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Monovalent Ions and Water Dipoles in Contact with Dipolar Zwitterionic Lipid Headgroups-Theory and MD Simulations
Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25,SI-1000 Ljubljana, Slovenia
SMARTEH Research and Development of Electronic Controlling and Regulating Systems,Trg tigrovcev 1, SI-5220 Tolmin, Slovenia
Laboratory of Biophysics, Faculty of Electrical Engineering, Tržaška 25, University of Ljubljana, SI-1000 Ljubljana, Slovenia
Laboratory of Clinical Biophysics, Orthopaedic Clinics and Faculty of Medicine, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia
* Author to whom correspondence should be addressed.
Received: 22 December 2012; in revised form: 20 January 2013 / Accepted: 21 January 2013 / Published: 29 January 2013
Abstract: The lipid bilayer is a basic building block of biological membranes and can be pictured as a barrier separating two compartments filled with electrolyte solution. Artificial planar lipid bilayers are therefore commonly used as model systems to study the physical and electrical properties of the cell membranes in contact with electrolyte solution. Among them the glycerol-based polar phospholipids which have dipolar, but electrically neutral head groups, are most frequently used in formation of artificial lipid bilayers. In this work the electrical properties of the lipid layer composed of zwitterionic lipids with non-zero dipole moments are studied theoretically. In the model, the zwitterionic lipid bilayer is assumed to be in contact with aqueous solution of monovalent salt ions. The orientational ordering of water, resulting in spatial variation of permittivity, is explicitly taken into account. It is shown that due to saturation effect in orientational ordering of water dipoles the relative permittivity in the zwitterionic headgroup region is decreased, while the corresponding electric potential becomes strongly negative. Some of the predictions of the presented mean-field theoretical consideration are critically evaluated using the results of molecular dynamics (MD) simulation.
Keywords: lipids; dipolar zwitterionic headgroups; relative permittivity; orientational ordering; water molecules; planar lipid bilayers
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Velikonja, A.; Perutkova, Š.; Gongadze, E.; Kramar, P.; Polak, A.; Maček-Lebar, A.; Iglič, A. Monovalent Ions and Water Dipoles in Contact with Dipolar Zwitterionic Lipid Headgroups-Theory and MD Simulations. Int. J. Mol. Sci. 2013, 14, 2846-2861.
Velikonja A, Perutkova Š, Gongadze E, Kramar P, Polak A, Maček-Lebar A, Iglič A. Monovalent Ions and Water Dipoles in Contact with Dipolar Zwitterionic Lipid Headgroups-Theory and MD Simulations. International Journal of Molecular Sciences. 2013; 14(2):2846-2861.
Velikonja, Aljaž; Perutkova, Šarka; Gongadze, Ekaterina; Kramar, Peter; Polak, Andraž; Maček-Lebar, Alenka; Iglič, Aleš. 2013. "Monovalent Ions and Water Dipoles in Contact with Dipolar Zwitterionic Lipid Headgroups-Theory and MD Simulations." Int. J. Mol. Sci. 14, no. 2: 2846-2861.