Cyclodextrins chiral discrimination

Chiral recognition of A-[Co(phen)3]3+ has been observed in a modified /3-cyclodextrin.772 Chiral discrimination has also been seen in photoinduced energy transfer from luminescent chiral lanthanoid complexes773 to [Co(phen)3]3+ and between photoexcited [Ru(bpy)3]2+ and [Co(phen)3]3+ co-adsorbed on smectite clays.774 The [Co(bpy)3]3+ ion has been incorporated into clays to generate ordered assemblies and also functional catalysts. When adsorbed onto hectorite, [Co(bpy)3]3+ catalyzes the reduction of nitrobenzene to aniline.775 The ability of [Co(phen)3]3+ to bind to DNA has been intensively studied, and discussion of this feature is deferred until Section 6.1.3.1.4. 

An understanding of the recognition of chirality at a molecular level has become of interest in many fields of chemistry and biology. In the past decade, many attempts to clarify the mechanism of chiral recognition on CSPs for liquid chromatography have been made by means of chromatography, NMR spectroscopy,199 202 X-ray analysis, and computational methods.203 - 206 The successful studies have been mostly carried out for the small-molecule CSPs, especially cyclodextrin-based CSPs and Pirkle-type (brush-type) CSPs. In contrast, only a few mechanistic studies on chiral discrimination at the molecular... 

Lyotropic polymeric LC, formed by dissolving two aromatic polyamides in concentrated sulphuric acid, have been studied using variable-director 13C NMR experiments.324 The experimental line shapes at different angles w.r.t the external field were used to extract macromolecular order and dynamic in these ordered fluids. An interesting application of lyotropic LC is for the chiral discrimination of R- and S-enantiomers, and has recently been demonstrated by Courtieu and co-workers.325 The idea was to include a chiral compound 1-deutero-l-phenylethanol in a chiral cage (e.g., /1-cyclodextrin) which was dissolved and oriented by the nematic mean field in a cromolyn-water system. Proton-decoupled 2H NMR spectrum clearly showed the quad-rupolar splittings of the R- and S-enantiomers. The technique is applicable to water-soluble solutes. 

RJ Tait, DO Thompson, VJ Stella, JF Stobaugh. Sulfobutyl ether /3-cyclodextrin as a chiral discriminator for use with capillary electrophoresis. Anal Chem 66 4013-4018, 1994. 

H Yamamura, A Akasaki, Y Yamada, K Kano, T Katsuhara, S Araki, M Kawai, T Tsuda. Capillary zone electrophoretic chiral discrimination using cationic cyclodextrin derivative determination of velocity and association... 

U Holzgrabe, H Mallwitz, SK Branch, TM Jefferies, M Wiese. Chiral discrimination by NMR spectroscopy of ephedrine and JV-methylephedrine induced by /3-cyclodextrin, heptakis(2,3-di-0-acetyl)-/3-cyclodextrin and hep-takis-(6-0-acetyl)-/3-cyclodextrin. Chirality 9 211-219, 1997. 

Reversible inclusion-type complexation, forming diastereomeric [SO-SA] molecule associates, is a favored resolution principle which has also been adapted for CE and MECK126 129. Cyclodextrin and derivatives are superior materials if extremely high efficiency capillary techniques are used. Small chiral discrimination effects are often sufficient for baseline resolution127. 

Schmidtchen, F.P. (2002) The anatomy of the energetics of molecular recognition by calorimetry Chiral discrimination of camphor by a-cyclodextrin, Chem.EurJ. 8, 3522-3529 ... 

Schurig, V, and Schmidt, R. (2003) Extraordinary chiral discrimination in inclusion gas chromatography. Thermodynamics of enantioselectivity between a racemic perfluorodiether and a modified 7-cyclodextrin. J. Chromatogr. 1000, 311-324. 

Yashima, E., Yamada, M., Yamamoto, C., Nakashima, M., and Okamoto, Y. (1997) Chromatographic enantioseparation and chiral discrimination in NMR by trisphenylcarbamate derivatives of cellulose, amylose, oligosaccharides, and cyclodextrins, Enantiomer 2, 225-240. 

A variety of chiral alignment media for organic solvents is known with the most widely used and best characterized being the poly(amino acids) PBLG and PCBLL. Both polymers form lyotropic mesophases and possess ot-helical structures for which many examples of enantiomeric differentiation have been shown. In addition to chiral poly(amino acids), it was demonstrated that achiral media with chiral cages like cyclodextrines serve as alignment media with the potential of chiral discrimination.121... 

Numerous chiral discrimination agents have also been investigated for CE, including natural and derivatized cyclodextrins (both charged and uncharged). 

FITC-labeled amino acids as model compounds were separated in sodium dodecyl sulfate/borate buffer at pH 9.4 with y-cyclodextrin as chiral discriminator. Separation speed achieved with the microchip was one order of magnitude faster than that with conventional CE. Bailey and co-workers demonstrated chiral and achiral separation of amphetamine and analogous compounds labeled with 4-fluoro-7-nitrobenzofurazane on an S-folded separation channel. Phosphate buffer with sulfated y-cyclodextrin and sodium dodecyl sulfate as additives was used. It is expected that chiral separations on microfabricated electrophoresis devices with high speed and high throughput will find its way into pharmaceutical and biomedical sciences as well as into other areas. 

Reliable techniques exist for liquid-liquid extraction of ephedrine from alkaline tissue samples. Gas chromatography-mass spectrometry measurement requires pentafluoropropionic acid derivatization. Blood and tissue measurements have been reported in several ephedrine-related deaths, and in clinical trials with therapeutic doses of the drug (Backer et al., 1997). More recently capillary electrophoresis has been used to separate and identify all 10 stereoisomers of the ephedrine family found in nutritional supplements. Chiral discrimination is effected by using hydroxypropyl-P-cyclodextrin (Flurer et al., 1995). 

Schneider, M. and Ballschmeter, K., Separation of diastereomeric and enantiomeric alkyl nitrates — Systematic approach to chiral discrimination on cyclodextrin LIPODEX-D, Chem. Eur. J., 2, 539-544, 1996. 

C. J. Easton, S. F. Lincoln, Chiral discrimination by modified cyclodextrins, Chem. Soc. Rev.,... 

As an alternative, papers have appeared in the thin-layer literature using TLC for chiral separations by putting the chiral discrimination reagent (antibiotic, cyclodextrin, etc.) into the mobile phase. The separations work as well as if the reagents had been coated or bonded to the silica gel (or in some cases, the reversed bonded phase). 

D Anna F, Riela S, Lo Meo P, Grattadauria M, Noto R. The binary pyrene/heptakis-(6-amino-6-deoxy)-P-cyclodextrin complex a suitable chiral discriminator. Spectrofluorimet-ric study of the effect of some a-amino acids and esters on the stability of the binary complex. Tetrahedron Asymmetry 2002 13 1755-60. 

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