• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.11
• /
• pp.6039-6046
• /
• 2013

Cr(VI)-heterocyclic complex[Cr(VI)-2-methylpyrazine] was synthesized by the reaction between of heterocyclic compound(2-methylpyrazine) and chromium trioxide, and characterized by IR and ICP analysis. The oxidation of benzyl alcohol using Cr(VI)-2-methylpyrazine in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order : cyclohexene${\rho}$) was Cr(VI)-2-methylpyrazine= -0.65(308K). The observed experimental data have been ratiolized. The hydride ion transfer causes the prior formation of a chromate ester in the rate-determining step.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.12 no.12
• /
• pp.5990-5996
• /
• 2011

6-Methylquinolinium dichromate[$(C_{10}H_9NH)_2Cr_2O_7$] was synthesized by the reaction of 6-methylquinoline with chromium trioxide in $H_2O$, and characterized by IR, ICP. The oxidation of benzyl alcohol using 6-methylquinolinium dichromate in various solvents showed that the reactivity increased with the increase of the dielectric constant(${\varepsilon}$), in the order: cyclohexene < chloroform < acetone < N,N- dimethylformamide. In the presence of hydrochloric acid($H_2SO_4$ solution), 6-methylquinolinium dichromate oxidized benzyl alcohol and its derivatives(p-$OCH_3$, m-$CH_3$, H, m-$OCH_3$, m-Cl, m-$NO_2$) smoothly in DMF. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant(${\rho}$) was -0.67(303K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

• Applied Chemistry for Engineering
• /
• v.23 no.2
• /
• pp.241-246
• /
• 2012

Cr(VI)-heterocyclic complex (2,2'-bipyridinium dichromate) was synthesized by the reaction between of 2,2'-bipyridine and chromium trioxide in $H_2O$, and characterized by IR and ICP. The oxidation of benzyl alcohol using 2,2'-bipyridinium dichromate in various solvents showed that the reactivity increased with the increase of the dielectric constant, in the order: cyclohexene < chloroform < acetone < N,N-dimethylformamide. In the presence of DMF solvent with acidic catalyst such as $H_2SO_4$ solution, 2,2'-bipyridinium dichromate oxidized the benzyl alcohol and its derivatives (p-$p-OCH_3$, $m-CH_3$, H, $m-OCH_3$, m-Cl, $m-NO_2$). Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant was -0.66 (303 K). The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

• Applied Chemistry for Engineering
• /
• v.22 no.6
• /
• pp.718-722
• /
• 2011

2,4'-Bipyridinium dichromate [$(C_{10}H_8N_2H)_2Cr_2O_7$] was synthesized by the reaction of 2,4'-bipyridinie with chromium trioxide in $H_2O$. The structure was characterized by IR and ICP analysis. The oxidation of benzyl alcohol using 2,4'-bipyridinium dichromate in various solvents showed that the reactivity increased with the increase in the order of the dielectric constant (${\varepsilon}$), in the order : cyclohexene < chloroform < acetone < N,N'-dimethylformamide. In the presence of hydrochloric acid, 2,4'-bipyridinium dichromate effectively oxidized benzyl alcohol and its derivatives ($p-CH_3$, H, m-Br, $m-NO_2$) in N,N'-dimethylformamide. Electron-donating substituents accelerated the reaction, whereas electron acceptor groups retarded the reaction. The Hammett reaction constant (${\rho}$) was -0.65 at 303 K. The observed experimental data was used to rationalize the hydride ion transfer in the rate-determining step.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.1
• /
• pp.21-26
• /
• 1995

Electrochemical reduction of oxygen has been carried out at glassy carbon electrode and carbon ultramicroelectrode, the surface of which is modified with a new Co(Ⅱ)-Schiff base complex, Co(Ⅱ)-3,4-bis(salicylidene diimine)toluene in 1 M KOH solution. The results obtained from cyclic voltammetric and chronoamperometric experiments are consistent with the formation of the reasonably stable superoxide ions as a primary electron transfer reaction product. The exchange rate constant obtained for oxygen reduction is about 0.02 cm/s.

• Bulletin of the Korean Chemical Society
• /
• v.30 no.3
• /
• pp.582-588
• /
• 2009

Direct electron transfer of hemoglobin (Hb) in the chitosan (CTS) and $TiO_2$ nanoparticles (nano-$TiO_2$) composite films was achieved by using a room temperature ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate ($BMIMPF_6$) modified carbon paste electrode (CILE) as the basal electrode. UV-Vis and FT-IR spectroscopy indicated that Hb in the film retained the native structure. Electrochemical investigation indicated that a pair of well-defined quasi-reversible redox peaks of Hb heme Fe(III)/Fe(II) was obtained with the formal potential located at -0.340 V (νs. SCE) in pH 7.0 phosphate buffer solution (PBS). The electrochemical parameters such as the electron transfer coefficient (α), the electron transfer number (n) and the standard electron transfer rate constant ($k_s$) were got as 0.422, 0.93 and 0.117 $s^{-1}$, respectively. The fabricated CTS/nano-$TiO_2$/Hb/CILE showed good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) and hydrogen peroxide ($H_2O_2$), which exhibited a potential application in fabricating a new kind of third generation biosensor.

