Molecular Dynamics Study of a Membrane-Water Interface

Abstract

A 200 ps molecular dynamics simulation of a membrane bilayer consisting of 202 dilauroylphosphatidylethanolamine molecules and 8108 water molecules at 315 K is conducted. Distribution functions of lipid groups, order parameters, and other properties of the lipid bilayer are calculated and compared with experimental measurements. A detailed analysis is conducted for the structure at the membrane-water interface. Water polarization profile, membrane dipole potential profile, and susceptibility profile are calculated. Simulation results suggest that the polarization of water is determined mainly by the distribution of lipid head groups in the interfacial region. The membrane dipole potential is mainly due to the ester groups linked to the glycerol backbone, while the contribution due to the phosphatidylethanolamine head groups is almost completely cancelled by the contribution due to oriented water molecules. The susceptibility profile suggests a dielectric constant around 30 for the head group-water interface and a dielectric constant around 10 for the ester group region. The ammonium groups of the DLPE membrane are found to form hydrogen bonds with water molecules, while no orientational preference is observed for water molecules around the choline groups of a previously simulated POPC ( 1 -palmitoyl-2-oleoyl-sn-glycerol-3-phosphatidylcholine) membrane. Correlations of the membrane surface charge density are also analyzed. The simulations which involved 32 808 atoms included Coulombic forces between all atom pairs evaluated by means of the fast multipole algorithm. Effects of cutting off Coulombic forces at a distance of 8 A are discussed.

Hydration and Lyotropic Melting of Amphiphilic Molecules: A Thermodynamic Study Using Humidity Titration Calorimetry

“…Its formation leads to a loss of energy of the phosphate groups (3) because TMA-phosphate interactions do not possess the characteristics of hydrogen bonding. On the other hand, the water dipoles associate with the charged TMA moieties via relatively weak polar interactions (38,44). Therefore the TMA groups energetically gain slightly when replacing the polar TMA-water with stronger TMA-phosphate contacts (43).…”

“…Hence, solvating water molecules probably screen direct interactions between the headgroups leading to the increase in their conformational and/or motional freedom. Molecular dynamics simulations show that, e.g., polarization due to water molecules almost completely cancel the polarization due to lipid headgroups, and thus the water obviously behaves like a classical medium with high dielectric constant (44,46,48,49).…”

Hydrogen Bonding Structure and Dynamics of Water at the Dimyristoylphosphatidylcholine Lipid Bilayer Surface from a Molecular Dynamics Simulation

“…The orientation and polarization of water in the interfacial region has been studied for both DLPE and DMPC; a clathrate shell is observed to form around the choline moiety. [24][25][26][27][28][29] The hydrogen bonding structure of water and of the lipid headgroups has been analyzed and the effect of employing different electrostatic cutoffs has been assessed. 25,28,30 Modeling of proton transport between water molecules near a phospholipid/water interface is not possible using conventional MD force fields.…”

“…[24][25][26][27][28][29] The hydrogen bonding structure of water and of the lipid headgroups has been analyzed and the effect of employing different electrostatic cutoffs has been assessed. 25,28,30 Modeling of proton transport between water molecules near a phospholipid/water interface is not possible using conventional MD force fields. Proton transport can be studied using quantum mechanical methods on small systems for short times 31 or by employing an empirical valence bond model that is incorporated into a conventional MD simulation.…”

Insights into the behavioral difference of water in the presence of GM1

“…Beside experiments, computer simulation also aids to understand the interfacial properties of water molecules [25,26]. The orientation and polarization of the interfacial water [27][28][29][30][31][32], water conductance through carbon nanotube [33], the hydrogen bonding structure of water and of the lipid headgroups has also been assessed [32,34,35] using MD simulations. Theory of solvation of small and large apolar species in water was also developed [36].…”