Effects of amino proton and denticity of quinoline-pyridine based dyes on Cd2+ and Zn2+ fluorescence sensing properties

Abstract

Zn2+ and Cd2+ are d10 metal ions with very different toxicity level but similar binding properties to most organic ligands. Herein, a series of quinoline-pyridine conjugates are synthesized and evaluated for binding properties on both metal ions. The effects of amino protons and number of N-donor atoms on the ligands binding to Cd2+ and Zn2+ were studied by UV–vis titration in aqueous solution. The association constant for Cd2+ is affected by amino protons and denticity of the ligands greater than that of Zn2+. As the results, the Cd2+/Zn2+ binding ratio can be tuned by the ligand design. L6, the ligand with 6 N atoms without the proton, exhibits the highest Cd2+/Zn2+ binding ratio with fluorescence enhancement at 480 nm. The ligand can be used for detecting Cd2+ with the detection limit of 69 nM in aqueous solution and monitoring Cd2+ within cells at the concentration range of 0.1−10 μM.