Showing papers on "Ferric published in 1978"

Ferric hydrous oxide sols

Abstract: The methods of preparation of ferric hydrous oxide sots consisting of particles, uniform in shape, of narrow size distribution are described in detail. To produce such sots, acidic solutions, containing ferric ions and nitrate, perchlorate, or chloride ions, respectively, were aged at elevated temperatures for times ranging from a few hours to a few weeks. Solids formed from the solutions containing chloride consisted of either β-FeOOH or α-Fe2O3 depending on the concentration of ferric and chloride ions, whereas particles generated in solutions containing nitrate or perchlorate ions consisted of α-Fe2O3. Particle shape varied greatly as the conditions of colloid preparation were altered. It was possible to produce systems consisting of cubic, ellipsoidal, pyramidal, rodlike, and spherical particles. Such dispersions differed greatly in color. Complete domains are given in terms of ferric salt and corresponding acid concentrations which delineate regions of particle formation of given chemical composition and shape. Electrokinetic measurements show relatively small difference in point of zero charge for the various sots studied.

Interpretation of the Mössbauer spectra of the four-iron ferredoxin from Bacillus stearothermophilus.

Abstract: The Mossbauer spectra of both oxidized and reduced ferredoxin from Bacillus stearothermophilus have been analysed using computer fits to theoretical spectra obtained from a spin Hamiltonian. A consistent set of parameters was obtained from fits to spectra obtained over a wide range of temperature and magnetic field. These results are interpreted in terms of a model for the active centre which is consistent with its electronic and magnetic properties in both redox states. In the model for the oxidized centre all four iron atoms have essentially the same valence, intermediate between ferric and ferrous, with one pair spin-up and the other pair spin-down. On reduction the extra electron goes predominantly to one pair of iron atoms which become ferrous with the other pair remaining substantially unchanged. Using this model it is possible to obtain relationships between the spin Hamiltonian parameters for individual iron atoms and those for the coupled centre. This can give further insight into the relation between the observed electron paramagnetic resonance and Mossbauer spectra.

The kinetics of dissolution of chalcopyrite in ferric ion media

Abstract: The kinetics of dissolution of chalcopyrite (CuFeS2) in ferric chloride-hydrochloric acid and in ferric sulfate-sulfuric acid solutions have been investigated using the rotating disk technique. Over the temperature range 50 to 100‡C, linear kinetics were observed in the chloride media while nonlinear kinetics were noted in the sulfate system. The apparent activation energy in the chloride system was about 11 kcal/mole. The rate increased with increasing ferric chloride concentrations but was insensitive to the concentrations of hydrochloric acid, the ferrous chloride reaction product and “inert≓ magnesium or lithium chlorides. Cupric chloride substantially accelerated the rate. Small amounts of sulfate in an otherwise all chloride system greatly reduce the chalcopyrite leaching rate; still larger amounts of sulfate make the system behave essentially like the slower-reacting ferric sulfate medium.

Siderophore electrochemistry: relation to intracellular iron release mechanism.

Abstract: Previous studies have shown that there is a major difference between the iron release mechanism of enterobactin, a catechol-based siderophore, and that of the hydroxamate-based siderophores such as ferrichrome. For ferric enterobactin there is an esterase that hydrolyzes the ligand during iron release. In contrast, iron is released by the hydroxamate-based siderophores and the ligands are reused in subsequent iron transport. It has been suggested that release of iron by hydroxamates occurs by reduction to the ferrous complex, a process that does not occur for ferric enterobactin. Cyclic voltammograms of ferrichrome A and ferrioxamine B exhibit reversible one-electron waves with pH-independent formal potentials (Ef-vs. the normal hydrogen electrode) -446 and -454 mV, respectively, within the range of physiological reductants. Ferric enterobactin also shows a reversible one-electron wave (at pH greater than 10) with Ef = -986 mV vs. the normal hydrogen electrode. From the pH dependence of this potential we estimate a reduction potential of -750 mV at pH 7. In sharp contrast to the value for the ferric hydroxamates, this value is well below the range of physiological reducing agents. The results demonstrate that the observed hydrolysis of enterobactin is a necessary prerequisite to in vivo release of iron from the siderophore via ferric ion reduction.

Ferric enterobactin transport system in Escherichia coli K-12. Extraction, assay, and specificity of the outer membrane receptor.

