Presence Of Ferric Ions Research Articles

Is it oxidative or free radical stress and why does it matter?

Although oxidative stress is generally considered to be caused by reactive oxygen species endowed with electrophilic properties, non-oxidizing free radicals also play a role in numerous degenerative diseases. The most biologically active is hydroxyl radical known to be produced in vivo under hypoxic conditions. In addition, as shown in this paper, hydroxyl radicals can be generated in vitro in the presence of ferric ions without any additional redox agents. This free radical can convert soluble human fibrinogen into an insoluble fibrin-like aggregate. It is argued that this novel phenomenon can explain the in vivo association of iron overload with fibrin-like deposits observed in degenerative diseases. In view of the fact that hydroxyl radials are also formed under the reductive conditions, true antioxidants i.e. reducing substances, may enhance rather than diminish free radical stress. On the other hand, numerous natural substances, such as polyphenols considered to be antioxidants, can reduce free radical stress by virtue of their direct scavenging of hydroxyl radicals and/or chelation of body free iron. In conclusion, it is suggested in this overview to revise the concept of oxidative stress and introduce a more adequate term of free radical stress.

Quantitative assessment of the effect of pyrite inclusions on chalcopyrite electrochemistry under oxidizing conditions

The present paper quantifies the separate and combined effects of pyrite (FeS2) inclusions, dissolved oxygen (0.001mol/L) and ferric ion (0.01–0.05mol/L) on the electrochemical behavior of chalcopyrite (CuFeS2) electrodes by means of potentiometry and linear sweep voltammetry. The experiments were carried out in 0.1mol/L H2SO4 solutions at room temperature (26±1°C). Naturally associated pyrite–chalcopyrite electrodes were selected with the aims to better represent the sulfide association in the ore, thus minimizing the voltage losses across the mineral–mineral contact. The presence of ferric ion and oxygen was shown to increase in approximately 53% the mixed potential of CuFeS2 electrodes; the dissolution current density increased up to 55 times. In the presence of these oxidants and pyrite (42% FeS2 of the electrode surface), the mixed potential was further increased in 14%. For these mixed electrodes, the dissolution current density increased by a factor of approximately 2.6 and 2.2, respectively, in solutions containing 0.001mol O2/L and 0.05molFe3+/L, and by 1.6 times in presence of both oxidants (0.001molO2/L with 0.05molFe3+/L). Therefore, more pronounced effect of pyrite inclusions on chalcopyrite oxidation rate was observed under the lower oxidizing conditions. The effects of the oxidants were described by electrochemical models. The galvanic effect of pyrite on the dissolution of this important sulfide was discussed by the kinetics of the half-cell reactions occurring in the pyrite–chalcopyrite coupling.

Neuroprotective and Cardioprotective Actions of an Association of Pyruvate, Vitamin E and Fatty Acids

Oxidative stress may involve overproduction of hydrogen peroxide which can generate highly cytotoxic hydroxyl radicals in the presence of ferrous ions. This work demonstrates that TCAT (Tricomponent Antioxidant Therapy), an association of pyruvate, vitamin E and fatty acids, provides neuronal and cardiac protection in oxidative stress, ex vivo. Mouse P19 neuron cultures were exposed for 30 min to low millimolar H2O2 concentrations in the absence or presence of Fe2+. Concentrations 1X (10 mmol/L pyruvate, 0.1 U/mL vitamin E and 0.1% fatty acids) and 3X of TCAT, respectively, prevented neuronal death caused by these treatments. Analysis of the contribution of TCAT components to neuroprotection showed that vitamin E and fatty acids enhanced pyruvate action whereas they displayed no neuroprotection by themselves. In contrast, vitamin E and fatty acids were as potent antioxidants as pyruvate in an in vitro cell-free assay, indicating that TCAT protection is modulated by the existence of the cellular membrane barriers. Isolated rat hearts were perfused under electrolysis or subjected to regional ischemia-reperfusion. TCAT 1X prevented the electrolysis-induced decrease in left ventricular pressure, heart rate and coronary flow. At 0.25X concentration, TCAT abolished the incidence of irreversible ventricular fibrillation in ischemia-reperfusion. The results indicate that TCAT could have a broad therapeutic utility in neurological and cardiac injuries associated with oxidative stress. The protective action of TCAT can surpass that of its components, revealing a benefit of the association.

