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1.
The `push' hypothesis for the antioxidant action of Zn2+ is based on its displacement of iron from a low molecular weight pro-oxidant complex. In this study, the chemical plausibility of that proposed function is investigated by cyclic voltammetry. As a model for a pro-oxidative low molecular weight iron complex the FeII/IIIEDTA couple was examined. This complex was selected for its well-defined electrochemical, iron stability constants, and similarity to other low molecular weight chelates in physiological fluids in terms of logical binding sites, i.e. amino, and carboxylate groups. Also investigated were iron complexes of nitrilotriacetic acid and DL-glutamic acid. Results demonstrate that approximately 90% of the cyclic voltammetric peak current for FeIIIEDTA reduction and the EC′ current for the mediated reduction of H2O2 by FeII/IIIEDTA (Fenton Reaction) are lost when Zn2+ is introduced to a 1:1 molar ratio relative to iron. All experiments were conducted in HEPES buffered solutions at pH 7.4. Iron (II/III) complexes of nitrilotriacetic acid and DL-glutamic acid followed the same trends. Cyclic voltammetric experiments indicate that Zn2+ displaces FeIII from EDTA despite the much larger stability constant for the iron complex (1025.1) versus zinc (1016.50). The hydrolysis aided displacement of FeIII from EDTA by Zn2+ is considered by the equilibria modeling program, HySS. With FeIII hydrolysis products included, Zn2+ is able to achieve 90% displacement of iron from EDTA, a result consistent with cyclic voltammetric observations. Published online December 2004  相似文献   

2.
The Fenton-type reaction between ferrous diethylenetriamine pentaacetic acid (Fe2+-DTPA, 50–200 μM) and H2O2 (20–1000 μM) in phosphate buffer at pH 7.0 results in consumption of dissolved oxygen. This observation differs from many prior reports that oxygen is liberated when more concentrated solutions of H2O2 are decomposed by iron salts. The rate and total quantity of oxygen consumed were dependent upon the concentrations of ferrous chelate, H2O2, and excess DTPA. Evidence is provided that both the ferrous-DTPA chelate and free DTPA can participate in the oxygen-consuming reactions. Oxygen was also consumed during the Fenton reaction between ferrous ions and H2O2 when DTPA and phosphate buffer were omitted. Under these conditions, oxygen evolution was observed at higher H2O2 concentrations (e.g., 400 μM). The consumption of oxygen during the Fenton-type reaction of an iron chelate at neutral pH may be relavant to events that take place in biologic systems.  相似文献   

3.
Due to its wide industrial application, chromium (Cr) is known to be a critical environmental pollutant. Contamination of water and agricultural soil by Cr inhibits crop productivity and their physiological and biochemical processes. The objective of the current work was to investigate the effects of appropriate reducing agents such as EDTA, iron sulfate (Fe2+), and zerovalent nano iron (Fe0 nanoparticles) on growth and physiology of sunflower plants under Cr(VI) stress. Results showed that the Cr uptake increased by increasing the amount of EDTA, leading to a significant reduction in morphological and physiological parameters except for MDA and H2O2 contents. Treatment with Fe0 nanoparticles and Fe2+ reduced Cr concentration in root and shoot, increased root and shoot dry weight, plastid pigments (chlorophyll and carotenoids) and proline contents; however, the level of MDA and H2O2 decreased significantly. All parameters were affected by Fe2+ during the first week of sampling; however, Fe0 nanoparticles affected all traits until the end of the third sampling stage. A statistically significant and positive correlation was found between root Cr concentration and MDA and H2O2 seedlings treated with EDTA, Fe2+, and Fe0 grown under Cr stress. From the result of this study, it can be concluded that sunflower has the potential for accumulation of Cr as a heavy metal, and treatment with Fe0 nanoparticles to prevent Cr uptake is more effective than other employed treatments.  相似文献   

