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

Examples of several molecular redox-active receptors containing a ferrocene redox centre and crown ether or bipyridyl moieties as binding site are pre sented. Their electrochemical recognition properties towards groups I and I I (crown ether-based receptors) and Cu+ (2,2'-bipyridine-based receptors) m etal cations have been investigated by cyclic voltammetry in homogeneous so lution. Among the four ferrocene-crown ether studied, Fee, allowed the effe ctive amperometric recognition of Ba2+ and Ca2+ cations owing to the growth of a new redox peak system at the expense of the original Fc/Fc(+) wave (t wo-wave behavior). In addition, comparison of the electrochemical features in the presence of Cu+ cations of ferrocene monosubstituted (Fcb(1)) and di substituted (Fcb(2)) by bipyridyl groups emphasized the beneficial "sandwic h" 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 amperometri c properties, studied by cyclic voltammetry, of the molecular receptors. Fu rthermore, capacity measurements using electrochemical impedance spectrosco py (EIS) appeared as a good method for detection and titration of metal cat ions with these polymer-modified electrodes. (C) 1999 Elsevier Science S.A. All rights reserved.