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Showing papers on "Reaction rate constant published in 1975"


Journal ArticleDOI
01 Jan 1975
TL;DR: In this paper, the reaction rates of formation of NO and N2 were determined from measurements carried out on flat premixed hydrocarbon/oxygen argon (or helium) flames, into which small amounts of ammonia, or cyanogen are added.
Abstract: From measurements carried out on flat premixed hydrocarbon/oxygen argon (or helium) flames, into which small amounts of ammonia, or cyanogen are added, overall reaction rates of formation of NO and N2 are determined. From similar measurements effected on nitrogen-diluted ethylene/oxygen flames, an overall rate of prompt NO formation is obtained. The discussion of these rate constants indicates that the relative importance of HCN molecules as intermediates in the fuel NO mechanism increases according to the following sequence of primary fuel nitrogen compounds: ammonia, cyanogen and molecular nitrogen; this last is found to behave like a true fuel nitrogen compound in the early flame stages. Experimental values of the total yield of nitric oxide obtained from the added nitrogen compounds have been determined; they are found to be in good agreement with yields calculated by numerical integration of the empirical overall reaction rates of NO and N2 formation, showing almost the same dependence of the NO yield on temperature, initial fuel nitrogen concentration and oxygen concentration.

537 citations


Journal ArticleDOI
TL;DR: Comparing biological activities of con jugated carbonyls their reactivity towards HS (k1) and the stability of the adducts must be considered and the equilibrium constants as well as the rate constants for forward and reverse reaction show an extreme variation depending on the carbonyl structure.
Abstract: 1. GSH reacts with conjugated carbonyls according to the equation: GSH+R-CH=CH-COR in equilibrium R-CH(SG)-CH2-COR. The forward reaction follows second order, the reverse reaction first order kinetics. It is assumed that this reaction reflects best the ability of conjugated carbonyls to inactivate SH groups in biological systems. 2. The rate of forward reaction increases with pH approx. parallel with alphaSH. Besides OH- ions also proton donors (e.g. buffers) increase the rate. The catalytic effect of pH and buffer is interpreted in view of the reaction mechanism. 3. The equilibrium constants as well as the rate constants for forward (k1) and reverse reaction show an extreme variation depending on the carbonyl structure. Acrolein and methyl vinyl ketone (k1 = 120 and 32 mol-1 sec-1, resp.) react more rapidly than any other carbonyl to give very stable adducts (half-lives for reverse reaction 4.6 and 60.7 days, resp). Somewhat less reactive are 4-hydroxy-2-alkenals and 4-ketopentenoic acid (k1 between 1 and 3 mol-1 sec-1), but they also form very stable adducts showing half-lives between 3.4 and 19 days. All other carbonyl studied react either very slowly (e.g. citral, ethly crotonate, mesityl oxide, acrylic acid) or form very labile adducts (crotonal, pentenal, hexenal, 3-methyl-butenone). Comparing biological activities of conjugated carbonyls their reactivity towards HS (k1) and the stability of the adducts must be considered.

240 citations



Journal ArticleDOI
TL;DR: The reaction product is proven to be a hydroxymethyl group and a reaction mechanism is proposed, and some implications of these results forpolynucleotide studies are discussed.
Abstract: A comprehensive description is given of both the equilibrium and the kinetic aspects of the reaction of formaldehyde with the exocyclic amino groups of derivatives of adenine, cytosine, and guanine; the results extend previous data in the literature to the point where formaldehyde can now be used as a quantitative probe of DNA structure and dynamic behavior. The main results are: (i) the reaction product is proven (by isolation followed by nuclear magnetic resonance (NMR) spectroscopy) to be a hydroxymethyl group; (ii) a dihydroxymethyl adduct is shown to exist at high formaldehyde concentrations; (iii) equilibrium constants at 25 degrees for forming the monoadduct with adenine and cytosine compounds are about 12 (M-1), while those for forming the dihydroxymethyl adduct are about 0.4 (M-1); (iv) the standard enthalpies for forming the monoadducts with adenine and cytosine compounds are about minus 4 to minus 6 kcal/mol; (v) indirect evidence is presented suggesting that a monohydroxymethyl group on adenine or cytosine derivatives exists preferentially as that rotational isomer which blocks Watson-Crick hydrogen bonding; (vi) in derivatives of guanine, it is shown that the N-1 endocyclic imino group can react with formaldehyde, as well as the amino group, the overall equilibrium constant being about 6 (M-1); (vii) all rate constants are reported, as well as their response to temperature, pH, and various solvent additives known to perturb DNA structure; (viii) using a series of substituted anilines, a linear free energy relation is obtained between the logarithm of both the forward and the reverse rate constant for the formaldehyde reaction and the amine pK, over a range of 10-8 change in amie basicity; (ix) using this relation, the pK's for protonating the nucleoside amino groups are estimated to lie in the range of minus 2 to minus 4; (x) a reaction mechanism is proposed; and (xi) some implications of these results forpolynucleotide studies are discussed.

