scholarly journals Study of catalase immobilized on a silicate matrix for non-aqueous biocatalysis

2005 ◽  
Vol 3 (2) ◽  
pp. 279-287 ◽  
Author(s):  
Elena Horozova ◽  
Nina Dimcheva
Keyword(s):  
Enzymatic Reaction ◽  
Energy Of Activation ◽  
Specific Rate ◽  
Uv Spectrophotometry ◽  
Silicate Matrix ◽  
Experimental Conditions ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Entropy Of Activation ◽  
Rate Limiting

AbstractCatalytic activity of catalase (CAT) immobilized on a modified silicate matrix to mediate decomposition of meta-chloroperoxibenzoic acid (3-CPBA) in acetonitrile has been investigated by means of quantitative UV-spectrophotometry. Under the selected experimental conditions, the kinetic parameters: the apparent Michaelis constat (KM), the apparent maximum rate of enzymatic reaction (Vmaxapp), the first order specific rate constants (ksp), the energy of activation (Ea) and the pre-exponential factor of the Arrhenius equation (Z0) were calculated. Conclusions regarding the rate-limiting step of the overall catalytic process were drawn from the calculated values of the Gibbs energy of activation ΔG*, the enthalpy of activation ΔH*, and the entropy of activation ΔS*.

scholarly journals Kinetics of the diamine oxidase reaction

1973 ◽  
Vol 131 (3) ◽  
pp. 459-469 ◽  
Author(s):  
William G. Bardsley ◽  
M. James C. Crabbe ◽  
Julian S. Shindler
Keyword(s):  
Diamine Oxidase ◽  
Experimental Conditions ◽  
Ph Values ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Deuterium Substitution ◽  
Effects Of Temperature ◽  
Rate Limiting ◽  
Kinetics Of ◽  
Oxidase Reaction

1. The oxidation of p-dimethylaminomethylbenzylamine was followed spectrophotometrically by measuring the change in E250 caused by the p-dimethylaminomethylbenzaldehyde produced under a wide variety of experimental conditions. 2. The effect of variations in concentrations of both substrates (amine and oxygen) and all products (aminoaldehyde, hydrogen peroxide and ammonia) on this reaction was studied and the results used to develop a formal mechanism. 3. The nature of the rate-limiting step was elucidated by studying the effects of alterations in ionic strength, dielectric constant and deuterium substitution on the velocity of the forward reaction. 4. Thermodynamic activation energy parameters were obtained at several pH values from the effects of temperature on the reaction.

scholarly journals Chlorates(VII) removal on Dowex™PSR-2 resin

2016 ◽  
Vol 71 (1) ◽  
pp. 105
Author(s):  
Dorota Kołodyńska ◽  
Aleksandra Łyko ◽  
Marzena Gęca ◽  
Zbigniew Hubicki
Keyword(s):  
Solution Concentration ◽  
Intraparticle Diffusion ◽  
Optimum Conditions ◽  
Order Model ◽  
Experimental Conditions ◽  
Freundlich Model ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Pseudo Second Order ◽  
Rate Limiting

<p>Lately there has been observed the increased presence of chlorates(VII) in the natural environment which can affect human health negatively. Therefore the removal of chlorate(VII) ions using the gel type resin functionalized with the tri-n-butyl ammonium (Dowex<sup>™</sup>PSR-2) from waters was studied. The main aim was to evaluate the effects of experimental conditions including contact time, initial solution concentration, pH and temperature on chlorate(VII) ions removal as well as the anion exchanger properties on chlorate(VII) ions sorption. It was found that only the pseudo second order model described the experimental data well and the intraparticle diffusion was not the rate-limiting step. According to the Freundlich model, the q<sub>e</sub> value was to be 69.26 mg/g at optimum conditions (pH 7.0 at 25 <sup>o</sup>C).<strong></strong></p>

The Kinetics of Reactions in and Near the Cytochrome b/f Complex of Chloroplast Thylakoids. I. Proton Deposition

