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Redox Activity (redox + activity)
Selected AbstractsBiomimetic Approach to Confer Redox Activity to Thin Chitosan FilmsADVANCED FUNCTIONAL MATERIALS, Issue 16 2010Eunkyoung Kim Abstract Electron transfer in biology occurs with individual or pairs of electrons, and is often mediated by catechol/o -quinone redox couples. Here, a biomimetic polysaccharide-catecholic film is fabricated in two steps. First, the stimuli-responsive polysaccharide chitosan is electrodeposited as a permeable film. Next, the chitosan-coated electrode is immersed in a solution containing catechol and the electrode is biased to anodically-oxidize the catechol. The oxidation products covalently graft to the chitosan films as evidenced by electrochemical quartz crystal microbalance (EQCM) studies. Cyclic voltammetry (CV) measurements demonstrate that the catechol-modified chitosan films are redox-active although they are non-conducting and cannot directly transfer electrons to the underlying electrode. The catechol-modified chitosan films serve as a localized source or sink of electrons that can be transferred to soluble mediators (e.g., ferrocene dimethanol and Ru(NH3) 6Cl3). This electron source/sink is finite, can be depleted, but can be repeatedly regenerated by brief (30 s) electrochemical treatments. Further, the catechol-modified chitosan films can i) amplify currents associated with the soluble mediators, ii) partially-rectify these currents in either oxidative or reductive directions (depending on the mediator), and iii) switch between regenerated-ON and depleted-OFF states. Physical models are proposed to explain these novel redox properties and possible precedents from nature are discussed. [source] Copper(I) Cuboctahedral Coordination Cages: Host,Guest Dependent Redox Activity,ANGEWANDTE CHEMIE, Issue 33 2009Qi-Ting He Redoxaktiver Käfig: Mit einem dreieckigen Benzimidazol-Ligand wurden Cu+ -Koordinationskäfige aufgebaut, die einen kuboktaedrischen Hohlraum aufweisen und deren Redoxaktivität über das Gast-Anion abgestimmt werden kann. [source] Polyoxometalates with Internal Cavities: Redox Activity, Basicity, and Cation Encapsulation in [Mn+P5W30O110](15-n)- Preyssler Complexes, with M: Na+, Ca2+, Y3+, La3+, Ce3+, and Th4+.CHEMINFORM, Issue 50 2007Jorge A. Fernandez Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Redox Activity and Structural Transition of Heptyl Viologen Adlayers on Cu(100),CHEMPHYSCHEM, Issue 7 2010Min Jiang Dr. Abstract The redox behaviour and potential-dependent adsorption structure of heptyl viologen (1,1,-diheptyl-4,4,-bipyridinium dichloride, DHV2+) on a Cu(100) electrode was investigated in a chloride-containing electrolyte solution by cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (EC,STM). The dicationic DHV molecules generate a few pairs of current waves in CV measurements which are ascribed to two typical one-electron transfer steps. STM images obtained in a KCl-containing electrolyte solution disclose a well-ordered c(2×2) chloride adlayer on a Cu(100) electrode surface. After injecting DHV2+ molecules into the KCl electrolyte solution, a highly ordered 2D "dot-array" structure in STM images emerges on the c(2×2)-Cl modified Cu(100) electrode surface. DHV2+ molecules spontaneously arrange themselves with their molecular planes facing the electrode surface and their long molecular axis parallel to the step edge. Such adsorption structure can be described by mirror domains and rotational domains which stably exist between 200 mV and ,100 mV. One-electron reduction of the dications DHV2+ around ,150 mV causes a phase transition from a ,dot-array' assembly to a stripe pattern formed by DHV.+ radical monocations in STM images which has a bilayer structure. With a further decrease of the applied electrode potential, the structure of the DHV.+ adlayer undergoes a change from a loose stripe phase to a more compact stripe phase, a subsequent decay of the compact structure, and finally the formation of a new dimer phase. A further electron transfer reaction at ,400 mV causes the formation of an amorphous phase on the chloride free electrode surface. In a reverse anodic sweep, the reproduction of the ordered DHV.