Modeling methods are required for predicting the chemical stability of macromolecular materials used in critical spacecraft components of satellites orbiting in the high-energy radiation environment of near earth and deep space planetary magnetic belts. Methods for establishing degradation mechanisms and predicting and simulating the total absorbed dose and ionization for long term space missions are presented herein. This investigation evaluates cross-linking, main-chain scission and elimination products in a linear series of narrowly dispersed poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers. A comparison is made of the scission radiation yield (Gs) and crosslinking (Gx) predicted for the simulated ionization data to the results of degradation in a ground-based simulation of the space radiation environment using a 60Co source. The influence of molecular weight on the stability of post-irradiated polymer is evident in the degree of change observed for each molecular weight series with respect to the degradation products produced by exposure to gamma radiation. The analysis of the specific polymer degradation products and changes in the average molecular weight (Mw) were performed using chemical analysis (FTIR and GPC) and thermal analysis (DSC). The analytical results for PMMA and polystyrene radiation-induced degradation products demonstrate that, depending on Mw, the amount and types of degradation products will vary with respect to crosslinking, chain scission and other oxidative pathways. The results support the preference for end group loss with free volume properties driving the observed differences in the G(s) and (Gx) values. The cross-linking observed for polystyrene is controlled by molecular weight as well wherein the lowest molecular weight molecules display greater resistance to cross-linking. This research investigation employs proven tools of analysis (NASA AP8 and AE8) that accurately predict the amount of energy applied to spacecraft materials during a typical near-earth, aggressive mission environment . Another model (SPENVIS) is applied to determine the amount of total energy absorbed by the spacecraft materials from proton, electron and Brehmsstralung radiation throughout the mission life. Another set of models (SRIM and CASINO) are used to asses the range of penetration of particles into the materials and the extent of ionization caused by the particle spectrum and fluence. The absorption coefficients for the PS and PMMA structure are determined to ensure good correlation between ground simulation and the true space environment. The total dose values are used to establish the total dose that is to be deposited during the ground simulation experiments. A 60Co irradiator was used as the ground simulation source. Dosimetry was used to determine the exposure time needed to deposit an equivalent amount of dose accumulation needed to simulate the total dose modeled for the space mission. Using gel permeation chromatography, previous studies have demonstrated that the characteristic Gaussian distribution of narrowly-dispersed PS and PMMA is perturbed by the accumulation of degradation products following irradiation. The change in distribution provides insight into the preferred path of degradation. The role of free volume in the glass transition temperature are reported with respect to Tg variation with molecular weight. Using differential scanning calorimetry. The role of free volume in the determination of the mechanism of radiation-induced degradation is a primary focus of this investigation when considering the ability of the main chain to recombine or undergo abstraction as opposed to crosslinking or scission where motion is restricted in the solid state. The subtle distinction of structural changes brought about by the loss of side groups, double bond formation and crosslinking have been characterized by infrared spectroscopy. The resultant spectra of irradiated polymers offer considerable information on verifying the extent of competing reactions that involve structural features of the molecule. These instrumental methods are the tools of research that will assess the affect of molecular structure on polymer radiation resistance, and will support the rationale explaining the preference for one degradation mechanism over another. This research investigation has yielded information on the affect of polymer molecular structure on radiation resistance. The work goes beyond previous studies that define empirical observations for a change in radiation resistance by virtue of a change in side group. The effect of free volume, stabilized intermediates and reactive intermediates are related to molecular weight and side group functionality. The understanding of the mechanistic rationale behind the effect of structural features on polymer radiation resistance are essential to the development of modeling systems for predicting polymer stability in space mission environments.

