Dynamics of ionized poly(4-hydroxystyrene)-type resist polymers with tert-butoxycarbonyl-protecting group.

The imaging reactions of resist materials used for nano-patterning have become radiation-chemical reactions, with the shortening of wavelengths of the exposure light sources in lithography systems. The most widely used patterning materials in industrial lithography are chemically amplified resists (CAR). Understanding the deprotonation mechanism of ionized polymers (radical cations) is important for acid generation in CARs. In this study, the dynamics of radical cations in poly(4-hydroxystyrene) (PHS)-type resist polymers, partially and totally protected by tert-butoxycarbonyl (t-BOC) groups, are investigated using a combination of electron pulse radiolysis experiments, acid yield measurements, and quantum chemical calculations. The t-BOC(oxy) group exhibits π-electron-donating behavior in the monomer cation but changes to electron-accepting behavior in the polymer cation, owing to the interaction between substituents. The destabilization of radical cations due to decreased intramolecular charge resonance may contribute to the high deprotonation efficiency of t-BOC-capped PHS polymers.

Recovery of platinum group metal resources from high-level radioactive liquid wastes by non-contact photoreduction.

Recovery of platinum group metals (PGMs) including palladium (Pd), rhodium (Rh), and ruthenium (Ru) from high-level radioactive liquid waste (HLLW) possesses enormous environmental and economic benefits. A non-contact photoreduction method was herein developed to selectively recover each PGM from HLLW. Soluble Pd(II), Rh(III), and Ru(III) ions were reduced to insoluble zero-valent metals and separated from simulated HLLW containing neodymium (Nd) as a representative for lanthanides, another main component in HLLW. Detailed investigation on the photoreduction of different PGMs revealed that Pd(II) could be reduced under 254- or 300-nm UV exposure using either ethanol or isopropanol as reductants. Only 300-nm UV light enabled the reduction of Rh(III) in the presence of ethanol or isopropanol. Ru(III) was the most difficult to reduce, which was only realized by 300-nm UV illumination in isopropanol solution. The effects of pH was also studied, suggesting that lower pH favored the separation of Rh(III) but hindered the reduction of Pd(II) and Ru(III). A delicate three-step process was accordingly designed to achieve the selective recovery of each PGM from simulated HLLW. Pd(II) was reduced by 254-nm UV light with the help of ethanol in the first step. Then Rh(III) was reduced by 300-UV light in the second step after the pH was adjusted to 0.5 to suppress the Ru(III) reduction. In the third step, Ru(III) was reduced by 300-nm UV light after isopropanol was added and the pH was adjusted to 3.2. The separation ratios of Pd, Rh, and Ru exceeded 99.8%, 99.9%, and 90.0%, respectively. Meanwhile, all Nd(III) still remained in the simulated HLLW. The separation coefficients between Pd/Rh and Rh/Ru exceeded 56,000 and 75,000, respectively. This work may provide an alternative method to recover PGMs from HLLW, which minimize the secondary radioactive wastes compared with other approaches.

Observation of dissociative quasi-free electron attachment to nucleoside via excited anion radical in solution.

Damage to DNA via dissociative electron attachment has been well-studied in both the gas and condensed phases; however, understanding this process in bulk solution at a fundamental level is still a challenge. Here, we use a picosecond pulse of a high energy electron beam to generate electrons in liquid diethylene glycol and observe the electron attachment dynamics to ribothymidine at different stages of electron relaxation. Our transient spectroscopic results reveal that the quasi-free electron with energy near the conduction band effectively attaches to ribothymidine leading to a new absorbing species that is characterized in the UV-visible region. This species exhibits a nearly concentration-independent decay with a time constant of ~350 ps. From time-resolved studies under different conditions, combined with data analysis and theoretical calculations, we assign this intermediate to an excited anion radical that undergoes N1-C1' glycosidic bond dissociation rather than relaxation to its ground state.

Effect of the solvation state of electron in dissociative electron attachment reaction in aqueous solutions.

