Distribution by Scientific Domains
Distribution within Chemistry

Terms modified by Fe2+

  • fe2+ ion

  • Selected Abstracts

    DNA Status on Thawed Semen from Fighting Bull: A Comparison Between the SCD and the SCSA Tests

    F Martnez-Pastor
    Contents The assessment of sperm chromatin status is compulsory in a complete spermiogram. Here we applied the sperm chromatin structure assay (SCSA) and the sperm chromatin dispersion (SCD) test to assess the chromatin status of three fighting bulls. Cryopreserved semen (two straws/bull) were analysed by duplicate after thawing and after 6 h at 37C with and without oxidative stress (1 mm FE2+). Results (SCD: percentage of spermatozoa with halo; SCSA: SD-DFI, %DFI and HDS) were analysed for differences between bulls and treatments, sensitivity and specificity (receiver operating characteristic curves) and repeatability (repeatability coefficients as 2SD of duplicate differences).%DFI for the three bulls was below 2% at 0 h, indicating no risk for fertility according to previous reports. It increased slightly for two of the bulls after FE2+ treatment (%DFI < 5%) and more pronouncedly for the other bull (C, %DFI,10%), which merits further investigation. SCD rendered higher percentage of halos for bull C, but could not discriminate between samples with and without oxidizing treatment (AUC: 0.52). SCSA (%DFI) showed a high discriminating ability between treatments (AUC: 0.96). The repeatability coefficient was also higher for SCD (5.9) than for %DFI (1.8), indicating lower repeatability for SCD. Overall, %DFI might be the most useful parameter for assessing sperm chromatin on fighting bull. SCD might yield different information than SCSA, hence further research is warranted. [source]


    ARCHAEOMETRY, Issue 2 2009
    Deep blue glasses coloured by octahedral Fe2+ cations are often reported as textbook examples of blue pigmentation. However, despite the possibility of laboratory synthesis under reducing conditions, to date there are no well-reported occurrences of their production and use in the past. A thorough historical, ethnographic, mineralogical, and chemico-physical investigation of the ,smaltini di calcara' from several baroque churches in Palermo, Sicily, has revealed that the blue enamels widely used for altar decorations in the 17th and 18th centuries are actually a unique case of ancient blue glasses pigmented by divalent iron cations in distorted octahedral coordination. This mixed-alkali glass was accidentally produced under severely reducing conditions in the local kilns during production of lime. [source]

    Atmospheric CO2 enrichment facilitates cation release from soil

    ECOLOGY LETTERS, Issue 3 2010
    L. 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]

    Prussian Blue-Modified Titanate Nanotubes: A Novel Nanostructured Catalyst for Electrochemical Reduction of Hydrogen Peroxide

    ELECTROANALYSIS, Issue 19 2010
    Damir Ivekovi
    Abstract Prussian blue (PB) modified titanate nanotubes (PB-TiNT) have been synthesized by the reaction of Fe2+ -modified TiNT with hexacyanoferrate(III) ions. The rate constant for heterogeneous catalytic reaction between PB-TiNT and H2O2 was found to be k=2104,dm3,mol,1,s,1, which is an order of magnitude higher than the values of k reported for conventionally prepared, electrochemically deposited PB films. On the PB-TiNT modified electrode with subnanomolar surface concentration of PB (,(PB)=2.810,11,mol/cm2), a stable, reproducible and linear response towards H2O2 was obtained in the concentration range 0.02,4,mM, with the sensitivity of 0.10,AM,1,cm,2 at ,150,mV. [source]

    Evaluation of Cu,Ethylenediamine Metal Ion Buffers as Calibrants for Ion-Selective Electrode Measurement of Copper in Fresh Water Systems

    ELECTROANALYSIS, Issue 10 2005
    Ling Zeng
    Abstract An investigation was made into the accuracy of cupric ion selective electrode (ISE) measurement of Cu in solutions approximating acidic freshwaters with Cu-ethylenediamine buffers used as the calibrants. This method overestimates the free Cu compared with calibration using Cu(NO3)2 standards, the standard addition method, and speciation modelling calculations. Statistical tests showed a small, but significant, difference between the intercepts of the linear Nernstian regressions of the calibration plots of Cu-en buffer standardisation and direct calibration with Cu(NO3)2 standards in matrix that matches the samples. The difference in the intercepts, which corresponds with Eo values of the electrode, is not well understood, but is possibly caused by potentially interfering cations such as Fe2+. The results of this study showed that down to 10,8,M Cu2+, where a linear Nernstian response is possible, the Cu ISE is probably better calibrated using Cu standards prepared in the same matrix as the sample solutions to avoid potential matrix effects. [source]

    DNA Hybridization at Magnetic Nanoparticles with Electrochemical Stripping Detection

