Stearate anions were successfully intercalated into the layered double hydroxide Mg4Al2(OH)12CO3.3H2O (LDH-CO3) by several methods to form LDH-SA. The intercalation method which involved the acid-base reaction between emulsified stearic acid (SA) and the carbonate anions in aqueous media was studied for the first time. This method led to the formation of more LDH-SA than well known methods such as melting the carboxylic acid in the presence of the LDH, allowing the interlayer region to swell in the presence of glycerol and reconstructing the calcined LDH in the presence of aqueous sodium stearate. Other literature methods involve ion-exchange of Cl- in LDH-Cl with stearate in aqueous sodium stearate, usually under N2 atmosphere. The methods developed in this study are more industrially viable because the more easily produced LDH-CO3 is used and no N2 atmosphere is necessary. The LDH-SA was successfully used to intercalate sodium polyvinyl sulphonate by an ion exchange with the intercalated stearate, without the need for a N2 atmosphere. This method of production could be useful for the production of nanocomposites in general, for example anionic polymer chains (such as DNA) and anionic clays. The same intercalation reaction was allowed to take place in situ during the formation of dextrin-alginate-glycerol film solutions in water-ethanol media. The stearate intercalated as a bilayer in the interlayer region of the LDH. The SA to LDH ratio was varied from 100% SA to 100% LDH. Around the middle of the series a minimum water vapour permeability (WVP) was obtained, which corresponded to an 80% reduction in WVP in comparison to the reference (blank) film. Around the middle of the series a maximum increase in Young’s modulus, corresponding to a 213% increase in comparison to the blank film, was obtained. Around the middle of the series a reduction in the intensity of the basal reflection and interlayer distance showed that some exfoliation (delamination) took place. / Thesis (PhD (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted

Catalysis plays an important part in our society. Numerous transition metal catalysts have been developed which can convert many different substrates in a wide range of reactions. Catalysis also plays an important role in nature and therefore special catalysts, enzymes, have evolved over time. Enzymes are tremendously efficient giving high yields and selectivities both regio and chemical but have a limited substrate and reaction scope. It was speculated that by combining the two, an ideal catalyst can be obtained. We planned to achieve this by introducing a transition metal, the catalytic centre, into the chiral environment of a double helical oligonucleotide. The transition metals were introduced by coordinating them to a ligand which was located in the chiral environment of a double helix. The ligand was either covalently bound (Chapter 2) or non-covalently bound (Chapter 3) to the oligonucleotide (Figure 1). Figure 1: A) covalent introduction of a transition metal into a nucleotide B) non-covalent introduction of a transition metal into a nucleotide For the covalent approach a phosphine ligand was chosen. A nucleoside was modified with an alkyne to which a phosphine moiety could be coupled via the copper catalysed 1,3-dipolar cycloaddition. The modified nucleoside was incorporated into an oligonucleotide before attempting to attach the phosphine moiety. The monomer was used as a ligand in allylic substitution and hydroformylation. In the non-covalent approach polyamide minor groove binders were functionalised with an amine linker. Phosphine moieties were connected via amide bond formation. Although the coupling worked effortlessly the phosphines oxidised during purification therefore dienes were also investigated.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Persisting challenges associated with remediation of heavy metals from aqueous media have stirred the need for enhancement of current technologies. Cellulosic agro waste materials (AWM) as well as ion-imprinted polymers (IIP) have received ardent attention from researchers. These materials are often employed in the following industries: water and wastewater treatment, medical, pharmaceutical and packaging. Applications in water and wastewater treatment have gained significant interest due to desirable features they possess. In the case of AWM, these features include a tuneable surface area and poor porosity, basic surface functional groups and chemical stability. Some desired features in IIP include adsorption sites compatible for the ion imprint obtained after leaching with suitable reagents, rigidity and reusability. The efficacy of