Spectroscopic Evidence for Mobilization of Amide Position Protons During CID of Model Peptide Ions

Infrared multiple photon dissociation (IRMPD) spectroscopy was used to study formation of b(2)(+) from nicotinyl-glycine-glycine-methyl ester (NicGGOMe). IRMPD shows that NicGGOMe is protonated at the pyridine ring of the nicotinyl group, and more importantly, that b(2)(+) from NicGGOMe is not protonated at the oxazolone ring, as would be expected if the species were generated on the conventional b(n)(+)/y(n)(+) oxazolone pathway, but at the pyridine ring instead. IRMPD data support a hypothesis that formation of b(2)(+) from NicGGOMe involves mobilization and transfer of an amide position proton during the fragmentation reaction. (J Am Soc Mass Spectrom 2009, 20, 1841-1845) (C) 2009 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry