Free radical yields in A:T polydeoxynucleotides, oligodeoxynucleotides, and monodeoxynucleotides at 4 K

Dose-response curves for free radical trapping in monomers, dimers, and polymers of dAMP and TMP have been measured. Powder samples pressed into pellets were X-irradiated and observed at 4 K using EPR at Q-band microwave frequencies. The initial free-radical yield (G value) and the destruction rate (k value) are reported for 22 samples. The absolute magnitude and relative changes in G are informative. For example, the duplex of homopolymers, poly(dA):poly(T)(Na), gives a large G of 6 while the closely related duplex of alternating ATs, poly(dA-T)(Na), gives a G value of 3. At G of around 6, the range of the bound electrons (e-) and electron loss centers (holes) is believed to be very limited. Two factors are suggested as important to limiting the range, proton transfer between strands and the low probability of radical transfer between strands. The lower G values are viewed as being due to relatively small increases in the range of e- and/or holes.