Salt-bridged macrocycles as building blocks for aqueous supramolecular nanotube formation

The programmed construction of nanotubular architectures through self-assembly remains a major challenge in supramolecular chemistry, especially when targeting pores with dimensions within the molecular scale (1-5 nm) in aqueous media. This work introduces a strategy that integrates covalent design with ionic hydrogen bonding interactions to generate discrete macrocycles that subsequently stack into nanotubes. Both supramolecular processes - cyclization and polymerization - were studied independently through a combination of ¹H NMR, DOSY NMR, mass spectrometry, fluorescence spectroscopy, and SAXS, as well as AFM, TEM, and Cryo TEM microscopy techniques. Custom engineered C shaped monomers can cyclize with high fidelity into heterodimeric rings by establishment of dual carboxylate : amidinium salt bridge interactions, a process that can take place in both polar and apolar solvents and that is stabilized by chelate cooperativity. In aqueous environments, hydrophobic π-π interactions between the macrocycles drive supramolecular polymerization, yielding nanotubes with a diameter of ca. 4 nm. This novel approach validates a versatile platform for bottom-up nanotube construction, enabling compatibility with water, and expands the design space for functional nanostructures.