Solvent Effects on the Racemization of Optically Active Tris(N-substituted carbamodithioato)cobalt (III) Complexes

1979 ◽  
Vol 32 (8) ◽  
pp. 1653 ◽  
Author(s):  
LR Gahan ◽  
MJ O'Conner
Keyword(s):  
Carbon Tetrachloride ◽  
Solvent Effects ◽  
Reaction Mechanisms ◽  
Activation Parameters ◽  
Optically Active ◽  
Isokinetic Relationship ◽  
First Order ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Wide Range

The thermal racemization in solution of some optically active tris(N-substituted carbamodithioato)- cobalt(III) complexes [N-substituents = diphenyl, dimethyl, diisopropyl, and tetramethylene (pyrrolidinyl)] has been measured polarimetrically in a range of solvents including dimethylformamide, acetonitrile, carbon tetrachloride, chlorobenzene, chloroform, toluene and ethanol. The metal-centred (Δ ↔ Λ) inversion reactions show first-order kinetics as expected for an intra- molecular process. Thermodynamic activation parameters for the reaction show that values of ΔS‡ occur over a wide range (from -124 to +60 J K-1 mol-1) as do the values of ΔH‡ (from 67�4 to 129�3 kJ mol-1). Values for ΔG‡ are reasonably constant. Although a similar mechanism for the metal-centred inversion is suggested for all compounds in the various solvents because of an observed isokinetic relationship between ΔH‡ and ΔS‡, with isokinetic temperatures in the range 312-369 K, it is clear that postulates of reaction mechanisms based on the value of ΔS‡ determined in only one solvent should be treated with caution. The optically active (-)546-tris(N,N-diisopropylcarbamodithioato)cobalt(III) complex photoracemizes in solution without decomposition. The rate of photoracemization is solvent-dependent being in the order bromoform � carbon tetrachloride ≈ chloroform �benzene.

scholarly journals Effect of heparin on thrombin inactivation by antithrombin-III

1978 ◽  
Vol 173 (3) ◽  
pp. 869-875 ◽  
Author(s):  
R Machovich ◽  
P Arányi
Keyword(s):  
Antithrombin Iii ◽  
Specific Activity ◽  
Activation Parameters ◽  
Heat Inactivation ◽  
Activation Entropy ◽  
First Order ◽  
Heparin Concentration ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Time Courses

The inactivation of thrombin by heat and by its physiological inhibitor, antithrombin-III, shows quite different dependence on heparin concentration. Heparin at 250 microgram/ml protects thrombin against heat inactivation, and thrombin behaves heterogeneously in this reaction. In the absence of heparin, the thermodynamic activation parameters change with temperature (deltaH+ = 733 kJ/mol and 210 kJ/mol at 50 and 58 degrees C respectively). When heparin is present, heat inactivation of the protected thrombin species proceeds with deltaH+ = 88 kJ/mol and is independent of temperature in the same range. On the other hand, heparin at 0.125-2.5 microgram/ml accelerates the thrombin-antithrombin-III reaction. Thrombin does not show heterogeneity in this reaction and the time courses at any heparin concentration and any temperature between 0 and 37 degrees C appear to follow first-order kinetics. Activation enthalpy is independent of heparin concentration or temperature, deltaH+ = 82-101 kJ/mol, varying slightly with antithrombin-III concentration and thrombin specific activity. Heparin seems to exert its effect by increasing activation entropy. On the basis of these data we suggest a mechanism of action of heparin in the thrombin-antithrombin-III reaction which accounts for all the important features of the latter and seems to unify the different hypotheses that have been advanced.

Thermolysis of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones in solution. Products, kinetics, substituent effects, and solvent effects

1981 ◽  
Vol 59 (1) ◽  
pp. 100-105 ◽  
Author(s):  
Lubomira M. Cabelkova-Taguchi ◽  
John Warkentin
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Charge Separation ◽  
Substituent Effects ◽  
Activation Parameters ◽  
Oxidative Cyclization ◽  
First Order ◽  
Temperature Range ◽  
Aryl Amine ◽  
First Order Kinetics

A series of 5,5-dimethyl-4-aryl-Δ1-1,2,4-triazolin-3-ones (Ar = C6H5, p-C6H4CH3, p-C6H4OCH3, p-C6H4Cl, and p-C6H4Br) were prepared from the corresponding 4-arylsemicarbazones of acetone by oxidative cyclization on alumina. The triazolinones decompose in solution to N2, CO, and isopropylidene aryl amine, with first order kinetics, in the temperature range 148–200 °C. Average activation parameters are ΔH≠ = 35 kcal mol−1 and ΔS≠ = 8 cal K−1 mol−1. Substituent effects are correlated through σ-constants but the thermolyses are relatively insensitive to substituents, with ρ = −0.17 at 172.5 °C. Solvent effects indicate a transition state that is less polar than the ground state.It is tentatively concluded that the triazolinone fragmentation, like the analogous thermolysis of a Δ3-1,3,4-oxadiazolin-2-one, may be a fully-concerted but nonsynchronous process with a transition state involving little, if any, charge separation. Other mechanisms, except for those involving highly polar (e.g. zwitterionic) transition states, have not been ruled out.

