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Showing papers on "Redox published in 2003"


Journal ArticleDOI
TL;DR: This review describes the main mitochondrial sources of reactive species and the antioxidant defences that evolved to prevent oxidative damage in all the mitochondrial compartments and discusses various physiological and pathological scenarios resulting from an increased steady state concentration of mitochondrial oxidants.
Abstract: The reduction of oxygen to water proceeds via one electron at a time. In the mitochondrial respiratory chain, Complex IV (cytochrome oxidase) retains all partially reduced intermediates until full reduction is achieved. Other redox centres in the electron transport chain, however, may leak electrons to oxygen, partially reducing this molecule to superoxide anion (O2−•). Even though O2−• is not a strong oxidant, it is a precursor of most other reactive oxygen species, and it also becomes involved in the propagation of oxidative chain reactions. Despite the presence of various antioxidant defences, the mitochondrion appears to be the main intracellular source of these oxidants. This review describes the main mitochondrial sources of reactive species and the antioxidant defences that evolved to prevent oxidative damage in all the mitochondrial compartments. We also discuss various physiological and pathological scenarios resulting from an increased steady state concentration of mitochondrial oxidants.

4,282 citations


Journal ArticleDOI
TL;DR: The network of redox signals from energy-generating organelles orchestrates metabolism to adjust energy production to utilization, interfacing with hormone signalling to respond to environmental change at every stage of plant development.
Abstract: Chloroplasts and mitochondria are the powerhouses of photosynthetic cells. The oxidation-reduction (redox) cascades of the photosynthetic and respiratory electron transport chains not only provide the driving forces for metabolism but also generate redox signals, which participate in and regulate every aspect of plant biology from gene expression and translation to enzyme chemistry. Plastoquinone, thioredoxin and reactive oxygen have all been shown to have signalling functions. Moreover, the intrinsic involvement of molecular oxygen in electron transport processes with the inherent generation of superoxide, hydrogen peroxide and singlet oxygen provides a repertoire of additional extremely powerful signals. Accumulating evidence implicates the major redox buffers of plant cells, ascorbate and glutathione, in redox signal transduction. The network of redox signals from energy-generating organelles orchestrates metabolism to adjust energy production to utilization, interfacing with hormone signalling to respond to environmental change at every stage of plant development.

1,279 citations


Journal ArticleDOI
TL;DR: Both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.
Abstract: Solid-oxide fuel cells (SOFCs) promise high efficiencies in a range of fuels. Unlike lower temperature variants, carbon monoxide is a fuel rather than a poison, and so hydrocarbon fuels can be used directly, through internal reforming or even direct oxidation. This provides a key entry strategy for fuel-cell technology into the current energy economy. Present development is mainly based on the yttria-stabilized zirconia (YSZ) electrolyte. The most commonly used anode materials are Ni/YSZ cermets, which display excellent catalytic properties for fuel oxidation and good current collection, but do exhibit disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels, and poor redox cycling causing volume instability. Here, we report a nickel-free SOFC anode, La0.75Sr0.25Cr0.5Mn0.5O3, with comparable electrochemical performance to Ni/YSZ cermets. The electrode polarization resistance approaches 0.2 Omega cm2 at 900 degrees C in 97% H2/3% H2O. Very good performance is achieved for methane oxidation without using excess steam. The anode is stable in both fuel and air conditions, and shows stable electrode performance in methane. Thus both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.

1,059 citations


Journal ArticleDOI
TL;DR: In biological systems, copper homeostasis has been characterized at the molecular level and is coordinated by several proteins such as glutathione, metallothionein, Cu-transporting P-type ATPases, Menkes and Wilson proteins and by cytoplasmic transport proteins called copper chaperones to ensure that it is delivered to specific subcellular compartments and thereby to copper-requiring proteins.

