Peroxidase-promoted aerobic oxidation of 2-nitropropane: mechanism of excited state formation

Using sensitized emission, the horseradish peroxidase-catalyzed aerobic oxidation of the toxic pollutant 2-nitropropane to nitrite and acetone is shown to produce the latter in the electronically excited triplet state. In turn, this chemiexcitation implies a hydroperoxide precursor. Taking into account the stoichiometry of the reaction and available isotopic data it is inferred that the hydroperoxide reacts with a second molecule of the substrate (aci form). While triplet acetone formed from isobutanal (enol form) is generated within the enzyme, in the present case triplet acetone is formed in the bulk solution.