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PubMed2004

Reduction of Cr(VI) in presence of some amino compounds.

The rate of reduction of Cr(VI) to Cr(III) in 0.05 M K2Cr2O7 has been studied and was found to be first order. The rate of reaction was measured in the absence of amino compounds and in the presence of o-nitroaniline, p-nitroaniline, m-toulidine, p-chloroaniline, and o-bromoaniline at four different temperatures. The rate of reaction was found to decrease with the addition of amines. Thermodynamic parameters DeltaG*, DeltaH*, and DeltaS* were calculated from the study.

Aniline Compounds↗
PubMed2005

Sorption of divalent metal ions on CrPO4.

The divalent metal ion sorption (Cu(2+), Cd(2+), Ni(2+), and Pb(2+)) on chromium phosphate (CrPO(4)) was studied as a function of pH, temperature, and concentration of metal ions. The sorption of metal ions is observed to increase with the increase in pH, temperature, and concentration of metal ions in solution. The mechanism of sorption is found to be the exchange of the hydrolyzed metal cations with the protons from solid at high temperature. The sorption at low temperature is found to be accompanied by the precipitation of the corresponding metal phosphates such as Pb(3)(PO(4))(2).

Adsorption↗
PubMed2005

Catalytic activity of active carbons impregnated before activation of pinewood sawdust and nutshells to be used on the control of atmospheric emissions.

This work analyses the catalytic activity of metal oxides impregnated on activated carbons to be used for the complete oxidation of benzene present in atmospheric emissions. When the impregnation step is performed before CO2 activation, the knowledge about catalytic activity is as yet quite scarce, being the main objective of the study here reported. Pinewood sawdust and nutshells were recycled to produce the activated carbons. Non-expensive metal oxides (CoO, Co3O4 and CrO3) were impregnated. When the impregnation was performed before CO2 activation instead of after activation, at 523 K the kinetic constants were 3.6-4.3 times higher for sawdust carbons, and 2.1-2.7 times higher for nutshell carbons, due to a better metal oxide dispersion on higher mesopore areas and on wider micropores. With Co3O4 as catalyst, a benzene conversion of 90% was reached at a lower temperature than with CrO3 (472 and 558 K, respectively). The carbons impregnated before CO2 activation allowed very good conversions at temperatures that guarantee carbon stability (lower than 575 K). The results obtained led to the conclusion that activated carbon is a suitable support for metal oxide catalyst aiming the complete oxidation of benzene, mainly if an adequately porous texture is induced, proceeding to the impregnation before CO2 activation.

Air Pollution↗
PubMed2005

Recycling Fe(III)/Cr(III) hydroxide, an industrial solid waste for the removal of phosphate from water.

Industrial solid waste, Fe(III)/Cr(III) hydroxide, was investigated to assess the capacity for the removal of phosphate from aqueous solution. Langmuir and Freundlich isotherms were used to model the adsorption equilibrium data. The system follows both isotherms. Adsorption capacity was found to be 6.5 mg/g. Kinetic studies show that the adsorption obeyed second order kinetics. Thermodynamic parameters were evaluated. Overall adsorption process was endothermic and spontaneous. Optimum pH for phosphate adsorption was found to be 4.0. Effect of coexisting anions has also been examined.

Adsorption↗
PubMed2005

Chromium recovery from chrome shaving generated in tanning process.

In this study, the chromium recovery conditions in the form of soluble chromate from chrome shaving (chromium-containing solid waste) by oxidation with air, oxygen and Na2O2 were investigated and basic Cr(III) sulphate solution using in the tanning was prepared from the chromate obtained. It has been determined that the oxidation agent is the most effective parameter affecting the chromate formation. While maximum oxidation yields in air and oxygen atmosphere at 850 degrees C were found to be 23.02 and 30.41%, respectively, the highest chromium recovery efficiency in the form of chromate (99.45%) occurred in the presence of eight times Na2O2 with respect to stoichiometric amount of chromium. The chromate generated in Na2O2 oxidation process where 99.45% of chromium in the chrome shaving can be recovered was leached with distilled water and pregnant chromate solution was prepared. The chromate ions in this solution were reduced by using Na2SO3 and Cr(III) sulphate solution was obtained.