    ELECTROANALYSIS, Issue 23 2004
    Ningning Zhu
    Abstract A simple and practical method for electrochemical DNA hybridization assay has been developed to take advantage of magnetic nanoparticles for ssDNA immobilization and zinc sulfide nanoparticle as oligonucleotide label. Magnetic nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then amino silane was coated onto the surface of magnetite nanoparticles. The magnetic nanoparticles have the advantages of easy preparation, easy surface modification and low cost. The target ssDNA with the phosphate group at the 5, end was then covalently immobilized to the amino group of magnetite nanoparticles by forming a phosphoramidate bond in the presence of 1-ethyl-3-(3-dimeth-ylaminopropyl)carbodiimide (EDAC). The zinc sulfide (ZnS) nanoparticle-labeled oligonucleotides probe was used to identify the target ssDNA immobilized on the magnetic nanoparticles based on a specific hybridization reaction. The hybridization events were assessed by the dissolution of the zinc sulfide nanoparticles anchored on the hybrids and the indirect determination of the dissolved zinc ions by anodic stripping voltammetry (ASV) at a mercury film glassy carbon electrode (GCE). The proposed method couples the high sensitivity of anodic stripping analysis for zinc ions with effective magnetic separation for eliminating nonspecific adsorption effects and offers great promise for DNA hybridization analysis. [source]

    Investigation of the stereodynamics of tris-(, -diimine),transition metal complexes by enantioselective dynamic MEKC

    ELECTROPHORESIS, Issue 2 2009
    Sabrina Bremer
    Abstract Enantiomerization of octahedral tris(, -diimine),transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe2+, Fe3+, and Ni2+) and the bidentate diimine ligand (1,10-phenanthroline and 2,2,-bipyridyl), the enantiomer separations were performed either in a 100,mM sodium tetraborate buffer (pH 9.3) or in a 100,mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ,H, and ,S, were calculated from temperature-dependent measurements between 10.0 and 35.0C in 2.5,K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2,-bipyridyl ligand show highly negative activation entropies between ,103 and ,116,J (K,mol),1 while the activation entropy of tris(1,10-phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni2+ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts. [source]

    Comparative mutagenic effects of structurally similar flavonoids quercetin and taxifolin on tester strains Salmonella typhimurium TA102 and Escherichia coli WP-2 uvrA

    Patrudu S. Makena
    Abstract Quercetin (QT) and Taxifolin (TF) are structurally similar plant polyphenols. Both have been reported to have therapeutic potential as anti-cancer drugs and antioxidants. Mutagenic effects of QT and TF were evaluated using Salmonella typhimurium TA102 and Escherichia coli WP-2 uvrA tester strains. Either in the presence or absence of S9 mix, QT was mutagenic to TA102 and WP2 uvrA. However, the mutagenicity of QT was significantly enhanced in the presence of S9 mix. Likewise, in the presence of Iron (Fe2+) and NADPH generating system (NGS) and absence of S9 mix, QT induced significantly high mutations in both TA102 and WP-2 uvrA. Mutagenicity of QT decreased in both strains in the presence of Iron (Fe2+) or NGS alone. TF was not mutagenic in the presence or absence of S9 mix in both TA102 and WP-2 uvrA 2, regardless of the presence of iron or NGS. Incorporation of antioxidants (ascorbate, superoxide dismutase (SOD), catalase (CAT)) and/or iron chelators (desferroxamine (DF) and ethylenediamine-tetraacetate (EDTA)) in the test systems markedly decreased QT-induced mutations in both tester strains. These results suggest that QT but not TF, could induce mutations in the presence or absence of rat liver S9 or Iron (Fe2+) and NGS in both tester strains by redox cycling and Fenton reactions to produce oxygen free radicals. Our results indicate that a minor structural variation between the two plant polyphenols could elicit a marked difference in their genotoxicities. These results provide a basis for further study into the potential use of QT in combination with iron supplements. Environ. Mol. Mutagen. 2009. 2009 Wiley-Liss, Inc. [source]

    Experimental study of flue gas desulfurization using landfill leachate

    Ding Sang-lan
    Abstract Because of the complexity of landfill leachate's composition, the reaction mechanism of SO2 in flue gas with landfill leachate was studied. The experimental results indicated that the factors influencing SO2 absorption efficiency using landfill leachate as the scrubbing medium were, in decreasing order of importance, pH, Fe2+, Mn2+, and Cl, as catalysts and the concentration of toluene and ethanol. Experiments showed that the pH of landfill leachate was the key factor governing both SO2 absorption and ammonia stripping. With the initial pH of 8.5, the terminal pH 6.0 and L/G ratio 3 L/m3, experimental results showed that average absorption efficiency of SO2 and the stripping efficiency of ammonia were 85 and 44%, respectively. The use of catalysts such as Fe2+ and Mn2+ was important for SO2 absorption when the pH value was below 7.0. The catalytic activity of Mn2+ was greater than that of Fe2+ although the reaction steps were very similar. Ethanol inhibits HSO3,/SO32, oxidation. The HSO3,/SO32, oxidation process improves the solubility of organics such as toluene in the leachate. The solute products of organics were water-soluble and biodegradable and could be used as substrates for bacteria in the post biotreatment. The factorial experiment results showed the effect of Cl,, Fe2+, and Mn2+ as catalysts on the HSO3,/SO32, oxidation has a greater positive impact than ethanol's inhibitory effect on the HSO3,/SO32, oxidation. 2006 American Institute of Chemical Engineers Environ Prog 26:25,32, 2007 [source]

