Showing papers on "Chromium published in 2000"
TL;DR: In this article, Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter.
Abstract: Borohydride reduction of an aqueous iron salt in the presence of a support material gives supported zero-valent iron nanoparticles that are 10−30 nm in diameter. The material is stable in air once it has dried and contains 22.6% iron by weight. The supported zero-valent iron nanoparticles (“Ferragels”) rapidly separate and immobilize Cr(VI) and Pb(II) from aqueous solution, reducing the chromium to Cr(III) and the Pb to Pb(0) while oxidizing the Fe to goethite (α-FeOOH). The kinetics of the reduction reactions are complex and include an adsorption phase. About 10% of the iron in the material appears to be located at active surface sites. Once these sites have been saturated, the reduction process continues but at a much lower rate, which is likely limited by mass transfer. Rates of remediation of Cr(VI) and Pb(II) are up to 30 times higher for Ferragels than for iron filings or iron powder on a (Fe) molar basis. Over 2 months, reduction of Cr(VI) was 4.8 times greater for Ferragels than for an equal weigh...
1,137 citations
TL;DR: The oligopeptide chromodulin appears to play a role in an autoamplification mechanism in insulin signaling, and the molecular agent responsible for transporting chromium from mobile pools to insulin-sensitive cells is probably the metal transport protein transferrin.
Abstract: Chromium has been known to be a micronutrient for mammals for four decades, but progress in elucidating the role of chromium has proceeded slowly. However, recent studies have shed light on a potential role of chromium in maintaining proper carbohydrate and lipid metabolism at a molecular level. The oligopeptide chromodulin binds chromic ions in response to an insulin-mediated chromic ion flux, and the metal-saturated oligopeptide can bind to an insulin-stimulated insulin receptor, activating the receptor's tyrosine kinase activity. Thus, chromodulin appears to play a role in an autoamplification mechanism in insulin signaling. The molecular agent responsible for transporting chromium from mobile pools to insulin-sensitive cells is probably the metal transport protein transferrin. Chromium from the popular dietary supplement chromium picolinate enters cells via a different mechanism. Release of chromium from chromium picolinate for use in cells requires reduction of the chromic center, a process that can lead potentially to the production of harmful hydroxyl radicals.
393 citations
TL;DR: Experimental and epidemiological data, and the underlying mechanisms, point to the occurrence of thresholds in chromium(VI) carcinogenesis, as quantified in human body compartments.
Abstract: Ten years have elapsed since the International Agency for Research on Cancer (IARC) evaluated the carcinogenicity of chromium and chromium compounds. Further studies performed during the last decade have provided further epidemiological, experimental and mechanistic data which support the IARC conclusions. A wealth of results indicate that, at variance with chromium(0) and chromium(III), chromium(VI) can induce a variety of genetic and related effects in vitro. The lack of carcinogenicity of chromium(0) and chromium(III) compounds in experimental animals is well established, and only a minority of animal carcinogenicity data with chromium(VI) compounds were positive (30 out of 70, i.e. 42.9%). Moreover, most positive studies used administration routes which do not mimic any human exposure and by-pass physiological defense mechanisms. Typically, positive results were only obtained at implantation sites and at the highest dose tested. Exposure to chromium(VI) has been known for more than a century to be associated with induction of cancer in humans. Carcinogenicity requires massive exposures, as is only encountered in well defined occupational settings, and is site specific, being specifically targeted to the lung and, in some cases, to the sinonasal cavity. Increased death rates for cancers at other sites, which were occasionally reported in some epidemiological studies, were almost invariably not statistically significant, and inconsistent (being counterbalanced by other studies which apparently showed decreased rates for the same cancers). As we recently quantified in human body compartments, chromium(VI) can be reduced in body fluids and non-target cells, which results in its detoxification, due to the poor ability of chromium(III) to cross cell membranes. In target cells, chromium(VI) tends to be metabolized by a network of mechanisms leading to generation of reduced chromium species and reactive oxygen species, which will result either in activation or in detoxification depending on the site of the intracellular reduction and its proximity to DNA. When introduced by the oral route, chromium(VI) is efficiently detoxified upon reduction by saliva and gastric juice, and sequestration by intestinal bacteria. If some chromium(VI) is absorbed by the intestine, it is massively reduced in the blood of the portal system and then in the liver. These mechanisms explain the lack of genotoxicity, carcinogenicity, and induction of other long-term health effects of chromium (VI) by the oral route. Within the respiratory tract, chromium(VI) is reduced in the epithelial-lining fluid, pulmonary alveolar macrophages, bronchial tree and peripheral lung parenchyma cells. Hence, lung cancer can only be induced when chromium(VI) doses overwhelm these defense mechanisms. The efficient uptake and reduction of chromium(VI) in red blood cells explains its lack of carcinogenicity at a distance from the portal of entry into the body. All experimental and epidemiological data, and the underlying mechanisms, point to the occurrence of thresholds in chromium(VI) carcinogenesis.
