Helical molecular programming: Supramolecular double helices by dimerization of helical oligopyridine-dicarboxamide strands

Helically preorganized oligopyridine-dicarboxamide strands are found to und ergo dimerization into double helical supramolecular architectures. Dimeriz ation of single helical strands with five or seven pyridine rings has been characterized by NMR and mass spectrometry in various solvent/ temperature conditions. Solution studies and stochastic dynamic simulations consistentl y show an increasing duplex stability with increasing strand length. The do uble helical structures of three different dimers was characterized in the solid phase by X-ray diffraction analysis. Both aromatic stacking and hydro gen bonding contribute the double helical arrangement of the oligopyridine- dicarboxamide strand. Inter-strand interactions involve extensive face-to-f ace overlap between aromatic rings, which is not possible in the single hel ical monomers. Most hydrogen bonds occur within each strand of the duplex a nd stabilize its helical shape. Some inter-strand hydrogen bonds are found in the crystal structures. Dynamic studies by NMR as well as by molecular m odeling computations yield structural and kinetic information on the double helices and on monomer-dimer interconversion. In addition, they reveal the presence of a spring-like extension/compression as well as rotational disp lacement motions.