Presence Of Ferric Ions Research Articles

Thermodynamics and kinetics of the cleavage of DNA catalyzed by bleomycin A5.

Microcalorimetry and UV-vis spectroscopy were used to conduct thermodynamic and kinetic investigations of the scission of calf thymus DNA catalyzed by bleomycin A5 (BLM-A5) in the presence of ferrous ion and oxygen. The molar reaction enthalpy for the cleavage, the Michaelis-Menten constant for calf thymus DNA and the turnover number of BLM-A5 were calculated by a novel thermokinetic method for an enzyme-catalyzed reaction to be -577 +/- 19 kJ.mol-1, 20.4 +/- 3.8 microm and 2.28 +/- 0.49 x 10-2 s-1, respectively, at 37.0 degrees C. This DNA cleavage was a largely exothermic reaction. The catalytic efficiency of BLM-A5 is of the same order of magnitude as that of lysozyme but several orders of magnitude lower than those of TaqI restriction endonuclease, NaeI endonuclease and BamHI endonuclease. By comparing the molar enthalpy change for the cleavage of calf thymus DNA induced by BLM-A5 with those for the scission of calf thymus DNA mediated by adriamycin and by (1,10-phenanthroline)-copper, it was found that BLM-A5 possessed the highest DNA cleavage efficiency among these DNA-damaging agents. These results suggest that BLM-A5 is not as efficient as a DNA-cleaving enzyme although the cleavage of DNA by BLM-A5 follows Michaelis-Menten kinetics. Binding of BLM-A5 to calf thymus DNA is driven by a favorable entropy increase with a less favorable enthalpy decrease, in line with a partial intercalation mode involved in BLM-catalyzed breakage of DNA.

Synthesis of polyquinoline ether and its optical sensor property in the presence of metal cations

AbstractSemirigid polyquinoline with a flexible ether linkage was prepared via Friedländer quinoline synthesis, of which monomer was obtained through a five‐step synthesis. We investigated the polymer as a fluorescent sensor toward ferric ion that used a quinoline unit as a fluoroionophore group. The polymer solution in dimethylformamide/tetrahydrofuran showed the hyperchromic shift of the absorption maximum upon addition of metal ions exhibiting that the effect was clearly manifested upon exposure to ferric ion. A fluorescence quenching was observed in the presence of ferric ion corresponding to an interaction of the ferric cation to the polyquinoline ether, which results in a photoinduced electron‐transfer quenching pathway showing a Stern–Volmer constant (KSV) of 7.17 × 103 (M−1). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1831–1837, 2002

Toxicity of hexavalent chromium to Daphnia magna: influence of reduction reaction by ferrous iron

The reaction kinetics of hexavalent chromium with ferrous ions were studied to determine the influence of reduction on the toxicity of chromium to aquatic organisms. The changes in chemical forms of the chromate in the presence of ferrous ions were examined in a bioassay system using Daphnia magna as a test organism. This study demonstrated that the reaction kinetics of chromate with ferrous ions showed a significant decrease of chromate concentration with the second-order rate coefficient ( k) for the reduction of Cr(VI) being determined as 55.2 M −1 s −1. The concentration of Cr(VI) remaining in the solution decreased as the ratio of ferrous ion to chromate increased, revealing a non-stoichiometric reaction due to oxygenation and the moderately alkaline pH of the solutions. The toxicity test indicated that the bioavailability of chromate to D. magna was reduced in the presence of Fe(II) and that it decreased further with increasing Fe(II) concentrations. However, the toxic effect of chromate to aquatic organisms was not controlled kinetically in the presence of ferrous ions. It was also found that LC 50 of chromate to D. magna decreased about 1.5-fold as the test period increased from 24 to 48 h in the presence of Fe(II).

Bleomycin A5 is analogous in mechanism to a DNA-cleaving enzyme: a microcalorimetric study

