Changhyun Roh

Korea Atomic Energy Research Institute (KAERI), Daiden, Daejeon, South Korea

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Publications (49)113.81 Total impact

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    ABSTRACT: 3D copper sulfide (Cu2S) with different morphologies for high performance supercapacitors were synthesized via a simple, costeffective successive ionic layer adsorption and reaction (SILAR) method. Further these Cu2S nanostructure demostrate excellent surface properties like uniform surface morphology, large surface area of Cu2S samples. X-ray diffraction (XRD) X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy of these samples confirmed the crystallinity and crystal structure of Cu2S. The electrochemical studies of Cu2S samples have been investigated by cyclic voltammetry, charge-discharge and electrochemical impedance spectroscopy techniques. The maximum specific capacitance of flower like and integrated nanotubes samples are found 761 and 470 F g-1 respectively, at a scan rate of 5 mV s−1. The electrodes are prepared using a simple four-beaker SILAR system at ambient conditions, thus providing an easy approach to fabricate high-power and high-energy supercapacitors. Further, the EIS analysis shows lower ESR value, high power performance, excellent rate as well as frequency response to flower like Cu2S sample. The Ragone plot shows better power and energy densities of all Cu2S nanostructured samples. The long-term cycling performance of Cu2S is examined with excellent retenation of 95%. The high surface area provided by the porous and more conductive 3D nickel foam have been utilized properly to enhance the electrochemical properties of copper sulfides with charge transport and storage.
    No preview · Article · Jan 2016 · RSC Advances
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    ABSTRACT: In this study, a simple one-step hydrothermal reaction is developed to prepare composite based on Prussian blue (PB)/reduced graphene oxide foam (RGOF) for efficient removal of radioactive cesium ((137)Cs) from contaminated water. Scanning electron microscopy and transmission electron microscopy show that cubic PB nanoparticles are decorated on the RGO surface. Owing to the combined benefits of RGOF and PB, the composite shows excellent removal efficiency (99.5%) of (137)Cs from the contaminated water. The maximum adsorption capacity is calculated to be 18.67 mg/g. An adsorption isotherm fit-well the Langmuir model with a linear regression correlation value of 0.97. This type of composite is believed to hold great promise for the clean-up of (137)Cs from contaminated water around nuclear plants and/or after nuclear accidents.
    Full-text · Article · Jan 2016 · Scientific Reports
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    Full-text · Dataset · Dec 2015
  • Van Hoa Nguyen · ChanKyu Kang · ChangHyun Roh · Jae-Jin Shim

    No preview · Article · Dec 2015 · Industrial & Engineering Chemistry Research
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    ABSTRACT: Prussian blue-functionalized magnetic nanoclusters were fabricated for the highly efficient removal of radioactive cesium (such as 137Cs) and rapid magnetic separation of absorbent from 137Cs-contaminated water. The magnetic nanoclusters, synthesized via the hydrothermal method, were coated with Prussian blue (PB) via a simple reaction with potassium hexacyanoferrate under acidic conditions. The resulting Prussian blue-functionalized magnetic nanoclusters had a large distribution coefficient, even in the presence of 3000 ppm competing ions such as K+, Na+, Ca2+ and Mg2+, and excellent removal efficiency (>99.7%) of radioactive cesium from contaminated water. Furthermore, they possess good saturation magnetization values (27.5 emu/g), allowing for rapid separation from an aqueous solution using an external magnetic field. Therefore, these magnetic adsorbents have promising applications for the treatment of radioactive cesium-contaminated water.
    Full-text · Article · Oct 2015 · Journal of Alloys and Compounds
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    ABSTRACT: Radioactive cesium (137Cs) has seriously become a human concern owing to exposure from a nuclear accident release at a nuclear plant. Many efforts have focused at the removal of radioactive cesium and remediation of a contaminated environment. To meet these demands, an effective sorbent based on magnetic composites functionalized with synthetic clay minerals was demonstrated. This sorbent shows a high removal efficiency of contaminated water containing suspended sorbents at a level of 0.5 mg ml−1 [137Cs of 84.68 Becquerel (Bq) gram (g)−1], decontaminated to 0.47 Bq g−1 (99.44 % removal efficiency) with just one treatment. The radioactive cesium is dramatically adsorbed into synthetic clay minerals. Subsequently, a rapid and easy sorbent separation from the radioactive cesium solution occurs after treatment using a magnetic field. Thus, a magnetic sodium-phlogopite sorbent can offer high potential for in situ remediation.