212 citations


Journal ArticleDOI
TL;DR: The application of a mathematical model developed by modification of the second-order chemical kinetic differential equation to hCG kinetic binding data demonstrated that reactant degradation had little significant effect on the derivation of the association rate constant, but caused significant overestimation of the dissociation rate constant values derived from association experiments.
Abstract: The kinetics of the reaction between human chorionic gonadotropin (hCG) and specific gonadotropin receptors in the rat testis were determined at 24 and 37 degrees, over a wide range of hormone concentrations. Hormone concentrations were corrected for the binding activity of the (-125I)hCG tracer preparations. Analysis of the experimental data was performed with an interactive nonlinear curve fitting program, based upon the second-order chemical kinetic differential equation. The mean values for the association rate constant (k1) were 4.7 x 10-7 M-1 min-1 at 24 degrees, and 11.0 x 10-7 M-1 min-1 at 37 degrees. At both temperatures, the values of kl were independent of hormone concentration. Initial dissociation rates were consistent with first order kinetics, with dissociation rate constant (k2) of 1.7 x 10 minus -3 and 4.6 x 10 minus -3 min minus -1 at 24 and 37 degrees, respectively. When studied over longer periods at 24 degrees, the dissociation process appeared to be multiexponential. The kinetics of degradation of (-125I)hCG and receptors were determined at both temperatures, and a mathematical model was developed by modification of the second-order chemical kinetic differential equation to take these factors into account. The application of such a model to hCG kinetic binding data demonstrated that reactant degradation had little significant effect on the derivation of the association rate constant (k1), but caused significant overestimation of the dissociation rate constant (k2) values derived from association experiments. The model was also applied by computer simulation to a theoretical analysis of the effects of degradation of free hormone and receptor sites upon kinetic and steadystate binding data. By this method, the initial velocities of hormone binding were shown to be less affected by degradation than the steady-state levels of hormone-receptor complex. Also, reactant degradation in simulated steady-state experiments caused an underestimate of the apparent equilibrium association constant, but had relatively less effect on the determination of binding site concentration.

206 citations


Journal ArticleDOI
TL;DR: The ion chemistry of HNO3 was studied at 298°K in this article, where the attachment of thermal electrons to HNO 3 to produce NO−2 was found to have a rate constant of (5±3) ×10−8 cm3/sec.
Abstract: The ion chemistry of HNO3 is studied at 298 °K. The attachment of thermal electrons to HNO3 to produce NO−2 is found to have a rate constant of (5±3) ×10−8 cm3/sec. HNO3 reacts rapidly (k∼10−9 cm3/sec) with a large variety of negative ions including Cl−, NO2−, O2−, and CO−3. HNO3 is also found to bond strongly to NO3−. The proton affinity of HNO3 is determined to be 176±7 kcal/mole. The present results indicate a strong similarity between protonated HNO3 and hydrated NO2+, suggesting that these ion species are identical. The implication of the present results for atomospheric ion chemistry is discussed.

