Low energy collisionally activated dissociation of Cu 2+(glycine)(H 2O), Cu 2+(glycine)(H 2O) 2, Cu 2+(glycine) 2, and Cu 2+(glycylglycine) 2

Abstract

Doubly charged complex ions of Cu(II) have been formed in an electrospray source from dilute aqueous solutions containing copper sulfate and glycine (G) or glycylglycine (glygly). The most prominent ions, Cu 2+GW, Cu 2+GW 2, Cu 2+G 2, and Cu 2+(glygly) 2 (W = water) were studied by low energy, collisionally activated dissociation (CAD) in a triple quadrupole instrument. At very low collision energy, background water adds to all ions, except Cu 2+(glygly) 2, with no charge reduction. Loss of the elements of water from Cu 2+G 2 and Cu 2+(glygly) 2 without loss of charge suggests the occurrence of intracomplex peptide bond formation. In charge reduction reactions, the two ions containing water as a ligand produce +H 3NCH 2 · as the only significant organic product ion, together with several singly charged copper containing ions. By contrast, Cu 2+(glygly) 2 produces CH 2NH 2 + and (glygly)H +, and Cu 2+G 2 produces GH +, G +, CH 2NH 2 +, and +H 3NCH 2 ·, the latter two becoming more important at high collision energy. The major product from both Cu 2+GW and Cu 2+GW 2 is [Cu,H 2,O] +, which is suggested to be [Cu(H)OH] + rather than [Cu(H 2O)] +. From the same two parent ions a stripping reaction at centre of mass collision energies above ∼3 eV leads to loss of water, but no charge reduction, in the formation of Cu 2+G. In all CAD spectra there is a large imbalance at low collision energy between the relative amounts of the singly charged copper-containing product ions and the expected organic ions originating from the ligands. It is suggested that the latter are discriminated against because of inefficient containment following coulomb explosion.