Showing papers on "Ferric published in 1982"

Perspectives in Iron Metabolism

Abstract: IN early times the earth had a reducing atmosphere, and an abundance of ferrous iron was present for incorporation into biologic molecules.1 Later, with an increase in atmospheric oxygen, iron existed largely in its less available ferric form,2 and special devices had to be developed by life forms for the acquisition of iron. Bacteria, for example, synthesize and excrete high-affinity chelating agents that extract otherwise unavailable iron from the surrounding environment.3 The roots of plants also secrete substances that augment iron absorption.4 In mammalian species a "shuttle" protein in the upper intestine — mucosal transferrin — appears to perform this . . .

Spectral evidence for the mineralogy of high‐albedo soils and dust on Mars

Abstract: Because of the lack of direct mineralogic data available for Mars, spectral remote sensing techniques and, in particular, earth-based reflectance spectroscopy remain the primary source of this information. Presented here are laboratory observations which further constrain the mineralogy and origin of the high-albedo soils and dust. Earth-based observations show the reflectance spectra of classical bright regions to be fairly uniform, with a strong Fe3+ → O2− charge transfer absorption edge extending from the near UV through the visible. This absorption is relatively smooth, unlike those observed for crystalline ferric oxides which have superimposed Fe3+ crystal field bands. Dilution of ferric oxide with a spectrally more neutral medium (montmorillonite) weakens the charge transfer and crystal field absorptions together and does not serve to make the ferric oxide spectrum more Mars-like (smoother). Nontronite (ferric-iron-bearing smectite clay) was also investigated for spectral agreement with telescopic observations. Pure nontronite has Fe3+ absorptions analogous to but different from ferric oxides. As in the previous case, the absorptions are very distinct and inappropriate for Mars. Admixture of neither montmorillonite nor ferric oxide serves to improve the nontronite spectrum. The conclusion is that nontronite is not a major component of martian soils, although the presence of other iron-poor clays cannot be totally excluded based on currently available observational data. The best spectral analogs known for high-albedo soil and dust are a specific type of palagonite from Hawaii: X-ray amorphous weathering products of mafic volcanic glass. The indication is therefore that ferric iron on Mars is likely to occur in poorly defined crystallo-graphic sites such as found in these amorphous materials. These materials form slowly under semiarid conditions at ambient temperature. Even low-temperature hydrothermal alteration of glass might provide enough ion mobility to favor some formation of crystalline clays over amorphous gels and may therefore not be the primary mechanism responsible for soil formation on Mars. The amorphous Hawaiian soils exist metastably for thousands of years on Earth. Similar materials on Mars would be expected to survive considerably longer under the present cold and dry climatic conditions.

Phytic Acid Determination in Soybeans

Abstract: Several established methods of phytic acid determination in soybeans were evaluated. Iron analysis methods, which rely on a 4:6 molar ratio of Fe:P, were eliminated because this ratio was not dependable. Three assay methods relying on phosphorus analysis were then compared. The anion-exchange method was considered most accurate but not convenient for routine analysis. Analysis of the ferric phytate precipitate and a new method, analysis of the supernatant before and after ferric chloride precipitation, were judged against the anion-exchange method under different extraction conditions. Based upon good agreement with anion-exchange column results and acceptable reproducibility, the best methods were (1) precipitate analysis of phosphorus after extraction with 3% TCA + 10% sodium sulfate, or (2) the supernatant difference method after extraction with 1.2% HCl.

A reassessment of podzol formation processes

Abstract: Summary Translocated (oxalate-soluble) Al and Fe are present predominantly in inorganic forms in the B2 horizons of the five pcdzol profiles examined: A1 as imogolite and proto-imogolite allophanes, and Fe as a separate oxide phase. Below the top few cm of the B2 horizon, over 75 per cent of the extractable (acid-plus alkali-soluble) organic matter is present as Al-fulvates, largely sorbed on allophanic material. The Bh horizons of the Iron Humus Podzol and Iron Podzol intergrades are distinguished by very high levels of organically bound Fe (soluble in EDTA solution), five to ten times more than in immediately adjacent A2 or B2 horizons, and also by larger humic acid contents than in comparable B2, levels in typical Iron Podzols. Inorganic forms of translocated Al and Fe are probably absent from two of the three Bh horizons examined, and also from the Bhg horizon overlying the thin iron pan in the Peaty Podzol. The organic matter in this Bhg horizon is saturated with Al rather than Fe. Chemical and physical processes which could lead to evolution of a profile along the genetic sequence, Iron Podzol, Iron Humus Podzol, Peaty Podzol, are postulated. During the formation of an Iron Podzol, positively charged inorganic sols carry aluminium, silicon and iron from the A2 and deposit them in the B2 horizon; subsequently, with the development of an H layer, colloidal humus migrates through the A2 and precipitates on the positive colloids at the top of the B2 horizon to form a Bh horizon, in which remobilized ferric species are trapped by the organic matter. In higher rainfall areas, occasional waterlogging above the oxide-impregnated B2 leads to a thin iron pan, separating permanently oxidizing conditions below from seasonally waterlogged and reducing conditions above.

