Yumi Yoshida

Ion transfer through a liquid membrane or a bilayer lipid membrane in the presence of sufficient electrolytes

Abstract Voltammograms for the ion transfer from one aqueous solution (W1) to another (W2) through a liquid membrane (LM) (VITTM) were recorded under various conditions by scanning the potential applied between two aqueous phases and measuring the current between two aqueous phases. A method of analysing the VITTM was proposed based on the comparison of the VITTM with voltammograms at the W1|LM and LM|W2 interfaces observed simultaneously with the VITTM. The membrane transport was demonstrated to be controlled mainly by the complementary ion transfers at the W1|LM and LM|W2 interfaces, when W1, LM and W2 contain sufficient electrolytes. The influence of different ions in LM or W2 on the membrane transport of an objective ion and the change in ion transfer reactions at the W1|LM and LM|W2 interfaces during the electrolysis under an applied membrane potential were elucidated taking into account the relation among the VITTM and voltammograms at two interfaces. The ion transport through a bilayer lipid membrane (BLM) was found to be analogous to that through an LM when the BLM contains sufficient ions, although the BLM is very much thinner than the LM.

Evaluation of distribution ratio in ion pair extraction using fundamental thermodynamic quantities

Abstract Equations were derived for the quantitative expressions of distribution ratios, D M , in ion pair extractions of a cation, M + , with a counter ion, X − , from water, W, to an organic solvent, O, in the absence and presence of a special complexing neutral ligand, L, in O by using standard transfer free energies of M + and X − from W to O, ion pair formation constants of M + with X − in W and O, the stability constant of the complex, (ML) + , in O and the ion pair formation constant of (ML) + with X − in O. The D M values calculated by substituting the constants determined by electrochemical methods into the derived equations agreed very well with those obtained experimentally by ion pair extraction, which means that the extraction processes assumed in the derivation of the equations was reasonable.

Redox reactions between NADH and quinone derivatives at a liquid/liquid interface

Abstract The redox process between NADH in an aqueous solution, W, and chloranil, CQ, or toluquinone, TQ, in 1,2-dichloroethane, DCE, at the W/DCE was investigated as the function of potential differences applied between W and DCE, E W/DCE . Two different redox reactions were found to occur depending on the potential difference at the W/DCE interface as well as the kind of quinone, Q. The reaction products between NADH and CQ were NAD + and CQ % s − when the electrolysis had been carried out by applying a constant E W/DCE in one potential range, Range A, and were NAD + in W and QH 2 in DCE at E W/DCE in another potential range, Range B. It was also demonstrated that the redox reaction could be controlled by selecting the ion transfer reaction occurring simultaneously with the redox reaction at the interface.

Physicochemical understanding of the selectivity at an ion selective electrode of the liquid membrane type and relation between the selectivity and distribution ratios in the ion-pair extraction

Abstract The potentials, E ISE , and selectivity coefficients, K pot ij , at an ion selective electrode (ISE) of liquid membrane type were related quantitatively to distribution ratios, D , of the primary ion, i z , and the interfering ion, j z , between an aqueous, W, and an organic, O, solutions, taking into account that all the E ISE , K pot ij and D terms could be expressed physicochemically by using standard Galvani potential differences, E 0 , (or standard free energies, Δ G 0 tr ) for transfers of i z and j z from water, W, to the ISE membrane, M, or organic solution, O, stability constants, K st , of complexes of i z and j z with an ionophore in M or O and formation constants of ion-pairs, K ip , of i z - and j z -species with coexisting counter ions in M or O. The equations theoretically derived for K pot ij indicated that the K pot ij in Nicolsky–Eisenman equation was a simple function of D in i z and j z when K pot ij at an ISE was determined under the conditions recommended by IUPAC for the separate solution and the fixed solution methods. Though the derived equations were verified experimentally by employing a Na + -ISE composed of a nitrobenzene membrane containing dibenzo-18-crown-6 as an example, they are considered to be generally applicable to the estimation of K pot ij at liquid membrane type ISE.

Voltammetric study on ion transport across a liquid membrane coupled with electron transport

Abstract The process of spontaneous transport of an ion from one aqueous solution (W1) to another (W2) through a liquid membrane (LM) coupled with the electron transfer was elucidated based on the ion or electron transfer voltammograms measured between W1 and W2 and at the W1∥LM or LM∥W2 interfaces. Based on the above fundamental research, the membrane separation of K+ from Na+ with the aid of electron transfer was discussed.