T8 PM Measurement/ Estimation of Environmentally Relevant Physico-Chemical Properties
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in 337-338

(ESC-1117-137742) Liposome-water partitioning of hydrophobic copper-organic complexes and their components.

Kaiser, S¹, Schwarzenbach, R^{1, 2}, Escher, B¹, ¹ EAWAG, Duebendorf, Switzerland² ETH, Zürich, Switzerland

ABSTRACT- This study is part of a project that develops concepts and methods to evaluate bioavailability and toxic effects of complexes of copper and hydrophobic ionogenic organic compounds. A first step in understanding bioavailability and passive uptake of these complexes is to investigate their partitioning into biological membranes. We used liposomes as model systems and studied the uptake of copper in the presence of hydrophobic ligands (oxines) as a function of concentration, pH and type of ligand. Our goal was to determine the influence of the mentioned factors on the uptake of hydrophobic copper complexes and to compare the partitioning of these complexes with that of its components. In the first step we investigated the ligand alone. The results showed higher liposome-water-partitioning coefficients (Klipw) for neutral oxine species than for their ionic species. The uptake of the latter is decreased due to their charge. However, Klipw of oxine anions were generally higher than those of the cations. This observation can be rationalized by the delocalisation of the negative charge of the anion over the aromatic ring system while the positive charge of the cation is localized at the nitrogen atom. It was also remarkable that the Klipw of all oxines were dependent on their hydrophobicity, expressed by Kow of the neutral species, and that there existed parallel regression lines between logKlipw of the three different species and logKow of the neutral species. In the second step we looked at Cu2+ and the copper-oxine complexes. The experiments with copper showed no detectable uptake of copper in liposomes. For the copper-oxine complexes we observed a dependency of their Klipw from their molecule size and the hydrophobicity of their ligands. In conclusion, partitioning of charged ligands and copper complexes is significant and by less than three orders of magnitude smaller than partitioning of the neutral species of the ligand. Hence we postulate that all species play a role and need to be considered in bioaccumulation and toxicity studies.

Key words: membrane-water partitioning, speciation, bioavailability, pesticide