Dans cette étude nous avons étudié la polymérisation de l’aniline en milieu aqueux micellaire eau-acide décylphosphonique (DcPA) ainsi qu’en milieu micellaire inverse acide décylphosphonique/eau/n-heptane : chloroforme (2 :1 v/v). Contrairement au système aqueux micellaire, la vitesse de polymérisation dans le système micellaire inverse augmente lorsque la concentration en DcPA dans le milieu réactionnel diminue. Ce résultat a été attribué à des différences de compacité de la couronne hydrophobe des micelles inverse, qui impactent la diffusion de l’aniline au cœur des gouttelettes d’eau, le lieu préférentiel de la polymérisation.La conductivité électrique maximale obtenue est de 3.6 S.cm-1. Cette valeur de conductivité est plus élevée de 4 ordres de grandeur comparée à la conductivité électrique de PANI dopée DcPA préparée par post-traitement de la PANI EB avec une solution de DcPA (2.3x10-4 S cm-1). Les analyses de diffraction des rayons X (DRX) ont révélé une structure lamellaire de la polyaniline préparée en milieu micellaire eau-DcPA dans laquelle les chaînes de polyaniline sont séparées par les longues chaînes alkyle du DcPA. Cette organisation diminue les interactions interchaînes de la polyaniline et contribue à l’augmentation de la solubilité en milieu organique de la polyaniline.La polyaniline dopée DcPA a été incorporée comme pigment dans un liant polymère polyvinyl butyral (PVB), puis appliqué sur un acier à faible teneur en carbone. Dans le cas de la polyaniline préparée dans le milieu aqueux micellaire de DcPA, la dispersion de polyanilinea été également appliquée après dialyse sur acier en couche mince, puis revêtue d’une couche de finition PVB. Les films PVB-PANI ont été exposés à des environnements neutres chlorurés (brouillard salin et milieu NaCl 3.5%). A partir de mesures de spectrométrie d’impédance électrochimique, nous avons montré que l’efficacité de la protection anticorrosion de la polyaniline dopée DcPA augmentait avec le taux de dopant DcPA du polymère. Ces résultats suggèrent un rôle actif du DcPA dans le mécanisme de protection. Ce rôle actif du DcPA a été confirmé par analyse de la surface métallique après exposition qui a révélé la présence de sels de phosphonates de fer insoluble. La protection anticorrosion apportée par polyaniline dopée DcPA apparaît supérieure à la polyaniline non dopée ainsi qu’à la polyaniline dopée HCl. / In this thesis, the polymerization of aniline in micellar solutions of decylphosphonic acid (DPA) as well as reversed micellar solutions of decylphosphonic acid / water / n-heptane : chroloform (2 : 1 vol/vol) was investigated. Unlike micellar solution, the polymerizations rate in the reversed micellar solution increases as the DPA concentration in the reaction medium decreases. This result was attributed to the packing density of DPA molecules in the surfactant shell of inverse micelles, which affects the diffusion of aniline into the inner of the water droplets in which the polymerization is preferred. The maximum electrical conductivity obtained is 3.6 S.cm-1. This value is four orders in magnitude greater than the value of DPA doped PANI prepared by postsynthesis treatment of the PANI-base with the solution of DPA (2.3 x 10-4 S.cm-1). The results of the X-ray diffraction analysis suggested the formation of layered structure of PANI backbone separated by long alkyl side chains of DPA. This organization reduces interchain interactions of the polyaniline and contributes to the increase in solubility of PANI in an organic solvent.The DPA doped PANI was incorporated as a pigment in the polymer binder polyvinyl butyral (PVB), and then applied to a steel material with a low content of carbon. In the case of the polyaniline prepared in the micellar solution of DPA, the dispersion of PANI was also applied to steel with thin layer after dialysis, and then coated with a top coat PVB. The PVB-PANI coatings applied on steel substrates are exposed in neutral saline corrosive media such as salt-spray or 3.5% NaCl solution. Based on the electrochemical impedance spectroscopy measurements, it is found that the corrosion protection efficiency of the DPA doped PANI increases with the amount of dopant of DPA. These results show an active role of DPA in the mechanism of protection. The active role of DPA was also confirmed by the analysis of the exposed metallic surface with the presence of insoluble phosphonate of iron. The corrosion protection provided by the DPA doped PANI appears better than the undoped polyaniline and the one doped with HCl.

