Presence Of Ferric Ions Research Articles

Dissolution of Nickel Ferrite in Aqueous Solutions Containing Oxalic Acid and Ferrous Salts

The dissolution of nickel ferrite in oxalic acid and in ferrous oxalate–oxalic acid aqueous solution was studied. Nickel ferrite was synthesized by thermal decomposition of a mixed tartrate; the particles were shown to be coated with a thin ferric oxide layer. Dissolution takes place in two stages, the first one corresponding to the dissolution of the ferric oxide outer layer and the second one being the dissolution of Ni1.06Fe1.96O4. The kinetics of dissolution during this first stage is typical of ferric oxides: in oxalic acid, both a ligand-assisted and a redox mechanism operates, whereas in the presence of ferrous ions, redox catalysis leads to a faster dissolution. The rate dependence on both oxalic acid and on ferrous ion is described by the Langmuir–Hinshelwood equation; the best fitting corresponds to K1ads=25.6 mol−1 dm−3 and k1max=9.17×10−7 mol m−2 s−1 and K2ads=37.1×103 mol−1 dm−3 and k2max=62.3×10−7 mol m−2 s−1, respectively. In the second stage, Langmuir–Hinshelwood kinetics also describes the dissolution of iron and nickel from nickel ferrite, with K1ads=20.8 mol−1 dm3 and K2ads=1.16×105 mol−1 dm3. For iron, k1max=1.02×10−7 mol of Fe m−2 s−1 and k2max=2.38×10−7 mol of Fe m−2 s−1; for nickel, the rate constants k1max and k2max are 2.4 and 1.79 times smaller, respectively. The factor 1.79 agrees nicely with the stoichiometric ratio, whereas the factor 2.4 implies the accumulation of some nickel in the residual particles. The rate of nickel dissolution in oxalic acid is higher than that in bunsenite by a factor of 8, whereas hematite is more reactive by a factor of 9 (in the absence of Fe(II)) and 27 (in the presence of Fe (II)). It may be concluded that oxalic acid operates to dissolve iron, and the ensuing disruption of the solid framework accelerates the release of nickel.

Transetherification of Allylic and Benzylic Ethers in the Presence of Ferric Ion

Alcoholysis of allylic, secondary and tertiary benzylic ethers is proceeded efficiently in the presence of catalytic amounts of ferric ion as anhydrous FeCl3 and Fe(ClO4)3.

Dissolution of Oxalate Precipitate and Destruction of Oxalate lon by Hydrogen Peroxide in Nitric Acid Solution.

This study aims at developing an oxalate precipitation process, which is applicable to a partitioning of long-lived radionuclides from the high-level radioactive liquid waste. In order to achieve this, a study for decomposition reaction of oxalic acid by hydrogen peroxide was first carried out. The decomposition rates of H2O2 and oxalic acid increased with an increase of nitric acid concentration, and especially those decomposition rates steeply increased at more than 2 M HNO3. Based on this result, the decomposition kinetics of H2O2 and oxalic acid were suggested in this work. Then, the dissolution of oxalate precipitate and the destruction of oxalate ion in the solution were examined. Oxalate precipitates were prepared by adding oxalic acid into a simulated radioactive waste containing 8 metallic elements. The precipitates obtained thereby were dissolved in various nitric acid concentrations and reacted with H2O2 at 90° C. When the oxalates were completely dissolved, most of the oxalates were decomposed by adding H2O2, but in a slurry state the decomposition yield of the oxalate decreased with an increase of the slurry density in the solution. Such phenomenon was considered to be due to a catalytic decomposition of H2O2 on a solid surface of oxalate and the decomposition mechanism was explained by a charge transfer from a surface of oxalate solid to H2O2, producing OH radicals which can destruct H2O2 explosively. Accordingly, the experimental condition for the decomposition of the oxalate precipitates was found to be most favorable at 3 M HNO3 under the initial concentrations of 0.2 M oxalate and 1M H2O2. At 3 M HNO3, oxalate precipitates could be safely and completely dissolved, and almost decomposed. Additionally, it was observed that the presence of ferric ion in the solution largely affects the decomposition rate of H2O2. This could be explained by a chain reaction of hydrogen peroxide with ferric ion in the solution.

