Neste trabalho, utilizamos o desenvolvimento recente do método DFT/LDA-1/2 para cálculos de estados excitados em materiais. Começamos com um resumo da teoria do funcional da densidade (DFT) e incluímos uma introdução ao método LDA-1/2 para cálculos de excitações em sólidos. Na compilação dos resultados esperamos ter demonstrado a utilidade do LDA-1/2 para cálculos de alinhamentos de bandas em junções semicondutor/semicondutor e semicondutor/isolante. A aplicação do método envolve o conhecimento da química básica dos sistemas. Para tanto, escolhemos sistemas importantes para diversas aplicações, e cujos modelos de simulação estão o limite ou fora do alcance de metodologias que envolvem alto custo computacional, mas que foram bem caracterizados experimentalmente. Concentramos nossas ações no estudo da capacidade preditiva do LDA-1/2 para alinhamentos de bandas, os chamados band offsets, particularmente importantes para a micro e optoeletrônica. Quando não foi possível compararmos nossos resultados com o experimento, procuramos a comparação com métodos estado-da-arte como GW. Bons resultados foram obtidos para band gaps e band offsets de interfaces A1As/GaAs, Si/SiO2, A1N/GaN e CdSe/CdTe, que representam os diferentes tipos de jun_c~oes poss__veis, com (e.g. A1As/GaAs, A1N/GaN) e sem (e.g. Si/SiO2, CdSe/CdTe) ^anions omuns, com (e.g. A1As/GaAs) e sem (e.g. CdSe/CdTe, Si/SiO2) casamento de parâmetros de rede e diferentes tipos de alinhamentos (\"straddling\", e.g. A1As/GaAs ou \"staggered\"e.g. CdSe/CdTe). Analisamos de maneira sistemática o comportamento do entorno do bandgap ao longo da interface, verificando plano a plano atômico o comportamento das bordas de valência e condução com LDA-1/2 em comparação com o LDA, ou comparando diferentes modelos dentro do LDA-1/2, como o caso do CdSe/CdTe e do Si/SiO2. Para o caso A1As/GaAs, aproveitamos o casamento de parâmetros de rede dos semicondutores constituintes e tentamos um modelo de interface de ligas A1xGa1-x As/GaAs para estudar a variação de valência, condução e bandgap em função da composição x. No AlN/GaN, estudamos também os offsets com as contribuições dos orbitais separadamente. Em todos os casos o LDA-1/2 levou-nos a resultados interessantes com modelos simples. A exploração de novas fronteiras de aplicação do método fez-se necessária com a diminuição da dimensionalidade dos sistemas, de 3D (bulk ) para 2D (interfaces) e depois para 1D, ou seja, _os quânticos (\"nanofios\"). Nosso material de estudo para os foi o ZnO que, além da motivação oriunda de conhecidas aplicações em optoeletrônica, apresenta desafios para simulações bulk com qualquer método, e que foi abordado com certo sucesso usando o LDA-1/2 anteriormente, sendo que para fios quânticos encontramos resultados interessantes em geometrias triangulares que facilitaram os modelos. Calculamos o bandgap ZnO bulk e de nanofios passivados e não passivados com hidrogênios usando LDA e LDA-1/2 sem polarização de spin. As estruturas de bandas e o bandgap como função do diâmetro do ano_o foram calculados e ajustes com funções de decaimento foram feitos para comparação, por extrapolação, dos bandgaps com valores experimentais. Foi possível comparar nossos resultados de fios com o bulk, e predizer uma faixa de variaação de bandgaps que os experimentais podem encontrar para nanofios triangulares de ZnO. Também foi feita análise de energias de confinamento em fios quânticos de ZnO, comparando o LDA com LDA-1/2. Finalmente, mostramos os resultados de uma oportunidade de aplicação do método a um material com defeitos, recentemente descoberto e promissor, e com enorme mercado potencial em fotocatálise, o Ti1-O4N. Nosso trabalho envolveu a aplicação do LDA-1/2 a um problema muito desafiador, e.g. a geração de energia limpa, especificamente a separação da molécula de água para produção de hidrogênio. O desafio maior vem da dificuldade de predição de bandgaps teoricamente, em particular para sistemas grandes como é o caso de modelos atomísticos com defeitos, devido aos altos custos computacionais envolvidos. Tais dificuldades forçam os pesquisadores a usarem parâmetros ajustáveis ou métodos semi-empíricos, ou modelos simplificados demais para descrever precisamente resultados experimentais. Isto dificulta o estudo dos sistemas fotocatalíticos potencialmente eficientes e que não foram ainda caracterizados ou otimizados. O LDA-1/2 é aqui validado para esta classe de materiais, abrindo assim a oportunidade para estudar sistemas mais realísticos e complexos para cálculos ainda mais precisos, particularmente para geração de energia limpa. Em particular, modelamos o TiO2 na estrutura rutile com nitrogênio substitucional, cuja estrutura eletrônica é ainda debatida. Foi a primeira aplicação do LDA-1/2 a sistemas com algum tipo de defeito, com ótimos resultados para o novo sistema Ti1- _O4N com vacâncias de Ti. / In this work, we used the recent development of DFT/LDA-1/2 method for calculations of excited states in materials. We begin with a summary of the density functional theory (DFT) and included an introduction to the method LDA-1/2 for calculations of excitations in solids. In compiling the results we hope to have demonstrated the usefulness of the LDA-1/2 for calculating alignments of bands at junctions semiconductor / semiconductor and semiconductor / insulator. The method involves the knowledge of basic chemical systems. To do this we chose systems important for