Narvaez, R. E.; Sánchez-Salas, N.; Chimal-Eguía, J. C.

    2015-01-01

    This paper presents the analysis efficiency of a chemical reaction model of four states, such that their activated states can occur at any point (fixed but arbitrary) of the transition from one state to another. This mechanism operates under a single heat reservoir temperature, unlike the internal combustion engines where there are two thermal sources. Different efficiencies are compared to this model, which operate at different optimum engine regimes. Thus, some analytical methods are used to give an approximate expression, facilitating the comparison between them. Finally, the result is compared with that obtained by other authors considered a general model of an isothermal molecular machine. Taking into account the above, the results seems to follow a similar behaviour for all the optimized engines, which resemble that observed in the case of heat engine efficiencies.

  17. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1994-01-01

    Quantum mechanical methods have been used to compute potential energy surfaces for chemical reactions. The reactions studied were among those believed to be important to the NASP and HSR programs and included the recombination of two H atoms with several different third bodies; the reactions in the thermal Zeldovich mechanism; the reactions of H atom with O2, N2, and NO; reactions involved in the thermal De-NO(x) process; and the reaction of CH(squared Pi) with N2 (leading to 'prompt NO'). These potential energy surfaces have been used to compute reaction rate constants and rates of unimolecular decomposition. An additional application was the calculation of transport properties of gases using a semiclassical approximation (and in the case of interactions involving hydrogen inclusion of quantum mechanical effects).

  18. Mediating chemical reactions using polysaccharides

    NASA Astrophysics Data System (ADS)

    Tyler, Lauren E.

    We have studied the NaBH4-mediated hydrogenation of select alkenes catalyzed by polysaccharide-stabilized nanoparticles. We compared the catalytic properties of Ni-based nanoparticles or Au/Co-based nanoparticles on the hydrogenation of cinnamic acid, cinnamide, cinnamyl alcohol, and ethyl cinnamate. We evaluated the possibility that the type of stabilizing polysaccharide surrounding the nanoparticle may affect the selectivity towards the alkene compounds that undergo the hydrogenation reaction. We found that the hydrogenation of cinnamide or ethyl cinnamate proceeded readily to 100% completion independent of the type of polysaccharide stabilizing the nanoparticle. However, the extent of the hydrogenation of cinnamyl alcohol and cinnamic acid varied greatly depending on the type of polysaccharide stabilizing the nanoparticle. In the course of these studies, we observed that some polysaccharides by themselves promoted the hydrolysis of ethyl cinnamate. Thus, we have raised the hypothesis that some polysaccharides may act as "esterases" and explored the interaction between select polysaccharides and a variety of ester compounds.

  19. Anatomy of an Elementary Chemical Reaction

    NASA Astrophysics Data System (ADS)

    Alexander, Andrew J.; Zare, Richard N.

    1998-09-01

    The alchemists of old sought the knowledge to transform one material to another-for example, base metals into gold-as a path to the elixir of life. As chemists have concerned themselves with the transformation from compound to compound, so they have become involved in trying to uncover the structures of molecules and the pathways that reactions follow. Classically, the study of reaction mechanisms in chemistry encompasses reaction kinetics, the study of velocities or rates of reactions, and reaction dynamics, the study of the nanoscopic motion and rearrangement of atoms during a reactive event. An essential aim of this article is to bring the reader to a favorable vantage point with a brief introduction to reactive dynamics, and from there to describe some examples of recent strategies that have been employed to promote a fundamental understanding of the anatomy of elementary chemical reactions. In the final section we ponder future directions for this rapidly evolving field of research.

  20. Concerted reactions of polynuclear metalloenzymes and their functional chemical models

    NASA Astrophysics Data System (ADS)

    Dzhabiev, T. S.; Shilov, A. E.

    2011-03-01

    The mechanisms of the many-electron oxidation of water by a chemical model of the manganese oxidase cofactor in photosynthesis photosystem II (manganese(IV) clusters) and nitrogen reduction in chemical models of nitrogenase cofactor (vanadium(II) and molybdenum(III) clusters) were considered. The hypothesis was suggested according to which polynuclear enzyme cofactors and their functional chemical models performed two important functions, catalyzed noncomplementary processes and effected many-substrate concerted reactions with decreased activation energies.

  1. Parameter Sensitivity Study of the Unreacted-Core Shrinking Model: A Computer Activity for Chemical Reaction Engineering Courses

    ERIC Educational Resources Information Center

    Tudela, Ignacio; Bonete, Pedro; Fullana, Andres; Conesa, Juan Antonio

    2011-01-01

    The unreacted-core shrinking (UCS) model is employed to characterize fluid-particle reactions that are important in industry and research. An approach to understand the UCS model by numerical methods is presented, which helps the visualization of the influence of the variables that control the overall heterogeneous process. Use of this approach in…

  2. Kinetics of Hydrogen Radical Reactions with Toluene Including Chemical Activation Theory Employing System-Specific Quantum RRK Theory Calibrated by Variational Transition State Theory.

    PubMed

    Bao, Junwei Lucas; Zheng, Jingjing; Truhlar, Donald G

    2016-03-01

    Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure. PMID:26841076

  3. Kinetics of Hydrogen Radical Reactions with Toluene Including Chemical Activation Theory Employing System-Specific Quantum RRK Theory Calibrated by Variational Transition State Theory.

    PubMed

    Bao, Junwei Lucas; Zheng, Jingjing; Truhlar, Donald G

    2016-03-01

    Pressure-dependent reactions are ubiquitous in combustion and atmospheric chemistry. We employ a new calibration procedure for quantum Rice-Ramsperger-Kassel (QRRK) unimolecular rate theory within a chemical activation mechanism to calculate the pressure-falloff effect of a radical association with an aromatic ring. The new theoretical framework is applied to the reaction of H with toluene, which is a prototypical reaction in the combustion chemistry of aromatic hydrocarbons present in most fuels. Both the hydrogen abstraction reactions and the hydrogen addition reactions are calculated. Our system-specific (SS) QRRK approach is adjusted with SS parameters to agree with multistructural canonical variational transition state theory with multidimensional tunneling (MS-CVT/SCT) at the high-pressure limit. The new method avoids the need for the usual empirical estimations of the QRRK parameters, and it eliminates the need for variational transition state theory calculations as a function of energy, although in this first application we do validate the falloff curves by comparing SS-QRRK results without tunneling to multistructural microcanonical variational transition state theory (MS-μVT) rate constants without tunneling. At low temperatures, the two approaches agree well with each other, but at high temperatures, SS-QRRK tends to overestimate falloff slightly. We also show that the variational effect is important in computing the energy-resolved rate constants. Multiple-structure anharmonicity, torsional-potential anharmonicity, and high-frequency-mode vibrational anharmonicity are all included in the rate computations, and torsional anharmonicity effects on the density of states are investigated. Branching fractions, which are both temperature- and pressure-dependent (and for which only limited data is available from experiment), are predicted as a function of pressure.

  4. Theoretical study of chemical reactions in solution

    SciTech Connect

    Yokogawa, D.

    2015-12-31

    Quantum chemical calculations in solution are becoming more and more important in chemistry. Reference interaction site model self-consistent field (RISM-SCF) is one of the powerful approaches to perform quantum chemical calculations in solution. In this work, we developed a new generation of RISM-SCF, where a robust fitting method was newly introduced. We applied the new method to tautomerization reaction of cytosine in aqueous phase. Our calculation reproduced experimentally obtained relative stabilities and relative free energies correctly.

  5. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2002-01-01

    A color-change reaction is described in which two colorless solutions are combined to afford a black mixture. Two more colorless solutions are combined to afford a white mixture. The black and white mixtures are then combined to afford a clear, colorless solution. The reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, vinegar, ammonia, bleach, Epsom salt, and laundry starch.

  6. Visualization of chemical reaction dynamics: Toward understanding complex polyatomic reactions

    PubMed Central

    SUZUKI, Toshinori

    2013-01-01

    Polyatomic molecules have several electronic states that have similar energies. Consequently, their chemical dynamics often involve nonadiabatic transitions between multiple potential energy surfaces. Elucidating the complex reactions of polyatomic molecules is one of the most important tasks of theoretical and experimental studies of chemical dynamics. This paper describes our recent experimental studies of the multidimensional multisurface dynamics of polyatomic molecules based on two-dimensional ion/electron imaging. It also discusses ultrafast photoelectron spectroscopy of liquids for elucidating nonadiabatic electronic dynamics in aqueous solutions. PMID:23318678

  7. Classification of Chemical Reactions: Stages of Expertise

    ERIC Educational Resources Information Center

    Stains, Marilyne; Talanquer, Vicente

    2008-01-01

    In this study we explore the strategies that undergraduate and graduate chemistry students use when engaged in classification tasks involving symbolic and microscopic (particulate) representations of different chemical reactions. We were specifically interested in characterizing the basic features to which students pay attention when classifying…

  8. Computer Animation of a Chemical Reaction.

    ERIC Educational Resources Information Center

    Eaker, Charles W.; Jacobs, Edwin L.

    1982-01-01

    Taking a prototype chemical reaction (molecular hydrogen plus hydrogen atom), constructs an accurate semiempirical, generalized diatomics-in-molecules potential energy surface, calculates motions of these atoms on this surface using REACTS trajectory program, and presents results as moving picture on a microcomputer graphics system. Provides…

  9. Chemical reactions in reverse micelle systems

    DOEpatents

    Matson, Dean W.; Fulton, John L.; Smith, Richard D.; Consani, Keith A.

    1993-08-24

    This invention is directed to conducting chemical reactions in reverse micelle or microemulsion systems comprising a substantially discontinuous phase including a polar fluid, typically an aqueous fluid, and a microemulsion promoter, typically a surfactant, for facilitating the formation of reverse micelles in the system. The system further includes a substantially continuous phase including a non-polar or low-polarity fluid material which is a gas under standard temperature and pressure and has a critical density, and which is generally a water-insoluble fluid in a near critical or supercritical state. Thus, the microemulsion system is maintained at a pressure and temperature such that the density of the non-polar or low-polarity fluid exceeds the critical density thereof. The method of carrying out chemical reactions generally comprises forming a first reverse micelle system including an aqueous fluid including reverse micelles in a water-insoluble fluid in the supercritical state. Then, a first reactant is introduced into the first reverse micelle system, and a chemical reaction is carried out with the first reactant to form a reaction product. In general, the first reactant can be incorporated into, and the product formed in, the reverse micelles. A second reactant can also be incorporated in the first reverse micelle system which is capable of reacting with the first reactant to form a product.

  10. Concordant chemical reaction networks and the Species-Reaction Graph.

    PubMed

    Shinar, Guy; Feinberg, Martin

    2013-01-01

    In a recent paper it was shown that, for chemical reaction networks possessing a subtle structural property called concordance, dynamical behavior of a very circumscribed (and largely stable) kind is enforced, so long as the kinetics lies within the very broad and natural weakly monotonic class. In particular, multiple equilibria are precluded, as are degenerate positive equilibria. Moreover, under certain circumstances, also related to concordance, all real eigenvalues associated with a positive equilibrium are negative. Although concordance of a reaction network can be decided by readily available computational means, we show here that, when a nondegenerate network's Species-Reaction Graph satisfies certain mild conditions, concordance and its dynamical consequences are ensured. These conditions are weaker than earlier ones invoked to establish kinetic system injectivity, which, in turn, is just one ramification of network concordance. Because the Species-Reaction Graph resembles pathway depictions often drawn by biochemists, results here expand the possibility of inferring significant dynamical information directly from standard biochemical reaction diagrams.

  11. Uncertainty Quantification for Nonlinear Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Srinivasan, G.; Robinson, B. A.; Aceves, A. B.; Tartakovsky, D. M.

    2006-12-01

    Systems of coupled chemical reactions are greatly affected by the inherent uncertainties in natural phenomena. These uncertainties can be parametric in nature due to measurement errors or insufficient data. Modeling uncertainties also arise at the molecular level when determining what fraction of the population of each chemical species participates in a chemical reaction at any given time. We present different methods used to quantify both modeling and parametric uncertainties. The application we focus on is that of chemical reactions in the subsurface that greatly affect the transport of contaminants in groundwater. The example considered here is the sorption of Neptunium Np-237 through a competitive ion exchange process. Np-237 is a key radio-nuclide of concern for the Yucca Mountain High Level Waste storage site due to its relatively long half-life, high solubility and low sorption properties. By quantifying the effects of modeling and parametric uncertainties, we can estimate the error associated with Np-237 sorptivity and hence its transport.

  12. Theoretical studies of chemical reaction dynamics

    SciTech Connect

    Schatz, G.C.

    1993-12-01

    This collaborative program with the Theoretical Chemistry Group at Argonne involves theoretical studies of gas phase chemical reactions and related energy transfer and photodissociation processes. Many of the reactions studied are of direct relevance to combustion; others are selected they provide important examples of special dynamical processes, or are of relevance to experimental measurements. Both classical trajectory and quantum reactive scattering methods are used for these studies, and the types of information determined range from thermal rate constants to state to state differential cross sections.

  13. Minimum Energy Pathways for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Walch, S. P.; Langhoff, S. R. (Technical Monitor)

    1995-01-01

    Computed potential energy surfaces are often required for computation of such parameters as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method to obtain accurate energetics, gives useful results for a number of chemically important systems. The talk will focus on a number of applications to reactions leading to NOx and soot formation in hydrocarbon combustion.

  14. Correlating the chemical composition and size of various metal oxide substrates with the catalytic activity and stability of as-deposited Pt nanoparticles for the methanol oxidation reaction

    DOE PAGES

    Megan E. Scofield; Wong, Stanislaus S.; Koenigsmann, Christopher; Bobb-Semple, Dara; Tao, Jing; Tong, Xiao; Wang, Lei; Lewis, Crystal S.; Vuklmirovic, Miomir; Zhu, Yimei; et al

    2015-12-09

    The performance of electrode materials in conventional direct alcohol fuel cells (DAFC) is constrained by (i) the low activity of the catalyst materials relative to their overall cost, (ii) the poisoning of the active sites due to the presence of partially oxidized carbon species (such as but not limited to CO, formate, and acetate) produced during small molecule oxidation, and (iii) the lack of catalytic stability and durability on the underlying commercial carbon support. Therefore, as a viable alternative, we have synthesized various metal oxide and perovskite materials of different sizes and chemical compositions as supports for Pt nanoparticles (NPs).more » Our results including unique mechanistic studies demonstrate that the SrRuO3 substrate with immobilized Pt NPs at its surface evinces the best methanol oxidation performance as compared with all of the other substrate materials tested herein, including commercial carbon itself. In addition, data from electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of electron transfer from bound Pt NPs to surface Ru species within the SrRuO3 substrate itself, thereby suggesting that favorable metal support interactions are responsible for the increased methanol oxidation reaction (MOR) activity of Pt species with respect to the underlying SrRuO3 composite catalyst material.« less

  15. Correlating the chemical composition and size of various metal oxide substrates with the catalytic activity and stability of as-deposited Pt nanoparticles for the methanol oxidation reaction

    SciTech Connect

    Megan E. Scofield; Wong, Stanislaus S.; Koenigsmann, Christopher; Bobb-Semple, Dara; Tao, Jing; Tong, Xiao; Wang, Lei; Lewis, Crystal S.; Vuklmirovic, Miomir; Zhu, Yimei; Adzic, Radoslav R.

    2015-12-09

    The performance of electrode materials in conventional direct alcohol fuel cells (DAFC) is constrained by (i) the low activity of the catalyst materials relative to their overall cost, (ii) the poisoning of the active sites due to the presence of partially oxidized carbon species (such as but not limited to CO, formate, and acetate) produced during small molecule oxidation, and (iii) the lack of catalytic stability and durability on the underlying commercial carbon support. Therefore, as a viable alternative, we have synthesized various metal oxide and perovskite materials of different sizes and chemical compositions as supports for Pt nanoparticles (NPs). Our results including unique mechanistic studies demonstrate that the SrRuO3 substrate with immobilized Pt NPs at its surface evinces the best methanol oxidation performance as compared with all of the other substrate materials tested herein, including commercial carbon itself. In addition, data from electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of electron transfer from bound Pt NPs to surface Ru species within the SrRuO3 substrate itself, thereby suggesting that favorable metal support interactions are responsible for the increased methanol oxidation reaction (MOR) activity of Pt species with respect to the underlying SrRuO3 composite catalyst material.

  16. Chemical reactions directed Peptide self-assembly.

    PubMed

    Rasale, Dnyaneshwar B; Das, Apurba K

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly.

  17. Chemical Reactions Directed Peptide Self-Assembly

    PubMed Central

    Rasale, Dnyaneshwar B.; Das, Apurba K.

    2015-01-01

    Fabrication of self-assembled nanostructures is one of the important aspects in nanoscience and nanotechnology. The study of self-assembled soft materials remains an area of interest due to their potential applications in biomedicine. The versatile properties of soft materials can be tuned using a bottom up approach of small molecules. Peptide based self-assembly has significant impact in biology because of its unique features such as biocompatibility, straight peptide chain and the presence of different side chain functionality. These unique features explore peptides in various self-assembly process. In this review, we briefly introduce chemical reaction-mediated peptide self-assembly. Herein, we have emphasised enzymes, native chemical ligation and photochemical reactions in the exploration of peptide self-assembly. PMID:25984603

  18. WATER AS A REACTION MEDIUM FOR CLEAN CHEMICAL PROCESSES.

    EPA Science Inventory

    Green chemistry is a rapid developing new field that provides us a pro-active avenue for the sustainable development of future science and technologies. When designed properly, clean chemical technology can be developed in water as a reaction media. The technologies generated f...

  19. Role of chemical composition in the enhanced catalytic activity of Pt-based alloyed ultrathin nanowires for the hydrogen oxidation reaction under alkaline conditions

    DOE PAGES

    Megan E. Scofield; Wong, Stanislaus S.; Zhou, Yuchen; Yue, Shiyu; Wang, Lei; Su, Dong; Tong, Xiao; Vukmirovic, Miomir B.; Adzic, Radoslav R.

    2016-05-19

    With the increased interest in the development of hydrogen fuel cells as a plausible alternative to internal combustion engines, recent work has focused on creating alkaline fuel cells (AFC), which employ an alkaline environment. Working in alkaline as opposed to acidic media yields a number of tangible benefits, including (i) the ability to use cheaper and plentiful precious-metal-free catalysts, due to their increased stability, (ii) a reduction in the amount of degradation and corrosion of Pt-based catalysts, and (iii) a longer operational lifetime for the overall fuel cell configuration. However, in the absence of Pt, no catalyst has achieved activitiesmore » similar to those of Pt. Herein, we have synthesized a number of crystalline ultrathin PtM alloy nanowires (NWs) (M = Fe, Co, Ru, Cu, Au) in order to replace a portion of the costly Pt metal without compromising on activity while simultaneously adding in metals known to exhibit favorable synergistic ligand and strain effects with respect to the host lattice. In fact, our experiments confirm theoretical insights about a clear and correlative dependence between measured activity and chemical composition. We have conclusively demonstrated that our as-synthesized alloy NW catalysts yield improved hydrogen oxidation reaction (HOR) activities as compared with a commercial Pt standard as well as with our as-synthesized Pt NWs. The Pt7Ru3 NW system, in particular, quantitatively achieved an exchange current density of 0.493 mA/cm2, which is higher than the corresponding data for Pt NWs alone. In addition, the HOR activities follow the same expected trend as their calculated hydrogen binding energy (HBE) values, thereby confirming the critical importance and correlation of HBE with the observed activities.« less

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  1. The smallest chemical reaction system with bistability

    PubMed Central

    Wilhelm, Thomas

    2009-01-01

    Background Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity. Results Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i) reactants, (ii) reactions, and (iii) terms in the corresponding ordinary differential equations (decreasing importance from i-iii). The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular). We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature. Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc.), we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.). This helps modelling multistable systems and it is important for corresponding synthetic biology projects. Conclusion The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with simple systems and for

  2. Quantum dynamics of fast chemical reactions

    SciTech Connect

    Light, J.C.

    1993-12-01

    The aims of this research are to explore, develop, and apply theoretical methods for the evaluation of the dynamics of gas phase collision processes, primarily chemical reactions. The primary theoretical tools developed for this work have been quantum scattering theory, both in time dependent and time independent forms. Over the past several years, the authors have developed and applied methods for the direct quantum evaluation of thermal rate constants, applying these to the evaluation of the hydrogen isotopic exchange reactions, applied wave packet propagation techniques to the dissociation of Rydberg H{sub 3}, incorporated optical potentials into the evaluation of thermal rate constants, evaluated the use of optical potentials for state-to-state reaction probability evaluations, and, most recently, have developed quantum approaches for electronically non-adiabatic reactions which may be applied to simplify calculations of reactive, but electronically adiabatic systems. Evaluation of the thermal rate constants and the dissociation of H{sub 3} were reported last year, and have now been published.

  3. Law of Localization in Chemical Reaction Networks

    NASA Astrophysics Data System (ADS)

    Okada, Takashi; Mochizuki, Atsushi

    2016-07-01

    In living cells, chemical reactions are connected by sharing their products and substrates, and form complex networks, e.g., metabolic pathways. Here we developed a theory to predict the sensitivity, i.e., the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Nonzero response patterns turn out to exhibit two characteristic features, localization and hierarchy. We present a general theorem connecting sensitivity with network topology that explains these characteristic patterns. Our results imply that network topology is an origin of biological robustness. Finally, we suggest a strategy to determine real networks from experimental measurements.

  4. Law of Localization in Chemical Reaction Networks.

    PubMed

    Okada, Takashi; Mochizuki, Atsushi

    2016-07-22

    In living cells, chemical reactions are connected by sharing their products and substrates, and form complex networks, e.g., metabolic pathways. Here we developed a theory to predict the sensitivity, i.e., the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Nonzero response patterns turn out to exhibit two characteristic features, localization and hierarchy. We present a general theorem connecting sensitivity with network topology that explains these characteristic patterns. Our results imply that network topology is an origin of biological robustness. Finally, we suggest a strategy to determine real networks from experimental measurements. PMID:27494502

  5. Law of Localization in Chemical Reaction Networks.

    PubMed

    Okada, Takashi; Mochizuki, Atsushi

    2016-07-22

    In living cells, chemical reactions are connected by sharing their products and substrates, and form complex networks, e.g., metabolic pathways. Here we developed a theory to predict the sensitivity, i.e., the responses of concentrations and fluxes to perturbations of enzymes, from network structure alone. Nonzero response patterns turn out to exhibit two characteristic features, localization and hierarchy. We present a general theorem connecting sensitivity with network topology that explains these characteristic patterns. Our results imply that network topology is an origin of biological robustness. Finally, we suggest a strategy to determine real networks from experimental measurements.

  6. Chemical Reaction Dynamics in Nanoscle Environments

    SciTech Connect

    Evelyn M. Goldfield

    2006-09-26

    The major focus of the research in this program is the study of the behavior of molecular systems confined in nanoscale environments. The goal is to develop a theoretical framework for predicting how chemical reactions occur in nanoscale environments. To achieve this goal we have employed ab initio quantum chemistry, classical dynamics and quantum dynamics methods. Much of the research has focused on the behavior of molecules confined within single-walled carbon nanotubes (SWCNTs). We have also studied interactions of small molecules with the exterior surface of SWCNTs. Nonequilibrium molecular dynamics of interfaces of sliding surface interfaces have also been performed.

  7. Molecular Dynamics Simulations of Chemical Reactions for Use in Education

    ERIC Educational Resources Information Center

    Qian Xie; Tinker, Robert

    2006-01-01

    One of the simulation engines of an open-source program called the Molecular Workbench, which can simulate thermodynamics of chemical reactions, is described. This type of real-time, interactive simulation and visualization of chemical reactions at the atomic scale could help students understand the connections between chemical reaction equations…

  8. Chemical repair activity of free radical scavenger edaravone: reduction reactions with dGMP hydroxyl radical adducts and suppression of base lesions and AP sites on irradiated plasmid DNA.

    PubMed

    Hata, Kuniki; Urushibara, Ayumi; Yamashita, Shinichi; Lin, Mingzhang; Muroya, Yusa; Shikazono, Naoya; Yokoya, Akinari; Fu, Haiying; Katsumura, Yosuke

    2015-01-01

    Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 10(8) dm(3) mol(-1) s(-1) and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10-1000 μmol dm(-3)) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.

  9. Chemical Potentials and Activities: An Electrochemical Introduction.

    ERIC Educational Resources Information Center

    Wetzel, T. L.; And Others

    1986-01-01

    Describes a laboratory experiment which explores the effects of adding inert salts to electrolytic cells and demonstrates the difference between concentration and chemical activity. Examines chemical potentials as the driving force of reactions. Provides five examples of cell potential and concentration change. (JM)

  10. The role of chemical reactions in the Chernobyl accident

    NASA Astrophysics Data System (ADS)

    Grishanin, E. I.

    2010-12-01

    It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000°C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

  11. The role of chemical reactions in the Chernobyl accident

    SciTech Connect

    Grishanin, E. I.

    2010-12-15

    It is shown that chemical reactions played an essential role in the Chernobyl accident at all of its stages. It is important that the reactor before the explosion was at maximal xenon poisoning, and its reactivity, apparently, was not destroyed by the explosion. The reactivity release due to decay of Xe-235 on the second day after the explosion led to a reactor power of 80-110 MW. Owing to this power, the chemical reactions of reduction of uranium, plutonium, and other metals at a temperature of about 2000 Degree-Sign C occurred in the core. The yield of fission products thus sharply increased. Uranium and other metals flew down in the bottom water communications and rooms. After reduction of the uranium and its separation from the graphite, the chain reaction stopped, the temperature of the core decreased, and the activity yield stopped.

  12. Systematic Error Estimation for Chemical Reaction Energies.

    PubMed

    Simm, Gregor N; Reiher, Markus

    2016-06-14

    For a theoretical understanding of the reactivity of complex chemical systems, accurate relative energies between intermediates and transition states are required. Despite its popularity, density functional theory (DFT) often fails to provide sufficiently accurate data, especially for molecules containing transition metals. Due to the huge number of intermediates that need to be studied for all but the simplest chemical processes, DFT is, to date, the only method that is computationally feasible. Here, we present a Bayesian framework for DFT that allows for error estimation of calculated properties. Since the optimal choice of parameters in present-day density functionals is strongly system dependent, we advocate for a system-focused reparameterization. While, at first sight, this approach conflicts with the first-principles character of DFT that should make it, in principle, system independent, we deliberately introduce system dependence to be able to assign a stochastically meaningful error to the system-dependent parametrization, which makes it nonarbitrary. By reparameterizing a functional that was derived on a sound physical basis to a chemical system of interest, we obtain a functional that yields reliable confidence intervals for reaction energies. We demonstrate our approach on the example of catalytic nitrogen fixation.

  13. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M. Allen; Mariella, Jr., Raymond P.; Carrano, Anthony V.; Balch, Joseph W.

    1996-01-01

    A silicon-based sleeve type chemical reaction chamber that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis.

  14. Silicon-based sleeve devices for chemical reactions

    DOEpatents

    Northrup, M.A.; Mariella, R.P. Jr.; Carrano, A.V.; Balch, J.W.

    1996-12-31

    A silicon-based sleeve type chemical reaction chamber is described that combines heaters, such as doped polysilicon for heating, and bulk silicon for convection cooling. The reaction chamber combines a critical ratio of silicon and silicon nitride to the volume of material to be heated (e.g., a liquid) in order to provide uniform heating, yet low power requirements. The reaction chamber will also allow the introduction of a secondary tube (e.g., plastic) into the reaction sleeve that contains the reaction mixture thereby alleviating any potential materials incompatibility issues. The reaction chamber may be utilized in any chemical reaction system for synthesis or processing of organic, inorganic, or biochemical reactions, such as the polymerase chain reaction (PCR) and/or other DNA reactions, such as the ligase chain reaction, which are examples of a synthetic, thermal-cycling-based reaction. The reaction chamber may also be used in synthesis instruments, particularly those for DNA amplification and synthesis. 32 figs.

  15. Regimes of chemical reaction waves initiated by nonuniform initial conditions for detailed chemical reaction models.

    PubMed

    Liberman, M A; Kiverin, A D; Ivanov, M F

    2012-05-01

    Regimes of chemical reaction wave propagation initiated by initial temperature nonuniformity in gaseous mixtures, whose chemistry is governed by chain-branching kinetics, are studied using a multispecies transport model and a detailed chemical model. Possible regimes of reaction wave propagation are identified for stoichiometric hydrogen-oxygen and hydrogen-air mixtures in a wide range of initial pressures and temperature levels, depending on the initial non-uniformity steepness. The limits of the regimes of reaction wave propagation depend upon the values of the spontaneous wave speed and the characteristic velocities of the problem. It is shown that one-step kinetics cannot reproduce either quantitative neither qualitative features of the ignition process in real gaseous mixtures because the difference between the induction time and the time when the exothermic reaction begins significantly affects the ignition, evolution, and coupling of the spontaneous reaction wave and the pressure wave, especially at lower temperatures. We show that all the regimes initiated by the temperature gradient occur for much shallower temperature gradients than predicted by a one-step model. The difference is very large for lower initial pressures and for slowly reacting mixtures. In this way the paper provides an answer to questions, important in practice, about the ignition energy, its distribution, and the scale of the initial nonuniformity required for ignition in one or another regime of combustion wave propagation.

  16. Shock induced chemical reactions in energetic structural materials

    NASA Astrophysics Data System (ADS)

    Reding, Derek J.

    Energetic structural materials (ESMs) constitute a new class of materials that provide dual functions of strength and energetic characteristics. ESMs are typically composed of micron-scale or nano-scale intermetallic mixtures or mixtures of metals and metal oxides, polymer binders, and structural reinforcements. Voids are included to produce a composite with favorable chemical reaction characteristics. In this thesis, a continuum approach is used to simulate gas-gun or explosive loading experiments where a strong shock is induced in the ESM by an impacting plate. Algorithms are developed to obtain equations of state of mixtures. It is usually assumed that the shock loading increases the energy of the ESM and causes the ESM to reach the transition state. It is also assumed that the activation energy needed to reach the transition state is a function of the temperature of the mixture. In this thesis, it is proposed that the activation energy is a function of temperature and the stress state of the mixture. The incorporation of such an activation energy is selected in this thesis. Then, a multi-scale chemical reaction model for a heterogeneous mixture is introduced. This model incorporates reaction initiation, propagation, and extent of completed reaction in spatially heterogeneous distributions of reactants. A new model is proposed for the pore collapse of mixtures. This model is formulated by modifying the Carol, Holt, and Nesterenko spherically symmetric model to include mixtures and compressibility effects. Uncertainties in the model result from assumptions in formulating the models for continuum relationships and chemical reactions in mixtures that are distributed heterogeneously in space and in numerical integration of the resulting equations. It is important to quantify these uncertainties. In this thesis, such an uncertainty quantification is investigated by systematically identifying the physical processes that occur during shock compression of ESMs which are

  17. Potential for exothermic chemical reactions in waste tanks

    SciTech Connect

    Van Tuyl, H.H.

    1983-02-03

    The potential for exothermic chemical reactions in waste tanks at Hanford is discussed. Organic chemicals have been added to Hanford waste tanks, particularly as ferrocyanides and when processing sludges at B Plant. Recent planned or ongoing activities involving stored wastes have possibly increased the potential for reaction of these wastes with nitrate salts in the waste tanks. Risk evaluations appear to be deficient in assessing the consequences of a deflagration, and in determining the probability of either a deflagration or detonation. The present question is whether current plans and recent safety-related documentation have given proper consideration to the available information about organic compounds in waste tanks. The principal organic additions to Hanford waste tanks are 1200 tonnes of organic carbon'' and 500 tonnes of Ni{sub 2}Fe(CN){sub 6}. 13 refs.

  18. Assessment of multireference perturbation methods for chemical reaction barrier heights.

    PubMed

    Fracchia, Francesco; Cimiraglia, Renzo; Angeli, Celestino

    2015-05-28

    A few flavors of multireference perturbation theory, two variants of the n-electron valence state perturbation theory and two of the complete active space perturbation theory, are here tested for the calculation of barrier heights for the set of chemical reactions included in the DBH24/08 database, for which very accurate values are available. The comparison of the results obtained with these approaches with those already published for other theoretical models indicates that multireference perturbation theory is a valuable tool for the description of a chemical reaction. Moreover, limiting the comparison to the perturbation theory approaches, one observes that the bad behavior found for single reference methods (such as Møller-Plesset to second and fourth order in the energy) is markedly improved upon moving to the multireference generalizations.

  19. Plasmon-driven sequential chemical reactions in an aqueous environment

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-06-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

  20. Plasmon-driven sequential chemical reactions in an aqueous environment.

    PubMed

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-06-24

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H(+) in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight.

  1. Plasmon-driven sequential chemical reactions in an aqueous environment

    PubMed Central

    Zhang, Xin; Wang, Peijie; Zhang, Zhenglong; Fang, Yurui; Sun, Mengtao

    2014-01-01

    Plasmon-driven sequential chemical reactions were successfully realized in an aqueous environment. In an electrochemical environment, sequential chemical reactions were driven by an applied potential and laser irradiation. Furthermore, the rate of the chemical reaction was controlled via pH, which provides indirect evidence that the hot electrons generated from plasmon decay play an important role in plasmon-driven chemical reactions. In acidic conditions, the hot electrons were captured by the abundant H+ in the aqueous environment, which prevented the chemical reaction. The developed plasmon-driven chemical reactions in an aqueous environment will significantly expand the applications of plasmon chemistry and may provide a promising avenue for green chemistry using plasmon catalysis in aqueous environments under irradiation by sunlight. PMID:24958029

  2. Heterogeneous chemical reactions: Preparation of monodisperse latexes

    NASA Technical Reports Server (NTRS)

    Vanderhoff, J. W.; Micale, F. J.; El-Aasser, M. S.; Sterk, A. A.; Bethke, G. W.

    1977-01-01

    It is demonstrated that a photoinitiated emulsion polymerization can be carried out to a significant conversion in a SPAR rocket prototype polymerization vessel within the six minutes allowed for the experiment. The percentage of conversion was determined by both dilatometry and gravimetric methods with good agreement. The experimental results lead to the following conclusions: (1) emulsion polymerizations can be carried out to conversions as high as 75%, using a stable micellized styrene-SLS system plus photoinitiator; (2) dilatometry can be used to accurately determine both the rate and conversion of polymerization; (3) thermal expansion due to the light source and heat of reaction is small and can be corrected for if necessary; (4) although seeded emulsion polymerizations are unfavorable in photoinitiation, as opposed to chemical initiation, polymerizations can be carried out to at least 15% conversion using 7940A seed particles, with 0.05% solids; and (5) photoinitiation should be used to initiate polymerization in the SPAR rocket experiments because of the mechanical simplicity of the experiment.

  3. Complex Chemical Reaction Networks from Heuristics-Aided Quantum Chemistry.

    PubMed

    Rappoport, Dmitrij; Galvin, Cooper J; Zubarev, Dmitry Yu; Aspuru-Guzik, Alán

    2014-03-11

    While structures and reactivities of many small molecules can be computed efficiently and accurately using quantum chemical methods, heuristic approaches remain essential for modeling complex structures and large-scale chemical systems. Here, we present a heuristics-aided quantum chemical methodology applicable to complex chemical reaction networks such as those arising in cell metabolism and prebiotic chemistry. Chemical heuristics offer an expedient way of traversing high-dimensional reactive potential energy surfaces and are combined here with quantum chemical structure optimizations, which yield the structures and energies of the reaction intermediates and products. Application of heuristics-aided quantum chemical methodology to the formose reaction reproduces the experimentally observed reaction products, major reaction pathways, and autocatalytic cycles.

  4. Chemical Characterization and Reactivity of Fuel-Oxidizer Reaction Product

    NASA Technical Reports Server (NTRS)

    David, Dennis D.; Dee, Louis A.; Beeson, Harold D.

    1997-01-01

    Fuel-oxidizer reaction product (FORP), the product of incomplete reaction of monomethylhydrazine and nitrogen tetroxide propellants prepared under laboratory conditions and from firings of Shuttle Reaction Control System thrusters, has been characterized by chemical and thermal analysis. The composition of FORP is variable but falls within a limited range of compositions that depend on three factors: the fuel-oxidizer ratio at the time of formation; whether the composition of the post-formation atmosphere is reducing or oxidizing; and the reaction or post-reaction temperature. A typical composition contains methylhydrazinium nitrate, ammonium nitrate, methylammonium nitrate, and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. Thermal decomposition reactions of the FORP compositions used in this study were unremarkable. Neither the various compositions of FORP, the pure major components of FORP, nor mixtures of FORP with propellant system corrosion products showed any unusual thermal activity when decomposed under laboratory conditions. Off-limit thruster operations were simulated by rapid mixing of liquid monomethylhydrazine and liquid nitrogen tetroxide in a confined space. These tests demonstrated that monomethylhydrazine, methylhydrazinium nitrate, ammonium nitrate, or Inconel corrosion products can induce a mixture of monomethylhydrazine and nitrogen tetroxide to produce component-damaging energies. Damaging events required FORP or metal salts to be present at the initial mixing of monomethylhydrazine and nitrogen tetroxide.

  5. Structure-activity relationships for chemical and glutathione S-transferase-catalysed glutathione conjugation reactions of a series of 2-substituted 1-chloro-4-nitrobenzenes.

    PubMed Central

    Van der Aar, E M; Bouwman, T; Commandeur, J N; Vermeulen, N P

    1996-01-01

    Glutathione S-transferases (GSTs) constitute an important class of phase II (de)toxifying enzymes, catalysing the conjugation of glutathione (GSH) with electrophilic compounds. In the present study, Km, kcat and kcat/Km values for the rat GST 1-1-, 3-3-, 4-4- and 7-7-catalysed conjugation reactions between GSH and a series of 10 different 2-substituted 1-chloro-4-nitrobenzenes, and the second-order rate constants (ks) of the corresponding base-catalysed reactions, were correlated with nine classical physicochemical parameters (electronic, steric and lipophilic) of the substituents and with 16 computer-calculated molecular parameters of the substrates and of the corresponding Meisenheimer complexes with MeS- as a model nucleophile for GS- (charge distributions and several energy values), giving structure-activity relationships. On the basis of an identical dependence of the base-catalysed as well as the GST 1-1- and GST 7-7-catalysed reactions on electronic parameters (among others, Hammett substituent constant sigma p and charge on p-nitro substituents), and the finding that the corresponding reactions catalysed by GSTs 3-3 and 4-4 depend to a significantly lesser extent on these parameters, it was concluded that the Mu-class GST isoenzymes have a rate-determining transition state in the conjugation reaction between 2-substituted 1-chloro-4-nitrobenzenes and GSH which is different from that of the other two GSTs. Several alternative rate-limiting transition states for GST 3-3 and 4-4 are discussed. Furthermore, based on the obtained structure-activity relationships, it was possible to predict the kcat/Km values of the four GST isoenzymes and the ks of the base-catalysed GSH conjugation of 1-chloro-4-nitrobenzene. PMID:8973562

  6. Spectroscopy and reactions of molecules important in chemical evolution

    NASA Technical Reports Server (NTRS)

    Becker, R. S.

    1974-01-01

    The research includes: (1) hot hydrogen atom reactions in terms of the nature of products produced, mechanism of the reactions and the implication and application of such reactions for molecules existing in interstellar clouds, in planetary atmospheres, and in chemical evolution; (2) photochemical reactions that can lead to molecules important in chemical evolution, interstellar clouds and as constituents in planetary atmospheres; and (3) spectroscopic and theoretical properties of biomolecules and their precursors and where possible, use these to understand their photochemical behavior.

  7. GREEN CHEMICAL SYNTHESIS THROUGH CATALYSIS AND ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    Green chemical synthesis through catalysis and alternate reaction conditions

    Encompassing green chemistry techniques and methodologies, we have initiated several projects at the National Risk Management Research laboratory that focus on the design and development of chemic...

  8. Prediction and Prevention of Chemical Reaction Hazards: Learning by Simulation.

    ERIC Educational Resources Information Center

    Shacham, Mordechai; Brauner, Neima; Cutlip, Michael B.

    2001-01-01

    Points out that chemical hazards are the major cause of accidents in chemical industry and describes a safety teaching approach using a simulation. Explains a problem statement on exothermic liquid-phase reactions. (YDS)

  9. Chemical and Free Radical-scavenging Activity Changes of Ginsenoside Re by Maillard Reaction and Its Possible Use as a Renoprotective Agent

    PubMed Central

    Yamabe, Noriko; Song, Kyung Il; Lee, Woojung; Han, Im-Ho; Lee, Ji Hwan; Ham, Jungyeob; Kim, Su-Nam; Park, Jeong Hill; Kang, Ki Sung

    2012-01-01

    Reactive oxygen species play critical role in kidney damage. Free radical-scavenging activities of Panax ginseng are known to be increased by heat-processing. The structural change of ginsenoside and the generation of Maillard reaction products (MRPs) are closely related to the increased free radical-scavenging activities. In the present study, we have demonstrated the Maillard reaction model experiment using ginsenoside Re and glycine mixture to identify the renoprotective effect of MRPs from ginseng or ginsenosides. Ginsenoside Re was transformed into less-polar ginsenosides, namely Rg2, Rg6 and F4 by heat-processing. The free radical-scavenging activity of ginsenoside Re-glycine mixture was increased in a temperature-dependant manner by heatprocessing. The improved free radical-scavenging activity by heat-processing was mediated by the generation of antioxidant MRPs which led to the protection of LLC-PK1 renal epithelial cells from oxidative stress. Although the free radical scavenging activities of less-polar ginsenosides were weak, they could protect LLC-PK1 cells from oxidative stress. Therefore, MRPs and less-polar ginsenosides contributed to the combined renoprotective effects against oxidative renal damage. PMID:23717126

  10. Incidents of chemical reactions in cell equipment

    SciTech Connect

    Baldwin, N.M.; Barlow, C.R.

    1991-12-31

    Strongly exothermic reactions can occur between equipment structural components and process gases under certain accident conditions in the diffusion enrichment cascades. This paper describes the conditions required for initiation of these reactions, and describes the range of such reactions experienced over nearly 50 years of equipment operation in the US uranium enrichment program. Factors are cited which can promote or limit the destructive extent of these reactions, and process operations are described which are designed to control the reactions to minimize equipment damage, downtime, and the possibility of material releases.

  11. Semiclassical methods in chemical reaction dynamics

    SciTech Connect

    Keshavamurthy, S.

    1994-12-01

    Semiclassical approximations, simple as well as rigorous, are formulated in order to be able to describe gas phase chemical reactions in large systems. We formulate a simple but accurate semiclassical model for incorporating multidimensional tunneling in classical trajectory simulations. This model is based on the existence of locally conserved actions around the saddle point region on a multidimensional potential energy surface. Using classical perturbation theory and monitoring the imaginary action as a function of time along a classical trajectory we calculate state-specific unimolecular decay rates for a model two dimensional potential with coupling. Results are in good comparison with exact quantum results for the potential over a wide range of coupling constants. We propose a new semiclassical hybrid method to calculate state-to-state S-matrix elements for bimolecular reactive scattering. The accuracy of the Van Vleck-Gutzwiller propagator and the short time dynamics of the system make this method self-consistent and accurate. We also go beyond the stationary phase approximation by doing the resulting integrals exactly (numerically). As a result, classically forbidden probabilties are calculated with purely real time classical trajectories within this approach. Application to the one dimensional Eckart barrier demonstrates the accuracy of this approach. Successful application of the semiclassical hybrid approach to collinear reactive scattering is prevented by the phenomenon of chaotic scattering. The modified Filinov approach to evaluating the integrals is discussed, but application to collinear systems requires a more careful analysis. In three and higher dimensional scattering systems, chaotic scattering is suppressed and hence the accuracy and usefulness of the semiclassical method should be tested for such systems.

  12. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1990-01-01

    The objective was to obtain accurate potential energy surfaces (PES's) for a number of reactions which are important in the H/N/O combustion process. The interest in this is centered around the design of the SCRAM jet engine for the National Aerospace Plane (NASP), which was envisioned as an air-breathing hydrogen-burning vehicle capable of reaching velocities as large as Mach 25. Preliminary studies indicated that the supersonic flow in the combustor region of the scram jet engine required accurate reaction rate data for reactions in the H/N/O system, some of which was not readily available from experiment. The most important class of combustion reactions from the standpoint of the NASP project are radical recombinaton reactions, since these reactions result in most of the heat release in the combustion process. Theoretical characterizations of the potential energy surfaces for these reactions are presented and discussed.

  13. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2014-03-01

    , they performed a sensitivity analysis for velocity, height and polydispersity and compared results against literature data for experimental studies of CLC beds with no reaction. Finally, they present an optimization space using simple non-reactive configurations. In Subtask 5.3, through a series of experimental studies, behavior of a variety of oxygen carriers with different loadings and manufacturing techniques was evaluated under both oxidizing and reducing conditions. The influences of temperature, degree of carrier conversion and thermodynamic driving force resulting from the difference between equilibrium and system O{sub 2} partial pressures were evaluated through several experimental campaigns, and generalized models accounting for these influences were developed to describe oxidation and oxygen release. Conversion of three solid fuels with widely ranging reactivities was studied in a small fluidized bed system, and all but the least reactive fuel (petcoke) were rapidly converted by oxygen liberated from the CLOU carrier. Attrition propensity of a variety of carriers was also studied, and the carriers produced by freeze granulation or impregnation of preformed substrates displayed the lowest rates of attrition. Subtask 5.4 focused on gathering kinetic data for a copper-based oxygen carrier to assist with modeling of a functioning chemical looping reactor. The kinetics team was also responsible for the development and analysis of supported copper oxygen carrier material.

