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 prod uct ions were observed from the precursor ions [M-2H+X](-) and [M-3H+2 X](-) where X stands for an alkali metal. The results are consistent w ith 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 me tal ion in [M-3H+2X](-) is likely attached to the other oxygen atom of the carboxylate terminus.