Effect of C12H25O– substituent position on the self-assembly behaviour of C6H5COO–Ala–Ala dipeptide

Three dipeptides based on the Ala–Ala building block with different substituent positions of the dodecyloxy group on the benzoyl residue at the N terminus were designed and synthesized (ortho-, meta- and para-16). All of them were able to spontaneously self-assemble in the mixed solvent of methanol and water (6/4, v/v). However, three dipeptides underwent a distinct kinetically controlled self-assembling process. The spectroscopic study also revealed that, for ortho-16, the phenylene groups and the peptide sequence loosely packed, while meta- and para-16 stacked into well-ordered structures with the formation of parallel β-sheets through supramolecular self-assembly. Intramolecular hydrogen bonding and steric hindrance of the dodecyloxy side chain were proposed to lead to the different self-assembling behaviour of the three isomers.