• KSBB Journal
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• v.18 no.5
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• pp.347-351
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• 2003

The extraction of glycyrrhizic acid from licorice using supercritical carbon dioxide (SCCO$_2$) was investigated with respect to the effects of extraction parameters such as the kind and amount of modifier, temperature, pressure, and extraction time. The conventional organic solvent extraction was also conducted for a quantitative comparison. The content of glycyrrhizic acid in crude extracts was analyzed by HPLC and the yield of glycyrrhizic acid was computed as a weight percent recovery. The optimal pressure and temperature for SCCO$_2$ extraction were found to be 40 MPa and 80$^{\circ}C$, respectively, when SCCO$_2$ was modified with 70% aqueous ethanol. Under the same pressure and temperature, the highest recovery was attained to be 104.57% in the first 60 min when the concentration of 60%, aqueous ethanol in SCCO$_2$ was 15%.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.280-285
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• 1992

Enantiomeric separation of free amino acids has been achieved by a reversed phase liquid chromatography with addition of a Cu(Ⅱ) complex of N-alkyl-L-proline (alkyl: propyl, pentyl or octyl) to the mobile phase. The amino acids eluted were detected by a postcolumn OPA system. N-alkyl-L-proline was prepared and used as a chiral ligand of Cu(Ⅱ) chelate for the enantiomeric separation. The concentration of the Cu(Ⅱ) chelate, the organic modifier and pH affect the enantiomeric separation of free amino acids. The retention behaviour, varied with change in pH and the concentration of the Cu(Ⅱ) chelate, was different compared with those of the derivatized amino acids. The elution orders between D- and L-forms were consistent except histidine showing that L-forms elute earlier than D-forms. The retention mechanism for the enantiomeric separation can be illustrated by the stereospecificity of the ligand exchange reaction and the hydrophobic interaction between the substituent of amino acids and reversed phase, $C_18$.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.285-289
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• 1992

Enantiomeric separation of underivatized amino acids using N-alkyl-L-proline (octyl, dodecyl or hexadecyl) coated HPLC has been accomplished. The anchoring N-alkyl groups of L-proline provides a permanent adsorption of there solving chiral agent on the hydrophobic interface layer of a reversed phase. The factors controlling retention and enantioselectivity such as the Cu(II) concentration, pH of the eluent, the type and concentration of organic modifier in the hydroorganic eluent, and extent of coating were examined. The elution orders between D- and L-amino acids were consistent, L-forms eluting first, except histidine and asparagine. The extremely high enantioselectivity $(\alpha$ upto 13 for proline) is observed. The retention mechanism for the chiral separation can be illustrated by a complexation and hydrophobic interaction.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.506-512
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• 2017

The purpose of this study was to improve release rate and bioavailability of nateglinide formulation. Polymorphism selection and particle size control were performed to enhance formulation dissolution rate, and a pH modifier was included in the formulation to overcome pH-dependent solubility of nateglinide. The enhanced dissolution rate was characterized by using a dissolution test. The results showed that H-type raw material had a higher dissolution rate than that of B-type raw material. There was 6.2% difference in dissolution between the two materials at 60 min. With regard to particle size, raw material with a $1.13{\mu}m$ particle size showed a 20% faster release rate than that of raw material with a $2.28{\mu}m$ particle size. Furthermore, fumaric acid was included in formulation as a pH modifier. That addition produced a greater than 50% improvement in dissolution rate. In conclusion, dissolution rate of nateglinide can be enhanced by optimizing its polymorphism and particle size; moreover, a synergistic effect on the enhancement of dissolution rate is obtained by including fumaric acid, a pH modifier, in the formulation.

• Korean Chemical Engineering Research
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• v.50 no.4
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• pp.678-683
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• 2012

Ceria is one of the most important catalytic materials which can be used in three-way catalysts, waste water treatment, petroleum refining, etc. So far, many methods have been studied to produce ceria nanoparticles. In this study, ceria nanoparticles were prepared via solvothermal synthesis using supercritical methanol in short reaction time using a batch reactor. The size of synthesized ceria nanoparticles in supercritical methanol is 6 nm without capping agent, which is smaller than that made in supercritical water at the same conditions of $400^{\circ}C$ and 30 MPa. Size difference results from density and critical point difference between water and methanol and slow reaction rate at the surface of ceria particles in supercritical methanol which reduces crystal growth rate. Several organic compounds were added to modify the surface of ceria nanoparticles, and in-situ surface modification was confirmed by FT-IR and TGA analysis. Surface modified ceria nanoparticles have excellent dispersibility in organic solvent. Size and shape of surface modified ceria particles can be controlled by adjusting molar ratio of modifier to precursor and selection of modifier.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.400.1-400.1
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• 2016

Interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Recently, polymer surface modifiers, such as poly(ethyleneimine) (PEI) and polyethylenimine ethoxylated (PEIE), were introduced to produce low WF electrodes and were reported to have good electron selectivity for inverted polymer solar cells (iPSCs) without an n-type metal oxide layer. To obtain more efficient solar cells, quantum dots (QDs) are used as effective sensitizers across a broad spectral range from visible to near IR. Additionally, they have the ability to efficiently generate multiple excitons from a single photon via a process called carrier multiplication (CM) or multiple exciton generation (MEG). However, in general, it is very difficult to prepare a bilayer structure with an organic layer and a QD interlayer through a solution process, because most solvents can dissolve and destroy the organic layer and QD interlayer. To present a more effective strategy for surpassing the limitations of traditional methods, we studied and fabricated the highly efficient iPSCs with mono-layered QDs as an effective multi-functional layer, to enhance the quantum yield caused by various effects of QDs monolayer. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer, which is verified by various analysis tools.

• Korean Chemical Engineering Research
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• v.49 no.5
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• pp.594-599
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• 2011

$SrAl_2O_4:Eu$ green phosphor was prepared by spray pyrolysis and its luminescence properties were controlled by replacing the Al sites with boron and using organic modifier or drying control chemical additive. It was clear that the substitution of B into the Al sites was helpful to obtain pure monoclinic $SrAl_2O_4$ phase and greatly enhance the emission intensity. In terms of the emission intensity, the optimal content of boron was about 1 at% with respect to the aluminum element. The luminescence intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor could be improved by the use of 0.2 M organic additives in the spray solution. Futhermore, using 0.5 M dimethylformamide(DMF) as a drying control chemical with organic additives made it possible to improve about 172% the emission intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor. According to XRD analysis, the organic additive and DMF used enhanced the crystallinity without any change in the crystal phase. When used only the organic additive without DMF, the surface area of the prepared $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor became enlarged. The use of DMF with the organic additive resulted in significant reduction in the surface area. It was concluded that the increase of the crystallinity as well as the reduction of surface area mainly contribute to the improvement in the luminescence intensity of $Sr_{0.9}Al_{1.98}B_{0.02}O_4:Eu_{0.1}$ phosphor prepared using DMF and organic additives.

• Journal of the Korean Chemical Society
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• v.42 no.2
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• pp.197-202
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• 1998

1-(2-Pyridylazo)-2-Naphthol (PAN) has been widely used as a spectrophotometric reagent and metallochromic indicator for many metal ions. In this work, the chelate reagent of PAN was used as mobile phase additive for the separation of metal ions by reversed phase chromatography. Metal ions could be detected by monitoring the effluent at 570 nm with spectrophotometric detector. In order to investigate retention behaviors of the metal ions, the chromatograms and capacity factors were obtained as the variation of pH, ionic strength and composition of organic modifier in mobile phase. Under the obtained optimum conditions, the mixtures of Fe(III), Ni(II), Cu(II), Zn(II) and Co(II) could be separated successfully and the calibration curves under the recommended conditions showed an excellent linearity. The detection limits(S/N) were feasible at the nanogram level.

• KSBB Journal
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• v.17 no.3
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• pp.261-265
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• 2002

The biologically active peptides in human blood can adjust the functions of many physiological systems. The peptides in human blood were separated on the five steps of linear gradient-elution mode by RP-HPLC with UV detection. The size of commercially available $C_{18}$ chromatographic column was 4.60$\times$150 mm with particle size of 5 $\mu\textrm{m}$ and pore size of 100 $\AA$. The mobile phases used were water in 0.75% trifluoroacetic acids (TFA) and organic modifier of acetonitrile. The isolation methods suggested in this work for peptides from the blood were composed of the formation of immiscible liquid layers and precipitation by centrifuge and chemicals of sodium citrate and trichloroacetic acid (TCA). The some peptides were identified based on the retention times previously constructed database.

• Journal of Pharmaceutical Investigation
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• v.41 no.1
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• pp.45-50
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• 2011

Nonclassical pathway of crystallization has been utilized to modify the properties and morphologies of inorganic and organic/inorganic materials. In here, the polymer-directed crystallization method has been applied to the pharmaceutical active ingredient to assess the applicability for as a particle engineering tool. The polymer-directed crystallization was successful to modifying the crystal size, habit and morphology, but it was not effective to discover the novel polymorphs of Sibutramine (SB). SB was selected as a model drug and polyacrylic acid (PAA), polyethylene imine (PEI) and chitosan (CHI) were added as a crystallization pathway modifier. SB was crystallized via drowning crystallization using methanol or ethanol as a solvent and water as a non-solvent. The significant interactions between polymer and the drug were confirmed by measuring the solubility of the drug in presence of polymer during the crystallization. The crystal forms of SB are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and optical microscope (OM). The polymer-directed crystallization seems to be able to modify the crystal properties of pharmaceutical active ingredient, which is critical in determining the bioavailability, processability, and stability.