A calix[4]pyrrole functionalized with an amidoindole ester for the selective recognition of the dihydrogen phosphate anion

A bisamidoindole ester-functionalized calix[4]pyrrole (2), which features additional hydrogen bond donors and acceptors, complexes dihydrogen phosphate (H₂PO₄⁻) with high affinity and selectivity. This binding takes place via distinct modes compared to those observed for meso-pyrrolic calix[4]pyrrole 1 and the parent calix[4]pyrrole, underscoring the impact of strategic functionalization on anion binding geometry and selectivity.