• Journal of dental hygiene science
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• v.21 no.2
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• pp.96-103
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• 2021

Background: We aimed to investigate the effect of Citrous limon extract (CLE) on oxidative stress-induced cytotoxicity and nitric oxide (NO) generation and the tooth bleaching effect of CLE as a substitute for hydrogen peroxide (H₂O₂) and determine the feasibility and application of CLE as a safe and effective natural tooth bleaching agent. Methods: The protective effect of CLE on H₂O₂-induced cytotoxicity in Raw264.7 macrophages was investigated by the MTT assay. The inhibitory effect of CLE on the generation of H₂O₂-induced NO was confirmed by the NO assay, and the changes in inducible nitric oxide synthase (iNOS) protein expression were confirmed by western blotting. Stained bovine teeth were treated with/without 15% and/or 35% CLE and H₂O₂, 15% sodium bicarbonate (NaHCO₃) for 3 hours, and were irradiated with/without bleaching light (BL) for 15 minutes. The color change of the treated bovine tooth surface was measured using a colorimeter. Results: The viability of Raw264.7 cells treated with each concentration of CLE and 500 μM H₂O₂ significantly increased as CLE increased, and NO generation and iNOS protein expression were significantly reduced in cells treated with 300 ㎍ CLE+/500 μM H₂O₂+ and 300 ㎍ CLE+/500 μM H₂O₂+/150 ㎍ NaHCO₃+. The bleaching effect of 35% CLE+ was higher than that of 15% CLE+ and 15% NaHCO₃+, and the effect was similar to that of 15% H₂O₂+. The 35% CLE+/15% NaHCO₃+ showed the greatest bleaching effect and was higher than that of the groups irradiated with the BL. The greatest bleaching effect was observed with 35% CLE+/15% NaHCO₃+, followed by 35% H₂O₂+/BL+. Conclusion: CLE inhibited oxidative stress-induced cytotoxicity and NO generation in Raw264.7 cells and, could replace H₂O₂, which causes side effects and risks in teeth breaching treatment. It showed greatest teeth bleaching effect when combined with NaHCO₃. CLE is an effective and safe natural tooth bleaching substitute.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.302-308
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• 2009

This study investigated the production of hydrogen over Ga (1.0, 2.0, and 5.0 mol%)-$TiO_2$ photocatalysts prepared by a solvothermal method. The absorption band was slightly blue-shifted upon the incorporation of the gallium ions, but the intensity of the photoluminescence (PL) curves of Ga-incorporated $TiO_2$s was distinguishably smaller, with the smallest case being the 2.0 mol% Ga-$TiO_2$, which was related to the recombination between the excited electrons and holes. $H_2$ evolution from photo splitting of water over Ga-incorporated $TiO_2$ in the liquid system was enhanced, compared to that over pure $TiO_2$; particularly, the production of 5.6 mL of $H_2$ gas after 8 h when 1.5 g of the 2.0 mol% Ga-incorporated $TiO_2$ was used.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.1-7
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• 2019

Japanese anise (Illicium anisatum L.) leaves were collected and ground after drying, then immersed with 50 % aqueous acetone for 3 days. After filtration, the extracts were fractionated with n-hexane, chloroform ($CHCl_3$), ethylacetate (EtOAc) and $H_2O$, and then freeze dried after concentration. A portion of EtOAc (3.12 g) and $H_2O$ (6.08 g) soluble fractions were chromatographed on a Sephadex LH-20 column with various aqueous MeOH solution to isolate the compounds. Compound 1 ((+)-catechin) was isolated from EtOAc soluble fraction. Compounds 2 (quercetin), 3 (quercitrin) and 4 (2''-O-rhamnosylvitexin) were isolated from $H_2O$ soluble fraction. For the first time, quercitrin (3) and 2''-O-rhamnosylvitexin (4) of the isolated compounds were obtained from the extracts of japanese anise leaves.

