Showing papers on "Radical ion published in 1986"
1,200 citations
01 Jan 1986
TL;DR: It was found that ferrous ion, but not ferric ion, was effective in forming 8-OH-dG, and the hydroxyl free radical scavenging agents, thiourea and ethanol, were very effective in quenching Fe(11) mediated 8- OH- dG formation, but superoxide dismutase had very little effect.
Abstract: DNA or 2-deoxyguanosine reacts with hydroxyl free radical to form 8-hydroxy-deoxyguanosine (8-OH-dG). We found that 8-OH-dG can be effectively separated from deoxyguanosine by high pressure liquid chromatography and very sensitively detected using electrochemical detection. The sensitivity of electrochemical detection is about one-thousand fold enhanced over optical detection. Utilizing deoxyguanosine in bicarbonate buffer it was found that ferrous ion, but not ferric ion, was effective in forming 8-OH-dG. The hydroxyl free radical scavenging agents, thiourea and ethanol, were very effective in quenching Fe(11) mediated 8-OH-dG formation, but superoxide dismutase had very little effect.
657 citations
TL;DR: Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs, acetophenones) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements, and the relative amounts of primary and tertiary radicals formed by reaction of the same ketones with p-cymene have been measured.
Abstract: Rate constants for triplet-state reaction of various ring-substituted benzophenones (BPs), acetophenones (APs), and ..cap alpha..,..cap alpha..,..cap alpha..-trifluoroacetophenones (TFAs) with toluene and p-xylene have been determined by a combination of flash kinetics, steady-state quenching, and quantum yield measurements. The relative amounts of primary and tertiary radicals formed by reaction of the same ketones with p-cymene have also been measured. For all three types of ketones, rate constants correlate well with triplet ketone reduction potentials. The magnitude of the kinetic isotope effects observed with toluene-d/sub 8/ and p-xylene-d/sub 10/ diminishes as the ketones become easier to reduce. All of the ketone triplets react with alkylbenzenes primarily by a charge-transfer mechanism, with the rate-determining step changing from complexation to hydrogen transfer as the ketones become harder to reduce. The least reactive AP triplets probably react significantly via simple hydrogen atom abstraction as well. Those ketones with n,..pi..* lowest triplets (all BPs and some APs) react with p-cymene to give primary/tertiary radical ratios that vary no more than a factor of 2 from the 0.40 value displayed by tert-butoxy radicals; those with ..pi..,..pi..* lowest triplets (TFAs and some APs) give ratios that favor primary radicals and that vary by an order of magnitude withmore » the triplet ketone reduction potential. The variation in cymene product ratios reflects different orientations for attack on cymene by n,..pi..* and ..pi..,..pi..* triplets and differing degrees of partial electron transfer within the exciplexes, which are not tight radical ion pairs.« less
184 citations
TL;DR: In this article, the authors used molecular orbital calculations on the distonic radical cations CH2(CH2)nN+H3 and their conventional isomers CH3(CH 2)nNH2+ (n = 0, 1, 2 and 3) to predict the relative energies of distonic ions.
156 citations
152 citations
137 citations
119 citations
TL;DR: Electron spin resonance spectroscopy has been used to monitor free radicals formed during CCl4 metabolism by perfused livers from phenobarbital-treated rats and found an additional free radical signal about two orders of magnitude more intense than that of the phenyl N-t-butylnitrone/CCl.
105 citations
TL;DR: This photoreaction constitutes an excellent model to study the chemical properties of the thymidine radical cation which is expected to be one of the primary consequences of the direct effects of ionizing radiation.
Abstract: The near ultraviolet photolysis of an aerated aqueous solution of thymidine containing 2-methyl-1,4-naphthoquinone gives rise to two main classes of photoproducts as a result of the initial formation of a pyrimidine radical cation. These photo-oxidation products have been separated by high performance liquid chromatography and further characterized by various spectroscopic techniques including fast atom bombardment mass spectrometry and high field 1H and 13C nuclear magnetic resonance analysis. This photoreaction constitutes an excellent model to study the chemical properties of the thymidine radical cation which is expected to be one of the primary consequences of the direct effects of ionizing radiation.
