title: Even-electron [M-H](+) ions generated by loss of AgH from argentinated peptides with N-terminal imine groups.
abstract: BACKGROUND
  Experiments were performed to probe the creation of apparent even-electron, [M-H](+) ions by CID of Ag-cationized peptides with N-terminal imine groups (Schiff bases).
  
  
  METHODS
  Imine-modified peptides were prepared using condensation reactions with aldehydes. Ag(+) -cationized precursors were generated by electrospray ionization (ESI). Tandem mass spectrometry (MS(n) ) and collision-induced dissociation (CID) were performed using a linear ion trap mass spectrometer.
  
  
  RESULTS
  Loss of AgH from peptide [M + Ag](+) ions, at the MS/MS stage, creates closed-shell [M-H](+) ions from imine-modified peptides. Isotope labeling unambiguously identifies the imine C-H group as the source of H eliminated in AgH. Subsequent CID of the [M-H](+) ions generated sequence ions that are analogous to those produced from [M + H](+) ions of the imine-modified peptides.
  
  
  CONCLUSIONS
  Experiments show (a) formation of novel even-electron peptide cations by CID and (b) the extent to which sequence ions (conventional b, a and y ions) are generated from peptides with fixed charge site and thus lacking a conventional mobile proton.
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh, PA, 15282, USA.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Plaviak
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh, PA, 15282, USA.
authors.forename: Sandra
authors.initials: S
authors.lastname: Osburn
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh, PA, 15282, USA.
authors.forename: Khiry
authors.initials: K
authors.lastname: Patterson
authors.affiliation: Department of Chemistry and Biochemistry, Duquesne University, 600 Forbes Ave, Pittsburgh, PA, 15282, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: van Stipdonk
mesh_terms: D001120:Arginine / Q000737:chemistry*; D004583:Electrons; D007097:Imines / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D013058:Mass Spectrometry; D010455:Peptides / Q000737:chemistry*; D018030:Silver Compounds / Q000737:chemistry*
chemical_list: D007097:Imines; D007477:Ions; D010455:Peptides; D018030:Silver Compounds; D001120:Arginine