PHOTOPHYSICAL STUDIES OF COPPER PHENANTHROLINES BOUND TO DNA

Electronic absorption and emission studies have been carried out for Cu(phen)2+, Cu(dmp)2+, and Cu(bcp)2+ interacting with a range of DNA duplexes, where phen denotes 1,10-phenanthroline, dmp denotes 2,9-dimethyl-1,10-phenanthroline, and bcp denotes 2,9- dimethyl-4,7-diphenyl-1,10-phenanthroline. Hypochromism is observed in the visible absorption bands of all three copper(I) complexes, but the bcp complex is unique in that binding to DNA causes the appearance of a measurable luminescence signal at room temperature. At low DNA-P/Cu ratios Cu(bcp)2+ appears to bind to DNA polymers in an aggregated form, but at high DNA-P/Cu ratios the complex binds as a monomer. The adduct of the bcp complex with DNA must be relatively rigid in the vicinity of the copper center because solvent-induced, exciplex quenching of the excited state is strongly inhibited. This suggests that the complex binds by intercalation, and emission polarization data support this model. The limiting emission intensity varies with the type of DNA used and is greater with poly(dA-dT)-poly(dA-dT) than with poly(dG-dC)·poly(dG-dC), possibly because propeller twisting facilitates intercalation. Interaction probably occurs within the major groove since T4 DNA, which is glycosylated in the major groove, does not induce monomer emission. None of the duplexes studied induced emission from Cu(dmp)2+, presumably because the dmp complex binds by another mechanism. Yeast tRNA was also effective at inducing emission from Cu(bcp)2+; hence the complex is also capable of intercalating into an A-form duplex. © 1990, American Chemical Society. All rights reserved.