SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The concentration of alpha-oxygen which can oxidize methane to methanol and benzene to phenol at RT, increases linearly with the amount of introduced extraframework Al on Fe/ZSM-5 catalysts prepared by solid-state exchange of FeCl3 and AlCl3 with H-ZSM-5.
We have determined the crystal structure of the chloroperoxidase (CPO) hydroperoxo reaction intermediate (CPO compound 0) at 1.75-A resolution. The intermediate was generated through controlled photoreduction of the CPO oxygen complex during x-ray data collection, which was monitored by recording of the crystal absorption spectra. Initially, the peroxo-anion species was formed and then protonated to yield compound 0. Quantum chemical calculations indicate that the peroxo-anion species is not stable and collapses instantaneously to compound 0. Compound 0 is present in the ferric low-spin doublet ground state and is characterized by a long O O bond length of 1.5 A and a Fe O bond distance of 1.8 A, which is also observed in the crystal structure.
Anaerobic enrichments with acetate as the electron donor and Fe(III) as the terminal electron acceptor were obtained from sediments of Salt Pond, a coastal marine basin near Woods Hole, Mass. A pure culture of a facultatively anaerobic Fe(III) reducer was isolated, and 16S rRNA analysis demonstrated that this organism was most closely related to Pantoea (formerly Enterobacter) agglomerans, a member of the family Enterobacteriaceae within the gamma subdivision of the Proteobacteria. This organism, designated strain SP1, can grow by coupling the oxidation of acetate or H(2) to the reduction of a variety of electron acceptors, including Fe(III), Mn(IV), Cr(VI), and the humic substance analog 2,6-anthraquinone disulfonate, but not sulfate. To our knowledge, this is the first mesophilic facultative anaerobe reported to couple acetate oxidation to dissimilatory metal reduction.
Two methods, centrifugation and flocculation, were evaluated to determine their efficiencies of recovery of Toxoplasma gondii oocysts from contaminated water samples. Demineralized and tap water replicates were inoculated with high numbers of sporulated or unsporulated T. gondii oocysts (1 x 10(5) and 1 x 10(4) oocysts). The strain, age, and concentration of the seeded oocysts were recorded. Oocysts were recovered either by centrifugation of the contaminated samples at various g values or by flocculation with two coagulants, Fe(2)(SO(4))(3) and Al(2)(SO(4))(3). The recovery rates were determined with the final pellets by phase-contrast microscopy. Sporulated oocysts were recovered more effectively by flocculation with Al(2)(SO(4))(3) (96.5% +/- 21.7%) than by flocculation with Fe(2)(SO(4))(3) (93.1% +/- 8.1%) or by centrifugation at 2,073 x g (82.5% +/- 6.8%). For the unsporulated oocysts, flocculation with Fe(2)(SO(4))(3) was more successful (100.3% +/- 26.9%) than flocculation with Al(2)(SO(4))(3) (90.4% +/- 19.1%) or centrifugation at 2,565 x g (97.2% +/- 12.5%). The infectivity of the sporulated oocysts recovered by centrifugation was confirmed by seroconversion of all inoculated mice 77 days postinfection. These data suggest that sporulated Toxoplasma oocysts purified by methods commonly used for waterborne pathogens retain their infectivity after mechanical treatment and are able to induce infections in mammals. This is the first step in developing a systematic approach for the detection of Toxoplasma oocysts in water.
The direct filtration system is widely used in the treatment of source waters with low and stable turbidity. We have previously indicated the importance of optimizing agitation strength GR and time TR in rapid mixing tanks in order to decrease filter head loss and treated water turbidity in direct filtration. In the present study, we employ a batch-type coagulation experimental apparatus that incorporates a high-sensitivity particle counter, where the particulate concentrations are measured continuously after injection of coagulant, in order to clarify the fundamental coagulation and microfloc formation dynamics. Specifically, it is shown that, after injection of the coagulant, coagulation and microfloc formation occur through distinct periods: an agglomeration preparation period, followed by an agglomeration progression period, and then finally an agglomeration stabilization period, and that optimization of the GR value is the most important consideration, although both the coagulant concentration and GR influence the time at which agglomeration begins in the preparatory period, the time at which agglomeration stabilizes after the progression period, and the concentration of initial particles with diameters of 1-3 microm at completion of agglomeration.
