- Electrochemical Reduction of Carbon Dioxide Using Iron-Sulfur Clusters as Catalyst Precursors
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The potential-current relationships of DMF solutions of a series of iron-sulfur compounds have revealed that in the presence of clusters 2- (R=PhCH2 or But) and 3- (M=Mo or W) the electroreduction of CO2 proceeds at the potential shifted by about 0.7 and 0.5 V, respectively, to the positive direction compared to the potential at which CO2 is reduced without any catalyst.When controlled potential electrolysis of a DMF solution containing 2- was carried out under CO2 at -2.0 V vs.SCE, phenylacetate and formate were formed as the products resulting from CO2 reduction.The cubane structure of this cluster collapsed rapidly under these conditions.However, when excess amount of PhCH2SH was added to the catholyte, the cluster structure was preserved during a relatively long period of electrolysis, and the yield of phenylacetate increased but that of formate decreased compared with the reaction in the absence of free PhCH2SH.
- Nakazawa, Makoto,Mizobe, Yasushi,Matsumoto, Yoichi,Uchida, Yasuzo,Tezuka, Meguru,Hidai, Masanobu
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- Glycerol electrooxidation in alkaline medium using Pd/c, Au/c and Pdau/c electrocatalysts prepared by electron beam irradiation
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Pd/C, Au/C and PdAu/C electrocatalysts with different atomic ratios prepared using electron beam irradiation were tested for glycerol electrooxidation in single alkaline direct glycerol fuel cell (ADGFC). X-ray diffractograms (XRD) of PdAu/C electrocataly
- Geraldes, Adriana N.,Silva, Dionisio F.,Silva, Ju?lio C.M.,Souza, Rodrigo F.B.,Spinace?, Estevam V.,Neto, Almir O.,Linardi, Marcelo,Santos, Mauro C.
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p. 831 - 840
(2014/06/24)
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- Polymerization-induced enhancement of binding and binding-induced polymerization
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We obtained the binding free energy of the complex [Co(C2O 4)3]3- to the peptide H-Lys-Gly-(Lys-Gly) 9-Lys-NH2, and to the monomers (aminoacids) forming the peptide, using the electron transfer reaction between [Ru(NH3) 5pz]2+ and [Co(C2O4) 3]3- as the probe. The polymerization of the monomers increases the negative free energy of binding and changes its character, non-cooperative for the monomers and anti-cooperative for the peptide. This increase in the negative free energy represents a driving force for the polymerization process that produces the peptide from the aminoacids (monomers) in such a way that the polymerization in the presence of the cobalt complex is more favourable, from a thermodynamic point of view, in 16.5 kJ/mol.
- Ortiz,Guichou,Chavanieu,Sánchez,Prado-Gotor
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p. 266 - 270
(2008/10/09)
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- Measurement of solvent dynamics effects on the electron transfer reaction of Co(NH3)4ox+ in mixed solvents: A quantitative approach
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For reactions involving electron transfer or nucleophilic attack on the transition state/excited state of metal complex in aquo-organic solvent mixtures, a linear relationship between logarithms of rate constant and solvent empirical parameters can be derived. Fe(CN)64- reduction of Co(NH3)4ox+ and ligand to metal charge transfer (LMCT) excited-state redox reaction of Co(NH3)4ox+ were studied in varying compositions of aqueous mixtures of methanol (MeOH) and 1,4-dioxane (Diox). A quantitative estimation of relative importance of the components was attempted. A number of empirical solvent parameters were used in the multiple regression equations. The correlation analysis showed significant information on the effect of solvent-solvent and solvent-solute interactions on reactivities. The addition of MeOH or Diox to the medium brings about marked structural changes in the prevailing water structure by making progressive desolvation between partners of the transition state/geminate radical pair which in all probability is highly solvated in the water medium. The positive sign of multiparametric coefficients suggested that the solvent mixture strongly solvates the transition state, and the negative sign of the coefficients shows the specific solvation of incipient reactants.
- Anbalagan,Geethalakshmi,Poonkodi
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p. 1918 - 1927
(2007/10/03)
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- Ultrasonic Irradiation of p-Nitrophenol in Aqueous Solution
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The kinetics and mechanism of the sonochemical reactions of p-nitrophenol have been investigated in oxygenated aqueous solutions.In the presence of ultrasound (20 kHz, 84 W) p-nitrophenol was degraded primarily by denitration to yield NO2-, NO3-, benzoquinone, hydroquinone, 4-nitrocatechol, formate, and oxalate.These reaction products and the kinetic observations are consistent with a model involving high-temperature reactions of p-nitrophenol in the interfacial region of cavitation bubbles.The main reaction pathway appears to be carbon-nitrogen bond cleavage.Reaction with hydroxyl radicals provides a secondary reaction channel.The average effective temperature of the interfacial region surrounding the cavitation bubbles was estimated to be T ca. 800 K.