Preparation of O-acylated low-molecular-weight carrageenans with potent anti-HIV activity and low anticoagulant effect

Depolymerization of λ- and κ-carrageenan was performed using ultrasonication at room temperature in the presence of ferrous ions, ascorbic acid and ethylenediaminetetraacetic acid. Tetrabutylammonium (TBA) salts of each depolymerized carrageenan were dissolved in N, N-dimethylformamide (DMF) and acylated by carboxylic acid anhydride at room temperature in the presence of dimethylaminopyridine and tributylamine as catalysts. The TBA salts of acylated carrageenans were dissolved in DMF and sulfated by pyridine–sulfur trioxide. The anti-HIV activities of each preparation were determined in a system in which MT-4 cells were infected with HTLV-III B. Sulfated samples prepared from low butanoylated or low hexanoylated derivatives had higher anti-HIV activities than dextran sulfate used as reference. Anticoagulant activity of these preparations was determined from the measurement of activated partial thromboplastin time (APTT). The butanoylated derivatives of λ-carrageenan with a degree of substitution of 1.1–1.5 had anticoagulant activities of 6.7–8.5 unit/mg, which were distinctly lower than that of dextran sulfate (avg. mol. wt. 0.7×10 4), 23.4 unit/mg. This result indicated clearly the decreasing effect of the substituted acyl group on anticoagulant activity. Hemolytic activity of these preparations was negligible.

New reaction pathways of dopamine under oxidative stress conditions: nonenzymatic iron-assisted conversion to norepinephrine and the neurotoxins 6-hydroxydopamine and 6, 7-dihydroxytetrahydroisoquinoline.

Aerial oxidation of dopamine at concentrations as low as 50 microM in the presence of ferrous ions in phosphate buffer (pH 7.4) led in the early stages (6-8 h) to the formation of the quinone of the neurotoxin 6-hydroxydopamine, 2, followed (24 h) by a complex product pattern comprising main components norepinephrine (5), 3, 4-dihydroxybenzaldehyde (4), and the neurotoxic alkaloid 6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (3). Product formation required the assistance of metal ions such as Mn(II), Zn(II), and iron, in either the ferrous or ferric form. Product yields were shown to vary linearly with iron and dopamine concentration in the early phases of the reaction (2 h). Biologically relevant antioxidants, like glutathione and ascorbate, and metal chelators, e. g., 2,2'-bipyridyl, inhibited dopamine conversion to products 2-5, but not substrate consumption, while hydroxyl radical scavengers such as DMSO and mannitol did not alter the course of the reaction. On the contrary, mannitol increased product yields, an effect seen for other monosaccharides. Catalase exhibited a significant inhibitory effect particularly on the formation of 3 and 4. By using (18)O(2), evidence was obtained for incorporation of the label into the carbonyl oxygen of 4, but not into the hydroxyl group of 5. On the basis of these and other results, a complete mechanistic picture of the oxidation is drawn involving conversion of dopamine to the corresponding o-quinone and its quinonemethide tautomer with concomitant reduction of O(2) to H(2)O(2). Nucleophilic attack by H(2)O to the quinonemethide gives rise to 5, while H(2)O(2) addition leads to benzaldehyde 4 via a beta-aminohydroperoxide intermediate. This latter reaction path also gives formaldehyde which yields the isoquinoline 3 by Pictet-Spengler condensation with dopamine. The quinone 2 results from H(2)O(2) attack at the 6-position of dopamine o-quinone in agreement with previous studies. These results provide an insight into new routes of nonenzymatic conversion of dopamine to its metabolite norepinephrine and neurotoxic species which may become operative under conditions relevant to neurodegeneration.

