Voltammetric study of the transfer of polyammonium ions at nitrobenzene / water interface.

The transfer of polyammonium ions, poly[(dimethylimino)-1,6-hexanediyl] (n = 140, n being the degree of polymerization) ion and poly[(dimethylimino)(2-oxo-1,2-ethanediyl)imino-alpha,omega-alkanediylimino(1-oxo-1,2-ethanediyl)(dimethylimino)-alpha',omega'-alkanediyl] ([-N+ (CH3)2CH2CONH(CH2)x NHCOCH2N+ (CH3)2(CH2)y-]n, x = 2, 3, 4, or 6, y = 3 or 6, and n = 30-130) ions, at a polarizable nitrobenzene / water interface has been studied by normal pulse voltammetry and cyclic voltammetry. Despite the polydispersity of the preparations, by normal pulse voltammetry, an S-shaped current-potential curve with a well-defined limiting current, and, by cyclic voltammetry, a pair of anodic and cathodic peak currents due to the transfer of polyammonium ions across the interface were observed within the potential window. The voltammetric behavior is described. Also, the effect of ion-pair formation of the polyammonium ions with supporting electrolyte anions in nitrobenzene- and water-phases on the half-wave or midpoint potential of the ion-transfer, and the relation between the structure of the polyammonium ions and the transfer potentials are discussed.     

Electrochemical study of the assisted transfer of silver ion by 1,5-cyclooctadiene at the 1,6-dichlorohexane/water interface.

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.     

Voltammetric behavior of the transfer of mono- and polyammonium ions across a phospholipid monolayer at the nitrobenzene/water interface.

The influence of a phospholipid, dipalmitoyl phosphatidylcholine, layer at a nitrobenzenelwater interface on the transfer of tetraethylammonium ion and a polyammonium anti-fungus agent, poly[(dimethylimino)(2-oxo-1,2-ethanediyl)imino1,6-hexanediylimino (1-oxo-1,2-ethanediyl)(dimethylimino)-1,6-hexanediyl] ion, across the interface was studied by normal pulse voltammetry. When the phospholipid was adsorbed to form a monolayer at the nitrobenzenelwater interface by its addition to the organic phase, the half-wave potential in the current vs. potential curves for the transfer of tetraethylammonium ion did not change, but the limiting current was significantly decreased at certain sampling times, indicating a retarding effect of the layer on the ion-transfer. On the other hand, in the current vs. potential curves for the transfer of the polyammonium ion, no significant change in either the half-wave potential or the limiting current was observed upon adding the phospholipid, indicating that the polyammonium ion can easily permeate through the phospholipid layer. The results suggest a new application of the voltammetric technique to the study of cell membrane permeability to polyionic bioactive compounds.     

Voltammetric determination of facilitated ion transfer across the water/1,2-dichloroethane interface

The facilitated transfer characteristics of Cd²⁺ ion by 4-morpholinoacetophenone-4-ethyl-3-thiosemicarbazone (MAPET) across water/1,2-dicholoroethane (1,2-DCE) interface and its electrochemical properties were investigated by voltammetric measurements. Cyclic voltammetry (CV) was employed to examine the transfer in the conditions of the ligand (organic phase) in excess and the obtained transfer peaks have reversible nature at different metal concentrations and scan rates. The dependence of the obtained half-wave transfer potential on MAPET concentration showed that the equilibrium is effectively displaced towards a 1: 3 (Cd²⁺: ligand) stoichiometry with an association constant of logβ ₃ ⁰ = 12.96 ± 0.09 for the Cd²⁺ ion, corresponding to the TIC/TID mechanism.     

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.     

