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 [b 2 − H + Ag] + and [a 2 − H + Ag] + ions have been determined by means of tandem mass spectrometry and confirmed by comparison with synthesized derivatives of the candidate [b 2 − H + Ag] + ion structure. The [b 2 − H + Ag] + ion was found to be an N-argentinated oxazolone, which could subsequently form the [a 2 − 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 [b 2 − H + Ag] + ion, which was postulated to be an argentinated ketene.