A new charge-associated mechanism to account for the production of fragment ions in the high-energy CID spectra of fatty acids
A new charge-associated mechanism to account for the production of fragment ions in the high-energy CID spectra of fatty acids
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DOI：
10.1016/j.jasms.2004.11.008
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发表时间：
2005-02-01
影响因子：
3.2
通讯作者：
Harvey, DJ
中科院分区：
文献类型：
--
作者：
Harvey, DJ
提出了一种新的机制，称为电荷辅助过程，作为电荷远程过程的附加机制，以解释在脂肪酸和相关化合物的正和负高能CID谱中发现的[M-CnH 2n +2]系列离子，当电离为闭壳层（[M-H]（-）或[M + X]（+））物种时。新机制是基础。通常用来解释衍生脂肪酸的电子碰撞光谱中的类似离子，由此衍生物上的正电荷从烷基链的不同位置夺取氢原子，留下引发链的自由基诱导裂解的自由基。有人提出，在高能量CID光谱的闭壳层离子，类似的氢迁移发生，但不成对的电子是避免电荷转移到烷基链。然后，该电荷引发链的协同断裂，得到烯丙基碳正离子（正离子谱）或碳负离子（负离子谱）。该机制避免了需要涉及自由基或从偶电子（闭壳层）离子损失氢原子，并为反应提供了驱动力，即形成具有稳定电荷的离子。还提出了一个扩展的机制，以占奇电子离子从这些化合物的形成。电荷辅助机制并不排除其他已被接受多年的机制的出现，但提供了一个替代过程，可以解释一些以前难以解释的光谱特征。(C)2004年美国质谱学会。
A new mechanism, termed a charge-assisted process, is proposed as an additional mechanism to the charge-remote process to account for ions of the [M - CnH2n+2] series found in the positive and negative high energy CID spectra of fatty acids and related compounds when ionized as closed-shell ([M - H](-) or [M + X](+)) species. The new mechanism is based. on that commonly invoked to account for similar ions in the electron-impact spectra of derivatized fatty acids whereby the positive charge on the derivative abstracts a hydrogen atom from various positions of the alkyl chain to leave a radical that initiates a radical-induced cleavage of the chain. It is proposed that in the high energy CID spectra of closed-shell ions, similar hydrogen migrations occur but unpairing of electrons is avoided by charge transfer to the alkyl chain. This charge then initiates a concerted cleavage of the chain to give an allylic carbonium (positive ion spectrum) or carbanion (negative ion spectrum). The mechanism avoids the need to involve radicals or loss of hydrogen atoms from even-electron (closed shell) ions and provides a driving force for the reaction, namely, the formation of ions with a stabilized charge. An extension of the mechanism is also proposed to account for the formation of odd-electron ions from these compounds. The charge-assisted mechanism does not rule out the occurrence of other mechanisms that have been accepted for many years but provides an alternative process that can account for some spectral features which were difficult to explain earlier. (C) 2004 American Society for Mass Spectrometry.