Showing papers on "Reaction rate constant published in 1983"
TL;DR: In this article, the rate constants of reactions of ozone with non-ionized solutes, such as aliphatic alcohols, olefins, chlorosubstituted ethylenes, substituted benzenes and carbohydrates, have been determined from the absolute rates with which ozone reacts in the presence of various concentrations of these compounds in water.
1,783 citations
TL;DR: The perhydroxyl radical (HO2) reaction with linoleic, linolenic, and arachidonic acids has been studied in aqueous ethanolic solutions by the stopped flow technique.
494 citations
TL;DR: In this article, the rate of colloidal gold formation in water-in-oil microemulsions was investigated by radiolytically reducing the HAuCl/sub 4/ pulse in water and in water in oil.
Abstract: Reduction of HAuCl/sub 4/ has been investigated pulse radiolytically in water and in water-in-oil microemulsions. Rate constants have been determined for Au/sup 3 +/ + e/sub aq//sup -/ ..-->.. Au/sup 2 +/, 2Au/sup 2 +/ ..-->.. Au/sup 3 +/ + Au/sup +/, and Au/sup +/ + R/sup -/. ..-->.. Au/sup 0/ + R (where R/sup -/. is an unidentified radical). On the longer time scale formation of colloidal gold, nAu/sup 0/ ..-->.. (Au/sup 0/)n, has been observed. Rate of colloidal gold formation has also been studied in the bombardment of HAuCl/sub 4/ solutions by 353-nm 60-mJ 3-5-ns laser pulses. Hydrodynamic diameters and polydispersities of empty and colloidal-gold-containing microemulsions have been determined by electron micrography. There are a number of advantages of forming colloidal particles in microemulsions. Under identical conditions a greater amount of colloidal particles is formed than that in water. Colloidal gold particles formed in microemulsions are smaller and more uniform than those obtained in homogeneous solutions.
337 citations
TL;DR: In this paper, the average survival time was shown to have a non-Kramers dependence on diffusivity, of the type found in the binding kinetics in heme proteins.
Abstract: Intramolecular reactions inside macromolecules (e.g., binding of ligands to iron inside heme proteins) may often be coupled to slow random fluctuations in the reaction center geometry. This motion is ‘‘perpendicular’’ to the reaction coordinate. It can be described as bounded diffusion in the presence of a binding potential field and an intramolecular rate constant which depends on the perpendicular degree of freedom. The diffusion equation is solved under the appropriate reflective boundary conditions. The transient decay of the total population is multiexponential (power law) for small diffusivity, changing to monoexponential kinetics for large diffusivity. For large times or large diffusivity, direct integration is very tedious, but an eigenvalue expansion converges rapidly. It also allows the calculation of the ‘‘average survival time’’ (an extension of the ‘‘first passage time’’) a natural candidate for replacing the reciprocal rate constant in multiexponential kinetics. An example is given for electron transfer between two loosely bound sites in a macromolecule. The average survival time shows a non‐Kramers dependence on diffusivity, of the type found in the binding kinetics in heme proteins.
322 citations
TL;DR: The rate of oxidation of ferrous iron in a seasonally anoxic lake was measured on 39 occasions with respect to both depth and time as discussed by the authors, and the data were consistent with the simple rate law for homogeneous chemical kinetics previously established for synthetic solutions.
317 citations
TL;DR: In this article, the reaction rates in the absence of accumulated product are described by a simple Langmuir form, rate = k · K[chloromethane]1 + K [chloromethrane]2 + K[ chloromethanes]
257 citations
TL;DR: In this paper, a theoretical framework for the description of nonequilibrium solvation and solvent participation in the reaction coordinate for solution reactions is presented, illustrated by a model of reactive dipole isomerization.
