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College Park, Maryland      June 6 - 10 , 2004

M3-B5 (2:45 PM): Bending Rigidity of Bio-Membranes Studied by Neutron Spin-Echo Technique (Invited)

D. Bossev (University of Maryland, College Park; National Institute of Standards and Technology), N. Rosov (National Institute of Standards and Technology)

The dynamics of multilamellar vesicles made of 1,2-Dimyristoyl-sn-Glycero-3-Phosphocholine (DMPC), is studied in the presence of cholesterol, addition of electrolyte, and as a function of temperature using Neutron Spin Echo (NSE) technique. NSE is the most direct method to monitor the thermal undulations of the lipid bilayers in solution because it is a unique scattering technique that covers the time scale of 0.01 ns to 100 ns, characteristic of these motions. We have used the Zilman-Granek approach to interpret the decay of the intermediate scattering function and to evaluate the bending modulus of elasticity, κ, of the lipid bilayers. To elucidate temperature effect on κ we have done measurements in a crystalline state of the bilayers (T < Tc, Tc = 24 ºC for DMPC) and in the liquid state (T > Tc). The bending modulus of elasticity in a crystalline state is one order of magnitude higher than that in the liquid state whereas in a liquid state κ is found to be independent of temperature. The presence of 30 % to 50 % cholesterol increases the bending modulus of elasticity of DMPC bilayers in a liquid state by a factor of 4 to 7. Presence of electrolyte (NaCl at 0.05 mol L-1) also stiffens the DMPC bilayers by a factor of 1.5 in a liquid state. Both, cholesterol and NaCl electrolyte, have a negligible effect onκ in a crystalline state. The results are compared to those obtained by other methods. The possible mechanisms of these effects are also discussed in the scope of DMPC bilayers structure.

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