Unprecedented Increase in Affinity for EuIII over AmIII through Silica Grafting of a Carbamoylmethylphosphine Oxide-Calix[4]arene Site

Grafting of a carbamoylmethylphosphine oxide (CMPO) calix[4]arene ligand to the silica surface yields an anchored host site that displays an unusual 22.4‐fold higher affinity (kD value) for EuIII relative to AmIII. This selective cation recognition is in stark contrast to a more flexible propoxy‐tethered CMPO‐calix[4]arene site on silica. A grafted CMPO‐calix[4]arene site on silica demonstrates affinity for EuIII over AmIII, which is unique when compared with a more flexible propoxy‐tethered CMPO‐calix[4]arene site as well as all previously reported CMPO‐calix[4]arene ligands. The results highlight the importance of rigidity when anchoring sites for cation recognition on solid surfaces.