Agoston Jerga

Organization of the interior of molecular capsules by hydrogen bonding

The enclosure of functional entities within a protective boundary is an essential feature of biological systems. On a molecular scale, free-standing capsules with an internal volume sufficiently large to house molecular species have been synthesized and studied for more than a decade. These capsules have been prepared by either covalent synthesis or self-assembly, and the internal volumes have ranged from 200 to 1,500 Å3. Although biological systems possess a remarkable degree of order within the protective boundaries, to date only steric constraints have been used to order the guests within molecular capsules. In this article we describe the synthesis and characterization of hexameric molecular capsules held together by hydrogen bonding. These capsules possess internal order of the guests brought about by hydrogen bond donors within, but not used by, the framework of the capsule. The basic building blocks of the hexameric capsules are tetrameric macrocycles related to resorcin[4]arenes and pyrogallol[4]arenes. The former contain four 1,3-dihydroxybenzene rings bridged together by -CHR- units, whereas the latter contain four 1,2,3-trihydroxybenzene rings bridged together. We now report the synthesis of related mixed macrocycles, and the main focus is on the macrocycle composed of three 1,2,3-trihydroxybenzene rings and one 1,3-dihydroxybenzene ring bridged together. The mixed macrocycles self-assemble from a mixture of closely related compounds to form the hexameric capsule with internally ordered guests.

Hydrogen-bonded molecular capsules are stable in polar media

Robust, very large hydrogen-bonded capsules which are even stable in 50:50 water-acetone mixtures have been characterized both in solution and in the solid state.

On the synthesis and structure of the very large spherical capsules derived from hexamers of pyrogallol[4]arenes

Abstract The acid-catalyzed condensation of pyrogallol and aldehydes yields pyrogallol[4]arenes, which associate in the form of hexameric capsules of extraordinary stability due to the presence of 48 intermolecular hydrogen bonds seaming the individual pyrogallol[4]arenes together.

Polymorphism of pure p-tert-butylcalix[4]arene: conclusive identification of the phase obtained by desolvation

In its pure form, the well-known host compound p-tert-butylcalix[4]arene forms at least two polymorphs; one of these phases is now identified as that formed upon guest removal.