Synthesis, DNA Binding, and DNA Photocleavage of the Ruthenium(II) Complexes [Ru(bpy)(btip)]²⁺ and [Ru(dmb)(btip)]²⁺ (bpy = 2,2′‐Bipyridine; btip = 2‐Benzo[b]thien‐2‐yl‐1H‐imidazo[4,5‐f] [1,10]phenanthroline; dmb = 4,4′‐Dimethyl‐2,2′‐bipyridine)

Abstract

(1; bpy = 2,2'-bipyridine) and [Ru(dmb) 2 A C H T U N G T R E N N U N G (btip)] 2+ (2; dmb = 4,4'-dimethyl-2,2'-bipyridine) were synthesized and characterized by elemental analysis, MS, and 1 H-NMR. The DNA-binding properties of the two complexes to calf-thymus DNA (CT-DNA) were investigated by different spectrophotometric methods and viscosity measurements. The results suggest that both complexes bind to CT-DNA through intercalation. Also, when irradiated at 400 nm, the two complexes promote the photocleavage of plasmid pBR-322 DNA. Thereby, under comparable experimental conditions, complex 1 cleaves DNA more effectively than complex 2 does. Mechanistic studies reveal that singlet oxygen ( 1 O 2 ) and hydroxyl radicals (OHC) play a significant role in the photocleavage.Introduction. -During the last decade, the interaction between transition-metal complexes and DNA has been extensively studied [1 -5]. Binding studies of small molecules to DNA are very important in the development of new therapeutic agents and DNA molecular probes [6 -18]. Polypyridyl ruthenium(II) complexes can bind to DNA by non-covalent interactions such as electrostatic binding, groove binding [19], intercalative binding, and partial intercalative binding [20]. The useful application of such complexes generally requires that they bind to DNA through intercalation. Therefore, the vast majority of studies has been focused on the interaction of transition-metal complexes containing fully planar ligands [21 -28]. In contrast, investigations with substituted ligands as DNA-binding reagents have been relatively few. However, some of these less-planar complexes also exhibit interesting DNA-binding properties [29]. Varying types and/or positions of substituents in intercalative ligands may create interesting differences in the spatial configuration and electron-density distribution of ruthenium(II)-polypyridyl complexes. This also results in differences in the spectroscopic properties and the DNA-binding potentials of such complexes, and will be helpful to more clearly understand the binding mechanism of these complexes to DNA. Therefore, further studies with ligands differing both in functionalization and degree of planarity are necessary.Herein, we report the synthesis and characterization of 2-benzo[b]thien-2-yl-1H-imidazo[4,5-f] [1,10]phenanthroline (btip), a new polypyridyl ligand, and its RuII complexes [Ru(bpy) 2

Synthesis, and Acid–Base and DNA-Binding Properties of a Thiophen-Appended Ruthenium Complex

“…[29] The intrinsic DNA binding constant K b illustrating the binding strength of the complex with ct-DNA was determined by a linear fitting of the changes in absorbance at 285 nm for the complex with increasing concentrations of the DNA to Eqn 2: [40] ½DNA ðe a À e f Þ ¼ ½DNA where the apparent absorption coefficients e a , e b and e f correspond to the extinction coefficient observed for the MLCT absorption band at a given DNA concentration, the extinction coefficient for the free ruthenium complex, and the extinction coefficient for the ruthenium complex in the fully bound form, respectively, and [DNA] is the the concentration of nucleotides in the DNA. A K b value of (7.11 AE 0.15) Â 10 5 M À1 was obtained from the ratio of the slope to the intercept, which is 1.4 times the binding constant of (4.98 AE 0.2) Â 10 5 M À1 observed under the same experimental conditions for [Ru(bpy) (Hpip)] 2þ , and is much greater than K b ¼ 2.85 Â 10 4 M À1 previously reported for the DNA intercalator [Ru(bpy) 2 (Hbtip)] 2þ , [28] indicating that the introduction of thiophen enlarges the conjugation plane of Hptip on [Ru(bpy) 2 (Hptip)] 2þ , thus being favourable for DNA binding. The hypochromism, DNA binding-induced red shifts suggest that the complex in this work most likely intercalatively binds to the DNA, involving a strong stacking interaction between Hptip and the base pairs of the DNA.…”

“…The 1 H NMR chemical shifts for the ligand and the complex were assigned based on comparison with those of a similar compound, [Ru (bpy) 2 (btip)] 2þ (where btip ¼ 2-benzo [b]thien-3-yl-H-imidazo [4,5-f] [1.10]phenanthroline) and the parent compound [Ru (bpy) 2 (Hpip)] 2þ (where Hpip ¼ 2-(4-phenyl)imidazo [4,5-f] [1,10]phenanthroline). [28,29] It is obvious that owing to the shielding effects of the adjacent bpy and Hptip moieties, the bpy H atoms of [Ru(bpy) 2 (Hptip)] 2þ exhibit two distinct sets of signals. The H a chemical shift at 8.89 ppm for Hptip experienced a large upshield shift to 8.09 ppm on complexation, while the single signal of H b gave a downfield shift of 0.43 ppm and split into multiplets.…”

Highly Charged Ruthenium(II) Polypyridyl Complexes as Effective Photosensitizer in Photodynamic Therapy

“…Following photo-activation,a progressive conversion of the supercoiled form of DNA (form I) to the relaxed/nicked form (form II) was observed with increasing Ru II concentrations, denoting ad ose-dependent DNA cleavage activity in the formation of single strand breaks (SSBs) on the plasmid. [48,49] This would be reasonablya ssociated to the ability of L to produce singlet oxygen when light-activated, as discussed above.…”

Photosensitive Organic-Inorganic Hybrid Materials for Room Temperature Gas Sensor Applications

“…The absorption bands in the UV range of Ru-TT (5 × 10 −5 M solution in methanol) spectrum are due to ligand-centered (LC) π-π* transitions. The 1 H -imidazo-phenantroline (ImPh) and pyridine π-π* transitions overlap in the 287 nm range [ 54 , 55 ]. Additionally, the π-π* transitions of substituted ImPh residues are in the region of 320–380 nm.…”