• BMB Reports
• /
• v.41 no.4
• /
• pp.305-309
• /
• 2008

Cobalt is an essential microelements in many biological processes involving enzymatic activity. We found that $Zn^{2+}$ and $Mg^{2+}$, which are in the active site of native calf intestine alkaline phosphatase (CIP), can be replaced by $Co^{2+}$ directly in solution. The effect of $Co^{2+}$ concentration on the substitution reaction was examined at ratios of [$Co^{2+}$]/[CIP] from 0:1 to 8:1. The quantity of $Zn^{2+}$ in CIP decreased progressively as the ratio was increased, but the amount of $Mg^{2+}$ changed in irrregular fashion. A series of active site models of the reaction mechanism of CIP are proposed. Low pH was found to promote the replacement of $Mg^{2+}$ by $Co^{2+}$. To understand how the substitution affects the enzyme, we also solved the secondary structure of CIP after reaction with $Co^{2+}$ in different conditions.

• Korean Chemical Engineering Research
• /
• v.48 no.6
• /
• pp.737-740
• /
• 2010

High leakage current and threshold voltage shift(${\Delta}Vth$) are demerits of a-Si:H TFT. These characteristics are influenced by gate insulator and active layer film quality, surface roughness, and process conditions. The purpose of this investigation is to improve off current($I_{off}$) and ${\Delta}V_{th}$ characteristics. Nitrogen-rich deposition condition was applied to gate insulator, and hydrogen-rich deposition condition was applied to active layer to reduce electron trap site and improve film density. $I_{off}$ improved from 1.01 pA to 0.18 pA at $65^{\circ}C$, and ${\Delta}V_{th}$ improved from -1.89 V to 1.22 V.

• Journal of The Korean Astronomical Society
• /
• v.14 no.2
• /
• pp.55-71
• /
• 1981

On the basis of observational constraints, particularly the relationship between metal abundance and cumulative stellar mass, a simple two-zone disk-halo model for the chemical evolution of our Galaxy was investigated, assuming different chemical processes in the disk and halo and the infall rates of the halo gas defined by the halo evolution. The main results of the present model calculations are: (i) The halo formation requires more than 80% of the initial galactic mass and it takes a period of $2{\sim}3{\times}10^9$ yrs. (ii) The halo evolution is divided into two phases, a fast collapse phase ($t=2{\sim}3{\times}10^8$ yrs) during which period most of the halo stars $({\sim}95%)$ are formed and a later slow collapse phase which is characterized by the chemical enrichment due to the inflow of external matter to the halo. (iii) The disk evolution is also divided into two phases, an active disk formation phase with a time-dependent initial mass function (IMF) up to $t{\approx}6{\times}10^9$ yrs and a later steady slow formation phase with a constant IMF. It is found that at the very early time $t{\approx}5{\times}10^8$ yrs, the metal abundance in the disk is rapidly increased to ${\sim}1/3$ of the present value but the total stellar mass only to ${\sim}10%$ of the present value, finally reaching about 80% of the present values toward the end of the active formation phase.

• Archives of Pharmacal Research
• /
• v.18 no.3
• /
• pp.173-178
• /
• 1995

Ciprofloxacin resistance mechanisms were studied by investigating the inhibitory effect of ciprofloxacin on the gyrase-mediated DNA supercoiling and the intracellular accumulation of ciprofloxacin in clinical isolates of Pseudomonas aeruginosa. A higher amount of ciprofloxacin was required to inhibit the gyrases purified from the ciprofloxacin-resistant strains than that from the sensitive strain. Reconstitution of heterologous gyrase subunits from different strains revealed alterations in the A and/or the B subunits of gyrase in these strains. In addition, the resistant strains accumulated approximately a half amount of ciprofloxacin inside the cells, compared to the sensitive strain. However, when the active efflux was blocked by carbonyl cyanide m-chlorophenyl hydrazone treatment, intracellular concentration of ciprofloxacin was elevated about 4-7 fold in these strains, while the sensitive strain was not significantly affected by this treatment, indicating that the ciprofloxacin-resistant strains developed a drug efflux system. Interestingly, these resistant strains expressed an envelope protein of approximately 51 kD. These studies suggest that alterations in the gyrase as well as the active drug-efflux system conferred dual ciprofloxacin resistance mechanisms to these clinical isolates of P. aeruginosa.

• Korean Chemical Engineering Research
• /
• v.57 no.2
• /
• pp.185-197
• /
• 2019

Deactivation of porous photocatalytic materials was studied using three types of microstructured particles: macroporous titania particles, titania microspheres, and porous silica microspheres containing CNTs and $TiO_2$ nanoparticles. All particles were synthesized by emulsion-assisted self-assembly using micron-sized droplets as micro-reactors. During repeated cycles of the photocatalytic decomposition reaction, the non-dimensionalized initial rate constants (a) were estimated as a function of UV irradiation time (t) from experimental kinetics data, and the results were plotted for a regression according to the exponentially decaying equation, $a=a_0\;{\exp}(-k_dt)$. The retardation constant ($k_d$) was then compared for macroporous titania microparticles with different pore diameters to examine the effect of pore size on photocatalytic deactivation. Nonporous or larger macropores resulted in smaller values of the deactivation constant, indicating that the adsorption of organic materials during the photocatalytic decomposition reaction hinders the generation of active radicals from the titania surface. A similar approach was adopted to evaluate the activation constant of porous silica particles containing CNT and $TiO_2$ nanoparticles to compare the deactivation during recycling of the photocatalyst. As the amount of CNTs increased, the deactivation constant decreased, indicating that the conductive CNTs enhanced the generation of active radicals in the aqueous medium during photocatalytic oxidation.

