Electrochemical recognition of alkali metal ions at the micro-water 1,2-dichloroethane interface using a calix[4]arene derivative

In this paper, a calix[4]arene derivative, 5,11,17,23-butyl-25,26,27,28-tetra-(ethanoxycarbonyl)-methoxy-calix[4]arene (L), is investigated as a host to recognize alkali metal ions (Li+, Na+, K+, Rb+ and Cs+) at the interface between two immiscible electrolyte solutions (ITIES). Well-defined cyclic voltammograms are obtained at the micro- and nano-water ∣ 1,2-dichloroethane (W ∣ DCE) interfaces supported at micro- and nano-pipets. The diffusion coefficient of this ionophore in the DCE phase is (3.8±0.4)×10−6 cm2 s−1. When the ion transfers across the interface, a 1:1 (metal:ionophore) complex is formed at the interface except for Cs+ ion. For the case of Cs+, a 1:2 (metal:ionophore) complex is verified from its special electrochemical response to the variation of [L] in the organic phase. The logarithms of the association constants of the LiL+, NaL+, KL+ and RbL+ complexes in the DCE phase (log β1o), are calculated to be 11.6, 13.0, 11.3 and 9.2, respectively, and the logarithm of the cumulative association constant of CsL2+ (log β2o) is found to be 7.9. The rate constants of these facilitated ion transfer processes are obtained using nano-pipet voltammetry. The large association constants, the rapid interfacial reaction rates and the ‘broad spectrum’ recognition of metal ions suggest that this ionophore might have many potential applications in ion recognition and the fabrication of electrochemical sensors.