Protonation sites in peptide dications and cation-radicals containing 尾-amino acid residues

详细信息	查看全文 | 推荐本文 |

• 作者：Christopher L. Moss ; Franti&scaron ; ek Ture膷ek ; ^{turecek@chem.washington.edu}
• 关键词：Peptide ion structure ; Peptide cation-radical ; Conformations&rsquo ; tautomer ; Transition state ; Fragmentation
• 刊名：International Journal of Mass Spectrometry
• 出版年：2012
• 期刊代码：43_13873806
• 类别：ch
• 出版时间：15 April, 2012
• 卷：316-318
• 期：Complete
• 页码：57-67
• 文件大小：1787 K

摘要

Protonation sites in a model pentapeptide Ala-Ala-尾Ab-Ala-Ala, where 尾Ab was 尾-aminobutyric acid, were studied by ab initio and density functional theory calculations. Gas-phase dication tautomers protonated at the N-terminus and amide oxygens were found to be substantially more stable than tautomers protonated at amide nitrogens. This order of ion stability did not change upon solvation with methanol. Conformational analysis of dication tautomers indicated similar degrees of internal solvation by hydrogen bonding in amide O- and N-protonated ions in the gas phase. Because of the low stability of amide N-protonated tautomers, their formation by electrospray of non-basic peptides is highly unlikely. Computational analysis of Ala-Ala-尾Ab-Ala-Ala cation-radicals indicated substantially lower transition-state energies for NC_伪 bond dissociations at Ala residues than for the NC_尾 bond dissociation at 尾Ab. The formation of 尾-radicals as z fragments was found to require a high threshold energy. Cleavage of the CONH₂ bond leading to b and y fragments was hampered by a high-energy transition state for the formation of an N-protonated cation-radical intermediate as well as by a high threshold energy for the fragment formation. The calculated energies for transition states and dissociation thresholds explain the less efficient NC_尾 bond dissociation upon electron capture or transfer in peptide ions containing 尾-amino acid residues.