"Revised and summarized version of (the author's) doctoral thesis submitted to the Department of Geography at the University of Edinburgh"--P. xii. / Titre de l'écran-titre (visionné le 11 juillet 2008). Description based on print version record. CaQQUQ Comprend des réf. bibliogr. (p. 107-113) et un index.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2000. / Includes bibliographical references (leaves 340-355). Also available on microfiche.

Thesis (M.A. in National Security Affairs)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Donald Abenheim. Includes bibliographical references (p.57-60). Also available online.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This research aims at diagnosing alternative conceptions to scientific knowledge of students in Elementary Education, Middle and Upper on acids and bases. The survey was conducted between 2008 and 2009 and applied to 26 primary school students (ninth year), 36 high school (third year) and 51 Degree in Chemistry (26 freshmen and 25 trainees) totaling 113 students. The instrument used for data collection was mainly made up of open questions where the students described their concepts of acids and bases. The overall results of this study showed that students, after receiving formal instruction on acids and bases continue to use simplistic views on the subject many times in this work, we found misconceptions even among senior college students in the Degree Course in Chemistry. We realize that in general, the Arrhenius model prevails among the students, however, can not be said if students really understand acids and bases as particles or if they perceive these substances as mere words. Confusion between the various theories acid base were very common here, which leads us to believe that the teaching content too complex for the primary and secondary education become conflicting for the student, which does not contribute to an appropriation of such knowledge. In short, we can infer that this inventory of alternative conceptions expressed by students for the contents acids and bases is necessary because the importance of these concepts disclosed and discussed primarily with science teachers. Therefore, we expect to support a significant learning effectively through reflection on students' previous conceptions, which are an important tool for the proposition didactic classroom, since the strong resistance to a conceptual change that students present. / Esta investigação tem como objetivo diagnosticar as concepções alternativas ao conhecimento científico de estudantes de Ensino Fundamental, Médio e Superior sobre ácidos e bases. A pesquisa foi realizada entre 2008 e 2009 e aplicada a 26 alunos de ensino fundamental (nono ano), 36 de ensino médio (terceiro ano) e 51 de Química Licenciatura (26 calouros e 25 formandos) totalizando 113 estudantes. O instrumento utilizado para a obtenção de dados foi essencialmente constituído por questões abertas onde os alunos descreveram seus conceitos sobre ácidos e bases. Os resultados gerais desse estudo mostraram que os estudantes, mesmo depois de receber o ensino formal sobre ácidos e bases continuam a usar concepções simplistas sobre o tema, muitas vezes, neste trabalho, verificamos concepções errôneas mesmo entre os estudantes formandos no curso de Química Licenciatura. Percebemos que em geral, o modelo de Arrhenius predomina entre os estudantes, porém, não se pode afirmar se os estudantes realmente entendem os ácidos e as bases como partículas ou se percebem tais substâncias como meras palavras. Confusões entre as várias teorias ácido base foram muito comuns aqui, o que nos leva a acreditar que o ensino de conteúdos muito complexos durante os ensinos fundamental e médio tornam-se conflitantes para o aluno, o que não contribui para uma apropriação de tais saberes. Em suma, pode-se inferir que este inventário das concepções alternativas manifestadas pelos estudantes para o conteúdo ácidos e bases se faz necessário visto a importância de que estas concepções sejam divulgadas e principalmente discutidas com os professores de ciências. Sendo assim, esperamos corroborar para uma aprendizagem efetivamente significativa, através da reflexão sobre as concepções prévias dos alunos, as quais são uma importante ferramenta para a proposição didática em sala de aula, visto a forte resistência a uma mudança conceitual que os estudantes apresentam.

