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The association of Na,K-ATPase subunits studied by circular dichroism, surface tension and dilatational elasticity

RIGOS, Carolina Fortes; NOBRE, Thatyane Morimoto; ZANIQUELLI, Maria Elisabete Darbello; WARD, Richard John; CIANCAGLINI, Pietro
Fonte: ACADEMIC PRESS INC ELSEVIER SCIENCE Publicador: ACADEMIC PRESS INC ELSEVIER SCIENCE
Tipo: Artigo de Revista Científica
ENG
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Different stoichiometries are observed between alpha and beta subunits of Na,K-ATPase that depend on the method employed to solubilize and purify the enzyme. It is not known whether this variability is due to loss of protein-protein association, or is a result of the replacement of essential phospholipids by detergent molecules. With the aim of understanding the effect of enzyme/surfactant ratio on both the catalytic activity and the enzyme structure, we have investigated the bulk and surface properties of the enzyme. The circular dichroism (CD) spectra, surface tension and dilatational surface elasticity results were compared with the residual ATPase activity of the Na,K-ATPase in different surfactant and protein concentrations. Na,K-ATPase in the (alpha beta)(2) form dissociated to the alpha beta form on dilution, and associated to the (alpha beta)(4) form when concentrated. These different stoichiometries have similar ATPase activities and are in equilibrium at C(12)E(8) concentrations below the CIVIC (0.053 mg mL(-1)). At detergent concentrations above the CIVIC the ATPase activity of all forms was abolished, which is concomitant with the dissociation of the a and subunits. (C) 2008 Elsevier Inc. All rights reserved.; FAPESP; CNPq; CAPES

gamma-zein secondary structure in solution by circular dichroism

BICUDO, Tatiana C.; BICUDO, Rogerio C.; FORATO, Lucimara A.; Beltramini, Leila Maria; BATISTA, Luiz A. R.; BERNARDES FILHO, Rubens; COLNAGO, Luiz A.
Fonte: JOHN WILEY & SONS INC Publicador: JOHN WILEY & SONS INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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The proline-rich N-terminal domain of gamma-zein has been reported in relevant process, which include its ability to cross the cell membranes. Evidences indicate that synthetic hexapeptide (PPPVHL), naturally found in N-terminal portion of gamma-zein, can adopt the polyproline II (PPII) conformation in aqueous solution. The secondary structure of gamma-zein in maize protein bodies had been analyzed by solid state Fourier transform infrared and nuclear magnetic resonance spectroscopies. However, it was not possible to measure PPII content in physiological environment since the beta-sheet and PPII signals overlap in both solid state techniques. Here, the secondary structure of gamma-zein has been analyzed by circular dichroism in SDS aqueous solution with and without ditiothreitol (DTT), and in 60% of 2-propanol and water with DTT The results show that gamma-zein has high helical content in all solutions. The PPII conformation was present at about 7% only in water/DTT solution. (c) 2007 Wiley Periodicals, Inc.

Dicroísmo circular magnético no espectro de absorção em calcógenos de európio; Magnetic Circular Dichroism in the Absorption Spectrum in Europium Chalcogenides

Manfrini, Maurício Alarcon
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 18/06/2007 PT
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Os calcógenos de európio (EuX, onde X representa O, S, Se ou Te) possuem propriedades magneto-ópticas únicas e interessantes, devido ao enorme magnetismo gerado dos elétrons na camada f do átomo pertencente a família dos terras raras, tornando estes materiais atraentes para aplicações na spintrônica (eletrônica baseada nos transporte de spins e não de carga). Neste trabalho investigamos em baixa temperatura o espectro de absorção utilizando luz circularmente polarizada na região próxima do limiar da banda para o telureto de európio EuTe e o seleneto de európio EuSe em alto campo magnético no ordenamento ferromagnético dos spins de Eu^{2+} da rede cristalina. As amostras crescidas por epitaxia por feixe molecular apresentaram um dicroísmo circular magnético intenso no espectro de absorção para a configuração de Faraday. O par de linhas estreitas observadas estão separadas de aproximadamente 200 meV para o EuTe e 300 meV para o EuSe. Em seguida, formulamos um modelo teórico para a interpretação deste espectro de absorção no arcabouço do modelo de transições eletrônicas entre o estado fundamental 4f^{7}({8}^S_{7/2}) e o estado excitado formado dos estados do caroço remanescente 4f^{6}({7}^F_{J=0...6}) mais o estado em que o elétron se encontra na banda de condução 5d(t_{2g})...

