Recognition mechanism

The dependence of chiral recognition on the formation of the diastereomeric complex imposes constraints on the proximity of the metal binding sites, usually either an hydroxy or an amine a to a carboxyHc acid, in the analyte. Principal advantages of this technique include the abiHty to assign configuration in the absence of standards, enantioresolve non aromatic analytes, use aqueous mobile phases, acquire a stationary phase with the opposite enantioselectivity, and predict the likelihood of successful chiral resolution for a given analyte based on a weU-understood chiral recognition mechanism. 

The chiral recognition mechanism for these types of phases was attributed primarily to hydrogen bonding and dipole—dipole interactions between the analyte and the chiral selector in the stationary phase. It was postulated that chiral recognition involved the formation of transient five- and seven-membered association complexes between the analyte and the chiral selector (117). 

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. 

The enantioselectivity of the macrocyclic CSPs are different in each of the operating modes, probably because of different separation mechanisms functioning in the different solvent modes. The possible chiral recognition mechanisms for three mobile phase compositions on glycopeptide phases are listed in Table 2-3 in descending order of strength. 

This observation is important in the study of the chiral recognition mechanism in this system. This may be a practical matter when determining the trace amount of one enantiomer in the presence of its dominant antipode. The smaller peak is always desired to be eluted first for best quantitation. 

The need for an overall and combined chemical structure and data search system became clear to us some time ago, and resulted in the decision to build CHIRBASE, a molecular-oriented factual database. The concept utilized in this database approach is related to the importance of molecular interactions in chiral recognition mechanisms. Solely a chemical information system permits the recognition of the molecular key fingerprints given by the new compound among thousands of fingerprints of known compounds available in a database. 

Polysaccharide-based CSPs incorporate derivatives of cellulose and amylose adsorbed on silica gel. The selectivity of these CSPs depends upon the nature of the substituents introduced during the derivatization process. The secondary structure of the modified polysaccharide is believed to play a role in selectivity, but the chiral recognition mechanisms have not been fully elucidated [55]. 

Macaudiere and co-workers performed a comparison of LC and SFC on a polymer based-CSP (Chiralpak OT) [64]. The chromatographic behavior of this CSP seemed to be quite different in SFC than in LC, although satisfactory separations were achieved with both techniques. The chiral recognition mechanisms may be altered by the nature (hexane-based or CO,-based) of the eluent. 

Lenzen S Hexose recognition mechanisms in pancreatic B-cells. Biochem Soc Trans 1990 18 105. 

Weinstein, H., R. Osman, and J. P. Green. 1979. The Molecular Basis of Structure-Activity Relationships Quantum Chemical Recognition Mechanisms in Drug-Receptor Interactions. In Computer-Assisted Drug Design. E. C. Olson and R. E. Christofferson, eds. American Chemical Society, Washington, D.C. 

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. 

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