MAIA JÚNIOR, Francisco Franciné. Cristais anidros das bases do ADN são semicondutores de Gap largo. 2011. 243 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2011. / Submitted by francisco lima (admir@ufc.br) on 2014-03-18T13:34:36Z No. of bitstreams: 1 2011_Tese_ffmaiajunior.pdf: 27698119 bytes, checksum: f4553d0bed3b17a38cc9b90fb8e55c88 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-05-19T19:27:28Z (GMT) No. of bitstreams: 1 2011_Tese_ffmaiajunior.pdf: 27698119 bytes, checksum: f4553d0bed3b17a38cc9b90fb8e55c88 (MD5) / Made available in DSpace on 2014-05-19T19:27:28Z (GMT). No. of bitstreams: 1 2011_Tese_ffmaiajunior.pdf: 27698119 bytes, checksum: f4553d0bed3b17a38cc9b90fb8e55c88 (MD5) Previous issue date: 2011 / Guanine (G), adenine (A), cytosine (C), and thymine (T) nucleotide bases are the essential building blocks of DNA (deoxyribonucleic acid), which contains the genetic information used to build living cells. DNA strands are also promising candidates to fabricate molecular nanodevices, since they are stable polymers easy to replicate. Despite the early suggestion of the possibility of using DNA as a nanoscale conductor almost ten years after the elucidation of its helical structure, charge carrier transport through DNA-based structures is still a matter of debate. Here, we present the structural, electronic and optical properties of anhydrous crystals of DNA nucleobases found after DFT (Density Functional Theory) calculations, as well as experimental measurements of optical absorption for powders of these crystals. Experimental measurements of the UV absorption spectra for the anhydrous crystals were carried out on these pellets using a Varian Cary 5000 UV-visible NIR spectrophotometer. The absorption spectrum of the samples was recorded in the wavelength range between 200 and 800 nm (50000-12500 cm-1). The computational simulations of the present work were performed using the CASTEP code, which is based in the DFT approach. The Local Density Approximation (LDA) exchange-correlation potential developed by Ceperley and Alder and parametrized by Perdew and Zunger was adopted as well. With respect to our choice of functional, a note of caution must be made: in anhydrous DNA bases crystals, van der Waals interactions along the molecular stacking axis and hydrogen bonding between molecules in the same stacking plane are relevant to explain their structural features, and it is well known that pure DFT methods are unable to give a good description of dispersive forces. Besides, the LDA approximation is not the best option to provide an accurate account of hydrogen bonds. However, some DFT studies of layered crystals such as graphite as well as guanine hydrated crystals have shown that the LDA gives reasonable values for atomic distances, notwithstanding the limitations of this functional. This and the relatively low cost of LDA computations have motivated us to its adoption instead of more sophisticated (and computationally expensive) means. Guanine and cytosine (adenine and thymine) anhydrous crystals are predicted from the DFT simulations to be direct (indirect) band gap semiconductors, with values 2.68 eV and 3.30 eV (2.83 eV and 3.32 eV), respectively, while the experimentally estimated band gaps we have measured are 3.7 eV and 3.8 eV (3.5 eV and 4.0 eV), in the same order. Our LDA figures for the energy gaps are smaller than experimental values, as expected, and the gaps estimated from the optical absorption measurements presented in this work are in general smaller than experimental data available in the literature (except for guanine). The LDA ordering of increasing band gaps is G < A < C < T, while the ordering of gaps obtained experimentally is not settled: our work finds (from optical absorption measurements) A < G < C < T in contrast with the X-ray measurements, that indicate the energy gap sequence G < C < A < T. For electrons and holes moving along selected hydrogen bonds (parallel to the molecular plane of a given nucleobase), effective masses are in general large, exception made to thymine. When the same electrons move along the pi-stacking axis, however, effective masses stay between 4.0 and 6.3 free electron masses (m0), which suggests that stackings of nucleobases behave like wide gap semiconductors for electrons. The perpendicular transport of holes is also favored for nucleobase stackings without thymine. Finally, the complex dielectric function was calculated for each anydrous DNA base crystal, and a very pronounced anisotropy was observed for polarized incident light in the cases of guanine, adenine, and thymine, but not for cytosine. / As bases nucleotídicas guanina (G), adenina (A), citosina (C) e timina (T) são bases nucleotídicasos blocos essenciais da molécula do ácido desoxiribonucleico (ADN), que contém a as informações genéticas usadas pelas células vivas. Filamentos de ADN são também candidatos promissores para fabricação nanodispositivos moleculares, visto que polímeros estáveis e de fácil replicação. Apesar desta sugestão inicial da possibilidade de usar o ADN como