Application of Photoactive Diruthenium Catalyst for New Organic Reactions: Syntheses of Imines, Isoquinolines, and Vinylstannanes

Gupta, Sreya POSTECH 2014 국내박사

Light had the potential to serve as an inexpensive, abundant, renewable, and nonpolluting reagent for chemical transformations. Thus developing new methodologies by employing metal-catalyst activated by visible light is the pivotal interest in the field of organic synthesis. In this thesis, we investigated important chemical transformation catalyzed by carbonyl bridged diruthenium complexes which is activated by visible light source. In chapter 1, Ru-catalyzed synthesis of N-unsubstituted imines from easily available alkyle azides under the photolytic condition has described. N-unsubstituted imines were generated by removal of N2 gas from azide precursors and subsequent migration of hydrogen atom under the house hold fluorescent light. This novel protocol has shown broad synthetic scope to construct various N-unprotected imines including unprecedented enolizable substrates. Mild reaction conditions used in this protocol even allowed obtaining fundamental physical parameters of N-unprotected imines, such as, existence of dynamic geometric isomers in the solution phase and dissociation energy of imino N-H bond. This novel synthetic route was successfully applied in one-pot imine generation/allylation sequence by using allylboron reagents; directly N-unprotected allylamines were formed without any undesirable side reactions. The above one-pot sequence has shown greater efficiency over prevailing methodologies in terms of enantio- and diastereoselectivity. Furthermore, this protocol also effective to synthesize N-unsubstituted imidates from various azidoethers. This is the first report of imidate synthesis in neutral reaction conditions which allowed constructing imidates having acid-labile functionality. Chapter 2 describes the Ru/Rh-tandem catalysis to synthesize isoquinoline from arylazides and internal alkynes by direct C-H bond activation. N-unsubstituted arylimines generated from the corresponding azides by the ruthenium catalysis were used as a directing group for rhodium-catalyst to activate the C-H bond at ortho-position of aromatic ring. Subsequent addition of various internal alkynes produces N-annulated isoquinolines. The essential merits of this cascade protocol are broad scope of applicable benzylic azides, including those having carbonyl and chiral functionalities. Additionally, this protocol is completely atom-economical as N2-gas is the only the byproduct. Furthermore, N-unsubstituted imidate synthesized by Ru-catalyst II from the corresponding azidoethers, also turned out to be the successful entity for direct synthesis of 1-alkoxyisoquinolines. The mechanism of the above transformation was established through the isolation and characterization (X-ray crystallography structure) of the important unknown intermediates. Previously we reported the hydrosilylation of aldehydes1 by using ruthenium catalyst under fluorescent light condition. We expected this catalyst can activate other metal-hydride species too. In the chapter 3, ruthenium-catalyzed addition of tin hydride to various internal alkynes (hydrostannation) under fluorescent light was described. The reaction was initiated by the formation of ruthenium hydride and tin radical species under the illumination of light. In the termination step, tin-radical and the hydrogen from ruthenium hydride species were added to the alkynes in anti-stereoselective way. In general, control the regio- and setreoselectivity of hydrostannation reaction is the formidable challenge. However, in above ruthenium photocatalyzed system, (Z)-β-selective vinylstannanes were obtained selectively for various internal alkynes and shown better activity over well-known radical initiators such as AIBN (azobisisobutyronitril) or BEt3 (triethylborane). To obtain insight into the hydrostannation mechanism, we conducted various experiments. The outcome of various control experiments strongly suggested the insolvent of radical mechanism and the formation of ruthenium-hydride (VI) as a key intermediate species under the fluorescent light. Additionally, the recyclability of the ruthenium catalyst added extra advantage of this novel methodology. 1 Do, Y.; Han, J.; Rhee, Y. H.; Park. J. Adv. Synth. Catal. 2011, 353, 3363.

