Hydration competition positive cooperativity results

Figure 5.34. Acid-base titration curves of the series of elastic Model Proteins I and i through v of Table 5.5 that exhibit systematic increases in hydrophobic-induced pK shifts and positive cooperativity resulting from competition for hydration between apolar and polar groups. (Inset) Slope of the Henderson-Hasselbalch equation with n = 1, and the slopes for...

From the analysis of the acid-base titration data in Figures 5.30 through 5.34, positive cooperativity results from the apolar-polar repulsive free energy of hydration, that is, from the competition for hydration between apolar (hydrophobic) and polar (e.g., charged) species. The general statement can be that the appearance on the scene of the first polar, for example, charged, species must do the work of destructuring hydrophobic hydration in order to achieve adequate hydration for itself. 

The Competition for Hydration Also Is Responsible for Large Hydrophobic-induced pKa Shifts with Positive Cooperativity That Results in Efficient Protein-based Machines... 

Both of these contractions result from hydrophobic association due to protonation of the carboxylate group. The underlying physical process is the competition for hydration between the charged carboxylate and the hydrophobic side chains of the valine (Val, V) residues (Urry, 1997). This competition, described as an apolar-polar repulsive free energy of hydration, results in increasing positive cooperativity of the add-base titration... 

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