Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-13T12:17:27Z No. of bitstreams: 1 arquivototal.pdf: 26917769 bytes, checksum: 9ff17103475ce4130305b157369d8448 (MD5) / Made available in DSpace on 2017-09-13T12:17:27Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 26917769 bytes, checksum: 9ff17103475ce4130305b157369d8448 (MD5) Previous issue date: 2015-03-06 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present work, we use first-principles calculations based on density functional theory, as implemented in the SIESTA code, to investigate the changes in the structural and electronic properties of the carbon, BN, and hybrid BxCyNz nanotubes produced by one or two of the following mechanisms: doping with carbon atoms, the application of external electric fields, by flattening of the cross section, the encapsulation of a carbon nanowire or the adsorption of hydrogen atoms (hydrogenation). We start with the study of double-walled boron nitride nanotubes (DWBNNTs), zig-zag and armchair, doped with carbon atoms, with chiral vectors (8,0)@(16,0) and (5,5)@(10,10), respectively. Two types of doping were considered: one C atom substituting a B atom on the inner wall (IW) and one C atom substituting a N atom on the outer wall (OW), which we call of CB[IW]@CN[OW], and the opposite situation results in CN[IW]@CB[OW]. In this sense, we generate a (type-p semiconductor)@(type-n semiconductor) and a (type-n semiconductor)@(type-p semiconductor), where the resulting DWBNNTs can be thought of as p-n junctions. At the same time, we apply an external electric field, with magnitude of 0,3 V/Å, in different directions, namely, perpendicular (Ey), parallel (Ex), and antiparallel (E􀀀x) to the line formed by the dopants. Thus, depending on the direction of the applied field, we observe an increase or decrease in the band gap energy between the defect levels (Eig), and such cases are related to the reverse and direct polarization of the p-n junction, respectively. Afterwards, we study the insertion of a carbon nanowire (CNW) inside a (10.0) zigzag carbon nanotube and inside a (10.0) zig-zag BN nanotube. Such systems were called CNW@SWCNT and CNW@SWBNNT, respectively. We produce the flattening of the nanotubes and verify the behavior of the atomic structure of the nanowire as the flattening of the nanotube increases. From the obtained results, it was possible to conclude that, for both CNW@SWCNT and CNW@SWBNNT, there is a critical distance dc (distance between the parallel planes of the flattened nanotubes (d)), with the value of 3.60 Å, so that we can summarize our findings as follows: in the case d > dc, the carbon nanowire does not undergo any deformation; and in the reverse case (d < dc), the carbon nanowire binds to the wall of the nanotube and undergoes deformations. Regarding the electronic properties, we verify that the encapsulation of the CNW inside the SWCNT and SWBNNT, produces a significant reduction of the band gap energy (Eg) of such systems. Moreover, we observe ABSTRACT viii the creation of Dirac points for some flattening ratios of the nanotubes. Finally, we carry out a study on the adsorption of hydrogen atoms (hydrogenation) on the surface of double-walled boron nitride nanotubes (DWBNNTs) and hybrid nanotubes of boron nitride and carbon (DW(BN)xCyNTs). Due to the fact that the nanotubes have two walls, we consider the following cases: (i) coverages of 2H, 4H, 8H, 12H, and 16H on the inner wall, (ii) coverages of 2H, 4H, 8H, 16H, and 32H on the outer wall, and (iii) coverages of 2H, 4H, 8H, 16H, and 32H on both walls. Curiously, we find that for all hydrogen coverages considered, a strong deformation occurs in the hydrogen regions, causing the cross section of the nanotubes take different polygonal shapes: ellipsoidal, rectangular, hexagonal or octahedral. For coverages of 16H and 32H only on the outer wall, we observe that some hydrogens desorbed from the wall forming isolated H2 molecules without preferential orientation. We verify that, in some cases, the bond angles between the B, N and H or C and H atoms exhibit characteristics of the sp3 hybridization. Regarding the structural stability, we verify that the adsorption of H atoms