Chiral molecules chromatographic studies

A chiral selector can also be dissolved in the IL solvent and be subsequently coated on the capillary wall [38]. In this approach, the achiral [C4CiIm]Cl was used to dissolve permethylated p-cyclodextrin (p-PM) and dimethylated P-cyclodextrin (p-DM). The chromatographic separations obtained from these two columns were compared to two commercially available CSPs based on p-PM and p-DM dissolved in polydimethylsiloxane. From a set of 64 chiral molecules separafed by fhe commercial p-PM column, only 21 of the molecules were enantioresolved by the IL-based p-PM column. Likewise, from a collecfion of 80 analytes separated by the p-DM column, only 16 analytes could be separated on the IL-based p-DM column. The authors also noted a considerable enhancement in the separation efficiency of fhe IL-based CSPs. This resulf, coupled to fhe loss of enantioselecfivify for mosf separations, suggests that the imidazolium cation may occupy the cavity of the cyclodextrin preventing the analyte-cyclodextrin inclusion complex-ation that is crucial for chiral recognition. The ability for ILs to form inclusion complexes wifh cyclodextrin molecules has been recently studied by Tran and coworkers using near-infrared spectromefry [39]. 

In the course of the development of CSPs, a broad variety of chiral molecules (and materials) has been the subject of scrutiny with respect to chromatographic enantiomer separation capacity. The chiral molecules studied as potential SOs cover virtually the entire chemical and structural diversity space, ranging from low-molecular-weight compounds to polymers of both synthetic and biological origin. So far, the (stiU ongoing) quest for efficient SOs has resulted in the synthesis of more than 1400 CSPs [94], the properties of which are documented in an almost intractable number of dedicated scientific publications. The outcome of these efforts is manifest in an enormously rich toolbox of more than 200 commercially available CSPs offered by various speciahzed suppliers. 

Our own interest in CyD modeling has evolved from the experimental study of molecular and chiral recognition of decalin isomers 1 by j8-CyD 2 [20, 8, 21]. These molecules provide a unique set for such studies since at room temperature the cis-isomer undergoes rapid ring inversions between the lb and Ic forms, which are enantiomers as well. Thus, decalin isomers allow us to study both molecular and chiral recognition. Chromatographic analysis by Sybilska s group [20] has shown that the trans isomer la forms weak complexes with 2 while the complexes with... 

The molecular imprinting strategy can be applied for the recognition of different kinds of templates from small organic molecules to biomacromolecules as proteins. Some examples of separations investigated with MIP monoliths in CEC and LC are shown in Table 2. The influence of the imprinted monolithic phase preparation procedure and of the separation conditions on the selectivity and chromatographic efficiency have been widely studied [154, 157, 161, 166, 167, 192]. The performance of imprinted monoliths as chromatographic stationary phase has also been compared to that of the traditional bulk polymer packed column [149, 160]. It was shown that the monolithic phases yielded faster analyses and improved chiral separations. 

In the area of cyclodextrin ethers the -compound has been converted into a set of five tris-Tbdms ethers, all substituted at their various 6-positions, which were separated by hplc and characterized by n.m.r. spectroscopy. Related work applied to y-cyclodextrin gave the various 6,6 -disubstituted ethers. 5-Bromo-l-pentene was used to produce the 2-0-mono-4-pentenyl ether of P-cyclodextrin which was then permethylated and the product was chemically bonded to silica gel to form an efficient hplc stationary phrase for the separation of enantiomers. Peroctyl a-cyclodextrin has been studied as a chiral receptor for the ephedrinium ion. Various octyl ethers of a-, P- and y-cyclodextrin ranging in their substitution from the diethers to completely alkylated products were characterized by electrospray mass spectrometry and n.m.r. methods applied to methylated derivatives. The 2,6-didodecyl derivative of p-cyclodextrin has been used as a potentiometric sensor. In the field of aromatic ethers, naphthyl carboxylate substituents have been bonded at the 6-positions and the products were able to transfer excitation energy to complexed merocyanine held in the cavities of those molecules. These phototransfer processes were extremely efficient.P-Substituted cyclodextrin derivatives with p-allyloxybenzoyl or various benzyl substituents at 0-2 or 0-3 were incorporated by hydrosilylation to give hydromethylpolysiloxane polymers used as chiral phases for chromatographic resolution of enantiomers. Cyclodextrins with complex benzyl-like eth are illustrated in 22 and 23. The latter were prepared as artificial redox enzymes. 

---