Chromium↗
PubMed2006

Sulphur mustard vapor breakthrough behaviour on reactive carbon systems.

Breakthrough behaviour of sulphur mustard, the deadliest of persistent chemical warfare agents, on carbon systems such as NaOH/CrO(3)/C, NaOH/CrO(3)/EDA/C and RuCl(3)/C has been studied and the data were compared with that of active carbon. Effects of bed lengths of carbons on breakthrough time have also been correlated. Thereafter, the effects of flow rate of air-sulphur mustard mixture, concentration and temperature on the kinetic parameters such as rate constant (k(v)) and kinetic saturation capacity (W(e)) were analyzed and interpreted by means of modified Wheeler equation. Rate constant was found to be increasing while W(e) was found to be invariable with the increase in air flow rate. Both k(v) and W(e) decreased with the increase of temperature, however, no significant effect on W(e) and k(v) was observed due to concentration change (0.3-0.6 mg/l). The values of kinetic saturation capacity were used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).

Air Pollutants↗
PubMed2006

Biosorption of Cr(III) from aqueous solution using algal biomass spirogyra spp.

In the present investigation, a fresh water green algae spirogyra spp. was used as an inexpensive and efficient biosorbent for Cr(III) removal from aqueous solution. The algal biomass was treated with 0.1M NaOH, 0.2M CaCl(2) and 5% HCHO. The biosorption efficiency was compared with untreated biomass. The effects of various physico-chemical parameters were studied, e.g. pH 3.0-6.0, initial metal ions concentration 20-150mgL(-1), algal dose 1.0-3.0gL(-1), and contact time 15-180min, respectively. Biosorption of Cr(III) is highly pH dependent. Maximum 81.02% adsorption of Cr(III) was observed with 0.2M CaCl(2) treated biomass at pH 5.0. Removal of Cr(III) was more than 70% in 45min of contact time with different treated and untreated algal biomass at concentration 30mgL(-1). Maximum metal uptake (Q(max)) was observed as 30.21mgg(-1) with 0.2M CaCl(2) treated algal biomass indicate good biosorbents than other treated and untreated biomass. The high values of correlation coefficient (r(2)<0.90) indicate equilibrium data of treated and untreated form of algal biomass well fitted in Freundlich than Langmuir isotherms model equations.

Adsorption↗
PubMed2004

Chromium-containing biomimetic cation triaqua-mu3-oxo-mu-hexapropionatotrichromium(III) inhibits colorectal tumor formation in rats.

The cation [Cr(3)O(propionate)(6)(H(2)O)(3)](+) has recently been found by oral or intravenous administration to increase insulin sensitivity and improve serum lipids in healthy and type 2 diabetic model rats. Serum insulin concentrations and, hence, insulin sensitivity are in part responsible for the relationship between diet and the incidence of colorectal cancer. This strongly suggested that the synthetic cation, which in vitro is able to stimulate insulin receptor tyrosine kinase activity in a fashion similar to the oligopeptide chromodulin, could influence the incidence of colorectal cancer. Consequently, the effects of the cation on the inhibition of colon tumorigenesis induced by 1,2-dimethylhydrazine in male Sprague Dawley rats were examined. Gavage administration of aqueous solutions of the complex (1000 microg Cr/kg body mass daily for 6 months) resulted in significantly decreased colon tumor incidence (P<0.003).

1,2-Dimethylhydrazine↗
PubMed2006

17O NMR study of oxo metalloporphyrin complexes: correlation with electronic structure of M=O moiety.

