Multiple one-electron oxidation and reduction of trinuclear bis(2,4-pentanedionato)ruthenium complexes with substituted diquinoxalino[2,3-a:2′,3′-c]phenazine ligands

The complexes (μ₃-L¹/L²)[Ru(acac)₂]₃, acac⁻ = 2,4-pentanedionato, L¹ = 2,3,8,9,14,15-hexachlorodiquinoxalino[2,3-a:2′,3′-c]phenazine and L² = 2,3,8,9,14,15- hexamethyldiquinoxalino[2,3-a:2′,3′-c]phenazine, undergo stepwise one-electron oxidation involving a total of three electrons and stepwise one-electron reduction with three (L²) or four electrons (L¹). All reversibly accessible states were characterized by UV–Vis–NIR spectroelectrochemistry. Oxidation leads to mixed-valent intermediates {(μ₃-L)[Ru(acac)₂]₃}⁺ and {(μ₃-L)[Ru(acac)₂]₃}²⁺ of which the Ru^IIIRu^IIRu^II combinations exhibit higher comproportionation constants K_c than the Ru^IIIRu^IIIRu^II states – in contrast to a previous report for the unsubstituted parent systems {(μ₃-L³)[Ru(acac)₂]₃}^+/2+, L³ = diquinoxalino[2,3-a:2′,3′-c]phenazine. No conspicuous inter-valence charge transfer absorptions were observed for the mixed-valent intermediates in the visible to near-infrared regions. The monocations and monoanions were characterized by EPR spectroscopy, revealing rhombic ruthenium(III) type signals for the former. Electron addition produces ruthenium(II) complexes of the reduced forms of the ligands L, a high resolution EPR spectrum with ¹⁴N and ^35,37Cl hyperfine coupling and negligible g anisotropy was found for {(μ₃-L¹)[Ru(acac)₂]₃}⁻. DFT calculations of (μ₃-L¹)[Ru(acac)₂]₃ confirm several ligand-centered low-lying unoccupied MOs for reduction and several metal-based high-lying occupied MOs for electron withdrawal, resulting in low-energy metal-to-ligand charge transfer (MLCT) transitions.     

Oligothiophene-2-yl-vinyl bridged mono- and binuclear ruthenium(II) tris-bipyridine complexes: Synthesis, photophysics, electrochemistry and electrogenerated chemiluminescence

A series of mono- and binuclear ruthenium(II) tris-bipyridine complexes tethered to oligothienylenevinylenes have been synthesized and characterized by ¹H NMR, ¹³C NMR and TOF-MS spectrometry. Photophysics, electrochemistry and electrogenerated chemiluminescence (ECL) properties of these complexes are investigated. The electronic absorption spectra of the mononuclear ruthenium complexes show a significant red shift both at MLCT (metal-to-ligand charge transfer) and π-π^∗ transitions of oligothienylenevinylenes with increase in the number of thiophenyl-2-yl-vinyl unit. For the binuclear complexes these two absorption bands are overlapped. All the metal complexes have very weak emission compared to that of the reference complex Ru(bpy)²⁺₃. The first reduction potentials of all mononuclear ruthenium complexes are less negative than that of Ru(bpy)²⁺₃, due to the moderate electron-withdrawing effect of oligothienylenevinylenes. For binuclear ruthenium complexes, only one Ru(II/III) oxidation peak (E_1/2 = 0.96 V vs. Ag/Ag⁺) was observed, suggesting a weak interaction between two metal centers. Three successive reduction processes of bipyridine ligands are similar among all ruthenium complexes except for RuTRu, which has a very sharp peak owing to the accumulation of neutral product on the electrode surface. All these ruthenium complexes exhibited different ECL property in CH₃CN solution without any additional reductant or oxidant. For three mononuclear ruthenium complexes, the ECL intensity strengthens with increase in the number of thiophene-2-yl-vinyl unit. However, the ECL efficiency dramatically decreased in the binuclear ruthenium complexes. The ECL efficiencies of all the reported complexes do not exceed that of Ru(bpy)²⁺₃, where the ECL efficiency decreases in the order of RuTRu > Ru3T > Ru2T > RuT > Ru2TRu (RuT,bis-2,2′-bipyridyl-(4-methyl-4′-(2-thienylethenyl)-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru2T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}-2,2′-bipyridine) ruthenium dihexafluorophosphate; Ru3T, bis-2,2′-bipyridyl-(4-methyl-4′-{(E)-2-{(E)-2-[5-((E)-2-thienylethenyl)-thienylethenyl]}}-2,2′-bipyridine) ruthenium dihexafluorophosphate; RuTRu, bis-2,2′-bipyridyl-ruthenium-bis-[2-((E)-4′-methyl-2, 2′-bipyridinyl-4)-ethenyl]-thienyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate; Ru2TRu, bis-2,2′-bipyridyl-ruthenium-(E)-1,2-bis-{2-[2-((E)-4′-methyl-2,2′-bipyridinyl-4)-ethenyl]-thienyl}-ethenyl-bis-2,2′-bipyridyl-ruthenium tetrahexafluorophosphate).     

