title: Internal configuration and electric potential in planar negatively charged lipid head group region in contact with ionic solution.
abstract: The lipid bilayer composed of negatively charged lipid 1-palmitoyl-3-oleoyl-sn-glycero-3-phosphatidylserine (POPS) in contact with an aqueous solution of monovalent salt ions was studied theoretically by using the mean-field modified Langevin-Poisson-Boltzmann (MLPB) model. The MLPB results were tested by using molecular dynamic (MD) simulations. In the MLPB model the charge distribution of POPS head groups is theoretically described by the negatively charged surface which accounts for negatively charged phosphate groups, while the positively charged amino groups and negatively charged carboxylate groups are assumed to be fixed on the rod-like structures with rotational degree of freedom. The spatial variation of relative permittivity, which is not considered in the well-known Gouy-Chapman (GC) model or in MD simulations, is thoroughly derived within a strict statistical mechanical approach. Therefore, the spatial dependence and magnitude of electric potential within the lipid head group region and its close vicinity are considerably different in the MLPB model from the GC model. The influence of the bulk salt concentration and temperature on the number density profiles of counter-ions and co-ions in the lipid head group region and aqueous solution along with the probability density function for the lipid head group orientation angle was compared and found to be in qualitative agreement in the MLPB and MD models.
authors.affiliation: Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia.
authors.forename: Alenka Maček
authors.initials: AM
authors.lastname: Lebar
authors.affiliation: Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia.
authors.forename: Aljaž
authors.initials: A
authors.lastname: Velikonja
authors.affiliation: Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia.
authors.forename: Peter
authors.initials: P
authors.lastname: Kramar
authors.affiliation: Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia. Electronic address: ales.iglic@fe.uni-lj.si.
authors.forename: Aleš
authors.initials: A
authors.lastname: Iglič
mesh_terms: D004560:Electricity; D008051:Lipid Bilayers / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D011789:Quantum Theory; D012996:Solutions
chemical_list: D008051:Lipid Bilayers; D012996:Solutions
keywords: 1-palmitoyl-3-oleoyl-sn-glycero-3-phosphatidylserine bilayer; Electric double layer; Ionic solution; MD simulations; MLPB model; Water dipole ordering