Probing the Dynamic Environment-Associated Conformational Conversion from Secondary to Supersecondary Structures in Oligo(phenanthroline dicarboxamide)s

The special structural features of the oligo(phenanthroline dicarboxamide)s and their dynamic environment-associated conformational conversion from secondary helical structure to supersecondary helix-turn structure, owing to the conversion of the CONH bond from s-cis form to s-trans form, have been experimentally and theoretically characterized by X-ray crystallographic, variable-temperature (1)H NMR, variable-temperature circular dichroism techniques, and computational studies. It has been demonstrated that the solvent effects together with intramolecular hydrogen bonds and pi-pi stacking play a key role in stabilizing both the secondary and supersecondary structures. Furthermore, by introducing the intramolecular F...H-N hydrogen bond to restrict the rotation about the CONH-aryl bonds, the oligomers 6 and 7 have been synthesized, which showed well-defined and predictable secondary helical conformations in solution and in the solid state.