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Sample records for reaction kinetics ligand

  1. Thermo-Kinetic Investigation of Comparative Ligand Effect on Cysteine Iron Redox Reaction

    Directory of Open Access Journals (Sweden)

    Masood Ahmad Rizvi

    2015-03-01

    Full Text Available Transition metal ions in their free state bring unwanted biological oxidations generating oxidative stress. The ligand modulated redox potential can be indispensable in prevention of such oxidative stress by blocking the redundant bio-redox reactions. In this study we investigated the comparative ligand effect on the thermo-kinetic aspects of biologically important cysteine iron (III redox reaction using spectrophotometric and potentiometric methods. The results were corroborated with the complexation effect on redox potential of iron(III-iron(II redox couple. The selected ligands were found to increase the rate of cysteine iron (III redox reaction in proportion to their stability of iron (II complex (EDTA < terpy < bipy < phen. A kinetic profile and the catalytic role of copper (II ions by means of redox shuttle mechanism for the cysteine iron (III redox reaction in presence of 1,10-phenanthroline (phen ligand is also reported.

  2. Thermo-Kinetic Investigation of Comparative Ligand Effect on Cysteine Iron Redox Reaction

    OpenAIRE

    Rizvi, Masood Ahmad; Teshima, Norio; Maqsood, Syed Raashid; Akhoon, Showket Ahmad; Peerzada, Ghulam Mustafa

    2015-01-01

    Transition metal ions in their free state bring unwanted biological oxidations generating oxidative stress. The ligand modulated redox potential can be indispensable in prevention of such oxidative stress by blocking the redundant bio-redox reactions. In this study we investigated the comparative ligand effect on the thermo-kinetic aspects of biologically important cysteine iron (III) redox reaction using spectrophotometric and potentiometric methods. The results were corroborated...

  3. Kinetic and mechanism formation reaction of complex compound Cu with di-n-buthildithiocarbamate (dbdtc) ligand

    Science.gov (United States)

    Haryani, S.; Kurniawan, C.; Kasmui

    2018-04-01

    Synthesis of complex compound is one field of research which intensively studied. Metal-dithiocarbamate complexes find wide-ranging applications in nanomaterial and metal separation science, and have potential use as chemotherapeutic, pesticides, and as additives to lubricants. However, the information about is reaction kinetic and mechanism are very much lacking. The research and analyzes results show that reaction synthesis ligand DBDTC and complex compounds Cu-DBDTC. Optimum reaction condition of formation of complex compounds Cu with DBDTC at pH=3, [DBDTC] = 4.10-3 M, and the time of reaction 5 minutes. Based the analysis varian reaction of complex compounds at pH 3 and 4, diffrence significance at the other pH: 5; 5,5; 6; 6,5 ; 7; and 8. The various of mole with reactants comosition difference sigbificance, those the time reaction for 5 and 6 minutes diffrence by significance with the other time, it is 3,4,8, and 10 minutes. The great product to at condition pH 6, the time optimum at 5 minutes and molar ratio of logam: ligand = 1:2. The reaction kinetic equation of complex compound Cu with chelathing ligand DBDTC is V=0.917106 [Cu2+]0.87921 [DBDTC]2.03021. Based on the kinetic data, and formed complex compounds estimation, the mechanism explaining by 2 stages. In the first stage formation of [Cu(DBDTC)], and then [Cu(DBDTC)2] with the last structure geomethry planar rectangle. The result of this research will be more useful if an effort is being done in reaction mechanism by chemical computation method for obtain intermediate, and for constant “k” in same stage, k1.k2. and compound complex constanta (β).

  4. Kinetics and mechanism of ligand-exchange reactions of Cd(II) chelates

    Energy Technology Data Exchange (ETDEWEB)

    Nivorozhkin, L.E.; Kalabin, G.A.; Nivorozhkin, A.L.; Valeev, R.B.; Minkin, V.I.

    1987-03-01

    Tetrahedral Cd(II) bis(5-thio(or seleno)pyrazole-4-carboxaldiminates) of types II and III have been synthesized for the first time. The kinetics of the degenerate ligand exchange and enantiomerization of the complexes obtained have been studied by dynamic /sup 111/Cd, /sup 77/Se, and /sup 1/H (s = 1/2) NMR. The rate of intramolecular enantiomerization (k = 1/tau) is more than an order of magnitude greater than the corresponding values for processes of degenerate ligand exchange (a second-order reaction) determined from the dynamics of the averaging of the /sup 111/Cd-/sup 77/Se and /sup 111/Cd-N=CH spin-spin coupling constants. The cleavage and formation processes of the Cd-Se and Cd-N bonds are isoenergetic (..delta.. G/sub 298//sup not equal to/ = 14.4 kcal/mole for chelate II with X = Se and R = CH/sub 2/C/sub 6/H/sub 5/). The free energies of activation of degenerate ligand exchange determined form the dynamics of the averaging of the /sup 111/Cd N=CH spin-spin coupling constant increase from 12.7 to 17.9 kcal/mole along the following series for R: C/sub 2/H/sub 5/ < Ar < CH/sub 2/C/sub 6/H/sub 5/ < t-C/sub 4/H/sub 9/ < cyclo-C/sub 6/H/sub 11/. Replacement of the sulfur atom in the chelate ring by selenium results in increases in the rates of ligand exchange. A mechanism of degenerate ligand exchange has been proposed.

  5. Development and Application of Ligand-Exchange Reaction Method ...

    African Journals Online (AJOL)

    Purpose: This paper presents an improved kinetic-spectrophotometric procedure for determining clonazepam (CZP) in pharmaceutical formulations and human serum. Methods: The method is based on ligand-exchange reaction. The reaction was followed spectrophotometrically by measuring the rate of change of ...

  6. Enzyme-catalyzed and binding reaction kinetics determined by titration calorimetry.

    Science.gov (United States)

    Hansen, Lee D; Transtrum, Mark K; Quinn, Colette; Demarse, Neil

    2016-05-01

    Isothermal calorimetry allows monitoring of reaction rates via direct measurement of the rate of heat produced by the reaction. Calorimetry is one of very few techniques that can be used to measure rates without taking a derivative of the primary data. Because heat is a universal indicator of chemical reactions, calorimetry can be used to measure kinetics in opaque solutions, suspensions, and multiple phase systems and does not require chemical labeling. The only significant limitation of calorimetry for kinetic measurements is that the time constant of the reaction must be greater than the time constant of the calorimeter which can range from a few seconds to a few minutes. Calorimetry has the unique ability to provide both kinetic and thermodynamic data. This article describes the calorimetric methodology for determining reaction kinetics and reviews examples from recent literature that demonstrate applications of titration calorimetry to determine kinetics of enzyme-catalyzed and ligand binding reactions. A complete model for the temperature dependence of enzyme activity is presented. A previous method commonly used for blank corrections in determinations of equilibrium constants and enthalpy changes for binding reactions is shown to be subject to significant systematic error. Methods for determination of the kinetics of enzyme-catalyzed reactions and for simultaneous determination of thermodynamics and kinetics of ligand binding reactions are reviewed. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Kinetic study on ligand exchange reaction between EC and 99mTc-GH

    International Nuclear Information System (INIS)

    Wu Chunying; Luo Shineng; Fang Ping; Huang Heyun; Xie Minhao; Meng Hong

    1995-01-01

    The ligand exchange reaction between EC and 99m Tc-GH and its influence factors such as concentrations of EC and pH were described. The concentration of EC has no influence on the exchange reaction rate constant, while pH is the most important influence factor. The rate constants of ligand exchange reaction at different pH values were determined. The results showed that in order to make the labelling yield of 99m Tc-EC higher than 90%, pH of the reaction must be higher than 8

  8. Kinetic modeling and fitting software for interconnected reaction schemes: VisKin.

    Science.gov (United States)

    Zhang, Xuan; Andrews, Jared N; Pedersen, Steen E

    2007-02-15

    Reaction kinetics for complex, highly interconnected kinetic schemes are modeled using analytical solutions to a system of ordinary differential equations. The algorithm employs standard linear algebra methods that are implemented using MatLab functions in a Visual Basic interface. A graphical user interface for simple entry of reaction schemes facilitates comparison of a variety of reaction schemes. To ensure microscopic balance, graph theory algorithms are used to determine violations of thermodynamic cycle constraints. Analytical solutions based on linear differential equations result in fast comparisons of first order kinetic rates and amplitudes as a function of changing ligand concentrations. For analysis of higher order kinetics, we also implemented a solution using numerical integration. To determine rate constants from experimental data, fitting algorithms that adjust rate constants to fit the model to imported data were implemented using the Levenberg-Marquardt algorithm or using Broyden-Fletcher-Goldfarb-Shanno methods. We have included the ability to carry out global fitting of data sets obtained at varying ligand concentrations. These tools are combined in a single package, which we have dubbed VisKin, to guide and analyze kinetic experiments. The software is available online for use on PCs.

  9. Design, Testing and Kinetic Analysis of Bulky Monodentate Phosphorus Ligands in the Mizoroki-Heck Reaction

    NARCIS (Netherlands)

    Dodds, Deborah L.; Boele, Maarten D. K.; van Strijdonck, Gino P. F.; de Vries, Johannes G.; van Leeuwen, Piet W. N. M.; Kamer, Paul C. J.

    A series of new monodentate phosphane ligands 2 have been evaluated in the MizorokiHeck arylation reaction of iodobenzene and styrene and compared with our previously reported ligands, 1, 3 and 4. The concept of rational ligand design is discussed, and we describe how the performance of this new

  10. Kinetic study on ligand exchange reaction between ethylenedicysteine and 99mTc- glucoheptonate (99mTc-GH)

    International Nuclear Information System (INIS)

    Wu, C.Y.; Ji, S.R.; Lu, C.X.; Ding, S.Y.; Chen, Z.P.; Lin, X.T.

    2002-01-01

    Aim: 99m Tc-L,L-ethylenedicysteine( 99m Tc-EC)is a new type of renal imaging agent. It can be labeled very easily and efficiently at room temperature through direct labeling at pH 12. The need for direct labeling at pH 12 does not compromise the simplicity and ease of preparation of 99m Tc-EC and its practical usefulness in daily routine. On the basis of the labeling experiments, we developed a ligand exchange labeling method, in which the labeling EC with 99m Tc can be performed at pH 8. In order to provide a theoretic basis, a detailed kinetic study of ligand exchange reaction between 99m Tc- glucoheptonate( 99m Tc-GH) and EC was carried out. Materials and Methods: 99m Tc-EC is prepared as follows: 99m Tc-GH + EC → 99m Tc-EC + GH, labeling can be easily performed by adding 99m TcO 4 - (2∼6ml generator elute) to glucoheptonate solution containing SnCl 2 .2H 2 O solution to form 99m Tc-GH, then freshly prepared 99m Tc-GH is transferred to the aqueous solution of different concentrations of EC at different pH value, after being shaken, 99m Tc-EC was formed. Radiolabeling yield(RLY) and radiochemical purity(RCP) of 99m Tc-GH and 99m Tc-EC were measured by Xinhua No.1 paper with developing system of Me 2 CO/H 2 O/con.NH 3 .H 2 O=9/3/1(V/V). 99m Tc-GH(RCP must be over 98%, 80ul, 3.6∼7.4MBq) was added to 1ml of 0.5mol/L phosphate buffer(pH 12) containing different amount of EC(150, 75, 50 and 15ug), the sample was taken out at different time intervals and RCP was determined. The solution of EC(30ul, 5g/L) was added to 1ml of 0.5mol/L phosphate buffer at different pH value(pH11, 10, 9, 8, 7), after completely vortexed, 99m Tc-GH(RCP must be over 98%, 80ul, 3.6∼7.4MBq) was then added, the sample was taken out and RCP was determined as above. The rate constant(k) of ligand exchange reaction at different concentrations of EC and different reaction pH values were calculated out by integrating. Plot ln[1/(1-RLY)] vs t(time) showed a liner relationship, and the rate

  11. Estimation of kinetic and thermodynamic ligand-binding parameters using computational strategies.

    Science.gov (United States)

    Deganutti, Giuseppe; Moro, Stefano

    2017-04-01

    Kinetic and thermodynamic ligand-protein binding parameters are gaining growing importance as key information to consider in drug discovery. The determination of the molecular structures, using particularly x-ray and NMR techniques, is crucial for understanding how a ligand recognizes its target in the final binding complex. However, for a better understanding of the recognition processes, experimental studies of ligand-protein interactions are needed. Even though several techniques can be used to investigate both thermodynamic and kinetic profiles for a ligand-protein complex, these procedures are very often laborious, time consuming and expensive. In the last 10 years, computational approaches have enormous potential in providing insights into each of the above effects and in parsing their contributions to the changes in both kinetic and thermodynamic binding parameters. The main purpose of this review is to summarize the state of the art of computational strategies for estimating the kinetic and thermodynamic parameters of a ligand-protein binding.

  12. Chemical kinetics and reaction mechanism

    International Nuclear Information System (INIS)

    Jung, Ou Sik; Park, Youn Yeol

    1996-12-01

    This book is about chemical kinetics and reaction mechanism. It consists of eleven chapters, which deal with reaction and reaction speed on reaction mechanism, simple reaction by rate expression, reversible reaction and simultaneous reaction, successive reaction, complicated reaction mechanism, assumption for reaction mechanism, transition state theory, successive reaction and oscillating reaction, reaction by solution, research method high except kinetics on reaction mechanism, high reaction of kinetics like pulsed radiolysis.

  13. Ligand-Controlled Synthesis of Azoles via Ir-Catalyzed Reactions of Sulfoxonium Ylides with 2-Amino Heterocycles.

    Science.gov (United States)

    Phelps, Alicia M; Chan, Vincent S; Napolitano, José G; Krabbe, Scott W; Schomaker, Jennifer M; Shekhar, Shashank

    2016-05-20

    An iridium-catalyzed method was developed for the synthesis of imidazo-fused pyrrolopyrazines. The presence or absence of a nitrogenated ligand controlled the outcome of the reaction, leading to simple β-keto amine products in the absence of added ligand and the cyclized 7- and 8-substituted-imidazo[1,2-a]pyrrolo[2,3-e]pyrazine products in the presence of ligand. This catalyst control was conserved across a variety of ylide and amine coupling partners. The substrate was shown to act as a ligand for the iridium catalyst in the absence of other ligands via NMR spectroscopy. Kinetic studies indicated that formation of the Ir-carbene was reversible and the slow step of the reaction. These mechanistic investigations suggest that the β-keto amine products form via an intramolecular carbene N-H insertion, and the imidazopyrrolopyrazines form via an intermolecular carbene N-H insertion.

  14. Ligand Exchange Kinetics of Environmentally Relevant Metals

    Energy Technology Data Exchange (ETDEWEB)

    Panasci, Adele Frances [Univ. of California, Davis, CA (United States)

    2014-07-15

    The interactions of ground water with minerals and contaminants are of broad interest for geochemists but are not well understood. Experiments on the molecular scale can determine reaction parameters (i.e. rates of ligand exchange, activation entropy, activation entropy, and activation volume) that can be used in computations to gain insight into reactions that occur in natural groundwaters. Experiments to determine the rate of isotopic ligand exchange for three environmentally relevant metals, rhodium (Rh), iron (Fe), and neptunium (Np), are described. Many environmental transformations of metals (e.g. reduction) in soil occur at trivalent centers, Fe(III) in particular. Contaminant ions absorb to mineral surfaces via ligand exchange, and the reversal of this reaction can be dangerous, releasing contaminants into the environment. Ferric iron is difficult to study spectroscopically because most of its complexes are paramagnetic and are generally reactive toward ligand exchange; therefore, Rh(III), which is diamagnetic and less reactive, was used to study substitution reactions that are analogous to those that occur on mineral oxide surfaces. Studies on both Np(V) and Np(VI) are important in their own right, as 237Np is a radioactive transuranic element with a half-life of 2 million years.

  15. Kinetic Isotope Effect Determination Probes the Spin of the Transition State, Its Stereochemistry, and Its Ligand Sphere in Hydrogen Abstraction Reactions of Oxoiron(IV) Complexes.

    Science.gov (United States)

    Mandal, Debasish; Mallick, Dibyendu; Shaik, Sason

    2018-01-16

    This Account outlines interplay of theory and experiment in the quest to identify the reactive-spin-state in chemical reactions that possess a few spin-dependent routes. Metalloenzymes and synthetic models have forged in recent decades an area of increasing appeal, in which oxometal species bring about functionalization of hydrocarbons under mild conditions and via intriguing mechanisms that provide a glimpse of Nature's designs to harness these reactions. Prominent among these are oxoiron(IV) complexes, which are potent H-abstractors. One of the key properties of oxoirons is the presence of close-lying spin-states, which can mediate H-abstractions. As such, these complexes form a fascinating chapter of spin-state chemistry, in which chemical reactivity involves spin-state interchange, so-called two-state reactivity (TSR) and multistate reactivity (MSR). TSR and MSR pose mechanistic challenges. How can one determine the structure of the reactive transition state (TS) and its spin state for these mechanisms? Calculations can do it for us, but the challenge is to find experimental probes. There are, however, no clear kinetic signatures for the reactive-spin-state in such reactions. This is the paucity that our group has been trying to fill for sometime. Hence, it is timely to demonstrate how theory joins experiment in realizing this quest. This Account uses a set of the H-abstraction reactions of 24 synthetic oxoiron(IV) complexes and 11 hydrocarbons, together undergoing H-abstraction reactions with TSR/MSR options, which provide experimentally determined kinetic isotope effect (KIE exp ) data. For this set, we demonstrate that comparing KIE exp results with calculated tunneling-augmented KIE (KIE TC ) data leads to a clear identification of the reactive spin-state during H-abstraction reactions. In addition, generating KIE exp data for a reaction of interest, and comparing these to KIE TC values, provides the mechanistic chemist with a powerful capability to

  16. Chemical kinetics of gas reactions

    CERN Document Server

    Kondrat'Ev, V N

    2013-01-01

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

  17. Study of substitution reactions of ligands in VO2+ complexes in toluene solutions by ESR method

    International Nuclear Information System (INIS)

    Lundkvist, R.; Panfilov, A.T.; Kalinichenko, N.B.; Marov, I.N.; AN SSSR, Moscow. Inst. Geokhimii i Analiticheskoj Khimii)

    1976-01-01

    Kinetics and equilibrium of stepwise substitution of ligands have been investigated at different temperatures for the complexes of oxovanadium (4) with salicylaldoxime, 8-oxyquinoline, acetylacetone, benzoylacetone, and tenoyltrifluoroacetone. The relative complexability of these ligands in toluene has been studied. The parameters of spin-Hamiltonian of EPR spectra of the VO 2+ complexes have been determined. The equilibrium constants, the rate constants, and activation energy have been found for the substitution reactions of ligands in the complexes VOA 2 : VOA 2 +HB=VOAB+HA; VOAB+HB=VOB 2 +HA, where HA and HB are the ligands with different donor atoms. The mixed complexes have been detected of the general formula VOAB, where HA is salicylaldoxime or 8-oxyquinoline and HB is β-diketone

  18. Precipitation kinetics of Mg-carbonates, influence of organic ligands and consequences for CO2 mineral sequestration

    International Nuclear Information System (INIS)

    Gautier, Q.

    2012-01-01

    Forming magnesium carbonate minerals through carbonation of magnesium silicates has been proposed as a safe and durable way to store carbon dioxide, with a possibly high potential to offset anthropogenic CO 2 emissions. To date however, chemical reactions involved in this process are facing strong kinetic limitations, which originate in the low reactivity of both Mg-silicates and Mg-carbonates. Numerous studies have focused on the dissolution of Mg-silicates, under the questionable hypothesis that this step limits the whole process. This thesis work focuses instead on the mechanisms and rates of formation of magnesium carbonates, which are the final products of carbonation reactions. The first part of the work is dedicated to studying the influence on magnesite precipitation kinetics of three organic ligands known to accelerate Mg-silicates dissolution rates: oxalate, citrate and EDTA. With help of mixed-flow reactor experiments performed between 100 and 150 C, we show that these ligands significantly reduce magnesite growth rates, through two combined mechanisms: (1) complexation of Mg 2+ cations in aqueous solution, which was rigorously estimated from a thermodynamic database established through a critical review of the literature, and (2) adsorption of ligands to a limited number of surface sites, leading to a decrease of the precipitation rate constant. The observed growth inhibition is maximal with citrate. We then used hydrothermal atomic force microscopy to probe the origin of the documented growth inhibition. Our observations show that citrate and oxalate interact with the crystal growth process on magnesite surface, modifying the shape of growth hillocks as well as the step generation frequency through spiral growth. We also show that the ligands adsorb preferentially on different kink-sites, which is probably related to their different structures and chemical properties. We propose that the stronger magnesite growth inhibition caused by citrate is related

  19. Nickel speciation and complexation kinetics in freshwater by ligand exchange and DPCSV

    NARCIS (Netherlands)

    Han Bin Xue,; Jansen, S.; Prasch, A.; Sigg, L.

    2001-01-01

    A technique of ligand exchange with DMG (dimethylglyoxime) and DPCSV was applied to determine Ni speciation in lake, river, and groundwater samples. The working conditions related to ligand-exchange equilibrium were optimized, and the ligand-exchange kinetics were examined. The observed

  20. Ligand-promoted protein folding by biased kinetic partitioning.

    Science.gov (United States)

    Hingorani, Karan S; Metcalf, Matthew C; Deming, Derrick T; Garman, Scott C; Powers, Evan T; Gierasch, Lila M

    2017-04-01

    Protein folding in cells occurs in the presence of high concentrations of endogenous binding partners, and exogenous binding partners have been exploited as pharmacological chaperones. A combined mathematical modeling and experimental approach shows that a ligand improves the folding of a destabilized protein by biasing the kinetic partitioning between folding and alternative fates (aggregation or degradation). Computationally predicted inhibition of test protein aggregation and degradation as a function of ligand concentration are validated by experiments in two disparate cellular systems.

  1. Thermodynamics of axial substitution and kinetics of reactions with amino acids for the paddlewheel complex tetrakis(acetato)chloridodiruthenium(II,III).

    Science.gov (United States)

    Santos, Rodrigo L S R; van Eldik, Rudi; de Oliveira Silva, Denise

    2012-06-18

    The known paddlewheel, tetrakis(acetato)chloridodiruthenium(II,III), offers a versatile synthetic route to a novel class of antitumor diruthenium(II,III) metallo drugs, where the equatorial ligands are nonsteroidal anti-inflammatory carboxylates. This complex was studied here as a soluble starting prototype model for antitumor analogues to elucidate the reactivity of the [Ru(2)(CH(3)COO)(4)](+) framework. Thermodynamic studies on equilibration reactions for axial substitution of water by chloride and kinetic studies on reactions of the diaqua complexes with the amino acids glycine, cysteine, histidine, and tryptophan were performed. The standard thermodynamic reaction parameters ΔH°, ΔS°, and ΔV° were determined and showed that both of the sequential axial substitution reactions are enthalpy driven. Kinetic rate laws and rate constants were determined for the axial substitution reactions of coordinated water by the amino acids that gave the corresponding aqua(amino acid)-Ru(2) substituted species. The results revealed that the [Ru(2)(CH(3)COO)(4)](+) paddlewheel framework remained stable during the axial ligand substitution reactions and was also mostly preserved in the presence of the amino acids.

  2. Mechanism of redox reactions induced by light and electron pulse in solutions of mixed ligand iron(II) complex cyanides

    International Nuclear Information System (INIS)

    Horvath, A.; Szoeke, J.; Wojnarovits, L.

    1991-01-01

    Redox reactions induced by light and electron pulse have been studied in aqueous solutions of mixed ligand iron(II) complex cyanides. The short lived intermediates have been identified by time resolved specroscopy, the results of detailed kinetic analysis have been discussed. (author) 6 refs.; 3 figs.; 2 tabs

  3. Kinetics of Bio-Reactions

    DEFF Research Database (Denmark)

    Villadsen, John

    2015-01-01

    his chapter predicts the specific rates of reaction by means of a mathematical expression, the kinetics of the reaction. This expression can be derived through a mechanistic interpretation of an enzymatically catalyzed reaction, but it is essentially of empirical nature for cell reactions. The mo...

  4. Colloidal nanoparticle size control: experimental and kinetic modeling investigation of the ligand-metal binding role in controlling the nucleation and growth kinetics.

    Science.gov (United States)

    Mozaffari, Saeed; Li, Wenhui; Thompson, Coogan; Ivanov, Sergei; Seifert, Soenke; Lee, Byeongdu; Kovarik, Libor; Karim, Ayman M

    2017-09-21

    Despite the major advancements in colloidal metal nanoparticles synthesis, a quantitative mechanistic treatment of the ligand's role in controlling their size remains elusive. We report a methodology that combines in situ small angle X-ray scattering (SAXS) and kinetic modeling to quantitatively capture the role of ligand-metal binding (with the metal precursor and the nanoparticle surface) in controlling the synthesis kinetics. We demonstrate that accurate extraction of the kinetic rate constants requires using both, the size and number of particles obtained from in situ SAXS to decouple the contributions of particle nucleation and growth to the total metal reduction. Using Pd acetate and trioctylphosphine in different solvents, our results reveal that the binding of ligands with both the metal precursor and nanoparticle surface play a key role in controlling the rates of nucleation and growth and consequently the final size. We show that the solvent can affect the metal-ligand binding and consequently ligand coverage on the nanoparticles surface which has a strong effect on the growth rate and final size (1.4 nm in toluene and 4.3 nm in pyridine). The proposed kinetic model quantitatively predicts the effects of varying the metal concentration and ligand/metal ratio on nanoparticle size for our work and literature reports. More importantly, we demonstrate that the final size is exclusively determined by the nucleation and growth kinetics at early times and not how they change with time. Specifically, the nanoparticle size in this work and many literature reports can be predicted using a single, model independent kinetic descriptor, (growth-to-nucleation rate ratio) 1/3 , despite the different metals and synthetic conditions. The proposed model and kinetic descriptor could serve as powerful tools for the design of colloidal nanoparticles with specific sizes.

  5. Ammonia formation by metal-ligand cooperative hydrogenolysis of a nitrido ligand

    Science.gov (United States)

    Askevold, Bjorn; Nieto, Jorge Torres; Tussupbayev, Samat; Diefenbach, Martin; Herdtweck, Eberhardt; Holthausen, Max C.; Schneider, Sven

    2011-07-01

    Bioinspired hydrogenation of N2 to ammonia at ambient conditions by stepwise nitrogen protonation/reduction with metal complexes in solution has experienced remarkable progress. In contrast, the highly desirable direct hydrogenation with H2 remains difficult. In analogy to the heterogeneously catalysed Haber-Bosch process, such a reaction is conceivable via metal-centred N2 splitting and unprecedented hydrogenolysis of the nitrido ligands to ammonia. We report the synthesis of a ruthenium(IV) nitrido complex. The high nucleophilicity of the nitrido ligand is demonstrated by unusual N-C coupling with π-acidic CO. Furthermore, the terminal nitrido ligand undergoes facile hydrogenolysis with H2 at ambient conditions to produce ammonia in high yield. Kinetic and quantum chemical examinations of this reaction suggest cooperative behaviour of a phosphorus-nitrogen-phosphorus pincer ligand in rate-determining heterolytic hydrogen splitting.

  6. Effects of electrostatic interactions on ligand dissociation kinetics

    Science.gov (United States)

    Erbaş, Aykut; de la Cruz, Monica Olvera; Marko, John F.

    2018-02-01

    We study unbinding of multivalent cationic ligands from oppositely charged polymeric binding sites sparsely grafted on a flat neutral substrate. Our molecular dynamics simulations are suggested by single-molecule studies of protein-DNA interactions. We consider univalent salt concentrations spanning roughly a 1000-fold range, together with various concentrations of excess ligands in solution. To reveal the ionic effects on unbinding kinetics of spontaneous and facilitated dissociation mechanisms, we treat electrostatic interactions both at a Debye-Hückel (DH) (or implicit ions, i.e., use of an electrostatic potential with a prescribed decay length) level and by the more precise approach of considering all ionic species explicitly in the simulations. We find that the DH approach systematically overestimates unbinding rates, relative to the calculations where all ion pairs are present explicitly in solution, although many aspects of the two types of calculation are qualitatively similar. For facilitated dissociation (FD) (acceleration of unbinding by free ligands in solution) explicit-ion simulations lead to unbinding at lower free-ligand concentrations. Our simulations predict a variety of FD regimes as a function of free-ligand and ion concentrations; a particularly interesting regime is at intermediate concentrations of ligands where nonelectrostatic binding strength controls FD. We conclude that explicit-ion electrostatic modeling is an essential component to quantitatively tackle problems in molecular ligand dissociation, including nucleic-acid-binding proteins.

  7. Characterization of ligand binding to melanocortin 4 receptors using fluorescent peptides with improved kinetic properties.

    Science.gov (United States)

    Link, Reet; Veiksina, Santa; Rinken, Ago; Kopanchuk, Sergei

    2017-03-15

    Melanocortin 4 (MC 4 ) receptors are important drug targets as they regulate energy homeostasis, eating behaviour and sexual functions. The ligand binding process to these G protein-coupled receptors is subject to considerable complexity. Different steps in the complex dynamic regulation can be characterized by ligand binding kinetics. Optimization of these kinetic parameters in terms of on-rate and residence time can increase the rapid onset of drug action and reduce off-target effects. Fluorescence anisotropy (FA) is one of the homogeneous fluorescence-based assays that enable continuous online monitoring of ligand binding kinetics. FA has been implemented for the kinetic study of melanocortin MC 4 receptors expressed on budded baculoviruses. However, the slow dissociation of the fluorescently labelled peptide NDP-α-MSH does not enable reaching equilibrium nor enable more in-depth study of the binding mechanisms. To overcome this problem, two novel red-shifted fluorescent ligands were designed. These cyclized heptapeptide derivatives (UTBC101 and UTBC102) exhibited nanomolar affinity toward melanocortin MC 4 receptors but had relatively different kinetic properties. The dissociation half-lives of UTBC101 (τ 1/2 =160min) and UTBC102 (τ 1/2 =7min) were shorter compared to that what was previously reported for Cy3B-NDP-α-MSH (τ 1/2 =224min). The significantly shorter dissociation half-life of UTBC102 enables equilibrium in screening assays, whereas the higher affinity of UTBC101 helps to resolve a wider range of competitor potencies. These two ligands are suitable for further kinetic screening of novel melanocortin MC 4 receptor specific ligands and could complement each other in these studies. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Biphasic kinetics in the reaction between amino acids or glutathione and the chromium acetate cluster, [Cr3O(OAc)6]+.

    Science.gov (United States)

    Chaudhary, Shveta; Van Horn, J David

    2006-11-07

    Kinetics for the breakdown of the trinuclear chromium acetate cluster with a series of monoprotic and diprotic amino acid ligands and with glutathione in aqueous media have been investigated spectrophotometrically at pH 3.5-5.5 and in a temperature range of 45-60 degrees C. Under pseudo-first-order conditions, reactions with these ligands exhibited biphasic kinetic behavior that can be accounted for by a consecutive two-step reaction, A-->B-->C, where A is assumed to be a forced ion pair, B an intermediate and C is the product; experimental data fit to a biexponential equation for the transformation. Rates for k(short), k(long), and k(obs) were determined by manual extrapolation of absorbance data or curve-fitting routines; associated activation parameters for each step of the reaction were calculated using the Eyring equation. Rates for the first and second steps of the reaction are on the order of approximately 10(-4) and approximately 10(-5)s(-1), respectively. The large negative values of DeltaS++ and smaller DeltaH++ in the first step indicate an associative step, while high positive values of DeltaS(double dagger) in the second step indicate dissociation. To account for the results mechanistically, the results are interpreted to be a first step of ligand exchange with a pseudo-axial aqua ligand, followed by a dissociative step involving acetate or oxo ligand displacement. The dissociative step is the rate determining step, with k(obs) approximately k(long). The results demonstrate reaction pathways that are available to the Cr(III) metal centers that may be physiologically relevant in the ligand-rich environment of biological systems. Under general conditions Cr(III) clusters may be expected to be broken down, unless some unique biological environment stabilizes the cluster. The present study has application to the processes related to Cr(III) transport and excretion, to potential mechanisms of Cr(III) action in a biological setting, and to the

  9. Catecholase activity of dicopper(II)-bispidine complexes: stabilities and structures of intermediates, kinetics and reaction mechanism.

    Science.gov (United States)

    Born, Karin; Comba, Peter; Daubinet, André; Fuchs, Alexander; Wadepohl, Hubert

    2007-01-01

    A mechanism for the oxidation of 3,5-di-tert-butylcatechol (dtbc) with dioxygen to the corresponding quinone (dtbq), catalyzed by bispidine-dicopper complexes (bispidines are various mono- and dinucleating derivatives of 3,7-diazabicyclo[3.3.1]nonane with bis-tertiary-amine-bispyridyl or bis-tertiary-amine-trispyridyl donor sets), is proposed on the basis of (1) the stoichiometry of the reaction as well as the stabilities and structures [X-ray, density functional theory (B3LYP, TZV)] of the bispidine-dicopper(II)-3,4,5,6-tetrachlorcatechol intermediates, (2) formation kinetics and structures (molecular mechanics, MOMEC) of the end-on peroxo-dicopper(II) complexes and (3) kinetics of the stoichiometric (anaerobic) and catalytic (aerobic) copper-complex-assisted oxidation of dtbc. This involves (1) the oxidation of the dicopper(I) complexes with dioxygen to the corresponding end-on peroxo-dicopper(II) complexes, (2) coordination of dtbc as a bridging ligand upon liberation of H(2)O(2) and (3) intramolecular electron transfer to produce dtbq, which is liberated, and the dicopper(I) catalyst. Although the bispidine complexes have reactivities comparable to those of recently published catalysts with macrocyclic ligands, which seem to reproduce the enzyme-catalyzed process in various reaction sequences, a strikingly different oxidation mechanism is derived from the bispidine-dicopper-catalyzed reaction.

  10. Kinetic studies of elementary chemical reactions

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  11. Chemistry and reaction kinetics of biowaste torrefaction

    NARCIS (Netherlands)

    Stelt, van der M.J.C.

    2011-01-01

    This thesis addresses the question of how the chemistry and reaction kinetics of torrefaction are influenced by reaction conditions and the effects occuring during the reaction. This research question can be specified by questions such as, what controls their kinetics during torrefaction and what

  12. Comparison of the kinetics of different Markov models for ligand binding under varying conditions

    International Nuclear Information System (INIS)

    Martini, Johannes W. R.; Habeck, Michael

    2015-01-01

    We recently derived a Markov model for macromolecular ligand binding dynamics from few physical assumptions and showed that its stationary distribution is the grand canonical ensemble [J. W. R. Martini, M. Habeck, and M. Schlather, J. Math. Chem. 52, 665 (2014)]. The transition probabilities of the proposed Markov process define a particular Glauber dynamics and have some similarity to the Metropolis-Hastings algorithm. Here, we illustrate that this model is the stochastic analog of (pseudo) rate equations and the corresponding system of differential equations. Moreover, it can be viewed as a limiting case of general stochastic simulations of chemical kinetics. Thus, the model links stochastic and deterministic approaches as well as kinetics and equilibrium described by the grand canonical ensemble. We demonstrate that the family of transition matrices of our model, parameterized by temperature and ligand activity, generates ligand binding kinetics that respond to changes in these parameters in a qualitatively similar way as experimentally observed kinetics. In contrast, neither the Metropolis-Hastings algorithm nor the Glauber heat bath reflects changes in the external conditions correctly. Both converge rapidly to the stationary distribution, which is advantageous when the major interest is in the equilibrium state, but fail to describe the kinetics of ligand binding realistically. To simulate cellular processes that involve the reversible stochastic binding of multiple factors, our pseudo rate equation model should therefore be preferred to the Metropolis-Hastings algorithm and the Glauber heat bath, if the stationary distribution is not of only interest

  13. Comparison of the kinetics of different Markov models for ligand binding under varying conditions

    Energy Technology Data Exchange (ETDEWEB)

    Martini, Johannes W. R., E-mail: jmartin2@gwdg.de [Max Planck Institute for Developmental Biology, Tübingen (Germany); Felix Bernstein Institute for Mathematical Statistics in the Biosciences, University of Göttingen, Göttingen (Germany); Habeck, Michael, E-mail: mhabeck@gwdg.de [Felix Bernstein Institute for Mathematical Statistics in the Biosciences, University of Göttingen, Göttingen (Germany); Max Planck Institute for Biophysical Chemistry, Göttingen (Germany)

    2015-03-07

    We recently derived a Markov model for macromolecular ligand binding dynamics from few physical assumptions and showed that its stationary distribution is the grand canonical ensemble [J. W. R. Martini, M. Habeck, and M. Schlather, J. Math. Chem. 52, 665 (2014)]. The transition probabilities of the proposed Markov process define a particular Glauber dynamics and have some similarity to the Metropolis-Hastings algorithm. Here, we illustrate that this model is the stochastic analog of (pseudo) rate equations and the corresponding system of differential equations. Moreover, it can be viewed as a limiting case of general stochastic simulations of chemical kinetics. Thus, the model links stochastic and deterministic approaches as well as kinetics and equilibrium described by the grand canonical ensemble. We demonstrate that the family of transition matrices of our model, parameterized by temperature and ligand activity, generates ligand binding kinetics that respond to changes in these parameters in a qualitatively similar way as experimentally observed kinetics. In contrast, neither the Metropolis-Hastings algorithm nor the Glauber heat bath reflects changes in the external conditions correctly. Both converge rapidly to the stationary distribution, which is advantageous when the major interest is in the equilibrium state, but fail to describe the kinetics of ligand binding realistically. To simulate cellular processes that involve the reversible stochastic binding of multiple factors, our pseudo rate equation model should therefore be preferred to the Metropolis-Hastings algorithm and the Glauber heat bath, if the stationary distribution is not of only interest.

  14. Discussion of the Investigation Method on the Reaction Kinetics of Metallurgical Reaction Engineering

    Science.gov (United States)

    Du, Ruiling; Wu, Keng; Zhang, Jiazhi; Zhao, Yong

    Reaction kinetics of metallurgical physical chemistry which was successfully applied in metallurgy (as ferrous metallurgy, non-ferrous metallurgy) became an important theoretical foundation for subject system of traditional metallurgy. Not only the research methods were very perfect, but also the independent structures and systems of it had been formed. One of the important tasks of metallurgical reaction engineering was the simulation of metallurgical process. And then, the mechanism of reaction process and the conversion time points of different control links should be obtained accurately. Therefore, the research methods and results of reaction kinetics in metallurgical physical chemistry were not very suitable for metallurgical reaction engineering. In order to provide the definite conditions of transmission, reaction kinetics parameters and the conversion time points of different control links for solving the transmission and reaction equations in metallurgical reaction engineering, a new method for researching kinetics mechanisms in metallurgical reaction engineering was proposed, which was named stepwise attempt method. Then the comparison of results between the two methods and the further development of stepwise attempt method were discussed in this paper. As a new research method for reaction kinetics in metallurgical reaction engineering, stepwise attempt method could not only satisfy the development of metallurgical reaction engineering, but also provide necessary guarantees for establishing its independent subject system.

  15. Multiscale simulations of ligand adsorption and exchange on gold nanoparticles.

    Science.gov (United States)

    Gao, Hui-Min; Liu, Hong; Qian, Hu-Jun; Jiao, Gui-Sheng; Lu, Zhong-Yuan

    2018-01-17

    We have developed a multiscale model that combines first-principles methods with atomistic and mesoscopic simulations to explore the molecular structures and packing density of the ligands present on the gold nanoparticle (AuNP) surface, as well as the adsorption/exchange reaction kinetics of cetyltrimethylammonium bromide (CTAB)/PEG-SH ligands on different facets of gold, namely, Au(111), Au(100), and Au(110). Our model predicts that on clean gold surfaces, CTAB adsorption is diffusion limited. Specifically, CTAB has the preferentially higher adsorption rate and coverage density on Au(100) and Au(110) surfaces, forming a more compact layer with respect to that on the Au(111) surface, which could result in greater growth of gold nanoparticles along the (111) direction. As opposed to CTAB adsorption, the exchange reaction between PEG-SH with CTAB shows no selectivity to different crystal faces, and the reaction process follows Langmuir diffusion kinetics. Kinetic analysis reveals that, in water, the exchange reaction is zeroth order with respect to the concentration of an incoming PEG-SH, indicative of a dissociative exchange mechanism. The observed rate constant decreases exponentially with the PEG-SH chain length, consistent with a diffusion process for the free PEG-SH in water. In particular, we show that the exchange efficiency increases as the chain rigidness and size of the incoming ligand and/or steric bulk of the initial protecting ligand shell are decreased. Our objectives are to provide a model to assess the kinetics and thermodynamics of the adsorption/exchange reaction process, and we expect that these findings will have important implications for routine surface characterization of AuNPs.

  16. Influence of Proton Acceptors on the Proton-Coupled Electron Transfer Reaction Kinetics of a Ruthenium-Tyrosine Complex.

    Science.gov (United States)

    Lennox, J Christian; Dempsey, Jillian L

    2017-11-22

    A polypyridyl ruthenium complex with fluorinated bipyridine ligands and a covalently bound tyrosine moiety was synthesized, and its photo-induced proton-coupled electron transfer (PCET) reactivity in acetonitrile was investigated with transient absorption spectroscopy. Using flash-quench methodology with methyl viologen as an oxidative quencher, a Ru 3+ species is generated that is capable of initiating the intramolecular PCET oxidation of the tyrosine moiety. Using a series of substituted pyridine bases, the reaction kinetics were found to vary as a function of proton acceptor concentration and identity, with no significant H/D kinetic isotope effect. Through analysis of the kinetics traces and comparison to a control complex without the tyrosine moiety, PCET reactivity was found to proceed through an equilibrium electron transfer followed by proton transfer (ET-PT) pathway in which irreversible deprotonation of the tyrosine radical cation shifts the ET equilibrium, conferring a base dependence on the reaction. Comprehensive kinetics modeling allowed for deconvolution of complex kinetics and determination of rate constants for each elementary step. Across the five pyridine bases explored, spanning a range of 4.2 pK a units, a linear free-energy relationship was found for the proton transfer rate constant with a slope of 0.32. These findings highlight the influence that proton transfer driving force exerts on PCET reaction kinetics.

  17. New L-Serine Derivative Ligands as Cocatalysts for Diels-Alder Reaction

    Science.gov (United States)

    Sousa, Carlos A. D.; Rodríguez-Borges, José E.; Freire, Cristina

    2013-01-01

    New L-serine derivative ligands were prepared and tested as cocatalyst in the Diels-Alder reactions between cyclopentadiene (CPD) and methyl acrylate, in the presence of several Lewis acids. The catalytic potential of the in situ formed complexes was evaluated based on the reaction yield. Bidentate serine ligands showed good ability to coordinate medium strength Lewis acids, thus boosting their catalytic activity. The synthesis of the L-serine ligands proved to be highly efficient and straightforward. PMID:24383009

  18. Hydrogen electrode reaction: A complete kinetic description

    International Nuclear Information System (INIS)

    Quaino, P.M.; Gennero de Chialvo, M.R.; Chialvo, A.C.

    2007-01-01

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

  19. Synthesis and thermal decomposition kinetics of Th(IV) complex with unsymmetrical Schiff base ligand

    International Nuclear Information System (INIS)

    Fan Yuhua; Bi Caifeng; Liu Siquan; Yang Lirong; Liu Feng; Ai Xiaokang

    2006-01-01

    A new unsymmetrical Schiff base ligand (H 2 LLi) was synthesized using L-lysine, o-vanillin and salicylaladyde. Thorium(IV) complex of this ligand [Th(H 2 L)(NO 3 )](NO 3 ) 2 x 3H 2 O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt = A x e -E/RT x 1/2 (1-α) x [-ln(1-α)] -1 . The kinetic parameters (E, A), activation entropy ΔS ≠ and activation free-energy ΔG ≠ were also calculated. (author)

  20. Preventing Corrosion by Controlling Cathodic Reaction Kinetics

    Science.gov (United States)

    2016-03-25

    3. DATES COVERED (From - To) 09/23/15 - 04/22/16 4. TITLE AND SUBTITLE Sa. CONTRACT NUMBER Preventing Corrosion by Controlling Cathodic Reaction...Preventing corrosion by controlling cathodic reaction kinetics Progress Report for Period: 1 SEP 2015-31 MAR 2016 John Keith Department of...25 March 2016 Preventing corrosion by controlling cathodic reaction kinetics Annual Summary Report: FY16 PI: John Keith, 412-624-7016,jakeith

  1. Toehold-Mediated Displacement of an Adenosine-Binding Aptamer from a DNA Duplex by its Ligand.

    Science.gov (United States)

    Monserud, Jon H; Macri, Katherine M; Schwartz, Daniel K

    2016-10-24

    DNA is increasingly used to engineer dynamic nanoscale circuits, structures, and motors, many of which rely on DNA strand-displacement reactions. The use of functional DNA sequences (e.g., aptamers, which bind to a wide range of ligands) in these reactions would potentially confer responsiveness on such devices, and integrate DNA computation with highly varied molecular stimuli. By using high-throughput single-molecule FRET methods, we compared the kinetics of a putative aptamer-ligand and aptamer-complement strand-displacement reaction. We found that the ligands actively disrupted the DNA duplex in the presence of a DNA toehold in a similar manner to complementary DNA, with kinetic details specific to the aptamer structure, thus suggesting that the DNA strand-displacement concept can be extended to functional DNA-ligand systems. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Combustion kinetics and reaction pathways

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  3. Reaction kinetics of polybutylene terephthalate polycondensation reaction

    NARCIS (Netherlands)

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

    2005-01-01

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

  4. Accuracy and precision of protein–ligand interaction kinetics determined from chemical shift titrations

    International Nuclear Information System (INIS)

    Markin, Craig J.; Spyracopoulos, Leo

    2012-01-01

    NMR-monitored chemical shift titrations for the study of weak protein–ligand interactions represent a rich source of information regarding thermodynamic parameters such as dissociation constants (K D ) in the micro- to millimolar range, populations for the free and ligand-bound states, and the kinetics of interconversion between states, which are typically within the fast exchange regime on the NMR timescale. We recently developed two chemical shift titration methods wherein co-variation of the total protein and ligand concentrations gives increased precision for the K D value of a 1:1 protein–ligand interaction (Markin and Spyracopoulos in J Biomol NMR 53: 125–138, 2012). In this study, we demonstrate that classical line shape analysis applied to a single set of 1 H– 15 N 2D HSQC NMR spectra acquired using precise protein–ligand chemical shift titration methods we developed, produces accurate and precise kinetic parameters such as the off-rate (k off ). For experimentally determined kinetics in the fast exchange regime on the NMR timescale, k off ∼ 3,000 s −1 in this work, the accuracy of classical line shape analysis was determined to be better than 5 % by conducting quantum mechanical NMR simulations of the chemical shift titration methods with the magnetic resonance toolkit GAMMA. Using Monte Carlo simulations, the experimental precision for k off from line shape analysis of NMR spectra was determined to be 13 %, in agreement with the theoretical precision of 12 % from line shape analysis of the GAMMA simulations in the presence of noise and protein concentration errors. In addition, GAMMA simulations were employed to demonstrate that line shape analysis has the potential to provide reasonably accurate and precise k off values over a wide range, from 100 to 15,000 s −1 . The validity of line shape analysis for k off values approaching intermediate exchange (∼100 s −1 ), may be facilitated by more accurate K D measurements from NMR

  5. Accuracy and precision of protein-ligand interaction kinetics determined from chemical shift titrations.

    Science.gov (United States)

    Markin, Craig J; Spyracopoulos, Leo

    2012-12-01

    NMR-monitored chemical shift titrations for the study of weak protein-ligand interactions represent a rich source of information regarding thermodynamic parameters such as dissociation constants (K ( D )) in the micro- to millimolar range, populations for the free and ligand-bound states, and the kinetics of interconversion between states, which are typically within the fast exchange regime on the NMR timescale. We recently developed two chemical shift titration methods wherein co-variation of the total protein and ligand concentrations gives increased precision for the K ( D ) value of a 1:1 protein-ligand interaction (Markin and Spyracopoulos in J Biomol NMR 53: 125-138, 2012). In this study, we demonstrate that classical line shape analysis applied to a single set of (1)H-(15)N 2D HSQC NMR spectra acquired using precise protein-ligand chemical shift titration methods we developed, produces accurate and precise kinetic parameters such as the off-rate (k ( off )). For experimentally determined kinetics in the fast exchange regime on the NMR timescale, k ( off ) ~ 3,000 s(-1) in this work, the accuracy of classical line shape analysis was determined to be better than 5 % by conducting quantum mechanical NMR simulations of the chemical shift titration methods with the magnetic resonance toolkit GAMMA. Using Monte Carlo simulations, the experimental precision for k ( off ) from line shape analysis of NMR spectra was determined to be 13 %, in agreement with the theoretical precision of 12 % from line shape analysis of the GAMMA simulations in the presence of noise and protein concentration errors. In addition, GAMMA simulations were employed to demonstrate that line shape analysis has the potential to provide reasonably accurate and precise k ( off ) values over a wide range, from 100 to 15,000 s(-1). The validity of line shape analysis for k ( off ) values approaching intermediate exchange (~100 s(-1)), may be facilitated by more accurate K ( D ) measurements

  6. Kinetic aspects of the Maillard reaction: a critical review

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    2001-01-01

    The literature concerning the kinetics of the Maillard reaction was critically discussed according to the initial, intermediate and advanced stages, as this is the way the Maillard reaction is traditionally analysed. For each stage, a division is made between simple kinetics and complex kinetics.

  7. A Kinetic Study of the Diels-Alder Reaction. An Experiment Illustrating Simple Second-Order Reaction Kinetics.

    Science.gov (United States)

    Silvestri, Michael G.; Dills, Charles E.

    1989-01-01

    Describes an organic chemistry experiment for teaching the basic concepts of chemical kinetics. Provides background information about first- and second-order reactions, experimental procedures of the Diels-Alder reaction between cyclopentadiene and dimethyl fumarate, and the experimental results. (YP)

  8. Kinetic investigation of uranyl-uranophile complexation. 1. Macrocyclic kinetic effect and macrocyclic protection effect

    International Nuclear Information System (INIS)

    Tabushi, I.; Yoshizawa, A.

    1986-01-01

    Equilibria and rates of ligand-exchange reactions between uranyl tricarbonate and dithiocarbamates and between uranyl tris-(dithiocarbamates) and carbonate were studied under a variety of conditions. The dithiocarbamates used were acyclic diethyl-dithiocarbamate and macrocyclic tris(dithiocarbamate). The acyclic ligand showed a triphasic (successive three-step) equilibrium with three different equilibrium constants while the macrocyclic ligand showed a clear monophasic (one-step) equilibrium with a much larger stability constant for the dithiocarbamate-uranyl complex. The macrocyclic ligand showed the S/sub N/2-type ligand-exchange rate in the forward as well as reverse process, while the first step of the acyclic ligand-exchange reaction proceeded via the S/sub N/1-type mechanism. This kinetic macrocyclic effect on molecularity is interpreted as the result of a unique topological requirement of uranyl complexation. The macrocyclic ligand also exhibited a clear protection effect, leading to the large stability constant. 19 references, 10 figures, 2 tables

  9. The Ligand Substitution Reactions of Hydrophobic Vitamin B ...

    African Journals Online (AJOL)

    NJD

    Vitamin B. 12. Derivatives. Reaction of Cobyric Acid. Heptapropyl Ester with Heterocyclic N-donor Ligands. Mohamed S.A. .... RESEARCH ARTICLE. M.S.A. Hamza ..... neutralized with NaHCO3 and treated with excess KCN to give. DCCbs-Pr.

  10. Metal- and Ligand-Accelerated Catalysis of the Baylis-Hillman Reaction.

    Science.gov (United States)

    Aggarwal, Varinder K.; Mereu, Andrea; Tarver, Gary J.; McCague, Ray

    1998-10-16

    The Baylis-Hillman reaction, the coupling of an unsaturated carbonyl compound/nitrile with aldehydes, is a valuable reaction but is limited in its practicality by poor reaction rates. We have endeavored to accelerate the reaction using Lewis acids and found that while conventional Lewis acids gave reduced rates group III, and lanthanide triflates (5 mol %) gave increased rates. The optimum metal salts were La(OTf)(3) and Sm(OTf)(3), which gave rate accelerations (k(rel)) of approximately 4.7 and 4.9, respectively, in reactions between tert-butyl acrylate and benzaldehyde when using stoichiometric amounts of DABCO. At low loadings of DABCO (up to 10 mol %), no reaction occurred due to association of DABCO with the metal. Use of additional ligands to displace the DABCO from the metal was studied, and the rate of reaction was found to increase further in most cases. Of the ligands tested, at 5 mol %, (+)-binol gave one of the largest rate accelerations (3.4-fold) and was studied in more detail. It was found that reactions occurred even at low DABCO concentration so that here the Lewis base and Lewis acid were able to promote the reaction without interference from each other. While the (+)-binol (and other chiral ligands) failed to provide any significant asymmetric induction, a substantial nonlinear effect was observed with binol. Thus, use of racemic binol gave no effect on the rate. In seeking to maximize the rate attainable, more soluble (liquid) ligands were studied. Diethyl tartrate and triethanolamine gave rate enhancements of 5.2x and 3.5x at 50 mol %, respectively, versus 1.5x and 2.3x at 5 mol %. The best protocol was to use 100 mol % DABCO, 50 mol % triethanolamine, and 5 mol % La(OTf)(3). This gave overall rate accelerations of between 23-fold and 40-fold depending on the acrylate and approximately 5-fold for acrylonitrile. A simple acid wash removed the reagents, leaving the product in the organic phase. While triethanolamine accelerated the reaction

  11. Accuracy and precision of protein-ligand interaction kinetics determined from chemical shift titrations

    Energy Technology Data Exchange (ETDEWEB)

    Markin, Craig J.; Spyracopoulos, Leo, E-mail: leo.spyracopoulos@ualberta.ca [University of Alberta, Department of Biochemistry (Canada)

    2012-12-15

    NMR-monitored chemical shift titrations for the study of weak protein-ligand interactions represent a rich source of information regarding thermodynamic parameters such as dissociation constants (K{sub D}) in the micro- to millimolar range, populations for the free and ligand-bound states, and the kinetics of interconversion between states, which are typically within the fast exchange regime on the NMR timescale. We recently developed two chemical shift titration methods wherein co-variation of the total protein and ligand concentrations gives increased precision for the K{sub D} value of a 1:1 protein-ligand interaction (Markin and Spyracopoulos in J Biomol NMR 53: 125-138, 2012). In this study, we demonstrate that classical line shape analysis applied to a single set of {sup 1}H-{sup 15}N 2D HSQC NMR spectra acquired using precise protein-ligand chemical shift titration methods we developed, produces accurate and precise kinetic parameters such as the off-rate (k{sub off}). For experimentally determined kinetics in the fast exchange regime on the NMR timescale, k{sub off} {approx} 3,000 s{sup -1} in this work, the accuracy of classical line shape analysis was determined to be better than 5 % by conducting quantum mechanical NMR simulations of the chemical shift titration methods with the magnetic resonance toolkit GAMMA. Using Monte Carlo simulations, the experimental precision for k{sub off} from line shape analysis of NMR spectra was determined to be 13 %, in agreement with the theoretical precision of 12 % from line shape analysis of the GAMMA simulations in the presence of noise and protein concentration errors. In addition, GAMMA simulations were employed to demonstrate that line shape analysis has the potential to provide reasonably accurate and precise k{sub off} values over a wide range, from 100 to 15,000 s{sup -1}. The validity of line shape analysis for k{sub off} values approaching intermediate exchange ({approx}100 s{sup -1}), may be facilitated by

  12. Effects of reaction-kinetic parameters on modeling reaction pathways in GaN MOVPE growth

    Science.gov (United States)

    Zhang, Hong; Zuo, Ran; Zhang, Guoyi

    2017-11-01

    In the modeling of the reaction-transport process in GaN MOVPE growth, the selections of kinetic parameters (activation energy Ea and pre-exponential factor A) for gas reactions are quite uncertain, which cause uncertainties in both gas reaction path and growth rate. In this study, numerical modeling of the reaction-transport process for GaN MOVPE growth in a vertical rotating disk reactor is conducted with varying kinetic parameters for main reaction paths. By comparisons of the molar concentrations of major Ga-containing species and the growth rates, the effects of kinetic parameters on gas reaction paths are determined. The results show that, depending on the values of the kinetic parameters, the gas reaction path may be dominated either by adduct/amide formation path, or by TMG pyrolysis path, or by both. Although the reaction path varies with different kinetic parameters, the predicted growth rates change only slightly because the total transport rate of Ga-containing species to the substrate changes slightly with reaction paths. This explains why previous authors using different chemical models predicted growth rates close to the experiment values. By varying the pre-exponential factor for the amide trimerization, it is found that the more trimers are formed, the lower the growth rates are than the experimental value, which indicates that trimers are poor growth precursors, because of thermal diffusion effect caused by high temperature gradient. The effective order for the contribution of major species to growth rate is found as: pyrolysis species > amides > trimers. The study also shows that radical reactions have little effect on gas reaction path because of the generation and depletion of H radicals in the chain reactions when NH2 is considered as the end species.

  13. Spectroscopic and Kinetic Characterization of Peroxidase-Like π-Cation Radical Pinch-Porphyrin-Iron(III Reaction Intermediate Models of Peroxidase Enzymes

    Directory of Open Access Journals (Sweden)

    Samuel Hernández Anzaldo

    2016-06-01

    Full Text Available The spectroscopic and kinetic characterization of two intermediates from the H2O2 oxidation of three dimethyl ester [(proto, (meso, (deuteroporphyrinato (picdien]Fe(III complexes ([FePPPic], [FeMPPic] and [FeDPPic], respectively pinch-porphyrin peroxidase enzyme models, with s = 5/2 and 3/2 Fe(III quantum mixed spin (qms ground states is described herein. The kinetic study by UV/Vis at λmax = 465 nm showed two different types of kinetics during the oxidation process in the guaiacol test for peroxidases (1–3 + guaiacol + H2O2 → oxidation guaiacol products. The first intermediate was observed during the first 24 s of the reaction. When the reaction conditions were changed to higher concentration of pinch-porphyrins and hydrogen peroxide only one type of kinetics was observed. Next, the reaction was performed only between pinch-porphyrins-Fe(III and H2O2, resulting in only two types of kinetics that were developed during the first 0–4 s. After this time a self-oxidation process was observed. Our hypotheses state that the formation of the π-cation radicals, reaction intermediates of the pinch-porphyrin-Fe(III family with the ligand picdien [N,N’-bis-pyridin-2-ylmethyl-propane-1,3-diamine], occurred with unique kinetics that are different from the overall process and was involved in the oxidation pathway. UV-Vis, 1H-NMR and ESR spectra confirmed the formation of such intermediates. The results in this paper highlight the link between different spectroscopic techniques that positively depict the kinetic traits of artificial compounds with enzyme-like activity.

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

    KAUST Repository

    Ebner, Davidâ C.; Bagdanoff, Jeffreyâ T.; Ferreira, Ericâ M.; McFadden, Ryanâ M.; Caspi, Danielâ D.; Trend, Raissaâ M.; Stoltz, Brianâ M.

    2009-01-01

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

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

    KAUST Repository

    Ebner, Davidâ C.

    2009-12-07

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

  16. Kinetics of gaseous uranium hexafluoride reaction with hydrogen chloride

    International Nuclear Information System (INIS)

    Ezubchenko, A.N.; Ilyukhin, A.I.; Merzlyakov, A.V.

    1993-01-01

    Kinetics of decrease of concentration of gaseous uranium hexafluoride in reaction with hydrogen chloride at temperatures close to room ones, was investigated by the method of IR spectroscopy. It was established that the process represented the first order reaction by both UF 6 and HCl. Activation energy of the reaction was determined: 7.6 ± 0.7 kcal/mol. Specific feature of reaction kinetics was noted: inversely proportional dependence of effective constant on UF 6 initial pressure. 5 refs., 3 figs

  17. Kinetic concepts of thermally stimulated reactions in solids

    Science.gov (United States)

    Vyazovkin, Sergey

    Historical analysis suggests that the basic kinetic concepts of reactions in solids were inherited from homogeneous kinetics. These concepts rest upon the assumption of a single-step reaction that disagrees with the multiple-step nature of solid-state processes. The inadequate concepts inspire such unjustified anticipations of kinetic analysis as evaluating constant activation energy and/or deriving a single-step reaction mechanism for the overall process. A more adequate concept is that of the effective activation energy, which may vary with temperature and extent of conversion. The adequacy of this concept is illustrated by literature data as well as by experimental data on the thermal dehydration of calcium oxalate monohydrate and thermal decomposition of calcium carbonate, ammonium nitrate and 1,3,5,7- tetranitro-1,3,5,7-tetrazocine.

