New secondary metabolites of Aspergillus wentii Wehmer. The positive and negative ion mass spectra produced by electron impact.

Abstract

The positive and negative ion mass spectra of three secondary metabolites of Aspergillus Wentii Wehmer, namely 15-acetoxyhexadecyl-, 15-oxohexadecyl- and 15-hydroxyhexadecylcitraconic anhydrides are reported and discussed. The positive ion mass spectra, which have been studied in detail by exact mass measurements and metastable ion detection using a defocusing method, show very weak molecular ions and complex fragmentation pathways, strongly influenced by the group on C-15. However, the negative ion mass spectra show very abundant molecular ions and little fragmentation, with the negative charge mainly retained by the anhydride moiety. The behavior of both positive and negative ions is in agreement with the charge localization concept, on the grounds of ionization energy and electron affinity considerations. positive and negative ion mass spectra are largely complementary, thus increasing their analytical value.