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Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase
Faculty of Science - Papers (Archive)
  • Tony Ly, University of Wollongong
  • Benjamin B Kirk, University of Wollongong
  • Pramesh I Hettiarachchi, University of Wollongong
  • Berwyck L Poad, Ucsd (University California, Sand Diego)
  • Adam J Trevitt, University of Wollongong
  • Gabriel da Silva, University of Melbourne
  • Stephen J Blanksby, University of Wollongong
RIS ID
42557
Publication Date
1-1-2011
Publication Details

Ly, T., Kirk, B. B., Hettiarachchi, P. I., Poad, B. L., Trevitt, A. J., da Silva, G. & Blanksby, S. J. (2011). Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase. Physical Chemistry Chemical Physics, 13 (36), 16314-16323.

Abstract

α-Carboxylate radical anions are potential reactive intermediates in the free radical oxidation of biological molecules (e.g., fatty acids, peptides and proteins). We have synthesised well-defined α-carboxylate radical anions in the gas phase by UV laser photolysis of halogenated precursors in an ion-trap mass spectrometer. Reactions of isolated acetate (CH2CO 2-) and 1-carboxylatobutyl (CH3CH 2CH2CHCO2-) radical anions with dioxygen yield carbonate (CO3-) radical anions and this chemistry is shown to be a hallmark of oxidation in simple and alkyl-substituted cross-conjugated species. Previous solution phase studies have shown that Cα-radicals in peptides, formed from free radical damage, combine with dioxygen to form peroxyl radicals that subsequently decompose into imine and keto acid products. Here, we demonstrate that a novel alternative pathway exists for two α-carboxylate Cα-radical anions: the acetylglycinate radical anion (CH3C(O)NHCHCO2-) and the model peptide radical anion, YGGFG-. Reaction of these radical anions with dioxygen results in concerted loss of carbon dioxide and hydroxyl radical. The reaction of the acetylglycinate radical anion with dioxygen reveals a two-stage process involving a slow, followed by a fast kinetic regime. Computational modelling suggests the reversible formation of the Cα peroxyl radical facilitates proton transfer from the amide to the carboxylate group, a process reminiscent of, but distinctive from, classical proton-transfer catalysis. Interestingly, inclusion of this isomerization step in the RRKM/ME modelling of a G3SX level potential energy surface enables recapitulation of the experimentally observed two-stage kinetics. © 2011 the Owner Societies

Grant Number
ARC/DP0986738
Citation Information
Tony Ly, Benjamin B Kirk, Pramesh I Hettiarachchi, Berwyck L Poad, et al.. "Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase" (2011) p. 16314 - 16323
Available at: http://works.bepress.com/berwyck_poad/2/