+ Site Statistics
+ Search Articles
+ PDF Full Text Service
How our service works
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ Translate
+ Recently Requested

Where does the electron go? Electron distribution and reactivity of peptide cation radicals formed by electron transfer in the gas phase

Where does the electron go? Electron distribution and reactivity of peptide cation radicals formed by electron transfer in the gas phase

Journal of the American Chemical Society 130(27): 8818-8833

We report the first detailed analysis at correlated levels of ab initio theory of experimentally studied peptide cations undergoing charge reduction by collisional electron transfer and competitive dissociations by loss of H atoms, ammonia, and N-C alpha bond cleavage in the gas phase. Doubly protonated Gly-Lys, (GK + 2H) (2+), and Lys-Lys, (KK + 2H) (2+), are each calculated to exist as two major conformers in the gas phase. Electron transfer to conformers with an extended lysine chain triggers highly exothermic dissociation by loss of ammonia from the Gly residue, which occurs from the ground ( X ) electronic state of the cation radical. Loss of Lys ammonium H atoms is predicted to occur from the first excited ( A ) state of the charge-reduced ions. The X and A states are nearly degenerate and show extensive delocalization of unpaired electron density over spatially remote groups. This delocalization indicates that the captured electron cannot be assigned to reduce a particular charged group in the peptide cation and that superposition of remote local Rydberg-like orbitals plays a critical role in affecting the cation-radical reactivity. Electron attachment to ion conformers with carboxyl-solvated Lys ammonium groups results in spontaneous isomerization by proton-coupled electron transfer to the carboxyl group forming dihydroxymethyl radical intermediates. This directs the peptide dissociation toward NC alpha bond cleavage that can proceed by multiple mechanisms involving reversible proton migrations in the reactants or ion-molecule complexes. The experimentally observed formations of Lys z (+*) fragments from (GK + 2H) (2+) and Lys c (+) fragments from (KK + 2H) (2+) correlate with the product thermochemistry but are independent of charge distribution in the transition states for NC alpha bond cleavage. This emphasizes the role of ion-molecule complexes in affecting the charge distribution between backbone fragments produced upon electron transfer or capture.

Please choose payment method:

(PDF emailed within 0-6 h: $19.90)

Accession: 034238620

Download citation: RISBibTeXText

PMID: 18597436

DOI: 10.1021/ja8019005

Related references

Where Does the Electron Go? Stable and Metastable Peptide Cation Radicals Formed by Electron Transfer. Journal of the American Society for Mass Spectrometry 28(1): 164-181, 2016

Probing peptide cation-radicals by near-UV photodissociation in the gas phase. Structure elucidation of histidine radical chromophores formed by electron transfer reduction. Journal of Physical Chemistry. B 119(10): 3948-3961, 2015

Ion/molecule reactions of cation radicals formed from protonated polypeptides via gas-phase ion/ion electron transfer. Journal of the American Chemical Society 128(36): 11792-8, 2006

Assigning structures to gas-phase peptide cations and cation-radicals. An infrared multiphoton dissociation, ion mobility, electron transfer, and computational study of a histidine peptide ion. Journal of Physical Chemistry. B 116(10): 3445-3456, 2012

Combining UV photodissociation action spectroscopy with electron transfer dissociation for structure analysis of gas-phase peptide cation-radicals. Journal of Mass Spectrometry 50(12): 1438-1442, 2015

The radicals formed by photoinduced electron transfer from hypocrellins to electron acceptors. Research on Chemical Intermediates 26(7-8): 763-774, 2000

Transition metals as electron traps. I. Structures, energetics, electron capture, and electron-transfer-induced dissociations of ternary copper-peptide complexes in the gas phase. Journal of Mass Spectrometry 44(5): 707-724, 2009

Cation-modulated electron-transfer channel: H-atom transfer vs proton-coupled electron transfer with a variable electron-transfer channel in acylamide units. Journal of the American Chemical Society 129(31): 9713-9720, 2007

Spontaneous Isomerization of Peptide Cation Radicals Following Electron Transfer Dissociation Revealed by UV-Vis Photodissociation Action Spectroscopy. Journal of the American Society for Mass Spectrometry 29(9): 1768-1780, 2018

Comprehensive analysis of Gly-Leu-Gly-Gly-Lys peptide dication structures and cation-radical dissociations following electron transfer: from electron attachment to backbone cleavage, ion-molecule complexes, and fragment separation. Journal of Physical Chemistry. a 118(1): 308-324, 2014

Transition metals as electron traps. II. Structures, energetics and electron transfer dissociations of ternary Co, Ni and Zn-peptide complexes in the gas phase. Journal of Mass Spectrometry 44(10): 1518-1531, 2009

The one-electron oxidation of porphyrins to porphyrin pi-cation radicals by peroxidases: an electron spin resonance investigation. Archives of Biochemistry and Biophysics 273(1): 158-164, 1989

Radicals formed in N-acetylproline by electron attachment: electron spin resonance spectroscopy and computational studies. Journal of Physical Chemistry. B 115(49): 14846-14851, 2012

The histidine effect. Electron transfer and capture cause different dissociations and rearrangements of histidine peptide cation-radicals. Journal of the American Chemical Society 132(31): 10728-10740, 2010

Energy distribution and redistribution and chemical reactivity. The generalized delta overlap-density method for ground state and electron transfer reactions: a new quantitative counterpart of electron-pushing. Journal of the American Chemical Society 123(10): 2265-2270, 2001