Interconverting Superstructures

Mild chemical stimuli can cause ordered films of a guanine derivative to reversibly disassemble from one supramolecular pattern and reassemble into an alternate one, according to researchers in France and Italy (Angew. Chem. Int. Ed. 2010, 49, 1963). The study deepens understanding of the formation mechanism and function of complex nucleobase architectures such as DNA and RNA. Paolo Samorì of the University of Strasbourg and Gian Piero Spada of the University of Bologna and coworkers showed via scanning tunneling microscopy that an octadecyl guanine compound readily adsorbs onto graphite from solution into an ordered interdigitated ribbon pattern. The group found that adding a minute quantity of potassium picrate causes the ribbon pattern to disassemble and the molecules to reassemble into an ordered macrocycle-based structure known as a quartet. Next, by sequestering the potassium ions with a cryptand, the team caused the quartet structure to revert to the ribbon pattern. The researchers were able to release the ions by gently acidifying the solution and to continue interconverting the surface structures.