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.     

On the Mechanism of Formation of Intratrack Yields of Water Radiolysis Products upon Irradiation with Fast Electrons and Positrons: 2. Concentration and Time Dependences of Yields

A mathematical model for the formation of main transient and final radiolysis products generated in tracks of fast electrons and positrons in water and aqueous solutions was constructed and described in terms of equations of inhomogeneous chemical kinetics in part 1 of this study. The model takes into account the reactions of a solute with epithermal electrons, thermal, and hydrated electrons; the ambipolar character of diffusion of charged intratrack particles; and new pathways of the formation of hydrogen and positronium due to the appearance of weakly bound states of electrons. In the present paper, the model was quantitatively fitted to experimental data on both time variation in the yields of radiolytic products (H₃O⁺, e _aq ⁻ , H, OH, OH⁻, H₂O₂) in pure water and the yields of hydrogen (H₂, H), hydrated electron (e _aq ⁻ ) and positronium (Ps) in various dilute and concentrated aqueous solutions.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 5, 2005, pp. 330–338.Original Russian Text Copyright © 2005 by Stepanov, Byakov.     

Reply to comment on the possible role of the reaction H+H2O→H2+OH in the radiolysis of water at high temperatures

In reply to “Comment on the possible role of reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures” (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) we present an alternative thermodynamic estimation of the reaction rate constant k. Based on the non-symmetric standard state convention we have calculated that the Gibbs energy of reaction Δ_rG=57.26 kJ mol^?1 and the reaction rate constant k=7.23×10^?5 M^?1 s^?1 at ambient temperature. Re-analysis of the thermodynamic estimation (Bartels, 2009 Comment on the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 78, 191–194) showed that the upper limit for the rate constant at 573 K is k=1.75×10⁴ M^?1 s^?1 compared to the value predicted by the diffusion-kinetic modelling (3.18±1.25)×10⁴ M^?1 s^?1 (Swiatla-Wojcik, D., Buxton, G.V., 2005. On the possible role of the reaction H+H₂O→H₂+OH in the radiolysis of water at high temperatures. Radiat. Phys. Chem. 74(3–4), 210–219). The presented thermodynamic evaluation of k(573) is based on the assumption that k can be calculated from Δ_rG and the rate constant of the reverse reaction which, as discussed, are both uncertain at high temperatures.     

Irradiation treatment of azo dye containing wastewater: An overview

The radiation-induced decolouration and degradation of aqueous solutions of azo dyes and their model compounds (anilines, phenols, triazines) are reviewed together with practical applications and the experimental methods (pulse radiolysis, steady-state gamma radiolysis, as well as end-product analysis) used for studying the reactions. The proposed mechanisms and the rate coefficients for the reactions of OH, e_aq⁻ and H water radiolysis intermediates with the dye molecules and with model compounds are summarized.     

Wastewater treatment with ionizing radiation

In water treatment by ionizing radiation ^·OH is suggested to initiate the degradation of organics. In these reactions mostly carbon centred radicals form. Here we show that other inorganic radicals also highly contribute to the initiation of degradation. Cl^? and HCO₃ ^? in the treated water reacting with ^·OH transform to Cl ₂ ^·? and CO ₃ ^·? . In their reactions C-centred radicals form, too. The reactions of e _aq ^? and H^· water radiolysis intermediates may also produce carbon centred radicals. The C-centred radicals react readily with dissolved O₂, this is the starting step of the gradual oxidation.     

The effect of interfacial mass transfer on steady-state water radiolysis

The effect of aqueous–gas interfacial transfer of volatile species on the γ-radiolysis of water was studied as a function of gas-to-liquid volume ratio at various solution pHs and cover gas compositions. Water samples with cover-gas headspace were irradiated at an absorbed dose rate of 2.5 Gy s^?1 and the radiolytic productions of H₂ in the cover gas and H₂O₂ in the water phase were monitored as a function of irradiation time. The experimental results were compared with computer simulations using a water radiolysis kinetics model that included primary radiolysis, subsequent reactions of the primary radiolysis products in the aqueous phase, and aqueous–gas interfacial transfer of the volatile species H₂ and O₂. This study shows that the impact of the interfacial mass transfer strongly depends on pH. At pH≤8 (lower than the pKa of ?H of 9.6) the effect of aqueous-to-gas phase transfer of the volatile species on the steady-state concentrations of the other radiolysis products is negligible. At higher pHs (≥8), radiolytic production of O₂ is slow but considerable, which results in significant increase in the steady-state concentrations of H₂ and H₂O₂ compared to those at lower pHs. Thus, in the presence of headspace, the interfacial transfer of both H₂ and O₂ becomes significant, and the aqueous concentrations of H₂ and O₂ are no longer independent of the interfacial surface area and water volume. Nevertheless, the accumulated mass of H₂(g) in the headspace is proportional to the aqueous concentration of H₂ at all pHs, and the gaseous concentration of H₂ in the headspace can be used to infer the aqueous concentration of H₂.     