Includes vita. / Title from PDF of title page. / Document formatted into pages; contains 172 pages. / Thesis (PH.D.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Modeling methods are required for predicting the chemical stability of macromolecular materials used in critical spacecraft components of satellites orbiting in the high-energy radiation environment of near earth and deep space planetary magnetic belts. Methods for establishing degradation mechanisms and predicting and simulating the total absorbed dose and ionization for long term space missions are presented herein. This investigation evaluates cross-linking, main-chain scission and elimination products in a linear series of narrowly dispersed poly(methyl methacrylate) (PMMA) and polystyrene (PS) polymers. A comparison is made of the scission radiation yield (Gs) and crosslinking (Gx) predicted for the simulated ionization data to the results of degradation in a ground-based simulation of the space radiation environment using a 60Co source. / ABSTRACT: The influence of molecular weight on the stability of post-irradiated polymer is evident in the degree of change observed for each molecular weight series with respect to the degradation products produced by exposure to gamma radiation. The analysis of the specific polymer degradation products and changes in the average molecular weight (Mw) were performed using chemical analysis (FTIR and GPC) and thermal analysis (DSC). The analytical results for PMMA and polystyrene radiation-induced degradation products demonstrate that, depending on Mw, the amount and types of degradation products will vary with respect to crosslinking, chain scission and other oxidative pathways. The results support the preference for end group loss with free volume properties driving the observed differences in the G(s) and (Gx) values. / ABSTRACT: The cross-linking observed for polystyrene is controlled by molecular weight as well wherein the lowest molecular weight molecules display greater resistance to cross-linking. This research investigation employs proven tools of analysis (NASA AP8 and AE8) that accurately predict the amount of energy applied to spacecraft materials during a typical near-earth, aggressive mission environment . Another model (SPENVIS) is applied to determine the amount of total energy absorbed by the spacecraft materials from proton, electron and Brehmsstralung radiation throughout the mission life. Another set of models (SRIM and CASINO) are used to asses the range of penetration of particles into the materials and the extent of ionization caused by the particle spectrum and fluence. The absorption coefficients for the PS and PMMA structure are determined to ensure good correlation between ground simulation and the true space environment. / ABSTRACT: The total dose values are used to establish the total dose that is to be deposited during the ground simulation experiments. A 60Co irradiator was used as the ground simulation source. Dosimetry was used to determine the exposure time needed to deposit an equivalent amount of dose accumulation needed to simulate the total dose modeled for the space mission. Using gel permeation chromatography, previous studies have demonstrated that the characteristic Gaussian distribution of narrowly-dispersed PS and PMMA is perturbed by the accumulation of degradation products following irradiation. The change in distribution provides insight into the preferred path of degradation. The role of free volume in the glass transition temperature are reported with respect to Tg variation with molecular weight. Using differential scanning calorimetry. / ABSTRACT: The role of free volume in the determination of the mechanism of radiation-induced degradation is a primary focus of this investigation when considering the ability of the main chain to recombine or undergo abstraction as opposed to crosslinking or scission where motion is restricted in the solid state. The subtle distinction of structural changes brought about by the loss of side groups, double bond formation and crosslinking have been characterized by infrared spectroscopy. The resultant spectra of irradiated polymers offer considerable information on verifying the extent of competing reactions that involve structural features of the molecule. These instrumental methods are the tools of research that will assess the affect of molecular structure on polymer radiation resistance, and will support the rationale explaining the preference for one degradation mechanism over another. / ABSTRACT: This research investigation has yielded information on the affect of polymer molecular structure on radiation resistance. The work goes beyond previous studies that define empirical observations for a change in radiation resistance by virtue of a change in side group. The effect of free volume, stabilized intermediates and reactive intermediates are related to molecular weight and side group functionality. The understanding of the mechanistic rationale behind the effect of structural features on polymer radiation resistance are essential to the development of modeling systems for predicting polymer stability in space mission environments. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

