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981.
Subhankar Singha Dokyoung Kim Basab Roy Sunderraman Sambasivan Hyunsoo Moon Alla Sreenivasa Rao Jin Yong Kim Taiha Joo Jae Woo Park Young Min Rhee Taejun Wang Ki Hean Kim Youn Ho Shin Junyang Jung Kyo Han Ahn 《Chemical science》2015,6(7):4335-4342
The donor–acceptor (D–A) type dipolar fluorophores, an important class of luminescent dyes with two-photon absorption behaviour, generally emit strongly in organic solvents but poorly in aqueous media. To understand and enhance the poor emission behaviour of dipolar dyes in aqueous media, we undertake a rational approach that includes a systematic structure variation of the donor, amino substituent of acedan, an important two-photon dye. We identify several factors that influence the emission behaviour of the dipolar dyes in aqueous media through computational and photophysical studies on new acedan derivatives. As a result, we can make acedan dyes emit bright fluorescence under one- and two-photon excitation in aqueous media by suppressing the liable factors for poor emission: 1,3-allylic strain, rotational freedom, and hydrogen bonding with water. We also validate that these findings can be generally extended to other dipolar fluorophores, as demonstrated for naphthalimide, coumarin and (4-nitro-2,1,3-benzoxadiazol-7-yl)amine (NBD) dyes. The new acedan and naphthalimide dyes thus allow us to obtain much brighter two-photon fluorescent images in cells and tissues than in their conventional forms. As an application of these findings, a thiol probe is synthesized based on a new naphthalimide dye, which shows greatly enhanced fluorescence from the widely used N,N-dimethyl analogue. The results disclosed here provide essential guidelines for the development of efficient dipolar dyes and fluorescence probes for studying biological systems, particularly by two-photon microscopy. 相似文献
982.
The excited-state lifetime of supersonically cooled adenine was measured in the gas phase by femtosecond pump-probe transient ionization as a function of excitation energy between 36?100 and 37?500cm(-1). The excited-state lifetime of adenine is ~2ps around the 0-0 band of the (1)L(b) ππ(?) state (36?105cm(-1)). The lifetime drops to ~1ps when adenine is excited to the (1)L(a) ππ(?) state with the pump energy at 36?800cm(-1) and above. The excited-state lifetimes of (1)L(a) and (1)L(b) ππ(?) states are differentiated in accordance with previous frequency-resolved and computational studies. 相似文献
983.
Juhyeon Ahn Wook-Jin Chung Ingo Pinnau Jingshe Song Naiying Du Gilles P. Robertson Michael D. Guiver 《Journal of membrane science》2010
Recently, high-free volume, glassy ladder-type polymers, referred to as polymers of intrinsic microporosity (PIM), have been developed and their reported gas transport performance exceeded the Robeson upper bound trade-off for O2/N2 and CO2/CH4. The present work reports the gas transport behavior of PIM-1/silica nanocomposite membranes. The changes in free volume, as well as the presence and volume of the void cavities, were investigated by analyzing the density, thermal stability, and nano-structural morphology. The enhancement in gas permeability (e.g., He, H2, O2, N2, and CO2) with increasing filler content shows that the trend is related to the true silica volume and void volume fraction. 相似文献
984.
Besma Mellah Rym Abidi Haiko Herchbach Kwanghyun No Jong Seung Kim Françoise Arnaud Hubscher Veronique 《Journal of inclusion phenomena and macrocyclic chemistry》2010,66(1-2):153-161
The binding properties of four amido derivatives of p-tetraphenyl tetrahomodioxacalix[4]arene towards alkali and alkaline-earth metal cations using UV-absorption spectrophotometry, 1H NMR and ESI-mass spectrometry techniques are reported. 相似文献
985.
Jeong-Hui Kwon Hyo-Jun Ahn Min-Sang Jeon Ki-Won Kim In-Shup Ahn Jou-Hyeon Ahn Guoxiu Wang Ho-Suk Ryu 《Research on Chemical Intermediates》2010,36(6-7):749-759
We investigated the first charge–discharge behavior and cycling property of Li batteries using MoS2 electrodes with multi-wall carbon nanotubes (MWNT) as a conducting agent. The MoS2 electrode was prepared using MWNT as the conducting agent. The battery gave a high first discharge capacity of 440 mAhg?1 with a plateau potential region at 1.1 V. The Li/MoS2 battery using MWNT showed a higher discharge capacity compared to acetylene black. After ten cycles of the battery using MWNT, the discharge capacity decreased to 120 mAhg?1, which corresponded to 30% of the first discharge capacity. Adding a carbon nanotube into the MoS2 electrode improved the first discharge behavior, but did not affect the cycling property of the Li/MoS2 cell. 相似文献
986.
