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Redox Potential (redox + potential)
Selected AbstractsControlling the Diameter of Polyaniline Nanofibers by Adjusting the Oxidant Redox Potential,ADVANCED MATERIALS, Issue 3 2007H. Ding A self-assembly process with no external template and no added acidic dopant is reported as a method providing quantitative control over the diameter d of the polyaniline (PANI) nanofibers produced. An experimental formula relating d to the standard redox potential of the oxidants is established. The PANI nanofibers in the figure have d,,,15,nm. [source] Additive Tuning of Redox Potential in Metallacarboranes by Sequential Halogen SubstitutionCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Patricia González-Cardoso Abstract The first artificially made set of electron acceptors is presented that are derived from a unique platform Cs[3,3,-Co(C2B9H11)2], for which the redox potential of each differs from its predecessor by a fixed amount. The sequence of electron acceptors is made by substituting one, two, or more hydrogen atoms by chlorine atoms, yielding Cs[3,3,-Co(C2B9H11,yCly)(C2B9H11,zClz)]. The higher the number of chlorine substituents, the more prone the platform is to be reduced. The effect is completely additive, so if a single substitution implies a reduction of 0.1,V of the redox potential of the parent complex, then ten substitutions imply a reduction of 1,V. [source] Can Electrophilicity Act as a Measure of the Redox Potential of First-Row Transition Metal Ions?CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2007Jan Moens Abstract Previous contributions concerning the computational approach to redox chemistry have made use of thermodynamic cycles and Car,Parrinello molecular dynamics simulations to obtain accurate redox potential values, whereas this article adopts a conceptual density functional theory (DFT) approach. Conceptual DFT descriptors have found widespread use in the study of thermodynamic and kinetic aspects of a variety of organic and inorganic reactions. However, redox reactions have not received much attention until now. In this contribution, we prove the usefulness of global and local electrophilicity descriptors for the prediction of the redox characteristics of first row transition metal ions (from Sc3+|Sc2+ to Cu3+|Cu2+) and introduce a scaled definition of the electrophilicity based on the number of electrons an electrophile ideally accepts. This scaled electrophilicity concept acts as a good quantitative estimate of the redox potential. We also identify the first solvation sphere together with the metal ion as the primary active region during the electron uptake process, whereas the second solvation sphere functions as a non-reactive continuum region. [source] Radii of Redox Components from Absolute Redox Potentials Compared with Covalent and Aqueous Ionic RadiiELECTROANALYSIS, Issue 9 2010Raji Heyrovska Abstract Aqueous standard potentials, referred to that of the SHE as zero, were recently shown to vary linearly with gaseous ionization potentials, with the absolute potential of SHE as the intercept. This enabled arriving at the absolute redox potentials of elements. Here, the distances between the oxidized and reduced forms in aqueous solutions have been evaluated. From the linear dependence of these distances on the covalent radii of atoms, the radii of the redox components have been obtained. The latter also vary linearly with the aqueous ionic radii estimated earlier from ion-water distances, and indicate the presence of aqueous molecular anions. [source] Experimentally Determined Redox Potentials of Individual (n,m),Single-Walled Carbon Nanotubes,ANGEWANDTE CHEMIE, Issue 41 2009Yasuhiko Tanaka Dr. Nanoröhren mit Potential: Durch Herstellen eines dünnen Films, der isolierte einwandige Nanoröhren (SWNTs) zurückhält, gelang es, die Redoxpotentiale vieler SWNTs mit unterschiedlichen Chiralitätsindizes (n,m) experimentell zu bestimmen. Die einfache Methode lässt sich auf alle einzelnen SWNTs mit messbarer Photolumineszenz (PL) im Nah-IR-Bereich anwenden (siehe Diagramm). [source] Redox Potentials of Methanophenazine and CoB-S-S-CoM, Factors Involved in Electron Transport in Methanogenic Archaea,CHEMBIOCHEM, Issue 4 2003Mario Tietze Dr. Potentially important: The redox potentials of methanophenazine and CoB-S-S-CoM (see scheme), two cofactors from methanogenic archaea, strongly support the view that methanophenazine plays a central role in the electron transport system of methane-producing archaea. These redox potentials were measured with a hanging mercury drop electrode as the working electrode and were compared to those of several phenazine ethers. [source] A Conceptual DFT Approach for the Evaluation and Interpretation of Redox Potentials.CHEMINFORM, Issue 49 2007Jan Moens 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] Electrochemical Genotyping by Using Two Ferrocene/Isoquinoline-Connected DNA Probes with Different Redox Potentials on a Single ElectrodeCHEMISTRY - A EUROPEAN JOURNAL, Issue 29 2009Reona Ikeda A single electrode: We describe an electrochemical single-nucleotide polymorphism genotyping protocol using a single electrode that is modified with a ferrocene/isoquinoline conjugate connected to DNA probes, which possess different redox potentials. Three types of zygotes (a wild-type homozygote, a mutant homozygote, and a heterozygote) were identified by a single square wave voltammetric measurement. [source] The Interplay of Inverted Redox Potentials and