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At least 1,243 records · Page 69Linked to original sources
PubMed2003

3-Boronoacrolein as an exceptional heterodiene in the highly enantio- and diastereoselective Cr(III)-catalyzed three-component [4+2]/allylboration.

This Communication reports the optimization of the first catalytic enantio- and diastereoselective hetero[4+2]/allylboration reaction to provide efficient access to alpha-hydroxyalkyl pyran derivatives. The key substrate 3-boronoacrolein pinacolate appears to be an exceptionally favorable heterodiene for use in Jacobsen's enantioselective reverse electron demand hetero[4+2] reaction with enol ethers, catalyzed by the tridentate (Schiff base)chromium complex 1. This one-pot three-component reaction was successfully applied to a concise total synthesis of (5R,6S)-6-acetoxy-5-hexadecanolide (2), the oviposition attractant pheromone of the female Culex mosquito capable of transmitting the West Nile virus.

Acrolein↗
PubMed1986

Experimental chelation therapy in chromium, lead, and boron intoxication with N-acetylcysteine and other compounds.

The usefulness of N-acetylcysteine (NAC) as a chelating agent was studied for the toxin potassium dichromate, lead tetraacetate, and boric acid. Mature Sprague-Dawley rats were intoxicated with these substances and placed in metabolic cages. Urinary excretion rates of intoxicant and total urine volume were determined during treatment with N-acetylcysteine, calcium EDTA, and/or dimercaptosuccinic acid, N-acetylcysteine proved to be the most effective agent at increasing the excretion of chromium and boron and was also able to reverse the oliguria associated with these toxins. Dimercaptosuccinic acid was most effective at the chelation of lead. NAC did not increase the excretion of lead. We conclude that NAC may be useful in intoxications due to chromate and borate and is effective at reversing the oliguria associated with these intoxicants.

Acetylcysteine↗
PubMed2000

Reduction of Fe(III), Cr(VI), U(VI), and Tc(VII) by Deinococcus radiodurans R1.

Deinococcus radiodurans is an exceptionally radiation-resistant microorganism capable of surviving acute exposures to ionizing radiation doses of 15,000 Gy and previously described as having a strictly aerobic respiratory metabolism. Under strict anaerobic conditions, D. radiodurans R1 reduced Fe(III)-nitrilotriacetic acid coupled to the oxidation of lactate to CO(2) and acetate but was unable to link this process to growth. D. radiodurans reduced the humic acid analog anthraquinone-2,6-disulfonate (AQDS) to its dihydroquinone form, AH(2)DS, which subsequently transferred electrons to the Fe(III) oxides hydrous ferric oxide and goethite via a previously described electron shuttle mechanism. D. radiodurans reduced the solid-phase Fe(III) oxides in the presence of either 0.1 mM AQDS or leonardite humic acids (2 mg ml(-1)) but not in their absence. D. radiodurans also reduced U(VI) and Tc(VII) in the presence of AQDS. In contrast, Cr(VI) was directly reduced in anaerobic cultures with lactate although the rate of reduction was higher in the presence of AQDS. The results are the first evidence that D. radiodurans can reduce Fe(III) coupled to the oxidation of lactate or other organic compounds. Also, D. radiodurans, in combination with humic acids or synthetic electron shuttle agents, can reduce U and Tc and thus has potential applications for remediation of metal- and radionuclide-contaminated sites where ionizing radiation or other DNA-damaging agents may restrict the activity of more sensitive organisms.

Anaerobiosis↗
PubMed1998

The major species of heavy metal aerosol resulting from water cooling systems and spray dryer systems during incineration processes

Trace toxic metals in municipal solid waste may escape from the incineration process in flue gas, in dry collected ash, in wet scrubbed ash, or as a suspended aerosol. Therefore, understanding the behavior of heavy metals in the flue gas and the best controls in the air pollution control equipment are important and necessary. The control conditions of water cooling and spray dryer systems during incineration processes significantly influence the formation of heavy metal compounds. The formation of chromium (Cr), lead (Pb), and cadmium (Cd) species under various control conditions (water cooling tower and spray dryer reactor) was investigated in this study. The object of the experiment is to understand the effects of water cooling and spray dryer systems individually on the formation of heavy metal species. The operating parameters that are evaluated include different control systems, control temperatures, and chlorine content. A thermodynamic equilibrium model was also used to evaluate experimental data. In order to match real incineration conditions, a two-stage simulation was performed in this experiment. The results showed that the relationship of speciation between the simulation prediction and X-ray diffraction (XRD) analysis is consistent for Cr compounds; both indicated that Cr2O3 is the major species. The relationship is almost the same for Cd compounds, but not for Pb compounds.

