Determination of bergenin based on the electrochemiluminescence quenching of tris(2,2′‐bipyridine)‐ruthenium(II)

Quenching effects of bergenin, based on the electrochemiluminescence (ECL) of the tris(2,2′‐bipyridyl)‐ruthenium(II) (Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution, is been described. The quenching behavior can be observed with a 100‐fold excess of bergenin over Ru(bpy)₃²⁺. In the presence of 0.1 m TPrA, the Stern–Volmer constant (K_SV) of the ECL quenching is as high as 1.16 × 10⁴ M^?1 for bergenin. The logarithmic plot of the inhibited ECL versus logarithmic plot of the concentration of bergenin was linear over the range 3.0 × 10^?6–1.0 × 10^?4 mol/L. The corresponding limit of detection was 6.0 × 10^?7 mol/L for bergenin (S/N = 3). In the mechanism of quenching it is believed that the competition of the active free radicals between Ru(bpy)₃²⁺/TPrA and bergenin was the key factor for the ECL inhibition of the system. Photoluminescence, cyclic voltammetry, coupled with bulk electrolysis, supports the supposition mechanism of the Ru(bpy)₃²⁺/TPrA–bergenin system. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of p‐Aminobenzenesulfonic acid based on the electrochemiluminescence quenching of tris (2,2’‐bipyridine)‐ ruthenium (II)

This study describes the quenching effects of p‐aminobenzenesulfonic acid (p‐ABSA) based on electrochemiluminescence (ECL) of the tris (2,2^’‐bipyridyl)‐ruthenium(II)(Ru(bpy)₃²⁺)/tri‐n‐propylamine (TPrA) system in aqueous solution. Quenching behaviours were observed with a 200‐fold excess of p‐ABSA over Ru(bpy)₃²⁺. In the presence of 0.1 M TPrA, the Stern‐Volmer constant (K_SV) of ECL quenching was as high as 1.39 × 10⁴ M^‐1 for p‐ABSA. The logarithmic plot of inhibited ECL versus concentration of p‐ABSA was linear over the range of 6.0 × 10^‐6 ‐3.0 × 10^‐4 mol/L. The corresponding limit of detection was 1.2 × 10^‐6 mol/L for p‐ABSA (S/N = 3). The mechanism of quenching is believed to involve an energy transfer from the excited‐state luminophore to a dimer of p‐ABSA and the adsorption of free radicals of p‐ABSA at the electrode surface that impeded the oxidation of the Ru(bpy)₃²⁺/TPrA system. Copyright © 2012 John Wiley & Sons, Ltd.     

Quantitative electrochemiluminescence detection of proteins: Avidin-based sensor and tris(2,2'-bipyridine) ruthenium(II) label

Quantitative electrochemiluminescence (ECL) detection of a model protein, bovine serum albumin (BSA) was achieved via biotin–avidin interaction using an avidin-based sensor and a well-developed ECL system of tris(2,2′-bipyridine) ruthenium(II) derivative as label and tri-n-propylamine (TPA) as coreactant. To detect the protein, avidin was linked to the glassy carbon electrode through passive adsorptions and covalent interaction with carboxylate-terminated carbon nanotubes that was used as binder to immobilize avidin onto the electrode. Then, biotinylated BSA tagged with tris(2,2′-bipyridine) ruthenium(II) label was attached to the prepared avidin surface. After binding of BSA labeled with tris(2,2′-bipyridine) ruthenium(II) derivative to the surface-immobilized avidin through biotin, ECL response was generated when the self-assembled modified electrode was immersed in a TPA-containing electrolyte solution. Such double protein labeling protocol with a biotin label for biorecognition and ruthenium label for ECL detection facilitated the detection of protein compared to the classical double antibody sandwich format. The ECL intensity was linearly proportional to the feed concentration of BSA over two orders of magnitude in the range of 15 nM to 7.5 μM. The detection limit was estimated to be 1.5 nM. Further application to the lysozyme analysis was carried out to validate the present approach for an effective and favorable protocol for the quantitative detection of proteins. The dynamic range of lysozyme was from 0.001 g L⁻¹ to 0.1 g L⁻¹ and the detection limit was 0.1 mg L⁻¹. Electrochemical impedance and cyclic voltammetric measurements along with some necessary control experiments were conducted to characterize the successful formation of self-assembled modified electrodes and to grant the whole detection process.     

