Study of fragmentation pathways of metastable negative ions in aliphatic dipeptides using the statistical theory

RATIONALE Dipeptide molecules are good model systems for investigation of resonant reactions of low‐energy electrons with proteins. The present work is devoted to the study of the processes of formation and fragmentation of negative ions in aliphatic dipeptides glycyl‐glycine and glycyl‐alanine. The metastable decays of negative ions were detected in these objects, and have been investigated with the aim of clarification of the mechanisms of fragmentation. METHODS The effective yield curves for negative ions as functions of electron energy were obtained using a magnetic sector mass spectrometer rebuilt for generation and detection of negative ions. For analysis of the observed metastable decays statistical and thermochemical approaches have been used. RESULTS The ions structures, the enthalpies of formation of neutral and charged particles, and the rate constants of dissociative reactions have been found. CONCLUSIONS Comparison of the experimental results with theoretical data leads to the conclusion that metastable ion decay proceeds with minimal structural changes avoiding complicated rearrangements and isomerization processes. Copyright © 2012 John Wiley & Sons, Ltd.