employing AWM and IIP for the remediation of toxic chromium from aqueous solution was explored. The current study is made up of part A and B. In part A, Macadamia nutshell powder was treated using HNO3, NaOH, as well as Fenton’s reagent. The three materials underwent a new modification which involved reacting treated adsorbents with cetyltrimethylammonium chloride (CTAC), followed by immobilization of 1,5' diphenylcarbazide (DPC) ligand. The adsorbents were ultimately washed, dried and stored for Cr(VI) batch adsorption experiments. Part B involved a synthesis of IIP and their non-imprinted polymer counterpart (NIP) for Cr(VI) sequestration in aqueous solution. This was done by precipitation polymerization of functional monomers, crosslinker and DPC-Cr(VI) complex as a template. Non-imprinted polymers were fashioned in a manner like that of IIP but with the exclusion of Cr(VI) ion template. Characterizations of the adsorbents were done using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray fluorescence (XRF), and carbon, hydrogen, nitrogen and sulphur (CHNS) analyzer. Batch adsorption experiments were done and parameters such as solution pH, adsorbent dosage, initial Cr(VI) concentration and contact time were optimized. Working solutions were analyzed using ultraviolet-visible (UV-Vis) and atomic absorption (AA) spectroscopy. Adsorption parameters found to be optimum for DPC immobilized cellulosic adsorbents were pH 1.4, adsorbent mass of 0.1 g, 100 mg/L initial concentration and 125 minutes of contact time. The adsorption parameters determined to be optimum for IIP and NIP were pH 2.6, 0.2 g adsorbent mass, 80 mg/L initial concentration and 240 minutes of contact time. Reusability studies demonstrated the potential of adsorbents to remove Cr(VI) ions from aqueous media after successive adsorption-desorption cycles. Selectivity studies indicated that DPC immobilized adsorbents as well as IIP were able to selectively adsorb Cr(VI) ions from aqueous media in the presence of Zn(II), Cu(II), Co(II) and NI(II) ions. Kinetic models revealed that DPC immobilized cellulosic adsorbents and synthetic IIP were most fitting for pseudo-second order and pseudo first order, respectively. On the other hand, adsorption isotherm studies demonstrated that DPC immobilized cellulosic adsorbents and synthetic polymers were best fit for Freundlich and Langmuir adsorption isotherm, respectively.

Basé sur les concepts de développement durable et de chimie verte, l’une des alternatives envisagées par les chimistes, pour une chimie plus propre, est de substituer les solvants organiques, pouvant être dangereux et toxiques, par des solvants plus verts. L’eau est un bon candidat pour cette substitution car c’est le solvant le moins cher dans nos contrées, et le plus sûr : il est non-toxique, ininflammable et non explosif. Afin de palier la faible solubilité de la majeure partie des composés organiques dans l’eau, les tensioactifs peuven têtre utilisés afin d’améliorer les rendements réactionnels. Les milieux ainsi obtenus sont difficilement recyclables car ils nécessitent une forte dilution afin de casser les agrégats et de récupérer les produits. C’est pourquoi, l’utilisation de tensioactifs photo-régulables est une bonne alternative car il est possible d’organiser/désorganiser les agrégats par irradiation lumineuse et ainsi récupérer les composés organiques en fin de réaction tout en recyclant le milieu réactionnel. Pour cela, nous avons synthétisé trois tensioactifs possédant une fonction azobenzène(anionique, cationique, non ionique), afin de les tester en catalyse micellaire. Certains de ces tensioactifs, après en avoir déterminé leurs propriétés physico-chimiques (cmc et spectre UV-Visible) ont été testés dans une réaction pallado-catalysée : la substitution allylique de Tsuji-Trost. Nous avons réussi à démontrer l’intérêt d’utiliser un tensioactif photo-régulable par rapport aux tensioactifs commerciaux en terme de rendement et de recyclabilité. D’autre part, la décarboxylation de Barton, décrite pour la première fois en 1983, permet la formation d’alcanes à partir d’acides carboxyliques en utilisant un dérivé d’étain comme donneur d’hydrogène. Depuis lors, cette réaction a toujours été utilisée comme étape clé en synthèse totale de composés naturels et en solvants organiques. De plus, cette réaction est historiquement réalisée par activation conventionnelle, thermique ou par irradiation ultra-violette. C’est pourquoi, nous avons décidé d’étudier cette décarboxylation radicalaire dans l’eau, en présence de tensioactifs et en utilisant des modes d’activation non conventionnels : les micro-ondes et les ultrasons. De plus, en lieu et place