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.     

Nitrite formation in aerated aqueous azide solutions: A radiation chemical study

Gamma radiolysis of oxygenated 1–10 mM azide solutions was carried out at various pH values. In oxygenated 10 mM azide solutions, H₂O₂ and NO ₂ ⁻ were observed as radiolytic products while NH3 was not. The concentration of H₂O₂ reached its maximum level at a dose of 1 kGy, whereas NO ₂ ⁻ yield increased non-linearly beyond 2 kGy in this system. Both in aerated and oxygenated systems, G(NO ₂ ⁻ ) and G(H₂O₂) were found to vary with N ₃ ⁻ concentration. The yield of NO ₂ ⁻ was found to be dependent on both dose rate and pH. On pulse radiolysis, NO ₂ ⁻ was found as a radiolytic product in aerated 1 mM azide solution at pH 6.8. In this system the intermediate generated exhibits absorbance around 250 nm. The overall results obtained during the present study reveal that in presence of both reducing radical (mainly e _aq ⁻ ) and oxygen, N ₃ ⁻ produced an intermediate possibly NH₂O ₂ ^• radical, which is the prime source for NO ₂ ⁻ generation.     

Effect of ascorbic acid and its derivatives on the radiation-chemical transformations of hydroxyl-containing organic compounds

The effect of ascorbic acid, 5,6-O-isopropylidyl-2,3-O-dimethylascorbic acid, and 2-O-glucopyranosylascorbic acid on the formation of main radiolysis products of ethanol and aqueous ethanol, ethylene glycol, α-methylglucopyranoside, and maltose solutions was studied by means of continuous radiolysis. The obtained results indicate that ascorbic acid effectively reacts with the carbon-centered hydroxyl-containing radicals derived from the substrates, thus decreasing the yield of their recombination and fragmentation products. It was found that the interaction of ascorbic acid and its derivatives with the carbon-centered radicals during the radiolysis of deaerated ethanol and its aqueous solutions may occur via both reducing and oxidizing mechanisms and that ascorbic acid in the aerated solutions acts as a hydrogen donor, reducing mainly the HO ₂ ^· radical to hydrogen peroxide.     

Semi-empirical calculations on the structure of the oxonium ion in various crystal sites and relative acidity scale

The structure of the H₃O⁺ ion embedded in a solid environment (H₃O⁺X^–, X^– = Cl^–, NO ₃ ^– , ClO ₄ ^– ) is studied using a modified version of CNDO/2. In this calculation the effect of the first shells of nearest neighbours is taken into account and the effects of second nearest neighbours are introduced by a simulation procedure. Electronic effects are also included. The ion structure is more planar in nitrate than in perchlorate environment and the hydrogen bonds are slightly bent. Trends in structural parameters are compared with chemical properties of the hydrogen bonds and parallels the Hammett acidity scale HNO₃ < HCl < HClO₄.     

Raman spectral study of the constitution and equilibria of nitric acid and d-nitric acid

From relative integrated intensity measurements of the symmetric stretching vibration of nitrate ion in nitric acid solutions (both HNO ₃ /H ₂ O and DNO ₃ /D ₂ O), the mass law concentration quotients, Q were obtained as functions of concentration. By extrapolation the limiting dissociation constants were estimated to be 24.4 and 15 respectively at 25°C. It is shown that this constant refers to a process in which the ion pair H ₃ O⁺ NO ₃ ^– is in equilibrium with the dispersed, solvated H ₃ O⁺ and NO ₃ ^– ions.     

The mechanism of nitrite formation in the radiation-induced oxidation of ammonia in aerated aqueous solutions

The mechanism of the radiation-induced conversion of ammonia to nitrites and nitrates in aerated aqueous solutions has been studied. The formation of the pernitrite ion, O=N-O-O^–, was detected at pH 10.5. The kinetics of its formation and decay were studied, andk _form was estimated at (2.3±0.2)·10⁷ L mol^–1 s^–1. The course of decay obeys first-order kinetics; the rate constant decreases at higher pH. Radiochemical yields of pernitrite, nitrite and nitrate at various pH and initial NH₃ concentrations were determined. A mechanism of ammonia oxidation in aqueous solution is proposed.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 280–283, February, 1993.     

