Studies on the photolytic breakdown of hydroperoxides and peroxidized fatty acids by using electron spin resonance spectroscopy. Spin trapping of alkoxyl and peroxyl radicals in organic solvents

Abstract

Spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to detect and distinguish between the carbon-centred, alkoxyl, and peroxyl radicals produced during the photolytic decomposition of hydroperoxides. Photolysis of tert-butyl and cumene hydroperoxides, and peroxidized fatty acids, in toluene, with low levels of u.v. light, is shown to lead to the initial production of alkoxyl radicals by homolysis of the oxygen-oxygen bond. Subsequent reaction of these radicals with excess hydroperoxide leads, by hydrogen abstraction, to the production of peroxyl radicals that can be detected as their corresponding adducts with the spin trap. Subsequent breakdown of these adducts produces alkoxyl radicals and a further species that is believed to be the oxidized spin-trap radical 5,5-dimethyl-1-pyrrolidone-2-oxyl. No evidence was obtained at low hydroperoxide concentrations, with either the cumene or lipid alkoxyl radicals, for the occurrence of beta-scission reactions; the production of low levels of carbon-centred radicals is believed to be due to the alternative reactions of hydrogen abstraction, ring closure, and/or 1,2 hydrogen shifts. Analogous experiments with 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO) led only to the trapping of alkoxyl radicals with no evidence for peroxyl radical adducts, this is presumably due to a decreased rate of radical addition because of increased steric hindrance.

Virgin olive oil: Free radical production studied with spin‐trapping electron paramagnetic resonance spectroscopy

“…Reaction of this spin trap with superoxide and hydroxyl radicals or radicals of a lipid nature derived from hydroxyl radicals produces spin-trapped adducts with characteristic EPR spectra (5,6). Moreover, spin trapping using DMPO has been used to detect and distinguish between carbon-centered, alkoxyl, and peroxyl radicals produced during metal ion-and lipoxygenase-catalyzed breakdown (7), as well as photolytic breakdown of peroxidized fatty acids (8).…”

The first 1H and 14N ENDOR spectra of an oxygen-centered radical adduct of DMPO-type nitrones

“…The sulfur analogues of alkoxyl radicals (thiyls) are also trapped at fast rate constants (-lo8 M-I s-' ) (13). spin trapping studies have suggested that oxygen-centered radicals may be important intermediates in radiolysis (14) and sonolysis (15) reactions, ozone-related chemistry (16,17), xanthinelxanthine oxidase systems (18), carcinogenesis (19), antitumour drug redox interactions (20)(21)(22), cigarette smoke (23), druglskin phototoxicity (24,25), neutrophil action (26a-c), peroxidation reactions (27)(28)(29)(30)(31), as well as myocardial ischemia/reperfusion injury (32a-c).…”

Evidence for L· against LOO· being spin-trapped by 4-POBN during the reaction of Fe2+-induced lipid peroxidation

“…b) The tate of formation of the spin trapping adducts with 4-POBN approached to zero when the reaction approximated anaerobiosis, c) No spectrum appeared in the presence of 4-POBN when the mixture was bubbled with nitrogen p¡ to the addition of fipoxygenase. It is apparent that they did not consid~r the fact that lipoxygenase is not active without oxygen or hydroperoxyl linoleic acid [14,17].…”

“…Rosen claimed that MNPOL-LOO was not stable as well [1]. Davies et al have trapped LOO" with DMPO produced from photolysis of hydroperoxides at room temperamre [17]. But Merritt et al have shown that the DMPO-LOO, if formed, were unstabte even at -80~ from the Pb(OAc)4-ROOH reaction [18].…”