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The Application of REDOR NMR to Understand the Conformation of Epothilone B
Lee, Jae-Ho,Kim, Moon-Su,Lee, Hyo Won,Lee, Ihl-Young C.,Kim, Hyun Kyoung,Kim, Nam Doo,Lee, SangGap,Seo, Hwajeong,Paik, Younkee MDPI 2017 INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES Vol.18 No.7
<P>The structural information of small therapeutic compounds complexed in biological matrices is important for drug developments. However, structural studies on ligands bound to such a large and dynamic system as microtubules are still challenging. This article reports an application of the solid-state NMR technique to investigating the bioactive conformation of epothilone B, a microtubule stabilizing agent, whose analog ixabepilone was approved by the U.S. Food and Drug Administration (FDA) as an anticancer drug. First, an analog of epothilone B was designed and successfully synthesized with deuterium and fluorine labels while keeping the high potency of the drug; Second, a lyophilization protocol was developed to enhance the low sensitivity of solid-state NMR; Third, molecular dynamics information of microtubule-bound epothilone B was revealed by high-resolution NMR spectra in comparison to the non-bound epothilone B; Last, information for the macrolide conformation of microtubule-bound epothilone B was obtained from rotational-echo double-resonance (REDOR) NMR data, suggesting the X-ray crystal structure of the ligand in the P450epoK complex as a possible candidate for the conformation. Our results are important as the first demonstration of using REDOR for studying epothilones. </P>
Lee, SangGap,Won, Soonho,Saun, Seung-bo,Lee, Soonchil IOP Pub 2007 Nanotechnology Vol.18 No.37
<P>We describe a magnetic resonance force microscopy experiment carried out using both a fast-relaxing spin system and a frequency-modulation mode detection method, presenting a validation of the measured signal and sensitivity. The detection method applied along with a self-excited cantilever oscillation worked stably without any serious interference due to spurious cantilever excitation despite application of first-harmonic microwave modulation, and thereby successfully created almost the maximum available signal. The signal could be measured without distortion while the magnetic field was swept at a rate of 1.9 G s<SUP>−1</SUP>. The measured sensitivity approached the thermal noise limit of the cantilever with a high quality factor. The experimental results for both signal and noise were in good agreement with theoretical predictions. </P>
Hwang, Young Jin,Jang, Jae Young,Lee, SangGap,Lee, Jiho,Lee, Woo Seung Elsevier 2018 Cryogenics Vol.89 No.-
<P>This paper reports the effects of a current sweep cycle method on reducing the screening current induced field (SCF) in a (RE)Ba2Cu3Ox (REBCO) coil. The screening current induced field in a REBCO coil causes two major problems: temporal magnetic field drift and a reduction of the central magnetic field. This is a critical problem in relation to REBCO coils, which require a homogeneous and stable magnetic field, during, for instance, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications (Itoh et al., 2013; Hemmi et al., 2005; Hahn et al., 2008; Amemiya et al., 2008; Otsuka et al., 2011; Yang et al., 2013; Ahn et al., 2009; Koyama et al., 2009; Kajikawa et al., 2015). In an effort to circumvent the SCF problem, the current sweep cycle method is investigated based on experiments in this study. The experimental results show that a greater SCF reduction in a REBCO coil can be obtained by increasing the overshooting of the current sweep cycle.</P>
Design of ferromagnetic shims for an HTS NMR magnet using sequential search method
Hongmin Yang,SangGap Lee,Minchul Ahn 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4
This study deals with the ferromagnetic shims design based on the spherical harmonic coefficient reduction method. The design method using the sequential search method is an intuitive method and has the advantage of quickly reaching the optimal result. The study was conducted for a 400 MHz all-REBCO magnet, which had difficulty in shimming due to the problem of SCF (screening current induced field). The initial field homogeneity of the magnet was measured to be 233.76 ppm at 20 mm DSV (Diameter Spherical Volume). In order to improve the field homogeneity of the magnet, the ferromagnetic shim with a thickness of 1 mil to 11 mil was constructed by a design method in which sequential search algorithm was applied. As a result, the field homogeneity of the magnet could be significantly improved to 0.24 ppm at 20 mm DSV and 0.05 ppm at 10 mm DSV.