in DWBNCNTs is more favorable than in DWBNNTs. Moreover, we conclude that is possible to control the band gap energy of the nanotubes through the hydrogen coverage. / No presente trabalho, usamos cálculos de primeiros princípios baseados na Teoria do Funcional da Densidade, como implementado no código SIESTA, para investigarmos as alterações nas propriedades estruturais e eletrônicas de nanotubos de carbono, de BN e híbridos BxCyNz, produzidas por um ou dois dos seguintes mecanismos: dopagem com átomos de carbono, aplicação de campos elétricos externos, pelo achatamento da secção transversal, encapsulamento de um nanofio de carbono ou pela adsorção de átomos de hidrogênio (hidrogenação). Iniciamos com o estudo de nanotubos de nitreto de boro de parede dupla (DWBNNTs), zig-zag e armchair, dopados com átomos de carbono, com vetores quirais (8,0)@(16,0) e (5,5)@(10,10), respectivamente. Duas situações de dopagem foram consideradas: um átomo de C substituindo um átomo de B na parede interna (IW) e um átomo de C substituindo um átomo de N na parede externa (OW) a qual chamamos de CB[IW]@CN[OW], e a situação oposta resulta em CN[IW]@CB[OW]. Neste sentido, construímos um (semicondutor do tipo-p)@(semicondutor do tipo-n) e um (semicondutor do tipo-n)@(semicondutor do tipo-p) onde os DWBNNTs resultantes podem ser pensados como junções p-n. Paralelamente, aplicamos um campo elétrico externo, com magnitude de 0,3 V/Å, em diferentes direções, a saber, perpendicular (Ey), paralelo (Ex) e anti-paralelo (E􀀀x) a linha formada pelos dopantes. Assim, dependendo da direção do campo aplicado, observamos um aumento ou diminuição do gap de energia entre os níveis de defeitos (Eig) e tais casos estão relacionados a polarização reversa e direta da junção p-n, respectivamente. Em seguida, estudamos a inserção de um nanofio de carbono (CNW) no interior de um nanotubo de carbono e de BN, ambos com vetor quiral (10.0). Tais sistemas foram chamados de CNW@SWCNT e CNW@SWBNNT, respectivamente. Nós produzimos o achatamento dos nanotubos e verificamos o comportamento da estrutura atômica do nanofio a medida que o achatamento do nanotubo aumenta. A partir dos resultados obtidos, foi possível concluir que para ambos os CNW@SWCNT e CNW@SWBNNT, existe uma distancia crítica dc (distância entre os planos paralelos dos nanotubos achatados (d)), com um valor de 3.60 Å, de tal forma que nós podemos resumir as nossas descobertas como: no caso de d > dc, o nanofio de carbono não sofre nenhuma deformação; e no caso reverso (d < dc), o nanofio de carbono liga-se a parede do nanotubo e sofre deformações. Em relação as propriedades eletrônicas, verificamos que o encapsulamento do CNW nos SWCNT e SWBNNT, produz uma significativa redução do gap de energia (Eg) de tais sisteRESUMO vi mas. Além disso, observamos a formação de pontos de Dirac para algumas taxas de achatamento dos nanotubos. Por último, nós realizamos um estudo da adsorção de átomos de hidrogênio (hidrogenação) sobre a superfície de um nanotubo de parede dupla de nitreto de boro (DWBNNTs) e um nanotubo híbrido de nitreto de boro e carbono (DW(BN)xCyNTs). Devido ao fato dos nanotubos possuírem duas paredes, consideramos os seguintes casos: (i) coberturas de 2H, 4H, 8H, 12H e 16H na parede interna, (ii) coberturas de 2H, 4H, 8H, 16H e 32H na parede externa e (iii) coberturas de 2H, 4H, 8H, 16H e 32H em ambas as paredes. Curiosamente, verificamos que em todas as coberturas de hidrogênio consideradas, uma forte deformação ocorre nos locais de hidrogênio, fazendo a secção transversal dos nanotubos se transformar em diferentes formas poligonais: elipsoidal, retangular, hexagonal ou octaedral. Para coberturas de 16H e 32H apenas na parede externa, observamos que alguns hidrogênios se dessorveram da parede formando moléculas de H2 isoladas sem orientação preferencial. Verificamos que em alguns casos, os ângulos de ligação entre os átomos de B, N e H ou C e H exibem características da hibridação sp3. Com relação a estabilidade estrutural, verificamos que a adsorção de átomos de H em DWBNCNTs é mais favorável do que em DWBNNTs. Ademais, concluímos que é possível controlar o gap de energia dos nanotubos através da cobertura de hidrogênio.

