Аннотация:The angle between lipid director and lipid membrane normal, called lipid tilt, is known to play an important role in membrane fusion and fission, defines membrane dynamics at short wavelengths, and generally helps to relax local curvature induced tensions. Molecular origin of tilt in homogeneous single-component lipid membranes has been attributed to the difference between area of lipid-water interface compared to cross-section of lipid hydrocarbon tails [1-5]: if lipids heads are large enough to prevent lipids tails from approaching each other, then lowering of the lipids free energy occurs via tilt of the lipids tails, that makes tails more close to each other relatively to the state in which their axes are parallel to the normal to the membrane's surface. We test that picture with a microscopic mean-field model of lipid membrane we used previously to describe a temperature-driven liquid-gel phase transition in lipid bilayers [6]. In our model free energy of lipid in a membrane consists of steric repulsion, van der Waals interaction, and hydrophobic tension. We argue that hydrophobic energy depends on cross-section area of hydrocarbon chains, rather then on area of lipid-water interface.
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