Gas phase reactivity of Cu+-aromatic amino acids

The reactions between Cu+ and the four natural aromatic amino acids (AAarom = Phe, Tyr, Trp and His) have been investigated by means of electrospray ionization mass spectrometry. Metal cation complexes ([Cu AAarom]+) were formed in the electrospray source and collision-induced fragmentations of the most abundant isotopic form, [63Cu AAarom]+, were studied for each amino acid. The same fragmentation pattern is observed for all the amino acids, the most important peak corresponding in all cases to the loss of CH2O2. Among the four aromatic amino acids, the [Cu Phe]+ complex was selected for a computational study of the potential energy surface. Several mechanisms were studied at the B3LYP level and most of the observed fragmentations start with the metal cation insertion into the CC backbone bond or into the CR bond of the amino acid.