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This Thesis aims to examine the effects of substituents on the adjacent proton accepting phenyl ring with respect to a new type of excited state intramolecular proton transfer (ESIPT) process discovered by Wan and co-workers. Therefore, a number of 2-phenylphenols 23-28 were synthesized with electron-donor and electron-acceptor substituents such as methyl, methoxy, and ketone moieties on the adjacent proton accepting phenyl ring. The results obtained from examination of photochemical deuterium exchange showed that all derivatives except for ketone 27 underwent deuterium exchange (Фex = 0.019 - 0.079), primarily at the 2’-position on photolysis in D2O-CH3CN. In general, compounds with methoxy moiety (ies) on the adjacent proton accepting ring showed higher deuterium exchange yields. Diol 28 has the potential to undergo photosolvolysis as well as ESIPT process since it has both a benzyl alcohol and a phenol chromophore on the same molecule. Irradiation of 28 in 1:1 H2O-CH3OH gave the corresponding methyl ether product in high yield. Photolysis of 28 in 1:1 D2O-CH3OH also showed that ESIPT competes very well with photosolvolysis. Thus, this work has established that ESIPT can compete efficiently with photosolvolysis. Semi-empirical AM1 (examination of HOMOs and LUMOs) calculations show a large degree of charge transfer in the electronic excited state (except 27), from the phenol ring to the attached phenyl ring of the studied compounds. The AM1 calculation for ketone 27 showed that the carbonyl oxygen is more basic than the carbon atoms of the benzene ring, which explains the lack of deuterium exchange observed for 27.

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La propagation d’une impulsion laser femtoseconde dans un milieu condensé trans- parent tel que l’eau conduit, dans les conditions appropriées, à la manifestation de phénomènes d’optiques non linéaires regroupés sous le terme de filamentation laser. Le faisceau laser correspondant voit alors sa propagation métamorphosée sous la forme de filaments de lumière intense. Au coeur de ces filaments, l’irradiance considérable provoque l’ionisation des atomes du milieu et la génération de plasmas. Produit de manière spontanée et auto-régulée, ces plasmas ont la particularité de combiner une densité importante d’événements d’ionisation avec des effets thermo-mécaniques minimisés. Leurs propriétés intrinsèques font de ces plasma une source d’ionisation singulière tout particulièrement en ce qui concerne les sciences qui s’intéressent à l’étude des effets des radiations ionisantes. Entre autres, les sciences des radiations étudient la physique, la chimie et la biologie de l’action des rayonnements ionisants sur des systèmes d’intérêt biologique. Dans ce contexte, cette dissertation s’intéresse à la filamentation d’impulsions laser femtosecondes proches infrarouges en solution aqueuse. L’eau représentant la compo- sante majeure des systèmes d’intérêt biologique, une solution aqueuse constitue une approximation satisfaisante d’un échantillon biologique plus concret. Tout d’abord, l’étude de la physique de la filamentation laser a permis de mieux appréhender l’interaction des impulsions assujetties au processus de filamentation dans l’eau, primordiale pour l’identification des conditions d’irradiation propices à une meilleure maîtrise des conséquences de la génération des plasmas photo-induits. Les effets d’un rayonnement ionisant en solution aqueuse sont notamment véhiculés au travers de la chimie déclenchée par l’ionisation de l’eau, qui implique une interaction entre les espèces réactives produites et les solutés dilués en solutions. L’étude des conséquences de l’irradiation laser sur des solutés inorganiques a permis d’élucider la nature de cette chimie sous rayonnements. De surcroît, il a été démontré comment la malléabilité qu’offre l’utilisation d’un laser se répercute sur la capacité à moduler les conséquences de l’irradiation. Enfin, l’étude a été étendue à l’irradiation de molécules d’ADN diluées en solution aqueuse. L’analyse détaillée des dommages occasionnés à l’ADN a permis de mettre en exergue la présence de lésions complexes caractéristiques d’une irradiation par un faisceau intense de rayonnements ionisants. / Abstract : The present study is part in a new framework in radiobiology, introduced a decade ago: femtosecond laser-induced "cold" low density plasmas for the highly localized deposition of energy at sub-cellular scales in systems of biological interest. Since in aqueous solutions the action of such plasmas is equivalent to the deposition of a dose by ionizing radiation, plasma-mediated effects on solutes involve the radiation chemistry of water. This chemistry corresponds to the interaction of solutes with radical oxygen species as well as with secondary low energy electrons, produced by the plasma. Here, to better understand the radiation chemistry underlying the generation of low density plasmas in aqueous environments, we harnessed the multi-filamentation of powerful femtosecond laser pulses as a way to achieve a self-regulated production of spatially homogeneous low density plasma foci in water. The "cold" low density plasma micro-channels generated by the filamentation of the femtosecond laser pulses in aqueous solutions constitute a source of dense ionization. We studied the femtosecond laser filamentation in inorganic solutions to account for the radiation-assisted chemistry triggered by laser ionization in aqueous environment. We highlighted that the trivial optical control of the spatio-temporal distribution of light filaments in the irradiated sample resulted in the modulation of the corresponding radical chemistry. We concluded that these spatially and temporally resolved plasmas could be developed as a tool for the unprecedented control of chemistry under ionizing radiation. The addition of a spatial light modulator to control the filamentation process improves significantly our control on the spatio-temporal distribution of the laser-induced plasma channels. From a bundle of entangled random low density plasma channels, usually produced by the non-linear propagation of the powerful laser beam, we were able to obtain a programmable matrix of mono-filaments to achieve a more pervasive and homogeneous energy deposition. This method of irradiation allowed us to perform a detailed analysis to determine, quantify and compare the consequences of the laser irradiation with those of a conventional source of ionizing radiation (Gamma-Rays) on organic molecules (e.g. DNA) desolved in aqueous solutions. We showed that each filament behaves as an independent intense micro beam of ionizing radiation, that is capable of inducing complex DNA damage. We believe that a better understanding of the laser-induced plasma-mediated effects in aqueous solutions of biological interest will further the adoption of such laser-based ionisation sources, and that this unorthodox approach to radiation sciences will open new fields of investigation at the frontiers of radiation and laser-driven chemistry. Moreover, one of the principal conclusions of this thesis argues in favour of a shift of paradigm in radiation sciences, shuch that the consequences of ionising radiation would not only be considered for their injurious effects but also for the fine modulation of the functions of systems of biological interest. This sentiment paves the way for new emerging techniques and applications in biomedical fields.

