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Modelling intramolecular electron transfer reactions in cytochromes and in photosynthetic bacteria reaction centres

Arnaut, Luís G.; Formosinho, Sebastião J.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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Electron transfer rates within protein systems with various donor acceptor distances, reaction-free energies and temperatures, are calculated as the product of an electron tunneling probability and a nuclear distortion activation term. The electronic factor is given by the frequency of electronic motion in the donor, the donor electron energy, the donor-acceptor distance and the protein refractive index. Nuclear distortion is obtained from bond lengths, force constants and bond orders of the co-factor bonds involved in the reaction coordinate. The nuclear factor is calculated according to thermal activation and nuclear tunneling mechanisms. The calculation of distance, free-energy and temperature dependence of photoinduced-intraprotein electron transfer rates in Ru/Zn-modified cytochromes and myoglobins does not rely on fitting unknown parameters to kinetic data and is in good agreement with the experiment. Systems with reduced masses lower than 100 a.m.u. may undergo sizable nuclear tunneling at room temperature.; http://www.sciencedirect.com/science/article/B6TGY-3VGT0HT-1M/1/dcf47d6786a1ab78c9d8f701f4591475

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)(2)((4,4 `-PO(3)H(2))(2)bpy)](2+) in TiO(2) Nanoparticle Films in Aqueous Environments

BRENNAMAN, M. Kyle; PATROCINIO, Antonio Otavio T.; SONG, Wenjing; JURSS, Jonah W.; CONCEPCION, Javier J.; HOERTZ, Paul G.; TRAUB, Matthew C.; IHA, Neyde Y. Murakami; MEYER, Thomas J.
Fonte: WILEY-BLACKWELL Publicador: WILEY-BLACKWELL
Tipo: Artigo de Revista Científica
ENG
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Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru-(bpy)(2)(4,4`-(PO(3)H(2))(2)bpy)](2+) surface-bound to TiO(2) (TiO(2)-Ru(II)). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, - were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO(2)(e(-))-Ru(3+) -> TiO(2)-Ru(2+). The appearance of pH-dependent decreases in the efficiency of formation of TiO(2)-Ru(3+) and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond-microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.; US Department of Energy (DOE), Office of Science...

Estudos espectroscópicos do processo de transferência de elétrons em um meio rígido; Study of the electron transfer process in a rigid medium

Nakaema, Marcelo Kiyoshi Kian
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 10/04/1996 PT
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Este trabalho teve como objetivo estudar a transferência de elétrons em um meio rígido através de técnicas espectroscópicas convencionais, tais como a fluorescência e a fotoacústica, e verificar a possibilidade de se determinar a taxa de transferência através destas técnicas. Foram utilizados como doador de elétrons a tetrafenilporfirina (TPP), como aceitador de elétrons a duroquinona (DQ), e como meio rígido o polimetilmetacrilato (PMMA) e o poliestireno (PS). As amostras foram estudadas na forma de filmes, com uma distribuição aleatória de doadores e aceitadores de elétrons. Com a espectroscopia de fotoacústica não foi possível se detectar a ocorrência da transferência de elétrons. Com a fluorescência, usando o modelo de Perrin, foi possível determinar o raio crítico de transferência, 72k para o par TPP/DQ em poliestireno. No entanto, verificou-se a impossibilidade de se determinar univocamente a taxa de transferência de elétrons. Nos filmes preparados com polimetilmetacrilato foi observada uma fotodegradação irreversível, o que inviabilizou seus estudos; The objective of this work was to study the electron transfer process in a rigid medium using conventional spectroscopic techniques, such as fluorescence and photoacoustic...

