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

• Published in: Journal of the American Society for Mass Spectrometry 2001-10, Vol.12 (10), p.1114-1119
• Main Authors: Chu, Ivan K, Rodriguez, Christopher F, Hopkinson, Alan C, Siu, K.W.Michael, Lau, Tai-Chu
• Format: Article
• Language: English
• Subjects: Amines; Amines - chemistry; Aminoacids, peptides. Hormones. Neuropeptides; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Cations; Chemistry; Coordination compounds; Copper; Copper - chemistry; Electrospraying; Enkephalins - chemistry; Exact sciences and technology; Fragmentation; Fundamental and applied biological sciences. Psychology; Indicators and Reagents; Ions; Mass spectrometry; Oligopeptides - chemistry; Organic chemistry; Peptides; Proteins; Reactivity and mechanisms; Spectrometry, Mass, Electrospray Ionization; Tryptophan; Tyrosine
• ISSN: 1044-0305; 1879-1123
• DOI: 10.1016/S1044-0305(01)00297-5

Fragmentation of some electrospray-generated complex ions, [ 63Cu 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 tyrosyl or tryptophanyl residue plus a basic residue, typically arginyl or lysyl. A typical viable amine is diethylenetriamine. Collision-induced dissociation (CID) of the M ·+ ion yields a prominent [M − 106] ·+ product ion for tyrosine-containing peptides, and a prominent [M − 129] ·+ ion for a tryptophan-containing peptide. These fragment ions are formed as a result of elimination 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. Structures for some of these unusual ions are proposed.