Thiocytosine as an example of nucleobase thioanalog hole trap in a DNA-mimetic system

Vjeran Gomzi, Janko N. Herak

Department of Biophysics, Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10000 Zagreb, Croatia

The excess electrons or holes in nucleic acids and related systems of stacked bases are trapped at sites determined by their electronic properties. The trapping sites for holes are determined predominantly by the lowest vertical ionization potentials (IP) of constituents. Here the calculations of IPs for a number of thioanalogs of the nucleic-acid bases and the base derivatives in the partial third-order electron propagator (P3) method are reported. That method has recently been used for calculation of IPs of a number of molecules and has shown excellent agreement with experimental data. To gain more information on the matter of hole transfer in a system of stacked DNA bases, detailed investigation of thiocytosine radical formed in cytosine monohydrate molecular crystals doped with thiocytosine has been performed. Experimental hyperfine couplings from previous ENDOR spectroscopy measurement have been confirmed using density functional (DFT) calculations. The structure of the radical has been confirmed establishing the protocol for reliable DFT calculations of electronic properties of point defects in crystal environment. References: [1] J.N. Herak, K. Sanković, E.O.Hole and E. Sagstuen, Phys. Chem. Chem. Phys., 2 (2000) 4971. [2] K. Sanković, E. Malinen, Z. Medunić, E. Sagstuen and J.N. Herak, Phys. Chem. Chem. Phys., 5 (2003) 1665. [3] V. Gomzi and J.N. Herak, J. Mol. Struct (THEOCHEM), 629 (2003) 71. [4] V. Gomzi and J.N. Herak, J. Mol. Struct (THEOCHEM), 683 (2004) 155.

Email: vgomzi@pharma.hr

Address: A. Kovacica 1, 10000 Zagreb, CROATIA