188 citations


Journal ArticleDOI
TL;DR: Spectral analysis of the reactions of compound (I) with L-cysteine and with papain showed that even under equimolar conditions the reaction is essentially stoicheimoetric and probably proceeds by specific attack at the sulphur atom distal from the pyridyl ring of compounds (I).
Abstract: 1. 4-(N-2-Aminoethyl2'-pyridyl disulphide)-7-nitrobenzo-2-oxa-1,3-diazole (compound I) was synthesized and evaluated as a fluorescent labelling reagent for thiol groups. 2. The design of compound (I) as one example of a general type of reporter group delivery reagent (2-pyridyl-S-S-X, where X contains an environmentally sensitive spectroscopic probe) is discussed. 3. The electronic absorption spectrum of compound (I) was determined over a wide range of pH and the spectral changes that accompany its reaction with low-molecular-weight thiols, e.g. L-cysteine, and with papain (EC 3.4.22.2) and bovine serum albumin are discussed. 4. A new value of epsilon343 for 2-thiopyridone (Py-2-SH) was determined as 8.08 X 10(3) +/- 0.08 X 10(3)M-1-cm-1. 5. Spectral analysis of the reactions of compound (I) with L-cysteine and with papain (in the pH range 3.5-8.0) showed that even under equimolar conditions the reaction (thiol-disulphide interchange to release Py-2-SH) is essentially stoicheimoetric and probably proceeds by specific attack at the sulphur atom distal from the pyridyl ring of compound (I). 6. The fluorescence-emission spectra of compound (I) and of the products of its reaction with papain and with ficin (EC 3.4.22.3) were determined. Compound (I) is highly fluorescent in aqueous solution. Excitation within the intense visible absorption band (lambda max. 481 nm, epsilon max. 2.52 X 10(4)M-1-cm-1) provides green fluorescence with an emission maximum at 540 nm. Both papain and ficin labelled by reaction with compound (I) are characterized by fluorescence-emission maxima (535 nm and 530 nm respectively) of even higher intensity. The fluorescence emission of the product of the reaction of papain with compound (I) was shown to be 25 times more intense than that of the product of the reaction of papain with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (Nbd chloride). 7. The second-order rate constants (k2) for the reactions of compound (I) and of Nbd chloride with GSH, papain, albumin, ficin, 2-benzimidazolylmethanethiol and 2-benzimidazolylethanethiol were determined at 25.0 degrees C and various pH values. At pH4 the values of k2(compound I)/k2(Nbd chloride) are: GSH, 288; albumin, 36; papain 3 X 10(3); ficin, 3 X 10(4). 8. The pH-k2 profiles for the reactions of compound (I) and of Nbd chloride with the two 2-benzimidazolylalkanethiols were determined. Of the four profiles only that for the reaction of compound (I) with 2-benzimidazolylmethanethiol is characterized by a striking rate maximum in acidic media.

173 citations


Journal ArticleDOI
TL;DR: The tiron semiquinone may be used as an indicator free radical for the formation of superoxide anion in biological systems because of the rapid rate of oxidation of the catechol by O2 compared to the rate of O2 formation is most enzyme systems.

150 citations


Journal ArticleDOI
TL;DR: The fluorescence of the supposedly buried tryptophan in ribonuclease T1 has been found to be collisionally quenched by acrylamide with a rate constant of 3 X 10(8) M--1 sec--1, and the dynamic character of a protein molecule is revealed.
Abstract: The fluorescence of the supposedly buried tryptophan in ribonuclease T1 has been found to be collisionally quenched by acrylamide with a rate constant of 3 X 10(8) M--1 sec--1. Only a slight decrease in the quenching rate is observed upon a 5-fold increase in the viscosity of the solution. For this to be the case, the diffusion of the quencher must be limited by the protein matrix. To explain the process of diffusion through this complex material, the formation of "holes" in the lattice of a protein due to nanosecond fluctuations must be invoked. Thus, the dynamic character of a protein molecule is revealed. The quenching rate constant has an activation energy of 9 kcal/mol which can be used to characterize the nature of the cohesive forces in the microenvironment about the indole ring. The mechanical properties of a portion of a protein matrix can, therefore, be described as one would for a fluid.