Gamma-ray induced decomposition of double nitrates of lanthanides with univalent and divalent cations

Double nitrates of Na and K having the composition 2M^INO₃·Ln^III(NO₃)₃·2H₂O(Ln^III=Pr, Nd, Sm, Eu, Gd, Tb and Dy) and of Ni and Cu with the composition 3M^II(NO₃)₂·2Ln^III(NO₃)₃·24H₂O (Ln^III=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) have been prepared and their -radiolytic decomposition studied up to 500 kGy. G(NO ₂ ^– ) values of K double nitrates at 230 kGy follow the order Dy³⁺>Pr³⁺=Nd³⁺=Sm³⁺>Tb³⁺>Eu³⁺> Gd³⁺·G(NO ₂ ³⁺ ) for NI double nitrates are higher than those of Cu double nitrates. Variation of G(NO ₂ ^– ) with cationic radii and the number of f electrons in lanthanide ion show a minimum at Eu. Thermal decomposition studies of double nitrates were also carried out.     

Effect of metal oxides on the gamma radiolysis of ammonium nitrate

The studies of radiation decomposition of ammonium nitrate in the presence of MnO₂, PbO and V₂O₅ with the absorbed dose reveal that MnO₂ retards while PbO and V₂O₅ accelerate the rate of radiolysis. G/NO ₂ ^– / values were found to increase with the mole% of V₂O₅ in an admixture. The results are explained on the basis of electron donor-acceptor properties of oxides affecting the equilibrium concentration of electrons present in pure ammonium nitrate in the presence of the added oxides.     

Radiolysis of aqueous cesium iodide

In hypothetical accident scenarios for Light Water reactors, the extent of release of iodine upon irradiation needs to be assessed for the purpose of evaluation of the applicable source term. In this context, an understanding of the behaviour of aqueous cesium iodide solutions subjected to high gamma-ray fluxes acquires significant importance. In the present work, gamma radiolysis of a cesium iodide solution (10^–2M I^–) with and without boron additive is investigated by irradiating with⁶⁰Co source at ambient temperature. Upon irradiation of the CsI solution, iodine is liberated, and the concentration of iodide in the KOH trap present in the radiolysis vessel increases with dose. The radiolytic products I ₃ ^– , IO ₃ ^– and H₂O₂ formed in the irradiated solution are also estimated and G values obtained are reported. G(I ₃ ^– ) and G(IO ₃ ^– ) are of the order of 10^–3 and 10^–4, respectively. G(H₂O₂) decreases with increase in dose. Addition of boron up to 200 ppm, does not appear to alter significantly the release fraction of iodine.     

State of the hydroxide ion in water and aqueous solutions

Conclusion Analysis of these experimental facts leads to the conclusion that in water and aqueous solutions of alkali metal hydroxides it is extremely probable that the hydroxide ion exists in the form H₃O₂ ^–. The marked displacement of the extrapolated chemical shift of the proton of the H₃O₂ ^– ion towards weak fields and the displacement of the frequency of the bending vibrations of the OH bond towards higher frequencies for hydroxide solutions indicate strong hydrogen bonding between the OH^– ion and the H₂O molecule. The comparatively low heat of hydration of the OH^– ion (111 cal/mole) compared with the heat of hydration of the H₊ ion (276 cal/mole) cannot, as has been shown, serve as proof that there is no strong electrostatic bond between the OH^– ion and a water molecule. All the heat of hydration is used up in the formation of this bond; this can be regarded as additional confirmation of the hydrophobic nature of the ion produced. The experimental data on the absolute value of the chemical shift of the proton of the H₃O₂ ^– ion indicate the important role played by the excited state of the proton in this complex. This conclusion agrees with the spectroscopic data.M. V. Lomonosov Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 12, No. 6, pp. 969–974, November–December, 1971.     

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/₅NO^3– ion, which then undergoes a slow dissociation to form Fe/CN/₄NO^2–. Only a small isotope effect k_H/k_D=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.Dedicated to Professor Schulte-Frohlinde on the occasion of his 60th birthday.     