Photo-activated cytotoxicity of a pyrenyl-terpyridine copper(II) complex in HeLa cells

Terpyridine copper(II) complexes [Cu(L)₂](NO₃)₂, where L is (4′-phenyl)-2,2′:6′,2′′-terpyridine (ph-tpy in 1) and [4′-(1-pyrenyl)]-2,2′:6′,2′′-terpyridine (py-tpy in 2), are prepared, characterized and their photocytotoxic activity studied. The crystal structure of complex 1 shows distorted octahedral CuN₆ coordination geometry. The 1:2 electrolytic and one-electron paramagnetic complexes show a visible band near 650 nm in DMF–H₂O. The complexes show emission band at 352 nm for 1 and 425 nm for 2 when excited at 283 and 346 nm, respectively. The Cu(II)–Cu(I) redox couple is observed near −0.2 V versus SCE in DMF–0.1 M TBAP. The complexes are avid partial-intercalative binders to calf thymus DNA giving binding constant (K_b) values of ∼10⁶ M⁻¹. Complex 2 with its photoactive pyrenyl moiety exhibits significant photocleavage of pUC19 DNA in red light via singlet oxygen pathway. Complex 2 also exhibits significant photo-activated cytotoxicity in HeLa cancer cells in visible light giving IC₅₀ value of 11.9 μM, while being non-toxic in dark with an IC₅₀ value of 130.5 μM.     

Electrochemiluminescence from Ru(bpy)3 immobilized in poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)-poly(vinyl alcohol) composite films

Electrochemical behavior and electrogenerated chemiluminescence (ECL) of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) immobilized in poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)-poly(vinyl alcohol) (PEDOT/PSS-PVA) composite films via ion-exchange have been investigated with tripropylamine (TPA) as the co-reactant at a glassy carbon electrode. The immobilized Ru(bpy)₃²⁺ performed a surface-controlled electrode reaction. The Ru(bpy)₃²⁺ modified electrode showed a fast ECL response to TPA, and was used for the ECL detection of TPA with high sensitivity. The ECL intensity was linearly related to concentrations of TPA over the range from 0.50 μmol L⁻¹ to 0.80 mmol L⁻¹, and the detection limit was 0.10 μmol L⁻¹ (S/N = 3). The as-prepared electrode exhibited good precision and long-term stability for TPA determination.     

