Interactions of DPPC with semitelechelic poly(glycerol methacrylate)s with perfluoroalkyl end groups.

Peggy Scholtysek, Zheng Li, Jörg Kressler, Alfred Blume

Index: Langmuir 28(44) , 15651-62, (2012)

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Abstract

Semitelechelic poly(glycerol methacrylate)s having a perfluoroalkyl end group (PGMA(n)-F(9)) were synthesized by ATRP. The interactions of these polymers with different degrees of polymerization with chiral or racemic dipalmitoylphosphatidylcholine (l-DPPC, d-DPPC, or rac-DPPC) monolayers at the air/water interface were studied. Langmuir trough measurements coupled with epifluorescence microscopy allowed for the observation of domain formation within the coexistence region of liquid-expanded (LE) and liquid-condensed (LC) states of DPPC in mixed DPPC-polymer films prepared by spreading a solution of both compounds in the same organic solvent (cospread films). Because of the incorporation of PGMA(n)-F(9) polymers into the LE phase and their line-active behavior, a formation of novel types of domains could be observed. During compression, a thinning out of the tips of two- to six-lobed flowerlike domain structures and consecutive spiral formation appeared for l- and d-DPPC within the two-phase coexistence region (LE/LC) of the monolayer. When rac-DPPC was used, symmetrical stripe formation was induced at the vertices of the domains and fingerprint-like structures were created by convection-inducing movements of the domains at the air/water interface. Additional investigations of the interaction of PGMA(n)-F(9) with DPPC vesicles using differential scanning calorimetry (DSC) supported the finding on the monolayer system that the incorporation of the polymers into the lipid monolayers is not solely driven by the perfluoroalkyl chain but significantly by the hydrophilic polymer part. Apparently, interactions of the PGMA chain with the lipid headgroups are important as the interactions increase with the elongation of the polymer chain, indicating that the polymer also has hydrophobic character.