    Full-text · Article · Aug 2015 · International journal of Environmental Science and Technology
  • Changhyun Roh · ChanKyu Kang · Jonathan R. Lloyd
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    ABSTRACT: Microbial processes can affect the environmental behavior of priority radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes and can contribute to the remediation of radionuclide-contaminated land. Underlying mechanisms that can control radionuclide solubility in biogeochemical systems can range from biosorption and biomineralization process, through direct (enzymatic) and indirect redox transformations. The mechanisms of enzyme-mediated reduction of problematic actinides, in principal, uranium (U), but including neptunium (Np), plutonium (Pu) and Americium (Am), are described in this review. In addition, the mechanisms by which the fission products technetium (Tc), cesium (Cs), and strontium (Sr) are removed from a solution by microorganisms are also described. The present review discusses the status of these microbiological processes, and the potential for cost-effective and scalable in situ remediation of radioactive waste.
    No preview · Article · Jul 2015 · Korean Journal of Chemical Engineering
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    ABSTRACT: Radioactive cesium (137 Cs) has inevitably become a human concern due to exposure from nuclear power plants and nuclear accident releases. Many efforts have been focused on removing cesium and the remediation of the contaminated environment. In this study, we elucidated the ability of Prussian blue-coated magnetic nanoparticles to eliminate cesium from radioactive contaminated waste. Thus, the obtained Prussian blue-coated magnetic nanoparticles were then characterized and examined for their physical and radioactive cesium adsorption properties. This Prussian blue-coated magnetic nanoparticle-based cesium magnetic sorbent can offer great potential for use in in situ remediation.
    Full-text · Article · Dec 2014 · Nanomaterials
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    Changhyun Roh
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    ABSTRACT: Recently, there has been a great deal of remarkable interest in finding bioactive compounds from nutritional foods to replace synthetic compounds. In particular, ortho-dihydroxyisoflavones and glycitein are of growing scientific interest owing to their attractive biological properties. In this study, 7,8-ortho-dihydroxyisoflavone, 6,7-ortho-dihydroxyisoflavone, 3',4'-ortho-dihydroxyisoflavone and 7,4'-dihydroxy-6-methoxyisoflavone were characterized using microorganism screened from soybean Doenjang. Three ortho-dihydroxyisoflavones and glycitein were structurally elucidated by 1H-NMR and GC-MS analysis. Furthermore, bacterial strains from soybean Doenjang with the capacity of biotransformation were screened. The bacterial strain, identified as Bacillus subtilis Roh-1, was shown to convert daidzein into ortho-dihydroxyisoflavones and glycitein. Thus, this study has, for the first time, demonstrated that a bacterial strain had a substrate specificity for multiple modifications of the bioactive compounds.
    Preview · Article · Dec 2014
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    Changhyun Roh · ChanKyu Kang
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    ABSTRACT: Microbial biotransformation is a great model system to produce drugs and biologically active compounds. In this study, we elucidated the fermentation and production of an anti-cancer agent from a microbial process for regiospecific hydroxylation of resveratrol. Among the strains examined, a potent strain showed high regiospecific hydroxylation activity to produce piceatannol. In a 5 L (w/v 3 L) jar fermentation, this wild type Streptomyces sp. in the batch system produced 205 mg of piceatannol (i.e., 60% yields) from 342 mg of resveratrol in 20 h. Using the product, an in vitro anti-cancer study was performed against a human cancer cell line (HeLa). It showed that the biotransformed piceatannol possessed a significant anticancer activity. This result demonstrates that a biotransformation screening method might be of therapeutic interest with respect to the identification of anti-cancer drugs.
    Preview · Article · Oct 2014 · Molecules
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    ABSTRACT: Obesity is the fifth leading cause of death globally. At least 2.8 million adults die each year as a result of being overweight. Therefore, the development of an efficient lipid inhibitor for the biological effects of obesity is highly needed. The discovery of bioactive compounds from food is one possible way to control obesity and to prevent or reduce the risks of various obesity-related diseases. In this study, we found that 7,3′,4′-trihydroxyisoflavone from Korean soybean paste has remarkable anti-obesity activity in vitro and in vivo. Treatment with 7,3′,4′-trihydroxyisoflavone significantly reduced the adipose tissue weight to 1.6/100 g of body weight in high-fat mice. In addition, in 7,3′,4′-trihydroxyisoflavone-treated mice, a significant reduction in the serum triglyceride and T-cholesterol was observed at 29 and 37 %, respectively. These results support the hypothesis that 7,3′,4′-trihydroxyisoflavone is expected to create a therapeutic interest in its use for the treatment of obesity.
