Ce mémoire présente une méthodologie théorique pour comprendre l'origine de différence de comportement dynamique de complexes alkylidènes, catalyseurs de type Schrock de la métathèse des oléfines, greffés un support de silice amorphe. Dans un travail antérieur, les différences entre les valeurs de l'anisotropie de déplacement chimique (CSA) obtenus par des mesures de RMN du solide et celles estimées par le calcul pour des systèmes figés avaient conduit à suggérer des régimes dynamiques différents pour ces complexes, certains étant proposés comme immobiles, d'autres comme mobiles. Dans le premier groupe se trouve les complexes du molybdène et dans le second les complexes du tungstène, rhénium et tantale. Dans le cadre de cette thèse, nous nous sommes donc attachés à mettre en place une méthodologie pour déterminer ces CSA et donc la nature de la dynamique de chaque système qui conduit au CSA moyenné. Nous nous sommes d'abord intéressés à des systèmes moléculaires pour révéler des interactions non covalentes entre les complexes et le support silice à partir d'une approche de type petit cluster en utilisant divers niveaux de calculs DFT et modèles moléculaires. Cette modélisation moléculaire de la silice étant insuffisante, nous avons entrepris une modélisation de la surface de silice amorphe par dynamique moléculaire classique dont les caractéristiques ont été comparées aux données expérimentales existantes. Le comportement dynamique de ces systèmes greffés sur silice amorphe a été simulé par dynamique moléculaire ab initio QM/MM, couplant une description quantique du complexe organométallique à une description classique du support. Ces études dynamiques ont conduit à des valeurs de CSA moyennées dans le temps de la dynamique. La comparaison de ces valeurs calculées et des valeurs expérimentales a permis d'apporter des éléments de réponse sur l'origine des différences de comportement dynamique de ces complexes alkylidènes. De façon remarquable des mouvements d'ensemble des espèces greffées par rapport à la surface de silice et des modifications de la coordination du métal par l'apparition d'interaction agostique contribuent à moyenner le CSA. / This work presents a theoretical study aimed at analyzing the origin of the differences in the dynamics of alkylidenes complexes, known as Schrock olefin metathesis catalysts, supported on amorphous silica. The difference between the experimental chemical shift anisotropies (CSA) obtained from solid state NMR measurements and the values computed for the most stable configurations have been used in previous work to suggest different dynamical behaviors for the supported complexes. Some of the complexes were suggested to have limited mobilities while others were suggested to be mobiles. In the first group, one finds Mo complexes, and in the second, W, Re and Ta complexes. In this thesis, a methodology was established to compute the CSA and to obtain information on the dynamics that average the CSA over time. In the first part of this work, molecular species were considered and the non covalent interactions between the surface and the grafted complexes were studied with various DFT levels of calculations and various molecular models. This molecular modeling being inappropriate, a better representation of the surface of amorphous silica was carried out with classical molecular dynamic methods. The nature of the surface was analyzed and compared with available experimental information. In a following step, the dynamic behavior of these complexes was determined using anab initio molecular dynamics (QM/MM) approach in which the metal fragments are treated at the quantum level and the support represented in a classical manner. These molecular dynamics studies yield time averaged CSA that are reasonably close to the experimental values and confirm in particular the partition into immobile (Mo) and mobile (W, Re, Ta) complexes. A detailed analysis of the results leads to a better understanding of the nature of the dynamics. Remarkably, motions relative to the silica surface and vibrations influencing the coordination sphere of the metal involving in particular agostic interactions both contribute to average the CSA.

