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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.

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.

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.

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.

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 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.

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.

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.

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.

Simultaneous photocatalytic degradation of non-emissive dye, acid blue1 (AB1) and emissive dyes (eosinY or thionine) in air-equilibrated aqueous suspension of TiO 2 semiconductor photocatalyst has been achieved at ambient conditions. Under visible light irradiation AB1 undergoes appreciable degradation in presence of a sensitizing dye (eosinY or thionine). However, concomitant decoloration of eosinY (EY) or thionine (Th) due to self-sensitized degradation was also noticed. Mechanistic proposals for the photocatalytic degradation of AB1 using a 150 W Xe lamp with a UV-filter ( λ > 420 nm) as well as without a UV-filter, are discussed. Formation of reactive O 2 − / HO 2 radicals is proposed to be responsible for the degradation of the selected dyes, AB1, EY and Th.

Kinetics of oxidation of catechol (H2cat) to benzoquinone (BQ) and, ascorbate (HA−) to dehydroascorbic acid (A) by [RuIII(tpy)(pic)(OH)]+ (1) (tpy = 2,2’6’,2”-terpyridine; pic− = picolinate) have been studied as function of [H2cat] (or [HA−]), ionic strength (0.01 − 0.25 M), temperature (10–30 °C) at a constant pH = 3.2, using stopped-flow and rapid-scan diode array spetrophotometric techniques. The rate of reaction of 1 with HA− was found to be very fast as compared to that of with H2cat. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism. Analysis of spectral and kinetic data revealed that the reaction of 1 with catechol proceeds by a straightforward outer-sphere electron transfer pathway, whereas, reduction of 1 with HA− involves ion-pair formation.

Mixed-ligand complexes of ruthenium(III) containing tridentate chiral Schiff-base ligands (H2TDL*s) derived from condensation of either d -glucose amine or l -alanine with 3,5-di-tertiarybutylsalicyldehyde, and triphenylphosphine (PPh3) or 2,2′-bipyridine (bipy) have been synthesized. The ruthenium(III)-complexes, [ R u III Cl ( TD L 1 * ) ( PP h 3 ) 2 ] {( H 2 TD L 1 * = N - 3 , 5 -di- ( tertiarybutyl ) salicylidine- D -glucosamine )},(1) [ R u III Cl ( TD L 2 * ) ( PP h 3 ) 2 ] H 2 TD L 2 * = { N - 3 , 5 -di- ( tertiarybutyl ) salicylidine- L -alanine } (2) and [ R u III ( TD L 2 * ) ( bipy ) H 2 O ] Cl (bipy = 2,2′-bipyridine) (3) were characterized by analytical, spectral (UV–vis and IR), molar conductivity, magnetic moment and electrochemical studies. Complex 1 exhibited remarkable enantioselcetivity toward epoxidation of unfunctionalized alkenes using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides in the 70–95% ee at ambient temperature. A lesser enantioselectivity was observed when complexes 2 and 3 were used in the epoxidation of enlisted alkenes under identical experimental conditions. A mechanism involving intermediacy of a high-valent Ru(V)-oxo species is proposed for the catalytic epoxidation process.

Visible light assisted photodegradation of various halocarbons, viz. chloro-phenols, trichloroethylene, 1,2-dichloroethane and 1,4-dichlorobenzene, has been achieved on the surface of dye-modified TiO 2 semiconductor. Thionine, eosinY, rhodamineB, methyleneblue, nileblueA and safranineO were used for the modification of TiO 2 semiconductor photocatalyst. After 5 h of irradiation with a 150 W Xenon lamp, over 55–72% degradation of pollutants has been achieved. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO 2 conduction band and formation of reactive • O 2 - / • HO 2 radicals, is proposed for the degradation of the enlisted organics to carbon dioxide. Efficacy of the photocatalytic system towards halocarbon degradation has been discussed in regard to excited state redox properties of the dyes selected for this study. Formation of • O 2 - radical has been substantiated by using a chemiluminescent probe luminol.