101 citations
TL;DR: In this paper, the aminoalkyl radical (CH3)2NCH2 (A) and its conjugated acid (CH 3)2HN+CH2(AH+) as well as the alkylamine radical cation (AH+) were observed to be disproportionate.
Abstract: Hydroxyl radical reactions with trimethylamine in aqueous solution lead to the formation of the aminoalkyl radical (CH3)2NCH2 (A) and its conjugated acid (CH3)2HN+CH2 (AH+) as well as to the alkylamine radical cation (CH3)3N+(N+). These radicals are transform ed into each other by hydrolytic reactions, e.g. [xxx] Radicals AH+ are more acidic (pKa ≈ 3.6) than the radicals N+(pKa ≈ 8.0). Consequently, N+ predom inate over AH+ under quasi equilibrium conditions (e.g. in the presence of phosphate buffer) and are the only species observed by ESR in acid solutions. Reacting with the protonated amine. OH radicals abstract hydrogen at nitrogen and at carbon with comparable ease. Reaction of OH radicals with the free amine may initially also generate N+, beside H-abstraction at carbon. Radicals A’ absorb more strongly at 260 nm (ε = 3390 dm3mol-1cm-1) than the radical cation N+(ε = 950 dm3mol-1cm-1). Radical A' has reducing properties whereas radicals AH+ and N+ have oxidizing properties and hence can be monitored with p-nitroacetophenone (the reducing radicals), and Fe(CN)64- , N ,N'-tetramethyl-p-phenylenediamine and 2,2'-azinobis-(3-ethyl-benzthiazoline- 6-sulphonate) (the oxidizing radicals). These radicals mainly (≥ 85 % ) disproportionate. one of the products being formaldehyde
64 citations
TL;DR: In this paper, the C-C bond dissociation energies of the radical cations of 5 and 6 were estimated by analysis of the thermochemical cycle using the bond dissociability energies and the oxidation potentials of the neutral molecules and the oxidization potential of the diphenylmethyl and cumyl radicals.
TL;DR: In this article, hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2−13.
Abstract: Hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2–13. From the intense satellite spectra of 1+–13+ not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the 13C isotopes in the central double bond. The former values range from 0.370 (8+) to 0.470 mT (4+) and the latter from 0.255 (8+) to 0.360 mT (4+) in the radical cations of bis(ethylenedithio)-TTF (8+) and tetracyano-TTF (4+). The radical cation of TTF (1+) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the 13C isotopes. The spin population in 1+–13+ resides, to a large extent, in the central S2C CS2 part of the π-system. It tends to increase (decrease) by substitution with electron-accepting (donating) groups in the 2,3,6,7-positions of TTF.
TL;DR: The most stable [C2H6O]- isomer is the distonic ion [CH2CH2OH2] as mentioned in this paper, which interconverts with a yet-unidentified isomer.
TL;DR: In this article, the resonance Raman, ESR and visible absorption spectra have been observed at room temperature for the 4, 4′-bipyridine radical anion in tetrahydrofuran.
Abstract: Resonance Raman, ESR and visible absorption spectra have been observed at room temperature for the 4, 4′-bipyridine radical anion in tetrahydrofuran and for 4, 4′-bipyridine adsorbed on metallic potassium. Based on the quinoid structure of the radical anion, as predicted by the MO theory, a normal coordinate analysis has been carried out. The relative Raman intensities have also been calculated satisfactorily for the totally symmetric modes of the radical anion. Thus, the main Raman bands are interpreted in terms of the molecular structure change caused by the resonant electronic transition in the visible region. The results are compared with those of the biphenyl radical anion, 2,2′-bipyridine radical anion and the methylviolegen radical cation reported in the literature.