Design of ferromagnetic shims for an HTS NMR magnet using sequential search method
Hongmin Yang,SangGap Lee,안민철 한국초전도저온학회 2021 한국초전도저온공학회논문지 Vol.23 No.4
This study deals with the ferromagnetic shims design based on the spherical harmonic coefficient reduction method. The designmethod using the sequential search method is an intuitive method and has the advantage of quickly reaching the optimal result. Thestudy was conducted for a 400 MHz all-REBCO magnet, which had difficulty in shimming due to the problem of SCF (screeningcurrent induced field). The initial field homogeneity of the magnet was measured to be 233.76 ppm at 20 mm DSV (DiameterSpherical Volume). In order to improve the field homogeneity of the magnet, the ferromagnetic shim with a thickness of 1 mil to11 mil was constructed by a design method in which sequential search algorithm was applied. As a result, the field homogeneityof the magnet could be significantly improved to 0.24 ppm at 20 mm DSV and 0.05 ppm at 10 mm DSV.
Catalytic oxidation of hydrogen at nanocrystalline palladium surfaces
Oh, Chanick,Hong, Kwan Soo,Lee, SangGap,Park, Chung-hyun,Yu, Insuk IOP Pub 2006 Journal of physics, an Institute of Physics journa Vol.18 No.13
<P>We studied hydrogen adsorption onto the oxidized nano-palladium surface using <SUP>1</SUP>H NMR. In the α phase, the incoming hydrogen molecules dissociate and form OH<SUB>ad</SUB>. We confirm that the <img SRC='http://ej.iop.org/images/0953-8984/18/13/001/cm210477ieqn1.gif' ALIGN='MIDDLE' ALT='\mathrm {OH_{ad}} \rightarrow \mathrm {H_2O}(\uparrow) '/> transformation occurs during the α–β phase transition by observing a decrease in OH<SUB>ad</SUB> resonance intensity.</P>
Characteristic Analysis of an HTS Flux-Switching Synchronous Generator With NI-Type HTS Field Coils
Kim, Jong Myung,Jang, Jae Young,Lee, SangGap,Hwang, Young Jin IEEE 2018 IEEE transactions on applied superconductivity Vol.28 No.3
<P>This paper presents the characteristics analysis of the flux-switching synchronous generator (FSG) applying no-insulation (NI)-type high-temperature superconducting (HTS) field coils. The HTS FSG can be cost effective, since the field coils and armature windings are both installed in the stator, while the rotor is only made of iron core with tooth. Along with low cost, since HTS field coils in the FSGs are located in the stationary part of the generator, FSG can be a solution for the design complexities of the excitation and cooling systems for HTS field coils. In addition, several studies on HTS coils without turn-to-turn insulation (NI) have been reported for HTS field coils for applying in electrical rotating machines. The NI-type winding technique enhances the stability of the HTS field coil since the overcurrent is automatically bypassed through the contacts between winding turns. Nevertheless, there is still an issue about whether the NI-type HTS field coil can be applied to the electrical rotating machines. In this study, we fabricated and tested an NI-type HTS field coil. In addition, a 600-kW HTS FSG was designed using a fundamental design process and the characteristics analysis of the generator was performed based on the test results of the fabricated NI-type field coil. The results show that the HTS FSG having NI-type HTS field coils is able to operate normally under normal operating conditions. However, the field current charging problem issue has been revealed through this study. Therefore, further research will need to improve the problem.</P>
Young Jin Hwang,Seungyong Hahn,SangGap Lee,Jae Young Jang,Jun Hee Han,Hunju Lee,Jaemin Kim,Hankil Yeom,Sangwon Yoon,Kyungmin Kim,Min Cheol Ahn Institute of Electrical and Electronics Engineers 2017 IEEE transactions on applied superconductivity Vol.27 No.4
<P>A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1-2 μm stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet.</P>