Stopped-flow kinetic measurements were used to compare the reactivities of [Ru(medtra)(H2O)] (medtra3− = N-methylethylenediaminetriacetate) (1) and [Ru(hedtra)(H2O)] (2) (hedtra3− = N-hydroxyethylethylenediaminetriacetate) with NO in aqueous solution at 15 °C, pH 7.2 (phosphate buffer). The measured second-order rate constants (3 × 103 and 6 × 104 M−1 s−1 for 1 and 2, respectively) are three to four order of magnitudes lower than that for the reaction between [RuIII(edta)(H2O)]− (3) with NO. However, NO scavenging studies of complexes 1–3, conducted by measuring the difference in nitrite production between treated and untreated murine macrophage cells, revealed that despite being less kinetically reactive toward NO, the [Ru(medtra)(H2O)] complex exhibited the highest NO scavenging ability and lowest toxicity of compounds 1–3.

A mixed-ligand ruthenium(III) catalyst complex, [Ru III (TDL*)(bipy)(H 2 O)]Cl ( 1 ) (TDL* = N -3,5-di-( t -butyl)salicylidine- d -glucosamine; bipy = 2,2′-bipyridine) exhibited catalytic activity toward enantioselective alkene epoxidation using tert -butyl hydroperoxide as terminal oxidant. Styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 1-methylcyclohexene and 1,2-dihydronaphthalene were effectively converted to their organic epoxides with moderate enantioselectivity (37–47% ee) at ambient temperature. A mechanism involving the formation of a high-valent Ru(V)-oxo species, and the subsequent oxo-transfer to the alkene through a metallaoxetane intermediate is proposed.

In this paper, visible light assisted degradation of various pollutants using different methods has been briefly reviewed. These methods have been broadly divided into two main categories. In the first category, the use of TiO2 semiconductor facilitating the photooxidative degradation of organic pollutants has been presented. This semiconductor has been treated in several ways. A major aim of these treatments is to maximize the range of wavelength in the visible light region for wastewater treatment. In the second category, various ways of degrading organic pollutants without the use of TiO2 semiconductor have been briefly outlined. The role of Fe(II)/Fe(III), etc., species in the sensitization process of various substrates helping it in the process to photocatalytic degradation reactions of organic pollutants has been highlighted. Also, the usage of semiconductors other than TiO2 has been critically analyzed.

The interaction of [PdII(mida)(Cl)]− (1) (mida2− = N-methyliminodiacetate) and [PdII(pydc)(Cl)]− (2) (pydc2− = pyridyl-2,6-dicarboxylate) with adenosine-5′-monophosphate (AMP), inosine-5′-monophosphate (IMP) and glutathione (GSH) was studied kinetically as a function of [L] (L = AMP, IMP, GSH) and [Cl−] and temperatures (10–35 °C) at pH 4.0. The kinetic results suggest that the reaction of 1 and 2 with the 5′-nucleotides (AMP, IMP) is characterized by the hydrolysis of chloro-complexes followed by the aquo-substitution with purine based 5′-nucleotides through its N7 atom. The reaction of 1 and 2 with GSH takes place through the direct chloride replacement with GSH. Kinetic data and activation parameters are interpreted in terms of an associative mechanism and discussed in reference to the data reported earlier. The [PtII(mida)(Cl)]− (3) and [PtII(pydc)(Cl)]− (4) complexes were prepared and allowed to interact with AMP and IMP and their reaction products were characterized by 1H NMR studies. The antitumor activity of 3 and 4 was examined against MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.

The reaction of [Ru III (edta)(H 2 O)] − (edta 4− = ethylenediaminetetraacetate) and [Ru III (hedtra)(H 2 O)] (hedtra 3− = N-hydroxyethylethylenediaminetriacetate) with various purine based 5′-nucleotides (Nu) viz. adenosin-5′-monophosphate (AMP), guanosin-5′-monophosphate (GMP), inosin-5′-monophosphate (IMP) was studied kinetically as a function of [Nu] at various temperatures (15–35 °C) at a fixed pH (4.5). Kinetic results suggest that the binding of 5′-nucleotides takes place in a rapid [Nu] dependent rate-determining step. Kinetic data and activation parameters are accounted for the operation of an associative mechanism. The antitumor activities of both [Ru III (edta)(H 2 O)] − ( 1 ) and [Ru III (hedtra)(H 2 O] ( 2 ) have been evaluated using MCF-7 (breast cancer), NCI-H460 (lung cancer) and SF-268 (CNS) cell lines.

Degradation of a pesticide (atrazine) in air-equilibrated aqueous mixture has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. Under 5 h of irradiation with a 150 W xenon lamp, appreciable degradation of atrazine has been observed. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O2 −/HO2 radicals is proposed for the degradation of the pesticide to carbon dioxide. Formation of O2 − radical has been evidenced by using a chemiluminescent probe, luminol.

