Reactions of <Emphasis Type="Italic">N,N</Emphasis>-dihexyloctanamide with nitrate and dodecane radicals: a pulse radiolysis study

Recently, completely incinerable N,N-dihexyloctanamide (DHOA) has been identified as a promising alternative to tri-n-butyl phosphate for the reprocessing of spent nuclear fuels. The present work deals with the pulsed radiolytic investigation on the reactions of DHOA with the radicals produced in the radiolysis of nitric acid and dodecane medium. The rate constants of the reactions of DHOA with solvated electron, nitrate radical and dodecane radicals have been measured and the transients have been characterized. In addition, the reactions of DHOA transients have also been studied.     

Electron Paramagnetic Resonance Study of Radical Pairs and Isolated Radicals Trapped in Irradiated Long-Chain Hydrocarbons at Low Temperatures

The intrinsic characteristics of radical pairs produced in squalane and in cetane receiving high gamma-dose are extensively studied with the EPR technique at temperatures from 77°K up to 150°K. The spectra of the paired radicals occur at g=4 with a very low transition probability in contrast to that of isolated radicals which appear at g=2 A well-resolved hyperfine spectrum corresponding to the species (CH₃CH₂.CH₂CH₃) is observed in cetane. The isothermal decay rates of radical pairs in cetane below 100°K are significantly slow; however, the decay kinetics at 150°K is first order with rate constant=1.86 min^?1. A relatively slower decay rate is obtained for isolated radicals suggesting that the decay mechanism of paired radicals is through geminate recombination. The relative inter-radical distance in radical pairs is known from a decay curve as a function of temperature. The yields of radical pairs are low in both matrices, only few percents of those of isolated radicals. The formation mechanisms of paired radicals with direct radiolytic bond scission process are discussed in connection with the experimental observations.     

Rate constants for reactions of perfluorobutylperoxyl radical with alkenes

Perfluorobutylperoxyl radicals were produced by radiolytic reduction of perfluorobutyl iodide in aerated methanol solutions. Rate constants for the reactions of this peroxyl radical with various organic compounds were determined by kinetic spectrophotometric pulse radiolysis. The rate constants for alkanes and alkenes were determined by competition kinetics using chlorpromazine as a reference. The results indicate that hydrogen abstraction from aliphatic compounds takes place with a rate constant that is too slow to measure in our system (<10⁵ M^?1 s^?1), and that abstraction of allylic and doubly allylic hydrogens is slow compared with addition. Addition to alkenes takes place with rate constants of the order of k = 10⁶ ? 10⁸ M^?1 s^?1. Good correlation was obtained between log k and the Taft substituent constants σ* for the various substituents on the double bond. Perfluorobutylperoxyl radical is found to be more reactive than trichloromethylperoxyl and other peroxyl radicals.     

A study of alkyl radicals in the matrix of polycrystallinen-alkane irradiated at 77 K

To reveal the reasons for the previously found absence of end radicals upon γ-radiolysis ofn-heptane polycrystals, we performed quantum-chemical calculations (SCF-MO, RHF, 6-31G^* basis set) of then-heptane molecule and its four radicals. The energies of the crystal lattice were calculated by the atom-atom potential method. Comparison of the experimental and calculated data showed that the absence of the end radicals is not related to the intermolecular interaction in the crystals. The most probable reason for the selective radical formation upon radiolysis can be a transfer of the excitation energy within then-heptane molecule occurring before the radical formation.     

Effect of gamma radiation on di- and trivalent cobalt nitrilotriacetates

Gamma irradiation of di- and trivalent cobalt nitrilotriacetic acid (NTA) chelates was performed both in the presence and absence of oxygen (air). A radiolytic mechanism is proposed where it has been shown that degradation of the cobalt chelates is due to OH radicals formed during radiolysis.     

Radiolytic degradation of pesticide 4-chloro-2-methylphenoxyacetic acid (MCPA)—Experimental data and kinetic modelling

The aqueous solutions of MCPA have been γ-irradiated in different conditions, where particular active radical species from water radiolysis predominate. The obtained data confirmed that largest yield of radiolytic decomposition is obtained in oxidation processes, where oxidation is carried out with hydroxyl radicals. The obtained data have been compared with kinetic modelling. A fair agreement was obtained for degradation of MCPA in different experimental conditions, including also irradiation in the presence of hydrogen peroxide, that in optimised conditions can be used to enhance the yield of decomposition. The obtained data have also shown a strong effect of the presence of large amount of chloride on yield of MCPA decomposition, which can be attributed to strong oxidation properties of chlorine radicals formed. It is also shown that MCPA can be completely decomposed in industrial wastes from various stages of MCPA production, although this is not accompanied by satisfactory reduction of toxicity of examined wastes.     