Development of small molecule and responsive polymer based colorimetric and fluorometric chemosensors

Gupta, Moumita University of Ulsan 2018 국내박사

Receipt of lump-sum distributions from retirement plans

Gupta, Shamlall University of Minnesota 1993 해외박사

Effekte der nicht-depolarisierenden Muskelrelaxanzien Pancuronium, Vecuronium, Pipecuronium und Atracurium auf den Katecholaminhaushalt des Ventrikelmyokards

Gupta, Robin Sen Universit¨at Hamburg 1997 국내박사

Digital X-ray Source Based on Carbon Nanotube Field Emitters; a Paradigm Shift in Medical X-ray Technology

GUPTA AMAR PRASAD 경희대학교 대학원 2023 국내박사

The art of Physics is understanding the phenomena and offering the new inventions to a real world problem. Continuously, driven by the question of HOW, WHY AND WHAT, the modern day Physicists do not just sit down and solves the equations of universe on paper, rather they raise from the chair and strive to invent things better than engineers could. This dissertation complies the series of works that offers and alternative solution to conventional X-ray source, which is more efficient, novel and well-suited with this generation of time. Since X-rays were discovered more than a century ago, most of the engineering techniques used to make X-ray sources haven't changed much. There haven't been many important technological improvements since the invention of thermionic electron sources, which are still utilized in practically all X-ray applications due to their ease of fabrication. However, nanomaterials and their efficient ways of fabrication have made it possible to replace traditional thermionic devices with cold cathode electron sources (field electron emission). The thermionic process of electron emission is inefficient because of the lagging time between heating up the filament and producing electrons. Thus, the filament-based thermionic emission is called analogue as the perfect pulses of electrons cannot be generated. Nanomaterials such as CNTs, composites of CNTs with other elements, metal tips, graphene, nanodiamond, silicon tips or any other nanostructure with high aspect ratio can be utilized to make cold cathode X-ray source based on field electron emission (FEE) process. In field emission-based cold cathode X-ray source, free electrons are usually extracted from the tips of nanostructure (cathode) inside a vacuum due to localized high electric field produced by an external voltage from gate or extractor. Because of the voltage dependence of the FEE process, the X-ray source can be digitalized with perfect pulses while using less power than filament-based X-ray sources. The smaller, lighter X-ray machines can be built with the digitalized X-ray system, which also emits less radiation. The fact that digital X-ray sources have rapid response times and precise radiation dose pulses is one of their most crucial features. Additionally, digital X-ray sources based on nanomaterials offer a significant opportunity for the effective integration of distributed X-ray sources into a single system. For these above reasons, researchers and engineers from all around the world are looking for a stable cold cathode electron emitter that can replace the hot filament inside the X-ray source. The work in my dissertation tries to find a way to connect the making and optimizing of X-ray source based on Carbon Nanotubes for high-speed radiographic imaging, especially with the goal of transforming the medical X-ray technology. This dissertation research includes the growth of carbon nanotubes on metal substrate for easier and economic way to mass produce the electron emitters. It also shades light on how metal substrate will advent the race of 3D field emitter. Using these field emitters and filament, open-type and closed type X-ray tubes are fabricated for medical purposes. Finally, I summarize this work's findings and outline the subsequent actions that will be taken to build the foundation for a new paradigm of X-ray source.

Essays in Finance

Gupta, Abhinav ProQuest Dissertations & Theses New York Universit 2022 해외박사(DDOD)

This dissertation is comprised of three chapters in finance. The first chapter examines how labor mobility frictions affect firm monopsony power and entrepreneurship. I exploit a natural experiment in the US immigration system that unexpectedly increased Green Card related job-switching frictions for Indian and Chinese immigrants in October 2005. Using matched employee-employer data, I confirm that this shock reduced inter-firm mobility for these employees. Reduced labor mobility increased incumbent firm value, with $28.7 billion in abnormal stock returns for firms with Indian and Chinese employees ten days following the announcement. A slowdown in internal promotions for Indian and Chinese employees suggests enhanced monopsony power as the primary channel. Immigration related mobility restrictions lowered the propensity of Indian and Chinese employees to join startups, reducing new firm formation and the funding/IPOs of existing startups for firms/markets more dependent on these employees. These results provide first causal evidence of the impact of labor mobility on business dynamism. Relative to conventional private ownership, private equity (PE) creates higher-powered incentives to maximize profits. The second chapter, co-authored with Atul Gupta, Sabrina Howell, and Constantine Yannelis, studies how PE affects the performance of U.S. nursing homes, an increasingly important sector where we exploit patient-level Medicare data. PE-owned nursing homes appear to select less risky patients, so we use distance as an instrument to control for unobserved selection. We find that PE ownership increases short-term mortality by 13%, reduces other measures of patient well-being, and increases revenue per patient by 10%. Clinical and operational changes including reductions in nursing staff and lower compliance with standards explain the declines in patient welfare.The final chapter, co-authored with Michael Bailey, Sebastian Hillenbrand, Theresa Kuchler, Robert Richmond, and Johannes Stroebel, examines the correlations between international trade and social connections. We use de-identified data from Facebook to construct a new and publicly available measure of the pairwise social connectedness between 170 countries and 332 European regions. We find that two countries trade more when they are more socially connected, especially for goods where information frictions may be large. The social connections that predict trade in specific products are those between the regions where the product is produced in the exporting country and the regions where it is used in the importing country. Once we control for social connectedness, the estimated effects of geographic distance and country borders on trade decline substantially.

