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981.
Park IW Yoo J Kim B Adhikari S Kim SK Yeon Y Haynes CJ Sutton JL Tong CC Lynch VM Sessler JL Gale PA Lee CH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(9):2514-2523
A ditopic ion-pair receptor (1), which has tunable cation- and anion-binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([1·F](-) and [1·Cl](-)) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li(+), Na(+), K(+), Cs(+), as their perchlorate salts), ion-dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [1·F](-), no appreciable interaction with the K(+) ion was seen. On the other hand, when this complex was treated with Li(+) or Na(+) ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li(+), Na(+), K(+), treating [1·F](-) with Cs(+) ions gave rise to a stable, host-separated ion-pair complex, [F·1·Cs], which contains the Cs(+) ion bound in the cup-like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [1·Cl](-). Here, no appreciable interaction was observed with Na(+) or K(+). In contrast, treating with Li(+) produces a tight ion-pair complex, [1·Li·Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [1·F](-), treatment of [1·Cl](-) with Cs(+) ions gives rise to a host-separated ion-pair complex, [Cl·1·Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co-transport) and antiport (nitrate-for-chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate-for-chloride anion exchange mechanism. 相似文献
982.
Yu CC Hsieh CR Hsiao G Chen PY Chang ML Yin HW Lee TH Lee CK 《Molecules (Basel, Switzerland)》2012,17(2):2082-2090
Two new abietane type diterpenoids, namely seco-helioscopinolide (1) and 3b,7b-dihydroxy-ent-abieta-8,13-diene-12,16-olide (2) were isolated from the aerial parts of Euphorbia formosana Hayata together with helioscopinolide A (3), helioscopinolide B (4), helioscopinolide C (5) and ent-(5b,8a,9b,10a,12a)-12-hydroxyatis-16-ene-3,14-dione (6). The structures of compounds 1-6 were elucidated by analyzing their spectroscopic data and comparison with the literature. Further biological tests by gelatin zymographic analysis revealed that 3-5 significantly up-regulated the expressions and activation of MMP-2 and -9 in human fibrosarcoma cell line HT1080. 相似文献
983.
Won Keun Son Ji Ho Youk Taek Seung Lee Won Ho Park 《Macromolecular rapid communications》2004,25(18):1632-1637
Summary: A feasible method for the preparation of antimicrobial ultrafine fibers with silver nanoparticles was developed by direct electrospinning of a cellulose acetate (CA) solution with small amounts of silver nitrate followed by photoreduction. Silver nanoparticles in ultrafine CA fibers were stabilized by interactions with carbonyl oxygen atoms in CA. Ultrafine CA fibers with silver nanoparticles showed very strong antimicrobial activity.
984.
The main toxicological concern of stevioside, a highly potent sweetener from S. rebaudiana, is its main metabolite, steviol. To determine very low levels of steviol in in vivo experiments, a sensitive liquid chromatography/atmospheric pressure chemical ionization mass spectrometry (LC/APCI-MS) method was developed for quantifying steviol in rat plasma after oral administration of a single dose of stevioside (0.5 g/kg). The sample preparation uses liquid-liquid extraction with tert-butyl methyl ether in an acidic environment. The retention time of steviol was 10.5 min. The assay was linear over the range 2-1000 ng/mL with a lower limit of detection of 1 ng/mL. The intra- and inter-day precision were <5 and <7%, respectively, and the accuracy was in the range 95-108%. The steviol concentration profile in rat plasma was determined. 相似文献
985.
Dr. Wen Liu Pilgun Oh Dr. Xien Liu Min‐Joon Lee Woongrae Cho Sujong Chae Prof. Dr. Youngsik Kim Prof. Dr. Jaephil Cho 《Angewandte Chemie (International ed. in English)》2015,54(15):4440-4457
High energy‐density lithium‐ion batteries are in demand for portable electronic devices and electrical vehicles. Since the energy density of the batteries relies heavily on the cathode material used, major research efforts have been made to develop alternative cathode materials with a higher degree of lithium utilization and specific energy density. In particular, layered, Ni‐rich, lithium transition‐metal oxides can deliver higher capacity at lower cost than the conventional LiCoO2. However, for these Ni‐rich compounds there are still several problems associated with their cycle life, thermal stability, and safety. Herein the performance enhancement of Ni‐rich cathode materials through structure tuning or interface engineering is summarized. The underlying mechanisms and remaining challenges will also be discussed. 相似文献
986.