755 citations


Journal ArticleDOI
TL;DR: It is apparent that the chalcogen amino acids cysteine, methionine, selenocysteines, and selenomethionine exhibit a unique biological chemistry that is the source of exciting research opportunities.
Abstract: Sulfur and selenium occur in proteins as constituents of the amino acids cysteine, methionine, selenocysteine, and selenomethionine. Recent research underscores that these amino acids are truly exceptional. Their redox activity under physiological conditions allows an amazing variety of posttranslational protein modifications, metal free redox pathways, and unusual chalcogen redox states that increasingly attract the attention of biological chemists. Unlike any other amino acid, the "redox chameleon" cysteine can participate in several distinct redox pathways, including exchange and radical reactions, as well as atom-, electron-, and hydride-transfer reactions. It occurs in various oxidation states in the human body, each of which exhibits distinctive chemical properties (e.g. redox activity, metal binding) and biological activity. The position of selenium in the periodic table between the metals and the nonmetals makes selenoproteins ideal catalysts for many biological redox transformations. It is therefore apparent that the chalcogen amino acids cysteine, methionine, selenocysteine, and selenomethionine exhibit a unique biological chemistry that is the source of exciting research opportunities.

674 citations


Journal ArticleDOI
TL;DR: Findings indicate that ROS production by mitochondria oxidizing physiological NADH‐dependent substrates is regulated by ΔΨ and by the NAD(P)H redox state over ranges consistent with those that exist at different levels of cellular energy demand.
Abstract: Mitochondrial production of reactive oxygen species (ROS) at Complex I of the electron transport chain is implicated in the etiology of neural cell death in acute and chronic neurodegenerative disorders. However, little is known regarding the regulation of mitochondrial ROS production by NADH-linked respiratory substrates under physiologically realistic conditions in the absence of respiratory chain inhibitors. This study used Amplex Red fluorescence measurements of H2O2 to test the hypothesis that ROS production by isolated brain mitochondria is regulated by membrane potential (DeltaPsi) and NAD(P)H redox state. DeltaPsi was monitored by following the medium concentration of the lipophilic cation tetraphenylphosphonium with a selective electrode. NAD(P)H autofluorescence was used to monitor NAD(P)H redox state. While the rate of H2O2 production was closely related to DeltaPsi and the level of NAD(P)H reduction at high values of DeltaPsi, 30% of the maximal rate of H2O2 formation was still observed in the presence of uncoupler (p-trifluoromethoxycarbonylcyanide phenylhydrazone) concentrations that provided for maximum depolarization of DeltaPsi and oxidation of NAD(P)H. Our findings indicate that ROS production by mitochondria oxidizing physiological NADH-dependent substrates is regulated by DeltaPsi and by the NAD(P)H redox state over ranges consistent with those that exist at different levels of cellular energy demand.

481 citations


Journal ArticleDOI
TL;DR: The immobilized GOD could electrocatalyze the reduction of dissolved oxygen and resulted in a great increase of the reduction peak current, which could be used for glucose detection with a high sensitivity and exclude the interference of commonly coex uric and ascorbic acid.

445 citations


Journal ArticleDOI
TL;DR: In this article, the structure and electrochemistry of FeF 3 :C-based carbon metal fluoride nanocomposites (CMFNCs) were investigated in detail from 4.5 to 1.5 V, revealing a reversible metal fluoride conversion process.
Abstract: The structure and electrochemistry of FeF 3 :C-based carbon metal fluoride nanocomposites (CMFNCs) was investigated in detail from 4.5 to 1.5 V, revealing a reversible metal fluoride conversion process. These are the first reported examples of a high-capacity reversible conversion process for positive electrodes. A reversible specific capacity of approximately 600 mAh/g of CMFNCs was realized at 70°C. Approximately one-third of the capacity evolved in a reaction between 3.5 and 2.8 V related to the cathodic reduction reaction of Fe 3+ to Fe 2+ . The remainder of the specific capacity occurred in a two-phase conversion reaction at 2 V resulting in the formation of a finer Fe:LiF nanocomposite. Upon oxidation, selective area electron diffraction characterization revealed the reformation of a metal fluoride. Evidence presented suggested that the metal fluoride is related to FeF 2 in structure. A pseudocapacitive reaction is proposed as a possible mechanism for the subsequent Fe 2+ → Fe 3+ oxidation reaction. Preliminary results of FeF 2 , NiF 2 , and CoF 2 CMFNCs were used in the discussion of the electrochemical properties of the reconverted metal fluoride.

