Life relies on polymers that are able to form a well-defined hierarchy of self-assembling structural levels. An essential attribute of biological macromolecules such as proteins and nucleic acids is their masterful control over the non-covalent forces that govern folding and self-assembly processes. For a long time only biopolymers were known to have such properties, whereas non-natural folded polymers (foldamers) have the potential for being similarly or even more versatile. A foldamer - a discrete chain molecule or oligomer - folds into a conformationally ordered state in solution, and its structure is stabilized by a collection of noncovalent interactions between adjacent monomer units. It is easy to admit that foldamer research has been motivated by the highly-ordered structures of the well-known biopolymers and the fact that the folding into a specific regular structure is the key to their functions such as molecular recognition, catalysis, and information storage. Therefore it is obvious that foldamers ability in mimicing the attributes of proteins, nucleic acids, and polysacharides can be interpreted with their folding into well-defined conformations, such as helices, sheets, turns, as seen in biological macromolecules.

Foldamers can be roughly classified into three categories with regard to their monomer types: peptidomimetic foldamers, nucleotidomimetic foldamers, and abiotic foldamers. The former two are inspired by the structures of proteins and nucleic acids, and are mainly based on the modification of the chemical structure of the monomer (amino acids and nucleotides), while the latter one utilizes aromatic interactions, charge-transfer interactions, and others, that are not general in the nature. Among them, inspired by sophisticated structures and functions of proteins, the peptidomimetic foldamers have been most actively investigated so far. The major advantage in peptidomimetic foldamers is that the amide groups, that combine monomers into the chain, also act as cross-linking points via hydrogen bonding between the amide proton and the carbonyl oxygen to fold the chain into a regular structure. Therefore these structures are able to easily form secondary structures (various helix-types, strand-like conformations, and turns) and are capable of forming higher-order selfassemblies too. That’s why they belong among the most intriguing models of unnatural polymers.

The importance of foldamers in chemistry and biochemistry can be verified by a number of interesting supramolecular properties including molecular self-assembly, molecular recognition, and host-guest chemistry. They have been studied as models of biological molecules and have been shown to display antimicrobial activity. They also have great potential application to the development of new functional materials.