Site-Specific Photochemical Reaction for Improved C=C Location Analysis of Unsaturated Lipids by Ultraviolet Photodissociation

Abstract

Unraveling the complexity of the lipidome requires the development of novel approaches to facilitate structural identification and characterization of lipid species with isomer-level discrimination. Ultraviolet photodissociation tandem mass spectrometry (UVPD MS/MS) is a promising tool for structure determination of lipids. The sensitivity of UVPD for lipid analysis however is limited mainly due to weak absorption of UV photons by a C=C. Herein, a C=C site-specific derivatization, the Paternò-Büchi (PB) reaction, was used to incorporate a chromophore to the C=C moiety in fatty acyls, leading to significantly improved UVPD efficiency and sensitivity for pinpointing C=C locations. The wavelength-dependent photodissociation of the PB products demonstrated 4-CF3-benzophenone as the best reagent for UVPD in terms of the efficiency of generating C=C diagnostic fragments and simplicity for C=C location assignments. We demonstrated the effectiveness of this approach for the shotgun profiling of C=C location isomers in different lipid classes from complex lipid extracts, highlighting its potential to advancing the identification of the C=C bond locations in unsaturated lipids.

Recent Advances in Mass Spectrometry-Based Structural Elucidation Techniques

“…Ions absorb high-energy UV photon(s) during UVPD, leading to the excitation of ions; thus, some unique high-energy dissociation pathways can be observed [ 53 ]. Single wavelength initiated UVPD (e.g., 157 nm, 193 nm, and 266 nm) has been utilized for the structural analysis of various biomolecules, including proteins, lipids, and carbohydrates [ 54 , 55 , 56 , 57 , 58 ].…”

Metabolic Pathway of Monounsaturated Lipids Revealed by In-Depth Structural Lipidomics by Mass Spectrometry

“…In particular, lipid analysis at the C=C location level has become mature with some important demonstrations on its applicability in biological studies [ 23 , 24 ]. The methods developed toward this purpose include ozone-induced dissociation, electron impact excitation of ions from organics, ultraviolet photodissociation, and chemical derivatizations (Paternò–Büchi [PB] reaction, epoxidation reaction, and photooxidation) [ 25 – 36 ]. These tools have not only advanced the lipid structure analysis to an unprecedented level, but also provided opportunities for biomedical analysis, such as discovery of new biomarkers for disease diagnosis [ 37 ].…”

Development of an Efficient On-Tissue Epoxidation Reaction Mediated by Urea Hydrogen Peroxide for MALDI MS/MS Imaging of Lipid C═C Location Isomers

“…Lipids, a vital type of biomolecule, have a significant role in various biological processes such as membrane construction, energy homeostasis, and signal transduction. , Among them, unsaturated lipids are a crucial subclass of lipids that contains one or multiple CC bonds in their fatty acyl chains . The number and location of lipid CC bonds affect their biophysical properties.…”

“…1,2 Among them, unsaturated lipids are a crucial subclass of lipids that contains one or multiple C�C bonds in their fatty acyl chains. 3 The number and location of lipid C�C bonds affect their biophysical properties. Disturbed lipid homeostasis has been implicated in many diseases, such as obesity, diabetes, and neurodegenerative diseases.…”