Synthesis and recognition properties of aromatic amide oligomers: Molecular zippers

A series of amide oligomers have been prepared from isophthalic acid and a bisaniline derivative. These compounds assemble into double-stranded zipper complexes in solution via hydrogen-bonding and edge-to-face aromatic interactions. The stability and structures of the complexes have been determined by H-1 NMR spectroscopy in chloroform solution. The stability of the complexes increases with increasing chain length, indicating cooperativity between the individual recognition sites in the oligomers. Oligomers which are complementary form more stable complexes than non-complementary systems with overhanging ends. Addition of polar solvents such as methanol destabilizes the complexes, because it competes for hydrogen-bonding interactions which appear to be the main driving force for binding in this system.