Cis-5-hydroperoxy-6-hydroxy-5,6-dihydrothymine: crystal structure and theoretical investigations of the electronic properties by DFT

The structure of cis-5-hydroperoxy-6-hydroxy-5,6-dihydrothymine was obtained using X-ray crystallography [space group P21n (Z = 4) with a = 11.428(2) A, b = 6.284(1) A, c = 11.882(2) A and β = 110.56(3) °]. Electronic properties of the thymine hydroxyhydroperoxide were determined, both in the solid state form and in the free molecule form, using LSD-DFT theory calculations. Only slight differences between the crystal structure and the optimized geometry are observed. On the other hand, the two structures exhibit significant differences in their electronic properties. In particular, the dipole moment of the crystal structure is larger than that of the theoretical geometry. This is probably due to the occurrence of hydrogen bonds in the crystal. A large hydrogen bond network, as well as unusual coulombic interactions between the different molecules in the crystal, are responsible for the molecular packing. These observations lead to a better understanding of the structural changes that occur during the hydroxyl radical-mediated decomposition of thymine.