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)<inf>3</inf>2+ (I), Ru(bipy) <inf>3</inf>2+. (II), Ru(terpy) <inf>2</inf>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 Mg2+ 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)<inf>2</inf>(CN)<inf>2</inf> or Ru(bipy)<inf>2</inf>(CN)<inf>2</inf> complexes. DNA is cleaved, upon visible irradiation of aerated solutions, in the presence of either I or II.