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 an rf quadrupole linear ion trap, leads to either peptide deprotonation (proton transfer) or electron deposition (electron transfer). The latter 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- 1,3-dimethyl-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. (C) 2004 Elsevier B.V. All rights reserved.