Polymer brushes are extremely versatile materials, as monomer choice allows the user to design a material with the desired physiochemical properties. Given the wide variety in monomer functionality, polymers can be fine-tuned for a specific application. In this work, polymer brushes bound to a silica support are designed and utilized to enhance performance of protein extraction and chromatographic separations. <br> The effectiveness of an analytical method is strongly affected by matrix composition, however, the presence of species other than the target analyte is usually unavoidable. An excellent technique will be able to identify and/or quantify the analyte even when its concentration is low compared with interfering molecules. Protein analysis is particularly challenging, since many proteins of clinical and scientific significance are present in complicated matrices such as plasma or cell lysates. <br>A common method to specifically separate a protein from a complicated matrix is solid phase extraction. In this method, a species (such as an antibody) with high specificity towards the target is immobilized onto a solid substrate (commonly beads or small particles for greater surface area). Next, the target is collected onto the surface, bound by the species. The solid substrate is rinsed of the liquid matrix, before elution of the target. Only the active species should interact with the analyte, and the surface should be otherwise inactive. However, nonspecific interactions lead to binding/adsorption of undesirable compounds. Therefore, an optimal substrate for protein extraction must be 1) easily and completely removable from the liquid phase, 2) have a high concentration of active sites for specific binding, and 3) exhibit low nonspecific binding. As part of this work, commercial magnetic particles were coated with a nonporous silica layer that tolerates the acid bath and silane coating necessary to attach a polymer layer. On the silane coating, a polymer layer was covalently bound; this layer contains epoxide active groups for immobilizing antibodies. These antibodies bind to the target molecule with high specificity, and low nonspecific binding. Obtained particles were evaluated for protein extraction, where antibodies as well as specifically engineered drug compounds were successfully bound to the particle surface.<br>Glycosylation influences several physiopathological processes in proteins. Glycans can act as receptors, modify protein solubility, and participate in folding conformation. Altered glycosylation is a common feature in tumorous cells. As such, many modifications in glycoproteins have been related to cancer, including increased branching of N-glycans or augmented units of sialic acid. Therefore, characterization of glycoproteins is important not only as a diagnostic tool, but also to monitor patients’ response to treatment. Furthermore, it is important in the growing field of monoclonal antibodies as drug carriers. <br>Among different methods used for glycosylation analysis, Hydrophilic Interaction Liquid Chromatography (HILIC) has showed important advantages over time-consuming digestion-MS based techniques. An adequate HILIC stationary phase can be used to rapidly differentiate glycoforms present in a sample. In the second part of this work, a polymer brush based bonded phase was developed as a HILIC stationary phase. The new polymer improved the separation of a model glycoprotein compared with a commercial HILIC column, while also exhibiting enhanced stability over a previous bonded phase synthetized in our group.<br><br>

O objetivo deste trabalho foi desenvolver biosensores de membranas baseados na técnica de Ressonância Plasmônica de Superfície (SPR) e aplicá-los no estudo da interação do citocromo c (cit c) com modelos de membranas. SPR é uma técnica ótica, que através de medidas de variações de índice de refração (n) próximas a uma interface mensura com alta sensibilidade a adsorção ou ligação de moléculas. Inicialmente desenvolvemos um sistema de gradiente de fluxo acoplado ao SPR, denominado FIG-SPR, e demonstramos a determinação automatizada da variação de n em função da concentração (dn/dC) de diferentes compostos e biopolímeros. O desenvolvimento dos biosensores de membranas iniciou-se com o estudo dos fatores que afetam a formação de uma membrana de bicamada híbrida (HBM). HBMs são compostas de uma monocamada de alcanotiol adsorvida sobre o ouro, e sobre esta uma camada fosfolipídica. A formação da HBM depende da fusão de vesículas em superfícies hidrofóbicas e que não é bem compreendido no nível molecular. Nossos estudos mostraram que na presença de cálcio e espermina a formação da HBM é