Showing papers on "Reaction rate constant published in 1970"
TL;DR: It is concluded that the association of repressor and operator is aided by electrostatic attraction between the phosphate groups of DNA and a positively charged binding site on the lac repressor.
786 citations
TL;DR: Results show that the lipid is essential for the enzymatic reduction of hemoprotein P-450 and that only the rapid phase of the reaction is adequate to support the observed rate of substrate hydroxylation.
438 citations
TL;DR: In this article, the curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine were investigated with a differential scanning calorimeter (DSC) operated isothermally.
Abstract: The curing reactions of epoxy resin with aliphatic diamines and the reaction of phenyl glycidyl ether with butylamine as a model for the curing reactions were investigated with a differential scanning calorimeter (DSC) operated isothermally. The heat of reaction of phenyl glycidyl ether with butylamine is equal to 24.5 ± 0.6 kcal/mole. The rate of reaction was followed over the whole range of conversion for both model and curing reactions. The reactions are accelerated by the hydrogen-bond donor produced in the system. The rate constants based on the third-order kinetics were determined and discussed for the model reaction and for the chemically controlled region of curing reactions. The activation energies for these rate constants are 13-14 kcal/mole. At a later stage of conversion, the curing reactions become controlled by diffusion of functional groups. The final extent of conversion is short of completion for most isothermally cured and even for postcured samples because of crosslinking. It was quantitatively indicated that the final conversion of isothermal cure corresponds to the transition of the system from a viscous liquid to a glass on the basis of the theory of glass transition temperature of crosslinked polymer systems.
436 citations
TL;DR: In this paper, an alternative representation is proposed by describing the progress of the reaction in terms of the porosity, grain size, gas phase and solid state diffusivities and a heterogeneous reaction rate constant, which is now independent of structure.
428 citations
TL;DR: In this article, the ion-molecule reactions in pure nitrogen and nitrogen containing traces of water were studied with a pulsed electron-beam mass spectrometer having a field-free high-pressure source.
Abstract: The ion–molecule reactions in pure nitrogen and nitrogen containing traces of water were studied with a pulsed electron‐beam mass spectrometer having a field‐free high‐pressure source. The reaction N2++2N2 = N4++N2 occurring in pure nitrogen was found to have a third‐order rate constant k = 8 × 10−29cc2molecule−2·sec−1 at 300°K and a negative temperature coefficient corresponding to an “activation energy” of − 2 kcal/mole at pressures up to 3.5 torr. The results for the reaction N++N2→N3+, investigated under the same conditions, indicated either third‐order dependence with k = 5 × 10−29cc2molecule−2·sec−1 and energy of activation − 1 kcal/mole or second‐order dependence with k = 1.3 × 10−12cc molecule−1·sec−1 with no temperature coefficient. The reaction mechanism in nitrogen in the torricelli range containing water vapor in the millitorr range was found to proceed by the following reaction sequence: N2+→N4+→H2O+→H3O+→H+(H2O)2→H+(H2O)n. The rate constants for all reactions were determined. The clustering ...
246 citations
TL;DR: The attachment rate for electrons to SF6 has been measured between 293 and 523°K in a helium-buffered flowing afterglow over the pressure range of 0.1 to 1.5 torr as discussed by the authors.
Abstract: The attachment rate for electrons to SF6 has been measured between 293 and 523°K in a helium‐buffered flowing afterglow over the pressure range of 0.1–1.5 torr. The attachment has a rate constant of 2.2 × 10−7 cm3/sec, independent of temperature and pressure. The primary reaction product over the measured range of temperatures is SF6−. However, the rate of production of SF5− increases rapidly with temperature.
188 citations
TL;DR: In this article, a pulsed electron-beam high-pressure mass spectrometer was used to investigate the reaction mechanism leading from O2+ to H 2 O n in the troposphere.
Abstract: The formation of H+(H2O)n clusters in moist oxygen is of interest since this process must occur in the troposphere and has been observed to occur in the D region of the ionosphere. The reaction mechanism leading from O2+ to H+(H2O)n was investigated with a pulsed electron‐beam high‐pressure mass spectrometer. At oxygen pressures in the torr range and for [O2]/[H2O]>102 the major reaction proceeds by the sequence O2+→O4+→O2+·H2O→H3O+·OH→H+(H2O)2→H+(H2O)n. The rate constants for all major steps were determined. Rate constants for parallel reactions which may become important at different conditions were also determined.
