Transcription inhibition by Rh(phi)(2)(phen)(3+)

Rh(phi)(2)(phen)(3+) (phi = 9,10-phenanthrenequinone diimine, phen = 1,10-phenanthroline) increases the melting temperature (DeltaT(m)) of a 15-mer duplex DNA by 21 degreesC and it is able to inhibit transcription in vitro; the concentration ratio of Rh(phi)(2)(phen)(3+) relative to DNA bases of the template required to inhibit the RNA transcribed by 50%, R-inh(50), was found to be 0.13; in contrast, Rh(phen)(2)(phi)(3+), which also possesses the intercalating phi ligand, exhibits only a +7 degreesC shift in T-m and R-inh(50) = 4.5; Rh(phen)(3)(3+), RhCl3, and ethidium bromide result in negligible or small DeltaT(m) and exhibit R-inh(50) values that range from 4.8 to 12.5; these results suggest that the intercalation of the phi ligand between the DNA bases and electrostatic binding are not the only means of duplex stabilization by these complexes.