A study of the interactions of some polypyridylruthenium(II) complexes with DNA using fluorescence spectroscopy, topoisomerisation and thermal denaturation

The nature of binding of Ru(phen) 3 2+ (I), Ru(bipy) 3 2+. (II), Ru(terpy) 2 2+ (III) (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridyl, terpy = 2,2′2,′′ -terpyridyl) to DNA, poly[d(G-C)] and poly[d(A-T)] has been compared by absorption, fluorescence, DNA melting and DNA unwinding techniques. I binds intercalatively to DNA in low ionic strength solutions. Topoisomerisation shows that it unwinds DNA by 22°±1 per residue and that it thermally stabilizes poly[d(A-T)] in a manner closely resembling ethidium. Poly[d(A-T)] induces greater spectral changes on I than poly[d(G-C)] and a preference for A-T rich regions is indicated. I binding is very sensitive to Mg 2+ concentration. In contrast to I the binding of II and III appears to be mainly electrostatic in nature, and causes no unwinding. There is no evidence for the binding of the neutral Ru(phen) 2(CN) 2 or Ru(bipy) 2(CN) 2 complexes. DNA is cleaved, upon visible irradiation of aerated solutions, in the presence of either I or II.