La spintronique est un nouveau domaine de recherche qui exploite l'influence de la caractéristique quantique de l’électron (le spin) sur la conduction électrique. Pour réaliser des composants de spintronique innovants, l’obtention des semi-conducteurs ferromagnétiques à température ambiante devenait un challenge international. Dans ce contexte, après les premières prédictions théoriques de la haute température de Curie de Zn1-xCoxO et les rapports contradictoires sur l'état magnétique de ce système, nous nous sommes attaché à étudier le semi-conducteur magnétique dilué Zn1-xCoxO. Une étude ab initio des propriétés structurales, électroniques et magnétiques du Zn1-xCoxO a été effectuée en utilisant la méthode de pseudopotentiels dans le cadre de la théorie de la fonctionnelle de la densité (DFT) avec les deux approximations GGA et GGA+U. En parallèle, des films minces de Zn1-xCoxO ont été synthétisés par co-pulvérisation cathodique magnétron en condition réactive avec différentes conditions d’élaboration. Les propriétés structurales, morphologiques, électriques et magnétiques ont été analysées par différentes techniques de caractérisation et confrontées à celles obtenues par l’étude ab inito. / Spintronic is a new field of research exploiting the effect of the quantum property of the electron (spin) on the electrical conduction. In order to realize innovative spintronic components, ferromagnetic semiconductors obtained at room temperature became an international challenge. In this context and following initial reports of high Curie temperature and contradictory reports on the magnetic states of this system, we investigated the diluted magnetic semiconductor Zn1-xCoxO. An ab initio study of structural, electronic and magnetic properties of Zn1-xCoxO was performed using the pseudopotentials method within the framework of density functional theory (DFT) with both GGA and GGA+U approximations. In parallel, thin films of Zn1-xCoxO were synthesised by reactive magnetron co-sputtering with different deposition conditions. The structural, morphological, electrical and magnetic properties were analyzed by various characterization techniques and compared with those obtained by ab inito study.

Die Photophysik und Photochemie von Flavinen sind aufgrund ihrer biologischen Funktion, inbesondere von Flavoproteinen, von großen Interesse. Flavoproteine spielen eine große Rolle in einer Vielzahl von biologischen Prozessen, z.B. Biolumineszenz, Entfernung von Radikalen, die bei oxidativem Stress entstehen, Photosynthese und DNA-Reparatur. Die spektroskopischen Eigenschaften des Flavin-Cofaktors machen diesen zu einem natürlichen Reporter für Veränderungen innerhalb des aktiven Zentrums. Deshalb sind die Flavoproteine eine der am meisten untersuchten Enzymfamilien. Eine biologische Aktivität des Flavins führt über einen elektronisch angeregten Zustand, wo dann, abhängig von der Aminosäureumgebung, ein bestimmter Mechanismus zu einem biologischen Prozess führt (Photozyklus). Ein wichtiges Analysetool zum Verständnis des anfänglichen Photoanregungsschritts der Flavine sind die elektronische und die Schwingungsspektroskopie. In dieser Arbeit wurden die Prozesse von Riboflavin (RF) während und nach optischer Anregung mit theoretischen Mitteln beleuchtet. Dazu wurden quantenchemische Berechnungen für Schwingungsspektren (vibratorische) von Riboflavin, auch Laktoflavin oder Vitamin B2 genannt, dem Grundmolekül der Chromophore biologischer Blaulichtrezeptoren, in dessen elektronischem Grundzustand und dessen niedrigsten angeregten Zustand durchgeführt. Weiterhin wurden vibronische (vibratorische+elektronische) Absorptionsspektren und ein vibronisches Emissionsspektrum berechnet. Die so berechneten Schwingungs- und elektronischen Spektren sind in guter qualitativer wie quantitativer Übereinstimmung mit gemessenen Werten, und helfen so, die experimentellen Signale der Photoanregung von Flavinen zuzuweisen. Unmittelbar nach der Photoanregung wurde ein Verlust des Doppelbindungscharakters im polaren Bereich des Ringssystems beobachtet, was zu der vibronischen Feinstruktur im elektronischen Absorptions- und Emissionsspektrum führte. Hier zeigte sich zudem, dass neben den vibronischen Effekten auch die Lösungsmitteleffekte wichtig für das quantitative