    Molecular modeling of metal complexation by a fluoroquinolone antibiotic

    Ludmilla Aristilde
    Abstract An understanding of the factors controlling the chemodynamics of fluoroquinolone antibiotics in different environmental matrices is a necessary prerequisite to the assessment of their potential impact on nontarget organisms in soils and receiving waters. Of particular interest are the complexes formed between fluoroquinolones and metal cations, which are believed to be important in the mechanism of sequestration of the antibiotic by minerals and natural organic matter. The structures of these complexes have not been fully resolved by conventional spectroscopy; therefore, molecular simulations may provide useful complementary insights. We present results from apparently the first molecular dynamics simulations of a widely used fluoroquinolone antibiotic, ciprofloxacin (Cipro), in aqueous complexes with five metal cations typically found in soils and surface waters: Ca2+, Mg2+, Fe2+, Na+, and K+. The interatomic potential functions employed in the simulations were validated by comparison with available structural data for solid-phase Cipro-hexahydrate and for the metal cations in aqueous solution. Although no comprehensive structural data on the aqueous complexes appear to be available, properties of the metal complexes predicted by our simulations agree with available data for solid-phase metal,Cipro complexes. Our results indicate that the ionic potential of the metal cation controls the stability of the complex formed and that the hydration number of the metal cation in aqueous solution determines its coordination number with O atoms in the metal,Cipro complex. In respect to environmental chemodynamics, our results imply that Cipro will form two configurations of bidendate chelates with metal centers on exposed surfaces of mineral oxides, water-bridged surface complexes with exchangeable cations in clay mineral interlayers, and cation-bridged complexes with functional groups in natural organic matter. [source]

    Reductive transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and methylenedinitramine with elemental iron

    Seok-Young Oh
    Abstract Reductive (pre)treatment with elemental iron is a potentiallyuseful method for degrading nitramine explosives in water and soil. In the present study, we examined the kinetics, products, and mechanisms of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) degradation with elemental iron. Both RDX and HMX were transformed with iron to formaldehyde, NH, N2O, and soluble products. The yields of formaldehyde were relatively constant (71% 5%), whereas the yields of NH and N2O varied, depending on the nitramine and the mechanism. The reactions most likely were controlled by a surface process rather than by external mass transfer. Methylenedinitramine (MDNA) was an intermediate of both RDX and HMX and was transformed quantitatively to formaldehyde with iron. However, product distributions and kinetic modeling results suggest that MDNA represented a minor reaction path and accounted for only 30% of the RDX reacted and 14% of the formaldehyde produced. Additional experiments showed that RDX reduction with elemental iron could be mediated by graphite and Fe2+ sorbed to magnetite, as demonstrated previously for nitroaromatics and nitrate esters. Methylenedinitramine was degraded primarily through reduction in the presence of elemental iron, because its hydrolysis was slow compared to its reactions with elemental iron and surface-bound Fe2+. Our results show that in a cast iron-water system, RDX may be transformed via multiple mechanisms involving different reaction paths and reaction sites. [source]

    Novel RuII Complexes with Bispidine-Based Bridging Ligands: Luminescence Sensing and Photocatalytic Properties

    Christoph Busche
    Abstract New ligands with a bidentate bipyridyl (bpy) and a tetradentate bispidine (bisp) subunit (bipyridyl = 2,2,-bipyridine derivative, bispidine = 3,7-diazabicyclo[3.3.1]nonane derivative) and their heterodinuclear {[Ru(bpy)3]2+ -[M(bisp)]2+} complexes (M = Cu2+, Fe2+) were prepared and characterized. The luminescence of the mononuclear RuII complexes (metal-free bisp subunit) is efficiently quenched in presence of CuII. An EPR spectroscopic study reveals thatvisible light irradiation does not alter the oxidation states of the two metal ions in {[Ru(bpy)3]2+ -[Cu(bisp)]2+}, i.e. there is energy rather than electron transfer. The heterodinuclear {[Ru(bpy)3]2+ -[Cu(bisp)]2+} complex shows a significantphotocatalytic activity in the aziridination of styrene. [source]

    Kinetics and Mechanism of Oxidation of Fe2+ by the Tris(biguanide)manganese(IV) Ion in Aqueous Acid Media

