Fragmentation reactions of some peptide b(3) ions: an energy-resolved study

摘要

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) - NH3) 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 b3 ions proposed by Cooper et al. (J. Am. Soc. Mass Spectrom. 2006; 17: 1654).