Selecting fixed-charge groups for electron-based peptide dissociations: A computational study of pyridinium tags

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• 作者：Thomas W. Chung ; Františ ; ek Tureč ; ek
• 关键词：Charge tags ; Electron capture ; Electron transfer ; Excited states ; Recombination energies
• 刊名：International Journal of Mass Spectrometry
• 出版年：2008
• 出版时间：1 October 2008
• 年：2008
• 卷：276
• 期：2-3
• 页码：127-135
• 全文大小：1289 K

文摘

Fixed-charge groups based on pyridiniummethylcarboxamide moieties are analyzed by electronic structure theory calculations at combined B3LYP-PMP2 and CCSD(T) levels of theory to establish the ion recombination energies and thermodynamic and kinetic stability of radicals after electron capture. The fixed-charge pyridinium groups carry electron-donating and electron-withdrawing substituents and have higher recombination energies than protonated peptides, as modeled for (GK + H)⁺ and (GR + H)⁺. The pyridinium and peptide radicals formed by electron attachment have overlapping manifolds of electronic states that may allow for unidirectional or reversible intramolecular electron transfer in charge-tagged peptides. The pyridinium groups have moderate kinetic stabilities toward dissociation by N–CH₂ bond cleavage after electron attachment. Alkylammonium ions coordinated to 18-crown-6-ether show extremely low recombination energies and may represent a special kind of charge tags. Electron attachment to [CH₃NH₃…18-crown-6-ether]⁺ complex forms a dipolar species resembling an organic electride, in which the ionic alkylammonium core is surrounded by a crown-solvated electron.