Abstract: We construct a theoretical framework for the description of nonequilibrium solvation and solvent participation in the reaction coordinate for solution reactions. The framework is illustrated by a model of reactive dipole isomerization. We show that a multidimensional reaction coordinate picture is equivalent to a one dimensional description in which a generalized friction characterizes and quantifies nonequilibrium solvation effects on the reaction rate. The adiabatic regime where equilibrium solvation and mean potential ideas are correct is identified. Several distinct regimes of nonequilibrium solvation are identified and described in molecular terms. In the effective mass regime, equilibrium solvation ideas give the reaction barrier curvature correctly, but solvent inertia modifies the barrier passage rate. In the nonadiabatic regime, the solvent is ‘‘frozen’’ during the barrier passage and cannot provide equilibrium solvation. In the polarization caging regime, the reacting species adjust to the moving solvent, rather than vice versa, and the solvent is heavily involved in the reaction coordinate. The rate constant in each of these regimes is related to reactive and solvent dynamics.
230 citations
TL;DR: The experimental rate constant of dissolution of oligoclase, 1.7 × 10 − 2 mol · m−2 · s−1 (Busenberg and Clemency, 1976), is compared with rate constants derived from mass-balance measurements of sodium in hydrological catchments.
227 citations
TL;DR: The patch-clamp technique of Mueller was modified to be suitable for single-channel measurements in lipid bilayers at potentials up to 500 mV, and it was found that the sublinear current-voltage behavior normally observed at low permeant ion concentrations and rather low potentials continues to be seen all the way up to500 mV.
213 citations
TL;DR: Fits of kinetic curves calculated from theoretical models to experimental kinetic curves showed that filament fragmentation was important to achieve a good fit, confirming the finding of Wegner and Savko.
Abstract: We measured the time course of skeletal muscle actin polymerization at different actin concentrations. In 0.1 M KCl with 1 mM Mg2+, log/log plots of the rate of the early, slow phase of polymerization vs. actin concentration were linear with slopes from 1.0 to 1.3. Computer-assisted calculations of similar curves from theoretical models with different sizes for the nucleus showed that no simple model gave a log/log plot with a slope less than 1.5. Addition of a first-order, monomer activation step before nucleation allowed models of any reasonable nucleus size to have a slope of 1. This is the first evidence that such a step is part of the kinetic pathway for actin polymerization. In 0.1 M KCl with 0.2 mM Ca2+, log/log plots of the rate of the slow phase vs. actin concentration were linear with slopes from 2.0 to 2.5. Monomer activation was not necessary to account for this slope. However, fits of kinetic curves calculated from theoretical models to experimental kinetic curves showed that filament fragmentation was important to achieve a good fit, confirming the finding of Wegner and Savko [Wegner, A., & Savko, P. (1982) Biochemistry 21, 1909-1913]. Our fit procedure also allowed us to estimate the size of the nucleus and the rate constants for activation, nucleation, and fragmentation. In 0.1 M KCl with 1 mM Mg2+, the nucleus was a dimer or trimer, and nucleation was fast. In 0.1 M KCl with 2.0 mM Ca2+, the nucleus was a trimer, and nucleation was slow.
207 citations
TL;DR: In this paper, the dark reaction of NOx and H2O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers.
Abstract: The dark reaction of NOx and H2O vapor in 1 atm of air was studied for the purpose of elucidating the recently discussed unknown radical source in smog chambers. Nitrous acid and nitric oxide were found to be formed by the reaction of NO2 and H2O in an evacuable and bakable smog chamber. No nitric acid was observed in the gas phase. The reaction is not stoichiometric and is thought to be a heterogeneous wall reaction. The reaction rate is first order with respect to NO2 and H2O, and the concentrations of HONO and NO initially increase linearly with time. The same reaction proceeds with a different rate constant in a quartz cell, and the reaction of NO2 and H218O gave H18ONO exclusively. Taking into consideration the heterogeneous reaction of NO2 and H2O, the upper limit of the rate constant of the third-order reaction NO + NO2 + H2O → 2HONO was deduced to be (3.0 ± 1.4) × 10−10 ppm−2-min−1, which is one order of magnitude smaller than the previously reported value. Nitrous acid formed by the heterogeneous dark reaction of NO2 and H2O should contribute significantly to both an initially present HONO and a continuous supply of OH radicals by photolysis in smog chamber experiments.
