Showing papers on "Reaction rate constant published in 1984"
TL;DR: In this paper, a homologous series of eight compounds of the general structure A-Sp-B where B is 4-biphenylyl, Sp is a rigid saturated hydrocarbon spacer, the steroidal 5-cap alpha-androstane skeleton, and A is one of a series of 8 different molecular groups with π.. electron networks was synthesized.
Abstract: A homologous series of eight compounds of the general structure A-Sp-B where B is 4-biphenylyl, Sp is a rigid saturated hydrocarbon spacer, the steroidal 5..cap alpha..-androstane skeleton, and A is one of a series of 8 different molecular groups with ..pi.. electron networks was synthesized. A liquid solution of these molecules in either 2-methyltetrahydrofuran or isooctane at room temperature was subjected to a 30-ps pulse of solvated electrons. Data are presented that demonstrate in these systems the dependence of the electron transfer rates on the exothermicity of the reaction and on solvent polarity. It is also noted that the electron transfer reactions are free ion reactions.
691 citations
TL;DR: In this article, it was shown that the cross-sectional area of etch pits on hydrolyzed feldspar grains is of the order of 10−9 to 10−8 cm2 and that the ratio of the effective to total surface area (which may or may not change with reaction progress) ranges from <0.01 to 1, depending on the grain size, dislocation density, and the extent of comminution damage on the surfaces of the grains.
596 citations
TL;DR: In this article, Giridih coal and crushed coconut shell were investigated in batch experiments after eliminating other sorbents in the initial screening tests, and they were found to adsorb cadmium from solution.
Abstract: The efficiency of Giridih coal and crushed coconut shell in removing cadmium from solution was investigated in batch experiments after eliminating other sorbents in the initial screening tests. Both sorbents were found to adsorb cadmium from solution. The batch sorption kinetics and equilibria may be described by a first order reversible reaction and Freundlich isotherm respectively. The first order rate constant for forward and reverse reactions have been calculated for both sorbents. In order to establish the rate limiting step the pore and film diffusion coefficients were evaluated from the half time equations. Film diffusion appears to be rate limiting. The cadmium adsorption for both the sorbents was found to be a function of pH of the reaction mixture, which increased with pH increase up to pH 10. A decreasing trend in sorption was observed beyond pH 10. The mechanism of sorption in terms of electrostatic forces and chemical interactions has been indicated with the aid of zero point of charge (pHzpc).
407 citations
TL;DR: In this article, the partitioning of radioactive trace elements between seawater and particulate matter from surface sediments and sediment traps was investigated in laboratory experiments, and the time dependence of Kd was described by an adsorption-desorption equilibrium (group I elements), followed by a lattice transport reaction step (group II elements).
370 citations
Journal Article•
TL;DR: Etude par radiolyse pulsee du mecanisme de decomposition en chaine, dans l'eau, de O 3 par OH ou O 2 −. Mise en jeu d'especes transitoires O 3 − et HO 3 (λ max =430±10 nm, and 350±20 nm) Constantes de vitesse des etapes elementaires.
Abstract: Etude par radiolyse pulsee du mecanisme de decomposition en chaine, dans l'eau, de O 3 par OH ou O 2 − . Mise en jeu d'especes transitoires O 3 − et HO 3 (λ max =430±10 nm, et 350±20 nm). Constantes de vitesse des etapes elementaires
312 citations
TL;DR: In this article, the authors implemented unimolecular rate theory for various types of reactions for any looseness of transition state, and the rate constant k(EJ) was weighted with the initial E and J distributions.
239 citations
TL;DR: In this article, the kinetics of the p-benzoquinone/hydroquinone Q/QH2 couple on a platinum electrode were analysed on the basis of the theory presented earlier (E Laviron, J Electroanal Chem, 146 (1983) 15) for the nine-member square scheme when the protonations are assumed to be at equilibrium.
239 citations
TL;DR: In this paper, a new technique for the determination of the kinetics of fast first order, or pseudo-first order, homogeneous chemical reactions coupled to heterogeneous election transfer reactions at electrodes is presented.
221 citations
TL;DR: In this paper, the authors investigated the kinetics of calcite dissolution in aqueous KCl-solutions far from equilibrium, between 1 and 62°C in the pH-range 2.7 to 8.4 have been investigated using a rotating disc apparatus.