It is generally considered that the pre-solvated electron and the solvated electron reacting with a solute yield the same product. Silver cyanide complex, Ag(CN)2-, is used as a simple probe to demonstrate unambiguously the existence of a different reduction mechanism for pre-hydrated electrons. Using systematic multichannel transient absorption measurements at different solute concentrations from millimolar to decimolar, global data analysis and theoretical calculations, we present the dissociative electron attachment on Ag(CN)2-. The short-lived silver complex, Ag0(CN)22-, formed by hydrated electron with nanosecond pulse radiolysis, can be observed at room temperature. However, at higher temperatures only the free silver atom, Ag0, is detected, suggesting that Ag0(CN)22- dissociation is fast. Surprisingly, pulse radiolysis measurements on Ag(CN)2- reduction, performed by a 7 ps electron pulse at room temperature, show clearly that a new reduced form of silver complex, AgCN-, is produced within the pulse. This species, absorbing at 560 nm, is not formed by the hydrated electron but exclusively by its precursor. DFT calculations show that the different reactivity of the hydrated and pre-hydrated electrons can be due to the formation of different electronic states of Ag0(CN)22-: the prehydrated electron can form an excited state of this complex, which mainly dissociates into Ag0CN- + CN-.

Deciphering the reaction between a hydrated electron and a hydronium ion at elevated temperatures.

The formation of a H˙ atom in liquid water from the reaction of a hydrated electron with a hydronium cation is a very challenging subject in chemical processes. Here picosecond pulse radiolysis measurements are performed at elevated temperatures, up to 350 °C, of acidic H2O and D2O solutions (up to 0.1 mol L(-1) HClO4) with the aim of investigating several issues related to this reaction. First, the red shift of the solvated electron absorption band in D2O with increasing temperature is found to be affected by the presence of D3O(+) in solution. The modified absorption spectra demonstrate the formation of a transient pair between D3O(+) and solvated electrons at elevated temperature (200-250 °C) when the concentration of D3O(+) is higher than 0.05 mol L(-1). For higher temperatures at 300 and 350 °C when the rate constant is almost diffusion controlled, the pair is no longer observable. Second, the presolvated electron in D2O is not scavenged up to 250 °C in solution containing 0.1 mol L(-1) D3O(+). Third, the decays in the picosecond range obtained under different conditions show that the rate constants are strongly affected by the temperature and by ionic strength. The model with an equation of log(k/k0) = 2A(I)(0.5)/1 + b(I)(0.5) gives a good fit of the experimental results by taking into account the variation of ionic strength, I, and, in particular, by considering the temperature dependence of the constant A.

Chemical repair activity of free radical scavenger edaravone: reduction reactions with dGMP hydroxyl radical adducts and suppression of base lesions and AP sites on irradiated plasmid DNA.

Reactions of edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) with deoxyguanosine monophosphate (dGMP) hydroxyl radical adducts were investigated by pulse radiolysis technique. Edaravone was found to reduce the dGMP hydroxyl radical adducts through electron transfer reactions. The rate constants of the reactions were greater than 4 × 10(8) dm(3) mol(-1) s(-1) and similar to those of the reactions of ascorbic acid, which is a representative antioxidant. Yields of single-strand breaks, base lesions, and abasic sites produced in pUC18 plasmid DNA by gamma ray irradiation in the presence of low concentrations (10-1000 µmol dm(-3)) of edaravone were also quantified, and the chemical repair activity of edaravone was estimated by a method recently developed by the authors. By comparing suppression efficiencies to the induction of each DNA lesion, it was found that base lesions and abasic sites were suppressed by the chemical repair activity of edaravone, although the suppression of single-strand breaks was not very effective. This phenomenon was attributed to the chemical repair activity of edaravone toward base lesions and abasic sites. However, the chemical repair activity of edaravone for base lesions was lower than that of ascorbic acid.

On the spur lifetime and its temperature dependence in the low linear energy transfer radiolysis of water.

