Get access

Leaving group effects on the selectivity of the gas-phase fragmentation reactions of side chain fixed-charge-containing peptide ions

Authors

  • Kade D. Roberts,

    1. Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
    Search for more papers by this author
  • Gavin E. Reid

    Corresponding author
    1. Department of Chemistry, Michigan State University, East Lansing, MI 48824, USA
    2. Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
    • 234 Chemistry Building, Michigan State University, East Lansing, Michigan, 48824, USA.
    Search for more papers by this author

Abstract

The effect of trialkylsulfonium versus quaternaryalkylammonium ions on the multistage gas-phase fragmentation reactions of side chain, fixed-charge, cysteine-containing peptides has been examined in a quadrupole linear ion trap. These tandem mass spectrometry experiments reveal that selective loss of dialkylsulfide from fixed-charge sulfonium ion derivatives is the dominant fragmentation pathway regardless of the degree of proton mobility, indicating that it is the most energetically favored fragmentation pathway. In contrast, the loss of trimethylamine from the side chain of fixed-charge ammonium-ion-containing cysteine derivatives appears to be less energetically favored, and as a result extensive charge-remote fragmentation is observed under low proton mobility conditions, while under conditions of high proton mobility, amide bond fragmentation reactions dominate. These findings are supported by molecular orbital calculations at the B3LYP/6-31 + G(d, p) level of theory, which showed that the neutral loss of dimethylsulfide is both thermodynamically and kinetically preferred over the loss of trimethylamine. Copyright © 2006 John Wiley & Sons, Ltd.

Ancillary