Molecular structure and interaction of dipalmitoyl phosphatidylcholine in multilayers. Comparative study with phosphatidylethanolamine

As a model of phospholipid bilayers in solid an oriented multilayer film (built-up film) of L-α-dipalmitoyl phosphatidylcholine (DPPC) was prepared from the monolayer by the dipping method. Structural analysis has been carried out by measuring infrared dichroism of the built-up film. The results were compared with those of the built-up film of L-α-dipalmitoyl phosphatidylethanolamine (DPPE). The tilting of the hydrocarbon chains is larger for DPPC than for DPPE. The orientation of the bisector of the two non-esterified PO bonds is closer to the film plane for DPPC than for DPPE. The strong hydrogen bonding interaction between the polar head groups was shown for DPPE, but not for DPPC. These features resemble the structural differences between dilauroyl phosphatidylethanolamine (DLPE) and dimyristoryl phosphatidylcholine (DMPC) in crystals. The hydrogen bonding interaction of DPPE found in solid remains even in the presence of water, namely, in the gel state. More closed packing of the hydrocarbon chains of solid DPPE than DPPC in solid was concluded on the basis of infrared and Raman spectra.