• Bulletin of the Korean Chemical Society
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• v.11 no.6
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• pp.521-527
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• 1990

The binding characteristics and analytical applications of anilinium ion complexes with 18-crown-6 were studied by polarography and NMR. First, the electrochemical reduction of the 10 species of mono and dimethylsubstituted anilinium ion complexes with 18-crown-6 as host in methanol are examined. The addition of 18-crown-6 to anilinium guest solution the polarographic waves remain well defined but shifted toward more negative potentials, indicating the complex formation. The values of formation constants, log Κ for 10 species of methylsubstituted anilinium ion complexes with 18-crown-6 varies from 2.7 to 4.8 in methanol at $25^{\circ}C$. The stability order of complexes for 18-crown-6 is anilinilum > 4-methyl > 3,4-dimethyl > 3-methyl > 3,5-dimethyl > 2,4-dimethyl > 2,5-dimethyl > 2,3-dimethyl > 2-methyl > 2,6-dimethylanilinium ion. The steric hindrance shows significant effect. Second, Proton NMR was used to elucidate their interaction characteristics. From the results of so called NMR titration techniques, the behaviors of binding sites on complexation, and the stoichiometry and stability order of complex were obtained. And the later results show the satisfactory agreement with the quantitative values obtained by polarography. Finally, the individual determinations of anilinium ion mixtures were also accomplished by addition of 18-crown-6. In some mixtures of methyl or dimethylanilinium ions the reduction peaks of differential pulse method appeared into one unresolved wave attributed to the small difference of half-wave potential, ${\Delta}E_{1/2}$. In the presence of 18-crown-6, the polarographic waves were resolved into individual maxima because of the shift toward more negative direction by the difference of selectivity of anilinium ions with 18-crown-6. It may be concluded that quantitative analysis of methylanilinium ion mixture make possible because the half-wave potential shift by the selectivity difference due to the steric hindrance between methyl group and 18-crown-6 on complexation.

• Analytical Science and Technology
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• v.5 no.3
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• pp.249-261
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• 1992

Electrochemical behavior of the heavy lanthanide complexes of alizarin red S(ARS) has been investigated by d. c. polarography, differential pulse polarography and cyclic voltammetry. The reduction mechanism at a mercury electrode of alizarin red S as a complexing ligand showed a one step of two-electron transfer and the electron process is found to be reversible. Alizarin red S forms a 3:1 adsorptive complexes with lanthanides and the complexes are reduced via one step of two-elctron. The reduction potential of complex wave($P_2$) shifted more negatively than the ligand wave($P_1$). The linear calibration curves of the decreacing $P_1$ and increasing $P_2$ is obtained when the lanthanide concentration varies from $2.0{\times}10^{-6}M$ to $6.4{\times}10^{-5}M$ under the condition of pH 9.5, 0.1M LiCl and $1{\times}10^{-3}M$ ARS.

• Journal of the Korean Chemical Society
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• v.39 no.1
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• pp.57-65
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• 1995

The electrochemical reduction of methylene blue (MB) in 1.0${\times}$10-2 M KNO3 aqueous solution was investigated by direct current (DC), differential pulse (DP) polarography, cyclic voltammetry (CV) and controlled potential coulometry (CPC). The electrode reduction of melthylene blue was processed CE reaction mechanism by two electrons transfer at the first reversible wave (- 0.18 volts vs. Ag/AgCl). MB was strongly adsorbed on the stationary mercury electrode and the reduction product of conptrolled potential electrolysis was rapidly auto-oxidized in air to the original methylene blue. Upon the basis of interpretation of cyclic voltammogram with pH change, possible CE electrode reaction mechanism was suggested.

