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The reduction of molecular oxygen (O2) and hydrogen peroxide (H2O2) by [RuII(edta)(pz)]2− (edta4− = ethylenediaminetetraacetate; pz = pyrazine) has been studied spectrophotometrically and kinetically in aqueous solution. Exposure of the aqua-analogue [RuII(edta)(H2O)]2− to O2 and H2O2 resulted in the formation of [RuIII(edta)(H2O)]− species, with subsequent formation of the corresponding RuVO complex. A working mechanism for the O2 and H2O2 reduction reactions mediated by the RuII(edta) complexes is proposed. The role of the coordinated water molecule (by its absence or presence in the primary coordination sphere) in controlling the mechanistic pathways, outer-sphere or inner-sphere, is discussed.

Reduction of carbon dioxide into formic acid using transition metal complexes as catalysts is a research area of abiding importance. Although ruthenium(II) complexes as ‘molecular catalysts’ have received much attention, use of ruthenium(III) complexes in the selective reduction of carbon dioxide into formic acid has recently been explored. This review focuses on the recent research progress in the use of a ruthenium(III) complex containing the ‘edta’ ligand (edta4- = ethylenediaminetetraacetate) as catalyst or mediator in the catalytic, electro-catalytic and photocatalytic conversion of bicarbonate to formate selectively. Details of the reaction mechanism pertaining to the overall catalytic process are discussed.

This review covers highlights of the work performed in the van Eldik group on inorganic reaction mechanisms over the past two decades in the form of a personal journey. Topics that are covered include, from NO to HNO chemistry, peroxide activation in model porphyrin and enzymatic systems, the wonder-world of RuIII(edta) chemistry, redox chemistry of Ru(iii) complexes, Ru(ii) polypyridyl complexes and their application, relevant physicochemical properties and reaction mechanisms in ionic liquids, and mechanistic insight from computational chemistry. In each of these sections, typical examples of mechanistic studies are presented in reference to related work reported in the literature.

This report provides our research progresses exploring the use of Ru(edta) complexes (edta4− = ethylenediaminetetraacetate) as a small-molecule model for mimicking the activity of the oxidoreductase family of enzymes (viz. oxidases, peroxidases, oxygenases, and reductases) in regard to small molecule activation (or transformation) with a focus on incorporating mechanistic information for a better understanding of the reaction pathways of such enzymatic reactions. Our research contributions reported herein show how the presence and absence of water molecule in the primary coordination sphere of the Ru(edta) complex governs the inner-sphere and outer-sphere pathways for the aforesaid enzyme mimicking activity of Ru(edta). Efforts were made to place our achievements into perspective along with the accomplishment of others.

The advancement of Ru(edta) complexes (edta4− = ethylenediamineteraacetate) mediated reactions, including NO generation and its utilization, has not been systematically reviewed to date. This review aims to report the research progress that has been made in exploring the application of Ru(edta) complexes in trapping and generation of NO. Furthermore, utilization of the potential of Ru(edta) complexes to mimic NO synthase and nitrite reductase activity, including thermodynamics and kinetics of NO binding to Ru(edta) complexes, their NO scavenging (in vitro), and antitumor activity will be discussed. Also, the role of [Ru(edta)(NO)] in mediating electrochemical reduction of nitrite, S-nitrosylation of biological thiols, and cross-talk between NO and H2S, will be covered. Reports on the NO-related chemistry of Fe(edta) complexes showing similar behavior are contextualized in this review for comparison purposes. The research contributions compiled herein will provide in-depth mechanistic knowledge for understanding the diverse routes pertaining to the formation of the [Ru(edta)(NO)] species, and its role in effecting the aforementioned reactions of biochemical significance.

The nitrite anion (NO2−) is an important source of nitric oxide (NO) or nitrosonium cations (NO+). In the present study, we have shown that [RuIII(edta)(NO+)] (edta4− = ethylendiaminetetraacetate) generated via decomposition of [RuIII(edta)(NO2)]2− at lower pH (3.5) could react with H2S to form a putative thionitrous acid (HSNO) bound Ru(edta) complex in aqueous solution. The reaction product [RuIII(edta)(NOSH)]− was characterized by IR, EPR and ESI-MS spectroscopy. Formation of N-coordinated [RuIII(edta)(NOSH)]− was further corroborated by DFT calculations.

