title: Effect of sodium chloride on a lipid bilayer.
abstract: Electrostatic interactions govern structural and dynamical properties of membranes and can vary considerably with the composition of the aqueous buffer. We studied the influence of sodium chloride on a pure POPC lipid bilayer by fluorescence correlation spectroscopy experiments and molecular dynamics simulations. Increasing sodium chloride concentration was found to decrease the self-diffusion of POPC lipids within the bilayer. Self-diffusion coefficients calculated from the 100 ns simulations agree with those measured on a millisecond timescale, suggesting that most of the relaxation processes relevant for lipid diffusion are faster than the simulation timescale. As the dominant effect, the molecular dynamics simulations revealed a tight binding of sodium ions to the carbonyl oxygens of on average three lipids leading to larger complexes with reduced mobility. Additionally, the bilayer thickens by approximately 2 A, which increases the order parameter of the fatty acyl chains. Sodium binding alters the electrostatic potential, which is largely compensated by a changed polarization of the aqueous medium and a lipid dipole reorientation.
authors.affiliation: Theoretical Molecular Biophysics Group, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Rainer A
authors.initials: RA
authors.lastname: Böckmann
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Hac
authors.forename: Thomas
authors.initials: T
authors.lastname: Heimburg
authors.forename: Helmut
authors.initials: H
authors.lastname: Grubmüller
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D002151:Calorimetry; D002244:Carbon / Q000737:chemistry; D002713:Chlorine / Q000737:chemistry; D003198:Computer Simulation; D004058:Diffusion; D004305:Dose-Response Relationship, Drug; D005227:Fatty Acids / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry; D008956:Models, Chemical; D015233:Models, Statistical; D010713:Phosphatidylcholines / Q000737:chemistry*; D012965:Sodium Chloride / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D055672:Static Electricity; D013997:Time Factors
chemical_list: D005227:Fatty Acids; D008051:Lipid Bilayers; D008055:Lipids; D010713:Phosphatidylcholines; D012965:Sodium Chloride; D002713:Chlorine; D002244:Carbon; C028694:1-palmitoyl-2-oleoylphosphatidylcholine