Catalytic constant determination

This equation contains a further term, ko, representing the solvent (water) term. In any given system, any of these terms may of course be negligible. The values of the catalytic constants and kon can be determined at the pH extremes. This equation states that the rate will be a minimum at an intermediate pH. It is easy to show that this occurs at a pH independent of ko, as expressed by... 

Hersh et al. found that the cationic complex [CpFe(CO)2(THF)]BF4 (23) can accelerate the [4 + 2] cycloaddition of acrolein and cyclopentadiene [32]. However, the catalytic activity was higher than expected from rate constants determined in stoichiometric experiments, indicating that a Brpnsted or Lewis acid impurity might accelerate this process and generating doubts about the role of 23. 

It has been shown by H naff (1963) that the rate of reaction of several carbonyl reagents (bisulphite, hydrazine, phenylhydrazine, semi-carbazide and hydroxylamine) with aqueous formaldehyde solutions is independent of the nature and concentration of the reagent, and is therefore determined by the rate of dehydration of methylene glycol. He obtained catalytic constants for hydrogen and hydroxide ions, and a detailed study of acid-base catalysis has been made by the same method by Bell and Evans (1966). 

The Flocculation Rate Constant. In principle Equation 1 contains all of the information to determine both v and kB from a single lightscattering experiment as has been demonstrated earlier with the clotting of fibrin( 3). However, the present turbidity measurements suffer from multiple scattering ), which makes an estimate of v from the previously proposed plot of (Mw — M0)/M0t vs. t2 unreliable. Therefore v was estimated with the catalytic constants recalculated from Gamier s data... 

The rate constants of O catalytic dismutation, determined for the nitroxides tested, increased with [H+], indicating that OOH, but not O2 oxidizes nitroxide ... 

Determine the Michaelis constant Km and the catalytic constant k3 for the enzyme under these conditions. 

Synthetic substrates allow rapid determination of the catalytic constants of an enzyme. Nevertheless, it is known that the environment of the peptide bond depends largely on physico-chemical conditions of the applied media, and imposed steric hindrance. Since these parameters are important, the hydrolysis of purified (3-casein was studied at different pHs. The kinetic analysis revealed that the mutant conserved the native trypsin capacity to hydrolyze peptide bonds containing arginyl and lysyl residues. The optimal pH of activity changed considerably according to the mutation. 

Experiments on the bromination of equilibrated ketone-acetal systems in methanol were also recently performed for substituted acetophenones (El-Alaoui, 1979 Toullec and El-Alaoui, 1979). Lyonium catalytic constants fit (57), but for most of the substituents the (fcA)m term is negligible and cannot be obtained with accuracy. However, the relative partial rates for the bromination of equilibrated ketone-acetal systems can be estimated. For a given water concentration, it was observed that the enol path is more important for 3-nitroacetophenone than for 4-methoxyacetophenone. In fact, the smaller the proportion of free ketone at equilibrium, the more the enol path is followed. From these results, it can be seen that the enol-ether path is predominant even if the acetal form is of minor importance. The proportions of the two competing routes must only depend on (i) the relative stabilities of the hydroxy-and alkyoxycarbenium ions, (ii) the relative reactivities of these two ions yielding enol and enol ether, respectively, and (iii) the ratio of alcohol and water concentrations which determines the relative concentrations of the ions at equilibrium. Since acetal formation is a dead-end in the mechanism, the amount of acetal has no bearing on the relative rates. Bromination, isotope exchange or another reaction can occur via the enol ether even in secondary and tertiary alcohols, i.e. when the acetal is not stable at all because of steric hindrance. 

Rate coefficient, 13 Rate constant, 13 catalytic, 268 determination of, 31 diffusion-limited, 135 first-order, 18, 31, 61 pressure dependence of, 261 pseudo-order, 23 second-order, 20... 

To those beginning work in this field, the study reported by Zhou and Notari on the kinetics of ceftazidime degradation in aqueous solutions may be used as a study design template. First-order rate constants were determined for the hydrolysis of this compound at several pH values and at several temperatures. The kinetics were separated into buffer-independent and buffer-dependent contributions, and the temperature dependence in these was used to calculate the activation energy of the degradation via the Arrhenius equation. Ceftazidime hydrolysis rate constants were calculated as a function of pH, temperature, and buffer by combining the pH-rate expression with the buffer contributions calculated from the buffer catalytic constants and the temperature dependencies. These equations and their parameter values were able to calculate over 90% of the 104 experimentally determined rate constants with errors less than 10%. 