  18. Kinetics of chemical reactions initiated by hot atoms

    International Nuclear Information System (INIS)

    Firsova, L.P.

    1977-01-01

    Modern ideas about kinetics of chemical reactions of hot atoms are generalized. The main points of the phenomenological theories (''kinetic theory'' of Wolfgang-Estrup hot reactions and the theory of ''reactions integral probability'' of Porter) are given. Physico-chemical models of elastic and non-elastic collisions are considered which are used in solving Boltzmann integro-differential equations and stochastic equations in the Porter theory. The principal formulas are given describing probabilities or yields of chemical reactions, initiated with hot atoms, depending on the distribution functions of hot particles with respect to energy. Briefly described are the techniques and the results of applying the phenomenological theories for interpretation of the experimental data obtained during nuclear reactions with hot atoms, photochemical investigations, etc. 96 references are given

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

    Science.gov (United States)

    Fedorenko, S. G.; Burshtein, A. I.

    2014-09-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-09-21

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

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

    International Nuclear Information System (INIS)

    Fedorenko, S. G.; Burshtein, A. I.

    2014-01-01

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

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

    NARCIS (Netherlands)

    Brands, C.M.J.

    2002-01-01

    Keywords: Maillard reaction, sugar isomerisation, kinetics, multiresponse modelling, brown colour formation, lysine damage, mutagenicity, casein, monosaccharides, disaccharides, aldoses, ketoses

    The aim of this thesis was to determine the kinetics of the Maillard reaction between

  3. : Recyclable, ligand free palladium(II) catalyst for Heck reaction

    Indian Academy of Sciences (India)

    well as heterogeneous palladium catalysts, generated from either palladium(0) compounds or palladium(II) acetate or chloride salts.6 Several ligands such as phosphines, phoshites, carbenes, thioethers have been successfully employed for this reaction.7 However, homogeneous catalysis results in problems of recovery.

  4. Organic ligand-induced dissolution kinetics of antimony trioxide

    Institute of Scientific and Technical Information of China (English)

    Xingyun Hu; Mengchang He

    2017-01-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb2O3 was investigated.Some representative LMWDOMs with carboxyl,hydroxyl,hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen,namely oxalic acid,citric acid,tartaric acid,EDTA,salicylic acid,phthalandione,glycine,thiolactic acid,xylitol,glucose and catechol.These LMWDOMs were dissolved in inert buffers at pH =3.7,6.6 and 8.6 and added to powdered Sb2O3 in a stirred,thermostatted reactor (25℃).The addition of EDTA,tartaric acid,thiolactic acid,citric acid and oxalic acid solutions at pH 3.7 and catechol at pH 8.6 increased the rate of release of antimony.In the 10 mmol/L thiolactic acid solution,up to 97% by mass of the antimony was released after 120 min reaction.There was no effect on the dissolution of Sb2O3 for the other ligands.A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found.All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb2O3 was not determined by the stability of the dissolved complex,but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface.This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands,but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals.

  5. Spectroscopy and reaction kinetics of HCO

    International Nuclear Information System (INIS)

    Guo, Yili.

    1989-01-01

    The high-resolution infrared spectrum of the C-H stretching fundamental of HCO has been studied by means of infrared flash kinetic spectroscopy. HCO was generated by flash photolysis of acetaldehyde or formaldehyde using a 308 nm (XeCl) excimer laser. The transient absorption was probed with an infrared difference frequency laser system. The high resolution spectra obtained were assigned and fitted with rotational, spin-rotational, and centrifugal distortion constants. The ν 1 band origin is 2434.48 cm/sup /minus/1/. New ground state constants have been derived from a least-squares fit combining the ν 1 data with previous microwave and FIR LMR measurements. A new set of spectroscopic constants for the (1, 0, 0) state, the equilibrium rotational constants, and the orientation of the transition dipole moment are also reported. The kinetics and product branching ratios of the HCO + NO 2 reaction have been studied using visible and infrared laser flash kinetic spectroscopy. The rate constant for the disappearance of HCO radical at 296 K is (5.7 +- 0.9) /times/ 10/sup /minus/11/ cm 3 molec/sup /minus/1/ sec/sup /minus/1/, and it is independent of the pressure of SF 6 buffer gas up to 700 torr. Less than 10% of the reaction goes through the most exothermic product channel, HNO + CO 2 . The product channel, H + CO 2 + NO, is responsible for 52% of the reaction. HONO has been observed, though not quantitatively, as a reaction product corresponding to the HONO + CO channel. 51 refs., 21 figs., 8 tabs

  6. A Ligand Structure-Activity Study of DNA-Based Catalytic Asymmetric Hydration and Diels-Alder Reactions

    NARCIS (Netherlands)

    Rosati, F.; Roelfes, J.G.

    A structure-activity relationship study of the first generation ligands for the DNA-based asymmetric hydration of enones and Diels-Alder reaction in water is reported. The design of the ligand was optimized resulting in a maximum ee of 83% in the hydration reaction and 75% in the Diels-Alder

  7. Organic ligand-induced dissolution kinetics of antimony trioxide.

    Science.gov (United States)

    Hu, Xingyun; He, Mengchang

    2017-06-01

    The influence of low-molecular-weight dissolved organic matter (LMWDOM) on the dissolution rate of Sb 2 O 3 was investigated. Some representative LMWDOMs with carboxyl, hydroxyl, hydrosulfuryl and amidogen groups occurring naturally in the solution were chosen, namely oxalic acid, citric acid, tartaric acid, EDTA, salicylic acid, phthalandione, glycine, thiolactic acid, xylitol, glucose and catechol. These LMWDOMs were dissolved in inert buffers at pH=3.7, 6.6 and 8.6 and added to powdered Sb 2 O 3 in a stirred, thermostatted reactor (25°C). The addition of EDTA, tartaric acid, thiolactic acid, citric acid and oxalic acid solutions at pH3.7 and catechol at pH8.6 increased the rate of release of antimony. In the 10mmol/L thiolactic acid solution, up to 97% by mass of the antimony was released after 120min reaction. There was no effect on the dissolution of Sb 2 O 3 for the other ligands. A weak correlation between dissolution rate with the dissociation constant of ligands and the stability of the dissolved complex was also found. All the results showed that the extent of the promoting effect of ligands on the dissolution of Sb 2 O 3 was not determined by the stability of the dissolved complex, but by the dissociation constant of ligands and detachment rate of surface chelates from the mineral surface. This study can not only help in further understanding the effect of individual low-molecular-weight organic ligands, but also provides a reference to deduce the effect of natural organic matters with oxygen-bearing functional groups on the dissolution of antimony oxide minerals. Copyright © 2016. Published by Elsevier B.V.

  8. NMRKIN: Simulating line shapes from two-dimensional spectra of proteins upon ligand binding

    International Nuclear Information System (INIS)

    Guenther, Ulrich L.; Schaffhausen, Brian

    2002-01-01

    The analysis of the shape of signals in NMR spectra is a powerful tool to study exchange and reaction kinetics. Line shapes in two-dimensional spectra of proteins recorded for titrations with ligands provide information about binding rates observed at individual residues. Here we describe a fast method to simulate a series of line shapes derived from two-dimensional spectra of a protein during a ligand titration. This procedure, which takes the mutual effects of two dimensions into account, has been implemented in MATLAB as an add-on to NMRLab (Guenther et al., 2000). In addition, more complex kinetic models, including sequential and parallel reactions, were simulated to demonstrate common features of more complex line shapes which could be encountered in protein-ligand interactions. As an example of this method, we describe its application to line shapes obtained for a titration of the p85 N-SH2 domain of PI3-kinase with a peptide derived from polyomavirus middle T antigen (MT)

  9. SABIO-RK: A data warehouse for biochemical reactions and their kinetics

    Directory of Open Access Journals (Sweden)

    Krebs Olga

    2007-03-01

    Full Text Available Systems biology is an emerging field that aims at obtaining a system-level understanding of biological processes. The modelling and simulation of networks of biochemical reactions have great and promising application potential but require reliable kinetic data. In order to support the systems biology community with such data we have developed SABIO-RK (System for the Analysis of Biochemical Pathways - Reaction Kinetics, a curated database with information about biochemical reactions and their kinetic properties, which allows researchers to obtain and compare kinetic data and to integrate them into models of biochemical networks. SABIO-RK is freely available for academic use at http://sabio.villa-bosch.de/SABIORK/.

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

    International Nuclear Information System (INIS)

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

    2007-01-01

    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 NE equilibrium reactions and a set of reactive transport equations of M-NE 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

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

    Science.gov (United States)

    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.

  12. Kinetics of a redox reaction in the system Ce(IV) β-diketonate - additional ligand

    International Nuclear Information System (INIS)

    Anufrieva, S.I.; Snezhko, N.I.; Pechurova, N.I.; Martynenko, L.N.; Spitsyn, V.I.

    1982-01-01

    Preparation of solutions containing stable compounds of Ce(IV) with organic ligands is difficult, because even strong Ce(IV) complexes undergo intramolecular reduction and have a tendency to hydrolysis. It is known that Ce(IV) β-diketonates have different resistances to reduction inorganic solvents, depending on the structure. Using spectrophotometric analysis we have investigated the oxidation-reduction characteristics of solutions of certain Ce(IV) β-diketonates in benzene in the absence and presence of neutral ligands containing donor O or N atoms

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

    Science.gov (United States)

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

    2011-01-01

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

  14. Analysis of kinetic reaction mechanisms

    CERN Document Server

    Turányi, Tamás

    2014-01-01

    Chemical processes in many fields of science and technology, including combustion, atmospheric chemistry, environmental modelling, process engineering, and systems biology, can be described by detailed reaction mechanisms consisting of numerous reaction steps. This book describes methods for the analysis of reaction mechanisms that are applicable in all these fields. Topics addressed include: how sensitivity and uncertainty analyses allow the calculation of the overall uncertainty of simulation results and the identification of the most important input parameters, the ways in which mechanisms can be reduced without losing important kinetic and dynamic detail, and the application of reduced models for more accurate engineering optimizations. This monograph is invaluable for researchers and engineers dealing with detailed reaction mechanisms, but is also useful for graduate students of related courses in chemistry, mechanical engineering, energy and environmental science and biology.

  15. Rate kernel theory for pseudo-first-order kinetics of diffusion-influenced reactions and application to fluorescence quenching kinetics.

    Science.gov (United States)

    Yang, Mino

    2007-06-07

    Theoretical foundation of rate kernel equation approaches for diffusion-influenced chemical reactions is presented and applied to explain the kinetics of fluorescence quenching reactions. A many-body master equation is constructed by introducing stochastic terms, which characterize the rates of chemical reactions, into the many-body Smoluchowski equation. A Langevin-type of memory equation for the density fields of reactants evolving under the influence of time-independent perturbation is derived. This equation should be useful in predicting the time evolution of reactant concentrations approaching the steady state attained by the perturbation as well as the steady-state concentrations. The dynamics of fluctuation occurring in equilibrium state can be predicted by the memory equation by turning the perturbation off and consequently may be useful in obtaining the linear response to a time-dependent perturbation. It is found that unimolecular decay processes including the time-independent perturbation can be incorporated into bimolecular reaction kinetics as a Laplace transform variable. As a result, a theory for bimolecular reactions along with the unimolecular process turned off is sufficient to predict overall reaction kinetics including the effects of unimolecular reactions and perturbation. As the present formulation is applied to steady-state kinetics of fluorescence quenching reactions, the exact relation between fluorophore concentrations and the intensity of excitation light is derived.

  16. Formation kinetics of gemfibrozil chlorination reaction products: analysis and application.

    Science.gov (United States)

    Krkosek, Wendy H; Peldszus, Sigrid; Huck, Peter M; Gagnon, Graham A

    2014-07-01

    Aqueous chlorination kinetics of the lipid regulator gemfibrozil and the formation of reaction products were investigated in deionized water over the pH range 3 to 9, and in two wastewater matrices. Chlorine oxidation of gemfibrozil was found to be highly dependent on pH. No statistically significant degradation of gemfibrozil was observed at pH values greater than 7. Gemfibrozil oxidation between pH 4 and 7 was best represented by first order kinetics. At pH 3, formation of three reaction products was observed. 4'-C1Gem was the only reaction product formed from pH 4-7 and was modeled with zero order kinetics. Chlorine oxidation of gemfibrozil in two wastewater matrices followed second order kinetics. 4'-C1Gem was only formed in wastewater with pH below 7. Deionized water rate kinetic models were applied to two wastewater effluents with gemfibrozil concentrations reported in literature in order to calculate potential mass loading rates of 4'C1Gem to the receiving water.

  17. Dissociation kinetics of open-chain and macrocyclic gadolinium(III)-aminopolycarboxylate complexes related to magnetic resonance imaging: catalytic effect of endogenous ligands.

    Science.gov (United States)

    Baranyai, Zsolt; Pálinkás, Zoltán; Uggeri, Fulvio; Maiocchi, Alessandro; Aime, Silvio; Brücher, Ernő

    2012-12-14

    The kinetics of the metal exchange reactions between open-chain Gd(DTPA)(2-) and Gd(DTPA-BMA), macrocyclic Gd(DOTA)(-) and Gd(HP-DO3A) complexes, and Cu(2+)  ions were investigated in the presence of endogenous citrate, phosphate, carbonate and histidinate ligands in the pH range 6-8 in NaCl (0.15 M) at 25 °C. The rates of the exchange reactions of Gd(DTPA)(2-) and Gd(DTPA-BMA) are independent of the Cu(2+) concentration in the presence of citrate and the reactions occur via the dissociation of Gd(3+)  complexes catalyzed by the citrate ions. The HCO(3)(-)/CO(3)(2-) and H(2)PO(4)(-) ions also catalyze the dissociation of complexes. The rates of the dissociation of Gd(DTPA-BMA), catalyzed by the endogenous ligands, are about two orders of magnitude higher than those of the Gd(DTPA)(2-). In fact near to physiological conditions the bicarbonate and carbonate ions show the largest catalytic effect, that significantly increase the dissociation rate of Gd(DTPA-BMA) and make the higher pH values (when the carbonate ion concentration is higher) a risk-factor for the dissociation of complexes in body fluids. The exchange reactions of Gd(DOTA)(-) and Gd(HP-DO3A) with Cu(2+) occur through the proton assisted dissociation of complexes in the pH range 3.5-5 and the endogenous ligands do not affect the dissociation rates of complexes. More insights into the interaction scheme between Gd(DTPA-BMA) and Gd(DTPA)(2-) and endogenous ligands have been obtained by acquiring the (13)C NMR spectra of the corresponding diamagnetic Y(III)-complexes, indicating the increase of the rates of the intramolecular rearrangements in the presence of carbonate and citrate ions. The herein reported results may have implications in the understanding of the etiology of nephrogenic systemic fibrosis, a rare disease that has been associated to the administration of Gd-containing agents to patients with impaired renal function. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Kinetics of subdiffusion-assisted reactions: non-Markovian stochastic Liouville equation approach

    International Nuclear Information System (INIS)

    Shushin, A I

    2005-01-01

    Anomalous specific features of the kinetics of subdiffusion-assisted bimolecular reactions (time-dependence, dependence on parameters of systems, etc) are analysed in detail with the use of the non-Markovian stochastic Liouville equation (SLE), which has been recently derived within the continuous-time random-walk (CTRW) approach. In the CTRW approach, subdiffusive motion of particles is modelled by jumps whose onset probability distribution function is of a long-tailed form. The non-Markovian SLE allows for rigorous describing of some peculiarities of these reactions; for example, very slow long-time behaviour of the kinetics, non-analytical dependence of the reaction rate on the reactivity of particles, strong manifestation of fluctuation kinetics showing itself in very slowly decreasing behaviour of the kinetics at very long times, etc

  19. Kinetic modeling of reactions in Foods

    NARCIS (Netherlands)

    Boekel, van M.A.J.S.

    2008-01-01

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

  20. The binding of quinone to the photosynthetic reaction centers: kinetics and thermodynamics of reactions occurring at the QB-site in zwitterionic and anionic liposomes.

    Science.gov (United States)

    Mavelli, Fabio; Trotta, Massimo; Ciriaco, Fulvio; Agostiano, Angela; Giotta, Livia; Italiano, Francesca; Milano, Francesco

    2014-07-01

    Liposomes represent a versatile biomimetic environment for studying the interaction between integral membrane proteins and hydrophobic ligands. In this paper, the quinone binding to the QB-site of the photosynthetic reaction centers (RC) from Rhodobacter sphaeroides has been investigated in liposomes prepared with either the zwitterionic phosphatidylcholine (PC) or the negatively charged phosphatidylglycerol (PG) to highlight the role of the different phospholipid polar heads. Quinone binding (K Q) and interquinone electron transfer (L AB) equilibrium constants in the two type of liposomes were obtained by charge recombination reaction of QB-depleted RC in the presence of increasing amounts of ubiquinone-10 over the temperature interval 6-35 °C. The kinetic of the charge recombination reactions has been fitted by numerically solving the ordinary differential equations set associated with a detailed kinetic scheme involving electron transfer reactions coupled with quinone release and uptake. The entire set of traces at each temperature was accurately fitted using the sole quinone release constants (both in a neutral and a charge separated state) as adjustable parameters. The temperature dependence of the quinone exchange rate at the QB-site was, hence, obtained. It was found that the quinone exchange regime was always fast for PC while it switched from slow to fast in PG as the temperature rose above 20 °C. A new method was introduced in this paper for the evaluation of constant K Q using the area underneath the charge recombination traces as the indicator of the amount of quinone bound to the QB-site.

  1. Ametryn degradation by aqueous chlorine: Kinetics and reaction influences

    International Nuclear Information System (INIS)

    Xu Bin; Gao Naiyun; Cheng Hefa; Hu Chenyan; Xia Shengji; Sun Xiaofeng; Wang Xuejiao; Yang Shaogui

    2009-01-01

    The chemical oxidation of the herbicide ametryn was investigated by aqueous chlorination between pH 4 and 10 at a temperature of 25 deg. C. Ametryn was found to react very rapidly with aqueous chlorine. The reaction kinetics can be well described by a second-order kinetic model. The apparent second-order rate constants are greater than 5 x 10 2 M -1 s -1 under acidic and neutral conditions. The reaction proceeds much more slowly under alkaline conditions. The predominant reactions were found to be the reactions of HOCl with neutral ametryn and the charged ametryn, with rate constants equal to 7.22 x 10 2 and 1.58 x 10 3 M -1 s -1 , respectively. The ametryn degradation rate increases with addition of bromide and decreases with addition of ammonia during the chlorination process. Based on elementary chemical reactions, a kinetic model of ametryn degradation by chlorination in the presence of bromide or ammonia ion was also developed. By employing this model, we estimate that the rate constants for the reactions of HOBr with neutral ametryn and charged ametryn were 9.07 x 10 3 and 3.54 x 10 6 M -1 s -1 , respectively. These values are 10- to 10 3 -fold higher than those of HOCl, suggesting that the presence of bromine species during chlorination could significantly accelerate ametryn degradation.

  2. Ligand exchange reactions of the heme group in hemoglobin and myoglobin as studied by pulse radiolysis

    International Nuclear Information System (INIS)

    Raap, I.A.

    1978-01-01

    In this thesis, the kinetic aspects of the ligand exchange reactions of hemoglobin are studied using the pulse radiolysis technique, in particular, the reactions of hydrated electrons with methemoglobin. A hitherto unobserved transient state of the heme group is observed which appears immediately after the rapid reduction process. The absorption spectrum of this new species has the characteristics of a ferrous low-spin state and can therefore be ascribed to the formation of a hemochrome non-equilibrium state. The subsequent relaxation of this intermediate structure into a deoxy-conformation is dependent on the amount of proton activity in the solution and on the presence of organic and inorganic phosphate anions. The final absorption spectrum of the heme group is shown to correspond to a ferrous high-spin state in the relaxed quaternary conformation. This is in agreement with the kinetics observen the binding of carbon monoxide and oxygen to partially reduced methemoglobin. At reduction degrees of methemoglobin as well as of valncy 8ybrids where there is an important contribution from species with two reduced subunits, the binding of carbon monoxide to hemoglobin occurs with on-rate constants characteristic for the tensed quaternary conformation. It is argued that this conformational change of hemoglobin (the R-to-T transition) takes place very rapidly, which suggests the participation of an activated relaxed conformation. In addition, it is found that there is a distinct heterogeneity in the binding of oxygen to partially reduced methemoglobin even at low degrees of reduction

  3. Internal Diffusion-Controlled Enzyme Reaction: The Acetylcholinesterase Kinetics.

    Science.gov (United States)

    Lee, Sangyun; Kim, Ji-Hyun; Lee, Sangyoub

    2012-02-14

    Acetylcholinesterase is an enzyme with a very high turnover rate; it quenches the neurotransmitter, acetylcholine, at the synapse. We have investigated the kinetics of the enzyme reaction by calculating the diffusion rate of the substrate molecule along an active site channel inside the enzyme from atomic-level molecular dynamics simulations. In contrast to the previous works, we have found that the internal substrate diffusion is the determinant of the acetylcholinesterase kinetics in the low substrate concentration limit. Our estimate of the overall bimolecular reaction rate constant for the enzyme is in good agreement with the experimental data. In addition, the present calculation provides a reasonable explanation for the effects of the ionic strength of solution and the mutation of surface residues of the enzyme. The study suggests that internal diffusion of the substrate could be a key factor in understanding the kinetics of enzymes of similar characteristics.

  4. Kinetic investigation of heterogeneous catalytic reactions by means of the kinetic isotope method

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, F; Dermietzel, J [Akademie der Wissenschaften der DDR, Leipzig. Zentralinstitut fuer Isotopen- und Strahlenforschung

    1978-09-01

    The application of the kinetic isotope method to heterogeneous catalytic processes is possible for surface compounds by using the steady-state relation. However, the characterization of intermediate products becomes ambiguous if sorption rates are of the same order of magnitude as surface reactions rates. The isotopic exchange reaction renders possible the estimation of sorption rates.

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

    Science.gov (United States)

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

    2016-06-01

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

  6. Deuterium secondary isotope kinetic effects in imine formation reactions

    International Nuclear Information System (INIS)

    Amaral, L. do; Rossi, M.H.

    1986-01-01

    The kinetic α-deuterium isotope effects, K D /K H , for reaction mechanisms is studied. The reaction of pH function to m-bromobenzaldehyde, semicarbazide nucleophile, methoxy-amine and hydroxylamine are analysed. (M.J.C.) [pt

  7. Reactions driving conformational movements (molecular motors) in gels: conformational and structural chemical kinetics.

    Science.gov (United States)

    Otero, Toribio F

    2017-01-18

    In this perspective the empirical kinetics of conducting polymers exchanging anions and solvent during electrochemical reactions to get dense reactive gels is reviewed. The reaction drives conformational movements of the chains (molecular motors), exchange of ions and solvent with the electrolyte and structural (relaxation, swelling, shrinking and compaction) gel changes. Reaction-driven structural changes are identified and quantified from electrochemical responses. The empirical reaction activation energy (E a ), the reaction coefficient (k) and the reaction orders (α and β) change as a function of the conformational energy variation during the reaction. This conformational energy becomes an empirical magnitude. E a , k, α and β include and provide quantitative conformational and structural information. The chemical kinetics becomes structural chemical kinetics (SCK) for reactions driving conformational movements of the reactants. The electrochemically stimulated conformational relaxation model describes empirical results and some results from the literature for biochemical reactions. In parallel the development of an emerging technological world of soft, wet, multifunctional and biomimetic tools and anthropomorphic robots driven by reactions of the constitutive material, as in biological organs, can be now envisaged being theoretically supported by the kinetic model.

  8. Molecular-weight-enlarged multiple-pincer ligands: synthesis and application in palladium-catalyzed allylic substitution reactions

    NARCIS (Netherlands)

    Ronde, N.J.; Totev, D.; Müller, Christian; Lutz, M.; Spek, A.L.; Vogt, D.

    2009-01-01

    Three different pincer ligand systems are synthesized via nucleophilic substitution reactions of polyaromatic benzyl bromides as support molecules and phenol derivatives as ligand precursors. Retention tests using a polymeric nanofiltration membrane show moderate to good retention in THF and CH2Cl2.

  9. Iteration scheme for implicit calculations of kinetic and equilibrium chemical reactions in fluid dynamics

    International Nuclear Information System (INIS)

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

    1995-01-01

    An iteration scheme for the implicit treatment of equilibrium chemical reactions in partial equilibrium flow has previously been described. 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 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. 10 refs., 2 figs

  10. Kinetical Analysis of the Mechanism of the Ligand Substitution Reaction between the Ethylenediamine-N,N{sup `}-bis[2-(2-hydroxyphenyl) acetato] cadmate (2) Ion and the Ethylenediaminetetraacetatoferrate (3) Ion; Echienjiami-N,N`-bisu[2-(2-hidorokishifueniru)asetato] kadomiume (2) san eion to echirenjiamintetoraasetato tetsu (3) san ion tono aida no haiishi okikae hanno no hanno sokudoron ni yoru kiko kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Katsuyama, Tetsuo.; Orihara, Katsuo.; Takahata, Yasuyuki.; Yokota, Toshiyuki. [Yamagata University, Yamagata (Japan). Department of Materials Science and Enginering

    1998-12-10

    The kinetics of the ligand substitution reaction between the ethylenediamine-N,N`- bis[2-(2-hydroxyphenyl) acetato] cadmate (2) ion and the ethylenediaminetetraacetatoferrate (3) ion were carried out at 25 degreeC and ionic strength=0.1 mol dm{sup -3}. The substitution reaction was shown to proceed by a chain reaction mechanism where the chain propageting steps are the reactions of metal complexes with metal ions. The properties of the metal chain reaction mechanism are discussed. The metal-substitution of [Fe (edta)]{sup -} with cadmium ion was studied by the use of the chain reactins. The observed rae constants of the reaction were separated into two rate constants. The mechamism of the reactions is discussed. (author)

  11. Kinetical Analysis of the Mechanism of the Ligand Substitution Reaction between the Ethylenediamine-N,N[sup ']-bis[2-(2-hydroxyphenyl) acetato] cadmate (2) Ion and the Ethylenediaminetetraacetatoferrate (3) Ion. Echienjiami-N,N'-bisu[2-(2-hidorokishifueniru)asetato] kadomiume (2) san eion to echirenjiamintetoraasetato tetsu (3) san ion tono aida no haiishi okikae hanno no hanno sokudoron ni yoru kiko kaiseki

    Energy Technology Data Exchange (ETDEWEB)

    Katsuyama, Tetsuo.; Orihara, Katsuo.; Takahata, Yasuyuki.; Yokota, Toshiyuki. (Yamagata University, Yamagata (Japan). Department of Materials Science and Enginering)

    1998-12-10

    The kinetics of the ligand substitution reaction between the ethylenediamine-N,N'- bis[2-(2-hydroxyphenyl) acetato] cadmate (2) ion and the ethylenediaminetetraacetatoferrate (3) ion were carried out at 25 degreeC and ionic strength=0.1 mol dm[sup -3]. The substitution reaction was shown to proceed by a chain reaction mechanism where the chain propageting steps are the reactions of metal complexes with metal ions. The properties of the metal chain reaction mechanism are discussed. The metal-substitution of [Fe (edta)][sup -] with cadmium ion was studied by the use of the chain reactins. The observed rae constants of the reaction were separated into two rate constants. The mechamism of the reactions is discussed. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

    Gary Blythe; John Currie; David DeBerry

    2008-03-31

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

  13. Reaction kinetics of bond rotations in graphene

    KAUST Repository

    Skowron, Stephen T.; Koroteev, Victor O.; Baldoni, Matteo; Lopatin, Sergei; Zurutuza, Amaia; Chuvilin, Andrey; Besley, Elena

    2016-01-01

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

  14. Reaction kinetics of bond rotations in graphene

    KAUST Repository

    Skowron, Stephen T.

    2016-04-12

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Gray, Patrick J. [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States); Department of Chemistry, The Ohio State University, 120 18th Avenue, Columbus, OH 43210 (United States); Olesik, John W., E-mail: olesik.2@osu.edu [Trace Element Research Laboratory, School of Earth Sciences, The Ohio State University, 125 S. Oval Mall, Columbus, OH 43210 (United States)

    2015-03-01

    Reaction gas flow rate dependent Ar{sub 2}{sup +} and Ar{sup +} signals are correlated to fundamental kinetic rate coefficients. A simple calculation, assuming that gas exits the reaction cell due only to effusion, is described to estimate the gas pressure in the reaction cell. The value of the product of the kinetic rate constant and the ion residence time in the reaction cell can be determined from experimental measurement of the decrease in an ion signal as a function of reaction gas flow rate. New kinetic rate constants are determined for the reaction of CH{sub 3}F with Ar{sup +} and Ar{sub 2}{sup +}. - Highlights: • How to determine pressure and the product of the kinetic rate constant times the ion residence time in reaction cell • Relate measured ICP-DRC-MS signals versus gas flow rate to kinetic rate constants measured previously using SIFT-MS • Describe how to determine previously unmeasured kinetic rate constants using ICP-DRC-MS.

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

    Science.gov (United States)

    Sobel, Sabrina G.; Cohen, Skyler

    2010-01-01

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

  17. Complex Reaction Kinetics in Chemistry: A Unified Picture Suggested by Mechanics in Physics

    Directory of Open Access Journals (Sweden)

    Elena Agliari

    2018-01-01

    Full Text Available Complex biochemical pathways can be reduced to chains of elementary reactions, which can be described in terms of chemical kinetics. Among the elementary reactions so far extensively investigated, we recall the Michaelis-Menten and the Hill positive-cooperative kinetics, which apply to molecular binding and are characterized by the absence and the presence, respectively, of cooperative interactions between binding sites. However, there is evidence of reactions displaying a more complex pattern: these follow the positive-cooperative scenario at small substrate concentration, yet negative-cooperative effects emerge as the substrate concentration is increased. Here, we analyze the formal analogy between the mathematical backbone of (classical reaction kinetics in Chemistry and that of (classical mechanics in Physics. We first show that standard cooperative kinetics can be framed in terms of classical mechanics, where the emerging phenomenology can be obtained by applying the principle of least action of classical mechanics. Further, since the saturation function plays in Chemistry the same role played by velocity in Physics, we show that a relativistic scaffold naturally accounts for the kinetics of the above-mentioned complex reactions. The proposed formalism yields to a unique, consistent picture for cooperative-like reactions and to a stronger mathematical control.

  18. Unravelling the Maillard reaction network by multiresponse kinetic modelling

    NARCIS (Netherlands)

    Martins, S.I.F.S.

    2003-01-01

    The Maillard reaction is an important reaction in food industry. It is responsible for the formation of colour and aroma, as well as toxic compounds as the recent discovered acrylamide. The knowledge of kinetic parameters, such as rate constants and activation energy, is necessary to predict its

  19. Kinetics of ion/molecule reactions in Xe++acteone system

    International Nuclear Information System (INIS)

    Vinogradov, P.S.; Misharin, A.S.

    2002-01-01

    A reaction of Xe+ ion with acetone and subsequent transformations of the product ions at a buffer gas pressure (He) of 1.1 Torr were studied by the flow reactor technique mass spectrometry. A kinetic scheme describing the evolution of the ionic composition has been determined. The rate constants of the key reactions involved in the scheme have been evaluated. A channel of the production of acetone cation in A state in a charge transfer reaction was observed. A production of slowly reacting isomer of the acetone cation in secondary reactions was detected. Its product in the reaction with acetone is the 'nonprotonated dimer'. The kinetics of the production of ternary ions - ( CH 3 CO + CH 3 COCH 3 )(m/e=101), CH 3 COCH 3 H + (m/e=59) as well as the production of ions of the fourth generation ( CH 3 CO + (CH 3 COCH 3 ) 2 ) (m/e=159) and (CH 3 COCH 3 ) 2 H + was observed. CH 3 CO + ion (m/e=43) was found as the main reaction product. The main pathways scheme of ionic transformations is shown. (nevyjel)

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

    International Nuclear Information System (INIS)

    Agirre, I.; Garcia, I.; Requies, J.; Barrio, V.L.; Gueemez, M.B.; Cambra, J.F.; Arias, P.L.

    2011-01-01

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

  1. Bayesian experts in exploring reaction kinetics of transcription circuits.

    Science.gov (United States)

    Yoshida, Ryo; Saito, Masaya M; Nagao, Hiromichi; Higuchi, Tomoyuki

    2010-09-15

    Biochemical reactions in cells are made of several types of biological circuits. In current systems biology, making differential equation (DE) models simulatable in silico has been an appealing, general approach to uncover a complex world of biochemical reaction dynamics. Despite of a need for simulation-aided studies, our research field has yet provided no clear answers: how to specify kinetic values in models that are difficult to measure from experimental/theoretical analyses on biochemical kinetics. We present a novel non-parametric Bayesian approach to this problem. The key idea lies in the development of a Dirichlet process (DP) prior distribution, called Bayesian experts, which reflects substantive knowledge on reaction mechanisms inherent in given models and experimentally observable kinetic evidences to the subsequent parameter search. The DP prior identifies significant local regions of unknown parameter space before proceeding to the posterior analyses. This article reports that a Bayesian expert-inducing stochastic search can effectively explore unknown parameters of in silico transcription circuits such that solutions of DEs reproduce transcriptomic time course profiles. A sample source code is available at the URL http://daweb.ism.ac.jp/~yoshidar/lisdas/.

  2. A kinetic model for the glucose/glycine Maillard reaction pathways

    NARCIS (Netherlands)

    Martins, S.I.F.S.; Boekel, van M.A.J.S.

    2005-01-01

    A comprehensive kinetic model for the glucose/glycine Maillard reaction is proposed based on an approach called multiresponse kinetic modelling. Special attention was paid to reactants, intermediates and end products: -fructose, N-(1-deoxy--fructos-1-yl)-glycine (DFG), 1-deoxy-2,3-hexodiulose and

  3. Haptoglobin preferentially binds β but not α subunits cross-linked hemoglobin tetramers with minimal effects on ligand and redox reactions.

    Science.gov (United States)

    Jia, Yiping; Wood, Francine; Buehler, Paul W; Alayash, Abdu I

    2013-01-01

    Human hemoglobin (Hb) and haptoglobin (Hp) exhibit an extremely high affinity for each other, and the dissociation of Hb tetramers into dimers is generally believed to be a prerequisite for complex formation. We have investigated Hp interactions with native Hb, αα, and ββ cross-linked Hb (ααXLHb and ββXLHb, respectively), and rapid kinetics of Hb ligand binding as well as the redox reactivity in the presence of and absence of Hp. The quaternary conformation of ββ subunit cross-linking results in a higher binding affinity than that of αα subunit cross-linked Hb. However, ββ cross-linked Hb exhibits a four fold slower association rate constant than the reaction rate of unmodified Hb with Hp. The Hp contact regions in the Hb dimer interfaces appear to be more readily exposed in ββXLHb than ααXLHb. In addition, apart from the functional changes caused by chemical modifications, Hp binding does not induce appreciable effects on the ligand binding and redox reactions of ββXLHb. Our findings may therefore be relevant to the design of safer Hb-based oxygen therapeutics by utilizing this preferential binding of ββXLHb to Hp. This may ultimately provide a safe oxidative inactivation and clearance pathway for chemically modified Hbs in circulation.

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

    International Nuclear Information System (INIS)

    Gourisse, D.

    1966-09-01

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

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

    Science.gov (United States)

    Liechty, Derek S.; Lewis, Mark J.

    2010-01-01

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

  6. Kinetics of Single-Enzyme Reactions on Vesicles: Role of Substrate Aggregation

    Science.gov (United States)

    Zhdanov, Vladimir P.

    2015-03-01

    Enzymatic reactions occurring in vivo on lipid membranes can be influenced by various factors including macromolecular crowding in general and substrate aggregation in particular. In academic studies, the role of these factors can experimentally be clarified by tracking single-enzyme kinetics occurring on individual lipid vesicles. To extend the conceptual basis for such experiments, we analyze herein the corresponding kinetics mathematically with emphasis on the role of substrate aggregation. In general, the aggregation may occur on different length scales. Small aggregates may e.g. contain a few proteins or peptides while large aggregates may be mesoscopic as in the case of lipid domains which can be formed in the membranes composed of different lipids. We present a kinetic model describing comprehensively the effect of aggregation of the former type on the dependence of the reaction rate on substrate membrane concentration. The results obtained with physically reasonable parameters indicate that the aggregation-related deviations from the conventional Michaelis-Menten kinetics may be appreciable. Special Issue Comments: This theoretical article is focused on single-enzyme reactions occurring in parallel with substrate aggregation on individual vesicles. This subject is related to a few Special Issue articles concerning enzyme dynamics6,7 and function8 and mathematical aspects of stochastic kinetics.9

  7. Kinetics of elementary atom and radical reactions

    International Nuclear Information System (INIS)

    Gordon, R.J.

    1990-06-01

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

  8. Kinetics of elementary atom and radical reactions: Progress report

    International Nuclear Information System (INIS)

    Gordon, R.J.

    1986-01-01

    Our research program is concerned with the kinetics of elementary gas phase reactions and energy transfer involving polyatomic molecules. We report here on three ongoing projects: The reaction of oxygen atoms with hydrogen molecules, the electronic relaxation of NH radicals, and the vibrational relaxation of highly excited SF 6 molecules. 10 refs., 5 figs

  9. Reactions of diiron m-aminocarbyne complexes containing nitrile ligands

    Directory of Open Access Journals (Sweden)

    Busetto Luigi

    2003-01-01

    Full Text Available The acetonitrile ligand in the mu-aminocarbyne complexes [Fe2{mu-CN(MeR}(mu-CO(CO(NCMe(Cp2][SO 3CF3] (R = Me, 2a, CH2Ph, 2b, Xyl, 2c (Xyl = 2,6-Me2C6H3 is readily displaced by halides and cyanide anions affording the corresponding neutral species [Fe2{mu-CN(MeR}(mu-CO(CO(X(Cp2 ] (X = Br, I, CN. Complexes 2 undergo deprotonation and rearrangement of the coordinated MeCN upon treatment with organolithium reagents. Trimethylacetonitrile, that does not contain acidic alpha hydrogens has been used in place of MeCN to form the complexes [Fe2{mu-CN(MeR}(mu-CO(CO(NCCMe3 (Cp2][SO3CF3] (7a-c. Attempts to replace the nitrile ligand in 3 with carbon nucleophiles (by reaction with RLi failed, resulting in decomposition products. However the reaction of 7c with LiCºCTol (Tol = C6H4Me, followed by treatment with HSO3CF3, yielded the imino complex [Fe2{mu-CN(MeXyl}(mu-CO(CO {N(HC(CºCC6H4Me-4CMe3}(Cp 2][SO3CF3 ] (8, obtained via acetilyde addition at the coordinated NCCMe3.

  10. Kinetic study of the dehydration reaction of lithium sulfate monohydrate crystals using microscopy and modeling

    Energy Technology Data Exchange (ETDEWEB)

    Lan, Shuiquan [Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612AZ Eindhoven (Netherlands); Zondag, Herbert [Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612AZ Eindhoven (Netherlands); Energy research Center of the Netherlands – ECN, P.O. Box 1, 1755ZG Petten (Netherlands); Steenhoven, Anton van [Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612AZ Eindhoven (Netherlands); Rindt, Camilo, E-mail: c.c.m.rindt@tue.nl [Department of Mechanical Engineering, Eindhoven University of Technology, Den Dolech 2, 5612AZ Eindhoven (Netherlands)

    2015-12-10

    Highlights: • Kinetics of Li{sub 2}SO{sub 4}·H{sub 2}O single crystals were modeled based on elementary processes. • Kinetics of nucleation and nuclei growth were studied by using optical microscopy. • A novel experiment was designed to visualize the reaction front into crystal bulk. • Fractional conversion was calculated and compared with TGA-experiments. - Abstract: Simulation of gas–solid reactions occurring in industrial processes requires a robust kinetic model to be applicable in a wide range of complicated reaction conditions. However, in literature it is often seen that even the same reaction under specific controlled conditions is interpreted with different kinetic models. In the present work, a phenomenological model based on nucleation and nuclei growth processes is presented to study the kinetics of the dehydration reaction of lithium sulfate monohydrate single crystals. The two elementary processes of the reaction, nucleation and nuclei growth, are characterized and quantified as a function of temperature by using optical microscopy experiments. The in-situ measured characteristics of the dehydration reaction provided confirmatory evidence that the rate of nucleation obeys an exponential law and the rate of nuclei growth is approximately constant. With knowledge acquired from the optical observations as inputs of the kinetic model, the fractional conversion of the dehydration reaction was calculated and compared with experimental results from thermogravimetric analysis (TGA). A satisfactory comparison was found both in isothermal and non-isothermal conditions. It is demonstrated that this knowledge-based model has a great potential to represent the gas–solid reaction kinetics in a wide range of process conditions regarding temperature, pressure and particle geometry.

  11. Reaction kinetics, reaction products and compressive strength of ternary activators activated slag designed by Taguchi method

    NARCIS (Netherlands)

    Yuan, B.; Yu, Q.L.; Brouwers, H.J.H.

    2015-01-01

    This study investigates the reaction kinetics, the reaction products and the compressive strength of slag activated by ternary activators, namely waterglass, sodium hydroxide and sodium carbonate. Nine mixtures are designed by the Taguchi method considering the factors of sodium carbonate content

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

    Science.gov (United States)

    Olanrewaju, Kazeem Bode

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

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

    KAUST Repository

    Hisatomi, Takashi

    2014-10-16

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

  14. Kinetics of heterogeneous catalytic reactions

    CERN Document Server

    Boudart, Michel

    2014-01-01

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

  15. Non-equilibrium reaction rates in chemical kinetic equations

    Science.gov (United States)

    Gorbachev, Yuriy

    2018-05-01

    Within the recently proposed asymptotic method for solving the Boltzmann equation for chemically reacting gas mixture, the chemical kinetic equations has been derived. Corresponding one-temperature non-equilibrium reaction rates are expressed in terms of specific heat capacities of the species participate in the chemical reactions, bracket integrals connected with the internal energy transfer in inelastic non-reactive collisions and energy transfer coefficients. Reactions of dissociation/recombination of homonuclear and heteronuclear diatomic molecules are considered. It is shown that all reaction rates are the complex functions of the species densities, similarly to the unimolecular reaction rates. For determining the rate coefficients it is recommended to tabulate corresponding bracket integrals, additionally to the equilibrium rate constants. Correlation of the obtained results with the irreversible thermodynamics is established.

  16. Molecular Dynamics Simulations and Kinetic Measurements to Estimate and Predict Protein-Ligand Residence Times.

    Science.gov (United States)

    Mollica, Luca; Theret, Isabelle; Antoine, Mathias; Perron-Sierra, Françoise; Charton, Yves; Fourquez, Jean-Marie; Wierzbicki, Michel; Boutin, Jean A; Ferry, Gilles; Decherchi, Sergio; Bottegoni, Giovanni; Ducrot, Pierre; Cavalli, Andrea

    2016-08-11

    Ligand-target residence time is emerging as a key drug discovery parameter because it can reliably predict drug efficacy in vivo. Experimental approaches to binding and unbinding kinetics are nowadays available, but we still lack reliable computational tools for predicting kinetics and residence time. Most attempts have been based on brute-force molecular dynamics (MD) simulations, which are CPU-demanding and not yet particularly accurate. We recently reported a new scaled-MD-based protocol, which showed potential for residence time prediction in drug discovery. Here, we further challenged our procedure's predictive ability by applying our methodology to a series of glucokinase activators that could be useful for treating type 2 diabetes mellitus. We combined scaled MD with experimental kinetics measurements and X-ray crystallography, promptly checking the protocol's reliability by directly comparing computational predictions and experimental measures. The good agreement highlights the potential of our scaled-MD-based approach as an innovative method for computationally estimating and predicting drug residence times.

  17. A kinetic study on non-catalytic reactions in hydroprocessing Boscan crude oil

    Energy Technology Data Exchange (ETDEWEB)

    A. Marafi; E. Kam; A. Stanislaus [Kuwait Institute for Scientific Research, Safat (Kuwait). Petroleum Refining Department, Petroleum Research and Studies Center

    2008-08-15

    Non-catalytic hydrothermal cracking reactions are known to associate with catalytic hydrocracking reactions. In a recent study on hydroprocessing of Boscan crude over a specific catalyst system containing three distinct catalysts, it was found that hydrodesulfurization (HDS) and hydrodemetallation (HDM) reactions continued even when the catalyst is severely deactivated. Since the reactor was packed with considerable amount of inert material besides the three catalysts, it will be advantage to determine if the inert materials can also facilitate hydroprocessing reactions. A series of kinetic experiments for the inert particles was undertaken under different space velocity and temperature conditions. The extent of catalytic and non-catalytic hydroprocessing reactions was assessed. Through statistical analysis, the initial reaction rate constant, reaction order and activation energy for various hydroprocessing reactions were then determined. The absolute average deviations (AAD) of the kinetics values obtained for inert materials are less than 10%. 25 refs., 7 figs., 4 tabs.

  18. Kinetics of catalytic reactions solutions manual

    CERN Document Server

    Vannice, M Albert

    2005-01-01

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

  19. Mechanistic rationalization of unusual sigmoidal kinetic profiles in the Machetti-De Sarlo cycloaddition reaction.

    Science.gov (United States)

    Mower, Matthew P; Blackmond, Donna G

    2015-02-18

    Unusual sigmoidal kinetic profiles in the Machetti-De Sarlo base-catalyzed 1,3-dipolar cycloaddition of acrylamide to N-methylnitroacetamide are rationalized by detailed in situ kinetic analysis. A dual role is uncovered in which a substrate acts as a precursor to catalyze its own reaction. Such kinetic studies provide a general protocol for distinguishing among different mechanistic origins of induction periods in complex organic reactions.

  20. Kinetic isotope effects in reaction of ferment oxidation of tritium-labelled D-galactosamine

    International Nuclear Information System (INIS)

    Akulov, G.P.; Korsakova, N.A.

    1992-01-01

    Primary, secondary and intramolecular kinetic isotopic effects in reaction of ferment oxidation of D-galactosamine labelled by tritium in position 6, were measured. When comparing values of the effects with previously obtained results for similar reaction D-[6- 3 H]galactose, it was ascertained that the presence of aminogroup in galactopyranosyl mainly affects kinetics of substrate-ferment complex formation stage. The possibility to use kinetic isotope effects for increase in molar activity of D-galactosamine, labelled by tritium in position 6, is shown

  1. A study of fundamental reaction pathways for transition metal alkyl complexes. I. The reaction of a nickel methyl complex with alkynes. Ii. The mechanism of aldehyde formation in the reaction of a molybdenum hydride with molybdenum alkyls

    Energy Technology Data Exchange (ETDEWEB)

    Huggins, John Mitchell [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)

    1980-06-12

    I. This study reports the rapid reaction under mild conditions of internal or terminal alkynes with methyl (acetyl-acetonato) (triphenylphosphine) nickel (1) in either aromatic or ether solvents. In all cases vinylnickel products 2 are formed by insertion of the alkyne into the nickel=methyl bond. These complexes may be converted into a variety of organic products (e.g. alkenes, esters, vinyl halides) by treatment with appropriate reagents. Unsymmetrical alkynes give selectively the one regioisomer with the sterically largest substituent next to the nickel atom. In order to investigate the stereochemistry of the initial insertion, a x-ray diffraction study of the reaction of 1 with diphenylacetylene was carried out. This showed that the vinylnickel complex formed by overall trans insertion was the product of the reaction. Furthermore, subsequent slow isomerization of this complex, to a mixture of it and the corresponding cis isomer, demonstrated that this trans addition product is the kinetic product of the reaction. In studies with other alkynes, the product of trans addition was not always exclusively (or even predominantly) formed, but the ratio of the stereoisomers formed kinetically was substantially different from the thermodynamic ratio. Isotope labeling, added phosphine, and other experiments have allowed us to conclude that the mechanism of this reaction does involve initial cis addition. However, a coordinatively unsaturated vinylnickel complex is initially formed which can undergo rapid, phosphine-catalyzed cis-trans isomerization in competition with its conversion to the isolable phosphine-substituted kinetic reaction products. II. The reaction of CpMo(CO)3H (1a) with CpMo(CO)3R (2, R= CH3, C2H5) at 50°C in THF gives the aldehyde RCHO and the dimers [CpMo(CO)3]2 (3a) and [CpMo(CO)2]2 (4a). Labeling one of the reactants with a methylcyclopentadienyl ligand

  2. Time-dependent photoluminescence spectroscopy as a tool to measure the ligand exchange kinetics on a quantum dot surface

    NARCIS (Netherlands)

    Koole, R.; Schapotschnikow, P.Z.; de Mello Donega, C.; Vlugt, T.J.H.; Meijerink, A.

    2008-01-01

    The exchange kinetics of native ligands that passivate CdSe quantum dots (hexadecylamine (HDA), trioctylphosphine oxide (TOPO), and trioctylphosphine (TOP)) by thiols is followed in situ. This is realized by measuring, in real-time, the decrease in emission intensity of the QDs upon addition of

  3. Ligand sphere conversions in terminal carbide complexes

    DEFF Research Database (Denmark)

    Morsing, Thorbjørn Juul; Reinholdt, Anders; Sauer, Stephan P. A.

    2016-01-01

    Metathesis is introduced as a preparative route to terminal carbide complexes. The chloride ligands of the terminal carbide complex [RuC(Cl)2(PCy3)2] (RuC) can be exchanged, paving the way for a systematic variation of the ligand sphere. A series of substituted complexes, including the first...... example of a cationic terminal carbide complex, [RuC(Cl)(CH3CN)(PCy3)2]+, is described and characterized by NMR, MS, X-ray crystallography, and computational studies. The experimentally observed irregular variation of the carbide 13C chemical shift is shown to be accurately reproduced by DFT, which also...... demonstrates that details of the coordination geometry affect the carbide chemical shift equally as much as variations in the nature of the auxiliary ligands. Furthermore, the kinetics of formation of the sqaure pyramidal dicyano complex, trans-[RuC(CN)2(PCy3)2], from RuC has been examined and the reaction...

  4. One ligand capable of in situ reaction in a mixed-ligand system with two new different frameworks

    KAUST Repository

    Wang, Xiaofang

    2017-12-24

    The in situ ligand 2,3-pyrazinedicarboxylic acid (2,3-H2pzdc) mixed with 1,1′-(1,4-butanediyl)bis(benzimidazole) (bbbi) is used to form two coordination polymers ([Cd(2,3-pzdc)(bbbi)] (1) and [Cd2Cl3(2-pzc)(bbbi)2] (2)) under hydrothermal conditions. Complex 1 was obtained in the absence of in situ reaction and 2 was synthesized with 2,3-H2pzdc in situ generating 2-pyrazinecarboxylate (2-pzc−). The structural details reveal that 1 has a 3D framework with dia topology, and 2 is a 2D layer structure and develops a 3D supramolecular structure via strong π⋯π stacking interactions. The ligand effects were compared for the two frameworks. In addition, fluorescence properties and thermal stabilities of 1 and 2 in the solid were studied.

  5. Kinetics Analysis of Synthesis Reaction of Struvite With Air-Flow Continous Vertical Reactors

    Science.gov (United States)

    Edahwati, L.; Sutiyono, S.; Muryanto, S.; Jamari, J.; Bayuseno, dan A. P.

    2018-01-01

    Kinetics reaction is a knowledge about a rate of chemical reaction. The differential of the reaction rate can be determined from the reactant material or the formed material. The reaction mechanism of a reactor may include a stage of reaction occurring sequentially during the process of converting the reactants into products. In the determination of reaction kinetics, the order of reaction and the rate constant reaction must be recognized. This study was carried out using air as a stirrer as a medium in the vertical reactor for crystallization of struvite. Stirring is one of the important aspects in struvite crystallization process. Struvite crystals or magnesium ammonium phosphate hexahydrates (MgNH4PO4·6H2O) is commonly formed in reversible reactions and can be generated as an orthorhombic crystal. Air is selected as a stirrer on the existing flow pattern in the reactor determining the reaction kinetics of the crystal from the solution. The experimental study was conducted by mixing an equimolar solution of 0.03 M NH4OH, MgCl2 and H3PO4 with a ratio of 1: 1: 1. The crystallization process of the mixed solution was observed in an inside reactor at the flow rate ranges of 16-38 ml/min and the temperature of 30°C was selected in the study. The air inlet rate was kept constant at 0.25 liters/min. The pH solution was adjusted to be 8, 9 and 10 by dropping wisely of 1 N KOH solution. The crystallization kinetics was examined until the steady state of the reaction was reached. The precipitates were filtered and dried at a temperature for subsequent material characterization, including Scanning Electron Microscope (SEM) and XRD (X-Ray diffraction) method. The results show that higher flow rate leads to less mass of struvite.

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

    International Nuclear Information System (INIS)

    Gokcen, Dincer; Bae, Sang-Eun; Brankovic, Stanko R.

    2011-01-01

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

  7. Chemical modification of protein A chromatography ligands with polyethylene glycol. I: Effects on IgG adsorption equilibrium, kinetics, and transport.

    Science.gov (United States)

    Weinberg, Justin; Zhang, Shaojie; Crews, Gillian; Carta, Giorgio; Przybycien, Todd

    2018-04-20

    Chemical modification of Protein A (ProA) chromatography ligands with polyethylene glycol (PEGylation) has been proposed as a strategy to increase the process selectivity and resin robustness by providing the ligand with a steric repulsion barrier against non-specific binding. This article comprises a comprehensive study of IgG adsorption and transport in Repligen CaptivA PriMAB resin with PEGylated ProA ligands that are modified using 5.2 and 21.5 kDa PEG chains. We studied the impact of the molecular weight of the PEG as well as the extent of PEGylation for the 5.2 kDa PEG modification. In all cases, PEGylation of ProA ligands decreases the resin average pore size, particle porosity, and static binding capacity for IgG proportional to the volume of conjugated PEG in the resin. Resin batch uptake experiments conducted in bulk via a stirred-tank system and with individual resin particles under confocal laser scanning microscopy suggests that PEGylation introduces heterogeneity into IgG binding kinetics: a fraction of the IgG binding sites are transformed from typical fast association kinetic behavior to slow kinetic behavior. pH gradient elution experiments of an IgG molecule on the modified resins show an increase in IgG elution pH for all modified resins, implying a decrease in IgG-ProA binding affinity on modification. Despite losses in static binding capacity for all resins with PEGylated ligands, the loss of dynamic binding capacity at 10% breakthrough (DBC 10% ) ranged more broadly from almost 0-47% depending on the PEG molecular weight and the extent of PEGylation. Minimal losses in DBC 10% were observed with a low extent of PEGylation with a smaller molecular weight PEG, while higher losses were observed at higher extents of PEGylation and with higher molecular weight PEG due to decreased static binding capacity and increased mass transfer resistance. This work provides insight into the practical implications for resin performance if PEGylation is

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

    International Nuclear Information System (INIS)

    Lalauze, Rene

    1973-01-01

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

  9. Digallane with redox-active diimine ligand: dualism of electron-transfer reactions.

    Science.gov (United States)

    Fedushkin, Igor L; Skatova, Alexandra A; Dodonov, Vladimir A; Chudakova, Valentina A; Bazyakina, Natalia L; Piskunov, Alexander V; Demeshko, Serhiy V; Fukin, Georgy K

    2014-05-19

    The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1), which consists of redox-active ligand 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian), has been studied. The reaction of 1 with I2 proceeds via one-electron oxidation of each of two dpp-Bian ligands to a radical-anionic state and affords complex (dpp-Bian)IGa-GaI(dpp-Bian) (2). Dissolution of complex 2 in pyridine (Py) gives monomeric compound (dpp-Bian)GaI(Py) (3) as a result of a solvent-induced intramolecular electron transfer from the metal-metal bond to the dpp-Bian ligands. Treatment of compound 3 with B(C6F5)3 leads to removal of pyridine and restores compound 2. The reaction of compound 1 with 3,6-di-tert-butyl-ortho-benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in 1 (the Ga-Ga bond and two dpp-Bian dianions) and results in mononuclear catecholate (dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q](2-)). Treatment of 4 with AgBF4 gives a mixture of [(dpp-Bian)2Ag][BF4] (5) and (dpp-Bian)GaF(Cat) (6), which both consist of neutral dpp-Bian ligands. The reduction of benzylideneacetone (BA) with 1 generates the BA radical-anions, which dimerize, affording (dpp-Bian)Ga-(BA-BA)-Ga(dpp-Bian) (7). In this case the Ga-Ga bond remains unchanged. Within 10 min at 95 °C in solution compound 7 undergoes transformation to paramagnetic complex (dpp-Bian)Ga(BA-BA) (8) and metal-free compound C36H40N2 (9). The latter is a product of intramolecular addition of the C-H bond of one of the iPr groups to the C═N bond in dpp-Bian. Diamagnetic compounds 3, 5, 6, and 9 have been characterized by NMR spectroscopy, and paramagnetic complexes 2, 4, 7, and 8 by ESR spectroscopy. Molecular structures of 2-7 and 9 have been established by single-crystal X-ray analysis.

  10. A kinetic reaction model for biomass pyrolysis processes in Aspen Plus

    International Nuclear Information System (INIS)

    Peters, Jens F.; Banks, Scott W.; Bridgwater, Anthony V.; Dufour, Javier

    2017-01-01

    Highlights: • Predictive kinetic reaction model applicable to any lignocellulosic feedstock. • Calculates pyrolysis yields and product composition as function of reactor conditions. • Detailed modelling of product composition (33 model compounds for the bio-oil). • Good agreement with literature regarding yield curves and product composition. • Successful validation with pyrolysis experiments in bench scale fast pyrolysis rig. - Abstract: This paper presents a novel kinetic reaction model for biomass pyrolysis processes. The model is based on the three main building blocks of lignocellulosic biomass, cellulose, hemicellulose and lignin and can be readily implemented in Aspen Plus and easily adapted to other process simulation software packages. It uses a set of 149 individual reactions that represent the volatilization, decomposition and recomposition processes of biomass pyrolysis. A linear regression algorithm accounts for the secondary pyrolysis reactions, thus allowing the calculation of slow and intermediate pyrolysis reactions. The bio-oil is modelled with a high level of detail, using up to 33 model compounds, which allows for a comprehensive estimation of the properties of the bio-oil and the prediction of further upgrading reactions. After showing good agreement with existing literature data, our own pyrolysis experiments are reported for validating the reaction model. A beech wood feedstock is subjected to pyrolysis under well-defined conditions at different temperatures and the product yields and compositions are determined. Reproducing the experimental pyrolysis runs with the simulation model, a high coincidence is found for the obtained fraction yields (bio-oil, char and gas), for the water content and for the elemental composition of the pyrolysis products. The kinetic reaction model is found to be suited for predicting pyrolysis yields and product composition for any lignocellulosic biomass feedstock under typical pyrolysis conditions

  11. 1D to 3D diffusion-reaction kinetics of defects in crystals

    DEFF Research Database (Denmark)

    Trinkaus, H.; Heinisch, H.L.; Barashev, A.V.

    2002-01-01

    Microstructural features evolving in crystalline solids from diffusion-reaction kinetics of mobile components depend crucially on the dimension of the underlying diffusion process which is commonly assumed to be three-dimensional (3D). In metals, irradiation-induced displacement cascades produce...... clusters of self-interstitials performing 1D diffusion. Changes between equivalent 1D diffusion paths and transversal diffusion result in diffusion-reaction kinetics between one and three dimensions. An analytical approach suggests a single-variable function (master curve) interpolating between the 1D...

  12. Hexacationic Dendriphos ligands in the Pd-catalyzed Suzuki-Miyaura cross-coupling reaction: scope and mechanistic studies

    NARCIS (Netherlands)

    Snelders, D.J.M.; van Koten, G.; Klein Gebbink, R.J.M.

    2009-01-01

    The combination of Pd2dba3·CHCl3and hexacationic triarylphosphine-based Dendriphos ligands (1-3) leads to a highly active catalytic system in the Suzuki-Miyaura cross-coupling reaction. Under relatively mild reaction conditions, nonactivated aryl bromides and activated aryl chlorides can be coupled

  13. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-02

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

  14. An Analogy Using Pennies and Dimes to Explain Chemical Kinetics Concepts

    Science.gov (United States)

    Cortes-Figueroa, Jose E.; Perez, Wanda I.; Lopez, Jose R.; Moore-Russo, Deborah A.