Dr. Hyewon Lee Rathi L. Srinivas Ankur Gupta Prof. Patrick S. Doyle 《Angewandte Chemie (International ed. in English)》2015,54(8):2477-2481
Although microRNAs (miRNAs) have been shown to be excellent indicators of disease state, current profiling platforms are insufficient for clinical translation. Here, we demonstrate a versatile hydrogel‐based microfluidic approach and novel amplification scheme for entirely on‐chip, sensitive, and highly specific miRNA detection without the risk of sequence bias. A simulation‐driven approach is used to engineer the hydrogel geometry and the gel‐reaction environment is chemically optimized for robust detection performance. The assay provides 22.6 fM sensitivity over a three log range, demonstrates multiplexing across at least four targets, and requires just 10.3 ng of total RNA input in a 2 hour and 15 minutes assay. 相似文献
987.
High‐Contrast Red–Green–Blue Tricolor Fluorescence Switching in Bicomponent Molecular Film 下载免费PDF全文
Hyeong‐Ju Kim Dr. Dong Ryeol Whang Chong Han Lee Prof. Soo Young Park 《Angewandte Chemie (International ed. in English)》2015,54(14):4330-4333
Highly efficient red–green–blue (RGB) tricolor luminescence switching was demonstrated in a bicomponent solid film consisting of (2Z,2′Z)‐2,2′‐(1,4‐phenylene)bis(3‐(4‐butoxyphenyl)acrylonitrile) (DBDCS) and (2Z,2′Z)‐3,3′‐(2,5‐bis(6‐(9H‐carbazol‐9‐yl)hexyloxy)‐1,4‐phenylene)bis(2‐(3,5‐bis(trifluoromethyl)phenyl)acrylonitrile) (m‐BHCDCS). Reversible RGB luminescence switching with a high ratiometric color contrast (λem=594, 527, 458 nm for red, green, and blue, respectively) was realized by different external stimuli such as heat, solvent vapor exposure, and mechanical force. It was shown that Förster resonance energy transfer in the bicomponent mixture could be efficiently switched on and off through supramolecular control. 相似文献
988.
Graphene Liquid Marbles as Photothermal Miniature Reactors for Reaction Kinetics Modulation 下载免费PDF全文
Wei Gao Hiang Kwee Lee Dr. Jonathan Hobley Prof. Tianxi Liu Dr. In Yee Phang Prof. Xing Yi Ling 《Angewandte Chemie (International ed. in English)》2015,54(13):3993-3996
We demonstrate the fabrication of graphene liquid marbles as photothermal miniature reactors with precise temperature control for reaction kinetics modulation. Graphene liquid marbles show rapid and highly reproducible photothermal behavior while maintaining their excellent mechanical robustness. By tuning the applied laser power, swift regulation of graphene liquid marble’s surface temperature between 21–135 °C and its encapsulated water temperature between 21–74 °C are demonstrated. The temperature regulation modulates the reaction kinetics in our graphene liquid marble, achieving a 12‐fold superior reaction rate constant for methylene blue degradation than at room temperature. 相似文献
989.
The Brownian-type molecular dynamics simulation is revisited and applied to study the thermal and geometric properties of four mono- and two polyvalent metallic clusters. For the thermal property, we report the specific heat at constant volume CV and study the solid-liquid-like transition by scrutinizing its characteristic. For the geometric property, we calculate the root mean square relative bond-length fluctuation delta as a function of increasing temperature. The thermal change in delta reflects the movement of atoms and hence is a relevant parameter in understanding the phase transition in clusters. The simulated results for the CV of alkali and aluminum clusters whose ground state structures exhibit icosahedral symmetry generally show one phase transition. In contrast, the tetravalent lead is quite often seen to exhibit two phase transitions, a premelting process followed by a progressive melting. In connection with the premelting scenario, it is found here that those (magic number) clusters identified to be of lesser stability (among other stable ones) according to the second energy difference are clusters showing a greater possibility of undergoing premelting process. This energy criterion applies to aluminum clusters nAl=28 and 38. To delve further into the thermal behavior of clusters, we have analyzed also the thermal variation of deltaT and attempted to correlate it with CV(T). It turns out that the premelting (if exist) and melting temperatures of the smaller size clusters (n less, similar 50) extracted from CV do not always agree quantitatively with that deduced from delta. 相似文献
990.
Many-body interaction in glycine-(water)3 complex using density functional theory method 总被引:4,自引:0,他引:4
Various configurations were investigated to find the most stable structures of glycine-(water)3 complex. Five different optimized conformers of glycine-(water)3 complex are obtained from density functional theory calculations using 6-311++G* basis set. Relaxation energy and many body interaction energies (two, three, and four body) are also calculated for these conformers. Out of the five conformers, the most stable conformer has the BSSE corrected total energy -513.917 967 7 Hartree and binding energy -27.28 Kcal/mol. It has been found that the relaxation energies, two body energies and three body energies have significant contribution to the total binding energy whereas four body energies are very small. The chemical hardness and chemical potential also confirmed the stability of the conformer having lowest total energy. 相似文献