several applications, and simulation models which are the limit or beyond the reach of methodologies involving high computational cost, but have been well characterized experimentally. We focus our actions in the study of the predictive capability of the LDA-1/2 for alignments of bands, the band called offsets, particularly important for micro and optoelectronics. When it was not possible to compare our results with experiment, we compared the methods with state of the art as GW. Good results were obtained for band gaps and band offsets of interfaces A1As/GaAs, Si/SiO2, A1N/GaN and CdSe / CdTe, which represent the different types of jun_c poss__veis-tions, with (eg A1As/GaAs, A1N/GaN) and without (eg Si/SiO2, CdSe / CdTe) ^ omuns anions with (eg A1As/GaAs) and without (eg CdSe / CdTe, Si/SiO2) matching network parameters and different types of alignments (\"straddling\" eg A1As/GaAs or \"staggered\" eg CdSe / CdTe). Systematically analyze the behavior of the environment along the interface bandgap, plane by plane scanning behavior of the edges atomic valence and conduction with LDA-half in comparison with LDA, or comparing templates within the LDA-1 / 2, as the case of CdSe / CdTe and Si/SiO2. For the case A1As/GaAs, we take the marriage of network parameters of semiconductor components and try an interface model alloys A1xGa1-x As / GaAs to study the variation of valence, conduction and bandgap as a function of composition x. In the AlN / GaN, we also studied the offsets with the contributions of the orbitals separately. In all cases the LDA-half led us to interesting results from simple models. The exploration of new frontiers of the method was necessary to decrease the dimensionality of the systems, the 3D (bulk) for 2D (interfaces) and then to 1D, ie, quantum _os (\"nanowires\"). Our study material for the ZnO was that, apart from the motivation coming from known applications in optoelectronics, presents challenges for bulk simulations with any method, and that was addressed with some success using the LDA-half earlier, and for wireless find interesting results in quantum triangular geometries that facilitated models. We calculate the bandgap and bulk ZnO nanowires passivated and not passivated with hydrogen using LDA and LDA-1/2 without spin polarization. The bandgap structures and strips as a function of the diameter of ano_o adjustments are calculated and decay functions for comparison were made by extrapolation of the bandgaps with experimental values. It was possible to compare our results with the bulk of wires, and predict a range of bandgaps that variaação can find experimental triangular ZnO nanowires. It was also made analysis of energy confinement in ZnO quantum wires, comparing LDA with LDA-1/2. Finally, we show the results of an opportunity to apply the method to a material with defects, newly discovered and promising, and with huge market potential in photocatalysis, the Ti1-O4N. Our work involved the application of LDA-1/2 to a very challenging problem, eg the generation of clean energy, specifically the separation of the water molecule for hydrogen production. The main challenge has been the difficulty of predicting bandgaps theoretically, in particular for large systems such as the model atomistic defects because of the high computational costs involved. These difficulties force the researchers to use adjustable parameters or semi-empirical methods, or other simplified models to accurately describe experimental results. This complicates the study of potentially efficient photocatalytic systems which have not yet been characterized or optimized. The LDA-1/2 is here validated for this class of materials, thus opening the opportunity to study more realistic and complex systems for more accurate calculations, particularly for clean energy generation. In particular, we modeled the structure of TiO2 in the rutile with substitutional nitrogen, whose electronic structure is still debated. It was the first application of the LDA-1/2 systems with some kind of defect, with excellent results for the new system Ti1-_O4N with Ti vacancies.

Cette thèse porte sur la modélisation ab initio des ligands et des nanoparticules magnétiques utilisés en médecine (hyperthermie magnétique, imagerie médicale ...). Les calculs sont effectués par le logiciel Quantum Espresso base sur théorie de la fonctionnelle de la densité et LDA + U. L'objectif est d'abord de comprendre la liaison des ligands sur des nanoparticules magnétiques, la nature de l'ionicité dans les particules, puis de décrire le changement d'anisotropie magnétique due aux liaisons chimiques sur la surface, et enfin de décrire la modification des propriétés optiques due également à la liaison de différents ligands sur la surface de nanoparticules hybrides d'or et d'oxyde de fer. / This thesis concerns the ab initio modeling of ligands and magnetic nanoparticles used in medicine (magnetic hyperthermia, medical imaging). Calculations are performed by the Quantum Espresso software based on density functional theory and LDA+U. The goal is first to understand the binding of ligands on magnetic nanoparticles, the nature of ionicity in the particles, then to describe the change in magnetic anisotropy due to the chemical bondings on surface, and finally to describe the change in optical properties due also to the bonding of various ligands or clusters on the surface of hybrid gold and iron oxide nanoparticles.

