Influence of primary structure on initial free radical products trapped in A:T polydeoxynucleotides X-irradiated at 4 K.
EPR measurements were made at Q-band microwave frequencies on powder samples pressed into pellets and X-irradiated at 4 K. Measurements were made at 4 K after no anneal, then after a 77 K anneal, and then after a 300 K anneal. In poly(dA):poly(T) the free radical distribution is approximately a simple sum of the distributions in the separate homopolymers. In poly(dA-T) the free radical distribution differs from that of poly(dA):poly(T). The clearest difference is that in poly-(dA):poly(T) the concentration of one-electron-reduced thymine (Tre.) is reduced relative to the total radical concentration. On warming the thymine-containing samples from 77 K to room temperature, the Tox. radical disappears and the (T-H5'). radical appears. Also, the Tre. radical disappears and the (T + H6). radical appears. There are three main conclusions. First, little or no transfer of free radicals between strands is needed to explain the data. Second, when A and T are interstacked, either the Tre. radical is less stable against recombination than other radical products or radical transfer occurs to an adjacent adenine. Third, in the poly- and oligonucleotides, the Tox. radical is a likely precursor to the (T-H5'). radical.
Department of Physics & Electronics Engineering, University of Scranton, Pennsylvania 18510.
R A
RA
Spalletta
W A
WA
Bernhard
D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals; D005615:Freezing; D011067:Poly dA-dT / Q000528:radiation effects*; D011089:Polydeoxyribonucleotides / Q000528:radiation effects*; D014965:X-Rays
D005609:Free Radicals; D011089:Polydeoxyribonucleotides; D011067:Poly dA-dT