两种喹啉类药物在水/硝基苯界面循环伏安研究

本文用循环伏安法研究了盐酸喹啉和8-羟基喹啉配合质子在水/硝基苯界面的转移过程, 讨论了水相pH值对其转移行为的影响, 探讨了有关转移过程的机理, 测定并计算了有关热力学参数。     

四苯卟啉及其第一过渡金属配合物推动H^+通过水/硝基苯界面的机理研究

应用具有以正反馈技术补偿溶液电阻降功能的微机联用四电极恒电位测试系统研究了四 苯卟啉(H~2TPP)及其第一过渡金属配合物(MTPP)对H^+在水/硝基苯界面转移的影响.结果表明,H~2TPP和MTPP对上述H^+转移过程均表现出一定程度的活性.当水相H^+浓度甚低于NB相的H~2TPP浓度时,后者推动H^+在W/NB界面的转移呈可逆并受扩散步骤控制.各MTPP对推动H^+通过W/NB界面的相对活性表现为NiTPP>MnTPP>CoTPP,CuTPP>ZnTPP,FcClTPP,与金属卟啉配合物的热稳定性一致.根据实验事实,提出有关H~2TPP推动H^+迁过W/NB界面的微观动力学机理.     

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface

The phase transfer mechanism of 18-molybdophosphate anion at the water/nitrobenzene interface has been investigated by chronopotentiometry with cyclic linear current-scanning (CLC) and cyclic voltammetry (CV). The transfer species is 18-molybdophosphtae anion with a charge number of 4, H₂[P₂Mo₁₈O₆₂]^4-. The transfer process is controlled by diffusion at a slow polarization rate and considerably influenced by pH of the aqueous phase. The stable forms and pH range of the heteropoly anion in the aqueous solution can be directly confirmed through voltammetric behavior. The theoretical analysis of the relationship between the transfer potential and solution pH is identical to the experimental results. The linear concentration relationship with the transfer peak current is suggested to be used in the determination of heteropoly acids (salts).     

Charge transfer between two immiscible electrolyte solutions: Part VI. Polarographic and voltammetric study of picrate ion transfer across the water/nitrobenzene interface

The transfer of the picrate ion across the interface between two immiscible electrolyte solutions, 0.05 M LiCl in water and 0.05 M tetrabutylammonium tetraphenylborate in nitrobenzene was investigated by electrolysis with the electrolyte dropping electrode and by cyclic voltammetry. Under the conditions of the experiments the charge-transfer process is controlled solely by diffusion. The maximum which appears on the polarogram of the picrate ion close to the limiting current can be suppressed by the addition of a surface-active substance (gelatine). The diffusion coefficients of the picrate ion in the aqueous and nitrobenzene phase were determined from the limiting polarographic current and from the peak current on the cyclic voltammogram. The value of the formal potential of the charge-transfer reaction, which was calculated from the half-wave potential or from the peak potential, is in good agreement with that inferred from the extraction data.     

Transfer behavior of cobaltous ion across the water/ nitrobenzene interface facilitated by 2,2'-bipyridine

The transfer behavior of cobaltous ion across the water/nitrobenzene interface facilitated by 2,2'-bipyridine has been investigated by cyclic voltammetry. The transfer species are successive complexes formed between Co(II) and bipyridine. Coupled chemical reactions occur not only in the aqueous phase but also in the organic phase during the electrolytic transfer. Irreversible transfer phenomena were found from voltammograms obtained in the Co(II)-bipyridine system and discussed.     

Facilitated ion transfer across the water/nitrobenzene interface Theory for single-scan voltammetry applied to a reversible system

The transfer of the metal cation across the interface between two immiscible electrolyte solutions facilitated by complex formation with a ligand at the interface was investigated both theoretically and experimentally. The theory of single-scan voltammetry was derived which enables the complex stoichiometry (1:1, 1:2 or 1:3. cation to ligand) to be determined as well as the thermodynamic and transport parameters of the facilitated charge transfer controlled by the diffusion of the ligand. Application of the theoretical results was illustrated for the transfer of Li⁺ and Cd²⁺ ions across the water/nitrobenzene interface facilitated by complexation with the neutral macrocyclic polyether diamine.     