d’étain, nous avons préféré l’utilisation de N-phénylmaléimide, déjà connu et étudié comme piège à radicaux, afin d’obtenir des maléimides substitués par des chaînes carbonées. Les rendements obtenus en milieux micellaires se sont avérés être aussi bons, voire meilleurs qu’en solvants organiques. / Based on concepts of sustainable development and green chemistry, one of the alternatives envisioned by chemists is to substitute organic solvents, which can be dangerous and toxic, for greener solvents. Water is the best candidate for this substitution because it is thesafest and cheapest solvent in our countries : this solvent is non-toxic, non-flammable and inexplosive. In order to overcome the low solubility of most of organic compounds in water, surfactants can be used to improve the reaction yields. Media thus obtained are difficult to recycle because they require high dilution in order to break aggregates and recover products. Therefore, using photo-switchable surfactants is a good alternative because they can organize/disorganize by light irradiation. Organic compounds could be recovered after reactions and the recyclability of the medium can be improved. For this purpose, we synthesized three surfactants having an azobenzene moiety (anionic,cationic, nonionic), to test them in micellar catalysis. Some of these surfactants, after determining their physicochemical properties (CMCs and UV-visible spectra) were studied in a pallado-catalyzed reaction, the allylic substitution of Tsuji-Trost. We have successfully demonstrated the value of using a photo-switchable surfactant compared to commercialones in terms of yields and recyclability. In other hand, Barton decarboxylation, described for the first time in 1983, permits the formation of alkanes from carboxylic acids, using tin derivatives as hydrogen donors. Since then, this reaction has always been used as a key step in total synthesis of natural compounds in organic solvents. In addition, historically, this reaction was carried out by conventional activation (heat or ultraviolet light). Therefore, we decided to study this radical decarboxylation in water, in the presence of surfactants and using unconventional activation modes : microwave and ultrasound. Moreover, instead of tin, we preferred the use of N-phenylmaleimide, already known and studied as a radical trap, to obtain maleimides substituted by carbon chains. Yields obtained in micellar media were found tobe at least as good as in organic solvents.

Au cours de ces dernières années, la microfluidique est devenue une technologie attrayante pour la synthèse en écoulement continu de dispersions colloïdales de nanocristaux. Ce procédé permet un contrôle optimal des paramètres de synthèse, offre une très bonne reproductibilité, et la possibilité de transposition à grande échelle. Dans une première partie, nous avons développé des synthèses microfluidiques et écologiques de cristaux ZIF 8, adaptables à une grande échelle de production, avec un écoulement monophasique ou biphasique (eau/alcane). La technologie microfluidique permet la synthèse rapide (10 min) de cristaux ZIF-8 avec une large variation de taille de particules (de 300 à 900 nm) simplement en faisant varier les paramètres expérimentaux (débit, température, ...). Les cristaux de ZIF-8 obtenus sont de forme géométrique dodécaèdrique rhombique, de structure cristalline sodalite et leur surface spécifique est d’environ 1700 m2/g. Puis, les propriétés catalytiques des particules ZIF-8 ont été évaluées. Des 3-cyanocoumarines et des cyanoesters α,β-insaturés ont été synthétisés avec des rendements variant de 89 à 95% via la réaction de Knoevenagel utilisant les particules ZIF-8 comme catalyseur hétérogène. Les particules de ZIF-8 peuvent être recyclées au minimum cinq fois. Dans la seconde partie de ce mémoire, nous avons synthétisé des QDs CdS dopé Mn2+ et Cu+ recouverts d’une coquille ZnS en microréacteur tubulaire avec un écoulement monophasique ou biphasique (eau/alcane). Différents paramètres expérimentaux (temps de séjour, température, pH, rapport molaire des précurseurs, concentration et nature des précurseurs, …) ont été évalués afin d’optimiser les propriétés optiques. Les QDs CdS dopé Mn2+ présentent uniquement l’émission de fluorescence liée à la transition 4T1→6A1 et leur rendement quantique de fluorescence est voisin de 10%. L’introduction d’une coquille ZnS en écoulement monophasique permet d’améliorer les propriétés optiques et de réduire les défauts des surfaces des QDs 6%Mn:CdS/ZnS (émission à 590 nm et rendement quantique de 20 %). L’introduction d’une coquille ZnS à la périphérie des QDs Cu:CdS ne permet pas d’améliorer de manière significative le rendement