10 results on '"Hyung-Jun Koo"'
Search Results
2. Synthesis and Functionalization of β-Glucan Particles for the Effective Delivery of Doxorubicin Molecules
- Author
-
Hojeong Jeon, Jonghoon Choi, Kyungwoo Lee, Youngmin Seo, Yonghyun Choi, Hyung-Jun Koo, Yejin Kwon, Kyobum Kim, and Jangsun Hwang
- Subjects
chemistry.chemical_classification ,General Chemical Engineering ,Microorganism ,General Chemistry ,engineering.material ,Polysaccharide ,lcsh:Chemistry ,Cell wall ,lcsh:QD1-999 ,chemistry ,Biochemistry ,medicine ,engineering ,Surface modification ,Molecule ,Doxorubicin ,Biopolymer ,Glucan ,medicine.drug - Abstract
β-Glucan, a polysaccharide biopolymer, is one of the constituents of cell walls of microorganisms, basidiomycetes, and plants. It has pathogen-associated molecular patterns, recognizing specific im...
- Published
- 2019
- Full Text
- View/download PDF
3. Cytotoxicity of Gallium–Indium Liquid Metal in an Aqueous Environment
- Author
-
Ji-Hye Kim, Kyobum Kim, Hyung-Jun Koo, Sungjun Kim, and Ju-Hee So
- Subjects
Liquid metal ,Aqueous solution ,Materials science ,Sonication ,Alloy ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Metal ,chemistry ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,engineering ,General Materials Science ,Gallium ,0210 nano-technology ,Indium ,Eutectic system - Abstract
Eutectic gallium-indium alloy (EGaIn) liquid metal is highly conductive, moldable, and extremely deformable and has attracted significant attention for many applications, ranging from stretchable electronics to drug delivery. Even though EGaIn liquid metal is generally known to have low toxicity, the toxicity of the metal, rather than a salt form of Ga or In, has not been systematically studied yet. In this paper, we investigate the time-dependent concentration of the ions released from EGaIn liquid metal in an aqueous environment and their cytotoxicity to human cells. It is observed that only the Ga ion is dominantly released from EGaIn when no external agitation is applied, whereas the concentration of the In ion drastically increases with sonication. The cytotoxicity study reveals that all human cells tested are viable in the growth media with naturally released EGaIn ions, but the cytotoxicity becomes significant with sonication-induced EGaIn releasates. On the basis of the comparative study with other representative toxic elements, that is, Hg and Cd, it could be concluded that EGaIn is reasonably safe to use in an aqueous environment; however, it should be cautiously handled when any mechanical agitation is applied.
- Published
- 2018
- Full Text
- View/download PDF
4. Flexible and Wearable Fiber Microsupercapacitors Based on Carbon Nanotube–Agarose Gel Composite Electrodes
- Author
-
Hyung-Jun Koo, Jinyun Liu, Paul V. Braun, and Sung-Kon Kim
- Subjects
Supercapacitor ,Materials science ,Composite number ,02 engineering and technology ,Carbon nanotube ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Capacitance ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,chemistry ,law ,Electrode ,Agarose ,General Materials Science ,Extrusion ,Composite material ,0210 nano-technology - Abstract
Fiber electrodes provide interesting opportunities for energy storage by providing both mechanical flexibility and the opportunity to impart multifunctionality to fabrics. We show here carbon nanotube (CNT)-embedded agarose gel composite fiber electrodes, with a diameter of ∼120 μm, consisting of 60 wt % CNTs that can serve as the basis for flexible and wearable fiber microsupercapacitors (mSCs). Via an extrusion process, CNT bundles are induced to align in an agarose filament matrix. Due to the shear alignment of the CNT bundles, the dehydrated filaments have an electrical conductivity as high as 8.3 S cm–1. The composite fiber electrodes are mechanically stable, enabling formation of twisted two-ply fiber mSCs integrated with a solid electrolyte. The fiber mSC shows a high capacitance (∼1.2 F cm–3), good rate retention (∼90%) at discharge current densities ranging from 5.1 to 38 mA cm–3, long cycle life under repeated charging/discharging (10% fade after 10 000 cycles) and good performance after at leas...