1988 ◽  
Vol 15 (5) ◽  
pp. 695 ◽  
Author(s):  
AB Hope ◽  
J Liggins ◽  
DB Matthews
Keyword(s):  
Rate Constant ◽  
Bimolecular Reaction ◽  
Plastoquinone Pool ◽  
Rate Limiting Step ◽  
Fixed Concentration ◽  
Wide Range ◽  
Entropy Of Activation ◽  
Electron Donation ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of proton deposition in the intrathylakoid spaces of pea chloroplasts were measured under a wide range of conditions. With duroquinol added to reduce the plastoquinone pool, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea added to inhibit photosystem II, but no ionophore present, the proton deposition, attributed to plastoquinol oxidation, was biphasic. About half the deposition had an apparent rate constant (k) of 150-200 s-1, the other half about 10 s-1. Valinomycin or nonactin (<0.1 �M) plus potassium ions made the deposition almost monophasic, with k = 140 s-1. When the state of reduction of the plastoquinone pool was varied by the addition of varied concentrations of duroquinol, in the presence of 1 �M nonactin, k for proton deposition varied from about 20 (0.01 mM duroquinol) up to a maximum of 140 s-1 (0.5 mM duroquinol). When temperature was varied between 4 and 23°C, with 1 �M nonactin, an Arrhenius plot of ln(k) for proton deposition was linear; the activation enthalpy was 67 kJ mol-1, the entropy of activation, 23 J K-1 mol-1. The data are analysed in terms of a bimolecular reaction between a varying concentration of plastoquinol and a fixed concentration of oxidised Rieske centre. The results are consistent with a rate constant, for the first electron donation by plastoquinol, of 28 s-1 (the rate-limiting step), followed by a relatively fast second electron donation to cytochrome b563 (low potential), followed by deposition of two protons. The speed of the second proton deposition is dependent on the membrane potential difference.

The thermal decomposition of silver azide

1979 ◽  
Vol 369 (1736) ◽  
pp. 83-104 ◽  
Keyword(s):  
Crystal Surface ◽  
Molar Fraction ◽  
X Rays ◽  
Silver Azide ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Transmission Electron ◽  
Valence Electrons ◽  
Electron Microscopes ◽  
Rate Limiting

The isothermal pyrolysis of single crystals ( ca . 5 x 0.1 x 0.1 mm 3 ) of silver azide has been investigated in the temperature range T ═ 513–558 K by using a thermobalance. The kinetic equation is found to be 1 – (1 – α ) ½ ═ t {2(1 – ∊) / B } u 0 exp (– E/kT) , where α is the molar fraction of decomposition, t the time, B the width of the crystal, ∊( ≪ 1) is an aspect ratio, u 0 ═ 10 2.5 –10 3.4 m s –1 , E ═ 1.23 ± 0.20 eV, and k is the Boltzmann constant. The reaction is topochemical, i. e. it is controlled by the movement of the phase boundary. The solid product (silver) has been examined with X-rays and with scanning and high voltage transmission electron microscopes. It is shown that silver aggregates in the form of ‘pebbles’ 7–14 μm in diameter, which protrude out of the decomposing surface, are randomly orientated but are probably monocrystalline. A mechanism based on Mott’s (1939) model is proposed. The rate-limiting step is the emission of valence electrons from silver azide into silver, and the decomposition is autocatalytic. The theoretical values of the activation energy and the pre-exponential factor are in general agreement with the experimental results. The mechanism has also been used to explain the effects of additives as observed by other workers. The topo­chemical and the autocatalytic characteristics of the reaction suggest that during pyrolysis a silver film covers the crystal surface.

A STUDY OF SOME REACTIONS OF THE CYCLOPENTYL RADICAL

1965 ◽  
Vol 43 (3) ◽  
pp. 570-581 ◽  
Author(s):  
Alvin S. Gordon
Keyword(s):  
Hydrogen Atom ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Energy Of Activation ◽  
Radical Reactions ◽  
Specific Rate ◽  
Exponential Factor ◽  
Allyl Radical ◽  
Specific Rate Constant ◽  
Activated Complex

The specific rate constant for opening the cyclopentyl radical has been determined to be 1014.5 exp –37 700/RT s−1. The energy of activation indicates that any eclipsed pairs of H atoms in the cyclic radical are not de-eclipsed in the activated complex. No evidence for the resulting five-membered linear radical can be found, only evidence for its breakdown products, allyl radical and ethylene.The disproportionation/combination ratio for methyl and cyclopentyl radicals is about 0.3. The energy of activation for methyl abstracting a hydrogen atom from cyclopentane has been confirmed as about 9.5 kcal/mole.Cyclopentyl radical also loses a hydrogen atom to form cyclopentene. The kinetic parameters are difficult to obtain because of radical–radical reactions which form cyclopentene. An analysis of the results indicates an energy of activation at least equal to that for opening the cyclopentyl ring.Evidence is presented to support the view that the cyclopentyl radical loses a molecule of hydrogen to form the resonance-stablized cyclopentenyl radical with an energy of activation close to that for opening the ring, and a pre-exponential factor about 1/10 of that for the opening of the ring.

scholarly journals KINETIKA MIKRO DEKOMPOSISI METANA MENJADI KARBON NANOTUBE PADA PERMUKAAN KATALIS Ni-Cu-Al

