Cellulose esters, chiral recognition

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. 

Polysaccharides, such as cellulose and amylose (Fig. 10), are the most abundant polymers on the earth and are known to have a chiral recognition ability. In 1951, Kotake resolved some amino acid derivatives by paper chromatography [35], However, their abilities and mechanical properties are not adequate for use as CSPs in HPLC. Fortunately, polysaccharides are readily modified to esters and carbamates by the reaction with acid chlorides and isocyanates, respectively, and these derivatives show very attractive chiral recognitiOTis based on their helical conformations. 

Both polymers are very poor chiral selectors in their native state but exhibit enhanced selectivity when derivatized as esters or carbamates derivatives. Microcrystalline cellulose triaeetate (MCTA) was the first derivative used in LC mostly in the reversed-phase mode. Chiral recognition by MCTA is mainly ascribed to its microcrystallinity as confirmed by Okamoto et al. [43,44] and then Francotte et al. [45], who have shown the influence of the crystalline arrangements on the enantioseparation. 

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