Mesophase lyotropic

Lyophobic colloids Lyotropic liquid crystals Lyotropic mesophases Lyotropic polymers Lyral [31906-04-4]... 

Many cellulose derivatives form Hquid crystalline phases, both in solution (lyotropic mesophases) and in the melt (thermotropic mesophases). The first report (96) showed that aqueous solutions of 30% hydroxypropylceUulose [9004-64-2] (HPC) form lyotropic mesophases that display iridescent colors characteristic of the chiral nematic (cholesteric) state. The field has grown rapidly and has been reviewed from different perspectives (97—101). 

T. K. Attwood, J. E. Lydon, C. Hall, G. L. Tiddy. The distinction between chromonic and amphiphilic lyotropic mesophases. Liquid Cryst 7 657-668,1990. 

Hentze H-P, Co CC, McKelvey CA, Kaler EW (2003) Templating Vesicles, Microemulsions and Lyotropic Mesophases by Organic Polymerization Processes. 226 197-223 Hergenrother PJ, Martin SF (2000) Phosphatidylcholine-Preferring Phospholipase C from B. 

Lyotropic LCs can also be described by a simple model. Such molecules usually possess the amphiphilic nature characteristic of surfactant, consisting of a polar head and one or several aliphatic chains. A representative example is sodium stearate (soap), which forms mesophases in aqueous solutions (Figure 8.4a). In lyotropic mesophases, not only does temperature play an important role, but also the solvent, the number of components in the solution and their concentration. Depending on these factors, different types of micelles can be formed. Three representative types of micelles are presented in Figure 8.4b-d. 

For aprotic polar organic solvents only few widely applicable alignment media are known. The lyotropic mesophase of poly(y-benzyl-L-glutamate) (PBLG) with DMF [37] has the disadvantage of a relatively strong minimum alignment. Bicellar... 

Lyotropic liquid crystals, 15 86, 98-101 amphiphilic molecules in, 25 99-101 Lyotropic mesophases, 20 79 Lyotropic polymer liquid crystals, 25 107-108 Lyral, 2 278 24 486 Lysergic acid, 2 100 Lysergic acid diethylamide (LSD-25),... 

Finally, much work remains to be done on concentrated micellar solutions, which have been poorly investigated compared to the dilute regime. Interesting properties, such as lyotropic mesophase behavior, are expected to be observed for these concentrated micellar solutions. 

R. Hermes and K. H. Bauer. Preparation and characterization of amphiphilic membranes with lyotropic mesophases for simulation of skin permeation resistance. Pharmazie 50 481-486 (1995). 

In addition to the cubic and/or inverse cubic forms described above, further transitional forms exist between the lamellar phase and the hexagonal mesophase (cubic, type II) or inverse hexagonal mesophase (cubic, type III) [6]. In contrast to the discontinuous phases of types I and IV, cubic mesophases of type II and III belong to the bieontinuous phases (Fig. 4f). A range of lyotropic mesophases are possible, depending on the mesogen concentration, the lipophilic or hydrophilic characteristics of the solvent, and the molecule itself [6]. 

The molecular structure of arsphenamin is a typical representative of a thermotropic mesogen. With its symmetrical arrangement of the atoms the same holds for disodium cromoglycate, DNCG [20], which forms both thermotropic liquid crystals and lyotropic mesophases in the presence of water. Micronized DNCG powder applied to the mucosa of the nose or the bronchi absorbs water from the high relative humidity of the respiration tract and is first transformed into a lyotropic mesophase and then into a solution depending on the amount of water available. 

For therapeutical purposes, a likewise frequently used group of drug compounds are the nonsteroidal anti-inflammatory drugs (NSAID). Among the best known representatives of the aryl acetic acid derivatives is diclofenac as well as ibuprofen, an aryl propionic acid derivative. As both have acidic properties, they dissociate while being dissolved and may form salts with amphiphilic properties. Together with appropriate counterions these amphiphilic organic acids may form lyotropic mesophases with water even at room or body temperature, for example, diclofenac diethylamine... 

Drug molecules with amphiphilic character may form lyotropic mesophases, and amphiphilic excipients in drug formulations also form lyotropic liquid crystals. Especially surfactants, which are commonly used as emulsifiers in dermal formulations, associate to micelles after dissolution in a solvent. With increasing concentration of these micelles the probability of interaction between these micelles increases and thus the formation of liquid crystals. 

Lyotropic liquid crystals are those which occur on the addition of a solvent to a substance, or on increasing the substance concentration in the solvent. There are examples of cellulose derivatives that are both thennotropic and lyotropic. However, cellulose and most cellulose derivatives form lyotropic mesophases. They usually have a characteristic "critical concentration" or "A point" where the molecules first begin to orient into the anisotropic phase which coexists with the isotropic phase. The anisotropic or ordered phase increases relative to the isotropic phase as the solution concentration is increased in a concentration range termed the "biphasic region." At the "B point" concentration the solution is wholly anisotropic. These A and B points are usually determined optically. 

Chanzy and Peguy (13) were the first to report that cellulose forms a lyotropic mesophase. They used a mixture of N-methyl-morpholine-N-oxide (MMNO) and water as the solvent. Solution birefringence occurred at concentrations greater than 20% (w/w) cellulose. The concentration at which an ordered phase formed increased as the cellulose D.P. decreased. The persistence length of cellulose in MMNO-H2O is not known but presumably it has an extended chain configuration in this solvent. Again the question arises as to what is the relevant axial ratio to be used for cellulose. This will be discussed further below. 

Cholesteric lyotropic mesophases of cellulose in LiCl-DMAC solutions at 1(>-15% (w/w) concentration have been observed by Ciferri and coworkers (19.59.61.62) and McCormick et al. (63). LiCl/DMAC ratios between 3/97 and 11/89 (w/w) were used. LiCl-DMAC does not degrade cellulose and does not react with the polymer (59). It does form a complex with the OH CToups on cellulose which is believed to result in dissolution (62). Optical rotary dispersions are negative, indicating the superhelicoidal structure has a left-handed twist. 

Presently, there are a large munber of reports of cellulose derivatives that form lyotropic mesophases (l-9>16.17.19.2Q.24.4Q-43.45.47-49.53.65-112). 

The difference between this system and an usual supersaturated solution is that two dimensions of the crystallites which are deposited are in the colloidal range, ca 10-200 nm. Only part of the phase diagram has been represented and exploited. For higher concencrations ( > 10 H ), gelation is complicated by some turbidity and existence of lyotropic mesophases. ... 

Note 2 The mesomorphic character of a lyotropic mesophase arises from the extended, ordered arrangement of the solvent-induced micelles. Hence, such mesophases should be regarded as based not on the structural arrangement of individual molecules (as in a non-amphiphilic or a thermotropic mesophase), but on the arrangement within multimolecular domains. 

Compound that can exhibit thermotropic as well as lyotropic mesophases. 

Note 5 If the mesogenic side-groups are rod-like (calamitic) in nature, the resulting polymer may, depending upon its detailed structure, exhibit any of the common types of calamitic mesophases nematic, chiral nematic or smectic. Side-on fixed SGPLC, however, are predominantly nematic or chiral nematic in character. Similarly, disc-shaped side-groups tend to promote discotic nematic or columnar mesophases while amphiphilic side-chains tend to promote amphiphilic or lyotropic mesophases. 

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