426 citations


Journal ArticleDOI
TL;DR: The diversity of cysteine's multiple roles in vivo is equally as fascinating as it is promising for future biochemical and pharmacological research.

407 citations


Journal ArticleDOI
TL;DR: In this article, the performance of carbon nanotubes paste electrodes (CNTPE) prepared by dispersion of multi-wall carbon Nanotubes (MWNT) within mineral oil is described.

395 citations


Journal ArticleDOI
TL;DR: A redox hydrogel with an apparent electron diffusion coefficient (D(app) of (5.8 +/- 0.5) x 10(-)(6) cm(2) s(-)(1)) is described, which results from the tethering of redox centers to the backbone of the cross-linked redox polymer backbone through 13 atom spacer arms.
Abstract: A redox hydrogel with an apparent electron diffusion coefficient (Dapp) of (5.8 ± 0.5) × 10-6 cm2 s-1 is described. The order of magnitude increase in Dapp relative to previously studied redox hydrogels results from the tethering of redox centers to the backbone of the cross-linked redox polymer backbone through 13 atom spacer arms. The long and flexible tethers allow the redox centers to sweep electrons from large-volume elements and to collect electrons of glucose oxidase efficiently. The spacer arms make the collection of electrons from glucose oxidase so efficient that glucose is electrooxidized already at −0.36 V versus Ag/AgCl, the reversible potential of the redox potential of the FAD/FADH2 centers of the enzyme at pH 7.2. The limiting current density of 1.15 mA cm-2 is reached at a potential as low as −0.1 V versus Ag/AgCl. The novel redox center of the polymer is a tris-dialkylated N,N‘-biimidazole Os2+/3+ complex. Its redox potential, −0.195 V versus Ag/AgCl, is 0.8 V reducing relative to that o...

Journal ArticleDOI
TL;DR: In this article, a series of binuclear FeIFeI complexes, (μ-SEt)2[Fe(CO)2L]2======¯¯¯¯(L = CO (1), PMe3====== ``(1-P)),(μ-SRS)[Fe(Co) 2L] 2======(R = CH2CH2======�
Abstract: A series of binuclear FeIFeI complexes, (μ-SEt)2[Fe(CO)2L]2 (L = CO (1), PMe3 (1-P)), (μ-SRS)[Fe(CO)2L]2 (R = CH2CH2 (μ-edt): L = CO (2), PMe3 (2-P); R = CH2CH2CH2(μ-pdt): L = CO (3), PMe3 (3-P); and R = o-CH2C6H4CH2 (μ-o-xyldt): L = CO (4), PMe3 (4-P)), that serve as structural models for the active site of Fe-hydrogenase are shown to be electrocatalysts for H2 production in the presence of acetic acid in acetonitrile. The redox levels for H2 production were established by spectroelectrochemistry to be Fe0Fe0 for the all-CO complexes and FeIFe0 for the PMe3-substituted derivatives. As electrocatalysts, the PMe3 derivatives are more stable and more sensitive to acid concentration than the all-CO complexes. The electrocatalysis is initiated by electrochemical reduction of these diiron complexes, which subsequently, under weak acid conditions, undergo protonation of the reduced iron center to produce H2. An (η2-H2)FeII–Fe0/I intermediate is suggested and probable electrochemical mechanisms are discussed.

