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Structure of the [M + H – H2O]+ Ion from Tetraglycine: A Revisit by Means of Density Functional Theory and Isotope Labeling

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journal contribution
posted on 23.06.2011, 00:00 by Udo H. Verkerk, Junfang Zhao, Michael J. Van Stipdonk, Benjamin J. Bythell, Jos Oomens, Alan C. Hopkinson, K.W. Michael Siu
Collision-induced dissociations of protonated 18O-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 [G4 + H – H2O]+ product ion is an N1-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 A 2010, 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.