n-Alkyl alcohols at the water/vapour and water/benzene interfaces: a study on phase transfer energies

Abstract

A preliminary study on the behaviour of molecular solutes at the interface of liquid water with other media is reported. The study is based on an extension of the polarizable continuum model (PCM) which gives solvation free energy as the difference between the quantum mechanically computed free energy of the molecule inserted in the medium and that of the isolated molecule. The PCM computational scheme is modified to take into account the position and orientation of the molecule with respect to the phase separation boundary. The energetic quantity object of this study is thus a position and orientation dependent free energy function. The other features of standard PCM, in particular the use of continuum solvent response functions, are maintained. The comparison with molecular dynamics simulations shows that this model gives reasonable results, also in the presence of a phase separation. The decomposition of the free energy values along the best energetic passage from one phase to another shows that the minimum and the maximum present in the free energy profile mainly depend on non-electrostatic dispersion and steric terms.