The role of the position of the basic residue in the generation and fragmentation of peptide radical cations

Abstract

Using simple di- and tripeptides GX, GGX, GXG, XG and XGG, the influence of the position of the basic residue, X (X = R, K and H), on the formation of peptide radical cations (M•+) from [CuII(tpy)M] 2+ complexes (where tpy = 2,2′:6′,2″-terpyridine) was probed. It was found that M•+ is formed with greatest abundance when the basic residue is at the C-terminus. For arginine containing peptides, this may be due to further fragmentation of GRG•+, RG•+ and RGG•+ at the MS2 stage. For lysine and histidine containing peptides, when the basic residue is not located at the C-terminus, competing fragmentation pathways that lead to peptide backbone cleavage are more facile than M•+ formation. In order ..