Journal Article
TL;DR: In this article, the reduction potentials of wine polyphenols and oxygen, as well as that of the Fe3+/Fe2+ couple, have been calculated for wine conditions and form the basis for discussing how these redox systems are likely to interact.
Abstract: The chemical, biochemical, and enological literature has been broadly surveyed to identify the reaction mechanisms of oxygen and of its intermediate reduction products that should apply to wine. The reduction potentials of redox couples derived from wine polyphenols and oxygen, as well as that of the Fe3+/Fe2+ couple, have been calculated for wine conditions and form the basis for discussing how these redox systems are likely to interact. Values obtained for wine quinone/catechol couples agree well with those reported for wine-model conditions. Catechol derivatives are oxidized sequentially to semiquinones and quinones, while oxygen is reduced in turn to hydroperoxyl radicals and hydrogen peroxide. The whole process is mediated by redox cycling of the Fe3+/Fe2+ couple, which is made possible by the lowering of its reduction potential by coordination of Fe3+ to hydroxy acids. Hydrogen peroxide is then further reduced by Fe2+ in the Fenton reaction to produce hydroxyl radicals, which oxidize saturated hydroxy compounds. Intermediate radicals may react with oxygen, providing an additional pathway for its reduction. Thus, both ferric and ferrous ions, which are present in wine, perform an important catalytic function. The antioxidant activity of bisulfite is largely restricted to its reaction with hydrogen peroxide. Direct reaction of sulfur dioxide with oxygen, which is a radical chain process, is prevented by the radical scavenging activity of polyphenols.

Journal ArticleDOI
TL;DR: It is demonstrated that the production of hydrogen gas by membrane vesicles of P. furiosus is directly coupled to the synthesis of ATP by means of a proton-motive force that has both electrochemical and pH components.
Abstract: Oxidative phosphorylation involves the coupling of ATP synthesis to the proton-motive force that is generated typically by a series of membrane-bound electron transfer complexes, which ultimately reduce an exogenous terminal electron acceptor This is not the case with Pyrococcus furiosus, an archaeon that grows optimally near 100°C It has an anaerobic respiratory system that consists of a single enzyme, a membrane-bound hydrogenase Moreover, it does not require an added electron acceptor as the enzyme reduces protons, the simplest of acceptors, to hydrogen gas by using electrons from the cytoplasmic redox protein ferredoxin It is demonstrated that the production of hydrogen gas by membrane vesicles of P furiosus is directly coupled to the synthesis of ATP by means of a proton-motive force that has both electrochemical and pH components Such a respiratory system enables rationalization in this organism of an unusual glycolytic pathway that was previously thought not to conserve energy It is now clear that the use of ferredoxin in place of the expected NAD as the electron acceptor for glyceraldehyde 3-phosphate oxidation enables energy to be conserved by hydrogen production In addition, this simple respiratory mechanism readily explains why the growth yields of P furiosus are much higher than could be accounted for if ATP synthesis occurred only by substrate-level phosphorylation The ability of microorganisms such as P furiosus to couple hydrogen production to energy conservation has important ramifications not only in the evolution of respiratory systems but also in the origin of life itself

Journal ArticleDOI
TL;DR: Novel role of AC as redox mediator in accelerating the reductive transformation of pollutants as well as a terminal electron acceptor in the biological oxidation of an organic substrate is described.
Abstract: Activated carbon (AC) has a long history of applications in environmental technology as an adsorbent of pollutants for the purification of drinking waters and wastewaters. Here we describe novel role of AC as redox mediator in accelerating the reductive transformation of pollutants as well as a terminal electron acceptor in the biological oxidation of an organic substrate. This study explores the use of AC as an immobilized redox mediator for the reduction of a recalcitrant azo dye (hydrolyzed Reactive Red 2) in laboratory-scale anaerobic bioreactors, using volatile fatty acids as electron donor. The incorporation of AC in the sludge bed greatly improved dye removal and formation of aniline, a dye reduction product. These results indicate that AC acts as a redox mediator. In supporting batch experiments, bacteria were shown to oxidize acetate at the expense of reducing AC. Furthermore, AC greatly accelerated the chemical reduction of an azo dye by sulfide. The results taken as a whole clearly suggest that AC accepts electrons from the microbial oxidation of organic acids and transfers the electrons to azo dyes, accelerating their reduction. A possible role of quinone surface groups in the catalysis is discussed.