Biodegradable Polyesters and Polyamides From Difunctionalized Lauric and Coconut Fatty Acids

In this work, a major fatty acid from coconut oil was used as starting material in preparing biodegradable polymers. Thus, polyesters and polyamides from varying proportions of monomers, hydroxy- and amino- derivatives of lauric acid were synthesized. Initially, the derivatives were prepared by regioselective chlorination of lauric acid, in the presence of ferrous ions in strong acid medium. Subsequent hydroxylation and amination procedures yielded the hydroxy- and amino- derivatives of lauric acid. These monomers were polymerized in a reaction tube by simple polycondensation method at 220–230 °C for 6–8 h without catalyst. Molecular weight determination using –COOH by end group titration and gel permeation chromatography (GPC) gave an average molar mass of 3,000–5,000 g mol−1 with n = 15–25 monomer units. Thermal properties such as glass transition (Tg) and decomposition (Td) temperatures were obtained using differential scanning calorimetry (DSC). The same processes of synthesis and determinations above were applied to coconut fatty acids, derived from saponification of coconut oil, and resulted to very similar conclusions. A quick biodegradation assay against fungus Aspergillus niger UPCC 4219 showed that the polymers prepared are more biodegradable than conventional plastics such as polypropylene, poly(ethyleneterepthalate) and poly(tetrafluoroethylene) but not as biodegradable as cellulosic (newsprint) paper.

Indirect Electrochemical Oxidation of Chlorophenols in Dilute Aqueous Solutions

The indirect electrochemical oxidation of chlorophenols was studied. The process involved the simultaneous reduction of water to produce protons that were used for the subsequent electrochemical reduction of oxygen to generate hydrogen peroxide. In the presence of ferrous ions, a Fenton’s reagent was produced. In the process, upon reaction with hydrogen peroxide, ferrous ions were converted to the ferric state and were then regenerated at the cathode to recover ferrous ion—an important reactant in Fenton’s reagent. A series of chlorophenols, including 4-mono-, 6-dichloro-, and 4-trichlorophenol, were studied. The degradation of monochlorophenols proceeded in decreasing order: 3-chlorophenol>2-chlorophenol∼4-chlorophenol; for dichloerophenols, the order was: 3, 5-dichlorophenol>3, 4-dichlorophenol>2, 3-dichlorophenol>2, 5-dichlorophenol>2, 4-dichlorophenol>2, 6-dichlorophenol;and for trichloro-phenols, the order followed: 2, 3, 5-trichlorophenol>2, 3, 6-trichlorophenol>2, 4, 5-trichlorophenol>2, 4, 6-trichlorophenol. The results indicated that the number and the relative locations (i.e., ortho, meta, or para) of chlorine substitution on the benzene ring played an important role in determining the rate and extent of chlorophenol oxidation. Regardless of the type of chlorine-substituted phenol, two major reaction pathways were responsible for the intermediate degradation of chlorophenols: hydroxyl radical attack (hydroxylation) and dechlorination. The detailed kinetics of the degradation of chlorophenols was studied in detail using 2-chlorophenol. Formic acid and acetic acid were the major end products that, in combination, contributed to 70% of the residual total organic carbon (TOC). Three other minor intermediates, 2-chloro-hydroquinone (2-Cl-HQ), 2-chloro-catechol (2-Cl-CA), and 4-hydroxyl,2,2’-dichlorodiphenyl ether (HDCDH), were observed; each contributed to a small percentage of the residual TOC.

Oxidation of oat β-glucan in aqueous solutions during processing.

The study investigated carbonyl group formation along the chain and the chain cleavage of cereal β-glucan during heat treatments, high pressure homogenisation, cold storage and ascorbic acid treatment of aqueous solutions of this soluble dietary fibre. The carbonyl group content and its distribution along the chain were simultaneously determined with the chain cleavage using a HPSEC/labelling method, originally developed for water-insoluble cellulose. Ascorbic acid treatment resulted in a relatively high degree of carbonyl content and extensive degradation of β-glucan, even in concentrations typically found in foods. The thermal oxidation of the β-glucan was considerable at 120°C in a β-glucan solution with co-extracted compounds from oat ingredient, and in the highly purified solutions in presence of ferrous ions. Oxidation also probably contributed to the molecular properties during high pressure homogenisation, even thou the main degradation mechanism is the hydrolysis caused by mechanical energy. In addition to the cleavage of the β-glucan chain, the formation of compact, high molar mass species or molecule clusters were obtained in the study after ascorbic acid, heat (120°C) and homogenisation treatments.

