Solvent Mixing Effect on Free-Energy Barrier and Stability for Molecular Recognition Driven by the Translational Motion of Solvent Molecules

Abstract

We calculated the potentials of mean force (PMFs) between a ring-like host and a spherical guest in a solvent mixture. We adopted hard-body interactions between particles to discuss the effects of solvent-particle translational motion. The PMFs were obtained using the three-dimensional Ornstein-Zernike equation coupled with the modified hypernetted-chain closure (3D-MHNC-OZ theory). The entropic stabilization at the recognition site is confirmed, and a free-energy barrier wall is observed surrounding it. The free-energy barrier for the solvent mixture is much lower than that for the one-component solvent. Similar barrier reduction for the association of two spherical solute molecules has also been reported, and the mixing effect also reduced the dimerization stability. By contrast, the mixing effect does not significantly reduce recognition stability in the present study. In this respect, the behavior of the host-guest association is different from that of the association of two spherical solute molecules.