Effects of B vitamins on the radiation-induced transformations of hydroxyl-containing organic compounds

In this work, the interaction of B vitamins with α-hydroxyl-containing carbon-centered radicals formed upon the irradiation of deaerated aqueous solutions of ethanol, ethylene glycol, α-methylglycoside, maltose, and α-glycerophosphate at pH 7 was studied by means of continuous radiolysis. Within the framework of the density functional theory, the homolytic bond dissociation enthalpies (BDEs) of -C-H, -O-H, and -N-H bonds and H-atom addition enthalpies (HAEs) at the -C=O and -C=N groups of the test compounds were calculated. The set of the experimental and theoretically calculated data suggests that vitamin B₂, nicotinamide and pyridoxal phosphate effectively oxidize α-hydroxyl-containing carbon-centered radicals, whereas vitamins B₁ and B₆ reduce these radicals to prevent their recombination and fragmentation reactions.     

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.     

Investigation of radiochemical conversions in extraction systems based on tributyl phosphate

The use of halogenated organic compounds under the effect of ionizing radiation requires a comprehensive knowledge of their radiation stability. There is little experimental evidence on the radiolysis of fluorine-containing organic compounds in the literature, while a theoretical generalization enabling one to predict the main radiolysis pathways is completely lacking. This paper is concerned with the identification of stable radiolysis products of trichloromethyl-1,1,2-trifluoro-2,2-dichloroethyl ether (C₃F₃Cl₅ O), γ-irradiated separately and the extraction system based on tributyl phosphate. Practically all the C₃F₃Cl₅O radiolysis products were identified with the aid of gas-liquid chromatography, GC-MS, IR, UV and NMR spectroscopy and elemental analysis. Upon C₃F₃Cl₅O radiolysis, the formation of CCl₄, Cl₂, COCl₂, C₂ Cl₆, freons of various composition and long-chained ethers like CFCl₂−CF₂−O−CCl₂−CCl₃ takes place. The identification of radiolysis products allows to draw well-founded conclusions on the mechanism of C₃F₃Cl₅O radiolysis, representing a wide class of chlorine- and fluorine-containing organic compounds.     

Radiolysis of pyridoxine (vitamin B6) in aqueous solution under different conditions

Aqueous solutions of pyridoxine (1 mM) without or with additive of K₃[Fe(CN)₆] (2.5 mM) were gamma-irradiated at different doses and dose rate of 2.16 kGy/h in the absence of air, in the presence of air or by their saturation with N₂O. The radiolytic products were analyzed with HPLC, mass spectrometry and UV spectroscopy. 2,4,5-Trihydroxymethyl-3-pyridinol, pyridoxal, isopyridoxal and 6-hydroxypyridoxine were formed by radiolysis in the absence of K₃[Fe(CN)₆], and their concentrations were much higher in samples saturated with N₂O. Pyridoxi-3,6-quinone was found by radiolysis under all the above-mentioned conditions but only in the presence of K₃[Fe(CN)₆]. Besides, the pyridoxal formation increased in the presence of this oxidizing agent. G values of pyridoxal formation and pyridoxine degradation were quantified. Some details of the radiolytic product formation were discussed.     

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.     

Radiation chemistry of CF2 Cl2 in the gas and liquid phases: Effect of doses rate

The dose rate dependence of CF₂ Cl₂ decomposition was studied in both, gas and liquid phase, for the range of 2.95·10^{1 7}–1.9·10^{1 9} eV·g^–1·h^–1. The major products were found to be CF₃Cl, CFCl₃, CF₂Cl–CF₂Cl and CF₂Cl–CFCl₂. The decomposition of CF₂Cl₂ was found to decrease with decreasing dose rate for the liquid phase, while an opposite trend was found for gas phase radiolysis. A new mechanism which explains these contrasting findings was suggested. The contribution of radical and of ionic (or molecular) processes to the yields of the various products was estimated.     

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.     

