<p>One of the most powerful aspects of conducting polymers is their ability to be nanostructured through innovative, synthetically manipulated, transformations, such as to tailor-make the polymers for specialized applications. In the exponentially increasing wide field of nanotechnology, some special attention is being paid to innovative hybrid dendrimer-core based polymeric smart materials. Star copolymers are a class of branched macromolecules having a central core with multiple linear polymer chains extending from the core. This intrinsic structural feature yields a unique 3D structure with extended conjugated linear polymer chains, resulting in star copolymers, which have higher ionic conductivities than their corresponding non-star conducting polymer counterparts. In this study an in-depth investigation was carried out into the preparation and characterization of specialized electronic &lsquo / smart materials&rsquo / . In particular, the preparation and characterization of novel conducting dendrimeric star copolymers which have a central poly(propylene imine) (PPI) dendrimer core with conducting polypyrrole (PPy) chains extending from the core was carried out. This involved, first, the preparation of a series of dendrimeric polypyrrole poly(propylene imine) star copolymers (PPI-co-PPy), using generations 1 to 4 (G1 to G4) PPI dendrimer precursors. The experimental approach involved the use of both chemical and electrochemical synthesis methods. The basic procedure involved a condensation reaction between the primary amine of a diamino functional PPI dendrimer surface and 2-pyrrole aldehyde, to afford the pyrrole functionalized PPI dendrimer (PPI-2Py). Polymerization of the intrinsically contained monomeric Py units situated within the dendrimer backbone was achieved via two distinctly different routes: the first involved chemical polymerization and the second was based on potentiodynamic oxidative electrochemical polymerization. The star copolymers were then characterized using various sophisticated analytical techniques, in-situ and ex-situ. Proton nuclear magnetic resonance spectroscopy (1HNMR) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structures. Scanning electron microscopy (SEM) was used to determine the morphology. Themogravimetric analysis (TGA) was used to study the thermal stability of the prepared materials. X-ray diffraction analysis (XRD) was used to study the structural make-up of phases, crystallinity and amorphous content. Hall effect measurements were carried out to determine the electrical conductivity of the chemically prepared star copolymers. The PPI-co-PPy exhibited improved thermal stability compared to PPI-2Py, as confirmed by TGA. SEM results showed that the surface morphology of the functionalized dendrimer and star copolymer differed. The surface morphology of the chemically prepared star copolymers resembled that of a flaky, waxy material, compared to the ordered morphology of the electrochemically grown star copolymers, which resembled that of whelk-like helixes. In the case the electrochemically grown star copolymers, SEM images recorded at higher magnifications showed that the whelk-like helixes of the star copolymers were hollow tubes with openings at their tapered ends, and had an average base diameter of 2.0 &mu / m. X-ray diffraction analysis of the first generation star copolymer G1PPI-co-PPy revealed a broadly amorphous structure associated with PPy, and crystalline peaks for PPI. Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivity of the star copolymer materials. Electrochemical impedance spectroscopy data showed that the G1PPI-co-PPy exhibited slightly higher ionic conductivity than pristine PPy in lithium perchlorate. The second generation star copolymer G2PPI-co-PPy electrochemically deposited on a platinum (Pt) electrode had a lower electrochemical charge transfer resistance compared to electrodeposited polypyrrole (PPy) on a Pt electrode, and bare Pt. The decrease in charge transfer resistance was attributed to an increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicated that G2PPI-co-PPI was a semiconductor, with a maximum phase angle shift of 45.3&deg / at 100 MHz. The star copolymer exhibited a 2- electron electrochemistry and a surface coverage of 99%. Results of Hall effect measurements showed that the star copolymer is a semiconducting material, having a conductivity of 0.7 S cm-1, in comparison to the 1.5 S cm-1 of PPy. To the best of my knowledge, these new star copolymers have not been reported in the open literature. Their properties make them potentially applicable for use in biosensors.</p>