Le premier chapitre de cette thèse concerne l'étude théorique des propriétés optiques linéaire et non linéaires de cibles organiques et organométalliques expérimentales de l'équipe, en particulier de dérivés carbo-benzéniques quadrupolaires. Les méthodes de calcul et d'analyse standard des états excités sont tout d'abord présentées, ainsi que deux outils d'analyse développés dans ce travail concernant : (i) le caractère transfert de charge en termes de densité de " trou " et de " particule ", et (ii) la visualisation du moment dipolaire de transition à partir de la densité de transition tronquée (TTD) aux principales mono-excitations. Les premiers états excités des chromophores calculés au niveau TD-DPT, ainsi qu'au niveau CAS-PT2 pour certains chromophores modèles, sont ensuite analysés. Les spectres d'absorption UV-visible à 1 photon des dérivés carbo-benzéniques s'inscrivent dans le cadre du modèle de Gouterman proposé pour les porphyrines, où les quatre premiers états excités mettent en jeu des combinaisons linéaires de mono-excitations impliquant les quatre mêmes orbitales moléculaires frontières. Les moments dipolaires calculés à partir des TTD rendent bien compte des intensités relatives des bandes d'absorption. Une analogie entre porphyrines et carbo-benzènes est ainsi argumentée. Les densités de " trou " et de " particule " ont été utilisées pour étudier le caractère transfert de charge des premiers états excités de complexes de palladium(II), construits à partir de ligands carbonés riches en électrons et de ligands phosphorés pauvres en électrons. L'efficacité d'absorption à deux photons (ADP), une propriété optique non linéaire du troisième ordre, est ensuite étudiée, Les sections efficaces d'ADP (sADP) ont été calculées, en utilisant la méthode " sum-over-state " (SOS), qui prend en compte la contribution de tous les états excités intermédiaires possibles. La plupart des dérivés carbo-benzéniques étudiés s'inscrivent dans le cadre du " modèle à trois niveaux ", c'est à dire que la contribution d'un état excité intermédiaire domine largement celle des autres. sADP ˜ (µ0i2*µif2)/?E2, où ?E est la différence entre l'énergie de l'état excité intermédiaire (autorisé à un photon) et la moitié de l'énergie de l'état excité final (autorisé à deux photons). Les propriétés d'ADP peuvent alors être analysées à partir des moments dipolaires de transition (µ0i et µif), qui peuvent être calculés à l'aide des TTD, et des énergies de ces deux transitions. Le second chapitre concerne des études du caractère bi- ou poly-radicalaire de molécules organiques réalisées dans le cadre d'une collaboration avec Georges Trinquier et Esmail Alikhani, animée par Jean-Paul Malrieu. Parmi les différents systèmes envisagés, notamment des carbo-benzènes de première, deuxième ou troisième génération ainsi que de nouveaux motifs dont le caractère bi- ou poly-radicalaire singulet à couches ouvertes est tout d'abord étudié par des calculs en symétrie de spin brisée. La décontamination de la solution MS = 0 de symétrie brisée a été ensuite effectuée soit (i) à géométrie constante selon la procédure de Labanowski et al., soit (ii) en optimisant la géométrie de l'état de spin singulet à couches ouvertes selon la " recette " proposée par Malrieu et al.. La stabilité de cet état pour des systèmes oligoacétyléniques de type carbo-mère a été comparée à celle obtenue pour des systèmes oligobenzéniques parents. Les résultats sont analysés en termes structuraux en faisant appel aux concepts de " motifs isolants de spin " et de " motifs stabilisants de spin ". La qualité des premiers est corrélée à l'aromaticité des motifs (1,4-phénylène > 1,2-éthynylène). Le radical trialcynylméthyle (TAM) est proposé comme un motif stabilisant de spin particulièrement performant. Sur la base de ces résultats, diverses cibles de synthèses sont proposées en série carbo-mère. / The first chapter of this thesis reports on the theoretical study of linear and nonlinear optical properties of organic and organometallic experimental targets developed in the group, especially quadrupolar carbo-benzene derivatives. Standard methods for the calculation and the analysis of excited states are presented first, as well as two theoretical tools developed in this work addressing: (i) the charge transfer character in terms of "hole" and "particle" densities and (ii) the visualization of the transition dipole moment from the transition density truncated to the main mono-excitations (TTD). The first excited states of the chromophores calculated at the TD-DFT level, and at the CAS- PT2 level for a few model chromophores, are then analyzed. The one-photon UV-visible absorption spectra of carbo-benzene derivatives fit with the Gouterman model originally proposed for porphyrins, where the four first excited states involve linear combinations of mono-excitations of the same four frontier molecular orbitals. The relative intensities of the absorption bands are analyzed from the transition dipole moments calculated from the TTDs. An analogy between porphyrins and carbo-benzenes is then argued. The "hole" and "particle" densities are used to study the charge transfer character of the first excited states of palladium(II) complexes, built from electron-rich carbon ligands and electron-poor phosphorus ligands. The two-photon absorption (TPA) efficiency, a third order nonlinear optical property, is then studied. For each two-photon allowed excited state, a TPA cross-section (sTPA) has been calculated, from the contribution of all possible intermediate excited states, using the "sum-over-state" (SOS) method. Most of the carbo-benzene derivatives fit with the "three level model", with a major contribution of one intermediate state to the TPA cross-section. sTPA ˜ (µ0i2*µif2)/?E2, where ?E is the difference between the energy of the intermediate state (one-photon allowed) and half the energy of the final state (two- photon allowed). The TPA efficiency can thus be analyzed from the transition dipole moments (µ0i and µif), which can be calculated from the TTDs, and the energies of the two transitions. In the second chapter, the stability of organic di- or poly-radicals was studied in collaboration with Jean-Paul Malrieu, Georges Trinquier and Esmail Alikhani. The di- or poly-radical open-shell singlet spin state of carbo-benzenes of first, second and third generation, and of related acyclic motifs, is first studied using broken-symmetry calculations. The spin-decontamination of the MS = 0 broken-symmetry solution is then performed either (i) at constant geometry according to the procedure of Labanowski et al. or (ii) following the "recipe" of Malrieu et al., yielding the optimized geometry of the open-shell singlet spin state. The stability of the latter for oligoacetylenic systems of the carbo-mer type has been compared to the one of parent oligobenzenic systems. A structural analysis of the results is discussed in terms of "spin insulating moieties" and "spin stabilizing moieties". The former may be related to aromaticity (1,4-phenylene > 1,2-ethynylene), while the latter may be related to spin delocalization. The trialkynylmethyle radical (TAM) is suggested as a particularly efficient spin stabilizing pattern. On the basis of these results, several carbo-meric synthesis targets are suggested.

