Helical secondary structures and supramolecular tilted chirality in N-terminal aryl amino acids with diversified optical activities

Abstract

Helix structures at atomic/molecular level have not been found in self-assembled peptide sequence with less than three residues. As β-sheet supramolecular secondary structures have been discovered in solid-state amino acids, we here report the conjugation of simple N-terminal aryl protecting group could give rise to helical supramolecular secondary structures in solid-state, which determines the optical activities of the adjacent aryl groups. The carboxylic acid-involved asymmetric H-bonds in N-terminal aryl amino acids induce the emergence of super-helical structures of amino acid residues and aryl groups. In most cases, supramolecular tilted chirality of aryl groups is opposite to that of amino acid sequences, of which handedness and helical pitch are determined by the H-bond modalities. Determining correlation between supramolecular tilted chirality of aryl segments and their chiroptical activities is firstly unveiled, which was verified by the computational results based on density functional theory. Most aryl amino acids self-assembled by nanoprecipitation method via crystallization induced self-assembly into rigid one-dimensional microstructures with ultra-high Young’s modulus. This study reveals the generic existence of chiral supramolecular structures in aggregated amino acid derivatives and gives an in-depth investigation into the structural-property relationships, which could guide the rational design and screening of chiroptical supramolecular materials.