179 citations
TL;DR: The distribution of rates among the various steps in the reaction requires that cooperativity in oxygen binding be attributed primarily to deviations of the successive dissociation velocity constants from their statistical values, and is consistent with the idea that the major change in reactivity occurs after 1 ligand molecule has dissociated from saturated hemoglobin.
167 citations
TL;DR: In this paper, the rate constants for the association of N2, O2, and CO2 to O2− and for N2 and CO 2 to O− have been measured at temperatures below 300°K.
Abstract: The temperature‐controlled flowing afterglow system has been utilized at temperatures below 300°K to measure the rate constants for the association of H2, N2, O2, CO2, N2O, and SO2 to O2+ with helium third body. Rate constants for the association of N2, O2, and CO2 to O2− and for the association of N2 and CO2 to O− have been measured at 200°K. Some of the ion clusters formed in this way reacted via binary neutral interchange reactions of the type A±·B+C → A±·C+B. Rate constants for these processes were obtained at and below 300°K. The observation of these reactions allows an ordering of ion cluster bond energies. The increasing order of binding energies to O2+ is H2, N2, O2, N2O, SO2, and H2O. For the O2− ion clusters the increasing order is N2, O2, H2O, CO2, and NO. In some cases, equilibria are observed allowing a determination of binding energy differences. The three‐body association rate constants increase with increasing binding energy of the ion cluster, in accord with theoretical expectation.
163 citations
TL;DR: Experiments imply that, for a deeper understanding of the biological action of AA, the following factors should also be considered: (a) secondary reactions after alkylation of, e.g. DNA (especially important for chromosomal aberrations) and protein; (b) lipid/water partition; (c) steric factors on the side of AA as well as the receptor molecule.
163 citations
TL;DR: In this article, it was shown that rotationq contributes a factor to the high pressure specific rate constant, kmuni, for a unimolecular reaction which is the ratio of the square root of the moments of inertia of the rotational partition functions of the activated complex and the molecule.
Abstract: Early theories of unimolecular reaction rates have considered the role of overall molecular rotations by using two ostensibly different approaches ; the results of both approaches are identical, however. Eyring1n2& postulated that all degrees of freedom of the reactants are in thermodynamic equilibrium with those of the activated complex (except that special considerations attach to that degree of freedom associated with the reaction coordinate). In this simple formulation, and without specific considerat of the conservation of angular momentum, rotationq contribute a factor to the high-pressure specific rate constant, kmuni, for a unimolecular reaction which is the ratio of the square root of the moments of inertia of the rotational partition functions of the activated complex and the molecule, i.e., (ZA+ZB+ZO+/ZAZBZC)’”. Another approach that was applied even earlier to a diatomic approximation for unimolecular decomposition reactions is that of Rice and Gershinowitz (RG).8 They pointed out that angular momentum conservation requires that the rotational quantum number does not change when the “activated complex” configuration at the top
TL;DR: In this article, the authors measured the reaction of CO2+ with atomic oxygen in a flowing afterglow system at 295°K at a rate constant 2.6 × 10−10cm3/sec and appeared to produce both O2+and O+ as product ions, approximately in the ratio 5:3.
TL;DR: In this paper, the binding of acridine orange to poly(α-l-glutamic acid) at pH 7.5 has been investigated by means of absorbance measurements at 492 nm.
Abstract: The binding of acridine orange to poly(α-l-glutamic acid) at pH 7.5 has been investigated by means of absorbance measurements at 492 nm. The equilibrium as well as chemical relaxation behavior is interpreted in the light of a basic model theory of cooperative binding. Binding and cooperativity are found to be stronger than in the previously studied case of proflavine. In principle, the static properties are analogous in both cases. The only distinct contrast is given by the fact that the degree of cooperativity is considerably affected by ionic strength and polymer to dye ratio. This is attributed to the effect of unfavorable electrostatic interactions which tend to prevent long aggregates of bound dye.
Temperature jump measurements resulted in relaxation curves which agreed very well with the predictions of the theory. Mean relaxation times of cooperative binding could be determined and evaluated in terms of an effective rate constant for recombination of free dye with bound aggregates of dye. The effect of varying the concentration of added KCl can be attributed to blocking of reaction sites by bound K+ ions. Extrapolation to zero KCl concentration yields a diffusion controlled rate constant for cooperative binding of monomer dye (kRo is approx. 1.5 × 109 M–1 sec–1). The life time of terminal elements of bound aggregates of dye turns out to be about 400 μsec.
TL;DR: The binding of oxygen with the ferrous enzyme in the presence of l-tryptophan is a reversible process, as are those with hemoglobin and myoglobin.
