“We demonstrated that the incorporation of metal atoms is fully compatible with the bottom-up strategy of building rosette assemblies via multiple hydrogen bonding,” Mercedes Crego-Calama told nanotechweb.org. “Normally this approach is carried out using biomolecules such as DNA that are less stable than the synthetic molecules presented here.”

Crego-Calama, Holger Schönherr and colleagues made double rosettes from gold-functionalized calix[4]arene dimelamine and 5,5-diethylbarbiturate. The rosettes self-assembled from a toluene solution into regular two-dimensional arrays, dubbed nanorod domains, on a highly oriented pyrolytic graphite surface, as seen in high-resolution atomic force microscopy images. The rows of rosettes were about 5 nm apart. The scientists prevented three-dimensional crystallization of the rosettes by ensuring that the solvent evaporated slowly.

“The formation of the nanometre-sized self-assembled aggregates relies on multiple hydrogen bonds,” added Crego-Calama. “Since these reversible interactions form under thermodynamically controlled conditions, the assemblies possess the ability to ‘proofread’ and correct mistakes during assembly.”

The scientists believe that the rosettes sorted themselves into domains containing molecules of the same chirality, and plan to investigate this further. “Despite the fact that the development of materials has often been inspired by chemistry from the biological world, materials that take advantage of inherent chirality have found relatively few applications,” said Crego-Calama. “It is therefore probable that much remains to be gained from novel applications of supramolecular chirality.”

The researchers, who reported their work in Nano Letters, also plan to use the assembly technique to create functional molecular devices.