Inhibition of the Fenton reaction by nitrogen monoxide

The toxicity of iron is believed to originate from the Fenton reaction which produces the hydroxyl radical and/or oxoiron(2+). The effect of nitrogen monoxide on the kinetics of the reaction of iron(II) bound to citrate, ethylenediamine-N,N′-diacetate (edda), ethylenediamine-N,N,N′,N′-tetraacetate (edta), (N-hydroxyethyl)amine-N,N′,N′-triacetate (hedta), and nitrilotriacetate (nta) with hydrogen peroxide was studied by stopped-flow spectrophotometry. Nitrogen monoxide inhibits the Fenton reaction to a large extent. For instance, hydrogen peroxide oxidizes iron(II) citrate with a rate constant of 5.8×10³ M⁻¹ s⁻¹, but in the presence of nitrogen monoxide, the rate constant is 2.9×10² M⁻¹ s⁻¹ . Similar to hydrogen peroxide, the reaction of tert-butyl hydroperoxide with iron(II) complexes is also efficiently inhibited by nitrogen monoxide. Generally, nitrogen monoxide binds rapidly to a coordination site of iron(II) occupied by water. The rate of oxidation is influenced by the rate of dissociation of the nitrogen monoxide from iron(II). Electronic Supplementary Material Supplementary material is available for this article at