This project is part of an international collaboration involving groups from Germany, Spain, and Switzerland, The concerted main goal is to synthesize, characterize, and optimize molecules that combine structural diversity and electrical response for an implementation in the construction of nanocircuits. Since neither carbon nanotubes nor DNA by itself spontaneously yield a clear strategy for their hybridization into "integrated" molecular wires capable of self-assembly, our research focuses on two promising alternatives: The first class of compounds that we will develop is described best as metal-modified oligonucleotides (MMOs), and the second class as self-assembling metal-organic frameworks (MOFs). MMOs are prepared by introducing chemically synthesized nucleoside derivatives with increased metal ion affinity into DNA oligonucleotides and subsequently incorporating metal ions. Implementation of metal ions is crucial as they will enable the charge transport along the DNA. MOFs instead consist of a one-dimensional metal polymer held together by e.g. a suitable nucleobase derivative. As an alternative to a bridging organic ligand, also inorganic bridges can be used, thus yielding inorganic-organic hybrid materials (referred to as MMX polymers due to their inherent sequence of two metals M and one ligand X). When incorporating ligands with a matching hydrogen bonding pattern into MMX polymers, these can serve as starting compounds for the self-assembly process using other systems such as oligonucleotides as a scaffold. Once the molecular-wire behavior is proven, a simple device will be tested.
The focus of our work in Zurich is thereby set to the structural investigation of the new molecular wires by NMR and X-ray (in collaboration with Dr. Eva Freisinger), as well as the elucidation of their exact metal ion binding properties, as the latter ones are responsible for the electrical charge transport.