The follow-up1 to Julia’s previous publication on assisted ion transfer at the three-phase junction was a long time coming. As in the previous paper, we used a squaramide-based ionophore to help transferring hydrophilic ions across the interface between to immiscible liquids, but here, the ionophore was functionalised with a ferrocene group to give it more controlled redox properties. However, this caused some unexpected issues. The molecule was very unstable in the solvent we normally use for the three-phase junction (TPJ) experiments, where it quickly oxidised. It was also stubbornly insoluble in other commonly used organic solvents for TPJ
Looking for a new solvent that may work, we stumbled on DMSO. There was one issue, however… DMSO is completely miscible with water which would normally exclude it from these kinds of measurements. Karolina, our amazing intern who performed many of the measurements, tried anyway and got beautiful, reproducible voltammetry. How?
A little investigation showed that the DMSO with the ionophore didn’t dissolve completely in the water. Instead, a relatively stable emulsion was formed. Numerous small droplets were formed on the electrode making lots of small three-phase junctions. This was enhancing the reproducibility of the measurements, and we could show that both very hydrophilic flouride and sulphate ions could be transferred. These voltammetric studies using the ferrocene-modified ion receptor indicate that it might shows that it is possible to identify an ionophore capable of transporting sulphate ions across immiscible liquid boundaries. Substituting the crown ether with an electron-withdrawing group that does not interact with cations could enhance its performance in potentiometric applications, which is a more practical technique than TPJ-measurements. It’s also necessary to work on the solubility in more commonly used solvents.
This work was done in collaboration with colleagues from Warsaw University, who synthesised the new ionophore.
- J. Maciejewska-Komorowska, K. Peret, M. Zaleskaya-Hernik, J. Romański, M. Jönsson-Niedziółka
Application of the oxidation reaction of a ferrocene derivative (FcSQC6) as driving force for the transfer of hydrophilic sulphate anions at a microemulsion three-phase electrode, Talanta 298, 128849 (2026). (link)(Preprint on ChemRxiv).