Abstract: An outer membrane preparation from cells of Escherichia coli K-12 grown in low iron medium was found to retain ferric enterobactin binding activity following solubilization in a Tris-HCl, Na2EDTA buffer containing Triton X-100. Activity was measured by means of a DEAE-cellulose column which separated free and receptor bound ferric enterobactin. The binding activity was greatly reduced in preparations obtained from cells grown in iron rich media or from cells of a colicin B resistant mutant grown in either high or low iron media. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis enabled correlation of this lack of activity to a single band missing in the outer membrane profile of the colicin B mutant. Evidence was obtained for in vitro competition between ferric enterobactin and colicin B for the extracted receptor. The binding specificity of the extracted receptor was examined by competition between ferric enterobactin and several iron chelates including a carbocyclic analogue of enterobactin, cis-1,5,9-tris(2,3-dihydroxybenzamido)cyclododecane. The ferric form of the latter compound supported growth of siderophore auxotrophs, apparently without hydrolysis to dihydroxybenzoic acid and resynthesis into enterobactin. These data may require revision of the accepted mechanism of enterobactin mediated iron utilization.

Phosphate sorption by reduced and reoxidized rice soils

Abstract: Intact cores of two rice soils of south-eastern Australia were flooded for 146 days to simulate part of a rice-upland crop rotation. The phosphorus sorptivity, and acetate (pH 4.8) and oxalate (pH 3.0) extractable iron levels were monitored for 210 days, before, during and after flooding. The effects of additional organic matter (rice straw) and the growing of rice plants were examined. In non-flooded soils phosphorus sorptivity was mainly influenced by clay content; there were no relationships between extractable iron and phosphorus sorbed. On flooding there were large increases in acetate and oxalate extractable iron and phosphorus sorptivity. Additional organic matter initially increased the rates of formation of extractable iron, and phosphorus sorptivity increased accordingly. However, with prolonged waterlogging, levels of oxalate iron and phosphorus sorptivity reached values dependent on the free iron oxide content of the soils. The growth of rice plants had no significant effects on phosphorus sorptivity or extractable iron at any time of sampling. During oxidation of previously flooded soils, levels of phosphorus sorptivity and oxalate iron decreased rapidly, but did not return to levels occurring before reduction. The results are consistent with domination of phosphorus sorption processes by ferrous hydrous oxides during the flooded (reduced) phase and by poorly crystalline ferric hydrous oxides during the post-flooding reoxidation phase. Agronomic implications of the results are mentioned.

Factors affecting metabolism and ferrous iron oxidation in suspensions and batch cultures of thiobacillus ferrooxidans: relevance to ferric iron leach solution regeneration

Abstract: Ferric iron in acid solution is the essential reagent for the bacterially–assisted solubilization of uranium from ores such as uraninite, and is also significant in the dissolution of metal sulphides The regeneration of ferric iron by bacterial reoxidation of ferrous sulphate is an essential step in the recycling of leach liquors in heap or other percolation leach systems Consequently it is of use to know the factors likely to affect bacterial development and activity The principal factor limiting growth in batch culture of Thiobacillus ferrooxidans on ferrous iron is ferric iron product inhibition of the rate of ferrous iron oxidation Ferric iron inhibits oxidation competitively, lowering substrate saturation coefficient (K s ) without affecting maximum attainable specific growth rate (μ max ) In normal batch culture, μ max was 0143h −1 , minimum observed K S was 36mM ferrous sulphate, μ max and growth yield coefficient was 035g dry wt/g atom iron oxidized Growth rates were exponential, measured as iron oxidation and fixation of labelled carbon dioxide Growth rate was not limited by carbon dioxide concentration, but exhaustion of carbon dioxide in sealed systems caused a switch from exponential to linear iron oxidation, indicating growth–uncoupled oxidation of the residual iron by the static population High potassium concentrations partially relieved ferric iron inhibition With non–growing cell suspensions, oxygen electrode methods indicated multiple K m values for ferrous iron oxidation: 07mM FeSO 4 between 04-43mM; 20-123mM between 100-400mM; and unmeasurably high between 400-700mM Above 07M ferrous sulphate became an inhibitory substrate Increased H + or uranyl sulphate inhibited non-competitively Efficiency of coupling of carbon dioxide fixation to Fe oxidation was decreased at low (25mM) and high (500mM) ferrous sulphate concentrations and was maximal in the 100-300mM range Ferric sulphate did not inhibit carbon dioxide fixation and so affected metabolism and growth only by its effect on ferrous iron oxidation

Coordination chemistry of microbial iron transport compounds: rhodotorulic acid and iron uptake in Rhodotorula pilimanae.