4.
Oxidative reactions can result in the formation of electronically excited species that undergo radiative decay depending on electronic transition from the excited state to the ground state with subsequent ultra‐weak photon emission (UPE). We investigated the UPE from the Fe2+–EDTA (ethylenediaminetetraacetic acid)–AA (ascorbic acid)–H2O2 (hydrogen peroxide) system with a multitube luminometer (Peltier‐cooled photon counter, spectral range 380–630 nm). The UPE, of 92.6 μmol/L Fe2+, 185.2 μmol/L EDTA, 472 μmol/L AA, 2.6 mmol/L H2O2, reached 1217 ± 118 relative light units during 2 min measurement and was about two times higher (P < 0.001) than the UPE of incomplete systems (Fe2+–AA–H2O2, Fe2+–EDTA–H2O2, AA–H2O2) and medium alone. Substitution of Fe2+ with Cr2+, Co2+, Mn2+ or Cu2+ as well as of EDTA with EGTA (ethylene glycol‐bis(β‐aminoethyl ether)‐N,N,N′,N′‐tetraacetic acid) or citrate powerfully inhibited UPE. Experiments with scavengers of reactive oxygen species (dimethyl sulfoxide, mannitol, sodium azide, superoxide dismutase) revealed the dependence of UPE only on hydroxyl radicals. Dimethyl sulfoxide at the concentration of 0.74 mmol/L inhibited UPE by 79 ± 4%. Plant phenolics (ferulic, chlorogenic and caffec acids) at the concentration of 870 μmol/L strongly enhanced UPE by 5‐, 13.9‐ and 46.8‐times (P < 0.001), respectively. It is suggested that augmentation of UPE from Fe2+–EDTA–AA–H2O2 system can be applied for detection of these phytochemicals.  相似文献   

5.
The ability of paraquat radicals (PQ+.) generated by xanthine oxidase and glutathione reductase to give H2O2-dependent hydroxyl radical production was investigated. Under anaerobic conditions, paraquat radicals from each source caused chain oxidation of formate to CO2, and oxidation of deoxyribose to thiobarbituric acid-reactive products that was inhibited by hydroxyl radical scavengers. This is in accordance with the following mechanism derived for radicals generated by γ-irradiation [H. C. Sutton and C. C. Winterbourn (1984) Arch. Biochem. Biophys.235, 106–115] PQ+. + Fe3+ (chelate) → Fe2+ (chelate) + PQ++ H2O2 + Fe2+ (chelate) → Fe3+ (chelate) + OH? + OH.. Iron-(EDTA) and iron-(diethylenetriaminepentaacetic acid) (DTPA) were good catalysts of the reaction; iron complexed with desferrioxamine or transferrin was not. Extremely low concentrations of iron (0.03 μm) gave near-maximum yields of hydroxyl radicals. In the absence of added chelator, no formate oxidation occurred. Paraquat radicals generated from xanthine oxidase (but not by the other methods) caused H2O2-dependent deoxyribose oxidation. However, inhibition by scavengers was much less than expected for a reaction of hydroxyl radicals, and this deoxyribose oxidation with xanthine oxidase does not appear to be mediated by free hydroxyl radicals. With O2 present, no hydroxyl radical production from H2O2 and paraquat radicals generated by radiation was detected. However, with paraquat radicals continuously generated by either enzyme, oxidation of both formate and deoxyribose was measured. Product yields decreased with increasing O2 concentration and increased with increasing iron(DTPA). These results imply a major difference in reactivity between free and enzymatically generated paraquat radicals, and suggest that the latter could react as an enzyme-paraquat radical complex, for which the relative rate of reaction with Fe3+ (chelate) compared with O2 is greater than is the case with free paraquat radicals.  相似文献   

6.
Summary The effect of trace elements (Fe, Ni) and chelating compounds on the activity of hydrogen (H2) uptake (Hup) hydrogenase, nitrogenase and rate and yield of H2 photoproduction from l-lactate in photosynthetic cultures of Rhodospirillum rubrum was investigated. Hup activity depended on the availability of Ni2+ and was inhibited by EDTA (0.3–0.5 mm ethylenedinitrilotetraacetic acid). Addition of EDTA (0.5 mm) to the culture medium caused a nearly complete inactivation of Hup activity and activation of nitrogenase, which was paralleled by a threefold increase in total H2 photoproduced from lactate. Hup mutants, isolated by transposon Tn5 mutagenesis, produced maximally twofold more H2 than the wild-type. Experiments with different chelating agents [EDTA, NTA (nitrilotriacetic acid), citrate, isocitrate] and varying concentrations of Fe2+ and Fe3+ showed that photosynthetic growth and nitrogenase activity of R. rubrum were strongly influenced by the iron supply. It is concluded that EDTA enhanced H2 photoproduction by (I) inhibition of biosynthesis of Hup hydrogenase and (II) mobilization of iron, thereby activating the biosynthesis of the nitrogenase complex. Correspondence to: M. Kern  相似文献   

