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Membranes 2017, 7(1), 5; doi:10.3390/membranes7010005

Effect of Sodium and Chloride Binding on a Lecithin Bilayer. A Molecular Dynamics Study

1
Physics Department (T38), Technische Universität München, James-Franck-Str. 1, Garching 85748, Germany
2
Institute of Physics, Albert-Ludwigs-Universität Freiburg, Hermann-Herder-Str. 3, Freiburg 79104, Germany
3
Freiburg Centre for Interactive Materials and Bioinspired Technologies, Georges-Köhler-Allee 105, Freiburg 79110, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Hsueh-Chia Chang
Received: 22 October 2016 / Revised: 12 January 2017 / Accepted: 14 January 2017 / Published: 25 January 2017
(This article belongs to the Special Issue Feature Papers)
View Full-Text   |   Download PDF [457 KB, uploaded 25 January 2017]   |  

Abstract

The effect of ion binding on the structural, mechanical, dynamic and electrostatic properties of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer in a 0.5 M aqueous NaCl solution is investigated using classical atomistic molecular dynamics simulation with different force-field descriptions for ion-ion and ion-lipid interactions. Most importantly, the repulsive Lennard–Jones parameters for the latter were modified, such that approximately similar binding of cations and anions to the lipid membrane is achieved. This was done to qualitatively improve the apparent ion-lipid binding constants obtained from simulations with the original force field (Berger lipids and GROMOS87 ions in combination with the SPC water model) in comparison to experimental data. Furthermore, various parameters characterizing membrane structure, elasticity, order and dynamics are analyzed. It is found that ion binding as observed in simulations involving the modified in comparison to the original force-field description leads to: (i) a smaller salt-induced change in the area per lipid, which is in closer agreement with the experiment; (ii) a decrease in the area compressibility and bilayer thickness to values comparable to a bilayer in pure water; (iii) lipid deuterium order parameters and lipid diffusion coefficients on nanosecond timescales that are very similar to the values for a membrane in pure water. In general, salt effects on the structural properties of a POPC bilayer in an aqueous sodium-chloride solution appear to be reproduced reasonably well by the new force-field description. An analysis of membrane-membrane disjoining pressure suggests that the smaller salt-induced change in area per lipid induced by the new force-field description is not due to the alteration of membrane-associated net charge, but must rather be understood as a consequence of ion-specific effects on the arrangement of lipid molecules. View Full-Text
Keywords: molecular dynamics; POPC bilayer; salt effects; lipid force field; ion force field; sodium chloride molecular dynamics; POPC bilayer; salt effects; lipid force field; ion force field; sodium chloride
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MDPI and ACS Style

Reif, M.M.; Kallies, C.; Knecht, V. Effect of Sodium and Chloride Binding on a Lecithin Bilayer. A Molecular Dynamics Study. Membranes 2017, 7, 5.

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