Influence of side-chain interactions on the self-assembly of discotic tricarboxyamides: a crystallographic insight

Abstract

Different assembly and behaviour of homologous discotic tricarboxyamides containing β-alanine and γ-aminobutyric acid have been investigated. From UV/Vis and FT-IR spectroscopy the tricarboxyamides have similar self-assembly patterns. But, the tricarboxyamide 2 containing γ-aminobutyric acid residues forms a gel in aromatic solvents after heating, cooling and ageing. However, the β-alanine analogue 1 failed to form a gel under the same conditions. From FE-SEM studies the tricarboxyamide 1 shows unbranched rod like morphology but the tricarboxyamide 2 exhibits an entangled fiber network. Finally, the X-ray crystallography reveals that both the tricarboxyamides 1 and 2 adopt 3-fold intermolecular H-bonded helical columnar structures. Detailed structural analysis shows that the individual helical columnar structures of tricarboxyamide 2 are themselves self-assembled through multiple hydrophobic interactions between side chains and thereby form a supramolecular network structure. However, the tricarboxyamide 1 columns are self-assembled into a supramolecular bundle-like structure. The result indicates that side chain interactions have a drastic effect on quaternary structure and function.