scholarly journals The kinetics of slow-binding and slow, tight-binding inhibition: the effects of substrate depletion

1993 ◽  
Vol 294 (1) ◽  
pp. 195-200 ◽  
Author(s):  
S G Waley
Keyword(s):  
Substrate Concentration ◽  
Dissociation Constants ◽  
Tight Binding ◽  
Slow Step ◽  
First Order ◽  
Initial Substrate ◽  
Binding Inhibition ◽  
Kinetics Of ◽  
Nanomolar Range ◽  
Step Mechanism

Inhibitors with dissociation constants in the micromolar to nanomolar range are important, but hard to characterize kinetically, especially when the substrate concentration in the assay is less than Km. When inhibition increases during the course of the assay (slow-binding inhibition) the concentration of substrate may decrease appreciably. Methods that take substrate depletion into account are described for analysing experiments in which the initial substrate concentration is below Km. Fitting progress curves gives the rate constants for the second (slow) step in a two-step mechanism. An approximate value for the overall dissociation constant may be determined from measurements of rates when the reaction is treated as a first-order process. When the concentrations of inhibitor and enzyme are comparable numerical methods are required. Procedures, suitable for implementation on a microcomputer, for the solution of the differential equations and the fitting of progress curves are described.

Osmium(VIII) Catalyzed Oxidation of Acetone and Ethylmethyl Ketone by Chloramine-T

1972 ◽  
Vol 27 (10) ◽  
pp. 1161-1163 ◽  
Author(s):  
S. P. Mushran ◽  
R. Sanehi ◽  
M. C. Agraval
Keyword(s):  
Acidic Medium ◽  
Present Note ◽  
Alkaline Media ◽  
Alkaline Solutions ◽  
Slow Step ◽  
First Order ◽  
Chloramine T ◽  
Kinetics Of ◽  
Catalyzed Oxidation ◽  
High Redox Potential

The Osmium (VIII) catalyzed oxidation of acetone and ethylmethyl ketone by chloramine-T, in highly alkaline solutions showed first order dependence to chloramine-T and osmium (VIII). The order of the reactions with respect to alkali and ketone were found to be fractional, being ~-0.82 and 0.3 respectively. No effects of ionic strength were evident. The mechanism has been proposed on the basis of the formation of a complex between N-chlorotoluene-p-sulfonamide and osmium (VIII) in the slow step, which in turn oxidizes the enol anion of the reducing substrate in the fast step.During the study of the mechanism of oxidations by chloramine-T, the kinetics of the oxidation of α-hydroxy acids 1 in presence of osmium (VIII) as catalyst, glycerol2 in neutral and alkaline media, p-cresol3 in an acidic medium, hexacyanoferrate (II)4 in a feebly acidic medium (pH 6-7) and aliphatic aldehydes 5 in alkaline media have been investigated.Despite the high redox potential6 of the chloramine-T/toluene sulfonamide system (1.138 V at pH 12), the oxidation of acetone does not take place in absence of catalyst and that of ethylmethyl ketone proceeds only in highly alkaline solutions7 (NaOH>0.01 M). In the present note the kinetics of the osmium (VIII) catalyzed oxidation of acetone and ethylmethyl ketone have been recorded.

The comparative chemistry of ammine and methylamine complexes of rhodium(III) and cobalt(III)

1977 ◽  
Vol 55 (17) ◽  
pp. 3166-3171 ◽  
Author(s):  
Thomas Wilson Swaddle
Keyword(s):  
Ionic Strength ◽  
Spectral Data ◽  
Electron Donor ◽  
Dissociation Constants ◽  
Base Hydrolysis ◽  
Acid Dissociation ◽  
Rate Coefficients ◽  
Acid Dissociation Constants ◽  
First Order ◽  
Kinetics Of