Solid-state electrochemiluminescence sensor through the electrodeposition of Ru(bpy)3/AuNPs/chitosan composite film onto electrode

Tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) has been successfully immobilized onto electrode through the electrodeposition of Ru(bpy)₃²⁺/AuNPs/chitosan composite film. In the experiments, chitosan solution was first mixed with Au nanoparticles (AuNPs) and Ru(bpy)₃²⁺. Then, during chronopotentiometry experiments in this mixed solution, a porous 3D network structured film containing Ru(bpy)₃²⁺, AuNPs and chitosan has been electrodeposited onto cathode due to the deposition of chitosan when pH value is over its pK_a (6.3). The applied current density is crucial to the film thickness and the amount of the entrapped Ru(bpy)₃²⁺. Additionally, these doping Ru(bpy)₃²⁺ in the composite film maintained their intrinsic electrochemical and electrochemiluminescence activities. Consequently, this Ru(bpy)₃²⁺/AuNPs/chitosan modified electrode has been used in ECL to detect tripropylamine, and the detection limit was 5 × 10⁻¹⁰ M.     

Tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence sensor based on carbon nantube dispersed in sol-gel-derived titania-Nafion composite films

A highly sensitive and stable tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) electrogenerated chemiluminescence (ECL) sensor was developed based on carbon nanotube (CNT) dispersed in mesoporous composite films of sol-gel titania and perfluorosulfonated ionomer (Nafion). Single-wall (SWCNT) and multi-wall carbon nanotubes (MWCNT) can be easily dispersed in the titania-Nafion composite solution. The hydrophobic CNT in the titania-Nafion composite films coated on a glassy carbon electrode certainly increased the amount of Ru(bpy)₃²⁺ immobilized in the ECL sensor by adsorption of Ru(bpy)₃²⁺ onto CNT surface, the electrocatalytic activity towards the oxidation of hydrophobic analytes, and the electronic conductivity of the composite films. Therefore, the present ECL sensor based on the CNT-titania-Nafion showed improved ECL sensitivity for tripropylamine (TPA) compared to the ECL sensors based on both titania-Nafion composite films without CNT and pure Nafion films. The present Ru(bpy)₃²⁺ ECL sensor based on the MWCNT-titania--Nafion composite gave a linear response (R² = 0.999) for TPA concentration from 50 nM to 1.0 mM with a remarkable detection limit (S/N = 3) of 10 nM while the ECL sensors based on titania-Nafion composite without MWCNT, pure Nafion films, and MWCNT-Nafion composite gave a detection limit of 0.1 μM, 1 μM, and 50 nM, respectively. The present ECL sensor showed outstanding long-term stability (no signal loss for 4 months).     

Solid-state anion interactions in the diastereoisomers of dinuclear ruthenium complexes based on 2,2′-bipyrimidine

The cations in the solid-state structures of meso-(ΛΔ)-[{Ru(bpy)₂}₂(μ-bpm)](PF₆)₄, meso-(ΛΔ)-[{Ru(Me₂bpy)₂}₂(μ-bpm)](tos)₄ · 2CH₃OH · 4H₂O and meso-(ΛΔ)-[{Ru(Me₄bpy)₂}₂(μ-bpm)](tos)₄ · 26H₂O (bpm = 2,2′-bipyrimidine; bpy = 2,2′-bipyridine; Me₂bpy = 4,4′-dimethyl-2,2′-bipyridine; Me₄bpy = 4,4′,5,5′-tetramethyl-2,2′-bipyridine; tos⁻ = toluene-4-sulfonate anion) exhibit similar features including comparable bond lengths and angles, and metal–metal separations of 5.56–5.59 Å. The counter-ions present in the structures reside in the clefts above and below the plane of the bridging ligand, but show considerable variation in location compared with their known occupancy in solution.     