Les matériaux isolants des câbles électriques des centrales nucléaires sont constitués d’élastomères ayant de bonnes capacités de résistance au vieillissement, comme les copolymères d’éthylène et de propylène (EPR, EPDM, …), car leurs conditions d’utilisation les soumettent à de faibles radiations et à des températures pouvant atteindre 50°C dans le bâtiment réacteur. L’objectif de la présente thèse est de contribuer à affiner la compréhension du vieillissement des isolants des câbles, en étudiant l’évolution de la structure et du comportement de matériaux modèles. Ces matériaux sont composés d’un EPDM amorphe réticulé au peroxyde et comprenant différent taux de charges micrométriques, constituées de trihydrate d’aluminium (ATH), utilisées pour leurs propriétés anti-feu. Aucun anti oxydant supplémentaire n’a été ajouté. L’approche utilisée dans cette étude consiste à réaliser des vieillissements thermiques accélérés dans une étuve ventilée à 130°C durant 20h, 30h et 40h, puis à caractériser l’évolution de la structure des matériaux, leur résistance à la traction et à la fissuration. La caractérisation expérimentale indique que l’oxydation, induit par le vieillissement, provoque un phénomène de rupture de chaînes prédominant, dont résulte la formation d’une quantité considérable de fraction soluble. La diminution de la densité de chaînes actives associée à l’accroissement de la partie soluble du matériau, constituée de chaînes libres devenant de plus en plus courtes durant le vieillissement, entraine une perte des propriétés mécaniques et de la résistance à la fissuration. / Insulating materials of electric cables in nuclear power plants are constituted by rubbers having good ageing resistance properties, like ethylene and propylene copolymers (EPR, EPDM …), because in service these cables are submitted to low irradiation and temperatures that could reach 50°C in the reactor building. The objective of this thesis is to contribute to improve the understanding of the ageing of cables insulating materials, by studying the evolution of the structure and the behavior of models materials. These materials are constituted an amorphous EPDM crosslinked with peroxide and including different ratio of micrometric fillers, constituted of aluminum trihydrate (ATH), used for its fire retardancy properties. Any antioxidants have been added. The approach used in this study consist to realize accelerated thermal ageing in air ventilated oven at 130°C during 20h, 30h and 40h, then characterizing the evolution of the structure of the materials, their tensile and crack propagation resistance. The experimental characterization show that the oxidation, resulted from the ageing, provoke a predominant chain scission phenomenon which leads to the formation of a large quantity of soluble fraction. The decrease of the density of active chains associated with the increase of the soluble part, constituted of free chains becoming shorter during the ageing, leads to a loss of tensile strength and crack propagation resistance.

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2018-2019 / Les apocaroténoïdes volatils sont des composés à l’arôme fruité qui contribuent de façon positive à la flaveur des fruits et à la fragrance des fleurs. La régulation de la production de ces composés dans les plantes est encore peu comprise. Ce projet visait à identifier des gènes clés impliqués dans le sentier de production des apocaroténoïdes, dans le but ultime d’améliorer l’arôme des fruits. Chez les tomates, SlCCD1 (Carotenoid Cleavage Dioxygenase 1), malgré sa localisation cytosolique, était considérée comme l’enzyme responsable d’effectuer le clivage oxydatif des caroténoïdes situés dans les plastes afin de libérer des apocaroténoïdes. Cependant, l’étude de lignées de tomates transgéniques et de fleurs de Viola odorata démontre que CCD1 n’est pas une enzyme clé dans la synthèse des apocaroténoïdes chez les fleurs et les fruits et que la présence d’enzymes capables d’accéder aux caroténoïdes est nécessaire. Ces enzymes peuvent être des CCDs localisées dans les plastes, comme VoCCD4 et VoCCD1-like chez V. odorata, ou des lipoxygénases comme TomloxC chez la tomate, capables de co-oxyder les caroténoïdes lors de l’oxydation des acides gras. L’accumulation des caroténoïdes dans les