Electrochemistry of Ru(edta) complexes (edta4− = ethylenediaminetetraacetate) progressed over a period of several decades, with significant increase in understanding of the electro-catalytic processes involving the substrate coordinated to the metal center. While electrochemistry studies of many Ru(edta) complexes were published in several papers, no attempt has been made to provide a comprehensive and systematic overview of its electrochemical properties, evaluating its application to catalytic electrochemical transformation of small molecules. In this article, results of the electrochemical studies of both mononuclear and binuclear complexes of Ru(edta) are reviewed with regard to electron-transfer reaction mechanism and activity. Their potential to act as redox mediators or catalysts in electrochemical transformations of small molecules and enzymatic reactions, are highlighted. This review aims to contribute to the mechanistic understanding of Ru(edta) complexes in catalysis of such electrochemical transformations.

Soft-robotics is gradually emerging as one of the promising fields of research and innovation. Owing to the blend of material-chemistry and conventional mechanics, complex motions have been successfully generated by flexible polymeric composites that act upon external activation stimuli. However, lack of robust deterministic models which can command reliable actuator performance, hinder their widespread deployments in diverse paradigms. The present article seeks to address the argument by modelling Ionic Polymer Metal Composites (IPMC) as multi-segmented chains of connected rigid bodies. A Cyclic-Coordinate-Descent (CCD) based Inverse Kinematic solver is employed to resolve the redundancy, by minimizing an objective function in joint space at gradual iterative steps. The algorithm is validated for its ability to model dissimilarly doped polymeric curvatures bearing distinct spatial postures. The 2-D shape estimation problem is addressed to generate patterns akin to original IPMCs for deployment on potential applications that anticipate a foresight of actuator geometry.

The reaction of [RuIII(EDTA)(H2O/OH)]−/2− (EDTA4− = ethylenediaminetetraacetate) with bisulfide (HS−) and persulfide (HSS−) leading to the formation of a dinuclear disulfur-bridged [(EDTA)R...

Ionic Polymer Metal Composites (IPMC) have emerged as an actuator for gripping soft as well as rigid objects, owing to their compliance and good scalability. Their use in precision gripping necessitates the absence of any ambivalence in its characterization to ensure grasp stability. This article proposes an alternative approach to model IPMCs, contrary to prior attempts that have employed cantilever deflection theories. The bending patterns of the actuator soaked in distilled water and LiCl solution are studied using a Tractrix based hyper-redundant kinematic algorithm. Two distinct gripper designs comprising of a conventional two jaw as well as a modified passive jaw gripper have been investigated to ascertain their traversed workspaces in the aforementioned mediums. A prior knowledge of this working-area ensures an effective design of target-specific gripper configurations adept to negotiate objects with varied surface profiles. The results obtained after experiments indicate that IPMCs infused in LiCl solution exhibit a characteristic curvilinearity, suited for ensuring surface contact with the object. However the ones hydrated in de-ionized water demonstrate linear bending, apt for generating point contact. Though the passive-jaw gripper showcases a smaller workspace with respect to the active ones, yet it conveys a vital information regarding the contact force exerted on an object surface by the polymer jaw.

[RuIII(EDTA)(H2O)]− (EDTA4− = ethylenediaminetetraacetate) catalyzes the oxidation of biological thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, penicillamine) using H2O2 as precursor oxidant. The kinetics of the oxidation process were studied spectrophotometrically as a function of [RuIII(EDTA)(H2O)]−, [H2O2], [RSH], and pH (4–8). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with [RuIII(EDTA)] catalyst complex to form [RuIII((EDTA)(SR)]2− intermediate species. In the subsequent reaction step the oxidant, H2O2, reacts directly with the coordinated S of the [RuIII((EDTA)(SR)]2− intermediate leading to formation of the disulfido (RSSR) oxidation product (identified by HPLC and ESI-MS studies) of thiols (RSH). Based on the experimental results, a working mechanism involving oxo-transfer from H2O2 to the coordinated thiols is proposed for the catalytic oxidation.

Ionic Polymer Metal Composites (IPMCs) has established itself as an ionomer rendering wide-ranging applications spanning the paradigm of robotics to medical appliances, thereby drawing significant research interests. Prior studies to characterize IPMCs have been conducted over several years but efforts on its kinematic modeling have remained inchoate. The bending profile of IPMC changes when placed in different ionic solutions. The IPMC trace along with its tip location characterizes its complete behavior upon low level actuation. This article aims at identifying the bending patterns of an IPMC actuator, decomposing it as a 20-link hyper-redundant serial manipulator. The Tractrix based inverse kinematics engine is used to study the polymer profile in distilled water, 1.5 N LiCl and NaCl solutions respectively. The proposed algorithm yields a natural curve (Tractrix) which resembles the profile traced by an actuated IPMC strip — enabling its use in potential applications which would require a foresight of the actuator workspace.

