Radical-induced fragmentation of phospholipid cations using metastable atom-activated dissociation mass spectrometry (MAD-MS)

Abstract

The fragmentation pattern of several protonated 1+ phosphatidylcholines (PCs) were studied using low energy collision induced dissociation (CID) and helium metastable atom-activated dissociation (He-MAD). He-MAD of the protonated compounds produced a dominant phosphocholine head group at m/z 184 as well as typical sn-1 and sn-2 glycerol fragments such as [M+H–Rx-1CHC=O]+ and [M+H-Rx-1CO2H]+. Within the aliphatic chain, He-MAD showed fragments consistent with high-energy collision induced dissociation (HE-CID) and products/pathways consistent with Penning ionization of the 1+ precursor ions to their respective radical dications. These Penning ionization products included both singly and doubly charged radical fragments, and the fragment ions are related to the number and position of double bonds in the acyl chains. Fragments created through HE-CID-like fragmentation followed classic charge remote fragmentation pathways including ladder-like fragmentation along the acyl chain, except for additional or missing peaks due to predictable rearrangement reactions. He-MAD therefore shows utility in being able to effectively fragment singly charged lipids into a variety of useful product ions using both radical and high-energy processes in the confines of a 3D ion trap.

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).…”

Collision-induced dissociation of doubly-charged barium-cationized lipids generated from liquid samples by atmospheric pressure matrix-assisted laser desorption/ionization provides structurally diagnostic product ions

“…Interestingly, with CTD a charge-increased species [L+H] 2+• was produced, as with metastable atom dissociation (MAD) [39]. Extensive information from the acyl chains was obtained through dissociation of [L+H] + and [L+H]…”

Multistage mass spectrometry of phospholipids using collision-induced dissociation (CID) and metastable atom-activated dissociation (MAD)

“…Upon the interaction with helium metastable atoms, the protonated form of POPC produces a variety of cleavages along the acyl chains. The 14 Da increments resemble high-energy CID (HE-CID) spectra, which suggests that a charge-remote-like mechanism is taking place in this process [33–35]. Conversely, MAD of the metal-adducted forms rarely cleaves the acyl chains, but instead forms abundant fragment ions arising from the glycerol backbone and head group.…”

“…The modification method, the connection between electronic components and the working principles are described elsewhere [32, 33]. …”

“…To date, MAD has been used in a variety of studies concerning peptide structures, including multiply charged cations and anions, 1+ cations, phosphorylated cations, disulfide bonds, to cleave the amide ring structure of proline and to differentiate isoleucine from leucine [30–32]. In addition to fragmenting peptides, MAD has been shown to provide high energy and radical-induced fragmentation of lipid cations [33]. In contrast to CID, which exclusively proceeds through even-electron mechanism, MAD produces both even-electron and odd-electron fragments.…”