The preparation and the electrochemical study of Disperse Blue 1‐chemically modified electrodes (DB1‐CME), as well as their efficiency for the electrocatalytic oxidation of NADH is described. The proposed mediator was immobilized by physical adsorption onto graphite electrodes. The electrochemical behavior of DB1‐CME was studied with cyclic voltammetry. The electrochemical redox reaction of DB1 was found to be reversible, revealing two well‐shaped pair of peaks with formal potentials 152 and ?42 mV, respectively, (vs. Ag/AgCl/3M KCl) at pH 6.5. The current Ip has a linear relationship with the scan rate up to 800 mV s?1, which is indicative for a fast electron transfer kinetics. The dissociation constants of the immobilized DB1 redox couple were calculated pK1=4 and pK2=5. The electrochemical rate constants of the immobilized DB1 were calculated k1°=18 s?1 and k2°=23 s?1 (Γ=2.36 nmol cm?2). The modified electrodes were mounted in a flow injection manifold, poised at +150 mV (vs. Ag/AgCl/3M KCl) and a catalytic current due to the oxidation of NADH was measured. The reproducibility was 1.4% RSD (n=11 for 30 μM NADH) The behavior of the sensor towards different reducing compounds was investigated. The sensor exhibited good operational and storage stability. 相似文献
The kinetics of the reduction of octacyanomolybdate(V) and octacyanotungstate(V) by sulphite ions has been studied over a wide pH range. The reaction is catalysed by alkali metal ions. The rate law is found to be of the form: The third order rate constants at [OH?] = 0.05 mol dm?3 for the reduction of Mo(CN)83? and W(CN)3?8 were determined as 6.2 x 103dm6mol?2 s?1 and 22.3 dm6mol?2s?1 respectively at 298 K for A+ = Na+ while Ka for the hydrogen sulphite ion was determined as 2.4 x 10?8 mol dm?3. It was established that the reaction proceeds via an outer-sphere mechanism. An explanation for the alkali metal ion catalysis is proposed. 相似文献
The mass transport and charge transfer kinetics of ozone reduction at Nafion coated Au electrodes were studied in 0.5 mol/L H2SO4 and highly resistive solutions such as distilled water and tap water. The diffusion coefficient and partition coefficient of ozone in Nafion coating are 1.78×10-6 cm2·s-1 and 2.75 at 25℃ (based on dry state thickness), respectively. The heterogeneous rate constants and Tafel slopes for ozone reduction at bare Au are 4.1×10-6 cm·s-1, 1.0×10-6 cm·s-1 and 181 mV, 207 mV in 0.5 mol/L H2SO4 and distilled water respectively and the corresponding values for Nafion coated Au are 5.5×10-6 cm·s-1, 1.1×10-6 cm·s-1 and 182 mV, 168 mV respectively. The Au microelectrode with 3 μm Nafion coating shows good linearity over the range 0-10 mmol/L ozone in distilled water with sensitivity 61 μA·ppm-1 ·cm-2, detection limit 10 ppb and 95% response time below 5 s at 25℃. The temperature coefficient in range of 11-30℃ is 1.3%. 相似文献
The kinetics of the p-benzoquinone/hydroquinone Q/QH2 couple on a platinum electrode are analysed on the basis of the theory presented earlier (E. Laviron, J. Electroanal. Chem., 146 (1983) 15) for the nine-member square scheme when the protonations are assumed to be at equilibrium, using experimental data from the literature. The square scheme is of the NN type. The Tafel plots and the variations of the experimental apparent rate constants between pH 0 and 7 are in good agreement with the theoretical predictions. The heterogeneous rate constants found for the elemental electrochemical steps are as follow: Q Q?, kh3=1/6×10?3 cm s?1; QH.QH?, kh5=0.11 cm s?1; QH+QH., kh2?160 cm s?1; kh4 for the reaction QH2+.QH2 is in the range 0.5–4 cm s?1. Between pH 0 and 7, the reaction sequence during the reduction is, for the most part, successively H+e?H+e?, e?H+H+e?, and e?H+e?H+ (reverse sequence during the oxidation). 相似文献