For the aquation of (CH3NH2)5RhCl2+, the first order rate coefficients are represented by ΔHaq* = 101.9 kJ mol−1 and ΔSaq* = −50.2 JK−1 mol−1 in 0.1 M HClO4, while for base hydrolysis the rate is first order in [(CH3NH2)5RhCl2+] and [OH−] at ionic strength 0.10 M and the rate coefficients (in M−1 s−1) are represented by ΔHOH*> = 108.6 kJ mol−1 and ΔSOH* = 74.1 J K−1 mol−1. Acid dissociation constants are reported for (RNH2)5MOH23+ (R = H or CH3; M = Rh or Co), and these, combined with spectral data, show CH3NH2 to be a poorer electron donor than NH3 in complexes of this type, contrary to expectations. The comparative kinetics of reactions of (RNH2)5MCl2+ support the assignment of an Ia mechanism to aquation when M = Rh or Cr, Id to aquation when M = Co, and Dcb for base hydrolysis in all these cases.

scholarly journals Kinetics of Oxidation of 3-Benzoylpropionic Acid byN-Chlorobenzamide in Aqueous Acetic Acid Medium

2011 ◽  
Vol 8 (2) ◽  
pp. 561-564 ◽  
Author(s):  
N. A. Mohamed Farook ◽  
G. A. Seyed Dameem
Keyword(s):  
Acetic Acid ◽  
Acid Medium ◽  
Reaction Medium ◽  
Activation Parameters ◽  
Slow Step ◽  
Aqueous Acetic Acid ◽  
Acetic Acid Medium ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Kinetics Of

The kinetics of oxidation of 3-benzoylpropionic acid(KA)byN-chlorobenzamide(NCB)in aqueous acetic acid medium in the presence of perchloric acid have been investigated. The observed rate of oxidation is first order dependence each in[KA],[NCB]and [H+]. The main product of the oxidation is the corresponding carboxylic acid. The rate decreases with the addition of benzamide, one of the products of the reaction. Variation in ionic strength of the reaction medium has no significant effect on the rate of oxidation. But the rate of the reaction is enhanced by lowering the dielectric constant of the reaction medium. Hypochlorous acidium ion (H2O+Cl), has been postulated as the reactive oxidizing species. A mechanism consistent with observed results have been proposed and the related rate law deduced. The activation parameters have been computed with respect to slow step of the mechanism.

Substrate-dependent, non-hyperbolic kinetics of pig brain prolyl oligopeptidase and its tight binding inhibition by JTP-4819

2002 ◽  
Vol 64 (3) ◽  
pp. 463-471 ◽  
Author(s):  
Jarkko I. Venäläinen ◽  
Risto O. Juvonen ◽  
Markus M. Forsberg ◽  
Arturo Garcia-Horsman ◽  
Antti Poso ◽  
...  
Keyword(s):  
Tight Binding ◽  
Prolyl Oligopeptidase ◽  
Pig Brain ◽  
Binding Inhibition ◽  
Kinetics Of

scholarly journals Kinetics of photocatalytic removal of 2-amino-5-chloropyridine from water

2004 ◽  
pp. 79-86 ◽  
Author(s):  
Biljana Abramovic ◽  
Vesna Anderluh ◽  
Andjelka Topalov ◽  
Ferenc Gaal
Keyword(s):  
Titanium Dioxide ◽  
Kinetic Model ◽  
Substrate Concentration ◽  
Zero Order ◽  
Direct Photolysis ◽  
Pyridine Moiety ◽  
Initial Substrate ◽  
Photocatalytic Removal ◽  
Kinetics Of ◽  
Initial Substrate Concentration

Titanium dioxide sensitized photocatalytic degradation of a pyridine pesticide analogue, 2-amino-5-chloropyridine, was investigated by monitoring the pyridine moiety degradation, as well as by monitoring the chloride generated in the process. Effect of the initial substrate concentration on the rate of its degradation is reported. Here we show that the kinetics of both reactions are of the zero-order in the entire investigated concentration range. The Langmuir-Hinshelwood kinetic model successfully described the influence of the initial substrate concentration on the rate of the pyridine moiety degradation. It was found that dechlorination of the substrate takes place by direct photolysis. The differences in the kinetics of pyridine moiety degradation and dechlorination were explained on the basis of the electrostatic potential for the investigated compound.

