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161.
A new cyclization route, triggered by epoxide opening, has been performed to provide the key intermediates for isoindolobenzapine alkaloids, lennoxamine and chilenine. The epoxide was prepared by the Stille reaction using vinyltributylstannane and the following dioxirane treatment. Cyclization under the treatment of BF3 · OEt2 provided an azepine moiety, and the oxidative cyclization toward the known precursor for the alkaloids has been achieved by reaction with a stoichiometric amount of Pd(OAc)2. This formal synthesis suggests a new route to the alkaloids. 相似文献
162.
Abstract The aliphatic polyesters are normally synthesized by ester interchange reactions or direct esterification of hydroxyacids or diacid/diol combinations. Biotransformation, utilizing the enzymes as catalysts, was accepted as an alternative route for the synthesis of aliphatic polyesters and offers various advantages compared with the conventional, metal-catalyzed polymerization reactions. Previous studies indicated that lipase-catalyzed polycondensation reactions between diols and diacids occurred preferentially at primary hydroxyl groups of diols, when diols contained both primary and secondary hydroxyl groups. In this work, we investigated lipase-catalyzed polycondensation of diacids and secondary hydroxyl group–containing diols, and successfully synthesized polyesters by polycondensation with secondary hydroxyl groups as well as primary hydroxyl groups. Various diols, glycerol, 1,2-propanediol, 1,3-butanediol, 2,3-butanediol, and 2,4-pentanediol were tested for the polycondensation. The polymerization was achieved by heating a mixture of lipase B, sebacic acid, and the diols in anhydrous toluene at 100 °C for 72 h. The resulting polymers were characterized by 1H and 13C NMR spectroscopy, Fourier transform–infrared spectroscopy, thermogravimetric analysis, and gel permeation chromatography. 相似文献
163.
Soaram Kim Hyunggil Park Giwoong Nam Hyunsik Yoon Jae-Young Leem 《Journal of Sol-Gel Science and Technology》2013,67(3):580-591
Sol–gel spin-coating was used to grow zinc oxide (ZnO) thin films doped with 0–2.5 at.% B on quartz substrates. The structural, optical, and electrical properties of the thin films were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD), photoluminescence (PL), ultraviolet–visible spectroscopy, and van der Pauw Hall-effect measurements. All the thin films had deposited well onto the quartz substrates and exhibited granular morphology. The average crystallite size, lattice constants, residual stress, and lengths of the bonds in the crystal lattice of the thin films were calculated from the XRD data. The PL spectra showed near-band-edge (NBE) and deep-level emissions, and B doping varied the PL properties and increased the efficiency of the NBE emission. The optical transmittance spectra for the undoped ZnO and boron-doped zinc oxide (BZO) thin films show that the optical transmittance of the BZO thin films was significantly higher than that of the undoped ZnO thin films in the visible region of the spectra and that the absorption edge of the BZO thin films was blue-shifted. In addition, doping the ZnO thin films with B significantly varied the absorption coefficient, optical band gap, Urbach energy, refractive index, extinction coefficient, single-oscillator energy, dispersion energy, average oscillator strength, average oscillator wavelength, dielectric constant, and optical conductivity of the BZO thin films. The Hall-effect data suggested that B doping also improved the electrical properties such as the carrier concentration, mobility, and resistivity of the thin films. 相似文献
164.
Ran Choi Dr. Sang‐Il Choi Dr. Chang Hyuck Choi Dr. Ki Min Nam Prof. Seong Ihl Woo Prof. Joon T. Park Prof. Sang Woo Han 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(25):8190-8198
Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs. 相似文献
165.
Hui‐Jun Yun Yun‐Ji Lee Seung‐Jin Yoo Prof. Dae Sung Chung Prof. Yun‐Hi Kim Prof. Soon‐Ki Kwon 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13242-13248
We describe herein the synthesis of novel donor–acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3‐benzothiadiazole as the electron acceptor for high‐performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto‐electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field‐effect transistor analyses, we found that the thiophene‐containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge‐carrier mobility up to 0.55 cm2 V?1 s?1. The outstanding charge‐transport characteristics of this polymer allowed the realization of high‐performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space‐charge‐limited current model. 相似文献
166.