scholarly journals A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate

2019 ◽  
Vol 8 (1) ◽  
pp. 719-729 ◽  
Author(s):  
Abdul Rehman ◽  
M.F.M. Gunam Resul ◽  
Valentine C. Eze ◽  
Adam Harvey
Keyword(s):  
Propylene Carbonate ◽  
Styrene Oxide ◽  
Activation Parameters ◽  
Green Solvent ◽  
Acid Base ◽  
First Order ◽  
First Order Kinetics ◽  
Thermodynamic Activation Parameters ◽  
Styrene Carbonate ◽  
Comprehensive Study

Abstract Synthesis of styrene carbonate (SC) via the fixation of CO2 with styrene oxide (SO) has been investigated using a combination of zinc bromide (ZnBr2) and tetrabutylammonium halides (TBAX) as acid-base binary homogeneous catalysts. The combination of ZnBr2 and TBAB had a synergistic effect, which led to about 6-fold enhancement in the rate of SC formation as compared to using TBAB alone as a catalyst. Propylene carbonate (PC) was chosen as a green solvent for a comprehensive study of reaction kinetics. The reaction followed a first-order kinetics with respect to SO, CO2, and TBAB, whereas a fractional order was observed for the ZnBr2 when used in combination with the TBAB. Arrhenius and Eyring’s expressions were applied to determine the kinetic and thermodynamic activation parameters, where activation energy (Ea) of 23.3 kJ mol−1 was obtained for the SC formation over the temperature range of 90-120°C. The thermodynamic analysis showed that positive values for enthalpy (ΔH‡ = 18.53 kJ mol−1), Gibbs free energy (ΔG‡ = 79.74 kJ mol−1), whereas a negative entropy (ΔS‡ = –162.88 J mol−1 K−1) was obtained. These thermodynamic parameters suggest that endergonic and kinetically controlled reactions were involved in the formation of SC from SO and CO2.

Kinetics of the acid-catalysed hydration of prop-2-en-1-ol. Evidence for a free, ion-dipole intermediate in the heterolysis of propane-1,2-diol

1982 ◽  
Vol 35 (11) ◽  
pp. 2221 ◽  
Author(s):  
KP Herlihy
Keyword(s):  
Activation Parameters ◽  
Optically Active ◽  
First Order ◽  
Aqueous Acid ◽  
First Order Kinetics ◽  
Pinacol Rearrangement ◽  
Free Ion ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Good Agreement

Prop-2-en-1-ol in aqueous acid solution gives propane-1,2-diol and propanal. At 100�C the amount of diol in this product ratio is found to decrease from 65% in 1 M HClO4 to 50% in 4 M HClO4. Pseudo-first-order kinetics are found to apply. The values obtained for the activation parameters, Ea and ΔS‡ and for a Hammett acidity plot, are similar to results reported for other alkenes. The relative rates of partitioning between regeneration of the substrate and rearrangement for the pinacol rearrangement of optically active propane-1,2-diol have been calculated previously. When these are compared with product ratios obtained from the hydration of prop-2-en-1-ol, good agreement is found between the respective values if it is assumed that the regenerated substrate has undergone complete racemization of configuration. This is interpreted to be evidence for a short-lived, but free ion-dipole as the intermediate in the heterolysis of propane-1,2-diol.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

The kinetics and the mechanism of oxidative decarboxylation of benzilic acid by acidic permanganate (stopped-flow technique) — An autocatalytic study

2004 ◽  
Vol 82 (9) ◽  
pp. 1372-1380 ◽  
Author(s):  
Sairabanu A Farokhi ◽  
Sharanappa T Nandibewoor
Keyword(s):  
Activation Parameters ◽  
Oxidative Decarboxylation ◽  
Two Stage ◽  
First Order ◽  
First Order Kinetics ◽  
Stage Process ◽  
Benzilic Acid ◽  
Reaction Constants ◽  
Kinetics Of ◽  
Good Agreement

The kinetics of the oxidation of benzilic acid by potassium permanganate in an acidic medium were studied spectrophotometrically. The reaction followed a two-stage process, wherein both stages of the reaction followed first-order kinetics with respect to permanganate ion and benzilic acid. The rate of the reaction increased with an increase in acid concentration. Autocatalysis was observed by one of the products, i.e., manganese(II). A composite mechanism involving autocatalysis has been proposed. The activation parameters of the reaction were calculated and discussed and the reaction constants involved in the mechanisms were calculated. There is a good agreement between the observed and calculated rate constants under different experimental conditions.Key words: oxidation, autocatalysis, benzilic acid, two-stage kinetics.

scholarly journals Purification and properties of a stable β-glucosidase from an extremely thermophilic anaerobic bacterium

1987 ◽  
Vol 243 (3) ◽  
pp. 779-787 ◽  
Author(s):  
M L Patchett ◽  
R M Daniel ◽  
H W Morgan
Keyword(s):  
Anaerobic Bacterium ◽  
Thermal Inactivation ◽  
First Order ◽  
First Order Kinetics ◽  
Purification And Properties ◽  
Wide Range ◽  
Optimum Ph ◽  
Exclusion Chromatography ◽  
Beta Glucosidase ◽  
Beta Galactosidase

