Gaseous dipeptide complexes with metal ions by electrospray ionization andtandem mass spectrometry

Electrospray ionization (ESI) and tandem mass spectrometry have been used t o investigate the gas-phase interactions of five metal ions and seven dipep tides. For silver ion, two complexes ([M+Ag](+) and [2M+Ag](+)) were obtain ed as well as the one complex ([2M+Met-H](+)) for transition-metal ions. Up on collision activation, there is an obvious difference in MS/MS data betwe en metal ion complex and the protonated molecule. The fragment pathway of e ach complex is related to the structures of dipeptide and the nature of met al ion which suggest that there are several interaction between the metal i ons and dipeptides in gas phase.