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 CD2Cl2/CD3OD (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.