Kinetics of acetal and orthobenzoate hydrolysis as probes of cyclodextrin-guest binding

2000 ◽  
Vol 78 (4) ◽  
pp. 436-443 ◽  
Author(s):  
Oswald S Tee ◽  
Samer MI Hussein ◽  
Isabelle E Turner ◽  
Ogaritte J Yazbeck
Keyword(s):  
Dissociation Constants ◽  
Substrate Binding ◽  
Dimethyl Acetal ◽  
First Order ◽  
Guest Binding ◽  
Hydrolysis Rates ◽  
Rate Of Hydrolysis ◽  
Acid Catalyzed ◽  
Kinetics Of ◽  
Hydrolysis Of

Acid-catalyzed hydrolysis of acetophenone dimethyl acetal (ADMA) and trimethyl orthobenzoate (TMOB) is retarded by cyclodextrins (CDs): α-CD, β-CD, hb-β-CD = "hydroxypropyl-β-cyclodextrin", and γ-CD. The observed first order rate constants (kobs) vary with [CD] in the manner expected for 1:1 binding between the substrates and the CDs. Similar behaviour was found recently for the hydrolysis of benzaldehyde dimethyl acetal (BDMA). With β-CD and hp-β-CD, the binding of all three substrates (BDMA, ADMA, TMOB) is strong and the CD-bound forms have very little reactivity. By contrast, substrate binding by α-CD is much weaker, and the CD-bound forms have appreciable, though reduced, reactivity. Substrate binding by γ-CD is also relatively weak, but the bound substrates have very low reactivities. The hydrolysis reactions of ADMA, TMOB, and BDMA have been evaluated as kinetic probes of the binding of guests to CD hosts. For α-CD, β-CD, and hp-β-CD, the addition of guests reduces the amount of free CD and thereby alleviates retardation of the hydrolysis by the CD. The resultant increases in hydrolysis rates can be analyzed to provide estimates of CD-guest dissociation constants, KG. For aliphatic alcohols and ketones binding to β-CD and hp-β-CD, all three probe reactions provide values of KG that agree well with each other and with literature values determined by other methods. The approach does not work well with α-CD because of its much weaker binding of the kinetic probes and their less pronounced dependence of kobs on [α-CD]. In the case of γ;-CD, the approach cannot be used because added guests cause a further lowering in the rate of hydrolysis, suggesting the formation of an unreactive ternary (substrate·CD·guest) complex.Key words: acetal, hydrolysis, cyclodextrin, host-guest, binding.

scholarly journals Optimization of o-cresol degrading microorganism and kinetics of degradation

2018 ◽  
Vol 18 (4) ◽  
pp. 702
Author(s):  
Krishnan Nhattuketty Shainy ◽  
Rajamanickam Usha
Keyword(s):  
Substrate Concentration ◽  
Cell Mass ◽  
Serial Transfer ◽  
Initial Substrate ◽  
Pseudomonas Monteilii ◽  
Petroleum Contaminated Soil ◽  
Kinetics Of Degradation ◽  
High Concentrations ◽  
Mass Increase ◽  
Kinetics Of

In the present study, Pseudomonas monteilii CR13 isolated from petroleum contaminated soil demonstrated the highest specific o-cresol degradation rate at all tested o-cresol concentrations and also was not disturbed by the starting substrate concentration used (o-cresol-500 mg/L). After a serial transfer of the isolate into a series of increasing o-cresol level, the organism demonstrated significant improvement on degradation ability up to 3000 mg/L. The optimum condition for the cell mass increase and biodegradation of o-cresol by Pseudomonas monteilii was in the minimal mineral medium of 3 at a pH of 6.5 and temperature 30 °C, stirring velocity of 160 rpm, and the substrate concentration of 500 mg/L. The biodegradation kinetic study was carried out by bacteria in different initial substrate concentrations (500–3000 mg/L). In the present test the μmax, Ks and the μ were found 0.332 h-1, 0.166 mg/L and 0.0282 mg/L for 500 mg/L of o-cresol, respectively. The organism is highly promising and could be used to remove high concentrations of o-cresol from highly polluted aquatic and soil regions. The cells could be immobilized on a suitable matrix and the efficiency of degradation could be effectively improved.

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