Investigação do processo de transferência de elétrons por espectroscopia fotoacústica e de fluorescência; Study the electron-transfer process by steady-state photoacoustic and fluorescence spectroscopy

Cornelio, Marinonio Lopes
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 25/04/1994 PT
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A espectroscopia fotoacústica e de fluorescência foram empregadas no estudo de reação da transferência de elétrons entre um doador (Octaetil-porfirina) dois tipos de aceitadores [Diclorodiciano-benzoquinona (DDQ) e Duroquinona (DQ)] em um meio rígido [poli (metil-metacrilato)] . Foram preparados filmes nos quais a concentração de doador foi mantida constante e a de aceitador foi variada. Observou-se um aumento exponencial da amplitude do sinal fotoacústico do doador em 620 nm, com o aumento da concentração de aceitadores nos filmes. O modelo de Perrin para a supressão de fluorescência foi aplicado aos dados de fotoacústica e o raio da esfera de ação, que representa a distância crítica para a ocorrência da transferência de elétrons, foi determinado. Os resultados obtidos foram: para DDQ37 angstron e para aDQ 32 a 34angstron. Era esperado um raio maior para a DDQ devido a sua maior elétron afinidade. Também foi aplicado a estes dados o modelo de Kaneko, desenvolvido para a supressão de fluorescência. Dele se obtém a distribuição de moléculas aceitadoras incorporadas na esfera de ação. Para uma mesma concentração de aceitadores (2,8mmoldm-3) , a probabilidade de encontrar uma molécula de DDQ na esfera de ação foi 27%...

Electron transfer by singlet excited state of porphyn and electron acceptor affinity in rigid medium: photoacoustic phase angle analysis

CORNÉLIO, Marinônio Lopes
Fonte: Editora Unesp Publicador: Editora Unesp
Tipo: Artigo de Revista Científica Formato: 83-92
ENG
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A espectroscopia fotoacústica obtém informações sobre amplitude e fase, da resposta de um sistema submetido a excitação por luz. Este artigo apresenta estudos do ângulo de fase no processo de transfereência de elétrons entre octaetilporfirina (OEP) e derivados de quinona ambos dispersos em uma matriz polimérica. Observou-se uma tendência no comportamento da fase para valores menores na região espectral próximo de 620 nm. Enquanto que para comprimentos de onda menores este efeito não foi apresentado. Estas medidas sugerem que a transferência de elétrons para o aceitador ocorreu com a participação do estado singleto excitado da octaetilporfirina.; Photoacoustic spectroscopy provides information about both amplitude and phase of the response of a system to an optical excitation process. This paper presents the studies of the phase in the electron transfer process between octaethylporphyn (OEP) and quinone molecules dispersed in a polymeric matrix. It was observed a tendency in the phase behavior to small values only in the spectral region near to 620 nm, while for shorter wavelength did not show any tendency. These measurements suggested that the electron transfer to acceptor occurred with the participation of octaethylporphyn singlet excited state.

Electron migration in DNA matrix: an electron transfer reaction

POY, Cecília Dominical; CORNÉLIO, Marinônio Lopes
Fonte: Editora Unesp Publicador: Editora Unesp
Tipo: Artigo de Revista Científica Formato: 99-109
ENG
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Este artigo apresenta uma área de pesquisa atual, ativa e interessante. Descreve a investigação da química de transferência de elétrons (TE) de um modo geral e resultados de TE em DNA em particular. Dois intercalantes de DNA foram utilizados: Ethidium Bromide como doador (D) e Methyl-viologen como receptor (A), o primeiro intercala-se entre as bases do DNA e o último na sua superfície. Utilizando o modelo de Perrin e medidas de Supressão de Fluorescência obteve-se a distância de migração do elétron; aqui a distância foi considerada o espaçamento linear entre as moléculas de doador e receptor ao longo da molécula de DNA. O valor determinado foi de 22,6 ± 1,1 angstrons e o número de pares de bases entre doador e receptor de 6,6. Na literatura os valores encontrados foram de 26 angstrons e de quase 8 pares de bases. Considera-se que a transferência de elétrons em DNA seja mediada através das interações através do espaço entre os elétrons do tipo p contido nos pares de bases.; This paper brings an active and provocative area of current research. It describes the investigation of electron transfer (ET) chemistry in general and ET reactions results in DNA in particular. Two DNA intercalating molecules were used: Ethidium Bromide as the donor (D) and Methyl-Viologen as the acceptor (A)...

