• Journal of the Korean Electrochemical Society
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• v.3 no.2
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• pp.69-71
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• 2000

Redox-active calix[4]arenes with carboxylic acid and disulfide groups were prepared and spontaneous deposition on silver and gold surfaces was observed. Owing to their unusual structure, the calix[4]arenes exhibit selective affinity fur alkaline earth metal ions in aqueous media. When annular ionophores are immobilized on the surface, voltammetric and spectroscopic studies show the entrapment of metal ions. Furthermore, it was possible to reversibly capture and remove the ions using strong chelating agents such as ethylenediaminetetraacetic acid (EDTA).

• BMB Reports
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• v.38 no.5
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• pp.550-554
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• 2005

YKR049C is a mitochondrial protein in Saccharomyces cerevisiae that is conserved among yeast species, including Candida albicans. However, no biological function for YKR049C has been ascribed based on its primary sequence information. In the present study, NMR spectroscopy was used to determine the putative biological function of YKR049C based on its solution structure. YKR049C shows a well-defined thioredoxin fold with a unique insertion of helices between two $\beta$-strands. The central $\beta$-sheet divides the protein into two parts; a unique face and a conserved face. The 'unique face' is located between ${\beta}2$ and ${\beta}3$. Interestingly, the sequences most conserved among YKR049C families are found on this 'unique face', which incorporates L109 to E114. The side chains of these conserved residues interact with residues on the helical region with a stretch of hydrophobic surface. A putative active site composed by two short helices and a single Cys97 was also well observed. Our findings suggest that YKR049C is a redox protein with a thioredoxin fold containing a single active cysteine.

• Proceedings of the Korean Society for Applied Microbiology Conference
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• 2001.06a
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• pp.62-72
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• 2001

The N-carbamoyl-D-amino acid amidohydrolase (D-carbamoylase) gene (dcb) from Agrobacterium tumefaciens AM 10 has been successfully cloned and expressed in Escherichia coli. Expression of D-carbamoylase gene under the 17 promoter in different host strains showed that the optimal expression was achieved in E. coli JM109 (DE3) with a 9-fold increase in enzyme production compared to the wild-type strain. The co-expression of the GroEL/ES protein with D-carbamoylase protein caused an in vivo solubilization of D-carbamoylase in an active form. The synergistic effect of GroEL/ES at 28$^{\circ}C$ led to 60 ％ solubilization of the total expressed target protein with a 6.2-fold increase in enzyme activity in comparison to that expressed without GroEL/ES and 43-fold increase in enzyme activity compared to A. tumefaciens AM 10. Attempts to express D-carbamoylase in an altered redox cytoplasmic milieu did not improve the enzyme production in an active form. The Histidyl-tagged D-carbamoylase was purified in a single step by Nickel-affinity chromatography and was found to have a specific activity of 9.5 U/mg protein.

• Bulletin of the Korean Chemical Society
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• v.12 no.3
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• pp.276-281
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• 1991

Electrochemical behaviors of optically active sparteine-Cu(II) dihalide complexes were investigated by polarography and cyclic voltammetry (CV). These Cu(II) complexes are rather easier to be reduced to Cu(I) states when comparison is made with other nonplaner copper complexes, We have assigned the CV peaks and polarographic waves related to the redox processes for these complexes. We could also observe the exchange reaction of Cu(II) ion in the complex with mercury metal in the cell having mercury pool. The redox mechanism of these complelxes is as follows; The 1st wave appeared at +0.47 V/+0.65 V corresponds to the reaction of $SpCuX_2+ e{\rightleftarrow}SpCuX_{2^-}$ and the 2nd one at +0.26 V/+0.21 V does the reaction of $SpCuX_{2 ^-} +e{\rightleftarrow}SpCuX_2^{2-}$. The 3rd one at -0.35 V/-0.27 V is dueto the reduction of mercury complex formed via exchange reaction. Where, X is chloride ion.

• Journal of Sensor Science and Technology
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• v.29 no.4
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• pp.215-219
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• 2020

MnCo₂S₄/CoS₂ electrode with highly accessible electroactive sites is prepared using the hydrothermal method. The electrode exhibits an areal capacitance of 0.75 Fcm^-2 at 6 mAcm^-2 in 1 M KOH. The capacitance is further increased to 2.06 Fcm^-2 by adding K₃Fe(CN)₆ and K₄Fe(CN)₆ (a redox couple) to KOH. This increment is associated with the redox-active properties of cobalt and manganese transition metals, as well as the ion pair of [Fe(CN)₆]^-3/[Fe(CN)₆]^-4. The capacitance retention of the MnCo₂S₄/CoS₂ electrode is 87.5% for successive 4000 charge-discharge cycles at 10 mAcm^-2 in a composite electrolyte system of KOH and ferri/ferrocyanide. The capacitance enhancement is supported by the lowest equivalent series resistance (0.62 Ωcm^-2) of MnCo₂S₄/CoS₂ in the presence of redox additive couple compared with the bare KOH electrolyte.