• Korean Journal of Agricultural and Forest Meteorology
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• v.5 no.1
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• pp.1-5
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• 2003

This study was carried out to investigate the chemical properties of rainwater in the Suwon area. Rainwater was collected from April to October in 1999 and 2000, and its chemical composition was analyzed. The pH of rainwater in April was higher than that of the months after June. Occurrence frequency of rain above pH 5.6 was 45.1%, which showed the highest ratio from rainwater samples during the investigation periods. Those of pH 5.0∼5.6 and 4.5∼4.9 range were 31.4 and 19.6%, respectively. The major cations in rainwater were $Ca^{2+}$ and N $H_{4}$$^{+}$, and S $O_{4}$$^{2-}$ made up more than 50% of total anion composition. Monthly variation of neutralization capacity of rainwater acidity by $Ca^{2+}$ and N $H_{4}$$^{+}$ decreased during the rainy season. The ratio of non-sea salt sulfate to nitrate (nss-S $O_{4}$$^{2-}$/N $O_{3}$$^{[-10]}$ ) was 2.1, which means anthropogenic S $O_{4}$$^{2-}$ contributed to acidity of rainwater two times more than N $O_{3}$$^{[-10]}$ . .

• Journal of the Korean Magnetics Society
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• v.14 no.2
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• pp.71-75
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• 2004

$\alpha$-LiFe $O_2$ powders have been prepared by a sol-gel method. The crystallographic and magnetic properties were characterized with a x-ray diffractometry, Mossbauer spectroscopy, and vibrating Samples magnetometry. The ${\gamma}$-LiFe $O_2$+LiFe$_{5}$ $O_{8}$ phase is observed in the Samples annealed at $600^{\circ}C$ for 3h in air and $\alpha$-LiFe $O_2$ phase is observed in the Samples annealed at $600^{\circ}C$ for 3 h in $H_2$(5％)/Ar(Bal.) gas atmosphere. The crystal structure of $\alpha$-LiFe $O_2$ is found to be cubic with a lattice a=4.193$\pm$0.0005 $\AA$. The Neel temperature of $\alpha$-LiFe $O_2$ is found to be 130$\pm$3 K.

• Applied Chemistry for Engineering
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• v.1 no.1
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• pp.35-43
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• 1990

A series of $TiO_2-SiO_2$catalysts were prepared by coprecipitation from the mixed solution of titanium tetrachloride and sodium silicate. Some of the samples were treated with 1N $H_2SO_4$ and used as modified catalysts. The catalytic activities of modified catalysts were higher than those of unmodified catalysts, and the effect of modification on the catalytic activity was higher for 2 - propanol dehydration than for cumene dealkylation. The catalytic activity of unmodified catalysts was correlated with their acid amount for the above two reactions. As $TiO_2-SiO_2$ catalysts had relatively large amount of weak acid sites and small amount of strong acid sites, the catalytic activity for 2 - propanol dehydration was higher than that for cumene dealkylation. The effect of modification on catalytic activity increased with increasing $TiO_2$content of the catalysts. Actually, $92-TiO_2-SiO_2/SO_4{^2}$had the highest increment in catalytic activity and $10-TiO_2-SiO_2/SO_4{^2}$had the lowest increment for the 2 - propanol dehydration.

• Applied Microscopy
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• v.34 no.4
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• pp.231-239
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• 2004

Cerebral microvessel endothelial cells that form blood-brain barrier (BBB) have tight junction for maintaining brain homeostasis. Occludin, one of tight junction protein, is crucial for BBB function. $H_2O_2$ induced occludin changes and effects in bovine brain BBB endothelial cells were examined in this study. The decrease of transendothelial electrical resistance (TEER) by $H_2O_2$ was due to disruption of occludin localization. Cytotoxicity test revealed that $H_2O_2$ did not cause cell death below 1 mM $H_2O_2$ within 4 hr. $H_2O_2$ caused intermittent disruption and loss of occludin at tight junctions and occludin disappeared with dose dependent manner from tight junction in confocal laser microscopy. But Western blot revealed that the total amounts of occludin increased by $H_2O_2$ administration. Transmission electron microscopy revealed that the ultrastructure of tight junction was not changed by $H_2O_2$. These data suggest that functional disruption of BBB by $H_2O_2$ was due to the localized loss of occludin in tight junction, but the expression of occludin increased in order to compensate the disrupted function in BBB.