Medidas magneto-óticas de tempos de relaxação Spin-Rede em KBr e nos halogenetos de Na e Cs e estudo de Dicroismo Circular Magnético do Ion Co++ em KCl.; Magneto-optical measurements of spin-lattice relaxation times in KBr, Na and Cs halides and Magnetic Circular Dichroism of Co++ dopped KCl.

Carvalho, Rene Ayres
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 15/02/1977 PT
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Neste trabalho, descrevemos um espectrômetro ótico para medidas de Dicroismo Circular Magnético (DCM), utilizado nas seguintes experiências: 1) Medidas de tempo de relaxação spin-rede (T1) para centros F em NaCl, NaBr, CsBr e CsCl, a temperatura de 1,8°K em campos magnéticos até 17000Gs. Verificamos a validade da teoria da referência (8) para explicar as diferenças observadas, no comportamento de 'T IND.1', para halogenetos com diferentes íons alcalinos, bem como diferentes estruturas. Comprovamos que a interação hiperfina ainda continua a ser o mecanismo mais importante para esses centros. Verificamos também que, para temperaturas entre 6°K e l5°K, os valores de experimentais para T1, em KBr, concordam razoavelmente com a teoria da referência (21). Esta terapia é uma extensão daquela da referência (8). 2) Espectros de DCM para KCl: Co++ e CaF2: Co++ foram obtidos para campos magnéticos ate 56KGs e temperaturas entre 1,8°K e 4,2 °K. Os resultados obtidos mostraram ser concordantes com a hipótese dos centros Co++ ocuparem sítios intersticiais na rede de KCl.; In this work we describe a Magnetic Circular Dicroism Spectrometer wich was used in the following experiments: 1) We measured the spin-lattice relaxation time (T1) for F centers in NaCl...

Estabilidade térmica da hemoglobina extracelular gigante de Glossoscolex paulistus (HbGp): estudos dos efeitos do pH do meio e do estado de oxidação do ferro por microcalorimetria diferencial de varredura (DSC), espectroscopia de absorção óptica e dicroísmo circular (CD); Thermal stability of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp): studies of the effects of the mediam pH iron oxidation state by differential of scanning microcalorimetry (DSC), optical absorption and circular dichroism (CD) spectroscopies

Carvalho, José Wilson Pires
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 11/08/2010 PT
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A estabilidade térmica em função do pH para três formas da hemoglobina extracelular gigante do anelídeo Glossoscolex paulistus (HbGp), monitorada atraves de DSC, CD e absorção óptica, e estudada no presente trabalho. Estes estudos possibilitaram a determinação de parâmetros importantes do processo de desnaturação e dissociação da proteína oligomerica em pH ácido, neutro e alcalino. A HbGp se mostrou mais estável no pH ácido do que em pH neutro e alcalino. No meio alcalino a HbGp sofre dissociação oligomérica gerando subunidades tais como o dodecâmero, o trímero e o monômero. Além disso, as técnicas de DSC, dicroísmo circular (CD) e absorção óptica permitiram o monitoramento da desnaturação da estrutura protéica global, da estrutura secundária e do centro ativo da HbGp, em função da temperatura. Por DSC foi determinado que o mecanismo do processo de desnaturação térmica da HbGp é irreversível. As variações de entalpia calorimétrica, ΔHcal, e de van Hoff, ΔHvH, nas formas oxi-, meta- e cianometa-HbGp são bem distintas, em todos os pHs estudados, indicando que o processo de desnaturação é bastante complexo, sugerindo que o pico de transição deve ser composto por varias transições. A ordem de estabilidade apresentada pela HbGp em termos dos valores de temperatura de transição (Tm) foi a seguinte: cianometa- > oxi- > meta- no intervalo de pH 5...

