Search for the Molecular Mechanism of Mercury Toxicity. Study of the Mercury(II)−Surfactant Complex Formation in Langmuir Monolayers

Surface pressure and electric surface potential measurements complemented with Brewster angle microscope observations have been used to study the interactions of Hg(2+) ions with selected surfactants spread in Langmuir monolayers. The chosen surfactants had the same hydrocarbon chain length (18 carbon atoms) and different polar groups, such as -COOH, -NH(2), -OH, and -SH, which can be found in natural cells. Our results indicate that Hg(2+) interacts strongly not only with the -SH group, which is believed to be the main target for mercury ions, but also with -COOH and -NH(2) groups. Another important finding is that hydracid or oxoacid mercury salts interact with surfactants differently. The observed differences were explained as being due to different coordination of mercury in the respective complexes. Similar experiments as for mercury salts have also been performed for other heavy metal ions (Cd(2+), Pb(2+), and Ag(+)). It turned out that the interactions with the investigated surfactants monolayers were considerably different, which was explained by different coordination properties of the above cations. The profound changes exerted by Hg(2+) ions on Langmuir monolayers of the selected herein surfactants (multilayer formation, induction of aggregation) may be related to natural membranes and can contribute to the elucidation of the molecular mechanism of mercury toxicity.