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 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 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 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 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.