Molecular motions in a liquid‐crystalline lipid bilayer. Molecular dynamics simulation

Abstract

AbstractThe results of a molecular dynamics study of a lipid bilayer are discussed. As a model we consider an ensemble of 2 × 10 flexible chains consisting of 16 groups in a box with lateral (x, y) periodicity conditions. The chains interact with each other and with the aqueous medium. Terminal groups are bound near to the bilayer surfaces by a harmonic potential. All numerical results are compared with those obtained for an isotropic polymer liquid with the same density as for the bilayer. From a study of the order parameters we conclude that the bilayer is in the liquid‐crystalline state with the chains expanding in the z‐direction normal to the surfaces. Segmental order parameters are in reasonable agreement with experimental NMR data. Dynamic properties discussed include the frequency spectrum of the velocity autocorrelation function of particles, the incoherent dynamic structure factor, dielectric absorption, and luminescence polarization. It is found that compared with the bulk polymer liquid, the molecular motions in the bilayer are quite different. Such features arise mainly from existing strong correlations in the bilayer and from a different molecular organization of the chains in the bilayer and in the bulk liquid.