A highly fluorescent chemosensor for Zn2+ and the recognition research on distinguishing Zn2+ from Cd2+

Abstract

A new fluorescent sensor, 2-(2-oxo-2-(quinolin-8-ylamino)ethoxy)-N-(pyridine-2-ylmethyl) benzamide (L), composed of a quinoline group as the fluorogenic unit and a pyridin-2-ylmethanamine as the binding unit for metal ions has been synthesized. The sensor shows excellent selectivity and sensitivity with a fluorescence enhancement to Zn²⁺ over other cations in acetonitrile aqueous solution. The X-ray crystal structure analysis reveals that sensor L coordinates to Zn²⁺via a 1 : 1 binding mode but to Cd²⁺via a 2 : 1 binding mode, which lead to a different spatial arrangement of the fluorogenic unit in these complexes. In addition, density functional theory calculations on L, and the Zn²⁺/L and Cd²⁺/L complexes also imply that the different structures of L significantly affect the molecular orbital energy levels and electron transition, which would result in the spectral changes to distinguish Zn²⁺ from Cd²⁺. The absorption study results may also suggest the Cd²⁺ in the complex can be displaced by Zn²⁺. Furthermore, the fluorescence imaging of Zn²⁺ in living cells was obtained.