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived by condensation of aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde) with 2-aminobenzoic acid, and bidentate ligands (2,2′-bipyridine or picolinic acid). [RuIII(cpsd)(bipy)(H2O)]+ (1), [RuIII(cpsd)(pic)(H2O)] (2), [RuIII(cppc)(bipy)(H2O)]2+ (3) and [RuIII(cppc)(pic)(H2O)]+ (4) complexes (where, cpsd2−=(N-(2-carboxyphenyl)salicylaldiminato); cppc−=N-2-carboxyphenylpyridine-2-carboxaldiminato; bipy=2,2′-bipyridine and pic−=picolinate) were characterized by analytical, spectral (IR and UV–Vis), conductance, magnetic moment and electrochemical studies. Catalysis of hydrocarbon oxidations for cyclohexene, cyclohexane, cyclohexanol, toluene, benzyl alcohol, and tetrahydrofuran have been studied using various O-atom transfer agents (t-BuOOH, H2O2, NaOCl, KHSO5 and pyridinium-N-oxide). The influence of product yield as a function of solvent was evaluated for CH2Cl2, CH3CN, and 1,4-dioxane. Coordinating solvents suppress the reactivity by inhibiting coordination of t-BuOOH, and compete for the RuV=O group through their own intrinsic C–H reactivity. The main pathway transfers the oxo group from the [RuO(TDL)(XY)] intermediate, TDL=cpsd2− and cppc2−; XY=bipy or pic−, with insertion of the oxo group into a C–H bond of all substrates tested (rather than olefin epoxidation for cyclohexene). A mechanism involving intermediacy of a high valent Ru(V)-oxo species is proposed for the catalytic oxidation processes.

Two series of complexes with formal oxidation state assignments of {Ru V (O 2− )} have been examined by molecular mechanics and molecular orbital methods at the level of PM3 calculations in order to assess the origin of differences in the activity of these complexes in the conversion of benzene to phenol by oxygen transfer. The first series includes complexes of general formula [RuO(hpsd)(XY)] n + with hpsd 2− (also known in the literature as amp 2− )=(2-hydroxyphenyl)salicyldiminato; XY=bpy(2,2 ′ -bipyridine) and other py-X, wherein the second pyridyl group of bpy is changed to X=–CH 2 N(CH 3 ) 2 (stronger σ-donor X), –CH 2 P(CH 3 ) 2 (better π-acceptor X), –CO 2 − (weak π-donor X), –CH 2 S − (strong π-donor X), and –CH 2 C(CH 3 ) 2 − (very strong σ-donor X). A second series of complexes, [RuO(TDL)(bpy)] n + was also studied with TDL=(tridentate ligand) of the parent hpsd 2− (or amp 2− ); cpsd 2− =( N -(2-carboxyphenyl)salicylaldiminato); cppc − =( N -2-carboxyphenylpyridine-2-carboxaldiminato); and hppc − =(2-hydroxyphenyl)2-pyridylcarboxaldiminato (or app − ). Experimentally, the activity order based upon the percentage yields of oxygenated products for [RuO(TDL)(bpy)] n + is as follows for TDL’s=hpsd 2− (91%) > cppc − (87%) > cpsd 2− (84%) > hppc − (80%). The rates approach toward saturation in reactivity as a function of the fractional positive charge on the apical O center: cppc − (0.233) > hpsd 2− (0.166) > cpsd 2− (0.105) > hppc − (0.041). The reactivity order follows chelate ring strain influences of the TDL, with 5,6-membered chelate rings; hpsd 2− and cppc − > 6,6; cpsd 2− > 5,5; hppc − . It was determined that the general structures of these complexes are best described as pentagonal pyramidal (rather than pseudo-octahedral) with the RuO unit apical, the three donors of hpsd 2− , cpsd 2− , cppc − or hppc − , and the two donors of XY ligands adopting a waffled arrangement around the Ru center as the remaining donors of the pentagonal set. The donor most trans to the apical RuO is approximately at 140°, rather than 180°. Ligands such as hpsd 2− (amp 2− ) are not retained in a single planar array, but rather with one of the aromatic donors turned upward to shield the approach of the RuO unit from one side. The ligand series [RuO(hpsd)(XY)] + averages angles between adjacent atoms of the pentagonal set of 75.4° instead of a theoretical 72.0°; angles between the apical RuO and adjacent donors average 111° but with wide deviations (±30°) depending upon the donors of the TDL. Small changes in the donor atom positions, and in the capability of the “ trans ” donor’s σ-donor strength, and whether it is a π-acceptor or a π-donor, modulate the degree of mixing of ligand orbitals and the LUMO/SOMO energy gap which influences reactivity. The presence of a π-acceptor ligand provides the most destabilization of Ru–O π bonding, and this appears to be the best way to increase the activity of these catalysts toward oxidation of C 6 H 6 to C 6 H 5 OH. Also, implicated in the activity of the catalysts is the need for two non-innocent phenolate donors that raise the energy of orbitals on the apical O atom. This increases the oxenoid character of the terminal O, and makes the insertion into a C–H bond more favored.

