Rare Tautomers of 1-Methyluracil and 1-Methylthymine: Tuning Relative Stabilities through Coordination to Pt-II Complexes

We have computationally explored how the relative stabilities of 1-methyluracil (1-MeUH) tautomers can be tuned through coordination of these tautomers to PtII complexes with a particular set of ligands. This has been done using density functional theory at the BP86/TZ2P level. Thus, we have examined the water/1-MeUH exchange reactions of [PtII(A)(B)(C)(OH2)]q + 1-MeUH to uncover: i) which tautomers are best stabilized by the PtII complex, and ii) how the net charge q in the complex affects the reaction energy. The net charge q depends on the ligands A, B, and C, which can be the neutral NH3 or anionic Cl−. To reveal the effect of solvation, all reaction systems are studied both in the gas phase and in water. Also the stabilization of tautomers of 1-methylthymine (1-MeTH) by cisplatin is investigated. The calculations reveal that relative energies of the metal (here: PtII)-complexed forms of the various tautomers (here: of 1-MeUH and 1-MeTH) do not parallel those of the free tautomers. Rather, a rare nucleobase tautomer, despite its low natural abundance, may become favored over the predominant one when complexed to a metal ion.