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- 저자 : Hwang Sungu (검색결과 25 건)
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Characteristics according to the Amount of HAp Added in Resin for Tooth Repair
Hwang, Sungu,Lim, Jinhyuck,Ryu, Suchak The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.6
A study was conducted to investigate the possibility of a composite material containing a composite resin as a matrix and hydroxyapatite (HAp) powder as a substitute material for tooth repair. As the content of HAp increased, hardness value (111.9 HV at 9%) increased and flexural strength (73.3 MPa at 9%) decreased. Observation of the microstructure after immersion in a simulated body fluid (SBF) solution confirmed a dense structure due to mutual coagulation and curing. It was thought that fine HAp recrystals were formed with the lapse of time, and they were entangled to form a condensation structure and had a dense structure. In addition, since the activity was shown by the ion migration on the surface of a tooth, it was highly likely that a biocompatible bond occurred during tooth contact. Therefore, it could be used as a substitute material for tooth repair.
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Lee, Taegon,Hwang, Sungu,Lim, Manho American Chemical Society 2015 The Journal of physical chemistry B Vol.119 No.5
<P>Like nitric oxide (NO), nitroxyl (HNO), a reduced form of NO, plays many biologically important roles including neurological function and vascular regulation. Although HNO is unstable in aqueous solution, it is exceptionally stable on binding to ferrous myoglobin (Mb) to form MbHNO. Various experimental and theoretical investigations has been carried out to unveil the structure of the active site and binding characteristics of MbHNO that can explain its functioning mechanism and the origin of its unusual stability. However, the binding dynamics of HNO to Mb, as well as the photochemical and photophysical processes associated with binding, have not been fully established. Herein, femtosecond vibrational spectroscopy was used to probe the photoexcitation dynamics of excited MbDNO in D<SUB>2</SUB>O solution at 294 K with a 575 nm pulse. Time-resolved spectra were described by three vibrational bands near 1380 cm<SUP>–1</SUP>, in the expected N–O stretching (ν<SUB>N–O</SUB>) mode of MbDNO, and all three bands showed instantaneous bleach that decays on a picosecond time scale. The three bands were assigned based on isotope shifts upon <SUP>15</SUP>N substitution and <I>ab initio</I> calculation of the vibrational frequency on a DNO-bound model heme. These three bands likely arise from Fermi interactions between the strong ν<SUB>N–O</SUB> mode and the weak overtone and combination modes of the N atom-related modes. The immediate appearance of the bleach in these bands and the picosecond decay of the bleach indicate that most of the photoexcited MbDNO undergoes picosecond geminate rebinding (GR) of DNO to Mb subsequent to its immediate deligation. Ultrafast and efficient GR of DNO likely arises from the bonding structure of the ligand and high reactivity between DNO and Mb.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2015/jpcbfk.2015.119.issue-5/jp509644m/production/images/medium/jp-2014-09644m_0006.gif'></P>
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Jang, Yun Hee,Hwang, Sungu,Cho, Keunchang,Lim, Manho,Joo, Taiha,Choi, Suhee,Kim, Jongwon,Joo, Sang‐,Woo John Wiley Sons, Ltd. 2011 Surface and interface analysis Vol.43 No.3
<P><B>Abstract</B></P><P>The potential‐induced adsorption change of 2‐amino‐4,5‐imidazoledicarbonitrile (AIDCN) on Ag electrode surfaces has been examined by surface‐enhanced Raman scattering (SERS) in an applied potential range between −1.0 and 0.2 V. Upon adsorption, AIDCN has a substantial interaction with the Ag metal surfaces via its two nitrile groups. The CN stretching peaks at ∼2200 cm<SUP>−1</SUP> appeared to be more intensified and redshifted at a negative potential. The deconvolution peak analysis of the CN bands at various voltages suggests that there should be a change in binding modes of AIDCN on Ag surfaces. This potential‐dependent orientation change appeared to be reversible. The density functional theory (DFT) calculation of AIDCN on Ag cluster atoms is used to explain its potential‐dependent adsorption. Copyright © 2010 John Wiley & Sons, Ltd.</P>
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DFT Calculation of Site-specific Acid Dissociation Constants of Purine Nucleobases
Jang, Yun Hee,Hwang, Sungu,Chung, Doo Soo The Chemical Society of Japan 2007 Chemistry letters Vol.36 No.12
<P>The intrinsic proton affinities of individual basic sites, so-called micro acid dissociation constants, of purine nucleobases in aqueous solution are calculated using an ab initio quantum-mechanical method in combination with the Poisson–Boltzmann continuum solvation model. Calculated micro acid dissociation constants as well as macro acid dissociation constants (p<I>K</I><SUB>a</SUB>) agree with recent experimental measurements mostly within a pH unit.</P>
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Density Functional Theoretical Studies on the Redox-dependent Hydrogen Bonding
Cho, Young Seuk,Hwang, Sungu The Chemical Society of Japan 2006 Chemistry letters Vol.35 No.12
<P>Redox-dependent hydrogen bonding has been a subject of extensive attraction since it provides a basis for external control for synthetic supramolecular system such as sensors, molecular electronics, and molecular machines. We performed density functional theoretical calculations on the nitrobenzene/arylurea interactions in order to understand the bonding and its dependence on the reduction/oxidation. We calculated the binding energy in the reduced and oxidized states and correlated the energy differences with the shift in half-wave potential, Δ<I>E</I><SUB>1/2</SUB>, for different <I>p</I>-substituted nitrobenzene/diphenylurea pairs.</P>