Visible light assisted degradation of aromatics, viz phenol, chlorophenol, 1,2-dichloroethane, trichloroethylene and surfactants, viz cetyl pyridinium chloride (CPC; cationic), sodium dodecylbenzene sulfonate (DBS; anionic) and neutral Triton-X 100 in air-equilibrated aqueous mixtures has been achieved on the surface of TiO2 semiconductor modified with methylene blue (MB) and rhodamine B (RB). Under 5 h of irradiation with a 150 W xenon lamp, over 40–75% degradation of pollutants has been observed. The failure of pollutants to degrade on non-conducting Al2O3 surface essentially suggests the role of semiconducting TiO2 photocatalyst in the photochemical process. A working mechanism involving excitation of surface adsorbed dye, followed by charge injection into the TiO2 conduction band and formation of reactive O2−/ HO2 radicals is proposed for the degradation of organics to carbon dioxide.

Photodegradation of organic pollutants, viz. phenol, chlorophenol, 1,2-dichloroethane and trichloroethylene in water has been achieved on the surface of TiO2 semiconductor modified with thionine and eosin Y by using visible light. After 5 h of irradiation with a 50 W tungsten lamp, over 55–72% degradation of pollutants is achieved. A working mechanism involving excitation of surface bound dye, followed by charge injection into the TiO2 conduction band is proposed.

Adsorption of dyes viz. thionine, eosin Y and rhodamine B on flyash has been investigated as a function of flyash and dye concentrations, contact time and pH. Photodegradation of dyes has been achieved by illuminating the reacting system containing dye and flyash with visible light.

Novel [MnIII(amp)(bipy)(Cl)] (1) (H2amp: N-(hydroxyphenyl)salicyldimine; bipy: 2,2′-bipyridyl) and [MnIII(app)(bipy)(Cl)]+ (2) (H2app: N-(hydroxyphenyl)pyridine-2-carboxaldimine; bipy: 2,2′-bipyridyl) complexes have been synthesized and characterized by physico-chemical methods. Complexes 1 and 2 have been employed as catalysts in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive highvalent Mn(V)-oxo species as catalytic intermediate is proposed for the catalytic processes.

[RuIII(amp)(bipy)(H2O)]+ complex (1) has been synthesized and characterized by physico-chemical methods. The complex 1 is found to be an effective catalyst in the oxidation of benzene to phenol by using tert-butylhydroperoxide (t-BuOOH). A high valent Ru(V)-oxo species as catalytic intermediate formed in the reaction of 1 with t-BuOOH is proposed to be the source of oxygen atom in the oxidized product. A mechanism involving stacking of benzene followed by the O atom insertion seems to be operative in the formation of phenol from benzene.

Cationic [RuIII(app)(pic)(H2O)]+ (1) complex (Happ=N-(hydroxyphenyl)pyridine-2-carboxaldimine; Hpic=picolinic acid) has been synthesized and characterized by physico-chemical methods and employed as catalyst in the oxidation of both saturated and unsaturated hydrocarbons using tert-butylhydroperoxide (t-BuOOH). A mechanism involving formation of and transfer from a reactive high valent Ru(V)-oxo species as catalytic intermediate is proposed for the catalytic processes.

