Synthesis of Permalloy (Ni-Fe) Nanosheets through Sonoelectrochemical Methods and its Magnetic Properties

Ryan Rhee,Kyounghoon Moon,Bongyoung Yoo 한국표면공학회 2018 한국표면공학회지 Vol.51 No.4

Permalloy(Ni80-Fe20) which is known for its soft magnetic properties is a well-known material that has been studied intensively. Permalloy nanoflakes were fabricated with the combination of electrodeposition and sonication process. Ultrasonic power was applied to the deposited alloy which produced nanoflakes in forms of sheet. High internal stress created cracks which helped the peeling of permalloy into nanosheets. Because of shape anisotropy, flakes could be aligned by magnetic field. The magnetic properties of the nanosheets were observed, and the variation of magnetic properties with the alignment of flake was also investigated.

Amino Acids Important for DNA Recognition by the Response Regulator OmpR

Rhee, Jee Eun,Sheng, Wanyun,Morgan, Leslie K.,Nolet, Ryan,Liao, Xiubei,Kenney, Linda J. American Society for Biochemistry and Molecular Bi 2008 The Journal of biological chemistry Vol.283 No.13

<P>Response regulators undergo regulated phosphorylation and dephosphorylation at conserved aspartic acid residues in bacterial signal transduction systems. OmpR is a winged helix-turnhelix DNA-binding protein that functions as a global regulator in bacteria and is also important in pathogenesis. A detailed mechanistic picture of how OmpR binds to DNA and activates transcription is lacking. We used NMR spectroscopy to solve the solution structure of the C-terminal domain of OmpR (OmpR(C)) and to analyze the chemical shift changes that occur upon DNA binding. There is little overlap in the interaction surface with residues of PhoB that were reportedly involved in protein/protein interactions in its head-to-tail dimer. Multiple factors account for the lack of overlap. One is that the spacing between the OmpR half-sites is shorter than observed with PhoB, requiring the arrangement of the two OmpR molecules to be different from that of the PhoB dimer on DNA. A second is the demonstration herein that OmpR can bind to its high affinity site as a monomer. As a result, OmpR(C) appears to be capable of adopting alternative orientations depending on the precise base composition of the binding site, which also contributes to the lack of overlap. In the presence of DNA, chemical shift changes occur in OmpR in the recognition alpha-helix 3, the loop between beta-strand 4 and alpha-helix 1, and the loop between beta-strands 5 and 6. DNA contact residues are Val(203) (T), Arg(207) (G), and Arg(209) (phosphate backbone). Our results suggest that OmpR binds to DNA as a monomer and then forms a symmetric or asymmetric dimer, depending on the binding site. We propose that during activation OmpR binds to DNA and undergoes a conformational change that promotes phosphorylation of the N-terminal receiver domain, the receiver domains dimerize, and then the second monomer binds to DNA. The flexible linker of OmpR enables the second monomer to bind in multiple orientations (head-to-tail and head-to-head), depending on the specific DNA contacts.</P>

The Critical Roles of Zinc: Beyond Impact on Myocardial Signaling

Sung Ryul Lee,Su Jin Noh,Julius Ryan Pronto,Yu Jeong Jeong,Hyoung Kyu Kim,In Sung Song,Zhelong Xu,Hyog Young Kwon,Se Chan Kang,Eun-Hwa Sohn,Kyung Soo Ko,Byoung Doo Rhee,Nari Kim,Jin Han 대한생리학회-대한약리학회 2015 The Korean Journal of Physiology & Pharmacology Vol.19 No.5