7.
Although considerably more oxidation-resistant than other P-type ATPases, the yeast PMA1 H+-ATPase of Saccharomyces cerevisiae SY4 secretory vesicles was inactivated by H2O2, Fe2+, Fe- and Cu-Fenton reagents. Inactivation by Fe2+ required the presence of oxygen and hence involved auto-oxidation of Fe2+ to Fe3+. The highest Fe2- (100 μM) and H2O2 (100 mM) concentrations used produced about the same effect. Inactivation by the Fenton reagent depended more on Fe2+ content than on H2O2 concentration, occurred only when Fe2+ was added to the vesicles first and was only slightly reduced by scavengers (mannitol, Tris, NaN3, DMSO) and by chelators (EDTA, EGTA, DTPA, BPDs, bipyridine, 1, 10-phenanthroline). Inactivation by Fe- and Cu- Fenton reagent was the same; the identical inactivation pattern found for both reagents under anaerobic conditions showed that both reagents act via OH·. The lipid peroxidation blocker BHT prevented Fenton-induced rise in lipid peroxidation in both whole cells and in isolated membrane lipids but did not protect the H+-ATPase in secretory vesicles against inactivation. ATP partially protected the enzyme against peroxide and the Fenton reagent in a way resembling the protection it afforded against SH-specific agents. The results indicate that Fe2+ and the Fenton reagent act via metal-catalyzed oxidation at specific metal-binding sites, very probably SH-containing amino acid residues. Deferrioxamine, which prevents the redox cycling of Fe2+, blocked H+-ATPase inactivation by Fe2+ and the Fenton reagent but not that caused by H2O2, which therefore seems to involve a direct non-radical attack. Fe-Fenton reagent caused fragmentation of the H+-ATPase molecule, which, in Western blots, did not give rise to defined fragments bands but merely to smears.  相似文献   

8.
A new hypothesis describing the role of the redox inactive Ca2+ ion in the expression of physiological oxidative damage is described. The hypothesis is based on the optimization of the chelation characteristics of iron complexes for pro-oxidant activity. In a previous investigation it was found that an excess of ligand kinetically hindered the Fenton reaction activity of the FeII/IIIEDTA complex (Bobier et al. 2003). EDTA, citrate, NTA, and glutamate were selected as models for the coordination sites likely encountered by mobile iron, i.e. proteins. The optimal [EDTA]:[FeIII] ratio for Fenton reaction activity as measured by electrocatalytic voltammetry in a solution was found to be 1:1. An excess of EDTA in the amount of 10:1 [ligand]:[metal] suppresses the Fenton reaction activity to nearly the control. It is expected that the physiological coordination characteristics of mobile Fe would have a very large excess of [ligand]:[metal] and thus not be optimized for the Fenton reaction. Introduction of Ca2+ in to a ratio of 10:10:1 [Ca2+]:[EDTA]:[FeIII] to the system reinvigorated the Fenton reaction activity to nearly the value of the optimal 1:1 [EDTA]:[FeIII] complex. The pH distribution diagrams of Ca2+ in the presence of EDTA and FeII/III indicate that Ca2+ has the ability to uptake excess EDTA without displacing either FeII of FeIII from their respective complexed forms. The similarity in the presence for hard ligand sites albeit with a lower binding constant for Ca2+ accounts for this action.  相似文献   

