Carboxylate and amine terminus directed fragmentations in gaseous dipeptide complexes with copper(II) and diimine ligands formed by electrospray

Singly and doubly charged peptide complexes with copper(II) and 2,2'-bipyridyl (bpy) are formed in the gas phase by electrospraying water-methanol solutions containing the components. Collisionally activated dissociations at low kinetic energies of singly charged complexes of the [Cu-II(peptide - H)(bpy)](.+) type provide information about the amino acid sequence for L-Phe-Leu, L-Leu-Phe, L-Phe-Pro, L-Pro-Phe, L-Phe-Met, L-Met-Phe, L-Ser-Phe, L-Asp-Phe, and L-His-Phe. Dissociations of doubly charged complexes of the [Cu-II(peptide)(bpy)](.2+) type also allow identification of the N- and C-terminal amino acid residues, Leucine and isoleucine residues are readily distinguished in L-Ala-Leu and L-Ala-ne through dissociations of their Cu complexes, Ion dissociation mechanisms, as elucidated by deuterium labeling, are discussed.