title: Phase-transition properties of glycerol-dipalmitate lipid bilayers investigated using molecular dynamics simulation.
abstract: The phase- and phase-transition properties of glycerol-dipalmitate (GDP) bilayer patches are investigated using molecular dynamics simulations. This permits to characterize the influence of introducing a second aliphatic lipid tail by comparison to previously reported simulations of glycerol-1-monopalmitate (GMP). To this purpose, a set of 67 simulations (up to 300ns duration) of 2×8×8GDP bilayer patches are performed, considering the two GDP isomers glycerol-1,3-dipalmitate (13GDP) and glycerol-1,2-dipalmitate (12GDP; racemic), two hydration levels (12GDP only), and temperatures in the range 250-370K. In agreement with experiment, the GDP simulations reveal an increase in the main transition temperature by about 25K relative to GMP, and the occurrence of non-bilayer phases at high temperatures (inverted-cylinder or stacked phases). Structurally, the GDP system tends to evidence a tighter packing of the chains, a reduced extent of tilting, increased order parameters and a reduced fluidity. These differences are easily interpreted in terms of two key changes in molecular properties when going from GMP to GDP: (i) the reduction of the headgroup polarity and hydration (from two free hydroxyl groups to a single one); (ii) the increase in the effective tail cross-section relative to the (hydrated) headgroup cross-section, conferring to GDP a particular wedge shape. These two effects contribute to the relative instability of the liquid-crystalline phase, the stability being recovered in nature when the diglyceride headgroup is functionalized by a bulky or/and polar substituent.
authors.affiliation: Laboratory of Physical Chemistry, ETH Zürich, Zürich, Switzerland. Electronic address: monika.laner@igc.phys.chem.ethz.ch.
authors.forename: Monika
authors.initials: M
authors.lastname: Laner
authors.affiliation: Laboratory of Physical Chemistry, ETH Zürich, Zürich, Switzerland. Electronic address: phil@igc.phys.chem.ethz.ch.
authors.forename: Philippe H
authors.initials: PH
authors.lastname: Hünenberger
mesh_terms: D005990:Glycerol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D056004:Molecular Dynamics Simulation; D044367:Phase Transition; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D005990:Glycerol
keywords: Diglyceride; GDP; Lipid bilayer; Long-timescale motions; Molecular dynamics; Phase transitions