Gamma Radiolysis Of Water Research Articles

Protection of endogenous β-carotene in LDL oxidized by oxygen free radicals in the presence of supraphysiological concentrations of melatonin

This study was designed to evaluate the effect of high concentrations of melatonin on the peroxidation of human low density lipoproteins (LDLs) initiated by O2•- and ethanol-derived peroxyl radicals (RO2•) from water gamma radiolysis in the presence of ethanol. LDL (3 g/l; total LDL concentration) was oxidized in the absence of melatonin or in its presence at three concentrations (50 × 10-6, 100 × 10-6 or 250 × 10-6 mol/l) in ethanol. Radiolytic yields (i.e. number of mole consumed or produced per Joule) of the markers of lipid peroxidation were determined (i.e. decrease in the endogenous antioxidants α-tocopherol and β-carotene, formation of conjugated dienes and of thiobarbituric acid-reactive substances [TBARS]). Melatonin decreased the yields of lipid peroxidation products and delayed the onset of the propagation phase for conjugated dienes and TBARS in a concentration-dependent manner. Nevertheless, melatonin did not protect endogenous α-tocopherol against peroxyl-induced oxidation (probably due to a lower scavenging capacity than that of α-tocopherol towards peroxyl radicals), but delayed the consumption of LDL endogenous β-carotene and decreased its rate of disappearance. The effect of melatonin seemed to be the highest for a melatonin concentration of 250 × 10-6 mol/l.

Application of gamma radiolysis of water for H2 production

The present work is devoted to the investigation of the effective use of radioactive waste for H2 production by g-radiolysis of water, through both experiments and simulation. We have suceeded in improving the efficiency of hydrogen production by g-radiolysis of water via the conversion of g-rays to lower energy electrons and photons by introducing high Z metals, such as Ta, Pd, W and Pb, into water. We have also used exothermic hydrogen occluders like Ta and Pd to absorb the produced hydrogen, suppressing recombination of hydrogen to water. Surface oxidation which must be avoided, was also prevented using Pd.

Reactions of hydroxyl radical with humic substances: bleaching, mineralization, and production of bioavailable carbon substrates.

In this study, we examine the role of the hydroxyl (OH*) radical as a mechanism for the photodecomposition of chromophoric dissolved organic matter (CDOM) in sunlit surface waters. Using gamma-radiolysis of water, OH* was generated in solutions of standard humic substances in quantities comparable to those produced on time scales of days in sunlit surface waters. The second-order rate coefficients of OH* reaction with Suwannee River fulvic (SRFA; 2.7 x 10(4) s(-1) (mg of C/L)(-1)) and humic acids (SRHA; 1.9 x 10(4) s(-1) (mg of C/L)(-1)) are comparable to those observed for DOM in natural water samples and DOM isolates from other sources but decrease slightly with increasing OH* doses. OH* reactions with humic substances produced dissolved inorganic carbon (DIC) with a high efficiency of approximately 0.3 mol of CO2/mol of OH*. This efficiency stayed approximately constant from early phases of oxidation until complete mineralization of the DOM. Production rates of low molecular weight (LMW) acids including acetic, formic, malonic, and oxalic acids by reaction of SRFA and SRHA with OH* were measured using HPLC. Ratios of production rates of these acids to rates of DIC production for SRHA and for SRFA were similar to those observed upon photolysis of natural water samples. Bioassays indicated that OH* reactions with humic substances do not result in measurable formation of bioavailable carbon substrates other than the LMW acids. Bleaching of humic chromophores by OH* was relatively slow. Our results indicate that OH* reactions with humic substances are not likely to contribute significantly to observed rates of DOM photomineralization and LMW acid production in sunlit waters. They are also not likely to be a significant mechanism of photobleaching except in waters with very high OH* photoformation rates.

Comparison of the effects of O 2•−/HO • free radical- and copper ions-oxidized LDL or lipoprotein(a) on the endothelial cell releases of tissue Plasminogen Activator and Plasminogen Activator Inhibitor-1

We investigated the effects of low density-lipoproteins (LDL) and lipoprotein(a) [Lp(a)] oxidized by O 2 •−/HO • free radicals generated by gamma radiolysis of water, on the release of tissue Plasminogen Activator (tPA) and of its main inhibitor Plaminogen Activator Inhibitor-1 (PAI-1) by human umbilical vein endothelial cells (HUVEC). These effects were compared to those of lipoproteins issued from the same preparations but oxidized by the classical copper ions procedure. The results showed that O 2 •−/HO • free radical oxidized LDL and Lp(a) led to a dramatic decrease of PAI-1 release but did not affect tPA release, whereas copper oxidation of lipoproteins resulted in an increase in PAI-1 release and a decrease in tPA release. Chemical analysis revealed that O 2 •−/HO • free radical oxidized lipoproteins exhibited very much lower levels of phosphatidylcholine hydroperoxides, lysophosphatidylcholine and oxysterols (7-ketocholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol) than copper oxidized LDL. Thus, the discordant effects of O 2 •−/HO • oxidized and copper oxidized LDL and Lp(a) on the endothelial releases of PAI-1 and tPA appeared to be due to qualitatively and/or quantitatively different formation of oxidized components by the two oxidation processes.

