Rollover Cyclometalation Pathway in Rhodium Catalysis: Dramatic NHC Effects in the C–H Bond Functionalization

Kwak, Jaesung,Ohk, Youhwa,Jung, Yousung,Chang, Sukbok American Chemical Society 2012 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.134 No.42

<P>Organometallic chelates are readily obtained upon coordination of metal species to multidentate ligands. Because of the robust structural nature, chelation frequently serves as a driving force in the molecular assembly and chemical architecture, and they are used also as an efficient catalyst in numerous reactions. Described herein is the development of a Rh(NHC) catalytic system for the hydroarylation of alkenes and alkynes with 2,2′-bipyridines (bipy) and 2,2′-biquinolines; the most representative chelating molecules. Initially generated (bipy)Rh(NHC) chelates become labile because of the strong <I>trans</I>-effect of <I>N</I>-heterocyclic carbenes, thus weakening a rhodium–pyridyl bond, which is <I>trans</I> to the bound NHC. Subsequent rollover cyclometalation leads to the C–H bond activation, eventually giving rise to double functionalization of chelate molecules. Density functional calculations are in good agreement with our mechanistic proposal based on the experimental data. The present study elucidated for the first time the dramatic NHC effects on the rollover cyclometalation pathway enabling highly efficient and selective bisfunctionalization of 2,2′-bipyridines and 2,2′-biquinolines.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2012/jacsat.2012.134.issue-42/ja308205d/production/images/medium/ja-2012-08205d_0021.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja308205d'>ACS Electronic Supporting Info</A></P>

Implementation of Convolutional Kernel Function Using 3-D TiO_<i>x</i> Resistive Switching Devices for Image Processing

Kwak, Myonghoon,Park, Jaesung,Woo, Jiyong,Hwang, Hyunsang Institute of Electrical and Electronics Engineers 2018 IEEE transactions on electron devices Vol.65 No.10

<P>We implemented a convolution operation in a convolutional neural network by introducing a 3-D integrated TiO<SUB><I>x</I></SUB>-based resistive switching device (RSD) array to act as the kernel. The 3-D integrated TiO<SUB><I>x</I></SUB>-based RSD exhibits a gradual SET/RESET behavior, which enables multilevel characteristics. A pair of layers in the 3-D structured array is used to achieve the positive and negative weights. Based on these results, we demonstrated the <TEX>$\textsf {3} \times \textsf {3}$</TEX> Laplace kernel for edge detection using images from the Columbia Object Image Library data set in a simulator to validate the convolution operation.</P>

TiO_<i>x</i>-Based RRAM Synapse With 64-Levels of Conductance and Symmetric Conductance Change by Adopting a Hybrid Pulse Scheme for Neuromorphic Computing

Park, Jaesung,Kwak, Myunghoon,Moon, Kibong,Woo, Jiyong,Lee, Dongwook,Hwang, Hyunsang IEEE 2016 IEEE electron device letters Vol.37 No.12

<P>We propose TiOx-based resistive switching device for neuromorphic synapse applications. This device is capable of 64-levels conductance states because of their optimized interface between the metal electrode and the TiOx film. To compensate the change in switching power with increasing pulse number, we propose the use of fixed voltage and current pulses in potentiation and depression conditions, respectively. By adopting a hybrid pulse scheme, the symmetry of conductance change under both potentiation and depression conditions is shown to be significantly improved. Both the improved conductance levels and the symmetry of conductance change are directly related with enhanced pattern recognition accuracy, which is confirmed by a neural network simulation.</P>

Microstructural engineering in interface-type synapse device for enhancing linear and symmetric conductance changes

Park, Jaesung,Lee, Chuljun,Kwak, Myunghoon,Chekol, Solomon Amsalu,Lim, Seokjae,Kim, Myungjun,Woo, Jiyong,Hwang, Hyunsang,Lee, Daeseok IOP 2019 Nanotechnology Vol.30 No.30

<P>The origins of the nonlinear and asymmetric synaptic characteristics of TiO<I> <SUB>x</SUB> </I>-based synapse devices were investigated. Based on the origins, a microstructural electrode was utilized to improve the synaptic characteristics. Under an identical pulse bias, a TiO<I> <SUB>x</SUB> </I>-based synapse device exhibited saturated conductance changes, which led to nonlinear and asymmetric synaptic characteristics. The formation of an interfacial layer between the electrode and TiO<I> <SUB>x</SUB> </I> layer, which can limit consecutive oxygen migration and chemical reactions, was considered as the main origin of the conductance saturation behavior. To achieve consecutive oxygen migration and chemical reactions, structural engineering was utilized. The resultant microstructural electrode noticeably improved the synaptic characteristics, including the unsaturated, linear, and symmetric conductance changes. These synaptic characteristics resulted in the recognition accuracy significantly increasing from 38% to 90% in a neural network-based pattern recognition simulation.</P>