In the spirit of the radiation chemical "spur model", the lifetime of a spur (τ(s)) is an important indicator of overlapping spurs and the establishment of homogeneity in the distribution of reactive species created by the action of low linear energy transfer (LET) radiation (such as fast electrons or γ irradiation). In fact, τ(s) gives the time required for the changeover from nonhomogeneous spur kinetics to homogeneous kinetics in the bulk solution, thus defining the so-called primary (or "escape") radical and molecular yields of radiolysis, which are obviously basic to the quantitative understanding of any irradiated chemical system. In this work, τ(s) and its temperature dependence have been determined for the low-LET radiolysis of deaerated 0.4 M aqueous solutions of H(2)SO(4) and pure liquid water up to 350 °C using a simple model of energy deposition initially in spurs, followed by random diffusion of the species of the spur during track expansion until spur overlap is complete. Unlike our previous τ(s) calculations, based on irradiated Fricke dosimeter simulations, the current model is free from any effects due to the presence of oxygen or the use of scavengers. In acidic solutions, the spur lifetime values thus obtained are in very good agreement with our previous calculations (after making appropriate corrections, however, to account for the possibility of competition between oxygen and Fe(2+) ions for H˙ atoms in the Fricke dosimeter, an effect which was not included in our original simulations). In this way, we confirm the validity of our previous approach. As expected, in the case of pure, oxygen-free water, our calculated times required to reach complete spur overlap are essentially the same (within uncertainty limits) as those found in acidic solutions. This explicitly reflects the fact that the diffusion coefficients for the hydrated electron and the H˙ atom that are involved in the overall calculation of the lifetime of spurs in neutral or acidic media, respectively, are of similar magnitude over the 25-350 °C temperature range studied.

Time-dependent yield of the hydrated electron in subcritical and supercritical water studied by ultrafast pulse radiolysis and Monte-Carlo simulation.

Fast kinetics and time-dependent yields of the hydrated electron (e(-)(aq)) in pure water under conditions of high temperature and pressure up to the supercritical region were investigated by picosecond and nanosecond pulse radiolysis experiments. More significant decays at short times followed by plateau components at longer times were observed with increasing temperature, suggesting faster spur reaction processes. In supercritical water, it was also found that the e(-)(aq) yields strongly depend on the pressure (density). Comparison of these measurements with Monte-Carlo computer simulations allowed us to identify spur reactions of e(-)(aq) that occur predominantly at high temperatures and also to provide new key information on certain spur model parameters. In particular, the experimental time-dependent e(-)(aq) yields were best reproduced if the electron thermalization distance decreases with increasing temperature. This "shrinkage" of spur sizes at high temperatures was attributed to an increase in the scattering cross sections of subexcitation electrons, likely originating from a decrease in the degree of structural order of water molecules as the temperature is increased.

Isotopic ratio and vertical distribution of radionuclides in soil affected by the accident of Fukushima Dai-ichi nuclear power plants.

The results of γ analyses of soil samples obtained from 50 locations in Fukushima prefecture on April 20, 2011, revealed the presence of a spectrum of radionuclides resulted from the accident of the Fukushima Dai-ichi nuclear power plant (FDNPP). The sum γ radioactivity concentration ranged in more than 3 orders of magnitude, depending on the sampling locations. The contamination of soils in the northwest of the FDNPP was considerable. The (131)I/(137)Cs activity ratios of the soil samples plotted as a function of the distance from the F1 NPPs exhibited three distinctive patterns. Such patterns would reflect not only the different deposition behaviors of these radionuclides, but also on the conditions of associated release events such as temperature and compositions and physicochemical forms of released radionuclides. The (136)Cs/(137)Cs activity ratio, on the other hand, was considered to only reflect the difference in isotopic compositions of source materials. Two locations close to the NPP in the northwest direction were found to be depleted in short-lived (136)Cs. This likely suggested the presence of distinct sources with different (136)Cs/(137)Cs isotopic ratios, although their details were unknown at present. Vertical γ activity profiles of (131)I and (137)Cs were also investigated, using 20-30 cm soil cores in several locations. About 70% or more of the radionuclides were present in the uppermost 2-cm regions. It was found that the profiles of (131)I/(137)Cs activity ratios showed maxima in the 2-4 cm regions, suggesting slightly larger migration of the former nuclide.