Highly fluorinated organic compounds are emerging environmental contaminants of concern, due to their persistence, ubiquitous distribution, bioaccumulation potential and toxicity. Ski waxes are sources of highly fluorinated chemicals to the environment that have not been investigated so far. Some contain fluorinated additives such as semifluorinated n-alkanes (SFAs). This thesis investigated the fate of SFAs after abrasion onto snow through skiing activities. Furthermore, perfluorinated alkyl acids (PFAAs) were found to be present in fluorinated ski waxes. A lot of attention has been paid to elucidating the environmental fate of PFAAs during the past decade. However, nothing was known so far about their release from melting snow packs. Analytical methods for quantification of SFAs in different environmental matrices were developed. The methods were used to investigate the fate of SFAs during snow melt and to study their occurrence in ski areas. Laboratory snow melt experiments and model-based fate simulations suggested that SFAs will sorb to the snow grain surface and particles in the bulk snow and, after snowmelt, will end up on the underlying (soil) surface. SFAs were detected and quantified for the first time in snow and soil samples taken from a ski area in Sweden. Comparison of concentrations in snow and soil did not give any evidence for long-term accumulation of SFAs in surface soil, but suggested volatilization of shorter chain homologues during snow melt. Such a volatilization could also explain an observed SFA pattern difference between snow and soil samples. Laboratory scale snow melt experiments were also used to investigate the behavior of PFAAs during snowmelt. PFAAs were released with the melt water from the snow pack in pulses. The pulses occurred early, late or with a so far unknown peak elution in the middle of the snowmelt, depending on the hydrophobicity of the PFAAs. These peak releases were further influenced by the age of the snow pack and thus the snow surface area and to a lesser extent by pH and ion concentrations.

Physisorption and reaction at silicon surfaces of a series of brominated organic molecules: bromoethane, 1,2-dibromoethane, 1-bromopropane, 1-bromobutane and 1-bromopentane were examined by Scanning Tunneling Microscopy (STM). On Si(111)-7×7, a widely-spaced “one-per-corner-hole” pattern was observed, formed by the physisorption and reaction of several alkyl bromides. This “one-per-corner-hole” pattern suggested long-range repulsion between the adsorbates. Density Functional Theory (DFT) calculations, performed by others in parallel with these experiments, showed that this long-range repulsion was due to lateral charge transfer in the Si(111)-7×7 surface consequent on the physisorption of an alkyl bromide or chemisorption of a Br atom. The reaction rate of bromine ‘abstraction’ (transfer of a Br-atom from the adsorbate to the silicon) was examined for two physisorbed states of 1 bromopentane on Si(111)-7×7, one vertical and one horizontal, each distinguishable by STM. The energy barrier was found to be significantly lower for abstraction of Br-atom from the vertical than for the horizontal 1 bromopentane, both for thermal and electron-induced reaction. This finding accords with previous DFT calculations for methyl bromide, for which theory exhibited a clear preference for a vertical transition state in the bromination of Si(111)-7×7. The effect of alkyl chain-length on the rate of thermally-induced dissociative attachment reactions was investigated for a series of primary bromo-alkanes (bromoethane, 1-bromopropane and 1-bromobutane) on a different face of silicon; Si(100)-c(4×2). These three bromo-alkanes all physisorbed exclusively ‘inter-row’, bridging the gap between Si dimer-rows of Si(100)-c(4×2). Thermal reaction was highly ‘localized’, i.e. the chemisorbed Br-atom was formed directly below the parent bromo-alkane. The thermal barrier heights were found experimentally to increase systematically with chain length. This trend was interpreted, on the basis of DFT calculations performed by the author, as being due to the extra energy required to lift the alkyl group in going from the initial physisorbed state to the more-nearly vertical transition state.

Tridentate "pincer" ligands provide a unique balance of stability and reactivity in organometallic chemistry. The development of diarylamido-based PNP pincer ligands has led to many applications in catalysis, including the potential to facilitate unique chemical transformations at transition metal centers. The main objective of this thesis was to explore transition metal chemistry supported by the PNP pincer framework for both early and late transition metals. In Chapter I, the history behind the design and synthesis of pincer complexes is described. The advantages and disadvantages of various pincer ligands are reviewed to show the reasoning behind the synthesis of the PNP pincer framework. Chapter II discusses the synthesis of novel Hf and Ta complexes involving the PNP ligand. Reactions of (PNP)HfCl3 with large alkyl Grignards led to double alkylation and triple alkylation was achieved with methyl Grignard. (PNP)HfMe3 and (PNP)Hf(CH2SiMe3)2Cl displayed remarkably irregular coordination environments about hafnium, in contrast to the approximately octahedral structure of (PNP)HfCl3. (PNP)HfMe3 was found to be thermally stable at 75 degrees C, whereas thermolysis of (PNP)Hf(CH2SiMe3)2Cl under similar conditions led to a mixture of products. The major decomposition product is believed to be a Hf alkylidene complex on the basis of in situ NMR spectroscopic observations (e.g., delta 248.2 ppm in the 13C{1H} NMR spectrum). The reaction of (PNP)TaF4 with an excess of ethyl Grignard led primarily to the double alkylation product, (PNP)Ta(CH2CH3)2F2. Repeating this reaction in the presence of excess ethyl Grignard and dioxane resulted in the formation of an ethylene complex, (PNP)Ta(=CHCH3)(C2H4). In Chapter III, a C-C reductive elimination study is described comparing two pincer ligand scaffolds: Me(PNP) ligand and TH(PNP) ligand. The tied ligand has previously been found to be more sterically demanding than the untied ligand, which has allowed for faster N-C cleavage, faster oxidative addition and a more selective alkyne dimerization catalyst. This study reveals that the tied ligand complex, TH(PNP)Rh(C6H4CF3)(Ph), undergoes slower reductive elimination of p-Ph-C6H4CF3 (< 4% after 7 h at 38 degrees C; t1/2 = 7.7 h at 64 degrees C; t1/2 = 2.13 h at 75 degrees C) than Me(PNP)Rh(C6H4CF3)(Ph) (t1/2 = 15.6 min at 38 degrees C).

