Non-covalent DNA binding studies of copper(I) bis-phenanthroline complexes

Fang Liu, Purdue University

Abstract

Binding studies of copper(I) complexes of two phenanthrolines, dmp (2,9-dimethyl-1,10-phenanthroline) and bcp (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), with DNA are described. The presence of the methyl substituent in the 2 and 9 positions allows us to focus on DNA binding because the reduction potential of the copper is too positive for significant nuclease activity (Sigman, 1976). In the course of this investigation we have relied on visible absorption, luminescence and circular dichroism spectroscopy, topoisomerization, as well as viscometry. For Cu(bcp)$\sb2\sp+$, the hypochroism in the visible absorption, an induced band in the circular dichroism spectrum in the visible region, and a dramatic increase in the luminescence intensity show the binding interaction of the complex with various types of DNA. The luminescence enhancement is consistent with rigid adduct formation with DNA because a potent solvent-induced quenching mechanism is inhibited. The facts that the complex unwinds ccs DNA and elongates the AT-rich DNA chains suggest that partial intercalation of the complex may occur. However, some type of condensation of DNA is also possible. The emission polarization results support either binding mode. All results indicate the nature of the binding interaction is dependent on the nucleotide-to copper (DNA-P/Cu) ratio. At low DNA-P/Cu ratios, the complex appears to bind to DNA in an aggregated form. Only at high DNA-P/Cu ratios does the complex intercalate or induce some type of condensation of the DNA. In contrast, Cu(dmp)$\sb2\sp+$ exhibits hypochromism in the visible absorption, but it is very weakly emissive in the presence of DNA. Viscometric titrations and circular dichroism results show that addition of Cu(dmp)$\sb2\sp+$ has no influence on the DNA. However, the Scatchard plot indicates that the binding strength of the complex to DNA is competitive with ethidium cation. Overall, the results suggest that the dmp complex binds to DNA by some type of groove binding but not by intercalation.

Degree

Ph.D.

Advisors

McMillin, Purdue University.

Subject Area

Chemistry

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