Chemiluminescent Aldehyde and β-Diketone Reactions Promoted by Peroxynitrite

Abstract

Peroxynitrite is shown here to promote the aerobic oxidation of isobutanal (IBAL) and 3-methyl-2,4-pentanedione (MP) in a pH 7.2 phosphate buffer into acetone plus formate and biacetyl plus acetate, respectively. These products are expected from dioxetane intermediates, whose thermolysis is known to be chemiluminescent (CL). Accordingly, the extent of total oxygen uptake by IBAL at different concentrations parallels the corresponding CL maximum intensities. The pH profile based on oxygen uptake data for the MP reaction matches the titration curve of peroxynitrous acid (pK(a) approximately 7), indicating that peroxynitrite anion is the oxidizing agent. Energy transfer studies with IBAL and the 9, 10-dibromoanthracene-2-sulfonate ion, a triplet carbonyl detector, indicates that triplet acetone (tau = 19 micros) is the energy donor. It is postulated that IBAL- or MP-generated triplet carbonyls are produced by the thermolysis of dioxetane intermediates, which are formed by the cyclization of alpha-hydroperoxide intermediates produced by insertion of dioxygen into the IBAL or MP enolyl radicals, followed by their reduction. Accordingly, EPR spin-trapping studies with 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) and 2-methyl-2-nitrosopropane (MNP) revealed the intermediacy of carbon-centered radicals, as expected for one-electron abstraction from the enol forms of IBAL or MP by peroxynitrite. The EPR data obtained with IBAL also reveal formation of the isopropyl radical produced by competitive nucleophilic addition of ONOO(-) to IBAL, followed by homolytic cleavage of this adduct and beta-scission of the resulting Me(2)CHCH(O(-))O(*). Superstoichiometric formation of fragmentation products from IBAL or MP attests to the prevalence of an autoxidation chain reaction, here proposed to be initiated by one-electron abstraction by ONOO(-) from the substrate. This work reveals the potential role of peroxynitrite as a generator of electronically excited species that may contribute to deleterious and pathological processes associated with excessive nitric oxide and aldehyde production.

Chemiexcitation of melanin derivatives induces DNA photoproducts long after UV exposure

“…This moiety undergoes thermolysis to two carbonyls, with one in an electronically excited triplet state having the high energy of a UV photon (> 3 eV, 70 kcal/mol, or 35,000 K) and capable of transferring its energy to DNA by a process that is independent of radiation (21). One of the few biologically-synthesized molecules that can initiate such “photochemistry in the dark” (22, 23) is peroxynitrite (ONOO – ) (24), which is generated by the reaction of O 2 •– with nitric oxide (NO • ). Peroxynitrite and NO • are stable enough to diffuse significant distances from the site of generation to the target molecule.…”

Peroxynitrite-Initiated Oxidation of Acetoacetate and 2-Methylacetoacetate Esters by Oxygen: Potential Sources of Reactive Intermediates in Keto Acidoses

“…However, a slightly different but significant profile was obtained by chemiluminescence, which reached a maximum around pH 7.2 and then declined with increasing pH. The roughly bell shaped pH curve obtained with EAA re- sembles the one reported for the acetoacetone/peroxynitrite system (29), suggesting dependence on H 2 PO 4 -(pK a ) 7.2) ion as an EAA enolization catalyst. Accordingly, as depicted in Figure 3, the light emission of the EAA/peroxynitrite system is also strongly dependent on the phosphate buffer concentration.…”

“…While the observed light emission may also be explained by the Russell reaction of the alkylperoxyl intermediate shown in Scheme 2, this does not seem to be the case, because the extent of oxygen consumption by structurally similar carbonyl compounds should be almost the same. Little or no oxygen consumption was observed in the oxidation of acetaldehyde and isobutyraldehyde initiated by peroxynitrite (29), whereas EAA and MAA depleted the dissolved oxygen within seconds. It could also be argued that the disparate oxygen consumption by EAA is due to different nucleophilic addition efficiencies.…”

Flow-injection chemiluminescence determination of tryptophan through its peroxidation and epoxidation by peroxynitrous acid

“…Moreover, it was also reported that the reaction of tryptophan with singlet oxygen also accompanied a chemiluminescence [35]. These chemiluminescence phenomena were considered as they originated from peroxidation and epoxidation of tryptophan by singlet oxygen and peroxynitrite [36,37]. Thus, The emitting species should be excited-state oxidation product resulted from decomposition of the formed dioxetane, epoxidized product of tryptophan by peroxynitrous acid [38,39], rather than the weak chemiluminescence of excited-state ONOOH * enhanced by tryptophan.…”