215 citations
TL;DR: In this article, rate constants were determined for the gas phase reactions of NO/sub 3/ radicals with a series of organics at 298 +/- 1 K using two experimental techniques, one by monitoring the enhanced decay rates of N/sub 2/O/sub 5/ in the presence of a reactive organic and the other employing a relative rate technique.
Abstract: In this work presented rate constants were determined for the gas-phase reactions of NO/sub 3/ radicals with a series of organics at 298 +/- 1 K using two experimental techniques, one by monitoring the enhanced decay rates of N/sub 2/O/sub 5/ in the presence of a reactive organic and the other employing a relative rate technique. Rate constants for the alkenes (apart from ethene) and acetaldehyde are in good agreement with the only previous set of literature values, while aromatic cm/sup -3/ hydrocarbons were observed for the first time to react with the NO/sub 3/ radical. Thus, the rate constant for m-xylene is comparable to that for ethene, and naphthalene reacts with the NO/sub 3/ radical a factor of 1.5 faster than does propene. Acetaldehyde is significantly more reactive than is formaldehyde toward NO/sub 3/ radicals, analogous to their reactions with O(/sup 3/P) atoms and OH radicals. The atmospheric implications of these data, with regard to the loss of NO/sub 3/ and organics and the formation of nitric acid and hence acid deposition, are briefly discussed. 7 figures, 2 tables.
177 citations
TL;DR: The rate constant of ADP dissociation is sufficiently slow to be the molecular step which limits the unloaded shortening velocity in cardiac muscle and is likely to beThe rate-limiting step of cross-bridge dissociation in muscle.
TL;DR: In this article, some simple theories are described for calculating rate constants for neutral chemical reactions in the gas phase which are dominated by long-range forces and have no barriers in the potential energy surface.
Abstract: Some simple theories are described for calculating rate constants for neutral chemical reactions in the gas phase which are dominated by long-range forces and have no barriers in the potential energy surface. The methods involve combining an adiabatic capture approach with the quantum mechanical sudden approximation of non-reactive energy transfer. A version of the technique is shown to work well in calculations on the O + OH reaction. The methods are applied to the diatom-diatom reactions SO + OH, NO + BrO, NO + ClO, CN + O2 and CH + O2. The results provide new information on the origin of the negative temperature dependence of the rate constants for reactions such as these.
TL;DR: In this paper, the one-electron reduction of pentaaminecobalt (III) attached to gold and mercury electrodes via thioalkylcarboxylate ligands containing varying numbers, n, of alkyl carbons was investigated.
Abstract: : Unimolecular electron-transfer rate constants, k sub et, are reported for the one-electron reduction of pentaaminecobalt (III) attached to gold and mercury electrodes via thioalkylcarboxylate ligands containing varying numbers, n, of alkyl carbons. While similar values of k sub et were found at mercury for each reaction, for close-packed monolayers at gold the k sub et values decreased by circa 10 to the 4th power as an increased from one to five. This effect is identified with increasingly nonadiabatic pathways as an increases, a linear plot of log k sub et versus n being obtained. The results provide estimates of the electronic transmission coefficient as a function of the surface-Co(III) separation distance.
TL;DR: The results imply a role for distal DNA in assembly-disassembly of specific CAP-DNA complexes, and are consistent with a model in which the subunits in the CAP dimer separate in the assembly- disassembly process.
TL;DR: In this paper, the absoluten Geschwindigkeiten der Reaktion (RG) verschiedener Aminosauren und Modellverbindungen (I)-(XIX) with Ozon in wasrigen Pufferlosungen werden gemessen.
Abstract: Die absoluten Geschwindigkeiten der Reaktion (RG) verschiedener Aminosauren und Modellverbindungen (I)-(XIX) mit Ozon in wasrigen Pufferlosungen (verschiedene pH-Werte) werden gemessen.
TL;DR: In this article, the relative reactivities of pulverized samples of 3 marcasite and 7 pyrite specimens from various sources were determined at 25°C and pH 2.0 in ferric chloride solutions with initial ferric iron concentrations of 10−3 molal.
TL;DR: In this article, the diffusion equation is solved analytically for the transport and kinetics of electrons and reactant in the layer of a modified electrode, and the reaction can take place in six different locations: at the electrode interface, at the electrolyte/layer interface, throughout the layer, or a reaction layer at the surface or in the middle of the layer.
TL;DR: Cinetique et mecanisme de l'oxydation de NADH par l'ion ferroceniumyle and quelques derives substitues de cet ion dans le propanol-1 aqueux as mentioned in this paper.