Computer simulation of electron transfer in molecular electronic devices

Correia, Helena M. G.; Ramos, Marta M. D.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /12/2005 ENG
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The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-Bis((2′-para-mercaptophenyl)-ethinyl)-anthracene] and an asymmetric [1,4-Bis((2′-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene] molecule bound to metal electrodes. Specifically addressed are the effects of voltage inversion on electron transfer between electrodes through both molecules. Our results show an electron transfer behaviour that reproduces the spatial symmetry of the molecules in agreement with experimental current-voltage data. The change in time of electron density and dimerisation at specific atomic sites is also discussed.; Fundação para a Ciência e a Tecnologia (FCT) - Programa Operacional “Ciência , Tecnologia, Inovação” - POCTI/CTM/41574/2001, SFRH/BD/11231/2002.; Comunidade Europeia (CE). Fundo Europeu de Desenvolvimento Regional (FEDER).

Studies on the metabolic role of the mitochondrial electron transfer proteins ETF and ETFDH in Saccharomyces cerevisiae

Rodrigues, Aurora; Vasconcelos, Filipe; Oliveira, Rui Pedro Soares de
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 27/02/2007 ENG
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The ETF (electron transfer flavoprotein) and ETFDH (ETF dehydrogenase) are flavoproteins involved in electron transfer from primary acyl-CoA dehydrogenases to ubiquinone of the mitochondrial electron transport system (ETS). ETF is a heterodimer composed of subunits ETFα and ETFβand ETFDH is associated to the mitochondrial inner membrane. Electron-donor metabolic reactions in which primary acyl-CoA dehydrogenases are known to catalyze reactions are β-oxidation, amino acid catabolism, choline catabolism and sarcosine and dimethylglycine catabolism. In mammalian cells, β-oxidation takes place in both mitochondria and peroxisomes, depending on fatty acid length and double bonds. For other eukaryotic organisms, it is exclusively peroxisomal and, hence, not directly coupled to ATP generation. The Saccharomyces cerevisiae orthologues of ETF and ETFDH are encoded by YPR004c (ETFα), YGR207c (ETFβ) and YOR356w (ETFDH) and have been demonstrated to be mitochondrial proteins. In this work, we aim at elucidate the role of ETF and ETFDH in yeast by exploring the possibility of involvement in the catabolism of amino acids, choline, sarcosine and dimethylglycine; in oxidative stress; and in heat shock. Mutant strains affected in these genes were tested for growth on media with different carbon sources. All mutant strains displayed normal growth when compared with their parental on glucose and on non-fermentable carbon sources: ethanol...

Modelling the effect of contact formation on electron transfer in single-molecule device

Ramos, Marta M. D.; Correia, Helena M. G.
Fonte: American Scientific Publishers Publicador: American Scientific Publishers
Tipo: Artigo de Revista Científica
Publicado em //2010 ENG
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The electric properties of single-molecule devices are very sensitive to details of contact formation between the molecule and the metallic electrodes. However the factors that control the electron transfer through the molecule in these devices, corresponding to slightly different molecule-metal attachments, are not well understood. In this work, we used a self-consistent molecular dynamics method to study the effect of symmetric and asymmetric contact realizations on electron transfer between two metallic electrodes through a spatially symmetric conjugated molecule. Our results showed that both symmetric and asymmetric electron transfer, with respect to voltage inversion, can be obtained with the same molecule in agreement with the experiments. Besides, a central factor determining the asymmetric electron transfer through a symmetric molecule, caused by the asymmetric contact realization, is the oscillation of the entire molecule between both electrodes and its distortion.; Fundação para a Ciência e a Tecnologia (FCT) – POCTI/CTM/41574/2001; CONC-REEQ/443/EEI/2005; FEDER

