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The influence of the catalyst on the kinetics of ethyl metacrylate synthesis
Miros aw Grzesik , Teresa Witczak
Polish Journal of Chemical Technology , 2007, DOI: 10.2478/v10026-007-0003-1
Abstract: The synthesis of ethyl metacrylate in the liquid phase was studied. Tungstophosphoric and molybdophosphoric acids, which belong to heteropolyacids group, were used as a catalyst. The chemical compounds from this group are often utilized in the catalysis with regard to their activity and selectivity. The rate equations, reaction rate constants and equilibrium constants have been determined. The reaction order and the kinetic parameters of the kinetic relations were determined by the integral method. All rate equations are formulated with activities taking the non ideal effects of the compounds into consideration. It was found that the kinetics of the esterification of the presented reactions was non-elementary
Chemical Kinetics for Synthesis of Triacetin from Biodiesel Byproduct  [cached]
Zahrul Mufrodi,Sutijan, Rochmadi,Arief Budiman
International Journal of Chemistry , 2012, DOI: 10.5539/ijc.v4n2p101
Abstract: The reaction kinetic of the glycerol acetylation with acetic acid catalyzed by sulfuric acid has been studied in the frame of continuous triacetin production. Glycerol, acetic acid and sulfuric acid catalyst were reacted in a batch reactor, in order to get reaction kinetics data. The mole ratio of catalyst to glycerol and temperature were studied during the experience. This study concluded that the selectivity of triacetin increased with increase in mole ratio of catalyst to glycerol. Increasing temperatures lead to increase selectivity of triacetin. It will decreased at the time of acetic acid has begun to evaporate. Triacetin synthesis is an exothermic reaction, a higher reaction temperature will cause in shifting the balance toward formation of reactants. This needs to be anticipated by taking one of the products so that the equilibrium shifting toward product formation.
Enzymatic Synthesis of Ampicillin: Nonlinear Modeling, Kinetics Estimation, and Adaptive Control
Monica Roman,Dan Seli teanu
Journal of Biomedicine and Biotechnology , 2012, DOI: 10.1155/2012/512691
Abstract: Nowadays, the use of advanced control strategies in biotechnology is quite low. A main reason is the lack of quality of the data, and the fact that more sophisticated control strategies must be based on a model of the dynamics of bioprocesses. The nonlinearity of the bioprocesses and the absence of cheap and reliable instrumentation require an enhanced modeling effort and identification strategies for the kinetics. The present work approaches modeling and control strategies for the enzymatic synthesis of ampicillin that is carried out inside a fed-batch bioreactor. First, a nonlinear dynamical model of this bioprocess is obtained by using a novel modeling procedure for biotechnology: the bond graph methodology. Second, a high gain observer is designed for the estimation of the imprecisely known kinetics of the synthesis process. Third, by combining an exact linearizing control law with the on-line estimation kinetics algorithm, a nonlinear adaptive control law is designed. The case study discussed shows that a nonlinear feedback control strategy applied to the ampicillin synthesis bioprocess can cope with disturbances, noisy measurements, and parametric uncertainties. Numerical simulations performed with MATLAB environment are included in order to test the behavior and the performances of the proposed estimation and control strategies.
Kinetics of Electrodeposition of Silver and Copper at Template Synthesis of Nanowires  [PDF]
P. G. Globa,E. A. Zasavitsky,V. G. Kantser,S. P. Sidelinikova,A. I. Dikusar
Physics , 2007,
Abstract: The results of investigation of kinetics of nanopores filling into membranes from aluminum oxide (pore diameter - 200 nm, porosity ~ 50%) at electrodeposition of copper and silver are described. It is shown, that at identical quantity of electricity passed through solutions, the degree of pores filling by metal (average thickness of a deposit) is various for copper and silver deposition. Calculated (according Faraday Law) and experimental dependences of deposition rates of these metals on quantity of electricity passed at direct and pulse currents are presented. Galvanodynamic i - v dependences have been obtained at various current scanning rates. The smaller rate of deposition allows to decrease concentration limitations of electrode process and to obtain higher average thickness of metal deposits and higher filling degree. The limiting values of quantity of electricity for direct and pulse currents were determined. The average thickness of silver and copper deposits was obtained. A degree of pores filling, the morphology and chemical microanalysis were studied on cross-section of the membrane, using TESCAN SEM equipped with an Oxford Instruments INCA Enerqy EDX-system.
Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate  [cached]
Michael North,Marta Omedes-Pujol
Beilstein Journal of Organic Chemistry , 2010, DOI: 10.3762/bjoc.6.119
Abstract: Propylene carbonate can be used as a green solvent for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate and dichloromethane. Reactions in both solvents obey overall second-order kinetics, the rate of reaction being dependent on the concentration of both the aldehyde and trimethylsilyl cyanide. The order with respect to VO(salen)NCS was determined and found to decrease from 1.2 in dichloromethane to 1.0 in propylene carbonate, indicating that in propylene carbonate, VO(salen)NCS is present only as a mononuclear species, whereas in dichloromethane dinuclear species are present which have previously been shown to be responsible for most of the catalytic activity. Evidence from 51V NMR spectroscopy suggested that propylene carbonate coordinates to VO(salen)NCS, blocking the free coordination site, thus inhibiting its Lewis acidity and accounting for the reduction in catalytic activity. This explanation was further supported by a Hammett analysis study, which indicated that Lewis base catalysis made a much greater contribution to the overall catalytic activity of VO(salen)NCS in propylene carbonate than in dichloromethane.
Deducing the Kinetics of Protein Synthesis In Vivo from the Transition Rates Measured In Vitro  [PDF]
Sophia Rudorf,Michael Thommen,Marina V. Rodnina,Reinhard Lipowsky
PLOS Computational Biology , 2014, DOI: doi/10.1371/journal.pcbi.1003909
Abstract: The molecular machinery of life relies on complex multistep processes that involve numerous individual transitions, such as molecular association and dissociation steps, chemical reactions, and mechanical movements. The corresponding transition rates can be typically measured in vitro but not in vivo. Here, we develop a general method to deduce the in-vivo rates from their in-vitro values. The method has two basic components. First, we introduce the kinetic distance, a new concept by which we can quantitatively compare the kinetics of a multistep process in different environments. The kinetic distance depends logarithmically on the transition rates and can be interpreted in terms of the underlying free energy barriers. Second, we minimize the kinetic distance between the in-vitro and the in-vivo process, imposing the constraint that the deduced rates reproduce a known global property such as the overall in-vivo speed. In order to demonstrate the predictive power of our method, we apply it to protein synthesis by ribosomes, a key process of gene expression. We describe the latter process by a codon-specific Markov model with three reaction pathways, corresponding to the initial binding of cognate, near-cognate, and non-cognate tRNA, for which we determine all individual transition rates in vitro. We then predict the in-vivo rates by the constrained minimization procedure and validate these rates by three independent sets of in-vivo data, obtained for codon-dependent translation speeds, codon-specific translation dynamics, and missense error frequencies. In all cases, we find good agreement between theory and experiment without adjusting any fit parameter. The deduced in-vivo rates lead to smaller error frequencies than the known in-vitro rates, primarily by an improved initial selection of tRNA. The method introduced here is relatively simple from a computational point of view and can be applied to any biomolecular process, for which we have detailed information about the in-vitro kinetics.