The combination of [RuIII(edta)(H2O)]− (edta4−=ethylenediamine-N,N,N′N′-tetraacetate) and [FeIII(CN)6]3− in aqueous solution results in the rapid formation of [RuIII(edta)(NC)FeIII(CN)5]4− (1), which has been isolated and characterized by physical methods. An aqueous solution of complex 1 shows two characteristic absorption maxima in the visible spectral region located at 420 and 620 nm. Examination of the same solution after 72 h shows that a spectral change has occurred, forming a species with a new band maximum at 870 nm. Spectral (IR, UV–Vis, 1H and 13C NMR spectra showing a paramagnetic complex, and time-dependent magnetic susceptibility data) provide evidence for the formation of a mixed-valence [RuIV(edta)(NC)FeII(CN)5]4− complex 2 by the process, which causes the appearance of the 870 nm band. The results are compared with the known reactions between [RuIII(NH3)5(H2O)]3+ and [Fe(CN)6]3−, which have been reported by Taube and co-workers (V.G. Poupopoulu, Z.W. Li, H. Taube, Inorg. Chim. Acta 225 (1994) 173) to sequentially form {[RuIII(NH3)5(H2O)]3+, [FeIII(CN)6]3−} ion-pairs, converting to a (RuIIICN− bridged-FeIII) binuclear complex (an analogue of 1, and upon intramolecular electron transfer, the (RuIVCN− bridged-FeII) binuclear complex (an analogue of 2). The events reported for the conversion of 1 into 2 ensue without appreciable accumulation of ion pairs as both [RuIII(edta)(H2O)]− and [FeIII(CN)6]3− are anionic. Magnetic susceptibility data imply that both 1 and 2 are paramagnetic S=1 ions. The d electron manifold filling is dxy2dxz2dyz1 in 1 and dxy2dxz1dyz1 in 2, whereas a filling of dxy2dxz2dyz0 seems to account for the prior observations with the [RuIV(NH3)5(NC)FeII(CN)5] system studied by Taube and co-workers.

New Schiff-base complexes of Nickel(II), NiL1 (where H2L1=N,N′-bis(2-hydroxyphenyl)ethylenediimine) and NiL2 (where H2L2=N-((2-hydroxyphenyl)acetylaldimine)-N′-(2-hydroxyphenyl)acetamide) have been prepared in good yield by direct interaction of 2-aminophenol, glyoxal/methylacetatotate and NiCl2 and characterised by physico-chemical analysis. Catalytic ability of NiL complex were examined and found that both the complexes can effectively catalyse the epoxidation of olefins viz. cyclohexene, 1-hexene, cis- and trans-stilbenes, indene with NaOCl.

The kinetics of the oxidation of [Ru III (edta)(H 2 O)] − (edta=ethylenediaminetetraacetate) (complex- 1 ) with pyridine N -oxide (PyO) to [Ru V (edta)O] − (complex- 2 ) and subsequent oxo-transfer from complex- 2 to dimethylsulfide (dms) leading to the formation of dimethylsulfoxide (dmso) have been studied spectrophotometrically. The rate of formation of oxo-complex ( 2 ) in the reaction of complex- 1 with PyO was found to be substitution controlled and first order both in complex- 1 and PyO concentrations. The rate of oxo transfer from complex- 2 to dms was found to be first order with respect to [complex- 2 ] and [dms]. Kinetic data and activation parameters are found to be consistent to the proposed mechanism.

[RuIII(amp)(bipy)Cl] complex (1) has been synthesised and characterised by physico–chemical methods. Complex-1 is found to be an effective catalyst in the oxidation of cyclohexene to cyclohexene-1-ol, cyclohexane to cyclohexanol and cyclohexanone, stilbenes to stilbene epoxides and benzaldehyde upon reaction with tert-butylhydroperoxide (t-BuOOH). A high valent Ru(V)-oxo species formed as a catalytic intermediate in the reaction of complex-1 with t-BuOOH is proposed as the source of oxygen in the oxidised product. Kinetic data suggests that the formation Ru(V)-oxo is substitution controlled. The results of the product distribution in the present investigation clearly indicate the high electrophilic nature of Ru=O bond in [RuV(amp)(bipy)O]+ intermediate complex which leads to high affinity for atomic hydrogen/hydride abstraction.

M(salen) complexes (M=Mn(III), Ni(II); salen=bis-(salicyldene)ethylenediamine) have been encapsulated in zeolite Y and characterised. Mn(salen)+ complex was also anchored in montmorillonite clay and characterised. Epoxidation of olefins, viz. cyclohexene, cyclooctene and 1-hexene with terminal oxidants (NaOCl, KHSO5) was carried out with the anchored catalyst complexes and found that the epoxidation of linear olefin (1-hexene) is selectively facile than cyclic olefins. Experimental results are compared with those reported for M(salen) complexes catalysed olefin epoxidation in homogeneous and heterogenised-homogeneous catalytic conditions.