favorecida, de tal forma que a monocamada de fosfolipídio alcança valores de espessura próximos àqueles previstos, cerca de 20 &#197;\'. Além disso, mostramos que em soluções de baixa força iônica a camada lipídica não é homogênea. Demonstramos também que a presença de cálcio na concentração 150 mM diminui o tempo de formação da monocamada lipídica cerca de 14 vezes quando comparado ao tempo indicado na literatura. A homogeneidade da HBM e a carga superficial da mesma foram verificadas com a adsorção e a dissociação de cit c e de albumina bovina (BSA). Utilizando HBMs de composição lipídica variada demonstramos a adsorção e a dissociação de cit c induzida por cálcio em HBMs mistas, incluindo um modelo mimético da membrana mitocondrial interna (IMM) constituído de fosfatidilcolina, fosfatidiletanolamina e cardiolipina (PC/PE/CL) na proporção (4,5:3,5:2,0). Demonstramos que a adsorção de cit c nativo segue um perfil cooperativo e padrões esperados de variação de afinidade e cooperatividade em pHs 6,8, 7,4 e 8,0. Um modelo matemático foi desenvolvido para tratar as curvas de ligação de cit c, que é uma adaptação do modelo de Hill para adsorção de proteínas em superfícies. Os resultados de SPR juntamente com dados obtidos por Microscopia de Força Atômica (AFM) sugerem que a ligação cooperativa de cit c com HBM ocorre devido à reorganização das moléculas de CL e formação de domínios fosfolipídicos. O tratamento dos resultados cinéticos da dissociação de cit c por cálcio indica a existência de duas constantes de velocidade de dissociação (kd), sendo a primeira constante (kd1) relacionada à perda das interações eletrostáticas entre a proteína e a HBM, e a segunda (kd2) à perda das interações hidrofóbicas. Além disso, a dissociação do cit c do modelo estudado requer uma concentração mínima de cálcio de 30 &#181;M para se tornar significativa. O estudo da interação entre moléculas de cit c foto-oxidadas (citc405) e a HBM de PC/PE/CL sugerem que ela ocorre com menor afinidade, nos três pHs estudados, se comparados aos resultados com cit c nativo. Além disso, nossos resultados sugerem que o citc405 não é facilmente dissociado por cálcio devido à perda da cooperatividade na interação. Possíveis implicações em eventos celulares destas descobertas, como a liberação do cit c da IMM e a iniciação da apoptose, são discutidas / The aim of this work was to develop membrane biosensors based on Surface Plasmon Resonance (SPR) and to apply them to study the interactions between cytochrome c (cyt c) and model membranes. SPR is an optical technique that provides high-sensitivity measurements of refractive index (n), allowing the characterization of the adsorption and desorption of molecules near interfaces. Initially we developed a flow gradient system connected to SPR, which was called FIG-SPR, and demonstrated the automated determination of the concentration gradient of refractive index (dn/dC) of different materials and biopolymers. The development of the membrane biosensors was initiated by studying the factors that affect the formation of a hybrid bilayer membrane (HBM). HBMs are composed of two monolayers: an alcanethiol monolayer adsorbed on gold over which is adsorbed a layer of phospholipids. The formation of an HBM depends on the fusion of phospholipid vesicles on hydrophobic surfaces, a process that is not well understood at the molecular level. Our results showed that in the presence of calcium and spermine the complete formation of an HBM is facilitated, i.e., the phospholipid monolayer reaches the expected thickness of about 20&#197;\'. However, in low ionic strength solutions the lipid layer that is formed is not homogeneous. We have also demonstrated that in the presence of 150 mM of calcium the time necessary for the formation of the lipid monolayer is reduced 14 times when compared to the times suggested in the literature. The homogeneity of the HBM and its superficial charge were verified with the adsorption and desorption of cyt c and bovine serum albumine (BSA). The adsorption and desorption of cyt c in different HBMs were studied including a model of the internal mitochondrial membrane (IMM), which is made of phosphatidylcholine, phosphatidylethanolamine and cardiolipin (PC/PE/CL) in the ratio (4,5: 3,5: 2,0). We demonstrated that the adsorption of native cyt c follows a cooperative profile showing expected changes in affinity and cooperativity in different solution pHs of 6,8, 7,4 and 8,0. A mathematical model, which is an adaptation of the Hill model for adsorption of proteins in surfaces, was developed to treat the binding curves of cyt c. The results of SPR together with those obtained by Atomic Force Microscopy (AFM) suggested that the cooperative binding of cyt c in HBMs occurs due to the reorganization of CL molecules and formation of phospholipid domains. The kinetic results of the dissociation of cyt c induced by calcium indicates the existence of two velocity constants (kd), being the larger (kd1) related to the dissociation of cyt c interacting electrostatically with the HBM, and the smaller (kd2) related to the dissociation of cyt c interacting hydrophobically with the HBM. Moreover, the dissociation of cyt c from the HBM requires a minimum calcium concentration of 30 &#181;M. The study of the interaction between photo-oxidized cyt c molecules (cytc405) and the PC/PE/CL HBM suggests that it occurs with smaller affinity when compared with the results obtained with the native cyt c. Moreover, cytc405 is not easily dissociated by calcium due to the loss of the interaction cooperativity with the HBM. Possible implications of these discoveries in cellular events, such as the release of cyt c from the IMM and the initiation of apoptosis, are discussed

Nesta tese, utilizamos técnicas de química quântica para o estudo de sistemas contendo átomos de silício e nitrogênio. Nesse contexto, o trabalho aqui apresentado procurou concentrar-se em três tópicos principais: aglomerados de silício e nitrogênio, a superfície Si(100) e a interação de um átomo de nitrogênio com essa superfície. Estudamos inicialmente os aglomerados de fórmula SiNN e Si3N2, onde procuramos caracterizar de forma rigorosa a estabilidade e a natureza das ligações químicas das várias espécies. Com relação ao sistema SiNN, os resultados utilizando cálculos de alto nível mostraram a necessidade de novos dados experimentais para a caracterização inequívoca dessa espécie. Além disso, obtivemos os primeiros resultados para as propriedades de quatro novas estruturas. Estudamos a estrutura de várias espécies com fórmula Si3N2, e obtivemos como mínimo global uma estrutura planar contendo apenas ligações Si-N. Para a simulação da superfície Si(100) utilizamos os aglomerados de fórmula Si9H12 e Si15H16. Apenas a metodologia do Funcional da Densidade indicou a existência de uma estrutura distorcida para o Si9H12. Os cálculos CASSCF mostraram a necessidade do uso de funções multideterminantais. Com relação ao aglomerado Si15H16, obteve-se uma estrutura distorcida com os dímeros alternados como a forma mais estável. Entretanto, o uso do CASSCF mostrou ser a forma simétrica a mais estável. Com base no estudo dos aglomerados Si9H12 e Si15H16, partimos para a investigação dos mecanismos envolvidos no processo de interação e incorporação de átomos de nitrogênio na superfície de silício. Estruturas com simetria de spin quarteto e dupleto foram estudadas, sendo os mecanismos bastante semelhantes, com o nitrogênio interagindo inicialmente com um dos silícios dímeros para em seguida poder formar duas outras estruturas, uma com o nitrogênio ligado aos dois silícios dímeros e outra com o nitrogênio inserido no interior do aglomerado. Esta última estrutura corresponde à forma mais estável. Os resultados mostram claramente que a reação é bastante favorável do ponto de vista energético. Questionamos também o uso de vínculos durante a otimização das estruturas por impedir um devido relaxamento apropriado dos átomos de silício da primeira e segunda camadas. / In this thesis, quantum chemical techniques were used to study molecular systems containing silicon and nitrogen atoms. ln this context, the work was concentrated on three main topics: silicon-nitrogen clusters, the Si(100) surface, and the interaction of a nitrogen atom with that surface. We studied initially the clusters SiNN and Si3N2, where we tried to characterize with rigour the stability and the nature of the chemical bonds of the various species. Concerning the system SiNN, using high level calculation, the results showed the necessity of new experimental data for the unequivocal characterization of this species. Moreover, the properties of four new structures were described for the first time in this study. The structures of various species with formula Si3N2 were studied, and the global minimum corresponds to a planar structure containing only Si-N bonds. For the simulation of Si(100) surface, the clusters Si9H12 and Si15H16 were used. Density Functional Theory predicted the existence of an asymmetric geometry for the Si9H12 cluster. The CASSCF calculations showed the necessity of using multideterminantal wave functions. Concerning the Si15H16 cluster, the most stable structure corresponds to a distorted one with alternated dimers. However, the CASSCF methodology showed that the symmetric structure is the most stable. Based on the