INCORPORATION OF EXOGENOUS MOLECULES INSIDE MONOLAYERS AND BILAYERS OF PHOSPHOLIPIDS - INFLUENCE OF THE MODE OF PREPARATION REVEALED BY SERRS AND SURFACE PRESSURE STUDIES

The aim of this work was to study the interaction of pirarubicin, an a nthracycline used in chemotherapy, with planar palmitoyloleoylphosphat idylcholine (POPC) monolayers and bilayers employed as membrane models . Different modes of preparation were used and compared, after a preli minary surface pressure study had been done to determine the character istics of the pirarubicin-POPC interaction and the level of pirarubici n incorporated in phospholipids. A first method consisted of studying the adsorption of the antibiotic (in aqueous solution) in a POPC monol ayer kept at a constant pressure. The final monolayer was composed of almost 11% of pirarubicin in the POPC/pirarubicin mixture at 25 mN/m. The second method consisted of spreading mixtures of POPC/pirarubicin (pirarubicin being now dissolved in an organic solvent) at the air-wat er interface: the maximum percentage of pirarubicin in the monolayer w as 38% at 25 mN/m. These two kinds of monolayers were then transferred by a Langmuir-Blodgett technique onto prisms previously coated with s ilver. Surface-enhanced resonance Raman spectroscopy gave information about the orientation of the molecules with respect to the silver coat ing. These spectra were compared with those of pure POPC bilayers tran sferred onto the prism and then put in contact with an aqueous solutio n of pirarubicin. Different results were observed for the orientation of pirarubicin in the bilayers (tilted or parallel to the silver), acc ording to the mode of preparation of the samples, underlining the impo rtance of the choice of the experimental protocol and precautions to t ake in the examination of the results.