Partial Anion Exchange Triggered Helical Conformation in Chiral Polyelectrolyte: Demonstration of “Sergeants and Soldiers Like Effect”

Abstract

Synthetic helical polymers have gained tremendous attention due to their superior efficiency in mimicking the complex self-assembly “helix” of biological systems. Prolinate-based chiral polyelectrolytes bearing chloride counter anion (poly-(L-)-Pro-Cl) is circular dichroism (CD) silent and exist as random coils. For instance, the same chiral polymer with methoxide counter anion (poly-(L-)-Pro-OMe) shows CD response with preferred-handed helical sense. Here we have used partial anion exchange of chloride anion with methoxide as a simple and effective technique to bring the induced CD, eventually helical sense to poly-(L-)-Pro-Cl. Even with 1 mol% of methoxide exchange, the obtained chiral random copolymer poly-(L-)-Pro-Cl_0.99-co-poly-(L-)-Pro-OMe_0.01 showed induced CD. The random copolymer poly-(L-)-Pro-Cl_0.50-co-poly-(L-)-Pro-OMe_0.50 with 50 mol% of the methoxide anion exchanged, showed induced CD identical to that of poly-(L-)-Pro–OMe. In partial anion exchange-induced random copolymers, methoxide-containing polymer units act as sergeants and chloride-containing units act as soldiers. Through the “sergeants- and soldiers-like effect,” partial anion exchange reactions trigger the helical sense into the polymer chains. CD analysis provided strong support for the study. Here, the study provides a novel approach to the helical amplification phenomenon, which corresponds to the “sergeants- and soldiers-like effect.”