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971.
972.
YAN Bing-Wen ZHANG Ling WANG Qin-SunNational Laboratory of Elemento-Organic Chemistry Nankai University Tianjin China 《中国化学》1996,14(4):354-358
A computer-assisted method is presented for optimization of mobile phase compositions and development distance in gradient two-step development HPTLC. The method is based on a system which can predict the final Rf values for gradient two-step development from values measured using five preliminary runs. The statistical scanning method is then used for optimization, using Rf difference as the selection criterion. The method was evaluated using a mixture of eight components. Excellent agreement was obtained between predicted and experimental results. Gradient two-step development HPTLC, mobile phase composition optimization, velopment distance optimizationde- 相似文献
973.
A new dinuclear copper complex, [Cu(C13H9N2O)Cl]2·(CH3CN)2 (C30H24Cl2Cu2N6O2),has been synthesized and characterized by X-ray structure determination. It crystallizes in the triclinic system, space group P1-, with a = 7.6677(14), b = 9.2375(17), c = 11.227(2) (A), α = 81.338(3),β= 88.173(4), γ = 66.199(3)°, V = 718.9(2) (A)3, Z = 1, Mr = 698.53, F(000) = 354, Dc = 1.613 g/cm3,μ(MoKα) = 1.705 mm-1, the final R = 0.0645 and wR = 0.1364 for 2474 unique reflections with 1809 observed ones (I> 2σ(Ⅰ)). In the title complex, each copper(Ⅱ) atom is located at the center of a distorted tetrahedron consisting of four coordinate atoms (one nitrogen atom, two oxygen anions,and one chlorine atom). Two copper(Ⅱ) atoms are bridged by two oxygen anions (O(1) and O(1a)) of two phenolates to form a Cu(Ⅱ)-Cu(Ⅱ) binuclear entity, and the distance between two copper(Ⅱ)atoms is 3.0144(15) (A). 相似文献
974.
Kanhaiya L. Yadav Amarjeet K. Narula Ramadhar Singh Subhas Chandra 《Applied biochemistry and biotechnology》2001,96(1-3):119-124
The direct current (dc) conductivity of poly(3-methyl thiophene) was measured in the temperature range of 77–300 K. The observed dc conductivity data were analyzed in the light of Mott’s variable range hopping model. Different Mott’s parameters such as
characteristic temperature (T
0), average hopping distance (R), average hopping energy (W), and density of states at the Fermi level (N [E
F
]) were evaluated. By taking the inverse of the coefficient of exponential decay of the localized states involved in the hopping
process as 0.5 nm, a realistic value of density of states at the Fermi level (N [E
F
]) was obtained that agrees well with the values reported earlier for other conjugated polymers. 相似文献
975.
REDOR technique was applied to natural abundance 13C nuclei coupled to a singly labeled 15N nucleus to determine the 13C, 15N interatomic distances simultaneously in crystalline ammonium [15N]
-glutamate monohydrate (1). Consequently, the interatomic C–N distances between 15N and 13C=O, 13Cα, 13Cβ, 13Cγ, and 13Cδ carbon nuclei for 1 were determined with a precision of ±0.15 Å, after the experimental conditions such as the location of samples in the rotor, length of π pulse etc. were carefully optimized. 13C-REDOR factors for three spin system, (ΔS/S0)CN1N2, and the sum of two isolated 2-spin system, (ΔS/S0)*=(ΔS/S0)CN1+(ΔS/S0)CN2, were further evaluated by the REDOR measurements on isotopically diluted 1 in a controlled manner. Subsequently, the intra- and intermolecular C–N distances were separated by searching the minima in the contour map of root mean square deviation (RMSD) between the theoretically and experimentally obtained (ΔS/S0)* values against two interatomic distances, rC–N1 and rC–N2. When the intramolecular C–N distance (rC–N1) of the particular carbon nucleus is substantially shorter than the intermolecular one (rC–N2), C–N distances within a single molecule were obtained with an accuracy of ±0.06 Å as in the cases of C=O, Cα and Cβ carbon nuclei. C–N distances between the molecule in question and the nearest neighboring molecules can be also obtained, although accuracy was lower. On the contrary, it was difficult to determine the interatomic distances in the same molecule when the intermolecular dipolar contribution is larger than the intramolecular one as in the case of Cδ carbon nucleus. 相似文献
976.
