Surface phase behavior and domain topography of ascorbyl palmitate monolayers.

L. BENEDINI; M. L. FANANI, ; , B. MAGGIO,; N. WILKE; P. MESSINA, ; S. PALMA; P. SCHULZ

LANGMUIR

AMER CHEMICAL SOC

Año: 2011 vol. 27 p. 10914 - 10919

0743-7463

ABSTRACT: Ascorbyl palmitate (ASC16) is a molecule ofpotential pharmacological interest due to its antioxidant propertiesand amphiphilic nature. The surface behavior of ASC16 wasstudied using Langmuir monolayers and Brewster angle microscopy.This molecule formed stable monolayers at room temperaturethat showed phase transition from a liquid-expanded toliquid-condensed or crystalline phase, depending on the subphaseconditions. Using a theoretical approach, we were able to explainthe behavior of the ASC16 film at different bulk pH values and saltconditions based on the surface pH and the dissociation fractionof the film. Both condensed phases corresponded to highly packedconditions with the crystalline phase occurring at a low chargedensity, showing molecular tilting and preferential growth atcharacteristic angles, while the liquid-condensed phase formed in highly charged surfaces revealed small flowerlike domainsprobably as a consequence of internal dipole repulsion. A smaller perpendicular dipole moment was observed for the crystalline thanthe liquid-condensed phase which may explain the domain features. In conclusion, ASC16 showed a complex surface behavior thatwas highly sensitive to subphase conditions.