    Basab Bijayi Dhar
    Abstract Tris(biguanide)manganese(IV), [Mn(LH2)3]4+ (LH2 = biguanide, C2N5H7), quantitatively oxidises Fe2+ to Fe3+ and is itself reduced to Mn2+ with almost quantitative (> 95%) release of biguanide. The reaction rate strongly depends on added Fe3+; in the presence of externally added Fe3+, the reaction shows a clear first-order dependence in [MnIV], whereas in the absence of any added Fe3+, an initial quick loss of MnIV is associated with a subsequent very sluggish decay. Two consecutive one-electron transfer inner-sphere steps are proposed for the entire redox process where [Mn(LH2)3]3+, the initial one-electron-reduced product of MnIV, is believed to be a steady-state intermediate. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Antioxidant capacity of rapeseed meal and rapeseed oils enriched with meal extract

    Aleksandra Szyd, owska-Czerniak
    Abstract Response surface methodology (RSM) was used to evaluate the quantitative effects of two independent variables: solvent polarity and temperature of the extraction process on the antioxidant capacity (AC) and total phenolics content (TPC) in meal rapeseed extracts. The mean AC and TPC results for meal ranged between 1181,9974,mol TE/100,g and 73.8,814,mg sinapic acid/100,g of meal. The experimental results of AC and TPC were close to the predicted values calculated from the polynomial response surface models equations (R2,=,0.9758 and 0.9603, respectively). The effect of solvent polarity on AC and TPC in the examined extracts was about 3.6 and 2.6 times greater, respectively, than the effect of processing temperature. The predicted optimum solvent polarity of ,,=,78.3 and 63.8, and temperature of 89.4 and 74.2C resulted in an AC of 10,014,mol TE/100,g and TPC of 863,mg SAE/100,g meal, respectively. The phenolic profile of rapeseed meal was determined by an HPLC method. The main phenolics in rapeseed meal were sinapine and sinapic acid. Refined rapeseed oils were fortified with an extract , rich in polyphenols , obtained from rapeseed meal. The supplemented rapeseed oil had higher AC and TPC than the refined oil without addition of meal extracts. However, AC and TPC in the enriched oils decreased during storage. The TPC in the studied meal extracts and rapeseed oils correlated significantly (p<0.0000001) positively with their AC (R2,=,0.9387). Practical applications: Many bioactive compounds extracted from rapeseed meal provide health benefits and have antioxidative properties. Therefore, it seems worth to consider the application of antioxidants extracted from the rapeseed meal for the production of rapeseed oils with potent AC. Moreover, antioxidants extracted from the rapeseed meal were added to refined rapeseed oil in order to enhance its AC. AC was then tested by FRAP assay. FRAP method is based on the reduction of the ferric tripyridyltriazine (Fe3+ -TPTZ) complex to the ferrous tripyridyltriazine (Fe2+ -TPTZ), and it is simple, fast, low cost, and robust method. FRAP method does not require specialized equipment and can be performed using automated, semi-automatic, or manual methods. Therefore the proposed FRAP method can be employed by the fat industry laboratories to asses the AC of rapeseed oils and meal. [source]

    Metal-Assisted Hybridization of Oligonucleotides, Evaluation of Circular 2,- O -Me RNA as Ligands for the TAR RNA Target

    Laurence Zapata
    Abstract Two complementary oligonucleotides were conjugated with terpyridine ligands at their nearby 5,- and 3,-ends. Addition of a stoichiometric amount of a transition metal (Zn2+, Fe2+) resulted in a large increase in the melting temperature of the duplex. The conjugation of TPY to stem-loop oligomers provided an efficient procedure for the cyclisation of the oligomer after the addition of metal ions. Such a short stem-loop oligomer was designed to target the HIV-1 TAR RNA through loop,loop interactions. The addition of Zn2+ ions yielded a good ligand (Kd = 30 nM) for this RNA structural element. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Functional characterization of an orphan cupin protein from Burkholderia xenovorans reveals a mononuclear nonheme Fe2+ -dependent oxygenase that cleaves ,-diketones

