Surface insertion of ascorbyl palmitate in phospholipid monolayers

MARIA L. FANANI; MILAGRO MOTTOLA; NATALIA WILKE; LUCIANO A. BENEDINI; BRUNO MAGGIO

Tucuman

Congreso; XLI Reunion Annual Sociedad Argentina de Biofísica; 2012

Sociedad Argentina de Biofísica

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 near 70mN/m. Subphase pH and ionic strength are determinant of both the features of ASC16 aggregates in the bulk phase and of the kinetic properties of ASC16 insertion in phospholipid monolayers. Those effects are due to different biophysical properties of the drug in its charged and neutral states. 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 disrupts the ASC16-enriched liquid-condensed phase promoting a rapid ASC16 insertion in the membrane.