results for the Si9H12 and Si15H16 clusters, we started to investigate the mechanism involved in the interaction and incorporation of a nitrogen atom into the silicon surface. Structures with quartet and doublet spin symmetry were studied, being their mechanisms very similar, with the nitrogen atom interacting initially with one silicon dimer; after that two other structures can be formed, one with the nitrogen bonded to two silicon dimers, and the other with the nitrogen bonded to one silicon dimer and two internal silicons. This last structure corresponds to the most stable species. The results show clearly that the reaction is very favorable energetically. The use of geometrical constraints during the optimization was questioned since it prevents the proper relaxation of the silicon atoms in the first and second layers.

Despite the central importance of porous electrodes to any advanced electrochemical system, there is no clear answer to “<i>How to make the best electrode</i>?”. The source of ambiguity lies in the incomplete understanding of convoluted material interactions at smaller – difficult to observe length and timescales. Such mesoscopic interactions, however, abide by the fundamental physical principles such as mass conservation. The porous electrodes are investigated in such a physics-based setting to comprehend the interplay among structural arrangement and off-equilibrium processes. As a result, a synergistic approach exploiting the complementary characteristics of controlled experiments and theoretical analysis emerges to allow mechanistic insights into the associated mesoscopic phenomena. The potential of this philosophy is presented by investigating three distinct electrochemical systems with their unique peculiarities.

L'hydrotraitement est un procédé catalytique important dans le raffinage du pétrole qui utilise des catalyseurs bimétalliques sulfurés NiWS ou NiMoS (ou CoMoS) supportés sur alumine. Leur mode conventionnel de préparation implique l’imprégnation d'une solution aqueuse de sels de Mo/W et de Ni/Co, puis l’activation par un agent sulfo-réducteur (H2S/H2). Pour répondre aux exigences environnementales et améliorer l'efficacité de l'hydrotraitement, des améliorations permanentes de la performance de ces systèmes catalytiques sont attendues. Ce travail se concentre sur la préparation de catalyseurs d'hydrotraitement hautement actifs par une approche de chimie de surface contrôlée (CSC) qui implique l'imprégnation successive de précurseurs moléculaires de MoV et NiII en solvant organique sur un support silice-alumine traité thermiquement. Dans la première partie de cette thèse, la genèse de la phase active du catalyseur CSC et conventionnel Mo et NiMo est étudiée par quick-XAS combinée à d’autres techniques (chimiométrie, XPS, RPE, STEM-HAADF, modélisation moléculaire). Nous proposons ainsi des structures moléculaires depuis les précurseurs oxydes de Mo et Ni supportés jusqu’aux nombreuses espèces intermédiaires (oxysulfure et sulfures) en fonction de la température. Cette analyse multi-technique permet d'abord de révéler les spécificités de la genèse des catalyseurs CSC et conventionnels qui peuvent expliquer leurs différentes activités catalytiques. Ensuite, elle révèle également de nouvelles connaissances sur les mécanismes d’insertion du Ni dans la phase NiMoS en fonction de la préparation. Dans la seconde partie, la possibilité de remplacer Co et Ni comme promoteurs est explorée. Ceci est entrepris en synthétisant des catalyseurs alternatifs de type XYMoS, où X et Y sont des métaux de transition 3d. Comme suggéré par des études de modélisation quantiques antérieures, certaines formulations XYMoS peuvent présenter un effet de synergie analogue à ceux des phases actives CoMoS et NiMoS. L’étude des formulations les plus prometteuses méritent d'être approfondies afin de mieux comprendre leur fonctionnement. / Hydrotreating is an important catalytic process in petroleum refining which uses sulfided bimetallic catalysts NiWS or NiMoS (or CoMoS) supported on alumina. Their conventional preparation involves an incipient wetness impregnation of an aqueous solution of Mo/W and Ni/Co salts, and then activation by a sulfo-reductive agent (such as H2S/H2). To meet environmental regulations and improve the energy efficiency of hydrotreatment, permanent improvements on the performance of these catalytic systems are expected. This work is thus focused on the preparation of highly active hydrotreating catalysts through a controlled surface chemistry (CSC) approach; which involves the successive impregnation of Mo5+ and Ni2+ molecular precursors in an organic solvent on a thermally treated silica-alumina