Verständnis der Photophysik der Flavine in Lösung sind. Um Details des optischen Anregungsprozesses als initialen, elementaren Schritt zur Signalweiterleitung zu entschlüsseln, wurden ultraschnelle (femtosekundenaufgelöste) Experimente durchgeführt, die die Photoaktivierung des Flavins untersuchen. Diese Arbeit soll zu einem weiteren Verständnis und der Interpretation dieser Experimente durch das Studium der Post-Anregungsschwingungsdynamik von Riboflavin und mikrosolvatisiertem Riboflavin beitragen. Dazu wurde eine 200 fs lange Molekulardynamik in angeregten Zuständen betrachtet. Durch die Analyse charakteristischer Atombewegungen und durch die Berechnungen zeitaufgelöster Emissionsspektren fand man heraus, dass nach der optischen Anregung Schwingungen im Ringssystem des Riboflavins einsetzen. Mit Hilfe dieser Berechnungen kann die Umverteilung der Energie im angeregten Zustand beobachtet werden. Neben den theoretischen Untersuchungen zu Riboflavin in der Gasphase und auch in Lösung wurde ein Modell für eine BLUF (Blue-Light Photoreceptor Using Flavin) Domäne, ein Flavin benutzender Photorezeptor, erstellt. Hierbei zeigt sich, dass man die in dieser Arbeit angewendeten Analysemethoden auch auf biologisch relevante Systeme anwenden kann. / The photophysics and photochemistry of flavins are due to their biological function, in particular of flavoproteins, of great interest. Flavoproteins play a major role in a variety of biological processes, eg Bioluminescence, removal of free radicals, resulting in oxidative stress, photosynthesis and DNA repair. The spectroscopic properties of the flavin cofactor make this a natural reporter for changes within the active site. Therefore flavoproteins are one of the most studied enzyme families. A biological activity of the flavin via an electronically excited state, which then performs a function of the amino acid environment, a specific mechanism to a biological process (photo cycle). An important analytical tool for the understanding of the initial step of the photoexcitation flavins are the electronic and vibrational spectroscopy. In this study, the processes of riboflavin (RF) during and after optical excitation illuminated by theoretical means. These quantum chemical calculations for the vibrational spectra (vibrational) of riboflavin, or vitamin B2 lactoflavin also been mentioned, the basic molecule of biological chromophores blue light receptors in the electronic ground state and the lowest excited state performed. Furthermore, vibronic (vibrational + electronic) absorption spectra and vibronic emission spectra were calculated. The calculated vibrational and electronic spectra are in good qualitative and quantitative agreement with measured values, and help to assign the experimental signals of the photo-excitation of flavins. Immediately after photoexcitation a loss of the double bond character was observed in the polar region of the ring system, leading to the vibronic fine structure in the electronic absorption and emission spectrum. It showed also that in addition to the vibronic effects, the solvent effects are important for a quantitative understanding of the photophysics of flavins in solution. To decipher details of the optical excitation process as initial, elementary step in signal transduction, ultrafast were performed (femtosecond-resolved) experiments that investigate the photoactivation of the flavin. This work will contribute to a further understanding and interpretation of these experiments by studying the post-excitation vibrational dynamics of riboflavin and riboflavin mikrosolvatisiertem. To a 200 fs long molecular dynamics in excited states was considered. By the analysis of characteristic atomic motions and by the calculations of time-resolved emission spectra, it was found that, after the optical excitation oscillations in the ring system of the riboflavin used. Using these calculations, the energy redistribution in the excited state can be observed. In addition to the theoretical studies of riboflavin in the gas phase and in solution, a model for a BLUF (Blue Light Photoreceptor Using flavin) domain, a flavin-use photoreceptor created. It is shown that one can apply the analytical methods employed in this work and to biologically relevant systems.