Há, no Brasil, uma enorme diversidade de espécies vegetais, e um conhecimento popular de várias propriedades medicinais das mesmas. Dentre os estudos realizados com extratos de plantas, há um interesse especial na atividade antioxidante. Este trabalho, focado em atividade antioxidante, é dividido em duas partes: a primeira, utiliza a técnica de RPE para estudar a ação dos antioxidantes neutralizando os radicais livres, enquanto que a segunda utiliza a TFD para, em simulação computacional, ajudar a entender os resultados obtidos na primeira parte. Foram analisados 10 extratos vegetais: Swartzia langsdorffii, Machaerium villosum, Pterogyne nitens, Maytenus ilicifolia (casca de raiz), Pera glabrata, Aegiphyla sellowiana, Copaifera langsdorffii, Chrysophyllum inornatum, Iryanthera juruensis (folhas e sementes), Didymopanax vinosum. O estudo da atividade antioxidante com RPE utiliza dois métodos diferentes: o primeiro método mede a atividade antioxidante por meio do controle da quantidade de radicais livres, TEMPOL e DPPH, em contato com o extrato vegetal, enquanto que o segundo método utiliza o spin trap DMPO em conjunto com a reação de Fenton (Fe2+ + H2O2 => Fe3+ + HO- + HO) para analisar a ação dos extratos vegetais contra o radical hidroxila (OH?). A simulação computacional dos compostos TEMPOL, DPPH e DMPO é realizada em um método de primeiros princípios na Teoria do Funcional da Densidade, com uso de pseudopotenciais. O código utilizado é o SIESTA. As conclusões indicam que o extrato de Iryanthera juruensis, tanto de folhas quanto de sementes, exibe atividades antioxidantes bastante acentuadas, em todos os métodos utilizados. A simulação computacional aponta o TEMPOL menos reativo que o DPPH, devido a menor energia liberada em sua reação de redução. Sabendo que algumas destas espécies já são usadas popularmente por propriedades medicinais, estudos futuros para a correta identificação do agente antioxidante e seu possível uso, tanto na indústria alimentícia quanto na farmacêutica, deverão ser realizados. / There is, in Brazil, a great diversity of vegetable species, and a popular knowledge of several medicinal properties of the some of them. In studies carried out with plants? extracts, there is special interest in antioxidant activities. This work, focused in antioxidant activity, is divided in two parts: the first uses EPR technique to study the antioxidant activities neutralizing free radicals, while the second one uses DFT, in computational simulation, to understand the results obtained from the first part. Ten vegetable extracts were analyzed: Swartzia langsdorffii, Machaerium villosum, Pterogyne nitens, Maytenus ilicifolia (bark root extracts), Pera glabrata, Aegiphyla sellowiana, Copaifera langsdorffii, Chrysophyllum inornatum, Iryanthera juruensis (leaves and seeds), Didymopanax vinosum. The study with EPR uses two different methods: the first method measures the antioxidant activity by monitoring the amount of free radicals, DPPH and TEMPOL, that are in contact with the plant extract, the second method uses spin trap DMPO with Fenton reaction (Fe2+ + H2O2 => Fe3+ + HO- + HO) for the study of the plant extract antioxidant activity against the hydroxyl radical (OH?). The computational simulation of TEMPOL, DPPH and DMPO is carried out using a method of first principles within the Density Functional Theory and pseudopotentials. The code is SIESTA. The conclusions indicate that the Iryanthera juruensis extract, as of leaves as of seeds, exhibits accentuated antioxidants activities, in all of the used methods. The computational simulation indicated that the TEMPOL is less reactive than the DPPH, because the lower energy in its reduction reaction. As some of these species are already used popularly by medicinal properties, future studies for correct identification of the antioxidant compounds and its possible use, as in the food industry as in the pharmaceutical industry, should be realized.