TL;DR: In this article, a comparative study of the electrode kinetics of oxygen reduction of platinum in perchloric, phosphoric, sulfuric, trifluoromethanesulfonic acids (all at pH = 0) and in potassium hydroxide (pH = 14) was made at 25°C using rotatating ringdisc electrode techniques.
TL;DR: In this paper, a theoretical study of the 2 e, 2H+ reaction is presented for a surface reaction (adsorbed species, Langmuir isotherm or monolayer-modified electrode), or for a heterogeneous electrochemical reaction with protonations taking place in solution near the electrode.
TL;DR: In this paper, the rates of coagulation of completely renneted casein micelles have been measured as functions of ionic strength, temperature, and concentration of Ca2+.
Abstract: The rates of coagulation of completely renneted casein micelles have been measured as functions of ionic strength, temperature, and concentration of Ca2+. At 25 °C and below, the rate constants for the coagulation were found to be low, but increased with temperature so that at 60 °C the particles were coagulating at almost maximum rate permitted by diffusion. This maximal rate at 60 °C was achieved at nearly all of the ionic strengths and concentrations of Ca2+ used. At lower temperatures the rate constant decreased with increasing ionic strength, the dependence being more marked at lower temperatures. Increasing concentration of Ca2+ also increased the rate at low and moderate temperatures. The implications of these results are discussed in terms of specific and non-specific ionic interactions and of hydrophobic bond formation.
TL;DR: In this article, Damjanovic et al. modified the rotating ringdisc electrode method to calculate most of the rate constants for the intermediate formation of H2O2 in the electroreduction of O2 to H 2O.
TL;DR: In this paper, the complex photophysical behavior of 2-(2′-hydroxyphenyl)benzoxazole (HBO) has been investigated using both steady-state absorption and fluorescence and time-resolved (picosecond) emission spectroscopy, and found to be consistent with the existence of various tautomeric and rotameric species in equilibrium.
TL;DR: In this article, the surface growth rate of a premixed flat flame is shown to be first order in the acetylene concentration, and the apparent first order rate is constant with respect to the C/H ratio.
Abstract: The total mass of soot in a premixed flat flame increases steeply with time through a process known as surface growth. In this paper we show that the surface growth rate is first order in the acetylene concentration, and we measure the apparent first order rate constant. We also show that the surface growth rate is not strongly temperature dependent, It is suggested that the C/H ratio of the soot may be important in determining its reactivity.
TL;DR: In this paper, the second-order rate constants and acid dissociation constants of primary amines were found to be overall second order, first order in CO2 and amine at temperatures between 5 and 30 °C.
Abstract: The kinetics of the reactions between carbon dioxide and a series of primary amines, both in aqueous solution, have been studied at temperatures between 5 and 30 °C. In all cases the reactions were found to be overall second order, first order in CO2 and amine. A Bronsted relationship was found to exist between the second-order rate constants and the acid dissociation constants of the amines. At 20 °C. log10k= 0.34 pKa+ 0.45. The mechanism of reactions between carbon dioxide and amines is discussed.
TL;DR: The p-nitrophenyl ester of (E)-ruthenoceneacrylic acid reacts in a complex to acylate..beta..-cyclodextrin, but with a poorer binding and rate constant than for the corresponding ferrocene derivative as discussed by the authors.
Abstract: The p-nitrophenyl ester of (E)-ruthenoceneacrylic acid reacts in a complex to acylate ..beta..-cyclodextrin, but with a poorer binding and rate constant than for the corresponding ferrocene derivative. The p-nitrophenyl ester of (E)-3-(carboxymethylene(-1,2-ferrocenocyclopentene is a mixture of two enantiomers. One enantiomer acylates ..beta..-cyclodextrin 5 900 000 times as fast in aqueous Me/sub 2/SO as it hydrolyzes under the same conditions (1.5 X 10/sup 8/ times as fast as hydrolysis in pure water at the same pH); the other enantiomer is 62-fold slower. These are the largest accelerations and enantiomeric selectives known for such reactions. Ferrocen-1,3-diacrylate esters react with ..beta..-cyclodextrin in processes in which the first and second acylation reveal important geometric effects. ..beta..-Cyclodextrin 6-tosylate is used to block unproductive binding and clarify the structural effects.