plastes ayant un impact important sur la nature des apocaroténoïdes produits, la synthèse de ces précurseurs a également été étudiée. L’analyse génétique de tomates qui présentent une accumulation anormale du lycopène a mis en évidence l’importance du gène de la phytoène synthase 1 (PSY1) dans le sentier et la façon dont différentes variations structurelles dans ses séquences promotrices et codantes peuvent affecter la couleur des fruits. Le phénotype des cultivars bicolores est notamment causé par une baisse vraisemblable de l’efficacité de la traduction de PSY1 due à une délétion dans sa région 5’UTR, tandis que les cultivars jaunes ry sont le résultat d’une perte de fonction de PSY1 suite à réarrangement complexe en aval du gène. Ces connaissances sur la synthèse des caroténoïdes et des apocaroténoïdes seront utiles afin d’améliorer l’arôme des tomates et de nombreuses autres espèces cultivées. / Volatile apocarotenoids are molecules with a fruity aroma that have a significant impact on the flavor of fruits and the fragrance of flowers. Despite their importance, the regulation of their synthesis in plants in still not fully understood. The main objective of this thesis was to identify key genes involved in the apocarotenoid pathway in order to ultimately improve the aroma of fruits. In tomatoes, SlCCD1 (Carotenoid Cleavage Dioxygenase 1), even if localized in cytosol, was considered the enzyme responsible for the oxidative cleavage of plastid-localized carotenoids. Analyses of transgenic tomato lines and Viola odorata flowers demonstrate that CCD1 is not a key enzyme in apocarotenoid synthesis in flowers and fruits, and that plastidial enzymes are associated with the production of apocarotenoid volatiles. In tomato, the lipoxygenase C co-oxidizes carotenoids while performing fatty acid oxidation. In V. odorata flowers, the considerable production of ionones correlates with the high expression of plastid-localized CCDs such as VoCCD4 and VoCCD1-like. Since carotenoid accumulation in plastid has an important impact on the nature of the apocarotenoids produced, our attention was also drawn to their synthesis. Genetic analysis of tomatoes that show unusual lycopene accumulation demonstrated the importance of the phytoene synthase 1 (PSY1) gene in the pathway, and the way different structural variation in its promoter or coding sequences can affect fruits color. Bicolor cultivars phenotype is notably due to a likely decrease of PSY1 translation efficiency caused by a deletion in the PSY1 5’UTR region. Similarly, yellow cultivars are the result of structural variations in the first or last exon of PSY1. This knowledge on carotenoid and apocarotenoid synthesis will be useful in order to improve the flavor of tomatoes and many other cultivated species.

As our world continues to develop and contend with the impacts of climate change, the scale up renewable energy technologies has never been more urgent. Alternative fuels derived from biomass-derived oxygenates and water splitting offer promising solutions for the transition towards sustainable chemical feedstocks and integration of clean renewable energy sources. However, this technology continues to be hampered by the need for scarce and costly precious metal catalysts. The work done in this thesis explored the facet-dependence of glycerol electrooxidation and studied the application of earth-abundant transition metal carbides (TMCs) and nitrides (TMNs) for reducing precious metal catalyst loadings in water electrolysis and electrooxidation of methanol and glycerol. Glycerol valorization has drawn significant interest in recent years due to the growth in biodiesel production leading to the market saturation of glycerol. While this molecule can be converted into a variety of value-added products, the possibilities have been limited by poor selectivity for C-C bond scission. The breaking of the C-C bonds in glycerol allows for complete extraction of energy from the molecule via complete glycerol oxidation, thereby opening the door for utilizing glycerol as an electrochemical fuel. While platinum (Pt) has been among the most popular catalysts, its tendency for poisoning due to adsorbed CO has hindered its activity. Previously demonstrated to enhance the catalytic activity of platinum (Pt) by reducing CO binding energy and increasing C-C bond scission selectivity in ethanol electrooxidation, TMCs were employed as catalyst supports for the glycerol electrooxidation reaction. This work used electrochemical techniques and in-situ IRRAS to study various loadings of Pt/TaC and Pt/WC to find enhanced C-C bond scission activity at reduced Pt loading because of the synergistic effects between Pt and TMCs. While Pt has remained the benchmark catalyst for glycerol electrooxidation