    FEBS JOURNAL, Issue 20 2009
    Stefan Leitgeb
    Cupins constitute a large and widespread superfamily of ,-barrel proteins in which a mononuclear metal site is both a conserved feature of the structure and a source of functional diversity. Metal-binding residues are contributed from two core motifs that provide the signature for the superfamily. On the basis of conservation of this two-motif structure, we have identified an ORF in the genome of Burkholderia xenovorans that encodes a novel cupin protein (Bxe_A2876) of unknown function. Recombinant Bxe_A2876, as isolated from Escherichia coli cell extract, was a homotetramer in solution, and showed mixed fractional occupancy of its 16.1 kDa subunit with metal ligands (0.06 copper; 0.11 iron; 0.17 zinc). Our quest for possible catalytic functions of Bxe_A2876 focused on Cu2+ and Fe2+ oxygenase activities known from related cupin enzymes. Fe2+ elicited enzymatic catalysis of O2 -dependent conversion of various ,-diketone substrates via a nucleophilic mechanism of carbon,carbon bond cleavage. Data from X-ray absorption spectroscopy (XAS) support a five-coordinate or six-coordinate Fe2+ center where the metal is bound by three imidazole nitrogen atoms at 1.98 . Results of structure modeling studies suggest that His60, His62 and His102 are the coordinating residues. In the ,best-fit' model, one or two oxygens from water and a carboxylate oxygen (presumably from Glu96) are further ligands of Fe2+ at estimated distances of 2.04 and 2.08 , respectively. The three-histidine Fe2+ site of Bxe_A2876 is compared to the mononuclear nonheme Fe2+ centers of the structurally related cysteine dioxygenase and acireductone dioxygenase, which also use a facial triad of histidines for binding of their metal cofactor but promote entirely different substrate transformations. [source]

    Characterization of Mycobacterium tuberculosis nicotinamidase/pyrazinamidase

    FEBS JOURNAL, Issue 4 2008
    Hua Zhang
    The nicotinamidase/pyrazinamidase (PncA) of Mycobacterium tuberculosis is involved in the activation of the important front-line antituberculosis drug pyrazinamide by converting it into the active form, pyrazinoic acid. Mutations in the pncA gene cause pyrazinamide resistance in M. tuberculosis. The properties of M. tuberculosis PncA were characterized in this study. The enzyme was found to be a 20.89 kDa monomeric protein. The optimal pH and temperature of enzymatic activity were pH 7.0 and 40 C, respectively. Inductively coupled plasma-optical emission spectrometry revealed that the enzyme was an Mn2+/Fe2+ -containing protein with a molar ratio of [Mn2+] to [Fe2+] of 1 : 1; furthermore, the external addition of either type of metal ion had no apparent effect on the wild-type enzymatic activity. The activity of the purified enzyme was determined by HPLC, and it was shown that it possessed similar pyrazinamidase and nicotinamidase activity, by contrast with previous reports. Nine PncA mutants were generated by site-directed mutagenesis. Determination of the enzymatic activity and metal ion content suggested that Asp8, Lys96 and Cys138 were key residues for catalysis, and Asp49, His51, His57 and His71 were essential for metal ion binding. Our data show that M. tuberculosis PncA may bind metal ions in a manner different from that observed in the case of Pyrococcus horikoshii PncA. [source]

    Inactivation of calcineurin by hydrogen peroxide and phenylarsine oxide

    FEBS JOURNAL, Issue 5 2000
    Evidence for a dithiol, disulfide equilibrium, implications for redox regulation
    Calcineurin (CaN) is a Ca2+ -and calmodulin (CaM)-dependent serine/threonine phosphatase containing a dinuclear Fe,Zn center in the active site. Recent studies have indicated that CaN is a possible candidate for redox regulation. The inactivation of bovine brain CaN and of the catalytic CaN A-subunit from Dictyostelium by the vicinal dithiol reagents phenylarsine oxide (PAO) and melarsen oxide (MEL) and by H2O2 was investigated. PAO and MEL inhibited CaN with an IC50 of 3,8 m and the inactivation was reversed by 2,3-dimercapto-1-propane sulfonic acid. The treatment of isolated CaN with hydrogen peroxide resulted in a concentration-dependent inactivation. Analysis of the free thiol content performed on the H2O2 inactivated enzyme demonstrated that only two or three of the 14 Cys residues in CaN are modified. The inactivation of CaN by H2O2 could be reversed with 1,4-dithiothreitol and with the dithiol oxidoreductase thioredoxin. We propose that a bridging of two closely spaced Cys residues in the catalytic CaN A-subunit by PAO/MEL or the oxidative formation of a disulfide bridge by H2O2 involving the same Cys residues causes the inactivation. Our data implicate a possible involvement of thioredoxin in the redox control of CaN activity under physiological conditions. The low temperature EPR spectrum of the native enzyme was consistent with a Fe3+,Zn2+ dinuclear centre. Upon H2O2 -mediated inactivation of the enzyme no significant changes in the EPR spectrum were observed ruling out that Fe2+ is present in the active enzyme and that the dinuclear metal centre is the target for the oxidative inactivation of CaN. [source]

    Energetics of overall metabolic reactions of thermophilic and hyperthermophilic Archaea and Bacteria

