Gas-phase ion/ion interactions between peptides or proteins and iron ions in a quadrupole ion trap

The gas-phase ion/ion reactions of iron ions with oppositely charged peptide and protein ions were studied in a quadrupole ion trap. Both Fe+ and FeCO2- were investigated as possible reactant ions for gas-phase cleavage of peptide and protein ions. Several types of reaction products were observed. Charge exchange lowered the charge states of the proteins. Attachment resulted in a complex of the protein ion and the iron ion. In some cases bonds were broken in the protein ions, but it is unclear whether this is due to an insertion of the iron ion into a bond or due to the energetic reaction of oppositely charged species. Some preference was observed for bond cleavage near sulfur. Two disulfide bonds were broken in one case, and bonds adjacent to a cysteine residue were broken in another. (C) 2001 Elsevier Science B.V.