Determination of DNA binding interactions for a new family of chiral ruthenium metal complexes

Binding of three new monomeric bis(bipyridy)ruthenium(II) dihydroxy anthraquinone complexes (1,8-DHAQ, 1,5-DHAQ and 1,4-DHAQ) and three new dimeric bis[bis(bipyridy)ruthenium(II)] anthraquinone complexes to duplex calf thymus DNA was examined by UV and CD spectrographic techniques. UV results show that the 1,8- and 1,5-DHAQ complexes upon binding to DNA, display hypochromicity, which is an indication of intercalative binding. The calculated binding constant for 1,8-DHAQ indicates binding strength increases with increasing salt concentration, while that for 1,5-DHAQ does not. 1,4-DHAQ forms a blue fiberous precipitate at all salt concentrations. Differences in monomeric behavior also indicates the location of the hydroxyl group has a prominent affect on the binding interactions. Interactions of 1,8-DHAQ with DNAs having varied %GC content shows a preference for poly dAdT DNA. CD results indicate that upon interaction with DNA, there is an optical enrichment in the dialysate of the least favored isomer. The DNA therefore, appears to have a preference for binding a single isomer. The dimers did not display hypochromicity or an optical enrichment with DNA, and therefore seems to suggest that there is no intercalative binding interaction between the two.