Anion recognition by diureido-calix[4]arenes in the 1,3-alternate conformation

A series of diureido-calix[4]arenes immobilised in the 1,3-alternate conformation was synthesised and systematically studied for their complexation ability. As revealed by H-1 NMR and UV/vis titrations, this structural motif leads to very efficient ligands for anion recognition with high binding constants in nonpolar solvents. The comparison with the corresponding ligands possessing the cone conformation indicates that diureido-calix[4]arene in a 1,3-alternate conformation are very promising anion receptors with pronounced binding ability towards carboxylates.