due to its high C-C scission activity, gold (Au) has also found popularity with its high catalytic activity attributed to greater resistance to CO poisoning, despite its favorability for partial glycerol oxidation. Previous studies have hinted at the significance of Au surface facets on glycerol oxidation activity and product selectivity, but none had used nanoparticles with controlled surface facets. This thesis sought to bridge the knowledge gap using precisely-synthesized Au nanocrystals with well-characterized {100}, {110}, and {111} surface facets to provide insight into glycerol electrooxidation on Au. Electrochemical techniques were used in parallel with in-situ IRRAS analysis to uncover the differences in product selectivity and oxidation activity between the three Au surfaces, with Au {111} exhibiting the greatest activity for C-C bond scission, while Au {110} showed the lowest onset potential due to facile AuOH- formation. Hydrogen (H₂) fulfills a critical role in modern society, not only as a renewable fuel, but also as a key chemical feedstock. Production of H₂ from water electrolysis creates opportunities for storing excess energy from renewable sources as an energy-dense fuel and reducing the environmental footprint of chemical processes requiring H₂. However, efforts have been hampered by the dependence on scarce Pt-group catalyst materials. This thesis explores the application of TMNs as an earth-abundant material for enhancing the activity of Pt in the hydrogen evolution reaction (HER). Combined with DFT calculations, the HER activity of monolayer Pt- and Au-modified TMN thin films was correlated with the ΔGH* values in a volcano-type relationship. Electrocatalytic experiments in acidic electrolyte showed that TMN-supported monolayer Pt exhibited similar HER activity to the Pt foil, correlating with intermediate hydrogen adsorption strength. TiN-supported Pt and Au powders were studied to extend the correlations from thin films. Furthermore, the electrochemical stability of TMNs was studied across a wide range of potentials and pH values to generate pseudo-Pourbaix diagrams and identify TMN candidates for HER, alcohol oxidation, ORR and OER applications. Using the pseudo-Pourbaix findings, Pt/TMN catalysts were selected for studying methanol electrooxidation activity. Methanol electrooxidation has drawn significant attention particularly due to interest in direct alcohol fuel cells. Much like the case for glycerol oxidation, while Pt has been the benchmark catalyst, it has been hindered by strong adsorption of CO. As the modification of Pt with other materials, such as ruthenium, has shown promising enhancements to methanol electrooxidation activity, the synergistic effects of Pt modification with TMNs were studied in this work. In the resulting electrochemical experiments, Pt/Mo₂N was found to exhibit negligible activity likely because of its oxidative instability. In contrast, Pt/TiN showed enhanced activity, and in-situ IRRAS experiments suggest that Pt/TiN enhanced the COads-free pathway leading to increased formic acid selectivity. This thesis demonstrated avenues for developing more optimized catalysts with reduced loadings of Pt and other precious metals for applications in alternative fuel production and utilization. The influence of Au surface facets on glycerol oxidation was examined and the synergistic effects between Pt and earth-abundant TMC and TMN materials were used to enhance the electrooxidation of biomass-derived oxygenates and H₂ production from water electrolysis. These electrochemical stability and activity trends can guide future catalyst design for other critical reactions such as oxygen evolution and challenging applications like glycerol electroreduction.

Les huiles végétales ont été identifiées depuis longtemps comme première ressource naturelle à fort potentiel permettant de remplacer le pétrole. Les acides gras insaturés obtenus à partir des huiles végétales constituent une alternative pour la production de biopolymères. La scission oxydative de l’acide oléique (C18:1) conduit aux acides azélaïque et pélargonique. Ces acides gras possèdent de nombreuses applications industrielles : en particulier l’acide azélaïque qui est le premier précurseur dans la fabrication du polymère (nylon-6: 9) utilisé dans l’industrie textile pour la production de vêtements. Actuellement, cette réaction est réalisée dans l’industrie via l’ozonolyse. Cependant, cette réaction pose de nombreux problèmes, l’ozone est un produit dangereux qui comporte un risque élevé d’explosion. L’objectif est donc de mettre au point un procédé de clivage oxydatif performant, moins couteux et moins polluant que l’ozonolyse. C’est ainsi que pour répondre aux principes de chimie durable, nous avons choisi