Metal-ion recognition. Competitive bulk membrane transport of transition and post transition metal ions using oxygen-nitrogen donor macrocycles as ionophores

Abstract

A series of competitive metal ion transport experiments have been performed. Each involved transport from an aqueous source phase across a chloroform membrane phase into an aqueous receiving phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) while the membrane phase incorporated an ionophore chosen from a series of single-ring and double-ring macrocyclic ligands (incorporating mixed oxygen–nitrogen donor sets) together with hexadecanoic acid. The transport process was ‘driven’ by a back flux of protons, maintained by buffering the source and receiving phases at pH 4.9 and 3.0, respectively. Transport selectivity for copper(II) was observed in all cases. The results confirm that consideration of the mass balance of the metal ions present across all three transport phases is important for a fuller understanding of the nature of the discrimination process for the present systems.