Fragmentation reactions of some peptide b 3 ions: an energy‐resolved study

The fragmentation reactions of b 3 ions of nominal structure AAA oxa , YAA oxa , AYA oxa and AAY oxa have been studied as a function of collision energy, allowing the construction of breakdown graphs expressing in a qualitative way the energy dependence of the fragmentation reactions. The primary fragmentation reactions of the AAA oxa b 3 ion involve formation of the a 3 * (a 3 – NH 3 ) ion and the b 2 ion, with the latter becoming the dominant product at higher internal energies. For both YAA oxa and AYA oxa b 3 ions the pathway to a 3 * is relatively minor with formation of b 2 the dominant primary fragmentation reaction. For the AAY oxa b 3 ion, in addition to a 3 *, abundant formation of the tyrosine (Y) iminium ion is observed with only minor formation of the b 2 ion. The results support and expand upon the detailed mechanism of fragmentation of b 3 ions proposed by Cooper et al . ( J . Am . Soc . Mass Spectrom . 2006; 17: 1654). Copyright © 2009 John Wiley & Sons, Ltd.