Conformationally regulated fluorescent sensors. Study of the selectivity in Zn 2+ versus Cd 2+ sensing

Abstract The Zn 2+ and Cd 2+ complexing properties of four ligands containing a 4,4′-substituted biphenyl moiety are described. Ligands 1 and 3 , containing only one 1-aza-18-crown-6 cavity, lead to selective complexation of Cd 2+ versus Zn 2+ . Ligand 4 , with two crown cavities linked to a tetramethylbenzidine unit, is able to form 1:1 complexes with Zn 2+ and Cd 2+ , showing a higher complexing constant with Zn 2+ than with Cd 2+ , probably due to enthalpic factors. Several complementary experiments suggest that the 1:1 complexes formed by ligand 4 involve both crown cavities acting together to give rise to clamp structures. The formation of this type of zinc complex gives rise to red sh…