Rate constants for reactions in viscous media: correlation between the viscosity of the solvent and the rate constant of the diffusion-controlled reactions

1988 ◽  
Vol 110 (14) ◽  
pp. 4494-4502 ◽  
Author(s):  
Andres F. Olea ◽  
J. K. Thomas
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Diffusion Controlled ◽  
Viscous Media

scholarly journals A Two-part Approach to the Determination of Intrinsic Rate Constants of an Alpha-amylase Catalysed Reaction

2020 ◽  
pp. 8-21
Author(s):  
Ikechukwu I. Udema
Keyword(s):  
Rate Constant ◽  
Rate Constants ◽  
Catalytic Efficiency ◽  
Intrinsic Rate ◽  
Product Formation ◽  
Intermolecular Potential ◽  
Diffusion Controlled ◽  
Quantitative Results ◽  
Intrinsic Rate Constant

Background: There is a need for equations with which to calculate the intrinsic rate constants that can further characterise enzyme catalysed reactions despite what seems to be conventional differences in methodology in the literature. Methods: Theoretical, experimental (Bernfeld method), and computational methods. Objectives: 1) To derive an alternative intrinsic rate constant equations consistent with their dimension, 2) derive electrostatic intermolecular potential energy equation, (xe), 3) calculate the intrinsic rate constants for forward (k1) and reverse (k2) reactions, and 4) define the dependence or otherwise of kinetic constants on diffusion and deduce the catalytic efficiency. Results and Discussion: The ultimate quantitative results were ~ 64.69 ±  0.49 exp (+3)/ min (k2) (and kd (s) = ~ 60.66 exp (+3)/ min), ~ 1594.48 ± 11.99 exp (+3) exp (+3) L/mol.min (k1) (and ka (s) = ~1482.47 exp (+3) L/mol.min), ~ 58.00 ± 10.83 exp (+3) /min, the apparent rate constant for reverse reaction (kb), and ~ 75.83 ± 10.83 exp (+3) /min, the rate constant for product formation (k3). The catalytic efficiency was: 3.025 exp (+ 9) L / mol.     Conclusion: The relevant equations were derived. Based on the derived equations the intrinsic rate constants can be calculated. Since k3 is > kb, then k3 is diffusion controlled and it appears that the enzyme has reached kinetic perfection. The evaluation of rate constants either from the perspective of diffusion dependency or independency cannot be valid without Avogadro number.

Kinetics of oxidation of Cu(I) complexes of cysteine and penicillamine: nature of intermediates and reactants at pH 10.0

1989 ◽  
Vol 67 (4) ◽  
pp. 736-745 ◽  
Author(s):  
Stephen P. Mezyk ◽  
David A. Armstrong
Keyword(s):  
Equilibrium Constant ◽  
Rate Constant ◽  
Rate Constants ◽  
Slow Component ◽  
Mixed Valence ◽  
Planar Geometry ◽  
Published Data ◽  
Diffusion Controlled ◽  
Square Planar ◽  
Thiolate Ligand

The Cu(I)•L2 complex with cysteine ligands at total Cu(I) concentrations of 10–30 μM was shown to be oxidised by cysteinyl radicals (RS•) with a diffusion-controlled rate constant k11a = 1.8 × 109 M−1 s−1. The corresponding reaction with the cysteine disulphide anion (RS•—SR−) proceeded at a slower rate, k11b = 2.7 × 108 M−1s−1. At higher Cu(I) concentrations, a slow and a fast component of absorption growth was observed. The slow component rate was independent of Cu(I) concentration, but it became more intense as the Cu(I) concentration rose. The yields and kinetic data were shown to be consistent with the presence of an equilibrium between the Cu(I)•L2 species and a second Cu(I) complex, Cu(I)2•L3, with an equilibrium constant of K1 = 162.[Formula: see text]This finding is consistent with the earlier work of Bagiyan etal. The rate constant of the oxidation of Cu(I)2•L3 by the cysteinyl radical was k12 = 1.0 × 109 M−1 s−1. Similar results were obtained with penicillamine, except the rate constants and equilibrium constant were smaller, (k11a = 4.5 × 108 M−1 s−1, k11b < 2 × 108 M−1 s−1, k12 = 5.5 × 108 M−1 s−1 and K1 = 113). This was attributed to the presence of the β-methyl groups in penicillamine, which exert a large steric effect.The ultraviolet spectra of the long-lived products, which are stable on a millisecond timescale, was consistent with a Cu(II)•L2 structure with a square planar geometry. The oxidation of the Cu(I)2.L3 species proceeded via intermediates, which relaxed to the final product spectra with rate constants of k13b = 2.6 and 1.1 × 104 s−1 for cysteine and penicillamine, respectively. Comparison of the spectra of the intermediates with published data showed that they were consistent with the presence of a bridging thiolate ligand between Cu(I) and Cu(II). Keywords: oxidation, copper, mixed valence, cysteine, penicillamine, complexation.

