Showing papers on "Reaction rate constant published in 1982"

Relationship between temperature and growth rate of bacterial cultures.

Abstract: The Arrhenius Law, which was originally proposed to describe the temperature dependence of the specific reaction rate constant in chemical reactions, does not adequately describe the effect of temperature on bacterial growth. Microbiologists have attempted to apply a modified version of this law to bacterial growth by replacing the reaction rate constant by the growth rate constant, but the modified law relationship fits data poorly, as graphs of the logarithm of the growth rate constant against reciprocal absolute temperature result in curves rather than straight lines. Instead, a linear relationship between in square root of growth rate constant (r) and temperature (T), namely, square root = b (T - T0), where b is the regression coefficient and T0 is a hypothetical temperature which is an intrinsic property of the organism, is proposed and found to apply to the growth of a wide range of bacteria. The relationship is also applicable to nucleotide breakdown and to the growth of yeast and molds.

Determination of the rate constant of enzyme modification by measuring the substrate reaction in the presence of the modifier

Abstract: On the basis of the equations derived previously [Tsou, C. L. (1965) Sheng Wu Hua Hsueh Yu Sheng Wu Wu Li Hsueh Pao 5, 398-408, 409-417] for the substrate reaction during the course of enzyme modification, the kinetic behavior of the system chymotrypsin-substrate-modifier has been studied. The kinetics of benzoyltyrosine ester hydrolysis during the course of irreversible inhibition of the enzyme has been found to be in satisfactory agreement with equations obtained previously. The apparent rate constant between the enzyme and an irreversible inhibitor can be easily obtained in one single experiment by following the course of substrate hydrolysis in the presence of the inhibitor. The results are also in accord with the assumption that diisopropyl fluorophosphate can be classified as an irreversible competitive inhibitor. For both phenylmethanesulfonyl fluoride and L-1-[(p-toluene-sulfonyl)amino]-2-phenylethyl chloromethyl ketone, the inhibition has been found to be in agreement with the kinetics of the complexing type; i.e., a noncovalent enzyme-inhibitor complex is formed before irreversible enzyme modification. Both the equilibrium constants for the complex formation and the first-order rate constants for the irreversible modification step have been determined also by following the course of substrate hydrolysis in the presence of the irreversible inhibitor.

Carbon dioxide hydration and dehydration kinetics in seawater1

Abstract: Rate constants for the hydration and dehydration reactions of carbon dioxide with water and with hydroxyl ion were measured in seawater by a pH-stat method at salinities (X lO:l) from 3.4 to 37.06 at 25°C and from 5” to 35°C at a salinity of 33.77. Transition state theory was used to extrapolate the rate constants to infinite dilution, with the following results at 25°C: kcoz = 0.037 ? 0.002. s-l, /COII-&~ = (7.1 + 0.7) x lo-l1 mol.dm-‘. s-‘, k,, = (7.6 + 1.1) x lo4 dm”* mol-’ * s-’ , and kIIcoB- = (1.8 f 0.3) x 10m4* s-l. The corresponding values in scawatcl of 33.77 salinity and 25°C calculated from equations fit to the experimental data are 0.036, 13.5 x 10 I’, 3.5 x 10d, and 1.40 x 10-4.

Kinetics of diffusion‐controlled processes in dense polymer systems. I. Nonentangled regimes

Abstract: We investigate diffusion‐controlled processes, where the reacting groups (A and B) are attached to long, flexible, macromolecules in melts or in concentrated solutions. We first give a general discussion of the rate constants, and are led to distinguish two fundamental types of behavior, depending on the rms displacement x(t) of one reacting group during a time t. (1) If t−1 x3(t) is an increasing function of time, the space volumes [∼ x3(t)] explored by A and B may overlap significantly without any reaction taking place: we call this regime noncompact exploration. It is obtained in the classical case where A and B belong to small molecules and where simple diffusion prevails [x(t)∼t1/2]. This regime leads to a second‐order rate constant k in the chemical kinetics which is well‐defined (independent of the time). (2) If x3(t)/t is a decreasing function of time, we have compact exploration: as soon as the space volumes explored by A and B overlap, the reaction takes place. Then the rate constant k is propor...

