Facilitating functionalization of benzene-1,3,5-tricarboxamides by switching amide connectivity

Abstract

Synthetic water-compatible supramolecular polymers based on benzene-1,3,5-tricarboxamides (BTAs) have attracted a lot of interest in recent years, as they are uniquely suited to generate functional multicomponent biomaterials. Their morphologies and intrinsic dynamic behaviour mimic fibrous structures found in nature. Moreover, their modularity allows control of the density of functionalities presented on the surface of the fibres when using functionalized BTA monomers. However, such moieties generally comprise a functionality on only one of three side chains, resulting in lengthy synthetic protocols and limited yields. In this work, we avert the need for desymmetrization of the core by starting from commercially available 5-aminoisophthalic acid. This approach eliminates the statistical reactions and reduces the number of synthetic steps. It also leads to the inversion of the connectivity of one of the amides to the benzene core. By combining spectroscopy, light scattering and cryogenic transmission electron microscopy, we confirm that the inversed amide BTAs (iBTAs) form intermolecular hydrogen bonds and assemble into supramolecular polymers, like previously used symmetrical BTAs, albeit with a slight decrease in water solubility. Solubility problems were overcome by incorporating iBTAs into conventional BTA-based supramolecular polymers. These two-component mixtures formed supramolecular fibres with a morphology and dynamic behaviour similar to BTA-homopolymers. Finally, iBTAs were decorated with a fluorescent dye to demonstrate the synthesis of functional monomers, and to visualize their co-assembly with BTAs. Our results show that functionality can be introduced into supramolecular polymers with monomers that slightly differ in their core structure while maintaining the structure and dynamics of the fibres.