Gas-Phase Fragmentation of [M + nH + OH]n•+ Ions Formed from Peptides Containing Intra-Molecular Disulfide Bonds

In this study, we systematically investigated gas-phase fragmentation behavior of [M + nH + OH](n center dot+) ions formed from peptides containing intra-molecular disulfide bond. Backbone fragmentation and radical initiated neutral losses were observed as the two competing processes upon low energy collision-induced dissociation (CID). Their relative contribution was found to be affected by the charge state (n) of [M + nH+ OH](n center dot+) ions and the means for activation, i.e., beam-type CID or ion trap CID. Radical initiated neutral losses were promoted in ion-trap CID and for lower charge states where mobile protons were limited. Beam-type CID and dissociation of higher charge states of [M + nH + OH](n center dot+) ions generally gave abundant backbone fragmentation, which was highly desirable for characterizing peptides containing disulfide bonds. The amount of sequence information obtained from CID of [M + nH + OH](n center dot+) ions was compared with that from CID of disulfide bond reduced peptides. For the 11 peptides studied herein, similar extent of sequence information was obtained from these two methods.