Aziridination-assisted mass spectrometry of nonpolar lipids with isomeric resolution

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.