Computational (DFT and TD DFT) study of the electron structure of the tautomers/conformers of uridine and deoxyuridine and the processes of intramolecular proton transfers

Six uridine and six deoxyuridine isomers were studied at the B3LYP and TD B3LYP theoretical level and 6–31+G(d) basis function. The stability and the excited states of the isomers were studied in order to clarify some known experimental data. It was established that the rotation of the oxo uracil ring in uridine is energetically more likely to occur in the excited state than in the ground state, driven by the bright ¹ ππ* state and the dark charge transfer ¹nπ* state. Very high energy barriers (on the S_o) were found for thermal intramolecular proton transfer processes.