Free radical intermediates in the oxidation of N-methylhydroxylamine and N,N-dimethylhydroxylamine by oxyhemoglobin

Nitroxide radicals have been detected in the methemoglobin formation reaction between oxyhemoglobin and the substituted hydroxylamine compounds, N-methylhydroxylamine and N,N-dimethylhydroxylamine, by ESR spectroscopy. The stability of these nitroxide radicals was considerably higher than that of the NH2O. radical derived from unsubstituted hydroxylamine. Only in the case of N-methylhydroxylamine the detection of the nitroxide radical required the use of a flow system, because the radical was found to undergo a rapid degradation with the concomitant formation of a secondary product, the beta-aminonitroxide CH3NO.CH2NH2. The nitroxide radical derived from N,N-dimethylhydroxylamine and oxyhemoglobin was stable for more than 1 hour. In addition, formation of low-spin iron-(III)-complexes from methemoglobin and excess substituted hydroxylamine was observed in both cases. Neither N-methylhydroxylamine nor N,N-dimethyldroxylamine formed the hemoglobin-nitric oxide complex found with unsubstituted hydroxylamine. Parallels and differences in the reaction path of un-, mono- and disubstituted hydroxylamines are discussed.