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91.
We report herein the gold-catalyzed tandem hydration/α-ketol rearrangement of 1-alkynylcyclobutanol derivatives, leading to cyclopentanones bearing an α-hydroxy substituted quaternary center. In the presence of water, coordination of gold catalyst onto alkynyl moiety triggers hydration rather than a direct ring expansion, which followed by unprecedented Au-catalyzed α-ketol rearrangement. The details and the scope of this method are presented. 相似文献
92.
Changwoo Nahm Sungjin Shin Woojin Lee Jae Ik Kim Dae-Ryong Jung Jongmin Kim Seunghoon Nam Sujin Byun Byungwoo Park 《Current Applied Physics》2013,13(2):415-418
Transparent and conductive Ga-doped ZnO (ZnO:Ga) films were post-annealed after sputter deposition, and their structural and electrical properties were investigated. Post-annealing led to an improvement of crystallinity along the [001] direction, but did not change lateral grain size. Therefore, carrier concentration and electron mobility of films were analyzed as a function of crystallinity. The electrical parameters were obtained with both optical reflectance based on the Drude free-electron model and the Hall method, and similar tendencies were observed within the two methods. Even though the lowest resistivity was demonstrated by the film annealed at 550 °C, the optimum values for carrier concentration and mobility were observed in films with different post-annealing temperatures. 相似文献
93.
In this work the set of entropies of shifts of finite type is proved to be the same as the set of entropies of renewal systems
that are shifts of finite type. The period of a finite set of words is the greatest common divisor of the lengths of the words.
We show that the period of a renewal system as a shift space and the minimum of the periods of its generating sets coincide
when the system is of finite type or mixing.
This work was supported by grant No.R04-2004-000-10157-0 from the Basic Research Program of the Korea Research Foundation. 相似文献
94.
Yeom HW 《Physical review letters》2006,97(18):189701; discussion 189702
95.
We report on the systematic tuning of the electronic band structure of atomic wires by controlling the density of impurity atoms. The atomic wires are self-assembled on Si(111) by substitutional gold adsorbates and extra silicon atoms are deposited as the impurity dopants. The one-dimensional electronic band of gold atomic wires, measured by angle-resolved photoemission, changes from a fully metallic to semiconducting one with its band gap increasing above 0.3 eV along with an energy shift as a linear function of the Si dopant density. The gap opening mechanism is suggested to be related to the ordering of the impurities. 相似文献
96.
Kong K Han M Yeom HW Miyamoto Y Sugino O Sasaki T Ohno T Yu BD 《Physical review letters》2002,88(12):125504
By carrying out first-principles calculations on diamond-forming processes, we predict a method for the heteroepitaxial growth of diamond on cubic beta-SiC(001). In the method, we used two processes: (i) the preformation of an sp(3)-like surface configuration of beta-SiC(001) by the adsorption of group-V surfactants; (ii) the successive growth of diamond by the segregation of the surfactants onto a surface and the desorption of surface hydrogen. Analyzing the segregation energies, we found that the atomic size effect plays a crucial role in the surfactant-mediated growth of diamond on beta-SiC(001). 相似文献
97.
Rotenberg E Koh H Rossnagel K Yeom HW Schäfer J Krenzer B Rocha MP Kevan SD 《Physical review letters》2003,91(24):246404
We present measurements of the Fermi surface and underlying band structure of a single layer of indium on Si(111) with square root 7 x square root 3 periodicity. Electrons from both indium valence electrons and silicon dangling bonds contribute to a nearly free, two-dimensional metal on a pseudo-4-fold lattice, which is almost completely decoupled at the Fermi level from the underlying hexagonal silicon lattice. The mean free path inferred from our data is quite long, suggesting the system might be a suitable model for studying the ground state of two-dimensional metals. 相似文献
98.
