Yufei Cheng

Electrodeposition of metallic gold clusters at the water/1,2-dichloroethane interface

Gold particles have been deposited at an immiscible electrolyte interface by electrochemical reduction of tetraoctylammonium tetrachloroaurate (TOAAuCl4) in 1,2-dichloroethane using potassium hexacyanoferrate(II)[K4Fe(CN)6] in water as the electron-transfer agent. The gold particles are formed at the interface and not in the bulk phases, and their growth was monitored in situ by transmission UV–VIS spectroscopy. The observed spectra have been qualitatively analysed using Mies theory.

A.C. impedance study of rate constants for two-phase electron-transfer reactions

The a.c. impedance technique has been used for the measurement of electron-transfer rate constants between organic and inorganic redox couples at the water/1,2-dichloroethane interface. The organic compounds studied were lutetium diphthalocyanine, bis(pyridine)(meso-tetraphenylporphyrinato)ruthenium(II) and 7,7,8,8-tetra-cyanoquinodimethane; Fe(CN)3–/4–6 was in all cases the aqueous redox couple. Electron-transfer rate constants were calculated using recent theoretical developments based on a continuum media model. It is concluded that Marcus theory can be used to predict the rate constants for two-phase reactions. Potential-dependent transfer coefficients have been found and it is shown that the origin of this effect is ionic adsorption in the form of interfacial ion pairing.

Electron transfer between bis(pyridine)meso-tetraphenylporphyrinato iron(II) and ruthenium(III) and the hexacyanof errate couple at the 1,2-dichlor

Abstract Oxidation and reduction of iron and ruthenium metalloporphyrin complexes with pyridine in 1,2-dichloroethane (1,2-DCE) have been investigated. Redox potential shifts are observed for the two compounds on complexation. Electron transfer reactions between these two complexes in the organic phase and the aqueous ferri-ferrocyanide couple have been studied at the 1,2-DCE/water interface, for which a quasi-reversible one-electron transfer was found, whereas reversible behaviour was observed at metallic electrodes. Possible explanations for this difference are discussed in terms of orientation and ligand effects.

Redox electrocatalysis by tetracyanoquinodimethane in phospholipid monolayers adsorbed at a liquid/liquid interface

Electron-transfer reactions at the water/1,2-dichloroethane interface with an adsorbed phospholipid monolayer have been studied for three organic redox couples: TCNQ, Ru(TPP)(py)2 and Lu(PC)2. The presence of a monolayer at the immiscible interface inhibited electron-transfer reactions to increasing extents on going from TCNQ to Ru(TPP)(py)2 to Lu(PC)2. This effect is attributed to the different Gibbs energies of transport across the monolayer of each species resulting from size effects, which prevent the approach of the redox centres present in the adjoining phase. Electron transfer mediated by TCNQ in a redox electrocatalytic cycle has been observed between the ruthenium(II) prophyrin complex, Ru(TPP)(py)2, and aqueous Fe(CN)3–/4–6. The differences in rates of electron transfer for the three compounds are discussed in terms of their structures and of the distances of closest approach between redox centres present in the different phases.

Electro-assisted solvent extraction of Cu2+, Ni2+ and Cd2+

Abstract A novel separation method, i.e. electro-assisted solvent extraction, based on the principles of two-phase electrochemistry, has been demonstrated for the successful separation of Ni 2+ , Cu 2+ and Cd 2+ ions. 2-Heptanone has been used as the organic solvent for the transfer of Ni 2+ , Cu 2+ and Cd 2+ facilitated by 2,2′;6′,2″-terpyridine. It is shown that extraction efficiency depends on the concentration ratio of ligand to metal ion and importantly, on the applied interfacial potential difference. It was found that Ni 2+ (not Cd 2+ or Cu 2+ ) extraction is suppressed in the presence of Mg 2+ ion due to competitive complexation.

A study of 2-heptanone and 2-octanone as solvents for two-phase electrochemistry. Part 1. Simple ion transfers

Abstract Transition metal ion (Cd2+, Co2+, Cu2+, Mn2+, Ni2+, Zn2+) transfer from water to methyl n-amyl ketone (2-heptanone) and methyl n-hexyl ketone (2-octanone) facilitated by nitrogen-containing ligands has been investigated by a.c. and d.c. voltammetry. For Cd2+, Cu2+ and Zn2+ in the presence of terpyridine as a ligand both facilitated and complex ion transfers are observed, while for the Co2+- and Ni2+-terpyridine systems only complex ion transfer takes place. The differences between the facilitated and complex ion transfers have been discussed in terms of the different mechanisms of the transfer reactions. This study shows that it is possible to use 2-heptanone and 2-octanone in electro-assisted solvent extraction and supported liquid membrane separation of metal ions, based on two-phase electrochemical principles.

Electroassisted separation of metals by solvent extraction and supported-liquid membranes

Electroassisted separation methods based on the use of electrically conducting supported liquid membranes and of liquid/liquid extraction under control of the interfacial Galvani potential are described. The control of interfacial potentials and the use of metal ion specific ligands have been employed to achieve specificity in metal ion separations and for the stripping and concentration of metal ion from dilute streams. It is shown that a supported liquid membrane can be used as an ion selective membrane for the electrolysis of specific metal ions. The interfacial potential for electroassisted solvent extraction is determined by the two-phase Nernst equation, which relates the distribution of ionic species to the Galvani potential and to the standard Gibbs energies of ionic transfer between an aqueous and an organic phase immiscible with water. It is shown that specificity in separations can be achieved in solvent extraction by controlling the Galvani potential.

Electrochemistry of anti-HIV agents

Square wave voltammetry has been used to study the electrochemical behaviour of anti-HIV drugs in aqueous solutions. The oxidation reaction of Carbovir (1) at a Pt microelectrode occurs at 1.12 V versus SCE and the peak current is proportional to the concentration. An electroanalytical technique for the determination of trace concentrations of Carbovir (1) is proposed and experimental conditions have been optimised. The effect of Cu(II) on the electrochemistry of nucleosides and nucleotides has also been studied. An equilibrium between the nucleotide-copper complex formed and the free nucleotide is observed.