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Velikonja A.,University of Ljubljana | Velikonja A.,SMARTEH Research and Development of Electronic Controlling and Regulating Systems | Slivnik T.,University of Ljubljana | Kralj-Iglic V.,University of Ljubljana | Iglic A.,University of Ljubljana
Electrochimica Acta | Year: 2013

The interface electrolyte-charged surface has been captured within the generalized LangevinPoisson-Boltzmann and Langevin-Bikerman models. Here we have modified the latter models to illus-trate the importance of the non-zero quadrupole moment of the water molecule within a triangularatomic model. It is shown that the local decrease of relative permittivity of electrolyte solution near thecharged surface is further pronounced due to quadrupole moment of the water molecule. The effect isstronger for larger magnitudes of surface charge density. © 2013 Elsevier Ltd. All rights reserved. Source


Santhosh P.B.,University of Ljubljana | Velikonja A.,University of Ljubljana | Velikonja A.,SMARTEH Research and Development of Electronic Controlling and Regulating Systems | Gongadze E.,University of Ljubljana | And 3 more authors.
Acta Chimica Slovenica | Year: 2014

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. The presence of positively charged iron oxide nanoparticles in the suspension of liposomes negligibly changed the results. The results of experiments were discussed theoretically within modified Langevin-Poisson-Boltzmann (MLPB) model leading to the conclusion that the membrane fluidity and ordering of the membrane lipids are primarily altered by the accumulation of calcium ions in the region of negatively charged phosphate groups within the head groups of the membrane lipids. Source


Velikonja A.,SMARTEH Research and Development of Electronic Controlling and Regulating Systems | Kramar P.,University of Ljubljana | Miklavcic D.,University of Ljubljana | Lebar A.M.,University of Ljubljana
IFMBE Proceedings | Year: 2015

This paper presents the study of electrical properties of hydrogenated planar lipid bilayers formed from thermophilic archaeal lipids extracted from Aeropyrum pernix K1. Study is focused on measuring electrical capacitance as parameter of the planar lipid bilayer thickness and breakdown voltage as parameter of planar lipid bilayer stability in electric field. The results show that both measured parameters of hydrogenated planar lipid bilayers formed from archeal lipids extracted from A. pernix K1 are not temperature dependant on measured temperature interval between 19 °C and 56 °C. Electrical capacitance is lower than in Molecular Dynamic simulations and in experiments using 2-Oleoyl-1-palmitoylsn- glycero-3-phosphocholine (POPC) lipids or 2-Oleoyl-1- palmitoyl-sn-glycero-3-phosphoserine (POPS) lipids. Breakdown voltage is higher than in experiments with POPC or POPS lipids. © Springer International Publishing Switzerland 2015. Source


Polak A.,University of Ljubljana | Velikonja A.,University of Ljubljana | Velikonja A.,SMARTEH Research and Development of Electronic Controlling and Regulating Systems | Kramar P.,University of Ljubljana | And 2 more authors.
Journal of Physical Chemistry B | Year: 2015

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. The experimental results show a slight increase of the capacitance and a 22% decrease of the voltage breakdown upon addition of C12E8 to pure POPC bilayers. These results were qualitatively confirmed by the MD simulations. They later revealed that the polyoxyethylene glycol molecules play a major role in the formation of hydrophilic pores in the bilayers above the electroporation threshold. The headgroup moieties of the latter are indeed embedded in the interior of the bilayer, which favors formation of water wires that protrude into its hydrophobic core. When the water wires extend across the whole bilayer, they form channels stabilized by the C12E8 head groups. These hydrophilic channels can transport ions across the membrane without the need of major lipid head-group rearrangements. (Chemical Presented). © 2014 American Chemical Society. Source


Santhosh P.B.,University of Ljubljana | Velikonja A.,University of Ljubljana | Velikonja A.,SMARTEH Research and Development of Electronic Controlling and Regulating Systems | Perutkova S.,University of Ljubljana | And 7 more authors.
Chemistry and Physics of Lipids | Year: 2014

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-Fe 2O3) 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. Membrane fluidity was assessed through the anisotropy measurements using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Though the interaction of both the types of nanoparticles reduced the membrane fluidity, the results were more pronounced in the negatively charged liposomes encapsulated with positively charged iron oxide nanoparticles due to strong electrostatic attractions. X-ray photoelectron spectroscopy results also confirmed the presence of significant quantity of positively charged iron oxide nanoparticles in negatively charged liposomes. Through thermally induced shape fluctuation measurements of the giant liposomes, a considerable reduction in the bending elasticity modulus was observed for cobalt ferrite nanoparticles. The experimental results were supported by the simulation studies using modified Langevin-Poisson-Boltzmann model. © 2013 Elsevier Ireland Ltd. Source

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