The reaction of hydrogen sulfide (H2S) and nitric oxide (NO) is of great physiological significance in human organisms. Our present studies show that Ru(III)(edta) (edta(4-) = ethylenediaminetetraacetate) mediates the S-nitrosylation of bisulfide ion (HS(-)) using NO to form [Ru(III)(edta)(SNO)](2-), the first-ever example of a ruthenium complex containing thionitrite (SNO(-)) in aqueous solution. The reaction product [Ru(III)(edta)(SNO)](2-) was characterized by IR, electron paramagnetic resonance, and electrospray ionization mass spectroscopy. Our studies further show that formation of the putative thionitrous acid coordinated to Ru(III)(edta) does not occur via the reaction of [Ru(III)(edta)NO](-) with HS(-).

The [RuIII(EDTA)(H2O)]− (EDTA4− = ethylenediaminetetraacetate) complex is shown to mediate the oxidation of thiols, RSH (RSH = cysteine, glutathione, N-acetylcysteine, and penicillamine), with peroxomonosulfate ion (HSO5−). The kinetics of the catalytic oxidation process were studied using stopped-flow and rapid scan spectrophotometry as a function of [RuIII(EDTA)(H2O)−], [HSO5−], and [RSH] at a constant pH (6.2). Spectral analyses and kinetic data are suggestive of a catalytic pathway in which the RSH reacts with the [RuIII(EDTA)] catalyst complex to form [RuIII(EDTA)(SR)]2− intermediate species. In a subsequent step the HSO5− ion reacts directly with the coordinated S-atom of [RuIII(EDTA)(SR)]2− yielding the disulfido species, RSSR, as a major oxidation product (as identified using HPLC and ESI-MS analyses) under the employed conditions. Based on the experimental data, a working mechanism is proposed for the [RuIII(EDTA)] catalyzed oxidation of thiols.

Reported in this paper is the first example of a ruthenium(III) complex, [RuIII(edta)] (edta4− = ethylenediaminetetraacetate), that catalyzes the conversion of bicarbonate to formate selectively over a visible light irradiated surface of carbon, nitrogen and sulfur doped TiO2 (represented as C–TiO2, N–TiO2 and S–TiO2, respectively) semiconductor photocatalyst particles. Formation of formate, the only reduction product, was identified by 13C NMR analysis of the reaction mixture. Based on the experimental findings a working mechanism involving activation of bicarbonate (HCO3−) through the formation of a [RuIII(edta)(HCO3)]2− intermediate complex followed by the photochemical reduction of the coordinated bicarbonate to produce formate at the surface of non-metal (C, N, S) doped TiO2 semiconductor particles is proposed. The efficacy of bicarbonate reduction over such photocatalysts decreased in the following order C–TiO2 > N–TiO2 > S–TiO2.

The complex [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) catalyzes the oxidation of captopril (CapSH) using primary oxidants, hydrogen peroxide (H2O2) and peroxomonosulfate ( $$ {\text{HSO}}_{5}^{ - } $$ ). The kinetics of the oxidation reaction were studied as a function of both oxidant (H2O2, $$ {\text{HSO}}_{5}^{ - } $$ ) and substrate (CapSH) concentrations using stopped-flow and rapid scan stopped-flow techniques. Spectral and kinetic data are suggestive of a pathway involving rapid formation of the intermediate complex [RuIII(edta)(CapS)]2− followed by direct attack of the oxidant (H2O2 or $$ {\text{HSO}}_{5}^{ - } $$ ) at the S atom of the coordinated CapS−. ESI–MS and HPLC analysis of the reaction products showed that captopril disulfide (CapSSCap) is the major oxidation product. A probable mechanism in agreement with the spectral and kinetic data is presented.

The reaction of [RuIII(edta)(SCN)]2− (edta4− = ethylenediaminetetraacetate; SCN− = thiocyanate ion) with the peroxomonosulfate ion (HSO5−) has been studied by using stopped-flow and rapid scan spectrophotometry as a function of [RuIII(edta)], [HSO5−], and temperature (15–30oC) at constant pH 6.2 (phosphate buffer). Spectral analyses and kinetic data are suggestive of a pathway in which HSO5− effects the oxidation of the coordinated SCN− by its direct attack at the S-atom (of SCN−) coordinated to the RuIII(edta). The high negative value of entropy of activation (ΔS≠ = −90 ± 6 J mol−1 deg−1) is consistent with the values reported for the oxygen atom transfer process involving heterolytic cleavage of the O-O bond in HSO5−. Formation of SO42−, SO32−, and OCN− was identified as oxidation products in ESI-MS experiments. A detailed mechanism in agreement with the spectral and kinetic data is presented.

