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The ion-transfer reaction at the 1,6-dichlorohexane (DCH) | water (W) interface in the presence of an organometallic cation, tetraphenylantimony (TPhSb + ), in DCH was studied voltammetrically. When TPhSb + salt with [(C 4 F 9 SO 2 ) 2 N] - ion was added to the DCH-phase and the W-phase was buffered at pH < 6, a reversible cyclic voltammogram due to the simple transfer of TPhSb + ion across the DCH | W interface was observed within the polarizable potential window. When the W-phase was buffered at pH > 7, the midpoint potential shifted to more positive potentials with increasing pH. The voltammogram could be attributed to the transfer of the OH - ion assisted by the formation of TPhSbOH, which is stable in DCH. Also, a 7reversible voltammogram due to the TPhSb + -assisted transfer of F - ion was observed at the TPhSb + (DCH) | F - (W, unbuffered) interfacial system. The same results were achieved when TPhSb[(C 4 F 9 SO 2 ) 2 N] in DCH was replaced by TPhSbOH or TPhSbF, indicating the applicability of the TPhSb + and TPhSbOH (DCH) | OH - (W) interfacial system to a pH sensor for alkaline solution and that of the TPhSb + and TPhSbF (DCH) | F - (W) interface to a F - ion sensor., (© 2022. The Author(s), under exclusive licence to The Japan Society for Analytical Chemistry.)

The non-Bornian solvation model has been applied to a theoretical consideration of the Gibbs free energy for the transfer of fluorinated anions, non-fluorinated cations, and non-fluorinated anions at the 2H,3H-decafluoropentane (DFP)/water (W) and 1,2-dichloroethane (DCE)/W interfaces. According to our previous experimental results, the fluorinated anions are more stable in DFP than DCE, while the non-fluorinated cations and anions are less stable in DFP. To understand this characteristic feature of DFP, energy decomposition analyses have been performed for the hypothetical transfer of ions at the DFP/DCE interface. In conclusion, the characteristics of DFP as a fluorous solvent should be explained in terms of the higher repulsive interaction of the solvent molecule with ions, particularly with non-fluorinated ions.

New appropriate reaction system was found for spectrophotometric determination of phosphate anion. This spectrophotometric method is based on the color development due to the formation of yellow molybdophosphate anion in acidic ethylene glycol-water (EG-W) mixed solution containing Mo(VI) species. The solution containing e.g. 20 mM Na(2)MoO(4), 0.1 M HCl, and 40% (v/v) EG is colorless, and becomes immediately yellow by addition of phosphate anion. Thus the method is simple, rapid, and easy to carry out. Although Si(IV) species is well known to interfere with the determination of phosphate anion in many cases, the EG-W Mo(VI) solution remains colorless after addition of silicate anion at 1 mM level, indicating that no yellow molybdosilicate anion was formed in the EG-W solution. Under an optimized condition, the absorbance at e.g. 400 nm of the EG-W P(V)-Mo(VI) solution was proportional to the concentration of phosphate anion with good reproducibility, and the detection limit was 1 µM. Also the present method is less interfered by high concentrations of potassium and ammonium cations and oxidative nitrite anion as well as silicate anion.

Voltammetric behaviors of various globular proteins, including cytochrome c, ribonuclease A, lysozyme, albumin, myoglobin, and alpha-lactalbumin, were studied at the polarized 1,2-dichloroethane/water (DCE/W) interface in the presence of four different anionic surfactants, that is, dinonylnaphthalenesulfonate (DNNS), bis(2-ethylhexyl)sulfosuccinate (Aerosol-OT; AOT), bis(2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoroheptyl)sulfosuccinate (BDFHS), and bis(2-ethylhexyl)phosphate (BEHP). When the W phase was acidic (pH = approximately 3.4), the surfactants (except for BEHP) added to DCE facilitated the adsorption of the above proteins to the DCE/W interface and gave a well-developed voltammetric wave due to the adsorption/desorption of the proteins. This voltammetric wave, which we here call "protein wave", is promising for direct label-free electrochemical detection of proteins. The current for the adsorption of a protein to the interface showed a linear dependence on the protein concentration in the presence of excess surfactant. The foot potential at which the protein wave appeared in cyclic voltammetry showed different values depending on the natures of the protein and surfactant. Multivariate analysis for the foot potentials determined for different proteins with different surfactants revealed that the protein selectivity should depend on the charged, polar, and nonpolar surface areas of a protein molecule. On the basis of these voltammetric studies, it was shown in principle that online electrochemical separation/determination of proteins could be performed using a two-step oil/water-type flow-cell system.

The tetraoctylammonium cation forms water-immiscible room temperature ionic liquids with dodecylsulfate and dodecylbenzenesulfonate anions. The ionic liquids are halogen-free and can be considered environmentally friendly solvents. At 25 degrees C, the solubilities of water in tetraoctylammonium dodecylsulfate and tetraoctylammonium dodecylbenzenesulfonate were 2.8 and 4.0%, respectively, and the densities were 0.92 and 0.93 g cm(-3). The ionic liquids formed stable interfaces with water at 25 degrees C. The possible use of tetraoctylammonium dodecylsulfate as chelate extraction solvent was evaluated by using 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione as extractant. Tetraoctylammonium dodecylsulfate showed high extraction performance for divalent transition metal cations.

The transfer of Ag+ ion across a polarized 1,6-dichlorohexane/water interface assisted by an alkene or olefin ligand, 1,5-cyclooctadiene (COD), was studied by cyclic voltammetry. Even if COD was absent from the organic phase, Ag+ ion gave a reversible voltammetric wave, and the formal potential of the non-assisted ion-transfer at the 1,6-dichlorohexane/water interface was determined from the reversible half-wave potential. By the addition of COD to the organic phase, the reversible half-wave potential shifted to more negative potentials with increasing concentration of COD. The concentration dependence of the half-wave potential revealed that the transfer of Ag+ ion is assisted by the formation of 1:1 and 1:2 Ag+-COD pi-complexes in 1,6-dichlorohexane with overall formation constants of (2.1 +/- 0.2) x 10(3) M(-1) and (7.8 +/- 1.0) x 10(3) M(-2), respectively. The formal potential and the formation constants coincide well with those obtained by the potentiometry of Ag+ ion in aqueous and organic media with a Ag electrode.

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]