  14. Chemical reactions of organic compounds on clay surfaces

    SciTech Connect

    Soma, Yuko; Soma, Mitsuyuki )

    1989-11-01

    Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Broensted or Lewis acidity of clay minerals.

  15. On the rate of relativistic surface chemical reactions.

    PubMed

    Veitsman, E V

    2004-07-15

    On the basis of special relativity and the classical theory of chemical reaction rates it is shown how the surface chemical reaction rates vary as v --> c, where v is the velocity of the object under study and c is the velocity of light. PMID:15178286

  16. Chemical kinetics computer program for static and flow reactions

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    General chemical kinetics computer program for complex gas mixtures has been developed. Program can be used for any homogeneous reaction in either one dimensional flow or static system. It is flexible, accurate, and easy to use. It can be used for any chemical system for which species thermodynamic data and reaction rate constant data are known.

  17. Stereodynamics: From elementary processes to macroscopic chemical reactions

    SciTech Connect

    Kasai, Toshio; Che, Dock-Chil; Tsai, Po-Yu; Lin, King-Chuen; Palazzetti, Federico; Aquilanti, Vincenzo

    2015-12-31

    This paper aims at discussing new facets on stereodynamical behaviors in chemical reactions, i.e. the effects of molecular orientation and alignment on reactive processes. Further topics on macroscopic processes involving deviations from Arrhenius behavior in the temperature dependence of chemical reactions and chirality effects in collisions are also discussed.

  18. Chemical Demonstrations with Consumer Chemicals: The Black and White Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes a dramatic chemical demonstration in which chemicals that are black and white combine to produce a colorless liquid. Reactants include tincture of iodine, bleach, white vinegar, Epsom salt, vitamin C tablets, and liquid laundry starch. (DDR)

  19. Structural cluster analysis of chemical reactions in solution

    NASA Astrophysics Data System (ADS)

    Gallet, Grégoire A.; Pietrucci, Fabio

    2013-08-01

    We introduce a simple and general approach to the problem of clustering structures from atomic trajectories of chemical reactions in solution. By considering distance metrics which are invariant under permutation of identical atoms or molecules, we demonstrate that it is possible to automatically resolve as distinct structural clusters the configurations corresponding to reactants, products, and transition states, even in presence of atom-exchanges and of hundreds of solvent molecules. Our approach strongly simplifies the analysis of large trajectories and it opens the way to the construction of kinetic network models of activated processes in solution employing the available efficient schemes developed for proteins conformational ensembles.

  20. Mesoscale simulations of shockwave energy dissipation via chemical reactions

    NASA Astrophysics Data System (ADS)

    Antillon, Edwin; Strachan, Alejandro

    2015-02-01

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock.

  1. Mesoscale simulations of shockwave energy dissipation via chemical reactions.

    PubMed

    Antillon, Edwin; Strachan, Alejandro

    2015-02-28

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock. PMID:25725713

  2. Mesoscale simulations of shockwave energy dissipation via chemical reactions.

    PubMed

    Antillon, Edwin; Strachan, Alejandro

    2015-02-28

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials that undergo volume-reducing chemical reactions under shockwave-loading conditions. We find that such chemical reactions can attenuate the shockwave and characterize how the parameters of the chemical model affect this behavior. The simulations show that the magnitude of the volume collapse and velocity at which the chemistry propagates are critical to weaken the shock, whereas the energetics in the reactions play only a minor role. Shock loading results in transient states where the material is away from local equilibrium and, interestingly, chemical reactions can nucleate under such non-equilibrium states. Thus, the timescales for equilibration between the various degrees of freedom in the material affect the shock-induced chemistry and its ability to attenuate the propagating shock.

  3. Chemical and genomic evolution of enzyme-catalyzed reaction networks.

    PubMed

    Kanehisa, Minoru

    2013-09-01

    There is a tendency that a unit of enzyme genes in an operon-like structure in the prokaryotic genome encodes enzymes that catalyze a series of consecutive reactions in a metabolic pathway. Our recent analysis shows that this and other genomic units correspond to chemical units reflecting chemical logic of organic reactions. From all known metabolic pathways in the KEGG database we identified chemical units, called reaction modules, as the conserved sequences of chemical structure transformation patterns of small molecules. The extracted patterns suggest co-evolution of genomic units and chemical units. While the core of the metabolic network may have evolved with mechanisms involving individual enzymes and reactions, its extension may have been driven by modular units of enzymes and reactions.

  4. An Analysis of the Algebraic Method for Balancing Chemical Reactions.

    ERIC Educational Resources Information Center

    Olson, John A.

    1997-01-01

    Analyzes the algebraic method for balancing chemical reactions. Introduces a third general condition that involves a balance between the total amount of oxidation and reduction. Requires the specification of oxidation states for all elements throughout the reaction. Describes the general conditions, the mathematical treatment, redox reactions, and…

  5. Power law behavior in chemical reactions.

    PubMed

    Claycomb, J R; Nawarathna, D; Vajrala, V; Miller, J H

    2004-12-22

    Reactions between metals and chloride solutions have been shown to exhibit magnetic field fluctuations over a wide range of size and time scales. Power law behavior observed in these reactions is consistent with models said to exhibit self-organized criticality. Voltage fluctuations observed during the dissolution of magnesium and aluminum in copper chloride solution are qualitatively similar to the recorded magnetic signals. In this paper, distributions of voltage and magnetic peak sizes, noise spectra, and return times are compared for both reactions studied. PMID:15606263

  6. Power law behavior in chemical reactions

    NASA Astrophysics Data System (ADS)

    Claycomb, J. R.; Nawarathna, D.; Vajrala, V.; Miller, J. H.

    2004-12-01

    Reactions between metals and chloride solutions have been shown to exhibit magnetic field fluctuations over a wide range of size and time scales. Power law behavior observed in these reactions is consistent with models said to exhibit self-organized criticality. Voltage fluctuations observed during the dissolution of magnesium and aluminum in copper chloride solution are qualitatively similar to the recorded magnetic signals. In this paper, distributions of voltage and magnetic peak sizes, noise spectra, and return times are compared for both reactions studied.

  7. FACILITATED CHEMICAL SYNTHESIS UNDER ALTERNATE REACTION CONDITIONS

    EPA Science Inventory

    The chemical research in the late 1990's witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into the atmo...

  8. The How and Why of Chemical Reactions

    ERIC Educational Resources Information Center

    Schubert, Leo

    1970-01-01

    Presents a discussion of some of the fundamental concepts in thermodynamics and quantum mechanics including entropy, enthalpy, free energy, the partition function, chemical kinetics, transition state theory, the making and breaking of chemical bonds, electronegativity, ion sizes, intermolecular energies and of their role in explaining the nature…

  9. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A new global potential energy surface (PES) is being generated for O(P-3) + H2 yields OH + H. This surface is being fit using the rotated Morse oscillator method, which was used to fit the previous POL-CI surface. The new surface is expected to be more accurate and also includes a much more complete sampling of bent geometries. A new study has been undertaken of the reaction N + O2 yields NO + O. The new studies have focused on the region of the surface near a possible minimum corresponding to the peroxy form of NOO. A large portion of the PES for this second reaction has been mapped out. Since state to state cross sections for the reaction are important in the chemistry of high temperature air, these studies will probably be extended to permit generation of a new global potential for reaction.

  10. Classical transition states for collinear chemical reactions

    NASA Astrophysics Data System (ADS)

    Maslen, V. W.

    An analysis of a simple model for the interaction region of the potential energy surface of a collinear atom-diatomic molecule reaction is used to interpret recent observations of periodic trajectories on accurate energy surfaces.

  11. Kinetics of Chemical Reactions in Flames

    NASA Technical Reports Server (NTRS)

    Zeldovich, Y.; Semenov, N.

    1946-01-01

    In part I of the paper the theory of flame propagation is developed along the lines followed by Frank-Kamenetsky and one of the writers. The development of chain processes in flames is considered. A basis is given for the application of the method of stationary concentrations to reactions in flames; reactions with branching chains are analyzed. The case of a diffusion coefficient different from the coefficient of temperature conductivity is considered.

  12. Peptide Bond Synthesis by a Mechanism Involving an Enzymatic Reaction and a Subsequent Chemical Reaction.

    PubMed

    Abe, Tomoko; Hashimoto, Yoshiteru; Zhuang, Ye; Ge, Yin; Kumano, Takuto; Kobayashi, Michihiko

    2016-01-22

    We recently reported that an amide bond is unexpectedly formed by an acyl-CoA synthetase (which catalyzes the formation of a carbon-sulfur bond) when a suitable acid and l-cysteine are used as substrates. DltA, which is homologous to the adenylation domain of nonribosomal peptide synthetase, belongs to the same superfamily of adenylate-forming enzymes, which includes many kinds of enzymes, including the acyl-CoA synthetases. Here, we demonstrate that DltA synthesizes not only N-(d-alanyl)-l-cysteine (a dipeptide) but also various oligopeptides. We propose that this enzyme catalyzes peptide synthesis by the following unprecedented mechanism: (i) the formation of S-acyl-l-cysteine as an intermediate via its "enzymatic activity" and (ii) subsequent "chemical" S → N acyl transfer in the intermediate, resulting in peptide formation. Step ii is identical to the corresponding reaction in native chemical ligation, a method of chemical peptide synthesis, whereas step i is not. To the best of our knowledge, our discovery of this peptide synthesis mechanism involving an enzymatic reaction and a subsequent chemical reaction is the first such one to be reported. This new process yields peptides without the use of a thioesterified fragment, which is required in native chemical ligation. Together with these findings, the same mechanism-dependent formation of N-acyl compounds by other members of the above-mentioned superfamily demonstrated that all members most likely form peptide/amide compounds by using this novel mechanism. Each member enzyme acts on a specific substrate; thus, not only the corresponding peptides but also new types of amide compounds can be formed.

  13. Nonequilibrium thermodynamics and a fluctuation theorem for individual reaction steps in a chemical reaction network

    NASA Astrophysics Data System (ADS)

    Pal, Krishnendu; Das, Biswajit; Banerjee, Kinshuk; Gangopadhyay, Gautam

    2015-09-01

    We have introduced an approach to nonequilibrium thermodynamics of an open chemical reaction network in terms of the propensities of the individual elementary reactions and the corresponding reverse reactions. The method is a microscopic formulation of the dissipation function in terms of the relative entropy or Kullback-Leibler distance which is based on the analogy of phase space trajectory with the path of elementary reactions in a network of chemical process. We have introduced here a fluctuation theorem valid for each opposite pair of elementary reactions which is useful in determining the contribution of each sub-reaction on the nonequilibrium thermodynamics of overall reaction. The methodology is applied to an oligomeric enzyme kinetics at a chemiostatic condition that leads the reaction to a nonequilibrium steady state for which we have estimated how each step of the reaction is energy driven or entropy driven to contribute to the overall reaction.

  14. Chemical reactions modulated by mechanical stress: extended Bell theory.

    PubMed

    Konda, Sai Sriharsha M; Brantley, Johnathan N; Bielawski, Christopher W; Makarov, Dmitrii E

    2011-10-28

    A number of recent studies have shown that mechanical stress can significantly lower or raise the activation barrier of a chemical reaction. Within a common approximation due to Bell [Science 200, 618 (1978)], this barrier is linearly dependent on the applied force. A simple extension of Bell's theory that includes higher order corrections in the force predicts that the force-induced change in the activation energy will be given by -FΔR - ΔχF(2)∕2. Here, ΔR is the change of the distance between the atoms, at which the force F is applied, from the reactant to the transition state, and Δχ is the corresponding change in the mechanical compliance of the molecule. Application of this formula to the electrocyclic ring-opening of cis and trans 1,2-dimethylbenzocyclobutene shows that this extension of Bell's theory essentially recovers the force dependence of the barrier, while the original Bell formula exhibits significant errors. Because the extended Bell theory avoids explicit inclusion of the mechanical stress or strain in electronic structure calculations, it allows a computationally efficient characterization of the effect of mechanical forces on chemical processes. That is, the mechanical susceptibility of any reaction pathway is described in terms of two parameters, ΔR and Δχ, both readily computable at zero force.

  15. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.

    1992-01-01

    The work on the NH + NO system which was described in the last progress report was written up and a draft of the manuscript is included in the appendix. The appendix also contains a draft of a manuscript on an Ar + H + H surface. New work which was completed in the last six months includes the following: (1) calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction; (2) calculations for the NH2 + O reaction; (3) calculations for the CH3 + O2 reaction; and (4) calculations for CH3O and the two decomposition channels--CH2OH and H + H2CO. Detailed descriptions of this work will be given in manuscripts; however, brief descriptions of the CH3 + OH and CH3 + O2 projects are given.

  16. Non-equilibrium effects in high temperature chemical reactions

    NASA Technical Reports Server (NTRS)

    Johnson, Richard E.

    1987-01-01

    Reaction rate data were collected for chemical reactions occurring at high temperatures during reentry of space vehicles. The principle of detailed balancing is used in modeling kinetics of chemical reactions at high temperatures. Although this principle does not hold for certain transient or incubation times in the initial phase of the reaction, it does seem to be valid for the rates of internal energy transitions that occur within molecules and atoms. That is, for every rate of transition within the internal energy states of atoms or molecules, there is an inverse rate that is related through an equilibrium expression involving the energy difference of the transition.

  17. Communication: Control of chemical reactions using electric field gradients.

    PubMed

    Deshmukh, Shivaraj D; Tsori, Yoav

    2016-05-21

    We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

  18. Communication: Control of chemical reactions using electric field gradients

    NASA Astrophysics Data System (ADS)

    Deshmukh, Shivaraj D.; Tsori, Yoav

    2016-05-01

    We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

  19. Developing Secondary Students' Conceptions of Chemical Reactions: The Introduction of Chemical Equilibrium.

    ERIC Educational Resources Information Center

    Van Driel, Jan H.; De Vos, Wobbe; Verloop, Nico; Dekkers, Hetty

    1998-01-01

    Describes an empirical study concerning the introduction of the concept of chemical equilibrium in chemistry classrooms in a way which challenges students' initial conceptions of chemical reactions. Contains 23 references. (DDR)

  20. Computed Potential Energy Surfaces for Chemical Reactions

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Walch, Stephen P.; Levin, Eugene

    1993-01-01

    A manuscript describing the calculations on the (1)CH2 + H2O, H2 + HCOH, and H2 + H2CO product channels in the CH3 + OH reaction, which were described in the last progress report, has been accepted for publication in J. Chem. Phys., and a copy of the manuscript is included in the appendix. The production of (1)CH2 in this reaction is important in hydrocarbon combustion since (1)CH2 is highly reactive and would be expected to insert into N2, possibly leading to a new source for prompt NO(x) (vide infra). During the last six months new calculations have been carried out for the NH2 + NO system, which is important in the thermal de-NO(x) process.

  1. Fluid flow and chemical reaction kinetics in metamorphic systems

    SciTech Connect

    Lasaga, A.C.; Rye, D.M. )

    1993-05-01

    The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

  2. 29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    29. NORTHWEST VIEW OF BOILER FEEDWATER CHEMICAL REACTION TANKS, WITH FORMER GENERAL OFFICE BUILDING IN BACKGROUND. - U.S. Steel Duquesne Works, Fuel & Utilities Plant, Along Monongahela River, Duquesne, Allegheny County, PA

  3. CHEMICAL REACTIONS SIMULATED BY GROUND-WATER-QUALITY MODELS.

    USGS Publications Warehouse

    Grove, David B.; Stollenwerk, Kenneth G.

    1987-01-01

    Recent literature concerning the modeling of chemical reactions during transport in ground water is examined with emphasis on sorption reactions. The theory of transport and reactions in porous media has been well documented. Numerous equations have been developed from this theory, to provide both continuous and sequential or multistep models, with the water phase considered for both mobile and immobile phases. Chemical reactions can be either equilibrium or non-equilibrium, and can be quantified in linear or non-linear mathematical forms. Non-equilibrium reactions can be separated into kinetic and diffusional rate-limiting mechanisms. Solutions to the equations are available by either analytical expressions or numerical techniques. Saturated and unsaturated batch, column, and field studies are discussed with one-dimensional, laboratory-column experiments predominating. A summary table is presented that references the various kinds of models studied and their applications in predicting chemical concentrations in ground waters.

  4. Chemical reactions of organic compounds on clay surfaces.

    PubMed Central

    Soma, Y; Soma, M

    1989-01-01

    Chemical reactions of organic compounds including pesticides at the interlayer and exterior surfaces of clay minerals and with soil organic matter are reviewed. Representative reactions under moderate conditions possibly occurring in natural soils are described. Attempts have been made to clarify the importance of the chemical nature of molecules, their structures and their functional groups, and the Brönsted or Lewis acidity of clay minerals. PMID:2533556

  5. Quantum chemical mechanism in parasitic reaction of AlGaN alloys formation

    NASA Astrophysics Data System (ADS)

    Makino, Osamu; Nakamura, Koichi; Tachibana, Akitomo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    2000-06-01

    The mechanism of parasitic reactions among trimethylaluminum (TMA), trimethylgallium (TMG), and NH 3 in atmospheric pressure (AP) MOVPE for growth of AlGaN is theoretically studied using the quantum chemical method. The calculations show that metal-nitrogen chain growth reaction easily proceeds through the successive reactions of 'complex formation with NH 3' and 'CH 4 elimination by the bimolecular mechanism'. Additionally, a parasitic reaction in APMOVPE using other raw material is also investigated. The calculated result shows that small change of raw material raises activation energy of parasitic reaction, and, thus, the parasitic reaction is suppressed. This result suggests a way to improve APMOVPE by a suitable choice of substituent.

  6. Quantifying chemical reactions by using mixing analysis.

    PubMed

    Jurado, Anna; Vázquez-Suñé, Enric; Carrera, Jesús; Tubau, Isabel; Pujades, Estanislao

    2015-01-01

    This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Besòs River Delta (NE Barcelona, Spain), where the River Besòs is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Besòs: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point.

  7. Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets.

    PubMed

    Bain, Ryan M; Pulliam, Christopher J; Thery, Fabien; Cooks, R Graham

    2016-08-22

    Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base-catalyzed Claisen-Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2-50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.

  8. Quantum chemical approach to estimating the thermodynamics of metabolic reactions.

    PubMed

    Jinich, Adrian; Rappoport, Dmitrij; Dunn, Ian; Sanchez-Lengeling, Benjamin; Olivares-Amaya, Roberto; Noor, Elad; Even, Arren Bar; Aspuru-Guzik, Alán

    2014-11-12

    Thermodynamics plays an increasingly important role in modeling and engineering metabolism. We present the first nonempirical computational method for estimating standard Gibbs reaction energies of metabolic reactions based on quantum chemistry, which can help fill in the gaps in the existing thermodynamic data. When applied to a test set of reactions from core metabolism, the quantum chemical approach is comparable in accuracy to group contribution methods for isomerization and group transfer reactions and for reactions not including multiply charged anions. The errors in standard Gibbs reaction energy estimates are correlated with the charges of the participating molecules. The quantum chemical approach is amenable to systematic improvements and holds potential for providing thermodynamic data for all of metabolism.

  9. Laser cutting with chemical reaction assist

    SciTech Connect

    Gettemy, D.J.

    1991-04-08

    This invention is comprised of a method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

  10. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, D.J.

    1992-11-17

    A method is described for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation. 1 figure.

  11. Laser cutting with chemical reaction assist

    DOEpatents

    Gettemy, Donald J.

    1992-01-01

    A method for cutting with a laser beam where an oxygen-hydrocarbon reaction is used to provide auxiliary energy to a metal workpiece to supplement the energy supplied by the laser. Oxygen is supplied to the laser focus point on the workpiece by a nozzle through which the laser beam also passes. A liquid hydrocarbon is supplied by coating the workpiece along the cutting path with the hydrocarbon prior to laser irradiation or by spraying a stream of hydrocarbon through a nozzle aimed at a point on the cutting path which is just ahead of the focus point during irradiation.

  12. Is the simplest chemical reaction really so simple?

    PubMed Central

    Jankunas, Justin; Sneha, Mahima; Zare, Richard N.; Bouakline, Foudhil; Althorpe, Stuart C.; Herráez-Aguilar, Diego; Aoiz, F. Javier

    2014-01-01

    Modern computational methods have become so powerful for predicting the outcome for the H + H2 → H2 + H bimolecular exchange reaction that it might seem further experiments are not needed. Nevertheless, experiments have led the way to cause theorists to look more deeply into this simplest of all chemical reactions. The findings are less simple. PMID:24367084

  13. Cu-free click cycloaddition reactions in chemical biology†

    PubMed Central

    Jewett, John C.

    2010-01-01

    Bioorthogonal chemical reactions are paving the way for new innovations in biology. These reactions possess extreme selectivity and biocompatibility, such that their participating reagents can form covalent bonds within richly functionalized biological systems—in some cases, living organisms. This tutorial review will summarize the history of this emerging field, as well as recent progress in the development and application of bioorthogonal copper-free click cycloaddition reactions. PMID:20349533

  14. Conservation-dissipation structure of chemical reaction systems.

    PubMed

    Yong, Wen-An

    2012-12-01

    In this Brief Report, we show that balanced chemical reaction systems governed by the law of mass action have an elegant conservation-dissipation structure. From this structure a number of important conclusions can be easily deduced. In particular, with the help of this structure we can rigorously justify the classical partial equilibrium approximation in chemical kinetics.

  15. Results of the 2010 Survey on Teaching Chemical Reaction Engineering

    ERIC Educational Resources Information Center

    Silverstein, David L.; Vigeant, Margot A. S.

    2012-01-01

    A survey of faculty teaching the chemical reaction engineering course or sequence during the 2009-2010 academic year at chemical engineering programs in the United States and Canada reveals change in terms of content, timing, and approaches to teaching. The report consists of two parts: first, a statistical and demographic characterization of the…

  16. Adsorption and catalysis: The effect of confinement on chemical reactions

    NASA Astrophysics Data System (ADS)

    Santiso, Erik E.; George, Aaron M.; Turner, C. Heath; Kostov, Milen K.; Gubbins, Keith E.; Buongiorno-Nardelli, Marco; Sliwinska-Bartkowiak, Małgorzata

    2005-10-01

    Confinement within porous materials can affect chemical reactions through a host of different effects, including changes in the thermodynamic state of the system due to interactions with the pore walls, selective adsorption, geometrical constraints that affect the reaction mechanism, electronic perturbation due to the substrate, etc. In this work, we present an overview of some of our recent research on some of these effects, on chemical equilibrium, kinetic rates and reaction mechanisms. We also discuss our current and future directions for research in this area.

  17. A Light-Activated Reaction Manifold.

    PubMed

    Hiltebrandt, Kai; Elies, Katharina; D'hooge, Dagmar R; Blinco, James P; Barner-Kowollik, Christopher

    2016-06-01

    We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels.

  18. Chemical kinetic reaction mechanism for the combustion of propane

    NASA Technical Reports Server (NTRS)

    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.

  19. ReactionMap: an efficient atom-mapping algorithm for chemical reactions.

    PubMed

    Fooshee, David; Andronico, Alessio; Baldi, Pierre

    2013-11-25

    Large databases of chemical reactions provide new data-mining opportunities and challenges. Key challenges result from the imperfect quality of the data and the fact that many of these reactions are not properly balanced or atom-mapped. Here, we describe ReactionMap, an efficient atom-mapping algorithm. Our approach uses a combination of maximum common chemical subgraph search and minimization of an assignment cost function derived empirically from training data. We use a set of over 259,000 balanced atom-mapped reactions from the SPRESI commercial database to train the system, and we validate it on random sets of 1000 and 17,996 reactions sampled from this pool. These large test sets represent a broad range of chemical reaction types, and ReactionMap correctly maps about 99% of the atoms and about 96% of the reactions, with a mean time per mapping of 2 s. Most correctly mapped reactions are mapped with high confidence. Mapping accuracy compares favorably with ChemAxon's AutoMapper, versions 5 and 6.1, and the DREAM Web tool. These approaches correctly map 60.7%, 86.5%, and 90.3% of the reactions, respectively, on the same data set. A ReactionMap server is available on the ChemDB Web portal at http://cdb.ics.uci.edu .

  20. Single-molecule chemical reaction reveals molecular reaction kinetics and dynamics.

    PubMed

    Zhang, Yuwei; Song, Ping; Fu, Qiang; Ruan, Mingbo; Xu, Weilin

    2014-06-25

    Understanding the microscopic elementary process of chemical reactions, especially in condensed phase, is highly desirable for improvement of efficiencies in industrial chemical processes. Here we show an approach to gaining new insights into elementary reactions in condensed phase by combining quantum chemical calculations with a single-molecule analysis. Elementary chemical reactions in liquid-phase, revealed from quantum chemical calculations, are studied by tracking the fluorescence of single dye molecules undergoing a reversible redox process. Statistical analyses of single-molecule trajectories reveal molecular reaction kinetics and dynamics of elementary reactions. The reactivity dynamic fluctuations of single molecules are evidenced and probably arise from either or both of the low-frequency approach of the molecule to the internal surface of the SiO2 nanosphere or the molecule diffusion-induced memory effect. This new approach could be applied to other chemical reactions in liquid phase to gain more insight into their molecular reaction kinetics and the dynamics of elementary steps.

  1. Computed potential energy surfaces for chemical reactions

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1988-01-01

    The minimum energy path for the addition of a hydrogen atom to N2 is characterized in CASSCF/CCI calculations using the (4s3p2d1f/3s2p1d) basis set, with additional single point calculations at the stationary points of the potential energy surface using the (5s4p3d2f/4s3p2d) basis set. These calculations represent the most extensive set of ab initio calculations completed to date, yielding a zero point corrected barrier for HN2 dissociation of approx. 8.5 kcal mol/1. The lifetime of the HN2 species is estimated from the calculated geometries and energetics using both conventional Transition State Theory and a method which utilizes an Eckart barrier to compute one dimensional quantum mechanical tunneling effects. It is concluded that the lifetime of the HN2 species is very short, greatly limiting its role in both termolecular recombination reactions and combustion processes.

  2. Chemical Looping Combustion Reactions and Systems

    SciTech Connect

    Sarofim, Adel; Lighty, JoAnn; Smith, Philip; Whitty, Kevin; Eyring, Edward; Sahir, Asad; Alvarez, Milo; Hradisky, Michael; Clayton, Chris; Konya, Gabor; Baracki, Richard; Kelly, Kerry

    2011-07-01

    Chemical Looping Combustion (CLC) is one promising fuel-combustion technology, which can facilitate economic CO2 capture in coal-fired power plants. It employs the oxidation/reduction characteristics of a metal, or oxygen carrier, and its oxide, the oxidizing gas (typically air) and the fuel source may be kept separate. This work focused on two classes of oxygen carrier, one that merely undergoes a change in oxidation state, such as Fe3O4/Fe2O3 and one that is converted from its higher to its lower oxidation state by the release of oxygen on heating, i.e., CuO/Cu2O. This topical report discusses the results of four complementary efforts: (1) the development of process and economic models to optimize important design considerations, such as oxygen carrier circulation rate, temperature, residence time; (2) the development of high-performance simulation capabilities for fluidized beds and the collection, parameter identification, and preliminary verification/uncertainty quantification (3) the exploration of operating characteristics in the laboratory-scale bubbling bed reactor, with a focus on the oxygen carrier performance, including reactivity, oxygen carrying capacity, attrition resistance, resistance to deactivation, cost and availability (4) the identification of mechanisms and rates for the copper, cuprous oxide, and cupric oxide system using thermogravimetric analysis.

  3. Automatic NMR-based identification of chemical reaction types in mixtures of co-occurring reactions.

    PubMed

    Latino, Diogo A R S; Aires-de-Sousa, João

    2014-01-01

    The combination of chemoinformatics approaches with NMR techniques and the increasing availability of data allow the resolution of problems far beyond the original application of NMR in structure elucidation/verification. The diversity of applications can range from process monitoring, metabolic profiling, authentication of products, to quality control. An application related to the automatic analysis of complex mixtures concerns mixtures of chemical reactions. We encoded mixtures of chemical reactions with the difference between the (1)H NMR spectra of the products and the reactants. All the signals arising from all the reactants of the co-occurring reactions were taken together (a simulated spectrum of the mixture of reactants) and the same was done for products. The difference spectrum is taken as the representation of the mixture of chemical reactions. A data set of 181 chemical reactions was used, each reaction manually assigned to one of 6 types. From this dataset, we simulated mixtures where two reactions of different types would occur simultaneously. Automatic learning methods were trained to classify the reactions occurring in a mixture from the (1)H NMR-based descriptor of the mixture. Unsupervised learning methods (self-organizing maps) produced a reasonable clustering of the mixtures by reaction type, and allowed the correct classification of 80% and 63% of the mixtures in two independent test sets of different similarity to the training set. With random forests (RF), the percentage of correct classifications was increased to 99% and 80% for the same test sets. The RF probability associated to the predictions yielded a robust indication of their reliability. This study demonstrates the possibility of applying machine learning methods to automatically identify types of co-occurring chemical reactions from NMR data. Using no explicit structural information about the reactions participants, reaction elucidation is performed without structure elucidation of

  4. Matrix isolation as a tool for studying interstellar chemical reactions

    NASA Technical Reports Server (NTRS)

    Ball, David W.; Ortman, Bryan J.; Hauge, Robert H.; Margrave, John L.

    1989-01-01

    Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

  5. An Efficient Chemical Reaction Optimization Algorithm for Multiobjective Optimization.

    PubMed

    Bechikh, Slim; Chaabani, Abir; Ben Said, Lamjed

    2015-10-01

    Recently, a new metaheuristic called chemical reaction optimization was proposed. This search algorithm, inspired by chemical reactions launched during collisions, inherits several features from other metaheuristics such as simulated annealing and particle swarm optimization. This fact has made it, nowadays, one of the most powerful search algorithms in solving mono-objective optimization problems. In this paper, we propose a multiobjective variant of chemical reaction optimization, called nondominated sorting chemical reaction optimization, in an attempt to exploit chemical reaction optimization features in tackling problems involving multiple conflicting criteria. Since our approach is based on nondominated sorting, one of the main contributions of this paper is the proposal of a new quasi-linear average time complexity quick nondominated sorting algorithm; thereby making our multiobjective algorithm efficient from a computational cost viewpoint. The experimental comparisons against several other multiobjective algorithms on a variety of benchmark problems involving various difficulties show the effectiveness and the efficiency of this multiobjective version in providing a well-converged and well-diversified approximation of the Pareto front.

  6. Binuclear metallohydrolases: complex mechanistic strategies for a simple chemical reaction.

    PubMed

    Schenk, Gerhard; Mitić, Nataša; Gahan, Lawrence R; Ollis, David L; McGeary, Ross P; Guddat, Luke W

    2012-09-18

    Binuclear metallohydrolases are a large family of enzymes that require two closely spaced transition metal ions to carry out a plethora of hydrolytic reactions. Representatives include purple acid phosphatases (PAPs), enzymes that play a role in bone metabolism and are the only member of this family with a heterovalent binuclear center in the active form (Fe(3+)-M(2+), M = Fe, Zn, Mn). Other members of this family are urease, which contains a di-Ni(2+) center and catalyzes the breakdown of urea, arginase, which contains a di-Mn(2+) center and catalyzes the final step in the urea cycle, and the metallo-β-lactamases, which contain a di-Zn(2+) center and are virulence factors contributing to the spread of antibiotic-resistant pathogens. Binuclear metallohydrolases catalyze numerous vital reactions and are potential targets of drugs against a wide variety of human disorders including osteoporosis, various cancers, antibiotic resistance, and erectile dysfunctions. These enzymes also tend to catalyze more than one reaction. An example is an organophosphate (OP)-degrading enzyme from Enterobacter aerogenes (GpdQ). Although GpdQ is part of a pathway that is used by bacteria to degrade glycerolphosphoesters, it hydrolyzes a variety of other phosphodiesters and displays low levels of activity against phosphomono- and triesters. Such a promiscuous nature may have assisted the apparent recent evolution of some binuclear metallohydrolases to deal with situations created by human intervention such as OP pesticides in the environment. OP pesticides were first used approximately 70 years ago, and therefore the enzymes that bacteria use to degrade them must have evolved very quickly on the evolutionary time scale. The promiscuous nature of enzymes such as GpdQ makes them ideal candidates for the application of directed evolution to produce new enzymes that can be used in bioremediation and against chemical warfare. In this Account, we review the mechanisms employed by binuclear

  7. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions

    PubMed Central

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-01-01

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea’) decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea’ under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea’ was determined. MW irradiation energy was partially transformed to reduce the Ea’, and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology. PMID:27118640

  8. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions

    NASA Astrophysics Data System (ADS)

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-04-01

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea’) decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea’ under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea’ was determined. MW irradiation energy was partially transformed to reduce the Ea’, and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology.

  9. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions.

    PubMed

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-04-27

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea') decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea' under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea' was determined. MW irradiation energy was partially transformed to reduce the Ea', and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology.

  10. A new type of power energy for accelerating chemical reactions: the nature of a microwave-driving force for accelerating chemical reactions.

    PubMed

    Zhou, Jicheng; Xu, Wentao; You, Zhimin; Wang, Zhe; Luo, Yushang; Gao, Lingfei; Yin, Cheng; Peng, Renjie; Lan, Lixin

    2016-01-01

    The use of microwave (MW) irradiation to increase the rate of chemical reactions has attracted much attention recently in nearly all fields of chemistry due to substantial enhancements in reaction rates. However, the intrinsic nature of the effects of MW irradiation on chemical reactions remains unclear. Herein, the highly effective conversion of NO and decomposition of H2S via MW catalysis were investigated. The temperature was decreased by several hundred degrees centigrade. Moreover, the apparent activation energy (Ea') decreased substantially under MW irradiation. Importantly, for the first time, a model of the interactions between microwave electromagnetic waves and molecules is proposed to elucidate the intrinsic reason for the reduction in the Ea' under MW irradiation, and a formula for the quantitative estimation of the decrease in the Ea' was determined. MW irradiation energy was partially transformed to reduce the Ea', and MW irradiation is a new type of power energy for speeding up chemical reactions. The effect of MW irradiation on chemical reactions was determined. Our findings challenge both the classical view of MW irradiation as only a heating method and the controversial MW non-thermal effect and open a promising avenue for the development of novel MW catalytic reaction technology. PMID:27118640

  11. Identifying individual chemical bonds in single-molecule chemical reaction products using nc-AFM

    NASA Astrophysics Data System (ADS)

    Wickenburg, Sebastian; de Oteyza, Dimas G.; Chen, Yen-Chia; Riss, Alexander; Tsai, Hsin-Zon; Pedramrazi, Zahra; Bradley, Aaron J.; Ugeda, Miguel M.; Gorman, Patrick; Etkin, Grisha; Mowbray, Duncan J.; Perez, Alejandro; Rubio, Angel; Crommie, Michael F.; Fischer, Felix R.

    2014-03-01

    Determining reaction pathways and products is an integral part of chemical synthesis. Ensemble measurements are commonly used, but identifying products of complex reactions at surfaces presents a significant challenge. Here we present a non-contact AFM (nc-AFM) study to directly address this issue. We followed the change of the chemical structures, from reactants to products of enediyne cyclization reactions on metal surfaces. Thermal annealing of enediynes induced a series of cyclization cascades leading to radical species and the formation of dimers. Atomically resolved nc-AFM images reveal the precise chemical structure and the formation of chemical bonds between single molecular units. With the support of DFT calculations, we identified the underlying chemical pathways and barriers, demonstrating the potential of this atomically resolved AFM technique to study unknown reaction products in surface chemistry at the single-molecule level.

  12. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    PubMed Central

    2015-01-01

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys.2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum under DFT by several fold. The approach also shows promise for free energy calculations when thermal noise can be controlled. PMID:25516726

  13. STM CONTROL OF CHEMICAL REACTIONS: Single-Molecule Synthesis

    NASA Astrophysics Data System (ADS)

    Hla, Saw-Wai; Rieder, Karl-Heinz

    2003-10-01

    The fascinating advances in single atom/molecule manipulation with a scanning tunneling microscope (STM) tip allow scientists to fabricate atomic-scale structures or to probe chemical and physical properties of matters at an atomic level. Owing to these advances, it has become possible for the basic chemical reaction steps, such as dissociation, diffusion, adsorption, readsorption, and bond-formation processes, to be performed by using the STM tip. Complete sequences of chemical reactions are able to induce at a single-molecule level. New molecules can be constructed from the basic molecular building blocks on a one-molecule-at-a-time basis by using a variety of STM manipulation schemes in a systematic step-by-step manner. These achievements open up entirely new opportunities in nanochemistry and nanochemical technology. In this review, various STM manipulation techniques useful in the single-molecule reaction process are reviewed, and their impact on the future of nanoscience and technology are discussed.

  14. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    DOE PAGES

    Kale, Seyit; Sode, Olaseni; Weare, Jonathan; Dinner, Aaron R.

    2014-11-07

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys. 2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum undermore » DFT by several fold. In conclusion, the approach also shows promise for free energy calculations when thermal noise can be controlled.« less

  15. Finding Chemical Reaction Paths with a Multilevel Preconditioning Protocol

    SciTech Connect

    Kale, Seyit; Sode, Olaseni; Weare, Jonathan; Dinner, Aaron R.

    2014-11-07

    Finding transition paths for chemical reactions can be computationally costly owing to the level of quantum-chemical theory needed for accuracy. Here, we show that a multilevel preconditioning scheme that was recently introduced (Tempkin et al. J. Chem. Phys. 2014, 140, 184114) can be used to accelerate quantum-chemical string calculations. We demonstrate the method by finding minimum-energy paths for two well-characterized reactions: tautomerization of malonaldehyde and Claissen rearrangement of chorismate to prephanate. For these reactions, we show that preconditioning density functional theory (DFT) with a semiempirical method reduces the computational cost for reaching a converged path that is an optimum under DFT by several fold. In conclusion, the approach also shows promise for free energy calculations when thermal noise can be controlled.

  16. Chemical reactions on solid surfaces of astrophysical interest

    NASA Astrophysics Data System (ADS)

    Biham, Ofer; Pirronello, Valerio; Vidali, Gianfranco

    Observed abundances of chemical species in interstellar clouds can be explained in most cases by reaction schemes involving only species in the gas phase. There is however clear evidence that reactions occurring on the surface of dust grains, helping the formation of key molecules, play a fundamental role into shaping the universe as we see it today. In this chapter we focus our attention on surface reactions on solids and in conditions close to those encountered in interstellar clouds. We will describe how experimental techniques of surface science have been used to study the recombination reaction of hydrogen on interstellar dust grain analogues and the oxidation of carbon monoxide in the interaction of oxygen atoms in water ice layers. Using theoretical methods and computer simulations, we show that it is possible to relate experimental results obtained in the laboratory to actual physical and chemical processes occurring in the interstellar space.

  17. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, James R.; Dodson, Michael G.

    1999-01-01

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846.

  18. Method and apparatus for controlling gas evolution from chemical reactions

    DOEpatents

    Skorpik, J.R.; Dodson, M.G.

    1999-05-25

    The present invention is directed toward monitoring a thermally driven gas evolving chemical reaction with an acoustic apparatus. Signals from the acoustic apparatus are used to control a heater to prevent a run-away condition. A digestion module in combination with a robotic arm further automate physical handling of sample material reaction vessels. The invention is especially useful for carrying out sample procedures defined in EPA Methods SW-846. 8 figs.

  19. A network dynamics approach to chemical reaction networks

    NASA Astrophysics Data System (ADS)

    van der Schaft, A. J.; Rao, S.; Jayawardhana, B.

    2016-04-01

    A treatment of a chemical reaction network theory is given from the perspective of nonlinear network dynamics, in particular of consensus dynamics. By starting from the complex-balanced assumption, the reaction dynamics governed by mass action kinetics can be rewritten into a form which allows for a very simple derivation of a number of key results in the chemical reaction network theory, and which directly relates to the thermodynamics and port-Hamiltonian formulation of the system. Central in this formulation is the definition of a balanced Laplacian matrix on the graph of chemical complexes together with a resulting fundamental inequality. This immediately leads to the characterisation of the set of equilibria and their stability. Furthermore, the assumption of complex balancedness is revisited from the point of view of Kirchhoff's matrix tree theorem. Both the form of the dynamics and the deduced behaviour are very similar to consensus dynamics, and provide additional perspectives to the latter. Finally, using the classical idea of extending the graph of chemical complexes by a 'zero' complex, a complete steady-state stability analysis of mass action kinetics reaction networks with constant inflows and mass action kinetics outflows is given, and a unified framework is provided for structure-preserving model reduction of this important class of open reaction networks.

  20. Equilibriumlike behavior in chemical reaction networks far from equilibrium.

    PubMed

    Lubensky, David K

    2010-06-01

    In an equilibrium chemical reaction mixture, the number of molecules present obeys a Poisson distribution. We report that, surprisingly, the same is true of a large class of nonequilibrium reaction networks. In particular, we show that certain topological features imply a Poisson distribution, whatever the reaction rates. Such driven systems also obey an analog of the fluctuation-dissipation theorem. Our results shed light on the fundamental question of when equilibrium concepts might apply to nonequilibrium systems and may have applications to models of noise in biochemical networks.

  1. Nucleic Acid Templated Chemical Reaction in a Live Vertebrate

    PubMed Central

    2016-01-01

    Nucleic acid templated reactions are enabled by the hybridization of probe-reagent conjugates resulting in high effective reagent concentration and fast chemical transformation. We have developed a reaction that harnesses cellular microRNA (miRNA) to yield the cleavage of a linker releasing fluorogenic rhodamine in a live vertebrate. The reaction is based on the catalytic photoreduction of an azide by a ruthenium complex. We showed that this system reports specific expression of miRNA in living tissues of a vertebrate. PMID:27413783

  2. Nucleic Acid Templated Chemical Reaction in a Live Vertebrate.

    PubMed

    Holtzer, Laurent; Oleinich, Igor; Anzola, Marcello; Lindberg, Eric; Sadhu, Kalyan K; Gonzalez-Gaitan, Marcos; Winssinger, Nicolas

    2016-06-22

    Nucleic acid templated reactions are enabled by the hybridization of probe-reagent conjugates resulting in high effective reagent concentration and fast chemical transformation. We have developed a reaction that harnesses cellular microRNA (miRNA) to yield the cleavage of a linker releasing fluorogenic rhodamine in a live vertebrate. The reaction is based on the catalytic photoreduction of an azide by a ruthenium complex. We showed that this system reports specific expression of miRNA in living tissues of a vertebrate.

  3. Chemical pathways in ultracold reactions of SrF molecules

    SciTech Connect

    Meyer, Edmund R.; Bohn, John L.

    2011-03-15

    We present a theoretical investigation of the chemical reaction SrF + SrF {yields} products, focusing on reactions at ultralow temperatures. We find that bond swapping SrF + SrF {yields} Sr{sub 2} + F{sub 2} is energetically forbidden at these temperatures. Rather, the only energetically allowed reaction is SrF + SrF {yields} SrF{sub 2} + Sr, and even then only singlet states of the SrF{sub 2} trimer can form. A calculation along a reduced reaction path demonstrates that this abstraction reaction is barrierless and proceeds by one SrF molecule ''handing off'' a fluorine atom to the other molecule.

  4. Researches on Preliminary Chemical Reactions in Spark-Ignition Engines

    NASA Technical Reports Server (NTRS)

    Muehlner, E.

    1943-01-01

    Chemical reactions can demonstrably occur in a fuel-air mixture compressed in the working cylinder of an Otto-cycle (spark ignition) internal-combustion engine even before the charge is ignited by the flame proceeding from the sparking plug. These are the so-called "prelinminary reactions" ("pre-flame" combustion or oxidation), and an exact knowledge of their characteristic development is of great importance for a correct appreciation of the phenomena of engine-knock (detonation), and consequently for its avoidance. Such reactions can be studied either in a working engine cylinder or in a combustion bomb. The first method necessitates a complicated experimental technique, while the second has the disadvantage of enabling only a single reaction to be studied at one time. Consequently, a new series of experiments was inaugurated, conducted in a motored (externally-driven) experimental engine of mixture-compression type, without ignition, the resulting preliminary reactions being detectable and measurable thermometrically.