Kinetics of the reduction of [Ru III (edta)(NC)Fe III (CN) 5 ] 4− (edta=ethylenediaminetetraacetate) with l -ascorbic acid (H 2 A) and the oxidation of [Ru III (edta)(NC)Fe II (CN) 5 ] 5− with peroxydisulfate (S 2 O 8 2− ) were studied spectrophotometrically. The rate of reduction was found to be first-order both with respect to [Ru III –Fe III ] and [H 2 A]. Similarly, the oxidation reaction was in first order in both Ru III –Fe II and S 2 O 8 2− concentrations. Based on the kinetic observations an Fe centered outersphere electron transfer mechanism has been suggested for both the oxidation and reduction processes.

The reaction of 5′-GMP (5′-GMP=guanosine-5′-monophosphate) with [RuII(edta)(H2O)]2− and [RuIII(edta)(H2O)]− (edta4−=ethylenediamine-N,N,N′,N′-tetraacetate) was followed by 1 H NMR spectroscopy for RuII and by spectrophotometric and kinetic methods for RuIII. The coordination of 5′-GMP for the RuII complex occurs at N-7, implicated by a downfield 0.21 ppm shift of the H-8 proton of 5′-GMP to 8.42 ppm for ca. 30% of the coordinated 5′-GMP and a 0.02 ppm upfield shift for another isomer (70%), coordinated via the N-3 purine donor. 0.01 ppm downfield shifts are also detected for the H-1′ proton of ribose ring upon metallation by [RuII(edta)]2−. Molecular mechanics energy-minimized structures show unhindered N-7 coordination and two N-3 rotomers with energy minima that minimize steric contacts between the ribose phosphate component of 5′-GMP and the [RuII(edta)]2− functionality. Figures illustrating the N-7 and N-3 modes of coordination are shown. Cyclic voltammetry and differential pulse polarography established an E1/2 value for the [RuII/III(edta)(5′-GMP)]n− couple as 0.01 V versus NHE at glassy carbon (pH ≅ 6, T = 22°C). The waves for both N-3 and N-7 are highly overlapped. When the complex is generated via substitution of the RuIII form, only the N-7 isomer is present in abundance. The RuIII complex exhibits an LMCT band at 582 nm which appears in a pH-dependent manner (pKa = 7.2). The origin of the LMCT band is attributed to deprotonation of coordinated 5′-GMP at N-1. At pH = 8.0, μ = 0.2, T = 27°C the addition of 5′-GMP is detectable by stopped-flow studies which established a second-order reaction between [RuIII(edta)(OH)]2− and 5′-GMP with k = 30 ± 4 M−1 s−1.

The development and intriguing aspects of the chemistry of Ru—pac (pac = polyaminopolycarboxylate) complexes are reviewed in this article. Kinetics and mechanistic aspects of Ru—pac complexes towards substitution reactions are discussed with reference to the role of the uncoordinated pendant group of the pac ligands in the remarkable lability of Ru pac complexes towards the aquo-substitution process. The catalytic ability of Ru pac complexes in various organic transformations are highlighted, along with the mechanistic details. The recent development of electrocatalytic systems with Ru—pac complexes for activation of small molecules is addressed. Most current investigations on the mixed-ligand complexes of ruthenium-containing pac ligands are included in this article. Applications of these mixed-ligand complexes to some biochemical processes or in developing new inorganic materials are discussed.

The oxidation of benzylcyclopropane using catalytic amounts of chromium oxide and an excess of aqueous tert-butyl hydroperoxide solution led efficiently to cyclopropylphenylketone with a high selectivity.

Reactions of Ru III L(H 2 O) (L = aminopolycarboxylate ligands viz. edta, pdta, hedtra) with dimethylsulfide (DMS) and dimethylsulfoxide (DMSO) were studied by using spectrophotometric, electrochemical and kinetic methods. [Ru III L(DMS)] complexes formed by the interaction of Ru III L(H 2 O) and DMS undergo oxidation when exposed to air to yield DMSO and Ru III L(H 2 O) back. Under identical condition [Ru III L(DMSO)] complexes do not undergo any further oxidation to produce dimethyl sulfone.

