A study of radicals arising in the low-temperature radiolysis of thiophene and some of its derivatives

EPR was used to investigate the radicals formed by radiolysis of furan, thiophene, and some of their substitution products having the general formula C₄H₃RS, where R = Cl, Br, COOH, C(CH₃)₃, and of di-tert-butylthiophene. By analyzing the EPR spectra it is shown that radicals formed by radiolysis of furan, thiophene, their alkyl substitution products, and 2-thiophene carboxylic acid arise in primary radiation-chemical events with splitting of the C-H bond in both ring and side chain. Characteristic of the radiolysis of these compounds is formation of secondary radicals by addition of hydrogen atoms at the double bond of the heteroaromatic ring. The values of the hyperfine splittings in the spectra of the secondary radicals are, for protons of methylene group 32 e [positions 2(5)] or 40 e [positions 3(4)], and 13 e for protons of the thiophene ring. In radiolysis of 2-chlorothiophene and 3-bromothiophene the main products are radicals with the unpaired electron localized on the sulfur atom.     

Radiolysis of iodotyrosines in aqueous-ethanol solutions

⁶⁰Co-gamma radiolysis of 3-iodotyrosine and 3,5-diiodotyrosine in aqueous-ethanol solutions has shown that the chemical effects are mainly determined by the interaction of radicals from the radiolysis of solvent and controlled by the composition of the solution. The influence of varying solvent composition and radiation dose on the amount of iodoamino acid converted and on the yields of the radiolysis products (I₂, I^–, IO ₃ ^– and H₂O₂) formed in aerated solutions at room termperature were investigated. The formation of I₂ is dependent upon the acidity of the solution and is mainly produced as an after-effect due to the interaction of H₂O₂ with I^– ions, both being radiolysis products. The variation of radiation-chemical yields with the solute and solvent composition, and the probable mechanisms for formation of the radiolysis products are discussed.     

Formation of 5-Hydroxy-5,6-Dihydrothymidine and cis-5,6-Dihydroxy-5,6-Dihydrothymidine in the Radiolysis of N2O-Saturated Aqueous Solutions of Thymidine, Thymidine 5"-Monophosphate, and DNA

The yields of formation of 5-hydroxy-5,6-dihydrothymidine and cis-5,6-dihydroxy-5,6-dihydrothymidine in the radiolysis of thymidine, thymidine 5"-monophosphate, and DNA in N₂O-saturated aqueous solutions were measured in order to study the mechanism of nucleic acid radiolysis. The above compounds were found to be main radiolysis products upon irradiation of thymidine and thymidine 5"-monophosphate. However, these compounds were formed in very low yields upon irradiation of DNA, and they amounted to less than 2% of the degradation yield of DNA thymine. The yield of the 5-hydroxythymidin-6-yl radical was evaluated by determining the amount of 5-hydroxy-5,6-dihydrothymidine formed in the radiolysis of the above compounds in the presence of cysteamine.     

Radiolysis of aqueous oxygen-free solutions of tryptophan at various pH values

Gamma radiolysis of 10^–2M aqueous oxygen-free tryptophan solutions irradiated at various pH values and in a N₂O atmosphere was investigated. The values of the radiation losses of tryptophan and the yields of NH₃ were determined. Using HPLC with an electrochemical detector the formation of hydroxylated radiation products of tryptophan was followed and the effect of pH on the radiolysis course discussed.     

Radiolysis study of genistein in methanolic solution

The aim of the present work was to identify products obtained from genistein by ionizing radiation and to enhance the antioxidant properties of genistein through radiation-induced transformation. Genistein dissolved in methanol was irradiated γ-rays at a dose of 100 kGy. NMR and (HR) EI-MS spectroscopy were used to identify radiolysis products (GM1 and GM2). We proposed that CH₂OH may be implicated in the formation GM1 and GM2 during radiolysis of genistein in methanol. The genistein in methanol solution showed higher DPPH radical scavenging activity after γ-irradiation. Then, the antioxidant activities of radiolysis products were evaluated and compared to those of genistein.     

