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Silybin (extracted from Silybum marianum) is the major active constituent of silymarin which possesses a wide range of medicinal properties. These properties may be, in part, due to the potent scavenging capacity of oxidizing free radicals. In this context, scavenging radicals (hydroxyl, azide, dibromide anion radicals, nitrite, carbonate, etc.) of silybin have been studied to understand the mechanistic aspects of its action against free radicals. The transients produced in these reactions have been assigned and the rate constants have been measured by pulse radiolysis techniques. Reduction potential determined both by cyclic voltammetry gave a value 0.62+/-0.02 V vs NHE at pH 9. Quantum chemical calculations have been performed to further confirm the different activities of individual hydroxyl groups with the difference of heat of formation. Moreover, silybin also protected plasmid pUC18 DNA from soft X-ray radiation which induced strand breaks. These results are expected to be helpful for a better understanding of the anti-oxidative properties of silybin.

The radiation-induced reactions of a water-soluble coumarin derivative, coumarin-3-carboxyl acid (C3CA), have been investigated in aqueous solutions by pulse radiolysis with a 35 MeV electron beam, final product analysis following 60Co γ-irradiations and deterministic model simulations. Pulse radiolysis revealed that C3CA reacted with both hydroxyl radicals (•OH) and hydrated electrons (e− aq) with near diffusion-controlled rate constants of 6.8 × 109 and 2.1 × 1010 M−1 s−1 was not confirmed by pulse radiolysis. Production of the fluorescent molecule, 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), was confirmed by final product analysis with a fluorescence spectrometer coupled to a high performance liquid chromatography (HPLC) system. Production yields of 7OH-C3CA following 2• − was not confirmed by pulse radiolysis. Production of the fluorescent molecule, 7-hydroxy-coumarin-3-carboxylic acid (7OH-C3CA), was confirmed by final product analysis with a fluorescence spectrometer coupled to a high performance liquid chromatography (HPLC) system. Production yields of 7OH-C3CA following 60Co γ-irradiations depended on the irradiation conditions and ranged from 0.025 to 0.18 (100 eV) −1. Yield varied with saturating gas, additive and C3CA concentration, implying the presence of at least two pathways capable of providing 7OH-C3CA as a stable product following the scavenging reaction of C3CA with •OH, including a peroxidation/elimination sequence and a disproportionation pathway. A reaction mechanism for the two pathways was proposed and incorporated into a deterministic simulation, showing that the mechanism can explain experimentally measured 7OH-C3CA yields with a constant conversion factor of 4.7% from •OH scavenging to 7OH-C3CA production, unless t-BuOH was added. [ABSTRACT FROM AUTHOR]

The flavonolignans (silybin and analogues) are important natural compounds with multiple biological activities operating at various cell levels. Many of these effects are connected with their radical scavenging activities. In the present study, free-radical scavenging and antioxidant activities of four natural flavonoids, namely silybin, naringenin, naringin, and hesperetin, have been studied using nanosecond pulse radiolysis techniques. The kinetics and mechanisms of the reactions of silybin and analogues with various oxidizing radicals (such as •OH,N3•, CCl3OO•, SO4•−) have been investigated. Furthermore, the transient species has been assigned and radical scavenging rate constants have also been measured. Moreover, the structure-activity relationships between chemical structures of the flavonoids and their radical scavenging activities are further analayzed by theoretical calculation. Combined our previous observation of the fast reparation of DNA damage and efficient DNA protection against radiation damage in vitro, it can be confirmed that test flavonoids are promising molecules to be used for their potential antioxidant properties. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 590-597, 2011 [ABSTRACT FROM AUTHOR]

