Langmuir-monolayer formation at the air/water interface (A/W) can be achieved by spreading amphiphilic molecules on a liquid subphase and compressing them into an ordered arrangement. The use of the Langmuir-Blodgett technique (LB) to prepare ultra thin films on solid surfaces from monolayers at A/W has considerable utility for studying surface interactions. In particular, the phase behavior of polyhedral oligomeric silsesquioxanes (POSS) was examined using a combination of LB and Brewster angle microscopy (BAM).Polymer fillers have been shown to reduce the cost and often improve the properties of high performance polymer composites. The utility of POSS as a potential nanofiller in blends with polymers such as poly(dimethylsiloxane) (PDMS) and poly(vinylacetate) (PVAc) was explored using surface pressure-area per monomer isotherms (P-A) and BAM. Substantial morphological differences are seen between polymer blends with heptasubstituted trisilanol-POSS and fully condensed octasubstituted-POSS due to differences in subphase affinity.Several poly(1-alkene-alt-maleic anhydride) (PXcMA) polymers were studied at both the gas/liquid interface as Langmuir films and at the gas/solid interface as Langmuir-Blodgett thin films on silicon substrates. A 0.01 M HCl solution (pH~2) was used during film deposition to ensure the carboxylic acids were fully protonated. The PXcMA polymers included X=1-hexene, 1-octene, 1-decene, and 1-octadecene (represented as PHcMA, POcMA, PDcMA, and PODcMA respectively). The P-A isotherms of these polymers were consistent with those obtained previously.1Tensiometry was used to determine the critical micelle concentrations (c.m.c.) of variable molar mass poly(dimethylsiloxane-b-(3-cyanopropyl)methylsiloxane-b-dimethylsiloxane) (PDMS-PCPMS-PDMS) triblock copolymers and a poly(dimethylsiloxane-b-2-ethyl-2-oxazoline) diblock copolymer. Dynamic light scattering (DLS) corroborated interfacial tension results. The polymers exhibited well-defined temperature-independent c.m.c.'s. These measurements ensured that the synthesis of cobalt nanoparticles for biocompatible magnetic fluids occurred above the c.m.c. / Master of Science

Wood is a complex biocomposite that exhibits a high work of fracture, making it an ideal model for multiphase man-made materials. Typically, man-made composites demonstrate interfacial fracture at failure due to abrupt transitions between neighboring phases. This phenomenon does not occur in wood because gradual phase transitions exist between regions of cellulose, hemicellulose, and lignin and therefore adhesion between adjacent phases is increased. The formation of interphases occurs as a consequence of the self-assembly process which governs the formation of wood. If this process was understood more thoroughly, perhaps tougher man-made, biobased composites could be prepared. To study self-assembly phenomena in wood, a system composed of a model copolymer (pullulan abietate, DS=0.027) representing the lignin-carbohydrate complex (LCC) and a model surface for cellulose fibers was used. The self-assembly of the polysaccharide pullulan abietate (DS=0.027) onto a regenerated cellulose surface prepared using the Langmuir-Blodgett (LB) technique was studied via surface plasmon resonance (SPR). Rapid, spontaneous, and desorption-resistant cellulose surface modification resulted when exposed to the model LCC. Adsorption was quantified using the de Feijter equation revealing that between 9-10 anhydroglucose units (AGUs) adsorb per nm&178; of cellulose surface area when cellulose is exposed to pullulan abietate (DS=0.027) compared to the adsorption of 6.6 AGUs per nm&178; of cellulose surface area when cellulose is exposed to unsubstituted pullulan. / Master of Science

Surface behavior of poly (epsilon-caprolactone) (PCL) have been studied at the air/water interface (A/W). PCL is a hydrophobic and crystalline polyester with a glass transition temperature around -60 degrees centigrade, a melting point around 55 degrees centigrade, excellent biocompatibility, and low toxicity. In the past decade, PCL based systems have attracted considerable interest for controlled-release drug delivery and as scaffolds for tissue engineering, that require a fundamental understanding of PCL's degradation mechanisms and crystallization properties. PCL spherulites were commonly observed in previous bulk studies. This thesis focuses on PCL crystallization in Langmuir monolayers. Brewster angle microscopy (BAM) studies show that square, distorted rectangular, and dendritic crystals form at the A/W interface. While dendritic structures have been observed in poly (ethylene oxide) (PEO) thin film on solid substrates, this study of PCL is the first time that dendritic morphologies have been observed at the A/W interface for a linear flexible-coil polymer. As far as