The oxidation processes of the radiation-generated, three-electron-bonded intermediates AcMet2 [S??S]+ and AcMet [S??Br] were investigated by pulse radiolysis via their reactions with tryptophan (TrpH). These intermediates were derived from N-acetyl-methionine amide (N-AcMetNH2) and N-acetyl-methionine methyl ester (N-AcMetOMe). The bimolecular rate constant k of the reaction between each intermediate and l-tryptophan (TrpH) was measured. For N-AcMetNH2, k for the reaction of AcMet2 [S??S]+ with TrpH were 3.4?×?108 and 2.2?×?108?dm3?mol?1?s?1 at pH?=?1 and 4.5, respectively. For N-AcMetOMe, k for the reaction of AcMet2 [S??S]+ with TrpH were 4.0?×?108 and 2.8?×?108?dm3?mol?1?s?1 at pH 1 and 4.5, respectively. The rate constants for the intermolecular transformation of Met [S??Br] into TrpH+ or Trp were also estimated. For N-AcMetNH2, k for the reaction of AcMet2 [S??Br] with TrpH were 2.6?×?108 and 3.3?×?108?dm3?mol?1?s?1 at pH 1 and 4.5, respectively. Related mechanisms were discussed. 相似文献
The oxidation of Na4Fe(CN)6 complex by S2O anion was found to follow an outer‐sphere electron transfer mechanism. We firstly carried out the reaction at pH=1. The specific rate constants of the reaction, kox, are (8.1±0.07)×10?2 and (4.3±0.1)×10?2 mol?1·L·s?1 at μ=1.0 mol·L?1 NaClO4, T=298 K for pH=1 (0.1 mol·L?1 HCl04) and 8, respectively. The activation parameters, obtained by measuring the rate constants of oxidation 283–303 K, were ΔH≠=(69.0±5.6) kJ·mol?1, ΔS≠=(?0.34±0.041)×102 J·mol?1·K?1 at pH=l and ΔH≠=(41.3±5.5) kJ·mol?1, ΔS≠=(?1.27±0.33)×102 J·mol?1·K?1 at pH=8, respectively. The cyclic voltammetry of Fe(CN) shows that the oxidation is a one‐electron reversible redox process with E1/2 values of 0.55 and 0.46 V vs. normal hydrogen electrode at μ=1.0 mol·L?1 LiClO4, for pH=1 and pH=8 (Tris). respectively. The kinetic results were discussed on the basis of Marcus theory. 相似文献
The inhibiting action of fullerene C60 on the liquid-phase initiated oxidation of cumene and ethylbenzene was studied. The apparent rate constants of inhibition by fullerene C60 of cumene and ethylbenzene oxidation were determined by measuring the amount of absorbed oxygen: (1.3±0.2)·103 and (2.0±0.3)·103 L mol?1 s?1, respectively. 相似文献
The inhibition of horseradish peroxidase (HRP)-cata-lyzed oxidation of indole-3-acetic acid (IAA) by a phenol, caffeic acid (CA), was studied using both a kinetic approach and computer simulation. The presence of CA resulted in a lag period in IAA oxidation. The lag period increased slowly with increasing [CA] until a critical concentration, [CA]cr, was reached, then it increased much faster when [CA] was greater than [CA]cr. The [CA]cr was proportional to [IAA] and did not depend upon [HRP]. Caffeic acid was oxidized by compound I and compound II of HRP with bimolecular rate constants (6.8 ± 107 and 2.1 ± 107M-1s?l), which were much higher than the corresponding rate constants for IAA oxidation (2.3 ± 103 and 2.0 ± 102M?1s?1). Our experimental data show that CA inhibits IAA oxidation because it is able to compete effectively as a peroxidase substrate. A model based on a detailed mechanism of IAA oxidation was investigated using computer simulation. A rate constant driving nonenzymatic hydroperoxide formation in IAA solution was determined, 3.0 × 10?-7 s?1. The model quantitatively describes the experimental results of this work and also qualitatively explains data published earlier. The critical inhibitor concentration is approximately equal to twice the concentration of hydroperoxide in IAA solution at the time of inhibitor addition. Therefore hydroperoxide Concentration can be calculated from the determination of critical inhibitor concentration. 相似文献
The reductions of Co(terpy)23+ and Co(edta)? complexes by ascorbic acid have been subjected to a detailed kinetic study in the range of pH =1–10.9. For each complex the rate law of the reaction is interpreted as a rate determining reaction between Co(III) complex and the ascorbic acid in the form of HA? (k1) and A2? (k2), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Co(III) complex. With given Ka1 and Ka2, the rate constants are k1 = 0.25 and 9.87 × 10?5 M?1s?1, k2 = 1.28 × 106 and 18.7 M?1s?1 for Co(terpy)23+and Co(edta)? complexes, respectively, at T = 25 °C and μ = 0.50M (terpy)and 1.0 M (edta) HClO4/LiClO4. The mechanism of the reaction is discussed on the basis of Marcus theory for outer sphere electron transfer process. Spin change and charge effect, duly considered, account for the non‐adiabatic behavior in the reduction of Co(edta)? complex. 相似文献
