Chiral ruthenium(II) anthraquinone complexes as dual inhibitors of topoisomerases I and II

Abstract  

DNA topoisomerases (I and II) have been one of the excellent targets in anticancer drug development. Here two chiral ruthenium(II) anthraquinone complexes, Δ- and Λ-[Ru(bpy)₂(ipad)]²⁺, where bpy is 2,2′-bipyridine and ipad is 2-(anthracene-9,10-dione-2-yl)imidazo[4,5-f][1,10]phenanthroline, were synthesized and characterized. As expected, both of the Ru(II) complexes intercalate into DNA base pairs and possess an obviously greater affinity with DNA. Topoisomerase inhibition and DNA strand passage assay confirmed that the two complexes are efficient dual inhibitors of topoisomerases I and II by interference with the DNA religation. In MTT cytotoxicity studies, two Ru(II) complexes exhibited antitumor activity against HeLa, MCF-7, HepG2 and BEL-7402 tumor cell lines. Flow cytometry analysis shows an increase in the percentage of cells with apoptotic morphological features in the sub-G1 phase for Ru(II) complexes. Nuclear chromatin cleavage has also been observed from AO/EB staining assay and alkaline single-cell gel electrophoresis (comet assay). The results demonstrated that Δ- and Λ-[Ru(bpy)₂(ipad)]²⁺ act as dual inhibitors of topoisomerases I and II, and cause DNA damage that can lead to cell cycle arrest and/or cell death by apoptosis.     

Targeting topoisomerase II with the chiral DNA-intercalating ruthenium(II) polypyridyl complexes

Many antitumor drugs act as topoisomerase inhibitors, and the inhibitions are usually related to DNA binding. Here we designed and synthesized DNA-intercalating Ru(II) polypyridyl complexes Δ--[Ru(bpy)₂(uip)]²⁺ and Λ-[Ru(bpy)₂(uip)]²⁺ (bpy is 2,2′-bipyridyl, uip is 2-(5-uracil)-1H-imidazo[4,5-f][1,10]phenanthroline). The DNA binding, photocleavage, topoisomerase inhibition, and cytotoxicity of the complexes were studied. As we expected, the synthesized Ru(II) complexes can intercalate into DNA base pairs and cleave the pBR322 DNA with high activity upon irradiation. The mechanism studies reveal that singlet oxygen (¹O₂) and superoxide anion radical (O₂^•−) may play an important role in the photocleavage. The inhibition of topoisomerases I and II by the Ru(II) complexes has been studied. The results suggest that both complexes are efficient inhibitors towards topoisomerase II by interference with the DNA religation and direct topoisomerase II binding. Both complexes show antitumor activity towards HELA, hepG2, BEL-7402, and CNE-1 tumor cells. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions

Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2′-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)₂(mppne)]²⁺ (bpy is 2, 2′–bipyridyl), [Ru(bpy)₂(mppae)]²⁺, [Ru(bpy)₂(mpppe)]²⁺, [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, ¹H NMR, fast-atom bombardment or electron-impact mass, UV–vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d _Ru→π*_sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d _Ru→π*_bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the ¹H NMR method. [Ru(bpy)₂(mppne)]²⁺, [Ru(bpy)₂(mppae)]²⁺ and [Ru(bpy)₂(mpppe)]²⁺ exhibit redox waves corresponding to the Ru^III/Ru^II couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH₃CN, 0.1 M tetrabutylammonium hexafluorophosphate)—corresponding voltammograms of [Ru(bpy)₂(sq-py)]⁺, [Ru(bpy)₂(sq-phen)]⁺ and [Ru(phen)₂(bsq)]⁺ are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)₂(mppne)]²⁺ and [Ru(bpy)₂(mppae)]²⁺ are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10⁵ to 10⁶ M⁻¹. Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)₂(mppne)]²⁺>[Ru(bpy)₂(mppae)]²⁺, although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)₂(sq)]⁺-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.Electronic Supplementary Material Supplementary material is available for this article at .     

