• Polymer(Korea)
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• v.37 no.3
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• pp.262-268
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• 2013

pH-sensitive P(MAA-co-PEGMA) hydrogel particles were prepared and their feasibility as smart delivery carriers for cosmetic ingredients was evaluated. P(MAA-co-PEGMA) hydrogel particles having an average size of approx. $2{\mu}m$ were synthesized via dispersion photopolymerization. There was a drastic change in the swelling ratio of P(MAA-co-PEGMA) particles at a pH of around 5 due to the ionization of MAA in the hydrogel and as the amount of MAA in the hydrogel increased, the swelling ratio increased at a pH above 5. The P(MAA-co-PEGMA) hydrogel particles showed a pH-sensitive release behavior. Thus, at pH 4 almost none of the albumin permeated through the skin while at pH 6 relatively high skin permeability was obtained. The albumin loaded in the P(MAA-co-PEGMA) hydrogel particles was hardly degraded in the presence of pepsin and its stability was maintained.

• Bulletin of the Korean Chemical Society
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• v.28 no.7
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• pp.1187-1194
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• 2007

The three major active isoflavonoids (calycosin-7-O-β -glucoside, isomucronulatol 7-O-β-glucoside, formononetin) and two main saponins (astragaloside I, astragaloside IV) in an extract of Radix Astragali were determined using rapid, sensitive, reliable HPLC/UV and LC-ESI-MS/MS methods. The separation conditions employed for HPLC/UV were optimized using a phenyl-hexyl column (4.6 × 150 mm, 5 μm) with the gradient elution of acetonitrile and water as the mobile phase at a flow rate of 1.0 mL/min and a detection wavelength of 230 nm. The specificity of the peaks was determined using a triple quadrupole tandem mass spectrometer equipped with an electrospray ionization (ESI) source that was operated in multiple reaction monitoring (MRM) in the positive mode. These methods were fully validated with respect to the linearity, accuracy, precision, recovery and robustness. The HPLC/UV method was applied successfully to the quantification of three major isoflavonoids in the extract of Radix Astragali. The results indicate that the established HPLC/UV and LC-ESI-MS/MS methods are suitable for the quantitative analysis and quality control of multi-components in Radix Astragali.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3629-3634
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• 2013

In this study, an improved method for the quantitative analysis of ginkgolic acids (GAs) in Ginkgo biloba leaf extract was developed. The samples were extracted with a mixture of chloroform and 50 % ethanol, after which the chloroform extract was dried and reconstituted in methanol. GAs with 13:0, 15:1, and 17:1 in the extract were successfully separated within 40 min and determined with high throughput performance using an online column-switching HPLC method using an SP column C8 SG80 ($4.6{\times}150mm$, $5{\mu}m$) and a Cadenza 5CD C18 column ($4.6{\times}150mm$, $3{\mu}m$). The developed HPLC method was validated for Ginkgo biloba leaf extract. The validation parameters were specificity, linearity, precision, accuracy, and limits of detection and quantitation (LODs and LOQs, respectively). It was found that all of the calibration curves showed good linearity ($r^2$ > 0.9993) within the tested ranges. The LODs and LOQs were all lower than $0.04{\mu}g/mL$. The established method was found to be simple, rapid, and high throughput for the quantitative analysis of GAs in ten commercial Ginkgo biloba leaf extract and dietary supplements. The samples were also analyzed in LC-electrospray ionization (ESI) tandem mass spectrometry (MS/MS) - multiple-ion reaction monitoring (MRM) mode to confirm the identification results that were obtained by the column switching HPLC-DAD method. The developed method is considered to be suitable for the routine quality control and safety assurance of Ginkgo biloba leaf extract.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.821-827
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• 2014

An isotope dilution liquid chromatography tandem mass spectrometry (ID LC-MS/MS) method has been developed and applied to the determination of arsenobetaine (AsB, ${(CH_3)_3}^+AsCH_2COO^-$) from oyster candidate certified reference material (CRM). The exact matching isotope dilution approach was adopted for accurate determination of AsB using $^{13}C_2$-labeled AsB as an internal standard. Efficiencies of different AsB extraction methods were evaluated using a codfish reference material and a simple sonication method was selected as the method of choice for the certification of the oyster candidate CRM. The hydrophilic interaction liquid chromatography (HILIC) combined with electrospray ionization tandem mass spectrometry (ESI/MS/MS) in selected reaction monitoring (SRM) mode was optimized for adequate chromatographic retention and robust quantification of AsB from codfish and oyster samples. By analyzing 12 subsamples taken from each 12 bottles systematically selected from the whole oyster CRM batch, the certified value of AsB was determined as $6.60mg{\cdot}kg^{-1}{\pm}0.31mg{\cdot}kg^{-1}$ and it showed excellent between-bottle homogeneity of less than 0.42%, which is represented by relative standard deviation of 12 bottles from the CRM batch. The major source of uncertainty was the certified value of the AsB standard solution.

