The Effect of Water on Intermolecular Interactions

Having considered intermolecular interaction in the absence of solvation, we now consider the consequence of addition of solvent to a system of interacting molecules. At the outset we note that the picture changes from one that considers the 

We consider first the effect of aqueous solvation on all intermolecular stabilizations that derive from the interaction of charged or dipolar species. Because of its small size and significant dipole and quadrupole, water interacts strongly with all ionic and dipolar species. A binding event of charged or dipolar compounds thus proceeds with a significant loss of favorable cohesive interactions between solutes and water. The effect is most profound for ionic interactions similar ameliorations of solute-solute interaction apply to multipole-multipole and dipole-induced dipole interactions. 

Gas phase ionic interaction energies are large, typically on the order of 50-200 kcal moF. The interaction of water with charged species is nearly as large as a result solution-phase ionic interactions are weak, seldom more than five kcal mol  

During the past decades a variety of physical models designed to rationalize the observed thermodynamic behavior of nonpolar solutes in water have been proposed. It is beyond the scope of this work to describe each in detail rather, the 

Putting aside issues of the molecular origin of hydrophobic effect , the more significant issue is the extent to which desolvation contributes to overall binding thermodynamics. A variety of experimental methodologies to evaluate the magnitude of this effect exist. The most commonly used tools are Hansch transfer parameters [30, 31]. Briefly, a series of eompounds are partitioned between water and water-saturated octanol. The value n is then derived for a substitutent according to the expression  

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