Thickening Broken and Critical Fluctuation of Phospholipid Bilayers

W. C. Hung ； F. Y. Chen

《Chinese Journal of Physics》 38卷5期 (2000/10) Pp. 939-948

並列摘要

It has been a puzzle that the phospholipid bilayers of a fluid phase fluctuate critically and at the same time are weakly thickened in full hydration, when the temperature T is lowered toward the ”main” transition [Chen et al., 1997, Phys. Rev. Lett. 79, 4026]. The osmotic pressure Q raises the transitional temperature, and their relation defines a transitional line. Exploring the fluid phase along the transition line down to the ”main” transition point enables one to find out the answer for this puzzle. This study measured dilauroyl-phosphatidylcholine (DLPC) bilayers by lamellar x-ray diffraction along isotherms varying from 1° to 35°C as a function of Q. The result shows that an intermediate phase of partial ordering in a chain up to a critical thickness D*1 emerges from the fluid phase along the transition line. As the transition is close to the ”main” transition point, the partial domain of the intermediate phase is water hydrolyzed so that the bilayer thickness is non-uniform, leading to a significant bilayer fluctuation and a weaker bilayer thickening. This gives a new explanation for the critical swelling of phospholipid bilayers near the ”main” transition.