    2011-01-01

    In this article, the authors present an analogy that uses coins and graphical analysis to teach kinetics concepts and resolve pseudo-first-order rate constants related to transition-metal complexes ligand-solvent exchange reactions. They describe an activity that is directed to upper-division undergraduate and graduate students. The activity…

  15. S,O-Ligand-Promoted Palladium-Catalyzed C-H Functionalization Reactions of Nondirected Arenes

    NARCIS (Netherlands)

    Naksomboon, K.; Valderas, C.; Gomez-Martinez, M.; Alvarez-Casao, Y.; Fernández Ibáñez, M.A.

    Pd(II)-catalyzed C-H functionalization of non directed arenes has been realized using an inexpensive and easily accessible type of bidentate S,O-ligand. The catalytic system shows high efficiency in the C-H olefination reaction of electron-rich and electron-poor arenes. This methodology is

  16. Reaction kinetics of dolomite rim growth

    Science.gov (United States)

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

    2014-04-01

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

  17. Radiation induced ligand loss from cobalt complexes

    International Nuclear Information System (INIS)

    Funston, A. M.; McFadyen, W.D.; Tregloan, P.A.

    2000-01-01

    Full text: Due to the rapid nature of ligand dissociation from cobalt(II) complexes the study of the rate of ligand dissociation necessitates the use of a technique such as pulse radiolysis. This allows the rapid reduction of the corresponding cobalt(III) complex by a reducing radical, such as the aquated electron, to form the cobalt(II) complex. However, to date, no systematic study of either the mechanism of reduction or the influence of the electronic structure on the rate of ligand dissociation has been carried out. In order to understand these processes more fully the mechanism of reduction of a range of related cobalt(III) complexes by the aquated electron and the subsequent rate of ligand dissociation from the resulting cobalt(II) complexes is being investigated. It has been found that a number of processes are observed following the initial rapid reaction of the cobalt(III) complex with the aquated electron. Ultimately ligand loss is observed. Depending upon the complex, the initial processes observed may include the formation of coordinated radicals and electron transfer within the complex. For complexes containing aromatic ligands such as 2,2'-bipyridine, 1,10-phenanthroline and dipyrido[3,2-a:2',3'-c]phenazine the formation of a coordinated radical is observed as the initial reduction step. The kinetics of ligand dissociation of these complexes has been determined. The loss of monodentate ligands is fast and has been indistinguishable from the reduction processes when aromatic ligands are also present in the complex. However, for diamine chelates and diimine chelates spectra of the transient species can be resolved

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

    International Nuclear Information System (INIS)

    Loureiro, Roi Meizoso; Amarelo, Tánia Carballeira; Abuin, Senen Paz; Soulé, Ezequiel R.; Williams, Roberto J.J.

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-09-20

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

  20. Deviation from the kinetic law of mass action for reactions induced by binary encounters in liquid solutions

    International Nuclear Information System (INIS)

    Doktorov, Alexander B; Kipriyanov, Alexey A

    2007-01-01

    In considering the irreversible chemical reaction A+B→ C+B in liquid solutions two many-particle approaches to the derivation of binary non-Markovian kinetic equations are compared: simple superposition decoupling and a method of extracting 'pair' channels from three-particle correlation evolution. It is shown that both methods provide an almost identical description of this reaction. However, in studies of reversible reactions in liquid solutions only the channel extraction method gives a correct physically clear description of the reaction though it consists of a sequence of steps: the development of integral encounter theory (IET), effective pairs approximation (EPA), modified encounter theory (MET), and the final regular form (RF) of kinetic equations. It is shown that the rate equations often encountered in the literature correspond to the independence of transient channels of 'scattering' in the bimolecular reversible reaction (A+B -B), while the independent transient channel of 'decay' in the reversible reactionA+B -C is defined solely by time integral convolution. In the general case transient channels in non-Markovian theory are not independent, and their interference manifests itself as a non-Markovian inhomogeneous source in binary non-Markovian kinetic equations in regular form. Based on the derived equations new universal kinetics (independent of models) of chemical equilibrium attainment have been obtained. It is shown that these kinetics can differ essentially from the kinetics corresponding to the kinetic law of mass action of formal chemical kinetics

  1. Kinetics of the Coupled Gas-Iron Reactions Involving Silicon and ...

    African Journals Online (AJOL)

    The kinetic study of coupled gas-iron reactions at 15600 has been carried out for the system involving liquid iron containing carbon and silicon and a gas phase consisting carbon monoxide, silicon monoxide and carbon dioxide. The coupled reactions are: (1) 200(g) = CO2 + C. (2) SiO (g) + CO (g) = Si ¸ CO (g). (3) SiO (g) + ...

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

    International Nuclear Information System (INIS)

    Cui, Zixiang; Duan, Huijuan; Xue, Yongqiang; Li, Ping

    2015-01-01

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

  3. CuInSe2 nano-crystallite reaction kinetics using solid state reaction from Cu2Se and In2Se3 powders

    International Nuclear Information System (INIS)

    Hsiang, Hsing-I; Lu, Li-Hsin; Chang, Yu-Lun; Ray, Dahtong; Yen, Fu-Su

    2011-01-01

    Highlights: → CuInSe 2 phase increased gradually accompanied with a decrease in γ-In 2 Se 3 and no intermediate phase during calcination. → CuInSe 2 formation from Cu 2 Se and In 2 Se 3 powders follows a one-dimensional diffusion-controlled reaction with apparent activation energy of about 122.5 kJ/mol. → The solid reaction kinetics may be dominated by the diffusion of In 3+ ions. - Abstract: The reaction mechanism and CuInSe 2 formation kinetics using a solid state reaction from Cu 2 Se and In 2 Se 3 powders synthesized using a heating up process were investigated using X-ray diffractomy (XRD) and transmission electron microscopy (TEM). It was observed that the CuInSe 2 phase increased gradually, accompanied with a decrease in γ-In 2 Se 3 with no intermediate phase as the calcination temperature and soaking time were increased. The reaction kinetics was analyzed using the Avrami and polynomial kinetic model, suggesting that CuInSe 2 formation from Cu 2 Se and In 2 Se 3 powders follows a diffusion-controlled reaction with an apparent activation energy of about 122.5-182.3 kJ/mol. Cu 2 Se and In 2 Se 3 phases react and directly transform into CIS without the occurrence of any intermediate phase and the size of the newly formed CuInSe 2 crystallites was close to that of the Cu 2 Se reactant particle based on the TEM results, which indicated that the solid reaction kinetics may be dominated by the diffusion of In 3+ ions.

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

    DEFF Research Database (Denmark)

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

    2000-01-01

    is therefore 'mixed 1D/3D migration' along a 3D path consisting of 1D segments, The defect reaction kinetics under mixed 1D/3D diffusion are different from pure 1D diffusion and pure 3D diffusion, both of which can be formulated within analytical rate theory models of microstructure evolution under irradiation....... Atomic-scale kinetic Monte Carlo (kMC) defect migration simulations are used to investigate the effects of mixed 1D/3D migration on defect reaction kinetics as a guide for implementing mixed 1D/3D migration into the analytical rate theory. The functional dependence of the sink strength on the size...

  5. Isothermal reaction calorimetry as a tool for kinetic analysis

    International Nuclear Information System (INIS)

    Zogg, Andreas; Stoessel, Francis; Fischer, Ulrich; Hungerbuehler, Konrad

    2004-01-01

    Reaction calorimetry has found widespread application for thermal and kinetic analysis of chemical reactions in the context of thermal process safety as well as process development. This paper reviews the most important reaction calorimetric principles (heat-flow, heat-balance, power-compensation, and Peltier principle) and their applications in commercial or scientific devices. The discussion focuses on the different dynamic behavior of the main calorimetric principles during an isothermal reaction measurement. Examples of available reaction calorimeters are further compared considering their detection limit, time constant as well as temperature range. In a second part, different evaluation methods for the isothermally measured calorimetric data are reviewed and discussed. The methods will be compared, focusing especially on the fact that reaction calorimetric data always contains additional informations not directly related to the actual chemical reaction such as heat of mixing, heat of phase-transfer/change processes or simple measurement errors. Depending on the evaluation method applied such disturbances have a significant influence on the calculated reaction enthalpies or rate constants

  6. Kinetics of the Br2-CH3CHO Photochemical Chain Reaction

    Science.gov (United States)

    Nicovich, J. M.; Shackelford, C. J.; Wine, P. H.

    1997-01-01

    Time-resolved resonance fluorescence spectroscopy was employed in conjunction with laser flash photolysis of Br2 to study the kinetics of the two elementary steps in the photochemical chain reaction nBr2 + nCH3CHO + hv yields nCH3CBrO + nHBr. In the temperature range 255-400 K, the rate coefficient for the reaction Br((sup 2)P(sub 3/2)) + CH3CHO yields CH3CO + HBr is given by the Arrhenius expression k(sub 6)(T) = (1.51 +/- 0.20) x 10(exp -11) exp(-(364 +/- 41)/T)cu cm/(molecule.s). At 298 K, the reaction CH3CO + Br2 yields CH3CBrO + Br proceeds at a near gas kinetic rate, k(sub 7)(298 K) = (1.08 +/- 0.38) x 10(exp -10)cu cm/(molecule.s).

  7. Reaction kinetics of resveratrol with thiyl and alkoxyl radicals

    International Nuclear Information System (INIS)

    Dzeba, I.; Mihaljevic, B.

    2011-01-01

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

  8. Kinetics of reactions of aquacobalamin with aspartic and glutamic acids and their amides in water solutions

    Science.gov (United States)

    Bui, T. T. T.; Sal'nikov, D. S.; Dereven'kov, I. A.; Makarov, S. V.

    2017-04-01

    The kinetics of aquacobalamin reaction with aspartic and glutamic acids, and with their amides in water solutions, is studied via spectrophotometry. The kinetic and activation parameters of the process are determined. It is shown that the reaction product is cobalamin-amino acid complex. The data are compared to results on the reaction between aquacobalamin and primary amines.

  9. Strain-induced structural changes and chemical reactions. 1: Thermomechanical and kinetic models

    International Nuclear Information System (INIS)

    Levitas, V.I.; Nesterenko, V.F.; Meyers, M.A.

    1998-01-01

    Strain-induced chemical reactions were observed recently (Nesterenko et al) in experiments in the shear band in both Ti-Si and Nb-Si mixtures. Reactions can start in the solid state or after melting of at least one component. One of the aims is to find theoretically whether there are possible macroscopic mechanisms of mechanical intensification of the above and other chemical reactions due to plastic shear in the solid state. Continuum thermodynamical theory of structural changes with an athermal kinetics, which includes martensitic phase transformations, plastic strain-induced chemical reactions and polymorphic transformations, is developed at finite strains. The theory includes kinematics, criterion of structural change and extremum principle for determination of all unknown variable parameters for the case with neglected elastic strains. Thermodynamically consistent kinetic theory of thermally activated structural changes is suggested. The concept of the effective temperature is introduced which takes into account that temperature can vary significantly (on 1,000 K) during the chemical reactions under consideration. The theory will be applied in Part 2 of the paper for the description of chemical reactions in the shear band

  10. Transport Properties of a Kinetic Model for Chemical Reactions without Barriers

    International Nuclear Information System (INIS)

    Alves, Giselle M.; Kremer, Gilberto M.; Soares, Ana Jacinta

    2011-01-01

    A kinetic model of the Boltzmann equation for chemical reactions without energy barrier is considered here with the aim of evaluating the reaction rate and characterizing the transport coefficient of shear viscosity for the reactive system. The Chapman-Enskog solution of the Boltzmann equation is used to compute the chemical reaction effects, in a flow regime for which the reaction process is close to the final equilibrium state. Some numerical results are provided illustrating that the considered chemical reaction without energy barrier can induce an appreciable influence on the reaction rate and on the transport coefficient of shear viscosity.

  11. The redox reaction kinetics of Sinai ore for chemical looping combustion applications

    International Nuclear Information System (INIS)

    Ksepko, Ewelina; Babiński, Piotr; Nalbandian, Lori

    2017-01-01

    Highlights: • Redox reaction kinetics of Fe-Mn-rich Sinai ore was determined by TGA. • The most suitable model for reduction was D3, while R3 for oxidation. • Activation energies 35.3 and 16.70 kJ/mole were determined for reduction and oxidation. • Repetitive redox reactions favor the formation of spinel phases in Sinai ore. • Multiple redox cycles induce formation of extensive porosity of the particles. - Abstract: The objective of this work was to study the use of Sinai ore, a Fe–Mn-based ore from Egypt, as a low-cost oxygen carrier (OC) in Chemical Looping Combustion (CLC). The Sinai ore was selected because it possesses relatively high amounts of iron and manganese oxides. Furthermore, those oxides have low cost, very favorable environmental and thermodynamic properties for the CLC process. The performance of the Sinai ore as an OC in CLC was compared to that of ilmenite (Norway Tellnes mine), the most extensively studied naturally occurring Fe-based mineral. The kinetics of the reduction and oxidation reactions with the two minerals were studied using a thermogravimetric analyzer (TGA). Experiments were conducted under isothermal conditions, with multiple redox cycles, at temperatures between 750 and 950 °C. For the reduction and oxidation reactions, different concentrations of CH_4 (10–25 vol.%) and O_2 (5–20 vol.%) were applied, respectively. The kinetic parameters, such as the activation energy (E_a), pre-exponential factor (A_0), and reaction order (n), were determined for the redox reactions. Furthermore, models of the redox reactions were selected by means of a model-fitting method. For the Sinai ore, the D3 model (3-dimensional diffusion) was suitable for modeling reduction reaction kinetics. The calculated E_a was 35.3 kJ/mole, and the reaction order was determined to be approximately 0.76. The best fit for the oxidation reaction was obtained for the R3 model (shrinking core). The oxidation (regeneration) reaction E_a was equal to 16

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

    Directory of Open Access Journals (Sweden)

    Kelath Murali Manoj

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

  13. Kinetic study of the reaction of chlorine atoms with hydroxyacetone in gas-phase

    Science.gov (United States)

    Stoeffler, Clara; Joly, Lilian; Durry, Georges; Cousin, Julien; Dumelié, Nicolas; Bruyant, Aurélien; Roth, Estelle; Chakir, Abdelkhaleq

    2013-12-01

    In this letter the kinetics of the reaction of hydroxyacetone CH3C(O)CH2OH with Cl atoms is investigated using the relative rate technique. Experiments are carried out in a 65 L multipass photoreactor in the temperature range of 281-350 K. A mid-infrared spectrometer based on a quantum cascade laser in external cavity emitting at 9.5 μm is used to analyze the reactants. The determined rate coefficient for the investigated reaction is (1.7 ± 0.3) × 10-11exp(381.5 ± 57.3/T). The results are presented and discussed in terms of precision and compared with those obtained previously. The impact of Cl atoms on the atmospheric life time of hydroxyacetone is also discussed. Developing analytical techniques to quantify this compound in the atmosphere. Several methods of measurement have been used including the technique of proton transfer mass spectrometry (PTR-MS) [2] and derivatization with a chemical agent such as dinitrophenylhydrazine (DNPH) [3,4] followed by GC/MS or HPLC analyses. The HA amount in the troposphere was found to be in the order of a few hundred parts per trillion by volume [4], Performing laboratory experiments in order to study the HA reactivity with atmospheric oxidants. The first study on the kinetic of the reaction between OH radicals and HA was made by Dagault et al. [5] whose work was performed at room temperature by flash photolysis-resonance fluorescence. The determined rate constant implies a lifetime of a few days for HA relative to oxidation by OH radicals. Orlando et al. performed mechanistic and kinetics studies of the reaction of HA with OH radicals and Cl atoms at room temperature using a relative method [6]. Products detection was performed using FTIR spectroscopy. Moreover, these authors studied the photolysis of HA to determine its quantum yield and UV absorption spectrum. These studies showed that HA is principally removed from the atmosphere by reaction with OH radicals. Kinetic studies of the reaction of OH radicals with HA as a

  14. Empirical potentials for recombination reactions of photo-dissociated ligands. Final report

    International Nuclear Information System (INIS)

    Elber, R.

    1998-01-01

    The aim of this research was to design an appropriate potential and simulation methodology to describe the effect of radiation on ligands bound to metal-proteins. As model systems the authors investigated myoglobin, hemoglobin and their mutants. The great advantage of the globins as a target for theoretical studies is the wealth of experimental data available for them. They focused on studies that combine fast spectroscopy with mutation experiments. The mutations make it possible to examine detailed changes in the kinetic curves with atomically detailed information. The first spectroscopy, which is in the same time scale as of ordinary molecular dynamics (sub nanoseconds), makes it possible to compare the results of the computations to raw experimental data

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

    NARCIS (Netherlands)

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

    2003-01-01

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

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

    NARCIS (Netherlands)

    Kumar Paramasivam Senthil, P.S.; Hogendoorn, Kees; Versteeg, Geert; Feron, P.H.M.

    2003-01-01

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

  17. The kinetics of the reduction reaction of plutonium(IV) with N,N-dimethylhydroxylamine

    International Nuclear Information System (INIS)

    Yanxin Chen; Honbing Tang; Jinping Liu; Hui He

    2011-01-01

    The kinetics of reduction reactions between N,N-dimethylhydroxylamine (DMHAN) and plutonium(IV) in nitric acid solution have been studied spectrophotometrically. The kinetic equation of the reaction is determined to be -d[Pu(IV)]/dt = k 0 [Pu(IV)][DMHAN] 1.18 /[H + ] 2.22 at the beginning, where, the rate constant of the reaction (k 0 ) is 10.5 ± 1.8(mol/L) 1.04 s -1 at 14.5 deg C. By regressing of the time-concentration curve of the reaction, The complete rate equation is calculated as -d[Pu(IV)] / dt = k[Pu(IV)] 2 [DMHAN] 1.18 /[H + ] 2.22 / 8.12[Pu(III)]+95.9[Pu(IV)] with the reaction constant k about 1,000(mol/L) 1.04 s -1 at 14.5 deg C and an ionic strength (μ) of 4.0 mol/L. (author)

  18. Reaction kinetics for preparation of silica film with Stoeber method

    International Nuclear Information System (INIS)

    Shang Mengying; Jiang Xiaodong; Liu Miao; Luo Xuan; Tang Yongjian; Cao Linhong

    2013-01-01

    A new formula was proposed to investigate the relationship between reaction time and tetraethylorthosilicate (TEOS) conversion rate for preparation of silica sol with Stöber method, by studying the reaction kinetics of TEOS hydrolytic process. An appropriate conversion rate was then determined and used to calculate the theoretical optimal reaction time. Meanwhile, silica sols were prepared by sol-gel process using TEOS as precursor and ammonia as catalyst. It was found that the reaction time decreases with an increasing amount of ammonia and water. The values of experimental optimal reaction time were obtained, and agree with the theoretical results (the errors are within 5%), which shows good applicability of our formula. (authors)

  19. Conductometric Studies Of Kinetics Of Ionic Reaction Between Ag And Cl- In Aqueous Solution

    Directory of Open Access Journals (Sweden)

    Md. Rezwan Miah

    2017-01-01

    Full Text Available In the present report conductometric studies on the kinetic of formation of AgCl by ionic reaction between Ag and Clamp61485 in aqueous solution have been presented. The order of the mentioned reaction was determined by a new conductometric approach using half-life method. The obtained result showed that the reaction follows a second-order kinetics. The second-order rate constant of the reaction was obtained conductometrically using different initial concentrations of the reactants in the range of 2.5-5.0 mM. The average value of the rate constant was obtained as 20.648 L molamp614851 samp614851 at 25 amp61616C.

  20. Isotopic studies on ligand exchange between complex and simple cyanides in water medium and in liquid hydrogen cyanide. Part 2. Radiocyanide ligand exchange study between hydrogen cyanide and octacyanotungstate(4) in water solutions of mineral acids

    International Nuclear Information System (INIS)

    Zielinski, M.

    1979-01-01

    Radiocyanide ligand exchange between potassium octacyanotungstate(4) and hydrogen cyanide in aqueous solutions of sulfuric acid and between octacyanotungstic(4) acid and hydrogen cyanide in aqueous solutions have been investigated experimentally. The observed enhancement of the rate of ligand exchange in acidic medium has been rationalized in terms of the proposed new general reaction scheme taking into account the reversible decomposition of complex cyanide at low pH, and irreversible one at high pH. The discussion on the results obtained has been carried out within the framework of derived formal kinetic equations. (author)

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

    Directory of Open Access Journals (Sweden)

    Xu Huan-Yan

    2014-01-01

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

  2. SABIO-RK: an updated resource for manually curated biochemical reaction kinetics

    Science.gov (United States)

    Rey, Maja; Weidemann, Andreas; Kania, Renate; Müller, Wolfgang

    2018-01-01

    Abstract SABIO-RK (http://sabiork.h-its.org/) is a manually curated database containing data about biochemical reactions and their reaction kinetics. The data are primarily extracted from scientific literature and stored in a relational database. The content comprises both naturally occurring and alternatively measured biochemical reactions and is not restricted to any organism class. The data are made available to the public by a web-based search interface and by web services for programmatic access. In this update we describe major improvements and extensions of SABIO-RK since our last publication in the database issue of Nucleic Acid Research (2012). (i) The website has been completely revised and (ii) allows now also free text search for kinetics data. (iii) Additional interlinkages with other databases in our field have been established; this enables users to gain directly comprehensive knowledge about the properties of enzymes and kinetics beyond SABIO-RK. (iv) Vice versa, direct access to SABIO-RK data has been implemented in several systems biology tools and workflows. (v) On request of our experimental users, the data can be exported now additionally in spreadsheet formats. (vi) The newly established SABIO-RK Curation Service allows to respond to specific data requirements. PMID:29092055

  3. Electro-kinetic separation of rare earth elements using a redox-active ligand

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Huayi; Cole, Bren E.; Qiao, Yusen; Bogart, Justin A.; Cheisson, Thibault; Manor, Brian C.; Carroll, Patrick J.; Schelter, Eric J. [Department of Chemistry, University of Pennsylvania, Philadelphia, PA (United States)

    2017-10-16

    Purification of rare earth elements is challenging due to their chemical similarities. All of the deployed separation methods rely on thermodynamic properties, such as distribution equilibria in solvent extraction. Rare-earth-metal separations based on kinetic differences have not been examined. Herein, we demonstrate a new approach for rare-earth-element separations by exploiting differences in the oxidation rates within a series of rare earth compounds containing the redox-active ligand [{2-(tBuN(O))C_6H_4CH_2}{sub 3}N]{sup 3-}. Using this method, a single-step separation factor up to 261 was obtained for the separation of a 50:50 yttrium-lutetium mixture. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Studies on ligand exchange reaction of functionalized mercaptothiadiazole compounds onto citrate capped gold nanoparticles

    International Nuclear Information System (INIS)

    Kalimuthu, Palraj; John, S. Abraham

    2010-01-01

    Mercaptothiadiazole ligands functionalized with thiol (2,5-dimercapto-1,3,4-thiadiazole (DMT)) and methyl (5-methyl-2-mercapto-1,3,4-thiadiazole (MMT)) groups capped onto citrate capped gold nanoparticles (C-AuNPs) by ligand exchange reaction was investigated by UV-vis spectroscopy, FT-IR spectroscopy and transmission electron microscopy (TEM) techniques. The surface plasmon resonance band at 522 nm for C-AuNPs was shifted to 530 nm after capping with DMT whereas an additional band was observed at 630 nm due to aggregation in addition to a shift in the band at 522 nm after capping of MMT onto C-AuNPs. Thus, capping of DMT onto C-AuNPs leads to the formation of stable AuNPs while capping of MMT leads to the formation of unstable AuNPs. FT-IR studies show that the citrate ions were completely replaced by both DMT and MMT ligands from the AuNPs. TEM images indicate that the size and shape of the AuNPs remain same after capping of these ligands.

  5. Energetics and kinetics of ferrocyanide and nitrate/nitrite reactions

    International Nuclear Information System (INIS)

    Scheele, R.D.; Burger, L.L.; Sell, R.L.

    1994-01-01

    During the 1950's, radiocesium scavenging at the Hanford site resulted in radioactive waste sludges containing ferrocyanide, nitrate, and nitrite. These waters are a concern since certain mixtures of ferrocyanide and nitrate and/or nitrite are known to explode when heated. The authors have used differential scanning calorimetry, thermogravimetric analysis, isothermal calorimetry and gravimetry, and accelerating rate calorimetry to measure the thermal behavior, the reaction enthalpies, and selected kinetic parameters for reactions between sodium nickel ferrocyanide, the suspected ferrocyanide form in Hanford wastes, and nitrate and/or nitrite. These studies indicate that the oxidation proceeds via multiple steps, the initial reaction begins near 200 degrees C, the initial step has a high activation energy (>200 kJ/mole-K), succeeding reaction steps have activation energies ranging from 90 to 160 kJ/mole-K, and that the oxidation yields about 50% of the theoretical heat of reaction for the most energetic reaction

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-12-31

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

  7. Accurate label-free reaction kinetics determination using initial rate heat measurements

    Science.gov (United States)

    Ebrahimi, Kourosh Honarmand; Hagedoorn, Peter-Leon; Jacobs, Denise; Hagen, Wilfred R.

    2015-01-01

    Accurate label-free methods or assays to obtain the initial reaction rates have significant importance in fundamental studies of enzymes and in application-oriented high throughput screening of enzyme activity. Here we introduce a label-free approach for obtaining initial rates of enzyme activity from heat measurements, which we name initial rate calorimetry (IrCal). This approach is based on our new finding that the data recorded by isothermal titration calorimetry for the early stages of a reaction, which have been widely ignored, are correlated to the initial rates. Application of the IrCal approach to various enzymes led to accurate enzyme kinetics parameters as compared to spectroscopic methods and enabled enzyme kinetic studies with natural substrate, e.g. proteases with protein substrates. Because heat is a label-free property of almost all reactions, the IrCal approach holds promise in fundamental studies of various enzymes and in use of calorimetry for high throughput screening of enzyme activity. PMID:26574737

  8. Nonequilibrium transition and pattern formation in a linear reaction-diffusion system with self-regulated kinetics

    Science.gov (United States)

    Paul, Shibashis; Ghosh, Shyamolina; Ray, Deb Shankar

    2018-02-01

    We consider a reaction-diffusion system with linear, stochastic activator-inhibitor kinetics where the time evolution of concentration of a species at any spatial location depends on the relative average concentration of its neighbors. This self-regulating nature of kinetics brings in spatial correlation between the activator and the inhibitor. An interplay of this correlation in kinetics and disparity of diffusivities of the two species leads to symmetry breaking non-equilibrium transition resulting in stationary pattern formation. The role of initial noise strength and the linear reaction terms has been analyzed for pattern selection.

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

    International Nuclear Information System (INIS)

    Haschke, J.M.

    1995-12-01

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

  10. Kinetics of the gas-phase tritium oxidation reaction

    International Nuclear Information System (INIS)

    Failor, R.A.

    1989-01-01

    Homogeneous gas-phase kinetics of tritium oxidation (2T 2 + O 2 →2T 2 O) have been studied with a model that accounts explicitly for radiolysis of the major species and the kinetics of the subsequent reactions of ionic, excited-state, and neutral species. Results from model calculations are given for 10 -4 -1.0 mol% T 2 in O 2 (298 K, 1 atm). As the reaction evolves three different mechanisms control T 2 O production, each with a different overall rate expression and a different order with respect to the T 2 concentration. The effects of self-radiolysis of pure T 2 on the tritium oxidation reaction were calculated. Tritium atoms, the primary product of T 2 self-radiolysis, altered the oxidation mechanism only during the first few seconds following the initiation of the T 2 -O 2 reaction. Ozone, an important intermediate in T 2 oxidation, was monitored in-situ by U.V. absorption spectroscopy for 0.01-1.0 mol% T 2 an 1 atm O 2 . The shape of the experimental ozone time profile agreed with the model predictions. As predicted, the measured initial rate of ozone production varied linearly with initial T 2 concentration ([T 2 ] 0.6 o ), but at an initial rate one-third the predicted value. The steady-state ozone concentration ([O 3 ]ss) was predicted to be dependent on [T 2 ] 0.3 o , but the measured value was [T 2 ] 0.6 o , resulting in four times higher [O 3 ]ss than predicted for a 1.0% T 2 -O 2 mixture. Adding H 2 to the T 2 -O 2 mixture, to provide insight into the differences between the radiolytic and chemical behavior of the tritium, produced a greater decrease in [O 3 ]ss than predicted. Adjusting the reaction cell surface-to-volume ratio showed implications of minor surface removal of ozone

  11. Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

    International Nuclear Information System (INIS)

    Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang; Gao, Ziwei

    2015-01-01

    A successive anchoring of Ti(NMe 2 ) 4 , cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, 13 C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, 13 C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated

  12. Ligand-tailored single-site silica supported titanium catalysts: Synthesis, characterization and towards cyanosilylation reaction

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Wei; Li, Yani; Yu, Bo; Yang, Jindou; Zhang, Ying; Chen, Xi; Zhang, Guofang, E-mail: gfzhang@snnu.edu.cn; Gao, Ziwei, E-mail: zwgao@snnu.edu.cn

    2015-01-15

    A successive anchoring of Ti(NMe{sub 2}){sub 4}, cyclopentadiene and a O-donor ligand, 1-hydroxyethylbenzene (PEA), 1,1′-bi-2-naphthol (Binol) or 2,3-dihydroxybutanedioic acid diethyl ester (Tartrate), on silica was conducted by SOMC strategy in moderate conditions. The silica, monitored by in-situ Fourier transform infrared spectroscopy (in-situ FT-IR), was pretreated at different temperatures (200, 500 and 800 °C). The ligand tailored silica-supported titanium complexes were characterized by in-situ FT-IR, {sup 13}C CP MAS-NMR, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and elemental analysis in detail, verifying that the surface titanium species are single sited. The catalytic activity of the ligand tailored single-site silica supported titanium complexes was evaluated by a cyanosilylation of benzaldehyde. The results showed that the catalytic activity is dependent strongly on the dehydroxylation temperatures of silica and the configuration of the ligands. - Graphical abstract: The ligand-tailored silica supported “single site” titanium complexes were synthesized by SOMC strategy and fully characterized. Their catalytic activity were evaluated by benzaldehyde silylcyanation. - Highlights: • Single-site silica supported Ti active species was prepared by SOMC technique. • O-donor ligand tailored Ti surface species was synthesized. • The surface species was characterized by XPS, {sup 13}C CP-MAS NMR, XANES etc. • Catalytic activity of the Ti active species in silylcyanation reaction was evaluated.

  13. Reaction mechanisms of metal complexes

    CERN Document Server

    Hay, R W

    2000-01-01

    This text provides a general background as a course module in the area of inorganic reaction mechanisms, suitable for advanced undergraduate and postgraduate study and/or research. The topic has important research applications in the metallurgical industry and is of interest in the science of biochemistry, biology, organic, inorganic and bioinorganic chemistry. In addition to coverage of substitution reactions in four-, five- and six-coordinate complexes, the book contains further chapters devoted to isomerization and racemization reactions, to the general field of redox reactions, and to the reactions of coordinated ligands. It is relevant in other fields such as organic, bioinorganic and biological chemistry, providing a bridge to organic reaction mechanisms. The book also contains a chapter on the kinetic background to the subject with many illustrative examples which should prove useful to those beginning research. Provides a general background as a course module in the area of inorganic reaction mechanis...

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  15. Thermodynamic criteria for estimating the kinetic parameters of catalytic reactions

    Science.gov (United States)

    Mitrichev, I. I.; Zhensa, A. V.; Kol'tsova, E. M.

    2017-01-01

    Kinetic parameters are estimated using two criteria in addition to the traditional criterion that considers the consistency between experimental and modeled conversion data: thermodynamic consistency and the consistency with entropy production (i.e., the absolute rate of the change in entropy due to exchange with the environment is consistent with the rate of entropy production in the steady state). A special procedure is developed and executed on a computer to achieve the thermodynamic consistency of a set of kinetic parameters with respect to both the standard entropy of a reaction and the standard enthalpy of a reaction. A problem of multi-criterion optimization, reduced to a single-criterion problem by summing weighted values of the three criteria listed above, is solved. Using the reaction of NO reduction with CO on a platinum catalyst as an example, it is shown that the set of parameters proposed by D.B. Mantri and P. Aghalayam gives much worse agreement with experimental values than the set obtained on the basis of three criteria: the sum of the squares of deviations for conversion, the thermodynamic consistency, and the consistency with entropy production.

  16. Receptor binding kinetics equations: Derivation using the Laplace transform method.

    Science.gov (United States)

    Hoare, Sam R J

    Measuring unlabeled ligand receptor binding kinetics is valuable in optimizing and understanding drug action. Unfortunately, deriving equations for estimating kinetic parameters is challenging because it involves calculus; integration can be a frustrating barrier to the pharmacologist seeking to measure simple rate parameters. Here, a well-known tool for simplifying the derivation, the Laplace transform, is applied to models of receptor-ligand interaction. The method transforms differential equations to a form in which simple algebra can be applied to solve for the variable of interest, for example the concentration of ligand-bound receptor. The goal is to provide instruction using familiar examples, to enable investigators familiar with handling equilibrium binding equations to derive kinetic equations for receptor-ligand interaction. First, the Laplace transform is used to derive the equations for association and dissociation of labeled ligand binding. Next, its use for unlabeled ligand kinetic equations is exemplified by a full derivation of the kinetics of competitive binding equation. Finally, new unlabeled ligand equations are derived using the Laplace transform. These equations incorporate a pre-incubation step with unlabeled or labeled ligand. Four equations for measuring unlabeled ligand kinetics were compared and the two new equations verified by comparison with numerical solution. Importantly, the equations have not been verified with experimental data because no such experiments are evident in the literature. Equations were formatted for use in the curve-fitting program GraphPad Prism 6.0 and fitted to simulated data. This description of the Laplace transform method will enable pharmacologists to derive kinetic equations for their model or experimental paradigm under study. Application of the transform will expand the set of equations available for the pharmacologist to measure unlabeled ligand binding kinetics, and for other time

  17. KEMOD: A mixed chemical kinetic and equilibrium model of aqueous and solid phase geochemical reactions

    International Nuclear Information System (INIS)

    Yeh, G.T.; Iskra, G.A.

    1995-01-01

    This report presents the development of a mixed chemical Kinetic and Equilibrium MODel in which every chemical species can be treated either as a equilibrium-controlled or as a kinetically controlled reaction. The reaction processes include aqueous complexation, adsorption/desorption, ion exchange, precipitation/dissolution, oxidation/reduction, and acid/base reactions. Further development and modification of KEMOD can be made in: (1) inclusion of species switching solution algorithms, (2) incorporation of the effect of temperature and pressure on equilibrium and rate constants, and (3) extension to high ionic strength

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

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Wiuf, C.

    2012-01-01

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

  19. Kinetics based reaction optimization of enzyme catalysed reduction of formaldehyde to methanol with synchronous cofactor regeneration

    DEFF Research Database (Denmark)

    Marpani, Fauziah Binti; Sárossy, Zsuzsa; Pinelo, Manuel

    2017-01-01

    regeneration of the reducing equivalents during reaction is required. Herein, we report the optimization of the enzymatic conversion of formaldehyde (CHOH) to CH3 OH by alcohol dehydrogenase, the final step of the enzymatic redox reaction of CO2 to CH3 OH, with kinetically synchronous enzymatic cofactor...... regeneration using either glucose dehydrogenase (System I) or xylose dehydrogenase (System II). A mathematical model of the enzyme kinetics was employed to identify the best reaction set-up for attaining optimal cofactor recycling rate and enzyme utilization efficiency. Targeted process optimization...... experiments were conducted to verify the kinetically modelled results. Repetitive reaction cycles were shown to enhance the yield of CH3 OH, increase the total turnover number (TTN) and the biocatalytic productivity rate (BPR) value for both system I and II whilst minimizing the exposure of the enzymes...

  20. Electrochemistry of oxo-technetium(V) complexes containing Schiff base and 8-quinolinol ligands

    International Nuclear Information System (INIS)

    Refosco, F.; Mazzi, U.; Deutsch, E.; Kirchhoff, J.R.; Heineman, W.R.; Seeber, R.

    1988-01-01

    The electrochemistry of six-coordinate, monooxo technetium(V) complexes containing Schiff base ligands has been studied in acetonitrile and N,N'-dimethylformamide solutions. The complexes have the general formula TcOCl(L B ) 2 or TcO(L T )(L B ), where L B represents a bidentate-N,O Schiff base ligand or a bidentate-N,O 8-quinolinol ligand and L T represents a tridentate-O,N,O Schiff base ligand. Cyclic voltammetry at a platinum-disk electrode, controlled-potential coulometry, and thin-layer spectroelectrochemistry were used to probe both the oxidation and the reduction of these complexes. The results of these studies, and previously reported results on the analogous Re(V) complexes, can be understood within a single general reaction scheme. The salient features of this scheme are (i) one-electron reduction of Tc(V) to Tc(IV), (ii) subsequent loss of a ligand situated cis to the Tc≡O linkage, and (iii) subsequent isomerization of this unstable Tc(IV) product to more stable complex in which the site trans to the Tc≡O linkage is vacant. The Tc(IV) complexes can also be reduced to analogous Tc(III) species, which appear to undergo the same ligand loss and isomerization reactions. The technetium complexes are 400-500 mV easier to reduce than are their rhenium analogues. The 8-quinolinol ligands, and especially the 5-nitro derivative, both thermodynamically and kinetically stabilize the Tc(IV) and Tc(III) oxidation states. These electrogenerated species are unusual in that they constitute the bulk of the known examples of monomeric Tc(IV) and Tc(III) complexes containing only N- and O-donating ligands. 34 refs., 9 figs., 1 tab

  1. Dependence of cancer cell adhesion kinetics on integrin ligand surface density measured by a high-throughput label-free resonant waveguide grating biosensor.

    Science.gov (United States)

    Orgovan, Norbert; Peter, Beatrix; Bősze, Szilvia; Ramsden, Jeremy J; Szabó, Bálint; Horvath, Robert

    2014-02-07

    A novel high-throughput label-free resonant waveguide grating (RWG) imager biosensor, the Epic® BenchTop (BT), was utilized to determine the dependence of cell spreading kinetics on the average surface density (v(RGD)) of integrin ligand RGD-motifs. v(RGD) was tuned over four orders of magnitude by co-adsorbing the biologically inactive PLL-g-PEG and the RGD-functionalized PLL-g-PEG-RGD synthetic copolymers from their mixed solutions onto the sensor surface. Using highly adherent human cervical tumor (HeLa) cells as a model system, cell adhesion kinetic data of unprecedented quality were obtained. Spreading kinetics were fitted with the logistic equation to obtain the spreading rate constant (r) and the maximum biosensor response (Δλmax), which is assumed to be directly proportional to the maximum spread contact area (Amax). r was found to be independent of the surface density of integrin ligands. In contrast, Δλmax increased with increasing RGD surface density until saturation at high densities. Interpreting the latter behavior with a simple kinetic mass action model, a 2D dissociation constant of 1753 ± 243 μm(-2) (corresponding to a 3D dissociation constant of ~30 μM) was obtained for the binding between RGD-specific integrins embedded in the cell membrane and PLL-g-PEG-RGD. All of these results were obtained completely noninvasively without using any labels.

  2. Quantitative analysis of protein-ligand interactions by NMR.

    Science.gov (United States)

    Furukawa, Ayako; Konuma, Tsuyoshi; Yanaka, Saeko; Sugase, Kenji

    2016-08-01

    Protein-ligand interactions have been commonly studied through static structures of the protein-ligand complex. Recently, however, there has been increasing interest in investigating the dynamics of protein-ligand interactions both for fundamental understanding of the underlying mechanisms and for drug development. NMR is a versatile and powerful tool, especially because it provides site-specific quantitative information. NMR has widely been used to determine the dissociation constant (KD), in particular, for relatively weak interactions. The simplest NMR method is a chemical-shift titration experiment, in which the chemical-shift changes of a protein in response to ligand titration are measured. There are other quantitative NMR methods, but they mostly apply only to interactions in the fast-exchange regime. These methods derive the dissociation constant from population-averaged NMR quantities of the free and bound states of a protein or ligand. In contrast, the recent advent of new relaxation-based experiments, including R2 relaxation dispersion and ZZ-exchange, has enabled us to obtain kinetic information on protein-ligand interactions in the intermediate- and slow-exchange regimes. Based on R2 dispersion or ZZ-exchange, methods that can determine the association rate, kon, dissociation rate, koff, and KD have been developed. In these approaches, R2 dispersion or ZZ-exchange curves are measured for multiple samples with different protein and/or ligand concentration ratios, and the relaxation data are fitted to theoretical kinetic models. It is critical to choose an appropriate kinetic model, such as the two- or three-state exchange model, to derive the correct kinetic information. The R2 dispersion and ZZ-exchange methods are suitable for the analysis of protein-ligand interactions with a micromolar or sub-micromolar dissociation constant but not for very weak interactions, which are typical in very fast exchange. This contrasts with the NMR methods that are used

  3. Reaction network modelling for kinetic parameters of pyrolytic reactions of CHON extractants in nuclear fuel processing waste management. Contributed Paper IT-07

    International Nuclear Information System (INIS)

    Gaikar, Vilas G.; Thaore, Vaishali

    2014-01-01

    The recovery and purification of plutonium (Pu) from uranium (U) and of U from Thorium (Th) in spent nuclear fuel reprocessing is accomplished by processes that employ organophosphorous compounds as extractants.The main objective of the present work was to develop a suitable kinetic model and to determine the kinetic parameters of the set of reactions involved in the pyrolysis of amides by fitting the experimental data in the reaction network model. The experimental data and analysis are expected to be useful in the steam pyrolysis of amide waste in fuel reprocessing in the nuclear industry. The basic approach was to understand the reaction mechanism of the steam pyrolysis of amides and then to estimate the reaction rate constants for the generation and consumption of different species by solving the model equations, allowing for the determination of important species in the reaction network

  4. Kinetic modeling of receptor-ligand binding applied to positron emission tomographic studies with neuroleptic tracers

    Energy Technology Data Exchange (ETDEWEB)

    Logan, J; Wolf, A P; Shiue, C Y; Fowler, J S

    1987-01-01

    Positron emission tomography (PET) with labeled neuroleptics has made possible the study of neurotransmitter-receptor systems in vivo. In this study we investigate the kinetics of the 3,4-dihydroxyphenylethylamine (dopamine) receptor-ligand binding using PET data from a series of experiments in the baboon with the /sup 18/F-labeled drugs spiperone, haloperidol, and benperidol. Models used to describe these systems are based on first-order kinetics which applies at high specific activity (low receptor occupancy). The parameters governing the uptake and loss of drug from the brain were found by fitting PET data from regions with little or no receptor concentration (cerebellum) and from experiments in which specific binding was blocked by pretreatment with the drug (+)-butaclamol. Receptor constants were determined by fitting data from receptor-containing structures. Correcting the arterial plasma activities (the model driving function) for the presence of drug metabolites was found to be important in the modeling of these systems.

  5. Kinetic study on bonding reaction of gelatin with CdS nanopaticles by UV-visible spectroscopy.

    Science.gov (United States)

    Tang, Shihua; Wang, Baiyang; Li, Youqun

    2015-04-15

    The chemical kinetics on gelatin-CdS direct conjugates has been systematically investigated as a function of different temperature and reactant concentration (i.e. Cd(2+), S(2-) and gelatin) by UV-visible spectroscopy, for the first time. The nonlinear fitting and the differential method were used to calculate the initial rate based on the absorbance-time data. A double logarithmic linear equation for calculating the rate constant (k) and the reaction order (n) was introduced. The reaction kinetic parameters (n, k, Ea, and Z) and activation thermodynamic parameters (ΔG(≠), ΔH(≠), and ΔS(≠)) were obtained from variable temperature kinetic studies. The overall rate equation allowing evaluation of conditions that provide required reaction rate could be expressed as: r = 1.11 × 10(8) exp(-4971/T)[Cd(2+)][gelatin](0.6)[S(2-)](0.6) (M/S) The calculated values of the reaction rate are well coincide with the experimental results. A suitable kinetic model is also proposed. This work will provide guidance for the rational design of gelatin-directed syntheses of metal sulfide materials, and help to understand the biological effects of nanoparticles at the molecular level. Copyright © 2015 Elsevier B.V. All rights reserved.

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

    Science.gov (United States)

    McCarrick, Thomas A.; McLafferty, Fred W.

    1984-01-01

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

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

    Directory of Open Access Journals (Sweden)

    J. Koralewska

    2008-06-01

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

  8. Reaction and Aggregation Dynamics of Cell Surface Receptors

    Science.gov (United States)

    Wang, Michelle Dong

    This dissertation is composed of both theoretical and experimental studies of cell surface receptor reaction and aggregation. Project I studies the reaction rate enhancement due to surface diffusion of a bulk dissolved ligand with its membrane embedded target, using numerical calculations. The results show that the reaction rate enhancement is determined by ligand surface adsorption and desorption kinetic rates, surface and bulk diffusion coefficients, and geometry. In particular, we demonstrate that the ligand surface adsorption and desorption kinetic rates, rather than their ratio (the equilibrium constant), are important in rate enhancement. The second and third projects are studies of acetylcholine receptor clusters on cultured rat myotubes using fluorescence techniques after labeling the receptors with tetramethylrhodamine -alpha-bungarotoxin. The second project studies when and where the clusters form by making time-lapse movies. The movies are made from overlay of the pseudocolored total internal reflection fluorescence (TIRF) images of the cluster, and the schlieren images of the cell cultures. These movies are the first movies made using TIRF, and they clearly show the cluster formation from the myoblast fusion, the first appearance of clusters, and the eventual disappearance of clusters. The third project studies the fine structural features of individual clusters observed under TIRF. The features were characterized with six parameters by developing a novel fluorescence technique: spatial fluorescence autocorrelation. These parameters were then used to study the feature variations with age, and with treatments of drugs (oligomycin and carbachol). The results show little variation with age. However, drug treatment induced significant changes in some parameters. These changes were different for oligomycin and carbachol, which indicates that the two drugs may eliminate clusters through different mechanisms.

  9. Organotellurium ligands – designing and complexation reactions

    Indian Academy of Sciences (India)

    Unknown

    membered rings it is negative and ~30 ppm only. Keywords. Organotellurium ligands; hybrid telluroether; platinum metal complexes; tellurium-125 NMR. 1. Introduction. Tellurium is the noblest metalloid which may act as a Lewis acid as well as Lewis base. The ligand chemistry of tellurium, which acts as a 'soft' donor, was ...

  10. Heterogeneous reaction mechanisms and kinetics relevant to the CVD of semiconductor materials

    Energy Technology Data Exchange (ETDEWEB)

    Creighton, J.R.; Coltrin, M.E.

    1994-03-01

    This report documents the state of the art in experimental and theoretical techniques for determining reaction mechanisms and chemical kinetics of heterogeneous reactions relevant to the chemical vapor deposition of semiconductor materials. It summarizes the most common ultra-high vacuum experimental techniques that are used and the types of rate information available from each. Several case studies of specific chemical systems relevant to the microelectronics industry are described. Theoretical methods for calculating heterogeneous reaction rate constants are also summarized.

  11. Determining Li+-Coupled Redox Targeting Reaction Kinetics of Battery Materials with Scanning Electrochemical Microscopy.

    Science.gov (United States)

    Yan, Ruiting; Ghilane, Jalal; Phuah, Kia Chai; Pham Truong, Thuan Nguyen; Adams, Stefan; Randriamahazaka, Hyacinthe; Wang, Qing

    2018-02-01

    The redox targeting reaction of Li + -storage materials with redox mediators is the key process in redox flow lithium batteries, a promising technology for next-generation large-scale energy storage. The kinetics of the Li + -coupled heterogeneous charge transfer between the energy storage material and redox mediator dictates the performance of the device, while as a new type of charge transfer process it has been rarely studied. Here, scanning electrochemical microscopy (SECM) was employed for the first time to determine the interfacial charge transfer kinetics of LiFePO 4 /FePO 4 upon delithiation and lithiation by a pair of redox shuttle molecules FcBr 2 + and Fc. The effective rate constant k eff was determined to be around 3.70-6.57 × 10 -3 cm/s for the two-way pseudo-first-order reactions, which feature a linear dependence on the composition of LiFePO 4 , validating the kinetic process of interfacial charge transfer rather than bulk solid diffusion. In addition, in conjunction with chronoamperometry measurement, the SECM study disproves the conventional "shrinking-core" model for the delithiation of LiFePO 4 and presents an intriguing way of probing the phase boundary propagations induced by interfacial redox reactions. This study demonstrates a reliable method for the kinetics of redox targeting reactions, and the results provide useful guidance for the optimization of redox targeting systems for large-scale energy storage.

  12. Study of kinetics of reaction of lithium deuteride powder with O2, CO2 and water vapor

    International Nuclear Information System (INIS)

    Li Gan; Lu Guangda; Jing Wenyong; Qin Cheng

    2004-01-01

    The kinetics of reaction of lithium deuteride powder with O 2 , CO 2 and water vapor is studied. The experimental results show that lithium deuteride reacts with O 2 and CO 2 at very small reaction rate but with water vapor at comparatively larger rate at room temperature (≅28 degree C). The reaction process with water vapor could be described using the unreacted shrinking core model. The second-order kinetics is appropriate for the chemical reaction on the surface of lithium deuteride and reaction rate constant is 0.281 kPa -1 ·min -1

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

    Science.gov (United States)

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

    2016-01-01

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

  14. KINETIC MODELS STUDY OF HYDRODESULPHURIZATION VACUUM DISTILLATE REACTION

    Directory of Open Access Journals (Sweden)

    AbdulMunem A. Karim

    2013-05-01

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

  15. Kinetic Studies of Oxidative Coupling of Methane Reaction on Model Catalysts

    KAUST Repository

    Khan, Abdulaziz M.

    2016-01-01

    the process to be commercialized despite the fact that great number of attempts to prepare catalysts were conducted so that it can be economically viable. Due to these limitations, understanding the mechanism and kinetics of the reaction can be utilized

  16. Kinetics of the hydrogen production reaction in a copper-chlorine water splitting plant

    International Nuclear Information System (INIS)

    Zamfirescu, C.; Naterer, G.F.; Dincer, I.

    2009-01-01

    The exothermic reaction of HCl with particulate Cu occurs during hydrogen production step in the thermochemical copper-chlorine (Cu-Cl) water splitting cycle. In this paper, this chemical reaction is modeled kinetically, and a parametric study is performed to determine the influences of particle size, temperature and molar ratios on the reaction kinetics. It is determined that the residence time of copper particles varies between 10 and 100 s, depending on the operating conditions. The hydrogen conversion at equilibrium varies between 55 and 85%, depending on the reaction temperature. The heat flux at the particle surface, caused by the exothermic enthalpy of reaction, reaches about 3,000 W/m 2 when the particle shrinks to 0.1% from its initial size. A numerical algorithm is developed to solve the moving boundary Stefan problem with a chemical reaction. It predicts the shrinking of copper particles based on the hypothesis that the chemical reaction and heat transfer are decoupled. The model allows for estimation of the temperature of the copper particle, assumed spherical, in the radial direction. The maximum temperature at the interface is higher than the melting point of CuCl by 10-50 o C, depending on the assumed operating conditions. (author)

  17. Configuration of a pulse radiolysis system for the study of gas-phase reactions and kinetic investigations of the reactions of hydroxyl radicals with methyl and ethyl radicals

    International Nuclear Information System (INIS)

    Fagerstroem, K.

    1993-01-01

    The work that is presented in this thesis deals with the assembling and testing of a pulse radiolysis system for kinetic studies of gas-phase reactions as well as with the kinetics of the gas-phase reactions of hydroxyl radicals with methyl and ethyl radicals. These radicals are very important as these are formed at an early stage in hydrocarbon combustion processes. The two studied reactions are key reactions in those processes. (6 refs., 4 figs., 2 tabs.)

  18. Reaction kinetic analysis of reactor surveillance data

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-02-15

    In the reactor pressure vessel surveillance data of a European-type pressurized water reactor (low-Cu steel), it was found that the concentration of matrix defects was very high, and a large number of precipitates existed. In this study, defect structure evolution obtained from surveillance data was simulated by reaction kinetic analysis using 15 rate equations. The saturation of precipitation and the growth of loops were simulated, but it was not possible to explain the increase in DBTT on the basis of the defect structures. The sub-grain boundary segregation of solutes was discussed for the origin of the DBTT increase.

  19. Binding equilibrium and kinetics of membrane-anchored receptors and ligands in cell adhesion: Insights from computational model systems and theory

    Science.gov (United States)

    Weikl, Thomas R.; Hu, Jinglei; Xu, Guang-Kui; Lipowsky, Reinhard

    2016-01-01

    ABSTRACT The adhesion of cell membranes is mediated by the binding of membrane-anchored receptor and ligand proteins. In this article, we review recent results from simulations and theory that lead to novel insights on how the binding equilibrium and kinetics of these proteins is affected by the membranes and by the membrane anchoring and molecular properties of the proteins. Simulations and theory both indicate that the binding equilibrium constant K2D and the on- and off-rate constants of anchored receptors and ligands in their 2-dimensional (2D) membrane environment strongly depend on the membrane roughness from thermally excited shape fluctuations on nanoscales. Recent theory corroborated by simulations provides a general relation between K2D and the binding constant K3D of soluble variants of the receptors and ligands that lack the membrane anchors and are free to diffuse in 3 dimensions (3D). PMID:27294442

  20. Modelling and experimental evaluation of reaction kinetics in reactive extraction for chiral separation of amines, amino acids and amino-alcohols

    NARCIS (Netherlands)

    Steensma, M.; Kuipers, N.J.M.; de Haan, A.B.; Kwant, Gerard

    2007-01-01

    This paper reports on determination of the intrinsic reaction kinetics in reactive extraction of chiral compounds. It is important to know the mass transfer rates and reaction kinetics separately for a reliable scale-up. A kinetic model is developed to interpret the experimental data from the

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

    Science.gov (United States)

    Lundberg, Dan; Stjerndahl, Maria

    2011-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Magnien, V

    2005-12-15

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

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

    Directory of Open Access Journals (Sweden)

    JUN WANG

    2010-01-01

    Full Text Available As a primary by-product in biodiesel production, glycerol can be used to prepare an important fine chemical, epichlorohydrin, by the glycerol chlorination reaction. Although this process has been applied in industrial production, unfortunately, less attention has been paid to the analysis and separation of the compounds in the glycerol chlorination products. In this study, a convenient and accurate method to determine the products in glycerol chlorination reaction was established and based on the results the kinetic mechanism of the reaction was investigated. The structure of main products, including 1,3--dichloropropan-2-ol, 2,3-dichloropropan-1-ol, 3-chloro-1,2-propanediol, 2-chloro-1,3-propanediol and glycerol was ascertained by gas chromatography–mass spectrometry and the isomers of the products were distinguished. Apidic acid was considered as the best catalyst because of its excellent catalytic effect and high boiling point. The mechanism of the glycerol chlorination reaction was proposed and a new kinetic model was developed. Kinetic equations of the process in the experimental range were obtained by data fitting and the activation energies of each tandem reaction were 30.7, 41.8, 29.4 and 49.5 kJ mol-1, respectively. This study revealed the process and mechanism of the kinetics and provides the theoretical basis for engineering problems.

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

    Science.gov (United States)

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

    2014-10-05

    In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. Copyright © 2014 Wiley Periodicals, Inc.

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

    International Nuclear Information System (INIS)

    Tomin, Vladimir I.; Ushakou, Dzmitryi V.

    2015-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-15

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

  7. 1,2- and 1,3-dihydroxylated and hydroxynitrogenated monoterpenes as chiral ligands in the asymmetric reformatsky reaction

    International Nuclear Information System (INIS)

    Ribeiro, Carlos Magno R.; Morita, Cristina M.; Maia, Monica P.

    2008-01-01

    This study describes the use of three (-)-α-pinene derivatives, one diol-1,2 [(-)- (1R, 2R, 3S, 5R)-2,6,6-trimethylbicyclo[3.1.1]heptane-2,3-diol 4] and two pyridine-hydroxy derivatives [(+)-(1R,2S,3R,5S)-2,6,6- trimethyl-3-(2-pyridinylmethyl)bicyclo[3.1.1]heptane-3-ol 7 and (-)-(1R,2S,3R,5S)-2,6,6-trimethyl-3-[2-(2-pyridinyl) ethyl]bicyclo[3.1.1]heptane-3-ol 8]; one diol-1,3 [(-)-(1S,2R,5S)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 5] derived from (+)-isopulegol 2 and one diol-1,3 [(+)-(1R,2R,5R)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanol 6] derived from (+)-neoisopulegol 3, as ligands in the asymmetric Reformatsky reaction. The best enantiomeric excess of β-hydroxy ester obtained in the Reformatsky asymmetric reaction was 18% using ligand 6, and the chemical yield of the reactions was 65% on average. (author)

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

    NARCIS (Netherlands)

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

    2013-01-01

    Motivated by recent progress on the interplay between graph theory, dynamics, and systems theory, we revisit the analysis of chemical reaction networks described by mass action kinetics. For reaction networks possessing a thermodynamic equilibrium we derive a compact formulation exhibiting at the

  9. BGK-type models in strong reaction and kinetic chemical equilibrium regimes

    International Nuclear Information System (INIS)

    Monaco, R; Bianchi, M Pandolfi; Soares, A J

    2005-01-01

    A BGK-type procedure is applied to multi-component gases undergoing chemical reactions of bimolecular type. The relaxation process towards local Maxwellians, depending on mass and numerical densities of each species as well as common velocity and temperature, is investigated in two different cases with respect to chemical regimes. These cases are related to the strong reaction regime characterized by slow reactions, and to the kinetic chemical equilibrium regime where fast reactions take place. The consistency properties of both models are stated in detail. The trend to equilibrium is numerically tested and comparisons for the two regimes are performed within the hydrogen-air and carbon-oxygen reaction mechanism. In the spatial homogeneous case, it is also shown that the thermodynamical equilibrium of the models recovers satisfactorily the asymptotic equilibrium solutions to the reactive Euler equations

  10. Preparation, characterization, and kinetics of thermolysis of nickel and copper nitrate complexes with 2,2 Prime -bipyridine ligand

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Dinesh; Kapoor, I.P.S. [Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273 009 (India); Singh, Gurdip, E-mail: gsingh4us@yahoo.com [Department of Chemistry, DDU Gorakhpur University, Gorakhpur 273 009 (India); Froehlich, Roland [Institut fuer Organische Chemie, Universitaet Muenster, D-48149 Muenster (Germany)

    2012-10-10

    Graphical abstract: Nickel and copper nitrate complexes with 2,2 Prime -bipyridine, nitrate and water ligands have been prepared and characterized by single crystal X-ray diffraction, FT-IR and CHN analyses. Thermolysis was performed by using TG, DTA and ignition delay measurements. The kinetics of thermolysis were also evaluated. Highlights: Black-Right-Pointing-Pointer Preparation and characterization of Ni and Cu nitrate complexes have been reported. Black-Right-Pointing-Pointer Thermolysis has been carried out using TG-DTA and ignition delay measurements. Black-Right-Pointing-Pointer Their thermal decomposition pathways have been proposed. Black-Right-Pointing-Pointer Oxides residues as end product of thermolysis were revealed by XRD patterns. Black-Right-Pointing-Pointer Kinetics of their isothermal decomposition was evaluated. - Abstract: Nickel and copper nitrate complexes with 2,2 Prime -bipyridine (bipy) as a N donor and nitrate and water as oxygen donor ligands of the general formula [M(NO{sub 3})(C{sub 10}H{sub 8}N{sub 2})(H{sub 2}O){sub 3}](NO{sub 3}), where M = Ni and Cu, have been obtained from the corresponding metal nitrate salts. These complexes were characterized by X-ray crystallography, FT-IR, and CHN analysis. Both the complexes have been found to be six coordinated. Their thermal decomposition behaviour was investigated by TG, DTA, and ignition delay measurements. TG-DTA examinations of these complexes revealed multistep thermal decomposition. The corresponding metal oxide residues obtained after thermolysis were identified from their X-ray diffraction patterns (XRD). Kinetics of isothermal decomposition of the complexes was established from both the model-fitting as well as isoconversional methods.

  11. Kinetic aspects of the embedded clusters: Reaction - Rate Theory

    International Nuclear Information System (INIS)

    Despa, F.; Apostol, M.

