Large Hydrogen Bond Molecular Capsules or Molecules Within Molecules:
Molecular capsules are container molecules capable of totally encapsulating molecules thus isolating them from the bulk. As such they can be used a nanoreactors. We are currently using diffusion NMR to characterize large hydrogen bond molecular capsules of resorcin[4]arenes (1) and pyrogallol[4]arenes (2).
We study in detail their self-assembly, structure, stability and guests’ affinity. Here, we could show, inter alia, that both 1 and 2 form spontaneously hexameric capsules in non-polar organic solvents. 1 forms a 16(H2O)8-type capsule and 2 forms a 26-type capsule. We also found that the hexameric capsule of 2 can act as a molecular switch, in which tertiary amines are expelled from the capsule upon protonation. Recently we become interested in the self-sorting in such self-assembly processes and in the interaction of 1 with nano-surfaces. We found that hetero-hexameric capsules are not formed between resorcin[4]arenes and pyrogallol[4]arenes but they do form between different members of the same family. We were able to show that octahydroxypyridine[4]arene (3) also forms hexameric capsule in solution, thus demonstrating that hexameric capsule are much more abundant than previously thought. The interaction of such hexameric capsules with different guests such as alcohols, amines and organic acids are also studied in a future goal to use these capsules as nanoreactors for chemical reactions between these guests. For example, recently we could demonstrate that diffusion NMR enables one to map alcohol sites in such hexameric capsules and to determine if they are encapsulated or are part of the backbone of the hexameric capsules.