de travailler avec les ultrasons et un système oxydant à base d’eau oxygénée, associée à des nanocatalyseurs sous forme de nanoparticules magnétisables de façon à pouvoir les séparer par application d’un champ magnétique. Ce travail aborde le sujet du développement d’un système permettant la production des monoacides et diacides sous ultrasons dans un réacteur soit discontinu (batch) ou soit à alimentation continue. L’aspect original des conclusions du travail est la vision par laquelle les ondes ultrasonores affectent la vitesse des réactions de clivage oxydatif qui passe de 5 h à 15 min pour des conversions très élevées supérieures à 98 %. En utilisant ce processus, le temps et l’énergie sont sauvés. La cavitation par ultrason est rapide et génère de fines émulsions du système biphasique dans tout le volume du réacteur qui affectent le transfert de matière interphase. Celui-ci est accéléré, ce qui permet de hautes conversions de l’huile de canola en mono et diacides gras (azélaïque et pélargonique) avec un temps de résidence aussi bas que 6 min dans le cas d’un réacteur continu et 15 min dans un réacteur discontinu, sans avoir recours à un solvant organique. La technique de production des acides carboxyliques sous ultrasons est une nouvelle technologie prometteuse pour la fabrication de biopolymères. / Vegetable oils have long been identified as a natural resource with high potential to replace petroleum. Unsaturated fatty acids obtained from vegetable oils are an alternative for the production of biopolymers. The oxidative cleavage of oleic acid (C18: 1) leads to azelaic and pelargonic acids. These fatty acids have many industrial applications: in particular azelaic acid which is a precursor in the manufacture of the polymer (nylon-6: 9) used in the textile industry for the production of clothing. Currently, this reaction is carried out in the industry via ozonolysis. However, this reaction poses many problems, since ozone is a dangerous product with a high risk of explosion. The objective is to develop an efficient oxidative cleavage process, less expensive and less polluting than ozonolysis. Thus, to meet the principles of sustainable chemistry, we chose to work with ultrasound and an oxidizing system based on hydrogen peroxide, associated with nanocatalysts in the form of magnetizable nanoparticles to separate them by a magnetic field. This work deals with the development of a system allowing the production of monoacids and diacids under ultrasound in a batch reactor or a continuous feed reactor. The original aspect of this work is the vision by which the ultrasonic waves affect the speed of the oxidative cleavage reactions which goes from 5 h to 15 min with conversions higher than 98%. Using this process, time and energy are saved. Ultrasonic cavitation is rapid and generates fine biphasic system emulsions throughout the reactor volume that affect interphase material transfer. The latter is accelerated which allows high conversions of canola oil into mono and di-fatty acids (azelaic and pelargonic) with a residence time as low as 6 min in the case of a continuous reactor and 15 min in a batch reactor, without the use of an organic solvent. The technique of producing carboxylic acids under ultrasound is a promising new technology for the manufacture of biopolymers. / Résumé en espagnol

L’objectif de ces travaux de thèse a consisté en le développement de nouveaux accepteurs sulfonylés pour l’élaboration de processus multicomposants radicalaires originaux. De nouvelles réactions de carbo-arylation, carbo-oximation et carbo-alcénylation d’oléfines ont ainsi été mises au point. Nous avons, dans un premier temps, étudié la faisabilité de nouvelles réactions de carbo-hétéroarylation basées sur deux modes d’activation des hétérocycles. Cette méthodologie s’est toutefois révélée être un réel défi en raison de la non-complémentarité des polarités du système, entrainant la formation de plusieurs réactions secondaires et des rendements assez faibles.Dans une seconde partie nous avons étudié le diastéréocontrôle lors de réactions de carbo-oximation d’allylsilanes et d’esters chiraux. Lors de ces processus, les produits de carbo-oximation sont obtenus avec de bons niveaux de diastéréocontrôle mais avec des rendements modestes en raison de l’encombrement stérique et de l’apparition de réactions secondaires. La configuration relative des diastéréoisomères majoritaires n’a pas encore pu être établie avec certitude, mais des modèles d’état de transition peuvent toutefois être proposés afin de prédire la stéréochimie la plus favorable.Dans le but de nous affranchir de l’utilisation d’une quantité stoechiométrique de diétain nous avons également développé de nouveaux accepteurs bi-fonctionnels capables d’agir à la fois