Specificity constants

The constant may depend on process variables such as temperature, rate of agitation or circulation, presence of impurities, and other variables. If sufficient data are available, such quantities may be separated from the constant by adding more terms ia a power-law correlation. The term is specific to the Operating equipment and generally is not transferrable from one equipment scale to another. The system-specific constants i and j are obtainable from experimental data and may be used ia scaleup, although j may vary considerably with mixing conditions. Illustration of the use of data from a commercial crystallizer to obtain the kinetic parameters i, andy is available (61). 

The ratio of specificity constants and determines the enantioselectivity of the reaction. Since (see Fig. 1)... 

Variables a andZ are specific constants reported by Tsonopoulos for some alcohols and water (e.g., methanol a = 0.0878, b = 0.0560 and water a = 0.0279, b = 0.0229). Tsonopoulos also gives specific prediction methods for haloalkanes and water pollutants. 

Liquid Viscosity The viscosity of both pure hydrocarbon and pure nonhydrocarbon hquids are most accurately predicted by the method of van Velzen et al. The basic equation (2-112) depends on group contributions which are dependent on stnic tiire for the calculation of compound-specific constants B and To-... 

The equation-specific constants for the SRK and PR equations are given by the following table ... 

The quantity kcat/Km is a rate constant that refers to the overall conversion of substrate into product. The ultimate limit to the value of k at/Km is therefore set by the rate constant for the initial formation of the ES complex. This rate cannot be faster than the diffusion-controlled encounter of an enzyme and its substrate, which is between 10 to 10 per mole per second. The quantity kcat/Km is sometimes called the specificity constant because it describes the specificity of an enzyme for competing substrates. As we shall see, it is a useful quantity for kinetic comparison of mutant proteins. 

The changes in the specificity constants, on the other hand, were as expected from the predictions. The ratio of the fccat/ m values for the Arg and Lys substrates (last column in Table 11.1) gives a measure of the relative specificities. This ratio decreases for the Ala 226 mutant and increases for the Ala 216 mutant as predicted. However, the changes in these values depend not... 

Where W is weight and Rj is a specific constant for the gas involved. This is the perfect gas equation. Going one step further, by making W, in pounds, equal to the molecular weight of the gas (one mole), the formula becomes ... 

The enantioselectivity of biocatalytic reactions is normally expressed as the enantiomeric ratio or the E value [la], a biochemical constant intrinsic to each enzyme that, contrary to enantiomeric excess, is independent of the extent of conversion. In an enzymatic resolution of a racemic substrate, the E value can be considered equal to the ratio of the rates of reaction for the two enantiomers, when the conversion is close to zero. More precisely, the value is defined as the ratio between the specificity constants (k st/Ku) for tho two enantiomers and can be obtained by determination of the k<-at and Km of a given enzyme for the two individual enantiomers. 

Table 1.4 I nfluence ofthe organic solvent on the enantioselectivity ofthe protease subtilisin in the kinetic resolution ofthe racemic alcohol (10) (expressed as the enatiomeric ratio E, that is the ratio of the specificity constants of the two enatiomers, (lfcat/ M)s/...

As an example, we mention the enzyme catalase, which catalyzes the decomposition of H2O2 to H2O and O2 at a turnover number of kcat = 10 and a high specificity constant of kcat/f M = 4 x 10 mol s . Such activities are orders of magnitude higher than those of heterogeneous catalysts. 

The first factor k. 1 = 35, is expected to be temperature dependent via an Arrhenius fjfpe relationship the second factor defines functionality dependence on molecular size the third factor indicates that smaller molecules are more likely to react than larger species, perhaps due to steric hindrance potentials and molecular mobility. The last term expresses a bulk diffusional effect on the inherent reactivity of all polymeric species. The specific constants were obtained by reducing a least squares objective function for the cure at 60°C. Representative data are presented by Figure 5. The fit was good. 

The specificity constant, kcJKm, is the second-order rate constant for the reaction of E and S to produce product. It has units of M Wn-1. 

Because you know the rate and the concentration of CH3CHO, solve for k, the rate-specific constant. 

Finally, substitute the rate-specific constant and the new concentration into the rate expression. 10. liter... 

A limited number of empirical correlations have been developed for metal droplet sizes generated by water atomization, as listed in Table 4.18. In these correlations p is a system-specific constant, is the atomizing angle, i.e., angle between water nozzle axis and metal delivery nozzle axis, A is a proportional constant specific to atomizer type, melt type and melt temperature, n is a parameter depending on atomizer type, APw is the water pressure, Uw is the water velocity, and mw is the mass flow rate of water. 

We expect that the trapping efficiency increases with decreasing crystal length lz for otherwise constant parameters, specifically constant pPy+, because the... 

Specificity constant Defined as kcJKm. It is a pseudo-second-order rate constant which, in theory, would be the actual rate constant if formation of the enzyme-substrate complex were the rate-determining step. 

After intravenous administration to rabbits, the t-amino acid derivatives of dapsone were rapidly (f1/2<2 min) and quantitatively converted to dapsone. The corresponding D-amino acid derivatives were also quantitatively converted to dapsone, but the f1/2 values ranged from 30 to 60 min. In human blood, the f1/2 values for hydrolysis of the L-amino acid prodrugs ranged from 1.7 to 20 min (Leuleucine peptidase, with decreasing specificity constants (kcat/Km) Leu=Ala>Phe>Lys=Gly. Interestingly, only L-Lys-dapsone was a substrate of trypsin, whereas only L-Phe-dapsone was a substrate of chymotrypsin. 

In this equation, the constant Kz, which can be easily inferred from the intercept, represents a system-specific constant that is related to the ion-exchange equilibrium constant K(Lmol ), the surface area 5 (in m the charge density on the surface, that is, the number of ion-exchange sites qx available for adsorption (in molm ), and the mobile phase volume Vo (in L) in the column as described by the following equation ... 

In enzyme-catalyzed kinetics, one must necessarily deal with the behavior of a multistep reaction scheme. For initial rate enzyme processes, one typically deals with collections of rate constants which appear in the form of the maximal velocity Um (shortened to U) or the specificity constant VJK (shortened to VIK). Accordingly, enzyme kineticists will use °V and °V/K as an easy way to indicate the respective isotope effects [(Um)H/(Um)D ] and [(VJK )u/(VJK )b], respectively. 

A measure and/or description of how specific an enzyme is toward a substrate or class of substrates or toward an effector or class of effectors. For effectors (or for ligands binding to macromolecules that are not enzymes), this specificity is readily measured by dissociation (or, association) constants. For enzymes, specificity is best quantitated by the Fmax/.K m ratio. See Specificity Constant. It is crucial, in the complete characterization of an enzyme, that the specificity of the enzyme be known in detail. 

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