Long-range electrostatic interactions with remote charges modulate cation-π interaction energies in water.

Chemical double mutant cycles using calix[4]pyrrole receptors have quantified the effect of remote charges on the free energy of interaction between an N-methyl pyridinium cation and a π-box in water. The cation-π interaction energies are 0.7-2.2 kcal mol-1 more favorable in negatively charged receptors than in their positively charged analogs.