Microcalorimetry, UV–VIS spectroscopy and HPLC were used to conduct thermodynamic and kinetic investigations of the scission of calf thymus DNA catalyzed by bleomycin A5 (BLM-A5) in the presence of ferrous ion and oxygen. The molar reaction enthalpy for the cleavage, the Michaelis constant for calf thymus DNA and the turnover number of BLM-A5 were calculated by a novel thermokinetic method for enzyme-catalyzed reactions to be −577±19kJmol−1, (2.04±0.38)×10−5moldm−3 and (2.28±0.49)×10−2s−1, respectively, at 37.00°C. This DNA cleavage was a fast and exothermic reaction. The catalytic efficiencies of BLM-A5 and of some DNA-cleaving enzymes, such as TaqI restriction endonuclease and NaeI endonuclease, are of the same order of magnitude. By comparing the molar enthalpy change for the cleavage of calf thymus DNA induced by BLM-A5 with those for the scission of calf thymus DNA mediated by adriamycin and by (1,10-phenanthroline)-copper, it was found that BLM-A5 possessed the highest DNA cleavage efficiency among these DNA-damaging agents. The UV–VIS spectral experiments showed that BLM-A5 itself remained unchanged chemically after the cleavage. The products of this scission, including four kinds of free nucleic acid bases, were separated and detected by HPLC. These results strongly suggest that BLM-A5 is analogous in mechanism to a DNA-cleaving enzyme, although it is much smaller than such type of enzymes. A possible mechanism for the cleavage of DNA catalyzed by BLM was suggested in this paper.

Anaerobic Reduction of a Sulfonated Azo Dye, Congo Red, by Sulfate-Reducing Bacteria

The capacity for anaerobic decolorization of a sulfonated azo dye, Congo Red, by a strain of a sulfate-reducing bacterium was evaluated. After optimizing the growth rate of the bacteria on a simple carbon source and terminal electron acceptor pair, lactate and sulfate, respectively, the effect of the dye concentration on their growth rate was analyzed. The decolorization rate was affected by the dye concentration in the growth medium. The azo-bond cleavage mechanism of reductive decolorization with the formation of benzidine was consistent with the results, as this metabolite was identified by high-performance liquid chromatography. Several fractions of the culture medium, including lysed cell extracts, were examined for the capacity to reduce the azo dye. This reduction capacity was found in the culture medium in which the cells had previously grown. The results showed that the mechanism of reductive decolorization of this sulfonated azo dye was extracellular and nonenzymatic, consistent with the production of sulfide anion by the microorganisms while growing on lactate and sulfate. The sulfide anions were the cause of the reduction leading to the disappearance of color in the medium. To increase the rate of decolorization, the presence of ferrous ion was also necessary together with the lactate and sulfate substrates.

Acid Refining of Synthesised Alloys Within the Quaternary System Fe–Si–Ca–AI: Effect of Ferric Ions

A systematic study of synthesis of different chemical composition of alloys within the quaternary Fe–Si–Ca–Al system, versus acid leaching refining using HCl with or without FeCl3 has been undertaken. Such study has the aim of achieving an adequate structural composition of Fe–Si alloys, in order to obtain high purity and fine particle size silicon by acid leaching, at more reduced costs. The experimental results show that an adequate control of Fe/Al and Si/Ca concentration ratios can hinder the formation of tetragonal and orthorhombic FeSi2 phases, and consequently promotes a successful refining of ferro-silicon alloys. The presence of ferric ion influences on a distinct way the rate of removal of Al–Fe–Si and Fe–Al–Si–Ca phases, increasing the first and decreasing the second one. The suitable starting composition which could give the expected results must be the following: 92–94% Si; 3–3.5% Fe; 3.5–4% Al and Ca ≤ 0.5%.

Formation of molecular chlorine in dark condition: Heterogeneous reaction of ozone with sea salt in the presence of ferric ion

Uptake coefficients of O3 on NaCl and synthetic sea salt (SSS) were found to be enhanced from < 10−5 to ∼ 3.5 × 10−2 in the presence of water‐soluble Fe3+ in the Fe/Na weight ratio larger than 0.1%. Cl2 release was observed without radiation in the reaction of O3 and a FeCl3/NaCl mixture with surface adsorbed water at the yields of 0.48 and 0.28 for Fe/Na ratio of 1.0 and 0.5 weight %, respectively. Only Br2 release was observed for a FeCl3/SSS sample. These results imply that when bromide is deficient in sea salt, Cl2 would be released from the sea salt with the coexistence of Fe3+. The estimate was made to show that the Cl2 releasing rate can be high enough to explain sporadically observed Cl2 at nighttime in a coastal area.

Structure of beta-lactam synthetase reveals how to synthesize antibiotics instead of asparagine.