Inactivation of deacetoxycephalosporin C synthase in extracts of Streptomyces clavuligerus during bioconversion of penicillin G to deacetoxycephalosporin G

By using cell-free extracts of Streptomyces clavuligerus containing deacetoxycephalosporin C synthase, we can convert penicillin G into deacetoxycephalosporin G. The degree of bioconversion was low (below 1% based on charged substrate) and decreased as substrate concentration was increased. Formation of product occurred during the first 2 h and then ceased. Addition of increasing levels of cofactors and/or substrate at the 2-h point did not result in more product. Preincubation of the crude extracts in the presence of ferrous ions plus either ascorbate or α-ketoglutarate led to complete loss of activity. Such inactivation could not be reversed by catalase, superoxide dismutase, mannitol, thiourea, dimethylsulfoxide, dithiothreitol, or β-mercaptoethanol.

Accumulation of aluminium in the cell wall pectin in cultured tobacco (Nicotiana tabacum L.) cells treated with a combination of aluminium and iron

ABSTRACTIn nutrient medium, aluminium (Al) accumulation in tobacco cells occurs only in the presence of ferrous ion [Fe(II)]. The localization of Al was examined to elucidate a mechanism of Al accumulation. After the digestion of Al‐treated cells with cellulase and pectolyase together, the resulting spheroplasts contained as much Al as the intact cells. However, the cell walls isolated from Al‐treated cells also contained as much Al as the intact cells. Comparison of sugar and Al contents in polysaccharide components extracted chemically from cell walls isolated from intact cells and spheroplasts revealed that the enzymes digested most of the cellulose and hemicellulose, but only half of the pectin, and that Al mainly existed in the pectin remaining in the spheroplasts. Gel‐permeation chromatography of the pectin fraction (NH4‐oxalate extract) from the cell walls of the intact cells indicated that Al was associated with small polysaccharides of approximately 3–7 kDa. These results suggest that a minor part of pectin is a major site of Al accumulation. The content of cell wall pectin increased during Al treatment in nutrient medium. Taken together, we hypothesize that Al may bind to the pectin newly produced during Al treatment.

Simultaneous removal of cod and color from dye manufacturing process wastewater using Photo‐Fenton oxidation process

The removal of COD and color present in dye manufacturing process wastewater were studied using the photo‐Fenton oxidation process. Emphasis of this study was placed on the effects of UV light intensity, ferrous and peroxide dosages, and the pH value on the process performance. Around 76% and 93% removals of COD and color can be achieved, respectively, under the experimental conditions of this study. Applying relatively higher UV power was found to accelerate the removals remarkably, and the enhanced effect becomes more and more significant as reaction carries on. The presence of ferrous ions enhanced the removal rate greatly during the initial reaction period, and after a certain time point the removal profiles became leveling off due to the lack of H2O2 residue in the reaction mixture. An excess of H2O2 does not necessarily result in relatively higher removals of COD and color. As for the pH effect, the values of pH = 3 and 4 were found optimum for the removals of COD and color, respectively. According to this study, the photo‐Fenton process can be considered as a promising technology for the treatment of dye manufacturing process wastewater.

Oxidative stress induces amyloid-like aggregate formation of NACP/alpha-synuclein in vitro.

The precursor of non-amyloid beta protein component of Alzheimer's disease amyloid (NACP/alpha-synuclein), found in Lewy bodies of Parkinson's disease (PD), is a presynaptic protein genetically linked to some familial types PD. Mechanisms of abnormal NACP/alpha-synuclein aggregation in neurodegenerative diseases are unclear. Since oxidative stress might play a role in PD pathogenesis, we investigated the role of iron and peroxide in NACP/alpha-synuclein aggregation. Immunoblot analysis showed that human NACP/alpha-synuclein (but not beta-synuclein) aggregated in the presence of ferric ion and was inhibited by the iron chelator deferoxamine. Ferrous ion was not effective by itself, but it potentially aggregated NACP/alpha-synuclein in the presence of hydrogen peroxide. NACP/ alpha-synuclein aggregates displayed strong thioflavine-S and congo-red reactivity, reminiscent of amyloid. This study suggests that NACP/alpha-synuclein aggregation might be closely related to oxidative reactions which may play a critical role in neurodegeneration in disorders with Lewy bodies.

