title: Diagnosing the protonation site of b2 peptide fragment ions using IRMPD in the X-H (X = O, N, and C) stretching region.
abstract: Charge-directed fragmentation has been shown to be the prevalent dissociation step for protonated peptides under the low-energy activation (eV) regime. Thus, the determination of the ion structure and, in particular, the characterization of the protonation site(s) of peptides and their fragments is a key approach to substantiate and refine peptide fragmentation mechanisms. Here we report on the characterization of the protonation site of oxazolone b(2) ions formed in collision-induced dissociation (CID) of the doubly protonated tryptic model-peptide YIGSR. In support of earlier work, here we provide complementary IR spectra in the 2800-3800 cm(-1) range acquired on a table-top laser system. Combining this tunable laser with a high power CO(2) laser to improve spectroscopic sensitivity, well resolved bands are observed, with an excellent correspondence to the IR absorption bands of the ring-protonated oxazolone isomer as predicted by quantum chemical calculations. In particular, it is shown that a band at 3445 cm(-1), corresponding to the asymmetric N-H stretch of the (nonprotonated) N-terminal NH(2) group, is a distinct vibrational signature of the ring-protonated oxazolone structure.
authors.affiliation: Laboratoire de Chimie Physique, Université Paris Sud, UMR8000 CNRS, Faculté des Sciences, Bât. 350, 91405, Orsay Cedex, France.
authors.forename: Rajeev K
authors.initials: RK
authors.lastname: Sinha
authors.forename: Undine
authors.initials: U
authors.lastname: Erlekam
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Bythell
authors.forename: Béla
authors.initials: B
authors.lastname: Paizs
authors.forename: Philippe
authors.initials: P
authors.lastname: Maître
mesh_terms: D054659:Diketopiperazines / Q000737:chemistry; D007536:Isomerism; D013058:Mass Spectrometry / Q000379:methods*; D009842:Oligopeptides / Q000737:chemistry*; D010081:Oxazolone / Q000737:chemistry; D011522:Protons; D013055:Spectrophotometry, Infrared / Q000379:methods*; D013816:Thermodynamics
chemical_list: D054659:Diketopiperazines; D009842:Oligopeptides; D011522:Protons; C081571:tyrosyl-isoleucyl-glycyl-seryl-arginine; D010081:Oxazolone