Liquid crystals liposomes

Phospholipids or similar water-insoluble amphiphilic natural substances aggregate in water to form bilayer liquid crystals which rearrange when exposed to ultrasonic waves to give spherical vesicles. Natural product vesicles are also called liposomes. Liposomes, as well as synthetic bilayer vesicles, can entrap substances in the inner aqueous phase, retain them for extended periods, and release them by physical process. 

Cholesterol s presence in liposome membranes has the effect of decreasing or even abolishing (at high cholesterol concentrations) the phase transition from the gel state to the fluid or liquid crystal state that occurs with increasing temperature. It also can modulate the permeability and fluidity of the associated membrane—increasing both parameters at temperatures below the phase transition point and decreasing both above the phase transition temperature. Most liposomal recipes include cholesterol as an integral component in membrane construction. 

Similar to Voltaren" Emulgel, oily droplets of an eutectic mixture of lidocaine and prilocaine are dispersed in a hydrogel to provide local anesthesia to the skin for injections and siugical treatment (Emla cream). A further possibility is the dermal administration of a liposome dispersion as a spray (Heparin PUR ratiopharm Spriih-gel "). After administration, water and isopropylic alcohol evaporate partially resulting in an increase of concentration and in a transition from the initial liposome dispersion into a lamellar liquid crystal [32]. The therapeutic effect appears to be influenced favorably by the presence of lecithins rather than by the degree of liposome dispersion. 

Tiddy, G.J.T., Surfactant-water liquid crystal phases, Phys. Rep., 57 1-46 (1980). Gregoriadis, G., ed.. Liposome Technology, Vols. I-III, CRC Press Inc., Boca Raton, FL, 1993. 

Unilamellar liposomes are nanoparticles made of a bilayer, most often phospholipidic, entrapping an internal aqueous core. Formed spontaneously in the presence of an excess of water and above the gel-to-liquid crystal phase tran-... 

Liquid crystals, liposomes, and artificial membranes. Phospholipids dissolve in water to form true solutions only at very low concentrations ( 10-10 M for distearoyl phosphatidylcholine). At higher concentrations they exist in liquid crystalline phases in which the molecules are partially oriented. Phosphatidylcholines (lecithins) exist almost exclusively in a lamellar (smectic) phase in which the molecules form bilayers. In a warm phosphatidylcholine-water mixture containing at least 30% water by weight the phospholipid forms multilamellar vesicles, one lipid bilayer surrounding another in an "onion skin" structure. When such vesicles are subjected to ultrasonic vibration they break up, forming some very small vesicles of diameter down to 25 nm which are surrounded by a single bilayer. These unilamellar vesicles are often used for study of the properties of bilayers. Vesicles of both types are often called liposomes.75-77... 

O-antigen of 180 structures of 430 Lipoprotein(s) 58 bacterial 428 Liposomes 392, 392-394 NMR spectra 396 Liquid crystals 392-394 Liquid crystalline phases 392 Lithium salts, in treatment of manic-depressive illness 564 Lithostatine 443 Liverworts 29... 

Safinya CR, Ewert KK, Ahmad A, Evans HM, Raviv U, Needleman DJ, Lin AJ, Slack NL, George CX, Samuel CE (2006) Cationic liposome-DNA complexes from liquid crystal science to gene delivery applications. Phil Transact Royal Soc A 364 2573-2596... 

The physical and chemical properties of photoisomerizable molecular films or photoisomerizable polymers are controlled by light. Photochemical control of the formation of liquid crystal phases, or sol-gel transitions,137 381 of polymers containing photoisomerizable components demonstrates signal regulation of the structure and properties of microscopic and macroscopic phases. Physicochemical properties of photoisomerizable membrane-mimetic assemblies such as liposomes,1241 mono-... 

Polyhedral niosomes were found to be thermoresponsive Fig. 7 (a). Above 35 °C, there was an increase in the release of CF from these niosomes even though the polyhedral shape was preserved until these vesicles were heated to 50 °C. Solulan C24-free polyhedral niosomes do not exhibit this thermoresponsive behavior [160] due to a decrease in the interaction of the polyoxyethylene compound solulan C24 with water at this temperature (due to decreased hydrogen bonding) as identified by viscometry [161]. This observed thermoresponsive behavior was used to design a reversible thermoresponsive controlled release system Fig. 7 (b). Thermoresponsive liposomal systems which rely on the changing membrane permeability, when the system transfers from the gel state (La) to the liquid crystal state (L 3) [162], are not reversible. This is not unex-... 

Second, in addition to the above, the fact that many expanded porphyrins are highly colored makes their use as dyes an obvious possibihty. Here their planar nature makes them particularly attractive as chromophores for use in liquid crystals and optical data storage applications. Also, these properties could make them of interest as photo-sensors in various clinical or pseudo-clinical situations. For instance, the high affinity by certain sapphyrins for enveloped viruses and cholesterol rich liposomes suggests that expanded porphyrins could be used to detect and/or destroy a variety of unwanted biological targets, including arterial sclerotic plaque. 

Li Y, Friberg S. Course Manual for the American Chemical Society Short Course on Surfactant Micelles, Liposomes, and Liquid Crystals in Emulsions and Microemulsions. 2002. 

The amphiphilic molecules can occur in lyotropic and thermotropic mesomorph, and the organization of lipid bilaycrs such as liposomes can exist in a temperature range where all the mesophases from gel state to liquid crystal state are favored. In the gel state the phospholipid acyl chains are closely packed and the molecular movements are deteriorized, while in the liquid crystalline slate, the fatty-acid moieties are in a more fluid stale and are able to move more freely. 

Liposomes belong to the class of lyotropic liquid crystals. Obviously, their physicochemical characteristics and their biocompatibility with cell membranes has given them several advantages they can dissolve, protect and deliver hydrophobic and hydrophilic molecules. Several applications of liposomes relate to a broad range of sciences and disciplines such as, biochemistry, chemistry, biology, medicine, biophysics, physics and mathematics. 

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