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

Three complexes of model nucleobases with exocyclic oxygen atoms (1-methylu racilate, mura; 1-methylcytosine, mcyt; 9-methylguanine, Hmgua) which conta in Pt-II bonded to a ring N atom and an alkali metal ion (Cs+, K+, Na+) bon ded to a keto oxygen of the bases, trans-Cs[Pt(NH3)(mura)I-2]. 4H(2)O 1, tr ans-K[Pt(NH3)(2)(mcyt)(2)][PF6](3). H2O 2, and trans-[Pt(NH3)(Hmgua)(2)(mcy t)Na(H2O)(2)][ClO4](3). 0.5H(2)O 3, have been prepared and their crystal st ructures determined. The compounds have been studied, among others, with re gard 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 fo r charge compensation and for this reason its binding to the platinated mur a is not fully unexpected, it is surprising to see that alkali metal ions e ven bind to cationic complexes of Pt-II containing neutral nucleobases (2, 3).