The complex [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) catalyzes the oxidation of thiourea (TU) by peroxomonosulfate ion (HSO5 −). The kinetics of the catalytic oxidation process was studied by using stopped-flow and rapid-scan spectrophotometry as a function of [RuIII(edta)(H2O)−], [HSO5 −] and [TU] at a constant pH of 6.2 (phosphate buffer) and temperature of 25 °C. Spectral and kinetic data are suggestive of a catalytic pathway involving rapid formation of a [RuIII(edta)(TU)]− intermediate complex by reaction of [RuIII(edta)(H2O)]− with TU, followed by the oxidation of the coordinated TU in which HSO5 − reacts directly with the S atom of TU coordinated to the RuIII(edta) complex. Analysis of the reaction mixture at the end of the reaction revealed the formation of formamidine disulfide (TU2) as a major product; however, thiourea dioxide (TUO2) and sulfate were also observed if the reaction mixture was kept for longer time periods. A detailed mechanism in agreement with the spectral and kinetic data is presented.

Reaction of [RuIII(EDTA)(CyS)]2− (edta4− = ethylenediaminetetraacetate; CySH = cysteine) with molecular oxygen (O2) have been studied as a function of pH (4.0-8.0) and cysteine concentration (0.2-2.0 mM) at room temperature (25 °C). Biological activities of the [Ru(EDTA)]/CySH/O2 system pertaining to cleavage of supercoiled plasmid DNA to its nicked open circular form has been explored in this work. Results are discussed in regard to the reaction of the ruthenium(III)-complex with molecular oxygen) and a working mechanism is proposed for the biological activities of the ruthenium(III)-complex in the presence of O2.

An effective procedure for selective reduction of O2 to H2O2 exploring the use of hydrogen sulfide, an obnoxious industrial pollutant as reductant is reported herein. The reduction of [Ru(III)(EDTA)pz](-) (EDTA(4-) = ethylenediaminetetraacetate; pz = pyrazine) by hydrogen sulfide resulting in the formation of a red [Ru(II)(EDTA)pz](2-) complex (λmax = 462 nm) has been studied spectrophotometrically and kinetically using both rapid scan and stopped-flow techniques. The time course of the reaction was followed as a function of [HS(-)]i, pH (5.5-8.5), and temperature. Alkali metal ions were found to have a positive influence (K(+) > Na(+) > Li(+)) on the reaction rate. Kinetic data and activation parameters are interpreted in terms of a mechanism (admittedly speculative) involving outer-sphere electron transfer between the reaction partners. Reaction of the red [Ru(II)(EDTA)pz](2-) complex with molecular oxygen regenerates the [Ru(III)(EDTA)pz](-) species in the reacting system along with the formation of H2O2, a partially reduced product of dioxygen (O2) reduction. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented.

The different RuIII(EDTA) complexes (EDTA4− = ethylenediaminetetraacetate) formed in aqueous solution are prospective in many ways and have unique features that make them significant for biochemical applications. The advancement of RuIII(EDTA) mediated bioinorganic reactions in terms of unravelling their mechanistic information has not been systematically reviewed to date. Hence, the subject of this review comprises the most recent advances in RuIII(EDTA) chemistry with regard to bioinorganic reaction mechanisms involving RuIII(EDTA) complexes. This review mainly covers the application of RuIII(EDTA) complexes as catalysts or mediators in homogeneous reaction systems for the activation of redox signalling molecules, viz. H2O2, thiols (RSH), NO and H2S, highlighting the authors’ own recent studies on such catalytic systems. Details of the reaction mechanisms have been revealed for peroxide activation, thiol oxidation, S-nitrosylation of thiols, and dioxygen activation involving RuIII(EDTA) complexes. This review also covers progress in unravelling the mechanism of RuIII(EDTA) mediated oxidation of thiols using KHSO5 as a precursor oxidant.