Myelin and oligodendrocytes (OLGs) are the apparent targets of the immune-mediated injury that underlies the development of multiple sclerosis (M8). Recovery from M8 clinical relapses likely reflects remyelination attributed to recruitment and differentiation of oligodendrocyte progenitor cells (OPCs), rather than to new process formation by previously myelinating OLGs. Newly emerging M8-directed immuno-modulatory therapies (statins and FTY720) can readily cross the blood-brain barrier and have been shown to impact signaling pathways implicated in cytoskeletal regulation, differentiation, migration, and survival; these are cellular events presumably important for myelin integrity and remyelination. / Statins inhibit the production of cholesterol (concentrated in the myelin membrane) and isoprenoids (post-translational attachments regulating the functions of proteins such as the Rho GTPases). We showed that treatment of human and rodent-derived OPCs with lipophilic statins induced an initial process extension associated with enhanced differentiation and impaired spontaneous migration, whereas prolonged treatment induced process retraction and cell death. Rodent and human mature OLGs demonstrated similar cytoskeletal and survival responses. Chronic simvastatin therapy of mice inhibited remyelination following demyelination induced by the OLG toxin, cuprizone, attributed to a block in OPC differentiation and consequent decrease in mature OLGs. Even fully myelinated animals treated with simvastatin over the long-term demonstrated a decrease in myelin in the brain by maintaining oligodendroglial cells in the pre-OLG state and preventing continual replacement of mature OLGs. / FTY720 is an agonist of G-protein-coupled receptors S1P1, 3, 4, and 5, that are associated with distinct receptor isotype-selective activation of Rho GTPases. In human OPCs, FTY720 could induce initial S1P3/5-dependent process retraction associated with an inhibition of differentiation, and subsequent S1P1-dependent process extension. Mature OLGs showed a dose-dependent cyclic modulation of process extension and retraction was observed over time. Both human OPCs and OLGs were rescued by FTY720 under death-promoting environments. Both cell types also demonstrated a cyclic and reciprocal modulation of S1P1 and S1P5 mRNA levels, reflected in the recurring receptor isotype-dependent functional responses over time. Studies using organotypic cerebellar slice cultures demonstrated that FTY720 did not impact myelin integrity under basal conditions, yet accelerated remyelination following lysolecithin-induced demyelination. Both treatment regimens were associated with an extension of OPC and mature OLG processes. / Our observations demonstrate that drug concentrations used to modulate immune function can have differential dose and time-dependent effects on OPCs, OLGs, as well as on myelin and remyelination processes. Our findings indicate the need to monitor the effects of putative immuno-modulatory therapies on myelin-related processes in MS patients.

<p>One of the most powerful aspects of conducting polymers is their ability to be nanostructured through innovative, synthetically manipulated, transformations, such as to tailor-make the polymers for specialized applications. In the exponentially increasing wide field of nanotechnology, some special attention is being paid to innovative hybrid dendrimer-core based polymeric smart materials. Star copolymers are a class of branched macromolecules having a central core with multiple linear polymer chains extending from the core. This intrinsic structural feature yields a unique 3D structure with extended conjugated linear polymer chains, resulting in star copolymers, which have higher ionic conductivities than their corresponding non-star conducting polymer counterparts. In this study an in-depth investigation was carried out into the preparation and characterization of specialized electronic &lsquo / smart materials&rsquo / . In particular, the preparation and characterization of novel conducting dendrimeric star copolymers which have a central poly(propylene imine) (PPI) dendrimer core with conducting polypyrrole (PPy) chains extending from the core was carried out. This involved, first, the preparation of a series of dendrimeric polypyrrole poly(propylene imine) star copolymers (PPI-co-PPy), using generations 1 to 4 (G1 to G4) PPI dendrimer precursors. The experimental approach involved the use of both chemical and electrochemical synthesis methods. The basic procedure involved a condensation reaction between the primary amine of a diamino functional PPI dendrimer surface and 2-pyrrole aldehyde, to afford the pyrrole functionalized PPI dendrimer (PPI-2Py). Polymerization of the intrinsically contained monomeric Py units situated within the dendrimer backbone was achieved via two distinctly different routes: the first involved chemical polymerization and the second was based on potentiodynamic oxidative electrochemical polymerization. The star copolymers were then characterized using various sophisticated analytical techniques, in-situ and ex-situ. Proton nuclear magnetic resonance spectroscopy (1HNMR) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structures. Scanning electron microscopy (SEM) was used to determine the morphology. Themogravimetric analysis (TGA) was used to study the thermal stability of the prepared materials. X-ray diffraction analysis (XRD) was used to study the structural make-up of phases, crystallinity and amorphous content. Hall effect measurements were carried out to determine the electrical conductivity of the chemically prepared star copolymers. The PPI-co-PPy exhibited improved thermal stability