The distribution of electron trapping in DNA: one-electron-reduced oligodeoxynucleotides of adenine and thymine.

A series of single- and double-stranded oligodeoxynucleotides of adenine and thymine, 8 to 12 nucleotides in length, were one-electron-reduced at 10 K in a > 8 M LiCl/H2O glass. The Q-band electron paramagnetic resonance (EPR) spectra of these radicals show that thymine is the dominant trapping site for mobile electrons in these oligomers. The spectra of the reduced oligomers in the series pd(AnT10-n).pd(A10-nTn) with n = 5-->10 showed a trend which is interpreted as either an increase in the probability of trapping at an adenine base in tracks of adenine > 7 base pairs in length, or the presence of different protonated states of the one-electron-reduced bases due to the adoption of a different conformational state for longer tracks of adenine, or a combination of these two possibilities. Analysis of the trends in the EPR spectra of the radicals as a function of sequence using multicomponent analysis is presented.