The Structure Research Of β-Cyclodextrin Inclusion Complexes With Aromatic Guest Molecules

Due to the unique structure with hydrophobic central cavity,β-cyclodextrin can selectively bind different guest molecules to form inclusion complexes in order to improve solubility, stability of guest molecules. Thus,β-cyclodextrin has been widely used in many different fields, such as pharmaceutics, analytics, food and environment, etc. The structure research of host-guest inclusion complex is the basic problem of molecular inclusion phenomena and supramolecular assembling, the study about this area is focused on all the time.In this paper,β-cyclodextrin was used as the host molecule and the o-aminobenzoic acid, m-aminobenzoic acid and p-aminobenzoic acid were used as the guest molecules. X-ray powder diffractometry, Fourier transform infrared, 1H nuclear magnetic resonance, circular dichroism, x-ray single crystal diffractometer and molecular simulation method were used to study the inclusion complex structure. The host and guest molecules with different molar ratio were dissolved in water or ethanol-water solvent, and agitated for 2 hours under 70℃, then cooled to room temperature, filtered with membrane filter. The products were stored under room temperature to volatilize the solvent, the solid inclusion complexes were gained. The products were put into vacuum dryer, dried till constant weight. The structures of inclusion complexes were studied, and the inclusion modes of the host-guest complexes were discussed by molecular simulation method.The results showed that: the inclusion complex of o-aminobenzoic acid andβ-cyclodextrin was made with the molar ratio of 1:1, the benzene ring was included into the cyclodextrin cavity, the amido and carboxyl pointed to the big end of cyclodextrin both, molecular dynamic simulation result indicated that the host-guest centroid distance was about 2 ?; the inclusion complex of m-aminobenzoic acid andβ-cyclodextrin was made with the molar ratio of 1:1, the benzene ring was included into the cyclodextrin cavity, the amido pointed to the big end of cyclodextrin and the carboxyl pointed to the small end, molecular dynamic simulation result indicated that the host-guest centroid distance was about 1.2 ?; the inclusion complex of p-aminobenzoic acid andβ-cyclodextrin was made with the molar ratio of 2:2, the benzene ring was included into the cyclodextrin cavity, the amido pointed to the big end of cyclodextrin and the carboxyl pointed to the small end, molecular dynamic simulation result indicated that the host-guest centroid distance was about 0.6 ?, the molecular simulation result was in accordance with the crystalline data; naproxen and β-cyclodextrin inclusion complex were synthesized with the molar ratio of 1:1, naphthaline ring was included into the cyclodextrin cavity, molecular simulation result indicated that the state which carboxyl pointed to the big end was the stable structure, molecular dynamic simulation showed that the host-guest centroid distance was about 4.5 ?; the hydrogen bond was observed by molecular silulation in the inclusion complexes of three isomers of aminobenzoic acid withβ-cyclodextrin, and the p-aminobenzoic acid was buried into cyclodextrin cavity deeply, the o-aminobenzoic acid was opposite.