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1.
The electrochemical properties of FAD adsorbed on graphite were studied with cyclic voltammetry. A film with a surface coverage of up to 2×10?8 mol cm?2 was formed after 4 h. The film-covered electrodes were stable for long times and they were investigated in buffers without any FAD. A single well-behaved wave was observed, k0≌1 s?1. The pH dependence of E1/2 was studied. On glassy carbon, platinum and gold much less FAD was adsorbed and it was removed with one rinse.  相似文献   

2.
Metal tetra-amino phthalocyanine complexes (MTAPc; where M is Co or Mn) were immobilized on screen-printed gold electrodes pre-modified with monolayers of benzylamino groups. The functionalized electrodes were then activated using benzene-1,4-dicarbaldehyde as a linker before MTAPc complexes were immobilized. The surface coverages for the modified electrodes confirmed the perpendicular orientation of the MTAPcs. The apparent electron transfer constant (kapp) for the electrodes is 2.2?×?10?5 cm.s?1 for both CoTAPc and MnTAPc modified electrodes as calculated with data from impedance measurements. The kapp values for the bare and benzylamino modified electrodes were found to be 1.2?×?10?4 cm.s?1 and 4.9?×?10?6 cm.s?1, respectively. The electrocatalysis of the modified electrodes towards detection of H2O2 gave significant peak current densities and electrocatalytic potentials at ?0.28 V and ?0.31 V for the MnTAPc and CoTAPc modified electrodes, respectively.  相似文献   

3.
Mass spectrometric studies of the ions present in H2/O2/N2 flames with potassium and chlorine added have demonstrated that ionization can occur in the forward steps of K + Cl ? K+ + Cl? (II), KCl + M ? K+ + Cl? + M (IV), where M is any third body. Variations of [K+] with time in these systems have been measured and establish that the rate coefficients (in ml molecule?1 s?1) of the ion-producing steps are k2 = 5 × 10?10T?12 exp(?10 500/T) and k4 = 2.2 × 107T?3.5 × exp(?60 800/T). Coefficients for ion-ion recombination have been obtained from k2 and k4 using the equilibrium constants of (II) and (IV) and are k?2 = 1.7 × 10?9T?12 and k?4 = 1.1 × 10?17T?3, with each one in the ml molecule?1 s?1 system of units. Replacement of the N2 in one of these flames with sufficient Ar to maintain the temperature constant leaves the measured k2 and k?2 unchanged, but lowers the observed k4 and k?4. This confirms that ion-recombination in the backward step in (II) is a two-body process, whereas in (IV) it is termolecular.  相似文献   

4.
cis- and trans - 2,3 - Dimethylenemethylenecyclopropane (C and T) interconvert at 160.0° with a small normal kinetic isotope effect (KIE) when the exo-methylene is deuterated, but the 1,3-shift products, 2-methylethylidenecyclopropane, show a large normal KIE, 1.35 and 1.31, when formed from C and T, respectively. This data can be interpreted in terms of either parallel reactions or a common trimethylenemethane diradical intermediate formed with a normal KIE of 1.11 and closing to 1,3-shift product with a normal KIE of 1.29 due to the effect of deuterium in the required 90° rotation of the exo-methylene carbon.The kinetics of the thermal 1,3- and 3,3-shifts of cis- and rans-3,4-dimethyl-1,2-dimethylenecyclobutane (CB and TB) were determined in a flow reactor. The first order rate constants are log kCB (sec?1) = 13.7 ? 42,200/2.3 RT and log kTB (sec?1) = 13.6 ? 41,900/2.3 RT (Ea in kcal/m) which compare favorably to that from the parent hydrocarbon. 1,2-dimethylenecyclobutane, after reasonable correction for dimethyl substitution.Rearrangement of TB and its bis(dideuteriomethylene) derivative at 230.0° revealed a normal KIE of 1.08. This KIE could be interpreted in terms of either a methylene rotational isotope effect in a concerted reaction or formation of a bisallyl diradical with the expected normal rotational IE on closure to the 1,3-shift product of 1.12 with no IE in the ring opening when the result is corrected for return of the biradical to starting material.The kinetics of intramolecular 2 + 2 cycloaddition of 1,2,8,9-decatetraene were determined in a flow reactor. The first order rate constant is log k(sec?1) = 9.4 ? 30,800/2.3 RT (Ea in kcal/m). These energetics are compared with those of other 2 + 2 cycloadditions. The major product is 3,4-dimethylenecyclooctene (DC) which is also found from the minor product, cis-7,8-dimethylenebicvyclo[4.2.0]octane (CO), at higher temperatures. The trans isomer, TO, also gives DC at about the same rate as CO.  相似文献   