support. In the first part of this thesis, the active phase genesis of CSC and conventional Mo and NiMo catalysts is studied by in situ quick-XAS combined with various other techniques (chemometrics, XPS, EPR, STEM-HAADF, molecular modeling). We thus propose molecular structures from the oxide of supported Mo and Ni precursors up to the numerous intermediate sulfided species as a function of temperature. This multi-technique analysis enables first to reveal the specific features of the genesis of CSC and conventional catalysts which may explain their different catalytic activities. Then, it also reveals new insights into the mechanisms of Ni promoter incorporation into the NiMoS phase as a function of the preparation. In the second part, the feasibility of replacing Co and Ni as promoters is explored. Using the CSC method, we attempted to synthesize alternative catalysts of the form XYMoS ternary sulfides, where X and Y are 3d transition metals. As suggested by previous quantum simulations, certain XY formulations possibly reveal a synergy effect as observed in CoMoS and NiMoS active phases. The most promising formulations merit further investigations.

Este trabalho teve como objetivo estudar a interação de polimetacrilato com vesículas de metacrilato de dioctadecildimetílamônio (DODAM) e brometo de dioctadecildimetilamônio (DODAB). A fotoirradiação de vesículas de DODAM a formou polimetacrilato na superfície vesicular do polímero, através da polimerização do contra-íon. Vesículas polimerizadas foram mais estáveis frenta á adição de metanol do que vesículas não polimerizadas. A estabilização da bicamada vesicular foi confirmada com o aumento da retenção da carboxifluoresceína (CF). Vesículas injetadas de DODAM retiveram cerca de 25% de CF, enquanto que vesículas polimerizadas retiveram cerca de 75%. Experimentos de temperatura de transição de fase por turbidez e tensão superfícial mostraram que o polimetacrilato formado na superfície vesicular diminui a temperatura de transição de fase e reduz a cooperatividade. A interação de fosfatase alcalina (Fal) com vesículas de DODAM e colinametacrilato de dicetilfosfato (DCM) foi estudada, como um primeiro passo para a construção de um micro-reator. Foi observada a precipitação na presença de DODAM, mas não em presença de DCM. Isto pode ser explicado pela forte interação entre a superfície de vesículas de dioctadecildimetilamônio (bicamada com carga negativa) com a fosfatase alcalina (carga negativa). Esta precipitação não foi observada com vesículas de DCM (bicamada negativa). Experimentos de monocamada confirmaram estes resultados. DCM e DODAM formaram monocamadas mistas estáveis, sugerindo que vesículas mistas poderiam ser usadas para superar as interações eletrostáticas fortes entre os surfactantes e a enzima. / This work had as objective studying the interaction of polymethacrylate with dioctadecyldimethylammonium methacrylate (DODAM) and brornide (DODAB). The fotoirradiation of vesicular suspensions of DODAM formed polymethacrylate on the vesicle surface though counter-ion polymerization. Polymerized vesicles were more stables on methanol addition than non-polymerized vesicles. Bilayer stability was confirmed with the retention of carboxyfluorescein (CF). DODAM injected vesicles without polymerization retained about 25% of CF, while polymerized DODAM retained about 75%. Experiments of phase transition temperature by turbidity and surface tension showed that polymethacrylate formed at vesicle surface drops phase transition temperature and reduces cooperativity. Polymethacrylic acid and polymethacrylic acid containing rodhamine B covalently linked was used to monitor polymer-vesicle interaction. Experiments showed that the polymer interacts electrostatically with the DODAB bilayer, causing precipitation and or aggregation. The polymer, initially on a confonnation with many hipercoiled hydrophobic regions, opens as interacts with DODAB vesicles. The interaction of alkaline phosphatase (Fal) with vesicles of DODAM and colina-methacrylate dicetylphosphate (DCM) was studied, as a preliminary step for a micro-reactor construction. Precipitation was observed in presence of DODAM, but not in presence of DCM. This may be explained by the strong interaction between the surface of dioctadecyldimethy lammonium vesicles (positive charged bylayer) with Fal (negative charge). This precipitation was not observed with DCM vesicles (negative charged bilayer). Monolayer experiments confirm these results. Experiments showed that DCM and DODAM form stabled mixed monolayers. Suggesting that mixed vesicles could be tried to overcome strong electrostatic interactions between surfactants and enzyme.