compared to PPI-2Py, as confirmed by TGA. SEM results showed that the surface morphology of the functionalized dendrimer and star copolymer differed. The surface morphology of the chemically prepared star copolymers resembled that of a flaky, waxy material, compared to the ordered morphology of the electrochemically grown star copolymers, which resembled that of whelk-like helixes. In the case the electrochemically grown star copolymers, SEM images recorded at higher magnifications showed that the whelk-like helixes of the star copolymers were hollow tubes with openings at their tapered ends, and had an average base diameter of 2.0 &mu / m. X-ray diffraction analysis of the first generation star copolymer G1PPI-co-PPy revealed a broadly amorphous structure associated with PPy, and crystalline peaks for PPI. Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivity of the star copolymer materials. Electrochemical impedance spectroscopy data showed that the G1PPI-co-PPy exhibited slightly higher ionic conductivity than pristine PPy in lithium perchlorate. The second generation star copolymer G2PPI-co-PPy electrochemically deposited on a platinum (Pt) electrode had a lower electrochemical charge transfer resistance compared to electrodeposited polypyrrole (PPy) on a Pt electrode, and bare Pt. The decrease in charge transfer resistance was attributed to an increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicated that G2PPI-co-PPI was a semiconductor, with a maximum phase angle shift of 45.3&deg / at 100 MHz. The star copolymer exhibited a 2- electron electrochemistry and a surface coverage of 99%. Results of Hall effect measurements showed that the star copolymer is a semiconducting material, having a conductivity of 0.7 S cm-1, in comparison to the 1.5 S cm-1 of PPy. To the best of my knowledge, these new star copolymers have not been reported in the open literature. Their properties make them potentially applicable for use in biosensors.</p>

Philosophiae Doctor - PhD / One of the most powerful aspects of conducting polymers is their ability to be nanostructured through innovative, synthetically manipulated, transformations, such as to tailor-make the polymers for specialized applications. In the exponentially increasing wide field of nanotechnology, some special attention is being paid to innovative hybrid dendrimer-core based polymeric smart materials. Star copolymers are a class of branched macromolecules having a central core with multiple linear polymer chains extending from the core. This intrinsic structural feature yields a unique 3D structure with extended conjugated linear polymer chains, resulting in star copolymers, which have higher ionic conductivities than their corresponding non-star conducting polymer counterparts. In this study an in-depth investigation was carried out into the preparation and characterization of specialized electronic smart materials. In particular, the preparation and characterization of novel conducting dendrimeric star copolymers which have a central poly(propylene imine) (PPI) dendrimer core with conducting polypyrrole (PPy) chains extending from the core was carried out. This involved, first, the preparation of a series of dendrimeric polypyrrole poly(propylene imine) star copolymers (PPI-co-PPy), using generations 1 to 4 (G1 to G4) PPI dendrimer precursors. The experimental approach involved the use of both chemical and electrochemical synthesis methods. The basic procedure involved a condensation reaction between the primary amine of a diamino functional PPI dendrimer surface and 2-pyrrole aldehyde, to afford the pyrrole functionalized PPI dendrimer (PPI-2Py). Polymerization of the intrinsically contained monomeric Py units situated within the dendrimer backbone was achieved via two distinctly different routes: the first involved chemical polymerization and the second was based on potentiodynamic oxidative electrochemical polymerization. The star copolymers were then characterized using various sophisticated analytical techniques, in-situ and ex-situ. Proton nuclear magnetic resonance spectroscopy (1HNMR) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structures. Scanning electron microscopy (SEM) was used to determine the morphology. Themogravimetric analysis (TGA) was used to study the thermal stability of the prepared materials. X-ray diffraction analysis (XRD) was used to study the structural make-up of phases, crystallinity and amorphous content. Hall effect measurements were carried out to determine the electrical conductivity of the chemically prepared star copolymers. The PPI-co-PPy exhibited improved thermal stability compared to PPI-2Py, as confirmed by TGA. SEM results showed that the surface morphology of the functionalized dendrimer and star copolymer differed. The surface morphology of the chemically prepared star copolymers resembled that of a flaky, waxy material, compared to the ordered morphology of the electrochemically grown star copolymers, which resembled that of whelk-like helixes. In the case the electrochemically grown star copolymers, SEM images recorded at higher magnifications showed that the whelk-like helixes of the star copolymers were hollow tubes with openings at their tapered ends, and had an average base diameter of 2.0 mu;m. X-ray diffraction analysis of the first generation star copolymer G1PPI-co-PPy revealed a broadly amorphous structure associated with PPy, and crystalline peaks for PPI. Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) techniques were used to study and model the electrochemical reactivity of the star copolymer materials. Electrochemical impedance spectroscopy data showed that the G1PPI-co-PPy exhibited slightly higher ionic conductivity than pristine PPy in lithium perchlorate. The second generation star copolymer G2PPI-co-PPy electrochemically deposited on a platinum (Pt) electrode had a lower electrochemical charge transfer resistance compared to electrodeposited polypyrrole (PPy) on a Pt electrode, and bare Pt. The decrease in charge transfer resistance was attributed to an increase in the conjugation length of the polymer as a result of the linking of the highly conjugated PPy to the PPI dendrimer. Bode impedimetric analysis indicated that G2PPI-co-PPI was a semiconductor, with a maximum phase angle shift of 45.3&deg; at 100 MHz. The star copolymer exhibited a 2- electron electrochemistry and a surface coverage of 99%. Results of Hall effect measurements showed that the star copolymer is a semiconducting material, having a conductivity of 0.7 S cm-1, in comparison to the 1.5 S cm-1 of PPy. To the best of my knowledge, these new star copolymers have not been reported in the open literature. Their properties make them potentially applicable for use in biosensors. / South Africa

No description available.

In recent years, metal-organic frameworks (MOFs) have been identified as promising adsorbents in a number of industrially relevant, yet challenging, separations, including the removal of propane from propane/propylene mixtures and the separation of mixtures of xylene isomers. The highly tuneable nature of MOFs - wherein structures may be constructed from a variety of diverse building blocks – has resulted in the publication of a staggering number of frameworks incorporating a wide range of network topologies, pore shapes and pore diameters. As a result, there are a huge number of candidate adsorbents to consider for a given separation. Molecular simulation techniques allow the identification of those structural features and characteristics of a MOF which exert the greatest influence on the adsorption and separation of the compounds of interest, providing insights which can both guide the selection and accelerate the development of adsorbents for a specific application. The separation of propane/propylene mixtures via adsorption has typically focused on selective adsorption of the olefin, propylene, via specific olefin-adsorbent interactions. These propylene-selective MOFs result in processes which selectively remove the most abundant species in the process stream and are typically characterised by high heats of adsorption, resulting in large adsorption units and adsorbents which are difficult to regenerate. In this work, the capability of MOFs to selectively adsorb propane over propylene is explored, potentially allowing for the design of smaller and more energy-efficient adsorption units. By studying a range of different MOFs as well as carbon-based model pores, it was found that the low-pressure selectivity of the structure is determined by the strength of the electrostatic interaction between propylene and the framework, while the adsorptive preference at industrially-relevant pressures is dominated by the enhanced packing efficiency of propylene over propane. The confinement of C3 molecules, however, may be employed to negate this entropic advantage and guide the development of materials which selectively adsorb propane over propylene. It has recently been reported that the adsorptive preference of a MOF for one xylene isomer over another may be predicted based solely on the pore size distribution of the structure. In this work, the impact of pore size on selectivity was studied systematically in both one-dimensional model pore systems of varying geometries and analogous published MOF structures. The ability of the framework to discriminate between xylene molecules in these systems was found to be determined primarily by the different packing arrangements available to the different isomers – while small pores were found to favour the slimmest of the isomers, larger pores were found to favour the more compact ortho- isomer. Finally, the adsorption and diffusion of xylene isomers in a more complex MOF, UiO-66(Zr), was studied in depth. Simulations were able to correctly predict the previously-reported preference of the MOF for ortho-xylene (oX). The smaller volume of the oX molecule compared to the other isomers was found to be responsible both for an enhanced entropic contribution and higher guest-host interaction energies. The importance of framework flexibility in the diffusion of xylene isomers in UiO-66(Zr) was also explored, with distortion of the structure in response to interaction with adsorbed molecules found to be essential in allowing xylenes to diffuse through the pore space.