  5. Reduction of chemical reaction networks through delay distributions.

    PubMed

    Barrio, Manuel; Leier, André; Marquez-Lago, Tatiana T

    2013-03-14

    Accurate modelling and simulation of dynamic cellular events require two main ingredients: an adequate description of key chemical reactions and simulation of such chemical events in reasonable time spans. Quite logically, posing the right model is a crucial step for any endeavour in Computational Biology. However, more often than not, it is the associated computational costs which actually limit our capabilities of representing complex cellular behaviour. In this paper, we propose a methodology aimed at representing chains of chemical reactions by much simpler, reduced models. The abridgement is achieved by generation of model-specific delay distribution functions, consecutively fed to a delay stochastic simulation algorithm. We show how such delay distributions can be analytically described whenever the system is solely composed of consecutive first-order reactions, with or without additional "backward" bypass reactions, yielding an exact reduction. For models including other types of monomolecular reactions (constitutive synthesis, degradation, or "forward" bypass reactions), we discuss why one must adopt a numerical approach for its accurate stochastic representation, and propose two alternatives for this. In these cases, the accuracy depends on the respective numerical sample size. Our model reduction methodology yields significantly lower computational costs while retaining accuracy. Quite naturally, computational costs increase alongside network size and separation of time scales. Thus, we expect our model reduction methodologies to significantly decrease computational costs in these instances. We anticipate the use of delays in model reduction will greatly alleviate some of the current restrictions in simulating large sets of chemical reactions, largely applicable in pharmaceutical and biological research.

  6. Reduction of chemical reaction networks through delay distributions

    NASA Astrophysics Data System (ADS)

    Barrio, Manuel; Leier, André; Marquez-Lago, Tatiana T.

    2013-03-01

    Accurate modelling and simulation of dynamic cellular events require two main ingredients: an adequate description of key chemical reactions and simulation of such chemical events in reasonable time spans. Quite logically, posing the right model is a crucial step for any endeavour in Computational Biology. However, more often than not, it is the associated computational costs which actually limit our capabilities of representing complex cellular behaviour. In this paper, we propose a methodology aimed at representing chains of chemical reactions by much simpler, reduced models. The abridgement is achieved by generation of model-specific delay distribution functions, consecutively fed to a delay stochastic simulation algorithm. We show how such delay distributions can be analytically described whenever the system is solely composed of consecutive first-order reactions, with or without additional "backward" bypass reactions, yielding an exact reduction. For models including other types of monomolecular reactions (constitutive synthesis, degradation, or "forward" bypass reactions), we discuss why one must adopt a numerical approach for its accurate stochastic representation, and propose two alternatives for this. In these cases, the accuracy depends on the respective numerical sample size. Our model reduction methodology yields significantly lower computational costs while retaining accuracy. Quite naturally, computational costs increase alongside network size and separation of time scales. Thus, we expect our model reduction methodologies to significantly decrease computational costs in these instances. We anticipate the use of delays in model reduction will greatly alleviate some of the current restrictions in simulating large sets of chemical reactions, largely applicable in pharmaceutical and biological research.

  7. Effects of incomplete mixing on chemical reactions under flow heterogeneities.

    NASA Astrophysics Data System (ADS)

    Perez, Lazaro; Hidalgo, Juan J.; Dentz, Marco

    2016-04-01

    Evaluation of the mixing process in aquifers is of primary importance when assessing attenuation of pollutants. In aquifers different hydraulic and chemical properties can increase mixing and spreading of the transported species. Mixing processes control biogeochemical transformations such as precipitation/dissolution reactions or degradation reactions that are fast compared to mass transfer processes. Reactions are local phenomena that fluctuate at the pore scale, but predictions are often made at much larger scales. However, aquifer heterogeities are found at all scales and generates flow heterogeneities which creates complex concentration distributions that enhances mixing. In order to assess the impact of spatial flow heterogeneities at pore scale we study concentration profiles, gradients and reaction rates using a random walk particle tracking (RWPT) method and kernel density estimators to reconstruct concentrations and gradients in two setups. First, we focus on a irreversible bimolecular reaction A+B → C under homogeneous flow to distinguish phenomena of incomplete mixing of reactants from finite-size sampling effects. Second, we analise a fast reversible bimolecular chemical reaction A+B rightleftharpoons C in a laminar Poiseuille flow reactor to determine the difference between local and global reaction rates caused by the incomplete mixing under flow heterogeneities. Simulation results for the first setup differ from the analytical solution of the continuum scale advection-dispersion-reaction equation studied by Gramling et al. (2002), which results in an overstimation quantity of reaction product (C). In the second setup, results show that actual reaction rates are bigger than the obtained from artificially mixing the system by averaging the concentration vertically. - LITERATURE Gramling, C. M.,Harvey, C. F., Meigs, and L. C., (2002). Reactive transport in porous media: A comparison of model prediction with laboratory visualization, Environ. Sci

  8. Program Helps To Determine Chemical-Reaction Mechanisms

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Radhakrishnan, K.

    1995-01-01

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

  9. Supersonic molecular beam experiments on surface chemical reactions.

    PubMed

    Okada, Michio

    2014-10-01

    The interaction of a molecule and a surface is important in various fields, and in particular in complex systems like biomaterials and their related chemistry. However, the detailed understanding of the elementary steps in the surface chemistry, for example, stereodynamics, is still insufficient even for simple model systems. In this Personal Account, I review our recent studies of chemical reactions on single-crystalline Cu and Si surfaces induced by hyperthermal oxygen molecular beams and by oriented molecular beams, respectively. Studies of oxide formation on Cu induced by hyperthermal molecular beams demonstrate a significant role of the translational energy of the incident molecules. The use of hyperthermal molecular beams enables us to open up new chemical reaction paths specific for the hyperthermal energy region, and to develop new methods for the fabrication of thin films. On the other hand, oriented molecular beams also demonstrate the possibility of understanding surface chemical reactions in detail by varying the orientation of the incident molecules. The steric effects found on Si surfaces hint at new ways of material fabrication on Si surfaces. Controlling the initial conditions of incoming molecules is a powerful tool for finely monitoring the elementary step of the surface chemical reactions and creating new materials on surfaces.

  10. Quantum and semiclassical theories of chemical reaction rates

    SciTech Connect

    Miller, W.H. |

    1995-09-01

    A rigorous quantum mechanical theory (and a semiclassical approximation thereto) is described for calculating chemical reaction rates ``directly``, i.e., without having to solve the complete state-to-state reactive scattering problem. The approach has many vestiges of transition state theory, for which it may be thought of as the rigorous generalization.

  11. 2011 Chemical Reactions at Surfaces Gordon Research Conference

    SciTech Connect

    Peter Stair

    2011-02-11

    The Gordon Research Conference on Chemical Reactions at Surfaces is dedicated to promoting and advancing the fundamental science of interfacial chemistry and physics by providing surface scientists with the foremost venue for presentation and discussion of research occurring at the frontiers of their fields.

  12. Chemical Reaction Engineering: Current Status and Future Directions.

    ERIC Educational Resources Information Center

    Dudukovic, M. P.

    1987-01-01

    Describes Chemical Reaction Engineering (CRE) as the discipline that quantifies the interplay of transport phenomena and kinetics in relating reactor performance to operating conditions and input variables. Addresses the current status of CRE in both academic and industrial settings and outlines future trends. (TW)

  13. Prediction of Rate Constants for Catalytic Reactions with Chemical Accuracy.

    PubMed

    Catlow, C Richard A

    2016-08-01

    Ex machina: A computational method for predicting rate constants for reactions within microporous zeolite catalysts with chemical accuracy has recently been reported. A key feature of this method is a stepwise QM/MM approach that allows accuracy to be achieved while using realistic models with accessible computer resources.

  14. Mapping students' ideas about chemical reactions at different educational levels

    NASA Astrophysics Data System (ADS)

    Yan, Fan

    Understanding chemical reactions is crucial in learning chemistry at all educational levels. Nevertheless, research in science education has revealed that many students struggle to understand chemical processes. Improving teaching and learning about chemical reactions demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the discipline. Thus, we have carried out a qualitative study using semi-structured interviews as the main data collection tool to explore students reasoning about reaction mechanism and causality. The participants of this study included students at different levels of training in chemistry: general chemistry students (n=22), organic chemistry students (n=16), first year graduate students (n=13) and Ph.D. candidates (n=14). We identified major conceptual modes along critical dimensions of analysis, and illustrated common ways of reasoning using typical cases. Main findings indicate that although significant progress is observed in student reasoning in some areas, major conceptual difficulties seem to persist even at the more advanced educational levels. In addition, our findings suggest that students struggle to integrate important concepts when thinking about mechanism and causality in chemical reactions. The results of our study are relevant to chemistry educators interested in learning progressions, assessment, and conceptual development.

  15. Molecular codes in biological and chemical reaction networks.

    PubMed

    Görlich, Dennis; Dittrich, Peter

    2013-01-01

    Shannon's theory of communication has been very successfully applied for the analysis of biological information. However, the theory neglects semantic and pragmatic aspects and thus cannot directly be applied to distinguish between (bio-) chemical systems able to process "meaningful" information from those that do not. Here, we present a formal method to assess a system's semantic capacity by analyzing a reaction network's capability to implement molecular codes. We analyzed models of chemical systems (martian atmosphere chemistry and various combustion chemistries), biochemical systems (gene expression, gene translation, and phosphorylation signaling cascades), an artificial chemistry, and random reaction networks. Our study suggests that different chemical systems possess different semantic capacities. No semantic capacity was found in the model of the martian atmosphere chemistry, the studied combustion chemistries, and highly connected random networks, i.e. with these chemistries molecular codes cannot be implemented. High semantic capacity was found in the studied biochemical systems and in random reaction networks where the number of second order reactions is twice the number of species. We conclude that our approach can be applied to evaluate the information processing capabilities of a chemical system and may thus be a useful tool to understand the origin and evolution of meaningful information, e.g. in the context of the origin of life.

  16. Molecular Codes in Biological and Chemical Reaction Networks

    PubMed Central

    Görlich, Dennis; Dittrich, Peter

    2013-01-01

    Shannon’s theory of communication has been very successfully applied for the analysis of biological information. However, the theory neglects semantic and pragmatic aspects and thus cannot directly be applied to distinguish between (bio-) chemical systems able to process “meaningful” information from those that do not. Here, we present a formal method to assess a system’s semantic capacity by analyzing a reaction network’s capability to implement molecular codes. We analyzed models of chemical systems (martian atmosphere chemistry and various combustion chemistries), biochemical systems (gene expression, gene translation, and phosphorylation signaling cascades), an artificial chemistry, and random reaction networks. Our study suggests that different chemical systems posses different semantic capacities. No semantic capacity was found in the model of the martian atmosphere chemistry, the studied combustion chemistries, and highly connected random networks, i.e. with these chemistries molecular codes cannot be implemented. High semantic capacity was found in the studied biochemical systems and in random reaction networks where the number of second order reactions is twice the number of species. We conclude that our approach can be applied to evaluate the information processing capabilities of a chemical system and may thus be a useful tool to understand the origin and evolution of meaningful information, e.g. in the context of the origin of life. PMID:23372756

  17. Computer simulation of chemical reactions in porous materials

    NASA Astrophysics Data System (ADS)

    Turner, Christoffer Heath

    Understanding reactions in nanoporous materials from a purely experimental perspective is a difficult task. Measuring the chemical composition of a reacting system within a catalytic material is usually only accomplished through indirect methods, and it is usually impossible to distinguish between true chemical equilibrium and metastable states. In addition, measuring molecular orientation or distribution profiles within porous systems is not easily accomplished. However, molecular simulation techniques are well-suited to these challenges. With appropriate simulation techniques and realistic molecular models, it is possible to validate the dominant physical and chemical forces controlling nanoscale reactivity. Novel nanostructured catalysts and supports can be designed, optimized, and tested using high-performance computing and advanced modeling techniques in order to guide the search for next-generation catalysts---setting new targets for the materials synthesis community. We have simulated the conversion of several different equilibrium-limited reactions within microporous carbons and we find that the pore size, pore geometry, and surface chemistry are important factors for determining the reaction yield. The equilibrium-limited reactions that we have modeled include nitric oxide dimerization, ammonia synthesis, and the esterification of acetic acid, all of which show yield enhancements within microporous carbons. In conjunction with a yield enhancement of the esterification reaction, selective adsorption of ethyl acetate within carbon micropores demonstrates an efficient method for product recovery. Additionally, a new method has been developed for simulating reaction kinetics within porous materials and other heterogeneous environments. The validity of this technique is first demonstrated by reproducing the kinetics of hydrogen iodide decomposition in the gas phase, and then predictions are made within slit-shaped carbon pores and carbon nanotubes. The rate

  18. Mixing, chemical reaction and flow field development in ducted rockets

    SciTech Connect

    Vanka, S.P.; Craig, R.R.; Stull, F.D.

    1984-09-01

    Calculations have been made of the three-dimensional mixing, chemical reaction, and flow field development in a typical ducted rocket configuration. The governing partial differential equations are numerically solved by an iterative finite-difference solution procedure. The physical models include the k approx. epsilon turbulence model, one-step reaction, and mixing controlled chemical reaction rate. Radiation is neglected. The mean flow structure, fuel dispersal patterns, and temperature field are presented in detail for a base configuration with 0.058 m (2 in.) dome height, 45/sup 0/ side arm inclination, and with gaseous ethylene injected from the dome plate at an eccentric location. In addition, the influences of the geometrical parameters such as dome height, inclination of the side arms, and location of the fuel injector are studied.

  19. Coriolis coupling and nonadiabaticity in chemical reaction dynamics.

    PubMed

    Wu, Emilia L

    2010-12-01

    The nonadiabatic quantum dynamics and Coriolis coupling effect in chemical reaction have been reviewed, with emphasis on recent progress in using the time-dependent wave packet approach to study the Coriolis coupling and nonadiabatic effects, which was done by K. L. Han and his group. Several typical chemical reactions, for example, H+D(2), F+H(2)/D(2)/HD, D(+)+H(2), O+H(2), and He+H(2)(+), have been discussed. One can find that there is a significant role of Coriolis coupling in reaction dynamics for the ion-molecule collisions of D(+)+H(2), Ne+H(2)(+), and He+H(2)(+) in both adiabatic and nonadiabatic context.

  20. Density functional study of chemical reaction equilibrium for dimerization reactions in slit and cylindrical nanopores.

    PubMed

    Malijevský, Alexandr; Lísal, Martin

    2009-04-28

    We present a theoretical study of the effects of confinement on chemical reaction equilibrium in slit and cylindrical nanopores. We use a density functional theory (DFT) to investigate the effects of temperature, pore geometry, bulk pressure, transition layering, and capillary condensation on a dimerization reaction that mimics the nitric oxide dimerization reaction, 2NO <==> (NO)(2), in carbonlike slit and cylindrical nanopores in equilibrium with a vapor reservoir. In addition to the DFT calculations, we also utilize the reaction ensemble Monte Carlo method to supplement the DFT results for reaction conversion. This work is an extension of the previous DFT study by Tripathi and Chapman [J. Chem. Phys. 118, 7993 (2003)] on the dimerization reactions confined in the planar slits.

  1. Development of a chemical oxygen - iodine laser with production of atomic iodine in a chemical reaction

    SciTech Connect

    Censky, M; Spalek, O; Jirasek, V; Kodymova, J; Jakubec, I

    2009-11-30

    The alternative method of atomic iodine generation for a chemical oxygen - iodine laser (COIL) in chemical reactions with gaseous reactants is investigated experimentally. The influence of the configuration of iodine atom injection into the laser cavity on the efficiency of the atomic iodine generation and small-signal gain is studied. (lasers)

  2. Students' Understandings of Chemical Bonds and the Energetics of Chemical Reactions.

    ERIC Educational Resources Information Center

    Boo, Hong Kwen

    1998-01-01

    Investigates Grade 12 students' understandings of the nature of chemical bonds and the energetics elicited across five familiar chemical reactions following a course of instruction. Discusses the many ways in which students can misconstruct concepts and principles. Contains 63 references. (DDR)

  3. Enhancement of activated sludge dewatering performance by combined composite enzymatic lysis and chemical re-flocculation with inorganic coagulants: Kinetics of enzymatic reaction and re-flocculation morphology.

    PubMed

    Chen, Zhan; Zhang, Weijun; Wang, Dongsheng; Ma, Teng; Bai, Runying

    2015-10-15

    The feasibility of combined process of composite enzymatic treatment and chemical flocculation with inorganic salt coagulants was investigated in this study. The evolution of extracellular polymeric substances (EPS) distribution, composition and morphological properties were analyzed to unravel the sludge conditioning mechanism. It was found that sludge filtration performance was deteriorated due to release of a large amount of biopolymers after enzymatic treatment. The change in EPS followed the pseudo-first-order kinetic equation well under enzymatic treatment. The feeding modes of enzymes had a significant influence on sludge lysis efficiency under compound enzymes treatment. Alpha amylase + protease was more effective in solubilization than other two addition modes (protease + α-amylase or simultaneous addition). The sludge floc re-formed and macromolecule biopolymers were effectively removed through coagulation process. At the same time, both of filtration rate and cake solid content of sludge treated with enzymes were improved with increasing dosage of coagulants, and ferric iron (FeCl3) had better performance in sludge dewaterability enhancement than polyaluminium chloride (PACl). In addition, sludge filtration property was slightly deteriorated, while the cake moisture reduction was favored at the optimal dosage of inorganic coagulants.

  4. PDF calculation of scalar mixing layer with simple chemical reactions

    NASA Astrophysics Data System (ADS)

    Kanzaki, Takao; Pope, Stephen B.

    1999-11-01

    A joint velocity-composition-turbulent frequency PDF(JPDF) model is used to simulate reactive mixing layer in a grid-generated turbulence with the influence of second-order irreversible chemical reactions. To investigate the effects of molecular mixing, a gas flow and a liquid flow are simulated. For a gas flow, the oxidation reaction (NO+ O3 arrow NO2 +O2 ) between nitricoxide (NO) and ozone (O3 ) is used. For a liquid flow, the saponification reaction(NaOH+HCOOCH3 arrow HCOONa+CH_3OH) between sodiumhydroxide(NaOH) and methylformate(HCOOCH_3) is used. The both cases are moderately fast reactions. Therefore, reactive scalar statistics are affected by turbulent mixing. The results of caliculation are compared with experimental data of Komori et al.(1994) and Bilger et al.(1991)

  5. Chemical research on red pigments after adverse reactions to tattoo.

    PubMed

    Tammaro, A; Toniolo, C; Giulianelli, V; Serafini, M; Persechino, S

    2016-03-01

    Currently, the incidence of tattooing is on the rise compared to the past, especially among adolescents, and it leads to the urgency of monitoring the security status of tattooing centers, as well as to inform people about the risks of tattoo practice. In our clinical experience, 20% of tattooed patients presented adverse reactions, like allergic contact dermatitis, psoriasis with Koebner's phenomena and granulomatous reactions, with the latter most prevalent and most often related to red pigment. Adverse reactions to tattoo pigments, especially the red one, are well known and described in literature. Great attention has to be focused on the pigments used, especially for the presence of new substances, often not well known. For this reason, we decided to perform a study on 12 samples of red tattoo ink, obtained by patients affected by different cutaneous reactions in the site of tattoo, to analyze their chemical composition. PMID:26934738

  6. Chemical research on red pigments after adverse reactions to tattoo.

    PubMed

    Tammaro, A; Toniolo, C; Giulianelli, V; Serafini, M; Persechino, S

    2016-03-01

    Currently, the incidence of tattooing is on the rise compared to the past, especially among adolescents, and it leads to the urgency of monitoring the security status of tattooing centers, as well as to inform people about the risks of tattoo practice. In our clinical experience, 20% of tattooed patients presented adverse reactions, like allergic contact dermatitis, psoriasis with Koebner's phenomena and granulomatous reactions, with the latter most prevalent and most often related to red pigment. Adverse reactions to tattoo pigments, especially the red one, are well known and described in literature. Great attention has to be focused on the pigments used, especially for the presence of new substances, often not well known. For this reason, we decided to perform a study on 12 samples of red tattoo ink, obtained by patients affected by different cutaneous reactions in the site of tattoo, to analyze their chemical composition.

  7. Active Chemical Thermodynamics promoted by activity of cortical actin

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Bhaswati; Chaudhuri, Abhishek; Gowrishankar, Kripa; Rao, Madan

    2011-03-01

    The spatial distribution and dynamics of formation and breakup of the nanoclusters of cell surface proteins is controlled by the active remodeling dynamics of the underlying cortical actin. To explain these observations, we have proposed a novel mechanism of nanoclustering, involving the transient binding to and advection along constitutively occuring ``asters'' of cortical actin. We study the consequences of such active actin-based clustering, in the context of chemical reactions involving conformational changes of cell surface proteins. We find that the active remodeling of cortical actin, can give rise to a dramatic increase in efficiency and extent of conformational spread, even at low levels of expression at the cell surface. We define a activity temperature (τa) arising due to actin activities which can be used to describe chemical thermodynamics of the system. We plot TTT (time-temparature-transformation) curves and compute the Arrhenius factors which depend on τa . With this, the active asters can be treated as enzymes whose enzymatic reaction rate can be related to the activity.

  8. A Light-Activated Reaction Manifold.

    PubMed

    Hiltebrandt, Kai; Elies, Katharina; D'hooge, Dagmar R; Blinco, James P; Barner-Kowollik, Christopher

    2016-06-01

    We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels. PMID:27151599

  9. Internal Active Thermal Control System (IATCS) Sodium Bicarbonate/Carbonate Buffer in an Open Aqueous Carbon Dioxide System and Corollary Electrochemical/Chemical Reactions Relative to System pH Changes

    NASA Technical Reports Server (NTRS)

    Stegman, Thomas W.; Wilson, Mark E.; Glasscock, Brad; Holt, Mike

    2014-01-01

    The International Space Station (ISS) Internal Active Thermal Control System (IATCS) experienced a number of chemical changes driven by system absorption of CO2 which altered the coolant’s pH. The natural effects of the decrease in pH from approximately 9.2 to less than 8.4 had immediate consequences on system corrosion rates and corrosion product interactions with specified coolant constituents. The alkalinity of the system was increased through the development and implementation of a carbonate/bicarbonate buffer that would increase coolant pH to 9.0 – 10.0 and maintain pH above 9.0 in the presence of ISS cabin concentrations of CO2 up to twenty times higher than ground concentrations. This paper defines how a carbonate/bicarbonate buffer works in an open carbon dioxide system and summarizes the analyses performed on the buffer for safe and effective application in the on-orbit system. The importance of the relationship between the cabin environment and the IATCS is demonstrated as the dominant factor in understanding the system chemistry and pH trends before and after addition of the carbonate/bicarbonate buffer. The paper also documents the corollary electrochemical and chemical reactions the system has experienced and the rationale for remediation of these effects with the addition of the carbonate/bicarbonate buffer.

  10. Theory of rotational transition in atom-diatom chemical reaction

    NASA Astrophysics Data System (ADS)

    Nakamura, Masato; Nakamura, Hiroki

    1989-05-01

    Rotational transition in atom-diatom chemical reaction is theoretically studied. A new approximate theory (which we call IOS-DW approximation) is proposed on the basis of the physical idea that rotational transition in reaction is induced by the following two different mechanisms: rotationally inelastic half collision in both initial and final arrangement channels, and coordinate transformation in the reaction zone. This theory gives a fairy compact expression for the state-to-state transition probability. Introducing the additional physically reasonable assumption that reaction (particle rearrangement) takes place in a spatially localized region, we have reduced this expression into a simpler analytical form which can explicitly give overall rotational state distribution in reaction. Numerical application was made to the H+H2 reaction and demonstrated its effectiveness for the simplicity. A further simplified most naive approximation, i.e., independent events approximation was also proposed and demonstrated to work well in the test calculation of H+H2. The overall rotational state distribution is expressed simply by a product sum of the transition probabilities for the three consecutive processes in reaction: inelastic transition in the initial half collision, transition due to particle rearrangement, and inelastic transition in the final half collision.

  11. Photo-induced chemical reaction of trans-resveratrol.

    PubMed

    Zhao, Yue; Shi, Meng; Ye, Jian-Hui; Zheng, Xin-Qiang; Lu, Jian-Liang; Liang, Yue-Rong

    2015-03-15

    Photo-induced chemical reaction of trans-resveratrol has been studied. UV B, liquid state and sufficient exposure time are essential conditions to the photochemical change of trans-resveratrol. Three principal compounds, cis-resveratrol, 2,4,6-phenanthrenetriol and 2-(4-hydroxyphenyl)-5,6-benzofurandione, were successively generated in the reaction solution of trans-resveratrol (0.25 mM, 100% ethanol) under 100 μW cm(-2) UV B radiation for 4h. cis-Resveratrol, originated from isomerization of trans-resveratrol, resulted in 2,4,6-phenanthrenetriol through photocyclisation reaction meanwhile loss of 2 H. 2,4,6-Phenanthrenetriol played a role of photosensitizer producing singlet oxygen in the reaction pathway. The singlet oxygen triggered [4+2] cycloaddition reaction of trans-resveratrol, and then resulted in the generation of 2-(4-hydroxyphenyl)-5,6-benzofurandione through photorearrangement and oxidation reaction. The singlet oxygen reaction was closely related to the substrate concentration of trans-resveratrol in solution.

  12. A chemical reaction network solver for the astrophysics code NIRVANA

    NASA Astrophysics Data System (ADS)

    Ziegler, U.

    2016-02-01

    Context. Chemistry often plays an important role in astrophysical gases. It regulates thermal properties by changing species abundances and via ionization processes. This way, time-dependent cooling mechanisms and other chemistry-related energy sources can have a profound influence on the dynamical evolution of an astrophysical system. Modeling those effects with the underlying chemical kinetics in realistic magneto-gasdynamical simulations provide the basis for a better link to observations. Aims: The present work describes the implementation of a chemical reaction network solver into the magneto-gasdynamical code NIRVANA. For this purpose a multispecies structure is installed, and a new module for evolving the rate equations of chemical kinetics is developed and coupled to the dynamical part of the code. A small chemical network for a hydrogen-helium plasma was constructed including associated thermal processes which is used in test problems. Methods: Evolving a chemical network within time-dependent simulations requires the additional solution of a set of coupled advection-reaction equations for species and gas temperature. Second-order Strang-splitting is used to separate the advection part from the reaction part. The ordinary differential equation (ODE) system representing the reaction part is solved with a fourth-order generalized Runge-Kutta method applicable for stiff systems inherent to astrochemistry. Results: A series of tests was performed in order to check the correctness of numerical and technical implementation. Tests include well-known stiff ODE problems from the mathematical literature in order to confirm accuracy properties of the solver used as well as problems combining gasdynamics and chemistry. Overall, very satisfactory results are achieved. Conclusions: The NIRVANA code is now ready to handle astrochemical processes in time-dependent simulations. An easy-to-use interface allows implementation of complex networks including thermal processes

  13. Dealing with chemical reaction pathways and electronic excitations in molecular systems via renormalized and active-space coupled-cluster methods

    SciTech Connect

    Piecuch, Piotr; Li, Wei; Lutz, Jesse J.; Włoch, Marta; Gour, Jeffrey R.

    2015-01-22

    Coupled-cluster (CC) theory has become the de facto standard for high-accuracy molecular calculations, but the widely used CC and equation-of-motion (EOM) CC approaches, such as CCSD(T) and EOMCCSD, have difficulties with capturing stronger electron correlations that characterize multi-reference molecular problems. This presentation demonstrates that many of these difficulties can be addressed by exploiting the completely renormalized (CR) CC and EOMCC approaches, such as CR-CC(2,3), CR-EOMCCSD(T), and CR-EOMCC(2,3), and their local correlation counterparts applicable to systems with hundreds of atoms, and the active-space CC/EOMCC approaches, such as CCSDt and EOMCCSDt, and their extensions to valence systems via the electron-attached and ionized formalisms.

  14. Reachability bounds for chemical reaction networks and strand displacement systems.

    PubMed

    Condon, Anne; Kirkpatrick, Bonnie; Maňuch, Ján

    2014-01-01

    Chemical reaction networks (CRNs) and DNA strand displacement systems (DSDs) are widely-studied and useful models of molecular programming. However, in order for some DSDs in the literature to behave in an expected manner, the initial number of copies of some reagents is required to be fixed. In this paper we show that, when multiple copies of all initial molecules are present, general types of CRNs and DSDs fail to work correctly if the length of the shortest sequence of reactions needed to produce any given molecule exceeds a threshold that grows polynomially with attributes of the system.

  15. Tailoring oxidation degrees of graphene oxide by simple chemical reactions

    SciTech Connect

    Wang Gongkai; Sun Xiang; Lian Jie; Liu Changsheng

    2011-08-01

    High quality graphene oxide (GO) with controllable degrees of oxidation was synthesized by simple chemical reactions inspired by approaches to unzip single wall carbon nanotubes using strong oxidizing agents. As compared to the conventional Hummers method, these reactions are less exo-therm involved without emission of toxic gases. The structural characteristics of the synthesized GO with various oxidation degrees were evaluated by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, thermal gravimetric analysis, and UV-vis-IR spectroscopy. GO with tailored degrees of oxidation displays tunable optoelectronic properties and may have a significant impact on developing graphene- or GO-based platforms for various technological applications.

  16. Complex wave patterns in an effective reaction-diffusion model for chemical reactions in microemulsions.

    PubMed

    Alonso, Sergio; John, Karin; Bär, Markus

    2011-03-01

    An effective medium theory is employed to derive a simple qualitative model of a pattern forming chemical reaction in a microemulsion. This spatially heterogeneous system is composed of water nanodroplets randomly distributed in oil. While some steps of the reaction are performed only inside the droplets, the transport through the extended medium occurs by diffusion of intermediate chemical reactants as well as by collisions of the droplets. We start to model the system with heterogeneous reaction-diffusion equations and then derive an equivalent effective spatially homogeneous reaction-diffusion model by using earlier results on homogenization in heterogeneous reaction-diffusion systems [S.Alonso, M.Bär, and R.Kapral, J. Chem. Phys. 134, 214102 (2009)]. We study the linear stability of the spatially homogeneous state in the resulting effective model and obtain a phase diagram of pattern formation, that is qualitatively similar to earlier experimental results for the Belousov-Zhabotinsky reaction in an aerosol OT (AOT)-water-in-oil microemulsion [V.K.Vanag and I.R.Epstein, Phys. Rev. Lett. 87, 228301 (2001)]. Moreover, we reproduce many patterns that have been observed in experiments with the Belousov-Zhabotinsky reaction in an AOT oil-in-water microemulsion by direct numerical simulations.

  17. Laser studies of chemical reaction and collision processes

    SciTech Connect

    Flynn, G.

    1993-12-01

    This work has concentrated on several interrelated projects in the area of laser photochemistry and photophysics which impinge on a variety of questions in combustion chemistry and general chemical kinetics. Infrared diode laser probes of the quenching of molecules with {open_quotes}chemically significant{close_quotes} amounts of energy in which the energy transferred to the quencher has, for the first time, been separated into its vibrational, rotational, and translational components. Probes of quantum state distributions and velocity profiles for atomic fragments produced in photodissociation reactions have been explored for iodine chloride.

  18. Crossed molecular beam studies of atmospheric chemical reaction dynamics

    SciTech Connect

    Zhang, Jingsong

    1993-04-01

    The dynamics of several elementary chemical reactions that are important in atmospheric chemistry are investigated. The reactive scattering of ground state chlorine or bromine atoms with ozone molecules and ground state chlorine atoms with nitrogen dioxide molecules is studied using a crossed molecular beams apparatus with a rotatable mass spectrometer detector. The Cl + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at four collision energies ranging from 6 kcal/mole to 32 kcal/mole. The derived product center-of-mass angular and translational energy distributions show that the reaction has a direct reaction mechanism and that there is a strong repulsion on the exit channel. The ClO product is sideways and forward scattered with respect to the Cl atom, and the translational energy release is large. The Cl atom is most likely to attack the terminal oxygen atom of the ozone molecule. The Br + O{sub 3} {yields} ClO + O{sub 2} reaction has been studied at five collision energies ranging from 5 kcal/mole to 26 kcal/mole. The derived product center-of-mass angular and translational energy distributions are quite similar to those in the Cl + O{sub 3} reaction. The Br + O{sub 3} reaction has a direct reaction mechanism similar to that of the Cl + O{sub 3} reaction. The electronic structure of the ozone molecule seems to play the central role in determining the reaction mechanism in atomic radical reactions with the ozone molecule. The Cl + NO{sub 2} {yields} ClO + NO reaction has been studied at three collision energies ranging from 10.6 kcal/mole to 22.4 kcal/mole. The center-of-mass angular distribution has some forward-backward symmetry, and the product translational energy release is quite large. The reaction proceeds through a short-lived complex whose lifetime is less than one rotational period. The experimental results seem to show that the Cl atom mainly attacks the oxygen atom instead of the nitrogen atom of the NO{sub 2} molecule.

  19. Chemical reaction fouling model for single-phase heat transfer

    SciTech Connect

    Panchal, C.B.; Watkinson, A.P.

    1993-08-01

    A fouling model was developed on the premise that the chemical reaction for generation of precursor can take place in the bulk fluid, in the thermalboundary layer, or at the fluid/wall interface, depending upon the interactive effects of flu id dynamics, heat and mass transfer, and the controlling chemical reaction. The analysis was used to examine the experimental data for fouling deposition of polyperoxides produced by autoxidation of indene in kerosene. The effects of fluid and wall temperatures for two flow geometries were analyzed. The results showed that the relative effects of physical parameters on the fouling rate would differ for the three fouling mechanisms; therefore, it is important to identify the controlling mechanism in applying the closed-flow-loop data to industrial conditions.

  20. Implementation of a vibrationally linked chemical reaction model for DSMC

    NASA Technical Reports Server (NTRS)

    Carlson, A. B.; Bird, Graeme A.

    1994-01-01

    A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

  1. Implementation of a vibrationally linked chemical reaction model for DSMC

    NASA Astrophysics Data System (ADS)

    Carlson, A. B.; Bird, Graeme A.

    1994-04-01

    A new procedure closely linking dissociation and exchange reactions in air to the vibrational levels of the diatomic molecules has been implemented in both one- and two-dimensional versions of Direct Simulation Monte Carlo (DSMC) programs. The previous modeling of chemical reactions with DSMC was based on the continuum reaction rates for the various possible reactions. The new method is more closely related to the actual physics of dissociation and is more appropriate to the particle nature of DSMC. Two cases are presented: the relaxation to equilibrium of undissociated air initially at 10,000 K, and the axisymmetric calculation of shuttle forebody heating during reentry at 92.35 km and 7500 m/s. Although reaction rates are not used in determining the dissociations or exchange reactions, the new method produces rates which agree astonishingly well with the published rates derived from experiment. The results for gas properties and surface properties also agree well with the results produced by earlier DSMC models, equilibrium air calculations, and experiment.

  2. Stochastic Generator of Chemical Structure. 3. Reaction Network Generation

    SciTech Connect

    FAULON,JEAN-LOUP; SAULT,ALLEN G.

    2000-07-15

    A new method to generate chemical reaction network is proposed. The particularity of the method is that network generation and mechanism reduction are performed simultaneously using sampling techniques. Our method is tested for hydrocarbon thermal cracking. Results and theoretical arguments demonstrate that our method scales in polynomial time while other deterministic network generator scale in exponential time. This finding offers the possibility to investigate complex reacting systems such as those studied in petroleum refining and combustion.

  3. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, Frank P.; Herbst, Ronald S.

    1995-01-01

    The isotopes of boron, .sup.10 B and .sup.11 B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF.sub.3 and a liquid BF.sub.3 . donor molecular addition complex formed between BF.sub.3 gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone.

  4. Separation of the isotopes of boron by chemical exchange reactions

    DOEpatents

    McCandless, F.P.; Herbst, R.S.

    1995-05-30

    The isotopes of boron, {sup 10}B and {sup 11}B, are separated by means of a gas-liquid chemical exchange reaction involving the isotopic equilibrium between gaseous BF{sub 3} and a liquid BF{sub 3} donor molecular addition complex formed between BF{sub 3} gas and a donor chosen from the group consisting of: nitromethane, acetone, methyl isobutyl ketone, or diisobutyl ketone. 1 Fig.

  5. Control of Ultracold Chemical Reactions Through Conical Intersections

    NASA Astrophysics Data System (ADS)

    Makrides, Constantinos; Petrov, Alexander; Kotochigova, Svetlana

    2016-05-01

    The pioneering work on obtaining a quantum degenerate sample of ground state KRb molecules is one of the great successes in ultracold physics. The early experimental and theoretical investigations to describe quantum chemical reactions of ultracold KRb molecules with residual ultracold K atoms have been based on probing their inelastic collision loss rates. A natural progression towards control of molecular reactivity would be to study the potential landscape of the collisional complex with the inherited degeneracies and intersections between two lowest electronic states. The topology of these surfaces provide us with a qualitative understanding of the reaction mechanism. Here we study how the ability to prepare unique initial states combined with the presence of conical intersections can be used to control the outcome of ultracold chemical reactions of alkali-metal atoms and molecules. We locate and determine properties of conical intersections for the KRbK molecular system and determine signatures of non-adiabatic passage through the conical intersection to distinguish between relaxation and reaction pathways. This work is supported by the ARO-MURI and NSF Grants.

  6. Phase and chemical equilibria in multicomponent fluid systems with a chemical reaction

    NASA Astrophysics Data System (ADS)

    Toikka, A. M.; Samarov, A. A.; Toikka, M. A.

    2015-04-01

    Studies of the phase and chemical equilibria in the systems with chemical reaction cover a wide range of problems related to both experimental determination of physicochemical characteristics of these systems and various aspects of thermodynamic analysis of the phase and chemical processes occurring there. The main goal of this review consists in systematization and analysis of available experimental data concerning the vapour-liquid and liquid-liquid equilibria in multicomponent systems where chemical reactions occur. The studies considered here have been mainly published in recent years, and they include rather detailed data on physicochemical properties, phase transitions and chemical processes in fluid systems, i.e., the data which are essential for thermodynamic analysis. Available approaches to the thermodynamic analysis of heterogeneous systems with chemical reactions are also discussed. Particular attention is paid to the studies of the simultaneous phase and chemical equilibria. We hope that this review could be useful both for fundamental studies of heterogeneous reactive systems and for solving applied problems on the design of combined reactive and mass-transfer processes. The bibliography includes 79 references.

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

    SciTech Connect

    Gray, S.K.

    1993-12-01

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

  8. Mesoscale simulations of shockwave energy dissipation via chemical reactions

    NASA Astrophysics Data System (ADS)

    Antillon, Edwin; Strachan, Alejandro

    2015-06-01

    We use a particle-based mesoscale model that incorporates chemical reactions at a coarse-grained level to study the response of materials under shockwave-loading conditions. An additional implicit variable (the particle size) is used to describe volume-reducing chemical reactions using an intra-molecular potential inspired by Transition State Theory, while the dynamics of the center-of-mass motion evolves according to inter-particle forces. The equations of motion are derived from a Hamiltonian and the model captures both: total energy conservation and Galilean invariance. We demonstrate that this model captures complex thermo-mechanical-chemical processes, and we use these features to explore materials with the capabilities to dissipate shocks-wave energy due to ballistic impacts. Our results characterize how the parameters of the chemical model affect shock-wave attenuation, and we elucidate on how the coupling between the different energy-transferring mechanisms influences nucleation of chemistry for conditions away from equilibrium.

  9. Physio-chemical reactions in recycle aggregate concrete.

    PubMed

    Tam, Vivian W Y; Gao, X F; Tam, C M; Ng, K M

    2009-04-30

    Concrete waste constitutes the major proportion of construction waste at about 50% of the total waste generated. An effective way to reduce concrete waste is to reuse it as recycled aggregate (RA) for the production of recycled aggregate concrete (RAC). This paper studies the physio-chemical reactions of cement paste around aggregate for normal aggregate concrete (NAC) and RAC mixed with normal mixing approach (NMA) and two-stage mixing approach (TSMA) by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Four kinds of physio-chemical reactions have been recorded from the concrete samples, including the dehydration of C(3)S(2)H(3), iron-substituted ettringite, dehydroxylation of CH and development of C(6)S(3)H at about 90 degrees C, 135 degrees C, 441 degrees C and 570 degrees C, respectively. From the DSC results, it is confirmed that the concrete samples with RA substitution have generated less amount of strength enhancement chemical products when compared to those without RA substitution. However, the results from the TSMA are found improving the RAC quality. The pre-mix procedure of the TSMA can effectively develop some strength enhancing chemical products including, C(3)S(2)H(3), ettringite, CH and C(6)S(3)H, which shows that RAC made from the TSMA can improve the hydration processes.

  10. [Recent results in research on oscillatory chemical reactions].

    PubMed

    Poros, Eszter; Kurin-Csörgei, Krisztina

    2014-01-01

    The mechanisms of the complicated periodical phenomenas in the nature (e.g. hearth beat, sleep cycle, circadian rhythms, etc) could be understood with using the laws of nonlinear chemical systems. In this article the newest result in the research of the subfield of nonlinear chemical dynamics aimed at constructing oscillatory chemical reactions, which are novel either in composition or in configuration, are presented. In the introductory part the concept of chemical periodicity is defined, then the forms as it can appear in time and space and the methods of their study are discussed. Detailed description of the experimental work that has resulted in two significant discoveries is provided. A method was developed to design pH-oscillators which are capable of operating under close conditions. The batch pH-oscillators are more convenient to use in some proposed applications than the equivalent CSTR variant. A redox oscillator that is new in composition was found. The permanganate oxidation of some amino acids was shown to take place according to oscillatory kinetics in a narrow range of the experimental parameters. The KMnO4 - glycine - Na2HPO4 system represents the first example in the family of manganese based oscillators where amino acids is involved. In the conclusion formal analogies between the simple chemical and some more complicated biological oscillatory phenomena are mentioned and the possibility of modeling periodic processes with the use of information gained from the studies of chemical oscillations is pointed out.

  11. Chemical activation through super energy transfer collisions.

    PubMed

    Smith, Jonathan M; Nikow, Matthew; Ma, Jianqiang; Wilhelm, Michael J; Han, Yong-Chang; Sharma, Amit R; Bowman, Joel M; Dai, Hai-Lung

    2014-02-01

    Can a molecule be efficiently activated with a large amount of energy in a single collision with a fast atom? If so, this type of collision will greatly affect molecular reactivity and equilibrium in systems where abundant hot atoms exist. Conventional expectation of molecular energy transfer (ET) is that the probability decreases exponentially with the amount of energy transferred, hence the probability of what we label "super energy transfer" is negligible. We show, however, that in collisions between an atom and a molecule for which chemical reactions may occur, such as those between a translationally hot H atom and an ambient acetylene (HCCH) or sulfur dioxide, ET of chemically significant amounts of energy commences with surprisingly high efficiency through chemical complex formation. Time-resolved infrared emission observations are supported by quasi-classical trajectory calculations on a global ab initio potential energy surface. Results show that ∼10% of collisions between H atoms moving with ∼60 kcal/mol energy and HCCH result in transfer of up to 70% of this energy to activate internal degrees of freedom.

  12. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a glass like'' material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  13. APOLLO: A computer program for the calculation of chemical equilibrium and reaction kinetics of chemical systems

    SciTech Connect

    Nguyen, H.D.

    1991-11-01

    Several of the technologies being evaluated for the treatment of waste material involve chemical reactions. Our example is the in situ vitrification (ISV) process where electrical energy is used to melt soil and waste into a ``glass like`` material that immobilizes and encapsulates any residual waste. During the ISV process, various chemical reactions may occur that produce significant amounts of products which must be contained and treated. The APOLLO program was developed to assist in predicting the composition of the gases that are formed. Although the development of this program was directed toward ISV applications, it should be applicable to other technologies where chemical reactions are of interest. This document presents the mathematical methodology of the APOLLO computer code. APOLLO is a computer code that calculates the products of both equilibrium and kinetic chemical reactions. The current version, written in FORTRAN, is readily adaptable to existing transport programs designed for the analysis of chemically reacting flow systems. Separate subroutines EQREACT and KIREACT for equilibrium ad kinetic chemistry respectively have been developed. A full detailed description of the numerical techniques used, which include both Lagrange multiplies and a third-order integrating scheme is presented. Sample test problems are presented and the results are in excellent agreement with those reported in the literature.

  14. Chemical Probes Allow Structural Insight into the Condensation Reaction of Nonribosomal Peptide Synthetases.

    PubMed

    Bloudoff, Kristjan; Alonzo, Diego A; Schmeing, T Martin

    2016-03-17

    Nonribosomal peptide synthetases (NRPSs) synthesize a vast variety of small molecules, including antibiotics, antitumors, and immunosuppressants. The NRPS condensation (C) domain catalyzes amide bond formation, the central chemical step in nonribosomal peptide synthesis. The catalytic mechanism and substrate determinants of the reaction are under debate. We developed chemical probes to structurally study the NRPS condensation reaction. These substrate analogs become covalently tethered to a cysteine introduced near the active site, to mimic covalent substrate delivery by carrier domains. They are competent substrates in the condensation reaction and behave similarly to native substrates. Co-crystal structures show C domain-substrate interactions, and suggest that the catalytic histidine's principle role is to position the α-amino group for nucleophilic attack. Structural insight provided by these co-complexes also allowed us to alter the substrate specificity profile of the reaction with a single point mutation.