• Journal of the Korean Chemical Society
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• v.44 no.3
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• pp.243-248
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• 2000

Oganic electroluminescent devices (OELD) with multilayer structures have been studied actively for the application to a flat-panel display. Netal-chelate complexes hrboxylate. These complexes were characterized by FT-IR, MS/FAB, $^1$H-NMR, UV-vis and photoluminescence (PL). More importantly, the electrochemical gap (Eg), electron affinity(EA) and ionization potential (IP) of these complex films were investigated. Data from cyclic voltammetry(CV) were compared with the bandgap obtained from UV-vis and discussed. Further studies on the EL of these new materials are now in progress.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2487-2493
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• 2014

Dimeric ${\beta}$-cyclodextrin linked by a thioether bridge was synthesized from a reaction of mono-6-iodo-6-deoxy-${\beta}$-cyclodextrin with sodium sulfide, and the structure was analyzed using nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The effects of thioether-bridged dimeric ${\beta}$-CD on the aqueous solubility of flavonols (myricetin, quercetin, and kaempferol) were investigated by ultraviolet-visible spectroscopy. The aqueous solubility of myricetin, quercetin, and kaempferol were enhanced 33.6-, 12.4-, and 10.5-fold following the addition of 9 mM of thioether-bridged dimeric ${\beta}$-CD. In comparison, the aqueous solubility of myricetin, quercetin, and kaempferol were enhanced 5.4-, 3.3-, and 2.7-fold using the same concentration of monomeric ${\beta}$-cyclodextrin. Furthermore, the formation of flavonol/thioether-bridged dimeric ${\beta}$-CD inclusion complexes was confirmed with nuclear magnetic resonance, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The results showed that the nature of the complexes significantly differed from that of free flavonols. Herein, we suggest that the thioether-bridged dimeric ${\beta}$-CD can act as an effective complexing agent for flavonols.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.388-393
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• 1999

Polyurethane foams are polymeric material with repeating groups of urethane and urea. When these are heated with ethylene glycol and K acetate catalyst at $200^{\circ}C$, the transesterification of them leads to soluble products. The mechanisms of the reaction were investigated from the molecular weight and the component distributions of the products by GPC and IR analysis. The degradation of the urethane groups was faster than that of urea groups in transesterification reaction. K acetate catalyst accelerated the rate of the transesterification because it had a high ionization tendency. Each reaction, using K or Sr acetate as a catalyst, progressed in the same reaction path but yielded different compositions in products because of the difference of the reaction rate.

• Journal of Applied Biological Chemistry
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• v.58 no.3
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• pp.237-240
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• 2015

The flowers of Chionanthus retusus Lindl. & Paxton were extracted with 80% aqueous MeOH at room temperature. The concentrated extract was partitioned as EtOAc, n-BuOH, and $H_2O$ fractions. From the EtOAc fraction, two triterpenoids and two sterols were isolated using the repeated silica gel ($SiO_2$) and octadecyl $SiO_2$ (ODS) column chromatographies. According to the results of physico-chemical and spectroscopic data including nuclear magnetic resonance, mass spectrometry, and infrared. The chemical structures of the compounds were respectively determined as ursolic acid (1), corosolic acid (2), ${\beta}$-sitosterol (3), and daucosterol (4). All the compounds were isolated for the first time from the flowers of Chionanthus retusus Lindl. & Paxton.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.676-680
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• 2003

Dissolution of magnetite powders by 0.05 M citric acid was investigated at $50^{\circ}C$. All the tests were performed in the pH range between 2.0 to 5.0, which was adjusted using nitric acid or sodium hydroxide. Concentration of each of the dissociated chemical species of citric acid under various solution pHs was calculated using the ionization constants. Variation of zeta potential of magnetite with pH changes was also investigated. The dissolution reaction was explained by comparing the concentration of the dissociated chemical species of citric acid with the zeta potential. Longer than 3 h of induction time was required to dissolve the magnetite. The dissolution behaviour of magnetite was well described by the equation. The physical meaning of each parameter was explained successfully from the model equation.

• Bulletin of the Korean Chemical Society
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• v.33 no.1
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• pp.143-148
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• 2012

The photodissociation dynamics of cyclopropyl bromide ($C_3H_5Br$) and cyclobutyl bromide ($C_4H_7Br$) at 234 nm was investigated. A two-dimensional photofragment ion-imaging technique coupled with a [2+1] resonanceenhanced multiphoton ionization scheme was utilized to obtain speed and angular distributions of the nascent $Br(^2P_{3/2})$ and $Br^*(^2P_{1/2})$ atoms. The recoil anisotropies for the Br and $Br^*$ channels were measured to be ${\beta}_{Br}=0.92{\pm}0.03$ and ${\beta}_{Br^*}=1.52{\pm}0.04$ for $C_3H_5Br$ and ${\beta}_{Br}=1.10{\pm}0.03$ and ${\beta}_{Br^*}=1.49{\pm}0.05$ for $C_4H_7Br$. The relative quantum yield for Br was found to be ${\Phi}_{Br}=0.13{\pm}0.03$ and for $C_3H_5Br$ and $C_4H_7Br$, respectively. The soft radical limit of the impulsive model adequately modeled the related energy partitioning. The nonadiabatic transition probability from the 3A' and 4A' potential energy surfaces was estimated and discussed.