9.
Fenton's reaction is comprised of hydrogen peroxide (H2O2) catalyzed by iron, producing the hydroxyl radical (·OH), a strong oxidant. ·OH in turn may react with H2O2 and iron and is capable of destroying a wide range of organic contaminants. In this laboratory study, Fenton's reaction was observed in aqueous and soil slurry systems using trichloroethylene (TCE) as the target contaminant, with the goal of maximizing TCE degradation while minimizing H2O2 degradation. Fenton's reaction triggers a complex matrix of reactions involving ·OH, H2O2, iron, TCE, and soil organics. In soil slurries with a high fraction of organic carbon (fOC), iron tends to sorb to soil organics and/or particles. In aqueous systems the optimal ratio of H2O2:Fe2+:TCE to degrade TCE in a timely fashion, minimize costs, and minimize H2O2 degradation is 300?mg/L: 25?mg/L: 60?mg/L (19:1:1 molar ratio), while soil slurries with a fOC up to approximately 1% and a soil:water ratio of 1:5 (weight ratio) require about ten times the amount of H2O2, the optimal ratio being 3000?mg/L: 5?mg/L: 60?mg/L (190:0.2:1 molar ratio). TCE degradation rates were observed to decrease in soil slurries with higher fOC because of competition by soil organic matter, which appears to act as a sink for ·OH. H2O2 degradation rates tended to increase in soil slurries with higher fOC, most likely due to increased demand for ·OH by soil organics, increased available iron and other oxidation processes.  相似文献   

10.
The uranium(IV) complexes [U(EDTA)(H2O)2], [U(HOEDTA)]+, and [U(DTPA)]? are well-formed in the pH fange 2–3 ([DTPA]5- = diethylenetriaminepentaacetate; [HOEDTA]3-  N-(2-hydroxyethyl)ethylenediaminetriacetate). Of these, only [U(DTPA)]- is extracted from an aqueous phase at pH 2 by the perchlorate salt of the primary amine, Primene JM-T. As the aqueous phase pH was raised, extraction occurred in all three cases and hydrolysed species may be extracted from EDTA and HOEDTA solutions but [U(DTPA)]? resists hydrolysis. The addition of sulphate had a marked effect on the extraction of U(IV) from EDTA and HOEDTA through the formation of [U(EDTA)(SO4)(H2O)]2- and [U(HOEDTA)(SO4)(H2O)n]?. The equilibrium constant, log β1, for: [(U(EDTA)(H2O)2] 2 [SO4]2? ? [U(EDTA)(SO4)(H2O)]2- 2 H2O was found to be 2.43 ± 0.04 (I = 1 mol dm?3, NaClO4; pH 2.0; 20 °C) from spectrophotometric data.With tri-n-octylphosphine oxide (TOPO) electronic spectroscopy showed that the same U(IV) complex was extracted at pH 2 for Cs2UCl6, U(IV)/ HOEDTA, and U(IV)/DTPA and the aminepoly- carboxylates were aqueous phase masking agents but with [U(EDTA)(H2O)2] oxidation gave a uranyl(VI) organic phase species.Uranium(IV) is strongly extracted from aqueous solutions of HOEDTA at pH 2 or 3 by bis(2-ethyl- hexyl)phosphoric acid (HBEHP) but less so from EDTA and DTPA. Since U(IV) is completely extracted from Cs2UCl6 it could be that the amine- polycarboxylates were aqueous phase masking agents although spectral evidence did not support this.  相似文献   

11.
Mesembryanthemum crystallinum L. plants were grown from seeds in perlite. At the age of 4 weeks (juvenile plants) or 6 weeks (adult plants), they were transferred on nutrient media with different Fe3+ content brought in as Fe2(SO4)3—EDTA complex (pH 6.0): control, iron deficit, and iron “excess”. Adult plants grown in media differing in iron content were subjected to salinity (300 mM NaCl) during the last 8 days of growth. Biochemical analyses were performed after plant fixation in liquid nitrogen; simultaneously, the samples for electron microscopy were taken. Different content of available Fe3+ in medium, especially under salinity conditions, changed sharply the content of chlorophyll and proline, the rate of lipid peroxidation, the level of H2O2, the activities of antioxidant enzymes in the leaves and roots, the number and sizes of plastoglobules, and ferritin formation in plastids. Joint action of salinity and iron deficit enhanced oxidative stress development, whereas iron excess hampered oxidative reaction development, reduced the rate of lipid peroxidation, and increased the chlorophyll content. At iron excess, plastoglobule lysis in plastids did not occur, their number and sizes increased, and ferritin deposits appeared, whereas the latter were absent at iron deficit.  相似文献   

