Hyonseok Hwang
Kangwon National University
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Hyonseok Hwang.
Journal of Materials Chemistry | 2010
Sangwon Ko; Hyunbong Choi; Moon-Sung Kang; Hyonseok Hwang; Heesun Ji; Jinho Kim; Jaejung Ko; Youngjin Kang
Three new organic dyes that contain the dithienosilole (DTS) moiety as spacer have been synthesized and their photophysical/electrochemical properties, theoretical calculation and dye-sensitized solar cell (DSSC) performance have been investigated. The overall conversion efficiencies for DSSCs based on these dyes range from 6.73 to 7.50%, comparable to a (3–5′-[N,N-bis(9,9-dimethylfluorene-2-yl)phenyl]2,2′-bithiophene-5-yl}-2-cyanoacrylic acid (JK-2)-sensitized device (7.63%), fabricated and measured under the same experimental conditions. The DSSC constructed from one of the three compounds shows a higher open-circuit voltage (VOC) compared to those of the other two dye sensitized solar cells due to an increased electron lifetime (τe) in the conduction band of TiO2.
Journal of Physical Chemistry A | 2009
Hyonseok Hwang; George C. Schatz; Mark A. Ratner
Coarse-grained (CG) molecular dynamics (MD) simulations are performed to study the insertion of cyclic peptide nanotubes into cell membranes and to examine whether cyclic peptide nanotubes can function as an ion channel and thereby as an antibacterial agent. To do so, the two coarse-grained (CG) models for lipid molecules and for proteins developed by Marrink et al. (J. Phys. Chem. B 2004, 108, 750) and by Shih et al. (J. Phys. Chem. B 2006, 110, 3674), respectively, were extended and modified. These CG models were verified by performing CG MD and all-atom (AA) MD simulations for a cyclic peptide nanotube, 8 x cyclo[(-d-Ala-l-Glu-d-Ala-l-Gln-)2], in water and by comparing the results from the two simulations. Comparison between static and dynamic (water transport) properties obtained from both simulations shows good agreement. To study nanotube insertion, a CG cyclic peptide nanotube, 8 x cyclo[(-Trp-d-Leu-)4], was prepared above the surface of a CG DPPC lipid bilayer, restrained with constraints, and equilibrated, and then a series of CG MD simulations were carried out by lifting the constraints imposed on the nanotube. The CG MD simulations show that the cyclic peptide nanotube spontaneously inserts into and reorients inside the lipid bilayer. After insertion, the long axis of the cyclic peptide nanotube is aligned approximately perpendicular to the bilayer plane indicating that the nanotube can function as an ion channel and as an antibacterial agent. Tilt structures of the cyclic peptide nanotubes inside the lipid bilayer are found to be in agreement with experiment and earlier AA simulations. Lipid flip-flop, a migration of lipid molecules from one leaflet to the other leaflet of the lipid bilayer, is also observed from the CG MD simulations. Finally, the CG MD simulations reveal that a lipid headgroup can be inserted into the cyclic peptide nanotube. This process is confirmed by an AA MD simulation.
Applied Spectroscopy | 2011
Soo Ryeon Ryu; Isao Noda; Chang-Hee Lee; Phil Ho Lee; Hyonseok Hwang; Young Mee Jung
In this study, we demonstrate the potentials and pitfalls of using various waterfall plots, such as conventional waterfall plots, two-dimensional (2D) gradient maps, moving window two-dimensional analysis (MW2D), perturbation-correlation moving window two-dimensional analysis (PCMW2D), and moving window principal component analysis two-dimensional correlation analysis (MWPCA2D), in the detection of the existence of band position shifts. Waterfall plots of the simulated spectral datasets are compared with conventional 2D correlation spectra. Different waterfall plots give different features in differentiating the behaviors of frequency shift versus two overlapped bands. Two-dimensional correlation spectra clearly show the very characteristic cluster pattern for both band position shifts and two overlapped bands. The vivid pattern differences are readily detectable in various waterfalls plots. Various types of waterfall plots of temperature-dependent infrared (IR) spectra of ethylene glycol, which does not have the actual band shift but only two overlapped bands, and of Fourier transform infrared (FT-IR) spectra of 2 wt% acetone in a mixed solvent of CHCl3/CCl4 demonstrate that waterfall plots are not able to unambiguously detect the difference between real band shift and two overlapped bands. Thus, the presence or lack of the asynchronous 2D butterfly pattern seems like the most effective diagnostic tool for band shift detection.
Journal of Organic Chemistry | 2011
Phil Ho Lee; Juntae Mo; Dongjin Kang; Dahan Eom; Chansoo Park; Chang-Hee Lee; Young Mee Jung; Hyonseok Hwang
Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield.
Journal of Chemical Physics | 2004
Hyonseok Hwang; Peter J. Rossky
In order to develop a more complete understanding of the limitations of mixed quantum-classical simulation methods, the origins of electronic dephasing are analyzed in a simple model of the condensed phase, namely, the spin-boson model with an ohmic spectral density. We focus on the decay of the thermally averaged nuclear overlap/phase function (NOPF). Considering the strong coupling/high temperature limit, a relationship is obtained at short time between the rate of electronic coherence loss and the electronic dephasing rate characteristic of a classical bath. Using this relationship, we clarify the origin of the decay of the NOPF. In the same limit, we also reproduce an earlier relationship between the electronic decoherence time and a solvation relaxation time. Finally, we point out that, for the spin-boson model, the exact quantum mechanical description of electronic dephasing is reproduced by mixed quantum/classical methods if a Gaussian distribution of quantum fluctuations around each classical phase space point is introduced. That spatial distribution of quantum fluctuations is functionally the same as that appearing in the Feynman-Kleinert variational local harmonic approximation, and also that implemented in existing classical trajectory-based estimates of coherence dissipation times.