Mechanism of radiation-induced reactions in aqueous solution of coumarin-3-carboxylic acid: effects of concentration, gas and additive on fluorescent product yield.

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 (60)Co 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 × 10(9) and 2.1 × 10(10) M(-1) s(-1), respectively. The reactivity of C3CA towards O(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 (60)Co 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.

Time-dependent radiolytic yield of OH• radical studied by picosecond pulse radiolysis.

Picosecond pulse radiolysis measurements using a pulse-probe method are performed to measure directly the time-dependent radiolytic yield of the OH(•) radical in pure water. The time-dependent absorbance of OH(•) radical at 263 nm is deduced from the observed signal by subtracting the contribution of the hydrated electron and that of the irradiated empty fused silica cell which presents also a transient absoption. The time-dependent radiolytic yield of OH(•) is obtained by assuming the yield of the hydrated electron at 20 ps equal to 4.2 × 10(-7) mol J(-1) and by assuming the values of the extinction coefficients of e(aq)(-) and OH(•) at 782 nm (ε(λ=782 nm) = 17025 M(-1) cm(-1)) and at 263 nm (ε(λ=263 nm) = 460 M(-1) cm(-1)), respectively. The value of the yield of OH(•) radical at 10 ps is found to be (4.80 ± 0.12) × 10(-7) mol J(-1).

Spin-trapping reactions of a novel gauchetype radical trapper G-CYPMPO.

Chemical reactions of a novel gauchetype spin trap, G-CYPMPO (sc-5-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphinan-2-yl)-5-methy-1-pyrroline N-oxide, O1-P1-C6-N1 torsion angle = 52.8°), with reactive oxygen species were examined by pulse radiolysis technique with 35 MeV electron beam and by electron spin resonance spectroscopy after (60)Co γ-ray irradiation. The spin-trapping reaction rate constants of G-CYPMPO toward the hydroxyl radical and the hydrated electron were estimated to be (4.2 ± 0.1) × 10(9) and (11.8 ± 0.2) × 10(9) M(-1)s(-1), respectively. Half-lives of the spin adducts, hydroxyl radical, and perhydroxyl radical adducted G-CYPMPO were estimated to be ∼35 and ∼90 min, respectively. A comparison of the results with earlier reports using different radical sources suggests that the purity of the solution and/or the radical generation technique may influence the stability of the spin adducts.

Nitration activates tyrosine toward reaction with the hydrated electron.

3-Nitrotyrosine has been reported as an important biomarker of oxidative stress that may play a role in a variety of diseases. In this work, transient UV-visible absorption spectra and kinetics observed during the reaction of the hydrated electron, e(aq)(-), with 3-nitrotyrosine and derivatives thereof were investigated. The absorption spectra show characteristics of aromatic nitro anion radicals. The absorptivity of radical anion product at 300 nm is estimated to be (1.0 ± 0.2) × 10(4) M(-1) cm(-1) at pH 7.3. The rate constants determined for the reaction of e(aq)(-) with 3-nitrotyrosine, N-acetyl-3-nitrotyrosine ethyl ester and glycylnitrotyrosylglycine at neutral pH (3.0 ± 0.3) × 10(10) M(-1) s(-1), (2.9 ± 0.2) × 10(10) M(-1) s(-1) and (1.9 ± 0.2) × 10(10) M(-1) s(-1), respectively, approach the diffusion-control limit and are almost two orders of magnitude higher than those for the reactions with tyrosine and tyrosine-containing peptides. The magnitude of the rate constants supports reaction of e(aq)(-) at the nitro group, and the product absorbance at 300 nm is consistent with formation of the nitro anion radical. The pH dependence of the second-order rate constant for e(aq)(-) decay (720 nm) in the presence of 3-nitrotyrosine shows a decrease with increasing pH, consistent with unfavorable electrostatic interactions. The pH dependence of the second-order rate constant for formation of radical anion (300 nm) product suggests that deprotonation of the amino group slows the rate, which indicates that deamination to form the 1-carboxy-2-(4-hydroxy-3-nitrophenyl)ethyl radical occurs. We conclude that the presence of the nitro group activates tyrosine and derivatives toward reaction with e(aq)(-) and can affect the redox chemistry of biomolecules exposed to oxidative stress.

