Chiral modified CyDs

CyDs are intrinsically chiral macrocydic hosts and this explains the recent trend of ITC application to eluddate the thermodynamics of chiral discrimination of enantiomeric and diastereomeric guest pairs by native and modified CyDs. It is... 

If both modified CyD and chiral guest exhibit a CD, this method is less suited for detecting complex formation (not shown in Scheme 10.4.1). 

Cyclodextrins were introduced as chiral selectors in GC in the 1980s and rapidly became estabhshed as the most powerfiil and versatile materials for GC enantioseparations. The first GC enantioseparation employing CyD as a chiral selector was reported by SybUska s group in 1983 [17]. A packed column was used in this study with a rather short lifetime and rather low peak efficiency. Later Venema and Tol-sma reported enantioseparation with a capillary column which was modified by heptakis(2,3,6-tri-0-methyl)- -CyD (TM- -CyD) [18]. This kind of capillary column... 

In 1992 Mayer and Schurig showed for the first time the possibility of enantioseparations in open tubular capillaries modified with a permethylated CyD derivative. This technique was used later with different chiral selectors but did not mature to become the method of choice for CEC enantioseparations, most likely due to the following conflict inherent in this technique. For a separation which occurs on the mobile phase/stationary phase interface and not in the bulk solution, retention of the analyte on the capillary wall (chiral stationary phase) is necessary for achieving a separation. On the other hand, any retentive analyte-capillary wall interactions are associated with a drastic decrease in peak efficiency in capillary electromigration techniques. However, this study stimulated research in both capillary enantioseparation techniques and in the use of CyD-based CSPs for CEC enantioseparations. 

Cyclodextrin derivatives have been successfully used also for enantioseparations in packed capillary CEC. In this technique CyDs are used covalently immobilized to silica gel [69], to particulate silica sintered as a monolith [70], or to a monolithic organic matrix [71, 72]. In addition, CyDs have been used as dynamic modifiers of the stationary phase [73], as well as chiral mobile phase additives in combination with an achiral stationary phase [74, 75]. 

Further development of the above-mentioned ideas [82] has been reported [83, 84]. Mono- and diaminated j8-CyDs were employed as chiral discriminators for a variety of chiral guest molecules [83, 84]. Thus, chiral centers less-symmetrically distributed inside the cavities of mono- and diaminated j8-CyDs, compared to native j8-CyD, do indeed lead to better chiral discrimination by the amino-modified hosts. The major findings [83, 84] may be summarized as follows (1) the direct correlation between the mode of penetration and chiral recognition established above for j8-CyD [82] holds for aminated j8-CyD, and may now be considered a general rule for CyD complexation reactions. We may further conclude that the origi-... 

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