Cadmium amino acid complexes

Keywords amino acids cadmium complexes crystal structures nucleobases thiolates vitamins... 

Keywords amino acids cadmium(II) peptides histidme cysteine thiolate ligands stability constants octahedral complexes polynuclear complexes... 

In the case of the common peptides the comparison of the stability constants of zinc(II) and cadmium(II) complexes reveals the same trends as reported for the amino acids Favored complexation with zinc(II) in almost all cases, except for the thiolate ligands. The binding of several side chain residues may enhance the stability of cadmium(II) complexes but the extent of this stabihzation is relatively low. This is true even for the aspartyl or histidyl residues which are generally considered as the most strongly coordinating side chains in the corresponding... 

Cadmium complexes acety(acetone, 2, 372 alcohols, 5, 964 amides, 5,944 amine oxides, 5,964 amines, 5,933 amino acids, 5, 938... 

Studies of the thermodynamics of formation of complexes of zinc with 2,2 -bipyridine in the presence of halide and thiocyanate ions in DMF has been carried out.205 The zinc complexes of 2,2 -bipyridine with A-(benzenesulfonyl)glycine and A-(toluene- -sulfonyl)glycine were synthesized and infrared data implied a structural analogy with the cadmium complexes. This suggests that the zinc promotes sulfonamide nitrogen deprotonation in the amino acid ligands in the solid state.206... 

Uptake of small organic metal complexes over transport systems of organic metabolites may be possible, for example, of small organic acids like citrate or amino acids. However, only few examples of such processes have been studied so far. Increased uptake of cadmium by an alga has been observed in the presence of citrate and has been attributed to accidental transport of the metal-citrate complex over a citrate transporter [212]. Transport systems of inorganic anions may also play a role in metal transport. Silver uptake by algae was enhanced in the presence of thiosulfate. In this case, the silver thiosulfate complex was transported over a sulfate uptake system [213]. It remains to be demonstrated how widespread these processes may be for metal uptake in the aquatic environment [12]. 

There are several such toxic agents that cause considerable medical, public and political concern. Two examples are discussed here the heavy metal ions (e.g. lead, mercury, copper, cadmium) and the fluorophosphonates. Heavy metal ions readily form complexes with organic compounds which are lipid soluble so that they readily enter cells, where the ions bind to amino acid groups in the active site of enzymes. These two types of inhibitors are discussed in Boxes 3.5 and 3.6. There is also concern that some chemicals in the environment, (e.g. those found in industrial effluents, rubbish tips and agricultural sprays), although present at very low levels, can react with enhanced reactivity groups in enzymes. Consequently, only minute amounts concentrations are effective inhibitors and therefore can be toxic. It is suggested that they are responsible for some non-specific or even specific diseases (e.g. breast tumours). 

A considerable number of NQR studies have been made on zinc and cadmium complexes, for example, the 35C1, 81Br and 127I NQR spectra of a number of CdX2-polyether complexes have been reported and indicate that the compounds are dimeric in solution, with symmetrical halogen bridges between the metal atoms.69 A number of amino acids and peptide complexes of cadmium(II) have been investigated by 14N NQR spectroscopy.70... 

Complexing of zinc and cadmium by amino acids, both natural and otherwise, and of polypeptides, has been the subject of study for many years because of the importance of zinc-protein systems and the physiological effect of cadmium compounds (see Section 56.1.14). 

There are a large number of preparative, structural and physical investigations in the area of amino acid complexes of zinc and cadmium and interesting structural features are often observed. 

A very large number of amino acid complexes of zinc and cadmium have been described. Among the most recent are complexes of zinc with histidine,254-256,258 threonine,258 tyrosine,257 glutamic acid,259 DL-nor-leudne, aspartic acid261 and tryptophan262 have been described. 

Chiral ligand-exchange chromatography resolves enantiomers on the basis of their ability to complex with transition metal ions, such as copper, zinc, and cadmium, as illustrated by the separation of amino acid racemates using copper102 (Fig. 2.21). The principle of exchange is similar to that... 

This is an area which has received almost no systematic study, in spite of occasional reports indicating that metals can have substantial effects. We may mention the general spectral intensification shown when conal-bumin binds two moles of Fe (Warner and Weber, 1953), which may be explained in part by the broad-band ultraviolet absorptivity of ferric ion with various ligands (Buck et al., 1954). We have already noted (Fig. 4) the substantial spectral effects of cadmium and zinc binding by thionein (Kagi and Vallee, 1961). The strong absorptivity of the cupric complexes of amino acids around 2300 A (Spies, 1952) is also pertinent here. 

Cadmium complexes with glydne, " histidine, alanine, " DL-norleucine, valine and numerous other amino acids have been reported. A study of the interaction of dipeptides with cadmium iom has also been described. ... 

Many of the biologically active zinc metalloproteins contain a zinc(II) ion bound to one or more imidazole ligands of the amino acid residue histidine. For this reason a large number of studies over an extended period have been carried out on zinc and cadmium complexes of imidazole, substituted imidazoles, histidine and related ligands. There has also been much recent activity in this field much structural information is available. 

Cadmium, 925-1022 acute poisoning, 1000 chronic poisoning, 1000 metallothioneins, 1021 poisoning therapy, 1001 toxicology, 999 Cadmium complexes alcohols, 964 amides, 944 amine oxides, 964 amines, 933 amino acids, 938... 

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