Solvation rules: aromatic interactions outcompete cation-π interactions in synthetic host-guest complexes in water.

Chemical double mutant cycles were used to measure the interaction of a N -methyl pyridinium cation with a π-box in a calix[4]pyrrole receptor. Although the cation-π interaction is attractive (-11 kJ mol -1 ), it is 7 kJ mol -1 less favourable than the corresponding aromatic interaction with the isosteric but uncharged tolyl group.