Gamma radiolysis of nitrilotriacetic acid (NTA) in aqueous solutions

Aqueous solutions of nitrilotriacetic acid (NTA) were irradiated with gamma-rays. In deaerated acidic solutions G (IDA, iminodiacetic acid) was found to be 3.0 and in aerated solutions 2.7. Both H and OH radicals abstracted alpha hydrogen from the NZA molecule. The dehydrogenated radical disproportionated to NTA and IDA; however in presence of air, the radical added with O₂ to give peroxy intermediate which was hydrolyzed to IDA and HO₂. The rate constants, for the reaction of OH-radical with NTA at pH 2.0, 6.0 and 10.0 as determined by competition kinetic methods were 0.61·10⁸, 5.5·10⁸ and 42·10⁸ dm³·mol^–1·s^–1, respectively. These indicated that the unprotonated form of NTA is more reactive than its protonated form. This has been attributed to the deactivation of alpha-hydrogen centers by protons through inductive effect.     

NOx-Sorbing Metal Oxides, MnOx–CeO2. Oxidative NO Adsorption and NOx–H2 Reaction

(n)MnO_x–(1–n)CeO₂ binary oxides have been studied for the sorptive NO removal and subsequent reduction of NO_x sorbed to N₂ at low temperatures (150 °C). The solid solution with a fluorite-type structure was found to be effective for oxidative NO adsorption, which yielded nitrate (NO^– ₃) and/or nitrite (NO^– ₂) species on the surface depending on temperature, O₂ concentration in the gas feed, and composition of the binary oxide (n). A surface reaction model was derived on the basis of XPS, TPD, and DRIFTS analyses. Redox of Mn accompanied by simultaneous oxygen equilibration between the surface and the gas phase promoted the oxidative NO adsorption. The reactivity of the adsorbed NO_x toward H₂ was examined for MnO_x–CeO₂ impregnated with Pd, which is known as a nonselective catalyst toward NO–H₂ reaction in the presence of excess oxygen. The Pd/MnO_x–CeO₂ catalyst after saturated by the NO uptake could be regenerated by micropulse injections of H₂ at 150 °C. Evidence was presented to show that the role of Pd is to generate reactive hydrogen atoms, which spillover onto the MnO_x–CeO₂ surface and reduce nitrite/nitrate adsorbing thereon. Because of the lower reducibility of nitrate and the competitive H₂–O₂ combustion, H₂–NO reaction was suppressed to a certain extent in the presence of O₂. Nevertheless, Pd/MnO_x–CeO₂ attained 65% NO-conversion in a steady stream of 0.08% NO, 2% H₂, and 6% O₂ in He at as low as 150 °C, compared to ca. 30% conversion for Pd/–Al₂O₃ at the same temperature. The combination of NO_x-sorbing materials and H₂-activation catalysts is expected to pave the way to development of novel NO_x-sorbing catalysts for selective deNO_x at very low temperatures.     

About the OH yield in the radiolysis of an aqueous/H2O2 system. Its optimisation for water treatment

Unless the radiolytic reducing species are neutralised or converted into oxidising species, an EB remediation system cannot be considered a true Advanced Oxidation Processes (AOP). A water/H₂O₂ system irradiated by UVC mercury lamps constitutes a widely used OH production method. Employing H₂O₂ in radiolysis as well, an enhancement of the oxidative efficiency of an EB treatment can be obtained. Pulse radiolysis measurements of an aerated aqueous/H₂O₂/KSCN system have been systematically undertaken to assess the optimal H₂O₂ concentration. By linearly fitting a competition kinetics relationship, it is found that the scavengeable extra-yield of OH is ΔG(OH)=0.24 μmol J^?1 (R=0,9958), while the maximum experimental yield is measured G(OH)_max=(0.52±0.02) μmol J^?1 when [H₂O₂]=5–10 mM. Exceeding these concentrations the OH yield drops off.     

Vibrational spectral studies of ion-ion and ion-solvent interactions. I. Zinc nitrate in water

Raman and infrared line parameters of Zn(NO₃)₂-H₂O systems ranging from dilute solutions (25°C) to ionic liquids of low water content (75°C) are reported. At 25°C the solutions contain a very low concentration of inner sphere [Zn(ONO₂)(H₂O)₅]⁺, outer sphere [Zn(H₂O)₆]²⁺[NO₃]^–, Zn(H₂O) ₆ ²⁺ , and NO ₃ ^– (aq.). In the ionic liquids the ion triplet also exists. Manifestations of a change from the octahedral coordination of zinc to tetrahedral coordination when the water content is very low include the appearance of a 285 cm^–1 band from the zinc nitrate bond and a shift to higher frequencies of the band from zinc-water.     

