G. Földiák

The Role of Free Radicals in the Pathogenesis of Amiodarone Toxicity

Free Radicals and Amiodarone Toxicity. Introduction: In vitro and in vivo studies were performed to elucidate the pathogenesis of amiodarone toxicity.

A computer controlled pulse radiolysis laboratory

In this paper the computer controlled, automated pulse radiolysis laboratory of the Institute of Isotopes of the Hungarian Academy of Sciences, Budapest, is introduced. The system is equipped with a Linac type accelerator which produces 50 ns–2.6 μs pulses of 4 MeV electrons, with an optical detection system and with computerized data acquisition.

Electron-capture detection of aromatic hydrocarbons

Abstract The detectabilities and some parameters of electron + aromatic hydrocarbon reactions were investigated in a constant-current, variable-frequency electron-capture detector. It was found that lower alkylbenzenes give weak signals in the detector, polymethylbenzenes, styrene, indene, naphthalenes and biphenyl exhibit medium responses, whereas the response factors of aromatics with three rings and those of diphenylthylene, diphenylacetalyne and azulene are relativity high. On the basis of the temperature dependence of the response factors the electron affinities and the electron absorption and desorption rate constants were determined for many aromatics, and the magnitudes of the response factors are discussed.

Addition and elimination kinetics in OH radical induced oxidation of phenol and cresols in acidic and alkaline solutions

Abstract The rates of the two consecutive reactions, OH radical addition and H 2 O/OH − elimination, were studied by pulse radiolysis in highly acidic (pH=1.3–1.9) and alkaline (pH≈11) solutions, respectively, for phenol and for the three cresol isomers. The rate coefficient of the addition as measured by the build-up of phenoxyl radical absorbance and by a competitive method is the same (1.4±0.1)×10 10 mol −1 dm 3 s −1 both in acidic and alkaline solution. The rate coefficient of the H 2 O elimination in acidic solution is (1.6±0.2)×10 6 s −1 , whereas the coefficient of the OH − elimination in alkaline solutions is 6–8 times higher. The kinetics of the phenoxyl radical formation was described by the two-exponential equation of the consecutive reactions: the first exponential is related to the pseudo-first-order addition, while the second to the elimination reaction. No considerable structure dependence was found in the rate coefficients, indicating that the methyl substitutent in these highly acidic or alkaline solutions influences neither the addition nor the elimination rate.

Mechanism of OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical

The OH radical-induced oxidation of p-cresol to p-methylphenoxyl radical was studied in aqueous solution in a wide pH range by means of pulse radiolysis combined with optical spectroscopy. OH-adduct cyclohexadienyl type radicals were identified as intermediates of the reaction. In the acidic pH range the first-order rate coefficient of phenoxyl radical formation was found linearly dependent on the H3O+ concentration yielding a bimolecular rate coefficient of 1.8 × 108 mol–1 dm3 s–1. In the alkaline range a linear dependence was found on the OH– concentration with rate coefficient of 4.9 × 1010 mol–1 dm3 s–1. These findings were interpreted in terms of acid-base catalysis of the H2O elimination from the OH-adduct. With the time resolution applied, 30 ns, the radical cation p-CH3C6H4OH+. was not observed as intermediate.

Pulse radiolysis of aqueous solutions of aromatic hydrocarbons in the presence of oxygen

Abstract The rate parameters of formation and decay of the corresponding OH-adduct and aryl-peroxy radicals in diluted water solutions of toluene, naphthalene and β-methylnaphthalene were determined. The parameter for the OH adduct formation is 5.1x109 mol-1dm3s-1 with toluene and it is 9.4 x 109mol-1dm3s-1 with naphthalene. The rate parameters for peroxy radical formation are about 4 x 108mol-1dm3s-1 for all compounds studied. In the dose range 5–15 Gy per pulse the decay of peroxy radicals is first order with rate parameter of ca 2 x 103s-1.

Radiolysis of liquid hydrocarbons

Abstract The radiation chemical reactions of hydrocarbons are controlled significantly by the structure and the energy relations of the irradiated compound, although the differences between the energies of the chemical reactions are six orders of magnitude smaller than the energy of the radiation.

Spectral characteristics of monosubstituted phenoxyl radicals

The absorption spectrum of the 2-chlorophenoxyl radical is compared with those of its isomer radicals, with those of the bromo- and methylphenoxyl radicals, and also with that of the phenoxyl itself. Spectra of the monosubstituted phenoxyls are very similar. Substitution on the phenoxyl radical in 4-position causes a significant enhancement in the extinction coefficient. 2-substitution causes a little blue-shift of the spectrum, the 3- and 4-substitutions, however, more significant red-shifts.

Biradical intermediates in 7.6 eV photon-induced isomerization of liquid alkylcyclohexanes

Abstract Structural isomerization to open-chain alkenes was observed in the photolysis of methylcyclohexane 1,2-dimethylcyclohexane, 1,3-dimethylcyclohexane and 1,4-dimethylcyclohexane; cis—trans geometrical isomerization was also found in the dimethylcyclohexanes. The results of deuterium labelling experiments on methylcyclohexane and examinations of the product distributions suggest that biradicals are intermediates of both types of isomerization. The lifetime of the biradical state is assumed to be a few times the rotation time around a CC.

Pulse radiolysis of silybin: One-electron oxidation of the flavonoid at neutral pH

Abstract One-electron oxidation of silybin, a flavonoid drug used in human therapy of liver, was investigated by pulse radiolysis at neutral pH. Phenoxyl radicals formed from the substrate by oxidising N . 3 radicals were identified by comparing the transient optical absorption spectra with those obtained from model compounds. The orto-methoxy-phenolic structure (ring B) is the exclusive target for one-electron oxidation of silybin. The 5.7-dihydroxy-chromanone moiety (ring A) withstands free-radical attack at neutral pH due to the chelatic H-bond (p K a = 10.2) existing between the 5-OH and 4-oxo groups. Hydroxyl radicals react with silybin at diffusion controlled rate ( k = 1.8 x 10 10 dm 3 mol -1 s -1 ). The reactivity of silybin towards free radicals at neutral pH is conform with the assumption that the physiological activity of the flavonoid is due to its chain-breaking antioxidant behaviour.