16518-46-0Relevant articles and documents
Reactions of simple and peptidic alpha-carboxylate radical anions with dioxygen in the gas phase
Ly, Tony,Kirk, Benjamin B.,Hettiarachchi, Pramesh I.,Poad, Berwyck L. J.,Trevitt, Adam J.,Da Silva, Gabriel,Blanksby, Stephen J.
, p. 16314 - 16323 (2011)
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.
Cage-Escape of Geminate Radical Pairs Can Produce Peroxynitrate from Peroxynitrite under a Wide Variety of Experimental Conditions
Hodges, George R.,Ingold
, p. 10695 - 10701 (2007/10/03)
The spontaneous and CO2-catalyzed decomposition of peroxynitrite yields HO? and -CO3? radicals, respectively, together with ?NO2. The geminate HOVNO2 and -CO3?/?NO2 pairs undergo competitive in-cage collapse to nitrate and diffusive separation. Free HO? and -CO3? radicals react with H2O2 and, in the presence of O2, suitable alcohols or formate to produce superoxide, which is trapped by the ?NO2 to form peroxynitrate. The formation of peroxynitrate may influence the rate of change in optical density at 302 nm, the wavelength normally employed to monitor peroxynitrite decay, leading to misleading kinetic traces. Tetranitromethane (TNM) was used as a colorimetric probe for superoxide to quantify the yield of free HO? (27-28%) and free -CO3? (32-33%). The yields of both of these free radicals are in excellent agreement with other recent estimates. Superoxide was also detected in some oxygenated aldehyde-catalyzed peroxynitrite decompositions both by peroxynitrate formation and by its reaction with TNM. Superoxide yields, measured with TNM, were aldehyde (RCHO) dependent (R = -O2CC6H4, CH3, CH3CH2, (CH3)3C and HOCH2CHOH; yields were 15, 9, 0.8, 0, and 30%, respectively).
