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.

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.

scholarly journals Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma

Blood ◽  
1990 ◽  
Vol 76 (3) ◽  
pp. 549-554
Author(s):  
J Pieters ◽  
T Lindhout ◽  
G Willems
Keyword(s):  
Unfractionated Heparin ◽  
Rate Constant ◽  
Calcium Ions ◽  
Order Rate Constant ◽  
Free Calcium ◽  
First Order ◽  
Factor Ixa ◽  
Factor Xia ◽  
Kinetics Of

Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.

Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 1. Polynuclear Hydroxyaluminum Cations

1971 ◽  
Vol 49 (10) ◽  
pp. 1683-1687 ◽  
Author(s):  
R. C. Turner ◽  
Wan Sulaiman
Keyword(s):  
Acetic Acid ◽  
Rate Constant ◽  
Empirical Equation ◽  
Decomposition Reaction ◽  
Order Rate Constant ◽  
Acetate Concentration ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Kinetics Of

The effect of varying 8-quinolinol and acetate concentration on the rate of decomposition of poly-nuclear hydroxyaluminum cations was studied. It was found that the concentration of the undissociated 8-quinolinol and acetic acid molecules determined the magnitude of the first order rate constant for the decomposition of the polynuclear hydroxyaluminum cations, except when the acetate concentrations were relatively high. With high acetate concentrations, it appeared that polynuclear acetate species were involved in the reactions. An empirical equation was developed showing the effect of 8-quinolinol and acetic acid molecule concentrations on the pseudo first order rate constant for the decomposition reaction.

Kinetics of Exchange of Dimethylsulfoxide between Hexakis(dimethylsulfoxide)chromium(III) and Solvent: Pressure Effect and Mechanism

1973 ◽  
Vol 51 (22) ◽  
pp. 3795-3798 ◽  
Author(s):  
Debra Lynn Carle ◽  
Thomas Wilson Swaddle
Keyword(s):  
Rate Constant ◽  
Pressure Effect ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

For the exchange of all six dimethylsulfoxide (DMSO) ligands in Cr(DMSO)63+ with perdeuterated DMSO solvent, the first-order rate constant (75°) = 5.5 × 10−5 s−1, while ΔH* = 23.1 kcal mol−1, ΔS* = − 11.8 cal deg−1 mol−1, and ΔV* = − 11.3 cm3 mol−1. These and other data are indicative of an associative interchange mechanism for substitution in Cr(III) DMSO complexes in DMSO.

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 Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma

Blood ◽  
1990 ◽  
Vol 76 (3) ◽  
pp. 549-554 ◽  
Author(s):  
J Pieters ◽  
T Lindhout ◽  
G Willems
Keyword(s):  
Unfractionated Heparin ◽  
Rate Constant ◽  
Calcium Ions ◽  
Order Rate Constant ◽  
Free Calcium ◽  
First Order ◽  
Factor Ixa ◽  
Factor Xia ◽  
Kinetics Of

Abstract Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.

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.

Kinetics of halogen substituted aniline transformation in anaerobic estuarine sediment

1996 ◽  
Vol 34 (7-8) ◽  
pp. 37-43 ◽  
Author(s):  
Sridhar Susarla ◽  
Shigeki Masunaga ◽  
Yoshitaka Yonezawa
Keyword(s):  
Rate Constant ◽  
Halogen Bond ◽  
Order Rate Constant ◽  
Quantitative Structure Activity Relationship ◽  
Estuarine Sediment ◽  
Substituted Anilines ◽  
First Order ◽  
The Relationship ◽  
Steric Constant ◽  
Kinetics Of

The kinetics of halogen substituted anilines were examined in estuarine sediment collected from Tsurumi river, Japan. Aniline was substituted with F, Cl, Br and I groups at meta or para positions on the aromatic ring. The transformation of all the compounds followed a first-order reaction kinetics with rate constants for the disappearance ranging between 0.002 to 0.006 day−1 or half lives between 108 and 669 days. Results indicated that para substituted anilines transformed two to four times faster compared to meta substituted ones. The rate of transformation followed the order: I &gt; Br &gt; Cl &gt; F. A quantitative structure-activity relationship was evaluated relating the first-order rate constant in sediment with several readily available molecular descriptors: carbon-halogen bond strength, Hammett sigma constants, Taft steric constant, and Lipophilic constant. In addition octanol/water partition coefficients and solubility were included in the correlation. The relationship obtained was only significant between the rate constant and lipophilic constant.

Article

1999 ◽  
Vol 77 (5-6) ◽  
pp. 1005-1008
Author(s):  
Ayla Khan ◽  
Alexei A Neverov ◽  
Anatoly K Yatsimirsky ◽  
R S Brown
Keyword(s):  
Rate Constant ◽  
Metal Ion ◽  
Order Rate Constant ◽  
Water Proton ◽  
First Order ◽  
Catalytic Rate Constant ◽  
Equilibrium Binding ◽  
Metal Ion Catalysis ◽  
Kinetics Of ◽  
Hydrolysis Of

The kinetics of methanolysis of acetyl imidazole (1) and acetyl pyrazole (2) have been investigated under anhydrous conditions in the presence of Zn(ClO4)2, Co(ClO4)2, and HClO4 at 25°C. In all cases, the plots of the pseudo-first-order rate constant for methanolysis (kobs) vs. [metal ion] or [HClO4] show saturation behavior indicative of equilibrium binding of the M2+ or H+ to the amide. Relative to the spontaneous methanolysis rate constant (ko), the catalytic rate constant obtained at saturation, kcat, is larger for metal-ion catalysis than for H+ catalysis. The (kcatH+/ko) ratio is 10.7 and 1.25 for 1 and 2, respectively, while the (kcatM2+/ko) for these divalent metals varies from 150-fold for 1 to between 700 and 5700-fold for 2. By contrast, in water, proton is far more effective at promoting the hydrolysis of 1 than are metals, the aqueous (kcatH+/ko) ratio being 560, while the (kcatZn2+ /ko) and (kcatNi2+/ko) ratios are 15 and 3.2, respectively.Key words: methanolysis, kinetics, metal-ion catalysis, acetyl imidazole, acetyl pyrazole.

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