• Biotechnology and Bioprocess Engineering:BBE
• /
• v.10 no.1
• /
• pp.47-51
• /
• 2005

The bioelectrochemical reduction of nitrate in the presence of various mediators including methyl viologen and azure A was studied using a 3-electrode voltammetric system. The catalytic potential for the reduction of the mediators was observed in the reactor, which for methyl viologen and azure A were -0.74 V and -0.32 V, respectively, with respect to the potential of Ag/AgCl reference electrode. This potential was then applied to a working electrode to reduce each mediator for enzymatic nitrate reduction. Nitrite, the product of the reaction, was measured to observe the enzymatic nitrate reduction in the reaction media. Methyl viologen was observed as the most efficient mediator among those tested, while azure A showed the highest electron efficiency at the intrinsic reduction potential when the mediated enzyme reactions were carried out with the freely solubilized mediator. The electron transfer of azure A with respect to time was due to the adhesion of azure A to the hydrophilic surface during the reduction. In addition, the use of the adsorbed mediator on conductive activated carbon was proposed to inhibit the change in the electron transfer rate during the reaction by maintaining a constant mediator concentration and active surface area of the electrode. Azure A showed better than nitrite formation than methyl viologen when used with activated carbon.

• Journal of Electrochemical Science and Technology
• /
• v.8 no.2
• /
• pp.96-100
• /
• 2017

Iridium(III) bis(2-phenylpyridinato-$N,C^{2^{\prime}}$)acetylacetonate ($(ppy)_2Ir(acac)$), a green dopant used in organic light-emitting devices (OLEDs), was subjected to electrochemical characterization to estimate its formal oxidation potential ($E^{o^{\prime}}$), HOMO energy level ($E_{HOMO}$), electron transfer rate constant ($k^{o^{\prime}}$), and diffusion coefficient ($D_o$). The employed combination of voltammetric methods, i.e., cyclic voltammetry (CV), chronocoulometry (CC), and the Nicholson method, provided meaningful insights into the electron transfer kinetics of $(ppy)_2Ir(acac)$, allowing the determination of $k^{o^{\prime}}$ and $D_o$. The quasi-reversible oxidation of $(ppy)_2Ir(acac)$ furnished information on $E^{o^{\prime}}$ and $E_{HOMO}$, allowing the latter parameter to be easily estimated by electrochemical methods without relying on expensive and complex ultraviolet photoemission spectroscopic (UPS) measurements.

• Analytical Science and Technology
• /
• v.9 no.3
• /
• pp.292-301
• /
• 1996

The synthesis of poly(ether)tailed bipyridine complex as redox reaction probes has advanced attempts to interpret very slow diffusion and heterogeneous electron transfer. Diffusion coefficients as low as $1.5{\times}10^{-15}cm^2/s$ have been observed for the oxidation of neat $Co(bpy(ppgm)_2)_{3^-}(ClO_4)_2$ with $LiClO_4$ electrolyte. Heterogeneous electron transfer rate constants of materials were found to vary with diffusion coefficient. The decrease in k as the diffusion coefficient decreases was actually caused by the decreasing D. Diffusion coefficient for compound of strong ion pairing anion($ClO{_4}^-$) was much smaller than the diffusion coefficient for compound of weak ion pairing anion($CF_3COO^-$).

• Journal of Microbiology and Biotechnology
• /
• v.22 no.10
• /
• pp.1446-1451
• /
• 2012

Levodopa or L-3,4-dihydroxyphenylalanine (L-DOPA) is the precursor of the neurotransmitter dopamine. L-DOPA is a famous treatment for Parkinson's disease symptoms. In this study, electroenzymatic synthesis of L-DOPA was performed in a three-electrode cell, comprising a Ag/AgCl reference electrode, a platinum wire auxiliary electrode, and a glassy carbon working electrode. L-DOPA had an oxidation peak at 376 mV and a reduction peak at -550 mV. The optimum conditions of pH, temperature, and amount of free tyrosinase enzyme were pH 7, $30^{\circ}C$, and 250 IU, respectively. The kinetic constant of the free tyrosinase enzyme was found for both cresolase and catacholase activity to be 0.25 and 0.4 mM, respectively. A cyclic voltammogram was used to investigate the electron transfer rate constant. The mean heterogeneous electron transfer rate ($k_e$) was $5.8{\times}10^{-4}$ cm/s. The results suggest that the electroenzymatic method could be an alternative way to produce L-DOPA without the use of a reducing agent such as ascorbic acid.