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Ressonancia paramagnetica eletronica de centros de hidrogenio em vidros alumino-boratos de bario. / Electron Paramagnetic Resonance of hydrogen centers in glasses aluminum barium borate.Walter Maigon Pontuschka 27 August 1979 (has links)
As diferentes formas com que o hidrogênio pode ocorrer nos vidros alumino-boratos de bário, ora na formação de ligações covalentes, ora ocupando posições intersticiais formando centros atômicos foram investigados por ressonância paramagnética eletrônica (RPE) e por medidas complementares de absorção no infravermelho. O estudo de cinética do centro de hidrogênio intersticial H IND. i revelou a presença de três tipos de armadilhas, com energias de ativação de (O,32±O,06}eV; (O,15±0,02}eV e (0,10±0,02}eV. Um estudo experimental da cinética do centro de elétron do boro (BEC), descoberto por D.L. Griscom, também foi realizado, incluindo o decaimento do BEC por exposição à luz visível, o que produziu o aumento de centros H IND. i observados por RPE, indicando a presença de centros H IND. i, ou prótons. Por outro lado, medidas de absorção no infravermelho de vidro hidrogenado revelaram a presença de pontes O-H...O. As distâncias entre átomos de oxigênio que encontramos são 2,69; 2,71 e 2,715 A SOB. 0. Sugerimos que a cada distância corresponde o lado de um polígono da cadeia de B-O, formadora do vidro. Propomos um modelo para o centro H IND. i, no qual os átomos de hidrogênio são capturados pelos polígonos por meio de forças atrativas de van der Waals. Avaliando a energia de van der Waals para polígonos de n lados e 2,70 A SOB. 0 de aresta, comparamos os resultados com as energias de ativação fornecidas por RPE, para determinar os números de lados dos polígonos (n = 5, 6 e 7). Acrescentamos a este trabalho um estudo de RPE de centros de prata em vidros alumino-boratos de bário irradiados com raios X a 77K. Em contraste com o que acontece com o hidrogênio, a presença de prata nos vidros altera consideravelmente as dimensões dos anéis de B-O. A constatação da ausência de centros sugere que a prata encontra dificuldade para difundir nestes vidros. / The different ways in which hydrogen can occur in barium alumino-borate glasses, either forming covalent bonds, or occupying interstitial positions forming atomic centers, were investigated by electron paramagnetic resonance (EPR) and complementary infrared absorption measurements. A study of the kinetics of interstitial hydrogen centers Hi0 revealed the presence of the three kinds of traps, whose activation energies are (.32 ± .06) eV; (.l5±.02)eV and (.l0±.02)eV. An experimental study of the kinetics of boron electron centers (BEC) was also carried out, including the decay of BEC when exposed to visible light. This exposure produced an increase of Hi0 centers, as observed by EPR, indicating the presence of Hi+ centers, or protons. On the other hand, I.R. absorption measurements of hydrogenated glass revealed the presence of O-HO bonds. The distances between oxygen atoms were found to be 2.69; 2.71; and 2.715 A. We suggest that each of these distances corresponds to a side of a polygon of the chain of B-O in the glass network. We propose a model for the Hi0 center where the hydrogen atoms are trapped by the polygons by means of attractive van der Waals forces. Evaluating the van der Waals energy for polygons of n sides, each side measuring 2.70 A, we compared the results with activation energies given by EPR, to determine the number of sides of the polygons (n= 5, 6 and 7). We studied, in addition, the EPR spectra of silver centers in barium alumino-borate glasses irradiated with X-rays at 77 K. In contrast to the behavior of hydrogen, the presence of silver in the glasses produces considerable alterations in the dimensions of the rings of B-O. The absence of Ag2+ suggests that silver has difficulty in diffusing in these glasses.
