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Dissociation of the peptide bond in protonated peptides
Author(s) -
Polce Michael J.,
Ren Da,
Wesdemiotis Chrys
Publication year - 2000
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/1096-9888(200012)35:12<1391::aid-jms85>3.0.co;2-1
Subject(s) - chemistry , oxazolone , protonation , peptide , peptide bond , stereochemistry , amide , proton affinity , dissociation (chemistry) , hydrogen bond , amino acid , crystallography , ion , molecule , organic chemistry , biochemistry
The dissociation of the amide (peptide) bond in protonated peptides, [M + H] + , is discussed in terms of the structures and energetics of the resulting N ‐terminal b n and C ‐terminal y n sequence ions. The combined data provide strong evidence that dissociation proceeds with no reverse barriers through interconverting proton‐bound complexes between the segments emerging upon cleavage of the protonated peptide bond. These complexes contain the C ‐terminal part as a smaller linear peptide (amino acid if one residue) and the N ‐terminal part either as an oxazolone or a cyclic peptide (cyclic amide if one residue). Owing to the higher thermodynamic stability but substantially lower gas‐phase basicity of cyclic peptides vs isomeric oxazolones, the N ‐terminus is cleaved as a protonated oxazolone when ionic (b n series) but as a cyclic peptide when neutral (accompanying the C ‐terminal y n series). It is demonstrated that free energy correlations can be used to derive thermochemical data about sequence ions. In this context, the dependence of the logarithm of the abundance ratio log[y 1 /b 2 ], from protonated GGX (G, glycine; X, varying amino acid) on the gas‐phase basicity of X is used to obtain a first experimental estimate of the gas‐phase basicity of the simplest b‐type oxazolone, viz. 2‐aminomethyl‐5‐oxazolone (b 2 ion with two glycyl residues). Copyright © 2000 John Wiley & Sons, Ltd.