Rare Tautomers of 1‐Methyluracil and 1‐Methylthymine: Tuning Relative Stabilities through Coordination to PtII Complexes

AbstractWe 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.