5.
Excited iodine atoms I(2P12) are formed by laser irradiation of C2F5I at 2950 Å. The mean radiative lifetime τ of these metastable atoms and their bimolecular rate constant k2 for deactivation in collissions with C2F5I were measured to be: τ = 108 ± 10 ms; k2 = (1.8 ± 0.1) × 10?17 cm3/molec s.  相似文献   

6.
The tracer diffusion coefficient, D1O, of oxide ions in LaFeO3 single crystal was determined over the temperature range of 900–1100°C by the gas-solid isotopic exchange technique using 18O as a tracer. For the determination of D1O, the depth profile of 18O was measured by means of a secondary ion mass spectrometer (SIMS). The surface exchange reaction was found to be slow and the surface exchange rate constant, k, was determined together with D1O. It was found that D1O at 950°C is proportional to P?0.58O2, where PO2 is an oxygen pressure. The vacancy mechanism was determined for the diffusion of oxide ions from the PO2 dependence. The vacancy diffusion coefficient, DV, for LaFeO3 was nearly the same as that for LaCoO3 at the same temperature. The activation energy for migration of oxide ion vacancies was 74 kJ · mole?1 for both oxides.  相似文献   

7.
Calcium arsenate dihydrate is precipitated at pH 7.0 and its dissolution in aqueous solutions at temperatures of 35, 40, 45 and 50°C and a pH of between 3.0 and 8.0 is investigated. The thermodynamic parameters ΔG0, ΔS0 and ΔH0 for the process are evaluated. Temperature dependence of solubility is obtained by the equations ?log KTCA = 9078.138T ? 34.0468 + 0.0821421 T  相似文献   

8.
Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(2P12) + O2 → Br(2P32) + O2 (k1), and Br(2P12) + NO → Br(2P32) + NO (k4) have been measured with a photodissociative IBr laser on the electronic transition 2P12?2P32 in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10?14 cm3 s?1 and (1.9 ± 0.6) × 10?12 cm3 s?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.  相似文献   

9.
The kinetics of the aminolysis of different nitrophenylacetates were investigated with n-butylamine in dioxane at 20°C. The reaction rate can be described up to high concentrations of amine (~1 mole dm?3) by the equation v=k2[ester][amine]+k3[ester][amine]2. The ratio k3k2 is larger for p-nitrophenylacetates than for o-nitrophenylacetates, while for 2,4-dinitrophenylacetates a third order term is not observed.  相似文献   

10.
In this study, an oxadiazole multi-wall carbon nanotube-modified glassy carbon electrode (OMWCNT?GCE) was used as a highly sensitive electrochemical sensor for hydrazine determination. The surface charge transfer rate constant, k s, and the charge transfer coefficient, ??, for electron transfer between GCE and electrodeposited oxadiazole were calculated as 19.4?±?0.5?s?1 and 0.51, respectively at pH?=?7.0. The obtained results indicate that hydrazine peak potential at OMWCNT?GCE shifted for 14, 109, and 136?mV to negative values as compared with oxadiazole-modified GCE, MWCNT?GCE, and activated GCE surface, respectively. The electron transfer coefficient, ??, and the heterogeneous rate constant, k??, for the oxidation of hydrazine at OMWCNT?GCE were also determined by cyclic voltammetry measurements. Two linear dynamic ranges of 0.6 to 10.0???M and 10.0 to 400.0???M and detection limit of 0.17???M for hydrazine determination were evaluated using differential pulse voltammetry. In addition, OMWCNT?GCE was shown to be successfully applied to determine hydrazine in various water samples.  相似文献   

11.
Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 103 M?1) cm?1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E12 = ?0.448 V vs NHE, and ΔSrcθ = ?6 cal · mol?1 · deg?1. Electron transfer kinetics with [CO(en)3]3+ led to k12 = 3100 M?1 s?, ΔH = 12.4 kcal · mol?1 and ΔS = ?0.9 cal · mol?1 · deg?1 (I = 0.10 M). For the related [Co(NH3)6]3+ complex, k13 = 1.9 × 104 M?1 s?1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.  相似文献   

12.
The photolysis of n-C3F7I and C2F5I has been studied with a frequency doubled dye laser at fixed frequency in the UV by detection of time resolved resonance fluorescence of the metastable iodine formed. The rate coefficient for quenching of I(2P12) by n-C3F7I has been obtained as k = (4.6 ± 0.3) × 10?17 cm3 molecule?1s?1. This value is by more than an order of magnitude lower than published values. Further proof is given for the value of the radiative lifetime of the metastable atoms which was obtained recently by this experimental method. This answers questions raised by Husain et al. on this subject in this journal.  相似文献   

