Zn2+ Binding‐Enabled Excited State Intramolecular Proton Transfer: A Step toward New Near‐Infrared Fluorescent Probes for Imaging Applications

• DOI: 10.1002/adhm.201200025
• Publication Date: 2012-05-11T13:45:35Z
• Authors: Yongqian Xu; Qin Liu; Bairui Dou; Brian Wright; Jingyun Wang; Yi Pang
• Keywords: Binding Sites; Microscopy, Fluorescence; Infrared Rays; Contrast Media; Humans; Nanoparticles; Protons; 01 natural sciences; Fluorescent Dyes; HeLa Cells; 0104 chemical sciences

AbstractIn order to facilitate the in vivo study of zinc‐related biology, it is essential to develop a zinc‐selective sensor that exhibits both near‐infrared (NIR) emission and larger Stokes shift. A fluorescent sensor, Zinhbo‐5, has been constructed by using bis(benzoxazole) ligand with 2, 2'‐dipicolylamine (DPA) as metal ion receptor. In aqueous solution, Zinhbo‐5 exhibits high sensitivity (Kd = 2.58 nM2) and selectivity for Zn2+ cation, revealing about 14‐fold fluorescence enhancement upon zinc binding to give green emission. Remarkably, Zn2+ binding to Zinhbo‐5 switches on the excited state intramolecular proton transfer (ESIPT), producing the desirable near‐infrared region (over 710 nm) with large Stokes shift (ca. 240 nm). The new probe is demonstrated to be useful for in vivo imaging of the intracellular Zn2+ ion. The Zinhbo‐5 is also useful for detecting zinc ion distribution during the development of living zebrafish embryos.