In this paper, we present the first example of a ruthenium(III) complex, [RuIII(edta)] (edta = ethylenediaminetetraacetate), that catalyzes the electrochemical conversion of hydrogen carbonate to formate selectively. The formation of an [RuIII(edta)(HCO3)]2– species through the reaction of the [RuIII(edta)(H2O)]– catalyst and hydrogen carbonate (HCO3–) was studied kinetically by using the stopped-flow technique. The value of the second-order rate constant for the formation of the [RuIII(edta)(HCO3)]2– complex was 82 ± 7 M–1 s–1 at 25 °C and pH = 6.4. Electrochemical reduction of hydrogen carbonate (HCO3–) was achieved by carrying out constant-potential bulk electrolysis at –0.4 V (vs. SCE) with a mercury-pool cathode at pH = 6.4. The formation of formate as the only reduction product was evidenced by a 13C NMR analysis of the reaction mixture obtained after electrolysis.

Reported here is the first example of a ruthenium(iii) complex [Ru(III)(EDTA)(H2O)](-) (EDTA(4-) = ethylenediaminetetraacetate) that mediates S-nitrosylation of cysteine in the presence of nitrite at pH 4.5 (acetate buffer) and results in the formation of [Ru(III)(EDTA)(SNOCy)](-). The kinetics of the reaction was studied by stopped-flow and rapid-scan spectrophotometry as a function of [Cysteine], [NO2(-)] and pH (3.5-8.5). Formation of [Ru(III)(EDTA)(SNOCy)](-), the product of the S-nitrosylation reaction, was identified by ESI-MS experiments. A working mechanism in agreement with the spectroscopic and kinetic data is presented.

The Fe(III) complex, [FeIII(HQS)3] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO2. The role of interfacial electron transfer in sensitization of TiO2 nanoparticles by surface adsorbed [FeIII(HQS)3] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO2-based dye-sensitized solar cell (DSSC) was fabricated using [FeIII(HQS)3] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm2. The solar to electric power conversion efficiency of the [FeIII(HQS)3] sensitized TiO2-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO2 by other Fe(II)-dye complexes.

Catalytic ability of [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) complex toward oxidation of thiosulfate (S2O32−) in presence of H2O2 has been explored in the present work. The kinetics of the catalytic oxidation of thiosulfate (S2O32−) has been studied spectrophotometrically as a function of [RuIII(edta)], [H2O2], [S2O32−] and pH. Spectral analyses and kinetic data indicate a catalytic pathway involving activation of both substrate (S2O32−) and oxidant (H2O2). Substrate activation pathway involves the formation of a red [RuIII(edta)(S2O3)]3− species through the reaction of the [RuIII(edta)(H2O)]− catalyst complex and the substrate (S2O32−). Hydrogen peroxide reacts directly with thiosulfate coordinated to the RuIII(edta) complex to yield sulfite as immediate oxidation product. Peroxide activation pathway is governed by the formation of [RuV(edta)(O)]− catalytic intermediate which oxidize thiosulfate, however, at slower rate ( k ox 2 = 0.012 M − 1 s − 1 at 25 °C) as compared to the rate of oxidation of the coordinated thiosulfate ( k ox 1 = 0.93 M − 1 s − 1 at 25 °C). Sulfite and sulfate were found to be the oxidation products of the above described catalytic oxidation process. A detailed mechanism in agreement with the spectral and kinetic data is presented.

Nafion based IPMC (Ion Polymeric Metal Composites) has been prepared by using a tetraaquaplatinum (II) complex, [Pt (H2O)4])ClO4)2. Fabrication of a robotic mini-hand comprising five micro-fingers of 5 mm length, 400 μm width at a pitch of 600 μm has been achieved by adopting mechanicalmicro milling' technique. The micro-fingers prepared from the IPMC material were found to actuate successfully under operating voltage of 2.5 V.

The interaction of a RuIII(edta) complex (edta4− = ethylenediaminetetraacetate) with human apo-transferrin (apo-hTf) has been investigated using fluorescence spectroscopic techniques. The results of fluorescence spectral studies point towards static quenching involving binding of RuIII(edta) with apo-hTf. The value of the apparent binding constant (KA) estimated at physiological buffer is 4.72 × 104 M−1. Antiproliferative activity of RuIII(edta) in MCF-7 (breast carcinoma) cells was evidened by microculture tetrazolium test (MTT). Our results taken together are suggestive of the fact that the RuIII(edta) complex can bind to apo-hTf, and induce cell death by inhibiting NF-κB activation. The results of the computational based in silico analysis studies further suggest that the RuIII(edta) that binds apo-hTf to form the [Ru-edta-hTf] complex, for which the binding of [Ru-edta-hTf] complex with transfrrin receptor (TfR) takes place not at the usual binding domain, but in the other domain of the receptor. The alteration of the binding domain of transferrin with its receptor may inactivate the observed transferrin-transferrin receptor mediated biological functions.