303 citations
TL;DR: In this article, the corrosion behavior of Fe, Cr, Ni, the ferritic alloys Fe 15Cr and Fe 35Cr and the austenitic alloys Alloy 800, Alloy 825 and Alloy 600 at temperatures between 400 and 700°C using discontinuous exposures and thermogravimetric experiments.
269 citations
TL;DR: It could be inferred that chromium toxicity is not located at the level of ALA synthesis, but, probably at the ALAD activity which was more severely affected during chlorophyll biosynthesis, which resulted in reduced totalchlorophyll content.
265 citations
TL;DR: Investigation of the interaction of calf thymus DNA with Cr(VI) and Cr(III) in aqueous solution at pH 6.5 found no interaction with DNA at low anion concentrations, and the biopolymer remained in the B family structure upon chromium complexation.
259 citations
01 Sep 2000-Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment
TL;DR: Dietary exposure of the UK population to lead is falling as a result of measures taken to reduce lead contamination of the environment and food and is well below the PTWI.
Abstract: Concentrations of aluminium, arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, tin and zinc were determined in samples from the 1997 UK Total Diet Study and used to estimate dietary exposures of the general UK population. Population average dietary exposures to aluminium (3.4mg/day), arsenic (0.065mg/day), cadmium (0.012mg/day), chromium (0.10mg/day), copper (1.2mg/day), mercury (0.003mg/day), nickel (0.13mg/day), tin (1.8mg/ day) and zinc (8.4mg/day) are similar to those from previous UK Total Diet Studies and are below the appropriate PTWIs, PMTDIs and TDIs. Dietary exposure of the UK population (0.026 mg/day) to lead is falling as a result of measures taken to reduce lead contamination of the environment and food and is well below the PTWI. There has been little change in UK estimates of selenium exposure since the 1994 Total Diet Study but current estimates (0.039mg/day) are lower than those derived from earlier Total Diet Studies.
252 citations
TL;DR: In this paper, a review of reduction reactions of chromium within natural environments is presented, and the ability of enzymes to reduce chromium to hexavalent states is evaluated using both aerobic and anaerobic bacteria.
Abstract: Chromium is a redox-dynamic element that has many industrial uses. As a consequence, it is often introduced at elevated levels into the surface environment through human activity. Additionally, ultramafic rocks such as serpentinite are commonly enriched in chromium, and thus can also lead to appreciable levels of this element within soils and waters. In the trivalent state, it poses little hazard to biological activity, but, unfortunately, in the hexavalent state it is very toxic to living matter. One must therefore assess the oxidation state of Cr in a given system and determine the potential for transformation between valence states. The objective of this paper to is review and provide new insight on reduction reactions of Cr(VI) within natural environments. A number of aerobic and anaerobic bacteria demonstrate the enzymatic ability to reduce Cr(VI) to Cr(III); two species can even grow using Cr(VI) as the terminal electron acceptor in respiration. The ability to reduce chromium in itself is not eviden...
231 citations
TL;DR: The copolymerization of 1,2-cyclohexene oxide (CHO) with carbon dioxide was performed, using supercritical carbon dioxide (scCO2) as both solvent and reactant, to produce an aliphatic polycarbonate as mentioned in this paper.
Abstract: The copolymerization of 1,2-cyclohexene oxide (CHO) with carbon dioxide was performed, using supercritical carbon dioxide (scCO2) as both solvent and reactant, to produce an aliphatic polycarbonate...
222 citations
TL;DR: The comet assay did not indicate the involvement of oxidative mechanisms in the DNA-damaging activity of trivalent chromium and it is speculated that its binding to cellular ligands may play a role in its genotoxicity.
