Radiation-chemical Degradation Research Articles

ALTERATION OF ACTIVE SUBSTANCE CONTENT IN "HEXACHLORAN DUST" PESTICIDE FORMULATION AT EXPOSURE TO ELECTRON BEAM

The most popular methods of organochlorinated pesticides (OCP) destruction, which are based on thermal dechlorination, are not ecologically safe. The other process – radiation-chemical degradation – has got some advantages. It does not involve high temperatures and expensive reagents. In this study, the effective OCP degradation was observed under irradiation of residuals of the active substance of ‘Hexachloran dust’ pesticide formulation, intended for utilization. Parameters for the preparation powder (dry form) exposure to electron beam are discussed. It is shown that at the exposure to electron beam at dose of 100 kGy, the degradation degree of hexachlorocyclohexane (HCH) isomers in a composition of active substance achieves 56.2–66.3%.

Evidence for Indirect Action of Ionizing Radiation in 18-Crown-6 Complexes with Halogenous Salts of Strontium: Simulation of Radiation-Induced Transformations in Ionic Liquid/Crown Ether Compositions.

Ionic liquid/crown ether compositions are an attractive alternative to traditional extractants in the processes for spent nuclear fuel and liquid radioactive wastes reprocessing. These compositions are exposed to ionizing radiation, and their radiation stability, especially in the presence of metal salts, is a crucial issue. In the present study, the macrocyclic 18C6·Sr(BF4)2 and 18C6·Sr(PF6)2 complexes simulating the components of metal loaded ionic liquid/crown ether extractants were synthesized and their structures were characterized by FTIR spectroscopy and single-crystal X-ray diffraction analysis. Inclusion of Sr2+ cation into the 18C6 cavity resulted in more symmetric D3d conformations of the macrocycle. The structural transformations of the crown ether were accompanied by an elongation of polyether C-O bonds that could increase the possibility of radiolytic cleavage of the macrocycle. However, EPR study of the synthesized compounds subjected to X-ray irradiation revealed predominant formation of macrocyclic -CH2-ĊH-O- radicals. This result demonstrated an evidence for indirect action of ionizing radiation on individual components of the complexes and was reasonably described by a positive "hole" transfer from primary macrocyclic radical cation to fluorous anion at the primary stages of radiolysis and a subsequent interaction of fluorine atom with 18C6 macrocycle in secondary radical reactions. The observed effects may be partially responsible for enhanced sensitivity of the ionic liquid/crown ether extractants to ionizing radiation due to chemical blocking of the crown ether with radiolytic HF, radiation-chemical degradation of the 18C6, and precipitation of a low-soluble SrF2.

Mechanisms of Radiation-Induced Degradation of CFCl3 and CF2Cl2 in Noble-Gas Matrixes: An Evidence for "Hot" Ionic Channels in the Solid Phase.

The X-ray-induced transformations of simple chlorofluorocarbons (CFCl3 and CF2Cl2) in solid noble-gas matrixes (Ne, Ar, Kr, and Xe) at 7 K were studied in order to elucidate basic mechanisms of the radiation-chemical degradation with possible implications for stratospheric and extraterrestrial ice chemistry. The decomposition of parent molecules and formation of products were monitored by FTIR spectroscopy, and the identification was supported by ab initio calculations at the CCSD(T) level. It was shown that the ionic reaction channels were predominating in most cases (except for CF2Cl2/Xe system). The primary radical cations (CFCl3+• and CF2Cl2+•) are either stabilized in matrixes or undergo fragmentation to yield the corresponding secondary cations (CFCl2+, CCl3+, CF2Cl+) and halogen atoms. The probability of fragmentation through different channels demonstrates a remarkable matrix dependence, which was explained by the effect of excess energy resulting from the exothermic positive hole transfer from matrix atoms to freon molecules. A qualitative correlation between "hot" ionic fragmentation at low temperatures and gas-phase ion energetics was found. However, dissociative electron attachment leads to formation of neutral radicals (CFCl2• or CF2Cl•) and chloride anions. One more possible way of dissociative electron attachment in the case of CF2Cl2 is formation of CF2•• and Cl2-•. A general scheme of the radiation-induced processes is proposed.

