title: Structure and dynamics of interfacial water in an Lalpha phase lipid bilayer from molecular dynamics simulations.
abstract: Based on molecular dynamics simulations, an analysis of structure and dynamics is performed on interfacial water at a liquid crystalline dipalmitoylphosphatidycholine/water system. Water properties relevant for understanding NMR relaxation are emphasized. The first and second rank orientational order parameters of the water O-H bonds were calculated, where the second rank order parameter is in agreement with experimental determined quadrupolar splittings. Also, two different interfacial water regions (bound water regions) are revealed with respect to different signs of the second rank order parameter. The water reorientation correlation function reveals a mixture of fast and slow decaying parts. The fast (ps) part of the correlation function is due to local anisotropic water reorientation whereas the much slower part is due to more complicated processes including lateral diffusion along the interface and chemical exchange between free and bound water molecules. The 100-ns-long molecular dynamics simulation at constant pressure (1 atm) and at a temperature of 50 degrees C of 64 lipid molecules and 64 x 23 water molecules lack a slow water reorientation correlation component in the ns time scale. The (2)H(2)O powder spectrum of the dipalmitoylphosphatidycholine/water system is narrow and consequently, the NMR relaxation time T(2) is too short compared to experimental results.
authors.affiliation: Department of Chemistry, Biophysical Chemistry, Umeå University, Sweden.
authors.forename: Ken
authors.initials: K
authors.lastname: Aman
authors.forename: Erik
authors.initials: E
authors.lastname: Lindahl
authors.forename: Olle
authors.initials: O
authors.lastname: Edholm
authors.forename: Pär
authors.initials: P
authors.lastname: Håkansson
authors.forename: Per-Olof
authors.initials: PO
authors.lastname: Westlund
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D003198:Computer Simulation; D017666:Deuterium Oxide / Q000737:chemistry; D008051:Lipid Bilayers / Q000737:chemistry*; D046911:Macromolecular Substances; D009682:Magnetic Resonance Spectroscopy; D008560:Membrane Fluidity; D008567:Membranes, Artificial; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D012680:Sensitivity and Specificity; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008567:Membranes, Artificial; D014867:Water; D015060:1,2-Dipalmitoylphosphatidylcholine; D017666:Deuterium Oxide