Propriedades físico-químicas da lectina KM+ monitoradas por dicroismo circular (CD) e fluorescência. Estimativa do conteúdo de estrutura secundaria por CD; Physico-chemical properties of lectin KM+ monitored by circular dichroism (CD) and fluorescence. Estimative of secondary structure content by CD

Lucca, Rosemeire Aparecida da Silva de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 01/07/1994 PT
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Uma nova lectina extraída da semente de Artocarpus integrifólia, denominada KM+ foi recentemente descrita. KM+ e haptotática para neutrófilos, promove a aglutinação de hemácias dos grupos A, B, 0, estimula a proliferação de linfócitos do baço de camundongos e liga-se em α D-manose, α metil manosidio e α D-glicose. Esta lectina é composta por quatro monômeros, com peso molecular de 13.150 daltons cada, unidos por interações não covalentes. KM+ contem 1,8% de carboidratos e apresentou quatro isoformas com pontos isoelétricos entre 4,2 e 5,2. Este trabalho teve como objetivos estudar modificações estruturais de KM+ em função de parâmetros como temperatura, força iônica, pH, agentes desnaturantes, ligação com D-manose, monitoradas por dicroísmo circular (CD) e fluorescência. CD também foi utilizado para estimar o conteúdo de estrutura secundaria de KM+, utilizando-se dois programas descritos na literatura: SSE (Secondary Structure Estimation), que utiliza o método dos mínimos quadrados para a estimativa da estrutura secundaria e obtenção dos espectros básicos, baseados nos dados cristalográficos de proteínas de .estrutura resolvida; CCA (Convex Constraint Analisys) que utiliza o algoritmo simplex e a partir dos espectros de CD das proteínas de referencia calcula os espectros das componentes básicas. Para a estimativa das frações de estrutura secundária o segundo método utiliza o programa Lincomb. Os espectros de CD foram registrados no intervalo de 185 a 260 nm. O conteúdo em estrutura secundária...

Expression, purification, and circular dichroism analysis of human CDK9

Leopoldino, A. M.; Canduri, F.; Cabral, H.; Junqueira, M.; Marqui, A, B. T. de; Apponi, L. H.; da Fonseca, I. O.; Domont, G. B.; Santos, D. S.; Valentini, S.; Bonilla-Rodriguez, G. O.; Fossey, Marcelo Andrés; Azevedo, W. F. de; Tajara, E. H.
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 614-620
ENG
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The human cyclin-dependent kinase 9 (CDK9) protein was expressed in E coli BL21 using the pET23a vector at 30 degrees C. Several milligrams of protein were purified from soluble fraction using ionic exchange and ATP-affinity chromatography. The structural quality of recombinant CDK9 and the estimation of its secondary structure were obtained by circular dichroism. Structural models of CDK9 presented 26% of helices in agreement with the spectra by circular dichroism analysis. This is the first report on human CDK9 expression in Escherichia coli and structure analysis and provides the first step for the development of CDK9 inhibitors. (c) 2006 Elsevier B.V. All rights reserved.

Conformational basis for the biological activity of TOAC-labeled angiotensin II and bradykinin: Electron paramagnetic resonance, circular dichroism, and fluorescence studies

Schreier, Shirley; Barbosa, Simone R.; Casallanovo, Fábio; Vieira, Renata de F. F.; Cilli, Eduardo Maffud; Paiva, Antonio C. M.; Nakaie, Clóvis R.
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 389-402
ENG
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N-Terminally and internally labeled analogues of the hormones angiotensin (AII, DRVYIHPF) and bradykinin (BK, RPPGFSPFR) were synthesized containing the paramagnetic amino acid 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4- carboxylic acid (TOAC). TOAC replaced Asp 1 (TOAC 1-AII) and Val 3 (TOAC 3-AII) in AII and was inserted prior to Arg 1 (TOAC 0-BK) and replacing Pro 3 (TOAC 3-BK) in BK. The peptide conformational properties were examined as a function of trifluoroethanol (TFE) content and pH. Electron paramagnetic resonance spectra were sensitive to both variables and showed that internally labeled analogues yielded rotational correlation times (TC) considerably larger than N-terminally labeled ones, evincing the greater freedom of motion of the N-terminus. In TFE, τ C increased due to viscosity effects. Calculation of τ Cpeptide/τ CTOAC ratios indicated that the peptides acquired more folded conformations. Circular dichroism spectra showed that, except for TOAC 1-AII in TFE, the N-terminally labeled analogues displayed a conformational behavior similar to that of the parent peptides. In contrast, under all conditions, the TOAC 3 derivatives acquired more restricted conformations. Fluorescence spectra of All and its derivatives were especially sensitive to the ionization of Tyr 4. Fluorescence quenching by the nitroxide moiety was much more pronounced for TOAC 3-AII The conformational behavior of the TOAC derivatives bears excellent correlation with their biological activity...