Temperature dependence of the Fricke dosimeter and spur expansion time in the low-LET high-temperature radiolysis of water up to 350 °C: a Monte-Carlo simulation study.

Monte-Carlo simulations of the radiolysis of the ferrous sulfate (Fricke) dosimeter with low-linear energy transfer (LET) radiation (such as (60)Co γ-rays or fast electrons) have been performed as a function of temperature from 25 to 350 °C. The predicted yields of Fe(2+) oxidation are found to increase with increasing temperature up to ∼100-150 °C, and then tend to remain essentially constant at higher temperatures, in very good agreement with experiment. By using a simple method based on the direct application of the stoichiometric relationship that exists between the ferric ion yields so obtained G(Fe(3+)) and the sum {3 [g(e(-)(aq) + H˙) + g(HO(2)˙)] + g(˙OH) + 2 g(H(2)O(2))}, where g(e(-)(aq) + H˙), g(HO(2)˙), g(˙OH), and g(H(2)O(2)) are the primary radical and molecular yields of the radiolysis of deaerated 0.4 M H(2)SO(4) aqueous solutions, the lifetime (τ(s)) of the spur and its temperature dependence have been determined. In the spirit of the spur model, τ(s) is an important indicator for overlapping spurs, giving the time required for the changeover from nonhomogeneous spur kinetics to homogeneous kinetics in the bulk solution. The calculations show that τ(s) decreases by about an order of magnitude over the 25-350 °C temperature range, going from ∼4.2 × 10(-7) s at 25 °C to ∼5.7 × 10(-8) s at 350 °C. This decrease in τ(s) with increasing temperature mainly originates from the quicker diffusion of the individual species involved. Moreover, the observed dependence of G(Fe(3+)) on temperature largely reflects the influence of temperature upon the primary free-radical product yields of the radiolysis, especially the yield of H˙ atoms. Above ∼200-250 °C, the more and more pronounced intervention of the reaction of H˙ atoms with water also contributes to the variation of G(Fe(3+)), which may decrease or increase slightly, depending on the choice made for the rate constant of this reaction. All calculations reported herein use the radiolysis database of Elliot (Atomic Energy of Canada Limited) and Bartels (University of Notre Dame) that contains all the best currently available information on the rate constants, reaction mechanisms, and g-values in the range 20 to 350 °C.

Temperature dependent absorption spectra of Br(-), Br2(•-), and Br3(-) in aqueous solutions.

The absorption spectra of Br(2)(•-) and Br(3)(-) in aqueous solutions are investigated by pulse radiolysis techniques from room temperature to 380 and 350 °C, respectively. Br(2)(•-) can be observed even in supercritical conditions, showing that this species could be used as a probe in pulse radiolysis at high temperature and even under supercritical conditions. The weak temperature effect on the absorption spectra of Br(2)(•-) and Br(3)(-) is because, in these two systems, the transition occurs between two valence states; for example, for Br(2)(-) we have (2)Σ(u) → (2)Σ(g) transition. These valence transitions involve no diffuse final state. However, the absorption band of Br(-) undergoes an important red shift to longer wavelengths. We performed classical dynamics of hydrated Br(-) system at 20 and 300 °C under pressure of 25 MPa. The radial distribution functions (rdf's) show that the strong temperature increase (from 20 to 300 °C) does not change the radius of the solvent first shell. On the other hand, it shifts dramatically (by 1 Å) the second maximum of the Br-O rdf and introduces much disorder. This shows that the first water shell is strongly bound to the anion whatever the temperature. The first two water shells form a cavity of a roughly spherical shape around the anion. By TDDFT method, we calculated the absorption spectra of hydrated Br(-) at two temperatures and we compared the results with the experimental data.

Pulse radiolysis study on free radical scavenger edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one). 2: A comparative study on edaravone derivatives.