we know, the crystallization of flexible-coil polymers at the A/W interface is a brand new area of research. These findings may provide an interesting model system for studying crystallization in confined geometries and the effect of crystallinity on enzyme catalyzed hydrolysis of this important biodegradable polymer at the A/W interface. The main objectives of this thesis were to investigate the phase behavior of PCL at the A/W interface, gain a deeper understanding of the nucleation and growth mechanism of PCL crystallization at the A/W interface through surface pressure-area isotherms and isobaric area relaxation analyses, and interpret the effects of molecular weight on the nucleation and growth mechanism, and morphologies of semicrystalline PCL crystallized in Langmuir monolayers at the A/W interface. / Master of Science

Cette thèse de doctorat étudie l’auto-assemblage de copolymères di-blocs et de nanoparticules métalliques à l’interface air-eau. Les nanoparticules métalliques peuvent interagir fortement avec la lumière grâce à l’oscillation collective des électrons de conduction. Ce phénomène, qu’on appelle le plasmon de surface localisé, offre d’importantes perspectives dans l’élaboration de matériaux optiques. Cependant, la force et la fréquence du plasmon de surface varient significativement en fonction de plusieurs paramètres dont l’arrangement des nanoparticules. Les copolymères à blocs, quant à eux, ont la capacité de former des domaines de morphologies définies à la surface de l’eau et représentent une voie simple pour organiser les nanoparticules en deux dimensions. Avec la technique Langmuir-Blodgett, il a été possible de former des monocouches composites de nanoparticules et de copolymères, et de les transférer sur des substrats solides. Les films composites Langmuir-Blodgett ont été caractérisés par microscopie à force atomique et par microscopie électronique en transmission. Plusieurs auto-assemblages, incluant des agrégats, des systèmes cœur-satellites, des cercles et des lignes de nanoparticules ont été observés. Les caractéristiques structurales de ces assemblages peuvent être ajustées avec précision en modifiant l’organisation des copolymères et la longueur des ligands thioalcanes à la surface des nanoparticules. De plus, une procédure de recroissance in situ a été développée pour augmenter la taille des nanoparticules incorporées sans altérer l’ordre des monocouches. Les propriétés optiques des auto-assemblages ont ensuite été étudiées expérimentalement et comparées à des simulations théoriques par l’approximation aux dipôles discrets. Une attention particulière a été portée aux nanocercles qui sont des structures hautement symétriques et compliquées à obtenir avec d’autres méthodes. Enfin, la thèse se termine par une série d’expériences préliminaires destinées à évaluer l’utilité de ce type de monocouches pour des applications de détection. / The present Ph. D. thesis treats the investigation of the self-assembly of block copolymers and metallic nanoparticles at the air-water interface. Metallic nanoparticles interact strongly with light because of the collective oscillation of the conduction electrons. This phenomenon is called the localized surface plasmon resonance and offer significant promise in the development of optical materials. However, the strength and frequency of the surface plasmon depend on several parameters, including details of the arrangement of the nanoparticles. As block copolymers can form nanodomains at the surface of water, they represent a simple way to organize nanoparticles in two dimensions. With the help of the Langmuir-Blodgett technique, it has been possible to form composite monolayers composed of nanoparticles and block copolymers, which are transferable on solid substrate. The Langmuir-Blodgett composite films have been characterized both by atomic force microscopy and transmission electron microscopy. Several self-assemblies, including aggregates, core-satellite structures, nanorings, and particle lines have been observed. The structural characteristics of these assemblies can be tuned precisely by modifying the copolymer organization and the capping ligand length at the nanoparticle surface. In addition, an in situ regrowth procedure has been developed to increase the size of the incorporated nanoparticles without losing the order of the monolayers. Then, optical properties of the self-assemblies have been investigated experimentally and compared to theoretical calculations by the discrete dipole approximation. Particular attention has been paid to the nanoring structures, which are highly symmetrical and complicated to obtain with other fabrication procedures. Finally, the thesis presents a series of preliminary experiments intended to assess the usefulness of the monolayers for sensing applications.

