Dissociation constant, conditional definition

Attempts have been made to deduce the structure of the predominant form of a potentially tautomeric compound from the shifts which occur in the ultraviolet spectrum of the compound in question on passing from neutral to basic or acidic solutions. The fact that no bathochromic shifts were observed for 2- and 4-hydroxy quinoline and 1-hydroxyisoquinoline under these conditions was taken as evidence that they existed in the oxo form [similar work on substituted quinol-4-ones led to no definite conclusions ]. A knowledge of the dissociation constants is essential to studies of this type, and the conclusions can, in any case, be only very tentative. A further dif-... 

For deductions to be made as to the state of the aromatic amino acid residues in proteins, the conditions under which the amino acids and the proteins are examined must be similar. Thin-film data on crystalline material are scarcely comparable with those obtained from the study of the same compounds when combined in macromolecules in solution, although they may have intrinsic interest of their own. Similarly, caution must be observed in comparing data obtained at low temperatures with those at room temperature where there is a possibility that ionic dissociation is involved. The meaning of pH at low temperatures in solid media and the values of the relevent dissociation constants are scarcely possible of definition. Keilin and Hartree (1949) have demonstrated the decolorization of certain dyes and indicators on cooling, which they ascribe to decrease of ionization. For instance, a red phenol-phthalein solution at pH 10.0 becomes colorless on cooling to — 15°C. 

Kapp, and the on- and off-rate constants of Qg are given in eqs. (1) ano (2) by their definitions under the three appropriate assumptions (i) under our experimental conditions the binding of Qg to the vacant site is a pseudo-first order reaction to the first approximation, (ii) the ratio of the amplitude of the fast decay component over that of the slow decay component in the decay kinetics following an actinic flash, is equal to the ratio of the fraction of the Qg-bound reaction centers over that of the Qg-unbound reaction centers in the dark, and (iii) the dissociation constant of Qg in the dark is equal to that following an actinic flash. 

Below are collected some acid-base constants, pK , the negative log of the acidity (dissociation) constant. See Chapter 5 for definitions and forms. First, the pK° values are given, followed by the conditional values at 25° and 0.1 M ionic strength, unless other conditions are stated. 

By assuming a definite formula for the polybromide attempts have been made to show that the relative proportions of the substance concerned in the reaction are in accord with the law of mass action. For example, with the polybromide KBr.nBrg of cone. 0, where the dissociation products are KBr of cone, and of cone. C2, the equilibrium condition is that KC=CiC, where K is the equilibrium constant. If the soln. are sat. with bromine, and the cone, of the free bromine in the soln. is constant, meaning that the cone, of the polybromide is proportional to the... 

The following entry defines the commonly used stability constants (stepwise, overall, conditional, association, dissociation, and pK) and relates the values to a rigorous thermodynamic definition of equilibrium constants. In addition, the article briefly outlines experimental techniques (potentiometric titration, spectroscopic methods involving ultraviolet/visible, infrared, Raman, fluorescence. and nuclear magnetic resonance spectroscopy), together with the numerical methods and computer programs that can be used to derive stability constants from such experimental data. 

---