Anion Dependence in the Partitioning between Proton and Electron Transfer in Ion/Ion Reactions

Gas-phase reactions of singly-charged anions with multiply-protonated peptides, in a RF quadrupole linear ion trap, leads to either peptide deprotonation (proton transfer) or electron deposition (electron transfer). The former process induces peptide backbone cleavage through a reaction scheme analogous to electron capture dissociation (ECD). Here we characterize the preferred reaction pathways of several anions with multiply-protonated peptides. These anions include sulfur dioxide, perfluoro-1,3dimethyl-cyclohexane, sulfur hexafluoride, anthracene, and 9,10 diphenylanthracene. In our ion/ion apparatus, we find some anions react exclusively via proton transfer, others react by proton and electron transfer, while another behaved predominantly as an electron transfer agent.