title: Rigidification of neutral lipid bilayers in the presence of salts.
abstract: We studied the influence of sodium and calcium chloride on the global and local membrane properties of fluid palmitoyl-oleoyl phosphatidylcholine bilayers, applying synchrotron small-angle x-ray diffraction, spin-labeling electron paramagnetic resonance spectroscopy, and differential scanning calorimetry, as well as simultaneous density and acoustic measurements. The salt concentration was varied over a wide range from 0 to 5 M. We found that NaCl leads to a continuous swelling of the bilayers, whereas the behavior of the bilayer separation dW in the presence of CaCl2 is more complex, showing an initial large dW value, which decreased upon further addition of salt and finally increased again in the high concentration regime. This can be understood by a change of balance between electrostatic and van der Waals interactions. We were further able to show that both salts lead to a significant increase of order within the lipid bilayer, leading to a decrease of bilayer elasticity and shift of main phase transition temperature. This effect is more pronounced for Ca2+, and occurs mainly in the high salt-concentration regime. Thus, we were able to reconcile previous controversies between molecular dynamics simulations and x-ray diffraction experiments regarding the effect of salts on neutral lipid bilayers.
authors.affiliation: Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz, Austria. Georg.Pabst@oeaw.ac.at
authors.forename: Georg
authors.initials: G
authors.lastname: Pabst
authors.forename: Aden
authors.initials: A
authors.lastname: Hodzic
authors.forename: Janez
authors.initials: J
authors.lastname: Strancar
authors.forename: Sabine
authors.initials: S
authors.lastname: Danner
authors.forename: Michael
authors.initials: M
authors.lastname: Rappolt
authors.forename: Peter
authors.initials: P
authors.lastname: Laggner
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D009994:Osmolar Concentration; D010539:Permeability; D044367:Phase Transition; D012492:Salts / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D012492:Salts