• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.446-451
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• 2018

In this study, different formulations of magnesium oxide and various modifiers (phosphoric acid, ferrous sulfate, pure acrylic emulsion, silicone acrylic emulsion, glass fiber, and polypropylene fiber) were used to prepare magnesium oxychloride cement composites. The compressive strength of the magnesium oxychloride cement was tested, and the softening coefficients of the composites after soaking in water were also calculated. The results showed that a magnesium oxychloride cement sample could not be coagulated when the MgO activity was 24.3%, but the coagulation effect of the magnesium oxide cement sample was excellent when the MgO activity was 69.5%. While pure acrylic emulsion, silicon-acrylic emulsion, and glass fiber showed insignificant modification effects on the magnesium oxychloride cement, ferrous sulfate heptahydrate, phosphoric acid, and polypropylene fiber could effectively improve its water resistance and compressive strength. When the phosphoric acid, ferrous sulfate heptahydrate, and polypropylene fiber contents were 0.47%, 0.73%, and 0.25%, respectively, the softening coefficient of a composite soaked in water reached 0.93 after 7 days, and the compressive strength reached 64.3 MPa.

• Journal of the Korean Chemical Society
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• v.8 no.2
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• pp.68-74
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• 1964

Water has the melting point, the boiling point, the heat of fusion, and the heat of vaporization all much higher than would be normally expected from the hydrogen compounds of the other members of the oxygen family. Another unique characteristic of ice-Ⅰ is its volume decrease which takes place in its melting. A number of significant efforts have been made in the past to explain these properties quantitatively. The authors, reasoning from the unusually great free surface energy of water and the characteristic volume change on melting, propose the structural model of liquid water as follows. On melting, fluidized vacancies of a molecular size are introduced. Thereupon, for the unusually great surface energy density, molecules surrounding the vacancies become to have close packed arrangement. But molecules not in direct contact with vacancies should still possess the original structure i. e., ice-Ⅰ. When a molecule adjacent to a vacancy jumps into the vacancy, the molecule attains the gaslike degree of freedom. Using the above model, the authors had developed the liquid partition function of water by applying the theory of significant structures in liquids. Molar volume, vapor pressure, entropy of fusion and entropy of vaporization were calculated over a wide temperature range. The results show good agreement with experimental observations.

• Journal of the Korean Chemical Society
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• v.55 no.5
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• pp.746-750
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• 2011

Fluorescence correlation spectroscopy (FCS) is an emerging fluorescence technique used to study the dynamics of proteins on a millisecond to microsecond time scale at the single-molecule level. Solution pH-modulated protein conformational changes can be manifested by binding rate, fluorescence lifetime, and binding specificity of a probe molecule. The fluorescence lifetime of Nile red (NR) bound to apomyoglobin (apoMb) was measured to be $6{\pm}0.3$ ns, much longer than that in water solution ($2.9{\pm}0.2$ ns). As the unfolding population of apoMb increased by lowering pH of solution, the fraction for the longer lifetime of NR decreased with an increasing fraction for the shorter lifetime of NR in water. Unlike 1-anilino-8-naphthalene sulfonic acid, which has many lifetimes due to nonspecific binding to the unfolded apoMb, NR bound to apoMb possesses only a single lifetime. These results suggest that NR binds specifically to native apoMb and thus can be utilized to probe the folding/unfolding dynamics of apoMb using FCS.

• Bulletin of the Korean Chemical Society
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• v.27 no.10
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• pp.1597-1600
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• 2006

The mononuclear iron complex 1, $Fe^{III}$(Hbida)Cl($H_2O$), was synthesized using a tripodal tetradentate ligand, N-(benzimidazol-2-ylmethyl)iminodiacetic acid (H3bida), which has two carboxylate groups, one benzimida- zoyl group, and one tertiary amine where it serves as a tetradentate chelating ligand for the octahedral Fe(III) ion. The four equatorial positions of the octahedral complex are occupied by two monodentate carboxylates, a benzimidazole nitrogen, and an oxygen of a water molecule. One of the axial positions is occupied by an apical nitrogen of the Hbida and the other by a chloride anion. The mononuclear octahedral complex 1 mimics the geometry of the key intermediate structure of the catalytic reaction cycle proposed for the FeSODs, which is a distorted octahedral geometry with three histidyl imidazoles, an aspartyl carboxylate, a superoxide anion, and a water molecule. The redox potential of complex 1, $E_{1/2}$ is -0.11V vs. Ag/AgCl (0.12 V vs. NHE), which is slightly lower than those reported for the most FeSODs. The magnetic susceptibility of complex 1 at room temperature is 5.83 $\mu$B which is close to that of the spin only value, 5.92 $\mu$B of high-spin d5 Fe(III).

• Bulletin of the Korean Chemical Society
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• v.25 no.2
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• pp.198-202
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• 2004

Hydrogen bond is an important factor in the structures of carbohydrates. Because of great strength, short range, and strong angular dependence, hydrogen bonding is an important factor stabilizing the structure of carbohydrate. In this study, conformational properties and the hydrogen bonds in GlcNAc( ${\beta}$1,3)Gal(${\beta}$)OMe in DMSO are investigated through NMR spectroscopy and molecular dynamics simulation. Lowest energy structure in the adiabatic energy map was utilized as an initial structure for the molecular dynamics simulations in DMSO. NOEs, temperature coefficients, SIMPLE NMR data, and molecular dynamics simulations proved that there is a strong intramolecular hydrogen bond between O7' and HO3' in GlcNAc( ${\beta}$1,3)Gal(${\beta}$)OMe in DMSO. In aqueous solution, water molecule makes intermolecular hydrogen bonds with the disaccharides and there was no intramolecular hydrogen bonds in water. Since DMSO molecule is too big to be inserted deep into GlcNAc(${\beta}$1,3)Gal(${\beta}$)OMe, DMSO can not make strong intermolecular hydrogen bonding with carbohydrate and increases the ability of O7' in GlcNAc(${\beta}$1,3)Gal(${\beta}$)OMe to participate in intramolecular hydrogen bonding. Molecular dynamics simulation in conjunction with NMR experiments proves to be efficient way to investigate the intramolecular hydrogen bonding existed in carbohydrate.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.828-832
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• 2014

