Influence of mercuric ions on the phosphorescence and photochemistry of DNA

Partial mercuration of DNA, such that roughly one mercuric ion is bound for every two thymine residues, results in an enhancement of the phosphorescence by a factor of ten and a small enhancement of the photosteady thymine dimer yield. Complete mercuration of DNA [one Hg(II) added per momoner unit] results in quenching of the phosphorescence intensity and an inhibition of thymine dimer production. The enhancement of the phosphorescence is interpreted in terms of a heavy-atom effect caused by the preferential binding of Hg(II) to the thymine residues. The quenching of both the thymine phosphorescence and the rate of thymine dimerization upon complete mercuration is probably due to energy transfer from thymine to another base, presumably adenine, which when mercurated acts as an energy trap.