Determination of the molar extinction coefficient for the ferric reducing/antioxidant power assay

The FRAP reagent contains 2,4,6-tris(2-pyridyl)- s-triazine, which forms a blue–violet complex ion in the presence of ferrous ions. Although the FRAP (ferric reducing/antioxidant power) assay is popular and has been in use for many years, the correct molar extinction coefficient of this complex ion under FRAP assay conditions has never been published, casting doubt on the validity of previous calibrations. A previously reported value of 19,800 is an underestimate. We determined that the molar extinction coefficient was 21,140. The value of the molar extinction coefficient was also shown to depend on the type of assay and was found to be 22,230 under iron assay conditions, in good agreement with published data. Redox titration indicated that the ferrous sulfate heptahydrate calibrator recommended by Benzie and Strain, the FRAP assay inventors, is prone to efflorescence and, therefore, is unreliable. Ferrous ammonium sulfate hexahydrate in dilute sulfuric acid was a more stable alternative. Few authors publish their calibration data, and this makes comparative analyses impossible. A critical examination of the limited number of examples of calibration data in the published literature reveals only that Benzie and Strain obtained a satisfactory calibration using their method.

Effect of support and second metal in catalytic in-situ generation of hydrogen peroxide by Pd-supported catalysts: application in the removal of organic pollutants by means of the Fenton process

A catalytic system for the generation of H2O2 from formic acid and oxygen at ambient conditions has been developed. Pd-supported catalysts (Pd/C, Pd/TiO2 and Pd/Al2O3) have been tested, showing that for bulk purposes Pd/Al2O3 is more favourable while for in-situ applications Pd/TiO2 seems to be preferable. However, when these catalysts were tested in the in-situ H2O2 generation for the oxidation of phenol by means of the Fenton process (in the presence of ferrous ion), Pd/TiO2 did not demonstrate the expected results, whereas Pd/Al2O3 showed to be an efficient catalyst. Therefore, Pd/Al2O3 is offered as a good catalyst for Fenton's reactions with in-situ generated H2O2. In order to optimize the operating cost of the process, different initial concentrations of formic acid have been tested with Pd/Al2O3, and it has been seen that lowering the initial amount of formic acid favours the efficiency of the process. The effect of the addition of a second metallic (Pt, Au, Fe, Cu) active phase was studied. Concerning H2O2 generation, best results were obtained with a Pd-Au catalyst for bulk production (long time) while for in-situ application Pd-Fe showed interesting results. The Pd-Fe catalyst also performed similarly to the semi-heterogeneous Fenton system involving Pd/Al2O3 and ferrous ion in the degradation of phenol. Therefore, Pd-Fe catalyst offered an interesting prospect for making a full heterogeneous catalyst for Fenton reaction involving in-situ generation of H2O2.

Dissolution of oxidised Co–Cu ores using hydrochloric acid in the presence of ferrous chloride

An investigation of the dissolution of four oxidised Co–Cu ores, from the Democratic Republic of Congo (DRC, ex-Zaire), in hydrochloric acid and FeCl 2 solution was conducted. Cobalt leaching in the absence of FeCl 2 was < 36% but copper leaching was > 70%. Addition of FeCl 2 resulted in the reduction of Co 3+ to soluble Co 2+. The leaching of cobalt was very rapid with only a slow rate of dissolution evident beyond 30 min. The ratio of ferrous ions to cobalt in the ore was important with a > 2:1 ratio required to achieve > 95% Co dissolution. Copper dissolution was also rapid and was not affected by the presence of ferrous ions. Both metals were present in several different minerals, of which only the most abundant, heterogenite and malachite, were detected by XRD.

In vivo NMR study of yeast fermentative metabolism in the presence of ferric irons

Mathematical modelling analysis of experimental data, obtained with in vivo NMR spectroscopy and 13C-labelled substrates, allowed us to describe how the fermentative metabolism in Saccharomyces cerevisiae, taken as eukaryotic cell model, is influenced by stress factors. Experiments on cellular cultures subject to increasing concentrations of ferric ions were conducted in order to study the effect of oxidative stress on the dynamics of the fermentative process. The developed mathematical model was able to simulate the cellular activity, the metabolic yield and the main metabolic fluxes occurring during fermentation and to describe how these are modulated by the presence of ferric ions.

A Sulfur Plugging Experiment in the Presence of Ferric Ion

Acid fracturing is widely used as an effective reconstruction measure in sour gas reservoirs, but sulfur and ferrous sulfide plugging are still problems in reservoir secondary damage. In order to simulate reservoir damage in the presence of ferric ion in residual acid, an artificial core with ferric ion and supersaturated natural sour gas was adopted as a sample. A depletion-type damage experiment was carried out to observe sulfur precipitation and plugging in the core. The results show that core color became dark and weight was increased. Permeability decreased with increased time and the decreasing trend was steep at the beginning and then down to smooth rate slowly. Trace pyrite was discovered using X-diffraction. Severe damage was formed by sulfur deposition in the presence of ferric ion.

