DNA-BINDING STUDIES OF CU(BCP)(2)+ AND CU(DMP)(2)+ - DNA ELONGATION WITHOUT INTERCALATION OF CU(BCP)(2)+

We have used a variety of physical methods to investigate the ways by which copper phenanthrolines bind to B-form DNA. To vary the composition of the DNA, we have employed poly(dG-dC).poly(dG-dC), M. lysodeikticus DNA, salmon testes DNA, and poly(dA-dT).poly(dA-dT) as hosts. The specific copper complexes we have studied are Cu(dmp)2+ and Cu(bcp)2+ where dmp and bcp denote 2,9-dimethyl-1,10-phenanthroline and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline, respectively. The results indicate that the dmp complex binds externally in a solvent-accessible site. However, the solvent cannot access the metal center as readily in the case of the bcp complex because Cu(bcp)2+ is emissive in the presence of DNA. Since the emission retains polarization, the complex does not rotate independently but tumbles with the macromolecule in solution. At low loadings of Cu(bcp)2+ the specific viscosity due to DNA molecules that are rich in adenine-thymine base pairs increases; however, the results are inconsistent with classical intercalative binding. They are more logically interpreted in terms of bridging structures in which one or more bcp complexes link DNA molecules together in solution. High loadings of Cu(bcp)2+ induce further condensation of the DNA and ultimately particulate formation. The techniques we have used in this work include absorption spectroscopy, circular dichroism, emission spectroscopy, emission polarization, and viscometry. The findings are relevant to the chemistry of copper complexes involving unmethylated phenanthrolines, systems widely being used to probe DNA structure.