Diffusion studies in viscous media

1965 ◽  
Vol 284 (1396) ◽  
pp. 9-16 ◽  
Keyword(s):  
Rate Constants ◽  
Sliding Friction ◽  
Liquid Paraffin ◽  
High Oxygen Concentration ◽  
Solvent Viscosity ◽  
Diffusion Controlled ◽  
Coefficient Of Sliding Friction ◽  
Diffusion Studies ◽  
Viscous Media ◽  
Quenching By Oxygen

The rate constants of quenching of the triplet state of naphthalene by α -iodonaphthalene, t -butyl hydroperoxide and oxygen have been studied in several solvents as a function of viscosity and temperature. The diffusion controlled rate constants for α -iodonaphthalene in hydroxylic media agree with those predicted by the equation k calc. = 8 RT /2000 ƞ ( ƞ being viscosity). This is interpreted as evidence for the validity of the Stokes‒Einstein expression, Stoke’s law with ‘slip’ (i. e. coefficient of sliding friction zero) being used for diffusing species comparable in size to the molecules comprising the medium. In liquid paraffin/ n -hexane mixtures, the ratio k obs : k calc. became progressively larger as the proportion of liquid paraffin n -hexane was increased and in 100% liquid paraffin the ratio was 4·5. This is interpreted as being due to breakdown of the Stokes‒Einstein expression in cases where the diffusing species is small compared with the molecules of the solvent. The observed rate constant for quenching by oxygen is also anomalously high, being over 100 times greater than predicted under conditions of high oxygen concentration and high solvent viscosity.

Rate constants for abstraction of bromine from bromotrichloromethane by butyl, cyclopropylmethyl, and phenyl radicals in solution

1988 ◽  
Vol 66 (1) ◽  
pp. 11-16 ◽  
Author(s):  
Lukose Mathew ◽  
John Warkentin
Keyword(s):  
Free Radicals ◽  
Temperature Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Radical Chain ◽  
Dichloromethane Solution ◽  
Chain Decomposition ◽  
Product Yields ◽  
Product Composition ◽  
Diffusion Controlled

The radical chain decomposition of cyclopropylmethyl (1-hydroxy-1-methylethyl)-diazene [Formula: see text] at 253–341 K in hexafluorobenzene or in dichloromethane solution containing bromotrichloromethane affords cyclopropylmethyl bromide, 4-bromo-1-butene, 1-bromo-5,5,5-trichloro-2-pentene, and 3,5-dibromo-1,1,1-trichloropentane from the cyclopropylmethyl portion of 1. Other major products are nitrogen, acetone, and chloroform. The rate constant for formation of cyclopropylmethyl bromide by attack of cyclopropylmethyl free radicals from 1 at bromine of BrCCl3[Formula: see text] was calculated from the product composition using the known rate constant for rearrangement of cyclopropylmethyl radicals to 3-buten-1-yl radicals. At 25 °C,[Formula: see text] and the temperature dependence is given by [Formula: see text], where θ = 2.3RT kcal/mol−1. Non-chain decomposition of (CH3)2C(OH)N=N—R (2, R = Bu, and 3, R = Ph) in the presence of excess 1,1,3,3-tetramethylisoindolin-2-yloxyl (4) and bromotrichloromethane afforded BuBr and PhBr, respectively, in yields determined by the relative concentrations of 4 and BrCCl3. Rate constants for coupling (kc) of Bu• and Ph• with 4 were assumed to be proportional to rate constants for diffusion controlled reactions, kd, which were estimated from measured viscosities. Values of [Formula: see text] and[Formula: see text], calculated from kc and product yields for reactions at 80 °C, are 0.26 × 109 and 1.55 × 109 M−1 s−1, respectively. The relative radical reactivities toward BrCCl3 at 80 °C are Ph, 6; cpm, 5; Bu, 1.

Determination of rate constants of redox reactions of second order from current-less potential-time curves by a simplified graphical-numerical method

1983 ◽  
Vol 48 (5) ◽  
pp. 1358-1367 ◽  
Author(s):  
Antonín Tockstein ◽  
František Skopal
Keyword(s):  
Numerical Method ◽  
Explicit Form ◽  
Rate Constant ◽  
Optimization Algorithm ◽  
Rate Constants ◽  
Redox Reactions ◽  
Second Order ◽  
Wide Region ◽  
Recurrent Formula

A method for constructing curves is proposed that are linear in a wide region and from whose slopes it is possible to determine the rate constant, if a parameter, θ, is calculated numerically from a rapidly converging recurrent formula or from its explicit form. The values of rate constants and parameter θ thus simply found are compared with those found by an optimization algorithm on a computer; the deviations do not exceed ±10%.