High throughput method for the analysis of cetrizine hydrochloride in pharmaceutical formulations and in biological fluids using a tris(2,2'-bipyridyl)ruthenium(II)-peroxydisulphate chemiluminescence system in a two-chip device

A fast, economic and sensitive chemiluminescence (CL) method has been developed for the analysis of cetrizine hydrochloride (CET) in pharmaceutical formulations and in biological fluids. The CL method is based on the oxidation of tris(2,2′-bipyridyl)ruthenium(II) (Ru (bipy)₃²⁺) by peroxydisulphate in a two-chip device. Up to 180 samples can be analysed per hour, consuming only minute quantities of reagents. Three instrumental setups were tested to find the most economical, sensitive and high throughput setup. In the first setup, a continuous flow of sample and CL reagents was used, whereas in the second setup, a fixed volume (2 μL) of (Ru (bipy)₃²⁺) was introduced into a continuous infusion of peroxydisulphate and the sample. In the third design, a fixed volume of sample (2 μL) was injected while the CL reagents were continuously infused. Compared to the first setup, a 200% signal enhancement was observed in the third setup. Various parameters that influence the CL signal intensity, including pH, flow rates and reagent concentrations, were optimized. A linear response was observed over the range of 50 μg L⁻¹ to 6400 μg L⁻¹ (R² = 0.9959) with RSD values of 1.1% (n = 15) for 1000 μg L⁻¹. The detection limit was found to be 15 μg L⁻¹ (S/N = 3). The amount of consumed sample was only 2 μL, from which the detected amount of CET was found to be 6.5 × 10⁻¹⁴ mol. This procedure was successfully applied to the analysis of CET in pharmaceutical formulations and biological fluids.     

Crosslinked poly(ethylene oxide) fouling resistant coating materials for oil/water separation

Potential fouling reducing coating materials were synthesized via free-radical photopolymerization of aqueous solutions of poly(ethylene glycol) diacrylate (PEGDA). Crosslinked PEGDA (XLPEGDA) exhibited high water permeability and good fouling resistance to oil/water mixtures. Water permeability increased strongly with increasing the water content in the prepolymerization water mixture, going from 10 to 150 L μm/(m² h bar) as prepolymerization water content increased from 60 to 80 wt.%. However, molecular weight cutoff decreased as water content increased. These materials were applied to polysulfone (PSF) UF membranes to form coatings on the surface of the PSF membranes. Oil/water crossflow filtration experiments showed that the coated PSF membranes had water flux values 400% higher than that of an uncoated PSF membrane after 24 h of operation, and the coated membranes had higher organic rejection than the uncoated membranes.     

Synthesis and characterization of some new mononuclear ruthenium complexes containing 4-(un)substituted dipyridylpyrazole ligands

A mononuclear ruthenium complex [Ru(bpy)₂(bpp)](PF₆) (1) and its halogenated and nitro derivatives [Ru(bpy)₂(Xbpp)](PF₆) (bpy = 2,2′-bipyridine; bpp = 3,5-bis(2-pyridyl)pyrazole; X = Cl, 2; X = Br, 3; X = I, 4; X = NO₂, 5) have been synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, elemental analysis. Complexes 2–5 have been further confirmed by X-ray diffraction. Their UV–Vis and emission spectroscopies, electrochemical measurements and acid–base properties are described. The results presented here reveal that the introduction of Cl, Br, I and NO₂ groups to the coordinated bpp⁻ ligand makes the absorption and emission maxima of the parent complex 1 blue-shifted, the oxidation potential of the Ru^II/Ru^III couple increased and the pK_a value decreased obviously. In addition, significant quenching of the emission by these groups is also observed.     

Tuning photophysical properties with ancillary ligands in Ru(II) mono-diimine complexes