Room temperature ferromagnetism in undoped and Fe doped ZnO nanorods: Microwave-assisted synthesis

One-dimensional (1D) undoped and Fe doped ZnO nanorods of average length ∼1 μm and diameter ∼50 nm have been obtained using a microwave-assisted synthesis. The magnetization ( M) and coercivity ( H c) value obtained for undoped ZnO nanorods at room temperature is ∼5×10 −3 emu/g and ∼150 Oe, respectively. The Fe doped ZnO samples show significant changes in M – H loop with increasing doping concentration. Both undoped and Fe doped ZnO nanorods exhibit a Curie transition temperature ( T c) above 390 K. Electron spin resonance and Mössbauer spectra indicate the presence of ferric ions. The origin of ferromagnetism in undoped ZnO nanorods is attributed to localized electron spin moments resulting from surface defects/vacancies, where as in Fe doped samples is explained by F center exchange mechanism.

ChemInform Abstract: Transetherification of Allylic and Benzylic Ethers in the Presence of Ferric Ion.

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Stimulation of proliferation in the colorectal mucosa by gastrin precursors is blocked by desferrioxamine

Precursors of the peptide hormone gastrin stimulate proliferation in the colorectal mucosa and promote the development of colorectal carcinoma. Gastrins bind two ferric ions selectively and with high affinity, and the biological activity of glycine-extended gastrin (Ggly) in vitro is dependent on the presence of ferric ions. The aim of the present study was to determine whether or not iron is required for biological activity of progastrin and Ggly in vivo. Rats that had undergone a colostomy were infused with Ggly, and proliferation was measured in the defunctioned rectal mucosa. Proliferation was also measured in the colonic mucosa of hGAS and MTI-Ggly mice, which, by definition, overexpress progastrin and Ggly, respectively. The requirement for iron was assessed by thrice-weekly injection of the chelating agent desferrioxamine (DFO). The proliferation index in the defunctioned rectal mucosa was significantly increased in the Ggly-infused rats, and the increase was significantly reduced after treatment with DFO. Treatment with DFO significantly reduced the crypt height and proliferation index in the colonic mucosa of hGAS and MTI-Ggly mice but had no effect on the same variables in wild-type mice. These observations are consistent with the hypothesis that the biological activity of progastrin and Ggly in vivo is dependent on the presence of ferric ions and further suggest that chelating agents may block the stimulatory effects of gastrin precursors in the development of colorectal carcinoma.

Adhesion of Acidithiobacillus ferrooxidans to mineral surfaces

Direct contact mechanism in bioleaching implies prior mineral adhesion of Acidithiobacillus ferrooxidans and subsequent enzymatic attack. Prior bacterial adaptation to sulfide mineral substrates influences bacterial ferrous ion oxidation rates. It is highly beneficial to understand major biooxidation mechanisms with reference to solution- and mineral-grown cells in order to optimize bioleaching reactions.For A. ferrooxidans grown in the presence of solid substrates such as sulfur, pyrite and chalcopyrite, bacterial adhesion is required for its enzymatic machinery to come into close contact for mineral dissolution. But when grown in solution substrate such as ferrous ions and thiosulfate, such an adhesion machinery is not required for substrate utilization. Proteinaceous compounds were observed on the surface of sulfur-grown cells. Such an induction of relatively hydrophobic proteins and down regulation of exposed polysaccharides leads to changes in cell surface chemistry. Sulfur-grown and pyrite- and chalcopyrite-grown bacterial cells were found to be more efficient in the bioleaching of chalcopyrite than those grown in the presence of ferrous ions and thiosulfate.

Electrochemically Induced Uptake and Release of Iron by Recombinant Horse H‐Chain Ferritin Covalently Immobilized on 6‐Mercaptohexanoic Acid Modified Gold Electrodes

AbstractFerritin composed entirely of the H‐chain subunit (rHF) was studied to determine whether electrochemical potential alone could induce rHF to take up or release iron. Horse rHF was expressed in E. coli, purified, and covalently immobilized on a self‐assembled monolayer of 6‐mercaptohexanoic acid on gold electrodes. Cyclic voltammetry was used to show that iron was released from rHF following electrochemical reduction, and iron uptake was induced by applying an oxidizing potential to rHF in the presence of ferrous ion.