Zinc has been considered as a vital constituent of proteins, including enzymes. Mobile reactive zinc (Zn²⁺) is the key form of zinc involved in signal transductions, which are mainly driven by its binding to proteins or the release of zinc from proteins, possibly via a redox switch. There has been growing evidence of zinc’s critical role in cell signaling, due to its flexible coordination geometry and rapid shifts in protein conformation to perform biological reactions. The importance and complexity of Zn²⁺ activity has been presumed to parallel the degree of calcium’s participation in cellular processes. Whole body and cellular Zn²⁺ levels are largely regulated by metallothioneins (MTs), Zn²⁺ importers (ZIPs), and Zn²⁺ transporters (ZnTs). Numerous proteins involved in signaling pathways, mitochondrial metabolism, and ion channels that play a pivotal role in controlling cardiac contractility are common targets of Zn²⁺. However, these regulatory actions of Zn²⁺ are not limited to the function of the heart, but also extend to numerous other organ systems, such as the central nervous system, immune system, cardiovascular tissue, and secretory glands, such as the pancreas, prostate, and mammary glands. In this review, the regulation of cellular Zn²⁺ levels, Zn²⁺-mediated signal transduction, impacts of Zn²⁺ on ion channels and mitochondrial metabolism, and finally, the implications of Zn²⁺ in health and disease development were outlined to help widen the current understanding of the versatile and complex roles of Zn²⁺.

The star formation quenching and transition epoch of the Horizon-AGN galaxies

Seyoung Jeon,Sukyoung K. Yi,San Han,Ryan A. Jackson,Jinsu Rhee 한국천문학회 2022 天文學會報 Vol.47 No.1

Improved Stability of Interfacial Energy-Level Alignment in Inverted Planar Perovskite Solar Cells

Im, Soeun,Kim, Wanjung,Cho, Wonseok,Shin, Dongguen,Chun, Do Hyung,Rhee, Ryan,Kim, Jung Kyu,Yi, Yeonjin,Park, Jong Hyeok,Kim, Jung Hyun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.22

<P>Even though poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been commonly used as a hole extraction layer (HEL) for p-i-n perovskite solar cells (PSCs), the cells’ photovoltaic performance deteriorates because of the low and unstable work functions (WFs) of PEDOT:PSS versus those of a perovskite layer. To overcome this drawback, we synthesized a copolymer (P(SS-<I>co</I>-TFPMA)) ionomer consisting of PSS and tetrafluoropropylmethacrylate (TFPMA) as an alternative to conventional PEDOT:PSS. The PEDOT:P(SS-<I>co</I>-TFPMA) copolymer solution and its film exhibited excellent homogeneity and high phase stability compared with a physical mixture of TFPMA with PEDOT:PSS solution. During spin coating, a self-organized conducting PEDOT:P(SS-<I>co</I>-TFPMA) HEL evolved and the topmost PEDOT:P(SS-<I>co</I>-TFPMA) film showed a hydrophobic surface with a higher WF compared to that of the pristine PEDOT:PSS film because of its chemically bonded electron-withdrawing fluorinated functional groups. Interestingly, the WF of the conventional PEDOT:PSS film dramatically deteriorated after being coated with a perovskite layer, whereas the PEDOT:P(SS-<I>co</I>-TFPMA) film represented a relatively small influence. Because of the superior energy-level alignment between the HEL and a perovskite layer even after the contact, the open-circuit voltage, short-circuit current, and fill factor of the inverted planar p-i-n PSCs (IP-PSCs) with PEDOT:P(SS-<I>co</I>-TFPMA) were improved from 0.92 to 0.98 V, 18.96 to 19.66 mA/cm<SUP>2</SUP>, and 78.96 to 82.43%, respectively, resulting in a 15% improvement in the power conversion efficiency vs that of IP-PSCs with conventional PEDOT:PSS. Moreover, the IP-PSCs with PEDOT:P(SS-<I>co</I>-TFPMA) layer showed not only improved photovoltaic performance but also enhanced device stability due to hydrophobic surface of PEDOT:P(SS-<I>co</I>-TFPMA) film.</P> [FIG OMISSION]</BR>

The Critical Roles of Zinc: Beyond Impact on Myocardial Signaling

Lee, Sung Ryul,Noh, Su Jin,Pronto, Julius Ryan,Jeong, Yu Jeong,Kim, Hyoung Kyu,Song, In Sung,Xu, Zhelong,Kwon, Hyog Young,Kang, Se Chan,Sohn, Eun-Hwa,Ko, Kyung Soo,Rhee, Byoung Doo,Kim, Nari,Han, Jin The Korean Society of Pharmacology 2015 The Korean Journal of Physiology & Pharmacology Vol.19 No.5