12.
In the absence of added Fe2+, the ATPase activity of isolatedSchizosaccharomyces pombe plasma membranes (5–7 μmolP i per mg protein per min) is moderately inhibited by H2O2 in a concentration-dependent manner. Sizable inactivation occurs only at 50–80 mmol/L H2O2. The process, probably a direct oxidative action of H2O2 on the enzyme, is not induced by the indigenous membrane-bound iron (19.3 nmol/mg membrane protein), is not affected by the radical scavengers mannitol and Tris, and involves a decrease of both theK m of the enzyme for ATP and theV of ATP splitting. On exposing the membranes to the Fenton reagent (50 μmol/L Fe2+ +20 mmol/L H2O2), which causes a fast production of HO radicals, the ATPase is 50–60% inactivated and 90% of added Fe2+ is oxidized to Fe3+ within 1 min. The inactivation occurs only when Fe2+ is added before H2O2 and can thus bind to the membranes. The lack of effect of radical scavengers (mannitol, Tris) indicates that HO radicals produced in the bulk phase play no role in inactivation. Blockage of the inactivation by the iron chelator deferrioxamine implies that the process requires the presence of Fe2+ ions bound to binding sites on the enzyme molecules. Added catalase, which competes with Fe2+ for H2O2, slows down the inactivation but in some cases increases its total extent, probably due to the formation of the superoxide radical that gives rise to delayed HO production.  相似文献   

13.
The capacity of non-illuminated nephrotoxin orellanine ([2,2′-bipyridine]-3,3′,4,4′-tetrol-1,1′-dioxide) to induce DNA damage in the presence of ferrous iron and dioxygen has been evaluated. Maximal single-strand breaks in plasmid DNA were obtained with a metal to ligand ratio 1:3. Instantaneous oxidation of Fe2+ in presence of orellanine under air was responsible for oxy-radical production concomitant to a stable ferric complex Fe(III)Or3 formation, leading to oxidative DNA breakage at physiological pH. DNA damage was lowered in the presence of SOD and catalase or DMSO, indicating a set of reactions that leads to oxyradical generation. Iron chelators such as DTPA and EDTA had no protecting effect, Desferal slightly protected. GSH acted as an oxy-radical scavenger, whereas cysteine induced stronger damage.

Closely related bipyridine compounds were also studied in presence of Fe2+ and O2 using a combination of spin-trapping and DNA-nicking experiments, none of which were able to chelate iron and induce damage at pH 7. Both catecholic moieties and aminoxide groups are required for observing breakage at physiological pH.  相似文献   

14.
Two iron(III) complexes, [Fe4OCl(O2CMe)3(O3PC6H9)3(py)5] (1) and [Fe7O2(O2CPh)9(O3PC6H9)4(py)6] (2), have been prepared through solution reactions of [Fe3O(O2CR)6(H2O)3]Cl (R = Me, Ph) with cyclohexenephosphonic acid. Both compounds contain triangular oxo-centered [Fe33-O)]7+ units. In complex 1, the fourth iron atom is capped on this triangular unit through O-P-O bridges, forming a tetranuclear cluster with a tetrahedral arrangement of iron atoms. In complex 2, two equivalent [Fe33-O)]7+ units are connected by the fourth iron atom through four phosphonate ligands, forming a heptanuclear cluster. Variable temperature susceptibility measurements were performed for 1 and 2. Both exhibit dominant antiferromagnetic interactions between the Fe(III) centers.  相似文献   

15.
Effect of heteroligands (L) on the properties of vanadium peroxides was investigated by preparing a number of peroxovanadium complexes, which were characterized by analysis, IR, UV/V and NMR spectra. X-ray structures for some were obtained. The vanadates(V) contain the cation M(I)=Na, K, NH4, Rb or Cs. Diperoxo complexes include M(I)[VO(O2)2L], where L=dipyridyl, o-phenanthroline; M(I)3[VO(O2)2(C2O4)]; K2[(nicotinic acid) {VO(O2)2}2]H2O;M(I)4[O{VO(O2)2}2 cystine]2H2O; H4[O{VO(O2)2(adenine)2)2]2H2O; and K2H2[O{VO(O2)2(adenosine)}2]2H2O. Monoperoxo vanadates(V) correspond to the formula M(I)2[VO(O2)L]2 for L=citrate and malate; M(I)2[VO(O2)L] for L=nitrilotriacetate; M(I)[VO(O2)L] for L=iminodiacetate, tartrate and EDTA; and [HVO2(O2)(adenosine)]2H2O. Syntheses of these heteroligand peroxovanadium compounds are sensitive to pH, temperature and the concentration of the components. The stability towards decomposition in solid state, mother-liquid and pure water solutions depends upon the heteroligand. Characteristic (V=O) and (O-O) stretching frequency bands in IR can be correlated with the corresponding bond lengths and the [peroxoV(V)] charge transfer bands in UV/V spectra. Intramolecular one-electron transfer in peroxo vanadates(V) can trigger the generation of radicals, and its dependency upon the nature of the heteroligand is discussed.  相似文献   