+ stacking phase occurs again on top of the chloride lattice. [source] Effect of Cyanato, Azido, Carboxylato, and Carbonato Ligands on the Formation of Cobalt(II) Polyoxometalates: Characterization, Magnetic, and Electrochemical Studies of Multinuclear Cobalt ClustersCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2007Laurent Lisnard Dr. Abstract Five CoII silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K20[{(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)}2Co(H2O)2],47,H2O (1) consists of two {(B-,-SiW9O33(OH))(,-SiW8O29(OH)2)Co3(H2O)} units connected by a {CoO4(H2O)2} group. In the chiral species K7[Co1.5(H2O)7)][(,-SiW10O36)(,-SiW8O30(OH))Co4(OH)(H2O)7],36,H2O (2), a {,-SiW10O36} and a {,-SiW8O30(OH)} unit enclose a mononuclear {CoO4(H2O)2} group and a {Co3O7(OH)(H2O)5} fragment. The two trinuclear CoII clusters present in 1 enclose a ,4 -O atom, while in 2 a ,3 -OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=,4 -O (1), ,3 -OH (2)) bridging angles in 2 (,av(Co-L-Co)=99.1°) than in 1 (,av(Co-L-Co)=92.8°). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of CoII centers, and indicated that two types of CoII centers in the structure were oxidized in separate waves. Redox activity of the seventh CoII center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K5Na3[(A-,-SiW9O34)Co4(OH)3(CH3COO)3],18,H2O (3) and K5Na3[(A-,-SiW9O34)Co4(OH)(N3)2(CH3COO)3],18,H2O (4) were characterized: in both, a tetrahedral {Co4(L1)(L2)2(CH3COO)3} (3: L1=L2=OH; 4: L1=OH, L2=N3) unit capped the [A-,-SiW9O34]10, trivacant polyanion. The octanuclear complex K8Na8[(A-,-SiW9O34)2Co8(OH)6(H2O)2(CO3)3],52,H2O (5), containing two {Co4O9(OH)3(H2O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed. [source] EXCHANGES OF INFORMATION, ENERGY & MATERIALS IN SYMBIOSESJOURNAL OF PHYCOLOGY, Issue 2000J.A. Raven Symbiosis is important in the cell and environmental biology of algae. Some examples involving the author and numerous collaborators include: 1) chloroplasts of eukaryotic algae arose from endosymbioses. Plastids are incapable of independent existence; most of the genes of the cyanobacterial photobiont have been lost, and the majority of the rest have been transferred to the nuclear genome. Some of the genes retained by the plastid are those whose transcription is controlled by environmental cues transduced by the organelle. The general trend is for organelle genes to be transferred to the nucleus, escaping plastid redox activities generating mutagenic free radicals; 2) symbioses involving potentially free-living photobionts include marine lichens and sponges with cyanobacterial symbionts. For the lichen, Lichina, inorganic carbon acquisition appears to involve inorganic carbon transport by the mycobiont, and for the sponge, Cymbastella, the flagellar activity of the sponge is probably important for inorganic carbon supply to the photobiont; 3) the Australasian fucalean, Notheia, is an obligate epiphyte on the fucaleans, Hormosira and Xiphophora; the four species involved all contain the hexitol, altritol. Notheia anomala is known to be phyletically-distant from the other five altritol-containing species. Can Notheia synthesize altritol, or is it obtained from the phorophyte?; 4) Sacoglossan gastropods retain kleptoplastids (not strictly symbionts) from ulvophycean (or rhodophycean) marine algae. Analyses of the natural abundance of stable carbon isotopes suggest significant contribution of kleptoplastid photosynthesis to the carbon and energy budget of the mollusks. [source] Assessment of the toxicity of mixtures of nickel or cadmium with 9,10-phenanthrenequinone to Daphnia magna: Impact of a reactive oxygen-mediated mechanism with different redox-active metalsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2007Fangli Xie Abstract Recently, we showed that reactive oxygen species (ROS) formation was involved in the toxicity of the redox-active metal Cu and