Made available in DSpace on 2015-04-14T14:33:59Z (GMT). No. of bitstreams: 1 448338.pdf: 64897 bytes, checksum: 29b4bece1e3a3f1f4624758dc0367583 (MD5) Previous issue date: 2013-03-19 / The present study aims at establishing the presupposition of intertemporal sustainability on the Social Security System, notedly in the General Regime of Social Security of Brazil. Therefore, starts with the concept of sustainability, noticing its historical evolution, especially from the perspective of sustainable development, to define sustainability as a multidimensional legal principle which determines social development on its material and immaterial aspect, in an inclusive, lasting, and equitable way of current and future generations. Subsequently, in light of this perspective, the presupposition of welfare sustainability will be characterized by addressing the various dimensions of sustainability (economical, social, ethical, environmental, legal, and political), and implication for Social Security. Finally, such theoretical presuppositions are applied to the main benefits held by the General Social Security Regime and selected based on their importance, defining whether they are in compliance with sustainability and making suggestions for adjustments, aiming at tailoring them to welfare sustainability / O presente estudo objetiva estabelecer os pressupostos intertemporais da sustentabilidade na previd?ncia social, notadamente no Regime Geral de Previd?ncia Social brasileiro. Para tanto, parte da concep??o de sustentabilidade, observando a sua evolu??o hist?rica, em especial sob a perspectiva do desenvolvimento sustent?vel, para definir a sustentabilidade como princ?pio jur?dico multidimensional que determina o desenvolvimento social, nos aspectos materiais e imateriais, de modo inclusivo, dur?vel e equ?nime, das atuais e futuras gera??es. Na sequ?ncia do estudo, caracterizam-se em face desta ?tica, os pressupostos da sustentabilidade previdenci?ria, abordando as diversas dimens?es da sustentabilidade (econ?mica, social, ?tica, ambiental e jur?dicopol?tica) e suas implica??es para a previd?ncia social. Por fim, aplicam-se estes pressupostos te?ricos aos principais benef?cios mantidos pelo Regime Geral de Previd?ncia Social, selecionados a partir de sua representatividade, definindo se est?o ou n?o em conformidade com a sustentabilidade e apresentando sugest?es de ajustes sempre com o intuito de adequ?-los ? sustentabilidade previdenci?ria

Pyrrolobenzodiazepines (PBDs) are a group of naturally occurring compounds that were discovered in the cultures of Streptomyces in the 1960s. Some natural PBDs discovered in these cultures, such as anthramycin and sibiromycin, were shown to possess a broad spectrum of anti-tumor activity. Since cancer is still a leading cause of death globally, the development of novel anti-proliferative derivatives of PBDs is essential for human welfare worldwide. Further synthesis and structure-activity relationship (SAR) studies of the parent natural products and their tetracyclic analogs will lead to the discovery of drug candidates. In this work, thirteen PBD analogues were synthesized using no more than three to four synthetic steps, beginning with commercially obtainable L-proline and isatoic anhydride. The MTT assay, which is a colorimetric assay that uses 3-(4,5-Dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) to assess cell metabolic activity, was initially implimented to test the in vitro cytotoxicity of the compounds using multiple cell lines, namely: SKBR-3, MCF-7, SKMEL-2, CaCo 2, HCT 116, and Mia Paca. Nearly all of the compounds decreased the cell viability of MCF-7 by roughly 20%. Additionally, the anti-proliferative activity of the PBD products were further evaluated by the NCI-60 Human Tumor Cell Lines Screen, which is a part of the National Cancer Institute’s Development Therapeutics Program - Drug Synthesis and Chemistry Branch.

