• Title/Summary/Keyword: lattice oxygen mechanism

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Recent Advances in Structural Studies of Antifreeze Proteins (구조 생물학을 이용한 Antifreeze protein의 최근 연구동향)

  • Lee, Jun-Hyuck;Lee, Sung-Gu;Kim, Hak-Jun
    • Ocean and Polar Research
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    • v.33 no.2
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    • pp.159-169
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    • 2011
  • Antifreeze proteins (AFPs) have ice binding affinity, depress freezing temperature and inhibit ice recystallization which protect cellular membranes in polar organisms. Recent structural studies of antifreeze proteins have significantly expanded our understanding of the structure-function relationship and ice crystal growth inhibition. Although AFPs (Type I-IV AFP from fish, insect AFP and Plant AFP) have completely different fold and no sequence homology, they share a common feature of their surface area for ice binding property. The conserved ice-binding sites are relatively flat and hydrophobic. For example, Type I AFP has an amphipathic, single ${\alpha}$-helix and has regularly spaced Thr-Ala residues which make direct interaction with oxygen atoms of ice crystals. Unlike Type I AFP, Type II and III AFP are compact globular proteins that contain a flat ice-binding patch on the surface. Type II and Type III AFP show a remarkable structural similarity with the sugar binding lectin protein and C-terminal domain of sialic acid synthase, respectively. Type IV is assumed to form a four-helix bundle which has sequence similarity with apolipoprotein. The results of our modeling suggest an ice-binding induced structural change of Type IV AFP. Insect AFP has ${\beta}$-helical structure with a regular array of Thr-X-Thr motif. Threonine residues of each Thr-X-Thr motif fit well into the ice crystal lattice and provide a good surface-surface complementarity. This review focuses on the structural characteristics and details of the ice-binding mechanism of antifreeze proteins.

Optical properties of HgTe and HgTe/CdTe core-shell structured nanocrystals (HgTe와 HgTe/CdTe core-shell 구조의 나노입자의 광학적 특성 비교)

  • Park, Byoung-Jun;Kim, Hyun-Suk;Cho, Kyoung-Ah;Kim, Jin-Hyong;Lee, Joon-Woo;Kim, Sang-Sig
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.07a
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    • pp.56-59
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    • 2004
  • HgTe and HgTe/CdTe core-shell structured nanocrystals(NCs) were synthesized in aqueous solution by colloidal method. HgTe and HgTe/CdTe NCs structure showed very similar XRD patterns because of the same lattice constant and crystal structure of both samples. The absorption and photoluminescence(PL) spectrum of the synthesized HgTe NCs revealed the strong exitonic peak in the IR region. The PL spectrum of HgTe/CdTe NCs have the intense peak in about 700nm shorter than that of HgTe by 400nm. The photocurrent measurement of colloidal NCs are performed using He-Ne laser for light source. The photocurrent of HgTe NCs shows the instant increased current response to light, but HgTe/CdTe NCs revealed a decreased current when lighted to the sample. In the vacuum condition, it shows reverse result that current increased under the illumination of light and it is thought that the molecules like the hydro-oxygen gas in the air give an important effect on the current mechanism.

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Kinetics and Mechanism of the Oxidation of Sulfur Dioxide on Nickel Oxide-${\alpha}$-Ferric Oxide System (산화니켈-${\alpha}$ 형 산화철 상에서 이산화황의 산화 반응메카니즘)

