The g-proteobacterium Shewanella oneidensis MR-1 reduces a wide range of terminal electron acceptors, including solid Fe(III) oxides. Pathways for Fe(III) oxide reduction by S. oneidensis include non-reductive (organic ligand-promoted) solubilization reactions, and either direct enzymatic, or indirect electron shuttling pathways. Results of the present study expand the spectrum of electron acceptors reduced by S. oneidensis to include the naturally occurring disulfide compounds cystine, oxidized glutathione, dithiodiglycolate, dithoidiproponiate and cystamine. Subsequent electron shuttling experiments demonstrated that S. oneidensis employs the reduced (thiol) form of the disulfide compounds (cysteine, reduced glutathione, mercaptoacetate, mercaptopropionate, and 2-nitro-5-thiobenzoate, cystamine) as electron shuttles to transfer electrons to extracellular Fe(III) oxides. The results of the present study indicate that microbial disulfide reduction may represent an important electron-shuttling pathway for electron transfer to Fe(III) oxides in anaerobic marine and freshwater environments.

Arsenic sorbs strongly to the surfaces of Fe(III) (hydr)oxides. Under aerobic conditions, oxygen acts as the terminal electron acceptor in microbial respiration and Fe(III) (hydr)oxides are highly insoluble, thus arsenic remains associated with Fe(III) (hydr)oxide phases. However, under anaerobic conditions Fe(III)-reducing microorganisms can couple the reduction of solid phase Fe(III) (hydr)oxides with the oxidation of organic carbon. When ferric iron is reduced to ferrous iron, arsenic is mobilized into groundwater. Although this process has been documented in a variety of pristine and contaminated environments, minimal information exists on the mechanisms causing this arsenic mobilization. Arsenic mobilization was studied by conducting controlled microcosm experiments containing an arsenic-bearing ferrihydrite and an Fe(III)-reducing microorganism, Geobacter metallireducens. Results show that arsenic mobility is strongly controlled by microbially-mediated disaggregation of arsenic-bearing iron nanoparticles. The most likely controlling mechanism of this disaggregation of iron oxide nanoparticles is a change in mineral phase from ferrihydrite to magnetite, a mixed Fe(III) and Fe(II) mineral, due to the microbially-mediated reduction of Fe(III). Although arsenic remained associated with the iron oxide nanoparticles and was not released as a hydrated oxyanion, the arsenic-bearing nanoparticles could be readily mobilized in aquifers. These results have significant implications for understanding arsenic behavior in aquifers with Fe(III) reducing conditions, and may aid in improving remediation of arsenic-contaminated waters. / Master of Science

Currently, the application of bioremediation requires extensive and costly monitoring due to limited understanding of the terminal electron accepting processes (TEAPs) that control biodegradation, which impairs the accurate quantification of contaminant mass loss. The measurement of redox conditions and evaluation of TEAPs are critical in assessing the capacity for bioremediation at any site. A series of batch microcosm experiments, using sediment collected from a gasoline-contaminated aquifer at Fort McCoy, Wisconsin, was designed to: 1) evaluate the role of Fe(III) in the development of TEAPs during biodegradation of benzene, toluene, ethylbenzene, and the xylenes (BTEX); 2) examine the biodegradation potential in different portions of the plume; and 3) compare methods of TEAP characterization. In general, the presence of Fe-oxides in microcosms inhibited methanogenesis. Although Fe-reducers did not actively degrade BTEX, Fe-reduction did occur, and most probable number (MPN) counts showed that added Fe(III) increased numbers of Fe-reducers in the microcosms. Methane production in microcosms constructed from sediment near the source area was ~5 times lower than levels produced by the mid-plume sediment. No Fe-reduction occurred in microcosms containing sediment from the source area. These results suggest that the source area has much lower biological activity than the mid-plume. TEAP characterization was conducted