Angewandte Chemie International Edition
Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Angewandte Chemie International Edition ,
A molecule that changes its conformation when irradiated with light: prototype of a light-controlled foldamer
The spatial structure of a protein is crucial to its function. The folding process that leads to a three-dimensional structure can be mimicked with foldamers. Foldamers are synthetic, flexible molecular chains than can adopt a stable, usually spiral-shaped structure in solution. In addition to providing insight into folding mechanisms, they have potential in the manufacture of “switchable” materials—materials whose structure, and thus properties, can be changed “on command”. Stefan Hecht and his team at the Max Planck Institute for Coal Research in Mülheim upon Ruhr have now succeeded for the first time in synthesizing a foldamer that changes its shape when irradiated with light.
Previous foldamers have typically been switched by the addition of triggering compounds, variation of the solvent composition, or changes in temperature. The Mülheim team has decided to use light as a stimulus instead. This allows for precise control over the time, place, and intensity of the switching command. “Our concept,” explains Hecht, “is based on a foldamer strand into which we have incorporated a photoisomerizable core moiety—a core moiety whose chemical structure changes with exposure to light.” To do this, the researchers attached two flat, kinked segments of a foldamer by means of a core segment, which resembles two repeat units of a foldamer building block. The length of the foldamer segments is of critical importance: it must be chosen so that each individual foldamer segment is too short to twist into a spiral on its own. The resulting complete strand must, in contrast, be long enough to fold into a spiral. If such a helix is then irradiated, the structure of the core segment changes within seconds and it can no longer arrange itself into a helix. The overall strand can thus also no longer form a spiral. Heating can reverse this shape change.
“Light-controlled systems like ours can give fundamental insights into folding and unfolding mechanisms,” says Hecht. “We are currently investigating whether our foldamer could be used as an intelligent delivery vehicle. Such a carrier can exist in two forms, one of which binds the cargo to be transported, the other releases it on command.”