Investigation of radiochemical conversions in extraction systems based on tributyl phosphate

The use of halogenated organic compounds under the effect of ionizing radiation requires a comprehensive knowledge of their radiation stability. There is little experimental evidence on the radiolysis of fluorine-containing organic compounds in the literature, while a theoretical generalization enabling one to predict the main radiolysis pathways is completely lacking. This paper is concerned with the identification of stable radiolysis products of trichloromethyl-1,1,2-trifluoro-2,2-dichloroethyl ether (C₃F₃Cl₅ O), γ-irradiated separately and the extraction system based on tributyl phosphate. Practically all the C₃F₃Cl₅O radiolysis products were identified with the aid of gas-liquid chromatography, GC-MS, IR, UV and NMR spectroscopy and elemental analysis. Upon C₃F₃Cl₅O radiolysis, the formation of CCl₄, Cl₂, COCl₂, C₂ Cl₆, freons of various composition and long-chained ethers like CFCl₂−CF₂−O−CCl₂−CCl₃ takes place. The identification of radiolysis products allows to draw well-founded conclusions on the mechanism of C₃F₃Cl₅O radiolysis, representing a wide class of chlorine- and fluorine-containing organic compounds.     

Effect of the B Vitamins on the Radiolysis of Aqueous Ethanol and Ethylene Glycol Solutions

The effects of vitamins B₁, B₂, and B₆ and pyridoxal phosphate on the formation of the final radiolysis products of aqueous ethanol and ethylene glycol solutions were studied. It was found that vitamin B₂ and pyridoxal phosphate effectively oxidize R^·CHOH species to suppress their recombination and fragmentation reactions, thereby increasing the yields of corresponding oxidation products. Vitamins B₁ and B₆ are capable of reducing alcohol radicals to the parent molecules and, hence, decreasing the yields of the main radiolysis products.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 5, 2005, pp. 325–329.Original Russian Text Copyright © 2005 by Lagutin, Shadyro.     

Effect of ascorbic acid and its derivatives on the radiation-chemical transformations of hydroxyl-containing organic compounds

The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO ₂ ^· radical to hydrogen peroxide.     

Radiolysis of the trichloromethane-water two-phase system

The radiolysis of the CHCl₃-water two-phase system in the absence of oxygen has been investigated by continuous -ray irradiation. The major products of radiolysis were determined to be the same, except for tetrachloromethane, as in the case of the radiolysis of pure CHCl₃, however, the radiolytical yields were different. The dependencies of gross radiation yields of the radiolysis products on the CHCl₃ volume fraction follow the two-phase rule of additivity. The partial yields of all products determined were calculated for both phases and revealed that the major products HCl and C₂H₂Cl₄ are formed in both phases. The other organic products are formed mainly in the organic phase. The decrease of organic product yields is probably caused by the presence of water in the organic phase. The radiolysis of CHCl₃-water did not proceed in the diffusional regime even at high absorbed doses due to the relatively high solubility of CHCl₃ in water andvice versa.     

Radiation yield of stable radiolysis products of 1-chlorobutane, 1-chlorobutene-2, 1-chloropropane, 2-chloropropane and 1,3-dichloropropane γ-irradiated in an oxygen-free atmosphere

The stable radiolysis products of 1-chlorobutane (1-CB), 1-chlorobutene-2 (1-CB-2), 1-chloropropane (1-CP), 2-chloropropane (2-CP) and 1,3-dichloropropane (1,3-DCP) gamma-irradiated in an oxygen-free atmosphere have been investigated. The pure radiolysis products were separated by preparative gas chromatography and identified by NMR and mass spectroscopy as well as qualitative gas chromatography. The compounds formed were determined by potentiometric analysis and quantitative gas chromatography. From 1-CB we have obtained in the gas phase: HCl, H₂, butane; in the liquid phase: 2-chlorobutane, 1,3-dichlorobutane and a mixture of oligomers of the initial compound (dimer and trimer). We have not recorded H₂ in 1-CB-2. The main gaseous products of radiolysis of 1-CP are HCl and H₂. Radiation yield of isomerization was determined. From 2-CP we have obtained in the gas phase: HCl and H₂; in the liquid phase: 2,2-dichloropropane and a mixture of oligomers of the initial compound (dimers and trimers). From 1,3-DCP we have found in the gas phase: HCl and H₂; in the liquid phase: 1-CP, 2-CP, 1,2-DCP and oligomers. Preliminary schemes for the formation of stable products are proposed.     

