Showing papers by "Debabrata Chatterjee published in 2014"

Nitrite reduction mediated by the complex RuIII(EDTA)

Abstract: Reported is the first example of a ruthenium(III)-complex, RuIII(EDTA) (EDTA4− = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [RuIII(EDTA)(NO+)]0. However, at pH below 5.0, the coordinated nitrite ion in the [RuIII(EDTA)(NO2)]2− complex undergoes proton-assisted decomposition, resulting in the formation of a [RuIII(EDTA)(NO+)]0 species.

Mechanism of the oxidation of thiosulfate with hydrogen peroxide catalyzed by aqua-ethylenediaminetetraacetatoruthenium(III)

Abstract: 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.

Electrochemical Conversion of Bicarbonate to Formate Mediated by the Complex RuIII(edta) (edta4– = ethylenediaminetetraacetate)

Abstract: 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.

RuIII(edta) mediated oxidation of azide in the presence of hydrogen peroxide. Azide versus peroxide activation

Abstract: The [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) complex catalyzes the oxidation of azide (N3−) with H2O2, mimicking the action of metallo-enzymes such as catalase and peroxidase in biochemistry. The kinetics of the catalytic oxidation process was studied by using stopped-flow and rapid-scan spectrophotometry as a function of [RuIII(edta)], [H2O2], [N3−] and pH. The catalytic activity of the different oxidizing species produced in the reaction of [RuIII(edta)(H2O)]− with H2O2 for the oxidation of azide was compared to the oxidation of coordinated azide in [RuIII(edta)N3]2− by H2O2. Detailed reaction mechanisms in agreement with the spectroscopic and kinetic data are presented for both reaction paths.

RuIII(EDTA) mediated S-nitrosylation of cysteine by nitrite

Abstract: Reported here is the first example of a ruthenium(III) complex [RuIII(EDTA)(H2O)]− (EDTA4− = ethylenediaminetetraacetate) that mediates S-nitrosylation of cysteine in the presence of nitrite at pH 4.5 (acetate buffer) and results in the formation of [RuIII(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 [RuIII(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.

Dye sensitization of a large band gap semiconductor by an iron(III) complex

Abstract: 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.