Abstract: The mechanism by which iron uptake is facilitated by the siderophore rhodotorulic acid (RA) in the yeast Rhodotorula pilimanae was investigated with radioactively labeled Fe and RA and kinetically inert, chromic-substituted RA complexes The weight of the evidence supports a model in which RA mediates iron transport to the cell but does not actually transport iron into the cell It is proposed that RA exchanges the ferric ion at the cell surface with a membrane-bound chelating agent that completes the active transport of iron into the cell Uptake of 55Fe in ferric rhodotorulate was much more rapid than uptake of RA itself Two exchange-inert chromic complexes of RA showed no uptake

The Dissolution of Sphalerite in Ferric Chloride Solutions

Abstract: The kinetics of dissolution of both sintered sphalerite disks and untreated sphalerite particles in ferric chloride-hydrochloric acid solutions have been investigated. Over the temperature interval 25 to 100°C, the dissolution occurred according to a linear rate law and with an associated apparent activation energy of about 10 kcal/mole. Most of the oxidized sulfide ion reported as elemental sulfur in the leach residues. The leaching rate was independent of the disk rotation speed and this fact, together with various hydrodynamic calculations, indicated that the reaction was chemically controlled. The dissolution rate increased as the 0.36 power of the ferric chloride concentration and it also increased substantially in the presence of dissolved CuCl2. The accumulation of the ferrous chloride reaction product severely retarded the leaching reaction, but the presence of dissolved zinc chloride only slightly impeded it. The leaching rate was relatively insensitive to low levels of HC1 (>1 M), but increased dramatically at higher acid concentrations because of direct acid attack of the ZnS.

Reduction of ferric iron by L-lactate and DL-glycerol-3-phosphate in membrane preparations from Staphylococcus aureus and interactions with the nitrate reductase system.

Abstract: Membrane fractions with L-lactate dehydrogenase, sn-glycerol-3-phosphate (G3P) dehydrogenase, and nitrate reductase activities were prepared from Staphylococcus aureus wild-type and hem mutant strains. These preparations reduced ferric to ferrous iron with L-lactate or G3P as the source of reductant, using ferrozine to trap the ferrous iron. Reduction of ferric iron was insensitive to 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) with either L-lactate or G3P as reductant, but oxalate and dicumarol inhibited reduction with L-lactate as substrate. The membranes had L-lactate- and G3P-nitrate reductase activities, which were inhibited by azide and by HQNO. Reduction of ferric iron under anaerobic conditions was inhibited by nitrate with preparations from the wild-type strain. This effect of nitrate was abolished by blocking electron transport to the nitrate reductase system with azide or HQNO. Nitrate did not inhibit reduction of ferric iron in heme-depleted membranes from the hem mutant unless hemin was added to restore L-lactate- and G3P-nitrate reductase activity. We conclude that reduced components of the electron transport chain that precede cytochrome b serve as the source of reductant for ferric iron and that these components are oxidized preferentially by a functional nitrate reductase system.

Ultraviolet spectroscopic study of ferric hydroxide complexation

Abstract: Ultraviolet absorbance spectra of ferric ions in 0.68m NaClO4 were studied as a function of pH at 4.0, 14.9, and 25.0°C. The results provided an evaluation of the stability constant for the formation of FeOH2+ which is *β1=[FeOH+][H+]/[Fe3+]. The enthalpy change for the reaction Fe3++H2O⇌ FeOH2++H+ was calculated as 10.0±0.3 kcal-mole−1. Increasing temperature was also found to promote the reaction Fe3++2H2O⇌ Fe(OH)2++2H+. Our results were combined with the results of other to produce an expression describing the first hydrolysis equilibrium at ionic strengths between 0 and 3m and temperatures between 4.0 and 45.0°C at 1 atm total pressure. At 25°C and 0.68m the ionic strength *β1=1.90×10-3

The iron-binding properties of hen ovotransferrin.

Abstract: 1. The distribution of iron between the two iron-binding sites in partially saturated ovotransferrin was studied by labelling with 55Fe and 59Fe and by gel electrophoresis in a urea-containing buffer. 2. When iron is added in the form of chelate complexes at alkaline pH, binding occurs preferentially at the N-terminal binding site. In acid, binding occurs preferentially at the C-terminal site. 3. When simple iron donors (ferric and ferrous salts) are used the metal is distributed at random between the binding sites, as judged by the gel-electrophoresis method. The double-isotope method shows a preference of ferrous salts for the N-terminal site. 4. Quantitative treatment of the results of double-isotope labelling suggests that in the binding of iron to ovotransferrin at alkaline pH co-operative interactions between the sites occur. These interactions are apparently absent in the displacement of copper and in the binding of iron at acid pH.

Ultrastructural localization of nonheme celluar iron with ferrocyanide.

