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1.
Lee JC Chang SW Liao CC Chi FC Chen CS Wen YS Wang CC Kulkarni SS Puranik R Liu YH Hung SC 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(2):399-415
A novel and convenient route for the synthesis of biologically potent and rare L-hexose derivatives from D-glucose is described. Conversion of diacetone-alpha-D-glucose (14) into 1,2:3,5-di-O-isopropylidene-beta-L-idofuranose (19) was efficiently carried out in two steps. Orthogonal isopropylidene rearrangement of compound 19 led to 1,2:5,6-di-O-isopropylidene-beta-L-idofuranose (27), which underwent regioselective epimerization at the C3 position to give the L-talo- and 3-functionalized L-idofuranosyl derivatives. Hydrolysis of compound 19 under acidic conditions furnished 1,6-anhydro-beta-L-idopyranose (35) in excellent yield, which was successfully transformed into the corresponding L-allo, L-altro, L-gulo, and L-ido derivatives via regioselective benzylation, benzoylation, triflation and nucleophilic substitution as the key steps. Applications of these 1,6-anhydro-beta-L-hexopyranoses as valuable building blocks to the syntheses of 4-methylcoumarin-7-yl-alpha-L-iduronic acid and the disaccharide moieties of bleomycin A(2) as well as heparan sulfate are highlighted. 相似文献
2.
We introduce a way to estimate the fluctuation of the refractive index during thin film deposition, through an optical monitor. The thicknesses and error-compensated thickness for each layer are analyzed. A novel monitoring method is thereby derived. The revised refractive index and the choice of highly sensitive monitoring wavelengths help us predict the termination points more accurately. The performance of a narrow-bandpass filter monitored by this method is demonstrated. 相似文献
3.
Yu-Lin Tsai Cheng-Chung Chang Chi-Chih Kang Ta-Chau Chang 《Journal of luminescence》2007,127(1):41-47
We have previously illustrated that the electron donor of carbazole moiety and the electron acceptor of methyl pyridinium cation in 3,6-bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC) molecule could form an intramolecular charge-transfer state. The intramolecular twist of the vinyl group in bridging the donor and acceptor plays an important role in the BMVC fluorescence. Here, we have synthesized three 9-aryl-substituted BMVC derivatives with different electronic properties for the design of the second generation of fluorescence probes. The steady-state solvatochromic studies show no appreciable change to the charge transfer of BMVC by substituting an anisole electron-donating group at 9-position of BMVC. However, substituting a 9-nitrobenzyl electron-withdrawing group in BMVC could restrict the charge transfer in the excited state. Moreover, the increase of the fluorescence yields of 9-anisole BMVC and 9-phenyl BMVC upon interaction with DNA is even higher than that in glycerol, while the fluorescence yield of 9-nitrobenzyl BMVC upon interaction with DNA is much lower than that in glycerol. Although 9-nitrobenzyl BMVC is a good G-quadruplex stabilizer, substituting an electron-withdrawing group at 9-position of BMVC is not recommended for the design of fluorescence probes. On the other hand, co-localization between 9-phenyl BMVC and MitoTracker Red in the merged image of cells indicates that the 9-phenyl BMVC is a potential fluorescent mitochondrial probe. 相似文献
4.
A vibration-insensitive interferometer is described to measure the thickness, refraction index and surface profile of thin-film stack at normal incidence. By satisfying the continuous boundary conditions of electric and magnetic fields at interfaces in a multilayer film stack, the reflection coefficient phase of the thin-film stack can be distinguished from the phase of spatial path difference, thus thickness and refraction index can be extracted. The experiment results showed that the measurement precision is significantly increased after the phase analysis was added into the reflectance analysis. 相似文献
5.
INFLUENCE OF ASIAN DUSTS ON THE PHYSICOCHEMICAL PROPERTIES OF ATMOSPHERIC AEROSOLS IN TAIWAN DISTRICT USING THE PENGHU ISLANDS AS AN EXAMPLE 总被引:1,自引:0,他引:1
Chung-Shin Yuan* Cheng-Chung Sau Ming-Chung Chen Institute of Environmental Engineering Sun Yat-sen University Kaohsiung China 《中国颗粒学报》2004,2(4):144-152
1. Introduction In the early months of each year, Asian dusts transport frequently from Northwest China and Mongolia to the Pa-cific-Rim countries (Kagawa et al., 2001; Uno et al., 2002). It causes significant environmental effects such as ambient air quality deterioration, atmospheric visibility impairment, radiation energy reduction, mineral deposition, and acid rain neutralization (Terada et al., 2002; Zhang & An, 1999). During Asian dust periods, significant increases of atmos-pheric … 相似文献
6.
