Synthesis and Recognition Properties of Amide-α-Cyclodextrin Derivatives and Their Imine-Bonded Dimers

The linking of multiple molecular receptors has attracted significant attention as a strategy for constructing unique complexes and controlling the binding states of guest molecules. In this study, we developed imine-bonded dimeric anion receptors capable of recognizing two anions via multipoint hydrogen bonding within each binding pocket. First, we synthesized per(5-N-carboxamide-5-dehydroxymethyl)-α-cyclodextrin derivatives (amide-α-CDs) bearing six aromatic amide groups directly attached to each pyranose ring. It was revealed that their anion recognition ability can be finely tuned by modulating the electron-withdrawing nature of the para-substituents. Moreover, leveraging the characteristic upright orientation of the six aromatic rings in the amide-α-CD, we synthesized amide-CD dimers by linking p-formylphenylamide groups with diamines. An X-ray diffraction analysis confirmed the formation of a well-defined tubular structure of the dimer. Subsequently, we demonstrated that the dimer linked by p-xylylenediimine encapsulated two anion molecules, such as acetate, benzoate, and nitrate, at its two binding sites. In contrast, halide ions, which were encapsulated by the monomer state of the amide-α-CD, did not interact with the dimer, indicating the change in anion selectivity upon the diimine linkage. These structural features and recognition properties suggest potential applications as an artificial ion channel or as a protein-mimetic receptor with multiple binding sites.