Structure of anionic phospholipid coatings on silica by dissipative quartz crystal microbalance
ABSTRACT The adsorption of anionic phospholipids on silica was investigated by the dissipative quartz crystal microbalance (QCM) technique. Liposomes composed of 1 mM 80:20 mol % of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC)/phosphatidic acid, POPC/phosphatidylglycerol, or POPC/phosphatidylserine in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) buffer at pH 7.4 (with or without 3 mM of CaCl2) were examined. We have previously demonstrated that similar phospholipid coatings can be used in capillary electrochromatography as a stationary phase for the separation of analytes. In this work, we focus on the formation of the coatings and on the type of lipid structure formed on silica. The QCM investigation comprised qualitative results based on changes in frequency and resistance, and quantitative modeling of the obtained results. The latter was performed using the dissipative QCM, which measures the quartz crystal impedance, combined with equivalent circuit analysis. A previously developed coating and cleaning procedure for phospholipid-coated fused silica capillaries was adopted in this study, and the same silica-coated crystal was used throughout the QCM study. We will demonstrate in this work that the type of lipid structure formed on silica, that is, a rather rigid supported lipid bilayer or a viscoelastic supported vesicle layer (SVL), is highly dependent on the lipid and solvent composition. We also show for the first time that the modeling of the dissipative QCM data can be used to extract a more quantitative picture of an adsorbed SVL, because, so far, published studies have merely used the QCM data in a qualitative sense.
SourceAvailable from: Susanne Wiedmer[Show abstract] [Hide abstract]
ABSTRACT: The reassembly of the S-layer protein SlpA of Lactobacillus brevis ATCC 8287 on positively charged liposomes was studied by small angle X-ray scattering (SAXS) and zeta potential measurements. SlpA was reassembled on unilamellar liposomes consisting of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine and 1,2-dioleoyl-3-trimethylammonium-propane, prepared by extrusion through membranes with pore sizes of 50nm and 100nm. Similarly extruded samples without SlpA were used as a reference. The SlpA-containing samples showed clear diffraction peaks in their SAXS intensities. The lattice constants were calculated from the diffraction pattern and compared to those determined for SlpA on native cell wall fragments. Lattice constants for SlpA reassembled on liposomes (a=9.29nm, b=8.03nm, and γ=84.9°) showed a marked change in the lattice constants b and γ when compared to those determined for SlpA on native cell wall fragments (a=9.41nm, b=6.48nm, and γ=77.0°). The latter are in good agreement with values previously determined by electron microscopy. This indicates that the structure formed by SlpA is stable on the bacterial cell wall, but SlpA reassembles into a different structure on cationic liposomes. From the (10) reflection, the lower limit of crystallite size of SlpA on liposomes was determined to be 92nm, corresponding to approximately ten aligned lattice planes.Biochimica et Biophysica Acta 05/2014; 1838(8). DOI:10.1016/j.bbamem.2014.04.022 · 4.66 Impact Factor
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ABSTRACT: Different types of lipid bilayers/monolayers have been used to simulate the cellular membranes in the investigation of the interactions between drugs and cells. However, to our knowledge, very few studies focused on the influence of the chosen membrane model upon the obtained results. The main objective of this work is to understand how do the nature and immobilization state of the biomembrane models influence the action of the local anaesthetic tetracaine (TTC) upon the lipid membranes. The interaction of TTC with different biomembrane models of dimyristoylphosphatidylcholine (DMPC) with and without cholesterol (CHOL) was investigated through several techniques. A quartz crystal microbalance with dissipation (QCM-D) was used to study the effect on immobilized liposomes, while phosphorus nuclear magnetic resonance ((31)P-NMR) and differential scanning calorimetry (DSC) were applied to liposomes in suspension. The effect of TTC on Langmuir monolayers of lipids was also investigated through surface pressure-area measurements at the air-water interface. The general conclusion was that TTC has a fluidizing effect on the lipid membranes and, above certain concentrations, induces membrane swelling or even solubilization. However, different models led to variable responses to the TTC action. The intensity of the disordering effect caused by TTC increased in the following order: supported liposomes<liposomes in solution<Langmuir monolayers. This means that extrapolation of the results obtained in in vitro studies of the lipid/anaesthetic interactions to in vivo conditions should be done carefully.Colloids and surfaces B: Biointerfaces 12/2013; 116C:63-71. DOI:10.1016/j.colsurfb.2013.12.042 · 4.29 Impact Factor
Conference Paper: Interaction between anaesthetics and model biomembrane systems[Show abstract] [Hide abstract]
ABSTRACT: Supported layers of vesicles of dimyristoyl and dipalmitoyl phosphatidylcholine containing cholesterol are adequate models for eukaryotic plasma membranes. In this work it was investigated the adsorption of unilamellar vesicles on the surface of oxidized gold, using a QCM-D, AFM and LSCFM. The results of all techniques indicate that a dense layer of intact liposomes irreversibly adsorbs on the gold surface. It was also investigated the interaction of some examples of local and general anaesthetics with these membrane models, using a QCM-D. Lidocaine, tetracaine, ropivacaine and levobupivacaine were chosen as local anaesthetics examples, and propofol as general anaesthetic. Simultaneously, the interaction of the anaesthetics with the same liposomes in suspension was studied, using DSC. The results showed that all the studied anaesthetics interacted with the used models, causing changes such as raised fluidity and depressed phase transition temperature.Bioengineering (ENBENG), 2011. ENBENG 2011. 1st Portuguese Meeting in; 01/2011