DNA-Binding and Photocleavage Properties of Ru(II) Polypyridyl Complexes with DNA and Their Toxicity Studies on Eukaryotic Microorganisms

Four Ru(II) polypyridyl complexes, [Ru(bpy)₂(7-NO₂-dppz)]²⁺, [Ru(bpy)₂(7-CH₃-dppz)]²⁺, [Ru(phen)₂(7-NO₂-dppz)]²⁺, and [Ru(phen)₂(7-CH₃-dppz)]²⁺ (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline), (7-Nitro-dppz = 7-Nitro dipyrido[3,2-a:2′-3′-c]phenazine, 7-CH₃-dppz = 7-Methyl dipyrido[3,2-a:2′-3′-c]phenazine), have been synthesized and characterized by IR, UV, elemental analysis, ¹H NMR, ¹³C-NMR, and mass spectroscopy. The DNA-binding properties of the four complexes were investigated by spectroscopic and viscosity measurements. The results suggest that all four complexes bind to DNA via an intercalative mode. Under irradiation at 365 nm, all four complexes were found to promote the photocleavage of plasmid pBR 322 DNA. Toxicological effects of the selected complexes were performed on industrially important yeasts (eukaryotic microorganisms).     

Ruthenium(II) mixed-ligand complexes containing 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline: Synthesis, DNA-binding and photocleavage studies

Two novel Ru(II) complexes [Ru(bpy)₂(MCMIP)]²⁺ (1) and [Ru(phen)₂(MCMIP)]²⁺ (2) (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline; MCMIP = 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra and ¹H NMR. The DNA-binding properties of the complexes were investigated by absorption, emission, melting temperature and viscosity measurements. Experimental results indicate that the two complexes can intercalate into DNA base pairs. Upon irradiation at 365 nm, two Ru(II) complexes were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II, and the mechanisms for DNA cleavage by the complexes were also investigated.     

Synthesis and properties of red emitter Ru(II) complexes based on 6,6′-disubstituted-4,4′-bipyrimidine

Heteroleptic complexes [Ru(bpy)₂(R₂bpm)]²⁺, where bpy = 2,2′-bipyridine and R₂bpm = 6,6′-diaryl-4,4′-bipyrimidine, have been synthesized and characterized, together with the homoleptic complex [Ru(R₂bpm)₃]²⁺, in which R₂bpm = 6,6′-diphenyl-4,4′-bipyrimidine. The substituent aryl on the bipyrimidine has significant effects on the properties of these complexes as compared to the parent [Ru(bpy)₂(bpm)]²⁺ complex. The complexes exhibit Ru-to-bpm charge transfer (CT) absorptions centered at about 540 nm and Ru-to-bpy CT absorptions centered at about 435 nm. The assignment of the low energy absorptions is supported by the relative ease of the reduction of the new complexes as compared to [Ru(bpy)₃]²⁺. The new complexes exhibit a relatively intense emission at room temperature, with lifetimes in the 10-50 ns range, with the homoleptic species exhibiting the higher-energy (maximum at 724 nm) and the longest-lived (τ = 48 ns) emission among the complexes. Luminescence lifetimes and quantum yields are governed by the energy gap law, indicating that direct deactivation to the ground state is the dominant relaxation pathway for 1-6, while thermally activated processes are inefficient.     

Electronic Effect of Substituents on the DNA Intercalation of Ruthenium(II)?Polypyridyl Complexes