Radiation-Chemical Degradation of Oxalic Acid in Water Solutions

Radiation-Chemical Degradation of Oxalic Acid in Water Solutions

Role of surfactant derived intermediates in the efficacy and mechanism for radiation chemical degradation of a hydrophobic azo dye, 1-phenylazo-2-naphthol

A combined methodology involving gamma and pulse radiolysis, product analysis and toxicity studies has been adopted to comprehend the degradation process of a model hydrophobic azo dye, 1-phenylazo-2-naphthol, emphasizing the role of the surfactant, which is an integral part of textile waste. Two new and important findings are underlined in this article. The first is the direct attestation of the hydrazyl radical-parent adduct, formed in the reaction of the dye with e−aq followed by protonation and subsequent addition to the unreacted dye molecule. This has been confirmed from concentration dependent studies. Secondly, we have clearly shown that in the reaction of hydroxyl radical with the dye in Triton X-100 media, the initially produced TX radicals cause reductive degradation of the dye. Identification and detailed analysis of HPLC and GCMS data reveals that similar products are formed in both the reactions of e−aq and OH radicals. Moreover, the cytotoxicity of 10−4moldm−3 dye was found to be reduced significantly after irradiation. Thus, the present study not only depicts new pathways for the degradation of hydrophobic azo dye, but also demonstrates the role of a surfactant in the entire process.

Effect of molecular weight on radiation chemical degradation yield of chain scission of γ-irradiated chitosan in solid state and in aqueous solution

Chitosan A1, A2 and A3 with molecular weight of 471, 207 and 100kDa respectively, produced from squid pen chitin was degraded by gamma rays in the solid state and in aqueous solution with various doses in air at ambient temperature. Effect of molecular weight on radiation chemical degradation yield of chain scission and degradation rate constants of γ-irradiated chitosan in solid state and in aqueous solution was investigated. The radiation chemical degradation yield G(s) and degradation rate values were calculated. The molecular weight changes were monitored by capillary viscometry method and the chemical structure changes were followed by UV analysis. The results showed that, the degradation of chitosan was faster in solution, than in solid state. The values of G(s) in solid state and in aqueous solution were respectively 1.1×10−8mol/J and 0.074×10−7mol/J for A1, 4.42×10−8mol/J and 0.28×10−7mol/J for A2 and 6.08×10−8mol/J and 0.38×10−7mol/J for A3. Degradation rate constants values ranged from 0.41×10−5 to 2.1×10−5kGy−1 in solid state, whereas in solution they ranged from 13×10−5 to 68×10−5kGy−1. The chitosan A3 was more sensitive to radiolysis than A1 and A2. The chain scission yield, G(s) and degradation rate constants seems to be greatly influenced by the initial molecular weight of the chitosan. Structural changes in irradiated chitosan are revealed by the apparition of absorption peaks at 261 and 295nm, which could be attributed to the formation of carbonyl groups. In both conditions the peak intensity was higher in chitosan A3 than in A1 and A2, the oxidative products decreased with increasing molecular weight of chitosan.

Mechanism of gas-phase degradation of polycyclic aromatic hydrocarbons by the action of ionizing radiation

The most comprehensive kinetic model for the gas-phase radiation-chemical degradation of polycyclic aromatic hydrocarbons is proposed on the basis of analysis of published data, which takes into account both the radical and ion-molecule mechanisms of the process. The model was verified by comparing the calculation results with the experimental data. It was shown that the efficiency of the process is lower in dry gas mixtures in which the ion-molecule mechanism plays the principal role in the degradation of aromatic molecules than in wet mixtures in which the radical mechanism dominates.

Radiation resistance of ionic and ionic-molecular crystals

The factors that determine the stability of ionic and ionic-molecular crystals in ionizing radiation fields are analyzed. The concepts of the fundamental reactivity (stability) of a solid (the ability of the ideal crystal lattice of the material, in which only intrinsic point defects—interstitial ions and vacancies—are present, to undergo radiation-chemical degradation) and the structure-sensitive reactivity determined by the presence of structural and extrinsic defects are introduced. Data on the radiation resistance of crystalline solids (alkali halides, silver halides, and silver azide) are summarized. It is pointed out that the AgHal crystalline matrix should be resistant toward radiation and alkali halide and AgN3 crystals should not.

