DNA Mediated Energy Transfer from 4',6-Diamidino-2-phenylindole to Ru(II)[(1,10-phenanthroline)2L]2+: Effect of Ligand Structure

Abstract

It was proposed that Ru(II)[(1,10-phenanthroline)<TEX>$_2$</TEX>dipyrido[3,2-a:2',3'-c]phenazine ([Ru(phen)<TEX>$_2$</TEX>DPPZ]<TEX>$^{2+}$</TEX>)complexes and 4',6-diamidino-2-phenylindole (DAPI) simultaneously bind to poly[d(A-T)<TEX>$_2$</TEX>] (Biophysics. J. 2003, 85, 3865). Förster type resonance energy transfer from excited DAPI to [Ru(phen)2DPPZ]<TEX>$^{2+}$</TEX> complexes was observed. In this study, we synthesized <TEX>$\Delta$</TEX>- and <TEX>$\wedge$</TEX>-[Ru(phenanthroline)<TEX>$_2$</TEX>dipyrido[3,2-a:2’3’c]6-azaphenazine] ([Ru(phen)<TEX>$_2$</TEX>DPAPZ]<TEX>$^{2+}$</TEX>) at which the DNA intercalating ligand DPPZ was replaced and we studied its binding properties to poly[d(A-T)<TEX>$_2$</TEX>] in the presence and absence of DAPI using polarized spectroscopy and fluorescence techniques. All the spectroscopic properties of the [Ru(phen)<TEX>$_2$</TEX>DPAPZ]<TEX>$^{2+}$</TEX>-poly[d(A-T)<TEX>$_2$</TEX>] complex were the same in the presence and absence of DAPI that blocks the minor groove of polynucleotide, suggesting both <TEX>$\Delta$</TEX>- and <TEX>$\wedge$</TEX>-[Ru(phen)<TEX>$_2$</TEX>DPAPZ]<TEX>$^{2+}$</TEX> complexes are located at the major groove of poly[d(A-T)2]. On the other hand, in contrast with [Ru(phen)<TEX>$_2$</TEX>DPPZ]<TEX>$^{2+}$</TEX>, both <TEX>$\Delta$</TEX>- and <TEX>$\wedge$</TEX>-[Ru(phen)<TEX>$_2$</TEX>DPAPZ]<TEX>$^{2+}$</TEX> exhibited almost twice the efficiency in the fluorescence quenching of DAPI that binds at the minor groove of poly[d(A-T)<TEX>$_2$</TEX>]. This observation indicates that the efficiency of the Förster type resonance energy transfer can be controlled by a small change in the chemical structure of the intercalated ligand.