TL;DR: The magnitude of the effect suggests that the contribution of substrate "freezing" to total rate enhancement by an enzyme can be considerably greater than previously supposed and may in fact be sufficient to complete the justification for enzyme catalysis.
Abstract: As a result of alkyl substitution in both aromatic ring and side chain, the rate constant for acid-catalyzed lactonization of hydrocoumaric acid is increased by factors as high as 1011 and, in comparison with the bimolecular esterification of phenol and acetic acid, by almost 1016. In the most favorable case studied, the half-life of the phenolic acid (imidazole buffer, pH 7, 30°C) is 6 sec, with 90% of the total rate being due to catalysis by the buffer species. The effect is attributed to a unique interlocking of methyl groups, which produces a severe conformational restriction of the side chain and increases greatly the population of the most productive conformer. This phenomenon is presented as a model for the conformational restraint imposed by an enzyme on its substrate. The magnitude of the effect suggests that the contribution of substrate „freezing” to total rate enhancement by an enzyme can be considerably greater than previously supposed and may in fact be sufficient to complete the justification for enzyme catalysis.
TL;DR: Squid giant axons were treated with tetrodotoxin (TTX) in concentrations ranging from 1 nM to 25 nM and the resulting decrease in sodium current was followed in time using the voltage clamp technique, suggesting that the over-all interaction is more complex than just a reversible reaction.
Abstract: Squid giant axons were treated with tetrodotoxin (TTX) in concentrations ranging from 1 nM to 25 nM and the resulting decrease in sodium current was followed in time using the voltage clamp technique. The removal of TTX from the bathing solution produced only partial recovery of the sodium current. This suggests that the over-all interaction is more complex than just a reversible reaction. By correcting for the partial irreversibility of the decrease in sodium current, a dissociation constant of 3.31 x 10(-9)M was calculated for the reaction between TTX and the reactive site of the membrane. The data obtained fit a dose-response curve modified to incorporate the correction for partial irreversibility when calculated for a one-to-one stoichiometry. The fit disagreed with that calculated for a reaction between two molecules of TTX with a single membrane-reactive site, but neither supported nor disproved the possibility of a complex formed by two reactive sites with one molecule of TTX. Values of the rate constants for the formation and dissociation of the TTX-membrane complex, k(1) and k(2), respectively, were obtained from the kinetic data. The values are: k(1) = 0.202 x 10(8)M(-1), and k(2) = 0.116 min(-1). The magnitude of the dissociation constant derived from these values is 5.74 x 10(-9)M, which has the same order of magnitude as that obtained from equilibrium measurements. Arrhenius plots of the rate constants gave values for the thermodynamic quantities of activation.
TL;DR: In this article, the authors studied the mechanism of reaction in 85% orthophosphoric acid as a function of temperature and impurity level in the electrolyte, and showed that the rate constants and Tafel slopes are dependent on impurity adsorption.
Abstract: Oxygen electrode kinetics in 85% orthophosphoric acid have been studied as a function of temperature and impurity level in the electrolyte. It is shown that the mechanism of reaction is the same as that in N perchloric acid, and that rate constants and Tafel slopes are dependent on impurity adsorption. Hydrogen peroxide is not a significant reaction product, at least at high temperatures. The activation energy of the reaction at the reversible potential was determined to be
TL;DR: In this article, the intrinsic behavior of nucleophilic substitution reactions of the type was investigated in a gas phase at 22.5" under thermal equilibrium conditions using the flowing afterglow technique, and the reaction probabilities were calculated for the reactions of oxide, hydroxide, alkoxide, phenyl, and benzylic anions with methyl chloride.