四甲铵阳离子在水/硝基苯界面传输的新极谱法研究

本文采用新极谱法, 包括半积分, 半微分, 1.5次微分及2.5次微分新极谱研究了四甲铵离子在水/硝基苯界面的传输, 从理论上讨论了峰高, 峰电位及峰宽对传输质点浓度, 扫描速率等因系的依赖关系, 用模拟电子线路在实验上对离子在两相界面传输的新极谱法理论进行了验证, 实验与理论接近, 得到了与金属电极/电解质溶液界面的氧化还原类似的结果.     

Mechanistic study of the oxidation of -ascorbic acid by chloranil at the nitrobenzene water interface

The redox reaction between -ascorbic acid in water and chloranil in nitrobenzene has been studied by means of polarography with an ascending water electrode as well as cyclic voltammetry with a stationary interface. Through accurate measurement of the limiting currents, it has been suggested that the redox reaction should be a two-electron reaction rather than a one-electron reaction described previously. A spectrophotometric technique has also been used to observe that the redox reaction proceeds spontaneously under certain conditions even without electrochemical control. Based on these findings, it has been concluded that the present heterogeneous charge transfer reaction is the ion transfer of chloranil semiquinone radical, which is driven by the homogeneous electron transfer between ascorbic acid and chloranil in the aqueous phase.     

Hydrodynamically induced chemical oscillation at a water/nitrobenzene interface

By measuring a time course of interfacial tension and interfacial electrical potential, we successfully observed oscillatory phenomena that were based on alternatively appearing adsorption and desorption processes of anionic surfactant molecules (sodium dodecyl sulfate (SDS)) at the water/nitrobenzene interface. These oscillation patterns were drastically modified by slightly changing the rate of SDS aqueous solution injection into the water phase. When 10 mM of SDS aqueous solution was injected at a low rate, for example, at less than 1 microl/min, abrupt adsorption was repeatedly followed by slow desorption of DS- ions; in other words, the sequence of the oscillation and relaxation processes was repeated. However, when it was injected at a higher rate, no remarkable periodic phenomenon occurred after the first oscillation. In addition, the rapid adsorption process was observed to be accompanied by a flip motion of the liquid/liquid interface and a flow along the interface. This is caused by a Marangoni convection that is brought about by the generation of heterogeneity of interfacial tension. Furthermore, by estimating the flow speed, it was determined that the faster flow tends to quench the periodic oscillation patterns.     

Transfer of actinide ion at the interface between aqueous and nitrobenzene solutions studied by controlled-potential electrolysis at the interface

A novel electrochemical method based on controlled-potential electrolysis has been developed for the elucidation of the ion transfer at the interface between two immiscible electrolyte solutions (ITIES). A relationship between the applied interfacial potential (E_app) and the amount of the ion transferred (A_tr) was investigated after an electrolytic equilibrium was attained by controlled-potential electrolysis. The A_tr was determined chemically or radiometrically instead of by current measurement. It was found that (i) controlled-potential electrolysis was applicable to the study of the transfer of such hydrophilic ions as transition metal ions which gave no appreciable current within the potential window in voltammetry or polarography at ITIES, (ii) controlled-potential electrolysis in combination with a sensitive analytical method enabled a study of the transfer reaction of an ion of very dilute concentration, and (iii) even when the transfer reaction of an ion was irreversible or quasi-reversible, a standard ion transfer potential could be determined by controlled-potential electrolysis without using a kinetic parameter. The controlled-potential electrolysis method developed was applied to the transfer reactions of actinide ions such as UO₂ ²⁺ and Am³⁺ from aqueous solution to nitrobenzene solution in the absence or presence of an ionophore facilitating the transfer. The Gibbs energy for the transfer of actinide ion and a stability constant of the complex between an actinide ion and the ionophore in nitrobenzene solution were determined from log D versus E_app plots (D the ratio of the concentration of the ion in nitrobenzene solution to that in aqueous solution). The feasibility of controlled-potential electrolysis as a method for electrolytic separation of actinide ions is discussed.     

