Capsules and cavitands : concave molecules built on the cyclotribenzylene (CTB) scaffold
Drake, Stephen D.
Thesis (Ph.D.)--Georgetown University, 2011.; Includes bibliographical references.; Text (Electronic thesis) in PDF format. Molecules possessing large, enforced concave surfaces are fairly prevalent in naturally occurring systems, but there are relatively few synthetic molecules that share these characteristics. Cyclotribenzylenes (CTBs) and cryptophanes are examples of synthetic molecules that meet these criteria and are also lend themselves to facile functionalization to create new platforms with which to explore recognition and supramolecular chemistry.; A series of C3-symmetric, pyridyl-substituted, extended cavity CTBs have been synthesized with the intent of exploring larger self-assembled molecular moieties and cavitand-containing coordination polymers through the exploitation of labile metal-pyridine bonds, with the strategic interest of incorporating an inherently chiral CTB ligand to explore the effect of the shape and chirality on the potential self-assembled aggregates. Reaction of these molecules with organic carboxylic acids has also provided nearly isostructural materials from acetone and MeOH, two solvents having opposite hydrogen bonding characteristics.; Additionally using the CTB scaffold, cyclotrianisidines ((+/-)-CTAs), an amine functionalized CTB, have been synthesized--both C3 symmetric and C1 symmetric--using a novel one-step method, avoiding the previously reported tedious and expensive synthetic route to the useful CTA supramolecular scaffold. The synthesis and characterization of CTAs of various symmetry and numbers of amino functional groups for future use as ligands is also explored and discussed.; Cryptophanes, molecules consisting of two bridged CTBs, have also been synthesized bearing endohedral and exohedral functional groups through the use of m-xylyl bridges and their derivatives. The introduction of interior pyridine functionalization--using bridges derived from 2,6-lutidine--have led to the observation of a stable, 'imploded' conformation of a cryptophane--the first reported in organic solvent at room temperature. These studies shed light on the conformational properties of cryptophanes in the context of other CTB containing molecules, and the ability of cryptophanes to selectively encapsulate substrates. Other approaches to incorporate nitrogen heteroatoms into cryptophane molecules are also highlighted within this thesis.; Lastly, the utility of m-xylyl bridges has also been exploited to functionalize the exterior of cryptophanes through the synthesis and characterization of a water soluble cryptophane bearing six exohedral carboxylic acid moieties. The synthesis and isolation of the syn and anti diastereomers of has been achieved and is described herein.
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