16.
[1+1] macrocyclic and [1+2] macroacyclic compartmental ligands (H2L), containing one N2O2, N3O2, N2O3, N4O2 or O2N2O2 Schiff base site and one O2On (n=3, 4) crown-ether like site, have been prepared by self-condensation of the appropriate formyl- and amine precursors. The template procedure in the presence of sodium ion afforded Na2(L) or Na(HL) · nH2O. When reacted with the appropriate transition metal acetate hydrate, H2L form M(L) · nH2O, M(HL)(CH3COO) · nH2O, M(H2L)(X)2 · nH2O (M=Cu2+, Co2+, Ni2+; X=CH3COO, Cl) or Mn(L)(CH3COO) · nH2O according to the experimental conditions used. The same complexes have been prepared by condensation of the appropriate precursors in the presence of the desired metal ion. The Schiff bases H2L have been reduced by NaBH4 to the related polyamine derivatives H2R, which form, when reacted with the appropriate metal ions, M(H2R)(X)2 (M= Co2+, Ni2+; X=CH3COO, Cl), Cu(R) · nH2O and Mn(R)(CH3COO) · nH2O. The prepared ligands and related complexes have been characterized by IR, NMR and mass spectrometry. The [1+1] cyclic nature of the macrocyclic polyamine systems and the site occupancy of sodium ion have been ascertained, at least for the sodium (I) complex with the macrocyclic ligand containing one N3O2 Schiff base and one O2O3 crown-ether like coordination chamber, by an X-ray structural determination. In this complex the asymmetric unit consists of one cyclic molecule of the ligand coordinated to a sodium ion by the five oxygen atoms of the ligand. The coordination geometry of the sodium ion can be described as a pentagonal pyramid with the metal ion occupying the vertex. In the mononuclear complexes with H2L or H2R the transition metal ion invariantly occupies the Schiff base site; the sodium ion, on the contrary, prefers the crown-ether like site. Accordingly, the heterodinuclear complexes [MNa(L)(CH3COO)x] (M=Cu2+, Co2+, Ni2, x=1; M=Mn3+, x=2) have been synthesised by reacting the appropriate formyl and amine precursors in the presence of M(CH3COO)n · nH2O and NaOH in a 1:1:1:2 molar ratio. The reaction of the mononuclear transition metal complexes with Na(CH3COO) · nH2O gives rise to the same heterodinuclear complexes. Similarly [MNa(R)(CH3COO)x] have been prepared by reaction of the appropriate polyamine ligand H2R with the desired metal acetate hydrate and NaOH in 1:1:2 molar ratio.  相似文献   

17.
The kinetics of the formation of the purple complex [FeIII(EDTA)O2]3−, between FeIII-EDTA and hydrogen peroxide was studied as a function of pH (8.22-11.44) and temperature (10-40 °C) in aqueous solutions using a stopped-flow method. The reaction was first-order with respect to both reactants. The observed second-order rate constants decrease with an increase in pH and appear to be related to deprotonation of FeIII-EDTA ([Fe(EDTA)H2O] ⇔ Fe(EDTA)OH]2− + H+). The rate law for the formation of the complex was found to be d[FeIIIEDTAO2]3−/dt=[(k4[H+]/([H+] + K1)][FeIII-EDTA][H2O2], where k4=8.15±0.05×104 M−1 s−1 and pK1=7.3. The steps involved in the formation of [Fe(EDTA)O2]3− are briefly discussed.  相似文献   

