BLM =* bilayer lipid membrane

FIGURE 24.4 FIA manifold used for the analysis of mixtures of artificial sweeteners using filter-supported BLMs. BLM bilayer lipid membrane CER carrier electrolyte reservoir E electrometer G ground P pump PS power supply R recorder RE reference electrode S syringe SI sample injector SWP Saran-Wrap partition UM ultrafiltration membrane W waste. 

In biological systems molecular assemblies connected by non-covalent interactions are as common as biopolymers. Examples arc protein and DNA helices, enzyme-substrate and multienzyme complexes, bilayer lipid membranes (BLMs), and aggregates of biopolymers forming various aqueous gels, e.g, the eye lens. About 50% of the organic substances in humans are accounted for by the membrane structures of cells, which constitute the medium for the vast majority of biochemical reactions. Evidently organic synthesis should also develop tools to mimic the Structure and propertiesof biopolymer, biomembrane, and gel structures in aqueous media. 

As first shown by Hladky and Haydon 7,8), it is possible to observe the current due to a single transmembrane channel by using extensions of the planar lipid hilaver approach of Mueller and Rudin 9). The basic system is shown in Fig. 2 and is commonly referred to as the black lipid membrane (BLM) method. This is because, as the lipid in the hole between the two chambers thins, the areas that have become planar bilayers are seen as black. Additional terms are bilayer lipid membranes or planar lipid bilayer membranes. These lipid bilayer membranes, particularly those which are solvent free, have capacitances which are very close to those of biological membranes. 

The use of Upid bilayers as a relevant model of biological membranes has provided important information on the structure and function of cell membranes. To utilize the function of cell membrane components for practical applications, a stabilization of Upid bilayers is imperative, because free-standing bilayer lipid membranes (BLMs) typically survive for minutes to hours and are very sensitive to vibration and mechanical shocks [156,157]. The following concept introduces S-layer proteins as supporting structures for BLMs (Fig. 15c) with largely retained physical features (e.g., thickness of the bilayer, fluidity). Electrophysical and spectroscopical studies have been performed to assess the appUcation potential of S-layer-supported lipid membranes. The S-layer protein used in aU studies on planar BLMs was isolated fromB. coagulans E38/vl. 

Phospholipids are amphiphilic substances i.e. their molecules contain both hydrophilic and hydrophobic groups. Above a certain concentration level, amphiphilic substances with one ionized or polar and one strongly hydrophobic group (e.g. the dodecylsulphate or cetyltrimethylammonium ions) form micelles in solution these are, as a rule, spherical structures with hydrophilic groups on the surface and the inside filled with the hydrophobic parts of the molecules (usually long alkyl chains directed radially into the centre of the sphere). Amphiphilic substances with two hydrophobic groups have a tendency to form bilayer films under suitable conditions, with hydrophobic chains facing one another. Various methods of preparation of these bilayer lipid membranes (BLMs) are demonstrated in Fig. 6.10. 

Fig. 6.10 Methods of preparation of bilayer lipid membranes. (A) A Teflon septum with a window of approximately 1mm2 area divides the solution into two compartments (a). A drop of a lipid-hexane solution is placed on the window (b). By capillary forces the lipid layer is thinned and a bilayer (black in appearance) is formed (c) (P. Mueller, D. O. Rudin, H. Ti Tien and W. D. Wescot). (B) The septum with a window is being immersed into the solution with a lipid monolayer on its surface (a). After immersion of the whole window a bilayer lipid membrane is formed (b) (M. Montal and P. Mueller). (C) A drop of lipid-hexane solution is placed at the orifice of a glass capillary (a). By slight sucking a bubble-formed BLM is shaped (b) (U. Wilmsen, C. Methfessel, W. Hanke and G. Boheim)...

Ti Tien, H., Bilayer Lipid Membrane (BLM), M. Dekker, New York, 1974. 

Mueller et al. [6] discovered in 1962 that when a small quantity of a phospholipid (2% wt/vol alkane solution) was carefully placed over a small hole (0.5 mm) in a thin sheet of Teflon or polyethylene (10-25 pm thick), a thin film gradually forms at the center of the hole, with excess lipid flowing towards the perimeter (forming a Plateau-Gibbs border ). Eventually, the central film turns optically black as a single (5 nm-thick) bilayer lipid membrane (BLM) forms over the hole. Suitable lipids for the formation of a BLM are mostly isolated from natural sources, e.g.,... 