(17)O NMR spectroscopy of oxo ligand of oxo metalloporphyrin can be considered as an excellent means to derive information about structure, electronic state, and reactivity of the metal bound oxo ligand. To show the utility of (17)O NMR spectroscopy of oxo ligand of oxo metalloporphyrin, (17)O NMR spectra of oxo ligands of dioxo ruthenium(VI), oxo chromium(IV), and oxo titanium(IV) porphyrins are measured. For all oxo metalloporphyrins, well-resolved (17)O NMR signals are detected in far high frequency region. The (17)O NMR signal of the metal bound oxo ligand shifts high frequency in order of Ru(VI)<Ti(IV)<Cr(IV), thus the (17)O NMR chemical shift does not directly correlate with the oxo-transfer reactivity, Ti(IV)<Cr(IV)<Ru(VI). On the other hand, the (17)O NMR shift of oxo ligand correlates with the bond strength of metal-oxo bond. This suggests that the (17)O NMR signal of metal bound oxo ligand is a sensitive probe to study the nature of metal-oxo bond in oxo metalloporphyrin. The effect of the electron-withdrawing meso-substituent on the (17)O NMR shift of the oxo ligand is also investigated. With increase in the electron-withdrawing effect of the meso-substituent, the (17)O NMR signal of the oxo ligand of oxo chromium(IV) porphyrin shifts high frequency while that of dioxo ruthenium(VI) porphyrin hardly change resonance position. The changes in metal-oxo bonds induced by the electron-withdrawing meso-substituent are discussed on the basis of the (17)O NMR shifts, the strengths of the metal-oxo bonds, and the oxo-transfer reaction rates.

Chromium Compounds↗
PubMed2006

The influence of chromium chloride-containing milk to glycemic control of patients with type 2 diabetes mellitus: a randomized, double-blind, placebo-controlled trial.

The aim of this study is to evaluate the effect and safety of chromium-containing milk powder in patients with type 2 diabetes mellitus. A randomized, double-blind, placebo-controlled trial was conducted in Taiwan. A total of 60 patients with type 2 diabetes mellitus, aged 30 to 75 years, and on a dose of gliclazide sulfonylurea agent (< or =160 mg/d) for at least 3 months were enrolled. Their glycosylated hemoglobin ranged from 7.5% to 12%, fasting plasma glucose (FPG) from 140 to 250 mg/dL, and body mass index from 20 to 35 kg/m(2). The subjects were divided into 2 groups, one group to receive chromium-containing milk powder (chromium 200 microg/20 g milk powder) and the other to receive placebo twice a day for 16 weeks. Frequently sampled intravenous glucose tolerance test (IVGTT) was performed before and after treatment. The chromium group demonstrated a lower FPG and fasting insulin (-38.1 +/- 9.2 vs 63 +/- 8. 5 mg/dL and -1.7 +/- 0.2 vs 1.9 +/- 0.3 microU/mL, respectively; P < .05), especially in male patients (-41 +/- 9.2 vs 85 +/- 11.7 mg/dL and -2.7 +/- 0.2 vs 3.1 +/- 0.3 microU/mL, respectively; P < .01), at the end of the study. Lower glycosylated hemoglobin was observed in chromium-treated male patients (-1.1 +/- 0. 5 vs 0.7 +/- 0. 2; P < .05). However, there were no significant changes in other metabolic parameters (lipid profiles including total cholesterol, triglyceride, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol), except improvement of insulin resistance (homeostasis model assessment for insulin resistance and insulin sensitivity index from frequently sampled intravenous glucose tolerance test) observed in male patients (-2.1 +/- 1.1 vs -0.41 +/- 1.12 and 0.18 +/- 0.11 vs -0.15 +/- 0. 2, respectively; P < .05). There were no adverse events in both groups, except for mild complaints in the chromium group on constipation (5%) and flatulence (5%). Intake of milk powder containing 400 microg/d of chromium for 16 weeks in subjects with type 2 diabetes mellitus resulted in lowering of FPG, fasting insulin, and improvement of metabolic control in male patients.

