Radiolysis Of Aqueous Solutions Research Articles

Dependence of Molecular Hydrogen Formation in Water on Scavengers of the Precursor to the Hydrated Electron

Molecular hydrogen yields have been measured in the γ radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parametrized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a “nonscavengable” hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted “nonscavengable” yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers.

Radiolysis of aqueous solutions with pulsed helium ion beams—2. Yield of SO4− formed by scavenging hydrated electron as a function of S2O2−8 concentration

Yields of SO4− in the radiolysis of aqueous (NH4)2S2O8 solutions with pulsed 24 MeV 4He2+ ion beams were measured in the concentration range from 1×10−4 to 1 mol dm−3. The yield increased with increasing the concentration, and it was smaller than that in electron beam pulse radiolysis in the concentration range measured. The results were compared with the reported Ge−aq derived from various scavengers. Though the yields agree well for low LET radiations, the result of the present research for 4He ion beams is smaller than the yield determined by a product analysis method. This suggests that once formed SO4− disappears by the intra-track reactions and that this effect is more important in ion beam radiolysis because of more dense production of the initial species. Simulation by the deterministic diffusion kinetic model supports it qualitatively.

Effect α-radiation of Po on aqueous solutions (history of French and Russian research)

A brief historic review of Russian R & D concerning Po as well as French and Russian data on α-induced radiolysis of aqueous solutions are presented.

Radiation-Induced Reactions of 2,4,6-Trinitrotoluene in Aqueous Solution

Radiolysis of aqueous solutions of TNT was examined to provide fundamental information concerning the reactions of TNT with radical species in water. γ-Radiation was used in conjunction with radical scavengers to compare yields for radiation-induced TNT transformation under oxidizing and reducing conditions and in the presence and absence of oxygen. Pulse radiolytic techniques were employed to determine rate constants and absorption spectra for the reactions of TNT with the hydroxyl radical and the aqueous electron. TNT was rapidly transformed under both reducing (1% tert-butyl alcohol, N 2 sparged) and oxidizing (N 2 O sparged) conditions although rates under reducing conditions were greater. The initial yield for transformation of a 350 μmol L -1 TNT solution under reducing conditions was 0.14 μmol/J as opposed to 0.10 μmol/J measured in oxidizing conditions. The reactions of TNT with reduced oxygen species were found to be highly inefficient in aqueous solution. Although TNT is transformed by both oxidizing and reducing radicals, TNT degradation yields in the absence of a radical scavenger were low, indicating that under these conditions there were significant secondary reactions in which the species resulting from reactions between TNT and the primary radicals further reacted to reform the parent compound. The bimolecular rate constant for the reaction between TNT and - OH was determined to be 4.3 x 10 8 mol -1 s -1 . Byproduct analyses from γ-radiolysis suggest that hydroxyl radical abstraction of a methyl hydrogen to form the trinitrotoluyl radical is an initial oxidative reaction. The bimolecular rate constant for the reaction between TNT and e aq - was measured as 3.5 x 10 10 mol -1 s -1 . These results provide quantitative and qualitative insight into the reactions between TNT and the various aqueous radicals produced in many remediation processes.

Gamma radiolysis of aqueous solution of acrylic and polyacrylic acid in the presence of Cu2+

The inhibitory action of cupric ions in the process of radiation polymerization of acrylic acid (AA) in aqueous solution was investigated as well as the reaction of the products of gamma radiolysis of water with polyacrylic acid (PAA) in the presence of cupric ions. In the case of AA-CuSO4 and PAA-CuSO4 systems irradiated at 77 K an external protective effect caused by copper ions was observed. This effect was connected with the electron transfer between a radical and the Cu2+ ion. During radiolysis of copper arcylate (A2Cu) and a system AA-A2Cu in aqueous solutions a protective effect exerted by copper ions was observed which seemed to be connected with the dispersion of the absorbed radiation energy by the groups: copper-ligands.

