关键词: 环糊精类固定相, 高效液相色谱, 手性识别机理

Abstract: Apartially phenyl carbamate derivative β-cyclodextrin bonded phase(CSP1) has been prepared to achieve two aims: firstly, we want to add more interaction sites to enhance the selectivity; secondly, we attend to increase hydrophobic effect to make it easy for the compound to get into the cone. The effect of structure of enantiomers, temperature and flow rate on enantioselectivity of a series of O,O-diethyl(p-methylbenzenesulfonamido)aryl (or alkyl)methylphosphonates has been investigated in order to obtain a better understanding of the separation mechanism. The results reveal that the substituent on the chiral carbon is a decisive factor for the separation. When the substituent is an aryl group, the enantiomer can get a good separation. On the contrary, the enantiomer cannot be recognized when the substituent group is an alkyl. It is obvious that the aryl group gives a dipole-dipole stacking interaction which contributes to the separation. Plots of lnα against 1/Tyields linear relationships under the conditions studied which can be used to determine the Gibbs-Helmholtz parameters Δ _(R,S)ΔH° and Δ _(R,S)ΔS°. The good linear relationships indicate that the same recognizing mechanism exists. According to the value of thermodynamic parameters, the separation mechanism is believed to depend on weak π-π interactions or weak hydrogen bonding. There is no great influence on enantioselectivity when the flow rate varied from 0.5 to 2.0 mL/min . The kinetics of the mass transfer suggests that inclusion complex formation may be slower than simple external cyclodextrin interaction. That the enantioselectivity does not decrease with the increase of the flow rate shows that the inclusion mechanism does not control the separation. More interaction sites have been added to the derivative cyclodextrin bonded phase which can afford π-π interactions, hydrogen bonding and dipole-dipole stackings. Dipole stacking contributes to the enantioselectivity between the aryl group connected to chiral carbon and the benzene group of CSP1.Hydrogen-bonding interactions can be involved between the N_H of the carbamate function of the CSP1 and the oxygen atom of the PO. Each glucose unit contains five chiral centres. Two of these chiral centres are on the C-2 and C-3 atoms. The carbamate groups on C-2 are located at the entrance of the cone and point in a clockwise direction whereas the hydroxyl groups on C-3 are located outside the cyclodextrin molecule and point in a counter-clockwise direction. In this way, the third chiral repulsive interaction can be involved. In conclusion, the chiral recognizing model involves one hydrogen-bonding interactions, stronger dipole stacking and repulsive interaction.

Key words: Cyclodextrin bonded phase, High performance liquid chromatography, Chiral recognition mechanism