DFT study of radicals formed in 2-thiothymine single crystals at 77 K: 1- and 2-molecule models revised

Two different radical types have been found by EPR spectroscopic measurements of γ-irradiated 2-thiothymine single crystals at 77 K. In this work an effort has been made to establish the model which describes the observed properties of the radicals taking into account their crystal environment. Density-functional geometry optimizations and single-point calculations using B3LYP functional and 6-311G(2d,p) basis set have been performed on one and two-molecule model structures. Based on results presented it was possible to find common points relating the structure of specific radical type to its experimentally observed behavior. The radicals of σ-type are thus expected to be neutral radicals formed by deprotonation at N3 while the radicals of presumed π-type are best described by neutral structures involving N1 deprotonation.