Animals↗
PubMed2006

Biphasic kinetics in the reaction between amino acids or glutathione and the chromium acetate cluster, [Cr3O(OAc)6]+.

Kinetics for the breakdown of the trinuclear chromium acetate cluster with a series of monoprotic and diprotic amino acid ligands and with glutathione in aqueous media have been investigated spectrophotometrically at pH 3.5-5.5 and in a temperature range of 45-60 degrees C. Under pseudo-first-order conditions, reactions with these ligands exhibited biphasic kinetic behavior that can be accounted for by a consecutive two-step reaction, A-->B-->C, where A is assumed to be a forced ion pair, B an intermediate and C is the product; experimental data fit to a biexponential equation for the transformation. Rates for k(short), k(long), and k(obs) were determined by manual extrapolation of absorbance data or curve-fitting routines; associated activation parameters for each step of the reaction were calculated using the Eyring equation. Rates for the first and second steps of the reaction are on the order of approximately 10(-4) and approximately 10(-5)s(-1), respectively. The large negative values of DeltaS++ and smaller DeltaH++ in the first step indicate an associative step, while high positive values of DeltaS(double dagger) in the second step indicate dissociation. To account for the results mechanistically, the results are interpreted to be a first step of ligand exchange with a pseudo-axial aqua ligand, followed by a dissociative step involving acetate or oxo ligand displacement. The dissociative step is the rate determining step, with k(obs) approximately k(long). The results demonstrate reaction pathways that are available to the Cr(III) metal centers that may be physiologically relevant in the ligand-rich environment of biological systems. Under general conditions Cr(III) clusters may be expected to be broken down, unless some unique biological environment stabilizes the cluster. The present study has application to the processes related to Cr(III) transport and excretion, to potential mechanisms of Cr(III) action in a biological setting, and to the pharmacokinetics of Cr(III) supplements for animal and human consumption.

Amino Acids↗
PubMed2006

Ascorbate is a pro-oxidant in chromium-treated human lung cells.

The human A549 lung cell line is used in this study as a model to evaluate chromium toxicity and mutagenesis since inhalation exposure of this metal gives rise to an epidemiology that indicates the lung as a target organ of chromium toxicity. Hexavalent chromium is considered the carcinogenic form of chromium, however it must be reductively activated following uptake into cells in order to react with intracellular constituents. We have previously established that the fluorescent dyes, dichlorofluorescein (DCF) and dihydrorhodamine, are effective indicators of the reductive activation of chromium and are sensitive measures of the formation of highly reactive chromium species (RCS) intracellularly. In order to examine the role of the two common intracellular reductants, glutathione and ascorbic acid (Vitamin C) in generating RCS intracellularly, we manipulated their intracellular levels through the use of buthionine sulfoximine (BSO) or by the addition of ascorbate into the culture media. We found that the high levels of glutathione in this cancer cell line lowered endogenous oxidation levels markedly, and that, by decreasing intracellular glutathione, BSO not only generated a higher background level of endogenous intracellular oxidation but the chromium-stimulated oxidation also increased markedly. Contrary to it appellation as an anti-oxidant, ascorbic acid stimulated a strong pro-oxidant response upon chromium treatment and this pro-oxidant response was evident regardless of the levels of glutathione in the cells. Based on these results, we conclude that ascorbic acid acts as a pro-oxidant in chromium-treated cells.

Antioxidants↗
PubMed2006

Chromium picolinate positively influences the glucose transporter system via affecting cholesterol homeostasis in adipocytes cultured under hyperglycemic diabetic conditions.

