Dataset Information

Trimethylation Enhancement Using 13C-Diazomethane: Gas-Phase Charge Inversion of Modified Phospholipid Cations for Enhanced Structural Characterization.

ABSTRACT: Methylation of phospholipids (PL) leads to increased uniformity in positive electrospray ionization (ESI) efficiencies across the various PL subclasses. This effect is realized in the approach referred to as "trimethylation enhancement using 13C-diazomethane" (13C-TrEnDi), which results in the methyl esterification of all acidic sites and the conversion of amines to quaternary ammonium sites. Collision-induced dissociation (CID) of these cationic modified lipids enables class identification by forming distinctive headgroup fragments based on the number of 13C atoms incorporated during derivatization. However, there are no distinctive fragment ions in positive mode that provide fatty acyl information for any of the modified lipids. Gas-phase ion/ion reactions of 13C-TrEnDi-modified phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylcholine (PC), and sphingomyelin (SM) cations with dicarboxylate anions are shown to charge-invert the positively charged phospholipids to the negative mode. An electrostatically bound complex anion is shown to fragment predominantly via a novel headgroup dication transfer to the reagent anion. Fragmentation of the resulting anionic product yields fatty acyl information, in the case of the glycerophospholipids (PE, PS, and PC), via ester bond cleavage. Analogous information is obtained from modified SM lipid anions via amide bond cleavage. Fragmentation of the anions generated from charge inversion of the 13C-TrEnDi-modified phospholipids was also found to yield lipid class information without having to perform CID in positive mode. The combination of 13C-TrEnDi modification of lipid mixtures with charge inversion to the negative-ion mode retains the advantages of uniform ionization efficiency in the positive-ion mode with the additional structural information available in the negative-ion mode without requiring the lipids to be ionized directly in both ionization modes.

SUBMITTER: Betancourt SK

PROVIDER: S-EPMC5648332 | biostudies-literature | 2017 Sep

REPOSITORIES: biostudies-literature

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Publications

Trimethylation Enhancement Using 13C-Diazomethane: Gas-Phase Charge Inversion of Modified Phospholipid Cations for Enhanced Structural Characterization.

Betancourt Stella K SK Canez Carlos R CR Shields Samuel W J SWJ Manthorpe Jeffrey M JM Smith Jeffrey C JC McLuckey Scott A SA

Analytical chemistry 20170815 17

Methylation of phospholipids (PL) leads to increased uniformity in positive electrospray ionization (ESI) efficiencies across the various PL subclasses. This effect is realized in the approach referred to as "trimethylation enhancement using 13C-diazomethane" (13C-TrEnDi), which results in the methyl esterification of all acidic sites and the conversion of amines to quaternary ammonium sites. Collision-induced dissociation (CID) of these cationic modified lipids enables cla ...[more]

PMID: 28764333

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Project description:Shotgun lipidomics has recently gained popularity for lipid analysis. Conventionally, shotgun analysis of glycerophospholipids via direct electrospray ionization tandem mass spectrometry (ESI-MS/MS) provides glycerophospholipid (GPL) class (i.e., headgroup composition) and fatty acyl composition. Reliant on low-energy collision-induced dissociation (CID), traditional ESI-MS/MS fails to define fatty acyl regiochemistry along the glycerol backbone or carbon-carbon double bond position(s) in unsaturated fatty acyl substituents. Therefore, isomeric GPLs are often unresolved, representing a significant challenge for shotgun-MS approaches. We developed a top-down shotgun-MS method utilizing gas-phase ion/ion charge inversion chemistry that provides near-complete GPL structural identification. First, in negative ion mode, CID of mass-selected GPL anions generates fatty acyl carboxylate anions via fragmentation of ester bonds linking the fatty acyl substituents at the sn-1 and sn-2 positions of the glycerol backbone. Product anions, including fatty acyl carboxylate ions, were then derivatized in the mass spectrometer via an ion/ion charge inversion reaction with tris-phenanthroline magnesium dications. Subsequent CID of charge-inverted fatty acyl complex cations yielded isomer-specific product ion spectra that permit (i) unambiguous assignment of carbon-carbon double bond position(s) and (ii) relative quantitation of isomeric fatty acyl substituents. The outlined strategy was applied to the analysis of targeted GPLs extracted from human plasma, including several proposed plasma biomarkers. A single experiment thus facilitates assignment of the GPL headgroup, fatty acyl composition, carbon-carbon double bond position(s) in unsaturated fatty acyl chains, and, in some cases, fatty acyl sn-position and relative abundances for isomeric fatty acyl substituents. Ultimately, this MSn platform paired with ion/ion chemistry permitted identification of major, and some minor, isomeric contributors that are unresolved using conventional ESI-MS/MS.

Dataset Information

Trimethylation Enhancement Using 13C-Diazomethane: Gas-Phase Charge Inversion of Modified Phospholipid Cations for Enhanced Structural Characterization.

Publications

Trimethylation Enhancement Using <sup>13</sup>C-Diazomethane: Gas-Phase Charge Inversion of Modified Phospholipid Cations for Enhanced Structural Characterization.

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