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No. of bitstreams: 1 vivianedasilvavaiss.pdf: 3626163 bytes, checksum: 3a5c810252b870e4922ae7564819b604 (MD5) Previous issue date: 2011-01-27 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os hidróxidos lamelares, dentre os quais se incluem os compostos tipo brucita e os hidróxidos duplos lamelares (HDL), apresentam inúmeras aplicações devido às suas propriedades, tais como: alta estabilidade térmica, capacidade de troca iônica, porosidade e elevada área específica, eletroquímicas, fotoquímicas e outras. A capacidade de adsorção e troca iônica apresentada por estes compostos faz com que estes materiais sejam amplamente utilizados na remoção de espécies aniônicas e contaminantes. Assim, por exemplo, tais materiais podem ser usados na remoção do excesso de fluoreto de água potável, pois fluoreto em excesso pode causar fluorose esquelética ou dental, e na desativação de agentes neurotóxicos, organofosforados que atacam o sistema nervoso. O presente trabalho, apresenta um estudo detalhado dos mecanismos de reação de H2O, HF e sarin com hidróxidos lamelares. Para tanto, foram utilizados cálculos ab initio baseados na Teoria do Funcional da Densidade com condições de contorno e o método CI-NEB (Climbing Image-Nudging Elastic Band) para calcular o caminho de reação e a barreira energética de cada reação envolvida nos processos. A reação de HF foi baseada num mecanismo proposto composto por quatro reações elementares: a adsorção de HF sobre a superfície dos hidróxidos, a dissociação do HF adsorvido, a dessorção da molécula de água formada na reação de dissociação e a formação do composto M(OH)2−xFx. Os resultados mostram que a formação do composto M(OH)2−xFx é espontânea. Este resultado está de acordo com trabalhos experimentais, que prevêem como estável o composto formado pela substituição de OH- por F- em hidróxidos lamelares. Foram analisadas duas propostas para a formação de hidroxila sobre a superfície de hidróxidos lamelares. Na primeira uma hidroxila da própria lamela do hidróxido migra para a superfície e na segunda uma molécula de água se dissocia sobre a superfície do hidróxido, formando uma molécula de água e hidroxila adsorvidas na superfície, sendo esta última proposta mais favorável segundo os cálculos realizados. Os trabalhos anteriores foram etapas necessárias para o objetivo central da tese: estudar a desativação do agente neurotóxico sarin. No processo de desativação do sarin foram estudados intermediários formados pela dissociação e quimissorção do agente sobre a superfície da brucita. Com base nos resultados dos três processos estudados pôde-se verificar que a reação de desativação do agente sarin utilizando a brucita é termodinamicamente mais estável do que a reação de hidrólise. Além disso, verificou-se que a água pode participar do processo de desativação como um catalisador. Tal estudo está no âmbito do Programa Pró-Defesa do ministério da Defesa em conjunto com a CAPES. / Layered hydroxides, including brucite-like compounds and layered double hydroxides (LDHs), present numerous applications due to their properties such as: high thermal stability, ion exchange capacity, porosity and high surface area, electrochemistry, photochemistry and others. The capacity of adsorption and ion exchange presented by these materials make them to be widely used in the removal of anionic species and contaminants. Thus, for example, such materials can be used in the removal of excess fluoride from drinking water, because fluoride in excess can cause dental or skeletal fluorosis, and degradation of nerve agents, like organophosphates that attack the nervous system. This work presents a detailed study of the reactions H2O, HF and sarin with layered hydroxides. Therefore, were used ab initio calculations based on Density Functional Theory (DFT) with periodic boundary conditions and the CI-NEB method (Climbing Image – nudging Elastic band) to calculate the reaction path and the energetic barrier for each reaction involved in the process. The reaction of HF was based on a proposed mechanism consisting of four elementary steps: the adsorption of HF on the surface of hydroxides, the dissociation of adsorbed HF, the desorption of water molecule formed in the dissociation reaction and the formation of the compound M(OH)2−xFx. The results show that the formation of the compound M(OH)2−xFx is spontaneous. This result agrees with experimental works, that predicts as stable the compound formed by replacing OH- by F- in layered hydroxides. Two proposals were analyzed for the formation of hydroxyl on the surface of layered hydroxides. In the first proposal a hydroxyl of the hydroxide lamella migrates to the surface and in the second proposal a water molecule dissociates on the surface of the hydroxides, forming a water molecule and hydroxyl adsorbed on the surface; the latter proposal is more favorable according to the calculations performed. The previous studies were necessary steps for the central goal of the thesis: to study the deactivation of the nerve agent sarin. In the deactivation process of the nerve agent sarin intermediates formed by dissociation and chemisorption of the agent on the surface of brucite were studied. Based on the results of the three cases studied it could be checked that the deactivation reaction of the agent sarin using brucite is thermodynamically more stable than the hydrolysis reaction. Moreover, it appears that water can participate in the deactivation process as a catalyst. This study has happened into the ambit of the Pro-Defense program of the Defense Menistry in conjunction with the CAPES.