    1995-07-01

    The main stages of the cluster growth process are reviewed using Reaction - Rate Theory. The precipitation stage is shown as a relaxation of the solute towards a cluster state characterized by a higher stability. The kinetic of the late stage of phase separation, the coarsening process, is analyzed by an off-centre diffusion mechanism. The theoretical results are compared to the experimental ones. (author). 37 refs, 6 figs

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

    Science.gov (United States)

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

    2012-01-01

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

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

    Science.gov (United States)

    Kocadağlı, Tolgahan; Gökmen, Vural

    2016-11-15

    The study describes the kinetics of the formation and degradation of α-dicarbonyl compounds in glucose/wheat flour system heated under low moisture conditions. Changes in the concentrations of glucose, fructose, individual free amino acids, lysine and arginine residues, glucosone, 1-deoxyglucosone, 3-deoxyglucosone, 3,4-dideoxyglucosone, 5-hydroxymethyl-2-furfural, glyoxal, methylglyoxal and diacetyl concentrations were determined to form a multiresponse kinetic model for isomerisation and degradation reactions of glucose. Degradation of Amadori product mainly produced 1-deoxyglucosone. Formation of 3-deoxyglucosone proceeded directly from glucose and also Amadori product degradation. Glyoxal formation was predominant from glucosone while methylglyoxal and diacetyl originated from 1-deoxyglucosone. Formation of 5-hydroxymethyl-2-furfural from fructose was found to be a key step. Multi-response kinetic modelling of Maillard reaction and caramelisation simultaneously indicated quantitatively predominant parallel and consecutive pathways and rate limiting steps by estimating the reaction rate constants. Copyright © 2016 Elsevier Ltd. All rights reserved.

  14. A study of butyl acetate synthesis. 4-reaction kinetics

    Directory of Open Access Journals (Sweden)

    Álvaro Orjuela Londoño

    2006-05-01

    Full Text Available This work was aimed at studying liquid-phase acetic acid and butyl alcohol esterification reaction (P atm =0.76 Bar,using an ion exchange resin (Lewatit K-2431 as catalyst. The effect of the absence of internal and external mass transport on catalyst particles was established in the research conditions used here. A set of assays to determine the effect of catalyst load (0.5%, 1%, 2% w/w temperature (73°C, 80°C, 87°C and molar ratio (1:2, 1:1, 2:1 acid/alcohol on reaction rate was carried out and both LHHW and pseudo-homogeneous kinetic expressions were obtained, these being in good agreement with the experimental data.

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

    Science.gov (United States)

    Yan, Yaw Kai; Subramaniam, R.

    2016-01-01

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

  16. Kinetic investigation of the chlorine reduction reaction on electrochemically oxidised ruthenium

    International Nuclear Information System (INIS)

    Thomassen, M.; Karlsen, C.; Borresen, B.; Tunold, R.

    2006-01-01

    The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm -3 and varying H + concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H + concentrations and that it can be satisfactorily described by the Erenburg mechanism, previously suggested for the chlorine evolution on RuO 2 and RTO. The expression of the kinetic current as a function of chlorine and H + concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential

  17. Bacillus anthracis o-succinylbenzoyl-CoA synthetase: reaction kinetics and a novel inhibitor mimicking its reaction intermediate.

    Science.gov (United States)

    Tian, Yang; Suk, Dae-Hwan; Cai, Feng; Crich, David; Mesecar, Andrew D

    2008-11-25

    o-Succinylbenzoyl-CoA (OSB-CoA) synthetase (EC 6.2.1.26) catalyzes the ATP-dependent condensation of o-succinylbenzoate (OSB) and CoA to form OSB-CoA, the fourth step of the menaquinone biosynthetic pathway in Bacillus anthracis. Gene knockout studies have highlighted this enzyme as a potential target for the discovery of new antibiotics. Here we report the first studies on the kinetic mechanism of B. anthracis OSB-CoA synthetase, classifying it as an ordered bi uni uni bi ping-pong mechanism. Through a series of pre-steady-state and steady-state kinetic studies in conjunction with direct binding studies, it is demonstrated that CoA, the last substrate to bind, strongly activates the first half-reaction after the first round of turnover. The activation of the first half-reaction is most likely achieved by CoA stabilizing conformations of the enzyme in the "F" form, which slowly isomerize back to the E form. Thus, the kinetic mechanism of OSB-CoA synthetase may be more accurately described as an ordered bi uni uni bi iso ping-pong mechanism. The substrate specificity of OSB-CoA synthetase was probed using a series of OSB analogues with alterations in the carboxylate groups. OSB-CoA shows a strong preference for OSB over all of the analogues tested as none were active except 4-[2-(trifluoromethyl)phenyl]-4-oxobutyric acid which exhibited a 100-fold decrease in k(cat)/K(m). On the basis of an understanding of OSB-CoA synthetase's kinetic mechanism and substrate specificity, a reaction intermediate analogue of OSB-AMP, 5'-O-{N-[2-(trifluoromethyl)phenyl]-4-oxobutyl}adenosine sulfonamide (TFMP-butyl-AMS), was designed and synthesized. This inhibitor was found to be an uncompetitive inhibitor to CoA and a mixed-type inhibitor to ATP and OSB with low micromolar inhibition constants. Collectively, these results should serve as an important forerunner to more detailed and extensive inhibitor design studies aimed at developing lead compounds against the OSB-CoA synthetase

  18. Dynamic Model of Basic Oxygen Steelmaking Process Based on Multizone Reaction Kinetics: Modeling of Decarburization

    Science.gov (United States)

    Rout, Bapin Kumar; Brooks, Geoffrey; Akbar Rhamdhani, M.; Li, Zushu; Schrama, Frank N. H.; Overbosch, Aart

    2018-03-01

    In a previous study by the authors (Rout et al. in Metall Mater Trans B 49:537-557, 2018), a dynamic model for the BOF, employing the concept of multizone kinetics was developed. In the current study, the kinetics of decarburization reaction is investigated. The jet impact and slag-metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburization such as residence time of metal drops in the emulsion, interfacial area evolution, initial size, and the effects of surface-active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass-transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effects of SiO2 and P2O5 in slag on the decarburization kinetics of a metal droplet in the emulsion. Further, a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag-metal emulsion. The model's prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data.

  19. Dynamic Model of Basic Oxygen Steelmaking Process Based on Multizone Reaction Kinetics: Modeling of Decarburization

    Science.gov (United States)

    Rout, Bapin Kumar; Brooks, Geoffrey; Akbar Rhamdhani, M.; Li, Zushu; Schrama, Frank N. H.; Overbosch, Aart

    2018-06-01

    In a previous study by the authors (Rout et al. in Metall Mater Trans B 49:537-557, 2018), a dynamic model for the BOF, employing the concept of multizone kinetics was developed. In the current study, the kinetics of decarburization reaction is investigated. The jet impact and slag-metal emulsion zones were identified to be primary zones for carbon oxidation. The dynamic parameters in the rate equation of decarburization such as residence time of metal drops in the emulsion, interfacial area evolution, initial size, and the effects of surface-active oxides have been included in the kinetic rate equation of the metal droplet. A modified mass-transfer coefficient based on the ideal Langmuir adsorption equilibrium has been proposed to take into account the surface blockage effects of SiO2 and P2O5 in slag on the decarburization kinetics of a metal droplet in the emulsion. Further, a size distribution function has been included in the rate equation to evaluate the effect of droplet size on reaction kinetics. The mathematical simulation indicates that decarburization of the droplet in the emulsion is a strong function of the initial size and residence time. A modified droplet generation rate proposed previously by the authors has been used to estimate the total decarburization rate by slag-metal emulsion. The model's prediction shows that about 76 pct of total carbon is removed by reactions in the emulsion, and the remaining is removed by reactions at the jet impact zone. The predicted bath carbon by the model has been found to be in good agreement with the industrially measured data.

  20. Kinetics of reactions of chromium, molybdenum and tungsten hexacarbonyls with hydroxylamine and trimethylamine oxide

    International Nuclear Information System (INIS)

    Maksakov, V.A.; Ershova, V.A.

    1994-01-01

    Mechanism of M(CO) 6 (M = Cr, Mo, W) reaction with hydroxylamine was studied. On the basis of kinetic data it was ascertained that as a result of the reaction CO oxidation to CO 2 and intramolecular transfer of amine formed to the central atom of metal occur. Mechanisms of M(CO) 6 reactions with hydroxylamine and trimethylamine oxide are compared

  1. Cerebral kinetics of the dopamine D{sub 2} receptor ligand [{sup 123}I]IBZM in mice

    Energy Technology Data Exchange (ETDEWEB)

    Meyer, Philipp T. [Department of Neurology, University Hospital Aachen, 52074 Aachen (Germany); Department of Nuclear Medicine, University Hospital Aachen, 52074 Aachen (Germany)], E-mail: pmeyer@ukaachen.de; Salber, Dagmar [C. and O. Vogt Institute of Brain Research, University Hospital Duesseldorf, 40225 Duesseldorf (Germany); Schiefer, Johannes [Department of Neurology, University Hospital Aachen, 52074 Aachen (Germany); Cremer, Markus [Institute of Neurosciences and Biophysics, Research Center Juelich, 52425 Juelich (Germany); Schaefer, Wolfgang M. [Department of Nuclear Medicine, University Hospital Aachen, 52074 Aachen (Germany); Kosinski, Christoph M. [Department of Neurology, University Hospital Aachen, 52074 Aachen (Germany); Langen, Karl-Josef [Institute of Neurosciences and Biophysics, Research Center Juelich, 52425 Juelich (Germany)

    2008-05-15

    Introduction: In vivo small animal imaging of the dopaminergic system is of great interest for basic and applied neurosciences, especially in transgenic mice. Small animal SPECT is particularly attractive because of its superior spatial resolution and tracer availability. We investigated the kinetics of the commercial dopamine D{sub 2} receptor (DZR) ligand [{sup 123}I]IBZM in mice as a prerequisite for an appropriate design of translational SPECT imaging between mice and humans. Methods: Cerebral kinetics of [{sup 123}I]IBZM under isoflurane anaesthesia were assessed by autoradiography in mice sacrificed at 30, 60, 120 and 200 min after iv injection. To explore the possible effects of isoflurane anaesthesia, an additional mice group was only anaesthetized for 20 min before being sacrificed at 140 min (putative time of single-scan SPECT analysis). Results: Maximum [{sup 123}I]IBZM uptake in the striatum (D{sub 2}R-rich; 10.5{+-}2.7 %ID/g) and cerebellum (D{sub 2}R-devoid; 2.4{+-}0.7 %ID/g) was observed at 30 min after injection. Thereafter, [{sup 123}I]IBZM uptake decreased slowly in striatum and rapidly in the cerebellum (200 min: 5.3{+-}1.9 and 0.4{+-}0.2 %ID/g, respectively). The striatum-to-cerebellum (S/C) [{sup 123}I]IBZM uptake ratio increased from 4.6{+-}1.2 at 30 min to 11.6{+-}2.6 at 120 min. The S/C ratio at 200 min was highly variable (17.8{+-}10.1), possibly indicating pseudo-equilibration in some animals. In mice, which were only anaesthetized between 120 and 140 min, a higher S/C ratio of 17.0{+-}5.1 was observed. Conclusions: The present study suggests that [{sup 123}I]IBZM is a suitable ligand for D{sub 2}R-SPECT in mice. Although a single-scan analysis may be a pragmatic semi-quantitative approach, tracer kinetic analyses on dynamic SPECT data should be pursued. The interfering effects of isoflurane anaesthesia need to be considered.

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

    KAUST Repository

    Hanson, Ronald K.; Pang, Genny A.; Chakraborty, Sreyashi; Ren, Wei; Wang, Shengkai; Davidson, David Frank

    2013-01-01

    We report a constrained-reaction-volume strategy for conducting kinetics experiments behind reflected shock waves, achieved in the present work by staged filling in a shock tube. Using hydrogen-oxygen ignition experiments as an example, we

  3. The Nanoconfined Free Radical Polymerization: Reaction Kinetics and Thermodynamics

    Science.gov (United States)

    Zhao, Haoyu; Simon, Sindee

    The reaction kinetics and thermodynamics of nanoconfined free radical polymerizations are investigated for methyl methacrylate (MMA) and ethyl methacrylate (EMA) monomers using differential scanning calorimetry. Controlled pore glass is used as the confinement medium with pore diameters as small as 7.5 nm; the influence of both hydrophobic (silanized such that trimethylsilyl groups cover the surface) and hydrophilic (native silanol) surfaces is investigated. Propagation rates increase when monomers are reacted in the hydrophilic pores presumably due to the specific interactions between the carbonyl and silanol groups; however, the more flexible EMA monomer shows weaker effects. On the other hand, initial rates of polymerization in hydrophobic pores are unchanged from the bulk. In both pores, the onset of autoacceleration occurs earlier due to the reduced diffusivity of confined chains, which may be compensated at high temperatures. In addition to changes in kinetics, the reaction thermodynamics can be affected under nanoconfinement. Specifically, the ceiling temperature (Tc) is shifted to lower temperatures in nanopores, with pore surface chemistry showing no significant effects; the equilibrium conversion is also reduced at high temperatures below Tc. These observations are attributed to a larger negative change in entropy on propagation for the confined system, with the MMA system again showing greater effects. Funding from ACS PRF is gratefully acknowledged.

  4. Determination of kinetic parameters of heterogeneous isotopic exchange reaction

    International Nuclear Information System (INIS)

    Huang, Ting-Chia; Tsai, Fuan-Nan

    1977-01-01

    A mathematical model has been proposed for a heterogeneous isotopic exchange reaction which involves film diffusion, surface chemical reaction and intraparticle diffusion. The exchange equation to predict the exchange fraction as a function of time for the spherical particles immersed in a solution of finite volume has been derived. The relations between the exchange fraction and dimensionless time are plotted with xi(=ak sub(f)/KD sub(e)), xi 1 (=K 1 a 2 /D sub(e)) and final fractional uptake as parameters. From the values of the kinetic parameters xi and xi 1 , the relative importance of each limiting step is discussed. Experimental results of the isotopic exchange reaction of calcium ion in both system CaCO 3 (s)/Ca 2+ (aq) and system calcium type resin Dowex 50W-X8/Ca 2+ (aq) are coincident with the theoretical equation proposed in this study. (auth.)

  5. Pressure-dependent kinetics of initial reactions in iso-octane pyrolysis.

    Science.gov (United States)

    Ning, HongBo; Gong, ChunMing; Li, ZeRong; Li, XiangYuan

    2015-05-07

    This study focuses on the studies of the main pressure-dependent reaction types of iso-octane (iso-C8H18) pyrolysis, including initial C-C bond fission of iso-octane, isomerization, and β-scission reactions of the alkyl radicals produced by the C-C bond fission of iso-octane. For the C-C bond fission of iso-octane, the minimum energy potentials are calculated at the CASPT2(2e,2o)/6-31+G(d,p)//CAS(2e,2o)/6-31+G(d,p) level of theory. For the isomerization and the β-scission reactions of the alkyl radicals, the optimization of the geometries and the vibrational frequencies of the reactants, transition states, and products are performed at the B3LYP/CBSB7 level, and their single point energies are calculated by using the composite CBS-QB3 method. Variable reaction coordinate transition state theory (VRC-TST) is used for the high-pressure limit rate constant calculation and Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) is used to calculate the pressure-dependent rate constants of these channels with pressure varying from 0.01-100 atm. The rate constants obtained in this work are in good agreement with those available from literatures. We have updated the rate constants and thermodynamic parameters for species involved in these reactions into a current chemical kinetic mechanism and also have improved the concentration profiles of main products such as C3H6 and C4H6 in the shock tube pyrolysis of iso-octane. The results of this study provide insight into the pyrolysis of iso-octane and will be helpful in the future development of branched paraffin kinetic mechanisms.

  6. Recoil implantation reactions in binary mixtures of catcher complexes and in mixed ligand catchers

    International Nuclear Information System (INIS)

    Sekine, Tsutomu; Sano, Masaaki; Yoshihara, Kenji

    1989-01-01

    Recoil implantation reactions were studied in binary mixtures of catcher complexes of tris(β-diketonato)metal(III) and in single-component catcher complexes of Cr(acac) n (dbm) 3-n where n=1 and 2. For the mixtures of M(acac) 3 and M(dbm) 3 , the products of 51 Cr(acac) 3 and 51 Cr(dbm) 3 were obtained as major components while 51 Cr(acac) 2 (dbm) and 51 Cr(acac)(dbm) 2 were seen as minor components. For the single component catcher complexes, predominant chemical species were parent retention type compounds. In addition to retentions there were product distributions which indicated a strong preference for acac pickup. The results were interpreted by a model which involves displacement reaction as a main process and ligand pickup reactions as side processes. (orig.)

  7. Pd-bound functionalized mesoporous silica as active catalyst for Suzuki coupling reaction: Effect of OAcˉ, PPh3 and Clˉ ligands on catalytic activity

    Science.gov (United States)

    Das, Trisha; Uyama, Hiroshi; Nandi, Mahasweta

    2018-04-01

    Three new palladium catalysts, PdCat-I, PdCat-II and PdCat-III, immobilized over heterogeneous silica support have been synthesized using different ligands attached to the palladium precursor. The ligands that have been used in this study are acetate, triphenylphosphine and chloride in PdCat-I, PdCat-II and PdCat-III, respectively. The ligands have different effect on stability of the compounds and impart different oxidation states to the metal center. The materials have been characterized by powder X-ray diffraction, nitrogen adsorption-desorption studies, transmission electron microscopy, thermal analysis, and different spectroscopic techniques. The Pd-content of the samples have been determined by ICP-AES analysis. The materials have been used as catalysts for Suzuki coupling reaction of aryl halides with phenylboronic acid under mild conditions. A comparative study has been carried out to ascertain the effect of the nature of different ligands on the outcome of the catalytic reactions. Products have been identified and estimated by 1H NMR and gas chromatography. The results show that the best yields are obtained with the catalyst containing triphenylphosphine as the ligand in methanol. Such type of work to study the effect of ligand on Suzuki coupling reaction over functionalized mesoporous silica heterogeneous catalysts have not been carried out so far.

  8. Kinetic studies on the reaction between dicyanocobinamide and hypochlorous acid.

    Directory of Open Access Journals (Sweden)

    Dhiman Maitra

    Full Text Available Hypochlorous acid (HOCl is a potent oxidant generated by myeloperoxidase (MPO, which is an abundant enzyme used for defense against microbes. We examined the potential role of HOCl in corrin ring destruction and subsequent formation of cyanogen chloride (CNCl from dicyanocobinamide ((CN2-Cbi. Stopped-flow analysis revealed that the reaction consists of at least three observable steps, including at least two sequential transient intermediates prior to corrin ring destruction. The first two steps were attributed to sequential replacement of the two cyanide ligands with hypochlorite, while the third step was the destruction of the corrin ring. The formation of (OCl(CN-Cbi and its conversion to (OCl2-Cbi was fitted to a first order rate equation with second order rate constants of 0.002 and 0.0002 µM(-1 s(-1, respectively. The significantly lower rate of the second step compared to the first suggests that the replacement of the first cyanide molecule by hypochlorite causes an alteration in the ligand trans effects changing the affinity and/or accessibility of Co toward hypochlorite. Plots of the apparent rate constants as a function of HOCl concentration for all the three steps were linear with Y-intercepts close to zero, indicating that HOCl binds in an irreversible one-step mechanism. Collectively, these results illustrate functional differences in the corrin ring environments toward binding of diatomic ligands.

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

    DEFF Research Database (Denmark)

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

    2007-01-01

    The reaction kinetics of the various species of mobile defects in irradiated materials are crucially dependent on the dimensionality of their migration. Sink strengths for one-dimensionally (1D) gliding interstitial loops undergoing occasional direction changes have been described analytically...

  10. Schiff base ligand

    Indian Academy of Sciences (India)

    Unknown

    Low-temperature stoichiometric Schiff base reaction in air in 3 : 1 mole ratio between benz- aldehyde and triethylenetetramine (trien) in methanol yields a novel tetraaza µ-bis(bidentate) acyclic ligand L. It was .... electrochemical work was performed as reported in ..... change in ligand shape through change in oxidation.

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

    International Nuclear Information System (INIS)

    Ang, Gaik Tin; Ooi, San Nee; Tan, Kok Tat; Lee, Keat Teong; Mohamed, Abdul Rahman

    2015-01-01

    Highlights: • Sea mango oil as feedstock for biodiesel via non-catalytic supercritical reaction. • Extracted sea mango oil with high FFA could produce high yield of FAME. • Employment of Response Surface Methodology for optimization of FAME. • Kinetic study for reversible transesterification and esterification reactions. - Abstract: Sea mango (Cerbera odollam) oil, which is rich in free fatty acids, was utilized to produce fatty acid methyl esters (FAME) via supercritical transesterification reaction. Sea mango oil was extracted from seeds and was subsequently reacted with methanol in a batch-type supercritical reactor. Response surface methodology (RSM) analysis was used to optimize important parameters, including reaction temperature, reaction time and the molar ratio of methanol to oil. The optimum conditions were found as 380 °C, 40 min and 45:1 mol/mol, respectively, to achieve 78% biodiesel content. The first kinetic modelling of FAME production from sea mango oil incorporating reversible transesterification and reversible esterification was verified simultaneously. The kinetic parameters, including reaction rate constants, k, the pre-exponential constant, A, and the activation energy, Ea, for transesterification and esterification were determined using an ordinary differential equation (ODE45) solver. The highest activation energy of 40 kJ/mol and the lowest reaction rate constant of 2.50 × 10 −5 dm 3 /mol s verified that the first stepwise reaction of TG to produce DG was the rate-limiting step

  12. Gas phase polymerization of propylene. Reaction kinetics and molecular weight distribution

    NARCIS (Netherlands)

    Meier, G.B.; Weickert, G.; van Swaaij, Willibrordus Petrus Maria

    2001-01-01

    Gas-phase polymerizations have been executed at different temperatures, pressures, and hydrogen concentrations using Me2Si[Ind]2ZrCl2 / methylaluminoxane / SiO2(Pennsylvania Quarts) as a catalyst. The reaction rate curves have been described by a kinetic model, which takes into account the initially

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

    KAUST Repository

    Hanson, Ronald K.

    2013-09-01

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

  14. The chemistry of separations ligand degradation by organic radical cations

    International Nuclear Information System (INIS)

    Mezyk, S.P.; Horne, G.P.; Mincher, B.J.; Zalupski, P.R.; Cook, A.R.; Wishart, J.F.

    2016-01-01

    Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R"."+), carbon-centered radicals (R".), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R"."+ as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

  15. Using a Multi-Tier Diagnostic Test to Explore the Nature of Students' Alternative Conceptions on Reaction Kinetics

    Science.gov (United States)

    Yan, Yaw Kai; Subramaniam, R.

    2018-01-01

    This study focused on grade 12 students' understanding of reaction kinetics. A 4-tier diagnostic instrument was developed for this purpose and administered to 137 students in the main study. Findings showed that reaction kinetics is a difficult topic for these students, with a total of 25 alternative conceptions (ACs) being uncovered. Except for…

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

    International Nuclear Information System (INIS)

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

    2014-01-01

    Scanning AC nano-calorimetry is a recently developed experimental technique capable of measuring the heat capacity of thin-film samples of a material over a wide range of temperatures and heating rates. Here, we describe how this technique can be used to study solid-gas phase reactions by measuring the change in heat capacity of a sample during reaction. We apply this approach to evaluate the oxidation kinetics of thin-film samples of zirconium in air. The results confirm parabolic oxidation kinetics with an activation energy of 0.59 ± 0.03 eV. The nano-calorimetry measurements were performed using a device that contains an array of micromachined nano-calorimeter sensors in an architecture designed for combinatorial studies. We demonstrate that the oxidation kinetics can be quantified using a single sample, thus enabling high-throughput mapping of the composition-dependence of the reaction rate.

  17. Presenting a new kinetic model for methanol to light olefins reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson mechanism

    Science.gov (United States)

    Javad Azarhoosh, Mohammad; Halladj, Rouein; Askari, Sima

    2017-10-01

    In this study, a new kinetic model for methanol to light olefins (MTO) reactions over a hierarchical SAPO-34 catalyst using the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism was presented and the kinetic parameters was obtained using a genetic algorithm (GA) and genetic programming (GP). Several kinetic models for the MTO reactions have been presented. However, due to the complexity of the reactions, most reactions are considered lumped and elementary, which cannot be deemed a completely accurate kinetic model of the process. Therefore, in this study, the LHHW mechanism is presented as kinetic models of MTO reactions. Because of the non-linearity of the kinetic models and existence of many local optimal points, evolutionary algorithms (GA and GP) are used in this study to estimate the kinetic parameters in the rate equations. Via the simultaneous connection of the code related to modelling the reactor and the GA and GP codes in the MATLAB R2013a software, optimization of the kinetic models parameters was performed such that the least difference between the results from the kinetic models and experiential results was obtained and the best kinetic parameters of MTO process reactions were achieved. A comparison of the results from the model with experiential results showed that the present model possesses good accuracy.

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

    Energy Technology Data Exchange (ETDEWEB)

    Magnien, V

    2005-12-15

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

  19. Kinetics based reaction optimization of enzyme catalyzed reduction of formaldehyde to methanol with synchronous cofactor regeneration.

    Science.gov (United States)

    Marpani, Fauziah; Sárossy, Zsuzsa; Pinelo, Manuel; Meyer, Anne S

    2017-12-01

    Enzymatic reduction of carbon dioxide (CO 2 ) to methanol (CH 3 OH) can be accomplished using a designed set-up of three oxidoreductases utilizing reduced pyridine nucleotide (NADH) as cofactor for the reducing equivalents electron supply. For this enzyme system to function efficiently a balanced regeneration of the reducing equivalents during reaction is required. Herein, we report the optimization of the enzymatic conversion of formaldehyde (CHOH) to CH 3 OH by alcohol dehydrogenase, the final step of the enzymatic redox reaction of CO 2 to CH 3 OH, with kinetically synchronous enzymatic cofactor regeneration using either glucose dehydrogenase (System I) or xylose dehydrogenase (System II). A mathematical model of the enzyme kinetics was employed to identify the best reaction set-up for attaining optimal cofactor recycling rate and enzyme utilization efficiency. Targeted process optimization experiments were conducted to verify the kinetically modeled results. Repetitive reaction cycles were shown to enhance the yield of CH 3 OH, increase the total turnover number (TTN) and the biocatalytic productivity rate (BPR) value for both system I and II whilst minimizing the exposure of the enzymes to high concentrations of CHOH. System II was found to be superior to System I with a yield of 8 mM CH 3 OH, a TTN of 160 and BPR of 24 μmol CH 3 OH/U · h during 6 hr of reaction. The study demonstrates that an optimal reaction set-up could be designed from rational kinetics modeling to maximize the yield of CH 3 OH, whilst simultaneously optimizing cofactor recycling and enzyme utilization efficiency. © 2017 Wiley Periodicals, Inc.

  20. Thermodynamic and Kinetic Response of Microbial Reactions to High CO2.

    Science.gov (United States)

    Jin, Qusheng; Kirk, Matthew F

    2016-01-01

    Geological carbon sequestration captures CO 2 from industrial sources and stores the CO 2 in subsurface reservoirs, a viable strategy for mitigating global climate change. In assessing the environmental impact of the strategy, a key question is how microbial reactions respond to the elevated CO 2 concentration. This study uses biogeochemical modeling to explore the influence of CO 2 on the thermodynamics and kinetics of common microbial reactions in subsurface environments, including syntrophic oxidation, iron reduction, sulfate reduction, and methanogenesis. The results show that increasing CO 2 levels decreases groundwater pH and modulates chemical speciation of weak acids in groundwater, which in turn affect microbial reactions in different ways and to different extents. Specifically, a thermodynamic analysis shows that increasing CO 2 partial pressure lowers the energy available from syntrophic oxidation and acetoclastic methanogenesis, but raises the available energy of microbial iron reduction, hydrogenotrophic sulfate reduction and methanogenesis. Kinetic modeling suggests that high CO 2 has the potential of inhibiting microbial sulfate reduction while promoting iron reduction. These results are consistent with the observations of previous laboratory and field studies, and highlight the complexity in microbiological responses to elevated CO 2 abundance, and the potential power of biogeochemical modeling in evaluating and quantifying these responses.

  1. Thermodynamic and kinetic response of microbial reactions to high CO2

    Directory of Open Access Journals (Sweden)

    Qusheng Jin

    2016-11-01

    Full Text Available Geological carbon sequestration captures CO2 from industrial sources and stores the CO2 in subsurface reservoirs, a viable strategy for mitigating global climate change. In assessing the environmental impact of the strategy, a key question is how microbial reactions respond to the elevated CO2 concentration. This study uses biogeochemical modeling to explore the influence of CO2 on the thermodynamics and kinetics of common microbial reactions in subsurface environments, including syntrophic oxidation, iron reduction, sulfate reduction, and methanogenesis. The results show that increasing CO2 levels decreases groundwater pH and modulates chemical speciation of weak acids in groundwater, which in turn affect microbial reactions in different ways and to different extents. Specifically, a thermodynamic analysis shows that increasing CO2 partial pressure lowers the energy available from syntrophic oxidation and acetoclastic methanogenesis, but raises the available energy of microbial iron reduction, hydrogenotrophic sulfate reduction and methanogenesis. Kinetic modeling suggests that high CO2 has the potential of inhibiting microbial sulfate reduction while promoting iron reduction. These results are consistent with the observations of previous laboratory and field studies, and highlight the complexity in microbiological responses to elevated CO2 abundance, and the potential power of biogeochemical modeling in evaluating and quantifying these responses.

  2. Bayesian inference of chemical kinetic models from proposed reactions

    KAUST Repository

    Galagali, Nikhil

    2015-02-01

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

  3. Can ligand addition to soil enhance Cd phytoextraction? A mechanistic model study.

    Science.gov (United States)

    Lin, Zhongbing; Schneider, André; Nguyen, Christophe; Sterckeman, Thibault

    2014-11-01

    Phytoextraction is a potential method for cleaning Cd-polluted soils. Ligand addition to soil is expected to enhance Cd phytoextraction. However, experimental results show that this addition has contradictory effects on plant Cd uptake. A mechanistic model simulating the reaction kinetics (adsorption on solid phase, complexation in solution), transport (convection, diffusion) and root absorption (symplastic, apoplastic) of Cd and its complexes in soil was developed. This was used to calculate plant Cd uptake with and without ligand addition in a great number of combinations of soil, ligand and plant characteristics, varying the parameters within defined domains. Ligand addition generally strongly reduced hydrated Cd (Cd(2+)) concentration in soil solution through Cd complexation. Dissociation of Cd complex ([Formula: see text]) could not compensate for this reduction, which greatly lowered Cd(2+) symplastic uptake by roots. The apoplastic uptake of [Formula: see text] was not sufficient to compensate for the decrease in symplastic uptake. This explained why in the majority of the cases, ligand addition resulted in the reduction of the simulated Cd phytoextraction. A few results showed an enhanced phytoextraction in very particular conditions (strong plant transpiration with high apoplastic Cd uptake capacity), but this enhancement was very limited, making chelant-enhanced phytoextraction poorly efficient for Cd.

  4. Kinetics of the reaction between H· and superheated water probed with muonium

    International Nuclear Information System (INIS)

    Alcorn, C.; Brodovitch, J.-C.; Ghandi, K.; Kennedy, A.; Percival, P.W.; Smith, M.

    2011-01-01

    Safe operation of a supercritical water cooled reactor requires knowledge of the reaction kinetics of transient species formed by the radiolysis of water in the temperature range 300-650"oC. By using a light isotope of the H·atom, it is possible to study its chemistry in water over this range of temperatures. Arguably, the most important reaction to study is that of the H·atom with the bulk solvent. This reaction could provide an in situ source of H_2 gas, which is added to CANDU reactors to suppress oxidative corrosion. The work described here concerns studies of the reaction of muonium with H_2O and D_2O at temperatures up to 450"oC.

  5. Electron and ligand transfer reactions between cyclometallated platinum(II) compounds and thallium(III) carboxylates

    NARCIS (Netherlands)

    Koten, G. van; Ploeg, A.F.M.J. van der; Vrieze, K.

    1982-01-01

    Reaction of trans-[(2-Me{2}NCH{2}C{6}H{4}{2}Pt}I{}I{] with Tl}I{}I{}I{(O{2}CR){3} (R = Me, i-Pr) gave direct elimination of Tl}I{(O{2}CR) and formation of the oxidative addition product [(2-Me{2}NCH{2}C{6}H{4}){2}Pt}I{}V{ (O{2}CR){2}], in two isomeric forms. A structure with the carbon ligands in

  6. Bacillus anthracis o-succinylbenzoyl-CoA synthetase: reaction kinetics and a novel inhibitor mimicking its reaction intermediate †

    Science.gov (United States)

    Tian, Yang; Suk, Dae-Hwan; Cai, Feng; Crich, David; Mesecar, Andrew D.

    2009-01-01

    O-succinylbenzoyl-CoA (OSB-CoA) synthetase (EC 6.2.1.26) catalyzes the ATP-dependent condensation of o-succinylbenzoate (OSB) and CoA to form OSB-CoA, the fourth step of the menaquinone biosynthetic pathway in Bacillus anthracis. Gene knockout studies have highlighted this enzyme as a potential target for the discovery of new antibiotics. Here we report the first studies on the kinetic mechanism of B. anthracis OSB-CoA synthetase, classifying it as an ordered Bi Uni Uni Bi ping-pong mechanism. Through a series of pre-steady-state and steady-state kinetic studies in conjunction with direct-binding studies, it is demonstrated that CoA, the last substrate to bind, strongly activates the first half-reaction after the first round of turnover. The activation of the first-half reaction is most likely achieved by CoA stabilizing conformations of the enzyme in the ‘F’ form, which slowly isomerize back to the E form. Thus, the kinetic mechanism of OSB-CoA synthetase may be more accurately described as an ordered Bi Uni Uni Bi Iso ping-pong mechanism. The substrate specificity of OSB-CoA synthetase was probed using a series of OSB analogs with alterations in the carboxylate groups. OSB-CoA shows a strong preference for OSB over all of the analogs tested as none were active except 4-(2-trifluoromethylphenyl)-4-oxobutyric acid which exhibited a 100-fold decrease in kcat/Km. Based on an understanding of OSB-CoA synthetase’s kinetic mechanism and substrate specificity, a reaction intermediate analog of OSB-AMP, 5’-O-(N-(2-trifluoromethylphenyl)-4-oxobutyl) adenosine sulfonamide (TFMP-butyl-AMS), was designed and synthesized. This inhibitor was found to be an uncompetitive inhibitor to CoA and a mixed-type inhibitor to ATP and OSB with low micromolar inhibition constants. Collectively, these results should serve as an important forerunner to more detailed and extensive inhibitor design studies aimed at developing lead compounds against the OSB-CoA synthetase class of

  7. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction

    Directory of Open Access Journals (Sweden)

    Cobbs Gary

    2012-08-01

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

  8. Stepwise kinetic equilibrium models of quantitative polymerase chain reaction.

    Science.gov (United States)

    Cobbs, Gary

    2012-08-16

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

  9. Kinetic study of the annealing reactions in Cu-Ni-Fe alloys

    International Nuclear Information System (INIS)

    Donoso, E.

    2014-01-01

    The thermal aging of a Cu-45Ni-4Fe, Cu-34Ni-11Fe and Cu-33Ni-22Fe alloys tempered from 1173 K have been studied from Differential Scanning Calorimetry (DSC) and microhardness measurements. The analysis of DSC curves, from room temperature to 950 K, shows the presence of one exothermic reaction associated to the formation of FeNi 3 phase nucleating from a modulate structure, and one endothermic peak attributed to dissolution of this phase. Kinetic parameters were obtained using the usual Avrami-Erofeev equation, modified Kissinger method and integrated kinetic functions. Microhardness measurements confirmed the formation and dissolution of the FeNi 3 phase. (Author)

  10. Kinetics and mechanism of the gas phase reaction of Cl atoms with iodobenzene

    DEFF Research Database (Denmark)

    Andersen, Mads Peter Sulbæk; Ponomarev, DA; Nielsen, OJ

    2001-01-01

    Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms with iodobenzene (C6H5I) in 20-700 Torr of N-2, air, or O-2 diluent at 296 K. The reaction proceeds with a rate constant k(Cl + QH(5)I) = (3.3 +/- 0.7) x 10(-11) cm(3) molecule(-1) s(-1) to give...

  11. Noise-Induced Modulation of the Relaxation Kinetics around a Non-Equilibrium Steady State of Non-Linear Chemical Reaction Networks

    OpenAIRE

    Ramaswamy, Rajesh; Sbalzarini, Ivo F; González-Segredo, Nélido

    2011-01-01

    Stochastic effects from correlated noise non-trivially modulate the kinetics of non-linear chemical reaction networks. This is especially important in systems where reactions are confined to small volumes and reactants are delivered in bursts. We characterise how the two noise sources confinement and burst modulate the relaxation kinetics of a non-linear reaction network around a non-equilibrium steady state. We find that the lifetimes of species change with burst input and confinement. Confi...

  12. Kinetic studies on the oxidation of oxyhemoglobin by biologically active iron thiosemicarbazone complexes: relevance to iron-chelator-induced methemoglobinemia.

    Science.gov (United States)

    Basha, Maram T; Rodríguez, Carlos; Richardson, Des R; Martínez, Manuel; Bernhardt, Paul V

    2014-03-01

    The oxidation of oxyhemoglobin to methemoglobin has been found to be facilitated by low molecular weight iron(III) thiosemicarbazone complexes. This deleterious reaction, which produces hemoglobin protein units unable to bind dioxygen and occurs during the administration of iron chelators such as the well-known 3-aminopyridine-2-pyridinecarbaldehyde thiosemicarbazone (3-AP; Triapine), has been observed in the reaction with Fe(III) complexes of some members of the 3-AP structurally-related thiosemicarbazone ligands derived from di-2-pyridyl ketone (HDpxxT series). We have studied the kinetics of this oxidation reaction in vitro using human hemoglobin and found that the reaction proceeds with two distinct time-resolved steps. These have been associated with sequential oxidation of the two different oxyheme cofactors in the α and β protein chains. Unexpected steric and hydrogen-bonding effects on the Fe(III) complexes appear to be the responsible for the observed differences in the reaction rate across the series of HDpxxT ligand complexes used in this study.

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

    International Nuclear Information System (INIS)

    Alves, Giselle M; Kremer, Gilberto M; Marques, Wilson Jr; Soares, Ana Jacinta

    2011-01-01

    The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solutions of the Boltzmann equations are determined through an expansion in Sonine polynomials up to the first order, using the Chapman–Enskog method, in a chemical regime for which the reaction process is close to its final equilibrium state. The non-equilibrium deviations are explicitly calculated for what concerns the thermal–diffusion ratio and coefficients of shear viscosity, diffusion and thermal conductivity. The theoretical and formal analysis developed in the present paper is complemented with some numerical simulations performed for different concentrations of reactants and products of the reaction as well as for both exothermic and endothermic chemical processes. The results reveal that chemical reactions without energy barrier can induce an appreciable influence on the transport properties of the mixture. Oppositely to the case of reactions with activation energy, the coefficients of shear viscosity and thermal conductivity become larger than those of an inert mixture when the reactions are exothermic. An application of the non-barrier model and its detailed transport picture are included in this paper, in order to investigate the dynamics of the local perturbations on the constituent number densities, and velocity and temperature of the whole mixture, induced by spontaneous internal fluctuations. It is shown that for the longitudinal disturbances there exist two hydrodynamic sound modes, one purely diffusive hydrodynamic mode and one kinetic mode

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

    Science.gov (United States)

    Alves, Giselle M.; Kremer, Gilberto M.; Marques, Wilson, Jr.; Jacinta Soares, Ana

    2011-03-01

    The kinetic model of the Boltzmann equation proposed in the work of Kremer and Soares 2009 for a binary mixture undergoing chemical reactions of symmetric type which occur without activation energy is revisited here, with the aim of investigating in detail the transport properties of the reactive mixture and the influence of the reaction process on the transport coefficients. Accordingly, the non-equilibrium solutions of the Boltzmann equations are determined through an expansion in Sonine polynomials up to the first order, using the Chapman-Enskog method, in a chemical regime for which the reaction process is close to its final equilibrium state. The non-equilibrium deviations are explicitly calculated for what concerns the thermal-diffusion ratio and coefficients of shear viscosity, diffusion and thermal conductivity. The theoretical and formal analysis developed in the present paper is complemented with some numerical simulations performed for different concentrations of reactants and products of the reaction as well as for both exothermic and endothermic chemical processes. The results reveal that chemical reactions without energy barrier can induce an appreciable influence on the transport properties of the mixture. Oppositely to the case of reactions with activation energy, the coefficients of shear viscosity and thermal conductivity become larger than those of an inert mixture when the reactions are exothermic. An application of the non-barrier model and its detailed transport picture are included in this paper, in order to investigate the dynamics of the local perturbations on the constituent number densities, and velocity and temperature of the whole mixture, induced by spontaneous internal fluctuations. It is shown that for the longitudinal disturbances there exist two hydrodynamic sound modes, one purely diffusive hydrodynamic mode and one kinetic mode.

  15. P-chiral 1-phosphanorbornenes: from asymmetric phospha-Diels-Alder reactions towards ligand design and functionalisation.

    Science.gov (United States)

    Möller, Tobias; Wonneberger, Peter; Sárosi, Menyhárt B; Coburger, Peter; Hey-Hawkins, Evamarie

    2016-02-07

    The principle of stereotopic face differentiation was successfully applied to 2H-phospholes which undergo a very efficient and highly stereoselective Diels-Alder reaction giving phosphorus-chiral 1-phosphanorbornenes with up to 87% yield. The observed reaction pathway has been supported by theoretical calculations showing that the cycloaddition reaction between 2H-phosphole 3a and the dienophile (5R)-(-)-menthyloxy-2(5H)-furanone (8) is of normal electron demand. Optically pure phosphanes were obtained by separation of the single diastereomers and subsequent desulfurisation of the sulfur-protected phosphorus atom. Finally, divergent ligand synthesis is feasible by reduction of the chiral auxiliary, subsequent stereospecific intramolecular Michael addition, and various functionalisations of the obtained key compound 13a. Furthermore, the unique structural properties of phospanorbornenes are presented and compared to those of phosphanorbornanes.

  16. Comparative study on ion-isotopic exchange reaction kinetics by application of tracer technique

    International Nuclear Information System (INIS)

    Lokhande, R.S.; Singare, P.U.

    2007-01-01

    The radioactive isotopes 131 I and 82 Br were used to trace the ion-isotopic exchange reactions using industrial grade ion exchange resins Amberlite IRA-400. The experiments were performed to understand the effect of temperature and concentration of ionic solution on kinetics of exchange reactions. Both the exchange reactions were greatly influenced by rise in temperature, which result in higher percentage of ions exchanged. For bromide ion-isotopic exchange reactions, the calculated values of specific reaction rate/min -1 , and amount of ions exchanged/mmol were obtained higher than that for iodide ion-isotopic exchange reactions under identical experimental conditions. The observed variation in the results for two ion-isotopic exchange reactions was due to the difference in the ionic size of bromide and iodide ions. (orig.)

  17. Pre-steady-state kinetics of Escherichia coli aspartate aminotransferase catalyzed reactions and thermodynamic aspects of its substrate specificity

    International Nuclear Information System (INIS)

    Kuramitsu, Seiki; Hiromi, Keitaro; Hayashi, Hideyuki; Morino, Yoshimasa; Kagamiyama, Hiroyuki

    1990-01-01

    The four half-transamination reactions [the pyridoxal form of Escherichia coli aspartate aminotransferase (AspAT) with aspartate or glutamate and the pyridoxamine form of the enzyme with oxalacetate or 2-oxoglutarate] were followed in a stopped-flow spectrometer by monitoring the absorbance change at either 333 or 358 nm. The reaction progress curves in all cases gave fits to a monophasic exponential process. Kinetic analyses of these reactions showed that each half-reaction is composed of the following three processes: (1) the rapid binding of an amino acid substrate to the pyridoxal form of the enzyme; (2) the rapid binding of the corresponding keto acid to the pyridoxamine form of the enzyme; (3) the rate-determining interconversion between the two complexes. This mechanism was supported by the findings that the equilibrium constants for half- and overall-transamination reactions and the steady-state kinetic constants agreed well with the predicted values on the basis of the above mechanism using pre-steady-state kinetic parameters. The significant primary kinetic isotope effect observed in the reaction with deuterated amino acid suggests that the withdrawal of the α-proton of the substrates is rate determining. The pyridoxal form of E. coli AspAT reacted with a variety of amino acids as substrates. The substrate specificity of the E. coli enzyme was much broader than that of pig isoenzymes, reflecting some subtle but distinct difference in microenvironment accommodating the side chain of the substrate between e. coli and mammalian AspATs

  18. Reaction kinetics of free fatty acids esterification in palm fatty acid distillate using coconut shell biochar sulfonated catalyst

    Science.gov (United States)

    Hidayat, Arif; Rochmadi, Wijaya, Karna; Budiman, Arief

    2015-12-01

    Recently, a new strategy of preparing novel carbon-based solid acids has been developed. In this research, the esterification reactions of Palm Fatty Acid Distillate (PFAD) with methanol, using coconut shell biochar sulfonated catalyst from biomass wastes as catalyst, were studied. In this study, the coconut shell biochar sulfonated catalysts were synthesized by sulfonating the coconut shell biochar using concentrated H2SO4. The kinetics of free fatty acid (FFA) esterification in PFAD using a coconut shell biochar sulfonated catalyst was also studied. The effects of the mass ratio of catalyst to oil (1-10%), the molar ratio of methanol to oil (6:1-12:1), and the reaction temperature (40-60°C) were studied for the conversion of PFAD to optimize the reaction conditions. The results showed that the optimal conditions were an methanol to PFAD molar ratio of 12:1, the amount of catalyst of 10%w, and reaction temperature of 60°C. The proposed kinetic model shows a reversible second order reaction and represents all the experimental data satisfactorily, providing deeper insight into the kinetics of the reaction.

  19. Kinetics of the reaction between H· and superheated water probed with muonium

    Energy Technology Data Exchange (ETDEWEB)

    Alcorn, C. [Mount Allison Univ., Sackville, NB (Canada); Brodovitch, J.-C. [Simon Fraser Univ., Burnaby, BC (Canada); Ghandi, K.; Kennedy, A. [Mount Allison Univ., Sackville, NB (Canada); Percival, P.W. [Simon Fraser Univ., Burnaby, BC (Canada); TRIUMF, Vancouver, BC (Canada); Smith, M. [Mount Allison Univ., Sackville, NB (Canada)

    2011-07-01

    Safe operation of a supercritical water cooled reactor requires knowledge of the reaction kinetics of transient species formed by the radiolysis of water in the temperature range 300-650{sup o}C. By using a light isotope of the H·atom, it is possible to study its chemistry in water over this range of temperatures. Arguably, the most important reaction to study is that of the H·atom with the bulk solvent. This reaction could provide an in situ source of H{sub 2} gas, which is added to CANDU reactors to suppress oxidative corrosion. The work described here concerns studies of the reaction of muonium with H{sub 2}O and D{sub 2}O at temperatures up to 450{sup o}C.

  20. Supramolecular architectures constructed using angular bipyridyl ligands

    International Nuclear Information System (INIS)

    Barnett, Sarah Ann

    2003-01-01

    This work details the synthesis and characterization of a series of coordination frameworks that are formed using bidentate angular N-donor ligands. Pyrimidine was reacted with metal(ll) nitrate salts. Reactions using Cd(NO 3 ) 2 receive particular focus and the analogous reactions using the linear ligand, pyrazine, were studied for comparison. In all cases, two-dimensional coordination networks were prepared. Structural diversity is observed for the Cd(ll) centres including metal-nitrate bridging. In contrast, first row transition metal nitrates form isostructural one-dimensional chains with only the bridging N-donor ligands generating polymeric propagation. The angular ligand, 2,4-bis(4-pyridyl)-1,3,5-triazine (dpt), was reacted with Cd(NO 3 ) 2 and Zn(NO 3 ) 2 . Whereas Zn(NO 3 ) 2 compounds exhibit solvent mediated polymorphism, a range of structures were obtained for the reactions with Cd(NO 3 ) 2 , including the first example of a doubly parallel interpenetrated 4.8 2 net. 4,7-phenanthroline, was reacted with various metal(ll) nitrates as well as cobalt(ll) and copper(ll) halides. The ability of 4,7-phenanthroline to act as both a N-donor ligand and a hydrogen bond acceptor has been discussed. Reactions of CuSCN with pyrimidine yield an unusual three-dimensional structure in which polymeric propagation is not a result of ligand bridging. The reaction of CuSCN with dpt yielded structural supramolecular isomers. (author)

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2008-02-08

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

  2. Study of kinetics and mechanism of diazo compound reactions using nuclear chemical polarization

    International Nuclear Information System (INIS)

    Gragerov, I.P.; Levit, A.F.; Kiprianova, L.A.; Buchachenko, A.L.; Sterleva, T.G.

    1975-01-01

    It has been established that at the rate-determining steps of the radical reactions in which aniline interacts with isoamyl nitrite and substituted diazo salts interact with sodium methylate, tertiary fatty amines, or phosphinic acid, no transfer of a single electron occurs. The processes of single electron transfer do not seem to play a decisive role in the kinetics of most transformations of diazo compounds. Chemical nuclear polarization is shown to be suitable for kinetic studies of fast radical processes

  3. Computation of restoration of ligand response in the random kinetics of a prostate cancer cell signaling pathway.

    Science.gov (United States)

    Dana, Saswati; Nakakuki, Takashi; Hatakeyama, Mariko; Kimura, Shuhei; Raha, Soumyendu

    2011-01-01

    Mutation and/or dysfunction of signaling proteins in the mitogen activated protein kinase (MAPK) signal transduction pathway are frequently observed in various kinds of human cancer. Consistent with this fact, in the present study, we experimentally observe that the epidermal growth factor (EGF) induced activation profile of MAP kinase signaling is not straightforward dose-dependent in the PC3 prostate cancer cells. To find out what parameters and reactions in the pathway are involved in this departure from the normal dose-dependency, a model-based pathway analysis is performed. The pathway is mathematically modeled with 28 rate equations yielding those many ordinary differential equations (ODE) with kinetic rate constants that have been reported to take random values in the existing literature. This has led to us treating the ODE model of the pathways kinetics as a random differential equations (RDE) system in which the parameters are random variables. We show that our RDE model captures the uncertainty in the kinetic rate constants as seen in the behavior of the experimental data and more importantly, upon simulation, exhibits the abnormal EGF dose-dependency of the activation profile of MAP kinase signaling in PC3 prostate cancer cells. The most likely set of values of the kinetic rate constants obtained from fitting the RDE model into the experimental data is then used in a direct transcription based dynamic optimization method for computing the changes needed in these kinetic rate constant values for the restoration of the normal EGF dose response. The last computation identifies the parameters, i.e., the kinetic rate constants in the RDE model, that are the most sensitive to the change in the EGF dose response behavior in the PC3 prostate cancer cells. The reactions in which these most sensitive parameters participate emerge as candidate drug targets on the signaling pathway. 2011 Elsevier Ireland Ltd. All rights reserved.

  4. Reaction of diazepam and related benzodiazepines with chlorine. Kinetics, transformation products and in-silico toxicological assessment.

    Science.gov (United States)

    Carpinteiro, Inmaculada; Rodil, Rosario; Quintana, José Benito; Cela, Rafael

    2017-09-01

    In this work, the reaction of four benzodiazepines (diazepam, oxazepam, nordazepam and temazepam) during water chlorination was studied by means of liquid chromatography-quadrupole-time of flight-mass spectrometry (LC-QTOF-MS). For those compounds that showed a significant degradation, i.e. diazepam, oxazepam and nordazepam, parameters affecting to the reaction kinetics (pH, chlorine and bromide level) were studied in detail and transformation products were tentatively identified. The oxidation reactions followed pseudofirst-order kinetics with rate constants in the range of 1.8-42.5 M -1  s -1 , 0.13-1.16 M -1  s -1 and 0.04-20.4 M -1  s -1 corresponding to half-life values in the range of 1.9-146 min, 1.8-87 h and 2.5-637 h for oxazepam, nordazepam and diazepam, respectively, depending of the levels of studied parameters. Chlorine and pH affected significantly the reaction kinetics, where an increase of the pH resulted into a decrease of the reaction rate, whereas higher chlorine dosages led to faster kinetics, as expected in this case. The transformation of the studied benzodiazepines occurs mainly at the 1,4-diazepine 7-membered-ring, resulting in ring opening to form benzophenone derivatives or the formation of a 6-membered pyrimidine ring, leading to quinazoline derivatives. The formation of these by-products was also tested in real surface water samples observing kinetics of oxazepam degradation slower in river than in creek water, while the degradation of the two other benzodiazepines occurred only in the simpler sample (creek water). Finally, the acute and chronical toxicity and mutagenicity of precursors and transformation products were estimated using quantitative structure-activity relationship (QSAR) software tools: Ecological Structure Activity Relationships (ECOSAR) and Toxicity Estimation Software Tool (TEST), finding that some transformation products could be more toxic/mutagenic than the precursor drug, but additional test would be needed

  5. The chemistry of separations ligand degradation by organic radical cations

    Energy Technology Data Exchange (ETDEWEB)

    Mezyk, S.P.; Horne, G.P. [California State University at Long Beach, Long Beach, CA 90840 (United States); Mincher, B.J.; Zalupski, P.R. [Idaho National Laboratory, Idaho Falls, ID 83415 (United States); Cook, A.R.; Wishart, J.F. [Chemistry Department, Brookhaven National Laboratory, New York, 11973 (United States)

    2016-07-01

    Solvent based extractions of used nuclear fuel use designer ligands in an organic phase extracting ligand complexed metal ions from an acidic aqueous phase. These extractions will be performed in highly radioactive environments, and the radiation chemistry of all these complexing agents and their diluents will play a major role in determining extraction efficiency, separation factors, and solvent-recycle longevity. Although there has been considerable effort in investigating ligand damage occurring in acidic water radiolysis conditions, only minimal fundamental kinetic and mechanistic data has been reported for the degradation of extraction ligands in the organic phase. Extraction solvent phases typically use normal alkanes such as dodecane, TPH, and kerosene as diluents. The radiolysis of such diluents produce a mixture of radical cations (R{sup .+}), carbon-centered radicals (R{sup .}), solvated electrons, and molecular products such as hydrogen. Typically, the radical species will preferentially react with the dissolved oxygen present to produce relatively inert peroxyl radicals. This isolates the alkane radical cation species, R{sup .+} as the major radiolytically-induced organic species that can react with, and degrade, extraction agents in this phase. Here we report on our recent studies of organic radical cation reactions with 2 ligands: CMPO and TODGA. Elucidating these parameters, and combining them with the known acidic aqueous phase chemistry, will allow a full, fundamental, understanding of the impact of radiation on solvent extraction based separation processes to be achieved. (authors)

  6. Aspartate aminotransferase: the kinetic barriers facing the covalent intermediates on the reaction pathway

    International Nuclear Information System (INIS)

    Kirsch, J.F.; Julin, D.A.; McLeish, M.; Wiesinger, H.

    1986-01-01

    The intermediates, aldimine (A), quinonoid (Q) and ketimine (K), along the transaminase reaction coordinate were probed by isotope transfer and solvent exchange kinetics. Less than 0.003% of 3 H is transferred from C/sub α/[ 3 H]-aspartate to pyridoxamine phosphate in the cytoplasmic aspartate aminotransferase (cAATase) reaction implying either that Q does not exist as a kinetically competent intermediate or that there is a rapid exchange of isotope with solvent. The ratio of the rate constants for C/sub α/ hydrogen exchange vs keto acid product formation (k/sub exge//k/sub prod/) are 2.5 and 0.5 for the reactions of cAATase with C/sub α/ [ 2 H]-aspartate and mitochondrial (m) AATase with C/sub α/[ 2 H]-glutamate respectively. The latter reaction was also probed from the α-keto-glutarate side with carbonyl 0-18 enriched keto acid. This experiment gave k/sub exge//k/sub prod/ = 1.0 for oxygen-18 exchange in α-ketoglutarate versus amino acid formation. The two exchange experiments with mAATase are interpreted in terms of a model in which the rate constant for diffusion of water from the active site is comparable with those for product forming steps

  7. Kinetic calorimetry in the study of the mechanism of low-temperature chemical reactions

    Science.gov (United States)

    Barkalov, I. M.; Kiryukhin, D. P.

    Chemical reactions are always followed by a change in the reacting system enthalpy, hence, calorimetry as a method of enthalpy and heat capacity measuring is a universal and, sometimes, even the only possible way of studying chemical reaction kinetics. Throughout its long history, the calorimeter, having preserved the positions of the main method of thermodynamic studies, has conquered a new field of application: that of kinetic study of chemical reactions. The advantages and disadvantages of the kinetic calorimeter are now obvious. First, the advantages are: (1) the possibility of measuring the rate of a chemical reaction without any special requirements being imposed on the reaction medium (solid, viscous, multicomponent systems); (2) the high efficiency: a large volume of kinetic information in one experiment and a non-destructive character of changes; (3) the possibility of measuring directly in the field of ionizing radiation (γ-radiation, accelerated electrons) and light; and (4) recording of the chemical conversion directly at the time of its occurrence. The disadvantages of this method are: (1) the high inertia of standard calorimeter systems (τC⋍102-103S), which restricts the possibilities of studying fast processes; and (2) the complexity of the correct organization of the calorimeter experiment when the parameters of the process are changed (overheating in the sample, conversion of the process to explosive and auto wave regimens). One of the oldest and most universal methods of studying the mechanism of chemical reactions, calorimetry, is now passing through a period of turbulent development due to the advances in electronics and computerization. The wide variety of types of calorimeter set-ups and the large assortment of measurement schemes in the currently described methods complicate the experimental selection of the necessary instrument rather than facilitate it. The basic principles of the method, the types of calorimeters, and the measuring

  8. Surface Reaction Kinetics of Ga(1-x)In(x)P Growth During Pulsed Chemical Beam Epitaxy

    National Research Council Canada - National Science Library

    Dietz, N; Beeler, S. C; Schmidt, J. W; Tran, H. T

    2000-01-01

    ... into the surface reaction kinetics during an organometallic deposition process. These insights will allow us to move the control point closer to the point where the growth occurs, which in a chemical been epitaxy process is a surface reaction layer (SRL...

  9. Using ground reaction force to predict knee kinetic asymmetry following anterior cruciate ligament reconstruction.

    Science.gov (United States)

    Dai, B; Butler, R J; Garrett, W E; Queen, R M

    2014-12-01

    Asymmetries in sagittal plane knee kinetics have been identified as a risk factor for anterior cruciate ligament (ACL) re-injury. Clinical tools are needed to identify the asymmetries. This study examined the relationships between knee kinetic asymmetries and ground reaction force (GRF) asymmetries during athletic tasks in adolescent patients following ACL reconstruction (ACL-R). Kinematic and GRF data were collected during a stop-jump task and a side-cutting task for 23 patients. Asymmetry indices between the surgical and non-surgical limbs were calculated for GRF and knee kinetic variables. For the stop-jump task, knee kinetics asymmetry indices were correlated with all GRF asymmetry indices (P kinetic asymmetry indices were correlated with the peak propulsion vertical GRF and vertical GRF impulse asymmetry indices (P kinetic asymmetries and therefore may assist in optimizing rehabilitation outcomes and minimizing re-injury rates. © 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  10. A Recyclable Cu-MOF-74 Catalyst for the Ligand-Free O-Arylation Reaction of 4-Nitrobenzaldehyde and Phenol.

    Science.gov (United States)

    Leo, Pedro; Orcajo, Gisela; Briones, David; Calleja, Guillermo; Sánchez-Sánchez, Manuel; Martínez, Fernando

    2017-06-16

    The activity and recyclability of Cu-MOF-74 as a catalyst was studied for the ligand-free C-O cross-coupling reaction of 4-nitrobenzaldehyde (NB) with phenol (Ph) to form 4-formyldiphenyl ether (FDE). Cu-MOF-74 is characterized by having unsaturated copper sites in a highly porous metal-organic framework. The influence of solvent, reaction temperature, NB/Ph ratio, catalyst concentration, and basic agent (type and concentration) were evaluated. High conversions were achieved at 120 °C, 5 mol % of catalyst, NB/Ph ratio of 1:2, DMF as solvent, and 1 equivalent of K₂CO₃ base. The activity of Cu-MOF-74 material was higher than other ligand-free copper catalytic systems tested in this study. This catalyst was easily separated and reused in five successive runs, achieving a remarkable performance without significant porous framework degradation. The leaching of copper species in the reaction medium was negligible. The O-arylation between NB and Ph took place only in the presence of Cu-MOF-74 material, being negligible without the solid catalyst. The catalytic advantages of using nanostructured Cu-MOF-74 catalyst were also proven.