comme accepteurs de radicaux nucléophiles et comme sources de radicaux électrophiles via l’α-scission du radical alkylsulfonyle généré. Nous avons mis au point une méthode de préparation de ces accepteurs extrêmement simple et efficace permettant l’accès à une large série de composés.Dans une dernière partie nous avons étendu les résultats obtenus lors des réactions de carbo-alcénylation en préparant de nouveaux accepteurs halogénés et sulfonylés très appauvris en électron par la présence de groupements électroattracteurs. Nous avons finalement réalisé un premier test concluant de carbo-alcénylation à partir d’un vinylsulfoxyde permettant d’envisager la réalisation de ces réactions en version énantiosélective à partir de vinylsulfoxydes énantioenrichis. / This thesis consists in the development of new sulfonylated acceptors for the elaboration of original free-radical multicomponent processes. Thereby, we have developed new free-radical carbo-arylation, carbo-oximation and carbo-alkenylation processes onto olefins.We have first studied the feasibility of new free-radical carbo-heteroarylation based on two different way of activation. This process proved to be very challenging due to the mismatch polarity between the different components, leading to the formation of side reactions and therefore relatively poor yield.In a second part, we examined the diastereocontrol arising from carbo-oximation of chiral allylsilanes and allylic esters. Carbo-oximation products are obtained with high level of selectivity, albeit in modest yields, due to steric hindrance and the formation of side-products. The relative configuration of the major diastereoisomer could not be established, but transition state models may be proposed to predict the most favorable stereochemistry. In order to overcome the use of stoechiometric amount of tin, we have developed new bi-functional reagents which can act both as a trap for nucleophilic radicals as well as a source of electrophilic radical via α-scission of generated alkylsulfonyl radicals. We have developed a very simple and efficient method for the preparation of these acceptors allowing an access to a wide range of compounds.In the final part, we extended the results obtained in the carbo-alkenylation reactions by preparing new activated halogenated and sulfonylated acceptors containing electron-withdrawing groups. We finally carried out a successful test on a carbo-alkenylation reaction using a vinylsulfoxide, offering an entry toward the development of such reactions in an enantioselective series starting from enantioenriched vinylsulfoxides.

Le trafic intracellulaire consiste en la formation et le transport de vésicules ou tubules qui acheminent des composants protéiques et lipidiques entre les différents organites ou avec la membrane plasmique. L’élaboration de ces tubulo-vésicules est initiée par le remodelage local d’une membrane, tout d’abord en générant une courbure puis un bourgeon qui, s’allongeant, forme la tubulo-vésicule. Enfin, la rupture de la membrane, ou scission, libère le transporteur nouvellement formé. Ces étapes repose sur un sculptage profond de la membrane. Ceci requière des forces générées par des moteurs moléculaires, lesquels s’associent aux cytosquelettes comme les microtubules ou les filaments d’actine. Afin de mieux comprendre comment le cytosquelette et leurs moteurs façonnent ces transporteurs, nous avons examiné le rôle de l’actine et de la myosine VI dans la formation de tubules membranaires aux mélanosomes. Les mélanosomes sont des organites apparentés aux lysosomes, générés dans les mélanocytes de la peau et de la choroïde de l’œil, et qui sont le lieu de synthèse et de stockage d’un pigment, la mélanine. Dans l’épiderme, ces compartiments spécialisés évoluent par différentes étapes de maturation qui aboutissent à leurs transferts aux cellules voisines, les kératinocytes. Les mélanosomes sont des organites dynamiques qui reçoivent et recyclent constamment des composants membranaires, comme la SNARE VAMP7. Nous résultats montrent que la myosine VI et son adapteur optineurine se localisent à un sous-domaine spécifique de la membrane des mélanosomes, ou elles contrôlent la scission de tubules. En effet, l’activité motrice de la myosine VI et le réseau d’actine branchée, dépendant des complexes Arp2/3 et WASH, permettent la constriction des membranes du tubule et son détachement du mélanosome. Un défaut de scission de ces tubes engendre des mélanosomes plus pigmentés, enrichis en cargos et au pH plus acide. L’altération de l’homéostasie du mélanosome affecte sa fonction, comme sa capacité à être sécrété et transféré aux kératinocytes. Nos résultats démontrent que la myosine VI en coopération avec le cytosquelette d’actine permet la constriction et fission