| Cyclodextrin (CD) is widely used in food, chemistry and medicine industries as itscylindrical structure which is internally hydrophobic and externally hydrophilic. This wideusage of CDs in industry is mainly attributed to its special structure which can form inclusioncomplex with guest molecules. In the formation process of host-guest inclusion complexes,the hydrophobicity of CDs is one of the important driving forces to form inclusion complexes.However, report on the hydrophobicity of CDs is fairly few. In this study, pyrene was used asa fluorescent probe to investigate the hydrophobicity of β-CD and three different derivatives(hydroxypropyl-β-CD, methyl-β-CD and sulfobutyl ether-β-CD) of it in different solvents.First, the differences of hydrophobicity of β-CD and its three derivatives in watersolution were studied. The results indicated that in same concentration, the hydrophobicitycapacity of β-CD was strongest among the four kinds of CDs. While the hydrophobicitycapacity of HP-β-CD and S-β-CD was nearly same and M-β-CD showed weakest capacity inhydrophobicity. The inclusion constants of the four kinds of CDs were also calculated and theresults indicated that the order of inclusion constants of them was M-β-CD, HP-β-CD,S-β-CD, β-CD in ascending order, which matched well with results from polaritymeasurement. This indicated that the introduced derived groups reduced the hydrophobicityof CDs.Second, the changes of hydrophobicity of β-CD and its derivatives in organic solutionwas studied. Methanol, ethanol, acetone and dimethy sulfoxide were chosen as organicsolution and the results indicated that the capacity of hydrophobicity of β-CD was higher thanthe three derivatives in organic solution with a low concentration (less than30%). And thecapacity of hydrophobicity of β-CD and its derivatives all reduced along with the enhancingconcentration of organic solution. Compared with other derivatives, this reducing trend wasmost obvious in β-CD. This was mainly due to the competitive cooperation between organicsolvents and pyrene.Meanwhile, the changes of hydrophobicity of β-CD and its derivatives in salt solutionwere also studied. The results showed that the hydrophobicity of β-CD was still stronger thanother kinds of derivatives in salt solution. And the hydrophobicity of β-CD increased alongwith the increasing concentration of salt solution while the hydrophobicity of otherderivatives was relatively stable. The reason for this phenomenon was that positive ions canform a cyclic structure with the narrow end of β-CD to increase the hydrophobicity of thecavity, while anions were not directly involved in changing the property of the cavity of β-CD.As for the derivatives, the similar structure was difficult to form because of the spaceobstacles of substituent groups. Therefore, the properties of cavities of the three derivativeswere almost unaffected.In addition, β-CD, M-β-CD, HP-β-CD and S-β-CD were analyzed by High PerformanceLiquid Chromatography (HPLC) with Amino column as separating column. The resultsindicated that the order of the retention time of the four kinds of CDs based on the polarforces with the stationary phase was β-CD, HP-β-CD, S-β-CD and M-β-CD in ascendingorder. The longer the retention time in positive phase column, the stronger the hydrophobicity of the cavity of CDs. This result was generally consistent with the result of β-CD and itsderivatives measured by pyrene probe.Finally, chiral molecules were separated by using the hydrophobicity of the cavity ofCDs. β-CD and three kinds of derivatives were chosen as mobile phases to separate thechlorthalidone enantiomers. The results showed that only β-CD and HP-β-CD can be used toseparate chlorthalidone enantiomers and the degree of separation were1.41and0.83,separately. While S-β-CD and M-β-CD can’t be used to separate chlorthalidone enantiomers.This indicated that the study on hydrophobicity of the cavity of CDs was significantlyimportant for the identification and separation of chiral molecules. |
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