Selective phosphatidylcholine double bond fragmentation and localisation using Paternò–Büchi reactions and ultraviolet photodissociation

Abstract

The effect of double bond functionalisation for selective double bond localisation by ultraviolet photodissociation of phosphatidylcholines is investigated. Paternò-Büchi reactions in nanoESI emitter tips enable attachment of acetophenone to double bonds of unsaturated phosphatidylcholines after 100 s of 254 nm light irradiation with about 50-80% reaction yield. Functionalized phosphatidylcholines dissociate upon 266 nm irradiation yielding double bond selective fragment ions in contrast to results for ultraviolet photodissociation of unmodified lipids. Ultraviolet photodissociation of Paternò-Büchi modified lipids results in a selectivity increase of up to 2.2 towards double bond localisation compared collision-induced dissociation experiments. Double bond localisation is also possible with ultraviolet photodissociation when alkali metal ion attachment to Paternò-Büchi modified phosphatidylcholines occurs in contrast to classic collision-induced dissociation experiments. The developed methodology is used to differentiate lipid double bond isomers and applied to phosphatidylcholines from egg yolk to identify 15 phosphatidylcholines. Results from this study demonstrate that locally depositing energy in close vicinity to cleavable bonds via ultraviolet photodissociation can result in increased dissociation selectivity. This method can help to disentangle contributions from different structural elements in complex tandem mass spectra of lipids and aid to the structural characterization of phospholipids in a "top-down" approach.

Large-scale lipid analysis with C=C location and sn-position isomer resolving power

“…1f, for analysis of PC 16:0/18:1(9Z) standard, m/z 489 and m/z 578 were diagnostic ions for the C=C location while m/z 396 and m/z 466 could serve as diagnostic ions for C18:1 at sn-2 and C16:0 at sn-2. A systematic screening was performed for a group of carbonyl compounds 52,53 (Supplementary Fig. 7 and Supplementary Table 3) using the nanoESI-MS platform shown in Fig.…”

An On‐Tissue Paternò–Büchi Reaction for Localization of Carbon–Carbon Double Bonds in Phospholipids and Glycolipids by Matrix‐Assisted Laser‐Desorption–Ionization Mass‐Spectrometry Imaging

“…In combination with electrospray ionization (ESI‐)MS, several techniques have recently emerged that exploit chemical derivatization of C=C bonds and subsequent generation of diagnostic fragments in a CID experiment. These include ozone‐induced dissociation (OzID) of selected ions within a collision cell, epoxidation reaction with acetone enabled by a cold plasma, and on‐line Paternò–Büchi (PB) photo‐derivatization . Very recently, a combination of MALDI‐MSI and CID/OzID, performed in the linear ion trap of a modified MALDI‐LTQ Orbitrap Elite mass spectrometer, was used to visualize the distributions of db‐ and sn ‐positional isomers of several phosphatidylcholines (PC) in mouse brain .…”

Double bond localization in unsaturated rhamnolipid precursors 3-(3-hydroxyalkanoyloxy)alkanoic acids by liquid chromatography–mass spectrometry applying online Paternò–Büchi reaction

“…Moreover, modifications of the initially introduced setup were reported, tackling particular drawbacks of this approach. For example, Wäldchen et al combined the PB reaction by ultraviolet photodissociation (UVPD), striving for an even higher selectivity in terms of the fragmentation via altered dissociation process [59]. Based on a different approach, Esch et al demonstrated the effect of charge switching, via derivatization with acetylpyridine, on the conversion to the targeted diagnostic fragments.…”