The lifetime of hydrogen adsorbed on a slightly oxidized nickel surface

1957 ◽  
Vol 240 (1222) ◽  
pp. 423-436 ◽  
Keyword(s):  
Oxide Film ◽  
Mass Spectrometer ◽  
Rate Constant ◽  
Molecular Beam ◽  
Copper Surface ◽  
Solid Surfaces ◽  
Nickel Surface ◽  
Order Process ◽  
Adsorbed Molecules ◽  
First Order

A method for investigating the lifetimes of adsorbed molecules on solid surfaces is described. A molecular beam of hydrogen was projected on to the surface of a spinning nickel disk, and the hydrogen evaporating from the surface at different times after deposition was collected and measured with a mass spectrometer. On a slightly oxidized nickel surface all the hydrogen was adsorbed. The subsequent evaporation was a first-order process with a rate constant of 4·5 x 10 11 exp ( -11·5 kcal/ RT ) S -1 . With a mixed molecular beam of hydrogen and deuterium no exchange was produced by the adsorption, which is considered to be molecular. Attempts to remove the oxide film from the nickel surface gave an un­stable surface on which no clear results were obtained. The lifetime of hydrogen on a copper surface was too short to measure.

Spectrochemical Behavior of Carcinogenic Polycyclic Aromatic Hydrocarbons in Biological Systems. Part II: A Theoretical Rate Model for BaP Metabolism in Living Cells

1996 ◽  
Vol 50 (11) ◽  
pp. 1352-1359 ◽  
Author(s):  
Ping Chiang ◽  
Kuang-Pang Li ◽  
Tong-Ming Hseu
Keyword(s):  
Rate Constant ◽  
Living Cells ◽  
Rate Model ◽  
Number Density ◽  
Order Process ◽  
Irreversible Reaction ◽  
First Order ◽  
Metabolism Rate ◽  
Polycyclic Aromatic ◽  
Kinetics Of

An idealized model for the kinetics of benzo[ a]pyrene (BaP) metabolism is established. As observed from experimental results, the BaP transfer from microcrystals to the cell membrane is definitely a first-order process. The rate constant of this process is signified as k1. We describe the surface–midplane exchange as reversible and use rate constants k2 and k3 to describe the inward and outward diffusions, respectively. The metabolism is identified as an irreversible reaction with a rate constant k4. If k2 and k3 are assumed to be fast and not rate determining, the effect of the metabolism rate, k4, on the number density of BaP in the midplane of the microsomal membrane, m3, can be estimated. If the metabolism rate is faster than or comparable to the distribution rates, k2 and k3, the BaP concentration in the membrane midplane, m3, will quickly be dissipated. But if k4 is extremely small, m3 will reach a plateau. Under conditions when k2 and k3 also play significant roles in determining the overall rate, more complicated patterns of m3 are expected.

scholarly journals The combination of carbon monoxide–haem with apoperoxidase

1969 ◽  
Vol 114 (4) ◽  
pp. 719-724 ◽  
Author(s):  
Charles Phelps ◽  
Eraldo Antonini
Keyword(s):  
Activation Energy ◽  
Carbon Monoxide ◽  
Rate Constant ◽  
Binding Sites ◽  
Order Process ◽  
First Order ◽  
Effects Of Ph ◽  
Kinetics Of

1. Static titrations reveal an exact stoicheiometry between various haem derivatives and apoperoxidase prepared from one isoenzyme of the horseradish enzyme. 2. Carbon monoxide–protohaem reacts rapidly with apoperoxidase and the kinetics can be accounted for by a mechanism already applied to the reaction of carbon monoxide–haem derivatives with apomyoglobin and apohaemoglobin. 3. According to this mechanism a complex is formed first whose combination and dissociation velocity constants are 5×108m−1sec.−1 and 103sec.−1 at pH9·1 and 20°. The complex is converted into carbon monoxide–haemoprotein in a first-order process with a rate constant of 235sec.−1 for peroxidase and 364sec.−1 for myoglobin at pH9·1 and 20°. 4. The effects of pH and temperature were examined. The activation energy for the process of complex-isomerization is about 13kcal./mole. 5. The similarity in the kinetics of the reactions of carbon monoxide–haem with apoperoxidase and with apomyoglobin suggests structural similarities at the haem-binding sites of the two proteins.

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. α-METHYLSTYRENE, β-METHYLSTYRENE, AND INDENE

1966 ◽  
Vol 44 (10) ◽  
pp. 1113-1118 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
Propagation Rate ◽  
Absolute Rate ◽  
Order Process ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Process Rate Constant ◽  
Propagation Rate Constant

Absolute rate constants for the copolymerization of α-methylstyrene and oxygen have been measured from 13 to 50 °C. The propagation and termination rate constants can be represented by[Formula: see text]Experiments with 2,6-di-t-butyl-4-methylphenol at 65 °C have shown that C6H5C(CH3):CH2 and C6H5C(CD3):CD2 have the same propagation rate constant but that chain termination involves a deuterium isotope effect (kt)H/(kt)D ≈ 1.5.Absolute rate constants for the copolymerization of oxygen with β-methylstyrene and with indene at 30 °C showed that a significant fraction of the oxidation chains were terminated by a kinetically first order process (rate constant kx). The rate constants for β-methylstyrene and indene at 30 °C are kp = 51 and 142 l mole−1 s−1, kt = 1.6 × 107 and 2.5 × 107 l mole−1 s−1, and kx = 0.61 and 1.2 s−1, respectively. The propagation rate constant for indene can be separated into a rate constant for the copolymerization with oxygen (kadd = 128 l mole−1 s−1) and a rate constant for hydrogen atom abstraction (kabstr = 14 l mole−1 s−1). In the presence of heavy water the first order process for indene had a deuterium isotope effect (kx)/(kx)D2O ≈ 3.

