Designing copper(II) ternary complexes to generate radical cations of peptides in the gas phase: Role of the auxiliary ligand

Abstract

A series of ternary copper(II) complexes of the type [Cu II(L)(M)]2+, where M represents the hexapeptides GGGFLR, YGGFLR and WGGFLR and L a set of 12 nitrogen donor ligands have been evaluated for their ability to form cationic peptide radicals, M+̇, in the gas phase. Although the fragmentation chemistry of these ions is complex, two main conclusions emerge: (i) Complexes containing a tri- or tetra-dentate ligand were found to be more effective at producing the peptide radical because in these instances competitive loss of the ligand from the complex is inhibited; (ii) The ligands ought not possess any acidic protons in order to prevent competitive loss of the protonated peptide, [M + H]+. T..