Mechanisms for ion formation during the electron impact-mass spectrometry of picolinyl ester and 4,4-dimethyloxazoline derivatives of fatty acids
Mechanisms for ion formation during the electron impact-mass spectrometry of picolinyl ester and 4,4-dimethyloxazoline derivatives of fatty acids
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DOI：
10.1016/s0009-3084(99)00133-4
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发表时间：
2000-03-01
影响因子：
3.4
通讯作者：
Christie, WW
中科院分区：
文献类型：
--
作者：
Hamilton, JTG;Christie, WW
质谱研究已经进行了同位素稳定的标记和氟化吡啶基酯和4，4-二甲基恶唑啉（DMOX）衍生物的脂肪酸，以建立离子形成的机制。相互氢转移被证明参与在m/= 126的离子与二甲基恶唑啉衍生物的形成和在m/z 164的离子与吡啶基酯。已经证明，在脂肪酸的羧基的α位包含氟原子可以增强重排，从而用甲酯和二甲基恶唑啉衍生物排出内部链片段。当两个氟原子插入到α位时，已经表明吡啶基酯发生类似的重排，尽管与其他衍生物中观察到的程度不同。提出并讨论了这种重新安排的机制。对于脂肪酸二甲基恶唑啉衍生物，M-15离子仅由环上甲基的损失产生，M-43离子至少有三种不同的形成机制。这种重排使得难以确定烷基链末端部分的身份。在质谱方面，吡啶甲酸酯似乎是脂肪酸结构表征的上级衍生物。(C)2000由Elsevier Science爱尔兰有限公司出版。保留所有权利。
Mass spectral studies have been conducted with isotopically stable labelled and fluorinated picolinyl esters and 4,4-dimethyloxazoline (DMOX) derivatives of fatty acids in order to establish mechanisms of ion formation. Reciprocal hydrogen transfer is shown to be involved in the formation of the ion at m/= 126 with dimethyloxazoline derivatives and for the ion at m/z 164 with picolinyl esters. Inclusion of a fluorine atom alpha to the carboxyl of a fatty acid has been demonstrated to enhance rearrangements for expulsion of internal chain fragments with both methyl ester and dimethyloxazoline derivatives. When two fluorine atoms are inserted into the alpha position a similar rearrangement has been shown to occur with picolinyl esters, although not nearly to the same extent as that observed with either of the other derivatives. Mechanisms for such rearrangements are proposed and discussed. With fatty acid dimethyloxazoline derivatives the M-15 ion arises solely from the loss of a methyl radical from the ring and the M-43 ion has at least three different mechanisms of formation. Such rearrangements make it difficult to establish the identity of the terminal moiety of the alkyl chain. In mass spectrometry terms the picolinyl ester would seem to be the superior derivative for structural characterisation of fatty acids. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.