mixtures of Cu plus a photomodified polycyclic aromatic hydrocarbon (PAH), phenanthrenequinone (PHQ), to Daphnia magna. It is unknown, however, if similar results can be observed for metals with lower or no redox activity and their mixtures with PHQ. In the present study using D. magna, the toxicity of Ni, a weakly redox-active metal, and of Cd, a non-redox active metal, was examined with or without PHQ. The abilities of Ni, Cd, PHQ, and binary mixtures of metal plus PHQ to generate ROS were measured using a 2,,7,-dichlorofluorescein fluorescence assay. The results were compared with the results of Cu and mixtures of Cu plus PHQ from a recent study by our group. The order of metal toxicity to D. magna was found to be Cd , Cu > Ni. As with Cu/PHQ mixtures, synergistic toxicity was observed for mixtures of Ni and PHQ, whereas additive toxicity was observed for mixtures of Cd and PHQ. Alone, PHQ had no impact on ROS levels in D. magna. Nickel alone caused elevated ROS, which was further enhanced in the presence of PHQ. Neither Cd nor Cd/PHQ mixtures increased ROS production. Attenuation of toxicity and ROS production was observed in response to treatment with low concentrations of L -ascorbic acid. These results indicate potential toxic interactions between metals and modified PAHs. With redox-active metals, such as Cu and Ni, and modified PAHs, such as PHQ, these interactions can involve ROS formation. [source] ATP-dependent modulation and autophosphorylation of rapeseed 2-Cys peroxiredoxinFEBS JOURNAL, Issue 7 2008Martin Aran 2-Cys peroxiredoxins (2-Cys Prx) are ubiquitous thiol-containing peroxidases that have been implicated in antioxidant defense and signal transduction. Although their biochemical features have been extensively studied, little is known about the mechanisms that link the redox activity and non-redox processes. Here we report that the concerted action of a nucleoside triphosphate and Mg2+ on rapeseed 2-Cys Prx reversibly impairs the peroxidase activity and promotes the formation of high molecular mass species. Using protein intrinsic fluorescence in the analysis of site-directed mutants, we demonstrate that ATP quenches the emission intensity of Trp179, a residue close to the conserved Cys175. More importantly, we found that ATP facilitates the autophosphorylation of 2-Cys Prx when the protein is successively reduced with thiol-bearing compounds and oxidized with hydroperoxides or quinones. MS analyses reveal that 2-Cys Prx incorporates the phosphoryl group into the Cys175 residue yielding the sulfinic-phosphoryl [Prx-(Cys175)-SO2PO32,] and the sulfonic-phosphoryl [Prx-(Cys175)-SO3PO32,] anhydrides. Hence, the functional coupling between ATP and 2-Cys Prx gives novel insights into not only the removal of reactive oxygen species, but also mechanisms that link the energy status of the cell and the oxidation of cysteine residues. [source] Redox Reactions and Electron Transfer Across the Red Cell MembraneIUBMB LIFE, Issue 7 2003Eleanor Kennett Abstract Plasma membrane electron transport systems appear to be ubiquitous. These systems are implicated in hormone signal transduction, cell growth and differentiation events as well as protection from oxidative stress. The red blood cell is constantly exposed to oxidative stress; protection against the reactive species generated during this process may be the main role of its membrane electron transport systems. Membrane redox activity has been studied for over three-quarters of a century, and yet many questions remain regarding its identity and likely roles: are electron transfers by distinct and specific mechanisms; what are the physiological donors and acceptors; and how do these systems affect metabolism? Current evidence suggests that the human erythrocyte membrane contains a number of distinct electron transfer systems, some of which, at least, involve membrane proteins, and NADH or ascorbate as electron donors. The activity of these systems appears to be closely related to the metabolic state of the cell, suggesting that mediation of reducing equivalents across