A novel insulating cross-arm (ICA) has been developed for new and existing overhead transmission lines of up to 400 kV. The cross-arm consists of four insulating members, end fittings, field grading devices and a nose connection for the attachment of the conductor. The two main structural elements of the assembly have a unique non-cylindrical geometry which gives them improved mechanical characteristics compared to conventional overhead line insulators. The profile for the compression insulator has been designed. After examining six profile variations, it was determined that the lateral orientation which would give the best performance would be with the flat face of the core facing upwards and tilted by 6o. Using the results obtained from performing flashover tests on a conventional 145 kV insulator, the elevation angle for the compression insulator was set to 6o. The dimensions of the compression insulator were calculated based on the assumption that the ICA would be used to uprate an OHL with L3 towers from 275 kV to 400 kV. The optimal insulator profile was determined to be an alternating profile with three different shed sizes, an arcing distance of 3083 mm and a creepage distance of 12470 mm. Electric field grading devices for the ICA were designed. For the LV end, a grading device resembling a ring which follows the general shape of the cross-section of the insulator was designed. For the HV end, an iterative process yielded two designs. First, the ‘butterfly’ grading device was a unibody piece of cast aluminium for all four ICA members. FEA simulations and tests in the laboratory showed that it could effectively control the electric field at voltages of up to 132 kV. The design was patented and the device was used on six cross-arms installed on a live line in Scotland in August 2013. Second, the ‘M-W’ grading device, was a solution made out of four components for managing the field at voltages of up to 400 kV. The device was designed to be easy to install and service, easy and cheap to manufacture and to have minimal visual impact. The compression insulator and the cross-arm assembly were subjected to a multitude of tests adapted from international standards and the Technical Specifications of National Grid. The performed tests aimed to test the electrical characteristics of the cross-arm and the quality of the materials and manufacturing process of the compression insulator. All of the tests were completed successfully except from the corona extinction test for which the appropriate equipment was not available at the time. Two trials were commissioned to examine how the cross-arm performs in a service-like environment. The snow and ice accretion patterns recorded at the mechanical trial site were used for optimising the profile of the compression insulator. The results after a year of continuous monitoring of leakage current and weather conditions at the live trial site showed that there were humidity and visibility thresholds, above 93% for the former and below 400 m for the latter, which increased the average leakage current by 15% on the tension insulators and by 20% on the compression insulators. It was found that when the longitudinal axis of the cross-arm was perpendicular to the weather the leakage current was higher because more of its surface was exposed. The performance of the novel compression insulators was found to be as good as that of the industry standard tension insulators, reaffirming the potency of the design. Finally, on-site observations showed that the ‘butterfly’ grading device could not effectively manage the electric field on the cross-arm at 400 kV, confirming the results of the FEA simulations and testing.

No description available.

Made available in DSpace on 2015-04-14T14:33:51Z (GMT). No. of bitstreams: 1 437993.pdf: 58370 bytes, checksum: 2d318bbae75d57b9dd1c25b84f068af5 (MD5) Previous issue date: 2012-03-20 / O princ?pio da igualdade, norma fundamental do Estado Social Democr?tico brasileiro, assume especial relevo quando se analisa o modelo de distribui??o de benef?cios previdenci?rios em fun??o do g?nero. A realiza??o do direito ? previd?ncia social, direito fundamental de segunda dimens?o, deve orientar-se pela isonomia no acesso aos bens jur?dicos, com vistas ? maior concretiza??o poss?vel. A m?xima j? h? muito preconizada de tratar igualmente os iguais e, em consequ?ncia, desigualmente os desiguais exige, na perspectiva material do aludido postulado, que se afira a adequa??o do modelo atual de concess?o de