Determination of ketotifen fumarate by capillary electrophoresis with tris(2,2′‐bipyridyl) ruthenium(II) electrochemiluminescence detection

On the basis of an europium (III)‐doped Prussian blue analog film modifying platinum electrode as the working electrode, a Ru(bpy)₃²⁺‐based electrochemiluminescence (ECL) assay coupled with capillary electrophoresis has been first established for the determination of ketotifen fumarate (KTF). Analytes were injected onto a separation capillary of 50 cm length (50 μm i.d., 360 μm o.d.) by electrokinetic injection for 10 s at 10 kV. Parameters related to the separation and detection were discussed and optimized. It was proved that 15 mm phosphate buffer at pH 8.0 could achieve the most favorable resolution, and the highest sensitivity of detection was obtained using the detection potential at 1.25 V and 5 mm Ru(bpy)₃²⁺ in 100 mm phosphate buffer at pH 8.0 in the detection reservoir. Under the optimized conditions, the ECL intensity was in proportion to KTF concentration over the range from 3.0 × 10^?8 to 5.0 × 10^?6 g mL^?1 with a detection limit of 2.1 × 10^?8 g mL^?1 (3σ). The relative standard deviations of the ECL intensity and the migration time were 0.95 and 0.26%, respectively. The developed method was successfully applied to determine KTF contents in pharmaceuticals and human urine with recoveries between 99.5 and 107.0%. Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanism of reaction of peroxomethyl radicals with copper(II)(glycine)2 and copper(II)(glycylglycylglycine) in aqueous solutions

The reactions of O₂CH₃ radicals with Cu^II(glycine)₂ and Cu^II(GGG), GGG = glycylglycylglycine, in aqueous solutions were studied.The results demonstrate that the peroxyl radicals oxidize the copper complexes forming relatively stable intermediates of the type L_mCu^III-OOCH₃. These intermediates decompose via oxidation of the ligands glycine and GGG, respectively. Substituents on the alkyl of the peroxyl radical affect somewhat the kinetics of reaction but not the mechanism of oxidation. It is suggested that analogous reactions are probably contributing to the radical-induced deleterious biological processes.     

Preparation of ruthenium(II) chloride complexes of polybasic amines

The reactions of RuCl₂[P(C₆H₅)₃]₃, RuCl₂(tmeda)₂, and RuCl₂(1,5-COD)(tmeda) with polybasic amines such as pyrazole have been studied. From the phosphine complex, a binuclear complex has been isolated in which one pyrazole has been incorporated, while reactions of the latter two with excess pyrazole lead to the replacement of a tmeda ligand by two pyrazoles.     

Effects of flexible bridging ligands on DNA-binding of dinuclear ruthenium(II)-2,2′-bipyridine complexes

For reactions of [{RuCl(bpy)₂}₂(μ-BL)]²⁺ (bpy = 2,2′-bipyridine, BL = H₂N(CH₂)_nNH₂ (n = 4-8, 12), [Ru₂-BL]²⁺) with mononucleotides, the MLCT absorption bands of [Ru₂-BL]²⁺ blue-shifted with hyperchromism for GMP and hypochromism for TMP with time. Reactions of [Ru₂-BL]²⁺ with GMP or TMP proceed via initial Cl⁻ ions replacement by coordination to N7 of GMP and N3 of TMP, respectively. In competition binding experiments for [Ru₂-BL]²⁺ with GMP versus TMP, only GMP selectively coordinated to ruthenium(II). For reactions with calf thymus (CT) DNA, [Ru₂-BL]²⁺ complexes selectively bind to guanine residues of DNA. The higher degrees of binding of [Ru₂-BL]²⁺ to CT-DNA were observed with increasing n values for H₂N(CH₂)_nNH₂, which may be explained by the length of the bridging ligands. Studies on the inhibition of the restriction enzyme Acc I revealed that [Ru₂-BL]²⁺ complexes appear to be covalently favorable for the type of difunctional binding. In addition, it is very interesting to observe that circular dichroism spectroscopy of the supernatants obtained following the reactions of CT-DNA with racemic [Ru₂-BL]²⁺ show enrichments of the solutions in the ΔΔ isomers, demonstrating preferences of the ΛΛ isomers for covalent binding to CT-DNA.     