Interfacial Energy Transfer during Gamma Radiolysis of Water on the Surface of ZrO2 and Some Other Oxides

The effect of an oxide interface on 60Co gamma radiolysis of water molecules was studied. On the basis of the molecular hydrogen yield when compared with the radiolysis of the control ampules without oxides, all the tested materials can be generally classified into three groups: I. Oxides that lower the H2 yield (MnO2, Co3O4, CuO, and Fe2O3); II. Oxides with H2 yields that are close to G values obtained in control experiments (MgO, CaO, SrO, BaO, ZnO, CdO, Cu2O, NiO, Cr2O3, Al2O3, CeO2, SiO2, TiO2, Nb2O5 and WO3); and III. Oxides that can increase the H2 yield as compared with the radiolysis of water without oxides (Ga2O3, Y2O3, La2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Yb2O3, Er2O3, HfO2, and ZrO2). For the third group, the H2 yield can be much greater than for the homogeneous process due to effective energy transfer at the oxide/water interface. There are several parameters, such as the oxide band-gap, water adsorption form, and energy migration distance that can collectively contribute to “enhanced” radiolys...

OH radicals and oxidizing products in the gamma radiolysis of water.

The production of OH radicals in the gamma radiolysis of water has been examined with radical scavenger techniques employing formic acid. OH radical yields were found to vary from 2.4 radicals/100 eV at the low scavenger concentration limit to 4.2 at a formic acid concentration of 3 M. An inverse Laplace transform technique was applied to the scavenger concentration dependence to obtain the temporal dependence of OH radicals in pure water. It was found that the relative decrease in OH radical yields from 200 ps to 3 ns was virtually the same for the transform of the scavenger data and the directly measured time-resolved results. The absolute yields for the time-resolved experiments are about 10% higher than expected from the present results with scavengers. The agreement can be considered to be good, and reasons for the observed difference are given. Approximately 40% of the OH radicals produced lead to the formation of hydrogen peroxide, which is the only other major oxidizing species in the gamma radiolysis of water. The net water decomposition for gamma rays was found to vary from an initial value of 5.6 +/- 0.3 molecules/100 eV to 3.8 +/- 0.2 molecules/100 eV at 1 micros.

Oxidation of Human High-Density Lipoproteins by ∙ OH and ∙ OH/O 2 ∙- Free Radicals

The aim of this work was to specify the mechanisms involved in the radical oxidation of human high-density lipoprotein (HDL) and to compare these mechanisms with those described previously for the oxidation of low-density lipoprotein (LDL) under the same experimental conditions (Bonnefont-Rousselot et al., Radiat, Res. 134, 271-282, 1993). The oxidation of HDL, initiated by .OH or .OH/O(.-)2 free radicals from gamma radiolysis of water, was evaluated as a function of increasing radiation dose by analyzing quantitatively the decrease of endogenous alpha-tocopherol and the formation of oxidation products (thiobarbituric acid-reactive substances and conjugated dienes). All qualitative conclusions were supported by quantitative data (radiation yields and concentrations of the oxidation markers at high radiation doses) and by the mechanisms of the kinetics, .OH free radicals in the absence of oxygen were less efficient in initiating HDL oxidation than in the presence of oxygen (action of .OH/O(.-)2 free radicals), which was in agreement with the enhancement of the action of .OH free radicals by oxygen. The remaining significant level of vitamin E in HDLs at high radiation doses in the absence of oxygen could be explained by a regeneration of vitamin E by an oxidation product that was able to reduce the alpha-tocopheroxyl radical. The yields related to the decrease in the vitamin E content of HDLs after exposure to radiation with .OH or .OH/O(.-)2 free radicals were slightly higher than those obtained previously in LDLs under similar experimental conditions. Moreover, in the presence of oxygen, .OH free radicals led to a lower formation of thiobarbituric acid-reactive substances in HDLs than in LDLs. Such discrepancies in the behavior of these two lipoprotein fractions could be related to the differences in the chemical composition of HDLs and LDLs.

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.

Radiation effect on polyadenylic acid in aqueous solution

In this study, dilute solution properties of polyadenylic acid (polyA), G values for single strand break formation G(ssb), Arrhenius parameters (25–45 °C), the kinetics of strand break in the absence and presence of radical scavengers have been studied. OH radicals were produced from gamma radiolysis of water, which is supposed to be the main primary radical causing single strand break formation.

