Study of Ni(II) ion-DNA interactions with methylene blue as fluorescent probe

Spectroscopic studies of the interactions of Ni(II) ion with herring sperm DNA have been performed in this contribution using methylene blue (MB) as the fluorescent probe molecule. MB binds to double helical DNA via the intercalative mode, and its fluorescence is efficiently quenched by the DNA nucleobases. The fluorescence intensity of the probe molecule increases distinctly when Ni(II) ion is added to the MB-DNA solution system. These results indicate that the Ni(II) ions may be complexed with the DNA helix and probably bind at N-7 of adenine or guanine; consequently, some intercalated MB molecules are released due to the binding of Ni(II) ions to N-7 nitrogen of the purines. The Ni(II) ion-DNA interactions are further investigated by performing the photobleaching experiments of the MB-DNA complex in the presence and absence of Ni(II) ion. The bi-exponential decay functions of the fluorescence intensity have been observed in both cases and the shortening of the slow decay component when added Ni(II) ion also agrees with the release of MB from the DNA duplex.