Showing papers on "Ferric published in 1979"
TL;DR: A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp and the two types were similar.
Abstract: A bipolarly flagellated magnetotactic spirillum containing intracellular chains of single domain-sized magnetite crystals was isolated by applying a magnetic field to sediments from a freshwater swamp. The organism was cultured in a chemically defined medium containing ferric quinate and succinate as sources of iron and carbon, respectively. Nonmagnetic variants of this isolate were maintained in chemically defined medium lacking ferric quinate. In contrast to magnetic cells, these had less iron and lacked measurable magnetic remanence and the intracytoplasmic crystals. In other respects, including moles percent guanine plus cytosine content, growth characteristics, nutrition, and physiology, the two types were similar. The isolate reduced nitrate without accumulating nitrite and produced ammonia during growth. Nitrate or ammonium ions served as a nitrogen source. The organism was microaerophilic and did not grow anaerobically with nitrate in the medium. In chemically defined medium, cells synthesized magnetite only if the initial O2 concentration in the atmosphere of sealed cultures was 6% (vol/vol) or less.
442 citations
248 citations
TL;DR: The reversibility of the stepwise reduction of Compound I to the ferric state via Compound II was confirmed in horseradish peroxidases A2 and C and the pH dependence of E'O (Compound II/ferric) was in accord with the equation.
224 citations
01 Jun 1979-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, it was shown that the principal rate limiting step for the acid ferric sulfate leaching of chalcopyrite appears to be a transport process through the elemental sulfur reaction product.
Abstract: The acid ferric sulfate leaching of chalcopyrite, CuFeS2 + 4Fe+3 = Cu+2 + 5Fe+2 + 2S0 was studied using monosize particles in a well stirred reactor at ambient pressure and dilute solid phase concentration in order to obtain fundamental details of the reaction kinetics. The principal rate limiting step for this electrochemical reaction appears to be a transport process through the elemental sulfur reaction product. This conclusion has been reached in other investigations and is supported by data from this investigation in which the reaction rate was found to have an inverse second order dependence on the initial particle diameter. Furthermore, the reaction kinetics were found to be independent of Fe+3, Fe+2, Cu+2 and H2SO4 in the range of additions studied. The unique aspect of this particular research effort is that data analysis, using the Wagner theory of oxidation, suggests that the rate limiting process may be the transport of electrons through the elemental sulfur layer. Predicted reaction rates calculated from first principles using the physicochemical properties of the system (conductivity of elemental sulfur and the free energy change for the reaction) agree satisfactorily with experimentally determined rates. Further evidence which supports this analysis includes an experimental activation energy of 20 kcal/mol (83.7 kJ/mol) which is approximately the same as the apparent activation energy for the transfer of electrons through elemental sulfur, 23 kcal/ mol (96.3 kJ/mol) calculated from both conductivity and electron mobility measurements reported in the literature.
219 citations
218 citations
TL;DR: Agrobactin was produced by A. tumefaciens in response to iron deficiency and was able to reverse the iron starvation in this organism precipitated by the presence of a ferric complexing agent not utilized by the cells.
162 citations
TL;DR: The relevant oxidation-reduction equilibria of the heme chromaphore are presented in terms of a thermodynamic model for the control of the observed cytochrome P450 redox potential through this modulation of the spin configuration of the five d-electrons of the ferric heme iron induced by the binding of Type I substrates.
130 citations
TL;DR: In this paper, the adsorption of EDTA on a well-defined hydrosol consisting of rod-like β-FeOOH particles was studied as a function of pH and temperature.
124 citations
109 citations
TL;DR: The results suggested that the ferric enzyme is reduced by the IAA free radical but not by IAA itself, and it was concluded that the catalytic cycle of ferrous and oxyperoxidases is not involved in the I AA oxidase reaction.
96 citations
TL;DR: A theoretical comparison showed that the "strengths" of the ferric chelates can be ranked: EDTA greater than phosphoprotein di-O-phosphorylserine greater than citrate greater than NTA.
