Combined Cation–π and Anion–π Interactions for Zwitterion Recognition

Brothers and enemies: Anion–π and cation–π interactions act in a synergistic way when gathered in the molecular cavity of a hemicryptophane host, affording an efficient contribution (−170 kJ mol−1) in zwitterion recognition. NMR titration experiments and calculations reveal the positioning of the guest in the cavity of the heteroditopic receptor. This study emphasizes the importance of anion–π bonds in host–guest chemistry.