Chiral stationary phases configuration

Although the chiral recognition mechanism of these cyclodexttin-based phases is not entirely understood, thermodynamic and column capacity studies indicate that the analytes may interact with the functionalized cyclodextrins by either associating with the outside or mouth of the cyclodextrin, or by forming a more traditional inclusion complex with the cyclodextrin (122). As in the case of the metal-complex chiral stationary phase, configuration assignment is generally not possible in the absence of pure chiral standards. 

Mobile phases used with this stationary phase are typically 0.01 N perchloric acid with small amounts of methanol or acetonitrile. One significant advantage of these phases is that both configurations of the chiral stationary phase are commercially available and can be obtained from J. T. Baker Inc. and Chiral Technologies, Inc. (Crownpak CR). 

Investigations on the stereochemistry of chiral semiochemicals may be carried out by (gas) chromatographic separation of stereoisomers using chiral stationary phases, e.g. modified cyclodextrins [32]. Alter natively, formation of diastereomers (e.g. Mosher s ester or derivatives involving lactic acid etc.) may be followed by separation on conventional achiral stationary phases. Assignment of the absolute configuration of the natural product will again need comparison with an authentic (synthetic) reference sample. 

Yang, S., Mushtaq, M., and Fu, P., Elution order absolute configuration of k-region dihydrodiol enantiomers of benz[a] anthracene derivatives in chiral stationary phase high performance liquid chromatography, J. Chromatogr., 371, 195, 1986. 

The central point of chirality in a molecule is known as the stereo-centre and diastereoisomers occur when there is more than one stereo-centre in a molecule. Stereo-centres are given the absolute configurations of Rectus (R) and Sinister (S). Diastereoisomers that differ in absolute configuration at the stereo-centres are called epimers. Diastereoisomers differ in conformation so it is actually possible to purify these mixtures by normal phase and reversed phase HPLC. However, better separation factors are often obtained using chiral stationary phases. 

Chirality evaluation of linalyl acetate and linalool have been introduced as new and substantial criteria in the authenticity control of lavender oils. In particular, linalyl acetate from genuine lavender oils has high enantiomeric purity favouring the R-configuration, irrespective of the Lavandula species, and storage or work-up conditions [32]. Using 2,3-di-0-acylated-6-0-silylated cyclodextrins as a new generation of chiral stationary phases in enantio-cGC, most of chiral compounds of Lavandula oil, are stereoanalyzed simultaneously (Fig. 6.37 Fig. 6.38). 

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