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971.
The seeds of Clitoria fairchildiana provided a new rotenoid, 6-hydroxy-2,3,9-trimethoxy-[1]benzopyrano[3,4-b][1]benzopyran-12(6H)-one. The structural elucidation was performed using detailed analyses of H- and 13C-NMR spectra including 2DNMR spectroscopic techniques (1H-13CHETCOR) and by comparison with spectrometric data from the literature. The anti-inflammatory activity was investigated using a capillary permeability assay. 相似文献
972.
973.
Huang S Xiao Z Wang F Zhou J Yuan G Zhang S Chen Z Thiel W von Ragué Schleyer P Zhang X Hu X Chen B Gan L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(18):5449-5456
[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results. 相似文献
974.
Balaban TS Linke-Schaetzel M Bhise AD Vanthuyne N Roussel C Anson CE Buth G Eichhöfer A Foster K Garab G Gliemann H Goddard R Javorfi T Powell AK Rösner H Schimmel T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(8):2267-2275
We report two crystal structures of a synthetic porphyrin molecule which was programmed for self-assembly. The same groups which ensure that bacteriochlorophylls c, d, and e can self-assemble into the chlorosomal nanorods, the photosynthetic antenna system of some green bacteria, have been engineered into desired positions of the tetrapyrrolic macrocycle. In the case of the 5,15-meso-substituted anchoring groups, depending upon the concentration, by using the same crystallization solvents, either a tetragonal or a layered structure of porphyrin stacks were encountered. Surprisingly, pi-pi interactions combined with extensive dispersive interactions, which also encompass cyclohexane, one of the crystallization solvents, win over putative hydrogen bonding. We are aware that our compounds differ considerably from the natural bacteriochlorophylls, but based upon our findings, we now question the hydrogen-bonding network, previously proposed to organize stacks of bacteriochlorophylls. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS) on various isomeric compounds support our challenge of current models for the chlorosomal antenna as these show structures, astonishingly similar to those of chlorosomes. 相似文献
975.
Lobinger P Jarzina H Roesky HW Singh S Kumar SS Schmidt HG Noltemeyer M Freyhardt HC 《Inorganic chemistry》2005,44(25):9192-9196
A novel synthetic approach is given for the preparation of a metal-organic lanthanide sol-gel precursor solution and its application for the production of coated conductors. Besides all other problems concerning the technical process itself, the key to a successful deposition of oxide layers is the choice of the precursor solution and the understanding of the mechanism of deposition. Moreover, the isolation and characterization of the species involved in the reaction is very important. Regarding the complex process occurring during the formation of the surface layer, it is obvious that the best choice should have a compound already containing the final composition of the layer. Two compounds of composition [Y(OAc)3(H2O)2]2 and [Y(OAc)3]2(H2O) were isolated from their precursor solution and characterized by X-ray structural analysis. A short outlook will give an insight into the possible bonding mechanisms of the surface layer. These experiments were made with the mixed metal-oxide system yttrium-stabilized zirconium oxide, which is widely used as a substrate for superconducting oxides. A study of the structure of hydrated yttrium acetates, by single-crystal X-ray diffraction, infrared spectra, and elemental analysis demonstrates that there are two separate structures for hydrated yttrium acetates, which play a role as an intermediate in the building of ceramic oxide layers for coated conductors. 相似文献
976.
We introduce two new types of inversive generators for pseudorandom numbers. These new methods offer several advantages over
the conventional inversive generator. For instance, we establish good correlation properties of our generators that cannot
be obtained for the conventional inversive generator with current methods. A new bound on character sums for finite fields
is the essential technical tool for this work.
Authors’ addresses: Harald Niederreiter, Department of Mathematics, National University of Singapore, 2 Science Drive 2, Singapore
117543, Republic of Singapore; Jo?l Rivat, Institut de Mathématiques de Luminy, Université de la Méditerranée, CNRS-UMR 6206,
163 avenue de Luminy, Case 907, 13288 Marseille Cedex 9, France 相似文献
977.
Walter J. Gutjahr Stefan Katzensteiner Peter Reiter Christian Stummer Michaela Denk 《Central European Journal of Operations Research》2008,16(3):281-306
This paper presents a new model for project portfolio selection, paying specific attention to competence development. The
model seeks to maximize a weighted average of economic gains from projects and strategic gains from the increment of desirable
competencies. As a sub-problem, scheduling and staff assignment for a candidate set of selected projects must also be optimized.
We provide a nonlinear mixed-integer program formulation for the overall problem, and then propose heuristic solution techniques
composed of (1) a greedy heuristic for the scheduling and staff assignment part, and (2) two (alternative) metaheuristics
for the project selection part. The paper outlines experimental results on a real-world application provided by the E-Commerce
Competence Center Austria and, for a slightly simplified instance, presents comparisons with the exact solution computed by
CPLEX. 相似文献
978.
Walter C. P. M. Blondel Bertrand Lehalle Gérard Maurice Xiong Wang Jean-François Stoltz 《Rheologica Acta》2000,39(5):461-468
Cryopreservation is widely used to preserve blood vessels for a while but is controversially suspected to affect the mechanical
behavior of these allografts. The aim of this study was to determine whether differences in the three-dimensional mechanical
behavior exist or not between fresh and cryopreserved arteries. Using a previously developed experimental system, in vitro
inflation tests were performed on twenty segments of human fresh and cryopreserved arteries, in static conditions. Opening
angles were also measured from images of rings in zero-stress state. The initial reference state was chosen as the unloaded
state and tests were performed on specimens stretched at natural “in vivo” length. Mechanical measures calculated are “natural”
(Hencky) strains (finite deformations), “true” (Cauchy) stresses in radial, circumferential, and longitudinal directions as
well as strain energy per unit volume. Tangent moduli are derived from radial and circumferential stress-strain characteristics
using non-linear curve fitting. Values of incremental and pressure-strain elastic parameters, wall stiffness, and compliance
per unit length are also calculated. Results are presented in terms of characteristics of stresses and strains in the three
directions, axial force, tangent moduli vs strains or stresses, and energy per unit volume, for both types of artery, with
reference to transmural pressure. Detailed numerical results are given at mean transmural pressure or in the physiological
range. Significant differences are indicated by statistic Student T-tests. Results obtained show that significant differences
exist between rheological properties of fresh and cryopreserved segments of human artery. Strains, stresses, axial force,
strain energy, and wall stiffness values highlight those differences whereas elastic parameters, compliance, and opening angle
do not. The usefulness of some parameters to compare the mechanical behavior existing between fresh and cryopreserved arteries
is therefore underlined.
Received: 3 January 2000 Revision received: 12 April 2000 Accepted: 8 May 2000 相似文献
979.
980.
Walter Taylor 《Algebra Universalis》1987,24(3):289-291