Controlling the Fenton Reaction in Wine

The fate of hydrogen peroxide in a model wine system was studied under a competitive scenario in the presence of ferrous ions and sulfur dioxide. The metal-catalyzed reduction of hydrogen peroxide (H(2)O(2)), referred to as the Fenton reaction, yields hydroxyl radicals capable of oxidizing ethanol to acetaldehyde and is now thought to be a key step in nonenzymatic wine oxidation. It appears that sulfur dioxide (SO(2)) exerts its protective function in wine by scavenging hydrogen peroxide in oxidizing wine, thereby diverting peroxide from the Fenton route. In this study, the factors affecting the rate and outcome of hydroxyl radical-mediated ethanol oxidation were examined under wine conditions. The exclusion of oxygen in the model wine led to conditions wherein ferric ions (50 microM) were rapidly reduced, presumably by 1-hydroxyethyl radicals. This resulted in the complete stoichiometric conversion of H(2)O(2) (300 microM) to hydroxyl radicals, giving an equimolar concentration of acetaldehyde ( approximately 300 microM). Surprisingly, the yield of acetaldehyde was markedly depressed in the presence of oxygen. The addition of a model phenol, 4-methylcatechol (4-MeC; 12 mM), did not protect the ethanol from hydroxyl radical-mediated oxidation under the conditions tested but rather appeared to slightly increase the rate of the Fenton reaction, perhaps by forming a complex with the added iron. The competition for H(2)O(2) in the presence of Fe(II) ions and SO(2) was also examined, and the effect of added 4-MeC, as well as dissolved oxygen, was investigated. Higher concentrations of 1-hydroxyethyl radicals, which were trapped by N-tert-butyl-alpha-phenylnitrone (PBN) and detected by electron paramagnetic resonance spectroscopy, were observed when oxygen was excluded and when 4-MeC was included.

Effect of hydroxy substituent on the prooxidant action of naphthoquinone compounds

Prooxidant activity of naphthoquinone compounds was analyzed by lipid peroxidation, and the formation of base adduct in DNA. Naphthoquinones with electron-repelling hydroxyl group in the benzene moiety such as juglone and shikonin of lower concentrations stimulated the microsomal lipid peroxidation, but lawsone and lapachol with hydroxyl group in the quinone moiety did not enhance the formation of lipid peroxides. Naphthoquinone-dependent lipid peroxidation was closely related to the enhancement of Fe 2+ autooxidation. Treatment of DNA with juglone a representative of 5-hydroxylated naphthoquinone stimulated the formation of 8-hydroxy-2′-deoxyguanosine, whereas lawsone and lapachol showed negligible formation of DNA base adduct. ESR spectra showed that juglone can form semiquinone radical in the presence of ferrous ion, but lawsone cannot. Biological toxicity of juglone with the potent electron-repelling group at 5-position may be due to the reactive oxygen species formed by semiquinone radical, but naphthoquinone compounds with an electron-repelling group in the quinone moiety, lawsone shows weak toxicity with only a little ability producing reactive oxygen species by the negligible formation of semiquinone.

A Comparison of Pseudomonas Aeruginosa Biofilm Development on ZnSe and TiO2 Using Attenuated Total Reflection Fourier Transform Infrared Spectroscopy

The growth of Pseudomonas aeruginosa PAO1 biofilms on ZnSe internal reflection elements (IREs) was compared with their growth on TiO(2)-coated ZnSe over several days using attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy. The effect of the TiO(2) coating on the IR spectra of reference compounds and cell suspensions was determined to aid in the interpretation of the data. The presence of TiO(2) on the surface of a ZnSe IRE tripled the size of the amide II peak and facilitated the detection of pyoverdin production due to its increased adsorption on the coated surface. A 50% increase in the length of the lag phase was observed for PAO1 growth on TiO(2)-coated surfaces as compared to growth on ZnSe. Biofilms on both surfaces exhibited a growth maximum for all components, followed by restructuring at the surface characterized by a decrease in the signal. The composition of biofilms grown on TiO(2) was relatively constant after the restructuring phase, while the extracellular polymeric substance (EPS) component of the biofilms grown on ZnSe gradually increased. The peak due to the carbohydrate component of EPS was much larger in the spectra of biofilms than in those of planktonic cells. The increase of the pyoverdin signal over time in the spectra of the biofilms on TiO(2) closely followed the overall increase in biomass. However, no signal from pyoverdin was detected in the presence of ferric ions.

Alignment of Polysaccharide–SWNT Composites by Metal–Ligand Interactions

Abstract The composite of terpyridine-modified polysaccharide (TPySPG) and single-walled carbon nanotube (SWNT) afforded sheet-like morphologies in the presence of ferric ion. On the basis of TEM images, it was proposed that the sheet-like morphologies are created by the metal–ligand interaction cross-linking TPySPG/SWNT components.