  15. Chemical reaction equilibrium in nanoporous materials: NO dimerization reaction in carbon slit nanopores.

    PubMed

    Lísal, Martin; Brennan, John K; Smith, William R

    2006-02-14

    We present a molecular-level simulation study of the effects of confinement on chemical reaction equilibrium in nanoporous materials. We use the reaction ensemble Monte Carlo (RxMC) method to investigate the effects of temperature, nanopore size, bulk pressure, and capillary condensation on the nitric oxide dimerization reaction in a model carbon slit nanopore in equilibrium with a bulk reservoir. In addition to the RxMC simulations, we also utilize the molecular-dynamics method to determine self-diffusion coefficients for confined nonreactive mixtures of nitric oxide monomers and dimers at compositions obtained from the RxMC simulations. We analyze the effects of the temperature, nanopore width, bulk pressure, and capillary condensation on the reaction equilibrium with respect to the reaction conversion, fluid structure, and self-diffusion coefficients. We show that the influence of the temperature, nanopore size, and capillary condensation on the confined reaction equilibrium is quite dramatic while the effect of the bulk pressure on the reaction equilibrium in the carbon slit nanopore is only moderate. This work is an extension of previous work by Turner et al. [J. Chem. Phys. 114, 1851 (2001)] on the confined reactive nitric oxide system.

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

    PubMed

    Kraka, Elfi; Cremer, Dieter

    2010-05-18

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

  17. Chemical reaction and dust formation studies in laboratory hydrocarbon plasmas.

    NASA Astrophysics Data System (ADS)

    Hippler, Rainer; Majumdar, Abhijit; Thejaswini, H. C.

    Plasma chemical reaction studies with relevance to, e.g., Titan's atmosphere have been per-formed in various laboratory plasmas [1,2]. Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH4 /N2 and CH4 /Ar gas mixtures by means of mass spectrometry. The main reaction scheme is production of H2 by fragmenta-tion of CH4 , but also production of larger hydrocarbons like Cn Hm with n up to 10 including formation of different functional CN groups is observed. [1] A. Majumdar and R. Hippler, Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition, Rev. Sci. Instrum. 78, 075103 (2007) [2] H.T. Do, G. Thieme, M. Frühlich, H. Kersten, and R. Hippler, Ion Molecule and Dust Particle Formation in Ar/CH4 , Ar/C2 H2 and Ar/C3 H6 Radio-frequency Plasmas, Contrib. Plasma Phys. 45, No. 5-6, 378-384 (2005)

  18. Chemical reaction network approaches to Biochemical Systems Theory.

    PubMed

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

    2015-11-01

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

  19. Determination of caffeine using oscillating chemical reaction in a CSTR.

    PubMed

    Gao, Jinzhang; Ren, Jie; Yang, Wu; Liu, XiuHui; Yang, Hua

    2003-07-14

    A new analytical method for the determination of caffeine by the sequential perturbation caused by different amounts of caffeine on the oscillating chemical system involving the manganese(II)-catalyzed reaction between potassium bromate and tyrosine in acidic medium in a CSTR was proposed. The method exposed for the first time in this work. It relies on the relationship between the changes in the oscillation amplitude of the chemical system and the concentration of caffeine. The calibration curve fits a second-order polynomial equation very well when the concentration of caffeine over the range 4.0 x 10(-6) - 1.2 x 10(-4) M (r = 0.9968). The effect of influential variables, such as the concentration of reaction components, injection point, temperature, flow rate and stirring rate were studied. Some aspects of the potential mechanism of action of caffeine on the chemical oscillating system were also discussed. A real sample was determined and the result was satisfactory.

  20. Mechano-chemical coupling in Belousov-Zhabotinskii reactions

    NASA Astrophysics Data System (ADS)

    Klika, Václav; Grmela, Miroslav

    2014-03-01

    Mechano-chemical coupling has been recently recognised as an important effect in various systems as chemical reactivity can be controlled through an applied mechanical loading. Namely, Belousov-Zhabotinskii reactions in polymer gels exhibit self-sustained oscillations and have been identified to be reasonably controllable and definable to the extent that they can be harnessed to perform mechanical work at specific locations. In this paper, we use our theoretical work of nonlinear mechano-chemical coupling and investigate the possibility of providing an explanation of phenomena found in experimental research by means of this theory. We show that mechanotransduction occurs as a response to both static and dynamic mechanical stimulation, e.g., volume change and its rate, as observed experimentally and discuss the difference of their effects on oscillations. Plausible values of the quasi-stoichiometric parameter f of Oregonator model are estimated together with its dependence on mechanical stimulation. An increase in static loading, e.g., pressure, is predicted to have stimulatory effect whereas dynamic loading, e.g., rate of volume change, is predicted to be stimulatory only up to a certain threshold. Further, we offer a physically consistent explanation of the observed phenomena why some Belousov-Zhabotinskii gels require an additional mechanical stimulation to show emergence of oscillation or why "revival" of oscillations in Belousov-Zhabotinskii reactions is possible together with indications for further experimental setups.

  1. Scaffolding Students' Online Critiquing of Expert- and Peer-generated Molecular Models of Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Chang, Hsin-Yi; Chang, Hsiang-Chi

    2013-08-01

    In this study, we developed online critiquing activities using an open-source computer learning environment. We investigated how well the activities scaffolded students to critique molecular models of chemical reactions made by scientists, peers, and a fictitious peer, and whether the activities enhanced the students' understanding of science models and chemical reactions. The activities were implemented in an eighth-grade class with 28 students in a public junior high school in southern Taiwan. The study employed mixed research methods. Data collected included pre- and post-instructional assessments, post-instructional interviews, and students' electronic written responses and oral discussions during the critiquing activities. The results indicated that these activities guided the students to produce overall quality critiques. Also, the students developed a more sophisticated understanding of chemical reactions and scientific models as a result of the intervention. Design considerations for effective model critiquing activities are discussed based on observational results, including the use of peer-generated artefacts for critiquing to promote motivation and collaboration, coupled with critiques of scientific models to enhance students' epistemological understanding of model purpose and communication.

  2. Holistic Metrics for Assessment of the Greenness of Chemical Reactions in the Context of Chemical Education

    ERIC Educational Resources Information Center

    Ribeiro, M. Gabriela T. C.; Machado, Adelio A. S. C.

    2013-01-01

    Two new semiquantitative green chemistry metrics, the green circle and the green matrix, have been developed for quick assessment of the greenness of a chemical reaction or process, even without performing the experiment from a protocol if enough detail is provided in it. The evaluation is based on the 12 principles of green chemistry. The…

  3. Preparation of activated carbon by chemical activation under vacuum.

    PubMed

    Juan, Yang; Ke-Qiang, Qiu

    2009-05-01

    Activated carbons especially used for gaseous adsorption were prepared from Chinesefir sawdust by zinc chloride activation under vacuum condition. The micropore structure, adsorption properties, and surface morphology of activated carbons obtained under atmosphere and vacuum were investigated. The prepared activated carbons were characterized by SEM, FTIR, and nitrogen adsorption. It was found that the structure of the starting material is kept after activation. The activated carbon prepared under vacuum exhibited higher values of the BET surface area (up to 1079 m2 g(-1)) and total pore volume (up to 0.5665 cm3 g(-1)) than those of the activated carbon obtained under atmosphere. This was attributed to the effect of vacuum condition that reduces oxygen in the system and limits the secondary reaction of the organic vapor. The prepared activated carbon has well-developed microstructure and high microporosity. According to the data obtained, Chinese fir sawdust is a suitable precursor for activated carbon preparation. The obtained activated carbon could be used as a low-cost adsorbent with favorable surface properties. Compared with the traditional chemical activation, vacuum condition demands less energy consumption, simultaneity, and biomass-oil is collected in the procedure more conveniently. FTIR analysis showed that heat treatment would result in the aromatization of the carbon structure. PMID:19534162

  4. Nature of the chemical reaction for furfural modified asphalt

    SciTech Connect

    Memon, G.M.; Chollar, B.H.

    1994-12-31

    Three of the most serious problems of asphalt pavements today are rutting, cracking, and susceptibility to moisture damage (stripping). Asphalt manufacturers have been mixing asphalts with polymers to produce polymer-modified asphalts with improved rheological properties. However, the costs for these improved polymer-modified asphalts are almost double that of regular asphalts. FHWA researchers have found that asphalt modified by the chemical, furfural (which is prepared by simple elimination reaction of aldopentoses obtained from oat hulls), exhibited better stripping properties and was less temperature susceptible than the virgin asphalt while costing less than polymer-modified asphalts. This paper discusses the possible structure of the furfural-modified asphalt, data for the virgin and furfural-modified asphalts and their Corbett fractions, data from a model reaction between phenol and furfural, and a possible explanation of this structure based on these data.

  5. Chemical characteristics of mineral trioxide aggregate and its hydration reaction

    PubMed Central

    2012-01-01

    Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed. PMID:23429542

  6. Thermal energy storage. [by means of chemical reactions

    NASA Technical Reports Server (NTRS)

    Grodzka, P. G.

    1975-01-01

    The principles involved in thermal energy storage by sensible heat, chemical potential energy, and latent heat of fusion are examined for the purpose of evolving selection criteria for material candidates in the low ( 0 C) and high ( 100 C) temperature ranges. The examination identifies some unresolved theoretical considerations and permits a preliminary formulation of an energy storage theory. A number of candidates in the low and high temperature ranges are presented along with a rating of candidates or potential candidates. A few interesting candidates in the 0 to 100 C region are also included. It is concluded that storage by means of reactions whose reversibility can be controlled either by product removal or by catalytic means appear to offer appreciable advantages over storage with reactions whose reversability cannot be controlled. Among such advantages are listed higher heat storage capacities and more favorable options regarding temperatures of collection, storage, and delivery. Among the disadvantages are lower storage efficiencies.

  7. Chemical characteristics of mineral trioxide aggregate and its hydration reaction.

    PubMed

    Chang, Seok-Woo

    2012-11-01

    Mineral trioxide aggregate (MTA) was developed in early 1990s and has been successfully used for root perforation repair, root end filling, and one-visit apexification. MTA is composed mainly of tricalcium silicate and dicalcium silicate. When MTA is hydrated, calcium silicate hydrate (CSH) and calcium hydroxide is formed. Formed calcium hydroxide interacts with the phosphate ion in body fluid and form amorphous calcium phosphate (ACP) which finally transforms into calcium deficient hydroxyapatite (CDHA). These mineral precipitate were reported to form the MTA-dentin interfacial layer which enhances the sealing ability of MTA. Clinically, the use of zinc oxide euginol (ZOE) based materials may retard the setting of MTA. Also, the use of acids or contact with excessive blood should be avoided before complete set of MTA, because these conditions could adversely affect the hydration reaction of MTA. Further studies on the chemical nature of MTA hydration reaction are needed. PMID:23429542

  8. Method for detecting pollutants. [through chemical reactions and heat treatment

    NASA Technical Reports Server (NTRS)

    Rogowski, R. S.; Richards, R. R.; Conway, E. J. (Inventor)

    1976-01-01

    A method is described for detecting and measuring trace amounts of pollutants of the group consisting of ozone, nitrogen dioxide, and carbon monoxide in a gaseous environment. A sample organic solid material that will undergo a chemical reaction with the test pollutant is exposed to the test environment and thereafter, when heated in the temperature range of 100-200 C., undergoes chemiluminescence that is measured and recorded as a function of concentration of the test pollutant. The chemiluminescence of the solid organic material is specific to the pollutant being tested.

  9. Chemical reactions of As complexation by glutathione: an XAFS study

    NASA Astrophysics Data System (ADS)

    Franco, M. W.; Vasconcelos, I. F.; Modolo, L. V.; Barbosa, F. A. R.

    2016-05-01

    In this study, the chemical reactions between As(III) and As(V) with glutathione, which is a target compound in As biochemistry due to its primordial role in As immobilization and intracellular reduction, in various molar ratios were investigated using As K-edge XAFS spectroscopy. Results showed a gradual substitution of As-O bonds in the coordination of aqueous As(III) and As(V) for three As-S bonds in the As+GSH complex. Moreover, the data showed reduction of As(V) to As(III) prior or concomitant to the As+GSH complex formation.

  10. Spatially resolved chemical reaction monitoring using magnetic resonance imaging.

    PubMed

    Feindel, Kirk W

    2016-06-01

    Over the previous three decades, the use of MRI for studying dynamic physical and chemical processes of materials systems has grown significantly. This mini-review provides a brief introduction to relevant principles of MRI, including methods of spatial localization, factors contributing to image contrast, and chemical shift imaging. A few historical examples of (1) H MRI for reaction monitoring will be presented, followed by a review of recent research including (1) H MRI studies of gelation and biofilms, (1) H, (7) Li, and (11) B MRI studies of electrochemical systems, in vivo glucose metabolism monitored with (19) F MRI, and in situ temperature monitoring with (27) Al MRI. Copyright © 2015 John Wiley & Sons, Ltd.

  11. Chemical Kinetic Reaction Mechanisms for Combustion of Hydrocarbon and Other Types of Chemical Fuels

    DOE Data Explorer

    The central feature of the Combustion Chemistry project at LLNL is the development, validation, and application of detailed chemical kinetic reaction mechanisms for the combustion of hydrocarbon and other types of chemical fuels. For the past 30 years, LLNL's Chemical Sciences Division has built hydrocarbon mechanisms for fuels from hydrogen and methane through much larger fuels including heptanes and octanes. Other classes of fuels for which models have been developed include flame suppressants such as halons and organophosphates, and air pollutants such as soot and oxides of nitrogen and sulfur. Reaction mechanisms have been tested and validated extensively through comparisons between computed results and measured data from laboratory experiments (e.g., shock tubes, laminar flames, rapid compression machines, flow reactors, stirred reactors) and from practical systems (e.g., diesel engines, spark-ignition engines, homogeneous charge, compression ignition (HCCI) engines). These kinetic models are used to examine a wide range of combustion systems.

  12. A stronger necessary condition for the multistationarity of chemical reaction networks.

    PubMed

    Soliman, Sylvain

    2013-11-01

    Biochemical reaction networks grow bigger and bigger, fed by the high-throughput data provided by biologists and bred in open repositories of models allowing merging and evolution. Nevertheless, since the available data is still very far from permitting the identification of the increasing number of kinetic parameters of such models, the necessity of structural analyses for describing the dynamics of chemical networks appears stronger every day. Using the structural information, notably from the stoichiometric matrix, of a biochemical reaction system, we state a more strict version of the famous Thomas' necessary condition for multistationarity. In particular, the obvious cases where Thomas' condition was trivially satisfied, mutual inhibition due to a multimolecular reaction and mutual activation due to a reversible reaction, can now easily be ruled out. This more strict condition shall not be seen as some version of Thomas' circuit functionality for the continuous case but rather as related and complementary to the whole domain of the structural analysis of (bio)chemical reaction systems, as pioneered by the chemical reaction network theory.

  13. Computational organic chemistry: bridging theory and experiment in establishing the mechanisms of chemical reactions.

    PubMed

    Cheng, Gui-Juan; Zhang, Xinhao; Chung, Lung Wa; Xu, Liping; Wu, Yun-Dong

    2015-02-11

    Understanding the mechanisms of chemical reactions, especially catalysis, has been an important and active area of computational organic chemistry, and close collaborations between experimentalists and theorists represent a growing trend. This Perspective provides examples of such productive collaborations. The understanding of various reaction mechanisms and the insight gained from these studies are emphasized. The applications of various experimental techniques in elucidation of reaction details as well as the development of various computational techniques to meet the demand of emerging synthetic methods, e.g., C-H activation, organocatalysis, and single electron transfer, are presented along with some conventional developments of mechanistic aspects. Examples of applications are selected to demonstrate the advantages and limitations of these techniques. Some challenges in the mechanistic studies and predictions of reactions are also analyzed.

  14. Single-collision studies of energy transfer and chemical reaction

    SciTech Connect

    Valentini, J.J.

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  15. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    NASA Astrophysics Data System (ADS)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

  16. Parameter estimation in complex flows with chemical reactions

    NASA Astrophysics Data System (ADS)

    Robinson, Daniel J.

    The estimation of unknown parameters in engineering and scientific models continues to be of great importance in order to validate them to available experimental data. These parameters of concern cannot be known beforehand, but must be measured experimentally, variables such as chemical species concentrations, pressures, or temperatures as examples. Particularly, in chemically reacting flows, the estimation of kinetic rate parameters from experimentally determined values is in great demand and not well understood. New parameter optimization algorithms have been developed from a Gauss-Newton formulation for the estimation of reaction rate parameters in several different complex flow applications. A zero-dimensional parameter estimation methodology was used in conjunction with a parameter sensitivity study and then applied to three-dimensional flow models. This new parameter estimation technique was applied to three-dimensional models for chemical vapor deposition of silicon carbide and gallium arsenide semiconductor materials. The parameter estimation for silicon carbide for several different operating points was in close agreement to experiment. The parameter estimation for gallium arsenide proved to be very accurate, being within four percent of the experimental data. New parameter estimation algorithms were likewise created for a three-dimensional multiphase model for methanol spray combustion. The kinetic rate parameters delivered results in close agreement to experiment for profiles of combustion species products. In addition, a new parameter estimation method for the determination of spray droplet sizes and velocities is presented. The results for methanol combustion chemical species profiles are in good agreement to experiment for several different droplet sizes. Lastly, the parameter estimation method was extended to a bio-kinetic application, namely mitochondrial cells, that are cardiac or respiratory cells found in animals and humans. The results for the

  17. Anthropogenic reaction parameters--the missing link between chemical intuition and the available chemical space.

    PubMed

    Keserű, György M; Soós, Tibor; Kappe, C Oliver

    2014-08-01

    How do skilled synthetic chemists develop good intuitive expertise? Why can we only access such a small amount of the available chemical space-both in terms of the reactions used and the chemical scaffolds we make? We argue here that these seemingly unrelated questions have a common root and are strongly interdependent. We performed a comprehensive analysis of organic reaction parameters dating back to 1771 and discovered that there are several anthropogenic factors that limit reaction parameters and thus the scope of synthetic chemistry. Nevertheless, many of the anthropogenic limitations such as narrow parameter space and the opportunity for rapid and clear feedback on the progress of reactions appear to be crucial for the acquisition of valid and reliable chemical intuition. In parallel, however, all of these same factors represent limitations for the exploration of available chemistry space and we argue that these are thus at least partly responsible for limited access to new chemistries. We advocate, therefore, that the present anthropogenic boundaries can be expanded by a more conscious exploration of "off-road" chemistry that would also extend the intuitive knowledge of trained chemists.

  18. Inorganic chemically active adsorbents (ICAAs)

    SciTech Connect

    Ally, M.R.; Tavlarides, L.

    1997-10-01

    Oak Ridge National Laboratory (ORNL) researchers are developing a technology that combines metal chelation extraction technology and synthesis chemistry. They begin with a ceramic substrate such as alumina, titanium oxide or silica gel because they provide high surface area, high mechanical strength, and radiolytic stability. One preparation method involves silylation to hydrophobize the surface, followed by chemisorption of a suitable chelation agent using vapor deposition. Another route attaches newly designed chelating agents through covalent bonding by the use of coupling agents. These approaches provide stable and selective, inorganic chemically active adsorbents (ICAAs) tailored for removal of metals. The technology has the following advantages over ion exchange: (1) higher mechanical strength, (2) higher resistance to radiation fields, (3) higher selectivity for the desired metal ion, (4) no cation exchange, (5) reduced or no interference from accompanying anions, (6) faster kinetics, and (7) easy and selective regeneration. Target waste streams include metal-containing groundwater/process wastewater at ORNL`s Y-12 Plant (multiple metals), Savannah River Site (SRS), Rocky Flats (multiple metals), and Hanford; aqueous mixed wastes at Idaho National Engineering Laboratory (INEL); and scrubber water generated at SRS and INEL. Focus Areas that will benefit from this research include Mixed Waste, and Subsurface Contaminants.

  19. Double group transfer reactions: role of activation strain and aromaticity in reaction barriers.

    PubMed

    Fernández, Israel; Bickelhaupt, F Matthias; Cossío, Fernando P

    2009-12-01

    Double group transfer (DGT) reactions, such as the bimolecular automerization of ethane plus ethene, are known to have high reaction barriers despite the fact that their cyclic transition states have a pronounced in-plane aromatic character, as indicated by NMR spectroscopic parameters. To arrive at a way of understanding this somewhat paradoxical and incompletely understood phenomenon of high-energy aromatic transition states, we have explored six archetypal DGT reactions using density functional theory (DFT) at the OLYP/TZ2P level. The main trends in reactivity are rationalized using the activation strain model of chemical reactivity. In this model, the shape of the reaction profile DeltaE(zeta) and the height of the overall reaction barrier DeltaE( not equal)=DeltaE(zeta=zeta(TS)) is interpreted in terms of the strain energy DeltaE(strain)(zeta) associated with deforming the reactants along the reaction coordinate zeta plus the interaction energy DeltaE(int)(zeta) between these deformed reactants: DeltaE(zeta)=DeltaE(strain)(zeta)+DeltaE(int)(zeta). We also use an alternative fragmentation and a valence bond model for analyzing the character of the transition states. PMID:19852009

  20. The quantum dynamics of electronically nonadiabatic chemical reactions

    NASA Astrophysics Data System (ADS)

    Truhlar, Donald G.

    1993-04-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally

  1. The quantum dynamics of electronically nonadiabatic chemical reactions

    NASA Technical Reports Server (NTRS)

    Truhlar, Donald G.

    1993-01-01

    Considerable progress was achieved on the quantum mechanical treatment of electronically nonadiabatic collisions involving energy transfer and chemical reaction in the collision of an electronically excited atom with a molecule. In the first step, a new diabatic representation for the coupled potential energy surfaces was created. A two-state diabatic representation was developed which was designed to realistically reproduce the two lowest adiabatic states of the valence bond model and also to have the following three desirable features: (1) it is more economical to evaluate; (2) it is more portable; and (3) all spline fits are replaced by analytic functions. The new representation consists of a set of two coupled diabatic potential energy surfaces plus a coupling surface. It is suitable for dynamics calculations on both the electronic quenching and reaction processes in collisions of Na(3p2p) with H2. The new two-state representation was obtained by a three-step process from a modified eight-state diatomics-in-molecules (DIM) representation of Blais. The second step required the development of new dynamical methods. A formalism was developed for treating reactions with very general basis functions including electronically excited states. Our formalism is based on the generalized Newton, scattered wave, and outgoing wave variational principles that were used previously for reactive collisions on a single potential energy surface, and it incorporates three new features: (1) the basis functions include electronic degrees of freedom, as required to treat reactions involving electronic excitation and two or more coupled potential energy surfaces; (2) the primitive electronic basis is assumed to be diabatic, and it is not assumed that it diagonalizes the electronic Hamiltonian even asymptotically; and (3) contracted basis functions for vibrational-rotational-orbital degrees of freedom are included in a very general way, similar to previous prescriptions for locally

  2. Assessment of reaction-rate predictions of a collision-energy approach for chemical reactions in atmospheric flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2010-06-01

    A recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates is assessed for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological nonequilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, significant differences can be found. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  3. A new mathematical solution for predicting char activation reactions

    USGS Publications Warehouse

    Rafsanjani, H.H.; Jamshidi, E.; Rostam-Abadi, M.

    2002-01-01

    The differential conservation equations that describe typical gas-solid reactions, such as activation of coal chars, yield a set of coupled second-order partial differential equations. The solution of these coupled equations by exact analytical methods is impossible. In addition, an approximate or exact solution only provides predictions for either reaction- or diffusion-controlling cases. A new mathematical solution, the quantize method (QM), was applied to predict the gasification rates of coal char when both chemical reaction and diffusion through the porous char are present. Carbon conversion rates predicted by the QM were in closer agreement with the experimental data than those predicted by the random pore model and the simple particle model. ?? 2002 Elsevier Science Ltd. All rights reserved.

  4. Solar photo-thermal catalytic reactions to produce high value chemicals

    SciTech Connect

    Prengle, H.W. Jr.; Wentworth, W.E. )

    1992-04-01

    This report presents a summary of the research work accomplished to date on the utilization of solar photo-thermal energy to convert low cost chemical feedstocks into high $-value chemical products. The rationale is that the solar IR-VIS-UV spectrum is unique, supplying endothermic reaction energy as well as VIS-UV for photochemical activation. Chemical market analysis and product price distribution focused attention on speciality chemicals with prices >$1.00/lb, and a synthesis sequence of n-paraffins to aromatics to partial oxidized products. The experimental work has demonstrated that enhanced reaction effects result from VIS-UV irradiation of catalytically active V2O5/SiO2. Experiments of the past year have been on dehydrogenation and dehydrocyclization of n-paraffins to olefins and aromatics with preference for the latter. Recent results using n-hexane produced 95% conversion with 56% benzene; it is speculated that aromatic yield should reach {approximately}70% by further optimization. Pilot- and commercial-scale reactor configurations have been examined; the odds-on-favorite being a shallow fluid-bed of catalyst with incident radiation from the top. Sequencing for maximum cost effectiveness would be day-time endothermic followed by night-time exothermic reactions to produce the products.

  5. Monte-Carlo simulations of chemical reactions in molecular crystals

    NASA Astrophysics Data System (ADS)

    Even, J.; Bertault, M.

    1999-01-01

    Chemical reactions in molecular crystals, yielding new entities (dimers, trimers,…, polymers) in the original structure, are simulated for the first time by stochastic Monte Carlo methods. The results are compared with those obtained by deterministic methods. They show that numerical simulation is a tool for understanding the evolution of these mixed systems. They are in kinetic and not in thermodynamic control. Reactive site distributions, x-ray diffuse scattering, and chain length distributions can be simulated. Comparisons are made with deterministic models and experimental results obtained in the case of the solid state dimerization of cinnamic acid in the beta phase and in the case of the solid state polymerization of diacetylenes.

  6. Miscible viscous fingering involving production of gel by chemical reactions

    NASA Astrophysics Data System (ADS)

    Nagatsu, Yuichiro; Hoshino, Kenichi

    2015-11-01

    We have experimentally investigated miscible viscous fingering with chemical reactions producing gel. Here, two systems were employed. In one system, sodium polyacrylate (SPA) solution and aluminum ion (Al3 +) solution were used as the more and less viscous liquids, respectively. In another system, SPA solution and ferric ion (Fe3 +) solution were used as the more and less viscous liquids, respectively. In the case of Al3 +, displacement efficiency was smaller than that in the non-reactive case, whereas in the case of Fe3 +, the displacement efficiency was larger. We consider that the difference in change of the patterns in the two systems will be caused by the difference in the properties of the gels. Therefore, we have measured the rheological properties of the gels by means of a rheometer. We discuss relationship between the VF patterns and the rheological measurement.

  7. Quantum instanton approximation for thermal rate constants of chemical reactions

    NASA Astrophysics Data System (ADS)

    Miller, William H.; Zhao, Yi; Ceotto, Michele; Yang, Sandy

    2003-07-01

    A quantum mechanical theory for chemical reaction rates is presented which is modeled after the [semiclassical (SC)] instanton approximation. It incorporates the desirable aspects of the instanton picture, which involves only properties of the (SC approximation to the) Boltzmann operator, but corrects its quantitative deficiencies by replacing the SC approximation for the Boltzmann operator by the quantum Boltzmann operator, exp(-βĤ). Since a calculation of the quantum Boltzmann operator is feasible for quite complex molecular systems (by Monte Carlo path integral methods), having an accurate rate theory that involves only the Boltzmann operator could be quite useful. The application of this quantum instanton approximation to several one- and two-dimensional model problems illustrates its potential; e.g., it is able to describe thermal rate constants accurately (˜10-20% error) from high to low temperatures deep in the tunneling regime, and applies equally well to asymmetric and symmetric potentials.

  8. Chemical Reactions in the Processing of Mosi2 + Carbon Compacts

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan S.; Lee, Kang N.; Maloy, Stuart A.; Heuer, Arthur H.

    1993-01-01

    Hot-pressing of MoSi2 powders with carbon at high temperatures reduces the siliceous grain boundary phase in the resultant compact. The chemical reactions in this process were examined using the Knudsen cell technique. A 2.3 wt pct oxygen MoSi2 powder and a 0.59 wt pct oxygen MoSi2 powder, both with additions of 2 wt pct carbon, were examined. The reduction of the siliceous grain boundary phase was examined at 1350 K and the resultant P(SiO)/P(CO) ratios interpreted in terms of the SiO(g) and CO(g) isobars on the Si-C-O predominance diagram. The MoSi2 + carbon mixtures were then heated at the hot-pressing temperature of 2100 K. Large weight losses were observed and could be correlated with the formation of a low-melting eutectic and the formation and vaporization of SiC.

  9. Importance of cytochromes in cyclization reactions: quantum chemical study on a model reaction of proguanil to cycloguanil.

    PubMed

    Arfeen, Minhajul; Patel, Dhilon S; Abbat, Sheenu; Taxak, Nikhil; Bharatam, Prasad V

    2014-10-30

    Proguanil, an anti-malarial prodrug, undergoes cytochrome P450 catalyzed biotransformation to the pharmacologically active triazine metabolite (cycloguanil), which inhibits plasmodial dihydrofolate reductase. This cyclization is catalyzed by CYP2C19 and many anti-malarial lead compounds are being designed and synthesized to exploit this pathway. Quantum chemical calculations were performed using the model species (Cpd I for active species of cytochrome and N4-isopropyl-N6-methylbiguanide for proguanil) to elucidate the mechanism of the cyclization pathway. The overall reaction involves the loss of a water molecule, and is exothermic by approximately 55 kcal/mol, and involves a barrier of approximately 17 kcal/mol. The plausible reaction pathway involves the initial H-radical abstraction from the isopropyl group by Cpd I, followed by two alternative paths- (i) oxygen rebound to provide hydroxyl derivative and (ii) loss of additional H-radical to yield 1,3,5-triazatriene, which undergoes cyclization. This study helped in understanding the role of the active species of cytochromes in this important cyclization reaction.

  10. A quasistationary analysis of a stochastic chemical reaction: Keizer's paradox.

    PubMed

    Vellela, Melissa; Qian, Hong

    2007-07-01

    For a system of biochemical reactions, it is known from the work of T.G. Kurtz [J. Appl. Prob. 8, 344 (1971)] that the chemical master equation model based on a stochastic formulation approaches the deterministic model based on the Law of Mass Action in the infinite system-size limit in finite time. The two models, however, often show distinctly different steady-state behavior. To further investigate this "paradox," a comparative study of the deterministic and stochastic models of a simple autocatalytic biochemical reaction, taken from a text by the late J. Keizer, is carried out. We compute the expected time to extinction, the true stochastic steady state, and a quasistationary probability distribution in the stochastic model. We show that the stochastic model predicts the deterministic behavior on a reasonable time scale, which can be consistently obtained from both models. The transition time to the extinction, however, grows exponentially with the system size. Mathematically, we identify that exchanging the limits of infinite system size and infinite time is problematic. The appropriate system size that can be considered sufficiently large, an important parameter in numerical computation, is also discussed.

  11. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Ziaul Huque

    2007-08-31

    This is the final technical report for the project titled 'Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks'. The aim of the project was to develop an efficient chemistry model for combustion simulations. The reduced chemistry model was developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) was used via a new network topology known as Non-linear Principal Components Analysis (NPCA). A commonly used Multilayer Perceptron Neural Network (MLP-NN) was modified to implement NPCA-NN. The training rate of NPCA-NN was improved with the GEneralized Regression Neural Network (GRNN) based on kernel smoothing techniques. Kernel smoothing provides a simple way of finding structure in data set without the imposition of a parametric model. The trajectory data of the reaction mechanism was generated based on the optimization techniques of genetic algorithm (GA). The NPCA-NN algorithm was then used for the reduction of Dimethyl Ether (DME) mechanism. DME is a recently discovered fuel made from natural gas, (and other feedstock such as coal, biomass, and urban wastes) which can be used in compression ignition engines as a substitute for diesel. An in-house two-dimensional Computational Fluid Dynamics (CFD) code was developed based on Meshfree technique and time marching solution algorithm. The project also provided valuable research experience to two graduate students.

  12. Site remediation via Dispersion by Chemical Reaction (DCR). Special report

    SciTech Connect

    Marion, G.M.; Payne, J.R.; Brar, G.S.

    1997-08-01

    The DCR (Dispersion by Chemical Reaction) technologies are a group of patented waste treatment processes using CaO (quicklime) for the immobilization of heavily oiled sludges, oil-contaminated soils, acid-tars, and heavy metals in Ca(OH)2 and CaCO3 matrices. The objectives of this project were to: (1) evaluate the DCR process for remediating soils contaminated with pesticides, petroleum hydrocarbons (oils and fuels), and heavy metals in cold regions and (2) evaluate DCR-treated oil-contaminated soil as a non-frost-susceptible (NFS) construction material. Three major studies evaluated the DCR process to remediate (1) hydrocarbons at Eareckson Air Force Station on Shemya in the Aleutians, (2) pesticide-contaminated soils from Rocky Mt. Arsenal, and (3) heavy-metal contaminated soils from a former zinc smelter site at Palmerton, Pennsylvania. The DCR process was successful in stabilizing liquid organics and heavy metals in contaminated soils. The chemical properties of soils contaminated by solid organics (asphalt tar and pesticides) were not generally improved by the DCR process, but even in these cases, the physical properties were improved for potential reuse as construction materials.

  13. Cross coupling reactions of polyfluoroarenes via C-F activation.

    PubMed

    Sun, Alex D; Love, Jennifer A

    2010-11-21

    This Perspective provides an overview of transition metal-catalyzed cross coupling reactions of polyfluoroarenes. When appropriate, stoichiometric C-F activation and subsequent reaction are briefly covered.

  14. Chemical Reaction and Flow Modeling in Fullerene and Nanotube Production

    NASA Technical Reports Server (NTRS)

    Scott, Carl D.; Farhat, Samir; Greendyke, Robert B.

    2004-01-01

    The development of processes to produce fullerenes and carbon nanotubes has largely been empirical. Fullerenes were first discovered in the soot produced by laser ablation of graphite [1]and then in the soot of electric arc evaporated carbon. Techniques and conditions for producing larger and larger quantities of fullerenes depended mainly on trial and error empirical variations of these processes, with attempts to scale them up by using larger electrodes and targets and higher power. Various concepts of how fullerenes and carbon nanotubes were formed were put forth, but very little was done based on chemical kinetics of the reactions. This was mainly due to the complex mixture of species and complex nature of conditions in the reactors. Temperatures in the reactors varied from several thousand degrees Kelvin down to near room temperature. There are hundreds of species possible, ranging from atomic carbon to large clusters of carbonaceous soot, and metallic catalyst atoms to metal clusters, to complexes of metals and carbon. Most of the chemical kinetics of the reactions and the thermodynamic properties of clusters and complexes have only been approximated. In addition, flow conditions in the reactors are transient or unsteady, and three dimensional, with steep spatial gradients of temperature and species concentrations. All these factors make computational simulations of reactors very complex and challenging. This article addresses the development of the chemical reaction involved in fullerene production and extends this to production of carbon nanotubes by the laser ablation/oven process and by the electric arc evaporation process. In addition, the high-pressure carbon monoxide (HiPco) process is discussed. The article is in several parts. The first one addresses the thermochemical aspects of modeling; and considers the development of chemical rate equations, estimates of reaction rates, and thermodynamic properties where they are available. The second part

  15. Bioorthogonal Chemical Activation of Kinases in Living Systems

    PubMed Central

    2016-01-01

    Selective manipulation of protein kinases under living conditions is highly desirable yet extremely challenging, particularly in a gain-of-function fashion. Here we employ our recently developed bioorthogonal cleavage reaction as a general strategy for intracellular activation of individual kinases. Site-specific incorporation of trans-cyclooctene-caged lysine in place of the conserved catalytic lysine, in conjunction with the cleavage partner dimethyl-tetrazine, allowed efficient lysine decaging with the kinase activity chemically rescued in living systems. PMID:27280167

  16. Active damping with a reaction mass actuator

    NASA Technical Reports Server (NTRS)

    Spanos, John; O'Brien, John

    1992-01-01

    This paper presents analytical and experimental results in actively damping flexible structures with reaction mass actuators. A two degree of freedom spring-mass model of a flexible structure is analyzed and the key parameters of actuator mass participation and pole-zero separation are related to the maximum damping achievable from rate feedback control. The main conclusion of the paper is that the larger the pole-zero separation the larger the amount of damping that can be imparted to a structural mode. Laboratory experiments conducted on an 8-foot truss structure support the analytical predictions.

  17. Chemical activation by mechanochemical mixing, microwave, and ultrasonic irradiation

    EPA Science Inventory

    The use of emerging MW-assisted chemistry techniques in conjunction with benign reaction media is dramatically reducing chemical waste ad reaction times in several organic syntheses and chemical transformations. This editorial comments on the recent developments in mechanochemica...

  18. Science Activities in Energy: Chemical Energy.

    ERIC Educational Resources Information Center

    Oak Ridge Associated Universities, TN.

    Presented is a science activities in energy package which includes 15 activities relating to chemical energy. Activities are simple, concrete experiments for fourth, fifth and sixth grades which illustrate principles and problems relating to energy. Each activity is outlined on a single card which is introduced by a question. A teacher's…

  19. Ab initio calculations of free energy barriers for chemical reactions in solution: proton transfer in [FHF]-.

    PubMed

    Muller, R P; Warshel, A

    1996-01-01

    This paper describes a hybrid ab initio quantum mechanical/molecular mechanics (QM/MM) method for calculating activation free energies of chemical reactions in solution, using molecular mechanics force fields for the solvent and an ab initio technique that incorporates the potential from the solvent in its Hamiltonian for the solute. The empirical valence bond (EVB) method is used as a reference potential for the ab initio free energy calculation, and drives the reaction along the proper coordinate, thus overcoming problems encountered by direct attempts to use molecular orbital methods in calculations of activation free energies. The utility of our method is illustrated by calculating the activation free energy for proton transfer between fluoride ions in the [FHF]-system, in both polar and nonpolar solution.

  20. A Case Study in Chemical Kinetics: The OH + CO Reaction.

    ERIC Educational Resources Information Center

    Weston, Ralph E., Jr.

    1988-01-01

    Reviews some important properties of the bimolecular reaction between the hydroxyl radical and carbon monoxide. Investigates the kinetics of the reaction, the temperature and pressure dependence of the rate constant, the state-to-state dynamics of the reaction, and the reverse reaction. (MVL)

  1. Chemical dynamics in the gas phase : quantum mechanics of chemical reactions.

    SciTech Connect

    Gray, S. K.

    2006-01-01

    This research program focuses on both the development and application of accurate quantum mechanical methods to describe gas phase chemical reactions and highly excited molecules. Emphasis is often placed on time-dependent or integrative approaches that, in addition to computational simplifications, yield useful mechanistic insights. Applications to systems of current experimental and theoretical interest are emphasized. The results of these calculations also allow one to gauge the quality of the underlying potential energy surfaces and the reliability of more approximate theoretical approaches such as classical trajectories and transition state theories.

  2. Capillary Action may Cool Systems and Precisely balance Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Kriske, Richard

    2011-10-01

    It is well known that it takes no work for Water to rise in a Capillary tube against the force of Gravity. There is a precise balance in this system that resembles Robert Millikan's ``Oil Drop'' experiment, where mass was balanced against the electrostatic force. If at the top of the capillary tube there is evaporation, one can see that the system is cooled as another water molecule has room to move up the column. Furthermore, if the evaporation process can be controlled one photon at a time, a precise balance is created between a photon, and the height/mass of the column. If other molecules are place in the column, they can be moved up and down the column, in a chromatograph way, in a fairly precise manner, by controlling evaporation and molecular weight. If in addition to all of this, the interface of the solution against the walls of the column have Fermi levels, it can be seen as a very precise Electrochemical Device. In the situation of nanotubes, as opposed to trees and plants, these properties can be used to create measure environmental properties and to Balance Chemical Reactions. Forests, and Plants may cool themselves and their environment using this process, and using this process coupled with more energetic photons through photosynthesis.

  3. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2005-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a novel procedure to speed up the training of NPCA. The same procedure termed L{sub 2}Boost can be used to increase the order of approximation of the Generalized Regression Neural Network (GRNN). It is pointed out that GRNN is a basic procedure for the emerging mesh free CFD. Also reported is an efficient simple approach of computing the derivatives of GRNN function approximation using complex variables or the Complex Step Method (CSM). The results presented demonstrate the significance of the methods developed and will be useful in many areas of applied science and engineering.

  4. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2004-12-01

    This is an annual technical report for the work done over the last year (period ending 9/30/2004) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the development of a procedure to speed up the training of NPCA. The developed procedure is based on the non-parametric statistical technique of kernel smoothing. When this smoothing technique is implemented as a Neural Network, It is know as Generalized Regression Neural Network (GRNN). We present results of implementing GRNN on a test problem. In addition, we present results of an in house developed 2-D CFD code that will be used through out the project period.

  5. Heat Diffusion in Gases, Including Effects of Chemical Reaction

    NASA Technical Reports Server (NTRS)

    Hansen, C. Frederick

    1960-01-01

    The diffusion of heat through gases is treated where the coefficients of thermal conductivity and diffusivity are functions of temperature. The diffusivity is taken proportional to the integral of thermal conductivity, where the gas is ideal, and is considered constant over the temperature interval in which a chemical reaction occurs. The heat diffusion equation is then solved numerically for a semi-infinite gas medium with constant initial and boundary conditions. These solutions are in a dimensionless form applicable to gases in general, and they are used, along with measured shock velocity and heat flux through a shock reflecting surface, to evaluate the integral of thermal conductivity for air up to 5000 degrees Kelvin. This integral has the properties of a heat flux potential and replaces temperature as the dependent variable for problems of heat diffusion in media with variable coefficients. Examples are given in which the heat flux at the stagnation region of blunt hypersonic bodies is expressed in terms of this potential.

  6. Detailed Chemical Kinetic Reaction Mechanism for Biodiesel Components Methyl Stearate and Methyl Oleate

    SciTech Connect

    Naik, C; Westbrook, C K; Herbinet, O; Pitz, W J; Mehl, M

    2010-01-22

    New chemical kinetic reaction mechanisms are developed for two of the five major components of biodiesel fuel, methyl stearate and methyl oleate. The mechanisms are produced using existing reaction classes and rules for reaction rates, with additional reaction classes to describe other reactions unique to methyl ester species. Mechanism capabilities were examined by computing fuel/air autoignition delay times and comparing the results with more conventional hydrocarbon fuels for which experimental results are available. Additional comparisons were carried out with measured results taken from jet-stirred reactor experiments for rapeseed methyl ester fuels. In both sets of computational tests, methyl oleate was found to be slightly less reactive than methyl stearate, and an explanation of this observation is made showing that the double bond in methyl oleate inhibits certain low temperature chain branching reaction pathways important in methyl stearate. The resulting detailed chemical kinetic reaction mechanism includes more approximately 3500 chemical species and more than 17,000 chemical reactions.

  7. Chemical reactions between Venus' surface and atmosphere - An update. (Invited)

    NASA Astrophysics Data System (ADS)

    Treiman, A. H.

    2013-12-01

    The surface of Venus, at ~740K, is hot enough to allow relatively rapid chemical reactions between it and the atmosphere, i.e. weathering. Venus chemical weathering has been explored in detail [1], to the limits of available data. New data from Venus Express (VEx) and new ideas from exoplanets have sparked a modest renewal of interest in Venus weathering. Venus' surface cannot be observed in visible light, but there are several NIR ';windows' through its atmosphere that allow surface imaging. The VIRTIS spectrometer on VEx viewed the surface through one window [2]; emissivity variations among lava flows on Imdr and Themis Regios have been explained as varying degrees of weathering, and thus age [3]. The VMC camera on VEx also provides images through a NIR window, which suggest variable degrees of weathering on some basaltic plains [4]. Indirect evidence for weathering may come from varying SO2 abundance at Venus' cloud tops; repeated rapid increases and gradual declines may represent volcanic eruptions followed by weathering to form sulfate minerals [5]. Continued geochemical modeling relevant to Venus weathering is motivated by expolanet studies [6]. Models have been extended to hypothetical exo-Venuses of different temperatures and surface compositions [7]. The idea that Venus' atmosphere composition can be buffered by reaction with its surface was explored in detail, and the derived constraint extended to other types of planets [8]. Several laboratories are investigating Venus weathering, motivated in part by the hope that they can provide real constraints on timescales of Venus volcanism [3]. Aveline et al. [9] are extending early studies [10] by reacting rocks and minerals with concentrated SO2 (to accelerate reaction rates to allow detectability of products). Kohler et al. [11] are investigating the stability of metals and chalcogenides as possible causes of the low-emissivity surfaces at high elevations. Berger and Aigouy [12] studied rock alteration on a

  8. Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory

    NASA Astrophysics Data System (ADS)

    Demeo, Stephen

    1995-09-01

    The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be performed by introductory students to understand different aspects of chemical change such as the concepts of reaction, compound, bonding, excess and limiting reactants, an empirical formula, balanced chemical equation, the conservation of matter and energy, the Law of the Conservation of Mass, and the Law of Constant Composition. These concepts, in turn, are important because they are fundamental to chemistry, are widely taught by chemistry teachers, and are deceptively difficult for introductory chemistry students to understand. The synthesis of zinc iodide has many scientific advantages over current syntheses of binary compounds from elements such as the syntheses of copper sulfide and magnesium oxide. For example, zinc iodide can be synthesized to 1% of theoretical mass in less than a half an hour and can be readily analyzed qualitatively as well as quantitatively by two different titrations. As a set of reactions, the synthesis and decomposition of zinc iodide is safe to perform, reliable, inexpensive, and does not pose a threat to the environment. The author has developed a small collection of teacher activities describing the synthesis and decomposition of zinc iodide. The activities are innovative because they contain improvements not found in the existing literature. Appropriate for high school and first year college chemistry teachers, all of the activities contain detailed procedures and discussions as well as safety and disposal requirements.

