Xu, Y., Liu, Q., Dou, B., Wright, B., Wang, J., and Pang, Y. (2012) Zn(2+) Binding-Enabled Excited State Intramolecular Proton Transfer: A Step toward New Near-Infrared Fluorescent Probes for Imaging Applications. Advanced Healthcare Materials. 1(4):485-492.
In 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 (K(d) = 2.58 nM(2) ) and selectivity for Zn(2+) cation, revealing about 14-fold fluorescence enhancement
upon zinc binding to give green emission. Remarkably, Zn(2+) 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 Zn(2+) ion. The Zinhbo-5 is also useful
for detecting zinc ion distribution during the development of living zebrafish embryos.