RIS ID
42557
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
Additional Grant Number
Included in
Life Sciences Commons, Physical Sciences and Mathematics Commons, Social and Behavioral Sciences Commons
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.