Structural models for the interaction of Cd(II) with DNA: trans-[Cd(9-RGH-N7)2(H2O)4]2+

Reactions of Cd(NO3)2 with the model nucleobases 9-alkylguanine in water at neutral pH, give the compounds trans-[Cd(9-RGH-N7)2(H2O)4](NO3)2(R = Me, Et), with the 9-alkylguanine ligands bound to the metal cation at the N(7) position. The X-ray structures of both compounds are reported. The six-coordinate Cd(II) complexes consist of a highly regular octahedral geometry in which the two 9-alkylguanine ligands are in a trans position to each other and approximately collinear with the metal cation. In addition, the networks of both compounds show interesting features. Thus, intramolecular H-bonds between O(6) and a coordinated water molecule are present, and self-association of guanines via H-bonding of N(3)-H⋯N(2) take place, leading to a 1D supramolecular polymeric ribbon. Density functional theory calculations have been applied to both compounds in order to study the stability of N(7) metalated guanine-guanine associations by comparing experimental and theoretical results. The potential relevance with regard to possible Cd(II)-DNA cross-links is briefly discussed.