Ionization potentials of nucleobase analogs using partial third-order electron propagator method

The excess electrons or holes transported in nucleic acids and related systems of stacked bases are trapped at the sites determined by their electronic properties. The trapping sites for holes are determined predominantly by the lowest ionization potentials (IP's) of the 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. It is shown that IN of the thioanalogs are lower than the values of the respective bases, justifying the use of the thioanalogs as hole traps in conjunction with the natural bases. The mercaptoguanines have the lowest IPs from all the molecules studied. The comparison of the results derived in the P3 and Koopmans approaches shows that these two methods might predict different ordering of the energy levels. (C) 2004 Elsevier B.V. All rights reserved.