Aromaticity in the Oxidized States of New ,-Electron Donors: 9-(1,3-Dithiol-2-ylidene)fluorene and 9-(1,3-Dithiol-2-ylidene)thioxanthene DerivativesCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2006Samia Amriou Dr. Abstract Derivatives of 9-(1,3-dithiol-2-ylidene)fluorene (9) and 9-(1,3-dithiol-2-ylidene)thioxanthene (10) have been synthesised using Horner,Wadsworth,Emmons reactions of (1,3-dithiol-2-yl)phosphonate reagents with fluorenone and thioxanthen-9-one. X-ray crystallography, solution electrochemistry, optical spectroscopy, spectroelectrochemistry and simultaneous electrochemistry and electron paramagnetic resonance (SEEPR), combined with theoretical calculations performed at the B3P86/6-31G** level, elucidate the interplay of the electronic and structural properties in these molecules. These compounds are strong two-electron donors, and the oxidation potentials depend on the electronic structure of the oxidised state. Two, single-electron oxidations (<) were observed for 9-(1,3-dithiol-2-ylidene)fluorene systems (9). In contrast, derivatives of 9-(1,3-dithiol-2-ylidene)thioxanthene (10) display the unusual phenomenon of inverted potentials (>) resulting in a single, two-electron oxidation process. The latter is due to the aromatic structure of the thioxanthenium cation (formed on the loss of a second electron), which stabilises the dication state (102+) compared with the radical cation. This contrasts with the nonaromatic structure of the fluorenium cation of system 9. The two-electron oxidation wave in the thioxanthene derivatives is split into two separate one-electron waves in the corresponding sulfoxide and sulfone derivatives 27,29 owing to destabilisation of the dication state. [source] Theoretical Study of One-electron Redox Potentials of Some NADH Model CompoundsCHINESE JOURNAL OF CHEMISTRY, Issue 1 2010Huajing Wang Abstract Several 1-benzyl-1,4-dihydronicotinamide derivatives, which are important NADH model compounds were studied theoretically in acetonitrile. The performances of various DFT methods including B3LYP, B1B95, B3PW91, MPW1B95, MPWKCIS, and M06 were tested to calculate the redox potentials. The first theoretical protocol to predict the redox potentials of these derivatives is B1B95, whose reliability has been tested against almost all the available experimental data. Strikingly, the mean absolute derivations (MAD) and root mean square (RMS) error of the current theoretical model equal 0.015 and 0.017, respectively. By using this method, the important thermodynamic properties of BNAHs were investigated and the mechanisms of hydride transfer progress were explained. Besides, para -substituents that have a big effect on these redox potentials of BNAH were systematically studied and carefully demonstrated. [source] Premature Salmonella Typhimurium growth inhibition in competition with other Gram-negative organisms is redox potential regulated via RpoS inductionJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2004E. Komitopoulou Abstract Aims:, To identify the role of oxidation,reduction (redox) potential in the premature growth inhibition and RpoS induction in Salmonella serotype Typhimurium in competitive growth experiments. Methods and Results:, Oxidation,reduction potential was measured throughout the growth of a minority population of Salm. Typhimurium in mixed cultures with other Gram-negative and Gram-positive organisms. A lux -based reporter was also used to evaluate RpoS activity in Salm. Typhimurium in competitor studies. In a mixed culture, the multiplication of a minority population of Salm. Typhimurium was inhibited when competing Gram-negative organisms entered the stationary phase. This was not seen when the competing flora was Gram-positive. The change in redox potential during growth in mixed cultures was closely linked to the inhibition of Salm. Typhimurium growth by Gram-negative competitors. An artificially induced drop in redox potential earlier during growth in mixed cultures with Gram-negative organisms reduced the time to RpoS induction in Salm. Typhimurium and thus inhibited its multiplication prematurely. In contrast, RpoS induction and growth inhibition were prevented under high redox potential conditions. Conclusions:, This work shows that the inhibitory activity of competitive organisms can be mediated through their effect on redox potential-regulated RpoS induction. Significance and Impact of the Study:, Redox potential is shown to be an important determinant of Salm. Typhimurium growth, an observation with practical implications both for its control and detection. [source] Redox potential of bulk soil and soil solution concentration of nitrate, manganese, iron, and sulfate in two GleysolsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2004Tim Mansfeldt Abstract While the reduction of nitrate-N, Mn(III,IV), Fe(III), and sulfate-S in soil has been studied intensively in the laboratory, field research has received only limited attention. This study investigated the relationship between redox potential (EH) measured in bulk soil and concentrations of nitrate, Mn2+, Fe2+, and sulfate in the soil solution of two Gleysols differing in drainage status from the Marsh area of Schleswig-Holstein, Northern Germany. The soils are silty-sandy and developed from calcareous marine sediments. Redox potentials were monitored weekly with permanently installed Pt electrodes, and soil solution was obtained biweekly by ceramic suction cups from 10, 30, 60, and 150,cm depth over one year. Median EH at 10, 