The role of halouracils in radiotherapy studied by electron transfer in atom-molecule collisions experiments

Antunes, Rodrigo Augusto Ferreira
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Tese de Doutorado
Publicado em //2011 ENG
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Dissertação para obtenção do Grau de Doutor em Engenharia Física; The role of ionising radiation as a source of damage to living tissues and cells has been recognized as a key issue regarding cellular DNA integrity and, ultimately, mutagenesis. The lethal effect of radiation, despite being most of the time undesired, can sometimes be useful, as is the case of radiation therapy. However, still the major concern in medicine is that only the cancerous cell material should be destroyed, keeping as much as possible healthy tissue unaffected. One way to control this damage seems to be the application of radiosensitizers that are incorporated into cancer cells. The cancer tissue doped with these radiation sensitizing molecules may be destroyed preferentially under radiation exposure, in very well defined places and even with radiation doses which may be low enough to prevent healthy cell material to be affected in the surrounding medium. This leads to nanodosimetry and so the sorts of interactions have now to be described at the molecular level. Upon irradiation, the most abundant secondary species produced along the radiation track are low energy electrons and so the study of electron induced damage to biological relevant molecules seems indubitably relevant. The research described in this thesis covers for the first time the study of electron transfer on two halouracils (5-chlorouracil and 5-fluorouracil) and isolated DNA/RNA basis (thymine and uracil)by atom-molecule collisions. In order to investigate such molecules...

Kinetics studies of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and superoxide reductases

Auchère, Françoise; Pauleta, Sofia R.; Tavares, Pedro; Moura, Isabel; Moura, José J. G.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2006 ENG
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J Biol Inorg Chem (2006) 11: 433–444 DOI 10.1007/s00775-006-0090-0; In this work we present a kinetic study of the superoxide-mediated electron transfer reactions between rubredoxin-type proteins and members of the three different classes of superoxide reductases (SORs). SORs from the sulfate-reducing bacteria Desulfovibrio vulgaris (Dv) and D. gigas (Dg) were chosen as prototypes of classes I and II, respectively, while SOR from the syphilis spirochete Treponema pallidum (Tp) was representative of class III. Our results show evidence for different behaviors of SORs toward electron acceptance, with a trend to specificity for the electron donor and acceptor from the same organism. Comparison of the different kapp values, 176.9+/-25.0 min(-1) in the case of the Tp/Tp electron transfer, 31.8+/-3.6 min(-1) for the Dg/Dg electron transfer, and 6.9+/-1.3 min(-1) for Dv/Dv, could suggest an adaptation of the superoxide-mediated electron transfer efficiency to various environmental conditions. We also demonstrate that, in Dg, another iron-sulfur protein, a desulforedoxin, is able to transfer electrons to SOR more efficiently than rubredoxin, with a kapp value of 108.8+/-12.0 min(-1), and was then assigned as the potential physiological electron donor in this organism.

Overexpression and purification of Treponema pallidum rubredoxin; kinetic evidence for a superoxide-mediated electron transfer with the superoxide reductase neelaredoxin

