| In this paper, a new chiral separation technology, aqueous two phase chiral extraction based on Polyethylene glycol (PEG)/salt contaning cyclodextrin derivatives as the chiral selector has been proposed for the separation of a-cyclohexyl-mandelic acid (CHMA) enantiomers. Chromatographic retention mechanism of CHMA was explanied by molecular simulation.The main contents can be summarized as follows:Firstly, based on the PEG/Ammonium sulphate aqueous two phase system (ATPS), a green, economical, novel approach coupled with high performance liquid chromatography was proposed for the chiral separation and determination of CHMA. The result showed that this new technique has good recognition ability for CHMA.The separation factor, a, was affected by various factors, including the molecular weight of PEG, the amount of PEG, pH, temperature, the amount of ethanol and HP-β-cyclodextrin, which influenced on either the formation of the host-guest complex or the distribution of the complex. The result showed that HP-β-cyclodextrin was inclined to recognize S-CHMA, aqueous two phase system based on PEG6000(3.0g)/Ammonium sulphate (2.0g) resolved in15.0mL CHMA(0.5mmol·L-1, pH=2.87) which contains0.1g HP-β-CD has a better recognition ability for CHMA under18℃.Under these conditions a could reached1.25after just one step extraction.Secondly, ATPS based on the PEG/Sodium citrate containing Cu2-β-CD as the selector has been applied in the chiral separation of CHMA racemic. The separation factor, a, was affected by various factors, including the molecular weight of PEG, pH, temperature, the amount of Cu2-β-CD, which influenced on either the formation of the host-guest complex or the distribution of the complex. The result showed that Cu2-β-CD was inclined to recognize R-CHMA, aqueous two phase system based on PEG6000(3.0g)/Sodium citrate (2.0g) resolved in15.0mL CHMA(0.5mmol·L-1, pH=8.96) which contains1.0g Cu2-β-CD has a better recognition ability for CHMA under9℃.Under these conditions a could reach1.36after just one step extraction.Thirdly, Host-guest complexation of β-cyclodextrin (β-CD) with α-cyclohexyl-mandelic acid enantiomers was simulated by quantum mechanics PM3method for understanding the chiral recognition mechanism. The modeling results can correctly predict the retention order and provide an atomistic account of how chiral discrimination takes place. Modeling results showed that the stabilization of complexes formed by (R/S)-CHMA enantiomers and β-CD were different. The hydrophobic block of benzene moiet of (R)-CHMA was located in the cavity of β-CD to form an inclusion molecule, while it is the cyclohexyl that be inserted in the cavity in the case of (S)-CHMA to form an inclusion molecule. What is more, as for (S)-CHMA/β-CD complex, there is an intermolecular hydrogen bonds. The stabilization energy of the (S)-CHMA/β-CD complex was lower than that of the (R)-CHMA/p-CD complex. The main driving forces responsible for chiral recognition are hydrophobic forces and weak hydrogen bondings.Finally, a novel type of temperature stimuli responsive polymer, β-CDE-grafted-PNIPAAm, was prepared by radical polymerization using cerium ammonium nitrate as the initiator. The structure and properties of the resultant were characterized by FT-IR,1H-NMR, DLS etc. The optical transmittance of the copolymers in the aqueous solution was examined by Vis instrument. The result showed that the LCST of β-CDE-grafted-PNIPAAm, about33.5℃, is slightly higher than that of PNIPAAm and that the optical transmittance of the product decreased in the case of the addition of sodium chloride and sodium dodecyl sulfate.Its critical micelle concentration is about0.0257mg·mL-1. What is more, under certain condition, it could form aqueous two phase system with dextran-40000.This thermosensitive product can be used to construct polymeric micelles as drug carriers and may have the potential applications in environmental control; they can also be used to separate and purify some biological materials. |
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