Molecular encapsulation in kinetically trapped, hydrogen-bonded pyrogallolarene hexamers

Pyrogallolarene and resorcinarene hexamers are hydrogen-bonded capsules that self-assemble in the solid state and can be studied in gaseous and solution phases. Guest loading within pyrogallolarene hexamers in solution has primarily been comprised of solvent molecules with some tertiary amines. A novel solvent-free method for loading guests into the interior of the hexamer has been shown to be effective for encapsulation of a variety of molecules. Aromatic and aliphatic compounds have particularly high guest loading within the hexamers and often result in kinetically stable guest-filled capsules in solution.;Kinetic studies of the encapsulation complexes of anthracene, biphenyl, fluoranthene, fluorene, naphthalene, norbornene and pyrene were performed in multiple solvents using 1H NMR. In all but one case the kinetically stable complexes completely exchanged the encapsulated guest for solvent resulting in guest release processes that were determined to be first order in capsule. Guest release requires the breakage of multiple hydrogen bonds simultaneously to create an opening in the hexamer for the guest to exit and solvent to enter. Small structural changes in both the solvent and the guest resulted in large differences in exchange rates. Those guests and solvents that were larger or had greater deviations from planarity had longer exchange rates due to the larger openings required for guest release.;Purification of the kinetically trapped species was successfully performed using size exclusion gel permeation chromatography. Chemical compartmentalization experiments were performed to determine the ability of the hexamer to sequester encapsulated guests from bulk solution and thereby isolate them from potential reactants. Both bromination and hydrogenation of the alkene functionality of norbornene resulted in no addition to the double bond for encapsulated norbornene. These results illustrate the high kinetic stability of the guest encapsulated pyrogallolarene hexamers in solution.;Monofunctionalization of the lower rim of pyrogallolarene was also attempted. A mixture of pyrogallolarenes was successfully synthesized with 0-3 terminal double bonds. Olefin metathesis with benzyl acrylate followed by hydrogenolysis successfully resulted in pyrogallolarenes with carboxylic acids on the lower rim. Peptide coupling to create an amide linkage has also been studied for use in attachment to polymers.