Yves Lion

QUANTUM YIELD OF SINGLET OXYGEN PRODUCTION BY XANTHENE DERIVATIVES

The singlet oxygen quantum yield (ϕ1o2) of 11 purified fluorescein derivatives was determined by reaction with singlet oxygen acceptors in aqueous and ethanolic solutions; in both solvents ϕ1o2 was enhanced with increasing halogenation. Tryptophan and 2,2,6,6‐tetramethylpiperidone were found to be unadapted for the determination of ϕ1o2, in our systems; however, the use of 9.10‐dipropionic anthracene acid andp‐nitrosodimethylaniline in conjunction with imidazole derivatives was suitable for 1O2 detection in water. Both methods lead to results in excellent agreement. As in ethanol. ϕ1o2, was equal to the triplet state quantum yield (ϕT), the comparison between the two solvents showed that ϕT in water was greater than in ethanol. The comparison between our values obtained with polychromatic light with published data obtained with monochromatic light suggests that the triplet quantum yield of fluorescein derivatives is wavelength independent.

ON THE PRODUCTION OF NITROXIDE RADICALS BY SINGLET OXYGEN REACTION: AN EPR STUDY

Abstract— The production of free radicals by reaction of 2,2,6,6‐tetramethyl‐4‐piperidinol with singlet oxygen was studied by EPR spectroscopy. The rate constant of the amine was found to be equal to 8 ×105M‐1s‐1 in ethanol and to 4 × 107M‐1s‐1 in phosphate buffer (pH 8). Competition experiments were performed with singlet oxygen quenchers such as NaN3, DABCO and the quenching rate constants were found to be consistent with the literature values. The EPR method proved to be a valuable technique to study the reaction of singlet O2 with the sterically hindered amine without any interfering effect.

Characterization of an acrylamide-based dry photopolymer holographic recording material

Recent work on an acrylamide-based photopolymer holographic recording medium is presented. The lifetime of recorded gratings is improved by the addition of cross-linking monomers. Shelf life is also improved. The effects of various constituents of the photosensitive material are studied to determine an optimum composition, and five xanthene dyes are compared as possible sensitizers for the system. With the most sensitive dye and optimum concentrations of the other constituents an improved formulation is presented with high sensitivity and very high diffraction efficiency. The new formulation also works well in reflection mode.

Characterization of DuPont photopolymer: determination of kinetic parameters in a diffusion model

We investigate the recording dynamics of Omnidex photopolymer film from DuPont. We use a reviewed version of the diffusion model proposed by Zhao and Mouroulis [J. Mod. Opt. 41, 1929 (1994)] in order to describe the recording response that combined photopolymerization and free-monomer diffusion process. Two different experiments are detailed that lead to the determination of material kinetic parameters. These values are introduced in the numerical model to provide quantitative simulations of a grating formation under various holographic exposures. Theoretical results are experimentally checked as a validation of the model. We extend its applications to several secondary investigations, such as volume-shrinkage influence on refractive-index distribution and spectral selectivity of reflection gratings. This study improves the understanding of the recording process and consequently allows to build more accurate holographic components in this material to be built.

On the mechanism of formation of free radicals induced in nucleic acid bases by ionizing radiation

Abstract The reaction of trapped electrons with nucleic acid bases was studied by electron spin resonance and spectrophotometry. Electrons were generated at 77 K by radiolysis of 8 mol dm −3 NaOH. For adenine, guanine and thymine the results showed that an intermediate step, corresponding probably to the anion stage, occurred in the formation of the hydrogen adduct radicals that were ultimately observed. The cytosine anion does not appear to protonate. The implications of these findings for γ radiolysis of the four bases are discussed.

Polarizing holographic beam splitter on a photoresist

A method to take advantage of high-spatial-frequency surface-relief gratings as polarizing beam splitters is described. The analogy between that kind of grating and a volume grating is the basis of the theoretical predictions. Results of rigorous calculations are presented. High polarizing performances are demonstrated. We illustrate the method with a practical realization that checks the validity of the calculations.