As propriedades da molécula de nitroxil livre e do ligante nitroxil em tetraamminas de Ru(II) (trans-[Ru(NH3)4(nitroxyl)n(L)]2+n, n = carga do nitroxil e L = NH3, py, P(OEt)3, H2O, Cl- and Br-) foram estudadas utilizando-se a teoria do funcional da densidade (DFT). De acordo com as energias calculadas para as conformações dos complexos de HNO, esses são mais estáveis do que os análogos desprotonados e a configuração singleto (trans-1[Ru(NH3)4(L)HNO]2+) é de menor energia em relação a correspondente tripleto <br /> (trans-3[Ru(NH3)4(L)HNO]2. A avaliação dos componentes &sigma; e &pi; na ligação <br /> L-Ru-HNO sugere que o aumento da estabilidade destes orbitais juntamente com o aumento das contribuições dos orbitais HNO estão correlacionacionado a menores valores de distâncias Ru-N(H)O e freqüências inferiores para os estiramentos &nu;NO. A estabilidade da ligação Ru-HNO também foi avaliada através de um estudo cinético teórico da dissociação de HNO a partir de <br /> trans-1[Ru(NH3)4(L)HNO]2+. De acordo com a ordem de estabilidade de ligação Ru-HNO em trans-1[Ru(NH3)4(L)HNO]2+ observa-se a seguinte ordem em função de L: H2O &gt; Cl- ~ Br- &gt; NH3 &gt; py &gt; P(OEt)3, que corresponde à ordem do efeito trans e influência trans medida experimentalmente para a série de L em complexos octaédricos. A mesma tendência foi também observada utilizando o modelo explícito solvente, considerando-se, assim, a presença de uma molécula de H2O juntamente com uma molécula de HNO no estado de transição. Para esta série, as energias calculadas para a ligação Ru-HNO estão no intervalo de 21,4 - 41,5 kcal.mol-1. Observou-se uma boa concordância entre os valores calculados de &Delta;G&dagger; HNO para substituição por H2O a partir do complexo trans-1[Ru(NH3)4(P(OEt)3HNO]2+ (28.5 kcal mol-1) e os dados experimentais disponíveis para reações de substituição em sistemas trans-[Ru(NH3)4(POEt)3(Lx)]2+ (19.4 e 24.0 kcal.mol-1 para Lx = isn e P(OET)3, respectivamente). Experimentos de voltametria cíclica foram realizados observando os processos de redução do ligante nitrosônio gerando nitroxil e podendo gerar amônia, o que foi também observado por cálculos envolvendo efeito de uma primeira esfera de solvatação. / The properties of free nitroxyl molecule and the nitroxyl ligand in Ru(II) tetraammines (trans-[Ru(NH3)4(nitroxyl)n(L)]2+n, n = nitroxyl charge and L = NH3, py, P(OEt)3, H2O, Cl- and Br-) were studied trough density functional theory (DFT). According to the calculated conformation energies the HNO complexes are more stable than the deprotonated analogues and the singlet configuration (trans-1[Ru(NH3)4(L)HNO]2+) is lower energy the than the corresponding triplet (trans-3[Ru(NH3)4(L)HNO]2+). Evaluation of the &sigma; and &pi; components in the L-Ru-HNO bond suggest that increased stability of these orbitals and enhanced contributions from the HNO orbitals correlate to shorter Ru-N(H)O distances and lower &nu;NO stretching frequencies. The stability of the Ru-HNO bond was also evaluated through a theoretical kinetic study on HNO dissociation from trans-1[Ru(NH3)4(L)HNO]2+. Accordingly, the order of the Ru-HNO bonding stability in trans-1[Ru(NH3)4(L)HNO]2+ as a function of L is: H2O &gt; Cl- ~ Br- &gt; NH3 &gt; py &gt; P(OEt)3, which parallels the order of the trans effect and trans influence series experimentally measured for L in octahedral complexes. The same trend was also observed using the explicit solvent model, thus considering the presence of both the HNO and H2O molecules in the transition state. For this series, the calculated bond energies for the Ru-HNO bond are in the range 21.4 to 41.5 kcal.mol-1. Good agreement was observed between the calculated &Delta;G&dagger; values for HNO substitution by H2O from the complex trans-1[Ru(NH3)4(P(OEt)3HNO]2+ (28.5 kcal mol-1) and the available experimental data for substitution reactions of trans-[Ru(NH3)4(POEt)3(Lx)]2+ (19.4 to 24.0 kcal.mol-1 for Lx = isn and P(OET)3, respectively). Cyclic voltammetry experiments were carried out observing the reduction processes of the nitrosonium ligand generating nitroxil and could generate ammonia, which was also observed by calculations involving the effect of a first sphere of solvation.

