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 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.

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.

The homogeneous decomposition reactions of gaseous formic acid

1960 ◽  
Vol 255 (1283) ◽  
pp. 444-455 ◽  
Keyword(s):  
Formic Acid ◽  
Kinetic Parameters ◽  
Rate Constant ◽  
Ion Pairs ◽  
Order Rate Constant ◽  
Second Order ◽  
Unimolecular Decomposition ◽  
Order Component ◽  
First Order ◽  
Homogeneous Decomposition

By use of reaction vessels with specially treated surfaces the homogeneous decomposition of formic acid has been studied kinetically in the range 436 to 532°C. Neither of the two simultaneous reactions ( a ) HCOOH = CO 2 + H 2 , ( b ) HCOOH = CO + H 2 O, is retarded by the usual inhibitors of chain processes. Each appears to be molecular. Reaction ( a ) is of the first order in the range 3 to 650 mm, the first-order rate constant being given by k CO 2 = 10 4⋅8 exp (–30600/ RT )s -1 . It is suggested tentatively that the abnormal kinetic parameters might be explained by regarding the reaction as a decarboxylation of (H + ) (HCOO¯) ion pairs present in minute concentration. Reaction ( b ) shows a pressure dependence most simply explained by a superposition of a predominant second-order component with a small first-order component. The most satisfactory interpretation of the second-order reaction is that it represents the unimolecular decomposition of dimer molecules, known to be present in formic-acid vapour. On this basis the rate constant is given by k CO dimer = 10 13⋅58 exp (–42600/ RT )s -1 , the kinetic parameters thus being in the normal range. The various alternative interpretations are discussed.

Studies on Horseradish Peroxidase. XI. On the Nature of Compounds I and II as Determined from the Kinetics of the Oxidation of Ferrocyanide

1973 ◽  
Vol 51 (4) ◽  
pp. 582-587 ◽  
Author(s):  
M. L. Cotton ◽  
H. B. Dunford
Keyword(s):  
Horseradish Peroxidase ◽  
Rate Constant ◽  
Active Sites ◽  
Ph Dependence ◽  
Order Rate Constant ◽  
Second Order ◽  
Compound I ◽  
Order Rate ◽  
Compound Ii ◽  
Kinetics Of

In order to investigate the nature of compounds I and II of horseradish peroxidase, the kinetics were studied of ferrocyanide oxidation catalyzed by these compounds which were prepared from three different oxidizing agents. The pH dependence of the apparent second-order rate constant for ferrocyanide oxidation by compound I, prepared from ethyl hydroperoxide and m-chloroperbenzoic acid, was interpreted in terms of an ionization on the enzyme with a pKa = 5.3, identical to that reported previously for hydrogen peroxide. The second-order rate constant for the compound II-ferrocyanide reaction also showed the same pH dependence for the three oxidizing substrates. However, with more accurate results, the compound II-ferrocyanide reaction was reinterpreted in terms of a single ionization with pKa = 8.5. The same dependence of ferrocyanide oxidation on pH suggests structurally identical active sites for compounds I and II prepared from the three different oxidizing substrates.

THE KINETICS OF THE CHELATION OF NICKEL (II) AND 1,10-PHENANTHROLINE

1964 ◽  
Vol 42 (4) ◽  
pp. 934-940 ◽  
Author(s):  
P. F. Barrett ◽  
W. MacF. Smith
Keyword(s):  
Ionic Strength ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Second Order ◽  
Hydrogen Ion ◽  
Kinetic Behavior ◽  
Ion Concentrations ◽  
Order Rate ◽  
Kinetics Of ◽  
Limiting Values

The kinetics of the formation of the bidentate monocomplex of 1,10-phenanthroline and nickel (II) have been examined spectrophotometrically at ionic strength 0.5 over the range of temperatures 8 to 37 °C and over the range of hydrogen ion concentrations 0.01 to 0.30 molar. The kinetic behavior over the range of conditions is consistent with that found at 25 °C by Margerum, Bystroff, and Banks. The limiting values for the second-order rate constant for the reaction at high acidities have been assessed and imply associated values of ΔH≠and ΔS≠ of 9.5 kcal mol−1 and −5.3 e.u. respectively.

Effect of Thrombomodulin on the Molecular Recognition and Early Catalytic Events in Thrombin-Protein C Interaction

1996 ◽  
Vol 76 (04) ◽  
pp. 556-560 ◽  
Author(s):  
Raimondo De Cristofaro
Keyword(s):  
Molecular Recognition ◽  
Perturbation Method ◽  
Rate Constant ◽  
Protein C ◽  
Order Rate Constant ◽  
Second Order ◽  
Concentration Addition ◽  
Order Rate ◽  
C Complex ◽  
Kinetics Of

SummaryA viscosity perturbation method allowed to compute the second order rate constant, k±15 for the formation of thrombin-Protein C complex, both in the absence and presence of thrombomodulin (TM) at pH 8.00 and 37° C. In the absence of TM the second order rate constant was found equal to 7.9 ± 0.6 × 103 M-1 sec-1, whereas it was enhanced to 9.9 ± 0.4 × 104 M-1 s-1 by a saturating (100 nM) TM concentration. Addition of 5 mM Ca++ to solution containing 100 nM TM induced a further increase of k+1 value up to 7.3 ± 0.5 × 105 M-1 s-1. Moreover, it was demonstrated that the thrombin-PC complex undergoes the acy-lation reaction more rapidly than it dissociates to form free thrombin and substrate (stickiness ratio = 2.4 ± 0.9). This tendency is even favored when thrombin is bound to TM both in the absence and presence of Ca++ (stickiness ratio = 9 ± 6 in the absence of Ca++ and 16 ± 10 in the presence of Ca++). Altogether these results demonstrate that TM is able to positively affect both the molecular encounter and the kinetics of the early catalytic events of the thrombin-Protein C interaction.

