Electron‐induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double‐bond positions and localization of acyl chains

Abstract

Glycerophospholipids are a highly abundant and diverse collection of biologically relevant lipids and distinction between isomeric and isobaric species is a fundamental aspect for confident identification. The ability to confidently assign a unique structure to a glycerophospholipid of interest is dependent on determining the number and location of the points of unsaturation and assignment of acyl chain position. The use of high energy electrons (>20 eV) to induce gas-phase dissociation of intact precursor ions results in diagnostic product ions for localizing double bond positions and determining acyl chain assignment. We describe a high resolution, tandem mass spectrometry method for structure characterization of glycerophospholipids using electron-induced dissociation (EID). Furthermore, the inclusion of nomenclature to systematically assign bond cleavage sites with acyl chain position and double bond location enables a uniform platform for lipid identification. The EID methodology detailed here combines novel application of an electron-based dissociation technique with high resolution mass spectrometry that facilitates a new experimental approach for lipid biomarker discovery and validation.

Quantitative structural multiclass lipidomics using differential mobility: electron impact excitation of ions from organics (EIEIO) mass spectrometry

“…This cleavage has not been observed by CID, and only infrequently in high energy EID (26) and metastable atom activation (27). This peak solves permutation of two chains at sn-1 and sn-2 (Table 2).…”

Recent advances in lipid separations and structural elucidation using mass spectrometry combined with ion mobility spectrometry, ion-molecule reactions and fragmentation approaches

“…A number of fragmentation approaches, including HCD, multistage CID, charge remote fragmentation, and charge transfer dissociation have been explored for this purpose, but have shown limited capabilities [35]. Recently, several novel fragmentation approaches have shown great promise for efficient C=C determination, including electron transfer dissociation (ETD) [36], helium metastable atom activated dissociation (He-MAD) [37,38], electron impact excitation of ions from organics (EIEIO)/electron-induced dissociation (EID) [39,40], radical-directed dissociation (RDD) [41] and ultraviolet photodissociation (UVPD) [42,43]. ETD and He-MAD utilize ions reactions with radical anions metastable or helium atoms to induce similar radical-based fragmentation pathways.…”

Charge transfer dissociation of phosphocholines: gas‐phase ion/ion reactions between helium cations and phospholipid cations

“…[24] The odd-electron fragments in Fig. 2(c) were also observed in MAD [12] and EID [24] spectra of the same lipid, which suggests analogous fragmentation pathways among CTD, MAD and EID. The odd-electron fragments must be generated via the introduction of radical species during the fragmentation process, indicating the involvement of radical cleavages in CTD.…”

“…[10,21,24] In contrast to this general preference for sn-2 ketene loss over sn-1 ketene loss, Ho and Huang show no such preference for sn-2 ketene loss in low-energy CID experiments in a quadrupole ion trap [16] and Jones et al observed a slight preference for sn-1 ketene loss over sn-2 ketene loss in the EID fragmentation of phospholipids. [24] The odd-electron fragments in Fig. 2(c) were also observed in MAD [12] and EID [24] spectra of the same lipid, which suggests analogous fragmentation pathways among CTD, MAD and EID.…”

“…ultraviolet photo -dissociation electron transfer reactions UVPD, [32] IRMPD [51] ), electron-based reactions (e.g. electron transfer dissociation (ETD), [29] electron impact excitation of ions from organics (EIEIO), [9] electron-induced dissociation (EID) [24,50] ) and radical-directed dissociation. [35,37] In OzESI/OzID, the exposure of unsaturated lipids to ozone molecules results in an ozonide, which then dissociates into fragment ion pair(s) with diagnostic mass separation that enables an unambiguous identification of sites of unsaturation.…”