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Results for “Chromium Compounds”

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PubMed2004

Chromium removal from aqueous solution by the ferrite process.

This research summarises the results of the study on the removal of chromium by applying the ferrite process to the solutions obtained from two different Cr(VI) reduction processes utilising sodium sulphite and ferrous sulphate as reducing agents. For both solutions containing trivalent chromium ions, the optimum treatment conditions were determined. The generated sludges were characterised by XRD analysis and physical tests. In addition, to explore the dissolution properties of the sludges obtained, they were contacted with the solutions of sulphuric, citric, tartaric, oxalic and ascorbic acids and EDTA. Also, the sludge samples were subjected to standard toxicity characterisation leaching procedure (TCLP) test of USEPA in order to determine the pollution potential. An efficient Cr(III) removal (about 100%) in the solution from the Cr(VI) reduction process utilising sodium sulphite as reducing agent was achieved when the solution was treated at pH 9 and 50 degrees C for 60 min in the presence of Fe2+/Cr3+ weight ratio of 16. For the other Cr(III) solution prepared from Cr(VI) reduction by ferrous sulphate, a Fe2+/Cr3+ weight ratio of 17.9 at the same conditions was found to produce complete removal of Cr(III). It was determined that the spynel chromium-iron compounds obtained in the process were in the form of chromite (Cr2FeO4). Dissolution experiments and TCLP tests show that the concentrations of the chromium dissolved from both sludges were below the limit given as 5 mg l(-1) by USEPA. The results showed that Cr(III) removal through ferrite process provides the advantages that the sludges generated are non-voluminous, easily separable and environmentally stable.

Chromium↗
PubMed1995

Characterization of the pre-mRNA binding site for yeast ribosomal protein L32: the importance of a purine-rich internal loop.

The structure of the RNA binding target for Saccharomyces cerevisiae ribosomal protein L32 was examined using chemical and enzymatic probes as well as thermodynamic methods. In vivo, the production of yeast RPL32 is regulated by a feedback mechanism whereby RPL32 binds to the 5' end of its transcript and inhibits splicing. The binding site of ribosomal protein L32 on the L32 RNA transcript can be reduced to fewer than 30 nucleotides which compromise a stem-internal loop-stem structural motif. The internal loop is closed by a potential G-U pair, is asymmetric and contains mostly purines. The existence of the two helical regions was confirmed by chemical and enzymatic probing. The reactivity of the loop region suggests a structure intermediate between that of single and double-stranded RNA. Base stacking continues into the loop, but two loop bases are extremely reactive to chemical agents. The interaction between the model RNA and the protein is specific and has a dissociation constant of approximately 10 nM. Several of the loop bases are critical for protein binding, as demonstrated by mutational data and chemical protection and modification interference studies. The internal loop destabilizes the RNA, and allows the RNA to melt in an all-or-none fashion.

Aniline Compounds↗
PubMedDate not supplied

Biomonitoring of chromium(VI) deposited in pulmonary tissues: pilot studies of a magnetic resonance imaging technique in a post-mortem rodent model.

The biomonitoring of individuals exposed to chromium(VI) by inhalation is often based on determinations of chromium in body fluids such as blood, plasma or urine, or on assessments of DNA damage in non-lung surrogate tissues such as peripheral blood lymphocytes. These techniques are of some use as biomarkers of internal exposure or biological effect, mainly in the case of soluble chromium(VI) compounds, but they provide at best only indirect information about chromium(VI) concentrations in the main target organ of interest - the lung. An urgent need exists for a non-invasive technique to permit the visualization and quantification of chromium(VI) in the lung of exposed humans. This study details the development of a lung imaging technique based on the detection of paramagnetic chromium using magnetic resonance imaging (MRI). The intracellular reductive conversion of chromium(VI) is a crucial bioactivation step in its carcinogenicity, and the MRI method described here relies on the conversion of non-paramagnetic (MRI 'silent') chromium(VI) to detectable paramagnetic species such as chromium(III). Initial studies with chromium(III) revealed that a range of 2.5-5 microg chromium(III) instilled in rat lung is considered to be the lower limit of detection of this method. It was possible to demonstrate the presence of 30 microg chromium(VI) in our post-mortem rat model. The ultimate objective of this work is to determine whether this technique has applicability to the biomonitoring of chromium(VI) inhalation exposures that result in internalized lung doses in human subjects.

Animals↗
PubMed2001

Cr(Salen)-catalyzed addition of 1,3-dichloropropene to aromatic aldehydes. A simple access to optically active vinyl epoxides.

[reaction: see text]. Chiral Cr(Salen) complex (1) prepared in situ from CrCl3 promotes the enantioselective addition of 1,3-dichloropropene to aromatic aldehydes in the presence of Mn as the stoichiometric reductant and Me3SiCl as a scavenger. The resulting 1,2-chlorohydrins obtained in good enantiomeric and diastereoisomeric excesses can be easily transformed into the corresponding chiral vinyl epoxides.

Aldehydes↗
PubMed1995

Effects of mixed silane coupling agent on porcelain tooth material and various dental alloys.

