• BMB Reports
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• v.38 no.5
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• pp.584-590
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• 2005

Glucose 6-phosphate dehydrogenase (EC 1.1.1.49) was purified from Aspergillus aculeatus, a filamentous fungus previously isolated from infected tongue of a patient. The enzyme, apparently homogeneous, had a specific activity of $220\;units\;mg^{-1}$/, a molecular weight of $105,000{\pm}5,000$ Dal by gel filtration and subunit size of $52,000{\pm}1,100$ Dal by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The substrate specificity was extremely strict, with glucose 6-phosphate (G6P) being oxidized by nicotinamide adenine dinucleotide phosphate (NADP) only. At assay pH of 7.5, the enzyme had $K_m$ values of $6\;{\mu}m$ and $75\;{\mu}m$ for NADP and G6P respectively. The $k_{cat}$ was $83\;s^{-1}$. Steady-state kinetics at pH 7.5 produced converging linear Lineweaver-Burk plots as expected for ternary-complex mechanism. The patterns of product and dead-end inhibition suggested that the enzyme can bind NADP and G6P separately to form a binary complex, indicating a random-order mechanism. The enzyme was irreversibly inactivated by heat in a linear fashion, with G6P providing a degree of protection. Phosphoenolpyruvate (PEP), adenosinetriphosphate (ATP), and fructose 6-phosphate (F6P), in decreasing order, are effective inhibitors. Zinc and Cobalt ions were effective inhibitors although cobalt ion was more potent; the two divalent metals were competitive inhibitors with respect to G6P, with $K_i$ values of $6.6\;{\mu}m$ and $4.7\;{\mu}m$ respectively. It is proposed that inhibition by divalent metal ions, at low NADPH /NADP ratio, is another means of controlling pentosephosphate pathway.

• Journal of Sensor Science and Technology
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• v.1 no.1
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• pp.85-92
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• 1992

A new potassium sensitive field effect transistor modified with 4'-aminobenzo-15-crown-5 was prepared and its response characteristics were evaluated. The response slope of $K^{+}-ISFET$ for pH was 30.0 mV/decade and the response time was mere than 3 minutes. And the response slope and time of the $K^{+}-ISFET$ for potassium ion as $19.5{\pm}0.2{\;}mV/decade$ and about 3 minutes, respectively. The linear response range of the sensor for potassium ion was $2.0{\times}10^{-4}{\sim}1.0{\times}10^{-2}M$. The selectivity coefficients of the $K^{+}-ISFET$ for the alkali and alkaline earth metal ions were also evaluated. Sodium, ammonium and calcium ions exhibited relatively significant interference. The long term stability of the sensor was remarkably improved and it could be used for more than 50 days.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.49-53
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• 1996

Crystal structures of N $a_{x}$W $O_3$(0.5$\leq$x$\leq$1.0) were investigated. Transmission electron microscopy (TEM) studies indicate that there is an ordering of sodium ions when x=0.75. The direction of ordering is [110] and the wavelength of ordering is twice of the interplanar distance of (110) plane. It has been confirmed that a superlattice containing eight N $a_{0.75}$W $O_3$is the unit cell of ordered structure. In this unit cell, Na sites at (100) and ($\frac{1}{2}$$\frac{1}{2}$$\frac{1}{2}$) are vacant. The ordered phase was preserved after the annealing at $600^{\circ}C$ in the air. In reduced N $a_{x}$W $O_3$with x=0.5 and 1.0, extra phases were found to coexist with the partially ordered perovskite phase. After annealing at $600^{\circ}C$, theses phases were transformed into the phases found in calcined specimens.ens.s.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.1
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• pp.139-147
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• 2007

For environmental remediation of a contaminated groundwater plume, the use of zero-valent metal represents one of the latest innovative technologies. In this study, the effects of denitrification by zero-valent iron adsorbed in mesoporous silicas have been studied for groundwater contaminant degradation. The mesoporous silica was functionalized with 3-mercaptopropyltrimethoxysilane (MPTS) ligands and the zero-valent iron precipitated in the mesopore of granular silica was made by $FeCl_2$ and $NaBH_4$. Hydrogen was exchanged with $Fe^{2+}$ ions in the granular silicas. And then the ions were reduced by sodium borohydride in the mesoporous silicas. The surface area of the silica determined via the BET method ranged from 858 to $1275m^2/g$. The reductive reaction of nitrate-nitrogen indicated that the degradation of nitrate-nitrogen appeared to be pseudo first-order with the observed reaction rate constant kobs ($0.1619h^{-1}$) and to be directly proportional to the specific surface area. Therefore, the mesoporous silica with nano zero-valent iron proposed as a novel treatment strategy for contaminated groundwater was successfully implemented herein for the removal of nitrate-nitrogen.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.527-532
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• 2014

$0.97Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3-0.03LaFeO_3$ lead-free piezoelectric ceramics were fabricated by a solid state reaction method. $LaFeO_3$ additives were added to $Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ for volatile compensation of bismuth and sodium ions in the sintering process. To create A-site vacancies, the mole ratio and charge valence of A-site ions ($Bi^{3+}$, $Na^+$ and $K^+$) were controlled. The improved piezoelectric properties were observed by addition of $LaFeO_3$ and control of A-site vacancies. In particular, a $d_{33}^*(S_{max}/E_{max})$ value of 614pm/V and an electric field induced strain of 0.33% was observed in $0.97Bi_{0.505}(Na_{0.78}K_{0.22})_{0.485}TiO_3-0.03LaFeO_3$ ceramic.