using a variety of methods, including geochemical indicators, redox dyes, MPN, and hydrogen concentrations. Monitoring of CH4 concentration yielded useful information in delineation of redox processes; Fe(II) monitoring was unreliable as a geochemical indicator. Redox dyes supplied basic information on reducing environments. MPN counts estimated microbial populations in lieu of faulty geochemical indicators, i.e., Fe(II). The measurement of H2 proved to be one of the more simple and reliable methods for TEAP identification. Results of this study indicate that TEAP characterization should include use of multiple methods; relying on geochemical indicators alone is not sufficient. / Master of Science

Neste trabalho, foram estudadas a oxidação do cicloexano e a epoxidação do (Z)- cicloocteno com iodosilbenzeno (PhIO) e H2O2 como oxidantes, comparando as FeIIIclorinas pentafluorossubstituídas com as FeIIIporfirinas, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl e [Fe(TF4TMAPP)](CF3SO3)5 como catalisadores em meio homogêneo e suportadas via ligação iônica e/ou covalente em matrizes de sílica quimicamente modificada. No caso do substrato (Z)-cicloocteno, os metalocomplexos utilizados levaram a rendimentos elevados para formação do ciclooctenóxido, tanto em meio homogêneo quanto heterogêneo, quando PhIO foi utilizado como oxidante. A atividade catalítica foi mantida mesmo após três reciclagens sucessivas. Com o H2O2 como oxidante, os rendimentos foram menores exceto com o metanol, quando se observa um aumento nos rendimentos de epoxidação, porque favorece a formação do intermediário ativo FeIIIhidroperóxido. Já os sistemas heterogeneizados apresentam desempenho bastante inferior quando comparado aos catalisadores em solução. Os melhores rendimentos foram observados com DCE um solvente mais viscoso que aumenta o tempo de vida da gaiola do solvente favorecendo o processo biomimético. Os catalisadores imobilizados foram caracterizados por espectroscopias UV-Vis e de RPE. Estas técnicas deram informações do estado de oxidação e de spin do metal, bem como a geometria do macrociclo na superfície da matriz sólida. Os resultados catalíticos puderam ser explicados pela natureza dos grupos funcionais que ligam o metalocomplexo à sílica, bem como, pelas informações fornecidas pela técnica de RPE quanto ao estado de oxidação do ferro e à geometria dos metalocomplexos imobilizados, dando consistência aos mecanismos propostos nos processos de oxidação. / In this work, the cyclohexane oxidation and the (Z)-cyclooctene epoxidation with iodosylbenzene (PhIO) e H2O2 as oxidants were studied. A comparison between fluorinated FeIIIchlorins and FeIIIporphyrins, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl, [Fe(TF4TMAPP)](CF3SO3)5 as catalysts was made either in solution or supported in silica matrices via eletrostatic interaction and/or covalent bonds. In the case of (Z)-cyclooctene epoxidation by PhIO, all the studied metallocomplexes achieved high yields for the epoxide production in both homogeneous and heterogeneous systems. The catalytic activity was maintained even after three successive recyclings. On the other hand, when H2O2 was used as oxidant the yields were lower. Differently, raised yields of epoxidation were observed when using methanol as solvent due to favored formation of the active intermediate FeIIIhydroperoxide. The performance of the heterogeneous systems was significantly lower than that of the catalysts in solution. The best yields were observed with DCE, a viscous solvent that probably raises the shelf life of the solvent cage favoring the biomimetic process. The supported systems were characterized by EPR and UV-Vis spectroscopies. These techniques gave information about the oxidation state and the metal spin, as well as the macrocycle geometry on the solid matrix surface. The catalytic results were explained by the nature of the functional groups that bound the metallocomplex to the silica matrix. In addition, the information obtained by the EPR technique regarding the state of oxidation of iron and the geometry of the supported metallocomplexes gave consistence to the proposed mechanisms in the oxidation processes.