145 citations


Journal ArticleDOI
TL;DR: The chemical shifts and line widths of the Watson-Crick ring NH resonances of the self-complementary duplex of d-ApTpGpApT have been monitored at low ionic strength and in the presence of Mg ions at neutral pH in aqueous solution to determine the thermodynamic parameters associated with fraying.
Abstract: The chemical shifts and line widths of the Watson-Crick ring NH resonances of the self-complementary duplex of d-ApTpGpApT have been monitored at low ionic strength and in the presence of Mg ions at neutral pH in aqueous solution to determine the thermodynamic parameters associated with fraying (D. J. Patel (1974), Biochemistry 13, 2396) at the terminal and internal base pairs as a function of temperature and pH. From studies in H2O-MeOH (3:2), the fraying process persists down to approximately -20 degrees for the internal TA base pair and down to and probably beyond -30 degrees for the terminal AT base pair. The observed average chemical shift at each of these base pairs as a function of temperature suggests rapid exchange on the nuclear magnetic resonance (NMR) time scale between helix and coil (chemical shift separation of 3.2 ppm) and have been utilized to determine the dissociation constant at the terminal and internal base pairs. Comparison of the reaction enthalpies elucidated from the chemical shift parameters with those reported from optical studies suggests that the symmetry related internal TA base pairs break in a coupled manner at low ionic strength, with the coupling removed in the presence of Mg ions and high salt. By contrast, the symmetry related terminal AT base pairs break independently of each other in the absence and presence of Mg ions and high salt. The terminal base pair exhibits a Tm of 10-15 degrees lower than that of the internal base pair in the hexanucleotide, with divalent Mg ions and high salt stabilizing the double helix as reflected in the Tm values of these base pairs. The observed line width changes as a function of temperature provide an estimate of the exchange rate of the proton from the coil form with water. The exchange reaction from the coil state is base catalyzed with rate constants in the diffusion limit.

136 citations


Journal ArticleDOI
TL;DR: In this article, rate constant measurements for charge transfer processes at various electrodes show the general sequence k s (Pt)> k s(glassy carbon)> K s (wax-impregnated graphite) > K s(carbon paste).

Journal ArticleDOI
TL;DR: It is suggested that O2- may reduce cytochrome c through a track composed of aromatic amino acids, and that little protein rearrangement is required for the formation of the activated complex.

Journal ArticleDOI
TL;DR: A model for the aggregation reaction was developed and the specific rate constant for the binding of free cells to aggregates was developed, which can be used to distinguish between aggregation-inducing substances of different molecular structures.
Abstract: . Reactions between selected strains of oral streptococci and saliva were studied spectrophotometrically. The curves of absorbance (700 nm) versus those of time were sigmoidal for aggregating saliva-bacteria mixtures. When the logarithm of the ratio of the change in absorbance to the remaining absorbance was plotted against the reaction time, straight lines were obtained. At a fixed concentration of bacteria, the slope of these lines for a series of dilutions of a selected saliva sample was a parabolic function of the volume of saliva in the reaction mixtures. A model for the aggregation reaction was developed which explained the shape of these parabolic curves. The parameters of the model can be calculated from the experimental data and can be used to estimate the concentration of aggregation-inducing substances in undiluted saliva. A method for calculating the specific rate constant for the binding of free cells to aggregates was developed. This rate constant is a characteristic feature of a given aggregation reaction and can, in principle, be used to distinguish between aggregation-inducing substances of different molecular structures.