• Korean Journal of Soil Science and Fertilizer
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• v.18 no.4
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• pp.352-358
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• 1985

Loss of cationic zeolites saturated with different ions, sodium, potasium, ammonium, magnesium and calcium ions, and changes of hydraulic conductivity were investigated in labortory. The 0.5 to 1mm sands and the zeolite particles passed 0.1mm sieve were used in the column tests. The amount of zeolite particle loss was in order of Na- > K- > $NH_4-$ saturated zeolites, and little loss was observed from Mg and Ca saturated zeolites. The loss of zeolite particles was mainly due to dispersion in solution, which was prominant when 0.01N dilute mono ionic solution and distilled water were percolated. The results also showed that the changes in hydraulic conductivity were greater in the columns where the loss of dispersed zeolite particles was higher.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.5
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• pp.533-540
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• 2024

In line with the development of electronic devices and technologies, the demand for improving ferroelectric materials' performance is increasing. Since K_0.5Na_0.5NbO₃ (KNN), an eco-friendly ferroelectric material that does not use lead and has a high Curie temperature, it is attracting attention to its usability as a high-temperature dielectric, and various studies are being conducted to increase performance. In a KNN having a perovskite structure, there was a simulation result that the KNN has higher spontaneous polarization when the A-site in which sodium ions exist is replaced with lithium ions. If the simulation results can be proven experimentally, the application range of KNN-based ferroelectric materials will increase. To this end, we tried to manufacture a K_1-xLi_xNbO₃ (KLN) with high electrical characteristics by fabricating niobium-deficient and potassium-excessive compositions, which attempt was made to solve the stoichiometry problem by volatilization and suppress secondary phases. If KLN's secondary phase suppression and relative permittivity improvement are successful, it will contribute to meeting the demand for developing electronic devices.

• Journal of Environmental Science International
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• v.10 no.4
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• pp.299-304
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• 2001

For the remediation of the contaminated soil with heavy metals, Cd, Cr, Cu, and Pb, the reaction parameters were optimized. Tartaric acid (TA) and oxalic acid(OA) as a washing agent and recovery of metals, The optimum washing conditions of TA and OA were in the ratio of 1 : 20 between soil and acid solution during 2hr reaction under unbuffered pH solutions. At the optimized reaction conditions, the removal efficiencies were compared with that of 0.1 M HCl and ethylenediamine tetraacetic acid(EDTA). TA showed higher efficiency on the removal of Pb than that of EDTA, which established for the remediation of contaminated soil with Pb and Cd metals. The recovery of metal ions from washing solution was achieved by adding calcium hydroxide and sodium sulfide by forming the precipitation of metal hydroxide and metal slfied. Optimum amounts of sodium sulgide and calcium hydroxide were Cd = 25g/$\ell$, Cu = 5~10g/$\ell$ and Pb = 5~10g/$\ell$ for the washing solution of OA and 2~5g/$\ell$ for the washing solution of TA, respectively. The amounts of $Na_2S$ and $CA(OH)_2$ for the tartaric acid was less than that of oxalic acid.

• Journal of the Korean Chemical Society
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• v.41 no.9
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• pp.488-494
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• 1997

Lithium and sodium ions have been intercalated into two dimensional structure of $FeMoO_4Cl$. The electronic localization and the large difference in unit cell parameter between the pristine material and the intercalates lead to the existence of large biphased domains. In the case of the lithium system, a narrow range of $Li_xFeMoO_4Cl$ ($0.95{\leq}x{\leq}1.06$) solid solution has been found around the $LiFeMoO_4Cl$ composition. The OCV curve fitting has been performed using Armand's model. The occurrence of several parts in the charge-discharge curve is related to the electronic and structural modifications of the material during the intercalation process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.6
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• pp.479-485
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• 2002

We have investigated the effects of various wafers cleaning on glass/Si bonding using 4 inch Pyrex glass wafers and 4 inch silicon wafers. The various wafer cleaning methods were examined; SPM(sulfuric-peroxide mixture, $H_2SO_4:H_2O_2$ = 4 : 1, $120^{\circ}C$), RCA(company name, $NH_4OH:H_2O_2:H_2O$ = 1 : 1 : 5, $80^{\circ}C$), and combinations of those. The best room temperature bonding result was achieved when wafers were cleaned by SPM followed by RCA cleaning. The minimum increase in surface roughness measured by AFM(atomic force microscope) confirmed such results. During successive heat treatments, the bonding strength was improved with increased annealing temperatures up to $400^{\circ}C$, but debonding was observed at $450^{\circ}C$. The difference in thermal expansion coefficients between glass and Si wafer led debonding. When annealed at fixed temperatures(300 and $400^{\circ}C$), bonding strength was enhanced until 28 hours, but then decreased for further anneal. To find the cause of decrease in bonding strength in excessively long annealing time, the ion distribution at Si surface was investigated using SIMS(secondary ion mass spectrometry). tons such as sodium, which had been existed only in glass before annealing, were found at Si surface for long annealed samples. Decrease in bonding strength can be caused by the diffused sodium ions to pass the glass/si interface. Therefore, maximum bonding strength can be achieved when the cleaning procedure and the ion concentrations at interface are optimized in glass/Si wafer direct bonding.