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We examined the partition of two amines, procaine and metoprolol, in ionic and charge-neutral forms between organic solvent (O) 1,2-dichloroethane and water (W) phases, each of which contained a common ion, [(C n F 2n+1 SO 2 ) 2 N] − , as tetrabutylammonium and Li + salts, respectively, to control the potential difference at the O|W interface, Δ O W ϕ. The interfacial system would be useful in the study of the partitioning of ionic species, which depends on Δ O W ϕ. With different pH levels, the dependence of the distribution ratio on Δ O W ϕ satisfied the prediction from the theoretical equation, giving the formal potentials for the transfer of the ionic forms at the O|W interface. We also examined the partition of nourseothricin, a mixture of streptothricin antibiotics with different sizes of lysine oligomers. They would exist as di-, tri-, tetra- and pentavalent cations in fully protonated forms. The distribution ratio for each ionic species could be determined simultaneously using an HPLC technique. The dependence of the distribution ratio on Δ O W ϕ for each species also satisfied the prediction, giving their formal potentials. Therefore, the present interfacial system can be applied when both ionic and charge-neutral species are partitioned and when the sample is of low purity or is a mixture. [ABSTRACT FROM AUTHOR]

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 electron transfer reaction across the 1,6-dichlorohexane (1,6-DCH)|water (W) interface where bis(pentamethylcyclopentadienyl)iron(II/III) ([FeII/III(C5Me5)2]0/+) as the organic redox couple in 1,6-DCH is present in excess has been studied by cyclic voltammetry. The 1,6-DCH|W interface gave a potential window where the transfer of [FeIII(C5Me5)2]+ ion as well as that of [FeII(C5Me5)2]0 across the interface can be neglected. When hexaammineruthenium(III) and cyano complexes of iron protoporphyrin IX and microperoxidase-11, which do not transfer across the 1,6-DCH|W interface in the potential range tested, are present in W as the aqueous reactant, well-defined voltammetric waves due to the heterogeneous electron transfer have been observed within the potential window. The voltammetric waves can be assigned to reversible one-electron transfer controlled by diffusion of the aqueous redox couple in W. The reversible half-wave potentials are consistent with those predicted from simple voltammetric experiments with a Pt electrode. [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]