A novel Hg2+-selective colorimetric sensor based on a cyclen–nitrobenzoxadiazole (NBD) conjugate was investigated. A cyclen derivative with three ester ligands was used as the binding site and the NBD moiety acted as the reporting chromogenic subunit. Interaction of 1 with Hg2+ ions resulted in a pronounced color change from pink to yellow, and fluorescence signaling was also possible. Selective colorimetric signaling of Hg2+ ions by NBD-functionalized cyclen with a detection limit of 1.5 × 10−6 M in aqueous environments was successfully achieved. 相似文献
167.
Eun Joung Choi Eunha Kim Youngjun Lee Ala Jo Seung Bum Park 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(5):1370-1374
Fluorescence imaging enables the uniquely sensitive observation of functional‐ and molecular‐recognition events in living cells. However, only a limited range of biological processes have been subjected to imaging because of the lack of a design strategy and difficulties in the synthesis of biosensors. Herein, we report a facile synthesis of emission‐tunable and predictable Seoul‐Fluors, 9‐aryl‐1,2‐dihydrolopyrrolo[3,4‐b]indolizin‐3‐ones, with various R1 and R2 substituents by coinage‐metal‐catalyzed intramolecular 1,3‐dipolar cycloaddition and subsequent palladium‐mediated C H activation. We also showed that the quantum yields of Seoul‐Fluors are controlled by the electronic nature of the substituents, which influences the extent of photoinduced electron transfer. On the basis of this understanding, we demonstrated our design strategy by the development of a Seoul‐Fluor‐based chemosensor 20 for reactive oxygen species that was not accessible by a previous synthetic route. 相似文献
168.
Rapid and sensitive detection of lower respiratory tract infections by stuffer‐free multiplex ligation‐dependent probe amplification
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Boram Chung Gi Won Shin Chan Kwon Park Woong Choi Yeun‐Jun Chung Hyung Kyu Yoon Gyoo Yeol Jung 《Electrophoresis》2014,35(4):511-514
Lower respiratory tract infection is one of the most common infectious diseases. However, conventional methods for detecting infectious pathogens are time‐consuming, and generally have a limited impact on early therapeutic decisions. We previously reported a rapid and sensitive method for detecting such pathogens using stuffer‐free multiplex ligation‐dependent probe amplification coupled with high‐resolution CE‐SSCP. In this study, we report an application of this method to the detection of respiratory pathogens. As originally configured, this method was capable of simultaneously detecting seven bacterial species responsible for lower respiratory tract infections, but its detection limit and assay time were insufficient to provide useful information for early therapeutic decisions. To improve sensitivity and shorten assay time, we added a target‐specific preamplification step, improving the detection limit from 50 pg of genomic DNA to 500 fg. We further decreased time requirements by optimizing the hybridization step, enabling the entire assay to be completed within 7 h while maintaining the same detection limit. Taken together, these improvements enable the rapid detection of infectious doses of pathogens (i.e. a few dozen cells), establishing the strong potential of the refined method, particularly for aiding early treatment decisions. 相似文献
169.
Keng Yoon Yeong Mohamed Ashraf Ali Chee Wei Ang Soo Choon Tan Hasnah Osman 《Tetrahedron letters》2014
A facile method to synthesize various 1,2-disubstituted benzimidazoles is developed. It is suggested that formation of a Meisenheimer adduct between the substrate, amine, and solvent aids the N-arylation process. The generality of the protocol is demonstrated by the efficient reactions involving numerous substituents ranging from electron-withdrawing groups to electron-donating groups. 相似文献
170.
Nucleophile‐Dependent Regio‐ and Stereoselective Ring Opening of 1‐Azoniabicyclo[3.1.0]hexane Tosylate
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Mi‐Kyung Ji Dietmar Hertsen Doo‐Ha Yoon Heesung Eum Hannelore Goossens Prof. Dr. Michel Waroquier Prof. Dr. Veronique Van Speybroeck Prof. Dr. Matthias D'hooghe Prof. Dr. Norbert De Kimpe Prof. Dr. Hyun‐Joon Ha 《化学:亚洲杂志》2014,9(4):1060-1067
1‐[(1R)‐(1‐Phenylethyl)]‐1‐azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2‐(3‐hydroxypropyl)aziridine upon reaction with p‐toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio‐ and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring‐opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways. 相似文献