TL;DR: In this paper, a model of complex formation followed by vibrational predissociation with a rate constant of 109 −1010 s−1 was proposed to explain the dependence of the quenching rate constants on collision energy.
Abstract: Vibrational quenching rate constants have been measured for NO+(v) ions in collision with 17 neutral molecules. The dependence of the quenching rate constants on collision energy have been determined from near thermal energy up to ∼ 1 eV in some of these cases. The experimental results can be satisfactorily interpreted using a model of complex formation followed by vibrational predissociation with a rate constant of the order of 109–1010 s−1.
TL;DR: The results obtained allowed us to assess the importance of knowing the carrier and removal status of Na6(CO3, Na3SO4, Na2SO3, and Na2CO4 in the determination of the concentration of these materials in the sediments.
Abstract: 38, 811. (37) Matthess, G.; Pekdeger, A. GWF, GasWasserfach: WasserlAbwasser 1980, 121, 214. (38) Davis, J. In “Contaminants and Sediments”: Baker, R. A,, Ed.; Ann Arbor Science: Ann Arbor, MI 1980; p 279. (39) Hansch, C.; Leo, A. In “Substituent Constants for Correlation Analysis in Chemistry and Biology”; Elsevier: Amsterdam, 1979. (40) Tute, M. S. Adv. Drug. Res. 1971, 6 , 1. (41) Mackay, D.; Bobra, A,; Shin, W. Y.; Yalkowsky, S. H.
TL;DR: The data indicates that softening kinetics of vegetables is more complex than has been formerly assumed.
Abstract: The rate of softening in several canned vegetables during the retort process was studied. The rate of softening is consistent with two simultaneous first order kinetic mechanisms; mechanism 1 acting on substrate “a” and mechanism 2 acting on substrate “b”. The rate constants for mechanism 1 are 20 times or more greater than the rate constantsfor mechanism 2. Approximately 85% to 97% of the firmness of the raw commodity is contributed by substrate “a” and the remaining firmness is contributed by substrate “b”. Mechanism 1 is probably due to pectic changes in the interlamellar layer. The biochemical nature of substrate 2 is a matter of speculation. The apparent Arrhenius activation energies range from 5.1 to 35.0 Kcal/mole. The data indicates that softening kinetics of vegetables is more complex than has been formerly assumed.
TL;DR: The authors extended the general polyatomic canonical variational theory formalism of Isaacson and one of the authors to improved canonical and microcanonical variational theories and calculated the rate constants for the reaction in the title over the temperature range 200-2500 K using all three variational models and the Melius-Blint ab initio potential energy surface.
Abstract: We have extended the general polyatomic canonical variational theory formalism of Isaacson and one of the authors to improved canonical and microcanonical variational theory. We have calculated the rate constants for the reaction in the title over the temperature range 200–2500 K using all three variational theories and the Melius–Blint ab initio potential energy surface. The results are compared to canonical variational calculations based on the reaction‐path interpolation scheme of Quack and Troe, to the trajectory calculations of Miller, and to experiment. We find that the microcanonical variational transition states have a strong energy dependence and the generalized free energy of activation curves have two maxima. Quantization effects appear to be important at the lower temperatures, and recrossing effects may be important at higher temperatures.
TL;DR: The mechanism of the process is discussed in terms of initial formation of a complex between ATP and protonated 1, followed by an intracomplex reaction which may involve a combination of nucleophilic or acid catalysis with electrostatic catalysis.