The kinetics of formation of ruthenium(II) nitrogen complexes

1970 ◽  
Vol 48 (11) ◽  
pp. 1639-1644 ◽  
Author(s):  
Clive M. Elson ◽  
I. J. Itzkovitch ◽  
John A. Page
Keyword(s):  
Activation Energy ◽  
Order Rate Constant ◽  
Second Order ◽  
Kcal Mole ◽  
Potential Reduction ◽  
First Order ◽  
Kinetics Of Formation ◽  
Controlled Potential ◽  
Kinetics Of ◽  
Electrolyte Ph

The formation of nitrogen monomers by the reaction of Ru(NH3)5(H2O)2+ and cis-Ru(NH3)4(H2O)22+ with N2 has been shown to be first order in N2 and second order overall. The formation of bridging N2 dimers by the reaction of the ruthenium(II) pentaammine and tetraammine with the monomers has been shown to be second order overall.The reactions were studied in a H2SO4–K2SO4 electrolyte pH 3.3, μ = 0.30. The ruthenium(II) species were prepared by controlled potential reduction of known ruthenium(III) species at −0.50 V at a Hg cathode. The reactions of the reduced species with N2 or the monomers were followed spectrophotometrically.The second order rate constant at 25 °C and the activation energy for the substrate Ru(NH3)5(H2O)2+ with the respective nucleophiles are: N2, 8.0 × 10−2 M−1 s−1, 22.0 ± 0.1 kcal/mole; Ru(NH3)5N22+, 3.6 × 10−2 M−1 s−1, 19.9 ± 0.5 kcal/mole; Ru(NH3)4(H2O)N22+, 2.7 × 10−2 M−1 s−1, 20.4 ± 0.8 kcal/mole. For the substrate cis-Ru(NH3)4(H2O)22+ the values are: N2, 1.0 × 10−1 M−1 s−1, 20.4 ± 0.2 kcal/mole; Ru(NH3)5N22+, 6.8 × 10−2 M−1 s−1, 18.2 ± 0.1 kcal/mole; Ru(NH3)4(H2O)N22+, 7.2 × 10−2 M −1 s−1, 17.1 ± 0.2 kcal/mole.

scholarly journals Kinetics of the reaction of thrombin and α2-macroglobulin

1985 ◽  
Vol 231 (2) ◽  
pp. 417-423 ◽  
Author(s):  
R D Feinman ◽  
A I Yuan ◽  
S R Windwer ◽  
D Wang
Keyword(s):  
Rate Constant ◽  
Gel Electrophoresis ◽  
Bond Formation ◽  
Covalent Bond ◽  
Thiol Group ◽  
Order Rate Constant ◽  
Second Order ◽  
Order Rate ◽  
Covalent Bond Formation ◽  
Kinetics Of

The kinetics of the reaction of alpha 2-macroglobulin (alpha 2M) with human thrombin were studied by recording the appearance of thiol groups spectrophotometrically and by measuring the distribution of protein species by denaturing non-reducing gel electrophoresis. The goals were to study the relation between the formation of various covalent enzyme-inhibitor complex species and the appearance of free thiol, and from the kinetic analysis, to try to characterize the chemical nature of the protein complexes. The kinetics of thiol-group release were observed to be biphasic, the early phase showing second-order behaviour, results consistent with previous reports in the literature. The observed second-order rate constant for thiol-group release was found to be faster than the second-order rate constant for the disappearance of the band corresponding to native alpha 2M on gel electrophoresis. This may be a reflection of the multiple products formed from the thioester. Alternatively, it is possible that covalent-bond formation is slower than some enzyme-induced change in the thioester centre, and this may be suggestive evidence for a reactive alpha 2M centre that does not contain an intact thioester. The kinetics of covalent-bond formation were found to be consistent with the internal cross-link of several alpha 2M chains by the bound proteinase, providing further evidence that the very-high-Mr species seen on gels may arise from dimers of the alpha 2M molecule held together by covalent bonds to the enzyme.

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.

Kinetics and Mechanism of the Cleavage of N-Phthaloylglycine in Buffers of Some Primary Amines

2002 ◽  
Vol 2002 (12) ◽  
pp. 593-595 ◽  
Author(s):  
M. Niyaz Khan ◽  
Norsaadah H. Ismail
Keyword(s):  
Kinetic Parameters ◽  
Rate Constant ◽  
Kinetic Studies ◽  
Order Rate Constant ◽  
Second Order ◽  
Kinetics And Mechanism ◽  
Primary Amines ◽  
Buffer Concentration ◽  
Nucleophilic Cleavage ◽  
The Relationship

Kinetic studies on the nucleophilic cleavage of N-phthaloylglycine (NPG) in buffers of 2-methoxyethylamine, and 2-hydroxyethylamine reveal the relationship: knapp = A1 [Am]T/(1 + A2 [Am]T) where A1 and A2 are constants (kinetic parameters) and knapp and [Am]T represent apparent nucleophilic second-order rate constant and total amine buffer concentration, respectively.

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