Ir(III)-Catalyzed Mild C–H Amidation of Arenes and Alkenes: An Efficient Usage of Acyl Azides as the Nitrogen Source

Ryu, Jaeyune,Kwak, Jaesung,Shin, Kwangmin,Lee, Donggun,Chang, Sukbok American Chemical Society 2013 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.135 No.34

<P>Reported herein is the development of the Ir(III)-catalyzed direct C–H amidation of arenes and alkenes using acyl azides as the nitrogen source. This procedure utilizes an in situ generated cationic half-sandwich iridium complex as a catalyst. The reaction takes place under very mild conditions, and a broad range of sp<SUP>2</SUP> C–H bonds of chelate group-containing arenes and olefins are smoothly amidated with acyl azides without the intervention of the Curtius rearrangement. Significantly, a wide range of reactants of aryl-, aliphatic-, and olefinic acyl azides were all efficiently amidated with high functional group tolerance. Using the developed approach, <I>Z</I>-enamides were readily accessed with a complete control of regio- and stereoselectivity. The developed direct amidation proceeds in the absence of external oxidants and releases molecular nitrogen as a single byproduct, thus offering an environmentally benign process with wide potential applications in organic synthesis and medicinal chemistry.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2013/jacsat.2013.135.issue-34/ja406383h/production/images/medium/ja-2013-06383h_0019.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja406383h'>ACS Electronic Supporting Info</A></P>

한국의 스마트 그리드 보안현황과 사이버 보안 추진방향

곽지섭(Jisup Kwak),김완홍(Wanhong Kim),강순희(Soonhee Kang),김재성(Jaesung Kim) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7

최근 스마트그리드에 대한 관심이 고조되고 국가에서 정책적으로 스마트그리드를 추진하고 있다. 한국형 스마트그리드는 영역별로 비즈니스모델의 도출이 가능하도록 전력망-소비자-운송-신재생-서비스의 5개 영역으로 구분하여 추진하고 있고 관련 기술(전력 · 통신 · 반도체 · 디스플레이 · 가전산업 등) 또한 세계적인 경쟁력을 갖추고 있으나 원천기술 · 부품소재에 대해서는 선진국에 비해 뒤처지고 있다. 현재까지의 전력망은 폐쇄망을 기본으로 하고 있어 보안문제가 크게 부각된 적이 없으나 스마트그리드가 전력인프라에 정보 · 통신인프라가 융합된 새로운 비즈니스 플랫폼이기때문에 기존 정보 · 통신산업에서 발생했던 보안문제가 나타날 우려가 높다. 이에 따라 한국에서는 기존의 “주요정보통신 기반시설 보호지침” 및 “전력계통 신뢰도 및 전기품질기준 유지기준”과 2010년 입법예정인 “지능형전력망 구축 및 이용 촉진에 관한 법률”을 통해 스마트그리드의 보안문제에 대처하고 있다. 현재의 폐쇄형 전력망도 침해사고가 증가하고 있는 추세여서 스마트그리드는 더더욱 이에 대한 대처가 필요하다. 전기의 공급이 중단되는 경우, 그 손실은 산정하기 어려울 정도로 크므로 사이버 테러로 인한 비정상적 제어 또는 소프트웨어 에러에도 불구하고 소비자에게 지속적인 전력공급이 가능할 수 있도록 Failsafe 개념의 도입이 필요하다. 스마트그리드는 초기 설계시부터 보안 이슈를 전면에 내걸고 문제를 해결하면서 개발을 추진해야 미래의 효율적 에너지 이용과 저탄소 녹색성장을 이룰 수 있을 것이다.

Improved Conductance Linearity and Conductance Ratio of 1T2R Synapse Device for Neuromorphic Systems

Moon, Kibong,Kwak, Myounghoon,Park, Jaesung,Lee, Dongwook,Hwang, Hyunsang IEEE 2017 IEEE electron device letters Vol.38 No.8

<P>We report on a 1-transisor/2-resistor (1T2R) synapse device with improved conductance linearity and conductance ratio under an identical pulse condition for hardware neural networks with high pattern-recognition accuracy. Utilizing an additional series-connected resistor, the conductance linearity of a synapse device was significantly improved owing to the reduced initial voltage drop on an resistive RAM (RRAM) device during depression conditions. Moreover, to maximize the conductance ratio of a synapse device, we utilized a steep subthreshold region of an MOSFET by a parallel connection of an RRAM and a transistor. A small change in voltage on the RRAM directly controlled the gate bias of the MOSFET, which causes a large change in the drain current. Compared with a conventional RRAM synapse device, the 1T2R synapse device shows an improved conductance linearity and conductance ratio (>x100). Finally, we confirmed an excellent classification accuracy by using a neural network simulation based on a multilayer perceptron.</P>

