title: Phase state and surface topography of palmitoyl-ceramide monolayers.
abstract: In cell biology (and in many biophysical) studies there is a natural tendency to consider ceramide as a highly condensed, solid-type lipid conferring rigidity and close packing to biomembranes. In the present work we advanced the understanding of the phase behavior of palmitoyl-ceramide restricted to a planar interface using Langmuir monolayers under strictly controlled and known surface packing conditions. Surface pressure-molecular area isotherms were complemented with molecular area-temperature isobars and with observations of the surface topography by Brewster Angle Microscopy. The results described herein indicate that palmitoyl-ceramide can exhibit expanded, as well as condensed phase states. Formation of three phases was found, depending on the surface pressure and temperature: a solid (1.80nm thick), a liquid-condensed (1.73nm thick, likely tilted) and a liquid-expanded (1.54nm thick) phase over the temperature range 5-62 degrees C. A large hysteretic behavior is observed for the S phase monolayer that may indicate high resistance to domain boundary deformation. A second (or higher) order S-->LC phase transition is observed at about room temperature while a first order LC-->LE transition occurs in a range of temperature encompassing the physiological one (observed above 30 degrees C at low surface pressure). This phase behavior broadens the view of ceramide as a type of lipid not-always-rigid but able to exhibit polymorphic properties.
authors.affiliation: Departamento de Química Biológica, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Facultad de Ciencias Químicas, CONICET, Univ. Nacional de Córdoba, Haya de la Torre y Medina Allende, Ciudad Universitaria, X5000HUA, Córdoba, Argentina. lfanani@fcq.unc.edu.ar
authors.forename: Maria Laura
authors.initials: ML
authors.lastname: Fanani
authors.forename: Bruno
authors.initials: B
authors.lastname: Maggio
mesh_terms: D002518:Ceramides / Q000737:chemistry*; D044367:Phase Transition; D011312:Pressure; D013499:Surface Properties; D013696:Temperature
chemical_list: D002518:Ceramides