The inclusion behavior of anthracene (ANT) in three cyclodextrins (betacyclodextrin, hydroxypropyl betacyclodextrin, and sulfobutylbetacyclodextrin) has been investigated by molecular dynamics (MD) simulations. The MD results showed that ANT could spontaneously enter the cavities of these three cyclodextrins. The difference is that when packaged with sulbutylbetacyclodextrin, ANT can only enter the cavity through the wide edge of sulbutylbetacyclodextrin. Then, the effects of 2-hydroxypropyl (HP) and sulphonated butyl (SBE) substituents on the structure of cyclodextrins were studied by analyzing the structural distortion of glucose units of each cyclodextrin.
It was found that neutral betacyclodextrins showed a conical structure, and the presence of HP or SBE groups greatly influenced the structure. The secondary edge Narrows due to the flipping of the glucose unit caused by the fluctuation of the substituent group. When ANT was included in the cavity, the cavity conformation of the three cyclodextrins was restored to a certain extent. At the same time, the substituent group extends along the cavity axis and interacts with the guest molecule.
By analyzing the interaction between each cyclodextrin and ANT, it was found that the substituting groups expanded the volume of the hydrophobic cavity. Both the substituent groups and the glucose units contribute to the interaction with the guest molecule. Conformational changes in the cyclodextrin ring lead to contraction of the cavity, which may allow it to bind tightly to ANT molecules.