Ces travaux abordent la problématique des mesures de sonde de Langmuir dans un environnement RF. Les mesures expérimentales ont montré que des courants DC négatifs (électroniques) étaient collectés sur la structure d'une antenne ICRF sous tension, pendant que des courants DC positifs (ioniques) sont recueillis par une sonde de Langmuir à l'autre bout du tube de flux magnétique ouvert connecté à l'antenne, la sonde étant au potentiel de la machine. Un modèle de tube de flux asymétrique, de type de sonde double, est présenté. Celui-ci modélise un plasma, confiné le long des lignes de champ magnétique, ayant à chaque extrémité une électrode dont l'une est polarisée à un potentiel RF et l'autre à la masse. L'électrode polarisée modélise le potentiel RF résultant de l'intégration, le long d'une ligne champ magnétique, du champ électrique rayonné par les straps d'une antenne ICRF, tandis que l'autre électrode modélise la sonde au potentiel de la machine. Ce modèle permet d'expliquer l'apparition de courants DC en émettant simplement l'hypothèse qu'il faut à la fois une asymétrie de la source RF par rapport à une masse fixe, une conductivité RF transverse non nulle autorisant des courants RF transverses ainsi qu'une caractéristique courant-tension non linéaire due aux gaines pour favoriser des courants négatifs du côté RF et des courants positifs côté sonde. Ce modèle permet également de modéliser les caractéristiques Courant DC - Tension DC d'une sonde en présence de RF et ainsi d'évaluer les propriétés du plasma. Dans ce cas l'électrode modélisant la sonde n'est plus à la masse, mais à un potentiel donné. Des résultats analytiques sont trouvés dans certaines limites / This work investigates the problematic of probe measurements in RF environment. DC currents flowing along magnetic field lines connected to powered ICRF antennas have been observed experimentally. Negative (i.e. net electron) current is collected on the powered ICRF antenna structure, while positive (i.e. net ion) current is collected by magnetically connected Langmuir probes. An asymmetric model based upon a double probe configuration was developed. The ICRF near field effect is mimicked by a ?driven? RF electrode at one extremity of an "active" open magnetic flux tube, where a purely sinusoidal potential is imposed. The other connection point is maintained at ground potential to model a collecting probe. This "active" flux tube can exchange transverse RF currents with surrounding "passive" tubes, whose extremities are grounded. With simple assumptions, an analytical solution is obtained. We can thus explain how DC currents are produced from RF sheaths. This model also makes it possible to model the characteristics DC Current' DC Voltage of a probe in the presence of RF and thus to evaluate some plasma properties. In this case the electrode at ground potential (probe) is polarized at a given potential. Analytical results are found within certain limits

L'auto-assemblage des copolymères à bloc (CPBs) attire beaucoup d'intérêt grâce à leur capacité de générer spontanément des matériaux ordonnés avec des propriétés uniques. Les techniques Langmuir-Blodgett (LB) et Langmuir-Schaefer (LS) sont couramment utilisées pour produire des monocouches ou des films ultraminces à l'interface air/eau suivi de transfert aux substrats solides. Les films LB/LS de CPBs amphiphiles s'auto-assemblent dans des morphologies variables dépendamment de la composition du CPB ainsi que d'autres facteurs. Dans notre travail, nous avons étudié les films LB/LS de polystyrène-b-poly(4-vinyl pyridine) (PS-P4VP) et leurs complexes supramoléculaires avec le naphtol (NOH), l'acide naphtoïque (NCOOH) et le 3-n-pentadécylphenol (PDP). La première partie de ce mémoire est consacré à l'investigation du PS-P4VP complexé avec le NOH et le NCOOH, en comparaison avec le PS-P4VP seul. Il a été démontré qu'un plateau dans l'isotherme de