title: Electron-capture and -transfer dissociation of peptides tagged with tunable fixed-charge groups: structures and dissociation energetics.
abstract: Pyridiniummethylcarbonyl moieties that were previously designed on the basis of electronic structure analysis are now utilized as fixed-charge tags with tunable electronic properties to be used for N-terminal peptide derivatization and sequencing by electron-transfer dissociation. Dipeptides AK and KA were derivatized at the peptide N-terminus with 4-dimethylaminopyridinium-N-acetyl (DMAP-ac) and pyridinium-N-acetyl (pyrid-ac) tags of increasing intrinsic recombination energies. Upon the capture of a free electron or electron transfer from fluoranthene anions, (DMAP-ac-AK+H)(2+), (DMAP-ac-KA+H)(2+), (pyrid-ac-AK+H)(2+) and (pyrid-ac-KA+H)(2+) ions, as well as underivatized (AK+2H)(2+), completely dissociated. The fixed-charge tags steered the dissociation upon electron transfer to form abundant backbone N-C(α) bond cleavages, whereas the underivatized peptide mainly underwent H-atom and side-chain losses. Precursor ion structures for the tagged peptides were analyzed by an exhaustive conformational search combined with B3LYP/6-31+G(d,p) geometry optimization and single-point energy calculations in order to select the global energy minima. Structures, relative energies, transition states, ion-molecule complexes, and dissociation products were identified for several charge-reduced species from the tagged peptides. The electronic properties of the charge tags and their interactions with the peptide moieties are discussed. Electrospray ionization and electron-transfer dissociation of larger peptides are illustrated with a DMAP-tagged pentapeptide.
authors.affiliation: Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA 98195-1700, USA.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Chung
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Moss
authors.forename: Magdalena
authors.initials: M
authors.lastname: Zimnicka
authors.forename: Richard S
authors.initials: RS
authors.lastname: Johnson
authors.forename: Robert L
authors.initials: RL
authors.lastname: Moritz
authors.forename: František
authors.initials: F
authors.lastname: Tureček
mesh_terms: D004583:Electrons; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D010455:Peptides