Ce travail est consacré à l'étude du dopage de la polyaniline et de ses dérivés substitutés (polyanisidine, poly(2-ethylaniline)) avec d'une part le chlorure d'aluminium AlCl3 ou le chlorure ferrique FeCl3, d'autre part avec leurs dérivés contenant les ligands mixtes chlorure-acétylacétonate (AlCl2(acac) ou (FeCl(acac)2). Les polymères dopés avec AlCl3 ou FeCl3 sont conducteurs, et leur conductivité électronique est de l'ordre de 10-3 S/cm. Des études spectroscopiques complémentaires (UV-VIS-Proche IR, IRTF, RPE, RMN du noyau 27Al (dans le cas du dopage avec AlCl3) et spectroscopie Mössbauer sur le noyau 57Fe (dans le cas du dopage avec FeCl3)), combinées avec l'analyse élémentaire, permettent de comprendre et d'identifier un même mécanisme de dopage. Celui-ci correspond en un premier temps à une dissociation de la molécule du dopant. La partie cationique résultant de cette dissociation est complexée sur les sites azote de type imine de la chaîne du polymère, tandis que la partie anionique s'incorpore à la matrice polymère afin de neutraliser la charge positive imposée à la chaîne du polymère. La sphère de coordination du complexe cationique est complétée par solvatation avec une molécule de nitrométhane. Le réarrangement des charges accompagnant le processus de dopage entraîne la création de radicaux cationiques mobiles sur la chaîne du polymère, donnant ainsi au polymère dopé des propriétés de conduction électronique. Ce mécanisme rend parfaitement compte de la présence de porteurs de charge et de la structure cationique des radicaux de la chaîne polymérique dopée mises en évidence par les expériences de spectroscopie RPE et d'absorption UV-VIS-Proche IR. La polyaniline dopée avec FeCl3 présente de faibles propriétés mécaniques, qui peuvent cependant être améliorées par un traitement ultérieur avec l'hexafluoroacetylacetone (HFAA). Ce traitement conduit à la transformation de la polyaniline dopée avec FeCl3 (acide de Lewis) en un polymère dopé avec HFeCl4 (acide de Brönsted), simultanément plastifié par HFAA. Le dopage avec les ligands mixtes (AlCl2(acac) ou (FeCl(acac)2), bien qu'inopérant en ce qui concerne la polyaniline, conduit clairement au dopage de la polyanisidine et de la poly(2-éthylaniline). Les chaînes de ces polymères dopés présentent une structure radicalaire cationique mise en évidence par les expériences d'absorption UV-VIS-Proche IR ; mais le mécanisme de dopage reste plus complexe à définir que dans le cas du dopage avec AlCl3 ou FeCl3. Le dopage avec AlCl2(acac) conduit à un polymère dopé avec AlCl3 avec Al(acac)3 incorporé à la matrice du polymère comme sous-produit. Le dopage avec FeCl(acac)2 donne un composé présentant davantage de sites de fer non équivalents qu'il en est attendu ; leur nature reste difficile à identifier par spectrométrie Mössbauer.

Iron is an essential element for life. It is involved in a number of biological processes, including iron sulfur (Fe/S) cluster assembly and heme biosynthesis. However it is also potentially toxic due to its ability to induce formation of reactive oxygen species (ROS) via Fenton chemistry. Therefore its uptake, trafficking and utilization must be regulated to avoid its toxicological effect. It has been recently discovered that Fe/S cluster biosynthesis machinery plays a key role in the cellular iron regulation and its disruption leads to impaired iron regulation and iron accumulation within mitochondria. The iron accumulation resulted from impaired Fe/S cluster assembly in the eukaryotic model organism Saccharomyces cerevisiae (baker’s yeast) was studied. Various biophysical (e.g. Mössbauer, EPR, UV-vis spectroscopy) and biochemical (e.g. Western blots, PCR, enzyme activity assay, etc.) techniques were used to characterize the iron content in yeast mitochondria isolated from several mutants strains. In these mutants one of the proteins involved in Fe/S cluster biosynthesis (Yah1p and Atm1p) is mutated and iron regulation and metabolism are disrupted. By integrating the results obtained from these different methods, it was determined that excess iron accumulates in the mutant mitochondria as inorganic phosphate Fe(III) nano-particles exhibiting superparamagnetic behaviors. Oxygen is required for iron accumulation and nanoparticle formation. The Fe(III) nano-particles can be chemically reduced to Fe(II) then largely exported from the mitochondria. These biophysical and biochemical methods were also used to examine the iron distribution in whole yeast cells of the Aft1-1up strain in which iron regulon genes are constitutively activated and compared to that of Yah1p-depleted and wild type yeast. Constitutive activation of iron regulon genes does not alter the cellular iron distribution significantly. However disruption of Fe/S cluster assembly by Yah1p depletion causes dramatic cellular iron redistribution: the vacuolar iron is largely evacuated and most of the cellular iron probably precipitates in mitochondria as Fe(III) nanoparticles. The results provide novel insights into iron trafficking and possible signal communications between organelles within cells.