• Journal of the Korean Chemical Society
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• v.37 no.12
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• pp.1053-1059
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• 1993

The determination of iron(Ⅱ), iron(Ⅲ) and total iron was studied by differential-pulse and Tast polarography in 0.1 M acetate buffer solution at pH 4.60, Half wave potentials of iron(Ⅱ)-DTPA and iron(Ⅲ)-DTPA complexes were -0.150V vs. SCE reference electrode. In the presence of DTPA the redox process of iron(Ⅱ) and iron(Ⅲ) was reversible. Linear calibration plots were obtained for iron(Ⅱ) and iron(Ⅲ) concentration of 0.2∼1.0 mM. The detection limits of iron(Ⅱ) and iron(Ⅲ)by Tast polarographic method were 0.05 mM and 0.07 mM, respectively.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.567-574
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• 1993

Mordant Red 19(MR19) is reduced at mercury electrode at -0.67 V vs. Ag/AgCl with two electrons per molecule in pH 9.2 buffer by differential pulse polarography and linear sweep voltammetry. The peak potential is dependent on the pH of solution. The exhaustive electrolysis, however, gives 4 electrons per molecule because of the disproportionation of the unstable hydrazo intermediate. The electrochemical reduction of lanthanide-MR19 complexes is observed at more cathodic potential than that of free ligand. The difference in peak potentials between complex and free ligand varies from 75 mV for $La^{3+}$ to 165 mV for $Tb^{3+}$ and increases with increasing the atomic number of lanthanide. The electrochemical reduction of lanthanide complexes with MR19 is due to the reduction of ligand itself, and it can be potentially useful as an indirect method for the determination of lanthanides. The shape of i-E curves and the scan rate dependence indicates the presence of adsorption and the adsorption was confirmed by potential double-step chronocoulometry and the effect of standing time. Also the surface excess of the adsorbed species and diffusion coefficients are determined. The composition of the complex is determined to be 1 : 2 by spectrophotometric and electrochemical methods.

• Analytical Science and Technology
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• v.7 no.3
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• pp.361-369
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• 1994

Voltammetric behavior of some light lanthanide ions($La^{3+}$, $Pr^{3+}$, $Nd^{3+}$, $Sm^{3+}$ and $Eu^{3+}$) in acetonitrile(AN) and dimethylformamide(DMF) has been investigated by direct current, differential pulse polarography and cyclic voltammetry. The reduction of $La^{3+}$, $Pr^{3+}$ and $Nd^{3+}$ in 0.1M TEAP proceeded directly to the metallic state through three-electron charge transfer of irreversible process where as $Sm^{3+}$ and $Eu^{3+}$ proceeded by charge transfer of two steps. As the results of the cyclic voltammetric investigation, the first step reduction of $Sm^{3+}$ and $Eu^{3+}$ were a quasireversible reaction, the second step reductions were an irreversible reaction. The cathodic peak currents of the differential pulse polarogram showed adsorptive properties at lower sweep rates and high concentrations of these metal ions. The peak potenital was shifted to a negative petential and the peak current decreased with the increase of percentage of water in AN. On the other hand, the peak potential was shifted to a positive potential and the peak current decreased with an increased percentage of water in DMF.

• Journal of the Korean Chemical Society
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• v.35 no.6
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• pp.673-679
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• 1991

The electrochemical reduction of N-tert-butylbenzothiazole-2-sulfenamide (TBBS; vulcanization accelerator) was investigated by direct current, differential pulse polarography, cyclic voltammetry and controlled potential coulometry. The electrode reduction of TBBS proceeded E-C-E-C reaction mechanism by four electrons transfer at irreversible one wave (-2.31 volts vs. Ag/0.1M AgN$O_3$ in AN). As the results of controlled potential electrolysis, mercaptobenzothiazole (MBT), benzothiazole disulfide (MBT dimer) and extricated sulfur were products which followed by cleavage of the sulfenamide (-S-N=) bond. Upon the basis of products analysis and polarogram interpretation with pH variable, electrochemical reaction mechanism was suggested.

