Premium
Negative ion fragmentations of deprotonated peptides. The unusual case of iso Asp: a joint experimental and theoretical study. Comparison with positive ion cleavages
Author(s) -
Andreazza Hayley J.,
Wang Tianfang,
Bagley Christopher J.,
Hoffmann Peter,
Bowie John H.
Publication year - 2009
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4107
Subject(s) - chemistry , deprotonation , endothermic process , cleavage (geology) , ion , stereochemistry , electrospray , mass spectrometry , medicinal chemistry , chromatography , organic chemistry , adsorption , geotechnical engineering , fracture (geology) , engineering
The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH 2 )], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH 2 )], Crinia angiotensin [APGDRIYVHPF(OH)] and their iso Asp isomers. It is not possible to differentiate between Asp‐ and iso Asp‐containing peptides (used in this study) using negative ion electrospray mass spectrometry. This is because the iso Asp residue cleaves to give the same fragment anions as those formed by δ and γ backbone cleavage of Asp. The iso Asp fragmentations are as follows: RNHCH(CO 2 H) − CHCONHR′ → [RNH − (HO 2 CCHCHCONHR′)] → RNH − +HO 2 CCHCHCONHR′ and RNHCH(CO 2 H) − CHCONHR′ → [RNH − (HO 2 CCHCHCONHR′] → − O 2 CCHCHCONHR′+RNH 2 . Calculations at the HF/6‐31+G(d)//AM1 level of theory indicate that the first of these iso Asp cleavage processes is endothermic (by +115 kJ mol −1 ), while the second is exothermic (−85 kJ mol −1 ). The barrier to the highest transition state is 42 kJ mol −1 . No diagnostic cleavage cations were observed in the electrospray mass spectra of the MH + ion of the Asp‐ and iso Asp‐containing peptides (used in this study) to allow differentiation between these two amino acid residues. Copyright © 2009 John Wiley & Sons, Ltd.