    Jan P. Amend
    Abstract Thermophilic and hyperthermophilic Archaea and Bacteria have been isolated from marine hydrothermal systems, heated sediments, continental solfataras, hot springs, water heaters, and industrial waste. They catalyze a tremendous array of widely varying metabolic processes. As determined in the laboratory, electron donors in thermophilic and hyperthermophilic microbial redox reactions include H2, Fe2+, H2S, S, S2O32,, S4O62,, sulfide minerals, CH4, various mono-, di-, and hydroxy-carboxylic acids, alcohols, amino acids, and complex organic substrates; electron acceptors include O2, Fe3+, CO2, CO, NO3,, NO2,, NO, N2O, SO42,, SO32,, S2O32,, and S. Although many assimilatory and dissimilatory metabolic reactions have been identified for these groups of microorganisms, little attention has been paid to the energetics of these reactions. In this review, standard molal Gibbs free energies (,Gr) as a function of temperature to 200C are tabulated for 370 organic and inorganic redox, disproportionation, dissociation, hydrolysis, and solubility reactions directly or indirectly involved in microbial metabolism. To calculate values of ,Gr for these and countless other reactions, the apparent standard molal Gibbs free energies of formation (,G) at temperatures to 200C are given for 307 solids, liquids, gases, and aqueous solutes. It is shown that values of ,Gr for many microbially mediated reactions are highly temperature dependent, and that adopting values determined at 25C for systems at elevated temperatures introduces significant and unnecessary errors. The metabolic processes considered here involve compounds that belong to the following chemical systems: H,O, H,O,N, H,O,S, H,O,N,S, H,O,Cinorganic, H,O,C, H,O,N,C, H,O,S,C, H,O,N,S,Camino acids, H,O,S,C,metals/minerals, and H,O,P. For four metabolic reactions of particular interest in thermophily and hyperthermophily (knallgas reaction, anaerobic sulfur and nitrate reduction, and autotrophic methanogenesis), values of the overall Gibbs free energy (,Gr) as a function of temperature are calculated for a wide range of chemical compositions likely to be present in near-surface and deep hydrothermal and geothermal systems. [source]

    Iron-mediated suppression of bloom-forming cyanobacteria by oxine in a eutrophic lake

    FRESHWATER BIOLOGY, Issue 5 2010
    Summary 1. Published studies show that cyanobacteria have higher Fe requirements than eukaryotic algae. To test whether Fe availability can affect formation of a cyanobacterial bloom, a strong Fe chelator, oxine (8-hydroxyquinoline, C9H7NO), was added to enclosures in eutrophic Lake 227 in the Experimental Lakes Area (ELA) (northwestern Ontario). 2. Aphanizomenon schindlerii growth was suppressed, and growth of eukaryotic chlorophytes significantly promoted in enclosures to which oxine had been added. Significant eukaryotic growth did not occur in enclosures treated with ammonium, suggesting that N supplied by degradation of oxine was not responsible for eukaryotic success in the oxine enclosures. 3. In situ Fe2+ measurements were unreliable because of interference from high concentrations of dissolved organic compounds. However, oxine rapidly promoted oxidation of Fe2+ to Fe3+ in deionised water, suggesting that rapid removal of Fe2+ also occurred in the oxine-treated enclosures. 4. In batch cultures, 10 ,m Fe and 10 ,m oxine (a 1 : 1 ratio) completely inhibited the growth of the cyanobacteria Synechococcus sp. and Anabaena flos-aquae and the chlorophytes Pseudokirchneriella subcapitata and Scenedesmus quadricauda. Increasing Fe 10-fold to 100 ,m Fe completely and partially reversed oxine inhibition in the two chlorophytes but could not overcome inhibition of the cyanobacteria, indicating that inhibition was Fe-mediated at least in the eukaryotes. Since oxine binds Fe3+ in a 1 : 3 ratio (Fe : oxine), inhibition at a 1 : 1 ratio indicates that not all of the Fe is bound, and a mechanism involving Fe other than chelation was at least partly responsible for inhibition. 5. Collectively, the enclosure and laboratory results suggest that the outcome of competition between cyanobacteria and eukaryotic algae in the oxine-treated enclosures in Lake 227 was likely a result of decreased availability of Fe, especially Fe2+. 6. The results suggest that remediation methods that dramatically restrict the supply rate of Fe2+ could reduce the relative abundance of cyanobacteria in eutrophic systems. [source]

    Microbiology and geochemistry of Little Hot Creek, a hot spring environment in the Long Valley Caldera

