Wheelan P, Zirrolli J A, Murphy R C
National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Biol Mass Spectrom. 1993 Aug;22(8):465-73. doi: 10.1002/bms.1200220808.
The low-energy collision-induced dissociation (CID) of the carboxylate anions generated by fast atom bombardment ionization of monohydroxy unsaturated fatty acids derived from oleic, linoleic, linolenic and arachidonic acids were studied in a tandem quadrupole mass spectrometer. The collisional activation spectra revealed structurally informative ions as to the position of the hydroxyl substituent in relationship to the sites of unsaturation. Five mechanisms are proposed for the fragmentation of hydroxyl substituted unsaturated fatty acids and are dependent upon the presence of alpha- or beta-unsaturation sites. These mechanisms include charge-remote allylic fragmentation, charge-remote vinylic fragmentation, charge-driven allylic fragmentation, charge-driven vinylic fragmentation, and homolytic fragmentation by an oxy-Cope rearrangement process. The assignment of specific fragmentation pathways was supported in many instances with deuterium-labeled analogs. Although no single fragmentation mechanism appears to predominate, a rational approach to the interpretation of these CID spectra is proposed. The CID spectra of unknown compounds could be used to establish the hydroxyl substituent position in relationship to certain sites of unsaturation but would not be indicative of all double bond locations. The oxy-Cope rearrangement is specific for a structural unit, namely the 3-hydroxy-1,5-diene moiety.
在串联四极杆质谱仪中，研究了由油酸、亚油酸、亚麻酸和花生四烯酸衍生的单羟基不饱和脂肪酸经快原子轰击电离产生的羧酸根阴离子的低能碰撞诱导解离（CID）。碰撞活化谱揭示了关于羟基取代基相对于不饱和位点位置的结构信息丰富的离子。针对羟基取代的不饱和脂肪酸的碎片化提出了五种机制，这些机制取决于α-或β-不饱和位点的存在。这些机制包括电荷远程烯丙基碎片化、电荷远程乙烯基碎片化、电荷驱动烯丙基碎片化、电荷驱动乙烯基碎片化以及通过氧-Cope重排过程的均裂碎片化。在许多情况下，用氘标记的类似物支持了特定碎片化途径的归属。尽管似乎没有单一的碎片化机制占主导地位，但提出了一种解释这些CID谱的合理方法。未知化合物的CID谱可用于确定羟基取代基相对于某些不饱和位点的位置，但不能指示所有双键位置。氧-Cope重排对一个结构单元具有特异性，即3-羟基-1,5-二烯部分。