The nature and role of defects is of primary importance to understand the physical properties of C and BN single walled nanotubes. Transmission electron microscopy (TEM) is a well known powerful tool to study the structure of defects in materials. However, in the case of SWNTs, the electron irradiation of the TEM may knock out atoms. This effect may alter the native structure of the tube, and has also been proposed as a potential tool for nanoengineering of nanotubular structures. Here we develop a theoretical description of the irradiation mechanism. First, the anisotropy of the emission energy threshold is obtained via density functional based calculations. Then, we numerically derive the total Mott cross section for different emission sites of carbon and boron nitride nanotubes with different chiralities. Using a dedicated STEM microscope with experimental conditions optimised on the basis of derived cross-sections, we are able to control the generation of defects in nanotubular systems. Either point or line defects can be obtained with a spatial resolution of a few nanometers. The structure, energetics and electronics of point and line defects in BN systems have been investigated. Stability of mono- and di- vacancy defects in hexagonal boron nitride layers is investigated, and their activation energies and reaction paths for diffusion have been derived using the nudged elastic band method (NEB) combined with density functional based techniques. We demonstrate that the appearance of extended linear defects under electron irradiation is more favorable than a random distribution of point defects and this is due to the existence of preferential sites for atom emission in the presence of pre-existing defects, rather than thermal vacancy nucleation and migration.

La demande d'une énergie durable et verte est très importante pour les gouvernements et les populations. De par l'augmentation rapide de la population humaine et l'industrialisation à l'échelle mondiale, c’est devenu un enjeu majeur. Une alternative à l’utilisation des combustibles fossiles qui peut être envisagée est l’utilisation, lorsque c’est possible, de dispositifs thermoélectriques. Ces derniers peuvent convertir la chaleur perdue, provenant de diverses sources, en énergie électrique. Cependant, les dispositifs thermoélectriques actuels sont limités en raison de leur faible efficacité, de la nature toxique des matériaux utilisés et de leurs coûts élevés. Le défi actuel dans ce domaine de recherche est de concevoir des matériaux hautement efficaces, respectueux de l'environnement et disponibles à des prix moins élevés. Parmi les matériaux thermoélectriques prometteurs pour la génération d'énergie, le composé Fe2VAl (matériau de la famille des composés Heusler), semble prometteur car il se comporte comme un semi-conducteur sur une large gamme de température et ce jusqu'à 1173 K. Néanmoins, la capacité thermoélectrique de ce composé est compromise par sa conductivité thermique élevée. L'objectif de cette thèse était de trouver de nouvelles stratégies afin d’améliorer l'efficacité thermoélectrique de Fe2VAll'aide de calculs ab initio et d'études expérimentales. Les calculs basés sur les premiers principes ont été effectués en utilisant le code informatique VASP (Vienna Ab-initio Simulation Package) basé sur la théorie de la fonctionnelle densité (DFT) avec comme but d’étudier la structure électronique du composé Fe2VAl. L'énergie de formation des défauts intrinsèques tels que les lacunes, les anti-sites et les défauts interstitiels, a été déterminée. Nous avons montré que la formation des défauts de type anti-sites est la plus probable. À l'aide du code BoltzTraP, basé sur la théorie du transport de Boltzmann dans l’approximation du temps de relaxation constant, les propriétés de transport électronique de Fe2VAl pur et contenant les défauts les plus favorables ont été calculées. La présence des différents défauts au sein du réseau n’entraine pas d'amélioration notable du coefficient de Seebeck. La conductivité thermique de réseau de Fe2VAl, à la fois sous forme pure et en présence des défauts d’anti-site les plus stables (AlV) a été analysée en utilisant les codes ShengBTE et almaBTE récemment développés. Uneamélioration significative du facteur de mérite (appelé ZT) est alors trouvée en présence de défauts de type anti-sites. Des composés Fe2VAl nanostructurés ont été synthétisés en parallèle par mécanosynthèse, autrement appelé