Spectral characteristics of the iron oxides with application to the Martian bright region mineralogy

Abstract: Reflectance spectra of eight polymorphs of FeOOH and Fe2O3 are determined in order to clarify the nature and significance of the iron oxide mineralogy on Mars. The effect of other components that might interfere with iron oxide absorption features is qualitatively constrained through the use of the Kebulka-Munk theory. It is found that the effect of temperature complicates the identification of a given Fe(3+) phase based on the position of the 6A1-4T1 absorption feature. While the Fe(3+) crystal field transitions are spin forbidden, most of the iron oxide polymorphs exhibit anomalously intense crystal field absorption features due to magnetic coupling between adjacent FeO6 octahedra. It is suggested that the resulting deviations from observed remotely sensed reflectance spectra of Mars may provide a basis for the exclusion of many iron oxide phases as significant components of the Martian Fe(3+) mineralogy. A comparison of these results with the visible region spectra of Martian bright regions indicates that the predominant Fe(3+)-bearing phase may be a magnetically disordered material, such as amorphous gels, some ferric sulphates, and other minerals in which Fe(3+) ions in the crystal structure are not magnetically coupled.

UV‐sensitive complex phosphorus: Association with dissolved humic material and iron in a bog lake1

Abstract: The concentration of uv-sensitive complex phosphorus compounds in water from an acid bog lake was linearly related to the concentration of dissolved high molecular weight humic material (DHM) both seasonally and diurnally. The first-order rate of photoreduction (Fe/sup 3 +/ to Fe/sup 2 +/) of DHM..iron equaled the rate of release of orthophosphate (SRP) from these compounds. The rate of photoreduction of DHM..iron was the same as the rate of photoreduction of ferric citrate under similar conditions. Reduced DHM..iron was auto-oxidizable (Fe/sup 2 +/ to Fe/sup 3 +/); ferrous citrate was not. These data support the view that orthophosphate sorbed to ferric iron..DHM complexes may be released by a mechanism involving uv-induced photoreduction of ferric iron to the ferrous state.

Iron Oxidation and Precipitation of Ferric Hydroxysulfates by Resting Thiobacillus ferrooxidans Cells.

Abstract: The oxidation of ferrous ions, in acid solution, by resting suspensions of Thiobacillus ferrooxidans produced sediments consisting of crystalline jarosites, amorphous ferric hydroxysulfates, or both. These products differed conspicuously in chemical composition and infrared spectra from precipitates formed by abiotic oxidation under similar conditions. The amorphous sediments, produced by bacterial oxidation, exhibited a distinctive fibroporous microstructure when examined by scanning electron microscopy. Infrared spectra indicated outer-sphere coordination of Fe(III) by sulfate ions, as well as inner-sphere coordination by water molecules and bridging hydroxo groups. In the presence of excess sulfate and appropriate monovalent cations, jarosites, instead of amorphous ferric hydroxysulfates, precipitated from bacterially oxidized iron solutions. It is proposed that the jarositic precipitates result from the conversion of outer-sphere (Td) sulfate, present in a soluble polymeric Fe(III) complex, to inner-sphere (C3v) bridging sulfate. The amorphous precipitates result from the further polymerization of hydroxo-linked iron octahedra and charge stabilized aggregation of the resulting iron complexes in solution. This view was supported by observations that bacterially oxidized iron solutions gave rise to either amorphous or jarositic sediments in response to ionic environments imposed after oxidation had been completed and the bacteria had been removed by filtration. Images

Kinetics of biosynthesis of iron-regulated membrane proteins in Escherichia coli.

Abstract: Using biological iron chelators to control specifically iron availability to Escherichia coli K-12 in conjunction with radioactive pulse-labels, we examined the biosynthesis of six iron-regulated membrane proteins. Iron deprivation induced the synthesis of five proteins, which had molecular weights of 83,000 (83K), 81K (Fep), 78K (TonA), 74K (Cir), and 25K. The kinetics of induction were the same in entA and entA + strains, but were affected by the initial iron availability in the media. Iron-poor cells induced rapidly (half-time, 10 min), whereas iron-rich cells began induction after a lag and showed a slower induction half-time (30 min). Within this general pattern of induction after iron deprivation, several different kinetic patterns were apparent. The 83K, 81K, and 74K proteins were coordinately controlled under all of the conditions examined. The 78K and 25K proteins were regulated differently. The synthesis of a previously unrecognized 90K inner membrane protein was inhibited by iron deprivation and stimulated by iron repletion. Both ferrichrome and ferric enterobactin completely repressed 81K and 74K synthesis when the siderophores were supplied at concentrations of 5 μM in vivo (half-time, 2.5 min). At concentrations less than 5 μM, however, both siderophores repressed synthesis only temporarily; the duration of repression was proportional to the amount of ferric siderophore added. The half-lives of the 81K and 74K mRNAs, as measured by rifampin treatment, were 1.2 and 1.6 min, respectively. The results of this study suggest that enteric bacteria are capable of instantaneously detecting and reacting to fluctuations in the extracellular iron concentration and that they store iron during periods of iron repletion for utilization during periods of iron stress. Neither iron storage nor iron regulation of envelope protein synthesis is dependent on the ability of the bacteria to form heme. Images