The monograph program of the International Agency for Research of on Cancer has evaluated many trace elements for their carcinogenicity to humans. Five groups of compounds were considered human carcinogens: arsenic and arsenic compounds, beryllium and beryllium compounds, cadmium and cadmium compounds, hexavalent chromium compounds, and nickel compounds. Antimony trioxide, cobalt and cobalt compounds, lead and inorganic lead compounds, methylmercury compounds, and metallic nickel were considered possibly carcinogenic to humans. Antimony trisulfide, trivalent chromium compounds, metallic chromium, ferric oxide, organolead compounds, metallic mercury, inorganic mercury compounds, selenium and selenium compounds, and titanium dioxide were not classifiable. Trace elements studied to a limited extent include copper, manganese, tin, vanadium, and zinc. Among the problems are the lack of relevant data, the definition of active species, the extrapolation of the results of experimental studies to humans, the methodological problems of epidemiologic studies, and the possible anticarcinogenic activity of some trace elements.
The subcellular site of oxidation of [1-14C]phytanic acid to pristanic acid and CO2 was examined by measurement of the release of 14CO2 in different organelles from human and rat tissues prepared by isopycnic density gradient centrifugation in Nycodenz. The activity of phytanic acid oxidation in human tissues (liver and cultured skin fibroblasts) paralleled that of the peroxisomal marker catalase. We also observed that Nycodenz (commonly used gradient material for isolation of subcellular organelles) has a strong inhibitory effect on the alpha-oxidation of phytanic acid. This inhibition is reversible and can be decreased or eliminated by dialysis of isolated organelles against isotonic solution. The dialysis of endoplasmic reticulum, mitochondrial, and peroxisomal fractions from human liver and cultured skin fibroblasts for 2 h against isotonic solution increased the specific activity of phytanic acid oxidation by 1.3-, 1.3-, and 5-21-fold, respectively, after removal of Nycodenz as compared with nondialyzed samples. After dialysis, the rate of oxidation of phytanic acid in peroxisomes from human liver and cultured skin fibroblasts was 4-26 times higher than that in mitochondria and 43-130 times than that in the endoplasmic reticulum, suggesting that, in human tissues, phytanic acid is oxidized to pristanic acid in peroxisomes. On the other hand, the oxidation of phytanic acid in rat liver paralleled the distribution of the mitochondrial marker cytochrome-c oxidase. The 18-fold higher rate of oxidation in dialyzed mitochondria (198.6 +/- 4.20 pmol/h/mg of protein) than in peroxisomes (11.0 +/- 0.5 pmol/h/mg of protein) demonstrates that, in rodents, phytanic acid is oxidized in mitochondria. 2-[5-(4-Chlorophenyl)pentyl]oxiran-2-carboxylic acid, an inhibitor of carnitine palmitoyltransferase I and mitochondrial fatty acid oxidation, inhibits the oxidation of phytanic acid in rat tissues (liver and cultured skin fibroblasts), whereas it has no effect on the oxidation of phytanic acid in human tissues (liver and cultured skin fibroblasts). The higher specific activity of phytanic acid oxidation in peroxisomes compared with that in mitochondria and the endoplasmic reticulum from human tissues and the inhibition of phytanic acid oxidation by 2-[5-(4-chlorophenyl)pentyl]oxiran-2-carboxylic acid in rat tissues (but not human tissues) demonstrate clearly that, in human tissues, phytanic acid is predominantly oxidized in peroxisomes.