REAKTOR ◽  
2011 ◽  
Vol 13 (3) ◽  
pp. 148 ◽  
Author(s):  
Praswasti Pembangun Dyah Kencana Wulan ◽  
Widodo Wahyu Purwanto ◽  
Yuswan Muharam
Keyword(s):  
Carbon Nanotube ◽  
Kinetic Model ◽  
Phase Transfer ◽  
Internal Diffusion ◽  
Exponential Factor ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Decomposition Of Methane ◽  
Rate Limiting ◽  
Kinetics Of

MICRO KINETICS OF DECOMPOSITION OF METHANE TO CARBON NANOTUBES OVER NI-CU-AL CATALYST. The main focus of this research was to obtain micro kinetics decomposition of methane producing carbon nanotube on the surface of the Ni-Cu-Al catalyst. Experimental kinetics data collected at a temperature range of 650-750oC and pressure of one atmosphere. The preliminary test was conducted to obtain the kinetics are not influenced by external and internal diffusion limitations as well as inter-phase transfer. Kinetics data were tested by micro kinetic model derived from the catalyst surface reaction mechanism. The most appropriate kinetic model becomes the rate-limiting step of methane decomposition reaction. Results of preliminary experiment showed that the kinetics of the external diffusion effect is negligible at flow rates above 150 mL/min. Internal diffusion can be ignored with a catalyst under 0.25 mm in diameter with a weight of 0.04 grams of catalyst and contact time 2.5x10-4. Rate equation analysis shows that the rate-limiting step is the adsorption which indicates that intermediate consumption (CH4I + I Û CH3I + HI) is faster than the formation of intermediate (adsorption of methane, CH4 + I Û CH4I). The activation energy obtained for 34.628 kJ/mol and pre-exponential factor of 6.583x106.  Fokus utama penelitian ini adalah memperoleh kinetika mikro dekomposisi metana yang menghasilkan Carbon Nanotube pada permukaan  katalis Ni-Cu-Al. Data kinetika eksperimen diambil pada rentang temperatur 650-750oC dan tekanan 1 atmosfer. Percobaan pendahuluan dilakukan untuk memperoleh daerah kinetika yang tidak dipengaruhi oleh limitasi difusi eksternal dan internal serta perpindahan antar fasa.  Data kinetika  diuji dengan model kinetika mikro yang diturunkan dari mekanisme reaksi permukaan katalis. Model kinetika yang paling sesuai menjadi tahap pembatas laju reaksi dekomposisi metana. Hasil percobaan pendahuluan kinetika menunjukkan bahwa pengaruh difusi eksternal dapat diabaikan pada laju alir di atas 150 mL/menit. Difusi internal dapat diabaikan dengan menggunakan katalis berdiameter di bawah 0,25 mm dengan berat katalis 0,04 gram pada waktu kontak 2,5x10-4. Analisis persamaan laju menunjukkan bahwa tahap pembatas laju adalah tahap adsorpsi yang menunjukkan bahwa konsumsi intermediate (CH4I + I Û CH3I + HI) lebih cepat dari pembentukan intermediate (adsorpsi metana,CH4 + I Û CH4I). Energi aktivasi yang diperoleh sebesar 34,628 kJ/mol dan faktor pre-eksponensial 6,583x106.

Enzyme-Catalyzed Decomposition of Dibenzoyl Peroxide in Organic Solvents

2001 ◽  
Vol 56 (7-8) ◽  
pp. 553-558 ◽  
Author(s):  
Elena Horozova ◽  
Nina Dimcheva ◽  
Zinaida Jordanova
Keyword(s):  
Reaction Rate ◽  
Specific Rate ◽  
Michaelis Constant ◽  
Exponential Factor ◽  
Maximum Reaction Rate ◽  
Enthalpy Of Activation ◽  
Maximum Reaction ◽  
Specific Rate Constant ◽  
Entropy Of Activation ◽  
Dibenzoyl Peroxide

Catalytic activity of catalase (CAT, EC 1.11.1.6), immobilized on carbon black NORIT and soot PM-100, with respect to decomposition of dibenzoyl peroxide (BPO) in non-aque-ous media (acetonitrile and tetrachloromethane), was investigated with a quantitative UV-spectrophotometrical approach. Progress of the above reaction was controlled by selected kinetic parameters: the apparent Michaelis constant (Kmapp), the specific rate constant (Ksp), the activation energy (Ea), the maximum reaction rate (Vmax), and the Arrhenius’ pre-exponential factor (Z0). Conclusions on the tentative mechanism of the catalytic process observed were drawn from the calculated values of the Gibbs energy of activation (ΔG*), the enthalpy of activation (ΔH*), and entropy of activation (ΔS*)

scholarly journals BIREFRINGENCE OF SPERMATOZOA

1972 ◽  
Vol 55 (2) ◽  
pp. 489-500 ◽  
Author(s):  
James Bearden ◽  
Irwin J. Bendet
Keyword(s):  
Ethylene Glycol ◽  
Disulfide Bonds ◽  
Human Sperm ◽  
Molecular Structures ◽  
Rate Limiting Step ◽  
Ionic Bonds ◽  
Entropy Of Activation ◽  
Enthalpy And Entropy ◽  
Sperm Nuclei ◽  
Rate Limiting

