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Ion-transfer reactions at the interface between fluorous solvent 1,1,1,2,3,4,4,5,5,5-decafluoropentane (DFP) and water (W) were investigated voltammetrically. Within the potential window at the DFP | W interface, various non-fluorinated ions, including tetraphenylarsonium and tetraphenylborate, and fluorinated ions, including fluorocomplex and perfluoro- n -alkanoate ions, gave reversible voltammetric waves for their ion transfer across the DFP | W interface. Based on the tetraphenylarsonium-tetraphenylborate assumption, the formal potentials of their ion transfer could be determined in terms of the Galvani potential difference. Also, formal potentials for the transfer of bis(perfluoroalkanesulfonyl)imide ions at the DFP | W interface were determined potentiometrically. The formal Gibbs energies for the transfer of ions from DFP to W, which would provide the criteria necessary for evaluating the fluorophilicity/hydrophilicity of ions were calculated from the formal potentials, and were compared with the transfer energies from 1,2-dichloroethane to W and those from the organic solvent to DFP, as quantitative scales of the ions' lipophilicity/hydrophilicity and fluorophilicity/lipophilicity. [ABSTRACT FROM AUTHOR]

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]

Abstract: The electron transfer (ET) reaction between bis(butylcyclopentadienyl)iron(II) ([FeII(C5H4Bu)2]) in 1,2-dichloroethane (1,2-DCE) and the hexacyanoferrate redox couple ([FeII/III(CN)6]4−/3−) in water (W) at the 1,2-DCE∣W interface has been studied by use of normal pulse voltammetry and cyclic voltammetry. In normal pulse voltammetry, S-shaped current vs. potential curves with well-defined limiting currents attributable to the interfacial ET reaction were observed. The voltammetric results can be explained well by the theoretical equations [M. Senda, Rev. Polarogr. (Jpn), 49 (2003) 219; 50 (2004) 60] according to a so-called IT-mechanism, that is, the [FeII(C5H4Bu)2] molecule is transferred from the 1,2-DCE to the W phase across the interface, then the ET reaction takes place homogeneously in the W phase between [FeIII(CN)6]3−(W) and [FeII(C5H4Bu)2](W) to produce [FeII(CN)6]4−(W) and [FeIII(C5H4Bu)2]+(W), which is followed by the transfer of the [FeIII(C5H4Bu)2]+ ion from the W to the 1,2-DCE phase across the interface to give the voltammetric current. Experimental results from cyclic voltammetry are also explained well by the IT-mechanism. [Copyright &y& Elsevier]

The usefulness of 1,6-dichlorohexane (1,6-DCH) and 1,4-dichlorobutane (1,4-DCB) as organic solvent (O) for ion-transfer voltammetry at O|water (W) interface has been examined, and the results are compared with those with 1,2-dichloroethane (1,2-DCE). The width of potential window of the 0.1 M tetraoctylammonium tetrakis(4-chlorophenyl)borate (O)|0.05 M Li2SO4 (W) interface increased in the sequence: O = 1,6-DCH > 1,4-DCB > 1,2-DCE. The voltammetric behavior of the transfer of various cations and anions at the 1,6-DCH|W and 1,4-DCB|W interfaces has been shown to be of reversible nature, and the midpoint potentials or the reversible half-wave potentials have been determined. The midpoint potentials of hydrophilic ions have also been determined by the analysis of anodic final rise or cathodic final decent of the voltammograms with the O|W interfaces, where the W contains a salt of the hydrophilic ion. Also, the effect of ion-pair formation in O on the midpoint potentials has also been discussed. [Copyright &y& Elsevier]

The transfer of streptothricin antibiotics containing a β-lysine monomer (ST-F), trimer (ST-D), and tetramer (ST-C) at a polarizable nitrobenzene (NB) | water (W) interface was studied by cyclic voltammetry. Under acidic conditions, the streptothricins existed in fully protonated forms, as ST-F 2 + , ST-D 4 + and ST-C 5 + cationic species. Within the potential range tested, ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer across the NB | W interface. The formal potentials, Δ O W ϕ 0 S ’ T , of ST-D 4 + and ST-C 5 + ions were determined. In the presence of a neutral ligand (L), dibenzo-18-crown-6, in NB, ST-F 2 + , ST-D 4 + and ST-C 5 + ions gave reversible voltammograms due to their transfer assisted by the formation of ST-FL 2 2 + , ST-DL 4 4 + and ST-CL 5 5 + complexes with the ligand in NB. Using the Δ O W ϕ 0 S ’ T -values, association constants between the NH 3 + -groups of ST-D 4 + and ST-C 5 + ions and the crown ether in NB were determined. The association constants were in agreement with each other. By assuming that the association constant of ST-F 2 + was equal to those of the ST-D 4 + and ST-C 5 + ions, the Δ O W ϕ 0 S ’ T of the ST-F 2 + ion was estimated. Interestingly, the determined Δ O W ϕ 0 S ’ T -value was increasingly negative in the order of ST-F 2 + (~ 0.24 V) > ST-D 4 + (0.199 V) > ST-C 5 + (0.194 V), indicating that the lysine oligomer affected the phase-transfer characteristics of streptothricin. [ABSTRACT FROM AUTHOR]

Abstract: The transfer of a biopolymer, ε-poly-L-lysine (εPL), at a polarized nitrobenzene (NB) | water (W) interface was studied voltammetrically. Despite the polydispersity of sample (n =25–35, n being the degree of polymerization), an S-shaped current-potential curve with a well-defined limiting current was observed in normal pulse voltammogram for the transfer of εPL at the NB | W (pH 3.0) interface. In the W-phase, εPL would exist in the fully protonated form, and the limiting current can be explained by the diffusion of the polycationic εPL species. Also a pair of anodic and cathodic peak currents was observed by cyclic voltammetry. The midpoint potential was in agreement with the half-wave potential in the normal pulse voltammogram. The influence of pH and the supporting electrolyte anions in both phases on the voltammograms has been also studied. By the addition of dibenzo-18-crown-6 (DB18C6) to NB, the half-wave potential shifted to negative potentials. This can be interpreted as being due to the εPL-transfer facilitated by the formation of εPL-DB18C6 complex in NB. The concentration dependence of the half-wave potential can be explained by the formation of 1:n εPL-DB18C6 complex. The results suggest the applicability of the voltammetric technique to compare the phase-transfer characteristics of εPL and the derivatives. [Copyright &y& Elsevier]