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.     

Mixed-valent and radical states of complexes [(bpy)2M(μ-abpy)M′(bpy)2], M,M′ = Ru or Os, abpy = 2,2′-azobispyridine: Electron transfer vs. hole transfer mechanism in azo ligand-bridged complexes

The title complexes were obtained as M^IIM′^II species [(bpy)₂M(μ-abpy)M′(bpy)₂](PF₆)₄, M,M′ = Ru or Os, using the new mononuclear precursor [(bpy)₂Os(abpy)](PF₆)₂ for the osmium-containing dinuclear complexes. One-electron reduction produces radical complexes [(bpy)₂M(μ-abpy)M′(bpy)₂]³⁺ and [(bpy)₂M(abpy)]⁺ with significant contributions from the metals, as evident from the EPR effects on successive replacement of ruthenium by osmium with its much higher spin-orbit coupling constant. The diruthenium and diosmium radical complexes were also studied by EPR at high-frequency (285 GHz), the latter shows an unusually large g anisotropy g₁ − g₃ = 0.25 in frozen solution. Further reduction was monitored by UV/Vis spectroelectrochemistry. Oxidation produced Os^III EPR signals for [(bpy)₂Os(abpy)]³⁺ and [(bpy)₂Os(μ-abpy)Ru(bpy)₂]⁵⁺, indicating a Ru^IIOs^III species for the latter. The diosmium(III,II) and diruthenium(III,II) mixed-valent species remained EPR silent at 4 K, however, they exhibit weak inter-valence charge transfer (IVCT) bands at about 1460 nm. Whereas the cyclic voltammetric response towards reduction is only marginally different for the three dinuclear complexes, successive replacement of ruthenium by osmium causes the first oxidation potential to decrease. The much higher comproportionation constant K_c for the mixed valent diosmium(III,II) state (K_c > 10¹⁵) in comparison to the diruthenium(III,II) analogue with K_c = 10¹⁰ confirms the electron transfer alternative for the valence exchange mechanism, in contrast to the hole transfer established for analogous dinuclear complexes with the formally related diacylhydrazido(2−) bridging ligands.     

Luminescent ruthenium(II) amidodipyridoquinoxaline biotin complexes that display higher avidin-induced emission enhancement

A series of luminescent ruthenium(II) amidodipyridoquinoxaline biotin (dpq-B) complexes [Ru(N-N)₂(N-N′)](PF₆)₂ (N-N = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 4,7-diphenyl-1,10-phenanthroline (Ph₂-phen); N-N′ = 2-((2-biotinamido)ethyl)amidodipyrido[3,2-f:2′,3′-h]quinoxaline (dpq-C2-B), 2-((6-biotinamido)hexyl)amidodipyrido[3,2-f:2′,3′-h]quinoxaline (dpq-C6-B)) has been designed as new luminescent probes for avidin. The electrochemical and photophysical properties of these complexes have been investigated. Upon irradiation, all the complexes exhibited metal-to-ligand charge-transfer (³MLCT) (dπ(Ru) → π^∗(diimine)) emission in fluid solutions at 298 K and in low-temperature glass. In aqueous buffer, the emission was extremely weak, probably a consequence of hydrogen-bonding interactions between the amide moiety of the dpq-B ligands and the water molecules. The avidin-binding properties of all the complexes have been studied by 4′-hydroxyazobenzene-2-carboxylic acid (HABA) assays, luminescence titrations, kinetics experiments and confocal microscopy using avidin-conjugated microspheres.     

Terpyridine-platinum(II) complexes are effective inhibitors of mammalian topoisomerases and human thioredoxin reductase 1