    No preview · Article · Apr 2014 · European Food Research and Technology
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    ABSTRACT: Here, we present a simple method for controlling the density of Au nanoparticles (Au NPs) on a modified silicon substrate, by destabilizing the colloidal Au NPs with 3-mercaptopropyltrimethoxylsilane (3-MPTMS) for microelectromechanical-system-based applications to reduce tribological issues. A silicon surface was pretreated with a 3-MPTMS solution, immediately after which thiolated Au NPs were added to it, resulting in their uniform deposition on the silicon substrate. Without any material property change of the colloidal Au NPs, we observed the formation of large clusters Au NPs on the modified silicon surface. Analysis by scanning electron microscopy with energy dispersive X-ray spectroscopy indicated that the addition of 3-MPTMS resulted in an alternation of the chemical characteristics of the solution. Atomic force microscopy imaging supported the notion that silicon surface modification is the most important factor on tribological properties of materials along with ligand-modified Au NPs. The density of Au NPs on a silicon surface was significantly dependent on several factors, including the concentration of colloidal Au NPs, deposition time, and concentration of 3-MPTMS solution, while temperature range which was used throughout experiment was determined to have no significant effect. A relatively high density of Au NPs forms on the silicon surface as the concentrations of Au NPs and 3-MPTMS are increased. In addition, the maximum deposition of Au NPs on silicon wafer was observed at 3 h, while the effects of temperature variation were minimal.
    No preview · Article · Mar 2014 · Bioprocess and Biosystems Engineering
  • Changhyun Roh
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    ABSTRACT: Highly branched fatty acids are of particular interest as they have polyketide-like structures with several chiral centers and regioselective fictionalization of such substances would offer convenient routes to new important pharmaceutical compounds. A novel biocatalyst from Bacillus cereus was cloned and expressed in Escherichia coli BL21 using pET expression system. It can be easily expressed in Escherichia coli with a high yield. The expressed recombinant enzyme was purified by Ni-NTA affinity chromatography and characterized. We elucidated that this enzyme catalyzes the oxidation of alkanoic acids (C8 to C17) and unsaturated fatty acids (C18). Substrate binding study showed the tightest binding fatty acid was myristic acid (C14), yielding a Kd value of 7.88 µM. This biocatalyst showed the activity of saturated fatty acids of shorter (C8,C10), which could not be observed from other enzyme.
    No preview · Article · Mar 2014 · Biocatalysis and Agricultural Biotechnology
  • ChanKyu Kang · ChangHyun Roh · Ruel A. Overfelt
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    ABSTRACT: Pressure-driven flows through optically transparent polydimethylsiloxane (PDMS) microfluidic channels using a syringe pump are common in many experimental applications. However, because of small changes, the pressure-induced deformations due to soft materials and shapes and patterns in the microchannels, which generate untargeted flow velocity and pressure drop, have been easily ignored. In this paper, we present a simple experimental investigation with circular-shaped, periodically arranged objects of three different characteristic dimensions, as well as various channel heights ranging from 15 μm to 200 μm. The resultant CCD images and pressure data were used to determine the extent of the start-up transients and evaluate the establishment of quasi-steady flow conditions. Channel deformation, measured by fluorescence intensity difference, was severe in shallow microchannels that had characteristically large obstacles. In addition, PDMS microchannel bulging effects in shallow microchannels exerted a greater deleterious effect on (ΔP/Δx)QS values than upon VQS for the experiments using a volumetrically controlled syringe pump. The discrepancy between experimental and theoretical (ΔP/Δx) increased with decreasing microchannel height. This means that the severe PDMS bulging observed in shallow microchannels using a syringe pump can generate large deviations from the desired experimental result. As a result, the slope of Darcy friction factors plotted against the Reynolds number indicates that the slope was strongly dependent on microfluidic channel height and the degree of PDMS bulging. The microfluidic channel with the greatest height exhibited the smallest bulging effect and was shown to be in relatively good agreement with predicted values, while the slope became much steeper than −1 as channel heights decreased.
