플레너리 세미나가 11월 21일(목)에 개최됩니다.참석 부탁드립니다.감사합니다.======================================연 사 : 조규학 박사님 (화학과 5회 졸업)제 목 : 화학과 인류의 미래일 시 : 2019년 11월 21일(목) 오후 4시 15분 장 소 : 화학관 1층 효천조규학강의실(330126호)-------------------------------------- < 효천 조규학 박사님(화학과 5회졸업) >
세미나가 이번주 목요일(11월 14일)에 개최됩니다.많은 참석 부탁드립니다.감사합니다.===============================================================================제 목 : Computational experiments on approximate mixed quantum-classical approaches based on mapping formalisms연 사 : 김현우 박사(KRICT)일 시 : 2019년 11월 14일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================================================ Computational experiments on approximate mixed quantum-classical approaches based on mapping formalisms Hyun Woo KimCenter for Molecular Modeling and Simulation, Korea Research Institute of Chemical Technology (KRICT), Daejeon, Korea. Corresponding Author: email@example.com Molecular dynamics (MD) simulations are applicable to study interesting chemical phenomena in multiple excited states with the help of approximate quantum dynamics methods. Representative examples are mixed quantum-classical (MQC) approaches such as surface hopping algorithms and mean-field approaches. As it is well-known that some MQC approaches are not accurate in the long-time limit because of their approximations, several methods are developed so far. Here, I will present computational analysis on approximate MQC approaches based on mapping formalisms including the application of machine learning algorithms. I tried to modify equations of motion by utilizing the quantum-classical Liouville equation in the mapping basis and its approximation which is called Poisson bracket mapping equation (PBME). I found several techniques such as trajectory-branching improve the performance of PBME. For applying machine learning algorithms, I generated a large amount of data from MD simulations with PBME and then applied machine learning algorithms to improve its performance. Machine learning models can predict corrections to PBME by including the information from a set of trajectories. I will discuss some issues such as the energy conservation along MQC trajectories.
세미나가 다음주 목요일(10월 31일)에 개최됩니다.많은 참석 부탁드립니다.감사합니다.===============================================================================제 목 : Functionalized Small & Medium Carbocycles연 사 : 권용훈 교수(서울대학교 응용생물화학부)일 시 : 2019년 10월 31일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================================================ Functionalized Small & Medium CarbocyclesYonghoon KwonDepartment of Applied Biology and ChemistrySeoul National University, Seoul 08826, KoreaThe development of ring closing alkyne metathesis (RCAM) followed by stereoselective reduction of the resulting alkyne has rendered opportunities to access macrolides as well as medium-sized carbocycles bearing Z- or E-alkenes.1 Beyond the selective formation of (Z)- or (E)-disubstituted alkenes, we recently demonstrated that a macrolide having a trisubstituted alkene with well-defined stereochemistry can be prepared by a RCAM/trans-selective hydrostannation sequence. This approach is complementary to ring closing alkene metathesis (RCM) since (stereoselective) formation of trisubstituted alkenes by RCM is problematic. Testing this method in the total synthesis of a complex natural product is desirable to broaden the generality of the strategy. Disciformycins A and B, isolated from cultures of Pyxidicoccus fallax by the Müller group in 2014,2 were chosen as our targets as they exhibit considerable antibacterial activity against Gram-positive bacteria. This presentation will describe details of unforeseen synthetic challenges and our endeavors to resolve these problems met along the way.3References1. Fürstner, A. Angew. Chem. Int. Ed. 2013, 52, 2794–2819.2. Surup, F.; Viehrig, K.; Mohr, K. I.; Herrmann, J.; Jansen, R.; Mülller, R. Angew. Chem. Int. Ed. 2014, 53, 13588–13591.3. Kwon, Y.; Schulthoff, S.; Dao, Q. M.; Wirtz, C.; Fürstner, A. Chem. Eur. J. 2018, 24, 109 –114.
