Investigation of intramolecular proton migration in a series of model, metal‐cationized tripeptides using in situ generation of an isotope label

In this study we used an isotope label, generated in situ , to investigate intramolecular proton migration or scrambling during formation of [b 2 +17+Li] + products by collision‐induced dissociation (CID) of Li + ‐cationized tripeptides. To generate the isotope label, we used a McLafferty‐type rearrangement of N‐terminally acetylated, C‐terminal peptide tert ‐butyl esters in which all amide positions were exchanged with deuterium. Using a set of small, model peptides, we show that intramolecular proton scrambling occurs during CID, particularly amongst adjacent sites along a peptide backbone, on the time scales employed for low‐energy collisional activation in an ion‐trap mass spectrometer. Copyright © 2005 John Wiley & Sons, Ltd.