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 [CuII(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 [CuII(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-Ile through dissociations of their Cu complexes. Ion dissociation mechanisms, as elucidated by deuterium labeling, are discussed.