Potential-dependent adsorption and transfer of poly(diallyldialkylammonium) ions at the nitrobenzene|water interface

Electrochemically driven adsorption and partition of a series of poly(diallyldialkylammonium) ions (PDADAA(+): alkyl = methyl, ethyl, propyl, and butyl) at the nitrobenzene (NB)|water (W) interface have been studied using voltammetry and electrocapillary measurements. When the phase-boundary potential, Δφ, that is, the inner potential of the W phase referred to that of the NB phase, is negative, poly(diallyldimethylammonium) (PDADMA(+)) shows little surface activity. The scanning of Δφ in the positive direction induces, first, the adsorption of PDADMA(+) at the interface and, then, the desorption of adsorbed PDADMA(+) ions into the NB phase, followed by the diffusion-limited transfer of PDADMA(+) from W to NB. The elongation of the dialkyl chains gives the stronger surface activity of PDADAA(+) even when Δφ < 0. The PDADAA(+) polyions studied are only slightly more hydrophilic than the corresponding monomers. However, the polycationic character of PDADAA(+) renders the adsorption, desorption, and ion transfer strongly dependent on Δφ and gives rise to unusual, M-shaped electrocapillary curves. The interplay of adsorption-desorption and ion transfer of PDADAA(+) ions induces the electrochemical instability of the interface and the emulsion formation on the NB side of the interface.     

水/硝基苯界面上水溶性冠醚推动碱土金属离子转移的循环伏安法研究

本文用循环伏安法研究了水/硝基苯界面上十种水溶性及两种非水溶性冠醚推动镁(II)、钙(II)、锶(II)、钡(II)四种碱土金属离子的转移, 讨论了实验条件下的转移机制, 估测了热力学函数.     

Electrochemical studies of the tetrabutyl- and tetramethyl-ammonium ion transfer across the water-1,2-dichloroethane interface: A comparison with the water—nitrobenzene interface

The results of electrochemical studies on the reaction of tetrabutyl- and tetramethylammonium (TBA⁺ and TMA⁺) ion transfer from water to 1,2-dichloroethane are presented in this paper and are compared with se of the water—nitrobenzene interface. The TMA⁺ ion transfer has been studied by the chronopotentiometric cyclic voltammetry methods and that of the TBA⁺ ion by the chronopotentiometric method only.It has been found that the reactions are diffusion controlled over the current density range up to about 1O μA cm^?2 and at polarization rates up to 0.15V s^?1. Diffusion coefficients of the studied ions have been detemined, as well as their formal potentials with respect to an ion-selective tetrabutylammonium electrode to a partition electrode containing tetraethylammonium picrate whose potential is close to zero. In additon, kinetic parameters of the transfer reaction have been determined for the tetrabutylammonium ion from data obtained at current densities over 10 μA cm^?2 (irreversible range).     

Direct observation of chemical oscillation at a water/nitrobenzene interface with a sodium-alkyl-sulfate system.

The oscillation of the interfacial tension and electrical potential at a water/nitrobenzene interface was observed with homologous anionic surfactant molecules, sodium-alkyl-sulfates. Concerning small molecules with a short hydrophobic carbon chain, the oscillation period and amplitude decreased with a decrease of the length of the alkyl chain. On the other hand, when surfactant molecules with a long hydrophobic carbon chain were used, no remarkable periodic oscillation occurred after the first oscillation. In all systems, an interfacial flow by Marangoni convection was observed when the oscillation took place. By monitoring the movement of carbon powder scattered on the liquid/liquid interface with a CCD camera, we could observe that the liquid/liquid interface expanded outward from the area on which the surfactant molecules adsorbed when the oscillation occurred. When the small molecule was used, the speed of expansion of the interface (flow speed) was small and shrinkage followed by expansion of the interface repeatedly occurred. However, when the large molecule was used, the flow speed was large and expansion occurred only one time. These results show that hydrodynamic factors and surface activities are important in chemical oscillation systems.