Radiation-induced destruction of hydroxyl-containing amino acids and dipeptides

The yields of molecular products resulting from radiolysis of hydroxyl-containing amino acids and dipeptides under various conditions were determined. The possibility of a new radiation-induced destruction pathway has been shown for serine and threonine, as well as for the dipeptides having residues of these amino acids at the N-terminal part of the respective molecule. This process includes formation of N-centered radicals from the starting molecules followed by their decomposition with elimination of side substituents. On radiolysis, serine and threonine were also shown to undergo free-radical destruction to form acetaldehyde and acetone, respectively. A mechanism has been proposed including consecutive stages of fragmentation of α-hydroxyl-containing carbon-centered radicals with elimination of ammonia and decomposition of the secondary radicals with elimination of CO₂. The yields of CO₂ obtained on radiolysis of serine and threonine were significantly higher (except for solutions at pH 12) than those for alanine and valine, which have no hydroxyl groups in their structures. The obtained data indicate that the hydroxyl-containing amino acids occupy a special place among other amino acids as regards the variety of radiation-induced reactions which they may undergo due to their structural features.     

Calculated and measured transient product yields in pulse radiolysis of aqueous solutions: Concentration dependence

Pulse radiolysis of aqueous solutions was modeled by using 54 equations for the reaction of water radiolysis intermediates with carefully selected rate coefficients. Yields of products formed in the hydrated electron+solute and hydroxyl radical+solute reactions were calculated and compared with the measured yields in wide concentration range. These reactions are in competition with the reactions of the water radiolysis intermediates with each other and with H₂O, H⁺ and H₂O₂. An empirical equation was developed for the calculation of scavenged product yields that can be used in cases when due to low rate coefficient, low solubility or very high absorbance, low solute concentrations are applied and a considerable fraction of the water radiolysis intermediates does not react with the solute.     

Gamma Radiolysis of the Highly Selective Ligands CyMe4BTBP and CyMe4BTPhen: Qualitative and Quantitative Investigation of Radiolysis Products

The highly selective nitrogen donor ligands CyMe₄BTBP and CyMe₄BTPhen where γ–irradiated under identical experimental conditions in 1–octanol with and without contact to nitric acid solution. Subsequently, solvent extraction experiments were carried out to evaluate the stability of the extractants against γ–radiation monitoring Am(III) and Eu(III) distribution ratios. Generally, decreasing distribution ratios with increasing absorbed dose were detected for both molecules. Furthermore, qualitative mass spectrometric analyses were performed and ligand concentrations were determined by HPLC-DAD after irradiation to investigate the radiolysis mechanism. An exponential decrease with increasing absorbed dose was observed for both ligands with a faster rate for CyMe₄BTPhen. Main radiolysis products indicated the addition of one or more diluent molecules (1–octanol) to the ligand via prior production of α-hydroxyoctyl radicals from diluent radiolysis. The addition of nitric acid during the irradiation lead to a remarkable stabilization of the system, as the extraction of Am(III) and Eu(III) did not change significantly over the whole examined dose range. Quantification of the remaining ligand concentration on the other hand showed decreasing concentrations with increasing absorbed dose. The stabilization of D values is therefore explained by the formation of 1–octanol addition products which are also able to extract the studied metal ions.     

辐照气氛对异丙氧基杯[4]冠-6辐解的影响

异丙氧基杯[4]冠-6(1,3-交替-25,27-二(2-丙氧基)杯[4]芳烃-26,28-冠-6, 简称BPC6)对高放废液中的放射性Cs离子具有很好的选择萃取性能, 然而在萃取过程中BPC6 会受到强辐射场辐照, 所以有必要研究其辐射稳定性. 本文应用气相色谱(GC)、傅里叶变换显微红外(Micro-FTIR)和核磁共振(NMR)谱等手段分析了BPC6 固体分别在O₂和N₂气氛下的γ辐照效应. 结果表明, 当剂量为1 MGy时, O₂气氛下BPC6 的辐解率明显高于N₂(分别约为10.4%和2.5%), 而且气体辐解产物也有很大差异, 在O₂气氛下主要为H₂、CH₄、CO和CO₂,而在N₂辐照气氛下还有C₂H₄、C₂H₆、C₃H₆和C₃H₈等产物. 通过综合分析气体与固体辐解产物, 我们提出BPC6在不同气氛下具有不同的辐解途径, 这将为BPC6 萃取体系的辐射效应研究提供新的方法与思路, 加深对其辐解机理的认识.     