Journal ArticleDOI
TL;DR: A rapid mixing and quenching device is described which operates efficiently in the range of 150 msec to several minutes as well as the usual time scale of 5-150 msec of the conventional apparatus to measure the initial rate of acylation by the tyrosyl-tRNA synthetase of Escherichia coli during the first turnover of the enzyme.
Abstract: A rapid mixing and quenching device is described which operates efficiently in the range of 150 msec to several minutes as well as the usual time scale of 5-150 msec of the conventional apparatus. This has been used to measure the initial rate of acylation of tRNATyr by the tyrosyl-tRNA synthetase of Escherichia coli during the first turnover of the enzyme, and also the rate constants of the partial reactions of amino acid activation and transfer to the tRNA. It is shown that at saturating conenctration of tRNA the reaction proceeds by a ternary complex mechanism. The rate-determining step is either the aminoacyltion process or a step preceding it. At low concentrations of tRNA the reaction proceeds by the stepwise process of formation of tyrosyl adenylate followed by acylation of the tRNA. The rate constants for these partial reactions are faster than that for the ternary complex reaction. But the prior binding of tRNA greatly decreases the rate of tyrosyl adenylate formation. Both pathways are probably important at physiological concentrations. 88% of the tyrosine from the tyrosyl adenylate complex is transferred to tRNA. The presence of added tyrosine and ATP reduces this to 78%. However, the addition of aliquots of ATP to a mixture of enzyme, tyrosine, and a saturating concentration of tRNA (i.e., ternary complex conditions) leads to at least 0.97 mol of tRNA being acylated/mol of ATP hydrolyzed. Trapping experiments show that the 12% of adenylated that is not transferred to tRNA is hydrolyzed on the enzyme rather than expelled into solution.

Journal ArticleDOI
TL;DR: In this article, the kinetics of calcite carbonate were studied by following changes in pH only on batch solutions of CaCl 2, NaHCO 3 and NaOH in the presence of calcitic seed crystals.

Journal ArticleDOI
TL;DR: In this paper, the rate equations of the overall process and the parallel reactions of the formation of N2 and N2O were derived, and the expected dependence of specificity on the reaction mixture composition and temperature has been examined.

Journal ArticleDOI
TL;DR: In this article, the pyrolysis of methane has been studied in a static system at temperatures of 995, 1038, 1068, and 1103 K and pressures from 25 to 700 Torr.
Abstract: The pyrolysis of methane has been studied in a static system at temperatures of 995, 1038, 1068, and 1103 K and pressures from 25 to 700 Torr. It was concluded that the initial stages of the reacti...

Journal ArticleDOI
TL;DR: Evidence is given that the stable complex is effected by Ca-2+-mediated salt bridges between the two membranes and that the rate constant of the transformation step derives from the statistics of the distribution and the rate of redistribution of Ca- 2+-occupied polar head groups on the membrane surfaces.

01 Jan 1975
TL;DR: In this paper, the authors used a conductance method and nuclear backscattering for reaction-rate measurements for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt.
Abstract: Intermetallic coumpound formation at metal–metal interfaces was observed for thin film couples of Al and transition metals such as Cr, Ti, Hf, Zr, Co, Ta, Pd, and Pt. The Al–Cr system was investigated in some detail using a conductance method and nuclear backscattering for reaction‐rate measurements. The compounds CrAl7 and Cr2Al11 were identified and their growth was found to be diffusion controlled. The temperature dependence of the rate constant for CrAl7 obeyed an Arrhenius plot from 300° to 450 °C with an activation energy of 1.91±0.1 eV. The Al‐rich phases of the remaining transition metals were investigated; the compounds either exhibited a planar interface with parabolic growth kinetics or an irregular interface with nonparabolic growth. An empirical relationship involving the melting point and stability of the compounds was proposed to explain the different growth kinetics.

Journal ArticleDOI
TL;DR: The rate of the reaction between cytochrome c peroxidase and hydrogen peroxide was investigated using the stopped-flow technique and the apparent bimolecular rate constant was determined between pH 3.3 and pH 11 as a function of ionic strength.
Abstract: The rate of the reaction between cytochrome c peroxidase and hydrogen peroxide was investigated using the stopped-flow technique. The apparent bimolecular rate constant was determined between pH 3.3 and pH 11 as a function of ionic strength. The pH dependence of the apparent bimolecular rate constant can be explained by assuming that two ionizable groups on the enzyme strongly influence the rate of the reaction. At 0.1 M ionic strength, a group with a pKa of 5.5 must be unprotonated and a group with a pKa of 9.8 must be protonated for the enzyme to react rapidly with hydrogen peroxide. The apparent acid dissociation constants depend upon the ionic strength. The true bimolecular rate constant has a value of (4.5 +/- 0.3) X 10(7) M-1 sec-1 and is independent of ionic strength.

