Biomimetic Self-Assembly: The fundamental goal of the research proposed herein is the discovery of new methods to control molecular aggregation using hydrogen bonding and pi-stacking interactions. The simplest aggregates to be developed are disc-and washer-shaped structures composed of three of six heterocyclic """"""""building-blocks."""""""" These building blocks self-associate as a result of complementary hydrogen bonding arrays on remote edges of the aromatic systems. Two strategies for generating higher levels of self-assembly will be investigated. The first is through pi- stacking of disc- and washer-shaped aggregates in solution or in molecular or liquid crystals, forming columnar or tubular structures. The second is by addition of optically active """"""""end-capping"""""""" heterocycles that will induce formation of a continuous pi-stacked and hydrogen-bonded helical structure, similar to the disc->washer->helix transition shown by the tobacco mosaic virus protein in forming the viral capsid. An alternative approach to helical structures uses heterocyclic units with geometries that prevent closure to form discs or washers. Substituents attached to the heteroaromatic compounds will be oriented toward the center of the disc (washer) or project out from its periphery. The internal groups determine the chemical nature of the interior of the column or tube, while the peripheral substituents adjust the morphology and properties of the aggregate. Aryl substituents will enhance crystallinity, alkyl chains of intermediate length solubility in a range of solvents, and long alkyl chains liquid crystallinity. Covalently linking heterocyclic subunits allows the formation of polymeric assemblies. Applications include: (1) biomimetic viral capsids for solution encapsulation (e.g. drug-deliver), (2) designed clathrates for separation, purification, and/or optical resolution of drugs and other organic compounds, or for storage of small quantities of toxic materials, (3) ion channels, (4) crystal engineering, and (5) new columnar and tubular mesophases.
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