condutor em nanoescala apenas dez anos após a elucidação da estrutura helicoidal do ADN, o transporte de portadores de cargas através de estruturas baseadas no ADN ainda são matéria de debate. Aqui, são apresentadas as propriedades estruturais, eletrônicas e ópticas dos cristais anidros das bases do ADN obtidas após cálculos baseados na teoria do funcional da densidade (DFT, do inglês Density Functional Theory), assim como medidas de absorção ótica para o pó desses cristais. Os experimentos do espectro absorção UV para os cristais foram realizadas sobre pastilhas usando o espectrometro Varian Cary 5000 UV-visible NIR, considerando o intervalo de 200 and 800 nm (50000-12500 cm-1). Os cálculos teóricos da presente tese foram desenvolvidos usando o pacote CASTEP, baseado na teoria DFT. Na descrição do potencial de troca e correlação, foi utilizada aproximação local da densidade (LDA, do inglês Local Density Approximation) desenvolvida por Cerpeley e Alder e parametrizado por Perdew e Zunger (CA-PZ). Sobre a escolha do funcional, uma observação deve ser feita: nos cristais anidros das bases do ADN, interações de van der Waals ao longo do eixo de empilhamento molecular e as ligações de hidrogênio entre as moléculas do mesmo plano são relevantes na explicação das suas características, e é bem conhecido que os métodos de DFT puro são incapazes de uma boa descrição das forças dispersivas. Além disso, a aproximação LDA não é a melhor opção para cálculos precisos das ligações de hidrogênio. Entretanto, alguns trabalhos DFT de cristais formados por camadas tais como grafite e o cristal hidratado da guanina mostraram que o funcional LDA fornece valores razoáveis para as distâncias atômicas, contrariando as limitações desse funcional. Isso e o baixo custo computacional foram as motivações que levaram a sua escolha em vez da adoção de funcionais mais sofisticados (e computacionalmente mais pesados). Os cristais de guanina e citosina (adenina e timina) são previstos terem gaps diretos (indiretos), com os valores experimentais estimados a partir da absorção de 3,7 eV e 3,8 eV (3,8 eV e 4,0 eV), na mesma ordem. Os resultados LDA mostraram gaps de energia menores do que os valores experimentais, como esperado, e os gaps experimentais estimados a partir da absorção ótica são, em geral, menores do que os valores experimentais disponíveis na literatura (exceto, para a guanina). A ordem crescente nos valores calculados dos gaps de energia para os cristais é dada por G < A < C < T, enquanto os valores experimentais obtidos nesta tese (a partir da absorção óptica) seguem a ordem A < G < C < T em contraste com as medidas de raios-x, que indicam a sequência G < C < A < T. Para os elétrons e buracos se movendo das ligações de hidrogênio (paralelas ao plano molecular da base), as massas efetivas são geralmente elevadas, exceto para a timina. Quando os mesmos elétrons se movimentam ao do eixo de empilhamento molecular, entretanto, as massas efetivas ficam entre 4,0 e 6,3m0, sugerindo estes cristais se comportam como semicondutores de gap largo ao longo das direções de empilhamento molecular. O transporte de buracos também é favorecido ao longo da direção de empilhamento, exceto para a timina. Finalmente, a função dielétrica complexa foi calculada para cada cristal anidro das bases do ADN, sendo observada uma forte anisotropia para a incidência de luz polarizada nos casos da guanina, adenina e timina, mas não para a citosina.

Dans le cadre de cette thèse, nous présentons l’extension des résultats sur le raisonnement avec des bases de croyances totalement ordonnées au cas partiellement ordonné. L’idée est de raisonner avec des bases logiques équipées d’un ordre partiel exprimant la certitude relative et de construire une fermeture déductive partiellement ordonnée. Au niveau syntaxique, nous pouvons soit utiliser un langage exprimant des paires de formules et des axiomes décrivant les propriétés de l’ordre, ou utiliser des formules en relation avec des poids symboliques partiellement ordonnés dans l’esprit de la logique possibiliste. Une sémantique possible consiste à supposer que cet ordre provient d’un ordre partiel sur les modèles. Elle exige la capacité d’induire un ordre partiel sur les sous-ensembles d’un ensemble, à partir d’un ordre partiel sur ses éléments. Parmi plusieurs définitions de relations d’ordre partiel ainsi définies, nous sélectionnons la plus pertinente pour représenter la notion de certitude relative, en accord avec la théorie des possibilités. Nous montrons les limites d’une sémantique basée sur un ordre partiel unique sur les modèles et proposons une sémantique plus générale qui utilise une relation d’ordre partiel entre les ensembles de modèles. Nous utilisons un langage de plus haut niveau qui exprime des conjonctions de paires de formules en relation, avec des axiomes qui décrivent les propriétés de la relation. Nous proposons deux approches syntaxiques pour inférer de nouvelles paires de formules à partir d’une base partiellement ordonnée, et compléter ainsi l’ordre sur le langage propositionnel. L’une des inférences est