Zinc has been considered as a vital constituent of proteins, including enzymes. Mobile reactive zinc ($Zn^{2+}$) is the key form of zinc involved in signal transductions, which are mainly driven by its binding to proteins or the release of zinc from proteins, possibly via a redox switch. There has been growing evidence of zinc's critical role in cell signaling, due to its flexible coordination geometry and rapid shifts in protein conformation to perform biological reactions. The importance and complexity of $Zn^{2+}$ activity has been presumed to parallel the degree of calcium's participation in cellular processes. Whole body and cellular $Zn^{2+}$ levels are largely regulated by metallothioneins (MTs), $Zn^{2+}$ importers (ZIPs), and $Zn^{2+}$ transporters (ZnTs). Numerous proteins involved in signaling pathways, mitochondrial metabolism, and ion channels that play a pivotal role in controlling cardiac contractility are common targets of $Zn^{2+}$. However, these regulatory actions of $Zn^{2+}$ are not limited to the function of the heart, but also extend to numerous other organ systems, such as the central nervous system, immune system, cardiovascular tissue, and secretory glands, such as the pancreas, prostate, and mammary glands. In this review, the regulation of cellular $Zn^{2+}$ levels, $Zn^{2+}$-mediated signal transduction, impacts of $Zn^{2+}$ on ion channels and mitochondrial metabolism, and finally, the implications of $Zn^{2+}$ in health and disease development were outlined to help widen the current understanding of the versatile and complex roles of $Zn^{2+}$.

Kobophenol A inhibits sodium nitroprusside-induced cardiac H9c2 cell death through suppressing activation of JNK and preserving mitochondrial anti-apoptotic Bcl-2 and Mcl-1.

Lee, Sung Ryul,Kwak, Jong Hwan,Noh, Su Jin,Pronto, Julius Ryan,Ko, Kyung Soo,Rhee, Byoung Doo,Xu, Zhelong,Kim, Nari,Han, Jin Pharmaceutical Society of Japan 2014 Chemical & pharmaceutical bulletin Vol.62 No.7

<P>Sodium nitroprusside (SNP) releases nitric oxide (NO), a powerful vasodilator, and thus widely used in intensive care unit for treating hypertension emergency. However, cardiac toxicity after SNP administration is a clinical problem. For finding a natural compound that suppressing SNP-induced cardiac toxicity, we tested the protective potential of kobophenol A (Kob A), purified from the root of Caragana sinica, against the toxic effects of SNP. The severe cardiac H9c2 cell death was induced by SNP (2?mM) treatment. Kob A ameliorated SNP-induced cardiac H9c2 cell death, and this protective effect of Kob A may be related to the inhibition of c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinase activation following SNP administration. In addition, the downregulation of cellular Bcl-2 and Mcl-1 levels by SNP exposure was strongly abrogated in the presence of Kob A. These biological properties of Kob A might provide insights into developing new cardioprotectant against SNP-induced cardiac cell death.</P>

Grain Boundary Healing of Organic-Inorganic Halide Perovskites for Moisture Stability

Chun, Do Hyung,Kim, Sungsoon,Chai, Sung Uk,Kim, Wook,Kim, Wanjung,Lee, Jung Hwan,Rhee, Ryan,Choi, Dukhyun,Kim, Jung Kyu,Shin, Hyunjung,Park, Jong Hyeok American Chemical Society 2019 NANO LETTERS Vol.19 No.9

<P>Although organic-inorganic halide perovskite (OIHP)-based photovoltaics have high photoconversion efficiency (PCE), their poor humidity stability prevents commercialization. To overcome this critical hurdle, focusing on the grain boundary (GB) of OIHPs, which is the main humidity penetration channel, is crucial. Herein, pressure-induced crystallization of OIHP films prepared with controlled mold geometries is demonstrated as a GB-healing technique to obtain high moisture stability. When exposed to 85% RH at 30 °C, OIHP films fabricated by pressure-induced crystallization have enhanced moisture stability due to the enlarged OIHP grain size and low-angle GBs. The crystallographic and optical properties indicate the effect of applying pressure onto OIHP films in terms of moisture stability. The photovoltaic devices with pressure-induced crystallization exhibited dramatically stabilized performance and sustained over 0.95 normalized PCE after 200 h at 40% RH and 30 °C.</P> [FIG OMISSION]</BR>