Neste trabalho, foram estudadas a oxidação do cicloexano e a epoxidação do (Z)- cicloocteno com iodosilbenzeno (PhIO) e H2O2 como oxidantes, comparando as FeIIIclorinas pentafluorossubstituídas com as FeIIIporfirinas, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl e [Fe(TF4TMAPP)](CF3SO3)5 como catalisadores em meio homogêneo e suportadas via ligação iônica e/ou covalente em matrizes de sílica quimicamente modificada. No caso do substrato (Z)-cicloocteno, os metalocomplexos utilizados levaram a rendimentos elevados para formação do ciclooctenóxido, tanto em meio homogêneo quanto heterogêneo, quando PhIO foi utilizado como oxidante. A atividade catalítica foi mantida mesmo após três reciclagens sucessivas. Com o H2O2 como oxidante, os rendimentos foram menores exceto com o metanol, quando se observa um aumento nos rendimentos de epoxidação, porque favorece a formação do intermediário ativo FeIIIhidroperóxido. Já os sistemas heterogeneizados apresentam desempenho bastante inferior quando comparado aos catalisadores em solução. Os melhores rendimentos foram observados com DCE um solvente mais viscoso que aumenta o tempo de vida da gaiola do solvente favorecendo o processo biomimético. Os catalisadores imobilizados foram caracterizados por espectroscopias UV-Vis e de RPE. Estas técnicas deram informações do estado de oxidação e de spin do metal, bem como a geometria do macrociclo na superfície da matriz sólida. Os resultados catalíticos puderam ser explicados pela natureza dos grupos funcionais que ligam o metalocomplexo à sílica, bem como, pelas informações fornecidas pela técnica de RPE quanto ao estado de oxidação do ferro e à geometria dos metalocomplexos imobilizados, dando consistência aos mecanismos propostos nos processos de oxidação. / In this work, the cyclohexane oxidation and the (Z)-cyclooctene epoxidation with iodosylbenzene (PhIO) e H2O2 as oxidants were studied. A comparison between fluorinated FeIIIchlorins and FeIIIporphyrins, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl, [Fe(TF4TMAPP)](CF3SO3)5 as catalysts was made either in solution or supported in silica matrices via eletrostatic interaction and/or covalent bonds. In the case of (Z)-cyclooctene epoxidation by PhIO, all the studied metallocomplexes achieved high yields for the epoxide production in both homogeneous and heterogeneous systems. The catalytic activity was maintained even after three successive recyclings. On the other hand, when H2O2 was used as oxidant the yields were lower. Differently, raised yields of epoxidation were observed when using methanol as solvent due to favored formation of the active intermediate FeIIIhydroperoxide. The performance of the heterogeneous systems was significantly lower than that of the catalysts in solution. The best yields were observed with DCE, a viscous solvent that probably raises the shelf life of the solvent cage favoring the biomimetic process. The supported systems were characterized by EPR and UV-Vis spectroscopies. These techniques gave information about the oxidation state and the metal spin, as well as the macrocycle geometry on the solid matrix surface. The catalytic results were explained by the nature of the functional groups that bound the metallocomplex to the silica matrix. In addition, the information obtained by the EPR technique regarding the state of oxidation of iron and the geometry of the supported metallocomplexes gave consistence to the proposed mechanisms in the oxidation processes.