Pulse radiolysis study of the reactivity of metal complexes of DTPA /diethylene triamine pentaacetic acid/ with OH radicals in aqueous solutions

Using the pulse radiolysis competition kinetic technique, OH radical rate constants with 12 metal DTPA complexes were determined in neutral aerated aqueous solutions. They are in the range of /1.3–5.9/×10⁹ dm³ mol^–1s^–1. To a first approximation, the rate constant was found to decrease linearly with an increase in the field strength of the metal ion (q/r²).     

Simulation of radiation-chemical transformations in aqueous nitric oxide and nitrite solutions

A kinetic model of radiation-chemical transformations of nitrogen oxide and nitrites in aqueous solutions is proposed. It includes the previously developed reaction scheme for water and H₂, H₂O₂, and O₂ solutions complemented by the reactions of water radiolysis products with NO and NO₂⁻. It has been shown that the model describes well experimental data on the decomposition of the compounds and the buildup of products depending on the absorbed dose in aqueous solutions at different pH values.     

Ferrous ion oxidations by √H, √OH and H2O2 in aerated FBX dosimetry system

In the ferrous ion, benzoic acid and xylenol orange (FBX) dosimetric system, benzoic acid (BA) increases the G(Fe³⁺) value. Xylenol orange (XO) controls the BA sensitized chain reaction as well as forms a complex with Fe³⁺. In the aerated FBX system each √H, √OH and H₂O₂ oxidizes 8.5, 6.6 and 7.6 Fe²⁺ ions, respectively; and these values respectively increase to 11.3, 7.6 and 8.6 in oxygenated solution. About 8% √OH reacts with XO and the remaining with BA. The above fractional values are due to this competition. This √OH reaction with XO oxidizes 1.8% and 2.1% ferrous ions only in aerated and oxygenated solutions, respectively. There is a competition between √H reactions with O₂ and with BA, but both lead to the production of H₂O₂. The oxidation of Fe²⁺ by √OH reactions at different concentrations of H₂O₂ is linear with absorbed dose while the √H reactions make the oxidation of Fe²⁺ non-linear with dose. This is due to competition reaction of H-adduct of BA between O₂ and Fe³⁺.     

Effect of outer cations and water of crystallization on the radiolytic decomposition of nitrates

The -ray induced decomposition of several inorganic nitrates CsNO₃, TlNO₃, Mg/NO₃/₂.6H₂O, Ca/NO₃/₂.4H₂O, Hg/NO₃/₂, Hg/NO₃/₂.2H₂O, Pb/NO₃/₂ and Al/NO₃/₃.9H₂O has been studied at an absorbed dose of {5 Mrads. G/NO ₂ ^– / is affected by the outer cation and depends mainly on its valency and ionic size. G/NO ₂ ^– / for hydrated mercuric nitrate is always higher as compared to that for the anhydrous mercuric nitrate at various doses. Water of crystallization might provide extra factors to facilitate the decomposition of the hydrated nitrate compared to that for the anhydrous salts. In most cases G/NO ₂ ^– / decreases exponentially with dose but in cases of CsNO₃, Mg/NO₃/₂.6H₂O and Al/NO₃/₃.9H₂O it varies linearly.     

Radiation-induced decomposition of cyclotrimethylenetrinitramine in aqueous solutions

Radiation-induced decomposition of cyclotrimethylenetrinitramine, a representative of heterocyclic nitramines, in dilute aqueous solutions saturated with argon, air, and N₂O has been investigated. Dose dependence curves have been obtained, and the initial yields of formation of nitrite ions and hydrogen peroxide have been measured, making up 0.122 and 0.049 in deaerated solutions, 0.050 and 0.065 in aerated solutions, and 0 and 0.074 μmol/J in N₂O-saturated solutions, respectively. The main radiolysis initial steps involve the reaction of dissociative electron capture with nitro-group elimination in the form of nitrite ion and the reaction of hydrogen atom abstraction from the methylene group by hydroxyl radicals and atomic hydrogen.