Kinetics of the Anation Reaction of Nickel(II) and 1,10-Phenanthroline in Ethanol

1972 ◽  
Vol 50 (23) ◽  
pp. 3861-3865 ◽  
Author(s):  
M. L. Sanduja ◽  
W. MacF. Smith
Keyword(s):  
Rate Constant ◽  
Sodium Perchlorate ◽  
Order Rate Constant ◽  
Stopped Flow ◽  
Tetrabutyl Ammonium ◽  
Kinetics Of Formation ◽  
Kinetics Of ◽  
Nickel Perchlorate ◽  
Anation Reaction ◽  
Made In

The kinetics of formation of the monophenanthroline complex of nickel(II) in ethanol has been studied using stopped-flow methods over the temperature range 7 to 35 °C. Tetrabutyl ammonium perchlorale in concentration 0.044 M does not affect the rate appreciably, sodium perchlorate at the same concentration depresses the rate significantly. Most measurements were made in the absence of electrolytes other than nickel perchlorate and a trace of perchloric acid. The second order rate constant is not significantly dependent on the nickel(II) concentration over a four-fold change in value indicating that the concentration of encounter pairs is small relative to the concentration of the free reactants. The rate constant at 25 °C (31 × 103 M−1 s−1)is consistent with a dissociative interchange mechanism and the rate constant for ethanol exchange on nickel. However, the value of ΔH≠ for the overall reaction (15.9 ± 1.0 kcal mol−1) is about 5 kcal mol−1 higher than that reported for ethanol exchange.

Kinetics of the Reaction of Nickel(II) and 2,2′-Bipyridine in Ethanol

1973 ◽  
Vol 51 (23) ◽  
pp. 3975-3977 ◽  
Author(s):  
M. L. Sanduja ◽  
W. MacF. Smith
Keyword(s):  
Kinetic Parameters ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Stopped Flow ◽  
Ligand Specificity ◽  
Temperature Range ◽  
Kinetics Of Formation ◽  
The Difference ◽  
Kinetics Of

The kinetics of formation of the monobipyridine complex of nickel(II) in ethanol has been studied with stopped-flow methods over the temperature range 7 to 35 °C. The value of the second order rate constant kf at 25 °C of 6.6 × 10−3M−1 s1 and the values of ΔH≠ (10.1 ± 1.0 kcal mol−1) and of ΔS≠ (−7.3 ± 3.4 cal deg−1 mol−1) are close to the corresponding values for ethanol exchange on nickel(II) and suggest that the mechanism is dissociative interchange. However the difference in the values of the kinetic parameters of this reaction and those previously reported for the reactions involving the chemically similar phenanthroline imply a degree of ligand specificity for the reactions in ethanol which is considerably larger than is the case for reactions in water and methanol and that a common Id mechanism with monodentate formation being rate controlling is not applicable to both reactions.

Kinetics of the anation reaction of nickel(II) and 1,10-phenanthroline in methanol–water mixtures

1969 ◽  
Vol 47 (20) ◽  
pp. 3773-3778 ◽  
Author(s):  
M. L. Sanduja ◽  
W. MacF. Smith
Keyword(s):  
Ionic Strength ◽  
Rate Constant ◽  
Rate Constants ◽  
Solvent Composition ◽  
Solvent Mixtures ◽  
Methanol Content ◽  
Dependent Rate ◽  
Kinetics Of Formation ◽  
Kinetics Of ◽  
Anation Reaction

The kinetics of formation of the monophenanthroline complex of nickel(II) has been studied spectrophotometrically in water–methanol mixtures of 0 to 97 weight % of methanol, at ionic strength 0.050, at varying acidities at 25 °C. Values for the rate constants for the acid independent and acid dependent reactions together with values for the equilibrium acid ionization quotient of phenanthrolium ion over the range of solvent mixtures have been determined. The values of the acid independent rate constant show little dependence on solvent compositions up to 76% methanol, then decrease and show no correlation with trends in the ionization quotient of phenanthrolium ion. The acid dependent rate constant shows only a modest dependence on solvent composition over most of the range of solvent compositions except in the range of highest methanol content where it is not significantly different from zero.