Isotopic effect in the radiolysis of water. Diffusion-kinetic modelling up to 300°C

Diffusion-kinetic calculations [1-3] have been analysed to determine the isotopic effect in the radiolysis of water with ionising radiation of linear energy transfer characteristics (LET) from 0.2 to 60 eV/nm and at temperatures up to 300°C. This analysis shows that, for low LET radiation, the spur decay of e^- _aq is slower in D₂O and results in a higher yield of e^- _aq, g(e^- _aq), at 10^-7 -10^-6s after the ionisation event. In low LET radiolysis, g(OD) ≈ g(OH) over the whole range of temperature but in high LET radiolysis g(OD) is clearly lower than g(OH). The isotopic effect on the yields of the radical products is enhanced by increasing LET but diminished by increasing temperature. The yields of the molecular products show the opposite isotopic effect to their radical precursors, namely g(D₂) is 10-20% lower than g(H₂) and g(D₂O₂) > g(H₂O₂). A particularly significant difference between g(D₂O₂) and g(H₂O₂) has been found at LET = 20 eV/nm. The isotopic dependence of the g-values estimated for fast neutron radiolysis is also presented.     

Influence of γ-radiation on the reactivity of montmorillonite towards H2O2

Compacted and water saturated bentonite will be used as an engineered barrier in deep geological repositories for radioactive waste in many countries. Due to the high dose rate of ionizing radiation outside the canisters holding the nuclear waste, radiolysis of the interlayer and pore water in the compacted bentonite is unavoidable. Upon reaction with the oxidizing and reducing species formed by water radiolysis (OH^•, e⁻_(aq), H^•, H₂O₂, H₂, HO₂^•, H₃O⁺), the overall redox properties in the bentonite barrier may change. In this study the influence of γ-radiation on the structural Fe(II)/Fe_Tot ratio in montmorillonite and its reactivity towards hydrogen peroxide (H₂O₂) was investigated in parallel experiments. The results show that under anoxic conditions the structural Fe(II)/Fe_Tot ratio of dispersed Montmorillonite increased from ≤3 to 25-30% after γ-doses comparable to repository conditions. Furthermore, a strong correlation between the structural Fe(II)/Fe_Tot ratio and the H₂O₂ decomposition rate in montmorillonite dispersions was found. This correlation was further verified in experiments with consecutive H₂O₂ additions, since the structural Fe(II)/Fe_Tot ratio was seen to decrease concordantly. This work shows that the structural iron in montmorillonite could be a sink for one of the major oxidants formed upon water radiolysis in the bentonite barrier, H₂O₂.     

Reactions of the dications C7H6, C7H7, and C7H8 with methane: Predominance of doubly charged intermediates

The reactions of methane with the dications C₇H₆²⁺, C₇H₇²⁺, and C₇H₈²⁺ generated by electron ionization of toluene are studied using mass-spectrometry tools. It is shown that the reactivity is dominated by the formation of doubly charged intermediates, which can either eliminate molecular hydrogen to yield doubly charged products or undergo charge-separation reactions leading to the formation of a methyl cation and the corresponding C₇H_n+1⁺ monocation. Typical processes observed for dications, like electron transfer or proton transfer, are largely suppressed. The theoretically derived mechanism of the reaction between C₇H₆²⁺ and CH₄ indicates that the formation of the doubly charged intermediate is kinetically preferred at low internal energies of the reactants. In agreement, the experimental results show a pronounced hydrogen scrambling and dominant formation of the doubly charged products at low collision energies, whereas direct hydride transfer prevails at larger collision energies.     