TL;DR: In this article, the efficiency of proton transfer from the donor cation radical to the acceptor anion radical is determined by the kinetic acidity and basicity of the radical ion pair.
TL;DR: Methode generale d'evaluation de l'acidite par combinaison du pk and des potentiels d'oxydation de l-acide and de la base conjuguee are revealed.
Abstract: Methode generale d'evaluation de l'acidite par combinaison du pk et des potentiels d'oxydation de l'acide et de la base conjuguee
TL;DR: In this article, the benzene rings of N-alkyltoluidine and benzene (or iodobenzene) in acetic acid were annelated with acetylenedicarboxylates by palladium(II) acetate to give N-alkylindole-2,3-dicar-carboxylate and naphthalene-1, 2,3,4-tetracaroxylate.
Abstract: Benzene rings of N-alkyltoluidine and benzene (or iodobenzene) in acetic acid were annelated with acetylenedicarboxylates by palladium(II) acetate to give N-alkylindole-2,3-dicarboxylate and naphthalene-1,2,3,4-tetracarboxylate. The formation of the products are explained in terms of toluidine radical cation intermediates.
TL;DR: In this article, the synthesis and full characterization of the title heterocycle are presented, which can be studied in its three stable oxidation states: diradical, radical action and dication.
TL;DR: In this article, the steric slowing of Diels-Alder dimerization appears to be necessary; 1,3-cyclohexadiene gave only dimer under conditions where its 1-isopropyl-4-methyl derivative gave a 96% yield of ascaridole.
Abstract: Alkylated 1,3-dienes are shown to oxygenate to endoperoxides by a cation radical chain mechanism. Steric slowing of Diels-Alder dimerization appears to be necessary; 1,3-cyclohexadiene gave only dimer under conditions where its 1-isopropyl-4-methyl derivative gave a 96% yield of ascaridole. The cation radical chain conditions tolerate more steric crowding than does the singlet oxygen reaction, as 4,4'-bihomoadamantenyl gave an 84% yield of its endoperoxide while singlet oxygen gave a mixture of several products. Oxygenation products were not observed from biadamantylideneethane which is sterically prohibited from assuming an s-cis conformation.
TL;DR: The oxidation of the phenacetin metabolites p-phenetidine and acetaminophen by peroxidases was investigated and the radical concentration was dependent on the square root of the enzyme concentration, indicating second-order decay of the radical, as is consistent with its dimerization or disproportionation.
TL;DR: The title compound can be isolated in at least three distinct oxidation states as mentioned in this paper, and the dication is easily reduced to the radical cation by a variety of reducing agents, yielding a mixed valence compound showing a conductivity of ≈ 2 × 10 −1 S cm −1.
TL;DR: In this paper, Nelsen and Clennan reported the oxygenation of biadamantylidene (1) to its dioxetane 2 by a radical cation chain reaction with ground state.
Abstract: Cyclic voltammetry studies allow estimation of the rate constant for addition of O2 to biadamantylidene cation radical (lo+) to be 5600 M-' s-' at room temperature and for the cleavage of biadamantylidene dioxetane cation radical to oxygen and 1'+ >800 s-]. Chlorination of the adamantane skeleton slows the overall rate of oxygen addition, and the face selectivity for oxygenation of S(C1) is 25:l in favor of attack from the olefin face syn to the chlorine. The implications of these findings for the mechanism of the reaction are discussed. The groups of Nelsen' and Clennan2 simultaneously reported the oxygenation of biadamantylidene (1) to its dioxetane 2 by a radical cation chain reaction with ground state. 302, which could be initiated by chemical or electrochemical oxidation (Scheme I) . Various acidic) and oxidizing reagents cause formation of 2, the epoxide of 1, and their decomposition products, but it was argued that the cation radical chain mechanism gives essentially only 2 . ' ~ ~ Ando and co-workers4 have contrasted the stereochemistry of dioxetane formation for analogues of 1 in the electrochemically initiated reaction with those of photogenerated IO2 and by photolysis with reducible sensitizers like 9,lO-dicyanoanthracene, which initially generates pairs of olefin cations and 02-.5 The use of 3'+,6 a powerful enough oxidant to form tetraalkylolefin cation radicals rapidly at low temperature, makes the cation radical chain oxygenation reaction preparatively useful? Conversion of isopropylideneadamantane (4) to dioxetane under
TL;DR: PCBA represents the first in the cyclobutylamine class of MAO inactivators and strongly supports involvement of a radical mechanism for MAO-catalyzed amine oxidations.
