Bilayer lipid membranes , scanning

Tsionsky M, Zhou IF, Amemiya S, Fan FRF, Bard AJ, Dryfe RAW (1999) Scanning electrochemical microscopy. 38. Application of SECM to the study of charge transfer through bilayer lipid membranes. Anal Chem 71(19) 4300-4305... 

Amemiya S, Bard AJ (2000) Scanning electrochemical microscopy. 40. Voltarametric ion-selective micropipet electrodes for probing ion transfer at bilayer lipid membranes. Anal Chem 72(20) 4940-4948... 

Gennis RB (1989) Biomembranes molecular structure and function. Springer, New York Yeagle P (1992) The structure of biological membranes. CRC Press, Boca Raton McElhaney RN (1986) Differential scanning calorimetric studies of lipid-protein interactions in model membrane systems. Biochim Biophys Acta 864(3-4) 361-42l HianikT, Passechnik VI (1995) Bilayer lipid membranes structure and mechanical properties. Kluwer, Netherlands... 

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... 

Lipofullerenes such as 35-37 self-assemble within lipid bilayers into rod-like structures of nanoscopic dimensions [61, 62]. These anisotropic superstructures may be important for future membrane technology. Significantly, lipofullerenes 35 and 37 have very low melting points, 22 and 67 °C (DSC, heating scan), respectively, with 35 being the first liquid fuUerene derivative at room temperature. 

Because the area under the peaks in the scanning calorimeter is proportional to the heat of transition, the instrument can be calibrated by running a known amount of membrane lipid suspended in water. It is necessary to assume, of course, that all of the lipid is in the bilayer conformation in water. If the lipid content of the membranes is known, the fraction of the lipids contributing to the peak observed for the membranes can then be calculated by comparing peak areas for the membranes and the lipids in water. Our preliminary results using this approach indicate that at least 60% of the lipids in the membranes participate in the phase change. Work is in progress to obtain more precision. 

Comparson of the transitions observed by differential scanning calorimetry in membranes of M. laidlawii and in water dispersions of the lipids from the membranes support the concept that most of the lipids exist as a smectic mesophase in the membranes. The evidence for a bilayer structure is straightforward in this case. Lipid transition temperatures are a function of fatty acid composition and correlate well with biological properties. The calorimeter possesses advantages over high resolution NMR for M. laidlawii, and perhaps in many other systems, because the data can be interpreted less ambiguously. In M. laidlawii membranes the bilayer appears to be compatible with the same physical properties observed in other membranes—a red-shifted ORD, lack of ft structure in the infrared, reversible dissociation by detergents, and poorly... 

The influence of plant sterols on the phase properties of phospholipid bilayers has been studied by differential scanning calorimetry and X-ray diffraction [206]. It is interesting that the phase transition of dipalmitoylglycerophosphocholine was eliminated by plant sterols at a concentration of about 33 mole%, as found for cholesterol in animal cell membranes. However, less effective modulation of lipid bilayer permeability by plant sterols as compared with cholesterol has been reported. The molecular evolution of biomembranes has received some consideration [207-209]. In his speculation on the evolution of sterols, Bloch [207] has suggested that in the prebiotic atmosphere chemical evolution of the sterol pathway if it did indeed occur, must have stopped at the stage of squalene because of lack of molecular oxygen, an obligatory electron acceptor in the biosynthetic pathway of sterols . Thus, cholesterol is absent from anaerobic bacteria (procaryotes). 

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