Synthesis and characterization of host-guest complexes: metal-organic nanocapsules using aryl-substituted pyrogallolarenes
Maerz, Andrew K.
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The desire to synthesize and control self-assembly of molecular nanocapsules has long been a focus within the supramolecular community due to the nanocapsules' potential applications as tools for encapsulation and delivery of host molecules, catalytic media sites, and gas sorption agents. Resorcinarenes (RsC) and pyrogallolarenes (PgC) have received considerable attention due to their preference to form the all-cis cone-shaped (rccc) structure, thus allowing dimeric and hexameric nanocapsule formation through complementary and structurally distinct intermolecular hydrogen bonding interactions or metal coordination. By changing the lower rim R group, one drastically alters the chemical environment. C-arylresorcinarenes, for example, adopt a more kinetically stable 1,2-chair rctt stereostructure but show interconversion to the thermodynamic product, the all-cis rccc cone. In contrast, our studies of the C-arylpyrogallolarenes unexpectedly suggest that the 1,2-chair rctt stereostructure is the thermodynamic product. Herein, we show that complexation of zinc and C-phenylpyrogallolarene, as well as other benzyl derivatives, induces a conformational flip in these macrocycles from chair to cone. This formation of the zinc-seamed metal-organic nanocapsules has been tracked via NMR, X-ray Diffraction and Mass Spectroscopy studies. The results yield several important trends that can be applied towards both the study of supramolecular self-assembly and the utilization of these host-guest capsular entities for other purposes.
2011 Freely available dissertations (MU)