Exocyclic oxygen atoms of platinated nucleobases as binding sites for alkali metal ions

Three complexes of model nucleobases with exocyclic oxygen atoms (1-methyluracilate, mura; 1-methylcytosine, mcyt; 9-methylguanine, Hmgua) which contain Pt-II bonded to a ring N atom and an alkali metal ion (Cs+, K+, Na+) bonded to a keto oxygen of the bases, trans-Cs[Pt(NH3)(mura)I-2]. 4H(2)O 1, trans-K[Pt(NH3)(2)(mcyt)(2)][PF6](3). H2O 2, and trans-[Pt(NH3)(Hmgua)(2)(mcyt)Na(H2O)(2)][ClO4](3). 0.5H(2)O 3, have been prepared and their crystal structures determined. The compounds have been studied, among others, with regard to the role of alkali metal ions for the rotation of nucleobases when bound to Pt-II. While in the case of 1 the alkali metal ion is necessary for charge compensation and for this reason its binding to the platinated mura is not fully unexpected, it is surprising to see that alkali metal ions even bind to cationic complexes of Pt-II containing neutral nucleobases (2, 3).