Made available in DSpace on 2015-04-22T22:02:01Z (GMT). No. of bitstreams: 1 Dissertacao Julio Rodolfo Pessoa Iank.pdf: 2962867 bytes, checksum: cae054b70271d4b5155110e9b2d9641e (MD5) Previous issue date: 2009-06-15 / Fundação de Amparo à Pesquisa do Estado do Amazonas / Currently the study of fullerene or buckyballs C60, C70, C82, etc. has generated great interest for theoretical research and experimental in discover its chemical and physical properties, including the ability of encapsulation of different chemicals species. These searches resulted in the development and possible production by synthesis of new buckyballs, but also with homologous series of C70 molecules with encapsulated metal ions that can be used as superconducting, photoluminescent materials, ferromagnetic materials and also in developing new systems of accumulation and storage of hydrogen gas. This study aims to examine the relative stability of C60 and its derivatives, through a theoretical and computational approach in DFT level with B3LYP hybrid functional using bases 3-21G and 6-31 G++. The results showed that buckyballs and their derivatives are stable against the fragmentation structural, changes were observed only from the C20, C18 and C16, and the latter buckyball does not support encapsulated hydrogen. The characterization of systems C60@(2, 5, 8, 11 and 15)H2 shows a large transfer of charge between hydrogens and carbons in all systems studied which suggests a high probability of acceptance of electrons and limited capacity of the containment least 15 molecules of H2 of encapsulated C60, at the same time demonstrates the great capacity of encapsulation of H2. Other relevant results showed high reactivity to only two molecular systems C60@11H2 and C60@15H2, demonstrating that the C60 is more reactive with high index of H2 encapsulated. / Atualmente o estudo de fulerenos ou buckyballs C60, C70, C82, etc tem geradoum grande interesse para pesquisa teórica e experimental em desvendar suas propriedades químicas e físicas, entre elas a capacidade de encapsulamento de diferentes substâncias químicas. Estas pesquisas resultaram no desenvolvimento e possível produção por síntese de novas buckyballs, como também séries homólogas com moléculas de C70, que podem ser usados como supercondutores, materiais fotoluminescentes, materiais ferromagnéticos e também no desenvolvimento de novos sistemas de acumulação e armazenamento de gás hidrogênio. Este trabalho tem por objetivo analisar as estabilidades relativas do C60 e seus derivados, através de uma abordagem teórico-computacional, em nível DFT com funcional híbrido B3LYP utilizando bases 3-21G e 6-31 G++. Os resultados mostraram que as buckyballs e seus derivados são estáveis frente à fragmentação estrutural, tendo sido observadas mudanças somente a partir do C20, C18 e C16, sendo que a última buckyball não suporta hidrogênio encapsulado. A caracterização de sistemas C60@(2, 5, 8, 11 e 15)H2 demonstra uma grande transferência de carga entre hidrogênios e carbonos em todos os sistemas estudados o que sugere uma altaprobabilidade de aceitação de elétrons e limitada capacidade de confinamento de pelo menos 15 moléculas de H2 encapsuladas do C60, ao mesmo tempo em que demonstra a grande capacidade de encapsulamento de H2. Outros resultados relevantes mostraram alta reatividade molecular somente para dois sistemas C60@11H2 e C60@15H2, demonstrando que o C60 é mais reativo com alto índice de H2 encapsulado.

Nanoligas bimetálicas têm atraído a atenção de pesquisadores nas últimas décadas devido a possibilidade de ajustar suas propriedades físico-químicas, tais como propriedades elétricas, ópticas, magnéticas e de reatividade, por meio da variação do número de átomos, da composição química e do formato geométrico. As nanoligas bimetálicas que combinam Pt com outros metais são especificamente interessantes na área de catálise heterogênea, devido a possibilidade de se obter materiais com propriedades distintas de seus respectivos sistemas unários no que se refere ao surgimento ou aumento da atividade catalítica, à seletividade e, muitas vezes, ao preço reduzido. Esse trabalho tem como objetivo investigar as propriedades estruturais, energéticas, eletrônicas e de estabilidade de nanoligas bimetálicas core-shell de 55 átomos que combinam Pt com metais de transição (MT) pertencentes às séries de transição 3d, 4d e 5d dos grupos de Fe a Zn. Esses sistemas foram estudados utilizando cálculos de primeiros princípios (ab initio) baseados na teoria do funcional da densidade, tal como implementada no código computacional VASP (Vienna Ab initio Simulation Package). As nanoligas putativas de mínimo global energético (pGMC) de composição Pt13MT42 e Pt42MT13 calculadas nesse estudo apresentaram características particulares quanto à geometria e ao arranjo das espécies metálicas na nanoliga. Ao que diz respeito aos arranjos core-shell, foram observados dois arranjos em que a fica Pt no caroço (Pt13Ag42 e Pt13 Au42) e sete arranjos em que a Pt fica na superfície (Pt42Fe13, Pt42Co13, Pt42Ni13, Pt42Cu13, Pt42Ru13, Pt42Rh13 e Pt42Os13). Os mecanismos que levam à formação destas e das demais nanoligas pGMC foram investigados com base em três fatores: raio atômico, energia de superfície e cargas de Bader. Verificou-se que raio e a energia de superfície competem como fator determinante pelas posições preferenciais de cada espécie metálica na nanoliga. Nos casos em que houve divergência, o raio apresentou-se como o fator de maior importância, entretanto, quando o raio das espécies são muitos próximos, a energia de superfície exerce um papel de maior importância. A partir da análise de cargas de Bader, observou-se ocorrência de transferência de carga da região do caroço para a região da superfície para a maioria das nanoligas. No mais, observou-se que as nanoligas core-shell contam com atração coulômbica de maior magnitude do que as demais nanoligas pGMC, como resultado de altas cargas de sinal oposto em cada uma das regiões. / Bimetallic nanoalloys have been attracting attention since the last decades due to the possibility of adjusting their physical-chemical properties, such as electrical, optical, magnetic and reactivity properties, by means of the variation of the number of atoms, chemical composition and geometry. Bimetallic nanoalloys that combine Pt with other metals are especially interesting for heterogeneous catalysis given the possibility of obtaining materials with properties that differ from their respective unary systems regarding the appearance or increase of catalytical activity, selectivity and, in many cases, reduced cost. The aim of this work is the evaluation of the stability and of structural, energetic and electronic properties of 55 atom core-shell bimetallic nanoalloys that combine Pt with transition metals (MT) from the 3d, 4d, and 5d transition periods from Fe to Zn groups. These systems were studied using first principle (ab initio) calculations based on density functional theory, as implemented in the VASP (Viena Ab initio Simulation Package) computer code. The nanoalloys with Pt13MT42 and Pt42MT13 compositions which were observed as putative global minimum configuration (pGMC) presented unique characteristics regarding their geommetry and the arrangement of the different metals within the nanoalloy. Considering the core-shell nanoalloys, two arrangements in which Pt is located in the core were observed (Pt13Ag42 e Pt13 Au42) as well as seven arrangements with Pt in the surface (Pt42Fe13, Pt42Co13, Pt42Ni13, Pt42Cu13, Pt42Ru13, Pt42Rh13 e Pt42Os13). The mechanisms that lead to the formation of these and of the remaining pGMC nanoalloys were investigated considering three factors: atomic radius, surface energy and Bader charges. It was verified that atomic radius and surface energy compete directly for the determination of preferential sites for the atoms in the nanoalloy. When these two factors diverge, the atomic radius is the most important factor. However, when the radii of the species involved are similar, the surface energy becomes the determining factor. In addition, Bader charges analysis showed that, for most nanoalloys, the core is positively charged and the shell accumulates negative charge, indicating that charge is transfered from the atoms in the core to the ones in the surface. Besides, the core-shell nanoalloys have a higher coulombic attraction in comparison with others pGMC, due to high quantities of charge with opposite sign in each region.

