The oxidative electrochemistry of truns-[Re(0)2(4-OMe-py)4]+ in the presence of DNA has been studied. The complex exhibits a reversible oxidation at E1/2(VW) = 1.00 V (vs Ag/AgCl) in buffer or in the presence of poly(dA)poly(dT). However, in the presence of calf thymus DNA or poly(dG)poly(dC), a dramatic catalytic enhancement is observed. An identical result is obtained with Fe(S-C1-~hen)3~+ (E1/2(IIIAI) = 1.02 V), but no electrocatalytic enhancement is observed with truns-[Re(0)2(py)2(dmap)2]+ (E112 = 0.90 V). Electrophoresis of plasmids electrolyzed at 1.2 V in the presence of trans-[Re(0)2(4-OMe-py)4]+ show relaxation from form I to form 11, and analogous reactions with 5'-end 32P-labeled synthetic oligonucleotides show piperidine-labile cleavage specifically at guanine. The combined results point to an electrocatalytic mechanism where the oxidized metal complex oxidizes guanine in DNA by one electron via an efficient, outer-sphere mechanism. Moreover, the experiments demonstrate a potential for the one-electron oxidation of guanine in double-helical DNA at neutral pH of between 0.90 and 1.00 V. This result should provide insight into the mechanisms of DNA oxidation by chemical agents and by ionizing radiation.
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Johnston et al. (1994) studied this question.