Rate constant for scavenging eaq- in nitrous oxide-saturated solutions

Abstract: The rate constant for reaction of hydrated electrons with N/sub 2/O in aqueous solutions has been determined to be (9.1 +- 0.2) x 10/sup 9/ M/sup -1/ s/sup -1/ from pulse radiolysis observations on the growth and the decay of the absorption of e/sub aq//sup -/. Improvements in instrumental response have allowed observations to be carried out directly on solutions saturated with N/sub 2/O at atmospheric pressure where the reaction period is only 2.9 ns. An approach to numerical simulation of the observed time dependence is described which allows one to take into account in detail the track processes which occur on this time scale as well as the pulse profile and instrumental characteristics. Critical comparisons of the observed growth and decay with the results of these simulations establish well-defined limits for the reaction period. By using the simulated responses to provide reference information we show that it is possible to use the integrated absorbance to evaluate the reaction period with an accuracy of a few percent. The approaches used here allow rate information to be obtained for reaction periods as low as approx. 0.3 ns even though the pulse duration and recording response periods are 1 order of magnitudemore » greater.« less

Rate Constants for Reactions of Aliphatic Carbon‐Centered Radicals in Aqueous Solution

Abstract: Absolute rate constants for reactions of aliphatic carbon‐centered radicals in aqueous solutions have been compiled and evaluated from the literature. Rate constants are included for reactions of radicals with inorganic and organic compounds and for decay by radical–radical reactions. The radicals were generated by radiolysis, photolysis, or other techniques, and their rate constants were determined generally by kinetic spectrophotometry. The tables include data for over 2,500 reactions of 373 radicals from 740 literature references.

Dynamical polar solvent effects on solution reactions: A simple continuum model

Abstract: The influence of polar solvent dynamics in solution reactions is investigated for a simple model. In this model, a charge is subject to a chemical free energy barrier, the successful crossing of which constitutes reaction. The retarding influence of the time dependent solvent polarization is described at the continuum Debye relaxation level. The reaction rate constant k is determined as a function of the barrier curvature, the charge‐solvent interaction strength, and the solvent polarization relaxation time. The reduction of k with increasingly slower solvent relaxation is found to depend sensitively on the magnitude of charge‐solvent interactions. When the latter are weak, the behavior of k differs qualitatively from a standard Kramers prediction. The analogous reaction problem for a dipole is discussed briefly. Directions for a more realistic treatment of polar solvent effects on reaction rates are described.

Outer-sphere electron-transfer reactions of ascorbate anions

Abstract: Rate constants for the one-electron oxidation of ascorbate dianion (A2-) by bis(terpyridine)cobalt(III)ion (8.5 × 106 dm3 mol-1 s-1) and pentaammine(pyridine)ruthenium(III) ion (6.0 × 109 dm3 mol-1 s-1), and of the monoanion (HA-) by tetraammine (bipyridine)ruthenium(III)ion (2.1 × 105 dm3 mol-1s-1) have been determined in aqueous solution at 25oC and ionic strength 0.1 (NaNO3 or NaClO4). It is shown that these rate constants, and other published rate constants for oxidation of HA- and A2-, are consistent with the Marcus cross relation, on the assumption that the self-exchange rate constants for both the HA-/HA and A2-/A-couples are 106 dm3 mol-1 s-1. One electron redox potentials for the ascorbate/dehydroascorbate system have been derived from scattered literature data.