This work introduces the concept of a novel thiocyanate ion (SCN-) detecting device. We show proof-of-principle of the device, namely IPMC film prepared by surface modification of the ionic-polymer film. In this work, naked-eye detection of thiocyanate ion (SCN-) by using iron exchanged ionic polymer-metal composites (IPMC) strip has been achieved. It was successfully applied to direct determination of thiocyanate at micro-molar level in water samples. The response time of the sensor in whole concentration ranges is very short (

Selective hydrogenation of bicarbonate to formate catalyzed by a ruthenium(III) complex, [RuIII(edta)] (edta4− = ethylenediaminetetraacetate), at moderate H2 pressure (2–8 atm) and temperature (30–40 °C) is reported. Formation of formate, the only reduction product, was identified by 13C NMR analysis of the resultant reaction mixture. Based on the spectral data, a working mechanism (admittedly speculative) involving the formation of ruthenium(III)-bicarbonate complex, [RuIII(edta)(HCO3)]2−, is proposed for the catalytic reaction.

In this work, we have developed a wrist band using Nafion based ionic polymer-metal composites (IPMC) for sensing the rhythm of human pulse bits. Each pulse bit produces dynamic deformation of IPMC band, and signals (voltage) are generated due to endo-ionic mobility inside the IPMC strip wrapped around the wrist. This work introduces the concept of a novel pulse bits rhythm sensing device. We show proof-of-principle of the mechano-electrical functions of the device, namely IPMC film prepared by surface platinization of the ionic-polymer film.

This paper presents the mechanistic aspects of the -O–O- bond activation by the Ru-pac (pac = polyaminocarboxylate) complex leading to the formation of various catalytic active species, viz. [RuIII(pac)(OOH)]2 − , [RuIV(pac)(OH)] − and [RuV(pac)(O)] − , and their reactivity towards oxidation of a few organic compounds.

This paper presents a short review related to the chemistry of Ru-edta complexes that exhibit catalytic properties in the presence of oxygen atom donors under homogeneous conditions that mimic biological enzymatic hydrocarbon oxidation by cytochrome P450. The results of our recently published work are reviewed in this paper. The mechanism of the reaction of [RuIII(edta)(H2O)]− with different oxygen atom donors leading to the formation of various catalytic active species, viz. [RuIII(edta)(OOH)]2−, [RuIV(edta)(OH)]− and [RuV(edta)(O)]−, along with their spectral characteristics, are analyzed. Details of the reaction mechanisms have been revealed for peroxide, O O bond activation involving the Ru-edta complex. Furthermore, various mechanistic aspects of the oxidation of organic substrate catalyzed by the Ru-edta complexes are also covered in this report.

The kinetics of the reduction of [RuIII(hedtra)(pz)] (hedtra3– = N-hydroxyethylethylenediaminetriacetate; pz = pyrazine) by biologically important reducing agents, Red (Red = L-ascorbic acid, catechol and cysteine), resulting in the formation of the corresponding red-coloured ruthenium(II) complex has been studied spectrophotometrically using both conventional mixing and stopped-flow techniques. The time course of the reaction was followed as a function of [Red], pH and temperature. Alkali metal ions were found to have an insignificant effect on the reaction rate. Kinetic data and activation parameters are interpreted in terms of an outer-sphere electron-transfer mechanism, and discussed with reference to the data reported for the corresponding RuIII–edta (edta4– = ethylenediamineteraacetate) complex. The antibacterial activity of the [RuIII(hedtra)(pz)] complex in inhibiting the growth has been explored. Results of the biological studies have been discussed in terms of the cleavage of chromosomal DNA of the bacteria by the [RuIII(hedtra)(pz)] complex in the presence of cysteine under aerobic conditions.

Hydrogen generation over carbon-, nitrogen- and sulfur-doped TiO2 semiconductor photocatalysts (represented as C–TiO2, N–TiO2 and S–TiO2, respectively) under visible light irradiation has been achieved using various sacrificial electron donors, namely triethanolamine, diethanolamine, monoethanolamine, triethylamine, MeOH, EtOH, EDTA, l-ascorbic acid and phenol. The highest initial rate of H2 production was found to be in the range 1,000–2,200 μmol/g/h at ambient conditions when triethanolamine was used as sacrificial electron donor. The efficacy of hydrogen production over these photocatalysts depends strongly on the nature of the sacrificial electron donor and decreases in the following order: C–TiO2 > S–TiO2 > N–TiO2. The results of the present studies suggest that the rate of H2 production is not simply governed by the reduction potential of the sacrificial electron donor but also by the kinetic barrier of the electron transfer process.