The removal of chlorinated organic herbicide in water by gamma-irradiation

In this study, the radiation-induced degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide in aqueous solution was studied under various conditions as a function of irradiation dose in the absence and presence of hydrogen peroxide. The obtained data confirmed that largest yield of radiolytic degradation is obtained in oxidation processes/ionizing radiation, where oxidation is carried out with hydroxyl radicals. For complete degradation of 50?ppm 2,4-D, a required dose was lower in the presence of hydrogen peroxide. The formed major toxic phenolic intermediates were 2,4-dichlorophenol (2,4-DCP) and 4-chlorophenol (4-CP). The chemical analysis of the 2,4-D and the intermediates resulted from the radiolytic degradation were performed using a gas chromatography associated to mass spectrometry (GC?CMS) with ion trap dedector (ITD) and ion chromatography (IC). The formation of chlorophenols in addition to chloride, formaldehyde and carboxylic acids was studied as a function of absorbed dose.     

Antioxidative properties of nitroxyl radicals and hydroxyamines in reactions with triplet and deaminated kynurenine

The reactions of triplet kynurenine and 4-(2-aminophenyl)-4-oxocrotonic acid, formed upon the thermal decomposition of kynurenine, with nitroxyl radicals and cyclic N-hydroxylamines were studied. Nitroxyl radicals were found to quench efficiently the triplet state of kynurenine (rate constant 3–6·.10⁸ L mol^-1 s^-1). The quenching proceeds via the spin-exchange mechanism and affords no new products. Neither nitroxyl radicals, nor hydroxyl-lamines react with 4-(2-aminophenyl)-4-oxocrotonic acid under conditions similar to physiological.     

Redox reactions of hydrogen adducts of thymine: Comparisons with the reactions of hydroxyl adducts

Hydrogen atoms form two kinds of adducts with thymine (oxidizing and reducing). Redox reactions of these two kinds, popularly known as 5-hydrogenated-6-thyminyl (reducing) and 6-hydrogenated-5-thyminyl (oxidizing), were investigated where ferric ions (oxidizing) and ferrous ions (reducing) were used as the corresponding redox partners. A steady-state gamma radiolytic system was chosen where hydroxyl radicals were scavenged using t-butyl alcohol in acidic (pH 1.8) solution. It is inferred that the redox potential of oxidizing hydrogenated thyminyl radicals lies between 0.77 and 1.4 V vs. NHE. The reducing hydrogenated thyminyl radical has a redox value less than 0.8 V because it efficiently undergoes electron transfer reaction with Fe(III). A probable range of redox values for hydroxyl adduct of thymine is included for comparison.     

The effect of anti-sinhibition of radiolytic hydrogen formation in Liquids

Attention is focused on that the phenomenon known as anti-inhibition in positronium chemistry is also observed in the radiolyses of liquids. In particular, the yield of radiolytic hydrogen from cyclohexane in the presence of molecular iodine increases when benzene is added to a cyclohexane solution. This effect is rationalized on the basis of the previously advanced idea on the similarity between the formation mechanisms of positronium and radiolytic hydrogen. The assumption that the enhancement of radiolytic hydrogen yield in aqueous nitrate or nitrite solutions taking place upon addition of Mn²⁺, Co^v2+, Zn²⁺, etc. ions is also the manifestation of the anti-inhibition effect, which has been known neither for positronium nor for radiolytic hydrogen in polar media, is substantiated.     

Radiation-induced crosslinking and cyclization in 1,2-polybutadiene

In order to get information on the radiolytic changes in 1,2-polybutadiene (1,2-PB) the sol and gel fractions, the conversion of double bonds, the structure and concentration of radicals, the formation of dienes and the formation of gaseous products were measured. In addition, the dose rate dependence and temperature dependence for the conversion of double bonds were determined. G values for double bond conversion depend on molecular weight and range from 20 to 200. G values for crosslinking are about 10. A mechanism for the double bond conversion is proposed which involves initiation by a transformation of the primary radical ion in the vinyl group into a carbonium ion and a radical. This is supported by ESR measurement. Reaction of the carbonium ion with a vinyl group in the same chain gives rise to cyclization, whereas reaction with a vinyl group in a neighboring chain results in crosslinking. A comparison of the G values for conversion of double bonds with the G values for crosslinking shows that the formation of cyclic rings exceeds the formation of crosslinks by a factor of about 10. The corresponding values in 1,4-cis- and 1,4-trans-polybutadiene are much smaller [G(cl) ? 2; G(db) ? 7]. The pendent vinyl groups in 1,2-polybutadiene therefore are more reactive than the vinylidene groups in 1,4-polybutadienes.     