Mixed salines, 3-methacryloxypropylsilytriisocyanate and 3-mercaptopropyltrimethoxysilane, were used as primers for adhesion of poly(methyl methacrylate) to porcelain teeth, precious alloys and nonprecious alloys. After thermocycle testing, the mean bond strength of the resin to porcelain, silver alloys and stainless steel were excellent. The fracture patterns of porcelain teeth after thermocycling followed by adherent testing were similar to those of specimens subjected to 48-hour water immersion at 37 degrees C. Two specimens failed cohesively in the porcelain and the other specimens failed in the resin. The mixed primer had no effect on cobalt-chromium alloy specimens.

Boron Compounds↗
PubMedDate not supplied

[In vitro exposure of U937 cells to potassium dichromate: study of apoptosis].

The aim of our study is to evaluate the genotoxic damage of cells treated with different concentrations of potassium dichromate. For this reason we have utilised U937 cells, a cellular line derived from acute promyelocytic leukaemia. Our results show that the minimum concentration of potassium dichromate induces apoptosis in the U937 cells and is of 600 microM, already after 12 hours, the cells treated with potassium dichromate with a concentration of 500 microM presented an apoptosis of 27% while the respective control showed a base apoptosis of 9.5%. Our experimental data indicate that the model adopted by us, may be a valid instrument to study the cytotoxic effects of compounds containing Chromium. In particular we have evidenced a clear genotoxic effect of these compounds demonstrated by a significant increase of the apoptosis percentage which is time and dose dependent.

Apoptosis↗
PubMed2002

Stereocontrolled [3 + 2] annulations with arene chromium tricarbonyl complexes: construction of spirocyclic compounds related to fredericamycin A.

[reaction: see text] An efficient method has been developed for the stereocontrolled construction of polycyclic and spirocyclic compounds, including the spirocyclic core of the antitumor agent fredericamycin A. The strategy involves a one-pot aldol addition/Brook rearrangement/cyclization sequence beginning from arene chromium tricarbonyl complexes and can formally be described as a [3 + 2] annulation.

Antibiotics, Antineoplastic↗
PubMed1989

Cytotoxic and neoplastic transforming effects of industrial hexavalent chromium pigments in Syrian hamster embryo cells.

Twenty eight moderately water-soluble to insoluble chromium (VI) compounds, such as zinc and lead chromate, industrial and laboratory synthesized pigments, and the analytical reagents strontium, barium and calcium chromate, were physicochemically characterized and studied for cytotoxicity and morphological transformation in cultured Syrian hamster embryo (SHE) cells. In vivo validation of malignancy of transformed SHE cells was performed. A high physicochemical diversity among the complex chromium pigments was revealed. The solubility of the compounds was greatly increased after incubation in a complete medium and even higher under cell culture conditions. The cytotoxic effects appeared to be due principally to extracellular solubilized chromium because the most solubilized compounds. Zn, Ca and Sr chromates, were equitoxic at about the same Cr concentration treatment and 8-fold more cytotoxic than less soluble compounds such as some Pb chromates and Ba chromate. However, certain physicochemical properties of lead chromate pigments could also influence their cytotoxic activity. All test compounds were, in a dose-dependent manner, efficient in inducing morphological transformation of SHE cells. Many of the Cr pigments, although physicochemically different, were similarly effective in transformation induction. Nevertheless, compounds among Zn and Pb chromates had various transforming potencies. Ba chromate was the least active in inducing transformation. Certain physicochemical properties could mediate the transforming activity but no particular relationship could be established between any one of the physicochemical parameters and the transforming potency. Cloned morphologically-transformed colonies of SHE cells were grown in soft agar medium and showed true neoplastic behaviour by tumour formation in syngeneic animals. These results show that various chromate pigments containing either Zn or Pb, of medium to very low aqueous solubility, induced neoplastic transformation of SHE cells.

Animals↗
PubMedDate not supplied

Mechanism of chromium(VI) carcinogenesis. Reactive intermediates and effect on gene expression.

Since chromium(VI) is unreactive toward DNA under physiological conditions in vitro, the ability of carcinogenic chromium(VI) compounds to damage DNA depends on the presence of cellular redox components that reduce chromium(VI) to reactive species capable of interacting with DNA. We have examined the role of glutathione and hydrogen peroxide in chromium(VI)-induced DNA damage in vitro. Upon reaction with chromium(VI), glutathione produced chromium(V) and glutathione thiyl radical reactive intermediates, whereas hydrogen peroxide produced chromium(V) and hydroxyl radical. Reaction of DNA with chromium(VI) in the presence of glutathione resulted in binding of chromium and glutathione to DNA with little or no DNA strand breakage. Reaction of DNA with chromium(VI) in the presence of hydrogen peroxide produced the 8-hydroxydeoxyguanosine adduct and extensive DNA strand breakage in the absence of significant Cr-DNA adduct formation. These results suggest that the nature of chromium(VI)-induced DNA damage will be strongly dependent on reactive intermediates such as chromium(V), glutathione thiyl radical, and hydroxyl radical, produced by cellular components active in chromium(VI) metabolism. In order to assess the ability of chromium(VI)-induced DNA damage to affect the normal template function of DNA, we investigated the effects of chromium(VI) on steady-state mRNA levels of various genes in chick embryo liver in vivo, and compared the effects to the levels of DNA damage observed. Chromium(VI) induced DNA-protein and DNA interstrand cross-links in chick embryo liver in vivo and suppressed the induction of 5-aminolevulinic acid synthase and cytochrome P-450 mRNA expression by porphyrinogenic drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