• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.183-183
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• 2014

Recently, multiferroic materials gain much attention due to their fascinating fundamental physical properties. These materials offer wide range of potential applications such as data storage, spintronic devices and sensors, where both electronic and magnetic polarizations can be coupled. Among single-phase multiferroic materials, $BiFeO_3$ is typical because of the room-temperature magnetoelectric coupling in view of long-range magnetic- and ferroelectric-ordering temperatures. However, $BiFeO_3$ is well known to have large leakage current and small spontaneous polarization due to the existence of oxygen vacancies and other defects. Furthermore the magnetic moment of pure $BiFeO_3$ is very weak owing to its antiferromagnetic nature. Recently, various attempts have been performed to improve the multiferroic properties of $BiFeO_3$ through the co-doping at the A and the B sites, by making use of the fact that the intrinsic polarization and magnetization are associated with the lone pair of $Bi^{3+}$ ions at the A sites and the partially-filled 3d orbitals of $Fe^{3+}$ ions at the B sites, respectively. In this study, $BiFeO_3$, $Bi_{0.9}Ho_{0.1}FeO_3$, $BiFe_{0.97}Ni_{0.03}O_3$ and $Bi_{0.9}Ho_{0.1}Fe_{0.97}Ni_{0.03}O_3$ bulk compounds were prepared by solid-state reaction and rapid sintering. High-purity $Bi_2O_3$, $Ho_2O_3$, $Fe_2O_3$ and $NiO_2$ powders with the stoichiometric proportions were mixed, and calcined at $500^{\circ}C$ for 24 h to produce the samples. The samples were immediately put into an oven, which was heated up to $800^{\circ}C$ and sintered in air for 1 h. The crystalline structure of samples was investigated at room temperature by using a Rigaku Miniflex powder diffractometer. The field-dependent and temperature-dependent magnetization measurements were performed with a vibrating-sample magnetometer and superconducting quantum-interference device.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.775-780
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• 1995

Thin films of titanium nitride are formed using the tetrakis-dimethyl-amino-titanium (TDMAT(Ti[N($CH_3$)$_2$]$_4$)) under various conditions. The formation of TiN films has been obtained from the thermal decomposition of the Ti-precursor and the gas phase reaction between TDMAT and ammonia(NH$_3$). The resistivity of the MOCVD film can be attributed to their impurity. Especially the curve fitting graph of XPS data is revealed that main impurities in the films as carbon and oxygen make various interstitial compounds which has influenced physical and electrical properties of the film. In the contact hole with the aspect ratio of 3:1 and the diameter of 0.5${\mu}{\textrm}{m}$, the SEM morphology shows that the step coverage is more decreased in the films formed y flowing ammonia additionally than the films formed by pyrolysis of TDMAT and the phenomenon is probably related with the activation energy.

• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.452-460
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• 1991

The chemical evidence for involvement of singlet oxygen during photoirradiation for 2-ethylanthracene [2-EA] and 9-phenylanthracene [9-PA] was based on the rapid decomposition of 1,3-diphenylisobenzofuran [DPBF] in methanol-water mixture and aqueous CTAB, and SDS micellar solutions. The average microenvironmental polarities of 2-EA and 9-PA were estimated by UV spectroscopic characteristics sensitive to the polarity of solvent. When 2-EA and 9-PA were solubilized in aqueous CTAB, SDS and Brij 35 solutions, their average microenvironmental polarities were polar, and their microenvironmental polarity parameter showed little dependence on the ionic properties of the micelles. The average microenvironmental polarity of 2-EA was similar to the polarity of 40% (w/w) aqueous ethanol, and that of 9-PA was similar to the polarity between 30 and 40% (w/w) aqueous ethanol. It was found that the greater part of these species might be distributed at the surface of micelles when they were solubilized in aqueous micellar solutions. The methanol-water mixture solution appeared to have characteristics more favorable for photooxidation reaction than aqueous micellar solutions.

• Korean Journal of Food Science and Technology
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• v.20 no.3
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• pp.287-292
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• 1988

The inhibition mechanism of DNA damage by lipid peroxidation was studied through the reaction systems of plasmid pBR322 DNA, linoleic acid and the ethanol extracts obtained from ginger and garlic. The DNA damage was greatly inhibited by the addition of ginger and garlic extracts, and their scavenging effects of active oxygens were also great. It is considered that the inhibitory effects of these extracts on the DNA damage are mainly due to their scavenging effects of active oxygen radicals.