• Journal of the Korean Institute of Gas
• /
• v.26 no.2
• /
• pp.14-20
• /
• 2022

In this study, the catalytic reaction characteristics for producing hydrogen using methanol steam reforming were investigated. Nickel and copper are frequently used in steam reforming reaction and methanol synthesis, were used as main active metals. As a support, hydrotalcite has a high specific surface area, excellent porosity and thermal stability, and has weak Lewis acid sites and basic properties. Hydrotalcite was used to identify catalysts of methanol steam reforming with catalytic activity and their properties. In this research, high reactivity was shown in the catalyst of copper metal with high reducibility. And increasing of active metal loading showed the higher the methanol conversion and hydrogen selectivity.

• Korean Journal of Pharmacognosy
• /
• v.34 no.4 s.135
• /
• pp.308-313
• /
• 2003

A bioassay-guided fractionation of the stem bark extract of Eucommia ulmoides Oliver (Eucommiaceae) led to the isolation of three iridoid constituents, genipin (1), geniposide (3), geniposidic acid (4) as well as $({\pm})-guaiacylglycerol$ (2) and fatty acid mixtures as active ingredients of the extract responsible for the antitumoral property. The EtOAc soluble part and BuOH soluble part of the extract demonstrated a potent inhibition on the proliferation of cultured human tumor cells such as A549 (non small cell lung), SK-OV-3 (ovary), SK-MEL-2 (melanoma), XF498 (central nerve system) and HCT-15 (colon) in vitro, whereas the remaining water soluble part exhibited a poor inhibition. The intensive investigation of the EtOAc soluble part and BuOH soluble part of the extract yielded genipin, guaiacylglycerol, geniposide, geniposidic acid and large amounts of fatty acid mixtures as active components.

• Journal of Electrochemical Science and Technology
• /
• v.8 no.3
• /
• pp.169-182
• /
• 2017

Iron and nitrogen codoped carbon (Fe-N/C) catalysts have emerged as one of the most promising replacements for state-of-the-art platinum-based electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells. During the last decade, significant progress has been achieved in Fe-N/C catalysts in terms of ORR activity improvement and active site identification. In this review, we focus on recent efforts towards advancing our understanding of the structure of active sites in Fe-N/C catalysts. We summarize the spectroscopic and electrochemical methods that are used to analyze active site structure in Fe-N/C catalysts, and the relationship between active site structure and ORR activity in these catalysts. We provide an overview of recently reported synthetic strategies that can generate active sites in Fe-N/C catalysts preferentially. We then discuss newly suggested active sites in Fe-N/C catalysts. Finally, we conclude this review with a brief future outlook.

• Journal of Microbiology
• /
• v.35 no.4
• /
• pp.300-308
• /
• 1997

The catechol 2,3-dioxygenase (C23O) encoded by the Pseudomonas putida xylE gene was over-produced in Escherichia coli and purified to homogeneity. The activity of the C23O required the reduced form of the Fe(II) ion since the enzyme was highly susceptible to inactivation with hydrogen perocide but reactivated with the addition of ferrous sulfate in conjunction with ascorbic acid. The C23O activity was abolished by treatment with the chemical reagents, diethyl-pyrocarbonate (DEPC), tetranitromethane (TNM), and 1-cyclohexy1-3-(2-morpholinoethyl) car-bodiimidemetho-ρ-toluenesulfontate (CMC), which are modifying reagents of histidine, tyrosine and glutamic acid, respectively. These results suggest that histidine, tyrosine and glutamic acid residues may be good active sites for the enzyme activity. These amino acid residues are conserved residues may be good active sites for the enzyme activity. These amino acid residues are conserved residues among several extradion dioxygenases and have the chemical potential to serveas ligands for Fe(II) coordination. Analysis of random point mutants in the C23O gene derived by PCR technique revealed that the mutated positions of two mutants, T179S and S211R, were located near the conserved His165 amd Hos217 residues, respectively. This finding indicates that these two positions, along with the conserved histidine residues, are specially effective regions for the enzyme function.

• The Korean Journal of Pesticide Science
• /
• v.19 no.2
• /
• pp.88-92
• /
• 2015

This study investigated the thermal stabilities of the four limonoidal active compounds like azadirachtin A, azadirachtin B, deacetylsalannin and salannin and of the two alkaloidal active compounds like matrine and oxymatrine in commercial biopesticides at incubated conditions ($30^{\circ}C$, $35^{\circ}C$, $40^{\circ}C$, $45^{\circ}C$, and $54^{\circ}C$). Half-lives of the limonoidal compounds in biopesticide ranged from 25.6 to 220 days. And the total limonoid contents changed over 15% after 14 days at all the conditions in the tested biopesticide containing neem extract. On the contrary, half-lives of the alkaloidal compounds in biopesticide showed the ranges from 231 to 346 days. And total alkaloidal compounds in all the tested biopesticides containing Sophora flavescens extracts decomposed below 15% after 14 days incubation at $54^{\circ}C$.