Physisorption and reaction at silicon surfaces of a series of brominated organic molecules: bromoethane, 1,2-dibromoethane, 1-bromopropane, 1-bromobutane and 1-bromopentane were examined by Scanning Tunneling Microscopy (STM). On Si(111)-7×7, a widely-spaced “one-per-corner-hole” pattern was observed, formed by the physisorption and reaction of several alkyl bromides. This “one-per-corner-hole” pattern suggested long-range repulsion between the adsorbates. Density Functional Theory (DFT) calculations, performed by others in parallel with these experiments, showed that this long-range repulsion was due to lateral charge transfer in the Si(111)-7×7 surface consequent on the physisorption of an alkyl bromide or chemisorption of a Br atom. The reaction rate of bromine ‘abstraction’ (transfer of a Br-atom from the adsorbate to the silicon) was examined for two physisorbed states of 1 bromopentane on Si(111)-7×7, one vertical and one horizontal, each distinguishable by STM. The energy barrier was found to be significantly lower for abstraction of Br-atom from the vertical than for the horizontal 1 bromopentane, both for thermal and electron-induced reaction. This finding accords with previous DFT calculations for methyl bromide, for which theory exhibited a clear preference for a vertical transition state in the bromination of Si(111)-7×7. The effect of alkyl chain-length on the rate of thermally-induced dissociative attachment reactions was investigated for a series of primary bromo-alkanes (bromoethane, 1-bromopropane and 1-bromobutane) on a different face of silicon; Si(100)-c(4×2). These three bromo-alkanes all physisorbed exclusively ‘inter-row’, bridging the gap between Si dimer-rows of Si(100)-c(4×2). Thermal reaction was highly ‘localized’, i.e. the chemisorbed Br-atom was formed directly below the parent bromo-alkane. The thermal barrier heights were found experimentally to increase systematically with chain length. This trend was interpreted, on the basis of DFT calculations performed by the author, as being due to the extra energy required to lift the alkyl group in going from the initial physisorbed state to the more-nearly vertical transition state.

No description available.

Quaternary ammonium compounds (QACs) are widely used in commercial and consumer applications as disinfectants, fabric softeners, hair conditioners, and emulsifying agents. The massive production and utilization of QACs has led to their extensive discharge into the environment, raising concerns globally. Several studies have reported on potential risks and detrimental effects of QACs on the natural environment and public wastewater treatment plants. Biological treatment has been found to be an effective way to remove QACs and especially aerobic treatment processes can provide rapid biodegradation via a consortium of bacteria. Although extensive research has been conducted on the fate and effect of QACs, relatively little is known about their effect on aerobic biological treatment processes, especially on nitrification. Research was conducted on the fate and effect of alkyl benzyl dimethyl ammonium chloride (AB), a QAC widely used as disinfectant, in mixed aerobic and nitrifying cultures. The results of this study demonstrated that up to 50 mg/L AB was efficiently degraded in a mixed aerobic culture fed with dextrin and peptone, although trace residual AB levels were observed. Nitrification of the produced ammonia was complete at an AB concentration of 20 mg/L after an acclimation period, but was almost completely inhibited at 50 mg/L. Mixed aerobic cultures maintained only with AB as external nitrogen and carbon source achieved a high degree of AB degradation at both 20 and 50 mg/L. Ammonia oxidation by a nitrifying culture, enriched with ammonium chloride and sodium bicarbonate, was inhibited with increasing AB concentration and completely ceased at 15 mg/L AB. Degradation or utilization of AB was not observed for all tested AB concentrations between 2 to 20 mg/L. Based on these experimental results, and assuming non-competitive inhibition, a relatively low value of the AB inhibition coefficient was obtained, which indicates a relatively high susceptibility of the ammonia oxidizers to AB. The results of this study have significant implications for both engineered and natural systems relative to the fate and effect of QACs.

