Liquid crystalline mesophases lyotropic

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

Thermotropic liquid crystalline (LC) phases or mesophases are usually formed by rod-like (calamitic) or disk-like (discotic) molecules. Spheroidal dendrimers are therefore incapable of forming mesophases unless they are flexible, because this would allow them to deform and subsequently line up in a common orientation. However, poly(ethyleneimine) dendrimers were reported to exhibit lyotropic liquid crystalline properties as early as 1988 [123],... 

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. 

The structure and function of cell membranes have long been associated with lyotropic liquid crystalline phases. Since most of the glycolipids are amphitropic (both thermotropic and lyotropic) their was an increase of interest in the comparison of the structures of both types of mesophases formed by the same compound. 

The appearance of a sharp central peak in the deuteron NMR spectrum for unaligned lyotropic liquid crystalline samples has been observed by several authors (30, 33, 34). This has been interpreted in terms of phase inhomogenities (35) or isotropic motion (36). However, recently Wennerstrom et al. showed for a lamellar amphiphile-water mesophase that this could be referred to double quantum transitions (37). It is expected that double quantum transition peaks appear in NMR spectra... 

FIGURE 2.3 51V NMR spectrum of vanadate in a nematic lyotropic liquid crystalline solution. The spectrum shows quadrupole-split signals from V and V4, while the signal of V2 is broadened. The quadrupole splittings are 200 Hz and 5.35 kHz for V and V4, respectively. The spectrum was obtained from a tetradecyltrimethylammonium bromide (TDTMABr) mesophase of composition TDTMABr, 160 mg decanol, 30 mg D20,450 mg NaCl, 10 mg. 

Similar to germanium sulfides or selenides, [SiqSeio] adamantine clusters also exist and have been found to form mesostractured semiconductors with Pt + when templated by the lyotropic liquid-crystalline phase of alkylpyridiniinn surfactant [Ci6H33NC5H5]Br. This mesophase designated as CiePyPtSnSe has a band gap of 1.5 eV. 

In this chapter lyotropic liquid crystalline polymers are considered, where micelle-like organizations of the macromolecules cause the formation of mesophases in defined concentration and temperature regions. For these polymers it has to be assumed that the polymer backbone or the monomer units must contain an amphiphilic character. 

S.A. El-Safty and T. Hanaoka, Monolithic Nanostructured Silicate Family Templated by Lyotropic Liquid-crystalline Nonionic Surfactant Mesophases. Chem. Mater., 2003, 15, 2892-2902. 

Lyotropic liquid crystalline cellulose derivatives exhibit unique optical properties because of their helicoidal supramolecular structure.The chiro-optical properties of the helicoidal structure can be described by a pitch p (or its inverse, the twist p ) p = 2o/fi, where is the reflection wavelength and h is the mean refractive index of a sheet, and the corresponding handedness of the twist right-handed helicoidal structure being assigned to a positive pitch p > 0) and left-handed helicoidal structures to a negative pitch p < The nematic mesophase can be... 

Hyde, S. T. Identification of Lyotropic Liquid Crystalline Mesophases. In Handbook of Applied Surface and Colloid Chemistry, Holmberg, K., Ed. Wiley Chichester UK, 2002 Chapter 16, pp 299-332. 

Self-assembly and molecular recognition of some biomolecules lead to lyotropic liquid-crystalline behavior with water [5]. These molecular complexes derived from biomolecules could be more important in view of biofunction. Nucleic acids such as DNA and RNA, which self-organize supramolecular complexes, show lyotropic mesophases [5]. Complexes of nucleic acid and cationic amphiliphic molecules form mesomorphic molecular arrangements, which can be used for drug delivery such as gene therapy [6]. 

Interesting examples of biomolecules that show lyotropic liquid crystallinity by association of identical molecules are guanosines and folic acids [168-171]. These molecules exhibit columnar mesophases due to the formation of hydrogen-bonded complexes in the presence of water. For example, folic acid 80 sodium salt exhibits cholesteric and hexagonal phases with water due to the formation of a tetramer, which stacks as shown in Fig. 23. The introduction of long alkyl chains into the guanosines leads to the assembly of ribbon-like structures in organic solvents [172]. 

Some Characteristics of Lyotropic Liquid-Crystalline Mesophases... 

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