A number of strategies have been so far employed for modifying the periphery of DNA with metal complexes. However, little has been done to explore the DNA core. Recently, we envisioned the use of charged or uncharged metal complexes as replacement building blocks in the interior of the DNA helix. Replacement of the hydrogen-bonded base pairing of natural DNA by alternative base pairing modes is expected to lead not only to expansion of the genetic alphabet but also to novel DNA structures and functions based on the controlled and periodic spacing of the building blocks along the helix axis.
This paper provides a summary of our recent progress devoted to the introduction of metal-assisted base pairs directed towards what we term the nano-assembly of metals into the DNA core. Specifically, we detail here syntheses of artificial β-C-nucleosides bearing a chelator nucleobase (o-phenylenediamine, catechol, 2-aminophenol, pyridine, or hydroxypyridone, and so on), their metal coordination properties with metal ions, and the incorporation of these building blocks into DNA oligomers. The present results raise the appealing possibility that this approach could lead eventually to a novel molecular architecture-type approach to the nano-assembly of multi-metal arrays.

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Metalloenzymes are ingeniously designed natural catalysts that demonstrate specific substrate recognition, marked rate enhancement, and appropriate selection of reaction pathways under mild reaction conditions. Such enzymic functions are quite attractive from the view point of supramolecular chemistry and expected to be clarified on a molecular basis. If we consider a simple holoenzyme, then such a supramolecule is composed of a specific apoprotein and an additional cofactors, such as a coenzyme. An apoprotein generally provides a binding site for both specific coenzyme and substrate molecules, which is well separated from a bulk aqueous phase. It is quite important for the constitution of an artificial metalloenzyme to select a right kind of molecular system that is qualified for simulation of the characteristic physicochemical functions of an apoprotein. There are two possible approaches to the constitution of an artificial holoenzyme. One approach is to design a specific molecule that is capable of performing functions of both apoprotein and coenzyme. Another approach is to set up a supramolecular system by noncovalent combination of an appropriate apoprotein model with a coenzyme model. The concept for molecular design of artificial metalloenzymes is presented in this paper, and some examples are shown by using bilayer membranes, macrocyclic compounds, dendrimers, and natural proteins as apoprotein functions.

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