  9. Chemical wave propagation preserved on an inhibitory field in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

    PubMed

    Nakata, Satoshi; Ezaki, Takato; Ikura, Yumihiko S; Kitahata, Hiroyuki

    2013-10-17

    The propagation of a chemical wave on an inhibitory field, which was wedged between two excitable fields, was investigated for the photosensitive Belousov-Zhabotinsky (BZ) reaction. With an increase in the width of the inhibitory field between the excitable fields (W), the chemical wave divided into two waves at W = Wα. The divided chemical waves then coalesced at W = Wβ with a decrease in W. Wα was larger than Wβ, i.e., hysteresis on the width of the inhibitory field was observed between the division and coalescence of the chemical wave. The experimental results were qualitatively reproduced by a numerical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that the chemical wave may be preserved on the inhibitory field due to an activator supplied from a chemical wave on the excitable field.

  10. Plasmon-assisted chemical reactions revealed by high-vacuum tip-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Lu, Shuaicheng; Sheng, Shaoxiang; Zhang, Zhenglong; Xu, Hongxing; Zheng, Hairong

    2014-08-01

    Tip-enhanced Raman spectroscopy (TERS) is the technique that combines the nanoscale spatial resolution of a scanning probe microscope and the highly sensitive Raman spectroscopy enhanced by the surface plasmons. It is suitable for chemical analysis at nanometer scale. Recently, TERS exhibited powerful potential in analyzing the chemical reactions at nanoscale. The high sensitivity and spatial resolution of TERS enable us to learn the reaction processes more clearly. More importantly, the chemical reaction in TERS is assisted by surface plasmons, which provides us an optical method to manipulate the chemical reactions at nanoscale. Here using our home-built high-vacuum tip-enhanced Raman spectroscopy (HV-TERS) setup, we successfully observed the plasmon-assisted molecule dimerization and dissociation reactions. In HV-TERS system, under laser illumination, 4-nitrobenzenethiol (4NBT) molecules can be dimerized to p,p'-dimercaptoazobenzene (DMAB), and dissociation reaction occurs for malachite green (MG) molecules. Using our HV-TERS setup, the dynamic processes of the reactions are clearly revealed. The chemical reactions can be manipulated by controlling the plasmon intensity through changing the power of the incident laser, the tunneling current and the bias voltage. We also investigated the role of plasmonic thermal effect in the reactions by measuring both the Stokes and anti- Stokes Raman peaks. Our findings extend the applications of TERS, which can help to study the chemical reactions and understand the dynamic processes at single molecular level, and even design molecules by the plasmon-assisted chemical reactions.

  11. An Activation Energy Experiment for a Second-Order Reaction in a Single Laboratory Period.

    ERIC Educational Resources Information Center

    Barile, Raymond C.; Michiels, Leo P.

    1983-01-01

    Describes modification of a chemical reaction to a single 4 1/2-hour laboratory period. Reaction kinetics between 2, 4-initrochlorobenzene and piperidine to form 2, 4-dinitrophenyl-piperidine and piperidinium hydrochloride are followed conductometrically at three temperatures to obtain data to calculate activation parameters. (Author/JN)

  12. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A. S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K. R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.

    2015-06-01

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.

  13. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes.

    PubMed

    Kabbani, Mohamad A; Tiwary, Chandra Sekhar; Autreto, Pedro A S; Brunetto, Gustavo; Som, Anirban; Krishnadas, K R; Ozden, Sehmus; Hackenberg, Ken P; Gong, Yongi; Galvao, Douglas S; Vajtai, Robert; Kabbani, Ahmad T; Pradeep, Thalappil; Ajayan, Pulickel M

    2015-01-01

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations.

  14. A reaction-based paradigm to model reactive chemical transport in groundwater with general kinetic and equilibrium reactions.

    PubMed

    Zhang, Fan; Yeh, Gour-Tsyh; Parker, Jack C; Brooks, Scott C; Pace, Molly N; Kim, Young-Jin; Jardine, Philip M; Watson, David B

    2007-06-16

    This paper presents a reaction-based water quality transport model in subsurface flow systems. Transport of chemical species with a variety of chemical and physical processes is mathematically described by M partial differential equations (PDEs). Decomposition via Gauss-Jordan column reduction of the reaction network transforms M species reactive transport equations into two sets of equations: a set of thermodynamic equilibrium equations representing N(E) equilibrium reactions and a set of reactive transport equations of M-N(E) kinetic-variables involving no equilibrium reactions (a kinetic-variable is a linear combination of species). The elimination of equilibrium reactions from reactive transport equations allows robust and efficient numerical integration. The model solves the PDEs of kinetic-variables rather than individual chemical species, which reduces the number of reactive transport equations and simplifies the reaction terms in the equations. A variety of numerical methods are investigated for solving the coupled transport and reaction equations. Simulation comparisons with exact solutions were performed to verify numerical accuracy and assess the effectiveness of various numerical strategies to deal with different application circumstances. Two validation examples involving simulations of uranium transport in soil columns are presented to evaluate the ability of the model to simulate reactive transport with complex reaction networks involving both kinetic and equilibrium reactions.

  15. Computational Analyses of Complex Flows with Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Bae, Kang-Sik

    The heat and mass transfer phenomena in micro-scale for the mass transfer phenomena on drug in cylindrical matrix system, the simulation of oxygen/drug diffusion in a three dimensional capillary network, and a reduced chemical kinetic modeling of gas turbine combustion for Jet propellant-10 have been studied numerically. For the numerical analysis of the mass transfer phenomena on drug in cylindrical matrix system, the governing equations are derived from the cylindrical matrix systems, Krogh cylinder model, which modeling system is comprised of a capillary to a surrounding cylinder tissue along with the arterial distance to veins. ADI (Alternative Direction Implicit) scheme and Thomas algorithm are applied to solve the nonlinear partial differential equations (PDEs). This study shows that the important factors which have an effect on the drug penetration depth to the tissue are the mass diffusivity and the consumption of relevant species during the time allowed for diffusion to the brain tissue. Also, a computational fluid dynamics (CFD) model has been developed to simulate the blood flow and oxygen/drug diffusion in a three dimensional capillary network, which are satisfied in the physiological range of a typical capillary. A three dimensional geometry has been constructed to replicate the one studied by Secomb et al. (2000), and the computational framework features a non-Newtonian viscosity model for blood, the oxygen transport model including in oxygen-hemoglobin dissociation and wall flux due to tissue absorption, as well as an ability to study the diffusion of drugs and other materials in the capillary streams. Finally, a chemical kinetic mechanism of JP-10 has been compiled and validated for a wide range of combustion regimes, covering pressures of 1atm to 40atm with temperature ranges of 1,200 K--1,700 K, which is being studied as a possible Jet propellant for the Pulse Detonation Engine (PDE) and other high-speed flight applications such as hypersonic

  16. Simple Chemical Solution Deposition of Co₃O₄ Thin Film Electrocatalyst for Oxygen Evolution Reaction.

    PubMed

    Jeon, Hyo Sang; Jee, Michael Shincheon; Kim, Haeri; Ahn, Su Jin; Hwang, Yun Jeong; Min, Byoung Koun

    2015-11-11

    Oxygen evolution reaction (OER) is the key reaction in electrochemical processes, such as water splitting, metal-air batteries, and solar fuel production. Herein, we developed a facile chemical solution deposition method to prepare a highly active Co3O4 thin film electrode for OER, showing a low overpotential of 377 mV at 10 mA/cm(2) with good stability. An optimal loading of ethyl cellulose additive in a precursor solution was found to be essential for the morphology control and thus its electrocatalytic activity. Our results also show that the distribution of Co3O4 nanoparticle catalysts on the substrate is crucial in enhancing the inherent OER catalytic performance.

  17. Computational molecular technology towards macroscopic chemical phenomena-molecular control of complex chemical reactions, stereospecificity and aggregate structures

    SciTech Connect

    Nagaoka, Masataka

    2015-12-31

    A new efficient hybrid Monte Carlo (MC)/molecular dynamics (MD) reaction method with a rare event-driving mechanism is introduced as a practical ‘atomistic’ molecular simulation of large-scale chemically reactive systems. Starting its demonstrative application to the racemization reaction of (R)-2-chlorobutane in N,N-dimethylformamide solution, several other applications are shown from the practical viewpoint of molecular controlling of complex chemical reactions, stereochemistry and aggregate structures. Finally, I would like to mention the future applications of the hybrid MC/MD reaction method.

  18. Response of a chemical wave to local pulse irradiation in the ruthenium-catalyzed Belousov-Zhabotinsky reaction.

    PubMed

    Nakata, Satoshi; Suzuki, Shogo; Ezaki, Takato; Kitahata, Hiroyuki; Nishi, Kei; Nishiura, Yasumasa

    2015-04-14

    The photo-sensitive Belousov-Zhabotinsky (BZ) reaction system was investigated to understand the response of wave propagation to local pulse stimulation in an excitable field. When the chemical wave was irradiated with a bright pulse or a dark pulse, the speed of wave propagation decreased or increased. The timing of pulse irradiation that significantly affected the speed of chemical wave propagation was different with the bright and dark pulses. That is, there is a sensitive point in the chemical wave. The experimental results were qualitatively reproduced by a numerical calculation based on a three-variable Oregonator model that was modified for the photosensitive BZ reaction. These results suggest that the chemical wave is sensitive to the timing of pulse irradiation due to the rates of production of an activator and an inhibitor in the photochemical reaction.

  19. Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks

    SciTech Connect

    Nelson Butuk

    2006-09-21

    This is an annual technical report for the work done over the last year (period ending 9/30/2005) on the project titled ''Mathematically Reduced Chemical Reaction Mechanism Using Neural Networks''. The aim of the project is to develop an efficient chemistry model for combustion simulations. The reduced chemistry model will be developed mathematically without the need of having extensive knowledge of the chemistry involved. To aid in the development of the model, Neural Networks (NN) will be used via a new network topology know as Non-linear Principal Components Analysis (NPCA). We report on the significant development made in developing a truly meshfree computational fluid dynamics (CFD) flow solver to be coupled to NPCA. First, the procedure of obtaining nearly analytic accurate first order derivatives using the complex step method (CSM) is extended to include computation of accurate meshfree second order derivatives via a theorem described in this report. Next, boosted generalized regression neural network (BGRNN), described in our previous report is combined with CSM and used to obtain complete solution of a hard to solve wave dominated sample second order partial differential equation (PDE): the cubic Schrodinger equation. The resulting algorithm is a significant improvement of the meshfree technique of smooth particle hydrodynamics method (SPH). It is suggested that the demonstrated meshfree technique be termed boosted smooth particle hydrodynamics method (BSPH). Some of the advantages of BSPH over other meshfree methods include; it is of higher order accuracy than SPH; compared to other meshfree methods, it is completely meshfree and does not require any background meshes; It does not involve any construction of shape function with their associated solution of possibly ill conditioned matrix equations; compared to some SPH techniques, no equation for the smoothing parameter is required; finally it is easy to program.

  20. Probing Isotope Effects in Chemical Reactions Using Single Ions

    SciTech Connect

    Staanum, Peter F.; Hoejbjerre, Klaus; Drewsen, Michael; Wester, Roland

    2008-06-20

    Isotope effects in reactions between Mg{sup +} in the 3p {sup 2}P{sub 3/2} excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only {approx}250 reactions with HD, the branching ratio between formation of MgD{sup +} and MgH{sup +} is found to be larger than 5. From an additional 65 reactions with H{sub 2} and D{sub 2} we find that the overall fragmentation probability of the intermediate MgH{sub 2}{sup +}, MgHD{sup +}, or MgD{sub 2}{sup +} complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

  1. Probing Isotope Effects in Chemical Reactions Using Single Ions

    NASA Astrophysics Data System (ADS)

    Staanum, Peter F.; Højbjerre, Klaus; Wester, Roland; Drewsen, Michael

    2008-06-01

    Isotope effects in reactions between Mg+ in the 3p P3/22 excited state and molecular hydrogen at thermal energies are studied through single reaction events. From only ˜250 reactions with HD, the branching ratio between formation of MgD+ and MgH+ is found to be larger than 5. From an additional 65 reactions with H2 and D2 we find that the overall fragmentation probability of the intermediate MgH2+, MgHD+, or MgD2+ complexes is the same. Our study shows that few single ion reactions can provide quantitative information on ion-neutral reactions. Hence, the method is well suited for reaction studies involving rare species, e.g., rare isotopes or short-lived unstable elements.

  2. CHEMICAL SYNTHESIS USING 'GREENER' ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The chemical research during the last decade has witnessed a paradigm shift towards "environmentally-friendly chemistry" more popularly known as "green chemistry" due to the increasing environmental concerns and legislative requirements to curb the release of chemical waste into ...

  3. SUBSTITUTION REACTIONS FOR THE DETOXIFICATION OF HAZARDOUS CHEMICALS

    EPA Science Inventory

    Chemical Treatment is one of several treatment techniques used for the remediation of toxic and hazardous chemicals. Chemical treatment in this report is defined as substitution of halogens by hydrogens for the conversion of halogenated organic toxicant into its native hydrocarb...

  4. Mixing and chemical reaction in sheared and nonsheared homogeneous turbulence

    NASA Technical Reports Server (NTRS)

    Leonard, Andy D.; Hill, James C.

    1992-01-01

    Direct numerical simulations were made to examine the local structure of the reaction zone for a moderately fast reaction between unmixed species in decaying, homogeneous turbulence and in a homogeneous turbulent shear flow. Pseudospectral techniques were used in domains of 64 exp 3 and higher wavenumbers. A finite-rate, single step reaction between non-premixed reactants was considered, and in one case temperature-dependent Arrhenius kinetics was assumed. Locally intense reaction rates that tend to persist throughout the simulations occur in locations where the reactant concentration gradients are large and are amplified by the local rate of strain. The reaction zones are more organized in the case of a uniform mean shear than in isotropic turbulence, and regions of intense reaction rate appear to be associated with vortex structures such as horseshoe vortices and fingers seen in mixing layers. Concentration gradients tend to align with the direction of the most compressive principal strain rate, more so in the isotropic case.

  5. Reactions of hydrazines with chemicals found in environment. Technical report

    SciTech Connect

    Judeikis, H.S.; Damschen, D.E.

    1992-01-24

    Reactions of hydrazine, monomethylhydrazine and unsymmetrical dimethylhydrazine with selected species of interest that are found in the environment have been investigated. Included are aqueous phase reactions that can occur in atmospheric aerosols, groundwater, or soils in contact with groundwater, as well as selected gas phase reactions. Reactants include oxygen and hydrogen peroxide (both reactants in the presence and absence of catalysts), ozone, nitrous acid, sulfur dioxide, and acetone (as a model for environmental ketones and aldehydes). Rate constants for the reactions have been determined, or upper limits set. In several instances, reaction products have been identified. By far, the fastest reactions measured were those involving the hydrazines and ozone with (second-order) rate constants up to 2.4 x 107 liter/mole-sec.

  6. Facile Synthesis of Single Crystal Vanadium Disulfide Nanosheets by Chemical Vapor Deposition for Efficient Hydrogen Evolution Reaction.

    PubMed

    Yuan, Jiangtan; Wu, Jingjie; Hardy, Will J; Loya, Philip; Lou, Minhan; Yang, Yingchao; Najmaei, Sina; Jiang, Menglei; Qin, Fan; Keyshar, Kunttal; Ji, Heng; Gao, Weilu; Bao, Jiming; Kono, Junichiro; Natelson, Douglas; Ajayan, Pulickel M; Lou, Jun

    2015-10-01

    A facile chemical vapor deposition method to prepare single-crystalline VS2 nanosheets for the hydrogen evolution reaction is reported. The electrocatalytic hydrogen evolution reaction (HER) activities of VS2 show an extremely low overpotential of -68 mV at 10 mA cm(-2), small Tafel slopes of ≈34 mV decade(-1), as well as high stability, demonstrating its potential as a candidate non-noble-metal catalyst for the HER. PMID:26293810

  7. Facile Synthesis of Single Crystal Vanadium Disulfide Nanosheets by Chemical Vapor Deposition for Efficient Hydrogen Evolution Reaction.

    PubMed

    Yuan, Jiangtan; Wu, Jingjie; Hardy, Will J; Loya, Philip; Lou, Minhan; Yang, Yingchao; Najmaei, Sina; Jiang, Menglei; Qin, Fan; Keyshar, Kunttal; Ji, Heng; Gao, Weilu; Bao, Jiming; Kono, Junichiro; Natelson, Douglas; Ajayan, Pulickel M; Lou, Jun

    2015-10-01

    A facile chemical vapor deposition method to prepare single-crystalline VS2 nanosheets for the hydrogen evolution reaction is reported. The electrocatalytic hydrogen evolution reaction (HER) activities of VS2 show an extremely low overpotential of -68 mV at 10 mA cm(-2), small Tafel slopes of ≈34 mV decade(-1), as well as high stability, demonstrating its potential as a candidate non-noble-metal catalyst for the HER.

  8. Acid-Base Chemistry According to Robert Boyle: Chemical Reactions in Words as well as Symbols

    ERIC Educational Resources Information Center

    Goodney, David E.

    2006-01-01

    Examples of acid-base reactions from Robert Boyle's "The Sceptical Chemist" are used to illustrate the rich information content of chemical equations. Boyle required lengthy passages of florid language to describe the same reaction that can be done quite simply with a chemical equation. Reading or hearing the words, however, enriches the student's…

  9. Design criteria for extraction with chemical reaction and liquid membrane permeation

    NASA Technical Reports Server (NTRS)

    Bart, H. J.; Bauer, A.; Lorbach, D.; Marr, R.

    1988-01-01

    The design criteria for heterogeneous chemical reactions in liquid/liquid systems formally correspond to those of classical physical extraction. More complex models are presented which describe the material exchange at the individual droplets in an extraction with chemical reaction and in liquid membrane permeation.

  10. Mapping Students' Conceptual Modes When Thinking about Chemical Reactions Used to Make a Desired Product

    ERIC Educational Resources Information Center

    Weinrich, M. L.; Talanquer, V.

    2015-01-01

    The central goal of this qualitative research study was to uncover major implicit assumptions that students with different levels of training in the discipline apply when thinking and making decisions about chemical reactions used to make a desired product. In particular, we elicited different ways of conceptualizing why chemical reactions happen…

  11. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, John; Escher, Claus

    1988-01-01

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction.

  12. Method of operating a thermal engine powered by a chemical reaction

    DOEpatents

    Ross, J.; Escher, C.

    1988-06-07

    The invention involves a novel method of increasing the efficiency of a thermal engine. Heat is generated by a non-linear chemical reaction of reactants, said heat being transferred to a thermal engine such as Rankine cycle power plant. The novel method includes externally perturbing one or more of the thermodynamic variables of said non-linear chemical reaction. 7 figs.

  13. Introducing Stochastic Simulation of Chemical Reactions Using the Gillespie Algorithm and MATLAB: Revisited and Augmented

    ERIC Educational Resources Information Center

    Argoti, A.; Fan, L. T.; Cruz, J.; Chou, S. T.

    2008-01-01

    The stochastic simulation of chemical reactions, specifically, a simple reversible chemical reaction obeying the first-order, i.e., linear, rate law, has been presented by Martinez-Urreaga and his collaborators in this journal. The current contribution is intended to complement and augment their work in two aspects. First, the simple reversible…

  14. Motivational Factors Contributing to Turkish High School Students' Achievement in Gases and Chemical Reactions

    ERIC Educational Resources Information Center

    Kadioglu, Cansel; Uzuntiryaki, Esen

    2008-01-01

    This study aimed to investigate the contribution of motivational factors to 10th grade students' achievement in gases and chemical reactions in chemistry. Three hundred fifty nine 10th grade students participated in the study. The Gases and Chemical Reactions Achievement Test and the Motivated Strategies for Learning Questionnaire were…

  15. Achieving Chemical Equilibrium: The Role of Imposed Conditions in the Ammonia Formation Reaction

    ERIC Educational Resources Information Center

    Tellinghuisen, Joel

    2006-01-01

    Under conditions of constant temperature T and pressure P, chemical equilibrium occurs in a closed system (fixed mass) when the Gibbs free energy G of the reaction mixture is minimized. However, when chemical reactions occur under other conditions, other thermodynamic functions are minimized or maximized. For processes at constant T and volume V,…

  16. Separation of chemical reaction intermediates by metal-organic frameworks.

    PubMed

    Centrone, Andrea; Santiso, Erik E; Hatton, T Alan

    2011-08-22

    HPLC columns custom-packed with metal-organic framework (MOF) materials are used for the separation of four small intermediates and byproducts found in the commercial synthesis of an important active pharmaceutical ingredient in methanol. In particular, two closely related amines can be separated in the methanol reaction medium using MOFs, but not with traditional C18 columns using an optimized aqueous mobile phase. Infrared spectroscopy, UV-vis spectroscopy, X-ray diffraction, and thermogravimetric analysis are used in combination with molecular dynamic simulations to study the separation mechanism for the best-performing MOF materials. It is found that separation with ZIF-8 is the result of an interplay between the thermodynamic driving force for solute adsorption within the framework pores and the kinetics of solute diffusion into the material pores, while the separation with Basolite F300 is achieved because of the specific interactions between the solutes and Fe(3+) sites. This work, and the exceptional ability to tailor the porous properties of MOF materials, points to prospects for using MOF materials for the continuous separation and synthesis of pharmaceutical compounds.

  17. Theoretical research program to study chemical reactions in AOTV bow shock tubes

    NASA Technical Reports Server (NTRS)

    Taylor, P.

    1986-01-01

    Progress in the development of computational methods for the characterization of chemical reactions in aerobraking orbit transfer vehicle (AOTV) propulsive flows is reported. Two main areas of code development were undertaken: (1) the implementation of CASSCF (complete active space self-consistent field) and SCF (self-consistent field) analytical first derivatives on the CRAY X-MP; and (2) the installation of the complete set of electronic structure codes on the CRAY 2. In the area of application calculations the main effort was devoted to performing full configuration-interaction calculations and using these results to benchmark other methods. Preprints describing some of the systems studied are included.

  18. Chemical modeling of irreversible reactions in nuclear waste-water-rock systems

    SciTech Connect

    Wolery, T.J.

    1981-02-01

    Chemical models of aqueous geochemical systems are usually built on the concept of thermodynamic equilibrium. Though many elementary reactions in a geochemical system may be close to equilibrium, others may not be. Chemical models of aqueous fluids should take into account that many aqueous redox reactions are among the latter. The behavior of redox reactions may critically affect migration of certain radionuclides, especially the actinides. In addition, the progress of reaction in geochemical systems requires thermodynamic driving forces associated with elementary reactions not at equilibrium, which are termed irreversible reactions. Both static chemical models of fluids and dynamic models of reacting systems have been applied to a wide spectrum of problems in water-rock interactions. Potential applications in nuclear waste disposal range from problems in geochemical aspects of site evaluation to those of waste-water-rock interactions. However, much further work in the laboratory and the field will be required to develop and verify such applications of chemical modeling.

  19. Phase and chemical equilibria in the transesterification reaction of vegetable oils with supercritical lower alcohols

    NASA Astrophysics Data System (ADS)

    Anikeev, V. I.; Stepanov, D. A.; Ermakova, A.

    2011-08-01

    Calculations of thermodynamic data are performed for fatty acid triglycerides, free fatty acids, and fatty acid methyl esters, participants of the transesterification reaction of vegetable oils that occurs in methanol. Using the obtained thermodynamic parameters, the phase diagrams for the reaction mixture are constructed, and the chemical equilibria of the esterification reaction of free fatty acids and the transesterification reaction of fatty acid triglycerides attained upon treatment with supercritical methanol are determined. Relying on our analysis of the obtained equilibria for the esterification reaction of fatty acids and the transesterification reaction of triglycerides attained upon treatment with lower alcohols, we select the optimum conditions for performing the reaction in practice.

  20. Chemical Synthesis Accelerated by Paper Spray: The Haloform Reaction

    ERIC Educational Resources Information Center

    Bain, Ryan M.; Pulliam, Christopher J.; Raab, Shannon A.; Cooks, R. Graham

    2016-01-01

    In this laboratory, students perform a synthetic reaction in two ways: (i) by traditional bulk-phase reaction and (ii) in the course of reactive paper spray ionization. Mass spectrometry (MS) is used both as an analytical method and a means of accelerating organic syntheses. The main focus of this laboratory exercise is that the same ionization…

  1. The canonical and other mechanisms of elementary chemical reactions.

    PubMed

    Aldegunde, Jesús; Aoiz, F Javier; Sáez-Rábanos, Vicente; Kendrick, Brian K; de Miranda, Marcelo P

    2007-11-21

    This article introduces a definition of the concept of elementary reaction mechanism that, while conforming to the traditional view of reaction mechanisms as dynamical processes whereby reagents are transformed into products, sharpens it by requiring reagent and product states to be completely specified and fully correlated. This leads to well-defined mathematical requirements for classification of a dynamical process as a reaction mechanism and also to a straightforward mathematical procedure for the determination of a special class of independent collision mechanisms that are dubbed "canonical". Canonical mechanisms result from an exact decomposition of the differential cross section of the reaction and form a complete orthogonal basis in terms of which all reaction mechanisms can be described. Examples involving the benchmark F + H2 and D + H2 reactions at energies ranging from ultralow to hyperthermal illustrate how canonical and other reaction mechanisms can be visualised and also how analysis of a reaction in terms of its canonical mechanisms can provide insight into its dynamics.

  2. Quantum chemical modeling of zeolite-catalyzed methylation reactions: toward chemical accuracy for barriers.

    PubMed

    Svelle, Stian; Tuma, Christian; Rozanska, Xavier; Kerber, Torsten; Sauer, Joachim

    2009-01-21

    The methylation of ethene, propene, and t-2-butene by methanol over the acidic microporous H-ZSM-5 catalyst has been investigated by a range of computational methods. Density functional theory (DFT) with periodic boundary conditions (PBE functional) fails to describe the experimentally determined decrease of apparent energy barriers with the alkene size due to inadequate description of dispersion forces. Adding a damped dispersion term expressed as a parametrized sum over atom pair C(6) contributions leads to uniformly underestimated barriers due to self-interaction errors. A hybrid MP2:DFT scheme is presented that combines MP2 energy calculations on a series of cluster models of increasing size with periodic DFT calculations, which allows extrapolation to the periodic MP2 limit. Additionally, errors caused by the use of finite basis sets, contributions of higher order correlation effects, zero-point vibrational energy, and thermal contributions to the enthalpy were evaluated and added to the "periodic" MP2 estimate. This multistep approach leads to enthalpy barriers at 623 K of 104, 77, and 48 kJ/mol for ethene, propene, and t-2-butene, respectively, which deviate from the experimentally measured values by 0, +13, and +8 kJ/mol. Hence, enthalpy barriers can be calculated with near chemical accuracy, which constitutes significant progress in the quantum chemical modeling of reactions in heterogeneous catalysis in general and microporous zeolites in particular.

  3. Iteration Scheme for Implicit Calculations of Kinetic and Equilibrium Chemical Reactions in Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Ramshaw, J. D.; Chang, C. H.

    1995-02-01

    An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described (J. D. Ramshaw and A. A. Amsden, J. Comput. Phys.59, 484 (1985); 71 , 224 (1987)). Here we generalize this scheme to kinetic reactions as well as equilibrium reactions. This extends the applicability of the scheme to problems with kinetic reactions that are fast in some regions of the flow field but slow in others. The resulting scheme thereby provides a single unified framework for the implicit treatment of an arbitrary number of coupled equilibrium and kinetic reactions in chemically reacting fluid flow.

  4. A Unified Approach to the Study of Chemical Reactions in Freshman Chemistry.

    ERIC Educational Resources Information Center

    Cassen, T.; DuBois, Thomas D.

    1982-01-01

    Provides rationale and objectives for presenting chemical reactions in a unified, logical six-stage approach rather than a piecemeal approach. Stages discussed include: introduction, stable electronic configurations and stable oxidation states, reactions between two free elements, ion transfer/proton transfer reactions, double displacement…

  5. The elimination of fast variables in complex chemical reactions. I. Macroscopic level

    NASA Astrophysics Data System (ADS)

    Janssen, J. A. M.

    1989-10-01

    The kinetics of complex chemical reactions is considered. Different time scales exist if one or more of the rate constants of the individual reaction steps is much larger than the others. Examples of specific reactions are given in which the intermediates vary on the fast time scale. They can be eliminated according to a standard scheme, the lowest order of which coincides with the steady-state approximation usually employed in textbooks on chemical kinetics.

  6. Chemical reaction model for oil and gas generation from type 1 and type 2 kerogen

    SciTech Connect

    Braun, R.L.; Burnham, A.K.

    1993-06-01

    A global model for the generation of oil and gas from petroleum source rocks is presented. The model consists of 13 chemical species and 10 reactions, including an alternate-pathway mechanism for kerogen pyrolysis. Reaction rate parameters and stoichiometry coefficients determined from a variety of pyrolysis data are given for both type I and type II kerogen. Use of the chemical reaction model is illustrated for typical geologic conditions.

  7. On the deduction of chemical reaction pathways from measurements of time series of concentrations

    NASA Astrophysics Data System (ADS)

    Samoilov, Michael; Arkin, Adam; Ross, John

    2001-03-01

    We discuss the deduction of reaction pathways in complex chemical systems from measurements of time series of chemical concentrations of reacting species. First we review a technique called correlation metric construction (CMC) and show the construction of a reaction pathway from measurements on a part of glycolysis. Then we present two new improved methods for the analysis of time series of concentrations, entropy metric construction (EMC), and entropy reduction method (ERM), and illustrate (EMC) with calculations on a model reaction system.

  8. A new extension of the polarizable continuum model: Toward a quantum chemical description of chemical reactions at extreme high pressure.

    PubMed

    Cammi, Roberto

    2015-11-15

    A quantum chemical method for studying potential energy surfaces of reactive molecular systems at extreme high pressures is presented. The method is an extension of the standard Polarizable Continuum Model that is usually used for Quantum Chemical study of chemical reactions at a standard condition of pressure. The physical basis of the method and the corresponding computational protocol are described in necessary detail, and an application of the method to the dimerization of cyclopentadiene (up to 20 GPa) is reported.

  9. Reduction of WO 3 to nano-WC by thermo-chemical reaction route

    NASA Astrophysics Data System (ADS)

    Kumar, Akshay; Singh, K.; Pandey, O. P.

    2009-02-01

    Thermo-chemical reaction route has been used to synthesize WC-nanoparticles from WO 3. Two different carbon sources are used to study the effect of these sources on synthesis. The as-prepared samples are characterized by using X-ray diffraction (XRD), differential thermal analyzer (DTA), thermo-gravimetric analysis (TGA) and transmission electron microscope (TEM). The results indicate that reduction of WO 3 to WC takes place by the adsorption of carbon at the surface of WO 3 forming porous structure at the defect sites through which carbon diffuses. As the concentration of adsorbed carbon increases the growth of carbon nanotube starts from this site which ultimately gets converted to carbon nano-fibers of higher chemical activity.

  10. Vicher: A Virtual Reality Based Educational Module for Chemical Reaction Engineering.

    ERIC Educational Resources Information Center

    Bell, John T.; Fogler, H. Scott

    1996-01-01

    A virtual reality application for undergraduate chemical kinetics and reactor design education, Vicher (Virtual Chemical Reaction Model) was originally designed to simulate a portion of a modern chemical plant. Vicher now consists of two programs: Vicher I that models catalyst deactivation and Vicher II that models nonisothermal effects in…

  11. Chemical Reaction CO+OH(•) → CO2+H(•) Autocatalyzed by Carbon Dioxide: Quantum Chemical Study of the Potential Energy Surfaces.

    PubMed

    Masunov, Artëm E; Wait, Elizabeth; Vasu, Subith S

    2016-08-01

    The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO2 to OH radical and CO molecule, hydrogen transfer from oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO2 medium. It may open a new venue for controlling reaction rates for chemical manufacturing. PMID:27351778

  12. Chemical Reaction CO+OH(•) → CO2+H(•) Autocatalyzed by Carbon Dioxide: Quantum Chemical Study of the Potential Energy Surfaces.

    PubMed

    Masunov, Artëm E; Wait, Elizabeth; Vasu, Subith S

    2016-08-01

    The supercritical carbon dioxide medium, used to increase efficiency in oxy combustion fossil energy technology, may drastically alter both rates and mechanisms of chemical reactions. Here we investigate potential energy surface of the second most important combustion reaction with quantum chemistry methods. Two types of effects are reported: formation of the covalent intermediates and formation of van der Waals complexes by spectator CO2 molecule. While spectator molecule alter the activation barrier only slightly, the covalent bonding opens a new reaction pathway. The mechanism includes sequential covalent binding of CO2 to OH radical and CO molecule, hydrogen transfer from oxygen to carbon atoms, and CH bond dissociation. This reduces the activation barrier by 11 kcal/mol at the rate-determining step and is expected to accelerate the reaction rate. The finding of predicted catalytic effect is expected to play an important role not only in combustion but also in a broad array of chemical processes taking place in supercritical CO2 medium. It may open a new venue for controlling reaction rates for chemical manufacturing.

  13. Why Do Lithium-Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect.

    PubMed

    Yao, Xiahui; Dong, Qi; Cheng, Qingmei; Wang, Dunwei

    2016-09-12

    As an electrochemical energy-storage technology with the highest theoretical capacity, lithium-oxygen batteries face critical challenges in terms of poor stabilities and low charge/discharge round-trip efficiencies. It is generally recognized that these issues are connected to the parasitic chemical reactions at the anode, electrolyte, and cathode. While the detailed mechanisms of these reactions have been studied separately, the possible synergistic effects between these reactions remain poorly understood. To fill in the knowledge gap, this Minireview examines literature reports on the parasitic chemical reactions and finds the reactive oxygen species a key chemical mediator that participates in or facilitates nearly all parasitic chemical reactions. Given the ubiquitous presence of oxygen in all test cells, this finding is important. It offers new insights into how to stabilize various components of lithium-oxygen batteries for high-performance operations and how to eventually materialize the full potentials of this promising technology. PMID:27381169

  14. Analysis of weblike network structures of directed graphs for chemical reactions in methane plasmas

    SciTech Connect

    Sakai, Osamu Nobuto, Kyosuke; Miyagi, Shigeyuki; Tachibana, Kunihide

    2015-10-15

    Chemical reactions of molecular gases like methane are so complicated that a chart of decomposed and/or synthesized species originating from molecules in plasma resembles a weblike network in which we write down species and reactions among them. Here we consider properties of the network structures of chemical reactions in methane plasmas. In the network, atoms/molecules/radical species are assumed to form nodes and chemical reactions correspond to directed edges in the terminology of graph theory. Investigation of the centrality index reveals importance of CH{sub 3} in the global chemical reaction, and difference of an index for each radical species between cases with and without electrons clarifies that the electrons are at an influential position to tighten the network structure.

  15. Why Do Lithium-Oxygen Batteries Fail: Parasitic Chemical Reactions and Their Synergistic Effect.

    PubMed

    Yao, Xiahui; Dong, Qi; Cheng, Qingmei; Wang, Dunwei

    2016-09-12

    As an electrochemical energy-storage technology with the highest theoretical capacity, lithium-oxygen batteries face critical challenges in terms of poor stabilities and low charge/discharge round-trip efficiencies. It is generally recognized that these issues are connected to the parasitic chemical reactions at the anode, electrolyte, and cathode. While the detailed mechanisms of these reactions have been studied separately, the possible synergistic effects between these reactions remain poorly understood. To fill in the knowledge gap, this Minireview examines literature reports on the parasitic chemical reactions and finds the reactive oxygen species a key chemical mediator that participates in or facilitates nearly all parasitic chemical reactions. Given the ubiquitous presence of oxygen in all test cells, this finding is important. It offers new insights into how to stabilize various components of lithium-oxygen batteries for high-performance operations and how to eventually materialize the full potentials of this promising technology.

  16. Activated coconut shell charcoal carbon using chemical-physical activation

    NASA Astrophysics Data System (ADS)

    Budi, Esmar; Umiatin, Nasbey, Hadi; Bintoro, Ridho Akbar; Wulandari, Futri; Erlina

    2016-02-01

    The use of activated carbon from natural material such as coconut shell charcoal as metal absorbance of the wastewater is a new trend. The activation of coconut shell charcoal carbon by using chemical-physical activation has been investigated. Coconut shell was pyrolized in kiln at temperature about 75 - 150 °C for about 6 hours in producing charcoal. The charcoal as the sample was shieved into milimeter sized granule particle and chemically activated by immersing in various concentration of HCl, H3PO4, KOH and NaOH solutions. The samples then was physically activated using horizontal furnace at 400°C for 1 hours in argon gas environment with flow rate of 200 kg/m3. The surface morphology and carbon content of activated carbon were characterized by using SEM/EDS. The result shows that the pores of activated carbon are openned wider as the chemical activator concentration is increased due to an excessive chemical attack. However, the pores tend to be closed as further increasing in chemical activator concentration due to carbon collapsing.

  17. Cutaneous reactions in nuclear, biological and chemical warfare.

    PubMed

    Arora, Sandeep

    2005-01-01

    Nuclear, biological and chemical warfare have in recent times been responsible for an increasing number of otherwise rare dermatoses. Many nations are now maintaining overt and clandestine stockpiles of such arsenal. With increasing terrorist threats, these agents of mass destruction pose a risk to the civilian population. Nuclear and chemical attacks manifest immediately while biological attacks manifest later. Chemical and biological attacks pose a significant risk to the attending medical personnel. The large scale of anticipated casualties in the event of such an occurrence would need the expertise of all physicians, including dermatologists, both military and civilian. Dermatologists are uniquely qualified in this respect. This article aims at presenting a review of the cutaneous manifestations in nuclear, chemical and biological warfare and their management.

  18. Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

    SciTech Connect

    Gallis, Michail A.; Bond, Ryan Bomar; Torczynski, John Robert

    2009-08-01

    This report summarizes the work completed during FY2009 for the LDRD project 09-1332 'Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows'. The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for high-temperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonic-flow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

  19. Real time monitoring of accelerated chemical reactions by ultrasonication-assisted spray ionization mass spectrometry.

    PubMed

    Lin, Shu-Hsuan; Lo, Ta-Ju; Kuo, Fang-Yin; Chen, Yu-Chie

    2014-01-01

    Ultrasonication has been used to accelerate chemical reactions. It would be ideal if ultrasonication-assisted chemical reactions could be monitored by suitable detection tools such as mass spectrometry in real time. It would be helpful to clarify reaction intermediates/products and to have a better understanding of reaction mechanism. In this work, we developed a system for ultrasonication-assisted spray ionization mass spectrometry (UASI-MS) with an ~1.7 MHz ultrasonic transducer to monitor chemical reactions in real time. We demonstrated that simply depositing a sample solution on the MHz-based ultrasonic transducer, which was placed in front of the orifice of a mass spectrometer, the analyte signals can be readily detected by the mass spectrometer. Singly and multiply charged ions from small and large molecules, respectively, can be observed in the UASI mass spectra. Furthermore, the ultrasonic transducer used in the UASI setup accelerates the chemical reactions while being monitored via UASI-MS. The feasibility of using this approach for real-time acceleration/monitoring of chemical reactions was demonstrated. The reactions of Girard T reagent and hydroxylamine with steroids were used as the model reactions. Upon the deposition of reactant solutions on the ultrasonic transducer, the intermediate/product ions are readily generated and instantaneously monitored using MS within 1 s. Additionally, we also showed the possibility of using this reactive UASI-MS approach to assist the confirmation of trace steroids from complex urine samples by monitoring the generation of the product ions.

  20. Accelerating chemical reactions: Exploring reactive free-energy surfaces using accelerated ab initio molecular dynamics

    PubMed Central

    Pierce, Levi C. T.; Markwick, Phineus R. L.; McCammon, J. Andrew; Doltsinis, Nikos L.

    2011-01-01

    A biased potential molecular dynamics simulation approach, accelerated molecular dynamics (AMD), has been implemented in the framework of ab initio molecular dynamics for the study of chemical reactions. Using two examples, the double proton transfer reaction in formic acid dimer and the hypothetical adiabatic ring opening and subsequent rearrangement reactions in methylenecyclopropane, it is demonstrated that ab initio AMD can be readily employed to efficiently explore the reactive potential energy surface, allowing the prediction of chemical reactions and the identification of metastable states. An adaptive variant of the AMD method is developed, which additionally affords an accurate representation of both the free-energy surface and the mechanism associated with the chemical reaction of interest and can also provide an estimate of the reaction rate. PMID:21548673

  1. Studying Chemical Reactions, One Bond at a Time, with Single Molecule AFM Techniques

    NASA Astrophysics Data System (ADS)

    Fernandez, Julio M.

    2008-03-01

    The mechanisms by which mechanical forces regulate the kinetics of a chemical reaction are unknown. In my lecture I will demonstrate how we use single molecule force-clamp spectroscopy and protein engineering to study the effect of force on the kinetics of thiol/disulfide exchange. Reduction of disulfide bond via the thiol/disulfide exchange chemical reaction is crucial in regulating protein function and is of common occurrence in mechanically stressed proteins. While reduction is thought to proceed through a substitution nucleophilic bimolecular (SN2) reaction, the role of a mechanical force in modulating this chemical reaction is unknown. We apply a constant stretching force to single engineered disulfide bonds and measure their rate of reduction by dithiothreitol (DTT). We find that while the reduction rate is linearly dependent on the concentration of DTT, it is exponentially dependent on the applied force, increasing 10-fold over a 300 pN range. This result predicts that the disulfide bond lengthens by 0.34 å at the transition state of the thiol/disulfide exchange reaction. In addition to DTT, we also study the reduction of the engineered disulfide bond by the E. coli enzyme thioredoxin (Trx). Thioredoxins are enzymes that catalyze disulfide bond reduction in all organisms. As before, we apply a mechanical force in the range of 25-450 pN to the engineered disulfide bond substrate and monitor the reduction of these bonds by individual enzymes. In sharp contrast with the data obtained with DTT, we now observe two alternative forms of the catalytic reaction, the first requiring a reorientation of the substrate disulfide bond, causing a shortening of the substrate polypeptide by 0.76±0.07 å, and the second elongating the substrate disulfide bond by 0.21±0.01 å. These results support the view that the Trx active site regulates the geometry of the participating sulfur atoms, with sub-ångström precision, in order to achieve efficient catalysis. Single molecule

  2. Solvation and chemical reaction of sodium in water clusters

    NASA Astrophysics Data System (ADS)

    Bobbert, C.; Schulz, C. P.

    Nam(H2O)n Clusters ( n = 1...200, m = 1...50) are formed in a recently build pick-up arrangement. Preformed water clusters traverse a sodium oven, where sodium atoms are picked up. At low sodium vapour pressure ( < 1×10-4 mbar) pure Na(H2O)n clusters are observed in the mass spectra. At high sodium vapour pressure ( > 1×10-3 mbar) the water cluster pick up more than 50 Na atoms and reaction products Na(NaOH)n ( n = 2, 4...50) dominate the mass spectra. The even number of NaOH units in the products indicate that also in a finite cluster the reaction occurs in pairs as in the macroscopic reaction.

  3. Applications of the ETS-NOCV method in descriptions of chemical reactions.

    PubMed

    Mitoraj, Mariusz Paweł; Parafiniuk, Monika; Srebro, Monika; Handzlik, Michał; Buczek, Agnieszka; Michalak, Artur

    2011-09-01

    The present study characterizes changes in the electronic structure of reactants during chemical reactions based on the combined charge and energy decomposition scheme, ETS-NOCV (extended transition state-natural orbitals for chemical valence). Decomposition of the activation barrier, ΔE (#), into stabilizing (orbital interaction, ΔE (orb), and electrostatic, ΔE (elstat)) and destabilizing (Pauli repulsion, ΔE (Pauli), and geometry distortion energy, ΔE (dist)) factors is discussed in detail for the following reactions: (I) hydrogen cyanide to hydrogen isocyanide, HCN → CNH isomerization; (II) Diels-Alder cycloaddition of ethene to 1,3-butadiene; and two catalytic processes, i.e., (III) insertion of ethylene into the metal-alkyl bond using half-titanocene with phenyl-phenoxy ligand catalyst; and (IV) B-H bond activation catalyzed by an Ir-containing catalyst. Various reference states for fragments were applied in ETS-NOCV analysis. We found that NOCV-based deformation densities (Δρ (i)) and the corresponding energies ΔE (orb)(i) obtained from the ETS-NOCV scheme provide a very useful picture, both qualitatively and quantitatively, of electronic density reorganization along the considered reaction pathways. Decomposition of the barrier ΔE(#) into stabilizing and destabilizing contributions allowed us to conclude that the main factor responsible for the existence of positive values of ΔE (#) for all processes (I, II, III and IV) is Pauli interaction, which is the origin of steric repulsion. In addition, in the case of reactions II, III and IV, a significant degree of structural deformation of the reactants, as measured by the geometry distortion energy, plays an important role. Depending on the reaction type, stabilization of the transition state (relatively to the reactants) originating either from the orbital interaction term or from electrostatic attraction can be of vital importance. Finally, use of the ETS-NOCV method to describe catalytic

  4. Theoretical studies of the dynamics of chemical reactions

    SciTech Connect

    Wagner, A.F.

