Mesomorphism lyotropic

Some drug substances can form mesophases with or without a solvent [19-26]. In the absence of a solvent, an increase in temperature causes the transition from the solid state to the liquid crystalline state, called thermotropic mesomorphism. Lyotropic mesomorphism occurs in the presence of a solvent, usually water. A further change in temperature may cause additional transitions. Thermotropic and/or lyotropic liquid crystalline mesophases of drug substances may interact with meso-morphous vehicles as well as with liquid crystalline structures in the human organism. Table 1 presents drug substances for which thermotropic or lyotropic mesomorphism has been proved. 

Liquid crystal As the name implies, this is an ordered yet fluid phase in which water, surfactant, and solubilizate combine to form anisotropic, organized structures. These are called lyotropic mesomorphic phases, as opposed to thermotropic mesomorphs, which form when certain organic crystals are heated. 

Tihe term lyotropic mesomorphism is used to describe the formation of thermodynamically stable liquid crystalline systems through the penetration of a solvent between the molecules of a crystal lattice. In contrast to the thermotropic mesomorphism shown by many pure substances, lyotropic mesomorphism always requires the participation of a solvent. Lyotropically mesomorphous systems, however, are usually as sensitive to changes in temperature as thermotropic systems. So far, lyotropic mesomorphism has been observed almost exclusively in lipid systems containing water. Lipids that show lyotropic mesomorphism frequently... 

The structure of the lyotropically mesomorphous lattice is made up of multimolecular units called mesoaggregates. These are surrounded by an intervening liquid. Lyotropic mesomorphism is therefore closely related to the tendency of lipids to accumulate at interfaces. The surface activity is a consequence of the same dualistic polar/non-polar molecular structure that causes the formation of micelles in solutions of association colloids (I, 2, 3, 4, 5, 6). 

The change from a crystalline into a liquid crystalline state can be brought about by changes in, for example, temperature or pressure. Furthermore, some molecules may be induced to form liquid crystals by the addition of a solvent such as water. This behavior is in reality a liquid crystalline formation in a two component system and is called solvent-induced liquid crystal formation or lyotropic mesomorphism (Small, 1986, p. 49). 

Chapman D, Williams RM, Ladbrooke BD. Physical studies of phospholipids. VI. Thermotropic and lyotropic mesomorphism of some 1,2-diacylphosphatidylcholines (lecithins). Chem. Phys. Lipids 1967 1 445-475. 

Patel, D.L. Gilbert, R.D. Lyotropic mesomorphic formation of cellulose in trifluoroacetic acid/chlorinated-alkane solvent mixtures at room temperature. J. Polym. Sci. Polym. Phys. Ed. 1981, 19 (8), 1231-1236. 

The phenomenon of increasing ability to form a mesophase as a function of amphi-philicity was also observed when the benzene hexakis(thioethers) 43 were oxidized into their hexakis(sulfones) 44 [142-144] (Fig. 29). In contrast to the nonliquid crystalline thioether series 43, the radial-polar hexasulfones 44 with chains containing between 7 and 15 carbon atoms exhibit a columnar hexagonal type of mesophase established by various methods, including X-ray diffractometry [142-144]. Their lyotropic mesomorphic behavior is also of interest and currently under investigation [145]. 

A number of studies have been reported concerning the solution behavior of some divalent earboxylate complexes ((91) M = Zn, Mn, Pb, Hg, Cd). Krafft points (the Krafft point is the temperature at which micelles become soluble) and critical micelle concentration (cmc) were determined in a variety of long-chain alcohols, and for different earboxylate chain lengths. However, the demonstration of their lyotropic mesomorphism was not clear and it appeared that lamellar phases were induced, although over small ranges of temperature and concentration. 

D. Chapman, R. M. Williams, and B. D. Ladbrooke, Physical Studies of Phospholipids. VI. Thermotropic and Lyotropic Mesomorphism of some 1,2-diacyl-phosphatidylcholines (Lecithins), Chem. Phys. Lipids 1, 445-475 (1971). 

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