Journal Article↗
PubMed2001

New method for divesting cobalt-chromium alloy castings: sandblasting with a mixed abrasive powder.

STATEMENT OF PROBLEM: Because the conventional divesting method for cobalt-chromium (Co-Cr) alloys is laborious, a more convenient method is desirable. PURPOSE: This study compared sandblasting with a mixed powder composed of aluminum oxide and glass beads to sandblasting with single powders (carborundum, aluminum oxide, and glass beads) when a Co-Cr casting was removed from the investment mold. MATERIAL AND METHODS: Rectangular plates with the 2 surfaces simulating the inner and outer surfaces of a removable partial denture framework were fabricated with Co-Cr alloys. Four kinds of sandblasting powders were used to remove the remnants of investment molds. Total time (seconds) required for each procedure was measured, as was the surface roughness (Ra) of each specimen after sandblasting. SEM was used to analyze the powders themselves and the sandblasted specimen surfaces. RESULTS: Glass beads alone and the mixed powder of aluminum oxide and glass beads generated a smoother surface compared with aluminum oxide and carborundum powders. The use of the mixed powder significantly reduced the time of the sandblasting procedure. SEM revealed that glass beads generated fewer scars, followed by the mixed powder and then aluminum oxide. The surface sandblasted by carborundum powder was always the roughest. CONCLUSION: Sandblasting Co-Cr castings with the mixed powder effectively decreased treatment time and resulted in smooth, clinically acceptable casting surfaces.

Aluminum Oxide↗
PubMed2006

Starved air combustion-solidification/stabilization of primary chemical sludge from a tannery.

The high concentration of trivalent chromium along with organic/inorganic compounds in tannery sludge causes severe ground water contamination in the case of land disposal and chronic air pollution during incineration. In the present investigation, the sludge was subjected to flow-through column test to evaluate the concentration of leachable organics (tannin, COD and TOC) and heavy metal ions (Cr(3+), Fe(2+)) present in it. The dried sludge was incinerated at 800 degrees C in an incinerator under starved oxygen supply (starved-air combustion) to prevent the conversion of Cr(3+) to Cr(6+). The efficiency of starved air combustion was studied under different loading rates of sludge. The calcined sludge was solidified/stabilized using fly ash and Portland cement/gypsum. The solidified bricks were tested for unconfined compressive strength and heavy metal leaching. Unconfined compressive strength of the blocks was in the range of 83-156 kg/cm(2). The stabilization of chromium (III) in the cement gel matrix was confirmed with scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDX). Leachability studies on solidified bricks were carried out to determine the metal fixation and dissolved organic (as COD) concentration in the leachate.

Adsorption↗
PubMed2006

Thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned solid wastes with calcium hydroxide.

The thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned wastes with Ca(OH)2 was studied. Ashes obtained after incineration of wastes at various temperatures were analysed by X-ray diffraction and EDX method. The main crystallized phases present in the ash obtained at 600 degrees C are Cr2O3 and NaCl. The diffractograms revealed an increase in the intensities of the chromium oxide peaks and a very notable decrease of the amount of sodium chloride at 1100 degrees C. EDX analysis revealed a total disappearance of the chlorine peak at this temperature. Scanning electron micrographs show that the waste lost its fibrous aspect when the temperature increases. Formation of aggregates was noted after 550 degrees C. Combustion of organic matters and decarbonation phenomenon are the main stages observed on GTA and DTA curves of sludges. These phenomena are, respectively, exothermic and endothermic. The diffractogram of sludges recorded at 550 degrees C, in the presence of a constant oxygen surplus, revealed the presence of CaCrO4 and CaCO3.

Calcium Carbonate↗
PubMed2006

Microbial community analysis of soils contaminated with lead, chromium and petroleum hydrocarbons.

The impact on the microbial community of long-term environmental exposure to metal and organic contamination was investigated. Twenty-four soil samples were collected along a transect dug in soils contaminated with road paint and paint solvents, mainly toluene. Chemical analysis along the transect revealed a range from high to low concentrations of metals (lead and chromium) and organic solvent compounds. Principal components analysis of microbial community structure based on denaturing gradient gel electrophoresis of the V3 region of the 16S rRNA gene and fatty acid methyl esters derived from phospholipids (phospholipid fatty acid analysis) showing samples with similar fingerprints also had similar contaminant concentrations. There was also a weak positive correlation between microbial biomass and the organic carbon concentration. Results indicated that microbial populations are present despite some extreme contaminant levels in this mixed-waste contaminated site. Nucleotide sequence determination of the 16S rRNA gene indicated the presence of phylogenetically diverse bacteria belonging to the alpha-, beta-, gamma-, and delta-Proteobacteria, the high and low G + C Gram-positive bacteria, green nonsulfur, OP8, and others that did not group within a described division. This indicates that soils contaminated with both heavy metals and hydrocarbons for several decades have undergone changes in community composition, but still contain a phylogenetically diverse group of bacteria (including novel phylotypes) that warrant further investigation.