Abstract: The absorption spectra of solvated electrons in pentanol, hexanol and octanol are measured from 22 to 200, 22 to 175 and 50 to150°C, respectively, at a fixed pressure of 15MPa, using nanosecond pulse radiolysis technique. The results show that the peak positions of the absorption spectra have a red-shift (shift to longer wavelengths) as temperature increases, similar to water and other alcohols. Including the above mentioned data, a compilation of currently available experimental data on the energy of absorption maximum (E max) of solvated electrons changed with temperature in monohydric alcohols, diols and triol is presented. E max of solvated electron is larger in those alcohols that have more OH groups at all the temperatures. The molecular structure effect, including OH numbers, OH position and carbon chain length, is investigated. For the primary alcohols with same OH group number and position, the temperature coefficient increases with increase in chain length. For the alcohols with same chain length and OH numbers, temperature coefficient is larger for the symmetric alcohols than the asymmetric ones. [ABSTRACT FROM AUTHOR]

Abstract: The absorption spectra of the hydrated electron in concentrated LiCl, LiClO4, Li2SO4, MgCl2 and Mg(ClO4)2 deuterated water solutions were measured by pulse radiolysis techniques from room temperature to 300°C at a constant pressure of 25MPa. With increasing temperature, the absorption band of the solvated electron for all solutions shifts to larger wavelengths. Whatever the temperature, shifts to shorter wavelengths of the absorption spectrum were observed as salt effects. The results on the shape and broadening of the absorption spectrum are discussed. [Copyright &y& Elsevier]

Abstract: In order to study radiation-induced fast phenomena, a new pulse radiolysis system with higher time resolution based on pulse-and-probe method was developed and utilized for practical work. A few picosecond electron beam generated from a linear accelerator, in which a laser photocathode RF-gun is introduced, was synchronized with a femtosecond laser pulse which is employed as the analyzing light. The synchronization precision between them was suppressed within 1.6ps (rms). Converting the fundamental laser into white light continuum or optical parametric amplification allows to measure in the wide wavelength from visible to infrared region. [Copyright &y& Elsevier]

Abstract: The reactions between edaravone and various one-electron oxidants such as OH, , , and , have been studied by pulse radiolysis techniques. The transient species produced by the reaction of edaravone with OH radical shows an absorption band with λ max =320nm, while the oxidation by , , and CCl3OO results in an absorption band with λ max =345nm. Different from the previous reports, the main transient species by the reaction of edaravone with OH radical in the absence of O2 is attributed to OH-adducts. At neutral condition (pH 7), the rate constants of edaravone reacting with OH, , , CCl3OO , and are estimated to be 8.5×109, 5.8×109, 6×108, 5.0×108 and 2.4×109 dm3 mol−1 s−1, respectively. From the pH dependence on the formation of electron adducts and on the rate constant of edaravone with hydrated electron, the pK a of edaravone is estimated to be 6.9±0.1. [Copyright &y& Elsevier]

Transient radicals (hydrated electron, (SCN)[sub 2][sup .-] and CO[sub 3][sup .-]) formed in supercritical water have been observed by the pulse radiolysis technique. The change of spectra of these radicals with temperature has been measured. It was found that the spectra and absorption coefficients of the radicals, e[sup -][sub aq] and (SCN)[sub 2][sup .-], are strongly dependent on the temperature of the water. Since it was found that the absorption spectrum and molar absorption coefficient of CO[sub 3][sup .-] radical seem to be almost independent of temperature, G-values of OH and e[sup -][sub aq] could be derived. Then, the absolute values of the absorption coefficients for the radicals could be calculated. The G-values of the radical products in water radiolysis tend to increase with increasing temperature up to 400°C. Based on the above observation, radiolysis of supercritical water is discussed. [ABSTRACT FROM AUTHOR]

Abstract: In the present work, laser photolysis techniques have been used to study the transient species of silybin (abbreviated as SLB) in ethanol solutions. It has been demonstrated that the exposure of silybin to 248nm excimer laser gives rise to monophotonic ionization with a high quantum yield. The transient species have been identified, and a series of related kinetics parameters have also been obtained. For the sake of comparison, we approached the problem using another way to reduce silybin, i.e. attack of solvated electrons, esol −, produced in pulse radiolysis. The rate constant for reaction of esol − was determined to be 3.8×109 dm3 mol−1 s−1 at 720nm, which is consistent with 4.6×109 dm3 mol−1 s−1, obtained by laser photolysis. [Copyright &y& Elsevier]

