Reaction competition in the fragmentation of protonated dipeptides

Alex G. Harrison, Imre G. Csizmadia, Ting Hua Tang, Ya Ping Tu

Research output: Contribution to journalArticle

44 Citations (Scopus)


A major low-energy fragmentation reaction of many protonated dipeptides involves cleavage of the amide bond resulting in formation of either the y''1 ion or the a1 ion. For a series of protonated dipeptides H - Val - Xxx - OH it is observed that log(y''1/a1) is a linear function of the proton affinity of the variable C-terminal amino acid. For the series of protonated dipeptides H - Xxx - Phe - OH log(a1/y''1) gives a poor correlation with the proton affinity or gas-phase basicity of H - Xxx - OH. However, a good limited correlation of log(a1/y''1) with the Taft-Topsom σ(α) for the alkyl group is observed when Xxx is an aliphatic amino acid. It is proposed that fragmentation occurs by initial formation of a proton-hound complex of an aziridinone and an amino acid which may fragment to form either a protonated amino acid (y''1) or an N-protonated aziridinone with the corresponding neutrals being an aziridinone and an amino acid. Ab initio calculations show that the N-protonated aziridinone is unstable and fragments by loss of CO to form the a1 immonium ion. However, the proton-bound complex of an aziridinone and an amine base is a stable species which exists in a potential well. Copyright (C) 2000 John Wiley and Sons, Ltd.

Original languageEnglish
Pages (from-to)683-688
Number of pages6
JournalJournal of Mass Spectrometry
Issue number6
Publication statusPublished - Jan 1 2000


  • Fragmentation mechanisms
  • Linear free energy correlations
  • Protonated dipeptides
  • Reaction competition

ASJC Scopus subject areas

  • Spectroscopy

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