30, 60, and 150,cm depths was 470, 410, 410, and 20 mV in the drained soil and 500, 480, 30, and ,170 mV in the undrained soil, respectively. A decrease in EH below critical values was accompanied in the soil solutions (pH 7.4 to 7.8) by disappearance of nitrate below 0 to 200 mV, appearance of Mn2+ below 350 mV, and Fe2+ below 0 to 50 mV. Both metals disappeared from soil solution after aeration. In the sulfide-bearing environment of the 150,cm depth of the undrained soil, however, the sulfate concentrations were highest at such EH values at which sulfate should be unstable. This discrepancy was reflected in the fact that at this depth bulk soil EH was about 400 mV lower than soil solution EH (250 mV). When investigating the dynamics of nitrate, Mn, and Fe in soils, bulk soil EH provides semi-quantitative information in terms of critical EH ranges. However, in sulfidic soil environments the interpretation of EH measured in bulk soil is uncertain. Redoxpotenzial des Bodens und Bodenlösungskonzentrationen von Nitrat, Mangan, Eisen und Sulfat in zwei Kalkmarschen Während die Reduktion von Nitrat-N, Mn(III,IV), Fe(III) und Sulfat-S in Böden intensiv im Labor untersucht worden ist, haben Felduntersuchungen sich damit kaum beschäftigt. In dieser Arbeit wurde die Beziehung zwischen dem Redoxpotenzial (EH) der Bodenmatrix und den Bodenlösungskonzentrationen von Nitrat, Mn2+, Fe2+ und Sulfat in zwei unterschiedlich drainierten Kalkmarschen Schleswig-Holsteins untersucht. Die Böden sind schluffig-sandig und haben sich aus kalkhaltigen marinen Sedimenten entwickelt. Über ein Jahr wurden in 10, 30, 60 und 150,cm Tiefe die EH wöchentlich mit permanent installierten Pt-Elektroden gemessen und die Bodenlösung zweiwöchentlich mittels keramischer Saugkerzen gewonnen. Der Medianwert des EH betrug in 10, 30, 60 und 150,cm Tiefe 470, 410, 410 und 20 mV im drainierten Boden und 500, 480, 30 und ,170 mV im nicht drainiertem Boden. Ein Abfall im EH unter kritische Werte war in der Bodenlösung (pH 7,4 bis 7,8) von einem Verschwinden des Nitrats unterhalb 0 bis 200 mV und einem Auftreten des Mn2+ unterhalb 350 mV und des Fe2+ unterhalb 0 bis 50 mV begleitet. Beide Metalle verschwanden nach Belüftung aus der Bodenlösung. Im sulfidhaltigen Milieu in 150,cm Tiefe des nicht drainierten Bodens waren die Konzentrationen des Sulfats jedoch bei solchen EH -Werten am höchsten, bei denen das Sulfat instabil sein sollte. Diese Unstimmigkeit spiegelt sich darin wieder, dass das EH in dieser Bodentiefe um ungefähr 400 mV niedriger war als das EH der Bodenlösung (250 mV). Wenn die Dynamik von Nitrat, Mn und Fe in Böden untersucht wird, stellt das in der Bodenmatrix gemessene EH semiquantitative Informationen im Sinne kritischer EH -Bereiche zur Verfügung. Im sulfidhaltigen Bodenmilieu ist die Interpretation des in der Bodenmatrix gemessenen EH jedoch unsicher. [source] Prediction of pKa and redox properties in the thioredoxin superfamilyPROTEIN SCIENCE, Issue 10 2004Efrosini Moutevelis Abstract Electrostatic interactions play important roles in diverse biological phenomena controlling the function of many proteins. Polar molecules can be studied with the FDPB method solving the Poisson-Boltzmann equation on a finite difference grid. A method for the prediction of pKas and redox potentials in the thioredoxin superfamily is introduced. The results are compared with experimental pKa data where available, and predictions are made for members lacking such data. Studying CxxC motif variation in the context of different background structures permits analysis of contributions to cysteine ,pKas. The motif itself and the overall framework regulate pKa variation. The reported method includes generation of multiple side-chain rotamers for the CxxC motif and is an effective predictive tool for functional pKa variation across the superfamily. Redox potential follows the trend in cysteine pKa variation, but some residual discrepancy indicates that a pH-independent factor plays a role in determining redox potentials for at least some members of the superfamily. A possible molecular basis for this feature is discussed. [source] Speciation of Arsenic under Dynamic ConditionsENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 6 2008J. Ackermann Abstract In periodically flooded soils, reductive conditions can occur, which favor the dissolution of Fe (hydr)oxides. Fe (hydr)oxides such as goethite are important sorbents for arsenate (AsV), which is the dominant As species in soils under aerobic conditions. Hence, the dissolution of Fe (hydr)oxides under reductive conditions can result in the mobilization and reduction of AsV and, thus, in an increase in the bioavailability of arsenic. The temporal dynamics of these processes and possible re-sorption or precipitation of arsenite (AsIII) formed are poorly understood. Under controlled laboratory conditions, the temporal change in the redox potential and arsenic speciation with time after a simulated flooding event in a quartz-goethite organic matter substrate, spiked with AsV, was examined. During a period of 6,weeks, substrate solutions were sampled weekly using micro-suction cups and analyzed for pH, AsIII and AsV, Fe, Mn and P concentrations. Redox potentials and matric potentials were determined in situ in the substrate-bearing cylinders. The redox potential and the ratio between AsIII and AsV concentrations remained unchanged during the experiment without organic matter application. With organic matter applied, the redox potential decreased and the AsIII