The reversibility of the stepwise reduction of Compound I to the ferric state via Compound II was confirmed in horseradish peroxidases A2 and C. The values of E'o (compound I/Compound II) and E'O (Compound II/ferric) were measured from equilibrium data coupled with the K2IrCl6-K3IrCl6 system in a narrow region of pH near 6.3. The ferric enzymes were also oxidized by ferricyanide to Compound II at alkaline pH and the values of E'O (Compound II/ferric) were measured from the equilibrium data. The pH dependence of E'O (Compound II/ferric) was in accord with the equation: E'O = EO + 0.058 log (Kr[H+] + [H+]2)/(KO + [H+]), where Kr and KO are proton dissociation constants in the ferric enzyme and Compound II, respectively. The pH-E'O (Compound I/Compound II) curves were likewise obtained from the equation, E'O = EO + 0.058 log (Kr + [H+]), where Kr is the proton dissociation constant in Compound II. The forward and backward rate constants were measured in each of one-electron transfer reactions of the peroxidases with the K2IrCl6-K3IrCl6 system at various pH values. The E'O values calculated on the assumption that the ratio of the rate constants equals the equilibrium constant were compared with those obtained from the equilibrium data.
Aluminium ions hydrolyse and polymerise into different species in water. Main aluminium species in aluminium coagulant solutions are monomeric Al species (Al1) and polymeric Al species Al13O4(OH)24(7+) (Al13). The aluminium species distribution in coagulant solutions can be influenced by many parameters. This paper studies influences of concentrations of total aluminium species (Al(t)) and other species--OH-, polysilicic acid and ferric species, which were added in aluminium coagulant solutions, on the aluminium species distribution through 27Al nuclear magnetic resonance (NMR) analysis. Results show that only Al1 and no Al13 exist in coagulant solutions at higher Al(t) concentrations (over 1 mol l(-1)), while both species exist at lower Al(t) concentrations (0.1 mol l(-1)). The increase of OH/Al value (molar ratio) increases the concentration of Al13 in coagulant solutions, while the addition of polysilicic acid and ferric species decreases the concentration of Al13.
BACKGROUND: Numerous substances are administered during dialysis for anticoagulation and the treatment of anemia and iron deficiency. The availability of current dialysis membranes is diverse, but assessment of the effects of different membranes on these routinely administered substances is lacking. This prospective study appraises specific effects of 7 dialysis membranes (4 low-flux membranes, 3 high-flux membranes) on the handling of 4 commonly administered agents (epoetin alfa, darbepoetin alfa, enoxaparin, and iron sucrose) during dialysis. METHODS: Using a different membrane sequentially, 6 stable hemodialysis patients were treated with epoetin alfa, enoxaparin, and iron sucrose, and 6 patients with darbepoetin alfa. Serum concentrations (predialyzer and postdialyzer) of each substance were assessed after administration and after 4 hours of dialysis (predialyzer). RESULTS: Overall, use of low-flux membranes resulted in similar serum concentrations for all compounds. However, use of high-flux membranes showed reduced antifactor Xa levels immediately (predialyzer, P = 0.028; postdialyzer, P = 0.027) and 4 hours after (P = 0.001) administration of enoxaparin compared with low-flux membranes. Variable changes in darbepoetin concentrations also were found between the high-flux membranes during dialysis (P = 0.009). Although peak serum concentrations of all compounds were inversely proportional to body weight, the percentage of change during dialysis was not related to dosage or body weight. CONCLUSION: High-flux membranes may require greater doses of enoxaparin to ensure adequate anticoagulation during dialysis and may be associated with variable changes in darbepoetin concentrations. For other compounds, no noteworthy difference among membranes was defined.
The T252A mutant of cytochrome P450cam is unable to form the oxoferryl "active oxygen" intermediate, as judged by its inability to hydroxylate its normal substrate, camphor. In the present study, we demonstrate that T252A P450cam is nonetheless able to epoxidize olefins, due to the action of a second oxidant. However, as shown in earlier radiolytic studies and by the ability of T252A to reduce dioxygen to hydrogen peroxide, the mutant retains the ability to form the hydroperoxo-ferric reaction cycle intermediate. The present results provide strong evidence that hydroperoxo-ferric P450 can serve as a second electrophilic oxidant capable of olefin epoxidation.
