Zinc selective chemosensors based on the flexible dipicolylamine and quinoline

Zinc sensor molecules containing quinoline have been synthesized, which show fluorescence in the presence of Zn2+. The nitrogen in quinoline is critical to fluorescence and fluorescence enhancement is promoted by deprotonating the sensor’s amide. One of the sensors is highly selective for Zn2+ over Cd2+ and other cations such as Hg2+, Fe2+, Mn2+ and Ca2+. This selectivity can be attributed to the increased absorption of the sensor in the presence of Zn2+ and the strong binding of Zn2+. Structural studies, including X-ray and NMR, show the ability of dipicolylamine (DPA) to bind in facial and meridional manners to Zn2+. Crystal structures of different compounds show Zn2+ coordinating to three, four, and five nitrogens from the compounds. They also indicate that the selectivity of DPA containing compounds towards Zn2+ may originate from Zn2+ being stable in different coordination environments.

Graphical abstractReceptor molecules containing quinoline and dipicolylamine bind Zn2+ and show fluorescence enhancement. Crystal structures and NMR spectra show the flexibility of dipicolylamine and different coordination geometries of Zn2+. The receptors have selective fluorescence for Zn2+ over other metal ions, including Cd2+.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Quinoline and bispicolylamine-based chemosensors. ► Selective zinc sensor. ► NMR characterization of zinc binding. ► Fluorescence enhancement due to zinc.