A Diffusion-Kinetic Model for Radiation-Chemical Transformations of Oxalic Acid and Oxalate Ions in Aqueous Solutions

A diffusion-kinetic model for the radiation-chemical degradation of oxalic acid and oxalates in aqueous solutions was developed. The model adequately describes published data on the formation of H2, H2O2, and CO2 over wide ranges of acid concentrations and pH values.

Radiation-chemical degradation of the paper insulation of power transformers

Radiation-chemical degradation of the paper insulation of power transformers

The pH-Dependent Radiation-Chemical Degradation of Ionol Incorporated into the Lipid Bilayer of Lecithin Liposomes

The pH-Dependent Radiation-Chemical Degradation of Ionol Incorporated into the Lipid Bilayer of Lecithin Liposomes

Radiation-Chemical Degradation of Azo Dye Solutions

The radiation-chemical discoloration of evacuated alcoholic solutions of the azo dye 1-(2-pyridylazo)-2-naphthol was studied using a pulse radiolysis technique. The spectral characteristics of radicals were determined, and the radiation-chemical yields of their formation and dye decomposition were measured. The degradation of the azo dye Acid Yellow 99 under irradiation with γ-quanta and vacuum UV radiation was compared. The radical mechanism of azo dye degradation in aqueous and alcoholic solutions under exposure to high-energy particles was confirmed.

Formation of Methyl Iodide in the Radiolysis of Aqueous Cesium Iodide and Acetic Acid Solutions

Volatile compounds of radioactive iodine, including methyl iodide, are released into the environment in the cases of serious accidents at nuclear power plants. The aim of this study was to find a conceivable mechanism of the radiation-chemical formation of methyl iodide in aerated aqueous solutions of cesium iodide and acetic acid. This provides the basis for subsequent investigations aimed at preventing the formation of methyl iodide. The radiation-chemical yield of methyl iodide formation in 10–3M CsI solutions containing CH3COOH (0.1 mol/l) decreased with increasing the pH. This fact is primarily explained by a decrease in the steady-state concentration of molecular iodine with increasing the pH. An increase in the pH of irradiated solutions up to pH ≥ 9 was found not only to prevent the formation of methyl iodide but also to enhance its radiation-chemical degradation.

The radiation-chemical degradation of polytetrafluoroethylene to low-molecular and functionalized perfluorinated compounds

The action of high energy radiation of relatively low dose in presence of reactive substances leads to a finely grained PTFE powder with functional groups, which can be mixed easily with liquids, solutions and polymers. The degradation of PTFE by high energy radiation with a high dose in presence of oxygen forms among other compounds perfluorinated carboxylic acids, whereas in inert atmosphere mixtures of perfluorinated alkenes and alkanes of different chain length ranges are obtained. An apparatus conception of a continuous degradation of PTFE was developed. Irradiation of perfluorinated alkanes and of gaseous degradation products of PTFE leads to a significant increasing of the yield of perfluorinated alkenes. Mechanisms of reactions are discussed. Recombinations of radicals obtained by irradiation form branched molecules. The reactions are diffusion controlled. Irradiation of high molecular PTFE leads to low branching. The degree of branching of molecules increases in correlation to decrease of viscosity of the reaction medium. Compounds with the highest degree of branching are obtained with the irradiation of gaseous perfluorocarbons, and reactions of increase of the carbon chain are observed in this case in a high extent.

Radiation processing of the degradation of polytetrafluoroethylene to low-molecular perfluorinated compounds

The production of aliphatic perfluorinated compounds by means of radiation-chemical degradation reaction of PTFE using an electron beam represents a new alternative of the synthesis of special active components, such as fluorocarbon surfactants, fluorine containing textile finishing agents, special dielectrics and others. A principle of process and an apparatus conception pertaining to it of a continuous degradation of PTFE to perfluoroalkenes and -alkanes in the favourable chain lengths ranges from six to fourteen carbon atoms, according to application, is described. An essential component of this conception is the use of a target which consists of a tempered thin layer which is led, in correspondence with dimension and intensity of the radiation field, in an inertly processed reactor. An embodiment of the reactor is presented in detail.