Abstract: The Prussian blue reaction was evaluated at the ultrastructural level as a cytochemical method to identify ferric and ferrous iron in rat bone marrow and splenic macrophages. Satisfactory tissue preservation and staining were achieved after fixation for 1 hr in 3% glutaraldehyde and exposure for 30 min to Perls's ferrocyanide solution before routine osmication and embedding. The acid ferrocyanide solution formed cuboidal and irregular electron-opaque deposits which localized ferric iron in the macrophage siderosomes and hyaloplasm. When thin sections were directly stained with the acid ferrocyanide, the stain deposits were much less distinct. The size and number of cytes exhibited sparse evenly distributed stain deposits. Several cells displayed abundant precipitates on the inner surface of the plasmalemma. Prussian blue precipitates were occasionally seen in mitochondria and nuclear euchromatin. Although osmium tetroxide post-fixation improved tissue preservation, it did not enhance the density of the ferri-ferrocyanide precipitate. The ferrocyanide solution yielded cuboidal deposits also in clots impregnated with ferritin, and electron diffraction analysis confirmed the symmetrical crystal structure of these stain precipitates. Smaller irregular precipitates were formed in clots impregnated with FeCl3, or Fe2 (SO4)3 solutions, despite the equally interpreted as indicating that the iron hydroxide core or protein structure of ferritin and hemosiderin contributed to the formation of the ultrastructurally evident cuboidal precipitates, but were not necessary for the formation of a colored reaction product. The acid ferrocyanide solution failed to stain clots formed in FeCI2, CuCI2 or CuCI solutions. Staining with a ferricyanide solution identified only sparse foci of ferrous iron in some siderosomes. This study demonstrates that the Prussian blue reaction can be used ultrastructurally to localize iron cations bound to some nonheme iron binding proteins.

Resonance Raman studies of hepatic microsomal cytochromes P-450: evidence for strong pi basicity of the fifth ligand in the reduced and carbonyl complex forms.

Abstract: Resonance Raman spectra have been measured for cytochromes P-450 purified from liver microsomes of phenobarbital-treated rabbits (PB P-450 and PB P-448) and of 3-methylcholanthrene-treated rabbits (MC P-448). In the reduced state, all three cytochromes P-450 exhibit Raman spectra of ferrous high-spin type but show the so-called "oxidation state marker" (band IV) at unusually low frequencies, indicating extensive delocalization of electrons from the iron dpi orbital to the porphyrin II (eg) orbital and, consequently, the strong pi basicity of the fifth ligand of the heme iron. The reduced CO complexes of the cytochromes P-450 also exhibit band IV at markedly lower frequencies than CO complexes of hemoglobin and myoglobin. These anomalies observed for the reduced form and CO complex disappear upon conversion of the cytochromes to the catalytically inactive form called cytochrome P-420. Oxidized PB P-450 shows a Raman spectrum which is characteristic of typical ferric low-spin heme compounds, whereas those of PB P-448 and MC P-448 are of the ferric high-spin type. PB P-450 is also clearly distinguishable from the two P-448 preparations in the reduced state. The reduced form of cytochrome P-420, produced by laser illumination, exhibits two sets of Raman lines and, therefore, seems to be a mixture of both high- and low-spin species.

Radiation Chemistry of the Ferrous Sulfate-Benzoic Acid-Xylenol Orange System

Abstract: GUPTA, B. L., BHAT, R. M., GOMATHY, K. R., AND SUSHEELA, B. Radiation Chemistry of the Ferrous Sulfate-Benzoic Acid-Xylenol Orange System. Radiat. Res. 75, 269-277 (1978). In the dosimetric system containing 0.20 mM ferrous ammonium sulfate, 5.0 mM benzoic acid, and 0.20 mM xylenol orange in 0.05 N sulfuric acid (FBX system), benzoic acid increases the G(Fe3+) value and ferric ions form a complex with xylenol orange. This paper presents the investigations carried out regarding the reactions of H202, OH, and H in the FBX system. The OH radicals were generated by the reaction of ferrous ions with H202. In the FBX system, each H202, OH, and H leads to the oxidation of 8, 7, and 11 ferrous ions, respectively. In the absence of xylenol orange, the above values respectively are 12, 11, and 13. The rate constant of the reaction of OH radical with xylenol orange in 0.05 N H2SO4 has been measured by competition kinetics using benzoic acid and its value has been found to be 7.9 X 109 M-' sec-L. In the absence of oxygen there is no radiolytic oxidation of ferrous ions in FBX system.

Investigation of calcium-iron-silicate glasses by the Mössbauer method

Abstract: The oxidation-reduction and coordination of iron atoms in calciumsilicate glasses has been studied as functions of the basic oxide content and partial oxygen pressure on the basis of Mossbauer spectra. It was found that the equilibrium concentration ratio NFe3+/NFe2+ increased as the CaO content or partial oxygen pressure increased. The coordination behavior of iron atoms was complicated. In the glasses containing a large amount of Fe2O3, the Fe2+ ion was always present in the octahedral site, while the Fe3+ ion showed amphoteric behaviour. The ratio in number of tetrahedrally coordinated to octahedrally coordinated ferric ions did not exhibit any remarkable variation for larger partial oxygen pressures (1 and 0.21 atm), but increased slightly with the CaO/SiO2 ratio for the small oxygen pressure (3 × 10−7 atm). In the glasses containing a small amount of Fe2O3, the Fe2+ ion was present in both tetrahedral and octahedral sites. However, the coordination state of the Fe3+ ion was not sufficiently clear in such glasses.