Spectroelectrochemical studies of some ruthenium(II) complexes with polypyridyl bridging ligands

Ruthenium(II) bis(2,2″-pyridyl) complexes with bridging ligands: 6,7-dichloro-2,3-di(2-pyridyl)quinoxaline; 2,3-di(2-pyridyl)-quinoxaline; 5-methyl-2,3-di(2-pyridyl) quinoxaline; 6,7-dibenzo-2,3-di(2-pyridyl)quinoxaline have been prepared. The electrochemical and spectroscopic properties of these complexes are reported. The resonance Raman spectroelectrochemical results indicate the presence of oxidation state sensitive marker bands in the resonance Raman spectra of the oxidized complexes. The spectroscopic data for the reduced complexes is similar for all four species. The resonance Raman data for the reduced species are dominated by 2,2″-bipyridyl vibrations.     

Reactivity of cationic carbonyl/phosphine ruthenium(II) compounds

Cis(or trans)-[RuCl₂(CO)₂(PPh₃)₂] react with two and one equivalents of AgBF₄ to give the recently reported [Ru(CO)₂(PPh₃)₂][BF₄]₂·CH₂Cl₂ (1) and novel [RuCl(CO)₂(PPh₃)₂][BF₄] · 1/2 CH₂Cl₂ (2), respectively. Cis-[RuCl₂(CO)₂(PPh₃)₂] also reacts with two equivalents of AgBF₄ in the presence of CO to give [Ru(CO)₃(PPh₃)₂][BF₄]₂ (3). Reactions of 1 and 2 with NaOMe and CO at 1 atm produce the carbomethoxy species [Ru(COOMe)₂(CO)₂(PPh₃)₂] (4) and [RuCl(COOMe)(CO)₂(PPh₃)₂] (5), respectively. Complex 4 can also be formed from the reaction of 3 with NaOMe and CO. Alternatively, 4 is formed from cis-[RuCl₂(CO)₂(PPh₃)₂] with NaOMe and CO at elevated pressure (10 atm); if these reactants are refluxed under 1 atm of CO, [Ru(CO)₃(PPh₃)₂] is the product. The reaction of [RuCl(CO)₃(PPh₃)₂][AlCl₄] with NaOMe provides an alternative route to the preparation of 5, but the product is contaminated with [RuCl₂(CO)₂(PPh₃)₂]. Compounds 1. 2, 4 and 5 have been characterised by IR, ¹H NMR and analysis, whilst the formulation of 3 is proposed from spectroscopic data only. This account also examines the reactivity of [Ru(CO)₂(PPh₃)₂][BF₄]₂ · CH₂Cl₂ with NaBH₄, conc. HCl, KI and, finally, MeCOONa in the presence of CO. The products of these reactions, namely cis-[RuH₂(CO)₂(PPh₃)₂], cis-[RuCl₂(CO)₂(PPh₃)₂], cis-[RuI₂(CO)₂(PPh₃)₂] and [Ru(OOCMe)₂(CO)₂(PPh₃)₂], have been identified by comparison of their spectra with previous literature.     