broyage hauteénergie. Les éléments constitutifs sont broyés en ajoutant différentes proportions de chlorure de sodium afin d'obtenir des échantillons poreux, NaCl servant d’agent structurant. Les poudres sont ensuite lavées soigneusement pour éliminer les traces de NaCl et consolidées à l'aide de la technique de frittage flash SPS. L’utilisation de cette nouvelle voie pour structurer et introduire de la porosité dans les échantillons afin de diminuer la conductivité thermique est assez concluante. Nous obtenons une porosité d'environ 15 à 20% en présence de NaCl (contre environ 5% sans sel). L'efficacité thermoélectrique estremarquablement augmentée pour ces échantillons poreux. Néanmoins, les échantillons broyés contenant 15% de porosité présentent des valeurs de ZT plus élevées que les échantillons à plus forte porosité. Ainsi, il est crucial de contrôler et d’optimiser la porosité pour obtenir une plus grande efficacité thermoélectrique. Notre étude montre ainsi clairement que la performance thermoélectrique peut être améliorée en modifiant la stœchiométrie et la morphologie des échantillons.Mots clés : Fe2VAl, matériaux, composés Heusler, thermoélectricité, calculs ab initio, enthalpie de formation, défauts, mécanosynthèse, porosité. / The requirement of a sustainable and green energy is increasing with the rapid rise in human population and industrialization. The traditional way of utilizing fossil fuels can be replaced by thermoelectric devices which can convert thewasted heat from various sources into electrical energy. However, the present day thermoelectric devices are limited due to their low efficiency, toxic nature and high costs. The current challenge in this field is to design highly efficient thermoelectric materials which are environment friendly and available at a reasonable price. Among promising thermoelectric materials forpower generation, the Heusler-type Fe2VAl attained a great attention due to its semiconducting nature over a wide temperature range up to 1173 K. Nonetheless, the thermoelectric use of this compound is jeopardized by its high thermalconductivity. The aim of this thesis was to find new strategies in enhancing the thermoelectric efficiency of Fe2VAl with the aid of ab initio calculations and experimental studies. First principles calculations have been performed using the computer code VASP (Vienna ab-initio Simulation Package) based on the Density Functional Theory (DFT) to study the electronic structure of the full Heusler compound Fe2VAl. The formation energy of the intrinsic point defects such as vacancies, antisites and interstitials is analyzed and antisite defects are found to be the most probable defects. With the aid of the BoltzTraP code based on the Boltzmann transport theory within the constant relaxation time approach, the electronic transport properties of Fe2VAl taking into account the effect of the most favorable defects have been calculated. The presenceof defects does not lead to a significant improvement of the Seebeck coefficient. The lattice thermal conductivities of Fe2VAl, both in pristine form and in presence of its most stable antisite defect (Al V) have been analyzed by ShengBTE and the recently developed code almaBTE. A significant enhancement of the figure of merit (also known as ZT) is found with the presence of antisite defects. Nanostructured Fe2VAl compounds have been synthesized in parallel by the ball milling technique. The constituent elements have been milled together with different contents of NaCl in order to obtain porous samples. The powders have been later washed thoroughly to remove the traces of NaCl. All the powders have been consolidated using Spark Plasma Sintering (SPS). This novel idea is quite successful in achieving a porosity of around 15–20% with NaCl whereas a porosity of ~5 % is found in the case of the samples without NaCl. The thermoelectric efficiency is enhanced remarkably in the porous samples. Nevertheless, the samples milled with 15 % porosity exhibit higher ZT valuesthan the samples with 20 % porosity. Thus, it is crucial to confine and control the porosity to obtain high thermoelectric efficiencies. Our study thus clearly shows that the thermoelectric performance can be enhanced by off-stoichiometry and the modification of the morphology of the samples.Key words: Fe2VAl, materials, Heusler compounds, thermoelectricity, ab initio calculations, formation enthalpy, defects, ball milling,porosity.

