Quantum mechanical investigations of the mechanisms and selectivities of synthetic organic reactions --- From organocatalysis to transition metal catalysis to substrate controlled asymmetric reactions

Cheong, Paul Ha-Yeon University of California, Los Angeles 2007 해외박사(DDOD)

Chapter 1 recounts the development of catalysts for Mannich-type reactions that afford anti-products with excellent diastereo- and enantioselectivities. Based on principles gained from the study of (S)-proline and (S)-pipecolic acid catalyzed Mannich-type reactions that afford enantiomerically enriched syn-products, (3 R,5R)-5-methyl-3-pyrrolidinecarboxylic acid (RR5M3PC) has been designed to catalyze the direct enantioselective anti-selective Mannich-type reactions. In accord with the design principles and in quantitative agreement with the theoretical predictions, reactions catalyzed by this catalyst afforded anti-products in good yields with excellent diastereo- and enantioselectivities (anti:syn 94:6--98:2, >97-->99% ee). This work has been published in two journals---Mitsumori, S.; Zhang, H.; Cheong, P. H.-Y.; Houk, K. N. Tanaka, F.; Barbas, C. F., J. Am. Chem. Soc. 2006, 128(4), 1040-1041 and Cheong, P. H.-Y.; Zhang, H. L.; Thayumanavan, R.; Tanaka, F.; Houk, K. N.; Barbas, C. F., Org. Len. 2006, 8(5), 811-814. Chapter 2 describes the computational investigations of the Hajos-Parrish-Eder-Sauer-Wiechert reaction catalyzed by various proline derivatives. Where available, quantitative agreements with experimental stereoselectivities were observed. Predictions were made for catalysts that have not been evaluated yet. Chapter 2 was published in two journals---Cheong, P. H.-Y.; Houk, K. N.; Warrier, J. S.; Hanessian, S., Adv, Synth. Cat. 2004, 396(9-10), 1111-1115 and Cheong, P. H.-Y.; Houk, K. N., Synthesis 2005, (9), 1533-1537. Chapter 3 is the density functional theory study of the mechanisms, transition structures, regioselectivity and stereoselectivity of proline-catalyzed alpha-aminoxylation reactions. The most favorable transition structure involves the nucleophilic attack of the (E)-proline enamine to the oxygen of the nitrosobenzene with proton transfer from the carboxylic acid to the nitrogen. Enamine attacks to the oxygen are favored over the attack on the nitrogen due to the greater basicity of the nitrogen. Previously proposed zwitterionic enaminium pathways are highly disfavored due to the energetic penalty associated with charge separations. This has been published in Cheong, P. H.-Y.; Houk, K. N., J. Am. Chem. Soc. 2004, 126(43), 13912-13913. Chapter 4 discusses the torsional steering control of stereoselectivity in the key epoxidation step of Guanacastepene A synthesis of Danishefsky. In this particular epoxidation reaction, the transition structure energetic difference is enhanced by the great asynchronicity of the forming C-0 bonds that intensifies the torsional interactions. This has been published in Cheong, P. H.-Y.; Yun, H.; Danishefsky, S. J.; Houk, K. N., Org. Lett. 2006, 8(8), 1513-1516. Chapter 5 illustrates how substantial differences in reductive elimination barriers control the ease of organometallic reactions. Rhodium dimer [Rh(CO) 2Cl]2 efficiently catalyzes the intra- and intermolecular (5+2) reactions of vinylcyclopropanes with alkynes and allenes, but not alkenes. This difference in reactivity is attributed to the difficulty of reductive elimination for the alkene. The computed reductive elimination transition structures show that the participation of the second pi-orbital in acetylene and allene reduces the barrier by 9∼45 kcal/mol, compared to ethylene, for which no such interactions are possible. Chapter 6 details the mechanism and origins of stereoselectivity for the Rh(I)-chiral bisphosphine hydrogenation of unprotected enamines. The hydrogenation step is found to be rate-determining. The origins of stereoselectivity were investigated by computing the hydrogenation transition structure involving the Josiphos ligand---the actual bisphosphine ligand used in the industrial process---and its various derivatives. Chapter 7 reports the mechanisms and origins of selectivity for the tris-gold phosphine oxonium fluoroborate, [(Ph3PAu)3O]BF 4, catalyzed rearrangement of 1,5-allenynes to cross-conjugated trienes. Experimental and computational evidence shows that the ene reaction proceeds through a unique nucleophilic addition of an allene double bond to a gold phosphine complexed gold phosphine acetylide, followed by a 1,5-hydrogen shift.

