Chiral stationary phases recognition mechanism

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. 

A number of specialised stationary phases have been developed for the separation of chiral compounds. They are known as chiral stationary phases (CSPs) and consist of chiral molecules, usually bonded to microparticulate silica. The mechanism by which such CSPs discriminate between enantiomers (their chiral recognition, or enantioselectivity) is a matter of some debate, but it is known that a number of competing interactions can be involved. Columns packed with CSPs have recently become available commercially. They are some three to five times more expensive than conventional hplc columns, and some types can be used only with a restricted range of mobile phases. Some examples of CSPs are given below ... 

HPLC Chiral Stationary Phases Containing Macrocyclic Antibiotics Practical Aspects and Recognition Mechanism... 

Anionic Catalysis Several bulky methacrylates afford highly isotactic, optically active polymers having a single-handed helical structure by asymmetric polymerization. The effective polymerization mechanism is mainly anionic but free-radical catalysis can also lead to helix-sense-selective polymerization. The anionic initiator systems can also be applied for the polymerization of bulky acrylates and acrylamides. The one-handed helical polymethacrylates show an excellent chiral recognition ability when used as a chiral stationary phase for high-performance liquid chromatography (HPLC) [97,98]. 

Yashima E, Okamoto Y, Chiral recognition mechanism of polysaccharides chiral stationary phase in The Impact of Stereochemistry on Drugs Development and Use (Aboul-Enein, HY, Wainer IW, Eds.), John Wiley Sons, New York, p. 345 (1997). 

The chiral recognition mechanisms in NLC and NCE devices are similar to conventional liquid chromatography and capillary electrophoresis with chiral mobile phase additives. It is important to note here that, to date, no chiral stationary phase has been developed in microfluidic devices. As discussed above polysaccharides, cyclodextrins, macrocyclic glycopeptide antibiotics, proteins, crown ethers, ligand exchangers, and Pirkle s type molecules are the most commonly used chiral selectors. These compounds... 

Figure 5.6 Chiral stationary phases classification according to chiral recognition mechanisms and chemical structures. (From Reference 256.)...

Approximately 70 chiral stationary phases (CSPs) have been marketed since 1981 [256]. A classification scheme has been proposed for the numerous commercially available CSPs which takes into account chiral recognition mechanism and chemical structure (Figure 5.6). 

DIRECT ENANTIOSEPARATION BY LIQUID CHROMATOGRAPHY WITH CHIRAL STATIONARY PHASES (CSPs) — CHIRAL SELECTORS AND CHIRAL RECOGNITION MECHANISMS... 

Booth, T.D. and Wainer, I.W. (1996a). Investigation of the Enantioselective Separations of alpha-alkylarylcarboxylic Acids on an Amylose tris(3,5-dimethylphenylcarbamate) Chiral Stationary Phase Using Quantitative Structure-Enantioselective Retention Relationships. Identification of a Conformationally Driven Chiral Recognition Mechanism. J.Chromat., 737A, 157-169. 

Aubry A. F., Gimenez, F., Farinotti, R., Wainer, 1. W. Enantioselective chromatography of the antimalarial agents chloro-quine, mefloquine, and enpiroline on a al-acid glycoprotein chiral stationary phase Evidence for a multiple-site chiral recognition mechanism. Chirality, 1992, 4, 30-35. 

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