13.
A nano-micelle with highly efficient peroxide activity was constructed by self-assembly of sodium dodecyl sulfate micellar, histidine and hematin in 50 mM phosphate buffer at 25 °C. UV–Vis spectrometry methods were utilized for characterization of the nanostructured material or artificial peroxidase (AP). The Michaelis–Menten (K m) and catalytic rate (k cat) constants of the AP were obtained to be 5.5 μM and 0.06 s?1, respectively, in 50 mM phosphate buffer solution at pH 8.0. The catalytic efficiency of AP was evaluated to be 0.011 μM?1 s?1. The AP was also immobilized on a functional multi-wall carbon nanotubes-gold nanoparticles (AuNPs) nano-complex modified glassy carbon electrode (GCE). The transmission electron microscopy method was utilized for the characterization of the nano-materials. The electron-transfer rate constant (k s) and the apparent Michaelis–Menten constant K m app of the AP modified GCE were evaluated to be 1.36 s?1 and 0.19 μM, respectively. For a biosensor without a redox protein, the properties of the AP modified GCE were significant and will further benefit from additional studies and improvement.  相似文献   

14.
In this study, direct electron transfer (ET) has been achieved between an immobilised non-symbiotic plant haemoglobin class II from Beta vulgaris (nsBvHb2) and three different screen-printed carbon electrodes based on graphite (SPCE), multi-walled carbon nanotubes (MWCNT-SPCE), and single-walled carbon nanotubes (SWCNT-SPCE) without the aid of any electron mediator. The nsBvHb2 modified electrodes were studied with cyclic voltammetry (CV) and also when placed in a wall-jet flow through cell for their electrocatalytic properties for reduction of H2O2. The immobilised nsBvHb2 displayed a couple of stable and well-defined redox peaks with a formal potential (E°′) of ?33.5 mV (vs. Ag|AgCl|3 M KCl) at pH 7.4. The ET rate constant of nsBvHb2, k s, was also determined at the surface of the three types of electrodes in phosphate buffer solution pH 7.4, and was found to be 0.50 s?1 on SPCE, 2.78 s?1 on MWCNT-SPCE and 4.06 s?1 on SWCNT-SPCE, respectively. The average surface coverage of electrochemically active nsBvHb2 immobilised on the SPCEs, MWCNT-SPCEs and SWCNT-SPCEs obtained was 2.85?×?10?10 mol cm?2, 4.13?×?10?10 mol cm?2 and 5.20?×?10?10 mol cm?2. During the experiments the immobilised nsBvHb2 was stable and kept its electrochemical and catalytic activities. The nsBvHb2 modified electrodes also displayed an excellent response to the reduction of hydrogen peroxide (H2O2) with a linear detection range from 1 μM to 1000 μM on the surface of SPCEs, from 0.5 μM to 1000 μM on MWCNT-SPCEs, and from 0.1 μM to 1000 μM on SWCNT-SPCEs. The lower limit of detection was 0.8 μM, 0.4 μM and 0.1 μM at 3σ at the SPCEs, the MWCNT-SPCEs, and the SWCNT-SPCEs, respectively, and the apparent Michaelis–Menten constant, $ {\hbox{K}}_{\rm{M}}^{\rm{app}} $ , for the H2O2 sensors was estimated to be 0.32 mM , 0.29 mM and 0.27 mM, respectively.  相似文献   

15.
Seeded supersonic NO beams were used to study the kinetic energy dependence of both the electronic (NO2*) and vibrational (NO23) chemiluminescence of the NO + O3 reaction. In addition the electronic CL is found to be enhanced by raising the NO internal temperature. This is shown to be due to enhanced reactivity of the NO(2Π,32) fine structure component. By difference NO(2Π12) is concluded to yield predominantly groundstate NO23. The excitation function for NO2* formation from NO(2Π32) is of the form σ32(E) = C(E/E0 - 1)n over the 3–6 kcal energy range where n = 2.4 ± 0.15, C = 0.163 Å2 and E0 = 3.2 ± 0.3 kcal/mole. Vibrational IR emission from NO23 has an energy dependence different from electronic NO2* emission, confirming that emitters are formed predominantly in distinct reaction channels rather than via a common precursor (either NO2* or NO23). The short wavelength cutoff of the CL spectra recorded at elevated collision energies E ? 15 kcal/mole corresponds to the total available energy. These and literature results are discussed in the light of general properties of the (generally unknown) ONO3 potential energy surfaces. The formation of electronically excited NO2* rather than energetically preferred O2 (1 Δg) (Gauthier and Snelling) can be rationalized in terms of surface hopping near a known intersection of potential energy surfaces more easily than by vibronic interaction in the asymptotic NO2 product.  相似文献   

