title: Effect of heavy water on phospholipid membranes: experimental confirmation of molecular dynamics simulations.
abstract: Although there were experimental indications that phospholipid bilayers hydrated with D(2)O express different biophysical properties compared with hydration by ordinary H(2)O, a molecular concept for this behavior difference was only recently proposed by a molecular dynamics simulations study [T. Róg et al., J. Phys. Chem. B, 2009, 113, 2378-2387]. Here we attempt to verify those theoretical predictions by fluorescence measurements on 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membranes. Specifically, we determine the water isotope effect on headgroup hydration and mobility, lateral lipid diffusion and lipid backbone packing. Time-dependent fluorescence shift experiments show significantly slower dynamics and lower hydration of the headgroup region for a bilayer hydrated with D(2)O, an observation in good agreement with the calculated predicted differences in duration of lipid-lipid and lipid-water bridges and extent of water penetration into the bilayer, respectively. The water isotope effect on the lipid order parameter of the bilayer core (measured by fluorescence anisotropy) and lateral diffusion of lipid molecules (determined by two-focus fluorescence correlation spectroscopy) is close to the experimental errors of the experiments, however also refers to slightly more rigid organization of phospholipid bilayers in heavy water. This study confirms the view that the water isotope effect can be particularly found in time-resolved physicochemical properties of the membrane. Together with the simulations our experiments provide a comprehensive, molecular view on the effect of D(2)O on phospholipid bilayers.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, vvi, Prague 8, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Beranová
authors.forename: Jana
authors.initials: J
authors.lastname: Humpolíčková
authors.forename: Jan
authors.initials: J
authors.lastname: Sýkora
authors.forename: Aleš
authors.initials: A
authors.lastname: Benda
authors.forename: Lukasz
authors.initials: L
authors.lastname: Cwiklik
authors.forename: Piotr
authors.initials: P
authors.lastname: Jurkiewicz
authors.forename: Gerhard
authors.initials: G
authors.lastname: Gröbner
authors.forename: Martin
authors.initials: M
authors.lastname: Hof
mesh_terms: D017666:Deuterium Oxide / Q000737:chemistry*; D005453:Fluorescence; D008051:Lipid Bilayers / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D010743:Phospholipids / Q000737:chemistry*; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D010743:Phospholipids; D017666:Deuterium Oxide