J. Barnes et Wa. Bernhard, IRREVERSIBLE PROTONATION SITES OF ONE-ELECTRON-REDUCED ADENINE - COMPARISONS BETWEEN THE C5 AND THE C2 OR C8 PROTONATION SITES, Journal of physical chemistry, 98(42), 1994, pp. 10969-10977
The reversible and irreversible protonation sites of one-electron-redu
ced adenine are shown to depend upon the environment adenine is reduce
d in. Reduction of 2'-deoxyadenosine in a PEG glass (polyethylene glyc
ol, 12 M monomer) at 77 K probably gives rise to the neutral, N1-proto
nated reduced adenine radical. Upon annealing to similar to 150 K, an
irreversible protonation at C2 or C8 is observed, in agreement with pu
lse radiolysis studies in aqueous solution (Candeias, L. P.; Steenken,
S. J. Phys. Chem. 1992, 96, 937-944). Upon reduction at 4 K in a high
-salt glass containing Li+ or Mg2+, 5'AMP protonates at the amino grou
p, which assumes an sp(3) conformation with one N-H bond perpendicular
to the ring plane. A second, irreversible protonation occurs at C5 up
on annealing to 40-80 K. This adenine radical is identified by a disti
nctive set of EPR and optical absorption spectra. The reaction pathway
leading to protonation at C5 could be a significant trap for mobile e
lectrons in X-irradiated, single-stranded DNA.