A comparative study using the pulse radiolysis technique was carried out to investigate transient absorption spectra and rate constants for the reactions of (•)OH and N(3)(•) with edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) and its four analogue compounds, 1,3-dimethyl-2-pyrazolin-5-one, 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one, 1-phenyl-3-trifluoromethyl-2-pyrazolin-5-one and 1-(4-chlorophenyl)-3-methyl-2-pyrazolin-5-one. The results showed that, unlike reaction mechanisms previously proposed, the phenyl group of edaravone played an important role in the reaction with (•)OH and OH adducts to the phenyl group were formed. Quantum chemical calculations also strongly supported this attribution and suggested that the most favorable site for attacks by (•)OH is the ortho position of the phenyl group. Moreover, the rate constants for the reactions of edaravone and its analogues towards (•)OH and N(3)(•) were about 8.0 × 10(9), and 4.0 × 10(9) dm(3) mol(-1) s(-1), respectively. Edaravone displayed higher reactivity compared to the others, in contrast to a previous report in which 3-methyl-1-(pyridin-2-yl)-2-pyrazolin-5-one showed the highest reactivity towards (•)OH.

Protective effects of silybin and analogues against X-ray radiation-induced damage.

Silybin (SLB) and similar analogues, namely, hesperetin (HESP), naringenin (NAN) and naringin (NAR), are believed to be active constituents of natural flavonoids that have been reported as chemopreventive agents for certain cancers. Moreover, SLB and analogues have been determined to fast repair DNA bases from oxidative damage by pulse radiolysis techniques. The present study was designed to evaluate the protective effects of SLB and analogues on soft X-ray-induced damage to plasmid DNA in vitro. The DNA damage was determined by agarose gel electrophoresis. SLB and analogues were found to protect DNA from radiation damage at micromolar concentrations. Among the compounds tested, HESP and SLB were the most effective in preventing X-ray-induced formation of DNA single-strand breaks (SSB). A comparison of these results with other experiments showed that the ability of SLB and analogues to inhibit DNA damage in vitro correlated with the ability of the compounds to scavenge free radicals. Our work revealed that natural flavonoids, SLB and analogues may be used as potent radioprotectors against radiation damage.

Pulse radiolysis studies on the temperature-dependent spectrum and the time-dependent yield of solvated electron in propane-1,2,3-triol.

With a revisit of the absorption coefficient of the solvated electron in propane-1,2,3-triol, the temperature-dependent behavior of the absorption spectrum of solvated electron was studied from room temperature to 573 K by pulse radiolysis techniques. The change in the absorption spectrum of solvated electron in propane-1,2,3-triol observed by cooling down from a high temperature to 333 K is compared with that occurring during the electron solvation process at 333 K. The effect of the specific molecular structure of propane-1,2,3-triol compared to other alcohols is discussed.

Free radical scavenging reactions and antioxidant activities of silybin: mechanistic aspects and pulse radiolytic studies.

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.

Effect of water density on the absorption maximum of hydrated electrons in sub- and supercritical water up to 400 degrees C.

The optical absorption spectra of the hydrated electron (e(aq) (-)) in supercritical (heavy) water (SCW) are measured by electron pulse radiolysis techniques as a function of water density at three temperatures of 380, 390, and 400 degrees C, and over the density range of approximately 0.2-0.65 g/cm(3). In agreement with previous work, the position of the e(aq) (-) absorption maximum (E(A(max) )) is found to shift slightly to lower energies (spectral "redshift") with decreasing density. A comparison of the present E(A(max) )-density data with other measurements already reported in the literature in subcritical (350 degrees C) and supercritical (375 degrees C) water reveals that at a fixed pressure, E(A(max) ) decreases monotonically with increasing temperature in passing through the phase transition at t(c). By contrast, at constant density, E(A(max) ) exhibits a minimum as the water passes above the critical point into SCW. These behaviors are explained in terms of simple microscopic arguments based on the crucial role played by local density and configurational fluctuations (associated with criticality) in providing pre-existing polymeric clusters, which act as trapping sites for electrons.