title: Methodology for the calculation of the potential of mean force for a cation-pi complex in water.
abstract: We report potential of mean force (PMF) calculations on the interaction between the p-sulfonatocalix[4]arene and a monovalent cation (Cs(+)). It has been recently shown from microcalorimetry and (133)Cs NMR experiments that the association with Cs(+) is governed by favourable cation-pi interactions and is characterized by the insertion of the cation into the cavity of the macrocycle. We show that the PMF calculation based upon a classical model is not able to reproduce both the thermodynamic properties of association and the insertion of the cation. In order to take into account the different contributions of the cation-pi interactions, we develop a new methodology consisting of changing the standard PMF by an additional contribution resulting from quantum calculations. The calculated thermodynamic properties of association are thus in line with the microcalorimetry and (133)Cs NMR experiments and the structure of the complex at the Gibbs free-energy minimum shows the insertion of the cation into the cavity of the calixarene.
authors.affiliation: Laboratoire de Thermodynamique des Solutions et des Polymères, UMR CNRS 6003, Université Blaise Pascal, 63177 Aubière Cedex, France.
authors.forename: Aziz
authors.initials: A
authors.lastname: Ghoufi
authors.forename: Pierre
authors.initials: P
authors.lastname: Archirel
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Morel
authors.forename: Nicole
authors.initials: N
authors.lastname: Morel-Desrosiers
authors.forename: Anne
authors.initials: A
authors.lastname: Boutin
authors.forename: Patrice
authors.initials: P
authors.lastname: Malfreyt