RESONANCE RAMAN PROBING OF THE INTERACTION BETWEEN DIPYRIDOPHENAZINE COMPLEXES OF RU(II) AND DNA

Resonance Raman (RR) spectroscopy has been used to probe the interacti on between dipyridophenazine (dppz) complexes of ruthenium(II), [Ru(L) (2)(dppz)](2+) (L = 1,10-phenanthroline (1) and 2,2-bipyridyl (2)), an d calf-thymus DNA. Ground electronic state RR spectra at selected prob e wavelengths reveal enhancement patterns which reflect perturbation o f the dppz-centered electronic transitions in the UV-vis spectra in th e presence of DNA. Comparison of the RR spectra recorded of the short- lived MLCT excited states of both complexes in aqueous solution with t hose of the longer-lived states of the complexes in the DNA environmen t reveals changes to excited state modes, suggesting perturbation of e lectronic transitions of the dppz ligand in the excited state as a res ult of intercalation. The most prominent feature, at 1526 cm(-1), appe ars in the spectra of both 1 and 2 and is a convenient marker band for intercalation. For 1, the excited state studies have been extended to the A and A enantiomers. The marker band appears at the same frequenc y for both but with different relative intensities. This is interprete d as reflecting the distinctive response of the enantiomers to the chi ral environment of the DNA binding sites. The results, together with s ome analogous data for other potentially intercalating complexes, are considered in relation to the more general application of time-resolve d RR spectroscopy for investigation of intercalative interactions of p hotoexcited metal complexes with DNA.