The formation and patterns of a monolayer are determined by the interplay of two fundamental interactions, adsorbate-substrate and intermolecular interactions. The binding strength between adsorbate and substrate affects the mobility of the adsorbate at the surface and the stability of the complex. The intermolecular interaction plays a significant role in the monolayer patterns on the epitaxial layer of the substrate. A monolayer can be formed either by a spontaneous self-assembly, or by fabrication via atomic-layer deposition (ALD). The physical and chemical properties of the resulting monolayer have a broad array of applications in fabricating functional materials for hydrophobic or hydrophilic surfaces, biological sensors, alternating the properties of the substrate, catalysis and forming ordered layered structures. In this dissertation, the investigation focuses primarily on the influence of the surface topology on the binding behaviour of adsorbate-surface complexes. The state of the art DFT-TS method is used to simulate the sulfur-containing amino acids at complex gold surfaces and examine the relationship between the binding strengths and the binding sites with various nearest neighbouring environments. The same method is also used to determine if a chemical reaction will take place for various catalytic silicon precursors at a silicon oxide surface. Simulating surface chemistry using the DFT-TS method requires intensive com- puting resources, including CPU use and computing time. Another focus of this dissertation is to increase the data generating speed by reducing the size of the sim- ulated systems without altering the outcome. A relatively small gold cluster is used to study the binding behaviours of small organic molecules on the cluster. The same strategy is also used to simulate the chemical reactions between various self-catalying silicon precursors and a water molecule. / Graduate / 2021-10-21

This thesis concerns my theoretical calculations and simulations in comparison with experimental measurements acquired by means of surface science techniques on bare surfaces and molecules adsorbed on surfaces. In the beginning of the thesis I briefly describe the density functional theory (DFT) method, which is used for calculations of geometric and electronic structure of surfaces and absorbed molecules. It is followed by a quick overview of the scanning probe microscopy (SPM) and X-ray spectroscopy techniques that provided experimental context for my calculations. In the later part of my thesis I introduce publications on which I participated. In these works, direct results of my DFT calculations or simulations based on DFT outputs helped to reveal geometric and electronic structure of acetophenone adsorbed on Si(111) surface, on-surface oligomerized organic molecules and boron atoms used for substitational doping of graphene. The simulations also enable us to probe a laser initiated CO hydrogenation in real time. A big part of my work was the development of some simulation methods for SPM imaging of molecules on surfaces with flexible tip apexes. These simulation methods helped to create a comprehensive overview of SPM techniques performed with flexible tip apexes. 1

Catalysis is a key area of chemistry. Through catalysis it is possible to achieve better synthetic routes, exploit molecules normally considered to be inactive and also attain novel chemical transformations. The development of new catalysts is crucial to furthering chemistry as a field. Computational chemistry, arising from applying the equations of quantum and classical mechanics to solving chemical problems, offers an essential route to investigating the underlying atomistic detail of catalysis. In this thesis calculations have been applied towards studying a number of different catalytic processes. The processing of renewable chemical sources via homogeneous reactions, specifically cardanol from cashew nuts, is discussed. All routes examined for monoreduction of a diene model by [Ru(H)(iPrOH)(Cl)(C₆H₆)] and [Ru(H)(iPrOH)(C₆H₆)]⁺ are energetically costly and would allow for total reduction of the