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Kim, Youngmin,Lee, Daewon,Kwon, Yonghyun,Kim, Tae-Wan,Kim, Kyoungsoo,Kim, Hyung Ju Elsevier 2019 Journal of Electroanalytical Chemistry Vol.838 No.-
<P><B>Abstract</B></P> <P>Here we report an efficient catalyst design strategy to develop high performance Pt-based electrocatalysts for oxygen reduction reaction (ORR). Finely-dispersed Pt nanoclusters supported on microporous graphene-like 3D carbon (Pt/MGTC) having a Pt size of <I>ca.</I> 1.3nm were synthesized by zeolite template-based carbon synthesis and subsequent Pt impregnation. The Pt/MGTC catalyst demonstrated about 2 times higher ORR activity than that of commercial Pt/C. In addition, the Pt/MGTC showed relatively stable ORR performance, maintaining an activity higher than that of Pt/C. This performance enhancement of electrocatalytic ORR on Pt/MGTC was attributed to the significant increase of Pt active sites and the efficient charge transport in Pt/MGTC.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly-dispersed Pt nanoclusters supported on microporous graphene-like 3D carbon (Pt/MGTC) were synthesized. </LI> <LI> The Pt/MGTC led to improved catalytic performances for electrochemical oxygen reduction reaction. </LI> <LI> This performance enhancement was attributed to many Pt active sites and efficient charge transport in Pt/MGTC. </LI> </UL> </P>
Regulation of Protein Structural Changes by Incorporation of a Small-Molecule Linker
Kim, Youngmin,Yang, Cheolhee,Kim, Tae Wu,Thamilselvan, Kamatchi,Kim, Yonggwan,Ihee, Hyotcherl MDPI 2018 INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES Vol.19 No.12
<P>Proteins have the potential to serve as nanomachines with well-controlled structural movements, and artificial control of their conformational changes is highly desirable for successful applications exploiting their dynamic structural characteristics. Here, we demonstrate an experimental approach for regulating the degree of conformational change in proteins by incorporating a small-molecule linker into a well-known photosensitive protein, photoactive yellow protein (PYP), which is sensitized by blue light and undergoes a photo-induced N-terminal protrusion coupled with chromophore-isomerization-triggered conformational changes. Specifically, we introduced thiol groups into specific sites of PYP through site-directed mutagenesis and then covalently conjugated a small-molecule linker into these sites, with the expectation that the linker is likely to constrain the structural changes associated with the attached positions. To investigate the structural dynamics of PYP incorporated with the small-molecule linker (SML-PYP), we employed the combination of small-angle X-ray scattering (SAXS), transient absorption (TA) spectroscopy and experiment-restrained rigid-body molecular dynamics (MD) simulation. Our results show that SML-PYP exhibits much reduced structural changes during photo-induced signaling as compared to wild-type PYP. This demonstrates that incorporating an external molecular linker can limit photo-induced structural dynamics of the protein and may be used as a strategy for fine control of protein structural dynamics in nanomachines.</P>
Characterization of the Vertical Position of the Trapped Charge in Charge-trap Flash Memory
Kim, Seunghyun,Kwon, Dae Woong,Lee, Sang-Ho,Park, Sang-Ku,Kim, Youngmin,Kim, Hyungmin,Kim, Young Goan,Cho, Seongjae,Park, Byung-Gook The Institute of Electronics and Information Engin 2017 Journal of semiconductor technology and science Vol.17 No.2
In this paper, the characterization of the vertical position of trapped charges in the charge-trap flash (CTF) memory is performed in the novel CTF memory cell with gate-all-around structure using technology computer-aided design (TCAD) simulation. In the CTF memories, injected charges are not stored in the conductive poly-crystalline silicon layer in the trapping layer such as silicon nitride. Thus, a reliable technique for exactly locating the trapped charges is required for making up an accurate macro-models for CTF memory cells. When a programming operation is performed initially, the injected charges are trapped near the interface between tunneling oxide and trapping nitride layers. However, as the program voltage gets higher and a larger threshold voltage shift is resulted, additional charges are trapped near the blocking oxide interface. Intrinsic properties of nitride including trap density and effective capture cross-sectional area substantially affect the position of charge centroid. By exactly locating the charge centroid from the charge distribution in programmed cells under various operation conditions, the relation between charge centroid and program operation condition is closely investigated.
Kim, Hyeong Seok,Han, Youngmin,Kang, Jae Seung,Kim, Hongbeom,Kim, Jae Ri,Koon, Wooil,Kim, Sun‐,Whe,Jang, Jin‐,Young John WileySons Ltd 2018 Journal of hepato-biliary-pancreatic sciences Vol.25 No.2
<P>ConclusionRobot PD is comparable to open PD in early outcomes. Robot PD is safe and feasible and enables early recovery; indication for robot PD is expected to expand in the near future.</P>
Kim, Kyung Hwan,Muniyappan, Srinivasan,Oang, Key Young,Kim, Jong Goo,Nozawa, Shunsuke,Sato, Tokushi,Koshihara, Shin-ya,Henning, Robert,Kosheleva, Irina,Ki, Hosung,Kim, Youngmin,Kim, Tae Wu,Kim, Jeongh American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.16
<P/><P>Proteins serve as molecular machines in performing their biological functions, but the detailed structural transitions are difficult to observe in their native aqueous environments in real time. For example, despite extensive studies, the solution-phase structures of the intermediates along the allosteric pathways for the transitions between the relaxed (R) and tense (T) forms have been elusive. In this work, we employed picosecond X-ray solution scattering and novel structural analysis to track the details of the structural dynamics of wild-type homodimeric hemoglobin (HbI) from the clam <I>Scapharca inaequivalvis</I> and its F97Y mutant over a wide time range from 100 ps to 56.2 ms. From kinetic analysis of the measured time-resolved X-ray solution scattering data, we identified three structurally distinct intermediates (I<SUB>1</SUB>, I<SUB>2</SUB>, and I<SUB>3</SUB>) and their kinetic pathways common for both the wild type and the mutant. The data revealed that the singly liganded and unliganded forms of each intermediate share the same structure, providing direct evidence that the ligand photolysis of only a single subunit induces the same structural change as the complete photolysis of both subunits does. In addition, by applying novel structural analysis to the scattering data, we elucidated the detailed structural changes in the protein, including changes in the heme–heme distance, the quaternary rotation angle of subunits, and interfacial water gain/loss. The earliest, R-like I<SUB>1</SUB> intermediate is generated within 100 ps and transforms to the R-like I<SUB>2</SUB> intermediate with a time constant of 3.2 ± 0.2 ns. Subsequently, the late, T-like I<SUB>3</SUB> intermediate is formed via subunit rotation, a decrease in the heme–heme distance, and substantial gain of interfacial water and exhibits ligation-dependent formation kinetics with time constants of 730 ± 120 ns for the fully photolyzed form and 5.6 ± 0.8 μs for the partially photolyzed form. For the mutant, the overall kinetics are accelerated, and the formation of the T-like I<SUB>3</SUB> intermediate involves interfacial water loss (instead of water entry) and lacks the contraction of the heme–heme distance, thus underscoring the dramatic effect of the F97Y mutation. The ability to keep track of the detailed movements of the protein in aqueous solution in real time provides new insights into the protein structural dynamics.</P>