    1993-12-01

    Recent research effort has focussed on several reactions pertinent to combustion. The formation of the formyl radical from atomic hydrogen and carbon monoxide, recombination of alkyl radicals and halo-alkyl radicals with halogen atoms, and the thermal dissociation of hydrogen cyanide and acetylene have been studied by modeling. In addition, the inelastic collisions of NCO with helium have been investigated.

  5. Theoretical Studies of Chemical Reactions following Electronic Excitation

    NASA Technical Reports Server (NTRS)

    Chaban, Galina M.

    2003-01-01

    The use of multi-configurational wave functions is demonstrated for several processes: tautomerization reactions in the ground and excited states of the DNA base adenine, dissociation of glycine molecule after electronic excitation, and decomposition/deformation of novel rare gas molecules HRgF. These processes involve bond brealung/formation and require multi-configurational approaches that include dynamic correlation.

  6. Chemical Principles Revisited. Redox Reactions and the Electropotential Axis.

    ERIC Educational Resources Information Center

    Vella, Alfred J.

    1990-01-01

    This paper suggests a nontraditional pedagogic approach to the subject of redox reactions and electrode potentials suitable for freshman chemistry. Presented is a method for the representation of galvanic cells without the introduction of the symbology and notation of conventional cell diagrams. (CW)

  7. Chemical reaction networks as a model to describe UVC- and radiolytically-induced reactions of simple compounds.

    PubMed

    Dondi, Daniele; Merli, Daniele; Albini, Angelo; Zeffiro, Alberto; Serpone, Nick

    2012-05-01

    When a chemical system is submitted to high energy sources (UV, ionizing radiation, plasma sparks, etc.), as is expected to be the case of prebiotic chemistry studies, a plethora of reactive intermediates could form. If oxygen is present in excess, carbon dioxide and water are the major products. More interesting is the case of reducing conditions where synthetic pathways are also possible. This article examines the theoretical modeling of such systems with random-generated chemical networks. Four types of random-generated chemical networks were considered that originated from a combination of two connection topologies (viz., Poisson and scale-free) with reversible and irreversible chemical reactions. The results were analyzed taking into account the number of the most abundant products required for reaching 50% of the total number of moles of compounds at equilibrium, as this may be related to an actual problem of complex mixture analysis. The model accounts for multi-component reaction systems with no a priori knowledge of reacting species and the intermediates involved if system components are sufficiently interconnected. The approach taken is relevant to an earlier study on reactions that may have occurred in prebiotic systems where only a few compounds were detected. A validation of the model was attained on the basis of results of UVC and radiolytic reactions of prebiotic mixtures of low molecular weight compounds likely present on the primeval Earth.

  8. Synthesis and chemical reactions of the steroidal hormone 17α-methyltestosterone.

    PubMed

    El-Desoky, El-Sayed Ibrahim; Reyad, Mahmoud; Afsah, Elsayed Mohammed; Dawidar, Abdel-Aziz Mahmoud

    2016-01-01

    Structural modifications of natural products with complex structures like steroids require great synthetic effort. A review of literature is presented on the chemistry of the steroidal hormone 17α-methyltestosterone that is approved by Food and Drug Administration (FDA) in the United States as an androgen for estrogen-androgen hormone replacement therapy treatment. The analog also offers special possibilities for the prevention/treatment of hormone-sensitive cancers. The testosterone skeleton has important functionalities in the molecule that can act as a carbonyl component, an active methylene compound, α,β-unsaturated enone and tertiary hydroxyl group in various chemical reactions to access stereoisomeric steroidal compounds with potent activity. In addition, microbiological methods of synthesis and transformation of this hormone are presented.

  9. Synthesis and chemical reactions of the steroidal hormone 17α-methyltestosterone.

    PubMed

    El-Desoky, El-Sayed Ibrahim; Reyad, Mahmoud; Afsah, Elsayed Mohammed; Dawidar, Abdel-Aziz Mahmoud

    2016-01-01

    Structural modifications of natural products with complex structures like steroids require great synthetic effort. A review of literature is presented on the chemistry of the steroidal hormone 17α-methyltestosterone that is approved by Food and Drug Administration (FDA) in the United States as an androgen for estrogen-androgen hormone replacement therapy treatment. The analog also offers special possibilities for the prevention/treatment of hormone-sensitive cancers. The testosterone skeleton has important functionalities in the molecule that can act as a carbonyl component, an active methylene compound, α,β-unsaturated enone and tertiary hydroxyl group in various chemical reactions to access stereoisomeric steroidal compounds with potent activity. In addition, microbiological methods of synthesis and transformation of this hormone are presented. PMID:26639430

  10. X-ray Microspectroscopy and Chemical Reactions in Soil Microsites

    SciTech Connect

    D Hesterberg; M Duff; J Dixon; M Vepraskas

    2011-12-31

    Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earth's surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

  11. EFFICIENT CHEMICAL TRANSFORMATIONS USING ALTERNATIVE REACTION CONDITIONS AND MEDIA

    EPA Science Inventory

    The diverse nature of chemical entities requires various green' strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable...

  12. Effect of Coriolis coupling in chemical reaction dynamics.

    PubMed

    Chu, Tian-Shu; Han, Ke-Li

    2008-05-14

    It is essential to evaluate the role of Coriolis coupling effect in molecular reaction dynamics. Here we consider Coriolis coupling effect in quantum reactive scattering calculations in the context of both adiabaticity and nonadiabaticity, with particular emphasis on examining the role of Coriolis coupling effect in reaction dynamics of triatomic molecular systems. We present the results of our own calculations by the time-dependent quantum wave packet approach for H + D2 and F(2P3/2,2P1/2) + H2 as well as for the ion-molecule collisions of He + H2 +, D(-) + H2, H(-) + D2, and D+ + H2, after reviewing in detail other related research efforts on this issue.

  13. Magnetohydrodynamic (MHD) stretched flow of nanofluid with power-law velocity and chemical reaction

    NASA Astrophysics Data System (ADS)

    Hayat, Tasawar; Rashid, Madiha; Imtiaz, Maria; Alsaedi, Ahmed

    2015-11-01

    This paper deals with the boundary layer flow of nanofluid over power-law stretched surface. Analysis has been carried out in the presence of applied magnetic field and chemical reaction. Heat and mass transfer characteristics are studied using heat and mass convective conditions. The governing partial differential equations are transferred to the nonlinear ordinary differential equations. Convergent series solutions are obtained for fluid velocity, temperature and concentrations fields. Influences of pertinent parameters including Hartman number, thermal and concentration Biot numbers and chemical reaction parameters are discussed on the velocity, temperature and concentration profiles. Graphical result are presented and discussed. Computations for local Nusselt and Sherwood numbers are carried out. It is observed that the heat transfer rate is enhanced by increasing power-law index, thermal Biot number and chemical reaction parameter while mass transfer rate increases for power-law index and chemical reaction parameter.

  14. Rheological monitoring of phase separation induced by chemical reaction in thermoplastic-modified epoxy

    SciTech Connect

    Vinh-Tung, C.; Lachenal, G.; Chabert, B.

    1996-12-31

    The phase separation induced by chemical reaction in blends of tetraglycidyl-diaminodiphenylmethane epoxy resin with an aromatic diamine hardener and a thermoplastic was monitored. Rheological measurements and morphologies are described.

  15. The Determination of Molecular Quantities from Measurements on Macroscopic Systems IV. Phases with Chemical Reactions

    NASA Astrophysics Data System (ADS)

    Liptay, Wolfgang; Wehning, Detlev; Becker, Jürgen; Rehm, Torsten

    1982-12-01

    A general method for the determination of molecular quantities from measurements in dense phases without chemical reactions has been presented in a previous paper [1], The method is extended to phases where chemical reactions may occur. The intimate relationship between the investigation of chemical equilibria and the determination of model molar quantities is shown. Some particular reactions have to be assumed as hypothesis. A scheme is developed, by which in favorable cases it is possible to falsify the assumed hypothesis or to estimate corresponding equilibrium constants and model molar quantities. Some special chemical reactions are treated, where observable quantities are insensitive to any variation of the concentrations of solutions and therefore such methods cannot contribute to the investigation of the systems.

  16. Reformulation and solution of the master equation for multiple-well chemical reactions.

    PubMed

    Georgievskii, Yuri; Miller, James A; Burke, Michael P; Klippenstein, Stephen J

    2013-11-21

    We consider an alternative formulation of the master equation for complex-forming chemical reactions with multiple wells and bimolecular products. Within this formulation the dynamical phase space consists of only the microscopic populations of the various isomers making up the reactive complex, while the bimolecular reactants and products are treated equally as sources and sinks. This reformulation yields compact expressions for the phenomenological rate coefficients describing all chemical processes, i.e., internal isomerization reactions, bimolecular-to-bimolecular reactions, isomer-to-bimolecular reactions, and bimolecular-to-isomer reactions. The applicability of the detailed balance condition is discussed and confirmed. We also consider the situation where some of the chemical eigenvalues approach the energy relaxation time scale and show how to modify the phenomenological rate coefficients so that they retain their validity.

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

    NASA Technical Reports Server (NTRS)

    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.

  18. Exact probability distributions of selected species in stochastic chemical reaction networks.

    PubMed

    López-Caamal, Fernando; Marquez-Lago, Tatiana T

    2014-09-01

    Chemical reactions are discrete, stochastic events. As such, the species' molecular numbers can be described by an associated master equation. However, handling such an equation may become difficult due to the large size of reaction networks. A commonly used approach to forecast the behaviour of reaction networks is to perform computational simulations of such systems and analyse their outcome statistically. This approach, however, might require high computational costs to provide accurate results. In this paper we opt for an analytical approach to obtain the time-dependent solution of the Chemical Master Equation for selected species in a general reaction network. When the reaction networks are composed exclusively of zeroth and first-order reactions, this analytical approach significantly alleviates the computational burden required by simulation-based methods. By building upon these analytical solutions, we analyse a general monomolecular reaction network with an arbitrary number of species to obtain the exact marginal probability distribution for selected species. Additionally, we study two particular topologies of monomolecular reaction networks, namely (i) an unbranched chain of monomolecular reactions with and without synthesis and degradation reactions and (ii) a circular chain of monomolecular reactions. We illustrate our methodology and alternative ways to use it for non-linear systems by analysing a protein autoactivation mechanism. Later, we compare the computational load required for the implementation of our results and a pure computational approach to analyse an unbranched chain of monomolecular reactions. Finally, we study calcium ions gates in the sarco/endoplasmic reticulum mediated by ryanodine receptors.

  19. Three model space experiments on chemical reactions. [Gibbs adsorption, equilibrium shift and electrodeposition

    NASA Technical Reports Server (NTRS)

    Grodzka, P.; Facemire, B.

    1977-01-01

    Three investigations conducted aboard Skylab IV and Apollo-Soyuz involved phenomena that are of interest to the biochemistry community. The formaldehyde clock reaction and the equilibrium shift reaction experiments conducted aboard Apollo Soyuz demonstrate the effect of low-g foams or air/liquid dispersions on reaction rate and chemical equilibrium. The electrodeposition reaction experiment conducted aboard Skylab IV demonstrate the effect of a low-g environment on an electrochemical displacement reaction. The implications of the three space experiments for various applications are considered.

  20. Ambient solid-state mechano-chemical reactions between functionalized carbon nanotubes

    PubMed Central

    Kabbani, Mohamad A.; Tiwary, Chandra Sekhar; Autreto, Pedro A.S.; Brunetto, Gustavo; Som, Anirban; Krishnadas, K.R.; Ozden, Sehmus; Hackenberg, Ken P.; Gong, Yongi; Galvao, Douglas S.; Vajtai, Robert; Kabbani, Ahmad T.; Pradeep, Thalappil; Ajayan, Pulickel M.

    2015-01-01

    Carbon nanotubes can be chemically modified by attaching various functionalities to their surfaces, although harsh chemical treatments can lead to their break-up into graphene nanostructures. On the other hand, direct coupling between functionalities bound on individual nanotubes could lead to, as yet unexplored, spontaneous chemical reactions. Here we report an ambient mechano-chemical reaction between two varieties of nanotubes, carrying predominantly carboxyl and hydroxyl functionalities, respectively, facilitated by simple mechanical grinding of the reactants. The purely solid-state reaction between the chemically differentiated nanotube species produces condensation products and unzipping of nanotubes due to local energy release, as confirmed by spectroscopic measurements, thermal analysis and molecular dynamic simulations. PMID:26073564

  1. Fractional electron number, temperature, and perturbations in chemical reactions.

    PubMed

    Miranda-Quintana, Ramón Alain; Ayers, Paul W

    2016-06-01

    We provide a perspective on the role of non-integer electron number in the density functional theory approach to chemical reactivity (conceptual DFT), emphasizing that it is important to not only treat reagents as open systems, but also as non-isolated systems, in contact with their surroundings. The special case of well-separated reagents is treated in some detail, as is the case where reagents interact strongly. The resulting expressions for the chemical potential of an acid, μacid = -(αI + A)/(1 + α), and a base, μbase = -(I + αA)/(1 + α), elucidate and generalize the assumptions inherent in the chemical potential models of Mulliken (α = 1) and Gazquez, Cedillo, and Vela (α = 3). In the strongly-interacting limit, it is appropriate to model the effects of the environment as a state-specific effective temperature, thereby providing a rigorous justification for the phenomenological effective-temperature model one of the authors previously proposed. The framework for the strongly interacting limit subsumes our model for weakly-interacting subsystems at nonzero temperature, the case of open but otherwise noninteracting subsystems, and the zero-temperature limit.

  2. "JCE" Classroom Activity #111: Redox Reactions in Three Representations

    ERIC Educational Resources Information Center

    Nieves, Edgardo L. Ortiz; Barreto, Reizelie; Medina, Zuleika

    2012-01-01

    This activity introduces students to the concept of reduction-oxidation (redox) reactions. To help students obtain a thorough understanding of redox reactions, the concept is explored at three levels: macroscopic, submicroscopic, and symbolic. In this activity, students perform hands-on investigations of the three levels as they work at different…

  3. Chemical reactions between CF2HCl and NH3 induced by IR double-beam excitation

    NASA Astrophysics Data System (ADS)

    Sigüenza, C. L.; Simeonov, S. A.; Díaz, L.; González-Díaz, P. F.

    1993-06-01

    Infrared multiphoton dissociation experiments with two wavelengths in different mixtures of chlorodifluoromethane and ammonia have been carried out. It is shown that the presence of ammonia in the sample induces a decrease in the chlorodifluoromethane dissociation yield. It has been observed that the distinct chemical reaction channels are differently activated as the time delay between the two laser pulses is varied. The ratio of the obtained products in the infrared multiphoton dissociation changes with the composition of the initial mixture and are not compatible with the mechanism suggested by Sugita and Arai for this reaction in single IR wavelength excitation if it is assumed to be the only contributing mechanism other than that for direct CF2HCl dissociation and subsequent C2F4 formation from the resulting CF2 radicals. It appears that, although for simultaneous two-wavelength irradiation the presence of an accumulated solid NH4Cl deposit does not significantly influence the reaction, this is no longer the case when time delays are introduced between the two beams.

  4. Non-stationary filtration mode during chemical reactions with the gas phase

    NASA Astrophysics Data System (ADS)

    Zavialov, Ivan; Konyukhov, Andrey; Negodyaev, Sergey

    2015-04-01

    An experimental and numerical study of filtration accompanied by chemical reactions between displacing fluid and solid skeleton is considered. Glass balls (400-500 μm in diameter) were placed in 1 cm gap between two glass sheets and were used as model porous medium. The baking soda was added to the glass balls. The 70% solution of acetic acid was used as the displacer. The modeling porous medium was saturated with a mineral oil, and then 70% solution of colored acetic acid was pumped through the medium. The glass balls and a mineral oil have a similar refractive index, so the model porous medium was optically transparent. During the filtration, the gas phase was generated by the chemical reactions between the baking soda and acetic acid, and time-dependent displacement of the chemical reaction front was observed. The front of the chemical reaction was associated with the most intensive gas separation. The front moved, stopped, and then moved again to the area where it had been already. We called this process a secondary oxidation wave. To describe this effect, we added to the balance equations a term associated with the formation and disappearance of phases due to chemical reactions. The equations were supplemented by Darcy's law for multiphase filtration. Nonstationarity front propagation of the chemical reaction in the numerical experiment was observed at Damköhler numbers greater than 100. The mathematical modelling was agreed well with the experimental results.

  5. RPMDRATE: Bimolecular chemical reaction rates from ring polymer molecular dynamics

    NASA Astrophysics Data System (ADS)

    Suleimanov, Yu. V.; Allen, J. W.; Green, W. H.

    2013-03-01

    We present RPMDRATE, a computer program for the calculation of gas phase bimolecular reaction rate coefficients using the ring polymer molecular dynamics (RPMD) method. The RPMD rate coefficient is calculated using the Bennett-Chandler method as a product of a static (centroid density quantum transition state theory (QTST) rate) and a dynamic (ring polymer transmission coefficient) factor. The computational procedure is general and can be used to treat bimolecular polyatomic reactions of any complexity in their full dimensionality. The program has been tested for the H+H2, H+CH4, OH+CH4 and H+C2H6 reactions. Catalogue identifier: AENW_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AENW_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: MIT license No. of lines in distributed program, including test data, etc.: 94512 No. of bytes in distributed program, including test data, etc.: 1395674 Distribution format: tar.gz Programming language: Fortran 90/95, Python (version 2.6.x or later, including any version of Python 3, is recommended). Computer: Not computer specific. Operating system: Any for which Python, Fortran 90/95 compiler and the required external routines are available. Has the code been vectorized or parallelized?: The program can efficiently utilize 4096+ processors, depending on problem and available computer. At low temperatures, 110 processors are reasonable for a typical umbrella integration run with an analytic potential energy function and gradients on the latest x86-64 machines.

  6. Effects of reversible chemical reaction on Li diffusion and stresses in spherical composition-gradient electrodes

    SciTech Connect

    Li, Yong; Zhang, Kai; Zheng, Bailin Zhang, Xiaoqian; Wang, Qi

    2015-06-28

    Composition-gradient electrode materials have been proven to be one of the most promising materials in lithium-ion battery. To study the mechanism of mechanical degradation in spherical composition-gradient electrodes, the finite deformation theory and reversible chemical theory are adopted. In homogeneous electrodes, reversible electrochemical reaction may increase the magnitudes of stresses. However, reversible electrochemical reaction has different influences on stresses in composition-gradient electrodes, resulting from three main inhomogeneous factors—forward reaction rate, backward reaction rate, and reaction partial molar volume. The decreasing transition form of forward reaction rate, increasing transition form of backward reaction rate, and increasing transition form of reaction partial molar volume can reduce the magnitudes of stresses. As a result, capacity fading and mechanical degradation are reduced by taking advantage of the effects of inhomogeneous factors.

  7. The modeling of chemical reactions and thermochemical nonequilibrium in particle simulation computations

    NASA Astrophysics Data System (ADS)

    Gallis, Michael A.; Harvey, John K.

    1998-06-01

    The treatment of chemical reactions and nonequilibrium energy exchange in Direct Simulation Monte Carlo calculations is examined. Details of a Maximum Entropy chemical reaction model are presented that is based on the classical scheme devised by Levine and Bernstein. Data are given for all of the significant reactions that occur in hypersonic reentry flight into the atmospheres of the Earth, Mars, and Venus. The method is an extension of that described and used previously by the authors (Gallis and Harvey [J. Fluid Mech. 312, 149 (1996); AIAA J. 34(7), 1378 (1996)]) and now includes carbon dioxide/nitrogen and ionic reactions. The model allows an appropriate dependence of each reaction on its controlling energy mode and avoids inappropriate use of equilibrium distributions to determine the reaction probabilities and post-collision energy reallocation. Sample flow solutions are given and comparisons are made with results obtained using continuum solvers.

  8. METHODOLOGICAL NOTES: Brusselator — an abstract chemical reaction?

    NASA Astrophysics Data System (ADS)

    Lavrova, Anastasiya I.; Postnikov, E. B.; Romanovsky, Yurii M.

    2009-12-01

    In this paper we consider the Brusselator and the Sel'kov model, which describes the irreversible reaction of glycolysis in the regime of self-sustained oscillations. We show that these two differently constructed models can be reduced to a single equation — a generalized Rayleigh equation. The physical basis for this generality is investigated. The advantages of this equation as a tool for qualitative and quantitative analyses, as well as the similarities and differences of the solutions realized for each of the two concrete models in the cases of almost harmonic and relaxation self-sustained oscillations, are discussed.

  9. Quantum chemical study of penicillin: Reactions after acylation

    NASA Astrophysics Data System (ADS)

    Li, Rui; Feng, Dacheng; Zhu, Feng

    The density functional theory methods were used on the model molecules of penicillin to determine the possible reactions after their acylation on ?-lactamase, and the results were compared with sulbactam we have studied. The results show that, the acylated-enzyme tetrahedral intermediate can evolves with opening of ?-lactam ring as well as the thiazole ring; the thiazole ring-open products may be formed via ?-lactam ring-open product or from tetrahedral intermediate directly. Those products, in imine or enamine form, can tautomerize via hydrogen migration. In virtue of the water-assisted, their energy barriers are obviously reduced.

  10. The Modification of Biocellular Chemical Reactions by Environmental Physicochemicals

    NASA Astrophysics Data System (ADS)

    Ishido, M.

    Environmental risk factors affect human biological system to different extent from modification of biochemical reaction to cellular catastrophe. There are considerable public concerns about electromagnetic fields and endocrine disruptors. Their risk assessments have not been fully achieved because of their scientific uncertainty: electromagnetic fields just modify the bioreaction in the restricted cells and endocrine disruptors are quite unique in that their expression is dependent on the exposure periods throughout a life. Thus, we here describe their molecular characterization to establish the new risk assessments for environmental physicochemicals.

  11. Ca + HF - The anatomy of a chemical insertion reaction

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.; Pattengill, M. D.; Mascarello, F. G.; Zare, R. N.

    1987-01-01

    A comprehensive first-principles theoretical investigation of the gas phase reaction Ca + HF - CaF + H is reported. Ab initio potential energy calculations are first discussed, along with characteristics of the computed potential energy surface. Next, the fitting of the computed potential energy points to a suitable analytical functional form is described, and maps of the fitted potential surface are displayed. The methodology and results of a classical trajectory calculation utilizing the fitted potential surface are presented. Finally, the significance of the trajectory study results is discussed, and generalizations concerning dynamical aspects of Ca + HF scattering are drawn.

  12. Collective Surfing of Chemically Active Particles

    NASA Astrophysics Data System (ADS)

    Masoud, Hassan; Shelley, Michael J.

    2014-03-01

    We study theoretically the collective dynamics of immotile particles bound to a 2D surface atop a 3D fluid layer. These particles are chemically active and produce a chemical concentration field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. For a 3D diffusion-dominated concentration field and Stokesian fluid we show that the surface dynamics of active particle density can be determined using nonlocal 2D surface operators. Remarkably, we also show that for both deep or shallow fluid layers this surface dynamics reduces to the 2D Keller-Segel model for the collective chemotactic aggregation of slime mold colonies. Mathematical analysis has established that the Keller-Segel model can yield finite-time, finite-mass concentration singularities. We show that such singular behavior occurs in our finite-depth system, and study the associated 3D flow structures.

  13. Collective surfing of chemically active particles.

    PubMed

    Masoud, Hassan; Shelley, Michael J

    2014-03-28

    We study theoretically the collective dynamics of immotile particles bound to a 2D surface atop a 3D fluid layer. These particles are chemically active and produce a chemical concentration field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. For a 3D diffusion-dominated concentration field and Stokesian fluid we show that the surface dynamics of active particle density can be determined using nonlocal 2D surface operators. Remarkably, we also show that for both deep or shallow fluid layers this surface dynamics reduces to the 2D Keller-Segel model for the collective chemotactic aggregation of slime mold colonies. Mathematical analysis has established that the Keller-Segel model can yield finite-time, finite-mass concentration singularities. We show that such singular behavior occurs in our finite-depth system, and study the associated 3D flow structures. PMID:24724685

  14. Reaction between Chromium(III) and EDTA Ions: an Overlooked Mechanism of Case Study Reaction of Chemical Kinetics.

    PubMed

    Cerar, Janez

    2015-01-01

    Widely cited and accepted explanation of reaction mechanism of the case study reaction of chemical kinetics between Cr(III) ions and ethylenediaminetetraacetic acid (EDTA) contradicts modern chromium(III) coordination chemistry data. Absorption UV and visible light spectra were recorded during the reaction between aqueous solution of Cr(NO(3))(3) and EDTA in order to obtain new information about this reaction. Analysis of the spectra showed that only very small fraction of intermediates may be present in solution during the course of the reaction. The reaction scheme was established and according to it calculations based on a simplified model were carried out. Literature data for constants were used if known, otherwise, adjusted values of their sound estimates were applied. Reasonable agreement of the model calculations with the experimental data was obtained for pH values 3.8 and 4.5 but the model failed to reproduce measured rate of reaction at pH 5.5, probably due to the use of the oversimplified model. PMID:26454587

  15. Reaction between Chromium(III) and EDTA Ions: an Overlooked Mechanism of Case Study Reaction of Chemical Kinetics.

    PubMed

    Cerar, Janez

    2015-01-01

    Widely cited and accepted explanation of reaction mechanism of the case study reaction of chemical kinetics between Cr(III) ions and ethylenediaminetetraacetic acid (EDTA) contradicts modern chromium(III) coordination chemistry data. Absorption UV and visible light spectra were recorded during the reaction between aqueous solution of Cr(NO(3))(3) and EDTA in order to obtain new information about this reaction. Analysis of the spectra showed that only very small fraction of intermediates may be present in solution during the course of the reaction. The reaction scheme was established and according to it calculations based on a simplified model were carried out. Literature data for constants were used if known, otherwise, adjusted values of their sound estimates were applied. Reasonable agreement of the model calculations with the experimental data was obtained for pH values 3.8 and 4.5 but the model failed to reproduce measured rate of reaction at pH 5.5, probably due to the use of the oversimplified model.

  16. Development of a novel fingerprint for chemical reactions and its application to large-scale reaction classification and similarity.

    PubMed

    Schneider, Nadine; Lowe, Daniel M; Sayle, Roger A; Landrum, Gregory A

    2015-01-26

    Fingerprint methods applied to molecules have proven to be useful for similarity determination and as inputs to machine-learning models. Here, we present the development of a new fingerprint for chemical reactions and validate its usefulness in building machine-learning models and in similarity assessment. Our final fingerprint is constructed as the difference of the atom-pair fingerprints of products and reactants and includes agents via calculated physicochemical properties. We validated the fingerprints on a large data set of reactions text-mined from granted United States patents from the last 40 years that have been classified using a substructure-based expert system. We applied machine learning to build a 50-class predictive model for reaction-type classification that correctly predicts 97% of the reactions in an external test set. Impressive accuracies were also observed when applying the classifier to reactions from an in-house electronic laboratory notebook. The performance of the novel fingerprint for assessing reaction similarity was evaluated by a cluster analysis that recovered 48 out of 50 of the reaction classes with a median F-score of 0.63 for the clusters. The data sets used for training and primary validation as well as all python scripts required to reproduce the analysis are provided in the Supporting Information.

  17. Development of a novel fingerprint for chemical reactions and its application to large-scale reaction classification and similarity.

    PubMed

    Schneider, Nadine; Lowe, Daniel M; Sayle, Roger A; Landrum, Gregory A

    2015-01-26

    Fingerprint methods applied to molecules have proven to be useful for similarity determination and as inputs to machine-learning models. Here, we present the development of a new fingerprint for chemical reactions and validate its usefulness in building machine-learning models and in similarity assessment. Our final fingerprint is constructed as the difference of the atom-pair fingerprints of products and reactants and includes agents via calculated physicochemical properties. We validated the fingerprints on a large data set of reactions text-mined from granted United States patents from the last 40 years that have been classified using a substructure-based expert system. We applied machine learning to build a 50-class predictive model for reaction-type classification that correctly predicts 97% of the reactions in an external test set. Impressive accuracies were also observed when applying the classifier to reactions from an in-house electronic laboratory notebook. The performance of the novel fingerprint for assessing reaction similarity was evaluated by a cluster analysis that recovered 48 out of 50 of the reaction classes with a median F-score of 0.63 for the clusters. The data sets used for training and primary validation as well as all python scripts required to reproduce the analysis are provided in the Supporting Information. PMID:25541888

  18. Concentration fluctuations in a mesoscopic oscillating chemical reaction system

    PubMed Central

    Qian, Hong; Saffarian, Saveez; Elson, Elliot L.

    2002-01-01

    Under sustained pumping, kinetics of macroscopic nonlinear biochemical reaction systems far from equilibrium either can be in a stationary steady state or can execute sustained oscillations about a fixed mean. For a system of two dynamic species X and Y, the concentrations nx and ny will be constant or will repetitively trace a closed loop in the (nx, ny) phase plane, respectively. We study a mesoscopic system with nx and ny very small; hence the occurrence of random fluctuations modifies the deterministic behavior and the law of mass action is replaced by a stochastic model. We show that nx and ny execute cyclic random walks in the (nx, ny) plane whether or not the deterministic kinetics for the corresponding macroscopic system represents a steady or an oscillating state. Probability distributions and correlation functions for nx(t) and ny(t) show quantitative but not qualitative differences between states that would appear as either oscillating or steady in the corresponding macroscopic systems. A diffusion-like equation for probability P(nx, ny, t) is obtained for the two-dimensional Brownian motion in the (nx, ny) phase plane. In the limit of large nx, ny, the deterministic nonlinear kinetics derived from mass action is recovered. The nature of large fluctuations in an oscillating nonequilibrium system and the conceptual difference between “thermal stochasticity” and “temporal complexity” are clarified by this analysis. This result is relevant to fluorescence correlation spectroscopy and metabolic reaction networks. PMID:12124397

  19. Theoretical Chemical Dynamics Studies of Elementary Combustion Reactions

    SciTech Connect

    Donald L. Thompson

    2009-09-30

    The objective of this research was to develop and apply methods for more accurate predictions of reaction rates based on high-level quantum chemistry. We have developed and applied efficient, robust methods for fitting global ab initio potential energy surfaces (PESs) for both spectroscopy and dynamics calculations and for performing direct dynamics simulations. Our approach addresses the problem that high-level quantum calculations are often too costly in computer time for practical applications resulting in the use of levels of theory that are often inadequate for reactions. A critical objective was to develop practical methods that require the minimum number of electronic structure calculations for acceptable fidelity to the ab initio PES. Our method does this by a procedure that determines the optimal configurations at which ab initio points are computed, and that ensures that the final fitted PES is uniformly accurate to a prescribed tolerance. Our fitting methods can be done automatically, with little or no human intervention, and with no prior knowledge of the topology of the PES. The methods are based on local fitting schemes using interpolating moving least-squares (IMLS). IMLS has advantages over the very effective modified-Shepard methods developed by Collins and others in that higher-order polynomials can be used and does not require derivatives but can benefit from them if available.

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

    PubMed

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

    2016-03-31

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

  1. Aligned carbon nanotube with electro-catalytic activity for oxygen reduction reaction

    DOEpatents

    Liu, Di-Jia; Yang, Junbing; Wang, Xiaoping

    2010-08-03

    A catalyst for an electro-chemical oxygen reduction reaction (ORR) of a bundle of longitudinally aligned carbon nanotubes having a catalytically active transition metal incorporated longitudinally in said nanotubes. A method of making an electro-chemical catalyst for an oxygen reduction reaction (ORR) having a bundle of longitudinally aligned carbon nanotubes with a catalytically active transition metal incorporated throughout the nanotubes, where a substrate is in a first reaction zone, and a combination selected from one or more of a hydrocarbon and an organometallic compound containing an catalytically active transition metal and a nitrogen containing compound and an inert gas and a reducing gas is introduced into the first reaction zone which is maintained at a first reaction temperature for a time sufficient to vaporize material therein. The vaporized material is then introduced to a second reaction zone maintained at a second reaction temperature for a time sufficient to grow longitudinally aligned carbon nanotubes over the substrate with a catalytically active transition metal incorporated throughout the nanotubes.

  2. Free Energies of Chemical Reactions in Solution and in Enzymes with Ab Initio Quantum Mechanics/Molecular Mechanics Methods

    NASA Astrophysics Data System (ADS)

    Hu, Hao; Yang, Weitao

    2008-05-01

    Combined quantum mechanics/molecular mechanics (QM/MM) methods provide an accurate and efficient energetic description of complex chemical and biological systems, leading to significant advances in the understanding of chemical reactions in solution and in enzymes. Here we review progress in QM/MM methodology and applications, focusing on ab initio QM-based approaches. Ab initio QM/MM methods capitalize on the accuracy and reliability of the associated quantum-mechanical approaches, however, at a much higher computational cost compared with semiempirical quantum-mechanical approaches. Thus reaction-path and activation free-energy calculations based on ab initio QM/MM methods encounter unique challenges in simulation timescales and phase-space sampling. This review features recent developments overcoming these challenges and enabling accurate free-energy determination for reaction processes in solution and in enzymes, along with applications.

  3. Free energies of chemical reactions in solution and in enzymes with ab initio quantum mechanics/molecular mechanics methods.

    PubMed

    Hu, Hao; Yang, Weitao

    2008-01-01

    Combined quantum mechanics/molecular mechanics (QM/MM) methods provide an accurate and efficient energetic description of complex chemical and biological systems, leading to significant advances in the understanding of chemical reactions in solution and in enzymes. Here we review progress in QM/MM methodology and applications, focusing on ab initio QM-based approaches. Ab initio QM/MM methods capitalize on the accuracy and reliability of the associated quantum-mechanical approaches, however, at a much higher computational cost compared with semiempirical quantum-mechanical approaches. Thus reaction-path and activation free-energy calculations based on ab initio QM/MM methods encounter unique challenges in simulation timescales and phase-space sampling. This review features recent developments overcoming these challenges and enabling accurate free-energy determination for reaction processes in solution and in enzymes, along with applications.

  4. Resonant Chemical Oscillations: Pattern Formation in Reaction-Diffusion Systems

    NASA Astrophysics Data System (ADS)

    Lin, Anna L.

    2003-03-01

    Using the Belousov-Zhabotinsky (BZ) chemical system we explore the resonant response of spatially-extended oscillatory and excitable media to periodic perturbation. Resonance in excitable media is particularly relevant to biological systems, where excitable dynamics (threshold response to stimulus and refractoriness) are common. Methods to quantify spatio-temporal patterns will be discussed and the resonant patterns in excitable and oscillatory media will be compared. Experimental observations are compared to the results from numerical simulations of the Brusselator and FitzHugh-Nagumo models and from a forced complex Ginzburg-Landau amplitude equation.

  5. Transmission coefficients for chemical reactions with multiple states: role of quantum decoherence.

    PubMed

    de la Lande, Aurélien; Řezáč, Jan; Lévy, Bernard; Sanders, Barry C; Salahub, Dennis R

    2011-03-23

    Transition-state theory (TST) is a widely accepted paradigm for rationalizing the kinetics of chemical reactions involving one potential energy surface (PES). Multiple PES reaction rate constants can also be estimated within semiclassical approaches provided the hopping probability between the quantum states is taken into account when determining the transmission coefficient. In the Marcus theory of electron transfer, this hopping probability was historically calculated with models such as Landau-Zener theory. Although the hopping probability is intimately related to the question of the transition from the fully quantum to the semiclassical description, this issue is not adequately handled in physicochemical models commonly in use. In particular, quantum nuclear effects such as decoherence or dephasing are not present in the rate constant expressions. Retaining the convenient semiclassical picture, we include these effects through the introduction of a phenomenological quantum decoherence function. A simple modification to the usual TST rate constant expression is proposed: in addition to the electronic coupling, a characteristic decoherence time τ(dec) now also appears as a key parameter of the rate constant. This new parameter captures the idea that molecular systems, although intrinsically obeying quantum mechanical laws, behave semiclassically after a finite but nonzero amount of time (τ(dec)). This new degree of freedom allows a fresh look at the underlying physics of chemical reactions involving more than one quantum state. The ability of the proposed formula to describe the main physical lines of the phenomenon is confirmed by comparison with results obtained from density functional theory molecular dynamics simulations for a triplet to singlet transition within a copper dioxygen adduct relevant to the question of dioxygen activation by copper monooxygenases.

  6. Regular Wave Propagation Out of Noise in Chemical Active Media

    SciTech Connect

    Alonso, S.; Sendina-Nadal, I.; Perez-Munuzuri, V.; Sancho, J. M.; Sagues, F.

    2001-08-13

    A pacemaker, regularly emitting chemical waves, is created out of noise when an excitable photosensitive Belousov-Zhabotinsky medium, strictly unable to autonomously initiate autowaves, is forced with a spatiotemporal patterned random illumination. These experimental observations are also reproduced numerically by using a set of reaction-diffusion equations for an activator-inhibitor model, and further analytically interpreted in terms of genuine coupling effects arising from parametric fluctuations. Within the same framework we also address situations of noise-sustained propagation in subexcitable media.

  7. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the Conceptual Landscape

    ERIC Educational Resources Information Center

    Yan, Fan; Talanquer, Vicente

    2015-01-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative…

  8. Hypersensitivity reactions to radiocontrast media: the role of complement activation.

    PubMed

    Szebeni, Janos

    2004-01-01

    Although intravenous use of radiocontrast media (RCM) for a variety of radiographic procedures is generally safe, clinically significant acute hypersensitivity reactions still occur in a significant percentage of patients. The mechanism of these anaphylactoid, or "pseudoallergic," reactions is complex, involving complement activation, direct degranulation of mast cells and basophils, and modulation of enzymes and proteolytic cascades in plasma. In this review, basic information on different RCMs and their reactogenicity is summarized and updated, and the prevalence, pathomechanism, prediction, prevention, treatment, and economic impact of hypersensitivity reactions are discussed. Particular attention is paid to the in vitro and in vivo evidence supporting complement activation as an underlying cause of RCM reactions.

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

    NASA Astrophysics Data System (ADS)

    Onida, Giovanni; Andreoni, Wanda

    1995-09-01

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

  10. Rate constants for chemical reactions in high-temperature nonequilibrium air

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1986-01-01

    In the nonequilibrium atmospheric chemistry regime that will be encountered by the proposed Aeroassisted Orbital Transfer Vehicle in the upper atmosphere, where air density is too low for thermal and chemical equilibrium to be maintained, the detailed high temperature air chemistry plays a critical role in defining radiative and convective heating loads. Although vibrational and electronic temperatures remain low (less than 15,000 K), rotational and translational temperatures may reach 50,000 K. Attention is presently given to the effects of multiple temperatures on the magnitudes of various chemical reaction rate constants, for the cases of both bimolecular exchange reactions and collisional excitation and dissociation reactions.

  11. The mineralogic evolution of the Martian surface through time: Implications from chemical reaction path modeling studies

    NASA Technical Reports Server (NTRS)

    Plumlee, G. S.; Ridley, W. I.; Debraal, J. D.; Reed, M. H.

    1993-01-01

    Chemical reaction path calculations were used to model the minerals that might have formed at or near the Martian surface as a result of volcano or meteorite impact driven hydrothermal systems; weathering at the Martian surface during an early warm, wet climate; and near-zero or sub-zero C brine-regolith reactions in the current cold climate. Although the chemical reaction path calculations carried out do not define the exact mineralogical evolution of the Martian surface over time, they do place valuable geochemical constraints on the types of minerals that formed from an aqueous phase under various surficial and geochemically complex conditions.

  12. From chemical reactions to evolution: Emergence of species

    NASA Astrophysics Data System (ADS)

    Carletti, T.; Fanelli, D.

    2007-01-01

    The Chemoton model constitutes a minimalistic description of a protocell unit. The original formulation assumes three coupled chemical networks, representing a proto-metabolism, a template duplication and the membrane growth. An improved version is here proposed that explicitly incorporates the effects of the volume changes, due to the membrane growth. A stochastic mechanism is also introduced that mimics a stochastic source of error in the template duplication process. Numerical simulations are performed to monitor the time evolution of a family of protocells, under the chemoton hypothesis. An open-ended Darwinian evolution under the pressure of the environment is reproduced thus allowing to conclude that differentiation into species is an emergent property of the model.

  13. New physical-chemical reactions useful for TES

    NASA Astrophysics Data System (ADS)

    Johnson, J. S., Jr.; Westmoreland, C. G.

    New options in materials for heat storage is the aim of the program. Chemical systems, including those having equilibria with high temperature coefficients, are tested by differential scanning calorimetry for evidence of enhanced heat capacity. The approach is high-risk and exploratory; and in the search for new classes of storage systems, relatively little weight is given the costs of members of the classes that are at present apparent. Several possibilities have been tested in a preliminary way. These include concentrated aqueous solutions of a hydrolyzable metal ion; aqueous solutions of polyethylene oxide-polypropylene oxide polymers, which when cross-lindked take up or eject water in temperature cycles; and soluble partially fluorinated organic compounds, in hope that hydrates might be formed and be melted in temperature ranges of interest (analogous to clathrates). Certain petroleum ester waxes have also been tested. No promising embodiments have been found so far, but the survey is too incomplete as yet to rule any out.

  14. Empirical Force Fields for Mechanistic Studies of Chemical Reactions in Proteins.

    PubMed

    Das, A K; Meuwly, M

    2016-01-01

    Following chemical reactions in atomistic detail is one of the most challenging aspects of current computational approaches to chemistry. In this chapter the application of adiabatic reactive MD (ARMD) and its multistate version (MS-ARMD) are discussed. Both methods allow to study bond-breaking and bond-forming processes in chemical and biological processes. Particular emphasis is put on practical aspects for applying the methods to investigate the dynamics of chemical reactions. The chapter closes with an outlook of possible generalizations of the methods discussed.

  15. Empirical Force Fields for Mechanistic Studies of Chemical Reactions in Proteins.

    PubMed

    Das, A K; Meuwly, M

    2016-01-01

    Following chemical reactions in atomistic detail is one of the most challenging aspects of current computational approaches to chemistry. In this chapter the application of adiabatic reactive MD (ARMD) and its multistate version (MS-ARMD) are discussed. Both methods allow to study bond-breaking and bond-forming processes in chemical and biological processes. Particular emphasis is put on practical aspects for applying the methods to investigate the dynamics of chemical reactions. The chapter closes with an outlook of possible generalizations of the methods discussed. PMID:27498633

  16. Systematic trends in photonic reagent induced reactions in a homologous chemical family.

    PubMed

    Tibbetts, Katharine Moore; Xing, Xi; Rabitz, Herschel

    2013-08-29

    The growing use of ultrafast laser pulses to induce chemical reactions prompts consideration of these pulses as "photonic reagents" in analogy to chemical reagents. This work explores the prospect that photonic reagents may affect systematic trends in dissociative ionization reactions of a homologous family of halomethanes, much as systematic outcomes are often observed for reactions between homologous families of chemical reagents and chemical substrates. The experiments in this work with photonic reagents of varying pulse energy and linear spectral chirp reveal systematic correlations between observable ion yields and the following set of natural variables describing the substrate molecules: the ionization energy of the parent molecule, the appearance energy of each fragment ion, and the relative strength of carbon-halogen bonds in molecules containing two different halogens. The results suggest that reactions induced by photonic reagents exhibit systematic behavior analogous to that observed in reactions driven by chemical reagents, which provides a basis to consider empirical "rules" for predicting the outcomes of photonic reagent induced reactions.

  17. Molecules in Motion: Chemical Reaction and Allied Dynamics in Solution and Elsewhere

    NASA Astrophysics Data System (ADS)

    Hynes, James T.

    2015-04-01

    After my acceptance of the kind invitation from Todd Martínez and Mark Johnson, Co-Editors of this journal, to write this article, I had to decide just how to actually do this, given the existence of a fairly personal and extended autobiographical account of recent vintage detailing my youth, education, and assorted experiences and activities at the University of Colorado, Boulder, and later also at Ecole Normale Supérieure in Paris ( 1 ). In the end, I settled on a differently styled recounting of the adventures with my students, postdocs, collaborators, and colleagues in trying to unravel, comprehend, describe, and occasionally even predict the manifestations and consequences of the myriad assortment of molecular dances that contribute to and govern the rates and mechanisms of chemical reactions in solution (and elsewhere). The result follows.

