Study of structural model of biological membranes by synchrotron radiation

The objective of this work has been to study, from the structural point of view, the process of incorporation of various types of hydrophobic compounds into the lamellar phase of liposomes and multilayers of the zwitterionic phospholipid DPPC. X-ray diffraction and scattering techniques using synchrotron radiation, have been used to monitor changes of several bilayer systems. Thermotropic phase transitions as well as the order of the lamellar packing were studied in situ experiments. The behavior of the Lβ' and Lα phases was followed as a function of the water content in dispersions of DPPC multi lamellar vesicles with the addition of the alkaloid Ellipticine in several concentrations. The results showed a decrease in the temperature of the pre-transition as well as that of the main transition (Pβ' ->Lα). The decrease of the lamellar spacing as a function of temperature in the liquid crystalline phase leads to the description of the thermal compression coefficient in the Lα phase. It was also proved that addition of the anionic lipid Cardiolipin to the DPPC/water system it is possible to promote the incorporation of Ellipticine. The aforementioned methods were used in another set of experiments to study the lamellar phases of DPPC with the addition of Polycyclic Aromatic Hydrocarbons known to have various degrees of carcinogenic activity. It was verified that the main transition temperature as well as the spacing of the multilammelar vesicles in the Lα phase have a change with the incorporation of these compounds. It was possible to show that the hydrophobic PAHs favor the formation of the liquid crystalline phase, causing a broadening of the Pβ' -> L α phase transition.The results obtained in this work are basically important in the development of thermo sensitive liposomes, which can act as drug carriers. They also contribute to the understanding of the perturbations caused by the interaction of highly hydrophobic molecules with the cellular membranes. (author)