THE THERMAL DECOMPOSITION OF PHENYLACETIC ACID

1960 ◽  
Vol 38 (8) ◽  
pp. 1261-1270 ◽  
Author(s):  
Margaret H. Back ◽  
A. H. Sehon
Keyword(s):  
Carbon Dioxide ◽  
Activation Energy ◽  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Rate Constant ◽  
Phenylacetic Acid ◽  
Order Process ◽  
First Order ◽  
Kinetics Of ◽  
Dissociation Step

The thermal decomposition of phenylacetic acid was investigated by the toluene-carrier technique over the temperature range 587 to 722 °C. The products of the pyrolysis were carbon dioxide, carbon monoxide, hydrogen, methane, dibenzyl, and phenylketene. From the kinetics of the decomposition it was concluded that the reaction[Formula: see text]was a homogeneous, first-order process and that the rate constant of this dissociation step was represented by the expression k = 8 × 1012.e−55,000/RT sec−1. The activation energy of this reaction may be identified with D(C6H5CH2—COOH). The possible reactions of carboxyl radicals are discussed.

Development of Sustained Release Multi-Component Microparticulate System of Diclofenac Sodium and Tizanidine Hydrochloride

1970 ◽  
Vol 1 (1) ◽  
pp. 97-105
Author(s):  
Kamlesh Dashora ◽  
Shailendra Saraf ◽  
Swarnalata Saraf
Keyword(s):  
Particle Size ◽  
Sustained Release ◽  
Cellulose Acetate ◽  
Rate Constant ◽  
Diclofenac Sodium ◽  
Order Rate Constant ◽  
Anomalous Transport ◽  
First Order ◽  
Sem Study ◽  
Transport Type

Sustained released tablets of diclofenac sodium (DIC) and tizanidine hydrochloride (TIZ) were prepared by using different proportions of cellulose acetate (CA) as the retardant material. Nine formulations of tablets having different proportion of microparticles developed by varied proportions of polymer: drug ratio ‘’i.e.’’; 1:9 -1:3 for DIC and 1:1 – 3:1 for TIZ. Each tablet contained equivalent to 100 mg of DIC and 6mg of TIZ. The prepared microparticles were white, free flowing and spherical in shape (SEM study), with  the particle size varying from 78.8±1.94 to 103.33±1.28 µm and 175.92± 9.82 to 194.94±14.28µm for DIC  and TIZ, respectively.  The first order rate constant K1 of formulations were found to be in the range of  K1 = 0.117-0.272 and 0.083- 0.189 %hr-1for DIC and TIZ, respectively. The value of exponent coefficient (n) was found to be in the range of 0.6328-0.9412  and 0.8589-1.1954 for DIC and TIZ respectively indicates anomalous  to  non anomalous transport type of diffusions among different formulations

scholarly journals Determination of exothermic batch reactor specific model parameters

2019 ◽  
Vol 292 ◽  
pp. 01063
Author(s):  
Lubomír Macků
Keyword(s):  
Rate Constant ◽  
Reaction Rate ◽  
Batch Reactor ◽  
Specific Model ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
First Order Reaction ◽  
Model Parameters ◽  
Reactor Model ◽  
First Order

An alternative method of determining exothermic reactor model parameters which include first order reaction rate constant is described in this paper. The method is based on known in reactor temperature development and is suitable for processes with changing quality of input substances. This method allows us to evaluate the reaction substances composition change and is also capable of the reaction rate constant (parameters of the Arrhenius equation) determination. Method can be used in exothermic batch or semi- batch reactors running processes based on the first order reaction. An example of such process is given here and the problem is shown on its mathematical model with the help of simulations.

The reaction of μ-oxo-bis(phthalocyaninato)iron(III) with hydrogen sulphide in the presence of pyridine: Evidence for axial coordination of dichloromethane

2005 ◽  
Vol 09 (03) ◽  
pp. 198-205 ◽  
Author(s):  
Fabrizio Monacelli ◽  
Elisa Viola
Keyword(s):  
Reaction Mechanism ◽  
Linear Function ◽  
Rate Constant ◽  
Hydrogen Sulphide ◽  
Stoichiometric Ratio ◽  
First Order ◽  
Axial Coordination ◽  
Elementary Sulphur ◽  
Increasing Function ◽  
Limiting Value