Since Upids are known to associate with DNA with high affinity, the adsorption of ssDNA at lipid membranes as a medium for DNA incorporation on a GC surface was extensively studied [60]. Exploiting DNA-Upid interactions, various approaches were designed for the incorporation of ssDNA [61] and dsDNA [62] at a modified bilayer lipid membrane (BLM) GC surface, such as (1) the formation of self-assembled BLMs over ssDNA previously adsorbed on GC, (2) the direct adsorption of ss- and dsDNA [62] into a previously BLM-modified GC and, (3) formation of a BLM with incorporated ssDNA at the GC surface using the monolayer folding technique [61]. 

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

Tien, H. T. Bilayer Lipid Membranes (BLM) Theory and Practice, Marcel Dekker New York, 1974. 

Description of the different mimetic systems will be the starting point of the presentation (Sect. 2). Preparation and characterization of monolayers (Langmuir films), Langmuir-Blodgett (LB) films, self-assembled (SA) mono-layers and multilayers, aqueous micelles, reversed micelles, microemulsions, surfactant vesicles, polymerized vesicles, polymeric vesicles, tubules, rods and related SA structures, bilayer lipid membranes (BLMs), cast multibilayers, polymers, polymeric membranes, and other systems will be delineated in sufficient detail to enable the neophyte to utilize these systems. Ample references will be provided to primary and secondary sources. 

A n oinhole which separates two compartments, b A schematic Fig. 58a. Formation of BLMs at at 1 K surfactant molecules in a bilayer lipid membrane diagram of the molecular organization... 

Bilayer lipid membranes (BLMs) 2D, 3D 30- to 50- Painting of the surfactant (or A-thick, 1- to 2- lipid), dissolved in a hydrocarbon mm-diameter mem- solvent, across a teflon pinhole brane, supported which separates two by a solvent compartments of aqueous solution surfactant reservoir the Plateau-Gibbs border or torus) and separating two aqueous solutions macroscopically Hours Convenient system for fundamental studies as simultaneous electrical and spectroscopic measurements were possible 385, 387... 

Membrane-mimetic compartments have provided a viable means for generating monodispersed catalytic particles [500], In particular, reversed micelles and microemulsions have been used extensively as hosts. A complete summary of work reported on the in situ generation of catalysts in membrane-mimetic media, including publications up to 1987, has been produced [500] and, therefore, will not be reiterated here. Attention will be focused on more recent research utilizing monolayers, bilayer lipid membranes (BLMs), Langmuir-Blodgett (LB) films, zeolites, and clay particles as membrane-mimetic templates. 

Glyceryl monooleate (GMO) (22) bilayer lipid membranes (BLMs) Ag Silver particulate films were generated photochemically in situ on the BLM surface and used in surface enhanced Raman spectroscopy 568... 

Bilayer lipid membranes (BLMs) prepared from glyceryl monooleate (GMO) (22), phosphatidylserine (16), and [n-C i sH31 C02(CH2)2]2N + (CH3)-CH2C6H4CH= H2, Cl"... 

Glyceryl monooleate (22) bilayer lipid membrane Nanometer-sized, single-domain, Fe304 particles attached to BLMs Electrical measurements and reflection spectroscopy were used for characterization 795... 

Tien HT (1974) Bilayer lipid membranes (BLM) Theory and practice. Marcel Dekker, New York... 

Independent of the assumptions A to C the cation selectivity of the membranes in the equilibrium domain is therefore controlled by the ratio of the complex formation constants (6) and should therefore be identical for different types of neutral carrier membranes.18 Figure 2 indicates that there is indeed a close parallelism between the selectivities of solvent polymeric membranes (SPM) and bilayer lipid membranes (BLM) modified with valinomycin 1, nonactin 2, trinactin 5, and tetranac-tin 6 (see also Ref. 18). This is in good agreement with findings from Eisenman s45 and Lev s15 research groups. 

A solution of brain lipids was brushed across a small hole in a 5-ml. polyethylene pH cup immersed in an electrolyte solution. As observed under low power magnification, the thick lipid film initially formed exhibited intense interference colors. Finally, after thinning, black spots of poor reflectivity suddenly appeared in the film. The black spots grew rapidly and evenutally extended to the limit of the opening (5, 10). The black membranes have a thickness ranging from 60-90 A. under the electron microscope. Optical and electrical capacitance measurements have also demonstrated that the membrane, when in the final black state, corresponds closely to a bimolecular leaflet structure. Hence, these membranous structures are known as bimolecular, black, or bilayer lipid membranes (abbreviated as BLM). The transverse electrical and transport properties of BLM have been studied usually by forming such a structure interposed between two aqueous phases (10, 17). 

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