Desde a identificação do vírus da imunodeficiência humana (HIV, do inglês Human Immunodeficiency Virus) como agente causador da Síndrome da Imunodeficiência Adquirida (AIDS ? do inglês Acquired Immunodeficiency Syndrome), a busca para tratamentos seguros e eficazes contra o HIV transformou-se no principal foco para a descoberta de uma nova droga em todo o mundo. A AIDS aparece como um dos principais problemas de saúde pública para as próximas décadas, onde será o maior determinante de mortalidade na faixa etária entre 20 e 50 anos em praticamente todos os países do mundo. Tendo como objetivo relacionar a atividade de compostos biflavonóides anti-HIV-1 com algumas de suas propriedades moleculares, serão utilizados métodos de Mecânica Molecular e Química Quântica. O método de cálculo semi-empírico AM1 foi empregado para calcular um conjunto de propriedades moleculares dos 14 compostos biflavonóides com atividade anti-HIV-1. A seguir utilizar-se-á métodos estatísticos com a finalidade de separar os 14 compostos em duas classes, ativos e não ativos, de forma que se relacione qual as propriedades, dentre as calculadas, são responsáveis pela atividade dos compostos biflavonóides estudados. As técnicas estatísticas utilizadas foram a Análise de Componentes Principais (PCA: Principal Components Analysis), Análise Hierárquica de Agrupamentos (HCA: Hierarquical Clusters Analysis) e Análise de Discriminates por Passos (SDA: Stepwise Discriminant Analysis). Os estudos com PCA, HCA, e SDA mostraram que as variáveis HOMO (Highest Occupied Molecular Orbital - Orbital Molecular Ocupado de Maior Energia), LUMO (Lowest Unoccupied Molecular Orbital ? Orbital Molecular Desocupado de Menor Energia), e Área superficial são responsáveis pela separação dos compostos com alta e baixa atividade anti-HIV-1. O comportamento destas três propriedades pode ser útil na tentativa de se obter outros compostos biflavonóides com elevada atividade inibidora anti-HIV-1. / A set of 25 quinone compounds with anti-trypanocidal activity was studied by using the Density Functional Theory (DFT) method in order to calculate electronic atomic and molecular properties to be correlated with the biological activity. The chemometric methods Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), Stepwise Discriminant Analysis (SDA), Kth nearest neighbor (KNN) and Soft Independent Modeling of Class Analogy (SIMCA) were used to obtain possible relationships between the calculated descriptors and the biological activity studied and predict the anti-trypanocidal activity of new quinone compounds from a test set. Four descriptors were responsible for the separation between the active and inactive compounds: T5 (torsion angle), HOMO-1 (energy of the first molecular orbital below HOMO), QTS1 (sum of absolute values of the atomic charges) and VOLS2 (volume of the substituent at region B). These descriptors give information on the kind of interaction that occurs between the compounds and the biological receptor. The prediction study was done with a set of three new quinone compounds by using the PCA, HCA, SDA, KNN and SIMCA. Beside the five chemometric methods, the neural network method was used by employing the backpropagation algorithm. The four variables (T5, QTS1, VOLS2 and HOMO-1) were employed to validate the models constructed previously. The architecture of networks consisting of four neurons at input layers, ten neurons at intermediary layers and two neurons at output layers was adopted to observe the root mean square error between the true and desired output over the entire training set. The percentage of correct classification was 87.5%, and only one compound was predicted wrong in the test set, which indicates that the model is robust and could be able to make predictions. The docking studies were carried out with two different programs in the approach of ligands: the Autodock and FlexX. The docking results on trypanothione reductase enzyme showed that all studied compounds stay at second hydrophobic pocket in the outer region of the active site called the Z-site. The residues that could be specifically involved in the binding of ligands are Lys62, Thr66, Thr397, Thr463, Leu399, Ser464, Glu466 and Glu467, where the residues Thr66, Thr463 and Leu399 are conserved in different trypanothiones and could be used for the development of selective inhibitors against to the parasite enzyme.