The spectroscopic properties of quercetin (QCT) were studied in the AOT reverse micelle by fluorescence spectroscopy. Because the molecular structure of QCT is completely planar, excited state intramolecular proton transfer (ESIPT) occurs between the -OH at C(5) and carbonyl oxygen via intramolecular hydrogen bonding. This ESIPT happens at the $S_1$ state but not at the $S_2$ state. Because QCT is a good donor-acceptor-conjugated molecule at the excited state, this molecule can emit strong fluorescence but shows no $S_1{\rightarrow}S_o$ emission due to this ESIPT. Since the $S_2{\rightarrow}S_1$ internal conversion was very slow due to the small Franck-Condon factors, $S_2{\rightarrow}S_o$ fluorescence emission was observed. All of the experimental results indicated that the QCT resided at the bound water interface and that the position of solute did not change significantly in the micelle at various water concentrations.

• Journal of Pharmaceutical Investigation
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• v.12 no.2
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• pp.37-44
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• 1982

In order to enhance water solubility, ketoprofen was made as lysine salt, such as acetylsalicylic acid lysine salt, ibuprofen lysine salt and amino acid salt of phenylbutazone. The purpose of this study was to make a comparison between ketoprofen lysine salt in aspects of analgesic, anti-inflammatory, and antipyretic effect. The experimental results were summerized as followings. 1. Ketoprofen lysinate was composed of one molecule of ketoprofen and one molecule of lysine. The product was water soluble and melting point was $92^{\circ}C{\sim}94^{\circ}C$. 2. Ketoprofen lysinate showed about 2 times stronger analgesic effect than that of ketoprofen while no difference in antipyretic effect was observed. 3. $LD_{50}$ of ketoprofen lysinate was higher than that of ketoprofen, suggesting ketoprofen lysinate as safer drug. 4. Blood concentration of ketoprofen lysinate was $156{\mu}g/ml$ while the concentration of ketoprofen was $116{\mu}g/ml$ in 30 min., suggesting long acting as well as high blood concentration.

• Journal of the Korean Chemical Society
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• v.67 no.5
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• pp.333-338
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• 2023

In this study, the H₂O reaction with SiO clusters was investigated using ab initio Monte Carlo simulations and density functional theory calculations. Three chemistry models, PBE1/DGDZVP (Model 1), PBE1/DGDZVP (Si atom), and aug-cc-pVDZ (O and H atoms), (Model 2) and PBE1/aug-cc-pVDZ (Model 3), were used. The average bond lengths, as well as the relative and reaction energies, were calculated using Models 1, 2, and 3. The average bond lengths of Si-O and O-H are 1.67-1.75 Å and 0.96-0.97 Å, respectively, using Models 1, 2, and 3. The most stable structures were formed by the H transfer from an H₂O molecule except for Si₃O₃-H₂O-1 cluster. The Si₃O₃ cluster with H₂O exhibited the lowest reaction energy. In addition, the Bader charge distributions of the Si_nO_n and (SiO)_n-H₂O clusters with n = 1-7 were calculated using Model 1. We determined that the reaction sites between H₂O and the SiO clusters possessed the highest fraction of electrons.

• Journal of the Korean Chemical Society
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• v.68 no.2
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• pp.74-81
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• 2024

A sulfonic acid-water-silanol system in SO₃H-functionalized MCM-41 was investigated using solid-state nuclear magnetic resonance techniques. The proton exchange rate between a water molecule and a silanol group in the S-PE-MCM-41 was determined by analyzing the 1D proton spectra, the proton EXSY spectrum, and ²H spin-lattice relaxation data under various hydration levels. Two kinds of water-bounding sites were found in the S-PE-MCM-41: weakly and strongly bound sites. Over several hours, water molecules bound to the weakly bound sites at the low hydration level migrated to the strongly bound sites. At high temperature, the S-PE-MCM-41 easily lost water molecules weakly bound to the silanol, while the strongly bound water molecules survived. Water molecules that participated in the hydration of the phenethyl sulfonate were involved in the hydrogenbonded silanol mechanism of proton conductivity. This phenomenon contributes higher proton conductivity to the S-PE-MCM-41 by the cooperation of sulfonyl and silanol groups in the proton transfer process, even at higher temperature.

• Journal of the Korean Ceramic Society
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• v.56 no.3
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• pp.284-290
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• 2019

Ternary MoS₂/graphene (G)-TiO₂ photocatalysts were prepared by a simple hydrothermal method. The morphology, phase structure, band gap, and catalytic properties of the prepared samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-vis spectrophotometry, and Brunauer-Emmett-Teller surface area measurement. The H₂ production efficiency of the prepared catalysts was tested in methanol-water mixture under visible light. MoS₂/G-TiO₂ exhibited the highest activity for photocatalytic H₂ production. For 5 wt.% and 1 wt.% MoS₂ and graphene (5MT-1G), the production rate of H₂ was as high as 1989 µmol^-1h^-1. The catalyst 5MT-1G showed H₂ production activity that was ~ 11.3, 5.6, and 4.1 times higher than those of pure TiO₂, 1GT, and 5MT, respectively. The unique structure and morphology of the MoS₂/G-TiO₂ photocatalyst contributed to its improved hydrogen production efficiency under visible light.