Since trivalent chromium (Cr(3+)) enhances glucose metabolism, interest in the use of Cr(3+)as a therapy for type 2 diabetes has grown in the mainstream medical community. Moreover, accumulating evidence suggests that Cr(3+) may also benefit cardiovascular disease (CVD) and atypical depression. We have found that cholesterol, a lipid implicated in both CVD and neurodegenerative disorders, also influences cellular glucose uptake. A recent study in our laboratory shows that exposure of 3T3-L1 adipocytes to chromium picolinate (CrPic, 10 nM) induces a loss of plasma membrane cholesterol. Concomitantly, accumulation of intracellularly sequestered glucose transporter GLUT4 at the plasma membrane was dependent on the CrPic-induced cholesterol loss. Since CrPic supplementation has the greatest benefit on glucose metabolism in hyperglycemic insulin-resistant individuals, we asked here if the CrPic effect on cells was glucose-dependent. We found that GLUT4 redistribution in cells treated with CrPic occurs only in cells cultured under high glucose (25 mM) conditions that resemble the diabetic-state, and not in cells cultured under non-diabetic (5.5 mM glucose) conditions. Examination of the effect of CrPic on proteins involved in cholesterol homeostasis revealed that the activity of sterol regulatory element-binding protein (SREBP), a membrane-bound transcription factor ultimately responsible for controlling cellular cholesterol balance, was upregulated by CrPic. In addition, ABCA1, a major player in mediating cholesterol efflux was decreased, consistent with SREBP transcriptional repression of the ABCA1 gene. Although the exact mechanism of Cr(3+)-induced cholesterol loss remains to be determined, these cellular responses highlight a novel and significant effect of chromium on cholesterol homeostasis. Furthermore, these findings provide an important clue to our understanding of how chromium supplementation might benefit hypercholesterolemia-associated disorders.

3T3-L1 Cells↗
PubMed2006

Molecular analysis of hprt mutations induced by chromium picolinate in CHO AA8 cells.

Chromium picolinate (CrPic) is a popular dietary supplement, marketed to the public for weight loss, bodybuilding, and control of blood sugar. Recommendations for long-term use at high dosages have led to questions regarding its safety. Previous studies have reported that CrPic can cause chromosomal aberrations and mutations. The purpose of the current work was to compare the mutagenicity of CrPic as a suspension in acetone versus a solution in DMSO, and to characterize the hprt mutations induced by CrPic in CHO AA8 cells. Treatments of 2% acetone or 2% DMSO alone produced no significant increase in 6-thioguanine (6-TG)-resistant mutants after 48 h exposures. Mutants resistant to 6-TG were generated by exposing cells for 48 h to 80 microg/cm(2) CrPic in acetone or to 1.0mM CrPic in DMSO. CrPic in acetone produced an average induced mutation frequency (MF) of 56 per 10(6) surviving cells relative to acetone solvent. CrPic in acetone was 3.5-fold more mutagenic than CrPic in DMSO, which produced an MF of 16.2. Characterization of 61 total mutations in 48 mutants generated from exposure to CrPic in acetone showed that base substitutions comprised 33% of the mutations, with transversions being predominant; deletions made up 62% of the mutations, with one-exon deletions predominating; and 1-4 bp insertions made up 5% of the characterized mutations. CrPic induced a statistically greater number of deletions and a statistically smaller number of base substitutions than have been measured in spontaneously generated mutants. These data confirm previous studies showing that CrPic is mutagenic, and support the contention that further study is needed to verify the safety of CrPic for human consumption.

Acetone↗
PubMed2004

The in vitro effect of pulpal pressure and luting agent on tensile bond strength of complete cast crowns.

