Synthesis and self-assembly of supramolecular dendritic "Bow-Ties":: Effect of peripheral functionality on association constants

Self-assembled polyester dendritic bow-ties with various peripheral groups were prepared, and their association constants were measured by H-1 NMR in CDCl3. The two complementary dendrons were prepared by attachment of either a bis(adamantylurea) or a glycinylurea to the focal point of the dendron. The parent self-assembled system with benzylidene acetals on one periphery and isopropylidene acetals on the other had an association constant of 520 M-1. Upon deprotection of one dendron, the association constant is increased by more than an order of magnitude as the solubility of the hydroxyl-terminated dendron in CDCl3 is decreased. In contrast, attachment of tri(ethylene oxide) units to the periphery of one dendron lowers the association constant by almost an order of magnitude. The causes of these relatively large changes in complex strength are discussed in terms of solubility, steric effects, competitive hydrogen bonding, and the structure of the dendritic scaffold.