Abstract: Molecular catalysis of ATP-hydrolysis by a number of protonated macrocyclic polyamines 1–9 has been investigated by 31P-NMR spectroscopy, and marked rate enhancements have been obtained. The largest acceleration is produced by the [24]-N6O2 macrocycle 1, and the process displays the following properties: 1. protonated 1 forms very stable complexes with ATP, as well as with ADP and AMP; 2. it enhances the rate of ATP-hydrolysis by a factor of 103 at pH = 8.5; the rate of hydrolysis is constant over a wide pH-range, from pH = 2.5 to 8.5; 3. 1 is more efficient than acyclic analogues; 4. the products of the reaction are orthophosphate (OP) and ADP, which is subsequently hydrolyzed to OP and AMP at a slower rate; 5. at pH > 6.5, a transient species is detected, which is tentatively identified as a phosphoramidate intermediate, resulting from phosphorylation of the macrocycle 1; 6. the reaction presents first-order kinetics and is catalytic. The mechanism of the process is discussed in terms of initial formation of a complex between ATP and protonated 1, followed by an intracomplex reaction which may involve a combination of nucleophilic or acid catalysis with electrostatic catalysis.
TL;DR: The kinetics of the reaction between human thrombin and antithrombin III were studied in the presence of heparin fractionated according to its molecular size and affinity for antithROMbin III to imply that interactions of both proteins with heparIn are involved in the expression of catalytic activity through a template mechanism.
TL;DR: The second-order reaction rate constant was found to be pressure dependent, varying by a factor of 96 in this range as discussed by the authors, and the rate constant decreases with increasing temperature and cannot be adequately described by a linear fit.
Abstract: The reaction CH + N/sub 2/ (hydrocarbon radical + nitrogen) --> products was studied at 297 K at total pressures between 25 and 787 torr The second-order reaction rate constant was found to be pressure dependent, varying by a factor of 96 in this range This reaction was also studied in the range 297 to 675 K at 100-torr total pressure The rate constant decreases with increasing temperature and cannot be adequately described by a linear fit in this range Transition-state (RRKM) theory calculations for the reaction proceeding through a long-lived intermediate, HCN/sub 2/ (diazomethane), sucessfully describe the data Stabiliztion of the adduct is the primary reaction channel at lower temperatures while metathesis dominates above 1000 K These calculations provide a consistent description of these and previous data from flame studies 10 figures, 4 tables
TL;DR: It is concluded that free energy relationships provide a sound basis for systematic analysis of reaction mechanisms of electron transfer proteins.
Abstract: Rate constants for the reduction of approximately 40 electron transfer proteins by photoreduced flavins have been determined by laser flash photolysis techniques. The data for a series of 12 homologous cytochromes and 10 homologous high redox potential ferredoxins (HiPIPs) are in excellent agreement with semi-empirical equations relating rate constant and thermodynamic redox potential that have proven applicable to nonbiological electron transfer systems. These correlations allow the establishment of relative reactivities within structurally homologous classes of biological oxidation-reduction proteins, including cytochromes and HiPIPs, and a variety of nonhomologous heme-, iron-sulfur-, copper-, and flavin-containing proteins. A qualitative correspondence is shown to exist between such relative reactivity and the extent of solvent exposure of the redox centers in a particular structural class. The implications of these results are considered, and it is concluded that free energy relationships provide a sound basis for systematic analysis of reaction mechanisms of electron transfer proteins.
TL;DR: In this article, a laboratory study of the kinetics of the S(IV)-O3 reaction in aqueous solution, including measurements of the effects of UV radiation, dissolved transition metals, and an antioxidant (hydroquinone) on the rate.
Abstract: Results are presented from a laboratory study of the kinetics of the S(IV)-O3 reaction in aqueous solution, including measurements of the effects of UV radiation, dissolved transition metals, and an antioxidant (hydroquinone) on the rate. On the basis of the results, relative rates of S(IV) conversion by O3 in tropospheric cloud water are compared with those predicted for H2O2 and for O2. The reaction mechanism is discussed, with an outline given of the elements of a possible reaction scheme. Application of the rate constants obtained to SO2 conversion in cloud water predicts conversion rates by ozone to be competitive with those by H2O2 at pH above about 4.5 and to dominate at pH above about 5.5. It is pointed out that since these pH's are typical for nonurban tropospheric cloud water, ozone is a potentially important contributor to the overall oxidative conversion of SO2 to sulfate in the nonurban troposphere.