Transfer of highly hydrophilic ions between immiscible liquids at the three-phase junction using a squaramide-based ion pair receptor

Abstract

Although many redox probes have been used for anion transfer studies in three-phase junction setups, no known molecule would enable the transfer of highly hydrophilic anions. In recent years, research has been emerging on ion pair receptors consisting of a crown ether cation binding site and a squaramide anion binding domain, which offer the ability to extract extremely hydrophilic sulphate salts. In this paper, we show that we can induce the transfer of sulphate and fluoride anions at a three-phase electrode setup using the oxidation of a squaramide-based compound in the organic phase. We evaluate the compound for the transfer of sulphate and fluoride ions and its selectivity towards other anions. We performed measurements of the transfer of ions in regular electrochemical cells, with a small organic drop deposited onto the surface of a glassy carbon electrode. These measurements demonstrate the potential of applying ion-transfer voltammetry in the characterization of organic compounds and sensing