Electron Capture Dissociation Studies of the Fragmentation Patterns of Doubly Protonated and Mixed Protonated-Sodiated Peptoids

摘要

The fragmentation patterns of a group of doubly protonated ([P + 2H]~(2+)) and mixed protonated-sodiated ([P + H + Na]~(2+)) peptide-mimicking oligomers, known as peptoids, have been studied using electron capturing dissociation (ECD) tandem mass spectrometry techniques. For all the peptoids studied, the primary backbone fragmentation occurred at the N-C_α bonds. The N-terminal fragment ions, the C-ions (protonated) and the C′-ions (sodiated) were observed universally for all the peptoids regardless of the types of charge carrier. The Cterminal ions varied depending on the type of charge carrier. The doubly protonated peptoids with at least one basic residue located at a position other than the N-terminus fragmented by producing the Z~?-series of ions. In addition, most doubly protonated peptoids also produced the Y-series of ions with notable abundances. The mixed protonated-sodiated peptoids fragmented by yielding the Z~(?′)-series of ions in addition to the C′-series. Chelation between the sodium cation and the amide groups of the peptoid chain might be an important factor that could stabilize both the N-terminal and the C-terminal fragment ions. Regardless of the types of the charge carrier, one notable fragmentation for all the peptoids was the elimination of a benzylic radical from the odd-electron positive ions of the protonated peptoids ([P + 2H]~(?+)) and the sodiated peptoids ([P + H + Na]~(?+)). The study showed potential utility of using the ECD technique for sequencing of peptoid libraries generated by combinatorial chemistry.