Side-Chain-Driven Dual Structural System of Poly-Arylopeptide: Selective Helical Formation Derived from Aromatic Ring Flips on the Backbone

A methodology for producing dual structural systems of macromolecules, which involves flipping the unsymmetrical aromatic rings on the main chain is presented. Previously, we reported a non-natural polypeptide containing an aromatic ring on the peptide backbone, called a poly arylopeptide. Herein, we used 2,6-naphthalene rings as axially unsymmetrical spacers, which has two geometrical isomers, anti and syn, to create dual structural properties. The miniscule energy difference between the two geometrical isomers can be amplified by incorporating the 2,6-naphthylene units into the polypeptide backbone, which creates a thermodynamic driving force for the formation of two specific global structures (i.e., 31-helix or 41-helix) biased toward one side geometrical isomer depending on the side chain. Additionally, the 31-helix can be switched to the 41-helix upon addition of a small amount of additives, indicating a conformational conversion from an identical sequence. The developmental dual helical systems exploit basic molecular geometry and can serve as a design platform for synthetic polymers.