Internal configuration and electric potential in planar negatively charged lipid head group region in contact with ionic solution.

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.

Specific electrical capacitance and voltage breakdown as a function of temperature for different planar lipid bilayers.

The breakdown voltage and specific electrical capacitance of planar lipid bilayers formed from lipids isolated from the membrane of archaeon Aeropyrum pernix K1 as a function of temperature were studied and compared with data obtained previously in MD simulation studies. Temperature dependence of breakdown voltage and specific electrical capacitance was measured also for dipalmitoylphosphatidylcholine (DPPC) bilayers and bilayers formed from mixture of diphytanoylphosphocholine (DPhPC) and DPPC in ratio 80:20. The breakdown voltage of archaeal lipids planar lipid bilayers is more or less constant until 50°C, while at higher temperatures a considerable drop is observed, which is in line with the results from MD simulations.

Binding of plasma proteins to titanium dioxide nanotubes with different diameters.

Titanium and titanium alloys are considered to be one of the most applicable materials in medical devices because of their suitable properties, most importantly high corrosion resistance and the specific combination of strength with biocompatibility. In order to improve the biocompatibility of titanium surfaces, the current report initially focuses on specifying the topography of titanium dioxide (TiO2) nanotubes (NTs) by electrochemical anodization. The zeta potential (ζ-potential) of NTs showed a negative value and confirmed the agreement between the measured and theoretically predicted dependence of ζ-potential on salt concentration, whereby the absolute value of ζ-potential diminished with increasing salt concentrations.

Electroporation threshold of POPC lipid bilayers with incorporated polyoxyethylene glycol (C12E8).

Electroporation relates to a phenomenon in which cell membranes are permeabilized after being exposed to high electric fields. On the molecular level, the mechanism is not yet fully elucidated, although a considerable body of experiments and molecular dynamic (MD) simulations were performed on model membranes. Here we present the results of a combined theoretical and experimental investigation of electroporation of palmitoy-oleoyl-phosphatidylcholine (POPC) bilayers with incorporated polyoxyethylene glycol (C12E8) surfactants.

Interactions of divalent calcium ions with head groups of zwitterionic phosphatidylcholine liposomal membranes.

The interaction of the divalent calcium ions with the zwitterionic lipid membranes was studied by measuring the lipid order parameter which is inversely proportional to the membrane fluidity. Small unilamellar lipid vesicles were prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and then treated with different concentrations of divalent calcium ions. An increase in the order parameter and decrease in the fluidity of the liposomal membranes were observed after treatment with the calcium ions.

Influence of nanoparticle-membrane electrostatic interactions on membrane fluidity and bending elasticity.

The aim of this work is to investigate the effect of electrostatic interactions between the nanoparticles and the membrane lipids on altering the physical properties of the liposomal membrane such as fluidity and bending elasticity. For this purpose, we have used nanoparticles and lipids with different surface charges. Positively charged iron oxide (γ-Fe2O3) nanoparticles, neutral and negatively charged cobalt ferrite (CoFe2O4) nanoparticles were encapsulated in neutral lipid 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine and negatively charged 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine lipid mixture.

Interaction between dipolar lipid headgroups and charged nanoparticles mediated by water dipoles and ions.

In this work, a theoretical model describing the interaction between a positively or negatively charged nanoparticle and neutral zwitterionic lipid bilayers is presented. It is shown that in the close vicinity of the positively charged nanoparticle, the zwitterionic lipid head groups are less extended in the direction perpendicular to the membrane surface, while in the vicinity of the negatively charged nanoparticle, the headgroups are more extended.This result coincides with the calculated increase in the osmotic pressure between the zwitterionic lipid surface and positively charged nanoparticle and the decrease of osmotic pressure between the zwitterionic lipid surface and the negatively charged nanoparticle.

Monovalent ions and water dipoles in contact with dipolar zwitterionic lipid headgroups-theory and MD simulations.

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.