Feasibility of a Two-Metal, Four-Purine Nucleobase Quartet Motif

A mixed-purine nucleobase complex of composition trans-[(NH3)2Pt(9-EtA-N1)(9-MeHx-N7)](NO3)2·2H2O (1) (9-EtA = 9-ethyladenine; 9-MeHx = 9-methylhypoxanthine) has been prepared and
characterized by X-ray crystallography. Cations of 1 are self-complementary as far as hydrogen bonding properties are
concerned and form H bonded dimers, containing four intermolecular hydrogen bonds in addition to two intramolecular ones.
The resulting mixed-purine square is considered a model compound
for a putative mixed-purine tetrad consisting of two adenines and
two guanines. In this model, the one-metal, four-nucleobase quartet
motif, as seen in guanine or uracil quartets of nucleic acids, with
the metal located in the center of the base tetrad, has been altered
to a two-metal, four-nucleobase motif, with the two metal ions
localized at the periphery.