===============================================================================제 목 : Development and Mechanistic Understanding of Transition Metal-Catalyzed C-C Bond Forming Reactions연 사 : 신광민 박사(MIT)일 시 : 2019년 10월 24일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================================================ Development and Mechanistic Understanding of Transition Metal-Catalyzed C-C Bond Forming ReactionsKwangmin ShinDepartment of Chemistry, Massachusetts Institute of Technology (MIT)The development of new transition metal catalysis for the construction of carbon-carbon bonds has a great impact on broad research fields such as organic synthesis, medicinal and materials chemistry. Here, I present my research effort in recent years toward the establishment of site-selective and/or stereoselective C-C bond forming reactions catalyzed by transition metal complexes. The first part of this talk will describe the development of site-selective Ir(III)-, Rh(III)- and Ru(II)-catalyzed oxidative C-H arylation reactions.[1-3] Mechanistic investigations of these arylation reactions, including isolation, CV and EPR studies of the key reaction intermediates and DFT calculations, will be discussed in detail. In the second part of this talk, the development of copper-hydride catalyzed stereoselective allylation of aldehydes with unactivated 1,3-dienes will be discussed. The effect of kinetic control (slow addition of aldehyde) on the chemo- and stereoselectivity of this allylation reaction will be explained. References Shin, K.; Park, S.-W.; Chang, S.* J. Am. Chem. Soc.2015, 137, 8584. Shin, K.; Park, Y.; Baik, M.-H.*; Chang, S.* Nat. Chem. 2018, 10, 218-224. Kim, J.†; Shin, K.†; Jin, S.; Kim, D.; Chang, S.* J. Am. Chem. Soc.2019, 141, 4137-4146. (†contributed equally) Li, C.†; Shin, K.†; Liu, R.Y.; Buchwald, S. L.* Angew. Chem., Int. Ed.2019, DOI: 10.1002/anie.201911008. (†contributed equally
===============================================================================제 목 : Development of new strong Brønsted acids and their application towards the synthesis of enantio-enriched O-heterocycles연 사 : 이성기 교수(Dept. of Emerging Material Science, DGIST)일 시 : 2019년 10월 10일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================================================ Development of new strong Brønsted acids and their application towards the synthesis of enantio-enriched O-heterocyclesSunggi Leesunggi.firstname.lastname@example.org Since the Akiyama and Terada groups reported chiral phosphoric acids as powerful catalysts in multiple asymmetric functional group transformations, various new Brønsted acids were introduced. Recently, we developed new class of strong Brønsted acids which can provide excellent catalytic activity and well-defined active sites at the same time.1,2 The new catalysts, imidodiphosphorimidates (IDPs), enable multiple transformations which were not possible with conventional organo- and transition-metal catalysts. The handling of cyclic aliphatic oxocarbenium ions in enantioselective reactions is the one of such challenges. Now, the enantioselective carbon-carbon bond formation on these highly reactive and small intermediates can be carried out using IDPs affording O-heterocycles bearing multisubstituted stereogenic centers.3,4 Various lactol acetates reacted with enol silanes in the presence of powerful pre-Lewis acid organocatalysts to furnish the desired oxygen heterocycles with high enantioselectivities. Additionally, 1,4- and 1,5-dicarbonyl compounds were transformed to multisubstituted O-heterocycles via catalytic chemo- and enantioselective additions of silyl nucleophiles. ReferencesKaib, P. S.; Schreyer, L.; Lee, S.; Properzi, R.; List, B. Angew. Chem. Int. Ed.2016, 55, 13200-13203. Lee, S.; Kaib, P. S.; List, B. Synlett2017, 28, 1478-1480.Lee, S.; Kaib, P. S.; List, B. J. Am. Soc. Chem. 2017, 139, 2156-2159.Lee, S.; Bae, H. Y.; List, B. Angew. Chem. Int. Ed.2018, 57, 12162-12166.
================================================== 제 목 : Extremely Active Chiral Catalysts for Challenging Chemical Reactions 연 사 : 배한용 교수님(성균관대학교 화학과)일 시 : 2019년 9월 5일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================== Extremely Active Chiral Catalysts for Challenging Chemical Reactions Hanyong BaeDepartment of Chemistry, Sungkyunkwan University2066, Seobu-ro, Jangan-gu, Suwon, 16419 Korea E-mail: email@example.comVisit our webpage: https://hanyongbae.wixsite.com/hbcatalysis Since its establishment as a field at the beginning of this century, organocatalysis has significantly advanced chemical synthesis in academia and industry. However, a common view suggesting that organocatalysts are generally less active than metal-based catalysts and enzymes still occasionally persists.In this talk, we will discuss our recent findings on biomimetic enantioselective reactions regarding efficient "direct" introduction of (thio)ester enolate equivalents via chiral Brønsted base catalysis. In the light of both mechanistic and environmental approaches, we developed different hydrogen bonding promoted asymmetric reactions that those are, decarboxylative aldol reaction of malonic acid half thioester with aldehyde which is inspired by polyketide biosynthesis, rate-accelerated Michael addition reaction of malonate with nitroolefin “on water” due to the hydrophobic amplification effect, and Mannich reaction of highly reactive thioester enolate precursor dithiomalonate with N-Boc imine/α-amido sulfone. The low catalytic activity, which is regarded as an intrinsic limitation of organocatalyst, could be addressed by taking advantage of nature's solution.As an “in-direct” approach, we will demonstrate a new class of chiral catalysts which enable the highly challenging enantioselective Mukaiyama aldol reaction of ketones in the presence of extremely low catalyst loading (down to 0.00009 mol%: 900 parts-per-billions, ppb). The developed highly acidic (pKa = 4.5 in acetonitrile) imidodiphosphorimidate catalysts were employed as potent catalysts for the Mukaiyama aldol reaction of commercially available silyl ketene acetals with ketones, via Lewis acid catalysis. Previously developed chiral disulfonimides (pKa = 8.4 in acetonitrile), which proved to be efficient catalysts of the Mukaiyama aldol reaction of aldehyde failed to achieve the desired transformation.[4,5] References H. Y. Bae, J. H. Sim, J. W. Lee, B. List, C. E. Song, Angew. Chem. Int. Ed.2013, 52, 12143. H. Y. Bae, C. E. Song, ACS Catal. 2015, 5, 3613. H. Y. Bae, M. J. Kim, J. H. Sim, C. E. Song, Angew. Chem. Int. Ed. 2016, 55, 10825. H. Y. Bae, B. List, Chem.-Eur. J. 2018, 24, 13767. H. Y. Bae, D. Höfler, P. S. J. Kaib, P. Kasaplar, C. K. De, A. Döhring, S. Lee, K. Kaupmees, I. Leito, B. List, Nature Chemistry2018, 10, 888.