Unsung voices : the transformation of writing and identity of Korean ESL students in U.S. secondary schools

Cheong, Cheong-hwa UMI Dissertation Services 2010 국내박사

PLC r2, a novel signaling component of high affinity IgE receptor through the amino terminal of βsubunit / Cheong Ho 著

Cheong, Ho Chonnam National Univ. Graduate School 1999 국내박사

Strukturuntersuchungen am Oberflaechenprotein des Archaebakteriums Methanoplanus limicola mit Hilfe von Elektronenmikroskopie

Cheong, Gang-Won Universitat Muenchen 1993 해외박사

본 논문에서 Archaebacteria인 Methanoplanus limicola(DSM 2279)의 최외각 단백질막(surface protein layer, S-layer)에 대한 생화학적 특성과 전자현 미경의 여러가지 방법을 이용하여 그의 구조에 대해 연구하였다. 냉동 파기법으로 얻은 replica와 ultra thin section의 전자현미경의 관찰 로 M. limicola의 세포막의 구조와 최외각 단백질 막의 구조에 대해 고찰하 였다. 분리한 단백질막을 음착색법(negative stain)으로 착색한 후, tilt series의 기술과 image analysis등을 이용하여 3차원 구조의 모델을 얻었다. M. limicola 의 최외각 단백질 막의 분자량은 SDS 전기영동법으로 당이 포함 된 당단백질(135 kDa)과 탈당된(deglycosylated) 단백질(115 kDa)의 분자량을 결정하였다. Lquid chromatography/mass spectrometry등을 이용하여 neutral sugar의 정량비와 정량을 분석하였으며, 또한 ninhydrin의 방법으로 amino sugar의 양을 결정하였다. 고분해능(high resolution)의 구조를 얻기 위해 서, 냉동 건조한 후 금속막을 입힌 후 공기와의 접촉없이 곧 전자현미경으로 옮긴 후, image을 얻었다. 이 image을 multivariate statistical analysis 와 correlation coefficient function 등을 이용하여, S-layer 당단백질의 안쪽면과 바깥쪽면의 각각의 symmetry를 밝혔다. 또한 image로부터 구조의 재구성법으로 각각의 면에 대한 3차원 구조를 얻었고, 이에 scanning tunneling microscopy로 얻은 당단백질막의 두께로 S-layer 당단백질의 양쪽 면구조를 결합하여 3차원 구조를 제시하므로, 단백질 3차원 구조연구에 대한 새로운 방법을 제시하였다. 보다 더 자연적인 상태에서 또 고분해능의 구조 를 연구하기 위해서 정재된 단백질을 급속냉동(액체질소 온도) 시킨 후, 초저 온(-170℃ 이하)에서 전자현미경 즉 cryo electronmicroscopy와 low dose 및 spot-scan등의 방법으로 전자현미경한 것을 image analysis로 고분해능(8 A) 의 구조를 얻었다. 이로써 S-layer 단백질 막의 기능에 대해 보다 많은 이 해가 가능하므로써 이를 응용으로 발전 시키는데 도움이 될 것이다. We consider two types of product form closed queueing networks (CQN); with state-independent exponential server queues; with state-dependent server queues. We first extend the dual property of queueing systems, from a single queue to a closed network of queues. We also show that a simple recursion for the throughput can be derived from the dual model of the single server case. Relaxing the dependency of round-trip times, we also propose an approximate dual model, which may be used to derive efficient algorithms for network performance measures. Next we provide some properties of CQN related to the network throughput and the normalization constant which may be of independent interest. We establish a set of simple closed form upper bounds on the network throughput. That is, let be a positive integer number, and TH(n) be the throughput of the network with n customers. We show that UB,, are upper bounds on the throughput of the network. When n = 2 is the well known result of Dallerg [12]. We also present a simple closed form lower bound on the network throughput, We show that LB is much sharper than the upper bound of Zahojan [(ill. We also provide an improved version of the Fixed Population Mean (FPM) proposed by Whitt [57],, which is conjectured to be a lower bound on the thmighput. We prove that it is in fact the lower bound for some cases. Each bound cm the throughput we propose in this thesis may be directly used to obtain the corresponding bound on the response (sojourn) time. Finally, based on the lower bound conjecture we reformulate a new conjkcture called the Migrating Critical Point (MCP) conjecture. The MCP conjecture asserts that the successive critical points of certain rational functions migrate at an accelerating rate. We provide a proof of MCP in the polynomial case, and some other special cases where the rational functions have exactly two poles.

