Dissociation constant values

On the basis of the dissociation constant values, it seems sensible to conclude that, in these moderately basic carbinolamines, the hydrogen atom of the hydroxyl group is suflQciently acid to be eliminated under the influence of an alkali and by its transfer to the nitrogen atom of the mesomeric anion, the formation of the amino-aldehyde form may result. Instead of the amino-aldehyde, however, the corresponding bimolecular ether (15a-c) can be obtained. " It can be concluded that the formation of the bimolecular ether (S l or 8 2 mechanism) and the formation of the amino-aldehyde (B-SeI or B-Se2 mechanism) are competitive reactions. It seems probable that where the first reaction can occur the latter one is pushed into the background. The triple tautomeric system postulated by Gadamer... 

It should be mentioned that a similar comparison of the dissociation constant values of uracil monoalkyl derivatives does not permit the determination of the sequence of dissociation on account of the small differences between the pEo values. However, the pH dependence of the XJV spectra showed that the first dissociation of uracil occurs at the NH group in position 1 and thus differently than in 6-azauracil. This, together with different acidity, represents the main differences between the properties of uracil and its 6-aza analogs. 

The p/<, of a base is actually that of its conjugate acid. As the numeric value of the dissociation constant increases (i.e., pKa decreases), the acid strength increases. Conversely, as the acid dissociation constant of a base (that of its conjugate acid) increases, the strength of the base decreases. For a more accurate definition of dissociation constants, each concentration term must be replaced by thermodynamic activity. In dilute solutions, concentration of each species is taken to be equal to activity. Activity-based dissociation constants are true equilibrium constants and depend only on temperature. Dissociation constants measured by spectroscopy are concentration dissociation constants." Most piCa values in the pharmaceutical literature are measured by ignoring activity effects and therefore are actually concentration dissociation constants or apparent dissociation constants. It is customary to report dissociation constant values at 25°C. 

A temperature change can have an effect on the degree of ionization of various moieties on a protein as well as on substrates and effectors. Since proton dissociation constants values) are thermodynamic parame-... 

Fig. 3. Experimental dose-response data on G-beads from previous work (Simons et al, 2003, 2004) fitted to simulations of the ternary complex model including soluble G protein (Fig. 1C). The inclusion of soluble G protein in the model (Fig. 1C) is required due to the presence of extra G protein from the solubilized receptors and without which resulted in simulations that overestimated bead-bound receptors. Note that the same equilibrium dissociation constant values were used for the interactions with G protein on bead as with soluble G protein (Gtotbead and Gtots0l). Although the individual kinetic reaction rate constants for the interactions with soluble G protein might be faster than those for the bead-bound G protein, their ratios (the equilibrium dissociation constants) are expected to remain the same. The calibrated GFP per bead as...

Some representative examples are given of plant sources of the cited compounds (further plant sources can be readily accessed via the Web). ICjo (concentration for 50% inhibition) values are given in round brackets. Ka (dissociation constant) or K (enzyme-inhibitor dissociation constant) values are given in square brackets. For convenience compounds are grouped into alkaloids (also encompassing N-containing aromatic pseudoalkaloids), phenolics, terpenes and other compounds and are listed alphabetically within these four groupings. 

If the initial concentration of the titrant is equal to that of oxygen-containing admixtures, the ATMe0 value obtained is half as high as the true concentration constant. A rise of the initial molality of the titrant reduces this deviation, but the dissociation constant values are somewhat underestimated. The results in Table 3.6.1 show that only the data corresponding to the initial titrant molalities of 5 X 10 3 mol kg-1 and higher can be used for averaging pA o without appreciable error. 

Comparison of the dissociation constant value with that obtained in the same melt at 450 °C by Shapoval [176] shows that the stability constant of oxides in molten salts decreases the rise in temperature. The p coo value obtained in Ref. [176] is pKCo0 = 2.7 in molality scale, the agreement of this value with the one presented in Table 3.7.3 is good enough, taking into account the fact that this value was obtained by polarographic measurements. 

Such selective binding occurs with 1 1 stoichiometry [32]. Erythromycin-binding affinities to E. coli and S. aureus ribosomes give apparent dissociation constant values of 1 x 10 and 1 x 10 M, respectively [33, 34]. 

This implies that every collision of a reactant molecule (substrate) with the enzyme leads to product formation. Because tor many enzymes (the Michaelis or apparent substrate-enzyme dissociation constant) values are in the micro- or submiaomolar range (10 M), one can compute the (the catalytic or... 

A series of nineteen 3 -(Oacyl) derivatives of etilefrine HCl was synthesized and dieir physical characteristics were evaluated. Correlations between structure and solubility, dissociation constant values, lipophUicity and esterase catalyzed hydrolysis were demonstrated. 3 -(OPivaloyl)-etilefrine showed favorable characteristics of solubility, lipophilicity and stability against enzymatic cleavage in blood."... 

If a strong acid is used, it is assumed that it fully dissociates in the aqueous portion of the mobile phase. In the case of perchloric acid there will be no HCIO molecules but only and CIO ions present. Usually the (dissociation constant) values of strong acids are >1. Other acids in this class include hydrochloric, hydrobromic, nitric, and sulfuric. 

Physical Parameters. Tricarballylic acid is usually obtained as large orthorhombic prisms from water or ether having mp 166°C. It has three dissociation constant values, namely Kj at 30°C = 3.25 x lO K2 = 2.65 x lO Kg = 1.48 x lO It is found that at 18°C, 50 g dissolve in 100 ml water and 0.9 g dissolve in 100 ml ether very soluble in ethanol. The trisodium salt is, however, neutral to litmus. 

The effects of organic acids in the reduction of pH and their antimicrobial activity vary considerably depending on their dissociation status. The amount of dissociation depends on the pH value of the enviromnent, and is described by the specific pK (dissociation constant) value for each acid, which defines the pH at a 50% dissociation rate. The lower the pK value, the stronger the acid, which relates to its ability to lower the pH of the enviromnent. Acids used as feed additives have pK values between 3 and 5, and are categorised as being of intermediate strength (table 1). 

---