Abstract: As part of a program directed toward an understanding of the intrinsic nature of anion-molecule re- actions involving organic constituents, rate constants have been measured, reaction channels have been identified, and intrinsic reaction probabilities (the ratios of the experimentally determined rate constants to the theoretical collision rate constants) have been calculated for the reactions of oxide, hydroxide, alkoxide, phenyl, and benzylic anions with methyl chloride. All measurements were made in the gas phase at 22.5" under thermal equilibrium conditions using the flowing afterglow technique. The highly charge-localized anions were found to react rapidly with methyl chloride with rate constants larger than 8 x 10-10 cm3 molecule-1 sec-1 whereas the charge-delocalized anions reacted only slowly with rate constants less than 3 x 10-11 cm3molecule-1 sec-l. The formation of chloride ion was the dominant reaction channel observed in all cases. Calculated reaction probabilities were larger than 0.20 for the reactions involving highly charge-localized anions and less than 0.03 for the charge-delocalized anion re- actions. These results obtained in a rarified medium provide evidence for a correlation well known from solution studies, namely, a correlation between the reactivity of an anion and the nature of the distribution of its charge. Solvated alkoxide ions could be established as the dominant negative ions in a low-pressure helium afterglow. This allowed an investigation of the effect of weak solvation on the rate of reaction of alkoxide ions with methyl chloride. Upon the association of one molecule of the conjugate acid to the alkoxide ion the specific rate for reaction decreased by at least a factor of three. n our continuing studies of the intrinsic kinetics and I energetics of anion-molecule reactions involving organic constituents, we have turned our attention to the intrinsic behavior of nucleophilic substitution reactions of the type
TL;DR: In this paper, the oestradiol-binding protein of calf uterine cytosol forms a slowly reversible complex, and the affinity constant measured under equilibrium conditions shows an inverse relationship with protein concentration, and does not appear to vary at temperatures between 0 and 18°.
Abstract: The oestradiol-binding protein of calf uterine cytosol forms a slowly reversible complex with oestradiol. Kinetic studies on the formation of this complex, carried out with crude or partially purified uterine cytosol preparations, indicate a reaction of the second order. The rate constant shows an inverse relationship with protein concentration. Dissociation of the complex appears to occur in two stages, both following first order reaction rate kinetics. Affinity constants calculated from association-dissociation kinetics, decrease with increasing temperature. The affinity constant measured under equilibrium conditions shows an inverse relationship with protein concentration, and does not appear to vary at temperatures between 0° and 18°. The treatment of the data from binding studies at equilibrium suggests a cooperative effect.
These findings indicate that the interaction between the oestradiol-binding protein, and its ligand cannot be described by simple reaction schemes; work with purified material, now under progress, could simplify interpretation by eliminating ambiguities due to eventual specific or unspecific protein-protein interactions in our present impure system.
TL;DR: In this article, it was shown that RSSR and RS· formed during the pulse radiolysis of aqueous solutions of cysteine react with oxygen with rate constants of 4·3 ± 0·3 × 10 8 dm 8 mol −1 s −1 and about 8 × 10 9 dm 3 mol − 1 s − 1 respectively.
TL;DR: In this article, an upper bound for the recombination reaction rate constant for O+CO+M → CO2+M has been obtained with He as the third body of < 4.8 × 10−35 cm6 molecule.
Abstract: The recombination of oxygen atoms with O2 has been monitored directly using kinetic absorption spectroscopy in the vacuum ultra-violet. Oxygen atoms were produced by photolysis of O2(λ > 175 nm) and the decay observed via the resonance absorption transitions (33S1→ 23PJ) in the region of 130 nm using a vacuum ultra-violet monochromator. The experimental arrangement is described, and the results for the recombination with Ar, Kr and He as third bodies are reported. An upper limit for the recombination reaction rate constant for O+CO+M → CO2+M has been obtained with He as the third body of < 4.8 × 10–35 cm6 molecule–2 s–1.
TL;DR: In this paper, the authors studied the hydrogen atom-ethylene system at 298°K employing the methods of resonance fluorescence and absorption by hydrogen atoms of Lyman α radiation at 1216 A. Their results indicate that stoichiometric factors obtained under low-pressure conditions may not be applicable to high pressure.
Abstract: The hydrogen atom–ethylene system was studied at 298°K employing the methods of resonance fluorescence and absorption by hydrogen atoms of Lyman α radiation at 1216 A. The contribution of hydrogen atom–radical reactions was evaluated under varying experimental conditions, and the rate of disappearance of H atoms in ethylene was measured under conditions where stoichiometric corrections became significant. Measurements in the literature of reaction rates for H+C2H4 at low total pressure are now in good agreement; however the limiting high‐pressure absolute rate constants thus far reported differ depending on the assignment of stoichiometric factors. Our results indicate that stoichiometric factors obtained under low‐pressure conditions may not be applicable to high pressure. Furthermore, extrapolations based on plots of inverse rate constant vs inverse pressure may be in error due to significant curvature in such plots. Our high‐pressure limiting rate constant for H+C2H4, extrapolated from data at pressure...
TL;DR: Oxygen of mass 18 was used as a stable tracer to measure the rate of exchange between the sulfite ion and water as a function of pH and total sulfite concentration as mentioned in this paper.
Abstract: Oxygen of mass 18 was used as a stable tracer to measure the rate of exchange between the sulfite ion and water as a function of pH and total sulfite concentration. A value for the rate constant of...
