Spontaneous Resolution of racemic hydrogen-bonded nanoassemblies on highly oriented pyrolytic graphite revealed by atomic force microscopy

COLL 229

Holger Schönherr1, Mercedes Crego-Calama2, G. Julius Vancso1, and David N. Reinhoudt2. (1) Department of Materials Science and Technology of Polymers, MESA+ Institute of Nanotechnology, University of Twente, P.O.Box 217, 7500 AE Enschede, Netherlands, (2) Laboratory of Supramolecular Chemistry and Technology, MESA+ Institute of Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede, Netherlands
We report on a high resolution AFM study on the 2-D structures formed by tetrarosettes, which are self-assembled from the two basic building blocks melamine-substituted calix[4]arene and 5,5-diethylbarbiturate. Racemic mixtures of these stable tetrarosette nanostructures, in which 15 building blocks are held together by 72 H-bonds, are spontaneously resolved into enantiopure domains in 2-D supramolecular assemblies on HOPG. Based on the real-space visualization of the arrangement of the nanostructures at the single rosette level, the presence of a chiral lattice structure and complementary domains with mirror symmetry were unveiled. These results constitute the first example of spontaneous resolution of a racemate of chiral nanostructures that are stable in solution by assembly on surfaces. In addition to revealing subtleties of the formation of 2-D nanostructures, our findings have important implications for the application of these arrays of functionalized nanorods, e.g., as scaffolds and templates for the deposition of metals and other materials.