Total structure characterization of unsaturated acidic phospholipids provided by vicinal di-hydroxylation of fatty acid double bonds and negative electrospray ionization mass spectrometry

Abstract

In the present work, the unsaturated fatty acid substituents of some phosphatidic acid, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol species were converted to their 1,2-di-hydroxy derivatives by OsO 4 . The subsequent electrospray ionization tandem low-energy mass spectrometry analysis of the deprotonated species allowed positional determination of the double bonds by the production of specific product-ions. The productions are formed by charge-remote and charge-proximate homolytic cleavages as well as charge-directed heterolytic cleavages and rearrangements. The commercial availability of pure species of the phospholipids in question was limited, and a number of species were therefore synthesized. The developed method was used to fully characterize the two isobaric phosphatidylglycerol species 16:0/16:1⌬ 9 and 16:0/16:1⌬ 10 extracted from the bacteria Methylococcus capsulatus. The presence of these fatty acids was supported by a gas-chromatography mass spectrometry investigation of the dimethyloxazoline derivatives of the species of the lipid extract. The present work demonstrates that a total structure characterization of acidic unsaturated phospholipids in isolate or in mixtures is accomplished by vicinal di-hydroxylation of olefinic sites and subsequent electrospray ionization mass spectrometry of the derivatized phospholipids. (J Am Soc Mass Spectrom 2005, 16, 46 -59)

Electrospray ionization multiple stage quadrupole ion-trap and tandem quadrupole mass spectrometric studies on phosphatidylglycerol from arabidopsis leaves

“…The fragmentation processes observed for the PG species bearing a ⌬ Ϫ ) is prominent due to the labile nature of the ␣-hydrogen of ⌬ 3 16:1-fatty acid substituent.°Recently,°Moe°et°al.° [28]°and°Thomas°et°al. [29]°described°ESI°tandem°mass°spectrometric°methods for location of the olefinic sites of phospholipids, following conversion to their 1,2-dihydroxy derivatives by OsO 4° [ 28]°or°on-line°ozonolysis°of°double°bonds°to yield both a terminal oxoalkanoyl and a terminal Chydroperoxy, C-methoxy alkanoyl radyl containing phospholipid°anions° [29].°These°approaches°are straightforward and should be useful, in particular, for locating the double-bond(s) of the fatty acid substituents from various isomers.…”

Ozone-induced dissociation on a modified tandem linear ion-trap: Observations of different reactivity for isomeric lipids

“…In contrast, low-energy CID spectra fail to provide any distinctive spectral features indicative of either (1) the position of carbon-carbon double-bond(s) or (2) the stereochemistry of the double bonds (cis or trans). Publications from our group and others have contrasted the CID mass spectra of double-bond variants of complex molecular lipids, demonstrating the inability of this approach to differentiate such isomers [21,22]. As such, a conventional CID spectrum of a mass-selected lipid provides little information to alert the analyst to the presence of isomeric variations in lipids (i.e., Is a mass-selected ionized lipid one species or, in fact, a mixture of several structurally distinct compounds?…”

Dissociation of proton-bound complexes reveals geometry and arrangement of double bonds in unsaturated lipids

“…This method derivatized double bonds to vicinal diols, which are readily cleaved upon CID, enabling identification of initial double bond location. 7 Another method employs ion-molecule reactions between unsaturated lipids and ozone in the gas-phase, namely ozone-induced dissociation (OzID) for online assignment of the double bond position(s). 8,9 Moreover, the differences in reaction rates for gas-phase ozonolysis (and thus product ion abundance) has been exploited to discriminate between lipid geometric isomers (i.e., cis/trans isomers).…”