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Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry.

ABSTRACT: Although marine oysters contain abundant amounts of ether-linked aminophospholipids, the structural identification of the various molecular species has not been reported. We developed a normal-phase silica liquid chromatography/negative-ion electrospray ionization/quadrupole multiple-stage linear ion-trap mass spectrometric (NPLC-NI-ESI/Q-TRAP-MS(3)) method for the structural elucidation of ether molecular species of serine and ethanolamine phospholipids from marine oysters. The major advantages of the approach are (i) to avoid incorrect selection of isobaric precursor ions derived from different phospholipid classes in a lipid mixture, and to generate informative and clear MS(n) product ion mass spectra of the species for the identification of the sn-1 plasmanyl or plasmenyl linkages, and (ii) to increase precursor ion intensities by "concentrating" lipid molecules of each phospholipid class for further structural determination of minor molecular species. Employing a combination of NPLC-NI-ESI/MS(3) and NPLC-NI-ESI/MS(2), we elucidated, for the first time, the chemical structures of docosahexaenoyl and eicosapentaenoyl plasmenyl phosphatidylserine (PS) species and differentiated up to six isobaric species of diacyl/alkylacyl/alkenylacyl phosphatidylethanolamine (PE) in the US pacific oysters. The presence of a high content of both omega-3 plasmenyl PS/plasmenyl PE species and multiple isobaric molecular species isomers is the noteworthy characteristic of the marine oyster. The simple and robust NPLC-NI-ESI/MS(n)-based methodology should be particularly valuable in the detailed characterization of marine lipid dietary supplements with respect to omega-3 aminophospholipids.

SUBMITTER: Chen S

PROVIDER: S-EPMC3566561 | biostudies-literature | 2012 Jul

REPOSITORIES: biostudies-literature

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Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry.

Chen Su S Belikova Natalia A NA Subbaiah Papasani V PV

Analytica chimica acta 20120529

Although marine oysters contain abundant amounts of ether-linked aminophospholipids, the structural identification of the various molecular species has not been reported. We developed a normal-phase silica liquid chromatography/negative-ion electrospray ionization/quadrupole multiple-stage linear ion-trap mass spectrometric (NPLC-NI-ESI/Q-TRAP-MS(3)) method for the structural elucidation of ether molecular species of serine and ethanolamine phospholipids from marine oysters. The major advantages ...[more]

PMID: 22713920

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Project description:Linear ion-trap multiple-stage mass spectrometric approach (MS(n)) towards nearly complete structural elucidation of triacylglycerol (TAG) including (1) assignment the fatty acid substituents on the glycerol backbone and (2) location of the double bond(s) on the unsaturated fatty acyl groups is reported. The characterization is established by the findings that MS(2) on the [M + Li](+) ions of TAG yields more abundant ions reflecting losses of the outer fatty acid substituents either as free acids (i.e., [M + Li - R(1)CO(2)H](+) and [M + Li - R(3)CO(2)H](+) ions) or as lithium salts (i.e., [M + Li - R(1)CO(2)Li](+) and [M + Li - R(3)CO(2)Li](+) ions) than the ions reflecting the similar losses of the inner fatty acid substituent (i.e., [M + Li - R(2)CO(2)Li](+) and [M + Li - R(2)CO(2)Li](+) ions). Further dissociation (MS(3) of [M + Li - R(n)CO(2)H](+) (n = 1, 2, or 3) gives rise to the ion series locating the double bonds along the fatty acid chain. These ions arise from charge-remote fragmentations involving beta-cleavage with gamma-H shift, analogous to those seen for the unsaturated long-chain fatty acids characterized as initiated ions. Significant differences in abundances in the ion pairs reflecting the additional losses of the fatty acid moieties, respectively, were also seen in the MS(3) spectra of the [M + Li - R(n)CO(2)H](+) and [M + Li - R(n)CO(2)Li](+) ions, leading to confirmation of the fatty acid substituents on the glycerol backbone. MS(n) on the [M + Na](+) and [M + NH(4)](+) adduct ions also affords location of fatty acid substituents on the glycerol backbone, but not the position of the double bond(s) along the fatty acid chain. Unique ions from internal losses of the glycerol residues were seen in the MS(3) spectra of [M + Alk - R(n)CO(2)H](+) (n = 1, 2, 3) and of [M + Alk - R(n)CO(2)Alk](+) (Alk = Li, Na, NH(4); n = 1, 3). They are signature ions for glycerides and the pathways leading to their formation may involve rearrangements.

Project description:Exact quantification of the molar ratios of isotopologous mixed O-methyl-O-methyl-d3-cellooligosaccharides (COS) comprising all combinations from fully methylated to fully deuteromethylated constituents within an individual degree of polymerization (DP) is the key step in the analysis of the substituent distribution over the polymer chains in methyl celluloses (MC). Deuteromethylation of MC is performed to level chemical differences, but due to a m/z range of 3 DP·ΔMe/Me-d3, bias during MS measurement cannot certainly be excluded. Therefore, ionization, ion transportation, and ion storage were studied with an electrospray ionization ion trap mass spectrometer (ESI-IT-MS) using binary equimolar mixtures of per-O-Me- and per-O-Me-d3-COS, defining the border cases of a particular Me/Me-d3-profile. Reference data of their molar ratio were determined after reductive amination with m-amino benzoic acid by HPLC-UV. COS of DP2-6 were measured as their sodium adducts at c = 10-6 M by syringe pump infusion. The impact of the RF voltage of the ion trap (TD), the octopole RF and DC voltages, and the Cap Exit potential on absolute and relative ion intensities were studied. Adapting the Cap Exit voltage was essential for correct quantification of DP2, while all COS of higher DP behaved insensitive with respect to bias. To check whether any bias occurs in the electrospray ionization process of the isotopologs, concentration-dependent measurements were performed with optimized instrumental settings for each DP. Intensity ratios IR = I (Me-d3)/I (Me) did not show any concentration-dependent trend and no selective ion suppression. Its decrease with DP observed under usually applied standard conditions (smart mode) is a consequence of discrimination according to m/z and can be overcome by appropriate instrumental settings of Oct 2 DC and TD. IR between 0.971 ± 0.008 and 1.040 ± 0.009 with no trend for DP (2-6) were obtained by averaging all measurements in the range 2 · 10-7 to 2 · 10-5 M total concentration. The DP-related optimized settings were applied to two MCs and compared with the results obtained under so far applied standard conditions.

Dataset Information

Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry.

Publications

Structural elucidation of molecular species of pacific oyster ether amino phospholipids by normal-phase liquid chromatography/negative-ion electrospray ionization and quadrupole/multiple-stage linear ion-trap mass spectrometry.

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