Stable products and radicals in the radiolysis of dichloromethane and 1,1,-dichloroethane gamma-irradiated in an oxygen-free atmosphere

Stable and transient products of the -radiolysis of dichloromethane (DCM) and 1,1-dichloroethane (11 DCE) have been investigated in an oxygen-free atmosphere. The stable products were separated by preparative gas chromatography and identified by NMR and mass spectroscopy. The quantitative determinations were performed by potentiometric and gas chromatographic analysis. The main products of radiolysis of DCM are dimers (11DCE, 12DCE, 112TCE, 1122TetraCE) and the product of dechlorination CM; in the case of 11DCE-dimers (133TCB, 2233TetraCB) and the product of dechlorination CE as well as products of isomerization and chlorination of the parent compound (12DCE, 112TCE). The gas products of both chlorides are HCl and H₂. The ESR investigations at 77 K indicate the formation of at least two kinds of radicals in both chlorides: CH₂Cl/CHCl₂=1/3 in DCM and CH₃CCl₂/CH₃CHCl=2.5/1 in 11DCE. An outline of the mechanism of radiolysis is proposed.     

Products of the Radiation-Chemical and Thermal Decomposition of Mercury Fulminate

The products of the radiation-chemical and thermal decomposition of mercury fulminate were examined by IR spectroscopy and X-ray diffraction analysis. Upon radiolysis to 20% conversion, the fulminate ion underwent decomposition (G (decomposition) = 20 molecule/100 eV) with the formation of HgO (G = 9 ± 1 molecule/100 eV), CN^– ions, and CO₂. The final solid products of the radiolysis are Hg(CNH)₂, a cyanide complex, the mercury carbonate oxide HgCO₃ · 3HgO, the mercury cyanide oxide Hg(CN)₂ · HgO, and paracyanogen (CN)_n. In the thermolysis, the final solid products of decomposition are the mercury carbonate oxide HgCO₃ · 2HgO, a cyanide complex, and the cluster Hg_nC_mN_oO_p.     

Observation of hydrated electron, (SCN)2 .- and CO3 .- radical in high temperature and supercritical water

Transient radicals (hydrated electron, (SCN)₂ ^.- and CO₃ ^.-) formed in supercritical water have been observed by the pulse radiolysis technique. The change of spectra of these radicals with temperature has been measured. It was found that the spectra and absorption coefficients of the radicals, e^- _aq and (SCN)₂ ^.-, are strongly dependent on the temperature of the water. Since it was found that the absorption spectrum and molar absorption coefficient of CO₃ ^.- radical seem to be almost independent of temperature, G-values of OH and e^- _aq could be derived. Then, the absolute values of the absorption coefficients for the radicals could be calculated. The G-values of the radical products in water radiolysis tend to increase with increasing temperature up to 400°C. Based on the above observation, radiolysis of supercritical water is discussed.     

The influence of iodine on the radiolysis of purex solvent

The effect of iodine on the radiolysis of TBP-dodecane-HNO₃ systems and the same systems containing the uranium, zirconium and palladium salts was examined. The results obtained indicate that the effect of iodine on the radiolysis products in the systems with and without uranium salt is similar. It has been found also that the effect of iodine on the retention of uranium and zirconium in organic phase depends on nitric acid concentration and is particularly high in the systems with low concentrations of HNO₃ containing uranium salt.     

Radiolysis of pyridoxine (vitamin B6) in aqueous solution under different conditions

Aqueous solutions of pyridoxine (1 mM) without or with additive of K₃[Fe(CN)₆] (2.5 mM) were gamma-irradiated at different doses and dose rate of 2.16 kGy/h in the absence of air, in the presence of air or by their saturation with N₂O. The radiolytic products were analyzed with HPLC, mass spectrometry and UV spectroscopy. 2,4,5-Trihydroxymethyl-3-pyridinol, pyridoxal, isopyridoxal and 6-hydroxypyridoxine were formed by radiolysis in the absence of K₃[Fe(CN)₆], and their concentrations were much higher in samples saturated with N₂O. Pyridoxi-3,6-quinone was found by radiolysis under all the above-mentioned conditions but only in the presence of K₃[Fe(CN)₆]. Besides, the pyridoxal formation increased in the presence of this oxidizing agent. G values of pyridoxal formation and pyridoxine degradation were quantified. Some details of the radiolytic product formation were discussed.