title: Transformation of [M + 2H](2+) Peptide Cations to [M - H](+), [M + H + O](+), and M(+•) Cations via Ion/Ion Reactions: Reagent Anions Derived from Persulfate.
abstract: The gas-phase oxidation of doubly protonated peptides is demonstrated here using ion/ion reactions with a suite of reagents derived from persulfate. Intact persulfate anion (HS2O8(-)), peroxymonosulfate anion (HSO5(-)), and sulfate radical anion (SO4(-•)) are all either observed directly upon negative nanoelectrospray ionization (nESI) or easily obtained via beam-type collisional activation of persulfate into the mass spectrometer. Ion/ion reactions between each of these reagents and doubly protonated peptides result in the formation of a long-lived complex. Collisional activation of the complex containing a peroxymonosulfate anion results in oxygen transfer from the reagent to the peptide to generate the [M + H + O](+) species. Activation of the complex containing intact persulfate anion either results in oxygen transfer to generate the [M + H + O](+) species or abstraction of two hydrogen atoms and a proton to generate the [M - H](+) species. Activation of the complex containing sulfate radical anion results in abstraction of one hydrogen atom and a proton to form the peptide radical cation, [M](+•). This suite of reagents allows for the facile transformation of the multiply protonated peptides obtained via nESI into a variety of oxidized species capable of providing complementary information about the sequence and structure of the peptide.
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, IN, 47907-2084, USA.
authors.forename: Alice L
authors.initials: AL
authors.lastname: Pilo
authors.forename: Jiexun
authors.initials: J
authors.lastname: Bu
authors.forename: Scott A
authors.initials: SA
authors.lastname: McLuckey
mesh_terms: D000838:Anions / Q000737:chemistry*; D002412:Cations / Q000737:chemistry*; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry*; D010545:Peroxides / Q000737:chemistry; D011522:Protons; D013431:Sulfates / Q000737:chemistry*
chemical_list: D000838:Anions; D002412:Cations; D010455:Peptides; D010545:Peroxides; D011522:Protons; D013431:Sulfates; C038288:peroxymonosulfate