Reaction of [RuII(tpy)(pic)(H2O)]+ (1) with KHSO5 resulting in the formation of [RuIV(tpy)(pic)(O)]+ (2) was studied kinetically as a function of [KHSO5], temperature (15–35°C), and pressure (10–30 MPa) at a fixed pH of 5.1 using spectrophotometric techniques. A suggested mechanism that is in agreement with the observed rate and activation parameters is presented. Complex 1 was found to induce DNA (pBluescript) cleavage in the presence of KHSO5, which proceeds via oxygen transfer from 2.

Fly ash samples collected from the Durgapur Thermal Power Station (DTPS) (Durgapur, West Bengal, India) were designated in regard to their respective collection points, that is, the discharge point...

The kinetics of oxidation of [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) with peroxydisulfate ( ) was studied spectrophotometrically as a function of [ ] at pH 6.0. Oxidation was found to be first order in both ruthenium complex and concentrations. The effect of alkali cations (K+, Na+, and Li+) is attributed to triple-ion formation through an alkali cation bridging between two negatively charged reactants, facilitating the electron-transfer process. Kinetic data and activation parameters are indicative of an outer-sphere electron-transfer process. A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to data reported for the [RuIII(edta)(H2O)]−/XO (XO = H2O2, t-BuOOH, and KHSO5) systems.

Visible light assisted hydrogen evolution from of water has been achieved over the surface of dye modified TiO 2 semiconductor. Thionine, eosin Y, rhodamine B, methylene blue, nile blue A and safranine O were used for surface modification of TiO 2 semiconductor photocatalyst. Upon prolonged illumination (15 h) with visible light (using a 150 W Xenon lamp) production of H 2 in micro-mole level (600–1500 μmol) has been achieved at ambient conditions. Efficacy of the photocatalytic system towards hydrogen evolution is plausibly governed by the excited state redox properties of the dyes adsorbed onto the surface of the TiO 2 photocatalyst.

Reported in this paper is the first example of a ruthenium complex, [Ru(III)(edta)(H(2)O)](-) (edta = ethylenediaminetetra-acetate), that catalyzes the oxidation of hydroxyurea in the presence of H(2)O(2), mimicking the action of peroxidase or catalase and shedding light on their possible mechanism of action.

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [Ru III (hpsd)(tmeda)(H 2 O)] + ( 1 ), [Ru III (hppc)(tmeda)(H 2 O)] 2+ ( 2 ), [Ru III (cpsd)(tmeda)(H 2 O)] + ( 3 ) and [Ru III (cppc)(tmeda)(H 2 O)] 2+ ( 4 ) complexes (where hpsd 2− = N-(hydroxyphenyl)salicylaldiminato); hppc − = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd 2− = (N-(2-carboxyphenyl)salicylaldiminato); cppc − = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1 – 4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis - and trans -stilbenes effectively at ambient temperature using tert -butylhydroperoxide ( t -BuOOH) as terminal oxidant. On the basis of Hammett correlation (log k rel vs. σ + ) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBu t ] radicaloid species is proposed for the catalytic epoxidation process.

Mixed-chelate [Ru(TDL)(XY)Z] type complexes (TDL = tridentate ligand; XY = bidentate ligand and Z = H2O or halide) are known to perform hydrocarbon oxidation under ambient conditions. The subject of this review comprises the use of various tri-dentate polypyridyl and Schiff-base complexes of ruthenium as catalysts for performing oxo-functionalization of a number of organic substrates using various precursor oxidants. The catalytic ability and mechanistic details of such ruthenium based catalyst complexes in the oxidation of saturated and unsaturated hydrocarbons under homogeneous reaction are systematically reviewed in this article highlighting the author’s own recent investigations on such catalytic systems.

RuIII-edta (edta, ethylenediaminetetraacetate) induced cleavage of pBluescript SK+ plasmid DNA in the presence of air with primary oxidant, PO (PO = H2O2, KHSO5) or reductant (L-ascorbic acid) has been studied at pH 7.2. The studies revealed that the RuIII-edta complex induces DNA cleavage in different ways. A mechanism suggesting the involvement of [RuV(edta)O]− in the oxidative cleavage of DNA is proposed for H2O2 and KHSO5. Generation of active oxygen radical species ( /OH•) is proposed for cleavage of DNA with RuIII-edta/ascorbate system. Results are discussed in reference to the data reported for the reaction of Ru-edta with DNA constituents, H2O2, KHSO5, and L-ascorbic acid.

