Hydration Forces

Force measurements on a wide variety of biologic macromolecules indicate that the perturbation of water structuring as hydrated surfaces closely approach can dominate interaction energetics. Forces with remarkably similar characteristics are observed for the repulsive interactions of charged polymer surfaces, of uncharged polymer surfaces, of charged solutes with uncharged surfaces, and of uncharged solutes with charged surfaces stressing the universality of the hydration force in aqueous solution. Repulsive interactions are caused by a disruption of the hydrogen bonding network of the intervening water between surfaces. The available measurements of forces between macromolecules that spontaneously assemble are consistent with an attractive hydration interaction. A water-order parameter theory has been developed that is successful for predicting force curve behaviors. The direct involvement of water structuring in the interaction between macromolecules has important consequences for recognition, assembly, and conformational transitions that underlie biologic function.