concentrations in the substrate solution increased while the total As concentrations in the substrate solution strongly decreased. An addition of goethite (1,g/kg) per se led to a decrease of the total As in the substrate solution (almost 50,%). In respect to the potential As availability for plants, and consequently, the transfer into the food chain, the results are difficult to evaluate. The lower the total As concentrations in the substrate solution, determined with decreasing redox potential, the least plant As uptake will occur. This effect may however be compensated by a shift of the molar P/AsV ratio in the solution in favor of AsV which is expected to increase the As uptake. [source] Redox potential of bulk soil and soil solution concentration of nitrate, manganese, iron, and sulfate in two GleysolsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2004Tim Mansfeldt Abstract While the reduction of nitrate-N, Mn(III,IV), Fe(III), and sulfate-S in soil has been studied intensively in the laboratory, field research has received only limited attention. This study investigated the relationship between redox potential (EH) measured in bulk soil and concentrations of nitrate, Mn2+, Fe2+, and sulfate in the soil solution of two Gleysols differing in drainage status from the Marsh area of Schleswig-Holstein, Northern Germany. The soils are silty-sandy and developed from calcareous marine sediments. Redox potentials were monitored weekly with permanently installed Pt electrodes, and soil solution was obtained biweekly by ceramic suction cups from 10, 30, 60, and 150,cm depth over one year. Median EH at 10, 30, 60, and 150,cm depths was 470, 410, 410, and 20 mV in the drained soil and 500, 480, 30, and ,170 mV in the undrained soil, respectively. A decrease in EH below critical values was accompanied in the soil solutions (pH 7.4 to 7.8) by disappearance of nitrate below 0 to 200 mV, appearance of Mn2+ below 350 mV, and Fe2+ below 0 to 50 mV. Both metals disappeared from soil solution after aeration. In the sulfide-bearing environment of the 150,cm depth of the undrained soil, however, the sulfate concentrations were highest at such EH values at which sulfate should be unstable. This discrepancy was reflected in the fact that at this depth bulk soil EH was about 400 mV lower than soil solution EH (250 mV). When investigating the dynamics of nitrate, Mn, and Fe in soils, bulk soil EH provides semi-quantitative information in terms of critical EH ranges. However, in sulfidic soil environments the interpretation of EH measured in bulk soil is uncertain. Redoxpotenzial des Bodens und Bodenlösungskonzentrationen von Nitrat, Mangan, Eisen und Sulfat in zwei Kalkmarschen Während die Reduktion von Nitrat-N, Mn(III,IV), Fe(III) und Sulfat-S in Böden intensiv im Labor untersucht worden ist, haben Felduntersuchungen sich damit kaum beschäftigt. In dieser Arbeit wurde die Beziehung zwischen dem Redoxpotenzial (EH) der Bodenmatrix und den Bodenlösungskonzentrationen von Nitrat, Mn2+, Fe2+ und Sulfat in zwei unterschiedlich drainierten Kalkmarschen Schleswig-Holsteins untersucht. Die Böden sind schluffig-sandig und haben sich aus kalkhaltigen marinen Sedimenten entwickelt. Über ein Jahr wurden in 10, 30, 60 und 150,cm Tiefe die EH wöchentlich mit permanent installierten Pt-Elektroden gemessen und die Bodenlösung zweiwöchentlich mittels keramischer Saugkerzen gewonnen. Der Medianwert des EH betrug in 10, 30, 60 und 150,cm Tiefe 470, 410, 410 und 20 mV im drainierten Boden und 500, 480, 30 und ,170 mV im nicht drainiertem Boden. Ein Abfall im EH unter kritische Werte war in der Bodenlösung (pH 7,4 bis 7,8) von einem Verschwinden des Nitrats unterhalb 0 bis 200 mV und einem Auftreten des Mn2+ unterhalb 350 mV und des Fe2+ unterhalb 0 bis 50 mV begleitet. Beide Metalle verschwanden nach Belüftung aus der Bodenlösung. Im sulfidhaltigen Milieu in 150,cm Tiefe des nicht drainierten Bodens waren die Konzentrationen des Sulfats jedoch bei solchen EH -Werten am höchsten, bei denen das Sulfat instabil sein sollte. Diese Unstimmigkeit spiegelt sich darin wieder, dass das EH in dieser Bodentiefe um ungefähr 400 mV niedriger war als das EH der Bodenlösung (250 mV). Wenn die Dynamik von Nitrat, Mn und Fe in Böden untersucht wird, stellt das in der Bodenmatrix gemessene EH semiquantitative Informationen im Sinne kritischer EH -Bereiche zur Verfügung. Im sulfidhaltigen Bodenmilieu ist die Interpretation des in der Bodenmatrix gemessenen EH jedoch unsicher. [source] Atmospheric CO2 enrichment facilitates cation release from soilECOLOGY LETTERS, Issue 3 2010L. Cheng Ecology Letters (2010) 13: 284,291 Abstract Atmospheric CO2 enrichment generally stimulates plant photosynthesis and nutrient uptake, modifying the local and global cycling of bioactive elements. Although nutrient cations affect the long-term productivity and carbon balance of terrestrial ecosystems, little is known about the effect of CO2 enrichment on cation availability in soil. In this study, we present evidence for a novel mechanism of CO2 -enhancement of cation release from soil in rice agricultural systems. Elevated CO2 increased organic C allocation belowground and net H+ excretion from roots, and stimulated root and microbial respiration, reducing soil redox potential and increasing Fe2+ and Mn2+ in soil solutions. Increased H+, Fe2+, and Mn2+ promoted Ca2+ and Mg2+ release from soil cation exchange sites. These results indicate that over the short term, elevated CO2 may stimulate cation release from soil and enhance