Isolation of a receptor for an elicitor of phytoalexins

Cheong, Jong Joo The University of Georgea 1993 해외박사

식물에 병변을 일으키는 진균류의 세포벽에서 유래한 소당류 유도신호체가 식물의 항생물질을 생성케 하는 기작을 식물세포의 신호체 인지체계의 모형으 로 사용 하였다. 일련의 실험들은 대두(콩) 세포로 부터 hepta-β-glucoside( HG)[7개의 포도당으로 구성된 소당류 분자]를 특이하게 인지하여 결합하는 수 용체를 확인하고 정제할수 있도록 구상되었다. 화학합성으로 얻어진 일군의 소당류들을 사용하여 구조와 활성의 관계를 조 사한 결과,HG의 비활성(비환원성) 부위의 분지된 삼당류의 구조와 분지당의 분포 양상이 소당류 유도신호체의 유도활성에 핵심적인 구조요소가 됨을 알게 되었다. 반면에 환원성 극단의 포도당은 전체물질의 활성에 영향을 주지 않고 화학적 변환이 가능하였다. 따라서 HG에 tyramine을 결합시킨후 이에 방사성 요오드를 부가하여 이를 대두 근막과의 결합반응 시험에 사용 하였다. 방사성 HG의 결합반응은 포화적,가역성 및 고도의 친화력을 보였다. (Kd=0. 75nM). HG 와 구조적으로 관련된 다양한 소당류를 가지고 경쟁저해반응을 실험한 결과 이 결합반응의 특이성이 증명 되었다. 이들 소당류의 결합강도와 유도신호체 로서의 활성 사이에 엄밀한 상관관계가 관찰되었다. 그러므로 이러한 결과로 확인된 신호결합 단백질은 HG에 대한 생리적 수용체로서의 기준을 충족하고 있다. 이 신호유도체를 결합하는 수용체는 식물의 원형질막에 융합되어 있는 (당) 단백질인 것으로 보인다. 이 신호결합 단백질을 비이온성 세제인 n-dode cylsucrose를 사용하여 용해하였다. 용해된 신호결합 단백질은 원래의 막에 융합된 형태에서 관찰된 구조 특이성 및 고도 친화력(Kd=1. 8nM)을 유지하고 있었다. 이 단백질을 크로마토그래피로써 부분 정제하여 본 결과,분자량 500 KDa 이상의 세제-단백질의 복합체의 형태로 존재하고 있음을 알게 되었다. 이 신호결합 단백질을 순수하게 정제하고 성질을 자세히 연구함으로써 HG가 대두 에 있어서 항생물질의 합성을 유도하는 신호전달체계를 어떻게 활성화 시키는 지를 분자 수준에서 이해하도록 하는 연구방향을 정립하게 할 수 있다.