scholarly journals Kinetics of the interaction of chymotrypsin with eglin c

1991 ◽  
Vol 280 (1) ◽  
pp. 27-32 ◽  
Author(s):  
B Faller ◽  
J G Bieth
Keyword(s):  
Rate Constant ◽  
Proteinase Inhibitor ◽  
Enzyme Inhibitor ◽  
Order Rate Constant ◽  
Stopped Flow ◽  
First Order ◽  
Wide Range ◽  
Eglin C ◽  
Pseudo First Order ◽  
Kinetics Of

The kinetics of binding of recombinant eglin c to bovine pancreatic chymotrypsin was studied by conventional and stopped-flow techniques. With nanomolar enzyme and inhibitor concentrations, the inhibition was fast and pseudo-irreversible (k(assoc.) = 4 x 10(6) m-1.s-1 at 7.4 and 25 degrees C). Reaction of the enzyme-inhibitor complex with alpha 1-proteinase inhibitor, an irreversible chymotrypsin ligand, resulted in a slow release of free eglin c, which was monitored by electrophoresis (k(dissoc.) approximately 1.6 x 10(-6) s-1, t1/2 approximately 5 days). The proflavin displacement method and a stopped-flow apparatus were used to monitor the association of chymotrypsin with eglin c under a wide range of inhibitor concentration and under pseudo-first-order conditions. At pH 7.4 and 25 degrees C or 5 degrees C, or at pH 5.0 and 25 degrees C, the pseudo-first-order rate constant of proflavin displacement increased linearly with eglin c up to the highest concentration tested, suggesting a one-step bimolecular association reaction: E + I in equilibrium with EI. However, kassoc. is much lower than the rate constant for a bimolecular reaction and its activation energy (66 kJ.mol-1 at pH 7.4 and 78 kJ.mol-1 at pH 5.0) is far too high for a diffusion-controlled step. The enzyme-inhibitor association may therefore occur via a loose pre-equilibrium complex EI* (Ki* much greater than 5 x 10(-4) M) that rapidly isomerizes (k2 much greater than 2 x 10(3) s-1) into an extremely stable final complex (Ki approximately 4 x 10(-13) M). Unlike other proteinase-inhibitor systems, the chymotrypsin-eglin association is virtually pH-independent.

Water attack at an sp2 hybridized-carbon: the hydroxyl σ-complex of 4,6-dinitrobenzofuroxan in water–DMSO–tetramethylammonium chloride mixtures

1980 ◽  
Vol 58 (12) ◽  
pp. 1155-1160 ◽  
Author(s):  
François Terrier ◽  
Habib Achassi Sorkhabi ◽  
François Millot ◽  
Jean-Claude Halle ◽  
Robert Schaal
Keyword(s):  
Water Molecule ◽  
Water Content ◽  
Rate Constant ◽  
Fold Increase ◽  
Order Rate Constant ◽  
Solvent Mixtures ◽  
First Order ◽  
Tetramethylammonium Chloride ◽  
Kinetics Of Formation ◽  
Kinetics Of

The kinetics of formation and decomposition of the hydroxyl-σ adduct 2 derived from 4,6-dinitrobenzofuroxan 1 have been studied in various water – dimethylsulphoxide (DMSO) – tetramethylammonium chloride (I = 0.5 M) mixtures. At pH < 7, the formation of 2 occurs exclusively from water attack at the 7-carbon of 1. This process is strongly favored by DMSO: the first-order rate constant k1H2O changes from 1.9 × 10−2 s−1 in water to 1.33 s−1 in 90% DMSO. Taking into account the decrease in the water content of the solutions, and assuming that only one water molecule participates in the reaction, this increase in k1H2O reflects a 103-fold increase in the ability of a water molecule to act as a nucleophile. This interesting result compares well with previous data reported by Murto for the solvolysis of 2,4-dinitrofluorobenzene in the same solvent mixtures.

