Diazaborines oxidize slowly with H 2 O 2 but rapidly with peroxynitrite in aqueous buffer.

Reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) and peroxynitrite (ONOO - ) oxidize arylboronic acids to their corresponding phenols. When used in molecular imaging probes and in ROS-responsive molecules, however, simple arylboronic acids struggle to discriminate between H 2 O 2 and ONOO - because of their fast rate of reaction with both ROS. Here, we show that diazaborines (DABs) react slowly with H 2 O 2 but rapidly with peroxynitrite in an aqueous buffer. In addition to their slow reaction with H 2 O 2 , the immediate product of DAB oxidation with H 2 O 2 and ONOO - can yield a kinetically trapped CN Z -isomer that slowly equilibrates with its E -isomer. Taken together, our work shows that diazaborines exhibit enhanced kinetic discrimination between H 2 O 2 and ONOO - compared to arylboronic acids, opening up new opportunities for diazaborine-based tools in chemical biology.