An ammonium/bis-ammonium switchable molecular shuttle

A pH shuttle has been developed in which the mean position of the macrocycle can be switched between dialkylammonium stations of differing acidities. With only the most basic binding site protonated (dibenzylammonium), the macrocycle resides almost exclusively on the protonated station; when the second ammonium group (diethylammonium) is generated by further protonation, a mixture of translational diastereomers is observed in CD2Cl2 at 298 K, with the diethylammonium binding site preferred by the crown ether macrocycle in a ratio of ∼2:1.