Oxidation of Nickel(II) and Manganese(II) by Peroxodisulfate in Aqueous Solution in the Presence of Molybdate. Crystal Structure of the (NH4)6[NiMo9O32].6H2O Product

1992 ◽  
Vol 45 (12) ◽  
pp. 1943 ◽  
Author(s):  
SJ Dunne ◽  
RC Burns ◽  
GA Lawrance
Keyword(s):  
Rate Constant ◽  
Linear Dependence ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
X Ray Diffraction ◽  
X Ray ◽  
First Order ◽  
Oxidant Concentration ◽  
Ph Range ◽  
Kinetics Of

Oxidation of Ni2+,aq, by S2O82- to nickel(IV) in the presence of molybdate ion, as in the analogous manganese system, involves the formation of the soluble heteropolymolybdate anion [MMogO32]2- (M = Ni, Mn ). The nickel(IV) product crystallized as (NH4)6 [NiMogO32].6H2O from the reaction mixture in the rhombohedra1 space group R3, a 15.922(1), c 12.406(1) � ; the structure was determined by X-ray diffraction methods, and refined to a residual of 0.025 for 1741 independent 'observed' reflections. The kinetics of the oxidation were examined at 80 C over the pH range 3.0-5.2; a linear dependence on [S2O82-] and a non-linear dependence on l/[H+] were observed. The influence of variation of the Ni/Mo ratio between 1:10 and 1:25 on the observed rate constant was very small at pH 4.5, a result supporting the view that the precursor exists as the known [NiMo6O24H6]4- or a close analogue in solution. The pH dependence of the observed rate constant at a fixed oxidant concentration (0.025 mol dm-3) fits dequately to the expression kobs = kH [H+]/(Ka+[H+]) where kH = 0.0013 dm3 mol-1 s-1 and Ka = 4-0x10-5. The first-order dependence on peroxodisulfate subsequently yields a second-order rate constant of 0.042 dm3 mol-1 s-1. Under analogous conditions, oxidation of manganese(II) occurs eightfold more slowly than oxidation of nickel(II), whereas oxidation of manganese(II) by peroxomonosulfuric acid is 16-fold faster than oxidation by peroxodisulfate under similar conditions.

Kinetic and Equilibrium Studies of the Reactions of Cyanide Ion with 1,3,5-Trinitrobenzene, 2,4,6-Trinitroanisole, and 2,4,6-Trinitrotoluene in Isopropanol

1974 ◽  
Vol 52 (1) ◽  
pp. 8-17 ◽  
Author(s):  
Leong Huat Gan ◽  
Albert Richard Norris
Keyword(s):  
Standard Enthalpy ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Stopped Flow ◽  
Cyanide Ion ◽  
Equilibrium Studies ◽  
Kinetics Of Formation ◽  
Kinetics Of

Equilibrium constants for the formation of 1:1 cyanide ion σ-complexes with 1,3,5-trinitrobenzene, 2,4,6-trinitroanisole, and 2,4,6-trinitrotoluene have been determined spectrophotometrically over a range of temperatures. Standard enthalpy (ΔH0) and entropy (ΔS0) changes associated with each reaction have been evaluated. The kinetics of formation of the σ-complexes have been investigated by means of a stopped-flow technique and the activation parameters characterizing the formation of each complex have been determined. Evidence is presented which indicates the cyanide ion – 2,4,6-trinitroanisole σ-complex formed in isopropanol contains the cyanide ion bonded exclusively at the C-3 position.

Kinetics of reconstitution of apotyrosinase by copper

1990 ◽  
Vol 68 (2) ◽  
pp. 476-479
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constant ◽  
Copper Concentration ◽  
Copper Ions ◽  
Copper Ion ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

Open-chain nitrogen compounds. Part XV. A kinetic study of the hydrolysis of 1-aryl-3-aryloxymethyl-3-methyltriazenes and related triazenes

1992 ◽  
Vol 70 (8) ◽  
pp. 2224-2233 ◽  
Author(s):  
Keith Vaughan ◽  
Donald L. Hooper ◽  
Marcus P. Merrin
Keyword(s):  
Rate Constant ◽  
Order Rate Constant ◽  
Buffer System ◽  
Open Chain ◽  
Nucleophilic Displacement ◽  
Ether Oxygen ◽  
Rate Of Hydrolysis ◽  
Electron Withdrawing Group ◽  
Ph Range ◽  
Kinetics Of