Photocatalytic decoloration kinetics of triazine (Reactive Red 11, Reactive Red 2, and Reactive Orange 84) and vinylsulfone type (Reactive Orange 16 and Reactive Black 5) of reactive dyes have been studied spectrophotometrically by following the decrease in dye concentration with time. At ambient conditions, over 90-95% decoloration of above dyes have been observed upon prolonged illumination (15 h) of the reacting system with a 150 W xenon lamp. It was found that the decoloration reaction followed first-order kinetics. The values of observed rate constants were found to be dependent of the structure of dyes at low dye concentration, but independent at higher concentration. It also reports for the first time the decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO(2) photocatalyst. Rate of decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO(2) photocatalyst is governed by the adsorptivity of the particular dye onto the surface of the TiO(2) photocatalyst.

[RuIV(tpy)(pic)(O)]+ (1) was synthesized by chemical oxidation of the corresponding aqua-complex [RuII(tpy)(pic)(H2O)]+ (2) and characterized by analytical, spectroscopic (UV–vis and IR) and magnetic moment studies. Complex 1 effected epoxidation of styrene and substituted styrenes, cis- and trans-stilbenes and cyclohexene, in CH3CN at room temperature. Epoxides were found to be the major product for styrenes and stilbenes, whereas, the oxidation of cyclohexene yielded allylic oxidation product. Detailed kinetic studies were performed under pseudo-first order conditions of excess alkene concentrations. A working mechanism in agreement with the rate and activation parameters is presented, and the results are discussed in reference to the data reported for the alkene oxidation by relevant RuIV O system in CH3CN.

Kinetics of oxidation of phenol by [RuIV(tpy)(pic)(O)]+ (tpy = 2,2′,6′,2″-terpyridine; pic− = picolinate) (1) has been studied in aqueous solution using a rapid scan stopped-flow spectrophotometer. Under pseudo-first order conditions of excess phenol concentrations, the rate of reaction was found to be first order in respect to both 1 and phenol concentrations. Quinones and [RuII(tpy)(pic)(H2O)]+ (2) were found to be the ultimate products of the reaction. Kinetic results were analyzed by using global kinetic analysis techniques and a working mechanism in agreement with the rate and activation parameters is presented. The experimental results are discussed in reference to data reported for the phenol oxidation by relevant RuIV O systems. Catalytic ability of 2 in effecting phenol oxidation in the presence of t-BuOOH has been explored.

Ruthenium complexes of various chiral ligands viz. porphyrins, Schiff-base, polypyridyl, pyridinebisoxazolines and pyridinebisimidazoline are known to perform asymmetric epoxidation of unfunctionalized alkenes with moderate to high enantioselectivity. The advancement of asymmetric epoxidation catalyzed by ruthenium chiral complexes has not been systematically reviewed till date. Hence, the subject of this review comprises the use of chiral complexes as catalysts for performing enantioselective epoxidation of olefins using various precursor oxidants. The catalytic ability and intriguing aspects of the ruthenium based catalyst complexes in asymmetric epoxidation under homogeneous reaction along with the mechanistic details are systematically reviewed in this article. This review highlights most recent investigations on the catalytic systems with chiral ruthenium complexes for olefin epoxidation.

The [CrIII(α-TDL1*)(bipy)(Cl)] (1) and [CrIII(TDL2*)(bipy)(Cl)] (2) complexes (where H2TDL1* = N-3,5-di-(t-butyl)salicylidine- d -glucosamine, H2TDL2* = N-3,5-di-(tertiarybutyl)salicylidine- l -alanine, bipy = bipyridyl) have been synthesized and characterized by analytical, spectral (UV–vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complexes 1 and 2 catalyzed the epoxidation of styrenes, stilbenes, 1-methylcyclohexene and 1,2-dihydronapthalene using aqueous tert-butyl hydroperoxide (t-BuOOH) as terminal oxidant. The selected alkenes were converted to their corresponding epoxides exhibiting moderate enantioselectivity at ambient temperature.

The [RuII(trpy)(pic)(H2O)]+ (1) was synthesized and characterized by analytical, spectral (UV–Vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complex 1 catalyzes the epoxidation of styrene and stilbenes in presence of tert-butyl hydroperoxide (t-BuOOH) in dichloromethane at room temperature. No epoxide formation was observed in presence of the radical trapping agent (benzoquinone). A mechanism involving formation of [Ru–O(t-Bu)–O] type of radicaloid intermediate as an active intermediate responsible for epoxide formation is proposed for the catalytic epoxidation process.