A Bis-Calix[4]pyrrole Enzyme Mimic that Constrains Two Oxoanions in Close Proximity

Herein we describe a large capsule-like bis-calix[4]pyrrole 1, which is able to host concurrently two dihydrogen phosphate anions within a relatively large internal cavity. Evidence for the concurrent, dual recognition of the encapsulated anions came from ¹H NMR and UV-vis spectroscopies and ITC titrations carried out in CD ₂Cl ₂/CD ₃OD (9/1, v/v) or dichloroethane (DCE), as well as single crystal X-ray diffraction analyses. Receptor 1 was also found to bind two dianionic sulfate anions bridged by two water molecules in the solid state. The resulting sulfate dimer was retained in DCE solution, as evidenced by spectroscopic analyses. Finally, receptor 1 was found capable of accommodating two trianionic pyrophosphate anions in the cavity. The present experimental findings are supported by DFT calculations along with ¹H NMR and UV-vis spectroscopies, ITC studies, and single crystal X-ray diffraction analyses.