Yields of light products in radiolysis of binary mixture isooctane-benzene and isooctane-hexafluoro-benzen

Radiolysis of binary mixtures isooctance-benzene and isooctane-hexafluorobenzene has been studied. The yields of light products of isooctane radiolysis, namely, G/H₂/, G/CH₄/, G/C₄H₁₀/ and G/C₄H₈/, have been determined for various electron ratios of benzene- and hexafluorobenzene. The acceptance of positive charges with benzene and of electrons with hexafluorobenzene is reponsible for deviations of radiation-chemical yields towards negative side from the additivity rule. Positive deviation of G/CH₄/, G/C₄H₁₀/ and G/C₄H₈/ yields at is attributed to indirect ionization of isooctane. Monomolecular reactions of C₈H ₁₈ ⁺ have been discussed.     

Radiolysis and corrosion of238Pu-doped UO2 pellets in chloride brine

Deaerated 5 M NaCl solution is irradiated in the presence of UO₂ pellets with α-radiation from²³⁸Pu. Experiments are conducted with²³⁸Pu doped pellets and others with²³⁸Pu dissolved in the brine. The radiolysis products and yields of mobilized U and Pu from the oxidative dissolution of UO₂ are determined. Results found for radiolysis products and for the oxidation/dissolution of pellets immersed in Pu containing brine are similar to results for Pu doped pellets, where the radiation chemical processes occur only in the liquid layer of some 10 σm thickness adjacent to the pellet. The yield of radiolysis products is comparable to earlier results, that of mobilized U from the pellets is < 1% of the total amount of oxidized species. Thus, the radiation chemical yield (G-value) for mobilized hexavalent U is < 0.01 ions/100 eV. In spite of the low radiation yield for the corrosion, the rate of UO₂dissolution is higher than expected for the concentrations of long-lived oxidizing radiolysis compounds found in the solutions.     

Simultaneous Spectrophotometric Determination of Group B Vitamins Using Parallel Factor Analysis: PARAFAC

In this work, a simple and rapid analytical procedure was applied for simultaneous determination of folic acid (vitamin B₀), thiamin (vitamin B₁), riboflavin (vitamin B₂) and pyridoxal (vitamin B₆) based on the absorbance data in the pH range 2.0‐12.0 at 25 °C using parallel factor analysis (PARAFAC). The effect of the pH as the most important factor on the sensitivity of the determination was studied. The spectral data were recorded in 400‐650 nm intervals and a 2‐12 pH range for all four vitamins. The calibration set was constructed in the concentration ranges of 4‐22, 1‐20, 6‐26, and 4‐20 μg mL^?;1 for B₆,B₂,B₁ and B₀, respectively. The root mean squares errors of prediction for the prediction set, (RMSEP), are 0.65, 0.63, 1.13 and 0.34 for B₀,B₁,B₂ and B₆, respectively. The recovery percent for the validation set are in the range of 90.6 to 107.0%. The effect of the experimental conditions and diverse species were discussed. The optimum values of these factors were searched according to the relative standard deviation of the prediction set of mixtures solutions.     

Calcination of SiO2-Aerogel in Inert Atmosphere

Thermal treatment of SiO₂-aerogel in inert atmosphere, in contrary to oxidizing atmosphere, yields a series of gas products with great range of mole masses (12–154 g mol^–1) and every product has specific way of evolving. These substances are represented by CO, CO₂, CH₄, CH₃OH, C₂H₆, C₂H₄ and aromates. Part of evolving products, which are formed during catalytic condensation, is trapped under the surface and after carbonisation it causes opacity of surface layer of aerogel.This revised version was published online in November 2005 with corrections to the Cover Date.     

The mechanism of the photochemical reactions of SO2 with isobutane excited at 3130 Å

