Green light-triggered generation of peroxynitrite with fluorescent reporting exploiting doxorubicin as a photoredox...

Peroxynitrite (ONOO^-) plays a dominant role in chemistry and biology owing to its dual action as an excellent oxidant and nucleophile. This makes ONOO^- a potent cytotoxic agent that can be used as an "unconventional" therapeutic agent, opening new avenues for innovative treatment modalities to tackle a variety of diseases. However, the lack of cell selectivity of ONOO^- makes its spatiotemporal control mandatory and highly challenging. Herein, we report a new molecular strategy to generate ONOO^- with precise spatiotemporal control using highly biocompatible green light as the only excitation source and the chemotherapeutic agent doxorubicin (DOX) as a photoredox catalyst in the presence of a nitroso derivative of amino-nitro-benzofurazan (NBF-NO) and physiological concentrations of glutathione (GSH). We demonstrate that the excited triplet state of DOX, populated after green light excitation of the drug, is quenched by GSHvia electron transfer, producing the DOX semiquinone radical anion. Under anaerobic conditions, this species is oxidized back to DOX by NBF-NO, with the consequent formation of the NBF-NO radical anion, which releases nitric oxide (NO) and converts to NBF as the sole stable photoproduct. On the other hand, under aerobic conditions, molecular oxygen competes with NBF-NO in the oxidation of the semiquinone radical anion, restoring DOX and, consequently, forming a superoxide anion (O₂˙^-), which generates ONOO^- through a well-known diffusion-controlled reaction with NO. In both cases, the highly fluorescent photoproduct NBF serves as an internal optical reporter, enabling real-time monitoring of the photocatalyzed reaction. This work establishes the photochemical foundations of a green-light activated ONOO^--generating platform, providing a mechanistic basis for ongoing biological and therapeutic investigations.