Auchère, Françoise; Sikkink, Robert; Cordas, Cristina; Raleiras, Patrícia; Tavares, Pedro; Moura, Isabel; Moura, José J. G.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2004 ENG
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J Biol Inorg Chem (2004) 9: 839–849 DOI 10.1007/s00775-004-0584-6; Superoxide reductases are a class of non-haem iron enzymes which catalyse the monovalent reduction of the superoxide anion O2- into hydrogen peroxide and water. Treponema pallidum (Tp), the syphilis spirochete, expresses the gene for a superoxide reductase called neelaredoxin, having the iron protein rubredoxin as the putative electron donor necessary to complete the catalytic cycle. In this work, we present the first cloning, overexpression in Escherichia coli and purification of the Tp rubredoxin. Spectroscopic characterization of this 6 kDa protein allowed us to calculate the molar absorption coefficient of the 490 nm feature of ferric iron, epsilon=6.9+/-0.4 mM(-1) cm(-1). Moreover, the midpoint potential of Tp rubredoxin, determined using a glassy carbon electrode, was -76+/-5 mV. Reduced rubredoxin can be efficiently reoxidized upon addition of Na(2)IrCl(6)-oxidized neelaredoxin, in agreement with a direct electron transfer between the two proteins, with a stoichiometry of the electron transfer reaction of one molecule of oxidized rubredoxin per one molecule of neelaredoxin. In addition, in presence of a steady-state concentration of superoxide anion, the physiological substrate of neelaredoxin...

The role of electron transfer in DNA building blocks: evaluation of strand breaks and their implications

Almeida, Diogo Alexandre Fialho de
Fonte: Faculdade de Ciências e Tecnologia Publicador: Faculdade de Ciências e Tecnologia
Tipo: Tese de Doutorado
Publicado em //2013 ENG
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Dissertação para obtenção do Grau de Doutor em Engenharia Física; Radiation-induced damage to biological systems, both direct and indirect processes, has increasingly come under scrutiny by the international scientific community due to recent findings that electrons are a very effective agent in damaging DNA/RNA. Indeed, much remains to be discovered regarding the exact physico-chemical processes that occur in the nascent stages of DNA/RNA damage by incident radiation. However, it is also known that electrons do not exist freely in the physiological medium, but rather solvated and/or pre-solvated states. This leads to the need for new techniques that can better explore the damaging role of “bound” electrons to DNA/RNA. The work presented in this thesis consists on the study of electron transfer in collisions of atomic species with molecules of biological relevance. In order to study these processes, two experimental setups were used. One setup consists of a crossed beam experiment where a neutral potassium beam is created and made to collide with an effusive molecular target beam. The anionic products that stem from electron transfer in potassium atom to the molecular target collisions are then extracted and time-of-flight (TOF) mass analysed. In the second setup a beam of anionic species is formed and made to collide with a molecular target. Collisions with three different anionic beams were performed (H-...

Electron migration in DNA matrix: an electron transfer reaction

POY,Cecília Dominical; CORNÉLIO,Marinônio Lopes
Fonte: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP Publicador: Fundação Editora da Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/1998 EN
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This paper brings an active and provocative area of current research. It describes the investigation of electron transfer (ET) chemistry in general and ET reactions results in DNA in particular. Two DNA intercalating molecules were used: Ethidium Bromide as the donor (D) and Methyl-Viologen as the acceptor (A), the former intercalated between DNA bases and the latter in its surface. Using the Perrin model and fluorescence quenching measurements the distance of electron migration, herein considered to be the linear spacing between donor and acceptor molecule along the DNA molecule, was obtained. A value of 22.6 (± 1.1) angstroms for the distance and a number of 6.6 base pairs between donor and acceptor were found. In current literature the values found were 26 angstroms and almost 8 base pairs. DNA electron transfer is considered to be mediated by through-space interactions between the p-electron-containing base pairs.

Electron-transfer functionality of synthetic coiled-coil metalloproteins

Ogawa,Michael Y.; Fan,Jiufeng; Fedorova,Anna; Hong,Jing; Kharenko,Olesya A.; Kornilova,Anna Y.; Lasey,Robin C.; Xie,Fei
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2006 EN
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The emerging field of metalloprotein design seeks to prepare artificial proteins whose properties can mimic, enhance, and perhaps improve upon many features found in natural metalloenzymes. This review summarizes our recent efforts to prepare synthetic metalloproteins built from alpha-helical coiled-coils and to incorporate electron-transfer functionality within these systems. We have recently designed a cysteine-containing random-coil peptide which forms a alpha-helical coiled-coil upon binding various metals. The CuI adduct can serve as photoinduced electron-transfer agent to exogenous acceptors and undergoes collisional electron-transfer in the inverted Marcus region to various ruthenium ammine acceptors. It is speculated that this unexpected result might be due to the positioning of the CuI cofactor within the hydrophobic core of the protein which prohibits close approach between the donor and acceptor to slow the high driving force reaction rates below the diffusion limit.