• Applied Chemistry for Engineering
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• v.20 no.2
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• pp.159-164
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• 2009

Monomers of oxetane high explosives were theoretically examined in terms of reactivity, reaction mechanism and process of polymerization substituted by azido $(-CH_2N_3)$, nitrato $(-CH_2ONO_2)$ and hydrazino $(-CH_2N_2H_3)$ which belong to the 5th class hazardous materials and have explosiveness under acid catalyst using MINDO/3, MNDO, and AMI methods for formal charge, heat of formation, and energy level. Nucleophilicity and base of oxetane high explosives could be explained by negative charge size of oxetane oxygen atom and reactivity of oxetane in the growth stage of polymerization under acid catalyzer could be expected to be governed by positive charge size of axial carbon atom and low LUMO energy of electrophile. It could be estimated that carbenium ion was more beneficial in the conversion process of oxetane high explosives than that of stabilization energy (13.90~31.02 kcal/mole) of oxonium ion. In addition, concentration of oxonium ion and carbenium ion in equilibrium state influenced mechanism and it was also estimated that $S_N1$ mechanism reacts faster than that of $S_N2$ in prepolymer growth stage considering quick equilibrium based on form and calculation of polymerization under acid catalyzer.

• Applied Biological Chemistry
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• v.40 no.6
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• pp.501-507
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• 1997

Chloroplasts isolated from Stevia rebaudiana Bertoni leaves contained an enzyme activity which catalyzed hydroxylation of ent-kaurenoic acid (ent-kaur-16-en-19-oic acid; ent-KA) to steviol (ent-13-hydroxy kaur-16-en-19-oic acid), the diterpenoid carboxylic alcohol which is the aglycone of sweet stevioside-related glycosides. $[^(14)C]-methylated$ ent-KA was used to localize ent-KA hydroxylase. $[^(14)C]-methyl-KA$ was most actively was transformed into methyl-steviol in chloroplast. The enzymatic activity was found in stroma fraction but not in thylakoid membrane in Stevia rebaudiana Bertoni. However, ent-KA 13-hydroxylase activity was not detected in stroma fraction of either Spinacia oleracea and Solidago altissima. The reaction products using $[^(14)C]-methyl-KA$ were purified and identified on TLC autoradiogram. The hydroxylation of ent-KA from stromal protein to form steviol required NADPH and oxygen. FAD and riboflavin stimulated the enzyme activity 1.5-and 1.7-fold, respectively. It also turned out that the activity of this enzyme using methyl-KA as a substrate was 16.7% that of ent-KA. The purified ent-KA 13-hydroxylase did not act on t-cinnamic acid, 4-hydroxyphenyl acetic acid, choline and resorcinol, known as monooxygenase and hydroxylase substrates.

• Journal of Korean Society for Atmospheric Environment
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• v.22 no.6
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• pp.799-807
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• 2006

The catalytic activity of $Pt/{\gamma}-Al_2O_3$ catalysts for the oxidation of toluene and toluene+xylene mixture was investigated in the microreactor of fixed-bed type. The calcination temperatures and loadings of $Pt/{\gamma}-Al_2O_3$ catalysts played the important role in the activity of catalysts for the oxidation of toluene. The increasing calcination temperatures and loadings of $Pt/{\gamma}-Al_2O_3$ catalysts increased the crystallite size of the platinum to result in the higher oxidation activity of catalysts. The catalytic activity for the toluene oxidation over $Pt/{\gamma}-Al_2O_3$ catalysts turned out to be increasing in the order of $500^{\circ}C\;<\;800^{\circ}C<600^{\circ}C\;<\;700^{\circ}C$ for calcination temperatures and 0.1 wt% < 0.3 wt% < 1.0 wt% for platinum loadings, respectively. The 1.0 wt% $Pt/{\gamma}-Al_2O_3$ catalysts calcined at $700^{\circ}C$ for 3 hrs in the air showed the highest activity for the oxidation of the toluene. The decrease of oxidation activity of $Pt/{\gamma}-Al_2O_3$ catalysts calcined at $800^{\circ}C$ might result from the decrease of active sites by sintering of platinum metals as well as ${\gamma}-Al_2O_3$ supports. The 1.0wt% $Pt/{\gamma}-Al_2O_3$ catalyst showed the activity from the lower temperature at $120^{\circ}C$, reached the light-off temperature ($T_{50%}$) at $180^{\circ}C$, and leveled off its activity at $340^{\circ}C$ with the conversion of 100% 'Mutual promotion' effects were observed for the binary mixture of toluene and xylene. The activity of the easy-to-oxidize toluene was slightly increased with the existence of the xylene. It might suggest the different mechanism for the oxidation of toluene and xylene on the $Pt/{\gamma}-Al_2O_3$ catalysts on different sites, and its reaction of gaseous oxygen.