benef?cios previdenci?rios afetados pelo g?nero. As esp?cies previdenci?rias em quest?o - aposentadoria por tempo de contribui??o e aposentadoria por idade - diferenciam homens e mulheres para a sua frui??o, demandando, em s?ntese, trinta e cinco anos de tempo de contribui??o para homens e trinta para mulheres, ou sessenta e cinco anos de idade para homens e sessenta anos para mulheres. Nesse desiderato anal?tico, diversos fatores hist?rico-sociol?gicos e jur?dicos (quer sob o vi?s doutrin?rio, jurisprudencial ou puramente normativo) devem ser sopesados, examinando as mudan?as de paradigma em rela??o ? participa??o e ? integra??o da mulher ?s mais diversas fun??es sociais e conduzindo a um cen?rio de composi??o da igualdade previdenci?ria. As vari?veis demonstram, em ?ltima an?lise, a impropriedade do quadro atual e a consequente disparidade na outorga das aposentadorias a homens e mulheres, segurados do regime geral de previd?ncia social. O crit?rio orientador de qualquer modifica??o no sistema deve convergir para a origem comum do direito envolvido e assumir como norte a raz?o de ser dos direitos fundamentais: a pessoa como valor fundamental, independentemente de sexo ou g?nero. Considerando, ent?o, a experi?ncia da legisla??o anterior a 1991, a possibilidade de recrudescimento das exig?ncias legais, a representatividade econ?mica, a participa??o dessas duas esp?cies de benef?cios no contexto do regime geral de previd?ncia, bem como todas as demais condicionantes que atuam sobre esse direito (? aposentadoria) em forma??o, algumas altera??es normativas podem ser propostas. As sugest?es principiam com a redu??o da idade ou do tempo de contribui??o para homens, perpassam pela majora??o desses requisitos para mulheres e mesclam redu??o para homens com majora??o para mulheres at? o termo m?dio. Prosseguem tamb?m com a formula??o de tabelas de transi??o para a minora??o dos impactos ?s popula??es atingidas, contemplando ainda a eleva??o dos atuais limites de idade e de tempo de contribui??o e facultando, ao final, a aplica??o das novas regras apenas para novos segurados.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The rice is the main component of the basic diet of the world-wide population, is therefore, of extreme importance for the food security. In function of this, related aspects its production and comsumption must continuously be monitored and be evaluated, so that its supply is guaranteed. In this study, was development and validated a methodology for determination of residues of 51 pesticides in polish rice grains, using the modified QuEChERS extraction method and Gas Chromatography coupled to Mass Spectrometry with Negative Chemical Ionization and Selected Ion Monitoring (GC-MS NCI-SIM). To that end, previous homogenized rice was spiked with 51 pesticides at 3 different spiking levels (10, 20 and 50 μg kg-1, 6 replicates at each level) and extracted by the modified QuEChERS method. Applying this method, 10 mL of acetonitrile was added to 10.0 g of rice matrix and the tubes were vigorously shaken by hand for 45 s. The tubes were uncapped, 3.0 g of anhydrous magnesium sulfate and 1.7 g of sodium acetate were added, the shaking procedure was repeated and the extract was centrifuged for 8 min. Furthermore, a dispersive clean-up was developed for extract purification. The upper layer (4 mL) of the extracts was transferred to another tube containing 600 mg of anhydrous magnesium sulfate and 500 mg of C18, the shaking procedure was repeated and the extract was centrifuged for 8 min. The extracts were analized by GC-MS NCI-SIM. The method validation was performed of the linear range of the analytical curves (7 concentration levels and 6 injections each), detection limit (LOD), quantification limit (LOQ), matrix effect, as well as precision (as RSD%) and accuracy (as recovery percent). In general, LOD, LOQ and r2 results, obtained from GC, were affected by standards prepared in matrix extract compared to the preparation in solvent. The linear calibration curves was between 1.0 or 2.0 to 100.0 ng mL-1 with r2 values ≥ 0,99. The GC-MS (NCI) allowing the quantification (recovery criteria 70-120% and RSD% values ≤ 20%) of 87% of the target compounds, that showed LOQm of 10 or 20 mg kg-1. Hence, it is possible to conclude, this method proved to be adequate for the multi-residue analysis of pesticides in rice, conciliating sensitivity and acceptable selectivity and all the validation parameters were within the limits suggested for validation of chromatographic