Wrapping up a helix

Metal ions make it possible to control molecular folding and unfolding.

A chemical system that sequentially forms helical molecules and then untwists them with the help of a metal ion has been unveiled by French researchers.

Much chemical research involves trying to copy nature, and in their work, Jean-Marie Lehn and his colleagues at the Institut de science et d’ing?nierie supramol?culaires in Strasbourg, France, might have managed to mimic protein folding/unfolding processes. They found that long straight ligands, based on pyridine and hydrazone groups, could wrap themselves around a lead(ii) ion to form a helix. Then, if a different ligand group, N(CH2CH2NH2)3 (tren), is added to the mix, the lead(ii) ion will swap allegiance and bind to tren, causing the helical complex to unravel, leaving behind the linear ligand. The process doesn’t stop there, because, as acid is added to the new lead-tren and straight ligand mixture, the lead ion is released, allowing the helical complex to form again, only to unravel when a base is added. As well as this protein mimicry, the system is an example of a molecular ion channel, which is specific to the metal ion involved in the process.

Lehn explains his motivation for this work as ’designing nano-objects that self-organise into well-defined superstructures and undergo molecular motions induced by and controlled via external triggers’.

Markus Albrecht at RWTH Aachen, Germany, explains why Lehn’s work is important: ’The function of biological systems in living cells depends on transport and movement processes. If chemists want to learn how to build related artificial systems, they have to learn to control the movement or dynamics of molecular building blocks. The described folding/unfolding "machinery" still is very simple but it is a starting point for the development of more complicated devices which will be able to mimic naturally occurring processes.’

Katharine Sanderson