Radiolytic degradation of 2,4-dichlorophenoxyacetic acid in dilute aqueous solution: pH dependence

The reactions of hydroxyl radical and hydrated electron intermediates of water radiolysis were studied in the radiolytic degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) at pH values of 4, 6 and 8. The hydrated electron reactions are also suggested to contribute to the aromatic ring decomposition in addition to the highly effective hydroxyl radical reactions. The experimental results suggest also some contribution from the O₂^−•/HO₂^• pair to the degradation. The degradation efficiency was found to be the highest at pH 8 and the lowest at pH 6.     

Reactions of stabilized criegee intermediates from the gas‐phase reactions of O3 with selected alkenes

The gas‐phase reactions of O₃ with 1‐octene, trans‐7‐tetradecene, 1,2‐dimethyl‐1‐cyclohexene, and α‐pinene have been studied in the presence of an OH radical scavenger, primarily using in situ atmospheric pressure ionization tandem mass spectrometry (API‐MS), to investigate the products formed from the reactions of the thermalized Criegee intermediates in the presence of water vapor and 2‐butanol (1‐octene and trans‐7‐tetradecene forming the same Criegee intermediate). With H₃O⁺(H₂O)_n as the reagent ions, ion peaks at 149 u ([M + H]⁺) were observed in the API‐MS analyses of the 1‐octene and trans‐7‐tetradecene reactions, which show a neutral loss of 34 u (H₂O₂) and are attributed to the α‐hydroxyhydroperoxide CH₃(CH₂)₅CH(OH)OOH, which must therefore have a lifetime with respect to decomposition of tens of minutes or more. No evidence for the presence of α‐hydroxyhydroperoxides was obtained in the 1,2‐dimethyl‐1‐cyclohexene or α‐pinene reactions, although the smaller yields of thermalized Criegee intermediates in these reactions makes observation of α‐hydroxyhydroperoxides from these reactions less likely than from the 1‐octene and trans‐7‐tetradecene reactions. Quantifications of 2,7‐octanedione from the 1,2‐dimethyl‐1‐cyclohexene reactions and of pinonaldehyde from the α‐pinene reactions were made by gas chromatographic analyses during reactions with cyclohexane and with 2‐butanol as the OH radical scavenger. The measured yields of 2,7‐octanedione from 1,2‐dimethyl‐1‐cyclohexene and of pinonaldehyde from α‐pinene were 0.110 ± 0.020 and 0.164 ± 0.029, respectively, and were independent of the OH radical scavenger used. Reaction mechanisms are presented and discussed. © 2001 Wiley Periodicals, Inc. Int J Chem Kinet 34: 73–85, 2002     

Effect of Solvation on Chemical Reactions,I. Addition of a Single Water Molecule to the H− + H2O → OH− + H2 Reaction

The gas phase chemical reaction, H^? + H₂O → H₂ + OH, and the effect of an additional water molecule on the reaction, H^?(H₂O) + H₂O → H₂ + OH(H₂O), have been investigated. The optimal structures and energies of the reactants, products, two stable intermediates, and the transition state connecting the two intermediates have been determined. The additional water molecule does not affect the potential surface congruently: it destabilizes the H(H₂O) minimum, but stabilizes the H₂ ?OH minimum and the transition state connecting the two intermediates. However, it stabilizes the products more than the H₂ ?OH^? minimum. Finally, in line with the reduction in the barrier height, the transition state for the H(H₂0) to H₂ ?OH^? isomerization moves further along the reaction path.     

Radiolysis of aqueous solutions of gadolinium nitrate

The specific effect due to Gd³⁺ ion on the radiolysis of aqueous nitrate solutions was determined by measurement of H₂, H₂O₂ and NO ₂ ^– radiolytic yields produced by gamma-irradiation of aerated and deaerated solutions of gadolinium, sodium and calcium nitrates in the concentration range of 10^–5 to 0.3M. Important O₂ consumption in aerated and O₂ evolution in deaerated Gd(NO₃)₂ solutions was found by radiolysis in comparison with the inert cations nitrates. In the former the Gd³⁺ ion generates an O₂ transporter producing an increase in the H₂O₂ yield and a decrease in the NO ₂ ^– yield, while in the latter it enhances the H₂ and NO ₂ ^– production with respect to the same nitrate concentration of the Na⁺ solutions.     

