Unusual Hypochlorous Acid (HClO) Recognition Mechanism Based on Chlorine-Oxygen Bond (Cl-O) Formation

One of the most important endogenous reactive oxygen species, hypochlorous acid (HClO), is involved in numerous pathological and physiological processes. Herein, a near-infrared fluorescence probe (CyHR) was designed and synthesized for ultrafast (within 0.2 s), sensitive (limit of detection=39.44 nm), and selective response to HClO. The reaction mechanism was systematically analyzed by MS, ¹ H NMR spectroscopy, HPLC-MS techniques, and theoretical calculations. The results indicated that HClO can be recognized by CyHR, which is based on chlorine-oxygen (Cl-O) bond formation. To the best of our knowledge, this study is the first to find Cl-O bonds among organic aromatic compounds, given that Cl-O bonds are common among inorganics. Through biological experiments, CyHR was successfully applied to image exogenous and endogenous HClO in macrophage cells (RAW 264.7). Thus, CyHR is a promising tool for HClO-related physiological and pathological studies and may provide a means for designing HClO-specific fluorescence probes.