plant growth. Over the long-term, however, CO2 -induced cation release may facilitate cation losses and soil acidification, negatively feeding back to the productivity of terrestrial ecosystems. [source] Speciation of Arsenic under Dynamic ConditionsENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 6 2008J. Ackermann Abstract In periodically flooded soils, reductive conditions can occur, which favor the dissolution of Fe (hydr)oxides. Fe (hydr)oxides such as goethite are important sorbents for arsenate (AsV), which is the dominant As species in soils under aerobic conditions. Hence, the dissolution of Fe (hydr)oxides under reductive conditions can result in the mobilization and reduction of AsV and, thus, in an increase in the bioavailability of arsenic. The temporal dynamics of these processes and possible re-sorption or precipitation of arsenite (AsIII) formed are poorly understood. Under controlled laboratory conditions, the temporal change in the redox potential and arsenic speciation with time after a simulated flooding event in a quartz-goethite organic matter substrate, spiked with AsV, was examined. During a period of 6,weeks, substrate solutions were sampled weekly using micro-suction cups and analyzed for pH, AsIII and AsV, Fe, Mn and P concentrations. Redox potentials and matric potentials were determined in situ in the substrate-bearing cylinders. The redox potential and the ratio between AsIII and AsV concentrations remained unchanged during the experiment without organic matter application. With organic matter applied, the redox potential decreased and the AsIII concentrations in the substrate solution increased while the total As concentrations in the substrate solution strongly decreased. An addition of goethite (1,g/kg) per se led to a decrease of the total As in the substrate solution (almost 50,%). In respect to the potential As availability for plants, and consequently, the transfer into the food chain, the results are difficult to evaluate. The lower the total As concentrations in the substrate solution, determined with decreasing redox potential, the least plant As uptake will occur. This effect may however be compensated by a shift of the molar P/AsV ratio in the solution in favor of AsV which is expected to increase the As uptake. [source] Degradation and sorption of selected organophosphate and carbamate insecticides in urban stream sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004Svetlana Bondarenko Abstract Monitorings studies show that urban surface streams in the United States are commonly contaminated with pesticides, and contamination by organophosphates and carbamates is of particular concern because of their aquatic toxicity. The degradation and sorption of four common organophosphate and carbamate insecticides were studied in urban creek sediments from southern California, USA. In sediment, malathion was quickly degraded under either aerobic or anaerobic conditions, with a half-life (t1/2) <3 d. Diazinon and chlorpyrifos were moderately persistent under aerobic conditions (t1/2 = 14,24 d). However, persistence of chlorpyrifos increased significantly under anaerobic conditions, and t1/2 was prolonged to 58 to 223 d. The greatest effect of redox potential was found with carbaryl. Although rapid dissipation occurred under aerobic conditions (t1/2 = 1.8,4.9 d), carbaryl became virtually nondegradable under anaerobic conditions (t1/2 = 125,746 d). The sorption coefficient consistently increased with time for all pesticides, and chlorpyrifos displayed greater sorption potential than the other pesticides. This study indicates that pesticides in sediment may become less available with time because of increased sorption, and pesticide persistence in sediment may vary greatly among compounds and with redox conditions. Under anaerobic conditions, long persistence may occur even for nonpersistent compounds. [source] Spatial variation of metals and acid volatile sulfide in floodplain lake sedimentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2003Corine van Griethuysena Abstract In risk assessment of aquatic sediments, much attention is paid to the immobilizing effect of acid volatile sulfide (AVS) on trace metals. The difference of AVS and simultaneously extracted metals (SEM) gives an indication of metal availability. In floodplain sediments, where changing redox conditions occur. AVS may play a major role in determining variation in metal availability. The importance of spatial heterogeneity has been recognized in risk assessment of trace-metal-polluted sediments. However, little is known about spatial variation of available metal fractions. We studied spatial variability of sediment, environmental conditions, total contaminant concentrations, and available metals (as SEM-AVS or SEM-AVS/fOC) in a floodplain lake. The top 5 cm of sediment was sampled at 43 locations. Data were analyzed with correlation and principal component analysis as well as with geostatistical methods. Trace metal and SEM concentrations and most sediment characteristics were more or less constant within 10%. In contrast, AVS concentrations were much more variable and showed a strong spatial dependence due to differences in lake depth, total sulfur pools, and redox potential (Eh), which resulted in crucial differences in trace-metal availability within the lake. The spatial pattern of SEM-AVS deviates from total or normalized trace-metal patterns. This particularly has implications for risk assessment of sediments prone to dynamic hydrological