The oxo-bridged complex ( py ) FePc - O - FePc ( py ) ( py = pyridine , Pc = phthalocyaninato dianion) reacts in dichloromethane with hydrogen sulphide giving elementary sulphur and the reduced ( py )2( FePc ) complex in the stoichiometric ratio 1:1. Under excess py and H2S , the reaction is first-order and the rate constant at a given py concentration is an increasing function of the reducing agent concentration, with asymptotic tendency to a limiting value. This latter depends on the pyridine concentration being higher the lower is the base concentration. When the reaction is carried out in pure pyridine, the rate constant is, instead, a strictly linear function of [ H2S ], with zero intercept. A reaction mechanism is proposed where the dichloromethane is directly involved in the axial coordination about the iron centers and H2S competes efficiently with both pyridine and solvent.

scholarly journals REGENERATION OF VISUAL PURPLE IN SOLUTION

1939 ◽  
Vol 23 (1) ◽  
pp. 21-39 ◽  
Author(s):  
Aurin M. Chase ◽  
Emil L. Smith
Keyword(s):  
Order Process ◽  
First Order ◽  
Color Changes ◽  
Violet Light ◽  
Frog Retina ◽  
Significant Difference ◽  
Kinetics Of ◽  
Photosensitive Substance ◽  
Subsequent Regeneration

1. Measurements of visual purple regeneration in solution have been made by a procedure which minimized distortion of the results by other color changes so that density changes caused by the regenerating substance alone are obtained. 2. Bleaching a visual purple solution with blue and violet light causes a greater subsequent regeneration than does an equivalent bleaching with light which lacks blue and violet. This is due to a photosensitive substance which has a gradually increasing effective absorption toward the shorter wavelengths. It is uncertain whether this substance is a product of visual purple bleaching or is present in the solution before illumination. 3. The regeneration of visual purple measured at 560 mµ is maximal at about pH 6.7 and decreases markedly at more acid and more alkaline pH's. 4. The absorption spectrum of the regenerating material shows only a concentration change during the course of regeneration, but has a higher absorption at the shorter wavelengths than has visual purple before illumination. 5. Visual purple extractions made at various temperatures show no significant difference in per cent of regeneration. 6. The kinetics of regeneration is usually that of a first order process. Successive regenerations in the same solution have the same velocity constant but form smaller total amounts of regenerated substance. 7. In vivo, the frog retina shows no additional oxygen consumption while visual purple is regenerating.

scholarly journals Horse liver alcohol dehydrogenase. A study of the essential lysine residue

1975 ◽  
Vol 149 (3) ◽  
pp. 627-635 ◽  
Author(s):  
S S Chen ◽  
P C Engel
Keyword(s):  
Alcohol Dehydrogenase ◽  
Rate Constant ◽  
Lysine Residue ◽  
Horse Liver Alcohol Dehydrogenase ◽  
First Order ◽  
Liver Alcohol Dehydrogenase ◽  
Horse Liver ◽  
Lysine Residues ◽  
Modified Enzyme ◽  
Covalent Complex

1. The inactivation of horse liver alcohol dehydrogenase by pyridoxal 5'-phosphate in phosphate buffer, pH8, at 10°C was investigated. Activity declines to a minimum value determined by the pyridoxal 5'-phosphate concentration. The maximum inactivation in a single treatment is 75%. This limit appears to be set by the ratio of the first-order rate constants for interconversion of inactive covalently modified enzyme and a readily dissociable non-covalent enzyme-modifier complex. 2. Reactivation was virtually complete on 150-fold dilution: first-order analysis yielded an estimate of the rate constant (0.164min-1), which was then used in the kinetic analysis of the forward inactivation reaction. This provided estimates for the rate constant for conversion of non-covalent complex into inactive enzyme (0.465 min-1) and the dissociation constant of the non-covalent complex (2.8 mM). From the two first-order constants, the minimum attainable activity in a single cycle of treatment may be calculated as 24.5%, very close to the observed value. 3. Successive cycles of modification followed by reduction with NaBH4 each decreased activity by the same fraction, so that three cycles with 3.6 mM-pyridoxal 5'-phosphate decreased specific activity to about 1% of the original value. The absorption spectrum of the enzyme thus treated indicated incorporation of 2-3 mol of pyridoxal 5'-phosphate per mol of subunit, covalently bonded to lysine residues. 4. NAD+ and NADH protected the enzyme completely against inactivation by pyridoxal 5'-phosphate, but ethanol and acetaldehyde were without effect. 5. Pyridoxal 5'-phosphate used as an inhibitor in steady-state experiments, rather than as an inactivator, was non-competitive with respect to both NADH and acetaldehyde. 6. The partially modified enzyme (74% inactive) showed unaltered apparent Km values for NAD+ and ethanol, indicating that modified enzyme is completely inactive, and that the residual activity is due to enzyme that has not been covalently modified. 7. Activation by methylation with formaldehyde was confirmed, but this treatment does not prevent subsequent inactivation with pyridoxal 5'-phosphate. Presumably different lysine residues are involved. 8. It is likely that the essential lysine residue modified by pyridoxal 5'-phosphate is involved either in binding the coenzymes or in the catalytic step. 9. Less detailed studies of yeast alcohol dehydrogenase suggest that this enzyme also possesses an essential lysine residue.

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