Structural investigation of Langmuir-Blodgett monolayers of L-α-dipalmitoylphosphatidylcholine by atomic force microscopy

Atomic force microscopy (AFM) was applied to observe the formation of solid phase domains from liquid phase regions on compression of Langmuir-Blodgett (LB) monolayers of L-α-dipalmitoylphosphatidylcholine (L-α-DPPC). The essential features in monolayers are remarkably similar to those observed by the fluorescence technique. However, many more detailed structural features are directly observed which cannot be resolved by fluorescence microscopy. Besides, AFM images clearly reveal that the chiral domain morphologies, which are directly related to the enantiomorphic configuration of the lipids composing the monolayer, remain intact upon transfer to solid substrates. More importantly, the observation of these rotative solid phase grains nearby chiral domains leads us to believe that there exist chiral nearest neighbor forces between chiral molecules, which can produce strongly chiral domain shapes. Finally, the influence of the compression rate on shape changes as well as microstructure within a single domain was also investigated using AFM.