DNA-binding studies of mixed-ligand (ethylenediamine)ruthenium(II) complexes

A series of mixed-ligand ruthenium(II) complexes of the type [Ru(en)(2)bpy](2+) (bpy=2,2-bipyridine; 1), [Ru(en)(2)phen](2+) (phen=1,10-phenantroline; 2), [Ru(en)(2)IP](2+) (IP=imidazo[4,5-f][1,10]phenanthroline; 3), and [Ru(en)(2)PIP](2+) (PIP=2-phenylimidazo[4,5-f][1,10]phenanthroline; 4) have been isolated and characterized by UV/VIS, IR, and (1)H-NMR spectral methods. The binding of the complexes with calf thymus DNA has been investigated by absorption, emission spectroscopy, viscosity measurements, DNA melting, and DNA photo-cleavage. The spectroscopic studies together with viscosity measurements and DNA melting studies support that complexes 1 and 2 bind to CT DNA (=calf thymus DNA) by groove mode. Complex 2 binds more avidly to CT DNA than complex 1, complexes 3 and 4 bind to CT DNA by intercalation mode, 4 binds more avidly to CT DNA than 3. Noticeably, the four complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA.     

η-Allyl-cobalt (II) complexes

(η³-Cyclooctenyl)Co(bisphosphine) compounds react with HBF₄ in the presence of alkenes with oxidation of the metal to give the novel, paramagnetic organocobalt(II) species [(η³-cyclooctenyl)Co(bisphosphine)]⁺BF₄⁻, (η³-2-RC₃H₄)Co(bisphosphine) complexes react similarly. The Co(II) compounds form adducts with CO and NO (the latter being diamagnetic) and undergo facile chemical and electrochemical reduction.     

Interactions of mixed ligand ruthenium(II) complexes containing an amino acid and 1,10-phenanthroline with DNA

Mixed ligand ruthenium(II) complexes containing an amino acid (AA) and 1,10-phenanthroline (phen), i.e. [Ru(AA)(phen)₂]ⁿ⁺ (n=1,2, AA=glycine (gly), l-alanine (l-ala), l-arginine (l-arg)) have been synthesized. The interactions of these complexes and [Ru(phen)₃]²⁺ with DNA have been examined by absorption, luminescence, and circular dichroism spectroscopic methods. Absorption spectral properties revealed that [Ru(AA)(phen)₂]⁺ (AA=gly, l-ala) interacted with CT-DNA by the electrostatic binding mode. [Ru(l-arg)(phen)₂]²⁺ exhibited the greatest hypochromicity, red shift, and binding constant, indicating that this complex may partially intercalate into the base-pairs of DNA. These results were also suggested by luminescence spectroscopy. CD spectral properties have been examined to understand the detailed interactions of the ruthenium(II) complexes with artificial DNA. In the case of Δ-[Ru(l-arg)(phen)₂]²⁺, the solution on adding [poly(dG-dC)]₂ exhibited two well-defined positive peaks, which the shorter and longer wavelength peaks were assigned as originating from the major and the minor groove binding modes, respectively. Then, the solution on adding [poly(dA-dT)]₂ exhibited only one positive peak, which was assigned as a peak corresponding to the minor groove binding mode.     

Self‐quenching in the electrochemiluminescence of Ru(bpy)32+ using ascorbic acid as co‐reactant

In this study, electrochemiluminescence (ECL) of Ru(bpy)₃²⁺ (bpy = 2,2′‐bipyridyl) using ascorbic acid (H₂A) as co‐reactant was investigated in an aqueous solution. When H₂A was co‐existent in a Ru(bpy)₃²⁺‐containing buffer solution, ECL peaks were observed at a potential corresponding to the oxidation of Ru(bpy)₃²⁺, and the intensity was proportional to H₂A concentration at lower concentration levels. The formation of the excited state *Ru(bpy)₃²⁺ was confirmed to result from the co‐reaction between Ru(bpy)₃³⁺and the intermediate of ascorbate anion radical (A⁻•), which showed the maximum ECL at pH = 8.8. It is our first finding that the ECL intensity would be quenched significantly when the concentration of H₂A was relatively higher, or upon ultrasonic irradiation. In most instances, quenching is observed with four‐fold excess of H₂A over Ru(bpy)₃²⁺. The diffusional self‐quenching scheme as well as the possible reaction pathways involved in the Ru(bpy)₃²⁺–H₂A ECL system are discussed in this study. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrochemiluminescence of tris(2,2′‐bipyridyl)ruthenium and its applications in bioanalysis: a review