Determinação de enantiômeros em extratos vegetais por cromatografia quiral e dicroísmo circular

Rinaldo, Daniel
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 105 f. : il.
POR
Relevância na Pesquisa
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pós-graduação em Química - IQ; Este trabalho abordou a determinação quali e quantitativa de enantiômeros de catequinas em extratos e infusões das folhas de espécies do gênero Byrsonima (Malpighiaceae), tais como: B.basiloba, B. cocolobifolia, B. crassa, B. intermedia e B. verbascifolia. O trabalho descreve a determinação rápida e eficiente de catequina, ent- catequina, epicatequina e ent-epicatequina por cromatografia líquida de alta eficiência acoplada a detector de arranjo de fotodiodos e dicrísmo circular, usando coluna de fase estaconária quiral. O método possui alta seletividade e permite identificar inequivocadamente diastereômeros de catequinas em matrizes complexas como extratos vegetais, com limites de detecção (0,42 a 0,77 μg mL-1 ) e quantificação (1,27 a 2,32 μg mL-1 ) satisfatórios para as condições analisadas, e valores de precisão (0,3 to 4,8%) e exatidão (70,0 a 110,2%) recomendados pela ANVISA. Com exceção da espécie B. intermedia, quatro espécies do gênero apresentaram em seus extratos e infusões os diastereômeros catequina, epicatequina e ent-epicatequina. Experimentos para avaliar a epimerização da catequina indicaram que a incomum ent-epicatequina não é um artefato...

Dicroísmo circular vibracional e eletrônico na determinação da configuração absoluta de benzopiranos de Peperomia obtusifolia e Piper gaudichaudianum (Piperaceae): implicações biológicas e biossintéticas

Batista Junior, João Marcos
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Tese de Doutorado Formato: 215 f. : il. -
POR
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57.90932%
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Pós-graduação em Química - IQ; Estudos fitoquímicos visando o isolamento de benzopiranos quirais foram realizados em Peperomia obtusifolia e Piper gaudichaudianum (Piperaceae). Da espécie P. obtusifolia foram isolados dois cromanos racêmicos, a peperobtusina A e o ácido 3,4-diidro-5-hidróxi-2,7-dimetil-8-(3-metil-2-butenil)-2-(4-metil-1,3-pentadienil)-2H-1- benzopirano carboxílico, bem como oito ésteres isoméricos deste último com os monoterpenos borneol e fenchol, inéditos na literatura. P. gaudichaudianum forneceu o cromeno ácido gaudichaudiânico, também como racemato. As misturas estereoisoméricas foram resolvidas por meio de cromatografia líquida de alta eficiência quiral e os estereoisômeros purificados tiveram sua configuração absoluta determinada por comparação dos espectros experimentais de dicroísmo circular vibracional e eletrônico com aqueles preditos por cálculos mecânico-quânticos ab initio. Peperobtusina A e o ácido 3,4-diidro-5-hidróxi-2,7-dimetil-8-(3-metil-2-butenil)- 2-(4-metil-1,3-pentadienil)-2H-1-benzopirano carboxílico foram assinalados como (+)-R...