Direct evidence for anthocyanidin synthase as a 2-oxoglutarate-dependent oxygenase: molecular cloning and functional expression of cDNA from a red forma of Perilla frutescens.

Anthocyanidin synthase (ANS), an enzyme of the biosynthetic pathway to anthocyanin, has been postulated to catalyze the reaction(s) from the colorless leucoanthocyanidins to the colored anthocyanidins. Although cDNAs have been isolated that encode putative ANS, which exhibits significant similarities in amino acid sequence with members of a family of 2-oxoglutarate-dependent oxygenases, no biochemical evidence has been presented which identifies the actual reaction that is catalyzed by ANS. Here we show that anthocyanidins are formed in vitro through 2-oxoglutarate-dependent oxidation of leucoanthocyanidins catalyzed by the recombinant ANS and subsequent acid treatment. A cDNA encoding ANS was isolated from red and green formas of Perilla frutescens by differential display of mRNA. Recombinant ANS tagged with maltose-binding-protein (MBP) was purified, and the formation of anthocyanidins from leucoanthocyanidins was detected by the ANS-catalyzed reaction in the presence of ferrous ion, 2-oxoglutarate and ascorbate, being followed by acidification with HCI. Equimolar stoichiometry was confirmed for anthocyanidin formation and liberation of CO2 from 2-oxoglutarate. The presumptive two-copy gene of ANS was expressed in leaves and stems of the red forma of P. frutescens but not in the green forma plant. This corresponds to the accumulation pattern of anthocyanin. The mechanism of the reaction catalyzed by ANS is discussed in relation to the molecular evolution of a family of 2-oxoglutarate-dependent oxygenases.

The role of ( E)-4-hydroxy-2-nonenal in platelet activation by low density lipoprotein and iron

( E)-4-Hydroxy-2-nonenal (HNE) is a highly reactive product of the oxidation of low density lipoprotein (LDL) which increases the platelet aggregation response to various agonists. HNE formation was increased during the enhanced platelet aggregation to thrombin, ADP, A23187 and epinephrine in the presence of LDL. The increase in platelet aggregation and HNE formation by LDL was inhibited by superoxide dismutase and catalase, suggesting superoxide and hydrogen peroxide produced by platelets during aggregation may be at least partly responsible. The responsiveness of platelets to LDL and the accompanying HNE formation was increased further in the presence of ferrous ion. The effect of ferrous ion on both platelet responses and HNE formation was decreased by superoxide dismutase, catalase and the antioxidants dipyridamole and probucol implicating platelet-derived free radicals. Ferrous ion caused an increase in the release of arachidonic acid from platelet membrane phospholipids in the presence of LDL which was probably caused by increased HNE production. The results suggest iron could increase platelet reactivity at sites of vascular injury by increasing HNE formation and promote the development of atherosclerotic lesions.

Reduction of 13-hydroperoxy-9,11-octadecadienoic acid by dopamine-melanin.

The effect of dopamine-melanin (DA-melanin), synthetic model of neuromelanin, on the stability of 13-hydroperoxyoctadecadienoic acid (13-HPODE) has been investigated using a reverse-phase high-performance liquid chromatography (HPLC) with UV detection. It was found that DA-melanin effectively accelerated the decomposition of 13-HPODE, both in the absence and in the presence of ferrous ions. The disappearance of 13-HPODE was accompanied by the formation of 13-hydroxyoctadecadienoic acid (13-HODE). The results obtained indicate that DA-melanin is able to reduce linoleic acid hydroperoxide to its stable hydroxyl derivative. The fatty acid hydroperoxide-reducing ability of DA-melanin appears to play an important role in the antioxidative activity of neuromelanin in the process of lipid peroxidation.

Sequence specificity of DNA cleavage by bisnetropsin-linked hydroxamic acid-metal complexes: highly specific cleavage by ferrous complexes.

Bisnetropsin-linked hydroxamic acids (BNHA) were shown to cleave DNA stands at a single residue with a preferred binding orientation in the presence of ferrous ion. In contrast, the corresponding cerium (III) complexes cleaved DNA with low sequence specificity.