This dissertation is devoted to our synthetic studies towards the total synthesis of the natural product Nakadomarin A, and Manzamine A using the Pauson-Khand reaction as the key step. Chapter 1 reviews past work using Pauson-Khand technology. Chapter 2 reviews the N-alkyl piperidine family of natural products. Chapter 3 reviews published total syntheses of Manzamine A and Nakadomarin A. Chapter 4 explores our work using the Pauson-Khand reaction to form the ABC rings of Nakadomarin A and subsequent B ring expansion to form the ABC ring core of Manzamine A. Chapter 5 explores our approaches to the furan portion, as well as, our approaches to the macrocyclic F ring. Finally Chapter 6 contains the description of the experiments performed along with relevant analytical data. / text

Percutaneous delivery of drugs promises many advantages over oral or intravenous administration, such as a better control of blood levels, a reduced incidence of systemic toxicity, an absence of hepatic first-pass metabolism, better patient compliance, etc. However, the dermal drug transport is limited by the unsuitable physicochemical properties of most drugs and the efficient barrier function of the skin. Thus, numerous attempts have been reported to improve topical absorption of drugs, concentrating mainly on the barrier function of the stratum corneum by use of penetration enhancers and/or skin warming. An alternative and interesting possibility for improved dermal permeability is the synthesis of derivatives or analogues with the aim of changing the physicochemical properties in favour of skin permeation, efficacy and therapeutic value. Cyclizine (I) is an anti-emetic drug primarily indicated for the prophylaxis and treatment of nausea and vomiting associated with motion sickness, post operation and Meniere's disease. It acts both on the emetic trigger zone and by damping the labyrinthine sensitivity. Pharmacologically it has anti-histaminic, antiserotonergic, local anaesthetic and vagolytic actions. It is widely used and also suitable for children from six year of age. Percutaneous absorption of (I) can, among others, avoid the "first-pass" effect and the discomfort of injection. The main objective of this study was to explore the feasibility of percutaneous absorption of (I) and its alkyl analogues via physicochemical characterization and assessment of their permeation parameters. The intent was also to establish a correlation between the physicochemical properties of these compounds and their percutaneous rate of absorption. To achieve these objectives, the study was undertaken by synthesizing the alkyl analogues and determining the physicochemical parameters relevant to skin transport. Identification and level of purity for the prepared analogues were confirmed by mass spectrometry (MS), nuclear magnetic resonance (NMR) spectrometry and infrared (IR) spectrometry. Experimental aqueous solubility (25 °c & 32 °C) and partition coefficient for each compound were determined. In vitro permeation studies were performed at pH 7.4, using Franz diffusion cells with human epidermal membranes. Diffusion experiments were conducted over a period of 24 hours maintaining a constant temperature (37 DC) by means of water bath. All samples were analysed by high pressure liquid chromatography (HPLC). Cyclizine (I) has a methyl group at N-4. Increasing the alkyl chain length on N-4 of the piperazine ring resulted' in compounds with lower melting points and higher water solubility than (I). (II) exhibited 3-fold increase in water solubility, followed by (IV) with about 2.5 fold increase. The water solubility of (III) was almost the same as that of (I). Log partition coefficients increased linearly with increasing alkyl chain length. The analogues therefore, possessed more favourable physicochemical properties to be delivered percutaneously. Indeed, the in vitro skin permeation data proved that these analogues could be delivered more easily than (I) itself. The flux of (I) was 0.132 ug/cm2/h in a saturated aqueous solution. Compound (II) resulted in a 53-fold (6.952 ug/cm2/h) increase in permeation compared to (I). (III) and (IV) resulted in a 2- and 5fold enhancement of permeation respectively. Based on the results of the study, it seems that increased aqueous solubility and low level of crystallinity play a vital role in optimizing percutaneous absorption of (I) and its alkyl analogues. But the importance of the effect of increased lipophilicity cannot be ignored. The low percutaneous• absorption of (I) might be attributed to its low aqueous solubility and increased crystallinity, as is evident from the higher melting point than the analogues. From all the permeability data using aqueous solutions, it is clear that compound (II) is the best permeant of this series and in addition it is known that this compound antagonizes the effects of histamine. / Thesis (M.Sc. (Pharm.))--North-West University, Potchefstroom Campus, 2004.

No description available.