Self-Assembled Cyclic Structures from Copper(II) Peptoids

Abstract

Metal-ligand coordination is a key interaction in the self-assembly of both biopolymers and synthetic oligomers. Although the binding of metal ions to synthetic proteins and peptides is known to yield high-order structures, the self-assembly of peptidomimetic molecules upon metal binding is still challenging. Herein we explore the self-assembly of three peptoid trimers bearing a bipyridine ligand at their C-terminus, a benzyl group at their N-terminus, and a polar group (N-ethyl-R) in the middle position (R=OH, OCH₃ , or NH₂ ) upon Cu²⁺ coordination. X-ray diffraction analysis revealed unique, highly symmetric, dinuclear cyclic structure or aqua-bridged dinuclear double-stranded peptoid helicates, formed by the self-assembly of two peptoid molecules with two Cu²⁺ ions. Only the macrocycle with the highest number of intermolecular hydrogen bonds is stable in solution, while the other two disassemble to their corresponding monometallic complexes.

Keywords: copper coordination; foldamer; peptide; peptoid; self-assembly.