proche des logiques conditionnelles de Lewis (qui traite le cas totalement ordonné) et d’un travail de Halpern. Elle est également proche du Système P. Nous reprenons la logique possibiliste symbolique proposée par Benferhat et Prade et comparons cette approche avec l’approche par certitude relative. Pour cela nous poursuivons l’étude de la logique possibiliste symbolique en démontrant un résultat de complétude. Nous étudions la question de la traduction d’une base partiellement ordonnée en base possibiliste symbolique et inversement. Nous proposons enfin des pistes pour une implémentation du système d’inférence de certitude relative et du système possibiliste symbolique. / In this thesis, we present results on the extension of the existing methods for reasoning with totally ordered belief bases to the partially ordered case. The idea is to reason from logical bases equipped with a partial order expressing relative certainty and to construct a partially ordered deductive closure. The difficult part lies in the fact that equivalent definitions in the totally ordered case are no longer equivalent in the partially ordered case. At the syntactic level we can either use a language expressing pairs of related formulas and axioms describing the properties of the ordering, or use formulas with partially ordered symbolic weights attached to them in the spirit of possibilistic logic. A possible semantics consists in assuming that the partial order on formulas stems from a partial order on interpretations. It requires the capability of inducing a partial order on subsets of a set from a partial order on its elements so as to extend possibility theory functions. Among different possible definitions of induced partial order relations, we select the one generalizing necessity orderings (closely related to epistemic entrenchments). We study such a semantic approach inspired from possibilistic logic, and show its limitations when relying on a unique partial order on interpretations. We propose a more general sound and complete approach to relative certainty, inspired by conditional modal logics, in order to get a partial order on the whole propositional language. Some links between our approach and several inference systems, namely conditional logic, modal epistemic logic and non-monotonic preferential inference are established. Possibilistic logic with partially ordered symbolic weights proposed by Benferhat and Prade is also revisited and we continue the study by proving a completeness result. A comparison with the relative certainty approach is made via mutual translations. We compare this approach with the relative certainty approach.We study the question of the translation of a partially ordered base into a symbolic possibilistic base and vice versa. The results for this translation highlight different assumptions underlying the two logics. We also offer steps toward implementation tools for the inference of relative certainty and for the symbolic possibilistic system.

Neste trabalho foi realizado o estudo por docagem e simulação de dinâmica molecular de doze derivados benzazólicos fluorescentes por ESIPT, interagindo com o dodecâmero de Dickerson-Drew na forma B-DNA. Estes doze ligantes foram divididos em dois grupos (A e B), sendo o primeiro grupo composto por derivados do 2-(2’-hidroxifenil)-benzoxazol e o segundo grupo composto por três derivados do 2-(4’-amino-2’-hidroxifenil)-benzazóis, alternando entre N, S e O no anel azólico, mais três bases de Tröger derivadas dos mesmos. Na análise da docagem molecular do grupo A, os derivados com grupamento –NH2 no anel fenólico apresentaram energias de interação mais favoráveis com o DNA, verificando um favorecimento ainda maior, para os ligantes que continham –NO2 como substituinte no anel benzoxazólico. Na análise da docagem molecular para grupo B, as bases de Tröger (4ac) apresentaram interações significativamente mais favoráveis, quando comparados com seus respectivos precursores (3ac). Na análise da DM, tanto o grupo A, quanto o B, apresentaram a formação de complexos estáveis. O grupo A apresentou uma indução a alterações estruturais mínimas no DNA, sendo as maiores alterações a abertura do Rise quando os ligantes estavam intercalados, acompanhado pelo desenrolamento do parâmetro Twist. Nas interações de sulco menor, o ligante 2a foi o que formou o complexo mais estável com o DNA. Na análise da DM do grupo B, as bases de Tröger apresentaram uma preferência maior por interações do tipo intercalação que seus precursores, sendo os primeiros, os quais induziram o oligonucleotídeo a maiores alterações estruturais. Durante todas as simulações os ligantes mantiveram-se com uma forte interação com o oligonucleotídeo, sem causar a desnaturação do mesmo. Devido às interações estáveis, e também as propriedades fotofísicas peculiares dos ligantes estudados, esta classe de moléculas pode atuar como possíveis sondas biológicas. / In this work we carried out a study by docking and molecular dynamics simulations of twelve ESIPT-fluorescent benzazoles, interacting with the Dickerson-Drew