  18. Detailed Chemical Kinetic Reaction Mechanisms for Incineration of Organophosphorus and Fluoro-Organophosphorus Compounds

    SciTech Connect

    Glaude, P A; Melius, C; Pitz, W J; Westbrook, C K

    2001-12-13

    A detailed chemical kinetic reaction mechanism is developed to describe incineration of the chemical warfare nerve agent sarin (GB), based on commonly used principles of bond additivity and hierarchical reaction mechanisms. The mechanism is based on previous kinetic models of organophosphorus compounds such as TMP, DMMP and DIMP that are often used as surrogates to predict incineration of GB. Kinetic models of the three surrogates and GB are then used to predict their consumption in a perfectly stirred reactor fueled by natural gas to simulate incineration of these chemicals. Computed results indicate that DIMP is the only one of these surrogates that adequately describes combustion of GB under comparable conditions. The kinetic pathways responsible for these differences in reactivity are identified and discussed. The most important reaction in GB and DIMP that makes them more reactive than TMP or DMMP is found to be a six-center molecular elimination reaction producing propene.

  19. Imaging Molecular Motion: Femtosecond X-Ray Scattering of an Electrocyclic Chemical Reaction.

    PubMed

    Minitti, M P; Budarz, J M; Kirrander, A; Robinson, J S; Ratner, D; Lane, T J; Zhu, D; Glownia, J M; Kozina, M; Lemke, H T; Sikorski, M; Feng, Y; Nelson, S; Saita, K; Stankus, B; Northey, T; Hastings, J B; Weber, P M

    2015-06-26

    Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.

  20. Buoyancy-driven instabilities induced by chemical reactions in vertical porous media

    NASA Astrophysics Data System (ADS)

    Almarcha, C.; Trevelyan, P. M. J.; de Wit, A.

    2008-11-01

    Classical Rayleigh-Taylor or double diffusive instabilities can be triggered by a simple A+B->C chemical reaction when two miscible solutions each containing one reactant are put in contact in the gravity field. A linear stability analysis of the evolving base state profiles is performed using a quasi-steady state approximation. This allows one to classify the various sources of instabilities as a function of the parameters which are the Rayleigh numbers and the ratio of diffusion coefficients of the chemical species. The resulting nonlinear dynamics due to this chemo-hydrodynamic feedback are then systematically analyzed to highlight how the chemical reaction can trigger or modify the hydrodynamical instabilities. It is also shown to what extent the resulting buoyancy-driven instabilities enhance the total reaction rate. Finally, related experiments are also performed in a vertical Hele-Shaw cell with an acid-base reaction.

  1. Students' Dilemmas in Reaction Stoichiometry Problem Solving: Deducing the Limiting Reagent in Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Waldrip, Bruce G.; Chandrasegaran, Antonia

    2009-01-01

    A qualitative case study was conducted to investigate the understanding of the limiting reagent concept and the strategies used by five Year 11 students when solving four reaction stoichiometry problems. Students' written problem-solving strategies were studied using the think-aloud protocol during problem-solving, and retrospective verbalisations…

  2. Students' Ideas about How and Why Chemical Reactions Happen: Mapping the conceptual landscape

    NASA Astrophysics Data System (ADS)

    Yan, Fan; Talanquer, Vicente

    2015-12-01

    Research in science education has revealed that many students struggle to understand chemical reactions. Improving teaching and learning about chemical processes demands that we develop a clearer understanding of student reasoning in this area and of how this reasoning evolves with training in the domain. Thus, we have carried out a qualitative study to explore students reasoning about chemical causality and mechanism. Study participants included individuals at different educational levels, from college to graduate school. We identified diverse conceptual modes expressed by students when engaged in the analysis of different types of reactions. Main findings indicate that student reasoning about chemical reactions is influenced by the nature of the process. More advanced students tended to express conceptual modes that were more normative and had more explanatory power, but major conceptual difficulties persisted in their reasoning. The results of our study are relevant to educators interested in conceptual development, learning progressions, and assessment.

  3. Chemical Reaction Rate Coefficients from Ring Polymer Molecular Dynamics: Theory and Practical Applications

    DOE PAGES

    Suleimanov, Yury V.; Aoiz, F. Javier; Guo, Hua

    2016-11-03

    This Feature Article presents an overview of the current status of ring polymer molecular dynamics (RPMD) rate theory. We first analyze the RPMD approach and its connection to quantum transition-state theory. We then focus on its practical applications to prototypical chemical reactions in the gas phase, which demonstrate how accurate and reliable RPMD is for calculating thermal chemical reaction rate coefficients in multifarious cases. This review serves as an important checkpoint in RPMD rate theory development, which shows that RPMD is shifting from being just one of recent novel ideas to a well-established and validated alternative to conventional techniques formore » calculating thermal chemical rate coefficients. We also hope it will motivate further applications of RPMD to various chemical reactions.« less

  4. Effect of water treatment chemicals on limestone/sulfur dioxide reaction in flue gas desulfurization systems

    SciTech Connect

    Dille, E.R.; Gaikwad, R.P.

    1994-12-31

    A simple laboratory test has been developed which simulates the reaction between limestone/water and sulfur dioxide in flue gas desulfurization systems. By adding various chemicals, in differing concentrations, to the limestone/water mixture, the quantitative impact on the sulfur dioxide/limestone reaction can be qualified and quantified. This paper will present the impact of several water treatment chemicals on the reaction of limestone and sulfur dioxide. An attempt has been made to predict the effect through mathematical correlations. All of the additive chemicals tend to decrease the rate of dissolution of limestone to various degrees. Some of the chemicals retard crystal growth thus adversely impacting solids separation in the thickener. The physical appearance of the crystal growth retarded limestone absorber slurry approaches a colloidal suspension.

  5. A New Method for Describing the Mechanism of a Chemical Reaction Based on the Unified Reaction Valley Approach.

    PubMed

    Zou, Wenli; Sexton, Thomas; Kraka, Elfi; Freindorf, Marek; Cremer, Dieter

    2016-02-01

    The unified reaction valley approach (URVA) used for a detailed mechanistic analysis of chemical reactions is improved in three different ways: (i) Direction and curvature of path are analyzed in terms of internal coordinate components that no longer depend on local vibrational modes. In this way, the path analysis is no longer sensitive to path instabilities associated with the occurrences of imaginary frequencies. (ii) The use of third order terms of the energy for a local description of the reaction valley allows an extension of the URVA analysis into the pre- and postchemical regions of the reaction path, which are typically characterized by flat energy regions. (iii) Configurational and conformational processes of the reaction complex are made transparent even in cases where these imply energy changes far less than a kcal/mol by exploiting the topology of the potential energy surface. As examples, the rhodium-catalyzed methanol carbonization, the Diels-Alder reaction between 1,3-butadiene and ethene, and the rearrangement of HCN to CNH are discussed.

  6. Research on Social Stability Mechanisms Based on Activation Energy and Gradual Activation Reaction Theory

    NASA Astrophysics Data System (ADS)

    Ning, Miao; Gu, Jifa

    This paper draws a comparison between social stability and chemical reaction process, and brings forward the concept of “social temperature” and “activation energy of social agent”. It is considered that social temperature turns out to be the macro symptom of social average energy, and its unceasing up-climbing roots in the energy accumulation of “inferiorization” process of social system; that “activation energy of social agent” stands for the social energy or temperature where individuals or groups reach the limit of their psychological bearing ability. This paper, basing on above concepts, elaborates on and demonstrates the gradual activation reaction mechanisms of social stability by a lot of concrete examples. It is thought that there is a threshold value for social stability, and the society will be unstable if social temperature goes higher than this value; that the larger the social average activation energy is, the higher the temperature threshold value of social stability will be; and considering that different groups have different activation energy, those fragile groups with low activation energy are often the risk source which might pose a threat to social stability.

  7. Mixing and chemical reaction in an idealized swirl chamber

    SciTech Connect

    Knio, O.M.; Worlikar, A.S.; Najm, H.N.

    1996-01-01

    A vorticity-based, low-Mach-number model for simulating combustion in closed chambers is constructed. Numerical scheme is based on a mixed finite-difference pseudo-spectral discretization of the governing equations. Discrete evolution equations are integrated in time using a predictor-corrector scheme, while discrete elliptic systems are inverted with the help of fast-Poisson solver. Scheme is applied to analyze mixing and combustion in an idealized swirl cavity, which consists of the annular space between a spinning inner cylinder and a stationary reaction. To this end, we assume that the oxidizer and fuel are initially separated by a thin mixed region, and carefully control mixing levels by varying the duration of the swirl-driven mixing period. The mixture is then ignited along the boundary of the inner cylinder. When pre-mixing is complete, an axisymmetric flame front is established, and the reactants are consumed as the front propagates radially outwards. When the charge is partially mixed, combustion in the early stages predominantly occurs within a non-uniform premixed front. As this non-uniform front approaches the outer cylinder, a transition to a distributed combustion regime occurs. Following the transition, the remaining fuel burns at a slow rate within non-premixed flames which wrap around the inner cylinder. Results show that the mixing time has substantial effects on the pressure rise within the cavity and on the evolution of the burnt fraction, and that these effects become more pronounced as the Damkoehler number increases.

  8. Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents.

    PubMed

    Dzhioev, Alan A; Kosov, Daniel S; von Oppen, Felix

    2013-04-01

    We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.

  9. Finite element modeling of contaminant transport in soils including the effect of chemical reactions.

    PubMed

    Javadi, A A; Al-Najjar, M M

    2007-05-17

    The movement of chemicals through soils to the groundwater is a major cause of degradation of water resources. In many cases, serious human and stock health implications are associated with this form of pollution. Recent studies have shown that the current models and methods are not able to adequately describe the leaching of nutrients through soils, often underestimating the risk of groundwater contamination by surface-applied chemicals, and overestimating the concentration of resident solutes. Furthermore, the effect of chemical reactions on the fate and transport of contaminants is not included in many of the existing numerical models for contaminant transport. In this paper a numerical model is presented for simulation of the flow of water and air and contaminant transport through unsaturated soils with the main focus being on the effects of chemical reactions. The governing equations of miscible contaminant transport including advection, dispersion-diffusion and adsorption effects together with the effect of chemical reactions are presented. The mathematical framework and the numerical implementation of the model are described in detail. The model is validated by application to a number of test cases from the literature and is then applied to the simulation of a physical model test involving transport of contaminants in a block of soil with particular reference to the effects of chemical reactions. Comparison of the results of the numerical model with the experimental results shows that the model is capable of predicting the effects of chemical reactions with very high accuracy. The importance of consideration of the effects of chemical reactions is highlighted.

  10. New chemical reactions in methane at high temperatures and pressures

    SciTech Connect

    Culler, T.S.; Schiferl, D. )

    1993-01-21

    The authors have used a Merrill-Bassett diamond anvil cell and Raman spectroscopy to study methane at high pressures (up to 13 GPa) and high temperatures (up to 912 K). At 2.5-5.0 GPa and 912 K, methane photoreacts with the laser light used for Raman spectroscopy and forms a graphitelike soot compound. At room temperature and pressure the Raman spectrum of the new material has an intense peak with a frequency of 1597 cm[sup [minus]1]. At higher pressures and temperatures (10-13 GPa and 948 K) a sample of [sup 13]CD[sub 4] methane photoreacted with the laser light and formed a hard, clear, solid film. At 0.34 GPa and 300 K, this film had Raman peaks at 541 and 1605 cm[sup [minus]1]. The 541-cm[sup [minus]1] peak may correspond to the 550-cm[sup [minus]1] peak found in some diamondlike carbon (DLC) films formed by chemical vapor deposition (CVD), but the 1605-cm[sup [minus]1] peak does not appear to have any such counterpart. Other possible Raman peaks were masked by interference from the diamond anvils. Thus, while the hard, clear film has some similarities to CVD DLC films, some important differences and questions remain. 35 refs., 5 figs.

  11. Molecular Beam Studies of Hot Atom Chemical Reactions: Reactive Scattering of Energetic Deuterium Atoms

    DOE R&D Accomplishments Database

    Continetti, R. E.; Balko, B. A.; Lee, Y. T.

    1989-02-01

    A brief review of the application of the crossed molecular beams technique to the study of hot atom chemical reactions in the last twenty years is given. Specific emphasis is placed on recent advances in the use of photolytically produced energetic deuterium atoms in the study of the fundamental elementary reactions D + H{sub 2} -> DH + H and the substitution reaction D + C{sub 2}H{sub 2} -> C{sub 2}HD + H. Recent advances in uv laser and pulsed molecular beam techniques have made the detailed study of hydrogen atom reactions under single collision conditions possible.

  12. Weber's law for biological responses in autocatalytic networks of chemical reactions.

    PubMed

    Inoue, Masayo; Kaneko, Kunihiko

    2011-07-22

    Biological responses often obey Weber's law, according to which the magnitude of the response depends only on the fold change in the external input. In this study, we demonstrate that a system involving a simple autocatalytic reaction shows such a response when a chemical is slowly synthesized by the reaction from a faster influx process. We also show that an autocatalytic reaction process occurring in series or in parallel can obey Weber's law with an oscillatory adaptive response. Considering the simplicity and ubiquity of the autocatalytic process, our proposed mechanism is thought to be commonly observed in biological reactions. PMID:21867048

  13. MuA Transposase: Organizing Two Reactions With One Active Site

    NASA Astrophysics Data System (ADS)

    Goldhaber-Gordon, Ilana; Baker, Tania A.

    2002-03-01

    Transposases are unusual proteins, performing at least two types of chemical reaction with a single active site. In the first reaction, the transposase cleaves the 3' end of a transposon DNA sequence. In the second reaction, the transposase transfers the cleaved 3' end into a new DNA molecule called the target. The final product is the transposon DNA attached by its 3' strands to the target DNA. The two reactions, DNA cleavage and DNA strand transfer, are chemically very similar, raising the question of how transposases avoid unintentionally cleaving the target. We have now observed that at least one transposase, the MuA protein, can cleave a target DNA --- when in the presence of a transposon DNA with a special (dideoxy nucleotide) termination. By exploring the protein's ability to cleave the target DNA under these unusual circumstances, we are learning how it prevents target cleavage when working with more standard DNA substrates.

  14. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule.

    PubMed

    Zheng, Peng; Arantes, Guilherme M; Field, Martin J; Li, Hongbin

    2015-06-25

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions.

  15. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    NASA Astrophysics Data System (ADS)

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-06-01

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions.

  16. Force-induced chemical reactions on the metal centre in a single metalloprotein molecule

    PubMed Central

    Zheng, Peng; Arantes, Guilherme M.; Field, Martin J.; Li, Hongbin

    2015-01-01

    Metalloproteins play indispensable roles in biology owing to the versatile chemical reactivity of metal centres. However, studying their reactivity in many metalloproteins is challenging, as protein three-dimensional structure encloses labile metal centres, thus limiting their access to reactants and impeding direct measurements. Here we demonstrate the use of single-molecule atomic force microscopy to induce partial unfolding to expose metal centres in metalloproteins to aqueous solution, thus allowing for studying their chemical reactivity in aqueous solution for the first time. As a proof-of-principle, we demonstrate two chemical reactions for the FeS4 centre in rubredoxin: electrophilic protonation and nucleophilic ligand substitution. Our results show that protonation and ligand substitution result in mechanical destabilization of the FeS4 centre. Quantum chemical calculations corroborated experimental results and revealed detailed reaction mechanisms. We anticipate that this novel approach will provide insights into chemical reactivity of metal centres in metalloproteins under biologically more relevant conditions. PMID:26108369

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

    PubMed

    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.

  18. Quantum theory of chemical reactions in the presence of electromagnetic fields.

    PubMed

    Tscherbul, T V; Krems, R V

    2008-07-21

    We present a theory for rigorous quantum scattering calculations of probabilities for chemical reactions of atoms with diatomic molecules in the presence of an external electric field. The approach is based on the fully uncoupled basis set representation of the total wave function in the space-fixed coordinate frame, the Fock-Delves hyperspherical coordinates, and the adiabatic partitioning of the total Hamiltonian of the reactive system. The adiabatic channel wave functions are expanded in basis sets of hyperangular functions corresponding to different reaction arrangements, and the interactions with external fields are included in each chemical arrangement separately. We apply the theory to examine the effects of electric fields on the chemical reactions of LiF molecules with H atoms and HF molecules with Li atoms at low temperatures and show that electric fields may enhance the probability of chemical reactions and modify reactive scattering resonances by coupling the rotational states of the reactants. Our preliminary results suggest that chemical reactions of polar molecules at temperatures below 1 K can be selectively manipulated with dc electric fields and microwave laser radiation.

  19. Effect of gravity field on the nonequilibrium/nonlinear chemical oscillation reactions

    NASA Astrophysics Data System (ADS)

    Fujieda, S.; Mori, Y.; Nakazawa, A.; Mogami, Y.

    2001-01-01

    Biological systems have evolved for a long time under the normal gravity. The Belousov-Zhabotinsky (BZ) reaction is a nonlinear chemical system far from the equilibrium that may be considered as a simplified chemical model of the biological systems so as to study the effect of gravity. The reaction solution is comprised of bromate in sulfuric acid as an oxidizing agent, 1,4-cyclohexanedione as an organic substrate, and ferroin as a metal catalyst. Chemical waves in the BZ reaction-diffusion system are visualized as blue and red patterns of ferriin and ferroin, respectively. After an improvement to the tubular reaction vessels in the experimental setup, the traveling velocity of chemical waves in aqueous solutions was measured in time series under normal gravity, microgravity, hyper-gravity, and normal gravity using the free-fall facility of JAMIC (Japan Microgravity Center), Hokkaido, Japan. Chemical patterns were collected as image data via CCD camera and analyzed by the software of NIH image after digitization. The estimated traveling velocity increased with increasing gravity as expected. It was clear experimentally that the traveling velocity of target patterns in reaction diffusion system was influenced by the effect of convection and correlated closely with the gravity field.

  20. Effect of gravity field on the nonequilibrium/nonlinear chemical oscillation reactions.

    PubMed

    Fujieda, S; Mori, Y; Nakazawa, A; Mogami, Y

    2001-01-01

    Biological systems have evolved for a long time under the normal gravity. The Belousov-Zhabotinsky (BZ) reaction is a nonlinear chemical system far from the equilibrium that may be considered as a simplified chemical model of the biological systems so as to study the effect of gravity. The reaction solution is comprised of bromate in sulfuric acid as an oxidizing agent, 1,4-cyclohexanedione as an organic substrate, and ferroin as a metal catalyst. Chemical waves in the BZ reaction-diffusion system are visualized as blue and red patterns of ferriin and ferroin, respectively. After an improvement to the tubular reaction vessels in the experimental setup, the traveling velocity of chemical waves in aqueous solutions was measured in time series under normal gravity, microgravity, hyper-gravity, and normal gravity using the free-fall facility of JAMIC (Japan Microgravity Center), Hokkaido, Japan. Chemical patterns were collected as image data via CCD camera and analyzed by the software of NIH image after digitization. The estimated traveling velocity increased with increasing gravity as expected. It was clear experimentally that the traveling velocity of target patterns in reaction diffusion system was influenced by the effect of convection and correlated closely with the gravity field.

  1. Sensitivity of chemical reaction networks: a structural approach. 1. Examples and the carbon metabolic network.

    PubMed

    Mochizuki, Atsushi; Fiedler, Bernold

    2015-02-21

    In biological cells, chemical reaction pathways lead to complex network systems like metabolic networks. One experimental approach to the dynamics of such systems examines their "sensitivity": each enzyme mediating a reaction in the system is increased/decreased or knocked out separately, and the responses in the concentrations of chemicals or their fluxes are observed. In this study, we present a mathematical method, named structural sensitivity analysis, to determine the sensitivity of reaction systems from information on the network alone. We investigate how the sensitivity responses of chemicals in a reaction network depend on the structure of the network, and on the position of the perturbed reaction in the network. We establish and prove some general rules which relate the sensitivity response to the structure of the underlying network. We describe a hierarchical pattern in the flux response which is governed by branchings in the network. We apply our method to several hypothetical and real life chemical reaction networks, including the metabolic network of the Escherichia coli TCA cycle.

  2. The Sugar Model: Autocatalytic Activity of the Triose Ammonia Reaction

    NASA Astrophysics Data System (ADS)

    Weber, Arthur L.

    2007-04-01

    Reaction of triose sugars with ammonia under anaerobic conditions yielded autocatalytic products. The autocatalytic behavior of the products was examined by measuring the effect of the crude triose ammonia reaction product on the kinetics of a second identical triose ammonia reaction. The reaction product showed autocatalytic activity by increasing both the rate of disappearance of triose and the rate of formation of pyruvaldehyde, the product of triose dehydration. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of autocatalytic molecules.

  3. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    NASA Astrophysics Data System (ADS)

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-01

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope 4He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O2. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  4. Chemical reactions studied at ultra-low temperature in liquid helium clusters

    SciTech Connect

    Huisken, Friedrich; Krasnokutski, Serge A.

    2012-11-27

    Low-temperature reaction rates are important ingredients for astrophysical reaction networks modeling the formation of interstellar matter in molecular clouds. Unfortunately, such data is difficult to obtain by experimental means. In an attempt to study low-temperature reactions of astrophysical interest, we have investigated relevant reactions at ultralow temperature in liquid helium droplets. Being prepared by supersonic expansion of helium gas at high pressure through a nozzle into a vacuum, large helium clusters in the form of liquid droplets constitute nano-sized reaction vessels for the study of chemical reactions at ultra-low temperature. If the normal isotope {sup 4}He is used, the helium droplets are superfluid and characterized by a constant temperature of 0.37 K. Here we present results obtained for Mg, Al, and Si reacting with O{sub 2}. Mass spectrometry was employed to characterize the reaction products. As it may be difficult to distinguish between reactions occurring in the helium droplets before they are ionized and ion-molecule reactions taking place after the ionization, additional techniques were applied to ensure that the reactions actually occurred in the helium droplets. This information was provided by measuring the chemiluminescence light emitted by the products, the evaporation of helium atoms by the release of the reaction heat, or by laser-spectroscopic identification of the reactants and products.

  5. Active Emulsions: Synchronization of Chemical Oscillators

    NASA Astrophysics Data System (ADS)

    Fraden, Seth

    2012-02-01

    We explore the dynamical behavior of emulsions consisting of nanoliter volume droplets of the oscillatory Belousov-Zhabotinsky (BZ) reaction separated by a continuous oil phase. Some of the aqueous BZ reactants partition into the oil leading to chemical coupling of the drops. We use microfluidics to vary the size, composition and topology of the drops in 1D and 2D. Addition of a light sensitive catalyst to the drops and illumination with a computer projector allows each drop to be individually perturbed. A variety of synchronous regimes are found that systematically vary with the coupling strength and whether coupling is dominated by activatory or inhibitory species. In 1D we observe in- and anti-phase oscillations, stationary Turing patterns in which drops stop oscillating, but form spatially periodic patterns of drops in the oxidized and reduced states, and more complex combinations of stationary and oscillatory drops. In 2D, the attractors are more complex and vary with network topology and coupling strength. For hexagonal lattices as a function of increasing coupling strength we observe right and left handed rotating oscillations, mixed oscillatory and Turing states and finally full Turing states. Reaction -- diffusion models based on a simplified description of the BZ chemistry and diffusion of messenger species reproduce a number of the experimental results. For a range of parameters, a simplified phase oscillator model provides an intuitive understanding of the complex synchronization patterns. [4pt] ``Coupled oscillations in a 1D emulsion of Belousov--Zhabotinsky droplets,'' Jorge Delgado, Ning Li, Marcin Leda, Hector O. Gonzalez-Ochoa, Seth Fraden and Irving R. Epstein, Soft Matter, 7, 3155 (2011).

  6. Observing single-molecule chemical reactions on metal nanoparticles

    NASA Astrophysics Data System (ADS)

    Emory, Steven R.; Ambrose, W. Patrick; Goodwin, Peter M.; Keller, Richard A.

    2001-06-01

    We report on the study of the photodecomposition of single Rhodamine 6G (R6G) dye molecules adsorbed on silver nanoparticles. The nanoparticles were immobilized and spatially isolated on polylysine-derivatized glass coverslips, and confocal laser microspectroscopy was used to obtain surface-enhanced Raman scatters (SERS) spectra from individual R6G molecules. The photodecomposition of these molecules was observed with 150-ms temporal resolution. The photoproduct was identified as graphitic carbon based on the appearance of bread SERS vibrational bands at 1592 cm-1 and 1340 cm-1 observed in both bulk and averaged single-molecule photoproduct spectra. In contrast, when observed at the single-molecule level, the photoproduct yielded sharp SERS spectra. The inhomogeneous broadening of the bulk SERS spectra is due to a variety of photoproducts in different surface orientations and is a characteristic of ensemble-averaged measurement of disordered systems. These single-molecule studies indicate a photodecomposition pathway by which the R6G molecule desorbs from the metal surface, an excited-state photoreaction occurs, and the R6G photoproduct(s) readsorbs to the surface. A SERS spectrum is obtained when either the intact R6G or the R6G photoproduct(s) are adsorbed on a SERS-active site. This work further illustrates the power of single-molecule spectroscopy (SMS) to reveal unique behaviors of single molecules that are not discernable with bulk measurements.

  7. Observing single molecule chemical reactions on metal nanoparticles.

    SciTech Connect

    Emory, S. R.; Ambrose, W. Patrick; Goodwin, P. M.; Keller, Richard A.

    2001-01-01

    We report the study of the photodecomposition of single Rhodamine 6G (R6G) dye molecules adsorbed on silver nanoparticles. The nanoparticles were immobilized and spatially isolated on polylysine-derivatized glass coverslips, and confocal laser microspectroscopy was used to obtain surface-enhanced Raman scattering (SERS) spectra from individual R6G molecules. The photodecomposition of these molecules was observed with 150-ms temporal resolution. The photoproduct was identified as graphitic carbon based on the appearance of broad SERS vibrational bands at 1592 cm{sup -1} and 1340 cm{sup -1} observed in both bulk and averaged single-molecule photoproduct spectra. In contrast, when observed at the single-molecule level, the photoproduct yielded sharp SERS spectra. The inhomogeneous broadening of the bulk SERS spectra is due to a variety of photoproducts in different surface orientations and is a characteristic of ensemble-averaged measurements of disordered systems. These single-molecule studies indicate a photodecomposition pathway by which the R6G molecule desorbs from the metal surface, an excited-state photoreaction occurs, and the R6G photoproduct(s) readsorbs to the surface. A SERS spectrum is obtained when either the intact R6G or the R6G photoproduct(s) are adsorbed on a SERS-active site. This work further illustrates the power of single-molecule spectroscopy (SMS) to reveal unique behaviors of single molecules that are not discernable with bulk measurements.

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

    PubMed

    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)], in contrast to previous work by Jones and Hore [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010)]. 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.

  9. The Role of Comprehensive Detailed Chemical Kinetic Reaction Mechanisms in Combustion Research

    SciTech Connect

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

    2008-07-16

    Recent developments by the authors in the field of comprehensive detailed chemical kinetic reaction mechanisms for hydrocarbon fuels are reviewed. Examples are given of how these mechanisms provide fundamental chemical insights into a range of combustion applications. Practical combustion consists primarily of chemical heat release from reactions between a fuel and an oxidizer, and computer simulations of practical combustion systems have become an essential tool of combustion research (Westbrook et al., 2005). At the heart of most combustion simulations, the chemical kinetic submodel frequently is the most detailed, complex and computationally costly part of a system model. Historically, the chemical submodel equations are solved using time-implicit numerical algorithms, due to the extreme stiffness of the coupled rate equations, with a computational cost that varies roughly with the cube of the number of chemical species in the model. While early mechanisms (c. 1980) for apparently simple fuels such as methane (Warnatz, 1980) or methanol (Westbrook and Dryer, 1979) included perhaps 25 species, current detailed mechanisms for much larger, more complex fuels such as hexadecane (Fournet et al., 2001; Ristori et al., 2001; Westbrook et al., 2008) or methyl ester methyl decanoate (Herbinet et al., 2008) have as many as 2000 or even 3000 species. Rapid growth in capabilities of modern computers has been an essential feature in this rapid growth in the size and complexity of chemical kinetic reaction mechanisms.

  10. Chemical Characterization and Reactivity Testing of Fuel-Oxidizer Reaction Product (Test Report)

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The product of incomplete reaction of monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) propellants, or fuel-oxidizer reaction product (FORP), has been hypothesized as a contributory cause of an anomaly which occurred in the chamber pressure (PC) transducer tube on the Reaction Control Subsystem (RCS) aft thruster 467 on flight STS-51. A small hole was found in the titanium-alloy PC tube at the first bend below the pressure transducer. It was surmised that the hole may have been caused by heat and pressure resulting from ignition of FORP. The NASA Johnson Space Center (JSC) White Sands Test Facility (WSTF) was requested to define the chemical characteristics of FORP, characterize its reactivity, and simulate the events in a controlled environment which may have lead to the Pc-tube failure. Samples of FORP were obtained from the gas-phase reaction of MMH with NTO under laboratory conditions, the pulsed firings of RCS thrusters with modified PC tubes using varied oxidizer or fuel lead times, and the nominal RCS thruster firings at WSTF and Kaiser-Marquardt. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC), ion chromatography (IC), inductively coupled plasma (ICP) spectrometry, thermogravimetric analysis (TGA) coupled to FTIR (TGA/FTIR), and mechanical impact testing were used to qualitatively and quantitatively characterize the chemical, thermal, and ignition properties of FORP. These studies showed that the composition of FORP is variable but falls within a limited range of compositions that depends on the fuel loxidizer ratio at the time of formation, composition of the post-formation atmosphere (reducing or oxidizing), and reaction or postreaction temperature. A typical composition contains methylhydrazinium nitrate (MMHN), ammonium nitrate (AN), methylammonium nitrate (MAN), and trace amounts of hydrazinium nitrate and 1,1-dimethylhydrazinium nitrate. The thermal decomposition

  11. Competition between charge exchange and chemical reaction - The D2/+/ + H system

    NASA Technical Reports Server (NTRS)

    Preston, R. K.; Cross, R. J., Jr.

    1973-01-01

    Study of the special features of molecular charge exchange and its competition with chemical reaction in the case of the D2(+) + H system. The trajectory surface hopping (TSH) model proposed by Tully and Preston (1971) is used to study this competition for a number of reactions involving the above system. The diatomics-in-molecules zero-overlap approximation is used to calculate the three adiabatic surfaces - one triplet and two singlet - which are needed to describe this system. One of the significant results of this study is that the chemical reaction and charge exchange are strongly coupled. It is also found that the number of trajectories passing into the chemical regions of the three surfaces depends very strongly on the surface crossings.-

  12. On the possibility of negative activation energies in bimolecular reactions

    NASA Technical Reports Server (NTRS)

    Jaffe, R. L.

    1978-01-01

    The temperature dependence of the rate constants for model reacting systems was studied to understand some recent experimental measurements which imply the existence of negative activation energies. A collision theory model and classical trajectory calculations are used to demonstrate that the reaction probability can vary inversely with collision energy for bimolecular reactions occurring on attractive potential energy surfaces. However, this is not a sufficient condition to ensure that the rate constant has a negative temperature dependence. On the basis of these calculations, it seems unlikely that a true bimolecular reaction between neutral molecules will have a negative activation energy.

  13. Surface modification of poly(ethylene terephthalate) fabric via photo-chemical reaction of dimethylaminopropyl methacrylamide

    NASA Astrophysics Data System (ADS)

    Mohamed, Nasser H.; Bahners, Thomas; Wego, Andreas; Gutmann, Jochen S.; Ulbricht, Mathias

    2012-10-01

    Photo-chemical reactions and surface modifications of poly(ethylene terephthalate) (PET) fabrics with the monomer dimethylaminopropyl methacrylamide (DMAPMA) and benzophenone (BP) as photo-initiator using a broad-band UV lamp source were investigated. The tertiary amino groups of the grafted poly(DMAPMA) chains were subsequently quaternized with alkyl bromides of different chain lengths to establish antibacterial activity. The surface composition, structure and morphology of modified PET fabrics were characterized by Fourier transform infrared spectroscopy (FTIR/ATR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). To evaluate the amount of quaternary and tertiary ammonium groups on the modified surface, PET was dyed with an acid dye which binds to the ammonium groups. Therefore, the color depth is a direct indicator of the amount of ammonium groups. The resulting antibacterial activity of the modified PET fabrics was tested with Escherichia coli. The results of all experiments show that a photochemical modification of PET is possible using DMAPMA, benzophenone and UV light. Also, the quaternization of tertiary amino groups as well as the increase in antibacterial activity of the modified PET by the established quaternary ammonium groups were successful.

  14. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods.

    PubMed

    Suleimanov, Yury V; Green, William H

    2015-09-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms--the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several single-molecule systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes. PMID:26575920

  15. Molecular dynamics study of phase separation in fluids with chemical reactions

    NASA Astrophysics Data System (ADS)

    Krishnan, Raishma; Puri, Sanjay

    2015-11-01

    We present results from the first d =3 molecular dynamics (MD) study of phase-separating fluid mixtures (AB) with simple chemical reactions (A ⇌B ). We focus on the case where the rates of forward and backward reactions are equal. The chemical reactions compete with segregation, and the coarsening system settles into a steady-state mesoscale morphology. However, hydrodynamic effects destroy the lamellar morphology which characterizes the diffusive case. This has important consequences for the phase-separating structure, which we study in detail. In particular, the equilibrium length scale (ℓeq) in the steady state suggests a power-law dependence on the reaction rate ɛ :ℓeq˜ɛ-θ with θ ≃1.0 .

  16. Molecular dynamics study of phase separation in fluids with chemical reactions.

    PubMed

    Krishnan, Raishma; Puri, Sanjay

    2015-11-01

    We present results from the first d=3 molecular dynamics (MD) study of phase-separating fluid mixtures (AB) with simple chemical reactions (A⇌B). We focus on the case where the rates of forward and backward reactions are equal. The chemical reactions compete with segregation, and the coarsening system settles into a steady-state mesoscale morphology. However, hydrodynamic effects destroy the lamellar morphology which characterizes the diffusive case. This has important consequences for the phase-separating structure, which we study in detail. In particular, the equilibrium length scale (ℓ(eq)) in the steady state suggests a power-law dependence on the reaction rate ε:ℓ(eq)∼ε(-θ) with θ≃1.0.

  17. Estimating the effective rate of fast chemical reactions with turbulent mixing of reactants

    SciTech Connect

    Vorotilin, V. P. Yanovskii, Yu. G.

    2015-07-15

    On the basis of representation of a turbulent fluid as an aggregation of independent turbulent particles (vortexes), we derive relations for the effective rate of chemical reactions and obtain a closed system of equations describing reactions with turbulent mixing of reactants. A variant of instantaneous reactions is considered that explains the proposed approach simply. In particular, the turbulent mixing events according to this approach are uniquely related to the acts of chemical interaction, which makes it possible to exclude from consideration the mixing of inert impurities–the most difficult point of the theory formulated using classical notions. The obtained system of equations is closed without introducing arbitrarily adopted correlations, by naturally introducing the concept of effective reaction and writing the equations of conservation for both the concentrations of reactants and their volumes.

  18. Automated Discovery of Elementary Chemical Reaction Steps Using Freezing String and Berny Optimization Methods.

    PubMed

    Suleimanov, Yury V; Green, William H

    2015-09-01

    We present a simple protocol which allows fully automated discovery of elementary chemical reaction steps using in cooperation double- and single-ended transition-state optimization algorithms--the freezing string and Berny optimization methods, respectively. To demonstrate the utility of the proposed approach, the reactivity of several single-molecule systems of combustion and atmospheric chemistry importance is investigated. The proposed algorithm allowed us to detect without any human intervention not only "known" reaction pathways, manually detected in the previous studies, but also new, previously "unknown", reaction pathways which involve significant atom rearrangements. We believe that applying such a systematic approach to elementary reaction path finding will greatly accelerate the discovery of new chemistry and will lead to more accurate computer simulations of various chemical processes.

  19. Stereodynamics of chemical reactions: quasi-classical, quantum and mixed quantum-classical theories

    NASA Astrophysics Data System (ADS)

    Xu, Wenwu; Zhao, Guangjiu

    2012-04-01

    In this review, some benchmark works by Han and coworkers on the stereodynamics of typical chemical reactions, triatomic reactions H + D2, Cl + H2 and O + H2 and polyatomic reaction Cl+CH4/CD4, are presented by using the quasi-classical, quantum and mixed quantum-classical methods. The product alignment and orientation in these A+BC model reactions are discussed in detail. We have also compared our theoretical results with experimental measurements and demonstrated that our theoretical results are in good agreement with the experimental results. Quasi-classical trajectory (QCT) method ignores some quantum effects like the tunneling effect and zero-point energy. The quantum method will be very time-consuming. Moreover, the mixed quantum-classical method can take into account some quantum effects and hence is expected to be applicable to large systems and widely used in chemical stereodynamics studies.

  20. Fluctuation Induced Structure in Chemical Reaction with Small Number of Molecules

    NASA Astrophysics Data System (ADS)

    Suzuki, Yasuhiro

    We investigate the behaviors of chemical reactions of the Lotka-Volterra model with small number of molecules; hence the occurrence of random fluctuations modifies the deterministic behavior and the law of mass action is replaced by a stochastic model. We model it by using Abstract Rewriting System on Multisets, ARMS; ARMS is a stochastic method of simulating chemical reactions and it is based on the reaction rate equation. We confirmed that the magnitude of fluctuations on periodicity of oscillations becomes large, as the number of involved molecules is getting smaller; and these fluctuations induce another structure, which have not observed in the reactions with large number of molecules. We show that the underling mechanism through investigating the coarse grained phase space of ARMS.

  1. Stereo and regioselectivity in ''Activated'' tritium reactions

    SciTech Connect

    Ehrenkaufer, R.L.E.; Hembree, W.C.; Wolf, A.P.

    1988-01-01

    To investigate the stereo and positional selectivity of the microwave discharge activation (MDA) method, the tritium labeling of several amino acids was undertaken. The labeling of L-valine and the diastereomeric pair L-isoleucine and L-alloisoleucine showed less than statistical labeling at the ..cap alpha..-amino C-H position mostly with retention of configuration. Labeling predominated at the single ..beta.. C-H tertiary (methyne) position. The labeling of L-valine and L-proline with and without positive charge on the ..cap alpha..-amino group resulted in large increases in specific activity (greater than 10-fold) when positive charge was removed by labeling them as their sodium carboxylate salts. Tritium NMR of L-proline labeled both as its zwitterion and sodium salt showed also large differences in the tritium distribution within the molecule. The distribution preferences in each of the charge states are suggestive of labeling by an electrophilic like tritium species(s). 16 refs., 5 tabs.

  2. Significance of vapor phase chemical reactions on CVD rates predicted by chemically frozen and local thermochemical equilibrium boundary layer theories

    NASA Technical Reports Server (NTRS)

    Gokoglu, Suleyman A.

    1988-01-01

    This paper investigates the role played by vapor-phase chemical reactions on CVD rates by comparing the results of two extreme theories developed to predict CVD mass transport rates in the absence of interfacial kinetic barrier: one based on chemically frozen boundary layer and the other based on local thermochemical equilibrium. Both theories consider laminar convective-diffusion boundary layers at high Reynolds numbers and include thermal (Soret) diffusion and variable property effects. As an example, Na2SO4 deposition was studied. It was found that gas phase reactions have no important role on Na2SO4 deposition rates and on the predictions of the theories. The implications of the predictions of the two theories to other CVD systems are discussed.

  3. Characterization of plastic deformation and chemical reaction in titanium-polytetrafluoroethylene mixture

    NASA Astrophysics Data System (ADS)

    Davis, Jeffery Jon

    1998-09-01

    The subject of this dissertation is the deformation process of a single metal - polymer system (titanium - polytetrafluoroethylene) and how this process leads to initiation of chemical reaction. Several different kinds of experiments were performed to characterize the behavior of this material to shock and impact. These mechanical conditions induce a rapid plastic deformation of the sample. All of the samples tested had an initial porosity which increased the plastic flow condition. It is currently believed that during the deformation process two important conditions occur: removal of the oxide layer from the metal and decomposition of the polymer. These conditions allow for rapid chemical reaction. The research from this dissertation has provided insight into the complex behavior of plastic deformation and chemical reactions in titanium - polytetrafluoroethylene (PTFE, Teflon). A hydrodynamic computational code was used to model the plastic flow for correlation with the results from the experiments. The results from this work are being used to develop an ignition and growth model for metal/polymer systems. Three sets of experiments were used to examine deformation of the 80% Ti and 20% Teflon materials: drop- weight, gas gun, and split-Hopkinson pressure bar. Recovery studies included post shot analysis of the samples using x-ray diffraction. Lagrangian hydrocode DYNA2D modeling of the drop-weight tests was performed for comparison with experiments. One of the reactions know to occur is Ti + C → TiC (s) which results in an exothermic release. However, the believed initial reactions occur between Ti and fluorine which produces TixFy gases. The thermochemical code CHEETAH was used to investigate the detonation products and concentrations possible during Ti - Teflon reaction. CHEETAH shows that the Ti - fluorine reactions are thermodynamically favorable. This research represents the most comprehensive to date study of deformation induced chemical reaction in metal/polymers.

  4. Simulation of Chemical Isomerization Reaction Dynamics on a NMR Quantum Simulator

    NASA Astrophysics Data System (ADS)

    Lu, Dawei; Xu, Nanyang; Xu, Ruixue; Chen, Hongwei; Gong, Jiangbin; Peng, Xinhua; Du, Jiangfeng

    2011-07-01

    Quantum simulation can beat current classical computers with minimally a few tens of qubits. Here we report an experimental demonstration that a small nuclear-magnetic-resonance quantum simulator is already able to simulate the dynamics of a prototype laser-driven isomerization reaction using engineered quantum control pulses. The experimental results agree well with classical simulations. We conclude that the quantum simulation of chemical reaction dynamics not computable on current classical computers is feasible in the near future.

  5. Non-invasive estimation of dissipation from non-equilibrium fluctuations in chemical reactions.

    PubMed

    Muy, S; Kundu, A; Lacoste, D

    2013-09-28

    We show how to extract an estimate of the entropy production from a sufficiently long time series of stationary fluctuations of chemical reactions. This method, which is based on recent work on fluctuation theorems, is direct, non-invasive, does not require any knowledge about the underlying dynamics and is applicable even when only partial information is available. We apply it to simple stochastic models of chemical reactions involving a finite number of states, and for this case, we study how the estimate of dissipation is affected by the degree of coarse-graining present in the input data.

  6. Reacting gas mixtures in the state-to-state approach: The chemical reaction rates

    SciTech Connect

    Kustova, Elena V.; Kremer, Gilberto M.

    2014-12-09

    In this work chemically reacting mixtures of viscous flows are analyzed within the framework of Boltzmann equation. By applying a modified Chapman-Enskog method to the system of Boltzmann equations general expressions for the rates of chemical reactions and vibrational energy transitions are determined as functions of two thermodynamic forces: the velocity divergence and the affinity. As an application chemically reacting mixtures of N{sub 2} across a shock wave are studied, where the first lowest vibrational states are taken into account. Here we consider only the contributions from the first four single quantum vibrational-translational energy transitions. It is shown that the contribution to the chemical reaction rate related to the affinity is much larger than that of the velocity divergence.

  7. Arrhenius' law in turbulent media and an equivalent tunnel effect. [in binary exchange chemical reactions

    NASA Technical Reports Server (NTRS)

    Tsuge, S.; Sagara, K.

    1978-01-01

    The indeterminacy inherent to the formal extension of Arrhenius' law to reactions in turbulent flows is shown to be surmountable in the case of a binary exchange reaction with a sufficiently high activation energy. A preliminary calculation predicts that the turbulent reaction rate is invariant in the Arrhenius form except for an equivalently lowered activation energy. This is a reflection of turbulence-augmented molecular vigor, and causes an appreciable increase in the reaction rate. A similarity to the tunnel effect in quantum mechanics is indicated. The anomaly associated with the mild ignition of oxy-hydrogen mixtures is discussed in this light.

  8. A Review of the Thermodynamic, Transport, and Chemical Reaction Rate Properties of High-temperature Air

    NASA Technical Reports Server (NTRS)

    Hansen, C Frederick; Heims, Steve P

    1958-01-01

    Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.

  9. The influence of the "cage" effect on the mechanism of reversible bimolecular multistage chemical reactions proceeding from different sites in solutions.

    PubMed

    Doktorov, Alexander B

    2016-08-28

    Manifestations of the "cage" effect at the encounters of reactants have been theoretically treated on the example of multistage reactions (including bimolecular exchange reactions as elementary stages) proceeding from different active sites in liquid solutions. It is shown that for reactions occurring near the contact of reactants, consistent consideration of quasi-stationary kinetics of such multistage reactions (possible in the framework of the encounter theory only) can be made on the basis of chemical concepts of the "cage complex," just as in the case of one-site model described in the literature. Exactly as in the one-site model, the presence of the "cage" effect gives rise to new channels of reactant transformation that cannot result from elementary event of chemical conversion for the given reaction mechanism. Besides, the multisite model demonstrates new (as compared to one-site model) features of multistage reaction course. PMID:27586911

  10. The influence of the "cage" effect on the mechanism of reversible bimolecular multistage chemical reactions proceeding from different sites in solutions.