Journal ArticleDOI
TL;DR: The principles of protein film voltammetry are outlined by discussing some recent results from this laboratory, and the potential dimension is introduced into enzyme kinetics.
Abstract: Protein film voltammetry is a relatively new approach to studying redox enzymes, the concept being that a sample of a redox protein is configured as a film on an electrode and probed by a variety of electrochemical techniques. The enzyme molecules are bound at the electrode surface in such a way that there is fast electron transfer and complete retention of the chemistry of the active site that is observed in more conventional experiments. Modulations of the electrode potential or catalytic turnover result in the movement of electrons to, from, and within the enzyme; this is detected as a current that varies in characteristic ways with time and potential. Henceforth, the potential dimension is introduced into enzyme kinetics. The presence of additional intrinsic redox centers for providing fast intramolecular electron transfer between a buried active site and the protein surface is an important factor. Centers which carry out cooperative two-electron transfer, most obviously flavins, produce a particularl...

Journal ArticleDOI
TL;DR: In this article, a vanadium chloride/polyhalide redox flow cell is described, which employs a polyhalide solution in the positive half-cell electrolyte and a V(II)/vanadium(III) chloride redox couple as the negative half-cells electrolyte.

Journal ArticleDOI
TL;DR: The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square wave voltammetry at different pH.
Abstract: The mechanism of electrochemical oxidation of quercetin on a glassy carbon electrode has been studied using cyclic, differential pulse and square-wave voltammetry at different pH. It proceeds in a cascade mechanism, related with the two catechol hydroxyl groups and the other three hydroxyl groups which all present electroactivity, and the oxidation is pH dependent. Quercetin also adsorbs strongly on the electrode surface; and the final oxidation product is not electroactive and blocks the electrode surface. The oxidation of the catechol 3,4-dihydroxyl electron-donating groups, occurs first, at very low positive potentials, and is a two electron two proton reversible reaction. The hydroxyl group oxidized next was shown to undergo an irreversible oxidation reaction, and this hydroxyl group can form a intermolecular hydrogen bond with the neighboring oxygen. The other two hydroxyl groups also have an electron donating effect and their oxidation is reversible.

Journal ArticleDOI
TL;DR: This work summarized the results of research into Adsorption of Hydrogen-Bonding Species:Oxygenated Organics and its implications for Atmospheric Implications, Needs for Laboratory Research, and Reactions to Reactions.
Abstract: 47893.3. Adsorption of Hydrogen-Bonding Species:Oxygenated Organics47903.4. Adsorption of Other Species 47923.5. Adsorption: Atmospheric Implications 47923.6. Adsorption: Needs for Laboratory Research 47934. Reactions of Atmospheric Trace Gases on IceSurfaces47944.1. Hydrolysis Reactions 47944.2. Halogen Activation Reactions 47954.3. Sulfur(IV) Oxidation Reactions 47974.4. Reactions: Atmospheric Implications 47974.5. Reactions: Needs for Laboratory Research 47985. Summary 47986. Acknowledgments 47987. References 4799

Journal ArticleDOI
TL;DR: In this paper, the role of the copper species in the CO oxidation reaction was investigated in terms of species transformation and change in the number of surface lattice oxygen ions, and the light-off behaviors were observed over both Cu and Cu2O powders.
Abstract: Carbon monoxide oxidation activities over Cu, Cu2O, and CuO were studied to seek insight into the role of the copper species in the oxidation reaction. The activity of copper oxide species can be elucidated in terms of species transformation and change in the number of surface lattice oxygen ions. The propensity of Cu2O toward valence variations and thus its ability to seize or release surface lattice oxygen more readily enables Cu2O to exhibit higher activities than the other two copper species. The non-stoichiometric metastable copper oxide species formed during reduction are very active in the course of CO oxidation because of its excellent ability to transport surface lattice oxygen. Consequently, the metastable cluster of CuO is more active than CuO, and the activity will be significantly enhanced when non-stoichiometric copper oxides are formed. In addition, the light-off behaviors were observed over both Cu and Cu2O powders. CO oxidation over metallic Cu powders was lighted-off because of a synergistic effect of temperature rises due to heat generation from Cu oxidation as well as CO oxidation over the partially oxidized copper species.