Langmuir, indicatif d'une transition de premier ordre, est absent à des concentrations élevées des solutions d'étalement des complexes. Cela a été corrélé avec l'absence de morphologie en nodules avec un ordre 2D hexagonal à basse pression de surface. L'ordre au-delà de la pression de cette transition, lorsque présente, change à un ordre 2D carré pour tout les systèmes. La deuxième partie du la mémoire considère à nouveau le système PS-P4VP/ PDP, pour lequel on a démontré antérieurement que la transition dans l'isotherme correspond a une transition 2D d'un ordre hexagonal à un ordre carré. Cela est confirmé par microscopie à force atomique, et, ensuite, on a procédé à une étude par ATR-IR des films LB pour mieux comprendre les changements au niveau moléculaire qui accompagnent cette transition. Il a été constaté que, contrairement à une étude antérieure dans la littérature sur un autre système, il n'y a aucun changement dans l'orientation des chaînes alkyles. Au lieu de cela, on a découvert que, aux pressions au-delà de celle de la transition, le groupe pyridine, qui est orienté à basse pression, devient isotrope et qu'il y a une augmentation des liaisons hydrogènes phénol-pyridine. Ces observations sont rationalisées par un collapse partiel à la pression de transition de la monocouche P4VP, qui à basse pression est ordonné au niveau moléculaire. Cette étude a mené à une meilleure compréhension des mécanismes moléculaires qui se produisent à l'interface air/eau, ce qui fournit une meilleure base pour la poursuite des applications possibles des films LB/LS dans les domaines de nanotechnologie. / Self-assembly of block copolymers (BCPs) attracts much interest due to their ability to spontaneously generate ordered materials with unique properties. For many applications, such as masks in nanolithography, separation membranes in medical diagnostics, and nanotemplates for nanowire fabrication, manufacturing into thin films is required. The Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques are commonly used to produce ultrathin or monolayer films at the air/water interface that are transferred to solid substrates. LB/LS films of amphiphilic BCPs self-assemble into various morphologies, depending on the BCP composition and other factors. In our work, we investigated LB/LS films of polystyrene-b-poly(4-vinyl pyridine) (PS-P4VP) and their supramolecular complexes with, naphthol (NOH), naphthoic acid (NCOOH) and 3-n-pentadecylphenol (PDP). The first part of the thesis was devoted to the investigation of PS-P4VP complexes with NOH and NCOOH, in comparison to PS-P4VP alone. It was shown that a plateau in the Langmuir isotherm, indicative of a first-order transition, is absent at high spreading solution concentrations for the complexes. This was correlated with an absence of the expected dot morphology with 2D hexagonal-like order at low surface pressure. Above the transition, when present, the morphology has 2D square order. The second part of the thesis re-examines the PS-P4VP/PDP system, which was previously shown to undergo a transition from 2D hexagonal to square order at the isotherm plateau pressure. This was confirmed here, and a detailed ATR-IR study of LB films was then undertaken to better understand molecular-level changes occurring at this transition. It was found that, contrary to another study in the literature on a different system, there is no change in alkyl chain orientation. Instead, it was found that the pyridine group loses its low-pressure orientation and there is increased phenol-pyridine hydrogen-bonding above the transition pressure, which is rationalized by a partial collapse of the low-pressure molecularly ordered P4VP monolayer at the transition pressure. This study leads to an improved understanding of the processes occurring at the air/water interface, which is a basis for the further possible applications of LB/LS films in nanotechnologies.

