Quantum-chemical investigation of the 1-methylthymine dimer photoproduct: Pyrimidine-(6-4)-pyrimidone adduct

One of the products of a photochemical reaction induced by UV irradiation of 1-methyltimine dimmer is pyrimidine(6-4)pyrimidone. Due to the low yield of this product, it is difficult to examine its geometry and vibrational spectrum. In this study we used quantum chemical methods to characterize pyrimidine(6-4)pyrimidone structure. Its three conformers were optimized and their structures were compared. Their vibrational frequencies in the harmonic approximation are briefly discussed. It is shown that the most significant changes in the infrared spectra arise from formation of hydrogen bonds. All calculations have been performed both in vacuum and in D2O