conditions, where AVS concentrations are also variable in time. [source] Assessing sediment contamination in estuariesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2001Peter M. Chapman Abstract Historic and ongoing sediment contamination adversely affects estuaries, among the most productive marine ecosystems in the world. However, all estuaries are not the same, and estuarine sediments cannot be treated as either fresh or marine sediments or properly assessed without understanding both seasonal and spatial estuarine variability and processes, which are reviewed. Estuaries are physicochemically unique, primarily because of their variable salinity but also because of their strong gradients in other parameters, such as temperature, pH, dissolved oxygen, redox potential, and amount and composition of particles. Salinity (overlying and interstitial) varies spatially (laterally, vertically) and temporally and is the controlling factor for partitioning of contaminants between sediments and overlying or interstitial water. Salinity also controls the distribution and types of estuarine biota. Benthic infauna are affected by interstitial salinities that can be very different than overlying salinities, resulting in large-scale seasonal species shifts in salt wedge estuaries. There are fewer estuarine species than fresh or marine species (the paradox of brackish water). Chemical, toxicological, and community-level assessment techniques for estuarine sediment are reviewed and assessed, including chemistry (grain size effects, background enrichment, bioavailability, sediment quality values, interstitial water chemistry), biological surveys, and whole sediment toxicity testing (single-species tests, potential confounding factors, community level tests, laboratory-to-field comparisons). Based on this review, there is a clear need to tailor such assessment techniques specifically for estuarine environments. For instance, bioavailability models including equilibrium partitioning may have little applicability to estuarine sediments, appropriate reference comparisons are difficult in biological surveys, and there are too few full-gradient estuarine sediment toxicity tests available. Specific recommendations are made to address these and other issues. [source] Haemodialysis induces mitochondrial dysfunction and apoptosisEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 12 2007D. S. C. Raj Abstract Background Mitochondria play a crucial role in the regulation of the endogenous pathways of apoptosis activated by oxidant stress. Nuclear factor-,B (NF-,B) is a central integration site for pro-inflammatory signals and oxidative stress. Materials and methods Peripheral blood mononuclear cells (PBMC) were isolated from eight end-stage renal disease (ESRD) patients before haemodialysis (Pre-HD) and during the last 10 min of HD (End-HD). A new polysulfone membrane (F70, Fresenius) was used for dialysis. Intracellular generation of reactive oxygen species (ROS), mitochondrial redox potential (,,m) and PBMC apoptosis were determined by flow-cytometry. Results Plasma levels of interleukin-6 (IL-6) (24·9 ± 7·0 vs. 17·4 ± 5·5 pg dL,1, P < 0·05), IL-6 soluble receptor (52·2 ± 4·9 vs. 37·6 ± 3·2 ng dL,1, P < 0·02) and IL-6 gp130 (405·7 ± 41·0 vs. 235·1 ± 38·4 ng dL,1, P < 0·02) were higher end-HD compared to pre-HD. IL-6 secretion by the isolated PBMC (24·0 ± 2·3 vs. 19·3 ± 3·5 pg dL,1, P < 0·02) increased end-HD. Percentage of lymphocytes exhibiting collapse of mitochondrial membrane potential (43·4 ± 4·6% vs. 32·6 ± 2·9%, P < 0·01), apoptosis (33·4 ± 7·1% vs. 23·7 ± 7·7%, P < 0·01), and generation of superoxide (20·7 ± 5·2% vs. 12·5 ± 2·9%, P < 0·02) and hydrogen peroxide (51·1 ± 7·8% vs.38·2 ± 5·9%, P < 0·04) were higher at end-HD than pre-HD. NF-,B activation (3144·1 ± 208·1 vs. 2033·4 ± 454·6 pg well,1, P < 0·02), expression of B-cell lymphoma protein-2 (6494·6 ± 1461 vs. 3501·5 ± 796·5 ng mL,1, P < 0·03) and heat shock protein-70 (9·81 ± 1·47 vs. 6·38 ± 1·0 ng mL,1, P < 0·05) increased during HD. Conclusions Intra-dialytic activation of cytokines, together with impaired mitochondrial function, promotes generation of ROS culminating in augmented PBMC apoptosis. There is concomitant activation of pathways aimed at attenuation of cell stress and apoptosis during HD. [source] Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactisFEBS JOURNAL, Issue 10 2010D. Michelon Lactococcus lactis can decrease the redox potential at pH 7 (Eh7) from 200 to ,200 mV in oxygen free Man,Rogosa,Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in Eh7 by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final Eh7 (,200 mV) was reached, only thiol-reactive reagents could restore the initial Eh7 value. Inhibition of the proton motive force showed no effect on maintaining the final Eh7 value. These results suggest that maintaining the exofacial thiol (,SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress. [source] Allosteric activation of pyruvate kinase via NAD+ in rat liver cellsFEBS JOURNAL, Issue 14 2001Anne Devin In isolated rat hepatocytes, it has previously been reported that a rise in the ATP content induces a proportional increase in cytosolic NAD+ concentration [Devin, A., Guérin, B. & Rigoulet, M. (1997) FEBS Lett.410, 329,332]. This occurs under physiological conditions such as various substrates or different energetic states. To investigate the effect of a physiological rise in cytosolic [NAD+] per se on glycolysis and gluconeogenesis, an increase in [NAD+] induced by