Ein Beitrag zur Friedenserziehung aus der Sicht der Dritten Welt

Cheong Yoo Seong Ludwing-Maximilians-Univ Muchen 1987 국내석사

KOMPSAT-2 고해상도 위성영상의 상대복사보정 및 검증

Jin, Cheong Gil 부경대학교 대학원 2012 국내석사

Korea possesses Korea Multi-Purpose SATellite(KOMPSAT)-2 which can acquire high resolution image of 1 meter. Those researches utilizing these high resolution image can draw reliable result only when validation and calibration of standard images are preceded, thus considerable effort to maintain quality of satellite image data. Especially, reliability of theme image that are prepared with technique using reflection of ground surface and solar radiation is depend on the validation and calibration at atmospheric radiation level. The purpose of this study is to validate and supplement radiometric calibration coefficient of KOMPSAT-2 image with relative radiometric calibration method. For the purpose, satellites which KOMPSAT-2 can refer were selected and the images taken from same target at the same day were compared. First of all, IKONOS and QuickBird Satellites whose resources and spectral bands were similar as KOMPSAT-2 were chosen and similarity of spectral response was figured out to obtain more accurate results. The comparison result of spectral response showed that area and range of lower part of graphs from each satellite were different that made matching rate low each other to some extent. In spite of this result, since more than 90% of matching rate could be obtained and radiation energy sensed by satellite sensor and lower area of spectral response graph were in proportion, it was thus judged that research with images from two reference satellites can be carried out. After that, the data for image comparison was sampled as DN average value using square polygon size 8m x 8m from arbitrary target. And then only those data whose deviation were within 2.5% were used by calculating standard deviation of overlapping pixels with lattice. This effort was made to improve accuracy of data by reducing geometric error of satellite and by removing effect caused by scattering that was existed in sampled pixels. The coefficient which has been used on reference image from reference satellites during relative radiometric calibration of KOMPSAT-2 with preset data was radiometric calibration coefficient which is provided during satellite image procurement. The coefficients that were used in images from reference satellites were validated through sufficient research, but these again went through validation process by absolute radiometric calibration. The absolute radiometric calibration result was quoted from field campaign data performed by Korea Aerospace Research Institute(KARI). Radiometric calibration coefficient of KOMPSAT-2 obtained by relative radiometric calibration technique were finally calculated as 0.0114294 at Blue Band, 0.0139369 at Green Band, 0.0148859 at Red Band, and 0.0151555 at Near Infra-Red Band. These results are expected to ensure reliability of various theme information generated by KOMPSAT-2 satellite through relative radiometric calibration and to attribute in reliability improvement with absolute radiometric calibration by applying them on KOMPSAT-3 which is due launch in future.

JAPANESE-SOUTH KOREAN RELATIONS UNDER AMERICAN OCCUPATION, 1945-1952 : THE POLITICS OF ANTI-JAPANESE SENTIMENT IN KOREA AND THE FAILURE OF DIPLOMACY

CHEONG, SUNG-HWA 1988 국내박사

(The) effects of Bouea macrophylla extract on prevention of photoaging and improvement of skin barrier function