Isolierbare,o-verbrückte sulfinsäurefluorid/BF3-addukte ArS(F)O⋯BF3[1]

Interaction of gaseous BF₃ with the sulfinic acid fluorides 1a,b yields the O-bridged adducts ArS(F)?BF₃ 2a,b (a: Ar= Ph, b:Ar = p-F(C₆H₄)). Their structure is established by low temperature ¹³C {¹H}-NMR and their reactions. Compounds of type 2 are intermediates in Lewis-acid catalyzed aromatic sulfinylation.     

A pulse radiolysis study of the reactivity of neptunoyl ions relative to inorganic free radicals

Conclusions 1. Pulse radiolysis was used to find the rate constants for the reactions of OH, HSO₄, NO₃, and Cl₂ radicals with neptunoyl ions.Change in the NO₃ and H⁺ ion concentrations do not affect the term k[NO₃ + NpO₂ ⁺], while k[Cl₂ ^– + NpO₂ ⁺] increases with increasing chloride concentration due to the formation of neptunoyl ion chlorocomplexes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 456–458, February, 1986.     

Water radiolysis with heavy ions of energies up to 28 GeV.: 1. Measurements of primary g values as track segment yields

Water radiolysis has been investigated with heavy ions having energies up to 28 GeV provided from the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIRS). Beams of ⁴He²⁺, ¹²C⁶⁺, ²⁰Ne¹⁰⁺, ²⁸Si¹⁴⁺, ⁴⁰Ar¹⁸⁺ and ⁵⁶Fe²⁶⁺ with respective energies of 150, 400, 400, 490, 500 and 500 MeV/u corresponding LET values of 2.2, 13, 30, 54, 92 and 183 eV/nm, respectively, were taken for the irradiation. The LET changes in sample solutions can be neglected due to their high energies for the irradiation of 1-cm cells. Primary g values have been determined for three important products, hydrated electron (e⁻_aq), hydroxyl radical (·OH), and hydrogen peroxide (H₂O₂) as track segment yields (differential yields) under the conditions of neutral pH.With increasing LET, the g values of e⁻_aq and ^·OH decrease from 2.4 and 2.6 in ⁴He²⁺ radiolysis to 0.9 and 1.1 (100 eV)⁻¹ in ⁵⁶Fe²⁶⁺ radiolysis, respectively. It was also found that the primary g value of e⁻_aq is smaller than that of ·OH for any type of ion beam. For the ¹²C⁶⁺ beam, other energies such as 290, 220, 135 MeV/u were taken for the irradiation to investigate the effects of type or atomic number of ions on the measured yields. Furthermore, effects of dissolved oxygen on enhancement of H₂O₂ production have also been investigated with aerated NaNO₃ solutions. The presence of dissolved oxygen caused 15–35% enhancement in H₂O₂ yields for all beams. In addition, the results of the present work were compared with reported track segment yields.     

A study of methanetetraol dehydration to carbonic acid

Two alternative dehydration reactions C(OH)₄ → (HO)₂CO + H₂O and C(OH)₄ + H₂O → (HO)₂CO + 2H₂O are studied by ab initio Becke3LYP/6–311 + G^** and MP2/6–31G^** methods. Calculated energy and geometry characteristics of intermediates and transition states predict a catalytic effect of one water molecule and the exothermism of the transformations. Relevant HF/6–311 + G^**, HF/6–31G^**, HF/6–31G, and HF/3–21G calculations were performed for comparison. © 1997 John Wiley & Sons, Inc.     

COD reduction of waste water streams of active pharmaceutical ingredient – Atenolol manufacturing unit by advanced oxidation-Fenton process

Active pharmaceutical intermediates (API) in waste waters have adverse effects on aquatic life and environment. The API have high COD value and low BOD₃ and hence difficult to treat biologically. In this study, advanced oxidation processes (AOPs) utilizing the H₂O₂/Fe⁺², Fenton reactions were investigated in lab-scale experiments for the degradation of Atenolol containing waste water streams. The experimental results showed that the Fenton process using H₂O₂/Fe⁺² was the most effective treatment process. With Fenton processes, COD reduction of wastewater can be achieved successfully. It is suggested that Fenton processes are viable techniques for the degradation of Atenolol from the waste water stream with relatively low toxic by-products in the effluent which can be easily biodegraded in the activated sludge process. Hence, the Fenton process with H₂O₂/Fe⁺² is considered a suitable pretreatment method to degrade the active pharmaceutical molecules and to improve the biodegradability of waste water.