Optical activity recognition mechanism

Among optically active polymers, polysaccharide derivatives are particularly valuable. Polysaccharides such as cellulose and amylose are the most readily available optically active polymers and have stereoregular sequences. Although the chiral recognition abilities of native polysaccharides are not remarkable, they can be readily converted to the esters and carbamates with high chiral recognition abilities. The chiral recognition mechanism of these derivatives has been clarified to some extent. 

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]. 

Type II sorbents are based on an inclusion mechanism. Chiral recognition by optically active polymers is based solely on the helicity of that polymer. Optically active polymers can be prepared by the asymmetric polymerization of triphenylmethyl methacrylate using a chiral anionic initiator [264]. Helical polymers are unique from the previously discussed chromatographic approaches because polar functional groups are not required for resolution [265]. These commercially available sorbents have been used to resolve enantiomers of a-tocopherol [266]. The distinction between this group (lib) and the sorbents containing cavities is vague (Ila). 

More than half of all drugs on the market are asymmetric molecules. Many of these are administered as racemates. Since biological recognition systems are based on optically active molecules, the two enantiomers of a racemic drug may interact by different mechanisms with these systems. One of the enantiomers may exert pharmacologically different or unwanted side effects [1-3]. The same is true for racemic pesticides and herbicides often only one of the enantiomers possesses the desired activity. 

Some optically active cationic and racemic anionic complexes were examined to elucidate the mechanism of chiral recognition of cations and anions capable of forming hydrogen bonds [313]. The chromatographic study showed that enantiomers of some anionic complexes form favourable ion pairs with cationic A-complexes (Table 31). 

Yoshida et al.86 employed HyperChem and performed MD calculations to verify the recognition mechanism of the MIP they synthesized for the separation of optically active tryptophan methyl ester. The computational modeling proved that the enantiomeric selectivity is conferred by the electrostatic and hydrogen bonding interactions between the functional molecule and the target tryptophan methyl ester along with the chiral space formed on the polymer surface. 

A materials-handling system must frequently have the abihty at some point to identify, sort, and divert parts, products, or unit loads. Peripheral accessories and equipment do this, ranging from simple mechanical diverters to sophisticated optical recognition reading devices, which can actudly read and identify alphanumeric characters and sort 20,000 items per hour and which are used mainly for check and mail handling. Whatever the complexity of the system, three basic elements must be considered identification of the item to be sorted or consoh-dated, recognition of the item, and the command to activate the mechanisms to divert the item. 

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