Self-Assembly of N-Terminal Aryl Amino Acids into Adaptive Single- and Double-Strand Helices.

Abstract

Helical structures are important features of many important biomacromolecules such as double helices and single α-helices in DNA and protein, respectively, yet the self-organization of short oligopeptides (<3) or independent amino acids into artificial helical structures on the atomic level remains mysterious. Here we present the direct construction of artificial double and single helices from N-terminated aryl amino acids (ferrocene phenylalanine (Phe) conjugates) despite both Phe and Phe-Phe dipeptide self-aggregations adopting supramolecular β-sheet structures, which also demonstrated chirality evolution exposed to small molecular binders. In the solid state, the box-shaped building unit stacks into a double helix with enantiomer-resolved handedness driven orthogonally by H-bonds and the CH-π interaction. The entire double helix is noncovalently linked except for the hybridization regions. Asymmetric H-bonds between carboxylic acids and amides facilitates the one-dimensional helical packing of amino acid residues. The ditopic building unit adopts intramolecular H-bonds, facilitating single-strand helix formation. In aqueous self-assemblies, the superhelical structures were retained, which underwent chirality transfer and handedness inversion upon complexation orthogonally by H-bonds and charge-transfer interaction, showing adaptivity to environmental factors.