Collective dynamics in fully hydrated phospholipid bilayers studied by inelastic X-ray scattering

The short wavelength density fluctuation of DLPC (dilaurylphosphatidylcholi ne) bilayers close to full hydration has been studied by the inelastic x-ra y scattering technique below and above the main transition temperature. The analysis based on a generalized three effective eigenmode theory allows us to construct the dispersion relation of the high frequency sound mode for the first time. The marl;rd softening of the excitation near k = 14 nm(-1), corresponding to the lipid chain-chain correlation peak in the structure f actor, in the L-alpha, phase implies prevalent occurrences of short-wavelen gth in-plane motions of lipid chains that might be of importance for transp ortation of small molecules across membranes. DOI: 10.1103/PhysRevLett.86.7 40.