Discrete Molecular Recognition Induced Higher-Order Structures: Fibrous Formation Triggered by Melamine Recognition with a Cationic Ethynylpyridine Macrocyclic Host

A tricationic shape-persistent macrocycle was obtained by methylation on the nitrogen atoms of the three 3,5-pyridylene groups of an alternating 2,6-/3,5-substituted ethynylpyridine macrocycle. The tricationic macrocycle recognized melamine in polar solvents such as DMSO and water, and the host-guest association in water induced a higher-order aggregate confirmed by UV-vis titration and dynamic light scattering experiments. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy indicated that fibrous network structures resulted from the stacking of the macrocycle and melamine complex.