Formation of molecular radical cations of enkephalin derivatives via collision-induced dissociation of electrospray-generated copper (II) complex ions of amines and peptides

Fragmentation of some electrospray-generated complex ions, [Cu-63(II)(amine )M](.2+), where M is an enkephalin derivative, produces the radical cation of the peptide, M.+. This ion has only been observed when M contains a tyro syl or tryptophanyl residue plus a basic residue, typically arginyl or lysy l. A typical viable amine is diethylenetriamine. Collision-induced dissocia tion (CID) of the M.+ ion yields a prominent [M - 106](.+) product ion for tyrosine-containing peptides, and a prominent [M - 129](.+) ion for a trypt ophan-containing peptide. These fragment ions are formed as a result of eli mination of the tyrosyl and tryptophanyl side chains. Dissociation of these ions, in turn, produces second generation product ions, many of which are typically absent in the fragmentation of protonated peptide ions. Structure s for some of these unusual ions are proposed. (C) 2001 American Society fo r Mass Spectrometry.