TL;DR: An appropriate boundary condition is derived which permits both the bimolecular association and dissociation steps to be simultaneously treated within the framework of the theory of Smoluchowski, Debye, and Collins, and Kimball.
TL;DR: The absolute rate constants have been measured for several gas-phase chlorine atom-molecule reactions at 25°C by resonance fluorescence as mentioned in this paper, and conditions under which no competing side reaction occurs were established and the reported rate constants were measured under these conditions.
Abstract: The absolute rate constants have been measured for several gas-phase chlorine atom-molecule reactions at 25°C by resonance fluorescence. These reactions and their corresponding rate constants in units of cm3 mole−1 sec−1 are:
The effects of varying the substrate pressure, total pressure, light intensity and chlorine-atom source on the value of the bimolecular rate constants have been investigated for all these reactions. Conditions under which no competing side reaction occurs were established and the reported rate constants were measured under these conditions. For reactions (2), (5), (6), (7), and 8, there is a discrepancy of a factor of two between the rate constants measured in this work and values in the literature; it is suggested that this is due to an error in the previously measured value of k/k upon which the relative measurements in the literature ultimately depend.
TL;DR: In this article, the rates of alkaline hydrolysis of the enantiomers of isopropyl methylphosphonofluoridate (Sarin) have been determined without and with varying concentrations of α-cyclodextrin (cyclohexaamylose) in aqueous 0.1M/KCl solution at pH 9.0 and 25°.
Abstract: The rates of alkaline hydrolysis of the enantiomers of isopropyl methylphosphonofluoridate (Sarin) have been determined without and with varying concentrations of α-cyclodextrin (cyclohexaamylose) in aqueous 0.1M/-KCl solution at pH 9.0 and 25°.
The pseudo first-order rate constants are reported. The observed kinetics and product analysis are consistent with a reaction scheme in which complex formation precedes the nucleophilic reaction of α-cyclodextrin with Sarin. Dissociation constants (Kdiss) of the inclusion complexes and rate constants (k2) for the nucleophilic reaction are reported. The results indicate a stereospecific formation of the inclusion complexes, (S)-(+)-Sarin forming a more stable complex than (R)-(-)-Sarin, as well as a stereospecific rate of reaction, (R)-{-)-Sarin reacting faster than (S)-(+)-Sarin. The α-cyclodextrin-Sarin system represents the first model reaction for enzyme inhibition showing typical properties as complex formation, saturation effects and stereospecificity.
TL;DR: The kinetic data of the reaction were calculated from the absorption rate of oxygen into the mechanically agitated sulphite solutions and it was found that the reaction order in oxygen depends on the oxygen concentration in the liquid phase at the interface.
TL;DR: In this article, the extinction coefficient of the methyl radical was found to have a maximum value of (1.02 ± 0.06) X 104 1 mole−1 cm−1 at 216.4 nm.
Abstract: Combination reactions of the methyl radical have been studied by following the decay of the absorbance of the methyl radical during the course of the reaction by means of kinetic spectroscopy. The limiting values of the second-order rate constants at high pressure were determined for two reactions at room temperature:
The extinction coefficient of the methyl radical was found to have a maximum value of (1.02 ± 0.06) X 104 1 mole−1 cm−1 at 216.4 nm. Integration of the extinction coefficient over the absorption band of the methyl radical gave an oscillator strength of 1.0 X 10−2.
TL;DR: An electrostatic interaction of the bacteriochlorophyll reaction-center complex and mammalian cytochrome c resulted, and a collision-independent electron-transfer with a halftime of 25 μsec can be attained by laser-flash excitation, indicating a good stoichiometry of the reaction.
TL;DR: In this paper, the combination-elimination reaction CH3+CF3+HF was studied in a fast-flow system and the relative rate constants k(v) for vibrational levels v = 1 − 4 were obtained.
Abstract: The combination–elimination reaction CH3 + CF3 → CH3CF3† → CH2CF2 + HF has been studied in a fast-flow system. Infrared chemiluminescence arising from the HF product has been observed from vibrational levels v = 1–4, and relative rate constants, k(v), have been obtained for HF formation in these levels. A study has also been made of the reaction CH2CF2 + Hg*(63P1) → CHCF + HF + Hg(61S0), which has been found to produce vibrationally-excited HF. Relative rate constants k(v) for vibrational levels v = 1–4 have been obtained. It appears that channelling of the potential energy into HF vibration, in the course of the elimination step, is more efficient in the first than in the second of these reactions. In the second reaction HF is eliminated with considerable rotational excitation.