diene if they were operating. While this accounts for the need of high temperatures, further work is required to elucidate the true mechanism of this small but surprisingly complex system. Gold-mediated protodecarboxylation was examined in tandem with experiment to find the subtle steric and electronic effects that dictate CO₂ extrusion from gold N-heterocyclic carbene activated benzene-derived carboxylic acids. The origin of a switch in the rate limiting step from decarboxylation to protodeauration with less activated substrates was also clearly demonstrated. Studies of gold systems are closed with examinations of 1,2-difluorobenzene C–H activation and CO₂ insertion by [Au(IPr)(OH)]. Calculations highlight that the proposed mechanism for oxazole-derived substrates cannot be extended to 1,2-difluorobenzene and instead a digold complex offers more congruent predicted kinetics. The lens of quantum chemistry was turned upon palladium-mediated methoxycarbonylation reactions. An extensive study was undertaken to attempt to understand the bidentate diphosphine ligand dependency on forming either methylpropanoate (MePro) or copolymers. Mechanisms currently suggested in literature are shown to be incongruous with the formation of MePro by Pd(OAc)₂ and bulky diphosphines. A possible alternative route is proposed in this thesis. Four mechanisms for methoxycarbonylation with Pd(2-PyPPh₂)ₙ are detailed. The most accessible route is found to be congruent with experimental reports of selectivity, acid dependency and slight steric modifications. A modification of 2-PyPPh₂ to 2-(4-NMe₂-6-Me)PyPPh₂ is shown to improve both selectivity and turnover, the latter by four orders of magnitude (highest transition state from 22.9 kcal/mol to 16.7 kcal/mol ∆G), and this new second generation in silico designed ligand is studied for its applicability to wider substrate scope and different solvents. The final chapter of this thesis is a mixed quantum mechanics and molecular mechanics (QM/MM) examination of an enzymatic reaction, discussing the need for certain conditions and the role of particular amino acid residues in an S[sub]N2 hydrolysis reaction.

Les fonctionnelles de la densité couramment utilisées ont rencontrées un succès spectaculaire dans la modélisation des systèmes physiques, chimiques, et biologiques. Toutefois, elles se sont avérées inadaptées pour décrire certaines situations, comme par exemple les forces de dispersion de London ou les phénomènes de corrélation forte. Dans le cadre de cette thèse, nous nous sommes intéressés à des développements récents de la formulation de l’énergie de corrélation exprimée à partir du théorème de fluctuation-dissipation et connexion adiabatique, visant à pallier ces problèmes. En particulier, différentes implémentations des méthodes au-delà de l’approximation de la phase aléatoire, qui permettent la prise en compte de la contribution d’échange dans le calcul de l’énergie de corrélation, ont été comparées. Ensuite, afin de réduire drastiquement la complexité numérique, une procédure d’orthogonalisation des vecteurs utilisées pour représenter la matrice diélectrique a été développée. Ces méthodes ont ensuite été appliquées au calcul de l’énergie de liaison de petits complexes moléculaires. La formulation de l’énergie de corrélation de la théorie de perturbation de Møller-Plesset dans le contexte matrice diélectrique est aussi présentée et testée. En parallèle, des calculs utilisant les méthodes semi-empiriques numériquement efficaces ont été conduits sur trois ensembles de molécules afin d’en tester les performances concernant les énergies de liaisons en les comparant aux valeurs de références disponibles dans la littérature / Commonly used density functionals have encountered a spectacular success in the modelling of physical, chemical or biological systems. However, they have proven to be unsuitable to describe some situations, such as London’s dispersion forces or strong correlation behaviour. In this thesis, we have been interested in recent developments in the formulation of the correlation energy from the adiabatic connection fluctuation dissipation