Various experimental techniques based on electron spin resonance (ESR) are presented for the detection of paramagnetic species directly in the 'hot' H-2/O flame and in the 'cold' plasma produced by microwave radiation.The concentration of atomic hydrogen in the H-2/O2 flame was traced by shifting the burner in the ESR cavity or by exhausting the H. atoms from different positions in the flame. In this way the 'steady-state' radical concentration during the change from the diffuse to oscillating and finally to a premixed flame is quantitatively determined and the optimal position for the most effective flame retardation with halogenated flame retardants is located.Diatomic gases, H-2, N2 and O2 under reduced pressure, and volatilized molecules of H2O, D2O, H2O2 and NH3, are effectively dissociated to their atoms when they are exposed to microwave radiation of 2450 MHz. At constant power of microwave radiation (5 to 100 W) the highest concentration of atomized gases, 2-3 x 10(16) spin/cm3, is reached in the vacuum interval from 0.8 to 1.5 Torr. With increasing pressure the atomized species gradually disappear as a consequence of recombination. The presence of HO. and HOO. radicals and the effect of the applied magnetic field on gas phase radical reactions were ascertained by introducing the spin-trapping technique, transforming the primary unstable radicals of the plasma to stable nitroxy spin-adducts of DMPO (5,5-dimethyl-1-pyrroline-N-oxide). The concentration relationship between the highly reactive HO. and HOO. radicals as products of the reaction .O. + HOH --> 2HO. was measured after freezing the radicals from the flowing plasma on the internal cryostat situated in the ESR cell and cooled with liquid nitrogen.Using a cross-flow experimental method, the kinetics of the rapid reaction between the colliding atomized gases with different molecules, introduced into the ESR cell from the opposite direction to the plasma flow, was studied.The reactivity of atomized oxygen with solid targets was measured directly in the ESR cavity. In this way the one-electron transfer from chelated cobalt(II) with a 3 d7 unpaired electron to atomized oxygen to form the complex Co(III)O.- was proved. Atomized oxygen can initiate surface cross-linking after its addition to a double bond when it is in contact with exposed films of natural rubber or polyisoprene.

Conference Article| November 01 1991 Menaquinone mediated free radical generation: a possible mutagenic mechanism ANDREW COOK; ANDREW COOK 1Biochemistry Division, School of Natural Sciences, Liverpool Polytechnic, Byrom St., Liverpool L3 3AF Search for other works by this author on: This Site PubMed Google Scholar ROMAN STOVICEK; ROMAN STOVICEK 1Biochemistry Division, School of Natural Sciences, Liverpool Polytechnic, Byrom St., Liverpool L3 3AF Search for other works by this author on: This Site PubMed Google Scholar ANNA D'ODORICO; ANNA D'ODORICO 1Biochemistry Division, School of Natural Sciences, Liverpool Polytechnic, Byrom St., Liverpool L3 3AF Search for other works by this author on: This Site PubMed Google Scholar ALEXANDER TKAC; ALEXANDER TKAC *Dept. of Physical Chemistry, Slovak Technical University, Radlinskeho 9, Bratislava, CS 81237, C.S.F.R. Search for other works by this author on: This Site PubMed Google Scholar RODNEY F. BILTON RODNEY F. BILTON 1Biochemistry Division, School of Natural Sciences, Liverpool Polytechnic, Byrom St., Liverpool L3 3AF Search for other works by this author on: This Site PubMed Google Scholar Biochem Soc Trans (1991) 19 (4): 426S. https://doi.org/10.1042/bst019426s Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter LinkedIn Cite Icon Cite Get Permissions Citation ANDREW COOK, ROMAN STOVICEK, ANNA D'ODORICO, ALEXANDER TKAC, RODNEY F. BILTON; Menaquinone mediated free radical generation: a possible mutagenic mechanism. Biochem Soc Trans 1 November 1991; 19 (4): 426S. doi: https://doi.org/10.1042/bst019426s Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1991 Biochemical Society1991 Article PDF first page preview Close Modal You do not currently have access to this content.

Differently substituted 4,4'-methylenediphenols I donate an electron to the AlCl2+ electron acceptor in the AlCl3-CH3NO2-benzene solution at laboratory temperature to give radical cations II of different stability. The symmetrical distribution of spin density in individual phenyl rings remains preserved. Nevertheless, an asymmetrical redistribution to equivalent positions (ortho, meta) in each of these rings take place owing to steric distortion in the process of formation of the ion-radical complex. The effect of voluminous substituents in ortho positions on stability of the primary complex of ion-radical with the AlCl4- counterion is discussed. This complex is subjected to fragmentation and subsequently gives rise to radical cations from 4,4'-biphenyldiols.