The reaction mechanisms for oxidation of CH3CCl2 and CCl3CH2 radicals, formed in the atmospheric degradation of CH3CCl3 have been elucidated. The primary oxidation products from these radicals are CH3CClO and CCl3CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH3CCl3 have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH3CCl3) = (5.4 ± 3) 10?12 exp(?3570 ± 890/RT) cm3 molecule?1 s?1. A value of this rate constant of 1.3 × 10?14 cm3 molecule?1 s?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH3 CCl3 reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH3CCl3) = (1.09 ± 0.35) × 10?14, ??(OH + CH3CClO) = (0.91 ± 0.32) × 10?14, ??(OH + CCl3CHO) = (178 ± 31) × 10?14, ??(OH + CCl2O) < 0.1 × 10?14; all in units of cm3 molecule?1 s?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed. 相似文献
An electrochemical method for the determination of carbaryl, after prior oxidation to 1,4-naphthoquinone in natural water and soils is reported. The coulometric oxidation of carbaryl at a platinum electrode was studied using 0.024 mol/L Britton-Robinson buffer (pH 7.0). The reduction of the oxidation product 1,4-naphthoquinone at a dropping mercury electrode was used for the indirect determination of carbaryl after separation on C18 Sep-pak cartridges by differential pulse polarography (detection limits: 0.41 mg L?1 of water and 0.47 mg kg?1 of soil) and directly without separation by adsorptive stripping voltammetry (detection limits: 5 μg L?1 of water and 7 μg kg?1 of soil, for 75 s preconcentration time). Relative errors were lower than 3.7% and relative standard deviations smaller than 4.5%. 相似文献
Kinetics of the photoaquation of hexacyanoferrate(II) ion in aqueous solution were studied potentiometrically and spectrophotometrically. Supposing the simplest mechanism (see Fig. 3. in text), the photoaquation in alkaline medium can be well described. The value of the constants at pH = ll.0 are: ø = 0.8-1.0, k6 = (3.0 ± 0.5) × 10?8 s?1 and k?6 = 1.5 ± 0.2 mol?1 dm3 s?1. To describe the photoaquation in neutral medium t was extended (k′ = 3.33 x 102 mol?1 dm3s?1). The quantum yield in acidic medium can be calculated by combination of ø values of different protonated complexes. The reversibility of photoaquation in alkaline medium is also explained by the scheme. 相似文献
The reaction of H2[OsBr6] with DMSO in ethanol solution resulted in DMSO complex [H(dmso-O)2][OsIII(dmso-S)2Br4] (1) described previously as an intermediate product in the reaction of K2[OsBr6] with DMSO and characterized by EAS and ESR spectra. The coordination of DMSO molecules was established by IR and 1H and 13C NMR spectroscopy. The oxidation state of osmium and trans arrangement of DMSO molecules in the anion were established by ESR. The behavior of complex 1 in solutions was studied by EAS, ESR, and mass-spectrometry: a displacement of Br? ions accompanied by the reduction of osmium to oxidation state +2 occurs in DMSO, a solvation with displacement of DMSO molecules is observed at the first stage in water and methanol (rate constants 2.3 × 10?4 and 1.7 × 10?3 s?1, respectively), the sequential substitution of DMSO molecules and osmium oxidation to form [OsIVBr6]2? ions takes place in 4 mol/L HBr. 相似文献
