Surface Phase Behavior and Domain Topography of Ascorbyl Palmitate Monolayers

BENEDINI LUCIANO, FANANI LAURA, MAGGIO BRUNO, WILKE NATALIA, PALMA SANTIAGO, MESSINA PAULA, SCHULZ PABLO

LANGMUIR

AMER CHEMICAL SOC

Lugar: Washington; Año: 2011 p. 10914 - 10919

0743-7463

Ascorbyl palmitate (ASC16) is a molecule of potential pharmacological interest due to its antioxidant properties and amphiphili  nature. The surface behavior of ASC16 was studied using Langmuir monolayers and Brewster angle microscopy. This molecule formed stable monolayers at room temperature that showed phase transition from a liquid-expanded to liquid-condensed or crystalline phase, depending on the subphase conditions. Using a theoretical approach, we were able to explain the behavior of the ASC16 film at different bulk pH values and salt conditions based on the surface pH and the dissociation fraction of the film. Both condensed phases corresponded to highly packed conditions with the crystalline phase occurring at a low chargedensity, showing molecular tilting and preferential growth at characteristic angles, while the liquid-condensed phase formed in highly charged surfaces revealed small flowerlike domains probably as a consequence of internal dipole repulsion. A smaller perpendicular dipole moment was observed for the crystalline than the liquid-condensed phase which may explain the domain features. In conclusion, ASC16 showed a complex surface behavior that was highly sensitive to subphase conditions.