The enzyme beta-lactam synthetase (beta-LS) catalyzes the formation of the beta-lactam ring in clavulanic acid, a clinically important beta-lactamase inhibitor. Whereas the penicillin beta-lactam ring is generated by isopenicillin N synthase (IPNS) in the presence of ferrous ion and dioxygen, beta-LS uses ATP and Mg2+ as cofactors. According to sequence alignments, beta-LS is homologous to class B asparagine synthetases (AS-Bs), ATP/Mg2+-dependent enzymes that convert aspartic acid to asparagine. Here we report the first crystal structure of a beta-LS. The 1.95 A resolution structure of Streptomyces clavuligerus beta-LS provides a fully resolved view of the active site in which substrate, closely related ATP analog alpha,beta-methyleneadenosine 5'-triphosphate (AMP-CPP) and a single Mg2+ ion are present. A high degree of substrate preorganization is observed. Comparison to Escherichia coli AS-B reveals the evolutionary changes that have taken place in beta-LS that impede interdomain reaction, which is essential in AS-B, and that accommodate beta-lactam formation. The structural data provide the opportunity to alter the synthetic potential of beta-LS, perhaps leading to the creation of new beta-lactamase inhibitors and beta-lactam antibiotics.

Reaction Mechanism from Leucoanthocyanidin to Anthocyanidin 3-Glucoside, a Key Reaction for Coloring in Anthocyanin Biosynthesis

In the conversion from colorless leucoanthocyanidin to colored anthocyanidin 3-glucoside, at least two enzymes, anthocyanidin synthase (ANS) and UDP-glucose:flavonoid 3-O-glucosyltransferase (3-GT), are postulated to be involved. Despite the importance of this reaction sequence for coloring in anthocyanin biosynthesis, the biochemical reaction mechanism has not been clarified, and the possible involvement of a dehydratase has not been excluded. Here we show that recombinant ANSs from several model plant species, snapdragon, petunia, torenia, and maize, catalyze the formation of anthocyanidin in vitro through a 2-oxoglutarate-dependent oxidation of leucoanthocyanidin. Crude extracts of Escherichia coli, expressing recombinant ANSs from these plant species, and purified recombinant enzymes of petunia and maize catalyzed the formation of anthocyanidin in the presence of ferrous ion, 2-oxoglutarate, and ascorbate. The in vitro formation of colored cyanidin 3-glucoside from leucocyanidin, via a cyanidin intermediate, was demonstrated using petunia ANS and 3-GT. The entire reaction sequence did not require any additional dehydratase but was dependent on moderate acidic pH conditions following the enzymatic steps. The present study indicated that the in vivo cytosolic reaction sequence involves an ANS-catalyzed 2-oxoglutarate-dependent conversion of leucoanthocyanidin (flavan-3,4-cis-diol) to 3-flaven-2,3-diol (pseudobase), most probably through 2,3-desaturation and isomerization, followed by glucosylation at the C-3 position by 3-GT.

Mechanisms of bioleaching of a refractory mineral of gold with Thiobacillus ferrooxidans

A quick, simple and reproducible method for the indirect determination of the population of the absorbed and suspended bacterias in the cultivation media is the Bradford's method. It has been used to evaluate the fraction of bacteria adhered to the mineral during the bioleaching process and the suspended fraction. It was observed that a significant fraction of the bacteria is adhered to the mineral surface. This proportion varies with the environmental conditions, mainly pH, the presence of ferric ions and the way to supply the mineral sulphide. It has also been observed that the fraction adhered to the solid shows a progressive loss of its oxidative activity. The results can help demonstrate that the sulphides leaching is due to the combination of the direct bacterial action on the sulphide mineral surface with the indirect leaching by the ferric ion produced by the bacteria into the solution.

A simple, highly sensitive and improved method for the measurement of bleomycin-detectable iron: the ‘catalytic iron index’ and its value in the assessment of iron status in haemochromatosis

In the presence of ferrous ions (Fe(2+)), the anti-tumour agent bleomycin will induce DNA degradation. Degradation of DNA into substances detectable by the thiobarbituric acid test has been used previously for the detection of iron in a form that is capable of catalysing the formation of the potentially harmful hydroxyl free radical. In the present paper, we describe the application of the ethidium-binding assay of DNA damage to the measurement of bleomycin-detectable iron, comparing its performance with the conventional method in the assessment of iron standard solutions and plasma samples from haemochromatosis patients. The ethidium-binding assay proved to be more responsive than the thiobarbituric acid test in the detection of DNA damage induced by very low concentrations of iron, but became saturated at higher iron concentrations. Agreement between the two versions of the assay in the identification of plasma samples containing bleomycin-detectable iron was good, but agreement on the actual concentrations of such iron in the positive samples was poor. This discrepancy is believed to be due to interference with the thiobarbituric acid assay by plasma. Consequently, it was not possible to obtain reliable estimates of free iron concentrations in plasma when using the conventional version of the bleomycin assay. We have devised a parameter of iron status called the catalytic iron index. For healthy, non-haemochromatotic individuals, the mean value of this parameter was found to be 0.81 (range 0.78-0.84; n=20). Elevated values were observed in some plasma samples from haemochromatosis patients, but these showed no correlation with serum ferritin levels. In contrast, correlations were seen with both serum iron and transferrin saturation levels, but only when these were above the normal range.