Effects of substituents on chain-transfer reactivities of p-substituted cumenes in radical polymerization of p-substituted styrenes

In order to study the effects of the substituents in both substrate and attacking radical on the chain-transfer reactivities of nuclear-substituted cumenes toward substituted polystyryl radicals, the polymerizations of p-substituted styrenes in the presence of p-substituted cumenes were carried out with α,α′-azobisisobutyronitrile as an initiator at 60°C, and their chain-transfer constants were determined. The relative chain transfer reactivities of p-substituted cumenes toward given p-substituted polystyryl radicals did not follow the Hammett equation, but were correlated with the modified Hammett equation, log(k/k₀) = pρ + γE_R, which was proposed by the present authors for evaluating the substituent effects in radical reactions. On the other hand, the relative reactivities of poly-(p-substituted styrene) radicals toward given p-substituted cumenes were correlated by the Hammett equation. Thus, it was concluded that the effects of the substituents in substrate cumene depended upon the contributions of both polar and resonance factors, while those in attacking polystyryl radical depended upon only a polar factor.     

A study of radiation effects on the extraction of americium(III) with acidic organophosphates

Radiation effects on the extraction of americium(III) with several dialkylphosphoric and monoalkylphosphoric acids have been studied comparatively. The extractants were exposed to⁶⁰Co γ-rays in the absence and presence of diluent and HNO₃. The Df of Am(III) was measured and the yield of radiolytic products was determined after γ-irradiation as a function of the absorbed dose. Di(hexoxyethyl)phosphoric acid was the most susceptible to radiation among the extractants studied and its extractability was weakened by radiation regardless of the presence or absence of diluent or HNO₃. Diisodecylphosphoric acid itself showed an enhancement upon irradiation but incurred a depressant effect upon intimate contact with HNO₃·Mono(2-ethylhexyl)phosphoric acid showed a decrease of the Df of Am(III), similarly to DIDPA in the presence of HNO₃ during γ-irradiation. All the above extractants gave H₃PO₄ as the principal radiolytic product upon γ-irradiation upon intimate contact with HNO₃ causing decreasing solely the extraction of Am(III). Di(2-ethylhexyl)phosphoric acid proved to be the most stable extractant to radiation among those studied.     

Laser-irradiation-induced surface graft polymerization method

A laser-induced surface graft polymerization method is reported in which surface radicals generated upon laser irradiation initiated radical polymerization. The radical concentrations generated upon excimer laser irradiation under vacuum on poly-(ethylene terephthalate) film surfaces were measured using a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl. The density of surface radicals increased with laser fluence at low fluences but decreased at high fluences. Upon laser irradiation and subsequent treatment with gaseous N,N-dimethylacrylamide, surface graft polymerization occurred. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 747–750, 1997     

Spectroscopic analysis of pindolol irradiated in the solid state

Pindolol ((2RS)-(1-(1H-indol-4-iloxy)-3- [(1-metyloetylo)amino]-2-propanol) in substantia was exposed to ionising radiation emitted by high energy electrons from an accelerator, in the standard sterilisation dose of 25 kGy and in higher doses from the range 50–400 kGy. The effects of irradiation were checked by spectrometric methods (UV, MS, FT-IR, EPR) and hyphenated methods (HPLC-MS) and the results were referred to those obtained for non-irradiated sample. EPR results indicated the presence of free radicals in irradiated samples, in the amount of 1.36 × 10¹⁶ spin g^?1 for 25 kGy and 3.70×10¹⁶ spin g^?1 for 400 kGy. The loss of pindolol content determined by HPLC was 1.34% after irradiation with 400 kGy, while the radiolytic yield of the total radiolysis for this dose of irradiation was 2.69×10⁷ mol J^?1. By means of HPLC-MS it was possible to separate and identify one product of radiolytic decomposition, which probably is 2-((R)-3-(1H-indol-4-yloxy)-2-hydroxypropylamino)propan-1-ol formed upon oxidation. In the range of sterilisation doses (25–50 kGy), pindolol was found to show high radiochemical stability and would probably be safely sterilised by the standard dose of 25 kGy.      