In experiments designed to determine the thermal stability and bonding strength of a natural nucleoprotein structure, the loss of birefringence as a function of time and temperature was investigated for both mammalian and nonmammalian sperm nuclei. At a constant temperature, this reaction was found to be first order for both types over a range of temperatures. The methods of chemical kinetics applied to results of these reactions, called birefringence melting reactions, produced values for the enthalpy and entropy of activation in the reactions, which gave some indication of the strength of binding in the nucleoprotein structure; and these results, plus those on the influence of chemicals on the structure, were consistent with the molecular structures which have been proposed by others for the nucleoprotein complex of sperm nuclei. For both bull and human sperm in ethylene glycol, the rate-limiting step in the melting reactions appeared to be the breakage of disulfide bonds. For squid sperm in ethylene glycol, and bull or squid sperm in ethylene glycol plus ß-mercaptoethanol, the identity of this step was more ambiguous, but a possibility consistent with these and other results would be a cooperative breakage of ionic bonds.

The story so far: molecular regulation of the heme oxygenase-1 gene in renal injury

2004 ◽  
Vol 286 (3) ◽  
pp. F425-F441 ◽  
Author(s):  
Eric M. Sikorski ◽  
Thomas Hock ◽  
Nathalie Hill-Kapturczak ◽  
Anupam Agarwal
Keyword(s):  
Renal Injury ◽  
Biological Effects ◽  
Enzymatic Reaction ◽  
Molecular Regulation ◽  
Heme Oxygenase 1 ◽  
Biliverdin Reductase ◽  
Disease States ◽  
Rate Limiting Step ◽  
Beneficial Response ◽  
Rate Limiting

Heme oxygenases (HOs) catalyze the rate-limiting step in heme degradation, resulting in the formation of iron, carbon monoxide, and biliverdin, the latter of which is subsequently converted to bilirubin by biliverdin reductase. Recent attention has focused on the biological effects of product(s) of this enzymatic reaction, which have important antioxidant, anti-inflammatory, and cytoprotective functions. Two major isoforms of the HO enzyme have been described: an inducible isoform, HO-1, and a constitutively expressed isoform, HO-2. A third isoform, HO-3, closely related to HO-2, has also been described. Several stimuli implicated in the pathogenesis of renal injury, such as heme, nitric oxide, growth factors, angiotensin II, cytokines, and nephrotoxins, induce HO-1. Induction of HO-1 occurs as an adaptive and beneficial response to these stimuli, as demonstrated by studies in renal and non-renal disease states. This review will focus on the molecular regulation of the HO-1 gene in renal injury and will highlight the interspecies differences, predominantly between the rodent and human HO-1 genes.

Inhibition and activation of Na+-Ca2+ exchange activity by quinacrine

1987 ◽  
Vol 252 (1) ◽  
pp. C24-C29 ◽  
Author(s):  
P. de la Pena ◽  
J. P. Reeves
Keyword(s):  
Inhibitory Effects ◽  
Experimental Conditions ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Amiloride Derivatives ◽  
High Concentrations ◽  
Rate Limiting ◽  
Sarcolemmal Vesicles ◽  
Stimulation Of ◽  
Exchange Activity

Quinacrine either inhibited or stimulated Na-Ca exchange in cardiac sarcolemmal vesicles, depending on the experimental conditions. When present in the assay medium for Na-Ca exchange, quinacrine inhibited both Nai-dependent Ca2+ uptake (Ki = 50 microM) and Nao-dependent Ca2+ efflux. Quinacrine's inhibition of Ca2+ efflux was attenuated by high concentrations of Na+. Quinacrine also blocked Na-Na and Ca-Ca exchange activities in the vesicles. The inhibitory effects of quinacrine on Na-Ca exchange activity are qualitatively similar to those reported previously for amiloride derivatives. When Na-loaded vesicles were preincubated with quinacrine and then assayed for Na-Ca exchange in a quinacrine-free medium, stimulation of exchange activity was observed. This stimulation was reversible on the removal of bound quinacrine and involved in a reduction in the apparent Km for extravesicular Ca2+. Stimulation of exchange activity under these conditions was also observed with the lipophilic cation tetraphenylphosphonium. Since Ca2+, quinacrine and tetraphenylphosphonium all bind strongly to sarcolemmal membranes, it is suggested that the observed stimulation of exchange activity involves a local electrostatic effect of the bound cations in accelerating a rate-limiting step in the reaction mechanism for Na-Ca exchange.

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