• Applied Chemistry for Engineering
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• v.34 no.2
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• pp.175-179
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• 2023

Herein we present a tested aqueous based redox flow battery (RFB) that employs phosphomolybdic acid and ferrocyanide as the negative and positive active species in an aqueous sodium hydroxide solution. The different concentrations of NaOH solution, such as 1.0, 1.2, 1.4, 1.5, and 1.6 M, were prepared for checking the electrochemical properties and stability. The NaOH concentration as a supporting electrolyte in the negative species appears to play an important role in the electrochemical properties of phosphomolybdic acid. Moreover, the optimum value of the concentration is necessary for the best performance. The resistance of the electrolyte decreased with increasing the concentration up to 1.5 M and then increased to 1.6 M. Hence, the decrease in electrolyte resistance appears to greatly influence the energy efficiency, which is improved by increasing the concentration of NaOH. In addition, the 1.5 M NaOH solution appears to be the concentration required for optimum performance.

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.239-243
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• 2019

In this study, anthraquinone-2,7-disulfonic acid (2,7-AQDS) is used as negative active material and Tiron is used as positive active material for aqueous redox flow battery (RFB). In previous results that used the 2,7-AQDS and Tiron, sulfuric acid ($H_2SO_4$) was a supporting electrolyte. However, in this study, ammonium chloride ($NH_4Cl$) is suggested as the electrolyte for the first time. By changing the supporting electrolyte from $H_2SO_4$ to $NH_4Cl$, the cell voltage of RFB is improved from 0.76 V to 1.01 V. To investigate the effect of $NH_4Cl$ supporting electrolyte of the performance of RFB, the full-cell tests of RFB using 2,7-AQDS and Tiron that are dissolved in $NH_4Cl$ supporting electrolyte are carried out, while cut-off voltage range is a main parameter to determine their performance. When the cut-off voltage range is 0.2~1.6 V, the hydrogen evolution occurs during charging step. To address the side reaction effect, the cut-off voltage range is changed to 0.2~1.2 V. When the revised cut-off voltage range is used and the current density of $40mA/cm^2$ is applied, hydrogen evolution is not observed and the optimal RFB shows the charge efficiency of 99% and discharge capacity of 3.3 Ah/L at 10cycle.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.108-111
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• 2003

Currently, molecular devices are reported utilizing active self-assembled monolayers containing the nitro group as the active component, which has active redox centers[1]. We confirm the electrical properties of 4,4-di(ethynylphenyl)-2'-nitro-1-benzenethiolate. To deposit the SAM layer onto gold electrode, we transfer the prefabricated Au(111) substrates into a 1mM self-assembly molecules in THF solution. Au(111) substrates were prepared by ion beam sputtering method of gold onto the silicon wafer. As a result, we measured current-voltage curve using ultra high vacuum scanning tunneling microscopy (UHV STM), I-V curve also clearly shows several current peaks between the negative bias region (-0.3958V) and the positive bias region (0.4658V), respectively.

• Journal of Hydrogen and New Energy
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• v.26 no.2
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• pp.170-178
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• 2015

In this study, we carry out a study on how to improve performance of vanadium redox flow battery (VRFB) through promoting reaction rate of rate determining vanadium reaction ($[VO]^{2+}/[VO_2]^+$). In order to do that, three different carbons like Vulcan (XC-72), CMK3 and MSU-F-C are adopted as the catalysts, while their catalytic activity and reaction reversibility are evaluated using half-cell tests. Their topological images are also measured by TEM. For estimation of the VRFB performance, multiple charge-discharge curves of VRFBs including the catalysts are measured by single cell tests. As a result of that, MSU-F-C shows relatively excellent catalytic activity and reaction reversibility as well as large surface area compared to those of Vulcan (XC-72) and CMK3. Also, in terms of the performance of VRFBs including the catalysts, VRFB including MSU-F-C indicates (i) low charging/discharging overpotentials and low internal resistance, (ii) high charge/discharge capacities and (iii) high energy efficiency. These VRFB performance data are well agreed with results on catalytic activity and reaction reversibility. The reason that MSU-F-C induces superior VRFB performances is attributed to (i) its large surface area and (ii) its hydrophilic surface functional groups that mainly consist of hydroxyl bonds that are supposed to play active surface site role for facilitaing $[VO]^{2+}/[VO_2]^+$ redox reaction. Based on the above results, it is found that adoption of MSU-F-C as catalyst for VRFB results in improvement in VRFB performance by promoting the languid $[VO]^{2+}/[VO_2]^+$ redox reaction.

• Economic and Environmental Geology
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• v.40 no.1 s.182
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• pp.29-45
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• 2007

Biogeochemical characteristics involving redox processes in groundwater from a riverine alluvial aquifer was investigated using multi-level monitoring wells (up to 30m in depth). Anaerobic conditions were predominant and high Fe ($14{\sim}37mg/L$) and Mn ($1{\sim}4mg/L$) concentrations were observed at 10 to 20 m in depth. Below 20 m depth, dissolved sulfide was detected. Presumably, these high Fe and Mn concentrations were derived from the reduction of Fe- and Mn-oxides because dissolved oxygen and nitrate were nearly absent and Fe and Mn contents were considerable in the sediments. The depth range of high Mn concentration is wider than that of high Fe concentration. Dissolved organics may be derived from the upper layers. Sulfate reduction is more active than Fe and Mn reduction below 20 m in depth. Disparity of calculated redox potential from the various redox couples indicates that redox states are in disequilibrium condition in groundwater. Carbonate minerals such as siderite and rhodochrosite may control the dissolved concentrations of Fe(II) and Mn(II), and iron sulfide minerals control for Fe(II) where sulfide is detected because these minerals are near saturation from the calculation of solubility equilibria.