Abstract: Chromium can be found in the environment in two main valence states: hexavalent (Cr(VI)) and trivalent (Cr(III)). Cr(VI) salts are well known human carcinogens, but the results from in vitro studies are often conflicting. Cr(VI) primarily enters the cells and undergoes metabolic reduction; however, the ultimate product of this reduction, Cr(III) predominates within the cell. In the present work, we compared the effects of tri- and hexavalent chromium on the DNA damage and repair in human lymphocytes using the alkaline single cell gel electrophoresis (comet assay). Potassium dichromate induced DNA damage in the lymphocytes, measured as the increase in comet tail moment. The effect was dose-dependent. Treated cells were able to recover within a 120-min incubation. Cr(III) caused greater DNA migration than Cr(VI). The lymphocytes did not show measurable DNA repair. Vitamin C at 50 μM reduced the extent of DNA migration. This was either due to a decrease in DNA strand breaks and/or alkali labile sites induced by Cr(VI) or to the formation of DNA crosslinks by Cr(VI) in the presence of vitamin C. Vitamin C, however, did not modify the effects of Cr(III). Catalase, an enzyme inactivating hydrogen peroxide, decreased the extent of DNA damage induced by Cr(VI) but not the one induced by Cr(III). Lymphocytes exposed to Cr(VI) and treated with endonuclease III, which recognizes oxidized pyrimidines, displayed greater extent of DNA damage than those not treated with the enzyme. Such an effect was not observed when Cr(III) was tested. The results obtained suggest that reactive oxygen species and hydrogen peroxide may be involved in the formation of DNA lesions by hexavalent chromium. The comet assay did not indicate the involvement of oxidative mechanisms in the DNA-damaging activity of trivalent chromium and we speculate that its binding to cellular ligands may play a role in its genotoxicity.
217 citations
TL;DR: The experimental results show that the chromium(III) complexes bind to DNA by non-intercalative mode and major groove binding is the preferred mode of interaction for these Schiff base complexes of chromium (III).
TL;DR: In this article, Fe(II)-Fe(III) layered double hydroxysalt green rusts, recently identified as a mineral in hydromorphic soils, were evaluated as potential Fe (II)-bearing phases for hexavalent chromium reduction.
Abstract: Hexavalent chromium, a byproduct of many industrial processes, is toxic and produces mobile aqueous oxyanions, whereas Cr(III) is relatively immobile in the environment and, moreover, essential in human glucidic metabolism. For this reason, Fe(II)-Fe(III) layered double hydroxysalt green rusts, recently identified as a mineral in hydromorphic soils, were evaluated as potential Fe(II)-bearing phases for hexavalent chromium reduction. Both considered synthetic varieties, the hydroxysulfate GR(SO{sub 4}{sup 2{minus}}) and the hydroxychloride GR(Cl{sup {minus}}), proved to be very reactive; their interaction with potassium chromate solutions leads to the rapid and complete reduction of Cr(VI) into Cr(III). The Cr(III)-bearing solid phase, studied by X-ray diffraction, Moessbauer, X-ray photoelectron, and Raman spectroscopies, was determined to be a poorly ordered Cr(III)-Fe(III) oxyhydroxide, similar to the 2 the line ferrihydrite. The comparison between the experimental redox potential and pH values for a theoretical equilibrium diagram bearing Cr and Fe phases indicated that the solubility of this solid solution, which may govern the behavior of chromium in the environment, is of the same order as that of pure Cr(OH){sub 3}.
TL;DR: In this paper, the kinetics of reduction and oxidation of soluble chromium in various soils (peat, clay, sand, and luvi-chromic cambisols) were studied at constant soil moisture and constant temperature.
Abstract: The kinetics of reduction and oxidation of soluble chromium in various soils (peat, clay, sand, and luvi-chromic cambisols) were studied at constant soil moisture and constant temperature. A total ...
TL;DR: Magnetotransport measurements were made on patterned, (110) oriented, thin films grown by the high-pressure, thermal decomposition of ${\mathrm{CrO}}_{3}$ onto rutile substrates as mentioned in this paper.