Five ruthenium(II) complexes, i.e., [Ru(bpy)₂(TIP)]²⁺ (bpy=2,2′‐bipyridine; TIP=2‐thiophenimidazo[4,5‐f] [1,10]phenanthroline; 1 ), [Ru(bpy)₂(5‐NTIP)]²⁺ (5‐NTIP=2‐(5‐nitrothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 2 ), [Ru(bpy)₂(5‐MOTIP)]²⁺ (5‐MOTIP=2‐(5‐methoxythiophen)imidazo[4,5‐f] [1,10]phenanthroline; 3 ), [Ru(bpy)₂(5‐BTIP)]²⁺ (5‐BTIP=2‐(5‐bromothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 4 ), and [Ru(bpy)₂(4‐BTIP)]²⁺ (4‐BTIP=2‐(4‐bromothiophen)imidazo[4,5‐f] [1,10]phenanthroline; 5 ), were synthesized and characterized by elemental analysis and UV/VIS, IR, and ¹H‐NMR spectroscopic methods. The photophysical and DNA‐binding properties were investigated by means of UV and fluorescence spectroscopic methods and viscosity measurements, respectively. The results suggest that all five complexes can bind to CT‐DNA with various binding strength. Complexes 2 and 3 showed the strongest and the weakest binding affinity, respectively, among these five complexes. Due to the substituent position of the Br‐atom in the ligand, complex 5 interacted stronger with CT‐DNA than complex 4 . The binding affinities of the complexes decreased in the order 2, 5, 4, 1 , and 3 .     

Strong and weak coupling in mixed-valence complexes bridged by 4,4′-azo-di(phenylcyanamido)

The complexes [{Ru(tpy^∗)(bpy)}₂(μ-adpc)][PF₆]₂ where tpy^∗ is 4,4′,4″-tri-(tert-butyl)-2,2′:6′,2″-terpyridine, bpy is 2,2′-bipyridine, and adpc²⁻ is 4,4′-azo-diphenylcyanamide dianion and trans,trans-[{Ru(tpy^∗)(pc)}₂(μ-adpc)] where pc⁻ is 2-pyrazine-carboxylato were prepared and characterized by cyclic voltammetry and spectroelectrochemical methods. Intervalence band properties and IR spectroelectrochemistry of the mixed-valence complexes [{Ru(tpy^∗)(bpy)}₂(μ-adpc)]³⁺ and trans,trans-[{Ru(tpy^∗)(pc)}₂(μ-adpc)]⁺ are consistent with delocalized and valence-trapped mixed-valence properties respectively. The reduction in mixed-valence coupling upon substituting a bipyridine ligand with 2-pyrazine carboxylato strongly suggests that hole-transfer superexchange is the dominant mechanism for metal-metal coupling in these complexes.     

[Ru(phen)2(dppz)] as an efficient optical probe for staining nuclear components

The ‘molecular light switch’ complexes [Ru(bpy)₂(dppz)]²⁺ (1) and [Ru(phen)₂(dppz)]²⁺ (2), where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and dppz = dipyrido[3,2-a:2′,3′-c]phenazine, have been explored as probes for diagnosing and staining nuclear components. The phen complex acts as a better staining agent for nonviable cells than for viable cells and exhibits a staining efficiency in tail region of comet more specific and stronger than the already known dye Hoechst 33258.     

The interesting DNA-binding properties of three novel dinuclear Ru(II) complexes with varied lengths of flexible bridges

Three binuclear Ru(II) complexes with two [Ru(bpy)₂(pip)]²⁺-based subunits {where bpy = 2,2′-bipyridine and pip = 2-phenylimidazo[4,5-f][1,10]phenanthroline} being linked by varied lengths of flexible bridges, were synthesized and characterized by ¹H NMR, elemental analysis, UV-visible (UV-vis) and photoluminescence spectroscopy. The structures of the three complexes were optimized by density functional theory calculations. The interaction of the complexes with calf thymus DNA was investigated by UV-vis and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The experimental results indicated that the three complexes bound to the DNA most probably in a threading intercalation binding mode with high DNA binding constant values three orders of magnitude greater than the DNA binding constant value reported for proven DNA intercalator, mononuclear counterpart [Ru(bpy)₂(p-mopip)]²⁺ {p-mopip = 2-(4-methoxylphenyl)imidazo[4,5-f][1,10]phenanthroline}.     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Selectivity at a three-base bulge site in the DNA binding of ΔΔ-[{Ru(phen)2}2(μ-dppm)]4+ [dppm is 4,6-bis(2-pyridyl)pyrimidine; phen is 1,10-phenanthroline]

