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·nH2O (1-MeC=1-methylcytosine; 9-EtGH=9-et

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·nH2O (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)2Cl2 (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)H2 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.