Abstract: 1-Phenylcyclobutylamine (PCBA) is shown to be both a substrate and a time-dependent irreversible inactivator of monoamine oxidase (MAO). Inactivation results in attachment to the flavin cofactor. For every molecule of PCBA leading to inactivation, 325 molecules are converted to product. The first metabolite formed is identified as 2-phenyl-1-pyrroline; then after a lag time, 3-benzoylpropanal and 3-benzoylpropionic acid are generated. The 3-benzoylpropanal is a product of MAO-catalyzed oxidation of 2-phenyl-1-pyrroline (presumably, of its hydrolysis product, gamma-aminobutyrophenone). The aldehyde is nonenzymatically oxidized by nascent hydrogen peroxide to the carboxylic acid. These results are consistent with a one-electron oxidation of PCBA to the amine radical cation followed by homolytic cyclobutane ring cleavage. The resulting radical can partition between cyclization (an intramolecular radical trap) to the 2-phenylpyrrolinyl radical and attachment to the flavin. The cyclic radical can be further oxidized by one electron to 2-phenyl-1-pyrroline. PCBA represents the first in the cyclobutylamine class of MAO inactivators and strongly supports involvement of a radical mechanism for MAO-catalyzed amine oxidations.
TL;DR: In this article, the authors showed that the viologen molecules can be reduced to radical cations in situ by optical excitation of the semiconductor, which results in a dramatic increase in the rate of radical cation dimer formation, compared with the bulk solution reaction.
TL;DR: The ring-opened radical cations of cyclopropane and several of its methyl derivatives have been characterized by ESR spectroscopy following their generation by γ irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K.
TL;DR: In this paper, the influence of the metal oxide surface on radical cation reactivity is discussed, and the intermediate formation of an immonium cation in an ECE route is revealed.
TL;DR: In this paper, the radical cations from aziridine and azetidine have been characterized by ESR spectroscopy following their generation in the solid state by gamma-gamma irradiation of dilute solutions of the parent compounds in the CFCl/sub 3/ matrix at 77 K.
Abstract: The radical cations from aziridine and azetidine have been characterized by ESR spectroscopy following their generation in the solid state by ..gamma.. irradiation of dilute solutions of the parent compounds in the CFCl/sub 3/ matrix at 77 K. The ESR parameters of the azetidine radical cation are typical of those for nitrogen-centered amine radical cations such as Me/sub 2/NH*/sup +/. On the other hand, the radical cation formed from aziridine has very different ESR parameters that compare closely to those for the isoelectronic C...C ring-opened form of the oxirane radical cation and the allyl radical. The radical cation formed from azetidine is therefore assigned a ring-closed structure with the unpaired electron in a 2p/sub z/ orbital on nitrogen perpendicular to the ring plane, whereas the cation from aziridine is an allylic C...C ring-opened planar isomer with the unpaired electron in a nonbonding ..pi.. orbital centered mainly on the two end carbon atoms. The neutral 1-aziridinyl and 1-azetidinyl radicals have been detected as radical products following the ..gamma.. irradiation of the parent compounds in the CFCl/sub 2/CF/sub 2/Cl and CF/sub 3/CCl/sub 3/ matrices. In particular, the 1-azetidinyl radical is produced cleanly from the azetidine radical cation in the CFCl/sub 2/CF/sub 2/Clmore » matrix at ca. 100 K.« less