Electron detachment dissociation of peptide di-anions: an electron–hole recombination phenomenon

A novel electron–ion reaction mimicking positron capture is reported for gas-phase polypeptide di-anions. Bombardment of the latter by >10 eV electrons produced electron detachment followed by backbone dissociation, noticeably cleavage of the N–Cα bond. On the other hand, reaction with hydrogen cations resulted in losses of neutral groups but not in backbone cleavage. It is proposed that the N–Cα dissociation is due to recombination along the peptide chain of a positive radical charge (hole) with a negative charge. The new reaction is likely to find application in mass spectrometry for primary structure determination of acidic polypeptides.