One-electron transfer to molecular oxygen or to peroxides triggers the creation of reactive oxygen radicals (O2., HO., HO2., RO., RO2.). In living systems the redox step proceeds either under enzymatic control or the radicals are formed randomly in the presence of potential electron donors. Successive depletion of radical scavengers leads to uncontrolled radical reactions, being involved in different pathological processes (e.g. lipid peroxidation, inflammation, lung oxygen toxicity, atherosclerosis, ischaemic-reperfusion-injury, activation of carcinogens) and in ageing.According to the interpretation of ESR and ENDOR spectra, two different one-electron transfer reactions are discussed: (a) intramolecular transfer from a sulfur containing ligand of haemoproteins to peroxy-radicals coordinated to the central iron atom of the haemin group; (b) intermolecular electron transfer to molecular oxygen from semiquinones resulting from oxidation of the chemical pro-carcinogen benzo(a)pyrene or by one-electron reduction of vitamin K1 and K2 with the coenzyme NADPH or in the presence of the enzyme glutathione reductase. In both cases the increased polarity of the environment stimulates the transient formation of the superoxide anion O2-.The control of random radical reactions is discussed with reference to the role of H-transfer cascades between radicals of different reactivities in the presence of vitamin E, vitamin C and the spin-trapper DMPO.

In a search for stable and safe tracers suitable for investigating systems for residence time distributions, such as those systems for which visual observation is not possible, sensitive high temperature systems etc., stable radicals proved valuable. An example is given of their application to determine residence time distributions in a scraped-film prepolymerization reactor operating at a temperature of 100–160 °C, where analysis of the resulting solid sample is difficult under normal conditions and where there are considerable health hazards when using radioactive tracers in a pilot plant environment. The method is described. Substantial time savings in obtaining response data can be achieved over those obtained from heat-resistant dye tracer injection measurements.

AbstractRadical species were generated from 4,4′;‐ and 2,2′;‐alkylidenebisphenols during oxidation with free and co‐ordinated [Co(III)]RO2˙Radicals. This simulates the participation of bisphenolic antioxidants in the process of stabilization of hydrocarbons. Phenoxyls are primarily formed, and, depending on the character of the alkylidene bridge, some of them are gradually transformed into phenoxy radicals of the galvinoxyl type. Oxidation of alkylidenebisphenols by oxygen complexed to Co(II) yields co‐ordinated cyclohexadienonyloxy radicals. The character of the alkyl substituents on the phenolic nuclei specifically influences the stability of the generated phenoxy radicals at the applied temperature. The ESR characteristics of the primarily formed phenoxyls, phenoxyls of the galvinoxyl type and co‐ordinated cyclohexadienonyloxyls are discussed.

AbstractThe phenoxy radicals obtained from 2,2′‐ and 4,4′‐biphenyldiols show, in nonpolar solvents, symmetrization of the unpaired electron spin density on the two phenyl rings in the temperature range 290–410 K. Below 270 K the paramagnetic systems became diamagnetic. This para‐diamagnetic conversion with temperature is reversible. According to INDO calculations the symmetrization of spin density is due to the formation of dimeric phenoxy radicals. The para‐diamagnetic conversion at various temperatures is explained by the reversible conversion of the radical dimer to the quinone‐hydroquinone pair.

AbstractDurch Einwirkung von Peroxidradikalen oder Hydroperoxiden wie z.B. (II) gehen die Hydroxylamine (I) in die Nitroxylradikale (III) über, die zu den Spin‐Addukten (IV) weiteroxidiert werden.

AbstractThe determination of the free radical distribution in the preflame and flame zones of a burning polymer (polypropylene) by ESR leads to the conclusion that in all phases of the burning polymer an exothermic reaction zone encloses an oxygen‐free pyrolytic zone. Whereas in the molten preflame zone (250–350°C) the polymer decomposes to oligomers, dimers, monomers, and the relevant free radicals or biradicals, in the gaseous flame zone the heat transport from the hot outer surface into the surrounding pyrolytic zone leads (with an increasing temperature gradient) to a progressive formation of thermodynamically more stable decomposition products. The CH. radicals generated at 400–800°C, after rapid cooling, yield polyaromaties with delocalized free electrons and the atomized carbon and its dimers at 800–1200°C, after cooling, yield graphite sheets with localized free electrons in its defects. Free radicals and paramagnetic species are trapped (a) in the gaseous pyrolytic products of heated polymers on the surface of a rotating cryostat, (b) in burning polymer drops by quenching in liquid nitrogen, and (c) in different zones of a burning diffuse flame. The superimposed ESR signals of the paramagnetic products are then qualitatively and quantitatively analyzed.

Hydroxyperoxides and cobalt-coordinated peroxy-radicals oxidize hydroxyolamines as e.g. Et2NOH, (PhCH2)2NOH, PhCH2PhNOH to the respective nitrones, and the spin adducts - nitrone and peroxy-radical - are formed. In contrast to hydroxyperoxides the coordinated peroxy radicals can oxidize the formed spin adduct, the methylene or methine groups next to nitrogen being converted into carbonyl groups. The radical intermediates corresponding to individual steps of the gradual oxidation have been identified by means of EPR spectra.

AbstractIn the reactions of meta‐ and para‐alkyl substituted benzoic acids with aryl Grignard reagents, in tetrahydrofuran solutions and in the presence of nickel salts, the ESR spectra of the anion radicals of carboxylates derived from the benzoic acids were observed which represent the intermediates in the formation of ketyl radicals.

