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 Zn ²⁺ 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.