    GEOBIOLOGY, Issue 2 2010
    T. J. VICK
    A culture-independent community census was combined with chemical and thermodynamic analyses of three springs located within the Long Valley Caldera, Little Hot Creek (LHC) 1, 3, and 4. All three springs were approximately 80 C, circumneutral, apparently anaerobic and had similar water chemistries. 16S rRNA gene libraries constructed from DNA isolated from spring sediment revealed moderately diverse but highly novel microbial communities. Over half of the phylotypes could not be grouped into known taxonomic classes. Bacterial libraries from LHC1 and LHC3 were predominantly species within the phyla Aquificae and Thermodesulfobacteria, while those from LHC4 were dominated by candidate phyla, including OP1 and OP9. Archaeal libraries from LHC3 contained large numbers of Archaeoglobales and Desulfurococcales, while LHC1 and LHC4 were dominated by Crenarchaeota unaffiliated with known orders. The heterogeneity in microbial populations could not easily be attributed to measurable differences in water chemistry, but may be determined by availability of trace amounts of oxygen to the spring sediments. Thermodynamic modeling predicted the most favorable reactions to be sulfur and nitrate respirations, yielding 40,70 kJ mol,1 e, transferred; however, levels of oxygen at or below our detection limit could result in aerobic respirations yielding up to 100 kJ mol,1 e, transferred. Important electron donors are predicted to be H2, H2S, S0, Fe2+ and CH4, all of which yield similar energies when coupled to a given electron acceptor. The results indicate that springs associated with the Long Valley Caldera contain microbial populations that show some similarities both to springs in Yellowstone and springs in the Great Basin. [source]

    Silicon-Doped LiFePO4 Single Crystals: Growth, Conductivity Behavior, and Diffusivity

    Ruhul Amin
    Abstract Single crystals of silicon doped LiFePO4 with a silicon content of 1% are grown successfully by the floating zone technique and characterized by single-crystal and powder X-ray diffraction, secondary ion mass spectroscopy, and chemical analysis. Electron paramagnetic resonance demonstrates the presence of only Fe2+; no traces of Fe3+ are found. Impedance spectroscopy as well as step-function polarization/depolarization (DC) measurements are carried out using the cells Ti/LiFe(Si)PO4/Ti and LiAl/LiI/LiFe(Si)PO4/LiI/LiAl. The electronic and ionic conductivities as well as the Li-diffusivity of the sample in the major crystallographic directions ([h00], [0k0], and [00l]) are determined. Within experimental error the transport properties along the b- and c-axes are found to be the same but differ significantly from the a-axis, which exhibits lower values. Compared to undoped LiFePO4, Si-doping leads to an increase of the ionic conductivity while the electronic conductivity decreases, which is in agreement with a donor effect. The activation energies of conductivities and diffusivities are interpreted in terms of defect chemistry and relevant Brouwer diagrams are given. [source]

    Bentonite as a Natural Adsorbent for the Sorption of Iron from the Ground Water Exploited from Aswan Area, Egypt

    Gharib M. Taha
    Sorption of dissolved Fe2+ on bentonite was studied using a batch technique. The distribution coefficient, Kd, was evaluated for a bentonite-iron system as a function of contact time, pH, sorbent and sorbate concentrations, and temperature. Sorption results were interpreted in terms of Freundlich's and Langmuir's equations. Thermodynamic parameters for the sorption system were determined at three temperatures: 298, 308, and 318K. The values of ,H(-4.0 kjmol,1) and ,G(-2.46 Kjmol,1) at 298K (25C) suggest that sorption of iron on bentonite is an exothermic and a spontaneous process. The ,G value became less negative at higher temperatures and, therefore, less iron was sorbed at higher temperatures. The desorption studies with 0.01M CaCl2 and deionized water at iron loading on bentonite showed that more than 90 wt% of the iron is irreversibly sorbed, probably due to the fixation of the iron by isomorphous replacement in the crystal lattice of the sorbent. [source]

    Kinetics of aerobic and anaerobic oxidations of ethanol by Fenton's reagent

    Mordechai L. Kremer
    For the first time, the time dependence of [H2O2] and [Fe2+] was followed during the aerobic oxidation of ethanol by Fenton's reagent. It was found that part of the ethanol was oxidized by dissolved O2 via the transient formation of H2O2. A model was set up based on FeO2+ as the key intermediate. Both one- and two-equivalent oxidations of ethanol occur, the former producing radical species derived from ethanol. No free radicals derived from H2O2 play part in the system. The relevant rate constants or their ratios were determined. The mechanism accounted successfully also for the anaerobic oxidation of ethanol. 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 541,553, 2008 [source]

    Promotion of the fenton reaction by Cu2+ ions: Evidence for intermediates

    Mordechai L. Kremer
    The promotion of the Fenton reaction by Cu2+ ions has been investigated using a wide range of [Cu2+]. Both the disappearance of Fe2+ and the evolution of O2 were followed as a function of time by quenching the reaction mixture with o -phenanthroline or with excess Fe2 + ions, respectively. Two series of experiments were performed. In one series [H2O2] was 5 10,4 mol dm,3, and in the other [H2O2] was reduced to 5 10,5 mol dm ,3. By stopping the reaction with excess Fe2+ ions, significant differences in the measured absorbance in the two series were observed. In the higher [H2O2] range, the absorbance decreased monotonically in time, due to O2 formation during the reaction. In the lower range, an initial transient rise of the absorbance was observed, indicating the formation of spectroscopically distinct intermediates in the system. A mechanism involving the intermediates FeOCu4+ and FeOCu5+ has been set up. Rate constants of the mechanism have been determined. 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 725,736, 2006 [source]