The theoretical part of the Master´s thesis describes ab initio methods in quantum chemistry and semiempirical methods, which represents a way in overcoming of main disadvantages in ab initio methods (costs, speed). The experimental part was focused on comparison highly accurate CCSD(T) method with used semiempirical methods (AM1, PM3, PM6, and PM7). The data were mostly compared on small model systems with ions, which are an essential part of many biological systems. Furthermore, the applicability of semiempirical methods was examined for the description of intra- and intermolecular hydrogen bonds and van der Waals interactions.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na área da catálise, interações de moléculas pequenas como H2,N2,O2, CO, NO etc, com aglomerados metálicos, têm nas suas adsorções químicas etapa fundamental nas atividades catalíticas. O paládio está entre os metais mais empregados em catalisadores usados em muitos processos catalíticos heterogêneos. Neste presente trabalho foi realizada uma série de cálculos baseado na Teoria do Funcional de Densidade (TFD ou DFT) empregando o método BP86/LANL2DZ/6-311+G(d,p) para estudar a adsorção da molécula NO que foi utilizada como protótipo molecular para interagir sobre aglomerados de paládio puros e dopados com metais de transição da primeira série de transição (Pd3M e Pd9M). Neste contexto, o escopo deste trabalho foi: (i) obter informações a respeito das possíveis alterações estruturais e eletrônicas ocorridas em aglomerados de paládio quando dopados com metais da primeira série de transição (MT), (ii) estudar as alterações no comportamento do átomo de paládio, nos seus respectivos aglomerados puros, frente aos aglomerados dopados com metais de transição da primeira série,(iii) buscar possíveis padrões de influência dos MT nas propriedades de aglomerados de paládio (ex: energias dos orbitais de fronteira, transferências eletrônicas de doação e retrodoação, densidades de spin, hibridizações dos orbitais responsáveis pelas ligações com moléculas adsorventes etc). Após a realização dos cálculos baseados na DFT, os resultados mostram que, para o estudo sobre os aglomerados contendo quatro átomos, foi obtida correlação direta entre a carga adquirida pelo metal M dentro do aglomerado metálico e os orbitais moleculares de fronteira LUMO calculados para Pd3M. Esta correlação direta não se mantém quando o tamanho do aglomerado de paládio é aumento de quatro para dez átomos. A energia de adsorção apresentada pela molécula de NO apresenta boa correlação com a energia do LUMO, independentemente do número de átomos e da geometria do aglomerado e da natureza do metal dopante. A molécula de NO adsorve mais favoravelmente no modo Bridge, independentemente de qual metal está dopando o aglomerado de Pd9M. Entretanto, para o aglomerado de Pd3M, o modo de adsorção dependerá da natureza do metal dopante. A mudança na geometria e no número de átomos de paládio existentes no aglomerado provoca mudanças no modo e na energia de adsorção da molécula de NO adsorvente. Uma investigação mais aprofundada deve encontrar outras possíveis correlações entre propriedades dos metais da primeira série e aglomerados de paládio dopados com os mesmos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Na área da catálise, interações de moléculas pequenas como H2,N2,O2, CO, NO etc, com aglomerados metálicos, têm nas suas adsorções químicas etapa fundamental nas atividades catalíticas. O paládio está entre os metais mais empregados em catalisadores usados em muitos processos catalíticos heterogêneos. Neste presente trabalho foi realizada uma série de cálculos baseado na Teoria do Funcional de Densidade (TFD ou DFT) empregando o método BP86/LANL2DZ/6-311+G(d,p) para estudar a adsorção da molécula NO que foi utilizada como protótipo molecular para interagir sobre aglomerados de paládio puros e dopados com metais de transição da primeira série de transição (Pd3M e Pd9M). Neste contexto, o escopo deste trabalho foi: (i) obter informações a respeito das possíveis alterações estruturais e eletrônicas ocorridas em aglomerados de paládio quando dopados com metais da primeira série de transição (MT), (ii) estudar as alterações no comportamento do átomo de paládio, nos seus respectivos aglomerados puros, frente aos aglomerados dopados com metais de transição da primeira série,(iii) buscar possíveis padrões de influência dos MT nas propriedades de aglomerados de paládio (ex: energias dos orbitais de fronteira, transferências eletrônicas de doação e retrodoação, densidades de spin, hibridizações dos orbitais responsáveis pelas ligações com moléculas adsorventes etc). Após a realização dos cálculos baseados na DFT, os resultados mostram que, para o estudo sobre os aglomerados contendo quatro átomos, foi obtida correlação direta entre a carga adquirida pelo metal M dentro do aglomerado metálico e os orbitais moleculares de fronteira LUMO calculados para Pd3M. Esta correlação direta não se mantém quando o tamanho do aglomerado de paládio é aumento de quatro para dez átomos. A energia de adsorção apresentada pela molécula de NO apresenta boa correlação com a energia do LUMO, independentemente do número de átomos e da geometria do aglomerado e da natureza do metal dopante. A molécula de NO adsorve mais favoravelmente no modo Bridge, independentemente de qual metal está dopando o aglomerado de Pd9M. Entretanto, para o aglomerado de Pd3M, o modo de adsorção dependerá da natureza do metal dopante. A mudança na geometria e no número de átomos de paládio existentes no aglomerado provoca mudanças no modo e na energia de adsorção da molécula de NO adsorvente. Uma investigação mais aprofundada deve encontrar outras possíveis correlações entre propriedades dos metais da primeira série e aglomerados de paládio dopados com os mesmos

Made available in DSpace on 2015-05-14T13:21:50Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2213786 bytes, checksum: 0cc6e2b3683929f526b695daf59e4b4a (MD5) Previous issue date: 2006-10-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present work the molecular properties of heterocyclic hydrogen complexes: oxirane (C2H4O), methyloxirane (H3C-C2H3O) and hydroxi-oxirane (HO-C2H3O), as well as the respective ring open reaction by fluoridric acid has been investigated by using quantum chemistry methods. In this way, molecular properties of hydrogen complexes, such as oxirane---HF (C2H4O---HF), methyloxirane---HF (H3C-C2H3O---HF) e hydroxi-oxirana---HF (HO-C2H3O---HF), has been investigated as well. The quantum chemistry methods used were: ab initio (HF) and DFT (B3LYP and PBE1PBE) with the base set 6-311++G(d,p). The optimized structures for the hydrogen complexes and the reaction products were used in order to obtain the structure of the transition state and reaction path. The results yield that the mechanism for ring open involving the reagent HO-C2H3O-HF was kinetically and thermodynamically more favorable. The nucleofilic attack to the more substituted carbon is the preferential one. The reactivity order of the ring opened mechanism was: HO-C2H3O-HF > H3C-C2H3O-HF > C2H4O-HF. / Este trabalho trata da investigação teórica de propriedades moleculares dos seguintes compostos heterocíclicos: oxirana (C2H4O), metil-oxirana (H3C-C2H3O) e hidroxi-oxirana (HO-C2H3O), e dos respectivos mecanismos de reações referente à abertura destes anéis, frente à adição do ácido fluorídrico (HF). Neste contexto, foram determinadas as propriedades moleculares dos complexos de hidrogênio, oxirana---HF (C2H4O---HF), metiloxirana--- HF (H3C-C2H3O---HF) e hidroxi-oxirana---HF (HO-C2H3O---HF), formados em uma das etapas do mecanismo. Os métodos de estrutura eletrônica empregados foram ab initio (HF) e DFT (B3LYP e PBE1PBE) com o conjunto de base 6-311++G(d,p). A partir das estruturas otimizadas para os complexos de hidrogênio e produtos das reações foram determinadas às estruturas dos estados de transição e os caminhos de reação para as reações propostas. Os resultados mostram que a reação de abertura do anel da oxirana substituída com hidroxila, HO-C2H3O-HF, é favorecida cinética e termodinamicamente. O ataque nucleofílico ao carbono mais substituído é o preferencial. A reatividade referente à abertura do anel dos complexos heterocíclicos obedece a seguinte ordem: HO-C2H3O-HF > H3C-C2H3O-HF > C2H4O-HF.