Interfacial electron-transfer reactions in colloidal semiconductor dispersions. Kinetic analysis

Abstract: A kinetic model is presented describing interfacial electron-transfer reactions in colloidal semiconductor dispersions induced by an ultrashort light pulse. The three elementary steps considered are (i) diffusion of charge carriers from the particle interior to the interphase, (ii) encounter-complex formation, and (iii) interfacial electron transfer. The first process is shown to occur so rapidly in colloidal particles that it does not contribute to the overall kinetics of the charge-transfer event. Steps ii and iii can be treated by solving the reaction-diffusion equation, thus obtaining an expression relating the observed bimolecular rate constant to the rate constant for heterogeneous electron transfer at the particle surface. The model is used to analyze the previously observed reduction of methylviologen (MV/sup 2 +/) by conduction-band electrons produced via laser excitation of TiO/sub 2/ colloids. The heterogeneous rate constant for electron transfer k/sub et/ follows a Tafel relation at pH greater than or equal to 5. Its value is k/sub et//sup 0/ = 4 x 10/sup -3/ cm/s at pH 5.4 where the conduction-band potential of the colloidal particle is equal to the standard potential of the MV/sup 2 +///sup +/ couple. The transfer coefficient obtained is 0.52. 3 figures.

Theory of highly exothermic electron transfer reactions

Abstract: The theory of highly exothermic homogeneous outer-sphere electron transfer reactions is discussed for transfers occurring over a range of distances. A finite rate of diffusion of reactants and their long-range force are treated by solving the diffusion equation numerically for the reactant pair distribution function. Steady-state solutions for the bimolecular rate constant are compared with experimental data as well as with our recent approximate analytic solution, which is found to agree in the present case. On the basis of short-time solutions, it is proposed that experiments which measure electron transfer rates at short times following the onset of reaction improve the possibility of observing the inverted effect in bimolecular systems. The chance of seeing it in linked systems (unimolecular reactions) is even greater. The relation between the prediction of an “inverted region” in the rate constant vs. ΔG° plot and the existence of a maximum in charge transfer spectral plots of intensity vs. absorption frequency is pointed out.

Reaction of nitrogen dioxide with alkenes and polyunsaturated fatty acids: addition and hydrogen-abstraction mechanisms

Abstract: The reactions of nitrogen dioxide in a carrier gas (nitrogen, oxygen, or air) with cyclohexene and a series of mono-, di-, and trienes is reported at NO/sub 2/ concentrations ranging from 70 ppM to 50%. A complete product analysis was made with cyclohexene, and these data allow the calculation of the fraction of the NO/sub 2/ that reacts by addition to the double bond or by abstraction of an allylic hydrogen. At high concentrations of NO/sub 2/, addition is the predominant process, in agreement with the literature. However, below 10,000 ppM (1%), hydrogen abstraction predominates. It is suggested this is because of competition between a reversible addition and an irreversible H-abstraction step, much as is the case for the well-known bromine atom reaction system. In fact, a kinetic analysis shows that the ratios of rate constants for addition and abstraction are similar for both NO/sub 2/ and the bromine atom. A less direct method (analysis of water formed) was used to estimate the addition to abstraction ratio for other alkenes and for esters of unsaturated fatty acids; these data are in agreement with the cyclohexene data. The autoxidation of unsaturated fatty acid esters initiated by NO/sub 2/ also was studied,more » and kinetic chain lengths and autoxidizability ratios are given.« less

Diffusion‐controlled vinyl polymerization. I. The gel effect

Abstract: It is well known that the reaction rate and molecular weight of vinyl polymers can change markedly during the course of polymerization and that these changes are due to the influence of diffusion on the termination reaction. The chain length dependence of the termination rate constant has been considered in this work and has resulted in a general method of treating the polymerization kinetics and molecular weight distribution. This method is independent of the form of the chain length dependency and is capable of dealing with both disproportionation and recombination modes of termination. A specific model for the termination rate constant with chain length dependence is proposed and is based on free volume theory and entanglement coupling. Master curves for the characteristics of the reaction rate and molecular weight distribution are presented with the application of this model.

Reaction Rate Studies for the Corrosion of Metals in Acids—I, Iron in Mineral Acids

Abstract: A detailed kinetic study of corrosion reactions of iron in HCl, H2SO4, and H3PO4 is made by a modified version of the gasometric technique. Reaction rates are measured at different tempera...

