Vitamins cadmium complexes

Vibrational spectroscopy cadmium complexes, 929 zinc complexes, 929 Vitamin... 

The total synthesis of vitamin Bn is arguably the most difficult challenge so far presented to synthetic organic chemists. It is therefore surprising that the application of a photocyclization reaction to a solution of this problem has escaped the attention of photochemistry reviewers. Irradiation of the optically active seco-corrin cadmium complex (120) in methanol gave the corrin (121), isolated as its Co complex, with a stereoselectivity of 95% (Scheme 38). Model... 

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

To date, only some hydrosoluble vitamins are known to interact as ligands with metal ions and, with some exceptions, very few solid phase stmctures of these complexes have been obtained (Scheme 2). Indeed, only a few cadmium complex structures have been described. 

In the following paragraphs, we will describe the most significant aspects of the known structures of cadmium complexes with vitamins, as obtained by X-ray diffraction analyses. 

Thiamine is a monovalent cation with a structure that corresponds to a substituted pyrimidine bonded to a substituted thiazole. This structure leads to the presence of a quaternary N atom attached to the thiazole ring. Thus, thiamine - so-called vitamin Bl - exists as salts of the physiological chloride anion or one of a wide variety of other counter anions. For solubility reasons, thiamine is commercially available as its hydrochloride salt, namely thiaminium(2+) dichloride. The structures of thiamine metal complexes correspond to two groups those containing the divalent thiaminium cation and a cadmium complex as counterion, and those in which there is a direct cadmium-thiamine interaction. 

Niacin and niacinamide (also known as nicotinic acid and nicotinamide, respectively) or vitamin B3, chemically 3-pyridinecarboxylic acid and 3-pyridinecarboxamide, are able to form various cadmium complexes with known crystal and molecular structures. In order to rationalize the analysis, hereafter the complexes have been differentiated according to the ligand and, within each case, we have only considered the most relevant structures. 

It has been established by polarography that cadmium(n) and mercury)n) form 1 1 and 2 1 complexes with vitamin B6.266 Activation parameters are reported. 

Cobalt, and sometimes cadmium, can substitute for zinc in many zinc enzymes such as CA, leading to complex interactions among the three metals in marine algae (Figure 5). The presence of cadmium in CA appears to explain its nutrient-like distribution in ocean waters (Figure 2(e)), and the identification of a unique Cd-CA enzyme in marine diatoms means that it functions as a micronutrient in these organisms. Cobalt also occurs in vitamin Bi2, an essential... 

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