Iron-induced oxidative stress has been implicated in several pathological processes. In the present work we provide evidence for the formation of a mangiferin:Fe(III) complex (2:1), shown by means of either iron-induced changes in the UV/visible spectrum of mangiferin or by reduction of the anodic current peak in the voltammogram of that compound; we demonstrate, in addition, that the ferric complex is more effective than mangiferin itself in scavenging superoxide radicals generated by pyrogallol autoxidation, as well as in protecting hepatocytes from reactive oxygen species mediated hypoxia/reoxygenation injury. Moreover, we found that the mangiferin:Fe(III) complex reacts more readily with horseradish peroxidase/H(2)O(2) than does mangiferin by itself. We postulate that mangiferin could afford protection against iron/reactive oxygen species-mediated pathological processes by means of both iron chelating and iron-stimulated superoxide radical scavenging activity.
Density functional theory (DFT) is applied to the dark section of the catalytic cycle of the enzyme cytochrome P450, namely, the formation of the active species, Compound I (Cpd I), from the ferric-hydroperoxide species (Cpd 0) by a protonation-assisted mechanism. The chosen 96-atom model includes the key functionalities deduced from experiment: Asp(251), Thr(252), Glu(366), and the water channels that relay the protons. The DFT model calculations show that (a) Cpd I is not formed spontaneously from Cpd 0 by direct protonation, nor is the process very exothermic. The process is virtually thermoneutral and involves a significant barrier such that formation of Cpd I is not facile on this route. (b) Along the protonation pathway, there exists an intermediate, a protonated Cpd 0, which is a potent oxidant since it is a ferric complex of water oxide. Preliminary quantum mechanical/molecular mechanical calculations confirm that Cpd 0 and Cpd I are of similar energy for the chosen model and that protonated Cpd 0 may exist as an unstable intermediate. The paper also addresses the essential role of Thr(252) as a hydrogen-bond acceptor (in accord with mutation studies of the OH group to OMe).
In this work, an electron paramagnetic resonance (EPR) strategy to study the heme-pocket structure of low-spin ferric heme proteins is optimized. Frozen solutions of ferric mouse neuroglobin (mNgb) are analyzed by means of electron spin echo envelope modulation and pulsed electron-nuclear double resonance techniques. The hyperfine and nuclear quadrupole couplings of the directly coordinating heme and histidine nitrogens are derived and are discussed in comparison with known data of other ferric porphyrin compounds. In combination with the hyperfine matrices of the imidazole protons, the 14N EPR parameters reveal structural information on the heme pocket of mNgb that is in agreement with previous X-ray diffraction data on neuroglobins.
This study investigated Fenton and Fenton-like reactions at low iron concentration (<or==10 mg l-1) to oxidize three commercial azo dyes, namely Red MX-5B, Reactive Black 5 and Orange G. In some local cases in Taiwan, wastewater color was found to be the only problem in meeting local effluent standards. This investigation reveals that both of these methods can remove the color of these dyes completely. Moreover they only produce little sludge in wastewater that meet local effluent standards and do not need to further treat. The effects of Fe2+, Fe3+, H2O2 and solution pH on dye decolorization are demonstrated in detail. The optimum pH for both Fenton and Fenton-like reactions in this study are about pH 2.5-3.0. Increasing the dose of ferric nitrate enhances the dye decolorization. The optimal levels of H2O2 required for the process are also examined. High levels of H2O2 appear to reduce dye decolorization. In addition, it is also found that decolorization of azo dyes undergoes a faster reaction rate than mineralization of azo dyes.