The binding of the stereoisomers of [{Ru(phen)₂}₂(μ-bpm)]⁴⁺, [{Ru(phen)₂}₂(μ-dppm)]⁴⁺ and [{Ru(phen)₂}₂(μ-bb)]⁴⁺ {phen is 1,10-phenanthroline; bpm is 2,2′-bipyrimidine, dppm is 4,6-bis(2-pyridyl)pyrimidine, bb is 1,2-bis[4-(4′-methyl-2,2′-bipyridyl)]ethane} to an oligonucleotide duplex [d(GCATCGAAAGCTACG)•d(CGTAGCCGATGC)] containing a three-base bulge has been studied using a fluorescence intercalator displacement assay. Of the dinuclear ruthenium complexes, the dppm-linked species showed the strongest binding to the oligonucleotide, with the ΔΔ isomer binding slightly more strongly than the meso isomer and the ΛΛ isomer exhibiting the weakest binding. In order to determine whether the ΔΔ-[{Ru(phen)₂}₂(μ-dppm)]⁴⁺ metal complex specifically bound at the three-base bulge site, a ¹H NMR study of the binding of the metal complex to the oligonucleotide duplex d(GCATCGAAAGCTACG)•d(CGTAGCCGATGC) was carried out. Although a detailed picture of the metal complex–oligonucleotide association could not be determined from the NMR results owing to the broadening of the resonances from the metal complex and nucleotide residues at the bulge site, the NMR results do indicate that the metal complex specifically binds at the three-base bulge site. The combined results of this study suggest that the dppm-bridged dinuclear ruthenium complexes have considerable potential as probes for the unusual secondary structure obtained by the insertion of a three-base bulge within duplex DNA.     

The Effects of Grafting of 2-Pyridyl to [Ru(bpy)2(Hpip)]2+ on Acid-Base and DNA-Binding Properties: Experimental and DFT Studies

Abstract

A new Ru(II) complex of [Ru(bpy)₂(Hppip)]²⁺ {bpy = 2,2′-bipyridine; Hppip = 2-(4-(pyridin- 2-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} has been synthesized by grafting of 2-pyridyl to parent complex [Ru(bpy)₂(Hpip)]²⁺ {Hppip = 2-(4-phenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline}. The acid-base properties of [Ru(bpy)₂(Hppip)]²⁺ studied by UV-visible and luminescence spectrophotometric pH titrations, revealed off-on-off luminescence switching of [Ru(bpy)₂(Hppip)]²⁺ that was driven by the protonation/deprotonation of the imidazolyl and the pyridyl moieties. The complex was demonstrated to be a DNA intercalator with an intrinsic DNA binding constant of (5.56 ± 0.2) × 10⁵ M^?1 in buffered 50 mM NaCl, as evidenced by UV-visible and luminescence titrations, reverse salt effect, DNA competitive binding with ethidium bromide, steady-state emission quenching by [Fe(CN)₆]^4-, DNA melting experiments and viscosity measurements. The density functional theory method was also used to calculate geometric/electronic structures of the complex in an effort to understand the DNA binding properties. All the studies indicated that the introduction of 2-pyridyl onto Hpip ligand is more favorable for extension of conjugate plane of the main ligand than that of phenyl, and for greatly enhanced ct-DNA binding affinity accordingly.     

Effect of ancillary ligands on the photophysical properties of Ru(II) complexes bearing a highly conjugated diimine ligand: A density functional theory study

Two bis-heteroleptic Ru(II) complexes [Ru(bpy)₂(pcip)]²⁺ (1, bpy = 2,2′-bipyridine, pcip = 2-[4-phenylcarboxy]-1H-imidazol[4,5-f][1,10]phenanthroline) and [Ru(phen)₂(pcip)]²⁺ (2, phen = 1,10-phenanthroline), bearing highly conjugated diimine ligands, were prepared and isolated as their PF₆ salts. The bpy-derivative 1 showed better photophysical properties (emission quantum yield, lifetime of the emitting state, and the radiative decay rate constant) than the phen-compound 2. These results followed by theoretical calculations at DFT level established a comprehensive understanding between the structural parameters and the photophysical properties, as well as of the influence of π conjugation and the symmetry of the molecules on spectroscopic characteristics. These results provide fundamental photophysical data for selecting ancillary ligands in the design and improvement of Ru-based light-harvesting complexes.     