theorem, to overcome these problems. In particular, different implementations of methods beyond the random phase approximation, which allow to take into account the exchange contribution in the computation of the correlation energy, have been compared. Then, in order to drastically decrease the numerical complexity, an orthogonalization procedure of the vectors used to represent the dielectric matrix has been developed. Then these approaches were applied to the calculation of the binding energy of small molecular complexes. The formulation of the correlation energy of the Møller-Plesset perturbation theory within the dielectric matrix context is also presented and tested. In parallel, calculations using numerically efficient semi-empirical methods were conducted over three molecular sets in order to test their performances regarding the binding energies by comparing them to reference values available in the literature

L’objectif principal de cette thèse était de comprendre par une approche conjointe théorie/expérience des réactions de polymérisation de monomères polaires, plus particulièrement de dérivés (méth)acryliques, réactions organocatalysées par des carbènes N-Hétérocycliques (NHC) utilisés seuls ou associés à une molécule organique (alcool) ou à un acide de Lewis. Pour cela un travail de rationalisation des effets électroniques et stériques apportés par le carbène a été réalisé à la fois sur les premières étapes du mécanisme de polymérisation par la théorie de la fonctionnelle de la densité (DFT) mais également sur les mécanismes potentiellement concurrents (cyclo-dimérisation) par deux méthodes théoriques: la DFT et la dynamique moléculaire (MD). L’ajout d’une molécule tierce comme un alcool ou un acide de Lewis (borane ou silane) a également été étudié théoriquement en détail afin de mieux comprendre l’effet de cette association sur la nature du mécanisme privilégié et sur l’efficacité de la polymérisation. / The main objective of this thesis was to understand, by a joint theoretical/experimental approach, polymerization reactions of polar monomers, especially (meth)acrylic derivatives, organocacatalyzed polymerizations by N-Heterocyclic carbenes (NHC) used alone or in combination with an organic molecule (alcohol) or a Lewis acid. Rationalization of both electronic and steric effects of the carbene was performed on the first steps of the polymerization mechanism by the functional density theory (DFT) and also on potentially competitive mechanisms (cyclodimerization) by two theoretical methods: DFT and molecular dynamics (MD). The addition of a third molecule such as an alcohol or a Lewis acid (borane or silane) has also been theoretically studied in detail in order to better understand the effect of this association on the nature of the privileged pathway and the effectiveness of the polymerization.

Dans cette thèse, de nouvelles stratégies pour la préparation de matériaux de type Metal-Organic-Frameworks (MOF) ont été étudiés et développés. L’électrodeposition bipolaire indirecte (IBED) a été utilisé pour préparer ZIF-8 et HKUST-1 sur des substrats métalliques de façon simple et avec une sélectivité spatiale. Ce concept devrait pouvoir être généralisée pour la synthèse de nombreux autres composés MOF, permettant ainsi une synthèse pas chère et verte, conduisant à de nouvelles générations de composites de type Janus basés sur des MOFs. En outre, des électrodes avec une structure hiérarchique macro-/ microporeux de HKUST-1 ont été préparées par une technique de dissolution-dépôt électrochimique. L'approche de synthèse mis au point est très pratique en ce qui concerne la durée des expériences, et ouvre diverses applications pour les MOFs. Enfin des nanoparticules de métaux nobles sur un substrat à base de MIL-101 ont été préparées comme la dernière partie de l'étude expérimentale par dépôt colloïdal. Ce concept peut être généralisé pour la synthèse d'autres composites nanoparticules métalliques / MOF, et pourrait améliorer l'activité catalytique des MOFs. En dehors de l'étude expérimentale, afin de comprendre mieux la catalyse de matériaux MOF, le comportement catalytique