Abstract: Cinetique et mecanisme de l'oxydation de NADH par l'ion ferroceniumyle et quelques derives substitues de cet ion dans le propanol-1 aqueux
TL;DR: It is argued on the basis of the magnitude of ka and the dependences of Ka and kd on temperature and salt concentration that a minimum reaction mechanism for the interaction of RNA polymerase with the λPR promoter to form an open complex (RPo) must be.
TL;DR: In this article, a flash photolysis/UV abosrption technique was used to study the HO2 + HO2 and DO2 + DO2 reactions in the gas phase.
Abstract: A flash photolysis/UV abosrption technique was used to study the HO2 + HO2 and DO2 + DO2 reactions in the gas phase. Rate constants were measured at pressures between 100 and 700 torr of Ar and N2, and at temperatures between 230 and 420 K with up to 10 torr of added water vapor. The overall disproportionation rate constants for the reaction is given as the sum of pressure-independent and pressure-dependent terms. A kinetic analysis shows that both reactions have a zero-pressure bimolecular component and a termolecular component which is linearly dependent on pressure up to 700 torr. A priori estimates of the vibrational frequencies of the product of the HO2 + HO2 reaction suggest binding energies of 12-20 kcal per mol (for the initial association).
TL;DR: In the presence of superoxide dismutase, the formation of this species was found to be inhibited, whereas that of Compound I was little affected, which suggests that this species is formed by the reaction of ferric catalase with O-2 and is probably the oxy form of this enzyme (Compound III).
TL;DR: Polymerized actin hydrolyzes bound ATP in a reaction that depends on the concentration of polymerized ATP‐actin, not on the rate of incorporation of ATP‐ actin into the polymer.
TL;DR: The discharge-flow resonance fluorescence technique has been used to obtain absolute rate data for the OH + HCl reaction at total pressures from 2 to 100 torr of helium and 2 to 25 tor r of 80% nitrogen plus 20% helium as mentioned in this paper.
Abstract: The discharge-flow resonance fluorescence technique has been used to obtain absolute rate data for the OH + HCl reaction at total pressures from 2 to 100 torr of helium and 2 to 25 torr of 80% nitrogen plus 20% helium. At 295 K the rate constant is (7.9 +/- 0.4) x 10/sup -13/ cm/sup 3/ molecule/sup -1/s/sup -1/. The results are independent of the pressure, the carrier gas, the surface-to-volume ratio, and the source of HCl but are dependent upon temperature. The interaction of flow dynamics, diffusion, and chemical reaction is discussed. Procedures are given to correct rate data for axial and radial diffusion.
TL;DR: In this paper, a CF4 plasma etching silicon has been simulated to identify dominant chemical processes and quantify the effects of various reaction and transport parameters, and the model unambiguously shows that fluorine atoms are the main reactive species in the plasma, that gas phase chemistry is clearly dominated by neutral reactions, an...
Abstract: A CF4 plasma etching silicon has been simulated to identify dominant chemical processes and to quantify the effects of various reaction and transport parameters. The model was a one‐dimensional plug‐flow reactor in which a packet of gas is followed through the plasma and into the afterglow region, allowing the simulation to be performed as an initial value problem in ordinary differential equations. Two temperature zones were used with all known significant reactions incorporated into the chemical mechanism with the best available rate constants. Adjustable parameters were included only for certain sticking coefficients, surface recombination rates, and surface polymerization rates. Appropriate adjustment of these parameters gives satisfactory agreement between the simulations and experimental measurements of downstream gas‐phase composition. The model unambiguously shows that fluorine atoms are the main reactive species in the plasma, that gas phase chemistry is clearly dominated by neutral reactions, an...
TL;DR: In this paper, it was shown that the dependences of the electronic coupling element and of the solvent reorganization energy on distance have important implications for intramolecular electron transfers and for the forward and back reaction rates and cage-escape yields in light-induced electron-transfer processes.
Abstract: It has been found that the dependences of the electronic coupling element and of the solvent reorganization energy on distance have important implications for intramolecular electron transfers and for the forward and back reaction rates and cage-escape yields in light-induced electron-transfer processes. An equation is presented for the net second order rate constant for bimolecular transfer. A derived difference in the optimum distance for the forward and back reactions is pointed out to have important implications for the formulation of steady-state quenching schemes and for the interpretation of cage-escape yields.
