Yeonjoon Kim

Angularly fused triquinanes from linear substrates through trimethylenemethane diyl [2 + 3] cycloaddition reaction.

Angularly fused triquinanes were synthesized from linear dienes and phenyl(propynyl)iodonium salt through trimethylenemethane (TMM) diyl mediated [2 + 3] cycloaddition reaction. TMM diyl intermediates were obtained from alkylidene carbenes generated from reactions of alkynyliodonium salts with nucleophiles.

APPROXIMATE RATE CONSTANTS FOR CYCLIZATIONS OF ALKYL RADICALS ONTO BENZYL OXIME ETHERS

Abstract The approximate rate constants for 5-exo and 6-exo cyclizations of alkyl radicals onto oxime ethers have been kinetically determined to be 4.2×10 7 s −1 and 2.4×10 6 s −1 at 80 °C, respectively. The competition studies gave similar results, confirming the effectiveness of rate constants obtained from kinetic studies.

Efficient Basin-Hopping Sampling of Reaction Intermediates through Molecular Fragmentation and Graph Theory.

Basin-hopping sampling has been widely used for searching local minima on a potential energy surface. Reaction intermediates including reactants and products are also local minima composed of a reaction path, but their brute-force sampling is too demanding because of large degrees of freedom. We developed an efficient Monte Carlo basin-hopping method to sample reaction intermediates through the fragmentation of molecules and a postanalysis scheme using the graph theory with a matrix representation of molecular structures. The former greatly reduces the dimension of a given potential energy surface, while the latter offers not only the effective screening of resulting local minima toward desirable intermediates but also their automatic ordering along a reaction path. We combined it with the density functional tight binding method for rapid calculations and tested its performance for organic reactions.

Effect of substitution and temperature on the reactivity of bicyclo[3.1.0]hex-1-ene system

Abstract Anions of allylmeldrums acids reacted with phenyl(propynyl)iodonium salt to produce bicyclo[3.1.0]hex-1-enes as the reactive intermediates through cyclopropanation reaction to yield various dimerization products. Depending on the substitution pattern on the intermediates, various dimeric products were obtained.

Retargeting Human-Object Interaction to Virtual Avatars

In augmented reality (AR) applications, a virtual avatar serves as a useful medium to represent a human in a different place. This paper deals with the problem of retargeting a human motion to an avatar. In particular, we present a novel method that retargets a human motion with respect to an object to that of an avatar with respect to a different object of a similar shape. To achieve this, we developed a spatial map that defines the correspondences between any points in the 3D spaces around the respective objects. The key advantage of the spatial map is that it identifies the desired locations of the avatars body parts for any input motion of a human. Once the spatial map is created offline, the motion retargeting can be performed in real-time. The retargeted motion preserves important features of the original motion such as the human pose and the spatial relation with the object. We report the results of a number of experiments that demonstrate the effectiveness of the proposed method.

Effects of titanium and post-rolling heat treatments on the fatigue behaviour of high strength low alloy steels

Abstract The effects of titanium and post-rolling treatments on the low cycle fatigue properties of weathering high strength low alloy steels were investigated. The post-controlled-rolling treatments were air colling, water spraying and normalizing. All the steels cyclically hardened, but the amounts of cyclic hardening varied with the post-rolling treatment. Water spraying produced initial cyclic hardening and softening, whereas air cooling or normalizing yielded cyclic hardening modes. The water-sprayed condition exhibited a better strain-life fatigue resistance than that of the air-cooled condition. Normalized titanium-bearing steel displayed the best strain-life fatigue resistance. The fatigue resistance was increased by adding titanium, compared with that of titanium-free steel. At 2.0% total strain the fatigue life was doubled by alloying with 0.1 wt.% Ti.

Poly(amide-imide) materials for transparent and flexible displays

Transparent polymers that can match the optical and thermal expansion properties of glass were synthesized for flexible devices. The key component currently missing for the next generation of transparent and flexible displays is a high-performance polymer material that is flexible, while showing optical and thermal properties of glass. It must be transparent to visible light and show a low coefficient of thermal expansion (CTE). While specialty plastics such as aromatic polyimides are promising, reducing their CTE and improving transparency simultaneously proved challenging, with increasing coloration the main problem to be resolved. We report a new poly(amide-imide) material that is flexible and displays glass-like behavior with a CTE value of 4 parts per million/°C. This novel polymer was successfully used as a substrate to fabricate transparent and flexible indium-gallium-zinc oxide thin-film transistors.

Efficient structural elucidation of microhydrated biomolecules through the interrogation of hydrogen bond networks

Microhydration of biomolecules is an important structural factor associated with their biological processes. However, there is no general way to elucidate stable hydrated structures even for simple amino acids because of the high complexity of chemical space increasing rapidly with the number of water molecules. Here, we propose a very efficient computational method to selectively sample the most stable structures of microhydrated molecules. The key idea is to utilize the unique structural patterns of H-bond networks obtained from their energetic features, i.e. their tendency to form more H-bonds. As a proof of concept, we could identify the new global minima of glycine·10(H2O) and for the first time, we found the minimum number of water molecules required to stabilize the zwitterionic form of tyrosine. Furthermore, the most stable structures of hydrated glycine and tyrosine indeed had common features, which were consistent with the X-ray data of proteins in water.

Feasibility of Activation Energy Prediction of Gas-Phase Reactions by Machine Learning

Machine learning based on big data has emerged as a powerful solution in various chemical problems. We investigated the feasibility of machine learning models for the prediction of activation energies of gas-phase reactions. Six different models with three different types, including the artificial neural network, the support vector regression, and the tree boosting methods, were tested. We used the structural and thermodynamic properties of molecules and their differences as input features without resorting to specific reaction types so as to maintain the most general input form for broad applicability. The tree boosting method showed the best performance among others in terms of the coefficient of determination, mean absolute error, and root mean square error, the values of which were 0.89, 1.95, and 4.49 kcal mol-1 , respectively. Computation time for the prediction of activation energies for 2541 test reactions was about one second on a single computing node without using accelerators.

Enhancing the Activity of Platinum-Based Nanocrystal Catalysts for Organic Synthesis through Electronic Structure Modification

We report a systematic study on the correlation of the modified electronic structure of nanocrystal catalysts with the adsorption properties of the substrate and the resultant catalytic activity by using Baeyer–Villiger oxidation catalyzed by composition‐controlled Pt‐based nanocubes (NCs) as a model heterogeneous catalysis reaction. The incorporation of 3d transition metals into Pt to form PtM (M=Zn, Co, and Ni) alloy NCs allowed fine‐tuning of the electronic structure of Pt. PtM NCs with a higher‐lying d band center exhibited higher catalytic performance owing to the enhanced initial activation of the carbonyl group of the substrate. This work emphasizes the importance of fine‐tuning the electronic structure of heterogeneous catalysts to advance their catalytic function.