N-Heterocyclic Carbene Boranes as Reactive Oxygen Species-Responsive Materials: Application to the Two-Photon Imaging of Hypochlorous Acid in Living Cells and Tissues
N-Heterocyclic carbene (NHC) boranes undergo oxidative hydrolysis to give imidazolium salts with excellent kinetic selectivity for HOCl over other reactive oxygen species (ROS), including peroxides and peroxynitrite. Selectivity for HOCl results from the electrophilic oxidation mechanism of NHC boranes, which stands in contrast to the nucleophilic oxidation mechanism of arylboronic acids with ROS. The change in polarity that accompanies the conversion of NHC boranes to imidazolium salts can control the formation of emissive excimers, forming the basis for the design of the first fluorescence probe for ROS based on the oxidation of B−H bonds. Two-photon microscope (TPM) ratiometric imaging of HOCl in living cells and tissues is demonstrated.
This work was supported by the National Research Foundation of Korea (2012R1A3A2048814 to J.Y.; 2016R1E1A1A02920873 to H.M.K.; and 2015R1D1A1A01059383 to J.B.). We thank Dr. Sung Hong Kim of the Korean Basic Science Institute (Daegu) for EI-MS, and Dr. Su Jin Kim of the Korean Basic Science Institute (Seoul) for ESI-MS analyses.
