Berlin 2008 – scientific programme
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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications
SYSA 5: Poster Session SYSA
SYSA 5.52: Poster
Tuesday, February 26, 2008, 14:30–20:00, Poster A
Adhesion between alkyl chains determines head group conformation in phosphocholine monolayers — •Olaf Soltwedel1, Christel Müller2, Heiko Ahrens1, Jens-Uwe Günther1, and Christiane A. Helm1 — 1Institut für Physik, Ernst-Moritz-Arndt Universität, Felix-Hausdorff-Str. 6, D-17487 Greifswald, Germany — 2Institut für physikalische Chemie, Johannes-Gutenberg Universität, Jakob-Welder Weg 11, D-50055 Mainz, German
Phosphatidylcholine monolayers at the air-water interface with different alkyl chain lengths are investigated with isotherms, X-ray reflectivity and Grazing Incidence X-ray diffraction. The length and symmetry of the alkyl chains is varied, C14-C14, C16-C16, C18-C18, C14-C18, C18-C14, C16-C18 and C18-C16. Increasing the alkyl chain length by 2 CH2-groups lowers the liquid-solid phase transition by about 15 mN/m. This is attributed to the increased adhesion between the ordered alkyl chains. The phase transition of C18-C14 and C14-C18 is between the one of C14-C14 and C16-C16, the analogue is observed for C16-C18 and C18-C16. To make it possible that the ordered part of the alkyl chains is the same for different chain lengths, the head group has to rearrange. In biological system, the bending of the glycerol occurs at the C2-atom, as it does in water-free choline crystals. But to maximize the thickness of the ordered alkyl chains, the head-group conformation has to change. The thermodynamic observations are supported by X-ray measurements.