The interaction of [Ru(NH3)5Cl]2+ and [Ru(NH3)6]3+ ions with DNA

The interaction of [Ru(NH3)5Cl]2+ and [Ru(NH3)6]3+ complex ions with calf thymus DNA has been studied at various r values (r = [Mn+]/[DNA-P]). Electronic spectra of metal-DNA solutions have been recorded and compared to the spectra of metal, as well as of DNA, solutions. Melting curves have been taken for the determination of DNA melting temperature (Tm) in the presence of the above complex ions. The results showed a biphasic melting of the DNA strands for relatively high r values. The Tm for the first phase increased with increasing r values, indicating metal ion interaction with the phosphate moieties of the DNA. The appearance of a second-phase melting, in connection with electronic spectra, pH values, and conductivity measurements of metal ion solutions, is indicative of the initial complexes' transformation to [Ru(NH3)5OH]2+, which binds preferentially to double-stranded rather than single-stranded DNA, thus leading to a second melting curve at a higher temperature than the first one.