On the Heterogeneous Nature of Cisplatin-1-Methyluracil Complexes: Coexistence of Different Aggregation Modes and Partial Loss of NH Ligands as Likely Explanation.

The conversion of the 1 : 1-complex of Cisplatin with 1-methyluracil (1MeUH), cis-[Pt(NH ) (1MeU-N3)Cl] (1 a) to the aqua species cis-[Pt(NH ) (1MeU-N3)(OH )] (1 b), achieved by reaction of 1 a with AgNO in water, affords a mixture of compounds, the composition of which strongly depends on sample history. The complexity stems from variations in condensation patterns and partial loss of NH ligands. In dilute aqueous solution, 1 a, and dinuclear compounds cis-[(NH ) (1MeU-N3)Pt(μ-OH)Pt(1MeU-N3)(NH ) ] (3) as well as head-tail cis-[Pt (NH ) (μ-1MeU-N3,O4) ] (4) represent the major components. In addition, there are numerous other species present in minor quantities, which differ in metal nuclearity, stoichiometry, stereoisomerism, and Pt oxidation state, as revealed by a combination of H NMR and ESI-MS spectroscopy. Their composition appears not to be the consequence of a unique and repeating coordination pattern of the 1MeU ligand in oligomers but rather the coexistence of distinctly different condensation patterns, which include μ-OH, μ-1MeU, and μ-NH bridging and combinations thereof. Consequently, the products obtained should, in total, be defined as a heterogeneous mixture rather than a mixture of oligomers of different sizes. In addition, a N complex, [Pt(NH )(1MeU)(N )] appears to be formed in gas phase during the ESI-MS experiment. In the presence of Na ions, multimers n of 1 a with n=2, 3, 4 are formed that represent analogues of non-metalated uracil quartets found in tetrastranded RNA.