Article pubs.acs.org/ac
Generation and Characterization of Gas-Phase Doubly Charged Biradical Peptide Ions (M2+••) Y. L. Elaine Wong,† Xiangfeng Chen,*,†,‡ Ri Wu,† Y. L. Winnie Hung,† Hoi Sze Yeung,§ and T.-W. Dominic Chan*,† †
Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong SAR Key Laboratory for Applied Technology of Sophisticated Analytical Instruments, Shandong Analysis and Test Centre, Shandong Academy of Sciences, Jinan, Shandong, People’s Republic of China § Bruker Scientific Instruments Hong Kong Co. Limited, Kowloon Bay, Hong Kong SAR ‡
S Supporting Information *
ABSTRACT: The gas-phase chemistry of peptide radical ions is attracting considerable interest in the fields of biology and mass spectrometry owing to its capability to provide sequence information on peptides and proteins. In this study, we observed that doubly charged peptide ions (M2+) can be produced from the collision-induced dissociation (CID) of Hg(II)-adducted peptide ions. The chemical nature and, thus, the dissociation pathways of this hydrogen-deficient biradical M2+ species is intriguing. We investigated the generation and dissociation behavior of this M2+ species under electron-capture dissociation (ECD) and CID conditions. The side-chain loss in the CID of the charge-reduced M+• ions formed by single-electron capture suggested that M2+ existed as a biradical ion. This ion underwent the combination of the two radical sites and conversion to hydrogen surplus species through structural rearrangement with increased energies. This study demonstrated a promising method to generate reactive doubly charged biradical precursor ions and, thus, help characterize novel biomolecules.
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series of a-/x-ions instead of a series of b-/y-ions, which are formed from the CID of even-electron protonated peptide ions. In electron-based dissociation methods, such as ECD17 and electron transfer dissociation (ETD),18 the even-electron multiply charged molecular ions are converted to chargereduced odd-electron species through the exothermic ionelectron recombination/electron transfer process. ECD/ETD presents numerous advantages compared with conventional even-electron dissociation methods, such as CID and infrared multiple-photon dissociation (IRMPD). The hydrogen surplus radical peptide/protein ions formed by ECD/ETD dissociate predominantly via the C−N cleavage; as a result, a series of c-/ z•-ions are formed. Although the dissociation efficiency of ECD/ETD for proteins is relatively low (typically