In this study, AlF3 thin films were deposited by pulse magnetron sputtering of Al targets with different ratios of CF4/O2 gas and at different sputtering powers. The optical and mechanical properties of the AlF3 thin films were analyzed. The transmittance spectra showed no obvious negative inhomogeneous refractive indices. Denser films
with a low optical absorption were obtained when high sputtering powers were used (larger than 30 W). The lowest extinction
coefficient (7.3 × 10−4 at 193 nm) of the films can be reached with 12 sccm O2 flow rate and at 160W sputtering power. All of the residual stresses were compressive and their trends were consistent with
the refractive indices. The lowest compressive stress (0.068 GPa) was obtained when the AlF3 films were prepared at 160W sputtering power. 相似文献
7.
Sheng-Hui Chen Kai Wu Chien-Cheng Kuo Sheng-Ju Ma Cheng-Chung Lee 《Optical Review》2009,16(4):479-482
A new method based on the polarization interferometer structure has been applied to measure the optical admittance, the refractive
index and thickness of a thin film. The structure is a vibration insensitive optical system. There is one Twyman-Green interferometer
part to induce a phase difference and one Fizeau interferometer part to induce the interference in the system. The intensities
coming from four different polarizers were measured at the same time to prevent mechanical vibration influence. Using the
polarization interferometer, the optical admittance, the refractive index and thickness of a single layer of Ta2O5 thin film has been measured. The measurement results were compared with the results obtained by ellipsometer. The results
meet reasonable values in both refractive index and thickness. 相似文献
8.
The laser-induced fluorescence excitation spectrum of the GeCl(2) A-X transition at ultraviolet wavelengths (300-320 nm) was recorded in a direct current discharge supersonic free jet expansion. The excitation spectrum contains several sharp peaks and a congested diffuse structure. Dispersed fluorescence spectra following the excitation of these GeCl(2) ultraviolet bands were successfully acquired for the first time. The analysis of the dispersed fluorescence spectra reveals the detailed vibrational structure of the X (1)A(1) state. We have assigned the vibrational structures corresponding to different isotopomers (Ge(35)Cl(2), Ge(35)Cl(37)Cl, and Ge(37)Cl(2)). The vibrational fundamental frequencies were determined: 409 cm(-1) (symmetric stretch), 159 cm(-1) (bend), and 352 cm(-1) (antisymmetric stretch) for the X (1)A(1) state of GeCl(2). Vibrational parameters of the ground electronic state including vibrational frequencies, anharmonicity, and bend-stretch coupling constant were determined. Our dispersed fluorescence spectra also clarify the vibrational assignments of the hot bands and provide more experimental data for unraveling the nature of the congested diffuse structure at shorter wavelengths in the excitation spectrum. 相似文献
9.
Hwang TS Juan N Chen HY Chen CC Lo SJ Chao I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(7):1616-1624
In an effort to manipulate the bond strengths of hydrogen bonds, we have studied a three-component chemical system consisting of a reaction center, a conjugated bridge, and a hydrogen-bonding site. Protonation of the reaction center triggers intramolecular charge transfer from the hydrogen-bonding site, altering its affinity to bind to an acceptor. Previously, we had found that this communication (signal transduction) between the reaction center and the hydrogen-bonding site does not necessarily die out with increasing length of the conjugated bridge. In certain cases, this signal transduction is maintained-and even amplified-over long distances (I. Chao, T.-S. Hwang, Angew. Chem. 2001, 113, 2775-2777; Angew. Chem. Int. Ed. 2001, 40, 2703-2705). In this study we report the results of an extensive theoretical investigation of this problem to provide insights into this intriguing phenomenon. In the systems we investigated it was found that the push-pull process between the hydrogen-bonding site and the protonatable reaction center was mediated with the greatest facility by conjugated bridges with low-lying pi and pi* orbitals. 相似文献
10.
A chiral and fluorescent columnar mesogen prepared from chiral binaphthols is reported. This liquid crystal comprises a C2-symmetric chiral core with two staggered aromatic planes. Its hexagonal columnar (Col(h)) mesophase was characterized by appropriate physical methods. 相似文献