The kinetics of hydyrolysis of a series of 1-aryl-3-aryloxymethyl-3-methyltriazenes, Ar-N=N-NMe-CH2OAr′, was studied over the pH range 2–7.5. Reactions were followed by the change in UV absorbance spectra of the triazenes. The aryloxymethyltriazenes decompose more slowly at pH 7.5 than the hydroxymethyltriazenes, Ar-N=NMe-CH2OH; the hydrolysis is favoured by the presence of an electron-withdrawing group in Ar′. A mixed isopropanol/buffer system was developed in order to improve solubility of the aryloxymethyl triazenes. Lowering the pH caused an increase in the rate of hydrolysis and under strongly acidic conditions an electron-withdrawing group in Ar′ actually slows down the reaction. A Hammett plot of the pseudo-first-order rate constant, kobs, is curved, indicating that two or more mechanisms operate simultaneously and that the contribution of each mechanism is substituent-dependent. A plot of kobs vs. [buffer] is linear; the slope of the plot affords the rate constant, kb for the buffer-catalyzed reaction for each substituent. A Hammett plot of kb vs. σ is linear with ρ = +0.55, suggesting that the buffer-catalyzed reaction involves nucleophilic displacement of the phenoxy group by the buffer anion. Further analysis afforded the specific acid-catalyzed rate constants, [Formula: see text], for each substituent; this component of the reaction has a negative ρ, consistent with a mechanism involving protonation at the ether oxygen. The postulation that specific acid catalysis is a component of the reaction mechanism was confirmed by the observation of a solvent deuterium isotope effect, 2.28 > kH/kD > 1.60. Only the p-NO2 and p-CN phenyloxymethyltriazenes showed any spontaneous decomposition.

scholarly journals Kinetic studies on the nitrite reductase of Wolinella succinogenes

1986 ◽  
Vol 233 (2) ◽  
pp. 553-557 ◽  
Author(s):  
R Blackmore ◽  
T Brittain
Keyword(s):  
Rate Constant ◽  
Nitrite Reductase ◽  
Flash Photolysis ◽  
Spectral Characteristics ◽  
Order Rate Constant ◽  
Second Order ◽  
Stopped Flow ◽  
Dependent Manner ◽  
Wolinella Succinogenes ◽  
Order Rate

The six haem groups of the nitrite reductase enzyme isolated from Wolinella succinogenes are rapidly reduced by the addition of dithionite (S2O4(2-)). The reduction, however, is not homogeneous. Two of the haem groups, namely those that show spectral characteristics typical of five-co-ordinated haem groups, are reduced in a dithionite-concentration-dependent fashion with a rate limit of 1.5 S-1. The other four haem groups, which show spectral characteristics very similar to those of normal six-co-ordinate c-haem groups, reduce in a linear dithionite-concentration-dependent manner with a second-order rate constant of 150 M-1/2 X S-1. The ratio of the amplitudes of the two reduction phases observed in stopped-flow studies is found to be dependent on the concentration of dithionite used. A model is proposed to account for these observations, and computer simulations show that the model represents a good fit to the experimental data. The two haem groups with five-co-ordinate spectral characteristics bind CO. Flash photolysis of the CO complex exhibits one major recombination process with a linear dependence in rate on CO concentration with a second-order rate constant of 2 × 106 M-1 × S-1. By contrast, stopped-flow mixing of the reduced protein with CO shows a very complex pattern of combination, with most of the observed absorbance change associated with a concentration-independent step. These findings are rationalized in terms of structural changes in the protein consequent to ligand binding.

Studies on Horseradish Peroxidase. VII. A Kinetic Study of the Oxidation of Iodide by Horseradish Peroxidase Compound II

1971 ◽  
Vol 49 (18) ◽  
pp. 3059-3063 ◽  
Author(s):  
R. Roman ◽  
H. B. Dunford ◽  
M. Evett
Keyword(s):  
Ionic Strength ◽  
Horseradish Peroxidase ◽  
Kinetic Study ◽  
Rate Constant ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Acid Dissociation ◽  
Ph Range ◽  
Compound Ii ◽  
Kinetics Of

The kinetics of the oxidation of iodide ion by horseradish peroxidase compound II have been studied as a function of pH at 25° and ionic strength of 0.11. The logarithm of the second-order rate constant decreases linearly from 2.3 × 105 to 0.1 M−1 s−1 with increasing pH over the pH range 2.7 to 9.0. The pH dependence of the reaction is explained in terms of an acid dissociation outside the pH range of the study.

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