The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO4 were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi3+. This indicates the accelerating effect of Bi3+ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb2+, Hg2+, Tl+, Ag+ and Sb3+, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as Mad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co2+, Zn2+, Fe3+ and Ni2+, exhibit no catalytic effect. These facts suggest that the presence of a Mad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the Mad, for example, Cuad, Cdad, Inad, Snad and Moad display no catalytic action.The catalytic activity depends on the degree of surface coverage by the Mad. The maximal effect of the Mad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the Mad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the 13C NMR spectra for the oxidation products, the adsorbed water on the Mad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid. 相似文献
Alkyl- and aryl-isothiocyanates undergo insertion reactions with platinum metal hydrides to yield the corresponding N-alkyl- and N-aryl-thioformamido derivatives, the structure and stereochemistry of which have been deduced using 1H NMR data. 相似文献
Perfluorocarboxylic acids (RFCOOH) (RF = CF3,C2F5 and (for Rh) C6F5) react with the species [M(NO)2(PPh3)2] (M = Ru, Os) and [M′(NO)(PPh3)3] (M′ = Rh, Ir) to yield new nitrosyl complexes [Ru(OCORF)3(NO)(PPh3)2], [OsH(OCORF)2(NO)(PPh3)2], [Os(OCORF)(NO)2(PPh3)2][OCORF], [Ir(OCORF)(NO)(PPh3)2][OCORF] and [Rh(OCORF)2(NO)(PPh3)2]. 相似文献
Proton NMR spectra of the dithioformate ligands in an extensive range of new platinum metal dithioformato complexes permit unambiguous assignment of stereochemistry. 相似文献
Reactions of some platinum group metal triphenylphosphine complexes with nitric acid afford nitrato(triphenylphosphine) derivatives in good yield; the complex “Rh(NO3) (NO)2(OPPh3)2” is positively identified as [Rh(NO3)2 (NO) (PPh3)2] 相似文献
Some platinum group metal hydrides react with N,N'-diarylcarbodiimides in boiling toluene to yield products containing novel bidentate N,N'-diarylformamidinate (ArNCHNAr) ligands. 相似文献
It is possible to generate conductive multilayer structures by reduction of methylene blue cations at the interface: clean surface of a platinum electrode/1 M aqueous electrolyte solution.The characteristics of the multilayer ordered phase generated in fluoride and nitrate solutions are presented and the mechanism of a fast charge transfer between electrode/organic film and organic film/aqueous solution interfaces is discussed. The conductivity of the film is interpreted by postulating formation of a mixed valence structure with the generation of a cation radical intermediate which is favoured in the solid state at characteristic potentials. 相似文献
Oxygen is shown to adsorb molecularly on gold as well as on Ag and Pt. UV and X-ray photoelectron spectroscopy and Auger electron spectroscopy have been employed to investigate electron states of molecularly adsorbed oxygen. 相似文献
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
Cyclic voltammetry has been used to study the heterogeneous electron transfer kinetics of horse heart cytochrome c in pH 7 tris/cacodylate media at several electrode surfaces. Reversible voltammetric responses (formal heterogeneous electron transfer rate constant>10?2 cm/s) were observed at bare gold electrodes and at tin-doped indium oxide semiconductor electrodes for certain experimental conditions. Quasireversible voltammetric responses were more typically observed at fluorine-doped tin oxide semiconductor electrodes, bare platinum electrodes, and at the indium oxide electrodes. Reaction rates at bare metal electrodes were strongly dependent on pretreatment procedures and experimental protocol. Reaction rates at metal oxide electrodes were strongly dependent on solution conditions, pretreatment procedures, and on the hydration state of the electrode surface. A general mechanistic scheme involving both interfacial electrostatic and chemical interactions is proposed for cytochrome c electrode reactions. The asymmetric distribution of surface charges on cytochrome c appears to play a dominant role in controlling electron transfer rates by its interaction with the electric field at the electrode surface. Electron transfer distances are also considered, and it is concluded that electron transfer between an electrode surface and the exposed heme edge of properly oriented cytochrome c molecules involves maximum distances of ca. 0.6–0.9 nm. 相似文献
In contrast to the behaviour of the analogous phosphonium betaines, neither the presence at arsenic of the electron-withdrawing 2-furyl substituent nor enclosure of the arsenic in the strained dibenzarsolium ring system promote betaine collapse via attack of betaine oxygen at the arsonium centre. Thus both 2-furyl(methyl)diphenylarsonium iodide and 5-methyl-5-phenyldibenzarsolium iodide on treatment with benzaldehyde and ethanolic sodium ethoxide give exclusive formation of olefin epoxide and tertiary arsine. 相似文献