• Journal of the Korean Chemical Society
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• v.33 no.1
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• pp.135-142
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• 1989

Methyl tert-butyl ether(MTBE) was synthesized from vapor phase reaction of methanol with iso-butylene over HZSM-5 catalysts, and effects of SiO$_2/Al_2O_3$ ratio in the HZSM-5 catalysts and reaction conditions on products distribution have been examined. Acid strength and acid type of each catalyst with different SiO$_2/Al_2O_3$ ratio were measured using pyridine adsorption followed by temperature programmed desorption(TPD) and IR analysis. Reactants and products adsorption characteristics on different acid sites have also been examined. As the SiO$_2/Al_2O_3$ ratio of HZSM-5 catalyst was increased, selectivity to MTBE was improved as a result of decrease in dimethylether(DME) formation at the strong acid sites. Conversion and selectivity to MTBE were also greatly enhanced as $i-C_4H_8/CH_3OH$ reactant ratio was increased, and overall about 80$^{\circ}$C was adequate for the MTBE synthesis. The properties of deposited coke on spent catalysts were examined by TG, DTA and IR spectrum analysis, indicating the amount of the coke deposit in the order of HY > H-Mordenite > HZSM-5. Even if the coke deposited on H-Mordenite was little more in amount than to that on HZSM-5, the former deactivated quickly due to its non-interconnected channel structure. For HY, owing to its lange pore size, significant $i-C_4H_8$ polymerization was occured, and rapid deactivation and severe coke formation has resulted within few hours.

• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.559-564
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• 2019

Hierarchical $ZnCo_2O_4$ hollow nanofibers were prepared by electrospinning and subsequent heat-treatment process. The spinning solution containing polystyrene (PS) nanobeads was electrospun to nanofibers. During heat-treatment process, PS nanobeads in the composite were decomposed and therefore generated numerous pores uniformly in the structure, which facilitated the heat transfer and gas penetration into the structure. The resulting hierarchical $ZnCo_2O_4$ hollow nanofibers were applied as an anode material for lithium-ion batteries. The discharge capacity of the nanofibers was $815mA\;h\;g^{-1}$ ($646mA\;h\;cm^{-3}$) after the 300th cycle at a high current density of $1.0A\;g^{-1}$. However, $ZnCo_2O_4$ nanopowders showed the discharge capacity of $487mA\;h\;g^{-1}$ ($450mA\;h\;cm^{-3}$) after 300th cycle. The excellent lithium ion storage property of the hierarchical $ZnCo_2O_4$ hollow nanofibers was attributed to the synergetic effects of the hollow nanofiber structure and the $ZnCo_2O_4$ nanocrystals composing the shell. The hierarchical hollow nanofiber structure introduced in this study can be extended to various metal oxides for various applications, including energy storage.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.295-298
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• 1989

Using the anisotropic etching characteristics or $N_2H_4-H_2O$ solution, Si diaphragm was fabricated for the integrated sensor. The optimal composition and temperature of the solution in Si etching process was established to be 50mol% $N_2H_4$ in water at $105{\pm}2^{\circ}C$ for both higher etch rate(=$2.6{\mu}m/min$) and better surface quality of etched {100} planes. Under the optimal etching condition, the electrochemical etch stop technique was employed to form Si diaphragm for pressure sensor and diaphragm thickness was exactly controlled to $20{\pm}2{\mu}m$.