Abstract: Estimates of the strength of iron binding to model phosphoproteins were obtained from equilibrium dialysis experiments. Iron-free phosvitin (chicken and frog) or alpha sl-casein (cow) was dialyzed against the iron(III) chelates of nitrilotriacetate (NTA), )ethylenedinitrilo)tetraacetate (EDTA), or citrate. Protein-bound metal was measured at equilibrium; competition of chelator and phosphoprotein for iron(III) was determined by reference to comprehensive equilibrium equations presented in the Appendix. Analysis of the iron-binding data for phosvitin suggested that clusters of di-O-phosphorylserine residues (SerP.SerP) were the most probable iron-binding sites. A stoichiometric equilibrium constant of 10(18.0) was calculated for the formation of the Fe3+(SerP.SerP) chelate. When comared on the basis of phosphate content, casein bound iron more weakly than phosvitin. However, if the stoichiometric equilibrium constant for the formation of the casein Fe3+(SerP.SerP) chelate (10(17.5) was adjusted to account for the fact that a smaller percentage of casein phosphoserines occurs in di-O-phosphorylserine clusters, the affinity of casein and phosvitin for iron was very similar. A theoretical comparison showed that the "strengths" of the ferric chelates can be ranked: EDTA greater than phosphoprotein di-O-phosphorylserine greater than citrate greater than NTA.
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01 Jan 1979
TL;DR: In this article, a hypothesis was proposed to explain clay decomposition and interlayering in acid, seasonally wet soils, under the influence of the periodic reduction and oxidation of iron.
Abstract: A hypothesis was proposed explaining clay decomposition and interlayering in acid, seasonally wet soils, under the influence of the periodic reduction and oxidation of iron. This process, termed ferrolysis, is as follows. In the wet season, reduction of ferric oxides produces dissolved ferrous iron , which displaces and mobilizes exchangeable bases. The bases (and dissolved ferrous iron) are partially removed by leaching. In the dry season, oxidation of exchangeable ferrous iron produces ferric oxides and exchangeable hydrogen leading to partial decomposition of the clay and release of aluminium and silica. Aluminium interlayers with trapped ferrous iron are formed in 2:1 clays by partial neutralization of exchangeable aluminium together with reduction of ferric oxides in the wet season; thus the cation exchange capacity decreases further. The implications of ferrolysis were tested by morphological, chemical and mineralogical analysis of several acid, seasonally wet soils from South-east Asia and different parts of Europe. The effects of various other processes, e.g. cheluviation and clay translocation, were also identified in some of these profiles. Until now, ferrolysis was not clearly distinguished from cheluviation (podzolization sensu stricto), clay translocation and desilication. Therefore, criteria are given to differentiate between the effects of these processes.
TL;DR: A method for simultaneous quantification of the various forms of iron added or endogenous to foods has been developed in this article, where the total, elemental, and soluble iron are determined with minimal pre-treatment by atomic absorption spectrophotometry.
Abstract: A method for the simultaneous quantification of the various forms of iron added or endogenous to foods has been developed. The total, elemental, and soluble iron are determined with minimal pre-treatment by atomic absorption spectrophotometry. The iron valences and complexed iron are measured spectrophotometrically using the bathophenanthroline reagent. The method was both reproducible and accurate in measuring iron added to plant material and to a formulated instant beverage. The procedure may be applied to determination of possible changes in the iron-fortified processed foods.
TL;DR: A series of concentrated ferric chloride solutions, both neutral and acidic, as well as the hydrated melt FeCl3⋅6H2O have been studied by x-ray diffraction as discussed by the authors, and the changes in the radial distribution curves by varying iron concentration or Cl−/Fe3+ ratio and least squares fitting of the structure functions for various solute models lead to an unambiguous conclusion with respect to the dominant species which are present in the solutions.
Abstract: A series of concentrated ferric chloride solutions, both neutral and acidic, as well as the hydrated melt FeCl3⋅6H2O have been studied by x‐ray diffraction. The changes in the radial distribution curves by varying iron concentration or Cl−/Fe3+ ratio and least squares fitting of the structure functions for various solute models lead to an unambiguous conclusion with respect to the dominant species which are present in the solutions. The existence of monochloro, dichloro, trichloro, and tetrachloro complexes, predicted by literature information in dilute solutions, has been established in the different solutions investigated. Octahedral complexes, mainly Fe(H2O)4Cl+2 and Fe(H2O)3Cl3, are the principal species occurring in neutral and acidic solutions while in the hydrated melt tetrahedral FeCl−4 predominates. Species of the type FeCl5(H2O)2− or FeCl3−6 as well as polymeric network are excluded. Hydration water molecules around Cl− anions has been found for both free chloride and chloride ions bonded to iron atoms. Second order interactions around Fe3+ ions are strongly suggested by the presence of a large peak at about 4.2 A in the distribution curves.
