title: Collective chain dynamics in lipid bilayers by inelastic x-ray scattering.
abstract: We investigated the application of inelastic x-ray scattering (IXS) to lipid bilayers. This technique directly measures the dynamic structure factor S(q,omega) which is the space-time Fourier transform of the electron density correlation function of the measured system. For a multiatomic system, the analysis of S(q,omega) is usually complicated. But for multiple bilayers of lipid, S(q,omega) is dominated by chain-chain correlations within individual bilayers. Thus IXS provides a unique probe for the collective dynamics of lipid chains in a bilayer that cannot be obtained by any other method. IXS of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylcholine + cholesterol at two different concentrations were measured. S(q,omega) was analyzed by three-mode hydrodynamic equations, including a thermal diffusive mode and two propagating acoustic modes. We obtained the dispersion curves for the phonons that represent the collective in-plane excitations of lipid chains. The effect of cholesterol on chain dynamics was detected. Our analysis shows the importance of having a high instrument resolution as well as the requirement of sufficient signal-to-noise ratio to obtain meaningful results from such an IXS experiment. The requirement on signal-to-noise also applies to molecular dynamics simulations.
authors.affiliation: Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA.
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Weiss
authors.forename: Poe-Jou
authors.initials: PJ
authors.lastname: Chen
authors.forename: Harald
authors.initials: H
authors.lastname: Sinn
authors.forename: Ercan E
authors.initials: EE
authors.lastname: Alp
authors.forename: Sow-Hsin
authors.initials: SH
authors.lastname: Chen
authors.forename: Huey W
authors.initials: HW
authors.lastname: Huang
mesh_terms: D000465:Algorithms; D018360:Crystallography, X-Ray / Q000379:methods*; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D004548:Elasticity; D008051:Lipid Bilayers / Q000737:chemistry*; D046911:Macromolecular Substances; D008560:Membrane Fluidity; D008968:Molecular Conformation; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity
chemical_list: D008051:Lipid Bilayers; D046911:Macromolecular Substances; D004134:Dimyristoylphosphatidylcholine