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Abstract: Theoretical equations of ac-voltammetric current or the equivalent admittance and/or impedance of the electron transfer reaction between a redox couple of A species, ARED and AOX, in organic (O) phase and another redox couple of B species, BOX and BRED, in aqueous or water (W) phase at the O∣W interface: ARED(O)+BOX(W)=AOX(O)+BRED(W) are derived when the electron transfer reaction is dc-voltammetric-reversible. The theoretical equations are discussed with reference to the mechanisms by which the electron transfer reaction may take place at the interface, that is, either by the heterogeneous electron transfer reaction mechanism at the interface or by the mechanism in which the homogeneous electron transfer reaction is associated with the ion transfer across the interface. [Copyright &y& Elsevier]

Abstract: The electron transfer reaction between bis(phthalocyaninato)lutetium(III) ([Lu(pc)2]0) in 1,2-dichloroethane (1,2-DCE) and hexacyanoferrate(II/III) redox couple ([Fe(CN)6]4−/3−) in water (W) at the interface was studied by the use of normal pulse voltammetry and ac-voltammetry. The ac-voltammetric results have reconfirmed that the electron transfer reaction between [Lu(pc)2] in 1,2-DCE and [Fe(CN)6]4−/3− in W takes place by way of the heterogeneous electron transfer at the interface, but not by the homogeneous electron transfer reaction associated with the ion transfer of redox species across the interface. The kinetic parameters of the heterogeneous electron transfer reaction at the interface were determined. [Copyright &y& Elsevier]

Abstract: The electron transfer (ET) reaction between bis(cyclopentadienyl)iron(II) ([FeII(C5H5)2]) in 1,2-dichloroethane (1,2-DCE) and in nitrobenzene (NB) and hexacyanoferrate redox couple ([FeII/III(CN)6]4−/3−) in water (W) at the interface has been studied by use of normal-pulse voltammetry. The voltammetric results indicate that the ET reaction between [FeII(C5H5)2] in O (O=1,2-DCE or NB) and [FeII/III(CN)6]4−/3− in W takes place not by way of the heterogeneous ET at O|W interface but by the mechanism in which a homogeneous ET reaction between [FeII(C5H5)2] (partially distributed from O) and [FeIII(CN)6]3− takes place in W phase and the resultant [FeIII(C5H5)2]+ ion is responsible for the current passage across the interface. From the limiting current, the forward rate constants of the homogeneous ET reaction: [Fe(C5H5)2]+[Fe(CN)6]3− =[Fe(C5H5)2]+ +[Fe(CN)6]4− in W phase, , were determined to be (3.2±2.0)×1010 M−1 s−1 and (2.0±1.3)×1010 M−1 s−1 with the 1,2-DCE|W (1.5M Li2SO4) and NB|W (1.5M Li2SO4) interfaces, respectively. These values are in the order of the rate constant of diffusion-controlled bimolecular reaction in solution. Also, the formal (standard) potentials of the transfer of [Fe(C5H5)2]+ ion at the interface, , were determined to be −0.015±0.014V and −0.087±0.015V with the 1,2-DCE|W (1.5M Li2SO4) and NB|W (1.5M Li2SO4) interfaces, respectively. [Copyright &y& Elsevier]

Abstract: Theory of normal-pulse voltammetric current of electron transfer (ET) reaction at organic solvent(O)/water(W) interface between a redox couple of A species, ARED and AOX, in O phase and another redox couple of B species, BOX and BRED, in W phase has been discussed. ARED is supposed to be a neutral molecule and AOX a cation, whereas both BRED and BOX are supposed to be highly hydrophilic. Then, two kinds of the reaction mechanism, that is, (1) the heterogeneous ET reaction: ARED(O)+BOX(W)=AOX(O)+BRED(W) at the O/W interface producing the voltammetric current, and (2) the transfer of ARED(O) molecule from O to W phase across the interface, then the homogeneous ET reaction: ARED(W)+BOX(W)=AOX(W)+BRED(W) in W phase, followed by the transfer of AOX(W) cation from W to O phase producing the voltammetric current, are considered. Theoretical equations of normal-pulse voltammetric current of the ET reaction at O/W interface are derived under the assumptions (i) that the ET reaction is pseudo-monomolecular with respect to A species, (ii) that the partition of ARED molecule between O and W phases is highly biased to O phase, and (iii) that the rate constants of homogeneous ET reaction in W phase are sufficiently large. Application of the theoretical equations to investigate the mechanism of the ET reaction at O/W interface has been discussed. [Copyright &y& Elsevier]