Abstract
The position and configuration of carbon-carbon double bonds in unsaturated fatty acids is crucial for their biological functions and influences health and disease. However, double bond isomers are not routinely distinguished by classical mass spectrometry workflows. Instead, they require sophisticated analytical approaches usually based on chemical derivatization and/or instrument modification. In this work, a novel strategy to investigate fatty acid double bond isomers (18:1) without prior chemical treatment or modification of the ion source was implemented by non-covalent adduct formation in the gas phase. Fatty acid adducts with sodium, pyridinium, trimethylammonium, dimethylammonium, and ammonium cations were characterized by a combination of cryogenic gas-phase infrared spectroscopy, ion mobility-mass spectrometry, and computational modeling. The results reveal subtle differences between double bond isomers and confirm three-dimensional geometries constrained by non-covalent ion-molecule interactions. Overall, this study on fatty acid adducts in the gas phase explores new avenues for the distinction of lipid double bond isomers and paves the way for further investigations of coordinating cations to increase resolution.Graphical abstract
Highlights
Lipids are essential biomolecules for all forms of life ranging from simple procaryotes to large multicellular organisms
Motivated by one of these previous studies, which showed that both C=C location and configuration in protonated deoxysphingolipids are distinguishable without chemical modification by gas-phase IR spectroscopy [36], we extended the application to fatty acids (FAs) in this work
Our results demonstrate that coordinating cations induce specific three-dimensional conformations of the lipid chain
Summary
Lipids are essential biomolecules for all forms of life ranging from simple procaryotes to large multicellular organisms. The development of MS-compatible approaches that enable the determination of C=C locations has boomed in recent years and has given rise to a variety of techniques, including ozone-induced dissociation (OzID) [7, 23, 24], Paternò-Büchi reactions [8, 9, 25], epoxidation [26,27,28] and other oxidation reactions [29], charge inversion [30, 31], radical-directed dissociation [32, 33], and ultraviolet photodissociation [34, 35] Most of those strategies require on- or offline chemical derivatization of the lipid and do not yield direct information about the C=C configuration
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