The mechanism of the reactions of electronically excited SO₂ with isobutane has been studied through the measurement of the initial quantum yields of product formation in 3130 Å irradiated gaseous binary mixtures of SO₂ and isobutane and ternary mixtures of SO₂, isobutane, C₆H₆ or CO₂. Under low-pressure conditions (P < 10 torr) the kinetic treatment of the present data shows that only one singlet and one triplet state, presumably the ¹B₁ and ³B₁ states, are involved in the photoreaction mechanism. The data give k_2a = 8.4 × 10⁹; SO₂(¹B₁) + isobutane → products (2a); k_5a ? k₅ = 8.7 × 10⁸ l./mol·sec; SO₂(³B₁) + isobutane → products (5a) SO₂(³B₁) + isobutane → (SO₂) + isobutane (5b) k_1a/k₁ = 0.145 ± 0.037; SO₂(¹B₁) + SO₂ → SO₂(³B₁) + SO₂ (1a) SO₂(¹B₁) + SO₂ → (2SO₂) (1b) k_2b/k₂ = 0.273 ± 0.018; SO₂(¹B₁) + isobutane → SO₂(³B₁) + isobutane (2b); SO₂(¹B₁) + isobutane → (SO₂) + isobutane (2c) error limits are ± 2 σ. The contribution from the excited SO₂(¹B₁) molecules to the quantum yields of the photolyses of SO₂–isobutane mixtures is not negligible. Under high-pressure conditions (P > 10 torr) the low-pressure mechanism coupled with the saturation effect on the phosphorescence lifetimes of SO₂(³B₁) molecules cannot alone rationalize the quantum yields. The evaluation suggests that some nonradiative intermediate state (X) is involved in the formation of “extra” triplet molecules. This ill-defined state decays largely nonradiatively to SO₂ in experiments at low pressures, X → SO₂ (12). In the presence of C₆H₆ the low-pressure data give k₇ = (8.5 ± 1.8) × 10¹⁰, and the high-pressure data give k₇ = (8.3 ± 0.6) × 10¹⁰ and (9.9 ± 0.9) × 10¹⁰l./mol·sec; SO₂(³B₁) + C₆H₆ → nonradiative products (7). These estimates are in good agreement with values directly measured from low-pressure lifetime studies, (8.1 ± 0.7) × 10¹⁰ and (8.8 ± 0.8) × 10¹⁰l./mol·sec.     

Radiolysis of aqueous oxygen-free solutions of tryptophan at various pH values

Gamma radiolysis of 10^–2M aqueous oxygen-free tryptophan solutions irradiated at various pH values and in a N₂O atmosphere was investigated. The values of the radiation losses of tryptophan and the yields of NH₃ were determined. Using HPLC with an electrochemical detector the formation of hydroxylated radiation products of tryptophan was followed and the effect of pH on the radiolysis course discussed.     

The B6‐vitamer Pyridoxal is a Sensitizer of UVA‐induced Genotoxic Stress in Human Primary Keratinocytes and Reconstructed Epidermis

UVA‐driven photooxidative stress in human skin may originate from excitation of specific endogenous chromophores acting as photosensitizers. Previously, we have demonstrated that 3‐hydroxypyridine‐derived chromophores including B₆‐vitamers (pyridoxine, pyridoxamine and pyridoxal) are endogenous photosensitizers that enhance UVA‐induced photooxidative stress in human skin cells. Here, we report that the B₆‐vitamer pyridoxal is a sensitizer of genotoxic stress in human adult primary keratinocytes (HEKa) and reconstructed epidermis. Comparative array analysis indicated that exposure to the combined action of pyridoxal and UVA caused upregulation of heat shock (HSPA6, HSPA1A, HSPA1L, HSPA2), redox (GSTM3, EGR1, MT2A, HMOX1, SOD1) and genotoxic (GADD45A, DDIT3, CDKN1A) stress response gene expression. Together with potentiation of UVA‐induced photooxidative stress and glutathione depletion, induction of HEKa cell death occurred only in response to the combined action of pyridoxal and UVA. In addition to activational phosphorylation indicative of genotoxic stress [p53 (Ser15) and γ‐H2AX (Ser139)], comet analysis indicated the formation of Fpg‐sensitive oxidative DNA lesions, observable only after combined exposure to pyridoxal and UVA. In human reconstructed epidermis, pyridoxal preincubation followed by UVA exposure caused genomic oxidative base damage, procaspase 3 cleavage and TUNEL positivity, consistent with UVA‐driven photooxidative damage that may be relevant to human skin exposed to high concentrations of B₆‐vitamers.     

