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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.

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.

Laser photolysis experiments on carboxymethylated chitin derivatives, such as carboxymethyl chitin (CM-chitin) and carboxymethyl chitosan (CM-chitosan), in aqueous solution by a 248 nm excimer laser were carried out for the first time. The transient absorption spectra of photolyzed CM-chitin or CM-chitosan solutions revealed a strong band with the maximum at 720 nm, which was assigned to the hydrated electron (eaq-). In the presence of argon, the eaq- decays by reacting with CM-chitin or CM-chitosan, and the rate constants are (6.1 +/- 0.1) x 10(7) M(-1) s(-1) and (3.7 +/- 0.1) x 10(7) M(-1) s(-1), respectively. Long-lived radicals with relatively weak absorption intensity were detected in the near-UV region. The absorption band was not notably characteristic and showed only an increasing absorption toward shorter wavelengths. It is similar to the signal of *CM-chitin or *CM-chitosan macroradicals formed by the reaction of CM-chitin or CM-chitosan with an OH* radical. It was assigned to *CM-chitin- or *CM-chitosan- macroradicals formed by eaq- + CM-chitin or CM-chitosan reaction. CM-chitin aqueous solutions were further examined by pulse radiolysis in order to confirm the site of the long-lived radical.

A re-examination of our Monte-Carlo modeling of the radiolysis of liquid water by low linear-energy-transfer (LET ~ 0.3 keV [micro][m.sup.-1]) radiation is undertaken herein in an attempt to reconcile the results of our simulation code with recently revised experimental hydrated electron ([e.sup.-.sub.aq]) yield data at early times. The thermalization distance of subexcitation electrons, the recombination cross section of the electrons with their water parent cations prior to thermalization, and the branching ratios of the different competing mechanisms in the dissociative decay of vibrationally excited states of water molecules were taken as adjustable parameters in our simulations. Using a global-fit procedure, we have been unable to find a set of values for those parameters to simultaneously reproduce (i) the revised [e.sup.-.sub.aq] yield of 4.0 [+ or -] 0.2 molecules per 100 eV at "time zero" (that is, a reduction of ~20% over the hitherto accepted value of 4.8 molecules per 100 eV), (ii) the newly measured [e.sup.-.sub.aq] decay kinetic profile from 100 ps to 10 ns, and (iii) the time-dependent yields of the other radiolytic species H*, *OH, [H.sub.2], and [H.sub.2][O.sub.2] (up to ~1 [micro]s). The lowest possible limiting "time-zero" yield of [e.sup.-.sub.aq] that we could in fact obtain, while ensuring an acceptable agreement between all computed and experimental yields, was ~4.4 to 4.5 molecules per 100 eV. Under these conditions, the mean values of the electron thermalization distance and of the geminate electron-cation recombination probability, averaged over the subexcitation electron "entry spectrum," are found to be equal to ~139 [Angstrom] and ~18%, respectively. These values are to be compared with those obtained in our previous simulations of liquid water radiolysis, namely ~88 [Angstrom] and ~5.5%, respectively. Our average electron thermalization distance is also to be compared with the typical size (~64-80 [Angstrom]) of the initial hydrated electron distributions estimated in current deterministic models of "spur" chemistry. Finally, our average probability for geminate electron-cation recombination agrees well with an estimated value of ~15% recently reported in the literature. In conclusion, this work shows that an adaptation of our calculations to a lower hydrated electron yield at early times is possible, but also suggests that the topic is not closed. Further measurements of the [e.sup.-.sub.aq] yields at very short times are needed. Key words: liquid water, radiolysis, electron-cation geminate recombination, electron thermalization distance, hydrated electron ([e.sup.-.sub.aq]), [e.sup.-.sub.aq] decay kinetics, time-dependent molecular and radical yields, Monte-Carlo simulations.

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The optical absorption spectra of the hydrated electron (eaq-) 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 °C, and over the density range of ∼0.2–0.65 g/cm3. In agreement with previous work, the position of the eaq- absorption maximum (EAmax) is found to shift slightly to lower energies (spectral “redshift”) with decreasing density. A comparison of the present EAmax-density data with other measurements already reported in the literature in subcritical (350 °C) and supercritical (375 °C) water reveals that at a fixed pressure, EAmax decreases monotonically with increasing temperature in passing through the phase transition at tc. By contrast, at constant density, EAmax 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. [ABSTRACT FROM AUTHOR]

Abstract: The yield of the hydrated electron in the picosecond time range has been re-evaluated with an ultrafast pulse radiolysis system using a laser photocathode RF-gun in combination with a conventional one, and a value of 4.1±0.2 per 100eV of absorbed energy at 20ps was derived. This is consistent with recent experimental results using a time correlation method [Bartels et al., J. Phys. Chem. A 104, 1686-1691 (2000)] and with Monte-Carlo calculations [Muroya et al., Can. J. Chem. 80 1367-1374 (2002)]. [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]

The reactivity of monochlorophenols and dichlorophenols towards •OH and hydrated electrons was investigated applying pulse radiolysis coupled with time resolved spectroscopy. Rate constants, transient spectra and stability of transient species were studied for mono and dichlorophenols. Reactivity of 3,4-dichlorophenol (3,4-DCP) towards •OH and hydrated electrons, its transient spectra and respective rate constants have been explained in detail as a model for the current pulse radiolysis experiments. The trends and behaviors in the reactivity of mono and dichlorophenols towards •OH and hydrated electrons were analyzed. All the corresponding OH-adducts demonstrated λ max values range between 295 and 435 nm and their rate constants exhibited a range of (3.4–21) x 109 dm3 mol−1 s−1. Likewise, e-adducts illustrated λ max values ranged between 295 and 355 nm and their rate constants displayed a range of (0.025–6.2) x 109 dm3 mol−1 s−1. Full geometry optimizations and electron charge density calculations based on DFT (density functional theory) presented the existence of a strong correlation of electron charge density and polarizability with the reactivity of chlorophenols towards hydrated electrons and •OH radical. This research represents the first thorough exploration of its kind, aiming to comprehend the reactivity of all dichlorophenols and their corresponding transient spectra through pulse radiolysis. • Mono- & dichlorophenols reactivity with e a q − &.•OH was probed via pulse radiolysis. • Transient spectra and rate constants were investigated for all MCPs and DCPs. • 3,4-DCP served as a model to display transient spectra, k values & decay profiles. • The trends of reactivity were correlated with electron charge density using DFT. [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]