A beta-glucosidase (EC 3.2.1.21) was purified to homogeneity from cell-free extracts of an extremely thermophilic anaerobic bacterium. The enzyme has an Mr of 43,000 as determined by molecular-exclusion chromatography, has a pI of 4.55 and shows optimum activity at pH 6.2. The enzyme is active against a wide range of aryl beta-glycosides and beta-linked disaccharides, with beta-galactosidase activity only slightly less than beta-glucosidase activity, and significant beta-xylosidase activity. Lineweaver-Burk plots for p-nitrophenyl beta-glucoside, o-nitrophenyl beta-glucoside and cellobiose substrates are biphasic concave-downwards. Inhibition of the beta-glucosidase by substrates and glucose is negligible. Thermal inactivation follows first-order kinetics, with t1/2 (65 degrees C) 45 h, t1/2 (75 degrees C) 47 min and t1/2 (85 degrees C) 1.4 min and a deactivation energy of 380 kJ/mol at pH 6.2. At pH 7.0, which is the optimum pH for thermostability, t1/2 (75 degrees C) is 130 min. At 75 degrees C, at pH 6.2, the thermostability is enhanced about 8-fold by 10% (w/v) glycerol, about 6-fold by 0.2 M-cellobiose and about 3-fold by 5 mM-dithiothreitol and 5 mM-2-mercaptoethanol.

scholarly journals Kinetics and Mechanism of Oxidation of Diethanolamine and Triethanolamine by Potassium Ferrate

2011 ◽  
Vol 8 (2) ◽  
pp. 903-909 ◽  
Author(s):  
Shan Jinhuan ◽  
Zhang Jiying
Keyword(s):  
Activation Parameters ◽  
Rate Equations ◽  
Potassium Ferrate ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Order Dependence ◽  
Rate Determining Step ◽  
Thermodynamic Activation Parameters ◽  
Plausible Mechanism ◽  
Kinetics Of

The kinetics of oxidation of diethanolamine and triethanolamine by potassium ferrate(VI)in alkaline liquids at a constant ionic strength has been studied spectrophotometrically in the temperature range of 278.2K-293.2K. The reaction shows first order dependence on potassium ferrate(VI), first order dependence on each reductant, The observed rate constant (kobs) decreases with the increase in [OH-], the reaction is negative fraction order with respect to [OH-]. A plausible mechanism is proposed and the rate equations derived from the mechanism can explain all the experimental results. The rate constants of the rate-determining step and the thermodynamic activation parameters are calculated.

scholarly journals KINETICS OF REACTION BETWEEN MALACHITE GREEN AND HYDROXYL ION IN THE PRESENCE OF REDUCING SUGARS

2015 ◽  
Vol 23 (23) ◽  
pp. 61-72
Author(s):  
Dayo Felix Latona ◽  
Adewumi Oluwasogo Dada
Keyword(s):  
Malachite Green ◽  
Activation Parameters ◽  
Cell Compartment ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Hydroxyl Ion ◽  
Kinetics Of Reaction ◽  
Kinetics Of ◽  
Sphere Mechanism

The reaction was studied via pseudo-first-order kinetics using a UV-1800 Shimadzu spectrophotometer with a thermostated cell compartment and interfaced with a computer. The reaction showed first order with respect to malachite green and sugar and hydroxyl ion concentrations. However, the reaction was independent of ionic strength and showed no dependence on the salt effect, indicating an inner sphere mechanism for the reaction. There was no polymerization of the reaction mixture with acrylonitrile, indicating the absence of radicals in the course of the reaction. Michaelis-Menten plot indicated the presence of a reaction intermediate in the rate-determining step. The activation parameters of the reaction have been calculated and products were elucidated by FTIR spectroscopy. The stoichiometry of the reaction is 1:1. A mechanism consistent with the above facts has been suggested.

Substituent and solvent effects on the reaction between 2,6-Di-t-butyl-α-(3,5-di-t-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)-p-tolyloxyl (galvinoxyl) and phenols

1978 ◽  
Vol 31 (6) ◽  
pp. 1201 ◽  
Author(s):  
N Nishimura ◽  
K Okahashi ◽  
T Yukutomi ◽  
A Fujiwara ◽  
S Kubo
Keyword(s):  
Carbon Tetrachloride ◽  
Binary Mixtures ◽  
Solvent Effects ◽  
Rate Constants ◽  
Isotope Effects ◽  
Mixed Solvents ◽  
Transition States ◽  
Activation Parameters ◽  
Substituted Phenols ◽  
Kinetic Behaviour

Rate constants and associated activation parameters for the reaction of galvinoxyl with substituted phenols were obtained in carbon tetrachloride and in cyclohexane-dioxan binary mixtures. Substantial isotope effects were observed for O-deuterated phenols. The rate constants are correlated with σ+ values. These findings are discussed by considering the polar contribution of substituents to the stabilization of the transition states. In the mixed solvents, the kinetic behaviour is well expressed by the equations which are based on the theory of Kondo and Tokura.

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