La mesure de composition isotopique est utilisée dans l'étude du cycle biogéochimique du zinc ; cycle largement impacté par les activités anthropiques. Toutefois, l'interprétation de ces mesures réalisées sur des échantillons naturels ou synthétiques requiert la connaissance des propriétés isotopiques du zinc en condition d'équilibre (qui servent de référence) et la compréhension des mécanismes à l'origine des variations de composition isotopique. Dans ce travail, nous avons déterminé en réalisant des calculs quantiques, les constantes d'équilibre de fractionnement isotopique du zinc dans des phases solides et liquides. Nous avons mis en évidence les paramètres cristallochimiques qui contrôlent les propriétés isotopiques : la constante de force interatomique du zinc, les longueurs de liaisons Zn-premiers voisins et la charge électronique de ces premiers voisins. Nous avons réalisé un développement méthodologique permettant de calculer les propriétés isotopiques dans les phases liquides à partir de trajectoires de dynamique moléculaire à un coût réduit en temps de calcul. Nous avons montré à travers la modélisation du zinc aqueux, qu'une description raisonnable des forces de van der Waals par une fonctionnelle d'échange et de corrélation non locale est nécessaire à la stabilisation à conditions ambiantes du complexe hexaaquo zinc par rapport à d'autres complexes, réconciliant ainsi calculs et expériences. Ce travail met à disposition des études expérimentales une base de données cohérente de constantes d'équilibres isotopiques. / Isotopic compositions are used to study the biogeochemical cycle of Zn, which is greatly impacted by anthropic activities. However, the interpretation of the measurements performed on natural or synthetic samples requires the knowledge of Zn isotope properties in equilibrium conditions (as reference) and the understanding of the mechanisms that are at the origin of the isotopic composition variations. In this work, we determined by performing quantum calculations, equilibrium Zn isotope fractionation constants in various phases including solids and liquids. We highlighted the crystal-chemical parameters controlling the isotopic properties : Zn interatomic force constant, Zn-first neighbours bond lengths and the electronic charge on atoms involved in the bonding. We carried out a methodological development in order to calculate isotopic properties in liquid phases from molecular dynamics trajectories at a reduced computational cost. We showed through the modelling of aqueous Zn that a reasonable description of van der Waals forces using a non-local exchange correlation functional is required to stabilise the experimentally observed hexaaquo zinc complex over other complexes at room temperature. This work provides a consistent database of equilibrium Zn isotope fractionation constants for experimental works.

