S. Mahadevan et M. Palaniandavar, SPECTROSCOPIC AND VOLTAMMETRIC STUDIES ON COPPER-COMPLEXES OF 2,9-DIMETHYL-1,10-PHENANTHROLINES BOUND TO CALF THYMUS DNA, Inorganic chemistry, 37(4), 1998, pp. 693-700
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.