Pulse radiolysis study of I− oxidation with radical anions Cl2 ⋅− in an aqueous solution

Radiation-chemical transformations of chloride solutions in the presence of iodide additives were studied by pulse radiolysis. Radical anion Cl₂ ^⋅− oxidize I⁻ ion, while in the secondary reactions Cl₂ reacts with I⁻ to form a mixed trihalide ion ICl₂ ⁻. A reaction model that satisfactorily describes the experimental data was proposed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1336–1340, June, 2005.     

ESR study of low-temperature radiolysis and photolysis of substitutedN′-furfurylidenebenzhydrazides

Low-temperature (77 K) γ- and UV irradiation of substitutedN′-furfurylidenebenzhydrazides produces paramagnetic particles in radiation-chemical yields of (0.05–0.5)/100 eV and quantum yields of 4·10⁻⁵–10⁻³, respectively. ESR study showed that hydrazyl radicals and HC·O and N·O₂ are the main products of radiolysis and photolysis, and the latter decay upon heating of the sample to 190 K, whereas the hydrazyl radicals survive up to 423 K. Further heating results in thermodestruction of the hydrazides, and the ESR spectrum exhibits only a singlet with splitting at 1 mT, which is characteristic of polyconjugated compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2078–2082, November, 1999.     

Effects of coenzyme Q<Subscript>0</Subscript>, ascorbic acid,and its glycoside on the radiation-induced dephosphorylation of organic phosphates in aqueous solutions

The effects of coenzyme Q₀, ascorbic acid, and 2-O-α-D-glucopyranosylascorbic acid on the radiation-induced dephosphorylation of 1-glycerophosphate, glucose-1-phosphate, and glucose-6-phosphate in deaerated aqueous solutions at pH 7 were studied by means of continuous radiolysis. It was found that the test compounds efficiently suppressed the radiation-induced dephosphorylation of organic phosphates in equimolar concentrations by interactions with water radiolysis products. At an organic phosphate to additive concentration ratio of 100: 1, ascorbic acid and coenzyme Q₀ can suppress the radiation-induced dephosphorylation of the initial substances in aqueous solutions by the reduction and oxidation of hydroxyl-containing carbon-centered radicals, respectively.     

辐照气氛对异丙氧基杯[4]冠-6辐解的影响

异丙氧基杯[4]冠-6(1,3-交替-25,27-二(2-丙氧基)杯[4]芳烃-26,28-冠-6, 简称BPC6)对高放废液中的放射性Cs离子具有很好的选择萃取性能, 然而在萃取过程中BPC6 会受到强辐射场辐照, 所以有必要研究其辐射稳定性. 本文应用气相色谱(GC)、傅里叶变换显微红外(Micro-FTIR)和核磁共振(NMR)谱等手段分析了BPC6 固体分别在O₂和N₂气氛下的γ辐照效应. 结果表明, 当剂量为1 MGy时, O₂气氛下BPC6 的辐解率明显高于N₂(分别约为10.4%和2.5%), 而且气体辐解产物也有很大差异, 在O₂气氛下主要为H₂、CH₄、CO和CO₂,而在N₂辐照气氛下还有C₂H₄、C₂H₆、C₃H₆和C₃H₈等产物. 通过综合分析气体与固体辐解产物, 我们提出BPC6在不同气氛下具有不同的辐解途径, 这将为BPC6 萃取体系的辐射效应研究提供新的方法与思路, 加深对其辐解机理的认识.     

A phosphate catalyzed reaction of iodine with hydrazine in aqueous solutions

Pulse radiolysis was utilized to study the kinetics of the iodine-hydrazine reaction in aqueous solutions containing phosphate buffer in the pH range 5.5 to 7. The reaction rate was found to be proportional to and [I^–]^–1, but did not show simple proportionality to [H⁺]^–1 and was considerably higher than that found earlier when the pH of solutions was adjusted with HClO₄ or H₃BO₃. The results are in a formal agreement with the assumption that in phosphate buffered solutions a complex N₂H₄. HPO ₄ ^2– is formed, reacting with I₂ with a rate constant which is greater than that ascribed earlier to the reaction of N₂H₄ with I₂/Ref. 1/.