  11. Kinetics of liquid lithium reaction with oxygen-nitrogen mixtures

    International Nuclear Information System (INIS)

    Gil, T.K.; Kazimi, M.S.

    1986-01-01

    A series of experiments have been conducted in order to characterize the kinetics of lithium chemical reaction with a mixture of oxygen and nitrogen. Three mixed gas compositions were used; 80% N 2 and 20% O 2 , 90% N 2 and 10% O 2 , and 95% N 2 and 5% O 2 . The reaction rate was obtained as a function of lithium temperature and the oxygen fraction. Liquid lithium temperature varied from 400 to 1100 0 C. By varying the composition, the degree of inhibition of the lithium-nitrogen reaction rate due to the presence of oxygen was observed. The results indicate that the lithium-nitrogen reaction rate depended on both the fraction of oxygen present and lithium temperature. The lithium nitride layer formed from the reaction also had a significant inhibition effect on the lithium-nitrogen reaction rate while the lithium-oxygen reaction rate was not as greatly hindered. LITFIRE, a computer code which simulates temperature and pressure history in a containment building following lithium spills, was modified by including (1) an improved model for the lithium-nitrogen reaction rate and (2) a model for the lithium-CO 2 reaction. LITFIRE was used to simulate HEDL's LC-2 and LA-5 experiments, and the predicted temperatures and pressures were in a reasonable agreement. Furthermore, LITFIRE was applied to a prototypical fusion reactor containment in order to simulate the consequences of a lithium spill accident. The result indicated that if nitrogen was used as containment building gas during the accident, the consequences of the accident would be less severe than those with air. The pressure rise in the building was found to be reduced by 50% and the maximum temperature of the combustion zone was limited to 900 0 C instead of 1200 0 C in the case of air

  12. A kinetic-theory approach for computing chemical-reaction rates in upper-atmosphere hypersonic flows.

    Science.gov (United States)

    Gallis, Michael A; Bond, Ryan B; Torczynski, John R

    2009-09-28

    Recently proposed molecular-level chemistry models that predict equilibrium and nonequilibrium reaction rates using only kinetic theory and fundamental molecular properties (i.e., no macroscopic reaction-rate information) are investigated for chemical reactions occurring in upper-atmosphere hypersonic flows. The new models are in good agreement with the measured Arrhenius rates for near-equilibrium conditions and with both measured rates and other theoretical models for far-from-equilibrium conditions. Additionally, the new models are applied to representative combustion and ionization reactions and are in good agreement with available measurements and theoretical models. Thus, molecular-level chemistry modeling provides an accurate method for predicting equilibrium and nonequilibrium chemical-reaction rates in gases.

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

    International Nuclear Information System (INIS)

    Bartling, Stephan; Meiwes-Broer, Karl-Heinz; Barke, Ingo; Pohl, Marga-Martina

    2015-01-01

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

  14. Thermodynamic and kinetic analysis of the reaction between biological catecholamines and chlorinated methylperoxy radicals

    Science.gov (United States)

    Dimić, Dušan S.; Milenković, Dejan A.; Marković, Jasmina M. Dimitrić; Marković, Zoran S.

    2018-05-01

    The antiradical potency of catecholamines (dopamine, epinephrine, norepinephrine, L-DOPA), metabolites of dopamine (homovanillic acid, 3-methoxytyramine and 3,4-dihydroxyphenylacetic acid) and catechol towards substituted methylperoxy radicals is investigated. The thermodynamic parameters, together with the kinetic approach, are used to determine the most probable mechanism of action. The natural bond orbital and quantum theory of atoms in molecules are utilised to explain the highest reactivity of trichloromethylperoxy radical. The preferred mechanism is dependent both on the thermodynamic and kinetic parameters . The number of chlorine atoms on radical, the presence of intra-molecular hydrogen bond and number of hydroxy groups attached to the aromatic ring significantly influence the mechanism. The results suggest that sequential proton loss electron transfer (SPLET) is the most probable for reaction with methylperoxy and hydrogen atom transfer (HAT) for reaction with trichloromethylperoxy radicals, with a gradual transition between SPLET and HAT for other two radicals. Due to the significant deprotonation of molecules containing the carboxyl group, the respective anions are also investigated. The HAT and SPLET mechanisms are highly competitive in reaction with MP radical, while the dominant mechanism towards chlorinated radicals is HAT. The reactions in methanol and benzene are also discussed.

  15. Quantitative modeling of the reaction/diffusion kinetics of two-chemistry photopolymers

    Science.gov (United States)

    Kowalski, Benjamin Andrew

    Optically driven diffusion in photopolymers is an appealing material platform for a broad range of applications, in which the recorded refractive index patterns serve either as images (e.g. data storage, display holography) or as optical elements (e.g. custom GRIN components, integrated optical devices). A quantitative understanding of the reaction/diffusion kinetics is difficult to obtain directly, but is nevertheless necessary in order to fully exploit the wide array of design freedoms in these materials. A general strategy for characterizing these kinetics is proposed, in which key processes are decoupled and independently measured. This strategy enables prediction of a material's potential refractive index change, solely on the basis of its chemical components. The degree to which a material does not reach this potential reveals the fraction of monomer that has participated in unwanted reactions, reducing spatial resolution and dynamic range. This approach is demonstrated for a model material similar to commercial media, achieving quantitative predictions of index response over three orders of exposure dose (~1 to ~103 mJ cm-2) and three orders of feature size (0.35 to 500 microns). The resulting insights enable guided, rational design of new material formulations with demonstrated performance improvement.

  16. Kinetics and Mechanism of the Reaction of Hydoxyl Radicals with Acetonitrile under Atmospheric Conditions

    Science.gov (United States)

    Hynes, A. J.; Wine, P. H.

    1997-01-01

    The pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to determine absolute rate coefficients for the reaction OH + CH3CN (1) and its isotopic variants, OH + CD3CN (2), OD + CH3CN (3), and OD + CD3CN (4). Reactions 1 and 2 were studied as a function of pressure and temperature in N2, N2/O2, and He buffer gases. In the absence of O2 all four reactions displayed well-behaved kinetics with exponential OH decays and pseudo-first rate constants which were proportional to substrate concentration. Data obtained in N2 over the range 50-700 Torr at 298 K are consistent with k(sub 1), showing a small pressure dependence. The Arrhenius expression obtained by averaging data at all pressures in k(sub 1)(T) = (1.1(sup +0.5)/(sub -0.3)) x 10(exp -12) exp[(-1130 +/- 90)/T] cu cm /(molecule s). The kinetics of reaction 2 are found to be pressure dependent with k(sub 2) (298 K) increasing from (1.21 +/- 0.12) x 10(exp -14) to (2.16 +/- 0.11) x 10(exp -14) cm(exp 3)/ (molecule s) over the pressure range 50-700 Torr of N2 at 298 K. Data at pressures greater than 600 Torr give k(sub 2)(T) = (9.4((sup +13.4)(sub -5.0))) x 10(exp -13) exp[(-1180 +/- 250)/T] cu cm/(molecule s). The rates of reactions 3 and 4 are found to be independent of pressure over the range 50-700 Torr of N2 with 298 K rate coefficient given by k(sub 3) =(3.18 +/- 0.40) x 10(exp -14) cu cm/(molecule s) and k(sub 4) = (2.25 +/-0.28) x 10(exp -14) cu cm/(molecule s). In the presence of O2 each reaction shows complex (non-pseudo-first-order) kinetic behavior and/or an apparent decrease in the observed rate constant with increasing [O2], indicating the presence of significant OH or OD regeneration. Observation of regeneration of OH in (2) and OD in (3) is indicative of a reaction channel which proceeds via addition followed by reaction of the adduct, or one of its decomposition products, with O2. The observed OH and OD decay profiles have been modeled by using a simple mechanistic

  17. alfa-Deuterium kinetic isotope effects in reactions of methyllithium. Is better aggregation the cause of lower reactivity?

    DEFF Research Database (Denmark)

    Holm, Torkil

    1996-01-01

    The value of kH/kD for alfa deuterium kinetic isotope effects for the reaction of methyllithium and methylmagnesium iodid with a series of substrates are consistently ca. 10-15 % higher for the lithium reagent. This may indicate a pre-equilibrium......The value of kH/kD for alfa deuterium kinetic isotope effects for the reaction of methyllithium and methylmagnesium iodid with a series of substrates are consistently ca. 10-15 % higher for the lithium reagent. This may indicate a pre-equilibrium...

  18. Cholesterol photo-oxidation: A chemical reaction network for kinetic modeling.

    Science.gov (United States)

    Barnaba, Carlo; Rodríguez-Estrada, Maria Teresa; Lercker, Giovanni; García, Hugo Sergio; Medina-Meza, Ilce Gabriela

    2016-12-01

    In this work we studied the effect of polyunsaturated fatty acids (PUFAs) methyl esters on cholesterol photo-induced oxidation. The oxidative routes were modeled with a chemical reaction network (CRN), which represents the first application of CRN to the oxidative degradation of a food-related lipid matrix. Docosahexaenoic acid (DHA, T-I), eicosapentaenoic acid (EPA, T-II) and a mixture of both (T-III) were added to cholesterol using hematoporphyrin as sensitizer, and were exposed to a fluorescent lamp for 48h. High amounts of Type I cholesterol oxidation products (COPs) were recovered (epimers 7α- and 7β-OH, 7-keto and 25-OH), as well as 5β,6β-epoxy. Fitting the experimental data with the CRN allowed characterizing the associated kinetics. DHA and EPA exerted different effects on the oxidative process. DHA showed a protective effect to 7-hydroxy derivatives, whereas EPA enhanced side-chain oxidation and 7β-OH kinetic rates. The mixture of PUFAs increased the kinetic rates several fold, particularly for 25-OH. With respect to the control, the formation of β-epoxy was reduced, suggesting potential inhibition in the presence of PUFAs. Copyright © 2016 Elsevier Inc. All rights reserved.

  19. Kinetics and mechanisms of the reactions of alkyl radicals with oxygen and with complexes of Co(III), Ru(III), and Ni(III)

    International Nuclear Information System (INIS)

    Kelley, D.

    1990-01-01

    The kinetics of the reactions of C 2 H 5 radical with Co(NH 3 ) 5 X 2+ , Ru(NH 3 ) 5 X 2+ , and Co(dmgH) 2 (X) (Y) (X = Br, Cl, N 3 , SCN; Y = H 2 O, CH 3 CN) complexes were studied using laser flash photolysis of ethylcobalt complexes. The kinetics were obtained by the kinetic probe method. Some relative rate constants were also determined by a competition method based on ethyl halide product ratios. The kinetics of colligation reactions of a series of alkyl radicals with β-Ni(cyclam) 2+ were studied using flaser flash photolysis of alkylcobalt complexes. Again, the kinetics were obtained by employing the kinetic probe competition method. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H 2 O 2+ were studied. Activation parameters were obtained for the unimolecular homolysis of C 2 H 5 Ni(cyclam)H 2 O 2+ . Kinetic and thermodynamic data obtained from these reactions were compared with those for the σ-bonded organometallic complexes. The kinetics of the unimolecular homolysis of a series of RNi(cyclam)H 2 O 2+ complexes were studied by monitoring the formation of the oxygen insertion product RO 2 Ni(cyclam)H 2 O 2+ . The higher rate constants for the reactions of alkyl radicals with oxygen in solution, as compared with those measured in the gas phase, were discussed. 30 refs

  20. Characterization and reaction studies of dimeric molybdenum(III) complexes with bridging dithiolate ligands. Catalytic reduction of acetylene to ethylene

    International Nuclear Information System (INIS)

    DuBois, M.R.; Haltiwanger, R.C.; Miller, D.J.; Glatzmaier, G.

    1979-01-01

    The complexes [C 5 H 5 MoSC/sub n/H/sub 2n/S] 2 (where n = 2 and 3) have been prepared by the reaction of ethylene sulfide and propylene sulfide, respectively, with C 5 H 5 MoH(CO) 3 or with [C 5 H 5 Mo(CO) 3 ] 2 . Cyclic voltammetry shows that each complex undergoes two reversible oxidations at 0.13 and 0.79 V vs. SCE (in acetonitrile with 0.1 M Bu 4 NBF 4 ). Both the one-electron and two-electron oxidation products have been synthesized and characterized by spectral and magnetic data. Electrochemical data for the oxidized complexes support the conclusion that the complexes have the same gross structural features in all three oxidation states. A single crystal of the monocation [C 5 H 5 MoSC 3 H 6 S] 2 BF 4 has been characterized by an x-ray diffraction study. The compound crystallizes in the space group C2/c with a = 18.266 (1) A, b = 9.206 (4) A, c = 12.911 (5) A, β = 100.83 (3) 0 , and V = 2128 A 3 . The metal ions of the cation are bridged by two 1,2-propanedithiolate ligands. The four sulfur atoms of these ligands form a plane which bisects the metal-metal distance. The neutral dimeric complexes undergo a unique reaction with alkenes and alkynes in which the hydrocarbon portion of the bridging dithiolate ligands is exchanged. The reaction has been characterized with olefinswith both electron-withdrawing and electron-donating substituents. When [C 5 H 5 MoSC 2 H 4 S] 2 (1) is reacted with acetylene at 25 0 C, ethene is produced and the complex [C 5 H 5 MoSC 2 H 2 S] 2 is isolated. The latter complex is reduced by hydrogen (2 atm) at 60 0 C to re-form 1. The utility of these reactions in the catalytic reduction of acetylene to ethylene has been investigated. The role of the sulfur ligands in this catalytic cycle is discussed. 50 references, 2 figures, 5 tables

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

    International Nuclear Information System (INIS)

    Adda, Y.

    1955-06-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

    Slavov, Chavdar Lyubomirov

    2009-07-09

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

  3. Kinetic isotope effect in the reaction of dehydration of fructose into 5-hydroxymethylfurfural

    International Nuclear Information System (INIS)

    Grin', S.A.; Tsimbaliev, S.R.; Gel'fand, S.Yu.

    1993-01-01

    Kinetic isotopic effect in the reaction of fructose dehydration into 5- hydroxymethylfurfural was determined. The results suggest hydrogen participation in the limiting stage of the process. The assumption that proton addition to 4, 5, 6 -trihydroxy - 2- on - hexal is the limiting stage is made

  4. The renneting of milk : a kinetic study of the enzymic and aggregation reactions

    NARCIS (Netherlands)

    Hooydonk, van A.C.M.

    1987-01-01

    The rennet-induced clotting of milk was studied under various conditions. The kinetics of the enzymic and aggregation reactions was analysed separately and, where possible, related to the physico-chemical properties of the casein micelle and its environment.

    The effects of important

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

    DEFF Research Database (Denmark)

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

    2009-01-01

    In this paper we have used a proposed mathematical model, describing the carbon-carbon bond format ion reaction between beta-hydroxypyruvate and glycolaldehyde to synthesise L-erythrulose, catalysed by the enzyme transketolase, for the analysis of the sensitivity of the process to its kinetic...

  6. General theory of the multistage geminate reactions of the isolated pairs of reactants. II. Detailed balance and universal asymptotes of kinetics.

    Science.gov (United States)

    Kipriyanov, Alexey A; Doktorov, Alexander B

    2014-10-14

    The analysis of general (matrix) kinetic equations for the mean survival probabilities of any of the species in a sample (or mean concentrations) has been made for a wide class of the multistage geminate reactions of the isolated pairs. These kinetic equations (obtained in the frame of the kinetic approach based on the concept of "effective" particles in Paper I) take into account various possible elementary reactions (stages of a multistage reaction) excluding monomolecular, but including physical and chemical processes of the change in internal quantum states carried out with the isolated pairs of reactants (or isolated reactants). The general basic principles of total and detailed balance have been established. The behavior of the reacting system has been considered on macroscopic time scales, and the universal long-term kinetics has been determined.

  7. Reaction kinetics in open reactors and serial transfers between closed reactors

    Science.gov (United States)

    Blokhuis, Alex; Lacoste, David; Gaspard, Pierre

    2018-04-01

    Kinetic theory and thermodynamics of reaction networks are extended to the out-of-equilibrium dynamics of continuous-flow stirred tank reactors (CSTR) and serial transfers. On the basis of their stoichiometry matrix, the conservation laws and the cycles of the network are determined for both dynamics. It is shown that the CSTR and serial transfer dynamics are equivalent in the limit where the time interval between the transfers tends to zero proportionally to the ratio of the fractions of fresh to transferred solutions. These results are illustrated with a finite cross-catalytic reaction network and an infinite reaction network describing mass exchange between polymers. Serial transfer dynamics is typically used in molecular evolution experiments in the context of research on the origins of life. The present study is shedding a new light on the role played by serial transfer parameters in these experiments.

  8. The influence of gas–solid reaction kinetics in models of thermochemical heat storage under monotonic and cyclic loading

    International Nuclear Information System (INIS)

    Nagel, T.; Shao, H.; Roßkopf, C.; Linder, M.; Wörner, A.; Kolditz, O.

    2014-01-01

    Highlights: • Detailed analysis of cyclic and monotonic loading of thermochemical heat stores. • Fully coupled reactive heat and mass transport. • Reaction kinetics can be simplified in systems limited by heat transport. • Operating lines valid during monotonic and cyclic loading. • Local integral degree of conversion to capture heterogeneous material usage. - Abstract: Thermochemical reactions can be employed in heat storage devices. The choice of suitable reactive material pairs involves a thorough kinetic characterisation by, e.g., extensive thermogravimetric measurements. Before testing a material on a reactor level, simulations with models based on the Theory of Porous Media can be used to establish its suitability. The extent to which the accuracy of the kinetic model influences the results of such simulations is unknown yet fundamental to the validity of simulations based on chemical models of differing complexity. In this article we therefore compared simulation results on the reactor level based on an advanced kinetic characterisation of a calcium oxide/hydroxide system to those obtained by a simplified kinetic model. Since energy storage is often used for short term load buffering, the internal reactor behaviour is analysed under cyclic partial loading and unloading in addition to full monotonic charge/discharge operation. It was found that the predictions by both models were very similar qualitatively and quantitatively in terms of thermal power characteristics, conversion profiles, temperature output, reaction duration and pumping powers. Major differences were, however, observed for the reaction rate profiles themselves. We conclude that for systems not limited by kinetics the simplified model seems sufficient to estimate the reactor behaviour. The degree of material usage within the reactor was further shown to strongly vary under cyclic loading conditions and should be considered when designing systems for certain operating regimes

  9. HYDROBIOGEOCHEM: A coupled model of HYDROlogic transport and mixed BIOGEOCHEMical kinetic/equilibrium reactions in saturated-unsaturated media

    Energy Technology Data Exchange (ETDEWEB)

    Yeh, G.T.; Salvage, K.M. [Pennsylvania State Univ., University Park, PA (United States). Dept. of Civil and Environmental Engineering; Gwo, J.P. [Oak Ridge National Lab., TN (United States); Zachara, J.M.; Szecsody, J.E. [Pacific Northwest National Lab., Richland, WA (United States)

    1998-07-01

    The computer program HYDROBIOGEOCHEM is a coupled model of HYDROlogic transport and BIOGEOCHEMical kinetic and/or equilibrium reactions in saturated/unsaturated media. HYDROBIOGEOCHEM iteratively solves the two-dimensional transport equations and the ordinary differential and algebraic equations of mixed biogeochemical reactions. The transport equations are solved for all aqueous chemical components and kinetically controlled aqueous species. HYDROBIOGEOCHEM is designed for generic application to reactive transport problems affected by both microbiological and geochemical reactions in subsurface media. Input to the program includes the geometry of the system, the spatial distribution of finite elements and nodes, the properties of the media, the potential chemical and microbial reactions, and the initial and boundary conditions. Output includes the spatial distribution of chemical and microbial concentrations as a function of time and space, and the chemical speciation at user-specified nodes.

  10. Neutral bidentate N-heterocyclic ligands - phase transfer reagents improving the kinetics of solvent extraction of Am(III) and Eu(III) ions with tetradentate 6,6'-bis-(diethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine

    International Nuclear Information System (INIS)

    Narbutt, J.; Krejzler, J.

    2008-01-01

    Poor kinetics of solvent extraction of Am(III) and Eu(III) ions from 1 M HNO 3 with 6,6'-bis-(diethyl-1,2,4-triazin-3-yl)-2,2'-bipyridine (etBTBP) has been improved by adding an auxiliary bidentate N-heterocyclic ligand to the extraction system. Two such ligands were studied, derivatives of bis-triazine and pyridine-triazine, which alone poorly extract the metal ions, but together with etBTBP they act as phase transfer reagents, improving the extraction kinetics to a different degree. The ability to transfer the metal ions from aqueous to organic phase depends on lipophilicity and acid/base properties of these auxiliary ligands, as well as on the mode of shaking the two liquid phases - gentle or vigorous. (orig.)

  11. THEORETICAL RESEARCH ON THE MULTI-CHANNEL REACTION MECHANISM AND KINETICS OF HNCS WITH OH-

    Directory of Open Access Journals (Sweden)

    Li-Jie Hou

    Full Text Available We presented a theoretical study on the detailed reaction mechanism and kinetics of the HNCS molecule with the OH-. The barrierless minimum energy path and the most favorable entrance channel have been determined by study the thermodynamic and kinetic characters of the channel with low energy barrier. The B3LYP/6-311++G** method was employed for all the geometrical optimizations and a multi-level extrapolation method based on the G3 energies was employed for further energy refinements. In addition, the analysis of the combining interaction between hydroxide ion and HNCS was performed by natural bond orbitals (NBO analysis. The calculation results indicated that the reaction of OH- with HNCS had four channels, and the channel of H-atom in HNCS direct extraction to OH- (OH-+HNCS→IM1→TS3→IM4→P2(SCN- +H2O in singlet state was the main channel with the low potential energy and high equilibrium constant and reaction rate constant. SCN- and H2O were main products.

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

    International Nuclear Information System (INIS)

    Feron, G.

    1963-09-01

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

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

    International Nuclear Information System (INIS)

    Jorge, Nelly Lidia; Romero, Jorge Marcelo; Grand, André; Hernández-Laguna, Alfonso

    2012-01-01

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

  14. Study on the kinetics of gel formation in the radiation crosslinking reaction

    International Nuclear Information System (INIS)

    Wang Mingjun; Liu Yuming

    1988-01-01

    From the kinetic equation of gel formation obtained by the authors, the mechanism of gel formation may be interpreted clearly as follows: (1) When the degree of crosslinking q g , the system is sol and the crosslinking reaction is only carried out between the sol molecules. (q g is the gel point). (2) When q=q g , there exists a beginning point where the gel is coexisted with the sol, and the system is still sol, and the crosslinking reaction is still carried out between the sol molecules. (3) When q>q g , the crosslinking reaction exceeds the gel point and the gel is coexisted with the sol. The kinetic equation shows clearly that the transformation from sol into gel is caused by crosslinking reaction of the uncrosslinked chain units between the sol and gel molecules. As a result the sol molecules are transformed into the gel molecules gradually, and the sol fraction is reduced. When the chain units P-barw(s)S(1-s)dq in sol are crosslinked with gel, the sol fraction in the system is reduced ds (where P-barw(s) is a function of the radiation dose and s is sol frection). The degree of crosslinking per unit dose (q 0 ) is a reduced function of dose (R). The equation for calculating its value for every irradiation dose is obtained. After knowing the correlation between P-bar W(s) vs R and q 0 vs R, the distribution of gel and sol in the process of radiation crosslinking can be discussed as well

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

    International Nuclear Information System (INIS)

    Korsse, J.

    1983-01-01

    The reactivity of the hydrated electron towards metal complexes is considered. Experiments are described involving metal EDTA and similar complexes. The metal ions studied are mainly Ni 2+ , Co 2+ and Cu 2+ . Rates of the reactions of the complexes with e - (aq) were measured using the pulse radiolysis technique. It is shown that the reactions of e - (aq) with the copper complexes display unusually small kinetic salt effects. The results suggest long-range electron transfer by tunneling. A tunneling model is presented and the experimental results are discussed in terms of this model. Results of approximate molecular orbital calculations of some redox potentials are given, for EDTA chelates as well as for series of hexacyano and hexaquo complexes. Finally, equilibrium constants for the formation of ternary complexes are reported. (Auth./G.J.P.)

  16. REACTION KINETICS SELF-PROPOGATION REGIME DURING PRE-IGNITION PERIOD

    Directory of Open Access Journals (Sweden)

    D. D. Polishchuk

    2015-11-01

    Full Text Available Self-propagation high temperature synthesis (SHS technological regulations application is mainly limited by transformation processes taking place in the pre-ignition period. Zn-S, Zn-Se, Ti-C and 3Ni-Al small sample systems ignition experimental study was carried out under heating conditions in inert atmosphere with temperature values T = 1200K.It was shown that at this temperature level a chemical reaction can be initiated, turning into a self-sustaining mode. Wherein the reaction limiting factors can be mass transfer processes. Ignition temperatures were determined and plotted via the samples size. A physical ignition model was developed assuming the pre-ignition period limiting reaction Arrhenius law.The inverse combustion problem solution made it possible to calculate the low-temperature (T = 800 ÷ 1200K reaction kinetic constant values. Comparison thus obtained values  with the known data of other researchers showed their good agreement.Activation energy values for the Zn-S system were used to calculate the heat wave propagation speed. This value appeared to coincide with experimental values.Obtained results analysis leads to the conclusion about the availability and justification for the proposed method of express-analysis of presupposed, but previously not studied SHS systems. The results thus obtained allow us to estimate conditions for the SHS technology implementation, the reactor characteristic sizes and the thermal wave’s propagation speed.

  17. Essential role of conformational selection in ligand binding.

    Science.gov (United States)

    Vogt, Austin D; Pozzi, Nicola; Chen, Zhiwei; Di Cera, Enrico

    2014-02-01

    Two competing and mutually exclusive mechanisms of ligand recognition - conformational selection and induced fit - have dominated our interpretation of ligand binding in biological macromolecules for almost six decades. Conformational selection posits the pre-existence of multiple conformations of the macromolecule from which the ligand selects the optimal one. Induced fit, on the other hand, postulates the existence of conformational rearrangements of the original conformation into an optimal one that are induced by binding of the ligand. In the former case, conformational transitions precede the binding event; in the latter, conformational changes follow the binding step. Kineticists have used a facile criterion to distinguish between the two mechanisms based on the dependence of the rate of relaxation to equilibrium, kobs, on the ligand concentration, [L]. A value of kobs decreasing hyperbolically with [L] has been seen as diagnostic of conformational selection, while a value of kobs increasing hyperbolically with [L] has been considered diagnostic of induced fit. However, this simple conclusion is only valid under the rather unrealistic assumption of conformational transitions being much slower than binding and dissociation events. In general, induced fit only produces values of kobs that increase with [L] but conformational selection is more versatile and is associated with values of kobs that increase with, decrease with or are independent of [L]. The richer repertoire of kinetic properties of conformational selection applies to kinetic mechanisms with single or multiple saturable relaxations and explains the behavior of nearly all experimental systems reported in the literature thus far. Conformational selection is always sufficient and often necessary to account for the relaxation kinetics of ligand binding to a biological macromolecule and is therefore an essential component of any binding mechanism. On the other hand, induced fit is never necessary and

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-10-05

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

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

    Directory of Open Access Journals (Sweden)

    Marwa Saied Shalaby

    2015-03-01

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

  20. Simplification of lipase design in the enzymatic kinetic resolution of amines by saturation transfer difference NMR

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Marcio S.; Pietrobom, Daniel, E-mail: s.marcio@ufabc.edu.br [Universidade Federal do ABC (CCNH/UFABC), Santo André, SP (Brazil). Centro de Ciências Naturais e Humanas

    2016-07-01

    In this work, we demonstrate a nuclear magnetic resonance (NMR) method for racemic amide and lipase interaction as a first-pass design method in the enzymatic kinetic resolution of amines. As a novel adaptation of commonly used protein-ligand screening NMR methodologies, this approach relies upon a lipase-amide interaction wherein the time-consuming is reduced drastically and new insights are produced during the development of biocatalysis reactions. (author)

  1. Hydrolysis reaction of 2,4-dichlorophenoxyacetic acid. A kinetic and computational study

    Science.gov (United States)

    Romero, Jorge Marcelo; Jorge, Nelly Lidia; Grand, André; Hernández-Laguna, Alfonso

    2015-10-01

    The degradation of the 2,4-dichlorophenoxyacetic acid in aqueous solution is an hydrolysis reaction. Two products are identified: 2,4-dichlorophenol and glycolic acid. Reaction is investigated as a function of pH and temperature, and it is first-order kinetics and pH-dependent. Reaction is modeled in gas phase, where a proton catalyses the reaction. Critical points of PES are calculated at B3LYP/6-311++G(3df,2p), and aug-cc-pvqz//6-311++G(3df,2p) levels plus ZPE at 6-311++G(3df,2p) level. The activation barrier is 21.2 kcal/mol. Theoretical results agree with the experimental results. A second mechanism related with a Cl2Phsbnd Osbnd CH2sbnd COOH⋯H2O complex is found, but with a rate limiting step of 38.4 kcal/mol.

  2. The kinetics of lanthanide complexation by EDTA and DTPA in lactate media.

    Science.gov (United States)

    Nash, K L; Brigham, D; Shehee, T C; Martin, A

    2012-12-28

    The interaction of trivalent lanthanide and actinide cations with polyaminopolycarboxylic acid complexing agents in lactic acid buffer systems is an important feature of the chemistry of the TALSPEAK process for the separation of trivalent actinides from lanthanides. To improve understanding of metal ion coordination chemistry in this process, the results of an investigation of the kinetics of lanthanide complexation by ethylenediamine-N,N,N',N'-tetraacetic acid (EDTA) and diethylenetriamine-N,N,N',N'',N''-pentaacetic acid (DTPA) in 0.3 M lactic acid/0.3 M ionic strength solution are reported. Progress of the reaction was monitored using the distinctive visible spectral changes attendant to lanthanide complexation by the colorimetric indicator ligand Arsenazo III, which enables the experiment but plays no mechanistic role. Under the conditions of these experiments, the reactions occur in a time regime suitable for study by stopped-flow spectrophotometric techniques. Experiments have been conducted as a function of EDTA/DTPA ligand concentration, total lactic acid concentration, and pH. The equilibrium perturbation reaction proceeds as a first order approach to equilibrium over a wide range of conditions, allowing the simultaneous determination of complex formation and dissociation rate constants. The rate of the complexation reaction has been determined for the entire lanthanide series (except Pm(3+)). The predominant pathway for lanthanide-EDTA and lanthanide-DTPA dissociation is inversely dependent on the total lactate concentration; the complex formation reaction demonstrates a direct dependence on [H(+)]. Unexpectedly, the rate of the complex formation reaction is seen in both ligand systems to be fastest for Gd(3+). Correlation of these results indicates that in 0.3 M lactate solutions the exchange of lanthanide ions between lactate complexes and the polyaminopolycarboxylate govern the process.

  3. Kinetics of H-D exchange in olefins with complicating reactions

    International Nuclear Information System (INIS)

    Trokhimets, A.I.

    1979-01-01

    The kinetics of H-D-exchange is considered for olefins under conditions when simple and complicated exchange occur together with hydrogenation. If hydrogenation takes place in the system, it is theoretically impossible to derive the integrated rate equation for the accumulation of deuterium in the olefin. The variation of the concentration of different deuteroolefins during the process can be calculated numerically. A method is proposed for evaluating the contribution of individual steps to the overall process and determining the rate constants of the most important reactions. (author)

  4. Optically Controlled Electron-Transfer Reaction Kinetics and Solvation Dynamics : Effect of Franck-Condon States

    NARCIS (Netherlands)

    Gupta, Kriti; Patra, Aniket; Dhole, Kajal; Samanta, Alok Kumar; Ghosh, Swapan K.

    2017-01-01

    Experimental results for optically controlled electron-transfer reaction kinetics (ETRK) and nonequilibrium solvation dynamics (NESD) of Coumarin 480 in DMPC vesicle show their dependence on excitation wavelength λex. However, the celebrated Marcus theory and linear-response-theory-based approaches

  5. A kinetic study of the redox reactions of complex cyanides of iron, molybdenum and tungsten with compounds of the group VI A elements

    International Nuclear Information System (INIS)

    Dennis, C.R.

    1981-01-01

    The kinetic study arises out of the fact that few is known about redox kinetics of complex cyanides of molybdenum and tungsten. The redox kinetics of the complex cyanides of iron with organic and inorganic compounds are well known in organic chemistry. This comparitive study is done to obtain more information on redox reactions of complex cyanides of molybdenum and tungsten considering its greater applicability in organic and inorganic chemistry because of the propitious reduction potential of this complex cyanide in acidic and alkaline mediums. Various redox systems are kinetically investigated regarding the influence of the oxidising agent, reducing agent hydrogen ions and alkaline-metal ions on the reaction rate. A reaction mechanism is proposed for every system

  6. Redox non-innocent ligands: versatile new tools to control catalytic reactions

    NARCIS (Netherlands)

    Lyaskovskyy, V.; de Bruin, B.

    2012-01-01

    In this (tutorial overview) perspective we highlight the use of "redox non-innocent" ligands in catalysis. Two main types of reactivity in which the redox non-innocent ligand is involved can be specified: (A) The redox active ligand participates in the catalytic cycle only by accepting/donating

  7. The role of high temperature heterogeneous reaction kinetics in the rate of radionuclide vaporisation during core-concrete interactions

    International Nuclear Information System (INIS)

    Raymond, D.P.; Clough, P.N.

    1989-09-01

    Heterogeneous reactions may cause enhanced release of radionuclides during the core-concrete interaction (CCl) stage of a PWR severe accident. The VANESA computer code models these CCI releases using chemical equilibrium assumptions; however, the possibility that chemical kinetics could prevent equilibrium from being achieved is considered in this report. Direct experimental evidence is lacking on these reactions. Therefore, some analogues studies are reviewed, including examples of Eyring's surface reaction rate theory; sequential vaporisation-oxidation processes; iron and steelmaking chemistry; radionuclide evaporation from solid UO 2 . This circumstantial evidence appeared to agree with the current assumptions, in VANESA and some UK modelling studies, that mass transfer, rather than chemical kinetics will limit the rate at which equilibrium is attained. (author)

  8. Toward a Kinetic Model for Acrylamide Formation in a Glucose-Asparagine Reaction System

    NARCIS (Netherlands)

    Knol, J.J.; Loon, W.A.M.; Linssen, J.P.H.; Ruck, A.L.; Boekel, van M.A.J.S.

    2005-01-01

    A kinetic model for the formation of acrylamide in a glucose-asparagine reaction system is pro-posed. Equimolar solutions (0.2 M) of glucose and asparagine were heated at different tempera-tures (120-200 C) at pH 6.8. Besides the reactants, acrylamide, fructose, and melanoidins were quantified after

  9. Preclusion of switch behavior in reaction networks with mass-action kinetics

    DEFF Research Database (Denmark)

    Feliu, Elisenda; Wiuf, C.

    2012-01-01

    We study networks taken with mass-action kinetics and provide a Jacobian criterion that applies to an arbitrary network to preclude the existence of multiple positive steady states within any stoichiometric class for any choice of rate constants. We are concerned with the characterization...... precludes the existence of degenerate steady states. Further, we relate injectivity of a network to that of the network obtained by adding outflow, or degradation, reactions for all species....

  10. The browning kinetics of the non-enzymatic browning reaction in L-ascorbic acid/basic amino acid systems

    Directory of Open Access Journals (Sweden)

    Ai-Nong YU

    Full Text Available Abstract Under the conditions of weak basis and the reaction temperature range of 110-150 °C, lysine, arginine and histidine were reacted with L-ascorbic acid at equal amount for 30-150 min, respectively and the formation of browning products was monitored with UV–vis spectrometry. The kinetic characteristics of their non-enzymatic browning reaction were investigated. The study results indicated that the non-enzymatic browning reaction of these three amino acids with L-ascorbic acid to form browning products was zero-order reaction. The apparent activation energies for the formation of browning products from L-ascorbic acid/lysine, L-ascorbic acid/arginine and L-ascorbic acid/histidine systems were 54.94, 50.08 and 35.31kJ/mol. The activation energy data indicated the degree of effects of reaction temperature on non-enzymatic browning reaction. Within the temperature range of 110-150 °C, the reaction rate of L-ascorbic acid/lysine system was the fastest one, followed by that of the L-ascorbic acid/arginine system. The reaction rate of L-ascorbic acid/histidine system was the slowest one. Based on the observed kinetic data, the formation mechanisms of browning products were proposed.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2010-09-15

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

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

    International Nuclear Information System (INIS)

    Harikrishna, R.; Ponrathnam, S.; Tambe, S.S.

    2014-01-01

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

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

    International Nuclear Information System (INIS)

    Basilevsky, M. V.; Mitina, E. A.; Odinokov, A. V.; Titov, S. V.

    2013-01-01

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

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

    International Nuclear Information System (INIS)

    Barnett, D.S.; Kazimi, M.S.

    1989-04-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2012-01-17

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

  16. Kinetics of the radiation-induced exchange reactions of H2, D2, and T2: a review

    International Nuclear Information System (INIS)

    Pyper, J.W.; Briggs, C.K.

    1978-01-01

    Mixtures of H 2 --T 2 or D 2 --T 2 will exchange to produce HT or DT due to catalysis by the tritium β particle. The kinetics of the reaction D 2 + T 2 = 2DT may play an important role in designing liquid or solid targets of D 2 --DT--T 2 for implosion fusion, and distillation schemes for tritium cleanup systems in fusion reactors. Accordingly, we have critically reviewed the literature for information on the kinetics and mechanism of radiation-induced self-exchange reactions among the hydrogens. We found data for the reaction H 2 + T 2 = 2HT in the gas phase and developed a scheme based on these data to predict the halftime to equilibrium for any gaseous H 2 + T 2 mixture at ambient temperature with an accuracy of +-10 percent. The overall order of the H 2 + T 2 = 2HT reaction is 1.6 based on an initial rate treatment of the data. The most probable mechanism for radiation-induced self-exchange reaction is an ion-molecule chain mechanism

  17. Programming chemical kinetics: engineering dynamic reaction networks with DNA strand displacement

    Science.gov (United States)

    Srinivas, Niranjan

    Over the last century, the silicon revolution has enabled us to build faster, smaller and more sophisticated computers. Today, these computers control phones, cars, satellites, assembly lines, and other electromechanical devices. Just as electrical wiring controls electromechanical devices, living organisms employ "chemical wiring" to make decisions about their environment and control physical processes. Currently, the big difference between these two substrates is that while we have the abstractions, design principles, verification and fabrication techniques in place for programming with silicon, we have no comparable understanding or expertise for programming chemistry. In this thesis we take a small step towards the goal of learning how to systematically engineer prescribed non-equilibrium dynamical behaviors in chemical systems. We use the formalism of chemical reaction networks (CRNs), combined with mass-action kinetics, as our programming language for specifying dynamical behaviors. Leveraging the tools of nucleic acid nanotechnology (introduced in Chapter 1), we employ synthetic DNA molecules as our molecular architecture and toehold-mediated DNA strand displacement as our reaction primitive. Abstraction, modular design and systematic fabrication can work only with well-understood and quantitatively characterized tools. Therefore, we embark on a detailed study of the "device physics" of DNA strand displacement (Chapter 2). We present a unified view of strand displacement biophysics and kinetics by studying the process at multiple levels of detail, using an intuitive model of a random walk on a 1-dimensional energy landscape, a secondary structure kinetics model with single base-pair steps, and a coarse-grained molecular model that incorporates three-dimensional geometric and steric effects. Further, we experimentally investigate the thermodynamics of three-way branch migration. Our findings are consistent with previously measured or inferred rates for

  18. Kinetics of heterogeneous chemical reactions: a theoretical model for the accumulation of pesticides in soil.

    Science.gov (United States)

    Lin, S H; Sahai, R; Eyring, H

    1971-04-01

    A theoretical model for the accumulation of pesticides in soil has been proposed and discussed from the viewpoint of heterogeneous reaction kinetics with a basic aim to understand the complex nature of soil processes relating to the environmental pollution. In the bulk of soil, the pesticide disappears by diffusion and a chemical reaction; the rate processes considered on the surface of soil are diffusion, chemical reaction, vaporization, and regular pesticide application. The differential equations involved have been solved analytically by the Laplace-transform method.

  19. Tunneling and reflection in unimolecular reaction kinetic energy release distributions

    Science.gov (United States)

    Hansen, K.

    2018-02-01

    The kinetic energy release distributions in unimolecular reactions is calculated with detailed balance theory, taking into account the tunneling and the reflection coefficient in three different types of transition states; (i) a saddle point corresponding to a standard RRKM-type theory, (ii) an attachment Langevin cross section, and (iii) an absorbing sphere potential at short range, without long range interactions. Corrections are significant in the one dimensional saddle point states. Very light and lightly bound absorbing systems will show measurable effects in decays from the absorbing sphere, whereas the Langevin cross section is essentially unchanged.

  20. Kinetics of Vinyl Polymerization of Methyl Methacrylate Initiated by Ce(IV-Vanillin Redox System

    Directory of Open Access Journals (Sweden)

    M. Palanivelu

    2012-01-01

    Full Text Available The kinetics of polymerization of methyl methacrylate initiated by Ce(IV-Vanillin redox system was studied in aqueous solution of sulfuric acid at 40°C. The rate of polymerization (Rp and the reaction orders with respect to monomer, initiator and ligand have been determined and found to be 1.5, 0.5 and 0.5 respectively. The effect of concentration of sulfuric acid on the polymerization was also studied. The rate of polymerization was found to increase with increasing temperature 30–60°C and decreases at higher temperature (>60°C. The overall activation energy (Ea was found to be 36.7 kJ/mol. A suitable kinetic scheme has been proposed.

  1. Specific ability of sulfur-ligands on removal of 203Hg-labeled organomercury from hemoglobin in comparison with nitrogen-ligands

    International Nuclear Information System (INIS)

    Hojo, Yasuji; Sugiura, Yukio; Tanaka, Hisashi

    1975-01-01

    Removal of 203 Hg-labeled organomercurials, bound to sulfhydryl groups of hemoglobin, by various chelating agents was investigated by the use of equilibrium dialysis. Organomercurials employed were chlormerodrin, methylmercury, ethylmercury and phenylmercury compounds. Higher and more specific effects of the sulfur-ligands, such as penicillamine and glutathione, on removal of organomercurial were found as compared with those of the nitrogen-ligands such as EDTA, glycine and polymethylenediamines. Linear correlation was observed between the degree of organomercury elimination from hemoglobin and the stability constant (log K 1 ) of 1:1 organomercury complex in both the sulfur- and nitrogen-ligand systems and at the same value of log K 1 , the elimination-effect of sulfur-ligands was extremely greater than that of the nitrogen-ligands. The relationship between the average percentage of removal and the Taft's polar substituent constant of organic moiety of the metal was also linear among the organomercury compounds other than chlormerodrin. The average removal percentage by sulfur-ligands increased in the order, ethylmercury>methylmercury>phenylmercury, while that of the nitrogen-ligands was not different among the organomercurials investigated. In addition, direct ligand-exchange reaction between hemoglobin-SH and the ligand coordinating-atom (S or N) against organomercurials rather than Ssub(N2) reaction via the ternary complex, hemoglobin-S-RHg-ligand, is postulated. (auth.)

  2. Kinetics of the glucose/glycine Maillard reaction pathways: influences of pH and reactant initial concentrations

    NARCIS (Netherlands)

    Martins, S.I.F.S.; Boekel, van M.A.J.S.

    2005-01-01

    A previously proposed kinetic model for the glucose/glycine Maillard reaction pathways has been validated by changing the initial pH (4.8, 5.5, 6.0, 6.8 and 7.5) of the reaction and reactant initial concentrations (1:2 and 2:1 molar ratios were compared to the 1:1 ratio). The model consists of 10

  3. Kinetics of evaporation of barium THD precursors used for organometallic chemical vapor deposition (OMCVD) thin films

    Science.gov (United States)

    Burtman, V.; Schieber, M.; Yitzchaik, S.; Yaroslavsky, Y.

    1997-04-01

    Various methods have been used to synthesize Ba(THD) 2 and its molecular structure has been studied using nuclear magnetic resonance. Compared with Raman and infrared spectroscopy it was found that NMR is very useful to determine quantitatively the decomposition through aging of Ba(THD) 2. The transport kinetics of Ba(THD) 2 has been studied under experimental conditions of a OMCVD reactor. It has been found that the freshly prepared Ba(THD) 2 by the reaction of Ba metal with THD ligand in anhydrous conditions with subsequent crystallization from methanol transported quantitatively without decomposition. A simple model shows that the transport kinetics corresponds to a diffusion controlled process.

  4. Catalytic behaviors of Co{sup II} and Mn{sup II} compounds bearing α-Diimine ligands for oxidative polymerization or drying oils

    Energy Technology Data Exchange (ETDEWEB)

    Lima, Gilvan E.S.; Nunes, Everton V.; Dantas, Roberta C.; Meneghetti, Mario R.; Meneghetti, Simoni M.P., E-mail: simoni.plentz@gmail.com [Universidade Federal de Alagoas (UFAL), Maceió, AL (Brazil). Grupo de Catálise e Reatividade Química; Simone, Carlos A. de [Universidade de Sao Paulo (USP), São Carlos, USP, SP (Brazil). Instituto de Física

    2018-05-01

    The oxidative polymerization of linseed oil was investigated comparing the classical catalysts cobalt(II) 2-ethylhexanoate and manganese(II) 2-ethylhexanoate and their derivatives modified by the presence of chelating nitrogen ligands, i.e., 2,2’-bipyridyl, 2-(acetyl-2,6-diisopropylphenylimine)- pyridine and [N-(2,6-diisopropylphenyl)imine]acenaphthoquinone. The suitable stoichiometries between the two precursor complexes with the three ligands were determined by UV-visible spectroscopy. All complexes were characterized by infrared spectroscopy, and one complex was characterized also by X-ray diffraction. The apparent kinetic constants of oxidative polymerization of linseed oil was determined, for each catalytic system, via the periodic measurements of the oil viscosity during the oxidation reaction. The results indicated that the modifications of the classical two complexes with the chelating nitrogen ligands improved the catalytic efficiency at least to the manganese complex. (author)

  5. Reactions of Cp2MCl2 (M=Ti or Zr with Imine-Oxime Ligands. Formation of Metallacycles

    Directory of Open Access Journals (Sweden)

    C. Tripathi

    2005-07-01

    Full Text Available The reactions of bis(cyclopentadienyltitanium(IV/zirconium(IV dichloridewith a series of imine-oxime ligands (LH2, derived by condensing benzil-α-monoxime and2-phenylenediamine, 4-phenylenediamine, 4-methyl-2-phenylenediamine, 2,6-diamino-pyridine, have been studied in anhydrous tetrahydrofuran in the presence of base andmetallocycles of the [Cp2M(L] (M=Ti or Zr type have been isolated. Tentative structureshave been proposed for the products based on elemental analysis, electrical conductance andspectral (electronic, IR and 1H-NMR data. Proton NMR spectra indicate that on the NMRtime scale there is rapid rotation of the cyclopentadienyl ring around the metal-ring axis at25oC. Studies were conducted to assess the growth inhibiting potential of the complexessynthesized and the ligands against various bacterial strains.

  6. Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions.

    Science.gov (United States)

    Mitra, Mainak; Nimir, Hassan; Demeshko, Serhiy; Bhat, Satish S; Malinkin, Sergey O; Haukka, Matti; Lloret-Fillol, Julio; Lisensky, George C; Meyer, Franc; Shteinman, Albert A; Browne, Wesley R; Hrovat, David A; Richmond, Michael G; Costas, Miquel; Nordlander, Ebbe

    2015-08-03

    Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L(1)) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L(2)), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [Fe(II)(CH3CN)(L)](2+) (L = L(1) (1); L(2) (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [Fe(IV)(O)(L)](2+) (L = L(1) (3); L(2) (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and Mössbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L(1)) and 2.5 h (L = L(2)). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([Fe(IV)(O)(N4Py)](2+)), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [Fe(IV)(O)(L(2))](2+) exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.

  7. Effect of the competition of Cu(II) and Ni(II) on the kinetic and thermodynamic stabilities of Cr(III)-organic ligand complexes using competitive ligand exchange (EDTA).

    Science.gov (United States)

    Cunha, Graziele da Costa; Goveia, Danielle; Romão, Luciane Pimenta Cruz; de Oliveira, Luciana Camargo

    2015-05-01

    The effect of competition of Cu(II) and Ni(II) on the kinetic stability of Cr(III) complexed with natural organic matter (NOM) was characterized using EDTA exchange with single-stage tangential-flow ultrafiltration. For a water sample from Serra de Itabaiana, 3% of spiked Cr(III) was exchanged, while for a sample from the Itapanhaú River, 7, 10, 10, and 21% was exchanged in experiments using Cr(III) alone and in combination with Cu(II), Ni(II), or Cu(II) + Ni(II), respectively. Times required to reach exchange equilibrium with EDTA were less than 360 min. The influence of competition from Ni(II) and Cu(II) on the availability of complexed Cr(III) was low, demonstrating preference of the ligand sites for Cr(III). This was correlated with sample humification, as confirmed by EPR and (13)C NMR analyses. Exchange efficiency was in the order Cu > Ni > Cr, and the process could be readily described by first order kinetics, with average rate constants of 0.35-0.37 h(-1). Copyright © 2015 Elsevier Ltd. All rights reserved.

  8. Synthesis Of Magnesium-Aluminum Layered Double Hydroxides By Mechanochemical Method And Its Solid State Reaction Kinetics

    Directory of Open Access Journals (Sweden)

    Hongbo Y.

    2015-06-01

    Full Text Available A mechanochemical method is developed in preparing magnesium-aluminum-layered double hydroxides (MgAl-LDHs. This approach includes activation process and diffusion process. In order to verify the LDHs structure and study the reaction kinetics, X-ray diffraction (XRD patterns, inductively coupled plasma(ICP and physical adsorption instrument were characterized. The results show that activation time can change the surface of particles and affect the reaction grade. During the diffusion process, reaction time is the most important factor. The reaction energy (ΔQ was calculated that is 6kJ/mol.

  9. Kinetic and reaction pathways of methanol oxidation on platinum

    International Nuclear Information System (INIS)

    McCabe, R.W.; McCready, D.F.

    1986-01-01

    Methanol oxidation kinetics were measured on Pt wires in a flow reactor at pressures between 30 and 130 Pa. The kinetics were measured as a function of oxygen-to-methanol equivalence ratio phi and wire temperature. In methanol-lean feeds (phi 2 CO, CO 2 , and H 2 O were the only products; in methanol-rich feeds (phi > 1), CO, H 2 , H 2 CO, CO 2 , and H 2 O were observed. Experiments with 18 O 2 showed that the principal methanol oxidation pathway does not involve C-O bond dissociation. However, the 18 O 2 experiments, together with other features of the methanol oxidation data, also provided evidence for a minor oxidation pathway (accounting for less than 1% of the product CO 2 ) which proceeds through a carbon intermediate. A mathematical model is presented which describes the principal CH 3 OH oxidation pathway as a series reaction involving adsorbed H 2 CO and CO intermediates. Consistent with experimental results, the model predicts that inhibition by adsorbed CO should be weaker for CH 3 OH and H 2 CO oxidation than for CO oxidation. 34 references, 10 figures, 2 tables

  10. Kinetics of protein–ligand unbinding: Predicting pathways, rates, and rate-limiting steps

    Science.gov (United States)

    Tiwary, Pratyush; Limongelli, Vittorio; Salvalaglio, Matteo; Parrinello, Michele

    2015-01-01

    The ability to predict the mechanisms and the associated rate constants of protein–ligand unbinding is of great practical importance in drug design. In this work we demonstrate how a recently introduced metadynamics-based approach allows exploration of the unbinding pathways, estimation of the rates, and determination of the rate-limiting steps in the paradigmatic case of the trypsin–benzamidine system. Protein, ligand, and solvent are described with full atomic resolution. Using metadynamics, multiple unbinding trajectories that start with the ligand in the crystallographic binding pose and end with the ligand in the fully solvated state are generated. The unbinding rate koff is computed from the mean residence time of the ligand. Using our previously computed binding affinity we also obtain the binding rate kon. Both rates are in agreement with reported experimental values. We uncover the complex pathways of unbinding trajectories and describe the critical rate-limiting steps with unprecedented detail. Our findings illuminate the role played by the coupling between subtle protein backbone fluctuations and the solvation by water molecules that enter the binding pocket and assist in the breaking of the shielded hydrogen bonds. We expect our approach to be useful in calculating rates for general protein–ligand systems and a valid support for drug design. PMID:25605901

  11. Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors.

    Science.gov (United States)

    Milanovsky, Georgy E; Petrova, Anastasia A; Cherepanov, Dmitry A; Semenov, Alexey Yu

    2017-09-01

    The reduction kinetics of the photo-oxidized primary electron donor P 700 in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P 700 , secondary quinone acceptor A 1 , iron-sulfur clusters and external electron donor and acceptors - methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl 2 NQ) and oxygen. PS I complexes containing various quinones in the A 1 -binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl 2 NQ) as well as F X -core complexes, depleted of terminal iron-sulfur F A /F B clusters, were studied. The acceleration of charge recombination in F X -core complexes by PhQ/PQ substitution indicates that backward ET from the iron-sulfur clusters involves quinone in the A 1 -binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P 700 + reduction with the kinetic model. The free energy gap ΔG 0 between F X and F A /F B clusters was estimated as -130 meV. The driving force of ET from A 1 to F X was determined as -50 and -220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A 1A -site, this reaction was found to be endergonic (ΔG 0  = +75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis-Menten kinetics. The second-order rate constants of ET from F A /F B , F X and Cl 2 NQ in the A 1 -site of PS I to external acceptors were estimated. The side production of superoxide radical in the A 1 -site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.

  12. Kinetics of the reactions of bromine atoms with a series of aliphatic aldehydes at 298 K

    Energy Technology Data Exchange (ETDEWEB)

    Szilagyi, I.; Imrik, K.; Dobe, S.; Berces, T. [Magyar Tudomanyos Akademia, Budapest (Hungary). Koezponti Kemiai Kutato Intezete

    1998-01-01

    The kinetics of the reactions of Br({sup 2}P{sub 3/2}) with selected aldehydes, i.e. ethanal (1), propanal (2), 2-methyl-propanal (3), 2.2-dimethyl-propanal (4) and trichloroacetaldehyde (5) were studied at 298{+-}2 K. Rate constants for overall reactions were measured using the fast flow technique with resonance fluorescence detection of Br. Complementary determinations were carried out by the laser flash photolysis method. The following rate constants were obtained in the kinetic measurements ({+-}2{sigma}): k{sub 1}=(2.1{+-}0.2) x 10{sup 12}, k{sub 2}=(4.3{+-}0.4) x 10{sup 12}, k{sub 3}=(6.3{+-}1.4) x 10{sup 12}, k{sub 4}=(8.5{+-}0.8) x 10{sup 12}, k{sub 5}{<=}1 x 10{sup 9}, all in cm{sup 3}mol{sup -1}s{sup -1} units. The probable mechanism for the reactions of bromine atoms with aliphatic aldehydes has been discussed. (orig.)

  13. Flow chemistry kinetic studies reveal reaction conditions for ready access to unsymmetrical trehalose analogues.

    Science.gov (United States)

    Patel, Mitul K; Davis, Benjamin G

    2010-10-07

    Monofunctionalization of trehalose, a widely-found symmetric plant disaccharide, was studied in a microreactor to give valuable kinetic insights that have allowed improvements in desymmetrization yields and the development of a reaction sequence for large scale monofunctionalizations that allow access to probes of trehalose's biological function.

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

    Science.gov (United States)

    Hoggett, J G; Kellett, G L

    1992-10-15

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

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

    International Nuclear Information System (INIS)

    Santon, J.P.

    1964-09-01

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

  16. Kinetics of transuranium element oxidation-reduction reactions in solution; Cinetique des reactions d'oxydo-reduction des elements transuraniens en solution

    Energy Technology Data Exchange (ETDEWEB)

    Gourisse, D [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

    1966-09-01

    A review of the kinetics of U, Np, Pu, Am oxidation-reduction reactions is proposed. The relations between the different activation thermodynamic functions (compensatory effect, formal entropy of the activated complex, magnitude of reactions velocities) are considered. The effects of acidity, ionic strength deuterium and mixed solvents polarity on reactions rates are described. The effect of different anions on reactions rates are explained by variations of the reaction standard free energy and variations of the activation free energy (coulombic interactions) resulting from the complexation of dissolved species by these anions. (author) [French] Une revue systematique de la cinetique des reactions d'oxydo-reduction des elements U, Np, Pu, Am, en solution perchlorique est proposee. Des considerations relatives aux grandeurs thermodynamiques d'activation associees aux actes elementaires (effet de compensation, entropie standard des complexes actives, rapidite des reactions) sont developpees. L'influence de l'acidite, de la force ionique, de l'eau lourde et de la polarite des solvants mixtes sur la vitesse des reactions est decrite. Enfin l'influence des differents anions sur la vitesse des reactions est expliquee par les variations de l'enthalpie libre standard de la reaction et de l'enthalpie libre d'activation (travail des forces electrostatiques) resultant de la complexation des especes dissoutes dans la solution. (auteur)

  17. Studies on Pd/NiFe2O4 catalyzed ligand-free Suzuki reaction in aqueous phase: synthesis of biaryls, terphenyls and polyaryls

    Directory of Open Access Journals (Sweden)

    Suresh B. Waghmode

    2011-03-01

    Full Text Available Palladium supported on nickel ferrite (Pd/NiF2O4 was found to be a highly active catalyst for the Suzuki coupling reaction between various aryl halides and arylboronic acids. The reaction gave excellent yields (70–98% under ligand free conditions in a 1:1 DMF/H2O solvent mixture, in short reaction times (10–60 min. The catalyst could be recovered easily by applying an external magnetic field. The polyaryls were similarly synthesized.

  18. Kinetic Titration Series with Biolayer Interferometry

    Science.gov (United States)

    Frenzel, Daniel; Willbold, Dieter

    2014-01-01

    Biolayer interferometry is a method to analyze protein interactions in real-time. In this study, we illustrate the usefulness to quantitatively analyze high affinity protein ligand interactions employing a kinetic titration series for characterizing the interactions between two pairs of interaction patterns, in particular immunoglobulin G and protein G B1 as well as scFv IC16 and amyloid beta (1–42). Kinetic titration series are commonly used in surface plasmon resonance and involve sequential injections of analyte over a desired concentration range on a single ligand coated sensor chip without waiting for complete dissociation between the injections. We show that applying this method to biolayer interferometry is straightforward and i) circumvents problems in data evaluation caused by unavoidable sensor differences, ii) saves resources and iii) increases throughput if screening a multitude of different analyte/ligand combinations. PMID:25229647

  19. Simultaneous determination of thermodynamic and kinetic parameters of aminopolycarbonate complexes of cobalt(II) and nickel(II) based on isothermal titration calorimetry data.

    Science.gov (United States)

    Tesmar, Aleksandra; Wyrzykowski, Dariusz; Muñoz, Eva; Pilarski, Bogusław; Pranczk, Joanna; Jacewicz, Dagmara; Chmurzyński, Lech

    2017-04-01

    The influence of the different side chain residues on the thermodynamic and kinetic parameters for complexation reactions of the Co 2 + and Ni 2 + ions has been investigated by using the isothermal titration calorimetry (ITC) technique supported by potentiometric titration data. The study was concerned with the 2 common tripodal aminocarboxylate ligands, namely, nitrilotriacetic acid and N-(2-hydroxyethyl) iminodiacetic acid. Calorimetric measurements (ITC) were run in the 2-(N-morpholino)ethanesulfonic acid hydrate (2-(N-morpholino) ethanesulfonic acid), piperazine-N,N'-bis(2-ethanesulfonic acid), and dimethylarsenic acid buffers (0.1 mol L -1 , pH 6) at 298.15 K. The quantification of the metal-buffer interactions and their incorporation into the ITC data analysis enabled to obtain the pH-independent and buffer-independent thermodynamic parameters (K, ΔG, ΔH, and ΔS) for the reactions under study. Furthermore, the kinITC method was applied to obtain kinetic information on complexation reactions from the ITC data. Correlations, based on kinetic and thermodynamic data, between the kinetics of formation of Co 2 + and Ni 2 + complexes and their thermodynamic stabilities are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

  20. Kinetic study of the Diels-Alder reaction of Li⁺@C₆₀ with cyclohexadiene: greatly increased reaction rate by encapsulated Li⁺.