TL;DR: In this article, the second order rate constant for the binding of the indoleamine 2,3-dioxygenase was determined to be 1.1 x 10" s-l at 24°C and pH 8.0.
TL;DR: In this article, the thermal decomposition of ferrous sulphate heptahydrate was carried out in air under dynamic and isothermal conditions, and the intermediate phases were identified by chemical analysis and an X-ray technique.
Abstract: The thermal decomposition of ferrous sulphate heptahydrate was carried out in air under dynamic and isothermal conditions. The intermediate phases were identified by chemical analysis and an X-ray technique. Ferrous sulphate heptahydrate is converted to tetrahydrate and monohydrate, but this conversion is accompanied by oxidation. Fe(OH)SO4 and Fe2O(SO4)2 are formed as oxidation products, and the latter decomposes to ferric oxide directly and/or through Fe2(SO4)3.
TL;DR: In this paper, the order of sorption affinities of transition metals for Na-montmorillonite, treated red clay, and hydrated ferric oxide was investigated.
Abstract: Experiments of sorption of Mn, Co, Ni, Cu and Zn on manganese oxides, hydrated ferric oxide, Na-montmorillonite and treated red clay are carried out in connection with the mechanisms by which transition metals are removed from seawater in marine environments. The order of sorption affinities of transition metals for Na-montmorillonite, treated red clay and hydrated ferric oxide is Mn
TL;DR: In this article, an x-ray scattering technique has been used to investigate the structure of iron-sulphate compounds with high concentration in a tetrahedral configuration and octahedral configuration.
Abstract: Ferric sulphate solutions of high concentration have been investigated by an x‐ray scattering technique. The experimental distribution curves show the main peaks at about 1.5, 2.0, 2.4, 2.8, 3.3, and 4.2 A. The presence in solution of sulphate groups in tetrahedral configuration and of hydrated iron complexes in octahedral configuration is in agreement with the peaks found at 1.5, 2.0, and 2.4 A. Water–water interactions from the solvent give the main contributions to the 2.8 A peak. The 3.3 A peak reveals the formation of inner iron–sulphate complexes of average form Fe(H2O)6−n(OSO3)+3−2nn, in which oxygens from sulphate groups substitute n water molecules of the hydrated Fe(H2O)3+6 ions. Least squares refinements of the i (s) curves are consistent with a structural unit in which about one sulphate tetrahedron shares a corner with one iron octahedron with an Fe–O–S angle of 135 deg. The same structural unit found for the iron–sulphate complexes in solution can be identified as the building unit of the crystalline structures of several iron–sulphate solid compounds. The large peak at about 4.2 A in the distribution curves strongly suggests a hydrogen bonded structure outside the inner coordination sphere of Fe3+. The introduction into the model of (H2O)I– (H2O)II interactions between water molecules pertaining to two subsequent hydration shells of Fe3+ resulted in a marked better agreement between experimental and calculated i (s) curves. Some indications have been obtained supporting the presence of hydration water around the sulphate groups.
TL;DR: In this article, photoelectron (XP) spectroscopies were used to identify the XP peaks of iron(II) and (III) fluorides, and a peak shift of 3.0-3.5 eV to higher binding energies was found for all iron orbitals upon oxidation.
Abstract: Iron(II) and (III) fluorides have been studied using X-ray emission (XE) and photoelectron (XP) spectroscopies. XE data enable the XP peaks to be identified unequivocally; in the iron(III) compound the F 2p and Fe 3d orbitals were shown to have almost identical energy. The F Kα XE peak profile showed the Fe–F band to be more covalent in ferric than ferrous fluoride. Whilst the F 1s binding energy was the same for both compounds a peak shift of 3.0–3.5 eV to higher binding energies was found for all iron orbitals upon oxidation. The rapid reduction of iron(III) to iron(II) by argonion bombardment was observed.
TL;DR: Pseudomonas cytochrome c peroxidase contains two hemes, one of which is shown to be in low-spin and one in high-spin state, and the ferrous enzyme binds carbon monoxide in a 1:1 molar ratio, whereas the ferric form is unreactive towards small anionic ligands like F- and CN-.
