Compostos de vanádio são extensivamente estudados, devido suas propriedades redox, eletroquímicas, catalíticas, magnéticas e biológicas. Nesta dissertação tivemos como foco de nosso trabalho o composto VOPO4.2H2O que apresenta uma forma lamelar com suas lamelas unidas por interações de Van der Waals. Essas fracas interações interlamelares fazem do fosfato de vanadila e de seus componentes análogos excelentes matrizes para a síntese de compostos de intercalação. A morfologia do VOPO4.2H2O mostrou-se sensível a alterações de temperatura e tempo durante síntese. Através da alteração destes parâmetros obtivemos um sólido lamelar com um grau de organização inferior a matriz sintetizada à 130oC e 16 horas, devido a existência da fase II-VOPO4 que foi constatada por difração de raios-X. A quantidade de dois mols de água por mol de VOPO4 manteve-se constante segundo as análises termogravimétricas. As imagens de microscopia eletrônica de varredura confirmaram a estrutura lamelar dos produtos, no entanto uma forma rosácea foi constatada em VOPO4/160oC, sugerindo a presença da fase VOHPO4.0,5H2O, precursora da fase (VO)2P2O7 que atua como catalisador seletivo na reação de oxidação do n-butano à anidrido malêico. A intercalação de íons lantanídeos na matriz VOPO4.2H2O produziu sólidos lamelares com cristalinidade inferior a matriz hospedeira, devido a distorção dos octaedros ocasionado pela redução dos íons vanádio (V) à (IV) apresentando uma diminuição na distância interlamelar com concomitante inserção de íons lantanídeos visando o balanceamento de carga na matriz. A reação de intercalação da matriz VOPO4.2H2O utilizando os tensoativos CTAB e CPC apresentaram resultados satisfatórios confirmados por difração de raios-X e espectrofotometria na região infravermelho. A intercalação de poli(óxido de etileno) assistida com brometo de cetiltrimetilamônio mostrou-se mais adequada apresentando sólidos organizados devido as moléculas de CTAB atuarem como agente diretivo. / Vanadium compounds are intensively studied due to their electrochemical, catalytic, magnetic and biological properties. In this work, our goal was to investigate the VOPO4.2H2O (vanadyl phosphate), which has a lamellar structure formed by VOPO4 sheets interconnected by weak interactions. Taking advantage of this structure, it is possible to synthesize several different intercalation compounds in which the guest species can vary from simple ions to polymeric species. The morphology of VOPO4.2H2O is very sensitive to temperature and time of reaction changes. By varying both parameters, several lamellar matrices have been synthesized. X-ray diffraction, thermal analysis and scanning electronic microscopy showed that depending on the synthetic conditions the arrangements VOPO4.2H2O can change the shape. For instance, in one of the experiments, a rose-like structure was produced, suggesting the presence of VOHPO40.5H2O phase, precursor of (VO)2P2O7 phase, which acts as oxidation catalyst of the n-butane to maleic anhydride. Intercalation of lanthanide ions leads to lamellar solids with low crystallinity in relation to the matrix due to octahedric distortion caused by reduction of vanadium ions (VV to VIV). Besides, it was observed a decrease of the interlamellar distance in function of the electroneutrality balance between the lamellar sheets. Intercalation compounds were produced by reacting surfactants molecules directly with the matrix under hydrothermal conditions. Surfactant-assisted intercalation of poly(ethylene oxide) into VOPO4.2H2O was conducted under soft conditions with the surfactant/matrix compound as a suspension in an aqueous polymer solution.

No description available.

Acyl groups in biochemical reactions are activated as acyl adenylates; such intermediates are generated by a reaction with ATP. Acyl adenylates are mixed carboxylic-phosphoric anhydrides which are potentially useful as biomimetic reagents for acylation reactions in water. These species have been reported to be unstable and have been isolated without purification. Since the adenylate portion is necessarily complex because it originates from ATP, we reasoned that using a simple alkyl group in place of adenosine might allow the biomimetic process to proceed without the difficulties reported. Our laboratory has developed routes towards such acyl phosphate alkyl monoesters and we have used them for several applications. Such materials react rapidly and selectively with amines in order to produce amides. While reactions utilizing lanthanide ions allow for the selective monoacylation of diols through bis-dentate chelates of the lanthanide. However, the efficiency of diol acylation is limited due to significant hydrolysis of the phosphate reagent and the requirement of a stoichiometric amount of the lanthanide ion. Therefore, three distinct approaches towards improving the efficiency of lanthanide promoted acylation were investigated: addition of an inert co-solvent in an attempt to reduce hydrolysis, eliminating the stoichiometric requirement of the lanthanide by addition of MgII, and the development of immobilized lanthanides as catalysts for acylation. Finally, aminoacyl phosphates are biomimetically activated amino acids and in principle should function as peptide synthesis reagents. The stability and solubility of the activated materials in water presents an opportunity to perform aqueous peptide coupling; such a process is limited by the fact that common peptide coupling agents are either insoluble or unstable in water. Therefore, we investigated the reactions of aminoacyl phosphates with amino acid esters. We find that peptides form readily in buffered solutions, establishing a basis for a general protocol for aqueous amino acid coupling and could be adapted for applications such as solid phase peptide synthesis.

