Browsing by Author "Kim, J"

Now showing 1 - 7 of 7
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    The chaperone activity of a-synuclein: Utilizing deletion mutants to map its interaction with target proteins
    (Wiley-Blackwell, 2012-03-01) Rekas, A; Ahn, KJ; Kim, J; Carver, JA
    a-Synuclein is the principal component of the Lewy body deposits that are characteristic of Parkinson's disease. In vivo, and under physiological conditions in vitro, a-synuclein aggregates to form amyloid fibrils, a process that is likely to be associated with the development of Parkinson's disease. a-Synuclein also possesses chaperone activity to prevent the precipitation of amorphously aggregating target proteins, as demonstrated in vitro. a-Synuclein is an intrinsically disordered (i.e., unstructured) protein of 140 amino acids in length, and therefore studies on its fragments can be correlated directly to the functional role of these regions in the intact protein. In this study, the fragment containing residues 61140 [a-syn(61140)] was observed to be highly amyloidogenic and was as effective a chaperone in vitro as the full-length protein, while the N- and C-terminal fragments a-syn(160) and a-syn(96140) had no intrinsic chaperone activity. Interestingly, full-length fibrillar a-synuclein had greater chaperone activity than nonfibrillar a-synuclein. It is concluded that the amyloidogenic NAC region (residues 6195) contains the chaperone-binding site which is optimized for target protein binding as a result of its beta-sheet formation and/or ordered aggregation by a-synuclein. On the other hand, the first 60 residues of a-synuclein modulate the protein's chaperone-active site, while at the same time protecting a-synuclein from fibrillation. On its own, however, this fragment [a-syn(160)] had a tendency to aggregate amorphously. As a result of this study, the functional roles of the various regions of a-synuclein in its chaperone activity have been delineated. Proteins 2012; (c) 2011 Wiley Periodicals, Inc.
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    Controlled atomic solubility in Mn‐rich composite material to achieve superior electrochemical performance for Li‐ion batteries
    (Wiley, 2019-12-16) Lee, J; Zhang, Q; Kim, J; Dupre, N; Avdeev, M; Jeong, M; Yoon, WS; Gu, L; Kang, B
    The quest for high energy density and high power density electrode materials for lithium-ion batteries has been intensified to meet strongly growing demand for powering electric vehicles. Conventional layered oxides such as Co-rich LiCoO2 and Ni-rich Li(NixMnyCoz)O2 that rely on only transition metal redox reaction have been faced with growing constraints due to soaring price on cobalt. Therefore, Mn-rich electrode materials excluding cobalt would be desirable with respect to available resources and low cost. Here, the strategy of achieving both high energy density and high power density in Mn-rich electrode materials by controlling the solubility of atoms between phases in a composite is reported. The resulting Mn-rich material that is composed of defective spinel phase and partially cation-disordered layered phase can achieve the highest energy density, ≈1100 W h kg−1 with superior power capability up to 10C rate (3 A g−1) among other reported Mn-rich materials. This approach provides new opportunities to design Mn-rich electrode materials that can achieve high energy density and high power density for Li-ion batteries. © 1999-2021 John Wiley & Sons, Inc.
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    Critical role of Ti4+ in stabilizing high-voltage redox reactions in Li-rich layered material
    (Wiley, 2021-07-01) Cho, M; Song, SH; Hong, S; Kim, KS; Avdeev, M; Yoo, JG; Ko, KT; Hong, J; Kim, J; Lee, S; Kim, H
    Li-rich layered oxide materials are considered promising candidates for high-capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti4+-substituted Li2IrO3 (Li2Ir0.75Ti0.25O3) is synthesized, which undergoes an oxygen redox reaction with suppressed voltage decay, yielding improved electrochemical performance and good capacity retention. It is shown that the increased bond covalency upon Ti4+ substitution results in structural stability, tuning the phase stability from O3 to O1′ upon de-lithiation during charging compared with O3 to T3 and O1 for pristine Li2IrO3, thereby facilitating the oxidation of oxygen. This work unravels the role of Ti4+ in stabilizing the cathode framework, providing insight for a fundamental design approach for advanced Li-rich layered oxide battery materials.© 2021 Wiley-VCH GmbH
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    High‐voltage‐driven surface structuring and electrochemical stabilization of Ni‐rich layered cathode materials for Li rechargeable batteries
    (Wiley, 2020-05-04) Song, SH; Cho, M; Park, I; Yoo, JG; Ko, KT; Hong, J; Kim, J; Jung, SK; Avdeev, M; Ji, S; Lee, S; Bang, J; Kim, H
    Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li+/Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as improved electrochemical performance upon electrochemical cycling at a high operating voltage of 4.9 V in the Ni‐rich NCM LiNi0.895Co0.085Mn0.02O2 is presented. The improved electrochemical performance at a high working voltage at 4.9 V is attributed to the removal of the resistive Ni2+O rock‐salt surface layer, which stabilizes the voltage profile and improves retention of the energy density during electrochemical cycling. The manifestation of the layered Ni2+O rock‐salt phase along with the structural evolution related to the metal dissolution are probed using in situ X‐ray diffraction, neutron diffraction, transmission electron microscopy, and X‐ray absorption spectroscopy. The findings help unravel the structural complexities associated with high working voltages and offer insight for the design of advanced battery materials, enabling the realization of fully reversible lithium extraction in Ni‐rich NCM materials. © 2020 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
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    Rational design of Li off-stoichiometric Ni-rich layered cathode materials for Li-ion batteries
    (Elsevier, 2022-11) Song, SH; Hong, S; Cho, M; Yoo, JG; Jin, HM; Lee, SH; Avdeev, M; Ikeda, K; Kim, J; Nam, SC; Yu, SH; Park, I; Kim, H
    The electrification trend in the automotive industry is fueling research on Ni-rich layered NCM cathode materials with high specific capacities. The simplest way to maximize the electrochemical performance of Ni-rich NCM is to tune the crystal structure by controlling the Li content and synthesis temperature. Herein, we demonstrate the critical roles of the Li content and synthesis temperature in determining the crystal structure of Li-excess Ni-rich NCM with enhanced electrochemical performance. The crystal structure of Li-excess Ni-rich NCM was systemically investigated using X-ray diffraction, neutron diffraction, and X-ray absorption spectroscopy, revealing that excess Li can be accommodated in Ni-rich NCM as the synthesis temperature decreases, resulting in stable cycle performance at high working voltage. We believe that our findings provide a rational reason for the excess amount Li required for optimization of the synthesis of Ni-rich NCM and offer insight for the simplest design of Ni-rich cathode materials that are stable under high-voltage operation. © 2022 Elsevier B.V.
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    Synthesis and physical properties of the new oxybismuthides BaTi2Bi2O and (SrF)2Ti2Bi2O with a d1 square net
    (Physical Society of Japan, 2012-12-11) Yajima, T; Nakano, K; Takeiri, F; Hester, JR; Yamamoto, T; Kobayashi, Y; Tsuji, N; Kim, J; Fujiwara, A; Kageyama, H
    We have recently reported the d(1) square-lattice compound BaTi(2)Sb(2)O, which shows superconductivity at T(c) = 1.2K coexisting with a charge- or spin-density wave (CDW/SDW) state. Here, we successfully prepared two new oxybismuthides, BaTi(2)Bi(2)O and (SrF)(2)Ti(2)Bi(2)O, as the first Pn = Bi compounds in the ATi(2)Pn(2)O family. The CDW/SDW state disappeared for both compounds, presumably owing to the considerable interaction between the Ti-3d and Bi-6s orbitals. The complete suppression of the CDW/SDW instability resulted in an enhanced T(c) of 4.6 K for BaTi(2)Bi(2)O. However, (SrF)(2)Ti(2)Bi(2)O exhibits no superconductivity, suggesting the importance of the interlayer interaction for superconductivity. © 2012, Physical Society of Japan
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    Understanding ion transport phenomena in heterostructured yttria-stabilized zirconia with respect to coordination chemistry
    (International Conference on Neutron Scattering, 2017-07-12) Lee, D; Sterbinsky, G; Soon, A; Stampfl, APJ; Kim, J; Moon, J
    Yttria-stabilized zirconia (xY -(1-x)ZrO , YSZ) has been exploited as a fast oxygen-ion conductor at elevated temperature, which is benefited from the formation of oxygen vacancies upon the stabilization of zirconia by yttria doping. Oxygen ion conduction in YSZ takes place by exchanging oxygen ions and vacancies within the cubic/tetragonal crystal framework, therefore, the coordination chemistry of a Zr ion by oxygen are of key importance in terms of crystal structure and crystal field to understand the origin of fast ionic conduction in YSZ. Herein, the Zr-Ometal-ligand interactions are modulated by heterostructuring of YSZ with Smdoped ceria, by which the vibrational properties of Zr-O bonding are altered.The coordination chemistry of the heterostructures is studied by X-ray absorption spectroscopy on Zr L edges, which is combined with neutron diffraction and inelastic neutron scattering studies. The coordination chemistry model for the heterostructures is suggested in conjunction with ab initio calculations.