The objective of this research is to develop and apply a HILIC UHPLC stationary phase that allows for separation of intact glycoproteins. In Chapter 1 I give an overview of the problems of current glycosylation profiling with regards to biotherapeutics, and my strategy to separate the intact glycoprotein with HILIC. Chapter 2 describes the methods used to produce the nonporous packing material and stationary phase. In Chapter 3 I describe previous work in developing a HILIC polyacrylamide stationary phase, and further improvements I have made. Chapter 4 describes development of an assay in collaboration with Genentech of therapeutic mAb glycosylation. In Chapter 5, I show HILIC-MS of digested ribonuclease B as a beginning step to analyze glycosylated biomarkers.

Les biocapteurs sont des outils de détection et d'analyse puissants qui ont été largement utilisés dans les domaines de la santé, de la recherche biomédicale et de l’environnement. Cependant, différents biocapteurs utilisent différents transducteurs qui varient par la nature des substrats utilisés et par la chimie de surface. Tous ces paramètres peuvent avoir un effet sur les réactions biomoléculaires aux interfaces et conduire à des variations de la mesure de la constante de dissociation Kd. Dans ce contexte, ce travail de thèse visait à comparer trois techniques différentes : biopuce avec une détection par fluorescence, biocapteur à fluorescence par champ évanescent et biocapteur par résonance de plasmon de surface (SPR). Ces trois techniques ont été comparées pour la détermination de la constant de dissociation de l'hybridation de l'ADN. Pour la biopuce à fluorescence classique, le substrat est une lame de verre et la mesure est effectuée à la fin de l'expérience. Dans le cas du biocapteur à fluorescence à champ évanescent, le polystyrène est le substrat et une détection en temps réel est réalisée. La SPR est réalisée sur un film d'or mince. C'est une technique en temps réel et sans marquage. Les deux techniques basées sur la fluorescence nécessitent de marquer les cibles avec un fluorophore avant la mesure. Un facteur important déterminant la performance de l'analyse est la chimie de surface du capteur. Ici, nous avons optimisé la chimie de la surface de l'or pour le greffage d'ADN modifié thiol. Nous avons étudié deux méthodes de nettoyage: la solution de piranha et le plasma d'oxygène, dans le but d'obtenir une surface d'or propre sans oxydation de l'or. Ensuite, nous avons optimisé les paramètres lors de la mesure SPR comme par exemple la structure interfaciale du capteur, la force ionique .... Enfin, ces trois techniques ont été utilisées pour mesurer la constante de formation du duplex ADN/ADN. Les résultats ont montré que les Kd sont du même ordre de grandeur pour les trois techniques. De plus, pour les trois techniques, une augmentation de la densité de sonde de surface a entraîné une baisse d’affinité telle que mesurée. / Biosensors are powerful detection and analysis tools that have been widely applied in pharmaceuticals, healthcare, biomedical research, and environmental monitoring. However different biosensors use different transducers and therefore different substrates and surface chemistries. All of these parameters may have an effect on the biomolecular reactions at the interface and lead to a deviation in dissociation constant Kd measurements. In this context, this PhD work aimed at comparing three different techniques: fluorescent microarray, evanescent field fluorescence biosensor and surface plasmon resonance (SPR) biosensor, to determine DNA hybridization Kd. For the classical fluorescence microarray, the substrate is a glass slide and the detection is performed at the end of the experiment. In the case of evanescent field fluorescence biosensor, polystyrene is the substrate and it permits a real-time detection. SPR is performed on thin gold film. It is a real-time and a label-free technique. The two fluorescent based techniques require to label the targets with fluorescent dyes prior to the measurements. One important factor determining the performance of the analysis is the surface chemistry of the sensor chip. Herein, we have optimized gold surface chemistry for thiol modified DNA grafting. We studied two cleaning methods: piranha solution and oxygen plasma, aiming at obtaining a clean gold surface without oxidation of the gold. Then, we optimized SPR assay parameters such as interfacial structure of sensor chip, ionic strength... After, these three techniques were used to measure the DNA hybridization Kd. The results showed that the Kds measured are similar for the three techniques. In addition, increasing surface probe density resulted in an increase of Kd of DNA hybridization.