BACKGROUND: Iron sucrose (Fe-S) and low-molecular-weight iron dextran (Fe-D) have been used successfully in the treatment of anaemia in chronic kidney disease patients. However, some side effects, such as endothelial cell dysfunction have been reported. Mechanisms by which iron can induce endothelial cell damage have not been completely understood. This study was designed to examine the effect of Fe-S and Fe-D on bovine aortic endothelial cells in vitro. METHODS: Cell proliferation was determined by [3H] thymidine incorporation, cytotoxicity by lactate dehydrogenase, pro-Caspase-3 by immunoblotting; and Caspase-3 activity using a colorimetric assay. Expression of the apoptosis stress pathway proteins Bcl-2 and Bax and cycle arrest proteins p53 and p21WAF/CIP1 were examined by immunoblot. Cell apoptosis was tested by terminal deoxynucleotidyltransferase-mediated nick-end labelling (TUNEL) and DNA fragmentation. RESULTS: Both iron preparations inhibited cell proliferation. This effect was more important and occurred at lower concentrations in Fe-S than Fe-D cultured cells. Expression of p53 and p21WAF/CIP1 increased in cells incubated with Fe-S, but not with Fe-D. Bcl-2 expression was significantly down-regulated in cells incubated with Fe-S in comparison with Fe-D, while Bax expression was not modified by the iron compounds. Pro-Caspase-3 expression and Caspase-3 activity increased only in cells treated with Fe-S. Apoptosis was present in cells treated with Fe-S. CONCLUSIONS: Our results demonstrate that Fe-S exerts a greater inhibitory effect on endothelial cell proliferation than Fe-D. The mechanisms involved in this process may be related, at least in part, to over expression of proteins related to the cell cycle arrest and apoptosis stress pathway.
Selective ion exchange is one of the preferred treatment technologies for removing low levels of perchlorate (ClO4-) from contaminated water because of its high efficiency and minimal impact on water quality through the addition or removal of chemicals and nutrients. However, the exceptionally high affinity of ClO4- for type I anion-exchange resins makes regeneration with conventional NaCl brine extremely difficult and costly for practical applications. The present study entails the development of a novel regeneration methodology applicable to highly selective anion-exchange resins. Tetrachloroferrate (FeCl4-) anions, formed in a solution of ferric chloride and hydrochloric acid (e.g., 1 M FeCl3 and 4 M HCl), were found to effectively displace Cl04- anions that were sorbed on the resin. A mass-balance analysis indicated that a nearly 100% recovery of ion-exchange sites was achieved by washing with as little as approximately 5 bed volumes of the regenerant solution in a column flow-through experiment There was no significant deterioration of the resin's performance with respect to ClO4- removal after repeated loading and regeneration cycles. Thus, the new methodology may offer a cost-effective means to regenerate ClO4- -loaded resins with improved regeneration efficiency, recovery, and waste minimization in comparison with conventional brine regeneration techniques.
Ferric myoglobin (Mb) is oxidized by H2O2 to a ferryl (FeIV = O) species and a protein radical, whereas ferrous Mb is similarly oxidized to the ferryl species without the protein radical. The protein radical is unstable and decays within 5 min, but the ferryl species is stable for more than 1 h. Previous studies have shown that styrene is oxidized to styrene oxide and benzaldehyde by ferric Mb and H2O2. We demonstrate here that the ferryl species produced from ferrous equine Mb and H2O2 does not epoxidize styrene. Furthermore, the EPR signal intensity of the protein radical formed from ferric equine Mb and the ability to oxidize styrene decrease in parallel as a function of the time separating the addition of H2O2 and styrene. The ability to oxidize styrene as a function of time after addition of H2O2 is lost much more rapidly with the H64V/K102Q/Y103F/Y146F/Y151F mutant of sperm whale Mb than with the native protein or the Y146F/Y151F mutant. The results indicate that styrene epoxidation requires a two-electron oxidized species of Mb in which the ferryl (FeIV = O) complex is coupled to a protein or highly transient (undetectable) porphyrin radical. Benzaldehyde formation appears to be catalyzed by the same oxidizing species. Styrene oxidation thus differs from linoleic acid oxygenation, which is catalyzed by the ferryl species alone.