Self-Assembled Cyclic Structures from Copper(II) Peptoids.

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, OCH , or NH ) upon Cu 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 Cu 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.