Studies of electron-transfer and charge-transfer coupling processes at a liquid/liquid interface by double-barrel micropipet technique

Investigation of a heterogeneous electron-transfer (ET) reaction at the water/1,2-dichloroethane interface employing a double-barrel micropipet technique is reported. The chosen system was the reaction between Fe(CN)(6)(3-) in the aqueous phase (W) and ferrocene in 1,2-dichloroethane (DCE). According to the generation and the collection currents as well as collection efficiency, the ET-ion-transfer (IT) coupling process at such an interface and competing reactions with the organic supporting electrolyte in the organic phase can be studied. In addition, this technique has been found to be an efficient method to distinguish and measure the charge-transfer coupling reaction between two ions (IT-IT) processes occurring simultaneously at a liquid/liquid interface. On this basis, the formal Gibbs energies of transfer of some ions across the W/DCE interface, such as NO3-, NO2-, Cl-, COO-, TBA(+), IPAs+, Cs+, Rb+, K+, Na+, and Li+, for which their direct transfers are usually difficult to obtain because of the IT-IT coupling processes, were quantitatively evaluated.

Mass-transfer kinetics of ytterbium extraction with sec-nonylphenoxy acetic acid

The extraction kinetics of ytterbium with sec-nonylphenoxy acetic acid (CA-100) in heptane have been investigated using a constant interfacial area cell with laminar flow. The influence of stirring speed and temperature on the rate indicated that the extraction rate was controlled by the experiment conditions. The plot of interfacial area on the rate showed a linear relationship. This fact together with the low solubility in water and strong surface activity of CA-100 at heptane-water interfaces made the interface the most probable locale for the chemical reactions. The influences of extractant concentration and hydrogen ion concentration on the extraction rate were investigated, and the forward and reverse rate equations for the ytterbium extraction with CA-100 were also obtained. Based on the experimental data, the apparent forward extraction rate constant was calculated. Interfacial reaction models were proposed that agree well with the rate equations obtained from experimental data.

Study on transfer and interfacial kinetics of neodymium and samarium in membrane based extraction

Extraction and interfacial kinetics of Nd3+ and Sm3+ with HER/EHP-kerosene in a hollow fiber membrane extractor were studied. The results show that the extraction reactions in the hollow fiber membrane extractor are the same as those in the liquid-liquid extraction, which can be expressed as a quasi-first-order reaction. The effect of acidity in aqueous phase, concentrations of extractant, Nd3+ and Sm3+ on extraction rate were discussed and the corresponding reaction series were obtained. The reaction equations, reaction rate constants and the separation constant were obtained.

Study of electron transfer across the liquid/ice-like matrix interface by scanning electrochemical microscopy

In this work, we report the findings of a study on scanning electrochemical microscopy (SECM) to investigate the interfacial electron-transfer (ET) reaction between the 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ(.-)) in 1,2-dichloroethane and ferricyanide in an ice-like matrix (a mixture of insulting ice and conductive liquid) under low temperatures. Experimental results indicate that the formed liquid/ice-like matrix interface is superficially similar in electrochemical characteristics to a liquid/liquid interface at temperatures above -20 degreesC. Furthermore, imaging data show that the surface of the ice-like matrix is microscopically flat and physically stable and can be applied as either a conductive or an insulting substrate for SECM studies. Perchlorate ion was selected as the common ion in both phases, the concentrations of which controlled the interfacial potential difference. The effect of perchlorate concentration in the DCE phase on interfacial reactions has been studied in detail. The apparent heterogeneous rate constants for TCNQ(.-) oxidation by Fe(CN)(6)(3-) in another phase under different temperatures have been calculated by a best-fit analysis, where the experimental approach curves are compared with the theoretically derived relationships. Reaction rate data obey Butler-Volmer formulation before and after the freezing point, which is similar to most other known cases of ET reactions at liquid/liquid interfaces. However, there is a sharp change observed for heterogeneous rate constants around the freezing point of the aqueous phase, which reflects the phase transition. At temperatures below -20 degreesC, surface-confined voltammograms for the reduction of ferricyanide were obtained, and the ice-like matrix became an insulating one, which indicates that the aqueous phase is really a frozen phase.