de Cu (II) dans le MOF-505 a été théoriquement étudié pour la réaction d'aldolisation Mukayiama par la théorie de densité fonctionnelle et comparé à celui d'un autre catalyseur, Cu-ZSM-5. En outre, le comportement catalytique d'amas homo- et hétéro-bimétalliques, qui sont des complexes métalliques qui représentent les agrégats métalliques dans les MOFs, a également été étudié théoriquement pour la réaction de cycloaddition de dioxyde de carbone et des oxydes d'éthylène. / In this thesis, new strategies for the preparation of Metal 0rganic Frameworks (MOF) materials with designed structures were studied and developed. Indirect bipolar electrodeposition (IBED) was used to prepare ZIF-8 and HKUST-1 on metal substrates in a straightforward and site-selective way. This concept is expected to be able to be generalized for the synthesis of many other MOF compounds, thus allowing a cheap and green synthesis, leading to new generations of MOF-based Janus-type composites. Furthermore, rationally designed hierarchical macro-/microporous HKUST-1 electrodes were prepared via an electrochemical dissolution-deposition technique. The developed synthesis approach is very practical in terms of the time consumption, and opens up MOFs for various applications. Finally, MIL-101-supported noble metal nanoparticles were prepared as the last part of the experimental studies via a simple colloidal deposition technique. This concept might be generalized for the synthesis of other metal nanoparticle/MOF composites, and might improve the catalytic activity of MOFs. Apart from the experimental study, in order to gain a deeper insight into the catalysis of MOF materials, the catalytic behavior of Cu(II) in the paddle-wheel unit of MOF-505 was theoretically investigated for the Mukaiyama aldol reaction via the density functional theory and compared to that of another catalyst, Cu-ZSM-5 zeolite. Besides, the catalytic behavior of homo-metallic clusters and hetero-bimetallic clusters, that are the metal complexes representing the metal clusters in MOFs, were also theoretically investigated for the cycloaddition reaction of carbon dioxide and ethylene oxides.

Mn+1AXn-Phasen sind thermodynamisch stabile nanolaminierte Ternärcarbide und -nitride, die sowohl metallische als auch keramische Eigenschaften aufweisen. Der Buchstabe M steht für ein frühes Übergangsmetall, der Buchstabe A für ein A-Element aus den Gruppen IIIA – VIA und X für Kohlenstoff und/oder Stickstoff. Die M-Atome bilden Oktaederschichten mit X-Atomen in ihren Zentren. Der Index n beschreibt die Dicke der Mn+1Xn-Lage, die zwischen zwei hexagonalen A-Schichten eingebettet ist. Die außergewöhnlichen Eigenschaften dieser Materialien haben ihren Ursprung in ihrer Mikrostruktur. Um einen Einblick auf atomarer Ebene zu gewinnen wird die Messmethode der gestörten γ-γ-Winkelkorrelation (PAC) angewendet. Die radioaktiven Sonden 111In/111Cd und 181Hf/181Ta werden durch Ionenimplantation und/oder durch Neutronenaktivierung in das Wirtsmaterial eingebracht, um den elektrischen Feldgradienten (EFG) zu messen, der am Gitterpatz des Sondenatoms herrscht. Das erste Ziel der Arbeit ist die Suche nach optimalen Ausheilparametern, mit denen ein möglichst hoher Anteil der Sonden die gleiche lokale Umgebung spürt. Der nächste Schritt ist die Bestimmung des Gitterplatzes der Sonden in der MAX-Struktur. Als Ergebnis kann festgestellt werden, dass 111In in den In- und Al-basierten MAX-Phasen fast ausschließlich den A-Platz besetzt, während 181Hf in Hf2InC auf dem M-Platz eingebaut wird. Als überraschendes Ergebnis zeigt diese Arbeit, dass die PAC-Methode bei Phasen mit gleichen Konstituenten, aber unterschiedlicher Mn+1Xn-Schichtdicke sensitiv auf die Änderung der Stapelfolge ist. Die Experimente werden mit umfangreichen Rechnungen auf Basis der Dichtefunktionaltheorie (DFT) verglichen, die hier erstmalig für nahezu alle Mitglieder der Familie der MAX-Verbindungen durchgeführt wurden. Die DFT-Rechnungen reproduzieren die gemessenen EFGs mit hoher quantitativer Genauigkeit und stützen die Hypothese, dass sich die Sonden auf den prognostizierten Gitterplätzen befinden.