The Effect of p-Toluidine on the Two-Step Electroreduction of Zn(II) in Water-Methanol and Water-Dimethylformamide

1999 ◽  
Vol 64 (4) ◽  
pp. 585-594 ◽  
Author(s):  
Barbara Marczewska
Keyword(s):  
Electron Transfer ◽  
Binary Mixtures ◽  
Rate Constant ◽  
Rate Constants ◽  
Electrode Surface ◽  
Mercury Electrode ◽  
Forward Rate ◽  
Solvent Molecules ◽  
Activated Complex

The acceleration effect of p-toluidine on the electroreduction of Zn(II) on the mercury electrode surface in binary mixtures water-methanol and water-dimethylformamide is discussed. The obtained apparent and true forward rate constants of Zn(II) reduction indicate that the rate constant of the first electron transfer increases in the presence of p-toluidine. The acceleration effect may probably be accounted for by the concept of the formation on the mercury electrode an activated complex, presumably composed of p-toluidine and solvent molecules.

Radiolysis studies on the corrosion inhibitors 1 -hexyn-3-ol, cinnamonitrile, and 1,3-diethyl-2-thiourea

1995 ◽  
Vol 73 (12) ◽  
pp. 2137-2142 ◽  
Author(s):  
A.J. Elliot ◽  
M.P. Chenier ◽  
D.C. Ouellette
Keyword(s):  
Hydrogen Atom ◽  
Hydroxyl Radical ◽  
Temperature Dependence ◽  
Rate Constant ◽  
Rate Constants ◽  
Corrosion Inhibitors ◽  
Hydrated Electron

In this publication we report: (i) the rate constants for reaction of the hydrated electron with 1-hexyn-3-ol ((8.6 ± 0.3) × 108 dm3 mol−1 s−1 at 18 °C), cinnamonitrile ((2.3 ± 0.2) × 1010 dm3 mol−1 s−1 at 20 °C), and 1,3-diethyl-2-thiourea ((3.5 ± 0.3) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile and diethylthiourea, the temperature dependence up to 200 °C and 150 °C, respectively, is also reported; (ii) the rate constants for the reaction of the hydroxyl radical with 1-hexyn-3-ol ((5.5 ± 0.5) × 109 dm3 mol−1 s−1 at 20 °C), cinnamonitrile ((9.2 ± 0.3) × 109 dm3 mol−1 s−1 at 21 °C), and diethylthiourea ((8.0 ± 0.8) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile, the temperature dependence up to 200 °C is also reported; (iii) the rate constant for the hydrogen atom reacting with 1-hexyn-3-ol ((4.3 ± 0.4) × 109 dm3 mol−1 s−1 at 20 °C). Keywords: radiolysis, corrosion inhibitors, rate constants.

Salt effects on nearly diffusion controlled electron-transfer reactions: bimolecular rate constants and cage escape yields in oxidative quenching of tris(2,2'-bipyridine)ruthenium(II)

1988 ◽  
Vol 92 (1) ◽  
pp. 156-163 ◽  
Author(s):  
Claudio Chiorboli ◽  
Maria Teresa Indelli ◽  
Maria Anita Rampi Scandola ◽  
Franco Scandola
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Salt Effects ◽  
Electron Transfer Reactions ◽  
Diffusion Controlled

An ICR mass spectrometry study of ion/molecule reactions between ethyl chloride and alkylamines

1991 ◽  
Vol 69 (2) ◽  
pp. 363-367
Author(s):  
Guoying Xu ◽  
Jan A. Herman
Keyword(s):  
Mass Spectrometry ◽  
Key Words ◽  
Rate Constant ◽  
Rate Constants ◽  
Ethyl Chloride ◽  
Ion Molecule Reactions ◽  
Mass Spectrometry Study ◽  
Ethyl Cation

Ion/molecule reactions in mixtures of ethyl chloride with C1–C4 alkylamines were studied by ICR mass spectrometry. Ethyl cation transfer to C1–C4 alkylamines proceeds mainly through diethylchloronium ions with rate constants ~3 × 10−10cm3 s−1. In the case of s-butylamine the corresponding rate constant is 0.5 × 10−10 cm3 s−1. Key words: ICR mass spectrometry, ion/molecule reactions, ethylchloride, methylamine, ethylamine, propylamines, butylamines

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