Ternary oxovanadium(IV) complexes of ONO-donor Schiff base and polypyridyl derivatives as protein tyrosine phosphatase inhibitors: synthesis, characterization, and biological activities

Abstract  A series of oxovanadium complexes with mixed ligands, a tridentate ONO-donor Schiff base ligand [viz., salicylidene anthranilic acid (SAA)], and a bidentate NN ligand [viz., 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq), dipyrido[3,2-a:2′,3′-c]phenazine (dppz), or 7-methyldipyrido[3,2-a:2′,3′-c]phenazine (dppm)], have been synthesized and characterized by elemental analysis, electrospray ionization mass spectrometry, UV–vis spectroscopy, Fourier transform IR spectroscopy, EPR spectroscopy, and X-ray crystallography. Crystal structures of both complexes, [V^IVO(SAA)(bpy)]·0.25bpy and [V^IVO(SAA)(phen)]·0.33H₂O, reveal that oxovanadium(IV) is coordinated with one nitrogen and two oxygen atoms from the Schiff base and two nitrogen atoms from the bidentate planar ligands, in a distorted octahedral geometry (VO₃N₃). The oxidation state of V(IV) with d ¹ configuration was confirmed by EPR spectroscopy. The speciation of VO–SAA–bpy in aqueous solution was investigated by potentiomtreic pH titrations, and the results revealed that the main species are two ternary complexes at a pH range of 7.0–7.4, and one is the isolated crystalline complex. The complexes have been found to be potent inhibitors against human protein tyrosine phosphatase 1B (PTP1B) (IC₅₀ approximately 30–61 nM), T-cell protein tyrosine phosphatase (TCPTP), and Src homology phosphatase 1 (SHP-1) in vitro. Interestingly, the [V^IVO(SAA)(bpy)] complex selectively inhibits PTP1B over the other two phosphatases (approximate ninefold selectivity against SHP-1 and about twofold selectivity against TCPTP). Kinetics assays suggest that the complexes inhibit PTP1B in a competitive and reversible manner. These suggest that the complexes may be promising candidates as novel antidiabetic agents. Graphical Abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of β-diketonato ruthenium(II) complexes with two 4-bromo or protected 4-ethynyl-2,2′-bipyridine ligands

Two new mononuclear mixed-ligand ruthenium(II) complexes with acetylacetonate ion (2,4-pentanedionate, acac) and functionalized bipyridine (bpy) in position 4, [Ru(bpyBr)₂(acac)](PF₆) (2; bpyBr = 4-Bromo-2,2′-bipyridine, acac = 2,4-pentanedionate ion) and [Ru(bpyOH)₂(acac)](PF₆) (3; bpyOH = 4-[2-methyl-3-butyn-2-ol]-2,2′-bipyridine) were prepared as candidates for building blocks. The ¹H NMR, ¹³C NMR, UV-Vis, electrochemistry and FAB mass spectral data of these complexes are presented.     

DNA-binding and photocleavage studies of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

New mixed polypyridyl {NMIP = 2′-(2″-nitro-3″,4″-methylenedioxyphenyl)imidazo-[4′,5′-f][1,10]-phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine} ruthenium(II) complexes [Ru(dmb)₂(NMIP)]²⁺ (1) and [Ru(bpy)₂(NMIP)]²⁺ (2) have been synthesized and characterized. The binding of these complexes to calf thymus DNA (CT-DNA) has been investigated with spectroscopic methods, viscosity and electrophoresis measurements. The experimental results indicate that both complexes could bind to DNA via partial intercalation from the minor/major groove. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation. Under comparable experimental conditions compared with [Ru(phen)₂(NMIP)]²⁺, during the course of the dialysis at intervals of time, the CD signals of both complexes started from none, increased to the maximum magnitude, then no longer changed, and the activity of effective DNA cleavage dependence upon concentration degree lies in the following order: [Ru(phen)₂NMIP]²⁺ > complex 2 > complex 1.     