Abstract: Magnetotransport measurements were made on patterned, (110) oriented ${\mathrm{CrO}}_{2}$ thin films grown by the high-pressure, thermal decomposition of ${\mathrm{CrO}}_{3}$ onto rutile substrates. The low-temperature Hall effect exhibits a sign reversal from positive to negative as the magnetic field is increased above 1 T, which may be interpreted within a simple two-band model as indicating the presence of highly mobile $({\ensuremath{\mu}}_{h}=0.25{\mathrm{m}}^{2}/\mathrm{V}\mathrm{}\mathrm{s})$ holes as well as a much larger number of less mobile electrons $(n=0.4$ electrons/Cr). Between 50 and 100 K, the field at which the sign reversal occurs rapidly increases and a contribution from the anomalous Hall effect becomes significant, while the large, positive transverse magnetoresistance (MR) observed at low temperatures changes over to a predominantly negative MR. These changes correlate with a thermally activated dependence in the resistivity of the form ${T}^{2}{e}^{\ensuremath{-}\ensuremath{\Delta}/T}$ with $\ensuremath{\Delta}\ensuremath{\approx}80\mathrm{K},$ reflecting the lack of temperature dependence in the resistivity at low temperatures and a ${T}^{2}$ behavior above 100 K. The high mobilities at low temperature which result in the observed positive MR reflect the suppression of spin-flip scattering expected for a half-metallic system. However, the changes in magnetotransport above the temperature $\ensuremath{\Delta}$ must be due to the onset of spin-flip scattering, even though ${k}_{B}\ensuremath{\Delta}$ is much less than the expected energy gap in the minority spin density of states. The significance of $\ensuremath{\Delta}$ is discussed in terms of recent models for another half-metallic system, the perovskite manganites, and the possible formation of ``shadow bands.''
TL;DR: In this article, the authors investigated the deposition processes of chromium species for the system chromia-forming alloy metallic interconnect/Sr-doped LaMnO 3 (LSM) electrode/3 mol % Y 2 O 3 -ZrO 2 (TZ3Y) electrolyte under various conditions at 900°C.
Abstract: Deposition processes of chromium (Cr) species for the system chromia-forming alloy metallic interconnect/Sr-doped LaMnO 3 (LSM) electrode/3 mol % Y 2 O 3 -ZrO 2 (TZ3Y) electrolyte have been investigated under various conditions at 900°C. Deposition of Cr species preferentially occurred on the zirconia electrolyte surface under both cathodic (O 2 reduction) and anodic (O 2 oxidation) polarization, and formed deposit rings at the edge of the LSM electrode. The deposit ring was ca. 60 μm wide after cathodic polarization for 50 h and ca. 89 μm for 129 h. Cr was not detected on the surface of the LSM electrode or inside the electrode body under the conditions studied. In the absence of polarization potentials, Cr deposits were also found on the zirconia electrolyte surface heated at 1100°C but not at 900°C. In all cases, energy despersive spectrometry analysis indicated that deposits mainly consisted of Cr and/or Cr-Mn, indicating the formation of Cr 2 O 3 and (Cr,Mn) 3 O 4 -type spinel phases. The results clearly demonstrated that the deposition of Cr species at the LSM electrode/TZ3Y electrolyte is not dominated by electrochemical reduction of high valent Cr vapor species to Cr 2 O 3 in competition with O 2 reduction. The driving force for the Cr deposition processes is most likely related to the Mn species, in particular the Mn 2+ ions, generated under polarization potentials or at high temperatures. The proposed deposition mechanism is consistent with the electrochemical behavior of LSM electrodes in the presence of chromia-forming alloy interconnect.
TL;DR: In this article, the effect of support on the catalytic activity of Cr2O3/SiO2 catalysts was investigated in the oxidative dehydrogenation of ethane into ethylene by carbon dioxide.
Abstract: The oxidative dehydrogenation of ethane into ethylene by carbon dioxide over an unsupported Cr2O3 and several supported Cr2O3 catalysts on metal oxides such as Al2O3, SiO2, TiO2, and ZrO2 was investigated and the effect of support on the catalytic activity was studied. The unsupported Cr2O3 shows medium catalytic activity in this reaction; the support will exert a quite different effect on catalytic behavior. The catalytic activity varies with the nature of supports. Cr2O3/SiO2 catalysts exhibit an excellent performance in this reaction. Cr2O3 loading also affects the catalytic activity; 8 wt.% Cr2O3/SiO2 catalysts can produce 55.5% ethylene yield at 61% ethane conversion at 650°C. Characterization indicates that the distribution of chromium oxide on supports and surface chromium species structure are influenced by the nature of supports. The acidity/basicity and redox property of catalysts determines the catalytic activity in the dehydrogenation of ethane by carbon dioxide.
TL;DR: In this paper, the authors investigated the pretreatment of a tannery wastewater, typified by the mixed effluent from tannery operations, and demonstrated 41.5% removal of total chemical oxygen demand (COD), 83.2% of chromium and 76.1% of suspended solid after 3h of plain settling.