In this work, interference and coherence phenomena, appearing in atomic and molecular ensembles interacting with coherent light sources, as electromagnetically induced transparency (EIT), coherent population trapping (CPT), and slow group velocity of light are investigated. The goal of the project is to make the steps towards various applications of these phenomena, first, by studying them in solid media (which are the most advantageous for applications), second, by suggesting some novel applications such as CPT-based plasma diagnostics, and realization of new types of solid-state lasers (based on suppression of excited-state absorption via EIT). The third goal of the project is extension of coherence and interference effects well-known in optics to the gamma-ray range of frequencies and, correspondingly, from atomic to nuclear transitions. A particular technique of chirped pulse compression applied to M??ossbauer transitions is considered and the possibility of compression of M??ossbauer radiation into ultrashort gamma-ray pulses is analyzed. The theoretical treatment of the interference and coherence effects is based on the semiclassical description of atom-light interaction, which is sufficient for correct analysis of the phenomena considered here. Coherent media are considered in two-, three-, and four-level approximations while their interaction with light is studied both analytically and numerically using the Maxwell-Bloch set of equations.

A suite of lightning strike glasses and unmelted starting materials has been studied by electron microscope and Mossbauer spectroscopy to determine Fe oxidation states. Nine of eleven samples are reduced compared to the starting materials; four of the glasses contain Fe0. Only one sample contained evidence of reduction by carbon, and the results support the reduction of Fe as intrinsic to the rapid, high temperature processing during lightning strikes.A thermodynamic modeling code is used to model the formation of moldavite tektites and the reduction of Fe from sediments around the Ries crater. During isentropic cooling from a strong shock, Fe3+ is reduced to Fe2+ at all modeled conditions. The best matches to an average moldavite composition and the compositions of the Bohemian and Bohemian:Radomilice sub-strewn fields occur with a mixture of surface and subsurface sands along a 4500 J/kg-K isentropic cooling path, consistent with an asteroid impact. The Lusatian and Moravian sub-strewn fields are better represented by starting materials of entirely surface sands, consistent with the uppermost layers of surface material having traveled the farthest from the impact.The thermodynamic code is also used to investigate the formation of lunar regolith agglutinates and reduction of Fe to Fe0. Forming Fe0 requires assuming Fe0 is miscible in silicate liquid at elevated temperatures and pressures. When Fe0 is included in the liquid solution, it is stable at modeled conditions. Simple separation of liquid from vapor is not sufficient to reproduce agglutinate glass. When the vapor phase is allowed to partially redeposit and some Fe0 is directly condensed from vapor, the resulting liquid better reproduces mare agglutinate glasses. This model cannot reproduce highland agglutinate glass, because the Al concentration remains too high in the liquid. The best match to mare glass is produced using the <10 µm fraction of the mare soil along the 8000 J/kg-K cooling isentrope at 100 bars, 4370 K with 95% vapor redeposition and 50% of the Fe(g) directly condensed as Fe0. The reduced fulgurite samples and the results of the impact models suggest that Fe reduction is intrinsic to the rapid, high temperature processing of silicates.

The study of magnetic properties and structures of Zn and Cd substituted mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray diffraction on powdered samples at about 300 K. Two series of mixed ferrites, (Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0) were synthesized. In the former series the effect of simultaneous site dilution by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated and in the latter the effect of single site dilution by Zn or Cd is also studied. The Mossbauer spectra show that the compounds transform with increase in x from ordered to disordered magnetic states. Systematic decrease in the hyperfine fields indicating weakening of the magnetic coupling with an increase in x is observed. We report the presence of a cross over effect with respect to the hyperfine fields on A and B sites at low concentration of diamagnetic ions in the simultaneously diluted series. Both series of compounds show no significant changes in isomer shifts with x. Differences in the evolution of Fe atoms on A and B sites between Zn and Cd based compounds are observed. The results of our analysis show that Zn and Cd ions occupy both tetrahedral and octahedral sites. The spinel structure of the compounds studied in this work is confirmed by X-ray diffraction (XRD). The lattice parameters derived from XRD show systematic change with x consistent with Vergard's law. In Cd based samples an increase of the lattice parameter with x is explained on the basis of the size difference of the cations involved. However, an anomalous behavior of the lattice parameter is observed in Zn based samples. The average grain sizes of the samples were determined from the line width of the (311) XRD intensity lines using the Scherrer formula. These vary between 50 nm and 70 nm for all the samples except for Zn and Al substituted samples which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The porosity, x-ray and bulk densities of the samples are also presented. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