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Contribuição do exchange na largura de linha de ressonância paramagnetica eletrônica do ion N POT. 2+ / Contribution of exchange in line width of the electron paramagnetic resonance ion \'N2 + I\'.Jose Carlos Sartorelli 24 June 1982 (has links)
Efetuamos medidas de RPE nos seguintes sais hexahidratados: fluorborato de níquel (Ni (BF IND. 4) IND. 2 6 H IND. 2 O) , perclorato de níquel (Ni(Cl O IND. 4) IND. 2 6 H IND. 2 O) e fluorsilicato de níquel (NiSi F IND. 6 6 H IND. 2 O). Os parâmetros da hamiltoniana de spin deste último sal foram redeterminados no intervalo de 100 K à 323 K. Os nossos resultados de RPE indicam a existência de anomalias no intervalo 153 K a 273 K que caracterizam uma transição de fase. Estudamos também as larguras de linha dos sais acima, separando as contribuições devido à interação spin- spin e a relaxação spin- rede. Os valores destas contribuições concordam perfeitamente com os calculados a partir de modelos teóricos. Desenvolvemos uma nova forma de linha que dá excelentes ajustes, por mínimos quadrados, das curvas experimentais. / We have performed EPR measurements in the following hexahidrated salts: nickel fluorborate (Ni(BF4)2 6H2O), nickel perchlorate (Ni(Cl04) 2 6H2O) and nickel fluorsilicate (NiSiF6 6 H20). The spin hamiltonian parameters of the last salt were determined once again in the range 100 - 323K. Our results of EPR indicate anomalies in the range 153 - 273K, which characterize a phase transition. Line widths of the above salts were also studied separating the contributions given by spin-spin interaction and spin-lattice relaxation. The values of these contributions agree with theoretical calculations. We have developped a new line form, which gives excellent fits, by least square fit, for the experimental data.
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Ressonância paramagnética eletrônica do fluorborato de zinco hexahidratado dopado com Mn2+ / Electron paramagnetic resonance of zinc fluoroborate hexahydrate doped with Mn2 +Eduardo di Mauro 04 April 1983 (has links)
Estudamos monocristais de Zn(BF4)26H2O dopados com Mn2+ no intervalo de temperatura de 94K à 353K empregando a técnica de Ressonância Paramagnética Eletrônica (RPE). Determinamos todos os parâmetros da Hamiltoniana de spin. Constatamos que o fator espectroscópico g = 2,000 ± 0,001 é constante com a temperatura. Calculamos o parâmetro D e através da curva de D versus T confirmamos a existência de uma transição de fase à 181K. Verificamos que este parâmetro D apresenta variação linear com a temperatura acima de 200K (D= (127 + 0,228T) Gauss), o que está de acordo com a previsão do modelo de Walsh. Com os espectros obtidos da variação angular do eixo c do cristal em relação ao campo magnético externo, constatamos que os resultados experimentais estão em excelente acordo com a teoria. Concluímos que o campo cristalino tem simetria trigonal em toda a faixa de temperatura pesquisada. / We have studied monocrystals of Zn(BF4)26H2O doped with Mn2+ in the range of the temperature of 94K to 353K employing the technics of Electron Paramagnetic Resonance (EPR). We have determined all the parameters of the spin Hamiltonian. We have verified that the temperature. We have calculated the parameter D and through the curve of D versus T confirmed the existence of a phase transition at 181K. We have verified that this parameter D shows linear variation with the temperature above 200K (D= (127 + 0,228T) Gauss), which agrees with the prevision of the Walshs model. With the spectra of the angular variation of the c axis of the crystal in relation to extern magnetic field, we have verified that the experimental results are in excellent agreement with the theory. We have concluded that the crystal field has trigonal symmetry in all range of temperature investigated.
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Spectroscopic and analytical characterization of the distribution of iron in intact mitochondria from Saccharomyces cerevisiaeHudder, Brandon Neal 30 October 2006 (has links)
Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy were used to examine the distribution of iron in mitochondria from Saccharomyces cerevisiae. These organelles were packed into EPR and Mössbauer cuvettes, affording spectra with unprecedented signal/noise ratios. EPR spectra of as-isolated intact mitochondria exhibited fourteen distinct signals, some of which were assigned according to previously reported g-values obtained using isolated proteins. Signals from adventitious manganese (II) and iron (III) were largely removed when mitochondria were isolated in buffers supplemented with the metal chelators EDTA or EGTA. Signals were simulated and intensities were quantified to afford spin concentrations and estimates of the concentration of EPR-active species in mitochondria. The effects of treating samples with chemical modifiers were examined. Packed samples were analyzed for protein and metal content, affording averaged values of 50 mg/mL [protein], 590 õM [Fe], 340 õM [Cu], and 17 õM [Mn]. 57Fe-enriched intact mitochondria isolated in the presence of metal chelators exhibited Mössbauer spectra dominated by three components. Approximately 60% of the 57Fe in the sample gave rise to a quadrupole doublet, most of which was diamagnetic. The parameters of this doublet are typical of S = 0 [4Fe-4S]2+ clusters and S = 0 ferrous heme groups. Spectra of samples reduced with dithionite, pH 8.5, suggested that at least half of this doublet arose from [4Fe-4S]2+ clusters. The second major component exhibited in the Mössbauer spectra arose from high-spin ferrous ions (10%-30%). The third major component (15%) came from iron exhibiting magnetic hyperfine interactions and is likely reflected in the Fe-containing species observed by EPR. The results presented here suggest that mitochondria contain ~ 600 õM of Fe overall, ~ 200 â 400 õM organized as [4Fe-4S]2+ clusters, with about 25 õM due to the [4Fe-4S]2+ cluster of aconitase. Approximately 60 õM â 200 õM of the Fe in mitochondria is high-spin ferrous ions, ~ 40 õM as the Rieske S = 1/2 [2Fe-2S]+ cluster of cytochrome bc1, and ~20 õM as the S = 1/2 [2Fe-2S]+ cluster of succinate dehydrogenase. The high-spin ferric hemes of the a3:CuB site of cytochrome oxidase and cytochrome c peroxidase each account for ~ 4 õM of Fe.
