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Typus
KomplettPlagiat
Bearbeiter
Klgn
Gesichtet
Yes.png
Untersuchte Arbeit:
Seite: 12, Zeilen: 1 ff. (entire page)
Quelle: Anézo 2003
Seite(n): 26, 27, Zeilen: 26:11ff; 27:1ff;
[Multilamellar vesicles (MLV) were the first liposomes to be characterized and consist of multiple bilayers forming a series of concentric shells with a diameter ranging from 5 to 50 μm. MLV are easy to] prepare, can be made in large quantities and high concentrations, and exhibit reproducible properties. They are thus suitable for a wide variety of biophysical studies. Drawbacks of MLV include the inhomogeneity in size and number of layers, the limited aqueous space for trapping solutes, and the close apposition of bilayers, which may affect membrane properties. The heterogeneity problem has been overcome by the introduction of small unilamellar vesicles (SUV), usually prepared by sonification of aqueous phospholipid dispersions. These vesicles have diameters from 10 to 50 nm and consist of a hollow sphere whose surface is single lipid bilayers. SUV are rather unsuitable for transport studies because of the too small size of the internal aqueous space. The radius of curvature of these vesicles is also much smaller than usually observed in cell membranes, resulting in packing constraints in the bilayers. The vesicle size was thus increased and large unilamellar vesicles (LUV), with diameters ranging from 50 to 500 nm, were produced. These vesicles are large enough to trap a significant amount of solute, necessary for transport experiments, and provide interesting drug delivery systems.

Planar bilayers membranes are traditionally created by painting a concentrated solution of phospholipid in solvent like hexane or decane over a small hole (about 1 mm diameter) immersed in an aqueous solution. Under appropriate conditions, the lipids spontaneously form bilayers across the hole. Because of their optical properties (lack of light reflectance), they are called black lipid membranes (BLM). The major advantages of planar membranes over vesicle preparations are their suitability for electrical measurements and for the study of membrane proteins. These systems are particularly appropriate for studying pores, channels or carriers that catalyze the transfer of charges across the bilayers. The unknown amount of residual solvent they contain as well as their relative instability may, however, generate some problems.

Lipids can be spread in a monolayer at an air/water interface – the polar headgroups are in contact with the aqueous phase, while the hydrocarbon chains extend in the gas phase. From the aqueous phase, the monolayer surface is similar to that of an entire membrane and surface properties can be investigated under variation of the surface density and the lateral surface pressure. Monolayers are especially useful for examining the behavior of molecules like lipases, known as being active at the membrane surface.

[page 26]

Multilamellar vesicles (MLV) were the first liposomes to be characterized and consist of multiple bilayers forming a series of concentric shells with a diameter ranging from 5 to 50 µm. MLV are easy to prepare, can be made in large quantities and high concentrations, and exhibit reproducible properties. They are thus suitable for a wide variety of biophysical studies. Drawbacks of MLV include the inhomogeneity in size and number of layers, the limited aqueous space for trapping solutes, and the close apposition of bilayers which may affect membrane properties. The heterogeneity problem has been overcome by the introduction of small unilamellar vesicles (SUV), usually prepared by sonification of aqueous phospholipid dispersions. These vesicles have diameters from 10 to 50 nm and consist of a hollow sphere whose surface is a single lipid bilayer. SUV are rather unsuitable for transport studies because of the too small size of the internal aqueous space. The radius of curvature of these vesicles is also much smaller than that usually observed in cell membranes, resulting in packing constraints in the bilayer. The vesicle size was thus increased and large unilamellar vesicles (LUV), with diameters ranging from 50 to 500 nm, were produced. These vesicles are large enough to trap a significant

[page 27]

amount of solute, necessary for transport experiments, and provide interesting drug delivery systems.

Planar bilayer membranes Planar bilayer membranes are traditionally created by painting a concentrated solution of phospholipid in a solvent like hexane or decane over a small hole (about 1 mm diameter) immersed in an aqueous solution. Under appropriate conditions, the lipids spontaneously form a bilayer across the hole. Because of their optical properties (lack of light reflectance), they are called black lipid membranes (BLM). The major advantages of planar membranes over vesicle preparations are their suitability for electrical measurements and for the study of membrane proteins. These systems are particularly appropriate for studying pores, channels, or carriers that catalyze the transfer of charges across the bilayer. The unknown amount of residual solvent they contain as well as their relative instability may, however, generate some problems.

Monolayers Lipids can be spread in a monolayer at an air/water interface: the polar headgroups are in contact with the aqueous phase, while the hydrocarbon chains extend in the gas phase. From the aqueous phase, the monolayer surface is similar to that of an entire membrane and surface properties can be investigated under variation of the surface density and the lateral surface pressure. Monolayers are especially useful for examining the behavior of molecules like lipases, known as being active at the membrane surface.

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(Klgn), WiseWoman

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