Nitric Oxide Oxygenation Reaction in Water at Room Temperature inside a Cage

Nitric oxide (NO) is a vital biological signaling molecule, but its overproduction can be toxic, necessitating its rapid conversion to nitrate (NO3–) via NO dioxygenase (NOD) enzymes. These Fe-containing enzymes bind NO to form {FeNO}6 or {FeNO}7 intermediates, a key step in NO3– formation upon reaction with O2. However, synthetic NOD models that function in water remain rare. Here, we report the stabilization of a mononuclear nonheme {FeNO}6 ⊂ Cage (2) nitrosyl complex within a water-soluble cationic Pd6L412+ nanocage using host–guest chemistry. In an aqueous solution at room temperature, the encapsulated {FeNO}6 complex is stable for days yet reacts readily with O2 to exclusively yield NO3–. We further show that a previously reported FeIV–O2•– ⊂ Cage complex (3) also reacts with NO to produce NO3– exclusively in water. Mechanistic investigations suggest the formation of a peroxynitrite intermediate. This study presents the first integrated model of NOD activity of both {FeNO}6 ⊂ Cage and FeIV–O2•– ⊂ Cage within the same supramolecular framework in water at ambient temperature, demonstrating both indirect and direct NOD pathways.