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排序方式: 共有331条查询结果,搜索用时 15 毫秒
1.
Tamaru SI Yamamoto M Shinkai S Khasanov AB Bell TW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(24):5270-5276
A dicarboxylate host (1) binds cationic monosaccharides such as D-glucosamine HCl (2), D-galactosamine-HCl (3), and D-mannosamine-HCl (4) with high affinity (K1 = 8.0 x 10(4)-2.0 x 10(5) M(-1)) in methanol. In circular dichroism (CD) spectroscopy a positive exciton-coupling band was observed near 290 nm; this indicates that the saccharides are recognized by multiple point interactions. Since the corresponding neutral monosaccharides are not significantly bound, one may conclude that complex formation is primarily due to the electrostatic interaction between NH3+ in the guest and one carboxylate in the host and secondarily due to hydrogen-bonding interactions of OH groups with the other carboxylate and/or nitrogen bases. Molar ratio plots and Job plots indicate that host 1 and cationic monosaccharide guests form CD-active, pseudo-cyclic 1:1 complexes at low guest concentration followed by the formation of CD-silent, acyclic 1:2 1-saccharide complexes at high guest concentration. The possible binding modes are discussed in detail on the basis of molecular mechanics calculations and chemical shift changes in 1H NMR spectra. The results of competition experiments with several cationic reference compounds bearing fewer OH groups than 2-4 are consistent with the proposed binding model. Thus, the present study is a rare example of saccharide recognition in a protic solvent, where in general, hydrogen-bonding interactions are rarely useful because of strong solvation energy. These are apparently the strongest saccharide complexes involving noncovalent interactions between host and guest. We believe that the findings are significant as a milestone toward development of new saccharide recognition systems ultimately useful in aqueous solution. 相似文献
2.
A. V. Kazakova N. D. Kushch L. I. Buravov E. B. Yagubskii S. V. Simonov L. V. Zorina S. S. Khasanov R. P. Shibaeva E. Canadell J. Yamada M. Umemiya 《Russian Chemical Bulletin》2007,56(1):49-55
New radical cation salts based on 2,5-bis(1,3-dithian-2-ylidene)-1,3,4,6-tetrathiapentalene (BDA-TTP) with copper(II) metal complex anions, β-(BDA-TTP)4Cu2Cl6 and (BDA-TTP)2CuCl4, were synthesized and structurally characterized. Single crystals were prepared by electrochemical oxidation of BDA-TTP under
galvanostatic conditions. X-ray diffraction study demonstrated that the salts have a layered structure, in which the conducting
BDA-TTP layers alternate with the [Cu2Cl6]2− or [CuCl4]2− anions. Both salts show the semiconductor-type temperature dependence of the conductivity.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 48–54, January, 2007. 相似文献
3.
Elena Laukhina Vladislava Tkacheva Salavat Khasanov Leokadia Zorina Jordi Gómez-Segura Angel Pérez del Pino Jaume Veciana Vladimir Laukhin Concepció Rovira 《Chemphyschem》2006,7(4):920-923
Temperature has great impact on the structure and size of the linked crystallites of the conducting topmost layer formed at the surface of a polycarbonate film via the reaction BEDT-TTF+IBr [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene]. We show that fine temperature control permits formation of a semiconducting topmost layer of alpha'-(BEDT-TTF)(2)(I(x)Br(1-x))(3) crystallites with either micro- or nanometre size, a result that opens a route to miniaturized conducting plastic materials. 相似文献
4.
Surface-ionization methods and devices of indication and identification of nitrogen-containing base molecules 总被引:2,自引:0,他引:2
The results of the development of methods and devices based on the effect of surface ionization (SI) and intended for the selective and sensitive registration and identification of the organic nitrogen base molecules in air and in mixtures of compounds for their chromatographic, ion mobility and mass-spectrometric analysis are presented. The main principles of the SI registration and identification of molecules are considered. The requirements that must be satisfied by devices implementing these principles are stated. The examples of the development of the effective and stable emitters, the simple-in-design diode SI detectors, the gas-chromatographic detectors, the SI gas analyzers of amines and the indicators and analyzers of narcotics including portable ones, SI ion mobility spectrometer and SI mass spectrometer are presented. They have a unique selectivity (up to 10(5)-10(8) with respect to organic solvents) and ionization efficiency (up to approximately 2 x 10(-1)) of amines and their derivatives, including the degradation products of chemical warfare agents, tobacco alkoloids, triazine herbicides, narcotics and other abused medicinal preparations, as well as the sensitivity of up to 6 C/g and picogram level detection limits with a response dynamic range of 5-8 orders of magnitude. 相似文献
5.
6.
Optics and Spectroscopy - A technique for detecting and measuring the weak optical anisotropy has been proposed and experimentally implemented. The strontium tetraborate activated by ytterbium... 相似文献
7.
The effect of the through-thickness inhomogeneity of SiO2 films on their refractive index is studied. The SiO2 films, deposited by tetraethoxysilane pyrolysis on plane-parallel oriented crystalline quartz substrates and on silicon plates, were etched layer-by-layer in Pliskin’s solution. The refractive index and the geometric thickness of films were calculated from the measured ellipsometric angles after each etching. The determination errors of the refractive indices as functions of the film thickness, which result from the measurement errors of the polarization angles and substrate parameters, are numerically analyzed. For SiO2 films thicker than 20nm, no effect of inhomogeneity is found. The refractive indices of thinner films were observed to depend on the thickness. The reasons for such dependences are discussed. 相似文献
8.
V. B. Efimov A. N. Izotov A. A. Levchenko L. P. Mezhov-Deglin S. S. Khasanov 《JETP Letters》2011,94(8):621-625
The structure of ice samples formed in the decay of a water impurity gel at temperatures above 4 K and atmospheric pressure
has been examined. The X-ray diffraction analysis indicates that three phases coexist in the initial sample at temperatures
of 85–110 K. These phases are amorphous ice occupying up to 30% of the sample volume, cubic-phase ice I
c metastable at low pressures (∼60%), and normal hexagonal ice I
h (≤6%). The characteristic sizes of crystals of the cubic and hexagonal phases are about 6 and 30 nm, respectively. The amorphous
phase at annealing above 110 K is gradually transformed to the crystalline phase both cubic and hexagonal. This transition
is accompanied by two processes, including a fast increase in the sizes of cubicphase nanocrystals and the partial transition
of the cubic phase I
c to the hexagonal one I
h. Hexagonal ice I
h prevails in the bulk of the sample above 200 K. 相似文献
9.
10.
B. M. Khasanov 《JETP Letters》2005,81(1):24-29
We study the effect of random porous matrices on the isotropic-nematic phase transition. Sufficiently close to the cleaning temperature, both random field and thermal fluctuations are important as disordering agents. A novel random field fixed point of the renormalization group equation was found that controls the transition from isotropic to the replica symmetric phase. Explicit evaluation of the exponents in d = 6 ? ε dimensions yields to a dimensional reduction and three-exponent scaling. 相似文献