Outer membrane cytochromes OmcB and OmcS of Geobacter sulfurreducens are two important components of the respiratory chain for extracellular Fe(III) reduction. OmcS is a loosely bound cell surface protein involved in the reduction of insoluble Fe(III). OmcB is an outer membrane protein and required for insoluble and soluble Fe(III) reduction. The objective of this study was to understand better the mechanism of dissimilatory Fe(III) reduction, focusing on the cell surface proteins by further localization, identification of protein-protein interactions, and biochemical characterization of OmcB and OmcS. OmcB was found to be surface-exposed but embedded in the outer membrane because mild protease treatment of cells resulted in partial degradation of OmcB. Removal of surface-exposed proteins inhibited Fe(III) reduction, which is at least partially due to the degradation of OmcB. Co-immunoprecipitation studies with outer surface proteins using an antibody against OmcS revealed that OmcS interacts with several proteins, of which some are implicated in Fe(III) reduction, such as PilA, OmpJ, and OmpB, and in electricity production, such as OmcZ. Other OmcS-associated proteins, which have not been studied, include a cytochrome (GSU2887), a hypothetical and a conserved hypothetical protein, and a putative protease with a PDZ domain. The results suggest that co-immunoprecipitation with other antibodies would help to identify more elements of electron transport pathways related to extracellular Fe(III) reduction. OmcB was purified via preparative sodium dodecylsulfate polyacrylamide gel electrophoresis (SDSPAGE) and anion-exchange chromatography. The molecular mass was determined as 82 kDa, and 11.5 hemes per molecule were found. OmcB was able to transfer electrons to either soluble or insoluble Fe(III). OmcS was purified by detergent extraction. The molecular mass was 47 kDa and it contains 6 heme groups. UV-visible, EPR, and NMR spectroscopies determined that all hemes are bis-histidyl hexacoordinated and low-spin in both oxidized and reduced forms. OmcS has a –212 mV midpoint redox potential, and donates electrons to soluble and insoluble metals and quinones. Transient state kinetics showed that OmcS reduces anthroquinone-2, 6-disulfonate 10 times faster than it reduces Fe(III) citrate. This study revealed valuable further details about the mechanism of Fe(III) reduction by G. sulfurreducens by identifying the localization, protein-protein interactions and biochemical characteristics of the components of extracellular electron transport.

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Made available in DSpace on 2017-07-21T18:53:17Z (GMT). No. of bitstreams: 1 hanna.pdf: 1540428 bytes, checksum: 5ef484decfdf0f2847bc9b139292d514 (MD5) Previous issue date: 2007-02-15 / The phytic acid depending on the pH value presents high potential quelante, quelanting metallic ions, inhibiting the production of species reactivates of oxygen, responsible for the destruction oxidative in biological systems. That potential quelante has been basing several applied studies to the antioxidant action in foods products, in environmental controls and as antioxidant in the human organism. The objective of this work was to study the degree of interaction of the phytic acid with the metallic ions Fe(II) and Fe(III), of biological importance, in near conditions of the physiologic and the stability of these complexes. Potentiometric titration were driven to determine the constants of formation of the complexes phytic acid-Fe(II) and phytic acid-Fe(III) in solution, under conditions of inert atmosphere, it ionic strength 0,1 mol.L-1 (KCl) at 36±0,1 ºC. For the system phytic acid- Fe(II), were determined seven constant of formation, corresponding to seven species formed in the range p[H] from 2,0 to 12,0. The first constant of formation of the complex phytic acid- Fe(II), it presented log K = 16,06 for the specie [MHL]9-, indicating that a great affinity exists among the ligand monoprotonated with the metal. For the system phytic acid-Fe(III) were determined seven constant of formation, seven species were detected in the range p[H] from 2,5 to 12,0. The first constant of formation of the complex presented log K = 18,87, very high value for the species [ML]9-, this denoted a strong interaction among the ligand deprotonated and the metallic ion. Studies spectroscopy in the region of the UV-Vis, were performed to accompany the formation of the complexes of the phytic acid with the metallic ions Fe(II) and Fe(III). In the studies of UV-Vis of the phytic acid in absence of the metallic ions, not occurred any absorption in the area of wavelength from 200 to 800 nm. Already for the ligand in the presence of the metallic ions two absorption bands were detected in 216 and 279 nm for the phytic acid-Fe(II) and 218 and 274 nm for the phytic acid Fe(III). Those are bands of transfer of electrons of the ligand for the metallic ion with formation of the linking coordinative. The complexes phytic acid-Fe(II) and phytic acid-Fe(III) were synthesized from the data potentiometric