Hydroxyl Radical Attack of Low-Density Lipoprotein Decreases Its Cellular Catabolism in the Absence of Significant Lipid Peroxidation

Low density lipoprotein (LDL) has been submitted to oxidative modification induced by gamma radiolysis of water under conditions generating either hydroxyl radical (OH·) alone, or a mixture of superoxide anion and OH·. Treatment of LDL with hydroxyl radical alone did not lead to significant lipid peroxidation as assessed thiobarbituric acid reactive substances (TBARS) and hydroperoxide measurement induced only very small change in the electrophoretic mobility of the particle. In contrast, superoxide and hydroxyl radical mixture induced a dose-dependent increase in lipid peroxidation, with a marked elevation of the negative net charge of the LDL. However, in both cases, a similar reduction of the uptake and degradation of modified LDL by the apo B/E receptor pathway of human fibroblasts was observed. This suggests that factors other than lipid peroxidation could play a role in LDL modification and influence their cellular metabolism.

Concentration- and pH-Dependent Ammonia Yields in the Reaction of Hydrated Electrons with Glycylglycine

Competition between recombination of the radicals formed in the gamma radiolysis of water (eaq-, OH, H) and the reaction of eaq- with glycylglycine is investigated in glycylglycine solutions of various concentrations and pH. First, the concentration dependence of the ammonia yields is measured in the glycylglycine solutions of between 0.5 mM and 1.0 M. The G values of ammonia appear to reach a plateau of 2.47 +/- 0.05 molecules/100 eV at the low concentrations (1-5 mM) and increase to 3.81 +/- 0.07 molecules/100 eV at the high concentration (1 M). Secondly, the pH dependence of the ammonia yields is measured at low (1 and 5 mM) and high (0.1 and 0.2 M) concentrations of glyclyglycine. For concentrated glyclyglycine solutions, the ammonia yields increase with increasing pH, as expected based on comparison of the probabilities of the competitive reactions. However, the G values of ammonia reach a maximum at pH 9.0 and then decrease as the pH increases for dilute solutions. The lower G values at higher pH for dilute glycylglycine solutions may result from increased interspur recombination since the rate constant for the reaction of eaq- with glycylglycine is decreased and, as a consequence, the scavenging capacity of glycylglycine for eaq- decreases approximately 4.7-fold from low to high pH.

Gamma Radiolysis of Water Solutions Relevant to the Nuclear Fuel Waste Management Program

The gamma radiolysis of water was investigated for conditions relevant to studies of the geological disposal of nuclear fuel waste. Chemical kinetic calculations were carried out for seven systems:...

Oxidation of UO 2 fuel by the products of gamma radiolysis of water

Abstract The kinetics of UO 2 fuel oxidation by the products of gamma radiolysis of water were studied as a function of absorbed dose rate. The oxidation of UO 2 during radiolysis was monitored by recording the corrosion potential of a UO 2 electrode as a function of time. Changes in the surface of UO 2 were determined using cathodic-stripping voltammetry (CSV) and X-ray photoelectron spectroscopy (XPS). The effects of specific radicals on UO 2 oxidation were determined by adding suitable scavengers to the solution to maximize the yield of a particular radical. The radical species formed during radiolysis of water are much more effective in causing UO 2 oxidation than the molecular oxidants formed during radiolysis of water or present in water from atmospheric sources. The oxidation of UO 2 in the presence of oxidants produced by the gamma radiolysis of water occurs in two distinct stages: (a) the formation of a thin layer ofUO 2 + x with a stoichiometry close to UO 2.33 and a thickness similar to that obtained (over longer exposure periods) in unirradiated oxygenated solutions; and (b) the subsequent oxidative dissolution of this surface layer to produce soluble U VI species and secondary phases, probably hydrated schoepite (UO 3 · xH 2O), on the UO 2 substrate. The first stage occurs in the potential range− 500 mV < E PCORR≲−100 mV (versus SCE). The second stage starts around E CORR∼− 100 mV and eventually achieves steady state at a value of E CORR determined by the gamma dose.

Copper-ligand interactions and physiological free radical processes. pH-dependent influence of Cu2+ ions on Fe2(+)-driven OH. generation.

Prior to comparative studies on the reactivity of various copper complexes with respect to OH. radicals, the influence of free Cu2+ ions on the superoxide-independent generation of OH. radicals through Fenton assays and water gamma radiolysis has been tested in the present work. Cu2+ ions have been shown to behave in a distinct manner towards each of these two production systems. As was logically expected from the noninvolvement of copper in OH. radical production through gamma radiolysis, no influence of Cu2+ ions has been observed on the amount of radicals detected in that case. In contrast, Cu2+ ions do influence OH. radical generation through iron-driven Fenton reactions, but differently depending on copper concentration. When present in high concentrations, Cu2+ ions significantly contribute to OH. radical production, which confirms previous observations on the reactivity of these in the presence of hydrogen peroxide. At lower levels corresponding to copper/iron ratios below unity on the contrary, Cu2+ ions behave as inhibitors of the OH. production in a pH-dependent manner over the 1-6 range investigated: the lower the pH, the greater the inhibition. The possible origin of this previously unreported inhibitory effect is discussed.

