On the mass spectrometric fragmentations of the bacterial sesterterpenes sestermobaraenes A–C

A 13C-labelling was introduced into each individual carbon of the recently discovered sestermobaraenes by the enzymatic conversion of the correspondingly 13C-labelled isoprenyl diphosphate precursors with the sestermobaraene synthase from Streptomyces mobaraensis. The main compounds sestermobaraenes A, B, and C were analysed by gas chromatography–mass spectrometry (GC–MS), allowing for a deep mechanistic investigation of the electron impact mass spectrometry (EIMS) fragmentation reactions of these sesterterpene hydrocarbons.

Electron-Impact Mass Spectrometry of PTCDA Molecules in the Gas Phase

The complete and dissociative ionizations of a 3,4,9,10-perylene-tetracarboxylic-dianhydride (C24H8O6, PTCDA) molecule in the gas phase have been studied, by using electron-impact mass spectrometry in an energy interval of 5–90 eV. The molecule is found to decay into the following fragment ions: the perylene core C20H8+ and its half C10H4+, as well as CO+, CO2+ , and O+ ions. The energy dependences of the cross-sections of the complete ionization of a PTCDA molecule and its fragment ions are analyzed. The energy of the complete ionization of a PTCDA molecule and the energies, at which its fragments appear, are determined. The temperature dependences of the formation of the most intensive fragment ions are measured, by using 80-eV electrons in a temperature interval of 320–500 K.