Hydroxyl radical formation in chondrocytes and cartilage as detected by electron paramagnetic resonance spectroscopy using spin trapping reagents

Chondrocytes have been shown to produce superoxide and hydrogen peroxide, suggesting possible formation of hydroxyl radical in these cells. In this study, we used electron spin resonance/spin trapping technique to detect hydroxyl radicals in chondrocytes. We found that hydroxyl radicals could be detected as α-hydroxyethyl spin trapped adduct of 4-pyridyl 1-oxide N-tert-butylnitrone (4-POBN) in chondrocytes stimulated with phorbol 12-myristate 13-acetate in the presence of ferrous ion. The formation of hydroxyl radical appears to be mediated by the transition metal-catalyzed Haber-Weiss reaction since no hydroxyl radical was detected in the absence of exogenous iron. The hydroxyl radical formation was inhibited by catalase but not by superoxide dismutase, suggesting that the hydrogen peroxide is the precursor. Cytokines, IL-1 and TNF enhanced the hydroxyl radical formation in phorbol 12-myristate 13-acetate treated chondrocytes. Interestingly, hydroxyl radical could be detected in unstimulated fresh human and rabbit cartilage tissue pieces in the presence of iron. These results suggest that the formation of hydroxyl radical in cartilage could play a role in cartilage matrix degradation.

Antiviral effects of ascorbic and dehydroascorbic acids in vitro

In the present study, ascorbic acid weakly inhibited the multiplication of viruses of three different families: herpes simplex virus type 1 (HSV-1), influenza virus type A and poliovirus type 1. Dehydroascorbic acid, an oxidized form of ascorbic acid and hence without reducing ability, showed much stronger antiviral activity than ascorbic acid, indicating that the antiviral activity of ascorbic acid is due to factors other than an antioxidant mechanism. Moreover, addition of 1 mM Fe3+, which oxidizes ascorbic acid to dehydroascorbic acid and also enhances the formation of hydroxyl radicals by ascorbic acid in the culture media, strongly enhanced the antiviral activity of ascorbic acid to a level significantly stronger than that of dehydroascorbic acid. Although both ascorbic acid and dehydroascorbic acid showed some cytotoxicity, the degree of cytotoxicity of the former was 10-fold higher than the latter, suggesting that the observed antiviral activity of ascorbic acid with and without ferric ion is, at least in part, a secondary result of the cytotoxic effect of the reagent, most likely due to the free radicals. However, the possibility that oxidation of ascorbic acid also contributed to the antiviral effects of ascorbic acid exists, in particular in the presence of ferric ion, since dehydroascorbic acid exhibited a very strong antiviral activity. Characterization of the mode of antiviral action of dehydroascorbic acid revealed that the addition of the reagent even at 11 h post infection almost completely inhibited the formation of progeny infectious virus in the infected cells, indicating that the reagent inhibits HSV-1 multiplication probably at the assembly process of progeny virus particles after the completion of viral DNA replication.

Antioxidant Properties of Catechins and Green Tea Extracts in Model Food Emulsions

Extraction of green tea with hot water provided an extract that was highly effective as an antioxidant for an oil-in-water emulsion at pH 5.5 during prolonged storage (40 days). Other components besides epigallocatechin gallate (EGCG) and epicatechin gallate (ECG) made important contributions to the antioxidant activity of the extract in an oil-in-water emulsion, since ECG, when pure, had no significant antioxidant activity (p > 0.05) and EGCG was completely oxidized within 15 days. Myricetin had a greater antioxidant effect in this system than EGCG or ECG at a concentration of 10-4 M in the absence of ferric ions, but all three flavonoids exhibited prooxidant effects in the presence of ferric ions. Keywords: Antioxidants; epigallocatechin gallate; epicatechin gallate; green tea; emulsions

Iron-mediated generation of the neurotoxin 6-hydroxydopamine quinone by reaction of fatty acid hydroperoxides with dopamine: a possible contributory mechanism for neuronal degeneration in Parkinson's disease.