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Spectroscopic and analytical characterization of the distribution of iron in intact mitochondria from Saccharomyces cerevisiaeHudder, Brandon Neal 30 October 2006 (has links)
Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy were used to examine the distribution of iron in mitochondria from Saccharomyces cerevisiae. These organelles were packed into EPR and Mössbauer cuvettes, affording spectra with unprecedented signal/noise ratios. EPR spectra of as-isolated intact mitochondria exhibited fourteen distinct signals, some of which were assigned according to previously reported g-values obtained using isolated proteins. Signals from adventitious manganese (II) and iron (III) were largely removed when mitochondria were isolated in buffers supplemented with the metal chelators EDTA or EGTA. Signals were simulated and intensities were quantified to afford spin concentrations and estimates of the concentration of EPR-active species in mitochondria. The effects of treating samples with chemical modifiers were examined. Packed samples were analyzed for protein and metal content, affording averaged values of 50 mg/mL [protein], 590 õM [Fe], 340 õM [Cu], and 17 õM [Mn]. 57Fe-enriched intact mitochondria isolated in the presence of metal chelators exhibited Mössbauer spectra dominated by three components. Approximately 60% of the 57Fe in the sample gave rise to a quadrupole doublet, most of which was diamagnetic. The parameters of this doublet are typical of S = 0 [4Fe-4S]2+ clusters and S = 0 ferrous heme groups. Spectra of samples reduced with dithionite, pH 8.5, suggested that at least half of this doublet arose from [4Fe-4S]2+ clusters. The second major component exhibited in the Mössbauer spectra arose from high-spin ferrous ions (10%-30%). The third major component (15%) came from iron exhibiting magnetic hyperfine interactions and is likely reflected in the Fe-containing species observed by EPR. The results presented here suggest that mitochondria contain ~ 600 õM of Fe overall, ~ 200 â 400 õM organized as [4Fe-4S]2+ clusters, with about 25 õM due to the [4Fe-4S]2+ cluster of aconitase. Approximately 60 õM â 200 õM of the Fe in mitochondria is high-spin ferrous ions, ~ 40 õM as the Rieske S = 1/2 [2Fe-2S]+ cluster of cytochrome bc1, and ~20 õM as the S = 1/2 [2Fe-2S]+ cluster of succinate dehydrogenase. The high-spin ferric hemes of the a3:CuB site of cytochrome oxidase and cytochrome c peroxidase each account for ~ 4 õM of Fe.
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EPR study of intrinsic near surface defects in SiCThomas, Sarah A. January 2009 (has links) (PDF)
Thesis (M.S.)--University of Alabama at Birmingham, 2009. / Title from PDF title page (viewed Jan. 21, 2010). Includes bibliographical references (p. 57-58) .
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An analysis of continuous wave and time domain electron paramagnetic resonance spectra with applications to biological systems /Nielsen, Robert D., January 2003 (has links)
Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 401-408).
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Studies on the structure and function of the myosin headBaumann, Bruce A. J. Logan, Timothy M. January 2003 (has links)
Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Tim Logan, Florida State University, College of Arts and Sciences, Program in Molecular Biophysics. Title and description from dissertation home page (viewed Oct. 3, 2003). Includes bibliographical references.
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Electron paramagnetic resonance spectroscopy of spin-labeled RNA : an emerging tool for the elucidation of RNA structure and dynamics /Edwards, Thomas Eugene, January 2003 (has links)
Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 148-174).
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Electron paramagnetic resonance study of Gd³⁺ in single crystals of yttrium vanadate (YVO₄)Zhao, Xinghai. January 1900 (has links)
Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains vi, 43 p. : ill. Includes abstract. Includes bibliographical references (p. 29).
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