Reaction of the phenylhydrazinium (PhN2H4+)_ion with the labile aquo complexes of [RuIII(HED-TA)(H2O)] (EDTA = ethylenediaminetetraacetate) was studied electrochemically employing sampled DC, cyclic voltammetry and differential pulse techniques in 0.2 M CH3COONa and H2SO4 mixture between pH 1.0 and 4.5 at 25°C. It produced two phenylhydrazinium complexes, namely [RuIII(HEDTA)(N2H4Ph)]+ and [RuIII(EDTA)(N2H4Ph)] in the rapid aquo-substitution reactions. The second-order rate contants, k1, for the formation of the former, and k2 for the latter are 0.98 and 36.85 M−1 s−1, respectively, as determined spectrophotometrically by following the intensity of the LMCT band at 420 nm. The complex, [RuIII(HEDTA)(N2H4Ph)]Cl·2H2O was prepared and characterised by physicochemical methods. These phenlhydrazinium complexes were reduced by two electrons at E 1 2 = −0.175 V vs SCE , producing one mole of NH3 and the corresponding RuIII-NH2Ph complexes in subsequent rapid decomposition steps. The unstable RuIII-NH2Ph complexes were rapidly hydrolysed to one mole of NH2Ph and the respective aquo complex. One-electron reduction steps for the regenerated aquo complex at ( E 1 2 ) − 0.254 V and the unhydrolysed RuIII-NH4Ph complex at −0.417 V were also observed. Phenylhydrazine was reduced to ammonia and aniline by constant potential coulometry at −0.200 V (Hg) vs SCE, in the presence of [RuIII(HEDTA)H2O)] at 100: 1 molar ratio. The turnover number (per mole of catalyst per hour) with respect to ammonia is 5.98 and 2.82 at pH 2.8 and 1.9, respectively. The probable mechanisms for the electroreduction of the above phenylhydrazinium complexes and the catalytic reduction of phenylhydrazine to NH3 and NH2Ph, are proposed.

The novel mixed-ligand complex [Ru III (TDL)(bipy)(H 2 O)] + ( 1 ) (TDL = N -3,5-ditertiarybutylsalicylidine- d -glucosamine; bipy = 2,2′-bipyridine) has been synthesized and characterized. Complex 1 found to catalyze the epoxidation of styrene and oxidize 1-indanol to 1-indanone in dichloromethane using t -BuOOH as a terminal oxidant. Enanantiomeric induction was observed in case of styrene epoxidation. Formation of a high valent Ru(V)-oxo species is proposed to be the catalytic oxidative species.

β-Methoxy alcohols are easily obtained from the one-pot reaction of alkenes with oxone ® in methanol, in the absence of any additive or catalyst. The use of other alcohols as solvents has shown that the efficiency of the process decreases with the steric hindrance of the alcohol.

Novel binuclear complexes of the type [{Ru(edtaH)}2L] [edta- = ethylenediaminetetraacetate, L = pyrazine, 4,4′-bipyridyl, 3,3′-dimethyl-4,4′-bipyridyl, trans-1,2-bis(4-pyridyl)ethylene)] have been synthesized and characterized by physicochemical methods. All the complexes showed weak metal-metal interaction, depending on the nature of the bridging ligand, L. The electrochemical and magnetic susceptibility measurements are consistent with weak interactions between the ruthenium centres.

Bentonite clays modified by exchanging Al3+, Co2+ and its Na+ form were used in etherification of cyclohexanol to dicyclohexyl ether. Product yields obtained for metal cation exchanged clays followed the order Al3+ > Co2+ > Na+. Bronsted acidity of the solid catalysts is suggested to play the key role in the studied reaction.

The K4[RuIII(hedtra)NCFeII(CN)5] (3) (hedtra=N-hydroxyethylethylenediaminetriacetate) complex has been synthesised and characterised by physicochemical analysis. The temperature dependence of intervalence transfer in 3 has been studied and compared with that observed in [RuIII(edta)NCFeII(CN)5]5− (1) and [RuIII(NH3)5NCFeII(CN)5]− (2), complexes. The charge type on the ruthenium centre of the binuclear complexes has been found to effect the intervalence thermochromism. This has been discussed in terms of a charge type effect on the temperature dependency of ΔE (vibrationally relaxed initial state/final state separation energy) and the χ (reorganisation energy) component of EIVCT (intervalence charge transfer energy).

Ni(salen) (salen = bis-(salicylidene)ethylenediamine) complex was encapsulated in zeolite Y and hydrogenations of cyclohexene, cyclooctene, 1-hexene and benzene were carried out with Ni(salen) encapsulated zeolite at moderately high temperature (40°C) and pressure (60 atm of H2).