Endothermic ion/molecule reactions Part VI. Reaction-induced dissociation of peptides containing basic residues using dimethyl- and trimethylamine

Protonated peptides containing the basic amino acids histidine, lysine or arginine are reacted at low beam energies in a tandem mass spectrometer with dimethyl- and trimethylamine. Proton transfer reactions are observed at clearly defined thresholds on the ion beam energy scale that are consistent with predicted endothermicites. At similar beam energies abundant sequence fragment ions are also observed that appear to result from alternate dissociation channels for a long-lived collision complex formed in the proton transfer reaction. The observed endothermicity and the selectivity for cleavages in which the charge is retained on basic residues are consistent with protonation of the molecular ion at those residues. Fragmentation induced by reactions with basic amines is referred to as reaction-induced dissociation to distinguish this process from collision-induced dissociations with inert gases.