The series of complexes [XRu(CO)(L-L)(L′)₂][PF₆] (X = H, TFA, Cl; L-L = 2,2′-bipyridyl, 1,10-phenanthroline, 5-amino-1,10-phenanthroline and 4,4′-dicarboxylic-2,2′-bipyridyl; L′₂ = 2PPh₃, Ph₂PC₂H₄PPh_2, Ph₂PCHCHPPh₂) have been synthesized from the starting complex K[Ru(CO)₃(TFA)₃] (TFA = CF₃CO₂) by first reacting with the phosphine ligand, followed by reaction with the L-L and anion exchange with NaPF₆. In the case of L-L = phenanthroline and L′₂ = 2PPh₃, the neutral complex Ru(Ph₃P)(CO)(1,10-phenanthroline)(TFA)₂ is also obtained and its solid state structure is reported. Solid state structures are also reported for the cationic complexes where L-L = phenanthroline, L₂ = 2PPh₃ and X = Cl and for L-L = 2,2′-bipyridyl, L₂ = 2PPh₃ and X = H. All the complexes were characterized in solution by a combination of ¹H and ³¹P NMR, IR, mass spectrometry and elemental analyses. The purpose of the project was to synthesize a series of complexes that exhibit a range of excited-state lifetimes and that have large Stokes shifts, high quantum yields and high intrinsic polarizations associated with their metal-to-ligand charge-transfer (MLCT) emissions. To a large degree these goals have been realized in that excited-state lifetimes in the range of 100 ns to over 1 μs are observed. The lifetimes are sensitive to both solvent and the presence of oxygen. The measured quantum yields and intrinsic anisotropies are higher than for previously reported Ru(II) complexes. Interestingly, the neutral complex with one phosphine ligand shows no MLCT emission. Under the conditions of synthesis some of the initially formed complexes with X = TFA are converted to the corresponding hydrides or in the presence of chlorinated solvents to the corresponding chlorides, testifying to the lability of the TFA Ligand. The compounds show multiple reduction potentials which are chemically and electrochemically reversible in a few cases as examined by cyclic voltammetry. The relationships between the observed photophysical properties of the complexes and the nature of the ligands on the Ru(II) is discussed.     

Glucose concentration determination based on silica sol-gel encapsulated glucose oxidase optical biosensor arrays

Optical biosensor arrays for rapidly determining the glucose concentrations in a large number of beverage and blood samples were developed by immobilizing glucose oxidase (GOD) on oxygen sensor layer. Glucose oxidase was first encapsulated in silica based gels through sol-gel approach and then immobilized on 96-well microarrays integrated with oxygen sensing film at the bottom. The oxygen sensing film was made of an organically modified silica film (ORMOSIL) doped with tris(4,7-diphenyl-1,10-phenanthroline) ruthenium dichloride (Ru(dpp)₃Cl₂). The oxidation reaction of glucose by glucose oxidase could be monitored through fluorescence intensity enhancement due to the oxygen consumption in the reaction. The luminescence changing rate evaluated by the dynamic transient method (DTM) was correlated with the glucose concentration with the wide linear range from 0.1 to 5.0 mM (Y = 13.28X − 0.128, R = 0.9968) and low detection limit (0.06 mM). The effects of pH and coexisting ions were systemically studied. The results showed that the optical biosensor arrays worked under a wide range of pH value, and normal interfering species such as Na⁺, K⁺, Cl⁻, PO₄³⁻, and ascorbic acid did not cause apparent interference on the measurement. The activity of glucose oxidase was mostly retained even after 2-month storage, indicating their long-term stability.     

Facilitated transport of Am(III) through a flat-sheet supported liquid membrane (FSSLM) containing tetra(2-ethyl hexyl) diglycolamide (TEHDGA) as carrier

Facilitated transport of Am(III) in nitric acid medium using tetra(2-ethyl hexyl) diglycolamide (TEHDGA) in n-dodecane as carrier was studied. It was aimed at finding out the physico-chemical model for the transport of Am(III) using TEHDGA/n-dodecane as carrier under various experimental parameters like feed acidity, carrier concentration, varying strippant, varying membrane pore size, etc. The feed acidity and carrier concentrations were varied from 1 M to 6 M HNO₃ and 0.1 M to 0.3 M TEHDGA/n-dodecane, respectively. The transport of Am(III) increased with increase in feed acidity and carrier concentration reaching maximum at 3 M HNO₃ and 0.2 M TEHDGA/n-dodecane, respectively. Several stripping agents were tested and 0.1 M HNO₃ was found to be the most suitable stripping agent for this system. Almost quantitative transport of Am(III) was observed at about 180 min with feed acidity of 3 M HNO₃, 0.1 M HNO₃ as strippant and 0.2 M TEHDGA/n-dodecane as carrier. The pore size of the membrane support was varied from 0.20 μm to 5 μm and the permeation coefficient increased with increase in pore size up to 0.45 μm (2.43 × 10⁻³ cm/s), and then decreased with further increase in pore size. The plot between permeation coefficient vs. (membrane thickness)⁻¹ was linear which showed that the Am(III) transport was membrane diffusion limited. The membrane diffusion coefficient calculated from the graph was found to be 1.27 × 10⁻⁶ cm²/s and its theoretical value was 1.22 × 10⁻⁶ cm²/s. The stability of the carrier against leaching out of the membrane support as well as the integrity of membrane support was studied over a period of 30 days and was found to be satisfactory within the studied time period.     