dodecamer in the canonical B-DNA form. These twelve ligands were divided into two groups (A and B), with the first group consisting of derivatives of 2-(2’-hydroxphenyl)-benzoxazole and the second group consisting of three derivatives of 2-(4’-amino-2’-hydroxyphenyl)-benzazoles, alternating between N, S and O in the azole ring and three Tröger bases derived from them. In the analysis of the molecular docking of group A, the derivatives with group –NH2 in the phenolic ring presented more favorable interaction energies with the DNA, and the score was even more favorable for the ligands which contained –NO2 as substituent in the benzoxazolic ring. In the analysis of the molecular docking for group B, the Tröger bases (4ac) presented significantly more favorable interactions, when compared with their respective precursors (3ac). In the analysis of the DM, both groups A and B formed stable complexes. Group A induced only slight structural distortions in the DNA, being the largest modifications the increase of the Rise parameter when the ligands were intercalated, accompanied by the unwinding of Twist parameter. Regarding minor groove interactions, the ligand 2a formed the most stable complex with the DNA. In the analysis of the DM both groups A and B, the Tröger bases presented a greater preference for intercalation interactions than their precursors and the Tröger bases induced the largest structural changes to the oligonucleotide. During all the simulations the ligands maintained a strong interaction with the oligonucleotide, without causing the denaturation of the same. Due to the stable interactions, and also the peculiar photophysical properties of the ligands studied, this class of molecules can act as possible biological probes.

Made available in DSpace on 2016-06-02T20:34:15Z (GMT). No. of bitstreams: 1 2091.pdf: 15515843 bytes, checksum: c1cd051b1487df8663ede9ea383cbe1a (MD5) Previous issue date: 2007-09-11 / Universidade Federal de Sao Carlos / Salen complexes are an important class of coordination compounds, which have been used to catalyze a wide variety of reactions. The salen complexes have emerged as efficient and practical catalysts for the asymmetric oxidation of various organic substrates. In this thesis, copper(II) and oxovanadium(IV) complexes of the salcn type ligand [salcn= N, N -bis- (salicylidene)-1,2-cyclohexanediamine] have been investigated as catalysts for oxidation of organic sulfide. The first part of this work describes the synthesis and characterization of the free ligands and copper(II) and oxovanadium(IV) complexes. The combination of four complementary techniques (IR, UV-vis, 1HNMR-13CNMR and X-ray) made possible the characterization of the free ligands and complexes. Six unpublished crystallographic structures were determined: four ligands and two oxovanadium(IV) complexes . In the second part of this research were studied catalytic properties of some complexes in oxidation of phenyl methyl sulfide using acetonitrile as the solvent and hydrogen peroxide and t-butylperoxide as the oxidant. The [Cu(salcn)] and [VO(salcn)] with electrons donors and electrons withdrawing substituents were tested for catalytic oxidation. The effect of reaction conditions on activity with various oxidants gave distinctly different yields. The complex trans-(±)-[Cu(5- Clsalcn) showed the best result, with 73% of the sulfide conversion. This is result was showed with hydrogen peroxide as the oxidant. The yields obtained for the other compounds vary of 11-32%. / Os complexos de salen são uma classe importante dos compostos de coordenação e são utilizados como catalisadores em uma grande quantidade de reações. Os complexos salen tem mostrado ser catalisadores eficientes e práticos para oxidações assimétricas de vários substratos. Nesta tese, complexos do tipo salcn [salcn = N, N -bis- (salicilideno)-1,2-ciclohexanodiamina) foram investigados como catalisadores em oxidação de sulfetos orgânicos. A primeira parte deste trabalho, descreve a síntese e caracterização dos ligantes e complexos de cobre(II) e oxovanádio(IV). A combinação das quatro técnicas complementares (IV, UVvis, RMN e raios-X) possibilitou a caracterização dos ligantes e complexos quirais. Seis estruturas cristalográficas inéditas foram determinadas: quatro ligantes e dois complexos de oxovanádio(IV). A segunda parte desta pesquisa foi o estudo das propriedades catalíticas dos complexos na oxidação do metilfenilsulfeto utilizando acetonitrila como solvente e peróxido de hidrogênio e terc-butil peróxido como agente oxidante. [Cu(salcn)] e [VO(salcn)] com substituintes doadores de elétrons e retiradores de elétrons foram testados e os efeitos das condições de reações na atividade catalítica com a variação dos agentes oxidantes mostraram rendimentos bem distintos. O complexo trans-(±)-[Cu(5-Clsalcn) apresentou o melhor resultado, com 73,5% de conversão do sulfeto a sulfóxido e/ou sulfona. Este resultado foi alcançado quando utilizado como doador de oxigênio o peróxido de hidrogênio. Os rendimentos obtidos para os outros complexos variam de 11-32%.

