Macrocyclic Aromatic Amide Foldamer: Synthesis, Twisted-to-Boxlike Conformational Switching, and Molecular Recognition.

In this study, a twisted macrocycle was synthesized via ring closure of a double-helical aromatic oligoamide foldamer with two disulfide bridges. Single-crystal X-ray structure and NMR spectroscopy demonstrate the twisted conformation of macrocycle both in the solid state and in solution. As a result of the rearrangement of hydrogen bonding preference, the twisted conformation could be transformed to boxlike through protonation of the pyridine segments of macrocycle. In addition, the NMR titration experiments revealed that flat aromatic guests (e. g., coronene and perylene) could bind to the boxlike macrocycle with a 1 : 1 binding stoichiometry. The addition of base to the host-guest complexes resulted in conformational reversal of the macrocycle from boxlike to twisted as well as the release of guest.