Gamma-Radiolysis of Water and Some Aqueous Solutions under N2Gas Bubbling

The γ-radiolysis of water subjected to gas bubbling has been studied using a specially desinged gasloop. During the irradiation, N2 gas was bubbled from the bottom of the irradiation vessel. As the N2 gas feed rate was raised, the apparent G(H2) value increased in keeping therewith, from 5 × l0−3 to 0.26. However in the presence of a sufficient amount of O2 or H2O2, G(H2) was raised almost to the level of the molecular yield. With reasonable assumptions, it could be concluded that 3∼5 × 10−6 mol/l of H2O2 was sufficient to reduce the back reaction of molecular products to less than 10% under the present experimental conditions. It was also found that the G(H2) value increased with CH3OH concentration roughly in proportion to log(CH3OH), and reached 3.1 with 0.1 mol/l CH3OH.

On the molecular hydrogen formation in the gamma radiolysis of water and aqueous solutions

The radiolytic hydrogen yield G H 2 from deaerated aqueous solutions of various di- and tri-positive metal ions was found to be in many cases independent of the solute concentration (up to 0·1 mol dm −3). However, in Cd 2+, Cu 2+, Cr 2+, Pb 2+ and acidic Hg 2+ solutions, G H 2 decreased with increasing solute concentration. The efficiency of these ions in reducing the hydrogen yield is in the order: Hg 2+>Pb 2+>Cr 2+≈Cu 2+>Cd 2+. The fact that all these metal ions are good scavengers for the reducing species produced in the radiolysis of water ( e aq − and H atoms) leads to the conclusion that they are not the main precursors of H 2. Homogeneous kinetics was used to express the dependence of G H 2 on solute concentration. The rate-determining step is considered to be the pseudo first-order disappearance of the H 2 precursor. It could be either the hydride ion produced by the reaction of subexcitation electrons with water as proposed by Platzman, the dry electrons suggested by Hamill, or the H 3O radicals of Sworski and Smaller. The chemical reactivity of the above ions toward the H 2 precursor is shown to be parallel to the rate of ligand substitution in the aquated metal ions as measured by Eigen. It is also shown that part (≈20 per cent) of the H 2 may be produced by a radical-radical reaction mechanism.

Gamma-Radiolysis of Water Using a Specially Designed Gamma-Irradiation Loop

The γ-radiolysis of water has been studied using a water-loop specially designed for this purpose. The water was circulated without contact with air during the irradiation. The apparent G(H2) value was found to be roughly 10-3. However a corresponding amount of O2 was not found, due to its comsumption by corroding reactions of the constituent materials under radiation field. In the presence of O2 and H2O2, the H2-yield curves vs. the irradiation dose were revealed a very distinctive characteristic: following a rapid increase with initial irradiation a plateau range has appeared. The H2-yield at this plateau range depended on the initial concentration of additives. Continued irradiation, however, caused a gradual further rise in the H2-yield above the plateau value at a rate corresponding to that found in the pure water system. These yield curves are discussed on the basis of the free radical model for the radiolysis of water.

Gamma-Radiolysis of Water and Some Aqueous Solutions under N2 Gas Bubbling

Gamma-Radiolysis of Water and Some Aqueous Solutions under N2 Gas Bubbling

Gamma-Radiolysis of Water Using a Specially Designed Gamma-Irradiation Loop

Gamma-Radiolysis of Water Using a Specially Designed Gamma-Irradiation Loop

THE REDUCING RADICALS PRODUCED IN WATER RADIOLYSIS: SOLUTIONS OF OXYGEN—HYDROGEN PEROXIDE—HYDROGEN ION1

The reducing radical H or H2O- arising from the gamma radiolysis of water is shown to react competitively with dissolved O2 and H2O2; the ratio of the respective rate constants is 2.0. lt also reacts in a simple competitive bimolecular fashion with hydrogen ion, H+, to give an acid form of the radical which reacts several thousand ttmes as fast with O2 as with H2O2. The rate constants for reaction of H with O2 and with H+ are equal. The yield of H deduced from the O2-H2O2 competition in neutral solution is 2.85, which is equal to the standard value of the total yield of reducing radicals. Thus essentially none of the reducing radicals appear to be generated initially in the acid form, a conclusion which disagrees with recently proposed interpretations of some other radiolytic reactions.