Mesomorphic crystalline solid

Membrane lipids can exist in a number of intermediate states or mesophases more ordered than the liquid but less so than the crystalline solid [102, 131, 136]. Such materials are called liquid crystals and their multiple intermediate phase character is termed mesomorphism. There are at least four types of mesomorphic behavior lyotropic, thermotropic, barotropic and ionotropic. These refer to the expression of the disparate liquid crystal phases by manipulating solvent (lyotrope) content, temperature, pressure, and salt concentration, respectively. Most membrane lipids exhibit the four types of mesomorphism. 

As noted above, lipids exist in a number of intermediate physical states or mesomorphs between the crystalline solid and the isotropic liquid. The stability of these phases depend on temperature and composition and each lipids pattern of dependency is conveniently described in the form of an isobaric temperature-composition phase diagram. Over the past few years two new and related methods of collecting mesomorphic phase information which are less time-consuming and more efficient... 

Ordinarily a crystalline solid melts sharply at a single, well-defined temperature to produce a Uquid phase that is amorphous and isotropic. A different behavior is exhibited by a class of organic compounds known as liquid crystals. The oldest examples are cholesterol derivatives, e.g., cholesteryl benzoate. This substance, for instance, does not have a sharp transition to amorphous Uquid at 145.5°C, but changes to a cloudy liquid, which becomes clear and isotropic only at 178.5°C. This cloudy intermediate state that possesses an ordered stmcture with some resemblance to a crystaUine soUd, while still in the liquid state, is called a mesophase or mesomorphic phase from the Greek mesos, meaning in between or intermediate. 

Although liquids are usually isotropic, some 200 cases are known of substances that exhibit anisotropy in the liquid state at temperatures just above their melting point. These liquids bear the unfortunate, but popular, name liquid crystals the term is inapt because the word crystal implies the existence of a precise space lattice. Lattice formation is not possible in the liquid state, but some form of molecular orientation can occur with certain types of molecules under certain conditions. Accordingly, the name anisotropic liquid is preferred to liquid crystal . The name mesomorphic state is used to indicate that anisotropic liquids are intermediate between the true liquid and crystalline solid states. 

The mesomorphic state is a mesophase between a crystalline solid and an isotropic liquid where the molecules are separated in parallel layers of quasicrystalUne order. Here, the molecules show optical activity. In this state, transition and supercooling are possible. 

Liquid crystal polymers (LCPs) were introduced over the last three decades. In the liquid state, either as a solution (lyotropic) or a melt (thermotropic), they lie between the boundaries of solid crystals and isotropic liquids. This polymeric state is also referred to as a mesomorphic structure, or a mesophase, a combined term adopted from the Greek language (mesos = intermediate morphe = form). This state does not meet all the criteria of a true solid or a true liquid, but it has characteristics similar to both a solid and a liquid. For instance, the anisotropic optical properties of LC polymeric fluids are like those of crystalline solids, but their molecules are free to move as in liquids. 

It is well known that matter exists in three different states depending upon the temperature sohd, hquid, and gas. Between the crystalline solid and the isotropic liquid (normal, isotropic hquid) there actually exists a series of transitions as temperature increases, giving rise to several new phases. These new phases have mechanical, optical, and stractural properties and are referred to as hquid-crystalline phases. Materials isolated from these phases are liquid crytals. A hquid crystal may, therefore, be as an intermediate phase or mesomorphic (meaning in between) phase which has hquidhke order in at least one direction and possesses a degree of anisotropy (also a kind of order). 

Liquid crystals belong to a range of materials, termed mesomorphic phases, that are intermediate between crystalline solids and simple, isotropic liquids. They are formed from compounds whose molecules have a strongly non-spherical shape, by heating or by dissolution in a suitable solvent. Many liquid crystals are formed from molecules that are, in fact, rod-shaped. 

A compound which displays liquid crystal properties is referred to as a mesogen and said to exhibit mesomorphism. Liquid crystals may be considered either as disordered solids or ordered liquids, and their properties are very dependent on temperature and the presence or absence of solvent. In thermotropic liquid crystals the phases of the liquid crystals may be observed to change as the temperature is increased. In lyotropic liquid crystals the ordered crystalline state is disrupted by the addition of a solvent, which is very commonly water. For these systems temperature changes may also be... 

Mesitylene, production from acetone, 1 164 Mesityl oxide, 14 589-590 characteristics of, 16 337 hydrogenation, 16 337-338 hydrogen peroxide treatment of, 16 338 Z-menthol from, 24 520 production of, 16 336-337 production from acetone, 1 164, 174 Mesogenic diols, 25 460 Mesogenic molecules, solids of, 15 82 Mesogens, 24 53, 54 Mesomixing, 16 683 Mesomorphic behavior, 24 53-54 Mesomorphic phase transitions, 15 102 Mesomorphism, 15 81. See also Liquid crystalline materials Mesophase pitch-based carbon fiber, 26 734-735... 

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. 

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