Electrochemiluminescence (ECL) of tris(2,2’‐bipyridyl)ruthenium(II) [Ru(bpy)₃²⁺] is an active research area and includes the synthesis of ECL‐active materials, mechanistic studies and broad applications. Extensive research has been focused on this area, due to its scientific and practical importance. In this mini‐review we focus on the bio‐related applications of ECL. After a brief introduction to Ru(bpy)₃²⁺ ECL and its mechanisms, its application in constructing an effective bioassay is discussed in detail. Three types of ECL assay are covered: DNA, immunoassay and functional nucleic acid sensors. Finally, future directions for these assays are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Substitution kinetics of tetracarbonyl(η-alkene)ruthenium complexes: ALKENE = ethene and methyl acrylate

The kinetics in heptane of displacement of the alkene ligands ethene and methyl acrylate from Ru(CO)₄(η²-alkene) by P(OEt)₃ have been measured. The reactions occur by reversible dissociation of the alkenes, and activation parameters are compared with those for dissociation of CO from Ru(CO)₅ and for reactions of the corresponding Os complexes. A linear free energy relationship for ligand dissociation from Ru(CO)₅, Ru(CO)₄(C₂H₄) and Ru(CO)₄(MA) has a gradient close to unity, indicating virtually complete bond breaking in the transition states. Competition parameters for reactions of what is probably a solvated Ru(CO)₄S intermediate have been measured for the alkenes and P(OEt)₃, and for eleven other P-donor nucleophiles. Correlations with the electronic and steric properties of the P-donors show negligible dependence on the electron donicity of the nucleophiles and a small but significant dependence on their sizes. The sizes were quantified by Tolman cone angles or by ‘cone angle equivalents’ derived directly from Brown's ligand repulsion energies (E_r). These correlations compared with those, reported elsewhere, for reactions of the probably solvated intermediates Co₂(CO)₅(μ²-C₂Ph₂) and H₃Re₃(CO)₁₁ formed by ligand dissociative processes. In all cases the discrimination between nucleophiles by the intermediates is weak confirming their high reactivity and the borderline nature of the mechanisms of these bimolecular reactions between I_d and I_a.     

Nickel(II) and copper(II) complexes of mixed benzene-triazolehemiporphyrazines

The kinetics of substitution reactions of [η-CpFe(CO)₃]PF₆ with PPh₃ in the presence of R-PyOs have been studied. For all the R-PyOs (R = 4-OMe, 4-Me, 3,4-(CH)₄, 4-Ph, 3-Me, 2,3-(CH)₄, 2,6-Me₂, 2-Me), the reactions yeild the same product [η⁵-CpFe(CO)₂PPh₃]PF₆, according to a second-order rate law that is first order in concentrations of [η⁵-CpFe(CO)₃]PF₆ and of R-PyO but zero order in PPh₃ concentration. These results, along with the dependence of the reaction rate on the nature of R-PyO, are consistent with an associative mechanism. Activation parameters further support the bimmolecular nature of the reactions: ΔH^≠ = 13.4 ± 0.4 kcal mol⁻¹, ΔS^≠ = −19.1 ± 1.3 cal k⁻¹ mol⁻¹ for 4-PhPyO; ΔH^≠ = 12.3 ± 0.3 kcal mol⁻¹, ΔS^≠ = 24.7 ±1.0 cal K⁻¹ mol⁻¹ for 2-MePyO. For the various substituted pyridine N-oxides studied in this paper, the rates of reaction increase with the increasing electron-donating abilities of the substituents on the pyridine ring or N-oxide basicities, but decrease with increasing ¹⁷O chemical shifts of the N-oxides. Electronic and steric factors contributing to the reactivity of pyridine N-oxides have been quantitatively assessed.     