Radiation Chemical Reactions in Aqueous Solutions of Methionine and Its Peptides

In our preceding paper (1) the radiation chemical degradation of eleven dipeptides and tripeptides was studied in aqueous oxygenated and oxygen-free solutions. Analysis of the products formed and of their yields, together with previous work by Garrison and Weeks (2), permitted establishment of the mechanism of the major radiation chemical reactions. In oxygen-free solutions, the peptide bond remains practically intact, the major reactions being reductive deamination of the N-terminal amino acid in the peptide and recombination either of two peptide radicals or of one peptide molecule with its radical (on the methyl or methylene groups), yielding dimersthat is, neutral peptides-or of one deaminated peptide radical with the original peptide or its radical (on the same groups), yielding acidic peptides. In oxygenated solutions, peptide bond cleavage to the amide and carbonyl derivatives, oxidative deamination to the ketoacyl peptide, and cleavage of the intermediary imine radical of the N-terminal amino acid to the lower aldehyde and the free C-terminal amino acid are the main reactions, besides oxidation on the methyl and methylene groups. Some effects of the structure of the peptide have also been pointed out (1). In our present work similar investigations were carried out with methionine peptides to study the effect of the -SCH3 group in methionine on the radiolysis of the peptides. For this purpose it was necessary to reinvestigate the radiolysis of methionine under the experimental conditions employed. The radiolysis of methionine in aqueous solutions has been studied by our group (3-5) as well as by Kumta et al. (6, 7) and by Shimazu et al. (8). The latter authors studied the radiolysis of methio-

The mechanism of the radiation chemical degradation of amino acids—V: Radiolysis of Norleucine, Leucine and Isoleucine in Aqueous Solution

Oxygenated and oxygen-free aqueous solutions of norleucine, leucine and isoleucine were irradiated with γ-rays. The products of the radiation chemical reactions in both media were determined. On the basis of these results the radiation chemical degradation pattern of these amino acids was elucidated and the effects of chain length and branching of the C chain discussed.

The Mechanism of the radiation chemical degradation of amino acids—IV: Radiolysis of valinein aqueous oxygenated and oxygen-free solutions

In the previous papers of this series (1–3) the mechanism of the radiation chemical degradation of the straight chain amino acids α-aminobutyric acid and norvaline was investigated in oxygenated and oxygen-free aqueous solution. In this paper the radiolysis of valine, an amino acid with a branched chain was studied under identical conditions with the purpose of elucidating the effect of branching of the C chain on the mechanism of the radiolytic degradation.

The mechanism of the radiation chemical degradation of amino acids-III: Radiolysis of norvaline in aqueous oxygenated and oxygen-free solutions

In our previous papers (1,2) the mechanism of the radiation chemical degradation of α-aminobutyric acid in oxygenated and oxygen-free solutions was elucidated and the degradation mechanism under these conditions compared. In this paper a similar study was undertaken with norvaline with the purpose of studying the effect of chain length on the degradation mechanism.

The mechanism of the radiation chemical degradation of amino acids—II: Degradation of α-aminobutyric acid in aqueous solution and nitrogen atmosphere and comparison with the degradation in oxygen atmosphere

In our previous paper (1) of this series the degradation of α-aminobutyric acid was studied in aqueous solution in oxygen atmosphere. A similar investigation has now been carried out in nitrogen atmosphere for the further elucidation of the reaction mechanism. Comparison of the products arising in oxygen and nitrogen atmosphere and their yields should make it possible to determine the effect of oxygen on the formation of the degradation products. A similar comparative study was made by Weeks and Garrison (2) on glycine, who on the basis of various literature sources and their own experimental results proposed a mechanism for the action of radiation on aqueous solutions of glycine under different conditions.