DSC study on the interactions between DDT and model membranes.

DOT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane) was a widely used chlorinated pesticide. It is characterized by a high environmental persistence time and accumulation in the fat tissues of living organisms. Furthermore, like other lipophilic substances, it can interact with biomembranes inducing membrane structure modification which could play a role both in the transport to the target tissues as well in the development of the toxicity. To this purpose we studied by means of Differential Scanning Calorimetry (DSC) thè hydrated multilamellar liposomes of both Dimyristoyl phosphatidylcholine (DMPC) and Dimyristoyl phosphatidyletanolamine (DMPE) in the presence of increasing amounts of DOT. Liposomes were prepared by mixing the appropriate amount of DMPC and DMPE in a NaCI 0.9 % w/w solution up to a final lipid concentration of about 20 % w/w. DSC scans were performed at a heating rate of 2.0°C/min in the thermal ranges of 5-40°C and 25-60°C for DMPC and DMPE samples respectively. The results on DDT/DMPC liposomes show significant Tm decrease and half width increase. The changes, more evident at low DDT concentration (up to 5.0 % w/w) suggest that the hydrophobic core is strongly affected by the presence of DDT molecules, their deep penetration into thè bilayer are only partially prevented by the potar interactions between the C-CI;i group and the DMPC polar head. In the presence of a greater DMPC amount, the Tm stays unchanged and half width increase slowly suggesting that the DDT solubility into the hydrophobic lipidic bilayer is limited. On the contrary DDT/DMPE liposomes show the presence of a phase segregation that takes piace in the presence of very small amount of DDT. This findings suggest that the DDT molecules interact mainly with the outer face of the bilayer and only secondly with the inner hydrophobic core as consequence of the setting up of strong polar interactions involving the more polar head group of DMPE head groups. Also in the high concentrated DDT/DMPE mixtures (DDT > 5.0 % w/w), the shape of the thermograms does not change, confirming the DDT limited solubility into the bilayer.