Models for the Study of Whole-Body Glucose Kinetics: A Mathematical Synthesis  [PDF]
Leslie L. McKnight,Secundino Lopez,Anna Kate Shoveller,James France
ISRN Biomathematics , 2013, DOI: 10.1155/2013/120974
Abstract: The maintenance of blood glucose homeostasis is complex and involves several key tissues. Most of these tissues are not easily accessible, making direct measurement of the physiological parameters involved in glucose metabolism difficult. The use of isotope tracer methodology and mathematical modeling allows indirect estimates of in vivo glucose metabolism through relatively noninvasive means. The purpose of this paper was to provide a mathematical synthesis of the models developed for describing glucose kinetics. As many of the models were developed using dogs, example data from the canine literature are presented. However, examples from the human and feline literature are also given in the absence of dog data. The glucose system is considered in both the steady and nonsteady states, and the models are examined by grouping them into schemes consisting of one, two, and three glucose compartments. Noncompartmental schemes are also considered briefly. 1. Introduction Glucose is a ubiquitous cellular fuel source for all mammalian tissues. As such, the regulation of glucose metabolism has been under extensive investigation for the past century. In healthy animals, several biological mechanisms ensure that the rate of appearance of glucose in the bloodstream tightly matches that of glucose uptake by tissues, resulting in relatively constant blood glucose concentrations irrespective of physiological condition. These control mechanisms are predominantly dictated by the energy status of the animal. In postabsorptive and fasting periods the body largely relies on endogenous glucose production via liver glycogenolysis or gluconeogenesis to maintain glucose homeostasis. In the postprandial period (or fed state) glucose uptake and utilization by tissues is increased in response to the absorption of glucose in the small intestine, giving rise to the subsequent stabilization of blood glucose concentrations. Both production and uptake are principally hormonally regulated by glucagon and insulin, but substrate availability, circulating free fatty acids (FFAs), and catecholamines (released in response to stress and/or exercise) also impact glucose metabolism. Dysregulation of glucose homeostasis, as seen in metabolic diseases including obesity and diabetes, has become a worldwide epidemic in humans [1] and companion animals [2]. These diseases share the common feature of progressive insulin resistance and hyperglycemia. The rat has been used extensively as a model for studying the etiology of these diseases (reviewed by [3]). However, the dog provides a model more
Kinetics and mechanism of NH3 synthesis over Fe(100) and K/Fe(100) model catalysts  [cached]
A. Z. Moshfegh,A. Reyhani
Iranian Journal of Physics Research , 2004,
Abstract: In this investigation kinetics and mechanism of NH3 synthesis over Fe(100) and K/Fe(100) model catalysts have been studied. In this context, adsorption kinetics of both N2/Fe (100) and H2/Fe (100)systems is initially investigated. By using statistical mechanic approach, we have determined the adsorption coefficient for N2 and H2 molecules as well as transition probability of different states of adsorption and dissociation of the reactants molecules. The effect of surface catalyst temperature on the reaction rate (TOF) is studied under different reactant partial pressures. The mechanism of NH3 synthesis is suggested based on LH surface reactions model. According to the obtained results, activation energy for the reaction over Fe (100) and K/Fe(100) (for θk=0.1ML) was determined 19.6 and 11.1 kcal/mole, respectively. The order of reaction on both catalysts with respect to PN2 and PH2 was unity and negative, respectively. Based on our data analysis, the NH3 synthesis obeys Temkin isotherm.
SYNTHESIS AND THERMAL DECOMPOSITION KINETICS OF LANTHANUM(III) COMPLEX WITH UNSYMMETRICAL SCHIFF BASE
CAIFENG,BI; XIAOKANG,AI; YUHUA,FAN; SHUANGYU,BI; SITAN,XIE;
Journal of the Chilean Chemical Society , 2007, DOI: 10.4067/S0717-97072007000400004
Abstract: a new unsymmetrical solid schiff base (lli) was synthesized using l-lysine, salicylaldehyde and furfural. solid lanthanum(iii) complex of this ligand [lal(no3)]no3-2h20 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 : da/dt = a · e-elrt. (1-a)2 y the kinetic parameters(δ, a), activation entropy δs* and activation free-energy δg* were also gained, e = 212.7 kj/molδlnla =44.12, ?s*=116.8 j/mol-kδδg*=148.1 kj/mol
SYNTHESIS AND THERMAL DECOMPOSITION KINETICS OF LANTHANUM(III) COMPLEX WITH UNSYMMETRICAL SCHIFF BASE  [cached]
BI CAIFENG,AI XIAOKANG,FAN YUHUA,BI SHUANGYU
Journal of the Chilean Chemical Society , 2007,
Abstract: A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, salicylaldehyde and furfural. Solid lanthanum(III) complex of this ligand [LaL(NO3)]NO3-2H(2)0 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 : da/dt = A · e-ElRT. (1-a)2 y The kinetic parameters(Δ, A), activation entropy ΔS* and activation free-energy ΔG* were also gained, E = 212.7 kJ/molΔlnLA =44.12, S*=116.8 J/mol-KΔΔG*=148.1 kJ/mol
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