The relation of ion pairs to protein hydration: An IR spectroscopic and X‐ray crystallographic survey

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Abstract
We report here a novel ir technique that we use to determine the apparent van't Hoff's energy for the distillation of water from protein amide and acid groups. The method is used to study the hydration properties of ten different proteins. The results show that water removal from the environment of ion‐paired acid groups (those ⩽ 4 Å from a basic group on the protein surface) requires less energy than water removal from the environment of nonpaired acid groups. These observations are supported by an analysis of the solvent distributions in protein crystal structures. A model is proposed for the interaction between water and protein acid groups, and this model is used to account for the distributions and properties of certain eye‐lens proteins.