An investigation of the pyrolysis of oligopeptides by Curie-point pyrolysis—tandem mass spectrometry

Abstract

The mechanisms of the thermal fragmentation of oligopeptides (ranging from three to six amino acid residues) upon Curie-point pyrolysis—mass spectrometry have been investigated. The results support the formation of diketopiperazines (DKP) or cyclic dipeptides as a major thermal decomposition mode. The pyrolysis—mass spectra illustrate that the formation of DKPs occurs via consecutive cyclizations for oligopeptides containing more than three amino acid units. For peptides that contain three or another odd number of amino acids, cyclization occurs with the eventual loss of the C-terminal amino acid. Peptides with an even number of amino acid units primarily produce DKPs. A significant number of peaks observed in the pyrolysis—mass spectra resulted from electron ionization (EI) fragmentations of the DKP. These fragmentations involve rearrangement and/or cleavage of the side groups followed by the breakup of the ring. No evidence was found for an EI N-terminal cleavage in straight-chained oligopeptides with more than three amino acids.