Lecithin-BLM

Some experimentally derived values of yy for foam and emulsion bilayers are listed in Table 3.16. Values of yy for BLMs are also given for comparison. These data are obtained on the basis of an experiment in which the rupture of BLM is caused by an external electric field of intensity U [456,463]. Using the i(U) dependence the value of yy for bilayers from lyso PC and lyso PE is found to be 0.5 to 1.510"11 J m 1 (Table 3.16). For egg lecithin BLM in n-decane yy is also evaluated [459,464], Depending on the adopted model, packing model [465] or liquid-crystalline model [464] two values of yy are obtained yy = 0.75-10" J m 1 and % = 2.M011 J m1. The latter value is also determined in [466] by studying microscopic holes in tube liposomes in electric field (Table 3.16). 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

Although the present finding that BLM formed from simple lipids alone can possess intrinsic low yb without the presence of protein layers, it in no sense invalidates the bimolecular leaflet model. Our study does suggest, however, that natural lipids such as lecithin when in a bilayer configuration could exist in natural membranes to give the results of low yt observed by earlier workers, which has been thought essential in the development of the concept of the bimolecular lipo-protein model based upon interfacial tension measurements. 

Out of a variety of polymerizable lipids tested for possible use of bilayer formation, only three systems exhibited BLM lifetimes of more than a few minutes (Table 2 26)). These BLMs were characterized by measuring their resistance and capacitance (Table 2., see26> for details). The data obtained were comparable with values obtained with egg lecithin the most frequently used material for preparing BLMs. 

Recently, Kotowski et al. (1988) immobilized GOD by glutaraldehyde in a conductive lecithin polypyrrole bilayer membrane (BLM). The membrane was formed by polymerization of pyrrole in the presence of ferric chloride and was arranged between two electrodes. Addition of glucose leads to the formation of anodic peaks at 200 mV which reflect the electron transfer from reduced GOD to polypyrrole in the BLM system. The peak current exhibits a nonlinear dependence on the concentration of glucose between 1 and 20 mmol/1. 

Liquid/liquid interfaces have been discussed in Chapter 8. A related approach involves using an expanding droplet of a nonaqueous solvent positioned above a stationary microelectrode (microelectrochemical measurements at expanding droplets, or MEMED) (18,19). More recent work has probed bilayer lipid membranes (BLMs). A BLM is produced by placing a small amount of a lipid, such as lecithin, on a small orifice ( 600 /xin... 

It turned out to be true that proteinoids, without any lipids, also form bimolecular membranes.Despite the fact that black proteinoid membranes are not as long-lived in the ultrathin state as phospholipid membranes, they last long enough to be examined. Those rich in hydrocarbon-rich amino acid side chains mostly display properties characteristic for BLMs. The same polymers are among those that most readily combine with lecithin. 

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