Circular dichroism of anthocyanidin 3-glucoside self-aggregates

Gavara, Raquel; Petrov, Vesselin; Quintas, Alexandre; Pina, Fernando
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /04/2013 ENG
Relevância na Pesquisa
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"Self-association constants for the flavylium cations of the six most common anthocyanidin 3-glucosides were determined by circular dichroism (CD) and UV–Vis spectroscopy. Along with previous 1H NMR results, all measurements were consistent with a monomer–dimer model. The CD spectra of the antho-cyanidin 3-glucosides were similar to the analogues 3,5-diglucosides. All dimers of the anthocyanidin 3-glucosides exhibited left-handed CD signals, with petunidin-3-glucoside and myrtillin having the most intense signals. In addition, the magnitude of the molar ellipticity, [h], was generally higher for the 3-glucosides than for the 3,5-diglucosides. For all six anthocyanins studied, the CD absorption spectra of their dimers showed evidence of the splitting of the monomer absorption into lower (J) and higher (H) energy bands. The angle and the distance between the dipolar moments of the two monomers comprising the dimer were obtained from the lower energy absorption band. While the angle was more or less similar in all six dimers, the separation distance between the monomer dipole moments differed dramatically. The intensity of the CD signal displayed a linear dependence with the inverse square of the dipole moment distances."

Investigation of self-assembling proline- and glycine-rich recombinant proteins and peptides inspired by proteins from a symbiotic fungus using atomic force microscopy and circular dichroism spectroscopy

Creasey, R.; Voelcker, N.; Schultz, C.
Fonte: Elsevier Science BV Publicador: Elsevier Science BV
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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Fiber-forming proteins and peptides are being scrutinized as a promising source of building blocks for new nanomaterials. Arabinogalactan-like (AGL) proteins expressed at the symbiotic interface between plant roots and arbuscular mycorrhizal fungi have novel sequences, hypothesized to form polyproline II (PPII) helix structures. The functional nature of these proteins is unknown but they may form structures for the establishment and maintenance of fungal hyphae. Here we show that recombinant AGL1 (rAGL1) and recombinant AGL3 (rAGL3) are extended proteins based upon secondary structural characteristics determined by electronic circular dichroism (CD) spectroscopy and can self-assemble into fibers and microtubes as observed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). CD spectroscopy results of synthetic peptides based on repeat regions in AGL1, AGL2 and AGL3 suggest that the synthetic peptides contain significant amounts of extended PPII helices and that these structures are influenced by ionic strength and, at least in one case, by concentration. Point mutations of a single residue of the repeat region of AGL3 resulted in altered secondary structures. Self-assembly of these repeats was observed by means of AFM and optical microscopy. Peptide (APADGK)(6) forms structures with similar morphology to rAGL1 suggesting that these repeats are crucial for the morphology of rAGL1 fibers. These novel self-assembling sequences may find applications as precursors for bioinspired nanomaterials.; Rhiannon G. Creasey...

Monitoring and modeling of protein processes using mass spectrometry, circular dichroism, and multivariate curve resolution methods

Navea, Susana; Tauler Ferré, Romà; Juan, Anna de
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artículo Formato: 162 bytes; application/msword
ENG
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11 pages, 10 figures.-- PMID: 16841894 [PubMed].-- Printed version published Jul 15, 2006.; Mass spectrometry has recently become one of the major analytical tools to study biomolecular structure and function. Ionization techniques, such as electrospray ionization (ESI), desorb biomolecules from solution to the gas phase keeping practically intact their natural structure. ESI applied to a protein solution produces a mixture of multiply charged ions, the ion charge distribution of which depends on the oligomeric form (mass) and on the protein surface exposed (amount of accommodated charges) of the related protein conformation. ESI-MS provides an efficient way to monitor protein processes; however, the ionic contributions of the different protein conformations involved usually overlap, and the use of chemometric tools is necessary to unravel the information related to the pure conformations that the biomolecule adopts along the process. Multivariate curve resolution-alternating least squares applied to MS-monitored protein processes provides the concentration profiles associated with the different protein conformations occurring during the process and the related pure mass spectra. The concentration profiles, in this context, the ionic contributions...

