Control of helical folding of macromolecules: Host-guest chemistry of helical macromolecules

The helical structure is one of the most significant motifs in macromolecules. In nature, helical structures are often found in biomacromolecules, and they appear to play a critical role in biological phenomena such as molecular recognition and information storage, as exemplified by the double helices of DNA and the alpha-helix of proteins. Some synthetic polymers and oligomers also adopt a helical conformation. Recently, the design and synthesis of macromolecules with a helical structure has attracted a great deal of interest, in view of their relationship to life science, as well as of their potential applications in materials science. This review deals mainly with 1) foldamers, 2) foldamer as receptors, and 3) helical folding in the cavity of helical polymers. The foldamer is any oligomer that folds into a conformationally ordered state in solution, the structure of which is stabilized by a collection of noncovalent interactions between nonadjacent monomer units. Recently, a number of examples of foldamers such as oligo (aromatic amide) and oligo (m-phenylene-ethynylene) have been reported. The foldamers can be employed as receptors for small molecules and metal ions confined within the helical cavity. The helical folding of oligomers in the cavity of helical polymers is also described.