    Kinetics of Fe(II) reduction of cis -halogeno(dodecylamine) bis(ethylenediamine)- cobalt(III) complex ion in aqueous solutions

    K. Santhakumar
    Kinetics of reduction of the surfactant complex ions, cis -chloro/bromo (dodecylamine)bis(ethylenediamine)cobalt(III) by iron(II) in aqueous solution was studied at 303, 308, and 313 K by spectrophotometry method under pseudo-first-order conditions, using an excess of the reductant. The second-order rate constant remains constant below critical micelle concentration (cmc), but increases with cobalt(III) concentration above cmc, and the presence of aggregation of the complex itself alters the reaction rate. The rate of reaction was not affected by the added [H+]. Variation of ionic strength (,) influences the reaction rate. Activation and thermodynamic parameters have been computed. It is suggested that the reaction of Fe2+ (aq) with cobalt(III) complex proceeds by the inner-sphere mechanism. 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 98,105, 2006 [source]

    Giant Room,Temperature Magnetodielectric Response in the Electronic Ferroelectric LuFe2O4

    ADVANCED MATERIALS, Issue 13 2006
    A. Subramanian
    A very large drop in dielectric constant upon application of small magnetic fields is observed at room temperature for LuFe2O4 (see figure). Such behavior is unprecedented and indicates a strong coupling of spins and electric dipoles at room temperature. This behavior of LuFe2O4 is apparently related to its ferroelectricity, which occurs through the highly unusual mechanism of Fe2+ and Fe3+ ordering. [source]

    Storage temperature and packaging condition affect the total phenolic content and antioxidant activity of black soybeans and koji

    Ru-Yue Huang
    Summary In this study, powders of steamed black soybeans and the Aspergillus awamori -fermented black soybeans (koji) were subjected to storage at 4 C and 25 C with or without deoxidant and desiccant for 120 days. It was found that total phenolic content and the antioxidant activity including the DPPH radicals scavenging effect, Fe2+ -chelating ability and reducing activity of the methanol extracts from black soybeans and koji decreased as the storage period was extended. Furthermore, storage temperature and packaging condition affected the antioxidant activity of the methanol extracts of black soybeans and koji. After 120-day storage, extract from black soybeans holding at 4 C with deoxidant and desiccant exhibited the highest residual of DPPH radicals scavenging effect, Fe2+ -chelating ability and reducing activity of 71.78%, 72.66% and 70.04%, respectively. Meanwhile, the highest residual of 77.78%, 81.71% and 85.05% respectively, was noted with extract from koji held at 25 C with deoxidant and desiccant. [source]

    Computational study of the solvation of protoporphyrin IX and its Fe2+ complex

    Teobaldo Cuya Guizado
    Abstract Molecular dynamics (MD) simulations of a well known hydrophobic structure, the heme (ferroprotoporphyrin IX) and its precursor in the heme synthesis, protoporphyrin IX (PPIX) are presented. The objective of the present study is to determine the stability of both structures in an aqueous medium, as well as the structure-solvent relation, hydration shells, and discuss their implications for biological processes. The density functional theory (DFT) is used for the electronic and structural characterization of both PPIX and its Fe2+ complex. A classical approach based on the Gromacs package is used for the MD. The radial distribution function g(r) is used to examine the allocation of water molecules around different regions of the porphyrins. The calculations demonstrate the heterogeneous character of the porphyrins with respect to the affinity with water molecules, the general hydrophobic character of the porphyrin ring bonded or not to the ion Fe, the hydrophilic character of the carboxylic oxygen that is unchanged upon iron binding, and the low hydrophilicity of Fe2+ in the heme. 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

    Competitive coordination between lead and oligoelements with respect to some therapeutic heavy-metal chelators

    C. Gourlaouen
    Abstract The competitive complexation of Ca2+, Fe2+, Cu2+, Zn2+, and Pb2+ toward ethylene diamine tetraacetate (EDTA), dimercaprol and D -penicillamine, three liganding agents commonly used in chelation therapy against heavy metal, especially lead, poisonings is examined by means of B3LYP calculations, natural population analyses, and the topological analysis of the electron localization function. It is shown that Pb2+ can displace any of Ca2+, Fe2+, Cu2+, or Zn2+ chelated by any of dimercaprol or D -penicillamine, but can only displace Ca2+ if EDTA is concerned. The first two chelators thus appear as better entities than EDTA to be used in chelation therapy, where in vivo selective complexation is essential. Moreover, the comparison of the bonding characteristics of Pb2+ with those of the other cations allows deriving three features to be taken into account in designing new chelators expecting to have an increased selectivity toward this cation. 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]