STATEMENT OF PROBLEM: The degree to which pulpal pressure may affect bond strength of complete cast crowns is unknown. PURPOSE: The aim of this in vitro study was to evaluate the effect of simulated pulpal pressure on the tensile bond strength of complete cast crowns luted with 2 different cements. MATERIAL AND METHODS: Forty-eight human mandibular canine teeth were cleaned and stored in saline solution. The crowns were prepared by 1 investigator, and standardization of the preparation was accomplished by fixing a dental handpiece in a parallelometer. Uniform grooves, 0.5 mm in depth, were prepared with burs with depth guides. The complete crowns were prepared with a 0.5-mm shoulder margin. Teeth were randomly divided into 2 groups of 24 teeth each (Group I and Group II). In Group I, bonding and tensile test procedures of the teeth were carried out under simulated pulpal pressure (15 cm of saline solution). In Group II, simulated pulpal pressure was not used. The roots were removed 1 mm below the cementoenamel junction to create direct communication with the pulp chamber. The remaining pulpal tissues were carefully removed, and crowns were embedded in acrylic resin. The acrylic resin was then penetrated by a stainless steel tube that connected the pulp chamber and the barrel of a disposable plastic 5-ml syringe. The pulp chambers were filled with physiological saline solution under elevated pressure to locate the area of greatest permeability on the dentinal surface. Crowns were cast (Co-Cr alloy) with a 20-mm bar to allow testing of the bond strength. Each of the 2 groups were further divided into 2 luting cement groups of 12 each (Group I, A and B, and Group II, A and B). Group IA/IIA and Group IB/IIB specimens were luted with a polycarboxylate luting cement (Poly-F Plus) and an adhesive luting cement (Superbond C&B), respectively. After storage in distilled water for 24 hours, all specimens were subjected to a tensile bond test in a universal testing machine at a crosshead speed of 0.5 mm/min until failure. The maximum load at fracture (Newton) was recorded. The results were then evaluated with 2-way analysis of variance and Tukey's honestly significant difference tests (alpha=.05). RESULTS: Simulated pulpal pressure increased the bond strength of cast complete crowns cemented with an adhesive luting agent (P=.01). No significant difference was found in the bond strength of complete cast crowns cemented with polycarboxylate cement with or without pulpal pressure. Superbond C&B adhesive luting agent showed significantly higher bond strength values for Group I (388.9+/-32.7) and Group II (300.9+/-66.8), when compared with polycarboxylate cement for Group I (221.3+/-17.3) and Group II (186.8+/-38.5) (P=.001). CONCLUSION: Simulated pulpal pressure had a positive effect on the retention of complete cast crowns when cemented with Superbond C&B adhesive luting agent. Superbond C&B significantly increased the retention of crowns in either the presence or absence of pulpal pressure.

Analysis of Variance↗
PubMed2005

Infrared (1.2-1.6 microm) luminescence in Cr4+:Yb3Al5O12 single crystal with 940 nm diode pumping.

Infrared (1.2-1.6 microm) luminescence in a ytterbium aluminium garnet (YbAG) crystal, doped with Cr (0.05at.%) ions, was investigated under CW laser diode pumping (lambda=940 nm). The Cr4+ emission band was observed with its peak at 1.34 microm and measured to be about 1.3 times with respect to Yb3+ IR luminescence (lambda=1.03 microm). We demonstrate that for the excitation wavelength of 940 nm Yb3+ ions act as sensitizers of the 3B2(3T2)-3B1(3A2) emission of Cr4+ ions. This crystal is promising as a high-efficient system for tunable laser (1.2-1.6 microm) output.

Aluminum↗
PubMed2006

Studies of the defect structures of the trigonal Cr3+-Vc centers in fluoroperovskites from EPR and optical spectra.

The EPR parameters (zero-field splitting D and g factors g(parallel), g(perpendicular)) and the first excited state splitting Delta(2E) of the trigonal Cr3+-Vc centers (Vc denotes the cation vacancy in a C3 axis) in Cr3+-doped fluoroperovskites KMgF3, KZnF3, CsCdF3, CsCaF3, RbCdF3 and BaLiF3 are studied from the high-order perturbation formulas. From the studies, the defect structures (characterized by the vacancy-induced displacements Delta x1 of Cr3+ ion and Delta x2 of the three F- ion between Cr3+ and Vc) of these trigonal Cr3+-Vc centers are determined. It is found that the signs of displacements Delta x1 and Delta x2 are consistent with the expectations based on the electrostatic interactions, and the magnitudes of Delta x1 and Delta x2 for Cr3+ in the inverse perovskite BaLiF3 are larger than those for Cr3+ in the classical perovskites. The results are discussed.

Calcium Compounds↗