Acyl groups in biochemical reactions are activated as acyl adenylates; such intermediates are generated by a reaction with ATP. Acyl adenylates are mixed carboxylic-phosphoric anhydrides which are potentially useful as biomimetic reagents for acylation reactions in water. These species have been reported to be unstable and have been isolated without purification. Since the adenylate portion is necessarily complex because it originates from ATP, we reasoned that using a simple alkyl group in place of adenosine might allow the biomimetic process to proceed without the difficulties reported. Our laboratory has developed routes towards such acyl phosphate alkyl monoesters and we have used them for several applications. Such materials react rapidly and selectively with amines in order to produce amides. While reactions utilizing lanthanide ions allow for the selective monoacylation of diols through bis-dentate chelates of the lanthanide. However, the efficiency of diol acylation is limited due to significant hydrolysis of the phosphate reagent and the requirement of a stoichiometric amount of the lanthanide ion. Therefore, three distinct approaches towards improving the efficiency of lanthanide promoted acylation were investigated: addition of an inert co-solvent in an attempt to reduce hydrolysis, eliminating the stoichiometric requirement of the lanthanide by addition of MgII, and the development of immobilized lanthanides as catalysts for acylation. Finally, aminoacyl phosphates are biomimetically activated amino acids and in principle should function as peptide synthesis reagents. The stability and solubility of the activated materials in water presents an opportunity to perform aqueous peptide coupling; such a process is limited by the fact that common peptide coupling agents are either insoluble or unstable in water. Therefore, we investigated the reactions of aminoacyl phosphates with amino acid esters. We find that peptides form readily in buffered solutions, establishing a basis for a general protocol for aqueous amino acid coupling and could be adapted for applications such as solid phase peptide synthesis.

No description available.

Nous nous sommes intéressés, dans ce travail de thèse, à des vitrocéramiques transparentes oxyfluorées pour la réalisation de dispositifs d'amplification optique, afin de s'affranchir des inconvénients des monocristaux (difficulté de synthèse et de mise en forme) et des verres (propriétés thermomécaniques et optiques insuffisantes) habituellement utilisés. Les vitrocéramiques, synthétisées par la dévitrification d'un verre à base de GeO2:PbO:PbF2, sont formées d'une phase amorphe oxyde dans laquelle sont réparties des nanocristallites fluorées. L'originalité de ce travail réside dans le développement de vitrocéramiques multi-dopées par ErF3, YbF3 et CeF3 pour optimiser les propriétés d'absorption de ces matériaux à 980 nm et leur intensité d'émission à 1.5 μm, qui correspond au maximum de transparence des fibres optiques de silice utilisées pour le transport de l'information. L'étude de la structure et de la morphologie des vitrocéramiques, en fonction de la nature des ions Ln3+ dopants et des conditions de traitement thermique, a permis d'obtenir une bonne compréhension des mécanismes de dévitrification. Elle a également mis en évidence la ségrégation des ions dopants Ln3+ dans les nanocristallites au détriment de la phase vitreuse. En parallèle, des études par spectroscopie optique et spectroscopie par résonance paramagnétique électronique nous ont renseignés sur la localisation des ions dopants dans le réseau de ß-PbF2 et nous ont permis de comprendre les propriétés optiques des vitrocéramiques. Les ions Er3+ et Yb3+ se répartissent, d'une part, sur des sites cubiques de ß-PbF2 et, d'autre part, forment des clusters, probablement des hexamères, dans une proportion qui dépend de la teneur en Ln3+ des matériaux. Les propriétés optiques des vitrocéramiques sont similaires à celles des monocristaux massifs de ß-PbF2 dopés, élaborés en tant que référence dans ce travail. Il en résulte que les vitrocéramiques sont potentiellement intéressantes pour des applications lasers, au même titre que les monocristaux, tout en présentant une synthèse beaucoup plus simple. Elles ouvrent la voie à la réalisation de dispositifs amplificateurs optiques de grande taille et de formes variées: plaques, fibres etc.

No description available.

Made available in DSpace on 2014-10-09T12:31:59Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:15Z (GMT). No. of bitstreams: 1 02571.pdf: 2380291 bytes, checksum: 94e6be3db24a9f0c5c1f13277cd435f2 (MD5) / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Four negative stains, hafnium chloride and europium, samarium and gadolinium nitrates, were tested in single particle electron microscopy as potential alternatives to uranyl acetate, which is recently being widely restricted for its toxicity. The new stains were applied to a structurally well-described plant photosystem I, visualized by a transmission electron microscope and classified in a single particle analysis. The quality of the stains was evaluated by the obtained resolution and ability to provide reliable structural information.

Made available in DSpace on 2014-06-11T19:35:07Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-07-31Bitstream added on 2014-06-13T20:06:30Z : No. of bitstreams: 1 rodrigues_ec_dr_araiq.pdf: 1115806 bytes, checksum: 386a1fe79443dfc59b7936e69cc0b5e7 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Foram sintetizados os 4-metoxibenzoatos de lantanídeos e ítrio trivalentes e no estado sólido. Esses compostos foram caracterizados e estudados utilizando-se as técnicas de análise elementar, complexometria, difratometria de raios x pelo método do pó, espectroscopia de absorção na região do infravermelho, termogravimetria-análise térmica diferencial simultânea (TG-DTA) e calorimetria exploratória diferencial (DSC). Os resultados permitiram obter informações sobre a estequiometria, desidratação, transformação polimórfica (transição de fase), modo de coordenação, comportamento térmico e decomposição térmica. / Solid 4-methoxybenzoates of trivalent lanthanides and yttrium have been synthesized. Elemental analysis, complexometry, X-ray powder diffractometry, infrared spectroscopy, simultaneous thermogravimetry and differential thermal analysis (TG-DTA), and differential scanning calorimetry (DSC) were used to characterize and to study the thermal behaviour of these compounds. The results led to information about the composition, dehydration, polymorphic transformation (phase transition), coordination mode, thermal behaviour and thermal decomposition of the isolated compounds.