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101.
Liao JH Chen CT Chou HC Cheng CC Chou PT Fang JM Slanina Z Chow TJ 《Organic letters》2002,4(18):3107-3110
[structure: see text] A push-pull conjugated molecule, 2,7-bis(1H-pyrrol-2-yl)ethynyl-1,8-naphthyridine (BPN), has been designed to bind selectively with octyl glucopyranoside (OGU). The BPN/OGU quadruple hydrogen-bonding complex adopts a rigid BPN conformation in which the proton donor (d) and acceptor (a) relays (daad) are resonantly conjugated through the ethynyl bridge, inducing pi-electron delocalization, i.e., a charge transfer effect. The excellent photophysical properties make BPN a highly sensitive probe for monitoring glucopyranoside to a detection limit of approximately 100 pM. 相似文献
102.
Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition. 相似文献
103.
The current-voltage curves of a composite bipolar membrane (CBM) were experimentally measured by varying the interface component between cation- and anion-exchange membranes for water and methanol solutions. In each solution system, 0.05 mol/l LiCl was used as the electrolyte. The interface component was varied by pasting the polymers or installing the thin membranes in the intermediate region of the CBM. The measured results show that the functional groups of the polymers and thin membranes enhanced the water and methanol splitting effect. This phenomenon can be explained by the protonation-deprotonation reactions occurring between these functional groups and the water or methanol molecules in the intermediate region of the CBM. The effect of transition metal compounds existing in the intermediate region of the CBM was also experimentally examined in this study. It was found that the effect of transition metal compounds on water or methanol splitting was not obvious. Copyright 1999 Academic Press. 相似文献
104.
We report difference frequency generation-based wavelength converters with multiple phase-matching wavelengths that use engineered quasi-phase-matching structures in LiNbO(3) waveguides. Multiple-channel wavelength conversion is demonstrated within the 1.5-mum band and between the 1.3- and 1.5-mum bands. With simultaneous use of M pump wavelengths, these devices can also be used to perform wavelength broadcasting, in which each of N input signals is converted into M output wavelengths. 相似文献
105.
106.
A simple and rapid polyamide chromatographic method for the detection of 12 kinds of preservatives and 3 kinds of artificial sweeteners were reported. The results indicated that the method was good in sensitivity, separability and reproducibility. 相似文献
107.
A newly developed self-consistent-field molecular orbital theory is described and tested. The intermediate neglect of differential overlap (INDO) approximation is used, and all interaction integrals are differentiated according to their dependence upon 2s and 2p AO's. The bonding parameter βl is reformulated so that the model is calibrated to only one specific molecular property, namely, the ionization energy of Hi. We expect that this model will not be biased toward any special families of molecules. 相似文献
108.
[reaction: see text] Rigid U-shaped molecules containing syn-facially situated quinoxaline rings have been synthesized in three steps, by a combination of the Diels-Alder reaction, the ruthenium-catalyzed oxidation, and the Zn(OAc)(2)-catalyzed condensation of the resulting bis-alpha-diketones with benzene-1,2-diamines. The unsymmetric bis-quinoxalines, with electronically different substituents, and the quinoxaline ring-attached alpha-diketones were also prepared. Their luminescence properties were examined and described. 相似文献
109.
Nafion membranes are used as semisolid electrolytes in methanol and hydrogen fuel cells. The ion conduction takes place through those hydrophilic channels in the Nafion that can provide continuous pathways through the membrane. There is as yet limited information about the density, the size, and the shape of these channels. We have developed two electrochemical methods of visualizing the pore structure which involve the creation of metal lithographs using the membrane pores as templates. In the experiments, the membrane is supported on a flat solid surface on one side, and is in contact with an electrolyte on the other side. Using hydrogen-terminated n-doped Si(111), we deposited gold from an electrolyte containing a gold salt. The Au ions traverse the membrane through the pores, reach the silicon surface, and are spontaneously reduced. A metallic Au deposit is formed on the silicon surface, at the base of the hydrophilic channel. The Au deposits are imaged after the membrane is dissolved. Another method involves supporting the membrane on a Pt surface and depositing silver wires through the hydrophilic channels of the membrane. The scanning electron microscope pictures of these wires provide an image of the size and the shape of the hydrophilic channels. 相似文献
110.
Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations. 相似文献