Selective zinc sensor based on pyrazoles and quinoline used to image cells

The synthesis, Zn²⁺ binding, crystal structure, and cell imaging studies of a new pyrazole amine quinoline receptor with a flexible binding pocket are described. Upon coordination to Zn²⁺, the absorption of the receptor increases at 364 nm and it fluoresces at 500 nm. The fluorescence response to Zn²⁺ is selective for Zn²⁺ and does not occur with other metal ions, not even Cd²⁺. In solution, the receptor forms 1:1 complexes with Zn²⁺, but in the solid-state two Zn²⁺ ions coordinate to the receptor. The aqueous solubility of the receptor allows for imaging of Zn²⁺ in living cells. Cells exposed to receptor and Zn²⁺ fluoresce when excited with visible light.