Formation of toroids by self-assembly of an α–α corner mimetic: supramolecular cyclization

Abstract

An α–α corner mimetic self-assembles to form a rod-like supramolecular structure which bends and closes end-to-end like a cyclization reaction to form uniform toroids. Each peptide fragment containing L-leucine, α-aminoisobutyric acid (Aib) and L-tyrosine forms rigid 3₁₀ helical structures stabilized by multiple intramolecular N–H⋯O hydrogen bonds. Two 3₁₀ helices are connected by the spacer 3-aminomethyl-benzylamine and maintain an angular distance of 120° and therefore mimic the α–α corner motif of a protein super secondary structure. The individual α–α corner subunits are themselves regularly interlinked through multiple water mediated intermolecular hydrogen-bonding interactions to form the rod-like supramolecular structure and toroids. The formation of the supramolecular structure has been proven with X-ray crystallography and other spectroscopic techniques. The cyclization of the supramolecular structure and toroid formation were studied by optical microscope, AFM and FE-SEM experiments. Despite other assignments such as exfoliation of graphene from graphite, the compound exhibits significant memory to finally produce the toroids.