Complexes of Cadmium with Vitamins and Derivatives

Although vitamins have different structures, sources, requirements, and mechanisms of action, they are classified according to their solubility in water or in fats. Vitamins A, D, E, and K are liposoluble, whereas the B-complex (Bi, B2, Bg, B12, niacin, pantothenic acid, biotin, and folic acid) and C vitamins are hydrosoluble. Moreover, there are some organic compounds related to vitamins that are usually classified with the B vitamins and are also hydrosoluble i.e., p-aminobenzoic acid is included among these substances with similarities to vitamins. 

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. 

Carballo, Castineiras, Dommguez-Martm, Garcia-Santos, and Nicl6s-Gutierrez 

There are also two known strucmres of cadmium complexes with 2-(a-hydroxybenzyl)thiamine (HBthiamine), an intermediate in thiamine catalysis with the a-hydroxybenzyl substituent in the C(2) position of the thiazolium ring. The complexes [Cd(HBthiamine)X3] (X = Cl or Br) are isotypic, with a structure similar to that of [Cd(thiamine)Cl3] [Cd-N = 2.251(3) A and 2.257(9) A]. In these structures the conformation of the thiamine skeleton is S (tp-p = 97 and -97°, 

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