Les minéraux absorbent la lumière proche des UV (comme TiO2, Fe2O3, MgO) présents dans les aérosols minéraux interagissent avec les gaz traces présents dans l'atmosphère et peuvent initier une nouvelle chimie hétérogène photo-induite potentiellement significative et actuellement peu documentée. Cette thèse vise à aborder différentes questions sur la réactivité des poussières minérales vers les composés organiques et évaluer l'impact de ces interactions sur plusieurs aspects des sciences de l'atmosphère. Nous avons étudié expérimentalement l'interaction physico-chimique d'aérosols minéraux, purs ou revêtus de matériaux organiques/inorganiques avec des gaz traces de plusieurs familles chimiques (alcools, cétones, acides carboxyliques), dans des conditions simulées proches de l'environnement reel (concernant l'humidité, la concentration en phase gazeuse, la longueur d'onde et l'intensité de l'irradiation, la pression et la température) évaluant les effets des conditions ambiantes sur la cinétique de capture et la génération de produits en phase gazeuse. Dans l'ensemble, nos résultats montrent clairement que les reactions photochimique des poussières minérales doit être considéré comme une source de composés réactifs et comme un processus clé affectant leur action sur la nucléation de la glace et les noyaux de condensation des nuages / Minerals that absorb light near UV/Vis present in dust aerosols interact with trace gases in the atmosphere and can initiate a new and potentially significant photo-induced heterogeneous chemistry, which is currently poorly documented. This thesis aims to address different issues of mineral dust reactivity towards organic compounds and, therefore, assesses the impact of these interactions on several aspects of atmospheric sciences. We investigated experimentally the physicochemical interaction of mineral aerosols (synthetic and natural), pure or coated with organic/inorganic materials with trace gases from several chemical families (alcohols, ketones, carboxylic acids, etc.), under simulated conditions close to the real environment (regarding to humidity, concentration in the gas phase, wavelength and intensity of irradiation, pressure and temperature). In a first approach, we studied the uptake of oxygenated organics onto different dust proxies such as SiO2, TiO2 and Arizona test dust (ATD) evaluating the effects of ambient conditions on the uptake kinetics and product generation. Then, we discussed the chemistry of 5 dicarboxylic acids (C4-C8) on ATD particles upon UV-A irradiation monitoring products in the gas phase as well as those whose stay adsorbed on the particulate phase. Lastly, we investigated the influence of nitrate anions on the uptake of acetone on ATD and SiO2 and in the photochemical product formation of glutaric acid on ATD. Overall, our results clearly show that photochemical processing of dust aerosols should be considered as a source of reactive compounds and as a key process affecting their action as ice nucleation and cloud condensation nuclei

The hydrophobicity of a surface is an important property in many areas of science and engineering. This is especially the case in mineral processing, where differences in surface hydrophobicity lie at the heart of the separation process of flotation. Chemicals are used to increase and decrease the natural hydrophobicity of minerals to attain a better separation between valuable and worthless material. Polymers are often used to reduce mineral surface hydrophobicity. Decades of empirically based decision making have produced a list of effective depressants. However the detailed study of how these polymer depressants affect surface hydrophobicity and mineral recovery lags