Surface insertion of ascorbyl palmitate on phospholipid monolayers

MARIA LAURA FANANI, MILAGRO MOTTOLA, NATALIA WILKE, LUCIANO BENEDINI, BRUNO MAGGIO

Congreso; XLI Reunión de la Sociadad Biofísica Argentina; 2012

Sociedad Biofísica Argentina

Ascorbyl palmitate (ASC16) is a molecule of potential pharmacological interest due to its antioxidant properties and amphiphilic nature. In this work we investigated its interaction with model lipid monolayers. ASC16 shows an ionizable OH group (pKa 4.2) that leads to a charged surface upon its insertion/adsorption to interface (1). When ASC16 is added to the subfase of a phospholipid monolayer it incorporates to the film showing a non-classical bimodal kinetics. From the analysis of mixed Langmuir films and Brewster angle microscopy we can conclude that the insertion kinetics of ASC16 leads to a two-dimensional phase transition from liquid-expanded (phospholipid-reach) film to a liquid-condensed phase enriched in the amphiphilic drug. The latter phase is highly stable at the interface reaching surface pressure values of ~65mN/m and a theoretical cut off value of near 70mN/m. Subphase pH and ionic strength are determinant of both the characteristics of ASC16 aggregates in the bulk phase and the kinetic properties of ASC16 insertion to phospholipid monolayers. Those effects are consequence of different biophysical properties of the charged and neutral drug. Additionally, we evaluated the insertion of ASC16 in phospholipid/cholesterol monolayers. In this condition the kinetic of insertion shows a fast hyperbolic increase. Preliminary results suggest that the presence of cholesterol disrupt the ASC16-enriched liquid-condensed phase promoting a rapid ASC16 insertion to the membrane. References: (1). Benedini, L., Fanani, M. L., Maggio, B., Wilke, N., Messina, P., Palma, S., and Schulz, P. (2011) Langmuir 27, 10914-10919