Spectroscopic Evidence for an Oxazolone Structure in Anionic b-Type Peptide Fragments

Infrared spectra of anionic b-type fragments generated by collision induced dissociation (CID) from deprotonated peptides are reported. Spectra of the b(2) fragments of deprotonated AlaAlaAla and AlaTyrAla have been recorded over the 800-1800 cm(-1) spectral range by multiple-photon dissociation (MPD) spectroscopy using an FTICR mass spectrometer in combination with the free electron laser FELIX. Structural characterization of the b-type fragments is accomplished by comparison with density functional theory calculated spectra at the B3LYP/6-31++G(d,p) level for different isomeric structures. Although diketopiperazine structures represent the energetically lowest isomers, the IR spectra suggest an oxazolone structure for the b(2) fragments of both peptides. Deprotonation is shown to occur on the oxazolone alpha-carbon, which leads to a conjugated structure in which the negative charge is practically delocalized over the entire oxazolone ring, providing enhanced gas-phase stability

Structure of anionic c-type peptide fragments elucidated by IRMPD spectroscopy

In contrast to protonated peptides, collision-induced dissociation of deprotonated peptides is known to yield abundant c- and z-type fragments, in addition to typical a-, b- and y-type ions. Here we investigate the isomeric structures of short anionic c-type peptide fragments using IR photodissociation spectroscopy. As for all N-terminal fragments of deprotonated peptides, an important structural question concerns the site of deprotonation, as no C-terminal COOH group is present in these products. Comparison of the experimental action spectra with spectra computed for several candidate structures suggests that the c1 and c2 ions investigated have linear peptide structures with a C-terminal C(O)NH2 amide group. Competition between deprotonation on the peptide bond nitrogen atom, forming an amidate anion, and on the residue side chain, depending on its gas-phase acidity, is observed

Spectroscopic Evidence for an Oxazolone Structure in Anionic b-Type Peptide Fragments

Infrared spectra of anionic b-type fragments generated by collision induced dissociation (CID) from deprotonated peptides are reported. Spectra of the b(2) fragments of deprotonated AlaAlaAla and AlaTyrAla have been recorded over the 800-1800 cm(-1) spectral range by multiple-photon dissociation (MPD) spectroscopy using an FTICR mass spectrometer in combination with the free electron laser FELIX. Structural characterization of the b-type fragments is accomplished by comparison with density functional theory calculated spectra at the B3LYP/6-31++G(d,p) level for different isomeric structures. Although diketopiperazine structures represent the energetically lowest isomers, the IR spectra suggest an oxazolone structure for the b(2) fragments of both peptides. Deprotonation is shown to occur on the oxazolone alpha-carbon, which leads to a conjugated structure in which the negative charge is practically delocalized over the entire oxazolone ring, providing enhanced gas-phase stability

Deamidation Reactions of Asparagine- and Glutamine-Containing Dipeptides Investigated by Ion Spectroscopy

Contains fulltext : 161495.pdf (publisher's version ) (Open Access

Deamidation reactions of protonated asparagine and glutamine investigated by ion spectroscopy

Contains fulltext : 156945pos.pdf (postprint version ) (Open Access

Structure of anionic c-type peptide fragments elucidated by IRMPD spectroscopy

In contrast to protonated peptides, collision-induced dissociation of deprotonated peptides is known to yield abundant c- and z-type fragments, in addition to typical a-, b- and y-type ions. Here we investigate the isomeric structures of short anionic c-type peptide fragments using IR photodissociation spectroscopy. As for all N-terminal fragments of deprotonated peptides, an important structural question concerns the site of deprotonation, as no C-terminal COOH group is present in these products. Comparison of the experimental action spectra with spectra computed for several candidate structures suggests that the c(1) and c(2) ions investigated have linear peptide structures with a C-terminal -C(=O)-NH2 amide group. Competition between deprotonation on the peptide bond nitrogen atom, forming an amidate anion, and on the residue side chain, depending on its gas-phase acidity, is observed. (C) 2012 Elsevier B.V. All rights reserved