Chemical Physics | 2001
Daren M. Lockwood; Hyonseok Hwang; Peter J. Rossky
Abstract The impact of electronic decoherence on electronic dynamics, and electron transfer (ET) reactions in particular, in condensed phase environments is discussed. Analytical expressions are considered for a common model system in which ET occurs between relatively displaced harmonic surfaces. We identify a relationship in the semi-classical Marcus limit between electronic decoherence and the Wigner distribution of nuclear configurations. Generalization to more complex surfaces is discussed. Additionally, we discuss electronic decoherence for ET via so-called bridge sites in materials, for both direct (superexchange) mechanisms and sequential mechanisms of ET. Quantitative simulation studies of factors affecting characteristic decoherence times for ET in solution are also presented and discussed.
RSC Advances | 2017
Dong Kyun You; Seon Hee Lee; Ji Hye Lee; Sang Woo Kwak; Hyonseok Hwang; Junseong Lee; Yongseog Chung; Myung Hwan Park; Kang Mun Lee
Phenanthroimidazole-based triarylborane compounds with an N-phenyl (1Ph, 2Ph) or N-biphenyl (1BP, 2BP) bridge were synthesized and characterized. All four compounds exhibit a dual emission pattern in their photoluminescence (PL) spectra, which can be separated into high- (λem = ca. 380 nm in THF) and low-energy (λem = ca. 480 nm) emissions. While the high-energy emission remains largely unchanged in different organic solvents, the low-energy emission exhibits clear signs of positive solvatochromism. The results of the photophysical analysis and theoretical calculations suggest that the high-energy emission corresponds to a π–π* transition band arising from the phenanthroimidazole, whereas the low-energy emission originates from an intramolecular charge transfer (ICT) transition between phenanthroimidazole and the triarylborane moiety. UV-vis titration experiments examining the association of 1Ph, 2Ph, 1BP, and 2BP with fluoride demonstrate that these compounds associate with a 1:1 binding stoichiometry in THF and binding constants (Ka) that are estimated to be around 1.0–3.0 × 104 M−1. These compounds show a ratiometrically increased fluorescence response in PL titration experiments upon binding of fluoride to the borane moiety, thereby giving rise to a ‘turn-on’ chemosensor for detection of fluoride anions. The ‘turn-on’ properties can be judged as a result of the reinforcement of π–π* transition on phenanthroimidazole and the restriction of ICT transition to triarylborane.
Inorganic Chemistry | 2017
Sang Woo Kwak; Byung Hoon Choi; Ji Hye Lee; Hyonseok Hwang; Junseong Lee; Hyoshik Kwon; Yongseog Chung; Kang Mun Lee; Myung Hwan Park
Novel salen-Al/triarylborane dyad complexes were prepared and characterized with their corresponding mononuclear compounds. The UV-vis and photoluminescence experiments for dyads exhibited photoinduced energy transfer from borane to the salen-Al moiety in an intramolecular manner. Theoretical calculation and fluoride titration results further supported these intramolecular energy-transfer features.
Journal of Chemical Physics | 2007
Hyonseok Hwang; George C. Schatz; Mark A. Ratner
An algorithm in which kinetic lattice grand canonical Monte Carlo simulations are combined with mean field theory (KLGCMC/MF) is presented to calculate ion currents in a model ion channel system. In this simulation, the relevant region of the system is treated by KLGCMC simulations, while the rest of the system is described by modified Poisson-Boltzmann mean field theory. Calculation of reaction field due to induced charges on the channel/water and membrane/water boundaries is carried out using a basis-set expansion method [Im and Roux, J. Chem. Phys. 115, 4850 (2001)]. Calculation of ion currents, electrostatic potentials, and ion concentrations, as obtained from the KLGCMC/MF simulations, shows good agreement with Poisson-Nernst-Planck (PNP) theory predictions when the channel and membrane have the same dielectric constant as water. If the channel and membrane have a lower dielectric constant than water, however, there is a considerable difference between the KLGCMC/MF and PNP predictions. This difference is attributed to the reaction field, which is missing in PNP theory. It is demonstrated that the reaction field as well as fixed charges in the channel play key roles in selective ion transport. Limitations and further development of the current KLGCMC/MF approach are also discussed.
ChemPhysChem | 2015
Yeonju Park; Yongil Seo; Boknam Chae; Dongjin Pyo; Hoeil Chung; Hyonseok Hwang; Young Mee Jung
In this study, the thermal denaturation mechanism and secondary structures of two types of human insulin nanoparticles produced by a process of solution-enhanced dispersion by supercritical fluids using dimethyl sulfoxide (DMSO) and ethanol (EtOH) solutions of insulin are investigated using spectroscopic approaches and molecular dynamics calculations. First, the temperature-dependent IR spectra of spherical and rod-shaped insulin nanoparticles prepared from DMSO and EtOH solution, respectively, are analyzed using principal component analysis (PCA) and 2D correlation spectroscopy to obtain a deeper understanding of the molecular structures and thermal behavior of the two insulin particle shapes. All-atom molecular dynamics (AAMD) calculations are performed to investigate the influence of the solvent molecules on the production of the insulin nanoparticles and to elucidate the geometric differences between the two types of nanoparticles. The results of the PCA, the 2D correlation spectroscopic analysis, and the AAMD calculations clearly reveal that the thermal denaturation mechanisms and the degrees of hydrogen bonding in the spherical and rod-shaped insulin nanoparticles are different. The polarity of the solvent might not alter the structure or function of the insulin produced, but the solvent polarity does influence the synthesis of different shapes of insulin nanoparticles.