Fragmentation Reactions of a2 Ions Derived From Deprotonated DipeptidesA Synergy Between Experiment and Theory †

The fragmentation reactions of a number of a2 ions ([M−H−CO2]-) derived from dipeptides have been studied by energy-resolved mass spectrometry, isotopic labeling, and MS3 experiments. The general reaction sequence leading eventually to a deprotonated amine, is shown to occur, a reaction sequence first proposed by Styles and O'Hair (Rapid Commun. Mass Spectrom. 1998, 12, 809) from a study of the a2 ion derived from glycylglycine. When an amidic …