Terpyridine-platinum(II) (TP-Pt(II)) complexes are known to possess DNA-intercalating activity and have been regarded as potential antitumor agents. However, their cytotoxic mechanism remains unclear. To investigate the possible mechanism, a series of TP-Pt(II) compounds were prepared and their biological activities assessed. The DNA binding activities of the aromatic thiolato[TP-Pt(II)] complexes were stronger than the aliphatic 2-hydroxylethanethiolato(2,2′:6′,2′′-terpyridine)platinum(II) [TP(HET)]. TP-Pt(II) complexes inhibited topoisomerase IIα or topoisomerase I activity at IC₅₀ values of about 5 μM and 10-20 μM, respectively, whereas the human thioredoxin reductase 1 (hTrxR1) activity was inhibited with IC₅₀ values in the range of 58-78 nM. At the cellular level, they possessed cytotoxicity with IC₅₀ values between 7 and 19 μM against HeLa cells. Additionally, using X-ray crystallography and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, we elucidated that the TP-Pt(II) complexes inhibited hTrxR1 activity by blocking its C-terminal active-site selenocysteine. Therefore, TP-Pt(II) complexes possess inhibitory activities against multiple biological targets, and they may be further studied as anticancer agents.     

Metal complexes of natural melophlins and their cytotoxic and antibiotic activities

Complexes of the natural melophlins A and C with Mg, Zn, Ga, La and Ru were prepared, characterized and tested for antimicrobial and cytotoxic effects. The lanthanum complex La(melophlinato C)₃ and the ruthenium complex chlorido(η⁶-p-cymene)(melophlinato C)ruthenium(II) inhibited cells of human A-498 kidney cancer at IC₅₀ = 0.54 μM and 1.0 μM, respectively, and so distinctly better than free melophlin C. Another synergistic effect of coordinating melophlins to bioactive metals was found in the growth inhibition of the melophlin C-resistant bacterium Micrococcus luteus by Ga, La and Ru complexes of melophlin C.     

Synthesis, characterization, photophysics and intramolecular energy transfer process in bimetallic rhenium(I)-ruthenium(II) complexes

Two new heterobimetallic complexes of rhenium(I) and ruthenium(II) [(CO)₃(NN)Re(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂ and already known monometallic complexes [Cl(NN)₂Ru(4,4′-bpy)](PF₆) and [(CO)₃(NN)Re(4,4′-bpy)](PF₆) and bimetallic complexes [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂, [(CO)₃(NN)Re(4,4′-bpy)Re(NN)(CO)₃](PF₆)₂ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized by spectral techniques. The photophysical properties of all the complexes are studied. It is found that attachment of rhenium(I) altered the photophysical characteristics of ruthenium(II). Excited state energy transfer from the rhenium(I) chromophore to the ruthenium(II) is observed upon excitation at 355 nm.     

Design,synthesis, DNA-binding affinity,cytotoxicity, apoptosis,and cell cycle arrest of Ru(II) polypyridyl complexes

A novel polypyridyl ligand CNPFIP (CNPFIP = 2-(5(4-chloro-2-nitrophenyl)furan-2-yl)-1H-imidazo[4,5f][1,10]phenanthroline) and its mononuclear Ru(II) polypyridyl complexes of [Ru(phen)₂CNPFIP]²⁺(1) (phen = 1,10-phenanthroline), [Ru(bpy)₂CNPFIP]²⁺(2) (bpy = 2,2′-bipyridine), and [Ru(dmb)₂CNPFIP]²⁺(3) (dmb = 4,4′-dimethyl-2,2′-bipyridine) have been synthesized successfully and characterized thoroughly by elemental analysis, UV/Vis, IR, NMR, and ESI-MS. The interaction of the Ru(II) complexes with calf thymus DNA (CT-DNA) was investigated by absorption titration, fluorescence, viscosity measurements. The experimental results suggest that three complexes bind to CT-DNA through an intercalative mode and the DNA-binding affinity of complex 1 is greater than that of complexes 2 and 3. The photocleavage of plasmid pBR322 DNA by ruthenium complexes 1, 2, and 3 was investigated. We have also tested three complexes for their antimicrobial activity against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) bacteria. The in vitro cytotoxicity of these complexes was evaluated by MTT assay, and complex 1 shows higher cytotoxicity than 2 and 3 on HeLa cells. The induced apoptosis and cell cycle arrest of HeLa cells were investigated by flow cytometry for 24 h. The molecular docking of ruthenium complexes 1, 2, and 3 with the active site pocket residues of human DNA TOP1 was performed using LibDock.     

