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Peptide derivatization as a strategy to form fixed‐charge peptide radicals
Author(s) -
Karnezis Asimo,
Barlow Christopher K.,
O'Hair Richard A. J.,
McFadyen W. David
Publication year - 2006
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.2671
Subject(s) - chemistry , peptide , radical , medicinal chemistry , fragmentation (computing) , electrospray ionization , derivatization , isopropyl , stereochemistry , ion , mass spectrometry , organic chemistry , chromatography , biochemistry , computer science , operating system
As a means of generating fixed‐charge peptide radicals in the gas phase we have examined the collision‐induced dissociation (CID) chemistry of ternary [Cu II (terpy)(TMPP‐M)] 2+ complexes, where terpy = 2,2′:6′2″‐terpyridine and TMPP‐M represents a peptide (M) modified by conversion of the N‐terminal amine to a [tris(2,4,6‐trimethoxyphenyl)phosphonium]acetamide (TMPP‐) fixed‐charge derivative. The following modified peptides were examined: oligoglycines, (Gly) n (n = 1–5), alanylglycine, glycylalanine, dialanine, trialanine and leucine‐enkephaline (YGGFL). The [Cu II (terpy)(TMPP‐M)] 2+ complexes are readily formed upon electrospray ionization (ESI) of a mixture of derivatized peptide and [Cu II (terpy)(NO 3 ) 2 ] and generally fragment to form transient peptide radical cations, TMPP‐M + . , which undergo rapid decarboxylation for the simple aliphatic peptides. This is contrasted with the complexes containing the unmodified peptides, which predominantly undergo fragmentation of the coordinated peptide. These differences demonstrate the importance of proton mobility in directing fragmentation of ternary copper(II) peptide complexes. In the case of leucine‐enkephaline, a sufficient yield of the radical cation was obtained to allow further CID. The TMPP‐YGGFL + . ion showed a rich fragmentation chemistry, including CO 2 loss, side‐chain losses of an isopropyl radical, 2‐methylpropene and p ‐quinomethide, and *a 1 and *a 4 sequence ion formation. In contrast, the even‐electron TMPP‐YGGFL + ion fragments to form *a n and *b n sequence ions as well as the [*b 4 + H 2 O] + rearrangement ion. Copyright © 2006 John Wiley & Sons, Ltd.