- Published
- 2017
- Full Text
- View/download PDF
5. Polymer Brushes Patterned with Micrometer-Scale Chemical Gradients Using Laminar Co-Flow
- Author
-
Chunjie Zhang, Paul V. Braun, Kristopher V. Waynant, and Hyung-Jun Koo
- Subjects
chemistry.chemical_classification ,Materials science ,Laminar flow ,Polymer ,Methacrylate ,Polymer brush ,Volumetric flow rate ,Reaction rate ,Reaction rate constant ,chemistry ,Chemical engineering ,Polymer chemistry ,General Materials Science ,Electrochemical gradient - Abstract
We present a facile microfluidic method for forming narrow chemical gradients in polymer brushes. Co-flow of an alkylating agent solution and a neat solvent in a microfluidic channel forms a diffusion-driven concentration gradient, and thus a gradient in reaction rate at the interface of the two flows, leading to a quaternization gradient in the underlying poly(2-(dimethylamino)ethyl methacrylate) polymer brush. The spatial distribution of the quaternized polymer brush is characterized by confocal Raman microscopy. The quaternization gradient length in the polymer brush can be varied with the injection flow rate and the distance from the co-flow junction. A chemical gradient in the polymer brush as narrow as 5 μm was created by controlling these parameters. The chemical gradient by laminar co-flow is compared with numerical calculations that include only one adjustable parameter: the reaction rate constant of the polymer brush quaternization. The calculated chemical gradient agrees with the experimental data, which validates the numerical procedures established in this study. Flow of multiple laminar streams of reactive agent solutions enables single-run fabrication of brush gradients with more than one chemical property. As one example, four laminar streams-neat solvent/benzyl bromide solution/propargyl bromide solution/neat solvent-generate multistep gradients of aromatic and alkyne groups. Because the alkyne functional group is a click-reaction available site, the alkyne gradient could allow small gradient formation with a wide variety of chemical properties in a polymer brush.
- Published
- 2014
- Full Text
- View/download PDF
6. General Method for Forming Micrometer-Scale Lateral Chemical Gradients in Polymer Brushes
- Author
-
Chunjie Zhang, Paul V. Braun, Hyung-Jun Koo, Kristopher V. Waynant, and Richard T. Haasch
- Subjects
chemistry.chemical_classification ,Microchannel ,General Chemical Engineering ,Diffusion ,Microfluidics ,Analytical chemistry ,General Chemistry ,Polymer ,Alkylation ,chemistry.chemical_compound ,Benzyl bromide ,chemistry ,Chemical engineering ,Materials Chemistry ,Fluorescence microscope ,Methyl iodide - Abstract
We report a general diffusion based method to form micrometer-scale lateral chemical gradients in polymer brushes via selective alkylation. A quaternized brush gradient is derived from a concentration gradient of alkylating agent formed by diffusion in permeable media around a microchannel carrying the alkylating agent. Polymer brushes containing both charge and aromatic gradients are formed using the alkylating agents, methyl iodide and benzyl bromide, respectively. The gradients are quantitatively characterized by confocal Raman spectroscopy and qualitatively by fluorescence microscopy. The length and gradient strength can be controlled by varying the diffusion time, concentrations, and solvents of the alkylating agent solutions. This microfluidic brush gradient generation method enables formation of 2-D chemical potential gradients with a diversity of shapes.
- Published
- 2014
- Full Text
- View/download PDF
7. On the Origin of the × Superstructure and the Anomalous Magnetic and Transport Properties of the Layered Compound Sr6V9S22O2
- Author
-
Raymond Brec, Michel Evain, Olivier Gourdon, M.-H. Whangbo, Chauvet O, Hyung-Jun Koo, Benoit Corraze, and S. Jobic
- Subjects
Inorganic Chemistry ,Octahedron ,Condensed matter physics ,Chemistry ,Mineralogy ,Fermi surface ,Electron ,Physical and Theoretical Chemistry ,Electronic band structure ,Superstructure (condensed matter) ,Charge density wave ,Instability - Abstract
We examined why the 1T-VS2 layer of the layered compound Sr6V9S22O2 has the × superstructure in terms of electronic band structure calculations and metal−metal bonding across the shared edges of adjacent VS6 octahedra. On the basis of this analysis we explored how the anomalous magnetic and transport properties of Sr6V9S22O2 can be explained. Our work shows that the × superstructure is not caused by a charge density wave instability associated with Fermi surface nesting but by the metal−metal bonding through the shared edges of adjacent VS6 octahedra. The weak and strong electron localizations observed for Sr6V9S22O2 were discussed in terms of three-center two-electron and two-center two-electron V−V bonds in the 1T-VS2 layers.
- Published
- 2001
- Full Text
- View/download PDF
8. Infrared and Optical Properties of β‘-(ET)2SF5CF2SO3: Evidence for a 45 K Spin-Peierls Transition
- Author
-
G. L. Gard, Christopher C. Homes, Urs Geiser, Javid Mohtasham, Janice L. Musfeldt, Zhengtao Zhu, Hau H. Wang, Hyung-Jun Koo, J. M. Pigos, Rolf W. Winter, John A. Schlueter, Brian H. Ward, B. R. Jones, and M.-H. Whangbo
- Subjects
Condensed matter physics ,Infrared ,Chemistry ,Peierls transition ,General Chemical Engineering ,Molecular vibration ,Materials Chemistry ,Infrared spectroscopy ,General Chemistry ,Electronic structure ,Electronic band structure ,Optical conductivity ,Spin-½ - Abstract
We measured the polarized infrared reflectance of β‘-(ET)2SF5CF2SO3 as a function of temperature and analyzed the spin-exchange interactions of this salt by calculating the spin−orbital interaction energies between adjacent spin sites. The observed changes in vibrational properties below the 45 K transition support a weak lattice distortion in combination with a spin gap in this material. The spin-exchange interaction is predicted to occur primarily along the (−a +b) diagonal direction, in good agreement with the spectral data. In addition, notable frequency shifts of vibrational modes point to a second transition between 100 and 200 K. The low-lying electronic excitation in the stack direction (assigned as a charge-transfer feature based upon our electronic band structure calculations) shows distinct changes with temperature that are consistent with trends in the vibrational spectrum. The pattern of a high-temperature transition preceding the spin-Peierls transition is discussed in relation to other low-...