Remarkable photocytotoxicity in hypoxic HeLa cells by a dipyridophenazine copper(II) Schiff base thiolate

Copper(II) complexes [Cu(satp)(L)] (1-3) of a Schiff base thiolate (salicylidene-2-aminothiophenol, H₂satp) and phenanthroline bases (L), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), were prepared, characterized and their anaerobic DNA photocleavage activity and hypoxic photocytotoxicity studied. The redox active complexes show the Cu(II)-Cu(I) couple near − 0.5 V for 1 and near 0.0 V vs. SCE (saturated calomel electrode) for 2 and 3. The one-electron paramagnetic complexes (~ 1.85 μ_B) are avid DNA binders giving K_b values within 1.0 × 10⁵ − 8.0 × 10⁵ M^− 1. Thermal melting and viscosity data along with molecular docking calculations suggest DNA groove and/or partial intercalative binding of the complexes. The complexes show anaerobic DNA cleavage activity in red light under argon via type-I pathway, while DNA photocleavage in air proceeds via hydroxyl radical pathway. The DFT (density functional theory) calculations reveal a thyil radical pathway for the anaerobic DNA photocleavage activity and suggest the possibility of generation of a transient copper(I) species due to bond breakage between the copper and sulfur to generate the thyil radical. An oxidation of the copper(I) species is likely by oxygen in an aerobic medium or by the buffer medium in an anaerobic condition. Complex 3 exhibits significant photocytotoxicity in HeLa cells (IC₅₀ = 8.3(± 1.0) μM) in visible light, while showing lower dark toxicity (IC₅₀ = 17.2(± 1.0) μM). A significant reduction in the dark toxicity is observed under hypoxic cellular conditions (IC₅₀ = 30.0(± 1.0) μM in dark), while retaining its photocytotoxicity (IC₅₀ = 8.0(± 1.0) μM).     

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

A novel Ru(II) complex, [Ru(bpy)₂(btppz)]Cl₂, where bpy = 2,2′-bipyridine and btppz = benzo[h]tripyrido[3,2-a:2′,3′-c:2″,3″-j]phenazine, has been synthesized and characterized. The pH effects on UV-visible (UV-vis) absorption and emission spectra of the complex have been studied and ground- and excited-state ionization constants of the complex have been derived. The calf thymus DNA (ct-DNA) binding properties of the complex were investigated with UV-vis absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, reverse salt titrations and viscosity measurements. The complex was demonstrated to act as dual molecular switches: pH-induced “on-off” emission switch with an on-off intensity ratio of ∼54 which is favorably compared with those reported for structurally analogous Ru(II) complexes, and a DNA molecular light switch with a luminescence enhancement factor of 22 as it intercalatively bound to the DNA.     

pH-sensitive Ru(II) and Os(II) bis(2,2′:6′,2″-terpyridine) complexes: A photophysical investigation

We have investigated the photophysical properties of two metal complexes, [M(tpy-py)₂][PF₆]₂, where tpy-py = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine and M = Ru(II) or Os(II), in acetonitrile and aqueous solutions at room temperature. Because the 4-pyridyl unit on the 4′-position of each tpy ligand contains a basic nitrogen atom, both of these compounds can exist in three different protonation states. We observed that the absorption and luminescence spectra of these compounds vary on changing the pH, because the protonation of the pendant pyridine unit makes it an electron acceptor by lowering the energy of its π^∗ orbital. We employed the absorption and luminescence spectral changes to study the acid-base reactions for these complexes, and found that the two protonation stages exhibit different pK_a values both in the electronic ground state and in the lowest (emitting) excited state. The absorption spectra and luminescence spectra and lifetimes of the deprotonated, mono-protonated and bis-protonated forms were also determined. While the absorption spectra of the variously protonated forms of both compounds can be intepreted in terms of a linear combination of two different and independent chromophores, namely M(tpy-py) and M(tpy-pyH⁺), the corresponding luminescence spectra exhibit a more complex behaviour, suggesting that the coupling between the two ligands in the lowest excited state is not negligible. Interestingly, at a low pH the luminescence of the Ru complex is switched on, whereas that of the Os complex is strongly quenched upon protonation of the pendant pyridine units. These compounds are of interest because they exhibit a luminescent signal in the red or far red spectral region that can be switched on or off by protons in solution. Hence, they could find applications as luminescent pH sensors and as molecular switches where a low-energy emission signal can be controlled by a chemical acid-base stimulation.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