No description available.

Metal-Organic Frameworks (MOFs) are nanoporous framework materials with tunable pore size and functionality, and hence attractive for gas separation membrane applications. Zeolitic Imidazolate Frameworks (ZIFs), a subclass of MOFs, are known for their high thermal and chemical stability. ZIF-8 has demonstrated potential to kinetically separate propane/propene in powder and membrane form. ZIF-8 membranes propane-propene separation performance is superior in comparison to polymer, mixed matrix and carbon membranes. The overarching theme of my research is to address challenges that hinder fabrication of MOF membranes on a commercial scale and in a reproducible and scalable manner. 1. Current approaches, are specific to a given ZIF, a general synthesis route is not available. Use of multiple steps for surface modification or seeding causes reproducibility and scalability issues. 2. Conventional fabrication techniques are batch processes, thereby limiting their commercialization. Here we demonstrate two new approaches that can potentially address these challenges. First, we report one step in situ synthesis of ZIF-8 membranes on more commonly used porous α-alumina supports. By incorporating sodium formate in the in situ growth solution, well intergrown ZIF-8 membranes were synthesized on unmodified supports. The mechanism by which sodium formate promotes heterogeneous nucleation was investigated. Sodium formate reacts with zinc source to form zinc oxide layer, which in turn promotes heterogeneous nucleation. Sodium formate promotes heterogeneous nucleation in other ZIF systems as well, leading to ZIF-7, Zn(Im)2 (ZIF-61 analogue), ZIF-90, and SIM-1 films. Thus one step in situ growth using sodium formate provides a simplified, reproducible and potentially general route for ZIF film fabrication. One step in situ route, although advantageous; is still conventional in nature and batch process with long synthesis time. This limits commercialization, due to scalability and manufacturing cost issues. Taking advantage of coordination chemistry of MOFs and using temperature as driving force, continuous well-intergrown membranes of HKUST-1 and ZIF-8 in relatively short time (15 min) using Rapid Thermal Deposition (RTD). With minimum precursor consumption and simplified synthesis protocol, RTD provides potential for a continuous, scalable, reproducible and commercializable route for MOF membrane fabrication. RTD-prepared MOF membranes show improved separation performances, indicating improved microstructure.

