An SCFab initio investigation of the “through-water” interaction of the phosphate anion with the Na⁺ cation

Abstract

SCFab initio computations in the supermolecule approach were carried out for the study of the hydration scheme of the dihydrogen phosphate anion, of the sodium cation and for the investigation of the direct and the through-water interaction of these two charged species. It is found that the energy balances of the direct phosphate-Na⁺ binding, involving their prior dehydration, or their through-water binding, allowing them to conserve their hydration shells, are of the same order of magnitude, indicating the competitivity of the two processes. This situation results in the existence of multiple possibilities for phosphate-Na⁺-water association. Appreciable energies of interaction exist between the different subunits of such systems. The Na⁺ cation and to a somewhat lesser extent the phosphate anion have a polarizing effect upon the charge distribution in the system over relatively appreciable distances. On the contrary, the charge transfers between the different components of the system are interpretable essentially in terms of displacements between adjacent units only.