Transient kinetics of electron transfer reactions of flavodoxin: ionic strength dependence of semiquinone oxidation by cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic acid and computer modeling of reaction complexes.

Abstract: Electron transfer reactions between Clostridum pasteurianum flavodoxin semiquinone and various oxidants [horse heart cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic [horse heart cytochrome c, ferricyanide, and ferric ethylenediaminetetraacetic acid (EDTA)] have been studied as a function of ionic strength by using stopped-flow spectrophotometry. The cytochrome c reaction is complicated by the existence of two cytochrome species which react at different rates and whose relative concentrations are ionic strength dependent. Only the faster of these two reactions is considered here. At low ionic strength, complex formation between cytochrome c and flavodoxin is indicated by a leveling off of the pseudo-first-order rate constant at high cytochrome c concentration. This is not observed for either ferricyanide or ferric EDTA. For cytochrome c, the rate and association constants for complex formation were found to increase with decreasing ionic strength, consistent with negative charges on flavodoxin interacting with the positively charged cytochrome electron transfer site. Both ferricyanide and ferric EDTA are negatively charged oxidants, and the rate data respond to ionic strength changes as would be predicted for reactants of the same charge sign. These results demonstrate that electrostatic interactions involving negatively charged groups are important in orienting flavodoxin with respect to oxidants during electron transfer. We have also carried out computer modeling studies of putative complexes of flavodoxin with cytochrome c and ferricyanide, which relate their structural properties to both the observed kinetic behavior and some more general features of physiological electron transfer processes. The results of this study are consistent with the ionic strength behavior described above.

Formation of monodispersed colloidal cubic haematite particles in ethanol + water solutions

Abstract: Cubic particles of colloidal haematite of narrow size distributions were prepared by aging ferric chloride solutions in water + ethanol mixtures. It was shown that α-Fe2O3 formed by phase transformation from β-FeOOH precipitated first. The kinetics of this conversion were followed at different temperatures, pH and chloride concentrations. The role of alcohol in the studied system is discussed and the rate of growth explained in terms of the theory of Burton, Cabrera and Frank.

Ferric reduction by foots of chlorotic bean plants: Indications for an enzymatic process

Abstract: Reduction of chelated ferric ions by the roots of iron‐stressed bean plants showed kinetics characteristic for reactions catalyzed by matrix‐bound enzymes. Assays for iron reducing compounds in the medium in which those plants had been standing for 1 day failed to yield indications for soluble reductants produced by iron‐stressed plants. The results suggest that the capacity to reduce chelated iron by the roots of iron‐stressed bean plants is due to a mambranebound enzyme in the root cortex.

Active transport of ferric schizokinen in Anabaena sp.

Abstract: The cyanobacterium Anabaena sp. strain ATCC 27898 was found to utilize the siderophore schizokinen to accumulate iron from the environment. This organism had previously been shown to produce schizokinen under low-iron conditions, and we observed that the iron-transport capability is also increased in response to iron limitation. Uptake activity was specific for ferric schizokinen displayed kinetics typical of a protein-mediated process with an apparent Km of 0.04 microM and saturation at high concentrations of substrate. Light-driven transport was blocked by uncouplers and by ATPase inhibitors. Transport in dark-adapted cells was additionally blocked by inhibitors of respiration. We conclude that ATP serves as an energy source for the cellular uptake of ferric schizokinen.

Ferric ion leaching of chalcopyrites from different localities

Abstract: Carefully sized and characterized chalcopyrite concentrates were produced from eleven different geographical localities, and were subsequently leached in both ferric chloride-hydrochloric acid and ferric sulfate-sulfuric acid media. When the leaching rates were corrected for the amount of CuFeS2 in the particular sample, similar leaching rates (±50 pet) were observed for all eleven chalcopyrites under all experimental conditions. Furthermore, all the relatively pure chalcopyrites leached according to the same reaction and yielded >95 pet elemental sulfur as a sulfidic reaction product. In light of the current experimental observations, various reasons are offered for the order of magnitude variations in the chalcopyrite leaching rates often reported in the literature.