    Science.gov (United States)

    Ueno, Hiroshi; Kawakami, Hiroki; Nakagawa, Koji; Okada, Hiroshi; Ikuma, Naohiko; Aoyagi, Shinobu; Kokubo, Ken; Matsuo, Yutaka; Oshima, Takumi

    2014-08-06

    We studied the kinetics of the Diels-Alder reaction of Li(+)-encapsulated [60]fullerene with 1,3-cyclohexadiene and characterized the obtained product, [Li(+)@C60(C6H8)](PF6(-)). Compared with empty C60, Li(+)@C60 reacted 2400-fold faster at 303 K, a rate enhancement that corresponds to lowering the activation energy by 24.2 kJ mol(-1). The enhanced Diels-Alder reaction rate was well explained by DFT calculation at the M06-2X/6-31G(d) level of theory considering the reactant complex with dispersion corrections. The calculated activation energies for empty C60 and Li(+)@C60 (65.2 and 43.6 kJ mol(-1), respectively) agreed fairly well with the experimentally obtained values (67.4 and 44.0 kJ mol(-1), respectively). According to the calculation, the lowering of the transition state energy by Li(+) encapsulation was associated with stabilization of the reactant complex (by 14.1 kJ mol(-1)) and the [4 + 2] product (by 5.9 kJ mol(-1)) through favorable frontier molecular orbital interactions. The encapsulated Li(+) ion catalyzed the Diels-Alder reaction by lowering the LUMO of Li(+)@C60. This is the first detailed report on the kinetics of a Diels-Alder reaction catalyzed by an encapsulated Lewis acid catalyst rather than one coordinated to a heteroatom in the dienophile.

  1. SUPECA kinetics for scaling redox reactions in networks of mixed substrates and consumers and an example application to aerobic soil respiration

    Science.gov (United States)

    Tang, Jin-Yun; Riley, William J.

    2017-09-01

    Several land biogeochemical models used for studying carbon-climate feedbacks have begun explicitly representing microbial dynamics. However, to our knowledge, there has been no theoretical work on how to achieve a consistent scaling of the complex biogeochemical reactions from microbial individuals to populations, communities, and interactions with plants and mineral soils. We focus here on developing a mathematical formulation of the substrate-consumer relationships for consumer-mediated redox reactions of the form A + BE→ products, where products could be, e.g., microbial biomass or bioproducts. Under the quasi-steady-state approximation, these substrate-consumer relationships can be formulated as the computationally difficult full equilibrium chemistry problem or approximated analytically with the dual Monod (DM) or synthesizing unit (SU) kinetics. We find that DM kinetics is scaling inconsistently for reaction networks because (1) substrate limitations are not considered, (2) contradictory assumptions are made regarding the substrate processing rate when transitioning from single- to multi-substrate redox reactions, and (3) the product generation rate cannot be scaled from one to multiple substrates. In contrast, SU kinetics consistently scales the product generation rate from one to multiple substrates but predicts unrealistic results as consumer abundances reach large values with respect to their substrates. We attribute this deficit to SU's failure to incorporate substrate limitation in its derivation. To address these issues, we propose SUPECA (SU plus the equilibrium chemistry approximation - ECA) kinetics, which consistently imposes substrate and consumer mass balance constraints. We show that SUPECA kinetics satisfies the partition principle, i.e., scaling invariance across a network of an arbitrary number of reactions (e.g., as in Newton's law of motion and Dalton's law of partial pressures). We tested SUPECA kinetics with the equilibrium chemistry

  2. Reduction reactions of water soluble cyano-cobalt(III)-porphyrins: Metal versus ligand centered processes

    International Nuclear Information System (INIS)

    Mosseri, S.; Neta, P.; Harriman, A.; Hambright, P.

    1990-01-01

    Reduction reactions of dicyano-cobalt(III)-porphyrins [potential in vivo cyanide scavenger drugs] were studied by radiolytic and electrochemical methods using the water soluble tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP). For [(CN)2CoIIITPPS]-, reduction occurs stepwise to the CoII, CoI, and finally to the phlorin anion. This behavior is similar to that of the cobalt porphyrins in the absence of cyanide, except that the cyanide ligand shifts the reduction potentials to much more negative values. On the other hand, under radiolytic conditions, [(CN)2CoIIITMPyP]- is reduced on the porphyrin macrocycle by one electron to give the CoIII pi-radical anion, which disproportionates into the initial complex and the two-electron ring reduced CoIII phlorin. The radical anion is also formed by intramolecular electron transfer subsequent to the reaction of CoIITMPyP and cyanide. The results are compared with the chemistry of Vitamin B-12

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-12-21

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

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

    International Nuclear Information System (INIS)

    Wu Yiming; Zhang Zhiping; Luo Ning

    2000-01-01

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

  5. The reaction kinetics of lithium salt with water vapor

    International Nuclear Information System (INIS)

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

    2002-01-01

    The interaction of lithium salt (LiH and/or LiD) with water vapor in the partial pressure range of 10 -5 -2657 Pa has been investigated. The reaction probability of water with LiH cleaved in an ultra high vacuum environment was obtained using the modulated molecular beam technique. This probability was 0.11 and independent of LiH surface temperature, suggesting a negligible activation energy for the reaction in agreement with quantum chemical calculations. The value gradually reduced, however, to 0.007 as the surface concentration of oxygen containing product approached full coverage. As the film grew beyond a monolayer, the phase lag of hydrogen product increased from 0 deg. C to 20 deg. C and the reaction probability reduced further until it approached our detection limit (∼10 -4 ). This phase lag was attributed to a diffusion-limited process in this regime. For micrometer thick hydroxide films grown in high moisture concentration environment on LiD and LiH, the reaction probability reduced to ∼4x10 -7 and was independent of exposure time. In this regime of thick hydroxide films (LiOH and/or LiOD), microcracks generated in the films to release stress provided easier pathways for moisture to reach the interface. A modified microscope, capable of both atomic force microscopy and nanoindentation, was also employed to investigate the surface morphology of hydroxide monohydrate (LiOH · H 2 O and/or LiOD · H 2 O) grown on hydroxide at high water vapor partial pressures and the kinetics of this growth

  6. A Ferrocene-Based Catecholamide Ligand: the Consequences of Ligand Swivel for Directed Supramolecular Self-Assembly

    Energy Technology Data Exchange (ETDEWEB)

    Mugridge, Jeffrey; Fiedler, Dorothea; Raymond, Kenneth

    2010-02-04

    A ferrocene-based biscatecholamide ligand was prepared and investigated for the formation of metal-ligand supramolecular assemblies with different metals. Reaction with Ge(IV) resulted in the formation of a variety of Ge{sub n}L{sub m} coordination complexes, including [Ge{sub 2}L{sub 3}]{sup 4-} and [Ge{sub 2}L{sub 2}({mu}-OMe){sub 2}]{sup 2-}. The ligand's ability to swivel about the ferrocenyl linker and adopt different conformations accounts for formation of many different Ge{sub n}L{sub m} species. This study demonstrates why conformational ligand rigidity is essential in the rational design and directed self-assembly of supramolecular complexes.

  7. Process and kinetics of the fundamental radiation-electrochemical reactions in the primary coolant loop of nuclear reactors

    International Nuclear Information System (INIS)

    Kozomara-Maic, S.

    1987-06-01

    In spite of the rather broad title of this report, its major part is devoted to the corrosion problems at the RA reactor, i.e. causes and consequences of the reactor shutdown in 1979 and 1982. Some problems of reactor chemistry are pointed out because they are significant for future reactor operation. The final conclusion of this report is that corrosion processes in the primary coolant circuit of the nuclear reactor are specific and that radiation effects cannot be excluded when processes and reaction kinetics are investigated. Knowledge about the kinetics of all the chemical reactions occurring in the primary coolant loop are of crucial significance for safe and economical reactor operation [sr

  8. Laccase-catalyzed removal of the antimicrobials chlorophene and dichlorophen from water: Reaction kinetics, pathway and toxicity evaluation.

    Science.gov (United States)

    Shi, Huanhuan; Peng, Jianbiao; Li, Jianhua; Mao, Liang; Wang, Zunyao; Gao, Shixiang

    2016-11-05

    As active agents in cleaning and disinfecting products, antimicrobials have been widely spread in the environment and have drawn extensive attention as potential threats to the ecological system and human health. In this study, the laccase-catalyzed removal of two emerging antimicrobials, chlorophene (CP) and dichlorophen (DCP), was investigated under simulated environmental conditions. Intrinsic reaction kinetics showed that the removal of CP and DCP followed second-order reaction kinetics, first-order with respect to both the enzyme and the substrate concentration. It was also found that fulvic acid could suppress the transformation of CP and DCP by reversing the oxidation reactions through its action as a scavenger of the free radical intermediates produced from reactions between laccase and the substrates. Several reaction products were identified by a quadrupole time-of-flight mass spectrometer, and detailed reaction pathways were proposed. For both CP and DCP, direct polymerization was the principal pathway, and the coupling patterns were further corroborated based on molecular modeling. The nucleophilic substitution of chlorine by the hydroxyl group was observed, and further oxidation products capable of coupling with each other were also found. Additionally, toxicity evaluation tests using Scenedesmus obliquus confirmed that the toxicity of CP and DCP was effectively eliminated during the reaction processes. Copyright © 2016 Elsevier B.V. All rights reserved.

  9. Kinetics in radiation chemistry

    International Nuclear Information System (INIS)

    Hummel, A.

    1987-01-01

    In this chapter the authors first briefly review the kinetics of first- and second-order processes for continuous and pulsed irradiation, without taking the effects of nonhomogeneous formation of the species into consideration. They also discuss diffusion controlled reactions under conditions where interactions of more than two particles can be neglected, first the kinetics of the diffusion-controlled reaction of randomly generated species (homogeneous reaction) and then that of isolated pairs of reactants. The latter is often called geminate kinetics when dealing with pairs of oppositely charged species; they shall use this term for the kinetics of isolated pairs in general. In the last section they discuss briefly the kinetics of groups of more than two reactants

  10. Kinetics of the reaction of CH3O2 radicals with NO2

    DEFF Research Database (Denmark)

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

    1999-01-01

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

  11. Coupling of kinetic Monte Carlo simulations of surface reactions to transport in a fluid for heterogeneous catalytic reactor modeling

    International Nuclear Information System (INIS)

    Schaefer, C.; Jansen, A. P. J.

    2013-01-01

    We have developed a method to couple kinetic Monte Carlo simulations of surface reactions at a molecular scale to transport equations at a macroscopic scale. This method is applicable to steady state reactors. We use a finite difference upwinding scheme and a gap-tooth scheme to efficiently use a limited amount of kinetic Monte Carlo simulations. In general the stochastic kinetic Monte Carlo results do not obey mass conservation so that unphysical accumulation of mass could occur in the reactor. We have developed a method to perform mass balance corrections that is based on a stoichiometry matrix and a least-squares problem that is reduced to a non-singular set of linear equations that is applicable to any surface catalyzed reaction. The implementation of these methods is validated by comparing numerical results of a reactor simulation with a unimolecular reaction to an analytical solution. Furthermore, the method is applied to two reaction mechanisms. The first is the ZGB model for CO oxidation in which inevitable poisoning of the catalyst limits the performance of the reactor. The second is a model for the oxidation of NO on a Pt(111) surface, which becomes active due to lateral interaction at high coverages of oxygen. This reaction model is based on ab initio density functional theory calculations from literature.

  12. Kinetics and mechanisms of iron redox reactions in silicate melts: The effects of temperature and alkali cations

    Energy Technology Data Exchange (ETDEWEB)

    Magnien, V.; Pinet, O. [CEA VALRHO, SCDV/LEBV, F-30207 Bagnols Sur Ceze, (France); Magnien, V.; Neuville, D. R.; Roux, J.; Richet, P. [IPGP, CNRS, Physique des Mineraux et Magmas, F-75252 Paris 05, (France); Cormier, L. [Univ Paris 06, IMPMC, F-75015 Paris, (France); Hazemann, J. L. [CNRS, Inst Neel, F-38043 Grenoble, (France); De Ligny, D. [Univ Lyon 1, LMLC, CNRS, UMR 5620, F-69622 Villeurbanne, (France); Pascarelli, S. [European Synchrotron Radiat Facil, F-38043 Grenoble, (France); Vickridge, I. [Univ Paris 06, INSP, F-75015 Paris, (France)

    2008-07-01

    The kinetics and the mechanisms of iron redox reactions in molten Fe-bearing pyroxene compositions have been investigated by Raman spectroscopy and X-ray absorption Near Edge Structure (XANES) experiments at the iron K-edge. The former experiments have been made only near the glass transition whereas the latter have also been performed from about 1300 to 2100 K. The same kinetics are observed with both techniques. They are described by characteristic times that depend primarily on temperature and not on the initial redox state. At high temperatures, where both kinds of reactions could be investigated, these times are similar for oxidation and reduction. From these characteristic times we have calculated as a function of temperature and composition a parameter termed effective redox diffusivity. For a given melt, the diffusivities follow two distinct Arrhenius laws, which indicate that the mechanisms of the redox reaction are not the same near the glass transition and at high temperatures. As is now well established, diffusion of divalent cations is the dominant mechanism at low temperatures but the enhanced kinetics observed for alkali-bearing melts indicate that Li{sup +} and Na{sup +} also participate in ionic transport. At super-liquidus temperatures, in contrast, diffusion of oxygen represents the dominant mechanism. (authors)

  13. THERMODYNAMICS OF PROTEIN-LIGAND INTERACTIONS AND THEIR ANALYSIS

    Directory of Open Access Journals (Sweden)

    Rummi Devi Saini

    2017-11-01

    Full Text Available Physiological processes are controlled mainly by intermolecular recognition mechanisms which involve protein–protein and protein–ligand interactions with a high specificity and affinity to form a specific complex. Proteins being an important class of macromolecules in biological systems, it is important to understand their actions through binding to other molecules of proteins or ligands. In fact, the binding of low molecular weight ligands to proteins plays a significant role in regulating biological processes such as cellular metabolism and signal transmission. Therefore knowledge of the protein–ligand interactions and the knowledge of the mechanisms involved in the protein-ligand recognition and binding are key in understanding biology at molecular level which will facilitate the discovery, design, and development of drugs. In this review, the mechanisms involved in protein–ligand binding, the binding kinetics, thermodynamic concepts and binding driving forces are discussed. Thermodynamic mechanisms involved in a few important protein-ligand binding are described. Various spectroscopic, non-spectroscopic and computational method for analysis of protein–ligand binding are also discussed.

  14. High-affinity multivalent wheat germ agglutinin ligands by one-pot click reaction

    Directory of Open Access Journals (Sweden)

    Henning S. G. Beckmann

    2012-06-01

    Full Text Available A series of six mono-, di-, and trivalent N,N’-diacetylchitobiose derivatives was conveniently prepared by employing a one-pot procedure for Cu(II-catalyzed diazo transfer and Cu(I-catalyzed azide–alkyne cycloaddition (CuAAC starting from commercially available amines. These glycoclusters were probed for their binding potencies to the plant lectin wheat germ agglutinin (WGA from Triticum vulgaris by an enzyme-linked lectin assay (ELLA employing covalently immobilized N-acetylglucosamine (GlcNAc as a reference ligand. IC50 values were in the low micromolar/high nanomolar range, depending on the linker between the two disaccharides. Binding enhancements β up to 1000 for the divalent ligands and 2800 for a trivalent WGA ligand, compared to N,N’-diacetylchitobiose as the corresponding monovalent ligand, were observed. Molecular modeling studies, in which the chitobiose moieties were fitted into crystallographically determined binding sites of WGA, correlate the binding enhancements of the multivalent ligands with their ability to bind to the protein in a chelating mode. The best WGA ligand is a trivalent cluster with an IC50 value of 220 nM. Calculated per mol of contained chitobiose, this is the best WGA ligand known so far.

  15. Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetic, and Rate Rule Optimizations for 2-Methylhexane

    KAUST Repository

    Mohamed, Samah; Cai, Liming; Khaled, Fathi; Banyon, Colin; Wang, Zhandong; Rachidi, Mariam El; Pitsch, Heinz; Curran, Henry J.; Farooq, Aamir; Sarathy, Mani

    2016-01-01

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxy-alkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model’s performance. The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model.

  16. Modeling Ignition of a Heptane Isomer: Improved Thermodynamics, Reaction Pathways, Kinetic, and Rate Rule Optimizations for 2-Methylhexane

    KAUST Repository

    Mohamed, Samah

    2016-03-21

    Accurate chemical kinetic combustion models of lightly branched alkanes (e.g., 2-methylalkanes) are important to investigate the combustion behavior of real fuels. Improving the fidelity of existing kinetic models is a necessity, as new experiments and advanced theories show inaccuracies in certain portions of the models. This study focuses on updating thermodynamic data and the kinetic reaction mechanism for a gasoline surrogate component, 2-methylhexane, based on recently published thermodynamic group values and rate rules derived from quantum calculations and experiments. Alternative pathways for the isomerization of peroxy-alkylhydroperoxide (OOQOOH) radicals are also investigated. The effects of these updates are compared against new high-pressure shock tube and rapid compression machine ignition delay measurements. It is shown that rate constant modifications are required to improve agreement between kinetic modeling simulations and experimental data. We further demonstrate the ability to optimize the kinetic model using both manual and automated techniques for rate parameter tunings to improve agreement with the measured ignition delay time data. Finally, additional low temperature chain branching reaction pathways are shown to improve the model’s performance. The present approach to model development provides better performance across extended operating conditions while also strengthening the fundamental basis of the model.

  17. A combined high-temperature experimental and theoretical kinetic study of the reaction of dimethyl carbonate with OH radicals

    KAUST Repository

    Khaled, Fathi; Giri, Binod; Szőri, Milá n; Mai, Tam V.-T.; Huynh, Lam K.; Farooq, Aamir

    2017-01-01

    The reaction kinetics of dimethyl carbonate (DMC) and OH radicals were investigated behind reflected shock waves over the temperature range of 872-1295 K and at pressures near 1.5 atm. Reaction progress was monitored by detecting OH radicals at 306.69 nm using a UV laser absorption technique. The rate coefficients for the reaction of DMC with OH radicals were extracted using a detailed kinetic model developed by Glaude et al. (Proc. Combust. Inst. 2005, 30(1), 1111-1118). The experimental rate coefficients can be expressed in Arrhenius form as: kexpt'l = 5.15 × 10(13) exp(-2710.2/T) cm(3) mol(-1) s(-1). To explore the detailed chemistry of the DMC + OH reaction system, theoretical kinetic analyses were performed using high-level ab initio and master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) calculations. Geometry optimization and frequency calculations were carried out at the second-order Møller-Plesset (MP2) perturbation level of theory using Dunning's augmented correlation consistent-polarized valence double-ζ basis set (aug-cc-pVDZ). The energy was extrapolated to the complete basis set using single point calculations performed at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory. For comparison purposes, additional ab initio calculations were also carried out using composite methods such as CBS-QB3, CBS-APNO, G3 and G4. Our calculations revealed that the H-abstraction reaction of DMC by OH radicals proceeds via an addition elimination mechanism in an overall exothermic process, eventually forming dimethyl carbonate radicals and H2O. Theoretical rate coefficients were found to be in excellent agreement with those determined experimentally. Rate coefficients for the DMC + OH reaction were combined with literature rate coefficients of four straight chain methyl ester + OH reactions to extract site-specific rates of H-abstraction from methyl esters by OH radicals.

  18. Kinetic and Mechanistic Study of the pH-Dependent Activation (Epoxidation) of Prodrug Treosulfan Including the Reaction Inhibition in a Borate Buffer.

    Science.gov (United States)

    Romański, Michał; Ratajczak, Whitney; Główka, Franciszek

    2017-07-01

    A prodrug treosulfan (T) undergoes a pH-dependent activation to epoxide derivatives. The process seems to involve an intramolecular Williamson reaction (IWR) but clear kinetic evidence is lacking. Moreover, a cis-diol system present in the T structure is expected to promote complexation with boric acid. As a result, the prodrug epoxidation would be inhibited; however, this phenomenon has not been investigated. In this article, the effect of pH on the kinetics of T conversion to its monoepoxide was studied from a mechanistic point of view. Also, the influence of boric acid on the reaction kinetics was examined. The rate constants observed for the activation of T (k obs ) in acetate, phosphate, and carbonate buffers satisfied the equation logk obs  = -7.48 + 0.96 pH. The reaction was inhibited in the excess of boric acid over T, and the k obs decreased with increasing borate buffer concentration. The experimental results were consistent with the inhibition model that included the formation of a tetrahedral, anionic T-boric acid monoester. To conclude, in nonborate buffers, the T activation to (2S,3S)-1,2-epoxybutane-3,4-diol 4-methanesulfonate follows IWR mechanism. A borate buffer changes the reaction kinetics and complicates kinetic analysis. Copyright © 2017 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

  19. Chemical kinetics and reaction dynamics

    CERN Document Server

    Houston, Paul L

    2006-01-01

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

  20. Site-specific chemical conjugation of human Fas ligand extracellular domain using trans-cyclooctene - methyltetrazine reactions.

    Science.gov (United States)

    Muraki, Michiro; Hirota, Kiyonori

    2017-07-03

    Fas ligand plays a key role in the human immune system as a major cell death inducing protein. The extracellular domain of human Fas ligand (hFasLECD) triggers apoptosis of malignant cells, and therefore is expected to have substantial potentials in medical biotechnology. However, the current application of this protein to clinical medicine is hampered by a shortage of the benefits relative to the drawbacks including the side-effects in systemic administration. Effective procedures for the engineering of the protein by attaching useful additional functions are required to overcome the problem. A procedure for the site-specific chemical conjugation of hFasLECD with a fluorochrome and functional proteins was devised using an inverse-electron-demand Diels-Alder reaction between trans-cyclooctene group and methyltetrazine group. The conjugations in the present study were attained by using much less molar excess amounts of the compounds to be attached as compared with the conventional chemical modification reactions using maleimide derivatives in the previous study. The isolated conjugates of hFasLECD with sulfo-Cy3, avidin and rabbit IgG Fab' domain presented the functional and the structural integrities of the attached molecules without impairing the specific binding activity toward human Fas receptor extracellular domain. The present study provided a new fundamental strategy for the production of the engineered hFasLECDs with additional beneficial functions, which will lead to the developments of the improved diagnostic systems and the effective treatment methods of serious diseases by using this protein as a component of novel molecular tools.

  1. Unravelling the kinetics of the formation of acrylamide in the Maillard reaction of fructose and asparagine by multiresponse modelling

    NARCIS (Netherlands)

    Knol, J.J.; Linssen, J.P.H.; Boekel, van M.A.J.S.

    2010-01-01

    A kinetic model for the formation of acrylamide in a fructose–asparagine reaction system at initial pH 5.5 is proposed, based on an approach called multiresponse kinetic modelling. The formation of acetic acid and formic acid from the degradation of fructose and its isomer glucose was included in

  2. Exploring the kinetic and thermodynamic aspects of four-electron electrochemical reactions: electrocatalysis of oxygen evolution by metal oxides and biological systems.

    Science.gov (United States)

    Wang, Vincent C-C

    2016-08-10

    Finding fundamental and general mechanisms for electrochemical reactions, such as the oxygen evolution reaction (OER) from water and reduction of CO2, plays vital roles in developing the desired electrocatalysts for facilitating solar fuel production. Recently, density functional theory (DFT) calculations have shown that there is a universal scaling relation of adsorption energy between key intermediate species, HO(ad) and HOO(ad), on the surface of metal oxides as OER electrocatalysts. In this paper, a kinetic and thermodynamic model for the four-electron electrochemical reaction based on previous OER mechanisms proposed by DFT calculations is developed to further investigate the electrocatalytic properties over a wide range of metal oxides and photosystem II. The OER activity of metal oxides (i.e. electrocatalytic current) calculated from the DFT-calculated equilibrium potentials with kinetic properties, such as the rate constants for interfacial electron transfer and catalytic turnover, can lead to a volcano-shaped trend that agrees with the results observed in experiments. In addition, the kinetic aspects of the impact on the electrocatalysts are evaluated. Finally, comparing the results of metal oxides and photosystem II, and fitting experimental voltammograms give further insights into kinetic and thermodynamic roles. Here, the general guidelines for designing OER electrocatalysts with unified kinetic and thermodynamic properties are presented.

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

    Science.gov (United States)

    Sattsangi, Prem D.

    2011-01-01

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

  4. Secondary ligand-directed assembly of Co(II) coordination polymers based on a pyridine carboxylate ligand

    International Nuclear Information System (INIS)

    Cao, Ke-Li; Zhang, Yi-Ping; Cai, Yi-Ni; Xu, Xiao-Wei; Feng, Yun-Long

    2014-01-01

    To investigate the influence of hydrogen bonds and secondary ligands on the structures and properties of the resulting frameworks, five new Co(II) compounds have been synthesized by the reactions of Co(II) salts and 3,5-bis(pyridin-4-ylmethoxy)benzoic acid (HL) with four rationally selected dicarboxylic acid ligands. Without secondary ligand, we got one compound [CoL 2 (H 2 O) 2 ] n ·2nH 2 O (1), which possesses a 1D chain structure. In the presence of ancillary ligands, namely, 1,3-adamantanedicarboxylic acid (H 2 adbc), terephthalic acid (H 2 tpa), thiophene-2,5-dicarboxylic acid (H 2 tdc) and 1,4-benzenedithioacetic acid (H 2 bdtc), four 3D structures [Co 2 L 2 (adbc)] n ·nH 2 O (2), [Co 2 L 2 (tpa)] n (3), [Co 2 L 2 (tdc)] n (4), [Co 2 L 2 (bdtc)(H 2 O)] n (5) were obtained, respectively. It can be observed from the architectures of 1–5 that hydrogen bonds and secondary ligands both have great effects on the spatial connective fashions, resulting in the formation of various dimensional compounds. The XRPD, TGA data of title polymers and the magnetic properties for 2 and 5 have also been investigated. - Graphical abstract: The structural differences show that the ancillary ligands have great effects on the spatial connective fashions, resulting in the formation of various dimensional compounds. - Highlights: • Five new Co(II) coordination polymers have been synthesized by solvothermal reactions based on 3,5-bis(pyridin-4-ylmethoxy)benzoic acid (HL). • The long-flexible ligand (HL) is a good candidate to produce interpenetrating architectures. • The secondary dicarboxylic acid ligands play important roles in the spatial connective fashions and the formation of various dimensional compounds. • The magnetism studies show that both 2 and 5 exhibit antiferromagnetic interactions

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

    NARCIS (Netherlands)

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

    2012-01-01

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

  6. Screening small-molecule compound microarrays for protein ligands without fluorescence labeling with a high-throughput scanning microscope.

    Science.gov (United States)

    Fei, Yiyan; Landry, James P; Sun, Yungshin; Zhu, Xiangdong; Wang, Xiaobing; Luo, Juntao; Wu, Chun-Yi; Lam, Kit S

    2010-01-01

    We describe a high-throughput scanning optical microscope for detecting small-molecule compound microarrays on functionalized glass slides. It is based on measurements of oblique-incidence reflectivity difference and employs a combination of a y-scan galvometer mirror and an x-scan translation stage with an effective field of view of 2 cm x 4 cm. Such a field of view can accommodate a printed small-molecule compound microarray with as many as 10,000 to 20,000 targets. The scanning microscope is capable of measuring kinetics as well as endpoints of protein-ligand reactions simultaneously. We present the experimental results on solution-phase protein reactions with small-molecule compound microarrays synthesized from one-bead, one-compound combinatorial chemistry and immobilized on a streptavidin-functionalized glass slide.

  7. Reaction kinetic model of the surface-mediated formation of PCDD/F from pyrolysis of 2-chlorophenol on a CuP/Silica suface

    Energy Technology Data Exchange (ETDEWEB)

    Lomnicki, S.; Khachatryan, L.; Dellinger, B. [Louisiana State Univ., Baton Rouge (United States). Dept. of Chemistry

    2004-09-15

    One of the major challenges in developing predictive models of the surface mediated pollutant formation and fuel combustion is the construction of reliable reaction kinetic mechanisms and models. While the homogeneous, gas-phase chemistry of various light fuels such as hydrogen and methane is relatively well-known large uncertainties exist in the reaction paths of surface mediated reaction mechanisms for even these very simple species. To date, no detailed kinetic consideration of the surface mechanisms of formation of complex organics such as PCDD/F have been developed. In addition to the complexity of the mechanism, a major difficulty is the lack of reaction kinetic parameters (pre-exponential factor and activation energy) of surface reactions, Consequently, numerical studies of the surface-mediated formation of PCDD/F have often been incorporated only a few reactions. We report the development of a numerical multiple-step surface model based on experimental data of surface mediated (5% CuO/SiO2) conversion of 2-monochlorphenol (2-MCP) to PCDD/F under pyrolytic or oxidative conditions. A reaction kinetic model of the catalytic conversion of 2-MCP on the copper oxide catalyst under pyrolytic conditions was developed based on a detailed multistep surface reaction mechanism developed in our laboratory. The performance of the chemical model is assessed by comparing the numerical predictions with experimental measurements. SURFACE CHEMKIN (version 3.7.1) software was used for modeling. Our results confirm the validity of previously published mechanism of the reaction and provides new insight concerning the formation of PCDD/F formation in combustion processes. This model successfully explains the high yields of PCDD/F at low temperatures that cannot be explained using a purely gas-phase mode.

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

    Science.gov (United States)

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

    2013-12-01

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

  9. Kinetic Modeling of the Reaction Rate for Quartz and Carbon Pellet

    Science.gov (United States)

    Li, Fei; Tangstad, Merete

    2018-04-01

    Kinetic modeling of quartz and carbon pellet at temperatures of 1898 K, 1923 K, and 1948 K (1625 °C, 1650 °C, and 1675 °C) was investigated in this study. The carbon materials used were charcoal, coke, coal, and preheated coal. The overall SiC producing reaction can be described by the reaction SiO2 + 3C = SiC + 2CO. In the SiC-producing step, the reaction rate of quartz and carbon pellet can be expressed as {d{ pct}}/dt = ( {1 - 0.40 × X_{fix - C}^{ - 0.86} × FC × {pct}} ) × A × \\exp ( { - E/{{RT}}} ) The carbon factor F C was used to describe the influence of different carbon materials that effect the gas-solid interface reaction. For charcoal, coke, coal, and preheated coal, the F C values were 0.83, 0.80, 0.94, and 0.83, respectively. The pre-exponential factor A values for the preceding four carbon materials were 1.06 × 1016 min-1, 4.21 × 1015 min-1, 3.85 × 109 min-1, and 1.00 × 1025 min-1, respectively. The activation energies E for the SiC-producing step were 570, 563, 336, and 913 kJ/mole for charcoal, coke, coal, and preheated coal pellets, respectively.

  10. Noise-induced modulation of the relaxation kinetics around a non-equilibrium steady state of non-linear chemical reaction networks.

    Science.gov (United States)

    Ramaswamy, Rajesh; Sbalzarini, Ivo F; González-Segredo, Nélido

    2011-01-28

    Stochastic effects from correlated noise non-trivially modulate the kinetics of non-linear chemical reaction networks. This is especially important in systems where reactions are confined to small volumes and reactants are delivered in bursts. We characterise how the two noise sources confinement and burst modulate the relaxation kinetics of a non-linear reaction network around a non-equilibrium steady state. We find that the lifetimes of species change with burst input and confinement. Confinement increases the lifetimes of all species that are involved in any non-linear reaction as a reactant. Burst monotonically increases or decreases lifetimes. Competition between burst-induced and confinement-induced modulation may hence lead to a non-monotonic modulation. We quantify lifetime as the integral of the time autocorrelation function (ACF) of concentration fluctuations around a non-equilibrium steady state of the reaction network. Furthermore, we look at the first and second derivatives of the ACF, each of which is affected in opposite ways by burst and confinement. This allows discriminating between these two noise sources. We analytically derive the ACF from the linear Fokker-Planck approximation of the chemical master equation in order to establish a baseline for the burst-induced modulation at low confinement. Effects of higher confinement are then studied using a partial-propensity stochastic simulation algorithm. The results presented here may help understand the mechanisms that deviate stochastic kinetics from its deterministic counterpart. In addition, they may be instrumental when using fluorescence-lifetime imaging microscopy (FLIM) or fluorescence-correlation spectroscopy (FCS) to measure confinement and burst in systems with known reaction rates, or, alternatively, to correct for the effects of confinement and burst when experimentally measuring reaction rates.

  11. A robust methodology for kinetic model parameter estimation for biocatalytic reactions

    DEFF Research Database (Denmark)

    Al-Haque, Naweed; Andrade Santacoloma, Paloma de Gracia; Lima Afonso Neto, Watson

    2012-01-01

    lead to globally optimized parameter values. In this article, a robust methodology to estimate parameters for biocatalytic reaction kinetic expressions is proposed. The methodology determines the parameters in a systematic manner by exploiting the best features of several of the current approaches...... parameters, which are strongly correlated with each other. State-of-the-art methodologies such as nonlinear regression (using progress curves) or graphical analysis (using initial rate data, for example, the Lineweaver-Burke plot, Hanes plot or Dixon plot) often incorporate errors in the estimates and rarely...

  12. Reaction of Non-Symmetric Schiff Base Metallo-Ligand Complexes Possessing an Oxime Function with Ln Ions

    Directory of Open Access Journals (Sweden)

    Jean-Pierre Costes

    2018-03-01

    Full Text Available The preparation of non-symmetric Schiff base ligands possessing one oxime function that is associated to a second function such as pyrrole or phenol function is first described. These ligands, which possess inner N4 or N3O coordination sites, allow formation of cationic or neutral non-symmetric CuII or NiII metallo-ligand complexes under their mono- or di-deprotonated forms. In presence of Lanthanide ions the neutral complexes do not coordinate to the LnIII ions, the oxygen atom of the oxime function being only hydrogen-bonded to a water molecule that is linked to the LnIII ion. This surprising behavior allows for the isolation of LnIII ions by non-interacting metal complexes. Reaction of cationic NiII complexes possessing a protonated oxime function with LnIII ions leads to the formation of original and dianionic (Gd(NO352− entities that are well separated from each other. This work highlights the preparation of well isolated mononuclear LnIII entities into a matrix of diamagnetic metal complexes. These new complexes complete our previous work dealing with the complexing ability of the oxime function toward Lanthanide ions. It could open the way to the synthesis of new entities with interesting properties, such as single-ion magnets for example.

  13. Kinetics of reaction of 1,10- decanedioland dimeric fatty acid C36

    International Nuclear Information System (INIS)

    Falah, A.

    2013-01-01

    Kinetic studies were carried out on the reaction between 1,10- Decanedioland dimeric fatty acid C 3 6 in melt phase. The reaction was performed at 140, 150, 160, 170, and 185 o C and followed by determining the acid value of the product. The polyesterfication reaction was found to be of overall second order with an activation energy of 39,91kj/mol up to (50, 44, 55,42, 63)% conversion at (140, 150, 160, 170, 185) o C and overall third order with an activation energy of 71.17 k j/ mol above (50, 44, 55, 42, 63)% conversion at (140, 150, 160, 170, 185) o C. The Degree of Polymerization, number average molecular weight and weight average molecular weight have been calculated during different times, the relationships between Degree of Polymerization, number average molecular weight, weight average molecular weight and the times is linear until, (50, 44, 55, 42, 63)%conversion at (140, 150, 160, 170, 185) o C. (author)

  14. Ligand-Receptor Interaction-Mediated Transmembrane Transport of Dendrimer-like Soft Nanoparticles: Mechanisms and Complicated Diffusive Dynamics.

    Science.gov (United States)

    Liang, Junshi; Chen, Pengyu; Dong, Bojun; Huang, Zihan; Zhao, Kongyin; Yan, Li-Tang

    2016-05-09

    Nearly all nanomedical applications of dendrimer-like soft nanoparticles rely on the functionality of attached ligands. Understanding how the ligands interact with the receptors in cell membrane and its further effect on the cellular uptake of dendrimer-like soft nanoparticles is thereby a key issue for their better application in nanomedicine. However, the essential mechanism and detailed kinetics for the ligand-receptor interaction-mediated transmembrane transport of such unconventional nanoparticles remain poorly elucidated. Here, using coarse-grained simulations, we present the very first study of molecular mechanism and kinetics behaviors for the transmembrane transport of dendrimer-like soft nanoparticles conjugated with ligands. A phase diagram of interaction states is constructed through examining ligand densities and membrane tensions that allows us to identify novel endocytosis mechanisms featured by the direct wrapping and the penetration-extraction vesiculation. The results provide an in-depth insight into the diffusivity of receptors and dendrimer in the membrane plane and demonstrate how the ligand density influences receptor diffusion and uptake kinetics. It is interesting to find that the ligand-conjugated dendrimers present superdiffusive behaviors on a membrane, which is revealed to be driven by the random fluctuation dynamics of the membrane. The findings facilitate our understanding of some recent experimental observations and could establish fundamental principles for the future development of such important nanomaterials for widespread nanomedical applications.

  15. Application of adjustable pulse lasers to studying rapid reaction kinetics of excited lanthanide complexing

    Energy Technology Data Exchange (ETDEWEB)

    Gruzdev, V.P. (Gosudarstvennyj Opticheskij Inst., Leningrad (USSR))

    1983-12-01

    Using some europium (3) ion complexes new possibilities to be opened by application of adjustable pulse lasers for studying rapid reactions of electron-excited metal ion complexing are demonstrated. The 6Zh rhodamine pulse laser is used as a source of nonequilibrium photoexcitation of an array of Eu/sup 3 +/ complexes in the luminescent kinetic spectroscopy method. The following results are obtained: for the first time the rate of reaction of acetate ion substitution for water molecules of an excited (/sup 5/D/sub 0/) ion of Eu/sup 3 +/ was measured to be (0.7+-0.2)x10/sup 7/ s/sup -1/; using direct experiments the lower limit for the rate of transition of one isomeric form of the excited Eu x EDTA complex into another one in an aqueous solution is determined to be 5x10/sup 5/ s/sup -1/ at 295 K; the kinetics of the excitation energy migration beteen aqueous solvates of Eu/sup 3 +/ and EuxEDTA complexes is investigated.

  16. Kinetic and theoretical studies on the protonation of [Ni(2-SC6H4N){PhP(CH2CH2PPh2)2}]+: nitrogen versus sulfur as the protonation site.

    Science.gov (United States)

    Petrou, Athinoula L; Koutselos, Andreas D; Wahab, Hilal S; Clegg, William; Harrington, Ross W; Henderson, Richard A

    2011-02-07

    The complexes [Ni(4-Spy)(triphos)]BPh(4) and [Ni(2-Spy)(triphos)]BPh(4) {triphos = PhP(CH(2)CH(2)PPh(2))(2), 4-Spy = 4-pyridinethiolate, 2-Spy = 2-pyridinethiolate} have been prepared and characterized both spectroscopically and using X-ray crystallography. In both complexes the triphos is a tridentate ligand. However, [Ni(4-Spy)(triphos)](+) comprises a 4-coordinate, square-planar nickel with the 4-Spy ligand bound to the nickel through the sulfur while [Ni(2-Spy)(triphos)](+) contains a 5-coordinate, trigonal-bipyramidal nickel with a bidentate 2-Spy ligand bound to the nickel through both sulfur and nitrogen. The kinetics of the reactions of [Ni(4-Spy)(triphos)](+) and [Ni(2-Spy)(triphos)](+) with lutH(+) (lut = 2,6-dimethylpyridine) in MeCN have been studied using stopped-flow spectrophotometry, and the two complexes show very different reactivities. The reaction of [Ni(4-Spy)(triphos)](+) with lutH(+) is complete within the deadtime of the stopped-flow apparatus (2 ms) and corresponds to protonation of the nitrogen. However, upon mixing [Ni(2-Spy)(triphos)](+) and lutH(+) a reaction is observed (on the seconds time scale) to produce an equilibrium mixture. The mechanistic interpretation of the rate law has been aided by the application of MSINDO semiempirical and ADF calculations. The kinetics and calculations are consistent with the reaction between [Ni(2-Spy)(triphos)](+) and lutH(+) involving initial protonation of the sulfur followed by dissociation of the nitrogen and subsequent transfer of the proton from sulfur to nitrogen. The factors affecting the position of protonation and the coupling of the coordination state of the 2-pyridinethiolate ligand to the site of protonation are discussed.

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

    Science.gov (United States)

    Basilevsky, M V; Odinokov, A V; Titov, S V; Mitina, E A

    2013-12-21

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ξ0 = ℏω0/k(B)T where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T → 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local

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

    Science.gov (United States)

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

    2011-01-01

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

  19. Ligand-controlled, tunable silver-catalyzed C-H amination.

    Science.gov (United States)

    Alderson, Juliet M; Phelps, Alicia M; Scamp, Ryan J; Dolan, Nicholas S; Schomaker, Jennifer M

    2014-12-03

    The development of readily tunable and regioselective C-H functionalization reactions that operate solely through catalyst control remains a challenge in modern organic synthesis. Herein, we report that simple silver catalysts supported by common nitrogenated ligands can be used to tune a nitrene transfer reaction between two different types of C-H bonds. The results reported herein represent the first example of ligand-controlled and site-selective silver-promoted C-H amination.

  20. Synchronous parallel kinetic Monte Carlo for continuum diffusion-reaction systems

    International Nuclear Information System (INIS)

    Martinez, E.; Marian, J.; Kalos, M.H.; Perlado, J.M.

    2008-01-01

    A novel parallel kinetic Monte Carlo (kMC) algorithm formulated on the basis of perfect time synchronicity is presented. The algorithm is intended as a generalization of the standard n-fold kMC method, and is trivially implemented in parallel architectures. In its present form, the algorithm is not rigorous in the sense that boundary conflicts are ignored. We demonstrate, however, that, in their absence, or if they were correctly accounted for, our algorithm solves the same master equation as the serial method. We test the validity and parallel performance of the method by solving several pure diffusion problems (i.e. with no particle interactions) with known analytical solution. We also study diffusion-reaction systems with known asymptotic behavior and find that, for large systems with interaction radii smaller than the typical diffusion length, boundary conflicts are negligible and do not affect the global kinetic evolution, which is seen to agree with the expected analytical behavior. Our method is a controlled approximation in the sense that the error incurred by ignoring boundary conflicts can be quantified intrinsically, during the course of a simulation, and decreased arbitrarily (controlled) by modifying a few problem-dependent simulation parameters

  1. Fast and calibration free determination of first order reaction kinetics in API synthesis using in-situ ATR-FTIR.

    Science.gov (United States)

    Rehbein, Moritz C; Husmann, Sascha; Lechner, Christian; Kunick, Conrad; Scholl, Stephan

    2018-05-01

    In early stages of drug development only sparse amounts of the key substances are available, which is problematic for the determination of important process data like reaction kinetics. Therefore, it is important to perform experiments as economically as possible, especially in regards to limiting compounds. Here we demonstrate the use of a temperature step experiment enabling the determination of complete reaction kinetics in a single non-isothermal experiment. In contrast to the traditionally used HPLC, the method takes advantage of the high measuring rate and the low amount of labor involved in using in-situ ATR-FTIR to determine time-dependent concentration-equivalent data. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Material Balance And Reaction Kinetics Modeling For Penex Isomerization Process In Daura Refinery

    Directory of Open Access Journals (Sweden)

    Hamadi Adel Sharif

    2017-01-01

    Full Text Available Penex Deisohexanizer isomerization of light straight run naphtha is a significant process for petroleum refining and proved to be effective technology to produce gasoline components with a high octane number. Modeling of the chemical kinetic reactions is an important tool because it is a better tool for optimization of the experimental data into parameters used for industrial reactors. The present study deals on the isomerization process in Daura refinery. Material balance calculations were done mathematically on the unit for the kinetics prediction purpose. A kinetic mathematical model was derived for the prediction rate constants K1 and K2 and activation energy Ea at operating temperatures range 120-180°C. According to the model, the results show that with increasing of temperature leads to increased K1 directly, where the K2 values proportional inversely. The activation energy results show that Ea1(nC6

  3. A spectroscopic study of the effect of ligand complexation on the reduction of uranium(VI) by anthraquinone-2,6-disulfonate (AH2DS)

    International Nuclear Information System (INIS)

    Wang, Z.; Wagnon, K.B.; Ainsworth, C.C.; Liu, C.; Rosso, K.M.; Fredrickson, J.K.

    2008-01-01

    In this paper, the reduction rate of uranyl complexes with hydroxide, carbonate, EDTA, and desferriferrioxamine B (DFB) by anthraquinone-2,6-disulfonate (AH 2 DS) is studied by stopped-flow kinetic technique under anoxic atmosphere. The apparent reaction rates varied with ligand type, solution pH, and U(VI) concentration. For each ligand, a single largest pseudo-1 st order reaction rate constant, k obs , within the studied pH range was observed, suggesting the influence of pH-dependent speciation on the U(VI) reduction rate. The maximum reaction rate found in each case followed the order of OH - > CO 3 2- > EDTA > DFB, in reverse order of the trend of the thermodynamic stability of the uranyl complexes and ionic sizes of the ligands. The pH-dependent rates were modeled using a second-order rate expression that was assumed to be dependent on a single U(VI) complex and an AH 2 DS species. By quantitatively comparing the calculated and measured apparent rate constants as a function of pH, species AHDS 3- was suggested as the primary reductant in all cases examined. Species UO 2 CO 3 (aq), UO 2 HEDTA - , and (UO 2 ) 2 (OH) 2 2+ were suggested as the principal electron acceptors among the U(VI) species mixture in each of the carbonate, EDTA, and hydroxyl systems, respectively. (orig.)

  4. Charge-Transfer Effects in Ligand Exchange Reactions of Au25 Monolayer-Protected Clusters.

    Science.gov (United States)

    Carducci, Tessa M; Blackwell, Raymond E; Murray, Royce W

    2015-04-16

    Reported here are second-order rate constants of associative ligand exchanges of Au25L18 nanoparticles (L = phenylethanethiolate) of various charge states, measured by proton nuclear magnetic resonance at room temperature and below. Differences in second-order rate constants (M(-1) s(-1)) of ligand exchange (positive clusters ∼1.9 × 10(-5) versus negative ones ∼1.2 × 10(-4)) show that electron depletion retards ligand exchange. The ordering of rate constants between the ligands benzeneselenol > 4-bromobenzene thiol > benzenethiol reveals that exchange is accelerated by higher acidity and/or electron donation capability of the incoming ligand. Together, these observations indicate that partial charge transfer occurs between the nanoparticle and ligand during the exchange and that this is a rate-determining effect in the process.

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

    Science.gov (United States)

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

    2008-01-01

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

  6. Deduction of kinetic mechanism in multisubstrate enzyme reactions from tritium isotope effects. Application to dopamine beta-hydroxylase

    International Nuclear Information System (INIS)

    Klinman, J.P.; Humphries, H.; Voet, J.G.

    1980-01-01

    Primary tritium isotope effects have been measured for the hydroxylation of [2-3H] dopamine catalyzed by dopamine beta-hydroxylase. Experimental values vary from 8.8 +/- 1.4 at 0.02 mM oxygen to 4.1 +/- 0.6 at 1.0 mM oxygen. It is shown that the observed dependence of the isotope effect on oxygen concentration provides unequivocal evidence for a kinetically significant dissociation of both dopamine and oxygen from enzyme, ternary complex. This approach, which is applicable to any multisubstrate enzyme characterized by detectable kinetic isotope effects, provides an alternate to classical methods for the elucidation of kinetic order in enzyme-catalyzed reactions

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1993-12-01

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

  8. Kinetic isotope effects in the CH4 + H→CH3 + H2 system. Predictions of the LMR six-body potential-energy reaction hypersurface

    International Nuclear Information System (INIS)

    Marriott, T.D.

    1976-01-01

    Scope of Study: The purpose of this study was two-fold. First, it served to test, in part, the usefulness of the LMR six-body potential-energy surface (LMR-PES) for transition-state theory predictions of the kinetic isotope effects for both the forward and reverse reactions of CH 4 + H reversible CH 3 + H 2 . In this regard the agreement between experimental and theoretical isotope effects, assuming the former to be accurate, provides information about the accuracy of the curvature of the potential energy surface for motion both parallel and perpendicular to the reaction coordinate. Second, these isotope effects were used to assess the validity of a number of qualitative and semi-quantitative interpretations of kinetic isotope effects developed in physical organic chemistry with regard to this reaction system. The force constants and geometries obtained numerically from the LMR-PES were found to produce reasonable harmonic approximations to the reactant normal mode frequencies. Neglecting tunneling, the LMR-PES reasonably reproduces the experimental k/sub H//k/sub D/ values for the reactions CH 4 + H(D), CH 3 + HD(DH) and CD 2 + HD(DH). Since previous theoretical treatments of primary deuterium kinetic isotope effects have neglected the bending normal mode frequencies, a semi-quantitative study of the effect of neglecting bending frequencies on the VP, EXC, and ZPE elements as well as the transition-state theory kinetic isotope effects was performed. The Swain-Schaad relationship between primary deuterium and tritium kinetic isotope effects was shown to hold to a reasonable degree of accuracy for the LMR-PES reaction system. A relationship between 13-carbon and 14-carbon kinetic isotope effects similar to the Swain-Schaad relationship was derived

  9. Kinetics of transuranium element oxidation-reduction reactions in solution; Cinetique des reactions d'oxydo-reduction des elements transuraniens en solution

    Energy Technology Data Exchange (ETDEWEB)

    Gourisse, D. [Commissariat a l' Energie Atomique, Fontenay-aux-Roses (France). Centre d' Etudes Nucleaires

    1966-09-01

    A review of the kinetics of U, Np, Pu, Am oxidation-reduction reactions is proposed. The relations between the different activation thermodynamic functions (compensatory effect, formal entropy of the activated complex, magnitude of reactions velocities) are considered. The effects of acidity, ionic strength deuterium and mixed solvents polarity on reactions rates are described. The effect of different anions on reactions rates are explained by variations of the reaction standard free energy and variations of the activation free energy (coulombic interactions) resulting from the complexation of dissolved species by these anions. (author) [French] Une revue systematique de la cinetique des reactions d'oxydo-reduction des elements U, Np, Pu, Am, en solution perchlorique est proposee. Des considerations relatives aux grandeurs thermodynamiques d'activation associees aux actes elementaires (effet de compensation, entropie standard des complexes actives, rapidite des reactions) sont developpees. L'influence de l'acidite, de la force ionique, de l'eau lourde et de la polarite des solvants mixtes sur la vitesse des reactions est decrite. Enfin l'influence des differents anions sur la vitesse des reactions est expliquee par les variations de l'enthalpie libre standard de la reaction et de l'enthalpie libre d'activation (travail des forces electrostatiques) resultant de la complexation des especes dissoutes dans la solution. (auteur)

  10. Heterogeneous reaction of particulate chlorpyrifos with NO3 radicals: Products, pathways, and kinetics

    Science.gov (United States)

    Li, Nana; Zhang, Peng; Yang, Bo; Shu, Jinian; Wang, Youfeng; Sun, Wanqi

    2014-08-01

    Chlorpyrifos is a typical chlorinated organophosphorus pesticide. The heterogeneous reaction of chlorpyrifos particles with NO3 radicals was investigated using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and a real-time atmospheric gas analysis mass spectrometer. Chlorpyrifos oxon, 3,5,6-trichloro-2-pyridinol, O,O-diethyl O-hydrogen phosphorothioate, O,O-diethyl ester thiophosphoric acid, diethyl hydrogen phosphate and a phosphinyl disulfide compound were identified as the main degradation products. The heterogeneous reaction pathways were proposed and their kinetic processes were investigated via a mixed-phase relative rate method. The observed effective rate constant is 3.4 ± 0.2 × 10-12 cm3 molecule-1 s-1.

  11. Noise-induced modulation of the relaxation kinetics around a non-equilibrium steady state of non-linear chemical reaction networks.

    Directory of Open Access Journals (Sweden)

    Rajesh Ramaswamy

    2011-01-01

    Full Text Available Stochastic effects from correlated noise non-trivially modulate the kinetics of non-linear chemical reaction networks. This is especially important in systems where reactions are confined to small volumes and reactants are delivered in bursts. We characterise how the two noise sources confinement and burst modulate the relaxation kinetics of a non-linear reaction network around a non-equilibrium steady state. We find that the lifetimes of species change with burst input and confinement. Confinement increases the lifetimes of all species that are involved in any non-linear reaction as a reactant. Burst monotonically increases or decreases lifetimes. Competition between burst-induced and confinement-induced modulation may hence lead to a non-monotonic modulation. We quantify lifetime as the integral of the time autocorrelation function (ACF of concentration fluctuations around a non-equilibrium steady state of the reaction network. Furthermore, we look at the first and second derivatives of the ACF, each of which is affected in opposite ways by burst and confinement. This allows discriminating between these two noise sources. We analytically derive the ACF from the linear Fokker-Planck approximation of the chemical master equation in order to establish a baseline for the burst-induced modulation at low confinement. Effects of higher confinement are then studied using a partial-propensity stochastic simulation algorithm. The results presented here may help understand the mechanisms that deviate stochastic kinetics from its deterministic counterpart. In addition, they may be instrumental when using fluorescence-lifetime imaging microscopy (FLIM or fluorescence-correlation spectroscopy (FCS to measure confinement and burst in systems with known reaction rates, or, alternatively, to correct for the effects of confinement and burst when experimentally measuring reaction rates.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2015-01-01

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

  13. Malonic acid concentration as a control parameter in the kinetic analysis of the Belousov-Zhabotinsky reaction under batch conditions.

    Science.gov (United States)

    Blagojević, Slavica M; Anić, Slobodan R; Cupić, Zeljko D; Pejić, Natasa D; Kolar-Anić, Ljiljana Z

    2008-11-28

    The influence of the initial malonic acid concentration [MA]0 (8.00 x 10(-3) sulfuric acid (1.00 mol dm(-3)) and cerium sulfate (2.50 x 10(-3) mol dm(-3)) on the dynamics and the kinetics of the Belousov-Zhabotinsky (BZ) reactions was examined under batch conditions at 30.0 degrees C. The kinetics of the BZ reaction was analyzed by the earlier proposed method convenient for the examinations of the oscillatory reactions. In the defined region of parameters where oscillograms with only large-amplitude relaxation oscillations appeared, the pseudo-first order of the overall malonic acid decomposition with a corresponding rate constant of 2.14 x 10(-2) min(-1) was established. The numerical results on the dynamics and kinetics of the BZ reaction, carried out by the known skeleton model including the Br2O species, were in good agreement with the experimental ones. The already found saddle node infinite period (SNIPER) bifurcation point in transition from a stable quasi-steady state to periodic orbits and vice versa is confirmed by both experimental and numerical investigations of the system under consideration. Namely, the large-amplitude relaxation oscillations with increasing periods between oscillations in approaching the bifurcation points at the beginning and the end of the oscillatory domain, together with excitability of the stable quasi-steady states in their vicinity are obtained.

  14. Interactions of nitrite with catalase: Enzyme activity and reaction kinetics studies.

    Science.gov (United States)

    Krych-Madej, Justyna; Gebicka, Lidia

    2017-06-01

    Catalase, a heme enzyme, which catalyzes decomposition of hydrogen peroxide to water and molecular oxygen, is one of the main enzymes of the antioxidant defense system of the cell. Nitrite, used as a food preservative has long been regarded as a harmful compound due to its ability to form carcinogenic nitrosamines. Recently, much evidence has been presented that nitrite plays a protective role as a nitric oxide donor under hypoxic conditions. In this work the effect of nitrite on the catalytic reactions of catalase was studied. Catalase was inhibited by nitrite, and this process was pH-dependent. IC 50 values varied from about 1μM at pH5.0 to about 150μM of nitrite at pH7.4. The presence of chloride significantly enhanced nitrite-induced catalase inhibition, in agreement with earlier observations. The kinetics of the reactions of nitrite with ferric catalase, its redox intermediate, Compound I, and catalase inactive form, Compound II, was also studied. Possible mechanisms of nitrite-induced catalase inhibition are analyzed and the biological consequences of the reactions of catalase with nitrite are discussed. Copyright © 2017 Elsevier Inc. All rights reserved.

  15. Interaction of 2-aminopyrimidine with dichloro-[1-alkyl-2-(naphthylazo imidazole]palladium(II complexes : Kinetic and mechanistic studies

    Directory of Open Access Journals (Sweden)

    Saha Sushanta

    2007-10-01

    Full Text Available Abstract Background The anticancer properties of cisplatin and palladium(II complexes stem from the ability of the cis-MCl2 fragment to bind to DNA bases. However, cisplatin also interacts with non-cancer cells, mainly through bonding molecules containing -SH groups, resulting in nephrotoxicity. This has aroused interest in the design of palladium(II complexes of improved activity and lower toxicity. The reaction of DNA bases with palladium(II complexes with chelating N,N/donors of the cis-MCl2 configuration constitutes a model system that may help explore the mechanism of cisplatin's anticancer activity. Heterocyclic compounds are found widely in nature and are essential to many biochemical processes. Amongst these naturally occurring compounds, the most thoroughly studied is that of pyrimidine. This was one of the factors that encouraged this study into the kinetics and mechanism of the interaction of 2-aminopyrimidine (2-NH2-Pym with dichloro-{1-alkyl-2-(α-naphthylazoimidazole}palladium(II [Pd(α-NaiRCl2, 1] and dichloro-{1-alkyl-2-(β-naphthylazoimidazole}palladium(II [Pd(β-NaiRCl2, 2] complexes where the alkyl R = Me (a, Et (b, or Bz (c. Results 2-NH2-Pym reacts with 1a, 1b, and 1c to yield [{1-alkyl-2-(α-naphthylazoimidazole}bis(2-aminopyrimidine]palladium(II (3a, 3b, 3c dichloride and with 2a, 2b, and 2c to yield [{1-alkyl-2-(β-naphthylazoimidazole}bis(2-aminopyrimidine]palladium(II (4a, 4b, 4c dichloride in an acetonitrile (MeCN medium. The products were characterized using spectroscopic techniques (FT-IR, UV-Vis, NMR. The ligand substitution reactions follow second order kinetics – first order dependence on the concentration of the Pd(II complex and 2-NH2-Pym. Addition of LiCl to the reaction does not influence its rate. The thermodynamic parameters (standard enthalpy of activation, Δ‡H° and standard entropy of activation, Δ‡S° were determined from variable temperature kinetic studies. The magnitude of the second order

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

    International Nuclear Information System (INIS)

    Kantoglu, O.; Ozbey, T.; Gueven, O.

    1995-01-01

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

  17. Experimental study of the reactions of limonene with OH and OD radicals: kinetics and products.

    Science.gov (United States)

    Braure, Tristan; Bedjanian, Yuri; Romanias, Manolis N; Morin, Julien; Riffault, Véronique; Tomas, Alexandre; Coddeville, Patrice

    2014-10-09

    The kinetics of the reactions of limonene with OH and OD radicals has been studied using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: OH + C10H16 → products (1), OD + C10H16 → products (2). The rate constants of the title reactions were determined using four different approaches: either monitoring the kinetics of OH (OD) radicals or limonene consumption in excess of limonene or of the radicals, respectively (absolute method), and by the relative rate method using either the reaction OH (OD) + Br2 or OH (OD) + DMDS (dimethyl disulfide) as the reference one and following HOBr (DOBr) formation or DMDS and limonene consumption, respectively. As a result of the absolute and relative measurements, the overall rate coefficients, k1 = (3.0 ± 0.5) × 10(-11) exp((515 ± 50)/T) and k2 = (2.5 ± 0.6) × 10(-11) exp((575 ± 60)/T) cm(3) molecule(-1) s(-1), were determined at a pressure of 1 Torr of helium over the temperature ranges 220-360 and 233-353 K, respectively. k1 was found to be pressure independent over the range 0.5-5 Torr. There are two possible pathways for the reaction between OH (OD) and limonene: addition of the radical to one of the limonene double bonds (reactions 1a and 2a ) and abstraction of a hydrogen atom (reactions 1b and 2b ), resulting in the formation of H2O (HOD). Measurements of the HOD yield as a function of temperature led to the following branching ratio of the H atom abstraction channel: k2b/k2 = (0.07 ± 0.03) × exp((460 ± 140)/T) for T = (253-355) K.

