GAS-PHASE COMPLEXES OF AMINO-ACIDS WITH CU(II) AND DIIMINE LIGANDS .2. AMINO-ACIDS WITH O, N AND S FUNCTIONAL-GROUPS IN THE SIDE-CHAIN

Ternary complexes of amino acids, Cu(II) and diimine ligand 2,2'-bipyr idyl (bpy) are obtained in the gas phase by electrospray ionization (E SI). The amino acids are found to bind to Cu(II) by their deprotonated carboxylate groups in the gas-phase complexes. Collisionally activate d dissociations at low ion kinetic energies of the [Cu(II)(AA - H)(bpy )](+.) complexes show decarboxylation followed by cleavages of the ami no acid side-chains that reveal interactions with the Cu atom of the s ide-chain functional groups. Hydroxy, sulfide and disulfide groups are transferred on to the Cu atom following collisional activation, but d o not displace the bpy ligand. The side-chain functional groups and th e CbetaH2=CalphaHNH2 fragment are found to compete for coordination to Cu(bpy)(+) in the products. The epsilon-amino group in lysine and the guanidyl group in arginine displace the bpy ligand following decarbox ylation. The fragmentations of the gas-phase [Cu(II(AA - H)(bpy)](+.) complexes are highly specific for the amino acid residues. Arginine an d lysine also form doubly charged ions by ESI that distinguish lysine from the isobaric glutamine.