Electron Transfer Involving the Phylloquinone (A1) Cofactor of Photosystem I Examined with Time Resolved Absorbance and Electron Paramagnetic Resonance Spectroscopy

Mula, Samuel Jr.
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
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The dependence of the electron transfer (ET) rate on the Photosystem I (PSI) cofactor phylloquinone (A1) is studied by time-resolved absorbance and electron paramagnetic resonance (EPR) spectroscopy. Two active branches (A and B) of electron transfer converge to the FX cofactor from the A1A and A1B quinone. The work described in Chapter 5 investigates the single hydrogen bond from the amino acid residue PsaA-L722 backbone nitrogen to A1A for its effect on the electron transfer rate to FX. Room temperature transient EPR measurements show an increase in the rate for the A1A- to FX for the PsaA-L722T mutant and an increased hyperfine coupling to the 2-methyl group of A1A when compared to wild type. The Arrhenius plot of the A1A- to FX ET in the PsaA-L722T mutant suggests that the increased rate is probably the result of a slight change in the electronic coupling between A1A- and FX. The reasons for the non-Arrhenius behavior are discussed. The work discussed in Chapter 6 investigates the directionality of ET at low temperature by blocking ET to the iron-sulfur clusters FX, FA and FB in the menB deletion mutant strain of Synechocyctis sp. PCC 6803, which is unable to synthesize phylloquinone, by incorporating the high midpoint potential (49 mV vs SHE) 2...

Electron Transfer Reactivity, Synthesis, Surface Chemistry and Liquid-Membrane Transport of Sarcophagine-Type Poly-Aza Cage Complexes

Walker, Glen William
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
EN
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The kinetics for outer-sphere electron transfer between a series of cobalt(II) poly-aza cage ligand complexes and the iron(III) sarcophagine-type hexa-aza cage complex, [Fe(sar)]3+ (sar = 3,6,10,13,16,19-hexaazabicyclo[6.6.6]icosane), in aqueous solution have been investigated and the Marcus correlation is used to deduce the electron self-exchange rate constant for the [Fe(sar)]3+/2+ couple from these cross-reactions. The deduced electron self-exchange rate constant is in relatively good agreement with the experimentally determined rate constant (k ex calc = 4 ´ 10 5 M -1 s -1 ; k ex obs = 8 ´ 10 5 M -1 s -1 ). The successful application of the Marcus correlation to the electron transfer reactions of the Fe cage complex is consistent with the trend for the Co, Mn, Ni and Ru cage complexes which all follow the pattern of outer-sphere electron transfer reactivity expected from the Marcus-Hush formalism. A comparison of predictions based on the Marcus correlation with the experimentally determined kinetics of an extended series of cross reactions involving cobalt cage complexes with low-spin-high-spin cobalt(III)/(II) couples shows that electron transfer reactions involving large spin changes at the metal centre are not necessarily anomalous in the context of the adiabatic Marcus-Hush formalism. The results of this study also show that for suitable systems...