Potentiation of oxygen toxicity by menadione in Saccharomyces cerevisiae

The cytotoxicity of molecular oxygen can be sharply increased in the yeast Saccharomyces cerevisiae by the use of redox compounds capable of shunting electrons in vivo and of spontaneous reoxidation under aerobic conditions. Among these redox compounds, menadione (Vitamin K3) is particularly able to stimulate the cyanide-resistant respiration of the yeast cells. Under steady-state conditions, the efficiency of menadione is modulated by the physiological state of the yeast cells and also depends on the availability of reducing agents within the cell. Menadione shows lethal effects towards yeast cells in the presence of O2 only, as a result of the production of toxic metabolites like O2-. and H2O2 which are actually detected in the extracellular fluid. Inhibitors of the enzymes scavenging O2-. and H2O2 generally potentiate the lethal effects of this redox compound. On the other hand, superoxide dismutase and/or catalase supplemented into the incubation buffer have been found to protect the cells to various extents from the cytotoxic effects of menadione. Our data support the following conclusions: When the cellular enzymatic defences are functional, the moderate lethality induced by menadione is principally mediated by O2-. ions acting on the outer side of the cell (peripheral region). In the presence of cyanide, but not of azide, the loss of viability also results from additional damage occurring within the inner cell region. In this case, intracellular injury can be caused by H2O2 alone but our data also suggest that during redox cycling more reactive species--O2-. and probably OH.--are generally intracellularly and are involved in the cytotoxic process.

A STUDY OF 1O2 PRODUCTION BY IMMOBILIZED SENSITIZER OUTSIDE THE SOLUTION. MEASUREMENT OF 1O2 GENERATION

Abstract— Recently, a new technique of 1O2 generation has been described by Midden and Wang. The sensitizer is immobilized on silica gel particles which are attached on one surface of a glass plate which is placed, sensitizer‐side down, above a solution leaving a small air space between the sensitizer and the solution. Applying the principle of the technique, i.e. generation of 1O2 in the gas phase above the solution, we first improved the long‐term stability of the dye (rose bengal) by using double stock transparent tape instead of rubber cement. Under these conditions, although the initial rate of production was higher in rubber cement, the rate of production reached a plateau after 30 min, whereas with double stick transparent tape, the rate of generation was linear up to 100 min. This result was explained by the fact that silica glass beads are embedded in the cement which could lead to the bleaching reaction of the dye. Different reactions have been investigated, the bleaching of N,N‐dimethyl‐4‐nitrosoaniline (RNO) in the presence of imidazole, destruction of anthracenedipropionic acid, formation of a stable nitroxide from a sterically hindered secondary amine and the influence of pH on the nitroxide yield. The yield was measured to be 5 × 1012 molecules of singlet oxygen produced per second per cm2 from the surface of the plate using the RNO bleaching reaction. This method of generating 1O2 also seems promising for studying the killing of mammalian cells by 1O2 as the sole damaging species.

Almost-common path interferometer using the separation of polarization states for digital phase-shifting shearography

An original experimental setup for shearography with metrological applications is presented. The simplicity and the efficiency of the setup are provided by a shearing device, a prism that separates the TE and TM polarization modes with a coating and a thin glass plate placed on its face. The use of this shearing device enables an in-line and almost-common path configuration for the shearing interferometer, a path that leads to high stability and a low sensitivity to external disturbances. Moreover, the sensitivity of the interferometer can be easily adjusted for different applications by varying the shearing amount with glass plates of different thicknesses or by moving the shearing device between two lenses along the optical axis. The temporal phase-shifting method is applied through the use of a liquid crystal variable retarder.

Formation de radicaux libres dans les constituants du DNA photosensibilises par la proflavine

Abstract Electron spin resonance spectroscopy has been used to study the photosensitization by proflavine of nucleotides of DNA. Under vacuum, this process induces, by a biphotonic mechanism, free radicals similar to those which result of direct action of ionising radiation. In the presence of oxygen, microwave saturation and annealing at 190°K allow ROO· radicals to be observed. The analysis of the influence of the incident wavelength and of the triplet state population in the photosensitizer versus the time of irradiation suggest that the biphotonic process implies the participation of this triplet and the successive absorption of one photon at 450 nm and of another with λ between 320 and 360 nm. As to the ROO· radicals, they need a physical process for desactivation of proflavine which corresponds to a transfer of excitation energy to the oxygen molecules, in the 1Σ+g excited state. The comparison of the shape of spectra obtained in the case of cytosine, thymine, 2-deoxy- d -ribose and related nucleotides suggests that in these nucleotides, the free radical induced by a biphotonic mechanism is localised in the base whereas the photodynamic component ROO· would be associated with the pentose moiety of nucleotide.