Identification of intermediate and product from methemoglobin-catalyzed oxidation of o-phenylenediamine in two-phase aqueous-organic system.

Methemoglobin (metHb) was used as a mimetic enzyme for peroxidase to catalyze the oxidation reaction of o-phenylenediamine (OPDA) with H2O2 functioning as an oxidant. A reaction intermediate was obtained in two-phase aqueous-organic system and an absorption peak at 710 nm was confirmed to be that of the intermediate in relation to OPDA. The isolated product and intermediate were characterized by UV-Vis and IR spectrophotometry and HPLC-tandem mass spectrometry. The results showed that the product is 2,3-diaminophenazine, the molecular mass of the intermediate is 212 daltons, and a conceivable structure of the intermediate is suggested. Combining the catalyzed reaction mechanism of peroxidase and our experimental results, a conceivable oxidation reaction mechanism of OPDA and H2O2 using metHb as catalyst is proposed.