title: Peptide dissociation patterns in secondary ion mass spectrometry under large argon cluster ion bombardment.
abstract: BACKGROUND
  The analysis of organic and biological substances by secondary ion mass spectrometry (SIMS) has greatly benefited from the use of cluster ions as primary bombarding species. Thereby, depth profiling and three-dimensional (3D) imaging of such systems became feasible. Large Ar(n)(+) cluster ions may constitute a further improvement in this direction.
  
  
  METHODS
  To explore this option, large Ar(n)(+) cluster ions (with n ~1500 Ar atoms per cluster) were used to investigate the emission of positive secondary ions from two peptide specimens (angiotensin I and bradykinin) by orthogonal time-of-flight SIMS using bombarding energies 6, 10 and 14 keV.
  
  
  RESULTS
  For both peptides, the protonated molecular ion is observed in the mass spectra. In addition, distinct fragmentation patterns were observed; these indicate that fragment ions under Ar cluster irradiation form primarily via cleavage of bonds along the peptide backbone whereas the rapture of side chains occurs much less frequently. These features appear to be similar to low-energy collision-induced dissociation pathways.
  
  
  CONCLUSIONS
  Tentatively, these findings can then be ascribed to the concerted action of the large number of Ar atoms in the impact zone of cluster at the surface: these low-energy Ar species (with an average energy of few eV) may effect the cleavage of the peptide bonds and lead, eventually, to the emission of the fragment ions.
authors.affiliation: Department of Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern, Germany. gnaser@rhrk.uni-kl.de
authors.forename: Hubert
authors.initials: H
authors.lastname: Gnaser
authors.forename: Makiko
authors.initials: M
authors.lastname: Fujii
authors.forename: Shunichirou
authors.initials: S
authors.lastname: Nakagawa
authors.forename: Toshio
authors.initials: T
authors.lastname: Seki
authors.forename: Takaaki
authors.initials: T
authors.lastname: Aoki
authors.forename: Jiro
authors.initials: J
authors.lastname: Matsuo
mesh_terms: D000803:Angiotensin I / Q000737:chemistry*; D001128:Argon / Q000737:chemistry*; D001920:Bradykinin / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D015394:Molecular Structure; D018629:Spectrometry, Mass, Secondary Ion / Q000295:instrumentation / Q000379:methods*
chemical_list: D007477:Ions; D001128:Argon; D000803:Angiotensin I; D001920:Bradykinin