Protein recognition in ferredoxin-P450 electron transfer in the class I CYP199A2 system from Rhodopseudomonas palustris

Bell, S.; Xu, F.; Johnson, E.; Forward, I.; Bartlam, M.; Rao, Z.; Wong, L.L.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
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CYP199A2 from Rhodopseudomonas palustris CGA009 is a heme monooxygenase that catalyzes the oxidation of para-substituted benzoic acids. CYP199A2 activity is reconstituted by a class I electron transfer chain consisting of the associated [2Fe-2S] ferredoxin palustrisredoxin (Pux) and a flavoprotein palustrisredoxin reductase (PuR). Another [2Fe-2S] ferredoxin, palustrisredoxin B (PuxB; RPA3956) has been identified in the genome. PuxB shares sequence identity and motifs with vertebrate-type ferredoxins involved in Fe-S cluster assembly but also 50% identity with Pux and it mediates electron transfer from PuR to CYP199A2, albeit with lower steady-state turnover activity: 99 nmol (nmol P450)(-1)min(-1) for 4-methoxybenzoic acid oxidation compared with 1,438 nmol (nmol P450)(-1 )min(-1) for Pux. This difference mainly arises from weak CYP199A2-PuxB binding (K (m) 34.3 vs. 0.45 microM for Pux) rather than slow electron transfer (k (cat) 19.1 vs. 37.9 s(-1) for Pux). Comparison of the 2.0-A-resolution crystal structure of the PuxB A105R mutant with other vertebrate-type, P450-associated ferredoxins revealed similar protein folds but also significant differences in some loop regions. Therefore, PuxB offers a platform for studying ferredoxin-P450 recognition in class I P450 systems. Substitution of PuxB residues at key locations with those in Pux shows that Ala42...

Electron transfer to sulfides and disulfides: intrinsic barriers and relationship between heterogeneous and homogeneous electron-transfer kinetics

Meneses, Ana Belén; Antonello, Sabrina; Arévalo, Maria Carmen; González Martín, Concepción C.; Sharma, Jadab; Wallette, Andrea N.; Workentin, Mark S.; Maran, Flavio
Fonte: John Wiley & Sons Publicador: John Wiley & Sons
Tipo: Artículo Formato: 2373 bytes; 220587 bytes; text/plain; application/pdf
ENG
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13 pages, 7 figures, 5 tables.-- PMID: 17616962 [PubMed].; The electron-acceptor properties of series of related sulfides and disulfides were investigated in N,N-dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron-transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the C(alkyl)-S or S-S bond. A generalized picture of how the intrinsic electron-transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative- and nondissociative-type acceptors...

Electron-transfer capacity of catechin derivatives and influence on the cell cycle and apoptosis in HT29 cells

Lozano, Carles; Juliá, Lluís; Jiménez, Aurora; Touriño, Sonia; Centelles, Josep J.; Cascante, Marta; Torres, Josep Lluís
Fonte: Wiley-Blackwell Publicador: Wiley-Blackwell
Tipo: Artículo Formato: 19968 bytes; application/msword
ENG
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12 pages, 5 figures, 2 tables.; Galloylated and nongalloylated catechin conjugates with cysteine derivatives have been synthesized and evaluated for their capacity to scavenge free radicals and to influence crucial functions (cell cycle, apoptosis) in HT29 colon carcinoma cells. We show that the nonphenolic part of the molecule modified the capacity of catechins to donate hydrogen atoms and to transfer electrons to free radicals. Nongalloylated derivatives did not significantly influence either the cell cycle or apoptosis. Among the galloylated species, 4β-[S-(O-ethyl-cysteinyl)]epicatechin 3-O-gallate, which showed a high electron-transfer capacity (5 e– per molecule), arrested the cell cycle and induced apoptosis as expected for galloylated catechins such as tea (–)-epigallocatechin 3-O-gallate. 4β-[S-(N-Acetyl-O-methyl-cysteinyl)]epicatechin 3-O-gallate, which showed the highest hydrogen-donating capacity (10 H per molecule) while keeping the electron-transfer capacity low (2.9 e– per molecule), did not trigger any significant apoptosis. The gallate moiety did not appear to be sufficient for the pro-apoptotic effect of the catechin derivatives in HT29 cells. Instead, a high electron-transfer capacity is more likely to be behind this effect. The use of stable radicals sensitive exclusively to electron transfer may help to design molecules with either preventive scavenging action (high hydrogen donation...