Heavy Metal Complex Formation with Amino Acids
Accumulation of heavy metal ions in the environment causes adverse health effects. “Soft” metal ions have a high affinity for thiol (-SH) groups, in e.g., amino acid L-cysteine, the cysteine-rich protein metallothionein, and tripeptide glutathione, which is the most abundant cellular thiol in the body and has important in vivo functions for protection against heavy metal ions. Uptake via food, drinking water and air of Hg(II), Pb(II) and Cd(II) can affect human metabolism by blocking enzymatic functions. Thiol-containing drugs, e.g. D-penicillamine (3,3´-dimethylcysteine), are clinically used for heavy metal detoxification. Similarly, metal based antitumor active complexes may interact with thiol-containing proteins, which could render their activities. We have applied a novel combination of different spectroscopic methods such as multi-nuclear NMR, EXAFS and vibrational spectroscopy for investigating the coordination of such metal ions to glutathione, cysteine and its derivatives, to elucidate the structure of their complexes, and to evaluate the distribution of these species in aqueous solution. The information on structure and bonding of heavy metal complexes with such thiol-containing small molecules can assist us to design new chelating agents/ drugs with improved efficiency for detoxification by increasing their bonding efficiency.