Bilayer model impedance

The polyelectrolyte-tethered bilayers were investigated by means of time dependent surface plasmon spectroscopy, impedance spectroscopy, FRAP, as well as NR [27], The NR data given in Fig. 12 were first calculated based on a model that included the substrate and a box for the polyelectrolyte multilayer (A), and an additional box for the lipid bilayer (C). However, in order to fit the experimental NR curve, a top layer had to be added that was approximated by a uniform coating with average scattering length density b/V shown in the inset of Fig. 12. The thickness of... 

Membrane structures that contain the visual receptor protein rhodopsin were formed by detergent dialysis on platinum, silicon oxide, titanium oxide, and indium—tin oxide electrodes. Electrochemical impedance spectroscopy was used to evaluate the biomembrane structures and their electrical properties. A model equivalent circuit is proposed to describe the membrane-electrode interface. The data suggest that the surface structure is a relatively complete single-membrane bilayer with a coverage of 0.97 and with long-term stability/... 

Membranes containing the visual pigment rhodopsin, a G-protein-linked receptor, were chosen as a model system for this work. Rhodopsin was one of the first integral membrane proteins whose amino acid sequence was determined (16-18). More than 40 receptors have been reported to have structural and functional homologies with rhodopsin (19). This chapter describes the use of electrochemical impedance spectroscopy to evaluate lipid bilayer membranes containing rhodopsin formed on electrode surfaces. 

At frequencies below 63 Hz, the double-layer capacitance began to dominate the overall impedance of the membrane electrode. The electric potential profile of a bilayer membrane consists of a hydrocarbon core layer and an electrical double layer (49). The dipolar potential, which originates from the lipid bilayer head-group zone and the incorporated protein, partially controls transmembrane ion transport. The model equivalent circuit presented here accounts for the response as a function of frequency of both the hydrocarbon core layer and the double layer at the membrane-water interface. The value of Cdl from the best curve fit for the membrane-coated electrode is lower than that for the bare PtO interface. For the membrane-coated electrode, the model gives a polarization resistance, of 80 kfl compared with 5 kfl for the bare PtO electrode. Formation of the lipid membrane creates a dipolar potential at the interface that results in higher Rdl. The incorporated rhodopsin may also extend the double layer, which makes the layer more diffuse and, therefore, decreases C. ... 

Electrochemical impedance spectroscopy provides a sensitive means for characterizing the structure and electrical properties of the surface-bound membranes. The results from impedance analysis are consistent with a single biomembrane-mimetic structure being assembled on metal and semiconductor electrode surfaces. The structures formed by detergent dialysis may consist of a hydrophobic alkyl layer as one leaflet of a bilayer and the lipid deposited by dialysis as the other. Proteins surrounded by a bound lipid layer may simultaneously incorporate into pores in the alkylsilane layer by hydrophobic interactions during deposition of the lipid layer. This model is further supported by the composition of the surface-bound membranes and by Fourier transform infrared analyses (9). 

For a simple planar bilayer membrane the impedance studies produce one semicircle on the complex plane plots according to the model RsiRmCm), from which the resistance, R, and capacitance, Cm, of the membrane can be simply determined. 

Pensado et al. [2001] Lithium. Cation and anion vacancies, LiH hydride barrier layer, LiOH outer layer Irreversible reactions with kinetic effects, barrier layer and outer layer dissolution Concentrations of cation and anion vacancies and barrier layer thickness First impedance analysis of bilayer structure and of hydride barrier layer. Cathodic reaction included in the model... 

Various planar membrane models have been developed, either for fundamental studies or for translational applications monolayers at the air-water interface, freestanding films in solution, solid supported membranes, and membranes on a porous solid support. Planar biomimetic membranes based on amphiphilic block copolymers are important artificial systems often used to mimic natural membranes. Their advantages, compared to artificial lipid membranes, are their improved stability and the possibility of chemically tailoring their structures. The simplest model of such a planar membrane is a monolayer at the air-water interface, formed when amphiphilic molecules are spread on water. As cell membrane models, it is more common to use free-standing membranes in which both sides of the membrane are accessible to water or buffer, and thus a bilayer is formed. The disadvantage of these two membrane models is the lack of stability, which can be overcome by the development of a solid supported membrane model. Characterization of such planar membranes can be challenging and several techniques, such as AFM, quartz crystal microbalance (QCM), infrared (IR) spectroscopy, confocal laser scan microscopy (CLSM), electrophoretic mobility, surface plasmon resonance (SPR), contact angle, ellipsometry, electrochemical impedance spectroscopy (EIS), patch clamp, or X-ray electron spectroscopy (XPS) have been used to characterize their... 

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