The formation of linoleic acid radical species under the oxidative conditions of the Fenton reaction (using hydrogen peroxide and Fe (II)) was monitored by FAB-MS and ES-MS using the spin trap 5,5-dimethyl-1-pyrrolidine-N-oxide, DMPO. Both the FAB and ES mass spectra were very similar and showed the presence of ions corresponding to carbon- and oxygen centered spin adducts (DMPO/L*, DMPO/LO*, and DMPO/LOO*). Cyclic structures, formed between the DMPO oxygen and the neighboring carbon of the fatty acid, were also observed. Electrospray tandem mass spectrometry of these ions was performed to confirm the proposed structure of these adducts. All MS/MS spectra showed an ion at m/z 114, correspondent to the [DMPO + H]+, and a fragment ion due to loss of DMPO (loss of 113 Da), confirming that they are DMPO adducts. ES-MS/MS spectra of alkoxyl radical adducts (DMPO/LO*) showed an additional ion at m/z 130 [DMPO - O + H]+, while ES MS/MS of peroxyl radical adducts (DMPO/LOO*) showed a fragment ion at m/z 146 [DMPO - OO + H]+, confirming both structures. Other fragment ions were observed, such as alkyl acylium radical ions, formed by cleavage of the alkyl chain after loss of water and the DMPO molecule. The identification of fragment ions observed in the MS/MS spectra of the different DMPO adducts suggests the occurrence of structural isomers containing the DMPO moiety both at C9 and C13. The use of ES tandem mass spectrometry, associated with spin trapping experiments, has been shown to be a valuable tool for the structural characterization of carbon and oxygen-centered spin adducts of lipid radicals.

中文翻译：

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通过质谱检测和表征亚油酸氧化产生的自由基加合物。

在Fenton反应的氧化条件下（使用过氧化氢和铁（II）），使用自旋阱5,5-二甲基-1-吡咯烷-N通过FAB-MS和ES-MS监测亚油酸自由基种类的形成氧化物，DMPO。FAB和ES质谱都非常相似，并显示了以碳和氧为中心的自旋加合物（DMPO / L *，DMPO / LO *和DMPO / LOO *）对应的离子的存在。还观察到在DMPO氧与脂肪酸的相邻碳之间形成的环状结构。对这些离子进行电喷雾串联质谱分析，以确认这些加合物的拟议结构。所有MS / MS光谱均显示对应于[DMPO + H] +的m / z 114离子，以及由于DMPO丢失（损失113 Da）而导致的碎片离子，证实它们是DMPO加合物。烷氧基自由基加合物（DMPO / LO *）的ES-MS / MS光谱显示m / z 130 [DMPO-O + H] +处有一个附加离子，而过氧基自由基加合物（DMPO / LOO *）的ES MS / MS显示m / z 146 [DMPO-OO + H] +处的碎片离子，确认了两个结构。观察到其他碎片离子，例如在水和DMPO分子失水后通过裂解烷基链形成的烷基alkyl离子。在不同DMPO加合物的MS / MS光谱中观察到的碎片离子的鉴定表明，在C9和C13处都存在含有DMPO部分的结构异构体。ES串联质谱法与自旋阱实验相关联的使用，已被证明是脂类自由基以碳和氧为中心的自旋加合物的结构表征的有价值的工具。