Microstructure Of Cholesterol/Phospholipid Complex Langmuir-Blodgett Films

The understanding of the effects of cholesterol on phospholipid monolayers and bilayers is important in biology. Langmuir monolayer at the air-liquid interface and Langmuir-Blodgett (LB) film are ideal systems to study the biomimetic membranes. Using LB technique, cholesterol and its mixture with lipids have been studied extensively. It has been well established that atomic force microscopy is a powerful technique to observe the surface topography and assembly at the molecular level.In this paper, using Atomic force microscopy (AFM) as a mainly tool, we investigated the microstructure of Cholesterol/phospholipid complex Langmuir-Blodgett Films. The paper consists of two parts:Part One: Preparation and Characterization of DPPC and Cholesterol LB Monolayer FilmsUsingπ-A isothems and AFM measurement, we investigated the phase separation and microstructure of dipalmitoylphosphatidylcholine(DPPC),Cholesterol LB monolayer films at 5 mN/m,15 mN/m,25 mN/m. Our experiment indicated that phase transition beginning with nucleation, then growth and fuse together with the increase of surface pressure. DPPC film has a larger limit area per molecular, a higher collapse surface pressure and better condensability than Cholesterol film. DPPC film is more stable than the LB film of cholesterol.Part Two: Microstructure of Cholesterol/DPPC Complex Langmuir-Blodgett Films The effect of cholesterol on the structure of DPPC monolayer has been studied by Atomic force microscopy (AFM). Mixed DPPC/Cholesterol monolayer have been deposited on mica using the Langmuir-Blodgett (LB) technique. AFM images showed that the area condensing effect of cholesterol on the DPPC monolayer is pronounced. Mixed LB films of Cholesterol and DPPC at a cholesterol concentration of 50(mol)% or more and at the surface pressure of 5mN/m is studied . Our experiment indicated that there exists an attractive intermolecular force between DPPC and Cholesterol. phase transition beginning with nucleation, then growth and fuse together with the increase of surface pressure. Increasing the mole fraction of cholesterol can reduce the surface pressure of phase transition.