  18. Exchange Reactions. Proceedings of the Symposium on Exchange Reactions

    International Nuclear Information System (INIS)

    1965-01-01

    The mechanisms and kinetics of chemical reactions are of great interest to chemists. The study of exchange reactions in particular helps to shed light on the dynamics of chemical change, providing an insight into the structures and the reactivities of the chemical species involved. The main theme of this meeting was the subject of oxidation-reduction reactions in which the net result is the transfer of one or more electrons between the different oxidation states of the same element. Other studies reported included the transfer of protons, atoms, complex ligands or organic radicals between molecules. Heterogeneous exchange, which is of importance in many cases of catalytic action, was also considered. For a long time isotopic tracers have formed the most convenient means of studying exchange reactions and today a considerable amount of work continues to be done with their aid. Consequently, several papers presented at this Symposium reported on work carried out by purely radiochemical tracer methods. In recognition, however, of the important role which nuclear magnetic resonance and electron spin resonance play in this field, in particular in the study of fast reactions, a number of reports on investigations in which these techniques had been used was included in the programme. By kind invitation of the United States Government the Symposium on Exchange Reactions was held from 31 May to 4 June at the Brookhaven National Laboratory, Upton, Long Island, N.Y., USA. It was attended by 46 participants from nine countries and one inter-governmental organization. The publication of these Proceedings makes the contents of the papers and the discussion available to a wider audience

  19. A kinetics database and scripts for PHREEQC

    Science.gov (United States)

    Hu, B.; Zhang, Y.; Teng, Y.; Zhu, C.

    2017-12-01

    Kinetics of geochemical reactions has been increasingly used in numerical models to simulate coupled flow, mass transport, and chemical reactions. However, the kinetic data are scattered in the literature. To assemble a kinetic dataset for a modeling project is an intimidating task for most. In order to facilitate the application of kinetics in geochemical modeling, we assembled kinetics parameters into a database for the geochemical simulation program, PHREEQC (version 3.0). Kinetics data were collected from the literature. Our database includes kinetic data for over 70 minerals. The rate equations are also programmed into scripts with the Basic language. Using the new kinetic database, we simulated reaction path during the albite dissolution process using various rate equations in the literature. The simulation results with three different rate equations gave difference reaction paths at different time scale. Another application involves a coupled reactive transport model simulating the advancement of an acid plume in an acid mine drainage site associated with Bear Creek Uranium tailings pond. Geochemical reactions including calcite, gypsum, and illite were simulated with PHREEQC using the new kinetic database. The simulation results successfully demonstrated the utility of new kinetic database.

  20. The Effects of One-Dimensional Glide on the Reaction Kinetics of Interstitial Clusters

    International Nuclear Information System (INIS)

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

    2000-01-01

    Collision cascades in metals produce small interstitial clusters and perfect dislocation loops that glide in thermally activated one-dimensional (1D) random walks. These gliding defects can change their Burgers vectors by thermal activation or by interactions with other defects. Their migration is therefore''mixed 1D/3D migration'' along a 3D path consisting of 1D segments. The defect reaction kinetics under mixed 1D/3D diffusion are different from pure 1D diffusion and pure 3D diffusion, both of which can be formulated within analytical rate theory models of microstructure evolution under irradiation. Atomic-scale kinetic Monte Carlo (kMC) defect migration simulations are used to investigate the effects of mixed 1D/3D migration on defect reaction kinetics as a guide for implementing mixed 1D/3D migration into the analytical rate theory. The functional dependence of the sink strength on the sixe and concentration of sinks under mixed 1D/3D migration is shown to lie between that for pure 1D and pure 3D migration and varies with L, the average distance between direction changes of the gliding defects. It is shown that the sink strength in simulations for spherical sinks of radius R under mixed 1D/3D migration for values of L greater than R can be approximated by an expression that varies directly as R2. For small L, the form of the transition from mixed 1D/3D to pure 3D diffusion as L decreases is demonstrated in the simulations, the results of which can be used in the future development of an analytical expression describing this transition region

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

    International Nuclear Information System (INIS)

    Battaglia, Francine

    2008-01-01

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

  2. Reaction kinetics and mechanisms of organosilicon fungicide flusilazole with sulfate and hydroxyl radicals.

    Science.gov (United States)

    Mercado, D Fabio; Bracco, Larisa L B; Arques, Antonio; Gonzalez, Mónica C; Caregnato, Paula

    2018-01-01

    Flusilazole is an organosilane fungicide used for treatments in agriculture and horticulture for control of diseases. The reaction kinetics and mechanism of flusilazole with sulfate and hydroxyl radicals were studied. The rate constant of the radicals with the fungicide were determined by laser flash photolysis of peroxodisulfate and hydrogen peroxide. The results were 2.0 × 10 9 s -1 M -1 for the reaction of the fungicide with HO and 4.6 × 10 8  s -1  M -1 for the same reaction with SO 4 - radicals. The absorption spectra of organic intermediates detected by laser flash photolysis of S 2 O 8 2- with flusilazole, were identified as α-aminoalkyl and siloxyl radicals and agree very well with those estimated employing the time-dependent density functional theory with explicit account for bulk solvent effects. In the continuous photolysis experiments, performed by photo-Fenton reaction of the fungicide, the main degradation products were: (bis(4-fluorophenyl)-hydroxy-methylsilane) and the non-toxic silicic acid, diethyl bis(trimethylsilyl) ester, in ten and twenty minutes of reaction, respectively. Copyright © 2017. Published by Elsevier Ltd.

  3. Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2'-bipyridine-6,6'-dicarboxylate (bda) ligand: how ligand environment influences the catalytic behavior.

    Science.gov (United States)

    Staehle, Robert; Tong, Lianpeng; Wang, Lei; Duan, Lele; Fischer, Andreas; Ahlquist, Mårten S G; Sun, Licheng; Rau, Sven

    2014-02-03

    A new water oxidation catalyst [Ru(III)(bda)(mmi)(OH2)](CF3SO3) (2, H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; mmi = 1,3-dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.

  4. A combined high-temperature experimental and theoretical kinetic study of the reaction of dimethyl carbonate with OH radicals

    KAUST Repository

    Khaled, Fathi

    2017-02-08

    The reaction kinetics of dimethyl carbonate (DMC) and OH radicals were investigated behind reflected shock waves over the temperature range of 872-1295 K and at pressures near 1.5 atm. Reaction progress was monitored by detecting OH radicals at 306.69 nm using a UV laser absorption technique. The rate coefficients for the reaction of DMC with OH radicals were extracted using a detailed kinetic model developed by Glaude et al. (Proc. Combust. Inst. 2005, 30(1), 1111-1118). The experimental rate coefficients can be expressed in Arrhenius form as: kexpt\\'l = 5.15 × 10(13) exp(-2710.2/T) cm(3) mol(-1) s(-1). To explore the detailed chemistry of the DMC + OH reaction system, theoretical kinetic analyses were performed using high-level ab initio and master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) calculations. Geometry optimization and frequency calculations were carried out at the second-order Møller-Plesset (MP2) perturbation level of theory using Dunning\\'s augmented correlation consistent-polarized valence double-ζ basis set (aug-cc-pVDZ). The energy was extrapolated to the complete basis set using single point calculations performed at the CCSD(T)/cc-pVXZ (where X = D, T) level of theory. For comparison purposes, additional ab initio calculations were also carried out using composite methods such as CBS-QB3, CBS-APNO, G3 and G4. Our calculations revealed that the H-abstraction reaction of DMC by OH radicals proceeds via an addition elimination mechanism in an overall exothermic process, eventually forming dimethyl carbonate radicals and H2O. Theoretical rate coefficients were found to be in excellent agreement with those determined experimentally. Rate coefficients for the DMC + OH reaction were combined with literature rate coefficients of four straight chain methyl ester + OH reactions to extract site-specific rates of H-abstraction from methyl esters by OH radicals.

  5. Kinetics of two simultaneous second-order reactions occurring in different zones

    International Nuclear Information System (INIS)

    Dole, M.; Hsu, C.S.; Patel, V.M.; Patel, G.N.

    1975-01-01

    Equations have been derived for the case of free radicals recombining according to the second-order kinetics with or without diffusion control under the conditions that there are two simultaneous spatially separated recombination reactions but that only the overall free-radical concentration can be observed. The properties of these equations are discussed and methods for determining the three independent parameters in the first case and five in the second developed. The resulting equations have been applied to the interpretation of data obtained in studying the decay of allyl chain free radicals in irradiated extended chain crystalline polyethylene

  6. Introduction to chemical kinetics

    CERN Document Server

    Soustelle, Michel

    2013-01-01

    This book is a progressive presentation of kinetics of the chemical reactions. It provides complete coverage of the domain of chemical kinetics, which is necessary for the various future users in the fields of Chemistry, Physical Chemistry, Materials Science, Chemical Engineering, Macromolecular Chemistry and Combustion. It will help them to understand the most sophisticated knowledge of their future job area. Over 15 chapters, this book present the fundamentals of chemical kinetics, its relations with reaction mechanisms and kinetic properties. Two chapters are then devoted to experimental re

  7. Kinetics and selectivity of the oxidation of methylbenzenes in Co(III)-CH3COOH-CF3COOH solutions. Comparison with nitration and hydroxylation reactions

    International Nuclear Information System (INIS)

    Rudakov, E.S.; Lobachev, V.L.

    1989-01-01

    Data have been obtained concerning the kinetics, substrate selectivity, and kinetic isotope effect for the first stage in the oxidation of a series of arenes, from benzene to hexamethylbenzene, by Co(III) acetate in CH 3 COOH-CF 3 COOH (1.9 M) solutions at 25 degree C. A similarity was noted between substrate selectivity for reactions of alkylbenzenes with Co(III) and electrophilic nitration reactions, which occur via an electron transfer step. It was also found that substrate selectivity for these reactions differs significantly from that found for electrophilic hydroxylation reactions, which occur via an intermediate slow step involving σ-complex formation

  8. Reaction of Tris(cyclopentadienyl)uranium compounds with amines, azides, and related ligands

    International Nuclear Information System (INIS)

    Rosen, R.K.

    1989-12-01

    The trivalent uranium compound, (MeC 5 H 4 ) 3 U(thf), serves as a one- or two-electron reducing agent towards azides, RN 3 . These reactions produce either the uranium(IV) azide, (MeC 5 H 4 ) 3 UN 3 , or uranium(V) imides, (MeC 5 H 4 ) 3 UNR. The role of steric and electronic effects upon this reaction has been investigated using several series of azides. For Me 3 XN 3 , the imides are produced when X = C or Si, both products are formed when X = Ge, and the azide is produced when X = Sn. For Ph 3 XN 3 , the azide is produced when X = C or Sn. For Ph 3-x CH 3 N 3 , the imide is produced when x = 2 and both compounds are produced when x = 1. For substituted phenylazides, RC 6 H 4 N 3 , only the imides are produced. The magnetic properties of uranium diimides, [(MeC 5 H 4 ) 3 U] 2 (μ-NRN), were investigated. Several uranium(III) amines, (MeC 5 H 4 ) 3 U(NH 2 R), were produced from (MeC 5 H 4 ) 3 U(thf) and RNH 2 , and NH 3 was found to be a better ligand towards (MeC 5 H 4 ) 3 U than is PMe 3

  9. Selective Electrocatalytic Activity of Ligand Stabilized Copper Oxide Nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Kauffman, Douglas R; Ohodnicki, Paul R; Kail, Brian W; Matranga, Christopher

    2011-01-01

    Ligand stabilization can influence the surface chemistry of Cu oxide nanoparticles (NPs) and provide unique product distributions for electrocatalytic methanol (MeOH) oxidation and CO{sub 2} reduction reactions. Oleic acid (OA) stabilized Cu{sub 2}O and CuO NPs promote the MeOH oxidation reaction with 88% and 99.97% selective HCOH formation, respectively. Alternatively, CO{sub 2} is the only reaction product detected for bulk Cu oxides and Cu oxide NPs with no ligands or weakly interacting ligands. We also demonstrate that OA stabilized Cu oxide NPs can reduce CO{sub 2} into CO with a {approx}1.7-fold increase in CO/H{sub 2} production ratios compared to bulk Cu oxides. The OA stabilized Cu oxide NPs also show 7.6 and 9.1-fold increases in CO/H{sub 2} production ratios compared to weakly stabilized and non-stabilized Cu oxide NPs, respectively. Our data illustrates that the presence and type of surface ligand can substantially influence the catalytic product selectivity of Cu oxide NPs.

  10. Ground reaction forces and knee kinetics during single and repeated badminton lunges.

    Science.gov (United States)

    Lam, Wing Kai; Ding, Rui; Qu, Yi

    2017-03-01

    Repeated movement (RM) lunge that frequently executed in badminton might be used for footwear evaluation. This study examined the influence of single movement (SM) and RM lunges on the ground reaction forces (GRFs) and knee kinetics during the braking phase of a badminton lunge step. Thirteen male university badminton players performed left-forward lunges in both SM and RM sessions. Force platform and motion capturing system were used to measure GRFs and knee kinetics variables. Paired t-test was performed to determine any significant differences between SM and RM lunges regarding mean and coefficient of variation (CV) in each variable. The kinetics results indicated that compared to SM lunges, the RM lunges had shorter contact time and generated smaller maximum loading rate of impact force, peak knee anterior-posterior force, and peak knee sagittal moment but generated larger peak horizontal resultant forces (Ps < 0.05). Additionally, the RM lunges had lower CV for peak knee medial-lateral and vertical forces (Ps < 0.05). These results suggested that the RM testing protocols had a distinct loading response and adaptation pattern during lunge and that the RM protocol showed higher within-trial reliability, which may be beneficial for the knee joint loading evaluation under different interventions.

  11. Full-dimensional analytical potential energy surface describing the gas-phase Cl + C2H6 reaction and kinetics study of rate constants and kinetic isotope effects.

    Science.gov (United States)

    Rangel, Cipriano; Espinosa-Garcia, Joaquin

    2018-02-07

    Within the Born-Oppenheimer approximation a full-dimensional analytical potential energy surface, PES-2017, was developed for the gas-phase hydrogen abstraction reaction between the chlorine atom and ethane, which is a nine body system. This surface presents a valence-bond/molecular mechanics functional form dependent on 60 parameters and is fitted to high-level ab initio calculations. This reaction presents little exothermicity, -2.30 kcal mol -1 , with a low height barrier, 2.44 kcal mol -1 , and intermediate complexes in the entrance and exit channels. We found that the energetic description was strongly dependent on the ab initio level used and it presented a very flat topology in the entrance channel, which represents a theoretical challenge in the fitting process. In general, PES-2017 reproduces the ab initio information used as input, which is merely a test of self-consistency. As a first test of the quality of the PES-2017, a theoretical kinetics study was performed in the temperature range 200-1400 K using two approaches, i.e. the variational transition-state theory and quasi-classical trajectory calculations, with spin-orbit effects. The rate constants show reasonable agreement with experiments in the whole temperature range, with the largest differences at the lowest temperatures, and this behaviour agrees with previous theoretical studies, thus indicating the inherent difficulties in the theoretical simulation of the kinetics of the title reaction. Different sources of error were analysed, such as the limitations of the PES and theoretical methods, recrossing effects, and the tunnelling effect, which is negligible in this reaction, and the manner in which the spin-orbit effects were included in this non-relativistic study. We found that the variation of spin-orbit coupling along the reaction path, and the influence of the reactivity of the excited Cl( 2 P 1/2 ) state, have relative importance, but do not explain the whole discrepancy. Finally, the

  12. The complex reaction kinetics of neptunium including redox and extraction process in 30% TBP-nitric acid system

    International Nuclear Information System (INIS)

    Hu Zhang; Zhan-yuan Liu; Xian-ming Zhou; Li Li

    2017-01-01

    In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO_3 system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium. (author)

  13. Principles of chemical kinetics

    CERN Document Server

    House, James E

    2007-01-01

    James House's revised Principles of Chemical Kinetics provides a clear and logical description of chemical kinetics in a manner unlike any other book of its kind. Clearly written with detailed derivations, the text allows students to move rapidly from theoretical concepts of rates of reaction to concrete applications. Unlike other texts, House presents a balanced treatment of kinetic reactions in gas, solution, and solid states. The entire text has been revised and includes many new sections and an additional chapter on applications of kinetics. The topics covered include quantitative rela

  14. An effective rate equation approach to reaction kinetics in small volumes: theory and application to biochemical reactions in nonequilibrium steady-state conditions.

    Science.gov (United States)

    Grima, R

    2010-07-21

    Chemical master equations provide a mathematical description of stochastic reaction kinetics in well-mixed conditions. They are a valid description over length scales that are larger than the reactive mean free path and thus describe kinetics in compartments of mesoscopic and macroscopic dimensions. The trajectories of the stochastic chemical processes described by the master equation can be ensemble-averaged to obtain the average number density of chemical species, i.e., the true concentration, at any spatial scale of interest. For macroscopic volumes, the true concentration is very well approximated by the solution of the corresponding deterministic and macroscopic rate equations, i.e., the macroscopic concentration. However, this equivalence breaks down for mesoscopic volumes. These deviations are particularly significant for open systems and cannot be calculated via the Fokker-Planck or linear-noise approximations of the master equation. We utilize the system-size expansion including terms of the order of Omega(-1/2) to derive a set of differential equations whose solution approximates the true concentration as given by the master equation. These equations are valid in any open or closed chemical reaction network and at both the mesoscopic and macroscopic scales. In the limit of large volumes, the effective mesoscopic rate equations become precisely equal to the conventional macroscopic rate equations. We compare the three formalisms of effective mesoscopic rate equations, conventional rate equations, and chemical master equations by applying them to several biochemical reaction systems (homodimeric and heterodimeric protein-protein interactions, series of sequential enzyme reactions, and positive feedback loops) in nonequilibrium steady-state conditions. In all cases, we find that the effective mesoscopic rate equations can predict very well the true concentration of a chemical species. This provides a useful method by which one can quickly determine the

  15. Effect of ionic strength on the kinetics of ionic and micellar reactions in aqueous solution

    International Nuclear Information System (INIS)

    Dung, M.H.; Kozak, J.J.

    1982-01-01

    The effect of electrostatic forces on the rate of reaction between ions in aqueous solutions of intermediate ionic strength is studied in this paper. We consider the kinetics of reactions involving simple ionic species (1--1 and 2--2 electrolyte systems) as well as kinetic processes mediated by the presence of micellar ions (or other charged organizates). In the regime of ionic strength considered, dielectric saturation of the solvent in the vicinity of the reacting ions must be taken into account and this is done by introducing several models to describe the recovery of the solvent from saturation to its continuum dielectric behavior. To explore the effects of ion size, charge number, and ionic strength on the overall rate constant for the process considered, we couple the traditional theory of ionic reactions in aqueous solution with calculations of the electrostatic potential obtained via solution of the nonlinear Poisson--Boltzmann equation. The great flexibility of the nonlinear Poisson--Boltzmann theory allows us to explore quantitatively the influence of each of these effects, and our simulations show that the short-range properties of the electrostatic potential affect primarily kinetically controlled processes (to varying degrees, depending on the ionic system considered) whereas the down-range properties of the potential play a (somewhat) greater role in influencing diffusion-controlled processes. A detailed examination is made of ionic strength effects over a broad range of ionic concentrations. In the regime of low ionic strength, the limiting slope and intercept of the curve describing the dependence of log k/sub D/ on I/sup 1/2//(1+I/sup 1/2/) may differ considerably from the usual Debye--Hueckel limiting relations, depending on the particular model chosen to describe local saturation effects

  16. Oxidation of β-lactam antibiotics by peracetic acid: Reaction kinetics, product and pathway evaluation.

    Science.gov (United States)

    Zhang, Kejia; Zhou, Xinyan; Du, Penghui; Zhang, Tuqiao; Cai, Meiquan; Sun, Peizhe; Huang, Ching-Hua

    2017-10-15

    Peracetic acid (PAA) is a disinfection oxidant used in many industries including wastewater treatment. β-Lactams, a group of widely prescribed antibiotics, are frequently detected in wastewater effluents and surface waters. The reaction kinetics and transformation of seven β-lactams (cefalexin (CFX), cefadroxil (CFR), cefapirin (CFP), cephalothin (CFT), ampicillin (AMP), amoxicillin (AMX) and penicillin G (PG)) toward PAA were investigated to elucidate the behavior of β-lactams during PAA oxidation processes. The reaction follows second-order kinetics and is much faster at pH 5 and 7 than at pH 9 due to speciation of PAA. Reactivity to PAA follows the order of CFR ∼ CFX > AMP ∼ AMX > CFT ∼ CFP ∼ PG and is related to β-lactam's nucleophilicity. The thioether sulfur of β-lactams is attacked by PAA to generate sulfoxide products. Presence of the phenylglycinyl amino group on β-lactams can significantly influence electron distribution and the highest occupied molecular orbital (HOMO) location and energy in ways that enhance the reactivity to PAA. Reaction rate constants obtained in clean water matrix can be used to accurately model the decay of β-lactams by PAA in surface water matrix and only slightly overestimate the decay in wastewater matrix. Results of this study indicate that the oxidative transformation of β-lactams by PAA can be expected under appropriate wastewater treatment conditions. Copyright © 2017. Published by Elsevier Ltd.

  17. Mineral solubility and free energy controls on microbial reaction kinetics: Application to contaminant transport in the subsurface

    Energy Technology Data Exchange (ETDEWEB)

    Taillefert, Martial [Georgia Inst. of Technology, Atlanta, GA (United States); Van Cappellen, Philippe [Univ. of Waterloo, ON (Canada)

    2016-11-14

    Recent developments in the theoretical treatment of geomicrobial reaction processes have resulted in the formulation of kinetic models that directly link the rates of microbial respiration and growth to the corresponding thermodynamic driving forces. The overall objective of this project was to verify and calibrate these kinetic models for the microbial reduction of uranium(VI) in geochemical conditions that mimic as much as possible field conditions. The approach combined modeling of bacterial processes using new bioenergetic rate laws, laboratory experiments to determine the bioavailability of uranium during uranium bioreduction, evaluation of microbial growth yield under energy-limited conditions using bioreactor experiments, competition experiments between metabolic processes in environmentally relevant conditions, and model applications at the field scale. The new kinetic descriptions of microbial U(VI) and Fe(III) reduction should replace those currently used in reactive transport models that couple catabolic energy generation and growth of microbial populations to the rates of biogeochemical redox processes. The above work was carried out in collaboration between the groups of Taillefert (batch reactor experiments and reaction modeling) at Georgia Tech and Van Cappellen (retentostat experiments and reactive transport modeling) at University of Waterloo (Canada).

  18. Curing behavior and reaction kinetics of binder resins for 3D-printing investigated by dielectric analysis (DEA)

    Science.gov (United States)

    Möginger, B.; Kehret, L.; Hausnerova, B.; Steinhaus, J.

    2016-05-01

    3D-Printing is an efficient method in the field of additive manufacturing. In order to optimize the properties of manufactured parts it is essential to adapt the curing behavior of the resin systems with respect to the requirements. Thus, effects of resin composition, e.g. due to different additives such as thickener and curing agents, on the curing behavior have to be known. As the resin transfers from a liquid to a solid glass the time dependent ion viscosity was measured using DEA with flat IDEX sensors. This allows for a sensitive measurement of resin changes as the ion viscosity changes two to four decades. The investigated resin systems are based on the monomers styrene and HEMA. To account for the effects of copolymerization in the calculation of the reaction kinetics it was assumed that the reaction can be considered as a homo-polymerization having a reaction order n≠1. Then the measured ion viscosity curves are fitted with the solution of the reactions kinetics - the time dependent degree of conversion (DC-function) - for times exceeding the initiation phase representing the primary curing. The measured ion viscosity curves can nicely be fitted with the DC-function and the determined fit parameters distinguish distinctly between the investigated resin compositions.

  19. Exquisite Modulation of the Active Site of Methanocaldococcus jannaschii Adenylosuccinate Synthetase in Forward Reaction Complexes.

    Science.gov (United States)

    Karnawat, Vishakha; Mehrotra, Sonali; Balaram, Hemalatha; Puranik, Mrinalini

    2016-05-03

    In enzymes that conduct complex reactions involving several substrates and chemical transformations, the active site must reorganize at each step to complement the transition state of that chemical step. Adenylosuccinate synthetase (ADSS) utilizes a molecule each of guanosine 5'-monophosphate (GTP) and aspartate to convert inosine 5'-monophosphate (IMP) into succinyl adenosine 5'-monophosphate (sAMP) through several kinetic intermediates. Here we followed catalysis by ADSS through high-resolution vibrational spectral fingerprints of each substrate and intermediate involved in the forward reaction. Vibrational spectra show differential ligand distortion at each step of catalysis, and band positions of substrates are influenced by binding of cosubstrates. We found that the bound IMP is distorted toward its N1-deprotonated form even in the absence of any other ligands. Several specific interactions between GTP and active-site amino acid residues result in large Raman shifts and contribute substantially to intrinsic binding energy. When both IMP and GTP are simultaneously bound to ADSS, IMP is converted into an intermediate 6-phosphoryl inosine 5'-monophosphate (6-pIMP). The 6-pIMP·ADSS complex was found to be stable upon binding of the third ligand, hadacidin (HDA), an analogue of l-aspartate. We find that in the absence of HDA, 6-pIMP is quickly released from ADSS, is unstable in solution, and converts back into IMP. HDA allosterically stabilizes ADSS through local conformational rearrangements. We captured this complex and determined the spectra and structure of 6-pIMP in its enzyme-bound state. These results provide important insights into the exquisite tuning of active-site interactions with changing substrate at each kinetic step of catalysis.

  20. Mechanistic pathways of recognition of a solvent-inaccessible cavity of protein by a ligand

    Science.gov (United States)

    Mondal, Jagannath; Pandit, Subhendu; Dandekar, Bhupendra; Vallurupalli, Pramodh

    One of the puzzling questions in the realm of protein-ligand recognition is how a solvent-inaccessible hydrophobic cavity of a protein gets recognized by a ligand. We address the topic by simulating, for the first time, the complete binding process of benzene from aqueous media to the well-known buried cavity of L99A T4 Lysozyme at an atomistic resolution. Our multiple unbiased microsecond-long trajectories, which were completely blind to the location of target binding site, are able to unequivocally identify the kinetic pathways along which benzene molecule meanders across the solvent and protein and ultimately spontaneously recognizes the deeply buried cavity of L99A T4 Lysozyme at an accurate precision. Our simulation, combined with analysis based on markov state model and free energy calculation, reveals that there are more than one distinct ligand binding pathways. Intriguingly, each of the identified pathways involves the transient opening of a channel of the protein prior to ligand binding. The work will also decipher rich mechanistic details on unbinding kinetics of the ligand as obtained from enhanced sampling techniques.

  1. Field-controlled electron transfer and reaction kinetics of the biological catalytic system of microperoxidase-11 and hydrogen peroxide

    Directory of Open Access Journals (Sweden)

    Yongki Choi

    2011-12-01

    Full Text Available Controlled reaction kinetics of the bio-catalytic system of microperoxidase-11 and hydrogen peroxide has been achieved using an electrostatic technique. The technique allowed independent control of 1 the thermodynamics of the system using electrochemical setup and 2 the quantum mechanical tunneling at the interface between microperoxidase-11 and the working electrode by applying a gating voltage to the electrode. The cathodic currents of electrodes immobilized with microperoxidase-11 showed a dependence on the gating voltage in the presence of hydrogen peroxide, indicating a controllable reduction reaction. The measured kinetic parameters of the bio-catalytic reduction showed nonlinear dependences on the gating voltage as the result of modified interfacial electron tunnel due to the field induced at the microperoxidase-11-electrode interface. Our results indicate that the kinetics of the reduction of hydrogen peroxide can be controlled by a gating voltage and illustrate the operation of a field-effect bio-catalytic transistor, whose current-generating mechanism is the conversion of hydrogen peroxide to water with the current being controlled by the gating voltage.

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

    DEFF Research Database (Denmark)

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

    1994-01-01

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

  3. Role of Re in Pt-Re/TiO2 catalyst for water gas shift reaction: A mechanistic and kinetic study.

    NARCIS (Netherlands)

    Azzam, K.G.H.; Babych, Igor V.; Seshan, Kulathuiyer; Lefferts, Leonardus

    2008-01-01

    Transient kinetic studies and in situ FTIR spectroscopy were used to follow the reaction sequences that occur during water gas shift (WGS) reaction over Pt–Re/TiO2 catalyst. Results pointed to contributions of an associative formate route with redox regeneration and two classical redox routes

  4. Exploring between the extremes: conversion-dependent kinetics of phosphite-modified hydroformylation catalysis.

    Science.gov (United States)

    Kubis, Christoph; Selent, Detlef; Sawall, Mathias; Ludwig, Ralf; Neymeyr, Klaus; Baumann, Wolfgang; Franke, Robert; Börner, Armin

    2012-07-09

    The kinetics of the hydroformylation of 3,3-dimethyl-1-butene with a rhodium monophosphite catalyst has been studied in detail. Time-dependent concentration profiles covering the entire olefin conversion range were derived from in situ high-pressure FTIR spectroscopic data for both, pure organic components and catalytic intermediates. These profiles fit to Michaelis-Menten-type kinetics with competitive and uncompetitive side reactions involved. The characteristics found for the influence of the hydrogen concentration verify that the pre-equilibrium towards the catalyst substrate complex is not established. It has been proven experimentally that the hydrogenolysis of the intermediate acyl complex remains rate limiting even at high conversions when the rhodium hydride is the predominant resting state and the reaction is nearly of first order with respect to the olefin. Results from in situ FTIR and high-pressure (HP) NMR spectroscopy and from DFT calculations support the coordination of only one phosphite ligand in the dominating intermediates and a preferred axial position of the phosphite in the electronically saturated, trigonal bipyramidal (tbp)-structured acyl rhodium complex. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. A General Ligand Design for Gold Catalysis allowing Ligand-Directed Anti Nucleophilic Attack of Alkynes

    Science.gov (United States)

    Wang, Yanzhao; Wang, Zhixun; Li, Yuxue; Wu, Gongde; Cao, Zheng; Zhang, Liming

    2014-01-01

    Most homogenous gold catalyses demand ≥0.5 mol % catalyst loading. Due to the high cost of gold, these reactions are unlikely to be applicable in medium or large scale applications. Here we disclose a novel ligand design based on the privileged biphenyl-2-phosphine framework that offers a potentially general approach to dramatically lowering catalyst loading. In this design, an amide group at the 3’ position of the ligand framework directs and promotes nucleophilic attack at the ligand gold complex-activated alkyne, which is unprecedented in homogeneous gold catalysis considering the spatial challenge of using ligand to reach antiapproaching nucleophile in a linear P-Au-alkyne centroid structure. With such a ligand, the gold(I) complex becomes highly efficient in catalyzing acid addition to alkynes, with a turnover number up to 99,000. Density functional theory calculations support the role of the amide moiety in directing the attack of carboxylic acid via hydrogen bonding. PMID:24704803

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

    Science.gov (United States)

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

    2016-01-01

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

  7. Non-equilibrium reactive flux: A unified framework for slow and fast reaction kinetics.

    Science.gov (United States)

    Bose, Amartya; Makri, Nancy

    2017-10-21

    The flux formulation of reaction rate theory is recast in terms of the expectation value of the reactive flux with an initial condition that corresponds to a non-equilibrium, factorized reactant density. In the common case of slow reactive processes, the non-equilibrium expression reaches the plateau regime only slightly slower than the equilibrium flux form. When the reactants are described by a single quantum state, as in the case of electron transfer reactions, the factorized reactant density describes the true initial condition of the reactive process. In such cases, the time integral of the non-equilibrium flux expression yields the reactant population as a function of time, allowing characterization of the dynamics in cases where there is no clear separation of time scales and thus a plateau regime cannot be identified. The non-equilibrium flux offers a unified approach to the kinetics of slow and fast chemical reactions and is ideally suited to mixed quantum-classical methods.

  8. The kinetics of free radical metathetical and addition reactions in silane solutions

    International Nuclear Information System (INIS)

    Aloni, R.

    1976-12-01

    In this work radiolytic technique was employed for the initiation of free radical chainreactions in silane solution. The kinetic analysis of the chain mechanism in various solutions enabled the determination of the Arrhenius parameters for metathesis, addition and unimolecular decomposition reactions which make up the chainpropagation sequence in the systems studied. The following radical reactions were investigated: chlorine atom abstraction from chloromethanes by SiCl 3 and Et 3 Si radicals, and chlorine atom abstraction from chloroethanes by Et 3 Si radicals; unimolecular decomposition reactions and hydrogen atom abstraction, *from the solvent, of chloroethyl radicals in triethylsilane solutions; addition and abstraction reactions of Et 3 Si radicals with chloroolefins. Arrhenius parameters were determined for abstraction of chlorine atom from CH 3 Cl, CH 2 Cl 2 , CHCl 3 and CCl 4 , by SiCl 3 radicals and from CCl 4 , CHCl 3 , CH 2 Cl 2 , CCl 3 CN, C 2 Cl 5 H, sym-C 2 Cl 4 H 2 , asym-C 2 Cl 4 H 2 , 1.1.1-C 2 Cl 3 H 3 , 1.1.1-C 2 Dl 3 F 3 and 1.1-C 2 Cl 2 H 4 by Et 3 Si radicals. (author)

  9. Cloud computing approaches for prediction of ligand binding poses and pathways.

    Science.gov (United States)

    Lawrenz, Morgan; Shukla, Diwakar; Pande, Vijay S

    2015-01-22

    We describe an innovative protocol for ab initio prediction of ligand crystallographic binding poses and highly effective analysis of large datasets generated for protein-ligand dynamics. We include a procedure for setup and performance of distributed molecular dynamics simulations on cloud computing architectures, a model for efficient analysis of simulation data, and a metric for evaluation of model convergence. We give accurate binding pose predictions for five ligands ranging in affinity from 7 nM to > 200 μM for the immunophilin protein FKBP12, for expedited results in cases where experimental structures are difficult to produce. Our approach goes beyond single, low energy ligand poses to give quantitative kinetic information that can inform protein engineering and ligand design.

  10. Kinetic and equilibrium studies of acrylonitrile binding to cytochrome c peroxidase and oxidation of acrylonitrile by cytochrome c peroxidase compound I.

    Science.gov (United States)

    Chinchilla, Diana; Kilheeney, Heather; Vitello, Lidia B; Erman, James E

    2014-01-03

    Ferric heme proteins bind weakly basic ligands and the binding affinity is often pH dependent due to protonation of the ligand as well as the protein. In an effort to find a small, neutral ligand without significant acid/base properties to probe ligand binding reactions in ferric heme proteins we were led to consider the organonitriles. Although organonitriles are known to bind to transition metals, we have been unable to find any prior studies of nitrile binding to heme proteins. In this communication we report on the equilibrium and kinetic properties of acrylonitrile binding to cytochrome c peroxidase (CcP) as well as the oxidation of acrylonitrile by CcP compound I. Acrylonitrile binding to CcP is independent of pH between pH 4 and 8. The association and dissociation rate constants are 0.32±0.16 M(-1) s(-1) and 0.34±0.15 s(-1), respectively, and the independently measured equilibrium dissociation constant for the complex is 1.1±0.2 M. We have demonstrated for the first time that acrylonitrile can bind to a ferric heme protein. The binding mechanism appears to be a simple, one-step association of the ligand with the heme iron. We have also demonstrated that CcP can catalyze the oxidation of acrylonitrile, most likely to 2-cyanoethylene oxide in a "peroxygenase"-type reaction, with rates that are similar to rat liver microsomal cytochrome P450-catalyzed oxidation of acrylonitrile in the monooxygenase reaction. CcP compound I oxidizes acrylonitrile with a maximum turnover number of 0.61 min(-1) at pH 6.0. Copyright © 2013 Elsevier Inc. All rights reserved.

  11. Kinetics and thermochemistry of the reversible gas phase reaction HONO+NH3->3N-HONO studied by infrared diode laser spectroscopy

    DEFF Research Database (Denmark)

    Pagsberg, P.; Ratajczak, E.; Sillesen, A.

    1994-01-01

    The kinetics of the reversible reaction HONO+NH3 reversible H3N-HONO (1) was studied by monitoring trans-HONO relaxation kinetics. The rate of approach towards equilibrium was studied as a function of the ammonia concentration to obtain values of the rate constants for the forward and reverse rea...

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

    International Nuclear Information System (INIS)

    Tarasevich, M.R.; Chalykh, A.E.; Bogdanovskaya, V.A.; Kuznetsova, L.N.; Kapustina, N.A.; Efremov, B.N.; Ehrenburg, M.R.; Reznikova, L.A.

    2006-01-01

    Studies are presented of the kinetics and mechanism of oxygen electroreduction reaction on CoPd catalysts synthesized on carbon black XC72. As shown both in model conditions and in the tests within the cathodes of hydrogen-oxygen fuel cells with proton conducting electrolyte, CoPd/C system features a higher activity, as compared to Co/C. The highest activity in the oxygen reduction reaction is demonstrated by the catalysts with the Pd:Co atomic ratio being 7:3 and 4:1. The structural studies (XPS and XRD, and also the data of CO desorption measurements) evidence the CoPd alloy formation, which is reflected in the negative shift of the bonding energy maximum as compared to Pd/C and in the appearance of the additional CO desorption maximums on the voltammograms. It is found by means of structural research that CoPd alloy is formed in the course of the catalyst synthesis which features a higher catalytic activity of the binary systems. Besides, CoPd/C catalyst is more stable in respect to corrosion than Pd supported on carbon black. The measurements on the rotating disc electrode and rotating ring-disc electrode evidence that CoPd/C system provides the predominant oxygen reduction to water in the practically important range of potentials (E > 0.7 V). The proximity of kinetic parameters of the oxygen reduction reaction on CoPd/C and Pt/C catalysts points to the similar reaction mechanism. The slow step of the reaction is the addition of the first electron to the adsorbed and previously protonated O 2 molecule. The assumptions are offered about the reasons causing the higher activity and selectivity of the binary catalyst towards oxygen reduction to water, as compared to Co/C. The studies of the most active catalysts within the fuel cell cathodes are performed

  13. Reversible alkyne insertion in the benzannulation reaction of Fischer carbene complexes with alkynes

    Energy Technology Data Exchange (ETDEWEB)

    Waters, M.L.; Bos, M.E.; Wulff, W.D. [Univ. of Chicago, IL (United States)

    1995-12-31

    The benzannulation reaction of Fischer carbene complexes with alkynes to give phenols is highly regioselective with terminal alkynes, and reasonably regioselective with internal alkynes. This has been attributed to steric factors in intermediates, where one form is favored due to close contact between the R substituent and a cis-CO ligand. Whether alkyne insertion is kinetically or thermodynamically controlled has not been determined. The authors now have evidence from regioselectivity studies that alkyne insertion into the metal-carbon bond is reversible. Implications of these results and further mechanistic considerations will be presented.

  14. Synthesis and properties of dioxo Tc(V) cationic complexes with nitrogen containing ligands

    International Nuclear Information System (INIS)

    Gambino, D.; Kremer, C.; Savio, E.; Leon, A.; Kremer, E.

    1990-01-01

    A series of Tc(V) cationic complexes was synthesized by electrochemical reduction of TcO 4 - . The electrolysis was performed in aqueous media containing amines as ligands: ethylenediamine (en), diethylenetriamine (dien), triethylenetetramine (trien) and 1,3-diaminopropane (1,3-dap). The combination of different techniques allows to propose the general formula [TcO 2 (amine) 2 ] + for these compounds. Electrodeposition of TcO 2 was a competitive reaction. The UV spectra were compared with those for other Tc(V) amine complexes. The presence of two peaks could be verified. Preliminary studies showed that kinetic stability decreased in the sequence en, 1,3-dap, trien, dien. The decomposition rate increased when the pH was lowered. (author) 16 refs.; 2 figs.; 3 tabs

  15. Reaction kinetics and transformation of carbadox and structurally related compounds with aqueous chlorine.

    Science.gov (United States)

    Shah, Amisha D; Kim, Jae-Hong; Huang, Ching-Hua

    2006-12-01

    The potential release of carbadox (CDX), a commonly used antibacterial agent in swine husbandry, into water systems is of a concern due to its carcinogenic and genotoxic effects. Until this study, the reactivity of carbadox (possessing quinoxaline N,N'-dioxide and hydrazone moieties) toward aqueous chlorine has yetto be investigated in depth. Chemical reactivity, reaction kinetics, and transformation pathways of carbadox and structurally related compounds with free chlorine under typical water treatment conditions were determined. This study found that only CDX and desoxycarbadox (DCDX), a main metabolite of CDX with no ring N-oxide groups, react rapidly with free chlorine while other structurally related compounds including olaquindox, quindoxin, quinoxaline N-oxide, quinoxaline, and quinoline N-oxide do not. The reaction kinetics of CDX and DCDX with chlorine are highly pH dependent (e.g., the apparent second-order rate constant, kapp, for CDX ranges from 51.8 to 3.15 x 10(4) M(-1)s(-1) at pH 4-11). The high reactivity of CDX and DCDX to chlorine involves deprotonation of their hydrazone N-H moieties where initial chlorine attack results in a reactive intermediate that is further attacked by nucleophiles in the matrix to yield non-chlorinated, hydroxylated, and larger molecular weight byproducts. All of the CDX's byproducts retain their biologically active N-oxide groups, suggesting that they may remain as active antibacterial agents.

  16. Kinetic study of the substitution of [Tc(tu)6]3+ by polyaminocarboxylic acids

    International Nuclear Information System (INIS)

    Torres, J.; Gonalez, R.; Kremer, C.; Kremer, E.; Leon, A.

    1997-01-01

    Substitution route has been traditionally proposed for the synthesis of new Tc complexes. In particular, Tc(III) coordination compounds can be successfully prepared by substitution on [Tc(tu) 6 ] 3+ (tu = thiourea). In this substitution reaction, TcO 2 is a side product that should be minimized. The success of these synthetic procedures is based on controlling the reaction conditions in order that pure substitution could be faster enough compared to decomposition. In this work, the substitution of [Tc(tu) 6 ] 3+ by polycarboxylic acids (ethylenediaminetetraacetate (edta), diethylenetriaminepentaacetate (dtpa), N-tris(2-amino-ethyl)amin N', N', N '' , N '' , N ''' , N ''' -hexaacetate (ttaha) and 3-bromo-2,4,6-trimethylacetanilideiminodiacetate (mebrofenin)) is kinetically studied in order to obtain the best conditions for preparing Tc(III) complexes. As a general conclusion, substitution constants are strongly dependent on the pH. k obs values fall in the range 0.1-13 x 10 -2 M -1 s -1 , depending on the pH value and the temperature. No strong differences are found with different incoming ligands. For the four ligands (L), a straight line is obtained when plotting log k obs /([L m- ]) vs. pH. This is consistent with a rate constant k obs = {k 0 + Σk n [H + ] n /K n }[L m- ], where n represents the charge of the incoming ligand and m is the maximum value of n. (orig.)

  17. Nonmonotonic Temperature Dependence of the Pressure-Dependent Reaction Rate Constant and Kinetic Isotope Effect of Hydrogen Radical Reaction with Benzene Calculated by Variational Transition-State Theory.

    Science.gov (United States)

    Zhang, Hui; Zhang, Xin; Truhlar, Donald G; Xu, Xuefei

    2017-11-30

    The reaction between H and benzene is a prototype for reactions of radicals with aromatic hydrocarbons. Here we report calculations of the reaction rate constants and the branching ratios of the two channels of the reaction (H addition and H abstraction) over a wide temperature and pressure range. Our calculations, obtained with an accurate potential energy surface, are based on variational transition-state theory for the high-pressure limit of the addition reaction and for the abstraction reaction and on system-specific quantum Rice-Ramsperger-Kassel theory calibrated by variational transition-state theory for pressure effects on the addition reaction. The latter is a very convenient way to include variational effects, corner-cutting tunneling, and anharmonicity in falloff calculations. Our results are in very good agreement with the limited experimental data and show the importance of including pressure effects in the temperature interval where the mechanism changes from addition to abstraction. We found a negative temperature effect of the total reaction rate constants at 1 atm pressure in the temperature region where experimental data are missing and accurate theoretical data were previously missing as well. We also calculated the H + C 6 H 6 /C 6 D 6 and D + C 6 H 6 /C 6 D 6 kinetic isotope effects, and we compared our H + C 6 H 6 results to previous theoretical data for H + toluene. We report a very novel nonmonotonic dependence of the kinetic isotope effect on temperature. A particularly striking effect is the prediction of a negative temperature dependence of the total rate constant over 300-500 K wide temperature ranges, depending on the pressure but generally in the range from 600 to 1700 K, which includes the temperature range of ignition in gasoline engines, which is important because aromatics are important components of common fuels.

  18. Kinetics of the high temperature oxygen exchange reaction on 238PuO2 powder

    International Nuclear Information System (INIS)

    Whiting, Christofer E.; Du, Miting; Felker, L. Kevin; Wham, Robert M.; Barklay, Chadwick D.; Kramer, Daniel P.

    2015-01-01

    Oxygen exchange reactions performed on PuO 2 suggest the reaction is influenced by at least three mechanisms: an internal chemical reaction, surface mobility of active species/defects, and surface exchange of gaseous oxygen with lattice oxygen. Activation energies for the surface mobility and internal chemical reaction are presented. Determining which mechanism is dominant appears to be a complex function including at least specific surface area and temperature. Thermal exposure may also impact the oxygen exchange reaction by causing reductions in the specific surface area of PuO 2 . Previous CeO 2 surrogate studies exhibit similar behavior, confirming that CeO 2 is a good qualitative surrogate for PuO 2 , in regards to the oxygen exchange reaction. Comparison of results presented here with previous work on the PuO 2 oxygen exchange reaction allows complexities in the previous work to be explained. These explanations allowed new conclusions to be drawn, many of which confirm the conclusions presented here. - Highlights: • PuO 2 Oxygen exchange kinetics can be influenced by at least 3 different mechanisms. • An internal chemical reaction controls the rate at high temperature and large SSA. • Surface mobility and surface exchange influence rate at lower temperatures and SSA. • Exchange temperatures may alter SSA and make data difficult to interpret.

  19. In situ synchrotron powder diffraction study of the setting reaction kinetics of magnesium-potassium phosphate cements

    Czech Academy of Sciences Publication Activity Database

    Viani, Alberto; Pérez-Estébanez, Marta; Pollastri, S.; Gualtieri, A. F.

    2016-01-01

    Roč. 79, January (2016), s. 344-352 ISSN 0008-8846 R&D Projects: GA MŠk(CZ) LO1219 Keywords : kinetics * reaction * X-ray diffraction * MgO * chemically bonded ceramics Subject RIV: JN - Civil Engineering Impact factor: 4.762, year: 2016 http://www.sciencedirect.com/science/article/pii/S0008884615002690

  20. Kinetics and mechanistic study of n-alkane hydroisomerization reaction on Pt-doped γ-alumina catalyst

    Directory of Open Access Journals (Sweden)

    Abhishek Dhar

    2017-12-01

    Full Text Available The catalysts γ-alumina (GA, the reference catalyst and Pt doped γ-alumina (PGA-s were synthesized using a simple sol-gel technique, in which at first preparation of porous base (GA, then impregnation of platinum salt over the base and finally reduction of platinum in the surface of the support were done. These catalysts prepared in different mole ratios of Pt:Al as 2:1, 1:1 and 1:2 are named as PGA-1, PGA-2 and PGA-3 respectively. The isomerization of n-alkanes (n-hexane, n-heptane and n-octane were investigated over the synthesized catalysts. The 2-methyl pentane (2-MP, 2,2-dimethyl pentane (2,2-DMP and 2,3-dimethyl hexane (2,3-DMH are the major products of respective isomerization of n-hexane, n-heptane and n-octane, besides a small amount of other branched isomers are also produced. The product distribution is comparable to that reported for Pt based other catalysts. The optimal mole ratios of Pt:Al is 1:1 (PGA-2 gives quite good catalytic activity for isomerization of n-alkane. Even through in reusability study, PGA-2 gives better performance than others. We have mainly focused on kinetic study, reaction mechanism behind isomerization and calculated the order of reactions and activation energies of the isomerization reactions in the present work. Keywords: Isomerization, n-alkanes, Catalyst, Reaction mechanism, Kinetics study, Activation energy

  1. Kinetics of the reaction of F atoms with O2 and UV spectrum of FO2 radicals in the gas phase at 295 K

    DEFF Research Database (Denmark)

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

    1994-01-01

    The ultraviolet absorption spectrum of FO2 radicals and the kinetics of the reaction of F atoms with O2 have been studied in the gas phase at 295 K using pulse radiolysis combined with kinetic UV spectroscopy. At 230 nm, sigma(FO2) = (5.08 +/- 0.70) X 10(-18) cm2 molecule-1. The kinetics of the r......The ultraviolet absorption spectrum of FO2 radicals and the kinetics of the reaction of F atoms with O2 have been studied in the gas phase at 295 K using pulse radiolysis combined with kinetic UV spectroscopy. At 230 nm, sigma(FO2) = (5.08 +/- 0.70) X 10(-18) cm2 molecule-1. The kinetics...

  2. Importance of (n,xn) reactions in evaluating kinetic parameters of subcritical assemblies: from classic to modern formalism

    Energy Technology Data Exchange (ETDEWEB)

    Talamo, Alberto; Gohar, Yousry, E-mail: alby@anl.gov [Argonne National Laboratory, Lemont, IL (United States); Dulla, Sandra; Ravetto, Piero [Politecnico di Torino (Italy)

    2011-07-01

    The importance of (n,xn) reactions must be taken into consideration while calculating the kinetic parameters of subcritical assemblies driven by an external neutron source. This study is divided into two parts, the first part is dedicated to the classic definition of the neutron source multiplication factor and two alternative calculation methodologies are compared. The second part considers a new definition of the kinetic parameters for subcritical assemblies, with particular emphasis on the delayed neutron fraction and generation time. This new definition has been modified to take into account the external neutron source and (n,xn) reactions, which increase the fraction of prompt neutrons. The developed theoretical framework has been applied by Monte Carlo and deterministic calculations to the YALINA Thermal subcritical assembly in Belarus. This facility can be driven by californium, deuterium-deuterium (D-D), or deuterium-tritium (D-T) external neutron sources. For the D-T neutron source, (n,xn) reactions must be taken into account in order to produce accurate results because the average energy of D-T source neutrons is 14.1 MeV, a value much higher than the threshold energy of the (n,2n) cross section of uranium isotopes. (author)

  3. Importance of (n,xn) reactions in evaluating kinetic parameters of subcritical assemblies: from classic to modern formalism

    International Nuclear Information System (INIS)

    Talamo, Alberto; Gohar, Yousry; Dulla, Sandra; Ravetto, Piero

    2011-01-01

    The importance of (n,xn) reactions must be taken into consideration while calculating the kinetic parameters of subcritical assemblies driven by an external neutron source. This study is divided into two parts, the first part is dedicated to the classic definition of the neutron source multiplication factor and two alternative calculation methodologies are compared. The second part considers a new definition of the kinetic parameters for subcritical assemblies, with particular emphasis on the delayed neutron fraction and generation time. This new definition has been modified to take into account the external neutron source and (n,xn) reactions, which increase the fraction of prompt neutrons. The developed theoretical framework has been applied by Monte Carlo and deterministic calculations to the YALINA Thermal subcritical assembly in Belarus. This facility can be driven by californium, deuterium-deuterium (D-D), or deuterium-tritium (D-T) external neutron sources. For the D-T neutron source, (n,xn) reactions must be taken into account in order to produce accurate results because the average energy of D-T source neutrons is 14.1 MeV, a value much higher than the threshold energy of the (n,2n) cross section of uranium isotopes. (author)

  4. A Spectroscopic Study of the effect of Ligand Complexation on the Reduction of Uranium(VI) by Anthraquinone-2,6-disulfonate (AH2DS)

    International Nuclear Information System (INIS)

    Wang, Zheming; Wagnon, Ken B.; Ainsworth, Calvin C.; Liu, Chongxuan; Rosso, Kevin M.; Fredrickson, Jim K.

    2008-01-01

    In this project, the reduction rate of uranyl complexes with hydroxide, carbonate, EDTA, and Desferriferrioxamine B (DFB) by anthraquinone-2,6-disulfonate (AH2DS), a potential electron shuttle for microbial reduction of metal ions (Newman and Kolter 2000), is studied by stopped-flow kinetics techniques under anoxic atmosphere. The apparent reaction rates varied with ligand type, solution pH, and U(VI) concentration. For each ligand, a single largest kobs within the studied pH range was observed, suggesting the influence of pH-dependent speciation on the U(VI) reduction rate. The maximum reaction rate found in each case followed the order of OH- > CO32- > EDTA > DFB, consistent with the same trend of the thermodynamic stability of the uranyl complexes and ionic sizes of the ligands. Increasing the stability of uranyl complexes and ligand size decreased the maximum reduction rate. The pH-dependent rates were modeled using a second-order rate expression that was assumed to be dependent on a single U(VI) complex and AH2DS species. By quantitatively comparing the calculated and measured apparent rate constants as a function of pH, species AHDS3- was suggested as the primary reductant in all cases examined. Species UO2CO3(aq) , UO2HEDTA-, and (UO2)2(OH)22+ were suggested as the principal electron acceptors among the U(VI) species mixture in carbonate, EDTA, and hydroxyl systems, respectively

  5. A Mathematical Model for the Multiphase Transport and Reaction Kinetics in a Ladle with Bottom Powder Injection

    Science.gov (United States)

    Lou, Wentao; Zhu, Miaoyong

    2017-12-01

    A computation fluid dynamics-population balance model-simultaneous reaction model (CFD-PBM-SRM) coupled model has been proposed to study the multiphase flow behavior and refining reaction kinetics in a ladle with bottom powder injection, and some new and important phenomena and mechanisms are presented. For the multiphase flow behavior, the effects of bubbly plume flow, powder particle motion, particle-particle collision and growth, particle-bubble collision and adhesion, and powder particle removal into top slag are considered. For the reaction kinetics, the mechanisms of multicomponent simultaneous reactions, including Al, S, Si, Mn, Fe, and O, at the multi-interface, including top slag-liquid steel interface, air-liquid steel interface, powder droplet-liquid steel interface, and bubble-liquid steel interface, are presented, and the effect of sulfur solubility in the powder droplet on the desulfurization is also taken into account. Model validation is carried out using hot tests in a 2-t induction furnace with bottom powder injection. The result shows that the powder particles gradually disperse in the entire furnace; in the vicinity of the bottom slot plugs, the desulfurization product CaS is liquid phase, while in the upper region of the furnace, the desulfurization product CaS is solid phase. The predicted sulfur contents by the present model agree well with the measured data in the 2-t furnace with bottom powder injection.

  6. Oxidation of ligand-protected aluminum clusters: An ab initio molecular dynamics study

    International Nuclear Information System (INIS)

    Alnemrat, Sufian; Hooper, Joseph P.

    2014-01-01

    We report Car-Parrinello molecular dynamics simulations of the oxidation of ligand-protected aluminum clusters that form a prototypical cluster-assembled material. These clusters contain a small aluminum core surrounded by a monolayer of organic ligand. The aromatic cyclopentadienyl ligands form a strong bond with surface Al atoms, giving rise to an organometallic cluster that crystallizes into a low-symmetry solid and is briefly stable in air before oxidizing. Our calculations of isolated aluminum/cyclopentadienyl clusters reacting with oxygen show minimal reaction between the ligand and O 2 molecules at simulation temperatures of 500 and 1000 K. In all cases, the reaction pathway involves O 2 diffusing through the ligand barrier, splitting into atomic oxygen upon contact with the aluminum, and forming an oxide cluster with aluminum/ligand bonds still largely intact. Loss of individual aluminum-ligand units, as expected from unimolecular decomposition calculations, is not observed except following significant oxidation. These calculations highlight the role of the ligand in providing a steric barrier against oxidizers and in maintaining the large aluminum surface area of the solid-state cluster material

  7. Classical Example of Total Kinetic and Thermodynamic Control: The Diels-Alder Reaction between DMAD and Bis-furyl Dienes.

    Science.gov (United States)

    Borisova, Kseniya K; Kvyatkovskaya, Elizaveta A; Nikitina, Eugeniya V; Aysin, Rinat R; Novikov, Roman A; Zubkov, Fedor I

    2018-04-20

    A rare example of chemospecificity in the tandem Diels-Alder reaction of activated alkynes and bis-dienes has been revealed. The reaction between bis-furyl dienes and DMAD occurs at 25-80 °C and leads to kinetically controlled "pincer" adducts, 4a,8a-disubstituted 1,4:5,8-diepoxynaphthalenes. On the contrary, only thermodynamically controlled "domino" adducts (2,3-disubstituted 1,4:5,8-diepoxynaphthalenes) are formed in the same reaction at 140 °C. The "pincer" adducts can be transformed to the "domino" adducts at heating. The rate constants for reactions of both types were calculated using dynamic 1 H NMR spectroscopy.

  8. Interplay between excitation kinetics and reaction-center dynamics in purple bacteria

    International Nuclear Information System (INIS)

    Caycedo-Soler, Felipe; RodrIguez, Ferney J; Quiroga, Luis; Johnson, Neil F

    2010-01-01

    Photosynthesis is arguably the fundamental process of life, since it enables energy from the Sun to enter the food chain on the Earth. It is a remarkable non-equilibrium process in which photons are converted to many-body excitations, which traverse a complex biomolecular membrane, where they are captured and fuel chemical reactions within a reaction center (RC) in order to produce nutrients. The precise nature of these dynamical processes-which lie at the interface between quantum and classical behavior and involve both noise and coordination-is still being explored. Here, we focus on a striking recent empirical finding concerning an illumination-driven transition in the biomolecular membrane architecture of the purple bacteria Rsp. photometricum. Using stochastic realizations to describe a hopping rate model for excitation transfer, we show numerically and analytically that this surprising shift in preferred architectures can be traced to the interplay between the excitation kinetics and the RC dynamics. The net effect is that the bacteria profit from efficient metabolism at low illumination intensities while using dissipation to avoid an oversupply of energy at high illumination intensities.

  9. Prediction and validation of burnout curves for Goettelborn char using reaction kinetics determined in shock tube experiments

    Energy Technology Data Exchange (ETDEWEB)

    Moors, J.H.J.; Banin, V.E.; Haas, J.H.P.; Weber, R.; Veefkind, A. [Eindhoven University of Technology, Eindhoven (Netherlands). Dept. of Applied Physics

    1999-01-01

    Using a shock tube facility the combustion characteristics of pulverised char ({lt} 10 {mu}m) were measured. A prediction was made for the burnout behaviour of a commercial sized char particle (75-90 {mu}m) in different ambient conditions using a `pseudo kinetic` approach. In this approach the kinetic rate of a surface containing micro pores is determined and these `pseudo kinetics` are then applied to the larger particle not taking into account the micro pores. Comparison of the predictions with measurements done with an isothermal plug flow reactor showed this approach to be valid within experimental error for low burnout. A linear decrease of the kinetic reaction rate with burnout is shown to predict the burnout behaviour in the complete range of burnout. A possible explanation for this linear decrease could be a growing fraction of non-combustible material in the char particles during burnout. 11 refs., 6 figs., 2 tabs.

  10. Investigation of the kinetic mechanism of the demanganization reaction between carbon-saturated liquid iron and CaF2-CaO-SiO2-based slags

    Science.gov (United States)

    Duan, Sheng-chao; Li, Chuang; Guo, Han-jie; Guo, Jing; Han, Shao-wei; Yang, Wen-sheng

    2018-04-01

    The demanganization reaction kinetics of carbon-saturated liquid iron with an eight-component slag consisting of CaO-SiO2-MgO-FeO-MnO-Al2O3-TiO2-CaF2 was investigated at 1553, 1623, and 1673 K in this study. The rate-controlling step (RCS) for the demanganization reaction with regard to the hot metal pretreatment conditions was studied via kinetics analysis based on the fundamental equation of heterogeneous reaction kinetics. From the temperature dependence of the mass transfer coefficient of a transition-metal oxide (MnO), the apparent activation energy of the demanganization reaction was estimated to be 189.46 kJ·mol-1 in the current study, which indicated that the mass transfer of MnO in the molten slag controlled the overall rate of the demanganization reaction. The calculated apparent activation energy was slightly lower than the values reported in the literature for mass transfer in a slag phase. This difference was attributed to an increase in the "specific reaction interface" (SRI) value, either as a result of turbulence at the reaction interface or a decrease of the absolute amount of slag phase during sampling, and to the addition of calcium fluoride to the slag.

