CHARGE-MIGRATION PHENOMENA IN GAMMA-IRRADIATED COSTACKING COMPLEXES OF DNA NUCLEOTIDES .2. ESR STUDY OF VARIOUS COMPLEXES IN FROZEN SOLUTION

The radiochemistry of various complexes formed by the costacking association of different DNA nucleotides in frozen solution has been investigated using the appropriate computer-assisted techniques. The existence of important charge migration phenomena has been revealed in all the nucleotide complexes: Positive charges migrate toward guanine, while negative charges migrate toward cytosine. The experimental data obtained are consistent with the assumption that electron affinity increases in the order G < A < T < C, with the converse true for electron donor properties. This leads to a large excess of cytosine anions and guanine cations and subsequently to the selective distribution of secondary radicals on the same constituents. In conclusion, it is confirmed that the radiochemistry of heterogeneous systems containing DNA bases in a stacking configuration cannot be considered to be simply the sum of the radiochemistries of the constituent subunits.