Mechanistic study of oscillations and bistability in the Briggs-Rauscher reaction

Abstract: A ten-step mechanism has been developed for the Briggs-Rauscher system which contains iodate, hydrogen peroxide, malonic acid, and manganese(I1) in acidic solution. The model is qualitatively identical with, though it differs quantitatively from, that proposed independently by Noyes and Furrow. It also bears strong similarities to the mechanistic suggestions of Cooke. Extensive numerical simulations of the reaction in a flow reactor show that the model predicts the observed topology of the "cross-shaped phase diagram" in which both bistability and oscillations appear as the input flows of the reactant species are varied. The observed hysteresis in the steady-state iodine concentration as a function of I2 flow and a variety of other dynamic behavior are also calculated in agreement with experiment. The remaining discrepancies between theory and experiment appear to result from an overestimation in the model of the stability of the nonradical steady state. A possible remedy for this problem is suggested. The Briggs-Rauscher (BR) reaction,' in which the acidic ox- idation of malonic acid by a mixture of hydrogen peroxide and iodate is catalyzed by manganous ion, is best known as the most visually impressive of the chemical oscillators. Under appropriate conditions and with the addition of a starch indicator, at room temperature a stirred batch solution goes through 15 or more cycles of colorless-gold-blue before expiring as a purplish solution with a strong odor of iodine. The BR reaction, however, exhibits a far richer collection of nonlinear dynamic phenomena than simple oscillation. In a flow reactor, complex oscillations* as well as multiple stable states3 accompanied by a variety of bifurcation and hysteresis phenomena have been obse~ed.~.~ The BR system was discovered some 8 years ago and is a hybrid of two other chemical oscillators, the Belousov-Zhabotinskii (BZ)5 and the Bray-Liebhafsky (BL) reactions,6 for which detailed mechanisms have been proposed and numerically evaluated.'~~ It is therefore surprising that until quite recently there had been no quantitative and very little qualitative discussion of the mechanism of the BR reaction. Cookeg has studied the BR and related systems experimentally and has made a number of mechanistic suggestions based on his results. No quantitative comparison between theory and exper- iment was carried out. More recently, Furrow and Noyes'O have conducted a systematic study of the reaction, investigating the kinetics of the reacting species taken two and three at a time. These authors have proposed a skeleton mechanism and have estimated rate constants for the elementary steps in that mech- anism. They have also reported a single numerical simulation1& with their model which shows that it can indeed give rise to oscillations. In this paper, we use a broad range of experimental data ob- tained mainly, but not exclusively, under flow conditions, to guide the construction of a mechanism for the BR reaction. Although we approach the problem from a rather different point of view, we have independently arrived at a mechanism similar to that of Cooke and nearly identical with that of Furrow and Noyes. We have carried out extensive calculations with our mechanism in an attempt to simulate not only the oscillatory behavior, but the multistability, hysteresis, and bifurcation phenomena as well. We find qualitative agreement with nearly all of the observed phe- nomena and quantitative agreement with some. Most of the discrepancies which remain between our calculations and the experimental results can be attributed to a single weakness of the model-its exaggeration of the stability of the nonradical steady state of the system. We suggest how the mechanism might be augmented to correct this failing. Modifications of the BR system in which malonic acid is re- placed by related organic specie^^^^*'^ are also known to oscillate. In particular, Furrow" has carried out a careful study of the BR reaction with methylmalonic acid and has found a significant lengthening of the oscillation period over that of the malonic acid system. By introducing Furrow's experimentally determined rate parameters for the methylmalonic acid-iodine reaction at the appropriate point in our model, we show that it indeed predicts the observed increase in the period of oscillation.

Analysis and optimization of methods using water-soluble carbodiimide for immobilization of biochemicals to porous glass.