Abstract: The absorption spectra of solvated electrons in 1-propanol and 2-propanol have been investigated from 22 to 270°C at a fixed pressure of 7MPa, by using both nanosecond pulse radiolysis and laser photolysis techniques. The results show that, even up to supercritical conditions, it is still possible to measure unambiguously the absorption spectra of solvated electron in these two propanols. The peak positions of the absorption spectra show a red-shift (shifts to longer wavelengths) as temperature increases, similar to water and other alcohols, but the temperature efficiency, dE max/dT, of 1-propanol is larger than that of 2-propanol. In addition, in clear contrast to that of pulse radiolysis, in laser photolysis experiments, an increase in the maximum absorbance of the absorption spectra of solvated electron with temperature up to ∼200°C is attributed to the increase of absorbance (CTTS absorption band) of I− anion at 248nm with increasing temperature. [Copyright &y& Elsevier]

Abstract: γ-Radiolysis and pulse radiolysis of phenol in aqueous solution up to supercritical condition have been carried out. G-values of phenol consumption and product formation have been determined. While dihydroxybenzenes were major products at room temperature, multi-ring compounds and benzene were formed above 300°C. This indicates reaction mechanism was changed above 300°C, where phenoxyl radical plays a predominant role. This is supported by the observation of phenoxyl radical in pulse radiolysis. In supercritical water, the G-values increased with decrease of density. [Copyright &y& Elsevier]

Graphical abstract Highlights • Fast reaction rate and high separation ratio of Re from aqueous solution were performed by γ irradiation. • Re(0) was produced together with ReO 2 and ReO 3 for the first time by γ irradiation. • Both steady state study and pulse radiolysis study were conducted. • OH− was believed to be coordinated with Re(VI) thus affecting the reaction rate. Abstract Rhenium (Re) is a good nonradioactive alternative of technetium-99 (99Tc), which is a β emitter causing long-term radioactive toxicity due to its long half-life and high yield in nuclear reactors. TcO 4 −, the dominant form of 99Tc, is very easy to migrate in the environment because of its high solubility. In this work, γ irradiation was applied to separate rhenium from aqueous solution in the presence of isopropanol. Re(VII) was reduced by hydrated electrons (e aq −) generated from γ-radiolysis of water, leading to the formation and precipitation of Re(0) and rhenium oxides (ReO 2 and ReO 3) nanoparticles. It was the first time that Re(0) was observed in the reduction products of Re(VII) by γ irradiation, which was confirmed by HR-TEM, EDX, XPS and XRD. The reduction of Re(VII) by γ irradiation was very fast and efficient in alkaline condition, whose separation ratio reached 93.6% after 2-h irradiation and the final separation ratio was as high as 98.1%. Increase in absorbed dose rate, isopropanol concentration, and pH, was conducive to the separation of Re overall. Further studies on the transient species by pulse radiolysis revealed that OH− might coordinate with the intermediate Re(VI) forming different complexes with different concentrations of OH−, thus affecting the reduction of Re(VII). This work not only demonstrates that γ irradiation could be a promising method for the efficient separation of Re(VII), but also gives a better understanding in the reaction mechanism. [ABSTRACT FROM AUTHOR]

Solvatochromic shift of 4,4′-bpyH in aqueous solutions at elevated temperatures up to supercritical conditions and in various organic solvents with different dielectric constants, is investigated by pulse-radiolysis technique. 4,4′-bpyH shows a stronger solvent–solute interaction in water than in organic solvents, perhaps due to the hydrogen bond between 4,4′-bpyH and water. At 380 °C, local density augmentation, namely ρ local – ρ bulk , in supercritical water becomes 280 kg m −3 ( ρ bulk = 208 kg m −3 ), and the density enhancement factor is 8.9. Density fluctuation maximizes when ρ bulk is around 120 kg m −3 . Density inhomogeneity decreases as temperature rises, but is still remarkable at 400 °C. [ABSTRACT FROM AUTHOR]