Self-assembling capsules higher structure

Figure 31.1 shows the structures of some of the calixarene and calixpyrrole derivatives that were found to self-assemble into dimeric capsules (see structures 2-5). The tetraureacalix[4]arenes (2) were found to from dimeric capsules with internal volumes estimated to be in the range of 160-200 [lib]. These dimeric capsules were found to encapsulate solvent molecules like chloroform and benzene and small ammonium salts [11]. In addition, it was demonstrated with the aid of diffusion NMR [16] that such dimers have a high affinity for charged systems, and it was found that tropylium cation and cobaltocenium cation have higher affinities than benzene and ferrocene, respectively, for the cavity of the dimer of 2 [17]. These and other studies demonstrated that indeed diffusion NMR is an excellent means to probe encapsulation [17, 18], a fact that was instrumental in the study of the large hexameric capsules of resorcin[4]arenes and pyrogallol[4]arenes as will be demonstrated below [18-20]. 

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