A quinoxaline-containing Schiff base probe for the selective and sensitive detection of Zn²⁺ and imaging application in living cells

A Schiff base probe, namely N '-(quinoxaline-2-ylmethylene) pyridinyl hydrazide (1) was produced by a simple condensation reaction and was fully characterized through H-1 NMR, C-13 NMR, and ESI-MS. Probe 1 was non-emissive while displaying a strong emission at 500 nm in the presence of Zn2+. This fluorescence enhancement was highly selective and sensitive toward Zn2+ over other common cations, with a detection limit of 0.16 mu mol center dot L-1. The coordination mode of 1 with Zn2+ was proposed by means of ESI-MS, H-1 NMR, and UV-Vis. The crystal structure of the 1-Zn2+ complex was characterized by X-ray single-crystal diffraction, further confirming the coordination behavior of the probe. The results showed that the probe can coordinate two independent Zn2+ ions via ONN and NN donor sets, which are connected by bridged CH3O- and Cl- to form a 1D chain. Finally, the probe was used to trace Zn2+ in HeLa cells.