Aziridination-assisted mass spectrometry of nonpolar lipids with isomeric resolution

Abstract

Characterization of nonpolar lipids is of significance, as they serve a variety of key biological functions and can naturally exist in isomeric forms. Electrospray ionization mass spectrometry (ESI-MS) is a powerful tool for most lipid analysis, but nonpolar lipids do not easily ionize in electrospray, complicating their analyses. In this work, we use the Du Bois catalyst (Rh2(esp)2) for aziridina-tion of carbon-carbon double bonds (C=C bond) of six nonpolar sterol lipids, simultaneously increasing ionization efficiency of nonpolar lipids and facilitating C=C bond identification. The incorporation of nitrogen expands the lipid categories detected by MS, and higher-energy C-trap dissociation of the aziridines generates diagnostic ions that can be used to locate C=C bond positions.

Mapping lipid C=C isomer profiles of human gut bacteria by a novel structural lipidomics workflow assisted by chemical epoxidation

“…For example, electron impact excitation of ions from organics (EIEIO) 28 , ultraviolet photodissociation (UVPD) 29 , hydrogen abstraction dissociation (HAD) 30 , and radical-directed dissociation 31 utilized special fragmentation methods to break down C=C to identify C=C position by MS n spectrum. Other ways that coupling derivatization of C=C double bonds with mass spectrometry such as Paternò-Büchi (PB) reaction 32 , epoxidation 33,34 , ozonolysis 35,36 , aziridination 37 and thio-ene reaction 38 turned C=C structure into other more unstable structures so that the C=C position can be determined from products MS n spectra. Although the above methods successfully help determine C=C position, the C=C geometry was still not resolved effectively due to the similar MS n spectra of geometric isomers.…”