SPECTROSCOPIC AND VOLTAMMETRIC STUDIES ON COPPER-COMPLEXES OF 2,9-DIMETHYL-1,10-PHENANTHROLINES BOUND TO CALF THYMUS DNA

The interaction of copper(II/I) complexes of a few 2,9-dimethyl-1,10-p henanthrolines with calf thymus DNA has been investigated using absorp tion and circular dichroic spectral and electrochemical techniques and viscometry. The observation of the usual hypochromism and the novel h yperchromism in the absorption spectra of [Cu-I(bcp)(2)](+) [bcp = 2,9 -dimethyl-4,7-diphenyl-1,10-phenanthroline] and thyl-4,7-bis(sulfonato phenyl)-1,10-phenanthroline] respectively in the presence of DNA and t he increase in viscosity of DNA at low loadings of both these complexe s have been interpreted in terms of bridging of a pair of DNA duplexes by the complex species. These tetrahedral copper(I) complexes, which lack minor groove binding because of substituents at the 4- and 7-posi tions of phen ring, are efficient in bridging the duplexes. The electr ochemical behaviors of [Cu-I(dmp)(2)](+) [dmp = 2,9-dimethyl-1,10-phen anthroline] and [Cu-I(bcp)(2)](+) bound to DNA have been compared with that of the analogous sulfonated complex [CU(dpsmp)(2)](2-/3-). The D NA binding constants determined reveal that dpsmp(2-) complex is engag ed in DNA binding less intimately than the bcp complex. While Coulombi c interactions are clearly more important than other types of interact ions for the former, nonclassical hydrophobic interactions for the lat ter. The Hill analysis of the absorbance data obtained as a function o f added DNA reveals Hill coefficients greater than unity, which may be construed as evidence for cooperative binding of the copper complexes to B-DNA.