methods. / O arroz é o principal componente da dieta básica da população mundial. É, portanto, de extrema importância para a segurança alimentar e, em função disso, aspectos relacionados à sua produção e consumo devem ser continuamentemonitorados e avaliados em profundidade, para que o seu suprimento seja garantido. Neste estudo, foi desenvolvida e validada uma metodologia para a determinação, em grãos de arroz polido, de resíduos de 51 pesticidas, analisados utilizando o método de extração QuEChERS modificado e Cromatografia Gasosa com Detecção por Espectrometria de Massas, operando no modo de Ionização Química Negativa e Monitoramento do Ion Selecionado (GC-MS NCI-SIM). Para isso, realizou-se a fortificação do arroz, previamente homogeinizado, com soluções contendo os 51 pesticidas, em 3 níveis de fortificação (10, 20 e 50 μg kg-1), 6 réplicas para cada nível, e aplicou-se o método QueChERS modificado. A extração por este método consistiu na pesagem de 10,0 g da matriz, adição de 10 mL de acetonitrila e procedeu-se a agitação manual e vigorosa, por cerca de 45 segundos. Acrescentou-se 3,0 g de sulfato de magnésio anidro e 1,7 g de acetato de sódio anidro, repetindo-se agitação. Foram, posteriormente, centrifugados por 8 minutos A purificação dos extratos foi realizada através de clean-up dispersivo, onde 4 mL do extrato foram transferidos para outro tubo já contendo 600 mg de sulfato de magnésio anidro e 500 mg de C18, repetindo-se a agitação e a centrifugação, e em seguida os extratos foram analisados por GC-MS NCI-SIM. Neste trabalho avaliouse os seguintes parâmetros de validação do método: faixa de linearidade das curvas analíticas (7 níveis de concentração e seis injeções cada), limite de detecção (LOD), limite de quantificação (LOQ), efeito matriz, bem como a precisão e a exatidão (em termos de percentual de recuperação). Em geral, os valores de LOD, LOQ e r2, obtidos por GC, foram influenciados pela utilização de extratos da matriz para o preparo das soluções analíticas. A faixa linear de concentração das curvas analíticas situou-se entre 1,0 ou 2,0 a 100,0 ng mL-1 com valores de r2 ≥ 0,99. A técnica GCMS NCI modo SIM promoveu a quantificação (critérios de recuperação entre 70 e 120% e valores de RSD% ≤ 20%) de 87% dos compostos que apresentaram LOQm de 10 ou 20 mg kg-1. Portanto, conclui-se que o método mostrou-se adequado à análise multirresíduo dos pesticidas em arroz, conciliando sensibilidade e seletividade adequadas, e todos os parâmetros de validação encontram-se dentro dos limites sugeridos para validação de métodos cromatográficos.

Après exposition par inhalation, les nanoparticules (NPs) peuvent atteindre les alvéoles pulmonaires, se retrouver au niveau de la barrière alvéolo-capillaire (BAC), et induire une toxicité locale et / ou franchir cette barrière pour se retrouver dans la circulation sanguine. Dans ce contexte, l’objectif de ce travail a été de développer des modèles de co-cultures in vitro simples à mettre en œuvre (utilisation de lignées cellulaires humaines), pour étudier les effets des NPs au niveau de la BAC. Dans un premier temps, des co-cultures de cellules épithéliales alvéolaires ou de phénotype proche (lignées A549 ou NCI-H441), et de macrophages (lignée THP-1), ont permis l’étude des effets pro-inflammatoires des NPs de SiO2 et de TiO2. Avec ces modèles nous avons montré l’importance de la coopération cellulaire mise en jeu lors des processus inflammatoires liés aux NPs, mais aussi le rôle du ratio cellulaire employé dans ces réponses. Dans un second temps, des co-cultures tridimensionnelles en chambres bicamérales associant des macrophages (lignée THP-1), des cellules épithéliales bronchiques (lignée Calu-3), et des cellules endothéliales pulmonaires microvasculaires (lignée HPMEC-ST1.6R), ont permis l’étude de l’impact de NPs fluorescentes de polystyrène sur l’intégrité de la BAC, et leur passage à travers cette barrière. Les cellules épithéliales Calu-3 permettent d’établir une barrière de qualité mais la membrane microporeuse servant de support aux cellules doit être optimisée pour ne pas être un frein au passage des NPs. Ce travail montre qu’un seul modèle ne permet pas d’étudier de façon optimale à la fois la toxicité et la translocation des NPs, et qu’une approche adaptée doit être envisagée en fonction du paramètre que l’on souhaite étudier. / After inhalation, nanoparticles (NPs) can reach the alveoli and the alveolo-capillary barrier (ACB), and consequently induce local toxicity and / or cross this barrier to