Molecular Recognition Based on β-cyclodextrin and Chemical Modified β-cyclodextrin as Receptor
|Keywords||Naproxen enantiomers β-cyclodextrin (β-CD) Dibromomethane Chiral discrimination Room tempearture phosphorescence (RTP)|
Chapter 1:The concept and application of cyclodextrin, modified cyclodextrin were introduced briefly. Summarized the different research technique of chiral discrimination and narrated the orgin and research development of chiral recognition simply.Chapter 2:Naproxen enantiomers possess strong room temperature phosphorescence (RTP) in (3-cyclodextrin (P-CD) system with a small amount of 1,2-dibromoethane (1, 2-DBE) under ambient conditions. The effects of pH, concentration ofβ-CD and 1, 2-DBE on the RTP of naproxen enantiomers have been investigated in detail. Time-resolved RTP spectroscopy shows that both naproxen enantiomers exhibit bi-exponential decay pattern with lifetimes ofτ1= 4.79±0.13 andτ2=1.51±0.096 ms for R-naproxen, andτ1= 6.67±0.15 andτ2= 2.13±0.061 ms for S-naproxen. The lifetime differences between these enantiomers areΔτ1=1.88 andΔτ2r=0.62 ms, indicating that chiral discrimination of naproxen enantiomers can be achieved inβ-CD/1,2-DBE system. Naproxen enantiomers can form stable complexes withβ-CD and 1,2-DBE in stoichiometric ratios of 1:1:2 and 1:1:1 (naproxen:β-CD:1,2-DBE) and the association constants are 3.20×103 M-4 and 2.43×103 M-3 for the S- and R-enantiomers respectively. The chiral discrimination of R-naproxen and S-naproxen is realized via their difference in interaction with the chiral cavity ofβ-CD due to their difference in stereochemical structure. Finally, molecular modeling is performed to determine the chiral recognition on a molecular level and the results are in good agreement with the experimental data.Chapter 3:S-naproxen-modified-β-CD (S-NPX-CDs 1-3) were synthesized by the reactions of (S)-(-)-naproxen with 6-amino-6-deoxy-,3-amino-3-deoxy-, and mono(2-amino-2-deoxy-altro).-β-CDs, respectively. All of them were characterized by HRMS and 1H and 13C NMR spectra. On this basis, the fluorescent and phosphorescent properties of 1 were studied preliminary. The fluorescent and phosphorescent properties of S-naproxen and S-naproxen-modified-β-CD in different medium were also compared, and the results showed that S-naproxen can enter intoβ-CD cavity, so the fluorescence and phosphorescence were enhance.Chapter 4:Firstly, the fluorescence and phosphorescence characteristics of S-NPX-CDs 1-3 were investigated. Then the molecular recognition of S-NPX-CDs 1-3 to small organic objective molecules were explored by RTP method, and the organic small molecules included dibromomethane, bromoform, isodiiodomethane, iodomethane, Carbon Tetrabromide,1,2-dibromomethane, formaldehyde, bromocyclohexane, methane, cyclohexane, formic acid, methanol, ethanol and acetic acid. Among them, only dibromomethane could significantly enhance the RTP signal of S-NPX-CD1, while it had no effect on S-NPX-CDs 2 and 3. Based on this, a RTP method for the determination trace dibromomethane was establised by S-NPX-CDs 1 as the receptor. Then it was applied to determine the content of dibromomethane in coal mine water and the results was in good agreement with the result of GC-MS method. Therefore, a potential RTP sensor of dibromomethane can be developed by S-NPX-CDs 1 as the receptor. Finally, the mechanism was investigated by 1HNMR, dichroism, UV absorption spectra and energy simulatione.