Cheong, Yongin Graduate School, Yonsei University 2017 국내석사

자외선 조사에 의해 발생한 피부 광노화는 주름형성, 쳐짐, 건조함, 피부두께 증가와 같은 증상으로 대표되며, 이는 세포외기질 분해와 밀접한 관계를 가지고 있다. 자외선 조사로 인해 MAPKs/AP-1 복합체 신호전달경로가 활성화되고 이를 통해 주름형성과 밀접한 관련이 있는 matrix metalloproteinases (MMPs)의 발현이 촉진된다. 또한, 활성화된 AP-1 복합체는 TGF-β/Smad 신호전달경로를 억제하여 콜라겐 합성을 저해한다. Bouea macrophylla는 옻나무과의 식물로 maprang 혹은 marian plum이라고도 불리우며, 이 식물의 항산화 효과는 이미 보고된 바 있다. 항산화 효과와 광노화 억제 효과는 밀접한 관계를 가진다고 발표한 논문들이 학계에 발표된 바 있어, Bouea macrophylla가 항광노화 효과에 효과적이라고 가정하였다. 이에 대한 연구는 현재까지 진행된 적 없어, 본 연구진은 Bouea macrophylla 추출물이 광노화와 피부장벽기능에 미치는 영향에 관한 실험을 진행하였다. UVB를 조사한 군과 비교하여, BME는 주름형성 억제, 피부두께 감소, 탄력성 증가에 효과적이었다. BME는 콜라겐 합성 유전자와 TGF-β/Smad 신호전달경로를 촉진하여 UVB조사에 의해 감소된 콜라겐 함량을 증진시켰다. BME는 MAPKs/AP-1 신호전달경로를 조절하여 MMP-3과 MMP-13의 발현을 증진시킬 뿐 아니라, MMP-2와 MMP-9의 발현 및 활성을 억제하였다. 또한, BME는 각질세포막 단백질과 필라그린 분해와 합성에 관련된 단백질의 발현을 조절하여 보습을 증진시켰다. 결론적으로, BME는 MAPKs/AP-1 신호전달경로를 억제하여 광노화로 인한 피부손상을 완화하였으며, 피부장벽기능과 관련된 단백질의 발현량을 조절해 피부장벽기능의 향상한다는 사실을 세포실험과 동물실험을 통해 확인할 수 있었다. BME는 광노화 및 피부장벽기능 감소와 관련된 현상들을 효과적으로 억제하므로, 화장품과 건강기능식품의 소재로 사용될 수 있을 것으로 예상된다. Ultraviolet B (UVB) irradiation is a major factor in skin photoaging, which stimulates wrinkle formation, sagging, dryness, and thickness. The mechanisms of photoaging are closely related to degradation of the extracellular matrix (ECM). UVB irradiation stimulates the mitogen-activated protein kinases (MAPKs)/activator protein-1 (AP-1) complex signaling pathway that promotes matrix metalloproteinases (MMPs) expression. Activation of the AP-1 complex also inhibits the transforming growth factor-β (TGF-β)/Smad signaling pathway that is related to collagen synthesis. Bouea macrophylla belongs to Anacardiaceae, which is also called maprang or marian plum. A previous study reported that Bouea macrophylla has an antioxidant property. This antioxidant property is associated with anti-photoaging effect. Therefore, we hypothesized that it might have anti-photoaging effect, but its preventive effect on photoaging has not been investigated yet. Thus, we evaluated the effects of Bouea macrophylla ethanol extract (BME) on photoaging and skin barrier function in vitro and in vivo. In compared to UVB-irradiated mice, BME significantly ameliorated wrinkle formation, skin thickening, and skin inelasticity. It also upregulated COL1A1, COL3A1, COL4A1, and COL7A1 mRNA levels through activation of the transforming growth factor-β (TGF-β)/Smad pathway, thereby recovering the content of collagen fiber reduced by UVB irradiation. Further, BME suppressed UVB-induced matrix metalloproteinase (MMP)-3 and MMP-13 expression and also inhibited MMP-2 and MMP-9 activity by mediating mitogen-activated protein kinases (MAPKs)/activator protein-1 (AP-1) complex. BME also improved skin moisture content by stimulating the expression of cornified envelope proteins (loricrin, involucrin, and transglutaminase), filaggrin and filaggrin processing enzymes (caspase-14, matriptase, and prostasin). This study shows that BME suppresses MMPs expression and stimulates collagen synthesis pathway through inactivation of MAPKs/AP-1 signaling pathway. Also, BME improves skin barrier function through regulation of the cornified envelope proteins, filaggrin and profilaggrin degradation. Thus, Bouea macrophylla can be a cosmeceutical and nutraceutical candidate for anti-photoaging and improvement of skin barrier function.

An inquiry into a plausible source of the differences between functionlism and reproduction theory in education

Cheong, Jeangon University of Illinois at Urbana-Champaign 1986 해외박사