Punam Thapa Yoo Jin Lee Tiep Tien Nguyen Donglan Piao Hwaryeong Lee Sujin Han Yeon Jin Lee Ah-Reum Han Hyukjae Choi Jee-Heon Jeong Joo-Won Nam Eun Kyoung Seo 《Molecules (Basel, Switzerland)》2021,26(6)
Alpinia oxyphylla Miquel (Zingiberaceae) has been reported to show antioxidant, anti-inflammatory, and neuroprotective effects. In this study, two new eudesmane sesquiterpenes, 7α-hydroperoxy eudesma-3,11-diene-2-one (1) and 7β-hydroperoxy eudesma-3,11-diene-2-one (2), and a new eremophilane sesquiterpene, 3α-hydroxynootkatone (3), were isolated from the MeOH extract of dried fruits of A. oxyphylla along with eleven known sesquiterpenes (4–14). The structures were elucidated by the analysis of 1D/2D NMR, high-resolution electrospray ionization mass spectrometry (HRESIMS), and optical rotation data. Compounds (1–3, 5–14) were evaluated for their protective effects against tert-butyl hydroperoxide (tBHP)-induced oxidative stress in adipose-derived mesenchymal stem cells (ADMSCs). As a result, treatment with isolated compounds, especially compounds 11 and 12, effectively reverted the damage of tBHP on ADMSCs in a dose-dependent manner. In particular, 11 and 12 at 50 µM improved the viability of tBHP-toxified ADMSCs by 1.69 ± 0.05-fold and 1.61 ± 0.03-fold, respectively. 相似文献
99.
Shinhui Lee Woog Jung Sanung Eom Hye Duck Yeom Heui-Dong Park Junho H. Lee 《Molecules (Basel, Switzerland)》2021,26(9)
Betulinic acid (BA) is a major constituent of Zizyphus seeds that have been long used as therapeutic agents for sleep-related issues in Asia. BA is a pentacyclic triterpenoid. It also possesses various anti-cancer and anti-inflammatory effects. Current commercially available sleep aids typically use GABAergic regulation, for which many studies are being actively conducted. However, few studies have focused on acetylcholine receptors that regulate wakefulness. In this study, we utilized BA as an antagonist of α3β4 nicotinic acetylcholine receptors (α3β4 nAChRs) known to regulate rapid-eye-movement (REM) sleep and wakefulness. Effects of BA on α3β4 nAChRs were concentration-dependent, reversible, voltage-independent, and non-competitive. Site-directed mutagenesis and molecular-docking studies confirmed the binding of BA at the molecular level and showed that the α3 subunit L257 and the β4 subunit I263 residues affected BA binding. These data demonstrate that BA can bind to a binding site different from the site for the receptor’s ligand, acetylcholine (ACh). This suggests that BA may be an effective antagonist that is unaffected by large amounts of ACh released during wakefulness and REM sleep. Based on the above experimental results, BA is likely to be a therapeutically useful sleep aid and sedative. 相似文献
100.
Dr. Kenji Hirai Dr. Bongjun Yeom Dr. Shu‐Hao Chang Dr. Hang Chi Dr. John F. Mansfield Dr. Byeongdu Lee Sungsik Lee Prof. Ctirad Uher Prof. Dr. Nicholas A. Kotov 《Angewandte Chemie (International ed. in English)》2015,54(31):8966-8970
Supramolecular chemistry utilizes coordination bonds to assemble molecular building blocks into a variety of sophisticated constructs. However, traditional coordination assemblies are based on organic compounds that have limited ability to transport charge. Herein, we describe coordination assembly of anisotropic FeS2 pyrite nanoparticles (NPs) that can facilitate charge transport. Zn2+ ions form supramolecular complexes with carboxylate end‐groups on NP surface, leading to multiparticle sheets with liquid‐crystal‐like organization. Conductivity and Hall carrier mobility of the p‐type layered semiconductor films with Zn2+ coordination bridging exceed those known for coordination compounds, some by several orders of magnitude. The nanoscale porosity of the assembled sheets combined with fast hole transport leads to high electrocatalytic activity of the NP films. The coordination assembly of NPs embraces the versatility of several types of building blocks and opens a new design space for self‐organized materials combining nanoscale and supramolecular structural motifs. 相似文献