Monolayer interactions between lipids and amphiphilic block copolymers

Interactions in binary mixed monolayers from lipids 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and amphiphilic poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyloxazoli ne) block copolymers were studied by using the Langmuir balance technique and Brewster angle microscopy. It is shown that monolayers from the satd. lipid (DPPC) are more sensitive to the presence of polymers in the film, resulting in phase sepn. and the formation of pure lipid domains at high surface pressure. The morphol. and compn. of such phase-sepd. lipid-polymer films were studied by fluorescence microscopy and ToF-SIMS. In contrast, in DOPC-contg. monolayers, the polymers tend to phase-sep. at low surface pressures only and homogeneous films are obtained upon further compression, due to higher lipid fluidity. The anal. of excess energy of mixing shows that while the sepn. effect in densely packed DPPC-contg. films is strongly dependent on the polymer size (with the larger polymer having a much stronger influence), in the case of monolayers with DOPC much smaller effects are obsd. The results are discussed in terms of the monolayer compn., lipid fluidity, and polymer size. [on SciFinder (R)]