Abstract: Two methods employing a water-soluble carbodiimide for carboxyl activation were investigated for the immobilization of biochemicals to succinamidopropyl-porous glass beads. Immobilization using the simultaneous method (simultaneous addition of carbodiimide and nucleophilic ligand to the beads) and large excess of carbodiimide and a small nucleophile should result in covalent binding to all accessible carboxyl groups. Results obtained with glycine methyl ester indicated that 40% of the total surface carboxyl groups were sterically accessible. Using these reaction conditions with the protein, chymotrypsinogen, suggests that a surface monolayer is immobilized. although far fewer sites are required assuming single point attachment. For ligands containing carboxyl groups and several nucleophilic groups (e. g., enzymes), however, biological inactivation may occur using the simultaneous method. Consequently, a sequential method (activation of the surface with carbodiimide followed by washing and addition of the biochemical to be immobilized) was optimized. Using optimal conditions (20 min activation time at pH 4.75 and room temperature; 2 min wash at pH 7 and 0 degrees C) and 0.1M carbodiimide, nearly half of the accessible surface sites remained in the O-acylisourea form and reacted with glycine methyl ester upon its addition. The amount of surface loading as a function of activation time was consistent with a model constructed using rate constants for O-acylisourea formation and hydrolysis previously derived from solution studies with acetic acid [Swaisgood and Natake, J. Biochem 74, 77 (1973)]. Measurement of reaction rates with glycine methyl ester following surface activation suggests that the rate of reaction with amino groups is at least eightfold greater than the hydrolysis rate. Either immobilization procedure gave comparable enzyme loading and specific activities for the case of sulfhydryl oxidase.

High‐pressure nmr study of dynamical effects on conformational isomerization of cyclohexane

Abstract: The effect of temperature and pressure on the conformational inversion of cyclohexane in solution has been investigated with use of /sup 1/H FT NMR spectroscopy. The solvents used in this study are methylcyclohexane-d/sub 14/, carbon disulfide, and acetone-d/sub 6/. The activation parameters as obtained from the temperature dependence of the rate constant are independent of solvent. However, the coalescence temperature in the methylcyclohexane-d/sub 14/ solvent is 1.5/sup 0/C higher than in the other two solvents. It is observed that the ring inversion in cyclohexane is accelerated when pressure is increased, and this pressure dependence of the rate constant is nonlinear. In the lower viscosity solvents, acetone-d/sub 6/ and carbon disulfide, the rate constant shows a larger pressure dependence than in the more viscous methylcyclohexane-d/sub 14/ solvent. The experimental data are interpreted with use of results of the stochastic models for isomerization reactions. In these models it is proposed that there are dynamical effects on isomerization because the reaction coordinate is coupled to the surrounding medium. We find that the observed activation volume is strongly pressure and solvent dependent as is the collisional contribution to the activation volume. Since the collision frequency reflecting the coupling of the reaction coordinate to themore » solvent mediums is proportional to solvent viscosity, the observed activation volume and the transmission coefficient kappa correlate well with the solvent viscosity. In addition, the experimental data indicate a non-monotonic transition between the inertial (weak coupling) and diffusive (strong coupling) regimes of isomerization reactions. Our results represent the first experimental proof of the predictions of stochastic models for isomerization reactions in condensed phases. 9 figures, 1 table.« less

Rate constants for the reaction of OH radicals with a series of alkanes and alkenes at 299 ± 2 K

Abstract: Using methyl nitrite photolysis in air as a source of hydroxyl radicals, relative rate constants for the reaction of OH radicals with a series of alkanes and alkenes have been determined at 299 ± 2 K. The rate constant ratios obtained are: relative to n-hexane = 1.00, neopentane 0.135 ± 0.007, n-butane 0.453 ± 0.007, cyclohexane 1.32 ± 0.04; relative to cyclohexane = 1.00, n-butane 0.341 ± 0.002, cyclopentane 0.704 ± 0.007, 2,3-dimethylbutane 0.827 ± 0.004, ethene 1.12 ± 0.05; relative to propene = 1.00, 2-methyl-2-butene 3.43 ± 0.13, isoprene 3.81 ± 0.17, 2,3-dimethyl-2-butene 4.28 ± 0.21. These relative rate constants are placed on an absolute basis using previous absolute rate constant data and are compared and discussed with literature data.