Synthesis and properties of electrochemiluminescent dinuclear Ru(II) complexes assembled with ester-bridged bis(bipyridine) ligands

New bridging ligands, such as bpy-(COOCH₂)-bpy (BL1), mbpy-(CH₂)₃COOCH₂-bpy (BL2), bpy-COO(CH₂)₆OOC-bpy (BL3), and bpy-COOCH₂PhPhCH₂OOC-bpy (BL4), have been synthesized and coordinated to [RuL₂(acetone)₂](PF₆)₂ for various [Ru(L)₂(BL)Ru(L)₂](PF₆)₄-type dinuclear ruthenium complexes (where BL = BL1, BL2, BL3, BL4, and L = bpy, o-phen, DTDP). Their electrochemical redox potentials, spectroscopic properties and relative electrochemiluminescence were investigated in detail. All dinuclear Ru complexes exhibit MLCT (metal-to-ligand charge transfer) absorption and luminescence bands in the visible region. ECL intensities of dinuclear ruthenium(II) complexes were affected not only by the kind of the ligand, but also by the nature of the bridging ligand. Among the synthesized dinuclear Ru complexes, [(DTDP)₂Ru(mbpy)-(CH₂)₃COOCH₂-(bpy)Ru(DTDP)₂](PF₆)₄ exhibited enhanced ECL intensities as high as 2.9 times greater than that of the reference, [Ru(o-phen)₃](PF₆)₂.     

Highly sensitive electrochemiluminescence determination of etamsylate using a low‐cost electrochemical flow‐through cell based on a tris(2, 2'‐bipyridyl)ruthenium(II)–Nafion‐modified carbon paste electrode

A simple and sensitive electrochemiluminescence (ECL) method for the determination of etamsylate has been developed by coupling an electrochemical flow‐through cell with a tris(2,2'‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)–Nafion‐modified carbon electrode. It is based on the oxidized Ru(bpy)₃²⁺ on the electrode surface reacting with etamsylate and producing an excellent ECL signal. Under optimized experimental conditions, the proposed method allows the measurement of etamsylate over the range of 8–1000 ng/mL with a correlation coefficient of r = 0.9997 (n = 7) and a limit of detection of 1.57 ng/mL (3σ), the relative standard deviation (RSD) for 1000 ng/mL etamsylate (n = 7) is 0.96%. The immobilized Ru(bpy)₃²⁺ carbon paste electrode shows good electrochemical and photochemical stability. This method is rapid, simple, sensitive and has good reproducibility. It has been successfully applied to the determination of the studied etamsylate in pharmaceutical preparations with satisfactory results. The possible ECL reaction mechanism has also been discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Generation of free radicals and electrochemiluminescence from simple aromatic molecules in aqueous solutions.

Oxide-covered aluminium electrodes were used to demonstrate that aromatic compounds, such as the simple derivatives of benzene, can be electrochemically excited at cathodically pulse-polarized conductor/insulator/electrolyte (C/I/E) tunnel junction electrodes (e.g. oxide-covered aluminium electrodes). The primary cathodic process at these electrodes was a tunnel emission of hot electrons into an aqueous electrolyte solution. Fluorescence (FL) and electrochemiluminescence (ECL) spectra were compared and the dependence of the electrochemiluminescence on the concentrations of benzene, toluene, phenol, p-cresol and aniline were measured and detailed mechanisms for the present electrochemiluminescence are proposed.     

Micellar effect on the photophysics of heteroleptic ruthenium(II)–phenanthrolinedisulfonato complexes

Luminescent heteroleptic ruthenium(II) complexes of type RuL_nX_3–n [L = 1,10‐phenanthroline (phen), X = 4,7 diphenyl phenanthroline disulfonate, (dpsphen) n = 0,1,2,3] were synthesized and their photophysical properties investigated in homogeneous and cationic (CTAB), anionic (SDS) and nonionic (Triton X‐100) micelles. The luminescent quantum yield and lifetime of the complexes were found to increase in the presence of micellar media and on the introduction of a disulfonate ligand into the coordination sphere. Both electrostatic and hydrophobic interactions play an important role in the micellar media. Thus, by changing the nature of the ligands and the medium, we were able to tune the photophysical properties of Ru(II) complexes. Copyright © 2015 John Wiley & Sons, Ltd.