The significant role that nitric oxide plays in human physiology is linked to the ability of NO to bind to iron forming mono-nitrosyl iron complexes. Protein-bound and low-molecular-weight dinitrosyl iron complexes (DNICs) are known to form in excess NO. Studies of such biological DNICs have relied on their paramagnetism and characteristic EPR signal of g value of 2.03. It has been suggested that DNICs act in vivo as NO storage (when protein-bound) and transfer agents (when released by, for example, free cysteine). Biological DNICs, mainly resulting from iron-sulfur cluster degradation, are difficult to extract and isolate, thereby preventing their full characterization. Thus, development of synthetic DNICs is a promising approach to model and better understand the formation and function of biological DNICs, the scope of donor ligands that might coexist with Fe(NO)2 units, the redox levels of bio-DNICs, and establish other spectroscopic techniques appropriate for characterization. A series of N-heterocyclic carbene (NHC) and imidazole (Imid) complexes has been characterized as mimics of histidine-containing DNICs. The pseudo-tetrahedral L2Fe(NO)2 complexes have NO stretching frequencies and redox potentials that suggest the NHCs are slightly better donors than Imids, however the two types of ligands have similar steric properties. Both the EPR-active, {Fe(NO)2}9 and the EPR-silent, {Fe(NO)2}10 states can be accessed and stabilized by the NHC. Nitric oxide transfer studies have shown that only the {Fe(NO)2}9 complexes are capable of transferring NO to a suitable NO trapping agent. Deprotonation of the distal nitrogen functionality in the imidazolate ligands of [(Imidazole)2Fe(NO)2]- leads to aggregation forming molecular squares of {Fe(NO)2}9 units bridged by the imidazolates. These interesting tetrameric complexes are examined by X-ray diffraction, EPR, and Mössbauer studies. The paramagnetic tetrameric complexes have multiple redox events observed by cyclic voltammetry. Mössbauer spectral data of the tetrameric complexes are compared with Mössbauer data obtained for a series of NHC-containing DNICs. Iron and cobalt-containing mononitrosyl N2S2 model complexes of the nitrile hydratase enzyme active site demonstrate sulfur-based reactivity resulting in the formation of polymetallic complexes. In all cases, shifts in the nitrosyl stretching frequencies demonstrate substantial transfer of electron density from the (NO)M(N2S2) moiety to the metal-acceptor site.

Investigam-se no presente trabalho as relações entre a composição superficial e as propriedades mecânicas e tribolõgicas de aços carbono implantados com nitrogenio. Os resultados dos testes de propriedades mecanicas e tribolõgicas foram extraídos da literatura. A análise da composição su perficial fdi realizada através da espectroscopia Wissbauer de elétrons de conversão (CEMS) e de raios-X de conversão (CXMS). Recozimentos em alto vácuo foram realizados para simular o aumento de temperatura nos processos tribolõgicos reais. Os resultados obtidos mostram que hã uma tendência para pre cipitação de carbonitretos de ferro, finamente distribuídos, em aços carbono implantados com nitrogénio. A quantidade de carbono pré-existente desempenha um papel relevante nessa tendência. Mostra-se que a melhoria das propriedades mecânicas e tribo lOgicas de aços carbono implantados com nitrogenio e fundamentalmente devida ao mecanismo de endurecimento por precipitação. Mostra- se também que a persistencia do efeito protetor em profundida des muito maiores do que a camada implantada, está associada com a difusão do nitrogenio liberado pela decomposição térmica dos com postos superficiais. / The relationships between the surface composition and the mechanical and tribological properties of carbon steels implanted with nitrogen were investigated. The results from the mechanical and tribological tests were extracted from the literature. The surface composition analysis was. performed with the conversion electron and X-ray Mdssbauer spectroscopy (CENS and CXMS). Thermal annealing was performed in high vacuum, in order to simulate the temperature increase in real tribological processes. The obtained results shown the tendency to iron carbonitrides precipitation, finely dispersed, induced by nitrogen implantation into carbon steels. The amount of carbon pre-existent plays a relevant rõle in this trend. It is shown that the improved mechanical and tribological performance of nitrogen-implanted carbon steels are mainly due to the precipitation hardening mechanism. It is shown also that the persistence of the protective action at greater depths is associated with the in-diffusion of nitrogen released by thermal decomposition of the compounds formed at the surface.