• Analytical Science and Technology
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• v.11 no.6
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• pp.460-468
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• 1998

Schiff base ligands such as $SOPDH_2$, $SNDH_2$, $EBNH_2$, and $PBNH_2$ and their Co(II) complexes such as [$Co(II)(SND)(H_2O)_2$], [$Co(II)(SOPD)(H_2O)_2$], [$Co(II)(EBN)(H_2O)$], and [$Co(II)(PBN)(H_2O)$] have been synthesized. The mole ratio of Shiff base ligand to cobalt(II) for the Co(II) complexes was found to be 1:1. Also these complexes have been configurated with hexa-coordination. Reduction of dioxygen was investigated by cyclic voltammetry at glassy carbon electrodes modified with Schiff base Co(II) complexes in 1 M KOH aqueous solution. At modified glassy carbon electrode with Schiff base Co(II) complexes, reduction peak current of oxygen was increased and peak potential was shifted to more positive direction compared to bare glassy carbon electrode. The electrokinetic parameters such as number of electron and exchange rate constant were calculated from the results of cyclic voltammogrms. The reduction of dioxygen at glassy carbon electrode has been $2e^-$ reaction pathway. Exchange rate constant at glassy carbon electrode modified with Co(II) complexes was increased 2~10 times compared to bare electrode.

• Journal of Life Science
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• v.27 no.5
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• pp.536-544
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• 2017

Abeliophyllum distichum Nakai is deciduous shrubs of flowering plant in Oleaceae. It is important plant resources and consists of one species in the world. Also the endemic plant of A. distichum has been protected and designed endangered plant in Korea. For this reason, study on the immature seeds of A. distichum (ADS) hasn't progressed. In the present study, we evaluated the antioxidant activity and inhibitory effects on proteins and mRNA levels were related in the whitening effect in B16F10 cells. ADS was effective for reaction oxygen species (ROS). ROS causes various diseases such as aging, inflammation, cancer, and etc. Antioxidant properties were evaluated DPPH, ABTS radical scavenging activity and Reducing power. Plants were known that contained phenolic compounds were related in antioxidant activity. Phenolic compounds were phytochemicals commonly named natural polyphenols. These are secondary metabolites of plants involved in the defense against different types of stresses. In results, ADS suppressed the expression and transcription of Tyrosinase, TRP-1, TRP-2, and Microphthalmia-associated transcription factor (MITF). Tyrosinase, tyrosinase-related protein 1 (TRP-1), tyrosinase-related protein 1 (TRP-2) are known to play an important role in melanin biosynthesis. MITF regulated the expression and transcription of Tyrosinase, TRP-1, and TRP-2. In conclusion, ADS was effective in both antioxidant activities and whitening effects. Also, they were associated with the content of phenolic compounds. We suggested that ADS can be use antioxidants and skin-whitening functional cosmetics material derived from natural plant resources.

• Korean Journal of Food Science and Technology
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• v.27 no.1
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• pp.19-24
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• 1995

The effect of several inhibitors such as ascorbic acid on the lipoxygenase in soybeans known to catalyze reaction resulting in racid off-flavors was examined in the soybean homogenates by the oxygen electrode method. Among 8 compounds added at homogenizing process, 10 mM ascorbic acid inhibited lipoxygenase-1 and lipoxygenase-2/3 activities to 41.7 and 49.8%, respectively. Inactivation of lipoxygenase-2/3 was highly accelerated by homogenization for 15 min at room temperature, so the activity was inhibited 70.8% comparing with the homogenization of 3 min. When soybean homogenates with 10 mM ascorbic acid was stored at $25^{\circ}C$ for 72 hrs, lipoxygenase-2/3 activities lowered to 52.8% whereas L-1 activities lowered to 15.8%. Since it is reported that lipoxygenase-2 is responsible for the off-flavor of soybean products, the inhibitory effect of ascorbic acid among several inhibitors investigated might be useful in soybean processing.