Gas-phase ion-molecule reactions of C-60 with the plasma of methyl acrylate

The gas-phase ion-molecule reactions of C-60 with the plasma generated from methyl acrylate under self-chemical ionization conditions were studied by use of a triple-quadrupole mass spectrometer. The adduct cation [C60C3H3O](+) and protonated molecular ion [C60H](+) were observed as the major product ions. The former adduct ion is formed by electrophilic reaction of C-60 with the ion [CH2=CHCO](+), a main fragment ion resulting from the methyl acrylate molecular ion [CH2=CHCOOCH3](+) through alpha cleavage. The latter ion is generated by proton transfer from protonated methyl acrylate to C-60. Semi-empirical quantum chemical calculations have been performed for the eight possible isomers of [C60C3H3O](+) at the Hartree-Fock level by use of the AMI method. The results show three types of cycloadducts as the most stable structures among the possible isomers.

Kinetic isotope effects of proton transfer reaction for amines by ultrasonic relaxation methods: Unexpected evidence from the results in ethylamine solutions

Ultrasonic absorption coefficients for ethylamine in heavy water (D2O) and in light water (H2O) have been measured in the frequency range from 0.8 to 220 MHz at 25 degrees C. A single relaxational process has been observed in these two kinds of solutions. From the concentration dependence of the ultrasonic relaxation parameters, and following the reaction mechanism proposed by Eigen et al. for ethylamine in H2O, the causes of the relaxations have been attributed to a perturbation of an equilibrium associated with a deuteron or proton transfer reaction. The rate and equilibrium constants have been estimated from deuterioxide or hydroxide ion concentration dependence of the relaxation frequency, and the kinetic isotope effects have been determined. In addition, the standard volume changes of the reactions have been calculated from the concentration dependence of the maximum absorption per wavelength, and the adiabatic compressibility has also been determined from the density and sound velocity for ethylamine in D2O and in H2O, respectively. These results are compared with those for propylamine and butylamine and are discussed in relation to the different kinetic properties between D2O and H2O, the reaction radii derived by Debye theory, and the structural properties of the reaction intermediate.

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH4+, Li+, Na+ and K+), anions (SO42- and NO3-) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. (C) 1997 Elsevier Science S.A.

Kinetics of electrocatalytic ascorbic acid at ultramicroelectrode modified by Eastman-AQ polymer containing tris(2,2-'-bipyridine) osmium(III/II) complexes as electron-transfer centers

The theoretical model[17] of an ultramicroelectrode modified with a redox species film is used as the diagnostic tool to characterize the catalytic oxidation of ascorbic acid at carbon fiber ultramicrodisk electrodes coated with an Eastman-AQ-Os(bpy)(3)(2+) film. The electrocatalytic behavior of ascorbic acid at the ultramicroelectrode modified by an Eastman-AQ polymer containing tris(2,2'-bipyridine) osmium(III/II) as mediators is described. In order to determine the five characteristic currents quantitatively, the radius of the ultramicroelectrode and the concentration of ascorbic acid are varied systematically. The kinetic zone diagram has been used to study the electrocatalytic system. This system with 0.5-2.75 mM ascorbic acid belongs to SR + E case, and the concentration profiles of the catalyst in the film are given in detail. Finally, optimizing the design of catalytic system is discussed.

DIRECT ELECTROCHEMICAL REACTIONS OF CYTOCHROME-C AT IODIDE-MODIFIED ELECTRODES

Quasi-reversible and direct electron transfer was observed between an iodide-modified Au electrode and cytochrome c, as well as between cytochrome c in an iodide-containing solution and a bare Au electrode. The results suggest that an electrostatic intera

ELECTROCHEMICAL STUDY OF CHOLINE DERIVATIVES TRANSFER ACROSS THE LIQUID LIQUID INTERFACE

Transfer behaviors across the water/nitrobenzene interface were studied for five choline derivatives by chronopotentiometry with linear current scanning, cyclic voltammetry and differential pulse voltammetry. The irreversible hydrolysis reactions coupled to the phase transfer of ions across the water/nitrobenzene interface were observed. The Gibbs energies of the transfer of choline derivatives show the effects of an additive constitution on hydrophobic property of the medicine.

HE PHASE TRANSFER OF CO(II) CATALYZED BY 2,2 '-BIPYRIDINE AT THE WATER/NITROBENZENE INTERFACE

The chemical reactions coupled with the phase transfer of Co(Ⅱ) catalyzed by 2,2′ -bipyridine across the water/nitrobenzene interface have been observed by using cyclic voltammetry (CV). Coupled chemical reactions both in the organic phase or in the aqueus phase influence the CV behavior of successive complex phase transfer obviously and an irreversible phenomenon similar to that existed at the metal electrode/electrolyte solution interface was observed. For different complexes, the phase transfer mechanism...