- Kotronarou, A.,Mills, G.,Hoffmann, M. R.
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p. 3630 - 3638
(2007/10/02)
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- The kinetics and mechanism of the decomposition reaction of the bis(oxalato)manganese(III) complex in an aqueous solution
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The kinetics and mechanism of the decomposition of the bis(oxalato)manganase(III) complex ion ([Mn(ox)2]-) were studied in acid solution in the absence and in the presence of oxygen at temperatures from 10 to 35°C. The decomposition reaction of [Mn(ox)2]- in the absence of oxygen was described by the first-order rate law of -d[[Mn(ox)2]-]/dt=k(obsd)[[Mn(ox)2]-], where the observed rate constant, k(obsd), increased proportionally with the increasing hydrogen-ion concentrations, being expressed as k(obsd)=k[H+] in the [H+] range of 0.006-0.1 M. The enthalpy and entropy changes of activation (ΔH≠ and ΔS≠) were 73.4±2.0 kJ mol-1 and -8.6±0.2 J K-1 mol-1 respectively. The rate of the decomposition of [Mn(ox)2]- decreased greatly upon the addition of a radical scavenger for CO2-. such as [Co(NH3)6]3+, [CoCl(NH3)5]2+, or molecular oxygen. In the presence of oxygen, the rate deviated greatly from the first-order rate law. On the other hand, the addition of [Co(NH3)6]3+ or [CoCl(NH3)5]2+ in the absence of oxygen did not change the first-order rate law, but did decrease the rate of reaction up to 40% of that in the absence of the radical scavenger. The mechanisms for the decomposition reaction of [Mn(ox)2]- are discussed in the light of the results obtained.
- Kimura,Ohota,Tsukahara
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p. 151 - 155
(2007/10/02)
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- Formation in Solution, Synthesis, and Electrochemical Study of Oxalato Complexes of N,N'-Ethylenebis(salicylideneiminato)-chromium(III) and -iron(III): Crystal Structures of Piperidinium (oxalato-O1O2)-chromate(III) and ferrate(III)
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Two new mononuclear complexes of formula and the binuclear *H2O, (3), where Hpip=piperidinium, salen=N,N'-ethylenebis(salycilideneiminate), and ox=oxalate, have been synthesized.Compounds (1) and (2) are isostructural, monoclinic, space group P21/n, Z=4, with a=24.425(3), b=6.847(1), c=14.271(2) Angstroem, and β=100.95(2) deg for (1) and a=24.363(4), b=6.991(2), c=14.105(3) Angstroem, and β=98.76(2) deg for (2).The stucture of (1) was solved by direct methods whereas that of (2) was solved by isomorphous replacement from the co-ordinates of (1).Both structures consist of (1-) mononuclear anions and piperidinium cations.The presence of the bidentate oxalate ligand in both complexes forces the salen ligand to adopt the non-planar cis-β configuration.The metal ions exhibit distorted octahedral geometry with the two co-ordinated oxygen atoms of the oxalate ligand and an oxygen and a nitrogen atom from the salen defining the best equatorial plane.The remaining two co-ordinating atoms of the quadridentate Schiff base are bent away from the oxalate ligand.The stability constant of the complex (1-) as well as the acidity constants of the complex (1+) have been determined by potentiometry in aqueous solution: log β1=4.80+/-0.03, pKa1=7.54+/-0.01, and pKa2=10.47+/-0.01 (25 deg C, 0.1 mol dm-3 NaNO3).Complexes (1) and (2) undergo one-electron reduction at a platinum electrode in dimethyl sulphoxide solution.The reduction process is totally irreversible due to an inner-sphere redox reaction in the case of Cr(III) and to the dissociation of the anionic oxalate ligand in the case of Fe(III).A reactivity scheme is proposed to explain their different electrochemical behaviour.
- Lloret, Francesc,Julve, Migual,Mollar, Miquel,Castro, Isabel,Latorre, Julio,at al.
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p. 729 - 738
(2007/10/02)
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- Photochemistry of Co(III)-penta-ammine Oxalate and Co(III)-tetra-ammine bis-Oxalate Complexes
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Photochemistry of Co(III)-penta-ammine oxalate and Co(III)-tetra-ammine bis-oxalate complexes has been studied in aqueous solution (pH = 4.63-2.7) using different wavelengths of irradiation under both aerobic and anaerobic media.Quantum yields of redox and aquated products have been determined.For penta-ammine oxalate complex the redox yield increases in the order 490 .- radical by oxygen (evidenced by formation of H2O2) in the latter case.In general the simple radical pair model is not sufficient to explain the photochemical behaviour of the complexes; the distribution of product yields depends on the spectroscopic state of excited species.
- Sarkar, Shyamal K.,Tarafdar, Pijush K.,Roy, Ansuman,Aditya, S.
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p. 1142 - 1146
(2007/10/02)
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