title: Structure of the [M + H - H2O]+ ion from tetraglycine: a revisit by means of density functional theory and isotope labeling.
abstract: Collision-induced dissociations of protonated (18)O-labeled tetraglycines labeled separately at either the first or the second amide bond established that water loss from the backbone occurs from the N-terminal residue. Density functional theory at B3LYP/6-311++G(d,p) predicted that the low-energy [G(4) + H - H(2)O](+) product ion is an N(1)-protonated 3,5-dihydro-4H-imidazol-4-one. The ion at the lowest energy, III, is 24.8 kcal mol(-1) lower than the protonated oxazole structure, II, proposed by Bythell et al. (J. Phys. Chem A2010, 114, 5076-5082). In addition, structure III has a predicted IR spectrum that provides a better match with the published experimental IRMPD spectrum than that of structure II.
authors: Department of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3.
authors: Udo H
authors: UH
authors: Verkerk
authors: Junfang
authors: J
authors: Zhao
authors: Michael J
authors: MJ
authors: Van Stipdonk
authors: Benjamin J
authors: BJ
authors: Bythell
authors: Jos
authors: J
authors: Oomens
authors: Alan C
authors: AC
authors: Hopkinson
authors: K W Michael
authors: KW
authors: Siu