A computational study on mixed-ligand N2P3 donor-set iron(II) and ruthenium(II) classical and non-classical hydrides

Iron and ruthenium classical and non-classical hydrides of the type [MH(N–N)P₃]⁺ and [M(η²-H₂)(N–N)P₃]²⁺ {M = Fe, Ru; N–N = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen); P = phosphites} were reported in 2004 together with an evaluation of the pseudo-aqueous pK_a values of the η²-H₂ complexes. The non-classical hydrides, even if doubly charged, showed a relatively low acidity, their pK_a values ranging between −5.4 and −4.3. Moreover, ruthenium(II) derivatives showed to be more acidic than the corresponding iron(II) complexes. Information about the structural and electronic proprieties of complexes of this type, which allowed to better understand the role of both the metal centres and the ancillary ligands in the acidity of the co-ordinated hydrogen molecule, was obtained on the basis of DFT B3LYP calculations.     

Determination of β-blockers in pharmaceutical preparations and human urine by high-performance liquid chromatography with tris(2,2′-bipyridyl)ruthenium(II) electrogenerated chemiluminescence detection

A highly selective and sensitive detection method based on tris(2,2′-bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] electrogenerated chemiluminescence (ECL) has been developed for the quantitative determination of β-blockers in both pharmaceutical preparations and human urine samples. The ECL emission is based on the reaction between electro-oxidized Ru(bpy)₃³⁺ and the secondary amino groups on the β-blockers. The ECL intensities for the β-blockers were strongly dependent on the pH at which the ECL detections were conducted, with the maximum intensities being obtained at pH 9.0. Under the optimal condition, the detection limit for atenolol and metoprolol were almost 0.5 μM (50 pmol) and 0.08 μM (8 pmol), respectively, with S/N of 3 and a linear working range that extends four orders of magnitude with relative standard deviations below 5% for 10 replicate injected samples. The concentrations of atenolol and metoprolol were determined in pharmaceutical preparations using flow injection analysis with Ru(bpy)₃²⁺ ECL detection based on standard addition method. The determined values by the present method showed acceptable agreement with the stated values by manufacturers. The determination of the five β-blockers in human urine samples was performed using HPLC-Ru(bpy)₃²⁺ ECL detection. The resulting chromatogram was much simpler than that obtained with HPLC-UV absorbance detection.     

A novel tris(2,2′-bipyridine)ruthenium(II)/tripropylamine cathodic electrochemiluminescence in acetonitrile for the indirect determination of hydrogen peroxide

A novel tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) cathodic electrochemiluminescence (ECL) was generated at −0.78 V at the Pt electrode in acetonitrile (ACN), which suggested that the cathodic ECL differed from conventional cathodic ECL. It was found that tripropylamine (TPrA) could enhance this cathodic ECL and the linear range (log-log plot) was 0.2 μM-0.2 mM. In addition, hydrogen peroxide (H₂O₂) could inhibit the cathodic ECL and was indirectly detected with the linear range of 27-540 μM. The RSD (n = 12) of the ECL intensity in the presence of 135 μM H₂O₂ was 0.87%. This method was also demonstrated for the fast determination of H₂O₂ in disinfectant sample and satisfactory results were obtained.     

