Structures of b and a product ions from the fragmentation of argentinated peptides

Argentinated (silver-containing) oligopeptides fragment under low- energy collision conditions to yield abundant argentinated product ions. The structures of the [b₂ - H + Ag]⁺ and [a₂ - H + Ag]⁺ ions have been determined by means of tandem mass spectrometry and confirmed by comparison with synthesized derivatives of the candidate [b₂ - H + Ag]⁺ ion structure. The [b₂ - H + Ag]⁺ ion was found to be an N-argentinated oxazolone, which could subsequently form the [a₂ - H + Ag]⁺ ion and other product ions after collision activation. Tripeptides containing proline as their second residue were observed to form a relatively less abundant [b₂ - H + Ag]⁺ ion, which was postulated to be an argentinated ketene.