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., 3 1 -helix or 4 1 -helix) biased toward one side geometrical isomer depending on the side chain. Additionally, the 3 1 -helix can be switched to the 4 1 -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.