    No preview · Article · Jan 2014 · RSC Advances
  • Changhyun Roh
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    ABSTRACT: Development of microbial and enzymatic platforms for the production of pharmaceuticals and other industrial chemicals is an important area of research. Flavonoid and isoflavonoid oxidation is of potential importance in the synthesis of active antioxidants for biological activity in human. Especially, ortho-dihydroxyisoflavones (7,8,4′-trihydroxyisoflavone, 6,7,4′-trihdyroxyisoflavone and 7,3′,4′-trihydroxyisoflavone) are a growing scientific interest to enhance their health-related quality in human. The roles of biocatalysts from microorganisms which are called as treasure islands for natural products of medicine and antibiotics are not well understood. Thus, substrate specificity study on enzymes may give a solution for elucidation their roles. In this study, it was elucidated an enzyme had substrate specificity for regiospecific multiple hydroxylation to 7,8,4′-trihydroxyisoflavone, 6,7,4′-trihdyroxyisoflavone and 7,3′,4′-trihydroxyisoflavone. We demonstrated here that the biotransformation of daidzein can be significantly improved by modulating the monooxygenase and redox partner. The studies presented here provide the basis for future strain optimization to improve ortho-dihydroxyisoflavones production.
    No preview · Article · Oct 2013 · Biocatalysis and Agricultural Biotechnology
  • Chankyu Kang · Ruel A Overfelt · Changhyun Roh
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    ABSTRACT: Understanding the mechanical properties of optically transparent polydimethylsiloxane (PDMS) microchannels was essential to the design of polymer-based microdevices. In this experiment, PDMS microchannels were filled with a 100 μM solution of rhodamine 6G dye at very low Reynolds numbers (∼10(-3)). The deformation of PDMS microchannels created by pressure-driven flow was investigated by fluorescence microscopy and quantified the deformation by the linear relationship between dye layer thickness and intensity. A line scan across the channel determined the microchannel deformation at several channel positions. Scaling analysis widely used to justify PDMS bulging approximation was allowed when the applied flow rate was as high as 2.0 μl/min. The three physical parameters (i.e., flow rate, PDMS wall thickness, and mixing ratio) and the design parameter (i.e., channel aspect ratio = channel height/channel width) were considered as critical parameters and provided the different features of pressure distributions within polymer-based microchannel devices. The investigations of the four parameters performed on flexible materials were carried out by comparison of experiment and finite element method (FEM) results. The measured Young's modulus from PDMS tensile test specimens at various circumstances provided reliable results for the finite element method. A thin channel wall, less cross-linker, high flow rate, and low aspect ratio microchannel were inclined to have a significant PDMS bulging. Among them, various mixing ratios related to material property and aspect ratios were one of the significant factors to determine PDMS bulging properties. The measured deformations were larger than the numerical simulation but were within corresponding values predicted by the finite element method in most cases.
    No preview · Article · Sep 2013 · Biomicrofluidics
  • Changhyun Roh · Rolf D Schmid
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    ABSTRACT: Although the use of lipases as biocatalysts has frequently been proposed, it is yet scarcely being implemented in industrial processes. This is mainly due to the difficulties associated with the discovery and engineering of new enzymes and the lack of versatile screening methods. In this study, we screened the available strategy from a metagenomic pool for the organic solvent-tolerant lipase with enhanced performance for industrial processes. A novel lipase was identified through functional screening from a metagenomic library of activated sludge in an Escherichia coli system. The gene encoding the lipase from the metagenomic pool, metalip1, was sequenced and cloned by PCR. Metalip1 encoding a polypeptide of 316 amino acids had typical residues essential for lipase such as pentapeptide (GXSXGG) and catalytic triad sequences (Ser160, Asp260, and His291). The deduced amino acid sequence of metalip1 showed high similarity to a putative lipase from Pseudomonas sp. CL-61 (80 %, ABC25547). Metalip1 was expressed in E. coli BL21 (DE3) with a his-tag and purified using a Ni-NTA chelating column and characterized. This enzyme showed high expression level and solubility in the heterologous E. coli host. This enzyme was active over broad organic solvents. Among organic solvents examined, dimethyl formamide was the best organic solvent for metalip1. We showed that function-based strategy is an effective method for fishing out an organic solvent-tolerant lipase from the metagenomic library. Also, it revealed high catalytic turnover rates, which make them a very interesting candidate for industrial application.
