Chemists in Japan have made nanotubular structures from cyclic peptides that could be used in molecular electronic devices.

Shunsaku Kimura at Kyoto University and co-workers made cyclic tri--peptides from the -amino acid, ACHC, which spontaneously assemble into a stacked columnar structure in solution. The researchers claim that the stacking of the molecules is promoted by the planar conformation of the cyclic peptides.  They say hydrogen bonding between the amide groups, which align perpendicular to the ring, stabilises the structure. The researchers found that the columnar structures associated together to form nanotube bundles. 



Kimura said an unusual and important property of the molecular assembly is that it has a macrodipole moment (all the dipole moments of the columns in the cluster line up in the same direction). 'Generally, molecular columns are expected to orient in an anti-parallel manner, to cancel out the total dipole moment for stabilization. Thus, this crystal structure of cyclo(ACHC)₃ is highly unique and will add a new aspect to molecular assemblies of cyclic  -amino acids.'

It is the macrodipole moment of the material makes it potentially useful for the fabrication of molecular electronic devices, as 'molecular dipole moments can influence the electron transfer reactions through a molecule,' said Kimura.

Kimura plans to develop nanotubular systems with interior and exterior functionalisation, which he expects will widen the scope of these structures to medicinal chemistry.

Richard Kelly