- Published
- 2001
- Full Text
- View/download PDF
9. Optical Spectra and Electronic Band Structure Calculations of β‘ ‘-(ET)2SF5RSO3 (R = CH2CF2, CHFCF2, and CHF): Changing Electronic Properties by Chemical Tuning of the Counterion
- Author
-
M.-H. Whangbo, Emilio Morales, I. Olejniczak, Zhengtao Zhu, Rolf W. Winter, Janice L. Musfeldt, Hyung-Jun Koo, B. R. Jones, Javid Mohtasham, John A. Schlueter, Brian H. Ward, A. D. Garlach, J. Dong, J. M. Pigos, Aravinda M. Kini, and G. L. Gard
- Subjects
Electronic correlation ,Chemistry ,General Chemical Engineering ,Infrared spectroscopy ,General Chemistry ,Electronic structure ,Molecular physics ,Optical conductivity ,Molecular solid ,Tight binding ,Computational chemistry ,Molecular vibration ,Materials Chemistry ,Condensed Matter::Strongly Correlated Electrons ,Electronic band structure - Abstract
We report the polarized infrared reflectance spectra, optical conductivity, and electronic band structure of metallic β‘ ‘-(ET)2SF5CHFSO3 and compare our results with those of the β‘ ‘-(ET)2SF5CH2CF2SO3 superconductor and the β‘ ‘-(ET)2SF5CHFCF2SO3 metal/insulator material. We discuss the electronic structure of these organic molecular solids in terms of band structure, many-body effects, and disorder. On the basis of spectral similarities between the superconductor and metallic salts and structural differences in the anion pocket of all three, we conclude that the unusual electronic excitations observed in the β‘ ‘-(ET)2SF5CHFCF2SO3 metal/insulator material are not caused by electron correlation but are due to disorder-related localization.
- Published
- 2000
- Full Text
- View/download PDF
10. Comparison of the Crystal and Electronic Structures of Three 2:1 Salts of the Organic Donor Molecule BEDT-TTF with Pentafluorothiomethylsulfonate Anions SF5CH2SO3-, SF5CHFSO3-, and SF5CF2SO3
- Author
-
Hyung-Jun Koo, Jack M. Williams, Rolf W. Winter, John A. Schlueter, Emilio Morales, Brian H. Ward, Seddon Y. Thomas, P. G. Nixon, Urs Geiser, Hsien-Hau Wang, M.-H. Whangbo, Gary L. Gard, and James P. Parakka
- Subjects
Chemistry ,General Chemical Engineering ,Inorganic chemistry ,General Chemistry ,Electronic structure ,Crystal structure ,Magnetic susceptibility ,Crystal ,chemistry.chemical_compound ,Crystallography ,X-ray crystallography ,Materials Chemistry ,Organic superconductor ,Electronic band structure ,Tetrathiafulvalene - Abstract
Salts of the donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), with pentafluorothiomethylsulfonate (SF{sub 5}CX{sub 2}SO{sub 3}{sup -}, X = H or F) anions have been prepared. Three phases, {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}SO{sub 3}, {beta}'-(ET){sub 2}SF{sub 5}CF{sub 2}SO{sub 3}, and {beta}'-(ET){sub 2}SF{sub 5}CHFSO{sub 3} were obtained by electrocrystallization with the corresponding LiSF{sub 5}CX{sub 2}SO{sub 3} electrolytes. The structures of these salts were determined by single-crystal X-ray diffraction, and their physical properties were examined by electrical resistivity measurements as well as by ESR and Raman spectroscopy. The {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}SO{sub 3}, {beta}'-(ET){sub 2}SF{sub 5}CHFSO{sub 3} and {beta}'-(ET){sub 2}SF{sub 5}CF{sub 2}SO{sub 3} salts are considerably different in their crystal structures, physical properties, and electronic structures despite the similarity in the structures of the SF{sub 5}CX{sub 2}SO{sub 3}{sup -} (X = H, F) anions. The {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}SO{sub 3} salt has two kinds of ET donor molecules with considerably different charge densities. The electronic structure of {beta}'-(ET){sub 2}SF{sub 5}CHFSO{sub 3} has both one-dimensional (1D) and two-dimensional (2D) Fermi surfaces which are similar to those found in the organic superconductor {beta}'-(ET){sub 2}SF{sub 5}CH{sub 2}CF{sub 2}SO{sub 3}. The ESR data for the {beta}'-(ET){sub 2}SF{sub 5}CF{sub 2}SO{sub 3} salt indicate that it opens a spin gapmore » below 45 K. The differences in the physical properties of the three salts were analyzed by calculating the HOMO-HOMO interaction energies between nearest-neighbor ET molecules in their donor molecule layers.« less
- Published
- 2000
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.