Chromium biologically active complexes

The nature of the anion making up the Cr(III) salt, as well as the gastrointestinal tract contents and the nutritional status of the animal, are important determinants of efficiency of absorption from the gastrointestinal tract. For example, oxalates are better absorbed than phytates (Chen et al. 1973). There is a suggestion that biologically active complexes of Cr(III) are even better absorbed, perhaps to the extent of 10%-25% (Mertz and Roginski 1971). Zinc status also influences chromium absorption (Hahn and Evans 1975). Both Cr(III) and Cr(VI) salts are better absorbed in the fasting than in the fed state (Mackenzie et al. 1959). 

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... 

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. 

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. 

METHODS OF CHARACTERIZATION OF BIOLOGICALLY ACTIVE CHROMIUM COMPLEXES OR COMPLEXES WITH BIOMOLECULES... 

Biaryls with axial chirality are potentially important as chiral ligands for asymmetrical reactions and also as intermediates for synthesizing biologically active natural biaryl compounds, for example, michellamine in Eq. 66. (ii -Disubstituted arene)chromium tricarbonyl complexes exist in two enantiomeric forms based on planar chirality. Biaryl coupling provides a new approach to synthesizing both optically pure atropisom-ers starting from a single chiral arene chromium complex (Eq. 75). ... 

Levina A, Mulyani I, Lay PA. 2007. Redox chemistry and biological activities of chromium(III) complexes. Jn Nutritional biochemistry of chromium(III). Ed JB Vincent. Amsterdam Elsevier Science. 

Finally, it should be noted that this chemistry may have biological relevance. Several metalloenzymes are believed to contain more than one metal ion bound at the active site. One relevant example is the glucose tolerance factor (GTF) which is important for the metabolic degradation of glucose (398-401). GTF is a low-molecular-weight protein which contains chromium(III). Its structure is not known, but it has been suggested that the active site contains a dinuclear chromium(III) complex (401). The fact that hydroxo-bridged dinuclear chromium(III) complexes exhibit reactions which are often very fast compared with those observed for the parent mononuclear species seems to support such a proposal. 

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