Charge variable PIB-based block copolymers as selective transmembrane ion transporters

Abstract

Artificial functional ionophores are essential for selective transmembrane ion transport since ion transport through biological membranes is an essential phenomenon and its disruption causes a variety of illnesses. Herein, we have designed charge variable (anionic, neutral, or cationic) polyisobutylene (PIB)-based amphiphilic block copolymers, and investigated their selective ion transport activity via an artificial membrane. Typical aggregation behaviour of the amphiphilic copolymers in an aqueous medium was monitored using ¹H NMR spectroscopy, critical aggregation concentration (CAC) measurement by fluorescence spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and field emission scanning electron microscopy (FESEM). The ionophoric activity of the block copolymers below their CAC was investigated through an artificial membrane using 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as a fluorescent pH probe. The ion selectivity of the PIB-based block copolymers was further monitored by varying different cations (Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) and anions (NO₂⁻, Cl⁻, Br⁻, I⁻, and ClO₄⁻). The anionic and cationic block copolymers exhibit potent selective ion transport activities towards K⁺ and NO₂⁻, respectively. Thus, the right charge on the hydrophilic side chains of the block copolymer and the nature of the ions determines the ion transport selectivity.