Indoor 222Rn concentrations and the corresponding lung cancer risk in Celein region, west of Al Khums, Libya

Paramagnetic products stabilized in both 4,4′(5′)-di-(tert-butylcyclohexano)-18-crown-6 (DtBuCH18C6) and its solution in 1-octanol upon low temperature (77 K) X-rays irradiation were studied by ESR spectroscopy. Macrocyclic –O–ĊH–CH₂– radicals and acyclic O = C(H)–ĊH–O– radicals were found as main radiolysis products in neat DtBuCH18C6. Fraction of acyclic radicals resulting from the macrocycle cleavage was about 50%. No radical products resulted from t-Bu and cyclohexyl fragments were observed. It was concluded that the primary events were essentially concerned with ionization of the polyether moiety. Irradiation of frozen DtBuCH18C6 solutions in 1-octanol resulted in formation of radicals both from crown ether and alcohol.     

Sequence dependence of DNA radioprotection by the thiols WR-1065 and WR-151326

Sequence-dependent variations of DNA structure modulate radiation-induced strand breakage. Thiols reduce breakage by scavenging damaging radiolytic OH ^. and repairing sugar radicals. As shown by sequencing gel electrophoresis, WR-1065 radioprotection is modulated by sequence, whereas that of WR-151326, a larger thiol, is more evenly distributed. Molecular modelling was performed on complexes of a 53 bp oligonucleotide (belonging to a natural restriction fragment) with one molecule of WR-1065 or WR-151326. Energy minimised structures exhibit a broadening of the minor groove of an AAATT motif upon WR-1065 binding, and a narrowing of the groove upon WR-151326 binding. Consequently, the accessibility to OH^˙ of H4′ (whose abstraction leads to strand breakage) increases near WR-1065, whereas it decreases near WR-151326. This modifies locally the otherwise homogeneous radioprotection. The effect of WR-151326 strengthens the protection at all tested binding sites, whereas that of WR-1065 diminishes it in some regions, in good agreement with the observed radioprotection distribution. Received: 24 April 1998 / Accepted: 4 August 1998 / Published online: 11 November 1998     

PHOTOCHEMISTRY OF 2-MERCAFTOPYRIDINES. PART 2. AN EPR AND SPIN-TRAPPING INVESTIGATION USING 2-METHYL-2-NITROSOPROPANE AND aci-NITROMETHANE AS SPIN TRAPS IN AQUEOUS SOLUTIONS*

Abstract Compounds possessing a pyridine-2-thione moiety show antimicrobial, antifungal and anticancer activities. Some of them are also photochemically active and upon UV irradiation generate free radicals. In this work, employing EPR and the spin traps 2-methyl-2-nitrosopropane (MNP) and aci-nitromethane (NM), we investigated the photochemistry in aqueous solutions of N-hydroxypyridine-2-thione (used here as a sodium salt, 2-S-PyrNONa), and pyridine-2-thione (2-S-PryH), as well as photochemistry of the respective disulfides, 2,2′-dithiobis(pyridine N-oxide) [(2-S-PyrN→O)₂] and 2,2′-dithiodipyridine [(2-S-Pyr)₂]. We found that UV irradiation of 2-S-PyrNONa and of 2-S-PyrH in the presence of MNP and NM generates EPR signals of reduced spin traps in addition to signals of MNP and NM adducts with aryl-thiyl radicals, 2–.S-PyrN→O and 2–.S-Pyr. The identification of the aromatic thiyl radicals was based on comparison of EPR spectra of spin adducts generated by irradiation of 2-S-PyrNONa and 2-S-PyrH with those produced by UV photolysis of the respective disulfides (2-S-PyrN→O), and (2-S-Pyr)₂. It is concluded that pyridine-2-thione and N-hydroxypyridine-2-thione possess a photoreducing capacity and generate aromatic thiyl radicals upon UV activation. This property may be relevant to biological action of agents containing the pyridine-2-thione moiety.     

Nitrite formation in the radiolysis of aerated aqueous solutions of ammonia

Gamma irradiation of aerated aqueous solutions of ammonia leads to the formation of nitrite as a radiolytic product. Its yield increases with increasing concentration of NH₃ as well as O₂. OH radicals react with NH₃ to give NH₂ radicals, which in the presence of O₂ form NH₂O₂ radicals. These radicals finally lead to the formation of nitrite. G(NO₂⁻) decreases with increasing radiation dose due to secondary reactions. Its initial yield, however, is more than 1/2G_OH, while hydrogen peroxide yield is less than the expected value viz. G(H₂O₂) + 1/2G(e_aq⁻), indicating its participation in reactions with radiation produced free radicals. G(H₂) is 0.35 in aerated aqueous solutions of 10⁻³ mol dm⁻³ NH₃ and 0.23 in the absence of oxygen. Implications of these results to the use of NH₃ in primary coolant water of pressurized water nuclear power reactors of the VVER type are discussed.