Journal ArticleDOI
TL;DR: In this article, the effect of AQ surface concentration on the kinetics of oxygen reduction has been investigated and the rate constant of the chemical reaction between semiquinone radical anion of AQ and molecular oxygen has been determined.

Journal ArticleDOI
TL;DR: A detailed investigation of the reductive nitrosylation of human met-Hb is reported, in which it is demonstrated the production of S-nitroso (SNO)-Hb through a heme-Fe(III)NO intermediate and the effective coupling of heme–iron and NO redox chemistries.
Abstract: Previous studies of the interactions of NO with human hemoglobin have implied the predominance of reaction channels that alternatively eliminate NO by converting it to nitrate, or tightly complex it on the α subunit ferrous hemes. Both channels could effectively quench NO bioactivity. More recent work has raised the idea that NO groups can efficiently transfer from the hemes to cysteine thiols within the β subunit (cysβ-93) to form bioactive nitrosothiols. The regulation of NO function, through its chemical position in the hemoglobin, is supported by response to oxygen and to redox agents that modulate the molecular and electronic structure of the protein. In this article, we focus on reactions in which Fe(III) hemes could provide the oxidative requirements of this NO-group transfer chemistry. We report a detailed investigation of the reductive nitrosylation of human met-Hb, in which we demonstrate the production of S-nitroso (SNO)-Hb through a heme-Fe(III)NO intermediate. The production of SNO-Hb is strongly favored (over nitrite) when NO is gradually introduced in limited total quantities; in this situation, moreover, heme nitrosylation occurs primarily within the β subunits of the hemoglobin tetramer. SNO-Hb can similarly be produced when Fe(II)NO hemes are subjected to mild oxidation. The reaction of deoxygenated hemoglobin with limited quantities of nitrite leads to the production of β subunit Fe(II)NO hemes, with SNO-Hb produced on subsequent oxygenation. The common theme of these reactions is the effective coupling of heme–iron and NO redox chemistries. Collectively, they establish a connectivity between hemes and thiols in Hb, through which NO is readily dislodged from storage on the heme to form bioactive SNO-Hb.

Journal ArticleDOI
TL;DR: In this article, Escherichia coli W3110 was genetically engineered for acetate production by using an approach that combines attributes of fermentative and oxidative metabolism (rapid growth, external electron acceptor) into a single biocatalyst.
Abstract: Microbial processes for commodity chemicals have focused on reduced products and anaerobic conditions where substrate loss to cell mass and CO2 are minimal and product yields are high. To facilitate expansion into more oxidized chemicals, Escherichia coli W3110 was genetically engineered for acetate production by using an approach that combines attributes of fermentative and oxidative metabolism (rapid growth, external electron acceptor) into a single biocatalyst. The resulting strain (TC36) converted 333 mM glucose into 572 mM acetate, a product of equivalent oxidation state, in 18 h. With excess glucose, a maximum of 878 mM acetate was produced. Strain TC36 was constructed by sequentially assembling deletions that inactivated oxidative phosphorylation (ΔatpFH), disrupted the cyclic function of the tricarboxylic acid pathway (ΔsucA), and eliminated native fermentation pathways (ΔfocA-pflB ΔfrdBC ΔldhA ΔadhE). These mutations minimized the loss of substrate carbon and the oxygen requirement for redox balance. Although TC36 produces only four ATPs per glucose, this strain grows well in mineral salts medium and has no auxotrophic requirement. Glycolytic flux in TC36 (0.3 μmol⋅min−1⋅mg−1 protein) was twice that of the parent. Higher flux was attributed to a deletion of membrane-coupling subunits in (F1F0)H+-ATP synthase that inactivated ATP synthesis while retaining cytoplasmic F1-ATPase activity. The effectiveness of this deletion in stimulating flux provides further evidence for the importance of ATP supply and demand in the regulation of central metabolism. Derivatives of TC36 may prove useful for the commercial production of a variety of commodity chemicals.