and characterized by absorption spectroscopy in the area of the infrared. The spectra for the system phytic acid in presence of the ions Fe(II), synthesized in pH=7,4, and Fe(III), pH=7,1, showed displacements in the areas of frequency of the groups O=PO3H2 of the phytic acid free. Those displacements, evidence that the ligant is coordinated to the metallic ions. Through the termogravimetry it verified that in the interval from 30 to 780 ºC the loss of total mass of the complex phytic acid-Fe(II) it was of 24,43 %. Of the room temperature up to 185 ºC, occurred the liberation of molecules of hydration water. In superior temperatures of this value the mass losses were relative to the decomposition of the compound, with liberation of constitution water and decomposition of the organic matter, with formation of double pyrophosphate of potassium and Fe(II) and potassium metaphosphate. The phytic acid-Fe(III) complexes presented thermal behavior similar to the complex phytic acid-Fe(II), however for the complex phytic acid-Fe(III) synthesized in pH 7,1 the loss of total mass of it was of 25,64 % in the area from 30 to 800 ºC, while the compound synthesized in pH 9,9 presented a loss of total mass of 31,98 % in the interval of temperature from 30 to 845 ºC. The obtained data, for the three complexes, indicate that the ligand is coordinated with the metallic ions so much in values of low pH as to you value of higher pH. / O ácido fítico dependendo do valor de pH apresenta alto potencial quelante, complexando íons metálicos, inibindo assim a produção de espécies reativas de oxigênio, responsáveis pela destruição oxidativa em sistemas biológicos. Esse potencial quelante tem fundamentado diversos estudos aplicados à ação antioxidante em produtos alimentícios, em controles ambientais e como antioxidante no organismo humano. O objetivo deste trabalho foi estudar o grau de interação do ácido fítico com os íons metálicos Fe(II) e Fe(III), de importância biológica, em condições próximas às fisiológicas e a estabilidade destes complexos. Titulações potenciométricas foram conduzidas para determinar as constantes de formação dos complexos ácido fítico-Fe(II) e ácido fítico-Fe(III) em solução, sob condições de atmosfera inerte, força iônica 0,100 mol.L-1 (KCl) a 36±0,1 ºC. Para o sistema ácido fítico- Fe(II), determinaram sete constantes de formação, correspondente a sete espécies formadas na faixa de p[H] de 2,0 a 12,0. A primeira constante de formação do complexo ácido fítico- Fe(II), apresentou log K=16,06 para a espécie [MHL]9-, indicando que existe uma grande afinidade entre o ligante monoprotonado com o metal. Para o sistema ácido fítico-Fe(III) foram determinadas sete constantes de formação, sete espécies foram detectadas na faixa de p[H] de 2,5 a 12,0. A primeira constante de formação do complexo apresentou log K=18,87, valor muito elevado para a espécie [ML]9-, isto denotou uma forte interação entre o ligante totalmente deprotonado e o íon Fe(III). Estudos espectroscópicos na região do UV-Vis foram realizados para acompanhar a formação dos complexos do ligante com os íons metálicos Fe(II) e Fe(III). Nos estudos de UV-Vis do ácido fítico em ausência dos íons metálicos não ocorreu nenhuma absorção na faixa de comprimento de onda de 200 a 800 nm. Já para o ligante na presença dos íons metálicos foram detectadas duas bandas de absorção em 216 e 279 nm para o ácido fítico-Fe(II) e 218 e 274 nm para o ácido fítico Fe(III). Essas são bandas de transferência de elétrons do ligante para o íon metálico com formação da ligação coordenativa. Os complexos ácido fítico-Fe(II) e ácido fítico-Fe(III) foram sintetizados a partir dos dados potenciométricos e caracterizados por espectroscopia de absorção na região do infravermelho. Os espectros para o sistema ácido fítico em presença do íon Fe(II), sintetizado em pH=7,4, e Fe(III), pH=7,1, mostraram deslocamentos nas regiões de freqüência dos grupamentos O=PO3H2 do ácido fítico livre. Esses deslocamentos evidenciam que o ligante encontra-se coordenado aos íons metálicos. Através da termogravimetria constatou-se que no intervalo de 30 a 780 ºC, a perda de massa total do complexo ácido fítico-Fe(II) foi de 24,43 %. Da temperatura ambiente até 185 ºC, ocorreu a liberação de moléculas de água de hidratação. Em temperaturas superiores deste valor as perdas de massa foram relativas à decomposição do complexo, com liberação de água de constituição e decomposição da matéria orgânica, com formação de pirofosfato duplo de potássio e Fe(II) e metafosfato de potássio. Os complexos ácido fítico-Fe(III) apresentaram comportamento térmico semelhante ao complexo ácido fítico-Fe(II), porém, para o complexo ácido fítico-Fe(III) sintetizado em pH 7,1 a perda de massa total do foi de 25,64 % na faixa de 30 a 800 ºC, enquanto que o complexo sintetizado em pH 9,9 apresentou uma perda de massa total de 31,98 % no intervalo de temperatura de 30 a 845 ºC. Os dados obtidos, para os três complexos, indicam que o ligante encontra-se coordenado com os íons metálicos tanto em valores de pH baixo como em valores de pH mais elevados.

