• Journal of Life Science
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• v.12 no.1
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• pp.26-31
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• 2002

Choline esters that are used with substrate of BChE-catalyzed hydrolyses were synthesized by two methods. First, 2-chloroethyl thiohexanoate, 2-chloroethyl thioheptanoate, and 2-chloroethyl thiooctanoate were synthesized by the treatment of hexanoyl chloride with ethylene sulfide. Hexanoyl thiocholine and octanoyl thiocholine were synthesized by using 2-chloroethyl thiohexanoate and 2-chloroethyl thiooctanoate with trimethyl amine. Second, after reaction of ethylene sulfide and dimethyl amine, followed by acylation with acid anhydride and then heptanonyl thiocholine, decanoyl thiocholine were synthesized by treatment of methyl iodide.

• Journal of the Korean Chemical Society
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• v.25 no.4
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• pp.207-213
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• 1981

Conformations of thioacetamide (TAA) and its protonated form were determined using the CNDO/2 method, and the intermolecular interaction energies between the protonated TAA and water were calculated. It was found that: (1) protonation occurs preferentially on the N rather than on the S atom, (2) the stabilization energy of intermolecular perturbation between the protonated TAA and water was also large for the N-protonated TAA. This causes preferential CS bond cleavage due to large antibonding nature of the CS bond in the LUMO, and leads to an orbital controlled reaction.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.749-757
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• 2019

Methyltrimethoxysilane (MTMS) and trimethylethoxysilane (TMES) as starting materials were dissolved in various types of solvents, and hydrolysis with water and polycondensation reaction were carried out using various types of catalysts to prepare non-fluorinated water-repellent coating solutions. The coating solutions were spin-coated on cold-rolled steel sheets, and thermally cured to prepare water-repellent coating films. The effect of types of catalysts and solvents on the water repellency of the resulting coating films was investigated during this process. When hydrochloric acid and nitric acid, which are strong acids, were used as catalysts, the solutions showed a white opaque state due to the aggregation of siloxane polymers. On the other hand, when acetic acid, phosphoric acid, and oxalic acid, which are weak acids, were used, they were in a stable and transparent state without precipitation. As a result, the contact angles of the coated films, prepared from hydrochloric acid and nitric acid, were $58^{\circ}$ and $92^{\circ}$, respectively, showing low water repellency. On the other hand, when acetic acid, phosphoric acid, and oxalic acid were used, the contact angles of the coated films were $101^{\circ}$, $103^{\circ}$ and $116^{\circ}$, respectively, showing high water repellency. In addition, when isopropanol and ethanol were used as solvents, phase separation occurred in the solutions due to the aggregation of siloxane polymers. On the other hand, when methanol, ethyl acetate, and methyl ethyl ketone were used as solvents, the solutions were transparent and showed a stable state without sedimentation.

• Journal of the Korean Chemical Society
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• v.34 no.6
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• pp.561-568
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• 1990

Voltammetric behavior of some light lanthanide ions (La$^{3+}$, Pr$^{3+}$, Nd$^{3+}$, Sm$^{3+}$, and Eu$^{3+}$) in various supporting electrolytes has been investigated by several electrochemical techniques. The peak potentials and the peak currents, their dependency on the concentration, temperature and pH effects, the reversibility of the electrode reactions are described. The reduction of La$^{3+}$, Pr$^{3+}$ and Nd$^{3+}$ in 0.1 M lithium chloride proceeds by a three-electron change directly to the metallic state (Ln$^{3+}$ ＋ 3e- → Ln$^0$) and charge transfer is totally irreversible. However, the reduction of Sm$^{3+}$ in 0.1 M tetramethylammonium iodide and Eu$^{3+}$ in 0.1 M lithium chloride proceeds in two stages (Ln$^{3+}$ ＋ e- → Ln$^{2+}$ and Ln$^{2+}$ ＋ 2e- → Ln$^0$). At pH values lower than ca.4 the hydrated lanthanide species (Ln(OH)$^{2+}$) reduced before the lanthanide ions (Ln$^{3+}$) due to the catalytic effect of hydrogen ions, and peak current increase with in the order Eu$^{3+}$ < Sm$^{3+}$ < Nd$^{3+}$ < Pr$^{3+}$ < La$^{3+}$ in differential pulse polarography. Some representative plots of $i_{pc}V^{-1/2} (proportional to current function) vs. V show considerable influence of hydrogen ion/lanthanide ion concentration in cyclic voltammetry. It is shown that a reaction of lanthanide ions with proton and/or water and catalytic reaction is enhanced at lower pH and at decreased lanthanide ion concentration.