Dans l'optique de produire de l'énergie à travers les réactions de fusion, nous sommes amenés à étudier des phénomènes physiques qui ont lieux dans les tokamaks. Les instabilités qui existent dans les tokamaks peuvent fortement dégrader le confinement et ont un impacte sur le fonctionnement de futurs réactions à fusion. Des mesures révèlent un fort transport radial. Même si ce transport radial est en partie est une conséquence des collisions, l'instabilité d'interchange est la source dominante à ce transport puisque le type de plasmas nous intéressant sont faiblement collisionnels. Dans la limite non collisionnelle, la description hamiltonienne permet de décrire le système dynamique des particules du plasmas dans un champ électromagnétique. Nous donnons de l'importance à cette description afin de pouvoir accéder aux outils hamiltoniens.Nous travaillons sur la modélisation et le contrôle hamiltonien du transport radial. Après avoir écrit le modèle hamiltonien des particules d'un plasma magnétisé, nous introduisons les réductions de ce modèle lagrangien en modèles eulériens réduits afin de s'adapter à certains calculs numériques et théoriques. Ces réductions donnent lieux aux équations fluides hamiltonien. Cependant, nous montrons que ces réductions peuvent faire perdre la propriété hamiltonienne. En particulier pour obtenir un modèle ayant la température des ions (puisqu'elle n'est pas négligeable au centre du plasma), nous montrons la procédure conservant la propriété hamiltonienne à partir du modèle sans température des ions.Quant à l'étude du transport radial, nous appliquons une des propriétés hamiltoniennes (le contrôle) afin de créer une barrière de transport par des perturbations du système. Nous étudions de manière idéale l'effet du contrôle à travers la dynamique lagrangienne des traceurs appelés particules test. Nous faisons particulièrement des efforts dans la prise en compte des contraintes numériques et expérimentales. Nous montrons notamment la robustesse du contrôle lors de l'application des perturbations par des sondes de Langmuir.Finalement, nous étudions l'application du contrôle dans un modèle eulérien décrivant la rétroaction du plasmas (à travers la densité et le potentiel électrique) lorsque nous appliquons les perturbations. Cette étape permet de prendre en compte le couplage du système plasma-perturbations. En utilisant un code fluide permettant de décrire le plasma de bord lors de perturbations générées par des sondes de Langmuir. Nous développons un algorithme permettant de calculer le contrôle en tout temps en fonction du potentiel électrique. Nous montrons alors que la valeur moyenne du potentiel électrique joue un rôle important pour l'application du contrôle dans un modèle fluide. / In order to produce energy through fusion reactions, we are led to study of physical phenomena that occur in tokamaks. The instabilities that exist in tokamaks can significantly degrade the confinement and have an impact on the operation of future fusion reactors. Measurements reveal a strong radial transport. Although this is partly a consequence of collisions, the interchange instability is the dominant source to transport since the type of plasmas that interest us are weakly collisional. Within non collisional limit, the Hamiltonian description used to describe the dynamical system of charged particles in an electromagnetic field. We give importance to this description in order to access the Hamiltonian tools.We are working on modeling and control Hamiltonian of radial transport. After writing the Hamiltonian model of particles in a magnetized plasma, we introduced some reductions from Lagrangian models to Eulerian reduced models in order to accommodate some theoretical and numerical calculations. These places give the Hamiltonian fluid equations. However, we show that these reductions may lose the Hamiltonian property. In particular for a model with the ion temperature (not neglected at the center of the plasma), we show the procedure preserving the Hamiltonian property from the model without ion temperature.As for the study of radial transport, we apply one of the Hamiltonian properties (the control) to create a transport barrier by perturbations of the system. We are looking ideally the effect of control through the Lagrangian dynamics of tracers called test particles. We make particular efforts in the consideration of numerical and experimental constraints. We show the robustness of control when applying perturbations by Langmuir probes.Finally, we study the application of control in an Eulerian model describing the feedback of plasma (through the density and the electric potential) when we apply the perturbations. This step allows to take into account the coupling of the system plasma-perturbations. We use a numerical code to describe the plasma at the edge during perturbations generated by Langmuir probes. We develop an algorithm to calculate the control at all times depending on the electric potential. Finally we show that the average value of electric potential plays an important role in the implementation of control in a fluid model.