Shock-tube measurement of the rate constant for excited hydroxyl(A2.SIGMA.+) formation in the hydrogen-oxygen reaction

Abstract: H/sub 2/-O/sub 2/ mixtures highly diluted with Ar were heated to temperatures in the range 1200 to 3200/sup 0/K behind reflected shock waves. The intensity and temporal variation of emission from the OH* A/sup 2/..sigma../sup +/-X/sup 2/II transition were studied in order to determine the reaction and rate constant for OH* formation. The OH* was found to be formed mainly by the reaction H + O + M = OH* + M under the experimental conditions below 2000/sup 0/K; thermal emission made significant contributions at higher temperatures. The rate constant was found to be k/sub 1/ = 1.2 x 10/sup 13/exp(-6940 cal/RT) cm/sup 6/mol/sup -2/s/sup -1/. This expression accounts for the OH* intensity and its temporal variation, including the ignition delay times t/sub m/ and t/sub m/ and t/sub 5/, for the experimental conditions used.

Arrhenius parameters of elementary reactions involved in the oxidation of neopentane

Abstract: The reactions of neopentyl radicals in an oxidising environment have been studied by adding neopentane to slowly reacting mixtures of H2+ O2 over the temperature range 380–520 °C. Over a wide range of mixture composition, the only detectable initial products at these temperatures are 3,3-dimethyloxetan (DMO), acetone, i-butene, methane, and formaldehyde. A relatively simple mechanism involving the formation of neopentylhydroperoxide (QOOH) radicals gives a quantitative interpretation of the product yields. Although the major source of i-butene is the C—C homolysis of neopentyl radicals, a significant proportion is formed in reaction (6)(CH3)2C(CH2OOH)CH2→(CH3)2CCH2+ HCHO + OH. (6)From measurements of the product ratios ([acetone]+[DMO])/[i-butene] and [acetone]/[DMO] at each temperature used, Arrhenius parameters have been determined for a number of the elementary steps. The recommended value of k3= 1.20 × 1013 exp (– 120 kJ mol–1/RT) S–1 for the 1,5p H-atom transfer in neopentylperoxy radicals is compared with previously determined parameters for the 1,4p H-atom transfer in ethylperoxy radicals. With the Arrhenius expressions for these two transfers as a basis, thermochemical calculations are used to obtain a self-consistent set of Arrhenius parameters from values of rate constants at 480 °C for primary, secondary and tertiary H-atom transfers in alkylperoxy radicals involving ring sizes in the transition state varying from 4 to 8 (CH3)3CCH2O2→(CH3)2C(CH2OOH)CH2. (3)

Kinetics of interaction of metal ions with two tetraazatetraacetate macrocycles

Abstract: The kinetics of formation of metal complexes of the macrocyclic ligands 1,4,7,10-tetraazacyclododecane-N,N’,N’’,N’’’tetraacetate (DOTA) and 1,4,8,11 -tetraazacyclotetradecane-N,N’,N”,N”’-tetraacetate (TETA) have been measured by stopped-flow spectrophotometry. Observations were made at 25 “ C and I = 0.25 M over a wide range of pH, and the reactive species was characterized as the monoprotonated form of the ligand. Metal ions examined were Mg2+, Ca2+, Sr2+, Ba2+, Zn2+, Ni2+, and Cu2+. With a number of systems, plots of the pseudo-first-order rate constant koM vs. [M2+] in excess were hyperbolic conforming to the expression ka = (A[M2+])(l + K[M2+])-I. K is considered a constant for formation of a preassociation complex. This may then proceed to a final complex (first-order rate constant AK-I) or be a “dead-end” complex, with reactants reacting by a second-order process, rate constant A. With the remaining systems, kobsd vs. [M2’] was linear as required for a second-order reaction.

The excitation of O(1S) in the reaction between N2(A 3Σ+u) and O(3P)

Abstract: The rate constant for the excitation of O(1S) in the reaction between N2(A,v′ = 0) and O(3P) has been measured in a discharge‐flow reactor at room temperature to be (2.1±0.4)×10−11 cm3 molecule−1 s−1. Combining this measurement with the previously determined rate constant for total quenching of N2(A) by O shows that the fraction of all quenching events which lead to O(1S) excitation is 0.75±0.13. These results are at variance with rate constants estimated from some auroral models and indicate that some revision of auroral models is in order.