the plasma membrane allows redox buffering of each environment, intra- and extracellular, by the other. We have decided to study this from a new perspective, NMR spectroscopy the area of our own technical expertise, hence this review is slanted towards this more recent analysis. IUBMB Life, 55: 375-385, 2003 [source] Formation of Poly(propylene)-Based Biocomposite Films and Their Use in the Attachment of Methylene BlueMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2010Jesica A. Cavallo Abstract Biocomposite PP -g- PAAc-CS films based on PP were generated and utilized as support of methylene blue, a thiazidic dye. Using a photograft polymerization of acrylic acid, the PP film was functionalized with carboxyl groups (PP -g- PAAc), which attached chitosan by electrostatic bond. A longer poly(acrylic acid) chain or a higher CS immobilization temperature led to a higher chain interpenetration and crosslinking reaction. Immobilized MB confirmed to possess redox activity from its reaction with ascorbic acid, where the dye decomposition rate () increases together with the chain interpenetration, then decreasing with the increase in the crosslinking degree. [source] Tocopheryl quinones and mitochondriaMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 5 2010Lars Gille Abstract In the past, the role of tocopherols and tocopheryl hydroquinones as antioxidants in mitochondria has been examined. However, structural properties of tocopherols and tocopheryl quinones (arrangement of polar/apolar moieties) have also been recognized as being crucial for the selective transport of RRR-,-congeners compared with other tocopherols in the cell, suggesting that these properties might be generally important for the binding of vitamin E-related compounds to proteins and enzymes in mitochondria. Therefore, direct modulation of mitochondrial activities, such as bioenergetics, production of reactive oxygen species and apoptosis, not exclusively related to the redox activity of these compounds is increasingly studied. This overview focuses on the influence of ,-/,-tocopheryl quinones and their parent ,-/,-tocopherols on mitochondrial functions, including formation of tocopheryl quinones, their analytical aspects, their potential as alternative substrates and their inhibitory activity for some mitochondrial functions. It is shown that the understanding of how tocopheryl quinones and tocopherols interfere with mitochondrial functions on the molecular level is still incomplete and that a better comprehension requires further research activities. [source] Mixed-Valence, Mixed-Spin-State, and Heterometallic [2×2] Grid-type Arrays Based on Heteroditopic Hydrazone Ligands: Synthesis and Electrochemical FeaturesCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2005Lindsay H. Uppadine Dr. Abstract An extended family of heterometallic [M12M22(L,)4]n+ [2×2] grid-type arrays 1,9 has been prepared. The three-tiered synthetic route encompasses regioselective, redox and enantioselective features and is based on the stepwise construction of heteroditopic hydrazone ligands A,C. These ligands contain ionisable NH and nonionisable NMe hydrazone units, which allows the metal redox properties to be controlled according to the charge on the ligand binding pocket. The 2-pyrimidine (R) and 6-pyridine (R,) substituents have a significant effect on complex geometry and influence both the electrochemical and magnetic behaviour of the system. 1H NMR spectroscopic studies show that the FeII ions in the grid can be low spin, high spin or spin crossover depending on the steric effect of substituents R and R,. This steric effect has been manipulated to construct an unusual array possessing two low-spin and two spin-crossover FeII centres (grid 8). Electrochemical studies were performed for the grid-type arrays 1,9 and their respective mononuclear precursor complexes 10,13. The grids function as electron reservoirs and display up to eight monoelectronic, reversible reduction steps. These processes generally occur in pairs and are assigned to ligand-based reductions and