Chiral phases cellulose derivatives

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). 

In another study, the authors reported a comparative study of the enantiomeric resolution of miconazole and the other two chiral drugs by high performance liquid chromatography on various cellulose chiral columns in the normal phase mode [79], The chiral resolution of the three drugs on the columns containing different cellulose derivatives namely Chiralcel OD, OJ, OB, OK, OC, and OE in normal phase mode was described. The mobile phase used was hexane-isopropanol-diethylamine (425 74 1). The flow rates of the mobile phase used were 0.5, 1, and 1.5 mL/min. The values of the separation factor (a) of the resolved enantiomers of econazole, miconazole, and sulconazole on chiral phases were ranged from 1.07 to 2.5 while the values of resolution factors (Rs) varied from 0.17 to 3.9. The chiral recognition mechanisms between the analytes and the chiral selectors are discussed. 

The requirements for homochirally pure a-amino acids have not ruled out any of these general synthetic methods (which all give racemic products), since resolution of DL-a-amino acids and their derivatives is a simple, albeit time-consuming, solution to this need. Classical methods for resolution include physical separation of the DL-amino acids themselves (by chromatography on a chiral phase e.g. resolution of DL-tryptophan over cellulose, see Section 4.15), fractional crystallisation of certain racemates or supersaturated solutions (through seeding with crystals of one enan-... 

Liquid crystalline (LC) solutions of cellulose derivatives form chiral nematic (cholesteric) phases. Chiral nematic phases are formed when optically active molecules are incorporated into the nematic state. A fingerprint texture is generally observed under crossed polarizers for chiral nematic liquid crystals when the axis of the helicoidal structure is perpendicular to the incident light (Fig. 2). 

Minguillon, C., Franco, P., Oliveros, L., Lopez, P. Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases. I. Influence of the degree of fixation on selectivity,... 

By using derivatives of cellulose 3,5-dimethylphenyl carbamate (Chiracel OD) as the chiral phase Bergman measured the enantiopurity of complexes of molybdenum (2.45) and iridium (2.46) (Figure 2.67). With the same type of stationary phase, Gladysz measured the ee of rhenium complexes ReCp(NO)P(C6H5)2Br (2.13), and uranyl-salophen complexes of uranium were analysed with a Chiracel ODH column. 

Carbamates. Many examples of cellulose derivatives as chiral stationary phases (CSPs) in liquid chromatography and capillary electrophoresis have been reported in the literature [43,44]. Chankvetadze et al. [43] used cellulose chlorophenyl carbamates as liquid chromatography stationary phases to resolve enantiomers of several chiral drugs including sedatives... 

Ichida, A. Shibata, T. Cellulose derivatives as stationary phases. In Chromatographic Chiral Separations) Zief, M., Crane, L.J., Eds. Marcel Dekker New York, 1988 Chap. 9. 

Chiral stationary phases that are currently available can be classified into those containing cavities (cellulose derivatives, cyclodextrins, synthetic polymers, crown ethers, and chiral imprinted gels), affinity phases (bovine serum albumin, human serum albumin, a-glycoprotein, enzymes), multiple hydrogen-bond phases, Ti-donor and Ti-acceptor phases, and chiral ligand exchange phases. This classification scheme was used in a review that gave numerous pharmaceutical examples of separation by... 

Cellulose is the most abundant biopolymer on earth. It can be used in different applications, namely in the form of fibers, and cellulose can be converted into numerous cellulose derivatives. Cellulose micro- and nanofibers have been the subject of intense research in the field of composites. Cellulose derivatives can show liquid crystalline chiral nematic phases, which can be used for the production of diverse composite systems. All-cellulosic composites based on liquid crystalline cellulosic matrices reinforced by cellulose micro- and nanofibers can show enhanced mechanical properties due to fiber orientation induced by the liquid crystalline matrix. Cellulose-based fibers electrospun from liquid crystalline phases can develop different structures, which are able to mimic the shape of plant tendrils on the nano- and microscale, opening new horizons for ceDulosic membrane applications. 

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