Atomic force microscopic study on the surface properties of phospholipid monolayers containing Ceramide 3

Abstract

The interactions between l-α-dipalmitoylphosphatidylcholine (DPPC) and 2 S,3 S,4 R-2-stearoylamide-1,3,4-octadecanetriol (Ceramide 3) in the mixed monolayers were investigated by using a surface pressure measurement and an atomic force microscopy (AFM). Mixed DPPC/Ceramide 3 monolayers were deposited on mica using the Langmuir–Blodgett (LB) technique for AFM. In the case of DPPC alone system, the phase transition from the liquid-expanded film to the liquid-condensed film was observed at 17 mN m −1 of surface pressure. Whereas in the case of Ceramide 3 alone system, no phase transition and only the liquid-condensed film were observed. In the mixed DPPC/Ceramide 3 systems, the average area per molecule in the liquid-condensed film was almost independent of the mole fraction of Ceramide 3, while that in the liquid-expanded film decreased with increasing the mole fraction of Ceramide 3. The observed negative deviation of the average area per molecule from the ideality relation indicated an attractive interaction between Ceramide 3 and DPPC in the liquid-expanded films, suggesting the higher packing density in the mixed DPPC/Ceramide 3 monolayers as compared with the pure components monolayers. The AFM images for the mixed DPPC/Ceramide 3 monolayers deposited at 10 mN m −1 of surface pressure on mica indicated elliptical domains, while those deposited at 30 mN m −1 of surface pressure indicated no domains. Ceramide 3 is likely to interact with DPPC in the liquid-expanded phase and consequently bring about phase separation.