    PubMed

    Doktorov, Alexander B

    2016-08-28

    Manifestations of the "cage" effect at the encounters of reactants have been theoretically treated on the example of multistage reactions (including bimolecular exchange reactions as elementary stages) proceeding from different active sites in liquid solutions. It is shown that for reactions occurring near the contact of reactants, consistent consideration of quasi-stationary kinetics of such multistage reactions (possible in the framework of the encounter theory only) can be made on the basis of chemical concepts of the "cage complex," just as in the case of one-site model described in the literature. Exactly as in the one-site model, the presence of the "cage" effect gives rise to new channels of reactant transformation that cannot result from elementary event of chemical conversion for the given reaction mechanism. Besides, the multisite model demonstrates new (as compared to one-site model) features of multistage reaction course.

  11. Ion-Molecule Reactions and Chemical Composition of Emanated from Herculane Spa Geothermal Sources

    PubMed Central

    Cosma, Constantin; Suciu, Ioan; Jäntschi, Lorentz; Bolboacă, Sorana D.

    2008-01-01

    The paper presents a chemical composition analysis of the gases emanated from geothermal sources in the Herculane Spa area (Romania). The upper homologues of methane have been identified in these gases. An ion-molecule reaction mechanism could be implicated in the formation of the upper homologues of methane. The CH4+ ions that appear under the action of radiation are the starting point of these reactions. The presence of hydrogen in the emanated gases may be also a result of these reactions. PMID:19325844

  12. Flow network QSAR for the prediction of physicochemical properties by mapping an electrical resistance network onto a chemical reaction poset.

    PubMed

    Ivanciuc, Ovidiu; Ivanciuc, Teodora; Klein, Douglas J

    2013-06-01

    Usual quantitative structure-activity relationship (QSAR) models are computed from unstructured input data, by using a vector of molecular descriptors for each chemical in the dataset. Another alternative is to consider the structural relationships between the chemical structures, such as molecular similarity, presence of certain substructures, or chemical transformations between compounds. We defined a class of network-QSAR models based on molecular networks induced by a sequence of substitution reactions on a chemical structure that generates a partially ordered set (or poset) oriented graph that may be used to predict various molecular properties with quantitative superstructure-activity relationships (QSSAR). The network-QSAR interpolation models defined on poset graphs, namely average poset, cluster expansion, and spline poset, were tested with success for the prediction of several physicochemical properties for diverse chemicals. We introduce the flow network QSAR, a new poset regression model in which the dataset of chemicals, represented as a reaction poset, is transformed into an oriented network of electrical resistances in which the current flow results in a potential at each node. The molecular property considered in the QSSAR model is represented as the electrical potential, and the value of this potential at a particular node is determined by the electrical resistances assigned to each edge and by a system of batteries. Each node with a known value for the molecular property is attached to a battery that sets the potential on that node to the value of the respective molecular property, and no external battery is attached to nodes from the prediction set, representing chemicals for which the values of the molecular property are not known or are intended to be predicted. The flow network QSAR algorithm determines the values of the molecular property for the prediction set of molecules by applying Ohm's law and Kirchhoff's current law to the poset

  13. The spliceosome catalyzes debranching in competition with reverse of the first chemical reaction.

    PubMed

    Tseng, Chi-Kang; Cheng, Soo-Chen

    2013-07-01

    Splicing of nuclear pre-mRNA occurs via two steps of the transesterification reaction, forming a lariat intermediate and product. The reactions are catalyzed by the spliceosome, a large ribonucleoprotein complex composed of five small nuclear RNAs and numerous protein factors. The spliceosome shares a similar catalytic core structure with that of fungal group II introns, which can self-splice using the same chemical mechanism. Like group II introns, both catalytic steps of pre-mRNA splicing can efficiently reverse on the affinity-purified spliceosome. The spliceosome also catalyzes a hydrolytic spliced-exon reopening reaction as observed in group II introns, indicating a strong link in their evolutionary relationship. We show here that, by arresting splicing after the first catalytic step, the purified spliceosome can catalyze debranching of lariat-intron-exon 2. The debranching reaction, although not observed in group II introns, has similar monovalent cation preferences as those for splicing catalysis of group II introns. The debranching reaction is in competition with the reverse Step 1 reaction influenced by the ionic environment and the structure of components binding near the catalytic center, suggesting that the catalytic center of the spliceosome can switch between different conformations to direct different chemical reactions.

  14. O/S-1/ interactions - The product channels. [collisional electron quenching and chemical reaction pathway frequencies

    NASA Technical Reports Server (NTRS)

    Slanger, T. G.; Black, G.

    1978-01-01

    The first measurements are reported of the reaction pathways for the interaction between oxygen atoms in the 4.19 eV S-1 state, and four molecules, N2O, CO2, H2O, and NO. Distinction is made between three possible paths - quenching to O(D-1), quenching to O(P-3), and chemical reaction. With N2O, the most reasonable interpretation of the data indicates that there no reaction, in sharp contrast with the interaction between O(D-1) and N2O, which proceeds entirely by reaction. Similarly, there is no reaction with CO2. With H2O, the reactive pathway is the dominant one, although electronic quenching is not negligible. With NO, O(D-1) is the preferred product.

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

    PubMed Central

    Kochhar, Gurpaul S.; Mosey, Nicholas J.

    2016-01-01

    Mechanochemistry, i.e. the application of forces, F, at the molecular level, has attracted significant interest as a means of controlling chemical reactions. The present study uses quantum chemical calculations to explore the abilities to mechanically eliminate activation energies, ΔE‡, for unimolecular and bimolecular reactions. The results demonstrate that ΔE‡ can be eliminated for unimolecular reactions by applying sufficiently large F along directions that move the reactant and/or transition state (TS) structures parallel to the zero-F reaction coordinate, S0. In contrast, eliminating ΔE‡ for bimolecular reactions requires the reactant to undergo a force-induced shift parallel to S0 irrespective of changes in the TS. Meeting this requirement depends upon the coupling between F and S0 in the reactant. The insights regarding the differences in eliminating ΔE‡ for unimolecular and bimolecular reactions, and the requirements for eliminating ΔE‡, may be useful in practical efforts to control reactions mechanochemically. PMID:26972114

  16. Chemical Signaling and Functional Activation in Colloidosome-Based Protocells.

    PubMed

    Sun, Shiyong; Li, Mei; Dong, Faqin; Wang, Shengjie; Tian, Liangfei; Mann, Stephen

    2016-04-13

    An aqueous-based microcompartmentalized model involving the integration of partially hydrophobic Fe(III)-rich montmorillonite (FeM) clay particles as structural and catalytic building blocks for colloidosome membrane assembly, self-directed membrane remodeling, and signal-induced protocell communication is described. The clay colloidosomes exhibit size- and charge-selective permeability, and show dual catalytic functions involving spatially confined enzyme-mediated dephosphorylation and peroxidase-like membrane activity. The latter is used for the colloidosome-mediated synthesis and assembly of a temperature-responsive poly(N-isopropylacrylamide)(PNIPAM)/clay-integrated hybrid membrane. In situ PNIPAM elaboration of the membrane is coupled to a glucose oxidase (GOx)-mediated signaling pathway to establish a primitive model of chemical communication and functional activation within a synthetic "protocell community" comprising a mixed population of GOx-containing silica colloidosomes and alkaline phosphatase (ALP)-containing FeM-clay colloidosomes. Triggering the enzyme reaction in the silica colloidosomes gives a hydrogen peroxide signal that induces polymer wall formation in a coexistent population of the FeM-clay colloidosomes, which in turn generates self-regulated membrane-gated ALP-activity within the clay microcompartments. The emergence of new functionalities in inorganic colloidosomes via chemical communication between different protocell populations provides a first step toward the realization of interacting communities of synthetic functional microcompartments. PMID:26923794

  17. Advanced deposition model for thermal activated chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Cai, Dang

    Thermal Activated Chemical Vapor Deposition (TACVD) is defined as the formation of a stable solid product on a heated substrate surface from chemical reactions and/or dissociation of gaseous reactants in an activated environment. It has become an essential process for producing solid film, bulk material, coating, fibers, powders and monolithic components. Global market of CVD products has reached multi billions dollars for each year. In the recent years CVD process has been extensively used to manufacture semiconductors and other electronic components such as polysilicon, AlN and GaN. Extensive research effort has been directed to improve deposition quality and throughput. To obtain fast and high quality deposition, operational conditions such as temperature, pressure, fluid velocity and species concentration and geometry conditions such as source-substrate distance need to be well controlled in a CVD system. This thesis will focus on design of CVD processes through understanding the transport and reaction phenomena in the growth reactor. Since the in situ monitor is almost impossible for CVD reactor, many industrial resources have been expended to determine the optimum design by semi-empirical methods and trial-and-error procedures. This approach has allowed the achievement of improvements in the deposition sequence, but begins to show its limitations, as this method cannot always fulfill the more and more stringent specifications of the industry. To resolve this problem, numerical simulation is widely used in studying the growth techniques. The difficulty of numerical simulation of TACVD crystal growth process lies in the simulation of gas phase and surface reactions, especially the latter one, due to the fact that very limited kinetic information is available in the open literature. In this thesis, an advanced deposition model was developed to study the multi-component fluid flow, homogeneous gas phase reactions inside the reactor chamber, heterogeneous surface

  18. Influences of chemical activators on incinerator bottom ash.

    PubMed

    Qiao, X C; Cheeseman, C R; Poon, C S

    2009-02-01

    This research has applied different chemical activators to mechanically and thermally treated fine fraction (<14 mm) of incinerator bottom ash (IBA), in order to investigate the influences of chemical activators on this new pozzolanic material. IBA has been milled and thermally treated at 800 degrees C (TIBA). The TIBA produced was blended with Ca(OH)(2) and evaluated for setting time, reactivity and compressive strength after the addition of 0.0565 mole of Na(2)SO(4), K(2)SO(4), Na(2)CO(3), K(2)CO(3), NaOH, KOH and CaCl(2) into 100g of binder (TIBA+Ca(OH)(2)). The microstructures of activated IBA and hydrated samples have been characterized by X-ray diffraction (XRD) and thermogravimetry (TG) analysis. Thermal treatment is found to produce gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)) phases. The thermally treated IBA samples are significantly more reactive than the milled IBA. The addition of Na(2)CO(3) can increase the compressive strength and calcium hydroxide consumption at 28-day curing ages. However, the addition of Na(2)SO(4), K(2)SO(4), K(2)CO(3), NaOH and KOH reduces the strength and hydration reaction. Moreover, these chemicals produce more porous samples due to increased generation of hydrogen gas. The addition of CaCl(2) has a negative effect on the hydration of TIBA samples. Calcium aluminium oxide carbonate sulphide hydrate (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33)(H(2)O)(11)) is the main hydration product in the samples with activated IBA, except for the sample containing CaCl(2). PMID:18718749

  19. Influences of chemical activators on incinerator bottom ash.

    PubMed

    Qiao, X C; Cheeseman, C R; Poon, C S

    2009-02-01

    This research has applied different chemical activators to mechanically and thermally treated fine fraction (<14 mm) of incinerator bottom ash (IBA), in order to investigate the influences of chemical activators on this new pozzolanic material. IBA has been milled and thermally treated at 800 degrees C (TIBA). The TIBA produced was blended with Ca(OH)(2) and evaluated for setting time, reactivity and compressive strength after the addition of 0.0565 mole of Na(2)SO(4), K(2)SO(4), Na(2)CO(3), K(2)CO(3), NaOH, KOH and CaCl(2) into 100g of binder (TIBA+Ca(OH)(2)). The microstructures of activated IBA and hydrated samples have been characterized by X-ray diffraction (XRD) and thermogravimetry (TG) analysis. Thermal treatment is found to produce gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)) phases. The thermally treated IBA samples are significantly more reactive than the milled IBA. The addition of Na(2)CO(3) can increase the compressive strength and calcium hydroxide consumption at 28-day curing ages. However, the addition of Na(2)SO(4), K(2)SO(4), K(2)CO(3), NaOH and KOH reduces the strength and hydration reaction. Moreover, these chemicals produce more porous samples due to increased generation of hydrogen gas. The addition of CaCl(2) has a negative effect on the hydration of TIBA samples. Calcium aluminium oxide carbonate sulphide hydrate (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33)(H(2)O)(11)) is the main hydration product in the samples with activated IBA, except for the sample containing CaCl(2).

  20. Diffusion-controlled reaction rate to an active site

    NASA Astrophysics Data System (ADS)

    Traytak, S. D.

    1995-02-01

    The diffusion-controlled reactions of chemically anisotropic reactants are treated for the simplest model of Solc and Stockmayer (Intern. J. Chem. Kinet. 5 (1973) 733) in the absence of rotational diffusion. Using the dual series relations approach we can find the effective steric factor with any necessary accuracy. A few simple analytical approximations for the effective steric factor are proposed. The derived results we compare with the relevant analytical approximations and numerical calculations available in the literature.

  1. Formation and decomposition of chemically activated and stabilized hydrazine.

    PubMed

    Asatryan, Rubik; Bozzelli, Joseph W; da Silva, Gabriel; Swinnen, Saartje; Nguyen, Minh Tho

    2010-06-01

    Recombination of two amidogen radicals, NH(2) (X(2)B1), is relevant to hydrazine formation, ammonia oxidation and pyrolysis, nitrogen reduction (fixation), and a variety of other N/H/X combustion, environmental, and interstellar processes. We have performed a comprehensive analysis of the N(2)H(4) potential energy surface, using a variety of theoretical methods, with thermochemical kinetic analysis and master equation simulations used to treat branching to different product sets in the chemically activated NH(2) + NH(2) process. For the first time, iminoammonium ylide (NH(3)NH), the less stable isomer of hydrazine, is involved in the kinetic modeling of N(2)H(4). A new, low-energy pathway is identified for the formation of NH(3) plus triplet NH, via initial production of NH(3)NH followed by singlet-triplet intersystem crossing. This new reaction channel results in the formation of dissociated products at a relatively rapid rate at even moderate temperatures and above. A further novel pathway is described for the decomposition of activated N(2)H(4), which eventually leads to the formation of the simple products N(2) + 2H(2), via H(2) elimination to cis-N(2)H(2). This process, termed as "dihydrogen catalysis", may have significant implications in the formation and decomposition chemistry of hydrazine and ammonia in diverse environments. In this mechanism, stereoselective attack of cis-N(2)H(2) by molecular hydrogen results in decomposition to N(2) with a fairly low barrier. The reverse termolecular reaction leading to the gas-phase formation of cis-N(2)H(2) + H(2) achieves non-heterogeneous catalytic nitrogen fixation with a relatively low activation barrier (77 kcal mol(-1)), much lower than the 125 kcal mol(-1) barrier recently reported for bimolecular addition of H(2) to N(2). This termolecular reaction is an entropically disfavored path, but it does describe a new means of activating the notoriously unreactive N(2). We design heterogeneous analogues of this

  2. Eliciting Students' Understandings of Chemical Reactions Using Two Forms of Essay Questions during a Learning Cycle.

    ERIC Educational Resources Information Center

    Cavallo, Ann M. L.; McNeely, Jack C.; Marek, Edmund A.

    2003-01-01

    Examines 9th grade students' explanations of chemical reactions using two forms of open-ended essay questions, those providing students with key terms to be used as "anchors" on which to base their essay, and those that do not provide terms. Results indicate that more misunderstandings were elicited by the use of key terms as compared to the…

  3. Effectiveness of Conceptual Change Text-Oriented Instruction on Students' Understanding of Energy in Chemical Reactions

    ERIC Educational Resources Information Center

    Tastan, Ozgecan; Yalcinkaya, Eylem; Boz, Yezdan

    2008-01-01

    The aim of this study is to compare the effectiveness of conceptual change text instruction (CCT) in the context of energy in chemical reactions. The subjects of the study were 60, 10th grade students at a high school, who were in two different classes and taught by the same teacher. One of the classes was randomly selected as the experimental…

  4. Chemical equilibrium and reaction modeling of arsenic and selenium in soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The chemical processes and soil factors that affect the concentrations of As and Se in soil solution were discussed. Both elements occur in two redox states differing in toxicity and reactivity. Methylation and volatilization reactions occur in soils and can act as detoxification pathways. Precip...

  5. Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

    NASA Technical Reports Server (NTRS)

    Kinnison, Douglas E.; Wuebbles, Donald J.

    1994-01-01

    Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O3, NO(x), Cl(x), HCl, N2O5, ClONO2 are calculated.

  6. Molecular Modeling as a Self-Taught Component of a Conventional Undergraduate Chemical Reaction Engineering Course

    ERIC Educational Resources Information Center

    Rothe, Erhard W.; Zygmunt, William E.

    2016-01-01

    We inserted a self-taught molecular modeling project into an otherwise conventional undergraduate chemical-reaction-engineering course. Our objectives were that students should (a) learn with minimal instructor intervention, (b) gain an appreciation for the relationship between molecular structure and, first, macroscopic state functions in…

  7. Using Drawing Technology to Assess Students' Visualizations of Chemical Reaction Processes

    ERIC Educational Resources Information Center

    Chang, Hsin-Yi; Quintana, Chris; Krajcik, Joseph

    2014-01-01

    In this study, we investigated how students used a drawing tool to visualize their ideas of chemical reaction processes. We interviewed 30 students using thinking-aloud and retrospective methods and provided them with a drawing tool. We identified four types of connections the students made as they used the tool: drawing on existing knowledge,…

  8. Stepwise chemical reaction strategy for highly sensitive electrochemiluminescent detection of dopamine.

    PubMed

    Zhang, Lei; Cheng, Yan; Lei, Jianping; Liu, Yueting; Hao, Qing; Ju, Huangxian

    2013-08-20

    A stepwise chemical reaction strategy based on the specific recognition of boronic acid to diol, and N-hydroxysuccinimide (NHS) ester to amine group, was designed to construct a "signal on" electrochemiluminescence (ECL) platform for highly sensitive detection of dopamine. A boronic acid-functionalized pyrene probe was synthesized and was self-assembled on the sidewalls of carbon nanotubes via π-π stacking interactions as capture probes on a glassy carbon electrode. Meanwhile, 3,3'-dithiodipropionic acid di(N-hydroxysuccinimide ester) (DSP)-functionalized CdTe quantum dots (QDs) were designed as signal probes and characterized with transmission electron microscopy and spectroscopic techniques. Upon stepwise chemical reaction of dopamine with boronic acid and then DSP-QDs, the QDs were captured on the electrode as ECL emitters for signal readout, leading to an ultralow background signal. By using O2 as an endogenous coreactant, the "signal on" ECL method was employed to quantify the concentration of dopamine from 50 pM to 10 nM with a detection limit of 26 pM. Moreover, the stepwise chemical reaction-based biosensor showed high specificity against cerebral interference and was successfully applied in the detection of dopamine in cerebrospinal fluid samples. The stepwise chemical reaction strategy should be a new concept for the design of highly selective analytical methods for the detection of small biomolecules.

  9. Facilitating High School Students' Use of Multiple Representations to Describe and Explain Simple Chemical Reactions

    ERIC Educational Resources Information Center

    Chandrasegaran, A. L.; Treagust, David F.; Mocerino, Mauro

    2011-01-01

    This study involved the evaluation of the efficacy of a planned instructional program to facilitate understanding of the macroscopic, submicroscopic and symbolic representational systems when describing and explaining chemical reactions by sixty-five Grade 9 students in a Singapore secondary school. A two-tier multiple-choice diagnostic instrument…

  10. Mapping Students' Modes of Reasoning When Thinking about Chemical Reactions Used to Make a Desired Product

    ERIC Educational Resources Information Center

    Weinrich, M. L.; Talanquer, V.

    2016-01-01

    The central goal of this study was to analyze the complexity of students' explanations about how and why chemical reactions happen in terms of the types of causal connections students built between expressed concepts and ideas. We were particularly interested in characterizing differences in the types of reasoning applied by students with…

  11. Two Experiments to Approach the Boltzmann Factor: Chemical Reaction and Viscous Flow

    ERIC Educational Resources Information Center

    Fazio, Claudio; Battaglia, Onofrio R.; Guastella, Ivan

    2012-01-01

    In this paper we discuss a pedagogical approach aimed at pointing out the role played by the Boltzmann factor in describing phenomena usually perceived as regulated by different mechanisms of functioning. Experimental results regarding some aspects of a chemical reaction and of the viscous flow of some liquids are analysed and described in terms…

  12. Turkish, Indian, and American Chemistry Textbooks Use of Inscriptions to Represent "Types of Chemical Reactions"

    ERIC Educational Resources Information Center

    Aydin, Sevgi; Sinha, Somnath; Izci, Kemal; Volkmann, Mark

    2014-01-01

    The purpose of this study was to investigate inscriptions used in "Types of Chemical Reactions" topic in Turkish, Indian, and American chemistry textbooks. We investigated both the types of inscriptions and how they were used in textbooks to support learning. A conceptual analysis method was employed to determine how those textbooks use…

  13. The Effective Concepts on Students' Understanding of Chemical Reactions and Energy

    ERIC Educational Resources Information Center

    Ayyildiz, Yildizay; Tarhan, Leman

    2012-01-01

    The purpose of this study was to determine the relationship between the basic concepts related to the unit of "Chemical Reactions and Energy" and the sub-concepts underlying for meaningful learning of the unit and to investigate the effectiveness of them on students' learning achievements. For this purpose, the basic concepts of the unit were…

  14. Volatile emission in dry seeds as a way to probe chemical reactions during initial asymptomatic deterioration

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The nature and kinetics of reactions in dry seeds determines how long they survive. We used gas chromatography to assay volatile organic compounds (VOC) emitted from seeds of three unrelated species as a means to non-invasively probe chemical changes during very dry, dry and humid (15, 33 and 75% RH...

  15. Remarkable nanoconfinement effects on chemical equilibrium manifested in nucleotide dimerization and H-D exchange reactions.

    PubMed

    Polak, Micha; Rubinovich, Leonid

    2011-10-01

    Nanoconfinement entropic effects on chemical equilibrium involving a small number of molecules, which we term NCECE, are revealed by two widely diverse types of reactions. Employing statistical-mechanical principles, we show how the NCECE effect stabilizes nucleotide dimerization observed within self-assembled molecular cages. Furthermore, the effect provides the basis for dimerization even under an aqueous environment inside the nanocage. Likewise, the NCECE effect is pertinent to a longstanding issue in astrochemistry, namely the extra deuteration commonly observed for molecules reacting on interstellar dust grain surfaces. The origin of the NCECE effect is elucidated by means of the probability distributions of the reaction extent and related variations in the reactant-product mixing entropy. Theoretical modelling beyond our previous preliminary work highlights the role of the nanospace size in addition to that of the nanosystem size, namely the limited amount of molecules in the reaction mixture. Furthermore, the NCECE effect can depend also on the reaction mechanism, and on deviations from stoichiometry. The NCECE effect, leading to enhanced, greatly variable equilibrium "constants", constitutes a unique physical-chemical phenomenon, distinguished from the usual thermodynamical properties of macroscopically large systems. Being significant particularly for weakly exothermic reactions, the effects should stabilize products in other closed nanoscale structures, and thus can have notable implications for the growing nanotechnological utilization of chemical syntheses conducted within confined nanoreactors.

  16. Motif analysis for small-number effects in chemical reaction dynamics

    NASA Astrophysics Data System (ADS)

    Saito, Nen; Sughiyama, Yuki; Kaneko, Kunihiko

    2016-09-01

    The number of molecules involved in a cell or subcellular structure is sometimes rather small. In this situation, ordinary macroscopic-level fluctuations can be overwhelmed by non-negligible large fluctuations, which results in drastic changes in chemical-reaction dynamics and statistics compared to those observed under a macroscopic system (i.e., with a large number of molecules). In order to understand how salient changes emerge from fluctuations in molecular number, we here quantitatively define small-number effect by focusing on a "mesoscopic" level, in which the concentration distribution is distinguishable both from micro- and macroscopic ones and propose a criterion for determining whether or not such an effect can emerge in a given chemical reaction network. Using the proposed criterion, we systematically derive a list of motifs of chemical reaction networks that can show small-number effects, which includes motifs showing emergence of the power law and the bimodal distribution observable in a mesoscopic regime with respect to molecule number. The list of motifs provided herein is helpful in the search for candidates of biochemical reactions with a small-number effect for possible biological functions, as well as for designing a reaction system whose behavior can change drastically depending on molecule number, rather than concentration.

  17. Motif analysis for small-number effects in chemical reaction dynamics.

    PubMed

    Saito, Nen; Sughiyama, Yuki; Kaneko, Kunihiko

    2016-09-01

    The number of molecules involved in a cell or subcellular structure is sometimes rather small. In this situation, ordinary macroscopic-level fluctuations can be overwhelmed by non-negligible large fluctuations, which results in drastic changes in chemical-reaction dynamics and statistics compared to those observed under a macroscopic system (i.e., with a large number of molecules). In order to understand how salient changes emerge from fluctuations in molecular number, we here quantitatively define small-number effect by focusing on a "mesoscopic" level, in which the concentration distribution is distinguishable both from micro- and macroscopic ones and propose a criterion for determining whether or not such an effect can emerge in a given chemical reaction network. Using the proposed criterion, we systematically derive a list of motifs of chemical reaction networks that can show small-number effects, which includes motifs showing emergence of the power law and the bimodal distribution observable in a mesoscopic regime with respect to molecule number. The list of motifs provided herein is helpful in the search for candidates of biochemical reactions with a small-number effect for possible biological functions, as well as for designing a reaction system whose behavior can change drastically depending on molecule number, rather than concentration. PMID:27608993

  18. Motif analysis for small-number effects in chemical reaction dynamics.

    PubMed

    Saito, Nen; Sughiyama, Yuki; Kaneko, Kunihiko

    2016-09-01

    The number of molecules involved in a cell or subcellular structure is sometimes rather small. In this situation, ordinary macroscopic-level fluctuations can be overwhelmed by non-negligible large fluctuations, which results in drastic changes in chemical-reaction dynamics and statistics compared to those observed under a macroscopic system (i.e., with a large number of molecules). In order to understand how salient changes emerge from fluctuations in molecular number, we here quantitatively define small-number effect by focusing on a "mesoscopic" level, in which the concentration distribution is distinguishable both from micro- and macroscopic ones and propose a criterion for determining whether or not such an effect can emerge in a given chemical reaction network. Using the proposed criterion, we systematically derive a list of motifs of chemical reaction networks that can show small-number effects, which includes motifs showing emergence of the power law and the bimodal distribution observable in a mesoscopic regime with respect to molecule number. The list of motifs provided herein is helpful in the search for candidates of biochemical reactions with a small-number effect for possible biological functions, as well as for designing a reaction system whose behavior can change drastically depending on molecule number, rather than concentration.

  19. Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd–Au Nanoshells

    PubMed Central

    Heck, Kimberly N.; Janesko, Benjamin G.; Scuseria, Gustavo E.

    2016-01-01

    Insight into the nature of transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions is obtainable from a number of surface spectroscopic techniques. Carrying out these investigations under actual reaction conditions is preferred but remains challenging, especially for catalytic reactions that occur in water. Here, we report the direct spectroscopic study of the catalytic hydrodechlorination of 1,1-dichloroethene in H2O using surface-enhanced Raman spectroscopy (SERS). With Pd islands grown on Au nanoshell films, this reaction can be followed in situ using SERS, exploiting the high enhancements and large active area of Au nanoshell SERS substrates, the transparency of Raman spectroscopy to aqueous solvents, and the catalytic activity enhancement of Pd by the underlying Au metal. The formation and subsequent transformation of several adsorbate species was observed. These results provide the first direct evidence of the room-temperature catalytic hydrodechlorination of a chlorinated solvent, a potentially important pathway for groundwater cleanup, as a sequence of dechlorination and hydrogenation steps. More broadly, the results highlight the exciting prospects of studying catalytic processes in water in situ, like those involved in biomass conversion and proton-exchange membrane fuel cells. PMID:19554693

  20. Stability of a laminar premixed supersonic free shear layer with chemical reactions

    NASA Technical Reports Server (NTRS)

    Menon, S.; Anderson, J. D., Jr.; Pai, S. I.

    1984-01-01

    The stability of a two-dimensional compressible supersonic flow in the wake of a flat plate is discussed. The fluid is a multi-species mixture which is undergoing finite rate chemical reactions. The spatial stability of an infinitesimal disturbance in the fluid is considered. Numerical solutions of the eigenvalue stability equations for both reactive and nonreactive supersonic flows are presented and discussed. The chemical reactions have significant influence on the stability behavior. For instance, a neutral eigenvalue is observed near the freestream Mach number of 2.375 for the nonreactive case, but disappears when the reaction is turned on. For reactive flows, the eigenvalues are not very dependent on the free stream Mach number.

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

    SciTech Connect

    Muramatsu, Y.; Grush, M.; Callcott, T.A.

    1997-04-01

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

  2. On a theory of stability for nonlinear stochastic chemical reaction networks

    SciTech Connect

    Smadbeck, Patrick; Kaznessis, Yiannis N.

    2015-05-14

    We present elements of a stability theory for small, stochastic, nonlinear chemical reaction networks. Steady state probability distributions are computed with zero-information (ZI) closure, a closure algorithm that solves chemical master equations of small arbitrary nonlinear reactions. Stochastic models can be linearized around the steady state with ZI-closure, and the eigenvalues of the Jacobian matrix can be readily computed. Eigenvalues govern the relaxation of fluctuation autocorrelation functions at steady state. Autocorrelation functions reveal the time scales of phenomena underlying the dynamics of nonlinear reaction networks. In accord with the fluctuation-dissipation theorem, these functions are found to be congruent to response functions to small perturbations. Significant differences are observed in the stability of nonlinear reacting systems between deterministic and stochastic modeling formalisms.

  3. Modeling pore collapse and chemical reactions in shock-loaded HMX crystals

    NASA Astrophysics Data System (ADS)

    Austin, R. A.; Barton, N. R.; Howard, W. M.; Fried, L. E.

    2014-05-01

    The localization of deformation in shock-loaded crystals of high explosive material leads to the formation of hot spots, which, if hot enough, initiate chemical reactions. The collapse of microscopic pores contained within a crystal is one such process that localizes energy and generates hot spots. Given the difficulty of resolving the details of pore collapse in shock compression experiments, it is useful to study the problem using direct numerical simulation. In this work, we focus on simulating the shock-induced closure of a single pore in crystalline β-HMX using a multiphysics finite element code. To address coupled thermal-mechanical-chemical responses, the model incorporates a crystal-mechanics-based description of thermoelasto-viscoplasticity, the crystal melting behavior, and transformation kinetics for a single-step decomposition reaction. The model is applied to stress wave amplitudes of up to 11 GPa to study the details of pore collapse, energy localization, and the early stages of reaction initiation.

  4. Diagnostic Criteria for the Characterization of Electrode Reactions with Chemically Coupled Reactions Preceding the Electron Transfer by Cyclic Square Wave Voltammetry.

    PubMed

    Helfrick, John C; Mann, Megan A; Bottomley, Lawrence A

    2016-08-18

    Theory for cyclic square wave voltammetry of electrode reactions with chemical reactions preceding the electron transfer is presented. Theoretical voltammograms were calculated following systematic variation of empirical parameters to assess their impact on the shape of the voltammogram. From the trends obtained, diagnostic criteria for this mechanism were deduced. When properly applied, these criteria will enable non-experts in voltammetry to assign the electrode reaction mechanism and accurately measure reaction kinetics. PMID:27443581

  5. Looking for chemical reaction networks exhibiting a drift along a manifold of marginally stable states.

    PubMed

    Brogioli, Doriano

    2013-02-01

    I recently reported some examples of mass-action equations that have a continuous manifold of marginally stable stationary states [Brogioli, D., 2010. Marginally stable chemical systems as precursors of life. Phys. Rev. Lett. 105, 058102; Brogioli, D., 2011. Marginal stability in chemical systems and its relevance in the origin of life. Phys. Rev. E 84, 031931]. The corresponding chemical reaction networks show nonclassical effects, i.e. a violation of the mass-action equations, under the effect of the concentration fluctuations: the chemical system drifts along the marginally stable states. I proposed that this effect is potentially involved in abiogenesis. In the present paper, I analyze the mathematical properties of mass-action equations of marginally stable chemical reaction networks. The marginal stability implies that the mass-action equations obey some conservation law; I show that the mathematical properties of the conserved quantity characterize the motion along the marginally stable stationary state manifold, i.e. they allow to predict if the fluctuations give rise to a random walk or a drift under the effect of concentration fluctuations. Moreover, I show that the presence of the drift along the manifold of marginally stable stationary-states is a critical property, i.e. at least one of the reaction constants must be fine tuned in order to obtain the drift.

  6. Organo- and nano-catalyst in greener reaction medium: Microwave-assisted expedient synthesis of fine chemicals

    EPA Science Inventory

    The use of emerging microwave (MW) -assisted chemistry techniques is dramatically reducing chemical waste and reaction times in several organic syntheses and chemical transformations. A brief account of our experiences in developing MW-assisted organic transformations, which invo...

  7. Reaction Product Identification in Extreme Chemical Environments by Broadband Rotational Spectroscopy

    NASA Astrophysics Data System (ADS)

    Pate, Brooks

    Molecular rotational spectroscopy has several advantages for detection of reaction intermediates and products under extreme laboratory conditions. Rotational spectroscopy has high sensitivity to the molecular structure and provides high spectral resolution in low pressure environments. Furthermore, quantum chemistry provides accurate estimates of the spectroscopic parameters. As a result, rotational spectroscopy can identify molecular species in complex reaction mixtures without the need for chromatographic separation and without the need for a previously recorded ``library spectrum'' of the molecule. The application of chirped pulse Fourier transform rotational spectroscopy methods for the identification of molecules of astrochemical interest formed in pulsed discharge sources will be described including recent advances for high-throughput mm-wave spectroscopy. The set of reaction products created in the experiment can provide insight into the reaction mechanism. Reactions involving the CN radical will be discussed. These reactions can be barrierless making them candidates for interstellar gas reactions. The possibility that interstellar cyanomethanimine is produced by gas phase radical-neutral reactions instead of surface chemistry on grain-supported ices will be discussed using recent spatially resolved chemical images in Sagittarius B2 observed with the Jansky Very Large Array. This work supported by NSF CHE 1213200.

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

    NASA Astrophysics Data System (ADS)

    Li, Tiejun; Lin, Feng

    2016-04-01

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

  9. Nonequilibrium thermodynamic formalism of nonlinear chemical reaction systems with Waage-Guldberg's law of mass action

    NASA Astrophysics Data System (ADS)

    Ge, Hao; Qian, Hong

    2016-06-01

    Macroscopic entropy production rate σ (tot) in the general nonlinear isothermal chemical reaction system with mass action kinetics is decomposed into a free energy dissipation rate and a house-keeping heat dissipation rate: σ (tot) =σ (fd) +σ (hk) ; σ (fd) = -d A /d t , where A is a generalized free energy function. This yields a novel nonequilibrium free energy balance equation d A /d t = -σ (tot) +σ (hk) , which is on a par with celebrated entropy balance equation d S /d t =σ (tot) +η (ex) where η (ex) is the rate of entropy exchange with the environment. For kinetic systems with complex balance, σ (fd) and σ (hk) are the macroscopic limits of stochastic free energy dissipation rate and house-keeping heat dissipation rate, which are both nonnegative, in the Delbrück-Gillespie description of the stochastic chemical kinetics. A full kinetic and thermodynamic theory of chemical reaction systems that transcends mesoscopic and macroscopic levels emerges.

  10. Miscible viscous fingering involving viscosity changes of the displacing fluid by chemical reactions

    NASA Astrophysics Data System (ADS)

    Nagatsu, Yuichiro; Iguchi, Chika; Matsuda, Kenji; Kato, Yoshihito; Tada, Yutaka

    2010-02-01

    In our previous study, we experimentally studied the effects of changes in the viscosity of the displaced more-viscous liquid by instantaneous reactions on miscible viscous fingering pattern [Y. Nagatsu, K. Matsuda, Y. Kato, and Y. Tada, "Experimental study on miscible viscous fingering involving viscosity changes induced by variations in chemical species concentrations due to chemical reactions," J. Fluid Mech. 571, 475 (2007)]. In the present study, experiments have been performed on the miscible viscous fingering involving changes in the viscosity of the displacing less-viscous liquid by instantaneous reactions in a radial Hele-Shaw cell. We have found that the shielding effect is suppressed and the fingers are widened when the viscosity is increased. As a result, the reaction makes the fingering pattern denser. In contrast, the shielding effect is enhanced, and the fingers are narrowed when the viscosity is decreased. As a result, the reaction makes the fingering pattern less dense. These results are essentially same as those obtained by the above-mentioned previous study. This shows that the effects of changes in the viscosity due to the instantaneous reactions are independent of whether the changes occur in the displaced liquid or in the displacing liquid. A mechanism for the independence is discussed.

  11. Detailed Chemical Kinetic Reaction Mechanisms for Combustion of Isomers of Heptane

    SciTech Connect

    Westbrook, C K; Pitz, W J; Curran, H C; Boercker, J; Kunrath, E

    2001-03-26

    Detailed chemical kinetic reaction mechanisms are developed for all nine chemical isomers of heptane (C{sub 7}H{sub 16}), following techniques and models developed previously for other smaller alkane hydrocarbon species. These reaction mechanisms are tested at high temperatures by computing shock tube ignition delay times and at lower temperatures by simulating ignition in a rapid compression machine. Although the corresponding experiments have not been reported in the literature for most of these isomers of heptane, intercomparisons between the computed results for these isomers and comparisons with available experimental results for other alkane fuels are used to validate the reaction mechanisms as much as possible. Differences in the overall reaction rates of these fuels are discussed in terms of differences in their molecular structure and the resulting variations in rates of important elementary reactions. Reaction mechanisms in this study are works in progress and the results reported here are subject to change, based on model improvements and corrections of errors not yet discovered.

  12. Chemical reactions at metallic and metal/semiconductor interfaces stimulated by pulsed laser annealing

    NASA Astrophysics Data System (ADS)

    Petit, E. J.; Caudano, R.

    1992-01-01

    Multilayer Al/Sb thin films have been evaporated on GaSb single crystals in ultra-high vacuum and pulsed-laser irradiated in-situ above the energy density threshold for surface melting. Superficial and interfacial chemical reactions have been characterized in-situ by Auger electron spectroscopy; and later, by X-ray photoelectron spectroscopy profiling, Rutherford backscattering spectrometry and scanning electron microscopy. The chemical reaction between the Al and Sb films is considered as a model reaction for laser-assisted synthesis of high-purity intermetallic compounds. The observation of a strong interfacial reaction between the melted film and the substrate is also a subject of great concern for optical data recording and laser alloying of ohmic contacts on semiconductors. We show that a suitable choice of the substrate and adding a low surface tension element into the metallic film can improve its stability during melting, and prevent inhomogeneous reaction and formation of holes, cracks and particles. Finally, other solutions are suggested to improve the control of these reactions.

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

    NASA Technical Reports Server (NTRS)

    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.

  14. Dynamics and Kinetics Study of "In-Water" Chemical Reactions by Enhanced Sampling of Reactive Trajectories.

    PubMed

    Zhang, Jun; Yang, Y Isaac; Yang, Lijiang; Gao, Yi Qin

    2015-11-12

    High potential energy barriers and engagement of solvent coordinates set challenges for in silico studies of chemical reactions, and one is quite commonly limited to study reactions along predefined reaction coordinate(s). A systematic protocol, QM/MM MD simulations using enhanced sampling of reactive trajectories (ESoRT), is established to quantitatively study chemical transitions in complex systems. A number of trajectories for Claisen rearrangement in water and toluene were collected and analyzed, respectively. Evidence was found that the bond making and breaking during this reaction are concerted processes in solutions, preferentially through a chairlike configuration. Water plays an important dynamic role that helps stabilize the transition sate, and the dipole-dipole interaction between water and the solute also lowers the transition barrier. The calculated rate coefficient is consistent with the experimental measurement. Compared with water, the reaction pathway in toluene is "narrower" and the reaction rate is slower by almost three orders of magnitude due to the absence of proper interactions to stabilize the transition state. This study suggests that the "in-water" nature of the Claisen rearrangement in aqueous solution influences its thermodynamics, kinetics, as well as dynamics.

  15. Do high school chemistry examinations inhibit deeper level understanding of dynamic reversible chemical reactions?

    NASA Astrophysics Data System (ADS)

    Wheeldon, R.; Atkinson, R.; Dawes, A.; Levinson, R.

    2012-07-01

    Background and purpose : Chemistry examinations can favour the deployment of algorithmic procedures like Le Chatelier's Principle (LCP) rather than reasoning using chemical principles. This study investigated the explanatory resources which high school students use to answer equilibrium problems and whether the marks given for examination answers require students to use approaches beyond direct application of LCP. Sample : The questionnaire was administered to 162 students studying their first year of advanced chemistry (age 16/17) in three high achieving London high schools. Design and methods : The students' explanations of reversible chemical systems were inductively coded to identify the explanatory approaches used and interviews with 13 students were used to check for consistency. AS level examination questions on reversible reactions were analysed to identify the types of explanations sought and the students' performance in these examinations was compared to questionnaire answers. Results : 19% of students used a holistic explanatory approach: when the rates of forward and reverse reactions are correctly described, recognising their simultaneous and mutually dependent nature. 36% used a mirrored reactions approach when the connected nature of the forward and reverse reactions is identified, but not their mutual dependency. 42% failed to recognize the interdependence of forward and reverse reactions (reactions not connected approach). Only 4% of marks for AS examination questions on reversible chemical systems asked for responses which went beyond either direct application of LCP or recall of equilibrium knowledge. 37% of students attained an A grade in their AS national examinations. Conclusions : Examinations favour the application of LCP making it possible to obtain the highest grade with little understanding of reversible chemical systems beyond a direct application of this algorithm. Therefore students' understanding may be attenuated so that they are

  16. Highly Stable and Active Catalyst for Sabatier Reactions

    NASA Technical Reports Server (NTRS)

    Hu, Jianli; Brooks, Kriston P.

    2012-01-01

    Highly active Ru/TiO2 catalysts for Sabatier reaction have been developed. The catalysts have shown to be stable under repeated shutting down/startup conditions. When the Ru/TiO2 catalyst is coated on the engineered substrate Fe-CrAlY felt, activity enhancement is more than doubled when compared with an identically prepared engineered catalyst made from commercial Degussa catalyst. Also, bimetallic Ru-Rh/TiO2 catalysts show high activity at high throughput.

  17. Effect of temperature oscillation on chemical reaction rates in the atmosphere

    NASA Technical Reports Server (NTRS)

    Eberstein, I. J.

    1974-01-01

    The effect of temperature fluctuations on atmospheric ozone chemistry is examined by considering the Chapman photochemical theory of ozone transport to calculate globally averaged ozone production rates from mean reaction rates, activation energies, and recombination processes.

  18. General chemical kinetics computer program for static and flow reactions, with application to combustion and shock-tube kinetics

    NASA Technical Reports Server (NTRS)

    Bittker, D. A.; Scullin, V. J.

    1972-01-01

    A general chemical kinetics program is described for complex, homogeneous ideal-gas reactions in any chemical system. Its main features are flexibility and convenience in treating many different reaction conditions. The program solves numerically the differential equations describing complex reaction in either a static system or one-dimensional inviscid flow. Applications include ignition and combustion, shock wave reactions, and general reactions in a flowing or static system. An implicit numerical solution method is used which works efficiently for the extreme conditions of a very slow or a very fast reaction. The theory is described, and the computer program and users' manual are included.

  19. A modified next reaction method for simulating chemical systems with time dependent propensities and delays.

    PubMed

    Anderson, David F

    2007-12-01

    Chemical reaction systems with a low to moderate number of molecules are typically modeled as discrete jump Markov processes. These systems are oftentimes simulated with methods that produce statistically exact sample paths such as the Gillespie algorithm or the next reaction method. In this paper we make explicit use of the fact that the initiation times of the reactions can be represented as the firing times of independent, unit rate Poisson processes with internal times given by integrated propensity functions. Using this representation we derive a modified next reaction method and, in a way that achieves efficiency over existing approaches for exact simulation, extend it to systems with time dependent propensities as well as to systems with delays.

  20. Method and apparatus for obtaining enhanced production rate of thermal chemical reactions

    DOEpatents

    Tonkovich, Anna Lee Y [Pasco, WA; Wang, Yong [Richland, WA; Wegeng, Robert S [Richland, WA; Gao, Yufei [Kennewick, WA

    2003-04-01

    The present invention is a method and apparatus (vessel) for providing a heat transfer rate from a reaction chamber through a wall to a heat transfer chamber substantially matching a local heat transfer rate of a catalytic thermal chemical reaction. The key to the invention is a thermal distance defined on a cross sectional plane through the vessel inclusive of a heat transfer chamber, reaction chamber and a wall between the chambers. The cross sectional plane is perpendicular to a bulk flow direction of the reactant stream, and the thermal distance is a distance between a coolest position and a hottest position on the cross sectional plane. The thermal distance is of a length wherein the heat transfer rate from the reaction chamber to the heat transfer chamber substantially matches the local heat transfer rate.