Synthesis of an amphiphilic ruthenium complex with swallow-tail bipyridyl ligand and its application in nc-DSC

An amphiphilic swallow-tail bipyridyl ligand, 4,4′-bis(dihexylmethyl)-2,2′-bipyridine, and its heteroleptic ruthenium (II) complex were synthesized starting from dichloro-(p-cymene)ruthenium (II) dimer. The complex was characterized by UV/Vis and FTIR spectrophotometers, NMR spectroscopy and cyclic voltammetry. The performance of this complex as charge transfer photosensitizer in nc-TiO₂ based dye sensitized solar cells was studied under standard AM 1.5 sunlight and by using an electrolyte consisting of 0.6 M N-methyl-N-butyl imidazolium iodide (BMII), 0.1 M LiI, 0.05 M I₂, 0.5 M 4-tert-butyl pyridine (TBP) in acetonitrile. The complex, CS9 in DMF, gave a photocurrent density of 12.62 mA/cm², 630 mV open circuit potential and 0.62 fill factor yielding 5.68% efficiency.     

Transition metal complexes (M = Cu, Ni and Mn) of Schiff-base ligands: Syntheses, crystal structures, and inhibitory bioactivities against urease and xanthine oxidase

Six new transition metal complexes (M = Cu(II), Ni(II) and Mn(III)) of tridentate (H₂L¹, HL²) and/or bidentate (HL³, HL⁴) Schiff-base ligands, obtained from the condensation of salicylaldehyde with glycine, N-(2-aminoethyl)morpholine, 4-(2-aminoethyl)phenylic acid and 4-(2-aminoethyl)benzsulfamide, respectively, were synthesized and structurally determined by single-crystal X-ray analysis. Complexes 1-6 were evaluated for their effect on the jack bean urease and xanthine oxidase (XO). Copper(II) complexes 1-3 (IC₅₀ = 0.43-2.25 μM) showed potent inhibitory activity against jack bean urease, comparable with acetohydroxamicacid (IC₅₀ = 42.12 μM), which is a positive reference. And these copper(II) complexes (IC₅₀ = 10.26-15.82 μM) also exhibited strong ability to inhibit activity of XO, comparable to allopurinol (IC₅₀ = 10.37 μM), which was used as a positive reference. Nickel(II) and manganese(III) complexes 4-6 showed weak inhibitory activity to jack bean urease (IC₅₀ = 4.36-8.25 μM) and no ability to inhibit XO (IC₅₀ > 100 μM).     

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.     

Structural, photophysical and electrochemical studies of [RuN6] complexes having polypyridine and azole mixed-donor sites

The mixed-ligand ruthenium(II) complexes [(phen)₂Ru(pzbzimH₃)](ClO₄)₂·3H₂O (1), [(phen)₂Ru(bzimH)₂](ClO₄)₂·3H₂O (2) and [(bpy)₂Ru(bpybzimH₂)](ClO₄)₂ (3), where phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine, pzbzimH₃ = pyrazole-3,5-bis(benzimidazole), bzimH = benzimidazole and bpybzimH₂ = 6,6′-bis(benzimidazole-2-yl)-2,2′-bipyridine have been synthesized and spectroscopically characterized. The X-ray structures of the three compounds have been determined which show that relative to the polypyridine ligands (phen or bpy) two donor nitrogens of the second ligand occupy cis position. In case of 3, bpybzimH₂ ligand is coordinated in puckered form where its bpy unit acts in a monodentate fashion. The electrochemical properties, absorption and emission spectral characteristics and lifetimes of luminescence decay of the complexes have been compared. Deprotonation of the azole NH moieties of the complexes lead to substantial lowering of redox potentials of the Ru^II/Ru^III couple as well as the MLCT and emission band energies. Spectrophotometric and spectrofluorometric titrations of complexes 1 and 3 have been carried out in 3:2 acetonitrile-water as a function of pH over the range 3.5-12.0 and the pK values have been determined. The kinetic parameters for the decay of the ³MLCT excited states of 1 at different pH at 298 K have been evaluated.     