TL;DR: The same two compounds I and II in a similar (54:46) ratio have been identified after acidic or thermal hydrolysis of DNA which had been reacted with 3,4-epoxy-1-butene under similar conditions.
Abstract: The reaction of guanosine with 3,4-epoxy-1-butene in acetic acid gives two main products of N-7 alkylation. After acidic hydrolysis the two aglycones have been isolated by h.p.l.c. and shown to be the regioisomeric 7-(2-hydroxy-3-buten-1-yl) guanine (I) and 7-(1-hydroxy-3-buten-2-yl) guanine (II), arising through nucleophilic attack by N-7 of the purine at the two oxirane carbons of 3,4-epoxy-1-butene. Spectral characteristics of both compounds are presented, including u.v., 1H-n.m.r. and mass spectra. Deoxyguanosine reacts with 3,4-epoxy-1-butene in 50% methanol-water at 37 degrees C to give the N-7 alkylated deoxynucleosides corresponding to I and II in a 59:41 ratio. The reaction rate depends on the nucleoside concentration, with second order rate constants at 37 degrees C of 1.6 X 10(-2) and 1.1 X 10(-2) h-1 M-1 for the formation of the two deoxynucleoside adduct corresponding to I and II, respectively. The same two compounds I and II in a similar (54:46) ratio have been identified after acidic or thermal hydrolysis of DNA which had been reacted with 3,4-epoxy-1-butene under similar conditions. The half life for the spontaneous depurination of I and II in the adducted DNA under physiological conditions (37 degrees C, pH 7.2) is 50 h.
TL;DR: Model calculations of the spermine binding kinetics according to an excluded-site model demonstrate that the sPermine molecules bound to DNA are mobile along the double helix.
Abstract: The condensation of DNA induced by spermine and spermidine is investigated by equilibrium titrations and stopped-flow and field-jump experiments using scattered light detection. The spermine concentration required for the cooperative condensation process is measured at different DNA concentrations; these data are used to evaluate both the condensation threshold degree of spermine binding and the binding constant of spermine according to an excluded-site model. Stopped-flow measurements of the spermine-induced condensation demonstrate the existence of two processes: (1) A "fast" reaction is observed in the millisecond time range, when the reactant concentrations are around 1 microM; it is associated with a characteristic induction period and is assigned to the intramolecular condensation reaction. (2) A slow reaction with time constants of, e.g., 100 s strongly dependent upon both spermine and DNA concentrations is assigned to an intermolecular DNA association. The unusual time course of the intramolecular condensation reaction with the induction period provides evidence for a "threshold kinetics". During the induction period, spermine molecules are bound to DNA, but the degree of binding remains below the threshold value. As soon as the degree of ligand binding arrives at the threshold, the DNA is condensed in a relatively fast reaction. Model calculations of the spermine binding kinetics according to an excluded-site model demonstrate that the spermine molecules bound to DNA are mobile along the double helix. A comparison of the experimental data with the results of Monte Carlo simulations suggests a rate constant of approximately 200 s-1 for spermine movement by one nucleotide residue.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: In this article, the kinetics and mechanism of the gaseous reaction of vinyl radicals with molecular oxygen have been studied between 297 and 602 K. The products formed in this temperature range are HCO and H/sub 2/CO.
Abstract: The kinetics and mechanism of the gaseous reaction of vinyl radicals with molecular oxygen have been studied between 297 and 602 K. The radicals were produced in a heated tubular reactor by the pulsed laser photolysis of C/sub 2/H/sub 3/Br at 193 nm. Reactant and product concentrations were monitored in real-time experiments using photoionization mass spectrometry. The products formed in this temperature range are HCO and H/sub 2/CO. The overall rate constant is pressure independent and is nearly constant with temperature. The magnitude of the rate constant, its temperature and pressure dependence, and the identity of the products of this reaction indicate that it proceeds by an addition mechanism in which the adduct rapidly rearranges to form an energy-rich dioxetanyl intermediate which decomposes into the observed products. Two other reactions (C/sub 2/H/sub 3/ + i-C/sub 4/H/sub 10/ and C/sub 3/H/sub 5/ (allyl radical) + O/sub 2/) were investigated at elevated temperatures, but no reaction was detected. An upper limit (5 X 10/sup -14/ cm/sup 3/ molecule/sup -1/ s/sup -1/) was established for the rate constants of both C/sub 2/H/sub 3/ + i-C/sub 4/H/sub 10/ at 600 K and C/sub 3/H/sub 5/ + O/sub 2/ at 900 K.