The naphthoimidazolium borane 4 is shown to be a selective probe for HOCl over other reactive oxygen species. Unlike other boronate-reactive oxygen species (ROS) fluorogenic probes that are oxidized by HOCl through a nucleophilic borono-Dakin oxidation mechanism, probe 4 is distinguished by its electrophilic oxidation mechanism involving B-H bond cleavage. Two-photon microscopy experiments in living cells and tissues with the probe 4 demonstrate the monitoring of endogenous HOCl generation and changes in HOCl concentrations generated in the endoplasmic reticulum during oxidative stress situations.
We thank the National Research Foundation of Korea for the financial support (2012R1A3A2048814 to J.Y., 2016-R1E1A1A02920873 to H.M.K., and 2018R1D1A1B07043568 to J.B.). We also thank the Western Seoul (LC\u2212MS) and Daegu (FAB) branches of the Korea Basic Science Institute for mass spectrometric data.