Journal ArticleDOI
TL;DR: In this article, the electro-oxidation of methanol was carried out on a platinised electrode in various alkaline media to examine the role of OH ads species and the influence of anions in the electrolyte on the methanoline oxidation reaction.

Journal Article
TL;DR: The hypothesis that a redox cycle within the mammalian cell cycle might provide a mechanistic link between the metabolic processes early in G(0)-G(1) and the activation of G(1)-regulatory proteins in preparation for the entry of cells into S phase is supported.
Abstract: The hypothesis that intracellular oxidation/reduction (redox) reactions regulate the G(0)-G(1) to S-phase transition in the mouse embryonic fibroblast cell cycle was investigated Intracellular redox state was modulated with a thiol-antioxidant, N-acetyl-L-cysteine (NAC), and cell cycle progression was measured using BrdUrd pulse-chase and flow cytometric analysis Treatment with NAC for 12 h resulted in an approximately 6-fold increase in intracellular low-molecular-weight thiols and a decrease in the MFI of an oxidation-sensitive probe, dihydrofluorescein diacetate, indicating a shift in the intracellular redox state toward a more reducing environment NAC-induced alterations in redox state caused selective delays in progression from G(0)-G(1) to S phase in serum-starved cells that were serum stimulated to reenter the cell cycle as well as to inhibit progression from G(1) to S phase in asynchronous cultures with no significant alterations in S phase, and G(2)+M transits NAC treatment also showed a 70% decrease in cyclin D1 protein levels and a 3-4-fold increase in p27 protein levels, which correlated with decreased retinoblastoma protein phosphorylation Cells released from the NAC treatment showed a transient increase in dihydrofluorescein fluorescence and oxidized glutathione content between 0 and 8 h after release, indicating a shift in intracellular redox state to a more oxidizing environment These changes in redox state were followed by an increase in cyclin D1, a decrease in p27, retinoblastoma protein hyperphosphorylation and subsequent entry into S phase by 8-12 h after the removal of NAC These results support the hypothesis that a redox cycle within the mammalian cell cycle might provide a mechanistic link between the metabolic processes early in G(1) and the activation of G(1)-regulatory proteins in preparation for the entry of cells into S phase

Journal ArticleDOI
TL;DR: The voltammogram of aryldiazonium tetrafluoroborates in acetonitrile (ACN), at low concentration, shows a first one-electron wave followed at a more negative potential by a small second wave; this last one corresponds to the reduction of the radical formed at the level of the first wave.
Abstract: The voltammogram of aryldiazonium tetrafluoroborates in acetonitrile (ACN), at low concentration, shows a first one-electron wave followed at a more negative potential by a small second wave; this last one corresponds to the reduction of the radical formed at the level of the first wave. Simulation of the voltammogram permits one to determine the standard redox potential of the radical/anion couple E°(Ph•/Ph-) = 0.05 V/SCE and the reduction mechanism of the diazonium cation. An electron transfer concerted with the cleavage of the C−N bond furnishes the aryl radical; this radical undergoes two competitive reactions: reduction at the electrode and H-atom transfer.

Journal ArticleDOI
TL;DR: LiNi 0.5 O 4 spinels, where M=Fe, Mg, Al, or Cu, and y = 0.4, have been studied as highvoltage cathode materials as discussed by the authors.

