Detection and characterization of complexes of methylmercury (II) with duplex deoxyribonucleic acid and synthetic copolymers by optical detection of magnetic resonance.

Complexes formed between Ch3HgOH and the polynucleotide duplexes poly(dA)-poly(dT) and poly(dG)-poly(dC) and calf thymus DNA have been detected and characterized byu luminescence and optically detected magnetic resonance (ODMR) spectroscopy. CH3HgOH is added by equilibrium dialysis at concentrations well below those previously found to cause denaturation of the duplex. Complexing of CH2HgII with the polynucleotide leads to heavy atom effects which are detected by the appearance of short-lived components in the phosphorescence decay. Heavy atom perturbed bases are identified by slow-passage ODMR frequencies and the lifetimes of phosphorescence transients induced by microwave rapid passage. Comparison of the zero-field splitting (zfs) parameters and signal polarity patterns with those found previously in specific mononucleotide and mononucleoside complexes with CH3HgII leads to the positive identification of complexed bases as well as the CH3HgII binding sites. We find that CH3HgOH at 10-5M complexes with N3 of thymine in poly(dA)-poly(dT) and with N7 of guanine in both poly (dG)-poly(dC) at pH 6, and calf thymus DNA at pH 6.8. When Ch3HgOH is added at 10-6M, we find that complexing occur at N3 of thymine. The thymine triplet state properties are altered, but not necessarily as the result of a heavy-atom, effect. Evidence for the presence of this type of complex in DNA treated with 10-5M CH3HgOH is provided by the presence of thymine triplet states with properties similar to those observed in poly(dA)-poly(dT) treated at 10-6M.