reach the bloodstream. In this context, the aim of this work was to develop co-culture in vitro models simple to implement (using human cell lines), to study effects of NPs on the ACB. In a first time, pro-inflammatory effects of SiO2 and TiO2 NPs were studied on co-cultures of alveolar epithelial cells (A549 and NCI-H441 cell lines), and macrophages (THP-1 cell line). We demonstrated the importance of cell cooperation during inflammatory processes caused by these NPs, and the role of the cellular ratio in these inflammatory responses. In a second time, effects of fluorescent polystyrene NPs on the ACB integrity, and their translocation were studied on three-dimensional co-cultures in bicameral chambers involving macrophages (THP-1 cell line), bronchial epithelial cells (Calu-3 cell line), and micro-vascular pulmonary endothelial cells (HPMEC ST1.6R cell line). The use of Calu-3 has provided a good barrier, but further investigations on microporous membranes are still needed to not interfere with NPs translocation. Altogether, these results show that a tailored approach should be considered in order to study toxicity or translocation of NPs.

This thesis work deals with the volume changes during the solidification of cast irons and peritectic steels. The volume changes in casting metals are related to the expansion and/or contraction of the molten metal during solidification. Often, different types of shrinkage, namely macro- and micro-shrinkage, affect the casting quality. In addition to that, exposure of the metal casting to higher contraction or expansion during the solidification might also be related to internal strain development in samples, which eventually leads to surface crack propagation in some types of steel alloys during continuous casting. In consequence, a deep understanding of the mechanisms and control of the solidification will improve casting quality and production. All of the experiments during the entire work were carried out on laboratory scale samples. Displacement changes during solidification were measured with the help of a Linear Variable Displacement Transformer (LVDT). All of the LVDT experiments were performed on samples inside a sand mould. Simultaneously, the cooling curves of the respective samples during solidification were recorded with a thermocouple. By combining the displacement and cooling curves, the volume changes was evaluated and later used to explain the influence of inoculants, carbon and cooling rates on volume shrinkages of the casting. Hypoeutectic grey cast iron (GCI) and nodular cast iron (NCI) with hypo-, hyper- and eutectic carbon compositions were considered in the experiments from cast iron group. High nickel alloy steel (Sandvik Sanbar 64) was also used from peritectic steel type. These materials were melted inside an induction furnace and treated with different types of inoculants before and during pouring in order to modify the composition. Samples that were taken from the LVDT experiments were investigated using a number of different  methods in order to support the observations from the displacement measurements:  Differential Thermal Analysis (DTA), to evaluate the different phase present; Dilatometry, to see the effect of cooling rates on contraction for the various types of alloys; metallographic studies with optical microscopy; Backscattered electrons (BSE) analysis on SEM S-3700N, to investigate the different types of oxide and sulphide nuclei; and bulk density measurements  by applying Archimedes' principle. Furthermore, the experimental volume expansion during solidification was compared with the theoretically calculated values for GCI and NCI. It was found that the casting shows hardly any shrinkage during early solidification in GCI, but in the eutectic region the casting expands until the end of solidification. The measured and the calculated volume changes are close to one another, but the former shows more expansion. The addition of MBZCAS (Si, Ca, Zr, Ba, Mn and Al) promotes more flake graphite, and ASSC (Si, Ca, Sr and Al) does not increase the number of eutectic cells by much. In addition to that, it lowers the primary austenite fraction, promotes more eutectic growth and decreases undercooled graphite and secondary dendritic arm spacing (SDAS). As a result, the volume expansion changes in the eutectic region. The expansion during the eutectic growth increase with an increase in the inoculant weight percentage. At the same time, the eutectic cells become smaller and increase in number. The effect of the inoculant and the superheat temperature shows a variation in the degree of expansion/contraction and the cooling rates for the experiments. Effective inoculation tends to homogenize the eutectic structure, reducing the undercooled and interdendritic graphite throughout the structure. In NCI experiments, it was found that the samples showed no expansion in the transversal direction due to higher micro-shrinkages in the centre, whereas in the longitudinal direction the samples shows expansion until solidification was complete.   