Uranyl solvation by a reference interaction site model

Abstract

We apply the one-dimensional reference interaction site model (RISM) to the solvation of uranyl in water. Uranyl aqua complexes with 4–6 explicit water ligands and an implicit water solvent, modeled by RISM to represent the further solvent environment, have been examined. The interaction of explicitly represented atoms of the aqua complexes are treated either by molecular mechanics or density functional theory, to build the free energy functional. A comparison of solvation energies and geometries of the aqua complexes for different numbers of explicit water ligands at the local minimum of the free energy surface indicate the interchangeability of explicit and implicit solvent models. Consequently the solvation energy is rather independent of the number of aqua ligands of the uranyl complex used as solute model, in contrast to results of a polarizable continuum model of solvation. For uranyl with four and five explicit water ligands in the first solvation shell we determined only a minor preference for the latter, in agreement with experiment. Other computational approaches tend to overestimate this preference.