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The binding mode of Delta- and Lambda-[Ru(1,10-phenanthroline)(2)dipyrido[3,2-a:2',3'-c]phenazine](2+) ([Ru(phen)(2)DPPZ](2+)) to DNA in the presence of 4',6-diamidino-2-phenylindole (DAPI) at a low and high [DAPI]/[DNA base] ratio (0.02 and 0.20, respectively) was investigated using electric absorption and circular dichroism spectroscopy. The spectral properties of both the Delta- and Lambda-[Ru(phen)(2)DPPZ](2+) were not altered in the presence of DAPI disregarding the [DAPI]/[DNA] ratio, suggesting that the presence of DAPI in the minor groove of DNA does not affect the binding mode of the [Ru(phen)(2)DPPZ](2+) complex to DNA. The transferring excited energy of DAPI to both Delta- and Lambda-[Ru(phen)(2)DPPZ](2+) occurs through Förster type resonance when they both spontaneously bound to DNA. At a high [DAPI]/[DNA] ratios, an upward bending curve in the Stern-Volmer plot, and a shortening the DAPI fluorescence decay time with increasing [Ru(phen)(2)DPPZ](2+) concentration were found. These results indicate that the quenching of the DAPI's fluorescence occurs through both the static and dynamic mechanisms. In contrast, the quenching mechanism at a low [DAPI]/[DNA] ratios was found to be purely static. The static quenching constant decreased linearly with respect to the [DAPI]/[DNA] ratio. Decrease in quenching efficiency can be explained by the association constant of [Ru(phen)(2)DPPZ](2+) to DNA while being within a quenchable distance from a DAPI molecule.

Cu complexes were synthesized by substituting the hydrogen of the amine group of basic ligand 2,2′‐dipicoylamine (dpca) (complex 2) with CH3CO (complex 1), phenyl (complex 3), and methyl (complex 4), respectively, and their DNA cleavage activity was investigated using linear dichroism (LD) and electrophoresis. The DNA cleavage efficiencies of Cu complexes 3 and 4 with phenyl and methyl, which are electron‐donating functional groups, turned out to be the highest, and LD magnitudes rapidly decreased at 260 nm. In particular, Cu complex 3 showed a rapid LD magnitude reduction to 63% of the total for 90 min, and to 50% of the total at 12 min. DNA cleavage efficiencies were high in the order of phenyl > methyl > HCH3CO, and the highest DNA cleavage efficiency was observed in the presence of electron‐donating groups. The electrophoresis results are also consistent with the changes in LD spectra over time. The Cu complexes (1–4) were found to cleave DNA through oxidative pathways, and the major reaction oxygen species involved in DNA cleavage were the superoxide radical (·O2−), singlet oxygen (1O2), and hydroxyl radical (·OH). [ABSTRACT FROM AUTHOR]

The oxidative DNA cleavage induced by the [Cu(2,2′-bipyridine) 2 (NO 3 )]NO 3 (Cu(bpy) 2 ) complex was examined using the linear dichroism (LD) technique. Using this method, the oxidative DNA cleavage by the Fenton mechanism was reported to occur through two sequential first-order reactions. As the Cu(bpy) 2 concentration increased, the rate constant of both first order reactions increased, as expected. The activation energy of the second step was estimated to be 0.190 kJ mol −1 . A similar method was applied for various synthetic polynucleotides. Poly[d(G-C) 2 ], poly(dG)·poly(dC), and poly(dA)·poly(dT) produced a time-dependent decrease in LD, which could be elucidated by a single component exponential decay. This observation is in contrast to Fenton-type oxidative DNA cleavage. On the other hand, poly[d(A-T) 2 ] produced a time-dependent decrease in the LD magnitude, which could be elucidated by two sequential first order reactions. [ABSTRACT FROM AUTHOR]

Abstract: The binding mode of Δ- and Λ-[Ru(1,10-phenanthroline)2dipyrido[3,2-a:2′,3′-c]phenazine]2+ ([Ru(phen)2DPPZ]2+) to DNA in the presence of 4′,6-diamidino-2-phenylindole (DAPI) at a low and high [DAPI]/[DNA base] ratio (0.02 and 0.20, respectively) was investigated using electric absorption and circular dichroism spectroscopy. The spectral properties of both the Δ- and Λ-[Ru(phen)2DPPZ]2+ were not altered in the presence of DAPI disregarding the [DAPI]/[DNA] ratio, suggesting that the presence of DAPI in the minor groove of DNA does not affect the binding mode of the [Ru(phen)2DPPZ]2+ complex to DNA. The transferring excited energy of DAPI to both Δ- and Λ-[Ru(phen)2DPPZ]2+ occurs through Förster type resonance when they both spontaneously bound to DNA. At a high [DAPI]/[DNA] ratios, an upward bending curve in the Stern–Volmer plot, and a shortening the DAPI fluorescence decay time with increasing [Ru(phen)2DPPZ]2+ concentration were found. These results indicate that the quenching of the DAPI''s fluorescence occurs through both the static and dynamic mechanisms. In contrast, the quenching mechanism at a low [DAPI]/[DNA] ratios was found to be purely static. The static quenching constant decreased linearly with respect to the [DAPI]/[DNA] ratio. Decrease in quenching efficiency can be explained by the association constant of [Ru(phen)2DPPZ]2+ to DNA while being within a quenchable distance from a DAPI molecule. [Copyright &y& Elsevier]

Ruthenium(II) polypyridyl dimer containing large planar aromatic bridging ligands [ μ -(tpphz)(phen) 4 Ru 2 ]4+ (phen = 1,10-phenanthroline, tpphz = tetrapyrido[3,2-a:2′,3′-c:3″, 2″-h:2‴, 3‴-j]phenazine, bis- Ru-tpphz) were synthesized and characterized by elemental analysis, and 1H nuclear magnetic spectroscopy. The binding mode of the synthesized bis- Ru-tpphz to DNA was compared with those of the bis -Ru-bip, and bis -Ru-tatpp complexes. The structures of the connecting bridge of bis -Ru complexes were different. The absorption and reduced linear dichroism spectrum showed that the planar linker moiety of the bis -Ru-tatpp complex is inserted between the DNA base-pairs despite the steric hindrance originating from its large ruthenium ligand part, whereas the bis -Ru-bip complex has flexible linker binds at the groove of the DNA. The binding mode of the bis- Ru-tpphz complex, which has fused shorter bridge ligands than the bis -Ru-tatpp complex, was in contrast with the other two complexes. The bis- Ru-tpphz complex binds either at the groove of the DNA or to the negatively charged phosphate group; intercalative binding was prevented by either short bridge structure or steric hindrances from the phenanthroline ligand. In conclusion, the structure of the bridge of the bis -Ru(II) complex plays an important role in determining the binding mode of these compounds to DNA. To have the mode of insertion, the bridge ligand structure must be fused and have a sufficiently long distance. [ABSTRACT FROM AUTHOR]