Electrochemical recognition of metal cations by redox-active receptors in homogeneous solution and in polymer films: some relevant examples

Abstract

Examples of several molecular redox-active receptors containing a ferrocene redox centre and crown ether or bipyridyl moieties as binding site are presented. Their electrochemical recognition properties towards groups I and II (crown ether-based receptors) and Cu + (2,2′-bipyridine-based receptors) metal cations have been investigated by cyclic voltammetry in homogeneous solution. Among the four ferrocene-crown ether studied, Fcc 3 allowed the effective amperometric recognition of Ba 2+ and Ca 2+ cations owing to the growth of a new redox peak system at the expense of the original Fc/Fc + wave (two-wave behavior). In addition, comparison of the electrochemical features in the presence of Cu + cations of ferrocene monosubstituted (Fcb 1) and disubstituted (Fcb 2) by bipyridyl groups emphasized the beneficial “sandwich” effect on the recognition behavior of ferrocene-based receptors. Polymer films coated onto electrodes surfaces by electropolymerization of pyrrole-substituted Fcc 3 and Fcb 2 retained the complexation and the amperometric properties, studied by cyclic voltammetry, of the molecular receptors. Furthermore, capacity measurements using electrochemical impedance spectroscopy (EIS) appeared as a good method for detection and titration of metal cations with these polymer-modified electrodes.