Model of the most abundant DNA interstrand cross-link of Transplatin : X-ray structures of two modifications and H bonding behavior in the solid state and in solution of trans-[Pt(NH3)(2)(1-MeC-N3)(9-EtGH-N7)](ClO4)(2)center dot nH(2)O (1-MeC=1-methylcytosine; 9-EtGH=9-ethylguanine)

The preparation, the crystal structure determination of two modifications, and the solution behavior of the mixed nucleobase complex trans-[Pt(NH3)(2)(1-MeC-N3)(9-EtGH-N7)](ClO4)(2).n H2O (n = 1.4 (2a) and 0 (2b)) with 1-MeC = 1-methylcytosine and 9-EtGH = 9-ethylguanine are reported. The compound is a model for the most abundant interstrand cross-link of trans-Pt(NH3)(2)Cl-2 (Transplatin) with double-stranded DNA. Characteristic features of this compound are the near-coplanarity of the two nucleobases and the intracomplex H bond between the exocyclic groups N(4)H-2 of 1-MeC and O(6) of 9-EtGH. Geometrical parameters responsible for the length of this H bond are studied. The compound can be considered a metal-modified Hoogsteen pair of cytosine and guanine. Its potential relevance to platinated DNA triplexes is also briefly discussed.