Propeller-Shaped Self-Assembled Molecular Capsules: Synthesis and Guest Entrapment

Molecular
containers or supramolecular capsules are a subject of great interest
because of their potential utilizations in various fields of chemistry,
medicine, and nanoscience. They have been utilized as nanovessels
for reactions and targeted drug delivery in recent years. Cyclotricatechylene
(CTC) is a bowl-shaped molecule in its crown structure. It has six
phenolic groups as potential hydrogen bond donors. In this work, we
utilize this hydrogen bonding capability of CTC to generate supramolecular
complexes with hydrogen bond acceptors such as 4,4′-bipyridine,
pyrazine, 2,2′-bipyridine, and phenanthroline. These supramolecular
entities were studied in the solid state by X-ray crystallography
and scanning electron microscopy. They are not soluble in low polar
solvents. Therefore, the hydrogen bonding behavior in solution could
not be studied by NMR. Except in the case of pyrazine, capsular supramolecular
assemblies were formed in all the cases. One of these capsules was
studied for guest entrapment. Planar molecules such as naphthalene
and pyrene were trapped inside its cavity with a little reorganization
of the capsular assembly.