title: Non-zwitterionic structures of aliphatic-only peptides mediated the formation and dissociation of gas phase radical cations.
abstract: We have investigated how the non-zwitterionic and zwitterionic structures of aliphatic-only tripeptides affect the formation and dissociation of peptide radical cations in the gas phase. The non-zwitterionic forms of the aliphatic-only peptides in their metal complexes play an important role in determining whether the electron transfer pathway predominates. We extended this study by synthesizing permanent non-zwitterionic and zwitterionic forms of aliphatic-only peptide radical cations and exploring their reactivities in the gas phase. Collision-induced dissociation spectra demonstrated the feasibility of generating both non-zwitterionic and zwitterionic forms. Radical cations in zwitterionic forms may indeed mediate the beta and gamma carbon-carbon bond cleavages of leucine and isoleucine side chains from the GlyGlyXle radical peptides; this feature allows leucine and isoleucine residues to be distinguished unambiguously.
authors.affiliation: Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Corey N W
authors.initials: CN
authors.lastname: Lam
authors.forename: Eric D L
authors.initials: ED
authors.lastname: Ruan
authors.forename: C Y
authors.initials: CY
authors.lastname: Ma
authors.forename: Ivan K
authors.initials: IK
authors.lastname: Chu
mesh_terms: D000107:Acetylation; D002412:Cations; D002942:Circular Dichroism; D003300:Copper; D005740:Gases; D008745:Methylation; D010455:Peptides / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D002412:Cations; D005740:Gases; D010455:Peptides; D003300:Copper