Kinetic Analysis of Photosterilization Rate of Escherichia coli Cells in Titanium Dioxide Suspension Associated with Redox Reactions of Iron Ions.

Photosterilization of Escherichia coli cells was investigated using TiO2 particles in the presence of ferric ion as an electron acceptor. Deactivation of the cells was recognized in the reaction mixture containing ferric ion at the initial concentration of CFe3, 0 = 1, 30 and 100 × 10-3 mol/m3 and the cell deactivation did not occur in the absence of ferric ion. The apparent sterilization rate constant, k', was determined from the photoreaction tests conducted under the varied conditions of average light intensity (Iobs = 0-22 W/m2) and TiO2 concentration (CTO = 0-0.1 kg/m3). A proportional relation was obtained between the values of k' and Iobs with the slope of k'/ Iobs = 3.8 × 10-5 m2/J at CTO = 0.01 kg/m3, while the value of k'/ Iobs increased with an increase in TiO2 concentration depicting a saturated profile up to CTO = 0.1 kg/m3 at Iobs = 8, 13 and 22 W/m2. This relation between the values of k'/ Iobs and CTO could be kinetically explained by considering the photoreactions of ferric and ferrous ions and the adsorption of TiO2 particles onto E. coli cells in the reaction mixture.

Acid Refining of Synthesised Alloys Within the Quaternary System Fe-Si-Ca-AI: Effect of Ferric Ions

A systematic study of synthesis of different chemical composition of alloys within the quaternary Fe-Si-Ca-AI system, versus acid leaching refining using HCI with or without FeCl3 has been undertaken. Such study has the aim of achieving an adequate structural composition of Fe-Si alloys, in order to obtain high purity and fine panicle size silicon by acid leaching, at more reduced costs. The experimental results show that an adequate control of Fe/Al and Si/Ca concentration ratios can hinder the formation of tetragonal and orthorhombic FeSl2 phases, and consequently promotes a successful refining of ferro-silicon alloys. The presence of ferric ion influences on a distinct way the rate of removal of Al-Fe-Si and Fe-Al-Si-Ca phases, increasing the first and decreasing the second one. The suitable starting composition which could give the expected results must be the following: 92-94% Si; 3-3.5% Fe; 3.5-4% Al and Ca < 0.5%.

Photo-Fenton degradation of dye in methanolic solution under both UV and visible irradiation

The photodegradation of methyl orange was examined in methanolic solution under both UV and visible irradiations in the presence of ferric ions and H 2O 2. The spin-trapping EPR technique was utilized to reveal the photo-Fenton reaction mechanism in the methanolic solution. It was found that different radicals were generated under UV and visible light irradiations. Possible mechanism of the photo-Fenton reaction in methanolic solution under both UV and visible light irradiations was proposed on the basis of experimental results. The intermediates produced during the photo-Fenton reaction were detected by IR and GC–MS spectra.

Scavenging effect of melatonin on hydroxyl radicals generated by alloxan

Alloxan can act as a generator of reactive oxygen species (ROS) as long as sufficient suitable reducing agents (e.g. reduced glutathione) and oxygen are available. Using electron spin resonance-spectroscopy and the oxygen-centered spin trap DEPMPO, we demonstrate that hydroxyl radicals (OH.) are formed in vitro by alloxan in the presence of glutathione (GSH) and chelated divalent iron. Furthermore, peroxidation of polyunsaturated fatty acids from phosphatidylcholine-containing liposomes with concomitant formation of malondialdehyde (MDA) was used as a further indicator for a preceding OH. formation. Melatonin, the main secretory product of the pineal gland, is an effective scavenger of OH.. The 50%-inhibitor concentration (IC50-value) for melatonin to scavenge OH. generated from the alloxan/GSH-reaction in the presence of ferrous ions was 23 micromol/L. In contrast to the ability to effectively scavenge OH., the potential of melatonin to prevent lipid peroxidation is considerably less pronounced.

Stabilization of soybean oil with heated quercetin and 5-caffeoylquinic acid in the presence of ferric ion.