아시아 여성 농민들의 씨앗 지키기 운동 : 한국의 전여농과 인도의 나바단야를 중심으로

Gupta, Snigdha 서울대학교 2020 국내석사

Investigation on Performance Enhancement of CNT Field Emitter Grown Directly on Fe/Ni/Cr Alloy Substrate for X-ray Source Applications

GUPTA AMAR PRASAD 경희대학교 대학원 2020 국내석사

Over the past 20 years, carbon nanotubes (CNTs) have attracted a wide range of scientific communities due to its extraordinary properties. This unique carbon allotrope possesses exceptional properties and its synthesis can be controlled thoroughly. It has been integrated into advanced electronic devices, including not only Field Emission (FE) cathodes, but sensors, energy storage devices, and circuit components. However, synthesizing CNTs on semiconducting materials like Silicon (Si) can limit its electrical property by increasing this resistance between CNTs and Si substrate. Thus, the rapid trend in synthesizing CNTs on metal substrates has taken its momentum. Recently, some groups are able to synthesize CNTs on metals substrate, especially stainless steel (SS) without using external catalysts. However, the substrate has to go through some pre-treatment processes such as oxidizing in air or treatment with acids. The research presented here demonstrates that the CNTs can be successfully grown on metal alloy substrates by chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD) without using external catalysts and any pre-treatment processes. The field emission properties of grown CNTs by two different processes are compared and analyzed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). Since the CVD grown CNTs are relatively thinner and with fewer defects, the field emission property of CVD grown CNTs are found to be more efficient compared to the PECVD counterpart. Understanding the need for a point source for high-resolution imaging, the pointed substrate is developed and its field emissions are measured depending on the number of pointed structures. Finally, the CVD grown CNTs are integrated into a compact electron gun and their field emissions are measured in a custom-built high vacuum chamber that can be used as both field emission chamber and portable open-type X-ray system. In addition, using the CNT based X-ray system; the feasibility of imaging the breast specimen is performed and its prospective use is discussed thoroughly.

New freedoms, new dependencies : new reproductive technologies, women's health and autonomy

Gupta, Jyotsna Agnihotri Rijksuniversiteit te Leiden 1996 국내박사

Exploring the role of hypoxia and propyl hydroxylases in modulating type 2 immunity