18.
The effect of lactic acid (lactate) on Fenton based hydroxyl radical (·OH) production was studied by spin trapping, ESR, and fluorescence methods using DMPO and coumarin-3-carboxylic acid (3-CCA) as the ·OH traps respectively. The ·OH adduct formation was inhibited by lactate up to 0.4mM (lactate/iron stoichiometry = 2) in both experiments, but markedly enhanced with increasing concentrations of lactate above this critical concentration. When the H2O2 dependence was examined, the DMPO-OH signal was increased linearly with H2O2 concentration up to 1 mM and then saturated in the absence of lactate. In the presence of lactate, however, the DMPO-OH signal was increased further with higher H2O2 concentration than 1 mM, and the saturation level was also increased dependent on lactate concentration. Spectroscopic studies revealed that lactate forms a stable colored complex with Fe3+ at lactate/Fe3+ stoichiometry of 2, and the complex formation was strictly related to the DMPO-OH formation. The complex formation did not promote the H2O2 mediated Fe3+ reduction. When the Fe3+-lactate (1:2) complex was reacted with H2O2, the initial rate of hydroxylated 3-CCA formation was linearly increased with H2O2 concentrations. All the data obtained in the present experiments suggested that the Fe3+-lactate (1:2) complex formed in the Fenton reaction system reacts directly with H2O2 to produce additional ·OH in the Fenton reaction by other mechanisms than lactate or lactate/Fe3+ mediated promotion of Fe3+/Fe2+ redox cycling.  相似文献   

19.
Barley (Hordeum vulgare L.) plants were grown in nutrient solutionscontaining the chelating agent, DTPA. The experiments replicatedthose reported in the preceding paper in which EDTA was thechelating agent used. The concentrations of all the chemicalspecies of metals were stimulated using the program NUTRIENT.The concentrations of DTPA used were chosen to give a similarrange of complexation as used in the EDTA experiments. The effectof complexation by DTPA on the uptakes of the metal ions Fe3+,Mn2+, Cu2+, and Zn2+ and on plant growth were sufficiently differentfrom those with EDTA to indicate some dependence on the natureof the chelating agent used. The biggest difference betweenthe EDTA and DTPA experiments occurred in the solutions containingthe largest concentrations of these reagents. With DTPA, chlorosiswas seen only in the early stages; otherwise the plants showednormal growth. A simple chemical model for metal uptake is discussed. Key words: DTPA, EDTA, micronutrients, trace metals, computer simulation, plants, absorption, iron, manganese, copper, zinc  相似文献   

20.
Under anaerobic conditions and in the absence of alternative electron acceptors, growth of the magnetic bacterium Aquaspirillum magnetotacticum MSI was iron concentration dependent. Weak chelation of the iron (with quinate, oxalate, or 2,3-dihydroxybenzoate) enhanced growth, whereas strong chelation (with EDTA, citrate, or nitrilotriacetic acid) retarded the growth of strain MSI relative to that of controls lacking chelators. Growth was proportional to the percentage of unchelated iron in medium containing EDTA in various molar ratios to iron. Addition of the respiratory inhibitors antimycin A (5 μM), NaCN (10 mM), and NaN3 (10 mM) inhibited growth with Fe(III) or NO3- as the terminal electron acceptor. Growth with O2 and NO3- was inhibited by 2-heptyl-4-hydroxyquinolone-N-oxide (HOQNO) but not with 2 mM Fe(III). Under strongly reducing conditions, strain MS1 survived but grew poorly and became irreversibly nonmagnetic. Growth and iron reduction in anaerobic cultures were stimulated by the provision of small amounts of O2 or H2O2. Slow infusion of air to cultures which had reduced virtually all of the Fe(III) in the medium (2 mM) supported a high rate of iron reoxidation (relative to killed controls) and growth in proportion to the amount of iron reoxidized. Oxygen consumption by iron-reducing cultures was predominantly biological, since NaCN and HOQNO both inhibited consumption. Inhibition of oxygen consumption (and iron reoxidation) by the addition of ferrozine and the inhibition of iron oxidation (and oxygen consumption) by the addition of HOQNO suggest that iron oxidation by strain MS1 is an aerobic respiratory process, perhaps tied to energy conservation. Iron oxidation was also necessary for magnetite synthesis, since in microaerobic denitrifying cultures, sequestration of reduced iron by ferrozine present in 10-fold molar excess to the available iron resulted in loss of magnetism and a severe drop in the average magnetosome number of the cells.  相似文献   

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