Flow-injection chemiluminescent determination of metoclopramide hydrochloride in pharmaceutical formulations and biological fluids using the [Ru(dipy)(3)(2+)]-permanganate system

A flow-injection (FI) methodology using (2,2′-dipyridyl) ruthenium(II) [Ru(dipy)₃²⁺] chemiluminescence (CL) was developed for the rapid and sensitive determination of metoclopramide hydrochloride. The method is based on the CL reaction of metoclopramide with Ru(dipy)₃²⁺ and KMnO₄ in a sulfuric acid medium. Under the optimum conditions, a calibration graph was obtained over the concentration range 0.005-3.5 μg ml⁻¹ with a limit of detection (S/N=2) of 1 ng ml⁻¹. The correlation coefficient was 0.99993 (n=8) with a relative standard deviation of 0.48% for 10 determinations of 1 μg ml⁻¹ of drug. The method was successfully applied to the determination of metoclopramide in pharmaceutical preparations and biological fluids after IP administration of 25 mg kg⁻¹ dose to rats. The elimination half-life was 2.5±0.4 h.     

Synthesis and properties of 6,6′-dithienyl-4,4′-bipyrimidine and its hetero- and homo-leptic Ru(II) complexes

Hetero- and homo-leptic Ru(II) complexes of a new 4,4′-bipyrimidine ligand, th₂bpm (6,6′-di(2″-thienyl)-4,4′-bipyrimidine), have been synthesized and characterized. The parent ligand th₂bpm has electron rich thiophene units on the periphery of a bidentate ligand which is capable of binding to metal ions. The heteroleptic complex of th₂bpm [Ru(bpy)₂th₂bpm]²⁺ (bpy = 2,2′-bipyridine) exhibits a Ru-to-bpm metal-to-ligand charge transfer (MLCT) absorption centered at 547 nm and a Ru-to-bpy MLCT absorption centered at 438 nm. The assignment of the low energy absorption is supported by the relative ease of electrochemical reduction of the new complex as compared to [Ru(bpy)₃]²⁺. The homoleptic complex, [Ru(th₂bpm)₃]²⁺, exhibits a Ru-to-bpm MLCT absorption at slightly higher energy (544 nm). Both complexes are emissive at room temperature in fluid solution and 5 is one of the lowest energy emitters based on tris-bidentate Ru(II) complexes known (λ_max = 770 nm). The luminescence spectra is red-shifted compared to [Ru(bpy)₃]²⁺ and this effect is ascribed to the delocalization in the acceptor ligand.     

Highly electrochemiluminescent Ru(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one ligand

A series of new ruthenium(II) complexes containing 1,3-dihydro-1,1,3,3-tetramethyl-7,8-diazacyclopenta[1]phenanthren-2-one (DTDP) ligand, such as [Ru(DTDP)_n(L)_3−n]²⁺ (L = 2,2′-bipyridyl (bpy), 4,4′-dimethyl-2,2′-bipyridyl (dmbpy), o-phenanthroline (o-phen), 5-chloro-o-phenanthroline (o-phen-Cl), 2,2′-bipyridine-4,4′-dicarboxaldehyde (bpy-(CHO)₂), n = 1, 2, 3) were synthesized and examined as ECL materials. All the complexes were characterized in terms of electrochemical redox potential and relative ECL intensity, and were compared to the well-known tris(o-phenanthroline) ruthenium(II) complex. Most of the synthesized Ru(II) complexes containing the DTDP ligand exhibited more intense ECL emissions than [Ru(o-phen)₃]²⁺. In particular, the ECL intensities of [Ru(DTDP)(o-phen)₂]²⁺ and [Ru(DTDP)(bpy-(CHO)₂)₂]²⁺ were observed to be as high as 9-fold and 20-fold greater, respectively, than the ECL intensity of [Ru(o-phen)₃]²⁺.     

Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), 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), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).