Radiotracer method for the study of the radiolysis of aqueous solutions of pyruvic acid

The purpose of this work is to study the radiolytic behavior of aqueous solutions of14C-pyruvic acid (oxygen-free). Several parameters were varied such as radiation dose, pH, etc. Gas chromatography, mass spectrometry and high performance liquid chromatography were used extensively for the analysis of radiolytic products. The more abundant product was dimethyltartaric acid. Other products identified were acetic, lactic, succinic, malonic and tricarballylic acids, acetaldehyde, carbon dioxide, and hydrogen. The yields of these products were influenced by the irradiation dose, concentration of the target compound and pH of the solution.

Concentration fluctuations in the radiolysis of aqueous solutions of peroxidase derived from horseradish roots

In a study of the 7-radiolysis of 1.2-2.4 ~M aqueous solutions of horseradish root peroxidase (HRP) saturated with oxygen and containing 0.i M HCO2Na, we discovered self-fluctuating reactions involving the products of the radiolytic transformations of HRP. Spectral changes occur upon the irradiation of this system as a result of reactions with H20 = and O2-(HO='), which are caused by the transformation of HRP to oxygenated forms, termed HRP-(1) and HRP-(II), and a peroxo complex, HRP-(III) [i]. In this case, the dose dependences of the concentrations of these forms have a fluctuating character. For example, the fluctuation period for initial HIRP concentration (Co) 1.6 ~M and dose 9.2 rad/sec is ~18 krad (in the antiphase) and the sum of the concentrations of the products corresponds to C o . The effect of the dose (0.8-9~ rad/sec) and Co indicates that the disproportionation of radicals O=(HO2") and HRP-(II) play the major role in the mechanism of the fluctuating reaction. After the irradiation, the concentrational fluctuations of HRP-(1) and HRP-(II) continue and are accompanied by the appearance of an HRP, whose concentration also fluctuates. These fluctuations are related to reactions apparently involving H20 = and the enzyme and the disproportionation of HRP-(II). These effects may account for the retention of biological activity of the enzyme under these conditions in doses up to i Mrad observed by Metodieva et al. [2].

ChemInform Abstract: Electrochemistry and Spectroelectrochemistry of Nitroxyl Free Radicals

This work reports electrochemical and spectroelectrochemical studies of the two nitroxyl radicals 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 3-carbamoyl-2,2,5,5-tetramethyl-3-pyrrolin-1-yloxy (3-carbamoyl-PROXYL). Oxidation and reduction reactions have been observed in aqueous media over the pH range 2-12 in the potential range -0.8 to +0.8 V by differential pulse voltammetry, cyclic voltammetry, and thin-layer UV-visible spectroelectrochemistry, and the reaction products have been characterized by IR, NMR, and ESR spectrometry. At pH values less than 10, characteristic electrochemical behavior is observed to be analogous for both radicals, and the products from electron transfer compare quite favorably with those found by pulse radiolysis of aqueous solutions of nitroxyl radicals. At pH 2-9, a stable cation from a reversible oxidation and hydroxylamine following an irreversible reduction, as well as hydroxylated cation at pH higher than 9, are the same as those obtained in pulse radiolysis experiments. Spectroscopic evidence indicates that behavior following reduction at high pH differs for the two radicals. At pH 12, reduced TEMPO may undergo structural changes leading to the formation of a new radical consisting of a seven-membered ring.

Detection of gaseous products in the radiolysis of aqueous solutions

A new technique for the direct determination of radiolytically produced gaseous products is discussed. The method consists of continuously bubbling a gas through a sample cell and monitoring the effluent with a mass spectrometer. It has been applied to the determination of H/sub 2/ and CO/sub 2/ produced in various aqueous solutions irradiated with /sup 60/Co ..gamma.. radiation. The yield of H/sub 2/ is found to be 0.51 molecules/100 eV in aerated ferrous sulfate solutions and in deaerated KBr solutions. The effect of saturating the ferrous sulfate solution with oxygen or addition of KNO/sub 2/ to the KBr solution is the same with a yield of H/sub 2/ of 0.43 molecules/100 eV. The yield of OH radicals as determined by the production of CO/sub 2/ in dilute oxygen-saturated formic acid solutions is 2.5 molecules/100 eV.

