ESR studies of trapped free radicals and polymer deposition in xylene plasmas

Rates of polymer deposition and radical trapping in xylene plasmas produced in a Siemens tube with 60-Hz current decreased linearly with increasing flow rate but increased linearly with power and decreased in the order ortho > meta > para at a constant flow rate and pressure. These results indicate that radical recombination and disproportionation are unimportant and that the polymerization rate equation is first order in free radical concentration.     

ESR study of free radicals formed upon UV irradiation of nitropentafluoroacetone in various solvents

The formation of CF₃C(O)CF₂N(O^.)O₂CF₂C(O)CF₃ free radicals upon the UV irradiation of nitropentafluoroacetone (1) in toluene and mesitylene is established by ESR. The most likely cause of their formation is the one-electron oxidation of the solvents by photoexcited1 followed by decay of the radical anion formed from1 with the expulsion of an NO₂ anion and attachment of the radical to a molecule of original1. The irradiation of 1 in triethylsilane results in the elimination of a fluoride ion and fixation of a CF₃COCFN(O^–)O' radical. UV irradiation of ketone1 in pentane results in the abstraction of a hydrogen atom from the solvent and the formation of a CF₃COCF₂N(OH)O ' radical.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 512–514, March, 1993.     

ESR study of free radicals in mango

An electron spin resonance (ESR) spectroscopic study of radicals induced in irradiated fresh mangoes was performed. Mangoes in the fresh state were irradiated with γ-rays, lyophilized and then crushed into a powder. The ESR spectrum of the powder showed a strong main peak at g = 2.004 and a pair of peaks centered at the main peak. The main peak was detected from both flesh and skin specimens. This peak height gradually decreased during storage following irradiation. On the other hand, the side peaks showed a well-defined dose–response relationship even at 9 days post-irradiation. The side peaks therefore provide a useful means to define the irradiation of fresh mangoes.     

ESR of cationic isoalloxazine free radicals

The ESR spectra in solution of a number of cationic isoalloxazine free radicals were recorded and interpreted in terms of hyperfine coupling constants. Two previously published interpretations are shown to be incorrect.     

ESR studies of the photodegradation of polyethylene containing trapped allylic free radicals

Changes produced in γ-irradiated polyethylene by subsequent ultraviolet irradiation have been investigated by ESR measurements, ultraviolet spectroscopy, and viscometric determination of average molecular weight. The photoinduced changes depend on the wavelength of irradiation. Upon irradiation at wave length greater than 3900 Å, main-chain scission occurs by reaction of trapped allylic radicals: A reduction in molecular weight sndicated by this reaction was verified by fractionation experiments and molecular weight determinations.     

An ESR study of free radicals formed in irradiated poly(alpha-methyl styrene) by gamma-radiation

The radiolysis of poly(α-methyl styrene) with γ-radiation has been studied at 77 and 300 K by ESR spectroscopy. The radical intermediates formed at these temperatures have been identified by utilization of the techniques of photobleaching, thermal annealing and simulation. The radical yields were found to be 0.105±0.005 at 77 K and 0.05±0.003 at 298 K.     

ESR spectra of free radicals formed during the gas-phase photo-oxidation of formaldehyde: thermal stability of the HOCH2OO radical

Formaldehyde/oxygen/nitrogen mixtures were photolyzed with UV light in a gas flow system. The reaction mixtures were analyzed by pumping a small fraction of the flowing gas through a microprobe, trapping the condensable compounds on a cold finger (T = 96 K), and measuring the ESR spectrum of the solid. The ESR spectra consisted of partly overlapping components from HO₂ and HOCH₂OO radicals, the latter having g-tensor values g₁ = 2.0025, g₂ = 2.0090 and g₃ = 2.0320. By simulating the experimental spectra with appropriate amplitude factors for their HO₂ and HOCH₂OO components, the concentration ratio [HO₂]/[HOCH₂OO] was determined. From these values and the H₂CO concentrations, measured by UV absorption, equilibrium constants k₁, k₋₁ for the reaction HO₂+H₂CO ⇌ HOCH₂OO were calculated. The expression k₁/k₋₁ = 2.4 × 10⁻²⁶ exp(15.2 kcal mol⁻¹/RT) cm³ was obtained from measurements in the temperature range 30–100° C.     