Depuis les années 70, la synthèse de carbonates organiques a rencontré un grand intérêt dans diverses applications de l’industrie chimique. Parmi ces composés, le carbonate de diméthyle, qui est à la base de la fabrication de certains polycarbonates, est particulièrement intéressant. C’est un excellent solvant, et plus récemment, il s’est révélé être un additif potentiel pour les essences grâce à son contenu élevé en oxygène. Encore aujourd’hui, au niveau industriel, la synthèse de carbonate de diméthyle est basée sur l’utilisation de réactifs dangereux tels que le phosgène ou le monoxyde de carbone. Pour s’aligner sur les demandes de la chimie verte, une recherche assidue a été développée afin de trouver une voie de synthèse plus propre mais efficace qui pourrait être appliquée au niveau industriel. Parmi celles-ci, la voie la plus appropriée est la réaction directe du CO2 et du méthanol en présence d’un catalyseur capable d’activer le dioxyde de carbone. Dans ce travail, l’activité des complexes de type métallophthalocyanines a été testée en conditions atmosphériques et sous haute pression et haute température. Les méthodes de spectroscopie infrarouge, UV-visible etRMN ont été mise en oeuvre pour caractériser les intermédiaires réactionnels formés. Les travaux ont démontré que ces complexes métalliques possèdent une capacité d’activation du CO2 et du méthanol pour former le carbonate de diméthyle, tout en ayant une activité catalytique encore trop faible pour envisager de développer un procédé industriel. Ce type de complexes a cependant montré une activité satisfaisante pour la synthèse de carbonate de propylène à partir de CO2 et d’oxyde de propylène. / Since the 1970’s, the synthesis of organic carbonates has been of a strong interest in applications in the chemical industry as an intermediate in the synthesis of polycarbonates, as a solvent and more recently as a possible additive in gasoline due to its high oxygen content. Until now, industrial dimethyl carbonate synthesis has been based on the use of harmful reagents such as phosgene and carbon monoxide. To bring it into line with the requirements of green chemistry, research has been carried out to find a cleaner way of synthesis that could be also applied at an industrial scale. It was found that one of the most suitable chemical routes is the use of carbon dioxide and methanol in the presence of a catalyst that is able to activate the CO2 molecule. In this work, the activity of metallophthalocyanine complexes was tested under atmospheric, as well as high pressure and high temperature conditions. Infrared, UV-visible and RMN spectroscopy has been used to attempt to identify the reaction intermediates. In this work metallophthalocyanine complexes have been shown to activate methanol and CO2 molecules by forming dimethyl carbonate. However, the yields are too low to develop a chemical process at the industrial scale. Nevertheless, this type of complex has shown to be active in the synthesis of propylene carbonate from carbon dioxide and propylene oxide.

L’oxydation catalytique du propylène en acroléine en phase gazeuse est un procédé complexe et fortement exothermique, faisant intervenir de nombreuses réactions consécutives et compétitives. Une des clés pour maximiser le rendement en acroléine est le contrôle rigoureux de la température du mélange réactionnel ; il s’agit de lever les limitations aux transferts thermiques, afin d’évacuer l’importante chaleur de réaction. Un échangeur-réacteur milli-structuré a ainsi été retenu pour intensifier le procédé. En effet, de par la taille millimétrique de ses canaux ainsi que le choix d’un dépôt du catalyseur industriel sur les parois internes de ceux-ci, les transferts de chaleur et de matière sont améliorés. Afin de réaliser ce dimensionnement, une étude préliminaire de la cinétique des réactions a été réalisée et un modèle cinétique a été déterminé. Ce dernier a été utilisé afin de dégager les conditions optimales de fonctionnement d’un canal réactif (température, nombre de canaux composition), et afin d’extrapoler ces conditions sur un agencement structuré des canaux réactifs. La forme des chambres de distribution et de collecte du réacteur-échangeur ainsi que sa structure ont été déterminées et optimisées afin d’atteindre un rendement élevé par un contrôle optimal de la température, de minimiser la maldistribution des fluides et d’assurer la sécurité du procédé. Ce réacteur-échangeur intensifié, à la géométrie complexe, a finalement été fabriqué par impression 3D, au sein du projet français FAIR (Fabrication Additive pour l’Intensification des Réacteurs) / The catalytic oxidation of propylene to acrolein is a complex and highly exothermic process carried out in the gas phase, involving consecutive and competitive reactions. To maximize the efficiency of this process, the temperature needs to be rigorously controlled and the thermal transfers must be maximized, in order to evacuate the heat released by the reactions. A millistructured reactor-exchanger has thus been chosen to intensify this process. Indeed, millimetric channels washcoated with an industrial catalyst provide intensified heat and mass transfer. To carry out this design, a preliminary study of the kinetics of these reactions was carried out and a kinetic model was determined. This model was then used to identify the optimal operating conditions of a single reactive channel (temperature, number of channels, composition), and to extrapolate these conditions for the design of an intensified reactor exchanger. The shape of the distribution and collect chambers of these reactive channels were then optimized to minimize maldistribution, maximize the acrolein yield with an optimal control of the temperature, and to ensure the safety of the process. This intensified reactor-exchanger with complex geometry was finally manufactured by 3D printing, within the French project FAIR (Additive Manufacturing for the Intensification of Reactors)