Christiane Ferradini

On the electronic structure of liquid water: Facts and reflections

Abstract Estimations of the water reorganization energy following excess electron (eexc−) production and of interband transition energies using magneto-optical Faraday rotation measurements in liquid water have been recently reported. In such a context, the electronic structure of liquid water is presently revisited. The existence of an Urbach tail extending below the water conduction band and its efficient participation in the eexc− trapping seem to be well substantiated. From thermodynamic considerations, a value V0∼−0.75 eV for the energy of the bottom of the conduction band with respect to vacuum, and a value Ut∼0.5 eV for the Urbach tail extension are now proposed. Reported semiempirical determinations of the energy gap Eg are presented and discussed, suggesting the average value Eg=8.7 ± 0.5 eV. On the whole, the main terms underlying the electronic structure of liquid water would thus have to be revised downwards; also the present values turn out to be close to the corresponding ones estimated for crystalline or amorphous ice.

The effect of pH on water radiolysis: A still open question — A minireview

The available data describing the influence of pH on the radiolysis of liquid water are not current and still raise a certain number of problems. Especially for alkaline media, the question of the values of the primary free radical and molecular yields is yet unsolved, the experimental data appearing contradictory. It is proposed here to briefly summarize the main results that have been obtained on this subject thus far. In the quest of finding a definitive explanation for these apparent disagreements, Monte-Carlo simulation methods could offer a most valuable tool to further develop our understanding of pH effects in the radiation chemistry of water and aqueous solutions.

A new estimate of the radical yield at early times in the radiolysis of liquid water

Abstract We have revisited earlier experiments on pulse radiolysis of aqueous solutions carried out at very high dose rates (intensities) up to 5×10 27 eV g −1 s −1 (∼10 12 Gy s −1 ). The ⋅ OH radical yield G ⋅ OH =4.6±0.25 molec./100 eV, derived from those studies, is here estimated to correspond to the time scale of ∼100 ps where, under these high irradiation-intensity conditions, spur overlap is assumed to be total. This ∼100 ps estimate is obtained with the aid of Monte Carlo simulation results of the nonhomogeneous chemical stage of water radiolysis. It is found that such a G ⋅ OH value at ∼100 ps compares well with the ⋅ OH yield values inferred from inverse Laplace transform analyses of ⋅ OH scavenger data and from Monte Carlo calculations, but strongly disagrees with direct measurements of G ⋅ OH (5.9±0.2 molec./100 eV at 200 ps).

On apparent contradictions in some photophysical properties of liquid water

Apparent inconsistency has appeared between essentially two sets of data relative to the optical absorption limit of liquid water on the one hand and to its photoionization threshold and band-gap energy on the other. Recent data prompt a renewed examination.

Are there protective enzymatic pathways to regulate high local nitric oxide (.NO) concentrations in cells under stress conditions

This paper examines, from a chemical perspective, the hypothesis of the existence of protective enzymes whose role would be to regulate the high local nitric oxide (NO) concentrations that are released in NO-generating cells in situations of response to oxidative stress. These enzymes should play the role, with respect to NO, either of a reductase or of a dismutase. The energetics of the intervening transformations is herein presented, along with a review of pertinent literature. An attempt is made in order to describe the physiognomy of such enzymes, in relation with the literature data. Experimental investigation is needed to further evaluate the validity of such a hypothesis.

Reactions of OH· and Br2̇ radicals with glutathione. A radiolysis study

Abstract Interactions of OH · and Br 2 radicals with glutathione (GSH) have been studied in buffered neutral aqueous solutions using γ and pulse radiolysis. In steady state radiolysis, initial G values of GSH loss and formation of GSSG have been measured for GSH concentrations ranging between 5 x 10 −5 and 5 x 10 −3 mol dm −3 . In pulse radiolysis experiments the absorption spectra and the kinetics of transients formed by the action of OH · radicals have been determined. It has been found that the bromide radical anion reacts with glutathione, producing quantitatively GSSG with a G value of 2.9×10 −7 molJ −1 . It is not the same for OH · radicals which show a non stoichiometric oxidation of thiol group of glutathione. The OH · -induced oxidation of glutathione in neutral aqueous solution by pulse radiolysis has been found to produce not only the sulphur-centered radical (GS · and GSSG∸) but at least one other alkyl radical.

One-electron oxidation of glutathione by azide radicals in neutral medium: A gamma and pulse radiolysis study

Abstract The selective interactions of azide radicals with glutathione (GSH) have been quantitatively studied in buffered neutral aqueous solutions using γ and pulse radiolysis. The sulfur centered GS and GSSG⨪ radicals are produced in pulse and γ radiolysis. Kinetic experiments and simulation allowed to estimate the rate constant of N3 with GSH which has been found to be equal to (9.5 ± 0.5) × 106M−1 s−1 at pH 7. In steady state radiolysis, we have found GSSG as the final product formed with an initial G value of 2.9 × 10−7 mol J−1.