Journal ArticleDOI
TL;DR: Even though the EC/MS/MS system is not able to mimic all oxidations performed by cytochrome P450, valuable information can be obtained concerning the sensitivity of the substrate towards oxidation and in which position of the molecule oxidations are likely to take place.
Abstract: The extent to which electrochemistry on-line with electrospray mass spectrometry can be used to mimic cytochrome P450 catalyzed oxidations has been investigated. Comparisons on the mechanistic level have been made for most reactions in an effort to explain why certain reactions can, and some cannot, be mimicked by electrochemical oxidations. The EC/MS/MS system used successfully mimics in cases where the P450 catalyzed reactions are supposed to proceed via a mechanism initiated by a one-electron oxidation, such as N-dealkylation, S-oxidation, P-oxidation, alcohol oxidation and dehydrogenation. The P450 catalyzed reactions initiated via direct hydrogen atom abstraction, such as O-dealkylation and hydroxylation of unsubstituted aromatic rings, generally had a too high oxidation potential to be electrochemically oxidized below the oxidation potential limit of water, and were not mimicked by the EC/MS/MS system. Even though the EC/MS/MS system is not able to mimic all oxidations performed by cytochrome P450, valuable information can be obtained concerning the sensitivity of the substrate towards oxidation and in which position of the molecule oxidations are likely to take place. For small-scale electrochemical synthesis of metabolites, starting from the drug, the EC/MS/MS system should be very useful for quick optimization of the electrochemical conditions. The simplicity of the system, and the ease and speed with which it can be applied to a large number of compounds, make it a useful tool in drug metabolism research.

Journal ArticleDOI
TL;DR: In this article, the authors summarized the literature concerning the structure, hydrolytic stability in solution, thermal stability in the solid state, redox-acid properties and applications of heteropoly-compounds with Wells-Dawson structure.
Abstract: The scientific literature concerning the structure, hydrolytic stability in solution, thermal stability in the solid state, redox-acid properties and applications of heteropoly-compounds (HPCs) with Wells–Dawson structure is summarized in the present work. Wells–Dawson heteropoly-anions possess the formula [(X n+ )2M18O62] (16−2n)− where X n+ represents a central atom (phosphorous(V), arsenic(V), sulfur(VI), fluorine) surrounded by a cage of M addenda atoms, such as tungsten(VI), molybdenum(VI) or a mixture of elements, each of them composing MO6 (M-oxygen) octahedral units. The addenda atoms are partially substituted by other elements, such as vanadium, transition metals, lanthanides, halogens and inorganic radicals. The Wells–Dawson heteropoly-anion is associated with inorganic (H + , alkaline elements, etc.) or organic countercations forming hybrid compounds. Wells–Dawson acids (phospho-tungstic H6P2W18O62·24H2O, phospho-molybdic H6P2Mo18O62·nH2O and arsenicmolybdic H6As2Mo18O62·nH2O) possess super-acidity and a remarkably stability both in solution and in the solid state. These properties make them suitable catalytic materials in homogeneous and heterogeneous liquid-phase reactions replacing the conventional liquid acids (HF, HCl, H2SO4, etc.). Although, the application of the acids in heterogeneous gas-phase reactions is less developed, there is a patented method to oxidize alkanes to carboxylic acids on a supported Wells–Dawson catalyst that combines acid and redox properties. Wells–Dawson anions possess the ability to accept or release electrons through an external potential or upon exposure to visible and UV radiation (electro and photochemical reactions). Additionally, Wells–Dawson HPCs catalyze the oxidation of organic molecules with molecular oxygen, hydrogen peroxide and iodosylarenes; epoxidation and hydrogenation in homogeneous and heterogeneous liquid-phase conditions. The ability of transition metal substituted Wells–Dawson HPCs to be reduced and re-oxidized without degradation of the structure is promising in the application of those HPCs replacing metalloporphyrins catalysts in redox and electrochemical reactions.

Journal ArticleDOI
TL;DR: In this article, supported bimetallic palladium and platinum catalysts promoted by metals of group 11 (Cu, Ag, and Au) were prepared by control surface deposition and tested in the liquid phase reduction of nitrates.