Anion binding properties for pyrophosphate derived from a 2,6-diamidopyridinedipyrromethane macrocycle

A 2,6-diamidopyridinedipyrromethane macrocyclic receptor was prepared by a Schiff base condensation reaction. The structures of the free macrocycle and its complex with H2P2O72− were analyzed by single crystal X-ray diffraction (SC-XRD). The stability constants for the binding of the receptor with tetrabutylammonium salts of HP2O73− were determined by isothermal titration calorimetry using acetonitrile solutions. According to the titration data, the receptor exhibited high affinity with HP2O73−. The crystal structure analysis demonstrated that the neutral sandwich-type pyrophosphate complex was formed via the protonation of the macrocyclic receptor.