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Very Smooth Ultrananocrystalline Diamond Film Growth by a Novel Pretreatment Technique
Park, Jong Cheon,Hwang, Sungu,Kim, Tae Gyu,Kim, Jin Kon,Chun, Ho Hwan,Shin, Sung Chul,Cho, Hyun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.2
<P>Very smooth ultrananocrystalline diamond (UNCD) film growth on SiC substrate was achieved by a novel pretreatment technique consisted of SiC surface texturing and deaggregation of nanodiamond (ND) seed particles. Texturing of SiC surfaces in Ar and SF6/O-2 plasmas was found to be able to provide normalized roughness values of 0.5-7.0 compared to the untreated surface. SiC surface plasma-textured and seeded with H-2 heat-treated ND particles at 600 degrees C showed the highest nucleation density of similar to 44.2x10(11) cm(-2) and a highly uniform coverage of surface with very fine ND seeds. The UNCD film grown with this new pretreatment technique showed a very smooth surface morphology consisted of small and uniformly distributed grains.</P>
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Jeong, Ji-Eun,Kim, Boram,Woo, Shinjae,Hwang, Sungu,Bazan, Guillermo C.,Woo, Han Young Royal Society of Chemistry 2015 Chemical Science Vol.6 No.3
<▼1><P>A new bioassay strategy based on the molecular beacon aptamer/conjugated polyelectrolyte demonstrates a fine-tuning of the detection range and limit of detection for weakly-binding targets.</P></▼1><▼2><P>A strategy to extend the detection range of weakly-binding targets is reported that takes advantage of fluorescence resonance energy transfer (FRET)-based bioassays based on molecular beacon aptamers (MBAs) and cationic conjugated polyelectrolytes (CPEs). In comparison to other aptamer-target pairs, the aptamer-based adenosine triphosphate (ATP) detection assays are limited by the relatively weak binding between the two partners. In response, a series of MBAs were designed that have different stem stabilities while keeping the constant ATP-specific aptamer sequence in the loop part. The MBAs are labeled with a fluorophore and a quencher at both termini. In the absence of ATP, the hairpin MBAs can be opened by CPEs <I>via</I> a combination of electrostatic and hydrophobic interactions, showing a FRET-sensitized fluorophore signal. In the presence of ATP, the aptamer forms a G-quadruplex and the FRET signal decreases due to tighter contact between the fluorophore and quencher in the ATP/MBA/CPE triplex structure. The FRET-sensitized signal is inversely proportional to [ATP]. The extension of the detection range is determined by the competition between opening of the ATP/MBA G-quadruplex by CPEs and the composite influence by ATP/aptamer binding and the stem interactions. With increasing stem stability, the weak binding of ATP and its aptamer is successfully compensated to show the resistance to disruption by CPEs, resulting in a substantially broadened detection range (from millimolar up to nanomolar concentrations) and a remarkably improved limit of detection. From a general perspective, this strategy has the potential to be extended to other chemical- and biological-assays with low target binding affinity.</P></▼2>
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Kang, Mijeong,Nag, Okhil Kumar,Hwang, Sungu,Kim, Inhong,Yang, Haesik,Kyhm, Kwangseuk,Woo, Han Young Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.47
<P>The solvent effects were studied in fluorescence resonance energy transfer (FRET) from a cationic polyfluorene copolymer (<B>FHQ</B>, <B>FPQ</B>) to a fluorescein (Fl)-labelled oligonucleotide (ssDNA-Fl). Upon addition of dimethyl sulfoxide (DMSO), the optical properties of polymers and the probe dye were substantially modified and the FRET-induced PL signal was enhanced 3.8–37 times, relative to that in phosphate buffer solution (PBS). The hydrophobic interaction between polymers and ssDNA-Fl is expected to decrease in the presence of DMSO, which induces the weaker polymer/ssDNA-Fl complexation with longer intermolecular donor–acceptor separation and perturbs the competition between the FRET and PL quenching processes such as photo-induced charge transfer. The gradual decrease in Fl PL quenching with increasing the DMSO content was investigated by measuring the Stern–Volmer quenching constants (3.3–4.2 × 10<SUP>6</SUP> M<SUP>−1</SUP> in PBS, 0.56–1.1 × 10<SUP>6</SUP> M<SUP>−1</SUP> in 80 vol% DMSO) and PL lifetime of the excited Fl* in polymer/ssDNA-Fl (600 ps in PBS and 2120 ps in 80 vol% DMSO for <B>FHQ</B>/ssDNA-Fl) in PBS/DMSO mixtures. The substantially reduced PL quenching would amplify the resulting FRET Fl signal. The signal amplification in real DNA detection was also demonstrated with fluorescein-labelled PNA (probe PNA) in the presence of a complementary target DNA and noncomplementary DNA in aqueous DMSO solutions. This approach suggests a simple way of modifying the fine-structure of polymer/ssDNA-Fl and improving the detection sensitivity in conjugated polymer-based FRET bioassays.</P> <P>Graphic Abstract</P><P>The FRET-induced fluorescence was substantially enhanced (3.8–37 times) upon addition of dimethyl sulfoxide in conjugated polymer-based FRET DNA detection in aq. buffer solution. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp01025a'> </P>
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