Identification of spin trapped carbon-centered radicals in soybean lipoxygenase-dependent peroxidations of ω-3 polyunsaturated fatty acids by LC/ESR, LC/MS, and tandem MS

With the combined techniques of on-line liquid chromatography/electron spin resonance (LC/ESR) and on-line liquid chromatography/mass spectrometry (LC/MS), we have previously characterized all classes of lipid-derived carbon-centered radicals (•Ld) formed from ω-6 polyunsaturated fatty acids (PUFAs: linoleic acid and arachidonic acid). In the present study, the carbon-centered radicals formed from two ω-3 PUFAs (linolenic acid and docosahexaenoic acid) resulting from their reactions with soybean lipoxygenase in the presence of α-[4-pyridyl 1-oxide]-N-tert-butylnitrone (POBN) were investigated using the combination of LC/ESR and LC/MS techniques. A total of 16 POBN trapped carbon-centered radicals formed from the peroxidation of linolenic acid and 11 formed from the peroxidation of docosahexaenoic acid were detected by LC/ESR, identified by LC/MS, and structurally confirmed by tandem mass analysis (MS/MS). The on-line ESR chromatograms and MS chromatograms obtained from two ω-3 PUFAs closely resembled each other not only because the four major β-scission products, including an ethyl radical and three isomeric pentenyl radicals, were formed from each PUFA, but also because isomeric POBN adducts of lipid dihydroxyallylic radicals from both PUFAs had almost identical chromatographic retention times. @2003 Elsevier Inc.