  11. Kinetics of the reaction between H· and superheated water probed with muonium

    International Nuclear Information System (INIS)

    Alcorn, Chris D.; Brodovitch, Jean-Claude; Percival, Paul W.; Smith, Marisa; Ghandi, Khashayar

    2014-01-01

    Highlights: • Rate constants for reactions of H with water resolve a controversy. • H reacts with superheated water via two channels. • The findings have important implications for the safety of some nuclear power reactors. - Abstract: Safe operation of supercritical water-cooled reactors requires knowledge of the kinetics of transient species formed by the radiolysis of water in the range 300–650 °C. Using muonium, it is possible to study aqueous H · atom chemistry over this temperature range. An important reaction to study is that of the H · atom with water itself, because it is a potential source of molecular H 2 . The concentration of H 2 is important to plant coolant chemistry, as H 2 is currently added to suppress oxidative corrosion in CANDU reactors. The reaction of muonium with H 2 O and D 2 O was studied experimentally up to 450 °C, and also via quantum chemical computations to investigate possible isotope effects. Our results suggest that although the H · atom abstraction from H 2 O is important at temperatures above 300 °C, the electron-producing channel (H · + H 2 O ⇌ H 3 O + + e aq - ) is significant at temperatures up to 300 °C, and becomes the dominant reaction channel at lower temperatures

  12. Synthetic Control of Kinetic Reaction Pathway and Cationic Ordering in High-Ni Layered Oxide Cathodes

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Dawei [Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton NY 11973 USA; Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory Physical Chemistry Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen Fujian 361005 China; Kou, Ronghui [X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne IL 60439 USA; Ren, Yang [X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne IL 60439 USA; Sun, Cheng-Jun [X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne IL 60439 USA; Zhao, Hu [Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton NY 11973 USA; Zhang, Ming-Jian [Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton NY 11973 USA; School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen Guangdong 518055 P. R. China; Li, Yan [Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne IL 60439 USA; Huq, Ashifia [Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge TN 37831 USA; Ko, J. Y. Peter [The Cornell High Energy Synchrotron Source, Cornell University, Ithaca NY 14853 USA; Pan, Feng [School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen Guangdong 518055 P. R. China; Sun, Yang-Kook [Department of Energy Engineering, Hanyang University, Seoul 133-791 South Korea; Yang, Yong [Collaborative Innovation Center of Chemistry for Energy Materials, State Key Laboratory Physical Chemistry Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen Fujian 361005 China; Amine, Khalil [Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne IL 60439 USA; Bai, Jianming [National Synchrotron Light Source II, Brookhaven National Laboratory, Upton NY 11973 USA; Chen, Zonghai [Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne IL 60439 USA; Wang, Feng [Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton NY 11973 USA

    2017-08-25

    Nickel-rich layered transition metal oxides, LiNi1-x(MnCo)(x)O-2 (1-x >= 0.5), are appealing candidates for cathodes in next-generation lithium-ion batteries (LIBs) for electric vehicles and other large-scale applications, due to their high capacity and low cost. However, synthetic control of the structural ordering in such a complex quaternary system has been a great challenge, especially in the presence of high Ni content. Herein, synthesis reactions for preparing layered LiNi0.7Mn0.15Co0.15O2 (NMC71515) by solid-state methods are investigated through a combination of time-resolved in situ high-energy X-ray diffraction and absorption spectroscopy measurements. The real-time observation reveals a strong temperature dependence of the kinetics of cationic ordering in NMC71515 as a result of thermal-driven oxidation of transition metals and lithium/oxygen loss that concomitantly occur during heat treatment. Through synthetic control of the kinetic reaction pathway, a layered NMC71515 with low cationic disordering and a high reversible capacity is prepared in air. The findings may help to pave the way for designing high-Ni layered oxide cathodes for LIBs.

  13. Correcting ligands, metabolites, and pathways

    NARCIS (Netherlands)

    Ott, M.A.; Vriend, G.

    2006-01-01

    BACKGROUND: A wide range of research areas in bioinformatics, molecular biology and medicinal chemistry require precise chemical structure information about molecules and reactions, e.g. drug design, ligand docking, metabolic network reconstruction, and systems biology. Most available databases,

  14. Elucidation of reaction mechanism for m -cresol hydrodeoxygenation over Fe based catalysts: A kinetic study

    Energy Technology Data Exchange (ETDEWEB)

    Hong, Yongchun; Wang, Yong

    2017-09-01

    Fe based catalysts are promising for hydrodeoxygenation (HDO) of lignin derived phenolics due to their high selectivity for aromatics. In this work, the reaction mechanism of m-cresol HDO on Fe catalysts and the kinetic consequence with Pd addition were elucidated by examining the effect of H2, H2O and m-cresol pressures on toluene formation rate on Fe and PdFe catalysts. A direct CO bond cleavage mechanism is proposed for HDO catalysis on both Fe and PdFe catalysts, while Pd provides a facilitated reaction pathway at the PdFe interface and therefore promotes the catalysis on Fe without changing the high selectivity towards aromatics.

  15. Kinetics of the rapid reaction Br/sub 2/ + 2 I/sup -/. -->. I/sub 2/ + 2 Br/sup -/ in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Rao, T S; Mali, S I; Dangat, V T [Presidency Coll., Calcutta (India). Dept. of Chemistry

    1979-01-01

    The displacement of iodine from aqueous iodide ion solutions by bromine is a rapid reaction whose kinetics has been studied by the competition technique. The reaction is of second order, having a specific rate of 6.85 x 10/sup 5/ M/sup -1/ s/sup -1/ at 25.0 /sup 0/C and energy of activation of 30.8 kJ mol/sup -1/. A mechanism for the reaction is proposed.

  16. Intrinsic reaction kinetics of coal char combustion by direct measurement of ignition temperature

    International Nuclear Information System (INIS)

    Kim, Ryang-Gyoon; Jeon, Chung-Hwan

    2014-01-01

    A wire heating reactor that can use a synchronized experimental method was developed to obtain the intrinsic kinetics of large coal char particles ranging in size from 0.4 to 1 mm. This synchronization system consists of three parts: a thermocouple wire for both heating and direct measurement of the particle temperature, a photodetector sensor for determining ignition/burnout points by measuring the intensity of luminous emission from burning particles, and a high-speed camera–long-distance microscope for observing and recording the movement of luminous zone directly. Coal char ignition was found to begin at a spot on the particle's external surface and then moved across the entire particle. Moreover, the ignition point determined according to the minimum of dT/dt is a spot point and not a full growth point. The ignition temperature of the spot point rises as the particle diameter increases. A spot ignition model, which describes the ignition in terms of the internal conduction and external/internal oxygen diffusion, was then developed to evaluate the intrinsic kinetics and predict the ignition temperature of the coal char. Internal conduction was found to be important in large coal char particles because its effect becomes greater than that of oxygen diffusion as the particle diameter increases. In addition, the intrinsic kinetics of coal char obtained from the spot ignition model for two types of coal does not differ significantly from the results of previous investigators. -- Highlights: • A novel technique was used to measure the coal char particle temperature. • The ignition point determined from a dT/dt minimum is a spot ignition point. • A spot ignition model was suggested to analyze the intrinsic reaction kinetics of coal char. • Internal conduction has to be considered in order to evaluate the intrinsic kinetics for larger particle (above 1 mm)

  17. Synthesis and study of new oxazoline-based ligands

    OpenAIRE

    Tilliet, Mélanie

    2008-01-01

    This thesis deals with the study of oxazoline-based ligands in metal-catalyzed asymmetric reactions. The first part describes the synthesis of six new bifunctinal pyridine-bis(oxazoline) ligands and their applications in asymmetric metal-catalysis. These ligands, in addition to a Lewis acid coordination site, are equipped with a Lewis basic part in the 4-position of the oxazoline rings. Dual activation by means of this system was probed in cyanide addition to aldehydes. The second part is con...

  18. Kinetic Modeling of the Reaction Rate for Quartz and Carbon Black Pellet

    Science.gov (United States)

    Li, Fei; Tangstad, Merete

    2018-06-01

    The kinetic modeling for the carbothermal reduction reaction rate in quartz and carbon black pellets is studied at different temperatures, under varying CO partial pressures in ambient atmosphere, varying carbon contents, different quartz particle sizes, and different crucible opening areas. Carbon black is produced by the cracking of natural gas. The activation energy of the SiC-producing step was determined to be 594 kJ/mol. The averaged pre-exponential factor A obtained from 1898 K, 1923 K, and 1948 K (1625 °C, 1650 °C, and 1675 °C) is 2.62E+16 min-1. The reaction rate of the gas-solid interface factor, fix-C content ( X fix-C), temperature ( T), and CO partial pressure ( X CO) can be expressed as follows: {{d/pct}}{{{d}t}} = (1 - 0.40 × X_{{{fix} - C}}^{ - 0.86} × {pct}) × 2.62 × 10^{16} × \\exp ( { - 594000/RT} ) × (2.6 - 0.015 × X_{co} ).

  19. Kinetic modeling of hydrocracking reaction in a trickle-bed reactor with Pt/Y-zeolite catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Lee, BalSang; Park, Myung-June; Kim, Young-A; Park, Eun Duck [Ajou University, Suwon (Korea, Republic of); Han, Jeongsik [Agency for Defense Development, Daejeon (Korea, Republic of); Jeong, Kwang-Eun; Kim, Chul-Ung; Jeong, Soon-Yong [Korea Research Institute of Chemical Technology (KRICT), Daejeon (Korea, Republic of)

    2014-03-15

    A kinetic model is developed to predict the entire distribution of hydrocarbon products for the hydrocracking reaction with Pt/Y-zeolite catalysts in a trickle-bed reactor. Operating conditions, such as temperature, pressure, and wax and H{sub 2} flow rates were varied to evaluate their effects on conversion and distribution, and kinetic parameters were estimated using the experimental data that covers the window of operating conditions. The comparison between experimental data and simulated results corroborated the validity of the developed model, and the quantitative prediction of the reactor performance was clearly demonstrated. To make evident the usefulness of the model, an optimization method, genetic algorithm (GA), was applied, and the optimal condition for the maximum production of C{sub 10}-C{sub 17} was successfully calculated.

  20. Kinetic modeling of hydrocracking reaction in a trickle-bed reactor with Pt/Y-zeolite catalysts

    International Nuclear Information System (INIS)

    Lee, BalSang; Park, Myung-June; Kim, Young-A; Park, Eun Duck; Han, Jeongsik; Jeong, Kwang-Eun; Kim, Chul-Ung; Jeong, Soon-Yong

    2014-01-01

    A kinetic model is developed to predict the entire distribution of hydrocarbon products for the hydrocracking reaction with Pt/Y-zeolite catalysts in a trickle-bed reactor. Operating conditions, such as temperature, pressure, and wax and H 2 flow rates were varied to evaluate their effects on conversion and distribution, and kinetic parameters were estimated using the experimental data that covers the window of operating conditions. The comparison between experimental data and simulated results corroborated the validity of the developed model, and the quantitative prediction of the reactor performance was clearly demonstrated. To make evident the usefulness of the model, an optimization method, genetic algorithm (GA), was applied, and the optimal condition for the maximum production of C 10 -C 17 was successfully calculated

  1. Recognition of damaged DNA by Escherichia coli Fpg protein: insights from structural and kinetic data

    International Nuclear Information System (INIS)

    Zharkov, Dmitry O.; Ishchenko, Alexander A.; Douglas, Kenneth T.; Nevinsky, Georgy A.

    2003-01-01

    Formamidopyrimidine-DNA glycosylase (Fpg) excises oxidized purines from damaged DNA. The recent determination of the three-dimensional structure of the covalent complex of DNA with Escherichia coli Fpg, obtained by reducing the Schiff base intermediate formed during the reaction [Gilboa et al., J. Biol. Chem. 277 (2002) 19811] has revealed a number of potential specific and non-specific interactions between Fpg and DNA. We analyze the structural data for Fpg in the light of the kinetic and thermodynamic data obtained by the method of stepwise increase in ligand complexity to estimate relative contributions of individual nucleotide units of lesion-containing DNA to its total affinity for this enzyme [Ishchenko et al., Biochemistry 41 (2002) 7540]. Stopped-flow kinetic analysis that has allowed the dissection of Fpg catalysis in time [Fedorova et al., Biochemistry 41 (2002) 1520] is also correlated with the structural data

  2. Characterization and kinetic study of Diels-Alder reaction: Detailed study on N-phenylmaleimide and furan based benzoxazine with potential self-healing application

    Directory of Open Access Journals (Sweden)

    Z. Stirn

    2016-07-01

    Full Text Available The Diels-Alder reaction between N-phenylmaleimide and benzoxazine bearing furan group was investigated for the purpose of successful appliance of self-healing in benzoxazine polymer networks. The reaction as a function of temperature/time was performed in molten state and in a solution, where also the kinetic study was performed. The Diels-Alder reaction leads to a mixture of two diastereomers: endo presented at lower cyclo-reversion temperature and exo at higher. Therefore, the conversion rates and exo/endo ratio were studied in detail for both systems. For instance, in molten state the Diels-Alder reaction was triggered by the temperature of the melting point at 60 °C with exo/endo ratio preferable to the endo adduct. The study of the kinetics in a solution revealed that the Diels-Alder reaction followed typical bimolecular reversible second-order reaction. The activation energies were close to the previous literature data; 48.4 and 51.9 kJ·mol–1 for Diels-Alder reaction, and 91.0 and 102.3 kJ·mol–1 for retro-Diels-Alder reaction, in acetonitrile and chloroform, respectively. The reaction equilibrium in a solution is much more affected by the retro-Diels-Alder reaction than in a molten state. This study shows detailed investigation of DA reaction and provides beneficial knowledge for further use in self-healing polymer networks.

  3. Ligand-mediated adhesive mechanics of two static, deformed spheres.

    Science.gov (United States)

    Sircar, Sarthok; Nguyen, Giang; Kotousov, Andrei; Roberts, Anthony J

    2016-10-01

    A self-consistent model is developed to investigate attachment/detachment kinetics of two static, deformable microspheres with irregular surface and coated with flexible binding ligands. The model highlights how the microscale binding kinetics of these ligands as well as the attractive/repulsive potential of the charged surface affects the macroscale static deformed configuration of the spheres. It is shown that in the limit of smooth, neutrally charged surface (i.e., the dimensionless inverse Debye length, [Formula: see text]), interacting via elastic binders (i.e., the dimensionless stiffness coefficient, [Formula: see text]) the adhesion mechanics approaches the regime of application of the JKR theory, and in this particular limit, the contact radius, R c , scales with the particle radius, R, according to the scaling law, [Formula: see text]. We show that static, deformed, highly charged, ligand-coated surface of micro-spheres exhibit strong adhesion. Normal stress distribution within the contact area adjusts with the binder stiffness coefficient, from a maximum at the center to a maximum at the periphery of the region. Although reported in some in vitro experiments involving particle adhesion, until now a physical interpretation for this variation of the stress distribution for deformable, charged, ligand-coated microspheres is missing. Surface roughness results in a diminished adhesion with a distinct reduction in the pull-off force, larger separation gap, weaker normal stress and limited area of adhesion. These results are in agreement with the published experimental findings.

  4. Kinetic and mechanisms of methanimine reactions with singlet and triplet molecular oxygen: Substituent and catalyst effects

    Science.gov (United States)

    Asgharzadeh, Somaie; Vahedpour, Morteza

    2018-06-01

    Methanimine reaction with O2 on singlet and triplet potential energy surfaces are investigated using B3PW91, M06-2X, MP2 and CCSD(T) methods. Thermodynamic and kinetic parameters are calculated at M06-2X method. The most favorable channel involves H-abstraction of CH2NH+O2 to the formation of HCN + H2O2 products via low level energy barrier. The catalytic effect of water molecule on HCN + H2O2 products pathway are investigated. Result shows that contribution of water molecule using complex formation with methanimine can decreases barrier energy of transition state and the reaction rate increases. Also, substituent effect of fluorine atom as deactivating group are investigated on the main reaction pathway.

  5. Discovery of a Significant Acetone•Hydroperoxy Adduct Chaperone Effect and Its Impact on the Determination of Room Temperature Rate Constants for Acetonylperoxy/Hydroperoxy Self-Reactions and Cross Reaction Via Infrared Kinetic Spectroscopy.

    Science.gov (United States)

    Grieman, F. J.; Hui, A. O.; Okumura, M.; Sander, S. P.

    2017-12-01

    In order to model the upper troposphere/lower stratosphere in regions containing acetone properly, the kinetics of the acetonylperoxy/hydroperoxy self-reactions and cross reaction have been studied over a wide temperature range using Infrared Kinetic Spectroscopy. We report here the determination of different rate constants for the acetonylperoxy chemistry that we obtained at 298 K compared to currently accepted values. A considerable increase in the observed HO2 self-reaction rate constant due to rate enhancement via the chaperone effect from the reaction between HO2 and the (CH3)2CO•HO2 hydrogen-bonded adduct, even at room temperature, was discovered that was previously ignored. Correct determination of the acetonylperoxy and hydroperoxy kinetics must include this dependence of the HO2 self-reaction rate on acetone concentration. Via excimer laser flash photolysis to create the radical reactants, HO2 absorption was monitored in the infrared by diode laser wavelength modulation detection simultaneously with CH3C(O)CH2O2absorption monitored in the ultraviolet at 300 nm as a function of time. Resulting decay curves were fit concurrently first over a short time scale to obtain the rate constants minimizing subsequent product reactions. Modeling/fitting with a complete reaction scheme was then performed to refine the rate constants and test their veracity. Experiments were carried out over a variety of concentrations of acetone and methanol. Although no effect due to methanol concentration was found at room temperature, the rate constant for the hydroperoxy self-reaction was found to increase linearly with acetone concentration which is interpreted as the adduct being formed and resulting in a chaperone mechanism that enhances the self-reaction rate: (CH3)2CO·HO2 + HO2 → H2O2 + O2 + (CH3)2CO Including this effect, the resulting room temperature rate constants for the cross reaction and the acetonylperoxy self-reaction were found to be 2-3 times smaller than

  6. The reaction kinetics of amino radicals with sulfur dioxide

    DEFF Research Database (Denmark)

    Gao, Yide; Glarborg, Peter; Marshall, Paul

    2015-01-01

    Application of the laser photolysis-laser-induced fluorescence method to the reaction NH2+SO2 in argon bath gas yields pressure-dependent, third-order kinetics which may be summarized as k = (1.49 ± 0.15) × 10-31 (T/298 K)-0.83cm6 molecule-2 s-1 over 292-555K, where the uncertainty is the 95......% confidence interval and includes possible systematic errors. The quenching of vibrationally excited NH2 is consistent with a high-pressure limit for NH2+SO2 of (1.62 ± 0.25) × 10-11cm3 molecule-1 s-1 over the temperature range 295-505K, where again the 95% confidence interval is shown. Ab initio analysis...... yields a H2N-SO2 dissociation enthalpy of 73.5 kJ mol-1, and comparison with RRKM theory and the exponential down model for energy transfer yields down = 350 cm-1 for Ar at room temperature....

  7. Kinetic mechanism for modeling of electrochemical reactions.

    Science.gov (United States)

    Cervenka, Petr; Hrdlička, Jiří; Přibyl, Michal; Snita, Dalimil

    2012-04-01

    We propose a kinetic mechanism of electrochemical interactions. We assume fast formation and recombination of electron donors D- and acceptors A+ on electrode surfaces. These mediators are continuously formed in the electrode matter by thermal fluctuations. The mediators D- and A+, chemically equivalent to the electrode metal, enter electrochemical interactions on the electrode surfaces. Electrochemical dynamics and current-voltage characteristics of a selected electrochemical system are studied. Our results are in good qualitative agreement with those given by the classical Butler-Volmer kinetics. The proposed model can be used to study fast electrochemical processes in microsystems and nanosystems that are often out of the thermal equilibrium. Moreover, the kinetic mechanism operates only with the surface concentrations of chemical reactants and local electric potentials, which facilitates the study of electrochemical systems with indefinable bulk.

  8. Reaction of Tris(cyclopentadienyl)uranium compounds with amines, azides, and related ligands

    Energy Technology Data Exchange (ETDEWEB)

    Rosen, R.K.

    1989-12-01

    The trivalent uranium compound, (MeC{sub 5}H{sub 4}){sub 3}U(thf), serves as a one- or two-electron reducing agent towards azides, RN{sub 3}. These reactions produce either the uranium(IV) azide, (MeC{sub 5}H{sub 4}){sub 3}UN{sub 3}, or uranium(V) imides, (MeC{sub 5}H{sub 4}){sub 3}UNR. The role of steric and electronic effects upon this reaction has been investigated using several series of azides. For Me{sub 3}XN{sub 3}, the imides are produced when X = C or Si, both products are formed when X = Ge, and the azide is produced when X = Sn. For Ph{sub 3}XN{sub 3}, the azide is produced when X = C or Sn. For Ph{sub 3-x}CH{sub 3}N{sub 3}, the imide is produced when x = 2 and both compounds are produced when x = 1. For substituted phenylazides, RC{sub 6}H{sub 4}N{sub 3}, only the imides are produced. The magnetic properties of uranium diimides, ((MeC{sub 5}H{sub 4}){sub 3}U){sub 2}({mu}-NRN), were investigated. Several uranium(III) amines, (MeC{sub 5}H{sub 4}){sub 3}U(NH{sub 2}R), were produced from (MeC{sub 5}H{sub 4}){sub 3}U(thf) and RNH{sub 2}, and NH{sub 3} was found to be a better ligand towards (MeC{sub 5}H{sub 4}){sub 3}U than is PMe{sub 3}.

  9. Kinetics modeling and reaction mechanism of ferrate(VI) oxidation of benzotriazoles.

    Science.gov (United States)

    Yang, Bin; Ying, Guang-Guo; Zhang, Li-Juan; Zhou, Li-Jun; Liu, Shan; Fang, Yi-Xiang

    2011-03-01

    Benzotriazoles (BTs) are high production volume chemicals with broad application in various industrial processes and in households, and have been found to be omnipresent in aquatic environments. We investigated oxidation of five benzotriazoles (BT: 1H-benzotriazole; 5MBT: 5-methyl-1H-benzotriazole; DMBT: 5,6-dimethyl-1H-benzotriazole hydrate; 5CBT: 5-chloro-1H-benzotriazole; HBT: 1-hydroxybenzotriazole) by aqueous ferrate (Fe(VI)) to determine reaction kinetics as a function of pH (6.0-10.0), and interpreted the reaction mechanism of Fe(VI) with BTs by using a linear free-energy relationship. The pK(a) values of BT and DMBT were also determined using UV-Visible spectroscopic method in order to calculate the species-specific rate constants, and they were 8.37 ± 0.0 and 8.98 ± 0.08 respectively. Each of BTs reacted moderately with Fe(VI) with the k(app) ranged from 7.2 to 103.8 M(-1)s(-1) at pH 7.0 and 24 ± 1 °C. When the molar ratio of Fe(VI) and BTs increased up to 30:1, the removal rate of BTs reached about >95% in buffered milli-Q water or secondary wastewater effluent. The electrophilic oxidation mechanism of the above reaction was illustrated by using a linear free-energy relationship between pH-dependence of species-specific rate constants and substituent effects (σ(p)). Fe(VI) reacts initially with BTs by electrophilic attack at the 1,2,3-triazole moiety of BT, 5MBT, DMBT and 5CBT, and at the N-OH bond of HBT. Moreover, for BT, 5MBT, DMBT and 5CBT, the reactions with the species HFeO(4)(-) predominantly controled the reaction rates. For HBT, the species H(2)FeO(4) with dissociated HBT played a major role in the reaction. The results showed that Fe(VI) has the ability to degrade benzotriazoles in water. Copyright © 2011 Elsevier Ltd. All rights reserved.

  10. DNA effects upon the reaction between acetonitrile pentacyanoferrate (II) and ruthenium pentammine pyrazine: Kinetic and thermodynamic evidence of the interaction of DNA with anionic species

    International Nuclear Information System (INIS)

    Grueso, E.; Prado-Gotor, R.; Lopez, M.; Gomez-Herrera, C.; Sanchez, F.

    2005-01-01

    The kinetics of the reaction between ruthenium pentaammine pyrazine and acetonitrile pentacyanoferrate (II) to obtain the binuclear anionic complex [Fe(CN) 5 pzRu(NH 3 ) 5 ] - , and the reverse (dissociation) process, have been studied in solutions containing DNA. The results corresponding to this reaction and those corresponding to the reverse (dissociation) process show a clear influence of DNA on their kinetics. The results can be interpreted using a modified Pseudophase Model. From the results obtained for the dissociation reaction one can conclude that the binuclear anionic complex [Fe(CN) 5 pzRu(NH 3 ) 5 ] - interacts with DNA

  11. Studies on the ruthenium complexes. IX. Kinetic studies on the deaquation-anation reaction of aquapentaammineruthenium(III) complexes

    Energy Technology Data Exchange (ETDEWEB)

    Ohyoshi, A; Hiraki, S I; Odate, T; Kohata, S; Oda, J [Kumamoto Univ. (Japan). Faculty of Engineering

    1975-01-01

    The deaquation-anation reaction of (Ru(OH/sub 2/)(NH/sub 3/)/sub 5/)X/sub 3/-type complexes in the solid state, as shown by the (Ru(OH/sub 2/)(NH/sub 3/)/sub 5/)X/sub 3/(s)..-->..(RuX(NH/sub 3/)/sub 5/)X/sub 2/(s)+H/sub 2/O(g) equation, where X is Cl, Br, I, and NO/sub 3/ respectively, was kinetically studied by means of thermogravimetry (TG) along with differential thermal analysis (DTA). The activation energy and entropy in the reaction process (Esub(a) kcal/mol, ..delta..S c.u.) are, respectively, found by isothermal kinetic study to be (22.7, - 7.1) for the chloride, (23.4, - 5.2) for the bromide, (26.7, 5.8) for the iodide, and (19.3 - 15.9) for the nitrate. The reaction seems to proceed through the following two steps, except in the case of the iodide: (Ru(OH/sub 2/)(NH/sub 3/)/sub 5/)X/sub 3/..-->..(RuX(OH/sub 2/)(NH/sub 3/)/sub 5/)X/sub 2/..-->..(RuX(NH/sub 3/)/sub 5/)X/sub 2/+H/sub 2/O. The first step is regarded as the rate-determining one.

  12. Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

    International Nuclear Information System (INIS)

    Martin del Campo, Julia S.; Patino, Rodrigo

    2011-01-01

    Research highlights: → The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. → A spectrophotometric method is proposed for kinetic and thermodynamic analysis. → The pH and the temperature influences are reported on physical chemical properties. → Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD ox ) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD ox as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, Δ f G o = -1784 ± 5 kJ mol -1 .

  13. Kinetic and thermodynamic study of the reaction catalyzed by glucose-6-phosphate dehydrogenase with nicotinamide adenine dinucleotide

    Energy Technology Data Exchange (ETDEWEB)

    Martin del Campo, Julia S. [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico); Patino, Rodrigo, E-mail: rtarkus@mda.cinvestav.mx [Departamento de Fisica Aplicada, Centro de Investigacion y de Estudios Avanzados - Unidad Merida, Carretera antigua a Progreso Km. 6, A.P. 73 Cordemex, 97310, Merida, Yucatan (Mexico)

    2011-04-20

    Research highlights: {yields} The reaction catalyzed by one enzyme of the pentose phosphate pathway was studied. {yields} A spectrophotometric method is proposed for kinetic and thermodynamic analysis. {yields} The pH and the temperature influences are reported on physical chemical properties. {yields} Relative concentrations of substrates are also important in the catalytic process. - Abstract: The enzyme glucose-6-phosphate dehydrogenase (G6PD, EC 1.1.1.49) from Leuconostoc mesenteroides has a dual coenzyme specificity with oxidized nicotinamide adenine dinucleotide (NAD{sub ox}) and oxidized nicotinamide adenine dinucleotide phosphate as electron acceptors. The G6PD coenzyme selection is determined by the metabolic cellular prevailing conditions. In this study a kinetic and thermodynamic analysis is presented for the reaction catalyzed by G6PD from L. mesenteroides with NAD{sub ox} as coenzyme in phosphate buffer. For this work, an in situ spectrophotometric technique was employed based on the detection of one product of the reaction. Substrate and coenzyme concentrations as well as temperature and pH effects were evaluated. The apparent equilibrium constant, the Michaelis constant, and the turnover number were determined as a function of each experimental condition. The standard transformed Gibbs energy of reaction was determined from equilibrium constants at different initial conditions. For the product 6-phospho-D-glucono-1,5-lactone, a value of the standard Gibbs energy of formation is proposed, {Delta}{sub f}G{sup o} = -1784 {+-} 5 kJ mol{sup -1}.

  14. Assessment of sorption properties and kinetic reaction of phosphorus reactive material to limit diffuse pollution

    Directory of Open Access Journals (Sweden)

    Bus Agnieszka

    2017-09-01

    Full Text Available Assessment of sorption properties and kinetic reaction of phosphorus reactive material to limit diffuse pollution. Polonite® is an effective reactive material (manufactured from opoka rock for removing phosphorus from aqueous solutions. In conducted experiments, Polonite® of grain size of 2–5 mm was used as a potential reactive material which can be used as a filter fulfillment to reduce phosphorus diffuse pollution from agriculture areas. Kinetic and equilibrium studies (performed as a batch experiment were carried out as a function of time to evaluate the sorption properties of the material. The obtained results show that Polonite® effectively removes such contamination. All tested concentrations (0.998, 5.213, 10.965 mg P-PO4·L−1 are characterized by a better fit to pseudo-second kinetic order. The Langmuir isotherm the best reflects the mechanism of adsorption process in case of Polonite® and based on the isotherm, calculated maximum adsorption capacity equals 96.58 mg P-PO4·g−1.

  15. Aziridine- and Azetidine-Pd Catalytic Combinations. Synthesis and Evaluation of the Ligand Ring Size Impact on Suzuki-Miyaura Reaction Issues

    Directory of Open Access Journals (Sweden)

    Hamza Boufroura

    2017-01-01

    Full Text Available The synthesis of new vicinal diamines based on aziridine and azetidine cores as well as the comparison of their catalytic activities as ligand in the Suzuki-Miyaura coupling reaction are described in this communication. The synthesis of three- and four-membered ring heterocycles substituted by a methylamine pendant arm is detailed from the parent nitrile derivatives. Complexation to palladium under various conditions has been examined affording vicinal diamines or amine-imidate complexes. The efficiency of four new catalytic systems is compared in the preparation of variously substituted biaryls. Aziridine- and azetidine-based catalytic systems allowed Suzuki-Miyaura reactions from aryl halides including chlorides with catalytic loadings until 0.001% at temperatures ranging from 100 °C to r.t. The evolution of the Pd-metallacycle ring strain moving from azetidine to aziridine in combination with a methylamine or an imidate pendant arm impacted the Suzuki-Miyaura reaction issue.

  16. New ' Bucky- ligands'. Potentially Monoanionic Terdentate Diamino Aryl Pincer Ligands Anchored to C60

    NARCIS (Netherlands)

    Koten, G. van; Meijer, M.D.; Gossage, R.A.; Jastrzebski, J.T.B.H.

    1998-01-01

    Two new methanofullerenes have been prepared by the reaction of C{6}{0} with diazo substituted, potentially monoanionic, terdentate diamino aryl ligands, yielding a mixture of the open valence [5, 6]- and closed valence [6,6]-isomers. Single isomers of the pure [6,6]-methanofullerenes were obtained

  17. Rates and equilibrium constants of the ligand-induced conformational transition of an HCN ion channel protein domain determined by DEER spectroscopy.

    Science.gov (United States)

    Collauto, Alberto; DeBerg, Hannah A; Kaufmann, Royi; Zagotta, William N; Stoll, Stefan; Goldfarb, Daniella

    2017-06-14

    Ligand binding can induce significant conformational changes in proteins. The mechanism of this process couples equilibria associated with the ligand binding event and the conformational change. Here we show that by combining the application of W-band double electron-electron resonance (DEER) spectroscopy with microfluidic rapid freeze quench (μRFQ) it is possible to resolve these processes and obtain both equilibrium constants and reaction rates. We studied the conformational transition of the nitroxide labeled, isolated carboxy-terminal cyclic-nucleotide binding domain (CNBD) of the HCN2 ion channel upon binding of the ligand 3',5'-cyclic adenosine monophosphate (cAMP). Using model-based global analysis, the time-resolved data of the μRFQ DEER experiments directly provide fractional populations of the open and closed conformations as a function of time. We modeled the ligand-induced conformational change in the protein using a four-state model: apo/open (AO), apo/closed (AC), bound/open (BO), bound/closed (BC). These species interconvert according to AC + L ⇌ AO + L ⇌ BO ⇌ BC. By analyzing the concentration dependence of the relative contributions of the closed and open conformations at equilibrium, we estimated the equilibrium constants for the two conformational equilibria and the open-state ligand dissociation constant. Analysis of the time-resolved μRFQ DEER data gave estimates for the intrinsic rates of ligand binding and unbinding as well as the rates of the conformational change. This demonstrates that DEER can quantitatively resolve both the thermodynamics and the kinetics of ligand binding and the associated conformational change.

  18. Microassay for measurement of binding of radiolabelled ligands to cell surface molecules

    International Nuclear Information System (INIS)

    Woof, J.M.; Burton, D.R.

    1988-01-01

    An improved technique for measuring the binding of radiolabelled ligands to cell surface molecules has been developed by modification of a procedure using centrifugation through a water-immiscible oil to separate free and cell-bound ligand. It maximises the percentage of ligand bound since cell-bound and free ligand can be separated easily and reproducibly even when very small reaction volumes are used. This permits low levels of ligand radiolabelling and relatively low numbers of cells to be used

  19. Density functional theoretical study on the C-F and C-O oxidative addition reaction at an AI center

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yong Seong [Dept. of Science Education, Kyungnam University, Masan (Korea, Republic of); Cho, Hyun; Hwang, Sungu [Dept. of Nanomechatronics Engineering, Pusan National University, Miryang (Korea, Republic of)

    2017-02-15

    In this study, B3LYP/LACVP** level calculations were chosen because the level of theory was applied successfully to calculations of the thermodynamic and kinetic features of the oxidative addition reactions of alkyl and aryl halides to pincer-type complexes. This study examined the effects of the substituents on the phenyl rings of the Al(I) center. Isopropyl side chains in the phenyl rings attached to N atoms of the pincer ligand were replaced with a methyl (Me) (2) or tertiary butyl ( t Bu) group. The oxidative addition of C[BOND]F and C[BOND]O bonds to an Al (I) center was investigated computationally by DFT calculations. The geometries, thermodynamic, and kinetic features were in good agreement with the experimental data, as in previous studies on the transition metal complexes. The computational results showed that the DFT calculations could provide qualitative insight into the reactivity and thermodynamics of the oxidative addition reactions of C[BOND]F bonds.

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

    Science.gov (United States)

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

    1997-01-01

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

  1. Dynamic Model of Basic Oxygen Steelmaking Process Based on Multi-zone Reaction Kinetics: Model Derivation and Validation

    Science.gov (United States)

    Rout, Bapin Kumar; Brooks, Geoff; Rhamdhani, M. Akbar; Li, Zushu; Schrama, Frank N. H.; Sun, Jianjun

    2018-04-01

    A multi-zone kinetic model coupled with a dynamic slag generation model was developed for the simulation of hot metal and slag composition during the basic oxygen furnace (BOF) operation. The three reaction zones (i) jet impact zone, (ii) slag-bulk metal zone, (iii) slag-metal-gas emulsion zone were considered for the calculation of overall refining kinetics. In the rate equations, the transient rate parameters were mathematically described as a function of process variables. A micro and macroscopic rate calculation methodology (micro-kinetics and macro-kinetics) were developed to estimate the total refining contributed by the recirculating metal droplets through the slag-metal emulsion zone. The micro-kinetics involves developing the rate equation for individual droplets in the emulsion. The mathematical models for the size distribution of initial droplets, kinetics of simultaneous refining of elements, the residence time in the emulsion, and dynamic interfacial area change were established in the micro-kinetic model. In the macro-kinetics calculation, a droplet generation model was employed and the total amount of refining by emulsion was calculated by summing the refining from the entire population of returning droplets. A dynamic FetO generation model based on oxygen mass balance was developed and coupled with the multi-zone kinetic model. The effect of post-combustion on the evolution of slag and metal composition was investigated. The model was applied to a 200-ton top blowing converter and the simulated value of metal and slag was found to be in good agreement with the measured data. The post-combustion ratio was found to be an important factor in controlling FetO content in the slag and the kinetics of Mn and P in a BOF process.

  2. Photodissociation dynamics of gaseous CpCo(CO)2 and ligand exchange reactions of CpCoH2 with C3H4, C3H6, and NH3.

    Science.gov (United States)

    Oana, Melania; Nakatsuka, Yumiko; Albert, Daniel R; Davis, H Floyd

    2012-05-31

    The photodissociation dynamics of CpCo(CO)(2) was studied in a molecular beam using photofragment translational energy spectroscopy with 157 nm photoionization detection of the metallic products. At 532 and 355 nm excitation, the dominant one-photon channel involved loss of a single CO ligand producing CpCoCO. The product angular distributions were isotropic, and a large fraction of excess energy appeared as product vibrational excitation. Production of CpCO + 2CO resulted from two-photon absorption processes. The two-photon dissociation of mixtures containing CpCo(CO)(2) and H(2) at the orifice of a pulsed nozzle was used to produce a novel 16-electron unsaturated species, CpCoH(2). Transition metal ligand exchange reactions, CpCoH(2) + L → CpCoL + H(2) (L = propyne, propene, or ammonia), were studied under single-collision conditions for the first time. In all cases, ligand exchange occurred via 18-electron association complexes with lifetimes comparable to their rotational periods. Although ligand exchange reactions were not detected from CpCoH(2) collisions with methane or propane (L = CH(4) or C(3)H(8)), a molecular beam containing CpCoCH(4) was produced by photolysis of mixtures containing CpCo(CO)(2) and CH(4).

  3. An Adaptor Domain-Mediated Auto-Catalytic Interfacial Kinase Reaction

    Science.gov (United States)

    Liao, Xiaoli; Su, Jing; Mrksich, Milan

    2010-01-01

    This paper describes a model system for studying the auto-catalytic phosphorylation of an immobilized substrate by a kinase enzyme. This work uses self-assembled monolayers (SAMs) of alkanethiolates on gold to present the peptide substrate on a planar surface. Treatment of the monolayer with Abl kinase results in phosphorylation of the substrate. The phosphorylated peptide then serves as a ligand for the SH2 adaptor domain of the kinase and thereby directs the kinase activity to nearby peptide substrates. This directed reaction is intramolecular and proceeds with a faster rate than does the initial, intermolecular reaction, making this an auto-catalytic process. The kinetic non-linearity gives rise to properties that have no counterpart in the corresponding homogeneous phase reaction: in one example, the rate for phosphorylation of a mixture of two peptides is faster than the sum of the rates for phosphorylation of each peptide when presented alone. This work highlights the use of an adaptor domain in modulating the activity of a kinase enzyme for an immobilized substrate and offers a new approach for studying biochemical reactions in spatially inhomogeneous settings. PMID:19821459

  4. Kinetic isotope effect studies of the S-adenosylmethionine synthetase reaction

    International Nuclear Information System (INIS)

    Markham, G.D.; Parkin, D.W.; Schramm, V.L.

    1986-01-01

    S-adenosylmethionine (AdoMet) synthetase catalyzes a unique substitution reaction at the 5' carbon of MgATP. Kinetic isotope effect (V/K) measurements have been used to investigate the mechanism of AdoMet synthetase from E. coli. Changes in 3 H/ 14 C ratios when AdoMet is formed from a mixture of either ([5'- 14 C]ATP and [5'- 12 C,1'- 3 H]ATP) or ([5'- 3 H]ATP and [5'- 1 H,1'- 14 C]ATP) were examined. The effects of varying the concentrations of the co-substrate methionine and the monovalent cation activator K + were investigated. Substitution of 14 C for 12 C at the 5' position of ATP yields a primary V/K kinetic isotope effect ( 12 C/ 14 C) of 1.128 +/- 0.004 at low K + and methionine concentrations. The observed isotope effect diminishes slightly to 1.107 +/- 0.003 when both K + and methionine are present at saturating concentrations, suggesting that MgATP has only a low commitment to catalysis from at conditions near Vmax. No secondary V/K 3 H isotope effect from [5'- 3 H]ATP was detected ( 1 H/ 3 H) = 0.997 +/- 0.003. The magnitude of the primary 14 C isotope effect and the small secondary 3 H effect demonstrate that AdoMet synthesis occurs with a S/sub N/ 2 transition state which is symmetric with respect to the sulfur nucleophile and the departing tripolyphosphate group

  5. Effect of the substitutional groups on the electrochemistry, kinetic of thermal decomposition and kinetic of substitution of some uranyl Schiff base complexes

    Energy Technology Data Exchange (ETDEWEB)

    Asadi, Zahra; Nasrollahi, Rahele; Ranjkeshshorkaei, Mohammad; Firuzabadi, Fahimeh Dehghani [Shiraz Univ. (Iran, Islamic Republic of). Chemistry Dept.; Dusek, Michal; Fejfarova, Karla [ASCR, Prague (Czech Republic). Inst. of Physics

    2016-05-15

    Uranyl(VI) complexes, [UO{sub 2}(X-saloph)(solvent)], where saloph denotes N,N{sup '}-bis(salicylidene)-1,2-phenylenediamine and X = NO{sub 2}, Cl, Me, H; were synthesized and characterized by 61H NMR, IR, UV-Vis spectroscopy, thermal gravimetry (TG), cyclic voltammetry, elemental analysis (C.H.N) and X-ray crystallography. X-ray crystallography of [UO{sub 2}(4-nitro-saloph)(DMF)] revealed coordination of the uranyl by the tetradentate Schiff base ligand and one solvent molecule, resulting in seven-coordinated uranium. The complex of [UO{sub 2}(4-nitro-saloph)(DMF)] was also synthesized in nano form. Transmission electron microscopy image showed nano-particles with sizes between 30 and 35 nm. The TG method and analysis of Coats-Redfern plots revealed that the kinetics of thermal decomposition of the complexes is of the first-order in all stages. The kinetics and mechanism of the exchange reaction of the coordinated solvent with tributylphosphine was investigated by spectrophotometric method. The second-order rate constants at four temperatures and the activation parameters showed an associative mechanism for all corresponding complexes with the following trend: 4-Nitro > 4-Cl > H > 4-Me. It was concluded that the steric and electronic properties of the complexes were important for the reaction rate. For analysis of anticancer properties of uranyl Schiff base complexes, cell culture and MTT assay was carried out. These results showed a reduction of jurkat cell line concentration across the complexes.

  6. Laboratory Studies of Stratospheric Bromine Chemistry: Kinetics of the Reactions of Bromine Monoxide with Nitrogen Dioxide and Atomic Oxygen.

    Science.gov (United States)

    Thorn, Robert Peyton, Jr.

    A laser flash photolysis - long path absorption technique has been employed to study the kinetics of the reaction rm BrO + NO_2 + M{k _{16}atopto} products as a function of temperature (248-346 K), pressure (16 -800 Torr), and buffer gas identity (rm N _2,CF_4). 351 nm photolysis of rm NO_2/Br_2/N_2 mixtures generated BrO. The BrO decay in the presence of excess NO_2 was followed by UV absorption at 338.3 nm. The reaction is in the falloff regime between third and second order over the entire range of conditions investigated. This is the first study where temperature dependent measurements of k_{16} (P,T) have been reported at pressures greater than 12 Torr; hence, these results help constrain choices of k_{16}(P,T) for use in modeling stratospheric BrO_{rm x} chemistry. The kinetics of the important stratospheric reaction rm BrO+O(^3P)_sp{to }{k_{14}}Br+O_2 in N_2 buffer gas have been studied as a function of temperature (233-328 K) and pressure (25 -150 Torr) using a novel dual laser flash photolysis/long path absorption/resonance fluorescence technique. 248 nm pulsed laser photolysis of rm Br_2/O _3/N_2 mixtures produces O atoms in excess over Br_2. After a delay sufficient for BrO to be generated, a 532 nm laser pulse photolyses a small fraction of the O_3 to generate O(^3P). The decay of O(^3P) in the presence of an excess, known concentration of BrO, as determined by UV absorption at 338.3 nm and by numerical simulation, is then followed by time-resolved atomic resonance fluorescence spectroscopy. The experimental results have shown the reaction kinetics to be independent of pressure, to increase with decreasing temperature, and to be faster than suggested by the only previous (indirect) measurement. The resulting Anhenius expression for k_{14}(T) is given below.rm k_{14 }(T) = 1.64times 10^{-11} exp (263/T) cm^3 molecule ^{-1} s^{-1} The absolute accuracy of k_{14 }(T) at any temperature within the range studied is estimated to be +/-25%. Possible kinetic

  7. Kinetics and

    Directory of Open Access Journals (Sweden)

    Mojtaba Ahmadi

    2016-11-01

    Full Text Available The aqueous degradation of Reactive Yellow 84 (RY84 by potassium peroxydisulfate (K2S2O8 has been studied in laboratory scale experiments. The effect of the initial concentrations of potassium peroxydisulfate and RY84, pH and temperature on RY84 degradation were also examined. Experimental data were analyzed using first and second-order kinetics. The degradation kinetics of RY84 of the potassium peroxydisulfate process followed the second-order reaction kinetics. These rate constants have an extreme values similar to of 9.493 mM−1min−1 at a peroxydisulfate dose of 4 mmol/L. Thermodynamic parameters such as activation (Ea and Gibbs free energy (ΔG° were also evaluated. The negative value of ΔGo and Ea shows the spontaneous reaction natural conditions and exothermic nature.

  8. Oxidation of fluoroquinolone antibiotics and structurally related amines by chlorine dioxide: Reaction kinetics, product and pathway evaluation.

    Science.gov (United States)

    Wang, Pei; He, Yi-Liang; Huang, Ching-Hua

    2010-12-01

    Fluoroquinolones (FQs) are a group of widely prescribed antibiotics and have been frequently detected in the aquatic environment. The reaction kinetics and transformation of seven FQs (ciprofloxacin (CIP), enrofloxacin (ENR), norfloxacin (NOR), ofloxacin (OFL), lomefloxacin (LOM), pipemidic acid (PIP) and flumequine (FLU)) and three structurally related amines (1-phenylpiperazine (PP), N-phenylmorpholine (PM) and 4-phenylpiperidine (PD)) toward chlorine dioxide (ClO(2)) were investigated to elucidate the behavior of FQs during ClO(2) disinfection processes. The reaction kinetics are highly pH-dependent, can be well described by a second-order kinetic model incorporating speciation of FQs, and follow the trend of OFL > ENR > CIP ∼ NOR ∼ LOM > > PIP in reactivity. Comparison among FQs and related amines and product characterization indicate that FQs' piperazine ring is the primary reactive center toward ClO(2). ClO(2) likely attacks FQ's piperazinyl N4 atom followed by concerted fragmentation involving piperazinyl N1 atom, leading to dealkylation, hydroxylation and intramolecular ring closure at the piperazine moiety. While FQs with tertiary N4 react faster with ClO(2) than FQs with secondary N4, the overall reactivity of the piperazine moiety also depends strongly on the quinolone ring through electronic effects. The reaction rate constants obtained in clean water matrix can be used to model the decay of CIP by ClO(2) in surface water samples, but overestimate the decay in wastewater samples. Overall, transformation of FQs, particularly for those with tertiary N4 amines, could be expected under typical ClO(2) disinfection conditions. However, the transformation may not eliminate antibacterial activity because of little destruction at the quinolone ring. Copyright © 2010 Elsevier Ltd. All rights reserved.

  9. Derivatized Pentadentate Macrocyclic Ligands and Their Transition Metal Complexes

    Directory of Open Access Journals (Sweden)

    Muhammad S. Khan

    2002-06-01

    Full Text Available The reaction of the pendant hydroxyethyl group in the planar pentadentate macrocyclic ligand,1,11-bis(2’-hydroxyethyl-4,8;12,16;17,21-trinitrilo-1,2,10,11-tetraazacyclohenicosa- 2,4,6,9,12,14,18,20-octaene (L2, derived from the condensation of 2,6-pyridinedialdehyde with 6,6’-bis(2’ hydroxyethylhydrazino -2,2’-bipyridine (L1, has been investigated. Esterification reactions are facile, and the reaction of the hydroxyethyl-substituted macrocycle with thionyl chloride yields a chloroethyl derivative. Metal complexes of the new derivatized macrocyclic ligands L3-6having general formula ML3-6X2.nH2O (M = Mn, Fe, Co, Ni, Cu, Zn are readily prepared.

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

    KAUST Repository

    Rachidi, Mariam El

    2015-01-01

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

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    Highlights: • Enzymatic treatment of triclosan in water by soybean and horseradish peroxidases. • pH, H_2O_2 concentration and enzyme dosage affected the removal efficiency of TCS. • The removal of TCS by SBP was more efficient than that of HRP. • K_C_A_T and K_C_A_T/K_M values for SBP toward TCS were much higher than those for HRP. • Polymers formed via radical coupling mechanism were nontoxic to the growth of alga. - Abstract: This study investigated and compared reaction kinetics, product characterization, and toxicity variation of triclosan (TCS) removal mediated by soybean peroxidase (SBP), a recognized potential peroxidase for removing phenolic pollutants, and the commonly used horseradish peroxidase (HRP) with the goal of assessing the technical feasibility of SBP-catalyzed removal of TCS. Reaction conditions such as pH, H_2O_2 concentration and enzyme dosage were found to have a strong influence on the removal efficiency of TCS. SBP can retain its catalytic ability to remove TCS over broad ranges of pH and H_2O_2 concentration, while the optimal pH and H_2O_2 concentration were 7.0 and 8 μM, respectively. 98% TCS was removed with only 0.1 U mL"−"1 SBP in 30 min reaction time, while an HRP dose of 0.3 U mL"−"1 was required to achieve the similar conversion. The catalytic performance of SBP towards TCS was more efficient than that of HRP, which can be explained by catalytic rate constant (K_C_A_T) and catalytic efficiency (K_C_A_T/K_M) for the two enzymes. MS analysis in combination with quantum chemistry computation showed that the polymerization products were generated via C−C and C−O coupling pathways. The polymers were proved to be nontoxic through growth inhibition of green alga (Scenedesmus obliquus). Taking into consideration of the enzymatic treatment cost, SBP may be a better alternative to HRP upon the removal and detoxification of TCS in water/wastewater treatment.

  12. Effect of strain on bond-specific reaction kinetics during the oxidation of H-terminated (111) Si

    International Nuclear Information System (INIS)

    Gokce, Bilal; Aspnes, David E.; Gundogdu, Kenan

    2011-01-01

    Although strain is used in semiconductor technology for manipulating optical, electronic, and chemical properties of semiconductors, the understanding of the microscopic phenomena that are affected or influenced by strain is still incomplete. Second-harmonic generation data obtained during the air oxidation of H-terminated (111) Si reveal the effect of compressive strain on this chemical reaction. Even small amounts of strain manipulate the reaction kinetics of surface bonds significantly, with tensile strain enhancing oxidation and compressive strain retarding it. This dramatic change suggests a strain-driven charge transfer mechanism between Si-H up bonds and Si-Si back bonds in the outer layer of Si atoms.

  13. Conformational diversity of flexible ligand in metal-organic frameworks controlled by size-matching mixed ligands

    International Nuclear Information System (INIS)

    Hua, Xiu-Ni; Qin, Lan; Yan, Xiao-Zhi; Yu, Lei; Xie, Yi-Xin; Han, Lei

    2015-01-01

    Hydrothermal reactions of N-auxiliary flexible exo-bidentate ligand 1,3-bis(4-pyridyl)propane (bpp) and carboxylates ligands naphthalene-2,6-dicarboxylic acid (2,6-H_2ndc) or 4,4′-(hydroxymethylene)dibenzoic acid (H_2hmdb), in the presence of cadmium(II) salts have given rise to two novel metal-organic frameworks based on flexible ligands (FL-MOFs), namely, [Cd_2(2,6-ndc)_2(bpp)(DMF)]·2DMF (1) and [Cd_3(hmdb)_3(bpp)]·2DMF·2EtOH (2) (DMF=N,N-Dimethylformamide). Single-crystal X-ray diffraction analyses revealed that compound 1 exhibits a three-dimensional self-penetrating 6-connected framework based on dinuclear cluster second building unit. Compound 2 displays an infinite three-dimensional ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster and V-shaped organic linkers. The flexible bpp ligand displays different conformations in 1 and 2, which are successfully controlled by size-matching mixed ligands during the self-assembly process. - Graphical abstract: Compound 1 exhibits a 3D self-penetrating 6-connected framework based on dinuclear cluster, and 2 displays an infinite 3D ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster. The flexible 1,3-bis(4-pyridyl)propane ligand displays different conformations in 1 and 2, which successfully controlled by size-matching mixed ligands during the self-assembly process.

  14. Conformational diversity of flexible ligand in metal-organic frameworks controlled by size-matching mixed ligands

    Energy Technology Data Exchange (ETDEWEB)

    Hua, Xiu-Ni; Qin, Lan; Yan, Xiao-Zhi; Yu, Lei; Xie, Yi-Xin; Han, Lei, E-mail: hanlei@nbu.edu.cn

    2015-12-15

    Hydrothermal reactions of N-auxiliary flexible exo-bidentate ligand 1,3-bis(4-pyridyl)propane (bpp) and carboxylates ligands naphthalene-2,6-dicarboxylic acid (2,6-H{sub 2}ndc) or 4,4′-(hydroxymethylene)dibenzoic acid (H{sub 2}hmdb), in the presence of cadmium(II) salts have given rise to two novel metal-organic frameworks based on flexible ligands (FL-MOFs), namely, [Cd{sub 2}(2,6-ndc){sub 2}(bpp)(DMF)]·2DMF (1) and [Cd{sub 3}(hmdb){sub 3}(bpp)]·2DMF·2EtOH (2) (DMF=N,N-Dimethylformamide). Single-crystal X-ray diffraction analyses revealed that compound 1 exhibits a three-dimensional self-penetrating 6-connected framework based on dinuclear cluster second building unit. Compound 2 displays an infinite three-dimensional ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster and V-shaped organic linkers. The flexible bpp ligand displays different conformations in 1 and 2, which are successfully controlled by size-matching mixed ligands during the self-assembly process. - Graphical abstract: Compound 1 exhibits a 3D self-penetrating 6-connected framework based on dinuclear cluster, and 2 displays an infinite 3D ‘Lucky Clover’ shape (2,10)-connected network based on the trinuclear cluster. The flexible 1,3-bis(4-pyridyl)propane ligand displays different conformations in 1 and 2, which successfully controlled by size-matching mixed ligands during the self-assembly process.

  15. Kinetic stable Cr isotopic fractionation between aqueous Cr(III)-Cl-H2O complexes at 25 °C: Implications for Cr(III) mobility and isotopic variations in modern and ancient natural systems

    Science.gov (United States)

    Babechuk, Michael G.; Kleinhanns, Ilka C.; Reitter, Elmar; Schoenberg, Ronny

    2018-02-01

    The stable Cr isotope fractionation preserved in natural substances has been attributed predominantly to Cr(III)-Cr(VI) redox transformations. However, non-redox reaction pathways (e.g., ligand-promoted dissolution, ligand exchange, adsorption of Cr(III)) are liable to contribute to isotopic fractionation in natural systems given that soluble Cr(III)-ligands have been directly documented or modeled in several marine, continental, and hydrothermal environments. This study isolates the stable Cr isotope fractionation accompanying Cl-H2O ligand exchange during the transformation of three aqueous species in the Cr(III)-Cl-H2O system, [CrCl2(H2O)4]+aq (abr. CrCl2+ or S1), [CrCl(H2O)5]2+aq (abr. CrCl2+ or S2), and [Cr(H2O)6]3+aq (abr. Cr3+ or S3), at low pH (≤2). In dilute HCl (0.01 to 1 M), Cr3+ is the kinetically favoured species and transformation of CrCl2+ to CrCl2+ to Cr3+ via 2 steps of dechlorination/hydrolyzation begins immediately upon dissolution of a Cr(III)-Cl solid. Individual species are separated with cation exchange chromatography at different stages of transformation and inter- and intra-species (across an elution peak of one species) isotopic fractionation of up to 1 and 2‰ (δ53/52Cr), respectively, is documented. Comparison of peak elution characteristics with Cr-Cl-H-O isotopologue mass abundances suggests mass-dependent sorting of isotopologues alone cannot explain intra-species fractionation, supporting a previously published proposal that preferential adsorption of light Cr isotopes on the resin is driven by vibrational energy effects. The transformation of CrCl2+ to CrCl2+ is faster than CrCl2+ to Cr3+ and the rates of both transformations increase with solution pH. Preferential reaction of light Cr(III) isotopes into product species occurs during each transformation, consistent with closed-system, kinetic fractionation during Cl-H2O ligand exchange. Inter-species fractionation is assessed using time-series experiments beginning from the

  16. Magnetic Pd-Fe{sub 3}O{sub 4} heterodimer nanocrystals as recoverable catalysts for ligand-free hiyama cross-coupling reactions

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Woong Sup; Byun, Sang Moon; Kwon, Jung Min; Kim, B. Moon [Dept. of Chemistry, College of Natural Sciences, Seoul National University, Seoul (Korea, Republic of)

    2016-12-15

    Ligand-free Hiyama cross-coupling reaction was achieved through the use of Pd-Fe{sub 3}O{sub 4} heterodimeric nanocrystals (1 mol% in Pd) as recyclable catalysts. The nanocrystal catalysts exhibited good activities accommodating a variety of substrates including aryl bromides and iodides with substituents of varying electronic and steric properties. Furthermore, the nanocrystal catalyst could be conveniently recovered with the aid of an external magnet and recycled five times without the loss of catalytic activity to a considerable degree.

  17. Parameterization of phosphine ligands demonstrates enhancement of nickel catalysis via remote steric effects

    Science.gov (United States)

    Wu, Kevin; Doyle, Abigail G.

    2017-08-01

    The field of Ni-catalysed cross-coupling has seen rapid recent growth because of the low cost of Ni, its earth abundance, and its ability to promote unique cross-coupling reactions. Whereas advances in the related field of Pd-catalysed cross-coupling have been driven by ligand design, the development of ligands specifically for Ni has received minimal attention. Here, we disclose a class of phosphines that enable the Ni-catalysed Csp3 Suzuki coupling of acetals with boronic acids to generate benzylic ethers, a reaction that failed with known ligands for Ni and designer phosphines for Pd. Using parameters to quantify phosphine steric and electronic properties together with regression statistical analysis, we identify a model for ligand success. The study suggests that effective phosphines feature remote steric hindrance, a concept that could guide future ligand design tailored to Ni. Our analysis also reveals that two classic descriptors for ligand steric environment—cone angle and % buried volume—are not equivalent, despite their treatment in the literature.

  18. Surface-Bound Ligands Modulate Chemoselectivity and Activity of a Bimetallic Nanoparticle Catalyst

    KAUST Repository

    Vu, Khanh B.

    2015-04-03

    "Naked" metal nanoparticles (NPs) are thermodynamically and kinetically unstable in solution. Ligands, surfactants, or polymers, which adsorb at a particle\\'s surface, can be used to stabilize NPs; however, such a mode of stabilization is undesirable for catalytic applications because the adsorbates block the surface active sites. The catalytic activity and the stability of NPs are usually inversely correlated. Here, we describe an example of a bimetallic (PtFe) NP catalyst stabilized by carboxylate surface ligands that bind preferentially to one of the metals (Fe). NPs stabilized by fluorous ligands were found to be remarkably competent in catalyzing the hydrogenation of cinnamaldehyde; NPs stabilized by hydrocarbon ligands were significantly less active. The chain length of the fluorous ligands played a key role in determining the chemoselectivity of the FePt NP catalysts. (Chemical Presented). © 2015 American Chemical Society.

  19. UV-visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

    DEFF Research Database (Denmark)

    Wallington, T.J.; Egsgaard, H.; Nielsen, O.J.

    1998-01-01

    Pulse radiolysis transient UV-visible absorption spectroscopy was used to study the UV-visible absorption spectrum (225-575 nm) of the phenyl radical, C6H5(.), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225-340 nm...

  20. Reactivity of monoolefin ligand in transition metal complexes

    International Nuclear Information System (INIS)

    Rybinskaya, M.I.

    1978-01-01

    The main tendencies in the coordinated olefin ligand property changes are discussed in the transition metal complexes in comparison with free olefins. The review includes the papers published from 1951 up to 1976. It has been shown that in complexes with transition metal cations olefin π-base acquires the ability to react with nucleophylic reagents. Olefin π-acids in complexes with zero valent metals are easily subjected to electrophylic reagent action. At coordination with transition metal cations the olefin properties are generally preserved, while in the zero-valent metal complexes the nonsaturated ligand acquires the properties of a saturated compounds. The ability of transition metal cations in complexes to intensify reactions of nucleophylic bimolecular substitution of vinyl halogen is clearly detected in contrast to the zero valent metal complexes. It has been shown that investigations of the coordinated olefin ligand reactivity give large possibilities in the further development of the organic synthesis. Some reactions are taken as the basis of important industrial processes