| Abstract
| - Careful examination of the X-ray structure of a ditopic hydrazide derivative 7 led to the concept thatwith malonyl groups as interhydrazide linkers hydrogen-bonding-mediated molecular duplex strands mightbe obtained. Complexation studies between 7, 8, and 9 confirmed this hypothesis. Two quadruple hydrogen-bonded heterodimers formed, in which spectator repulsive secondary electrostatic interaction was foundto play an important role in determining the stability of the complexes. Extensive studies on 1−4 indicatedthat the hydrogen-bonding mode could persist in longer oligomeric hydrazide derivatives with chainextension from monomer to tetramer. Molecular duplex strands via two to fourteen interstrand hydrogenbonds were obtained. In addition to affecting the stability of the duplex strands, spectator repulsivesecondary electrostatic interaction also played an important role in determining dynamic behavior of theduplex strands as exemplified by variable temperature 1H NMR experiments. IR studies confirmed strongerhydrogen bonding in the longer oligomers. The assemblies of 1−4 on HOPG were also studied by STMtechnology. Molecular mechanical calculations further revealed double-helical structures for the longeroligomers. The results provide new opportunities for development of polymeric helical duplexes withwell-defined structures.
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