ealizaram-se cálculos ab initio e semi-empíricos em 5-hidrotriptofano (5-OH-trp), 7-aza-triptofano (7-aza-trp) e triptofano (trp), determinando as superfícies de energia potencial (SEP) do estado fundamental (EF) e do primeiro estado excitado (1EE), em função dos ângulos X IND. 1 e X IND. 2, medidos nos diedros N-C IND.alfa-C IND.beta-C IND.gama e C IND.alfa-C IND.beta-C IND.gama- C IND.delta2, respectivamente. Esses compostos foram estudados nos estados de protonação zwitteriônico, neutro e aniônico. A SEP do EF na forma zwitteriônica fo obtida pelo método semi-empírico AM1 e utilizada como referência para os cálculos ab initio. Os cálculos de 1EE foram feitos utilizando o método de Interação de Configurações com excitações simples (ICS) e orbitais internos congelados. As energias de transição entre o EF e o 1EE após as otimizações foram obtidas pelo método semi-empírico INDO/S-CIS, permitindo a obtenção dos espectros teóricos de absorção ótica, pelas energias de transição das geometrias otimizadas no EF, e de fluorescência de estado estacionário, pelas energias de transição das geometrias otimizadas no 1EE. Medidas experimentais dos espectros de absorção ótica e de fluorescência de estado estacionário e resolvida no tempo foram realizadas com o 5-OH-trp e o 7-aza-trp em solução tampão fosfato, pH 7,4. Os decaimentos fluorescentes ajustados a mais de uma exponencial foram estudados em termos das populações relativas de Boltzmann nos EF e 1EE. As taxas do decaimento não-radiativo de transferência de elétrons no 1EE foram obtidas pela implementação computacional da Teoria de Marcus e do Método da Expansão de Perturbação Renormalizada (EPR). Além disso, otimizações de estruturas de estados de transição (ET) na SEP dos 1EE foram realizadas pelo Método Sunchronous Transiti-Guided Quasi-Newton e pelo algoritmo de Berny modificado. Para aproximar as condições experimentais, foram ) realizadas simulações por dinâmica molecular (DM) usando o método híbrido QM/MM no EF do 5-OH-trp na forma zwitteriônica, na presença do solvente aquoso representado explicitamente. Os resultados obtidos dos cálculos ab initio foram usados como referência para o início dessas simulações. As conformações visitadas no EF, os espectros teóricos de absorção ótica e as camadas de solvatação do solvente aquoso em torno do reagente são discutidas. / Semi-empirical and ab-initio calculations were performed on 5-hydroxytryptophan (5-OH-trp), 7-aza-tryptophan (7-aza-trp) and tryptophan (trp). The potential energy surface (PES) of the ground state (GS) and the lowest exited state (1ES) was determined as a function X IND. 1 e X IND. 2 angles corresponding to the dihedrals N-C IND.alfa-C IND.beta-C IND.gama e C IND.alfa-C IND.beta-C IND.gama- C IND.delta2, respectively. The compounds were studied in the zwitterionic, neutral and anionic states. The PES of the GS was obtained using the AM1 semi-empirical method and was used as a reference for the ab-initio calculations. The configuration interaction method with single excitations (CIS) was used for the calculations of the 1ES with frozen internal orbitals. After geometry optimization of GS, the transition energies to 1ES were obtained by INDO/S-CIS, giving the theoretical optical absorption spectrum. Similarly, following the geometry optimization of 1ES, the transition energies to GS were determined, giving the fluorescence emission spectrum. Experimental results were obtained for optical absorption and fluorescence spectra of 5-OH-trp and 7-aza-trp in phosphate buffer solution, pH 7.4. The fluorescence decay of the compounds was also examined. Decay profiles fitted to multiexponential function were analyzed in terms of Boltzmann relative populations in the GS and 1ES. The non-radioactive electron transfer rates in the excited state were obtained by computational implementation of the Marcus Theory with renormalized perturbation expansion method (RPE). In this study, optimizations of the transition states in the PES of the ground and lower excited states were performed by the Synchronous Transit-Guided Quasi-Newton method and the Berny algorithm modified. For further comparison with experimental conditions, molecular dynamic simulations for the zwitterionic 5-OH-trp were performed using the hybrid QM/MM method with explicit representation of the aqueous solvent. To start the simulations the results from ab-initio calculations were used. The conformations for the GS, the theoretical absorption spectrum and the solvation layers were compared to the experimental results