Journal ArticleDOI
TL;DR: In this paper, the initial yield of solvated electrons in all solvents studied was reduced in the presence of a high concentration of scavengers, and exhibited a semilogarithmic dependence on the scavenger concentration.

Journal ArticleDOI
TL;DR: The reaction mechanism and decay behavior of aspartase activity for immobilized Escherichia coli cells were investigated by using a sectional packed column.
Abstract: The reaction mechanism and decay behavior of aspartase activity for immobilized Escherichia coli cells were investigated by using a sectional packed column. Reaction within the immobilized cell column proceeded at zero-order on substrate solutions ranging in concentration from 0.1 to 1.0M, and the initial reaction rate was found to be 1.556 X 10(-2) mol/min/liter of immobilized cells. The effect of temperature on the reaction rate constant was investigated. The Arrhenius plot was a straight line at temperatures below 43 degrees C, and the activation energy for immobilized cells was calculated to be 12.36 kcal/mol. Aspartase activity in the immobilized cell column decayed exponentially and uniformly in all sections of a column. Its half-life was approximately 120 days. The rate of formation of L-aspartic acid was shown to be independent of column dimensions.

Journal ArticleDOI
TL;DR: In this article, a statistical model of chemical reaction is applied to collisions of O(1D) atoms with the molecules H2, N2, CO, CO 2, N2O, O3, and H2O.
Abstract: A statistical model of chemical reaction is applied to collisions of O(1D) atoms with the molecules H2, N2, CO, CO2, N2O, O3, and H2O. Rate constants for reaction and deactivation are computed over the temperature range 100−2100°K. Competition among various product channels is investigated. In most cases quantitative agreement with experiment is achieved.

Journal ArticleDOI
TL;DR: In this paper, the absolute rate constants for the reaction of OH radicals with propylene and the four butenes have been determined over the temperature range 297-425 K using a flash photolysis-resonance fluorescence technique.
Abstract: Absolute rate constants for the reaction of OH radicals with propylene and the four butenes have been determined over the temperature range 297–425 °K using a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained are: k1(propylene) =4.1×10−12 e(1080±300)/RT cm3 molecule−1⋅sec−1, k1(1‐butene) =7.6×10−12 e(930±300)/RT cm3 molecule−1⋅sec−1, k1(isobutene) =9.2×10−12 e(1000±300/RT cm3 molecule−1⋅sec−1, k1(cis‐2‐butene) =1.04×10−11 e(970±300)/RT cm3 molecule−1⋅sec−1, and k1(trans‐2‐butene) =1.12±10−11 e(1090±300)/RT cm3 molecule−1⋅sec−1. The room temperature rate constants are compared and discussed with respect to the literature values.

Journal ArticleDOI
TL;DR: In this article, the effect of changing reagent vibrational and rotational energy on the reaction rate has been analyzed for over 20 chemical reactions, including simple rearrangement (exchange) reactions as well as collision induced dissociation and quenching of electronically excited states.
Abstract: The effect of changing reagent vibrational and rotational energy on the reaction rate has been analyzed for over 20 chemical reactions. In most cases the selectivity in energy requirements could be characterized by a single (’’consumption potential’’) parameter, even when the reactivity varied by many orders of magnitude. The reactions analyzed covered atom–diatom and diatom–diatom collisions and included both simple rearrangement (’’exchange’’) reactions as well as collision induced dissociation (CID) and quenching of electronically excited states. The results were derived both from experiments and classical trajectory computations and include the variation in reactivity at both a given total collision energy and at a given translational (and rotational) temperature. In all cases the analysis was based on evaluating the surprisal of the energy consumption, i.e., the observed (or computed) reaction rate constant was compared to the rate expected on prior grounds when all states (at a given total energy) r...

Journal ArticleDOI
TL;DR: In this article, the standard rate constant decreases as the number of the coordinated 2,2′-bipyridine decreases and is interpreted on the basis of the extension of ligand π-orbitals.