TL;DR: In this article, a dissociation constant of 10−9.8 ± 0.3 pK units at room temperature (22 ± 3°C) was obtained, in close agreement with reported values at 25°C corrected to zero ionic strength.
TL;DR: In vivo exposure of animals to air containing a few parts per million NO or NO2 gives rise to significant accumulations of both Hb-NO and methemoglobin, the latter being the major product, and the implications of these chemical changes in terms of health effects of NOx and oxidant air pollution are discussed.
TL;DR: In this article, the effect of pH on the nature of the complexes formed between iron and humic acid was investigated and it was shown that at an initial suspension pH greater than 3 the iron occurs in the ferric form, although it is difficult to assess to what extent it is in combination with organic matter.
Abstract: Summary
Mossbauer specttoscopy has been used to provide information on the effect of pH on the nature of the complexes formed between iron and humic acid. At an initial suspension pH greater than 3 the iron occurs in the ferric form, although it is difficult to assess to what extent it is in combination with organic matter. On lowering the pH, iron is reduced with a considerable proportion of the ferrous iron entering solution, partly as a solvated ion and partly as complex forms. Raising the pH leads to re-oxidation and the precipitation of a considerable proportion of the iron in an inorganic form with Mossbauer parameters similar to those of β-FeOOH. No evidence was obtained for Fe(III) in solution or for Fe(II) in any form at pH values greater than 4.
TL;DR: In this article, the uptake of iron by wheat seedlings was investigated using half-strength Hoagland's nutrient solution containing 2.0 μM ferric chloride labelled with59Fe.
Abstract: The uptake of iron by wheat seedlings was investigated using half-strength Hoagland's nutrient solution containing 2.0 μM ferric chloride labelled with59Fe. The iron content of root tissue, which includes adsorbed iron, was depressed by the presence in the solution of the synthetic ligands EDTA and polymaleic acid (PMA) and by the natural ligands, humate, fulvate and a water-extractable soil polycarboxylate. The patterns of change in iron content of the shoots were in all cases different from those of the roots and were of two types. EDTA and humate increased the iron content of the shoots to maximum values, at ligand concentrations of 5.0 μM and 2.5 mg l−1 respectively, and decreased it at higher concentrations. Fulvate, water-extractable soil polycarboxylate and PMA increased the iron content of the shoots up to the maximum ligand concentrations tested (25 mg l−1). These results are discussed in the light of the likely solution chemistry of iron and the various ligands.
TL;DR: Iron uptake by washed suspensions of iron-deficiently grown Mycobacterium smegmatis from 55Fe(III)-exochelin fractions was greatest from the fractions containing the compounds that naturally predominate in culture filtrates, suggesting that the whole complex was being transported.
Abstract: Summary: Exochelins are a group of extracellular iron chelators produced by mycobacteria. Iron uptake by washed suspensions of iron-deficiently grown Mycobacterium smegmatis from 55Fe(III)-exochelin fractions (at about 1 μm) was greatest from the fractions containing the compounds that naturally predominate in culture filtrates. Uptake from the major fraction, as well as from combined exochelins, had a K
m of about 6 μm and was unaffected by the presence of a large excess of desferriexochelin; it was inhibited by more than 90% by electron transport inhibitors, uncouplers of oxidative phosphorylation, thiol reagents and by anaero-biosis and low temperature. Uptake of iron from 55Fe-salicylate, which is mediated by myco-bactin, was insensitive to these inhibitors and a 10-fold excess of ferric salicylate did not inhibit 55Fe-exochelin uptake. Thus mycobactin is probably not involved in the transport of iron from ferriexochelin at physiological concentrations. The rate of uptake of iron from 55Fe-exochelin into iron-sufficiently grown cells, which contain less than 0·05% of the concentration of mycobactin found in iron-deficiently grown cells, was only slightly lower than the rate of uptake into iron-deficiently grown cells.
Uptake of ferri[3H]exochelin, which could only be carried out at high and probably non-physiological concentrations (about 60 μm), was also extremely sensitive to metabolic inhibitors suggesting that the whole complex was being transported. At these high external concentrations of ferriexochelin a second, non-saturable, inhibitor-insensitive iron uptake process occurred. This process was inhibited in iron-deficiently grown cells by ferric salicylate and may therefore involve mycobactin. A similar but not identical second system which was not sensitive to ferric salicylate was found in iron-sufficiently grown cells; this might indicate yet another pathway of iron uptake from ferriexochelin.