L’objectif de cette thèse a consisté en la synthèse d’un polymère à empreinte moléculaire (MIP) permettant l’extraction du phosmet, un pesticide organophosphoré largement utilisé en oléiculture. La recherche du monomère fonctionnel (MF) disposant de la meilleure capacité à interagir de manière non-covalente avec le phosmet en présence du solvant porogène le plus approprié a été réalisée pour la toute première fois au moyen d’un capteur à acétylcholinestérase. Cette stratégie innovante a permis une meilleure compréhension des mécanismes cinétiques à l’œuvre lors de l’interaction MF-molécule cible. De par l’importance de son rôle dans la détermination de la structure d’un MIP, le choix d’un agent réticulant aux caractéristiques physico-chimiques adéquates a permis de sélectionner le meilleur MIP en s’appuyant sur l’étude des isothermes d’adsorption selon les modèles de Freundlich et Langmuir. La procédure d’extraction du phosmet selon la procédure MISPE (Molecularly Imprinted Solid Phase Extraction) a été effectuée par le biais d’une cartouche SPE dont la capacité a été évaluée à partir d’une solution standard. La validation du choix des réactifs de MIP sélectionnés a été confortée par la réalisation d’une expérience de réactivité croisée appliquée à une molécule analogue au phosmet. L’extraction du phosmet de l’huile d’olive a pu être effectuée avec succès selon un protocole d’extraction en flux inverse optimisé. Cette étude ouvre ainsi la voie à la recherche de nouvelles interactions MFs-molécules cibles au moyen de biocapteurs enzymatiques inhibant des composés toxiques tels que les herbicides, fongicides et autres pesticides. / The objective of this thesis has been the synthesis of a molecularly imprinted polymer (MIP) for the extraction of phosmet, an organophosphorus pesticide widely used in olive growing. The search for the functional monomer (FM) having the best ability to interact non-covalently with phosmet in the presence of the most suitable pore-forming solvent was carried out for the first time by means of an acetylcholinesterase sensor. This innovative strategy allowed us to better understand the kinetic mechanisms of FM-template interaction. Because of the importance of its role in determining the structure of a MIP, the selection of a crosslinking agent with adequate physicochemical characteristics made it possible to select the best MIP, whose adsorption isotherms were studied according to Freundlich and Langmuir models. Extraction of phosmet using a Molecularly Imprinted Solid Phase Extraction (MISPE) procedure was carried out via an SPE cartridge, whose capacity was evaluated from a standard solution. The choice of reagents and experimental conditions were validated by carrying out selectivity assays using another organophosphorus insecticide. Extraction of phosmet from olive oil was successfully carried out according to an optimized reverse flow extraction protocol. This work opens new opportunities for studying new FM-template interactions by means of enzymatic biosensors capable of detecting other inhibitors such as herbicides, fungicides and other pesticides.

O ácido politiofeno acético (PTAA) é um derivado do politiofeno bastante versátil. Sua solubilidade em alguns solventes orgânicos e em soluções básicas aquosas lhe confere extensa processabilidade na forma de filmes finos, característica importante para dispositivos e sensores. Neste trabalho, investigou-se a formação de filmes de PTAA com as técnicas de automontagem e Langmuir-Blodgett (LB). Os filmes automontados foram preparados com dois policátions, hidrocloreto de poli-alilamina (PAH) e cloreto de poli-dialildimetilamônio (PDAC). O crescimento dos filmes depende do pH das soluções e do tipo de policátion, sugerindo dependência do mecanismo de crescimento com as interações específicas polímeropolímero. A conformação do PTAA em filme tem correlação com sua conformação em solução, apontando para um efeito de memória. Por outro lado, a energia de superfície destes filmes não sofre influência da arquitetura nem dessas diferenças conformacionais. Ou seja, embora o volume do filme possa ser distinto, as superfícies possuem propriedades semelhantes. A morfologia dos filmes foi caracterizada a partir de imagens de AFM utilizando conceitos de geometria fractal e estatística. A dimensão fractal dos filmes é semelhante, indicando o mesmo processo de crescimento dos filmes, independentemente das condições da deposição. Os filmes obtidos em pH ácido tinham tamanho de grão e comprimentos de correlação maiores, sugerindo a deposição de cadeias mais enoveladas. Foi possível fabricar