Epr and endor of free radicals formed during the aerobic oxidation of chlorogenic acid and of caffeic acid in strongly alkaline solution

The proton hyperline coupling constants in three free radicals which are formed during the aerobic oxidation of either chlorogenic acid or of caffeic acid in strongly alkaline solution have been measured using EPR and ENDOR spectroscopy and the three radicals thus characterised. Possible identities for the free radicals are discussed.     

ESR spectra of free radicals of 3,3-disubstituted 1,2,3,4-tetrahydropyridines produced during electrochemical reduction

The polarographic properties (potentials, number of electrons, reversibility) of the electrochemical reduction of 3,5-diethoxycarbonyl-3-(p-nitrobenzoyl)-6-(p-nitrophenyl)-1,2,3,4-tetrahydropyridine and its derivatives in dimethylformamide have been determined. In the course of the electrochemical generation, ESR spectra of primary radical anions of p-nitrobenzoyl structure were obtained along with ESR spectra of nitrophenyl-p-substituted free radicals formed as a result of further reduction.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1103–1110, August, 1998.     

Intramolecular reactions of free radicals formed from artemisinin

Two cyclic alkoxyl radicals are formed as a result of peroxide bridge scission in artemisinin. Intramolecular reactions of these radicals induce the cascade of reactions of isomerization, decyclization, and decomposition of formed free radicals. It includes 14 reactions of intramolecular free radical hydrogen transfer, 17 reactions of decyclization of alkoxyl and alkyl radicals, and 4 reactions of decomposition of alkoxyl, acyl, and carboxyl radicals. The enthalpies of these 35 reactions are calculated. Using intersection parabolas method, activation energies and rate constants of all these reactions are calculated. The most rapid reactions are selected for every intermediate free radical. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 554–565, 2005     

A pulse radiolysis study of free radicals formed by one-electron oxidation of the antimalarial drug pyronaridine

Free radicals from one-electron oxidation of the antimalarial drug pyronaridine have been studied by pulse radiolysis. The results show that pyronaridine is readily oxidised to an intermediate semi-iminoquine radical by inorganic and organic free radicals, including those derived from tryptophan and acetaminophen. The pyronaridine radical is rapidly reduced by both ascorbate and caffeic acid. The results indicate that the one-electron reduction potential of the pyronaridine radical at neutral pH lies between those of acetaminophen (707 mV) and caffeic acid (534 mV). The pyronaridine radical decays to produce the iminoquinone, detected by electrospray mass spectrometry, in a second-order process that density functional theory (DFT) calculations (UB3LYP/6-31+G*) suggest is a disproportionation reaction. Important calculated dimensions of pyronaridine, its phenoxyl and aminyl radical, as well as the iminoquinone, are presented. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Intermediate free radicals in the oxidation of wastewaters

The cleaning action on wastewater as obtained through oxidation methods has been investigated by means of EPR spectroscopy to achieve qualitative and quantitative information on the radicals produced upon utilising peracetic acid and hydrogen peroxide with and without UV irradiation. The DEPMPO spin trap was employed to detect hydroxyl and carbon-centred short living radicals during water disinfection, either in the absence or in the presence of UV-C irradiation. Moreover, three different kinds of water (wastewater, demineralized water, distilled water) were analysed in order to assess the contribution of Fenton reactions to the radical production. The spectroscopic results are discussed in relation to the efficiency of the different oxidising agents and UV irradiation in wastewater disinfection evaluated as Escherichia coli, faecal and total coliforms inactivation.     

ESR,spectroscopic, and quantum-chemical studies on the electronic structures of complexes formed by Cu(I) with radicals

The optical and ESR spectra have been examined for complexes of Cu(I) with various radicals, which contain various numbers of Cl ions in the central-atom coordination sphere. The spin-Kamiltonian parameters have been determined for all these radical complexes, and the observed ESR spectra have been compared with those calculated with allowance for second-order effects. The observed values for the isotropic and anisotropic components of the HFI constant from the central ion have been used to estimate the contributions from the 4s and 3d² _z orbitals of the copper ion to the unpaired-electron MO. Quantum-chemical calculations have been performed by the INDO method on the electronic structures and geometries of complexes formed by CH₂OH with Cu(I) for various Cl contents in the coordination sphere. The radical is coordinated by the orbital on the carbon atom, and the stabilities of the radical complexes decrease as the number of Cl ions in the coordination sphere increases. A geometry close to planar is proposed for the CuCl₄ ^–3 fragment in a complex containing four Cl ions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 32–38, January–February, 1986.