Dr. Jeeyeon Kim Youngjoo Ahn Dr. Kyeng Min Park Don‐Wook Lee Prof. Kimoon Kim 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(40):12168-12173
We report glyco‐pseudopolyrotaxanes composed of cucurbit[6]uril‐based mannose wheels (ManCB[6]) threaded on polyviologen (PV), which not only effectively induce bacterial aggregation, but also exhibit high inhibitory activity against bacterial binding to host cells. Three glyco‐pseudopolyrotaxanes ( 1 – 3 ), which have 10, 5, and 3 ManCB[6] wheels, respectively, on a PV string, were prepared and characterized. Bacterial aggregation assays and hemagglutination inhibition assays illustrated the specific and multivalent interaction between the glyco‐pseudopolyrotaxanes and E. coli ORN178. Compound 3 was especially effective at inducing bacterial aggregation and showed 300 times higher inhibitory potency than monomeric methyl‐α‐mannoside (Me‐αMan) for ORN178‐induced hemagglutination. Furthermore, we demonstrated their inhibitory activities for the adhesion of ORN178 bacteria to urinary epithelial cells as a model of urinary tract infection. Our findings suggest that these supramolecular carbohydrate clusters are potentially useful in antiadhesion therapy. 相似文献
987.
Namgee Jung Yoon-Hwan Cho Kwang-Hyun Choi Ju Wan Lim Yong-Hun Cho Minjeh Ahn Yun Sik Kang Yung-Eun Sung 《Electrochemistry communications》2010,12(6):754-757
The cathode electrode structure of the direct methanol fuel cell (DMFC) was improved by a novel catalyst ink preparation method. Regulation of the solvent polarity in the cathode catalyst ink caused increases in the electrochemical active surface (EAS) for the oxygen reduction reaction (ORR) as well as decreases in the methanol crossover effect. In a two-step preparation, agglomerates consisting of catalyst and Nafion ionomers were decreased in size, and polar groups in the ionomers formed organized networks in the cathode catalyst layer. Despite Pt catalysts in the cathode being only 0.5 mg cm? 2, the maximum power density of the improved membrane electrode assembly (MEA) was 120 mW cm? 2, at 3 M methanol, which was much larger than that of traditional MEA (67 mW cm? 2). 相似文献
988.
Despite gaps in our knowledge of how phytochemicals interfere with cellular functions, several natural plant products are utilized to prevent or treat a wide range of diseases. Identification of an agent with therapeutic potential requires multiple steps involving in vitro studies, efficacy and toxicity studies in animal models, and then human clinical trials. This review provides a brief introduction on natural products that may help to treat and/or prevent bronchial asthma and describes our current understanding of their molecular mechanisms based on various in vitro, in vivo, and clinical studies. We focus on the anti-inflammatory and anti-vascular actions of the plant products and other roles beyond the anti-oxidative effects. 相似文献
989.
Sang-Young Lee Jong Hyeok Park Pilkyu Park Jong Hun Kim Soonho Ahn Kyeong-Jik Lee Hyung-Dong Lee Jae-Sung Park Deok-Hyeong Kim Yeon Uk Jeong 《Journal of Solid State Electrochemistry》2010,14(6):951-956
Multi-walled carbon nanotube (MWCNT) with bundle-type morphology was introduced as a new functional additive working as a
particle connector or an expansion absorber in the anodes of lithium-ion batteries. By controlling the dispersion process,
the MWCNT bundles were successfully divided and dispersed between the host particles. The composite anode consisting of rounded
shape natural graphite and 2 wt.% of MWCNT exhibited the capacity of 300 mAh g−1 at 3 C rate and excellent cyclability. The well-dispersed MWCNT bundles made it possible to relieve the large strains developed
at high discharge C rates and to keep the electrical contact between the host particles during repeated intercalation/deintercalation.
This study has also emphasized that when high C-rate applications of lithium-ion batteries are targeted, it is important to
get optimum content of MWCNT as well as uniform dispersion of their bundles in the composite anodes. 相似文献
990.
Silyl-bridged dimers of a ppy-BMes(2) (ppy = 2-phenylpyridine, Mes = mesityl) photochrome were found to undergo photochromic switching involving a single boryl unit only. A through-space intramolecular energy transfer was found to be responsible for the single-chromophore isomerization phenomenon and fluorescence quenching. Steric congestion in the diboryl molecules was found to have an impact on photoisomerization quantum efficiency. 相似文献