60Co Gamma radiolysis of aqueous solutions of ferrousbis–(nitrilotriacetate) and ferrous-ethylenediaminetetraacetate

Abstract Gamma radiolysis of aqueous solutions (pH 5.0) of Fe(NTA)2 4− and FeEDTA2-in presence of N2O, Br− and 2-propanol revealed that the H2O2 and Br− oxidised Fe(II), and the H atom abstracted hydrogen from ligand, while the OH did both; this revealed no steric protection of metal centre in these compounds. The rate constants detemined in the competition kinetic study with 2-propanol for metal oxidation reaction are k[OH+Fe(NTA)2 4−]=4.1×109 M−1 s−1 and k(OH+FeEDTA2−)=6.5×109 M−1 S−1, and those for hydrogen abstraction are 1.2×109 and 1.4×109 M−1 s−1 respectively.

Some aspects of the gamma radiolysis of aqueous solutions of urea in the context of chemical evolution

Some aspects of the gamma radiolysis of aqueous solutions of urea in the context of chemical evolution

Pulse radiolysis of pentacyanonitrosylferrate/II/ ions in aqueous solutions

Pulse radiolysis of aqueous solutions of sodium pentacyanonitrosylferrate/II/ Na2[Fe/CN/5NO] /sodium nitroprusside/ was studied in the presence of ethylene glycol as an OH radical scavenger. The rate constants of the one-electron reduction of nitroprusside ion were measured with e q − and with radicals derived from some alcohols /ethylene glycol, ethanol, 2-propanol/ as reducing species. The results show that the transition state for the reduction by alcohol radicals is polar. The only observed product of reduction is the Fe/CN/5NO3− ion, which then undergoes a slow dissociation to form Fe/CN/4NO2−. Only a small isotope effect kH/kD=1.08 was observed in D2O solutions for the dissociation reaction. This suggests an intramolecular electron transfer as rate-determining step for the dissociation reaction.

Investigation of the formation possibilities of alkyl iodides in nuclear power plants

The radiolytic decomposition of ion-exchange resins used in Czechoslovak nuclear power plants for the purification of the reactor coolant and chemical control of H 3BO 3 concentration in the coolant was studied with regard to the determination of sources of aliphatic hydrocarbons, which are potential precursors of alkyl iodides. On irradiation of ion-exchange resins in deaerated borate solution, C 1-C 4 hydrocarbons are formed. These hydrocarbons are produced also in the radiolysis of the emulsion of turbine oil in the same solution. The radiation stability of cation-exchange resins is higher than that of anion-exchange resins. Radiolytic and thermal reactions occuring in the gaseous mixtures containing I 2, CH 4, H 2O, and air/Ar give rise to CH 3I. CH 3I is produced also in the radiolysis of aqueous solutions containing CH 4 and I 2 or I -.

Radiolysis of aqueous solutions of gadolinium nitrate

The use of gadolinium nitrate for liquid regulation of the reactivity of nuclear reactors is attractive because this substance has a large neutron-absorption cross section and is highly soluble in coolants. The authors carried out experimental investigations on a special loop of the VVR-M reactor. The investigations established that gadolinium nitrate in aqueous solutions is a radiation-stable chemical compound and can be used as a neutron absorber in the liquid regulation of the reactivity of low temperature nuclear reactors. Nitrogen or air may be used as the gaseous cushion of the volume compensator. The radiolysis of water in the presence of gadolinium nitrate in a closed system leads to the generation of a gaseous phase containing a detonating mixture of H/sub 2/ and O/sub 2/. In an open system with degassing no generation of a gaseous phase is observed. The results of the investigations have been used in designing the liquid reactivity regulation system of the PIK reactor.

Radiation chemistry of overirradiated aqueous solutions of hydrogen cyanide and ammonium cyanide

The radiolysis of aqueous solutions (O2-free) of HCN and NH4CN was examined at very large doses of60Co gamma radiation (up to 230 Mrad). In this dose range the cyanide initially present (0.12 M) is decomposed and only its radiolytic products participate in the radiation-induced chemical process. It has been found that the weight of the dry residue containing the mixture of nonvolatile radiolytic products increases as doses increase up to 40 Mrad (up to about 4 g/l), but with further dose increases remains practically unchanged (NH4CN) or decreases slightly (HCN). Carboxylic and amino acids are present in overirradiated samples. At increasing doses their concentrations decrease, with the exception of oxalic and malonic acids, which are continually produced and accumulate. This is also the case with the abundant NH3 and CO2, as well as with several other products that were generated at lower radiation-chemical yields. The molecular weights of the radiolytic products are up to 20,000 daltons throughout the dose range studied. Their amounts gradually change with increasing doses above 30 Mrad: The compounds with Mw between 2,000 and 6,000 daltons become more abundant, while the amounts of polymers with Mw between 6,000 and 20,000 decrease. The relevance of these findings for studies of chemical evolution is considered.