Structure, speciation, DNA binding and nuclease activity of two bipyridyl-zinc complexes bearing trimethylaminomethyl groups

The Zn(II) complexes of two bipyridyl derivatives with trimethylaminomethyl groups, [Zn(L¹)₃](ZnBr₄)(ClO₄)₂Br₄ · 12H₂O (1) and [Zn(L²)₃](ClO₄)₈ · H₂O (2) (L¹ = [4,4′-(Me₃NCH₂)₂-bpy]²⁺, L² = [5,5′-(Me₃NCH₂)₂-bpy]²⁺ and bpy = 2,2′-bipyridyl), were synthesized and characterized. The structure of complex 1 has been determined by X-ray diffraction, and the configuration of ligand-coordinated Zn(II) ion can be well described as distorted octahedral. Species distribution of both complexes in aqueous solution was investigated by potentiometeric titration. DNA-binding ability of both complexes was studied by UV spectroscopy titration. Under hydrolytic condition, both complexes (150 μM) can effectively cleave plasmid pBR322 DNA from supercoiled to nicked form, giving hydrolysis rate constants of 2.63 × 10⁻⁵ and 9.92 × 10⁻⁵ s⁻¹, respectively (pH 7.75, 37 °C). The result shows that complex 2 is one of the most active artificial nucleases based on zinc.     

Mercaptoethanesulfonic acid (CoM imitator) interaction studies with nickel(II) complexes of pyridyl groups containing tetradentate ligands: Synthesis, structure, spectra and redox properties

Nickel(II) complexes of N,N′-dimethyl-N,N′-bis(pyridyl-2yl-methyl)ethylene-diamine (L¹), N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,2-diaminopropane (L²) and N,N′-dimethyl-N,N′-bis(pyridyl-2-ylmethyl)-1,3-diaminopropane (L³) were prepared and their spectroscopic and redox properties studied. The distorted octahedral structure was determined for [NiL³ClCH₃OH](ClO₄) by using X-ray crystallography. The electronic spectral behavior of the complexes at different pHs was analyzed; it is shown that a new band grew at the expense of the other band intensity in acid media. The redox properties of ligands and their complexes show the peaks of Ni(II) → Ni(III) and Ni(II) → Ni(0) as these were detected at low concentration while Ni(II) → Ni(I) process was detectable clearly at high concentration. Furthermore, the interaction studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN₄ chromophores are discussed.     

4′-(4-Pyridyl)-2,2′:6′,2″-terpyridine as ligand in the lead(II) complexes, [Pb(pyterpy)(MeOH)I2] · MeOH and [Pb(pyterpy)(μ-AcO)]2(ClO4)2

Two new lead(II) complexes with the ligand 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (pyterpy), [Pb(pyterpy)(MeOH)I₂] · MeOH and [Pb(pyterpy)(μ-AcO)]₂(ClO₄)₂, have been synthesized and characterized by CHN elemental analysis, ¹H NMR-, ¹³C NMR-, IR spectroscopy and structurally analyzed by X-ray single-crystal diffraction. The thermal stabilities of these compounds were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). The single crystal X-ray analyses show that the coordination number in these complexes is six with three “pyterpy” N-donor atoms and two or three of the anionic ligands. The arrangement of donor atoms in these complexes suggest a gap or hole in the coordination geometry of the lead atoms, possibly occupied by a stereoactive lone pair of electrons on lead(II) and the coordination sphere is hemidirected. The potentially tetradentate ligand 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine (pyterpy) acts as a tridentate donor to Pb(II). The noncoordinated pyridyl group interacts with hydrogen atoms of adjacent molecules and forms normal hydrogen bonds in [Pb(pyterpy)(MeOH)I₂] · MeOH and weak C-H?N interactions for [Pb(pyterpy)(μ-AcO)]₂(ClO₄)₂, thus extending the monomeric structures into one-dimensional networks.     

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.