• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.111-115
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• 2015

To produce patterns with high resolution in gravure printing, it is important to increase ink transfer ratio. The ink which has higher affinity with substrate can be transferred more from the roll to the substrate due to the good wettability between ink and substrate. However, it is difficult to evaluate the affinity between the substrate and the ink which is viscoelastic in nature. In this study, we suggest a practical method to evaluate the interfacial interaction between the ink and various substrates.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3218-3224
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• 2012

Uniform and well dispersed metal sulfide semiconductor nanoparticles incorporated into matrices of alginate biopolymer are prepared by using a facile in situ method. The reaction was accomplished by impregnation of alginate with divalent metal ions followed by reaction with thioacetamide. XRD analysis showed that the nanoparticles incorporated in the polymer matrix were of cubic structure with the average particle diameter of 1.8 to 4.8 nm. Field emission scanning electron microscopy and high resolution transmission electron microscopy images indicated that the particles were well dispersed and distributed uniformly in the matrices of alginate polymer. FT-IR spectra confirmed the presence of alginate in the nanocomposite. The crystalline nature and thermal stability of the alginate polymer was found to be influenced by the nature of the divalent metal ions used for the synthesis. The proposed method is considered to be a simple and greener approach for large scale synthesis of uniform sized nanoparticles.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1722-1726
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• 2013

A kinetic study on nucleophilic substitution reactions of phenyl Y-substituted-phenyl carbonates (5a-5j) with ethylamine in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$ is reported. The plots of $k_{obsd}$ vs. [amine] are linear for the reactions of substrates possessing a strong electron-withdrawing group (EWG) but curve upward for those of substrates bearing a weak EWG, indicating that the electronic nature of the substituent Y in the leaving group governs the reaction mechanism. The reactions have been concluded to proceed through a stepwise mechanism with one or two intermediates (a zwitterionic tetrahedral intermediate $T^{\pm}$ and its deprotonated form $T^-$) depending on the nature of the substituent Y. Analysis of Bronsted-type plots and dissection of $k_{obsd}$ into microscopic rate constants have revealed that the reactions of substrates possessing a strong EWG (e.g., 5a-5f) proceed through $T^{\pm}$ with its formation being the rate-determining step, while those of substrates bearing a weak EWG (e.g., 5g-5j) proceed through $T^{\pm}$ and $T^-$.

• Journal of Microbiology and Biotechnology
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• v.27 no.1
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• pp.77-83
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• 2017

Lignocellulosic biomass represents a potentially large resource to supply the world's fuel and chemical feedstocks. Enzymatic bioconversion of this substrate offers a reliable strategy for accessing this material under mild reaction conditions. Owing to the complex nature of lignocellulose, many different enzymatic activities are required to function in concert to perform efficient transformation. In nature, large multienzyme complexes are known to effectively hydrolyze lignocellulose into constituent monomeric sugars. We created artificial complexes of enzymes, called rosettazymes, in order to hydrolyze glucuronoxylan, a common lignocellulose component, into its cognate sugar ${\small{D}}$-xylose and then further convert the ${\small{D}}$-xylose into ${\small{D}}$-xylonic acid, a Department of Energy top-30 platform chemical. Four different types of enzymes (endoxylanase, ${\alpha}$-glucuronidase, ${\beta}$-xylosidase, and xylose dehydrogenase) were incorporated into the artificial complexes. We demonstrated that tethering our enzymes in a complex resulted in significantly more activity (up to 71%) than the same amount of enzymes free in solution. We also determined that varying the enzyme composition affected the level of complex-related activity enhancement as well as overall yield.

• Bulletin of the Korean Chemical Society
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• v.34 no.3
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• pp.768-772
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• 2013

Layered mixed metal hydroxy double salts (HDS) with the formulas $(Cu_{0.75}Ni_{0.25})_2(OH)_3NO_3$ ((Cu, Ni)-HDS) and $Cu_2(OH)_3NO_3$ ((Cu, Cu)-HDS) were prepared via slow hydrolysis reactions of CuO with $Ni(NO_3)_2$ and $Cu(NO_3)_2$, respectively. The crystal structures, morphologies, bonding natures, and magnetic properties of (Cu, Ni)-HDS and (Cu, Cu)-HDS were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transformation infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and a superconducting quantum interference device (SQUID). Even though (Cu, Ni)-HDS has a similar layered structure to that of (Cu, Cu)-HDS, the bonding nature of (Cu, Ni)-HDS is slightly different from that of (Cu, Cu)-HDS. Therefore, the magnetic properties of (Cu, Ni)-HDS are significantly different from those of (Cu, Cu)-HDS. The origin of the abnormal magnetic properties of (Cu, Ni)-HDS can be explained in terms of the bonding natures of the interlayer and intralayer structures.