    No preview · Article · Sep 2013 · Applied biochemistry and biotechnology
  • Changhyun Roh
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    ABSTRACT: The roles of cytochrome P450 monooxygenases (CYPs) from Streptomyces spp. which are called the "treasure islands" for natural products for medicine and antibiotics are not well understood. Substrate specificity studies on CYPs may give a solution for elucidation of their roles. Based on homology sequence information, the CYP105D7 of a soluble cytochrome P450 known as heme protein from Streptomyces avermitilis MA4680 was expressed using the T7 promoter of the bacterial expression vector pET24ma, over-expressed in Escherichia coli system and characterized. An engineered whole cell system for daidzein hydroxylation was constructed using an exogenous electron transport system from ferredoxin reductase (PdR) and ferredoxin (Pdx). Also, an in vitro reaction study showed the purified CYP105D7 enzyme, using NADH-dependent-reducing equivalents of a redox partner from Pseudomonas putida, hydroxylated daidzein at the 3' position of the B ring to produce 7,3,'4' trihydroxyisoflavone. The hydroxylated position was confirmed by GC-MS analysis. The turnover number of the enzyme was 0.69 μmol 7,3,'4'-trihydroxyisoflavone produced per μmol P450 per min. This enzyme CYP105D7 represents a novel type of 3'-hydroxylase for daidzein hydroxylation. A P450 inhibitor such as coumarin significantly (ca.98%) inhibited the daidzein hydroxylation activity.
    No preview · Article · Mar 2013 · Molecules
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    Changhyun Roh · Uhee Jung
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    ABSTRACT: Obesity is a global health problem. It is also known to be a risk factor for the development of metabolic disorders, type 2 diabetes, systemic hypertension, cardiovascular disease, dyslipidemia, and atherosclerosis. In this study, we screened crude extracts from 400 plants to test their anti-obesity activity using porcine pancreatic lipase assay (PPL; triacylglycerol lipase, EC 3.1.1.3) in vitro activity. Among the 400 plants species examined, 44 extracts from plants, showed high anti-lipase activity using 2,4-dinitrophenylbutyrate as a substrate in porcine pancreatic lipase assay. Furthermore, 44 plant extracts were investigated for their inhibition of lipid accumulation in 3T3-L1 cells. Among these 44 extracts examined, crude extracts from 4 natural plant species were active. Salicis Radicis Cortex had the highest fat inhibitory activity, whereas Rubi Fructus, Corni Fructus, and Geranium nepalense exhibited fat inhibitory capacity higher than 30% at 100 μg/mL in 3T3-L1 adipocytes, suggesting anti-obesity activity. These results suggest that four potent plant extracts might be of therapeutic interest with respect to the treatment of obesity.
    Preview · Article · Dec 2012 · International Journal of Molecular Sciences
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    ABSTRACT: Obesity is a global health problem. It is also known to be a risk factor for the development of metabolic disorders, type 2 diabetes, systemic hypertension, cardiovascular disease, dyslipidemia, and atherosclerosis. In this study, we elucidated that Buddleja officinalis Maximowicz extract significantly inhibited lipid accumulation during 3T3-L1 adipocyte differentiation. Furthermore, Buddleja officinalis Maximowicz extract reduced the body weight gain induced through feeding a high-fat diet to C57BL/6 mice. The treatment of Buddleja officinalis Maximowicz extract significantly reduced the adipose tissue weight to 2.7/100 g of body weight in high-fat mice. When their adipose tissue morphology was investigated for histochemical staining, the distribution of cell size in the high-fat diet groups was hypertrophied compared with those from Buddleja officinalis Maximowicz extract-treated mice. In addition, in Buddleja officinalis Maximowicz extract-treated mice, a significant reduction of serum triglyceride and T-cholesterol was observed at to 21% and 17%, respectively. The discovery of bioactive compounds from diet or dietary supplementation is one of possible ways to control obesity and to prevent or reduce the risks of various obesity-related diseases. These results support that Buddleja officinalis Maximowicz extract is expected to create the therapeutic interest with respect to the treatment of obesity.
    Full-text · Article · Dec 2012 · Molecules

Publication Stats

305 Citations
113.81 Total Impact Points

Institutions

  • 2010-2015
    • Korea Atomic Energy Research Institute (KAERI)
      • • Advanced Radiation Technology Institute
      • • Radiation Research Division for Biotechnology
      Daiden, Daejeon, South Korea
  • 2014
    • Korea Institute of Energy Research
      Sŏul, Seoul, South Korea
  • 2012
    • Auburn University
      • Department of Mechanical Engineering
      AUO, Alabama, United States
  • 2007-2010
    • Seoul National University
      • • Department of Chemical and Biological Engineering
      • • Institute of Molecular Biology and Genetics
      Sŏul, Seoul, South Korea
  • 2005-2008
    • Universität Stuttgart
      • Institute of Technical Biochemistry
      Stuttgart, Baden-Württemberg, Germany