Journal ArticleDOI
TL;DR: In this article, the rate constants for the reaction of O+2(a 4 Πu) metastable ions with N2, Ar, CO, CO+, CO2, CO+2, H2, and O2H+ have been measured for the relative kinetic energies 0.04-2 eV in a flow-drift tube.
Abstract: Rate constants for the reaction of O+2(a 4Πu) metastable ions with N2, Ar, CO, CO2, H2, and O2, which do not react with O+2(X 2Πg, v=0) ground‐state ions, have been measured for the relative kinetic energies 0.04–2 eV in a flow‐drift tube. With the exception of O2 and CO, most of the rate constants are near the respective Langevin limits. The rate constant for the reaction with CO exhibits a pronounced minimum at 0.3 eV; the other reactions show much less variation with energy. Up to 2 eV, quenching of the a 4Πu metastable state to the X 2Πg ground state of O+2 appears to be small compared to the reactive losses of O+2(a 4Πu) ions. The reactive process is charge transfer, except for CO and H2. For CO, CO+ and CO+2 are formed roughly in the ratio 5:1 and for H2, only O2H+ is formed.

Journal Article
TL;DR: Reaction rates and the failure of catalase to inhibit the reaction demonstrated that hydrogen peroxide is of no importance, and the lag phase of the reaction suggests that oxidation products of 4-dimethylaminophenol produced by the reaction between oxyhemoglobin and 4-Dimethylam inophenol are essential intermediates.
Abstract: The rate of oxidation by hydrogen peroxide of human hemoglobin, virtually free from catalase, glutathione peroxidase, and superoxide dismutase, was found to be proportional to the concentrations of hemoglobin and hydrogen peroxide, the second-order rate constant at pH 7.4 and 37° being k = 125 M-1 sec-1. Formation of ferrihemoglobin by reduced glutathione in air was found to be slow, gaining its maximal velocity after a lag phase. Kinetic data and the effect of catalase or glutathione peroxidase demonstrated that hydrogen peroxide is an essential intermediate which produces ferrihemoglobin in solutions of hemoglobin and reduced glutathione. The much higher rate of ferrihemoglobin formation by phenylhydroxylamine than by hydrogen peroxide and the failure of catalase to inhibit the reaction showed that hydrogen peroxide is not an important intermediate in the formation of ferrihemoglobin by phenylhydroxylamine. The reaction rate was found to be proportional to the concentrations of phenylhydroxylamine and hemoglobin. The second-order rate constant was calculated to be k = 2350 M-1 sec-1. With the formation of ferrihemoglobin by 4-dimethylaminophenol also, reaction rates and the failure of catalase to inhibit the reaction demonstrated that hydrogen peroxide is of no importance. The lag phase of the reaction suggests that oxidation products of 4-dimethylaminophenol produced by the reaction between oxyhemoglobin and 4-dimethylaminophenol are essential intermediates.


Journal Article
TL;DR: In this paper, the authors studied the kinetics of the crystal growth of calcium oxalate monohydrate using the technique of seeded crystal growth from stable supersaturated solution, and found that the incorporation of lattice ions into the crystal is governed by a bimolecular surface-controlled reaction step.
Abstract: The kinetics of the crystal growth of calcium oxalate monohydrate has been studied using the technique of seeded crystal growth from stable supersaturated solution. The rate law takes the form minus dc/dt equals kN-2 in which the rate of loss of lattice ion from solution is proportional to the square of the supersaturation. It is proposed that the incorporation of lattice ions into the crystal is governed by a bimolecular surface-controlled reaction step. The rate is independent of the hydrodynamics of the system but is proportional to the solid to solution ratio in the supersaturated solution. The specific rate constant, k (M-minus-1 min-minus-1 [mg/dl]minus-1), is nearly independent of the solid to solution ratio, however. The rate of crystal growth was found not to vary with the calcium to oxalate molar ratio in the range 1.5 to 0.75, although the rate did increase at both higher and lower ratios. The method was found to be simple, rapid, and reproducible and lends itself to the quantitative study of inhibitors of crystal growth.