quantique de fluorescence. Dans la dernière partie, la synthèse en microréacteur avec écoulement monophasique ou biphasique (eau/alcane) de QDs ZnS dopé Mn2+ a été développée. Les QDs obtenus possèdent un rendement quantique de 13% s’ils sont préparés en écoulement monophasique / In recent years, microfluidics has become an attractive technology for the continuous flow synthesis of colloidal nanocrystals. This technology allows a good control of the synthesis parameters, a good reproducibility and the possibility of the application on a large scale. In a first part, we have developed continuous and ecological syntheses of the ZIF-8 crystals for the large scale, either with a monophasic or a biphasic flow (water/alkane). The microfluidic technology allows the fast synthesis (10 min) of ZIF-8 crystals over a wide size range (from ca. 300 to 900 nm) simply by varying the experimental parameters (flow rates, temperature,…). ZIF-8 crystals with the stable rhombic dodecahedron shape, of sodalite structure and with a high specific surface area (ca. 1700 m2.g-1) were obtained. Next, the catalytic properties of ZIF-8 crystals were evaluated. These particles were demonstrated to be an efficient heterogeneous catalyst for the Knoevenagel synthesis of α,β-unsaturated cyanoesters and of 3-cyanocoumarins using 2-hydroxy aromatic aldehydes and ethyl cyanoacetate as starting materials (yields ranging from 89 to 95%). The ZIF-8 particles can be recycled at least five times with negligible changes in catalytic performances. In the second part, we synthesized the Mn2+ or Cu+-doped CdS QDs coated with a ZnS shell in a tubular microreactor using a monophasic or a biphasic flow (water/alkane). Various experimental parameters (time, temperature, pH, molar ratio, concentration and nature of the starting materials) were evaluated to optimize the optical properties of the dots. The obtained Mn2+ doped CdS QDs exhibited a photoluminescence emission related to the 4T1 → 6A1 transition with quantum yields higher than 10%. The introduction of a ZnS shell with the monophasic flow allows to improve the optical properties and to reduce the surface defects of the 6% Mn:CdS/ZnS QDs (strong emission at 590 nm and quantum yields of ca. 20%). The introduction of a ZnS shell on the surface of Cu doped CdS QDs does not significantly improve the quantum yields. Finally, the synthesis of Mn2+-doped ZnS QDs with monophasic or biphasic flow (water/alkane) was developed. The dots have a photoluminescence quantum yield of 13% if they are prepared in a monophasic water flow

L'objectif principal de ce travail de thèse est la synthèse et l'étude des propriétés en solution de nouveaux copolymères amphiphiles di- et triblocks à gradient de styrène et d'acide acrylique qui sont capables d'association réversible en milieu aqueux. Nous avons étudié la cinétique et le mécanisme de la polymérisation radicalaire contrôlée par l’intermédiaire d’un nitroxyde (NMP), afin de déterminer les caractéristiques quantitatives des réactions de terminaison réversible lors de ce processus. Puis la NMP a été utilisée pour la synthèse de deux architectures différentes de copolymère à gradient: copolymères di- et triblocs. L'auto-assemblage des copolymères à gradient dans l'eau a été étudiée par DLS, SANS et TEM. Les changements réversibles du nombre d'agrégation au cours des cycles de pH ont été observés. De plus, nous avons étudié l'effet du pH et de la force ionique sur les propriétés rhéologiques en solution de copolymères triblocs à gradient. Nous nous sommes également intéressés à synthétiser des brosses de polymère sur surface d'or et étudié leur propriétés pH et électro-sensibles en milieu aqueux. / The main goal of our work was the synthesis and the study of solution properties of novel amphiphilic di- and triblock-gradient copolymers based on styrene and acrylic acid which are capable of reversible association in aqueous solution. We studied the kinetics and the mechanism of nitroxide-mediated radical polymerization (NMP) in order to determine the quantitative characteristics of the reversible termination reaction in this process. Then NMP was employed to the synthesis of two different block-gradient copolymer architectures: di- and triblock-gradient copolymers. The self-assembly of the block-gradient copolymers in water was studied by DLS, SANS and TEM. The reversible changes of aggregation numbers in cycles of pH were observed. We also investigated the effect of pH and ionic strength on rheological properties of triblock-gradient copolymer solution. Then, we synthesized polymer brushes on the gold-coated surface and studied their pH- and electro-responsive properties in aqueous media.

