engleski

DFT study of radicals formed in 2-thiothymine single crystals at 77K

Two different radical types have been found by EPR spectroscopic measurements of gamma- irradiated 2-thiothymine single crystals at 77 K. As the assignment to the theoretically modeled systems has been of limited success, 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. Calculations of EPR spectroscopic parameters using Becke Three-parameter density functional have been performed for a set of model structures. Based on results presented it was possible to fmd common points relating the structure of specific radical type to its experimentally observed behavior. The radicals of sigma-type are thus expected to be neutral radicals formed by or at least involving deprotonation of the N3-H-S'2 hydrogen bond. The radicals of the presumed pi-type are described by charged structures involving redistribution of protons over several H-bonds, probably including 04 protonation of one, and S2 protonation of the other, neighboring 2-thiothymine molecule from the same crystal plane.

2-thiothymine, radicals, DFT study

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