Ionization constants variation with temperature

From the variation, with temperature, of the equilibrium constant of the overall reaction, the heat of the reaction has been shown to depend on pH, and values of 1.9—2.2 Kcal./mole have been obtained. Heats of ionization of groups at the active center of potato phosphorylase have been calculated, and are shown in Table XX. 

Corresponding dependencies in van t Hoff coordinates, although almost linear, show different directions in their slope, which is dependent on the particular pH chosen for this particular model (Figure 2-f8). Note that in this model the effect of temperature on the change of the dissociation constants of the buffer species and model basic analyte species were taken into account on the basis of standard relationship of the equilibrium constant with the temperature (Ki = exp[AG/i r]). It has been shown that the dissociation constants of particular acidic species and basic species show some specific variations of their ionization constants with temperature in methanoFwater and acetoni-trUe/water mobile phases [40,41],... 

FIGURE 3-3 Variation of ionization constants with temperature. All values are on the molal scale. Data from Handbook of Chemistry and Physics 53d ed., p. D-121, Chemicai Rubber, Cleveland, OMo, 1972-1973.)... 

The gel collapse induced by ionization was first observed experimentally by Philippova et al. In this study, PMAA gel was gradually ionized by titration with sodium methoxide in media with different polarities. Water, methanol, dioxane, and their mixtures were used as solvents, coveting the range of dielectric constants from 78 to 2. Water and methanol are nearly -solvents for uncharged PMAA at room temperature therefore, by varying the content of water/methanol mixtures, the dielectric constant of the medium is changed without a significant variation of the solvent quality. 

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