Ce travail porte sur l'étude de la capacité d'absorption du CO2 par différents types d'amines dissoutes en milieux aqueux et non aqueux. Ce dernier est constitué d'un mélange de chlorure de choline et d'éthylène glycol dans une proportion molaire respectivement de 1 pour 2. Ce solvant, communément appelé "Ethaline", appartient à la catégorie dite des « Solvants à Eutectique Profond » ainsi désignés car leur composition eutectique permet d'obtenir des mélanges généralement liquides à température ambiante. Pour ce faire un appareil d'équilibre liquide-vapeur avec analyse en ligne de la phase vapeur par GC a été réalisé et son fonctionnement validé. Les isothermes d'absorption du CO2 ainsi que la volatilité (composition de la phase vapeur) des mélanges étudiés, avec et sans CO2, ont été déterminées à différentes températures et pour différentes compositions en amines. Le domaine de pression exploré est particulièrement large : du Pascal à 800 kPa. L'étude a montré que la substitution de l'eau par "l'Ethaline" conduit à une capacité d'absorption du CO2 presque identique à celle de la MEA et DEA en solution aqueuse. Par contre dans le cas de la MDEA on observe une capacité d'absorption plus faible en milieu « Ethaline » qu'en milieu aqueux. Les isothermes d'absorption du CO2 des trois classes d'amines en milieu aqueux et non aqueux ont été corrélés par les modèles semi empiriques de (Gabrielsen et al., 2005) initialement établis par ces auteurs pour les solutions aqueuses (un modèle pour les amines primaires et secondaires conduisant à la formation de carbamates en présence de CO2, un modèle pour les amines tertiaires donnant des sels d'ammonium avec le CO2). Nous avons montré que ces deux modèles représentent avec succès les isothermes d'absorption en milieu non aqueux. Les constantes d'équilibre et les enthalpies de réaction qui s'en déduisent montrent que ces dernières sont plus faibles (en valeur absolue) pour la MEA et TMDEA en solution éthaline qu'en solution aqueuse. Dans le cas de la MDEA la nature du solvant n'a qu'une influence minime sur l'enthalpie de réaction. Les valeurs expérimentales des volatilités des amines dans les différents mélanges Amine- CO2 en milieu aqueux ont été corrélées par différents modèles semi-empiriques. Trois modèles thermodynamiques de coefficients d'activité ; le modèle de Wilson, NRTL et UNIQUAC ont été utilisés afin de restituer les données expérimentales de l'équilibre liquide-vapeur des systèmes aqueux d'amines (sans CO2). Une représentation satisfaisante des résultats expérimentaux par les trois modèles a été obtenue / This work focuses on the study of the absorption capacity of CO2 by different types of dissolved amines in aqueous and non-aqueous media. The latter consists of a mixture of choline chloride and ethylene glycol in a molar proportion of 1 to 2 respectively. This solvent, commonly called "Ethaline", belongs to the category called "Deep Eutectic Solvents" so designated because their eutectic composition makes it possible to obtain mixtures that are generally liquid at room temperature. With this aim, a liquid-vapor equilibrium apparatus with on-line analysis of the vapor phase by GC was performed and its operation validated. The CO2 absorption isotherms and the volatility (composition of the vapor phase) of the studied mixtures, with and without CO2, were determined at different temperatures and for different amine compositions. The explored pressure range is particularly large: from 1 Pa to 800 kPa. The study showed that the substitution of water by "Ethaline" leads to a CO2 absorption capacity almost identical to that of MEA and DEA in aqueous solution. On the other hand, in the case of MDEA, a lower absorption capacity is observed in Ethaline than in aqueous medium. In the hypothesis of a use of the DES+amine solvent for CO2 capture in post-combustion process, a decrease of the vapor pressure of the solvent (comparing to that of water+amine) has an advantage because of the low solvent loss due to vaporization in the absorber. The second advantage is most likely a lower effect of equipment corrosion, the third positive point is a lower enthalpy of absorption of MEA and MDEA in (1 ChCl : 2 EG) comparing to aqueous medium, resulting in a possible saving of energy in the regenerator of almost 40%. The disadvantage of the use of amines in "Ethaline" solution is the high viscosity of this solvent which decreases the kinetics of material transfer and reaction with CO2. The CO2 absorption isotherms and the experimental values of the amine volatilities in the different Amine-H2O-CO2 mixtures were well correlated by different semi-empirical models. Three thermodynamic models based on the activity coefficients; the Wilson model, NRTL and UNIQUAC were used to restitute experimental data for the liquid-vapor equilibrium of aqueous amine systems (without CO2). A satisfactory representation of the experimental results by the three models was obtained