The theoretical and measured volume changes agreed with each other. The austenite fraction and number of micro-shrinkage pores decreased with increase in carbon content. The nodule count and distribution changes with carbon content. The thermal contraction of NCI is not influenced by the variation in carbon content at lower cooling rates. The structural analysis and solidification simulation results for NCI show that the nodule size and count distribution along the cross-sections at various locations are different due to the variation in cooling rates and carbon concentration. Finer nodule graphite appears in the thinner sections and close to the mold walls. A coarser structure is distributed mostly in the last solidified location. The simulation result indicates that finer nodules are associated with higher cooling rate and a lower degree of microsegregation, whereas the coarser nodules are related to lower cooling rate and a higher degree of microsegregation. As a result, this structural variation influences the micro-shrinkage in different parts. The displacement change measurements show that the peritectic steel expands and/or contracts during the solidification. The primary austenite precipitation during the solidification in the metastable region is accompanied by gradual expansion on the casting sides. Primary δ-ferrite precipitation under stable phase diagram is complemented by a severe contraction during solidification. The microstructural analysis reveals that the only difference between the samples is grain refinement with Ti addition. Moreover, the severe contraction in solidification region might be the source for the crack formation due to strain development, and further theoretical analysis is required in the future to verify this observation. / <p>QC 20170228</p>

Ce mémoire présente une méthodologie théorique pour comprendre l'origine de différence de comportement dynamique de complexes alkylidènes, catalyseurs de type Schrock de la métathèse des oléfines, greffés un support de silice amorphe. Dans un travail antérieur, les différences entre les valeurs de l'anisotropie de déplacement chimique (CSA) obtenues par des mesures de RMN du solide et celles estimées par le calcul pour des systèmes figés avaient conduit à suggérer des régimes dynamiques différents pour ces complexes, certains étant proposés comme immobiles, d'autres comme mobiles. Dans le premier groupe se trouve les complexes du molybdène et dans le second les complexes du tungstène, rhénium et tantale. Dans le cadre de cette thèse, nous nous sommes donc attachés à mettre en place une méthodologie pour déterminer ces CSA et donc la nature de la dynamique de chaque système qui conduit au CSA moyenné. Nous nous sommes d'abord intéressés à des systèmes moléculaires pour révéler des interactions non covalentes entre les complexes et le support silice à partir d'une approche de type petit cluster en utilisant divers niveaux de calculs DFT et modèles moléculaires. Cette modélisation moléculaire de la silice étant insuffisante, nous avons entrepris une modélisation de la surface de silice amorphe par dynamique moléculaire classique dont les caractéristiques ont été comparées aux données expérimentales existantes. Le comportement dynamique de ces systèmes greffés sur silice amorphe a été simulé par dynamique moléculaire ab initio QM/MM, couplant une description quantique du complexe organométallique à une description classique du support. Ces études dynamiques ont conduit à des valeurs de CSA moyennées dans le temps de la dynamique. La comparaison de ces valeurs calculées et des valeurs expérimentales a permis d'apporter des éléments de réponse sur l'origine des différences de comportement dynamique de ces complexes alkylidènes. De façon remarquable des mouvements d'ensemble des espèces greffées par rapport à la surface de silice et des modification de la coordination du métal par l'apparition d'interaction agostique contribuent à moyenner le CSA.