Guest Encapsulation and Self-Assembly of a Cavitand-Based Coordination Capsule

摘要

The synthesis and spectro-scopic characterization of a cavitand-based coordination capsule 1.4BF_4 of nanometer dimensions is described.Encapsulation studies of large aromatic guests as well as aliphatic guests were performed by using ~1H NMR spectros-copy in [D_1]chloroform.In addition to the computational analysis of the shape and geometry of the capsule,an experimental approach to estimate the interior size of the cavity is discussed.The cavity provides a highly rigid binding space in which molecules with lengths of approximately 14 A can be selectively accommodated.The rigid cavity distinguished slight structural differences in the flexible alkyl-chain guests as well as the rigid aromatic guests.The detailed thermodynamic studies revealed that not only CH-pi interactions between the methyl groups on the guest termini and the aromatic cavity walls,but also desolvation of the innercavity play a key role in the guest encapsulation.The cavity preferentially selected the hydrogen-bonded hetero-dimers of a mixture of two or three carboxylic acids 18-20.The chiral capsule encapsulated a chiral guest to show diastereoselection.