The d.c. polarographic current-potential curves of Cd(II)-EDTA complexes were examined in the pH range 0.5–10.0, to elucidate the mechanism of their electrode processes and to determine the relevant electrochemical kinetic parameters. It was shown that the first wave observed below pH 3 at ?0.58 to ?0.65 V vs. SCE is the reversible reduction wave of Cd(II) aquo-ion with kinetically-controlled limiting current, and the second wave observed above pH 1.5 at ?0.75 to ?1.21 V vs. SCE corresponds to the simultaneous irreversible reduction of four complex species, CdH3L+, CdH2L, CdHL? and CdL2?, where CdHpL(p?2)+ and L4? denote the protonated complex species with p protons and the unprotonated EDTA ion, respectively. Analysis of the dependence of limiting current on the hydrogen ion concentration led to the conclusion that the preceding reaction determining the behaviour of limiting current is CdH3L+?Cd2++H3L? with k3d=6.3×102 s?1 and k3f=3.3×106 s?1M?1, where k3d and k3f are the dissociation and formation rate constants, respectively. On the other hand, from analysis of the dependence of half-wave potentials of the second wave on the hydrogen ion concentration, the kinetic parameters of the four complex species were evaluated, and are given in Table 1. Further, it was shown that the cathodic rate constants of these four charge transfer processes at some reference potential together with those of Cd(II)-HEDTA complexes fulfil the linear free energy relationship. 相似文献
The dark reduction kinetics of micromolar concentrations of Fe(III) in aqueous solution were studied in the presence of millimolar concentrations of ferrozine (FZ) over the pH range 4.0–7.0. A pseudo-first-order kinetics model was used to describe Fe(III) reduction at pH 4.0 and 5.0, and the reduction rate decreased with increasing pH or initial Fe(III) concentration. A more molecular-based kinetics model was developed to describe Fe(III) reduction at pH 6.0 and 7.0. From this model, the intrinsic rate constants (k1) of Fe(III) reduction by FZ in the dark were obtained as 0.133 ± 0.004 M?1 s?1 at pH 6.0 and 0.101 ± 0.009 M?1 s?1 at pH 7.0. It was also found in this model that a higher pH, a higher concentration of Fe(III), a lower concentration of FZ and less incubation time led to a lower fraction of Fe(III) reduction by FZ in the dark. 相似文献
The usefulness of a C60‐fullerene modified gold (Au) electrode in mediating the oxidation of methionine in the presence of potassium ions electrolyte has been demonstrated. During cyclic voltammetry, an oxidation peak of methionine appearing at +1.0 V vs. Ag/AgCl was observed. The oxidation current of methionine is enhanced by about 2 times using a C60 modified gold electrode. The current enhancement is significantly dependent on pH, temperature and C60 dosage. Calibration plot reveals linearity of up to 0.1 mM with a current sensitivity of close to 50 mA L mol?1 and detection limit of 8.2×10?6 M. The variation of scan rate study shows that the system undergoes diffusion‐controlled process. Diffusion coefficient and rate constant of methionine were determined using hydrodynamic method (rotating disk electrode) with values of 1.11×10?5 cm2 s?1 and 0.0026 cm s?1 respectively for unmodified electrode while the values of diffusion coefficient and rate constant of methionine using C60 modified Au electrode are 5.7×10?6 cm2 s?1 and 0.0021 cm s?1 respectively. 相似文献
Inspired by the cubic Mn4CaO5 cluster of natural oxygen‐evolving complex in Photosystem II, tetrametallic molecular water oxidation catalysts, especially M4O4 cubane‐like clusters (M=transition metals), have aroused great interest in developing highly active and robust catalysts for water oxidation. Among these M4O4 clusters, however, copper‐based molecular catalysts are poorly understood. Now, bio‐inspired Cu4O4 cubanes are presented as effective molecular catalysts for electrocatalytic water oxidation in aqueous solution (pH 12). The exceptional catalytic activity is manifested with a turnover frequency (TOF) of 267 s?1 for [(LGly‐Cu)4] at 1.70 V and 105 s?1 for [(LGlu‐Cu)4] at 1.56 V. Electrochemical and spectroscopic study revealed a successive two‐electron transfer process in the Cu4O4 cubanes to form high‐valent CuIII and CuIIIO. intermediates during the catalysis. 相似文献