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

Abstract

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.