Made available in DSpace on 2016-06-02T20:34:15Z (GMT). No. of bitstreams: 1 2092.pdf: 25701742 bytes, checksum: 780ff1a21d9df6f0d764a7c43de388dc (MD5) Previous issue date: 2007-12-14 / Universidade Federal de Sao Carlos / In order to find inorganic compounds with biological properties as chemotherapeutic agents that could increase the possibilities in the treatment of some diseases, copper complexes with Schiff base ligands were prepared and characterized. In this work we prepared 63 compounds, being 19 symmetrical tetradentate Schiff base ligands and their respective copper complexes, 16 copper complexes with unsymmetrical tetradentate Schiff base ligands and 9 copper complexes with tridentate Schiff base ligands derived from ethylenediamine, trans-1,2-diaminocyclohexane and orto-phenylenediamine, with salicylaldehyde or substituted salicylaldehyde. All were characterized by vibracional spectroscopy (infrared), electronic spectroscopy (ultraviolet-visible) and others methods such as solubility, melting points. Some complexes were studied by cyclic voltammetry and magnetic susceptibility. The structures of [Cu(3-MeOsalen)], [Cu(3- EtOsalen)] and [Cu(4-DEAsalen)], have been determined by single crystal X-ray diffraction. The cytotoxicity of the symmetrical complex [Cu(4-DEAsalen)], was evaluated using HPV-16 and HPV-18 infected cells. Cytotoxicity tests using spleen cells of BALB/c mice were performed using 5 tridentate complexes. The characterization results show that the synthesis had been successful with good yields. The effect of the substitution on the aromatic ring was compared for compounds within a series and between different series. / Em busca de compostos inorgânicos com propriedades biológicas que pudessem, através da atuação como agentes quimioterápicos, contribuir para aumentar as possibilidades no tratamento de algumas doenças, foram sintetizados e caracterizados complexos de cobre com ligantes bases de Schiff do tipo salen, foram estudados no total 63 compostos, sendo 19 complexos tetradentados simétricos com seus respectivos ligantes; 16 complexos tetradentados assimétricos e 9 complexos tridentados. Todos, complexos e ligantes, foram caracterizados pelas técnicas de espectroscopia vibracional (região do infravermelho) e eletrônica (região do ultravioleta-visível) entre outras técnicas como pontos de fusão e solubilidade, foram realizadas medidas de susceptibilidade magnética e estudos eletroquímicos para alguns complexos. Os complexos [Cu(3-MeOsalen)], [Cu(3-EtOsalen)] e [Cu(4-DEAsalen)], tiveram suas estruturas determinadas por difração de raios-x, método de monocristal. Foram realizados testes de toxicidade para o complexo simétrico [Cu(4-DEAsalen)], em relação à células infectadas com dois tipos de HPV e testes de toxicidade em células esplênicas com alguns complexos tridentados. Os meios de caracterização empregados indicam que as sínteses foram bem sucedidas com rendimentos bastante eficientes, foram feitas comparações com respeito aos efeitos dos substituintes no anel aromático dentro de uma mesma série de compostos e também foram comparados os resultados obtidos para as diferentes séries de trabalho.