de membranes aux mélanosomes. Les intermédiaires de transport ainsi formés recyclent des protéines cargos pour leur possible réutilisation, et participent ainsi au maintien de l’homéostasie et de la fonction de ces organites. / Intracellular transport among organelles and the plasma membrane occurs through the formation and transport of vesicular and tubular membrane carriers. The formation of these carriers requires first the bending of membrane and the generation of a bud, followed by its elongation to form the tubule-vesicle. Lastly, the carrier is released from the membrane source by the scission of the membrane. Importantly, all these different steps need an accurate orchestration to properly deform the membrane. The actions exerted by molecular motors onto microtubule and actin cytoskeletons provide forces onto membrane that contribute to its remodeling during the biogenesis of carrier. Actin filaments (F-actin) and myosins are thought to participate in the initiation and the fission of carriers. However, the role of actin machinery during carrier biogenesis remains elusive. We thus decided to address the role of F-actin and the actin-based motor myosin VI in the formation of tubular intermediates at melanosome. Melanosomes are lysosome-related organelles of skin melanocytes and eye pigment cells that function in the synthesis and storage of the melanin pigment. Melanosomes originate from endosomes and progressively mature into fully pigmented compartments, which fate is to be secreted and transferred to neighboring keratinocytes. Melanosomes are dynamic organelles that constantly receive, but also recycle proteins such as the SNARE VAMP7 through the formation and release of tubular intermediates. Our work reveals that myosin VI, together with Arp2/3- and WASH-mediated branched actin localize at specific melanosomal subdomains where they promote the constriction and scission of tubular intermediates. This fission event allows the export of components such as VAMP7 from melanosomes and promotes their maturation and subsequent transfer to keratinocytes. Altogether, our results uncover a new role for myosin VI and F-actin in the constriction and scission of membrane tubules at melanosome that is required for organelle homeostasis and function.

The reaction between the tetrahedrane cluster RCCo3(CO)9{R = CHO (1), H (3)} and the redox-active diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3- dione (bpcd) leads to the replacement of two CO groups and formation of RCCo3(CO)7(bpcd) {R = CHO (2), H (4)}. Clusters 2 and 4 are thermally unstable and readily transform into the new P-C bond cleavage cluster 5. All three clusters 2, 4, and 5 have been isolated and fully characterized in solution by IR and 31P NMR spectroscopy. VT 31P NMR data indicate that the bpcd ligand in RCCo3(CO)7(bpcd) is fluxional at 187 K in THF. Clusters 2, 4, and 5 have been structurally characterized by X-ray diffraction analyses.

Cette thèse rapporte l'étude d'un procédé original de filage continu par coagulation de nanotubes de carbone afin d'obtenir une fibre composite aux propriétés balistiques remarquables. Elle s'intéresse à la caractérisation des fonctions chimiques de surface, de la morphologie et des dimensions des nanotubes aux différentes étapes du procédé. Y sont détaillées une étude quantitative des effets et cinétiques de scission des nanotubes par les ultrasons. Elle présente de plus des travaux relatifs au développement d'une ligne continue de filage des nanotubes de carbone en voie solvant. Des méthodes originales de caractérisation mécanique in-situ de fibre gel sont proposées, permettant notamment un meilleur contrôle des paramètres physicochimiques liés au procédé. Nous espérons que les résultats obtenus participeront à une meilleure compréhension des effets des traitements utilisés pour l'obtention de dispersion homogène de nanotubes de carbone et à un développement des procédés continus de filage textile. / This thesis deals with an original continuous spinning process of carbon nanotubes by coagulation. It focuses on characterization of surface chemical functions, morphology and dimensions of carbon nanotubes at each stage of the process. We present a quantitative study about the effects and kinetics of nanotubes scission induced by ultrasound. We present also the development of a continuous wet-spinning line. We propose methods for in-situ mechanical characterization of gel fibers, which enable a better control of physico-chemical parameters of the process. We hope that these results will participate to a better global comprehension of the effects of treatments used to obtain homogeneous carbon nanotubes suspension and to the development of continuous spinning process of high performance textile fibers.