Paolo Cerreia Vioglio Luca Catalano Dr. Vera Vasylyeva Prof. Carlo Nervi Prof. Michele R. Chierotti Prof. Giuseppe Resnati Prof. Roberto Gobetto Prof. Pierangelo Metrangolo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):16819-16828
Solid‐state nuclear magnetic resonance (SSNMR) spectroscopy is a versatile characterization technique that can provide a plethora of information complementary to single crystal X‐ray diffraction (SCXRD) analysis. Herein, we present an experimental and computational investigation of the relationship between the geometry of a halogen bond (XB) and the SSNMR chemical shifts of the non‐quadrupolar nuclei either directly involved in the interaction (15N) or covalently bonded to the halogen atom (13C). We have prepared two series of X‐bonded co‐crystals based upon two different dipyridyl modules, and several halobenzenes and diiodoalkanes, as XB‐donors. SCXRD structures of three novel co‐crystals between 1,2‐bis(4‐pyridyl)ethane, and 1,4‐diiodobenzene, 1,6‐diiodododecafluorohexane, and 1,8‐diiodohexadecafluorooctane were obtained. For the first time, the change in the 15N SSNMR chemical shifts upon XB formation is shown to experimentally correlate with the normalized distance parameter of the XB. The same overall trend is confirmed by density functional theory (DFT) calculations of the chemical shifts. 13C NQS experiments show a positive, linear correlation between the chemical shifts and the C?I elongation, which is an indirect probe of the strength of the XB. These correlations can be of general utility to estimate the strength of the XB occurring in diverse adducts by using affordable SSNMR analysis. 相似文献
977.
One novel complex Mn2(phen)2(p-CBA)4(H2O) has been hydrothermally syn- thesized from p-chlorobenzoic acid (p-CBA), 1,10-phenanthroline (phen) and anhydrous man- ganese(Ⅱ) sulfate and then characterized. Crystal data for this complex: monoclinic, space group C2/c, with a = 2.3416(3), b = 1.5604(2), c =1.5605(2) nm, β = 121.048(2)o, V = 4.8849(12) nm3, Dc = 1.510 g/cm3, Mr = 555.26, Z = 8, μ = 0.798 mm-1, F(000) = 2256, GOOF = 1.032, the final R = 0.0393 and wR = 0.0816. The crystal structure shows that two neighboring manganese(Ⅱ ) ions are linked together by two bridge-chelating p-chlorobenzoic groups and one bridging water molecule, forming a cage structure with the Mn–Mn bond distance of 0.3512 nm. Each manganese(Ⅱ ) ion is coordinated by two nitrogen atoms of one 1,10-phenanthroline molecule and four oxygen atoms from three p-chlorobenzoic acid anions and one water molecule, giving a distorted octahedral coordination geometry. The cyclic voltammetric behavior of the complex was also investigated. 相似文献
978.
WANG Shan-Peng TAO Xu-Tang DONG Chun-Ming JIAO Zheng-Bo JIANG Min-Hua 《结构化学》2007,26(10):1184-1188
A Bridgman growth furnace was modified by adding adiabatic material between two furnace tubes. The appropriate temperature gradient of 10~30 ℃/cm at the growth interface was obtained by adjusting the distance between the two sections and controlling their temperature. The infrared nonlinear optical (NLO) crystal LiInS2 was successfully grown by the accelerated crucible rotation technique (ACRT). The crystal was characterized by using XRD and transmission microscopy. It is found that the UV-VIS-NIR and Mid-IR transmittances are about 40%. 相似文献
979.
J. A. Cuesta-Albertos C. Matrán J. Rodríguez-Rodríguez 《Journal of Theoretical Probability》2003,16(2):363-376
Let P be a probability distribution on
d
and let
be the family of the uniform probabilities defined on compact convex sets of
d
with interior non-empty. We prove that there exists a best approximation to P in
, based on the L
2-Wasserstein distance. The approximation can be considered as the best representation of P by a convex set in the minimum squares setting, improving on other existent representations for the shape of a distribution. As a by-product we obtain properties related to the limit behavior and marginals of uniform distributions on convex sets which can be of independent interest. 相似文献
980.
Antonio Siconolfi 《Transactions of the American Mathematical Society》2003,355(5):1987-2009
We deal with the metrics related to Hamilton-Jacobi equations of eikonal type. If no convexity conditions are assumed on the Hamiltonian, these metrics are expressed by an - formula involving certain level sets of the Hamiltonian. In the case where these level sets are star-shaped with respect to 0, we study the induced length metric and show that it coincides with the Finsler metric related to a suitable convexification of the equation.