Electrons and Ions Moving Across Liquid Membranes

Oxidation and reduction reactions can be carried out by interfacing the aqueous solution containing the reducing agent and the aqueous solution containing the oxidizing agent by a layer of a water immiscible solvent (e.g. CH2Cl2, the liquid membrane): in the membrane a lipophilic redox system C has to be present, which transports electrons from the aqueous reducing phase to the aqueous oxidizing phase and, in its oxidized form C+, X− anions in the opposite direction. Metal complexes have been tested as carriers for the transport of electrons across liquid membranes. In particular, transition metal complexes of lipophilic versions of cyclam and 2,2′-bipyridine have been investigated. The three-phase redox processes can be controlled by varying the potential of the C/C+ couple in the CH2Cl2 solution. Further selectivity effects derive from the kinetics of the electron transfer process at the membrane/aqueous phase interface. The possibility to perform light driven electron transport processes mediated by a metal centred carrier is discussed.