Acid‐bacterial and ferric sulfate leaching of pyrite single crystals

Abstract: Pyrite single-crystal cubes were cut, polished. and x-rayed to produce orientations of (100), (110), (111), and (112). These crystallographically developed surfaces then were prepared to expose an area of 1 cm2, and the remainder of the crystal was coated with an acid-resistant silicone cement. Crystals with representative orientations then were leached in ferric sulfate solutions adjusted to a pH of 2.3 with H2SO4 containing up to 6 × 103 ppm of Fe3+ at 30 and 55°C. Leaching was also conducted in acid-bacterial lixiviants containing Thiobacillus ferrooxidans at 30°C and a thermophilic microorganism at 55°C. Surface corrosion and pitting associated with pyrite leaching were examined by scanning electron microscopy. Pyrite leaching in ferric sulfate solutions was observed to be different when compared to acid-bacterial leaching. Ferric sulfate leaching required nearly 2 × 103 ppm of Fe3+ at 30°C while acid-bacterial leaching at 30°C occurred without additions of Fe3+, and values of Fe3+ never exceeded 102 ppm. Because of precipitate formation, an accurate assessment of the role of crystallographic orientation on the leaching of pyrite is difficult.

Properties and proteolysis of ferric enterobactin outer membrane receptor in Escherichia coli K12.

Abstract: A protein with a relative subunit molecular weight of 81000 (81K) has been isolated in virtually pure form from the outer membrane of low iron grown cells of Escherichia coli K12. The 81K protein, which is part of the receptor complex for translocation of the siderophore ferric enterobactin, displays activity in vitro for binding both ferric enterobactin and colicin B. The dissociation constant for the 81K-ferric enterobactin compound at 4 degrees C in 2% Triton-0.1 M Tris, pH 7, was determined to be 10 nM. The N-terminal amino acid was identified as phenylalanine, and the amino acid composition was shown to be similar to that published for the ferric aerobactin-cloacin receptor of Enterobacter cloacae. A plasmid-bearing strain of E. coli was employed to confirm that degradation of 81K to a slightly smaller, inactive form (81K) is performed by a second outer membrane component, protein a. The endoproteolytic action of protein a was verified by the finding of alanine as the N-terminal residue of 81K. A survey of enteric species suggests that the 81K-protein a interaction is confined to the K12 strain of E. coli.

Photochemical reduction of iron. II. Plant related factors

Abstract: Photochemical reduction of ferric iron induced by ultraviolet (UV) and blue radiation is enhanced by certain di‐ and tri‐carboxylic acids. Iron photoreduction proceeds according to the following relative rates in Fe3+‐organic acid solutions containing the major plant acids listed: tartaric >oxalic>citric> malic>aconitic > fumaric ≥succinic≥FeCl3 (control). Any sensitized ferric to ferrous photoreduction occurring in plant foliage exposed to sunlight or artificial light would make iron more available to the tissues for metabolism. Iron is translocated within plants primarily complexed with citric acid (Tiffin, 1972). Citric acid is decarboxylated during Fe‐citrate photoreduction‐oxidation. Ferric iron photoreduction is thus accompanied by citrate degradation. In plant foliage, the fate of ferric citrate taken up the stem depends upon many plant‐related factors. Chelated iron is translocated predominately to actively growing regions where enzymatic reactions largely determine the immediate fate. In...

A Raman study of aqueous solutions of ferric nitrate, ferrous chloride and ferric chloride in the glassy state

Abstract: Raman spectra have been obtained for aqueous solutions of Fe(NO3)3, FeCl2 and FeCl3 in the glassy state where R = moles of water/moles of salt = 10–20. The predominant jonic species in these solutions are [Fe(H2O)6]3+, [Fe(H2O)6]2+ and trans- [Fecl2(H2O)4]+, respectively. The second dominant ferric species in the glassy FeCl3 solution (R = 20) seems to be the [FeCl(H2O)5]2+ ion, which is inferred from comparison of the frequencies of the FeOH2 stretching Raman bands.

Iron-57 ENDOR of the nitrogenase molybdenum-iron protein

Abstract: In order to obtain a more complete characterization of the metal atoms in the EPR-visible center of MoFe, an /sup 75/F ENDOR study was performed and is examined in this report. Despite the complexity of the MoFe cluster, a spectra was obtained from six individual and distinct iron sites. Hyperfine coupling tensor of each were determined. Results show that the FeMo-co cluster must have an extraordiarily complex structure, for no two iron sites have the same characteristics. Since the site inequivalence must have a structural origin, this result will provide a stringent test of any postulated model for the cluster. ENDOR results also give a starting point for discussions of the cluster charge. They also suggest that no more than 3 equiv can be associated with the formally ferric/ferrous iron couple during reduction (or superoxidation) of the molybdenum cofactor of MoFe.