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

¹ Carnegie Mellon University
² Chalk River Laboratories

^* To whom correspondence should be addressed. E-mail: nagle{at}andrew.cmu.edu.

Submitted on June 20, 2007
Revised on July 23, 2007
Accepted on 20 August 2007

	Abstract

X-ray diffuse scattering was measured from oriented stacks and unilamellar vesicles of dioleoylphatidylcholine (DOPC) lipid bilayers to obtain the temperature dependence of the structure and of the material properties. The area per molecule A was 75.5Ų (45°C), 72.4Ų (30°C) and 69.1Ų (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 in Kelvins. 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.

Key Words: bending modulus, interactions, low angle x-ray diffraction, membrane structure, thermal expansivity