X-ray magnetic circular dichroism study of the decoupling of the magnetic ordering of the Er and Co sublattices in Er1−xYxCo2 systems

Chaboy, Jesús; Laguna-Marco, M. A.; Maruyama, H.; Ishimatsu, N.; Isohama, Y.; Kawamura, N.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 259768 bytes; application/pdf
ENG
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11 pages, 9 figures, 1 table.-- PACS number(s): 75.30.Kz, 61.10.Ht; We present an x-ray magnetic circular dichroism (XMCD) study performed at the Co K edge and at the Er L2,3 edges in the Er1−xYxCo2 series. Our results indicate that both Er and Co magnetic sublattices order at the same temperature for all the investigated compounds. In the case of the Er0.6Y0.4Co2 compounds, XMCD data do not show the decoupling of the magnetic ordering for both Er and Co sublattices. Moreover, no experimental evidence of the occurrence of an inverse itinerant electron metamagnetism has been found for applied magnetic fields of up to µ0H=10 T. In addition, a nonzero magnetic moment is found at the Co sites in the case of the Er0.5Y0.5Co2 compound.; This work was partially supported by Spanish Grant No. CICYT-MAT2005-06806-C04-04. The synchrotron radiation experiments were performed at SPring-8 (Proposals Nos. 2004A0020-NSc-np and 2005A0176-NSc-np).; Peer reviewed

Relationship between the magnetic moment of Lu and the magnetic behavior of (YyLu1−y)(Co1−xAlx)2 from x-ray absorption spectroscopy and x-ray magnetic circular dichroism

Chaboy, Jesús; Laguna-Marco, M. A.; Piquer, Cristina; Maruyama, H.; Kawamura, N.; Ishimatsu, N.; Suzuki, M.; Takagaki, M.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 259768 bytes; application/pdf
ENG
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10 pages, 2 tables, 8 figures.-- PACS number(s): 75.50.Cc, 75.30.Kz, 61.10.Ht, 87.64.Ni; We present an x-ray magnetic circular dichroism (XMCD) study performed at both the Co K edge and the Lu L2,3 edges on (YyLu1−y)(Co1−xAlx)2 systems. The XMCD spectra reflect the different magnetic character of these systems, allowing us to monitor the transition from weak to strong ferromagnetism. The XMCD at the Lu L2,3 edges indicates the existence of an ordered 5d moment at the lutetium sites that is coupled antiparallel to the Co moment. Estimates of the magnetic moment of Lu have been obtained by applying the XMCD sum rules. Our results show that there is a correlation between the Lu 5d–induced magnetic moment and the magnetic character of the (YyLu1−y)(Co1−xAlx)2 compounds. These results suggest that the developing of the Lu moment plays an important role in reinforcing the magnetic interactions and favoring the ferromagnetic character of the Lu-rich compounds.; This work was partially supported by Spanish Grants No. MAT2005-06806-C04-02 and No. MAT2005-06806-C04-04. The synchrotron radiation experiments were performed at SPring-8 (Proposals No. 2004A0020-NSc-np and No. 2006A1107).; Peer reviewed

57Fe Mössbauer and x-ray magnetic circular dichroism study of magnetic compensation of the rare-earth sublattice in Nd2−xHoxFe14B compounds

Chaboy, Jesús; Piquer, Cristina; Plugaru, N.; Bartolomé, Fernando; Laguna-Marco, M. A.; Plazaola, F.
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 728556 bytes; application/pdf
ENG
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12 pages, 8 figures, 3 tables.-- PACS number(s): 61.10.Ht, 76.80. y, 71.20.Lp, 75.50.Bb; We present here a study of the magnetic properties of the Nd2−xHoxFe14B series. The macroscopic properties of these compounds evolve continuously from those of Nd2Fe14B to those of Ho2Fe14B as Ho gradually replaces Nd. The system shows a compensation of the rare-earth sublattice magnetization for a critical concentration, xc=0.55, that is reflected into the anomalous behavior of both macroscopic and microscopic magnetic probes. The combined analysis of magnetization, 57Fe Mössbauer spectroscopy and Fe K-edge x-ray magnetic circular dichroism (XMCD) measurements suggests that the origin of the anomalous magnetic behavior found at xc=0.55 is mainly due to the Ho sublattice. Moreover, the analysis of the Fe K-edge XMCD signals reveal the presence of a rare-earth contribution, reflecting the coupling of the rare-earth and Fe magnetic moments, which can lead to the possibility of disentangling the magnetic behavior of both Fe and R atoms using a single absorption edge.; This work was partially supported by Spanish CICYTMAT2005-06806-C04-04 grant. M. A. L.-M. acknowledges a FPI grant from spanish MEC. The synchrotron radiation experiments were performed at SPring-8 (Proposal No. 2002A0153-NS2-np).; Peer reviewed

