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Lebar AM, Velikonja A, Kramar P, Iglič A. Internal configuration and electric potential in planar negatively charged lipid head group region in contact with ionic solution. Bioelectrochemistry 2016; 111:49-56. [PMID: 27209203 DOI: 10.1016/j.bioelechem.2016.04.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2015] [Revised: 04/19/2016] [Accepted: 04/19/2016] [Indexed: 11/17/2022]
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.
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Affiliation(s)
- Alenka Maček Lebar
- Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia
| | - Aljaž Velikonja
- Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia
| | - Peter Kramar
- Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia
| | - Aleš Iglič
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaška 25, SI-1000 Ljubljana, Slovenia.
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Velikonja A, Kramar P, Miklavčič D, Maček Lebar A. Specific electrical capacitance and voltage breakdown as a function of temperature for different planar lipid bilayers. Bioelectrochemistry 2016; 112:132-7. [PMID: 26948707 DOI: 10.1016/j.bioelechem.2016.02.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 02/15/2016] [Accepted: 02/23/2016] [Indexed: 12/16/2022]
Abstract
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. The breakdown voltage of DPPC planar lipid bilayer at melting temperature is considerably higher than in the gel phase. Specific electrical capacitance of planar lipid bilayers formed from archaeal lipids is approximately constant for temperatures up to 40°C and then gradually decreases. The difference with MD simulation predictions is discussed. Specific electrical capacitance of DPPC planar lipid bilayers in fluid phase is 1.75 times larger than that of the gel phase and it follows intermediated phases before phase transition. Increase in specific electrical capacitance while approaching melting point of DPPC is visible also for DPhPC:DPPC mixture.
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Affiliation(s)
- Aljaž Velikonja
- University of Ljubljana, Faculty of Electrical Engineering, Slovenia
| | - Peter Kramar
- University of Ljubljana, Faculty of Electrical Engineering, Slovenia
| | - Damijan Miklavčič
- University of Ljubljana, Faculty of Electrical Engineering, Slovenia
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Kulkarni M, Flašker A, Lokar M, Mrak-Poljšak K, Mazare A, Artenjak A, Čučnik S, Kralj S, Velikonja A, Schmuki P, Kralj-Iglič V, Sodin-Semrl S, Iglič A. Binding of plasma proteins to titanium dioxide nanotubes with different diameters. Int J Nanomedicine 2015; 10:1359-73. [PMID: 25733829 PMCID: PMC4340467 DOI: 10.2147/ijn.s77492] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
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. We investigated binding of various plasma proteins with different sizes and charges using the bicinchoninic acid assay and immunofluorescence microscopy. Results showed effective and comparatively higher protein binding to NTs with 100 nm diameters (compared to 50 or 15 nm). We also showed a dose-dependent effect of serum amyloid A protein binding to NTs. These results and theoretical calculations of total available surface area for binding of proteins indicate that the largest surface area (also considering the NT lengths) is available for 100 nm NTs, with decreasing surface area for 50 and 15 nm NTs. These current investigations will have an impact on increasing the binding ability of biomedical devices in the body leading to increased durability of biomedical devices.
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Affiliation(s)
- Mukta Kulkarni
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
| | - Ajda Flašker
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
| | - Maruša Lokar
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
| | - Katjuša Mrak-Poljšak
- Department of Rheumatology, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Anca Mazare
- Department of Materials Science and Engineering, University of Erlangen Nuremberg, Erlangen, Germany
| | - Andrej Artenjak
- Sandoz Biopharmaceuticals Mengeš, Lek Pharmaceuticals dd, Menges, Slovenia
| | - Saša Čučnik
- Department of Rheumatology, University Medical Centre Ljubljana, Ljubljana, Slovenia
| | - Slavko Kralj
- Department for Materials Synthesis, Institute Jožef Stefan (IJS), Ljubljana, Slovenia
| | - Aljaž Velikonja
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
| | - Patrik Schmuki
- Department of Materials Science and Engineering, University of Erlangen Nuremberg, Erlangen, Germany
| | | | - Snezna Sodin-Semrl
- Department of Rheumatology, University Medical Centre Ljubljana, Ljubljana, Slovenia
- Faculty of Mathematics, Natural Science and Information Technology, University of Primorska, Koper, Slovenia
| | - Aleš Iglič
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
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Polak A, Velikonja A, Kramar P, Tarek M, Miklavčič D. Electroporation threshold of POPC lipid bilayers with incorporated polyoxyethylene glycol (C12E8). J Phys Chem B 2014; 119:192-200. [PMID: 25495217 DOI: 10.1021/jp509789m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
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.
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Affiliation(s)
- Andraž Polak
- University of Ljubljana , Faculty of Electrical Engineering, Tržaška cesta 25, SI-1000 Ljubljana, Slovenia
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Gongadze E, Velikonja A, Perutkova Š, Kramar P, Maček-Lebar A, Kralj-Iglič V, Iglič A. Ions and water molecules in an electrolyte solution in contact with charged and dipolar surfaces. Electrochim Acta 2014. [DOI: 10.1016/j.electacta.2013.07.147] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Santhosh PB, Velikonja A, Gongadze E, Iglič A, Kralj-Iglič V, Ulrih NP. Interactions of divalent calcium ions with head groups of zwitterionic phosphatidylcholine liposomal membranes. Acta Chim Slov 2014; 61:215-222. [PMID: 25125103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023] Open
Abstract
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.
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Santhosh PB, Velikonja A, Perutkova Š, Gongadze E, Kulkarni M, Genova J, Eleršič K, Iglič A, Kralj-Iglič V, Ulrih NP. Influence of nanoparticle-membrane electrostatic interactions on membrane fluidity and bending elasticity. Chem Phys Lipids 2013; 178:52-62. [PMID: 24309194 DOI: 10.1016/j.chemphyslip.2013.11.009] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Revised: 11/21/2013] [Accepted: 11/22/2013] [Indexed: 11/18/2022]
Abstract
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. 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.
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Affiliation(s)
- Poornima Budime Santhosh
- Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia
| | - Aljaž Velikonja
- Laboratory of Biocybernetics, Faculty of Electrical Engineering, University of Ljubljana, Tržaska 25, SI-1000 Ljubljana, Slovenia; SMARTEH Research and Development of Electronic Controlling and Regulating Systems, Trg Tigrovcev 1, SI-5220 Tolmin, Slovenia
| | - Šarka Perutkova
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaska 25, SI-1000 Ljubljana, Slovenia; Institute of Cell Biology, Faculty of Medicine, University of Ljubljana, Lipičeva 2, SI-1000 Ljubljana, Slovenia
| | - Ekaterina Gongadze
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaska 25, SI-1000 Ljubljana, Slovenia
| | - Mukta Kulkarni
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaska 25, SI-1000 Ljubljana, Slovenia
| | - Julia Genova
- Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria
| | | | - Aleš Iglič
- Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana, Tržaska 25, SI-1000 Ljubljana, Slovenia
| | - Veronika Kralj-Iglič
- Laboratory of Clinical Biophysics, Faculty of Health Sciences, University of Ljubljana, Vrazov trg 2, SI-1000 Ljubljana, Slovenia
| | - Nataša Poklar Ulrih
- Department of Food Science and Technology, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia; Centre of Excellence for Integrated Approaches in Chemistry and Biology of Proteins (CipKeBiP), Jamova 39, SI-1000 Ljubljana, Slovenia.
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