• Journal of the Korean Chemical Society
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• v.58 no.1
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• pp.92-99
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• 2014

The pH sensitive hydrogels composed of N-isopropylacrylamide (NIPA) and acryloyl phenylalanine (APA) were prepared by redox polymerization using N,N'-methylenebisacrylamide (MBA) as a crosslinker. Anti-inflammatory and analgesic agent, Keterolac Tromethamine (KT), was loaded successfully into poly(NIPA-co-APA) copolymeric hydrogels by swelling equilibrium method. To understand the nature of drug in the polymeric matrix, the newly synthesized drug loaded poly(NIPA-co-APA) copolymeric hydrogels were characterized by using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. The scanning electron microscopy (SEM) technique result indicates the spherical smooth surface of the hydrogels. The drug (KT) releasing nature of the poly(NIPA-co-APA) hydrogels was studied in pH 1.2 and 7.4. Effects of drug loading, crosslinking agent, pH and the ionic strength of the external medium on swelling of hydrogels were also investigated.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1188-1194
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• 2013

Transparent $TiO_2$ thin films have been prepared by sol-gel spin coating method. The sols used for deposition of thin films were prepared with different ethanol content. The effect of ethanol (solvent) concentration and annealing temperature on the performance of $TiO_2$ thin film solar cells has been studied. The results indicate that the as deposited films are amorphous in nature. $TiO_2$ thin films annealed at temperatures above $350^{\circ}C$ exhibited crystalline nature with anatase phase. The results also indicated that the crystallinity of the films improved with increase of annealing temperature. The high resolution transmission electron microscope images showed lattice fringes corresponding to the anatase phase of $TiO_2$. The band gap of the deposited films has been found to decrease with increase in annealing temperature and increase with increase in ethanol concentration. The dependents of photovoltaic efficiency of the dye-sensitized $TiO_2$ thin film solar cells (DSSCs) with the amount of ethanol used to prepare thin films was determined from photocurrent-voltage curves.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.04a
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• pp.26-27
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• 1995

Most of synthetic polymeric membranes used in ultrafiltration, reverse osmosis and microfiltration processes are prepared by phase inversion(or phase separation) technique. In this technique, a homogeneous polymer solution is cast into thin film or hollow fiber shape and then immersed into a nonsolvent coagulant bath. The exchange of solvent and nonsolvent across the interface between casting solution and coagu!ant can make the casting solution phase-separate and form a membrane with a symmetric or asymmetric structure. Because of importance of this technique in membrane field, many investigations have been dedicated to elucidate the mechanism of membrane formation by phase inversion technique.[1-10] These investigation have suggested that the structure formation and permeation properties of phase inversion membrane depend on the variables such as the nature and content of casting solution and coagulant, temperature of casting solution and coagulant, and the diffusional exchange rate of solvent and nonsolvent etc. which can be related to the thermodynamic and kinetic properties of the casting system. The variables such as the nature and content of casting solution can also be the important factor affecting the structure formation and permeation property of the phase inversion membrane.

• Bulletin of the Korean Chemical Society
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• v.6 no.1
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• pp.23-29
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• 1985

The charge-transfer complexing properties of 1-methyl nicotinamide (MNA), an acceptor, and adenine, a donor, were investigated in water and SDS micellar solutions in relation to the intramolecular interaction in nicotinamide adenine dinucleotide ($NAD^+$). The spectral and thermodynamic parameters of MNA-indole and methyl viologen-adenine complex formations were determined, and the data were utilized to evaluate the charge-transfer abilities of MNA and adenine. The electron affinity of nicotinamide was estimated to be 0.28 eV from charge-transfer energy $of{\sim}300$ nm for MNA-indole. The large enhancement of MNA-indole complexation in SDS solutions by entropy effect was attributed to hydrophobic nature of indole. The complex between adenine and methyl viologen showed an absorption band peaked near 360 nm. The ionization potential of adenine was evaluated to be 8.28 eV from this. The much smaller enhancement of charge-transfer interaction involving adenine than that of indole in SDS solutions was attributed to weaker hydrophobic nature of the donor. The charge-transfer energy of 4.41 eV (280 nm) was estimated for nicotinamide-adenine complex. The spectral behaviors of $NAD^+$ were accounted to the presence of intramolecular interaction in $NAD^+$, which is only slightly enhanced in SDS solutions. The replacement of nicotinamide-adenine interaction in $NAD^+$ by intermolecular nicotinamide-indole interaction in enzyme bound $NAD^+$, and guiding role of adenine moiety in $NAD^+$ were discussed.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2593-2597
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for reactions of 2,4-dinitrophenyl X-substituted benzoates (X = 4-MeO, H and 4-$NO_2$) with a series of Z-substituted pyridines in 80 mol % $H_2O$/20 mol % DMSO at $25.0{\pm}0.1^{\circ}C$. The Br${\o}$nsted-type plots exhibit downward curvature (e.g., $\beta_2$ = 0.89 ~ 0.96 when $pK_a$ < 9.5 while $\beta_1$ = 0.38 ~ 0.46 when $pK_a$ > 9.5), indicating that the reaction proceeds through a stepwise mechanism with a change in rate-determining step (RDS). The ${pK_a}^o$, defined as the $pK_a$ at the center of Br${\o}$nsted curvature, has been analyzed to be 9.5 regardless of the electronic nature of the substituent X in the benzoyl moiety. Dissection of $k_N$ into the microscopic rate constants $k_1$ and $k_2/k_{-1}$ ratio has revealed that $k_1$ is governed by the electronic nature of the substituent X but the $k_2/k_{-1}$ ratio is not. Theoretical calculations also support the argument that the electronic nature of the substituent X in the benzoyl moiety does not influence the $k_2/k_{-1}$ ratio.