Simultaneous in-plane and out-of-plane exchange bias using a single antiferromagnetic layer resolved by x-ray magnetic circular dichroism

Nogués i Sanmiquel, Josep; Stepanow, S.; Bollero, A. Sort Viñas, Jordi; Dieny, B.; Nolting, F.; Gambardella, Pietro
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2009 ENG
Relevância na Pesquisa
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This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.; We present a study of exchange bias in ferromagnet/antiferromagnet/ferromagnet (FM/AFM/FM) trilayers, with in-plane and out-plane easy axes. Using element-specific x-ray magnetic circular dichroism, we demonstrate that simultaneous in-plane and out-of-plane exchange bias can be induced using a single antiferromagnet and zero field cooling, whereas field cooling only induces exchange bias to the layer with easy axis parallel to the cooling field. Our results further evidence the presence of pinned uncompensated moments in both the FM and AFM layers, implying that the AFM layer is capable of supporting uncompensated spins in two orthogonal directions at the same time.

Investigating the Spontaneous Resolution of an Abiotic Metallofoldamer Using Solid???State Circular Dichroism Spectroscopy

Benavidez, Ann
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Undergraduate Thesis
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Joseph M. Fox; Crystals of an abiotic metallofoldamer were used to investigate the viability of solid???state circular dichroism spectroscopy (solid???state CD) as an alternative to X???ray diffraction studies in spontaneous resolution analysis. The metallofoldamer is devoid of chiral centers and the molecules assemble into secondary structures with helical chirality. Although the metallofoldamer complexes racemize in solution, they produce a single enantiomerically pure crystal when subjected to vapor diffusion in a crystallization experiment. CD spectra of microcrystalline samples were obtained by scanning pellets of each crushed crystal mixed with KBr. The reliability, efficiency, and effectiveness of solid???state CD in spontaneous resolution analysis were established. Thus, it was demonstrated that an enantiomerically pure helical molecule can be produced from a dynamic macromolecule without any element of central chirality. A hypothesis for the evolutionary origin of chirality is discussed. Interestingly, all seven crystals characterized thus far have been left???handed. The probability of such an occurrence is 1 in 64. It is plausible that a chiral contaminant serves as a nucleation site for crystallization.; Howard Hughes Medical Institute and the Donald W. Harward Fellows Award.; Chemistry

Temperature-Dependent Magnetic Circular Dichroism of Lutetium Bisphthalocyanine

Dunford, Cara; Williamson, Bryce; Krausz, Elmars
Fonte: American Chemical Society Publicador: American Chemical Society
Tipo: Artigo de Revista Científica
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Magnetic circular dichroism (MCD) and absorption spectra are reported for the Q, RV, and IV band regions (6000-19000 cm-1) of lutetium bisphthalocyanine in poly(methyl methacrylate) films and Ar matrixes. Weak, temperature-independent MCD of the IV band (∼7500 cm-1) is consistent with its assignment to the intervalence transition of a delocalized mixed-valence system. The temperature-dependent MCD of the Q (∼15300 cm-1) and RV (∼11000 cm-1) bands is quantified by moment analysis and interpreted to indicate excited-state spin-orbit splittings due to weak mixing of metal and ligand π Orbitals. The spectra are semiquantitatively consistent with interpretation of these bands as arising from fully allowed transitions terminating in exciton coupling states derived principally from π* ← π excitations of the individual ligands.

Circular dichroism as a means to follow DNA gymnastics: on the shoulders of giants

Mills,M.; Lin,C.; Chauhan,M.; Klump,H.H.
Fonte: South African Journal of Science Publicador: South African Journal of Science
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2009 EN
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This is the first report of DNA stem-loops self-assembled by 'foot-loop' interactions into either two-dimensional strings or three-dimensional spirals, distinguished by circular dichroism spectroscopy. All subunits are linked by cooperative Watson-Crick hydrogen bonds.