exogenous nicotinamide addition was obtained without a change in redox potential, ATP/ADP ratio and ATP concentration. Using dihydroxyacetone as substrate, we found that an increase in cytosolic [NAD+] decreases gluconeogenesis and enhances glycolysis without significant alteration of dihydroxyacetone consumption rate. These modifications are the consequence of an allosteric activation of pyruvate kinase via cytosolic NAD+ content. Thus, in addition to the well-known thermodynamic control of glycolysis by pyridine-nucleotide redox status, our study points to a new mechanism of glycolytic flux regulation by NAD+ concentration at the level of pyruvate kinase activity. [source] Characterization of a nif-regulated flavoprotein (FprA) from Rhodobacter capsulatusFEBS JOURNAL, Issue 3 20002S] ferredoxin, Redox properties, molecular interaction with a [2Fe A flavoprotein from Rhodobacter capsulatus was purified as a recombinant (His)6 -tag fusion from an Escherichia coli clone over-expressing the fprA structural gene. The FprA protein is a homodimer containing one molecule of FMN per 48-kDa monomer. Reduction of the flavoprotein by dithionite showed biphasic kinetics, starting with a fast step of semiquinone (SQ) formation, and followed by a slow reduction of the SQ. This SQ was in the anionic form as shown by EPR and optical spectroscopies. Spectrophotometric titration gave a midpoint redox potential for the oxidized/SQ couple of Em1 = +20 mV (pH 8.0), whereas the SQ/hydroquinone couple could not be titrated due to the thermodynamic instability of SQ associated with its slow reduction process. The inability to detect the intermediate form, SQ, upon oxidative titration confirmed this instability and led to an estimate of Em2 , Em1 of > 80 mV. The reduction of SQ by dithionite was significantly accelerated when the [2Fe,2S] ferredoxin FdIV was used as redox mediator. The midpoint redox potential of this ferredoxin was determined to be ,275 ± 2 mV at pH 7.5, consistent with FdIV serving as electron donor to FprA in vivo. FdIV and FprA were found to cross-react when incubated together with the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, giving a covalent complex with an Mr of , 60 000. Formation of this complex was unaffected by the redox states of the two proteins. Other [2Fe,2S] ferredoxins, including FdV and FdVI from R. capsulatus, were ineffective as electron carriers to FprA, and cross-reacted poorly with the flavoprotein. The possible function of FprA with regard to nitrogen fixation was investigated using an fprA -deleted mutant. Although nitrogenase activity was significantly reduced in the mutant compared with the wild-type strain, nitrogen fixation was apparently unaffected by the fprA deletion even under iron limitation or microaerobic conditions. [source] Mapping the archaeological soil archive of sand and gravel mineral reserves in BritainGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 1 2009Ingrid Ward Primary sand and gravel deposits in Britain play an important role in preserving our cultural heritage and are also a valuable aggregate resource. While an understanding of the extrinsic properties of the soil archive (such as pH, redox, groundwater) can provide a firstorder assessment of the potential risk to any archaeologically sensitive deposits, we have very poor definition of spatial variations in the extrinsic properties of soil that influence archaeological preservation at a regional and national scale. Developments in digital geological mapping, remote sensing, and geochemical survey data undertaken by the British Geological Survey (BGS) have, however, significantly extended capabilities in this respect and can potentially be used to provide a primary assessment of the sensitivity of the present soil archive and the potential risk from changes to the soil process on cultural material in areas earmarked for aggregate extraction. Two of the major factors affecting archaeological preservation,soil acidification and groundwater,can be mapped or predicted at scales of better than 1:50,000 across increasingly large parts of the country using a combination of regional hydrogeological, geophysical, and geochemical data. Additional data from site investigations may further refine preservation potential as a function of changes in redox potential and acidity. These data, maps and models can be used to (1) better establish a baseline for archaeological preservation at a regional and national scale and (2) improve our understanding of how the physical and chemical properties of the near surface environment can be managed to sustainably preserve archaeological materials in areas impacted by sand and gravel extraction. © 2009 Wiley Periodicals, Inc. [source] Isolation of Solid Solution Phases in Size-Controlled LixFePO4 at Room TemperatureADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Genki Kobayashi Abstract State-of-the-art LiFePO4 technology has now opened the door for lithium ion batteries to take their place in large-scale applications such as plug-in hybrid vehicles. A high level of safety, significant cost reduction, and huge power generation are on the verge of being guaranteed for the most advanced energy storage system. The room-temperature phase diagram is essential to understand the facile electrode reaction of LixFePO4 (0,<,x,<,1), but it has not been fully understood. Here, intermediate solid solution phases close to x,=,0 and x,=,1 have been isolated at room temperature. Size-dependent modification of the phase diagram, as