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.