• Korean Chemical Engineering Research
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• v.44 no.4
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• pp.399-403
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• 2006

There has been numerous reports for the synthesis of mesoporous $TiO_2$ thin films due to not only the high surface area and regular mesoscale pores but also wide band gap and photo activity. However, the synthesis has been restricted by the limited reproducibility mainly due to the extraordinarily fast hydrolysis and condensation rate of titania precursors. In this report, molar composition of reaction batch (HCl/Ti and Ti/P123) and exterior condition (humidity and temperature) during coating and anealing process. Thereafter, the mesoporous $TiO_2$ thin films were characterized by XRD and TEM

• Microbiology and Biotechnology Letters
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• v.16 no.5
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• pp.363-368
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• 1988

Molecular cloning of gene for $\alpha$-acylamino-$\beta$-lactam acylhydrolase (ALAH) III from Acetobacter turbidans has been attempted by immunochemical detection method, in which polyclonal antibody from mouse Balb/c against this enzyme was employed as a probe. As a cloning vector, λ gtll was chosen for this purpose. Two positive clones has been selected from genomic libraries of A. turbidans, which had somewhat different binding affinities on anti-ALAH III umm and anti-$\beta$-galactosidase. By restriction analysis, both clones has been turned out to lose one of EeoRI sites. From these results, it concluded that deletion of DNA between lacZ gene and inserted DNA has occurred during replication of these clones in host cells.

• Journal of the Korean Wood Science and Technology
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• v.43 no.1
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• pp.76-85
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• 2015

In this study, we investigated optimal reaction conditions for furfural production from lignocellulosic biomass by two-stage acid treatment. Furfural produced by this method was recovered using XAD-4 resin. Oxalic and sulfuric acid were used as catalysts for the first stage of treatment. The concentration of xylose in the hydrolysate obtained from the first stage was $18.86g/{\ell}$ with oxalic acid and $19.35g/{\ell}$ with sulfuric acid. The concentration of oligosaccharide was relatively high when sulfuric acid was used. Maximum yield of furfural, that is, 55.10% ($6.71g/{\ell}$), was obtained when oxalic acid was used for the first stage and $0.1m{\ell}$ of sulfuric acid was used for the second stage of treatment for 90 min. Furfural production yield increased with increasing the reaction time. Most of the furfural produced by this two-stage treatment method was recovered using XAD-4 resin.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.4
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• pp.343-352
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• 2022

Co/Al₂O₃ nanopowder was used as a catalyst to investigate the effect of catalyst support, reduction temperature, sodium borohydride (NaBH₄) concentration, sodium hydroxide (NaOH) concentration, and reaction temperature on the characteristics of NaBH₄ hydrolysis. The Co/Al₂O₃ nanopowder showed a high catalytic activity among various catalysts. Catalyst reduction at 250℃ exhibited a relatively good activity. The activity decreased with an increase in the NaBH₄ concentration. Conversely, the activity increased and then decreased with an increase in the NaOH concentration. Additionally, the activity increased with an increase in the reaction temperature. The value of apparent activation energy was 40.81 kJ/mol, which was lower than the other Co-based catalysts. Thus, Co/Al₂O₃ nanopowder catalyst can be widely used for NaBH₄ hydrolysis owing to its superior catalytic activity.

• Journal of Life Science
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• v.27 no.11
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• pp.1381-1392
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• 2017

This review described solvent-tolerant lipases and their potential industrial, biotechnological and environmental impacts. Although organic solvent-tolerant lipase was first reported in organic solvent-tolerant bacterium, many organic solvent-tolerant lipases are in not only solvent-tolerant bacteria but also solvent-intolerant bacterial and fungal strains, such as the well-known Bacillus, Pseudomonas, Streptomyces and Aspergillus strains. As these lipases are not easily inactivated in organic solvents, there is no need to immobilize them in order to prevent an enzyme inactivation by solvents. Therefore, the solvent-tolerant lipases have the potential to be used in many biotechnological and biotransformation processes. With the solvent-tolerant lipases, a large number insoluble substrates become soluble, various chemical reactions that are initially impossible in water systems become practical, synthesis reactions (instead of hydrolysis) are possible, side reactions caused by water are suppressed, and the possibility of chemoselective, regioselective and enantioselective transformations in solvent and non-aqueous systems is increased. Furthermore, the recovery and reuse of enzymes is possible without immobilization, and the stabilities of the lipases improve in solvent and non-aqueous systems. Therefore, lipases with organic-solvent tolerances have attracted much attention in regards to applying them as biocatalysts to biotransformation processes using solvent and non-aqueous systems.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.634-638
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• 1998

Monodisperse, spherical $PMSQ/TiO_2$ composite fine powders were prepared by modified sol-gel process where 300 nm $TiO_2$ fine powders were used as seed particles for hetero-condensation with hydrolyzed MTMS (Methyltrimethoxysilane). The reaction was carried out under $N_2$ atmosphere at ambient temperature using $NH_3$ as a catalyst. Methanol was used as a solvent. Powder was obtained by the filtration of the solution with a glass filter and washing with acetone. The stirring rate, reaction temperature, $[H_2O]/[MTMS]$ and $[MTMS]/[TiO_2]$ ratio were varied to investigate shapes and sizes of particles. Monodisperse particles of $1-2{\mu}m$ diameter were obtained with [MTMS]=0.2 M, $[NH_3]=0.6M$, $[H_2O]/[MTMS]=100$, $[MTMS]/[TiO_2]=10-50$ at ambient temperature with mild stirring condition. These composite particles had a contact angle of almost 180 degree contact angle with water, which proves their excellent hydrophobicity. The study of UV absorption spectra showed that they have UV protecting effect.