Metal-free double helices from abiotic backbones.

There is a general interest in designing biomimetic materials, such as the double helical structures of biopolymers, by the self-assembly of synthetic organic moieties. This interest stems from their structural versatility, biocompatibility, robustness and a relative experimental simplicity. The self-assembly process requires a combination of several non-covalent interactions between two intertwined strands. Besides the combination of metal-ligand binding, base pair interactions and peptide stacking interactions, in the last few years, hybridized synthetic foldamers have proven to be useful in this context. The molecular rigidity and the extent of intra- vs. intermolecular interactions within the strand play an important role in the intertwining processes. A dynamic equilibrium exists between the monomer and the dimer. In general, the combination of the enthalpic gain (from the interaction of the two strands) and entropic loss (upon hybridization) controls the duplex formation. There are now a variety of metal-free double helices from abiotic backbones, with potential applications in antigene therapy, studies on evolution and conducting materials. A tutorial review of some general guidelines and illustrative examples is presented.