Linear ion-trap MSn with high-resolution MS reveals structural diversity of 1-O-acylceramide family in mouse epidermis1-O-acylceramide is a new class of epidermal ceramide (Cer) found in humans and mice. Here, we report an ESI linear ion-trap (LIT) multiple-stage MS (MSn) approach with high resolution toward structural characterization of this lipid family isolated from mice. Molecular species desorbed as the [M + H]+ ions were subjected to LIT MS2 to yield predominately the [M + H − H2O]+ ions, followed by MS3 to cleave the 1-O-acyl residue to yield the [M + H − H2O − (1-O-FA)]+ ions. The structures of the N-acyl chain and long-chain base (LCB) of the molecule were determined by MS4 on [M + H − H2O − (1-O-FA)]+ ions that yielded multiple sets of specific ions.
Characterization of phthiocerol and phthiodiolone dimycocerosate esters of M. tuberculosis by multiple-stage linear ion-trap MSBoth phthiocerol/phthiodiolone dimycocerosate (PDIM) and phenolic glycolipids are abundant virulent lipids in the cell wall of various pathogenic mycobacteria, which can synthesize a wide range of complex high-molecular-mass lipids. In this article, we describe linear ion-trap MSn mass spectrometric approach for structural study of PDIMs, which were desorbed as the [M + Li]+ and [M + NH4]+ ions by ESI. We also applied charge-switch strategy to convert the mycocerosic acid substituents to their N-(4-aminomethylphenyl) pyridinium (AMPP) derivatives and analyzed them as M + ions, following alkaline hydrolysis of the PDIM to release mycocerosic acids.