• Journal of the Korean Chemical Society
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• v.33 no.5
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• pp.496-503
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• 1989

The chemical behavior of trivalent lanthanide (Pr(III) and Yb(III)) and 2, 2, 6, 6-tetramethyl-3, 5-heptanedione(dipivaloylmethane) complexes was investigated by the use of direct current, differential pulse polarography and cyclic voltammetry. In this study, it was founded that the reduction of trivalent lanthanide complexes was observed by one electron transfer process at Epc = -0. 13 V and -0.80 V of Pr(III), and -0.02 V of Yb(III) vs. Ag-AgCl electrode. Also, it was founded that the treatment of DP and CV to the case of a first-order chemical equilibrium reaction preceding a reversible and irreversible one electron transfer reaction, (a >0. 5) the socalled ErCr electrode process. The equilibrium constant (lnK) obtained, of various solvents, these constant were founded to be increases with decreasing dielectric constant of the solvents. Plots of lnK for these reaction against ln(l/D) for the solvents was fairly straight lines, and the behavior of the heavier lanthanides was decreased equilibrium constant with increasing atomic number.

• Journal of the Korean Chemical Society
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• v.38 no.2
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• pp.136-145
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• 1994

Polymeric complexes such as M(Ⅱ)(PVPS)(SND), M(Ⅱ)(PVPS)(SOPD) have been prepared with monomeric complexes, M(Ⅱ)(SND) and M(Ⅱ)(SOPD)[M: Co(Ⅱ), Ni(Ⅱ), and Cu(Ⅱ)] and polymer PVPS. These complexes have been indentified by elemental analysis, spectroscopy, and T.G.A. From the results, it was found that M(Ⅱ)(PVPS)(SND), M(Ⅱ)(PVPS)(SOPD) complexes were penta-coordinated configuration. Electrochemical properties of these complexes studied by cyclic voltammetry and differential pulse polarography in 0.1 M TEAP-DMF solution at glassy carbon electrode. Co(Ⅱ)(PVPS)(SND) and Co(Ⅱ)(PVPS)(SOPD) showed irreversible two step reduction, such as Co(Ⅲ)/Co(Ⅱ) and Co(Ⅱ)/Co(Ⅰ), and Ni(Ⅱ)(PVPS)(SND), Ni(Ⅱ)(PVPS)(SOPD), Cu(Ⅱ)(PVPS)(SND), and Cu(Ⅱ)(PVPS)(SOPD) complexes showed irreversible one step reduction, such as Ni(Ⅱ)/Ni(Ⅰ) and Cu(Ⅱ)/Cu(Ⅰ), respectively.

• Journal of the Korean Chemical Society
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• v.34 no.6
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• pp.561-568
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• 1990

Voltammetric behavior of some light lanthanide ions (La$^{3+}$, Pr$^{3+}$, Nd$^{3+}$, Sm$^{3+}$, and Eu$^{3+}$) in various supporting electrolytes has been investigated by several electrochemical techniques. The peak potentials and the peak currents, their dependency on the concentration, temperature and pH effects, the reversibility of the electrode reactions are described. The reduction of La$^{3+}$, Pr$^{3+}$ and Nd$^{3+}$ in 0.1 M lithium chloride proceeds by a three-electron change directly to the metallic state (Ln$^{3+}$ ＋ 3e- → Ln$^0$) and charge transfer is totally irreversible. However, the reduction of Sm$^{3+}$ in 0.1 M tetramethylammonium iodide and Eu$^{3+}$ in 0.1 M lithium chloride proceeds in two stages (Ln$^{3+}$ ＋ e- → Ln$^{2+}$ and Ln$^{2+}$ ＋ 2e- → Ln$^0$). At pH values lower than ca.4 the hydrated lanthanide species (Ln(OH)$^{2+}$) reduced before the lanthanide ions (Ln$^{3+}$) due to the catalytic effect of hydrogen ions, and peak current increase with in the order Eu$^{3+}$ < Sm$^{3+}$ < Nd$^{3+}$ < Pr$^{3+}$ < La$^{3+}$ in differential pulse polarography. Some representative plots of $i_{pc}V^{-1/2} (proportional to current function) vs. V show considerable influence of hydrogen ion/lanthanide ion concentration in cyclic voltammetry. It is shown that a reaction of lanthanide ions with proton and/or water and catalytic reaction is enhanced at lower pH and at decreased lanthanide ion concentration.