Au-delà de son importance dans l’industrie nucléaire, la chimie d’oxydoréduction de l’uraniumretient de plus en plus l’attention des chercheurs. En effet, la capacité toute particulière descomplexes d’uranium à bas degré d’oxydation à promouvoir des réductions originales par desvoies inhabituelles suscite actuellement un grand intérêt, tout particulièrement leur aptitude àactiver dans des conditions douces des petites molécules telles CO, CO2, N2, ou encore descomposés aromatiques et des azotures. Les composés d’uranium, de part leurs propriétés decoordination tout à fait uniques pourraient offrir une alternative aux métaux de transitionclassiques pour la conception de catalyseurs. Cependant, comparativement aux métaux du bloc d,les processus polyélectroniques sont rares dans la chimie de l’uranium à bas degré d’oxidation quiest dominée par les transferts monoélectroniques. C’est pourquoi le développement de nouveauxcomplexes d’uranium capables de réaliser des réductions poly-électroniques est particulièrementintéressant. Le premier objectif de ce travail était d’associer à l’uranium des ligands non-innocentsservant de réservoir d’électrons. Ainsi nous avons utilisé des bases de Schiff p-conjuguées pourexplorer la chimie de cet élément à bas degree d’oxydation. Cela nous a permis d’isoler descomplexes riches en électrons dans lesquels des électrons sont stockés sur le ligand via laformation de liaisons C-C. Ces mêmes liaisons sont rompues en présence d’agent oxydant, et lesélectrons sont libérés pour réaliser des transformations polyélectroniques. Ce procédé a étéobservé pour plusieurs bases de Schiff, permettant de moduler les propriétés des composés. Dansune seconde approche, nous nous sommes intéressés à la synthèse et à l’étude de la réactivité denouveaux complexes d’uranium trivalent supportés par des ligands silanolates. De nouveauxcomposés dinucléaires d’uranium à basse valence ont été obtenus. Ces composés très réactifsdécomposent spontanément en clivant des groupements tertiobutyls des ligands, conduisant à laformation de complexes d’uranium(IV). En parallèle, un complexe monoanionique mononucléaired’U(III) a été isolé, nous permettant de comparer la réactivité de l’uranium trivalent dans différentsenvironnements stériques et électroniques. Ces études de réactivité ont permis de stabiliser unexemple rare de dimère d’uranium ponté par un groupement CS22- et ont mis en évidence lacapacité de l’uranium trivalent à promouvoir la dismutation de CO2 en carbonate et CO. La réactionde ces composés d’uranium trivalent vis-à-vis d’azotures organiques et inorganiques a produit denouveaux nitrures et nitrènes d’uranium originaux. Enfin, la capacité de ces agents réducteurspuissants à transférer des électrons au toluène a permis d’isoler une famille de complexessandwiches inversés où deux cations uranium sont liés de part et d’autre d’un cycle aromatique. / Beyond its importance in nuclear industry the redox chemistry uranium is attracting increasinginterest because complexes of low-valent uranium can promote unusual reductive chemistrythrough unusual reaction pathways, including attractive examples of CO, CO2, N2, arenes andazides activation in mild condition. Due to the unique coordination and bonding properties ofuranium, its compounds could provide an attractive alternative to transition metals for thecatalytic transformation of small molecules. However, metal-based multi-electron processesremain uncommon in uranium chemistry especially in comparison with the d-block metals, thechemistry of low-valent uranium being dominated by single-electron transfers. In this context, thefirst aim of this project was to investigate the association of low-valent uranium to a non-innocentligand acting as an independent electron reservoir at a same molecule. Accordingly, weinterrogated the use of highly p-delocalized Schiff bases ligands for supporting low-valent uraniumchemistry. This led to the isolation of electron-rich complexes which are stabilized by storingelectrons on the ligands through the formation of C-C bonds. Interestingly, these C-C bonds can becleaved by oxidizing agents and the electrons released to participate in multi-electron redoxreactions. This process was observed within different Schiff-base ligand scaffolds, allowing atuning of the properties of the compounds. The second part of this work was dedicated to thesynthesis of novel trivalent uranium complexes supported by siloxy ligands and the study of theirredox reactivity and coordination properties. Novel dinuclear highly-reactive low-valent uraniumassemblies were developed. The study of their limited stability revealed that these compounds arespontaneously decomposing through the cleavage of tBu groups from the supporting ligandsresulting in the formation of U(IV) species. In parallel, a mononuclear trivalent uranium atecomplex was obtained, allowing to compare the reactivity of U(III) in different steric and electronicenvironements. Hence we became interested in studying the redox reactivity of these compoundswith different substrates including CO2, CS2, azides and arenes. These investigations led to thestabilization of a rare CS22- sandwich complex of uranium, and highlited the ability of U(III) topromote reductive disproportionation of CO2 to carbonate and CO. The reaction of these trivalenturanium siloxide species with organic and inorganic azides produced original uranium imidos andnitridos compounds with original topologies. Finally the capacity of these strongly reducing agentsto transfer electrons to the toluene fragment lead to the isolation of a family of arenes invertedsandwich complexes.