Bacteria↗
PubMed1995

Shear bond strengths of four resin cements to cobalt-chromium alloy.

PURPOSE: To evaluate the shear bond strengths of four resin cements to cobalt-chromium (Co-Cr) alloy using two adhesive primers. MATERIALS AND METHODS: The adhesive luting agents Imperva Dual (ID), Panavia 21 (P21), Super-Bond C&B (SB) and Bistite Resin Cement (BR), and the adhesive primers Metal Primer (MP) and Cesead Opaque Primer (COP) were used. Two sizes of dental casting alloy disks were nonprimed or primed and cemented with each adhesive luting agent. The specimens were stored in water at 37 degrees C for 1 day, and then immersed alternately in water baths at 4 degrees C and 60 degrees C for 1 minute each for up to 100,000 thermocycles before shear mode testing at a cross-head speed of 0.5 mm/minute. RESULTS: The application of COP was effective for improving the shear bond strengths of ID, SB or BR to Co-Cr alloy compared with nonprimed specimens and those primed with MP. However, when Co-Cr alloy was cemented with P21, there were no significant differences in bond strengths between the three groups at all thermocycles.

Analysis of Variance↗
PubMed2004

Bone formation within alumina tubes: effect of calcium, manganese, and chromium dopants.

Alumina tubes (1.3mm outer diameter, 0.6mm inner diameter, 15 mm length) doped with Ca, Mn, or Cr at nominal concentrations of 0.5 and 5.0 mol% were implanted into femoral medullary canals of female rats for 16 weeks. Tissue formation within tubes was determined by histology and histomorphometry. Addition of Ca to alumina promoted hypertrophic bone formation at the advancing tissue fronts and tube entrances, and appeared to retard angiogenesis by limiting ongoing cellular migration into the tube. It is speculated that the presence of a secondary phase of calcium hexaluminate, probably having a solubility greater than that of alumina, possibly increased the level of extracellular Ca and, consequently, stimulated osteoclastic activity at the bone-ceramic interface. Addition of Mn significantly enhanced osteogenesis within the tubes. However, it is not possible to determine whether phase composition or microstructure of the ceramic was responsible for this because both were significantly altered by Mn addition. Addition of Cr to the alumina apparently stimulated bone remodelling as indicated by increased cellular activity and bone resorption at the tissue-implant interface. Cr was incorporated into the alumina as a solid solution and the tissue response was speculated to be an effect of surface chemistry rather than microstructure. The work demonstrates that doping a bioinert ceramic with small amounts of specific elements can significantly alter tissue ingrowth, differentiation, and osteogenesis within a porous implant.

Aluminum↗
PubMed1995

Competing pathway involved in allylic acetoxylation of androst-5-en-17-one, and oxidation of allylic alcohols with chromium oxides.

Allylic acetoxylation of androst-5-en-17-one (1) with bromine and silver acetate gave 6 alpha- and 6 beta-acetoxyandrost-4-en-17-ones [4 (3%) and 5 (12%)] and 5 alpha-bromo-6 beta-acetoxy steroid 8 (4%) along with the expected product 4 beta-acetoxy derivative 2 (45%). Treatment of 5 alpha,6 beta-bromide 12, an intermediate of the acetoxylation reaction, with silver acetate also produced the acetates 2, 4, 5, and 8 in relative yields similar to those above. These results indicate that the 6-acetates 4 and 5 are produced through a competing pathway involving formation of a bridged carbonium ion 13 followed by attack of an acetate anion. Oxidation of the axial allylic alcohol, 5-en-4 beta-ol 3, with Jones reagent yielded no trace of the previously reported androst-5-ene-4,17-dione (18) but instead gave a 1:4 mixture of 5 beta,6 beta-epoxy-4-one 16 and 4 beta,5 beta-epoxy-6-one 17 in high yield. In contrast, a 1:4 mixture of androst-4-ene-6,17-dione (10) and compound 18 was obtained upon treatment with chromium trioxide in pyridine. Similar results were also found with the oxidation of another axial allylic alcohol, 4-en-6 beta-ol 7.

Acetylation↗
PubMed1985

Low level chromium (VI) inhalation effects on alveolar macrophages and immune functions in Wistar rats.

