Fig. 4.

Structure elucidation of β-hydroxy fatty acid ceramide. a The experimental MS/MS spectrum, which was annotated as Ceramide [BS] (d18:1/26:0) by mass spectrometry experts, is shown in the bottom panel. The substructure ions with rearranged hydrogens were assigned to the diagnostic ions for ceramide [BS]. b The brief scheme to generate the base peak ion, m/z 340.2797 in (a), from the ceramide [BS] structure is shown as scheme A with the heat of formation calculated by the MOPAC program. c The brief scheme to generate the base peak from γ-hydroxy fatty acid ceramide is shown as scheme B with the heat of formation. In addition, the practical scheme arising from the α-elimination process at the hydroxy moiety is described as scheme C. These heat of formation data were used as important evidence to define the unknown lipid structure as ceramide [BS] from the mass fragmentation patterns