The metal complex Δ-[Ru(Me2phen)2dppz]2+ (Me2phen = 2,9-dimethyl-1,10-phenanthroline; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) has been synthesised and its binding to the hexanucleotide d(GTCGAC)2 studied by 1H NMR spectroscopy. The crystal structure of rac-[Ru(Me2phen)2dppz](PF6)2·2H2O has been determined. Addition of Δ-[Ru(Me2phen)2dppz]2+ to d(GTCGAC)2 induced significant broadening of the Me2phen and dppz resonances and large upfield shifts of the dppz resonances, consistent with the metal complex binding through intercalation of the dppz ligand. Also indicative of intercalation are the observed upfield shifts of the T2 and G4 imino protons and the 17 °C increase in the melting temperature of
the hexanucleotide upon addition of the metal complex. NOE cross-peaks from the Me2phen protons were only observed to hexanucleotide minor groove H1′ and H4′/H5′/H5″ protons in NOESY spectra of the hexanucleotide with added metal complex. In addition, NOEs were also observed between the H13/14 protons of the dppz ligand and the hexanucleotide major groove T2methyl and sugar H2′/H2″ protons. From the combined NMR data it is concluded that the dppz-based ruthenium(II) complex Δ-[Ru(Me2phen)2dppz]2+ intercalates from the minor groove of the hexanucleotide mini-duplex d(GTCGAC)2.
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