===============================================================================제 목 : Transmission Electron Microscope Toward Atomic Structure and Dynamics of Molecules연 사 : 유병국 박사(California Institute of Technology)일 시 : 2019년 8월 29일(목) 오후 4시 30분장 소 : 화학관 2층 서병인강의실 (330226호실)================================================================================ Transmission Electron Microscope Toward Atomic Structure and Dynamics of MoleculesPresenter: Dr. Byung-Kuk Yoo1 (California Institute of Technology)Structure of molecules is the determiner of their properties. Transmission Electron Microscope (TEM) has versatile advantages for scientists thanks to its atomic spatial resolution. As a CryoEM method, micro electron-diffraction (MicroED) has determined a variety of macromolecules with sub-Angstrom resolution until very recently. Moreover, this technique has been further advanced to address the broad needs in structure determination of small molecules. In the first part of the presentation, how MicroED is used to determine the atomic structure of an inorganic molecule will be demonstrated. A heterometallic Mn/Ca cluster (Mn4CaOn) is a synthetic model compound for oxygen-evolving complex of the natural enzyme: photosystem II, which has been vigorously studied as an important biological water oxidation catalyst. Having powder samples of this molecule directly from the synthesis, we were able to collect suitable crystallographic data from nano- and micro-crystals as a movie while the crystals are continuously rotated and solved the structure in atomic resolution in minutes. Our results prove that MicroED is ideal to determine structures for (in)organic chemists in the fields of drug discovery with minimal crystallization trials.In the second part of the talk, I explore TEM as an in-situ tool in pursuit of understanding dynamics. Unlike the conventional TEM, femtosecond time-resolved TEM has a time resolution that is 10 orders of magnitude better than that of TEM. Instead of using thermionic electrons in TEM, laser-driven single pulses of electrons allow various modes of detection such as imaging, diffraction, and spectroscopy, all with unprecedented spatiotemporal resolution; sub-nanometer and femtosecond. I will discuss the development of 4D Ultrafast EM and summarize the up-to-date accomplishments that represent its broad capability in chemical, materials, and biological sciences. As one of those examples, I will introduce how this technique provides a structural dynamic probe for catalytic active site in photocatalytic materials and visualizes the femtosecond atomic movement at the titanium active center in a single-site photocatalyst. Our findings contribute fundamental insights for developing advanced photocatalysts and suggest broad ranges of applications in materials science.1 Staff Scientist @Howard Hughes Medical Institute Research Laboratory, Broad Center for the Biological SciencesDivision of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
===================================================================================== 제 목 : Chemical Synthesis and Catalysis Harnessing Organosilanes연 사 : 전준하 교수(Department of Chemistry & Biochemistry University of Texas Arlington)일 시 : 2019년 8월 7일(수) 오후 4시장 소 : 화학관 2층 서병인강의실 (330226호실)===================================================================================== Chemical Synthesis and Catalysis Harnessing OrganosilanesJunha JeonDepartment of Chemistry and Biochemistry The University of Texas at ArlingtonArlington, Texas 76019 E-mail: firstname.lastname@example.orgEnvironmentally benign, stable, and abundant organosilanes are increasingly utilized in an impressively wide range of synthetic applications involving biomedically relevant agents, catalysts, and drug delivery vehicles. Despite the advances on organosilane chemistry, much less success has been achieved on broadly applicable, highly regio-, stereo-, and chemoselective silylation of unactivated C–C and C–H bonds. The goals of our research research program are to develop highly efficient synthetic methods for preparation of high-value synthetic building blocks and bioactive molecules and to advance our understanding of the associated catalytic mechanisms. Success in these endeavors will accelerate the use of a variety of novel small molecules to be employed in drug discovery and development, thus contributing to the promotion of human health. In this talk, our efforts toward expanding the dimension of organosilicon chemistry directed toward chemical synthesis and catalysis will be presented. Specifically, the progress on design and application of redox neutral and oxidative C–C and C–H silylation methodologies harnessing a traceless hydrosilyl acetal and our new discovery on catalytic hydrogen atom transfer from hydrosilanes to vinylarenes for hydrosilylation and polymerization will be discussed.