In inhalation chambers, 5-week-old male Wistar rats of the strain TNO-W-74 were continuously exposed to submicron aerosols of sodium dichromate in concentrations from 25 (low level) to 200 micrograms/m3 Cr (high level). Subacute exposure (28 days) to 25 and 50 micrograms/m3 Cr resulted in "activated" alveolar macrophages with stimulated phagocytic activities, and significantly elevated antibody responses to injected SRBC's. After subchronic (90 days) low level exposure there was a more pronounced effect on activation of the alveolar macrophages, with increased phagocytic activities. However, at high Cr (VI) exposure level (200 microgram/m3), inhibited phagocytic function of the alveolar macrophages was seen. In rats which were exposed to this chromium aerosol concentration for 42 days, the lung clearance of inert iron oxide was reduced significantly. The humoral immune system was still stimulated at subchronic low chromium aerosol concentrations of 100 micrograms/m3, but significantly depressed at 200 micrograms/m3 Cr. These results show that respiratory defence and immunologic functions were stimulated or inhibited depending on dose and time of chromium (VI) inhalation.

Aerosols↗
PubMed2005

Chemistry of the lichen Hypogymnia physodes transplanted to an industrial region.

Lichens produce a great number of secondary metabolites that participate in ecological interactions and respond to environmental changes. We examined the influence of heavy metal accumulations on lichen secondary metabolism. Thalli of Hypogymnia physodes were transplanted for 6 months to the Cracow-Silesia industrial region. Based on heavy metal accumulations in lichen, two of the investigated sites were classified as highly polluted. The highest concentrations of Cd, Pb, and Zn were found in lichens transplanted in the vicinity of a Zn-Pb smelter. Significant accumulations of Cr and Ni were detected in Hypogymnia transplanted near a chemical industry. Physodic, physodalic, hydroxyphysodic acids, and atranorin were identified and analyzed in extracts obtained from specimen samples. The most detrimental changes were observed in lichen transplanted into the vicinity of a chemical industry producing chromium, phosphor, and sulfur compounds that contained 340-fold higher Cr levels than control thalli. Decreases in the levels of physodic acid, hydroxyphysodic acid, and atranorin were detected, and one additional polar compound (probably product of degradation of lichen acids) appeared in the extract. The content of physodalic acid increased in every thalli sample transplanted, suggesting a possible role of this compound in defense against stress caused by accumulated pollutants. The levels of physodic acid decreased in thalli from both of the most polluted sites compared to those of the controls--but were not changed in thalli transplanted to less polluted sites. Our results illustrate that lichen compounds are sensitive to heavy metal accumulation and could be used as biomarkers in environmental studies.

Environmental Monitoring↗
PubMed1991

Role of metabolites in propanil-induced hemolytic anemia.

Hemolytic anemia and methemoglobinemia induced by exposure to certain arylamines, such as aniline and dapsone, are known to be mediated by their N-hydroxylamine metabolites. The arylamide propanil (3,4-dichloropropionanilide), a herbicide used extensively in rice fields, is also thought to induce methemoglobinemia through the action of metabolites. However, the hemolytic potential of this compound has not previously been reported. The present studies were undertaken to determine the hemolytic potential of propanil, and, if positive, the role of metabolites in this hemotoxicity. The survival of previously administered 51Cr-labeled erythrocytes in rats was reduced in a dose-dependent manner by ip administration of both propanil and its deacylated metabolite, 3,4-dichloroaniline (ED50 for both ca. 1.8 mmol/kg). When labeled erythrocytes were exposed in vitro to propanil or 3,4-dichloroaniline and then readministered to rats, no decrease in erythrocyte survival was observed, which indicated that these compounds were not direct-acting hemolytic agents. In contrast, erythrocyte survival was markedly reduced by ip administration or in vitro exposure to N-hydroxy-3,4-dichloroaniline. In addition, N-hydroxy-3,4-dichloroaniline was detected in the blood of propanil-treated rats in amounts sufficient to account for the hemolytic activity of the parent compound. These data indicate that N-hydroxy-3,4-dichloroaniline mediates propanil-induced hemolytic anemia, and that occupational exposure to propanil may result in an increased risk of hemolytic episodes.

Anemia, Hemolytic↗
PubMed2005

Chromium(VI) sorptive removal from aqueous solutions by nanocrystalline akaganèite.

In this study, akaganeite (beta-FeO(OH)) an ironoxyhydroxide material, was used as a low-cost potential adsorbent for the removal of hexavalent chromium from aqueous solutions. The influence of agitation speed, solution pH, initial chromium concentration, sorbent concentration and temperature were evaluated at batch kinetic runs. It was shown that the solid diffusion model, in comparison to simple reaction kinetic models, described better the sorption kinetics. Freundlich and Frumkin isotherm best fitted the equilibrium results. Akaganeite presented a sorption capacity approximately 80 mg Cr(VI) g(-1), under the conditions studied. Flotation was used as a downstream process for the effective removal of the loaded material.

Adsorption↗