The effect of heated quercetin (400 mg/kg of oil) or 5-caffeoylquinic acid (5-CQA) and the presence of ferric ion (2.2 mg/kg of oil) on the stability of soya oil oxidized in an oxidative stability index (OSI) instrument was investigated. After heating the phenolic at 100 degrees C or 150 degrees C, the OSI values of treated oils were not significantly (p < 0.001) different, whereas, at 200 degrees C, the values decreased significantly with addition of quercetin, but not with 5-CQA. However, the antioxidative activity of quercetin remained significantly greater than that of 5-CQA. The antioxidative potency of quercetin was reduced significantly by addition of ferric palmitate (FP), but that of 5-CQA was not. Reaction between the ortho-dihydroxy groups of the quercetin and ferric ion may reduce the number of hydroxyls available to react with free radicals. Chelating action of 5-CQA might be provided by ortho-dihydroxy grouping of the quinic acid moiety.

Photophysical and photochemical properties of a water-soluble perylene diimide derivative

The absorbance maximum of synthesized water soluble perylene 4-carboxylphenyl-bis-diimide (PECA) is found to be about 50nm lower in water, as compared to absorbance in organic solvents, and the singlet energy is 61.4kcalmol−1 in aqueous solutions, compared to 54.4kcalmol−1 in organic solvents. The fluorescence quantum yields were similar in both media but radiative and fluorescence lifetimes are found to be enhanced about twice (τf from 8 to 15ns), and the rate of fluorescence is decreased twofold in aqueous solution, as compared to organic solutions. PECA is proven to produce reactive superoxide anion and/or hydroperoxy radical in aqueous solutions, in the pH range of 6–12 (φPECAO2−=0.062 at pH=9). The superoxide/hydroperoxy formation is found to be enhanced in the presence of ferric ions (φPECAO2−=0.10 at pH=9). The quantum yield of fluorescence emission, Qf, was measured to be 1.00 at pH 11.85, and 0.87 at pH 6.60. The difference is attributed to an aggregation effect due to low solubility in neutral aqueous solution. Fluorescence quenching by Co+2 ions has yielded a quenching rate of 2.3×1012M−1s−1 for perylene diimide. The degradation of bromacil and 2,4-dichlorophenoxyacetic acid (2,4-D) pesticides in neutral aqueous solutions has proven that PECA/Fe+3 solar photocatalyst is as reactive as singlet oxygen in photo oxidations for organic pollutants. High thermal and photo stabilities and the regain of catalysts on precipitation, are the advantages with respect to classical triplet organic photosensitizers (methylene blue, rose bengal, etc.) employed for singlet oxygen photodegradations.

Dissolution of Oxalate Precipitate and Destruction of Oxalate Ion 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.

Sensitive determination of dissolved sulfide in estuarine water by solid-phase extraction and high-performance liquid chromatography of methylene blue

A sensitive method involving solid-phase extraction and HPLC analysis of methylene blue has been developed to measure nanomolar levels of dissolved sulfide in oxic surface waters. The procedure included 1) a preconcentration step, in which methylene blue generated from sulfide reaction with n, n-dimethyl- p-phenylenediamine in acidic conditions in the presence of ferric ion was absorbed onto Waters tC 18 cartridge; and 2) a determination step, in which methylene blue was separated by HPLC in a gradient elution to minimize natural organic matter interference and detected by absorbance. The concentrations of the dissolved sulfide, quantified by standard addition, were about 2.1–4.7 n M in oxic surface waters from Galveston Bay, Texas.

Thermodynamics of the cleavage of DNA induced by adriamycin: a microcalorimetric study

Microcalorimetry was used to measure the change in enthalpy for the scission of calf thymus DNA (ct-DNA) induced by adriamycin (ADM) in the presence of ferric ions, Vitamin C, and oxygen. At 298.15 K and pH 7.4, the overall molar reaction enthalpy for this cleavage was −147.1 kJ/mol, noticeably higher than that by the mixture of Fe 3+, Vitamin C, and O 2. Under the same conditions, the enthalpy change for the damage of ct-DNA by the mixture of adriamycin, ferrous ions, and oxygen, however, was nearly zero, indicating that this mixture can not induce any detectable degradation of DNA. These results suggest that both the activated adriamycin and hydroxyl radical attack DNA strands during the cleavage. A possible mechanism for the cleavage of DNA induced by adriamycin is proposed based on the calorimetric measurements. A novel thermodynamic model for the interactions of DNA with small molecules is also suggested. This is a convenient method to calculate both the binding constant ( K b) and the standard thermodynamic parameters (Δ b H m 0, Δ b G m 0, and Δ b S m 0) for the binding of adriamycin-Fe 3+ complex to ct-DNA by the calorimetric data. This nucleotide binding reaction is driven by a favorable enthalpy change, with a large unfavorable entropy change. This result indicates that the binding results in structural changes accompanied by an increase in the order of the whole system, implying that an intercalation mode is involved in adriamycin-mediated breakage of DNA.