  • Kyu Yong Lee;Yong Rok Kim;Sung Han Lee
    • Journal of the Korean Chemical Society
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    • v.27 no.3
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    • pp.183-188
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    • 1983
  • The catalytic oxidation of $SO_2$ has been investigated in the presence of vacuum-activated 10 mol % Ni-doped ${\alpha}-Fe_2O_3$ under various partial pressures of $SO_2\;and\;O_2$ at temperatures from 320 to $440{\circ}C$. Over the temperature range $320{\sim}440{\circ}C$, the activation energy is 13.8 $kcal{\cdot}mol^{-1}$. The oxidation rates have been correlated with 1.5 order kinetics; first order with respect to $SO_2$ and 0.5 order with respect to $O_2$. From the kinetic data and conductivity measurements, the adsorption, oxidation mechanism of $SO_2$ and the defect structure of vacuum-activated 10 mol % Ni-doped {\alpha}-Fe_2O_3$ are suggested. $O_2\;and\;SO_2$ appear to be adsorbed essentially as ionic species. Two surface sites, probably an $O^{2-}$ lattice and an oxygen vacancy which is induced by Ni-doping, might be required to adsorb $SO_2\;and\;O_2$. The conductivity measurements and kinetic data indicate that the adsorption process of $SO_2\;{(SO_2+O^{2-}}_{(latt)}{\rightleftharpoons}{{SO_3}^-}_{(ads)}+e')$ is the rate-determining step.

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The Effect of Trivalent Cation Doping on the Low Temperature Phase Stability of 2Y-TZP (3가 양이온 산화물이 첨가된 2Y-TZP의 저온 상안정성)

  • Jang, Ju-Woong;Kim, Hak-Kwan;Lee, Deuk-Yong;Kim, Dae-Joon;Park, Sun-Min
    • Journal of the Korean Ceramic Society
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    • v.39 no.11
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    • pp.1055-1062
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    • 2002
  • The phase stability and the Low Temperature Degradation(LTD) mechanism of Tetragonal Zirconia Polycrystals(TZP), sintered specimens of $Y_2O_3$-Stabilized Zirconia(2Y-TZP), doped with trivalent cations, were evaluated by investigating meachnical properties, Raman spectra, lattice parameter variation and the oxygen vacancy behavior under applied electric field. XRD observation was put forward on 2Y-TZP doped with trivalent cation whose ionic radii were larger than $Zr^{4+}(Sc^{3+},\;Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+},\;La^{3+})$ up to 2 mol% and sintered at 1500 h for 1h. For $La^{3+}$ doping, the stability of tetragonal phase was degraded due to the formation of the pyrochlore phase $(La_2Zr_2O_7)$ as the dopant content increased above exceeded 0.5 mol%. As the dosage increased, tetragonal phase maintained for the case of $Sc^{3+}$, whose radius was similar to $Zr^{4+}$, on the other hand, the cubic phase was formed for the cases of $Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+}$. As the radii of dopant cation increased, c/a ratio increased and it was experimentally observed that the amount of monoclinic phase decreased when the specimens were annealed at $220{\circ}C$ for 500 h.

Studies on Chemical Properties and Thermal Analysis of (Sr,M)FeO3-y System (M=Ca) ((Sr,M)FeO3-y계(M=Ca)의 화학적 성질과 열분석에 대한 연구)

  • Lee, Eun-Seok
    • Applied Chemistry for Engineering
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    • v.8 no.6
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    • pp.954-959
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    • 1997
  • The solid solutions of the $Sr_{1-X}M_XFeO_{3-y}$ (x=0.1, 0.2, 0.3, 0.4, 0.5, M=Ca) system having perovskite structures were prepared in air by heat treatment at 1473 K for 18hr. X-ray diffraction assigns cubic system for all the samples and shows that the lattice volume of each system decreases with increasing x value until x=0.3, but increases abruptly from x=0.4. The mole fractions of $Fe^{4+}$ ion($\tau$ value), the amounts of oxygen vacancy (y value) and finally nonstoichiometric chemical formulas for each composition were determined from Mohr salt analysis. TG/DTA thermal analysis (temperature range: 300~1173K) exhibits that 3-y values of the samples having x=0.1 and 0.2, decrease with temperature and increase almost reversibly with decreasing temperature. The samples of $x{\geq}0.3$, however, didn't show the reversible weight change and the 3-y values of them were nearly 2.5 in cooling process. Conductivities of each sample were varied within the semiconductivity range at relatively low temperature. And the conductivity at constant temperature decreases steadily with x value. The conduction mechanism of this ferrite system may be proposed as a hopping model of conducting electrons between the mixed valence states. At high temperature semiconductivity of each sample changed into metallic property.

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