well as the systematic variation of lattice parameters inside the solid-solution compositional domain closely related to the electrochemical redox potential, are demonstrated. These experimental results reveal that the excess capacity that has been observed above and below the two-phase equilibrium potential is largely due to the bulk solid solution, and thus support the size-dependent miscibility gap model. [source] Transient Leakance and Infiltration Characteristics during Lake Bank FiltrationGROUND WATER, Issue 1 2009B. Wiese Infiltration capacity of bank filtration systems depends on water extraction and hydraulic resistance of the bed sediments. Lakebed hydraulics may be especially affected by clogging, which is dependent on settlement of fine particles, redox potential, and other factors. In the field, most of these processes are difficult to quantify, and thus, when calculating response to pumping the water flux across the sediment surface is assumed to be linearly dependent on the hydraulic gradient. However, this assumption was not adequate to describe conditions at a bank filtration site located at Lake Tegel, Berlin, Germany. Hence, we first assumed the leakage coefficient (or leakance) is spatially distributed and also temporally variant. Furthermore, observations show that the leakance is considerably higher in shallow than in deeper areas; hence, leakance was assumed to be dependent on the existence and thickness of an unsaturated zone below the lake. The proposed explanation of spatial and temporal variability in leakance involves a hypothesis for redox dependent and reversible biogeochemical clogging, supported by geochemical observations in surface water and ground water. Four leakance approaches are implemented in the ground water flow code MODFLOW2000 and calibrated by inverse modeling using the parameter estimation software PEST. These concepts are evaluated by examining the fit to the hydraulic heads, to infiltration measurements, transport modeling results, and considering the degrees of freedom due to the number of calibration parameters. The leakage concept based on the assumption of the influence of an unsaturated zone on clogging processes best explains the field data. [source] Denitrification in a hyporheic riparian zone controlled by river regulation in the Seine river basin (France)HYDROLOGICAL PROCESSES, Issue 5 2009F. Curie Abstract The purpose of this paper is to study denitrification and the conditions for its development in a hyporheic zone. The study site is the riparian zone of a former branch of the Seine River, where the river stage is kept almost constant during the year by hydraulic regulation. Hydrological and geochemical surveys were performed by monitoring four wells, ten shorter piezometers and the river over a 15-month period. The water fluxes originating from the chalky hillsides and the river converge in a zone parallel to the river that acts as a drainage flow path through the floodplain. The riparian zone between this flow path and the river shows an important depletion of nitrate during the summer and autumn period, which cannot be explained by a simple mixing of waters coming from the river and the chalky hillsides. It can be attributed to denitrification as it occurs when oxygen concentration is below 2 mg l,1, and goes along with a consumption of dissolved organic carbon and a decrease of redox potential. The river completely controls these hydro-geochemical conditions. It also keeps the wetness of the riparian zone almost constant, which allowed us to isolate the high temperatures in summer and autumn as an important triggering factor for denitrification through its influence on the reaction rate and oxygen deficits. We also found a small isotopic enrichment of nitrate, suggesting that denitrification occurs after diffusion of nitrate through the sediment and riparian zone matrix, which is consistent with the hyporheic functioning of the study site. Copyright © 2008 John Wiley & Sons, Ltd. [source] Controlling the Diameter of Polyaniline Nanofibers by Adjusting the Oxidant Redox Potential,ADVANCED MATERIALS, Issue 3 2007H. Ding A self-assembly process with no external template and no added acidic dopant is reported as a method providing quantitative control over the diameter d of the polyaniline (PANI) nanofibers produced. An experimental formula relating d to the standard redox potential of the oxidants is established. The PANI nanofibers in the figure have d,,,15,nm. [source] Theoretical studies on effects of hydrogen bonds attaching to cysteine ligands on 4Fe-4S clustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Y. Kitagawa Abstract The effect of hydrogen bonds attaching to sulfur atoms of cysteine ligands on 4Fe-4S cluster is examined by using UB3LYP method. Calculated results indicate that an existence of the hydrogen bonds scarcely changes SOMO-SUMO gap, shapes of Kohn-Sham orbitals, and magnetic interactions between Fe ions, although it stabilizes Kohn-Sham orbital energies of SOMO and SUMO about 1.0 eV. And they also make a reduced state stable in comparison with an oxidized state. In addition, the point charges of +0.1e (e: elementary electric charge) at the position of the hydrogen atoms give almost same results to the hydrogen bonds quantitatively. The results suggest that a positive environment from the hydrogen bonds around the clusters is important for a redox potential of 4Fe-4S clusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] | ||||||||||||||||||||||||||||||||||||||||