Molecular Dynamics Simulation of a Dipalmitoylphosphatidylcholine Bilayer with NaCl

Abstract

Molecular dynamics simulations are performed on two hydrated dipalmitoylphosphatidylcholine bilayer systems: one with pure water and one with added NaCl. Due to the rugged nature of the membrane/electrolyte interface, ion binding to the membrane surface is characterized by the loss of ion hydration. Using this structural characterization, binding of Na(+) and Cl(-) ions to the membrane is observed, although the binding of Cl(-) is seen to be slightly weaker than that of Na(+). Dehydration is seen to occur to a different extent for each type of ion. In addition, the excess binding of Na(+) gives rise to a net positive surface charge density just outside the bilayer. The positive density produces a positive electrostatic potential in this region, whereas the system without salt shows an electrostatic potential of zero.

Effect of NaCl and KCl on Phosphatidylcholine and Phosphatidylethanolamine Lipid Membranes: Insight from Atomic-Scale Simulations for Understanding Salt-Induced Effects in the Plasma Membrane

“…For all considered POPC bilayers we computed the electrostatic potential from the Poisson equation by twice integrating over charge densities, see Figure 5 (top). For a salt-free POPC membrane we found that the overall potential difference between the membrane center and the aqueous phase is ∼0.55 V. This value is in agreement with numerous computational studies, 6,12,15,21,27,47,48 while corresponding experimental values are in the range of 200-600 mV. [49][50][51][52][53] Addition of NaCl leads to a pronounced change in the electrostatic potential of a PC membrane: The peak of the potential in the region of the lipidwater interface increases and is shifted toward the water phase, reflecting most likely a considerable reorientation of head group dipoles.…”

“…Considering the plasma membrane of eukaryotic cells, the computational studies that have been carried out by far have focused on the effect of monovalent 6,12,14,15 (NaCl) and divalent 11 (CaCl 2 ) salts on bilayers comprised of zwitterionic PCs. This setup essentially corresponds to the outer leaflet of the plasma membrane.…”

“…11 The binding of cations has been found to have a significant impact on the structural and dynamical properties of PC membranes: It leads to a drop in the area per lipid accompanied by an enhanced ordering of lipid acyl chains and the slowing down of lateral diffusion in the membrane plane. 6,11,12,15 The understanding of salt-induced effects on plasma membranes is largely incomplete, however. This is due to the lack of studies on the effect of salt ions on phosphatidylethanolamine (PE) lipid membranes.…”

Direct Imaging of Lipid-Ion Network Formation under Physiological Conditions by Frequency Modulation Atomic Force Microscopy

“…Therefore, the surface group is more likely to be a phosphate group associated with cations than a choline group associated with anions. This is consistent with previous studies by IR spectroscopy [9] and molecular dynamics simulations [12,30]. These studies have suggested that the metal cations specifically bind to phosphate groups, while chloride anions remain solvated near the surface.…”

Ion Dynamics in Cationic Lipid Bilayer Systems in Saline Solutions

“…[28][29][30][31][32][33][34][35][36][37][38][39][40][41] As for molecular-level computational studies, the increase in computing power in the past few years has made it possible to extend computer simulations beyond the relatively long relaxation times of tens to hundreds of nanoseconds required for equilibration of ions in lipid/water systems. Although most computational studies by far have focused on the effects of salt ions on zwitterionic (neutral) lipid bilayers, 33,[42][43][44][45][46][47][48][49][50][51][52][53] there is also an increasing number of studies on anionic [54][55][56][57][58][59] and cationic 60,61 lipid bilayers. Most simulations have addressed the effect of ions on the structural and electrostatic properties of lipid membranes.…”