title: Surface phase behavior and domain topography of ascorbyl palmitate monolayers.
abstract: Ascorbyl palmitate (ASC(16)) is a molecule of potential pharmacological interest due to its antioxidant properties and amphiphilic nature. The surface behavior of ASC(16) 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 ASC(16) 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 charge density, 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, ASC(16) showed a complex surface behavior that was highly sensitive to subphase conditions.
authors.affiliation: Instituto de Química del Sur (INQUISUR-CONICET), Departamento de Química, Universidad Nacional del Sur, 8000FTN Bahía Blanca, Argentina.
authors.forename: Luciano
authors.initials: L
authors.lastname: Benedini
authors.forename: Maria Laura
authors.initials: ML
authors.lastname: Fanani
authors.forename: Bruno
authors.initials: B
authors.lastname: Maggio
authors.forename: Natalia
authors.initials: N
authors.lastname: Wilke
authors.forename: Paula
authors.initials: P
authors.lastname: Messina
authors.forename: Santiago
authors.initials: S
authors.lastname: Palma
authors.forename: Pablo
authors.initials: P
authors.lastname: Schulz
mesh_terms: D001205:Ascorbic Acid / Q000031:analogs & derivatives* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D008968:Molecular Conformation; D010316:Particle Size; D013499:Surface Properties
chemical_list: D008567:Membranes, Artificial; D001205:Ascorbic Acid; C031226:6-O-palmitoylascorbic acid