TL;DR: Although Cr(VI) did not have a significant effect on C source utilization, sulphate reduction was severely inhibited by 500 µmol−1 Cr( VI) and only ca 10% of the sulphate reducing activity detected in control biofilms occurred in the presence of Cr(II).
Abstract: The ability of sulphate-reducing bacterial biofilms to reduce hexavalent chromium (Cr(VI)) to insoluble Cr(III), a process of environmental and biotechnological significance, was investigated. The reduction of chromate to insoluble form has been quantified and the effects of chromate on the carbon source utilization and sulphate-reducing activity of the bacterial biofilms evaluated. Using lactate as the carbon/energy source and in the presence of sulphate, reduction of 500 micromol l-1 Cr(VI) was monitored over a 48-h period where 88% of the total chromium was removed from solution. Mass balance calculations showed that ca 80% of the total chromium was precipitated out of solution with the bacterial biofilm retaining less than 10% of the chromium. Only ca 12% of the chromate added was not reduced to insoluble form. Although Cr(VI) did not have a significant effect on C source utilization, sulphate reduction was severely inhibited by 500 micromol-1 Cr(VI) and only ca 10% of the sulphate reducing activity detected in control biofilms occurred in the presence of Cr(VI). Low levels of sulphide were also produced in the presence of chromate, with control biofilms producing over 10-times more sulphide than Cr(VI)-exposed biofilms. Sulphide- or other chemically-mediated Cr(VI) reduction was not detected. The biological mechanism of Cr(VI) reduction is likely to be similar to that found in other sulphate-reducing bacteria.
TL;DR: In this paper, the kinetics and equilibrium of chromium sorption onto chitin were studied with respect to pH, particle size, initial metal ion concentration, sorbent concentration and stirring rate.
Journal Article•
TL;DR: Fungus Aspergillus niger 405 showed a good affinity for binding of Cu2+, Zn2+ and Ni2+ in single and multicomponent-equimass solution, while in multi-component solution it occurred only for copper and zinc.
Abstract: Fungal mycelium pellets of Aspergillus niger 405 has been used for adsorption of different metals. The biosorption of copper(II), zinc(II), nickel(II) and chromium(VI) is being studied over a range off metal ion concentrations, adsorption time, pH and co-anions. The process of uptake obeyed both the Langmuir and Freundlich isotherms. The results showed better biosorption for the first three metal ions between pH 4 and 6. On the contrary, pH values over a range of 3 to 7 had no influence on sorption of chromium. Comparison of metal uptake in single and multi-component aqueous solutions of Cu-Zn-Ni-Cr have been also undertaken. Fungus Aspergillus niger 405 showed a good affinity for binding of Cu2+, Zn2+ and Ni2+ in single and multicomponent-equimass solution, while in multi-component solution it occurred only for copper and zinc.
TL;DR: The investigations reveal that the process of decolorization is concomitant with the exponential growth phase of the fungus and has requirement for a biodegradable substrate such as glucose and suggests that dye uptake process mediated by A. foetidus has a potential for large-scale treatment of textile mill discharges.
TL;DR: In this article, the corrosion protection provided on AISI 304 stainless steel by various coatings was investigated by XRD and SEM/EDS as well as its tribological properties (hardness and wear resistance).
Abstract: Nitride based hard coatings are widely used for mechanical applications. Among these coatings, chromium nitrides are especially interesting because they combine good tribological properties with relative chemical inertness. Corrosion-resistant nitrogen-doped chromium thin films were deposited by using an industrial magnetron reactive sputtering device. A precise control of the composition has permitted separate synthesis of the defined compounds that exist in the binary diagram Cr–N: Cr 2 N and CrN. Potentiodynamic methods were used to investigate the corrosion protection provided on AISI 304 stainless steel by various coatings. At the same time, coating microstructure was investigated by XRD and SEM/EDS as well as its tribological properties (hardness and wear resistance). The CrN coatings exhibit the higher wear resistance whereas the Cr 2 N films show the better hardness. Cr 2 N coatings or CrN coatings have an inert intrinsic behaviour either in acidic or in chloride solutions. However, their capability of protecting the substrate from any corrosion is limited due to defects and porosity. However, as a function of deposition parameters, these coatings can enhance the substrate lifetime in aggressive environments.
TL;DR: The proposed method was applied successfully to the determination of Cr(III) and Cr(VI) in spiked and river water samples and recovery of the chromium was 96.3+/-0.2% at 95% confidence level.