Gupta, Anupriya 한림대학교 대학원 2023 국내박사

Type 2 inflammation is a key component of various allergic and inflammatory diseases, including atopic dermatitis (AD) and asthma. AD is a chronic inflammatory skin disease characterized by eczema and itching. The dysregulation of immune responses and altered cellular metabolism play key roles in AD pathogenesis. The mechanistic target of rapamycin complex (mTORC) signaling pathway has recently emerged as a critical regulator of immune responses and a potential target for immunomodulatory therapies. Additionally, the impact of environmental factors, including hypoxia, on AD development remains poorly understood, especially in relation to type 2 inflammation. Using a mouse model of MC903-induced AD-like skin inflammation, we investigated the role of mTORC signaling in AD pathogenesis. Activation of mTORC1, evidenced by the phosphorylation of ribosomal protein S6, was observed upon MC903 treatment. Interestingly, we found dual roles of mTORC1 in regulating type 2 inflammation in AD. Raptor-deficient mice displayed significantly reduced skin inflammation, accompanied by decreased eosinophil recruitment and IL-4 production, suggesting that mTORC1 promotes type 2 immunity and contributes to the pro-inflammatory cascade in AD. Furthermore, we explored the impact of hypoxia and its regulatory mechanisms on AD. Inhibiting prolyl hydroxylase (PHD), an enzyme that stabilizes hypoxia-inducible factor (HIF), using the inhibitor DMOG, attenuated MC903-induced AD-like symptoms. Intriguingly, PHD inhibition led to the downregulation of key mediators of type 2 inflammation, including thymic stromal lymphopoietin (TSLP) and interleukin-33 (IL-33), through the reactive oxygen species (ROS) pathway. These findings suggest that targeting PHD and modulating HIF signaling may provide a novel therapeutic approach for alleviating type 2 inflammation in AD. In conclusion, this study highlights the intricate relationship between mTORC signaling, hypoxia-inducible factor (HIF) regulation, and type 2 inflammation in AD. We demonstrate that mTORC1 promotes type 2 immunity, while inhibiting PHD and suppressing HIF signaling attenuate AD-like symptoms and downregulate type 2 cytokines. These findings shed light on the complex molecular mechanisms underlying AD pathogenesis and offer potential targets for future therapeutic interventions to modulate type 2 inflammation in AD. Further investigations into these pathways are warranted to fully understand their clinical implications and therapeutic potential. 제2형 염증은 아토피 피부염(AD)과 천식을 포함한 다양한 알레르기 및 염증성 질환의 핵심 요소입니다. 아토피 피부염은 습진과 가려움증을 특징으로 하는 만성 염증성 피부 질환입니다. 면역 반응의 조절 장애와 세포 대사의 변화는 AD 발병에 중요한 역할을 합니다. 라파마이신 복합체(mTORC) 신호 전달 경로의 기계적 표적은 최근 면역 반응의 중요한 조절자이자 면역 조절 치료의 잠재적 표적으로 부상하고 있습니다. 또한 저산소증을 포함한 환경 요인이 AD 발병에 미치는 영향은 특히 2형 염증과 관련하여 아직 제대로 이해되지 않고 있습니다. MC903으로 유도된 AD 유사 피부 염증의 마우스 모델을 사용하여 AD 발병에서 mTORC 신호의 역할을 조사했습니다. MC903 처리 시 리보솜 단백질 S6의 인산화에 의해 입증된 mTORC1의 활성화가 관찰되었습니다. 흥미롭게도 알츠하이머병의 2형 염증을 조절하는 데 있어 mTORC1의 이중 역할이 발견되었습니다. 랩터가 결핍된 마우스는 호산구 모집 및 IL-4 생산 감소와 함께 피부 염증이 현저히 감소한 것으로 나타났는데, 이는 mTORC1이 제2형 면역을 촉진하고 AD에서 염증성 캐스케이드에 기여한다는 것을 시사합니다. 또한 저산소증과 그 조절 메커니즘이 알츠하이머병에 미치는 영향을 탐구했습니다. 저산소증 유도 인자(HIF)를 안정화시키는 효소인 프롤릴 하이드 록실라제(PHD)를 억제제 DMOG를 사용하여 억제하면 MC903에 의해 유발된 AD 유사 증상이 약화되었습니다. 흥미롭게도 PHD를 억제하면 활성 산소 종(ROS) 경로를 통해 흉선 간질 림포포이에틴(TSLP)과 인터루킨-33(IL-33)을 포함한 제2형 염증의 주요 매개체가 하향 조절되었습니다. 이러한 연구 결과는 PHD를 표적으로 삼고 HIF 신호를 조절하는 것이 알츠하이머병의 2형 염증을 완화하는 새로운 치료 접근법을 제공할 수 있음을 시사합니다. 결론적으로, 이 연구는 알츠하이머병에서 mTORC 신호, 저산소증 유도 인자(HIF) 조절 및 제2형 염증 사이의 복잡한 관계를 강조합니다. 우리는 mTORC1이 제2형 면역을 촉진하는 반면, PHD를 억제하고 HIF 신호를 억제하면 AD 유사 증상이 약화되고 제2형 사이토카인이 하향 조절된다는 사실을 입증했습니다. 이러한 연구 결과는 알츠하이머병 발병의 기저에 있는 복잡한 분자 메커니즘을 밝히고 알츠하이머병의 2형 염증을 조절하기 위한 향후 치료적 개입의 잠재적 표적을 제공합니다. 이러한 경로의 임상적 의미와 치료 잠재력을 완전히 이해하기 위해서는 이러한 경로에 대한 추가 조사가 필요합니다.