국내 인바운드 창업 프로그램에 지원한 사하라 이남 아프리카 스타트업 연구: 현황과 과제

이종현(Jonghyun LEE),곽재성(Jaesung KWAK) 한국아프리카학회 2020 한국아프리카학회지 Vol.61 No.-

본 연구의 목적은 국내 인바운드 창업 프로그램에 지원한 사하라 이남 아프리카 스타트업을 대상으로 “왜 아프리카 스타트업은 경쟁력이 없을까?”라는 문제에 답을 제시하는 것이다. 이를 위해 기존 문헌을 중심으로 창업 및 액셀러레이팅에 대한 이론적 검토 및 선행 연구 경향을 분석하고, 국내 대표 인바운드 액셀러레이팅 프로그램의 지원서 설문조사, 서류평가 결과, 그리고 비대면 전문가 인터뷰를 통해 사하라 이남 아프리카 스타트업의 경쟁력 현황과 시사점을 도출하였다. 연구결과 아프리카 스타트업 생태계는 타 대륙보다 경쟁력이 부족한 부분이 있지만, 성장 가능성이 큰 영역임을 확인할 수 있었다. 특히, 스타트업이 사회적인 문제를 해결하고 개선하는 중요 역할을 하고 있어, 국제개발협력의 다양한 지원 수단을 통해 스타트업을 적절히 육성하고 사회경제 분야에 이바지할 수 있도록 관심을 가져야 한다. 본 연구는 국내 시장에 관심이 있는 스타트업에 대한 연구가 부족한 상황에서 향후 미래 성공 가능성이 있는 아프리카 스타트업을 대상으로 진행한 의미가 있으며, 장기적으로 개별 스타트업 생태계에 관한 다양한 연구의 지평을 열었다는 점에서도 의의를 찾을 수 있다. This study has its focus on the issue of the competitiveness of Sub-Saharan African start-ups that applied for inbound entrepreneur program in Korea. As for the research methodology. the study adopts desk review, survey and in-depth interviews. The results of the study indicate that Sub-Saharan start-ups have shown less competitiveness than those from other regions, but with a room for future development. Furthermore, as start-ups are increasingly playing an important role in solving and improving social problems, it is necessary to pay attention to the Sub-Saharan business ecosystem to contribute to the social economic standard of the region. This study has an importance in drawing implications about the way to promote start-ups through development cooperation.

Bax-induced cell death of Arabidopsisis meditated through reactive oxygen-dependent and -independent processes

Baek, Dongwon,Nam, Jaesung,koo, Yoon Duck,kim, Doh Hoon,Lee, Jiyoung,jeong, Jae Cheol,Kwak, Sang-soo,chung, Woo Sik,lim, Chae Oh,bahk, Jeong Dong,hong, Jong Chan,lee, Sang Yeol,Kawai-yamada, Maki,Uchi Springer-Verlag 2004 Plant Molecular Biology Vol.56 No.1

Mechanistic Studies of the Rhodium-Catalyzed Direct C–H Amination Reaction Using Azides as the Nitrogen Source

Park, Sae Hume,Kwak, Jaesung,Shin, Kwangmin,Ryu, Jaeyune,Park, Yoonsu,Chang, Sukbok American Chemical Society 2014 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.136 No.6

<P>Direct C–H amination of arenes offers a straightforward route to aniline compounds without necessitating aryl (pseudo)halides as the starting materials. The recent development in this area, in particular in the metal-mediated transformations, is significant with regard to substrate scope and reaction conditions. Described herein are the mechanistic details on the Rh-catalyzed direct C–H amination reaction using organic azides as the amino source. The most important two stages were investigated especially in detail: (i) the formation of metal nitrenoid species and its subsequent insertion into a rhodacycle intermediate, and (ii) the regeneration of catalyst with concomitant release of products. It was revealed that a stepwise pathway involving a key Rh(V)–nitrenoid species that subsequently undergoes amido insertion is favored over a concerted C–N bond formation pathway. DFT calculations and kinetic studies suggest that the rate-limiting step in the current C–H amination reaction is more closely related to the formation of Rh–nitrenoid intermediate rather than the presupposed C–H activation process. The present study provides mechanistic details of the direct C–H amination reaction, which bears both aspects of the inner- and outer-sphere paths within a catalytic cycle.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2014/jacsat.2014.136.issue-6/ja411072a/production/images/medium/ja-2013-11072a_0019.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja411072a'>ACS Electronic Supporting Info</A></P>