Speciation of metal complexes of medicinal interest: relationship between solution equilibria and pharmaceutical properties

: Biospeciation of essential and toxic metal ions, metal complexes with biological or medicinal activity are discussed in the paper in order to emphasize the importance of the distribution of metal ions in biological milieu. The exact knowledge of the chemical species present in the different organs/compartments/fluids/cells may provide essential information about the pharmacokinetic properties and the biological effect of the metal ion or the drug candidate metal complex. The transport of essential and toxic metal ions in the blood serum is discussed first, which is followed by the description of biodistribution of several important metal complexes with medicinal interest such as (i) anticancer, (ii) insulin-enhancing and (iii) MRI contrast agents in biological fluids.