REACTIONS OF ACTIVE OXYGEN AND NITROGEN SPECIES STUDIED BY EPR AND SPIN-TRAPPING

The reactions of hydrogen peroxide (H2O2) with nitrite (NO2-) and of s uperoxide (O2.-) with nitric oxide (NO.) were studied using EPR and sp in trapping techniques. These reactions reportedly have a common perox ynitrite (OONO-) intermediate. It has been suggested that this interme diate when protonated rapidly decomposes producing hydroxyl radicals ( .OH) and the nitrogen dioxide radical (NO2.). The production of .OH in the reaction between H2O2 and NO- was confirmed in spin trapping expe riments using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO). H 2O2 and NO- were mixed at neutral pH and then the pH was decreased to pH 3-3.5 in the presence of DMPO or DMPO and ethanol. In these experim ents, the EPR spectrum of the DMPO-OH adduct was obtained in addition to a weak EPR spectrum consisting of a triplet of triplets (a(N) = 1.4 15 mT and a(N)beta = 0.35 mT) indicating the addition of a nitrogen ce ntered radical to DMPO. The formation of .OH was confirmed using ethan ol as an .OH scavenger. The DMPO-hydroxyethyl adduct was produced from the reaction of .OH with ethanol. However, in experiments using an ex cess of ethanol, the formation of DMPO-OH was not prevented. This sugg ests that the DMPO-OH formed in the decomposition of HOONO does not en tirely originate from a direct addition of .OH to DMPO. The reaction o f O-2-radical-anion with NO. was carried out in deaerated and air-satu rated solutions at pH 12.3 where the dismutation of O-2-radical-anion is minimal. The pH was then decreased to pH 3-3.5 in the presence of D MPO or DMPO and ethanol. In these experiments, the most prominent EPR spectrum obtained was a triplet of triplets (a(N) = 1.415 mT and a(N)b eta = 0.35 mT) suggesting the addition of a nitrogen centered radical to DMPO. The formation of DMPO-OH was minimal and there was no formati on of DMPO-hydroxyethyl adducts in the presence of ethanol. The result s suggest that NO. in solution yields additional reactive species whic h act as nitrating agents in the presence of DMPO.