Locating Carbon–Carbon Double Bonds in Unsaturated Phospholipids by Epoxidation Reaction and Tandem Mass Spectrometry

Abstract

The presence of carbon-carbon double bonds (C═Cs) in unsaturated phospholipids is closely related to lipid conformations and physiochemical activities. Previously, we have demonstrated that epoxidation reaction facilitated by low-temperature plasma (LTP) enabled the structural analysis of unsaturated fatty acids (FAs). Epoxidation of the C═C leads to the production of an epoxide, which can be easily cleaved via collision-induced dissociation (CID) to produce diagnostic ions indicative of the C═C bond locations in FAs. In this work, we further developed this method for analysis of phospholipids. Tandem mass spectrometry analysis with epoxidation reaction was performed in both positive and negative ion mode to analyze phosphatidylcholines (PCs), phosphatidic acids (PAs), phosphatidylethanolamines (PEs), phosphatidylglycerols (PGs), and phosphatidylinositols (PIs). The developed method was applied in a shotgun lipidomics approach to characterize phospholipids in a bovine liver extract.

Positional determination of the carbon–carbon double bonds in unsaturated fatty acids mediated by solvent plasmatization using LC–MS

“…S12-S15. Though the isomeric variety of longer FAs are not well known, the isomers of C16:1 and C18:1 found in our study were consistent with previous reports 15,16,19,20,26,29 . The double bond position of MUFAs from biological samples, thus, were confirmed by this method.…”

“…Determination of the positions and number of double bonds, as well as the chain length, is crucial for understanding the precise physiological functions of each FA species. Many methods have been established for the positional determination of double bonds by modifying the target FAs at the double bond positions or the terminal carboxyl group to yield diagnostic fragment ions [8][9][10][11][13][14][15][16][17][18][19][20][21][22][23][24][25][26] . CID-mediated fragmentation on ESI-MS or EI-mediated fragmentation on GC-MS of unsaturated FAs cannot always produce informative product ions to determine the double bond positions, especially in case of PUFAs with many double bonds.…”

A lipidomic workflow capable of resolving sn- and CC location isomers of phosphatidylcholines

“…16,17 Localization of C]C has been recently achieved by paring C]C derivatization with subsequent MS/MS via CID, such as the Paternò-Büchì (PB) reaction 18,19 and epoxidation reaction. [20][21][22] These approaches are capable of determining C]C locations in various classes of lipids but they cannot provide information on the sn-positions of fatty acyls. Several MS/MS techniques utilizing ion activation/dissociation other than CID or combined with CID turn out to be quite informative for obtaining both sn-position and (or) C]C location from GPs.…”

A method to determine the double bond position in unsaturated fatty acids by solvent plasmatization using liquid chromatography-mass spectrometry

“…Two types of eicosatrienoic acid (C20:3), sciadonic acid (C20:3 ω-6 cis- 5,11,14) and dihomo-γ-linolenic acid (C20:3 ω-6 cis- 8,11,14), were examined. Dihomo-γ-linolenic acid contains three methylene-interrupted double bonds, whereas sciadonic acid contains two methylene-interrupted double bonds and one isolated double bond ( Figure 5C).…”

“…For example, acetonitrilerelated adducts of FA methyl esters produce diagnostic fragment ions from which the double bond position can be determined (11,12). Epoxidation of the double bond of FAs by low-temperature plasma successfully produces the informative diagnostic fragment ions from free FAs and lipidconjugated FAs after CID fragmentation (13,14). Paper-spray ionization followed by CID also successfully epoxidize FAs and produce the same type of diagnostic fragment ions to identify the position of carbon-carbon double bonds (15).…”