Made available in DSpace on 2015-05-14T13:21:30Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1275793 bytes, checksum: 6f184080723f11f294f29a4ddad08f39 (MD5) Previous issue date: 2013-08-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this study a flow-batch analyzer (FBA) was utilized and its performance was evaluated for the determination of Fe(III) in edible without external pretreatment. The FBA method uses the reaction between Fe(III) and thiocyanate in organic medium. The formed red complex was monitored by employing a light emitting diode (LED, λmax = 520 nm) and a phototransistor linked to the mixing chamber by optical fibers. All standard solutions were prepared in-line and all analytical processes were carried out by simply changing the operational parameters in FBA control software. Comparing with the reference method, no statistically significant differences were observed when applying the paired t-test at a 95% confidence level. For the three types of samples studied the estimated standard deviation was less than 0.03 mg kg-1 (n = 3). The analytical frequency was 95 h-1, the limit of detection was 0.004 mg kg-1 and the limit of quantification was 0.013 mg kg-1. The recovery study shows results between 98.4% and 104.2%. The FBA method showed better analytical features when compared with previous automatic flow methods. Thus, the automated method proposed is potentially useful as an alternative for the determination of other ions in similar samples or in other viscous matrices without external pretreatment. / Neste estudo, um analisador em fluxo-batelada (FBA) foi desenvolvido e seu desempenho foi avaliado na determinação de Fe (III) em óleos comestíveis sem pré-tratamento da amostra. O método utiliza a reação entre os íons Fe(III) e o tiocianato solubilizado em meio orgânico. O complexo vermelho formado foi monitorado utilizando um diodo emissor de luz (LED, λmax = 520 nm) e um fototransistor acoplados ao interior da câmara de mistura por meio de fibras ópticas. As soluções-padrão foram preparadas em linha e todas as etapas de análise foram efetuadas através de simples alterações nos parâmetros operacionais no programa de gerenciamento do sistema. Ao comparar os resultados obtidos com o método proposto e com o de referência, não foram observadas diferenças estatisticamente significativas ao se aplicar o teste t pareado com nível de confiança de 95%. Para os três tipos de amostras em estudo o desvio-padrão relativo estimado foi menor que 0,03 mg kg-1 (n = 3). A frequência analítica foi de 95 h-1, o limite de detecção foi 0,004 mg kg-1 e o limite de quantificação foi de 0,013 mg kg-1. Estudos com amostras fortificadas mostraram resultados de recuperação entre 98,4% e 104,2% para ambas as matrizes. De modo geral, o método proposto apresentou melhor desempenho analítico quando comparado com analisadores em fluxo automático anteriores. Assim, o método automático proposto é potencialmente útil como uma alternativa para a determinação de outros íons em amostras semelhantes aos óleos investigados ou em outras matrizes viscosas sem necessidade de um pré-tratamento.