Is Structured Near Cavities and Planar Surfaces

Water Is Structured Near Cavities and Planar Surfaces 

Computer simulations by Postma et al. 110] show that water molecules around small empty cavities behave much like water molecules around nonpolar solutes the first-shell water molecules orient to avoid pointing their hydrogen-bonding groups toward the cavity and wasting hydrogen bonds. In addition, 

So far we have considered the insertion of a single nonpolar molecule into water. This is sometimes called hydrophobic hydration or hydrophobic solvation. Now consider bringing two nonpolar solutes together in w-ater. This is called hydrophobic interaction. 

Potentials of Mean Force Describe Interactions in Fluids 

Imagine putting two solute molecules in water. Brownian motion separates them by different distances r at different times. Suppose you plot how often the solute molecules are found at separation r, for all possible values r = 0 to r 00. This is the radial distribution function g(r) (see page 461). iv(r), the potential of mean force (pmf), is dehned as the corresponding free energy, 

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