Electrospray tandem mass spectrometry of alkali metal-containing anionic complexes of tripeptide

Collision-induced dissociation mass spectra of alkali metal-containing anionic tripeptides are reported. Both N-terminal and C-terminal product ions were observed from the precursor ions [M-2H+X](-) and [M-3H+2X](-) where X stands for an alkali metal. The results are consistent with precursor ion structures in which an alkali metal ion is centrally located for bonding with the amino terminus, the amide nitrogen atoms, and an oxygen atom of the carboxylate terminus; the second alkali metal ion in [M-3H+2X](-) is likely attached to the other oxygen atom of the carboxylate terminus.