Probing mercury species-DNA interactions by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection

The interactions of inorganic mercury Hg(II), methylmercury (MeHg(I)), ethylmercury (EtHg(I)), and phenylmercury (PhHg(I)) with DNA have been probed by capillary electrophoresis with on-line electrothermal atomic absorption spectrometric detection (CE-ETAAS) in combination with circular dichroism and Fourier transform infrared spectroscopy. The CE-ETAAS assay allows sensitive probing of the level of DNA damage by mercury species, extraction of thermodynamic and kinetic information on the interactions of mercury species with DNA, and provides direct evidence for the formation of mercury species-DNA adducts. The binding affinity of mercury species to DNA increases in order of Hg(II) < EtHg(I) similar to PhHg(I) similar to MeHg(I). The interactions of mercury species with DNA follow a first-order kinetics for mercury species and zero-order kinetics for DNA. Mercury highly covalently coordinates to endocyclic and exocyclic N sites of DNA bases. However, the interactions of DNA with mercuric species cause no transition of the DNA original conformation. The results reveal that organomercuric species exhibit stronger affinity and faster binding to DNA and show more potential damage to DNA than Hg(II) in view of the kinetic and thermodynamic evaluations. Moreover, MeHg(I) exhibits the fastest binding to DNA, suggesting that MeHg(I) enjoys superiority over the other mercuric species for rapid formation of a stable complex with DNA, whereas Hg(II) shows the slowest binding to DNA. The present study provides new evidence and understanding of the binding modality of mercuric species to DNA.