The current study discusses the preparation and long-term performance of polymer composites used for various purposes under different ageing conditions. The first part deals with the preparation and characterization of polymer nanocomposites based on poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types with different specific surface areas and different hydroxyl-group concentrations; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). The nanocomposite with EBA–13 showed better overall nanoparticle dispersion while EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates. The activity of hindered phenolic antioxidant (0.2 wt%) in all EBA nanocomposites was assessed by determining the oxidation induction time using DSC. The composites containing uncoated aluminium oxide nanoparticles showed a much shorter initial OIT than the pristine polymer with the same initial concentration of antioxidant, indicating adsorption of antioxidant onto the nanoparticle surfaces. Composites containing coated nanoparticles showed a significantly smaller decrease in the initial OIT, suggesting the replacement of hydroxyl groups with organic silane tails, decreasing the concentration of available adsorption sites on the nanoparticle surfaces. The decrease in OIT with increasing ageing time in dry air at 90 °C of the nanocomposites was slower than that of the unfilled pristine polymer, suggesting a slow release of antioxidant from adsorption sites. The EBA nanocomposites exposed to liquid water at 90°C showed faster decrease of OIT than samples exposed to dry or humid air. The migration rate of antioxidant was controlled by the boundary conditions in the case of ageing in humid air and liquid water. The antioxidant diffusivity was lower for the composites containing uncoated ND than for the composites containing ND coated with octyltriethoxysilane or aminopropyltriethoxysilane. The migration and chemical consumption of deltamethrin DM, (synthetic pyrethroid) and synergist piperonyl butoxide from molded polyethylene sheets was also studied. Deltamethrin and piperonyl butoxide are often used for food  storage and insect control purposes. DM showed no signs of crystallization and remained in a liquid state after being cooled to room temperature. Exposure of polyethylene compound sheets to liquid water (at 80 &amp; 95 °C), caused degradation and hydrolysis of the ester bond in the DM, present in the prepared material, and generated species containing hydroxyl groups. Liquid chromatography and infrared spectroscopy showed a significant migration of the active species in liquid water, whereas in air at 80 °C (60 and 80 %RH) the loss of DM and PBO was negligible over 30 days. The long-term performance of medium-density polyethylene stabilized with six different phenolic antioxidants (0.1 wt%) in aqueous chlorinated media at 70 °C was studied. The results were compared with data for previously studied solutions of antioxidants in squalane (a liquid, low molar mass analogue of polyethylene). A linear relationship was established between the time to reach antioxidant depletion in polyethylene tape samples and the time in squalane samples. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion. / <p>QC 20121109</p> / Cable insulation materials / Loss of deltamethrin and pipronyl butoxide from polyethylene / long-term performance of polyethylene in chlorine dioxide water

Les dérivés phosphorylés de nucléosides naturels ou d'analogues (appelés nucléotides) sont des composés primordiaux largement utilisés comme outils biologiques. Certains d'entre eux présentent également un fort potentiel thérapeutique en particulier comme agents antiviraux ou antitumoraux. La préparation des dérivés polyphosphorylés de nucléosides demeure cependant un challenge du fait de rendements de synthèse parfois faibles et des multiples étapes de purification longues et fastidieuses. Ce manuscrit relève donc de la problématique globale de synthèse de ces composés. Le premier chapitre est consacré à l’étude non exhaustive des méthodes de synthèse décrites dans la littérature pour ces dérivés, en rappelant les avantages et inconvénients de ces approches. Le deuxième chapitre rapporte la voie de synthèse en milieux aqueux de nucléotides, et de quelques analogues, que nous avons développée. Des résultats préliminaires de mécanosynthèse basée sur cette même approche sont également présentés. Enfin, le troisième chapitre porte sur deux voies de synthèse supportée de nucléotides. L’une implique la cytidine et son ancrage sur polyéthylène glycol afin de fournir les dérivés 5’-di- et triphosphate correspondants. L’autre porte sur le développement d’un support tétrapode inédit en vue de son utilisation pour la synthèse de dérivés de l'adénosine. / Phosphorylated derivatives of endogenous nucleosides or analogues (called nucleotides) are crucial compounds widely used as biological tools. Some of them also have a high therapeutic potential, in particular as antiviral or antitumor agents. However, the synthesis of polyphosphorylated derivatives of nucleosides remains a challenge due to low yields as well as long and tedious multiple purification steps. Thus, this manuscript is dealing with the overall problem of synthesis of these compounds. The first chapter is devoted to the non-exhaustive study of the synthetic methods described in the literature for such compounds, recalling the advantages and disadvantages of these approaches. In the second chapter, we report our contribution to an original synthetic pathway in aqueous media of some nucleotides and analogues. Some preliminary results of mecanosynthesis based on the same approach are also presented. Finally, the third chapter refers to supported synthesis of nucleotides with two different approaches. One involves cytidine and its anchoring on polyethylene glycol in order to provide the corresponding 5'-di- and triphosphate derivatives. The other concerns the development of a novel tetrapod support that may be valuable for the synthesis of adenosine derivatives.