behind applied investigations. The aim of this thesis was to study the adsorption of commonly used depressants on model surfaces and to interrogate the action of these polymers in reducing surface hydrophobicity. We have modelled the degree of hydrophobicity of common minerals in order to study polymer depressants with methods not commonly used in studies of surface characterisation in flotation. The model surfaces (self-assembled monolayers, SAMs) allowed us to use the quartz crystal microbalance with dissipation monitoring (QCM-D) to study the adsorption of polymers. The QCM-D can be used to obtain adsorption isotherms, adsorption kinetics, water content of adsorbed layers, and information on the conformation of the adsorbed polymer. The results from the QCM-D were correlated with the contact angle data from the captive bubble measurements, with which we assessed the hydrophobicity of the surface before and after polymer adsorption. Three of the polymers layers were probed with dynamic dewetting studies, in order to test other modes of depressant action. Three types of polymers were studied - a polyacrylamide (Polymer-H), a polyelectrolyte CMC (carboxymethyl cellulose) and a group of dextrins (Dextrin-TY, a phenyl succinate substituted dextrin (PS Dextrin) and a styrene oxide substituted dextrin (SO Dextrin)). These polymers are commonly used or have potential to be used in the depression of talc and graphite. Polymer-H was used to investigate the hydrophobic bonding between a non-ionic polymer depressant and chemically inert and non charged surfaces by probing the influence of substrate hydrophobicity on polymer adsorption and reduction of contact angle. Three different model surfaces were used (mixed self-assembled 0.5 SAM, 0.7 SAM or single self-assembled 1.0 SAM monolayers) with advancing contact angles between 75?? and 119??. The study of Polymer-H found that the substrate hydrophobicity is an important factor in adsorption of this polymer and the change in contact angle upon adsorption depends on adsorbed amount. The effectiveness of Polymer-H to reduce surface hydrophobicity was established to correlate with its conformation and morphology. CMC was investigated to find out how a stimulus responsive polymer depressant can be used in flotation. It was established that the adsorbed amount and rate of adsorption of CMC increase with decreasing of pH or increasing of ionic strength. It was shown that the surface hydrophobicity of a CMC pre-adsorbed layer changes with the environment and these alterations are fully reversible. A switch of ionic strength (from 10-2 M KCl to 10-1 M KCl) caused partial dehydration of the adsorbed layer and a decrease of the receding contact angle by 20??. A pH switch (pH = 9 to pH = 3) resulted in a 40?? change in receding contact angle. The CMC investigation showed that the use of a stimulus responsive polymer presents opportunities for exploiting solution conditions as a means to effect a better mineral separation in flotation The adsorption of three dextrin-based polymers on a model hydrophobic surface has been characterized using the quartz crystal microbalance with dissipation monitoring (QCM-D). The three polymers (one standard dextrin and two dextrins with different aromatic group substitutions) exhibited varying affinities and capacity for adsorption on the hydrophobic substrate. The effect of the three polymers on the static contact angle of the surface was studied using captive bubble contact angle measurements. The three polymers were seen to reduce the receding contact angle by similar amounts (approximately 14 degrees) in spite of having varying adsorbed amounts and differences in adsorbed layer water content. Although no differences were observed in the ability of the polymers to reduce the static contact angle, measurements of the dewetting dynamics between a rising air bubble and the polymer covered substrate yielded stark differences between the polymers, with one polymer slowing the dewetting dynamics by an order of magnitude more than the other two polymers. The differences in dewetting behaviour correlate with the adsorbed layer characteristics determined by QCM-D. / Thesis (PhD)--University of South Australia, 2010