Differentiation of 1-O-alk-1'-enyl-2-acyl and 1-O-alkyl-2-acyl glycerophospholipids by multiple-stage linear ion-trap mass spectrometry with electrospray ionization - PubMed (original) (raw)

Differentiation of 1-O-alk-1'-enyl-2-acyl and 1-O-alkyl-2-acyl glycerophospholipids by multiple-stage linear ion-trap mass spectrometry with electrospray ionization

Fong-Fu Hsu et al. J Am Soc Mass Spectrom. 2007 Nov.

Abstract

We described linear ion-trap mass spectrometric approaches applying MS(3) and MS(4) toward to the structural characterization of 1-O-alk-1'-enyl-2-acyl-, 1-O-alkyl-2-acyl-, and diacyl-glycerophospholipids (GPL) as the [M - H](-) ions desorbed by ESI in negative-ion mode. Further dissociation of the [lM - H - R(2)CO(2)H - polar head group](-) ions from the [M - H](-) ions of GPL that have undergone the consecutive losses of the fatty acid substituent at sn-2 and the polar head group readily gives the structural information of the radyl group at sn-1, resulting in structural differentiation among the 1-O-alk-1'-enyl-2-acyl-, 1-O-alkyl-2-acyl, and diacyl-glycerolphospholipid molecules. The distinction between a 1-O-alk-1'-enyl-2-acyl- and a 1-O-alkyl-2-acyl-GPL is based on the findings that the MS(3) (or MS(4)) spectrum of the [M - H - R(2)CO(2)H - polar head group](-) ion from the former compound is dominated by the alkenoxide anion that represents the radyl moiety at sn-1, while the spectrum from the latter compound is dominated by the ion at m/z 135 arising from further loss of the 1-O-alkyl group as an alcohol. Another important notion is that the optimal collision energy required for acquiring the former spectrum is significantly lower than that required for obtaining the latter spectrum. Using the approaches, we are able to reveal the structures of several isobaric isomers in GPL mixtures of biological origin. Because the [M - H](-) ions are readily formed by various GPL classes (except glycerophosphocholine) in the negative-ion mode, these mass spectrometric approaches should have broad application in the structural identification of GPLs.

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Figures

Figure 1

Figure 1

The LIT MS2 spectra of the [M – H]− ions of _p_18:1/18:1-GPEtn at m/z 726 (a), of _a_18:0/18:0-GPEtn at m/z 732 (d), of 18:0/18:1- GPEtn at m/z 744 (g), their MS3 spectra of the ions at m/z 462 (726 → 462) (b), at m/z 466 (732 → 466) (e), at m/z 480 (744→ 480) (h), and their MS4 spectra of the ions at m/z 401 (726 → 462 → 401) (c), at m/z 405 (732 → 466 → 405) (f), and at m/z 419 (744 → 480 → 419) (i).

Figure 2

Figure 2

The LIT MS2 spectrum of the [M – H]− ion of _p_18:0/18:2-GPEtn at m/z 726 (a), its MS3 spectrum of the ion at m/z 464 (726 → 464) (b), its MS4 spectrum of the ion at m/z 403 (726 → 464 → 403) (c), and the MS2 spectrum of the ion at m/z 728 (d), which is consisted of both a _p_18:0/18:1-GPEtn and an _a_18:0/18:2-GPEtn structures.

Figure 3

Figure 3

The LIT MS2 spectrum of the [M – H]− ions of _a_18:0/18:1-GPIns at m/z 849 (a), and its MS3 spectra of the ions at m/z 405 (849 → 405) (b), and at m/z 687 (849 → 687) (c). The MS2 spectrum of the ion at m/z 847 (d), as well as its MS3 of the ions at m/z 405 (e), and at m/z 685 (f) represents mainly an _a_18:0/18:2-GPIns structure, along with the minor 17:0/18:2-GPIns and p18:1/18:1-GPIns species; while the MS2 spectrum of the ion at m/z 933 (g), and its MS3 spectra of the ions at m/z 489 (933 → 489) (h), and at m/z 771 (933 → 771) (i), represent an _a_24:0/18:1-GPIns structure.

Figure 4

Figure 4

The LIT MS2 spectrum of the ion at m/z 772 (a), its MS3 spectrum of the ion at m/z 685 (772 → 685) (b), and its MS4 spectrum of the ion at m/z 405 (772 → 685 → 405) (c), from isobaric isomers of _a_18:0/18:2-GPSer, 17:0/18:2-GPSer and _p_18:0/18:1-GPSer.

Figure 5

Figure 5

The LIT MS2 spectrum of the ion at m/z 750 (a), its MS3 spectrum of the ion at m/z 436 (750 → 436) (b), and its MS4 spectrum of the ion at m/z 375 (750 → 436 → 375) (c), from a major _p_18:0/20:4-GPEtn structure together with two minor _p_18:1/20:3-GPEtn and _p_16:0/22:4-GPEtn isomers.

Scheme 1

Scheme 1

The fragmentation pathways proposed for the [M – H] − ions of (A) Plasmenylethanolamine, and (B) Plasmanlyethanolamine

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