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Temperature Dependence of Structure, Bending Rigidity, and Bilayer Interactions of Dioleoylphosphatidylcholine Bilayers

Jianjun Pan ^*, Stephanie Tristram-Nagle ^*, Norbert Kuerka   and John F. Nagle ^* 

^* Department of Physics, and Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania; Canadian Neutron Beam Centre, National Research Council, Chalk River, Ontario, Canada; and Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University, Bratislava, Slovakia

Correspondence: Address reprint requests to John F. Nagle, Dept. of Physics, Carnegie Mellon University, Pittsburgh, PA 15213. Tel.: 412-268-2764, Fax: 412-681-0648; E-mail: nagle{at}cmu.edu.

X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphosphatidylcholine lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area/molecule, A, was 75.5 Ų at 45°C, 72.4 Ų at 30°C, and 69.1 Ų at 15°C, which gives the area expansivity _A = 0.0029/deg at 30°C, and we show that this value is in excellent agreement with the polymer brush theory. The bilayer becomes thinner with increasing temperature; the contractivity of the hydrocarbon portion was _Dc = 0.0019/deg; the difference between _A and _Dc is consistent with the previously measured volume expansivity _Vc = 0.0010/deg. The bending modulus K_C decreased as exp(455/T) with increasing T (K). Our area compressibility modulus K_A decreased with increasing temperature by 5%, the same as the surface tension of dodecane/water, in agreement again with the polymer brush theory. Regarding interactions between bilayers, the compression modulus B as a function of interbilayer water spacing D'_W was found to be nearly independent of temperature. The repulsive fluctuation pressure calculated from B and K_C increased with temperature, and the Hamaker parameter for the van der Waals interaction was nearly independent of temperature; this explains why the fully hydrated water spacing, D'_W, that we obtain from our structural results increases with temperature.