The following values were determined for the specific acid-catalytic constants for an antiinflammatory dmg ... 

The catalyst has been designed as given in Ref The proposed process of knowledge extraction consists in planning HTE experiments in a way allowing for the discrimination of the models of catalytic reactions, determination of the kinetic constants, and relating them to the catalyst microstructure. The proposed forward modeling is realized by the application of the... 

We shall assume that the amount of SH+ present is throughout much smaller than [S] or [A,]. If the first step is rate determining, then the reaction will be first order with respect to both catalyst and substrate, with a catalytic constant depending on the nature of Aj. It is reasonable to suppose that, for a series of similar catalysts the catalytic constants will run parallel with their acid strengths, but since acids do not dissociate in the aprotic solvents being considered, some other reaction must be... 

Forman and Fridovich (1973) using an indirect assay whereby O2 was generated either by the action of xanthine oxidase on xanthine or by the mechanical infusion of potassium superoxide in tetrahydrofuran. The generated OJ was allowed to react with ferricytochrome c or with tetra-nitromethane and the product formation was monitored spectroscopically. Details of the two assays are given in Section 11.3. Addition of superoxide dismutase inhibits the formation of products. A rate constant of 2 X 10 M sec was determined for all three enzymes. This value agreed with the rate constant determined by pulse radiolysis for the copper/zinc enzyme (Klug-Roth et al., 1973 Fielden et al., 1974). The mechanism of action of the superoxide dismutases has been investigated by the technique of pulse radiolysis which is described in Section II.2. The bovine erythrocyte copper/zinc enzyme is the most studied form as far as the molecular and catalytic properties are concerned (Rotilio and Fielden,... 

Relative to small molecules, the effects of mass transfer on conversion and catalytic constants will be greater for macromolecular substrates. Since diffusion of substrates and products to and from the catalyst will be largely determined by the size of macroporous particles, this variable is particularly important when assessing catalytic supports for enzyme-catalyzed polymer synthesis and modification reactions. To our knowledge, no systematic studies have been reported on how size of macroporous resins influences enzyme activity. 

In the case of nitrite nucleophile, however, the favourable situation was met that the role of this anion in aromatic nucleophilic substitutions had been thoroughly investigated and host-guest complexation happened under the experimental conditions of catalytic rate constant determination. 

The equilibrium lies to the right, and the rate constants determined, in C6D6, by H NMR spectroscopy are those for the regeneration of the catalytically active species. Exchange between the methyl groups of free Al(CH3)3 and those in the heterobimetallic species was slow on the NMR timescale. The rate constants (presumably obtained at an unstated room temperature) were independent of the value of [Al(CH3)3] and decreased in the order Ti > Zr > Hf, which was reasonable if the dissociation involves breaking a metal-ligand bond. Kinetics experiments conducted with substrates in which Cp had been replaced by ethenebis(indenyl) (EBI) or ethenebis(tetrahydroindenyl) indicated that the zirconocene methyl cation will be a superior carboalumination catalyst. 

Substitutions at the active site specifically R392A, M153A and Q384N (Figure 5.26B-D) give rise to voltammetry that is distinctly different from the wild-type enzyme (Figure 5.26A) both in waveform and in nitrate concentration dependence. The Michaelis constants determined from solution assays vary considerably (from 400 pM for the WT enzyme to 66 mM for the R392A variant) and this is reflected in the nitrate concentration dependence of the voltammetry. Another outcome of this study was the connection made between the potential dependence of the catalytic current and the observation that the rate of nitrate reduction in solution assays has been found to increase as the concentration of reductant decreases. 

The membrane-bound ATP(synth)ase affinity (Michaelis constant K ) for its substrates was found quite variable for ADP, from less than T yM (1) to almost 200 yM (2). In fact, this was predictable (3), inasmuch as the chemiosmotic mechanism of phosphorylation makes that, as soon as ADP is added, the proton channels open, the proton gradient A]5f + lowers, and consequently the catalytic constant and/or the enzyme number, because of their AvL+-dependent activation (4), decrease. That is, is not constant in the kinetic determination of K. ... 

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