16.
《Electroanalysis》2003,15(4):249-253
Cyclic voltammetric measurements were made using well‐characterized microcrystalline boron‐doped diamond thin‐film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002 cm/s were observed in 0.1 M NaClO4/CH3CN, 0.1 M TBAClO4/CH3CN, and 0.1M TBAClO4/CH2Cl2, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron‐doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes.  相似文献   

17.
Sadik Cogal 《Analytical letters》2018,51(11):1666-1679
Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant ks (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM?1?cm?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.  相似文献   

18.
The electrochemical redox properties of a surface‐confined thin solid film of nanostructured cobalt(II) tetracarboxyphthalocyanine integrated with multiwalled carbon nanotube (nanoCoTCPc/MWCNT) have been investigated. This novel nanoCoTCPc/MWCNT material was characterized using SEM, TEM, zeta analysis and electrochemical methods. The nanoCoTCPc/MWCNT nanohybrid material exhibited an extra‐ordinarily high conductivity (15 mS cm?1), which is more than an order of magnitude greater than that of the MWCNT‐SO3H (527 µS cm?1) and three orders of a magnitude greater than the nanoCoTCPc (4.33 µS cm?1). The heterogeneous electron transfer rate constant decreases as follows: nanoCoTCPc/MWCNT (kapp≈19.73×10?3 cm s?1)>MWCNT‐SO3H (kapp≈11.63×10?3 cm s?1)>nanoCoTCPc (kapp≈1.09×10?3 cm s?1). The energy‐storage capability was typical of pseudocapacitive behaviour; at a current density of 10 µA cm?2, the pseudocapacitance decreases as nanoCoTCPc/MWCNT (3.71×10?4 F cm?2)>nanoCoTCPc (2.57×10?4 F cm?2)>MWCNT‐SO3H (2.28×10?4 F cm?2). The new nanoCoTCPc/MWCNT nanohybrid material promises to serve as a potential material for the fabrication of thin film electrocatalysts or energy‐storage devices.  相似文献   

19.
The electrochemical kinetics of the benzoquinone (Q)/hydroquinone (H2Q) redox couple at platinum electrodes in aqueous solutions has been found to be extremely sensitive to the nature of species adsorbed on the electrode surface at monolayer coverages. Experimental measurements were based on thin-layer cyclic voltammetry; the use of thin-layer electrodes was dictated by the need to minimize surface contamination. Bulky neutral or anionic aromatic adsorbates led to the familiar U-shaped rate-vs.-pH curves; the rate minimum occurred near pH 4. Kinetic effects due to oriental changes of chemisorbed species were noted only when the rate was low. Adsorbed 1 atoms led to comparatively rapid reactivity (rate constant k° > 10?3 cm s?1) and virtual independence of pH. Profound retardation resulted from pretreatment ofthe surface with CN? and SCN?; total irreversibility (k° < 10?6 cm s?1) was observed at pH 4, with a further decrease in rate at pH 7. In contrast, when the surface contained n layer of chemisorbed phenyltriethylammonium cations, the electrode rate increased with increasing pH. The results indicate that different reaction pathways predominate when different absorbates are present.  相似文献   

20.
The preparation and electrochemical characterization of glassy carbon electrodes modified with plumbagin were investigated by employing cyclic voltammetry, chronoamperometry and rotating disc electrode techniques. The cyclic voltammograms of the electroreduction of oxygen showed an enhanced current peak at approximately −0.289 V in air-saturated phosphate buffer pH = 7 and scan rate 10 mV s−1. The thermodynamic and kinetic parameters of the reduction of oxygen at glassy carbon have been evaluated using cyclic voltammetry. The experimental parameters were optimized and the mechanism of the catalytic process was discussed. The obtained values of E°′ (V vs. Ag/AgCl), the apparent electron transfer rate constant ks (s−1), heterogeneous rate constant for the reduction of O2 at the surface of the modified electrode kh (M−1 s−1) and α (charge transfer coefficient of oxygen) were as follows: −0.146, 23.4, 9.9 × 103 and 0.57, respectively. In addition, plumbagin exhibited strong catalytic activity toward the reduction of H2O2.  相似文献   

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