o FeP04 nas condições ambiente cristaliza em uma estrutura tipo berlinita, que é análoga ao quartzo. O estudo do comportamento sob pressão de compostos isoestruturais ao quartzo é importante tanto do ponto de vista tecnológico quanto de Geociências. No FeP04, transformações de fase ocorrem a pressões particularmente baixas, o que o torna um sistema modelo particularmente interessante para o estudo dessa classe de compostos. Nesse trabalho, foi investigada a composição de fases de amostras de FeP04 de alta pureza processadas sob alta pressão (1,5 GPa, 2,5 GPa, 4,0 GPa e 7,7 GPa) e temperaturas de até 300°C, em uma câmara de alta pressão do tipo toroidal. O uso de um aquecimento moderado é uma garantia que o tratamento térmico atua como um alterador das condições cinéticas e nâo das condições de estabilidade termodinâmica. Isso permite que se dêem condições para o sistema evoluir para a situação de equilíbrio, permitindo a identificação de eventuais fases metaestáveis. As amostras foram estudadas usando diferentes técnicas de análise estrutural: difração de raios X, espectroscopia Raman e espectroscopia Mossbauer. Os resultados não indicaram a coexistência de fases de alta pressão cristalinas e amorfas, como previamente referido na literatura. Para a amostra processada a 1,5 GPa e 300°C, foi observada a formação de uma nova fase cristalina, não identificada em trabalhos anteriores. Para amostras processadas a pressões de 2,5 GPa, ou maiores, foi confirmada a formação da fase tipo Cmem, de acordo com outros autores. No entanto, essa fase sempre coexiste com outra fase minoritária, que parece ser uma deformação da estrutura produzida em pressões mais baixas. / At ambient conditions, FeP04 crystallizes in a berlinite-type structure, which is anaIogous to the quartz structure. A better understanding of the pressure behavior of quartz-like materiaIs is important not only in Geosciences but also for several technological appIications. The pressure induced phase transitions in FeP04 happen at reIativeIy Iow pressures, which makes this compound a very convenient model for the study of this class of materiaIs. ln this work, we have investigated the phase composition of high-purity FeP04 sampIes previously submitted at high-pressure (1.5 GPa, 2.5 GPa, 4 GPa, and 7.7 GPa) and temperatures up to 300°C in a toroidal-type high-pressure chamber. The empIoyment of moderate heating assures that the thermal treatment only changes the reaction kinetics, but not the thermodynamics stabiIity conditions. This enabIes the system evolution for an equiIibrium state, and the identification of possible metastabIe phases. The sampIes have been studied by several techniques of structural anaIysis: X-ray difIraction, Raman spectroscopy, and Mossbauer spectroscopy. The resuIts do not give any evidence for the coexistence of amorphous and crystalline high-pressure phases, as referred in the literature. For the sampIe processed at 1.5 GPa and 300°C, we observed the formation of a new crystalline phase, which was not identified in previous works. For the samples processed at 2.5 GPa, or higher, we confirmed the formation of a phase with Cmem symmetry, in agreement with other authors. However, this phase aIways coexists with a minor phase that seems to be a deformation of a structure produced at Iower pressures.

Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-06-21T12:54:56Z No. of bitstreams: 1 texto completo.pdf: 2722629 bytes, checksum: 4eef2d96be645ea417447cc013733a98 (MD5) / Made available in DSpace on 2017-06-21T12:54:56Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2722629 bytes, checksum: 4eef2d96be645ea417447cc013733a98 (MD5) Previous issue date: 2002-11-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A drenagem ácida é um problema ambiental capaz de comprometer a qualidade dos recursos hídricos, que decorre da oxidação de sulfetos. A adoção de medidas corretivas ou preventivas depende de uma correta avaliação, não apenas do potencial de geração ácida, mas também da velocidade em que esse processo ocorre. Supõe-se que a cinética de oxidação dos sulfetos está na dependência das características químicas e mineralógicas das amostras, em particular do tamanho e da cristalinidade dos sulfetos presentes. Assim sendo, o presente trabalho foi conduzido com o objetivo de identificar as características químicas e mineralógicas que mais influenciam na dinâmica de geração ácida de amostras provenientes de ambientes geoquímicos distintos, bem como sugerir métodos rápidos para se avaliar a cinética de oxidação de sulfetos. Foram utilizadas amostras de substratos rochosos, em diferentes graus de intemperismo, contendo sulfetos provenientes de distintas províncias geológicas do Brasil, relacionadas à mineração de ouro, carvão, zinco, chumbo, níquel e urânio, além de um solo tiomórfico. As amostras de geomateriais, moídas a 0,149 mm, foram caracterizadas por meio de análises químicas incluindo pH, teores totais de elementos maiores e menores, potencial de acidificação, potencial de neutralização e balanço ácido-base. A caracterização mineralógica foi feita por difratometria de raios-x, espectroscopia Mössbauer, magnetização de saturação e microscopia eletrônica de varredura, com ênfase nos sulfetos. A cinética de oxidação dos sulfetos, presentes nas amostras, foi avaliada por meio de experimento de intemperismo simulado, em que as amostras foram submetidas à oxidação, em condições de laboratório, sob diferentes doses de H 2 O 2 e CaCO 3 , por um período de 357 dias. A solução em contato com as amostras foram drenadas a cada 21 dias, determinando-se o pH, acidez titulável e concentrações de S-sulfato, As, Cu, Cd, Fe, Mn, Ni, Pb e Zn, na solução de equilíbrio. Os resultados obtidos permitem concluir que o método do balanço ácido-base (BAB) não foi eficiente para se avaliar a capacidade de geração ácida de todas as amostras, em particular do substrato de rocha ultrabásica. Com exceção dos carbonatos e sulfetos, os demais minerais presentes nas amostras não apresentaram influência marcante na cinética de geração de drenagem ácida. A taxa de geração ácida foi determinada, primordialmente, pelo tamanho dos cristais dos sulfetos, sendo que a presença de pirita framboidal , pirrotita e marcassita imprimiu um ritmo particularmente acelerado na cinética de oxidação, em relação aos outros sulfetos. As expectativas de desenvolvimento de um método analítico capaz de simular a cinética de drenagem ácida, comum para amostras de naturezas geoquímicas distintas, foram pouco promissoras nas condições experimentais utilizadas. / Acid drainage is an environmental problem that affects the quality of water, which arises from sulfide oxidation. Adopting corrective or preventive measures depends on a suitable evaluation of not only the acid generation potential, but also on the reaction kinetics. It is hypotesized that the kinetics of sulfide oxidation depends on the chemical and mineralogical characteristics of samples, especially the size and cristalinity of sulfides. Nevertheless, ranking those characteristics based on the relative importance is still a matter of debate. Thus, the present work was performed in order to identify the chemical and mineralogical features that influences the acid generation dynamics in samples from different geochemical environments, as well as to suggest fast methods to evaluate the kinetics of sulfide oxidation. Samples of rocky substrats, on diferents weatering grades, containing sulfides from different geological provinces of Brazil, related to the mining of gold, coal, zinc, lead, nickel and uranium, and a thiomorphic soil were used. The samples were characterized through chemical analyses including pH, total contents of major and minor elements, acidification potential, neutralization potential and acid-base accounting (ABA). The mineralogical characterization was made by X-ray difractometry, Mössbauer spectroscopy, magnetization saturation and scanning electronic microscopy, with emphasis in sulfides. The kinetics of sulfide oxidation in samples was evaluated through simulated weathering experiment by submitting the samples to the oxidation at in vitro conditions, under different doses of H 2 O 2 and CaCO 3 , during a 357 days period. The equilibrium solutions were drained every 21 days, in order to determine pH, tritable acidity and S- sulfate, As, Cd, Fe, Mn, Ni, Pb and Zn concentrations. The results showed that the ABA method was not efficient to evaluate the acid generation potential overall the samples, especially to the ultrabasic rocky substrat. Excepting the carbonates and sulfides, other minerals in the samples did not influence the kinetics of acid drainage generation. The acid drainage rate was primarily determined by the size of the sulfides crystals, and the xpresence of framboidal pyrite, pyrrhotite and marcasite promoted a particularly fast rate to the oxidation kinetics. Expectations for developing a common static method that simulates the kinetics of acid drainage, suitable for all samples of different geochemical natures, were poorly promising at these experimental conditions.

O campo hiperfino e o gradiente de campo elétrico (GCE) foram obtidos experimentalmente, no intervalo de temperatura de 4,2°K até 700°K, através da tecnica do efeito Mössbauer no Fe57, para o composto intermetálico HfFe2 tipo fase de Laves e para os compostos "pseudo binários" HfFe2-xSix com x=0,05;0,1;0,3. / Hyperfine fields and the electric field gradient (EFG) were experimentally obtained, in temperature interval of 4.2 K to 700 K for the laves phase intermetalic compound HfFe2 and for the "pseudo" thernary compounds HfFe2-xSix with x= 0.05 ;0.1; 0.3.