The double helical structure of DNA is a source of inspiration to many researchers. The way that a single strand can pass on specific information, by acting as the template for new DNA formation, means that it could potentially be used in molecular computers. However, the relatively low stability of DNA, and the fact that ‘mistakes’ in passing on genes are a necessary part of evolution mean that there is wide interest in more stable synthetic systems that display similar, or even improved, recognition.

In a step towards this lofty goal, Yoshio Furusho and co-workers from the Japan Science and Technology Agency and Nagoya University in Japan1 report the preparation of short oligomeric strands which fold into a helix, and are capable of recognizing a complementary strand and forming a double helix much like that in DNA. “The exquisite functions of DNA stimulated us to develop artificial molecules capable of processing molecular information,” says Furusho. “We have been actively involved in the design and synthesis functional molecules with a double helical structure since 2003.”

Each monomer unit of the oligomer is constructed from a meta-terphenyl structure—a central phenyl group bears two further phenyl substituents at carbons 1 and 3—to which a binding group is attached. These building blocks are then connected together with a simple diacetylene linker to the helical oligomers. Furusho and co-workers prepared a variety of short oligomers from dimers to tetramers bearing different sequences of two complementary binding groups—an amidine (A) or a carboxylic acid (C)—which are known to interact strongly by the formation of a salt-bridge.

Fig. 1: Recognition and double helix formation occurs only between self complementary strands. A = amidine, C=Carboxylate.

When mixtures of dimers or trimers bearing different combinations of binding units were prepared, a self-sorting process occurred whereby double helices were formed specifically between complementary strands (Fig. 1). Self-sorting was also observed based purely on the length of the oligomers—mixtures of monomers and homo-dimers and tetramers—so that over time, double helices were formed only between strands of the same length.

“This is the first system which sorts by both sequence and chain length,” explained Furusho, “in the future, we hope to devise a totally self-replicating system based on this technology.”