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

Area of Science:

• Bioinorganic Chemistry
• Supramolecular Chemistry
• Catalysis

Background:

• Nitric oxide (NO) is a crucial biological messenger, but its excess is toxic.
• Nitric oxide dioxygenase (NOD) enzymes detoxify NO by converting it to nitrate (NO₃^-).
• Developing synthetic models of NOD enzymes that function in aqueous environments is challenging.

Purpose of the Study:

• To create stable, water-soluble synthetic models of NOD enzymes.
• To investigate the mechanism of NO conversion to nitrate within a supramolecular host.
• To demonstrate both direct and indirect NOD pathways using integrated models.

Main Methods:

• Host-guest chemistry utilizing a water-soluble cationic Pd₆L₄¹²⁺ nanocage.
• Encapsulation of a mononuclear nonheme {FeNO}⁶ nitrosyl complex within the nanocage.
• Reaction studies with O₂ and NO in aqueous solution, followed by mechanistic investigations.

Main Results:

• The encapsulated {FeNO}⁶ complex remained stable in water for days.
• The complex reacted with O₂ to exclusively produce nitrate (NO₃^-).
• A previously reported Fe^IV-O₂^•- complex also converted NO to NO₃^-, suggesting a peroxynitrite intermediate.

Conclusions:

• The study presents the first integrated model of NOD activity within a single supramolecular framework in water.
• Demonstrated both indirect and direct NOD pathways under ambient conditions.
• Highlights the potential of host-guest chemistry in stabilizing reactive species for biomimetic catalysis.