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Atomic Force Microscopy Imaging and Force Spectroscopy of Supported Lipid Bilayers
Published on: July 22, 2015
Structural and topographical characteristics of dipalmitoyl phosphatidic acid in Langmuir monolayers
J Miñones1, J M Rodríguez Patino, J Miñones
1Faculty of Pharmacy, Department of Physical Chemistry, University of Santiago de Compostela, Campus Sur, Santiago de Compostela 15706, Spain. jminones@usc.es
Abstract:
Dipalmitoyl phosphatidic acid (DPPA) monolayers at the air-water interface were studied from surface pressure (Pi)-area (A) isotherms and at the microscopic level with Brewster angle microscopy (BAM) under different conditions of temperature, pH, and ionic strength. BAM images were recorded simultaneously with Pi-A isotherms during the monolayer compression-expansion cycles. DPPA monolayers show a structural polymorphism from the liquid-expanded (LE)-liquid-condensed (LC) transition region at lower surface pressures toward liquid-condensed and solid (S) structures at higher surface pressures. An increase in temperature, pH, or ionic strength provokes an expansion in the monolayer structure. The results obtained from the Pi-A measurements are confirmed by the monolayer topography and relative reflectivity. The measurements of relative reflectivity upon monolayer compression showed an increase in relative monolayer thickness of 1.25 and 3.3 times throughout the full monolayer compression from the liquid-expanded to the liquid-condensed and solid states, respectively.
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