Des mesures de radiolyse impulsionnelle avec des paquets d’électron de 7 picosecondes ont été effectuées dans des systèmes D₂O et D₂SO₄ / D₂O purs afin d'étudier l'effet isotopique sur la réactivité de l'électron solvaté (es⁻), du radical hydroxyle (OH•) et de son radical cation cationique (H₂O•⁺). Dans le système D₂O, le spectre d'absorption molaire de l’électron solvaté dans D₂O a été déterminé entre 250 et 1500 nm en utilisant la méthode du point isosbestique. Sur la base de ce coefficient d'extinction, le rendement radiolytique de es⁻ dans D₂O juste après l'impulsion d'électrons de 7 ps a été déterminé à (4,4 ± 0,2) × 10⁻⁷ mol J⁻¹, ce qui coïncide avec celui dans H₂O. Le rendement du radical OD• juste après l'impulsion d'électrons s'est révélée être (5,0 ± 0,2) × 10⁻⁷ mol J⁻¹. Dans le cas de l’électron solvaté la vitesse de déclin dans D₂O est plus lent que dans H₂O, tandis que la vitesse de déclin de OD• est similaire à celui de OH•. Dans le système D₂SO₄ /D₂O, la réactivité de D₂O•⁺ a été sondée dans des solutions d'acide sulfurique deutérées de diverses concentrations et comparée à celle de H₂O•⁺. Le soluté oxydé, le radical sulfate a été observé à 7 ps et des rendements plus élevés ont été trouvés dans les solutions deutérées. Les effets isotopiques révèlent la compétition entre deux réactions ultra-rapides : le transfert de protons vers H₂O (D₂O) et le transfert d'électrons de H₂O•⁺ (D₂O•⁺). Les simulations par la théorie de la densité fonctionnelle décryptent le mécanisme du transfert d’électrons : elles se font par migration de charge sub-femtoseconde et ne sont pas affectées par la substitution isotopique. / Picosecond pulse radiolysis measurements were performed in neat D₂O and D₂SO₄/D₂O system in order to study the isotopic effect on the reactivity of the solvated electron(es⁻), the hydroxyl radical (OH•) and its precursor—water cation radical (H₂O•⁺). In D₂O system, the molar absorption coefficient spectra of spectrum in D₂O was determined between 250 to 1500 nm using the isosbestic point method. Based on this extinction coefficient, the radiolytic yield of es⁻ in D₂O just after the 7 ps electron pulse was determined to be (4.4 ± 0.2) × 10⁻⁷ mol J⁻¹, which coincides with the one for in H₂O. The yield of the radical OD• just after the 7 ps electron pulse was found to be (5.0 ± 0.2) × 10⁻⁷ mol J⁻¹. In the spurs of ionization, the decay rate of es⁻ is slower in D₂O than that in H₂O, whereas the decay rate of OD• is similar to the one of OH•. In D₂SO₄/D₂O system, the reactivity of and D₂O•⁺ was probed in deuterated sulfuric acid solutions of various concentrations and compared with that of H2O•⁺. The oxidized solute sulfate radical was observed at 7 ps and remarkably higher yields are found in deuterated solutions. The isotopic effects reveal the competition between two ultrafast reactions: proton transfer toward H₂O (D₂O) and electron transfer from H₂SO4⁻ to H₂O•⁺ (D₂O•⁺). Density functional theory simulations decipher the electron transfer mechanism: it proceeds via sub-femtosecond charge migration and is not affected by isotopic substitution.

Acquisition of X-ray crystallographic data is always accompanied by structural degradation owing to the absorption of energy. The application of high-fluency X-ray sources to large biomolecules has increased the importance of finding ways to curtail the onset of X-ray-induced damage. A significant effort has been under way with the aim of identifying strategies for protecting protein structure. A comprehensive model is presented that has the potential to explain, both qualitatively and quantitatively, the structural changes induced in crystalline protein at 100 K. The first step is to consider the qualitative question: what are the radiation-induced intermediates and expected end products? The aim of this paper is to assist in optimizing these strategies through a fundamental understanding of radiation physics and chemistry, with additional insight provided by theoretical calculations performed on the many schemes presented.