filmes autossustentados sem degradação aparente do material a partir de filmes automontados de PAH/PTAA, entrecruzando termicamente os grupos ácido carboxílico e amina. Este é o primeiro relato de filmes deste tipo com derivado do politiofeno. Os filmes LB de PTAA foram obtidos sem adjuvantes, mas as condições de deposição precisam ser aprimoradas. Para explorar a elevada afinidade química entre compostos contendo enxofre e metais pesados, filmes foram utilizados para detecção espectroscópica e eletroquímica. Espectros de fotoluminescência e UV-Vis demonstraram que os metais interagem apenas com os estados excitados resultando na supressão da fluorescência; no entanto, sem especificidade e apenas para longos períodos de exposição. Espectros de FTIR mostraram a presença dos sais na matriz dos filmes. Por sua vez, voltametrias cíclicas permitiram detectar Pb+2 e Hg+2, mas a irreversibilidade dos processos eletroquímicos, causando alargamento dos picos de oxirredução, inviabiliza a detecção simultânea. / Polythiophene acetic acid (PTAA) is a versatile polythiophene derivative. Its solubility in some organic solvents and in basic aqueous solutions makes it attractive for processing thin films, an important feature for the fabrication of devices and sensors. In this thesis, we investigate the formation of PTAA films using the layer-by-layer (LbL) and the Langmuir- Blodgett (LB) techniques. The LbL films were prepared with poly(allylamine hydrochloride) (PAH) and poly(diallydimethylammonium chloride) (PDAC), with film growth depending on the pH of the solutions and type of polycation, thus indicating that the growth mechanism depends on polymer-polymer interactions. The conformation of the PTAA molecules in solid state was correlated with that in solution, in a kind of memory effect. The surface energy of the films was not affected by the film architecture or different conformations. The film morphology was characterized with AFM images using concepts of fractal geometry and statistics. The fractal dimension was similar for all films, and therefore the overall growth obeys the same process regardless of the deposition conditions. Nevertheless, films obtained at acidic pH exhibited larger grain size and correlation lengths than those produced at basic pHs, suggesting deposition of more coiled chains. It was also possible to fabricate selfsustained films without apparent PTAA degradation from the PAH/PTAA LbL films, upon thermal crosslinking of carboxylic acid and amine groups. This is the first report of such films with a polythiophene derivative. LB films of PTAA were obtained without co-spreading materials, but the deposition conditions need to be optimized. To explore the high chemical affinity between PTAA and compounds containing sulfur and heavy metals, some films were used for spectroscopic and electrochemical detection. The UV-Vis and photoluminescence spectra indicated that the metals affect only the excited states, leading to fluorescence quenching after long exposure times and without specificity for the metals. The FTIR spectra pointed to salts in the films. Pb+2 and Hg+2 ions could be detected using cyclic voltammetry, but their simultaneous detection was hampered by the irreversibility of the electrochemical processes which caused broadening of the oxi-reduction peaks.

As ligações de hidrogênio (LH), fundamentais na determinação da estrutura da água, proteínas, etc., são muito importantes no reconhecimento molecular e nos mecanismos de reações enzimáticas. A determinação da energia das LHs intramoleculares em proteínas e intermoleculares entre uma proteína e o solvente água, porque fornece informações sobre a estrutura secundária, terciária e quaternária das proteínas. Um método para quantificar e qualificar as LHs foi desenvolvido utilizando critérios de distância, geométricos e energéticos a partir das trajetórias obtidas por simulações de dinâmica molecular. O método foi testado com o monômero de uma fosfolipase A2 homodimérica, sem atividade catalítica, isolada do veneno da Bothrops asper(BaspMT-II). No dímero, a análise das LHs mostrou que elas são também essenciais na manutenção da estrutura quaternária. Essa análise permitiu identificar movimentos do tipo dobradiça acompanhados da formação transitória, na interface dimérica, de LHs controladas pelo triptofano na posição 77. Esses movimentos podem estar associados à ação danosa às membranas, uma vez que podem promover a inserção da região C-terminal na membrana. Estudos prévios mostraram que o peptídeo sintético (3Y codificado pelos aminoácidos 115-129 da BaspMT-II) apresenta atividade