Quenching of triplet states by nitroxyl radicals in the presence of surfactants

The quenching of anthracene and sodium anthracene-2-sulfonate triplets by several nitroxyl radicals in the presence of ionic surfactants provides information on micelle-substrate interactions on a microsecond to millisecond time scale.     

Electrical properties of some free nitroxyl radicals

D.C. and a.c. electrical conductivity of some free radicals is measured, and a “hopping” mechanism for the conduction is proposed, on the basis of the low values of mobility and the frequency dependence of the conductivity.     

The kinetic use of stable nitroxyl radicals in reactions of phosphites

Conclusions It was shown by the method of radical acceptors-stable nitroxyl radicals-that phosphoranyl radicals, formed in the reaction of tert-butylhydroperoxide with triethyl phosphite, are converted to phosphoranyl peroxide radicals in the presence of oxygen. The rate constant of formation of phosphoranyl peroxide radicals found at 20° is 250 times lower than the rate constant of the disproportionation of primary phosphoranyl radicals according to the reaction with the free radical.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2454–2458, November, 1973.     

Relative rate constants of reactions of alkyl radicals of methacrylates and acrylates with oxygen and stable nitroxyl radicals

Conclusions In methacrylates and acrylates undergoing oxidation, stable nitroxyl radicals react with the alkyl radicals of the monomers. The relative rate constants of the reactions of and O₂ with alkyl radicals for the different esters range from 0.36 to 5.20.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 753–756, April, 1977.We thank V. A. Golubev for providing the stable nitroxyl radicals.     

Reaction of nitroxyl radicals with dichlorocarbene

Conclusions The reaction of aromatic nitroxyl radicals with dichlorocarbene, generated under phase transfer catalysis conditions, leads to the corresponding hydrazine derivatives through the abstraction of the oxygen atom from the nitroxyl radicals and formation of aminyl radicals.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 470–472, February, 1989.     

Energy transfer in the course of triplet state quenching of aromatic hydrocarbons by nitroxyl radicals

Quenching of triplet states of aromatic hydrocarbons by nitroxyl radicals has been investigated by the flash photolysis method. There are two different mechanisms of triplet quenching: quenching occurs via enhanced intersystem crossing on exchange interaction with the radical for the triplet states of aromatic hydrocarbons which have low triplet energy (E_T < 14700 cm^?1); for very high triplet energies, energy transfer from the triplet molecule to the nitroxyl radical occurs. The energy of the excited nitroxyl radical was estimated to be 18000 cm^?1.     

Reactions of hydrazobenzene and tetranitromethane with nitroxyl radicals

The values of isotropic HFS constantsa _N were obtained for nitroxyl radicals (NR) of the piperidine series in hexane and water. The interrelation between rate constants for NR reduction and oxidation reactions, isotropic HFS constantsa _N, inductive constants of the piperidine substituents, and electrochemical characteristics of NR were found. The dependence of the rate constants for the reduction of NR by hydrazobenzene (HB) and its oxidation by tetranitromethane (TNM) upon the Hammett type inductive constants _EPR, obtained using HFS constantsa _N as the basis, was analyzed. The solvent effect on the reduction and oxidation reaction rate constants, the kinetic isotopic effect of the reduction reaction for a number of NR-HB systems, and alternative reaction mechanisms are considered.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1074–1079, June, 1993.     

Interaction of chlorine dioxide with nitroxyl radicals

The formation of charge transfer complexes between chlorine dioxide and nitroxyl radicals (2,2,6,6-tetramethylpiperidin-1-oxyl, 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidin-1-oxyl, 4-acetylamido-2,2,6,6-tetramethylpiperidin-1-oxyl, 2,2,5,5-tetramethyl-4-phenyl-3-imidazolin-1-oxyl, and bis(4-methoxyphenyl) nitroxide) in acetone, acetonitrile, n-heptane, diethyl ether, carbon tetrachloride, toluene, and dichloromethane was found by spectrophotometry at –60—+20 °C. The thermodynamic parameters of complex formation were determined. The radical structure affects its complex formation ability. The charge transfer complex is transformed into the corresponding oxoammonium salt.     

Reaction products of nitronyl nitroxyl radicals with acids

Study of the structures of compounds generated by the reactions of 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazole-1-oxyl 3-oxide with trifluoromethanesulfonic and picric acids demonstrated that these reactions produced salts of disproportionation products of nitronyl nitroxyl.     

Photochemistry of kynurenine, a tryptophan metabolite: properties of the triplet state

Photolysis of aqueous kynurenine (KN) solutions results in the formation of triplet kynurenine TKN. In low pH solutions, triplet formation occurs with almost 100% efficiency, while in neutral solutions the triplet quantum yield is PhiT = 0.018 +/- 0.004. The dissociation constant of TKN, which is attributed to deprotonation of the anilino group, has a pKa value of 4.7. Similar triplet absorption spectra were obtained under direct and acetone-sensitized photolysis. The large difference in quantum yields as a function of pH is attributed to excited-state properties of the first excited singlet state of KN. The rate constant quenching for TKN by oxygen is kq = 2 x 10(9) M(-1) s(-1).     

Rotational mobility of nitroxyl radicals in polyesters

Rotational mobility of nitroxyl radicals in polyester films was investigated at temperatures from ?180 to +240°C by ESR spin-probe techniques. Evidence obtained indicated that mobility of radicals was related to polymer structure and reflected increased volume made available to the probe molecule by the polymer matrix. A single correlation time, which followed the form τ_C = τ₀ exp {E_a/RT}, was calculated for the temperature range of rapid reorientation (～10⁹ Hz) of nitroxyl radicals. E_a ranged from 5 to 25 kcal/mole for various systems. Uniaxially oriented semicrystalline polymer matrix restricted radical mobility to a greater extent than a semicrystalline biaxially oriented sample. Effective local viscosity encountered by a nitroxyl radical in several polymers was calculated as 9–13 poise.     

Stable nitroxyl radicals with a hydrogen atom at α-carbon atom of nitroxyl group

Nitroxyl radicals containing the diphenylmethyl group as one of the substituents at the nitroxyl group are stable compounds that can be isolated in an individual state.N-(2-Hydroxy-3-methyl-2-phenylcyclohexyl)-N-diphenylmethylnitroxyl was characterized by X-ray diffraction analysis for the first time.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 400–408, February, 1996.