Putting gels in a twist

Chiral handles induce helical nanostructures in organogels.

Helical nanostructures are widespread in nature. Some of them, including the amyloid fibrils associated with a number of diseases, are highly undesirable, and research is directed at understanding why they form and to how to stop them forming.

To add another twist to the tale, researchers have now obtained helical nanostructures in the sol-gel transition of synthetic aromatic molecules, using chiral ’handles’.

Previously, the group of Ayyappanpillai Ajayaghosh at Trivandrum, India, had shown that oligo-(p-phenylenevinylene)s (OPVs) can form gels by stacking aromatic rings, which act as light-harvesting devices.1 Now, in collaboration with Bert Meijer’s group at the Technical University of Eindhoven, the Netherlands, the researchers have modified the OPVs by introducing chiral centres remote from the stacking centres.2 The so-called chiral handles consist of branched hydrocarbons.

By letting these compounds form organogels from non-polar solvents, the researchers obtained birefringent, fibrous materials. Using electron microscopy, they discovered left-handed helical fibres of up to 50nm diameter, 150nm helical pitch, and several micrometres in length. During the gelation process, the authors also observed characteristic changes in the circular dichroism spectra which they attribute to a hierarchic mechanism of assembly.

While the OPVs bear no resemblance to natural fibril-forming peptides, it would be interesting to know in more detail how the chirality of the individual molecules influences the assembly of chiral fibrils, both in biochemical and in synthetic molecular systems.

Michael Gross