Chromatographic studies on the radiolysis of DNA in aqueous solution.

Radiation-induced degradation of double-stranded DNA from calf thymus in aqueous solution with sodium phosphate was studied by conventional gel chromatography and by high-performance liquid-gel permeation chromatography. Comparison of the data after radiolysis of aqueous solutions of DNA under anaerobic and aerobic conditions indicates that double-strand breakage is not enhanced by oxygen. An increase of ionic strength impedes the break-down of the DNA molecules, so that loss of DNA can only be observed at doses above 100 Gy. Only reactions of OH-radicals contribute to the fragmentation of DNA, while the presence of hydrated electrons, H.-or formate radicals does not lead to a loss of highly polymerized DNA up to doses of 1500 Gy. High-performance liquid-chromatography proved to be an excellent method of studying the degradation of macromolecules as a function of dose.

Formation of 5-S-cystamine-5,6-dihydrothymine in radiolysis of aqueous solutions of thymine and cystamine

1. A method for synthesis of 5-S-cystamine-5,6-dihydrothymine was developed. 2. This compound is stable in neutral and acid solutions but rapidly decomposes according to a first-order reaction at pH 10–12. It was found that decomposition is due to acidbase dissociation of 5-S-cystamine-5,6-dihydrothymine (pK ∼ 11.1) and that the rate of decomposition increases with an increase in the pH of the solutions. 3. The products of cross-linking of these compounds, 5-S-cystamine-6-hydroxythymine and 5-S-cystamine-5,6-dihydrothymine, are formed in radiolysis of deaerated acid solutions containing thymine and cystamine.

Radiolysis of aqueous solutions of cobalt/II/ and cobalt/III/ 2,2′-bis-[aminoethyl]ether-tetraacetate complexes

Radiolysis of aqueous solutions of di- and trivalent cobalt with 2,2′-bis/aminoethyl/ether-tetraacetic acid /BAETA/ was investigated, both in absence and in presence of oxygen. A radiolytic mechanism has been proposed where it has been shown that the degradation of the chelation is due to OH only.

On the γ-radiolysis of aqueous solution of cerium (III) nitrilotriacetate

Radiolysis of aqueous solutions (pH 5.5–10.0) of cerium (III) nitrilotriacetate (C) has been studied both in deoxygenated solutions and in the presence of various scavengers like t-butanol, N 2O and Br -. Both H and OH radicals directly degrade the ligand and H 2O 2 oxidises the central metal ion. The radiolytic products iminodiacetic acid (IDA), Ce(IV) and the carbonyl compounds formaldehyde and glyoxalic acid and their yields are consistent with the proposed mechanism.

Oxidation of α-tocopherol in micelles and liposomes by the hydroxyl, perhydroxyl, and superoxide free radicals

Rates of oxidation of α-tocopherol by the hydroxyl- and superoxide free radicals were measured. The radicals were produced in known yields by radiolysis of aqueous solutions with gamma rays. Two main systems were used to dissolve the tocopherol; micelles, made up from charged and uncharged amphiphiles, and membranes made from dimyristyl phosphatidylcholine which could be charged by addition of stearyl amine or dicetyl phosphate. The HO. radicals were efficient oxidants of α-tocopherol in all systems, with up to 83% of radicals generated in micelle and 32% in membrane suspensions initiating the oxidation. The HO 2 ̇ radical was an even more effective oxidant, but when most of it was in the O form at neutral or alkaline pH, the oxidation rates became low. Tocopherol held in positively charged micelles or membranes was oxidized at a higher rate by the O than in uncharged or negative particles. Possible biological significance of these results is discussed.