As propriedades da molécula de nitroxil livre e do ligante nitroxil em tetraamminas de Ru(II) (trans-[Ru(NH3)4(nitroxyl)n(L)]2+n, n = carga do nitroxil e L = NH3, py, P(OEt)3, H2O, Cl- and Br-) foram estudadas utilizando-se a teoria do funcional da densidade (DFT). De acordo com as energias calculadas para as conformações dos complexos de HNO, esses são mais estáveis do que os análogos desprotonados e a configuração singleto (trans-1[Ru(NH3)4(L)HNO]2+) é de menor energia em relação a correspondente tripleto <br /> (trans-3[Ru(NH3)4(L)HNO]2. A avaliação dos componentes &sigma; e &pi; na ligação <br /> L-Ru-HNO sugere que o aumento da estabilidade destes orbitais juntamente com o aumento das contribuições dos orbitais HNO estão correlacionacionado a menores valores de distâncias Ru-N(H)O e freqüências inferiores para os estiramentos &nu;NO. A estabilidade da ligação Ru-HNO também foi avaliada através de um estudo cinético teórico da dissociação de HNO a partir de <br /> trans-1[Ru(NH3)4(L)HNO]2+. De acordo com a ordem de estabilidade de ligação Ru-HNO em trans-1[Ru(NH3)4(L)HNO]2+ observa-se a seguinte ordem em função de L: H2O &gt; Cl- ~ Br- &gt; NH3 &gt; py &gt; P(OEt)3, que corresponde à ordem do efeito trans e influência trans medida experimentalmente para a série de L em complexos octaédricos. A mesma tendência foi também observada utilizando o modelo explícito solvente, considerando-se, assim, a presença de uma molécula de H2O juntamente com uma molécula de HNO no estado de transição. Para esta série, as energias calculadas para a ligação Ru-HNO estão no intervalo de 21,4 - 41,5 kcal.mol-1. Observou-se uma boa concordância entre os valores calculados de &Delta;G&dagger; HNO para substituição por H2O a partir do complexo trans-1[Ru(NH3)4(P(OEt)3HNO]2+ (28.5 kcal mol-1) e os dados experimentais disponíveis para reações de substituição em sistemas trans-[Ru(NH3)4(POEt)3(Lx)]2+ (19.4 e 24.0 kcal.mol-1 para Lx = isn e P(OET)3, respectivamente). Experimentos de voltametria cíclica foram realizados observando os processos de redução do ligante nitrosônio gerando nitroxil e podendo gerar amônia, o que foi também observado por cálculos envolvendo efeito de uma primeira esfera de solvatação. / The properties of free nitroxyl molecule and the nitroxyl ligand in Ru(II) tetraammines (trans-[Ru(NH3)4(nitroxyl)n(L)]2+n, n = nitroxyl charge and L = NH3, py, P(OEt)3, H2O, Cl- and Br-) were studied trough density functional theory (DFT). According to the calculated conformation energies the HNO complexes are more stable than the deprotonated analogues and the singlet configuration (trans-1[Ru(NH3)4(L)HNO]2+) is lower energy the than the corresponding triplet (trans-3[Ru(NH3)4(L)HNO]2+). Evaluation of the &sigma; and &pi; components in the L-Ru-HNO bond suggest that increased stability of these orbitals and enhanced contributions from the HNO orbitals correlate to shorter Ru-N(H)O distances and lower &nu;NO stretching frequencies. The stability of the Ru-HNO bond was also evaluated through a theoretical kinetic study on HNO dissociation from trans-1[Ru(NH3)4(L)HNO]2+. Accordingly, the order of the Ru-HNO bonding stability in trans-1[Ru(NH3)4(L)HNO]2+ as a function of L is: H2O &gt; Cl- ~ Br- &gt; NH3 &gt; py &gt; P(OEt)3, which parallels the order of the trans effect and trans influence series experimentally measured for L in octahedral complexes. The same trend was also observed using the explicit solvent model, thus considering the presence of both the HNO and H2O molecules in the transition state. For this series, the calculated bond energies for the Ru-HNO bond are in the range 21.4 to 41.5 kcal.mol-1. Good agreement was observed between the calculated &Delta;G&dagger; values for HNO substitution by H2O from the complex trans-1[Ru(NH3)4(P(OEt)3HNO]2+ (28.5 kcal mol-1) and the available experimental data for substitution reactions of trans-[Ru(NH3)4(POEt)3(Lx)]2+ (19.4 to 24.0 kcal.mol-1 for Lx = isn and P(OET)3, respectively). Cyclic voltammetry experiments were carried out observing the reduction processes of the nitrosonium ligand generating nitroxil and could generate ammonia, which was also observed by calculations involving the effect of a first sphere of solvation.