pH effects on optical and DNA binding properties of a thiophene-containing ruthenium(II) complex

A new ruthenium(II) complex, [Ru(bpy)₂(Htip)]Cl₂ {where bpy = 2,2′-bipyridine and Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}, has been synthesized and characterized by ¹H NMR spectroscopy, elemental analysis, and mass spectrometry. The pH effects on UV-Vis absorption and emission spectra of the complex have been studied, and the ground- and excited-state acidity ionization constant values have been derived. The calf thymus (ct) DNA binding properties of the complex have been investigated with UV-Vis absorption and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The molecular structures and electronic properties of [Ru(bpy)₂(Htip)]²⁺ and deprotonated form [Ru(bpy)₂(tip)]⁺ have also been investigated by means of density functional theory calculations in an effort to understand the DNA binding properties. The results suggest that the complex undergo three-step successive protonation/deprotonation reactions with one of which occurring over physiological pH region, and act as a ct-DNA intercalator with an intrinsic DNA binding constant value on 10⁵ M⁻¹ order of magnitude that is insensitive to pH.     

Synthesis and characterisation of bis(2,2′-bipyridine)(4-carboxy-4′-(pyrid-2-ylmethylamido)-2,2′-bipyridine)ruthenium(II) di(hexafluorophosphate): Comparison of spectroelectrochemical properties with related complexes

The new complex, [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂ NHCO-bpy)](PF₆)₂ · 3H₂O (1), where 4-HCOO-4′-pyCH₂NHCO-bpy is 4-(carboxylic acid)-4′-pyrid-2-ylmethylamido-2,2′-bipyridine, has been synthesised from [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ (H₂dcbpy is 4,4′-(dicarboxylic acid)-2,2′-bipyridine) and characterised by elemental analysis and spectroscopic methods. An X-ray crystal structure determination of the trihydrate of the [Ru(bpy)₂(H₂dcbpy)](PF₆)₂ precursor is reported, since it represented a different solvate to an existing structure. The structure shows a distorted octahedral arrangement of the ligands around the ruthenium(II) centre and is consistent with the carboxyl groups being protonated. A comparative study of the electrochemical and photophysical properties of [Ru^II(bpy)₂(4-HCOO-4′-pyCH₂NHCO-bpy)]²⁺ (1), [Ru(bpy)₂(H₂dcbpy)]²⁺ (2), [Ru(bpy)₃]²⁺ (3), [Ru(bpy)₂Cl₂] (4) and [Ru(bpy)₂Cl₂]⁺ (5) was then undertaken to determine their variation upon changing the ligands occupying two of the six ruthenium(II) coordination sites. The ruthenium(II) complexes exhibit intense ligand centred (LC) transition bands in the UV region, and broad MLCT bands in the visible region. The ruthenium(III) complex, 5, displayed overlapping LC bands in the UV region and a LMCT band in the visible. 1, 2 and 3 were found, via cyclic voltammetry at a glassy carbon electrode, to exhibit very positive reversible formal potentials of 996, 992 and 893 mV (versus Fc/Fc⁺) respectively for the Ru(III)/Ru(II) half-cell reaction. As expected the reversible potential derived from oxidation of 4 (−77 mV (versus Fc/Fc⁺)) was in excellent agreement with that found via reduction of 5 (−84 mV (versus Fc/Fc⁺)). Spectroelectrochemical experiments in an optically transparent thin-layer electrochemical cell configuration allowed UV-Vis spectra of the Ru(III) redox state to be obtained for 1, 2, 3 and 4 and also confirmed that 5 was the product of oxidative bulk electrolysis of 4. These spectrochemical measurements also confirmed that the oxidation of all Ru(II) complexes and reduction of the corresponding Ru(III) complex are fully reversible in both the chemical and electrochemical senses.