to the CoIII/CoII redox couple. Individual metal ions in the heterometallic grid motif can be selectively addressed electrochemically (e.g., either the CoIII or FeII ions can be targeted in grids 2 and 5). The FeII oxidation potential is governed by the charge on the ligand binding unit, rather than the spin state, thus permitting facile electrochemical discrimination between the two types of FeII centre in 7 or in 8. Such multistable heterometallic [2×2] gridlike arrays are of great interest for future supramolecular devices incorporating multilevel redox activity. Une famille de complexes hétérométalliques [M12M22(L,)4]n+du type grille [2×2] 1,9 a été préparée. Les trois approches synthétiques multiétapes des ligands hydrazone hétéroditopiques A,C possèdent chacune des caractéristiques régio-, rédox-, énantio-sélectives. Ces ligands possèdent un groupement NH ionisable et un groupement hydrazone non-ionisable NMe, qui permettent un contrôle des propriétés rédox du métal complexé en fonction de la charge de la cavité coordinante. Les substituants 2-pyrimidine (R) et 6-pyridine (R,) influencent de manière significative la géométrie des complexes formés ainsi que leurs propriétés électrochimiques et magnétiques. Les études par spectroscopie RMN1H montrent que les ions FeII, dans ces complexes, possèdent une configuration électronique soit de bas spin, soit de haut spin ou encore de transition de spin en fonction de l'encombrement stérique du substituant. Cet effet stérique a été utilisé pour construire des grilles originales possédant deux cations FeIIde bas spin et deux cations FeIIà transition de spin (grille 8). Des études électrochimiques détaillées ont été réalisées pour les assemblages du type grille 1,9 et leurs précurseurs mononucléaires 10,13. Ces grilles fonctionnent comme réservoir à électrons. Jusqu'à huit étapes de réduction monoélectronique réversibles peuvent être observées. Ces transferts d'électrons se font généralement par paire et interviennent sur le ligand à l'exception des deux premières réductions correspondant aux couples CoIII/CoII. Chaque cation métallique d'une grille peut être sollicité sélectivement par voie électrochimique (les ions CoIIIou FeIIpeuvent être ciblés dans les grilles 2 et 5). Le potentiel d'oxydation du FeIIest tributaire de la charge des ligands et non de l'état de spin, permettant une discrimination électrochimique parmi les deux types de FeIIdans 7 ou 8. De telles grilles [2×2] hétérométalliques ont des niveaux de stabilité multiples et présentent un grand intérêt pour des systèmes supramoléculaires possédant une multiplicité de niveaux d'oxydo-réduction. [source] A Dual Electrochrome of Poly-(3,4-Ethylenedioxythiophene) Doped by N,N,-Bis(3-sulfonatopropyl)-4-4,-bipyridinium,Redox Chemistry and Electrochromism in Flexible DevicesCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 1 2010Shweta Bhandari Abstract An electrochromic zwitterionic viologen, N,N,-bis(3-sulfonatopropyl)-4-4,-bipyridinium, has been used for the first time for doping poly (3,4-ethylenedioxythiopene) (PEDOT) films during electropolymerization. Slow and fast diffusional rates for the monomer at deposition potentials of +1.2 and +1.8,V, respectively yielded the viologen-doped PEDOT films with granular morphology and with dendrite-like shapes. The dual electrochrome formed at +1.8,V, showed enhanced coloration efficiency, larger electrochemical charge storage capacity, and superior redox activity in comparison to its analogue grown at +1.2,V, thus demonstrating the role of dendritic shapes in amplifying electrochromism. Flexible electrochromic devices fabricated with the viologen-doped PEDOT film grown at +1.8,V and Prussian blue with an ionic liquid-based gel electrolyte film showed reversible coloration between pale and dark purple with maximum coloration efficiency of 187,cm2,C,1 at ,=693,nm. The diffusional impedance parameters and switching kinetics of the device showed the suitability of this dual electrochrome formed as a single layer for practical electrochromic cells. [source] | ||||||||||||||||