La thèse consiste en l'étude de la racémisation d'hydrogéno-phénylphosphinates d'alkyle, des molécules centrées sur un phosphore stéréogénique. Pour cela, nous avons synthétisé les composés d'intérêt puis étudié leur cinétique de racémisation en utilisant l'HPLC chirale et la RMN du phosphore. La première étude théorique (SMD//M06-2X/6-31++G**) sur l’énantiomérisation d’un phosphinate d’alkyle après une SN2 par un alcool a montré comme mécanisme le plus favorable une syn-addition de l’alcool sur la double liaison P=O du phosphinate à l’opposé du groupement alkoxy. Les études cinétiques d’inversion du phosphinate d’éthyle dans l’éthanol à reflux ont montré une barrière de 135 kJ.mol-1 en moyenne, en excellent accord avec ce modèle (136 kJ.mol-1). L’ajout de base lors de l’étude cinétique ont montré une accélération de l’inversion avec une barrière maximum mesurée à 121,5 kJ.mol-1 montrant un effet de catalyse basique. Les modèles cinétiques et théoriques réalisés à ce jour ont suggéré que la base activerait l’alcool pour faciliter son addition. Les premiers résultats sur l’influence du groupement alkyle ont montré une dépendance globale de l’inversion à la taille du groupement, mais certains modèles DFT, notamment avec l’adamantyle, n’étaient pas en accord avec cette hypothèse. / This thesis is about the racemization of alkyl hydrogeno-phenylphosphinate, a molecule centered on a stereogenic phosphorus atom. We have synthetized compounds of interest, and studied their kinetic of racemization with chiral HPLC and phosphorus NMR. The first theoretical study (SMD//M06-2X/6-31++G**) about the enantiomerization of alkyl phosphinate after an SN2 with an alcohol have shown that the most favored mechanism was a syn-addition of the alcohol onto the double bond P=O on the opposite side of the alkoxy group. Kinetic studies with ethyl phosphinate in ethanol under reflux have shown an inversion barrier around 135 kJ.mol-1, in excellent agreement with this model (136 kJ.mol-1). The addition of a basic compound during kinetic measurements has shown a decreasing of the barrier to 121.5 kJ.mol-1, showing a catalytic effect. Kinetic and theoretical models have suggested that the mechanism would go through an activation of the alcohol by the basic compound which would facilitate its addition. The first tests about the nature of the alkyl group of phosphinate and alcohol have shown a general dependency of the barrier with the hindrance, but some DFT models, especially with adamantyl, have been in disagreement with this hypothesis.

On appelle biominéraux l’ensemble des minéraux fabriqués par le vivant. Ce sont des matériaux essentiels, présents dans la quasi-totalitédes espèces vivantes. Néanmoins les caractéristiques structurales, chimiques ainsi que les mécanismes de formation, et l’évolution de cesmatériaux sont encore fortement débattus. Cela s’explique notamment par les difficultés à étudier expérimentalement des espèces chimiquesévoluant en milieux biologiques.Bien que tout aussi complexe, une approche théorique, à l’échelle moléculaire, peut aider à la caractérisation de ces matériaux biologiqueset notamment la caractérisation de leurs interfaces formées avec les milieux biologiques environnants. Cela étant essentiel pour une meilleurecompréhension de la formation et de l’évolution de ces minéraux.Les oxalates de calcium constituent une famille de biominéraux très importante dans le monde du vivant. Ils constituent notamment les principales espèces cristallinesrencontrées dans les calculs rénaux où ils peuvent exister sous trois phases possédant différents degrés d'hydratation. Au cours de cette thèse, nous avons effectuéles simulations des propriétés spectroscopique IR et RMN des ces trois phases, ce qui permet d'obtenir une signature propre à chacune d'entre elle, aidant ainsi àl'identification de ces phases à partir des spectres obtenus expérimentalement.Les phosphates de calcium font aussi partie des biominéraux. Ils composent la majeure partie du minéral osseux des mammifères. Ce minéral se trouvesous la forme de nanoparticules décrites comme possédant un cœur cristallin d’hydroxyapatite substituées entourée d'une couche hydratée et désordonnée en surface.Durant ce travail de thèse, nous nous sommes intéressés à ces deux composantes. Concernant le cœur cristallin des particules, nous avons étudié en particulierle cas des substitutions par des carbonates car il s'agit de la substitution prédominante dans les apatites biologiques. En couplant ce travail à des expériencesde RMN solide nous pouvons proposé une localisation précise de ces substituants au sein de la maille d’hydroxyapatite.La couche désordonnée de surface est encore très mal comprise à l'heure actuelle et de nombreux modèles structuraux sont proposés dans la littérature pour la décrire. Nous avonsconsidéré un certain nombre d'entre eux pour lesquels nous avons modélisé les propriétés RMN, qui confrontées à celle issues de l'expérience nous ontpermis d'identifier les points forts et faibles des différentes hypothèses. / Biominerals are all the minerals produced by living organisms. They are essential materials, present in almost all living species. Nevertheless,the structural, chemical properties and, formation mechanisms and the evolution of these materials are still heavily debated. This is due in particular to thedifficulties of experimentally studying chemical species evolving in biologicalenvironments. Although, equally complex, a theoretical approach at the molecular level can help in the characterization of these biological materialsand in particular the characterization of their interfaces formed with the surrounding biological media. This is essential for a better understandingof the formation and evolution of these minerals.Calcium oxalates are essential biominerals that are very common in the living world. They constitute the main crystalline speciesencountered in kidney stones where they can exist in three phases possessing different degrees of hydration. In this, thesis we carried outsimulations to predict the IR and NMR spectroscopic properties of these three phases. Thsi enabled us to obtain specificsignature of each polyhydrate, and thus makes it possible to obtain a signature specific to each of them, thus helpingthe identification of these phases from the experimentally spectra obtained.Calcium phosphates are part of the bio/biological minerals. They make up the major part of the bone mineral of mammals. This mineral is in the form of nanoparticles havinga crystalline core of hydroxyapatite and a hydrated and disordered surface layer.During this thesis we were interested in these two components. Concerning the crystalline core of the particles, we studied in particularthe case of carbonate substitutions because of its predominant substitution in biological apatites. By combining this work with solid state NMR experimentswe can propose a precise localization of these substituents within the hydroxyapatite crystalline cell.The disordered surface layer is still very poorly understood and many structural models are proposed in the literature to describe it. We haveconsidered a number of them for which we have modeled the NMR properties which were then confronted with experimental results. The comparaisonmade it possible to identify the strengths and weaknesses of the various hypotheses.