bactericida e citolítica. Um outro peptídeo (3W), mutante de 3Y, no qual três resíduos tirosina são substituidos por triptofano, apresenta um aumento do dano às membranas e do efeito miotóxico. Os mecanismos de ação desses peptídeos e as suas estruturas foram estudados por dinâmica molecular, dicroísmo circular (DC), microscopia de fluorescência e monocamadas de Langmuir (Mlang). As adsorções dos peptídeos em monocamadas de ácido dimiristoil fosfatídico (DMPA) e dimiristoilfosfatidilcolina (DMPC) se processam por mecanismos diferentes ocasionados pelas diferentes naturezas físico-químicas dos resíduos tirosina e triptofano. A microscopia de fluorescência acoplada a Mlang de DMPA com 3W adsorvido mostra um aumento da fluidez da monocamada, enquanto que o 3Y modifica os domínios do DMPA para pequenas estruturas circulares. Foram realizadas simulações dos peptídeos 3Y e 3W em meio aquoso e nas regiões interfaciais água/n-hexano e água/bicamadas de DMPC. Os resultados confirmam os obtidos por Mlang, demonstrando que os peptídeos interagem diferentemente com as membranas por adotar conformações alternativas definidas previamente. Essas conformações, diferentes das observadas em meio aquoso, dependem da natureza da interface. As estruturas encontradas no final das simulaçoes corroboram o mecanismo proposto por Mlang, assim como as estruturas sugeridas por DC. Isso sugere que a atividade biológica reduzida do peptídeo 3Y ocorre porque os seus dois resíduos Leu se adsorvem na interface sem penetrá-la. Ao contrário de 3W, os resíduos carregados do peptídeo 3Y não estão localizados corretamente para promover uma interação suficientemente atrativa para permitir a sua inserção na membrana celular. / Hydrogen bonds (HB) are highly important in the determination of the structure of the water and proteins. They also play a important role in molecular recognition and in enzyme reaction mechanisms. The determination of protein/water intermolecular and protein intramolecular HB energies provide information with respect to the formation and stabilization of secondary, tertiary and quaternary protein structure. A method that quantifies and qualifies the properties of HB was developed using distance, geometric and energy criteria as applied to data obtained from the atomic trajectories generated by molecular dynamics simulations. The method was tested with a monomer of a catalytically inactive homodimeric phospholipase A2 from Bothrops asper(BaspMT-II) venom. HBs at dimmer interface are essential for maintaining the quaternary structure, and are highly conserved during hinge-like movements of the dimmer. HB formed by tryptophan residue at position 77 controls this movement. These motions can be associated to the membrane damaging action since they facilitate the insertion of the C-terminus into the cellular membrane. Previous studies have shown that synthetic peptide (3Y, coding the amino acids 115-129 of BaspMT-II ) presents bactericidal and cytolitic activities. A peptide variant ( 3W ), in which tyrosine residues were substituted by tryptophan residues, presents an enhanced membrane damaging activity increased miotoxic effect. The mechanism of action of the peptides and their structures were studied by molecular dynamics simulations, circular dichroism (CD), fluorescence microscopy and Langmuir monolayers (Mlang). The adsorption of the peptides on a monolayer composed of dimiristoyl phosphatidic acid (DMPA) and dimiristoylphosphatidyl choline (DMPC) occurs through different processes due to the differences in the physic-chemical nature of the tyrosine and tryptophan residues. Fluorescence microscopy together with Mlang of DMPA with adsorbed 3W indicates an increase of the membrane fluidity while small circular domains are formed with DMPA. Simulations were conducted with the 3Y and 3W peptides in aqueous media, is a water/n-hexane and water/DMPC bilayers. The results confirm the Mlang results, showing that the peptides interact differently with the membranes by adopting alternative previously defined conformations. These two conformations, both of which are different to those observed in water, are dependent of the nature of the interfaces. The final simulated configurations confirm the mechanism proposed by Mlang and the structures proposed by CD. It is suggest that the reduced biological activity of the 3Y peptide is due to the two Leu residues that only adsorb to the cellular membrane without penetrating the bilayer. In contrast to the 3W peptide, no charged residue is correctly located to promote the interaction and insertion of the 3Y peptide into the membrane.