Exposure of dopamine to an excess of linoleic acid 13-hydroperoxide (13-hydroperoxyoctadecadienoic acid) in the presence of ferrous ions in Tris buffer, pH 7.4, resulted in a relatively fast, oxygen-independent reaction exhibiting first-order kinetics with respect to both catecholamine and metal concentrations. Product analysis in the early stages revealed the presence of significant amounts of the quinone of the neurotoxin 6-hydroxydopamine, together with some aminochrome and ill-defined melanin-like material. Quinone formation required the presence of iron, either in the ferrous or ferric form, and was unaffected by peroxidase, catalase, and hydroxyl radical scavengers, e.g. mannitol, as well as biologically relevant antioxidants, like ascorbate and glutathione. Hydrogen peroxide proved as effective as linoleic acid hydroperoxide in inducing dopamine oxidation and conversion to 6-hydroxydopamine quinone. Metal chelators, including EDTA and bipyridyl, markedly suppressed quinone formation without, however, inhibiting dopamine oxidation. These and other results are consistent with a hydroxyl radical independent hydroxylation/oxidation mechanism basically different from the Fenton reaction, which involves direct interaction of the peroxide with a dopamine-Fe(III) chelate generated during the process.

Homogeneous oxidation of phenols in aqueous solution with hydrogen peroxide and ferric ions

The chemical oxidation of phenol and chlorophenols with hydrogen peroxide in the presence of soluble iron can be economically attractive at low oxidant consumption, leading then to intermediates that are more easily biodegradable. The homogeneous oxidation of phenol and chlorophenols in aqueous solutions with hydrogen peroxide is studied at oxidant : phenol ratio of about 4:1 and 16:1 (mol/mol) at various catalyst concentrations, at ambient temperature without pH control. Ferric chloride, ferric and ferrous sulphate and ferrous ammonium sulphate are used as oxidation catalysts. Ferric salts induce higher oxidation rates than ferrous ones and the nature of the anions present does not affect reaction rate. 4-Chlorophenol is found to be most resistant to oxidation and 2,4,6-Trichlorophenol is not attacked by hydrogen peroxide in the presence of ferric ions at the experimental conditions studied.

Preparation and anti-HIV activity of low-molecular-weight carrageenans and their sulfated derivatives

Lambda-, kappa-, and iota-carrageenan were depolymerized in the presence of ferrous ions or ferrous ions plus ascorbic acid at room temperature. Tetrabutyl-ammonium salts of lambda-, kappa- and iota-carrageenan were dissolved in N,N-dimethylformamide and sulfated by the addition of pyridine-sulfur trioxide in N,N-dimethylformamide. Then, the sulfated carrageenans were depolymerized by the incubation with ferrous ions and ascorbic acid. The anti-HIV activities of the various preparations were determined in a system in which MT-4 cells were infected with HTLV-IIIB. The activity of lambda-carrageenan was similar to that of dextran sulfate and the depolymerized lambda-carrageenan retained high activity. The activities of kappa- and iota-carrageenan and their depolymerized forms were about 6% of that of lambda-carrageenan. The sulfation of kappa-and iota-carrageenan increased the activities of these compounds to the same level as that of lambda-carrageenan. However, the sulfation of lambda-carrageenan did not affect its activity. Depolymerized sulfated kappa- and iota-carrageenan with mean molecular weights of 50,000 (81,000-46,000) had higher anti-HIV activity than dextran sulfate and all other preparations of carrageenan tested.

Electrochemical Impedance Spectroscopy Study of Nickel‐Iron Deposition: I. Experimental Results

Results of an electrochemical impedance spectroscopy study of nickel‐iron codeposition are presented. Impedance spectra are influenced in a complicated manner by the applied current density, rotation speed, and concentration of ferrous ions. Spectra are particularly sensitive to current density and ferrous‐ion concentration. As a basis for comparison, an experimental and theoretical study of nickel deposition from an iron‐free bath is presented. It is found that it is the inductive loop of the impedance spectra that changes most dramatically in the presence of ferrous ions.