2-Ethyl-10-[3-(dimethylamino-2-methyl)propyl]phenothiazine hydrochloride (ethylisobutrazine hydrochloride) forms an orange-red complex with platinum(IV) at room temperature (26 ± 2 °C) in hydrochloric acid-sodium acetate buffer medium containing copper(II) ions. The complexation is complete within 10 min. The complex exhibits an absorption maximum at 529 nm with a molar absorptivity of 1.90 × 104 liters mol?1 cm?1. Beer's law is obeyed over the concentration range 0.4–7.8 ppm of platinum. A 50-fold molar excess of the chromogenic reagent is necessary for the development of maximum color intensity. Job's method of continuous variation, the molar-ratio method, and the slope-ratio method indicate a 1:1 composition for the complex. The effects of pH, time, temperature, reagent concentration, order of addition of reagents, and interference of various ions are reported. The reagent has also been used successfully for the determination of platinum in minerals and alloys. 相似文献
The frequency dependence of the double-layer capacitance has been studied at the interface Hg/0.116 M KCl in water at ?1.200 V vs. a reversible calomel electrode at 25°C. Two drop electrodes attached to 0.1-mm platinum wire have been used, one sessile with a narrow wedge, the other pendant with a widely open wedge between drop surface and support. The operation of the a.c. resistor-ratio arms bridge has been analysed in a manner generally applicable to series-R, C measurements. On that basis the effect of stray capacitances could be compensated and the frequency dispersion due to the measuring system reduced to a minimum. Both electrodes show a low-frequency dispersion of the measured series capacitance C(ω) and resistance R(ω), ω being the angular frequency. This dispersion has been analysed with a simple R, C network. In series with the bulk resistance R3 this network has two mutually parallel series R, C's: R1, C1 of the drop itself and R2, C2 of its edge (neck). From the actual C(ω), R(ω) data follow correct capacitance data C1, while R2 and C2 show a relatively stronger dependence on frequency and kind of electrode (pendant or sessile). Moreover, a sessile electrode exhibits a wedge or shielding effect above a much smaller ω (=ωh >ω1, the frequency above which the edge effect becomes insignificant) than a pendant electrode. Conclusions drawn from this information are: in the frequency domain (ωh?ω1) diffusive mass transport may be studied without interference from any geometric effect, which is probably also true at small electrolyte concentrations. This study should be performed with a pendant electrode, since it has the largest (ωh?ω1) domain. 相似文献
The electrocatalytic oxidation of methanol has been investigated on platinium+palladium alloy electrodes of different compositions in acid, neutral and alkaline aqueous solutions.The surface characteristics (composition and roughness factor) of the alloys and the stability of the electrodes in contact with different electrolytic solutions have been studied using cyclic voltammetry. In particular, a surface enrichment in platinum due to a preferential dissolution of palladium and an increase of the roughness factor with an increase of the palladium content has been shown.The electrocatalytic activity of different alloys for methanol oxidation has been characterized by exchange current densities obtained from extrapolation of Tafel lines of calculated equilibrium potential. The plot of these current densities vs. the surface composition leads to a synergistic effect, particularly important in alkaline medium. A reasonable explanation of this enhanced electroactivity at about 15 at.% in Pd is given on the basis of a decrease of electrode poisoning. 相似文献
High-resolution vibrational spectra of nucleic acid components adsorbed on a silver electrode were obtained using a spectroelectrochemical method based on the large-intensity enhancement for Raman scattering at electrode surfaces.The laser surface Raman spectra of purine, adenine, adenosine, deoxyadenosine, adenine mononucleotides, adenylyl-3′, 5′-adenosine and polyriboadenylic acid were recorded in the range of 150–3500 cm?1. The intensities of the vibrational bands were highly dependent upon the electrochemical preparation of the electrode, the applied potential and the nature of the adsorbate species. High-intensity spectra in rather dilute bulk solutions were obtained.The phosphate derivatives of adenosine exhibited strongly enhanced Raman scattering. Spectral band frequencies corresponded closely with normal Raman spectra of these molecules in solution. The adenine ring breathing mode at 740 cm?1 and the adenine ring skeletal vibration at 1335 cm?1 produced prominent Raman scattering. A strong band at about 240 cm?1 for the adenine mononucleotides was attributed to silver/adsorbed phosphate group vibrations. 相似文献
Spiro[2.nalkanes (n = 2, 4, 5) react with platinum complexes to form compounds of composition PtCl2(spiroalkane). These materials have been characterized by infrared and nuclear magnetic resonance spectra, and the point of insertion has been shown to be the cyclopropyl carbon—carbon bond opposite the spiro carbon. 相似文献