Isomerism of the covalent anion of the dimer of uracil and 1-methyl-cytosine: ab initio study Original Research Article

Theoretical ab initio calculations have been performed to determine the distribution of an excess electron in the covalent anion of the dimer of uracil and 1-methyl-cytosine (U–MC). Due to the multitude of possible isomers, this system may present an interesting model for future experimental investigations of the electron attachment and transfer in dimers of nucleic acid bases. The major conclusions of this work are (i) three isomeric structures of the covalent U–MC anion have been found in the calculations. The anion where the excess electron is located at the MC molecule was found to be the most stable; (ii) a noticeable ring distortion was found in the molecule where the excess electron is localized; (iii) the covalent U–MC anions are non-planar, hydrogen-bonded systems; and (iv) the out-of-plane deformed site of the base molecule where the excess electron localizes in the dimer anion is positioned opposite to the site involved in the hydrogen bond.