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首页> 外文期刊>Lipids >Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α-Tocopherol: The Hydroperoxide Pathway
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Autoxidation of Conjugated Linoleic Acid Methyl Ester in the Presence of α-Tocopherol: The Hydroperoxide Pathway

机译：α-生育酚存在下共轭亚油酸甲酯的自氧化作用：氢过氧化物途径

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摘要

Autoxidation of conjugated linoleic acid (CLA) methyl ester follows at least partly Farmer’s hydroperoxide theory. A mechanism for this hydroperoxide pathway has been proposed based on autoxidation of 9-cis,11-trans-CLA methyl ester. This investigation aims at confirming and further clarifying the mechanism by analyzing the hydroperoxides produced from 10-trans,12-cis-CLA methyl ester and by theoretical calculations. Five methyl hydroxyoctadecadienoates were isolated by HPLC and characterized by UV, GC-MS, and 1D- and 2D-NMR techniques. In addition, an HPLC method for the separation of the intact hydroperoxides was developed. The autoxidation of 10-trans,12-cis-CLA methyl ester in the presence of high amount of α-tocopherol (20%) was diastereoselective in favor of one geometric isomer, namely Me 9-OOH-10t,12c, and produced new positional isomers 10- and 14-hydroperoxides (Me 10-OOH-11t,13t; Me 14-OOH-10t,12c; and Me 14-OOH-10t,12t). Importantly, one of these new isomers, which was characterized as an intact hydroperoxide, had an unusual cis,trans geometry where the cis double bond is adjacent to the hydroperoxyl-bearing methine carbon. Further insight to the mechanism was provided by calculating the relative energies for different conformations of the precursor lipid, the allylic carbon–hydrogen bond dissociation enthalpies, and the spin distributions on the intermediate pentadienyl radicals. As a result, a better understanding of the isomeric distribution of the product hydroperoxides was achieved and a modified mechanism that accounts for these calculations is presented.
机译：共轭亚油酸（CLA）甲酯的自氧化反应至少部分遵循了Farmer的氢过氧化物理论。已经提出了基于9-顺式，11-反式-CLA甲酯的自氧化的氢过氧化物途径的机理。本研究旨在通过分析由10-反式，12-顺式-CLA甲酯产生的氢过氧化物并通过理论计算来确认和进一步阐明其机理。通过HPLC分离出五种甲基羟基十八碳二烯酸甲酯，并通过UV，GC-MS，1D和2D-NMR技术进行了表征。另外，开发了用于分离完整氢过氧化物的HPLC方法。在存在大量α-生育酚（20％）的情况下10-反式12-顺式CLA甲酯的自氧化具有非对映选择性，有利于一种几何异构体，即Me 9-OOH-10t，12c，并产生了新的位置异构体10-和14-氢过氧化物（Me 10-OOH-11t，13t; Me 14-OOH-10t，12c; Me 14-OOH-10t，12t）。重要的是，这些新的异构体之一被表征为完整的氢过氧化物，具有不寻常的顺式，反式几何构型，其中顺式双键与带有氢过氧基的次甲基碳相邻。通过计算前体脂质不同构象的相对能量，烯丙基碳氢键解离焓以及中间戊二烯基上的自旋分布，可以进一步了解该机理。结果，获得了对产物氢过氧化物的异构体分布的更好理解，并提出了解释这些计算的改进机理。

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