Direct Detection of Nitroxyl in Aqueous Solution Using a Tripodal Copper(II) BODIPY Complex

The synthesis, photophysical properties, and a biological application of BODIPY-triazole 1 (BOT1) are described. BOT1 juxtaposes a BODIPY fluorophore with a tripodal ligand platform via a triazole bridge. The triazole linker is afforded by azide-alkyne click chemistry and comprises the third arm of the tripodal architecture. BOT1 binds Cu2+ in aqueous solution to form a Cu-II[BOT1] complex in which emission from the BODIPY moiety is efficiently quenched. This complex exhibits a prompt turn-on response when exposed to nitroxyl, and this emission response is specific to HNO over other reactive nitrogen and oxygen species. Notably, Cu-II[BOT1] does not fluoresce in the presence of nitric oxide, making this system the first discrete molecular probe capable of detecting HNO over NO under physiologically relevant conditions. Fluorescence microscopy experiments establish that Cu-II[BOT1] is membrane-permeable and can successfully signal the presence of HNO in live cells.