Metal-Mediated Assembly of 1,N6-Ethenoadenine: From Surfaces to DNA Duplexes

The design of multinuclear metal complexes requires a match of the ligand-to-metal vectors and the preferred coordination geometries of the metal ions. Only a few ligands are known with a parallel orientation of N -> M vectors that brings the metal ions into close proximity. We establish here the adenine derivative 1,N-6-ethenoadenine (epsilon A) as an ideal bis(monodentate) ligand. Scanning tunneling microscope images of alkylated epsilon A on graphite surface clearly indicate that these ligands bind to Ag(I) ions. The molecular structures of [Ag-2(1)(2)](ClO4)(2) and [Ag-2(2)(2)](ClO4)(2) (1, 9-ethyl-1,N-6-ethenoadenine; 2, 9-propyl-1,N-6-propylenoadenine) confirm that dinuclear complexes with short Ag center dot center dot center dot Ag distances are formed (3.0256(3) and 2.984(1) angstrom, respectively). The structural motif can be extended to divalent metal ions, as was shown by determining the molecular structure of [Cu-2(1)(2)(CHO2)(2)(OH2)(2)](NO3)(2)center dot 2H(2)O with a Cu center dot center dot center dot Cu distance of 3.162(2) angstrom. Moreover, when introducing the 1,N-6-ethenoadenine deoxyribonucleoside into parallel-stranded DNA duplexes, even dinuclear Ag(I)-mediated base pairs are formed, featuring the same transoid orientation of the glycosidic bonds as the model complexes. Hence, 1,N-6-ethenoadenine and its derivatives are ideally suited as bis(monodentate) ligands with a parallel alignment of the N -> M vectors for the construction of supramolecular metal complexes that require two metal ions at close distance.