Des recherches sur de nouvelles sources énergétiques ont été initiées pour faire face à la hausse de la demande mondiale. Dans le domaine nucléaire, la filière Th-U est envisagée pour compléter ou remplacer la filière U-Pu. Toutefois, des améliorations technologiques sont nécessaires avant l’aboutissement industriel de ce projet, notamment sur l’adaptation du procédé de retraitement du combustible U-Pu à celui du cycle Th-U, qui consiste à dissoudre le combustible en milieu acide nitrique, suivi d’une extraction liquide-liquide. Or, contrairement à l’uranium, l’oxyde de thorium n’est pas soluble dans HNO₃ concentré. Un ajout de petites quantités de fluorures est nécessaire à l’obtention d’une dissolution totale. Cependant, la dissolution reste lente et le milieu HNO₃-HF est très corrosif. L’objectif de cette étude est de comprendre les réactions mises en jeu afin d’optimiser la composition de la solution pour diminuer la corrosion et améliorer la cinétique de dissolution. La poudre d’oxyde de thorium synthétisée en laboratoire est solubilisée dans des conditions expérimentales et selon un protocole prédéfinis. L’effet des caractéristiques du solide, de la méthode de dissolution et du milieu de dissolution ont été étudiés. La morphologie de l’oxyde a une forte influence sur la vitesse de dissolution. L’impact majeur des ultrasons de puissance est l’augmentation de la température, qui améliore considérablement la vitesse de dissolution. Le remplacement des fluorures par d’autres complexants du thorium n’a pas permis d’atteindre une dissolution quantitative de l’oxyde. L’augmentation des concentrations de HF et de HNO₃ accélère la dissolution, mais une concentration trop importante de fluorure mène à la formation d’un précipité blanc qui passive la surface. Sur la base de cette étude, un mécanisme réactionnel a été proposé. L’étape limitante est la formation d’un complexe activé. L’écriture et la résolution des équations cinétiques et des équilibres thermodynamiques a permis d’établir une relation analytique exprimant le taux de dissolution de ThO₂ en fonction des paramètres expérimentaux. La simulation des résultats expérimentaux à l’aide de cette relation a ensuite permis de déterminer les constantes thermodynamiques et cinétiques rendant compte de tous les phénomènes observés, validant ainsi le mécanisme proposé. / Studies of new energy sources are necessary to meet the rising global demand. In the nuclear area, Th-U cycle has been reinvestigated to supplement or replace the currently used U-Pu cycle. This project though needs further improvement to be operated in an industrial plant, especially on the reprocessing process, which consists in fuel dissolution in nitric acid medium, followed by liquid-liquid extraction. Still, unlike uranium, thorium oxide does not dissolve in concentrated nitric acid. Small amounts of fluoride are required to achieve the dissolution. The dissolution is rather slow and HNO₃-HF mixture is very corrosive. The aim of this project is thus to find an efficient dissolution method which both decreases corrosion and improves dissolution rate. The synthetized thorium oxide powder has been dissolved in chosen conditions. Effects of solid parameters, dissolution method and dissolution medium have been studied. Results show a strong dependence on oxide crystallinity. No improvement on dissolution rate was observed with power ultrasounds, except for the temperature increase, which greatly enhances dissolution rate. No other complexing agents than fluoride allows total dissolution. Rising HNO₃ and HF concentrations increases dissolution rate until the amount of fluorides is so high that a precipitate forms at the surface. This study led to the proposal of a dissolution mechanism whose limiting step is the formation of an activated complex. Based on kinetics and equilibrium equations, initial dissolution rate was then written as a function of the different studied parameters. Experimental results were finally fitted by this relation to find kinetics and thermodynamics constants, proving the accuracy of the proposed mechanism.