Heteroatom-directed supramolecular helical-rich architectures in N-terminal protected pyridyl aromatic amino acids

Supramolecular helical structures formed by the assembly of biological and bio-inspired building blocks (typically amino acids, peptides and proteins) are an intriguing class of materials with prospective applications in sustainable biomedical technologies and electronics. Specifically, short peptide or single amino acid building blocks can give rise to ideal materials candidates in terms of low cost, adjustability, and compatibility. Yet, to date, reliable helical topologies with specific handedness have been highly challenging to obtain. Herein, we present simple N-terminal protected aromatic pyridyl amino acids that display helicity at the molecular level confirmed by single-crystal X-ray diffraction analysis. The helical structure is stabilized by strong intermolecular hydrogen bonding between the pyridyl nitrogen and carboxylic acid groups. By comparing the specific l and d isomers with the dl racemic mixture, we explicitly demonstrate the influence of amino acid chirality on supramolecular crystal packing, self-assembly, and electromechanical properties. Atomic force microscopy (AFM) nanoindentation analysis confirms the strong rigidity of the dl assembly with very high Young's modulus (31.8 ± 11.9 GPa) attributed to the stacked face-to-face dimers with macrocyclic architectures. The present study provides an effective strategy for precisely formulating supramolecular helical structures, which could pave the way for the development of new bio-electronic applications of smart chiroptical materials from functionalised amino acids.