AbstractIn the reactions of alkyl‐substituted‐benzenecarboxylic and ‐2‐hydroxybenzenecarboxylic acids (ArCOOH) with alkyl‐substituted phenyl Grignard reagents (RMgX) in the presence of nickel, ketyl radicals ArCO−R are formed. The para substituents (H, Me, Et, Isopr and t‐Bu) of R increase the non‐equivalence of its ortho protons (a change of a2H = 0.43 mT, a6H = 0.422 mT to 0.435 mT, 0.395mT respectively, on substituting t‐butyl for H at position 4). The oxido anion group originating from 2‐hydroxybenzenecarboxylic acid has a strong push effect and nearly doubles the unpaired spin density on the phenyl ring R.

Reaction of diphenylamine with coordinated peroxy-radicals and various hydroperoxides (tert-butyl hydroperoxide, cumene hydroperoxide, tetraline hydroperoxide) has been studied in non-polar solvents by the EPR method. From this kinetic study the activation energies of H-transfer (105 ± 2 kJ/mol in the temperature range -40 to -10 °C) and e-transfer (97 ± 2 kJ/mol in the temperature range 10 to 50 °C) have been determined. From the activation energies it follows that, in a reaction mixture containing simultaneously a hydroperoxide and initiating peroxy-radicals, oxidation of diphenylamine goes by the both parallel mechanisms until the final concentration of nitroxyl radical reaches the value of about 1.7 . 1021 spin/l.

AbstractQualitative and quantitative free radical transformations between polypropylene alkyl radicals, oxygen, and brominated flame retardants in the molten and gaseous phases of thermally treated samples are described. By ESR technique it has been proved that, depending on the applied pressure during pyrolysis, highly reactive peroxy radicals or less reactive radicals of the retardant are formed. For flame‐retarded samples, compared with polypropylene without additives, the concentration of the primary alkyl radicals transferred from the molten to the gaseous phase is reduced by two orders of magnitude (from 7 × 1014 to 7 × 1012 spins/0.02 g), whereas the limiting oxygen index [LOI] is raised from 17–18% to 25–26%. The great variety of physical and chemical processes proceeding in molten polymer in the preflame zone and burning gaseous phase calls for use of different retardant types with a programmed release of Br and HBr with the temperature increase. The chain oxidation of the “fuel,” a product of the endothermic decomposition of polymer, determines the temperature of self‐ignition according to the number of initiating alkyl and allyl radicals formed per unit time; the [LOI] index depends more on the length of the kinetic chain of propagation reactions in the stationary process of oxidation at a given pressure.

Chemischer InformationsdienstVolume 12, Issue 10 Preparative Organic Chemistry ChemInform Abstract: FORMATION OF PARAMAGNETIC PRODUCTS IN REACTIONS OF ORGANOMETALLIC COMPOUNDS. PART XI. ANION RADICALS OF ALKYL-SUBSTITUTED DIBENZOTHIOPHENE SULFONES A. STASKO, A. STASKOSearch for more papers by this authorL. MALIK, L. MALIKSearch for more papers by this authorA. TKAC, A. TKACSearch for more papers by this authorP. PELIKAN, P. PELIKANSearch for more papers by this author A. STASKO, A. STASKOSearch for more papers by this authorL. MALIK, L. MALIKSearch for more papers by this authorA. TKAC, A. TKACSearch for more papers by this authorP. PELIKAN, P. PELIKANSearch for more papers by this author First published: March 10, 1981 https://doi.org/10.1002/chin.198110156AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue10March 10, 1981 RelatedInformation

Durch die Dehydrocyclisierung von 4,4'(H-, Et-, i-Pr-, t-Bu-)-diphenylsulfonen entstehen Anionradikale der 3,6(dialkylsubstituierten)-Dibenzothiophensulfone. Mit Hilfe der ESR-Spektroskopie wurden folgende Aufspaltungskonstanten ermittelt: a^'' ~ 0,02 ... 0,05 mT, ~ 0,3 m T und oft*"* ~ 0,2 (<0,2) mT. Die Bestimmung der Ladung und der Spindichteverteilung dieser Radikale sowie die Zuordnung ihrer Aufspaltungskonstanten erfolgte auf G r u n d von Alkylsubstitution und INDO-Berechnungen.

AbstractFrom a series of antioxidants comprising 2,2′‐biphenyldiols, 2,2′‐thiobisphenols and 2,2′‐dithiobisphenol, free phenoxyls were prepared by oxidation with tert‐butylperoxyls co‐ordinated to Co(III) in non‐polar media at ambient temperature. Both the effect of extended conjugation as a consequence of the direct bond between the two aromatic nuclei and, also, the steric effect of alkyl substituents could be observed. In the presence of free tert‐butylperoxyls in excess, primary phenoxyls are transformed into cyclohexadienonyloxyls, which form stable radical complexes with Co(III). A mechanism for the formation of the cyclohexadienonyloxyls is suggested.