Chromium biological activity

Another interesting study is the determination of the distribution of Cr valence states in human cells after in vitro exposure to soluble or particulate chromium compounds. The chromium biological activity depends strongly upon its oxidation state and solubihty. Several hexavalent chromium, Cr(VI),... 

Finally, in 1797, the Frenchman L. N. Vauquelin discovered the oxide of a new element in a Siberian mineral, now known as crocoite (PbCr04), and in the following year isolated the metal itself by charcoal reduction. This was subsequently named chromium (Greek xpco ia, chroma, colour) because of the variety of colours found in its compounds. Since their discoveries the metals and their compounds have become vitally important in many industries and, as one of the biologically active transition elements, molybdenum has been the subject of a great deal of attention in recent years, especially in the field of nitrogen fixation (p. 1035). 

It appears that chromium(III) is an essential trace element in mammalian metabolism and, together with insulin, is responsible for the clearance of glucose from the blood-stream. Tungsten too has been found to have a role in some enzymes converting CO2 into formic acid but, from the point of view of biological activity, the focus of interest in this group is unquestionably on molybdenum. 

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Under laboratory conditions, chromium is mutagenic, carcinogenic, and teratogenic to a wide variety of organisms, and Cr 6 has the greatest biological activity. However, information is lacking... 

Hexavalent chromium (Cr+6) is the most biologically active chromium chemical species, although little is known about the properties of organochromium compounds, water-soluble species, or their interactions in complex mixtures... 

Yeates, G.W., V.A. Orchard, T.W. Speir, J.L. Hunt, andM.C.C. Hermans. 1994. Impact of pasture contamination by copper, chromium, arsenic timber preservative on soil biological activity. Biol. Fertil. Soils 18 200-208. 

The synthesis and characterization of materials showing biological activity similar to that of GTF isolated from yeast is a logical objective. As already mentioned, Mertz found aqua and similar complexes of chromium to be more active than chelates with strong ligands. An exception to this was an unspecified cysteine complex,1193 prepared by C. L. Rollinson, which showed marked, but erratic, behaviour in GTF tests. Further investigation of this observation would be interesting, particularly as the crystal structure of a cysteine complex is now known.1185... 

It has been suggested that GTF is not a chromium complex.1091 This arises from the failure to isolate a biologically active Crm complex from extracts of brewers yeast grown in a medium containing added Crm. Two fractions showed biological activity, but further purification resulted in the loss of chromium and the isolation of biologically active chromium-free compounds. One of these was largely tyramine (formed from tyrosine residues), but pure tyramine does not show GTF-type properties. The activity of this fraction must therefore be due to the minor component... 

In humans and animals, chromium(ni) is an essential nutrient that plays a role in glucose, fat, and protein metabolism by potentiating the action of insulin (Anderson 1981). The biologically active form of chromium, called glucose tolerance factor (GTF), is a complex of chromium, nicotinic acid, and possibly amino acids (glycine, cysteine, and glutamic acid). Both humans and animals are capable of converting... 

Chromium(III) is an essential nutrient required for normal energy metabolism. The National Research Council recommends a dietary intake of 50-200 pg/day (NRC 1989). The biologically active form is an unidentified organic complex of chromium(ni) often referred to as GTF. Chromium(in) picolinate is a common form of chromium(III) nutritional supplementation. 

Davis CM, Sumrall KH, Vincent JB. 1996. A biologically active form of chromium may activate a membrane phosphotyrosine phosphatase (PTP). Biochemistry 35 12963-12969. 

Evans GW, Pouchnik DJ. 1993. Composition and biological activity of chromium-pyridine carboxylate complexes. J Inorg Biochem 49 177-187. 

The present overview deals with the application of Fischer chromium carbene complexes in the benzannulation reaction for the preparation of highly substituted aromatic compounds. Before focussing on specific arenes (Section 8.5), details of the mechanism are given (Section 8.2), and the scope and limitations of the reaction are defined (Section 8.3). A short description of the experimental procedure is given thereafter (Section 8.4). Finally, the contribution deals with the application of the chromium carbene benzannulation to natural compounds and molecules with biological activity (Section 8.6). 

Due to its versatility with respect to the scope and substitution pattern, both in terms of the chromium carbene and the alkyne, the benzannulation reaction has been recognized as a valuable methodology for the synthesis of complex biologically active compounds. 

Group 6B includes both chromium and molybdenum as essential trace elements. The oxidation state of Cr is of critical importance to its biological activity. The most common oxidation state is Cr3+ or Cr(III). Chromium(VI) is used in electroplating and in other industrial applications and is recognized as a carcinogen when inhaled. The essentiality of Cr was discovered when weaning rats were fed Cr-deficient diets,... 

Biological Implications of Chemical Forms. The biological availability of many trace elements is influenced by their valence state. Ferrous iron is believed to be more readily available than the ferric form, and selenium is better absorbed in its high oxidation state than in its lower ones. The organism is able to oxidize or reduce some, but not all, trace elements to their biologically active form. It is important, therefore, to determine the valence state in biological material, particularly in those cases where great differences of availability or toxicity exist, as in the case of chromium or of mercury. 

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