TL;DR: In this paper, the authors assess the types of rocks and the geochemical processes responsible for the chromium presence in the water in the Leon Guanajuato Valley, Central Mexico.
TL;DR: A Gram-negative bacterium was isolated from a chromium-contaminated site that was capable of reducing hexavalent chromium to an insoluble precipitate, thereby removing this toxic chromium species from solution, and was a pseudomonad with high similarity to Pseudomaonas synxantha.
Abstract: A Gram-negative bacterium (CRB5) was isolated from a chromium-contaminated site that was capable of reducing hexavalent chromium to an insoluble precipitate, thereby removing this toxic chromium species from solution. Analysis of the 16S rRNA from the isolate revealed that it was a pseudomonad with high similarity to Pseudomaonas synxantha. CRB5 was tolerant to high concentrations of chromate (500 mg l(-1)) and can reduce Cr(VI) under aerobic and anaerobic conditions. It also exhibited a broad range of reduction efficiencies under minimal nutrient conditions at temperatures between 4 degrees C and 37 degrees C and at pH levels from 4 to 9. As reduction increased, so did total cellular protein, indicating that cell growth was a requirement for reduction. Under low nutrient conditions with CRB5 or when using non-sterile contaminated groundwater from the site, reduction of Cr(VI) was followed by a increase in solution turbidity as a result of the formation of fine-grained Cr(III) precipitates, most probably chromium hydroxide mineral phases such as Cr(OH)3. Chromium adsorption and precipitation, as observed by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM/EDS), revealed that the surfaces of the cells were uniformly stained with bound Cr(III) and amorphous precipitates (as determined by selected area electron diffraction; SAED). A mass balance of chromium in a batch bioreactor revealed that up to 30% of the total Cr was as settable precipitates or bound to cells.
TL;DR: In this article, the authors used soft X-ray core-level photoemission and adsorption spectroscopies to study the reaction of aqueous sodium chromate solutions (50μM Na 2 CrO 4, pH 6 and 8.5) with clean surfaces of magnetite (111) prepared under UHV conditions.
TL;DR: Although there is no direct evidence of chromium deficiencies in humans, dietary supplements exist to provide supraphysiological doses of absorbable chromium3+.
Abstract: If chromium is an essential metal it must have a specific role in an enzyme or cofactor, and a deficiency should produce a disease or impairment of function. To date, no chromium-containing glucose tolerance factor has been characterized, the purpose of the low-molecular-weight chromium-binding protein is questionable, and no direct interaction between chromium and insulin has been found. Furthermore, chromium3+ is treated like the toxic metals arsenic, cadmium, lead and mercury in animals. Chromium3+ may be involved in chromium6+-induced cancers because chromium6+ is converted to chromium3+ in vivo, and chromium3+ is genotoxic and mutagenic. Although there is no direct evidence of chromium deficiencies in humans, dietary supplements exist to provide supraphysiological doses of absorbable chromium3+. Chromium3+ may act clinically by interfering with iron absorption, decreasing the high iron stores that are linked to diabetes and heart disease. If so, this would make chromium3+ a pharmacological agent, not an essential metal.
TL;DR: Chromium is readily transferred from transferrin to apoLMWCr at near neutral pH and reduction of the chromic center of Cr(pic)3 may be required for the supplement to release chromium; thus, release of chromium is related to a mechanism by which Cr (pic) 3 may generate hydroxyl radicals in cells.
Abstract: A recent model for the role of chromium in insulin signaling requires that the oligopeptide low-molecular-weight chromium-binding substance (LMWCr) tightly bind four chromic ions before the oligopeptide obtains a conformation required for binding to the tyrosine kinase active site of the insulin receptor. To test this model, the chromium-binding constant of LMWCr was determined, and the ability of LMWCr to remove chromium from Cr2-transferrin and the nutritional supplement chromium picolinate, Cr(pic)3, was examined. These results are consistent with the model of the mode of action of LMWCr; a Hill study indicates the four chromic ions bind to apoLMWCr in a highly cooperative fashion (n =3.47) with a binding constant of 1.54x 10(21). Chromium is readily transferred from transferrin to apoLMWCr at near neutral pH. The results also suggest that reduction of the chromic center of Cr(pic)3 may be required for the supplement to release chromium; thus, release of chromium is related to a mechanism by which Cr(pic)3 may generate hydroxyl radicals in cells.
TL;DR: In this article, the first homogeneous model system for 1,3,5-triazacyclohexane complexes of the Phillips catalyst has been presented, which is based on the MAO activation.